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magnetic reconnection has long been invoked as the physical mechanism underlying much of solar activity . for example , reconnection is believed to be the process driving many of the observed dynamic solar events ranging from spicules to the largest and most energetic manifestations of solar activity , coronal mass ejections ( cme ) and eruptive flares . in spite of the long and intensive study of reconnection in the solar atmosphere , the process is still not well understood , especially in three dimensions . one of the main difficulties in developing a comprehensive understanding is that reconnection may take on different forms depending on the details of the physical situation . consequently , any theory that can provide some unifying insight into the nature of reconnection would be of great benefit to understanding many aspects of solar activity . this is the compelling motivation behind studies of magnetic helicity . since magnetic helicity is believed to be conserved during reconnection in general , the hope is that helicity conservation may allow one to determine the final state of a reconnecting system without having to calculate the detailed dynamics of the evolution . helicity conservation may also be able to provide some valuable information on the dynamics . in this paper we argue , however , that helicity plays a negligible role in determining the evolution of reconnecting magnetic fields in the sun s corona . it should be emphasized that by the term `` helicity '' , we refer in this paper solely to the global relative helicity [ ] , which defines a single invariant . we are not referring to the helicity density which defines an infinite set of possible invariants . only the global helicity is believed to be conserved during reconnection . the basic theory for using helicity conservation to determine the evolution of magneto - plasmas has been developed by taylor [ 1986 ] . for taylor s theory to be applicable to the solar corona , three key statements must be true . first , the helicity ( global ) is conserved during reconnection . our numerical simulations agree well with this statement the higher the magnetic reynolds number of the simulation , the better the agreement . second , helicity is the only topological quantity that is generally conserved during reconnection . we believe that this assumption is also true , but our simulations can not test it , because they all begin with a potential field in which a simple shear or twist flow is imposed on the photospheric boundary . there are no knots or disconnected flux in the coronal field , and no braiding motions or higher - order topologies produced by the boundary flows . since the complete topology of our fields is contained in the helicity density , it is unlikely that there are any global topological invariants other than helicity available to be conserved . it appears , therefore , that the first two requirements for taylor s theory are valid for our simulations , and probably for the corona as well . the final requirement is that _ complete reconnection _ occurs , _ i.e. _ , the reconnection continues until the magnetic energy achieves its lowest possible state . note that this statement does not say anything about helicity , it is actually a model for reconnection . unfortunately , this statement is completely wrong for our simulations and , we believe , also for the sun . the physical reason for the failure of complete reconnection in the corona is that it requires the formation of numerous current sheets , or sheet - like current structures . but we , and others , have found from both 2.5d and 3d simulations that due to photospheric line - tying , current sheets do not form easily in the corona [ e.g. , ; ; ] . it is instructive to note that the taylor theory is closely related to parker s nonequilibrium theory for coronal heating [ ] . the nonequilibrium theory also proposes that in a 3d system , current sheets will form spontaneously throughout the coronal volume . but , there have been numerous simulations testing nonequilibrium [ _ e.g. _ , ; ; ] , and to our knowledge , no simulation produces these current sheets . this does not mean that current sheets can not form or that reconnection does not occur in the corona . many simulations find that current sheets readily form at magnetic separatrices [ _ e.g. _ , ] , and intense current concentrations do form at those locations where the photospheric motions produce exponentially growing gradients in footpoint displacements , in particular , at stagnation points of the flow [ _ e.g. _ , ; ; ; ] . but since reconnection occurs only at these very specific locations , it is far from complete , and taylor s theory can not be used to determine either the final state of the field or its evolution . we assert , therefore , that while the global helicity is conserved , it plays little role in determining the corona s dynamics and evolution . this conclusion is also evident from observations . the taylor theory would predict that the coronal field evolves towards a linear force - free field . for an infinite system like the corona , the only linear force - free field with finite energy is the field which is current - free in any finite volume [ _ berger , _ 1985 ] . therefore if the theory held , the coronal field would evolve _ via _ reconnection to the potential field , in which case there would be no need for cmes or eruptive flares . it may be argued that the taylor theory should not be applied to the corona as a whole , since the helicity is not uniquely defined for an infinite system . but , in fact , the taylor prediction for an infinite system is completely sensible . if reconnection could proceed freely , indeed it would be energetically favorable for the field to transfer all its shear and twist to the outermost field lines that extend toward infinity , such as the field lines at the poles . by transferring all the shear / twist to the longest field lines , the field conserves its helicity , but brings its energy down to the potential field value . the only problem with this type of evolution for the solar corona is that it is never observed . one could argue , however , that a taylor process may occur in some small portion of the corona , such as an active region , in which case the field should evolve to a linear force - free state inside this bounded domain . but this prediction also disagrees with observations . the canonical result from vector magnetograms and from h@xmath0 observations is that the field is strongly sheared near photospheric polarity - reversal lines ( `` neutral '' lines ) , and unsheared or weakly sheared far from these lines [ _ e.g. _ , ; ] . ( by shear we mean that the field lines appear to be greatly stretched out along the reversal line . ) we show below that such a shear distribution can explain the formation of prominences / filaments , which lends strong support to the observations . but this observed localization of the shear is _ not _ compatible with a linear force - free field . in order to demonstrate this point , consider a simple analytic model for the field . take the active region to consist of a 2.5d linear force - free field arcade : @xmath1 since this field must satisfy , @xmath2 , where @xmath3 is a constant , we find that @xmath4 , and the force - free equation reduces to the usual helmholtz form , @xmath5 . one possible solution is : @xmath6 where the wavenumbers @xmath7 , and @xmath3 are related by , @xmath8 . we have chosen the form of the flux function in equation ( 2 ) so that it corresponds to a bipolar arcade with a photospheric polarity reversal line at @xmath9 , and a width @xmath10 ( this periodic solution actually corresponds to an infinite set of arcades . ) if the wavelengths in the vertical and horizontal direction are equal , @xmath11 , then @xmath12 , and the solution reduces to the potential field . however , if the vertical wavelength becomes larger than the horizontal one @xmath13 ( we expect the force - free field to inflate upward ) , then the solution corresponds to a field with finite shear , @xmath14 . assuming that our bipolar arcade is at disk center , then the observed shear of the field at the photosphere would be given by the angle , @xmath15 . if the field is potential then @xmath16 , which implies that @xmath17 , and the field lines are perpendicular to the polarity reversal line ( the @xmath18 axis ) . for the nonpotential case we find from equations ( 1 ) and ( 2 ) that @xmath19 . hence , @xmath20 . the shear is constant throughout the region rather than being localized near the polarity - reversal line . although this result has been derived for only one family of solutions , it seems likely to hold true in general . a linear force - free field must has a constant ratio of electric current magnitude to magnetic field magnitude , and hence must have shear everywhere . but a broad shear distribution is in total disagreement with numerous observations of the solar field [ _ e.g. _ , ; ] . we conclude , therefore , that complete reconnection does not occur even in small regions of the corona , and that helicity conservation is of limited usefulness for determining the structure and evolution of the coronal field . we verify this conclusion with large - scale 3d numerical simulations in the following sections . the goal of our simulations is to understand the formation and eruption of solar prominences and the accompanying cme , but as will be demonstrated below , the simulations also address the issues of the role of helicity conservation in magnetic reconnection and the applicability of the taylor theory to the corona . the first simulation concerns the formation of prominences . solar prominences or filaments consist of huge masses of cool ( @xmath21 k ) , dense ( @xmath22 @xmath23 ) material apparently floating high up in the hot ( @xmath24 k ) , tenuous ( @xmath25 @xmath23 ) corona [ _ e.g. _ , ] . prominences reach heights of over @xmath26 km , which is approximately three orders of magnitude greater than the gravitational scale height of the cool material . hence , the most basic question concerning prominences is the origin of their gravitational support . it must be due to the magnetic field ; the field lines in the corona must have hammock - like geometry so that high - density plasma can be supported stably in the hammock [ ] . a characteristic feature of all prominences is that they form over photospheric polarity - reversal lines which exhibit strong shear . since many prominences are also observed to be very long compared to their width or height , 2.5d models for their magnetic structure ( a magnetic arcade ) have usually been considered . both numerical simulations and analytic theory showed , however , that 2.5d models of a sheared bipolar arcade can not produce field lines with the necessary dips to support prominence material [ ; ] . this led many to consider more complicated topologies involving multi - polar systems or topologies with flux disconnected from the photosphere , the so - called flux ropes [ _ e.g. _ , ; ] . we have shown , however , that the lack of dipped field lines is only an artifact of assuming translational symmetry , and that a sheared 3d bipolar field readily develops the correct geometry to support prominences [ ; ] . our previous results were based on a 3d static equilibrium code that computed the force - free field in the corona given the connectivity of the field lines at the photosphere . here we present results from recent fully time - dependent 3d simulations of photospheric shearing of a bipolar field . since we include the dynamics , these simulations also address the issues of current - sheet formation , reconnection , and eruption . the code uses a highly - optimized parallel version of our 3d flux - corrected transport algorithms to solve the ideal mhd equations in a finite - volume representation . the code is thoroughly documented and available on the web under the auspices of nasa s hpcc program ( _ see http://www.lcp.nrl.navy.mil/hpcc-ess/_ ) . the computational domain consists of the rectangular box , @xmath27 . we use a fixed , but very large non - uniform cartesian mesh of @xmath28 points . the initial magnetic field is that due to a point dipole located at ( 0,0,-2 ) and oriented along the @xmath29-axis , so that the polarity reversal line at the photospheric plane ( z = 0 ) corresponds to the @xmath18-axis . as boundary conditions , we impose line - tying with an assumed shear flow and no flow - through conditions at the bottom , and zero gradient conditions on all quantities at the sides and top . the initial plasma density is uniform , and we neglect the effects of both plasma pressure and gravity in this simulation , corresponding to a zero beta approximation . note , however , that the plasma is fully compressible and all alfven waves are included in the calculation , we shear the field by imposing a flow at the photosphere that is localized near the polarity reversal line . the shear vanishes for @xmath30 , and for @xmath31 it has the form : @xmath32 where the time scale for achieving the maximum shear @xmath33 . even though we performed the simulations on the latest architecture massively - parallel machines , it is still not possible to use observed solar values for the shear properties . our shear extends over roughly half the width of the strong field region on the photosphere , wider than is observed , and the average shearing velocity is approximately 10% the alfven speed in the strong field region , rather than the 1% typical of the sun . but even with these limitations , dipped field lines form readily in the corona . plate 1 shows the magnetic configuration halfway through the shearing , at @xmath34 . it is evident that the strongly sheared field lines have dipped central portions . the dips form as a result of the balance of forces between the increased magnetic pressure of the low - lying sheared field lines and the increased tension of the unsheared overlying field . since the unsheared flux is strongest at the center of the system , the downward tension force is strongest there , producing a local minimum in the height of the sheared flux . also shown in the plate is the half - maximum iso - surface of electric current magnitude . as expected , the current is concentrated where the gradient of the shear is largest , in the boundary between the sheared and unsheared field . the field of plate 1 reproduces all the basic observed features of prominences ; hence , we conclude that the magnetic structure of solar prominences and filaments is simply that of a sheared 3d field . it is tempting to conjecture that continued shearing of this field eventually leads to eruption . this is the basic hypothesis of the tether - cutting model , which proposes that reconnection of the sheared field either with itself or with the unsheared flux destroys the force balance between sheared and unsheared flux , thereby allowing the field to erupt outward explosively [ ; ] . note that the tether - cutting model is physically similar to the taylor theory since both hypothesize that reconnection transfers shear from inner to outer field lines . our simulation , however , shows no evidence for either tether - cutting or a taylor process . we continued the shearing up to @xmath35 , twice as far as shown in plate 1 . we then set the photospheric velocity to zero , and let the system relax for another 100 alfven times . the total magnetic energy and helicity are shown in figure 1 . the system appears to achieve a stable equilibrium with negligible loss of either energy or helicity . a key point is that the system appears stable , even though some `` reconnection '' does occur . by @xmath36 the imposed boundary shear is so extreme that even with our large grid we can not resolve it numerically , which produces `` current - sheets '' in the corona , in particular , the current structure seen in plate 1 . as a result , reconnection ( or perhaps more appropriately diffusion ) occurs , and helical field lines begin to appear at this time . however , the appearance of helical lines is confined to the regions of strongest shear , and does not propagate outward as would be necessary for tether - cutting or for a taylor process . we conclude , therefore , that our simulation rules out both tether - cutting and the taylor theory as viable models for the corona . there are two fundamental reasons for the lack of eruption in the simulation described above . first , line - tying inhibits magnetic reconnection in a topologically smooth field such as a simple bipole . second , eruption of the low - lying sheared flux requires the overlying unsheared field to open as well , but the aly - sturrock limit implies that no closed configuration can have sufficient energy to reach this open state [ ; ] . we have argued that a multi - polar magnetic topology overcomes both these problems , and have proposed a `` breakout '' model for prominence eruptions and coronal mass ejections [ ; ] . line - tying does not inhibit current - sheet formation at the separatrix surfaces between flux systems , and these current sheets can lead to sustained reconnection at separator lines [ ] . furthermore , a multi - flux topology makes it possible to transfer the unsheared overlying flux to neighboring flux systems , thereby allowing the sheared field to erupt outward while keeping the unsheared flux closed . this allows the system to erupt explosively while still satisfying the aly - sturrock energy limit [ ] . we show below results from our first 3d simulation of the breakout model . the simulation domain in this case consists of the region : @xmath37 , with a fixed , non - uniform grid of @xmath38 points . the initial magnetic field is that due to three point dipoles : one located at ( 0 , 25 , -50 ) , with magnitude unity , and pointing in the @xmath39 direction ; another located at ( 0 , 1 , -1 ) , with magnitude 10 , and pointing in the @xmath40 direction ; and the third at ( 0 , 0 , -0.5 ) , with magnitude 10 and pointing in the @xmath41 direction . the initial density and pressure were chosen so that the average plasma beta near the base is less than 0.1 . ( this simulation did not use the zero - beta approximation . ) . shows the initial potential field of the simulation . the magnetic topology consists of four flux systems due to four distinct polarity regions at the photosphere . there are two toroidal separatrix surfaces that define the boundaries of these flux systems , and their intersection in the corona defines a separator line , along which rapid reconnection can occur [ ] . this configuration corresponds to a so - called delta - sunspot region . we impose similar boundary conditions as in the previous simulation , and apply a shearing motion localized near the circular polarity - reversal line of the delta - spot located at the center of the bottom plane . the shear is such that it produces a rotation of @xmath42 over a time interval of 100 alfven times . . shows the effect of this shear . all field lines shown in plates 2 and 2b are traced from exactly the same set of positions at the photosphere . it is evident that field lines with footpoints near the polarity reversal line have been twisted through almost a full rotation , ( this sheared flux system corresponds to the sheared prominence bipole of plate 1 ) . a careful examination of the field lines in 2b reveals that some of the unsheared delta - spot flux overlying the sheared flux has become open , _ i.e. _ , it extends to the top boundary of the simulation box rather than closing down over the sheared field . this transfer occurs as a result of reconnection between the delta - spot flux and the neighboring open flux system . the effect of another @xmath43 rotation is shown in plate 2c . almost all the delta spot flux in now open . we show in figure 2 the total magnetic energy and helicity of the system , equivalent to figure 1 . near the end of the second shearing phase there is clearly a burst of impulsive energy release and helicity ejection through the top of the system . the helicity within the simulation volume decreases much faster than the energy , because of the eruption . therefore , the evolution of our simulated corona is the exact opposite of a taylor process ! of course , this claim is somewhat overstated because we expect that , in fact , the helicity of the whole system ( including the erupted field ) stays constant , whereas the magnetic energy of the whole system decreases . it is interesting to note , however , that since solar telescopes observe only a finite coronal volume , eruptive opening of the magnetic field in that volume implies that the observed helicity decreases to zero , but the observed magnetic energy asymptotes to the open field value , which is generally well above the potential field value . in this sense , an anti - taylor process is an appropriate approximation for the evolution of coronal regions observed during an eruption . a key result of our 3d delta - spot simulation is that that even though a great deal of reconnection occurs , it is far from complete . the reconnection is confined to the separator line between the sheared and unsheared regions . consequently , the field never approaches a linear force - free field . instead it evolves toward an open state in which the currents are concentrated in a thin sheet . this also is opposite to what is expected for a taylor process . in summary , we conclude that while helicity is conserved and may well be the only topological quantity that is generally conserved during reconnection , the actual amount of reconnection in the sun s corona is determined by the detailed magnetic topology of the particular region . consequently , the global helicity by itself yields little information on coronal evolution . moore , r. l. and roumeliotis , g. , triggering of eruptive flares : destabilization of the preflare magnetic field configuration , in _ eruptive solar flares _ , edited by z. svestka , b. v. jackson , and m. e. machado , p. 69 , springer , berlin , 1992 .

we demonstrate that conservation of global helicity plays only a minor role in determining the nature and consequences of magnetic reconnection in the solar atmosphere . first , we show that observations of the solar coronal magnetic field are in direct conflict with taylor s theory . next , we present results from three - dimensional mhd simulations of the shearing of bipolar and multi - polar coronal magnetic fields by photospheric footpoint motions , and discuss the implications of these results for taylor s theory and for models of solar activity . the key conclusion of this work is that significant magnetic reconnection occurs only at very specific locations and , hence , the sun s magnetic field can not relax completely down to the minimum energy state predicted by conservation of global helicity .

<s>[INST]magnetic reconnection has long been invoked as the physical mechanism underlying much of solar activity . for example , reconnection is believed to be the process driving many of the observed dynamic solar events ranging from spicules to the largest and most energetic manifestations of solar activity , coronal mass ejections ( cme ) and eruptive flares . in spite of the long and intensive study of reconnection in the solar atmosphere , the process is still not well understood , especially in three dimensions . one of the main difficulties in developing a comprehensive understanding is that reconnection may take on different forms depending on the details of the physical situation . consequently , any theory that can provide some unifying insight into the nature of reconnection would be of great benefit to understanding many aspects of solar activity . this is the compelling motivation behind studies of magnetic helicity . since magnetic helicity is believed to be conserved during reconnection in general , the hope is that helicity conservation may allow one to determine the final state of a reconnecting system without having to calculate the detailed dynamics of the evolution . helicity conservation may also be able to provide some valuable information on the dynamics . in this paper we argue , however , that helicity plays a negligible role in determining the evolution of reconnecting magnetic fields in the sun s corona . it should be emphasized that by the term `` helicity '' , we refer in this paper solely to the global relative helicity [ ] , which defines a single invariant . we are not referring to the helicity density which defines an infinite set of possible invariants . only the global helicity is believed to be conserved during reconnection . the basic theory for using helicity conservation to determine the evolution of magneto - plasmas has been developed by taylor [ 1986 ] . for taylor s theory to be applicable to the solar corona , three key statements must be true . first , the helicity ( global ) is conserved during reconnection . our numerical simulations agree well with this statement the higher the magnetic reynolds number of the simulation , the better the agreement . second , helicity is the only topological quantity that is generally conserved during reconnection . we believe that this assumption is also true , but our simulations can not test it , because they all begin with a potential field in which a simple shear or twist flow is imposed on the photospheric boundary . there are no knots or disconnected flux in the coronal field , and no braiding motions or higher - order topologies produced by the boundary flows . since the complete topology of our fields is contained in the helicity density , it is unlikely that there are any global topological invariants other than helicity available to be conserved . it appears , therefore , that the first two requirements for taylor s theory are valid for our simulations , and probably for the corona as well . the final requirement is that _ complete reconnection _ occurs , _ i.e. _ , the reconnection continues until the magnetic energy achieves its lowest possible state . note that this statement does not say anything about helicity , it is actually a model for reconnection . unfortunately , this statement is completely wrong for our simulations and , we believe , also for the sun . the physical reason for the failure of complete reconnection in the corona is that it requires the formation of numerous current sheets , or sheet - like current structures . but we , and others , have found from both 2.5d and 3d simulations that due to photospheric line - tying , current sheets do not form easily in the corona [ e.g. , ; ; ] . it is instructive to note that the taylor theory is closely related to parker s nonequilibrium theory for coronal heating [ ] . the nonequilibrium theory also proposes that in a 3d system , current sheets will form spontaneously throughout the coronal volume . but , there have been numerous simulations testing nonequilibrium [ _ e.g. _ , ; ; ] , and to our knowledge , no simulation produces these current sheets . this does not mean that current sheets can not form or that reconnection does not occur in the corona . many simulations find that current sheets readily form at magnetic separatrices [ _ e.g. _ , ] , and intense current concentrations do form at those locations where the photospheric motions produce exponentially growing gradients in footpoint displacements , in particular , at stagnation points of the flow [ _ e.g. _ , ; ; ; ] . but since reconnection occurs only at these very specific locations , it is far from complete , and taylor s theory can not be used to determine either the final state of the field or its evolution . we assert , therefore , that while the global helicity is conserved , it plays little role in determining the corona s dynamics and evolution . this conclusion is also evident from observations . the taylor theory would predict that the coronal field evolves towards a linear force - free field . for an infinite system like the corona , the only linear force - free field with finite energy is the field which is current - free in any finite volume [ _ berger , _ 1985 ] . therefore if the theory held , the coronal field would evolve _ via _ reconnection to the potential field , in which case there would be no need for cmes or eruptive flares . it may be argued that the taylor theory should not be applied to the corona as a whole , since the helicity is not uniquely defined for an infinite system . but , in fact , the taylor prediction for an infinite system is completely sensible . if reconnection could proceed freely , indeed it would be energetically favorable for the field to transfer all its shear and twist to the outermost field lines that extend toward infinity , such as the field lines at the poles . by transferring all the shear / twist to the longest field lines , the field conserves its helicity , but brings its energy down to the potential field value . the only problem with this type of evolution for the solar corona is that it is never observed . one could argue , however , that a taylor process may occur in some small portion of the corona , such as an active region , in which case the field should evolve to a linear force - free state inside this bounded domain . but this prediction also disagrees with observations . the canonical result from vector magnetograms and from h@xmath0 observations is that the field is strongly sheared near photospheric polarity - reversal lines ( `` neutral '' lines ) , and unsheared or weakly sheared far from these lines [ _ e.g. _ , ; ] . ( by shear we mean that the field lines appear to be greatly stretched out along the reversal line . ) we show below that such a shear distribution can explain the formation of prominences / filaments , which lends strong support to the observations . but this observed localization of the shear is _ not _ compatible with a linear force - free field . in order to demonstrate this point , consider a simple analytic model for the field . take the active region to consist of a 2.5d linear force - free field arcade : @xmath1 since this field must satisfy , @xmath2 , where @xmath3 is a constant , we find that @xmath4 , and the force - free equation reduces to the usual helmholtz form , @xmath5 . one possible solution is : @xmath6 where the wavenumbers @xmath7 , and @xmath3 are related by , @xmath8 . we have chosen the form of the flux function in equation ( 2 ) so that it corresponds to a bipolar arcade with a photospheric polarity reversal line at @xmath9 , and a width @xmath10 ( this periodic solution actually corresponds to an infinite set of arcades . ) if the wavelengths in the vertical and horizontal direction are equal , @xmath11 , then @xmath12 , and the solution reduces to the potential field . however , if the vertical wavelength becomes larger than the horizontal one @xmath13 ( we expect the force - free field to inflate upward ) , then the solution corresponds to a field with finite shear , @xmath14 . assuming that our bipolar arcade is at disk center , then the observed shear of the field at the photosphere would be given by the angle , @xmath15 . if the field is potential then @xmath16 , which implies that @xmath17 , and the field lines are perpendicular to the polarity reversal line ( the @xmath18 axis ) . for the nonpotential case we find from equations ( 1 ) and ( 2 ) that @xmath19 . hence , @xmath20 . the shear is constant throughout the region rather than being localized near the polarity - reversal line . although this result has been derived for only one family of solutions , it seems likely to hold true in general . a linear force - free field must has a constant ratio of electric current magnitude to magnetic field magnitude , and hence must have shear everywhere . but a broad shear distribution is in total disagreement with numerous observations of the solar field [ _ e.g. _ , ; ] . we conclude , therefore , that complete reconnection does not occur even in small regions of the corona , and that helicity conservation is of limited usefulness for determining the structure and evolution of the coronal field . we verify this conclusion with large - scale 3d numerical simulations in the following sections . the goal of our simulations is to understand the formation and eruption of solar prominences and the accompanying cme , but as will be demonstrated below , the simulations also address the issues of the role of helicity conservation in magnetic reconnection and the applicability of the taylor theory to the corona . the first simulation concerns the formation of prominences . solar prominences or filaments consist of huge masses of cool ( @xmath21 k ) , dense ( @xmath22 @xmath23 ) material apparently floating high up in the hot ( @xmath24 k ) , tenuous ( @xmath25 @xmath23 ) corona [ _ e.g. _ , ] . prominences reach heights of over @xmath26 km , which is approximately three orders of magnitude greater than the gravitational scale height of the cool material . hence , the most basic question concerning prominences is the origin of their gravitational support . it must be due to the magnetic field ; the field lines in the corona must have hammock - like geometry so that high - density plasma can be supported stably in the hammock [ ] . a characteristic feature of all prominences is that they form over photospheric polarity - reversal lines which exhibit strong shear . since many prominences are also observed to be very long compared to their width or height , 2.5d models for their magnetic structure ( a magnetic arcade ) have usually been considered . both numerical simulations and analytic theory showed , however , that 2.5d models of a sheared bipolar arcade can not produce field lines with the necessary dips to support prominence material [ ; ] . this led many to consider more complicated topologies involving multi - polar systems or topologies with flux disconnected from the photosphere , the so - called flux ropes [ _ e.g. _ , ; ] . we have shown , however , that the lack of dipped field lines is only an artifact of assuming translational symmetry , and that a sheared 3d bipolar field readily develops the correct geometry to support prominences [ ; ] . our previous results were based on a 3d static equilibrium code that computed the force - free field in the corona given the connectivity of the field lines at the photosphere . here we present results from recent fully time - dependent 3d simulations of photospheric shearing of a bipolar field . since we include the dynamics , these simulations also address the issues of current - sheet formation , reconnection , and eruption . the code uses a highly - optimized parallel version of our 3d flux - corrected transport algorithms to solve the ideal mhd equations in a finite - volume representation . the code is thoroughly documented and available on the web under the auspices of nasa s hpcc program ( _ see http://www.lcp.nrl.navy.mil/hpcc-ess/_ ) . the computational domain consists of the rectangular box , @xmath27 . we use a fixed , but very large non - uniform cartesian mesh of @xmath28 points . the initial magnetic field is that due to a point dipole located at ( 0,0,-2 ) and oriented along the @xmath29-axis , so that the polarity reversal line at the photospheric plane ( z = 0 ) corresponds to the @xmath18-axis . as boundary conditions , we impose line - tying with an assumed shear flow and no flow - through conditions at the bottom , and zero gradient conditions on all quantities at the sides and top . the initial plasma density is uniform , and we neglect the effects of both plasma pressure and gravity in this simulation , corresponding to a zero beta approximation . note , however , that the plasma is fully compressible and all alfven waves are included in the calculation , we shear the field by imposing a flow at the photosphere that is localized near the polarity reversal line . the shear vanishes for @xmath30 , and for @xmath31 it has the form : @xmath32 where the time scale for achieving the maximum shear @xmath33 . even though we performed the simulations on the latest architecture massively - parallel machines , it is still not possible to use observed solar values for the shear properties . our shear extends over roughly half the width of the strong field region on the photosphere , wider than is observed , and the average shearing velocity is approximately 10% the alfven speed in the strong field region , rather than the 1% typical of the sun . but even with these limitations , dipped field lines form readily in the corona . plate 1 shows the magnetic configuration halfway through the shearing , at @xmath34 . it is evident that the strongly sheared field lines have dipped central portions . the dips form as a result of the balance of forces between the increased magnetic pressure of the low - lying sheared field lines and the increased tension of the unsheared overlying field . since the unsheared flux is strongest at the center of the system , the downward tension force is strongest there , producing a local minimum in the height of the sheared flux . also shown in the plate is the half - maximum iso - surface of electric current magnitude . as expected , the current is concentrated where the gradient of the shear is largest , in the boundary between the sheared and unsheared field . the field of plate 1 reproduces all the basic observed features of prominences ; hence , we conclude that the magnetic structure of solar prominences and filaments is simply that of a sheared 3d field . it is tempting to conjecture that continued shearing of this field eventually leads to eruption . this is the basic hypothesis of the tether - cutting model , which proposes that reconnection of the sheared field either with itself or with the unsheared flux destroys the force balance between sheared and unsheared flux , thereby allowing the field to erupt outward explosively [ ; ] . note that the tether - cutting model is physically similar to the taylor theory since both hypothesize that reconnection transfers shear from inner to outer field lines . our simulation , however , shows no evidence for either tether - cutting or a taylor process . we continued the shearing up to @xmath35 , twice as far as shown in plate 1 . we then set the photospheric velocity to zero , and let the system relax for another 100 alfven times . the total magnetic energy and helicity are shown in figure 1 . the system appears to achieve a stable equilibrium with negligible loss of either energy or helicity . a key point is that the system appears stable , even though some `` reconnection '' does occur . by @xmath36 the imposed boundary shear is so extreme that even with our large grid we can not resolve it numerically , which produces `` current - sheets '' in the corona , in particular , the current structure seen in plate 1 . as a result , reconnection ( or perhaps more appropriately diffusion ) occurs , and helical field lines begin to appear at this time . however , the appearance of helical lines is confined to the regions of strongest shear , and does not propagate outward as would be necessary for tether - cutting or for a taylor process . we conclude , therefore , that our simulation rules out both tether - cutting and the taylor theory as viable models for the corona . there are two fundamental reasons for the lack of eruption in the simulation described above . first , line - tying inhibits magnetic reconnection in a topologically smooth field such as a simple bipole . second , eruption of the low - lying sheared flux requires the overlying unsheared field to open as well , but the aly - sturrock limit implies that no closed configuration can have sufficient energy to reach this open state [ ; ] . we have argued that a multi - polar magnetic topology overcomes both these problems , and have proposed a `` breakout '' model for prominence eruptions and coronal mass ejections [ ; ] . line - tying does not inhibit current - sheet formation at the separatrix surfaces between flux systems , and these current sheets can lead to sustained reconnection at separator lines [ ] . furthermore , a multi - flux topology makes it possible to transfer the unsheared overlying flux to neighboring flux systems , thereby allowing the sheared field to erupt outward while keeping the unsheared flux closed . this allows the system to erupt explosively while still satisfying the aly - sturrock energy limit [ ] . we show below results from our first 3d simulation of the breakout model . the simulation domain in this case consists of the region : @xmath37 , with a fixed , non - uniform grid of @xmath38 points . the initial magnetic field is that due to three point dipoles : one located at ( 0 , 25 , -50 ) , with magnitude unity , and pointing in the @xmath39 direction ; another located at ( 0 , 1 , -1 ) , with magnitude 10 , and pointing in the @xmath40 direction ; and the third at ( 0 , 0 , -0.5 ) , with magnitude 10 and pointing in the @xmath41 direction . the initial density and pressure were chosen so that the average plasma beta near the base is less than 0.1 . ( this simulation did not use the zero - beta approximation . ) . shows the initial potential field of the simulation . the magnetic topology consists of four flux systems due to four distinct polarity regions at the photosphere . there are two toroidal separatrix surfaces that define the boundaries of these flux systems , and their intersection in the corona defines a separator line , along which rapid reconnection can occur [ ] . this configuration corresponds to a so - called delta - sunspot region . we impose similar boundary conditions as in the previous simulation , and apply a shearing motion localized near the circular polarity - reversal line of the delta - spot located at the center of the bottom plane . the shear is such that it produces a rotation of @xmath42 over a time interval of 100 alfven times . . shows the effect of this shear . all field lines shown in plates 2 and 2b are traced from exactly the same set of positions at the photosphere . it is evident that field lines with footpoints near the polarity reversal line have been twisted through almost a full rotation , ( this sheared flux system corresponds to the sheared prominence bipole of plate 1 ) . a careful examination of the field lines in 2b reveals that some of the unsheared delta - spot flux overlying the sheared flux has become open , _ i.e. _ , it extends to the top boundary of the simulation box rather than closing down over the sheared field . this transfer occurs as a result of reconnection between the delta - spot flux and the neighboring open flux system . the effect of another @xmath43 rotation is shown in plate 2c . almost all the delta spot flux in now open . we show in figure 2 the total magnetic energy and helicity of the system , equivalent to figure 1 . near the end of the second shearing phase there is clearly a burst of impulsive energy release and helicity ejection through the top of the system . the helicity within the simulation volume decreases much faster than the energy , because of the eruption . therefore , the evolution of our simulated corona is the exact opposite of a taylor process ! of course , this claim is somewhat overstated because we expect that , in fact , the helicity of the whole system ( including the erupted field ) stays constant , whereas the magnetic energy of the whole system decreases . it is interesting to note , however , that since solar telescopes observe only a finite coronal volume , eruptive opening of the magnetic field in that volume implies that the observed helicity decreases to zero , but the observed magnetic energy asymptotes to the open field value , which is generally well above the potential field value . in this sense , an anti - taylor process is an appropriate approximation for the evolution of coronal regions observed during an eruption . a key result of our 3d delta - spot simulation is that that even though a great deal of reconnection occurs , it is far from complete . the reconnection is confined to the separator line between the sheared and unsheared regions . consequently , the field never approaches a linear force - free field . instead it evolves toward an open state in which the currents are concentrated in a thin sheet . this also is opposite to what is expected for a taylor process . in summary , we conclude that while helicity is conserved and may well be the only topological quantity that is generally conserved during reconnection , the actual amount of reconnection in the sun s corona is determined by the detailed magnetic topology of the particular region . consequently , the global helicity by itself yields little information on coronal evolution . moore , r. l. and roumeliotis , g. , triggering of eruptive flares : destabilization of the preflare magnetic field configuration , in _ eruptive solar flares _ , edited by z. svestka , b. v. jackson , and m. e. machado , p. 69 , springer , berlin , 1992 .[/INST] we demonstrate that conservation of global helicity plays only a minor role in determining the nature and consequences of magnetic reconnection in the solar atmosphere . first , we show that observations of the solar coronal magnetic field are in direct conflict with taylor s theory . next , we present results from three - dimensional mhd simulations of the shearing of bipolar and multi - polar coronal magnetic fields by photospheric footpoint motions , and discuss the implications of these results for taylor s theory and for models of solar activity . the key conclusion of this work is that significant magnetic reconnection occurs only at very specific locations and , hence , the sun s magnetic field can not relax completely down to the minimum energy state predicted by conservation of global helicity . </s>

paraesophageal hernia ( peh ) is a rare condition , occurring in about 5% of all hiatal hernia . various advantages , such as reduced post - operative pain , shorter hospital stay and rapid convalescence , make laparoscopy the surgical technique of choice for repair by fundoplication of the peh , especially in high risk elderly population . there are high chances of complications related to carbon dioxide ( co2 ) insufflation , such as subcutaneous emphysema , pneumothorax , pneumomediastinum , and pneumopericardium . increasing airway pressures and end - tidal carbon dioxide ( etco2 ) and decreasing peripheral oxygen saturation ( spo2 ) may indicate development of pneumothorax . we report a case of laparoscopic repair of a giant peh , in whom early diagnosis and prompt management of life - threatening subcutaneous emphysema and pneumothorax was possible because of vigilant monitoring . a 60 kg , 70 year woman presented to the hospital with complaints of post - prandial epigastric pain , occasional post - prandial dyspnea , and regurgitation of food since 4 years . conservative anti - reflux medication had not benefited her . oral contrast computerized tomography scan showed herniation of stomach , spleen , and pancreas into the thoracic cavity [ figure 1 ] . the patient was diagnosed as a case of large type iv ( giant ) peh and scheduled for laparoscopic repair of the peh with nissen fundoplication . chest x - ray of the patient showing a radio - opaque rounded shadow alongside the cardiac silhouette . pre - operative evaluation revealed that the patient was a known hypertensive controlled on oral amlodipine 5 mg and atenolol 50 mg taken once daily . she had grade iii dyspnea with a breath holding time of 14 s. airway examination was normal but she had mild degree of thoracolumbar kyphoscoliosis . pulmonary function tests revealed a restrictive pattern of lung disease and arterial blood gas analysis on room air showed ph 7.39 , pao2 70 mmhg and paco2 36 mmhg . the patient was pre - medicated with oral alprazolam 0.25 mg and ranitidine 150 mg , the night before surgery and again 2 h prior to surgery . on arrival in the operating room , pulse rate was 66/min , blood pressure ( bp ) 138/84 mmhg and spo2 93% on room air . patient was given morphine 0.1 mg / kg and midazolam 1 mg intravenous ( iv ) . after pre - oxygenation , a rapid sequence induction / intubation was performed after administration of thiopentone 4 mg / kg and suxamethonium 1.5 mg / kg iv . anesthesia was maintained with oxygen , nitrous oxide ( n2o ) , isoflurane ( 0.5 - 1% ) , and rocuronium . controlled ventilation was instituted with a tidal volume of 600 ml and a rate of 12/min using a penlon a-200 sp ventilator . the vital parameters , end - tidal carbon dioxide ( etco2 ) , and airway pressures were monitored . co2 pneumoperitoneum was created by using pressure - controlled high flow insufflator to an intra - abdominal pressure ( iap ) of 12 - 15 mmhg . the intra - operative period was uneventful for approximately 6 h but toward the end of the surgery , the patient 's pulse rate and bp showed a rising trend along with an increasing airway pressures and etco2 values . the plane of anesthesia was deepened and the anesthesia circuit and endotracheal tube checked for kinks or obstruction . we tried to decrease the peak airway pressures by decreasing the tidal volume from 600 to 550 ml and the respiratory rate was increased to 14/min . however , within a span of 7 - 8 min , the peak airway pressures reached 50 cmh2o and etco2 values approached 90 mmhg . chest auscultation revealed decreased air entry over the left hemithorax and arterial blood gas analysis showed an uncompensated respiratory acidosis ( ph 7.25 , pao2 102 mmhg and paco2 98 mmhg ) . a diagnosis of iatrogenic left pneumothorax with subcutaneous emphysema was made [ figure 2 ] . an intercostal drain was inserted and within 10 min , the airway pressures and etco2 returned to baseline values . however , to continue the procedure , surgeons had to increase the co2 insufflation rate from 6 to 8 l / min . at the end of the surgery , chest x - ray showed subcutaneous emphysema in the neck and thorax and intercostal drain in situ , without any evidence of pneumothorax or pneumomediastinum . post - operative pain was managed with morphine 3 mg in 8 ml saline via the thoracic epidural catheter 12 hourly . weaning from the ventilator was gradually done and trachea extubated after 48 h. the chest drain was removed after complete lung expansion , on the third post - operative day . giant peh is a hiatal hernia in which besides the stomach and gastroesophageal junction , other viscera , such as colon , small bowel , spleen , or pancreas are present in the hernia sac . its incidence is higher in the elderly population possibly as a result of progressive weakening and enlargement of the diaphragmatic hiatus with advancing age . there is a associated high risk of catastrophic complications that include bleeding , strangulation , incarceration , volvulus and perforation and so it should be repaired electively soon after recognition to prevent the development of these potentially life - threatening complications . repair of peh can be difficult for the surgeon as there is a need to resect a large sac . the main anesthetic considerations include geriatric age group , associated comorbidities , concomitant multiple drug therapies , presence of gastro - esophageal reflux , and low cardiopulmonary reserve due to herniation of abdominal contents into the thorax , compounded by kyphoscoliosis and old age . the intra - operative concerns are related mainly to the surgical positioning and the effects of co2 pneumoperitoneum . the patient is placed in supine position , with slight ( 10 - 15 ) reverse trendelenberg , legs abducted and the operator standing between the legs . in the post - operative period , pain relief and need for elective ventilation are the main concerns . left pneumothorax is one of the most common intra - operative complications since the left parietal pleura is exposed and can be torn during dissection around the diaphragmatic hiatus . the incidence of pneumothorax varies from 0 to 8% depending on the surgeon 's expertise . although subcutaneous emphysema itself is not a serious complication , but it may be the harbinger of pneumothorax . the risk factors for the development of subcutaneous emphysema are etco2 of 50 mmhg or greater , the use of six or more operative ports and operative time over 200 min . all these risk - factors were present in our patient . whenever surgical emphysema is detected during laparoscopic surgery , pneumothorax must be ruled out . if not associated with pneumothorax , the only treatment required is to temporarily interrupt the surgery and increase the minute ventilation to allow co2 elimination . the presence of pneumothorax , on the other hand , requires urgent and aggressive management . strategies for further management include insertion of an intercostal drain , application of positive end - expiratory pressure , and plugging the pleural rent . insertion of an intercostal drain , although the treatment of choice for pneumothorax due to other causes , is not indicated in laparoscopic surgeries , as it causes loss of pneumoperitoneum , creating suboptimal conditions for the continuation of surgery . joris et al used peep as an alternative to chest tube placement and found that peep largely corrected the respiratory changes associated with pneumothorax . it helps by decreasing the pressure gradient between the abdominal and pleural cavities not only during inspiration but also during expiration and subsequently inflating the lung . re - expansion of the lung with peep can mechanically seal the surgically induced tear in the parietal pleura . an alternative treatment is to ask the surgeon to plug the rent in the pleura with the help of omentum . although this may be time consuming , it has been successfully used by singhal et al . in our patient , however , the increasing airway pressures and rising etco2 levels made ventilation difficult , necessitating chest tube insertion before patient condition deteriorated further . although pneumoperitoneum was lost , surgeons were able to complete the surgery with lower iap using higher insufflation rate of co2 . to conclude , awareness of the risk and high index of suspicion for development of pneumothorax any sudden and brisk increase in these parameters should prompt a search for subcutaneous emphysema or pneumothorax .

giant paraesophageal hernia is an uncommon morbid disorder which may present a risk of catastrophic complications and should be repaired electively as soon as possible . laparoscopic fundoplication is the mainstay of surgical management of this disorder due to several advantages such as lower post - operative morbidity and pain . we report a case of a 70-year - old patient with a giant paraesophageal hernia , who developed subcutaneous emphysema with pneumothorax during laparoscopic fundoplication . early diagnosis was possible by close clinical evaluation and simultaneous monitoring of end - tidal carbon dioxide levels and airway pressures . although positive end - expiratory pressure application is an effective way of managing pneumothorax secondary to the passage of gas into the interpleural space , insertion of an intercostal drain may be used in an emergent situation .

<s>[INST]paraesophageal hernia ( peh ) is a rare condition , occurring in about 5% of all hiatal hernia . various advantages , such as reduced post - operative pain , shorter hospital stay and rapid convalescence , make laparoscopy the surgical technique of choice for repair by fundoplication of the peh , especially in high risk elderly population . there are high chances of complications related to carbon dioxide ( co2 ) insufflation , such as subcutaneous emphysema , pneumothorax , pneumomediastinum , and pneumopericardium . increasing airway pressures and end - tidal carbon dioxide ( etco2 ) and decreasing peripheral oxygen saturation ( spo2 ) may indicate development of pneumothorax . we report a case of laparoscopic repair of a giant peh , in whom early diagnosis and prompt management of life - threatening subcutaneous emphysema and pneumothorax was possible because of vigilant monitoring . a 60 kg , 70 year woman presented to the hospital with complaints of post - prandial epigastric pain , occasional post - prandial dyspnea , and regurgitation of food since 4 years . conservative anti - reflux medication had not benefited her . oral contrast computerized tomography scan showed herniation of stomach , spleen , and pancreas into the thoracic cavity [ figure 1 ] . the patient was diagnosed as a case of large type iv ( giant ) peh and scheduled for laparoscopic repair of the peh with nissen fundoplication . chest x - ray of the patient showing a radio - opaque rounded shadow alongside the cardiac silhouette . pre - operative evaluation revealed that the patient was a known hypertensive controlled on oral amlodipine 5 mg and atenolol 50 mg taken once daily . she had grade iii dyspnea with a breath holding time of 14 s. airway examination was normal but she had mild degree of thoracolumbar kyphoscoliosis . pulmonary function tests revealed a restrictive pattern of lung disease and arterial blood gas analysis on room air showed ph 7.39 , pao2 70 mmhg and paco2 36 mmhg . the patient was pre - medicated with oral alprazolam 0.25 mg and ranitidine 150 mg , the night before surgery and again 2 h prior to surgery . on arrival in the operating room , pulse rate was 66/min , blood pressure ( bp ) 138/84 mmhg and spo2 93% on room air . patient was given morphine 0.1 mg / kg and midazolam 1 mg intravenous ( iv ) . after pre - oxygenation , a rapid sequence induction / intubation was performed after administration of thiopentone 4 mg / kg and suxamethonium 1.5 mg / kg iv . anesthesia was maintained with oxygen , nitrous oxide ( n2o ) , isoflurane ( 0.5 - 1% ) , and rocuronium . controlled ventilation was instituted with a tidal volume of 600 ml and a rate of 12/min using a penlon a-200 sp ventilator . the vital parameters , end - tidal carbon dioxide ( etco2 ) , and airway pressures were monitored . co2 pneumoperitoneum was created by using pressure - controlled high flow insufflator to an intra - abdominal pressure ( iap ) of 12 - 15 mmhg . the intra - operative period was uneventful for approximately 6 h but toward the end of the surgery , the patient 's pulse rate and bp showed a rising trend along with an increasing airway pressures and etco2 values . the plane of anesthesia was deepened and the anesthesia circuit and endotracheal tube checked for kinks or obstruction . we tried to decrease the peak airway pressures by decreasing the tidal volume from 600 to 550 ml and the respiratory rate was increased to 14/min . however , within a span of 7 - 8 min , the peak airway pressures reached 50 cmh2o and etco2 values approached 90 mmhg . chest auscultation revealed decreased air entry over the left hemithorax and arterial blood gas analysis showed an uncompensated respiratory acidosis ( ph 7.25 , pao2 102 mmhg and paco2 98 mmhg ) . a diagnosis of iatrogenic left pneumothorax with subcutaneous emphysema was made [ figure 2 ] . an intercostal drain was inserted and within 10 min , the airway pressures and etco2 returned to baseline values . however , to continue the procedure , surgeons had to increase the co2 insufflation rate from 6 to 8 l / min . at the end of the surgery , chest x - ray showed subcutaneous emphysema in the neck and thorax and intercostal drain in situ , without any evidence of pneumothorax or pneumomediastinum . post - operative pain was managed with morphine 3 mg in 8 ml saline via the thoracic epidural catheter 12 hourly . weaning from the ventilator was gradually done and trachea extubated after 48 h. the chest drain was removed after complete lung expansion , on the third post - operative day . giant peh is a hiatal hernia in which besides the stomach and gastroesophageal junction , other viscera , such as colon , small bowel , spleen , or pancreas are present in the hernia sac . its incidence is higher in the elderly population possibly as a result of progressive weakening and enlargement of the diaphragmatic hiatus with advancing age . there is a associated high risk of catastrophic complications that include bleeding , strangulation , incarceration , volvulus and perforation and so it should be repaired electively soon after recognition to prevent the development of these potentially life - threatening complications . repair of peh can be difficult for the surgeon as there is a need to resect a large sac . the main anesthetic considerations include geriatric age group , associated comorbidities , concomitant multiple drug therapies , presence of gastro - esophageal reflux , and low cardiopulmonary reserve due to herniation of abdominal contents into the thorax , compounded by kyphoscoliosis and old age . the intra - operative concerns are related mainly to the surgical positioning and the effects of co2 pneumoperitoneum . the patient is placed in supine position , with slight ( 10 - 15 ) reverse trendelenberg , legs abducted and the operator standing between the legs . in the post - operative period , pain relief and need for elective ventilation are the main concerns . left pneumothorax is one of the most common intra - operative complications since the left parietal pleura is exposed and can be torn during dissection around the diaphragmatic hiatus . the incidence of pneumothorax varies from 0 to 8% depending on the surgeon 's expertise . although subcutaneous emphysema itself is not a serious complication , but it may be the harbinger of pneumothorax . the risk factors for the development of subcutaneous emphysema are etco2 of 50 mmhg or greater , the use of six or more operative ports and operative time over 200 min . all these risk - factors were present in our patient . whenever surgical emphysema is detected during laparoscopic surgery , pneumothorax must be ruled out . if not associated with pneumothorax , the only treatment required is to temporarily interrupt the surgery and increase the minute ventilation to allow co2 elimination . the presence of pneumothorax , on the other hand , requires urgent and aggressive management . strategies for further management include insertion of an intercostal drain , application of positive end - expiratory pressure , and plugging the pleural rent . insertion of an intercostal drain , although the treatment of choice for pneumothorax due to other causes , is not indicated in laparoscopic surgeries , as it causes loss of pneumoperitoneum , creating suboptimal conditions for the continuation of surgery . joris et al used peep as an alternative to chest tube placement and found that peep largely corrected the respiratory changes associated with pneumothorax . it helps by decreasing the pressure gradient between the abdominal and pleural cavities not only during inspiration but also during expiration and subsequently inflating the lung . re - expansion of the lung with peep can mechanically seal the surgically induced tear in the parietal pleura . an alternative treatment is to ask the surgeon to plug the rent in the pleura with the help of omentum . although this may be time consuming , it has been successfully used by singhal et al . in our patient , however , the increasing airway pressures and rising etco2 levels made ventilation difficult , necessitating chest tube insertion before patient condition deteriorated further . although pneumoperitoneum was lost , surgeons were able to complete the surgery with lower iap using higher insufflation rate of co2 . to conclude , awareness of the risk and high index of suspicion for development of pneumothorax any sudden and brisk increase in these parameters should prompt a search for subcutaneous emphysema or pneumothorax .[/INST]giant paraesophageal hernia is an uncommon morbid disorder which may present a risk of catastrophic complications and should be repaired electively as soon as possible . laparoscopic fundoplication is the mainstay of surgical management of this disorder due to several advantages such as lower post - operative morbidity and pain . we report a case of a 70-year - old patient with a giant paraesophageal hernia , who developed subcutaneous emphysema with pneumothorax during laparoscopic fundoplication . early diagnosis was possible by close clinical evaluation and simultaneous monitoring of end - tidal carbon dioxide levels and airway pressures . although positive end - expiratory pressure application is an effective way of managing pneumothorax secondary to the passage of gas into the interpleural space , insertion of an intercostal drain may be used in an emergent situation .</s>

View photo . Singer Beyonce, center holding camera, walks with her husband, rapper Jay-Z, right of her, as they tour Old Havana, … Sure enough , Beyoncé and Jay-Z may have 99 problems but the State Department's Office of Foreign Assets Control (OFAC) Ain't One. OFAC, which enforces sanctions against Cuba, assured Republican Representatives Mario Diaz-Balart and Ileana Ros-Lehtinen in a letter Tuesday that the pop power-duo's recent trip to the island on their fifth anniversary had the governmental green light. The Florida lawmakers had written to the Treasury Department demanding to know whether the trip fell afoul of Cold War-era restrictions on Americans' travel to Cuba. "It is our understanding that the travelers in question traveled to Cuba pursuant to an educational exchange trip organized by a group authorized by OFAC to sponsor and organize programs to promote people-to-people contact in Cuba," Alastair Fitzpayne, Assistant Treasury Secretary for Legislative Affairs, wrote in the letter, which was obtained by Yahoo News. Fitzpayne, however, also seemed to put a little distance between OFAC and the globetrotting couple, who gave vast sums to President Barack Obama's reelection campaign. He noted that "organizations holding people-to-people licenses must certify in writing to OFAC that any travel that they conduct will consist of a full-time schedule of educational activities that will result in meaningful interaction between the travelers and individuals in Cuba." But OFAC "does not request the identities of the travelers on each trip," he said. Ros-Lehtinen was unimpressed. "If the tourist activities undertaken by Beyonce and Jay-Z in Cuba are classified as an educational exchange trip, then it is clear that the Obama Administration is not serious about denying the Castro regime an economic lifeline that US tourism will extend to it," the Cuban-born lawmaker said in a statement. "That was a wedding anniversary vacation that was not even disguised as a cultural program," Ros-Lehtinen said. "As more human rights activists engage in hunger strikes, I don't think they will see any evidence of how this scam endeavor will help them become independent of the regime." If you’re inclined to dig through Treasury's regulations, here they are, but it’s probably enough to say that, as part of a 60-year-old embargo imposed after Fidel Castro seized power, Americans aren’t supposed to go there. And lawmakers like Ros-Lehtinen and Diaz-Balart have denounced tourism in Cuba because it provides the Communist government there with sorely needed foreign currency. The embargo, first imposed by Dwight Eisenhower in 1960 and tightened by many of his successors, aimed to punish Castro’s government for nationalizing U.S. property, to dissuade other Latin American countries from following in Castro’s revolutionary footsteps, and, ultimately, to drive Castro from power. Tourism to Cuba -- notably from Europe and Canada -- has increased over the years as the island has seen the development of luxury hotels. Americans have been going there in larger numbers as well, and advice on how to go there illegally has proliferated online. With the Soviet Union long gone, Americans have also softened their support for the embargo. That's not to say that everyone approves. In March, Republican Senator Marco Rubio ripped American visitors to Cuba. "Cuba is not a zoo where you pay an admission ticket and you go in and you get to watch people living in cages to see how they are suffering," Rubio said in a speech. ||||| White House press secretary Jay Carney dismissed rapper Jay Z's claim that he spoke to the White House to get approval for a recent trip to Cuba. "I guess nothing rhymes with Treasury," Carney said during his daily briefing Thursday. As he said earlier in the week, Carney again said that the Treasury Department was responsible for approving the trip and said that "from the president on down," no one at the White House was involved in approving the trip. In a rap released Thursday, Jay-Z said: “I turned Havana into Atlanta…Boy from the hood, I got White House clearance…Obama said, ‘Chill, you gonna get me impeached. You don’t need this s—t anyway, chill with me on the beach.’” (PHOTOS: 10 lyrical shout-outs to Obama) When pressed on whether Obama spoke with Jay-Z about Cuba at all, Carney insisted he did not. "It’s a song," he said. "The president did not communicate with Jay-Z over this trip." Florida Republican lawmakers Sen. Marco Rubio and Reps. Mario Diaz-Balart and Ileana Ros-Lehtinen have critizied Jay-Z and Beyonce's trip to the communist island, and asked the administration to explain why they were allowed to go. Read more about: Jay Carney, Cuba, Jay-Z ||||| 5 years ago (CNN) – It seemed like White House Press Secretary Jay Carney was waiting for the question when he was asked Thursday about Jay-Z's newest rap, which focuses on his U.S. government-approved trip to Cuba with wife Beyonce last week. In the rap, Jay-Z suggested their clearance came from the White House, when it actually came from the Treasury Department. Follow @politicalticker "I turned Havana into Atlanta… Boy from the 'hood, I got White House clearance. ..Obama said 'chill you gonna get me impeached.' (But) you don't need this – expletive – anyway. Chill with me on the beach," the lyrics stated. In one of the most bizarre exchanges in the White House press briefing room, a reporter read the lyrics to Carney, asking about the White House approval. And Carney, without missing a beat, hit back. "I guess nothing rhymes with Treasury," he said. Treasury Secretary Jack Lew was nominated by President Barack Obama earlier year and subsequently confirmed by the Senate. (Actually, secretary kind of rhymes with treasury.) Pressed further on whether the president had a conversation with Jay-Z, Carney shot down the speculation. "I am absolutely saying that the White House and the president on down had nothing to do with anybody's personal, anybody's travel to Cuba," he said. "That is something the Treasury handles." Due to the U.S. government's travel embargo with Cuba, Americans are prohibited from visiting the communist country for tourism. U.S. citizens can apply for licenses to go anyway, provided they show substantial proof they intend to visit for specific reasons, such as for business or education. And they must also provide a detailed itinerary. After two members of Congress called for an investigation of the power couple's controversial trip and explanation of the type of travel license issued, the Treasury Department responded in a letter, giving more details about the licenses. "It is our understanding that the travelers in question traveled to Cuba pursuant to an educational exchange trip organized by a group authorized by OFAC [the Office of Foreign Assets Control] to sponsor and organize programs to promote people-to-people contact in Cuba," the letter read. - CNN's Ashley Killough, Kevin Liptak and Erin McPike contributed to this report.

– The flap over Jay-Z and Beyonce's trip to Cuba resulted in what has to be one of the odder exchanges in Jay Carney's tenure as White House spokesman. In this afternoon's news briefing, Donovan Slack of Politico noted that Jay-Z released a rap today in which he suggests that President Obama himself cleared the trip. Slack quoted the line in full: Jay-Z: "I turned Havana into Atlanta. Boy from the hood, I got White House clearance. Obama said chill, you gonna get me impeached. You don’t need this (expletive) anyway, chill with me on the beach." Credit Carney for a decent comeback: "I guess nothing rhymes with Treasury, because Treasury offers and gives licenses for travel, as you know, and the White House has nothing to do with it." (Treasury had cleared it as an "educational" trip, reports Yahoo News.) Pressed to clarify, Carney—now being called "Jay C" by headline writers—insisted that neither Obama nor anyone in the White House was involved. "It's a song, Donovan. The president did not communicate with Jay-Z over this trip."

<s>[INST]View photo . Singer Beyonce, center holding camera, walks with her husband, rapper Jay-Z, right of her, as they tour Old Havana, … Sure enough , Beyoncé and Jay-Z may have 99 problems but the State Department's Office of Foreign Assets Control (OFAC) Ain't One. OFAC, which enforces sanctions against Cuba, assured Republican Representatives Mario Diaz-Balart and Ileana Ros-Lehtinen in a letter Tuesday that the pop power-duo's recent trip to the island on their fifth anniversary had the governmental green light. The Florida lawmakers had written to the Treasury Department demanding to know whether the trip fell afoul of Cold War-era restrictions on Americans' travel to Cuba. "It is our understanding that the travelers in question traveled to Cuba pursuant to an educational exchange trip organized by a group authorized by OFAC to sponsor and organize programs to promote people-to-people contact in Cuba," Alastair Fitzpayne, Assistant Treasury Secretary for Legislative Affairs, wrote in the letter, which was obtained by Yahoo News. Fitzpayne, however, also seemed to put a little distance between OFAC and the globetrotting couple, who gave vast sums to President Barack Obama's reelection campaign. He noted that "organizations holding people-to-people licenses must certify in writing to OFAC that any travel that they conduct will consist of a full-time schedule of educational activities that will result in meaningful interaction between the travelers and individuals in Cuba." But OFAC "does not request the identities of the travelers on each trip," he said. Ros-Lehtinen was unimpressed. "If the tourist activities undertaken by Beyonce and Jay-Z in Cuba are classified as an educational exchange trip, then it is clear that the Obama Administration is not serious about denying the Castro regime an economic lifeline that US tourism will extend to it," the Cuban-born lawmaker said in a statement. "That was a wedding anniversary vacation that was not even disguised as a cultural program," Ros-Lehtinen said. "As more human rights activists engage in hunger strikes, I don't think they will see any evidence of how this scam endeavor will help them become independent of the regime." If you’re inclined to dig through Treasury's regulations, here they are, but it’s probably enough to say that, as part of a 60-year-old embargo imposed after Fidel Castro seized power, Americans aren’t supposed to go there. And lawmakers like Ros-Lehtinen and Diaz-Balart have denounced tourism in Cuba because it provides the Communist government there with sorely needed foreign currency. The embargo, first imposed by Dwight Eisenhower in 1960 and tightened by many of his successors, aimed to punish Castro’s government for nationalizing U.S. property, to dissuade other Latin American countries from following in Castro’s revolutionary footsteps, and, ultimately, to drive Castro from power. Tourism to Cuba -- notably from Europe and Canada -- has increased over the years as the island has seen the development of luxury hotels. Americans have been going there in larger numbers as well, and advice on how to go there illegally has proliferated online. With the Soviet Union long gone, Americans have also softened their support for the embargo. That's not to say that everyone approves. In March, Republican Senator Marco Rubio ripped American visitors to Cuba. "Cuba is not a zoo where you pay an admission ticket and you go in and you get to watch people living in cages to see how they are suffering," Rubio said in a speech. ||||| White House press secretary Jay Carney dismissed rapper Jay Z's claim that he spoke to the White House to get approval for a recent trip to Cuba. "I guess nothing rhymes with Treasury," Carney said during his daily briefing Thursday. As he said earlier in the week, Carney again said that the Treasury Department was responsible for approving the trip and said that "from the president on down," no one at the White House was involved in approving the trip. In a rap released Thursday, Jay-Z said: “I turned Havana into Atlanta…Boy from the hood, I got White House clearance…Obama said, ‘Chill, you gonna get me impeached. You don’t need this s—t anyway, chill with me on the beach.’” (PHOTOS: 10 lyrical shout-outs to Obama) When pressed on whether Obama spoke with Jay-Z about Cuba at all, Carney insisted he did not. "It’s a song," he said. "The president did not communicate with Jay-Z over this trip." Florida Republican lawmakers Sen. Marco Rubio and Reps. Mario Diaz-Balart and Ileana Ros-Lehtinen have critizied Jay-Z and Beyonce's trip to the communist island, and asked the administration to explain why they were allowed to go. Read more about: Jay Carney, Cuba, Jay-Z ||||| 5 years ago (CNN) – It seemed like White House Press Secretary Jay Carney was waiting for the question when he was asked Thursday about Jay-Z's newest rap, which focuses on his U.S. government-approved trip to Cuba with wife Beyonce last week. In the rap, Jay-Z suggested their clearance came from the White House, when it actually came from the Treasury Department. Follow @politicalticker "I turned Havana into Atlanta… Boy from the 'hood, I got White House clearance. ..Obama said 'chill you gonna get me impeached.' (But) you don't need this – expletive – anyway. Chill with me on the beach," the lyrics stated. In one of the most bizarre exchanges in the White House press briefing room, a reporter read the lyrics to Carney, asking about the White House approval. And Carney, without missing a beat, hit back. "I guess nothing rhymes with Treasury," he said. Treasury Secretary Jack Lew was nominated by President Barack Obama earlier year and subsequently confirmed by the Senate. (Actually, secretary kind of rhymes with treasury.) Pressed further on whether the president had a conversation with Jay-Z, Carney shot down the speculation. "I am absolutely saying that the White House and the president on down had nothing to do with anybody's personal, anybody's travel to Cuba," he said. "That is something the Treasury handles." Due to the U.S. government's travel embargo with Cuba, Americans are prohibited from visiting the communist country for tourism. U.S. citizens can apply for licenses to go anyway, provided they show substantial proof they intend to visit for specific reasons, such as for business or education. And they must also provide a detailed itinerary. After two members of Congress called for an investigation of the power couple's controversial trip and explanation of the type of travel license issued, the Treasury Department responded in a letter, giving more details about the licenses. "It is our understanding that the travelers in question traveled to Cuba pursuant to an educational exchange trip organized by a group authorized by OFAC [the Office of Foreign Assets Control] to sponsor and organize programs to promote people-to-people contact in Cuba," the letter read. - CNN's Ashley Killough, Kevin Liptak and Erin McPike contributed to this report.[/INST]– The flap over Jay-Z and Beyonce's trip to Cuba resulted in what has to be one of the odder exchanges in Jay Carney's tenure as White House spokesman. In this afternoon's news briefing, Donovan Slack of Politico noted that Jay-Z released a rap today in which he suggests that President Obama himself cleared the trip. Slack quoted the line in full: Jay-Z: "I turned Havana into Atlanta. Boy from the hood, I got White House clearance. Obama said chill, you gonna get me impeached. You don’t need this (expletive) anyway, chill with me on the beach." Credit Carney for a decent comeback: "I guess nothing rhymes with Treasury, because Treasury offers and gives licenses for travel, as you know, and the White House has nothing to do with it." (Treasury had cleared it as an "educational" trip, reports Yahoo News.) Pressed to clarify, Carney—now being called "Jay C" by headline writers—insisted that neither Obama nor anyone in the White House was involved. "It's a song, Donovan. The president did not communicate with Jay-Z over this trip."</s>

melatonin synthesis by the pineal gland represents one circadian rhythm controlled by the suprachiasmatic nuclei ( scn ) of the hypothalamus . the light - dark pattern incident on the retina sets the timing of the scn , which in turn restricts the timing of melatonin synthesis to the dark phase of the 24-hour cycle ( i.e. , during subjective night ) . across mammalian species , melatonin concentrations are highest at night irrespective of the photic niche of the animal nocturnal , crepuscular , or diurnal . with the exception of retinal light exposure , neither environmental ( e.g. , exercise , diet ) nor endogenous ( e.g. , sleep ) stimuli affect melatonin synthesis . in contrast to melatonin production , however , the timing of corticosteroid synthesis is closely related to the photic niche of the species , with peak levels occurring at the daily transition from quiescence to activity . thus , peak levels of corticosteroids in diurnal mammals occur in the morning , whereas peak levels occur in the evening for nocturnal mammals . the daily pattern of corticosteroid production is influenced by several interacting systems , only one of which is the master clock in the scn . recently , clow and colleagues proposed a three - part control mechanism for the cortisol awakening response ( car ) in humans . at least two of these three mechanisms are explicitly under the influence of the scn : a preawakening reduced sensitivity to adrenocorticotropic hormone ( acth ) and a postawakening enhanced sensitivity to acth . the third mechanism , influenced by the scn , is a light - sensitive sympathetic pathway to the adrenal that is independent of the pituitary [ 2 , 3 ] . although regulation of the adrenal is complex , with the multiple control mechanisms that can be differentially important to corticosteroid production , the scn plays an important role in anticipatory corticosteroid production . under natural conditions , one might expect a close correspondence between circadian time , as measured by a reliable marker like dim light melatonin onset ( dlmo ) phase , and the awakening time . in fact , burgess and eastman [ 5 , 6 ] as well as crowley and colleagues have shown that wake times and dlmo are correlated when participants are on an unrestricted schedule . on the other hand , wilhelm and colleagues have shown that car is relatively unaffected by circadian time . rather , they concluded that car is determined mainly by the act of awakening from sleep . nevertheless , these authors readily conceded that car has some relationship to circadian time because of the known neural ( albeit indirect ) connections between the scn and the adrenal and because empirical evidence demonstrates that the amplitude of the car varies with circadian time . the purpose of the present analysis was to examine the association of circadian phase ( measured from salivary dlmo time ) with the time of peak cortisol in the morning during a two - week study of late - sleeping young adults . this report is a secondary analysis of a parent study that tested the effects of an advanced sleep - wake schedule and a morning light exposure intervention on circadian phase advances . the protocol allowed us to examine car in young adults before and after an advance in the sleep - wake schedule and attempt to dissociate the influences of sleep timing and circadian phase on car . twenty - five participants ( ages 1830 ; mean standard deviation ( sd ) was 21.8 3.0 years ; 13 females ) who reported a misalignment between their self - reported sleep - wake times and their obligatory morning work or study schedules at least once per week completed the study . all participants were considered to be otherwise healthy and without any medical concern or drug use ; specific details regarding race , gender , psychological disorders , affect ( positive and negative ) , drug use , and bed times are provided in sharkey et al . . after a baseline week on their usual schedules , participants were placed on individualized sleep - wake schedules for another week . participants were instructed to maintain a strict phase - advanced , 7.5-hour sleep duration schedule for the second week of the experiment . they were required to be in bed , in the dark , and to try to sleep during the scheduled sleep times . the advanced schedules were designed to enable participants to meet their obligatory work or school commitments . participants were randomly assigned to receive morning blue - light or dim - light for the second week . both groups sat with a commercially available light - treatment device containing short - wavelength ( blue ) light - emitting diodes ( apollo p2 golite , philips respironics , pittsburgh , pa , usa ) . the blue - light group ( n = 12 ; 6 females ) faced the light - treatment device , receiving approximately 225 lux of short - wavelength light ( max 470 nm ; full width half maximum 20 nm ) at the corneas for one hour after rising in the morning , while the dim - light group ( n = 13 ; 7 females ) received less than 1 lux of the same blue light because the light - treatment device was positioned orthogonal to their line of gaze during the light exposure . the daysimeter is a headset device that is used to continuously measure circadian light , or cla , exposures . at the end of the baseline week and again following the postintervention week ( friday evenings ) , participants came to the laboratory for an overnight session that included evening saliva collection for circadian phase assessment ( dlmo ) and morning saliva collection for determining cortisol levels . the timing of evening saliva collection was determined by each participant 's predicted baseline dlmo phase , calculated from self - reported sleep schedules using the algorithm developed by burgess and eastman . participants used salivettes ( sarstedt , nmbrecht , germany ) to give 1 ml saliva samples for melatonin and cortisol assays . samples for melatonin assay were taken every 30 minutes from 3.5 hours before the predicted dlmo to 2 hours after predicted baseline dlmo . samples for cortisol assay were obtained immediately upon awakening and every subsequent hour for 4 hours . all saliva samples were frozen at 20c and were later radioimmunoassayed for evening melatonin and morning cortisol ( alpco , salem , nh , usa ) . this study was approved by the institutional review board ( irb ) at rhode island hospital and by the irb at rensselaer polytechnic institute ; participants were paid for their participation in the study . additional details of the study methods and results can be found in sharkey et al . . the area under the curve ( auc ) was calculated based on the method described by pruessner et al . whereby samples collected at 0 ( upon awakening ) , 60 , 120 , 180 , and 240 minutes postawakening are all included . dlmo phase and auc were subjected to mixed design ( 2 groups , dim - light and blue - light ) , repeated measures ( 2 weeks ) analyses of variance ( anovas ) ( pasw statistics , 18.0 ) . post hoc , two - tailed student 's t - tests were performed to test the main effects and interactions between the variables . regression analyses were performed to evaluate the associations among peak morning cortisol time , circadian phase ( dlmo time ) , and rising time . goodness of fit was evaluated using the r values and an f - test was used to check the statistical significance of the overall fit ( pasw statistics , 18.0 ) . home monitoring confirmed that all participants complied with the prescribed protocol ; those in the dim - light and blue - light groups followed instructions with regard to usage of the light - treatment device . based upon visual inspection of the actigraphy data , sleep logs , telephone call - ins to the laboratory , and self - reports , all participants went to bed and arose at the prescribed times and there was no evidence that participants awoke during the prescribed sleep opportunity period . as previously reported , the time of dlmo showed a significant main effect of weeks ( f1,23 = 61.4 , p < 0.001 ) , but the main effect of groups and the groups - by - weeks interaction were not statistically significant ( f1,23 = 1.27 , n.s . and , resp . ) . on average , both groups of subjects exhibited a 1.4 0.9 h phase advance of dlmo . the mean dlmo times for all subjects were 23 : 24 1 : 16 h after week 1 and 21 : 59 1 : 03 h after week 2 . the morning blue - light treatment did not differentially affect the time of dlmo during week 2 with respect to a dim - light exposure at the same time . we examined daily light exposures from the daysimeter for the two groups and found that they were not significantly different between groups . mixed design anovas using the total ( log ) circadian light ( cla ) exposures ( as detailed in ) showed no significant main effect of groups ( f1,22 = 0.059 , n.s . ) , of weeks ( f1,22 = 0.037 , n.s . ) , nor a significant groups - by - weeks interaction ( f1,22 = 0.134 , n.s . ) . figure 1 shows the mean morning cortisol concentrations obtained from both groups during both weeks . using auc as the dependent measure , we found a significant main effect of weeks ( f1,23 = 12.6 , p = 0.002 ) and a significant main effect of groups ( f1,23 = 15.9 , p = 0.001 ) , but the groups - by - weeks interaction was not statistically significant ( f1,23 = 3.3 , n.s . ) . during week 1 , the mean sd morning cortisol auc was 2.3 0.6 g / dl for the dim - light group and 1.5 0.5 g / dl for the blue - light group . during week 2 , the mean sd morning cortisol auc was 1.8 0.5 g / dl for the dim - light group and 1.3 0.2 g / dl for the blue - light group . linear regression analyses were used to test the strengths of associations among the measured times of peak cortisol concentration , rising , and dlmo . these associations are illustrated by the six plots in figure 2 for both study weeks . the maximum cortisol concentrations were obtained from participants one hour after rising 86% of the time . however , the peak cortisol concentration times obtained from one subject during the first baseline week was at 10:00 h , four hours after rising . it seems unlikely that morning peak cortisol levels would have occurred four hours after rising , particularly since the second highest cortisol concentration was one hour after rising for this subject , like the peak for nearly all of the other subjects during both study weeks . thus , the circled values in figure 2 from this one subject during the baseline week were omitted from the regression analyses . dlmo phase was significantly associated with peak cortisol concentration time on week 1 ( r = 0.28 ; f1,22 = 8.76 ; p = 0.007 ) but not on week 2 ( r = 0.12 ; f1,23 = 3.14 ; n.s . ) as shown in the top row of plots in figure 2 . peak cortisol concentration time was , however , strongly associated with rising time both on week 1 ( r = 0.86 ; f1,22 = 140 ; p < 0.0001 ) and on week 2 ( r = 0.85 ; f1,23 = 133 ; p < 0.0001 ) as shown in the second row of plots in figure 2 . the associations between rising time and dlmo phase for both weeks are shown in the bottom row of plots . on week 1 , the association was statistically significant ( r = 0.25 ; f1,22 = 7.18 ; p = 0.01 ) , while it was not on the week two ( r = 0.15 ; f1,23 = 4.11 ; n.s . ) . as implied by the findings from wilhelm and colleagues , the present study shows that the timing of morning peak cortisol secretion was more strongly associated with awakening than with circadian phase position , as measured by dlmo time . . showed a much higher correlation between rising time and dlmo phase than was shown here . both groups found a strong correlation between rising time and dlmo phase for subjects on unrestricted sleep schedules . importantly , however , both laboratories also found a lower correlation between rising time and dlmo phase for subjects on strict sleep schedules . this weak relationship between rising time and dlmo phase was also shown during the second week of the present study , consistent with these earlier findings [ 57 ] . since the relationship between dlmo phase and rising time is also relatively low , although statistically significant , during the first week of the present study , it is perhaps reasonable to infer that the subjects in the present study were not necessarily on a completely unrestricted sleep schedule . it will be recalled that these subjects were selected for participation in the study because their work and school schedules were sometimes at odds with their natural rising time . on the other hand , because of the sampling constraints for the study , intersubject sleep schedule variability may have been lower , thus reducing the correlation with dlmo phase due to restricted range . in other words , the advance in circadian phase during the second week could have systematically shifted the morning downward slope of cortisol concentration to an earlier time relative to the fixed waking schedule , resulting in lower cortisol auc between weeks . alternatively , habituation to the experiment and/or placing the subjects on a regular sleep - wake pattern during the second week may have reduced their stress levels with consequent lower cortisol auc between weeks . on the other hand , self - assessment questionnaires showed no evidence that subjects in either group reported a reduction in stress from already low values in the second week . an explanation for significant differences in cortisol auc between groups and study weeks remains unresolved . from a clinical perspective , notwithstanding the unresolved differences between morning cortisol levels in the two groups , these data and those by burgess and eastman and by crowley et al . suggest future research to determine whether it is important to coordinate personal light exposures with scheduled sleep . circadian phase is determined by the daily retinal light exposure , but the scheduled time of waking can be unrelated to daily light exposures . in general , and indeed as shown by sharkey and colleagues , changing sleep schedule will produce concomitant changes in the patterns of daily retinal light exposures . broadly then , adjusting bedtime and wake time will , albeit indirectly , affect circadian phase . once the first - order magnitude change in light patterns due to scheduling has adjusted circadian phase ( e.g. , changing time zones ) , idiosyncratic behavior , with opportunities for differences in personal retinal light exposures from both natural and electric lighting during waking hours , will undoubtedly produce second - order changes to circadian phase . viewing a sunrise one morning ( but not the next ) or reading in bed one evening ( but not the next ) can change a person 's circadian phase from one day to the next . rising according to a fixed schedule will not , therefore , be perfectly correlated with these second - order , idiosyncratic changes in circadian phase . consequently , the correlation between circadian phase ( dlmo ) and morning peak cortisol ( car ) would be expected to be , and indeed was in the present study , lower during the second week with fixed sleep schedules than during the first week with more whether this second - order misalignment between circadian phase and morning cortisol peak has clinical significance is unknown . as reported by sharkey and colleagues , there were no significant changes in the psychological well - being of subjects from the first week to the second week despite the drop in the correlation between dlmo and car . it remains a subject for future study to determine if misalignment between circadian phase and fixed rising times has clinical significance and , if it does , how that misalignment might be effectively and practically resolved with controlled light exposures . in summary , the present study demonstrates that rising time and peak cortisol concentration time , usually car , are closely related , whereas rising time and dlmo phase are less well - correlated , especially for individuals on restricted sleep schedules . thus , neither car nor rising time should be considered unambiguous markers of circadian phase , although rise times can be used to estimate a window within which sampling may detect dlmo phase . thus , the results of the present study are consistent with the findings from wilhelm et al . moreover , the recommendations put forward from the latter groups for estimating dlmo phase using rising time are applicable for individuals with either unrestricted or restricted sleep schedules , recognizing the larger uncertainty in those estimates for individuals in the latter group . finally , it would appear important for future clinical research to determine if it is necessary to be concerned with the misalignment of circadian phase and peak morning cortisol and , if it is important , how the light - dependent circadian phase can be controlled so that it can be coordinated with scheduled waking .

the present study was aimed at further elucidating the relationship between circadian phase , rising time , and the morning cortisol awakening response ( car ) . the results presented here are a secondary analysis of experimental data obtained from a study of advanced sleep - wake schedules and light exposures on circadian phase advances measured by dim - light melatonin onset ( dlmo ) . the present results demonstrate that morning car is strongly related to rising time and more weakly related to dlmo phase .

<s>[INST]melatonin synthesis by the pineal gland represents one circadian rhythm controlled by the suprachiasmatic nuclei ( scn ) of the hypothalamus . the light - dark pattern incident on the retina sets the timing of the scn , which in turn restricts the timing of melatonin synthesis to the dark phase of the 24-hour cycle ( i.e. , during subjective night ) . across mammalian species , melatonin concentrations are highest at night irrespective of the photic niche of the animal nocturnal , crepuscular , or diurnal . with the exception of retinal light exposure , neither environmental ( e.g. , exercise , diet ) nor endogenous ( e.g. , sleep ) stimuli affect melatonin synthesis . in contrast to melatonin production , however , the timing of corticosteroid synthesis is closely related to the photic niche of the species , with peak levels occurring at the daily transition from quiescence to activity . thus , peak levels of corticosteroids in diurnal mammals occur in the morning , whereas peak levels occur in the evening for nocturnal mammals . the daily pattern of corticosteroid production is influenced by several interacting systems , only one of which is the master clock in the scn . recently , clow and colleagues proposed a three - part control mechanism for the cortisol awakening response ( car ) in humans . at least two of these three mechanisms are explicitly under the influence of the scn : a preawakening reduced sensitivity to adrenocorticotropic hormone ( acth ) and a postawakening enhanced sensitivity to acth . the third mechanism , influenced by the scn , is a light - sensitive sympathetic pathway to the adrenal that is independent of the pituitary [ 2 , 3 ] . although regulation of the adrenal is complex , with the multiple control mechanisms that can be differentially important to corticosteroid production , the scn plays an important role in anticipatory corticosteroid production . under natural conditions , one might expect a close correspondence between circadian time , as measured by a reliable marker like dim light melatonin onset ( dlmo ) phase , and the awakening time . in fact , burgess and eastman [ 5 , 6 ] as well as crowley and colleagues have shown that wake times and dlmo are correlated when participants are on an unrestricted schedule . on the other hand , wilhelm and colleagues have shown that car is relatively unaffected by circadian time . rather , they concluded that car is determined mainly by the act of awakening from sleep . nevertheless , these authors readily conceded that car has some relationship to circadian time because of the known neural ( albeit indirect ) connections between the scn and the adrenal and because empirical evidence demonstrates that the amplitude of the car varies with circadian time . the purpose of the present analysis was to examine the association of circadian phase ( measured from salivary dlmo time ) with the time of peak cortisol in the morning during a two - week study of late - sleeping young adults . this report is a secondary analysis of a parent study that tested the effects of an advanced sleep - wake schedule and a morning light exposure intervention on circadian phase advances . the protocol allowed us to examine car in young adults before and after an advance in the sleep - wake schedule and attempt to dissociate the influences of sleep timing and circadian phase on car . twenty - five participants ( ages 1830 ; mean standard deviation ( sd ) was 21.8 3.0 years ; 13 females ) who reported a misalignment between their self - reported sleep - wake times and their obligatory morning work or study schedules at least once per week completed the study . all participants were considered to be otherwise healthy and without any medical concern or drug use ; specific details regarding race , gender , psychological disorders , affect ( positive and negative ) , drug use , and bed times are provided in sharkey et al . . after a baseline week on their usual schedules , participants were placed on individualized sleep - wake schedules for another week . participants were instructed to maintain a strict phase - advanced , 7.5-hour sleep duration schedule for the second week of the experiment . they were required to be in bed , in the dark , and to try to sleep during the scheduled sleep times . the advanced schedules were designed to enable participants to meet their obligatory work or school commitments . participants were randomly assigned to receive morning blue - light or dim - light for the second week . both groups sat with a commercially available light - treatment device containing short - wavelength ( blue ) light - emitting diodes ( apollo p2 golite , philips respironics , pittsburgh , pa , usa ) . the blue - light group ( n = 12 ; 6 females ) faced the light - treatment device , receiving approximately 225 lux of short - wavelength light ( max 470 nm ; full width half maximum 20 nm ) at the corneas for one hour after rising in the morning , while the dim - light group ( n = 13 ; 7 females ) received less than 1 lux of the same blue light because the light - treatment device was positioned orthogonal to their line of gaze during the light exposure . the daysimeter is a headset device that is used to continuously measure circadian light , or cla , exposures . at the end of the baseline week and again following the postintervention week ( friday evenings ) , participants came to the laboratory for an overnight session that included evening saliva collection for circadian phase assessment ( dlmo ) and morning saliva collection for determining cortisol levels . the timing of evening saliva collection was determined by each participant 's predicted baseline dlmo phase , calculated from self - reported sleep schedules using the algorithm developed by burgess and eastman . participants used salivettes ( sarstedt , nmbrecht , germany ) to give 1 ml saliva samples for melatonin and cortisol assays . samples for melatonin assay were taken every 30 minutes from 3.5 hours before the predicted dlmo to 2 hours after predicted baseline dlmo . samples for cortisol assay were obtained immediately upon awakening and every subsequent hour for 4 hours . all saliva samples were frozen at 20c and were later radioimmunoassayed for evening melatonin and morning cortisol ( alpco , salem , nh , usa ) . this study was approved by the institutional review board ( irb ) at rhode island hospital and by the irb at rensselaer polytechnic institute ; participants were paid for their participation in the study . additional details of the study methods and results can be found in sharkey et al . . the area under the curve ( auc ) was calculated based on the method described by pruessner et al . whereby samples collected at 0 ( upon awakening ) , 60 , 120 , 180 , and 240 minutes postawakening are all included . dlmo phase and auc were subjected to mixed design ( 2 groups , dim - light and blue - light ) , repeated measures ( 2 weeks ) analyses of variance ( anovas ) ( pasw statistics , 18.0 ) . post hoc , two - tailed student 's t - tests were performed to test the main effects and interactions between the variables . regression analyses were performed to evaluate the associations among peak morning cortisol time , circadian phase ( dlmo time ) , and rising time . goodness of fit was evaluated using the r values and an f - test was used to check the statistical significance of the overall fit ( pasw statistics , 18.0 ) . home monitoring confirmed that all participants complied with the prescribed protocol ; those in the dim - light and blue - light groups followed instructions with regard to usage of the light - treatment device . based upon visual inspection of the actigraphy data , sleep logs , telephone call - ins to the laboratory , and self - reports , all participants went to bed and arose at the prescribed times and there was no evidence that participants awoke during the prescribed sleep opportunity period . as previously reported , the time of dlmo showed a significant main effect of weeks ( f1,23 = 61.4 , p < 0.001 ) , but the main effect of groups and the groups - by - weeks interaction were not statistically significant ( f1,23 = 1.27 , n.s . and , resp . ) . on average , both groups of subjects exhibited a 1.4 0.9 h phase advance of dlmo . the mean dlmo times for all subjects were 23 : 24 1 : 16 h after week 1 and 21 : 59 1 : 03 h after week 2 . the morning blue - light treatment did not differentially affect the time of dlmo during week 2 with respect to a dim - light exposure at the same time . we examined daily light exposures from the daysimeter for the two groups and found that they were not significantly different between groups . mixed design anovas using the total ( log ) circadian light ( cla ) exposures ( as detailed in ) showed no significant main effect of groups ( f1,22 = 0.059 , n.s . ) , of weeks ( f1,22 = 0.037 , n.s . ) , nor a significant groups - by - weeks interaction ( f1,22 = 0.134 , n.s . ) . figure 1 shows the mean morning cortisol concentrations obtained from both groups during both weeks . using auc as the dependent measure , we found a significant main effect of weeks ( f1,23 = 12.6 , p = 0.002 ) and a significant main effect of groups ( f1,23 = 15.9 , p = 0.001 ) , but the groups - by - weeks interaction was not statistically significant ( f1,23 = 3.3 , n.s . ) . during week 1 , the mean sd morning cortisol auc was 2.3 0.6 g / dl for the dim - light group and 1.5 0.5 g / dl for the blue - light group . during week 2 , the mean sd morning cortisol auc was 1.8 0.5 g / dl for the dim - light group and 1.3 0.2 g / dl for the blue - light group . linear regression analyses were used to test the strengths of associations among the measured times of peak cortisol concentration , rising , and dlmo . these associations are illustrated by the six plots in figure 2 for both study weeks . the maximum cortisol concentrations were obtained from participants one hour after rising 86% of the time . however , the peak cortisol concentration times obtained from one subject during the first baseline week was at 10:00 h , four hours after rising . it seems unlikely that morning peak cortisol levels would have occurred four hours after rising , particularly since the second highest cortisol concentration was one hour after rising for this subject , like the peak for nearly all of the other subjects during both study weeks . thus , the circled values in figure 2 from this one subject during the baseline week were omitted from the regression analyses . dlmo phase was significantly associated with peak cortisol concentration time on week 1 ( r = 0.28 ; f1,22 = 8.76 ; p = 0.007 ) but not on week 2 ( r = 0.12 ; f1,23 = 3.14 ; n.s . ) as shown in the top row of plots in figure 2 . peak cortisol concentration time was , however , strongly associated with rising time both on week 1 ( r = 0.86 ; f1,22 = 140 ; p < 0.0001 ) and on week 2 ( r = 0.85 ; f1,23 = 133 ; p < 0.0001 ) as shown in the second row of plots in figure 2 . the associations between rising time and dlmo phase for both weeks are shown in the bottom row of plots . on week 1 , the association was statistically significant ( r = 0.25 ; f1,22 = 7.18 ; p = 0.01 ) , while it was not on the week two ( r = 0.15 ; f1,23 = 4.11 ; n.s . ) . as implied by the findings from wilhelm and colleagues , the present study shows that the timing of morning peak cortisol secretion was more strongly associated with awakening than with circadian phase position , as measured by dlmo time . . showed a much higher correlation between rising time and dlmo phase than was shown here . both groups found a strong correlation between rising time and dlmo phase for subjects on unrestricted sleep schedules . importantly , however , both laboratories also found a lower correlation between rising time and dlmo phase for subjects on strict sleep schedules . this weak relationship between rising time and dlmo phase was also shown during the second week of the present study , consistent with these earlier findings [ 57 ] . since the relationship between dlmo phase and rising time is also relatively low , although statistically significant , during the first week of the present study , it is perhaps reasonable to infer that the subjects in the present study were not necessarily on a completely unrestricted sleep schedule . it will be recalled that these subjects were selected for participation in the study because their work and school schedules were sometimes at odds with their natural rising time . on the other hand , because of the sampling constraints for the study , intersubject sleep schedule variability may have been lower , thus reducing the correlation with dlmo phase due to restricted range . in other words , the advance in circadian phase during the second week could have systematically shifted the morning downward slope of cortisol concentration to an earlier time relative to the fixed waking schedule , resulting in lower cortisol auc between weeks . alternatively , habituation to the experiment and/or placing the subjects on a regular sleep - wake pattern during the second week may have reduced their stress levels with consequent lower cortisol auc between weeks . on the other hand , self - assessment questionnaires showed no evidence that subjects in either group reported a reduction in stress from already low values in the second week . an explanation for significant differences in cortisol auc between groups and study weeks remains unresolved . from a clinical perspective , notwithstanding the unresolved differences between morning cortisol levels in the two groups , these data and those by burgess and eastman and by crowley et al . suggest future research to determine whether it is important to coordinate personal light exposures with scheduled sleep . circadian phase is determined by the daily retinal light exposure , but the scheduled time of waking can be unrelated to daily light exposures . in general , and indeed as shown by sharkey and colleagues , changing sleep schedule will produce concomitant changes in the patterns of daily retinal light exposures . broadly then , adjusting bedtime and wake time will , albeit indirectly , affect circadian phase . once the first - order magnitude change in light patterns due to scheduling has adjusted circadian phase ( e.g. , changing time zones ) , idiosyncratic behavior , with opportunities for differences in personal retinal light exposures from both natural and electric lighting during waking hours , will undoubtedly produce second - order changes to circadian phase . viewing a sunrise one morning ( but not the next ) or reading in bed one evening ( but not the next ) can change a person 's circadian phase from one day to the next . rising according to a fixed schedule will not , therefore , be perfectly correlated with these second - order , idiosyncratic changes in circadian phase . consequently , the correlation between circadian phase ( dlmo ) and morning peak cortisol ( car ) would be expected to be , and indeed was in the present study , lower during the second week with fixed sleep schedules than during the first week with more whether this second - order misalignment between circadian phase and morning cortisol peak has clinical significance is unknown . as reported by sharkey and colleagues , there were no significant changes in the psychological well - being of subjects from the first week to the second week despite the drop in the correlation between dlmo and car . it remains a subject for future study to determine if misalignment between circadian phase and fixed rising times has clinical significance and , if it does , how that misalignment might be effectively and practically resolved with controlled light exposures . in summary , the present study demonstrates that rising time and peak cortisol concentration time , usually car , are closely related , whereas rising time and dlmo phase are less well - correlated , especially for individuals on restricted sleep schedules . thus , neither car nor rising time should be considered unambiguous markers of circadian phase , although rise times can be used to estimate a window within which sampling may detect dlmo phase . thus , the results of the present study are consistent with the findings from wilhelm et al . moreover , the recommendations put forward from the latter groups for estimating dlmo phase using rising time are applicable for individuals with either unrestricted or restricted sleep schedules , recognizing the larger uncertainty in those estimates for individuals in the latter group . finally , it would appear important for future clinical research to determine if it is necessary to be concerned with the misalignment of circadian phase and peak morning cortisol and , if it is important , how the light - dependent circadian phase can be controlled so that it can be coordinated with scheduled waking .[/INST]the present study was aimed at further elucidating the relationship between circadian phase , rising time , and the morning cortisol awakening response ( car ) . the results presented here are a secondary analysis of experimental data obtained from a study of advanced sleep - wake schedules and light exposures on circadian phase advances measured by dim - light melatonin onset ( dlmo ) . the present results demonstrate that morning car is strongly related to rising time and more weakly related to dlmo phase .</s>

SEC. 1. SHORT TITLE. This Act may be cited as the ``Las Vegas Wash Wetlands Restoration and Lake Mead Water Quality Improvement Act of 2000''. SEC. 2. FINDINGS AND PURPOSES. (a) Findings.--Congress finds that-- (1) the Las Vegas Wash is a significant ecosystem of desert wetland created by treated effluent return flows, urban runoff, and flood events from the Las Vegas Valley; (2) a healthy wetland ecosystem in the Las Vegas Wash would improve water quality in the Las Vegas Bay, the Lake Mead National Recreation Area, and the lower Colorado River, which is critical habitat for endangered and threatened fish and wildlife populations; (3) the Secretary of the Interior delivers municipal, industrial, and agricultural water from the Colorado River to millions of people in Nevada, Arizona, and California; (4) a significant concern relating to water quality in Lake Mead is the transmission of contaminants to the Colorado River through the Las Vegas Wash from shallow ground water seepage originating at an industrial complex located in the southeast part of the Las Vegas Valley, Nevada; (5) such industrial complex was constructed by the Federal Government during World War II to manufacture products required by the Department of Defense, including perchlorate, which is an essential component of rocket fuel used exclusively by the Federal Government; (6) over the past 20 years the Las Vegas Wash wetland has been significantly eroded and deteriorated by flash floods, increasing treated effluent flows, urban runoff, and polluted shallow groundwater seepage; (7) the loss of the Las Vegas Wash wetland is having an adverse impact on wildlife habitat; (8) the Las Vegas Wash wetland is a unique opportunity to experience a wetland environment providing educational, cultural, environmental, and recreation benefits to the community of southern Nevada; (9) as recommended by a citizens' water quality advisory committee in 1998, the Las Vegas Wash Coordination Committee, including Federal, State, and local agencies, was formed to establish a comprehensive adaptive management plan for the Las Vegas Wash wetland; (10) from 1998 to 1999, the Committee engaged in an extensive public process to evaluate the multifaceted challenges associated with the restoration of the Las Vegas Wash wetland; (11) in October of 1999, the Committee initiated a process for public comment on a comprehensive adaptive management plan; (12) in January 2000, the adaptive management plan was approved by the Board of the Southern Nevada Water Authority, which is the coordinating agency for the Committee; and (13) the adaptive management plan calls for a partnership among Federal, State and local agencies with an interest in Las Vegas Wash wetland. (b) Purposes.--The purposes of this Act are-- (1) to recognize the importance of the restoration of the Las Vegas Wash wetland to water quality in the Colorado River and a desert wetland ecosystem; (2) to direct the affected Federal agencies to participate constructively in the implementation of the Las Vegas Wash Wetland Restoration and Lake Mead Water Quality Improvement Project under the comprehensive adaptive management plan; and (3) to authorize such sums as are necessary for the affected Federal agencies to carry out specific tasks required by the Project in partnership with the authority and other State and local agencies involved in the Las Vegas Wash Coordination Committee. SEC. 3. DEFINITIONS. In this Act, the following definitions apply: (1) Authority.--The term ``Authority'' means the Southern Nevada Water Authority, organized under the law of the State of Nevada. (2) Committee.--The term ``Committee'' means the 28-member Las Vegas Wash Coordination Committee, including representatives of-- (A) the Army Corps of Engineers; (B) the Environmental Protection Agency; (C) the United States Fish and Wildlife Service; (D) the National Park Service; (E) the Bureau of Reclamation; (F) the Natural Resources Conservation Service; (G) the Southern Nevada Water Authority; (H) the Nevada Division of Environmental Protection, Clark County, Nevada (including the Clark County Department of Parks and Recreation); (I) the Clark County Sanitation District; (J) the cities of Las Vegas, North Las Vegas, and Henderson, Nevada; (K) the Clark County Regional Flood Control District; (L) other Federal, State, and local agencies; (M) environmental groups; and (N) private citizens. (3) Project.-- (A) In general.--The term ``Project'' means the Las Vegas Wash Wetlands Restoration and Lake Mead Water Quality Improvement Project. (B) Inclusions.--Such term includes the programs, features, components, projects, and activities identified in the Comprehensive Adaptive Management Plan for the Las Vegas Wash developed by the Committee and dated January 20, 2000. SEC. 4. PARTICIPATION IN THE PROJECT. (a) In General.--In addition to any other authority granted under Federal law, the Secretary of the Army, the Administrator of the Environmental Protection Agency, the Secretary of Agriculture, and the Secretary of the Interior may participate in the continued development and implementation of the Project. (b) Federal Assistance.--The Secretary of the Army, the Administrator of the Environmental Protection Agency, and the Secretary of the Interior shall provide with respect to the Project such technical assistance, interagency coordination, and funding for-- (1) the collection and modeling of hydrologic data for water quality; and (2) the design and construction of-- (A) erosion control facilities; (B) wetland restoration features; (C) ground water interdiction facilities; (D) treated effluent transport diffusion and reuse features; (E) water quality improvement facilities; and (F) any other project features developed under the Las Vegas Wash Comprehensive Adaptive Management Plan. (c) Authorization of Appropriations.--There are authorized to be appropriated such sums as may be necessary to carry out this Act.

Directs the Administrator and the Secretaries of the Army and Interior to provide, with respect to the Project, technical assistance, interagency coordination, and funding for: (1) the collection and modeling of hydrologic data for water quality; and (2) the design and construction of erosion control facilities, wetland restoration features, ground water interdiction facilities, treated effluent transport diffusion and reuse features, water quality improvement facilities, and other project features developed under the Las Vegas Wash Comprehensive Adaptive Management Plan. Authorizes appropriations.

<s>[INST]SEC. 1. SHORT TITLE. This Act may be cited as the ``Las Vegas Wash Wetlands Restoration and Lake Mead Water Quality Improvement Act of 2000''. SEC. 2. FINDINGS AND PURPOSES. (a) Findings.--Congress finds that-- (1) the Las Vegas Wash is a significant ecosystem of desert wetland created by treated effluent return flows, urban runoff, and flood events from the Las Vegas Valley; (2) a healthy wetland ecosystem in the Las Vegas Wash would improve water quality in the Las Vegas Bay, the Lake Mead National Recreation Area, and the lower Colorado River, which is critical habitat for endangered and threatened fish and wildlife populations; (3) the Secretary of the Interior delivers municipal, industrial, and agricultural water from the Colorado River to millions of people in Nevada, Arizona, and California; (4) a significant concern relating to water quality in Lake Mead is the transmission of contaminants to the Colorado River through the Las Vegas Wash from shallow ground water seepage originating at an industrial complex located in the southeast part of the Las Vegas Valley, Nevada; (5) such industrial complex was constructed by the Federal Government during World War II to manufacture products required by the Department of Defense, including perchlorate, which is an essential component of rocket fuel used exclusively by the Federal Government; (6) over the past 20 years the Las Vegas Wash wetland has been significantly eroded and deteriorated by flash floods, increasing treated effluent flows, urban runoff, and polluted shallow groundwater seepage; (7) the loss of the Las Vegas Wash wetland is having an adverse impact on wildlife habitat; (8) the Las Vegas Wash wetland is a unique opportunity to experience a wetland environment providing educational, cultural, environmental, and recreation benefits to the community of southern Nevada; (9) as recommended by a citizens' water quality advisory committee in 1998, the Las Vegas Wash Coordination Committee, including Federal, State, and local agencies, was formed to establish a comprehensive adaptive management plan for the Las Vegas Wash wetland; (10) from 1998 to 1999, the Committee engaged in an extensive public process to evaluate the multifaceted challenges associated with the restoration of the Las Vegas Wash wetland; (11) in October of 1999, the Committee initiated a process for public comment on a comprehensive adaptive management plan; (12) in January 2000, the adaptive management plan was approved by the Board of the Southern Nevada Water Authority, which is the coordinating agency for the Committee; and (13) the adaptive management plan calls for a partnership among Federal, State and local agencies with an interest in Las Vegas Wash wetland. (b) Purposes.--The purposes of this Act are-- (1) to recognize the importance of the restoration of the Las Vegas Wash wetland to water quality in the Colorado River and a desert wetland ecosystem; (2) to direct the affected Federal agencies to participate constructively in the implementation of the Las Vegas Wash Wetland Restoration and Lake Mead Water Quality Improvement Project under the comprehensive adaptive management plan; and (3) to authorize such sums as are necessary for the affected Federal agencies to carry out specific tasks required by the Project in partnership with the authority and other State and local agencies involved in the Las Vegas Wash Coordination Committee. SEC. 3. DEFINITIONS. In this Act, the following definitions apply: (1) Authority.--The term ``Authority'' means the Southern Nevada Water Authority, organized under the law of the State of Nevada. (2) Committee.--The term ``Committee'' means the 28-member Las Vegas Wash Coordination Committee, including representatives of-- (A) the Army Corps of Engineers; (B) the Environmental Protection Agency; (C) the United States Fish and Wildlife Service; (D) the National Park Service; (E) the Bureau of Reclamation; (F) the Natural Resources Conservation Service; (G) the Southern Nevada Water Authority; (H) the Nevada Division of Environmental Protection, Clark County, Nevada (including the Clark County Department of Parks and Recreation); (I) the Clark County Sanitation District; (J) the cities of Las Vegas, North Las Vegas, and Henderson, Nevada; (K) the Clark County Regional Flood Control District; (L) other Federal, State, and local agencies; (M) environmental groups; and (N) private citizens. (3) Project.-- (A) In general.--The term ``Project'' means the Las Vegas Wash Wetlands Restoration and Lake Mead Water Quality Improvement Project. (B) Inclusions.--Such term includes the programs, features, components, projects, and activities identified in the Comprehensive Adaptive Management Plan for the Las Vegas Wash developed by the Committee and dated January 20, 2000. SEC. 4. PARTICIPATION IN THE PROJECT. (a) In General.--In addition to any other authority granted under Federal law, the Secretary of the Army, the Administrator of the Environmental Protection Agency, the Secretary of Agriculture, and the Secretary of the Interior may participate in the continued development and implementation of the Project. (b) Federal Assistance.--The Secretary of the Army, the Administrator of the Environmental Protection Agency, and the Secretary of the Interior shall provide with respect to the Project such technical assistance, interagency coordination, and funding for-- (1) the collection and modeling of hydrologic data for water quality; and (2) the design and construction of-- (A) erosion control facilities; (B) wetland restoration features; (C) ground water interdiction facilities; (D) treated effluent transport diffusion and reuse features; (E) water quality improvement facilities; and (F) any other project features developed under the Las Vegas Wash Comprehensive Adaptive Management Plan. (c) Authorization of Appropriations.--There are authorized to be appropriated such sums as may be necessary to carry out this Act.[/INST]Directs the Administrator and the Secretaries of the Army and Interior to provide, with respect to the Project, technical assistance, interagency coordination, and funding for: (1) the collection and modeling of hydrologic data for water quality; and (2) the design and construction of erosion control facilities, wetland restoration features, ground water interdiction facilities, treated effluent transport diffusion and reuse features, water quality improvement facilities, and other project features developed under the Las Vegas Wash Comprehensive Adaptive Management Plan. Authorizes appropriations.</s>

abnormal fetal growth is associated with multiple adverse outcomes for the mother and the newborn , such as perinatal morbidities , developmental disorders , and learning disabilities.1 abnormal fetal growth is usually assessed through multiple indices , including low birth weight ( lbw ) , small size relative to gestational age , macrosomia , and prematurity . high parity ( hp ) , defined as having 5 pregnancies of 20 weeks of gestation , is among various risk factors which have been hypothesized for fetal growth abnormalities . 2 although hp has been recognized to be a potential risk factor for abnormal fetal growth , the exact etiological mechanism is not well understood . studies investigating whether increasing parity has an adverse effect on fetal growth have yielded inconsistent results . some studies have confirmed a negative effect evidenced by lbw and prematurity,35 while others revealed no association or even an increased frequency of macrosomia.6,7 this inconsistency has been attributed , among other factors , to inadequate sampling of high parity women , especially in developed countries , as well as failure to adequately adjust for strong confounders . hp is rarely seen in developed countries due to the widespread use of contraceptive measures and family planning . nonetheless , it is still common in many developing countries , especially in the arab world where a cultural preference for larger families is still prevalent.2 oman , an arab country characterized by an especially high birthrate,8 was accordingly selected as an ideal location for a new study that aims to investigate the association between high parity and three fetal growth indices : lbw , prematurity , and macrosomia . this population - based retrospective cohort study was conducted from january 2006 to august 2006 in bidbid , a city located about 30 kilometers west of muscat , the capital of oman . bidbid was also the catchment population for an ongoing community trial entitled delaying the development of diabetes mellitus type 2 in oman , also known as the amal study . this community trial , which was conducted from 2004 through 2008 , aimed to estimate the prevalence of prediabetes among adults in bidbid and to apply appropriate interventions to prevent the occurrence of diabetes . the study was approved by the medical research and ethics committee at sultan qaboos university . the target population for the present study consisted of 541 parous women who had previously enrolled in the amal study . of those women , the enrolled women had a total of 1,939 singleton pregnancies during the duration of the study . miscarriages , twin pregnancies , and pregnancies of less than 20 weeks of gestation were excluded . information about parity , lbw , and associated factors was obtained from maternal health cards which recorded salient information for each pregnancy , such as sociodemographic data , prepregnancy risk factors , obstetric and medical history , clinical findings at each antenatal visit , investigations , details of delivery , and postnatal findings . parity was defined both dichotomously ( < 5 , 5 ) and by multiple categories ( 1 , 23 , 45 , 67 , 89 , and 10 ) . lbw was defined as < 2500 g. individual pregnancies , rather than women , were the unit of analysis for this study , with the cumulative incidence of lbw reported per 100 pregnancies . outcomes of interest were : ( 1 ) lbw ( defined as < 2500 g ) . ( 2 ) macrosomia ( defined as > 4000 g ) , and ( 3 ) prematurity ( defined as < 37 weeks of gestation ) . multilevel logistic regression ( mllr ) analysis was used to assess the effect of parity on the aforementioned outcomes . multilevel regression modeling was preferred over conventional regression due to its ability to adjust for the dependency that exists among same - woman pregnancies.9 two series of mllr were conducted in order to separately assess both dichotomous parity and categorical parity . two sets of subanalyses were conducted within each series : a crude model and an adjusted model . in the crude model , parity was treated as the only predictor of occurrence of lbw . in the adjusted model , adjustment was made for the following confounders : maternal age , educational status of mothers , family income , past history of lbw , and year of delivery . similar crude and adjusted models were generated for the other outcomes : prematurity and macrosomia . the trend of association between categorical parity and outcomes was tested using the cochran armitage test for trend , and a cutoff value for statistical significance was taken at p < 0.05 . chi - square analyses were used to evaluate the statistical significance of differences among proportions of categorical data . the nonparametric fisher s exact test ( two - tailed ) replaced the chi - square test in cases of small sample size where the expected frequency was less than 5 in any of the cells in 2 2 tables . all statistical analyses were performed using sas software ( version 9.1 ; sas institute , cary , nc ) . a total of 1939 pregnancies were enumerated of which 944 ( 48.7% ) were hp and 995 ( 51.3% ) were low parity ( lp ) . table 1 compares lp and hp pregnancies with respect to important baseline characteristics existing at the beginning of each pregnancy . compared to lp pregnancies , hp pregnancies were shown to be associated with the following maternal characteristics : older age , higher body mass index ( bmi ) , illiteracy , higher family income , and increased frequency of both lbw and gestational diabetes mellitus . frequencies of recorded newborns with disease outcomes of interest were as follows : 191 lbw , 69 prematurity , and 34 macrosomia . fewer cases of lbw ( 80 vs 111 ) and prematurity ( 28 vs 41 ) were documented among hp pregnancies as compared to lp pregnancies . thus , the incidence of lbw among hp pregnancies ( 8.5 per 100 pregnancies ; 80/944 ) was lower than among lp pregnancies ( 11.1 per 100 pregnancies ; 111/995 ) . the difference in incidence risk of lbw was not statistically significant ( p = 0.06 ) . hp pregnancies also had a lower incidence of prematurity ( 3.0 per 100 pregnancies ; 28/944 ) than lp pregnancies ( 4.1 per 100 pregnancies ; 41/995 ) , and the difference was not statistically significant ( p = 0.26 ) . more macrosomia cases occurred among hp pregnancies ( 22 vs 12 ) , yielding a higher incidence of macrosomia among hp pregnancies ( 2.3 per 100 pregnancies ; 22/944 ) than lp pregnancies ( 1.2 per 100 pregnancies ; 12/995 ) , but the difference was not statistically significant ( p = 0.61 ) . hp pregnancies exhibited a 24% reduction in the risk of lbw ( relative risk [ rr ] = 0.76 ; 95% confidence interval [ ci ] : 0.441.1 ) and an 18% reduction in risk of prematurity ( rr = 0.82 ; 95% ci : 0.541.27 ) relative to lp pregnancies . additionally , the risk of having a macrosomic baby was higher among hp pregnancies ( rr = 1.8 ; 95% ci : 1.22.4 ) . using parity of 23 as the reference category , the adjusted mllr model revealed a preventive dose - response relation between parity and the risk of both lbw and prematurity ( trend , p = 0.04 ) . the adjusted rr sequence also showed a correlation between increasing parity and elevated risk of macrosomia , but with a plateau trend rather than a dose - response relation ( trend , p = 0.37 ) . this retrospective population - based cohort study explored whether parity has an effect on the occurrence of lbw , prematurity , and macrosomia . the results showed that higher parity was positively associated with macrosomia and negatively associated with both lbw and prematurity . primiparity was found to be associated with an increased risk of lbw compared to multiparity . the increased risk of lbw among primiparous women may be explained by the lower average age of primiparous women , which is known to be associated with greater risk of both prematurity and pre - eclampsia ; the latter also necessitating delivery before term.10,11 for multiparous pregnancies , higher parity was found to be associated with a decreased risk of lbw in a negative dose - response fashion . this finding may be explained by the association between higher parity and maternal hyperglycemia , which tends to result in higher birth weight.12 although the overall trend suggested reduction in risk of lbw as parity increases , it is worth mentioning that the reduction in risk of lbw in each subcategory of parity was not statistically significant , and this might be attributed to statistical instability caused by a small category - specific sample size . these results are in line with previous studies reporting that high parity is associated with a decreased risk of lbw and an increased risk of macrosomia.3,1315 for example , a prospective cohort study of 1098 pregnancies in finland found a steady increase in average birth weight in correlation with higher parity.12 other studies have found high parity to be associated with an increased risk of lbw;35 however , at least some of these results have been attributed to placental complications such as atresia or abruption . thus , their apparent disagreement with the present study s results might be due to the absence of this factor . others reporting conflicting results have postulated that observed elevations of the risk of lbw were caused by the additional domestic workload undertaken by women , along with each additional child.16 we do not reach a similar conclusion , despite the fact that the majority of pregnancies included in the present study were among illiterate women from low- or middle - income families with extensive domestic responsibilities . this study s use of prospectively documented data among a population with an overall prevalence of hp is one of its strengths . this feature substantially increased the statistical stability of the data notwithstanding the need to adjust for multiple confounders within smaller subcategories . a possible residual confounder is the nutritional status of the women , as sufficient information to adjust for this factor was not available . with estimates as high as 27.6% , oman has the second highest annual incidence proportion of hp pregnancies in the world ( after the united arab emirates),2 as well as the highest reported incidence proportion of extreme parity ( 10 ) in the world ( 11.3%).17 several explanations have been proposed for these high figures , including limited use of contraceptive measures , cultural idealization of large family size , suboptimal female education , and shortcomings in the implementation of the national birth spacing policy . local attitudes towards and limitations of family planning are illustrated by a survey which estimated that the prevalence of contraceptive use among omani women is only 12.7% , and only 64.3% of users believed contraceptives were desirable.18 another survey of omani high school students reported that around 43% of boys and 20.8% of girls stated a preference to have six or more children in the future.19 this indicates that widespread hp is likely to remain the status quo , even among younger , more educated generations . given such high rates of hp in oman , it is especially important for the local medical community to understand its potential health impacts in order to provide better health services for multiparous women and their children . in conclusion , this study provides evidence that high parity is associated with a lower risk of lbw and prematurity as well as a higher risk of macrosomia . these results could be usefully considered in designing effective national health policy programs aimed at improving the health of mothers and children in oman and similar populations . these results can be used to address more targeted family planning programs at the local community level . for example , the observed increased risk of macrosomia can be used to educate women who are at risk of having macrosomic babies because of predisposing conditions such as diabetes mellitus . these findings should not be interpreted in isolation from other potential consequences of high parity . further studies are needed to explore , for example , the social and economic effects of larger nuclear family size on both mothers and their families .

the objective of this retrospective cohort study was to explore the potential causal relation between parity and fetal growth indices , including low birth weight ( lbw ) , macrosomia , and prematurity . the study was nested on a community trial in a city in oman . the study analyzed 1939 pregnancies among 479 participants . of these , 944 pregnancies ( 48.7% ) were high parity ( 5 ) . obtained newborns with outcomes of interest were as follows : 191 lbw , 34 macrosomic , and 69 premature . associations were measured using multilevel logistic regression modeling . compared to low parity ( lp , defined as < 5 ) , high parity was found to be associated with less risk of lbw ( relative risk [ rr ] = 0.76 ; 95% confidence interval [ ci ] : 0.441.1 ) and prematurity ( rr = 0.82 ; 95% ci : 0.541.27 ) , but greater risk of macrosomia ( rr = 1.8 ; 95% ci : 1.22.4 ) . this study provides evidence that with increasing parity , risks of lbw and prematurity decrease , while risk of macrosomia increases .

<s>[INST]abnormal fetal growth is associated with multiple adverse outcomes for the mother and the newborn , such as perinatal morbidities , developmental disorders , and learning disabilities.1 abnormal fetal growth is usually assessed through multiple indices , including low birth weight ( lbw ) , small size relative to gestational age , macrosomia , and prematurity . high parity ( hp ) , defined as having 5 pregnancies of 20 weeks of gestation , is among various risk factors which have been hypothesized for fetal growth abnormalities . 2 although hp has been recognized to be a potential risk factor for abnormal fetal growth , the exact etiological mechanism is not well understood . studies investigating whether increasing parity has an adverse effect on fetal growth have yielded inconsistent results . some studies have confirmed a negative effect evidenced by lbw and prematurity,35 while others revealed no association or even an increased frequency of macrosomia.6,7 this inconsistency has been attributed , among other factors , to inadequate sampling of high parity women , especially in developed countries , as well as failure to adequately adjust for strong confounders . hp is rarely seen in developed countries due to the widespread use of contraceptive measures and family planning . nonetheless , it is still common in many developing countries , especially in the arab world where a cultural preference for larger families is still prevalent.2 oman , an arab country characterized by an especially high birthrate,8 was accordingly selected as an ideal location for a new study that aims to investigate the association between high parity and three fetal growth indices : lbw , prematurity , and macrosomia . this population - based retrospective cohort study was conducted from january 2006 to august 2006 in bidbid , a city located about 30 kilometers west of muscat , the capital of oman . bidbid was also the catchment population for an ongoing community trial entitled delaying the development of diabetes mellitus type 2 in oman , also known as the amal study . this community trial , which was conducted from 2004 through 2008 , aimed to estimate the prevalence of prediabetes among adults in bidbid and to apply appropriate interventions to prevent the occurrence of diabetes . the study was approved by the medical research and ethics committee at sultan qaboos university . the target population for the present study consisted of 541 parous women who had previously enrolled in the amal study . of those women , the enrolled women had a total of 1,939 singleton pregnancies during the duration of the study . miscarriages , twin pregnancies , and pregnancies of less than 20 weeks of gestation were excluded . information about parity , lbw , and associated factors was obtained from maternal health cards which recorded salient information for each pregnancy , such as sociodemographic data , prepregnancy risk factors , obstetric and medical history , clinical findings at each antenatal visit , investigations , details of delivery , and postnatal findings . parity was defined both dichotomously ( < 5 , 5 ) and by multiple categories ( 1 , 23 , 45 , 67 , 89 , and 10 ) . lbw was defined as < 2500 g. individual pregnancies , rather than women , were the unit of analysis for this study , with the cumulative incidence of lbw reported per 100 pregnancies . outcomes of interest were : ( 1 ) lbw ( defined as < 2500 g ) . ( 2 ) macrosomia ( defined as > 4000 g ) , and ( 3 ) prematurity ( defined as < 37 weeks of gestation ) . multilevel logistic regression ( mllr ) analysis was used to assess the effect of parity on the aforementioned outcomes . multilevel regression modeling was preferred over conventional regression due to its ability to adjust for the dependency that exists among same - woman pregnancies.9 two series of mllr were conducted in order to separately assess both dichotomous parity and categorical parity . two sets of subanalyses were conducted within each series : a crude model and an adjusted model . in the crude model , parity was treated as the only predictor of occurrence of lbw . in the adjusted model , adjustment was made for the following confounders : maternal age , educational status of mothers , family income , past history of lbw , and year of delivery . similar crude and adjusted models were generated for the other outcomes : prematurity and macrosomia . the trend of association between categorical parity and outcomes was tested using the cochran armitage test for trend , and a cutoff value for statistical significance was taken at p < 0.05 . chi - square analyses were used to evaluate the statistical significance of differences among proportions of categorical data . the nonparametric fisher s exact test ( two - tailed ) replaced the chi - square test in cases of small sample size where the expected frequency was less than 5 in any of the cells in 2 2 tables . all statistical analyses were performed using sas software ( version 9.1 ; sas institute , cary , nc ) . a total of 1939 pregnancies were enumerated of which 944 ( 48.7% ) were hp and 995 ( 51.3% ) were low parity ( lp ) . table 1 compares lp and hp pregnancies with respect to important baseline characteristics existing at the beginning of each pregnancy . compared to lp pregnancies , hp pregnancies were shown to be associated with the following maternal characteristics : older age , higher body mass index ( bmi ) , illiteracy , higher family income , and increased frequency of both lbw and gestational diabetes mellitus . frequencies of recorded newborns with disease outcomes of interest were as follows : 191 lbw , 69 prematurity , and 34 macrosomia . fewer cases of lbw ( 80 vs 111 ) and prematurity ( 28 vs 41 ) were documented among hp pregnancies as compared to lp pregnancies . thus , the incidence of lbw among hp pregnancies ( 8.5 per 100 pregnancies ; 80/944 ) was lower than among lp pregnancies ( 11.1 per 100 pregnancies ; 111/995 ) . the difference in incidence risk of lbw was not statistically significant ( p = 0.06 ) . hp pregnancies also had a lower incidence of prematurity ( 3.0 per 100 pregnancies ; 28/944 ) than lp pregnancies ( 4.1 per 100 pregnancies ; 41/995 ) , and the difference was not statistically significant ( p = 0.26 ) . more macrosomia cases occurred among hp pregnancies ( 22 vs 12 ) , yielding a higher incidence of macrosomia among hp pregnancies ( 2.3 per 100 pregnancies ; 22/944 ) than lp pregnancies ( 1.2 per 100 pregnancies ; 12/995 ) , but the difference was not statistically significant ( p = 0.61 ) . hp pregnancies exhibited a 24% reduction in the risk of lbw ( relative risk [ rr ] = 0.76 ; 95% confidence interval [ ci ] : 0.441.1 ) and an 18% reduction in risk of prematurity ( rr = 0.82 ; 95% ci : 0.541.27 ) relative to lp pregnancies . additionally , the risk of having a macrosomic baby was higher among hp pregnancies ( rr = 1.8 ; 95% ci : 1.22.4 ) . using parity of 23 as the reference category , the adjusted mllr model revealed a preventive dose - response relation between parity and the risk of both lbw and prematurity ( trend , p = 0.04 ) . the adjusted rr sequence also showed a correlation between increasing parity and elevated risk of macrosomia , but with a plateau trend rather than a dose - response relation ( trend , p = 0.37 ) . this retrospective population - based cohort study explored whether parity has an effect on the occurrence of lbw , prematurity , and macrosomia . the results showed that higher parity was positively associated with macrosomia and negatively associated with both lbw and prematurity . primiparity was found to be associated with an increased risk of lbw compared to multiparity . the increased risk of lbw among primiparous women may be explained by the lower average age of primiparous women , which is known to be associated with greater risk of both prematurity and pre - eclampsia ; the latter also necessitating delivery before term.10,11 for multiparous pregnancies , higher parity was found to be associated with a decreased risk of lbw in a negative dose - response fashion . this finding may be explained by the association between higher parity and maternal hyperglycemia , which tends to result in higher birth weight.12 although the overall trend suggested reduction in risk of lbw as parity increases , it is worth mentioning that the reduction in risk of lbw in each subcategory of parity was not statistically significant , and this might be attributed to statistical instability caused by a small category - specific sample size . these results are in line with previous studies reporting that high parity is associated with a decreased risk of lbw and an increased risk of macrosomia.3,1315 for example , a prospective cohort study of 1098 pregnancies in finland found a steady increase in average birth weight in correlation with higher parity.12 other studies have found high parity to be associated with an increased risk of lbw;35 however , at least some of these results have been attributed to placental complications such as atresia or abruption . thus , their apparent disagreement with the present study s results might be due to the absence of this factor . others reporting conflicting results have postulated that observed elevations of the risk of lbw were caused by the additional domestic workload undertaken by women , along with each additional child.16 we do not reach a similar conclusion , despite the fact that the majority of pregnancies included in the present study were among illiterate women from low- or middle - income families with extensive domestic responsibilities . this study s use of prospectively documented data among a population with an overall prevalence of hp is one of its strengths . this feature substantially increased the statistical stability of the data notwithstanding the need to adjust for multiple confounders within smaller subcategories . a possible residual confounder is the nutritional status of the women , as sufficient information to adjust for this factor was not available . with estimates as high as 27.6% , oman has the second highest annual incidence proportion of hp pregnancies in the world ( after the united arab emirates),2 as well as the highest reported incidence proportion of extreme parity ( 10 ) in the world ( 11.3%).17 several explanations have been proposed for these high figures , including limited use of contraceptive measures , cultural idealization of large family size , suboptimal female education , and shortcomings in the implementation of the national birth spacing policy . local attitudes towards and limitations of family planning are illustrated by a survey which estimated that the prevalence of contraceptive use among omani women is only 12.7% , and only 64.3% of users believed contraceptives were desirable.18 another survey of omani high school students reported that around 43% of boys and 20.8% of girls stated a preference to have six or more children in the future.19 this indicates that widespread hp is likely to remain the status quo , even among younger , more educated generations . given such high rates of hp in oman , it is especially important for the local medical community to understand its potential health impacts in order to provide better health services for multiparous women and their children . in conclusion , this study provides evidence that high parity is associated with a lower risk of lbw and prematurity as well as a higher risk of macrosomia . these results could be usefully considered in designing effective national health policy programs aimed at improving the health of mothers and children in oman and similar populations . these results can be used to address more targeted family planning programs at the local community level . for example , the observed increased risk of macrosomia can be used to educate women who are at risk of having macrosomic babies because of predisposing conditions such as diabetes mellitus . these findings should not be interpreted in isolation from other potential consequences of high parity . further studies are needed to explore , for example , the social and economic effects of larger nuclear family size on both mothers and their families .[/INST]the objective of this retrospective cohort study was to explore the potential causal relation between parity and fetal growth indices , including low birth weight ( lbw ) , macrosomia , and prematurity . the study was nested on a community trial in a city in oman . the study analyzed 1939 pregnancies among 479 participants . of these , 944 pregnancies ( 48.7% ) were high parity ( 5 ) . obtained newborns with outcomes of interest were as follows : 191 lbw , 34 macrosomic , and 69 premature . associations were measured using multilevel logistic regression modeling . compared to low parity ( lp , defined as < 5 ) , high parity was found to be associated with less risk of lbw ( relative risk [ rr ] = 0.76 ; 95% confidence interval [ ci ] : 0.441.1 ) and prematurity ( rr = 0.82 ; 95% ci : 0.541.27 ) , but greater risk of macrosomia ( rr = 1.8 ; 95% ci : 1.22.4 ) . this study provides evidence that with increasing parity , risks of lbw and prematurity decrease , while risk of macrosomia increases .</s>

interactions between cosmic microwave background ( cmb ) photons and the hot , ionized plasma in galaxy clusters introduce changes in the spectrum of the cmb . at wavelengths of 1 cm we observe this sunyaev - zeldovich effect ( sze ) @xcite as a decrease in the intensity of the cmb ; this decrement @xmath1 at projected cluster radius @xmath2 can be expressed as @xmath3 where @xmath4 is the thomson cross section , @xmath5 is the electron rest mass , @xmath6 is the electron number density and @xmath7 is the boltzmann constant . note that the fractional change in the cmb temperature @xmath8 is independent of redshift ; it depends only on properties of the icm . higher order corrections to this expression and a consideration of the effects of cluster peculiar velocities on the cmb spectrum can be found elsewhere ( e.g. , @xcite ) . the typical central decrement for a massive @xmath9 galaxy cluster is @xmath10 mk , and for typical radio telescope system temperatures the sze decrement is only a few parts in @xmath11 of the power detected by the receiver , making sze observations challenging . characteristics of radio interferometry make it well suited to meet this challenge . perhaps the most important of these is that only the correlated portion of the receiver output is signal , while the uncorrelated output serves as noise ; differential ground spillover and detector noise are naturally separated from the cluster decrement . another is that interferometry effectively simultaneously differences over the sky , easily filtering the smoothly distributed @xmath123 k background from the cluster sze decrement we seek . finally , with interferometry one obtains information on many scales simultaneously ; by placing some dishes at larger separations it is straightforward to filter out point source contributions . -10pt , and the synthesized beam is represented by the white ellipse in the lower left of each frame . [ fig : szclusters],title="fig:",scaledwidth=100.0% ] -10pt over the past several years , carlstrom , joy and collaborators have developed sensitive , low noise receivers and used them at the bima and ovro observatories to obtain high quality sze data on a sample of 27 intermediate redshift clusters @xcite . figure [ fig : szclusters ] contains greyscale sze images and signal to noise contour overlays of 6 clusters . the contours are spaced by 2@xmath13 , and the white ellipses in the lower left of each frame represent the fwhm of the synthesized beam . as demonstrated by figure [ fig : szclusters ] , the interferometric sze imaging experiment does deliver high signal to noise sze images of intermediate redshift clusters . we use these sze data to constrain the cluster icm distribution , and , in combination with published measurements of the icm temperature , these data enable estimates of cluster icm masses and mass fractions @xcite . in combination with x - ray images of galaxy clusters , the sze data allow one to estimate cluster sizes and measure direct , distance - ladder - independent distances . the x - ray surface brightness @xmath14 at projected cluster radius @xmath2 can be expressed as @xmath15 where @xmath6 is the electron number density , @xmath16 is the temperature dependent cooling coefficient and @xmath17 . note that @xmath14 depends on the square of the electron density , and is highly redshift dependent . because of the different dependence on the electron density , observations of @xmath14 and @xmath8 provide a direct measure of the line of sight distance through the cluster . with additional assumptions about the cluster geometry , we can combine this line of sight size with the angular size of the cluster on the sky to estimate the cluster angular diameter distance @xmath18 . we are currently using archival x - ray data to finalize distance estimates in our ensemble of 27 sze clusters @xcite . -10pt to -10pt the difficulty of detecting x - ray emission from high redshift clusters even with the high quality x - ray instruments available today is made clear by eqn . [ eq : xray ] . indeed , it is the redshift independent nature of the sze ( see eqn . [ eq : deltat ] ) that makes it an ideal tool for studying collapsed structures at high redshift . the current best instruments for sze studies of high redshift clusters do not have the sensitivity required to detect sizeable numbers of clusters in a non - targeted search within reasonable observing times of 1 mth to 1 yr . therefore , we have proposed to build a new array composed of ten 2.5 m dishes and a wide - band digital correlator . this array , when operating at 1 cm , is optimized for high redshift cluster detection and will be approximately 100 times more sensitive than our current sze imaging experiment on bima . in this era of large telescopes it may be surprising to learn that the best telescope size for sze cluster studies is 2.5 m. there are two main reasons for this . first , the angular size @xmath19 of the primary beam of a radio telescope scales with the dish diameter @xmath20 as @xmath21 , where @xmath22 is the observation wavelength . @xmath19 determines the field size in a survey , and cluster signal on scales larger than @xmath23 is lost . for 1 cm observations on a 6.1 m dish , the fwhm of the primary beam is @xmath24 arcmin , whereas for the 2.5 m telescopes @xmath25 arcmin . the primary beam of a 2.5 m dish is better matched to cluster angular scales than a 6.1 m dish . second , as is shown graphically in figure [ fig : dishes ] , interferometry samples the cluster visibility , which is the fourier transform of the cmb decrement distribution on the sky . cluster visibilities typically fall off exponentially with distance from the origin @xmath26 ( as opposed to point sources whose fourier transforms are independent of @xmath26 ) . therefore , with smaller dishes one samples a region of the u - v plane where there is significantly more cluster flux . -10pt to -10pt the proposed wide - band digital correlator will enable us to use a larger fraction of the signal output from the 10 ghz bandwidth receivers . currently , the maximum bandwidth at bima is @xmath12800 mhz ; thus , the proposed 8 ghz correlator will increase the sensitivity by an order of magnitude . in addition to higher throughput , the wide - band correlator provides enhanced image quality . as is apparent in figure [ fig : wideband ] , the fraction of the u - v plane sampled in a 7 hr exposure with the old correlator ( top left ) is much smaller than the fraction sampled in the same exposure with the new correlator ( bottom left ) . this additional u - v coverage leads to a synthesized beam ( right panels ) which has smaller sidelobes . this enhanced image quality simplifies structure detection in sze images . x - ray samples of high redshift clusters are disappointingly small , primarily because of the strong redshift dependence of cluster emission ( see eqn . [ eq : xray ] ) ; only the most luminous clusters at each redshift tend to be found . however , with this sensitive new sze array , we will be able to carry out a survey of @xmath10 deg@xmath27 per month and detect all clusters more massive than @xmath28 @xmath29 , independent of their redshift . interestingly , the cluster selection function from such a survey is essentially a cut in cluster binding mass . so not only will an sze survey yield a sizeable high redshift cluster sample for the first time , but the survey will also deliver a sample which is much easier to understand than typical x - ray samples at intermediate redshift . we determine the survey mass limit as a function of redshift through mock observations of n - body plus sph simulations of galaxy clusters . these mock sze observations include noise and have exposures tuned so that we will be able to survey 1 deg@xmath27 in a month . the n - body plus sph simulations are state of the art simulations sampled from four different cosmological models : ( 1 ) scdm : standard , biased @xmath30 cdm , ( 2 ) ocdm : unbiased @xmath31 cdm , ( 3 ) lcdm : unbiased @xmath31 and @xmath32 cdm , and ( 4 ) @xmath33cdm : @xmath34 but cdm power spectrum with @xmath35 ( see @xcite for more details ) . these simulations include only gas dynamics and gravity . we use three particle species ; this allows us to follow tidal fields from surrounding large scale structure while still resolving the dynamics in the cluster core . we incorporate no early heating of the icm from galaxy formation . to determine the detection limit at each redshift we use outputs of the 48 simulations from the appropriate redshift ; with this approach the morphological evolution of galaxy clusters is naturally included . we determine the detection probability in each mock observation by fitting a cluster model and determining the @xmath36 between the best fitting and null models . we set our detection threshold at 5@xmath13 . figure [ fig : selection ] ( left ) is a plot of limiting mass versus redshift . the uncertainties on the limiting mass correspond to the scatter about the best fit @xmath36-binding mass relation , determined using mock observations of the entire cluster ensemble at each redshift ; this scatter is an indication of the morphological sensitivity of the detection threshold . we find that the limiting mass is independent of cosmological model at least for the four models tested . also in figure [ fig : selection ] ( right ) is a press - schechter estimate of the surface density of clusters more massive than @xmath37 @xmath29 as a function of redshift for three cosmological models ( noted on the figure ) . these models are all normalized to produce the correct cluster abundance at the present epoch . note the cosmological sensitivity of the cluster surface densities ; we expect to find very few clusters with our survey if @xmath30 , whereas for more favored , low @xmath38 models we expect hundreds of clusters @xcite . in figure [ fig : survey ] we plot the survey yield after one month ( dotted line ) and one year ( solid line ) , where we have assumed that the currently favored model @xmath31 and @xmath32 is correct ( if @xmath39 the cluster count increases ) . for comparison we also plot the yield of 200 clusters from a deep rosat pspc x - ray cluster survey @xcite . note that after a one month sze survey we will have more redshift @xmath40 clusters than the deep rosat survey . after one year we expect to have @xmath12100 clusters at redshifts @xmath41 and almost 400 clusters at redshifts @xmath40 @xcite . this highly sensitive probe for massive collapsed structures in the high redshift universe constitutes an exceedingly powerful test of current structure formation models . the sze survey itself will yield a list of galaxy clusters and constraints on the cluster surface density . cluster redshifts , masses , gas distributions and galaxy populations can then be examined through followup observations with x - ray satellites and 8 m class telescopes like the vlt . we anticipate that the scope and number of scientific issues addressed with followup observations of the high redshift clusters from the sze survey will lead to enormous progress in cosmology . jjm is supported by chandra fellowship grant pf8 - 1003 , awarded through the chandra science center . the chandra science center is operated by the smithsonian astrophyical observatory for nasa under contract nas8 - 39073 . jec acknowledges support from the david and lucile packard foundation and the james s. mcdonnell foundation .

interferometric observations of the sunyaev - zeldovich effect ( sze ) toward clusters of galaxies provide sensitive cosmological probes . we present results from 1 cm observations ( at bima and ovro ) of a large , intermediate redshift cluster sample . in addition , we describe a proposed , higher sensitivity array which will enable us to survey large portions of the sky . simulated observations indicate that we will be able to survey one square degree of sky per month to sufficient depth that we will detect all galaxy clusters more massive than @xmath0 , regardless of their redshift . we describe the cluster yield and resulting cosmological constraints from such a survey . _ to appear in the proceedings of the vlt opening symposium _

<s>[INST]interactions between cosmic microwave background ( cmb ) photons and the hot , ionized plasma in galaxy clusters introduce changes in the spectrum of the cmb . at wavelengths of 1 cm we observe this sunyaev - zeldovich effect ( sze ) @xcite as a decrease in the intensity of the cmb ; this decrement @xmath1 at projected cluster radius @xmath2 can be expressed as @xmath3 where @xmath4 is the thomson cross section , @xmath5 is the electron rest mass , @xmath6 is the electron number density and @xmath7 is the boltzmann constant . note that the fractional change in the cmb temperature @xmath8 is independent of redshift ; it depends only on properties of the icm . higher order corrections to this expression and a consideration of the effects of cluster peculiar velocities on the cmb spectrum can be found elsewhere ( e.g. , @xcite ) . the typical central decrement for a massive @xmath9 galaxy cluster is @xmath10 mk , and for typical radio telescope system temperatures the sze decrement is only a few parts in @xmath11 of the power detected by the receiver , making sze observations challenging . characteristics of radio interferometry make it well suited to meet this challenge . perhaps the most important of these is that only the correlated portion of the receiver output is signal , while the uncorrelated output serves as noise ; differential ground spillover and detector noise are naturally separated from the cluster decrement . another is that interferometry effectively simultaneously differences over the sky , easily filtering the smoothly distributed @xmath123 k background from the cluster sze decrement we seek . finally , with interferometry one obtains information on many scales simultaneously ; by placing some dishes at larger separations it is straightforward to filter out point source contributions . -10pt , and the synthesized beam is represented by the white ellipse in the lower left of each frame . [ fig : szclusters],title="fig:",scaledwidth=100.0% ] -10pt over the past several years , carlstrom , joy and collaborators have developed sensitive , low noise receivers and used them at the bima and ovro observatories to obtain high quality sze data on a sample of 27 intermediate redshift clusters @xcite . figure [ fig : szclusters ] contains greyscale sze images and signal to noise contour overlays of 6 clusters . the contours are spaced by 2@xmath13 , and the white ellipses in the lower left of each frame represent the fwhm of the synthesized beam . as demonstrated by figure [ fig : szclusters ] , the interferometric sze imaging experiment does deliver high signal to noise sze images of intermediate redshift clusters . we use these sze data to constrain the cluster icm distribution , and , in combination with published measurements of the icm temperature , these data enable estimates of cluster icm masses and mass fractions @xcite . in combination with x - ray images of galaxy clusters , the sze data allow one to estimate cluster sizes and measure direct , distance - ladder - independent distances . the x - ray surface brightness @xmath14 at projected cluster radius @xmath2 can be expressed as @xmath15 where @xmath6 is the electron number density , @xmath16 is the temperature dependent cooling coefficient and @xmath17 . note that @xmath14 depends on the square of the electron density , and is highly redshift dependent . because of the different dependence on the electron density , observations of @xmath14 and @xmath8 provide a direct measure of the line of sight distance through the cluster . with additional assumptions about the cluster geometry , we can combine this line of sight size with the angular size of the cluster on the sky to estimate the cluster angular diameter distance @xmath18 . we are currently using archival x - ray data to finalize distance estimates in our ensemble of 27 sze clusters @xcite . -10pt to -10pt the difficulty of detecting x - ray emission from high redshift clusters even with the high quality x - ray instruments available today is made clear by eqn . [ eq : xray ] . indeed , it is the redshift independent nature of the sze ( see eqn . [ eq : deltat ] ) that makes it an ideal tool for studying collapsed structures at high redshift . the current best instruments for sze studies of high redshift clusters do not have the sensitivity required to detect sizeable numbers of clusters in a non - targeted search within reasonable observing times of 1 mth to 1 yr . therefore , we have proposed to build a new array composed of ten 2.5 m dishes and a wide - band digital correlator . this array , when operating at 1 cm , is optimized for high redshift cluster detection and will be approximately 100 times more sensitive than our current sze imaging experiment on bima . in this era of large telescopes it may be surprising to learn that the best telescope size for sze cluster studies is 2.5 m. there are two main reasons for this . first , the angular size @xmath19 of the primary beam of a radio telescope scales with the dish diameter @xmath20 as @xmath21 , where @xmath22 is the observation wavelength . @xmath19 determines the field size in a survey , and cluster signal on scales larger than @xmath23 is lost . for 1 cm observations on a 6.1 m dish , the fwhm of the primary beam is @xmath24 arcmin , whereas for the 2.5 m telescopes @xmath25 arcmin . the primary beam of a 2.5 m dish is better matched to cluster angular scales than a 6.1 m dish . second , as is shown graphically in figure [ fig : dishes ] , interferometry samples the cluster visibility , which is the fourier transform of the cmb decrement distribution on the sky . cluster visibilities typically fall off exponentially with distance from the origin @xmath26 ( as opposed to point sources whose fourier transforms are independent of @xmath26 ) . therefore , with smaller dishes one samples a region of the u - v plane where there is significantly more cluster flux . -10pt to -10pt the proposed wide - band digital correlator will enable us to use a larger fraction of the signal output from the 10 ghz bandwidth receivers . currently , the maximum bandwidth at bima is @xmath12800 mhz ; thus , the proposed 8 ghz correlator will increase the sensitivity by an order of magnitude . in addition to higher throughput , the wide - band correlator provides enhanced image quality . as is apparent in figure [ fig : wideband ] , the fraction of the u - v plane sampled in a 7 hr exposure with the old correlator ( top left ) is much smaller than the fraction sampled in the same exposure with the new correlator ( bottom left ) . this additional u - v coverage leads to a synthesized beam ( right panels ) which has smaller sidelobes . this enhanced image quality simplifies structure detection in sze images . x - ray samples of high redshift clusters are disappointingly small , primarily because of the strong redshift dependence of cluster emission ( see eqn . [ eq : xray ] ) ; only the most luminous clusters at each redshift tend to be found . however , with this sensitive new sze array , we will be able to carry out a survey of @xmath10 deg@xmath27 per month and detect all clusters more massive than @xmath28 @xmath29 , independent of their redshift . interestingly , the cluster selection function from such a survey is essentially a cut in cluster binding mass . so not only will an sze survey yield a sizeable high redshift cluster sample for the first time , but the survey will also deliver a sample which is much easier to understand than typical x - ray samples at intermediate redshift . we determine the survey mass limit as a function of redshift through mock observations of n - body plus sph simulations of galaxy clusters . these mock sze observations include noise and have exposures tuned so that we will be able to survey 1 deg@xmath27 in a month . the n - body plus sph simulations are state of the art simulations sampled from four different cosmological models : ( 1 ) scdm : standard , biased @xmath30 cdm , ( 2 ) ocdm : unbiased @xmath31 cdm , ( 3 ) lcdm : unbiased @xmath31 and @xmath32 cdm , and ( 4 ) @xmath33cdm : @xmath34 but cdm power spectrum with @xmath35 ( see @xcite for more details ) . these simulations include only gas dynamics and gravity . we use three particle species ; this allows us to follow tidal fields from surrounding large scale structure while still resolving the dynamics in the cluster core . we incorporate no early heating of the icm from galaxy formation . to determine the detection limit at each redshift we use outputs of the 48 simulations from the appropriate redshift ; with this approach the morphological evolution of galaxy clusters is naturally included . we determine the detection probability in each mock observation by fitting a cluster model and determining the @xmath36 between the best fitting and null models . we set our detection threshold at 5@xmath13 . figure [ fig : selection ] ( left ) is a plot of limiting mass versus redshift . the uncertainties on the limiting mass correspond to the scatter about the best fit @xmath36-binding mass relation , determined using mock observations of the entire cluster ensemble at each redshift ; this scatter is an indication of the morphological sensitivity of the detection threshold . we find that the limiting mass is independent of cosmological model at least for the four models tested . also in figure [ fig : selection ] ( right ) is a press - schechter estimate of the surface density of clusters more massive than @xmath37 @xmath29 as a function of redshift for three cosmological models ( noted on the figure ) . these models are all normalized to produce the correct cluster abundance at the present epoch . note the cosmological sensitivity of the cluster surface densities ; we expect to find very few clusters with our survey if @xmath30 , whereas for more favored , low @xmath38 models we expect hundreds of clusters @xcite . in figure [ fig : survey ] we plot the survey yield after one month ( dotted line ) and one year ( solid line ) , where we have assumed that the currently favored model @xmath31 and @xmath32 is correct ( if @xmath39 the cluster count increases ) . for comparison we also plot the yield of 200 clusters from a deep rosat pspc x - ray cluster survey @xcite . note that after a one month sze survey we will have more redshift @xmath40 clusters than the deep rosat survey . after one year we expect to have @xmath12100 clusters at redshifts @xmath41 and almost 400 clusters at redshifts @xmath40 @xcite . this highly sensitive probe for massive collapsed structures in the high redshift universe constitutes an exceedingly powerful test of current structure formation models . the sze survey itself will yield a list of galaxy clusters and constraints on the cluster surface density . cluster redshifts , masses , gas distributions and galaxy populations can then be examined through followup observations with x - ray satellites and 8 m class telescopes like the vlt . we anticipate that the scope and number of scientific issues addressed with followup observations of the high redshift clusters from the sze survey will lead to enormous progress in cosmology . jjm is supported by chandra fellowship grant pf8 - 1003 , awarded through the chandra science center . the chandra science center is operated by the smithsonian astrophyical observatory for nasa under contract nas8 - 39073 . jec acknowledges support from the david and lucile packard foundation and the james s. mcdonnell foundation .[/INST] interferometric observations of the sunyaev - zeldovich effect ( sze ) toward clusters of galaxies provide sensitive cosmological probes . we present results from 1 cm observations ( at bima and ovro ) of a large , intermediate redshift cluster sample . in addition , we describe a proposed , higher sensitivity array which will enable us to survey large portions of the sky . simulated observations indicate that we will be able to survey one square degree of sky per month to sufficient depth that we will detect all galaxy clusters more massive than @xmath0 , regardless of their redshift . we describe the cluster yield and resulting cosmological constraints from such a survey . _ to appear in the proceedings of the vlt opening symposium _ </s>

SECTION 1. COMMISSION TO REVIEW BENEFITS PROVIDED BY EACH STATE TO DISABLED VETERANS. (a) Establishment.--There is established a commission to be known as the ``State Veterans' Benefits Commission''. (b) Duties.--The Commission shall evaluate-- (1) the total amount of benefits provided by each State to a covered veteran residing in such State (including those benefits that a State provides to a resident regardless of whether the resident is a covered veteran); and (2) the method in which each State establishes the amount of benefits for veterans based on the disability rating of the veteran. (c) Membership.-- (1) In general.--The Commission shall be composed of seven members appointed as follows: (A) One individual appointed by the Speaker of the House of Representatives. (B) One individual appointed jointly by the President of the Senate and the President pro tempore of the Senate. (C) One individual appointed by the minority leader of the House of Representatives. (D) One individual appointed by the minority leader of the Senate. (E) Three individuals appointed by the President. (2) Appointments.--Appointments under paragraph (1) shall be made not later than 30 days after the date of the enactment of this Act. (3) Qualifications.--Of the seven individuals appointed under paragraph (1)-- (A) not less than three shall be disabled veterans; and (B) not less than one shall be a medical doctor. (4) Chairperson and vice chairperson.--The Chairperson and Vice Chairperson of the Commission shall be elected by the members. (5) Terms.--Each member shall be appointed for the life of the Commission. (6) Vacancy.--A vacancy in the Commission shall be filled in the manner in which the original appointment was made. (d) Meetings.-- (1) Initial meeting.--Not later than 30 days after each member is appointed under subsection (c)(1), the Commission shall hold its initial meeting. (2) Meetings.--The Commission shall meet at the call of the Chairperson or a majority of its members. (3) Quorum.--A majority of the Commission shall constitute a quorum but a lesser number may hold hearings. (e) Pay.-- (1) Rates of pay.--Except as provided in paragraph (2), members shall serve without pay. (2) Travel expense.--Each member shall receive travel expenses, including per diem in lieu of subsistence, in accordance with applicable provisions under subchapter I of chapter 57 of title 5, United States Code. (f) Staff.-- (1) Director.--The Commission shall have a director who shall be appointed by the Chairperson. (2) Staff.--Subject to rules prescribed by the Commission, the Chairperson may appoint additional personnel as the Chairperson considers appropriate. (3) Applicability of certain civil service laws.--The director and staff of the Commission shall be appointed subject to the provisions of title 5, United States Code, governing appointments in the competitive service, and shall be paid in accordance with the provisions of chapter 51 and subchapter III of chapter 53 of that title relating to classification and General Schedule pay rates. (4) Experts and consultants.--Subject to rules prescribed by the Commission, the Chairperson may procure temporary and intermittent services under section 3109(b) of title 5, United States Code. (5) Staff to federal agencies.--Upon request of the Chairperson, the head of any Federal department or agency may detail, on a reimbursable basis, any of the personnel of that department or agency to the Commission to assist it in carrying out its duties under this section. (g) Powers of Commission.-- (1) Hearings and sessions.--The Commission may, for the purpose of carrying out this Act, hold hearings, sit and act at times and places, take testimony, and receive evidence as the Commission considers appropriate. The Commission may administer oaths or affirmations to witnesses appearing before it. (2) Powers of members and agents.--Any member or agent of the Commission may, if authorized by the Commission, take any action which the Commission is authorized to take by this section. (3) Obtaining official data.--The Commission may secure directly from any department or agency of the United States information necessary to enable it to carry out this Act. Upon request of the Chairperson of the Commission, the head of that department or agency shall furnish that information to the Commission. (4) Mails.--The Commission may use the United States mails in the same manner and under the same conditions as other departments and agencies of the United States. (5) Administrative support services.--Upon the request of the Commission, the Administrator of General Services shall provide to the Commission, on a reimbursable basis, the administrative support services necessary for the Commission to carry out its responsibilities under this Act. (h) Report.--Not later than 60 days after the initial meeting under subsection (d)(1), the Commission shall submit to the Committee on Veterans' Affairs of the House of Representatives and the Committee on Veterans' Affairs of the Senate a report on the evaluation made under subsection (b), including-- (1) the results of the evaluation; (2) a list of States ranked in order of the amount of benefits provided to covered veterans residing in the State; (3) the recommended amount of benefits the Commission determines necessary for a State to provide covered veterans residing in the State to ensure that such veterans have adequate care, assistance, and financial security; (4) recommendations as to how States can improve the benefits provided to covered veterans residing in the State; (5) relevant background and statistical information associated with the recommendations under paragraphs (3) and (4); and (6) other information the Commission determines appropriate. (i) Termination.--The Commission shall terminate on the date that is two months after the date on which the Commission submits the report pursuant to subsection (h). (j) Covered Veteran Defined.--In this section, the term ``covered veteran'' means a veteran with a disability that is-- (1) rated total for the purposes of disability compensation under chapter 11 of title 38, United States Code; and (2) based upon an impairment reasonably certain to continue throughout the life of the veteran.

Establishes the State Veterans' Benefits Commission to evaluate the total amount of benefits provided by each state to resident veterans with a total and permanent disability rating, as well as the method in which each state establishes the amount of such benefits based on such disability rating. Requires the Commission to report evaluation results to the congressional veterans committees.

<s>[INST]SECTION 1. COMMISSION TO REVIEW BENEFITS PROVIDED BY EACH STATE TO DISABLED VETERANS. (a) Establishment.--There is established a commission to be known as the ``State Veterans' Benefits Commission''. (b) Duties.--The Commission shall evaluate-- (1) the total amount of benefits provided by each State to a covered veteran residing in such State (including those benefits that a State provides to a resident regardless of whether the resident is a covered veteran); and (2) the method in which each State establishes the amount of benefits for veterans based on the disability rating of the veteran. (c) Membership.-- (1) In general.--The Commission shall be composed of seven members appointed as follows: (A) One individual appointed by the Speaker of the House of Representatives. (B) One individual appointed jointly by the President of the Senate and the President pro tempore of the Senate. (C) One individual appointed by the minority leader of the House of Representatives. (D) One individual appointed by the minority leader of the Senate. (E) Three individuals appointed by the President. (2) Appointments.--Appointments under paragraph (1) shall be made not later than 30 days after the date of the enactment of this Act. (3) Qualifications.--Of the seven individuals appointed under paragraph (1)-- (A) not less than three shall be disabled veterans; and (B) not less than one shall be a medical doctor. (4) Chairperson and vice chairperson.--The Chairperson and Vice Chairperson of the Commission shall be elected by the members. (5) Terms.--Each member shall be appointed for the life of the Commission. (6) Vacancy.--A vacancy in the Commission shall be filled in the manner in which the original appointment was made. (d) Meetings.-- (1) Initial meeting.--Not later than 30 days after each member is appointed under subsection (c)(1), the Commission shall hold its initial meeting. (2) Meetings.--The Commission shall meet at the call of the Chairperson or a majority of its members. (3) Quorum.--A majority of the Commission shall constitute a quorum but a lesser number may hold hearings. (e) Pay.-- (1) Rates of pay.--Except as provided in paragraph (2), members shall serve without pay. (2) Travel expense.--Each member shall receive travel expenses, including per diem in lieu of subsistence, in accordance with applicable provisions under subchapter I of chapter 57 of title 5, United States Code. (f) Staff.-- (1) Director.--The Commission shall have a director who shall be appointed by the Chairperson. (2) Staff.--Subject to rules prescribed by the Commission, the Chairperson may appoint additional personnel as the Chairperson considers appropriate. (3) Applicability of certain civil service laws.--The director and staff of the Commission shall be appointed subject to the provisions of title 5, United States Code, governing appointments in the competitive service, and shall be paid in accordance with the provisions of chapter 51 and subchapter III of chapter 53 of that title relating to classification and General Schedule pay rates. (4) Experts and consultants.--Subject to rules prescribed by the Commission, the Chairperson may procure temporary and intermittent services under section 3109(b) of title 5, United States Code. (5) Staff to federal agencies.--Upon request of the Chairperson, the head of any Federal department or agency may detail, on a reimbursable basis, any of the personnel of that department or agency to the Commission to assist it in carrying out its duties under this section. (g) Powers of Commission.-- (1) Hearings and sessions.--The Commission may, for the purpose of carrying out this Act, hold hearings, sit and act at times and places, take testimony, and receive evidence as the Commission considers appropriate. The Commission may administer oaths or affirmations to witnesses appearing before it. (2) Powers of members and agents.--Any member or agent of the Commission may, if authorized by the Commission, take any action which the Commission is authorized to take by this section. (3) Obtaining official data.--The Commission may secure directly from any department or agency of the United States information necessary to enable it to carry out this Act. Upon request of the Chairperson of the Commission, the head of that department or agency shall furnish that information to the Commission. (4) Mails.--The Commission may use the United States mails in the same manner and under the same conditions as other departments and agencies of the United States. (5) Administrative support services.--Upon the request of the Commission, the Administrator of General Services shall provide to the Commission, on a reimbursable basis, the administrative support services necessary for the Commission to carry out its responsibilities under this Act. (h) Report.--Not later than 60 days after the initial meeting under subsection (d)(1), the Commission shall submit to the Committee on Veterans' Affairs of the House of Representatives and the Committee on Veterans' Affairs of the Senate a report on the evaluation made under subsection (b), including-- (1) the results of the evaluation; (2) a list of States ranked in order of the amount of benefits provided to covered veterans residing in the State; (3) the recommended amount of benefits the Commission determines necessary for a State to provide covered veterans residing in the State to ensure that such veterans have adequate care, assistance, and financial security; (4) recommendations as to how States can improve the benefits provided to covered veterans residing in the State; (5) relevant background and statistical information associated with the recommendations under paragraphs (3) and (4); and (6) other information the Commission determines appropriate. (i) Termination.--The Commission shall terminate on the date that is two months after the date on which the Commission submits the report pursuant to subsection (h). (j) Covered Veteran Defined.--In this section, the term ``covered veteran'' means a veteran with a disability that is-- (1) rated total for the purposes of disability compensation under chapter 11 of title 38, United States Code; and (2) based upon an impairment reasonably certain to continue throughout the life of the veteran.[/INST]Establishes the State Veterans' Benefits Commission to evaluate the total amount of benefits provided by each state to resident veterans with a total and permanent disability rating, as well as the method in which each state establishes the amount of such benefits based on such disability rating. Requires the Commission to report evaluation results to the congressional veterans committees.</s>

in many ways the study of random graphs traces its history back to the seminal work of erds and rnyi showing that there exists a rapid transition between the regimes of a random graph consisting of many small components , a random graph having one `` giant '' component , and a random graph being connected @xcite . because of their central role in the history of random graphs these phase transitions have been extensively studied , see for instance @xcite , among numerous others . we contribute to this ongoing discussion by providing a sharp transition for the emergence of both the giant component and connectivity for the stochastic kronecker graph , a generalization of the standard erds - rnyi binomial random graph model , @xmath3 . more formally , recall that the kronecker or tensor product of two matrices @xmath4 and @xmath5 is a matrix @xmath6 . for @xmath7 , j \in [ n ] , s \in [ p],$ ] and @xmath8 $ ] the entry @xmath9 is @xmath10 , that is @xmath11.\ ] ] letting @xmath0^{k \times k}$ ] be a symmetric matrix , the @xmath12-order stochastic kronecker graphgenerated by @xmath13 is formed by taking the @xmath14-fold kronecker product of @xmath13 , denoted @xmath15 , and using this as the probability matrix for a graph with independent edges . that is , each edge @xmath16 is present independently with probability @xmath17 . the stochastic kronecker graph was originally proposed as a model for the network structure of the internet with the property that it could be easily fit to real world data , especially in the case where the generating matrix was @xmath18 $ ] where @xmath19 @xcite . as such , there have been several papers analyzing structural properties of the stochastic kronecker graph when the generating matrix is a @xmath20 matrix @xcite . most relevant to this current work are the results of mahdian and xu @xcite who anaylzed the connectivity , diameter , and the emergence of the giant component with @xmath21 , and the work of the first author and horn who analyzed the emergence and size of the giant component for arbitrary @xmath22 @xcite . in this work we consider the case of an arbitrarily sized generating matrix , and develop necessary and sufficient conditions for the emergence of the giant component and connectivity . the key tool to analyzing these graphs is to tie the structure of the graph to a fixed markov chain on the underlying generating matrix . using this underlying structure , one can analyze the graph structure more completely than with traditional tools . given a @xmath12-order stochastic kronecker graph with generating matrix @xmath13 , we define @xmath23 to be the weighted graph on @xmath24 $ ] , where weights are as given in @xmath13 . we will occasionally refer to @xmath25 as the underlying graph of @xmath26 . we also define the backbone graph of the matrix @xmath13 , @xmath27 , as the subgraph of @xmath23 consisting of the edges assigned weight 1 . that is , @xmath27 is a graph on the vertices @xmath24 $ ] where @xmath16 is an edge if and only if @xmath28 . when the matrix @xmath13 is clear , we will neglect the dependence on @xmath13 and write simply @xmath25 and @xmath29 . our primary results can be summarized as follows . [ t : master ] let @xmath26 be @xmath12-order stochastic kronecker graph generated by a symmetric matrix @xmath0^{k \times k}$ ] which has column sums @xmath30 . let @xmath31 be the number of vertices of @xmath26 . 1 . if @xmath25 is disconnected or bipartite , then the largest component of @xmath26 has size @xmath32 [ m : disc_bip ] 2 . if @xmath25 is connected and non - bipartite and @xmath33 , then there is some @xmath34 such that with probability at least @xmath35 there are at least @xmath36 isolated vertices in @xmath26 . [ m : small ] 3 . if @xmath25 is connected , non - bipartite , @xmath37 , and the @xmath38 s are not identically one , then there is a positive constant @xmath39 such that with probability at least @xmath35 , the largest component of @xmath26 has size @xmath40 , that is , @xmath26 has a giant component . [ m : giant_bound ] 4 . if @xmath25 is connected , non - bipartite , and @xmath41 , then there is a positive constant @xmath39 such that with probability at least @xmath35 the largest component of @xmath26 has size @xmath40 . [ m : giant ] 5 . if @xmath25 is connected , non - bipartite , and @xmath42 , then there is a positive constant @xmath39 such that @xmath26 has at least @xmath43 isolated vertices with probability at least @xmath44 . [ m : discon_c1 ] 6 . if @xmath25 is connected , non - bipartite , @xmath45 , and @xmath29 has a vertex of degree zero , then there is some positive constant @xmath39 such that @xmath26 has at least @xmath46 isolated vertices with probability at least @xmath44.[m : discon ] 7 . if @xmath25 is connected and non - bipartite , @xmath45 , and @xmath29 has no vertices of degree zero , then there is a constant @xmath47 such that @xmath26 is connected with probability at least @xmath48 . [ m : connect_bound ] 8 . if @xmath25 is connected and non - bipartite and @xmath49 , then there is a constant @xmath47 such that @xmath26 is connected with probability at least @xmath50 . [ m : connected ] we note that item ( [ m : connected ] ) above is typical for the emergence of connectivity ; that is , the graph is connected asymptotically almost surely precisely when asymptotically almost surely the minimum degree is at least 1 . in fact , taking ( [ m : discon_c1 ] ) , ( [ m : discon ] ) , ( [ m : connect_bound ] ) , and ( [ m : connected ] ) together we can see that a stochastic kronecker graph is connected precisely when the minimum degree is at least 1 asymptotically almost surely . from this viewpoint , the slightly unnatural seeming condition on the backbone graph @xmath29 is simply the condition needed to assure that @xmath26 has no isolated vertices . the folklore in the study of random graphs asserts that , in general , the giant component should emerge when the average expected degree is 1 , see for instance @xcite . as the average expected degree in a @xmath12-order stochastic kronecker graphis @xmath51 , this suggests that the transition occurs when @xmath52 . however , as parts ( [ m : small ] ) and ( [ m : giant ] ) of theorem [ t : master ] show , the transition actually occurs when @xmath53 . noting that the expected degrees in stochastic kronecker graphs follow a multinomial distribution ( see section [ defsec ] ) , this condition can be seen as equivalent ( asymptotically ) to the condition that _ median _ expected degree is at least one . thus our results may suggest that the average expected degree is not as deeply connected to giant component as previously thought , because in many of the standard random graph models , such as the erds - rnyi random graph , the average and the median expected degree agree . that is , it may be that the median is truly the determining factor for such structures . it is also worth noting that spencer has conjectured based in part on @xcite , that the correct intuition is that the emergence of the giant component is tied to the second order average degree @xcite . to prove theorem [ t : master ] , we will develop several general results on @xmath26 , and then apply these results to the specific situations above . in particular , we are able to tie the adjacency structure of @xmath26 to a finite state markov chain on @xmath25 . using this association , we can take advantage of the finite structure of @xmath25 to build theory regarding the asymptotically growing structure @xmath26 . given a stochastic kronecker graph @xmath26 generated by @xmath13 , let @xmath54 be the adjacency matrix of @xmath26 and @xmath55 the diagonal matrix of degrees in @xmath26 . let @xmath56 be the column sums of @xmath13 ( note that we can assume these are nondecreasing without loss of generality ) , and let @xmath57 be the diagonal matrix of column sums in @xmath13 . we note that there are multiple means of describing the entries of the probability matrix @xmath15 to take advantage of the kronecker product structure . one point of view that is particularly helpful is to define a bijection @xmath58^t$ ] , so that each vertex of @xmath26 is represented by a word of length @xmath14 in @xmath24 $ ] . we will often identify the vertex to its corresponding word , and write @xmath59 . given an appropriate choice of bijection , for any two vertices @xmath60 and @xmath61 , the probability that @xmath60 and @xmath61 are adjacent is @xmath62 that is to say , we take the product of entries of the generating matrix @xmath13 , where entries correspond to the pairs of components in the words representing @xmath60 and @xmath61 . we will sometimes use the notation @xmath63 to refer to the @xmath64 position in @xmath15 , where we index the matrix by the ordered words obtained via the kronecker product , and we note that @xmath65 . we shall use the notation @xmath66 to indicate that @xmath60 is adjacent to @xmath61 . when ambiguous , we write @xmath67 to indicate that @xmath60 is adjacent to @xmath61 in the graph @xmath26 . now , suppose that @xmath68 has @xmath69 coordinates equal to 1 , @xmath70 coordinates equal to 2 , and so on . it is straightforward to calculate that @xmath71 } } = c_1^{a_1}c_2^{a_2}\dots c_k^{a_k}.\ ] ] from this we can see that the stochastic kronecker graph is defined precisely so that the expected adjacency matrix @xmath72 , and the expected degree matrix @xmath73 . at times we will wish to emphasize the graph structure of @xmath15 , and thus will use @xmath74 to refer to the weighted complete graph with weights given by @xmath15 . moreover , it will frequently be of interest to know the number of coordinates in @xmath68 equal to each symbol in @xmath24 $ ] . to that end , we define the _ signature _ of @xmath61 to be @xmath75 , where @xmath76 is the proportion of symbols in @xmath68 equal to @xmath77 . for example , if @xmath78 and @xmath79 , we would have @xmath80 . we will denote by @xmath81 the space of possible signatures . often we will establish an underlying signature for a vertex and then take @xmath14 to infinity ; this will generally result in noninteger values for the number of letters of a particular value in @xmath68 . this can be overlooked , however , as rounding to the next integer appropriately will not change the asymptotic features of the vertices , and so we will often assume that a vertex can take any signature . let @xmath82 . we will make frequent use of the simple observation that @xmath83 } } \right ) } } = t { \ensuremath{\left\langle \sigma(v ) , l \right\rangle}},\ ] ] where @xmath84 represents the standard dot product . let @xmath74 be the weighted complete graph on @xmath85 , with the weight of edge @xmath86 equal to @xmath87 . let @xmath61 be a vertex in @xmath74 with signature @xmath88 . define @xmath89 to be a random variable that takes values in @xmath90 , where @xmath89 is the signature of a randomly chosen neighbor of @xmath61 according to the probability distribution defined by the weights of the edges . that is , @xmath91 that is to say , @xmath89 is the signature of the vertex obtained after taking one step in the uniform random walk on @xmath74 . for each @xmath92 $ ] , let @xmath93 be the random variable that takes values in @xmath24 $ ] , with @xmath94 . note that for @xmath59 fixed , we have @xmath95 thus we can consider @xmath89 as giving the signature of a randomly chosen neighbor of @xmath61 , chosen according to the product distribution @xmath96 . as the signature is independent of order , for the purposes of analyzing @xmath89 , we may write this distribution as @xmath97 . therefore , for all @xmath92 $ ] , letting @xmath98 be the @xmath99 component of the signature @xmath89 , we have @xmath100 } } = \frac{1}{t}\sum_{j=1}^k ( \sigma_jt ) { { \mathbb{p}}}(x^{(j)}=i)= \sum_{j=1}^k \sigma_j \frac{p_{ij}}{c_j}.\ ] ] on the other hand , let @xmath101 , the transition probability matrix for the uniform random walk on @xmath25 and notice that the matrix product @xmath102 has @xmath99 coordinate @xmath103}}\ ] ] thus , @xmath104}}$ ] . therefore , we can think of the distribution of a random walk on @xmath25 as the expected signature of a vertex in a random walk on @xmath105 . let @xmath106 be the stationary distribution of the random walk on @xmath25 , so @xmath107 . it is a simple exercise to verify that @xmath108 . we will show in section [ structural ] that the collection of signatures close to @xmath109 will in fact , asymptotically almost surely , form a connected subgraph in @xmath26 , and further , by leveraging the convergence of the markov chain on @xmath25 , we can assure a giant component . for a given graph @xmath26 , the normalized laplacian matrix for @xmath26 is the matrix @xmath110 . we denote the eigenvalues of @xmath111 by @xmath112 . if there is any ambiguity , we write @xmath113 to specify that the eigenvalues are from the normalized laplacian , and more generally @xmath114 to denote the @xmath99 smallest eigenvalue of a hermitian matrix @xmath115 . we sometimes refer to these as the laplacian eigenvalues of @xmath26 . we shall use the following standard facts from spectral graph theory . [ t : standards ] let @xmath26 be a graph with laplacian eigenvalues @xmath116 . then 1 . @xmath26 is connected if and only if @xmath117 . if @xmath26 is connected , then the diameter @xmath118 of @xmath26 satisfies @xmath119 . 3 . let @xmath120 denote the probability transition matrix of a random walk on @xmath26 . then @xmath121 is an eigenvalue of @xmath111 with eigenvector @xmath61 if and only if @xmath122 is an eigenvalue of @xmath120 with eigenvector @xmath61 . among our key tools will be the following theorem from chung and the first author @xcite that gives spectral concentration in the normalized laplacian of a general random graph . [ t : indepspec ] let @xmath26 be a random graph with independent edges generated according to the matrix @xmath123 . let @xmath124 be the diagonal matrix of expected degrees and let @xmath125 denote the minimum expected degree . if @xmath126 , then with probability at least @xmath127 , for all @xmath77 @xmath128 we also make use of standard tools in spectral graph theory , chief among them the cheeger inequality . for two sets @xmath129 of vertices in a graph @xmath26 , define @xmath130 to be the number of edges ( or , in a weighted graph , the total weight of edges ) for which one endpoint is in @xmath131 and the other in @xmath132 . note that an edge with both endpoints in @xmath133 is counted twice in this definition . define @xmath134 . when the underlying graph is clear , we drop the subscript @xmath26 in the notation . the cheeger constant of a set @xmath131 with @xmath135 is defined to be @xmath136 and cheeger constant of @xmath26 is @xmath137 the spectrum of a graph is related to the cheeger constant via the cheeger ineqaulity @xcite . for @xmath26 any graph , let @xmath138 be the smallest nontrivial eigenvalue of @xmath139 . then @xmath140 as we will frequently be discussing markov chains , we will pass regularly between considering row vectors and column vectors . we will always treat the signature of a vertex @xmath61 as a row vector , as well as the vector @xmath141 . the all - ones vector , @xmath142 , will be considered a row vector as well . however , eigenvectors of a matrix are typically assumed to be right eigenvectors , and are thus column vectors . any other usages should be made clear by context . in order to understand the rate of convergence of a markov chain we will use the relative pointwise distance . if @xmath109 is the limiting distribution of the markov chain , the relative pointwise distance of a distribution @xmath143 from @xmath109 is @xmath144 as we are interested in an overall rate of convergence we define @xmath145 it is well known that the rate of decay of the relative pointwise distance can be controlled by the spectral information of the markov chain as given in the following theorem , see for instance @xcite . [ tvdist ] let @xmath146 be the eigenvalues of the transition probability matrix of a uniform random walk on a connected , non - bipartite ( weighted ) graph @xmath26 . set @xmath147 . for any @xmath148 we have @xmath149 , where @xmath150 denotes the minimum degree in @xmath26 . the phrase _ asymptotically almost surely _ in this paper will always refer to asymptotics with respect to @xmath14 , unless otherwise noted . the norm @xmath151 will refer to the @xmath152-norm unless otherwise noted . to prove the thresholds for connectivity and emergence of the giant component in a stochastic kronecker graph @xmath26 ( theorem [ t : master ] , items ( [ m : giant ] ) and ( [ m : connected ] ) ) , we will use the following structure . first , we show that @xmath26 contains a small set of vertices that is connected asymptotically almost surely , in particular , those vertices that are close to stationarity under the markov chain described in section [ mcdescription ] . we shall refer to this set as the `` connected core '' of the graph . although this will not be enough vertices to form a giant component , we can then show that under certain conditions , a positive fraction of the vertices in @xmath26 can be connected by a path to the connected core . the thresholds given are precisely those conditions needed to ensure that a positive fraction of the vertices exhibit this behavior . in retrospect , the arguments used by horn and the first author in @xcite to show the emergence of the giant component in the case where the generating matrix is @xmath153 can be viewed as a special case of our technique . specifically , as the underlying markov chain has only two states , the degree of each vertex is controlled by a single parameter , which significantly simplifies the argument . as a consequence , the authors in @xcite were able to analyze the giant component directly via counting techniques , without appealing to the underlying markov chain . in this section , we develop much of the underlying structure in @xmath26 via the random walk on @xmath25 . we begin with some elementary observations on the vertex degrees in @xmath26 and @xmath74 . [ agoodneighbor ] let @xmath61 be a vertex with signature @xmath143 in a @xmath12-order stochastic kronecker graph @xmath26 , such that @xmath154 . let @xmath155 . for any @xmath156 , we have 1 . [ concingbar ] @xmath61 has at least @xmath157 neighbors in @xmath74 with signature @xmath158 such that @xmath159 } } \right\|_{}}}\leq \delta$ ] . [ agoodneighborg ] with probability at least @xmath160 , @xmath61 has at least @xmath161 neighbors in @xmath26 with signature @xmath158 such that @xmath159 } } \right\|_{}}}\leq \delta$ ] . by the hoeffding inequality , we have that for any @xmath77 , @xmath162 } } \right| } } > \delta t\right)\leq 2e^{-2\delta^2 t}\ ] ] for any @xmath156 . therefore , by the union bound , we have @xmath163\hbox { such that } t{\ensuremath{\left| z^{(v)}_i-{\ensuremath{{{\mathbb{e}}}\!\left [ z^{(v)}_i \right ] } } \right|}}>\delta t\right)\leq 2ke^{-2\delta^2t}.\ ] ] this verifies item ( [ concingbar ] ) . for item ( [ agoodneighborg ] ) , note that by ( [ concingbar ] ) , we have that the expected number of neighbors of @xmath61 with signature @xmath158 in the desired range is at least @xmath157 . by chernoff bounds , then , with probability at least @xmath160 , we have at least @xmath161 neighbors with such a signature @xmath158 . as an immediate corollary of this result we have the following . [ c : tight ] let @xmath61 be a vertex with signature @xmath143 in a @xmath12-order stochastic kronecker graph @xmath26 , such that @xmath164 . let @xmath165 . with probability at least @xmath166 , @xmath61 has at least @xmath167 neighbors @xmath60 with @xmath168 . recall from section [ mcdescription ] that @xmath169 is the stationary distribution of the random walk on @xmath25 , with @xmath170 for all @xmath77 . given @xmath171 , define @xmath172 , \sigma_i(v)>(1-\epsilon)\pi_i\}$ ] . notice that if @xmath173 with signature @xmath143 , then we have , for all @xmath77 , @xmath174 by stationarity of @xmath109 . hence , if @xmath175 , then @xmath176}}$ ] is also in @xmath177 . we will show that under appropriate conditions , this set of vertices @xmath177 is connected asymptotically almost surely , forming the small connected core described above . to do this , we will show that vertices in @xmath177 have exponentially large degree in @xmath14 , and then use theorem [ t : indepspec ] to show the first eigenvalue in @xmath177 is bounded away from zero . we first must address the degree of vertices in @xmath177 . to that end , we have the following lemma : [ se_degree ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by @xmath13 and let @xmath178 be fixed , and assume @xmath25 is connected and nonbipartite . for sufficiently large @xmath14 there is a constant @xmath179 , depending only on @xmath13 and @xmath180 , such that for all @xmath181 , @xmath182 . to prove this lemma , we make use of the following standard observation about binomial random variables . [ o : sqrt ] let @xmath183 be fixed constants and let @xmath184 . there exists constants @xmath185 and @xmath186 , depending on @xmath187 and @xmath188 such that if @xmath189 , then @xmath190\right ) } } > c.\ ] ] let @xmath61 be an arbitrary vertex in @xmath177 . consider a collection of independent , identically distributed random variables , @xmath191 , taking on values in @xmath192 each with probability @xmath193 , where @xmath194 for all @xmath77 . let @xmath195 be the count of the number of @xmath77 s in these variables , that is , @xmath196 . for @xmath197 , let @xmath198 be the event that @xmath199 . we then have that , for all @xmath200 , @xmath201 } } & \geq { \ensuremath{\left ( t - { \ensuremath{\left ( p_it - c\sqrt{t } \right ) } } \right ) } } \frac{p_j}{1-p_i } \\ & = { \ensuremath{\left ( ( 1-p_i)t + c\sqrt{t } \right ) } } \frac{p_j}{1-p_i } \\ & = p_jt + \frac{c p_j}{1-p_i}\sqrt{t } \\ & \geq p_jt + c p \sqrt{t}. \end{aligned}\ ] ] to apply this observation to the context of @xmath89 we first consider the unweighted graph @xmath202 on @xmath24 $ ] where @xmath203 if and only if there is an unweighted walk of length 2 between @xmath77 and @xmath204 in @xmath25 . since @xmath25 is connected and non - bipartite , @xmath202 is connected and thus there exists a breadth - first traversal of @xmath202 . as noted above , by the definition of @xmath177 , for every @xmath77 we have @xmath205 . further , by the pigeonhole principle , there is some index @xmath77 such that @xmath206 . let @xmath207 be one such index and let @xmath208 be a breadth - first traversal of @xmath202 starting at @xmath207 . recall that we may analyze @xmath89 from the point of view of the product distribution @xmath209 where each @xmath93 is an independent random variable that takes values in the set of neighbors of @xmath77 in @xmath25 . let the random variables @xmath210 be the number of times that @xmath93 takes on the value @xmath204 . we note that we can ignore the indices that @xmath93 can not take on , and so define @xmath211 . we recursively define the events @xmath212 as follows . the event @xmath213 is the event that for all @xmath214 , @xmath215 } } - 2\alpha_1\sqrt{t } \leq z_{us_1 } \leq { \ensuremath{{{\mathbb{e}}}\!\left [ z_{us_1 } \right ] } } - \alpha_1\sqrt{t}.$ ] for all @xmath216 the event @xmath217 is the event that for all @xmath218 , @xmath219 } } - 2\alpha_i\sqrt{t } \leq z_{us_i } \leq { \ensuremath{{{\mathbb{e}}}\!\left [ z_{us_i } \mid \cap_{j=1}^{i-1 } \mathcal{a}_j \right ] } } - \alpha_i\sqrt{t},\ ] ] where the @xmath220 s are fixed constants to be chosen later . we note that by observation [ o : sqrt ] , as @xmath221 is a sum of independent indicator variables , each with probability @xmath193 , each of these events occurs with positive probability . thus it suffices to show that @xmath222 is contained in the event @xmath223 . for sufficiently large @xmath14 the event @xmath213 assures that @xmath224 by the choice of @xmath207 , specifically that @xmath225 } } \geq ( 1-{\epsilon})\pi_{s_1 } + \frac{\epsilon}{k}$ ] . since the sequence @xmath226 is a breadth - first search of @xmath202 , we have that for all @xmath227 , there exists index @xmath228 such that @xmath229 . thus there is some vertex @xmath60 that is a neighbor to both @xmath226 and @xmath230 in @xmath25 . now consider the effect of the conditioning on the event @xmath231 on @xmath221 . by ( [ abovecalculations ] ) and the definition of @xmath231 we have that @xmath232 } } \geq { \ensuremath{{{\mathbb{e}}}\!\left [ z_{us_i } \right ] } } + \alpha_{i-1}p_{u}\sqrt{t } \geq { \ensuremath{{{\mathbb{e}}}\!\left [ z_{us_i } \right ] } } + \alpha_{i-1}p_{\min}\sqrt{t}$ ] where @xmath233 } p_i$ ] . furthermore , this gives that @xmath234 } } \geq ( 1-\epsilon)\pi_{s_i}t + \alpha_{i-1}p_{\min}\sqrt{t}$ ] . thus choosing @xmath235 suffices to assure that the event @xmath222 is contained in @xmath177 , as desired . [ t : sepsilon ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . further suppose that @xmath236 and fix @xmath237 if @xmath238 , and @xmath239 if @xmath240 . let @xmath241 be the subgraph of @xmath26 induced by @xmath177 . for @xmath14 sufficiently large , there is a constant @xmath242 , depending on @xmath13 and @xmath180 , such that @xmath241 is connected with diameter @xmath243 with probability at least @xmath244 . notice that the bound on @xmath245 is always positive ( or infinite ) , since @xmath246 for all @xmath77 , so @xmath247 . we will proceed by showing that there exists a constant @xmath197 such that the graph @xmath241 has @xmath248 asymptotically almost surely . as noted in theorem [ t : standards ] , this implies that @xmath241 is connected asymptotically almost surely , with diameter @xmath249 . recall that the expected degree of a vertex with signature @xmath143 is @xmath250 and thus any vertex @xmath181 has expected degree at least @xmath251 where @xmath252 we note that by the restriction on @xmath180 , @xmath253 and thus @xmath242 . this implies that every vertex in @xmath177 has expected degree exponentially increasing with @xmath14 . let @xmath254 be the subgraph of @xmath74 induced by @xmath255 , so the weight of each edge in @xmath254 is the probability of that edge appearing in @xmath241 . now , by lemma [ se_degree ] , there is some constant @xmath185 such that for every vertex @xmath61 in @xmath254 we have @xmath256 . now for any positive constant @xmath125 , there exists some small positive constant @xmath257 such that @xmath258 and thus , by theorem [ t : indepspec ] , in order to complete the proof it suffices to show that @xmath254 has constant spectral gap . indeed , by theorem 3 , if there exists a constant @xmath259 with @xmath260 , then by theorem 3 , @xmath261 with probability at least @xmath262 , and by the above , we have that @xmath263 for any @xmath156 with probability at least @xmath262 , as desired . to determine the spectral gap in @xmath254 , we use cheeger s inequality . let @xmath264 with @xmath265 . note that @xmath266 where the constant @xmath185 is the constant provided by lemma [ se_degree ] . thus , we have @xmath267 now , let @xmath268 and let @xmath269 be the eigenvalues of @xmath270 . note that @xmath271 is the laplacian matrix for @xmath25 , and as @xmath25 is connected and non - bipartite , @xmath272 . now , @xmath273 , and thus has eigenvalues @xmath274 , where @xmath275\cup\{0\}$ ] . hence , the smallest nonzero eigenvalue of @xmath276 is @xmath277 , which occurs with multiplicity @xmath14 . thus by cheeger s inequality , @xmath278 . therefore , combining these results we have @xmath279 hence @xmath280 is bounded below by a constant and @xmath254 has constant spectral gap , as desired . this establishes that the graph @xmath26 contains a small connected core asymptotically almost surely provided @xmath281 . we now turn our attention to the second half of our fundamental structure . here we wish to determine which vertices will be connected by a path to the connected core . to that end , define @xmath282 . we wish to show that any vertex in @xmath283 may be connected by a path to @xmath177 asymptotically almost surely . [ t : snakeone ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . fix @xmath284 . let @xmath121 be the spectral gap of @xmath25 and let @xmath285 . for @xmath14 sufficiently large , any vertex @xmath286 is connected to @xmath177 by a path of length at most @xmath287 with probability at least @xmath288 . let @xmath286 . define @xmath289 and for each @xmath290 , let @xmath291 be a neighbor of @xmath292 such that @xmath293 ( if such a neighbor exists ) . for @xmath294 define @xmath295 . now , we note that if such a sequence exists , then @xmath296 and further @xmath297 thus , since @xmath287 is a fixed constant , we have that by corollary [ c : tight ] for sufficiently large @xmath14 such a sequence fails to exist with probability at most @xmath298 it now suffices to show that @xmath299 . by the choice of @xmath287 and theorem [ tvdist ] , we know that @xmath300 and thus @xmath301 but then as @xmath302 we have that for sufficiently large @xmath14 , @xmath299 . we now turn to the case that the stochastic kronecker graph has only small components , that is , the largest component is of size at most @xmath303 . these correspond to items ( [ m : disc_bip ] ) and ( [ m : small ] ) in theorem [ t : master ] . the first of these result follows from standard results on the component sizes of ( non - stochastic ) kronecker graphs which we include in the following lemma for completeness . [ t : smallcomps ] if @xmath241 is a disconnected or bipartite graph on @xmath2 vertices , then the largest component of @xmath304 has size @xmath305 . first , suppose @xmath241 is not connected . let @xmath59 be a vertex in @xmath304 . now for any neighbor @xmath306 of @xmath61 each coordinate @xmath307 must be adjacent to @xmath291 in @xmath241 and hence in the same component as @xmath291 . thus , the size of the component containing @xmath61 is at most the product of the sizes of the components in @xmath241 of the vertices @xmath291 . since @xmath241 is disconnected the largest component in @xmath241 has size at most @xmath308 and thus the largest component in @xmath304 has size at most @xmath309 . now , suppose @xmath241 is a connected bipartite graph with bipartition @xmath310 and again consider a vertex @xmath311 and a neighbor @xmath60 of @xmath61 , with @xmath312 . now since @xmath291 and @xmath307 are adjacent in @xmath241 , they are on different sides of the bipartition @xmath310 . thus the component containing @xmath61 and @xmath60 is bipartite with @xmath60 and @xmath61 on different sides of the bipartition . furthermore , the side of the bipartition containing @xmath61 has @xmath313 vertices . thus for all @xmath314 there are @xmath315 components of @xmath304 of size @xmath316 . it is worth noting that this size is symmetric and so that components counted for a given @xmath77 are also counted for @xmath317 . now maximizing @xmath316 over the choice of @xmath77 , we have the largest component occurs where either @xmath318 or @xmath319 . as @xmath320 , we maximize with respect to @xmath321 to obtain that the largest of component of @xmath304 has size at most @xmath322 for @xmath323 . this lemma resolves item ( [ m : disc_bip ] ) in theorem [ t : master ] as it implies that the underlying graph for @xmath15 is disconnected with small component sizes . [ t : small ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by @xmath0^{k \times k}$ ] with column sums @xmath324 . if @xmath25 is connected , non - bipartite , and @xmath325 , then there exists some @xmath326 such that with probability at least @xmath327 there are at least @xmath328 isolated vertices in @xmath26 . we consider two cases , according to whether @xmath329 or @xmath330 . if @xmath330 , then as @xmath33 we may set @xmath331 , so that @xmath332 . let @xmath39 be a solution to @xmath333 in the interval @xmath334 $ ] . such an @xmath39 exists as @xmath39 and @xmath335 are continuous functions , @xmath336 , and @xmath337 . let @xmath338 . let @xmath339 where each @xmath340 takes values independently uniformly from @xmath341 . note that @xmath342 can be thought of as the natural logarithm of the expected degree of a vertex of @xmath26 chosen uniformly at random . now by hoeffding bounds we have that @xmath343 thus there are at most @xmath344 vertices of @xmath26 with expected degree larger than @xmath345 . the sum of the expected degrees of vertices with expected degree smaller than @xmath345 is at most @xmath346 . thus by chernoff bounds with probability at least @xmath347 there are at most @xmath348 edges incident to vertices with expected degree at most @xmath345 . combining this with the vertices with expected degree at least @xmath345 we have that there are at most @xmath349 non - isolated vertices in @xmath26 . for the second case , if @xmath329 , then we note that @xmath350 . as @xmath351 , we have that @xmath352 , and the expected degree of every vertex in @xmath26 is @xmath353 . note then that by linearity of expectation , we have that the expected number of edges in @xmath26 is @xmath354 . as @xmath355 , we have that the expected number of edges in @xmath26 is at most @xmath356 for some @xmath357 . by chernoff bounds , then , the number of edges in @xmath26 is at most @xmath358 with probability at least @xmath359 . but then the number of nonisolated vertices in @xmath26 is at most @xmath360 , and the result follows . the preceding theorem resolves item ( [ m : small ] ) in theorem [ t : master ] . we now turn our attention to proving item ( [ m : giant ] ) in theorem [ t : master ] . to prove this result , we will use the structure outlined in section [ structural ] , and in particular , theorems [ t : sepsilon ] and [ t : snakeone ] regarding the existence of a connected core of vertices and the vertices that can be connected by a path to @xmath361 . in order to apply these theorems , however , we must verify that the conditions are met . we thus begin with several additional lemmas addressing the case that @xmath362 . [ l : c_prod ] let @xmath363 be such that @xmath364 . then @xmath365 with equality if and only if the @xmath38 s are identically 1 . define @xmath366 , where @xmath367 is defined to be 0 and define @xmath368 . as @xmath369 , and all the @xmath370 , it suffices to show that @xmath371 for @xmath372 . we note that since the @xmath38 s are increasing and @xmath373 is a monotonically increasing function @xmath374 , and thus @xmath375 for all @xmath204 . we note that if @xmath376 , then the previous argument implies that @xmath236 . thus suppose that @xmath37 and yet the @xmath38 s are not identically 1 . as this implies that @xmath377 and @xmath42 , there is some minimal @xmath204 such that @xmath378 . but then as @xmath379 , @xmath380 and @xmath381 , we have that @xmath382 , as desired . [ l : uniform ] let @xmath13 be a symmetric matrix in @xmath383^{k \times k}$ ] with non - identical column sums @xmath363 . further suppose that the associated weighted graph @xmath25 is connected and non - bipartite . let @xmath384 be a strictly monotonically increasing function on @xmath385 and let @xmath141 be the vector @xmath386 . if @xmath115 is the transition matrix for the uniform random walk on @xmath25 , then @xmath387 for all @xmath388 . we first note that @xmath389 and consider @xmath390 note that as @xmath384 is strictly increasing , @xmath391 and @xmath392 for @xmath393 . further , as @xmath25 is connected , @xmath394 for some @xmath77 and @xmath204 with @xmath395 , giving that @xmath396 . to complete the proof it would suffice to show that @xmath397 is the transition probability matrix for the uniform random walk on some connected , non - bipartite graph with the same degree sequence as @xmath25 . to that end , fix some @xmath398 and note that @xmath399 , and so let @xmath400 . it is clear that @xmath401 is symmetric and has the desired column sums , thus it suffices to show that the associated graph @xmath202 is connected and non - bipartite . we note that @xmath402 if and only if there is a length @xmath287 walk between @xmath77 and @xmath204 in @xmath25 . we note that if @xmath287 is odd , then the edges present in @xmath202 are a superset of the edges in @xmath25 , and thus @xmath202 is connected and non - bipartite . thus suppose @xmath287 is even and let @xmath403 be an odd length cycle in @xmath25 . consider the walk in @xmath202 formed by starting at vertex @xmath61 and traversing the cycle @xmath403 in steps of length @xmath287 . as @xmath287 is even and the length of the cycle is odd , it will take an odd number of steps in @xmath202 to return to the vertex @xmath61 . thus , there is a closed walk in @xmath202 of odd length and hence @xmath202 is non - bipartite . we note that as @xmath287 is even @xmath202 contains self - loops at all vertices and edges between pairs of vertices that are connected by a walk of length 2 . thus in order to show that @xmath202 is connected it suffices to show that there is an even length walk between any two vertices in @xmath25 . for any two distinct vertices @xmath60 and @xmath61 in @xmath25 such a walk can be constructed by taking a walk from each vertex to the odd cycle @xmath403 and then traversing @xmath403 in both directions . as @xmath403 is an odd cycle , these two traversals will have opposite parity , and thus one of those walks will have even length . these two lemmas immediately give part ( [ m : giant ] ) of our main theorem , as follows . [ t : giant ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . if @xmath404 , then there are constants @xmath405 , depending only on @xmath13 , such that for sufficiently large @xmath14 , @xmath26 has a giant component with probability at least @xmath406 . first , if @xmath350 , we note that the minimum degree in @xmath74 is at least exponential in @xmath14 , and hence by theorem [ t : indepspec ] together with the spectral properties of kronecker products used in theorem [ t : sepsilon ] , @xmath26 is connected with probability at least @xmath407 , and the result follows immediately . if not , then by lemma [ l : c_prod ] , we have that @xmath236 . fix @xmath408 by theorem [ t : sepsilon ] , there is some constant @xmath409 which depends only on @xmath13 such that @xmath177 is connected with probability at least @xmath410 . fix some positive constant @xmath185 . let @xmath61 be an arbitrary vertex such that @xmath411 and let @xmath412 . noting that @xmath413 , we have that for sufficiently large @xmath14 and all @xmath414 , @xmath415 where the first inequality follows from lemma [ l : uniform ] . let @xmath416 and note that this implies that @xmath417 and so by theorem [ t : snakeone ] there is a constant @xmath287 such that with probability at least @xmath418 the vertex @xmath61 is connected to @xmath177 by a path of length at most @xmath287 . observing that a constant fraction of the vertices have the desired signature by chernoff bounds completes the proof . a slight modification of this argument gives part ( [ m : giant_bound ] ) of the main theorem . [ t : giant_bound ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . if @xmath419 such that the @xmath38 s are not all equal , then there are constants @xmath405 , depending only on @xmath13 , such that for sufficiently large @xmath14 , @xmath26 has a giant component with probability at least @xmath420 . since the @xmath38 s are not all equal , we have that @xmath421 by lemma [ l : c_prod ] . fix @xmath239 satisfying the hypotheses of theorem [ t : sepsilon ] ; we shall further restrict @xmath245 as needed below . then by theorem [ t : sepsilon ] there is some constant @xmath422 such that @xmath177 is connected with probability at least @xmath410 . let @xmath423 and note that by theorem [ tvdist ] , @xmath424 for all @xmath425 . note that for all @xmath372 , if @xmath426 , then we have @xmath427 let @xmath428 be the largest integer such that @xmath429 . then we have , for all @xmath430 , @xmath431\ln c_i + \sum_{i = l+1}^k \left(1-\frac{{\epsilon}}{2}\right)\pi_i\ln c_i\\ \nonumber & = & \sum_i \left(1-\frac{{\epsilon}}{2}\right)\pi_i\ln c_i+\frac{{\epsilon}}{2}\sum_{i=1}^l \pi_i\ln c_i\\ \label{epsilonthing } & \geq & \sum_i\left(1-\frac{{\epsilon}}{2}\right)\pi_i\ln c_i + \frac{{\epsilon}}{2}k\ln c_1 \end{aligned}\ ] ] for all @xmath425 . here we further restrict @xmath245 to be sufficiently small that the quantity in ( [ epsilonthing ] ) is positive . moreover , if @xmath432 , we may apply lemma [ l : uniform ] to obtain a constant @xmath433 such that @xmath434 for all @xmath432 . since @xmath287 is a fixed constant , this implies that there is some @xmath435 such that for all @xmath436 , we have @xmath437 . let @xmath185 be a constant to be fixed later . we notice that for @xmath14 sufficiently large all vertices @xmath61 such that @xmath438 are contained in @xmath439 . thus by theorem [ t : snakeone ] these vertices are connected to @xmath440 with probability at least @xmath441 where @xmath442 . at this point it suffices to show that a constant fraction of the vertices in @xmath26 are adjacent to @xmath439 . to this end , let @xmath443 be the set of vertices @xmath444 such that @xmath445 for @xmath446 and @xmath447 . by chernoff bounds and observation [ o : sqrt ] , we have that a constant fraction of the vertices of @xmath26 are in @xmath443 . furthermore , for every vertex @xmath448 , @xmath449 } } \geq 1 now by part ( [ concingbar ] ) of lemma [ agoodneighbor ] , for all @xmath450 , @xmath451 } } \geq 1 - e^{-1}.\ ] ] thus , any fixed vertex in @xmath450 has a neighbor @xmath60 such that @xmath452 with probability at least @xmath453 . we further note that any such neighbor is a member of @xmath439 . taking @xmath454 and applying chernoff bounds completes the proof . finally , we turn to the connectivity of @xmath26 . we note that part ( [ m : connected ] ) of the main theorem follows immediately from theorem [ t : indepspec ] by observing that the minimum degree in @xmath105 is exponential in @xmath14 and exploiting the spectral properties of the kronecker product , as mentioned in the proof of theorem [ t : giant ] . however , in keeping with the theme of this paper we provide an alternative proof which exploits the markov chain structure . [ t : const_diam ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . if @xmath455 , then there is some constant @xmath242 , depending only on @xmath13 such that @xmath26 is connected with probability at least @xmath244 . we first note that as @xmath49 , @xmath456 and thus for any signature @xmath143 , @xmath457 . thus every vertex is in @xmath458 and hence by theorem [ t : snakeone ] for every @xmath178 , every vertex is connected to @xmath177 by a path of constant length with probability at least @xmath459 . thus it suffices to show that there is some @xmath178 such that @xmath177 is connected . but as @xmath460 for all @xmath77 , this implies that @xmath236 and thus by theorem [ t : sepsilon ] there is some constant @xmath461 , depending only on @xmath13 , such that @xmath177 is connected with probability at least @xmath462 . the following two theorems address the case that @xmath463 . we note that we will always have a giant component in this case , unless @xmath464 . however , the connectivity no longer depends entirely on the degrees in the graph , but is determined based on how the weight is distributed among the vertices . in particular , the backbone graph will determine the behavior . [ t : discon ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by @xmath0^{k \times k}$ ] with column sums @xmath465 . if @xmath25 is connected and non - bipartite and the backbone graph @xmath29 has a vertex of degree zero , then there is a constant @xmath184 such that with probability at least @xmath466 the graph @xmath26 has at least @xmath467 isolated vertices . note that as the backbone graph @xmath29 has a vertex of degree 0 , there exists a vertex @xmath468 such that for all vertices @xmath60 , @xmath469 . we note that in this case we have @xmath470}},\end{aligned}\ ] ] where the last inequality comes from the upper bound on @xmath471 . thus we have that @xmath472}}}.$ ] thus it suffices to find a large collection of vertices in @xmath26 whose degrees are independent and where @xmath449}}$ ] is small . to that end suppose that there is some @xmath77 such that @xmath473 , that is , the degree of vertex @xmath474 in @xmath29 is not zero . thus there is some @xmath475 such that @xmath204 has degree zero in @xmath29 . now let @xmath476 be the set of vertices in @xmath26 whose signature @xmath143 has @xmath477 , @xmath478 , and @xmath479 for @xmath480 . since @xmath45 and @xmath481 , we know that @xmath482 and thus the degrees of all vertices in @xmath476 are independent . we note that there is a choice of constant @xmath185 such that if @xmath483 then the expected number of isolated vertices in @xmath476 is @xmath484 , and thus by chernoff bounds with probability at least @xmath485 there are at least @xmath467 isolated vertices in @xmath26 . now suppose that the degree of @xmath474 in @xmath29 is zero . choose some index @xmath486 arbitrarily and consider the set @xmath476 as above . as @xmath204 is arbitrary there may be some edges between vertices of @xmath487 . thus we note that when @xmath488 , we have @xmath489 } } & = \sum_{u \in s^{(j)}_{t_j } } \sum_{v \in s^{(j)}_{t_j } } { \ensuremath{{{\mathbb{p}}}\!\left ( u \sim v\right ) } } \\ & = 2\binom{t}{t_j } \sum_{i=0}^{t_j } \binom{t_j}{i } \binom{t - t_j}{t_j - i}p_{jj}^{t_j - i } p_{j1}^{i } p_{1j}^i p_{11}^{t- t_j - i } \\ & \leq 2\binom{t}{t_j}\binom{t - t_j}{t_j } p_{11}^{t- 2t_j}{\ensuremath{\left ( p_{11}p_{jj } + p_{1j}^2 \right)}}^{t_j}\\ & \leq 2t^{t_j}t^{t_j}p_{11}^{t-2t_j}(p_{11}p_{jj}+p_{1j}^2)^{t_j}\end{aligned}\ ] ] in particular , there is a constant @xmath257 such that @xmath490 } } \leq { \ensuremath{\left ( c't^2 \right)}}^{t_j}p_{11}^t$ ] . as @xmath491 , this implies that the probability of an edge in @xmath487 is exponentially small provided @xmath492 . thus , again choosing @xmath493 and conditioning on @xmath494 gives the desired result . a slight simplification of this result gives part ( [ m : discon_c1 ] ) of theorem [ t : master ] . [ t : bconn ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . if @xmath495 and the backbone graph @xmath29 has no vertices of degree zero , then there is a constant @xmath496 such that @xmath26 is connected with probability at least @xmath407 . first we note that @xmath377 as otherwise the only edges present in @xmath25 are those present in the backbone graph , and in particular , @xmath25 is a perfect matching contradicting the non - bipartiteness . thus we have that @xmath236 and thus by theorem [ t : sepsilon ] there is some @xmath178 and @xmath497 such that @xmath498 is connected with probability at least @xmath499 . now in a similar manner as the proof of theorem [ t : snakeone ] it suffices to show that asymptotically almost surely , from every vertex @xmath500 there is a sequence @xmath501 such that @xmath502 and @xmath503 . by imposing the additional condition that @xmath504 , we may take @xmath505 by theorem [ tvdist ] and the markov chain viewpoint . to that end fix an arbitrary vertex @xmath61 and consider the behavior of @xmath89 from the point of view of the product distribution @xmath506 where @xmath507 is the number of @xmath77 s in the label for @xmath61 . notice that for those indicies @xmath77 where @xmath508 , @xmath93 is the identity distribution . furthermore , these coordinates perfectly respect the action of the markov chain given by @xmath115 . let @xmath204 be the first index with @xmath509 , so that @xmath510 . suppose that @xmath511 . note then any neighbor @xmath60 of @xmath61 in @xmath512 immediately satisfies that @xmath513 . otherwise , we have @xmath514 . but then @xmath449 } } \geq c_j^{\frac{\epsilon}{s k { \ensuremath{\left\| l \right\|_{\infty}}}}t}$ ] and @xmath509 , and thus by lemma [ agoodneighbor ] , there is a constant @xmath185 such that @xmath515 applying chernoff bounds to assure the existence of such a vertex completes the proof . we note that in principle these techniques can be extended to analyze the emergence of connectivity and the giant component in generalizations of the stochastic kronecker graph , such as the multiplicative attribute graph @xcite . in fact , based on the work in @xcite , it is likely that similar transition points will hold . that is , the multiplicative attribute graph will have a giant component when the median expected degree is 1 and become connected when the probability of an isolated vertex goes to zero . perhaps a more interesting direction would to resolve the size of the largest component in the case when @xmath516 . by letting @xmath517 we see that this regime includes the erds - rnyi graph @xmath518 at criticality . thus it seems likely that in order to understand the size of the largest component of the stochastic kronecker graph when @xmath519 it will require a deeper understanding of why the branching process for @xmath520 terminates with a largest component of size @xmath521 @xcite . as a possible intermediate stage , consider a @xmath522-regular , connected , non - bipartite graph @xmath241 on @xmath2 vertices and let @xmath13 be @xmath523 times the adjacency matrix of @xmath241 . what is the size of the largest component in the @xmath12-order stochastic kronecker graph generated by @xmath13 ? from a natural coupling with @xmath524 it is clear that it should be at least @xmath525 . on the other hand , since the degree of every vertex is still asymptotically poisson with parameter 1 , the branching process point of view would indicate that the size of the largest component should be @xmath526 . however , we note that if @xmath241 is the @xmath522-regular graph formed by two copies of @xmath527 joined by a perfect matching , then @xmath304 consists of @xmath528 copies of @xmath529 with relatively few edges between them . furthermore , as the expected degree within each of these copies of @xmath529 is @xmath530 , the largest component in each of these components is @xmath531 , seemingly indicating that the overall size of the largest component is relatively small . thus , it seems likely that any resolution of the case where @xmath532 will necessitate a deeper understanding of the branching process at criticalility , and specifically , how the branching process interacts with the underlying network of potential edges .

stochastic kronecker graphs are a model for complex networks where each edge is present independently according to the kronecker ( tensor ) product of a fixed matrix @xmath0^{k \times k}$ ] . we develop a novel correspondence between the adjacencies in a general stochastic kronecker graph and the action of a fixed markov chain . using this correspondence we are able to generalize the arguments of horn and radcliffe on the emergence of the giant component from the case where @xmath1 to arbitrary @xmath2 . we are also able to use this correspondence to completely analyze the connectivity of a general stochastic kronecker graph .

<s>[INST]in many ways the study of random graphs traces its history back to the seminal work of erds and rnyi showing that there exists a rapid transition between the regimes of a random graph consisting of many small components , a random graph having one `` giant '' component , and a random graph being connected @xcite . because of their central role in the history of random graphs these phase transitions have been extensively studied , see for instance @xcite , among numerous others . we contribute to this ongoing discussion by providing a sharp transition for the emergence of both the giant component and connectivity for the stochastic kronecker graph , a generalization of the standard erds - rnyi binomial random graph model , @xmath3 . more formally , recall that the kronecker or tensor product of two matrices @xmath4 and @xmath5 is a matrix @xmath6 . for @xmath7 , j \in [ n ] , s \in [ p],$ ] and @xmath8 $ ] the entry @xmath9 is @xmath10 , that is @xmath11.\ ] ] letting @xmath0^{k \times k}$ ] be a symmetric matrix , the @xmath12-order stochastic kronecker graphgenerated by @xmath13 is formed by taking the @xmath14-fold kronecker product of @xmath13 , denoted @xmath15 , and using this as the probability matrix for a graph with independent edges . that is , each edge @xmath16 is present independently with probability @xmath17 . the stochastic kronecker graph was originally proposed as a model for the network structure of the internet with the property that it could be easily fit to real world data , especially in the case where the generating matrix was @xmath18 $ ] where @xmath19 @xcite . as such , there have been several papers analyzing structural properties of the stochastic kronecker graph when the generating matrix is a @xmath20 matrix @xcite . most relevant to this current work are the results of mahdian and xu @xcite who anaylzed the connectivity , diameter , and the emergence of the giant component with @xmath21 , and the work of the first author and horn who analyzed the emergence and size of the giant component for arbitrary @xmath22 @xcite . in this work we consider the case of an arbitrarily sized generating matrix , and develop necessary and sufficient conditions for the emergence of the giant component and connectivity . the key tool to analyzing these graphs is to tie the structure of the graph to a fixed markov chain on the underlying generating matrix . using this underlying structure , one can analyze the graph structure more completely than with traditional tools . given a @xmath12-order stochastic kronecker graph with generating matrix @xmath13 , we define @xmath23 to be the weighted graph on @xmath24 $ ] , where weights are as given in @xmath13 . we will occasionally refer to @xmath25 as the underlying graph of @xmath26 . we also define the backbone graph of the matrix @xmath13 , @xmath27 , as the subgraph of @xmath23 consisting of the edges assigned weight 1 . that is , @xmath27 is a graph on the vertices @xmath24 $ ] where @xmath16 is an edge if and only if @xmath28 . when the matrix @xmath13 is clear , we will neglect the dependence on @xmath13 and write simply @xmath25 and @xmath29 . our primary results can be summarized as follows . [ t : master ] let @xmath26 be @xmath12-order stochastic kronecker graph generated by a symmetric matrix @xmath0^{k \times k}$ ] which has column sums @xmath30 . let @xmath31 be the number of vertices of @xmath26 . 1 . if @xmath25 is disconnected or bipartite , then the largest component of @xmath26 has size @xmath32 [ m : disc_bip ] 2 . if @xmath25 is connected and non - bipartite and @xmath33 , then there is some @xmath34 such that with probability at least @xmath35 there are at least @xmath36 isolated vertices in @xmath26 . [ m : small ] 3 . if @xmath25 is connected , non - bipartite , @xmath37 , and the @xmath38 s are not identically one , then there is a positive constant @xmath39 such that with probability at least @xmath35 , the largest component of @xmath26 has size @xmath40 , that is , @xmath26 has a giant component . [ m : giant_bound ] 4 . if @xmath25 is connected , non - bipartite , and @xmath41 , then there is a positive constant @xmath39 such that with probability at least @xmath35 the largest component of @xmath26 has size @xmath40 . [ m : giant ] 5 . if @xmath25 is connected , non - bipartite , and @xmath42 , then there is a positive constant @xmath39 such that @xmath26 has at least @xmath43 isolated vertices with probability at least @xmath44 . [ m : discon_c1 ] 6 . if @xmath25 is connected , non - bipartite , @xmath45 , and @xmath29 has a vertex of degree zero , then there is some positive constant @xmath39 such that @xmath26 has at least @xmath46 isolated vertices with probability at least @xmath44.[m : discon ] 7 . if @xmath25 is connected and non - bipartite , @xmath45 , and @xmath29 has no vertices of degree zero , then there is a constant @xmath47 such that @xmath26 is connected with probability at least @xmath48 . [ m : connect_bound ] 8 . if @xmath25 is connected and non - bipartite and @xmath49 , then there is a constant @xmath47 such that @xmath26 is connected with probability at least @xmath50 . [ m : connected ] we note that item ( [ m : connected ] ) above is typical for the emergence of connectivity ; that is , the graph is connected asymptotically almost surely precisely when asymptotically almost surely the minimum degree is at least 1 . in fact , taking ( [ m : discon_c1 ] ) , ( [ m : discon ] ) , ( [ m : connect_bound ] ) , and ( [ m : connected ] ) together we can see that a stochastic kronecker graph is connected precisely when the minimum degree is at least 1 asymptotically almost surely . from this viewpoint , the slightly unnatural seeming condition on the backbone graph @xmath29 is simply the condition needed to assure that @xmath26 has no isolated vertices . the folklore in the study of random graphs asserts that , in general , the giant component should emerge when the average expected degree is 1 , see for instance @xcite . as the average expected degree in a @xmath12-order stochastic kronecker graphis @xmath51 , this suggests that the transition occurs when @xmath52 . however , as parts ( [ m : small ] ) and ( [ m : giant ] ) of theorem [ t : master ] show , the transition actually occurs when @xmath53 . noting that the expected degrees in stochastic kronecker graphs follow a multinomial distribution ( see section [ defsec ] ) , this condition can be seen as equivalent ( asymptotically ) to the condition that _ median _ expected degree is at least one . thus our results may suggest that the average expected degree is not as deeply connected to giant component as previously thought , because in many of the standard random graph models , such as the erds - rnyi random graph , the average and the median expected degree agree . that is , it may be that the median is truly the determining factor for such structures . it is also worth noting that spencer has conjectured based in part on @xcite , that the correct intuition is that the emergence of the giant component is tied to the second order average degree @xcite . to prove theorem [ t : master ] , we will develop several general results on @xmath26 , and then apply these results to the specific situations above . in particular , we are able to tie the adjacency structure of @xmath26 to a finite state markov chain on @xmath25 . using this association , we can take advantage of the finite structure of @xmath25 to build theory regarding the asymptotically growing structure @xmath26 . given a stochastic kronecker graph @xmath26 generated by @xmath13 , let @xmath54 be the adjacency matrix of @xmath26 and @xmath55 the diagonal matrix of degrees in @xmath26 . let @xmath56 be the column sums of @xmath13 ( note that we can assume these are nondecreasing without loss of generality ) , and let @xmath57 be the diagonal matrix of column sums in @xmath13 . we note that there are multiple means of describing the entries of the probability matrix @xmath15 to take advantage of the kronecker product structure . one point of view that is particularly helpful is to define a bijection @xmath58^t$ ] , so that each vertex of @xmath26 is represented by a word of length @xmath14 in @xmath24 $ ] . we will often identify the vertex to its corresponding word , and write @xmath59 . given an appropriate choice of bijection , for any two vertices @xmath60 and @xmath61 , the probability that @xmath60 and @xmath61 are adjacent is @xmath62 that is to say , we take the product of entries of the generating matrix @xmath13 , where entries correspond to the pairs of components in the words representing @xmath60 and @xmath61 . we will sometimes use the notation @xmath63 to refer to the @xmath64 position in @xmath15 , where we index the matrix by the ordered words obtained via the kronecker product , and we note that @xmath65 . we shall use the notation @xmath66 to indicate that @xmath60 is adjacent to @xmath61 . when ambiguous , we write @xmath67 to indicate that @xmath60 is adjacent to @xmath61 in the graph @xmath26 . now , suppose that @xmath68 has @xmath69 coordinates equal to 1 , @xmath70 coordinates equal to 2 , and so on . it is straightforward to calculate that @xmath71 } } = c_1^{a_1}c_2^{a_2}\dots c_k^{a_k}.\ ] ] from this we can see that the stochastic kronecker graph is defined precisely so that the expected adjacency matrix @xmath72 , and the expected degree matrix @xmath73 . at times we will wish to emphasize the graph structure of @xmath15 , and thus will use @xmath74 to refer to the weighted complete graph with weights given by @xmath15 . moreover , it will frequently be of interest to know the number of coordinates in @xmath68 equal to each symbol in @xmath24 $ ] . to that end , we define the _ signature _ of @xmath61 to be @xmath75 , where @xmath76 is the proportion of symbols in @xmath68 equal to @xmath77 . for example , if @xmath78 and @xmath79 , we would have @xmath80 . we will denote by @xmath81 the space of possible signatures . often we will establish an underlying signature for a vertex and then take @xmath14 to infinity ; this will generally result in noninteger values for the number of letters of a particular value in @xmath68 . this can be overlooked , however , as rounding to the next integer appropriately will not change the asymptotic features of the vertices , and so we will often assume that a vertex can take any signature . let @xmath82 . we will make frequent use of the simple observation that @xmath83 } } \right ) } } = t { \ensuremath{\left\langle \sigma(v ) , l \right\rangle}},\ ] ] where @xmath84 represents the standard dot product . let @xmath74 be the weighted complete graph on @xmath85 , with the weight of edge @xmath86 equal to @xmath87 . let @xmath61 be a vertex in @xmath74 with signature @xmath88 . define @xmath89 to be a random variable that takes values in @xmath90 , where @xmath89 is the signature of a randomly chosen neighbor of @xmath61 according to the probability distribution defined by the weights of the edges . that is , @xmath91 that is to say , @xmath89 is the signature of the vertex obtained after taking one step in the uniform random walk on @xmath74 . for each @xmath92 $ ] , let @xmath93 be the random variable that takes values in @xmath24 $ ] , with @xmath94 . note that for @xmath59 fixed , we have @xmath95 thus we can consider @xmath89 as giving the signature of a randomly chosen neighbor of @xmath61 , chosen according to the product distribution @xmath96 . as the signature is independent of order , for the purposes of analyzing @xmath89 , we may write this distribution as @xmath97 . therefore , for all @xmath92 $ ] , letting @xmath98 be the @xmath99 component of the signature @xmath89 , we have @xmath100 } } = \frac{1}{t}\sum_{j=1}^k ( \sigma_jt ) { { \mathbb{p}}}(x^{(j)}=i)= \sum_{j=1}^k \sigma_j \frac{p_{ij}}{c_j}.\ ] ] on the other hand , let @xmath101 , the transition probability matrix for the uniform random walk on @xmath25 and notice that the matrix product @xmath102 has @xmath99 coordinate @xmath103}}\ ] ] thus , @xmath104}}$ ] . therefore , we can think of the distribution of a random walk on @xmath25 as the expected signature of a vertex in a random walk on @xmath105 . let @xmath106 be the stationary distribution of the random walk on @xmath25 , so @xmath107 . it is a simple exercise to verify that @xmath108 . we will show in section [ structural ] that the collection of signatures close to @xmath109 will in fact , asymptotically almost surely , form a connected subgraph in @xmath26 , and further , by leveraging the convergence of the markov chain on @xmath25 , we can assure a giant component . for a given graph @xmath26 , the normalized laplacian matrix for @xmath26 is the matrix @xmath110 . we denote the eigenvalues of @xmath111 by @xmath112 . if there is any ambiguity , we write @xmath113 to specify that the eigenvalues are from the normalized laplacian , and more generally @xmath114 to denote the @xmath99 smallest eigenvalue of a hermitian matrix @xmath115 . we sometimes refer to these as the laplacian eigenvalues of @xmath26 . we shall use the following standard facts from spectral graph theory . [ t : standards ] let @xmath26 be a graph with laplacian eigenvalues @xmath116 . then 1 . @xmath26 is connected if and only if @xmath117 . if @xmath26 is connected , then the diameter @xmath118 of @xmath26 satisfies @xmath119 . 3 . let @xmath120 denote the probability transition matrix of a random walk on @xmath26 . then @xmath121 is an eigenvalue of @xmath111 with eigenvector @xmath61 if and only if @xmath122 is an eigenvalue of @xmath120 with eigenvector @xmath61 . among our key tools will be the following theorem from chung and the first author @xcite that gives spectral concentration in the normalized laplacian of a general random graph . [ t : indepspec ] let @xmath26 be a random graph with independent edges generated according to the matrix @xmath123 . let @xmath124 be the diagonal matrix of expected degrees and let @xmath125 denote the minimum expected degree . if @xmath126 , then with probability at least @xmath127 , for all @xmath77 @xmath128 we also make use of standard tools in spectral graph theory , chief among them the cheeger inequality . for two sets @xmath129 of vertices in a graph @xmath26 , define @xmath130 to be the number of edges ( or , in a weighted graph , the total weight of edges ) for which one endpoint is in @xmath131 and the other in @xmath132 . note that an edge with both endpoints in @xmath133 is counted twice in this definition . define @xmath134 . when the underlying graph is clear , we drop the subscript @xmath26 in the notation . the cheeger constant of a set @xmath131 with @xmath135 is defined to be @xmath136 and cheeger constant of @xmath26 is @xmath137 the spectrum of a graph is related to the cheeger constant via the cheeger ineqaulity @xcite . for @xmath26 any graph , let @xmath138 be the smallest nontrivial eigenvalue of @xmath139 . then @xmath140 as we will frequently be discussing markov chains , we will pass regularly between considering row vectors and column vectors . we will always treat the signature of a vertex @xmath61 as a row vector , as well as the vector @xmath141 . the all - ones vector , @xmath142 , will be considered a row vector as well . however , eigenvectors of a matrix are typically assumed to be right eigenvectors , and are thus column vectors . any other usages should be made clear by context . in order to understand the rate of convergence of a markov chain we will use the relative pointwise distance . if @xmath109 is the limiting distribution of the markov chain , the relative pointwise distance of a distribution @xmath143 from @xmath109 is @xmath144 as we are interested in an overall rate of convergence we define @xmath145 it is well known that the rate of decay of the relative pointwise distance can be controlled by the spectral information of the markov chain as given in the following theorem , see for instance @xcite . [ tvdist ] let @xmath146 be the eigenvalues of the transition probability matrix of a uniform random walk on a connected , non - bipartite ( weighted ) graph @xmath26 . set @xmath147 . for any @xmath148 we have @xmath149 , where @xmath150 denotes the minimum degree in @xmath26 . the phrase _ asymptotically almost surely _ in this paper will always refer to asymptotics with respect to @xmath14 , unless otherwise noted . the norm @xmath151 will refer to the @xmath152-norm unless otherwise noted . to prove the thresholds for connectivity and emergence of the giant component in a stochastic kronecker graph @xmath26 ( theorem [ t : master ] , items ( [ m : giant ] ) and ( [ m : connected ] ) ) , we will use the following structure . first , we show that @xmath26 contains a small set of vertices that is connected asymptotically almost surely , in particular , those vertices that are close to stationarity under the markov chain described in section [ mcdescription ] . we shall refer to this set as the `` connected core '' of the graph . although this will not be enough vertices to form a giant component , we can then show that under certain conditions , a positive fraction of the vertices in @xmath26 can be connected by a path to the connected core . the thresholds given are precisely those conditions needed to ensure that a positive fraction of the vertices exhibit this behavior . in retrospect , the arguments used by horn and the first author in @xcite to show the emergence of the giant component in the case where the generating matrix is @xmath153 can be viewed as a special case of our technique . specifically , as the underlying markov chain has only two states , the degree of each vertex is controlled by a single parameter , which significantly simplifies the argument . as a consequence , the authors in @xcite were able to analyze the giant component directly via counting techniques , without appealing to the underlying markov chain . in this section , we develop much of the underlying structure in @xmath26 via the random walk on @xmath25 . we begin with some elementary observations on the vertex degrees in @xmath26 and @xmath74 . [ agoodneighbor ] let @xmath61 be a vertex with signature @xmath143 in a @xmath12-order stochastic kronecker graph @xmath26 , such that @xmath154 . let @xmath155 . for any @xmath156 , we have 1 . [ concingbar ] @xmath61 has at least @xmath157 neighbors in @xmath74 with signature @xmath158 such that @xmath159 } } \right\|_{}}}\leq \delta$ ] . [ agoodneighborg ] with probability at least @xmath160 , @xmath61 has at least @xmath161 neighbors in @xmath26 with signature @xmath158 such that @xmath159 } } \right\|_{}}}\leq \delta$ ] . by the hoeffding inequality , we have that for any @xmath77 , @xmath162 } } \right| } } > \delta t\right)\leq 2e^{-2\delta^2 t}\ ] ] for any @xmath156 . therefore , by the union bound , we have @xmath163\hbox { such that } t{\ensuremath{\left| z^{(v)}_i-{\ensuremath{{{\mathbb{e}}}\!\left [ z^{(v)}_i \right ] } } \right|}}>\delta t\right)\leq 2ke^{-2\delta^2t}.\ ] ] this verifies item ( [ concingbar ] ) . for item ( [ agoodneighborg ] ) , note that by ( [ concingbar ] ) , we have that the expected number of neighbors of @xmath61 with signature @xmath158 in the desired range is at least @xmath157 . by chernoff bounds , then , with probability at least @xmath160 , we have at least @xmath161 neighbors with such a signature @xmath158 . as an immediate corollary of this result we have the following . [ c : tight ] let @xmath61 be a vertex with signature @xmath143 in a @xmath12-order stochastic kronecker graph @xmath26 , such that @xmath164 . let @xmath165 . with probability at least @xmath166 , @xmath61 has at least @xmath167 neighbors @xmath60 with @xmath168 . recall from section [ mcdescription ] that @xmath169 is the stationary distribution of the random walk on @xmath25 , with @xmath170 for all @xmath77 . given @xmath171 , define @xmath172 , \sigma_i(v)>(1-\epsilon)\pi_i\}$ ] . notice that if @xmath173 with signature @xmath143 , then we have , for all @xmath77 , @xmath174 by stationarity of @xmath109 . hence , if @xmath175 , then @xmath176}}$ ] is also in @xmath177 . we will show that under appropriate conditions , this set of vertices @xmath177 is connected asymptotically almost surely , forming the small connected core described above . to do this , we will show that vertices in @xmath177 have exponentially large degree in @xmath14 , and then use theorem [ t : indepspec ] to show the first eigenvalue in @xmath177 is bounded away from zero . we first must address the degree of vertices in @xmath177 . to that end , we have the following lemma : [ se_degree ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by @xmath13 and let @xmath178 be fixed , and assume @xmath25 is connected and nonbipartite . for sufficiently large @xmath14 there is a constant @xmath179 , depending only on @xmath13 and @xmath180 , such that for all @xmath181 , @xmath182 . to prove this lemma , we make use of the following standard observation about binomial random variables . [ o : sqrt ] let @xmath183 be fixed constants and let @xmath184 . there exists constants @xmath185 and @xmath186 , depending on @xmath187 and @xmath188 such that if @xmath189 , then @xmath190\right ) } } > c.\ ] ] let @xmath61 be an arbitrary vertex in @xmath177 . consider a collection of independent , identically distributed random variables , @xmath191 , taking on values in @xmath192 each with probability @xmath193 , where @xmath194 for all @xmath77 . let @xmath195 be the count of the number of @xmath77 s in these variables , that is , @xmath196 . for @xmath197 , let @xmath198 be the event that @xmath199 . we then have that , for all @xmath200 , @xmath201 } } & \geq { \ensuremath{\left ( t - { \ensuremath{\left ( p_it - c\sqrt{t } \right ) } } \right ) } } \frac{p_j}{1-p_i } \\ & = { \ensuremath{\left ( ( 1-p_i)t + c\sqrt{t } \right ) } } \frac{p_j}{1-p_i } \\ & = p_jt + \frac{c p_j}{1-p_i}\sqrt{t } \\ & \geq p_jt + c p \sqrt{t}. \end{aligned}\ ] ] to apply this observation to the context of @xmath89 we first consider the unweighted graph @xmath202 on @xmath24 $ ] where @xmath203 if and only if there is an unweighted walk of length 2 between @xmath77 and @xmath204 in @xmath25 . since @xmath25 is connected and non - bipartite , @xmath202 is connected and thus there exists a breadth - first traversal of @xmath202 . as noted above , by the definition of @xmath177 , for every @xmath77 we have @xmath205 . further , by the pigeonhole principle , there is some index @xmath77 such that @xmath206 . let @xmath207 be one such index and let @xmath208 be a breadth - first traversal of @xmath202 starting at @xmath207 . recall that we may analyze @xmath89 from the point of view of the product distribution @xmath209 where each @xmath93 is an independent random variable that takes values in the set of neighbors of @xmath77 in @xmath25 . let the random variables @xmath210 be the number of times that @xmath93 takes on the value @xmath204 . we note that we can ignore the indices that @xmath93 can not take on , and so define @xmath211 . we recursively define the events @xmath212 as follows . the event @xmath213 is the event that for all @xmath214 , @xmath215 } } - 2\alpha_1\sqrt{t } \leq z_{us_1 } \leq { \ensuremath{{{\mathbb{e}}}\!\left [ z_{us_1 } \right ] } } - \alpha_1\sqrt{t}.$ ] for all @xmath216 the event @xmath217 is the event that for all @xmath218 , @xmath219 } } - 2\alpha_i\sqrt{t } \leq z_{us_i } \leq { \ensuremath{{{\mathbb{e}}}\!\left [ z_{us_i } \mid \cap_{j=1}^{i-1 } \mathcal{a}_j \right ] } } - \alpha_i\sqrt{t},\ ] ] where the @xmath220 s are fixed constants to be chosen later . we note that by observation [ o : sqrt ] , as @xmath221 is a sum of independent indicator variables , each with probability @xmath193 , each of these events occurs with positive probability . thus it suffices to show that @xmath222 is contained in the event @xmath223 . for sufficiently large @xmath14 the event @xmath213 assures that @xmath224 by the choice of @xmath207 , specifically that @xmath225 } } \geq ( 1-{\epsilon})\pi_{s_1 } + \frac{\epsilon}{k}$ ] . since the sequence @xmath226 is a breadth - first search of @xmath202 , we have that for all @xmath227 , there exists index @xmath228 such that @xmath229 . thus there is some vertex @xmath60 that is a neighbor to both @xmath226 and @xmath230 in @xmath25 . now consider the effect of the conditioning on the event @xmath231 on @xmath221 . by ( [ abovecalculations ] ) and the definition of @xmath231 we have that @xmath232 } } \geq { \ensuremath{{{\mathbb{e}}}\!\left [ z_{us_i } \right ] } } + \alpha_{i-1}p_{u}\sqrt{t } \geq { \ensuremath{{{\mathbb{e}}}\!\left [ z_{us_i } \right ] } } + \alpha_{i-1}p_{\min}\sqrt{t}$ ] where @xmath233 } p_i$ ] . furthermore , this gives that @xmath234 } } \geq ( 1-\epsilon)\pi_{s_i}t + \alpha_{i-1}p_{\min}\sqrt{t}$ ] . thus choosing @xmath235 suffices to assure that the event @xmath222 is contained in @xmath177 , as desired . [ t : sepsilon ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . further suppose that @xmath236 and fix @xmath237 if @xmath238 , and @xmath239 if @xmath240 . let @xmath241 be the subgraph of @xmath26 induced by @xmath177 . for @xmath14 sufficiently large , there is a constant @xmath242 , depending on @xmath13 and @xmath180 , such that @xmath241 is connected with diameter @xmath243 with probability at least @xmath244 . notice that the bound on @xmath245 is always positive ( or infinite ) , since @xmath246 for all @xmath77 , so @xmath247 . we will proceed by showing that there exists a constant @xmath197 such that the graph @xmath241 has @xmath248 asymptotically almost surely . as noted in theorem [ t : standards ] , this implies that @xmath241 is connected asymptotically almost surely , with diameter @xmath249 . recall that the expected degree of a vertex with signature @xmath143 is @xmath250 and thus any vertex @xmath181 has expected degree at least @xmath251 where @xmath252 we note that by the restriction on @xmath180 , @xmath253 and thus @xmath242 . this implies that every vertex in @xmath177 has expected degree exponentially increasing with @xmath14 . let @xmath254 be the subgraph of @xmath74 induced by @xmath255 , so the weight of each edge in @xmath254 is the probability of that edge appearing in @xmath241 . now , by lemma [ se_degree ] , there is some constant @xmath185 such that for every vertex @xmath61 in @xmath254 we have @xmath256 . now for any positive constant @xmath125 , there exists some small positive constant @xmath257 such that @xmath258 and thus , by theorem [ t : indepspec ] , in order to complete the proof it suffices to show that @xmath254 has constant spectral gap . indeed , by theorem 3 , if there exists a constant @xmath259 with @xmath260 , then by theorem 3 , @xmath261 with probability at least @xmath262 , and by the above , we have that @xmath263 for any @xmath156 with probability at least @xmath262 , as desired . to determine the spectral gap in @xmath254 , we use cheeger s inequality . let @xmath264 with @xmath265 . note that @xmath266 where the constant @xmath185 is the constant provided by lemma [ se_degree ] . thus , we have @xmath267 now , let @xmath268 and let @xmath269 be the eigenvalues of @xmath270 . note that @xmath271 is the laplacian matrix for @xmath25 , and as @xmath25 is connected and non - bipartite , @xmath272 . now , @xmath273 , and thus has eigenvalues @xmath274 , where @xmath275\cup\{0\}$ ] . hence , the smallest nonzero eigenvalue of @xmath276 is @xmath277 , which occurs with multiplicity @xmath14 . thus by cheeger s inequality , @xmath278 . therefore , combining these results we have @xmath279 hence @xmath280 is bounded below by a constant and @xmath254 has constant spectral gap , as desired . this establishes that the graph @xmath26 contains a small connected core asymptotically almost surely provided @xmath281 . we now turn our attention to the second half of our fundamental structure . here we wish to determine which vertices will be connected by a path to the connected core . to that end , define @xmath282 . we wish to show that any vertex in @xmath283 may be connected by a path to @xmath177 asymptotically almost surely . [ t : snakeone ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . fix @xmath284 . let @xmath121 be the spectral gap of @xmath25 and let @xmath285 . for @xmath14 sufficiently large , any vertex @xmath286 is connected to @xmath177 by a path of length at most @xmath287 with probability at least @xmath288 . let @xmath286 . define @xmath289 and for each @xmath290 , let @xmath291 be a neighbor of @xmath292 such that @xmath293 ( if such a neighbor exists ) . for @xmath294 define @xmath295 . now , we note that if such a sequence exists , then @xmath296 and further @xmath297 thus , since @xmath287 is a fixed constant , we have that by corollary [ c : tight ] for sufficiently large @xmath14 such a sequence fails to exist with probability at most @xmath298 it now suffices to show that @xmath299 . by the choice of @xmath287 and theorem [ tvdist ] , we know that @xmath300 and thus @xmath301 but then as @xmath302 we have that for sufficiently large @xmath14 , @xmath299 . we now turn to the case that the stochastic kronecker graph has only small components , that is , the largest component is of size at most @xmath303 . these correspond to items ( [ m : disc_bip ] ) and ( [ m : small ] ) in theorem [ t : master ] . the first of these result follows from standard results on the component sizes of ( non - stochastic ) kronecker graphs which we include in the following lemma for completeness . [ t : smallcomps ] if @xmath241 is a disconnected or bipartite graph on @xmath2 vertices , then the largest component of @xmath304 has size @xmath305 . first , suppose @xmath241 is not connected . let @xmath59 be a vertex in @xmath304 . now for any neighbor @xmath306 of @xmath61 each coordinate @xmath307 must be adjacent to @xmath291 in @xmath241 and hence in the same component as @xmath291 . thus , the size of the component containing @xmath61 is at most the product of the sizes of the components in @xmath241 of the vertices @xmath291 . since @xmath241 is disconnected the largest component in @xmath241 has size at most @xmath308 and thus the largest component in @xmath304 has size at most @xmath309 . now , suppose @xmath241 is a connected bipartite graph with bipartition @xmath310 and again consider a vertex @xmath311 and a neighbor @xmath60 of @xmath61 , with @xmath312 . now since @xmath291 and @xmath307 are adjacent in @xmath241 , they are on different sides of the bipartition @xmath310 . thus the component containing @xmath61 and @xmath60 is bipartite with @xmath60 and @xmath61 on different sides of the bipartition . furthermore , the side of the bipartition containing @xmath61 has @xmath313 vertices . thus for all @xmath314 there are @xmath315 components of @xmath304 of size @xmath316 . it is worth noting that this size is symmetric and so that components counted for a given @xmath77 are also counted for @xmath317 . now maximizing @xmath316 over the choice of @xmath77 , we have the largest component occurs where either @xmath318 or @xmath319 . as @xmath320 , we maximize with respect to @xmath321 to obtain that the largest of component of @xmath304 has size at most @xmath322 for @xmath323 . this lemma resolves item ( [ m : disc_bip ] ) in theorem [ t : master ] as it implies that the underlying graph for @xmath15 is disconnected with small component sizes . [ t : small ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by @xmath0^{k \times k}$ ] with column sums @xmath324 . if @xmath25 is connected , non - bipartite , and @xmath325 , then there exists some @xmath326 such that with probability at least @xmath327 there are at least @xmath328 isolated vertices in @xmath26 . we consider two cases , according to whether @xmath329 or @xmath330 . if @xmath330 , then as @xmath33 we may set @xmath331 , so that @xmath332 . let @xmath39 be a solution to @xmath333 in the interval @xmath334 $ ] . such an @xmath39 exists as @xmath39 and @xmath335 are continuous functions , @xmath336 , and @xmath337 . let @xmath338 . let @xmath339 where each @xmath340 takes values independently uniformly from @xmath341 . note that @xmath342 can be thought of as the natural logarithm of the expected degree of a vertex of @xmath26 chosen uniformly at random . now by hoeffding bounds we have that @xmath343 thus there are at most @xmath344 vertices of @xmath26 with expected degree larger than @xmath345 . the sum of the expected degrees of vertices with expected degree smaller than @xmath345 is at most @xmath346 . thus by chernoff bounds with probability at least @xmath347 there are at most @xmath348 edges incident to vertices with expected degree at most @xmath345 . combining this with the vertices with expected degree at least @xmath345 we have that there are at most @xmath349 non - isolated vertices in @xmath26 . for the second case , if @xmath329 , then we note that @xmath350 . as @xmath351 , we have that @xmath352 , and the expected degree of every vertex in @xmath26 is @xmath353 . note then that by linearity of expectation , we have that the expected number of edges in @xmath26 is @xmath354 . as @xmath355 , we have that the expected number of edges in @xmath26 is at most @xmath356 for some @xmath357 . by chernoff bounds , then , the number of edges in @xmath26 is at most @xmath358 with probability at least @xmath359 . but then the number of nonisolated vertices in @xmath26 is at most @xmath360 , and the result follows . the preceding theorem resolves item ( [ m : small ] ) in theorem [ t : master ] . we now turn our attention to proving item ( [ m : giant ] ) in theorem [ t : master ] . to prove this result , we will use the structure outlined in section [ structural ] , and in particular , theorems [ t : sepsilon ] and [ t : snakeone ] regarding the existence of a connected core of vertices and the vertices that can be connected by a path to @xmath361 . in order to apply these theorems , however , we must verify that the conditions are met . we thus begin with several additional lemmas addressing the case that @xmath362 . [ l : c_prod ] let @xmath363 be such that @xmath364 . then @xmath365 with equality if and only if the @xmath38 s are identically 1 . define @xmath366 , where @xmath367 is defined to be 0 and define @xmath368 . as @xmath369 , and all the @xmath370 , it suffices to show that @xmath371 for @xmath372 . we note that since the @xmath38 s are increasing and @xmath373 is a monotonically increasing function @xmath374 , and thus @xmath375 for all @xmath204 . we note that if @xmath376 , then the previous argument implies that @xmath236 . thus suppose that @xmath37 and yet the @xmath38 s are not identically 1 . as this implies that @xmath377 and @xmath42 , there is some minimal @xmath204 such that @xmath378 . but then as @xmath379 , @xmath380 and @xmath381 , we have that @xmath382 , as desired . [ l : uniform ] let @xmath13 be a symmetric matrix in @xmath383^{k \times k}$ ] with non - identical column sums @xmath363 . further suppose that the associated weighted graph @xmath25 is connected and non - bipartite . let @xmath384 be a strictly monotonically increasing function on @xmath385 and let @xmath141 be the vector @xmath386 . if @xmath115 is the transition matrix for the uniform random walk on @xmath25 , then @xmath387 for all @xmath388 . we first note that @xmath389 and consider @xmath390 note that as @xmath384 is strictly increasing , @xmath391 and @xmath392 for @xmath393 . further , as @xmath25 is connected , @xmath394 for some @xmath77 and @xmath204 with @xmath395 , giving that @xmath396 . to complete the proof it would suffice to show that @xmath397 is the transition probability matrix for the uniform random walk on some connected , non - bipartite graph with the same degree sequence as @xmath25 . to that end , fix some @xmath398 and note that @xmath399 , and so let @xmath400 . it is clear that @xmath401 is symmetric and has the desired column sums , thus it suffices to show that the associated graph @xmath202 is connected and non - bipartite . we note that @xmath402 if and only if there is a length @xmath287 walk between @xmath77 and @xmath204 in @xmath25 . we note that if @xmath287 is odd , then the edges present in @xmath202 are a superset of the edges in @xmath25 , and thus @xmath202 is connected and non - bipartite . thus suppose @xmath287 is even and let @xmath403 be an odd length cycle in @xmath25 . consider the walk in @xmath202 formed by starting at vertex @xmath61 and traversing the cycle @xmath403 in steps of length @xmath287 . as @xmath287 is even and the length of the cycle is odd , it will take an odd number of steps in @xmath202 to return to the vertex @xmath61 . thus , there is a closed walk in @xmath202 of odd length and hence @xmath202 is non - bipartite . we note that as @xmath287 is even @xmath202 contains self - loops at all vertices and edges between pairs of vertices that are connected by a walk of length 2 . thus in order to show that @xmath202 is connected it suffices to show that there is an even length walk between any two vertices in @xmath25 . for any two distinct vertices @xmath60 and @xmath61 in @xmath25 such a walk can be constructed by taking a walk from each vertex to the odd cycle @xmath403 and then traversing @xmath403 in both directions . as @xmath403 is an odd cycle , these two traversals will have opposite parity , and thus one of those walks will have even length . these two lemmas immediately give part ( [ m : giant ] ) of our main theorem , as follows . [ t : giant ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . if @xmath404 , then there are constants @xmath405 , depending only on @xmath13 , such that for sufficiently large @xmath14 , @xmath26 has a giant component with probability at least @xmath406 . first , if @xmath350 , we note that the minimum degree in @xmath74 is at least exponential in @xmath14 , and hence by theorem [ t : indepspec ] together with the spectral properties of kronecker products used in theorem [ t : sepsilon ] , @xmath26 is connected with probability at least @xmath407 , and the result follows immediately . if not , then by lemma [ l : c_prod ] , we have that @xmath236 . fix @xmath408 by theorem [ t : sepsilon ] , there is some constant @xmath409 which depends only on @xmath13 such that @xmath177 is connected with probability at least @xmath410 . fix some positive constant @xmath185 . let @xmath61 be an arbitrary vertex such that @xmath411 and let @xmath412 . noting that @xmath413 , we have that for sufficiently large @xmath14 and all @xmath414 , @xmath415 where the first inequality follows from lemma [ l : uniform ] . let @xmath416 and note that this implies that @xmath417 and so by theorem [ t : snakeone ] there is a constant @xmath287 such that with probability at least @xmath418 the vertex @xmath61 is connected to @xmath177 by a path of length at most @xmath287 . observing that a constant fraction of the vertices have the desired signature by chernoff bounds completes the proof . a slight modification of this argument gives part ( [ m : giant_bound ] ) of the main theorem . [ t : giant_bound ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . if @xmath419 such that the @xmath38 s are not all equal , then there are constants @xmath405 , depending only on @xmath13 , such that for sufficiently large @xmath14 , @xmath26 has a giant component with probability at least @xmath420 . since the @xmath38 s are not all equal , we have that @xmath421 by lemma [ l : c_prod ] . fix @xmath239 satisfying the hypotheses of theorem [ t : sepsilon ] ; we shall further restrict @xmath245 as needed below . then by theorem [ t : sepsilon ] there is some constant @xmath422 such that @xmath177 is connected with probability at least @xmath410 . let @xmath423 and note that by theorem [ tvdist ] , @xmath424 for all @xmath425 . note that for all @xmath372 , if @xmath426 , then we have @xmath427 let @xmath428 be the largest integer such that @xmath429 . then we have , for all @xmath430 , @xmath431\ln c_i + \sum_{i = l+1}^k \left(1-\frac{{\epsilon}}{2}\right)\pi_i\ln c_i\\ \nonumber & = & \sum_i \left(1-\frac{{\epsilon}}{2}\right)\pi_i\ln c_i+\frac{{\epsilon}}{2}\sum_{i=1}^l \pi_i\ln c_i\\ \label{epsilonthing } & \geq & \sum_i\left(1-\frac{{\epsilon}}{2}\right)\pi_i\ln c_i + \frac{{\epsilon}}{2}k\ln c_1 \end{aligned}\ ] ] for all @xmath425 . here we further restrict @xmath245 to be sufficiently small that the quantity in ( [ epsilonthing ] ) is positive . moreover , if @xmath432 , we may apply lemma [ l : uniform ] to obtain a constant @xmath433 such that @xmath434 for all @xmath432 . since @xmath287 is a fixed constant , this implies that there is some @xmath435 such that for all @xmath436 , we have @xmath437 . let @xmath185 be a constant to be fixed later . we notice that for @xmath14 sufficiently large all vertices @xmath61 such that @xmath438 are contained in @xmath439 . thus by theorem [ t : snakeone ] these vertices are connected to @xmath440 with probability at least @xmath441 where @xmath442 . at this point it suffices to show that a constant fraction of the vertices in @xmath26 are adjacent to @xmath439 . to this end , let @xmath443 be the set of vertices @xmath444 such that @xmath445 for @xmath446 and @xmath447 . by chernoff bounds and observation [ o : sqrt ] , we have that a constant fraction of the vertices of @xmath26 are in @xmath443 . furthermore , for every vertex @xmath448 , @xmath449 } } \geq 1 now by part ( [ concingbar ] ) of lemma [ agoodneighbor ] , for all @xmath450 , @xmath451 } } \geq 1 - e^{-1}.\ ] ] thus , any fixed vertex in @xmath450 has a neighbor @xmath60 such that @xmath452 with probability at least @xmath453 . we further note that any such neighbor is a member of @xmath439 . taking @xmath454 and applying chernoff bounds completes the proof . finally , we turn to the connectivity of @xmath26 . we note that part ( [ m : connected ] ) of the main theorem follows immediately from theorem [ t : indepspec ] by observing that the minimum degree in @xmath105 is exponential in @xmath14 and exploiting the spectral properties of the kronecker product , as mentioned in the proof of theorem [ t : giant ] . however , in keeping with the theme of this paper we provide an alternative proof which exploits the markov chain structure . [ t : const_diam ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . if @xmath455 , then there is some constant @xmath242 , depending only on @xmath13 such that @xmath26 is connected with probability at least @xmath244 . we first note that as @xmath49 , @xmath456 and thus for any signature @xmath143 , @xmath457 . thus every vertex is in @xmath458 and hence by theorem [ t : snakeone ] for every @xmath178 , every vertex is connected to @xmath177 by a path of constant length with probability at least @xmath459 . thus it suffices to show that there is some @xmath178 such that @xmath177 is connected . but as @xmath460 for all @xmath77 , this implies that @xmath236 and thus by theorem [ t : sepsilon ] there is some constant @xmath461 , depending only on @xmath13 , such that @xmath177 is connected with probability at least @xmath462 . the following two theorems address the case that @xmath463 . we note that we will always have a giant component in this case , unless @xmath464 . however , the connectivity no longer depends entirely on the degrees in the graph , but is determined based on how the weight is distributed among the vertices . in particular , the backbone graph will determine the behavior . [ t : discon ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by @xmath0^{k \times k}$ ] with column sums @xmath465 . if @xmath25 is connected and non - bipartite and the backbone graph @xmath29 has a vertex of degree zero , then there is a constant @xmath184 such that with probability at least @xmath466 the graph @xmath26 has at least @xmath467 isolated vertices . note that as the backbone graph @xmath29 has a vertex of degree 0 , there exists a vertex @xmath468 such that for all vertices @xmath60 , @xmath469 . we note that in this case we have @xmath470}},\end{aligned}\ ] ] where the last inequality comes from the upper bound on @xmath471 . thus we have that @xmath472}}}.$ ] thus it suffices to find a large collection of vertices in @xmath26 whose degrees are independent and where @xmath449}}$ ] is small . to that end suppose that there is some @xmath77 such that @xmath473 , that is , the degree of vertex @xmath474 in @xmath29 is not zero . thus there is some @xmath475 such that @xmath204 has degree zero in @xmath29 . now let @xmath476 be the set of vertices in @xmath26 whose signature @xmath143 has @xmath477 , @xmath478 , and @xmath479 for @xmath480 . since @xmath45 and @xmath481 , we know that @xmath482 and thus the degrees of all vertices in @xmath476 are independent . we note that there is a choice of constant @xmath185 such that if @xmath483 then the expected number of isolated vertices in @xmath476 is @xmath484 , and thus by chernoff bounds with probability at least @xmath485 there are at least @xmath467 isolated vertices in @xmath26 . now suppose that the degree of @xmath474 in @xmath29 is zero . choose some index @xmath486 arbitrarily and consider the set @xmath476 as above . as @xmath204 is arbitrary there may be some edges between vertices of @xmath487 . thus we note that when @xmath488 , we have @xmath489 } } & = \sum_{u \in s^{(j)}_{t_j } } \sum_{v \in s^{(j)}_{t_j } } { \ensuremath{{{\mathbb{p}}}\!\left ( u \sim v\right ) } } \\ & = 2\binom{t}{t_j } \sum_{i=0}^{t_j } \binom{t_j}{i } \binom{t - t_j}{t_j - i}p_{jj}^{t_j - i } p_{j1}^{i } p_{1j}^i p_{11}^{t- t_j - i } \\ & \leq 2\binom{t}{t_j}\binom{t - t_j}{t_j } p_{11}^{t- 2t_j}{\ensuremath{\left ( p_{11}p_{jj } + p_{1j}^2 \right)}}^{t_j}\\ & \leq 2t^{t_j}t^{t_j}p_{11}^{t-2t_j}(p_{11}p_{jj}+p_{1j}^2)^{t_j}\end{aligned}\ ] ] in particular , there is a constant @xmath257 such that @xmath490 } } \leq { \ensuremath{\left ( c't^2 \right)}}^{t_j}p_{11}^t$ ] . as @xmath491 , this implies that the probability of an edge in @xmath487 is exponentially small provided @xmath492 . thus , again choosing @xmath493 and conditioning on @xmath494 gives the desired result . a slight simplification of this result gives part ( [ m : discon_c1 ] ) of theorem [ t : master ] . [ t : bconn ] let @xmath26 be a @xmath12-order stochastic kronecker graph generated by a matrix @xmath0^{k \times k}$ ] such that @xmath25 is connected and non - bipartite . if @xmath495 and the backbone graph @xmath29 has no vertices of degree zero , then there is a constant @xmath496 such that @xmath26 is connected with probability at least @xmath407 . first we note that @xmath377 as otherwise the only edges present in @xmath25 are those present in the backbone graph , and in particular , @xmath25 is a perfect matching contradicting the non - bipartiteness . thus we have that @xmath236 and thus by theorem [ t : sepsilon ] there is some @xmath178 and @xmath497 such that @xmath498 is connected with probability at least @xmath499 . now in a similar manner as the proof of theorem [ t : snakeone ] it suffices to show that asymptotically almost surely , from every vertex @xmath500 there is a sequence @xmath501 such that @xmath502 and @xmath503 . by imposing the additional condition that @xmath504 , we may take @xmath505 by theorem [ tvdist ] and the markov chain viewpoint . to that end fix an arbitrary vertex @xmath61 and consider the behavior of @xmath89 from the point of view of the product distribution @xmath506 where @xmath507 is the number of @xmath77 s in the label for @xmath61 . notice that for those indicies @xmath77 where @xmath508 , @xmath93 is the identity distribution . furthermore , these coordinates perfectly respect the action of the markov chain given by @xmath115 . let @xmath204 be the first index with @xmath509 , so that @xmath510 . suppose that @xmath511 . note then any neighbor @xmath60 of @xmath61 in @xmath512 immediately satisfies that @xmath513 . otherwise , we have @xmath514 . but then @xmath449 } } \geq c_j^{\frac{\epsilon}{s k { \ensuremath{\left\| l \right\|_{\infty}}}}t}$ ] and @xmath509 , and thus by lemma [ agoodneighbor ] , there is a constant @xmath185 such that @xmath515 applying chernoff bounds to assure the existence of such a vertex completes the proof . we note that in principle these techniques can be extended to analyze the emergence of connectivity and the giant component in generalizations of the stochastic kronecker graph , such as the multiplicative attribute graph @xcite . in fact , based on the work in @xcite , it is likely that similar transition points will hold . that is , the multiplicative attribute graph will have a giant component when the median expected degree is 1 and become connected when the probability of an isolated vertex goes to zero . perhaps a more interesting direction would to resolve the size of the largest component in the case when @xmath516 . by letting @xmath517 we see that this regime includes the erds - rnyi graph @xmath518 at criticality . thus it seems likely that in order to understand the size of the largest component of the stochastic kronecker graph when @xmath519 it will require a deeper understanding of why the branching process for @xmath520 terminates with a largest component of size @xmath521 @xcite . as a possible intermediate stage , consider a @xmath522-regular , connected , non - bipartite graph @xmath241 on @xmath2 vertices and let @xmath13 be @xmath523 times the adjacency matrix of @xmath241 . what is the size of the largest component in the @xmath12-order stochastic kronecker graph generated by @xmath13 ? from a natural coupling with @xmath524 it is clear that it should be at least @xmath525 . on the other hand , since the degree of every vertex is still asymptotically poisson with parameter 1 , the branching process point of view would indicate that the size of the largest component should be @xmath526 . however , we note that if @xmath241 is the @xmath522-regular graph formed by two copies of @xmath527 joined by a perfect matching , then @xmath304 consists of @xmath528 copies of @xmath529 with relatively few edges between them . furthermore , as the expected degree within each of these copies of @xmath529 is @xmath530 , the largest component in each of these components is @xmath531 , seemingly indicating that the overall size of the largest component is relatively small . thus , it seems likely that any resolution of the case where @xmath532 will necessitate a deeper understanding of the branching process at criticalility , and specifically , how the branching process interacts with the underlying network of potential edges .[/INST] stochastic kronecker graphs are a model for complex networks where each edge is present independently according to the kronecker ( tensor ) product of a fixed matrix @xmath0^{k \times k}$ ] . we develop a novel correspondence between the adjacencies in a general stochastic kronecker graph and the action of a fixed markov chain . using this correspondence we are able to generalize the arguments of horn and radcliffe on the emergence of the giant component from the case where @xmath1 to arbitrary @xmath2 . we are also able to use this correspondence to completely analyze the connectivity of a general stochastic kronecker graph . </s>

an important topic in modern wireless communications is the subject of decentralized networks . by definition , a decentralized network of separate transmitter - receiver pairs has no central controller to allocate the network resources among the active users . as such , resource allocation must be performed locally at each node . in general , users are not already aware of the number of active users and the channel gains . also , users are not aware of each other s codebooks implying multiuser detection is not possible , i.e. , users treat each other as noise . multiuser interference is known to be the main factor limiting the achievable rates in such networks particularly in the high signal - to - noise ratio ( snr ) or interference limited regime . therefore , all users must follow a distributed signaling scheme such that the destructive effect of interference on each user is minimized , while the resources are fairly shared among users . most of distributed schemes reported in the literature rely on either _ game - theoretic _ approaches or _ cognitive radios_. cognitive radios @xcite have the ability to sense the unoccupied portion of the available spectrum and use this information in resource allocation . although such smart radios avoid the use of a central controller , they require sophisticated detection techniques for sensing the spectrum holes and dynamic frequency assignment which add to the overall system complexity @xcite . distributed strategies based on game theoretic arguments have already attracted a great deal of attention . in @xcite , the authors introduce a non - cooperative game theoretic framework to investigate the spectral efficiency issue when several users compete over an unlicensed band with no central controller . reference @xcite offers a brief overview of game theoretic dynamic spectrum sharing . although these schemes enable us to understand the dynamics of distributed resource allocation , they usually suffer from complexity in software and convergence issues as they rely on iterative algorithms . spread spectrum communications is a natural setup to share the same bandwidth by several users . this area has attracted tremendous attention by different authors during the past decades in the context of centralized uplink / downlink multiuser systems . appealing characteristics of spread spectrum systems have motivated researchers to utilize these schemes in networks without a certain infrastructure , i.e. , packet radio or ad - hoc networks@xcite . in direct sequence spread spectrum systems , the signal of each user is spread using a pseudo - random noise ( pn ) code . the challenging point is that in a network without a central controller , if two users use the same spreading code , they will not be capable of recovering the data at the receiver side due to the high amount of interference . distributed code assignment techniques are developed in @xcite . in @xcite , using a greedy approximation algorithm and invoking graph theory , a distributed code assignment protocol is suggested . another category of research is devoted to devise distributed schemes in the reverse link ( uplink ) of cellular systems . distributed power assignments algorithms are proposed in @xcite . reference @xcite proposes a distributed scheduling method called the token - bucket on - off scenario utilized by autonomous mobile stations where its impact on the overall throughput of the reverse link is investigated . furthermore , decentralized rate assignments in a multi - sector code division multiple access wireless network are discussed in @xcite . being a standard technique in spread spectrum communications and due to its interference avoidance nature , frequency hopping is the simplest spectrum sharing method to use in decentralized networks . as different users typically have no prior information about the codebooks of the other users , the most efficient method is avoiding interference by choosing unused channels . as mentioned earlier , searching the spectrum to find spectrum holes is not an easy task due to the dynamic spectrum usage . as such , fh is a realization of a transmission scheme without sensing , while avoiding the collisions as much as possible . frequency hopping is one of the standard signaling schemes adopted in ad - hoc networks . in short range scenarios , bluetooth systems @xcite are the most popular examples of a wireless personal area network or wpan . using fh over the unlicensed ism band , a bluetooth system provides robust communication to unpredictable sources of interference . a modification of frequency hopping called dynamic frequency hopping ( dfh ) , selects the hopping pattern based on interference measurements in order to avoid dominant interferers . the performance of a dfh scheme when applied to a cellular system is assessed in @xcite . distributed rate assignment strategies are recently adopted in the context of medium access control . it is well - known @xcite that the capacity region @xmath1 of a multiple access channel with @xmath2 users is a polytope with a @xmath3 corner points . let each corner point of @xmath1 be an @xmath2-tuple whose elements are among the numbers @xmath4 and @xmath5 . with no cooperation among the users , the authors in @xcite propose that each user selects a codebook of rate @xmath6 with probability @xmath7 for @xmath8 . assuming the receiver is aware of the rate selection of all users , the average sum rate of the network is @xmath9 where @xmath10 is @xmath11 if @xmath12 and @xmath13 otherwise . finally , the numbers @xmath14 and @xmath15 are derived to maximize @xmath16 . major differences of this scenario with a decentralized wireless network are _ 1 ) _ the capacity region of a multiuser interference channel is unknown . _ 2 ) _ in case transmitters have different choices to select the transmission rate , a certain receiver is not guaranteed to be aware of the transmission rate of interferers . _ 3 ) _ any user is already unaware of the gains of channels connecting the interferers transmitters to its receiver . also , any user is never capable of finding the amount of interference it imposes on other users . it is well - known that in the low snr regime continuous transmission of @xmath17 gaussian signals is optimal . however , as snr increases , this scheme turns out to be quite inefficient . for instance , the achievable rate of each user eventually saturates , i.e. , the achieved sum multiplexing gain as snr tends to infinity . ] ( smg ) is equal to zero . using the results in @xcite , it is easy to see that by using a masking strategy where each user quits transmitting its gaussian signals independently from transmission to transmission , a nonzero smg of @xmath18 is attained in a decentralized network of @xmath2 users . this is an interesting result in the sense that if the number of active users tends to infinity , the achieved smg settles on @xmath19 . in the present paper , we answer the following questions : _ question 1- _ is it possible to achieve an smg larger than @xmath20 as the number of users becomes large ? we propose a distributed signaling scheme where each user spread its gaussian signal along a spreading code consisting of @xmath17 elements selected according a globally known probability mass function ( pmf ) over a finite alphabet @xmath21 . thereafter , the resulting sequence is punctured independently from symbol to symbol with a certain probability representing the masking operation . for example , assuming @xmath22 , let the generated spreading code have length @xmath23 and be given by @xmath24 also , an @xmath17 sequence of @xmath11 s ( representing @xmath25 ) and @xmath13 s ( representing @xmath26 ) with length @xmath23 is generated as @xmath27 finally , denoting the gaussian signal to be transmitted by @xmath28 , the sequence @xmath29 is transmitted in @xmath23 consecutive transmission slots called a transmission frame . this process is repeated independently from transmission frame to transmission frame . we notice that since different users are not aware of each other s signals and the spreading / masking sequences , the noise plus interference vector at the receive side of any user is a mixed gaussian random vector . we assume the knowledge of interference probability density function ( pdf ) at the receiver side of each user . we are able to see that using the proposed randomized spreading scheme , the number of active users and the gains of channels conveying the interferers signals can be easily found by inspecting the interference pdf and solving a set of linear equation . assuming all users are _ frame - synchronous _ , we derive achievable rates for the users in three steps : _ step 1- _ using singular value decomposition ( svd ) of the signal space at the receiver side any user , the interference vector is mapped in the signal space and the complement space and a subspace @xmath30 of @xmath31 , the complement space @xmath32 of @xmath30 is the set of elements in @xmath31 that are perpendicular to any element in @xmath30 . ] of the signal space . _ step 2- _ a conditional version of entropy power inequality is used to derive a lower bound on the mutual information between the input and output of each user along any transmission frame . the conditioning is made over the contents of the interference vector mapped in the complement space of the signal space . _ step 3- _ the resulting lower bound in the previous step highly depends on the differential entropy of mixed gaussian random vectors . since there is no closed formula on the differential entropy of a mixed gaussian vector , a key lemma is used to find computable bounds on this differential entropy . this leads us to the final formulation of the achievable rate . in a decentralized network of @xmath2 users , we are able to show that by regulating the length of the transmission frame and the probabilistic structure of the spreading / masking sequences , the resulting lower bound scales like @xmath33 where @xmath34 . this is exactly the smg of a centralized orthogonal resource allocation scheme where multiuser interference is completely avoided . our focus is not particularly on the high snr regime . in fact , the length of the transmission frame and the probabilistic parameters of the spreading / masking codes are sensitive to the choice of snr . our proposed achievable rate for any user in general depends on the gains of the channels conveying the interference . as mentioned earlier , each user is capable of finding the channel gains , however , if each user attempts to maximize its achievable rate over the length of the transmission frame and other code parameters , different users come up with different choices which results in inconsistency . to circumvent this difficulty , assuming the channel gains are realizations of @xmath17 continuous random variables , each user selects the code parameters such that the average of achievable rate per user over different realizations of the channel gains is maximized . this leads to a consistent and distributed method to design the best randomization algorithm in constructing the spreading / masking sequences . an interesting observation is that even in the simplest scenario where the underlying alphabet is @xmath0 and no masking is applied , the elements of the spreading codes are not equiprobable over @xmath0 . for example , our simulation results show that in a network of @xmath35 users at @xmath36 , the elements of the spreading code must be selected to be @xmath11 with a probability of @xmath37 and @xmath38 with a probability of @xmath39 or vice versa . _ question 2- _ what is the highest achievable rate under the masking protocol ? can one do better than masking ? one may raise the question if masking the transmitted signals independently from transmission slot to transmission slot is by itself sufficient , i.e. , by selecting the pdf of the transmitted signals properly ( probably non - gaussian ) , there is no need for spreading . using an extremal inequality of liu - viswanath @xcite , we are able to show that transmission of gaussian signals along with spreading and masking yields higher achievable rates that the largest achievable rate with masking alone . the rest of the paper is organized as follows . section ii offers the system model . in this section , we introduce the randomized spreading coding and discuss how all user can consistently design their spreading / masking sequences . section iii presents the development of achievable rates based on the three steps mentioned earlier . system design is brought in section iv where we offer several design examples . finally , section v prove the supremacy of blending spreading and masking over masking alone . conclusion remarks are given in section vi . * notation- * throughout the paper , we denote random quantities in bold case such as @xmath28 and @xmath40 . a realization of @xmath28 is denoted by @xmath41 . a circularly symmetric complex gaussian random vector @xmath42 of length @xmath43 with zero mean and covariance matrix @xmath44 is denoted by @xmath45 . a bernoulli random variable @xmath46 with @xmath47 $ ] is denoted by @xmath48 . for a sequence @xmath49 and a set @xmath50 where @xmath51 , we define @xmath52 . we use @xmath53 for the expectation operator , @xmath54 for the probability of an event @xmath55 , @xmath56 for the indicator function of an event @xmath55 and @xmath57 for the pdf of a random variable @xmath28 . also , @xmath58 denotes the mutual information between random variables @xmath28 and @xmath59 , @xmath60 the differential entropy of a continuous random variable @xmath28 , @xmath61 the entropy of a discrete random variable @xmath28 , and the binary entropy function is denoted by @xmath62 for @xmath63 $ ] . for any @xmath63 $ ] , @xmath64 denotes @xmath65 . the dirac delta function is denoted by @xmath66 . for integers @xmath67 , a @xmath68 matrix in which all elements are @xmath13 or @xmath11 is shown by @xmath69 or @xmath70 respectively . for sets @xmath71 and @xmath72 , the set @xmath73 denotes a set with elements in @xmath71 and not in @xmath72 . the cardinality of a set @xmath71 is denoted by @xmath74 . for any two vectors of the same size @xmath75 and @xmath76 , the vector @xmath77 is the element - wise product of @xmath75 and @xmath76 . for two function @xmath78 and @xmath79 of a variable @xmath80 , we write @xmath81 if @xmath82 and @xmath83 if @xmath84 . the notation @xmath85 is defined similarly . we consider a decentralized communication network of @xmath2 users . the static and non frequency - selective gain of the channel from the @xmath86 transmitter to the @xmath87 receiver is shown by @xmath88 which is in general a complex number . in a decentralized network , there is no communication or cooperation among different users . due to the fact that the network has no fixed infrastructure and there is no central controller to manage the network resources among users , resource allocation and rate assignment must be performed locally at every transmitter . a main feature of such networks is that the @xmath86 user is not already informed about the channel gains @xmath89 concerning the links connecting different transmitters to the @xmath86 receiver . in fact , every receiver has only access to the interference pdf and the knowledge about the number of active users and the channel gains @xmath89 can only be inferred through analyzing this pdf . also , different users are not aware of each other s codebooks . as such , no multiuser detection is possible and users treat the interference as noise . in this part , we introduce a distributed signaling strategy using randomized spreading / masking . for positive integers @xmath90 and @xmath91 , the codebook of the @xmath86 user consists of @xmath92 codewords where a typical codeword @xmath93 is a sequence of @xmath17 circularly symmetric complex gaussian random variables with zero mean and variance @xmath94 . the @xmath86 user transmits @xmath93 in @xmath90 _ transmission frames _ where each transmission frame consists of @xmath91 _ transmission slots_. in a typical transmission frame , one of the signals in the codeword @xmath93 is transmitted . to transmit @xmath95 , the @xmath86 user randomly constructs two independent sequences called the spreading and the masking codes . the spreading code is a @xmath96 vector @xmath97 over an alphabet @xmath98 where the elements of @xmath97 are @xmath17 with a globally known pmf @xmath99 . the masking code is a @xmath96 vector @xmath100 whose elements are independent @xmath101 random variables for some @xmath102 $ ] . thereafter , the @xmath86 user transmits @xmath103 in the @xmath104 transmission frame . the vector @xmath105 is called the randomized signature code of the @xmath86 user in the @xmath104 transmission frame . we remark that the spreading and masking codes of the @xmath86 user over different transmission frames are constructed independently . the alphabet @xmath21 has the property that for any @xmath106 , we have @xmath107 . the received vector at the receiver side of the @xmath86 user in a typical transmission frame is given by @xmath108 where @xmath109 is a @xmath110 random vector representing the ambient noise at the @xmath86 receiver . also , @xmath111 is a normalization factor ensuring the average transmission power per symbol of the @xmath86 user is @xmath94 , i.e.,@xmath112 in ( [ e1 ] ) , we have made the assumption that all active users in the network are frame - synchronous meaning their transmission frames start and end at similar time instants . this is not necessarily a valid assumption in a decentralized network , however , this makes the presentation of the subject much easier . it is clear that the transmitted signals of each user along its transmission frames are correlated while signals transmitted in different transmission frames are independent . hence , we assume any new active user is capable of detecting the correlated segments along the interference plus noise process , and therefore , synchronizing itself with former active users in the network . however , in case different users are not frame - synchronous and users are not aware of the asynchrony pattern , the communication channel of any user is not ergodic anymore and one must perform outage analysis . using joint typicality at the receiver side of the @xmath86 user , any data rate @xmath113 is achievable where @xmath114 the term @xmath115 indicates that the @xmath86 user is also embedding information in the sequence of @xmath17 signature codes . in fact , one can assume the codeword of any user consists of two sequences , namely , the sequence of gaussian signals and the sequence of randomized signature codes . due to the fact that the signature code of any user is not known to other users and on the other hand , the signature codes are independently changing over different transmission frames , the noise plus interference at the receiver side of any user has a mixed gaussian pdf . this makes @xmath116 have no closed expression . therefore , we need to obtain a tight lower bound on this quantity whose computation only needs data that can be inferred from the noise plus interference pdf at the receiver side of the @xmath86 user and be fed back to its associated transmitter in order to regulate the transmission rate . throughout the paper , the interference term at the receiver side of the @xmath86 user is denoted by @xmath117 , i.e. , @xmath118 . one can state @xmath117 as @xmath119 where @xmath120 @xmath121 and @xmath122 in general , we assume that the @xmath86 receiver is aware of @xmath123 which can be done through a training sequence sent by the @xmath86 transmitter . assuming the channel gains are realizations of @xmath17 random variables with a continuous pdf , then the number of gaussian components in the mixed gaussian pdf of the interference in any transmission slot at the receiver side of the @xmath86 user is @xmath124 if masking is not performed and @xmath125 if masking and spreading are both applied . these levels consist of @xmath126 where @xmath127 . as such , as far as @xmath128 , the number of active users can be obtained by finding the number of interference power levels . however , if @xmath129 for some @xmath130 and masking is not performed , the interference pdf in any transmission slot is gaussian ( the interference vector on any transmission frame is still mixed gaussian ) with power @xmath131 . therefore , the number of active users can not be derived by investigating the interference pdf in one transmission slot . in this case , it can be verified that the joint pdf of any two transmission slots in a transmission frame is a mixed gaussian pdf with @xmath132 gaussian components . this yields a method to find @xmath2 in case @xmath21 has only two elements . by symmetry , characterization of @xmath133 demands the knowledge of an arbitrary reordering of the sequence @xmath134 . in this paper , we derive a lower bound @xmath135 on @xmath133 which is only a function of the magnitude of the channel gains . therefore , we need to obtain an arbitrary reordering of @xmath136 . let @xmath137 be a reordering of @xmath134 based on magnitude , i.e. , @xmath138 . we consider the following cases : _ case 1- _ if @xmath139 , let @xmath140 and @xmath141 be the two largest elements in @xmath21 such that @xmath142 . denoting the @xmath143 largest interference plus noise power levels on each transmission slot by @xmath144 , we have @xmath145 and @xmath146 for @xmath147 . these @xmath143 linear equations yield @xmath148 . _ case 2- _ let masking be the only ingredient in constructing the signatures , i.e. , spreading is not applied . denoting the @xmath143 largest interference plus noise power levels on each transmission slot by @xmath144 , we have @xmath149 and @xmath150 for @xmath147 . these @xmath143 linear equations yield @xmath148 . _ case 3- _ let @xmath129 for some @xmath151 and masking is performed on top of spreading . then , we can apply the same procedure in case 2 . _ case 4- _ let @xmath129 for some @xmath151 and masking is not applied . the joint pdf of the interference plus noise on any two transmission slots inside a transmission frame is a bivariate mixed gaussian pdf in which the gaussian components have covariance matrices of the form @xmath152 where @xmath153 for @xmath154 . the @xmath155 largest elements among the off - diagonal elements of these matrices correspond to @xmath156 for @xmath147 . these elements together with the diagonal element @xmath157 yield @xmath148 . therefore , we have shown that the @xmath86 user can find @xmath2 and a reordering of the sequence @xmath134 . an important issue in a decentralized network is to propose a globally known utility function to be optimized by all user without any cooperation . as mentioned earlier , the receivers can infer the number of active users in the network and the channel gains by inspecting the interference pdf . we consider a scenario where this information is fed back to the transmitters . as mentioned earlier , there is no closed formulation on @xmath133 . however , we are able to develop a lower bound @xmath135 for @xmath133 which is tight enough to guarantee @xmath158 in general , @xmath135 depends on @xmath159 . as such , we denote it explicitly by @xmath160 . assuming @xmath89 are realizations of independent @xmath161 random variables @xmath162 , we propose that the @xmath86 user selects @xmath91 , @xmath163 and @xmath164 based on @xmath165 after selecting @xmath91 and @xmath99 using ( [ rule ] ) , the @xmath86 user regulates its actual transmission rate at @xmath166 using the realization of @xmath167 . one can write @xmath116 as @xmath168 the term @xmath169 is the achievable rate of the @xmath86 user as if this user knew the randomized signature code @xmath170 already , i.e. , the achievable rate of the @xmath86 user can be in general larger than the case where the signature matrices are already revealed to the receiver side . the extra term @xmath171 is bounded from above by @xmath172 which is not a function of snr . therefore , @xmath173 as such , we ignore the term . this enables us to compute @xmath171 directly . ] @xmath171 and focus on developing a tight lower bound on @xmath169 . to develop a lower bound on @xmath169 , our major tools are linear processing of the channel output based on singular value decomposition of the signature code @xmath170 , a conditional version of entropy power inequality and a key upper bound on the differential entropy of a mixed gaussian random vector . we have @xmath174 in the following , we find a lower bound on @xmath175 for any @xmath176 . * step 1- * the matrix @xmath177 has two eigenvalues , namely zero and @xmath178 . the eigenvector corresponding to @xmath178 is @xmath179 and the the eigenvectors corresponding to zero are @xmath180 orthonormal vectors denoted by @xmath181 and @xmath182 which together with the columns of @xmath183 make an orthonormal basis for @xmath184 . let us define @xmath185 @xmath186 and @xmath187 writing the svd of @xmath179 , @xmath188 the @xmath86 receiver constructs the vector @xmath189 upon reception of @xmath190 . we have @xmath191 we define @xmath192_{1}\notag\\ & = & \frac{\beta\vec{s}^{\dagger}\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right)}{\|\vec{s}\|_{2}}\end{aligned}\ ] ] @xmath193_{1}=\beta h_{i , i}\|\vec{s}\|_{2}\boldsymbol{x}_{i}+\boldsymbol{\varphi}_{i}\ ] ] and @xmath194_{2}^{k}\notag\\&=&\left[u_{i}^{\dagger}(\vec{s})\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right)\right]_{2}^{k}\notag\\ & \stackrel{}{=}&\left[u_{i}^{\dagger}(\vec{s})\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right)\right]_{2}^{k}\notag\\&=&\left[\begin{pmatrix } \frac{\vec{s}^{\dagger}}{\|\vec{s}\|_{2 } } \\ g_{i}^{\dagger}(\vec{s } ) \end{pmatrix}\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right)\right]_{2}^{k}\notag\\ & = & g_{i}^{\dagger}(\vec{s})\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right).\notag\\\end{aligned}\ ] ] we have the following thread of equalities , @xmath195 where @xmath196 is by the fact that @xmath197 and @xmath198 are independent , i.e. , @xmath199 . * step 2- * in this part , we use the following lemma without proof . let @xmath200 and @xmath201 be @xmath202 complex random vectors and @xmath203 be any random quantity ( scalar or vector ) with densities . also , assume that the conditional densities @xmath204 and @xmath205 exist . if @xmath200 and @xmath201 are conditionally independent given @xmath203 , then @xmath206 we have @xmath207 on the other hand , we know that @xmath208 . defining @xmath209 and @xmath210 , it is clear that @xmath211 and @xmath212 are conditionally independent given the collection of random variables @xmath213 . as the conditional densities @xmath214 and @xmath215 exist , by lemma 1 , @xmath216 where @xmath196 is by the fact that the collection @xmath197 is independent of @xmath198 . dividing both sides of ( [ poe ] ) by @xmath217 , @xmath218 by ( [ gh1 ] ) , ( [ gh2 ] ) and ( [ gh3 ] ) , @xmath219 * step 3- * we start by stating the following lemma . let @xmath220 be a @xmath202 mixed gaussian random vector with the pdf @xmath221 where @xmath222 for @xmath8 and @xmath223 . then , @xmath224 let us define the random matrix @xmath225 such that @xmath226 and let @xmath227 be a zero mean gaussian vector with covariance matrix @xmath228 . then , one can easily see that @xmath229 in which @xmath230 is the conventional square root of a positive semi - definite matrix . using the inequalities @xmath231 and noting that @xmath232 , the result is immediate . the vector @xmath117 has a mixed gaussian distribution where the covariance matrices of its separate gaussian components correspond to different realizations of the matrix @xmath233 . this together with lemma 2 yields @xmath234 where we have used the fact that @xmath235 . one has@xmath236 where @xmath196 follows by the fact that the matrix @xmath237 is unitary , i.e. , @xmath238 , @xmath239 is by ( [ bw3 ] ) and @xmath240 is a direct consequence of lemma 2 . having @xmath241 , the vector @xmath242 is a complex gaussian vector . hence , @xmath243 by the same token , @xmath244 using ( [ lj1 ] ) and ( [ lj2 ] ) in ( [ pork ] ) , @xmath245 moreover , @xmath246 . hence , @xmath247 appearing in ( [ goosht ] ) can be bounded from below as @xmath248 substituting ( [ bone ] ) in ( [ goosht ] ) , @xmath249 where @xmath250 finally , we get the following lower bound on @xmath251 denoted by @xmath160 , i.e. , @xmath252 an important observation is that if the @xmath86 user sets its transmission rate at @xmath253 , then @xmath254 to prove this , we need some preliminary results in linear analysis . _ definition 2_- let @xmath31 be an euclidean space over @xmath255 and @xmath30 be a subspace of @xmath31 . we define @xmath256 let @xmath31 be an euclidean space over @xmath255 . if @xmath30 is a subspace of @xmath31 , then for each @xmath257 , there are unique elements @xmath258 and @xmath259 such that @xmath260 . _ definition 3_- in the setup of lemma 4 , @xmath261 is called the projection of @xmath262 in @xmath30 and is denoted by @xmath263 . by the same token , @xmath264 . _ definition 4_- let @xmath31 be an euclidean space over @xmath255 and @xmath265 and @xmath266 be subspaces of @xmath31 . we define @xmath267 let @xmath31 be an euclidean vector space over @xmath255 and @xmath265 and @xmath266 be subspaces of @xmath31 . then , @xmath268 let @xmath269 be a @xmath270 matrix such that @xmath271 . then , for any @xmath272 matrix @xmath273 , we have @xmath274 . regulating its transmission rate at @xmath160 , the @xmath86 user achieves an snr scaling of @xmath275 using the fact that for any matrix @xmath269 , @xmath276 , it is easy to see that for any @xmath277 and @xmath278 , we have @xmath279 scales like @xmath280 and @xmath281 scales like @xmath282 . this yields @xmath283 where @xmath196 is by the fact that @xmath284 . we show that @xmath285\right)\ ] ] holds almost surely . let us write @xmath286)=\mathrm{dim}(\mathrm{span}(\vec{\boldsymbol{s}}_i)\cup\mathrm{csp}(\boldsymbol{s}_{i})).\ ] ] using this in lemma 4 , @xmath287)&=&\mathrm{dim}(\mathrm{span}(\vec{\boldsymbol{s}}_i))+\mathrm{dim}(\mathrm{proj}(\mathrm{csp}(\boldsymbol{s}_{i});(\mathrm{span}(\vec{\boldsymbol{s}}_i))^{\perp}))\notag\\ & = & \mathbb{1}_{\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}}+\mathrm{dim}(\mathrm{proj}(\mathrm{csp}(\boldsymbol{s}_{i});(\mathrm{span}(\vec{\boldsymbol{s}}_i))^{\perp})).\end{aligned}\ ] ] on the other hand , by the definition of @xmath288 , @xmath289 it is easily seen that for any @xmath290 , the @xmath291 column of the matrix @xmath292 yields the proper linear combination of the columns of @xmath288 which constructs the projection of the @xmath291 column of @xmath293 into the space @xmath294 , i.e. , @xmath295_{k}=\mathrm{proj}\left([\boldsymbol{s}_{i}]_{k};\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i}))\right).\ ] ] therefore , @xmath296_{k}\big\}_{k=1}^{k-1}\right)&=&\mathrm{proj}\left(\mathrm{span}\left(\big\{[\boldsymbol{s}_{i}]_{k}\big\}_{k=1}^{k-1}\right);\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i}))\right)\notag\\ & = & \mathrm{proj}(\mathrm{csp}(\boldsymbol{s}_{i});\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i}))).\end{aligned}\ ] ] however , @xmath297_{k}\big\}_{k=1}^{k}\right)=\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i})\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i}).\ ] ] by ( [ bzz1 ] ) and ( [ bzz2 ] ) , @xmath298 using ( [ bzz5 ] ) and ( [ bzz4 ] ) in ( [ bzz6 ] ) , @xmath299)&=&\mathbb{1}_{\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}}+\mathrm{dim}(\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i})\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i}))\notag\\ & = & \mathbb{1}_{\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}}+\mathrm{rank}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i})\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i})\notag\\ & \stackrel{(a)}{=}&\mathbb{1}_{\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}}+\mathrm{rank}(\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i})\end{aligned}\ ] ] where @xmath196 follows by lemma 5 as @xmath288 has independent columns . taking expectation from both sides , @xmath300)\right\}=\pr\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}+\mathrm{e}\left\{\mathrm{rank}(\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i})\right\}.\ ] ] using this in ( [ bghm ] ) , @xmath301)-\mathrm{rank}(\boldsymbol{s}_{i})\right\}\notag\\ & = & \pr\left\{\vec{\boldsymbol{s}}_{i}\notin\mathrm{csp}(\boldsymbol{s}_{i})\right\}.\end{aligned}\ ] ] this completes the proof . finally , the following proposition proves that @xmath133 and @xmath135 have the snr scaling . @xmath135 and @xmath133 have the same snr scaling . see appendix a. an important consequence of proposition 1 is the following observation . since , all the users utilize the same algorithm to construct their randomized signature codes , the achievable smg is @xmath302\right)\right\}}{k}.\ ] ] computing @xmath303\right)\right\}$ ] can be quite a tedious task specially for @xmath304 . let the underlying alphabet to construct the spreading codes be @xmath0 . here , we examine two particular rscs by computing the achieved @xmath305 through simulations for the cases where masking is applied or ignored . in each case , we assume the elements of any randomized spreading code are selected independently and uniformly over @xmath0 , i.e. , @xmath306 . in case masking is applied , we set @xmath307 . taking @xmath308 , the results are sketched in fig . it is seen that _ 1- _ by increasing @xmath2 , the achieved @xmath305 approaches unity in both cases . this is the smg of a frequency division scenario where interference is completely avoided . _ 2- _ masking improves the smg . using a uniform pmf @xmath306 . it is assumed that @xmath308 . in case masking is applied , we have @xmath307 . ] _ example 1- _ let us consider an rsc scheme where @xmath309 , i.e. , no spreading is applied . in this case , for each @xmath310 , the vector @xmath311 is simply a @xmath101 random variable for some @xmath102 $ ] . hence , @xmath312\right)\right\}&=&\pr\left\{\boldsymbol{s}_{1}\notin\mathrm{span}\big(\left\{\boldsymbol{s}_{2},\boldsymbol{s}_{3},\cdots,\boldsymbol{s}_{n-1},\boldsymbol{s}_{n}\right\}\big)\right\}\notag\\ & = & \bar{\varepsilon}\pr\left\{0\notin\mathrm{span}\big(\left\{\boldsymbol{s}_{2},\boldsymbol{s}_{3},\cdots,\boldsymbol{s}_{n-1},\boldsymbol{s}_{n}\right\}\big)\right\}\notag\\ & & + \varepsilon\pr\left\{1\notin\mathrm{span}\big(\left\{\boldsymbol{s}_{2},\boldsymbol{s}_{3},\cdots,\boldsymbol{s}_{n-1},\boldsymbol{s}_{n}\right\}\big)\right\}\notag\\ & \stackrel{(a)}{=}&\varepsilon\pr\left\{1\notin\mathrm{span}\big(\left\{\boldsymbol{s}_{2},\boldsymbol{s}_{3},\cdots,\boldsymbol{s}_{n-1},\boldsymbol{s}_{n}\right\}\big)\right\}\notag\\ & \stackrel{(b)}{=}&\varepsilon\pr\left\{\boldsymbol{s}_{2}=\boldsymbol{s}_{3}=\cdots=\boldsymbol{s}_{n-1}=\boldsymbol{s}_{n}=0\right\}\notag\\ & = & \varepsilon(1-\varepsilon)^{n-1}\end{aligned}\ ] ] where @xmath196 is by the fact that @xmath313 and @xmath239 is by the fact that @xmath314 whenever @xmath315 for @xmath316 . maximizing @xmath317 over @xmath164 , a sum multiplexing gain of @xmath18 is achieved . increasing @xmath2 , the achieved @xmath305 drops to @xmath318 . comparing this to the results in fig . [ f2 ] , spreading the signals ( @xmath308 compared to @xmath309 ) can highly improve the sum multiplexing gain in the network . _ example 2- _ let @xmath320 and @xmath22 . for @xmath321 , elements of @xmath170 are @xmath17 random variables taking the values @xmath13 , @xmath11 and @xmath38 with probabilities @xmath322 , @xmath323 and @xmath324 respectively . we have @xmath325 however , @xmath326 similarly , @xmath327 therefore , @xmath328 this expression is maximized at @xmath306 uniformly for any @xmath102 $ ] and @xmath329 . thus , @xmath330 this function is maximized at @xmath331 and @xmath332 where an smg of @xmath333 is achieved . we notice that _ 1- _ although one s intuition expects @xmath307 is the best choice of the on - off probability , the _ optimum _ masking probability is not @xmath334 . _ 2- _ compared to the sum multiplexing gain of @xmath334 achieved in example 1 without spreading , we see that spreading in fact increases the achieved smg . @xmath319 _ remark 1- _ for any @xmath335 matrix @xmath71 and a @xmath336 diagonal matrix @xmath337 we have @xmath338 . using this , for any @xmath176 one can write @xmath339 where we have replaces @xmath340 and by definition , @xmath341 are nonzero eigenvalues of the matrix @xmath342 . for sufficiently large snr values , one can write @xmath160 given in ( [ fuv ] ) as @xmath343 there are three major factors playing role in the formulation of @xmath160 in the high snr regime , namely , the _ multiplexing gain per user _ , @xmath344 the _ interference entropy factor _ , @xmath345 and the _ channel plus signature factor _ @xmath346 in fact , @xmath347 in general , @xmath348 does not depend on the user index . also , assuming the channel gains are realizations of @xmath17 continuous random variables , the entropy @xmath349 is not a function of @xmath350 , i.e. , @xmath351 does not depend on the user index either . in this case , a simple argument shows that @xmath352 the interplay between @xmath348 , @xmath351 and @xmath353 determines the behavior of the achievable rate . this behavior highly depends on the randomized algorithm in constructing the signature codes . as we will see in the next section , a larger @xmath348 is usually achieved at the cost of a larger @xmath351 . it is clear that a larger @xmath351 reduces the rate specially in moderate ranges of snr . however , due to the fact that @xmath348 has also increased , the rate is lifted up is the high snr regime . these opposing effects identify a tradeoff between rate in moderate snr and high snr regime . @xmath319 in this section , we assume the channel gains @xmath354 are realizations of independent @xmath161 random variables @xmath355 representing rayleigh fading . in the previous section , we have developed a lower bound @xmath356 where @xmath357 and @xmath358 the global design criteria is to choose @xmath91 , @xmath99 and @xmath164 based on @xmath359 _ example 3- _ let us consider a network with @xmath320 users . for @xmath321 , we define @xmath360 in this case , we have _ 1- _ @xmath361 . _ 2- _ since @xmath362 , for each @xmath363 , we have @xmath364 and @xmath365 . _ 3- _ for each @xmath277 and @xmath366 , we have @xmath367 . indeed , @xmath368 and if @xmath369 , then @xmath370 . therefore , @xmath371 can be written as @xmath372 * scheme a- * let @xmath331 and @xmath22 with @xmath373 and @xmath374 for some @xmath375 $ ] . to simplify the expression for @xmath371 in ( [ lol ] ) , we make the following observations : _ 1- _ if @xmath179 has only one nonzero element , then @xmath376 _ 2- _ if @xmath179 has no zero elements , then @xmath377 as such , it is easy to see that _ 1- _ if @xmath179 has only one nonzero element , then @xmath378 _ 2- _ if @xmath379 , then @xmath380 _ 3- _ if @xmath381 , then @xmath382 finally , it is shown in appendix a that @xmath383 simulation results indicate that @xmath384 is maximized at @xmath385 . setting @xmath385 , @xmath386 it is also evident that @xmath387 and @xmath388 * scheme b- * assuming no spreading is performed , let @xmath309 . noting the fact that @xmath389 and @xmath390 , @xmath391 it is easily seen that @xmath392 . therefore , @xmath393 @xmath394 and @xmath395 fig . [ f5 ] sketches @xmath396 for the schemes a and b. it is seen that there is a tradeoff between the rates at medium and high snr values . [ f8 ] demonstrates the best @xmath164 chosen by the users . it is seen that any user in both schemes starts with @xmath397 at @xmath398 . selecting @xmath397 in scheme b leads to @xmath399 . however , @xmath400 is kept at zero as well . therefore , by increasing snr , the average achievable rate starts to saturate , and hence , users switch to @xmath401 for @xmath402 to avoid saturation . in scheme a , @xmath164 is set at @xmath11 for snr values up to @xmath403 . the yields @xmath404 which can be considered as a reason for poor performance of scheme a in the range @xmath405 compared to scheme b. since @xmath406 is larger than @xmath407 , the average achievable rate per user becomes eventually larger in scheme a compared to scheme b as snr increases . in schemes a and b for different snr values . ] in schemes a and b for different snr values . ] in schemes a and b in terms of @xmath164 . ] in schemes a and b in terms of @xmath164 . ] _ example 4- _ we consider a decentralized network of @xmath408 users . we present the following scenarios : the signature sequence of any user consists of an spreading code over the alphabet @xmath0 where @xmath373 and @xmath374 , i.e. , masking is not applied . the purpose of this example is to show that in contrast to example 3 , the optimum value of @xmath409 is not necessarily @xmath334 . before proceeding , let us explain why the common intuition is to set @xmath385 . it is well - known that in an additive noise channel with a stationary noise process , as far as the correlation function$ ] is the function @xmath410\boldsymbol{\mathsf{x}}^{\dagger}[t-\delta t]\}$ ] for @xmath411 . ] is fixed , a stationary gaussian noise process yields the least mutual information between the input and output . we call this the _ gaussian _ bounding technique . using this fact , one can obtain a lower bound on @xmath169 as @xmath412 it is easy to see that @xmath413 and @xmath414 therefore . then , one can use the identity @xmath415 for any @xmath335 and @xmath416 matrices @xmath71 and @xmath72 . ] , @xmath417 and @xmath418 finally , we come up with the following lower bound on @xmath251 , @xmath419 it is straightforward to see that this lower bound is maximized at @xmath309 and @xmath385 for any realization of the channel gains . hence , @xmath420 although , this lower bound suggests to set @xmath309 and in case @xmath421 , it requires @xmath385 , we demonstrate that taking a @xmath421 and regulating at some @xmath422 yield achievable rates larger than the threshold @xmath423 in fact , @xmath424 is the maximum average achievable rate by regulating the transmission rate of the @xmath86 user at @xmath425 . in ( [ wind ] ) , we have used the fact that @xmath426 is an exponential random variable with parameter @xmath11 and @xmath427 is a @xmath428 random variable . let @xmath35 . in this case , @xmath429 . to compute @xmath384 , we notice that _ 1- _ for any @xmath277 , @xmath430 . _ 2- _ in appendix b , it is shown that @xmath431 in contrast to example 3 , computing @xmath384 in closed form is a tedious task . as such , we calculate @xmath432 through simulations . setting the snr at @xmath433 , fig . [ f77 ] sketches @xmath432 in terms of @xmath373 for different values of @xmath91 . in spite of one s intuition , the average achievable rate per user has a double - hump shape and is not maximized at @xmath385 . it is seen that the best performance is obtained at @xmath434 and @xmath435 . @xmath319 in schemes a and b in terms of @xmath164 . ] _ remark 2- _ to gain some insight on why @xmath432 is double - hump in example 4 , one can study the multiplexing gain per user given in ( [ mg ] ) . let us consider a network with @xmath436 users . ] where the signature codes only consist of spreading over the alphabet @xmath22 . in general , one can write @xmath437 therefore , @xmath438 the term @xmath439 can be easily calculated as @xmath440 on the other hand , computation of the term @xmath441 is not an easy task . however , the point is that both @xmath439 and @xmath441 have a global maximum at @xmath385 . hence , there is a chance that their difference is maximized at some @xmath422 . this is exactly what happens here . as an example , fig . [ f77c ] sketches multiplexing gain per user in terms of @xmath442 in a network with @xmath443 users . it is assumed that the spreading code length is @xmath444 . in terms of @xmath373 in a network of @xmath443 users with @xmath444 . ] _ remark 3- _ the expression for the smg given in ( [ canada ] ) does not depend on the spreading / masking strategy . in fact , one can consider a more general scheme where the @xmath86 user randomly selects its code @xmath170 out of a globally known set of codes @xmath445 based on a globally known pmf . in case @xmath320 , @xmath446 taking @xmath331 , let us assume that @xmath447 consists of @xmath448 vectors in @xmath449 no two of which are parallel with each other . therefore , @xmath450 since @xmath448 can be arbitrarily large , the smg of a network of two users is equal to @xmath11 . in this case , it is easy to see that @xmath451 if @xmath408 , taking a set of arbitrarily large non - parallel vectors in some space @xmath184 is by no means a necessarily appropriate collection . let @xmath452 consist of @xmath448 vectors in @xmath184 . for each @xmath8 and @xmath453 , we denote by @xmath454 the number of distinct subsets @xmath455 of @xmath447 of size @xmath456 such that @xmath457 . we denote these subsets explicitly by @xmath458 . assuming all users select their codes equally likely over @xmath447 , @xmath459\right)\right\}=\frac{1}{l}\sum_{l=1}^{l}\pr\left\{\vec{\mathfrak{c}}_{l}\notin\mathrm{csp}\left([\vec{\boldsymbol{s}}_{2}|\vec{\boldsymbol{s}}_{3}|\cdots|\vec{\boldsymbol{s}}_{n-1}|\vec{\boldsymbol{s}}_{n}]\right)\right\}.\end{aligned}\ ] ] for each @xmath8 , @xmath460\right)\right\}=\sum_{r=1}^{l-1}\sum_{m=1}^{\omega_{l , r}}\pr\left\{\forall\vec{\mathfrak{b}}\in\mathfrak{b}_{l , r}(m),\exists j\geq 2 : \vec{\boldsymbol{s}}_{j}=\vec{\mathfrak{b}}\right\}.\end{aligned}\ ] ] it is easy to see that and @xmath461 elements of @xmath462 are chosen by @xmath463 and @xmath464 users respectively , this can happen in @xmath465 different ways . ] @xmath466 for any @xmath8 and @xmath467 . therefore , @xmath312\right)\right\}=\frac{1}{l^{n}}\sum_{l=1}^{l}\sum_{r=1}^{l-1}\omega_{l , r}\rho_{r , n}\end{aligned}\ ] ] where @xmath468 finally , the achieved smg is @xmath469 we remark that there is no closed formula for @xmath470 , however , one can use the recursion @xmath471 to compute this quantity . by ( [ bool ] ) , one can easily see that @xmath305 is maximized if @xmath454 is as large as possible for each @xmath8 and @xmath453 . we know that @xmath472 . this upper bound is achieved if @xmath447 consists of @xmath473 independent vectors in @xmath184 . in this case , @xmath474 it is not hard to see that @xmath475 . hence , @xmath476 to get the largest smg , one may let @xmath477 yielding @xmath478 which is the result obtained in example 1 via masking without spreading . we have already seen that applying masking on top of spreading can result in larger achievable rates due to increasing the attained multiplexing gain . however , our results so far are based on the achievable rate @xmath160 which is only a lower bound on the _ capacity _ of the @xmath86 user . in deriving @xmath160 , the pdf of the transmitted signals is taken to be complex gaussian which is not necessarily optimal . as such , we have no optimality arguments so far . in this section , we question the optimality of masking without spreading . in fact , we are interested to see if at any snr level , there is an optimal pdf such that generating the transmitted signals based on this pdf makes spreading unnecessary . for this purpose , we define the _ masking capacity _ of a user as the largest achievable rate by this user assuming all users follow the masking strategy with no spreading applied . we also require _ fairness _ conditions by which we imply that users generate their signals using the same pdf . fixing @xmath102 $ ] , the masking capacity of the @xmath86 user is defined by @xmath479 where @xmath480 in which @xmath481 is the masking coefficient of the @xmath86 user which is a @xmath101 random variable and @xmath482 is the @xmath161 ambient noise random variable . the parameter @xmath164 is designed based on maximizing a globally available utility function such as @xmath432 assuming @xmath354 are realizations of @xmath17 random variables with a continuous pdf . we focus on a decentralized network of @xmath320 users . we call the users as user # 1 and user # 2 . according to the results in example 3 ( scheme b ) , the decision rule to regulate @xmath164 is @xmath483}\mathrm{e}\left\{\varepsilon\log\left(1+\frac{2^{-\mathscr{h}(\varepsilon)}|\boldsymbol{h}_{1,1}|^{2}\gamma}{\varepsilon\left(1+\frac{|\boldsymbol{h}_{2,1}|^{2}\gamma}{\varepsilon}\right)^{\varepsilon}}\right)\right\}.\end{aligned}\ ] ] the main result of the paper is the following . there exist @xmath484 and @xmath485 $ ] such that for any @xmath486 , it is possible to achieve rates larger than @xmath487 for sufficiently large values of @xmath94 where @xmath488 is given in ( [ pel ] ) . to prove theorem 1 , we need the following lemma . let @xmath489 and @xmath490 be circularly symmetric complex gaussian random variables with variances @xmath491 and @xmath492 respectively and @xmath493 be independent of @xmath494 . then , the answer to the optimization problem @xmath495 is a circularly symmetric complex gaussian @xmath493 for any @xmath496 and any @xmath497 . also , if @xmath498 , the same conclusion holds for any @xmath499 . this is a direct consequence of theorem 1 in @xcite . our strategy is to find an upper bound on @xmath500 for arbitrary @xmath102 $ ] and proposing an achievable rate which surpasses this upper bound . we proceed as follows . we have @xmath501 where @xmath196 follows by the fact that @xmath502 , @xmath239 is by the fact that the mutual information between the input and output of the channel increases if a `` genie '' provides the receiver side of user # 1 with @xmath503 , @xmath240 follows by the fact that @xmath504 and @xmath505 are identically distributed and the fact that @xmath506 and finally @xmath507 follows by the fact that for any complex random variable @xmath493 and @xmath508 , we have @xmath509 . also , we have @xmath510 and @xmath511 in the last equality in ( [ ee1 ] ) . denoting the upper bound in ( [ ee1 ] ) by @xmath512 , @xmath513 it is trivial that @xmath514 which follows by the maximum entropy lemma@xcite . applying lemma 1 , if @xmath515 or @xmath516 , or equivalently , @xmath517 or @xmath516 , the answer to the optimization @xmath518 is a complex gaussian @xmath504 . we note that the power of the optimum gaussian signal @xmath504 is not necessarily @xmath94 . let the optimum @xmath504 be a @xmath519 random variable . we distinguish the following cases . _ case 1- _ if @xmath520 and @xmath521 , then @xmath522 . _ case 2- _ if @xmath523 , @xmath524 and @xmath525 , then @xmath526 . _ case 3- _ if @xmath527 and @xmath528 , then @xmath529 . verification of these cases is a straightforward task which is omitted here for the sake of brevity . therefore , as far as @xmath517 , the term @xmath530 saturates by increasing @xmath94 . using this fact together with ( [ koo ] ) and ( [ th2 ] ) , @xmath531 as far as @xmath517 . on the other hand , if @xmath532 and @xmath528 , @xmath533 using this together with ( [ koo ] ) and ( [ th2 ] ) , @xmath534 as far as @xmath532 and @xmath535 . however , we can remove the condition @xmath528 by a simple arguement . let us fix @xmath536 . it is clear that @xmath537 for @xmath538 . since @xmath539 , we get @xmath540 . hence , ( [ s444 ] ) holds for all @xmath532 regardless of the values of @xmath541 and @xmath536 . to recap , we have shown that @xmath542 we end this subsection with the following corollary . if @xmath543 , @xmath544 by the results in example 3 , @xmath545 for every @xmath546 . however , by ( [ s555 ] ) , @xmath547 for all @xmath543 . this concludes the proof . applying spreading on top of masking , we show that there is a range of @xmath164 such that it is possible to achieve rates larger than @xmath548 as far as @xmath94 is sufficiently large . to transmit its gaussian signal @xmath549 , user # @xmath550 spreads @xmath197 along a @xmath551 random vector @xmath552 consisting of @xmath17 random numbers taking values in a finite alphabet @xmath21 with equal probability . thereafter , this user applies the masking process by constructing the @xmath551 masking vector @xmath553 consisting of @xmath17 bernoulli random variables taking the values @xmath13 and @xmath11 with probabilities @xmath554 and @xmath164 respectively . we assume that @xmath552 and @xmath553 are known to both ends of user # @xmath550 . finally , this user transmits @xmath555 in two consecutive transmission slots where @xmath111 is to ensure the total transmission power per symbol @xmath197 is @xmath94 . assuming both users are synchronous , the following vector is received at the receiver side of user # 1 @xmath556 where @xmath557 is a vector of independent @xmath161 random variables representing the ambient noise samples at the receiver side of user # 1 . the achievable rate for this user is @xmath558 by our results in section iii , @xmath559 hence , @xmath560 we are interested in values of @xmath164 so that @xmath561 is strictly satisfied . by ( [ s555 ] ) and ( [ e33 ] ) , it is sufficient to show that there is a range for @xmath164 such that @xmath562 let @xmath22 . in this case the elements of @xmath563 and @xmath564 are @xmath17 random variables taking the values @xmath13 , @xmath11 and @xmath38 with probabilities @xmath554 , @xmath565 and @xmath566 respectively . the event @xmath567 occurs if and only if @xmath568 or @xmath569 while @xmath570 . then , one can easily see that @xmath571 . this can also be deduced from ( [ boro ] ) . substituting this in ( [ x2 ] ) requires @xmath572 this simplifies to @xmath573 for @xmath532 and @xmath574 for @xmath517 . solving these inequalities , we get @xmath575 . it is not hard to see that @xmath576 given in ( [ pel ] ) is in the interval @xmath577 for all @xmath578 . setting @xmath579 and @xmath580 , we see that @xmath488 and @xmath581 is larger than @xmath582 for large values of @xmath94 . this completes the proof of theorem 1 . next , we demonstrate that increasing the size of the underlying alphabet can expand the range of @xmath164 for which achieving a rate larger than @xmath548 is possible . _ remark 3- _ if @xmath583 , the elements of @xmath563 and @xmath564 are @xmath17 random variables taking the values @xmath13 , @xmath584 , @xmath38 , @xmath11 and @xmath585 with probabilities @xmath554 , @xmath586 , @xmath587 , @xmath586 and @xmath586 respectively . the event @xmath567 occurs if and only if @xmath568 or @xmath569 while @xmath570 or @xmath588 or @xmath589 . we get @xmath590 . substituting this in ( [ x2 ] ) requires @xmath591 hence , @xmath592 for @xmath532 and @xmath593 for @xmath517 . solving these inequalities , @xmath594 . we proposed an approach towards communication in decentralized wireless networks of separate transmitter - receiver pairs . a randomized signaling scheme was introduced in which each user locally spreads its gaussian signal along a randomly generated spreading code comprised of a sequence of nonzero elements over a certain alphabet . along with spreading , each transmitter also masks its output independently from transmission to transmission . using a conditional version of entropy power inequality and a key lemma on the differential entropy of mixed gaussian random vectors , achievable rates were developed for the users . assuming the channel gains are realization of independent continuous random variables , each user finds the optimum parameters in constructing the randomized spreading and masking sequences by maximizing the average achievable rate per user . it was seen that as the number of users increases , the achievable sum multiplexing gain of the network approaches that of a centralized orthogonal scheme where multiuser interference is completely avoided . it was observed that in general the elements of a spreading code are not equiprobable over the underlying alphabet . this particularly happens if the number of active users is greater than three . finally , using the recently developed extremal inequality of liu - viswanath , we presented an optimality result showing that transmission of gaussian signals via spreading and masking yields higher achievable rates than the maximum achievable rate attained by applying masking only . by proposition 1 , @xmath595 in this appendix , we prove that @xmath596 by ( [ e14 ] ) , it suffices to show that @xmath597 . let us consider the _ informed _ @xmath86 user where the receiver is aware of @xmath170 and @xmath241 . the achievable rate of this virtual user is @xmath598 . it is clear that @xmath599 . however , @xmath600 where @xmath196 follows by the fact that fixing @xmath601 converts the channel of the @xmath86 informed user to an additive gaussian channel . on the other hand , @xmath602 noting that @xmath603 scales like @xmath604\right)\log\gamma$ ] , we conclude that the first term on the right hand side of ( [ bol12 ] ) scales like @xmath605\right)\right\}\log\gamma$ ] . by the same token , the second term on the right hand side of ( [ bol12 ] ) scales like @xmath606 . therefore , @xmath607 is upper bounded by a quantity which scales like @xmath608)\}-\mathrm{e}\{\mathrm{rank}(\boldsymbol{s}_{i})\}\big)\log\gamma$ ] . the result of the proposition is immediate . let @xmath609 . therefore , @xmath610 to compute @xmath611 , we have @xmath612 where @xmath196 is by the fact that the terms @xmath613 , @xmath614 and @xmath615 are zero . on the other hand , it is easy to see that @xmath616 . this implies @xmath617 . therefore , @xmath618 using ( [ lol1 ] ) and ( [ lol2 ] ) , @xmath619 let @xmath620 . we have @xmath621 where @xmath196 is by the fact that @xmath622 for any @xmath623 and @xmath239 is by the fact that for any two distinct numbers @xmath624 , the knowledge about @xmath625 can be obtained by knowing @xmath626 and @xmath627 by the fact that @xmath628 . let us define @xmath629 by ( [ nol ] ) , @xmath630 . let @xmath55 be the event where @xmath631 , while @xmath632 of the elements of @xmath633 , namely , @xmath634 and @xmath635 are @xmath11 and the rest are @xmath38 for some @xmath636 and @xmath637 . also , let @xmath638 be the event where @xmath639 , @xmath640 for @xmath641 and @xmath642 for @xmath643 . it is clear that @xmath644 we know that @xmath645 and @xmath646 . hence , using ( [ mol ] ) , @xmath647 a. sahai , n. hoven , s. m. mishra and r. tandra , `` fundamental tradeoffs in robust spectrum sensing for opportunistic frequency reuse '' , _ technical reports _ , march 2006 , available online at http:// www.eecs,berkeley.edu/ sahai / papers / cognitivetechreport06.pdf . s. srivastava , s. tripathi , d. sanghi and a. k. chaturvedi , `` a code allocation protocol for maximizing throughput in cdma based ad - hoc networks '' , _ ieee wireless commun . and networking conf . 2 , pp . 1385 - 1390 , march 2003 . t. salonidis , p. bhagwat , l. tassiulas and r. lamaire , `` distributed topology construction of bluetooth wireless personal area networks '' , _ ieee journal on selected areas in commun . 633 - 643 , march 2005 . z. kostic and n. sollenberger , `` performance and implementation of dynamic frequency hopping in limited - bandwidth cellular systems '' , _ ieee trans . on wireless comm . _ , vol . 1 , no . 1 , pp . 28 - 36 , jan . 2002

this paper addresses a unified approach towards communication in decentralized wireless networks of separate transmitter - receiver pairs . different transmitters are connected to different receivers through channels with static and non - frequency selective gains . in general , users are unaware of each other s codebooks and there is no central controller to assign the resources in the network to the users . a randomized signaling scheme is introduced in which each user locally spreads its gaussian signal along a randomly generated spreading code comprised of a sequence of nonzero elements over a certain alphabet . along with spreading , each transmitter also masks its output independently from transmission to transmission . using a conditional version of entropy power inequality and a key lemma on the differential entropy of mixed gaussian random vectors , achievable rates are developed for the users . assuming the channel gains are realization of independent continuous random variables , each user finds the optimum parameters in constructing the randomized spreading and masking sequences by maximizing the average achievable rate per user . it is seen that as the number of users increases , the achievable sum multiplexing gain of the network approaches that of a centralized orthogonal scheme where multiuser interference is completely avoided . an interesting observation is that in general the elements of a spreading code are not equiprobable over the underlying alphabet . this is in contrast to the customary use of binary pn codes in spread spectrum communications in which the code elements may be selected with equal probability over @xmath0 . this particularly happens if the number of active users is greater than three . finally , using the recently developed extremal inequality of liu - viswanath , we present an optimality result showing that transmission of gaussian signals via spreading and masking yields higher achievable rates than the maximum achievable rate attained by applying masking only . = 1

<s>[INST]an important topic in modern wireless communications is the subject of decentralized networks . by definition , a decentralized network of separate transmitter - receiver pairs has no central controller to allocate the network resources among the active users . as such , resource allocation must be performed locally at each node . in general , users are not already aware of the number of active users and the channel gains . also , users are not aware of each other s codebooks implying multiuser detection is not possible , i.e. , users treat each other as noise . multiuser interference is known to be the main factor limiting the achievable rates in such networks particularly in the high signal - to - noise ratio ( snr ) or interference limited regime . therefore , all users must follow a distributed signaling scheme such that the destructive effect of interference on each user is minimized , while the resources are fairly shared among users . most of distributed schemes reported in the literature rely on either _ game - theoretic _ approaches or _ cognitive radios_. cognitive radios @xcite have the ability to sense the unoccupied portion of the available spectrum and use this information in resource allocation . although such smart radios avoid the use of a central controller , they require sophisticated detection techniques for sensing the spectrum holes and dynamic frequency assignment which add to the overall system complexity @xcite . distributed strategies based on game theoretic arguments have already attracted a great deal of attention . in @xcite , the authors introduce a non - cooperative game theoretic framework to investigate the spectral efficiency issue when several users compete over an unlicensed band with no central controller . reference @xcite offers a brief overview of game theoretic dynamic spectrum sharing . although these schemes enable us to understand the dynamics of distributed resource allocation , they usually suffer from complexity in software and convergence issues as they rely on iterative algorithms . spread spectrum communications is a natural setup to share the same bandwidth by several users . this area has attracted tremendous attention by different authors during the past decades in the context of centralized uplink / downlink multiuser systems . appealing characteristics of spread spectrum systems have motivated researchers to utilize these schemes in networks without a certain infrastructure , i.e. , packet radio or ad - hoc networks@xcite . in direct sequence spread spectrum systems , the signal of each user is spread using a pseudo - random noise ( pn ) code . the challenging point is that in a network without a central controller , if two users use the same spreading code , they will not be capable of recovering the data at the receiver side due to the high amount of interference . distributed code assignment techniques are developed in @xcite . in @xcite , using a greedy approximation algorithm and invoking graph theory , a distributed code assignment protocol is suggested . another category of research is devoted to devise distributed schemes in the reverse link ( uplink ) of cellular systems . distributed power assignments algorithms are proposed in @xcite . reference @xcite proposes a distributed scheduling method called the token - bucket on - off scenario utilized by autonomous mobile stations where its impact on the overall throughput of the reverse link is investigated . furthermore , decentralized rate assignments in a multi - sector code division multiple access wireless network are discussed in @xcite . being a standard technique in spread spectrum communications and due to its interference avoidance nature , frequency hopping is the simplest spectrum sharing method to use in decentralized networks . as different users typically have no prior information about the codebooks of the other users , the most efficient method is avoiding interference by choosing unused channels . as mentioned earlier , searching the spectrum to find spectrum holes is not an easy task due to the dynamic spectrum usage . as such , fh is a realization of a transmission scheme without sensing , while avoiding the collisions as much as possible . frequency hopping is one of the standard signaling schemes adopted in ad - hoc networks . in short range scenarios , bluetooth systems @xcite are the most popular examples of a wireless personal area network or wpan . using fh over the unlicensed ism band , a bluetooth system provides robust communication to unpredictable sources of interference . a modification of frequency hopping called dynamic frequency hopping ( dfh ) , selects the hopping pattern based on interference measurements in order to avoid dominant interferers . the performance of a dfh scheme when applied to a cellular system is assessed in @xcite . distributed rate assignment strategies are recently adopted in the context of medium access control . it is well - known @xcite that the capacity region @xmath1 of a multiple access channel with @xmath2 users is a polytope with a @xmath3 corner points . let each corner point of @xmath1 be an @xmath2-tuple whose elements are among the numbers @xmath4 and @xmath5 . with no cooperation among the users , the authors in @xcite propose that each user selects a codebook of rate @xmath6 with probability @xmath7 for @xmath8 . assuming the receiver is aware of the rate selection of all users , the average sum rate of the network is @xmath9 where @xmath10 is @xmath11 if @xmath12 and @xmath13 otherwise . finally , the numbers @xmath14 and @xmath15 are derived to maximize @xmath16 . major differences of this scenario with a decentralized wireless network are _ 1 ) _ the capacity region of a multiuser interference channel is unknown . _ 2 ) _ in case transmitters have different choices to select the transmission rate , a certain receiver is not guaranteed to be aware of the transmission rate of interferers . _ 3 ) _ any user is already unaware of the gains of channels connecting the interferers transmitters to its receiver . also , any user is never capable of finding the amount of interference it imposes on other users . it is well - known that in the low snr regime continuous transmission of @xmath17 gaussian signals is optimal . however , as snr increases , this scheme turns out to be quite inefficient . for instance , the achievable rate of each user eventually saturates , i.e. , the achieved sum multiplexing gain as snr tends to infinity . ] ( smg ) is equal to zero . using the results in @xcite , it is easy to see that by using a masking strategy where each user quits transmitting its gaussian signals independently from transmission to transmission , a nonzero smg of @xmath18 is attained in a decentralized network of @xmath2 users . this is an interesting result in the sense that if the number of active users tends to infinity , the achieved smg settles on @xmath19 . in the present paper , we answer the following questions : _ question 1- _ is it possible to achieve an smg larger than @xmath20 as the number of users becomes large ? we propose a distributed signaling scheme where each user spread its gaussian signal along a spreading code consisting of @xmath17 elements selected according a globally known probability mass function ( pmf ) over a finite alphabet @xmath21 . thereafter , the resulting sequence is punctured independently from symbol to symbol with a certain probability representing the masking operation . for example , assuming @xmath22 , let the generated spreading code have length @xmath23 and be given by @xmath24 also , an @xmath17 sequence of @xmath11 s ( representing @xmath25 ) and @xmath13 s ( representing @xmath26 ) with length @xmath23 is generated as @xmath27 finally , denoting the gaussian signal to be transmitted by @xmath28 , the sequence @xmath29 is transmitted in @xmath23 consecutive transmission slots called a transmission frame . this process is repeated independently from transmission frame to transmission frame . we notice that since different users are not aware of each other s signals and the spreading / masking sequences , the noise plus interference vector at the receive side of any user is a mixed gaussian random vector . we assume the knowledge of interference probability density function ( pdf ) at the receiver side of each user . we are able to see that using the proposed randomized spreading scheme , the number of active users and the gains of channels conveying the interferers signals can be easily found by inspecting the interference pdf and solving a set of linear equation . assuming all users are _ frame - synchronous _ , we derive achievable rates for the users in three steps : _ step 1- _ using singular value decomposition ( svd ) of the signal space at the receiver side any user , the interference vector is mapped in the signal space and the complement space and a subspace @xmath30 of @xmath31 , the complement space @xmath32 of @xmath30 is the set of elements in @xmath31 that are perpendicular to any element in @xmath30 . ] of the signal space . _ step 2- _ a conditional version of entropy power inequality is used to derive a lower bound on the mutual information between the input and output of each user along any transmission frame . the conditioning is made over the contents of the interference vector mapped in the complement space of the signal space . _ step 3- _ the resulting lower bound in the previous step highly depends on the differential entropy of mixed gaussian random vectors . since there is no closed formula on the differential entropy of a mixed gaussian vector , a key lemma is used to find computable bounds on this differential entropy . this leads us to the final formulation of the achievable rate . in a decentralized network of @xmath2 users , we are able to show that by regulating the length of the transmission frame and the probabilistic structure of the spreading / masking sequences , the resulting lower bound scales like @xmath33 where @xmath34 . this is exactly the smg of a centralized orthogonal resource allocation scheme where multiuser interference is completely avoided . our focus is not particularly on the high snr regime . in fact , the length of the transmission frame and the probabilistic parameters of the spreading / masking codes are sensitive to the choice of snr . our proposed achievable rate for any user in general depends on the gains of the channels conveying the interference . as mentioned earlier , each user is capable of finding the channel gains , however , if each user attempts to maximize its achievable rate over the length of the transmission frame and other code parameters , different users come up with different choices which results in inconsistency . to circumvent this difficulty , assuming the channel gains are realizations of @xmath17 continuous random variables , each user selects the code parameters such that the average of achievable rate per user over different realizations of the channel gains is maximized . this leads to a consistent and distributed method to design the best randomization algorithm in constructing the spreading / masking sequences . an interesting observation is that even in the simplest scenario where the underlying alphabet is @xmath0 and no masking is applied , the elements of the spreading codes are not equiprobable over @xmath0 . for example , our simulation results show that in a network of @xmath35 users at @xmath36 , the elements of the spreading code must be selected to be @xmath11 with a probability of @xmath37 and @xmath38 with a probability of @xmath39 or vice versa . _ question 2- _ what is the highest achievable rate under the masking protocol ? can one do better than masking ? one may raise the question if masking the transmitted signals independently from transmission slot to transmission slot is by itself sufficient , i.e. , by selecting the pdf of the transmitted signals properly ( probably non - gaussian ) , there is no need for spreading . using an extremal inequality of liu - viswanath @xcite , we are able to show that transmission of gaussian signals along with spreading and masking yields higher achievable rates that the largest achievable rate with masking alone . the rest of the paper is organized as follows . section ii offers the system model . in this section , we introduce the randomized spreading coding and discuss how all user can consistently design their spreading / masking sequences . section iii presents the development of achievable rates based on the three steps mentioned earlier . system design is brought in section iv where we offer several design examples . finally , section v prove the supremacy of blending spreading and masking over masking alone . conclusion remarks are given in section vi . * notation- * throughout the paper , we denote random quantities in bold case such as @xmath28 and @xmath40 . a realization of @xmath28 is denoted by @xmath41 . a circularly symmetric complex gaussian random vector @xmath42 of length @xmath43 with zero mean and covariance matrix @xmath44 is denoted by @xmath45 . a bernoulli random variable @xmath46 with @xmath47 $ ] is denoted by @xmath48 . for a sequence @xmath49 and a set @xmath50 where @xmath51 , we define @xmath52 . we use @xmath53 for the expectation operator , @xmath54 for the probability of an event @xmath55 , @xmath56 for the indicator function of an event @xmath55 and @xmath57 for the pdf of a random variable @xmath28 . also , @xmath58 denotes the mutual information between random variables @xmath28 and @xmath59 , @xmath60 the differential entropy of a continuous random variable @xmath28 , @xmath61 the entropy of a discrete random variable @xmath28 , and the binary entropy function is denoted by @xmath62 for @xmath63 $ ] . for any @xmath63 $ ] , @xmath64 denotes @xmath65 . the dirac delta function is denoted by @xmath66 . for integers @xmath67 , a @xmath68 matrix in which all elements are @xmath13 or @xmath11 is shown by @xmath69 or @xmath70 respectively . for sets @xmath71 and @xmath72 , the set @xmath73 denotes a set with elements in @xmath71 and not in @xmath72 . the cardinality of a set @xmath71 is denoted by @xmath74 . for any two vectors of the same size @xmath75 and @xmath76 , the vector @xmath77 is the element - wise product of @xmath75 and @xmath76 . for two function @xmath78 and @xmath79 of a variable @xmath80 , we write @xmath81 if @xmath82 and @xmath83 if @xmath84 . the notation @xmath85 is defined similarly . we consider a decentralized communication network of @xmath2 users . the static and non frequency - selective gain of the channel from the @xmath86 transmitter to the @xmath87 receiver is shown by @xmath88 which is in general a complex number . in a decentralized network , there is no communication or cooperation among different users . due to the fact that the network has no fixed infrastructure and there is no central controller to manage the network resources among users , resource allocation and rate assignment must be performed locally at every transmitter . a main feature of such networks is that the @xmath86 user is not already informed about the channel gains @xmath89 concerning the links connecting different transmitters to the @xmath86 receiver . in fact , every receiver has only access to the interference pdf and the knowledge about the number of active users and the channel gains @xmath89 can only be inferred through analyzing this pdf . also , different users are not aware of each other s codebooks . as such , no multiuser detection is possible and users treat the interference as noise . in this part , we introduce a distributed signaling strategy using randomized spreading / masking . for positive integers @xmath90 and @xmath91 , the codebook of the @xmath86 user consists of @xmath92 codewords where a typical codeword @xmath93 is a sequence of @xmath17 circularly symmetric complex gaussian random variables with zero mean and variance @xmath94 . the @xmath86 user transmits @xmath93 in @xmath90 _ transmission frames _ where each transmission frame consists of @xmath91 _ transmission slots_. in a typical transmission frame , one of the signals in the codeword @xmath93 is transmitted . to transmit @xmath95 , the @xmath86 user randomly constructs two independent sequences called the spreading and the masking codes . the spreading code is a @xmath96 vector @xmath97 over an alphabet @xmath98 where the elements of @xmath97 are @xmath17 with a globally known pmf @xmath99 . the masking code is a @xmath96 vector @xmath100 whose elements are independent @xmath101 random variables for some @xmath102 $ ] . thereafter , the @xmath86 user transmits @xmath103 in the @xmath104 transmission frame . the vector @xmath105 is called the randomized signature code of the @xmath86 user in the @xmath104 transmission frame . we remark that the spreading and masking codes of the @xmath86 user over different transmission frames are constructed independently . the alphabet @xmath21 has the property that for any @xmath106 , we have @xmath107 . the received vector at the receiver side of the @xmath86 user in a typical transmission frame is given by @xmath108 where @xmath109 is a @xmath110 random vector representing the ambient noise at the @xmath86 receiver . also , @xmath111 is a normalization factor ensuring the average transmission power per symbol of the @xmath86 user is @xmath94 , i.e.,@xmath112 in ( [ e1 ] ) , we have made the assumption that all active users in the network are frame - synchronous meaning their transmission frames start and end at similar time instants . this is not necessarily a valid assumption in a decentralized network , however , this makes the presentation of the subject much easier . it is clear that the transmitted signals of each user along its transmission frames are correlated while signals transmitted in different transmission frames are independent . hence , we assume any new active user is capable of detecting the correlated segments along the interference plus noise process , and therefore , synchronizing itself with former active users in the network . however , in case different users are not frame - synchronous and users are not aware of the asynchrony pattern , the communication channel of any user is not ergodic anymore and one must perform outage analysis . using joint typicality at the receiver side of the @xmath86 user , any data rate @xmath113 is achievable where @xmath114 the term @xmath115 indicates that the @xmath86 user is also embedding information in the sequence of @xmath17 signature codes . in fact , one can assume the codeword of any user consists of two sequences , namely , the sequence of gaussian signals and the sequence of randomized signature codes . due to the fact that the signature code of any user is not known to other users and on the other hand , the signature codes are independently changing over different transmission frames , the noise plus interference at the receiver side of any user has a mixed gaussian pdf . this makes @xmath116 have no closed expression . therefore , we need to obtain a tight lower bound on this quantity whose computation only needs data that can be inferred from the noise plus interference pdf at the receiver side of the @xmath86 user and be fed back to its associated transmitter in order to regulate the transmission rate . throughout the paper , the interference term at the receiver side of the @xmath86 user is denoted by @xmath117 , i.e. , @xmath118 . one can state @xmath117 as @xmath119 where @xmath120 @xmath121 and @xmath122 in general , we assume that the @xmath86 receiver is aware of @xmath123 which can be done through a training sequence sent by the @xmath86 transmitter . assuming the channel gains are realizations of @xmath17 random variables with a continuous pdf , then the number of gaussian components in the mixed gaussian pdf of the interference in any transmission slot at the receiver side of the @xmath86 user is @xmath124 if masking is not performed and @xmath125 if masking and spreading are both applied . these levels consist of @xmath126 where @xmath127 . as such , as far as @xmath128 , the number of active users can be obtained by finding the number of interference power levels . however , if @xmath129 for some @xmath130 and masking is not performed , the interference pdf in any transmission slot is gaussian ( the interference vector on any transmission frame is still mixed gaussian ) with power @xmath131 . therefore , the number of active users can not be derived by investigating the interference pdf in one transmission slot . in this case , it can be verified that the joint pdf of any two transmission slots in a transmission frame is a mixed gaussian pdf with @xmath132 gaussian components . this yields a method to find @xmath2 in case @xmath21 has only two elements . by symmetry , characterization of @xmath133 demands the knowledge of an arbitrary reordering of the sequence @xmath134 . in this paper , we derive a lower bound @xmath135 on @xmath133 which is only a function of the magnitude of the channel gains . therefore , we need to obtain an arbitrary reordering of @xmath136 . let @xmath137 be a reordering of @xmath134 based on magnitude , i.e. , @xmath138 . we consider the following cases : _ case 1- _ if @xmath139 , let @xmath140 and @xmath141 be the two largest elements in @xmath21 such that @xmath142 . denoting the @xmath143 largest interference plus noise power levels on each transmission slot by @xmath144 , we have @xmath145 and @xmath146 for @xmath147 . these @xmath143 linear equations yield @xmath148 . _ case 2- _ let masking be the only ingredient in constructing the signatures , i.e. , spreading is not applied . denoting the @xmath143 largest interference plus noise power levels on each transmission slot by @xmath144 , we have @xmath149 and @xmath150 for @xmath147 . these @xmath143 linear equations yield @xmath148 . _ case 3- _ let @xmath129 for some @xmath151 and masking is performed on top of spreading . then , we can apply the same procedure in case 2 . _ case 4- _ let @xmath129 for some @xmath151 and masking is not applied . the joint pdf of the interference plus noise on any two transmission slots inside a transmission frame is a bivariate mixed gaussian pdf in which the gaussian components have covariance matrices of the form @xmath152 where @xmath153 for @xmath154 . the @xmath155 largest elements among the off - diagonal elements of these matrices correspond to @xmath156 for @xmath147 . these elements together with the diagonal element @xmath157 yield @xmath148 . therefore , we have shown that the @xmath86 user can find @xmath2 and a reordering of the sequence @xmath134 . an important issue in a decentralized network is to propose a globally known utility function to be optimized by all user without any cooperation . as mentioned earlier , the receivers can infer the number of active users in the network and the channel gains by inspecting the interference pdf . we consider a scenario where this information is fed back to the transmitters . as mentioned earlier , there is no closed formulation on @xmath133 . however , we are able to develop a lower bound @xmath135 for @xmath133 which is tight enough to guarantee @xmath158 in general , @xmath135 depends on @xmath159 . as such , we denote it explicitly by @xmath160 . assuming @xmath89 are realizations of independent @xmath161 random variables @xmath162 , we propose that the @xmath86 user selects @xmath91 , @xmath163 and @xmath164 based on @xmath165 after selecting @xmath91 and @xmath99 using ( [ rule ] ) , the @xmath86 user regulates its actual transmission rate at @xmath166 using the realization of @xmath167 . one can write @xmath116 as @xmath168 the term @xmath169 is the achievable rate of the @xmath86 user as if this user knew the randomized signature code @xmath170 already , i.e. , the achievable rate of the @xmath86 user can be in general larger than the case where the signature matrices are already revealed to the receiver side . the extra term @xmath171 is bounded from above by @xmath172 which is not a function of snr . therefore , @xmath173 as such , we ignore the term . this enables us to compute @xmath171 directly . ] @xmath171 and focus on developing a tight lower bound on @xmath169 . to develop a lower bound on @xmath169 , our major tools are linear processing of the channel output based on singular value decomposition of the signature code @xmath170 , a conditional version of entropy power inequality and a key upper bound on the differential entropy of a mixed gaussian random vector . we have @xmath174 in the following , we find a lower bound on @xmath175 for any @xmath176 . * step 1- * the matrix @xmath177 has two eigenvalues , namely zero and @xmath178 . the eigenvector corresponding to @xmath178 is @xmath179 and the the eigenvectors corresponding to zero are @xmath180 orthonormal vectors denoted by @xmath181 and @xmath182 which together with the columns of @xmath183 make an orthonormal basis for @xmath184 . let us define @xmath185 @xmath186 and @xmath187 writing the svd of @xmath179 , @xmath188 the @xmath86 receiver constructs the vector @xmath189 upon reception of @xmath190 . we have @xmath191 we define @xmath192_{1}\notag\\ & = & \frac{\beta\vec{s}^{\dagger}\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right)}{\|\vec{s}\|_{2}}\end{aligned}\ ] ] @xmath193_{1}=\beta h_{i , i}\|\vec{s}\|_{2}\boldsymbol{x}_{i}+\boldsymbol{\varphi}_{i}\ ] ] and @xmath194_{2}^{k}\notag\\&=&\left[u_{i}^{\dagger}(\vec{s})\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right)\right]_{2}^{k}\notag\\ & \stackrel{}{=}&\left[u_{i}^{\dagger}(\vec{s})\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right)\right]_{2}^{k}\notag\\&=&\left[\begin{pmatrix } \frac{\vec{s}^{\dagger}}{\|\vec{s}\|_{2 } } \\ g_{i}^{\dagger}(\vec{s } ) \end{pmatrix}\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right)\right]_{2}^{k}\notag\\ & = & g_{i}^{\dagger}(\vec{s})\left(\vec{\boldsymbol{w}}_{i}+\vec{\boldsymbol{z}}_{i}\right).\notag\\\end{aligned}\ ] ] we have the following thread of equalities , @xmath195 where @xmath196 is by the fact that @xmath197 and @xmath198 are independent , i.e. , @xmath199 . * step 2- * in this part , we use the following lemma without proof . let @xmath200 and @xmath201 be @xmath202 complex random vectors and @xmath203 be any random quantity ( scalar or vector ) with densities . also , assume that the conditional densities @xmath204 and @xmath205 exist . if @xmath200 and @xmath201 are conditionally independent given @xmath203 , then @xmath206 we have @xmath207 on the other hand , we know that @xmath208 . defining @xmath209 and @xmath210 , it is clear that @xmath211 and @xmath212 are conditionally independent given the collection of random variables @xmath213 . as the conditional densities @xmath214 and @xmath215 exist , by lemma 1 , @xmath216 where @xmath196 is by the fact that the collection @xmath197 is independent of @xmath198 . dividing both sides of ( [ poe ] ) by @xmath217 , @xmath218 by ( [ gh1 ] ) , ( [ gh2 ] ) and ( [ gh3 ] ) , @xmath219 * step 3- * we start by stating the following lemma . let @xmath220 be a @xmath202 mixed gaussian random vector with the pdf @xmath221 where @xmath222 for @xmath8 and @xmath223 . then , @xmath224 let us define the random matrix @xmath225 such that @xmath226 and let @xmath227 be a zero mean gaussian vector with covariance matrix @xmath228 . then , one can easily see that @xmath229 in which @xmath230 is the conventional square root of a positive semi - definite matrix . using the inequalities @xmath231 and noting that @xmath232 , the result is immediate . the vector @xmath117 has a mixed gaussian distribution where the covariance matrices of its separate gaussian components correspond to different realizations of the matrix @xmath233 . this together with lemma 2 yields @xmath234 where we have used the fact that @xmath235 . one has@xmath236 where @xmath196 follows by the fact that the matrix @xmath237 is unitary , i.e. , @xmath238 , @xmath239 is by ( [ bw3 ] ) and @xmath240 is a direct consequence of lemma 2 . having @xmath241 , the vector @xmath242 is a complex gaussian vector . hence , @xmath243 by the same token , @xmath244 using ( [ lj1 ] ) and ( [ lj2 ] ) in ( [ pork ] ) , @xmath245 moreover , @xmath246 . hence , @xmath247 appearing in ( [ goosht ] ) can be bounded from below as @xmath248 substituting ( [ bone ] ) in ( [ goosht ] ) , @xmath249 where @xmath250 finally , we get the following lower bound on @xmath251 denoted by @xmath160 , i.e. , @xmath252 an important observation is that if the @xmath86 user sets its transmission rate at @xmath253 , then @xmath254 to prove this , we need some preliminary results in linear analysis . _ definition 2_- let @xmath31 be an euclidean space over @xmath255 and @xmath30 be a subspace of @xmath31 . we define @xmath256 let @xmath31 be an euclidean space over @xmath255 . if @xmath30 is a subspace of @xmath31 , then for each @xmath257 , there are unique elements @xmath258 and @xmath259 such that @xmath260 . _ definition 3_- in the setup of lemma 4 , @xmath261 is called the projection of @xmath262 in @xmath30 and is denoted by @xmath263 . by the same token , @xmath264 . _ definition 4_- let @xmath31 be an euclidean space over @xmath255 and @xmath265 and @xmath266 be subspaces of @xmath31 . we define @xmath267 let @xmath31 be an euclidean vector space over @xmath255 and @xmath265 and @xmath266 be subspaces of @xmath31 . then , @xmath268 let @xmath269 be a @xmath270 matrix such that @xmath271 . then , for any @xmath272 matrix @xmath273 , we have @xmath274 . regulating its transmission rate at @xmath160 , the @xmath86 user achieves an snr scaling of @xmath275 using the fact that for any matrix @xmath269 , @xmath276 , it is easy to see that for any @xmath277 and @xmath278 , we have @xmath279 scales like @xmath280 and @xmath281 scales like @xmath282 . this yields @xmath283 where @xmath196 is by the fact that @xmath284 . we show that @xmath285\right)\ ] ] holds almost surely . let us write @xmath286)=\mathrm{dim}(\mathrm{span}(\vec{\boldsymbol{s}}_i)\cup\mathrm{csp}(\boldsymbol{s}_{i})).\ ] ] using this in lemma 4 , @xmath287)&=&\mathrm{dim}(\mathrm{span}(\vec{\boldsymbol{s}}_i))+\mathrm{dim}(\mathrm{proj}(\mathrm{csp}(\boldsymbol{s}_{i});(\mathrm{span}(\vec{\boldsymbol{s}}_i))^{\perp}))\notag\\ & = & \mathbb{1}_{\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}}+\mathrm{dim}(\mathrm{proj}(\mathrm{csp}(\boldsymbol{s}_{i});(\mathrm{span}(\vec{\boldsymbol{s}}_i))^{\perp})).\end{aligned}\ ] ] on the other hand , by the definition of @xmath288 , @xmath289 it is easily seen that for any @xmath290 , the @xmath291 column of the matrix @xmath292 yields the proper linear combination of the columns of @xmath288 which constructs the projection of the @xmath291 column of @xmath293 into the space @xmath294 , i.e. , @xmath295_{k}=\mathrm{proj}\left([\boldsymbol{s}_{i}]_{k};\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i}))\right).\ ] ] therefore , @xmath296_{k}\big\}_{k=1}^{k-1}\right)&=&\mathrm{proj}\left(\mathrm{span}\left(\big\{[\boldsymbol{s}_{i}]_{k}\big\}_{k=1}^{k-1}\right);\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i}))\right)\notag\\ & = & \mathrm{proj}(\mathrm{csp}(\boldsymbol{s}_{i});\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i}))).\end{aligned}\ ] ] however , @xmath297_{k}\big\}_{k=1}^{k}\right)=\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i})\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i}).\ ] ] by ( [ bzz1 ] ) and ( [ bzz2 ] ) , @xmath298 using ( [ bzz5 ] ) and ( [ bzz4 ] ) in ( [ bzz6 ] ) , @xmath299)&=&\mathbb{1}_{\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}}+\mathrm{dim}(\mathrm{csp}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i})\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i}))\notag\\ & = & \mathbb{1}_{\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}}+\mathrm{rank}(\boldsymbol{g}_{i}(\vec{\boldsymbol{s}}_{i})\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i})\notag\\ & \stackrel{(a)}{=}&\mathbb{1}_{\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}}+\mathrm{rank}(\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i})\end{aligned}\ ] ] where @xmath196 follows by lemma 5 as @xmath288 has independent columns . taking expectation from both sides , @xmath300)\right\}=\pr\{\vec{\boldsymbol{s}}_{i}\neq0_{k\times 1}\}+\mathrm{e}\left\{\mathrm{rank}(\boldsymbol{g}_{i}^{\dagger}(\vec{\boldsymbol{s}}_{i})\boldsymbol{s}_{i})\right\}.\ ] ] using this in ( [ bghm ] ) , @xmath301)-\mathrm{rank}(\boldsymbol{s}_{i})\right\}\notag\\ & = & \pr\left\{\vec{\boldsymbol{s}}_{i}\notin\mathrm{csp}(\boldsymbol{s}_{i})\right\}.\end{aligned}\ ] ] this completes the proof . finally , the following proposition proves that @xmath133 and @xmath135 have the snr scaling . @xmath135 and @xmath133 have the same snr scaling . see appendix a. an important consequence of proposition 1 is the following observation . since , all the users utilize the same algorithm to construct their randomized signature codes , the achievable smg is @xmath302\right)\right\}}{k}.\ ] ] computing @xmath303\right)\right\}$ ] can be quite a tedious task specially for @xmath304 . let the underlying alphabet to construct the spreading codes be @xmath0 . here , we examine two particular rscs by computing the achieved @xmath305 through simulations for the cases where masking is applied or ignored . in each case , we assume the elements of any randomized spreading code are selected independently and uniformly over @xmath0 , i.e. , @xmath306 . in case masking is applied , we set @xmath307 . taking @xmath308 , the results are sketched in fig . it is seen that _ 1- _ by increasing @xmath2 , the achieved @xmath305 approaches unity in both cases . this is the smg of a frequency division scenario where interference is completely avoided . _ 2- _ masking improves the smg . using a uniform pmf @xmath306 . it is assumed that @xmath308 . in case masking is applied , we have @xmath307 . ] _ example 1- _ let us consider an rsc scheme where @xmath309 , i.e. , no spreading is applied . in this case , for each @xmath310 , the vector @xmath311 is simply a @xmath101 random variable for some @xmath102 $ ] . hence , @xmath312\right)\right\}&=&\pr\left\{\boldsymbol{s}_{1}\notin\mathrm{span}\big(\left\{\boldsymbol{s}_{2},\boldsymbol{s}_{3},\cdots,\boldsymbol{s}_{n-1},\boldsymbol{s}_{n}\right\}\big)\right\}\notag\\ & = & \bar{\varepsilon}\pr\left\{0\notin\mathrm{span}\big(\left\{\boldsymbol{s}_{2},\boldsymbol{s}_{3},\cdots,\boldsymbol{s}_{n-1},\boldsymbol{s}_{n}\right\}\big)\right\}\notag\\ & & + \varepsilon\pr\left\{1\notin\mathrm{span}\big(\left\{\boldsymbol{s}_{2},\boldsymbol{s}_{3},\cdots,\boldsymbol{s}_{n-1},\boldsymbol{s}_{n}\right\}\big)\right\}\notag\\ & \stackrel{(a)}{=}&\varepsilon\pr\left\{1\notin\mathrm{span}\big(\left\{\boldsymbol{s}_{2},\boldsymbol{s}_{3},\cdots,\boldsymbol{s}_{n-1},\boldsymbol{s}_{n}\right\}\big)\right\}\notag\\ & \stackrel{(b)}{=}&\varepsilon\pr\left\{\boldsymbol{s}_{2}=\boldsymbol{s}_{3}=\cdots=\boldsymbol{s}_{n-1}=\boldsymbol{s}_{n}=0\right\}\notag\\ & = & \varepsilon(1-\varepsilon)^{n-1}\end{aligned}\ ] ] where @xmath196 is by the fact that @xmath313 and @xmath239 is by the fact that @xmath314 whenever @xmath315 for @xmath316 . maximizing @xmath317 over @xmath164 , a sum multiplexing gain of @xmath18 is achieved . increasing @xmath2 , the achieved @xmath305 drops to @xmath318 . comparing this to the results in fig . [ f2 ] , spreading the signals ( @xmath308 compared to @xmath309 ) can highly improve the sum multiplexing gain in the network . _ example 2- _ let @xmath320 and @xmath22 . for @xmath321 , elements of @xmath170 are @xmath17 random variables taking the values @xmath13 , @xmath11 and @xmath38 with probabilities @xmath322 , @xmath323 and @xmath324 respectively . we have @xmath325 however , @xmath326 similarly , @xmath327 therefore , @xmath328 this expression is maximized at @xmath306 uniformly for any @xmath102 $ ] and @xmath329 . thus , @xmath330 this function is maximized at @xmath331 and @xmath332 where an smg of @xmath333 is achieved . we notice that _ 1- _ although one s intuition expects @xmath307 is the best choice of the on - off probability , the _ optimum _ masking probability is not @xmath334 . _ 2- _ compared to the sum multiplexing gain of @xmath334 achieved in example 1 without spreading , we see that spreading in fact increases the achieved smg . @xmath319 _ remark 1- _ for any @xmath335 matrix @xmath71 and a @xmath336 diagonal matrix @xmath337 we have @xmath338 . using this , for any @xmath176 one can write @xmath339 where we have replaces @xmath340 and by definition , @xmath341 are nonzero eigenvalues of the matrix @xmath342 . for sufficiently large snr values , one can write @xmath160 given in ( [ fuv ] ) as @xmath343 there are three major factors playing role in the formulation of @xmath160 in the high snr regime , namely , the _ multiplexing gain per user _ , @xmath344 the _ interference entropy factor _ , @xmath345 and the _ channel plus signature factor _ @xmath346 in fact , @xmath347 in general , @xmath348 does not depend on the user index . also , assuming the channel gains are realizations of @xmath17 continuous random variables , the entropy @xmath349 is not a function of @xmath350 , i.e. , @xmath351 does not depend on the user index either . in this case , a simple argument shows that @xmath352 the interplay between @xmath348 , @xmath351 and @xmath353 determines the behavior of the achievable rate . this behavior highly depends on the randomized algorithm in constructing the signature codes . as we will see in the next section , a larger @xmath348 is usually achieved at the cost of a larger @xmath351 . it is clear that a larger @xmath351 reduces the rate specially in moderate ranges of snr . however , due to the fact that @xmath348 has also increased , the rate is lifted up is the high snr regime . these opposing effects identify a tradeoff between rate in moderate snr and high snr regime . @xmath319 in this section , we assume the channel gains @xmath354 are realizations of independent @xmath161 random variables @xmath355 representing rayleigh fading . in the previous section , we have developed a lower bound @xmath356 where @xmath357 and @xmath358 the global design criteria is to choose @xmath91 , @xmath99 and @xmath164 based on @xmath359 _ example 3- _ let us consider a network with @xmath320 users . for @xmath321 , we define @xmath360 in this case , we have _ 1- _ @xmath361 . _ 2- _ since @xmath362 , for each @xmath363 , we have @xmath364 and @xmath365 . _ 3- _ for each @xmath277 and @xmath366 , we have @xmath367 . indeed , @xmath368 and if @xmath369 , then @xmath370 . therefore , @xmath371 can be written as @xmath372 * scheme a- * let @xmath331 and @xmath22 with @xmath373 and @xmath374 for some @xmath375 $ ] . to simplify the expression for @xmath371 in ( [ lol ] ) , we make the following observations : _ 1- _ if @xmath179 has only one nonzero element , then @xmath376 _ 2- _ if @xmath179 has no zero elements , then @xmath377 as such , it is easy to see that _ 1- _ if @xmath179 has only one nonzero element , then @xmath378 _ 2- _ if @xmath379 , then @xmath380 _ 3- _ if @xmath381 , then @xmath382 finally , it is shown in appendix a that @xmath383 simulation results indicate that @xmath384 is maximized at @xmath385 . setting @xmath385 , @xmath386 it is also evident that @xmath387 and @xmath388 * scheme b- * assuming no spreading is performed , let @xmath309 . noting the fact that @xmath389 and @xmath390 , @xmath391 it is easily seen that @xmath392 . therefore , @xmath393 @xmath394 and @xmath395 fig . [ f5 ] sketches @xmath396 for the schemes a and b. it is seen that there is a tradeoff between the rates at medium and high snr values . [ f8 ] demonstrates the best @xmath164 chosen by the users . it is seen that any user in both schemes starts with @xmath397 at @xmath398 . selecting @xmath397 in scheme b leads to @xmath399 . however , @xmath400 is kept at zero as well . therefore , by increasing snr , the average achievable rate starts to saturate , and hence , users switch to @xmath401 for @xmath402 to avoid saturation . in scheme a , @xmath164 is set at @xmath11 for snr values up to @xmath403 . the yields @xmath404 which can be considered as a reason for poor performance of scheme a in the range @xmath405 compared to scheme b. since @xmath406 is larger than @xmath407 , the average achievable rate per user becomes eventually larger in scheme a compared to scheme b as snr increases . in schemes a and b for different snr values . ] in schemes a and b for different snr values . ] in schemes a and b in terms of @xmath164 . ] in schemes a and b in terms of @xmath164 . ] _ example 4- _ we consider a decentralized network of @xmath408 users . we present the following scenarios : the signature sequence of any user consists of an spreading code over the alphabet @xmath0 where @xmath373 and @xmath374 , i.e. , masking is not applied . the purpose of this example is to show that in contrast to example 3 , the optimum value of @xmath409 is not necessarily @xmath334 . before proceeding , let us explain why the common intuition is to set @xmath385 . it is well - known that in an additive noise channel with a stationary noise process , as far as the correlation function$ ] is the function @xmath410\boldsymbol{\mathsf{x}}^{\dagger}[t-\delta t]\}$ ] for @xmath411 . ] is fixed , a stationary gaussian noise process yields the least mutual information between the input and output . we call this the _ gaussian _ bounding technique . using this fact , one can obtain a lower bound on @xmath169 as @xmath412 it is easy to see that @xmath413 and @xmath414 therefore . then , one can use the identity @xmath415 for any @xmath335 and @xmath416 matrices @xmath71 and @xmath72 . ] , @xmath417 and @xmath418 finally , we come up with the following lower bound on @xmath251 , @xmath419 it is straightforward to see that this lower bound is maximized at @xmath309 and @xmath385 for any realization of the channel gains . hence , @xmath420 although , this lower bound suggests to set @xmath309 and in case @xmath421 , it requires @xmath385 , we demonstrate that taking a @xmath421 and regulating at some @xmath422 yield achievable rates larger than the threshold @xmath423 in fact , @xmath424 is the maximum average achievable rate by regulating the transmission rate of the @xmath86 user at @xmath425 . in ( [ wind ] ) , we have used the fact that @xmath426 is an exponential random variable with parameter @xmath11 and @xmath427 is a @xmath428 random variable . let @xmath35 . in this case , @xmath429 . to compute @xmath384 , we notice that _ 1- _ for any @xmath277 , @xmath430 . _ 2- _ in appendix b , it is shown that @xmath431 in contrast to example 3 , computing @xmath384 in closed form is a tedious task . as such , we calculate @xmath432 through simulations . setting the snr at @xmath433 , fig . [ f77 ] sketches @xmath432 in terms of @xmath373 for different values of @xmath91 . in spite of one s intuition , the average achievable rate per user has a double - hump shape and is not maximized at @xmath385 . it is seen that the best performance is obtained at @xmath434 and @xmath435 . @xmath319 in schemes a and b in terms of @xmath164 . ] _ remark 2- _ to gain some insight on why @xmath432 is double - hump in example 4 , one can study the multiplexing gain per user given in ( [ mg ] ) . let us consider a network with @xmath436 users . ] where the signature codes only consist of spreading over the alphabet @xmath22 . in general , one can write @xmath437 therefore , @xmath438 the term @xmath439 can be easily calculated as @xmath440 on the other hand , computation of the term @xmath441 is not an easy task . however , the point is that both @xmath439 and @xmath441 have a global maximum at @xmath385 . hence , there is a chance that their difference is maximized at some @xmath422 . this is exactly what happens here . as an example , fig . [ f77c ] sketches multiplexing gain per user in terms of @xmath442 in a network with @xmath443 users . it is assumed that the spreading code length is @xmath444 . in terms of @xmath373 in a network of @xmath443 users with @xmath444 . ] _ remark 3- _ the expression for the smg given in ( [ canada ] ) does not depend on the spreading / masking strategy . in fact , one can consider a more general scheme where the @xmath86 user randomly selects its code @xmath170 out of a globally known set of codes @xmath445 based on a globally known pmf . in case @xmath320 , @xmath446 taking @xmath331 , let us assume that @xmath447 consists of @xmath448 vectors in @xmath449 no two of which are parallel with each other . therefore , @xmath450 since @xmath448 can be arbitrarily large , the smg of a network of two users is equal to @xmath11 . in this case , it is easy to see that @xmath451 if @xmath408 , taking a set of arbitrarily large non - parallel vectors in some space @xmath184 is by no means a necessarily appropriate collection . let @xmath452 consist of @xmath448 vectors in @xmath184 . for each @xmath8 and @xmath453 , we denote by @xmath454 the number of distinct subsets @xmath455 of @xmath447 of size @xmath456 such that @xmath457 . we denote these subsets explicitly by @xmath458 . assuming all users select their codes equally likely over @xmath447 , @xmath459\right)\right\}=\frac{1}{l}\sum_{l=1}^{l}\pr\left\{\vec{\mathfrak{c}}_{l}\notin\mathrm{csp}\left([\vec{\boldsymbol{s}}_{2}|\vec{\boldsymbol{s}}_{3}|\cdots|\vec{\boldsymbol{s}}_{n-1}|\vec{\boldsymbol{s}}_{n}]\right)\right\}.\end{aligned}\ ] ] for each @xmath8 , @xmath460\right)\right\}=\sum_{r=1}^{l-1}\sum_{m=1}^{\omega_{l , r}}\pr\left\{\forall\vec{\mathfrak{b}}\in\mathfrak{b}_{l , r}(m),\exists j\geq 2 : \vec{\boldsymbol{s}}_{j}=\vec{\mathfrak{b}}\right\}.\end{aligned}\ ] ] it is easy to see that and @xmath461 elements of @xmath462 are chosen by @xmath463 and @xmath464 users respectively , this can happen in @xmath465 different ways . ] @xmath466 for any @xmath8 and @xmath467 . therefore , @xmath312\right)\right\}=\frac{1}{l^{n}}\sum_{l=1}^{l}\sum_{r=1}^{l-1}\omega_{l , r}\rho_{r , n}\end{aligned}\ ] ] where @xmath468 finally , the achieved smg is @xmath469 we remark that there is no closed formula for @xmath470 , however , one can use the recursion @xmath471 to compute this quantity . by ( [ bool ] ) , one can easily see that @xmath305 is maximized if @xmath454 is as large as possible for each @xmath8 and @xmath453 . we know that @xmath472 . this upper bound is achieved if @xmath447 consists of @xmath473 independent vectors in @xmath184 . in this case , @xmath474 it is not hard to see that @xmath475 . hence , @xmath476 to get the largest smg , one may let @xmath477 yielding @xmath478 which is the result obtained in example 1 via masking without spreading . we have already seen that applying masking on top of spreading can result in larger achievable rates due to increasing the attained multiplexing gain . however , our results so far are based on the achievable rate @xmath160 which is only a lower bound on the _ capacity _ of the @xmath86 user . in deriving @xmath160 , the pdf of the transmitted signals is taken to be complex gaussian which is not necessarily optimal . as such , we have no optimality arguments so far . in this section , we question the optimality of masking without spreading . in fact , we are interested to see if at any snr level , there is an optimal pdf such that generating the transmitted signals based on this pdf makes spreading unnecessary . for this purpose , we define the _ masking capacity _ of a user as the largest achievable rate by this user assuming all users follow the masking strategy with no spreading applied . we also require _ fairness _ conditions by which we imply that users generate their signals using the same pdf . fixing @xmath102 $ ] , the masking capacity of the @xmath86 user is defined by @xmath479 where @xmath480 in which @xmath481 is the masking coefficient of the @xmath86 user which is a @xmath101 random variable and @xmath482 is the @xmath161 ambient noise random variable . the parameter @xmath164 is designed based on maximizing a globally available utility function such as @xmath432 assuming @xmath354 are realizations of @xmath17 random variables with a continuous pdf . we focus on a decentralized network of @xmath320 users . we call the users as user # 1 and user # 2 . according to the results in example 3 ( scheme b ) , the decision rule to regulate @xmath164 is @xmath483}\mathrm{e}\left\{\varepsilon\log\left(1+\frac{2^{-\mathscr{h}(\varepsilon)}|\boldsymbol{h}_{1,1}|^{2}\gamma}{\varepsilon\left(1+\frac{|\boldsymbol{h}_{2,1}|^{2}\gamma}{\varepsilon}\right)^{\varepsilon}}\right)\right\}.\end{aligned}\ ] ] the main result of the paper is the following . there exist @xmath484 and @xmath485 $ ] such that for any @xmath486 , it is possible to achieve rates larger than @xmath487 for sufficiently large values of @xmath94 where @xmath488 is given in ( [ pel ] ) . to prove theorem 1 , we need the following lemma . let @xmath489 and @xmath490 be circularly symmetric complex gaussian random variables with variances @xmath491 and @xmath492 respectively and @xmath493 be independent of @xmath494 . then , the answer to the optimization problem @xmath495 is a circularly symmetric complex gaussian @xmath493 for any @xmath496 and any @xmath497 . also , if @xmath498 , the same conclusion holds for any @xmath499 . this is a direct consequence of theorem 1 in @xcite . our strategy is to find an upper bound on @xmath500 for arbitrary @xmath102 $ ] and proposing an achievable rate which surpasses this upper bound . we proceed as follows . we have @xmath501 where @xmath196 follows by the fact that @xmath502 , @xmath239 is by the fact that the mutual information between the input and output of the channel increases if a `` genie '' provides the receiver side of user # 1 with @xmath503 , @xmath240 follows by the fact that @xmath504 and @xmath505 are identically distributed and the fact that @xmath506 and finally @xmath507 follows by the fact that for any complex random variable @xmath493 and @xmath508 , we have @xmath509 . also , we have @xmath510 and @xmath511 in the last equality in ( [ ee1 ] ) . denoting the upper bound in ( [ ee1 ] ) by @xmath512 , @xmath513 it is trivial that @xmath514 which follows by the maximum entropy lemma@xcite . applying lemma 1 , if @xmath515 or @xmath516 , or equivalently , @xmath517 or @xmath516 , the answer to the optimization @xmath518 is a complex gaussian @xmath504 . we note that the power of the optimum gaussian signal @xmath504 is not necessarily @xmath94 . let the optimum @xmath504 be a @xmath519 random variable . we distinguish the following cases . _ case 1- _ if @xmath520 and @xmath521 , then @xmath522 . _ case 2- _ if @xmath523 , @xmath524 and @xmath525 , then @xmath526 . _ case 3- _ if @xmath527 and @xmath528 , then @xmath529 . verification of these cases is a straightforward task which is omitted here for the sake of brevity . therefore , as far as @xmath517 , the term @xmath530 saturates by increasing @xmath94 . using this fact together with ( [ koo ] ) and ( [ th2 ] ) , @xmath531 as far as @xmath517 . on the other hand , if @xmath532 and @xmath528 , @xmath533 using this together with ( [ koo ] ) and ( [ th2 ] ) , @xmath534 as far as @xmath532 and @xmath535 . however , we can remove the condition @xmath528 by a simple arguement . let us fix @xmath536 . it is clear that @xmath537 for @xmath538 . since @xmath539 , we get @xmath540 . hence , ( [ s444 ] ) holds for all @xmath532 regardless of the values of @xmath541 and @xmath536 . to recap , we have shown that @xmath542 we end this subsection with the following corollary . if @xmath543 , @xmath544 by the results in example 3 , @xmath545 for every @xmath546 . however , by ( [ s555 ] ) , @xmath547 for all @xmath543 . this concludes the proof . applying spreading on top of masking , we show that there is a range of @xmath164 such that it is possible to achieve rates larger than @xmath548 as far as @xmath94 is sufficiently large . to transmit its gaussian signal @xmath549 , user # @xmath550 spreads @xmath197 along a @xmath551 random vector @xmath552 consisting of @xmath17 random numbers taking values in a finite alphabet @xmath21 with equal probability . thereafter , this user applies the masking process by constructing the @xmath551 masking vector @xmath553 consisting of @xmath17 bernoulli random variables taking the values @xmath13 and @xmath11 with probabilities @xmath554 and @xmath164 respectively . we assume that @xmath552 and @xmath553 are known to both ends of user # @xmath550 . finally , this user transmits @xmath555 in two consecutive transmission slots where @xmath111 is to ensure the total transmission power per symbol @xmath197 is @xmath94 . assuming both users are synchronous , the following vector is received at the receiver side of user # 1 @xmath556 where @xmath557 is a vector of independent @xmath161 random variables representing the ambient noise samples at the receiver side of user # 1 . the achievable rate for this user is @xmath558 by our results in section iii , @xmath559 hence , @xmath560 we are interested in values of @xmath164 so that @xmath561 is strictly satisfied . by ( [ s555 ] ) and ( [ e33 ] ) , it is sufficient to show that there is a range for @xmath164 such that @xmath562 let @xmath22 . in this case the elements of @xmath563 and @xmath564 are @xmath17 random variables taking the values @xmath13 , @xmath11 and @xmath38 with probabilities @xmath554 , @xmath565 and @xmath566 respectively . the event @xmath567 occurs if and only if @xmath568 or @xmath569 while @xmath570 . then , one can easily see that @xmath571 . this can also be deduced from ( [ boro ] ) . substituting this in ( [ x2 ] ) requires @xmath572 this simplifies to @xmath573 for @xmath532 and @xmath574 for @xmath517 . solving these inequalities , we get @xmath575 . it is not hard to see that @xmath576 given in ( [ pel ] ) is in the interval @xmath577 for all @xmath578 . setting @xmath579 and @xmath580 , we see that @xmath488 and @xmath581 is larger than @xmath582 for large values of @xmath94 . this completes the proof of theorem 1 . next , we demonstrate that increasing the size of the underlying alphabet can expand the range of @xmath164 for which achieving a rate larger than @xmath548 is possible . _ remark 3- _ if @xmath583 , the elements of @xmath563 and @xmath564 are @xmath17 random variables taking the values @xmath13 , @xmath584 , @xmath38 , @xmath11 and @xmath585 with probabilities @xmath554 , @xmath586 , @xmath587 , @xmath586 and @xmath586 respectively . the event @xmath567 occurs if and only if @xmath568 or @xmath569 while @xmath570 or @xmath588 or @xmath589 . we get @xmath590 . substituting this in ( [ x2 ] ) requires @xmath591 hence , @xmath592 for @xmath532 and @xmath593 for @xmath517 . solving these inequalities , @xmath594 . we proposed an approach towards communication in decentralized wireless networks of separate transmitter - receiver pairs . a randomized signaling scheme was introduced in which each user locally spreads its gaussian signal along a randomly generated spreading code comprised of a sequence of nonzero elements over a certain alphabet . along with spreading , each transmitter also masks its output independently from transmission to transmission . using a conditional version of entropy power inequality and a key lemma on the differential entropy of mixed gaussian random vectors , achievable rates were developed for the users . assuming the channel gains are realization of independent continuous random variables , each user finds the optimum parameters in constructing the randomized spreading and masking sequences by maximizing the average achievable rate per user . it was seen that as the number of users increases , the achievable sum multiplexing gain of the network approaches that of a centralized orthogonal scheme where multiuser interference is completely avoided . it was observed that in general the elements of a spreading code are not equiprobable over the underlying alphabet . this particularly happens if the number of active users is greater than three . finally , using the recently developed extremal inequality of liu - viswanath , we presented an optimality result showing that transmission of gaussian signals via spreading and masking yields higher achievable rates than the maximum achievable rate attained by applying masking only . by proposition 1 , @xmath595 in this appendix , we prove that @xmath596 by ( [ e14 ] ) , it suffices to show that @xmath597 . let us consider the _ informed _ @xmath86 user where the receiver is aware of @xmath170 and @xmath241 . the achievable rate of this virtual user is @xmath598 . it is clear that @xmath599 . however , @xmath600 where @xmath196 follows by the fact that fixing @xmath601 converts the channel of the @xmath86 informed user to an additive gaussian channel . on the other hand , @xmath602 noting that @xmath603 scales like @xmath604\right)\log\gamma$ ] , we conclude that the first term on the right hand side of ( [ bol12 ] ) scales like @xmath605\right)\right\}\log\gamma$ ] . by the same token , the second term on the right hand side of ( [ bol12 ] ) scales like @xmath606 . therefore , @xmath607 is upper bounded by a quantity which scales like @xmath608)\}-\mathrm{e}\{\mathrm{rank}(\boldsymbol{s}_{i})\}\big)\log\gamma$ ] . the result of the proposition is immediate . let @xmath609 . therefore , @xmath610 to compute @xmath611 , we have @xmath612 where @xmath196 is by the fact that the terms @xmath613 , @xmath614 and @xmath615 are zero . on the other hand , it is easy to see that @xmath616 . this implies @xmath617 . therefore , @xmath618 using ( [ lol1 ] ) and ( [ lol2 ] ) , @xmath619 let @xmath620 . we have @xmath621 where @xmath196 is by the fact that @xmath622 for any @xmath623 and @xmath239 is by the fact that for any two distinct numbers @xmath624 , the knowledge about @xmath625 can be obtained by knowing @xmath626 and @xmath627 by the fact that @xmath628 . let us define @xmath629 by ( [ nol ] ) , @xmath630 . let @xmath55 be the event where @xmath631 , while @xmath632 of the elements of @xmath633 , namely , @xmath634 and @xmath635 are @xmath11 and the rest are @xmath38 for some @xmath636 and @xmath637 . also , let @xmath638 be the event where @xmath639 , @xmath640 for @xmath641 and @xmath642 for @xmath643 . it is clear that @xmath644 we know that @xmath645 and @xmath646 . hence , using ( [ mol ] ) , @xmath647 a. sahai , n. hoven , s. m. mishra and r. tandra , `` fundamental tradeoffs in robust spectrum sensing for opportunistic frequency reuse '' , _ technical reports _ , march 2006 , available online at http:// www.eecs,berkeley.edu/ sahai / papers / cognitivetechreport06.pdf . s. srivastava , s. tripathi , d. sanghi and a. k. chaturvedi , `` a code allocation protocol for maximizing throughput in cdma based ad - hoc networks '' , _ ieee wireless commun . and networking conf . 2 , pp . 1385 - 1390 , march 2003 . t. salonidis , p. bhagwat , l. tassiulas and r. lamaire , `` distributed topology construction of bluetooth wireless personal area networks '' , _ ieee journal on selected areas in commun . 633 - 643 , march 2005 . z. kostic and n. sollenberger , `` performance and implementation of dynamic frequency hopping in limited - bandwidth cellular systems '' , _ ieee trans . on wireless comm . _ , vol . 1 , no . 1 , pp . 28 - 36 , jan . 2002[/INST] this paper addresses a unified approach towards communication in decentralized wireless networks of separate transmitter - receiver pairs . different transmitters are connected to different receivers through channels with static and non - frequency selective gains . in general , users are unaware of each other s codebooks and there is no central controller to assign the resources in the network to the users . a randomized signaling scheme is introduced in which each user locally spreads its gaussian signal along a randomly generated spreading code comprised of a sequence of nonzero elements over a certain alphabet . along with spreading , each transmitter also masks its output independently from transmission to transmission . using a conditional version of entropy power inequality and a key lemma on the differential entropy of mixed gaussian random vectors , achievable rates are developed for the users . assuming the channel gains are realization of independent continuous random variables , each user finds the optimum parameters in constructing the randomized spreading and masking sequences by maximizing the average achievable rate per user . it is seen that as the number of users increases , the achievable sum multiplexing gain of the network approaches that of a centralized orthogonal scheme where multiuser interference is completely avoided . an interesting observation is that in general the elements of a spreading code are not equiprobable over the underlying alphabet . this is in contrast to the customary use of binary pn codes in spread spectrum communications in which the code elements may be selected with equal probability over @xmath0 . this particularly happens if the number of active users is greater than three . finally , using the recently developed extremal inequality of liu - viswanath , we present an optimality result showing that transmission of gaussian signals via spreading and masking yields higher achievable rates than the maximum achievable rate attained by applying masking only . = 1 </s>

mature microrna ( mirna ) molecules are approximately 22-nucleotide - long single - stranded rnas that generally repress the expression of protein coding genes . specifically , they preferentially bind to 3 untranslated regions ( utrs ) of messenger rnas ( mrnas ) and interfere with their stability and translational efficiency ( 1,2 ) . the first mirnas and their target genes were identified via classical forward genetic techniques in 1993 , but it was not until 2001 that many more mirnas were discovered experimentally and found to be abundant and widespread ( 35 ) . since then there has been a dramatic growth in the number of annotated mirnas ( figure 1 ) . figure 1.the growth of the human mirna genes in mirbase database and the growth of the human experimentally determined mirna target interactions in tarbase . the growth of the human mirna genes in mirbase database and the growth of the human experimentally determined mirna target interactions in tarbase . a crucial aspect of the functional analysis of mirnas is the annotation of their protein - coding targets . a number of computational algorithms have been developed for the prediction of such targets ( 6 ) . although these programs are very important to guide wet lab experiments , they still lack in sensitivity and specificity ( 7,8 ) . in parallel , and as support for these programs , a number of experimental procedures have been developed to provide indirect or direct support for predicted mirna target interactions and results from a growing number of such experiments have been published ( figure 1 ) . the need for a systematic documentation of such experimentally supported targets was covered by the first version of tarbase ( 9 ) . in 2006 , the database recorded over 550 entries with mirna target interactions in human , mouse , fruit fly , worm and zebrafish . here we present a substantially updated and extended version of this database , tarbase5.0 , documenting over 1300 entries . the new database now contains all of the information included in the previous version , plus : specific cells lines ( if any ) used in the experiments , cell - type - specific expression of the gene product and its potential involvement in carcinogenesis , differential expression of mirnas in specific tissues , developmental or pathological events that a specific mirna is involved in and any annotated types of mirna - related mis - regulation in those events , hgnc symbols as defined by hugo ( in order to provide consistent gene naming ) . additionally , both the underlying sql database and the user interface have been extensively redesigned with several added external links such as a direct link to the paper 's abstract on the pubmed site . specific cells lines ( if any ) used in the experiments , cell - type - specific expression of the gene product and its potential involvement in carcinogenesis , differential expression of mirnas in specific tissues , developmental or pathological events that a specific mirna is involved in and any annotated types of mirna - related mis - regulation in those events , hgnc symbols as defined by hugo ( in order to provide consistent gene naming ) . the tarbase5.0 database can be directly accessed from the http://microrna.gr/tarbase web page . tarbase5.0 contains data extracted from a total of 203 scientific papers resulting in 1333 entries describing a regulatory interaction between a mirna and a target 3 utr ( summarized in table 1 ) . table 1.a list of all tarbase5.0 entriesorganismnumber of papersnumber of entriesmicroarray datapsilac datahomo sapiens110285328474mus musculus2810513d . elegans1814plants2130danio rerio11rat22total203514341474 a list of all tarbase5.0 entries the tarbase5.0 data set contains mirna targets that tested either positive ( induces target gene repression ) or negative ( no influence on target gene expression ) . for each experiment with a positive outcome the target site is described by the mirna that binds it , the gene in which it occurs , the nature of the experiments that were conducted to test it , the sufficiency of the site to induce translational repression and/or cleavage , and the paper from which all these data is extracted . additionally , for each mirna and protein - coding gene , the database contains links to several other relevant and useful databases such as ensembl ( 10 ) , hugo ( 11 ) , ucsc genome browser ( 12 ) and swissprot ( 13 ) . there are a number of direct and indirect experimental procedures that have been developed to test a possible mirna the entries in tarbase5.0 are classified into four categories : true or false in the cases where an assay provides direct experimental evidence , or microarray and/or psilac in the cases that present only indirect evidence from high - throughput techniques to measure mirna - mediated global transcriptomic or proteomic changes . to overexpress a mirna , expression constructs can be engineered using the mature mirna , the precursor ( hairpin ) mirna , or the pri - mirna sequence for transfection into in vitro or in vivo transformed cells . also , silencing of a specific mirna can be accomplished by introducing chemically modified oligonucleotides that are perfectly complimentary to the mature mirna ( antagomirs ) ( 14 ) . these methods for modifying mirna expression allow for several types of follow - up techniques to quantify and interpret differences in target gene expression . below we provide a more detailed description of each of the four categories : true or false : the most commonly used method for providing direct experimental evidence is the reporter gene assay . in its simplest form , an expression vector containing a reporter gene [ i.e. luciferase or green fluorescent protein ( gfp ) ] is first modified by cloning the predicted target 3utr downstream of the reporter gene , and then transfected into a cell line of interest in the absence and presence of the cognate mirna . despite the general utility of this approach to assay for 3utr - mediated effects on reporter protein expression , it is not informative for the precise location of the mirna response element ( mre ) or number of mirna target sites in the 3utr . integration of the reporter gene assay with site directed mutagenesis of the predicted mre ( and , further , restoring the complementarity of the mirna mre interaction by mutating the mature mirna sequence ) yields a much more specific and direct result . to measure effects on reporter mrna levels , the most commonly applied technique is quantitative rt - pcr ( qrt - pcr ) . measuring effects on both protein and mrna levels can help provide information about the mode of mirna - mediated silencing : mrna translational repression or immediate risc - mediated mrna cleavage and degradation . a mirna mre interaction is reported as true or false based on the results of the reporter gene assay . microarray and/or psilac : these high - throughput approaches measure global changes in the transcriptome ( 15 ) or proteome ( 8,16 ) given the presence or absence of a mirna . despite their power for large - scale analysis , these techniques only provide indirect evidence about a mirna 's targets since it is not possible to distinguish between primary direct targets and secondary indirect targets . other high - throughput methods like degradome sequencing ( 17,18 ) are also immensely useful but only in the scenarios where a mirna induces risc - mediated mrna cleavage . in order to facilitate user interaction , the query function is divided into several functionally related subgroups . the initial screen of the tarbase5.0 user interface allows users to query based on mirna , gene and organism . for more advanced queries , the user can utilize the extended query options . in this case , the search menus are arranged into four functionally related groups . target interaction : the validity of the interaction ( field support type , either true or false ) , the function of the interaction which can be either translational repression or mrna cleavage ( field datatype ) , the sufficiency of a single target site to exert the specific function ( field s_s_s ) and the number of mirna response elements present in the specific utr ( field mre ) . the second group contains the fields that refer to the experimental methods that led to the reported result . target interaction ( i.e. reporter gene assays ) while indirect support refers to experimental procedures that provide more global , system - wide mirna - mediated effects ( i.e. microarrays ) . the third group corresponds to biological properties of the mirna or target gene : biological functions ( field protein type ) , specific expression profiles ( field mirna expression ) or the physiological processes in which this interaction is involved ( field event or pathology ) . the fourth and final group contains some general query features such as the scientific paper ( searchable by author or pmid ) . , the results screen ( figure 2 ) shows only the repression type , the mirna identifier , the target gene identified by the hgnc symbol ( if it is a human gene ) , the common gene name , the refseq isoform i d ( particularly relevant in cases of gene variants or snp haplotypes ) , the affected biological processes and the paper containing the information presented . users can opt to view more detailed information by clicking on the + box so that the expanded results view is opened ( figure 2 ) . the additional information is divided into three categories : mirna information , gene information and experimental conditions . the mirna information category contains the properties of the specific mirna such as the mirna 's sequence [ extracted from mirbase ( 19 ) ] , the number and sequences of the mres , their locations within the gene 's 3utr , and the affected tissues ( extracted from the paper ) . the gene information category gathers mostly biological properties of the target gene like the protein type , ensembl and swissprot ids and chromosome location , providing direct links to ensembl , swissprot and the ucsc browser respectively . moreover , expression profiles and tumor involvement are also provided for human genes ( information extracted from the ensembl egenetics database ) . finally , the experimental conditions category provides the nature of the direct or indirect evidence for the mirna target gene interaction . the cell lines used to carry out the specific experiment are also presented in order to render the experimental conditions more complete and reproducible . even though several computational programs exist to predict mirna targets , the necessity for a systematic collection and description of mirna targets with experimental support led to the development of tarbase . the continuously expanding number of known and newly identified mirnas and their targets , combined with their central role in biological systems , renders this field particularly dependent on centralized information that is accurate , up - to - date , comprehensive and easy to browse or download . in order to satisfy these requirements , we have made extensive updates and modifications and present the new version of the database , tarbase5.0 . the tarbase data files can be freely downloaded and used according to the gnu public license . funding for open access charge : aristeia award from general secretary research and technology , greece .

tarbase5.0 is a database which houses a manually curated collection of experimentally supported microrna ( mirna ) targets in several animal species of central scientific interest , plants and viruses . mirnas are small non - coding rna molecules that exhibit an inhibitory effect on gene expression , interfering with the stability and translational efficiency of the targeted mature messenger rnas . even though several computational programs exist to predict mirna targets , there is a need for a comprehensive collection and description of mirna targets with experimental support . here we introduce a substantially extended version of this resource . the current version includes more than 1300 experimentally supported targets . each target site is described by the mirna that binds it , the gene in which it occurs , the nature of the experiments that were conducted to test it , the sufficiency of the site to induce translational repression and/or cleavage , and the paper from which all these data were extracted . additionally , the database is functionally linked to several other relevant and useful databases such as ensembl , hugo , ucsc and swissprot . the tarbase5.0 database can be queried or downloaded from http://microrna.gr/tarbase .

<s>[INST]mature microrna ( mirna ) molecules are approximately 22-nucleotide - long single - stranded rnas that generally repress the expression of protein coding genes . specifically , they preferentially bind to 3 untranslated regions ( utrs ) of messenger rnas ( mrnas ) and interfere with their stability and translational efficiency ( 1,2 ) . the first mirnas and their target genes were identified via classical forward genetic techniques in 1993 , but it was not until 2001 that many more mirnas were discovered experimentally and found to be abundant and widespread ( 35 ) . since then there has been a dramatic growth in the number of annotated mirnas ( figure 1 ) . figure 1.the growth of the human mirna genes in mirbase database and the growth of the human experimentally determined mirna target interactions in tarbase . the growth of the human mirna genes in mirbase database and the growth of the human experimentally determined mirna target interactions in tarbase . a crucial aspect of the functional analysis of mirnas is the annotation of their protein - coding targets . a number of computational algorithms have been developed for the prediction of such targets ( 6 ) . although these programs are very important to guide wet lab experiments , they still lack in sensitivity and specificity ( 7,8 ) . in parallel , and as support for these programs , a number of experimental procedures have been developed to provide indirect or direct support for predicted mirna target interactions and results from a growing number of such experiments have been published ( figure 1 ) . the need for a systematic documentation of such experimentally supported targets was covered by the first version of tarbase ( 9 ) . in 2006 , the database recorded over 550 entries with mirna target interactions in human , mouse , fruit fly , worm and zebrafish . here we present a substantially updated and extended version of this database , tarbase5.0 , documenting over 1300 entries . the new database now contains all of the information included in the previous version , plus : specific cells lines ( if any ) used in the experiments , cell - type - specific expression of the gene product and its potential involvement in carcinogenesis , differential expression of mirnas in specific tissues , developmental or pathological events that a specific mirna is involved in and any annotated types of mirna - related mis - regulation in those events , hgnc symbols as defined by hugo ( in order to provide consistent gene naming ) . additionally , both the underlying sql database and the user interface have been extensively redesigned with several added external links such as a direct link to the paper 's abstract on the pubmed site . specific cells lines ( if any ) used in the experiments , cell - type - specific expression of the gene product and its potential involvement in carcinogenesis , differential expression of mirnas in specific tissues , developmental or pathological events that a specific mirna is involved in and any annotated types of mirna - related mis - regulation in those events , hgnc symbols as defined by hugo ( in order to provide consistent gene naming ) . the tarbase5.0 database can be directly accessed from the http://microrna.gr/tarbase web page . tarbase5.0 contains data extracted from a total of 203 scientific papers resulting in 1333 entries describing a regulatory interaction between a mirna and a target 3 utr ( summarized in table 1 ) . table 1.a list of all tarbase5.0 entriesorganismnumber of papersnumber of entriesmicroarray datapsilac datahomo sapiens110285328474mus musculus2810513d . elegans1814plants2130danio rerio11rat22total203514341474 a list of all tarbase5.0 entries the tarbase5.0 data set contains mirna targets that tested either positive ( induces target gene repression ) or negative ( no influence on target gene expression ) . for each experiment with a positive outcome the target site is described by the mirna that binds it , the gene in which it occurs , the nature of the experiments that were conducted to test it , the sufficiency of the site to induce translational repression and/or cleavage , and the paper from which all these data is extracted . additionally , for each mirna and protein - coding gene , the database contains links to several other relevant and useful databases such as ensembl ( 10 ) , hugo ( 11 ) , ucsc genome browser ( 12 ) and swissprot ( 13 ) . there are a number of direct and indirect experimental procedures that have been developed to test a possible mirna the entries in tarbase5.0 are classified into four categories : true or false in the cases where an assay provides direct experimental evidence , or microarray and/or psilac in the cases that present only indirect evidence from high - throughput techniques to measure mirna - mediated global transcriptomic or proteomic changes . to overexpress a mirna , expression constructs can be engineered using the mature mirna , the precursor ( hairpin ) mirna , or the pri - mirna sequence for transfection into in vitro or in vivo transformed cells . also , silencing of a specific mirna can be accomplished by introducing chemically modified oligonucleotides that are perfectly complimentary to the mature mirna ( antagomirs ) ( 14 ) . these methods for modifying mirna expression allow for several types of follow - up techniques to quantify and interpret differences in target gene expression . below we provide a more detailed description of each of the four categories : true or false : the most commonly used method for providing direct experimental evidence is the reporter gene assay . in its simplest form , an expression vector containing a reporter gene [ i.e. luciferase or green fluorescent protein ( gfp ) ] is first modified by cloning the predicted target 3utr downstream of the reporter gene , and then transfected into a cell line of interest in the absence and presence of the cognate mirna . despite the general utility of this approach to assay for 3utr - mediated effects on reporter protein expression , it is not informative for the precise location of the mirna response element ( mre ) or number of mirna target sites in the 3utr . integration of the reporter gene assay with site directed mutagenesis of the predicted mre ( and , further , restoring the complementarity of the mirna mre interaction by mutating the mature mirna sequence ) yields a much more specific and direct result . to measure effects on reporter mrna levels , the most commonly applied technique is quantitative rt - pcr ( qrt - pcr ) . measuring effects on both protein and mrna levels can help provide information about the mode of mirna - mediated silencing : mrna translational repression or immediate risc - mediated mrna cleavage and degradation . a mirna mre interaction is reported as true or false based on the results of the reporter gene assay . microarray and/or psilac : these high - throughput approaches measure global changes in the transcriptome ( 15 ) or proteome ( 8,16 ) given the presence or absence of a mirna . despite their power for large - scale analysis , these techniques only provide indirect evidence about a mirna 's targets since it is not possible to distinguish between primary direct targets and secondary indirect targets . other high - throughput methods like degradome sequencing ( 17,18 ) are also immensely useful but only in the scenarios where a mirna induces risc - mediated mrna cleavage . in order to facilitate user interaction , the query function is divided into several functionally related subgroups . the initial screen of the tarbase5.0 user interface allows users to query based on mirna , gene and organism . for more advanced queries , the user can utilize the extended query options . in this case , the search menus are arranged into four functionally related groups . target interaction : the validity of the interaction ( field support type , either true or false ) , the function of the interaction which can be either translational repression or mrna cleavage ( field datatype ) , the sufficiency of a single target site to exert the specific function ( field s_s_s ) and the number of mirna response elements present in the specific utr ( field mre ) . the second group contains the fields that refer to the experimental methods that led to the reported result . target interaction ( i.e. reporter gene assays ) while indirect support refers to experimental procedures that provide more global , system - wide mirna - mediated effects ( i.e. microarrays ) . the third group corresponds to biological properties of the mirna or target gene : biological functions ( field protein type ) , specific expression profiles ( field mirna expression ) or the physiological processes in which this interaction is involved ( field event or pathology ) . the fourth and final group contains some general query features such as the scientific paper ( searchable by author or pmid ) . , the results screen ( figure 2 ) shows only the repression type , the mirna identifier , the target gene identified by the hgnc symbol ( if it is a human gene ) , the common gene name , the refseq isoform i d ( particularly relevant in cases of gene variants or snp haplotypes ) , the affected biological processes and the paper containing the information presented . users can opt to view more detailed information by clicking on the + box so that the expanded results view is opened ( figure 2 ) . the additional information is divided into three categories : mirna information , gene information and experimental conditions . the mirna information category contains the properties of the specific mirna such as the mirna 's sequence [ extracted from mirbase ( 19 ) ] , the number and sequences of the mres , their locations within the gene 's 3utr , and the affected tissues ( extracted from the paper ) . the gene information category gathers mostly biological properties of the target gene like the protein type , ensembl and swissprot ids and chromosome location , providing direct links to ensembl , swissprot and the ucsc browser respectively . moreover , expression profiles and tumor involvement are also provided for human genes ( information extracted from the ensembl egenetics database ) . finally , the experimental conditions category provides the nature of the direct or indirect evidence for the mirna target gene interaction . the cell lines used to carry out the specific experiment are also presented in order to render the experimental conditions more complete and reproducible . even though several computational programs exist to predict mirna targets , the necessity for a systematic collection and description of mirna targets with experimental support led to the development of tarbase . the continuously expanding number of known and newly identified mirnas and their targets , combined with their central role in biological systems , renders this field particularly dependent on centralized information that is accurate , up - to - date , comprehensive and easy to browse or download . in order to satisfy these requirements , we have made extensive updates and modifications and present the new version of the database , tarbase5.0 . the tarbase data files can be freely downloaded and used according to the gnu public license . funding for open access charge : aristeia award from general secretary research and technology , greece .[/INST]tarbase5.0 is a database which houses a manually curated collection of experimentally supported microrna ( mirna ) targets in several animal species of central scientific interest , plants and viruses . mirnas are small non - coding rna molecules that exhibit an inhibitory effect on gene expression , interfering with the stability and translational efficiency of the targeted mature messenger rnas . even though several computational programs exist to predict mirna targets , there is a need for a comprehensive collection and description of mirna targets with experimental support . here we introduce a substantially extended version of this resource . the current version includes more than 1300 experimentally supported targets . each target site is described by the mirna that binds it , the gene in which it occurs , the nature of the experiments that were conducted to test it , the sufficiency of the site to induce translational repression and/or cleavage , and the paper from which all these data were extracted . additionally , the database is functionally linked to several other relevant and useful databases such as ensembl , hugo , ucsc and swissprot . the tarbase5.0 database can be queried or downloaded from http://microrna.gr/tarbase .</s>

deep artificial neural networks ( anns ) have recently been very successful at solving image categorization problems . early successes with the mnist database @xcite were expanded to the more difficult but similarly sized cifar-10 dataset @xcite and street - view house numbers dataset @xcite . more recently , many groups have achieved better results on these small datasets ( e.g. @xcite ) and as well as success on larger datasets ( e.g. @xcite ) . this work culminated with the application of deep neural networks to imagenet @xcite , a very large and challenging dataset . the relative success of deep anns in general and convolutional neural networks in particular on these datasets have put them well ahead of other methods in terms of image categorization by machines . given that deep anns are approaching human performance on some datasets ( or even passing it , for example on mnist ) suggests that these models may be able to shed light on how the human visual system solves these same tasks . there has recently been considerable effort to take deep anns and make them more biologically plausible by introducing neural `` spiking '' @xcite , such that connected nodes in the network transmit information via instantaneous single bits ( spikes ) , rather than transmitting real - valued activities . while one goal of this work is to better understand the brain by trying to reverse engineer it @xcite , another goal is to build energy - efficient neuromorphic systems that use a similar communication method for image categorization @xcite . we first train a network on static images using traditional deep learning techniques ; we call this the _ static network_. we then take the parameters ( weights and biases ) from the static network and use them to connect spiking neurons , forming the _ dynamic network _ ( or spiking network ) . the challenge is to train the static network in such a way that a ) it _ can _ be transferred into a spiking network , and b ) the classification error of the dynamic network is as close to that of the static network as possible ( this means the error rate is as low as possible , since we do not expect the dynamic network to perform better than the static one ) . we base our network off that of krizhevsky et al . @xcite , which achieved 11% error on the cifar-10 dataset ( a larger variant of the model won the imagenet 2012 competition ) . the original network consists of five layers : two generalized convolutional layers , followed by two locally - connected non - convolutional layers , followed by a fully - connected softmax classifier . a generalized convolutional layer consists of a set of convolutional weights followed by a neural nonlinearity , then a pooling layer , and finally a local response normalization layer . the locally - connected non - convolutional layers are also followed by a neural nonlinearity . in the case of the original network , the nonlinearity is a rectified linear ( relu ) function , and both pooling layers perform overlapping max - pooling . code for the original network and details of the network architecture and training can be found at https://code.google.com / p / cuda - convnet2/. to make the static network transferable to spiking neurons , a number of modifications are necessary . first , we remove the local response normalization layers . this computation would likely require some sort of lateral connections between neurons , which are difficult to add in the current framework since the resulting network would not be feedforward . second , we changed the pooling layers from max pooling to average pooling . again , computing max pooling would likely require lateral connections between neurons , making it difficult to implement without significant changes to the training software . while the neural engineering framework can be used to compute a max function in a feedforward manner @xcite , this method requires prohibitively many neurons to achieve reasonable accuracy . average pooling , on the other hand , is very easy to compute in spiking neurons , since it is simply a weighted sum . the other modifications using leaky integrate - and - fire neurons and training with noise are the main focus of this paper , and are described in detail below . our network uses a modified leaky integrate - and - fire ( lif ) neuron nonlinearity instead of the rectified linear nonlinearity . past work has kept the rectified linear nonlinearity for the static network and substituted in the spiking integrate - and - fire ( if ) neuron model in the dynamic network @xcite , since the static firing curve of the if neuron model is a rectified line . our motivations for using the lif neuron model are that a ) it is more biologically realistic than the if neuron model @xcite , and b ) it demonstrates that alternative models can be used in such networks . the methods applied here are transferable to other neuron types , and could be used to train a network for the idiosyncratic neuron types employed by some neuromorphic hardware ( e.g. @xcite ) . the lif neuron dynamics are given by the equation @xmath0 where @xmath1 is the membrane voltage , @xmath2 is the input current , and @xmath3 is the membrane time constant . when the voltage reaches @xmath4 , the neuron fires a spike , and the voltage is held at zero for a refractory period of @xmath5 . once the refractory period is finished , the neuron obeys equation [ eqn : lifode ] until another spike occurs . given a constant input current @xmath6 , we can solve equation [ eqn : lifode ] for the time it takes the voltage to rise from zero to one , and thereby find the steady - state firing rate @xmath7^{-1 } & \text{if } j > v_{th } \\ 0 & \text{otherwise } \end{cases}. \label{eqn : lifss}\end{aligned}\ ] ] theoretically , we should be able to train a deep neural network using equation [ eqn : lifss ] as the static nonlinearity and make a reasonable approximation of the network in spiking neurons , assuming that the spiking network has a synaptic filter that sufficiently smooths a spike train to give a good approximation of the firing rate . the lif steady state firing rate has the particular problem that the derivative approaches infinity as @xmath8 , which causes problems when employing backpropagation . to address this , we added smoothing to the lif rate equation . equation [ eqn : lifss ] can be rewritten as @xmath9^{-1}\end{aligned}\ ] ] where @xmath10 . if we replace this hard maximum with a softer maximum @xmath11 , then the lif neuron loses its hard threshold and the derivative becomes bounded . further , we can use the substitution @xmath12 \label{eqn : softrelusigma}\end{aligned}\ ] ] to allow us control over the amount of smoothing , where @xmath13 as @xmath14 . figure [ fig : softlif ] shows the result of this substitution . ; the soft lif function smooths this threshold . the right panel shows the derivatives of the response functions . the hard lif function has a discontinuous and unbounded derivative at @xmath15 ; the soft lif function has a continuous bounded derivative , making it amenable to use in backpropagation . ] training neural networks with various types of noise on the inputs is not a new idea . denoising autoencoders @xcite have been successfully applied to datasets like mnist , learning more robust solutions with lower generalization error than their non - noisy counterparts . in a spiking neural network , the neuron receiving spikes in a connection ( called the post - synaptic neuron ) actually receives a filtered version of each spike . this filtered spike is called a post - synaptic current ( or potential ) , and the shape of this signal is determined by the combined dynamics of the pre - synaptic neuron ( e.g. how much neurotransmitter is released ) and the post - synaptic neuron ( e.g. how many ion channels are activated by the neurotransmitter and how they affect the current going into the neuron ) . this post - synaptic current dynamics can be characterized relatively well as a linear system with the impulse response given by the @xmath16-function @xcite : @xmath17 the filtered spike train can be viewed as an estimate of the neuron activity . for example , if the neuron is firing regularly at 200 hz , filtering spike train will result in a signal fluctuating around 200 hz . we can view the neuron output as being 200 hz , with some additional `` noise '' around this value . by training our static network with some random noise added to the output of each neuron for each training example , we can simulate the effects of using spikes on the signal received by the post - synaptic neuron . figure [ fig : noise ] shows how the variability of filtered spike trains depends on input current for the lif neuron . since the impulse response of the @xmath16-filter has an integral of one , the mean of the filtered spike trains is equal to the analytical rate of equation [ eqn : lifss ] . however , the statistics of the filtered signal vary significantly across the range of input currents . just above the firing threshold , the distribution is skewed towards higher firing rates ( i.e. the median is below the mean ) , since spikes are infrequent so the filtered signal has time to return to near zero between spikes . at higher input currents , on the other hand , the distribution is skewed towards lower firing rates ( i.e. the median is above the mean ) . in spite of this , we used a gaussian distribution to generate the additive noise during training , for simplicity . we found the average standard deviation to be approximately @xmath18 across all positive input currents for an @xmath16-filter with @xmath19 . the final steady - state soft lif curve used in training is given by @xmath20^{-1 } + \eta(j ) \label{eqn : softlifnoise}\end{aligned}\ ] ] where @xmath21 and @xmath22 is given by equation [ eqn : softrelusigma ] . ) . the solid line shows the mean of the filtered spike train ( which matches the analytical rate of equation [ eqn : lifss ] ) , the ` x'-points show the median , the solid error bars show the 25th and 75th percentiles , and the dotted error bars show the minimum and maximum . the spike train was filtered with an @xmath16-filter ( equation [ eqn : alpha ] ) with @xmath23 s. ( note that this is different than the @xmath19 used in simulation , to better display the variation . ) ] finally , we convert the trained static network to a dynamic spiking network . the parameters in the spiking network ( i.e. weights and biases ) are all identical to that of the static network . the convolution operation also remains the same , since convolution can be rewritten as simple connection weights ( synapses ) @xmath24 between pre - synaptic neuron @xmath25 and post - synaptic neuron @xmath26 . ( how the brain might _ learn _ connection weight patterns , i.e. filters , that are repeated at various points in space , is a much more difficult problem that we will not address here . ) similarly , the average pooling operation can be written as a simple connection weight matrix , and this matrix can be multiplied by the convolutional weight matrix of the following layer to get direct connection weights between neurons . the only component of the network that actually changes , then , when moving from the static to the dynamic network , is the neurons themselves . the most significant change is that we replace the soft lif rate model ( equation [ eqn : softlifnoise ] ) with the lif spiking model ( equation [ eqn : lifode ] ) . we also remove the additive gaussian noise used in training . additionally , we add post - synaptic filters to the neurons , which filter the incoming spikes before passing the resulting currents to the lif neuron equation . as stated previously , we use the @xmath16-filter for our synapse model , since it has both strong biological support @xcite , and removes a significant portion of the high - frequency variation produced by spikes . we pick the decay time constant @xmath27 ms , typical for excitatory ampa receptors in the brain @xcite . we tested our network on the cifar-10 dataset . this dataset is composed of 60000 @xmath28 pixel labelled images from ten categories . we used the first 50000 images for training and the last 10000 for testing , and augmented the dataset by taking random @xmath29 patches from the training images and then testing on the center patches from the testing images . this methodology is similar to krizhevsky et al . @xcite , except that they also used multiview testing where the classifier output is the average output of the classifier run on nine random patches from each testing image ( increasing the accuracy by about 2% ) . table [ tab : mods ] shows the effect of each modification on the network classification error . our original static network based on the methods of @xcite achieved 14.63% error , which is higher than the 11% achieved by the original paper since a ) we are not using multiview testing , and b ) we used a shorter training time ( 160 epochs versus 520 epochs ) . .effects of successive modifications to cifar-10 error . we first show the original static ( non - spiking ) network based on @xcite . modifications 1 - 5 are cumulative , which each one applied in addition to the previous ones . rows 6 - 8 show the results of running static networks 3 - 5 in spiking neurons , respectively . row 9 shows the best architecture for spiking implementation , network 4 , trained for additional epochs , and row 10 shows this highly - trained network in spiking neurons . this is the best spiking - network result on cifar-10 to date . [ cols="^,<,^",options="header " , ] our results demonstrate that it is possible to train accurate deep convolutional networks for image classification using more biologically accurate leaky integrate - and - fire ( lif ) neurons , as opposed to the traditional rectified - linear or sigmoid neurons . such a network can be run in spiking neurons , and training with noise decreases the amount of error introduced when running in spiking versus rate neurons . the first main contribution of this paper is to demonstrate that state - of - the - art deep spiking networks can be trained with lif neurons . other state - of - the - art methods use integrate - and - fire ( if ) neurons @xcite , which are easier to fit to the rectified linear units commonly used in deep convolutional networks , but are biologically implausible . by smoothing the lif response function so that its derivative remains bounded , we are able to use this more biologically plausible neuron with a standard convolutional network trained by backpropagation . this idea of smoothing the neuron response function is applicable to other neuron types , too . many other neuron types have discontinuous response functions ( e.g. the fitzhugh - nagumo neuron ) , and our smoothing method allows such neurons to be used in deep convolutional networks . we found that there was very little error introduced by switching from the soft response function to the hard response function with lif neurons for the amount of smoothing that we used . however , for neurons with harsh discontinuities that require more smoothing , it may be necessary to slowly relax the smoothing over the course of the training so that , by the end of the training , the smooth response function is arbitrarily close to the hard response function . the other main contribution of this paper is to demonstrate that training with noise on neuron outputs can decrease the error introduced when transitioning to spiking neurons . training with noise on neuron outputs improved the performance of the spiking network considerably ( the error decreased by 3.4% ) . this is because noise on the output of the neuron simulates the variability that a spiking network encounters when filtering a spike train . there is a tradeoff between too little training noise , where the resultant dynamic network is not robust enough against spiking variability , and too much noise , where the accuracy of the static network is decreased . since the variability produced by spiking neurons is not gaussian ( figure [ fig : noise ] ) , our additive gaussian noise is a rough approximation of the variability that the spiking network will encounter . future work includes training with noise that is more representative of the variability seen in spiking networks , to accommodate both the non - gaussian statistics at any particular input current , and the changing statistics across input currents . direct comparison with other spiking neural networks is difficult , since the amount of error introduced when converting from a static to a spiking network is heavily dependent on the firing rates of the neurons . nevertheless , we found our network to perform favourably with other spiking networks , achieving the best published result for a spiking network on cifar-10 , and the best result for a lif neuron spiking network on mnist . we also report our average firing rates for each layer and for the entire network , to facilitate comparison with future networks . the firing rates for the convolutional layers of our network are higher than typical in visual cortex @xcite . future work includes looking at methods to lower firing rates , though this may involve sparsification of neural firing having fewer neurons fire for a particular stimulus which can be difficult in convolutional networks . other future work includes implementing max - pooling and local contrast normalization layers in spiking networks . networks could also be trained offline as described here and then fine - tuned online using an stdp rule , such as the one described in @xcite , to help further reduce errors associated with converting from rate - based to spike - based networks , while avoiding difficulties with training a network in spiking neurons from scratch . y. cao , y. chen , and d. khosla , `` spiking deep convolutional neural networks for energy - efficient object recognition , '' _ international journal of computer vision _ 113 , no . 1 , pp . 5466 , nov 2014 . p. u. diehl , d. neil , j. binas , m. cook , s .- c . liu , and m. pfeiffer , `` fast - classifying , high - accuracy spiking deep networks through weight and threshold balancing , '' in _ ieee international joint conference on neural networks ( ijcnn ) _ , 2015 . b. v. benjamin , p. gao , e. mcquinn , s. choudhary , a. r. chandrasekaran , j .- bussat , r. alvarez - icaza , j. v. arthur , p. a. merolla , and k. boahen , `` neurogrid : a mixed - analog - digital multichip system for large - scale neural simulations , '' _ proceedings of the ieee _ , vol . 102 , no . 5 , pp . 699716 , 2014 . p. vincent , h. larochelle , y. bengio , and p .- a . manzagol , `` extracting and composing robust features with denoising autoencoders , '' in _ international conference on machine learning ( icml ) _ , 2008 , pp . 10961103 . p. jonas , g. major , and b. sakmann , `` quantal components of unitary epscs at the mossy fibre synapse on ca3 pyramidal cells of rat hippocampus . '' _ the journal of physiology _ , vol . 472 , pp . 615663 , 1993 . d. garbin , o. bichler , e. vianello , q. rafhay , c. gamrat , l. perniola , g. ghibaudo , and b. desalvo , `` variability - tolerant convolutional neural network for pattern recognition applications based on oxram synapses , '' in _ ieee international electron devices meeting ( iedm ) _ , 2014 , pp . 28.4.128.4.4 . b. nessler , m. pfeiffer , l. buesing , and w. maass , `` bayesian computation emerges in generic cortical microcircuits through spike - timing - dependent plasticity . '' _ plos computational biology _ , vol . 9 , no . 4 , p. e1003037 , apr 2013

we train spiking deep networks using leaky integrate - and - fire ( lif ) neurons , and achieve state - of - the - art results for spiking networks on the cifar-10 and mnist datasets . this demonstrates that biologically - plausible spiking lif neurons can be integrated into deep networks can perform as well as other spiking models ( e.g. integrate - and - fire ) . we achieved this result by softening the lif response function , such that its derivative remains bounded , and by training the network with noise to provide robustness against the variability introduced by spikes . our method is general and could be applied to other neuron types , including those used on modern neuromorphic hardware . our work brings more biological realism into modern image classification models , with the hope that these models can inform how the brain performs this difficult task . it also provides new methods for training deep networks to run on neuromorphic hardware , with the aim of fast , power - efficient image classification for robotics applications .

<s>[INST]deep artificial neural networks ( anns ) have recently been very successful at solving image categorization problems . early successes with the mnist database @xcite were expanded to the more difficult but similarly sized cifar-10 dataset @xcite and street - view house numbers dataset @xcite . more recently , many groups have achieved better results on these small datasets ( e.g. @xcite ) and as well as success on larger datasets ( e.g. @xcite ) . this work culminated with the application of deep neural networks to imagenet @xcite , a very large and challenging dataset . the relative success of deep anns in general and convolutional neural networks in particular on these datasets have put them well ahead of other methods in terms of image categorization by machines . given that deep anns are approaching human performance on some datasets ( or even passing it , for example on mnist ) suggests that these models may be able to shed light on how the human visual system solves these same tasks . there has recently been considerable effort to take deep anns and make them more biologically plausible by introducing neural `` spiking '' @xcite , such that connected nodes in the network transmit information via instantaneous single bits ( spikes ) , rather than transmitting real - valued activities . while one goal of this work is to better understand the brain by trying to reverse engineer it @xcite , another goal is to build energy - efficient neuromorphic systems that use a similar communication method for image categorization @xcite . we first train a network on static images using traditional deep learning techniques ; we call this the _ static network_. we then take the parameters ( weights and biases ) from the static network and use them to connect spiking neurons , forming the _ dynamic network _ ( or spiking network ) . the challenge is to train the static network in such a way that a ) it _ can _ be transferred into a spiking network , and b ) the classification error of the dynamic network is as close to that of the static network as possible ( this means the error rate is as low as possible , since we do not expect the dynamic network to perform better than the static one ) . we base our network off that of krizhevsky et al . @xcite , which achieved 11% error on the cifar-10 dataset ( a larger variant of the model won the imagenet 2012 competition ) . the original network consists of five layers : two generalized convolutional layers , followed by two locally - connected non - convolutional layers , followed by a fully - connected softmax classifier . a generalized convolutional layer consists of a set of convolutional weights followed by a neural nonlinearity , then a pooling layer , and finally a local response normalization layer . the locally - connected non - convolutional layers are also followed by a neural nonlinearity . in the case of the original network , the nonlinearity is a rectified linear ( relu ) function , and both pooling layers perform overlapping max - pooling . code for the original network and details of the network architecture and training can be found at https://code.google.com / p / cuda - convnet2/. to make the static network transferable to spiking neurons , a number of modifications are necessary . first , we remove the local response normalization layers . this computation would likely require some sort of lateral connections between neurons , which are difficult to add in the current framework since the resulting network would not be feedforward . second , we changed the pooling layers from max pooling to average pooling . again , computing max pooling would likely require lateral connections between neurons , making it difficult to implement without significant changes to the training software . while the neural engineering framework can be used to compute a max function in a feedforward manner @xcite , this method requires prohibitively many neurons to achieve reasonable accuracy . average pooling , on the other hand , is very easy to compute in spiking neurons , since it is simply a weighted sum . the other modifications using leaky integrate - and - fire neurons and training with noise are the main focus of this paper , and are described in detail below . our network uses a modified leaky integrate - and - fire ( lif ) neuron nonlinearity instead of the rectified linear nonlinearity . past work has kept the rectified linear nonlinearity for the static network and substituted in the spiking integrate - and - fire ( if ) neuron model in the dynamic network @xcite , since the static firing curve of the if neuron model is a rectified line . our motivations for using the lif neuron model are that a ) it is more biologically realistic than the if neuron model @xcite , and b ) it demonstrates that alternative models can be used in such networks . the methods applied here are transferable to other neuron types , and could be used to train a network for the idiosyncratic neuron types employed by some neuromorphic hardware ( e.g. @xcite ) . the lif neuron dynamics are given by the equation @xmath0 where @xmath1 is the membrane voltage , @xmath2 is the input current , and @xmath3 is the membrane time constant . when the voltage reaches @xmath4 , the neuron fires a spike , and the voltage is held at zero for a refractory period of @xmath5 . once the refractory period is finished , the neuron obeys equation [ eqn : lifode ] until another spike occurs . given a constant input current @xmath6 , we can solve equation [ eqn : lifode ] for the time it takes the voltage to rise from zero to one , and thereby find the steady - state firing rate @xmath7^{-1 } & \text{if } j > v_{th } \\ 0 & \text{otherwise } \end{cases}. \label{eqn : lifss}\end{aligned}\ ] ] theoretically , we should be able to train a deep neural network using equation [ eqn : lifss ] as the static nonlinearity and make a reasonable approximation of the network in spiking neurons , assuming that the spiking network has a synaptic filter that sufficiently smooths a spike train to give a good approximation of the firing rate . the lif steady state firing rate has the particular problem that the derivative approaches infinity as @xmath8 , which causes problems when employing backpropagation . to address this , we added smoothing to the lif rate equation . equation [ eqn : lifss ] can be rewritten as @xmath9^{-1}\end{aligned}\ ] ] where @xmath10 . if we replace this hard maximum with a softer maximum @xmath11 , then the lif neuron loses its hard threshold and the derivative becomes bounded . further , we can use the substitution @xmath12 \label{eqn : softrelusigma}\end{aligned}\ ] ] to allow us control over the amount of smoothing , where @xmath13 as @xmath14 . figure [ fig : softlif ] shows the result of this substitution . ; the soft lif function smooths this threshold . the right panel shows the derivatives of the response functions . the hard lif function has a discontinuous and unbounded derivative at @xmath15 ; the soft lif function has a continuous bounded derivative , making it amenable to use in backpropagation . ] training neural networks with various types of noise on the inputs is not a new idea . denoising autoencoders @xcite have been successfully applied to datasets like mnist , learning more robust solutions with lower generalization error than their non - noisy counterparts . in a spiking neural network , the neuron receiving spikes in a connection ( called the post - synaptic neuron ) actually receives a filtered version of each spike . this filtered spike is called a post - synaptic current ( or potential ) , and the shape of this signal is determined by the combined dynamics of the pre - synaptic neuron ( e.g. how much neurotransmitter is released ) and the post - synaptic neuron ( e.g. how many ion channels are activated by the neurotransmitter and how they affect the current going into the neuron ) . this post - synaptic current dynamics can be characterized relatively well as a linear system with the impulse response given by the @xmath16-function @xcite : @xmath17 the filtered spike train can be viewed as an estimate of the neuron activity . for example , if the neuron is firing regularly at 200 hz , filtering spike train will result in a signal fluctuating around 200 hz . we can view the neuron output as being 200 hz , with some additional `` noise '' around this value . by training our static network with some random noise added to the output of each neuron for each training example , we can simulate the effects of using spikes on the signal received by the post - synaptic neuron . figure [ fig : noise ] shows how the variability of filtered spike trains depends on input current for the lif neuron . since the impulse response of the @xmath16-filter has an integral of one , the mean of the filtered spike trains is equal to the analytical rate of equation [ eqn : lifss ] . however , the statistics of the filtered signal vary significantly across the range of input currents . just above the firing threshold , the distribution is skewed towards higher firing rates ( i.e. the median is below the mean ) , since spikes are infrequent so the filtered signal has time to return to near zero between spikes . at higher input currents , on the other hand , the distribution is skewed towards lower firing rates ( i.e. the median is above the mean ) . in spite of this , we used a gaussian distribution to generate the additive noise during training , for simplicity . we found the average standard deviation to be approximately @xmath18 across all positive input currents for an @xmath16-filter with @xmath19 . the final steady - state soft lif curve used in training is given by @xmath20^{-1 } + \eta(j ) \label{eqn : softlifnoise}\end{aligned}\ ] ] where @xmath21 and @xmath22 is given by equation [ eqn : softrelusigma ] . ) . the solid line shows the mean of the filtered spike train ( which matches the analytical rate of equation [ eqn : lifss ] ) , the ` x'-points show the median , the solid error bars show the 25th and 75th percentiles , and the dotted error bars show the minimum and maximum . the spike train was filtered with an @xmath16-filter ( equation [ eqn : alpha ] ) with @xmath23 s. ( note that this is different than the @xmath19 used in simulation , to better display the variation . ) ] finally , we convert the trained static network to a dynamic spiking network . the parameters in the spiking network ( i.e. weights and biases ) are all identical to that of the static network . the convolution operation also remains the same , since convolution can be rewritten as simple connection weights ( synapses ) @xmath24 between pre - synaptic neuron @xmath25 and post - synaptic neuron @xmath26 . ( how the brain might _ learn _ connection weight patterns , i.e. filters , that are repeated at various points in space , is a much more difficult problem that we will not address here . ) similarly , the average pooling operation can be written as a simple connection weight matrix , and this matrix can be multiplied by the convolutional weight matrix of the following layer to get direct connection weights between neurons . the only component of the network that actually changes , then , when moving from the static to the dynamic network , is the neurons themselves . the most significant change is that we replace the soft lif rate model ( equation [ eqn : softlifnoise ] ) with the lif spiking model ( equation [ eqn : lifode ] ) . we also remove the additive gaussian noise used in training . additionally , we add post - synaptic filters to the neurons , which filter the incoming spikes before passing the resulting currents to the lif neuron equation . as stated previously , we use the @xmath16-filter for our synapse model , since it has both strong biological support @xcite , and removes a significant portion of the high - frequency variation produced by spikes . we pick the decay time constant @xmath27 ms , typical for excitatory ampa receptors in the brain @xcite . we tested our network on the cifar-10 dataset . this dataset is composed of 60000 @xmath28 pixel labelled images from ten categories . we used the first 50000 images for training and the last 10000 for testing , and augmented the dataset by taking random @xmath29 patches from the training images and then testing on the center patches from the testing images . this methodology is similar to krizhevsky et al . @xcite , except that they also used multiview testing where the classifier output is the average output of the classifier run on nine random patches from each testing image ( increasing the accuracy by about 2% ) . table [ tab : mods ] shows the effect of each modification on the network classification error . our original static network based on the methods of @xcite achieved 14.63% error , which is higher than the 11% achieved by the original paper since a ) we are not using multiview testing , and b ) we used a shorter training time ( 160 epochs versus 520 epochs ) . .effects of successive modifications to cifar-10 error . we first show the original static ( non - spiking ) network based on @xcite . modifications 1 - 5 are cumulative , which each one applied in addition to the previous ones . rows 6 - 8 show the results of running static networks 3 - 5 in spiking neurons , respectively . row 9 shows the best architecture for spiking implementation , network 4 , trained for additional epochs , and row 10 shows this highly - trained network in spiking neurons . this is the best spiking - network result on cifar-10 to date . [ cols="^,<,^",options="header " , ] our results demonstrate that it is possible to train accurate deep convolutional networks for image classification using more biologically accurate leaky integrate - and - fire ( lif ) neurons , as opposed to the traditional rectified - linear or sigmoid neurons . such a network can be run in spiking neurons , and training with noise decreases the amount of error introduced when running in spiking versus rate neurons . the first main contribution of this paper is to demonstrate that state - of - the - art deep spiking networks can be trained with lif neurons . other state - of - the - art methods use integrate - and - fire ( if ) neurons @xcite , which are easier to fit to the rectified linear units commonly used in deep convolutional networks , but are biologically implausible . by smoothing the lif response function so that its derivative remains bounded , we are able to use this more biologically plausible neuron with a standard convolutional network trained by backpropagation . this idea of smoothing the neuron response function is applicable to other neuron types , too . many other neuron types have discontinuous response functions ( e.g. the fitzhugh - nagumo neuron ) , and our smoothing method allows such neurons to be used in deep convolutional networks . we found that there was very little error introduced by switching from the soft response function to the hard response function with lif neurons for the amount of smoothing that we used . however , for neurons with harsh discontinuities that require more smoothing , it may be necessary to slowly relax the smoothing over the course of the training so that , by the end of the training , the smooth response function is arbitrarily close to the hard response function . the other main contribution of this paper is to demonstrate that training with noise on neuron outputs can decrease the error introduced when transitioning to spiking neurons . training with noise on neuron outputs improved the performance of the spiking network considerably ( the error decreased by 3.4% ) . this is because noise on the output of the neuron simulates the variability that a spiking network encounters when filtering a spike train . there is a tradeoff between too little training noise , where the resultant dynamic network is not robust enough against spiking variability , and too much noise , where the accuracy of the static network is decreased . since the variability produced by spiking neurons is not gaussian ( figure [ fig : noise ] ) , our additive gaussian noise is a rough approximation of the variability that the spiking network will encounter . future work includes training with noise that is more representative of the variability seen in spiking networks , to accommodate both the non - gaussian statistics at any particular input current , and the changing statistics across input currents . direct comparison with other spiking neural networks is difficult , since the amount of error introduced when converting from a static to a spiking network is heavily dependent on the firing rates of the neurons . nevertheless , we found our network to perform favourably with other spiking networks , achieving the best published result for a spiking network on cifar-10 , and the best result for a lif neuron spiking network on mnist . we also report our average firing rates for each layer and for the entire network , to facilitate comparison with future networks . the firing rates for the convolutional layers of our network are higher than typical in visual cortex @xcite . future work includes looking at methods to lower firing rates , though this may involve sparsification of neural firing having fewer neurons fire for a particular stimulus which can be difficult in convolutional networks . other future work includes implementing max - pooling and local contrast normalization layers in spiking networks . networks could also be trained offline as described here and then fine - tuned online using an stdp rule , such as the one described in @xcite , to help further reduce errors associated with converting from rate - based to spike - based networks , while avoiding difficulties with training a network in spiking neurons from scratch . y. cao , y. chen , and d. khosla , `` spiking deep convolutional neural networks for energy - efficient object recognition , '' _ international journal of computer vision _ 113 , no . 1 , pp . 5466 , nov 2014 . p. u. diehl , d. neil , j. binas , m. cook , s .- c . liu , and m. pfeiffer , `` fast - classifying , high - accuracy spiking deep networks through weight and threshold balancing , '' in _ ieee international joint conference on neural networks ( ijcnn ) _ , 2015 . b. v. benjamin , p. gao , e. mcquinn , s. choudhary , a. r. chandrasekaran , j .- bussat , r. alvarez - icaza , j. v. arthur , p. a. merolla , and k. boahen , `` neurogrid : a mixed - analog - digital multichip system for large - scale neural simulations , '' _ proceedings of the ieee _ , vol . 102 , no . 5 , pp . 699716 , 2014 . p. vincent , h. larochelle , y. bengio , and p .- a . manzagol , `` extracting and composing robust features with denoising autoencoders , '' in _ international conference on machine learning ( icml ) _ , 2008 , pp . 10961103 . p. jonas , g. major , and b. sakmann , `` quantal components of unitary epscs at the mossy fibre synapse on ca3 pyramidal cells of rat hippocampus . '' _ the journal of physiology _ , vol . 472 , pp . 615663 , 1993 . d. garbin , o. bichler , e. vianello , q. rafhay , c. gamrat , l. perniola , g. ghibaudo , and b. desalvo , `` variability - tolerant convolutional neural network for pattern recognition applications based on oxram synapses , '' in _ ieee international electron devices meeting ( iedm ) _ , 2014 , pp . 28.4.128.4.4 . b. nessler , m. pfeiffer , l. buesing , and w. maass , `` bayesian computation emerges in generic cortical microcircuits through spike - timing - dependent plasticity . '' _ plos computational biology _ , vol . 9 , no . 4 , p. e1003037 , apr 2013[/INST] we train spiking deep networks using leaky integrate - and - fire ( lif ) neurons , and achieve state - of - the - art results for spiking networks on the cifar-10 and mnist datasets . this demonstrates that biologically - plausible spiking lif neurons can be integrated into deep networks can perform as well as other spiking models ( e.g. integrate - and - fire ) . we achieved this result by softening the lif response function , such that its derivative remains bounded , and by training the network with noise to provide robustness against the variability introduced by spikes . our method is general and could be applied to other neuron types , including those used on modern neuromorphic hardware . our work brings more biological realism into modern image classification models , with the hope that these models can inform how the brain performs this difficult task . it also provides new methods for training deep networks to run on neuromorphic hardware , with the aim of fast , power - efficient image classification for robotics applications . </s>

biomolecular motors have clear promise for transport applications in micro- and nanofabricated devices although control of motion remains a major challenge [ 14 ] . toward that end , we constructed a microfabricated thermoelectric controller for rapid and reversible actuation using myosin , the biomolecular motor of muscle , and its partner filament , actin [ 5 , 6 ] . thermal control of kinesin - microtubule motility using thermally responsive polymers has also been demonstrated as a possible temperature - dependent control mechanism for biomolecular motors . we present here novel applications of our thermoelectric control system to investigate changes in actin - myosin motility when ca - regulated thin ( actin ) filaments are used , and when thin - filament ca - regulatory protein mutations are introduced that underlie an inherited cardiovascular disease , familial hypertrophic cardiomyopathy ( fhc ) [ 810 ] . results provide insights into mechanisms of altered function when thin filaments are reconstituted with human cardiac ca - regulatory proteins troponin ( tn ) and tropomyosin ( tm ) , and further modulated by fhc - related mutations in cardiac tn . in the heart and thin filaments are comprised of three major proteins : actin , tm , and tn that is itself a complex of three polypeptides . ca activates thin filaments by binding to tn , leading to structural changes that ultimately expose myosin - binding sites on actin subunits . our previous work on the thermoelectric controller utilized only myosin and unregulated f - actin , that is , ca - independent motility achieved using actin filaments without tn or tm [ 5 , 6 ] . this study was initiated because ca - regulated thin filaments could have several advantages over unregulated f - actin in a thermoelectric nanoactuator . an additional benefit is that the ca - regulatory proteins tn and tm at saturating ca can enhance function of the actomyosin system [ 1220 ] . these effects of tn and tm on actomyosin function , however , appear to vary markedly over the limited temperature ranges studied previously [ 16 , 18 , 21 ] and thus could introduce nonlinearities to a thermoelectric nano - actuator . it affects several fundamental aspects of muscle structure and function [ 2224 ] although temperature effects on muscle function appear to be greater at low temperatures used in many experiments than at physiological temperature ; examples are isometric tetanic tension [ 2527 ] and maximum mechanical power output . temperature also modulates the control of striated muscle contraction by ca regulatory proteins tn and tm , although there are both qualitative and quantitative discrepancies on this point in the striated muscle literature [ 22 , 26 , 29 , 30 ] . interestingly , mild hypothermia has been reported to be a positive inotropic effector in living cardiac muscle due to interplay between temperature and cardiac thin filament ca regulation . our thermo - electric controller allows us to address these issues and more in a single experiment through rapid exploration of broad temperature regimes surrounding physiological temperature . some mutations in tn and tm alter thin - filament function in ways that might make the mutant proteins useful in biomolecular motor - based transport applications . in particular , mutations associated with familial hypertrophic cardiomyopathy ( fhc)one of a growing number of diseases caused by mutations in the genes for sarcomere proteins including thin - filament ca - regulatory proteins [ 810]may be especially useful in bionanomechanical systems even though those mutations are devastating for patients [ 3241 ] . the molecular basis by which these mutations alter thin - filament function and bring about cardiovascular disease is unknown [ 8 , 10 , 42 ] . our thermoelectric controller could provide important insight into mechanisms by which these mutations in myofilament proteins alter contractile function , and directly or indirectly signal changes in gene expression that underlie the progression to pathological cardiac hypertrophy in fhc . florida state university 's institutional animal care and use committee approved all procedures and protocols involving vertebrate animals . adult new zealand white rabbits were housed in florida state university 's laboratory animal resources facility and were handled in accordance with the current national institutes of health / national research council guide for the care and use of laboratory animals . briefly , rabbits were injected i m with 3 mg acepromazine + 10 mg / kg xylazine + 50 mg / kg ketamine . following verification of appropriate surgical depth of anesthesia back and leg muscles were removed for acetone powder , or back muscles only for myosin preparation [ 12 , 13 , 43 ] . myosin and the soluble chymotryptic digest fragment heavy meromyosin ( hmm ) were prepared from fast skeletal muscle as described [ 12 , 13 , 43 , 44 ] . hmm was made from myosin stored < 5 weeks in glycerol ( 1 : 1 ) at 20c ; hmm was used within 3 days after preparation . rabbit muscle actin was purified from muscle acetone powder as described [ 12 , 13 , 43 , 45 ] . f - actin was labeled with rhodamine phalloidin ( rhph ; molecular probes ) for fluorescence microscopy ( figure 1(a ) ) . f - actin ( 33 g / ml ) and rhph ( 1 m ) were incubated in actin buffer ( ab ) with 1 mm dtt at 4c overnight ; fluorescently labeled f - actin was stable at 4c for at least 2 weeks . recombinant human -tm was expressed in e. coli as a homodimeric fusion protein with maltose binding protein ( mbp ) ; -tm was purified following removal of the mbp affinity tag via thrombin cleavage [ 13 , 33 ] . after removal of the mbp tag , recombinant -tm has two extra amino acids ( gs- ) at the n - terminus ; gs- is a conservative alternative to the as - dipeptide in bacterially expressed tm that substitutes functionally for acetylation of tm 's n - terminus [ 46 , 47 ] . purified tn from human cardiac muscle ( ctn ) was obtained from research diagnostics ( flanders , nj ) , or coexpressed recombinantly ( rhctn ) in e. coli as a fusion protein with glutathione s - transferase ( gst ) ; the ternary rhctn complex was purified following removal of the gst affinity tag via cleavage with tev protease . fhc mutations of rhctn were introduced via site - directed mutagenesis to the bacterial coexpression plasmid ; changes were verified by dna sequencing . proteins were assessed by coomassie - stained tricine - sds page and quantitative analysis with a kodak edas 290 digital imaging system . the speed of rhph f - actin over hmm - coated surfaces was measured to assess the kinetics of actomyosin interactions and , for reconstituted thin filaments , their regulation by ca . all aspects of the motility experiments with unregulated f - actin , such as flow cell assembly , solution preparation , assay procedures , and data collection were conducted as described [ 5 , 13 , 43 , 49 ] . [ hmm ] applied to flow cells was 250 g ml in the majority of assays to achieve high density of hmm ( ) on the nitrocellulose - coated motility surface ; to reduce in a limited set of experiments , 75 g ml hmm was applied to the flow cell . the standard motility buffer ( mb ) contained 10 mm ethylene glycol - bis(2-aminoethylether)-n , n , n,n-tetraacetic acid ( egta ) , 20 mm 3-(n - morpholino)propanesulfonic acid ( mops ) , [ k ] = 50 mm , [ na ] = 15 mm , pmg 3 ( pmg = log10[mg ] , where [ mg ] is in molar units ) , and appropriate amounts of tris , and acetate ( anion ) to obtain an ionic strength of 0.085 m at ph 7 . concentrations of ca , mg , na , k were determined taking into account known metal ion binding constants and their enthalpies [ 32 , 50 ] ; solution composition was chosen to minimize enthalpic changes in ph in flow cells when temperature was varied . glucose ( 3 mg / ml ) , 0.1 mg / ml glucose oxidase , 0.018 mg / ml catalase ( boeringher - mannheim ) , and 40 mm dithiothreitol ( dtt ) were added immediately prior to an assay to minimize photooxidation and photobleaching . experiments were conducted at saturating [ ca ] ( pca 5 , where pca = log10[ca ] , with [ ca ] in molar units ) or , where indicated , at low [ ca ] ( pca 9 ) ; note that [ ca ] does not affect sliding speed of unregulated f - actin [ 12 , 14 ] . methylcellulose ( final concentration 0.3% ) , dialyzed against sodium azide ( 0.02% ) , was added to mb to prevent actin filament diffusion away from the assay surface [ 12 , 49 , 51 ] . solutions for assays with reconstituted thin filaments were the same as for unregulated f - actin , except for the last two solutions : the buffer applied to the flow cell before mb contained 75 nm each of -tm and either native ctn or recombinant hctn and was incubated for three minutes before infusing mb containing the same concentrations of tn and tm [ 12 , 13 , 32 , 50 ] . the minimum concentrations of native or wt tn and tm added to mb to obtain well - regulated filaments at 30c were determined by titrations and applying the following criteria : filament sliding was inhibited at pca 9 , while motility was fast and uniform at pca 5 and standard temperature of 30c [ 12 , 13 , 32 , 50 ] . in a limited set of motility experiments , standard mb was modified to vary metabolite concentrations ( table 1 ) as follows : either 5.3 g ml sucrose phosphorylase and 10 mm sucrose were added to reduce inorganic phosphate ( pi ) or acetate was partially replaced by pi to achieve the high pi condition ( sucrose phosphorylase was not added ) ; contaminating adp was reduced to < 1 m by addition of creatine phosphate ( cp ) and creatine phosphokinase ( ck ) . motility data were collected while varying temperature by employing modified flow cells containing microfabricated au heater and thermometer elements ( figure 1(a ) ) , where the thermometer is located immediately adjacent to the viewing region . in experiments using the thermoelectric heater , cooling was achieved by circulating chilled water through a copper coil wrapped around the microscope objective ; in a limited set of experiments , assays at constant temperature were achieved by circulating temperature - controlled water through the coil surrounding the objective [ 13 , 43 ] . stacks of frames ( one stack for each second of temperature transient data , or 1012 stacks for each constant temperature experiment from one flow cell ) were created from digitized movies . linear regression analyses were performed using microsoft excel 2000 or sigmaplot ( windows versions 8.0 and 11.2 ; spss inc . a transition temperature ( tt ) was estimated from arrhenius transformed speed versus temperature data that exhibited a change in slope with temperature . to obtain tt , the data were divided into two parts ( high- and low - temperature regimes ) that were separated by two adjacent points on the arrhenius plot 's temperature axis ; several such divisions of each dataset were processed using the following algorithm . linear regressions were obtained for each regime , and the intersection point determined for those regressions . in general , the intersection point does not fall between the two data points that separate the high and low temperature regimes . the small number of intersection points that did fall between the high- and low - temperature regimes were considered to be candidates for tt ; in the few instances when there was more than one candidate point , the median value was chosen for tt . to examine sliding of ca - regulated thin filaments over a broad range of temperatures , we employed a thermoelectric controller ( figure 1(a ) ) that enables both rapid and continuous variation of a flow cell 's temperature . figure 1(b ) shows sliding speed ( solid symbols ) as a function of time for thin filaments reconstituted with native ctn-tm at pca 5 during three heating phases of cyclic heating and cooling ( ~2060c ) . speed increased with temperature during the heating phase of each cycle over most of the range examined . as temperature increased during the third cycle , however , sliding speed of regulated actin reached a maximum at 54c , and then speed declined above 58c ( figure 1(b ) ) . this anomalous decline in speed for regulated thin filaments is particularly evident in figure 1(c ) , solid symbols where data from all three heating cycles of figure 1(b ) were combined to show the temperature dependence of sliding speed . superposition of the data from three cycles suggests that brief exposure to elevated temperature over at least the first two cycles was fully reversible . comparison of regulated versus unregulated f - actin sliding speed at high temperature suggests that the anomalous decline for regulated thin - filament speed is more likely due to an effect of temperature on tntm rather than on actin or hmm . regulated filament speed at pca 5 ( solid symbols ) was at least as fast as that for unregulated f - actin ( open symbols ) at each temperature over the range examined ( 2060c ) ( figure 1(c ) ) , consistent with previous reports over more limited temperature ranges [ 12 , 13 , 16 , 20 ] . the speed of unregulated f - actin , however , increased continuously over the entire temperature range even at the highest temperatures examined , where regulated thin - filament speed declined . to test the hypothesis that tntm is responsible for the anomalous decline in speed ( figure 1 ) , we examined the effect of temperature on regulated thin - filament motility at pca 9 , that is , in the absence of activating ca . figure 2(a ) shows sliding speed ( red symbols ) as a function of time for thin filaments reconstituted with rhctn-tm at pca 9 during five heating phases of cyclic heating and cooling . note that the peak temperature ( gray line ) increased with each cycle , as in figure 1(b ) . data from all five heating cycles of figure 2(a ) were combined to show the temperature dependence of sliding speed in figure 2(b ) . as expected in the absence of ca , regulated thin filaments exhibited little or no motion ( note red symbols at speed ~0 ) over a broad range of temperatures ( ~2043c ) . above ~43c , filament sliding was observed indicating loss of ca regulation ( red symbols ; figure 2 ) although the average speed was generally less than or similar to that of unregulated f - actin ( open symbols ; figure 2(b ) ) . as for native ctn ( figure 1(c ) , solid symbols ) , rhctn wt regulated thin filaments at pca 5 ( figure 2(b ) , solid symbols ) were faster than unregulated f - actin ( figure 2(b ) , open symbols ) ; an anomalous decline in speed with wt rhctn ( figure 2(b ) , solid black circles ) occurred at slightly a higher temperature ( by 45c ) than for native ctn ( figure 1(c ) , solid symbols ) , suggesting increased stability of the recombinantly expressed protein or its interactions with f - actin--tm . the apparent loss of ca - regulation , indicated in figure 2 by thin filament sliding ( nonzero speeds ) at pca 9 for temperatures above 43c , is completely reversible because thin - filaments stopped moving after temperature was lowered during the cooling phase of each cycle at pca 9 ( figure 2(a ) ) . arrhenius analysis of the data in figure 1(c ) reveals that the activation energy ( ea ) for regulated thin - filament speed at pca 5 exhibited two distinct values , with a change in the slope at tt ~ 38c ( figure 3 , solid symbols and black solid lines ) . for regulated thin filaments ( figure 3 , solid symbols and black solid lines ) , ea at temperatures below physiological ( 100.4 kj / mol ) was > 2-fold greater than ea for the higher - temperature regime ( 41.8 kj / mol ) , while the latter value was closer to that of unregulated f - actin ( 61.9 kj / mol ) ( figure 3 , open symbols and black dashed line ) . temperature has a dramatic , nonlinear effect on the viscosity of water , and the speed of filament sliding varies inversely with solvent viscosity [ 43 , 56 ] ; we therefore asked whether temperature - dependent changes in solvent viscosity could explain the nonlinear arrhenius relation ( figure 3 ) . the data in figure 3 were processed to remove the temperature dependence of solvent viscosity by first normalizing viscosity with respect to that of water at 37c ( i.e. , body temperature ) , and second assuming that speed varies inversely with solvent viscosity [ 43 , 56 ] . after removing the effects of viscosity , slopes of the arrhenius plots were reduced ( figure 3 , blue lines ) . ea for unregulated f - actin decreased from 61.9 kj mol to 47.0 kj mol ( figure 3 , blue dashed line ) . for regulated thin filaments , ea decreased from 100.4 to 83.9 kj mol for t < 38c , and from 41.8 to 26.6 kj mol for t > 38c ( figure 3 , black versus blue solid lines ) . the latter value of ea is suggestive of a diffusion - limited process , in accord with the previously observed inverse relationship between speed and viscosity [ 43 , 56 ] . despite the reduction of slopes for regulated thin - filaments , the ratio of ea 's between the two temperature regimes increased from 2.4 to 3.1 . ea 's for regulated thin - filament sliding speed with respect to that of unregulated f - actin increased from 1.6 to 1.8 . it is clear from this analysis that it is important to consider temperature - dependent changes in solvent viscosity when evaluating actin filament sliding speed . nonlinearities in the arrhenius plot ( figure 3 ) , however , can not be explained by temperature - dependent changes in solvent viscosity . because the temperature dependence of maximum filament sliding speed is influenced by the presence and function of tntm ( figures 13 ) , and fhc - related mutations in troponin profoundly influence the ca dependence of myofilament function [ 810 , 57 ] , we utilized the thermoelectric controller to investigate temperature effects on thin filaments reconstituted with rhctn-tm when one of three fhc - related mutations tni r145 g , tni k206q , or tnt r278c was incorporated into the troponin complex ( section 2 ) . at pca 5 , filament sliding speed for two mutants ( tni k206q and tnt r278c ) was faster than wt over the range of temperatures examined , consistent with previously reported data for tni k206q using recombinant rat cardiac tn . in contrast , speed with tni r145 g was similar to wt ( figure 4 ) . the micromechanical thermal assays with thin filaments containing fhc mutations in rhctn suggest that either the mutant troponins are intrinsically less thermally stable , or the regulatory interaction of mutant troponin with f - actin--tm is less stable , or both ( figure 4(a ) ) . all three of the fhc mutants exhibited anomalous declines in speed at lower temperatures than wt rhctn , with the ctnt r278c and ctni r145 g mutations resulting in 4 - 5c decreases , and the ctni k206q mutation leading to a larger , 8 - 9c decrease in the temperature at which the anomalous decline in speed occurred as temperature continued to rise ( figure 4(a ) ) . arhennius analysis suggests that there was little effect of the fhc mutations on tt for thin filaments reconstituted with wt or mutant rhctn , with values of 3841c where they could be unambiguously determined ( figure 4(b ) ) . this was similar to the value of tt = ~38c obtained with native ctn ( figure 3 ) . the slopes of the high- and low - temperature regimes were more similar for the two fastest mutants ( ctnt r278c and ctni k206q ) compared with wt or the ctni r145 g mutant ( figure 4(b ) ) ; in fact , it was not possible to unambiguously identify a value of tt from data with tni k206q by the algorithm used ( section 2 ) . when the data for unregulated f - actin from figure 2(b ) ( open symbols ) were plotted in arrhenius form ( figure 4(b ) , gray dashed lines ) , a value of tt ~ 33c was obtained in contrast to the dataset in figures 1 and 3 , where tt for unregulated f - actin could not be determined because there were not sufficient points below tt to define a low - temperature regime . to address whether changes in the number of cross - bridges and distribution of cross - bridge states could be responsible for differences in sliding speed and ea between unregulated f - actin and regulated thin filaments at saturating ca , we studied the effects of altered hmm density , and metabolite concentrations which are known to affect the fraction of weakly versus strongly bound cross - bridges . solutions were modified in the following ways , and compared with a control condition that was itself modified in comparison with assays reported in figures 14 ( section 2 ) : decreased [ atp ] from 2 mm ( control ) to 200 m , increased [ pi ] from ~1 m ( control ) to 4 mm , or reduced hmm density ( ) from 0.25 mg / ml ( control ) to 0.075 mg / ml ( figure 5 ) . in these experiments only , motility assays were performed at steady - state temperatures of 27 , 32 , 37 , or 42c so that we could calculate metabolite concentrations in the presence of cp / ck to buffer atp / adp and reduce adp ( section 2 ) , conditions that did not apply to the nonsteady state temperature assays reported in figures 14 . sliding speed increased with temperature for each condition tested for both regulated thin filaments at pca 5 and unregulated f - actin ( figure 5 ) as expected for the temperature range examined . sliding speed with respect to the control condition was reduced significantly for the low atp condition at the two highest temperatures for unregulated f - actin ( figure 5(a ) ) and at the three highest temperature points for regulated thin filaments ( figure 5(b ) ) . sliding speed at high pi ( figure 5 ) was higher than in control conditions at the two lower temperatures for both regulated thin filaments and unregulated f - actin . decreasing had little effect on unregulated f - actin sliding speed ( figure 5(a ) ) but decreased regulated thin - filament speed significantly at the three lowest temperatures ( 27 , 32 , and 37c , figure 5(b ) ) . addition of tntm was typically associated with increased speed , but not at low atp , which is in good agreement with the results of homsher et al . . the fraction of motile filaments at reduced increased over the three lowest temperatures ( 27 , 32 , and 37c ) for unregulated f - actin ( inset , figure 5(a ) ) , but over the entire temperature range for regulated thin filaments ( inset figure 5(b ) ) . in this study , we utilized microfabricated thermoelectric devices to rapidly and reversibly investigate the influence of temperature on myosin - driven sliding of ca - regulated , muscle thin filaments over a wide temperature range ( 2060c ) . to investigate molecular mechanisms of normal cardiac function and pathophysiology , thin filaments were reconstituted with human cardiac tn and tm , or with fhc - related mutants of human cardiac tn . the major results of this study are as follows . at pca 5 , sliding speed of regulated thin filaments increased reversibly with increasing temperature ( 2054c ) as expected and was faster than unregulated f - actin over that range . loss of ca - regulation occurred at both pca 5 and pca 9 at the upper end of the temperature range examined ; this suggests thermal unfolding of the cardiac regulatory proteins and/or their dissociation from actin . arrhenius analysis indicates two temperature regimes with different ea ; the transition temperature between those regimes was higher for regulated thin filaments than unregulated f - actin , and this is explained by a simple model . factors that alter cross - bridge number and kinetics[atp ] , [ pi ] , and hmm alter the temperature dependence of sliding speed of both regulated thin filaments and unregulated f - actin in qualitatively similar ways that provide insight into rate limiting factors . three fhc mutants in ctn ( ctni r145 g , ctni k206q , and ctnt r278c ) destabilize regulatory protein structure and/or interactions with f - actin - tm and may also alter the kinetics of thin filament sliding at pca 5 . a custom thermoelectric controller that was used in this study ( figure 1(a ) ) , and miniaturized versions thereof , provide a novel approach to evaluate contractile protein function over a wide range of temperatures and multiple temperature cycles . the multiple datasets collected this way with native and wt regulatory proteins ( figures 13 ) complement and expand the range of information that can be obtained using conventional motility assays [ 16 , 58 , 59 ] and traditional approaches to studying protein structure in solution [ 6063 ] . our device provides a simpler readout of temperature than relying on intensity of the fluorescent label . speed of unregulated f - actin increased monotonically over the temperature range used ( figures 1 - 2 , open symbols ) , indicating that hmm and actin are not affected detrimentally at temperatures below 60c ; this is consistent with previous functional measurements [ 5 , 64 ] and structural assays showing that the structure of ph - stabilized f - actin in solution is thermally stable up to 78c , while unfolding of subfragment 1 ( s1 ) was reported for temperatures greater than 58c in the presence of analogs of atp or adppi . dysregulation of thin filaments at elevated temperatures was observed at both pca 5 ( figures 1 - 2 ) and pca 9 ( figure 2 ) , suggesting that altered function was likely due to dissociation of tntm from actin or denaturation of tn and/or tm . at pca 5 , the anomalous decline in sliding speed for regulated thin filaments above 54c suggests a loss of regulation ( dysregulation ) because as temperature increased , speed decreased toward that of unregulated f - actin ( figure 1(c ) ) . at pca 9 , filament sliding was observed at temperatures above 43c ; speed increased with temperature and was generally lower than , but approached that of unregulated f - actin ( figure 2 ) , indicating that ctn stabilizes actintm at pca 5 . taken together , these results from microthermal heater assays provide functional correlates that are consistent with previous solution studies showing half - maximal dissociation of tm from ph - stabilized f - actintm complex ( no tn ) at 4648c , and unfolding of tm alone in solution that was resolved into two separate calorimetric domains with maxima of 42 and 51c [ 61 , 62 ] . more generally , our results demonstrate that microthermal heater assays can provide unique , molecular level insights into muscle thin - filament function , particularly when the maximum temperature is limited such that the effects of temperature on ca regulation are fully reversible ( figure 2(a ) ) . comparison of temperature - dependence of regulated thin - filament sliding at pca 5 with that of unregulated f - actin provides insights into the roles of cardiac troponin and tropomyosin . this is important in light of the observation that not only do tn - tm modulate the thin filament side of actomyosin interactions but ctn can also directly accelerate myosin atpase activity even in the absence of actin and tm . this direct effect of ctn on myosin kinetics is presumed to at least partially underlie tntm 's enhancement of maximum unloaded sliding speed under a wide variety of conditions ( e.g. , figures 1(c ) , 2(b ) , 3 , 4(b ) , and 5 ) , although it is also possible that there are differences in the myosin binding interface due to tms1 interactions or regulatory protein - induced structural changes in actin itself . while it is clear that tntm modulate filament sliding speed primarily by affecting the number of cross - bridges at submaximal ca activation [ 12 , 14 , 50 ] , the most straightforward mechanism by which tntm could directly enhance actomyosin kinetics at saturating ca is through a reduction in the time that cross - bridges spend in the strongly bound state ( ts ) under the unloaded conditions of a motility assay , as observed experimentally . the maximum sliding speed ( sm ) for regulated thin filaments at saturating ca or for unregulated f - actin is simply related to myosin step size ( dx ) and ts as proposed by uyeda et al . : ( 1)sm = dxts . to accommodate the observed , biphasic arrhenius plots ( figures 3 and 4(b ) ) , we assume that dx = 0.0055 m for all conditions examined and rewrite ( 1 ) to express ts as the sum of two exponential terms : ( 2)sm=0.0055(aebt+cedt ) , which , when fit to the data for regulated thin filaments in figure 3 , yields sm = 0.0055/(0.301e + 0.00145e ) with r = 0.97 . separating the two terms and plotting them as rates , we can see that one varies little with temperature ( black solid line ; figure 6 ) and while the other is highly temperature sensitive ( red solid line ; figure 6 ) . assuming that the more highly temperature - dependent term is similar for both regulated thin filaments and unregulated f - actin , regression estimates were obtained for unregulated f - actin sliding in figure 3 , c = 0.0225 and d = 0.0676 ( r = 0.97 ) , and the corresponding rate prediction was plotted in figure 6 ( black dashed line ) . if the intersections of the red line with the two black lines in figure 6 are related to discontinuities in the arrhenius plots ( figures 3 and 4(b ) ) and thus values of tt , then the simple analysis of ( 1 ) , ( 2 ) is in accord with observations that the transition from high to low ea will occur at higher temperature for regulated thin filaments ( red and solid black lines ) than for unregulated f - actin ( red and dashed black lines ) . in this model , the rate limitation for filament sliding at a given temperature would be the lower of the two rates from the red line and one black line : at low temperatures , the steeper , red value is limiting , while the shallower , black value is limited at elevated temperatures ( figure 6 ) . the temperature dependence of unloaded filament sliding speed has been reported to vary as a function of temperature in some but not all conditions [ 16 , 58 , 59 ] . for unregulated f - actin , arrhenius plots have been previously reported to be linear within 2060c and 725c , but nonlinear within 342c with a transition temperature ( tt ) of 15.4c , and 1035c with a tt ~ 25c [ 58 , 67 ] . tt depends not only on the experimental conditions but also on whether ca - regulatory proteins are present . the arrhenius plot of fish myofibrillar atpase at saturating ca exhibited a discontinuity , while this was not the case for in vitro motility sliding speed and actin - activated mgatpase activity with fish myosin and unregulated f - actin . for regulated thin filaments , homsher et al . reported a break in the arrhenius plot around 12.5c that was not observed for unregulated f - actin within the 725c temperature range . in this study using micromechanical thermal assays , discontinuities in arrhenius plots for regulated thin filaments ( figures 3 and 4(b ) ) occurred at a higher temperature than when tt could be identified for unregulated f - actin ( figure 4(b ) ) . while there is no universal agreement in the limited data available on absolute values for tt for filament sliding , there does appear to be general agreement that tntm modulates the temperature dependence of unloaded filament sliding . our data suggest that this modulation of tt by human cardiac tntm occurs around physiological temperature . the existence of discontinuities in arrhenius plots suggests that different factors are rate - limiting to filament sliding above and below tt . prior experiments with regulated thin filaments at subsaturating levels of ca suggested that the number of cross - bridges is limiting to sliding speed at 30c [ 12 , 50 ] . the data in figure 5 indicate that sliding speed is markedly sensitive to a reduction in the density ( ) of hmm on the flow cell surface at 27 and 32c for both unregulated f - actin and especially regulated thin filaments at maximal ca activation . at higher temperatures ( 37 and 42c ) , however , there was little or no effect of the same reduction in on sliding speed for either unregulated f - actin or regulated thin filaments ( figure 5 ) . in addition , the fraction of moving filaments at low increased with temperature for regulated thin filaments at pca 5 over the entire temperature range ( figure 5(b ) , inset ) , while for unregulated f - actin , the fraction started at a lower value and plateaued ( figure 5(a ) , inset ) . taken together , these observations suggest an increase in strong cross - bridges with temperature for both unregulated f - actin and regulated thin filaments , consistent with previous reports using in vitro assays and permeabilized muscle fibers [ 7072 ] . thus , it appears that tntm can modulate at least one rate - limiting factor , and also tt , around physiological temperature : once a temperature ( tt ) is attained at which the availability of cross - bridges is great enough to guarantee continuous filament sliding , further increase of speed with temperature will only depend on less temperature - sensitive kinetic rates that are associated with transitions between strongly bound cross - bridge states , and will therefore be characterized by low ea ( figure 6 , cross - over from red to black lines ) . in addition to the number of cross - bridges , filament sliding speed can be altered by variations in the substrate and products of the atpase reaction through modulation of actomyosin kinetics . according to the model implicit in ( 1 ) , changes in metabolite concentration would primarily influence ts , and therefore sm , and also the number of attached cross - bridges . for example , tntm could affect the kinetics of atp - induced cross - bridge dissociation that has been suggested to limit filament sliding speed , at least in fast skeletal muscle at low temperature [ 16 , 73 ] . when [ atp ] was reduced to 200 m a substrate concentration that is similar to the apparent kd for sarcomere shortening velocity and filament sliding speed [ 16 , 53 , 74 , 75]inhibition of speed was greater for regulated thin filaments at pca 5 than unregulated f - actin ( figure 5 ) , as reported by homsher et al . . inhibition of sm at low atp levels is explained by slower atp - induced detachment of cross - bridges at the end of attached phase the cycle , which increases ts ( 1 ) ; the fraction of strongly attached cross - bridges would also increase , although the dominant factor in determining sm in this instance is slower cross - bridge cycling . the relatively greater inhibition of regulated thin - filament sliding was accentuated at higher , more physiological temperatures ( figure 5 ) . the net result was a generally shallow slope of speed versus temperature for both regulated thin filaments and unregulated f - actin ( figure 5 ) that corresponds to a regime of relatively low ea . the expectation would then be that reduced [ atp ] should shift tt to a lower temperature ( figure 6 ) although it was not resolved in this experiment , likely because of the lower limit of temperature examined . there are some interesting parallels with reduced [ atp ] effects , along with significant differences , when the concentration of product pi was increased from micromolar levels to 4 mm ( table 1 ) , that is , the highest concentration that we could achieve without necessitating an increase in ionic strength . temperature has previously been shown to modulate the effect of pi on isometric force in muscle fibers , although there is disagreement about whether pi is either more [ 29 , 76 ] or less inhibitory of isometric force as temperature increases . while pi inhibits isometric force , elevated pi increases sliding speed for both regulated thin filaments at pca 5 and unregulated f - actin , although the effect predominates at lower temperatures and is more pronounced for regulated thin - filaments ( figure 5 ) . maximum velocity of sarcomere shortening [ 52 , 70 , 78 , 79 ] and unloaded sliding of unregulated f - actin have previously been reported to increase with elevated pi . this is generally understood to be the result of reversal of cross - bridge attachment , which decreases ts as demonstrated at the single molecule level by baker et al . , thus reducing the number of strongly attached cross - bridges and increasing sm ( 1 ) . the relatively greater enhancement of sliding speed at lower temperatures results in a generally shallow slope of speed versus temperature for both regulated thin filaments and unregulated f - actin ( figure 5 ) that corresponds to a regime of relatively low ea ; in contrast to the result with low atp , the expectation is that elevated pi should shift tt to a higher temperature ( figure 6 ) . taken together , the data in figure 5 illustrate that the relative importance of factors which influence cross - bridge cycling kinetics and/or filament sliding speed varies with temperature around the physiological range , and which are rate - limiting also varies as implicated in figure 6 . this suggests that energetic state may impact cardiac function when core body temperature varies , such as in mild hypothermia or with exercise , in ways that may seem counterintuitive . figure 4 illustrates that the microthermal heater can be used to study effects of disease - related mutations in human cardiac ca regulatory proteins on function of individual thin filaments . this clearly goes beyond , and will ultimately help explain , prior work that examined physical properties of the mutant proteins in bulk solution , and the ca - dependence of function . ctn mutations may influence not just sm ( tni k206q and tnt r278c ) , but also the temperature dependence of ea ( tni k206q and tnt r278c ) and possibly tt ( tni k206q ) . the mutations may also influence the temperature at which thin - filament structure is affected to the extent that dysregulation occurs and ca dependent function is altered , whether the disease - related change in function is most relevant in the myofilaments , or perhaps in the nucleus . for all three tn mutants examined ( tni r145 g , tni k206q , and tnt r278c ) mutations destabilized thin - filament structure and function at lower temperatures than wt ; this effect was particularly noticeable for an fhc mutant of human cardiac tm ( e180 g ) that causes extreme shifts in ca sensitivity [ 33 , 40 ] . thus , we anticipate that the thermoelectric heater will be generally useful for characterization of clinically relevant mutants of thin filament protein structural stability through assessment of function at the level of individual thin filaments . results demonstrate the utility of our thermoelectric controller for investigating molecular mechanisms underlying biomolecular motor function , and cardiovascular diseases related to altered biomechanics of cardiac myofilament proteins . this assay provides a novel view of structure - function relationships for cardiac thin filaments .

microfabricated thermoelectric controllers can be employed to investigate mechanisms underlying myosin - driven sliding of ca2 + -regulated actin and disease - associated mutations in myofilament proteins . specifically , we examined actin filament sliding with or without human cardiac troponin ( tn ) and -tropomyosin ( tm)propelled by rabbit skeletal heavy meromyosin , when temperature was varied continuously over a wide range ( 2063c ) . at the upper end of this temperature range , reversible dysregulation of thin filaments occurred at pca 9 and 5 ; actomyosin function was unaffected . tn - tm enhanced sliding speed at pca 5 and increased a transition temperature ( tt ) between a high activation energy ( ea ) but low temperature regime and a low ea but high temperature regime . this was modulated by factors that alter cross - bridge number and kinetics . three familial hypertrophic cardiomyopathy ( fhc ) mutations , ctni r145 g , ctni k206q , and ctnt r278c , cause dysregulation at temperatures 58c lower ; the latter two increased speed at pca 5 at all temperatures .

<s>[INST]biomolecular motors have clear promise for transport applications in micro- and nanofabricated devices although control of motion remains a major challenge [ 14 ] . toward that end , we constructed a microfabricated thermoelectric controller for rapid and reversible actuation using myosin , the biomolecular motor of muscle , and its partner filament , actin [ 5 , 6 ] . thermal control of kinesin - microtubule motility using thermally responsive polymers has also been demonstrated as a possible temperature - dependent control mechanism for biomolecular motors . we present here novel applications of our thermoelectric control system to investigate changes in actin - myosin motility when ca - regulated thin ( actin ) filaments are used , and when thin - filament ca - regulatory protein mutations are introduced that underlie an inherited cardiovascular disease , familial hypertrophic cardiomyopathy ( fhc ) [ 810 ] . results provide insights into mechanisms of altered function when thin filaments are reconstituted with human cardiac ca - regulatory proteins troponin ( tn ) and tropomyosin ( tm ) , and further modulated by fhc - related mutations in cardiac tn . in the heart and thin filaments are comprised of three major proteins : actin , tm , and tn that is itself a complex of three polypeptides . ca activates thin filaments by binding to tn , leading to structural changes that ultimately expose myosin - binding sites on actin subunits . our previous work on the thermoelectric controller utilized only myosin and unregulated f - actin , that is , ca - independent motility achieved using actin filaments without tn or tm [ 5 , 6 ] . this study was initiated because ca - regulated thin filaments could have several advantages over unregulated f - actin in a thermoelectric nanoactuator . an additional benefit is that the ca - regulatory proteins tn and tm at saturating ca can enhance function of the actomyosin system [ 1220 ] . these effects of tn and tm on actomyosin function , however , appear to vary markedly over the limited temperature ranges studied previously [ 16 , 18 , 21 ] and thus could introduce nonlinearities to a thermoelectric nano - actuator . it affects several fundamental aspects of muscle structure and function [ 2224 ] although temperature effects on muscle function appear to be greater at low temperatures used in many experiments than at physiological temperature ; examples are isometric tetanic tension [ 2527 ] and maximum mechanical power output . temperature also modulates the control of striated muscle contraction by ca regulatory proteins tn and tm , although there are both qualitative and quantitative discrepancies on this point in the striated muscle literature [ 22 , 26 , 29 , 30 ] . interestingly , mild hypothermia has been reported to be a positive inotropic effector in living cardiac muscle due to interplay between temperature and cardiac thin filament ca regulation . our thermo - electric controller allows us to address these issues and more in a single experiment through rapid exploration of broad temperature regimes surrounding physiological temperature . some mutations in tn and tm alter thin - filament function in ways that might make the mutant proteins useful in biomolecular motor - based transport applications . in particular , mutations associated with familial hypertrophic cardiomyopathy ( fhc)one of a growing number of diseases caused by mutations in the genes for sarcomere proteins including thin - filament ca - regulatory proteins [ 810]may be especially useful in bionanomechanical systems even though those mutations are devastating for patients [ 3241 ] . the molecular basis by which these mutations alter thin - filament function and bring about cardiovascular disease is unknown [ 8 , 10 , 42 ] . our thermoelectric controller could provide important insight into mechanisms by which these mutations in myofilament proteins alter contractile function , and directly or indirectly signal changes in gene expression that underlie the progression to pathological cardiac hypertrophy in fhc . florida state university 's institutional animal care and use committee approved all procedures and protocols involving vertebrate animals . adult new zealand white rabbits were housed in florida state university 's laboratory animal resources facility and were handled in accordance with the current national institutes of health / national research council guide for the care and use of laboratory animals . briefly , rabbits were injected i m with 3 mg acepromazine + 10 mg / kg xylazine + 50 mg / kg ketamine . following verification of appropriate surgical depth of anesthesia back and leg muscles were removed for acetone powder , or back muscles only for myosin preparation [ 12 , 13 , 43 ] . myosin and the soluble chymotryptic digest fragment heavy meromyosin ( hmm ) were prepared from fast skeletal muscle as described [ 12 , 13 , 43 , 44 ] . hmm was made from myosin stored < 5 weeks in glycerol ( 1 : 1 ) at 20c ; hmm was used within 3 days after preparation . rabbit muscle actin was purified from muscle acetone powder as described [ 12 , 13 , 43 , 45 ] . f - actin was labeled with rhodamine phalloidin ( rhph ; molecular probes ) for fluorescence microscopy ( figure 1(a ) ) . f - actin ( 33 g / ml ) and rhph ( 1 m ) were incubated in actin buffer ( ab ) with 1 mm dtt at 4c overnight ; fluorescently labeled f - actin was stable at 4c for at least 2 weeks . recombinant human -tm was expressed in e. coli as a homodimeric fusion protein with maltose binding protein ( mbp ) ; -tm was purified following removal of the mbp affinity tag via thrombin cleavage [ 13 , 33 ] . after removal of the mbp tag , recombinant -tm has two extra amino acids ( gs- ) at the n - terminus ; gs- is a conservative alternative to the as - dipeptide in bacterially expressed tm that substitutes functionally for acetylation of tm 's n - terminus [ 46 , 47 ] . purified tn from human cardiac muscle ( ctn ) was obtained from research diagnostics ( flanders , nj ) , or coexpressed recombinantly ( rhctn ) in e. coli as a fusion protein with glutathione s - transferase ( gst ) ; the ternary rhctn complex was purified following removal of the gst affinity tag via cleavage with tev protease . fhc mutations of rhctn were introduced via site - directed mutagenesis to the bacterial coexpression plasmid ; changes were verified by dna sequencing . proteins were assessed by coomassie - stained tricine - sds page and quantitative analysis with a kodak edas 290 digital imaging system . the speed of rhph f - actin over hmm - coated surfaces was measured to assess the kinetics of actomyosin interactions and , for reconstituted thin filaments , their regulation by ca . all aspects of the motility experiments with unregulated f - actin , such as flow cell assembly , solution preparation , assay procedures , and data collection were conducted as described [ 5 , 13 , 43 , 49 ] . [ hmm ] applied to flow cells was 250 g ml in the majority of assays to achieve high density of hmm ( ) on the nitrocellulose - coated motility surface ; to reduce in a limited set of experiments , 75 g ml hmm was applied to the flow cell . the standard motility buffer ( mb ) contained 10 mm ethylene glycol - bis(2-aminoethylether)-n , n , n,n-tetraacetic acid ( egta ) , 20 mm 3-(n - morpholino)propanesulfonic acid ( mops ) , [ k ] = 50 mm , [ na ] = 15 mm , pmg 3 ( pmg = log10[mg ] , where [ mg ] is in molar units ) , and appropriate amounts of tris , and acetate ( anion ) to obtain an ionic strength of 0.085 m at ph 7 . concentrations of ca , mg , na , k were determined taking into account known metal ion binding constants and their enthalpies [ 32 , 50 ] ; solution composition was chosen to minimize enthalpic changes in ph in flow cells when temperature was varied . glucose ( 3 mg / ml ) , 0.1 mg / ml glucose oxidase , 0.018 mg / ml catalase ( boeringher - mannheim ) , and 40 mm dithiothreitol ( dtt ) were added immediately prior to an assay to minimize photooxidation and photobleaching . experiments were conducted at saturating [ ca ] ( pca 5 , where pca = log10[ca ] , with [ ca ] in molar units ) or , where indicated , at low [ ca ] ( pca 9 ) ; note that [ ca ] does not affect sliding speed of unregulated f - actin [ 12 , 14 ] . methylcellulose ( final concentration 0.3% ) , dialyzed against sodium azide ( 0.02% ) , was added to mb to prevent actin filament diffusion away from the assay surface [ 12 , 49 , 51 ] . solutions for assays with reconstituted thin filaments were the same as for unregulated f - actin , except for the last two solutions : the buffer applied to the flow cell before mb contained 75 nm each of -tm and either native ctn or recombinant hctn and was incubated for three minutes before infusing mb containing the same concentrations of tn and tm [ 12 , 13 , 32 , 50 ] . the minimum concentrations of native or wt tn and tm added to mb to obtain well - regulated filaments at 30c were determined by titrations and applying the following criteria : filament sliding was inhibited at pca 9 , while motility was fast and uniform at pca 5 and standard temperature of 30c [ 12 , 13 , 32 , 50 ] . in a limited set of motility experiments , standard mb was modified to vary metabolite concentrations ( table 1 ) as follows : either 5.3 g ml sucrose phosphorylase and 10 mm sucrose were added to reduce inorganic phosphate ( pi ) or acetate was partially replaced by pi to achieve the high pi condition ( sucrose phosphorylase was not added ) ; contaminating adp was reduced to < 1 m by addition of creatine phosphate ( cp ) and creatine phosphokinase ( ck ) . motility data were collected while varying temperature by employing modified flow cells containing microfabricated au heater and thermometer elements ( figure 1(a ) ) , where the thermometer is located immediately adjacent to the viewing region . in experiments using the thermoelectric heater , cooling was achieved by circulating chilled water through a copper coil wrapped around the microscope objective ; in a limited set of experiments , assays at constant temperature were achieved by circulating temperature - controlled water through the coil surrounding the objective [ 13 , 43 ] . stacks of frames ( one stack for each second of temperature transient data , or 1012 stacks for each constant temperature experiment from one flow cell ) were created from digitized movies . linear regression analyses were performed using microsoft excel 2000 or sigmaplot ( windows versions 8.0 and 11.2 ; spss inc . a transition temperature ( tt ) was estimated from arrhenius transformed speed versus temperature data that exhibited a change in slope with temperature . to obtain tt , the data were divided into two parts ( high- and low - temperature regimes ) that were separated by two adjacent points on the arrhenius plot 's temperature axis ; several such divisions of each dataset were processed using the following algorithm . linear regressions were obtained for each regime , and the intersection point determined for those regressions . in general , the intersection point does not fall between the two data points that separate the high and low temperature regimes . the small number of intersection points that did fall between the high- and low - temperature regimes were considered to be candidates for tt ; in the few instances when there was more than one candidate point , the median value was chosen for tt . to examine sliding of ca - regulated thin filaments over a broad range of temperatures , we employed a thermoelectric controller ( figure 1(a ) ) that enables both rapid and continuous variation of a flow cell 's temperature . figure 1(b ) shows sliding speed ( solid symbols ) as a function of time for thin filaments reconstituted with native ctn-tm at pca 5 during three heating phases of cyclic heating and cooling ( ~2060c ) . speed increased with temperature during the heating phase of each cycle over most of the range examined . as temperature increased during the third cycle , however , sliding speed of regulated actin reached a maximum at 54c , and then speed declined above 58c ( figure 1(b ) ) . this anomalous decline in speed for regulated thin filaments is particularly evident in figure 1(c ) , solid symbols where data from all three heating cycles of figure 1(b ) were combined to show the temperature dependence of sliding speed . superposition of the data from three cycles suggests that brief exposure to elevated temperature over at least the first two cycles was fully reversible . comparison of regulated versus unregulated f - actin sliding speed at high temperature suggests that the anomalous decline for regulated thin - filament speed is more likely due to an effect of temperature on tntm rather than on actin or hmm . regulated filament speed at pca 5 ( solid symbols ) was at least as fast as that for unregulated f - actin ( open symbols ) at each temperature over the range examined ( 2060c ) ( figure 1(c ) ) , consistent with previous reports over more limited temperature ranges [ 12 , 13 , 16 , 20 ] . the speed of unregulated f - actin , however , increased continuously over the entire temperature range even at the highest temperatures examined , where regulated thin - filament speed declined . to test the hypothesis that tntm is responsible for the anomalous decline in speed ( figure 1 ) , we examined the effect of temperature on regulated thin - filament motility at pca 9 , that is , in the absence of activating ca . figure 2(a ) shows sliding speed ( red symbols ) as a function of time for thin filaments reconstituted with rhctn-tm at pca 9 during five heating phases of cyclic heating and cooling . note that the peak temperature ( gray line ) increased with each cycle , as in figure 1(b ) . data from all five heating cycles of figure 2(a ) were combined to show the temperature dependence of sliding speed in figure 2(b ) . as expected in the absence of ca , regulated thin filaments exhibited little or no motion ( note red symbols at speed ~0 ) over a broad range of temperatures ( ~2043c ) . above ~43c , filament sliding was observed indicating loss of ca regulation ( red symbols ; figure 2 ) although the average speed was generally less than or similar to that of unregulated f - actin ( open symbols ; figure 2(b ) ) . as for native ctn ( figure 1(c ) , solid symbols ) , rhctn wt regulated thin filaments at pca 5 ( figure 2(b ) , solid symbols ) were faster than unregulated f - actin ( figure 2(b ) , open symbols ) ; an anomalous decline in speed with wt rhctn ( figure 2(b ) , solid black circles ) occurred at slightly a higher temperature ( by 45c ) than for native ctn ( figure 1(c ) , solid symbols ) , suggesting increased stability of the recombinantly expressed protein or its interactions with f - actin--tm . the apparent loss of ca - regulation , indicated in figure 2 by thin filament sliding ( nonzero speeds ) at pca 9 for temperatures above 43c , is completely reversible because thin - filaments stopped moving after temperature was lowered during the cooling phase of each cycle at pca 9 ( figure 2(a ) ) . arrhenius analysis of the data in figure 1(c ) reveals that the activation energy ( ea ) for regulated thin - filament speed at pca 5 exhibited two distinct values , with a change in the slope at tt ~ 38c ( figure 3 , solid symbols and black solid lines ) . for regulated thin filaments ( figure 3 , solid symbols and black solid lines ) , ea at temperatures below physiological ( 100.4 kj / mol ) was > 2-fold greater than ea for the higher - temperature regime ( 41.8 kj / mol ) , while the latter value was closer to that of unregulated f - actin ( 61.9 kj / mol ) ( figure 3 , open symbols and black dashed line ) . temperature has a dramatic , nonlinear effect on the viscosity of water , and the speed of filament sliding varies inversely with solvent viscosity [ 43 , 56 ] ; we therefore asked whether temperature - dependent changes in solvent viscosity could explain the nonlinear arrhenius relation ( figure 3 ) . the data in figure 3 were processed to remove the temperature dependence of solvent viscosity by first normalizing viscosity with respect to that of water at 37c ( i.e. , body temperature ) , and second assuming that speed varies inversely with solvent viscosity [ 43 , 56 ] . after removing the effects of viscosity , slopes of the arrhenius plots were reduced ( figure 3 , blue lines ) . ea for unregulated f - actin decreased from 61.9 kj mol to 47.0 kj mol ( figure 3 , blue dashed line ) . for regulated thin filaments , ea decreased from 100.4 to 83.9 kj mol for t < 38c , and from 41.8 to 26.6 kj mol for t > 38c ( figure 3 , black versus blue solid lines ) . the latter value of ea is suggestive of a diffusion - limited process , in accord with the previously observed inverse relationship between speed and viscosity [ 43 , 56 ] . despite the reduction of slopes for regulated thin - filaments , the ratio of ea 's between the two temperature regimes increased from 2.4 to 3.1 . ea 's for regulated thin - filament sliding speed with respect to that of unregulated f - actin increased from 1.6 to 1.8 . it is clear from this analysis that it is important to consider temperature - dependent changes in solvent viscosity when evaluating actin filament sliding speed . nonlinearities in the arrhenius plot ( figure 3 ) , however , can not be explained by temperature - dependent changes in solvent viscosity . because the temperature dependence of maximum filament sliding speed is influenced by the presence and function of tntm ( figures 13 ) , and fhc - related mutations in troponin profoundly influence the ca dependence of myofilament function [ 810 , 57 ] , we utilized the thermoelectric controller to investigate temperature effects on thin filaments reconstituted with rhctn-tm when one of three fhc - related mutations tni r145 g , tni k206q , or tnt r278c was incorporated into the troponin complex ( section 2 ) . at pca 5 , filament sliding speed for two mutants ( tni k206q and tnt r278c ) was faster than wt over the range of temperatures examined , consistent with previously reported data for tni k206q using recombinant rat cardiac tn . in contrast , speed with tni r145 g was similar to wt ( figure 4 ) . the micromechanical thermal assays with thin filaments containing fhc mutations in rhctn suggest that either the mutant troponins are intrinsically less thermally stable , or the regulatory interaction of mutant troponin with f - actin--tm is less stable , or both ( figure 4(a ) ) . all three of the fhc mutants exhibited anomalous declines in speed at lower temperatures than wt rhctn , with the ctnt r278c and ctni r145 g mutations resulting in 4 - 5c decreases , and the ctni k206q mutation leading to a larger , 8 - 9c decrease in the temperature at which the anomalous decline in speed occurred as temperature continued to rise ( figure 4(a ) ) . arhennius analysis suggests that there was little effect of the fhc mutations on tt for thin filaments reconstituted with wt or mutant rhctn , with values of 3841c where they could be unambiguously determined ( figure 4(b ) ) . this was similar to the value of tt = ~38c obtained with native ctn ( figure 3 ) . the slopes of the high- and low - temperature regimes were more similar for the two fastest mutants ( ctnt r278c and ctni k206q ) compared with wt or the ctni r145 g mutant ( figure 4(b ) ) ; in fact , it was not possible to unambiguously identify a value of tt from data with tni k206q by the algorithm used ( section 2 ) . when the data for unregulated f - actin from figure 2(b ) ( open symbols ) were plotted in arrhenius form ( figure 4(b ) , gray dashed lines ) , a value of tt ~ 33c was obtained in contrast to the dataset in figures 1 and 3 , where tt for unregulated f - actin could not be determined because there were not sufficient points below tt to define a low - temperature regime . to address whether changes in the number of cross - bridges and distribution of cross - bridge states could be responsible for differences in sliding speed and ea between unregulated f - actin and regulated thin filaments at saturating ca , we studied the effects of altered hmm density , and metabolite concentrations which are known to affect the fraction of weakly versus strongly bound cross - bridges . solutions were modified in the following ways , and compared with a control condition that was itself modified in comparison with assays reported in figures 14 ( section 2 ) : decreased [ atp ] from 2 mm ( control ) to 200 m , increased [ pi ] from ~1 m ( control ) to 4 mm , or reduced hmm density ( ) from 0.25 mg / ml ( control ) to 0.075 mg / ml ( figure 5 ) . in these experiments only , motility assays were performed at steady - state temperatures of 27 , 32 , 37 , or 42c so that we could calculate metabolite concentrations in the presence of cp / ck to buffer atp / adp and reduce adp ( section 2 ) , conditions that did not apply to the nonsteady state temperature assays reported in figures 14 . sliding speed increased with temperature for each condition tested for both regulated thin filaments at pca 5 and unregulated f - actin ( figure 5 ) as expected for the temperature range examined . sliding speed with respect to the control condition was reduced significantly for the low atp condition at the two highest temperatures for unregulated f - actin ( figure 5(a ) ) and at the three highest temperature points for regulated thin filaments ( figure 5(b ) ) . sliding speed at high pi ( figure 5 ) was higher than in control conditions at the two lower temperatures for both regulated thin filaments and unregulated f - actin . decreasing had little effect on unregulated f - actin sliding speed ( figure 5(a ) ) but decreased regulated thin - filament speed significantly at the three lowest temperatures ( 27 , 32 , and 37c , figure 5(b ) ) . addition of tntm was typically associated with increased speed , but not at low atp , which is in good agreement with the results of homsher et al . . the fraction of motile filaments at reduced increased over the three lowest temperatures ( 27 , 32 , and 37c ) for unregulated f - actin ( inset , figure 5(a ) ) , but over the entire temperature range for regulated thin filaments ( inset figure 5(b ) ) . in this study , we utilized microfabricated thermoelectric devices to rapidly and reversibly investigate the influence of temperature on myosin - driven sliding of ca - regulated , muscle thin filaments over a wide temperature range ( 2060c ) . to investigate molecular mechanisms of normal cardiac function and pathophysiology , thin filaments were reconstituted with human cardiac tn and tm , or with fhc - related mutants of human cardiac tn . the major results of this study are as follows . at pca 5 , sliding speed of regulated thin filaments increased reversibly with increasing temperature ( 2054c ) as expected and was faster than unregulated f - actin over that range . loss of ca - regulation occurred at both pca 5 and pca 9 at the upper end of the temperature range examined ; this suggests thermal unfolding of the cardiac regulatory proteins and/or their dissociation from actin . arrhenius analysis indicates two temperature regimes with different ea ; the transition temperature between those regimes was higher for regulated thin filaments than unregulated f - actin , and this is explained by a simple model . factors that alter cross - bridge number and kinetics[atp ] , [ pi ] , and hmm alter the temperature dependence of sliding speed of both regulated thin filaments and unregulated f - actin in qualitatively similar ways that provide insight into rate limiting factors . three fhc mutants in ctn ( ctni r145 g , ctni k206q , and ctnt r278c ) destabilize regulatory protein structure and/or interactions with f - actin - tm and may also alter the kinetics of thin filament sliding at pca 5 . a custom thermoelectric controller that was used in this study ( figure 1(a ) ) , and miniaturized versions thereof , provide a novel approach to evaluate contractile protein function over a wide range of temperatures and multiple temperature cycles . the multiple datasets collected this way with native and wt regulatory proteins ( figures 13 ) complement and expand the range of information that can be obtained using conventional motility assays [ 16 , 58 , 59 ] and traditional approaches to studying protein structure in solution [ 6063 ] . our device provides a simpler readout of temperature than relying on intensity of the fluorescent label . speed of unregulated f - actin increased monotonically over the temperature range used ( figures 1 - 2 , open symbols ) , indicating that hmm and actin are not affected detrimentally at temperatures below 60c ; this is consistent with previous functional measurements [ 5 , 64 ] and structural assays showing that the structure of ph - stabilized f - actin in solution is thermally stable up to 78c , while unfolding of subfragment 1 ( s1 ) was reported for temperatures greater than 58c in the presence of analogs of atp or adppi . dysregulation of thin filaments at elevated temperatures was observed at both pca 5 ( figures 1 - 2 ) and pca 9 ( figure 2 ) , suggesting that altered function was likely due to dissociation of tntm from actin or denaturation of tn and/or tm . at pca 5 , the anomalous decline in sliding speed for regulated thin filaments above 54c suggests a loss of regulation ( dysregulation ) because as temperature increased , speed decreased toward that of unregulated f - actin ( figure 1(c ) ) . at pca 9 , filament sliding was observed at temperatures above 43c ; speed increased with temperature and was generally lower than , but approached that of unregulated f - actin ( figure 2 ) , indicating that ctn stabilizes actintm at pca 5 . taken together , these results from microthermal heater assays provide functional correlates that are consistent with previous solution studies showing half - maximal dissociation of tm from ph - stabilized f - actintm complex ( no tn ) at 4648c , and unfolding of tm alone in solution that was resolved into two separate calorimetric domains with maxima of 42 and 51c [ 61 , 62 ] . more generally , our results demonstrate that microthermal heater assays can provide unique , molecular level insights into muscle thin - filament function , particularly when the maximum temperature is limited such that the effects of temperature on ca regulation are fully reversible ( figure 2(a ) ) . comparison of temperature - dependence of regulated thin - filament sliding at pca 5 with that of unregulated f - actin provides insights into the roles of cardiac troponin and tropomyosin . this is important in light of the observation that not only do tn - tm modulate the thin filament side of actomyosin interactions but ctn can also directly accelerate myosin atpase activity even in the absence of actin and tm . this direct effect of ctn on myosin kinetics is presumed to at least partially underlie tntm 's enhancement of maximum unloaded sliding speed under a wide variety of conditions ( e.g. , figures 1(c ) , 2(b ) , 3 , 4(b ) , and 5 ) , although it is also possible that there are differences in the myosin binding interface due to tms1 interactions or regulatory protein - induced structural changes in actin itself . while it is clear that tntm modulate filament sliding speed primarily by affecting the number of cross - bridges at submaximal ca activation [ 12 , 14 , 50 ] , the most straightforward mechanism by which tntm could directly enhance actomyosin kinetics at saturating ca is through a reduction in the time that cross - bridges spend in the strongly bound state ( ts ) under the unloaded conditions of a motility assay , as observed experimentally . the maximum sliding speed ( sm ) for regulated thin filaments at saturating ca or for unregulated f - actin is simply related to myosin step size ( dx ) and ts as proposed by uyeda et al . : ( 1)sm = dxts . to accommodate the observed , biphasic arrhenius plots ( figures 3 and 4(b ) ) , we assume that dx = 0.0055 m for all conditions examined and rewrite ( 1 ) to express ts as the sum of two exponential terms : ( 2)sm=0.0055(aebt+cedt ) , which , when fit to the data for regulated thin filaments in figure 3 , yields sm = 0.0055/(0.301e + 0.00145e ) with r = 0.97 . separating the two terms and plotting them as rates , we can see that one varies little with temperature ( black solid line ; figure 6 ) and while the other is highly temperature sensitive ( red solid line ; figure 6 ) . assuming that the more highly temperature - dependent term is similar for both regulated thin filaments and unregulated f - actin , regression estimates were obtained for unregulated f - actin sliding in figure 3 , c = 0.0225 and d = 0.0676 ( r = 0.97 ) , and the corresponding rate prediction was plotted in figure 6 ( black dashed line ) . if the intersections of the red line with the two black lines in figure 6 are related to discontinuities in the arrhenius plots ( figures 3 and 4(b ) ) and thus values of tt , then the simple analysis of ( 1 ) , ( 2 ) is in accord with observations that the transition from high to low ea will occur at higher temperature for regulated thin filaments ( red and solid black lines ) than for unregulated f - actin ( red and dashed black lines ) . in this model , the rate limitation for filament sliding at a given temperature would be the lower of the two rates from the red line and one black line : at low temperatures , the steeper , red value is limiting , while the shallower , black value is limited at elevated temperatures ( figure 6 ) . the temperature dependence of unloaded filament sliding speed has been reported to vary as a function of temperature in some but not all conditions [ 16 , 58 , 59 ] . for unregulated f - actin , arrhenius plots have been previously reported to be linear within 2060c and 725c , but nonlinear within 342c with a transition temperature ( tt ) of 15.4c , and 1035c with a tt ~ 25c [ 58 , 67 ] . tt depends not only on the experimental conditions but also on whether ca - regulatory proteins are present . the arrhenius plot of fish myofibrillar atpase at saturating ca exhibited a discontinuity , while this was not the case for in vitro motility sliding speed and actin - activated mgatpase activity with fish myosin and unregulated f - actin . for regulated thin filaments , homsher et al . reported a break in the arrhenius plot around 12.5c that was not observed for unregulated f - actin within the 725c temperature range . in this study using micromechanical thermal assays , discontinuities in arrhenius plots for regulated thin filaments ( figures 3 and 4(b ) ) occurred at a higher temperature than when tt could be identified for unregulated f - actin ( figure 4(b ) ) . while there is no universal agreement in the limited data available on absolute values for tt for filament sliding , there does appear to be general agreement that tntm modulates the temperature dependence of unloaded filament sliding . our data suggest that this modulation of tt by human cardiac tntm occurs around physiological temperature . the existence of discontinuities in arrhenius plots suggests that different factors are rate - limiting to filament sliding above and below tt . prior experiments with regulated thin filaments at subsaturating levels of ca suggested that the number of cross - bridges is limiting to sliding speed at 30c [ 12 , 50 ] . the data in figure 5 indicate that sliding speed is markedly sensitive to a reduction in the density ( ) of hmm on the flow cell surface at 27 and 32c for both unregulated f - actin and especially regulated thin filaments at maximal ca activation . at higher temperatures ( 37 and 42c ) , however , there was little or no effect of the same reduction in on sliding speed for either unregulated f - actin or regulated thin filaments ( figure 5 ) . in addition , the fraction of moving filaments at low increased with temperature for regulated thin filaments at pca 5 over the entire temperature range ( figure 5(b ) , inset ) , while for unregulated f - actin , the fraction started at a lower value and plateaued ( figure 5(a ) , inset ) . taken together , these observations suggest an increase in strong cross - bridges with temperature for both unregulated f - actin and regulated thin filaments , consistent with previous reports using in vitro assays and permeabilized muscle fibers [ 7072 ] . thus , it appears that tntm can modulate at least one rate - limiting factor , and also tt , around physiological temperature : once a temperature ( tt ) is attained at which the availability of cross - bridges is great enough to guarantee continuous filament sliding , further increase of speed with temperature will only depend on less temperature - sensitive kinetic rates that are associated with transitions between strongly bound cross - bridge states , and will therefore be characterized by low ea ( figure 6 , cross - over from red to black lines ) . in addition to the number of cross - bridges , filament sliding speed can be altered by variations in the substrate and products of the atpase reaction through modulation of actomyosin kinetics . according to the model implicit in ( 1 ) , changes in metabolite concentration would primarily influence ts , and therefore sm , and also the number of attached cross - bridges . for example , tntm could affect the kinetics of atp - induced cross - bridge dissociation that has been suggested to limit filament sliding speed , at least in fast skeletal muscle at low temperature [ 16 , 73 ] . when [ atp ] was reduced to 200 m a substrate concentration that is similar to the apparent kd for sarcomere shortening velocity and filament sliding speed [ 16 , 53 , 74 , 75]inhibition of speed was greater for regulated thin filaments at pca 5 than unregulated f - actin ( figure 5 ) , as reported by homsher et al . . inhibition of sm at low atp levels is explained by slower atp - induced detachment of cross - bridges at the end of attached phase the cycle , which increases ts ( 1 ) ; the fraction of strongly attached cross - bridges would also increase , although the dominant factor in determining sm in this instance is slower cross - bridge cycling . the relatively greater inhibition of regulated thin - filament sliding was accentuated at higher , more physiological temperatures ( figure 5 ) . the net result was a generally shallow slope of speed versus temperature for both regulated thin filaments and unregulated f - actin ( figure 5 ) that corresponds to a regime of relatively low ea . the expectation would then be that reduced [ atp ] should shift tt to a lower temperature ( figure 6 ) although it was not resolved in this experiment , likely because of the lower limit of temperature examined . there are some interesting parallels with reduced [ atp ] effects , along with significant differences , when the concentration of product pi was increased from micromolar levels to 4 mm ( table 1 ) , that is , the highest concentration that we could achieve without necessitating an increase in ionic strength . temperature has previously been shown to modulate the effect of pi on isometric force in muscle fibers , although there is disagreement about whether pi is either more [ 29 , 76 ] or less inhibitory of isometric force as temperature increases . while pi inhibits isometric force , elevated pi increases sliding speed for both regulated thin filaments at pca 5 and unregulated f - actin , although the effect predominates at lower temperatures and is more pronounced for regulated thin - filaments ( figure 5 ) . maximum velocity of sarcomere shortening [ 52 , 70 , 78 , 79 ] and unloaded sliding of unregulated f - actin have previously been reported to increase with elevated pi . this is generally understood to be the result of reversal of cross - bridge attachment , which decreases ts as demonstrated at the single molecule level by baker et al . , thus reducing the number of strongly attached cross - bridges and increasing sm ( 1 ) . the relatively greater enhancement of sliding speed at lower temperatures results in a generally shallow slope of speed versus temperature for both regulated thin filaments and unregulated f - actin ( figure 5 ) that corresponds to a regime of relatively low ea ; in contrast to the result with low atp , the expectation is that elevated pi should shift tt to a higher temperature ( figure 6 ) . taken together , the data in figure 5 illustrate that the relative importance of factors which influence cross - bridge cycling kinetics and/or filament sliding speed varies with temperature around the physiological range , and which are rate - limiting also varies as implicated in figure 6 . this suggests that energetic state may impact cardiac function when core body temperature varies , such as in mild hypothermia or with exercise , in ways that may seem counterintuitive . figure 4 illustrates that the microthermal heater can be used to study effects of disease - related mutations in human cardiac ca regulatory proteins on function of individual thin filaments . this clearly goes beyond , and will ultimately help explain , prior work that examined physical properties of the mutant proteins in bulk solution , and the ca - dependence of function . ctn mutations may influence not just sm ( tni k206q and tnt r278c ) , but also the temperature dependence of ea ( tni k206q and tnt r278c ) and possibly tt ( tni k206q ) . the mutations may also influence the temperature at which thin - filament structure is affected to the extent that dysregulation occurs and ca dependent function is altered , whether the disease - related change in function is most relevant in the myofilaments , or perhaps in the nucleus . for all three tn mutants examined ( tni r145 g , tni k206q , and tnt r278c ) mutations destabilized thin - filament structure and function at lower temperatures than wt ; this effect was particularly noticeable for an fhc mutant of human cardiac tm ( e180 g ) that causes extreme shifts in ca sensitivity [ 33 , 40 ] . thus , we anticipate that the thermoelectric heater will be generally useful for characterization of clinically relevant mutants of thin filament protein structural stability through assessment of function at the level of individual thin filaments . results demonstrate the utility of our thermoelectric controller for investigating molecular mechanisms underlying biomolecular motor function , and cardiovascular diseases related to altered biomechanics of cardiac myofilament proteins . this assay provides a novel view of structure - function relationships for cardiac thin filaments .[/INST]microfabricated thermoelectric controllers can be employed to investigate mechanisms underlying myosin - driven sliding of ca2 + -regulated actin and disease - associated mutations in myofilament proteins . specifically , we examined actin filament sliding with or without human cardiac troponin ( tn ) and -tropomyosin ( tm)propelled by rabbit skeletal heavy meromyosin , when temperature was varied continuously over a wide range ( 2063c ) . at the upper end of this temperature range , reversible dysregulation of thin filaments occurred at pca 9 and 5 ; actomyosin function was unaffected . tn - tm enhanced sliding speed at pca 5 and increased a transition temperature ( tt ) between a high activation energy ( ea ) but low temperature regime and a low ea but high temperature regime . this was modulated by factors that alter cross - bridge number and kinetics . three familial hypertrophic cardiomyopathy ( fhc ) mutations , ctni r145 g , ctni k206q , and ctnt r278c , cause dysregulation at temperatures 58c lower ; the latter two increased speed at pca 5 at all temperatures .</s>

mesoporous sba-15 silica molecular sieves of large pore diameter ( up to 30 nm ) and area ( up to 1000 m g ) show excellent homogeneity and stability and can be well controlled for adsorption / desorption processes . mesoporous silica materials , especially mesoporous sba-15 molecular sieves , have been modified with 3-mercaptopropyl , 3-aminopropyl , octyl , or octadecyl groups for the separation and analysis of inorganic ions , organic compounds , and biological molecules [ 25 ] . magnetic separation is a useful tool because of its fast recovery , high efficiency , and low high cost . inclusion of magnetic components in modified materials allows convenient and economical magnetic separation instead of centrifugation and filtration steps on application of an appropriate magnetic field [ 79 ] . because of their potential applications in this approach , the preparation of co , co / fe , -fe2o3 , -fe2o3 , and fe3o4 magnetic sba-15 materials have been reported [ 1015 ] . we propose a convenient and effective procedure for iron doping of mesoporous sba-15 silica because of its excellent magnetic properties . then fe was transformed to the oxide form by calcination in the air . finally , ferric oxide in sba-15 was reduced with h2 [ 7 , 15 , 16 ] . fourier - transform infrared ( ft - ir ) spectroscopy , powder x - ray diffraction ( xrd ) , mssbauer spectra ( ms ) , surface area analysis , scanning electron microscopy ( sem ) , and transmission electron microscopy ( tem ) techniques were used to characterize the material . the iron content in fe - sba-15 was determined by atom adsorption spectroscopy ( aas ) . with the development of petroleum refining and chemical engineering , the release of harmful organic chemicals into the environment has attracted global attention because of their toxicity and widespread use , especially aromatic compounds considered as carcinogenic . the aim of the present study was to develop a method for preparing magnetic sba-15 for use as a sorbent to remove benzene and related derivatives from water . the adsorption of benzene , toluene , and ethyl benzene on magnetic sba-15 particles was determined by gas chromatography ( gc ) . benzene , toluene , and ethyl benzene were purchased from sigma ( st . louis , mo , usa ) . deionized water was prepared using a millipore unit ( bedford , ma , usa ) . sba-15 was soaked in 0.1 mol l hcl for 24 h , filtered , washed with deionized water , and dried in an oven at 100c for 8 h. a sample of 2 g of sba-15 was dispersed in 1 mol l fe(no3)3 solution by ultrasonication for 2 h. the material was filtered under low pressure and dried in an oven at 100c . samples were calcined in a muffle furnace at 750c for 6 h to obtain a red powder , which was then reduced under a h2 flow ( 35 ml min ) at 800c for 6 h. the final product was designated fe - sba-15 . ft - ir spectra of sba-15 particles were recorded before and after modification on a nicolet ( usa ) 360 ft - ir instrument . powder xrd patterns were measured on a d / max-2400 ( rigaku , japan ) instrument using cu k radiation . fe mssbauer spectra were collected using a conventional constant acceleration spectrometer ( wissel , german ) with a 25 m ci source of co in palladium at room temperature . the percentage of fe , fe(ii ) , and fe(iii ) were calculated and contributor of magnetic behavior was confirmed . nitrogen adsorption - desorption experiments were carried out at 76.53 k on an asap 2010 accelerated surface area and porosimetry system ( micromeritics , usa ) . the brunauer - emmett - teller ( bet ) surface area ( sbet ) was calculated from the linearity of the bet equation . the surface area , volume and pore diameter were calculated from pore size distribution curves using the barrett - joyner - halenda ( bjh ) formula . the surface morphology of powders was observed under a jsm-6380lv scanning electron microscope ( jeol , japan ) . for tem observation , samples were dispersed in ethanol , deposited on a grid of holey copper and transferred to a jem-1230 emission electron microscope ( jeol , japan ) at an accelerating voltage of 100 kv . a lakeshore ( usa ) 7304 vibrating sample magnetometer was used to record magnetization curves of the samples . a sample of 10 mg of fe - sba-15 was heated in a mixture of hydrochloric acid and nitric acid to completely dissolve the iron and transferred to a 25-ml volumetric flask and made up to volume with water . the solution was centrifuged at 10000 rpm and the iron concentration was determined on an aa-6800 instrument ( shimadzu , japan ) . standard fe solutions ( 0 , 2.0 , 4.0 , 8.0 , 10.0 g ml ) were measured to generate a standard curve . benzene , toluene , and ethyl benzene , were dissolved in deionized water at a concentration of 1.0 ppm each . then 20 mg of fe - sba-15 was added to the aqueous solution and sonicated at room temperature ( approx . 20c ) for 30 s to form a homogeneous dispersion . after standing for 5 min , fe - sba-15 finally , 1.0 l of the eluate was analyzed on a varian ( usa ) cp-3380 gas chromatograph and the content of the aromatic compounds was calculated . figure 2 shows ft - ir spectra of fe(no3)3 , sba-15 , fe(no3)3-sba-15 , fe2o3-sba-15 , and fe - sba-15 . the ir vibration for the no3 ion at 1385 cm is evident in curves a and c , but not in b , indicating that fe(no3)3-sba-15 was prepared successfully . fe2o3-sba-15 was obtained by transformation from the nitrate to the oxide form , as confirmed by the disappearance of the peak at 1385 cm after calcination ( curve d ) . the peak at 1385 cm also disappeared after fe2o3-sba-15 reduction ( curve e ) . the material was red after fe(no3)3-sba-15 calcination at 750c , suggesting that iron oxide is mainly in the form of -fe2o3 ( hematite ) . hematite is extremely stable under ambient conditions and is often the end product of the transformation of other iron oxides . xrd patterns of the materials are shown in figure 3 . in the narrow - angle range peaks for sba-15 are evident at 0.8 , 1.4 and 1.7. for fe - sba-15 , there is one prominent peak at 0.9 and two peaks at 1.5 and 1.8. these results indicate that magnetic fe - sba-15 still has a high degree of hexagonal symmetry [ 1 , 19 ] and retains the structure of sba-15 after calcination at 750c and reduction at 800c , indicating that sba-15 has good hydrothermal stability . peaks for iron are evident at 44.6 and 65 in the wide - angle xrd pattern for fe - sba-15 [ 20 , 21 ] . residual iron oxides may be a result of surface passivation , which can be explained by the following equations for reduction of fe2o3 with hydrogen : ( 1)3fe2o3+h22fe3o4+h2o , fe3o4 + 4h23fe+4h2o(1x)fe3o4+(14x)h23fe(1x)o+(14x)h2o , fe(1x)o+h2(1x)fe+h2o figure 4 shows mssbauer spectra of fe - sba-15 and table 1 shows mssbauer parameters of fe - sba-15 . from the calculation of fe mssbauer spectra , the percentage of fe , fe(ii ) , and fe(iii ) in the prepared materials were 17.0% , 64.5% , and 18.5% , respectively . the above results could also confirm that the reduction process followed the equations and the reduction was not complete under this condition . furthermore , it can be seen that the magnetic behavior of fe - sba-15 was contributed by fe3o4 . figure 5 shows nitrogen adsorption - desorption isotherms for the materials , which exhibit a typical type iv isotherm with an h1 hysteresis loop as defined by iupac . however , there was a shift in hysteresis position to lower relative pressure and a decreasing trend . the shift of the sharp inflection from p / p0 0.60 to 0.80 is characteristic of a diameter in the mesopore range [ 27 , 28 ] . the bet surface area changed from 524 to 308 m g and the pore diameter decreased from 72.8 to 72.6 on modification of sba-15 with fe . the decrease in surface area and pore diameter , probably caused by filling of the pores with small iron particles , indicates successful iron doping within the mesoporous channels of sba-15 . the pore diameter and d100 data for the two materials indicate that the mesopore uniformity of the parent sba-15 silica was retained in the modified material . large fibrous structures of 3080 m in length and 1020 m in diameter are clearly evident in figure 6 . compared to the parent sba-15 , the size of the modified material decreased on both a microscopic and macroscopic scale , suggesting that the particle size can change on ultrasonication . the tem images in figure 7 provide direct evidence that the material comprises well - ordered hexagonal arrays of mesopores ( 1d channel ) and a 2d hexagonal structure . the tem image of fe - sba-15 ( figure 6(b ) ) shows that the structure is the same as in the parent sba-15 silica . tem and xrd results also confirmed that modification occurred within pores and that the sba-15 structure did not change . the modified material retained the mesopore uniformity of the original inorganic wall structure of the parent sba-15 silica . figure 8 shows that fe - sba-15 exhibited strong magnetic behavior with a magnetization value of 8.8 emu g , confirming that fe - sba-15 was magnetic with potential as a magnetic adsorbent for removal of aromatic compounds from water . using aas data , the iron content of fe - sba-15 was calculated as a = 0.0794c + 0.0249 ( r = 0.9993 ) , where a is the sample absorbance and c is the sample concentration . the iron load was thus determined to be 19.1 wt.% in the modified material , in accordance with its strong magnetic behavior . large iron metallic particles that formed in fe - sba-15 can be observed in figure 6(b ) . after 5 min , a magnet was fixed to the vessel wall to attract the material . following the absorption process , fe - sba-15 was redispersed in methanol to desorb the aromatic compounds and the efficiency of magnetic separation was assessed by gc . analytical data for benzene , toluene , and ethyl benzene compared to standards revealed removal of 90.6% , 88.7% , and 85.4% , respectively , demonstrating that fe - sba-15 can be used as a sorbent in water . it is worth noting that fe - sba-15 can be reused after washing several times with methanol and vacuum drying . magnetic fe - sba-15 was prepared from mesoporous silica molecular sieves via a simple iron ion doping of sba-15 , transformation to fe2o3 and then reduction to magnetic iron particles using h2 . results confirm that the modified material retained the well - ordered hexagonal mesoporous structure after calcination at 800c . mesoporous silica materials may have further application potential , such as in sensing materials , solid supports , and nanobioelectronics , especially as magnetic sorbents allow the reuse of adsorbent materials for several cycles .

magnetic fe - sba-15 mesoporous silica molecular sieves were prepared , characterized , and used for magnetic separation . wet impregnation , drying , and calcination steps led to iron inclusion within the mesopores . iron oxide was reduced to the metal form with hydrogen , and the magnetic fe - sba-15 was obtained . fourier - transform infrared spectroscopy confirmed the preparation process from the oxide to metal forms . the structure of magnetic materials was confirmed by mssbauer spectra . powder x - ray diffraction data indicated that the structure of fe - sba-15 retained the host sba-15 structure . brunauer - emmett - teller analysis revealed a decrease in surface area and pore size , indicating fe - sba-15 coating on the inner surfaces . scanning electron micrographs confirmed the decrease in size for modified sba-15 particles . from scanning electron micrographs , it was found that the size of the modified sba-15 particles decreased . transmission electron micrographs also confirmed that modified sba-15 retained the structure of the parent sba-15 silica . fe - sba-15 exhibited strong magnetic properties , with a magnetization value of 8.8 emu g1 . the iron content in fe - sba-15 was determined by atom adsorption spectroscopy . fe - sba-15 was successfully used for the magnetic separation of three aromatic compounds in water . our results suggest wide applicability of fe - sba-15 magnetic materials for the rapid and efficient separation of various compounds .

<s>[INST]mesoporous sba-15 silica molecular sieves of large pore diameter ( up to 30 nm ) and area ( up to 1000 m g ) show excellent homogeneity and stability and can be well controlled for adsorption / desorption processes . mesoporous silica materials , especially mesoporous sba-15 molecular sieves , have been modified with 3-mercaptopropyl , 3-aminopropyl , octyl , or octadecyl groups for the separation and analysis of inorganic ions , organic compounds , and biological molecules [ 25 ] . magnetic separation is a useful tool because of its fast recovery , high efficiency , and low high cost . inclusion of magnetic components in modified materials allows convenient and economical magnetic separation instead of centrifugation and filtration steps on application of an appropriate magnetic field [ 79 ] . because of their potential applications in this approach , the preparation of co , co / fe , -fe2o3 , -fe2o3 , and fe3o4 magnetic sba-15 materials have been reported [ 1015 ] . we propose a convenient and effective procedure for iron doping of mesoporous sba-15 silica because of its excellent magnetic properties . then fe was transformed to the oxide form by calcination in the air . finally , ferric oxide in sba-15 was reduced with h2 [ 7 , 15 , 16 ] . fourier - transform infrared ( ft - ir ) spectroscopy , powder x - ray diffraction ( xrd ) , mssbauer spectra ( ms ) , surface area analysis , scanning electron microscopy ( sem ) , and transmission electron microscopy ( tem ) techniques were used to characterize the material . the iron content in fe - sba-15 was determined by atom adsorption spectroscopy ( aas ) . with the development of petroleum refining and chemical engineering , the release of harmful organic chemicals into the environment has attracted global attention because of their toxicity and widespread use , especially aromatic compounds considered as carcinogenic . the aim of the present study was to develop a method for preparing magnetic sba-15 for use as a sorbent to remove benzene and related derivatives from water . the adsorption of benzene , toluene , and ethyl benzene on magnetic sba-15 particles was determined by gas chromatography ( gc ) . benzene , toluene , and ethyl benzene were purchased from sigma ( st . louis , mo , usa ) . deionized water was prepared using a millipore unit ( bedford , ma , usa ) . sba-15 was soaked in 0.1 mol l hcl for 24 h , filtered , washed with deionized water , and dried in an oven at 100c for 8 h. a sample of 2 g of sba-15 was dispersed in 1 mol l fe(no3)3 solution by ultrasonication for 2 h. the material was filtered under low pressure and dried in an oven at 100c . samples were calcined in a muffle furnace at 750c for 6 h to obtain a red powder , which was then reduced under a h2 flow ( 35 ml min ) at 800c for 6 h. the final product was designated fe - sba-15 . ft - ir spectra of sba-15 particles were recorded before and after modification on a nicolet ( usa ) 360 ft - ir instrument . powder xrd patterns were measured on a d / max-2400 ( rigaku , japan ) instrument using cu k radiation . fe mssbauer spectra were collected using a conventional constant acceleration spectrometer ( wissel , german ) with a 25 m ci source of co in palladium at room temperature . the percentage of fe , fe(ii ) , and fe(iii ) were calculated and contributor of magnetic behavior was confirmed . nitrogen adsorption - desorption experiments were carried out at 76.53 k on an asap 2010 accelerated surface area and porosimetry system ( micromeritics , usa ) . the brunauer - emmett - teller ( bet ) surface area ( sbet ) was calculated from the linearity of the bet equation . the surface area , volume and pore diameter were calculated from pore size distribution curves using the barrett - joyner - halenda ( bjh ) formula . the surface morphology of powders was observed under a jsm-6380lv scanning electron microscope ( jeol , japan ) . for tem observation , samples were dispersed in ethanol , deposited on a grid of holey copper and transferred to a jem-1230 emission electron microscope ( jeol , japan ) at an accelerating voltage of 100 kv . a lakeshore ( usa ) 7304 vibrating sample magnetometer was used to record magnetization curves of the samples . a sample of 10 mg of fe - sba-15 was heated in a mixture of hydrochloric acid and nitric acid to completely dissolve the iron and transferred to a 25-ml volumetric flask and made up to volume with water . the solution was centrifuged at 10000 rpm and the iron concentration was determined on an aa-6800 instrument ( shimadzu , japan ) . standard fe solutions ( 0 , 2.0 , 4.0 , 8.0 , 10.0 g ml ) were measured to generate a standard curve . benzene , toluene , and ethyl benzene , were dissolved in deionized water at a concentration of 1.0 ppm each . then 20 mg of fe - sba-15 was added to the aqueous solution and sonicated at room temperature ( approx . 20c ) for 30 s to form a homogeneous dispersion . after standing for 5 min , fe - sba-15 finally , 1.0 l of the eluate was analyzed on a varian ( usa ) cp-3380 gas chromatograph and the content of the aromatic compounds was calculated . figure 2 shows ft - ir spectra of fe(no3)3 , sba-15 , fe(no3)3-sba-15 , fe2o3-sba-15 , and fe - sba-15 . the ir vibration for the no3 ion at 1385 cm is evident in curves a and c , but not in b , indicating that fe(no3)3-sba-15 was prepared successfully . fe2o3-sba-15 was obtained by transformation from the nitrate to the oxide form , as confirmed by the disappearance of the peak at 1385 cm after calcination ( curve d ) . the peak at 1385 cm also disappeared after fe2o3-sba-15 reduction ( curve e ) . the material was red after fe(no3)3-sba-15 calcination at 750c , suggesting that iron oxide is mainly in the form of -fe2o3 ( hematite ) . hematite is extremely stable under ambient conditions and is often the end product of the transformation of other iron oxides . xrd patterns of the materials are shown in figure 3 . in the narrow - angle range peaks for sba-15 are evident at 0.8 , 1.4 and 1.7. for fe - sba-15 , there is one prominent peak at 0.9 and two peaks at 1.5 and 1.8. these results indicate that magnetic fe - sba-15 still has a high degree of hexagonal symmetry [ 1 , 19 ] and retains the structure of sba-15 after calcination at 750c and reduction at 800c , indicating that sba-15 has good hydrothermal stability . peaks for iron are evident at 44.6 and 65 in the wide - angle xrd pattern for fe - sba-15 [ 20 , 21 ] . residual iron oxides may be a result of surface passivation , which can be explained by the following equations for reduction of fe2o3 with hydrogen : ( 1)3fe2o3+h22fe3o4+h2o , fe3o4 + 4h23fe+4h2o(1x)fe3o4+(14x)h23fe(1x)o+(14x)h2o , fe(1x)o+h2(1x)fe+h2o figure 4 shows mssbauer spectra of fe - sba-15 and table 1 shows mssbauer parameters of fe - sba-15 . from the calculation of fe mssbauer spectra , the percentage of fe , fe(ii ) , and fe(iii ) in the prepared materials were 17.0% , 64.5% , and 18.5% , respectively . the above results could also confirm that the reduction process followed the equations and the reduction was not complete under this condition . furthermore , it can be seen that the magnetic behavior of fe - sba-15 was contributed by fe3o4 . figure 5 shows nitrogen adsorption - desorption isotherms for the materials , which exhibit a typical type iv isotherm with an h1 hysteresis loop as defined by iupac . however , there was a shift in hysteresis position to lower relative pressure and a decreasing trend . the shift of the sharp inflection from p / p0 0.60 to 0.80 is characteristic of a diameter in the mesopore range [ 27 , 28 ] . the bet surface area changed from 524 to 308 m g and the pore diameter decreased from 72.8 to 72.6 on modification of sba-15 with fe . the decrease in surface area and pore diameter , probably caused by filling of the pores with small iron particles , indicates successful iron doping within the mesoporous channels of sba-15 . the pore diameter and d100 data for the two materials indicate that the mesopore uniformity of the parent sba-15 silica was retained in the modified material . large fibrous structures of 3080 m in length and 1020 m in diameter are clearly evident in figure 6 . compared to the parent sba-15 , the size of the modified material decreased on both a microscopic and macroscopic scale , suggesting that the particle size can change on ultrasonication . the tem images in figure 7 provide direct evidence that the material comprises well - ordered hexagonal arrays of mesopores ( 1d channel ) and a 2d hexagonal structure . the tem image of fe - sba-15 ( figure 6(b ) ) shows that the structure is the same as in the parent sba-15 silica . tem and xrd results also confirmed that modification occurred within pores and that the sba-15 structure did not change . the modified material retained the mesopore uniformity of the original inorganic wall structure of the parent sba-15 silica . figure 8 shows that fe - sba-15 exhibited strong magnetic behavior with a magnetization value of 8.8 emu g , confirming that fe - sba-15 was magnetic with potential as a magnetic adsorbent for removal of aromatic compounds from water . using aas data , the iron content of fe - sba-15 was calculated as a = 0.0794c + 0.0249 ( r = 0.9993 ) , where a is the sample absorbance and c is the sample concentration . the iron load was thus determined to be 19.1 wt.% in the modified material , in accordance with its strong magnetic behavior . large iron metallic particles that formed in fe - sba-15 can be observed in figure 6(b ) . after 5 min , a magnet was fixed to the vessel wall to attract the material . following the absorption process , fe - sba-15 was redispersed in methanol to desorb the aromatic compounds and the efficiency of magnetic separation was assessed by gc . analytical data for benzene , toluene , and ethyl benzene compared to standards revealed removal of 90.6% , 88.7% , and 85.4% , respectively , demonstrating that fe - sba-15 can be used as a sorbent in water . it is worth noting that fe - sba-15 can be reused after washing several times with methanol and vacuum drying . magnetic fe - sba-15 was prepared from mesoporous silica molecular sieves via a simple iron ion doping of sba-15 , transformation to fe2o3 and then reduction to magnetic iron particles using h2 . results confirm that the modified material retained the well - ordered hexagonal mesoporous structure after calcination at 800c . mesoporous silica materials may have further application potential , such as in sensing materials , solid supports , and nanobioelectronics , especially as magnetic sorbents allow the reuse of adsorbent materials for several cycles .[/INST]magnetic fe - sba-15 mesoporous silica molecular sieves were prepared , characterized , and used for magnetic separation . wet impregnation , drying , and calcination steps led to iron inclusion within the mesopores . iron oxide was reduced to the metal form with hydrogen , and the magnetic fe - sba-15 was obtained . fourier - transform infrared spectroscopy confirmed the preparation process from the oxide to metal forms . the structure of magnetic materials was confirmed by mssbauer spectra . powder x - ray diffraction data indicated that the structure of fe - sba-15 retained the host sba-15 structure . brunauer - emmett - teller analysis revealed a decrease in surface area and pore size , indicating fe - sba-15 coating on the inner surfaces . scanning electron micrographs confirmed the decrease in size for modified sba-15 particles . from scanning electron micrographs , it was found that the size of the modified sba-15 particles decreased . transmission electron micrographs also confirmed that modified sba-15 retained the structure of the parent sba-15 silica . fe - sba-15 exhibited strong magnetic properties , with a magnetization value of 8.8 emu g1 . the iron content in fe - sba-15 was determined by atom adsorption spectroscopy . fe - sba-15 was successfully used for the magnetic separation of three aromatic compounds in water . our results suggest wide applicability of fe - sba-15 magnetic materials for the rapid and efficient separation of various compounds .</s>

gene - expression profiling allows simultaneous , semi - quantitative measurements of thousands of different mrna species in a single experiment . it was considered logical to assume that different cancers will have distinct gene - expression patterns and that the expression of many genes will be associated with clinically relevant disease outcomes in particular cancer types . consequently , it was assumed these associations might be exploited to develop a new generation of multi - gene diagnostic tests , in particular prognostic and treatment response predictors . it has quickly become apparent that cancers of different organs have very different gene - expression patterns ; indeed , this fact led to the development of a novel gene - expression - based molecular diagnostic test to assign a histological origin to metastatic cancers that present as ' cancers of unknown primary ' . gene - expression profiling results also prompted re - evaluation of disease classification for certain tumors , most prominently breast cancer . breast cancer used to be considered as a single disease with variable histological appearance and variable expression of estrogen receptor ( er ) and other molecular markers . gene - expression profiling studies revealed surprisingly large - scale molecular differences between er - positive and er - negative cancers that suggested that these two different types of breast cancers are distinct diseases [ 2 - 4 ] . a new molecular classification schema was proposed , but how many molecular classes there are and what method is best to assign these classes continues to be debated . currently , there is no standard , readily available , gene - expression - based test to determine the molecular class of breast cancer in the clinic the goal of this analysis is to identify disease subsets that show similar gene - expression patterns within a larger cohort of cases . during this analysis , consequently , the emerging molecular subsets may or may not differ in prognosis or response to various therapies . a parallel research effort has focused on developing supervised outcome predictors . this approach relies on comparing cases with known outcome ( such as recurrence versus no recurrence ) . the goal of the analysis is to identify differentially expressed genes between outcome groups and use these genes to develop a multi - gene outcome predictor . investigators who developed the first generation of supervised prognostic and treatment response predictors started with the then prevailing notion that breast cancer is a single disease , and all subtypes of breast cancer were included in the analysis . unsupervised molecular classification identified three major and robust groups of breast cancers that differ in the expression of several hundred to a few thousand genes . these include basal - like breast cancers , which are negative for er , progesterone receptor ( pr ) and human epidermal growth factor receptor 2 ( her2 ) ; low histological grade er - positive breast cancers ( also called luminal a ) ; and high grade , highly proliferative er - positive cancers ( luminal b ) . several smaller and less stable molecular subsets ( such as normal - like , her-2-positive and claudin - low ) have also been proposed but are less consistently seen and are distinguished by substantially smaller molecular differences . importantly , among the various molecular subsets , one group , the luminal a class that includes low grade er - positive cancers , stands out with a very favorable prognosis with or without adjuvant endocrine therapy . if one understands these close associations between clinical phenotype , molecular class and prognosis , it is no longer surprising that comparing gene - expression profiles of breast cancers that recurred ( mostly the er - negative and the high grade , er - positive cancers ) and those that did not ( low grade , er - positive cancers ) in the absence of any systemic therapy ( or after anti - estrogen therapy alone in the case of er - positive cancers ) yields a very large number of differentially expressed genes . the relative position of individual genes in a rank - ordered gene list varies greatly , but the consistency of the gene list membership is fairly high across various datasets . functional annotation indicates that the majority of these prognostic genes are proliferation - related genes and the remainder are mostly er - associated and , to a lesser extent , immune - related genes [ 10 - 12 ] . because these genes function together in a coordinated manner in the regulation and execution of complex biological processes , such as cell proliferation , or originate from a particular cell type , such as immune cell infiltrate , it is therefore expected that a large number of nominally different prognostic signatures can be constructed that all perform equally well . for example , a particular gene may be highly significantly discriminating in two datasets but it is ranked 5th among the most discriminating genes in one dataset ( based on p - value or fold difference ) but only 35th in another dataset ( which is still very high considering the thousands of comparisons ! ) . in multivariate prediction model building , the top few informative features are usually combined and genes are added incrementally to increase the predictive performance . however , because many of the genes are highly correlated with each other , adding genes lower on the list yields less and less improvement in the model as a result of lack of independence . therefore , the gene in question will be included in a predictor developed from the first dataset ( because it is ranked as 5th ) and will work well on validation in the second dataset ; but if a new predictor were to be developed from the second dataset , this gene may not be included in the predictor ( because it is ranked 35th ) . these three features of the breast cancer prognostic gene space - the large number of individually prognostic features , the unstable rankings , and the highly correlated expression of informative genes - explain why it is easy to construct many different prognostic predictors that perform equally well even if they rely on nominally different genes in the model . however , this does not mean that all published prognostic gene signatures are equally ready for clinical use . before adoption in the clinic , a molecular diagnostic assay has to be standardized , the reproducibility within and between laboratories and stability of results over time have to be demonstrated , and its predictive accuracy has to be validated in the right clinical context , preferably in multiple independent cohorts of patients . most importantly , clinical utility implies that the assay improves clinical decision making and complements or replaces older standard methods , which in turn leads to better patient outcomes . the predictive performance of a multivariate model largely depends on the number of independent informative genes included in the model , the magnitude of differential expression of the informative genes and the complexity of the background . should be apparent that prediction of er status , histological grade of breast cancer , or better or worse prognosis associated with these clinical phenotypes should be relatively easy when considering all breast cancers together , and that such predictions can therefore yield predictors with good overall accuracy . indeed , prognostic gene signatures developed for breast cancer in general or for er - positive cancers tend to have good performance characteristics [ 12,15 - 17 ] . however , the first - generation prognostic signatures share some limitations . because these were invariably developed by analyzing all subtypes of breast cancers together , they tend to assign high risk category to almost all er - negative cancers ( which are almost always high grade ) , even though a substantial majority of these cancers have good prognosis . similarly , the good- and poor - prognosis er - positive cancers , as assigned by gene profiling , tend to correspond to the clinically low grade / low proliferation versus high grade / high proliferation subsets , respectively . this strong correlation between prognostic risk as predicted by gene signatures and routine clinical variables , such as histological grade , proliferation rate and er status , limits the practical value of these tests . efforts are under way to develop simple multivariate prognostic models that use routine pathological variables ( such as er , histologic grade and her2 status ) , and these could eventually rival the performance of the first - generation prognostic gene signatures . however , standardization of the pathological assessment of breast cancer and reducing the inter - observer variability remains an important challenge . predicting clinical outcome , such as prognosis or response to chemotherapy , within clinically and molecularly more homogeneous subsets ( such as triple - negative breast cancers or high grade , er - positive cancers ) would be highly desirable . it seems that fewer genes are associated with outcome in homogeneous disease subsets and the magnitude of association is modest when currently available datasets are analyzed . this leads to predictors that are specific for a particular dataset from which they were developed . these prediction models are fitted to the dataset and rely on features that have no or limited generalizability . this means that they fail to validate when applied to independent data or may demonstrate only nominally significant predictive value ( that is , they may predict outcome slightly better than chance ) . for example , if the good - prognosis group has a recurrence rate of 30% compared with 50% in the poor - risk group , these may be significantly different but the risk of recurrence in the good - risk group is still too high to safely forego adjuvant chemotherapy . it seems that for certain clinical prediction problems , the currently available breast cancer gene - expression datasets may not contain enough information to be able to develop highly accurate predictors . this may reflect limitations of the sample sizes for the subsets of interest and , as more data become available , the empirically developed models may improve . however , it is also possible that major advances will need to take place in our understanding of how the 10,000 to 12,000 genes expressed in breast cancer interact before we can construct more accurate prediction models . current statistical methods can not readily adjust for different levels of gene - expression change that may be required for a functional effect . the level of expression change that results in a functional change may be different from gene to gene : for some genes a 15 to 20% increase in mrna expression level may lead to functional consequences , whereas for others a 100 to 150% change may be needed . new bioinformatics approaches , such as examining the information content of the correlation matrix of gene - expression values or applying network analysis tools to the data , may also reveal additional prognostic information that is not readily revealed by studying gene - expression levels alone . new analytical platforms , such as next generation sequencing , will generate more comprehensive expression data than the current array - based methods and will also yield extensive nucleotide sequence information . the information content of these currently nascent datasets may be highly relevant to prognosis or treatment response of cancers and certainly warrants further exploration . the predictive performance of multi - gene signatures depends on the number and robustness of informative genes that are associated with the outcome to be predicted . for example , it is possible to predict the prognosis of er - positive breast cancers relatively accurately because prognosis is closely related to the proliferative status of these cancers and proliferation affects the expression of several hundreds of genes that regulate and execute cell division . not surprisingly , several different models that use different genes and different algorithms can be built with each performing similarly . on the other hand , predicting response to individual drugs based on gene - expression signatures has proved substantially more difficult . fewer genes are significantly associated with these outcomes , measured on current analytical platforms ( gene - expression arrays ) , and therefore prediction models invariably contain substantial amounts of ' noise ' ( predictive features that are specific to the dataset , not the actual outcome ) and have poorer predictive performance on independent datasets . larger datasets and new analytical platforms ( such as next generation sequencing ) that broaden the portfolio of variables that can be used for model building are expected to lead to improved predictors for these currently difficult classification problems . er : estrogen receptor ; her2 : human epidermal growth factor receptor 2 ; pr : progesterone receptor .

a large number of prognostic and predictive signatures have been proposed for breast cancer and a few of these are now available in the clinic as new molecular diagnostic tests . however , several other signatures have not fared well in validation studies . some investigators continue to be puzzled by the diversity of signatures that are being developed for the same purpose but that share few or no common genes . the history of empirical development of prognostic gene signatures and the unique association between molecular subsets and clinical phenotypes of breast cancer explain many of these apparent contradictions in the literature . three features of breast cancer gene expression contribute to this : the large number of individually prognostic genes ( differentially expressed between good and bad prognosis cases ) ; the unstable rankings of differentially expressed genes between datasets ; and the highly correlated expression of informative genes .

<s>[INST]gene - expression profiling allows simultaneous , semi - quantitative measurements of thousands of different mrna species in a single experiment . it was considered logical to assume that different cancers will have distinct gene - expression patterns and that the expression of many genes will be associated with clinically relevant disease outcomes in particular cancer types . consequently , it was assumed these associations might be exploited to develop a new generation of multi - gene diagnostic tests , in particular prognostic and treatment response predictors . it has quickly become apparent that cancers of different organs have very different gene - expression patterns ; indeed , this fact led to the development of a novel gene - expression - based molecular diagnostic test to assign a histological origin to metastatic cancers that present as ' cancers of unknown primary ' . gene - expression profiling results also prompted re - evaluation of disease classification for certain tumors , most prominently breast cancer . breast cancer used to be considered as a single disease with variable histological appearance and variable expression of estrogen receptor ( er ) and other molecular markers . gene - expression profiling studies revealed surprisingly large - scale molecular differences between er - positive and er - negative cancers that suggested that these two different types of breast cancers are distinct diseases [ 2 - 4 ] . a new molecular classification schema was proposed , but how many molecular classes there are and what method is best to assign these classes continues to be debated . currently , there is no standard , readily available , gene - expression - based test to determine the molecular class of breast cancer in the clinic the goal of this analysis is to identify disease subsets that show similar gene - expression patterns within a larger cohort of cases . during this analysis , consequently , the emerging molecular subsets may or may not differ in prognosis or response to various therapies . a parallel research effort has focused on developing supervised outcome predictors . this approach relies on comparing cases with known outcome ( such as recurrence versus no recurrence ) . the goal of the analysis is to identify differentially expressed genes between outcome groups and use these genes to develop a multi - gene outcome predictor . investigators who developed the first generation of supervised prognostic and treatment response predictors started with the then prevailing notion that breast cancer is a single disease , and all subtypes of breast cancer were included in the analysis . unsupervised molecular classification identified three major and robust groups of breast cancers that differ in the expression of several hundred to a few thousand genes . these include basal - like breast cancers , which are negative for er , progesterone receptor ( pr ) and human epidermal growth factor receptor 2 ( her2 ) ; low histological grade er - positive breast cancers ( also called luminal a ) ; and high grade , highly proliferative er - positive cancers ( luminal b ) . several smaller and less stable molecular subsets ( such as normal - like , her-2-positive and claudin - low ) have also been proposed but are less consistently seen and are distinguished by substantially smaller molecular differences . importantly , among the various molecular subsets , one group , the luminal a class that includes low grade er - positive cancers , stands out with a very favorable prognosis with or without adjuvant endocrine therapy . if one understands these close associations between clinical phenotype , molecular class and prognosis , it is no longer surprising that comparing gene - expression profiles of breast cancers that recurred ( mostly the er - negative and the high grade , er - positive cancers ) and those that did not ( low grade , er - positive cancers ) in the absence of any systemic therapy ( or after anti - estrogen therapy alone in the case of er - positive cancers ) yields a very large number of differentially expressed genes . the relative position of individual genes in a rank - ordered gene list varies greatly , but the consistency of the gene list membership is fairly high across various datasets . functional annotation indicates that the majority of these prognostic genes are proliferation - related genes and the remainder are mostly er - associated and , to a lesser extent , immune - related genes [ 10 - 12 ] . because these genes function together in a coordinated manner in the regulation and execution of complex biological processes , such as cell proliferation , or originate from a particular cell type , such as immune cell infiltrate , it is therefore expected that a large number of nominally different prognostic signatures can be constructed that all perform equally well . for example , a particular gene may be highly significantly discriminating in two datasets but it is ranked 5th among the most discriminating genes in one dataset ( based on p - value or fold difference ) but only 35th in another dataset ( which is still very high considering the thousands of comparisons ! ) . in multivariate prediction model building , the top few informative features are usually combined and genes are added incrementally to increase the predictive performance . however , because many of the genes are highly correlated with each other , adding genes lower on the list yields less and less improvement in the model as a result of lack of independence . therefore , the gene in question will be included in a predictor developed from the first dataset ( because it is ranked as 5th ) and will work well on validation in the second dataset ; but if a new predictor were to be developed from the second dataset , this gene may not be included in the predictor ( because it is ranked 35th ) . these three features of the breast cancer prognostic gene space - the large number of individually prognostic features , the unstable rankings , and the highly correlated expression of informative genes - explain why it is easy to construct many different prognostic predictors that perform equally well even if they rely on nominally different genes in the model . however , this does not mean that all published prognostic gene signatures are equally ready for clinical use . before adoption in the clinic , a molecular diagnostic assay has to be standardized , the reproducibility within and between laboratories and stability of results over time have to be demonstrated , and its predictive accuracy has to be validated in the right clinical context , preferably in multiple independent cohorts of patients . most importantly , clinical utility implies that the assay improves clinical decision making and complements or replaces older standard methods , which in turn leads to better patient outcomes . the predictive performance of a multivariate model largely depends on the number of independent informative genes included in the model , the magnitude of differential expression of the informative genes and the complexity of the background . should be apparent that prediction of er status , histological grade of breast cancer , or better or worse prognosis associated with these clinical phenotypes should be relatively easy when considering all breast cancers together , and that such predictions can therefore yield predictors with good overall accuracy . indeed , prognostic gene signatures developed for breast cancer in general or for er - positive cancers tend to have good performance characteristics [ 12,15 - 17 ] . however , the first - generation prognostic signatures share some limitations . because these were invariably developed by analyzing all subtypes of breast cancers together , they tend to assign high risk category to almost all er - negative cancers ( which are almost always high grade ) , even though a substantial majority of these cancers have good prognosis . similarly , the good- and poor - prognosis er - positive cancers , as assigned by gene profiling , tend to correspond to the clinically low grade / low proliferation versus high grade / high proliferation subsets , respectively . this strong correlation between prognostic risk as predicted by gene signatures and routine clinical variables , such as histological grade , proliferation rate and er status , limits the practical value of these tests . efforts are under way to develop simple multivariate prognostic models that use routine pathological variables ( such as er , histologic grade and her2 status ) , and these could eventually rival the performance of the first - generation prognostic gene signatures . however , standardization of the pathological assessment of breast cancer and reducing the inter - observer variability remains an important challenge . predicting clinical outcome , such as prognosis or response to chemotherapy , within clinically and molecularly more homogeneous subsets ( such as triple - negative breast cancers or high grade , er - positive cancers ) would be highly desirable . it seems that fewer genes are associated with outcome in homogeneous disease subsets and the magnitude of association is modest when currently available datasets are analyzed . this leads to predictors that are specific for a particular dataset from which they were developed . these prediction models are fitted to the dataset and rely on features that have no or limited generalizability . this means that they fail to validate when applied to independent data or may demonstrate only nominally significant predictive value ( that is , they may predict outcome slightly better than chance ) . for example , if the good - prognosis group has a recurrence rate of 30% compared with 50% in the poor - risk group , these may be significantly different but the risk of recurrence in the good - risk group is still too high to safely forego adjuvant chemotherapy . it seems that for certain clinical prediction problems , the currently available breast cancer gene - expression datasets may not contain enough information to be able to develop highly accurate predictors . this may reflect limitations of the sample sizes for the subsets of interest and , as more data become available , the empirically developed models may improve . however , it is also possible that major advances will need to take place in our understanding of how the 10,000 to 12,000 genes expressed in breast cancer interact before we can construct more accurate prediction models . current statistical methods can not readily adjust for different levels of gene - expression change that may be required for a functional effect . the level of expression change that results in a functional change may be different from gene to gene : for some genes a 15 to 20% increase in mrna expression level may lead to functional consequences , whereas for others a 100 to 150% change may be needed . new bioinformatics approaches , such as examining the information content of the correlation matrix of gene - expression values or applying network analysis tools to the data , may also reveal additional prognostic information that is not readily revealed by studying gene - expression levels alone . new analytical platforms , such as next generation sequencing , will generate more comprehensive expression data than the current array - based methods and will also yield extensive nucleotide sequence information . the information content of these currently nascent datasets may be highly relevant to prognosis or treatment response of cancers and certainly warrants further exploration . the predictive performance of multi - gene signatures depends on the number and robustness of informative genes that are associated with the outcome to be predicted . for example , it is possible to predict the prognosis of er - positive breast cancers relatively accurately because prognosis is closely related to the proliferative status of these cancers and proliferation affects the expression of several hundreds of genes that regulate and execute cell division . not surprisingly , several different models that use different genes and different algorithms can be built with each performing similarly . on the other hand , predicting response to individual drugs based on gene - expression signatures has proved substantially more difficult . fewer genes are significantly associated with these outcomes , measured on current analytical platforms ( gene - expression arrays ) , and therefore prediction models invariably contain substantial amounts of ' noise ' ( predictive features that are specific to the dataset , not the actual outcome ) and have poorer predictive performance on independent datasets . larger datasets and new analytical platforms ( such as next generation sequencing ) that broaden the portfolio of variables that can be used for model building are expected to lead to improved predictors for these currently difficult classification problems . er : estrogen receptor ; her2 : human epidermal growth factor receptor 2 ; pr : progesterone receptor . [/INST]a large number of prognostic and predictive signatures have been proposed for breast cancer and a few of these are now available in the clinic as new molecular diagnostic tests . however , several other signatures have not fared well in validation studies . some investigators continue to be puzzled by the diversity of signatures that are being developed for the same purpose but that share few or no common genes . the history of empirical development of prognostic gene signatures and the unique association between molecular subsets and clinical phenotypes of breast cancer explain many of these apparent contradictions in the literature . three features of breast cancer gene expression contribute to this : the large number of individually prognostic genes ( differentially expressed between good and bad prognosis cases ) ; the unstable rankings of differentially expressed genes between datasets ; and the highly correlated expression of informative genes .</s>

half - doped perovskite manganites re@xmath3a@xmath3mno@xmath4 ( re - rare earth , a - alkaline earth ) exhibit very specific properties quite different from manganites with other @xmath5 electron concentrations.@xcite generally , for large size re and a cations or when external pressure is applied@xcite these compounds are in the a - type antiferromagnetic ( af ) , metallic state at low temperatures showing no or only weak sign of charge ordering , and the occupied @xmath5 electron states are predominantly @xmath6 like . recently it has been reported that the a - phase may develop an intrinsic charge - stripe modulation , which controls the transport properties.@xcite with decreasing size of the cations , which implies a decrease of the bandwidth , charge ordering is observed which at lower temperatures is accompanied by the formation of peculiar ferromagnetic ( fm ) zigzag chains@xcite that are staggered antiferromagnetically . this ce spin order , a notation introduced in the pioneering work of wollan and koehler@xcite and goodenough@xcite , is accompanied by a checkerboard charge order ( co ) and directed occupied orbitals on the mn@xmath7 sites amplifying double exchange ( de ) along one lattice diagonal . the ce - structure is a particularly fascinating manifestation of the control of magnetic order due to the orbital degree of freedom@xcite in combination with charge ordering . although a number of approaches have been followed to explain this structure , the mechanism for its stability is still not clear and hotly debated with emphasis put on the role of the de,@xcite the coulomb interaction,@xcite or the coupling to the lattice degrees of freedom.@xcite the ce phase has been observed experimentally both in cubic ( nd , pr)@xmath3(sr , ca)@xmath3mno@xmath4@xcite and in layered lasr@xmath8mn@xmath8o@xmath9@xcite and la@xmath3sr@xmath10mno@xmath11@xcite manganites . in some cases it can coexist with the a - type af spin ordering.@xcite regarding co in the ce phase , some experiments are interpreted in terms of almost perfect co @xcite while others@xcite are considered to be consistent with a smooth charge density wave ( cdw ) of the @xmath5 electron density . although , it is plausible that the complex spin and orbital arrangement in the charge - ordered manganites can result from the competition between de@xcite and af superexchange interactions ( @xmath12 ) , the role played by the co and jahn - teller ( jt ) interactions@xcite in the system is still unclear . finally in systems like e.g. pr@xmath3ca@xmath3mno@xmath4 co and ce - type orbital correlations are found to develop well above the neel temperature@xcite or even coexist with fm spin state,@xcite which indicates that these orbital correlations are not primarily driven by magnetic interactions . this work focuses on a microscopic understanding of the stability of the ce - phase which appears to be the ground state of narrow band manganites at and near quarter - filling . we argue here that the key interaction , apart from the nearest - neighbor coulomb repulsion @xmath13 which supports the charge ordering,@xcite is the next - nearest neighbor jt interaction . this interaction between orbitals at next - nearest neighbor mn@xmath7 ions emerges from the jt - distortions of the mn@xmath7 octahedra which is amplified by the breathing distortion of the intermediate mn@xmath14 octahedra . we show that this interaction generates a narrow regime in the @xmath13-@xmath15 phase diagram where the ce - phase ( and sometimes the c - phase ) is stable . otherwise one encounters a homogeneous fm phase at small @xmath15 fully controlled by de and a conventional nearest - neighbor af phase at larger @xmath15 . an important feature of further neighbor jt interactions are the displacements of the mn@xmath14 ions . we are only aware of work by radaelli _ _ et al.__@xcite where detailed lattice coordinates for the ce - phase in la@xmath3ca@xmath3mno@xmath4 are reported . in particular they observed that the 4 planar o(2 ) move towards the mn@xmath14 ion and the mn@xmath14 ions are found to be displaced from their regular perovskite positions , while the mn@xmath7 ions are not shifted . this observation confirms the importance of the breathing distortion and also shows the mechanism of the further neighbor jt - distortion in the ce - phase . as a consequence the appearance of new bragg reflections in the ce - phase would be associated not primarily with quadrupolar electronic orbital order but rather with the displacements of ions associated with the ce orbital order.@xcite an alternative long - ranged jt based interaction was recently proposed by khomskii and kugel@xcite and by calderon , millis and ahn.@xcite they employ elasticity theory to derive the orbital interaction between jt - distorted mn@xmath7o@xmath16 octahedra for the perfectly charge ordered case . we have also investigated the consequences of this interaction . our numerical simulations confirm the estimate presented in ref . that for perfect charge ordering the af ce phase is stable . yet in this model this requires large nearest neighbor coulomb repulsion @xmath13 , while for moderate values of @xmath13 the ce phase gets unstable . the finite temperature diagonalization@xcite used in our study allows to include the full interplay of spin and orbital states , and to monitor the onset of different orders as function of temperature . this gives us the ability for an unbiased investigation of the formation of different spin - orbital orderings emerging from all multi - electron configurations in the cluster . in this paper we concentrate on the stability and temperature dependence of spin , orbital , and charge ordered states in the two - dimensional ( 2d ) realistic model for half - doped manganites . in our microscopic spin - orbital model co develops as a result of nearest - neighbor coulomb repulsion @xmath13 and as a consequence of further neighbor jt interactions , while the spin - orbital order results from the competition between de ( i.e. kinetic energy ) , af superexchange and further neighbor jt interactions . as shown in sec . [ sec : nnnjt ] the latter interaction can lead to a co state at low temperatures even in the absence of inter - site coulomb repulsion . furthermore we argue that a topological sign in the hopping amplitudes of @xmath5 orbitals@xcite invoked in one - dimensional ( 1d ) models for the ce phase is not sufficient to explain the formation of ce spin - orbital structure in the 2d model studied by us . further motivations to put effort in a better understanding of the interplay of spin , charge , orbitals and lattice in the formation of the ce - phase are the following : it has been argued that the intrinsic mechanism that leads to colossal magnetoresistance are tendencies towards ce - type charge and orbital ordering in the vicinity of @xmath17.@xcite furthermore a ce - insulator to fm - metal transition has been observed in relatively small magnetic field , which is accompanied by a major change of the optical conductivity on a surprisingly large energy scale ( @xmath18 ev).@xcite such dramatic changes in relatively weak magnetic fields are a clear manifestation of the subtle interplay between spin , orbital and co. the present study provides a basis for further investigations of the temperature dependence of e.g. the optical conductivity and the study of spin and orbital excitations in the ce - phase , as well as the effect of doping into the quarter filled state . the paper is organized as follows . in sec . [ sec : model ] we present the model hamiltonian , and describe in sec . [ sec : lanczos ] the finite - temperature lanczos method . [ sec : numerics ] contains numerical results for different two - site correlation functions characterizing the charge , orbital and spin structure . these correlation functions are evaluated as functions of temperature and collected in a form of semi - quantitative phase diagrams in three different regimes : ( i ) including nearest - neighbor effective orbital - orbital ( oo ) interactions ( sec . [ sec : nnjt ] ) ; ( ii ) assuming the elastic form of oo coupling at different distances ( sec . [ sec : elastic ] ) ; ( iii ) considering the local form of next- and nearest - neighbor oo coupling ( sec . [ sec : nnnjt ] ) , while in sec . [ sec : stacking ] the effect of charge stacking is discussed . the paper is summarized in sec . [ sec : summary ] . in the appendix the stability of the ce versus the c phase is analysed for a 1d band model with lifted orbital degeneracy . we consider the generic fm kondo lattice model for manganites@xcite with the mn @xmath5 electrons coupled to the core @xmath0 spins via the hund coupling @xmath19 . the model is augmented by inter - site coulomb repulsion @xmath13 and cooperative jt interactions and treated in the limit of infinite on - site coulomb repulsion between two @xmath5 electrons on the same site ( @xmath20 ) : @xmath21 the first term describes the motion of the @xmath5 electrons , @xmath22 with a constraint that allows only for mn@xmath14 and mn@xmath7 configurations , @xmath23 , where all other alternative @xmath5 states are projected out . here and in the following the index @xmath24 ( @xmath25 ) denotes the @xmath5 orbital ( spin ) orthogonal to the @xmath26 ( @xmath27 ) one , respectively . the hopping matrix elements depend on the basis chosen . for the basis @xmath28 with @xmath29 and @xmath30 they are given by , @xmath31=\frac{t}{4}\left ( \begin{array}{cc } 3 & \mp\sqrt{3}\\ \mp\sqrt{3 } & 1 \end{array}\right ) , \ ] ] where , @xmath32(@xmath33 ) refer to the @xmath34(@xmath35 ) direction , respectively . the second term of hamiltonian ( [ eq : h_total ] ) stands for the hund interaction between @xmath5 electrons spin and the @xmath36 @xmath0 core spin @xmath37 , @xmath38 resulting in the parallel alignment of spins between @xmath0 and @xmath5 electrons at each site in the limit @xmath39 which corresponds to the realistic situation in manganites . the @xmath40 part of the total hamiltonian alone represents the de mechanism and yields a fm ground state with @xmath41 orbitals being occupied which is favored by the kinetic energy in 2d model . such a fully spin polarized case at finite @xmath42 leads to _ the orbital @xmath43-@xmath44 model _ as considered in refs . . here , we are interested in the more complex case where both spin and orbital degrees of freedom play an active role . therefore , an af ( @xmath45 ) coupling between nearest - neighbor @xmath0 spins is also incorporated , @xmath46 in our numerical studies we assume @xmath47 for the core spins which decreases the resulting hilbert space considerably . we have tested that this assumption gives similar results as in the @xmath36 case when @xmath19 is renormalized@xcite by the factor @xmath48 . moreover , to promote the charge ordering as observed experimentally in half - doped manganites we include the coulomb repulsion ( @xmath49 ) between @xmath5 electrons on neighboring sites,@xcite @xmath50 with @xmath51 . this term reduces the probability of occupancy of neighboring sites by @xmath5 electrons . the form of the inter - site oo interactions included in the @xmath52 term of the hamiltonian will be specified in the following section . to investigate the possible spin and orbital orderings in our spin - orbital model ( [ eq : h_total ] ) we have calculated the temperature dependence of different two - site correlation functions given by the operator expectation value : @xmath53 of two - site operators , @xmath54 with @xmath55 , @xmath56 , @xmath57 , or @xmath58 with @xmath59.@xcite here , @xmath60 , @xmath61 is the number of basis states @xmath62 that span @xmath63 , @xmath64 number of sites in the cluster and @xmath65 is the partition function . the calculation of ( [ eq : a_r_exact ] ) would , however , require a complete diagonalization of a @xmath66 matrix of the hamiltonian . therefore , we use for the calculation of @xmath67 a generalization of the exact diagonalization technique developed by jakli and prelovek.@xcite in this approach the trace of the thermodynamic expectation value is performed by a monte carlo sampling leading to the following approximate expression : @xmath68 where the first sum is performed over a restricted number @xmath69 of random states @xmath70 being initial states in the lanczos algorithm to generate a set @xmath71 of eigenfunctions of @xmath63 with respective eigenvalues @xmath72 . @xmath73 is the number of lanczos functions in the expansion of a given state @xmath70 . in the same manner the partition function is approximated by , @xmath74 it has been shown@xcite that the results get very accurate already for @xmath69 , @xmath75 . even though we exploit the translational symmetry the calculations are restricted to small clusters ( @xmath76 is used in this paper ) as only @xmath77 subspaces can be treated separately , while a similar symmetry in the orbital sector does not exist . although a @xmath78 cluster is large enough to capture the ce - type correlations , boundary conditions can influence further neighbor interactions . to assess such finite size effects quantitatively , a full diagonalization on larger clusters would be necessary . in the case of the co ce phase this would involve at least a @xmath79 site cluster , which is far beyond numerical realization . in the numerical studies we assume @xmath47 for the core spins and the limit of strong hund s coupling @xmath80 . the numerical results are almost identical for all @xmath81 in the whole range of temperatures considered by us . the coulomb repulsion @xmath82 and the af - exchange @xmath83 are free parameters , and the data is summerized in form of a phase diagram in the @xmath84 plane . the hopping parameter @xmath43 is chosen as energy unit . we focus in this study on co states and thus assume finite positive values for @xmath13 in all the calculations . in perovskite manganites the effective hopping @xmath43 strongly depends on the lattice parameters and distortions _ e.g. _ increases with contraction of the mn@xmath33o bond length and also depends on the mn@xmath33o@xmath33mn bond angle.@xcite thus , its value can be only roughly estimated as @xmath85ev.@xcite a major difficulty when searching for spin structures like those indicated in fig . [ fig : spins ] , and the same applies to charge and orbital order , is that in a cluster with periodic boundary conditions translational ( and rotational ) symmetries are not broken . therefore we have to investigate correlation functions and compare their features with the different spin configurations ( presented in fig . [ fig : spins ] ) . schematic view of different spin patterns found in the 2d model in presence of checkerboard co ( half - doped case ) . thick ( thin ) arrows represent states with total spin @xmath86 ( @xmath36 ) with ( without ) an @xmath5 electron present at a given site , respectively . the shaded lines in c and ce phases indicate the direction of de carrier propagation . the preferred directional @xmath5 orbitals occupied at sites @xmath86 are parallel to the shaded paths.,width=226 ] we shall consider three different forms for the orbital interaction term @xmath52 and show that one has to go beyond the nearest - neighbor interactions to obtain the ce - type correlations . we begin the description of our calculations with a simplified model ( without @xmath87 term ) but including the crystal - field splitting of @xmath5 orbitals @xmath88 , @xmath89 where @xmath90 is the @xmath91 component of the pseudospin operator . this orbital splitting accounts for the elongation of octahedra along the c - axis in layered compounds , which favors @xmath92 over @xmath41 orbital occupation , and also counterbalances the trend towards occupation of @xmath41 orbitals , which is strongly favored by the kinetic energy in the 2d - model . although , the model without @xmath87 interactions can lead to the stability of the ce - type orbital pattern,@xcite the magnetic structure was fm . in a wide range of parameters @xmath93 , @xmath94 , @xmath95 no stabilization of the af ce spin phase was found , indicating that the inter - chain coupling is quite strong and can not be neglected in realistic models for half - doped co manganites . such a conclusion agrees this recent density - functional calculations showing a considerable band dispersion normal to the chains.@xcite thus , we argue that the _ topological effect _ considered in 1d model approximations , which gave a simple explanation of the existence of the ce spin - orbital phase at half - doping , is not likely to be the decisive mechanism in a more realistic 2d case investigated here . our simulations with purely electronic interactions do not provide evidence for 1d fm chains that are coupled antiferromagnetically to neighbor chains , which is the basic assumption that could justify such 1d models . therefore , in the following sections we concentrate on the electron - lattice coupling@xcite and present a mechanism stabilizing the ce spin / orbital state in manganites . phase diagram indicating the character of the dominant spin correlations found at small temperatures @xmath96 . the calculations include the nearest - neighbor oo effective interactions ( @xmath97 ) . @xmath98 indicates representative points for which the correlation functions are presented below.,width=132 ] the first aim of our study of the spin - orbital model ( [ eq : h_total ] ) in half - doped manganites is to investigate the role of nearest - neighbor oo coupling played in co state . there are two different mechanisms contributing to this interaction : ( i ) the cooperative jt effect@xcite and ( ii ) superexchange interactions.@xcite neglecting more complex spin - orbital terms@xcite both effects can be described by the following simple term derived before for undoped lamno@xmath4 compound,@xcite @xmath99 where the two - site orbital operator , @xmath100 , between nearest - neighbor mn sites in the @xmath28 basis , @xmath101 is described in terms of pseudospin operators : @xmath102 , and @xmath103 . the prefactor of the mixed term @xmath104 is negative in the @xmath34 direction and positive in the @xmath35 direction . the nearest - neighbor oo term can lead to _ attraction _ of electrons on neighboring sites with different orbital orientations but having the coulomb repulsion ( [ eq : h_v ] ) included in the model we avoid phase separation . temperature dependence of the charge ( a ) , orbital ( b ) , and spin ( c ) two - site correlation functions calculated for neighbors at different distances @xmath105 for the phase with fm spin correlations . parameters : @xmath106 , @xmath97 , @xmath107 , @xmath108.,width=377 ] temperature dependence of the correlations as in fig . but for the phase with af spin correlations . parameters : @xmath109 , @xmath97 , @xmath110 , @xmath108.,width=377 ] temperature dependence of the charge ( a ) , orbital ( b ) , and spin - charge ( c ) correlation functions calculated for the phase with c spin correlations . parameters : @xmath106 , @xmath97 , @xmath111 , @xmath108.,width=377 ] as shown in fig . [ fig : oonn_phase ] for large values of the superexchange interaction between core spins ( @xmath112 ) an af spin ground state is realized while with decreasing @xmath15 the kinetic energy of the @xmath5 electrons ( @xmath113 ) starts to play an active role via the de mechanism@xcite breaking some of the af bonds which leads to 1d fm chains which form straight lines ( c phase ) . further decrease of @xmath15 yields fm correlations in both @xmath34 and @xmath35 directions . as the kinetic energy is controlled by the inter - site coulomb repulsion @xmath13 and suppressed in the limit of @xmath114 we find the af region increasing in size with increasing @xmath82 . we discuss now in more detail the temperature dependence of the different correlation functions . starting from the fm region ( see fig . [ fig : corr_fm_nn ] ) we find the evolution of weak co for @xmath115 with nearest - neighbor @xmath116 charge correlations smaller than the @xmath117 and @xmath118 next - neighbor ones which is consistent with the alternating order of mn@xmath1 and mn@xmath2 ions . the orbital correlations are positive between all neighbors indicating the preference of @xmath6 orbital occupancy due to the kinetic energy which is quite large in the fm state . although all spin correlation functions are positive , they remain highly anisotropic as @xmath119 as a result of the strong competition between the de mechanism and af superexchange interaction between core spins . next , we consider the af spin state in the case of large @xmath15 and @xmath13 ( see fig . [ fig : corr_af_nn ] ) . increasing coulomb repulsion ( @xmath109 ) we find more distinct and almost isotropic alternation of the @xmath5 charge which now sets in already at @xmath120 . here , the orbital correlations are correlated with the onset of the af spin order at @xmath121 . for @xmath122 the spin - spin correlations are strong and represent an almost isotropic af spin state . for intermediate values of @xmath15 and moderate coulomb repulsion we find the phase with predominantly c spin correlations at @xmath122 ( see fig . [ fig : oonn_phase ] ) . as presented in fig . [ fig : corr_c_nn ] for @xmath123 and @xmath124 the charge correlations are similar to those obtained for the fm state shown in fig . [ fig : corr_fm_nn ] ( a ) while the spin ordering changes dramatically . moreover for @xmath122 the orbital correlations are weaker than those found in the fm state discussed above indicating the orbital tendency towards in - plane directional - type order . a convenient way to distinguish between phases with c or ce and other spin correlations is to evaluate a _ combined spin - charge correlation function _ being restricted to sites occupied by @xmath5 electrons , @xmath125 . analyzing the localized limit presented in fig . [ fig : spins ] ( or its by @xmath126 rotated version ) one can easily see that , for the c phase one should find @xmath127 for @xmath128 and @xmath129 for @xmath130 while for the ce phase only @xmath129 for @xmath128 with any other spin - charge correlations remaining small . in the case presented in fig . [ fig : corr_c_nn ] @xmath125 functions are negative ( positive ) for nearest - neighbors along diagonal ( next - nearest - neighbors along @xmath34/@xmath35 direction ) , respectively , in agreement with the arguments presented above . furthermore , nearest - neighbor spin - charge correlations are small as a result of averaging over different cluster orientations ( rotated by angles @xmath131 , @xmath132 ) . it is straightforward to see why the c - structure is favored by the nearest - neighbor jt interaction . the c - phase can be viewed as a realization of the alternating orbital structure of lamno@xmath4 but with a modulated charge density . hence this structure is compatible with the nearest - neighbor jt interaction , whereas in the ce - structure this interaction is frustrated . the role of local lattice distortions due to the jt effect , which creates an anisotropic strain field decaying as @xmath133 and thereby promotes long - range orbital ordering , was considered by khomskii ( see ref . ) . following these arguments , we treat the oo term as an elastic interaction which is active also between @xmath5 electrons on next - nearest - neighbor sites along @xmath34 or @xmath35 direction , @xmath134 where @xmath135 refers to next nearest - neighbors along @xmath34 and @xmath35 direction with @xmath136 which follows from the @xmath137 decay of elastic interactions.@xcite the existence of longer - range oo interactions is justified by its cooperative lattice - driven nature where an orbital flip on a single mn site distorts not only the neighboring oxygens but also positions of other manganese ions around it . here , the jt coupling preferring the tilting of the orbitals from the uniform orbital state leads to an alternating orbital order ( see fig . [ fig : ce_orb ] ) and in this way compensates for the kinetic energy gain in uniform @xmath41 orbital state favored in the 2d model . here we neglect non - central elastic interactions between neighboring mn sites in @xmath138 direction as their strength does not scale with @xmath139 ( see ref . ) and thus would involve introduction of an additional parameter in the model . schematic configuration of the charge - orbital ordered ce phase . the sites * a * and * b * indicate two orbital mn@xmath7 sublattices while empty circles stand for the mn@xmath14 ions . the dashed - line box indicates a typical orbitals orientation around a given mn@xmath14 ion.,width=226 ] phase diagram as in fig . including the nearest- and next - neighbor elastic interactions ( @xmath97 , @xmath136 ) . @xmath98 indicates a representative point in the ce region for which the correlation functions are presented here.,width=132 ] temperature dependence of the two - site correlations as in fig . but for the phase with ce spin and orbital correlations promoted by elastic interactions ( @xmath97 , @xmath136 ) . other parameters : @xmath140 , @xmath141 , @xmath108 . the inset in ( b ) shows the orbital correlations in the rotated basis : @xmath142.,width=377 ] the ce phase is favored as compared to the c phase by the oo coupling between second neighbors ( @xmath143 ) along @xmath34/@xmath35 direction . however , this interaction is only active ( not screened ) when strong charge ordering takes place ( large @xmath82 case ) and here the ce phase can persist even for small values of @xmath15 as long as the @xmath5 kinetic energy is sufficiently suppressed by a large @xmath13 ( see fig . [ fig : elastic_phase ] ) . thus , one has to assume large inter - site coulomb repulsion ( where almost perfect mn@xmath1/mn@xmath2 charge ordering@xcite is realized ) and small superexchange interaction [ see an example for @xmath144 and @xmath145 in fig . [ fig : corr_ce_el ] ] . in the @xmath28 basis , which we use in most of the numerical evaluations , the spin and orbital correlation functions with @xmath146 become large as @xmath119 while all the others remain very small in the whole range of temperatures . such small orbital correlations imply either that the respective orbitals are uncorrelated or that they order in such a way , that the occupied orbitals are linear combinations with almost equal amplitude expressed in the basis used for the measurement of correlation functions.@xcite this difficulty is not present in su(2 ) symmetric models , and appears here as consequence of the cubic symmetry in the orbital sector . therefore , the same functions were evaluated also in the @xmath142 basis as presented in the inset of fig . [ fig : corr_ce_el ] ( b ) . in the new orbital basis the function @xmath147 is more pronounced and saturates for @xmath148 at @xmath149 close to its maximum value @xmath150 indicating almost perfect ce orbital structure ( see fig . [ fig : ce_orb ] ) . shorter range @xmath151 correlations should become small when averaged over differently oriented clusters ( rotated by angles @xmath131 ) [ see fig . [ fig : spins ] ( d ) ] . from fig . [ fig : spins ] ( d ) one can see that a similar pattern as found for the two - site orbital correlations should be found for the @xmath125 functions . in our cluster in ideal ce state only electrons at distance @xmath128 can contribute to the charge - spin correlations ( being negative in this case ) which do not vanish when averaged over different cluster orientations . as shown in fig . [ fig : corr_ce_el ] ( c ) the @xmath125 correlations obtained here are consistent with the above characterization of the ce pattern with a strong negative signal dominating at distance @xmath128 . the existence of charge - ordered insulating state concomitant with orbital and spin order of the ce - type@xcite was observed in different half - doped manganites with small one - electron bandwidth.@xcite the average change in the orbital occupation can be studied calculating @xmath152 which changes between @xmath153 and @xmath154 for the uniform @xmath41 and @xmath92 orbital states , respectively , for the case with one @xmath5 electron per two mn sites . furthermore , when the orbital state involves @xmath41 and @xmath92 orbitals in the same proportion one finds @xmath155 . in fig . [ fig : tz_susc_el ] ( a ) we see that increasing the coulomb interaction from @xmath106 to @xmath109 the orbital ordering hardly changes for @xmath122 with @xmath152 only slightly decreasing to @xmath156 for @xmath109 . this indicates that as long as the system is in the fm state ( see fig . [ fig : elastic_phase ] ) the ground state is dominated by the @xmath6 orbital promoted by the kinetic energy term . further increase in the coulomb inter - site repulsion to @xmath140 leads to a drastic change in the orbital order when system enters the ce phase region ( see fig . [ fig : elastic_phase ] ) . here , @xmath157 for @xmath122 indicating dominating role played by the @xmath158 orbitals . this fact is consistent with our results for the two - site orbital correlation functions [ see inset in fig . [ fig : corr_ce_el](b ) ] . temperature dependence of the average value of the @xmath159 orbital operator ( a ) and the inverse of the staggered charge susceptibility @xmath160 ( b ) obtained for different values of the inter - site repulsion @xmath82 in the presence of elastic interactions ( @xmath97 , @xmath136 ) . other parameters : @xmath141 , @xmath108.,width=226 ] a change in the inter - site coulomb interaction is directly connected with the robustness of the charge ordering as seen in figs . [ fig : corr_fm_nn ] - [ fig : corr_c_nn ] ( a ) and fig . [ fig : corr_ce_el ] ( a ) . although the characteristic temperature of the co ( @xmath161 ) can be roughly estimated from the charge - charge correlation functions it can be more precisely extracted from the staggered charge susceptibility,@xcite @xmath162 : @xmath163 which at high temperatures follows a curie - weiss law @xmath164 . from fig . [ fig : tz_susc_el ] ( b ) one can easily estimate @xmath165 , @xmath166 , and @xmath167 for @xmath168 , @xmath169 , and @xmath170 , respectively , in agreement with the mean - field solution@xcite which for @xmath114 predicts , @xmath171 . although the model considered in the previous section with longer - range oo elastic coupling leads to the ce - type spin and orbital correlations , this phase is found only in a very extreme case of almost perfect mn@xmath14/mn@xmath7 co ( that is for strong coulomb repulsion ) which may not be very realistic in the light of some experimental facts indicating the cdw character of charge redistribution between different manganese ions.@xcite therefore in this section we derive the further neighbor oo interactions from a microscopic model including apart from the jt - distortion of the mn@xmath7 octahedra the breathing distortion around the mn@xmath14 ions as well . we then show that this interaction is capable to produce the zigzag ( spin and orbital ) phase in a region of small coulomb repulsion changing the previous phase diagrams in a drastic way . to assess the gain in lattice energy connected with the formation of the ce long - range orbital order we follow the work of millis for lamno@xmath4 by treating the lattice distortions classically.@xcite the effect of lattice displacements is described by assuming arbitrary values of four different lattice distances @xmath172 ( @xmath173 ) ( see fig . [ fig : distortions ] ) which are expressed by @xmath174 , @xmath175 uniform deformation along the @xmath34 and @xmath35 direction of the mn lattice , and @xmath176 displacements of o ions along the mn o mn bonds within the @xmath177 planes : @xmath178 where @xmath35 is the lattice constant of the ideal perovskite.@xcite moreover , we assume @xmath5 charge stacking in the @xmath179 direction with the respective mn mn distance being @xmath180 . schematic representation of the lattice distortions contributing to the second neighbor jt - interaction . the corresponding ce orbital order for the 5 atom structure above is indicated in fig . by dashed lines . different mn@xmath7 , mn@xmath14 , and o ions are presented by full , shaded and empty circles , respectively . the distances between the mn@xmath14 ion and the mn@xmath7 ions in @xmath181 [ @xmath182 and @xmath183 [ @xmath184 directions , respectively , are identical . the arrow indicates the displacement of the central mn@xmath14 ion when @xmath185.,width=283 ] phase diagram as in fig . including the local nearest- and next - neighbor oo interactions with @xmath97 and @xmath186 ( spring constants @xmath187 ) . @xmath98 indicate representative points in the ce region for which the correlation functions are presented here . the dashed arrow presents the direction of the transition from the localized ce to the itinerant electron a - phase at low temperatures.,width=132 ] in order to define orbital sublattices ( a and b ) we introduce a transformation which describes the tilting of orbitals by making two different transformations at both sublattices,@xcite @xmath188 = \left [ \begin{array}{cc } \cos\left(\frac{\pi}{4}\pm\phi\right ) & \sin\left(\frac{\pi}{4}\pm\phi\right ) \\ -\sin\left(\frac{\pi}{4}\pm\phi\right ) & \cos\left(\frac{\pi}{4}\pm\phi\right ) \end{array}\right ] \left [ \begin{array}{c } \end{array}\right ] , \ ] ] where @xmath33 ( @xmath32 ) refers to @xmath189 ( @xmath190 ) sublattice , respectively , and @xmath191 . here , @xmath192 and @xmath193 stands for local basis orbitals : @xmath41 and @xmath92 at site @xmath194 , respectively . in the rotated basis @xmath195 we assume for the transformed operators : @xmath196 ( @xmath197 ) for @xmath189 ( @xmath198 ) sublattice , respectively . at intermediate values of @xmath199 one can reach , e.g. , @xmath200/@xmath201 ( @xmath202/@xmath203)-type orbital ordering at @xmath204 ( @xmath205 ) , respectively . the rotation ( [ eq : rotation ] ) does not include complex orbital order which was proposed as a possible orbital order in manganites at smaller doping.@xcite the classical energy of the distorted lattice @xmath206 ( per mn site ) is given by,@xcite @xmath207 + k_1\left(u_1 ^ 2 + u_2 ^ 2\right),\ ] ] normalized per mn ion , where @xmath208 ( @xmath209 ) are the nearest - neighbor mn o ( mn mn ) spring constant , respectively . here the force constants include the factor @xmath210 , and hence have the dimension of an energy . next , we have to add the energy of the breathing mode ( bm ) describing the attraction between oxygen ions and the unoccupied mn@xmath2 site : @xmath211 here , all oxygens are equally attracted towards the central manganese ion . the bm induces charge alternation on neighboring mn sites and contributes to the effective inter - site charge - charge repulsion ( @xmath13 ) . the coupling constant to the breathing distortion is written as @xmath212 , where @xmath213 denotes the coupling to the jt distortion . the term describing the jt coupling depends on the character of the occupied orbital at a mn@xmath1 site . the jt interaction describes the coupling between the occupied @xmath5 orbital at a particular mn@xmath7 ion and the distortions of the surrounding oxygen ions , as introduced by millis.@xcite in the orbitally rotated state ( [ eq : rotation ] ) this energy has the following form , @xmath214\sin(2\phi)\right . \nonumber\\ & - & \left.\sqrt{3}\cos(2\phi)\left[\frac{1}{2}\left(\delta_x - \delta'_x\right ) + u_2 - u_1\right]\right\},\end{aligned}\ ] ] and depends on the rotation angle @xmath199 and on the deformation of the lattice . the optimal values of the ionic displacements for a given angle @xmath199 are found by minimization of the total energy , @xmath215 , which for ( [ eq : e_l])-([eq : jt ] ) and neglecting higher - order nonlinear terms gives , [ eq : dis ] @xmath216 } { 2\left(k_1 + 2k_2\right ) } , \\ \delta'_x & = & \frac{-\lambda\left[2\beta -\sin(2\phi)+\sqrt{3}\cos(2\phi)\right ] } { 2\left(k_1 + 2k_2\right ) } , \\ \delta_z & = & \frac{-\lambda\left[\beta+\sin(2\phi)\right]}{k_1 + 2k_2 } , \\ u_1 & = & \frac{-\lambda\left[2\beta+\sin(2\phi)+\sqrt{3}\cos(2\phi)\right ] } { 4k_1 } , \\ u_2 & = & \frac{-\lambda\left[2\beta+\sin(2\phi)-\sqrt{3}\cos(2\phi)\right ] } { 4k_1 } .\end{aligned}\ ] ] this yields for the total energy of the distorted lattice , @xmath217 + 2k_1+k_2\right\ } .\nonumber \\\end{aligned}\ ] ] this implies a change of the volume of the lattice with respect to the ideal perovskite ( @xmath218 ) @xmath219 . hence the volume decreases with increasing bm coupling @xmath220 , but does not depend on the character of the orbital order . the relative strength of the effective next- and nearest - neighbor jt interactions can be obtained by comparing the lattice stiffnesses of the orbital modulations in the undoped ( @xmath221 ) and the quarter - filled ( @xmath222 ) case , respectively . for _ undoped _ lamno@xmath4 the lattice energy was found to be [ see eq . ( 2.14 ) in ref . ] , @xmath223\right\ } , \label{eq : e^0}\ ] ] in the half - doped case the orbital alternation at mn@xmath7 neighbors is driven by the mn@xmath14 ion shift . the energy ( 21 ) can be decomposed @xmath224 , where @xmath225 is the gain of energy due to the mn@xmath14 displacement : @xmath226 . \label{eq : de}\ ] ] this cooperative energy does not depend on the breathing mode coupling @xmath220 directly , though there is an indirect dependence via @xmath227 influencing the optimal value for @xmath199 . contrary to the undoped case ( [ eq : e^0 ] ) , where the mn - mn potential ( @xmath228 ) is necessary to obtain finite orbital stiffness , in the half - doped case ( [ eq : de ] ) the mn - o interaction alone can lead to cooperative jt effect stabilizing the alternating orbital order . assuming @xmath229ev , @xmath230 ev , and @xmath231 ( see ref . ) one finds for the @xmath232 ( @xmath233 ) orbital order the ce energy contribution per mn ion @xmath234 mev . in table [ tab : ene ] we present the ratio @xmath235 , characterizing the stability of the ce orbital order , as function of the bm coupling strength @xmath220 and the ratio of spring constants @xmath236 . the largest relative gain in energy due to the mn@xmath14 ions shift ( @xmath237 ) is obtained for the @xmath238 orbital order ( @xmath233 ) which for small bm coupling ( @xmath239 ) can reach up to @xmath240 of the total lattice energy , whereas for larger values of @xmath220 , although @xmath225 is not changed , the total lattice energy increases rapidly as @xmath241 being dominated by the distortions of the mno@xmath16 octahedra rather then by their displacements . furthermore , with increasing mn lattice stiffness ( @xmath242 ) both the @xmath235 ratio and the shift of unoccupied mn@xmath14 ions [ @xmath243 decrease . .[tab : ene ] the relative energy gain , @xmath235 , associated with the mn@xmath14 ion displacement ( see fig . ) for the orbital orderings given by @xmath233 and @xmath244 presented as function of @xmath220 and @xmath236 . [ cols="<,^,^,^,^",options="header " , ] correlation functions in the case of a ce ground state ( as in fig . ) but obtained for the local oo interaction ( 26 ) with spring constants @xmath187 ( @xmath245 ) . other parameters : @xmath106 , @xmath97 , @xmath141 , @xmath108.,width=377 ] charge correlations in the case of a fm ground state as obtained for the local oo interaction with spring constants @xmath187 ( @xmath245 ) . other parameters : @xmath246 , @xmath97 , @xmath247 , @xmath108.,width=132 ] comparing the cooperative part [ @xmath248 of both jt energy contributions [ ( [ eq : e^0 ] ) and ( [ eq : de ] ) ] we end up with a simple relation between different oo interaction strengths , @xmath249 for @xmath250 the @xmath133 scaling of elastic interactions@xcite is recovered . in the above estimate we have neglected the superexchange interaction which can also contribute to the effective @xmath251 [ see _ e.g. _ eq . ( 2.7 ) in ref . ] . the relative strength of both spring constants in the co case can be assessed from the relative length of different bonds in the half - doped mno@xmath8 plane . as measured for low - temperature la@xmath252ca@xmath252mno@xmath4 superstructure@xcite the length of all four in - plane mn@xmath14-o bonds is very similar ( @xmath253 ) . neglecting the effect of mn - o - mn bond bending and assuming @xmath254 ( see fig . [ fig : distortions ] ) one obtains the relation , @xmath255 by using eqs . ( [ eq : dis ] ) . the above assessment together with ( [ eq : kappa_ratio ] ) underlines the importance of mn@xmath7mn@xmath7 orbital coupling ( @xmath222 ) in co manganites . the structural data of radaelli _ et al._@xcite may be used in combination with eqs . ( [ eq : dis ] a - e ) to infer the values for @xmath213 and @xmath220 . we have not attempted to determine the force constants as well , but assume @xcite @xmath230 ev . using basically data for the jt - distortion of mn@xmath7o in - plane bonds ( @xmath256 and @xmath257 ) and the mn@xmath14 displacement , we obtain for @xmath258 @xmath259 and @xmath260 ev , respectively . we note that the ratio @xmath261 is rather close to the values determined by millis@xcite for lamno@xmath4 . this also implies that the energy gain due to the breathing distortion is substantial [ see eq . ( [ eq : e_tot ] ) ] . we return to the many - body theory for a translation invariant system . as the oo interaction between further mn@xmath7 neighbors is mediated by an mn@xmath14 ion we introduce the following effective three - site interaction , @xmath262 where the operator @xmath263 is defined as in eq . ( [ eq : tij ] ) , and @xmath264 denotes three neighboring sites along @xmath34 or @xmath35 direction . the reasoning here is similar as for the nearest - neighbor jt interaction in eq . ( [ eq : h_oo ] ) , i.e. , the expectation value of the operator @xmath263 in an orbital ordered state depends on the orbital angle precisely as in eq . ( [ eq : de ] ) , namely @xmath265 $ ] . the @xmath266 factor in eq . ( [ eq:3site ] ) reflects the charge state of mn@xmath14 and favors co in the quarter - filled system , while the contribution of the interaction ( [ eq:3site ] ) would vanish in the undoped compound . investigating the model ( [ eq : h_total ] ) with both nearest - neighbor ( [ eq : h_oo ] ) and three - site ( [ eq:3site ] ) oo couplings we find a strong change in the low - temperature phase diagram ( see fig . [ fig : oonnn_phase ] ) as compared with the previous ones ( figs . [ fig : oonn_phase ] and [ fig : elastic_phase ] ) . assuming @xmath245 ( which corresponds to @xmath267 ) , the ce - like correlations set in already at rather small inter - site repulsion ( @xmath268 ) while for stronger coulomb interactions ( @xmath269 ) the spin correlations have predominantly af character . furthermore , the fm region is quite small and can be found only for @xmath270 and @xmath271 . when decreasing the ratio @xmath236 ( and keeping the value of @xmath139 constant ) the fm region shrinks at the expense of the ce region . next , we present the two - site correlations for one representative ( @xmath106 , @xmath141 ) point in the ce region in fig . [ fig : oonnn_phase ] . from fig . [ fig : corr_ce_nnn ] ( a ) one sees that the ce state can exist for less pronounced co than in the elastic strain model considered in sec . [ sec : elastic ] , where almost perfect mn@xmath7/mn@xmath14 co was necessary to stabilize the zigzag state ( see fig . [ fig : corr_ce_el ] ) . moreover , the evolution of ce - type orbital order with decreasing temperature is here correlated with the onset of co [ compare fig . [ fig : corr_ce_nnn ] ( a)-(b ) with [ fig : corr_ce_el ] ( a)-(b ) ] . regarding @xmath125 correlations , the ce - type spin order develops at lower temperatures than the charge and orbital order but at higher temperature than previously found for the strain induced interactions . the three - site term ( [ eq:3site ] ) which is active for a mn@xmath7mn@xmath14mn@xmath7 sequence along the @xmath34 and @xmath35 direction , respectively , promotes not only orbital alternation on neighboring mn@xmath7 sites but also strengthens co. this is clearly seen in the charge correlations which are now stronger than those _ e.g. _ in fig . [ fig : corr_fm_nn ] , although the same coulomb repulsion ( @xmath106 ) was assumed in both cases . going from the ce to the fm phase ( as indicated by an arrow in fig . [ fig : oonnn_phase ] ) one finds that the cdw is now reduced at low temperatures in the fm state ( fig . [ fig:<nn > ce ] ) , while the charge modulation is still rather strong at higher temperatures ( @xmath121 ) above the nel temperature where the electron kinetic energy is quenched due to the random @xmath0 spin orientations . this behavior is a clear manifestation of the de mechanism . we note that the ce - type orbital correlations are still present in the fm phase in fig . [ fig : oonnn_phase ] for @xmath272 , whereas for smaller values for @xmath13 @xmath273-@xmath274 orbital correlations dominate , which are characteristic for the metallic a - phase . finally , we consider possible mechanisms stabilizing the charge stacking of ce - ordered planes @xcite as observed in most charge - ordered manganites at doping @xmath275 . any interaction stabilizing such a stacking must overcome the inter - site charge - charge repulsion . there are two interactions which contribute to such a repulsion : ( i ) the electron - electron coulomb force @xmath13 ; and ( ii ) the bm coupling . both interactions will effectively tend to maximize the number of mn@xmath7mn@xmath14 bonds . the bm coupling contribution to the inter - site charge - charge repulsion ( @xmath276 ) can be estimated comparing the lattice energies with charge alternating and stacked along the @xmath179 direction which leads to the estimate @xmath277 ^ 2 /(2k_1)$ ] . assuming typical values for @xmath278 and @xmath279 ( see ref . ) together with our previous estimate @xmath280 one can obtain _ @xmath281 for the @xmath142 ce orbital order . in a multi - layer system the oo interaction along the @xmath179 direction is given by the nearest - neighbor coupling @xmath221 , which in the @xmath28 basis has the form,@xcite @xmath282 energy gained by @xmath5 electron stacked in the @xmath179 direction as function of charge modulation @xmath283 obtained for @xmath246 , @xmath186 and different values of @xmath251.,width=264 ] this interaction together with the @xmath222 coupling , which controls the ce - orbital order in the @xmath177 plane , in a charge - ordered case yields an approximate orbital model of the form , @xmath284 where @xmath56 ( @xmath285 ) are defined with respect to the @xmath142 orbital basis . defining @xmath286 and assuming that in the @xmath177 planes of a bilayer system @xmath287 and @xmath288 orbitals are occupied on two neighboring sites in the @xmath179 direction , the @xmath221 coupling [ see eq . ( [ eq : stacking ] ) ] rotates orbitals towards the @xmath289 configuration and leads to binding of two electrons with energy @xmath290 . for charge disproportion with mn@xmath291 ions alternating in the @xmath177 planes and assuming that the @xmath251 ( @xmath139 ) two ( three)-site interaction scales as @xmath292 with @xmath293 ( @xmath48 ) , respectively , one finds for the energy gain ( per mn ion ) due to charge stacking along @xmath179 direction for a 3d lattice : @xmath294 -2\delta^2v .\ ] ] the last term stands for the effective coulomb repulsion at given charge modulation . with charge modulation sufficiently reduced @xmath295 ( see fig . [ fig : stacking ] ) the oo inter - plane coupling can stabilize charge - stacked phase ( @xmath296 ) . such stabilization is strengthened ( weakened ) by increasing @xmath251 ( @xmath139 ) oo interaction , respectively . for smaller charge disproportion ( @xmath297 ) and considerable charge on mn@xmath298 sites the @xmath221 in - plane coupling [ neglected in eq . ( [ eq : stacking ] ) ] can also play an important role in the inter - plane charge modulation . however , when the co is strongly reduced the orbital ground state is too complex to be analyzed analytically . a further mechanism stabilizing the observed @xmath5 charge stacking along the @xmath179 direction results from the af inter - plane superexchange interaction.@xcite yet , the magnetic interaction ( @xmath299 ) results mainly from the @xmath300 superexchange which is of the order of only a few mev.@xcite thus , the antiferromagnetism in the @xmath179 direction observed in most of the ce structures appears to be a _ result _ rather than the _ origin _ of the stacking pattern of the charge / orbital order . we have investigated the potential of different electron - lattice mechanisms to stabilize the ce spin - orbital ordered phase in charge ordered half - doped manganites ( filled with one @xmath5 electron per two mn ions ) . our study is based on a generalized de model containing the @xmath5 orbital degrees of freedom , and also including inter - site coulomb repulsion ( @xmath13 ) and af superexchange ( @xmath15 ) between core spins . the effect of three types of orbital interactions derived from the cooperative jt effect have been studied : ( i ) nearest neighbor jt - coupling , which is responsible for the alternating orbital order in undoped lamno@xmath4 , ( ii ) in addition second neighbor jt - interaction with a strength as expected for elastic strain , and ( iii ) a 2nd neighbor jt interaction which accounts for the breathing distortion of the mn@xmath14 octahedra and is in general stronger than ( ii ) . a particular feature of this interaction , which has been proposed based on the classical model considerations in sec . [ sec : nnnjt ] , are the displacements of the mn@xmath14 ions in the ce - phase . we have studied these models employing finite temperature diagonalization on a @xmath78 cluster with periodic boundary conditions , thereby keeping the translational invariance . the evolution of the different phases with temperature is monitored by the calculation of correlation functions for charge , orbital and spin , respectively . starting out from the generalized fm kondo lattice model ( [ eq : h_total ] ) without any orbital interaction ( @xmath301 ) we find the orbital correlations dominated by the @xmath6 orbitals which are favored by the kinetic energy.@xcite this orbital state is characteristic for the metallic a - phase in wide - band manganites at half doping . for small af superexchange interactions ( @xmath302 ) between @xmath0 core spins the fm state is found in the spin sector , while for larger values of @xmath15 the ground state is that of a regular 2 sublattice antiferromagnet . even for large coulomb repulsion @xmath13 we found no evidence for c or ce structures for some intermediate values of the parameter @xmath15 . the inclusion of the nearest - neighbor jt - interaction ( i ) , however , was found to stabilize the af - c phase in a wide parameter range in the @xmath303 phase diagram . to obtain the more complex ce orbital and spin state not only the kinetic energy must be reduced by increasing the coulomb repulsion @xmath13 but also a further neighbor _ antiferro - orbital _ interaction must be included in the model . this interaction results from the electron - lattice coupling and is a generalization of the jt interaction which was found to play an important role in the parent lamno@xmath4 compound.@xcite in co compounds at quarter - filling the effect of the oo coupling will be dominated by interactions between further distant mn neighbors . we have shown that such interactions can produce the ce structure in both _ spin and orbital _ sectors . in the case of the three - site effective interaction ( @xmath143 ) the zigzag chains are found to be stable not only for modest inter - site repulsion ( @xmath268 ) but even in the limit of @xmath304 and provided @xmath251 is small , where the co is induced entirely by the three - site orbital coupling ( [ eq:3site ] ) . this effective next - nearest - neighbor oo coupling was derived taking into account the cooperative nature of both mn@xmath7o and mn@xmath7mn@xmath14 bonds length deformation . the free relaxation of the latter length leads in presence of co to orbital alternation in planar directions , and the pattern of directed orbitals typical for the orbital ce structure appears . consequently , with the help of the orbital topology,@xcite this gives rise to the ce af spin ordering for realistic values for @xmath15 . an important aspect of the second neighbor jt - interaction ( iii ) is its 3-site structure which involves a coupling to the charge at the mn@xmath14 ion . this implies that the evolution of the ce orbital correlations with temperature are linked to the evolution of co , while the magnetic ce correlations develop at lower temperature similar to pr@xmath3ca@xmath3mno@xmath4@xcite . this is different from ( ii ) , where first co develops , then oo and finally at lowest temperature af spin order . as discussed in sec . [ sec : parameters ] we did not find the ce spin and/or orbital phase considering a pure electronic model , i.e. , neglecting the electron - lattice coupling . although , the topological effect combined with the de mechanism leads to the preference of the ce over c phase when all @xmath5 ( bridge and corner ) orbitals are degenerate,@xcite the situation is more complex when such degeneracy is lifted by jt lattice distortions . as described in the appendix , one finds band insulators in both cases while the stability of the ce versus the c phase strongly depends on the crystal - field splittings ( @xmath305 , @xmath306 ) . an important issue is the degree of charge ordering in the ce phase . the ce spin - orbital structures obtained in our simulations appear in the regime of relatively strong co , as infered from our calculated charge correlation functions . our calculations also suggest that the second neighbor jt coupling even for small or vanishing coulomb repulsion can lead to a pronounced charge modulation . these results are consistent with the simple physical picture , that de perpendicular to the fm chains must be strongly suppressed to allow af superexchange to trigger the ce structure , which may not be the case for weak co. on the other hand , a recent study by mahadevan , terakura and sarma@xcite based on the band structure approach arrived at the conclusion that the charge difference between the two mn species in the ce phase is basically negligible , which would imply the absence of a significant breathing distortion of mn@xmath14 octahedra . further experimental information on the degree of lattice distortion in the ce phase will certainly help to test the proposed jt based mechanism for the stability of the ce phase . the charge modulations determined in our calculations may be influenced by numerical limitations which overestimate quantum fluctuations : ( i ) spins @xmath47 are used to describe @xmath0 electrons ; ( ii ) the calculations are made using a 2d cluster ; ( iii ) the oxygen ions are not present explicitly in the cluster and thus only _ dynamical _ interactions are included ( @xmath307 ) , which are mediated by oxygen displacements , while possible _ static _ lattice effects@xcite are neglected . certainly each of these approximations weakens the charge ordering and the spin - orbital order . it is , however , not straightforward to decide whether the region of the ce - phase in the phase diagram may grow or shrink , if quantum fluctuations are suppressed . finally we note that further neighbor jt interactions can also play an important role in the charge stripe formation at other commensurate carrier concentrations . for @xmath308 ( @xmath309 ) the dominant coupling arises from the nearest- ( next nearest- ) neighbor oo interactions , respectively , with a pronounced electron - hole asymmetry present . in the latter case with small inter - site coulomb repulsion ( @xmath13 ) the bi - stripe state@xcite would be preferred while larger values of @xmath13 would favor a `` wigner crystal '' charge arrangement.@xcite we would like to thank g. khaliullin , m. mayr and a. m. ole for stimulating discussions and valuable comments . j. b. acknowledges the support of the mpi fr festkrperforschung , stuttgart . the financial support by the polish state committee of scientific research ( kbn ) of poland , project no . 5 p03b 055 20 is also acknowledged ( j. b. ) . a quite appealing explanation for the stability of the ce as compared to the c phase was suggested in refs . by considering a 1d model , where in the ce phase a gap opens as a consequence of a topological sign in the hopping matrix - elements . however , the intra - site coulomb repulsion @xmath42 ( leading to some redistribution of the @xmath5 charge ) can destabilize the ce phase.@xcite here we investigate how these arguments are modified when orbital degeneracy is lifted due to jt distortions . we consider the hamiltonian : @xmath310 which contains the kinetic energy @xmath311 of an electron hopping along a fm chain@xcite with possible @xmath5 level shift at the bridge sites ( @xmath312 ) and level splitting at corner sites ( @xmath313 ) considered in two different orbital basis @xmath28 and @xmath314/@xmath315 orbitals are located between the split energy levels at the corners assuming @xmath316 . both kinds of level shifts can result from the lattice distortions . at the bridge site only the orbital @xmath317 ( @xmath315 ) is considered while the orthogonal one @xmath318 ( @xmath319 ) , respectively , is decoupled in chain direction . in momentum space this leads to a @xmath320 matrix problem : @xmath321 \left(\begin{array}{c } d_{b , k}\\ d_{x , k}\\ d_{z , k}\end{array } \right ) , \ ] ] where @xmath322 ( @xmath323 ) and @xmath324 ( @xmath325 ) are the hopping elements for the ce ( c ) phase , respectively , in the @xmath28 orbital basis . electron dispersion for the zigzag chain of the ce phase ( solid lines ) and for the linear chain of the c phase ( dashed lines ) calculated for different crystal - field splittings in the @xmath28 orbital basis at corner sites ( @xmath305 ) . the orbitals at the bridge sites are degenerate ( assuming @xmath326).,width=188 ] phase diagram of the chain model illustrating the stability of the ce against the c phase as function of the crystal - field splittings defined with respect to the orbital basis ( a ) @xmath28 and ( b ) @xmath327 , respectively.,width=188 ] calculating the band energies ( see fig . [ fig : bands ] ) one can easily determine the character of the stable phase . for the degenerate band model ( @xmath328 ) the c phase is metallic while in the ce phase a gap opens due to the _ topological sign_.@xcite the opening of the gap stabilizes the ce phase . when the degeneracy between @xmath41 and @xmath92 states at the corner sites ( @xmath329 ) is lifted , the c phase becomes insulating as well and for sufficiently large @xmath5 level splittings it can have a _ lower _ energy than the ce phase when the chain is doped with one electron per two mn sites [ see fig . [ fig : bands](b ) ] . the region of stability of the ce phase increases for positive ( negative ) @xmath305 when @xmath330(@xmath331 ) , respectively [ see fig . [ fig:1d_phase](a ) ] . generally , the ce phase is stabilized with respect to c , when the occupied bridge state approaches the lower energy level of the corner states . in a real half - doped crystal where in the ce phase mn@xmath33o bond lengths shrink ( expand ) in the @xmath179 direction [ @xmath177 plane ] , respectively , one would expect an energetic preference , due to the jt effect , for orbitals with stronger @xmath6 than @xmath332 character . thus , in the 1d model the relevant part of the phase diagram ( fig . [ fig:1d_phase ] ) is the region with @xmath333 and @xmath334 , i.e. , where the ce structure dominates . to relate our mean - field considerations to the model from sec . [ sec : nnjt ] the stability of the ce phase versus c was also considered with level splitting at the corner sites defined with respect to the orbital basis @xmath327 . such a splitting , directly related to the nearest - neighbor jt interaction ( [ eq : h_oo ] ) when @xmath335 , is operative in the c phase but vanishes by symmetry in the ce orbital phase . as shown in fig . [ fig:1d_phase](b ) the ce phase is stable for small splittings ( @xmath336 ) and in the @xmath335 , @xmath330 region . the latter is the relevant parameter range in the case of nearest neighbor jt interactions , and hence the model suggests the ce phase as stable phase . this , however , is in conflict with our numerical study of the 2d model , where only the c phase was found to be stable . as in 2d the nearest neighbor jt interaction stabilizes the c structure , whereas this interaction is frustrated in the ce phase . this effect is not included in the 1d model . a. e. bocquet , t. mizokawa , t. saitoh , h. namatame , and a. fujimori , , 3771 ( 1992 ) ; t. saitoh , a. e. bocquet , t. mizokawa , h. namatame , a. fujimori , m. abbate , y. takeda , and m. takano , _ ibid . _ * 51 * , 13 942 ( 1995 ) ; s. satpathy , zoran s. popovic and filip r. vukajlovic , , 960 ( 1996 ) .

we have analyzed different correlation functions in a realistic spin - orbital model for half - doped manganites . using a finite - temperature diagonalization technique the ce phase was found in the charge - ordered phase in the case of small antiferromagnetic interactions between @xmath0 electrons . it is shown that a key ingredient responsible for stabilization of the ce - type spin and orbital - ordered state is the cooperative jahn - teller ( jt ) interaction between next - nearest mn@xmath1 neighbors mediated by the breathing mode distortion of mn@xmath2 octahedra and displacements of mn@xmath2 ions . the topological phase factor in the mn - mn hopping leading to gap formation in one - dimensional models for the ce phase as well as the nearest neighbor jt coupling are not able to produce the zigzag chains typical for the ce phase in our model .

<s>[INST]half - doped perovskite manganites re@xmath3a@xmath3mno@xmath4 ( re - rare earth , a - alkaline earth ) exhibit very specific properties quite different from manganites with other @xmath5 electron concentrations.@xcite generally , for large size re and a cations or when external pressure is applied@xcite these compounds are in the a - type antiferromagnetic ( af ) , metallic state at low temperatures showing no or only weak sign of charge ordering , and the occupied @xmath5 electron states are predominantly @xmath6 like . recently it has been reported that the a - phase may develop an intrinsic charge - stripe modulation , which controls the transport properties.@xcite with decreasing size of the cations , which implies a decrease of the bandwidth , charge ordering is observed which at lower temperatures is accompanied by the formation of peculiar ferromagnetic ( fm ) zigzag chains@xcite that are staggered antiferromagnetically . this ce spin order , a notation introduced in the pioneering work of wollan and koehler@xcite and goodenough@xcite , is accompanied by a checkerboard charge order ( co ) and directed occupied orbitals on the mn@xmath7 sites amplifying double exchange ( de ) along one lattice diagonal . the ce - structure is a particularly fascinating manifestation of the control of magnetic order due to the orbital degree of freedom@xcite in combination with charge ordering . although a number of approaches have been followed to explain this structure , the mechanism for its stability is still not clear and hotly debated with emphasis put on the role of the de,@xcite the coulomb interaction,@xcite or the coupling to the lattice degrees of freedom.@xcite the ce phase has been observed experimentally both in cubic ( nd , pr)@xmath3(sr , ca)@xmath3mno@xmath4@xcite and in layered lasr@xmath8mn@xmath8o@xmath9@xcite and la@xmath3sr@xmath10mno@xmath11@xcite manganites . in some cases it can coexist with the a - type af spin ordering.@xcite regarding co in the ce phase , some experiments are interpreted in terms of almost perfect co @xcite while others@xcite are considered to be consistent with a smooth charge density wave ( cdw ) of the @xmath5 electron density . although , it is plausible that the complex spin and orbital arrangement in the charge - ordered manganites can result from the competition between de@xcite and af superexchange interactions ( @xmath12 ) , the role played by the co and jahn - teller ( jt ) interactions@xcite in the system is still unclear . finally in systems like e.g. pr@xmath3ca@xmath3mno@xmath4 co and ce - type orbital correlations are found to develop well above the neel temperature@xcite or even coexist with fm spin state,@xcite which indicates that these orbital correlations are not primarily driven by magnetic interactions . this work focuses on a microscopic understanding of the stability of the ce - phase which appears to be the ground state of narrow band manganites at and near quarter - filling . we argue here that the key interaction , apart from the nearest - neighbor coulomb repulsion @xmath13 which supports the charge ordering,@xcite is the next - nearest neighbor jt interaction . this interaction between orbitals at next - nearest neighbor mn@xmath7 ions emerges from the jt - distortions of the mn@xmath7 octahedra which is amplified by the breathing distortion of the intermediate mn@xmath14 octahedra . we show that this interaction generates a narrow regime in the @xmath13-@xmath15 phase diagram where the ce - phase ( and sometimes the c - phase ) is stable . otherwise one encounters a homogeneous fm phase at small @xmath15 fully controlled by de and a conventional nearest - neighbor af phase at larger @xmath15 . an important feature of further neighbor jt interactions are the displacements of the mn@xmath14 ions . we are only aware of work by radaelli _ _ et al.__@xcite where detailed lattice coordinates for the ce - phase in la@xmath3ca@xmath3mno@xmath4 are reported . in particular they observed that the 4 planar o(2 ) move towards the mn@xmath14 ion and the mn@xmath14 ions are found to be displaced from their regular perovskite positions , while the mn@xmath7 ions are not shifted . this observation confirms the importance of the breathing distortion and also shows the mechanism of the further neighbor jt - distortion in the ce - phase . as a consequence the appearance of new bragg reflections in the ce - phase would be associated not primarily with quadrupolar electronic orbital order but rather with the displacements of ions associated with the ce orbital order.@xcite an alternative long - ranged jt based interaction was recently proposed by khomskii and kugel@xcite and by calderon , millis and ahn.@xcite they employ elasticity theory to derive the orbital interaction between jt - distorted mn@xmath7o@xmath16 octahedra for the perfectly charge ordered case . we have also investigated the consequences of this interaction . our numerical simulations confirm the estimate presented in ref . that for perfect charge ordering the af ce phase is stable . yet in this model this requires large nearest neighbor coulomb repulsion @xmath13 , while for moderate values of @xmath13 the ce phase gets unstable . the finite temperature diagonalization@xcite used in our study allows to include the full interplay of spin and orbital states , and to monitor the onset of different orders as function of temperature . this gives us the ability for an unbiased investigation of the formation of different spin - orbital orderings emerging from all multi - electron configurations in the cluster . in this paper we concentrate on the stability and temperature dependence of spin , orbital , and charge ordered states in the two - dimensional ( 2d ) realistic model for half - doped manganites . in our microscopic spin - orbital model co develops as a result of nearest - neighbor coulomb repulsion @xmath13 and as a consequence of further neighbor jt interactions , while the spin - orbital order results from the competition between de ( i.e. kinetic energy ) , af superexchange and further neighbor jt interactions . as shown in sec . [ sec : nnnjt ] the latter interaction can lead to a co state at low temperatures even in the absence of inter - site coulomb repulsion . furthermore we argue that a topological sign in the hopping amplitudes of @xmath5 orbitals@xcite invoked in one - dimensional ( 1d ) models for the ce phase is not sufficient to explain the formation of ce spin - orbital structure in the 2d model studied by us . further motivations to put effort in a better understanding of the interplay of spin , charge , orbitals and lattice in the formation of the ce - phase are the following : it has been argued that the intrinsic mechanism that leads to colossal magnetoresistance are tendencies towards ce - type charge and orbital ordering in the vicinity of @xmath17.@xcite furthermore a ce - insulator to fm - metal transition has been observed in relatively small magnetic field , which is accompanied by a major change of the optical conductivity on a surprisingly large energy scale ( @xmath18 ev).@xcite such dramatic changes in relatively weak magnetic fields are a clear manifestation of the subtle interplay between spin , orbital and co. the present study provides a basis for further investigations of the temperature dependence of e.g. the optical conductivity and the study of spin and orbital excitations in the ce - phase , as well as the effect of doping into the quarter filled state . the paper is organized as follows . in sec . [ sec : model ] we present the model hamiltonian , and describe in sec . [ sec : lanczos ] the finite - temperature lanczos method . [ sec : numerics ] contains numerical results for different two - site correlation functions characterizing the charge , orbital and spin structure . these correlation functions are evaluated as functions of temperature and collected in a form of semi - quantitative phase diagrams in three different regimes : ( i ) including nearest - neighbor effective orbital - orbital ( oo ) interactions ( sec . [ sec : nnjt ] ) ; ( ii ) assuming the elastic form of oo coupling at different distances ( sec . [ sec : elastic ] ) ; ( iii ) considering the local form of next- and nearest - neighbor oo coupling ( sec . [ sec : nnnjt ] ) , while in sec . [ sec : stacking ] the effect of charge stacking is discussed . the paper is summarized in sec . [ sec : summary ] . in the appendix the stability of the ce versus the c phase is analysed for a 1d band model with lifted orbital degeneracy . we consider the generic fm kondo lattice model for manganites@xcite with the mn @xmath5 electrons coupled to the core @xmath0 spins via the hund coupling @xmath19 . the model is augmented by inter - site coulomb repulsion @xmath13 and cooperative jt interactions and treated in the limit of infinite on - site coulomb repulsion between two @xmath5 electrons on the same site ( @xmath20 ) : @xmath21 the first term describes the motion of the @xmath5 electrons , @xmath22 with a constraint that allows only for mn@xmath14 and mn@xmath7 configurations , @xmath23 , where all other alternative @xmath5 states are projected out . here and in the following the index @xmath24 ( @xmath25 ) denotes the @xmath5 orbital ( spin ) orthogonal to the @xmath26 ( @xmath27 ) one , respectively . the hopping matrix elements depend on the basis chosen . for the basis @xmath28 with @xmath29 and @xmath30 they are given by , @xmath31=\frac{t}{4}\left ( \begin{array}{cc } 3 & \mp\sqrt{3}\\ \mp\sqrt{3 } & 1 \end{array}\right ) , \ ] ] where , @xmath32(@xmath33 ) refer to the @xmath34(@xmath35 ) direction , respectively . the second term of hamiltonian ( [ eq : h_total ] ) stands for the hund interaction between @xmath5 electrons spin and the @xmath36 @xmath0 core spin @xmath37 , @xmath38 resulting in the parallel alignment of spins between @xmath0 and @xmath5 electrons at each site in the limit @xmath39 which corresponds to the realistic situation in manganites . the @xmath40 part of the total hamiltonian alone represents the de mechanism and yields a fm ground state with @xmath41 orbitals being occupied which is favored by the kinetic energy in 2d model . such a fully spin polarized case at finite @xmath42 leads to _ the orbital @xmath43-@xmath44 model _ as considered in refs . . here , we are interested in the more complex case where both spin and orbital degrees of freedom play an active role . therefore , an af ( @xmath45 ) coupling between nearest - neighbor @xmath0 spins is also incorporated , @xmath46 in our numerical studies we assume @xmath47 for the core spins which decreases the resulting hilbert space considerably . we have tested that this assumption gives similar results as in the @xmath36 case when @xmath19 is renormalized@xcite by the factor @xmath48 . moreover , to promote the charge ordering as observed experimentally in half - doped manganites we include the coulomb repulsion ( @xmath49 ) between @xmath5 electrons on neighboring sites,@xcite @xmath50 with @xmath51 . this term reduces the probability of occupancy of neighboring sites by @xmath5 electrons . the form of the inter - site oo interactions included in the @xmath52 term of the hamiltonian will be specified in the following section . to investigate the possible spin and orbital orderings in our spin - orbital model ( [ eq : h_total ] ) we have calculated the temperature dependence of different two - site correlation functions given by the operator expectation value : @xmath53 of two - site operators , @xmath54 with @xmath55 , @xmath56 , @xmath57 , or @xmath58 with @xmath59.@xcite here , @xmath60 , @xmath61 is the number of basis states @xmath62 that span @xmath63 , @xmath64 number of sites in the cluster and @xmath65 is the partition function . the calculation of ( [ eq : a_r_exact ] ) would , however , require a complete diagonalization of a @xmath66 matrix of the hamiltonian . therefore , we use for the calculation of @xmath67 a generalization of the exact diagonalization technique developed by jakli and prelovek.@xcite in this approach the trace of the thermodynamic expectation value is performed by a monte carlo sampling leading to the following approximate expression : @xmath68 where the first sum is performed over a restricted number @xmath69 of random states @xmath70 being initial states in the lanczos algorithm to generate a set @xmath71 of eigenfunctions of @xmath63 with respective eigenvalues @xmath72 . @xmath73 is the number of lanczos functions in the expansion of a given state @xmath70 . in the same manner the partition function is approximated by , @xmath74 it has been shown@xcite that the results get very accurate already for @xmath69 , @xmath75 . even though we exploit the translational symmetry the calculations are restricted to small clusters ( @xmath76 is used in this paper ) as only @xmath77 subspaces can be treated separately , while a similar symmetry in the orbital sector does not exist . although a @xmath78 cluster is large enough to capture the ce - type correlations , boundary conditions can influence further neighbor interactions . to assess such finite size effects quantitatively , a full diagonalization on larger clusters would be necessary . in the case of the co ce phase this would involve at least a @xmath79 site cluster , which is far beyond numerical realization . in the numerical studies we assume @xmath47 for the core spins and the limit of strong hund s coupling @xmath80 . the numerical results are almost identical for all @xmath81 in the whole range of temperatures considered by us . the coulomb repulsion @xmath82 and the af - exchange @xmath83 are free parameters , and the data is summerized in form of a phase diagram in the @xmath84 plane . the hopping parameter @xmath43 is chosen as energy unit . we focus in this study on co states and thus assume finite positive values for @xmath13 in all the calculations . in perovskite manganites the effective hopping @xmath43 strongly depends on the lattice parameters and distortions _ e.g. _ increases with contraction of the mn@xmath33o bond length and also depends on the mn@xmath33o@xmath33mn bond angle.@xcite thus , its value can be only roughly estimated as @xmath85ev.@xcite a major difficulty when searching for spin structures like those indicated in fig . [ fig : spins ] , and the same applies to charge and orbital order , is that in a cluster with periodic boundary conditions translational ( and rotational ) symmetries are not broken . therefore we have to investigate correlation functions and compare their features with the different spin configurations ( presented in fig . [ fig : spins ] ) . schematic view of different spin patterns found in the 2d model in presence of checkerboard co ( half - doped case ) . thick ( thin ) arrows represent states with total spin @xmath86 ( @xmath36 ) with ( without ) an @xmath5 electron present at a given site , respectively . the shaded lines in c and ce phases indicate the direction of de carrier propagation . the preferred directional @xmath5 orbitals occupied at sites @xmath86 are parallel to the shaded paths.,width=226 ] we shall consider three different forms for the orbital interaction term @xmath52 and show that one has to go beyond the nearest - neighbor interactions to obtain the ce - type correlations . we begin the description of our calculations with a simplified model ( without @xmath87 term ) but including the crystal - field splitting of @xmath5 orbitals @xmath88 , @xmath89 where @xmath90 is the @xmath91 component of the pseudospin operator . this orbital splitting accounts for the elongation of octahedra along the c - axis in layered compounds , which favors @xmath92 over @xmath41 orbital occupation , and also counterbalances the trend towards occupation of @xmath41 orbitals , which is strongly favored by the kinetic energy in the 2d - model . although , the model without @xmath87 interactions can lead to the stability of the ce - type orbital pattern,@xcite the magnetic structure was fm . in a wide range of parameters @xmath93 , @xmath94 , @xmath95 no stabilization of the af ce spin phase was found , indicating that the inter - chain coupling is quite strong and can not be neglected in realistic models for half - doped co manganites . such a conclusion agrees this recent density - functional calculations showing a considerable band dispersion normal to the chains.@xcite thus , we argue that the _ topological effect _ considered in 1d model approximations , which gave a simple explanation of the existence of the ce spin - orbital phase at half - doping , is not likely to be the decisive mechanism in a more realistic 2d case investigated here . our simulations with purely electronic interactions do not provide evidence for 1d fm chains that are coupled antiferromagnetically to neighbor chains , which is the basic assumption that could justify such 1d models . therefore , in the following sections we concentrate on the electron - lattice coupling@xcite and present a mechanism stabilizing the ce spin / orbital state in manganites . phase diagram indicating the character of the dominant spin correlations found at small temperatures @xmath96 . the calculations include the nearest - neighbor oo effective interactions ( @xmath97 ) . @xmath98 indicates representative points for which the correlation functions are presented below.,width=132 ] the first aim of our study of the spin - orbital model ( [ eq : h_total ] ) in half - doped manganites is to investigate the role of nearest - neighbor oo coupling played in co state . there are two different mechanisms contributing to this interaction : ( i ) the cooperative jt effect@xcite and ( ii ) superexchange interactions.@xcite neglecting more complex spin - orbital terms@xcite both effects can be described by the following simple term derived before for undoped lamno@xmath4 compound,@xcite @xmath99 where the two - site orbital operator , @xmath100 , between nearest - neighbor mn sites in the @xmath28 basis , @xmath101 is described in terms of pseudospin operators : @xmath102 , and @xmath103 . the prefactor of the mixed term @xmath104 is negative in the @xmath34 direction and positive in the @xmath35 direction . the nearest - neighbor oo term can lead to _ attraction _ of electrons on neighboring sites with different orbital orientations but having the coulomb repulsion ( [ eq : h_v ] ) included in the model we avoid phase separation . temperature dependence of the charge ( a ) , orbital ( b ) , and spin ( c ) two - site correlation functions calculated for neighbors at different distances @xmath105 for the phase with fm spin correlations . parameters : @xmath106 , @xmath97 , @xmath107 , @xmath108.,width=377 ] temperature dependence of the correlations as in fig . but for the phase with af spin correlations . parameters : @xmath109 , @xmath97 , @xmath110 , @xmath108.,width=377 ] temperature dependence of the charge ( a ) , orbital ( b ) , and spin - charge ( c ) correlation functions calculated for the phase with c spin correlations . parameters : @xmath106 , @xmath97 , @xmath111 , @xmath108.,width=377 ] as shown in fig . [ fig : oonn_phase ] for large values of the superexchange interaction between core spins ( @xmath112 ) an af spin ground state is realized while with decreasing @xmath15 the kinetic energy of the @xmath5 electrons ( @xmath113 ) starts to play an active role via the de mechanism@xcite breaking some of the af bonds which leads to 1d fm chains which form straight lines ( c phase ) . further decrease of @xmath15 yields fm correlations in both @xmath34 and @xmath35 directions . as the kinetic energy is controlled by the inter - site coulomb repulsion @xmath13 and suppressed in the limit of @xmath114 we find the af region increasing in size with increasing @xmath82 . we discuss now in more detail the temperature dependence of the different correlation functions . starting from the fm region ( see fig . [ fig : corr_fm_nn ] ) we find the evolution of weak co for @xmath115 with nearest - neighbor @xmath116 charge correlations smaller than the @xmath117 and @xmath118 next - neighbor ones which is consistent with the alternating order of mn@xmath1 and mn@xmath2 ions . the orbital correlations are positive between all neighbors indicating the preference of @xmath6 orbital occupancy due to the kinetic energy which is quite large in the fm state . although all spin correlation functions are positive , they remain highly anisotropic as @xmath119 as a result of the strong competition between the de mechanism and af superexchange interaction between core spins . next , we consider the af spin state in the case of large @xmath15 and @xmath13 ( see fig . [ fig : corr_af_nn ] ) . increasing coulomb repulsion ( @xmath109 ) we find more distinct and almost isotropic alternation of the @xmath5 charge which now sets in already at @xmath120 . here , the orbital correlations are correlated with the onset of the af spin order at @xmath121 . for @xmath122 the spin - spin correlations are strong and represent an almost isotropic af spin state . for intermediate values of @xmath15 and moderate coulomb repulsion we find the phase with predominantly c spin correlations at @xmath122 ( see fig . [ fig : oonn_phase ] ) . as presented in fig . [ fig : corr_c_nn ] for @xmath123 and @xmath124 the charge correlations are similar to those obtained for the fm state shown in fig . [ fig : corr_fm_nn ] ( a ) while the spin ordering changes dramatically . moreover for @xmath122 the orbital correlations are weaker than those found in the fm state discussed above indicating the orbital tendency towards in - plane directional - type order . a convenient way to distinguish between phases with c or ce and other spin correlations is to evaluate a _ combined spin - charge correlation function _ being restricted to sites occupied by @xmath5 electrons , @xmath125 . analyzing the localized limit presented in fig . [ fig : spins ] ( or its by @xmath126 rotated version ) one can easily see that , for the c phase one should find @xmath127 for @xmath128 and @xmath129 for @xmath130 while for the ce phase only @xmath129 for @xmath128 with any other spin - charge correlations remaining small . in the case presented in fig . [ fig : corr_c_nn ] @xmath125 functions are negative ( positive ) for nearest - neighbors along diagonal ( next - nearest - neighbors along @xmath34/@xmath35 direction ) , respectively , in agreement with the arguments presented above . furthermore , nearest - neighbor spin - charge correlations are small as a result of averaging over different cluster orientations ( rotated by angles @xmath131 , @xmath132 ) . it is straightforward to see why the c - structure is favored by the nearest - neighbor jt interaction . the c - phase can be viewed as a realization of the alternating orbital structure of lamno@xmath4 but with a modulated charge density . hence this structure is compatible with the nearest - neighbor jt interaction , whereas in the ce - structure this interaction is frustrated . the role of local lattice distortions due to the jt effect , which creates an anisotropic strain field decaying as @xmath133 and thereby promotes long - range orbital ordering , was considered by khomskii ( see ref . ) . following these arguments , we treat the oo term as an elastic interaction which is active also between @xmath5 electrons on next - nearest - neighbor sites along @xmath34 or @xmath35 direction , @xmath134 where @xmath135 refers to next nearest - neighbors along @xmath34 and @xmath35 direction with @xmath136 which follows from the @xmath137 decay of elastic interactions.@xcite the existence of longer - range oo interactions is justified by its cooperative lattice - driven nature where an orbital flip on a single mn site distorts not only the neighboring oxygens but also positions of other manganese ions around it . here , the jt coupling preferring the tilting of the orbitals from the uniform orbital state leads to an alternating orbital order ( see fig . [ fig : ce_orb ] ) and in this way compensates for the kinetic energy gain in uniform @xmath41 orbital state favored in the 2d model . here we neglect non - central elastic interactions between neighboring mn sites in @xmath138 direction as their strength does not scale with @xmath139 ( see ref . ) and thus would involve introduction of an additional parameter in the model . schematic configuration of the charge - orbital ordered ce phase . the sites * a * and * b * indicate two orbital mn@xmath7 sublattices while empty circles stand for the mn@xmath14 ions . the dashed - line box indicates a typical orbitals orientation around a given mn@xmath14 ion.,width=226 ] phase diagram as in fig . including the nearest- and next - neighbor elastic interactions ( @xmath97 , @xmath136 ) . @xmath98 indicates a representative point in the ce region for which the correlation functions are presented here.,width=132 ] temperature dependence of the two - site correlations as in fig . but for the phase with ce spin and orbital correlations promoted by elastic interactions ( @xmath97 , @xmath136 ) . other parameters : @xmath140 , @xmath141 , @xmath108 . the inset in ( b ) shows the orbital correlations in the rotated basis : @xmath142.,width=377 ] the ce phase is favored as compared to the c phase by the oo coupling between second neighbors ( @xmath143 ) along @xmath34/@xmath35 direction . however , this interaction is only active ( not screened ) when strong charge ordering takes place ( large @xmath82 case ) and here the ce phase can persist even for small values of @xmath15 as long as the @xmath5 kinetic energy is sufficiently suppressed by a large @xmath13 ( see fig . [ fig : elastic_phase ] ) . thus , one has to assume large inter - site coulomb repulsion ( where almost perfect mn@xmath1/mn@xmath2 charge ordering@xcite is realized ) and small superexchange interaction [ see an example for @xmath144 and @xmath145 in fig . [ fig : corr_ce_el ] ] . in the @xmath28 basis , which we use in most of the numerical evaluations , the spin and orbital correlation functions with @xmath146 become large as @xmath119 while all the others remain very small in the whole range of temperatures . such small orbital correlations imply either that the respective orbitals are uncorrelated or that they order in such a way , that the occupied orbitals are linear combinations with almost equal amplitude expressed in the basis used for the measurement of correlation functions.@xcite this difficulty is not present in su(2 ) symmetric models , and appears here as consequence of the cubic symmetry in the orbital sector . therefore , the same functions were evaluated also in the @xmath142 basis as presented in the inset of fig . [ fig : corr_ce_el ] ( b ) . in the new orbital basis the function @xmath147 is more pronounced and saturates for @xmath148 at @xmath149 close to its maximum value @xmath150 indicating almost perfect ce orbital structure ( see fig . [ fig : ce_orb ] ) . shorter range @xmath151 correlations should become small when averaged over differently oriented clusters ( rotated by angles @xmath131 ) [ see fig . [ fig : spins ] ( d ) ] . from fig . [ fig : spins ] ( d ) one can see that a similar pattern as found for the two - site orbital correlations should be found for the @xmath125 functions . in our cluster in ideal ce state only electrons at distance @xmath128 can contribute to the charge - spin correlations ( being negative in this case ) which do not vanish when averaged over different cluster orientations . as shown in fig . [ fig : corr_ce_el ] ( c ) the @xmath125 correlations obtained here are consistent with the above characterization of the ce pattern with a strong negative signal dominating at distance @xmath128 . the existence of charge - ordered insulating state concomitant with orbital and spin order of the ce - type@xcite was observed in different half - doped manganites with small one - electron bandwidth.@xcite the average change in the orbital occupation can be studied calculating @xmath152 which changes between @xmath153 and @xmath154 for the uniform @xmath41 and @xmath92 orbital states , respectively , for the case with one @xmath5 electron per two mn sites . furthermore , when the orbital state involves @xmath41 and @xmath92 orbitals in the same proportion one finds @xmath155 . in fig . [ fig : tz_susc_el ] ( a ) we see that increasing the coulomb interaction from @xmath106 to @xmath109 the orbital ordering hardly changes for @xmath122 with @xmath152 only slightly decreasing to @xmath156 for @xmath109 . this indicates that as long as the system is in the fm state ( see fig . [ fig : elastic_phase ] ) the ground state is dominated by the @xmath6 orbital promoted by the kinetic energy term . further increase in the coulomb inter - site repulsion to @xmath140 leads to a drastic change in the orbital order when system enters the ce phase region ( see fig . [ fig : elastic_phase ] ) . here , @xmath157 for @xmath122 indicating dominating role played by the @xmath158 orbitals . this fact is consistent with our results for the two - site orbital correlation functions [ see inset in fig . [ fig : corr_ce_el](b ) ] . temperature dependence of the average value of the @xmath159 orbital operator ( a ) and the inverse of the staggered charge susceptibility @xmath160 ( b ) obtained for different values of the inter - site repulsion @xmath82 in the presence of elastic interactions ( @xmath97 , @xmath136 ) . other parameters : @xmath141 , @xmath108.,width=226 ] a change in the inter - site coulomb interaction is directly connected with the robustness of the charge ordering as seen in figs . [ fig : corr_fm_nn ] - [ fig : corr_c_nn ] ( a ) and fig . [ fig : corr_ce_el ] ( a ) . although the characteristic temperature of the co ( @xmath161 ) can be roughly estimated from the charge - charge correlation functions it can be more precisely extracted from the staggered charge susceptibility,@xcite @xmath162 : @xmath163 which at high temperatures follows a curie - weiss law @xmath164 . from fig . [ fig : tz_susc_el ] ( b ) one can easily estimate @xmath165 , @xmath166 , and @xmath167 for @xmath168 , @xmath169 , and @xmath170 , respectively , in agreement with the mean - field solution@xcite which for @xmath114 predicts , @xmath171 . although the model considered in the previous section with longer - range oo elastic coupling leads to the ce - type spin and orbital correlations , this phase is found only in a very extreme case of almost perfect mn@xmath14/mn@xmath7 co ( that is for strong coulomb repulsion ) which may not be very realistic in the light of some experimental facts indicating the cdw character of charge redistribution between different manganese ions.@xcite therefore in this section we derive the further neighbor oo interactions from a microscopic model including apart from the jt - distortion of the mn@xmath7 octahedra the breathing distortion around the mn@xmath14 ions as well . we then show that this interaction is capable to produce the zigzag ( spin and orbital ) phase in a region of small coulomb repulsion changing the previous phase diagrams in a drastic way . to assess the gain in lattice energy connected with the formation of the ce long - range orbital order we follow the work of millis for lamno@xmath4 by treating the lattice distortions classically.@xcite the effect of lattice displacements is described by assuming arbitrary values of four different lattice distances @xmath172 ( @xmath173 ) ( see fig . [ fig : distortions ] ) which are expressed by @xmath174 , @xmath175 uniform deformation along the @xmath34 and @xmath35 direction of the mn lattice , and @xmath176 displacements of o ions along the mn o mn bonds within the @xmath177 planes : @xmath178 where @xmath35 is the lattice constant of the ideal perovskite.@xcite moreover , we assume @xmath5 charge stacking in the @xmath179 direction with the respective mn mn distance being @xmath180 . schematic representation of the lattice distortions contributing to the second neighbor jt - interaction . the corresponding ce orbital order for the 5 atom structure above is indicated in fig . by dashed lines . different mn@xmath7 , mn@xmath14 , and o ions are presented by full , shaded and empty circles , respectively . the distances between the mn@xmath14 ion and the mn@xmath7 ions in @xmath181 [ @xmath182 and @xmath183 [ @xmath184 directions , respectively , are identical . the arrow indicates the displacement of the central mn@xmath14 ion when @xmath185.,width=283 ] phase diagram as in fig . including the local nearest- and next - neighbor oo interactions with @xmath97 and @xmath186 ( spring constants @xmath187 ) . @xmath98 indicate representative points in the ce region for which the correlation functions are presented here . the dashed arrow presents the direction of the transition from the localized ce to the itinerant electron a - phase at low temperatures.,width=132 ] in order to define orbital sublattices ( a and b ) we introduce a transformation which describes the tilting of orbitals by making two different transformations at both sublattices,@xcite @xmath188 = \left [ \begin{array}{cc } \cos\left(\frac{\pi}{4}\pm\phi\right ) & \sin\left(\frac{\pi}{4}\pm\phi\right ) \\ -\sin\left(\frac{\pi}{4}\pm\phi\right ) & \cos\left(\frac{\pi}{4}\pm\phi\right ) \end{array}\right ] \left [ \begin{array}{c } \end{array}\right ] , \ ] ] where @xmath33 ( @xmath32 ) refers to @xmath189 ( @xmath190 ) sublattice , respectively , and @xmath191 . here , @xmath192 and @xmath193 stands for local basis orbitals : @xmath41 and @xmath92 at site @xmath194 , respectively . in the rotated basis @xmath195 we assume for the transformed operators : @xmath196 ( @xmath197 ) for @xmath189 ( @xmath198 ) sublattice , respectively . at intermediate values of @xmath199 one can reach , e.g. , @xmath200/@xmath201 ( @xmath202/@xmath203)-type orbital ordering at @xmath204 ( @xmath205 ) , respectively . the rotation ( [ eq : rotation ] ) does not include complex orbital order which was proposed as a possible orbital order in manganites at smaller doping.@xcite the classical energy of the distorted lattice @xmath206 ( per mn site ) is given by,@xcite @xmath207 + k_1\left(u_1 ^ 2 + u_2 ^ 2\right),\ ] ] normalized per mn ion , where @xmath208 ( @xmath209 ) are the nearest - neighbor mn o ( mn mn ) spring constant , respectively . here the force constants include the factor @xmath210 , and hence have the dimension of an energy . next , we have to add the energy of the breathing mode ( bm ) describing the attraction between oxygen ions and the unoccupied mn@xmath2 site : @xmath211 here , all oxygens are equally attracted towards the central manganese ion . the bm induces charge alternation on neighboring mn sites and contributes to the effective inter - site charge - charge repulsion ( @xmath13 ) . the coupling constant to the breathing distortion is written as @xmath212 , where @xmath213 denotes the coupling to the jt distortion . the term describing the jt coupling depends on the character of the occupied orbital at a mn@xmath1 site . the jt interaction describes the coupling between the occupied @xmath5 orbital at a particular mn@xmath7 ion and the distortions of the surrounding oxygen ions , as introduced by millis.@xcite in the orbitally rotated state ( [ eq : rotation ] ) this energy has the following form , @xmath214\sin(2\phi)\right . \nonumber\\ & - & \left.\sqrt{3}\cos(2\phi)\left[\frac{1}{2}\left(\delta_x - \delta'_x\right ) + u_2 - u_1\right]\right\},\end{aligned}\ ] ] and depends on the rotation angle @xmath199 and on the deformation of the lattice . the optimal values of the ionic displacements for a given angle @xmath199 are found by minimization of the total energy , @xmath215 , which for ( [ eq : e_l])-([eq : jt ] ) and neglecting higher - order nonlinear terms gives , [ eq : dis ] @xmath216 } { 2\left(k_1 + 2k_2\right ) } , \\ \delta'_x & = & \frac{-\lambda\left[2\beta -\sin(2\phi)+\sqrt{3}\cos(2\phi)\right ] } { 2\left(k_1 + 2k_2\right ) } , \\ \delta_z & = & \frac{-\lambda\left[\beta+\sin(2\phi)\right]}{k_1 + 2k_2 } , \\ u_1 & = & \frac{-\lambda\left[2\beta+\sin(2\phi)+\sqrt{3}\cos(2\phi)\right ] } { 4k_1 } , \\ u_2 & = & \frac{-\lambda\left[2\beta+\sin(2\phi)-\sqrt{3}\cos(2\phi)\right ] } { 4k_1 } .\end{aligned}\ ] ] this yields for the total energy of the distorted lattice , @xmath217 + 2k_1+k_2\right\ } .\nonumber \\\end{aligned}\ ] ] this implies a change of the volume of the lattice with respect to the ideal perovskite ( @xmath218 ) @xmath219 . hence the volume decreases with increasing bm coupling @xmath220 , but does not depend on the character of the orbital order . the relative strength of the effective next- and nearest - neighbor jt interactions can be obtained by comparing the lattice stiffnesses of the orbital modulations in the undoped ( @xmath221 ) and the quarter - filled ( @xmath222 ) case , respectively . for _ undoped _ lamno@xmath4 the lattice energy was found to be [ see eq . ( 2.14 ) in ref . ] , @xmath223\right\ } , \label{eq : e^0}\ ] ] in the half - doped case the orbital alternation at mn@xmath7 neighbors is driven by the mn@xmath14 ion shift . the energy ( 21 ) can be decomposed @xmath224 , where @xmath225 is the gain of energy due to the mn@xmath14 displacement : @xmath226 . \label{eq : de}\ ] ] this cooperative energy does not depend on the breathing mode coupling @xmath220 directly , though there is an indirect dependence via @xmath227 influencing the optimal value for @xmath199 . contrary to the undoped case ( [ eq : e^0 ] ) , where the mn - mn potential ( @xmath228 ) is necessary to obtain finite orbital stiffness , in the half - doped case ( [ eq : de ] ) the mn - o interaction alone can lead to cooperative jt effect stabilizing the alternating orbital order . assuming @xmath229ev , @xmath230 ev , and @xmath231 ( see ref . ) one finds for the @xmath232 ( @xmath233 ) orbital order the ce energy contribution per mn ion @xmath234 mev . in table [ tab : ene ] we present the ratio @xmath235 , characterizing the stability of the ce orbital order , as function of the bm coupling strength @xmath220 and the ratio of spring constants @xmath236 . the largest relative gain in energy due to the mn@xmath14 ions shift ( @xmath237 ) is obtained for the @xmath238 orbital order ( @xmath233 ) which for small bm coupling ( @xmath239 ) can reach up to @xmath240 of the total lattice energy , whereas for larger values of @xmath220 , although @xmath225 is not changed , the total lattice energy increases rapidly as @xmath241 being dominated by the distortions of the mno@xmath16 octahedra rather then by their displacements . furthermore , with increasing mn lattice stiffness ( @xmath242 ) both the @xmath235 ratio and the shift of unoccupied mn@xmath14 ions [ @xmath243 decrease . .[tab : ene ] the relative energy gain , @xmath235 , associated with the mn@xmath14 ion displacement ( see fig . ) for the orbital orderings given by @xmath233 and @xmath244 presented as function of @xmath220 and @xmath236 . [ cols="<,^,^,^,^",options="header " , ] correlation functions in the case of a ce ground state ( as in fig . ) but obtained for the local oo interaction ( 26 ) with spring constants @xmath187 ( @xmath245 ) . other parameters : @xmath106 , @xmath97 , @xmath141 , @xmath108.,width=377 ] charge correlations in the case of a fm ground state as obtained for the local oo interaction with spring constants @xmath187 ( @xmath245 ) . other parameters : @xmath246 , @xmath97 , @xmath247 , @xmath108.,width=132 ] comparing the cooperative part [ @xmath248 of both jt energy contributions [ ( [ eq : e^0 ] ) and ( [ eq : de ] ) ] we end up with a simple relation between different oo interaction strengths , @xmath249 for @xmath250 the @xmath133 scaling of elastic interactions@xcite is recovered . in the above estimate we have neglected the superexchange interaction which can also contribute to the effective @xmath251 [ see _ e.g. _ eq . ( 2.7 ) in ref . ] . the relative strength of both spring constants in the co case can be assessed from the relative length of different bonds in the half - doped mno@xmath8 plane . as measured for low - temperature la@xmath252ca@xmath252mno@xmath4 superstructure@xcite the length of all four in - plane mn@xmath14-o bonds is very similar ( @xmath253 ) . neglecting the effect of mn - o - mn bond bending and assuming @xmath254 ( see fig . [ fig : distortions ] ) one obtains the relation , @xmath255 by using eqs . ( [ eq : dis ] ) . the above assessment together with ( [ eq : kappa_ratio ] ) underlines the importance of mn@xmath7mn@xmath7 orbital coupling ( @xmath222 ) in co manganites . the structural data of radaelli _ et al._@xcite may be used in combination with eqs . ( [ eq : dis ] a - e ) to infer the values for @xmath213 and @xmath220 . we have not attempted to determine the force constants as well , but assume @xcite @xmath230 ev . using basically data for the jt - distortion of mn@xmath7o in - plane bonds ( @xmath256 and @xmath257 ) and the mn@xmath14 displacement , we obtain for @xmath258 @xmath259 and @xmath260 ev , respectively . we note that the ratio @xmath261 is rather close to the values determined by millis@xcite for lamno@xmath4 . this also implies that the energy gain due to the breathing distortion is substantial [ see eq . ( [ eq : e_tot ] ) ] . we return to the many - body theory for a translation invariant system . as the oo interaction between further mn@xmath7 neighbors is mediated by an mn@xmath14 ion we introduce the following effective three - site interaction , @xmath262 where the operator @xmath263 is defined as in eq . ( [ eq : tij ] ) , and @xmath264 denotes three neighboring sites along @xmath34 or @xmath35 direction . the reasoning here is similar as for the nearest - neighbor jt interaction in eq . ( [ eq : h_oo ] ) , i.e. , the expectation value of the operator @xmath263 in an orbital ordered state depends on the orbital angle precisely as in eq . ( [ eq : de ] ) , namely @xmath265 $ ] . the @xmath266 factor in eq . ( [ eq:3site ] ) reflects the charge state of mn@xmath14 and favors co in the quarter - filled system , while the contribution of the interaction ( [ eq:3site ] ) would vanish in the undoped compound . investigating the model ( [ eq : h_total ] ) with both nearest - neighbor ( [ eq : h_oo ] ) and three - site ( [ eq:3site ] ) oo couplings we find a strong change in the low - temperature phase diagram ( see fig . [ fig : oonnn_phase ] ) as compared with the previous ones ( figs . [ fig : oonn_phase ] and [ fig : elastic_phase ] ) . assuming @xmath245 ( which corresponds to @xmath267 ) , the ce - like correlations set in already at rather small inter - site repulsion ( @xmath268 ) while for stronger coulomb interactions ( @xmath269 ) the spin correlations have predominantly af character . furthermore , the fm region is quite small and can be found only for @xmath270 and @xmath271 . when decreasing the ratio @xmath236 ( and keeping the value of @xmath139 constant ) the fm region shrinks at the expense of the ce region . next , we present the two - site correlations for one representative ( @xmath106 , @xmath141 ) point in the ce region in fig . [ fig : oonnn_phase ] . from fig . [ fig : corr_ce_nnn ] ( a ) one sees that the ce state can exist for less pronounced co than in the elastic strain model considered in sec . [ sec : elastic ] , where almost perfect mn@xmath7/mn@xmath14 co was necessary to stabilize the zigzag state ( see fig . [ fig : corr_ce_el ] ) . moreover , the evolution of ce - type orbital order with decreasing temperature is here correlated with the onset of co [ compare fig . [ fig : corr_ce_nnn ] ( a)-(b ) with [ fig : corr_ce_el ] ( a)-(b ) ] . regarding @xmath125 correlations , the ce - type spin order develops at lower temperatures than the charge and orbital order but at higher temperature than previously found for the strain induced interactions . the three - site term ( [ eq:3site ] ) which is active for a mn@xmath7mn@xmath14mn@xmath7 sequence along the @xmath34 and @xmath35 direction , respectively , promotes not only orbital alternation on neighboring mn@xmath7 sites but also strengthens co. this is clearly seen in the charge correlations which are now stronger than those _ e.g. _ in fig . [ fig : corr_fm_nn ] , although the same coulomb repulsion ( @xmath106 ) was assumed in both cases . going from the ce to the fm phase ( as indicated by an arrow in fig . [ fig : oonnn_phase ] ) one finds that the cdw is now reduced at low temperatures in the fm state ( fig . [ fig:<nn > ce ] ) , while the charge modulation is still rather strong at higher temperatures ( @xmath121 ) above the nel temperature where the electron kinetic energy is quenched due to the random @xmath0 spin orientations . this behavior is a clear manifestation of the de mechanism . we note that the ce - type orbital correlations are still present in the fm phase in fig . [ fig : oonnn_phase ] for @xmath272 , whereas for smaller values for @xmath13 @xmath273-@xmath274 orbital correlations dominate , which are characteristic for the metallic a - phase . finally , we consider possible mechanisms stabilizing the charge stacking of ce - ordered planes @xcite as observed in most charge - ordered manganites at doping @xmath275 . any interaction stabilizing such a stacking must overcome the inter - site charge - charge repulsion . there are two interactions which contribute to such a repulsion : ( i ) the electron - electron coulomb force @xmath13 ; and ( ii ) the bm coupling . both interactions will effectively tend to maximize the number of mn@xmath7mn@xmath14 bonds . the bm coupling contribution to the inter - site charge - charge repulsion ( @xmath276 ) can be estimated comparing the lattice energies with charge alternating and stacked along the @xmath179 direction which leads to the estimate @xmath277 ^ 2 /(2k_1)$ ] . assuming typical values for @xmath278 and @xmath279 ( see ref . ) together with our previous estimate @xmath280 one can obtain _ @xmath281 for the @xmath142 ce orbital order . in a multi - layer system the oo interaction along the @xmath179 direction is given by the nearest - neighbor coupling @xmath221 , which in the @xmath28 basis has the form,@xcite @xmath282 energy gained by @xmath5 electron stacked in the @xmath179 direction as function of charge modulation @xmath283 obtained for @xmath246 , @xmath186 and different values of @xmath251.,width=264 ] this interaction together with the @xmath222 coupling , which controls the ce - orbital order in the @xmath177 plane , in a charge - ordered case yields an approximate orbital model of the form , @xmath284 where @xmath56 ( @xmath285 ) are defined with respect to the @xmath142 orbital basis . defining @xmath286 and assuming that in the @xmath177 planes of a bilayer system @xmath287 and @xmath288 orbitals are occupied on two neighboring sites in the @xmath179 direction , the @xmath221 coupling [ see eq . ( [ eq : stacking ] ) ] rotates orbitals towards the @xmath289 configuration and leads to binding of two electrons with energy @xmath290 . for charge disproportion with mn@xmath291 ions alternating in the @xmath177 planes and assuming that the @xmath251 ( @xmath139 ) two ( three)-site interaction scales as @xmath292 with @xmath293 ( @xmath48 ) , respectively , one finds for the energy gain ( per mn ion ) due to charge stacking along @xmath179 direction for a 3d lattice : @xmath294 -2\delta^2v .\ ] ] the last term stands for the effective coulomb repulsion at given charge modulation . with charge modulation sufficiently reduced @xmath295 ( see fig . [ fig : stacking ] ) the oo inter - plane coupling can stabilize charge - stacked phase ( @xmath296 ) . such stabilization is strengthened ( weakened ) by increasing @xmath251 ( @xmath139 ) oo interaction , respectively . for smaller charge disproportion ( @xmath297 ) and considerable charge on mn@xmath298 sites the @xmath221 in - plane coupling [ neglected in eq . ( [ eq : stacking ] ) ] can also play an important role in the inter - plane charge modulation . however , when the co is strongly reduced the orbital ground state is too complex to be analyzed analytically . a further mechanism stabilizing the observed @xmath5 charge stacking along the @xmath179 direction results from the af inter - plane superexchange interaction.@xcite yet , the magnetic interaction ( @xmath299 ) results mainly from the @xmath300 superexchange which is of the order of only a few mev.@xcite thus , the antiferromagnetism in the @xmath179 direction observed in most of the ce structures appears to be a _ result _ rather than the _ origin _ of the stacking pattern of the charge / orbital order . we have investigated the potential of different electron - lattice mechanisms to stabilize the ce spin - orbital ordered phase in charge ordered half - doped manganites ( filled with one @xmath5 electron per two mn ions ) . our study is based on a generalized de model containing the @xmath5 orbital degrees of freedom , and also including inter - site coulomb repulsion ( @xmath13 ) and af superexchange ( @xmath15 ) between core spins . the effect of three types of orbital interactions derived from the cooperative jt effect have been studied : ( i ) nearest neighbor jt - coupling , which is responsible for the alternating orbital order in undoped lamno@xmath4 , ( ii ) in addition second neighbor jt - interaction with a strength as expected for elastic strain , and ( iii ) a 2nd neighbor jt interaction which accounts for the breathing distortion of the mn@xmath14 octahedra and is in general stronger than ( ii ) . a particular feature of this interaction , which has been proposed based on the classical model considerations in sec . [ sec : nnnjt ] , are the displacements of the mn@xmath14 ions in the ce - phase . we have studied these models employing finite temperature diagonalization on a @xmath78 cluster with periodic boundary conditions , thereby keeping the translational invariance . the evolution of the different phases with temperature is monitored by the calculation of correlation functions for charge , orbital and spin , respectively . starting out from the generalized fm kondo lattice model ( [ eq : h_total ] ) without any orbital interaction ( @xmath301 ) we find the orbital correlations dominated by the @xmath6 orbitals which are favored by the kinetic energy.@xcite this orbital state is characteristic for the metallic a - phase in wide - band manganites at half doping . for small af superexchange interactions ( @xmath302 ) between @xmath0 core spins the fm state is found in the spin sector , while for larger values of @xmath15 the ground state is that of a regular 2 sublattice antiferromagnet . even for large coulomb repulsion @xmath13 we found no evidence for c or ce structures for some intermediate values of the parameter @xmath15 . the inclusion of the nearest - neighbor jt - interaction ( i ) , however , was found to stabilize the af - c phase in a wide parameter range in the @xmath303 phase diagram . to obtain the more complex ce orbital and spin state not only the kinetic energy must be reduced by increasing the coulomb repulsion @xmath13 but also a further neighbor _ antiferro - orbital _ interaction must be included in the model . this interaction results from the electron - lattice coupling and is a generalization of the jt interaction which was found to play an important role in the parent lamno@xmath4 compound.@xcite in co compounds at quarter - filling the effect of the oo coupling will be dominated by interactions between further distant mn neighbors . we have shown that such interactions can produce the ce structure in both _ spin and orbital _ sectors . in the case of the three - site effective interaction ( @xmath143 ) the zigzag chains are found to be stable not only for modest inter - site repulsion ( @xmath268 ) but even in the limit of @xmath304 and provided @xmath251 is small , where the co is induced entirely by the three - site orbital coupling ( [ eq:3site ] ) . this effective next - nearest - neighbor oo coupling was derived taking into account the cooperative nature of both mn@xmath7o and mn@xmath7mn@xmath14 bonds length deformation . the free relaxation of the latter length leads in presence of co to orbital alternation in planar directions , and the pattern of directed orbitals typical for the orbital ce structure appears . consequently , with the help of the orbital topology,@xcite this gives rise to the ce af spin ordering for realistic values for @xmath15 . an important aspect of the second neighbor jt - interaction ( iii ) is its 3-site structure which involves a coupling to the charge at the mn@xmath14 ion . this implies that the evolution of the ce orbital correlations with temperature are linked to the evolution of co , while the magnetic ce correlations develop at lower temperature similar to pr@xmath3ca@xmath3mno@xmath4@xcite . this is different from ( ii ) , where first co develops , then oo and finally at lowest temperature af spin order . as discussed in sec . [ sec : parameters ] we did not find the ce spin and/or orbital phase considering a pure electronic model , i.e. , neglecting the electron - lattice coupling . although , the topological effect combined with the de mechanism leads to the preference of the ce over c phase when all @xmath5 ( bridge and corner ) orbitals are degenerate,@xcite the situation is more complex when such degeneracy is lifted by jt lattice distortions . as described in the appendix , one finds band insulators in both cases while the stability of the ce versus the c phase strongly depends on the crystal - field splittings ( @xmath305 , @xmath306 ) . an important issue is the degree of charge ordering in the ce phase . the ce spin - orbital structures obtained in our simulations appear in the regime of relatively strong co , as infered from our calculated charge correlation functions . our calculations also suggest that the second neighbor jt coupling even for small or vanishing coulomb repulsion can lead to a pronounced charge modulation . these results are consistent with the simple physical picture , that de perpendicular to the fm chains must be strongly suppressed to allow af superexchange to trigger the ce structure , which may not be the case for weak co. on the other hand , a recent study by mahadevan , terakura and sarma@xcite based on the band structure approach arrived at the conclusion that the charge difference between the two mn species in the ce phase is basically negligible , which would imply the absence of a significant breathing distortion of mn@xmath14 octahedra . further experimental information on the degree of lattice distortion in the ce phase will certainly help to test the proposed jt based mechanism for the stability of the ce phase . the charge modulations determined in our calculations may be influenced by numerical limitations which overestimate quantum fluctuations : ( i ) spins @xmath47 are used to describe @xmath0 electrons ; ( ii ) the calculations are made using a 2d cluster ; ( iii ) the oxygen ions are not present explicitly in the cluster and thus only _ dynamical _ interactions are included ( @xmath307 ) , which are mediated by oxygen displacements , while possible _ static _ lattice effects@xcite are neglected . certainly each of these approximations weakens the charge ordering and the spin - orbital order . it is , however , not straightforward to decide whether the region of the ce - phase in the phase diagram may grow or shrink , if quantum fluctuations are suppressed . finally we note that further neighbor jt interactions can also play an important role in the charge stripe formation at other commensurate carrier concentrations . for @xmath308 ( @xmath309 ) the dominant coupling arises from the nearest- ( next nearest- ) neighbor oo interactions , respectively , with a pronounced electron - hole asymmetry present . in the latter case with small inter - site coulomb repulsion ( @xmath13 ) the bi - stripe state@xcite would be preferred while larger values of @xmath13 would favor a `` wigner crystal '' charge arrangement.@xcite we would like to thank g. khaliullin , m. mayr and a. m. ole for stimulating discussions and valuable comments . j. b. acknowledges the support of the mpi fr festkrperforschung , stuttgart . the financial support by the polish state committee of scientific research ( kbn ) of poland , project no . 5 p03b 055 20 is also acknowledged ( j. b. ) . a quite appealing explanation for the stability of the ce as compared to the c phase was suggested in refs . by considering a 1d model , where in the ce phase a gap opens as a consequence of a topological sign in the hopping matrix - elements . however , the intra - site coulomb repulsion @xmath42 ( leading to some redistribution of the @xmath5 charge ) can destabilize the ce phase.@xcite here we investigate how these arguments are modified when orbital degeneracy is lifted due to jt distortions . we consider the hamiltonian : @xmath310 which contains the kinetic energy @xmath311 of an electron hopping along a fm chain@xcite with possible @xmath5 level shift at the bridge sites ( @xmath312 ) and level splitting at corner sites ( @xmath313 ) considered in two different orbital basis @xmath28 and @xmath314/@xmath315 orbitals are located between the split energy levels at the corners assuming @xmath316 . both kinds of level shifts can result from the lattice distortions . at the bridge site only the orbital @xmath317 ( @xmath315 ) is considered while the orthogonal one @xmath318 ( @xmath319 ) , respectively , is decoupled in chain direction . in momentum space this leads to a @xmath320 matrix problem : @xmath321 \left(\begin{array}{c } d_{b , k}\\ d_{x , k}\\ d_{z , k}\end{array } \right ) , \ ] ] where @xmath322 ( @xmath323 ) and @xmath324 ( @xmath325 ) are the hopping elements for the ce ( c ) phase , respectively , in the @xmath28 orbital basis . electron dispersion for the zigzag chain of the ce phase ( solid lines ) and for the linear chain of the c phase ( dashed lines ) calculated for different crystal - field splittings in the @xmath28 orbital basis at corner sites ( @xmath305 ) . the orbitals at the bridge sites are degenerate ( assuming @xmath326).,width=188 ] phase diagram of the chain model illustrating the stability of the ce against the c phase as function of the crystal - field splittings defined with respect to the orbital basis ( a ) @xmath28 and ( b ) @xmath327 , respectively.,width=188 ] calculating the band energies ( see fig . [ fig : bands ] ) one can easily determine the character of the stable phase . for the degenerate band model ( @xmath328 ) the c phase is metallic while in the ce phase a gap opens due to the _ topological sign_.@xcite the opening of the gap stabilizes the ce phase . when the degeneracy between @xmath41 and @xmath92 states at the corner sites ( @xmath329 ) is lifted , the c phase becomes insulating as well and for sufficiently large @xmath5 level splittings it can have a _ lower _ energy than the ce phase when the chain is doped with one electron per two mn sites [ see fig . [ fig : bands](b ) ] . the region of stability of the ce phase increases for positive ( negative ) @xmath305 when @xmath330(@xmath331 ) , respectively [ see fig . [ fig:1d_phase](a ) ] . generally , the ce phase is stabilized with respect to c , when the occupied bridge state approaches the lower energy level of the corner states . in a real half - doped crystal where in the ce phase mn@xmath33o bond lengths shrink ( expand ) in the @xmath179 direction [ @xmath177 plane ] , respectively , one would expect an energetic preference , due to the jt effect , for orbitals with stronger @xmath6 than @xmath332 character . thus , in the 1d model the relevant part of the phase diagram ( fig . [ fig:1d_phase ] ) is the region with @xmath333 and @xmath334 , i.e. , where the ce structure dominates . to relate our mean - field considerations to the model from sec . [ sec : nnjt ] the stability of the ce phase versus c was also considered with level splitting at the corner sites defined with respect to the orbital basis @xmath327 . such a splitting , directly related to the nearest - neighbor jt interaction ( [ eq : h_oo ] ) when @xmath335 , is operative in the c phase but vanishes by symmetry in the ce orbital phase . as shown in fig . [ fig:1d_phase](b ) the ce phase is stable for small splittings ( @xmath336 ) and in the @xmath335 , @xmath330 region . the latter is the relevant parameter range in the case of nearest neighbor jt interactions , and hence the model suggests the ce phase as stable phase . this , however , is in conflict with our numerical study of the 2d model , where only the c phase was found to be stable . as in 2d the nearest neighbor jt interaction stabilizes the c structure , whereas this interaction is frustrated in the ce phase . this effect is not included in the 1d model . a. e. bocquet , t. mizokawa , t. saitoh , h. namatame , and a. fujimori , , 3771 ( 1992 ) ; t. saitoh , a. e. bocquet , t. mizokawa , h. namatame , a. fujimori , m. abbate , y. takeda , and m. takano , _ ibid . _ * 51 * , 13 942 ( 1995 ) ; s. satpathy , zoran s. popovic and filip r. vukajlovic , , 960 ( 1996 ) .[/INST] we have analyzed different correlation functions in a realistic spin - orbital model for half - doped manganites . using a finite - temperature diagonalization technique the ce phase was found in the charge - ordered phase in the case of small antiferromagnetic interactions between @xmath0 electrons . it is shown that a key ingredient responsible for stabilization of the ce - type spin and orbital - ordered state is the cooperative jahn - teller ( jt ) interaction between next - nearest mn@xmath1 neighbors mediated by the breathing mode distortion of mn@xmath2 octahedra and displacements of mn@xmath2 ions . the topological phase factor in the mn - mn hopping leading to gap formation in one - dimensional models for the ce phase as well as the nearest neighbor jt coupling are not able to produce the zigzag chains typical for the ce phase in our model . </s>

Image copyright Rebecca Burrell Image caption Brian O'Callaghan-Westropp and his wife Zoe Holohan were on their honeymoon A newly married Irishman is confirmed dead after being caught up in wildfires in Greece. Brian O'Callaghan-Westropp, who was on honeymoon with his wife Zoe Holohan, became separated trying to escape the flames in the seaside resort of Mati. In a statement, the two families said they were "deeply saddened" by his death. They also asked for privacy "as we grieve and as Zoe makes her recovery". Greece's citizen protection minister said on Thursday that arson is the suspected cause of the forest fire. Mr O'Callaghan-Westropp, who was originally from County Clare, worked for a catering company and volunteered for Blood Bikes East, which provides an emergency medical transport service around hospitals in Dublin. The organisation paid tribute to Mr O'Callaghan-Westropp in a post on its Facebook page, describing him as a diligent colleague and dear friend whose influence will last for decades to come. Ms Holohan, from Dublin, remains in hospital after suffering burns to her head and hands. The couple were travelling in a vehicle when they were forced to flee. Ms Holohan was able to escape to a nearby beach and was admitted to hospital last night. Death of Irish citizen Orla O'Hanrahan, the Irish Ambassador to Greece, confirmed the death of Mr O'Callaghan-Westropp in an interview with RTÉ. "Our sympathies and hearts go out to his family at this time," she said. Media playback is unsupported on your device Media caption Irishman on honeymoon is confirmed dead after Greek wildfires More than 70 people have died in the wildfires which have devastated a number of Greek villages and holiday resorts. Irish Foreign Affairs Minister Simon Coveney confirmed one Irish citizen had been hospitalised with burns. Mr Coveney said his department was also providing consular assistance to the person's family. Devastating wildfires More than 70 people have died in the wildfires, which have devastated a number of Greek villages and holiday resorts. Media playback is unsupported on your device Media caption Wildfires cause devastation in Greece Greek Prime Minister Alexis Tsipras has declared three days of mourning, while Italy, Germany, Poland and France have all sent help in the form of planes, vehicles and fire fighters. Spain and Cyprus have also offered assistance. ||||| NEOS VOUTZAS, Greece — The first fire alarm sounded in Kineta, a town an hour west of Athens, the capital, at 12:30 p.m. on Monday. Then, at 4:57 p.m., the authorities received calls on their 199 hotline reporting flames near Rafina, east of the capital. Just about an hour later, the wildfire had reached Neos Voutzas, to the northeast, and then, powered by gale-force winds, it moved “like a lava flow” down the hill to the seaside town of Mati, fire officials said. Greeks on Wednesday were still piecing together one of the nation’s worst disasters in recent memory. But many were asking how so many scattered fires had broken out in so short a span and spread with such fatal velocity. Suspicion of arson combined with grief and recrimination as shattered Greeks sifted through the ruins of fires that killed at least 81 people. ||||| ATHENS (Reuters) - The number of dead from a fire which ripped through a Greek coastal town reached at least 81 on Wednesday as frantic relatives tried to track down people missing from the inferno and officials began the grim task of identifying bodies. Hundreds of people were trapped in the eastern resort of Mati on Monday night as flames whipped around them. Many jumped into the sea to survive but others died from suffocation, either in their cars or trapped on the edge of steep cliffs. One of the victims was Irishman Brian O’Callaghan-Westrop, Ireland’s ambassador to Athens Orla O’Hanrahan told Ireland’s RTE. The broadcaster said he was on his honeymoon. He and his wife Zoe, who survived, had got married last week. The Greek anti-terrorist service was investigating suggestions that the blaze - one of several throughout the Attica region - was started deliberately, a security source said. Arson is often thought to be behind some fires in a crude attempt to clear forest land for building. The fire brigade said the death in hospital of one person who had initially survived brought the toll up to 81. The service had also received dozens of calls reporting missing people, but it was unclear if some of them were among those already found dead, a spokesperson said. Some people appeared on television to plead for help. “I’m looking for my mum,” a young woman told Greece’s SKAI TV between sobs. The fire broke out on Monday at 4:57 p.m. (1357 GMT), an hour which is observed as a siesta time in rural Greek communities. Mati was popular with local tourists, including pensioners. An aerial view shows burnt houses and trees following a wildfire in the village of Mati, near Athens, Greece, July 25, 2018. Antonis Nicolopoulos/Eurokinissi via REUTERS CHALLENGING TASK Rescue teams combed through the area and the sea on Wednesday trying to locate anything which could offer clarity on the missing, who are thought to number about 40. “We took our cars and went down to the sea and got into the sea to escape, but there were people who did not make it,” said Mati resident Agni Gantona. “We got into the water and stayed there for about five hours until the boats came to pick us up. We were at the beach with about 250, 300 people. “Some were burned, some were near fainting from the smoke and the flames. Groups of us, we were holding each other by the hand and shouting each other’s names, because we could not see from the smoke.” With most of the corpses badly charred, identification of the dead will be challenging, experts said. “Work has started on identifying the victims of the wildfires but the majority of the bodies are totally charred,” Grigoris Leon, head of the Hellenic Society of Forensic Medicine, told Reuters. Slideshow (12 Images) It was unclear what caused the fire, which spread rapidly through the community. But some suggested that the sheer force of winds, thick pine, fire and panic was a deadly combination making even the most well-executed evacuation plan futile. “Armaggeddon,” wrote the daily newspaper Ethnos on its front page. It carried a photo of a burned Greek flag hanging among the branches of a charred tree.

– An Irish couple's idyllic Greek honeymoon has become a disaster from which only one will return. Days after arriving in the seaside resort of Mati, Brian O'Callaghan-Westropp became separated from his new bride as they ran to escape a fast-moving wildfire; he is now among the 81 dead, per Reuters. O'Callaghan-Westropp and Zoe Holohan—who arrived in Greece on Saturday following their Thursday wedding in Kells—were forced to abandon their car in gridlock as winds pushed flames toward the sea. They ran in that direction but became separated close to the water, reports the Irish Times. Holohan reached a beach and realized her husband was no longer with her. The Irish ambassador to Greece confirmed O'Callaghan-Westropp's body was later found, per the BBC. "Our sympathies and hearts go out to his family at this time," said Orla O'Hanrahan. She added Holohan was admitted to a hospital Tuesday with burns to her head and hands and is expected to fully recover. She's one of an estimated 200 people injured, per the Guardian. With another 40 missing, officials expect the death toll to continue to climb as rescue workers comb through as many as 2,500 burned homes. Identification of the deceased won't be easy. "Sometimes it’s difficult to see the people; they look like charcoal," the New York Times quotes a Red Cross volunteer as saying. Per the Times, an investigation into the cause will only begin when all the fires are out, though arson is suspected given "the proliferation of so many small fires" in drought-affected areas.

<s>[INST]Image copyright Rebecca Burrell Image caption Brian O'Callaghan-Westropp and his wife Zoe Holohan were on their honeymoon A newly married Irishman is confirmed dead after being caught up in wildfires in Greece. Brian O'Callaghan-Westropp, who was on honeymoon with his wife Zoe Holohan, became separated trying to escape the flames in the seaside resort of Mati. In a statement, the two families said they were "deeply saddened" by his death. They also asked for privacy "as we grieve and as Zoe makes her recovery". Greece's citizen protection minister said on Thursday that arson is the suspected cause of the forest fire. Mr O'Callaghan-Westropp, who was originally from County Clare, worked for a catering company and volunteered for Blood Bikes East, which provides an emergency medical transport service around hospitals in Dublin. The organisation paid tribute to Mr O'Callaghan-Westropp in a post on its Facebook page, describing him as a diligent colleague and dear friend whose influence will last for decades to come. Ms Holohan, from Dublin, remains in hospital after suffering burns to her head and hands. The couple were travelling in a vehicle when they were forced to flee. Ms Holohan was able to escape to a nearby beach and was admitted to hospital last night. Death of Irish citizen Orla O'Hanrahan, the Irish Ambassador to Greece, confirmed the death of Mr O'Callaghan-Westropp in an interview with RTÉ. "Our sympathies and hearts go out to his family at this time," she said. Media playback is unsupported on your device Media caption Irishman on honeymoon is confirmed dead after Greek wildfires More than 70 people have died in the wildfires which have devastated a number of Greek villages and holiday resorts. Irish Foreign Affairs Minister Simon Coveney confirmed one Irish citizen had been hospitalised with burns. Mr Coveney said his department was also providing consular assistance to the person's family. Devastating wildfires More than 70 people have died in the wildfires, which have devastated a number of Greek villages and holiday resorts. Media playback is unsupported on your device Media caption Wildfires cause devastation in Greece Greek Prime Minister Alexis Tsipras has declared three days of mourning, while Italy, Germany, Poland and France have all sent help in the form of planes, vehicles and fire fighters. Spain and Cyprus have also offered assistance. ||||| NEOS VOUTZAS, Greece — The first fire alarm sounded in Kineta, a town an hour west of Athens, the capital, at 12:30 p.m. on Monday. Then, at 4:57 p.m., the authorities received calls on their 199 hotline reporting flames near Rafina, east of the capital. Just about an hour later, the wildfire had reached Neos Voutzas, to the northeast, and then, powered by gale-force winds, it moved “like a lava flow” down the hill to the seaside town of Mati, fire officials said. Greeks on Wednesday were still piecing together one of the nation’s worst disasters in recent memory. But many were asking how so many scattered fires had broken out in so short a span and spread with such fatal velocity. Suspicion of arson combined with grief and recrimination as shattered Greeks sifted through the ruins of fires that killed at least 81 people. ||||| ATHENS (Reuters) - The number of dead from a fire which ripped through a Greek coastal town reached at least 81 on Wednesday as frantic relatives tried to track down people missing from the inferno and officials began the grim task of identifying bodies. Hundreds of people were trapped in the eastern resort of Mati on Monday night as flames whipped around them. Many jumped into the sea to survive but others died from suffocation, either in their cars or trapped on the edge of steep cliffs. One of the victims was Irishman Brian O’Callaghan-Westrop, Ireland’s ambassador to Athens Orla O’Hanrahan told Ireland’s RTE. The broadcaster said he was on his honeymoon. He and his wife Zoe, who survived, had got married last week. The Greek anti-terrorist service was investigating suggestions that the blaze - one of several throughout the Attica region - was started deliberately, a security source said. Arson is often thought to be behind some fires in a crude attempt to clear forest land for building. The fire brigade said the death in hospital of one person who had initially survived brought the toll up to 81. The service had also received dozens of calls reporting missing people, but it was unclear if some of them were among those already found dead, a spokesperson said. Some people appeared on television to plead for help. “I’m looking for my mum,” a young woman told Greece’s SKAI TV between sobs. The fire broke out on Monday at 4:57 p.m. (1357 GMT), an hour which is observed as a siesta time in rural Greek communities. Mati was popular with local tourists, including pensioners. An aerial view shows burnt houses and trees following a wildfire in the village of Mati, near Athens, Greece, July 25, 2018. Antonis Nicolopoulos/Eurokinissi via REUTERS CHALLENGING TASK Rescue teams combed through the area and the sea on Wednesday trying to locate anything which could offer clarity on the missing, who are thought to number about 40. “We took our cars and went down to the sea and got into the sea to escape, but there were people who did not make it,” said Mati resident Agni Gantona. “We got into the water and stayed there for about five hours until the boats came to pick us up. We were at the beach with about 250, 300 people. “Some were burned, some were near fainting from the smoke and the flames. Groups of us, we were holding each other by the hand and shouting each other’s names, because we could not see from the smoke.” With most of the corpses badly charred, identification of the dead will be challenging, experts said. “Work has started on identifying the victims of the wildfires but the majority of the bodies are totally charred,” Grigoris Leon, head of the Hellenic Society of Forensic Medicine, told Reuters. Slideshow (12 Images) It was unclear what caused the fire, which spread rapidly through the community. But some suggested that the sheer force of winds, thick pine, fire and panic was a deadly combination making even the most well-executed evacuation plan futile. “Armaggeddon,” wrote the daily newspaper Ethnos on its front page. It carried a photo of a burned Greek flag hanging among the branches of a charred tree.[/INST]– An Irish couple's idyllic Greek honeymoon has become a disaster from which only one will return. Days after arriving in the seaside resort of Mati, Brian O'Callaghan-Westropp became separated from his new bride as they ran to escape a fast-moving wildfire; he is now among the 81 dead, per Reuters. O'Callaghan-Westropp and Zoe Holohan—who arrived in Greece on Saturday following their Thursday wedding in Kells—were forced to abandon their car in gridlock as winds pushed flames toward the sea. They ran in that direction but became separated close to the water, reports the Irish Times. Holohan reached a beach and realized her husband was no longer with her. The Irish ambassador to Greece confirmed O'Callaghan-Westropp's body was later found, per the BBC. "Our sympathies and hearts go out to his family at this time," said Orla O'Hanrahan. She added Holohan was admitted to a hospital Tuesday with burns to her head and hands and is expected to fully recover. She's one of an estimated 200 people injured, per the Guardian. With another 40 missing, officials expect the death toll to continue to climb as rescue workers comb through as many as 2,500 burned homes. Identification of the deceased won't be easy. "Sometimes it’s difficult to see the people; they look like charcoal," the New York Times quotes a Red Cross volunteer as saying. Per the Times, an investigation into the cause will only begin when all the fires are out, though arson is suspected given "the proliferation of so many small fires" in drought-affected areas.</s>

Vitamin D tablets are displayed, Wednesday, Nov. 9, 2016, in New York. Doctors are warning about vitamin D again, and it isn't the "we need more" news you might expect. Instead, they say there's an epidemic... (Associated Press) Vitamin D tablets are displayed, Wednesday, Nov. 9, 2016, in New York. Doctors are warning about vitamin D again, and it isn't the "we need more" news you might expect. Instead, they say there's an epidemic of needless testing and too many people taking too many pills for a deficiency that very few... (Associated Press) Doctors are warning about vitamin D again, and it's not the "we need more" news you might expect. Instead, they say there's too much needless testing and too many people taking too many pills for a problem that few people truly have. The nutrient is crucial for strong bones and may play a role in other health conditions, though that is far less certain. Misunderstandings about the recommended amount of vitamin D have led to misinterpretation of blood tests and many people thinking they need more than they really do, some experts who helped set the levels write in Thursday's New England Journal of Medicine . Correctly interpreted, less than 6 percent of Americans ages 1 to 70 are deficient and only 13 percent are in danger of not getting enough. That's concerning, "but these levels of deficiency do not constitute a pandemic," the authors write. Yet people may think there is one. Blood tests for vitamin D levels — not advised unless a problem like bone loss is suspected — are soaring. Under Medicare, there was an 83-fold increase from 2000 to 2010, to 8.7 million tests last year, at $40 apiece. It's Medicare's fifth most common test, just after cholesterol levels and ahead of blood sugar, urinary tract infections and prostate cancer screening. "I'm not sure when it got popular to check everybody for vitamin D deficiency," but patients often ask for it, especially baby boomers, said Dr. Kenny Lin, a Georgetown University family physician and preventive medicine expert. Vitamin D pill use also grew, from 5 percent of Americans in 1999 to 19 percent in 2012. That may be due to many reports suggesting harm from too little of "the sunshine vitamin," called that because our skin makes vitamin D from sun exposure. It's tough to get enough in winter or from dietary sources like milk and oily fish, though many foods and drinks are fortified with vitamin D and labels soon will have to carry that information. Too much vitamin D can lead to high levels of calcium in the blood, which can cause nausea, constipation, kidney stones, an abnormal heart rhythm and other problems. "We're not saying that moderate-dose supplements are risky, but more is not necessarily better," said Dr. JoAnn Manson of Brigham and Women's Hospital in Boston. She and several other advisers to the Institute of Medicine, which set the RDA, or recommended dietary allowance, wrote the journal article. People vary, biologically, in how much of any vitamin they need. The institute estimated this by comparing various intake and blood levels with measures of bone health. They estimated that, on average, people need about 400 international units of vitamin D per day, and 600 for people over 70. To be safe and ensure that everyone gets enough, they set the RDA at the high end of the spectrum of the population's needs — 600 to 800 units, depending on age. So by definition, nearly everyone's true requirement is below that. Many people and their doctors regard the RDA and its corresponding blood levels as a threshold that everyone needs to be above, the authors write. As a result, people often are told they are inadequate or deficient in D when, in fact, they're not. "If you're chasing a lab number, that will lead to many people getting higher amounts of vitamin D than they need," and labs vary a lot in the quality of testing, Manson said. The bottom line: Get 600 to 800 units a day from food or supplements and skip the blood test unless you have special risk factors, Manson said. A big study she is helping lead is testing whether higher levels lower the risk of cancer, heart disease, stroke, memory loss, depression, diabetes, bone loss or other problems. Nearly 26,000 people have been taking 2,000 units of D-3 (the most active form of vitamin D, also known as cholecalciferol) or dummy pills every day for five years. Results are expected in early 2018. ___ Marilynn Marchione can be followed at http://twitter.com/MMarchioneAP ||||| Vitamin D, also known as the sunshine vitamin, is produced by the body as a response to sun exposure; it can also be consumed in food or supplements. Having enough vitamin D is important for a number of reasons, including maintaining healthy bones and teeth; it may also protect against a range of conditions such as cancer, type 1 diabetes, and multiple sclerosis. Vitamin D has multiple roles in the body, helping to: Maintain the health of bones and teeth. Support the health of the immune system, brain, and nervous system. Regulate insulin levels and aid diabetes management. Support lung function and cardiovascular health. Influence the expression of genes involved in cancer development. What is vitamin D? Vitamin D is actually not a vitamin. Vitamin D is actually not a vitamin. Despite the name, vitamin D is considered a pro-hormone and not actually a vitamin. Vitamins are nutrients that cannot be created by the body and therefore must be taken in through our diet. However, vitamin D can be synthesized by our body when sunlight hits our skin. It is estimated that sensible sun exposure on bare skin for 5-10 minutes 2-3 times per week allows most people to produce sufficient vitamin D, but vitamin D breaks down quite quickly, meaning that stores can run low, especially in winter. Recent studies have suggested that a substantial percentage of the global population is vitamin D deficient. Health benefits of vitamin D This section looks at the potential health benefits of vitamin D, from assisting good bone health to possible cancer prevention. 1) Vitamin D for healthy bones Vitamin D is vital for bone health. Vitamin D is vital for bone health. Vitamin D plays a substantial role in the regulation of calcium and maintenance of phosphorus levels in the blood, two factors that are extremely important for maintaining healthy bones. We need vitamin D to absorb calcium in the intestines and to reclaim calcium that would otherwise be excreted through the kidneys. Vitamin D deficiency in children can cause rickets, a disease characterized by a severely bow-legged appearance due to softening of the bones. In adults, vitamin D deficiency manifests as osteomalacia (softening of the bones) or osteoporosis. Osteomalacia results in poor bone density and muscular weakness. Osteoporosis is the most common bone disease among post-menopausal women and older men. 2) Reduced risk of flu Children given 1,200 International Units of vitamin D per day for 4 months during the winter reduced their risk of influenza A infection by over 40 percent. 3) Reduced risk of diabetes Several observational studies have shown an inverse relationship between blood concentrations of vitamin D in the body and risk of type 2 diabetes. In people with type 2 diabetes, insufficient vitamin D levels may negatively effect insulin secretion and glucose tolerance. In one particular study, infants who received 2,000 International Units per day of vitamin D had an 88 percent lower risk of developing type 1 diabetes by the age of 32. 4) Healthy infants Children with normal blood pressure who were given 2,000 International Units (IU) per day had significantly lower arterial wall stiffness after 16 weeks compared with children who were given only 400 IU per day. Low vitamin D status has also been associated with a higher risk and severity of atopic childhood diseases and allergic diseases, including asthma, atopic dermatitis, and eczema. Vitamin D may enhance the anti-inflammatory effects of glucocorticoids, making it potentially useful as a supportive therapy for people with steroid-resistant asthma. 5) Healthy pregnancy Pregnant women who are deficient in vitamin D seem to be at greater risk of developing preeclampsia and needing a cesarean section. Poor vitamin D status is associated with gestational diabetes mellitus and bacterial vaginosis in pregnant women. It is also important to note that high vitamin D levels during pregnancy were associated with an increased risk of food allergy in the child during the first 2 years of life. 6) Cancer prevention Vitamin D is extremely important for regulating cell growth and for cell-to-cell communication. Some studies have suggested that calcitriol (the hormonally active form of vitamin D) can reduce cancer progression by slowing the growth and development of new blood vessels in cancerous tissue, increasing cancer cell death, and reducing cell proliferation and metastases. Vitamin D influences more than 200 human genes, which could be impaired when we do not have enough vitamin D. Vitamin D deficiency has also been associated with an increased risk of cardiovascular disease, hypertension, multiple sclerosis, autism, Alzheimer's disease, rheumatoid arthritis, asthma severity, and swine flu, however more reliable studies are needed before these associations can be proven. Many of these benefits occur through Vitamin D's positive effect on the immune system Recommended intake of vitamin D The amount of vitamin D you need depends on your age. The amount of vitamin D you need depends on your age. Vitamin D intake can be measured in two ways: in micrograms (mcg) and International Units (IU). One microgram of vitamin D is equal to 40 IU of vitamin D. The recommended intakes of vitamin D throughout life were updated by the U.S. Institutes of Medicine (IOM) in 2010 and are currently set at: Infants 0-12 months - 400 IU (10 mcg). Children 1-18 years - 600 IU (15 mcg). Adults to age 70 - 600 IU (15 mcg). Adults over 70 - 800 IU (20 mcg). Pregnant or lactating women - 600 IU (15 mcg). Vitamin D deficiency Although the body can create vitamin D, there are many reasons deficiency can occur. For instance, darker skin color and the use of sunscreen reduce the body's ability to absorb the ultraviolet radiation B (UVB) rays from the sun needed to produce vitamin D. A sunscreen with sun protection factor (SPF) 30 can reduce the body's ability to synthesize the vitamin by 95 percent. To start vitamin D production, the skin has to be directly exposed to sunlight, not covered by clothing. People who live in northern latitudes or areas of high pollution, work at night and stay home during the day, or are homebound should aim to consume extra vitamin D from food sources whenever possible. Infants who are exclusively breast-fed need a vitamin D supplement, especially if they are dark-skinned or have minimal sun exposure. The American Academy of Pediatrics recommends that all breastfed infants receive 400 IU per day of an oral vitamin D supplement; drops made specifically for babies are available. Although vitamin D supplements can be taken, it is best to obtain any vitamin or mineral through natural sources wherever possible. Symptoms of vitamin D deficiency Symptoms of vitamin D deficiency may include: Getting sick or infected more often. Fatigue. Painful bones and back. Depressed mood. Impaired wound healing. Hair loss. Muscle pain. If Vitamin D deficiency continues for long periods of time it can result in: obesity diabetes hypertension depression fibromyalgia chronic fatigue syndrome osteoporosis neurodegenerative diseases, such as Alzheimer's disease Vitamin D deficiency may also contribute to the development of certain cancers, especially breast, prostate, and colon cancers. We explain this in a little more detail later. Vitamin D food sources Sunlight is the most common and efficient source of vitamin D. The richest food sources of vitamin D are fish oil and fatty fish. Here is a list of foods with good levels of vitamin D: cod liver oil, 1 tablespoon: 1,360 IU herring, fresh, raw, 4 ounces: 1,056 IU swordfish, cooked, 4 ounces: 941 IU raw maitake mushrooms, 1 cup: 786 IU salmon, sockeye, cooked, 4 ounces: 596 IU sardines, canned, 4 ounces: 336 IU fortified skim milk, 1 cup: 120 IU tuna, canned in water, drained, 3 ounces: 68 IU egg, chicken, whole large: 44 IU Potential health risks of consuming vitamin D The Upper Level limit recommended for vitamin D is 4,000 IU per day. However, the National Institutes of Health (NIH) has suggested that vitamin D toxicity is unlikely at daily intakes below 10,000 IU per day. Excessive consumption of vitamin D (hypervitaminosis D) can lead to over calcification of bones and hardening of blood vessels, kidney, lungs, and heart. The most common symptoms of hypervitaminosis D are headache and nausea but can also include loss of appetite, dry mouth, a metallic taste, vomiting, constipation, and diarrhea. It is best to get your required Vitamin D from natural sources. When choosing supplements, choose your brand carefully as the FDA does not monitor safety or purity of supplements. If you want to buy Vitamin D supplements, then there is an excellent selection on online with thousands of customer reviews. It is the total diet or overall eating pattern that is most important in disease prevention and achieving good health. It is better to eat a diet with a variety than to concentrate on one individual nutrient as the key to good health.

– With winter gloom soon to be upon us, more people may turn to vitamin D pills to stay strong. But they should think twice, according to the New England Journal of Medicine. Contrary to reports claiming up to 50% of people are vitamin D deficient, per Medical News Today, researchers say less than 6% of Americans under 70 are vitamin D deficient (excluding infants) and only 13% are at risk of getting too little. That means some of the 19% of Americans taking vitamin D pills as of 2012 probably don't need them, per the AP. Not only that, but too much vitamin D—which your body makes naturally with sun exposure and helps build strong bones—can cause health problems like nausea, constipation, kidney stones, and an abnormal heart rhythm because of high levels of calcium in the blood. Researchers at the Institute of Medicine, which sets the recommended dietary allowance, acknowledge they're partly to blame for the confusion. Most people under 70 need 400 international units of vitamin D per day, while those over 70 need 600. But to make sure the RDA covered everyone, researchers set it at 600 to 800 units. Now, some doctors mistakenly believe patients are vitamin D deficient if their levels don't fall within that range. The result: blood tests for vitamin D levels have seen "an 83-fold increase from 2000 to 2010, to 8.7 million tests last year, at $40 apiece," per the AP. In fact, the blood test is now Medicare's fifth most common. Researchers' advice: Stick to the RDA and avoid a blood test unless you have special risk factors for a vitamin D deficiency. (A lack of vitamin D might've killed Wolfgang Mozart.)

<s>[INST]Vitamin D tablets are displayed, Wednesday, Nov. 9, 2016, in New York. Doctors are warning about vitamin D again, and it isn't the "we need more" news you might expect. Instead, they say there's an epidemic... (Associated Press) Vitamin D tablets are displayed, Wednesday, Nov. 9, 2016, in New York. Doctors are warning about vitamin D again, and it isn't the "we need more" news you might expect. Instead, they say there's an epidemic of needless testing and too many people taking too many pills for a deficiency that very few... (Associated Press) Doctors are warning about vitamin D again, and it's not the "we need more" news you might expect. Instead, they say there's too much needless testing and too many people taking too many pills for a problem that few people truly have. The nutrient is crucial for strong bones and may play a role in other health conditions, though that is far less certain. Misunderstandings about the recommended amount of vitamin D have led to misinterpretation of blood tests and many people thinking they need more than they really do, some experts who helped set the levels write in Thursday's New England Journal of Medicine . Correctly interpreted, less than 6 percent of Americans ages 1 to 70 are deficient and only 13 percent are in danger of not getting enough. That's concerning, "but these levels of deficiency do not constitute a pandemic," the authors write. Yet people may think there is one. Blood tests for vitamin D levels — not advised unless a problem like bone loss is suspected — are soaring. Under Medicare, there was an 83-fold increase from 2000 to 2010, to 8.7 million tests last year, at $40 apiece. It's Medicare's fifth most common test, just after cholesterol levels and ahead of blood sugar, urinary tract infections and prostate cancer screening. "I'm not sure when it got popular to check everybody for vitamin D deficiency," but patients often ask for it, especially baby boomers, said Dr. Kenny Lin, a Georgetown University family physician and preventive medicine expert. Vitamin D pill use also grew, from 5 percent of Americans in 1999 to 19 percent in 2012. That may be due to many reports suggesting harm from too little of "the sunshine vitamin," called that because our skin makes vitamin D from sun exposure. It's tough to get enough in winter or from dietary sources like milk and oily fish, though many foods and drinks are fortified with vitamin D and labels soon will have to carry that information. Too much vitamin D can lead to high levels of calcium in the blood, which can cause nausea, constipation, kidney stones, an abnormal heart rhythm and other problems. "We're not saying that moderate-dose supplements are risky, but more is not necessarily better," said Dr. JoAnn Manson of Brigham and Women's Hospital in Boston. She and several other advisers to the Institute of Medicine, which set the RDA, or recommended dietary allowance, wrote the journal article. People vary, biologically, in how much of any vitamin they need. The institute estimated this by comparing various intake and blood levels with measures of bone health. They estimated that, on average, people need about 400 international units of vitamin D per day, and 600 for people over 70. To be safe and ensure that everyone gets enough, they set the RDA at the high end of the spectrum of the population's needs — 600 to 800 units, depending on age. So by definition, nearly everyone's true requirement is below that. Many people and their doctors regard the RDA and its corresponding blood levels as a threshold that everyone needs to be above, the authors write. As a result, people often are told they are inadequate or deficient in D when, in fact, they're not. "If you're chasing a lab number, that will lead to many people getting higher amounts of vitamin D than they need," and labs vary a lot in the quality of testing, Manson said. The bottom line: Get 600 to 800 units a day from food or supplements and skip the blood test unless you have special risk factors, Manson said. A big study she is helping lead is testing whether higher levels lower the risk of cancer, heart disease, stroke, memory loss, depression, diabetes, bone loss or other problems. Nearly 26,000 people have been taking 2,000 units of D-3 (the most active form of vitamin D, also known as cholecalciferol) or dummy pills every day for five years. Results are expected in early 2018. ___ Marilynn Marchione can be followed at http://twitter.com/MMarchioneAP ||||| Vitamin D, also known as the sunshine vitamin, is produced by the body as a response to sun exposure; it can also be consumed in food or supplements. Having enough vitamin D is important for a number of reasons, including maintaining healthy bones and teeth; it may also protect against a range of conditions such as cancer, type 1 diabetes, and multiple sclerosis. Vitamin D has multiple roles in the body, helping to: Maintain the health of bones and teeth. Support the health of the immune system, brain, and nervous system. Regulate insulin levels and aid diabetes management. Support lung function and cardiovascular health. Influence the expression of genes involved in cancer development. What is vitamin D? Vitamin D is actually not a vitamin. Vitamin D is actually not a vitamin. Despite the name, vitamin D is considered a pro-hormone and not actually a vitamin. Vitamins are nutrients that cannot be created by the body and therefore must be taken in through our diet. However, vitamin D can be synthesized by our body when sunlight hits our skin. It is estimated that sensible sun exposure on bare skin for 5-10 minutes 2-3 times per week allows most people to produce sufficient vitamin D, but vitamin D breaks down quite quickly, meaning that stores can run low, especially in winter. Recent studies have suggested that a substantial percentage of the global population is vitamin D deficient. Health benefits of vitamin D This section looks at the potential health benefits of vitamin D, from assisting good bone health to possible cancer prevention. 1) Vitamin D for healthy bones Vitamin D is vital for bone health. Vitamin D is vital for bone health. Vitamin D plays a substantial role in the regulation of calcium and maintenance of phosphorus levels in the blood, two factors that are extremely important for maintaining healthy bones. We need vitamin D to absorb calcium in the intestines and to reclaim calcium that would otherwise be excreted through the kidneys. Vitamin D deficiency in children can cause rickets, a disease characterized by a severely bow-legged appearance due to softening of the bones. In adults, vitamin D deficiency manifests as osteomalacia (softening of the bones) or osteoporosis. Osteomalacia results in poor bone density and muscular weakness. Osteoporosis is the most common bone disease among post-menopausal women and older men. 2) Reduced risk of flu Children given 1,200 International Units of vitamin D per day for 4 months during the winter reduced their risk of influenza A infection by over 40 percent. 3) Reduced risk of diabetes Several observational studies have shown an inverse relationship between blood concentrations of vitamin D in the body and risk of type 2 diabetes. In people with type 2 diabetes, insufficient vitamin D levels may negatively effect insulin secretion and glucose tolerance. In one particular study, infants who received 2,000 International Units per day of vitamin D had an 88 percent lower risk of developing type 1 diabetes by the age of 32. 4) Healthy infants Children with normal blood pressure who were given 2,000 International Units (IU) per day had significantly lower arterial wall stiffness after 16 weeks compared with children who were given only 400 IU per day. Low vitamin D status has also been associated with a higher risk and severity of atopic childhood diseases and allergic diseases, including asthma, atopic dermatitis, and eczema. Vitamin D may enhance the anti-inflammatory effects of glucocorticoids, making it potentially useful as a supportive therapy for people with steroid-resistant asthma. 5) Healthy pregnancy Pregnant women who are deficient in vitamin D seem to be at greater risk of developing preeclampsia and needing a cesarean section. Poor vitamin D status is associated with gestational diabetes mellitus and bacterial vaginosis in pregnant women. It is also important to note that high vitamin D levels during pregnancy were associated with an increased risk of food allergy in the child during the first 2 years of life. 6) Cancer prevention Vitamin D is extremely important for regulating cell growth and for cell-to-cell communication. Some studies have suggested that calcitriol (the hormonally active form of vitamin D) can reduce cancer progression by slowing the growth and development of new blood vessels in cancerous tissue, increasing cancer cell death, and reducing cell proliferation and metastases. Vitamin D influences more than 200 human genes, which could be impaired when we do not have enough vitamin D. Vitamin D deficiency has also been associated with an increased risk of cardiovascular disease, hypertension, multiple sclerosis, autism, Alzheimer's disease, rheumatoid arthritis, asthma severity, and swine flu, however more reliable studies are needed before these associations can be proven. Many of these benefits occur through Vitamin D's positive effect on the immune system Recommended intake of vitamin D The amount of vitamin D you need depends on your age. The amount of vitamin D you need depends on your age. Vitamin D intake can be measured in two ways: in micrograms (mcg) and International Units (IU). One microgram of vitamin D is equal to 40 IU of vitamin D. The recommended intakes of vitamin D throughout life were updated by the U.S. Institutes of Medicine (IOM) in 2010 and are currently set at: Infants 0-12 months - 400 IU (10 mcg). Children 1-18 years - 600 IU (15 mcg). Adults to age 70 - 600 IU (15 mcg). Adults over 70 - 800 IU (20 mcg). Pregnant or lactating women - 600 IU (15 mcg). Vitamin D deficiency Although the body can create vitamin D, there are many reasons deficiency can occur. For instance, darker skin color and the use of sunscreen reduce the body's ability to absorb the ultraviolet radiation B (UVB) rays from the sun needed to produce vitamin D. A sunscreen with sun protection factor (SPF) 30 can reduce the body's ability to synthesize the vitamin by 95 percent. To start vitamin D production, the skin has to be directly exposed to sunlight, not covered by clothing. People who live in northern latitudes or areas of high pollution, work at night and stay home during the day, or are homebound should aim to consume extra vitamin D from food sources whenever possible. Infants who are exclusively breast-fed need a vitamin D supplement, especially if they are dark-skinned or have minimal sun exposure. The American Academy of Pediatrics recommends that all breastfed infants receive 400 IU per day of an oral vitamin D supplement; drops made specifically for babies are available. Although vitamin D supplements can be taken, it is best to obtain any vitamin or mineral through natural sources wherever possible. Symptoms of vitamin D deficiency Symptoms of vitamin D deficiency may include: Getting sick or infected more often. Fatigue. Painful bones and back. Depressed mood. Impaired wound healing. Hair loss. Muscle pain. If Vitamin D deficiency continues for long periods of time it can result in: obesity diabetes hypertension depression fibromyalgia chronic fatigue syndrome osteoporosis neurodegenerative diseases, such as Alzheimer's disease Vitamin D deficiency may also contribute to the development of certain cancers, especially breast, prostate, and colon cancers. We explain this in a little more detail later. Vitamin D food sources Sunlight is the most common and efficient source of vitamin D. The richest food sources of vitamin D are fish oil and fatty fish. Here is a list of foods with good levels of vitamin D: cod liver oil, 1 tablespoon: 1,360 IU herring, fresh, raw, 4 ounces: 1,056 IU swordfish, cooked, 4 ounces: 941 IU raw maitake mushrooms, 1 cup: 786 IU salmon, sockeye, cooked, 4 ounces: 596 IU sardines, canned, 4 ounces: 336 IU fortified skim milk, 1 cup: 120 IU tuna, canned in water, drained, 3 ounces: 68 IU egg, chicken, whole large: 44 IU Potential health risks of consuming vitamin D The Upper Level limit recommended for vitamin D is 4,000 IU per day. However, the National Institutes of Health (NIH) has suggested that vitamin D toxicity is unlikely at daily intakes below 10,000 IU per day. Excessive consumption of vitamin D (hypervitaminosis D) can lead to over calcification of bones and hardening of blood vessels, kidney, lungs, and heart. The most common symptoms of hypervitaminosis D are headache and nausea but can also include loss of appetite, dry mouth, a metallic taste, vomiting, constipation, and diarrhea. It is best to get your required Vitamin D from natural sources. When choosing supplements, choose your brand carefully as the FDA does not monitor safety or purity of supplements. If you want to buy Vitamin D supplements, then there is an excellent selection on online with thousands of customer reviews. It is the total diet or overall eating pattern that is most important in disease prevention and achieving good health. It is better to eat a diet with a variety than to concentrate on one individual nutrient as the key to good health.[/INST]– With winter gloom soon to be upon us, more people may turn to vitamin D pills to stay strong. But they should think twice, according to the New England Journal of Medicine. Contrary to reports claiming up to 50% of people are vitamin D deficient, per Medical News Today, researchers say less than 6% of Americans under 70 are vitamin D deficient (excluding infants) and only 13% are at risk of getting too little. That means some of the 19% of Americans taking vitamin D pills as of 2012 probably don't need them, per the AP. Not only that, but too much vitamin D—which your body makes naturally with sun exposure and helps build strong bones—can cause health problems like nausea, constipation, kidney stones, and an abnormal heart rhythm because of high levels of calcium in the blood. Researchers at the Institute of Medicine, which sets the recommended dietary allowance, acknowledge they're partly to blame for the confusion. Most people under 70 need 400 international units of vitamin D per day, while those over 70 need 600. But to make sure the RDA covered everyone, researchers set it at 600 to 800 units. Now, some doctors mistakenly believe patients are vitamin D deficient if their levels don't fall within that range. The result: blood tests for vitamin D levels have seen "an 83-fold increase from 2000 to 2010, to 8.7 million tests last year, at $40 apiece," per the AP. In fact, the blood test is now Medicare's fifth most common. Researchers' advice: Stick to the RDA and avoid a blood test unless you have special risk factors for a vitamin D deficiency. (A lack of vitamin D might've killed Wolfgang Mozart.)</s>

a major goal of cosmology is to determine the fundamental cosmological parameters that describe our universe . observations of anisotropies in the cosmic microwave background ( cmb ) provide unique data in achieving this goal through a determination of their power spectrum . an accurate measurement of the cmb power spectrum requires a good knowledge of the various galactic foregrounds which have their own frequency and power spectra . this is particularly important for all - sky , high - sensitivity cmb experiments such as _ wmap _ ( bennett et al . 2003 ) and _ planck _ ( tauber 2000 ) . for example , the cmb power spectrum expected from observations with the _ planck _ satellite will be accurate to @xmath14 per cent over the @xmath15-range @xmath16 ; this corresponds to a temperature accuracy of better than @xmath17k over the angular range @xmath18 to 5 arcmin . the galactic foregrounds should therefore be estimated to better than this value , otherwise the cmb data will be degraded . the @xmath1-dmr data ( bennett et al . 1996 ) covering @xmath19 at frequencies of 31.5 , 53 and 90 ghz are constrained by knowledge of the foregrounds ; this is also the case for the the _ wmap _ data , particularly on the largest angular scales discussed here . the challenge is to make use of the largest sky coverage possible to reduce the sample variance on such large angular scales ( @xmath20 ) ; the area available has normally been restricted to galactic latitudes @xmath21 or @xmath22 . in this paper we attempt to improve on available knowledge of the foregrounds and apply it to the @xmath1-dmr data in order to determine whether the fraction of sky available for cosmological assessment can be extended . the recent _ wmap _ analysis of the 1st year observations ( bennett et al . 2003a ) uses the 23 ghz channel as a basis for a galactic mask which eliminates @xmath2321 per cent of the sky from detailed cmb analysis ( bennett et al . 2003b ) . previous studies of galactic foregrounds relevant to the cmb at frequencies less than 100 ghz have used the 408 mhz map of haslam et al . ( 1982 ) as the synchrotron template and fir dust emission ( iras or dirbe ) as a template for the free - free which was thought to be correlated with dust and hi ( kogut et al . 1996a , b ) . it was widely established that at @xmath24 ghz a dust - correlated foreground was present ( de oliveira - costa et al . 1997 ; leitch et al . 1997 ; kogut 1999 ) although it was at a level which significantly exceeded the free - free emission expected from the partial h@xmath0 surveys available at the time . this dust - correlated anomalous emission has been ascribed to spinning dust ( draine & lazarian 1998a , hereafter dl98 , 1998b ) and appears to fit the expected narrow frequency spectrum ( de oliveira - costa et al . 1998 , 1999 , 2000 , 2002 ) , although mukherjee et al . ( 2001 ) weaken some of these arguments and claim that definitive statements about the origin of the dust - correlated component can not be made based on data at 10 and 15 ghz alone . bennett et al . ( 2003b ) find a dust - correlated component which they interpret as synchrotron emission with a flatter spectral index . lagache ( 2003 ) , however , argues that this emission is intrinsic to the dust itself and arises from small , cold grains . this is discussed further in section [ sec : wmap_comparison ] . a significant development now available for assessing and quantifying the galactic foregrounds is the unambiguous identification of the free - free component independent of the quasi - correlated dust . the new h@xmath0 surveys by the wisconsin h - alpha mapper , wham ( reynolds et al . 1998 ; haffner 1999 ) , and the southern h - alpha sky survey atlas , shassa ( gaustad et al . 2001 ) , now make this possible . they can be used to produce an all - sky free - free template when corrected for h@xmath0 absorption by dust and when evaluated at the electron temperature appropriate to the ionized gas in the local region of the milky way ( dickinson et al . 2003 ) . in the present paper , using cross - correlation techniques , we quantify the synchrotron and free - free emission , leaving a clearer estimate of the microwave emission associated with galactic dust . we use the @xmath1-dmr data at 31.5 , 53 and 90 ghz ( bennett et al . 1996 ) to identify an anomalous dust - correlated component which previously contained an unknown amount of free - free emission . our results are strengthened by including correlations with a 19.2 ghz survey of the sky ( cottingham 1987 ; boughn et al . 1992 ) . our present study leads to a frequency spectral index @xmath25 for the synchrotron emission ; although @xmath25 varies with position this global value is adequate for predicting the actual ( small ) contribution at higher radio frequencies ( @xmath26 ghz ) . we also investigate the effects of dust absorption and electron temperature in deriving the free - free template . finally , we utilise our improved understanding of the three galactic templates to re - examine the determination of the quadrupole normalization @xmath10 and the scalar fluctuation index @xmath11 from the @xmath1-dmr data ( grski et al . we extend the area of sky available by using data closer to the galactic plane and examine the stability of @xmath27 and @xmath11 values as a function of the latitude range included in the analyses . the synchrotron emission from the galaxy originates in relativistic cosmic ray ( cr ) electrons spiralling in galactic magnetic fields . these electrons will have a a range of spectral energy distributions depending on their age and the environment of origin ( e.g. supernova explosions or diffuse shocks in the interstellar medium ) . the variations in cr electron spectral index will translate into variations in the frequency spectral index of the synchrotron continuum emission . synchrotron emission , with its temperature spectral index of @xmath28 to @xmath29 ( @xmath30 ) , dominates over thermal bremsstrahlung ( free - free ) emission with @xmath31 at frequencies below @xmath14 ghz over most regions of the sky . exceptions are the galactic ridge and the brighter features of the local gould belt system ( dickinson et al . 2003 ) the only all - sky map at sufficiently low frequency to provide a template of galactic synchrotron emission is the 408 mhz survey by haslam et al . this has a resolution of 51 arcmin and has a brightness temperature scale `` absolutely calibrated '' with the 404 mhz @xmath32 survey of pauliny - toth & shakeshaft ( 1962 ) . in the present investigation we will derive ( for the sky area analysed ) a mean spectral index between 408 mhz and 19.2 ghz from the cottingham ( 1987 ) survey and 31.5 , 53 and 90 ghz from the @xmath1-dmr survey . it is important to remember that the spectral index of galactic synchrotron emission varies with frequency and position on the sky . the analysis of low - frequency surveys by lawson et al . ( 1987 ) indicates that the brighter regions away from the galactic plane have typical spectral indices of @xmath33 and @xmath34 at 100 and 800 mhz respectively . furthermore , the value of @xmath25 evaluated between any pair of frequencies separated by a factor of @xmath35 varies typically by @xmath36 over the sky ( reich & reich 1988 ) . bennett et al . ( 2003b ) propose a model using _ wmap _ data which includes a flat spectrum synchrotron component ( @xmath37 ) in regions of star formation near the galactic plane and a steep spectrum component ( @xmath38 ) from the galactic halo . at frequencies higher than @xmath35 ghz no reliable zero levels can be measured for large - area surveys at intermediate and high latitudes where cmb measurements are normally conducted and as a consequence , large area spectral index maps can not be made . however , the spectral index of smaller angular scale ( @xmath39 and less ) structures can be estimated from cross - correlation analyses of maps at different frequencies . for example , hancock et al . ( 1997 ) found a spectral index of @xmath40 at 10 ghz from bremsstrahlung data at 10,15 and 33 ghz . it is interesting to note that the steepening of the brightness temperature spectral index by 0.5 at higher frequencies expected from synchrotron losses would lead to @xmath41 at higher frequencies ; this is the value at these frequencies expected from the local cr electron spectrum ( platania et al . 1998 ) . for the free - free template , we use the all - sky h@xmath0 template described in dickinson et al . the all - sky map is a composite of h@xmath0 data from the wham survey of the northern sky ( reynolds et al . 1998 ; haffner 1999 ) and shassa survey in the southern sky ( gaustad et al . 2001 ) . the shassa data are first smoothed to the wham resolution of @xmath42 and are preferred at declinations @xmath43 . it should be noted that the all - sky template is a first attempt at producing a high - sensitivity all - sky h@xmath0 map . shassa data have significantly lower sensitivity than data from the wham survey ; the noise levels are estimated as @xmath44 and @xmath45 rayleigh ( @xmath46 ) respectively , where @xmath47 photons s@xmath6 @xmath48 sr@xmath49 erg s@xmath6 @xmath48 sr@xmath50 for @xmath51 k gas . baseline uncertainties exist in both data - sets , particularly shassa data which results in loss of information on angular scales @xmath52 for data at @xmath53 due to the @xmath54 field - of - view of each pointing . however , the shassa background levels are fitted to wham data where wham data exist ( @xmath55 ) with an assumed cosecant law for declinations further south . the different observing strategies result in different beam shapes which have not been accounted for . finally , large h@xmath0 signals ( emission and absorption ) from bright stars have been filtered using different techniques ; the wham team use data from nearby unaffected pixels , while the shassa team use a median filter to reduce star residuals . however , all these possible systematics are significantly reduced when the data , at a resolution of @xmath56 , are convolved with the dmr beam at @xmath57 resolution . indeed , we have explicitly verified this by comparing the power spectra of the high - latitude h@xmath0emission after varying the latitude at which the surveys are matched and adjusting baselines . recently , finkbeiner ( 2003 ) has produced an all - sky h@xmath0 map at 6 arcmin resolution which includes higher resolution data from the virginia - tech sky survey ( dennison et al . the differences in the power spectrum of our h@xmath0 map with that given by finkbeiner ( 2003 ) are less than 10 per cent for @xmath58 and less than 30 per cent everywhere . the optical h@xmath0 line ( @xmath59 nm ) is well known to be a good tracer of the free - free continuum emission at radio wavelengths since they are both emitted by the same ionized gas . since they are both proportional to the emission measure ( @xmath60 ) there is a well - defined relationship between the h@xmath0 line intensity @xmath61 and the radio continuum brightness temperature @xmath62 ( osterbrock 1989 ; valls - gabaud 1998 ; dickinson et al . there is a strong dependence on frequency since free - free emission scales as @xmath63 at ghz frequencies . there is also a modest dependence on the electron temperature @xmath64 ( @xmath65 ) . in the galaxy , @xmath64 can range between 3000 k and 15000 k ( shaver et al . 1983 ) ; the majority of hii regions have @xmath64 between 5000 and 10000 k ( reynolds 1985 ) . shaver et al . ( 1983 ) show that the mean electron temperature of hii regions at the galactocentric radius of the sun ( @xmath66 kpc ) is 7200 k with an r.m.s . spread of 1200 k. in the region of the galaxy covered in the present study where @xmath9 the ionized hydrogen will be typically within @xmath14 kpc of the sun and accordingly we adopt a value of @xmath51 k. with this value of @xmath64 , the conversions from h@xmath0 to free - free continuum for frequencies 31.5 , 53 and 90 ghz are 5.25 , 1.71 and 0.54 @xmath2k @xmath67 respectively . in section [ sec : results_foregrounds ] we will use this prior information to allow a fixed free - free component to be subtracted giving a clearer separation of the foregrounds . we will take a variation of @xmath68 k from the local value of 7000 k as in indication of the upper and lower bounds allowed . other caveats become important at the few per cent level : i ) the helium abundance is usually taken to be 8 per cent with a spread of a few per cent ii ) the emitting medium is assumed to be optically thick ( case b ) to the lyman continuum photons . a major uncertainty when using the h@xmath0 template is the absorption of h@xmath0 by foreground dust . the absorption can be estimated using the @xmath69 m maps given by schlegel , finkbeiner & davis ( 1998 , hereafter sfd ) . the absorption at h@xmath0@xmath70 in magnitudes using their temperature - corrected column density map ( @xmath71 ) in units of mjy sr@xmath6 is then @xmath72 where @xmath73 is the fraction of dust _ in front _ of the h@xmath0 actually causing absorption in the line of sight . the corrected h@xmath0 intensity is then @xmath74 . although there are uncertainties in this relationship due to different reddening values expected from different dust populations , the largest uncertainty is in @xmath73 , the fraction of dust lying in front of the h@xmath0-emitting region . dickinson et al . ( 2003 ) show that for a range of longitudes ( @xmath75 ) , and for @xmath76 , @xmath77 , while for local high latitude regions such as orion and the gum nebula , there is little or no absorption by dust ( @xmath78 ) . for much of the high latitude sky , @xmath71 is @xmath79 mjy sr@xmath6 and therefore the absorption is likely to be small ( @xmath80 mag ) . at lower galactic latitudes @xmath81 , the dust absorption strongly increases to 1 mag and above . for the majority of the galactic plane ( @xmath82 ) , the absorption is too great to make any reliable estimate of the true h@xmath0 intensity . finally , the scattering of h@xmath0 light from dust at high galactic latitudes could , in principle , cause a degeneracy in the analysis since the scattered h@xmath0 light would be directly correlated with the dust . however , wood & reynolds ( 1999 ) predict that this accounts for less than 20 per cent of high latitude h@xmath0 emission . since the anomalous component is larger than the free - free component at frequencies higher than @xmath83 ghz ( see sections [ sec : results_foregrounds ] and [ sec : results_anomalous ] ) , this systematic will not significantly affect our results within the errors . as templates for the thermal and anomalous dust - correlated emission , we utilise the @xmath1-dirbe data repixelised into the healpix pixelisation scheme . this was achieved using the publicly available calibrated individual observations ( cio ) files together with the dirbe sky and zodi atlas ( dsza , both products being described in hauser et al . 1998 ) , allowing the construction of dirbe full sky maps corrected for the zodiacal emission according to the model of kelsall et al . in particular , we use the dirbe 140 @xmath2 m data at @xmath84 resolution : although the 100 @xmath2 m data has the best sensitivity , there remain more noticeable artifacts present in the sky map after zodiacal correction . while this is not likely to present a problem after the data has been convolved with the dmr beam profile ( @xmath57 fwhm ) , our choice allows maximal consistency with previous analyses by the dmr team ( banday et al . 1996 ; grski et al . 1996 ; kogut et al . 1996a , 1996b ) . furthermore , the sfd version of the 100 @xmath2 m sky map has been used to correct for dust absorption in the h@xmath0 template , thus our choice allows some additional independence in the dust correlation results . dl98 have suggested that the anomalous dust - correlated signal which we re - investigate in this work should be significantly correlated with 12 @xmath2 m emission , so that the corresponding dirbe sky map may prove a better tracer for this foreground component . however , the 12 @xmath2 m map contains residual zodiacal artifacts in the region of the ecliptic plane which remain significant even after smoothing to dmr resolution . the impact of this could be minimised by excluding a region close to the ecliptic plane , but we prefer to make use of the greatest sky coverage possible . further , de oliveira - costa et al . ( 2002 ) have tested this hypothesis , but it is clear from their fig . 4 that even after considerable processing of the 12 @xmath2 m dirbe data for the removal of both zodiacal emission and point sources , the longer wavelength data at 100 , 140 and 240 @xmath2mremain equally viable for correlation studies . finally , in order to attempt to isolate the anomalous dust - correlated component signal , it is necessary to identify and subtract the thermal dust emission . we have employed the predictions of finkbeiner , davis & schlegel ( 1999 , hereafter fds ) for the thermal dust emission at dmr wavelengths . fds consider 8 models based on the 100 and 240 @xmath2 m maps from sfd , and test them against the @xmath1-firas data . the inconsistency of extrapolations of the sfd maps using single component power - law emissivity functions with the firas data over the range 200 - 2100 ghz motivated the development of generalised two - component models . we have considered fds models 7 and 8 as plausible tracers of the thermal dust component emission . masi et al . ( 2001 ) have demonstrated that model 8 extrapolated to 410 ghz is well correlated with the boomerang data at that frequency , and a recent analysis of the maxima data ( jaffe et al . 2003 ) also see consistency with these extrapolated dust models . it should be remembered that the fds models are formally correct only on scales comparable to or larger than the firas beam , hence the fds predictions of model 7/8 should be well - matched to our purposes . in this analysis , we utilise the @xmath1-dmr 4-year sky maps ( bennett et al . 1996 ) at 31.5 , 53 and 90 ghz in galactic coordinates and the healpix pixelisation scheme with a resolution parameter of @xmath85 , corresponding to 12288 pixels on the sky . inverse - noise - variance weighted combinations of the a and b channels are formed at each of the three dmr frequencies , the weights being ( 0.618 , 0.382 ) , ( 0.579 , 0.421 ) and ( 0.382 , 0.618 ) at 31.5 , 53 and 90 ghz respectively . the dominant feature visible in the sky maps ( given that the dipole anisotropy of amplitude @xmath23 3 mk is largely removed in the pre - map - making data processing ) is the enhanced emission along the galactic plane . this emission is indeed a combination of the synchrotron , free - free and dust emission that we are interested in , however , the distribution and spectral behaviour at the lowest latitudes ( @xmath86 ) is sufficiently complex that we do not attempt to fit or model it , considering only the mid- and high - latitude galactic emission . contrary to previous analyses , we attempt to fit our templates to somewhat lower latitudes , the results of which are discussed in section [ sec : results_foregrounds ] . in addition to the @xmath1-dmr data , we also consider correlations of the foreground templates with a 19.2 ghz survey of the sky ( cottingham 1987 ; boughn et al . such an investigation is clearly of interest here since 19.2 ghz is close to the frequency at which the dl98 models for spinning dust show a maximum in spectral behaviour . even if the anomalous dust - correlated component is not the putative rotational dust emission , the coupling amplitude of the dust template at 19.2 ghz should enable the spectrum of this foreground to be established , in particular since the frequency of observation is well - removed from that where a significant thermal dust contribution is present . the data are available in the @xmath1 quadcube format ( white & stemwedel , 1992 ) with 24,576 pixels on the full sky of size @xmath87 , and contains observations of angular resolution 3 fwhm . a small region close to the south ecliptic pole was not observed . the typical noise level is quoted as 1.5 mk per resolution element , but there is both variation in the number of observations per pixel and pixel - pixel covariance . in contrast to the analysis of de oliveira - costa et al . ( 1998 ) we take account of the former , but the information is not available for the latter . some attempt to provide additional constraints on the noise uncertainty is performed by scaling the noise level by a factor in the range 0.9 - 1.1 , and including this parameter in our later statistical analysis . each of the three dmr maps , the 19.2 ghz data , and the foreground sky map templates ( after convolution to the correct angular resolution ) are decomposed into harmonic coefficients using a basis of orthonormal functions explicitly computed on the incompletely sampled sky ( grski 1994 ) , a procedure which is directly analogous to the expansion of a full - sky map in terms of spherical harmonic coefficients . this technique has the advantage of allowing exact exclusion of the monopole and dipole components from the analysis ( which are unimportant for the investigation of cosmological anisotropy ) , and makes full use of all of the available spatial ( phase ) information . we have adopted several definitions for the area of sky coverage , in particular the standard galactic cut defined as the region with galactic latitude , @xmath88 , above 20@xmath89 with additional regions at ophiuchus ( up to @xmath90 at @xmath91 ) and orion ( down to @xmath92 at @xmath93 ) based on the dirbe 140 @xmath2 m map ( banday et al . 1997 , but recomputed explicitly for the healpix scheme ) , together with more aggressive and conservative cuts of @xmath88 greater than 15@xmath89 and 30@xmath89 respectively . for each sky coverage a new basis of orthonormal functions is computed . this procedure must also be performed separately for the 19.2 ghz data due to its different pixelisation scheme and pixel resolution ( and indeed for the foreground templates matched to the same pixelisation and angular resolution ) . the measured map coefficients in the new orthogonal basis at a given frequency , @xmath94 , can then be written in vector form as @xmath95 where @xmath96 , @xmath97 and @xmath98 are the coefficients describing the true cmb distribution , the noise and one foreground template map respectively . @xmath99 is now a coupling constant ( with units @xmath2k @xmath100 ) to be determined by minimizing @xmath101 where * m * is the covariance matrix describing the correlation between different fourier modes on the cut - sky and is dependent on assumed cmb model parameters and the instrument noise . full details of its computation can be found in grski ( 1994 ) and grski et al . ( 1996 ) . by minimising the @xmath102 with respect to @xmath99 we find that the coupling constant @xmath99 has an exact solution @xmath103 and a gaussian error given by @xmath104 the contribution of component @xmath105 to the observed sky is the map @xmath106 ( where @xmath107 is in the natural units of the foreground template map so that this scaled quantity is in @xmath2k ) . in this analysis , however , we treat multiple foreground templates and all three dmr channels simultaneously . this forces the cmb distribution ( in thermodynamic units ) to be invariant between the three frequencies , and suppresses the sensitivity of the method to noise features in the individual dmr maps which are clearly not common to all three frequencies , thus allowing an improved determination of the extent of chance cosmic or noise alignments with the template maps . we have tested the impact of such chance alignments to the method by repeating the fits after rotation of the foreground templates . we only find significant correlations when the templates are correctly aligned . moreover , the r.m.s values of the coupling coefficients derived from the rotated sky maps are consistent with the errors determined directly in the analysis . the full details of this method are contained in grski et al . the 19.2 ghz data are treated in a similar fashion , but we do not extend the method to include it in a simultaneous fit with the dmr data to the foreground templates because of complications introduced by its different angular resolution and noise properties . having solved for the values of the coupling coefficients and their gaussian errors , we are then in a position to compute the likelihood of the foreground corrected data as a function of a given set of input cosmological parameters as contained in the matrix @xmath108 of equation [ eqn : chi2 ] . indeed , this also allows us to assess the sensitivity of the coupling constant fits to the assumed cosmological power spectrum . we consider a full grid of power law models specified by the rms quadrupole normalisation amplitude @xmath10 and a spectral index @xmath11 as in grski et al . the cosmological implications of the foreground corrections as reappraised in this work are discussed in section [ sec : results_cmb ] . in order to quantify the uncertainty in the h@xmath0 template resulting from dust absorption , we generate corrected h@xmath0 templates for three values of @xmath73 0.0 , 0.5 and 1.0 which are then fitted successively to the data over the full @xmath10 , @xmath11 grid of cosmological models , and also test templates corrected assuming values of @xmath73 running from 0 to 1 in steps of 0.01 for a scale - invariant spectrum with @xmath10 @xmath2318 @xmath2k . since the correction is non - linear in @xmath73 ( see section [ sec : ff_template ] ) , modifications to the template are made _ before _ convolution with the appropriate beam response , at the 1 effective angular resolution of the h@xmath0 template ( see section [ sec : results_dmr_ff ] for full discussion ) . we also analyse the dmr and 19.2 ghz data after correction for free - free emission using the h@xmath0 templates scaled by the factors given in table 4 of dickinson et al . this enables us to test the impact of cross - talk between the templates , which is likely to be present at some level due to the large - scale cosecant variation with latitude of the galactic emission present in each template ( see section [ sec : results_19ghz ] ) . finally , in an attempt to unambiguously identify the _ anomalous _ dust - correlated emission , we use the fds models of _ thermal _ dust emission and subtract them from the observed data before correlation studies are performed ( see section [ sec : results_anomalous ] ) . to305 mm \5 . forced / unforced fits to the h@xmath0 data . open symbols are fits that are made to the dust and synchrotron templates _ after _ correcting the dmr data for the free - free contribution predicted by the h@xmath0 template ; filled symbols correspond to fits made to the three templates simultaneously in which no constraints have been placed on the h@xmath0 template correlation . \6 . electron temperature . the free - free predictions from the h@xmath0 template depend upon the electron temperature ; the dashed boxes in the middle panels show the range of predicted free - free emission for temperatures 5000 to 9000 k ( open symbols are for 7000 k ) . the results obtained from an analysis using only the dirbe and synchrotron templates , consistent with previous work by the @xmath1-dmr team ( kogut et al . 1996b ) , are shown with their errors by full - line boxes in the upper and lower panels of each figure show slightly different results to the previous analysis of kogut et al . ( 1996b ) . however , this is not surprising since they used an earlier release of the dirbe 140 @xmath2 m map and the data were analysed in the quadcube format . ] . this allows a direct assessment of the impact of the inclusion of a free - free template on the analysis by comparison with results in which such a template has not been utilised . the results presented here have been derived assuming a scale - invariant spectrum ( @xmath11 = 1 ) for the cmb contribution with an r.m.s quadrupole normalisation of @xmath10 = 18 @xmath2k . however , as part of our studies of the impact of the foreground correction for cosmological interpretations of the dmr data , we have determined the coupling parameters over a grid in @xmath10 and @xmath11 . we compute an average of the @xmath0 coefficients weighted by the likelihood function over the grid and find that the marginalised coupling coefficients are essentially identical to those shown here , and that no conclusions derived from later analysis are compromised by adopting these values as canonical . as described above , we have adopted three galactic cuts , and also computed correlations in which the coupling to the h@xmath0 template has been left unconstrained , or where we have fixed and subtracted the predicted free - free contribution according to the spectral behaviour predicted in dickinson et al . ( 2003 ) , determined for an electron temperature of 7000 k , the mean value in the solar neighbourhood ( see section [ sec : ff_template ] ) . our better understanding of the foregrounds allows us to correct for them over a larger region of the sky and reassess the value of @xmath10 and @xmath11 . the most significant changes in general result from an analysis made with an aggressive @xmath9 galactic cut , yet even here the results are compatible with earlier results at better than the @xmath112 level , although the error is slightly smaller , suggesting some possibility of making use of modestly larger sky coverage for the inference of cosmological parameters . interestingly , what might be considered our best model for the foreground correction with this aggressive galactic cut , utilising the fds model 7 dust template to correct for thermal dust emission , the h@xmath0 template from dickinson et al . ( 2003 ) to trace the free - free emission ( fixed assuming that the electron temperature is 7000 k ) , together with unrestricted fits to the dirbe 140 @xmath2 m and 408 mhz sky surveys to correct for anomalous dust - correlated and synchrotron emission respectively results in shifts in @xmath10 and @xmath11 of only @xmath113 @xmath2k and @xmath114 relative to the previous standard uncorrected result . all results with @xmath115 are consistent with values of @xmath10 = 15.3 @xmath2k and @xmath11 = 1.2 . ) at angular scales @xmath116 . best - fitting models to 19.2 ghz and dmr data are shown for each foreground component : synchrotron ( dotted line ) , free - free ( dot - dashed line ) , thermal dust ( dashed line ) and anomalous dust ( heavy dotted line between 19 and 90 ghz ) . units have been converted to thermodynamic temperature fluctuations relative to @xmath117 k ; cmb fluctuations are represented as a horizontal line at a level of @xmath118 for comparison . data from this paper are : synchrotron 19.2 ghz ( open triangle ) , anomalous emission at 31.5 , 53 and 90 ghz ( open circles ) and total dust emission at 90 ghz ( filled circle ) . the thick solid line gives an estimate total foreground level by adding all the foreground models in quadrature . the frequency channels for the _ wmap _ ( short vertical dashed lines ) and _ planck _ ( short vertical solid lines ) cmb satellites are shown at the top of the figure . the low and high frequency instruments ( lfi and hfi ) for _ planck _ are drawn as heavy and fine lines respectively . , scaledwidth=50.0% ] fig . [ fig : foregrounds ] summarises the integrated amplitudes of galactic foregrounds at large ( @xmath116 ) angular scales over the most important frequencies for cmb studies . our best models for synchrotron ( @xmath119 scaled to the 408 mhz map ) , free - free ( scaled h@xmath0 predictions assuming @xmath51 k ; dot - dashed line ) and thermal dust model ( fds7 ; dashed line ) emissions are plotted in terms of thermodynamic temperature units ( relative to @xmath120 k ) . the best - fit anomalous component is shown ( heavy dotted line ) over the range @xmath121 ghz . data points are shown for synchrotron at 19.2 ghz ( open triangle ) anomalous dust at 19.2 , 31.5 , 53 and 90 ghz ( open circles ) , total dust at 90 ghz ( filled circle ) . the cmb signal is plotted at a level of @xmath122 k. the approximate total foreground level is represented by adding the four components in quadrature , with the anomalous component set to 52 @xmath2k ( the value at 19.2 ghz ) for frequencies below 19.2 ghz . this suggests that the minimum foreground contamination for these data , is @xmath123 ghz . this is in good agreement with the _ wmap _ analysis which predicts the minimum to lie at @xmath124 ghz . the amplitudes for each of the foreground signals are now relatively well known as shown in fig . [ fig : foregrounds ] . strictly , fig . [ fig : foregrounds ] applies only for angular scales of @xmath125 and larger , and for all - sky observations with a galactic cut of @xmath126 . for different galactic cuts , there are likely to be variations of a factor of @xmath127 for reasonable galactic cuts as indicated in table 1 . observations covering smaller regions of sky , perhaps cleaner regions ( for example , away from the north polar spur ) , may be have reduced foreground contamination by a factor of @xmath128 . finally , at higher @xmath15-values ( smaller angular scales ) , it is known that diffuse galactic foregrounds reduce in amplitude . the power spectra of galactic emission have a typical power - law indices ( @xmath129 ) of @xmath130 ( giardino et al . 2001 ) . thus at @xmath131 angular scales , the galactic foregrounds , in terms of @xmath132 , will be reduced by a factor @xmath128 . however , at angular scales @xmath133 , discrete extragalactic sources become the dominant foreground . with relevance to the satellite missions _ wmap _ and _ planck _ , our analysis implies that the lowest level of foreground contamination from diffuse galactic foregrounds at least on a 7angular scale will be between 50 and 100 ghz . this has been confirmed by bennett et al ( 2003b ) and seems to hold to yet smaller scales @xmath23 1 . our study also predicts that for the _ wmap _ experiment , the predominant foreground at 22 , 30 and perhaps 40 ghz , will be due to the dust - correlated component . this is indeed found to be the case by the recent _ wmap _ analysis , although the interpretation of the physical origin of the emission remains open to debate . more accurate determination of its spectral behaviour , allied to lower frequency observations ( 5 - 15 ghz ) and higher angular resolution observations , should allow the mechanism behind this unexpected foreground to be ascertained . moreover , given the likely region of minimal foreground contamination in frequency space , the importance of the _ planck_-lfi instrument to the _ planck _ mission as a whole can not be overemphasised . the @xmath1 datasets were developed by the nasa goddard space flight center under the guidance of the @xmath1 science working group and were provided by the nssdc . the wisconsin h - alpha mapper project is funded by the national science foundation . the southern h - alpha sky survey atlas project is supported by the nsf . we acknowledge dave cottingham for providing us with a copy of the 19.2 ghz survey .

with the advent of all - sky h@xmath0 surveys it is possible to determine a reliable free - free template of the diffuse interstellar medium ( dickinson , davies & davis 2003 ) which can be used in conjunction with the synchrotron and dust templates to correct cmb observations for diffuse galactic foregrounds . we have used the @xmath1-dmr data at 31.5 , 53 and 90 ghz and employed cross - correlation techniques to re - evaluate the foreground contributions , particularly that due to dust which is known to be partially correlated with h@xmath0 ( and free - free ) emission . the dmr microwave maps are found to contain , as well as the expected synchrotron and free - free components , a component tightly correlated to the 140 @xmath2 m dust maps of dirbe . at 31.5 , 53 and 90 ghz this emission is @xmath3 , @xmath4 and @xmath5 @xmath2k/(mjy sr@xmath6 ) at 140 @xmath2 m respectively . when corrected for the contribution from thermal dust following model 7 of finkbeiner , davis & schlegel ( 1999 ) , a strong anomalous dust - correlated emission component remains , which is well - fitted by a frequency spectrum of the form @xmath7 where @xmath8 2.5 in the dmr frequency range ; this is the dominant foreground at 31.5 ghz . the result implies the presence of an emission component with a dust - like morphology but a synchrotron - like spectrum . we discuss the possible origins of this component and compare it with the recent _ wmap _ interpretation . the better knowledge of the individual foregrounds provided by the present study enables a larger area of the sky ( @xmath9 ) to be used to re - appraise the cmb quadrupole normalisation , @xmath10 , and the scalar perturbations spectral index , @xmath11 . we find @xmath10@xmath12 with a power - law spectral index of @xmath13 . these values are consistent with previous @xmath1-dmr analyses and the _ wmap _ 1-year analysis . [ firstpage ] cosmic microwave background - cosmological parameters - radio continuum : general - ism : dust , extinction

<s>[INST]a major goal of cosmology is to determine the fundamental cosmological parameters that describe our universe . observations of anisotropies in the cosmic microwave background ( cmb ) provide unique data in achieving this goal through a determination of their power spectrum . an accurate measurement of the cmb power spectrum requires a good knowledge of the various galactic foregrounds which have their own frequency and power spectra . this is particularly important for all - sky , high - sensitivity cmb experiments such as _ wmap _ ( bennett et al . 2003 ) and _ planck _ ( tauber 2000 ) . for example , the cmb power spectrum expected from observations with the _ planck _ satellite will be accurate to @xmath14 per cent over the @xmath15-range @xmath16 ; this corresponds to a temperature accuracy of better than @xmath17k over the angular range @xmath18 to 5 arcmin . the galactic foregrounds should therefore be estimated to better than this value , otherwise the cmb data will be degraded . the @xmath1-dmr data ( bennett et al . 1996 ) covering @xmath19 at frequencies of 31.5 , 53 and 90 ghz are constrained by knowledge of the foregrounds ; this is also the case for the the _ wmap _ data , particularly on the largest angular scales discussed here . the challenge is to make use of the largest sky coverage possible to reduce the sample variance on such large angular scales ( @xmath20 ) ; the area available has normally been restricted to galactic latitudes @xmath21 or @xmath22 . in this paper we attempt to improve on available knowledge of the foregrounds and apply it to the @xmath1-dmr data in order to determine whether the fraction of sky available for cosmological assessment can be extended . the recent _ wmap _ analysis of the 1st year observations ( bennett et al . 2003a ) uses the 23 ghz channel as a basis for a galactic mask which eliminates @xmath2321 per cent of the sky from detailed cmb analysis ( bennett et al . 2003b ) . previous studies of galactic foregrounds relevant to the cmb at frequencies less than 100 ghz have used the 408 mhz map of haslam et al . ( 1982 ) as the synchrotron template and fir dust emission ( iras or dirbe ) as a template for the free - free which was thought to be correlated with dust and hi ( kogut et al . 1996a , b ) . it was widely established that at @xmath24 ghz a dust - correlated foreground was present ( de oliveira - costa et al . 1997 ; leitch et al . 1997 ; kogut 1999 ) although it was at a level which significantly exceeded the free - free emission expected from the partial h@xmath0 surveys available at the time . this dust - correlated anomalous emission has been ascribed to spinning dust ( draine & lazarian 1998a , hereafter dl98 , 1998b ) and appears to fit the expected narrow frequency spectrum ( de oliveira - costa et al . 1998 , 1999 , 2000 , 2002 ) , although mukherjee et al . ( 2001 ) weaken some of these arguments and claim that definitive statements about the origin of the dust - correlated component can not be made based on data at 10 and 15 ghz alone . bennett et al . ( 2003b ) find a dust - correlated component which they interpret as synchrotron emission with a flatter spectral index . lagache ( 2003 ) , however , argues that this emission is intrinsic to the dust itself and arises from small , cold grains . this is discussed further in section [ sec : wmap_comparison ] . a significant development now available for assessing and quantifying the galactic foregrounds is the unambiguous identification of the free - free component independent of the quasi - correlated dust . the new h@xmath0 surveys by the wisconsin h - alpha mapper , wham ( reynolds et al . 1998 ; haffner 1999 ) , and the southern h - alpha sky survey atlas , shassa ( gaustad et al . 2001 ) , now make this possible . they can be used to produce an all - sky free - free template when corrected for h@xmath0 absorption by dust and when evaluated at the electron temperature appropriate to the ionized gas in the local region of the milky way ( dickinson et al . 2003 ) . in the present paper , using cross - correlation techniques , we quantify the synchrotron and free - free emission , leaving a clearer estimate of the microwave emission associated with galactic dust . we use the @xmath1-dmr data at 31.5 , 53 and 90 ghz ( bennett et al . 1996 ) to identify an anomalous dust - correlated component which previously contained an unknown amount of free - free emission . our results are strengthened by including correlations with a 19.2 ghz survey of the sky ( cottingham 1987 ; boughn et al . 1992 ) . our present study leads to a frequency spectral index @xmath25 for the synchrotron emission ; although @xmath25 varies with position this global value is adequate for predicting the actual ( small ) contribution at higher radio frequencies ( @xmath26 ghz ) . we also investigate the effects of dust absorption and electron temperature in deriving the free - free template . finally , we utilise our improved understanding of the three galactic templates to re - examine the determination of the quadrupole normalization @xmath10 and the scalar fluctuation index @xmath11 from the @xmath1-dmr data ( grski et al . we extend the area of sky available by using data closer to the galactic plane and examine the stability of @xmath27 and @xmath11 values as a function of the latitude range included in the analyses . the synchrotron emission from the galaxy originates in relativistic cosmic ray ( cr ) electrons spiralling in galactic magnetic fields . these electrons will have a a range of spectral energy distributions depending on their age and the environment of origin ( e.g. supernova explosions or diffuse shocks in the interstellar medium ) . the variations in cr electron spectral index will translate into variations in the frequency spectral index of the synchrotron continuum emission . synchrotron emission , with its temperature spectral index of @xmath28 to @xmath29 ( @xmath30 ) , dominates over thermal bremsstrahlung ( free - free ) emission with @xmath31 at frequencies below @xmath14 ghz over most regions of the sky . exceptions are the galactic ridge and the brighter features of the local gould belt system ( dickinson et al . 2003 ) the only all - sky map at sufficiently low frequency to provide a template of galactic synchrotron emission is the 408 mhz survey by haslam et al . this has a resolution of 51 arcmin and has a brightness temperature scale `` absolutely calibrated '' with the 404 mhz @xmath32 survey of pauliny - toth & shakeshaft ( 1962 ) . in the present investigation we will derive ( for the sky area analysed ) a mean spectral index between 408 mhz and 19.2 ghz from the cottingham ( 1987 ) survey and 31.5 , 53 and 90 ghz from the @xmath1-dmr survey . it is important to remember that the spectral index of galactic synchrotron emission varies with frequency and position on the sky . the analysis of low - frequency surveys by lawson et al . ( 1987 ) indicates that the brighter regions away from the galactic plane have typical spectral indices of @xmath33 and @xmath34 at 100 and 800 mhz respectively . furthermore , the value of @xmath25 evaluated between any pair of frequencies separated by a factor of @xmath35 varies typically by @xmath36 over the sky ( reich & reich 1988 ) . bennett et al . ( 2003b ) propose a model using _ wmap _ data which includes a flat spectrum synchrotron component ( @xmath37 ) in regions of star formation near the galactic plane and a steep spectrum component ( @xmath38 ) from the galactic halo . at frequencies higher than @xmath35 ghz no reliable zero levels can be measured for large - area surveys at intermediate and high latitudes where cmb measurements are normally conducted and as a consequence , large area spectral index maps can not be made . however , the spectral index of smaller angular scale ( @xmath39 and less ) structures can be estimated from cross - correlation analyses of maps at different frequencies . for example , hancock et al . ( 1997 ) found a spectral index of @xmath40 at 10 ghz from bremsstrahlung data at 10,15 and 33 ghz . it is interesting to note that the steepening of the brightness temperature spectral index by 0.5 at higher frequencies expected from synchrotron losses would lead to @xmath41 at higher frequencies ; this is the value at these frequencies expected from the local cr electron spectrum ( platania et al . 1998 ) . for the free - free template , we use the all - sky h@xmath0 template described in dickinson et al . the all - sky map is a composite of h@xmath0 data from the wham survey of the northern sky ( reynolds et al . 1998 ; haffner 1999 ) and shassa survey in the southern sky ( gaustad et al . 2001 ) . the shassa data are first smoothed to the wham resolution of @xmath42 and are preferred at declinations @xmath43 . it should be noted that the all - sky template is a first attempt at producing a high - sensitivity all - sky h@xmath0 map . shassa data have significantly lower sensitivity than data from the wham survey ; the noise levels are estimated as @xmath44 and @xmath45 rayleigh ( @xmath46 ) respectively , where @xmath47 photons s@xmath6 @xmath48 sr@xmath49 erg s@xmath6 @xmath48 sr@xmath50 for @xmath51 k gas . baseline uncertainties exist in both data - sets , particularly shassa data which results in loss of information on angular scales @xmath52 for data at @xmath53 due to the @xmath54 field - of - view of each pointing . however , the shassa background levels are fitted to wham data where wham data exist ( @xmath55 ) with an assumed cosecant law for declinations further south . the different observing strategies result in different beam shapes which have not been accounted for . finally , large h@xmath0 signals ( emission and absorption ) from bright stars have been filtered using different techniques ; the wham team use data from nearby unaffected pixels , while the shassa team use a median filter to reduce star residuals . however , all these possible systematics are significantly reduced when the data , at a resolution of @xmath56 , are convolved with the dmr beam at @xmath57 resolution . indeed , we have explicitly verified this by comparing the power spectra of the high - latitude h@xmath0emission after varying the latitude at which the surveys are matched and adjusting baselines . recently , finkbeiner ( 2003 ) has produced an all - sky h@xmath0 map at 6 arcmin resolution which includes higher resolution data from the virginia - tech sky survey ( dennison et al . the differences in the power spectrum of our h@xmath0 map with that given by finkbeiner ( 2003 ) are less than 10 per cent for @xmath58 and less than 30 per cent everywhere . the optical h@xmath0 line ( @xmath59 nm ) is well known to be a good tracer of the free - free continuum emission at radio wavelengths since they are both emitted by the same ionized gas . since they are both proportional to the emission measure ( @xmath60 ) there is a well - defined relationship between the h@xmath0 line intensity @xmath61 and the radio continuum brightness temperature @xmath62 ( osterbrock 1989 ; valls - gabaud 1998 ; dickinson et al . there is a strong dependence on frequency since free - free emission scales as @xmath63 at ghz frequencies . there is also a modest dependence on the electron temperature @xmath64 ( @xmath65 ) . in the galaxy , @xmath64 can range between 3000 k and 15000 k ( shaver et al . 1983 ) ; the majority of hii regions have @xmath64 between 5000 and 10000 k ( reynolds 1985 ) . shaver et al . ( 1983 ) show that the mean electron temperature of hii regions at the galactocentric radius of the sun ( @xmath66 kpc ) is 7200 k with an r.m.s . spread of 1200 k. in the region of the galaxy covered in the present study where @xmath9 the ionized hydrogen will be typically within @xmath14 kpc of the sun and accordingly we adopt a value of @xmath51 k. with this value of @xmath64 , the conversions from h@xmath0 to free - free continuum for frequencies 31.5 , 53 and 90 ghz are 5.25 , 1.71 and 0.54 @xmath2k @xmath67 respectively . in section [ sec : results_foregrounds ] we will use this prior information to allow a fixed free - free component to be subtracted giving a clearer separation of the foregrounds . we will take a variation of @xmath68 k from the local value of 7000 k as in indication of the upper and lower bounds allowed . other caveats become important at the few per cent level : i ) the helium abundance is usually taken to be 8 per cent with a spread of a few per cent ii ) the emitting medium is assumed to be optically thick ( case b ) to the lyman continuum photons . a major uncertainty when using the h@xmath0 template is the absorption of h@xmath0 by foreground dust . the absorption can be estimated using the @xmath69 m maps given by schlegel , finkbeiner & davis ( 1998 , hereafter sfd ) . the absorption at h@xmath0@xmath70 in magnitudes using their temperature - corrected column density map ( @xmath71 ) in units of mjy sr@xmath6 is then @xmath72 where @xmath73 is the fraction of dust _ in front _ of the h@xmath0 actually causing absorption in the line of sight . the corrected h@xmath0 intensity is then @xmath74 . although there are uncertainties in this relationship due to different reddening values expected from different dust populations , the largest uncertainty is in @xmath73 , the fraction of dust lying in front of the h@xmath0-emitting region . dickinson et al . ( 2003 ) show that for a range of longitudes ( @xmath75 ) , and for @xmath76 , @xmath77 , while for local high latitude regions such as orion and the gum nebula , there is little or no absorption by dust ( @xmath78 ) . for much of the high latitude sky , @xmath71 is @xmath79 mjy sr@xmath6 and therefore the absorption is likely to be small ( @xmath80 mag ) . at lower galactic latitudes @xmath81 , the dust absorption strongly increases to 1 mag and above . for the majority of the galactic plane ( @xmath82 ) , the absorption is too great to make any reliable estimate of the true h@xmath0 intensity . finally , the scattering of h@xmath0 light from dust at high galactic latitudes could , in principle , cause a degeneracy in the analysis since the scattered h@xmath0 light would be directly correlated with the dust . however , wood & reynolds ( 1999 ) predict that this accounts for less than 20 per cent of high latitude h@xmath0 emission . since the anomalous component is larger than the free - free component at frequencies higher than @xmath83 ghz ( see sections [ sec : results_foregrounds ] and [ sec : results_anomalous ] ) , this systematic will not significantly affect our results within the errors . as templates for the thermal and anomalous dust - correlated emission , we utilise the @xmath1-dirbe data repixelised into the healpix pixelisation scheme . this was achieved using the publicly available calibrated individual observations ( cio ) files together with the dirbe sky and zodi atlas ( dsza , both products being described in hauser et al . 1998 ) , allowing the construction of dirbe full sky maps corrected for the zodiacal emission according to the model of kelsall et al . in particular , we use the dirbe 140 @xmath2 m data at @xmath84 resolution : although the 100 @xmath2 m data has the best sensitivity , there remain more noticeable artifacts present in the sky map after zodiacal correction . while this is not likely to present a problem after the data has been convolved with the dmr beam profile ( @xmath57 fwhm ) , our choice allows maximal consistency with previous analyses by the dmr team ( banday et al . 1996 ; grski et al . 1996 ; kogut et al . 1996a , 1996b ) . furthermore , the sfd version of the 100 @xmath2 m sky map has been used to correct for dust absorption in the h@xmath0 template , thus our choice allows some additional independence in the dust correlation results . dl98 have suggested that the anomalous dust - correlated signal which we re - investigate in this work should be significantly correlated with 12 @xmath2 m emission , so that the corresponding dirbe sky map may prove a better tracer for this foreground component . however , the 12 @xmath2 m map contains residual zodiacal artifacts in the region of the ecliptic plane which remain significant even after smoothing to dmr resolution . the impact of this could be minimised by excluding a region close to the ecliptic plane , but we prefer to make use of the greatest sky coverage possible . further , de oliveira - costa et al . ( 2002 ) have tested this hypothesis , but it is clear from their fig . 4 that even after considerable processing of the 12 @xmath2 m dirbe data for the removal of both zodiacal emission and point sources , the longer wavelength data at 100 , 140 and 240 @xmath2mremain equally viable for correlation studies . finally , in order to attempt to isolate the anomalous dust - correlated component signal , it is necessary to identify and subtract the thermal dust emission . we have employed the predictions of finkbeiner , davis & schlegel ( 1999 , hereafter fds ) for the thermal dust emission at dmr wavelengths . fds consider 8 models based on the 100 and 240 @xmath2 m maps from sfd , and test them against the @xmath1-firas data . the inconsistency of extrapolations of the sfd maps using single component power - law emissivity functions with the firas data over the range 200 - 2100 ghz motivated the development of generalised two - component models . we have considered fds models 7 and 8 as plausible tracers of the thermal dust component emission . masi et al . ( 2001 ) have demonstrated that model 8 extrapolated to 410 ghz is well correlated with the boomerang data at that frequency , and a recent analysis of the maxima data ( jaffe et al . 2003 ) also see consistency with these extrapolated dust models . it should be remembered that the fds models are formally correct only on scales comparable to or larger than the firas beam , hence the fds predictions of model 7/8 should be well - matched to our purposes . in this analysis , we utilise the @xmath1-dmr 4-year sky maps ( bennett et al . 1996 ) at 31.5 , 53 and 90 ghz in galactic coordinates and the healpix pixelisation scheme with a resolution parameter of @xmath85 , corresponding to 12288 pixels on the sky . inverse - noise - variance weighted combinations of the a and b channels are formed at each of the three dmr frequencies , the weights being ( 0.618 , 0.382 ) , ( 0.579 , 0.421 ) and ( 0.382 , 0.618 ) at 31.5 , 53 and 90 ghz respectively . the dominant feature visible in the sky maps ( given that the dipole anisotropy of amplitude @xmath23 3 mk is largely removed in the pre - map - making data processing ) is the enhanced emission along the galactic plane . this emission is indeed a combination of the synchrotron , free - free and dust emission that we are interested in , however , the distribution and spectral behaviour at the lowest latitudes ( @xmath86 ) is sufficiently complex that we do not attempt to fit or model it , considering only the mid- and high - latitude galactic emission . contrary to previous analyses , we attempt to fit our templates to somewhat lower latitudes , the results of which are discussed in section [ sec : results_foregrounds ] . in addition to the @xmath1-dmr data , we also consider correlations of the foreground templates with a 19.2 ghz survey of the sky ( cottingham 1987 ; boughn et al . such an investigation is clearly of interest here since 19.2 ghz is close to the frequency at which the dl98 models for spinning dust show a maximum in spectral behaviour . even if the anomalous dust - correlated component is not the putative rotational dust emission , the coupling amplitude of the dust template at 19.2 ghz should enable the spectrum of this foreground to be established , in particular since the frequency of observation is well - removed from that where a significant thermal dust contribution is present . the data are available in the @xmath1 quadcube format ( white & stemwedel , 1992 ) with 24,576 pixels on the full sky of size @xmath87 , and contains observations of angular resolution 3 fwhm . a small region close to the south ecliptic pole was not observed . the typical noise level is quoted as 1.5 mk per resolution element , but there is both variation in the number of observations per pixel and pixel - pixel covariance . in contrast to the analysis of de oliveira - costa et al . ( 1998 ) we take account of the former , but the information is not available for the latter . some attempt to provide additional constraints on the noise uncertainty is performed by scaling the noise level by a factor in the range 0.9 - 1.1 , and including this parameter in our later statistical analysis . each of the three dmr maps , the 19.2 ghz data , and the foreground sky map templates ( after convolution to the correct angular resolution ) are decomposed into harmonic coefficients using a basis of orthonormal functions explicitly computed on the incompletely sampled sky ( grski 1994 ) , a procedure which is directly analogous to the expansion of a full - sky map in terms of spherical harmonic coefficients . this technique has the advantage of allowing exact exclusion of the monopole and dipole components from the analysis ( which are unimportant for the investigation of cosmological anisotropy ) , and makes full use of all of the available spatial ( phase ) information . we have adopted several definitions for the area of sky coverage , in particular the standard galactic cut defined as the region with galactic latitude , @xmath88 , above 20@xmath89 with additional regions at ophiuchus ( up to @xmath90 at @xmath91 ) and orion ( down to @xmath92 at @xmath93 ) based on the dirbe 140 @xmath2 m map ( banday et al . 1997 , but recomputed explicitly for the healpix scheme ) , together with more aggressive and conservative cuts of @xmath88 greater than 15@xmath89 and 30@xmath89 respectively . for each sky coverage a new basis of orthonormal functions is computed . this procedure must also be performed separately for the 19.2 ghz data due to its different pixelisation scheme and pixel resolution ( and indeed for the foreground templates matched to the same pixelisation and angular resolution ) . the measured map coefficients in the new orthogonal basis at a given frequency , @xmath94 , can then be written in vector form as @xmath95 where @xmath96 , @xmath97 and @xmath98 are the coefficients describing the true cmb distribution , the noise and one foreground template map respectively . @xmath99 is now a coupling constant ( with units @xmath2k @xmath100 ) to be determined by minimizing @xmath101 where * m * is the covariance matrix describing the correlation between different fourier modes on the cut - sky and is dependent on assumed cmb model parameters and the instrument noise . full details of its computation can be found in grski ( 1994 ) and grski et al . ( 1996 ) . by minimising the @xmath102 with respect to @xmath99 we find that the coupling constant @xmath99 has an exact solution @xmath103 and a gaussian error given by @xmath104 the contribution of component @xmath105 to the observed sky is the map @xmath106 ( where @xmath107 is in the natural units of the foreground template map so that this scaled quantity is in @xmath2k ) . in this analysis , however , we treat multiple foreground templates and all three dmr channels simultaneously . this forces the cmb distribution ( in thermodynamic units ) to be invariant between the three frequencies , and suppresses the sensitivity of the method to noise features in the individual dmr maps which are clearly not common to all three frequencies , thus allowing an improved determination of the extent of chance cosmic or noise alignments with the template maps . we have tested the impact of such chance alignments to the method by repeating the fits after rotation of the foreground templates . we only find significant correlations when the templates are correctly aligned . moreover , the r.m.s values of the coupling coefficients derived from the rotated sky maps are consistent with the errors determined directly in the analysis . the full details of this method are contained in grski et al . the 19.2 ghz data are treated in a similar fashion , but we do not extend the method to include it in a simultaneous fit with the dmr data to the foreground templates because of complications introduced by its different angular resolution and noise properties . having solved for the values of the coupling coefficients and their gaussian errors , we are then in a position to compute the likelihood of the foreground corrected data as a function of a given set of input cosmological parameters as contained in the matrix @xmath108 of equation [ eqn : chi2 ] . indeed , this also allows us to assess the sensitivity of the coupling constant fits to the assumed cosmological power spectrum . we consider a full grid of power law models specified by the rms quadrupole normalisation amplitude @xmath10 and a spectral index @xmath11 as in grski et al . the cosmological implications of the foreground corrections as reappraised in this work are discussed in section [ sec : results_cmb ] . in order to quantify the uncertainty in the h@xmath0 template resulting from dust absorption , we generate corrected h@xmath0 templates for three values of @xmath73 0.0 , 0.5 and 1.0 which are then fitted successively to the data over the full @xmath10 , @xmath11 grid of cosmological models , and also test templates corrected assuming values of @xmath73 running from 0 to 1 in steps of 0.01 for a scale - invariant spectrum with @xmath10 @xmath2318 @xmath2k . since the correction is non - linear in @xmath73 ( see section [ sec : ff_template ] ) , modifications to the template are made _ before _ convolution with the appropriate beam response , at the 1 effective angular resolution of the h@xmath0 template ( see section [ sec : results_dmr_ff ] for full discussion ) . we also analyse the dmr and 19.2 ghz data after correction for free - free emission using the h@xmath0 templates scaled by the factors given in table 4 of dickinson et al . this enables us to test the impact of cross - talk between the templates , which is likely to be present at some level due to the large - scale cosecant variation with latitude of the galactic emission present in each template ( see section [ sec : results_19ghz ] ) . finally , in an attempt to unambiguously identify the _ anomalous _ dust - correlated emission , we use the fds models of _ thermal _ dust emission and subtract them from the observed data before correlation studies are performed ( see section [ sec : results_anomalous ] ) . to305 mm \5 . forced / unforced fits to the h@xmath0 data . open symbols are fits that are made to the dust and synchrotron templates _ after _ correcting the dmr data for the free - free contribution predicted by the h@xmath0 template ; filled symbols correspond to fits made to the three templates simultaneously in which no constraints have been placed on the h@xmath0 template correlation . \6 . electron temperature . the free - free predictions from the h@xmath0 template depend upon the electron temperature ; the dashed boxes in the middle panels show the range of predicted free - free emission for temperatures 5000 to 9000 k ( open symbols are for 7000 k ) . the results obtained from an analysis using only the dirbe and synchrotron templates , consistent with previous work by the @xmath1-dmr team ( kogut et al . 1996b ) , are shown with their errors by full - line boxes in the upper and lower panels of each figure show slightly different results to the previous analysis of kogut et al . ( 1996b ) . however , this is not surprising since they used an earlier release of the dirbe 140 @xmath2 m map and the data were analysed in the quadcube format . ] . this allows a direct assessment of the impact of the inclusion of a free - free template on the analysis by comparison with results in which such a template has not been utilised . the results presented here have been derived assuming a scale - invariant spectrum ( @xmath11 = 1 ) for the cmb contribution with an r.m.s quadrupole normalisation of @xmath10 = 18 @xmath2k . however , as part of our studies of the impact of the foreground correction for cosmological interpretations of the dmr data , we have determined the coupling parameters over a grid in @xmath10 and @xmath11 . we compute an average of the @xmath0 coefficients weighted by the likelihood function over the grid and find that the marginalised coupling coefficients are essentially identical to those shown here , and that no conclusions derived from later analysis are compromised by adopting these values as canonical . as described above , we have adopted three galactic cuts , and also computed correlations in which the coupling to the h@xmath0 template has been left unconstrained , or where we have fixed and subtracted the predicted free - free contribution according to the spectral behaviour predicted in dickinson et al . ( 2003 ) , determined for an electron temperature of 7000 k , the mean value in the solar neighbourhood ( see section [ sec : ff_template ] ) . our better understanding of the foregrounds allows us to correct for them over a larger region of the sky and reassess the value of @xmath10 and @xmath11 . the most significant changes in general result from an analysis made with an aggressive @xmath9 galactic cut , yet even here the results are compatible with earlier results at better than the @xmath112 level , although the error is slightly smaller , suggesting some possibility of making use of modestly larger sky coverage for the inference of cosmological parameters . interestingly , what might be considered our best model for the foreground correction with this aggressive galactic cut , utilising the fds model 7 dust template to correct for thermal dust emission , the h@xmath0 template from dickinson et al . ( 2003 ) to trace the free - free emission ( fixed assuming that the electron temperature is 7000 k ) , together with unrestricted fits to the dirbe 140 @xmath2 m and 408 mhz sky surveys to correct for anomalous dust - correlated and synchrotron emission respectively results in shifts in @xmath10 and @xmath11 of only @xmath113 @xmath2k and @xmath114 relative to the previous standard uncorrected result . all results with @xmath115 are consistent with values of @xmath10 = 15.3 @xmath2k and @xmath11 = 1.2 . ) at angular scales @xmath116 . best - fitting models to 19.2 ghz and dmr data are shown for each foreground component : synchrotron ( dotted line ) , free - free ( dot - dashed line ) , thermal dust ( dashed line ) and anomalous dust ( heavy dotted line between 19 and 90 ghz ) . units have been converted to thermodynamic temperature fluctuations relative to @xmath117 k ; cmb fluctuations are represented as a horizontal line at a level of @xmath118 for comparison . data from this paper are : synchrotron 19.2 ghz ( open triangle ) , anomalous emission at 31.5 , 53 and 90 ghz ( open circles ) and total dust emission at 90 ghz ( filled circle ) . the thick solid line gives an estimate total foreground level by adding all the foreground models in quadrature . the frequency channels for the _ wmap _ ( short vertical dashed lines ) and _ planck _ ( short vertical solid lines ) cmb satellites are shown at the top of the figure . the low and high frequency instruments ( lfi and hfi ) for _ planck _ are drawn as heavy and fine lines respectively . , scaledwidth=50.0% ] fig . [ fig : foregrounds ] summarises the integrated amplitudes of galactic foregrounds at large ( @xmath116 ) angular scales over the most important frequencies for cmb studies . our best models for synchrotron ( @xmath119 scaled to the 408 mhz map ) , free - free ( scaled h@xmath0 predictions assuming @xmath51 k ; dot - dashed line ) and thermal dust model ( fds7 ; dashed line ) emissions are plotted in terms of thermodynamic temperature units ( relative to @xmath120 k ) . the best - fit anomalous component is shown ( heavy dotted line ) over the range @xmath121 ghz . data points are shown for synchrotron at 19.2 ghz ( open triangle ) anomalous dust at 19.2 , 31.5 , 53 and 90 ghz ( open circles ) , total dust at 90 ghz ( filled circle ) . the cmb signal is plotted at a level of @xmath122 k. the approximate total foreground level is represented by adding the four components in quadrature , with the anomalous component set to 52 @xmath2k ( the value at 19.2 ghz ) for frequencies below 19.2 ghz . this suggests that the minimum foreground contamination for these data , is @xmath123 ghz . this is in good agreement with the _ wmap _ analysis which predicts the minimum to lie at @xmath124 ghz . the amplitudes for each of the foreground signals are now relatively well known as shown in fig . [ fig : foregrounds ] . strictly , fig . [ fig : foregrounds ] applies only for angular scales of @xmath125 and larger , and for all - sky observations with a galactic cut of @xmath126 . for different galactic cuts , there are likely to be variations of a factor of @xmath127 for reasonable galactic cuts as indicated in table 1 . observations covering smaller regions of sky , perhaps cleaner regions ( for example , away from the north polar spur ) , may be have reduced foreground contamination by a factor of @xmath128 . finally , at higher @xmath15-values ( smaller angular scales ) , it is known that diffuse galactic foregrounds reduce in amplitude . the power spectra of galactic emission have a typical power - law indices ( @xmath129 ) of @xmath130 ( giardino et al . 2001 ) . thus at @xmath131 angular scales , the galactic foregrounds , in terms of @xmath132 , will be reduced by a factor @xmath128 . however , at angular scales @xmath133 , discrete extragalactic sources become the dominant foreground . with relevance to the satellite missions _ wmap _ and _ planck _ , our analysis implies that the lowest level of foreground contamination from diffuse galactic foregrounds at least on a 7angular scale will be between 50 and 100 ghz . this has been confirmed by bennett et al ( 2003b ) and seems to hold to yet smaller scales @xmath23 1 . our study also predicts that for the _ wmap _ experiment , the predominant foreground at 22 , 30 and perhaps 40 ghz , will be due to the dust - correlated component . this is indeed found to be the case by the recent _ wmap _ analysis , although the interpretation of the physical origin of the emission remains open to debate . more accurate determination of its spectral behaviour , allied to lower frequency observations ( 5 - 15 ghz ) and higher angular resolution observations , should allow the mechanism behind this unexpected foreground to be ascertained . moreover , given the likely region of minimal foreground contamination in frequency space , the importance of the _ planck_-lfi instrument to the _ planck _ mission as a whole can not be overemphasised . the @xmath1 datasets were developed by the nasa goddard space flight center under the guidance of the @xmath1 science working group and were provided by the nssdc . the wisconsin h - alpha mapper project is funded by the national science foundation . the southern h - alpha sky survey atlas project is supported by the nsf . we acknowledge dave cottingham for providing us with a copy of the 19.2 ghz survey .[/INST] with the advent of all - sky h@xmath0 surveys it is possible to determine a reliable free - free template of the diffuse interstellar medium ( dickinson , davies & davis 2003 ) which can be used in conjunction with the synchrotron and dust templates to correct cmb observations for diffuse galactic foregrounds . we have used the @xmath1-dmr data at 31.5 , 53 and 90 ghz and employed cross - correlation techniques to re - evaluate the foreground contributions , particularly that due to dust which is known to be partially correlated with h@xmath0 ( and free - free ) emission . the dmr microwave maps are found to contain , as well as the expected synchrotron and free - free components , a component tightly correlated to the 140 @xmath2 m dust maps of dirbe . at 31.5 , 53 and 90 ghz this emission is @xmath3 , @xmath4 and @xmath5 @xmath2k/(mjy sr@xmath6 ) at 140 @xmath2 m respectively . when corrected for the contribution from thermal dust following model 7 of finkbeiner , davis & schlegel ( 1999 ) , a strong anomalous dust - correlated emission component remains , which is well - fitted by a frequency spectrum of the form @xmath7 where @xmath8 2.5 in the dmr frequency range ; this is the dominant foreground at 31.5 ghz . the result implies the presence of an emission component with a dust - like morphology but a synchrotron - like spectrum . we discuss the possible origins of this component and compare it with the recent _ wmap _ interpretation . the better knowledge of the individual foregrounds provided by the present study enables a larger area of the sky ( @xmath9 ) to be used to re - appraise the cmb quadrupole normalisation , @xmath10 , and the scalar perturbations spectral index , @xmath11 . we find @xmath10@xmath12 with a power - law spectral index of @xmath13 . these values are consistent with previous @xmath1-dmr analyses and the _ wmap _ 1-year analysis . [ firstpage ] cosmic microwave background - cosmological parameters - radio continuum : general - ism : dust , extinction </s>

ms is primarily an autoimmune disease involving several arms of the cellular and humoral immune systems resulting ultimately in axonal degeneration . the disease prevalence has been on the rise in several areas around the world including the middle east ( 1 , 2 ) . the diagnosis requires proof of the disease activity on sequential examinations and central nervous system magnetic resonance imaging ( mri ) . genetic , viral along with environmental factors are possible candidate etiologies of the disease ( 3 , 4 ) . the effector cells include different categories of the t - lymphocytes , b - lymphocytes , natural killer cells , and the oligodendrocytes . the deregulated immune inflammatory mediators include ifn- , tumor necrosis factor ( tnf ) , and several interleukins . this unusual combination of abnormally acting cells and factors interact in a very complex schema to produce the clinical manifestations of ms ( 47 ) . the myelin generating , supporting and feeding cells , the oligodendrocytes , are attacked by this immune army , leading to thinning and disappearance of the myelin sheath . the degradation of myelin gradually leads to electrical instability , poor axonal conduction and functional aberrations along the whole neuron ( 4 ) . depending on the location and degree of damage , the lesions show up along the white matter and its tracts in the cns in order of frequency along the basal and lateral ganglia , brain stem , spinal cord , and optic nerves . muscle spasms , visual problems ( nystagmus , diplopia ) , chronic pain , dizziness , headaches , dysarthria , dysphagia , urinary and bowel incontinence are some of those manifestations ( 4 , 7 ) . the patterns and severity of the symptoms are grouped into four subtypes ( 8) : the relapsing remitting ms ( rrms ) : affects almost 80% of the patients with a course of flare - ups alternating with improvements . the symptoms are dynamic and sometimes abrupt with differing degrees of recovery and periods of stability or slow progression . secondary progressive ms ( spms ) : progressive course of symptoms after an initial course of a relapsing remitting pattern with or without periods of regression or stability . the treatments of multiple sclerosis , which can be effective at relieving the symptoms , usually have no or little effect on the actual demyelination and immune disturbances . interferons , natalizumab , fingolimod , glatiramer actetate and others may allow to hit one or more of the abnormalities found in ms rather than restore the normal immune balance and that explains the lack of full remissions or cure with all these medications carrying the price tags of several thousands of dollars yearly ( 911 ) . other strategies involve attacking the leukocyte specific adhesion molecules , tipping the balance to producing immune suppressors like il-4 , il-10 and tgf - beta , inhibiting il-2 , blocking certain specific molecules like cd20 and cd52 have been shown to control ms at least for a period of time ( 913 ) . the bm - mnscs are progenitor cells with regenerative and immune modulatory and growth stimulating properties . they may induce angiogenesis and differentiate into different types of cells of the nervous system . the bm - mnscs include the hematopoietic and mesenchymal cells found in the bone marrow in small numbers ( 1416 ) . the bm - mnscs have been found in several studies to be well tolerated and to have the ability to generate neurons , counteract fibrosis and oxidation . they are easy to handle technically and to inject using sterile methods ( 1619 ) . stem cell therapies have given the ms and neuro - regenerative fields a breath of hope with the promise of regenerating and immune modulating properties . the stem cell immune modulator properties make them capable of breaking the process that leads to ms . stem cells have several useful properties including their ability to self - renew , remodeling , differentiation , immune modulation , and immune balance restoration . mesenchymal stem cells are also known to be immune modulators , a property that may be of utmost importance ( 20 , 21 ) . to quantify , monitor and evaluate the ms patients receiving this therapy we resorted to the edss which is a validated , reproducible tool that quantifies disability in eight functional systems and allows to quantitatively assign a functional system score in each case ( 22 ) . there has been a lot of data but a scarcity of randomized studies . in 2011 , connick et al . administered intravenous autologous bone - marrow - derived mesenchymal stem cells at a mean dose was 1.610 cells per kg to secondary progressive ms patients in an open - label study . they noted improvement after treatment in visual acuity and visual evoked response latency with an increase in the optic nerve area . starting in 2009 , patients with ms were enrolled sequentially on this study using bone marrow derived stem cells . the study was reviewed and approved by the scientific committee and institutional review board at the hospital . the patients had to have confirmed disease by 2 neurologists based on the clinical picture , the mri showing progression on two occasions , and the presence of change over time correlating with the mri findings . the patients had also to have progressive disease despite treatment using at least 2 standard lines of therapy and have adequate renal , hepatic , pulmonary and cardiac functions . all patients signed an informed consent and received full explanation of the protocol , expected outcomes and adverse events . the patients were given 3 days of granulocyte - colony stimulating factor at 10 mg / kg divided in 2 equal doses prior to bone marrow collection . on the day of the procedure , the bone marrow was collected under sterile conditions under local or general anesthesia and adequate sedation . about three milliliters per kg of marrow were collected from the posterior iliac crests bilaterally . the marrow was aspirated using a gauge 8 jamshidi needle into a syringe containing heparin sodium at 10% concentration . the collected bm - mnscs were separated using density gradient centrifugation before counting the cells using a neubauer chamber . the resulting cells were re - suspended to prepare 5~10 ml bm - mnscs to be injected intrathecally . the intrathecally injected cells were adjusted to about 0.5 million mononuclear cells per kilogram of body weight at the l4~l5 level under sterile conditions and the rest of the cells were given intravenously . 22 sequential patients , 10 males and 12 females aged 22 to 56 years were accrued . seven patients were classified as having the spms type , eight as ppms , and seven as rrms . pretreatment edss scores ranged between 1 and 8.5 with an average of 5.5 ( table 1 ) . the patients tolerated the procedures well in general with manageable pain at the site of bone marrow aspiration in most patients . headaches due to sterile meningitis and fever occurred in 12 of the 22 patients ( 54% ) but were easily treated with steroids and pain medications . one patient had nausea and vomiting that lasted for few hours and was easily controlled . 1 shows an interesting phenomenon we observed on the mris demonstrating a significant decrease in the number and intensity of some of the demyelinated areas after the treatment . 16 of the 20 evaluable patients improved as assessed by their edss score ( 80% ) . it meant being able to ambulate or eat independently when they needed much more help in the past and that resulted in significant subjective quality of life improvement . there were no other long term effects noted to prevent repeating the procedure where it was found to be useful . there were also no issues to prevent the use of other therapies especially the newer agents where the neurologist felt the necessity . the response seems to vary from one patient to another as reported in other studies ( 16 , 19 ) although it was our impression that the lesser the symptoms and their duration , the better the response in general ( table 2 ) . the pathobiology of the disease makes it a logical conclusion given the fact that the inflammatory process is at least partially reversible up to the point of neuronal death where it becomes permanent . when comparing the pre and post edss scores , we found a trend towards improvement of the patients functional capacity but the p value did not reach statistical significance probably due to our sample size and the study design as a phase ii rather than a randomized trial . however , comparing the expected edss scores to the post treatment values , the p value and statistical significance improved significantly to a two - tailed p value of 0.04 . one has to keep in mind that the patients progression can be unpredictable and does not usually follow a clear pattern . the 95% confidence interval was 1.003 to 2.653 with a mean of 5.3 before treatment and 4.475 after therapy . the standard deviation widened from 2.5 to 3.2 post treatment indicating the difference in responses seen among patients . even when the expected worsening is accounted for , the improvement shows a wide standard deviation again reflecting the variations among the patients responses . when comparing the pre and post edss scores , we found a trend towards improvement of the patients functional capacity but the p value did not reach statistical significance probably due to our sample size and the study design as a phase ii rather than a randomized trial . however , comparing the expected edss scores to the post treatment values , the p value and statistical significance improved significantly to a two - tailed p value of 0.04 . one has to keep in mind that the patients progression can be unpredictable and does not usually follow a clear pattern . the 95% confidence interval was 1.003 to 2.653 with a mean of 5.3 before treatment and 4.475 after therapy . the standard deviation widened from 2.5 to 3.2 post treatment indicating the difference in responses seen among patients . even when the expected worsening is accounted for , the improvement shows a wide standard deviation again reflecting the variations among the patients responses . the available treatments for ms usually aim at providing symptom relief with no or little effect on the intricate pathobiology of the disease , effector cells and intermediary molecules . there is no available cure but rather calming treatments to maintain function for as long as possible . due to the presence of a big gap in the treatment of ms and the major permanent disability that results , we felt the need to look for alternative ways and new approaches to treat this disease . to assess the patients , we used a validated assessment tool which is the edss score . several growth factors like g - csf , stem cell factor ( scf ) , the fibroblast growth factor ( fgf ) and others may help reduce the ischemia and enhance the migration and proliferation of the stem cells . there is evidence that the growth factors like the ones released from the stem cells may help improve neuronal regeneration ( 24 ) . the transplanted bone marrow cells infiltrate the brain and may help regenerate new elements or combat the neurodegenerative process , fibrosis and oxidative insults . several studies reported significant improvement among patients with neurodegenerative conditions with no significant adverse events . in this study , we report a significant improvement in 80% of the patients treated for progressive ms with minor adverse events and great tolerability as reported by other groups ( 16 , 19 , 25 ) . others used bm - mnscs to treat cerebral palsey , giving five intrathecal injections , they reported significant clinical improvement with no safety issues ( 16 , 26 ) . the bone marrow contains several types of progenitors including the hematopoietic and mesenchymal stem cells in addition to mature differentiated cells . the bm - mnscs seem to concentrate in injured areas and act through paracrine effects to reduce the inflammatory process . the bm - mnscs also contribute to vascular repair and stimulate endogenous stem cells to proliferate and contribute to the repair process . the bm - mnscs may generate neurons ; counteract fibrosis and oxidation ( 2729 ) . there are several auto - immune conditions that reportedly showed a good response to stem cell therapy using different methods . these conditions include crohn s disease , graft versus host disease ( gvhd ) , lupus , and others ( 30 ) . in this report , we summarized the course of 22 patients treated with bone marrow derived stem cells . the cells were given using intravenous and intrathecal routes . our list of patients adds to the current evidence that the bm - mnscs are safe and partially effective in many patients with ms . those cells can be combined with other immunotherapeutic approaches as well as growth factors in the future and tested extensively in phase iii studies to demonstrate and prove their efficacy beyond doubt . the injections could be repeated theoretically to sustain the improvement or add to it over time should the patient benefit from this approach . it is not clear at this time what is the best number of injections , the injection schedule , or whether it is beneficial to add growth factors to maximize this effect . it is also important for the regulatory agencies to keep up with the progress being made in the stem cell science and assist in its proper implementation and benefit . a very large number of hurdles remain but we have to keep in mind the special aspects of this line of therapy requiring new methodologies to keep abiding by the scientific methods and medical ethics . the very concept of cellular therapy entails a fundamental new look at our concepts of pharmacodynamics and pharmacokinetics along with new roles for using new differentiation growth factors and special in vivo microenvironments reaching a re - definition of the different phases of the clinical studies . cell therapy may be the future pathway to solve a large number of debilitating and disabling situations if we can channel this effort into the correct paths .

stem cell therapy , an evolving , progressive field of therapeutics has shown several successes in areas where classic treatments failed to prevent or stop disability . starting in 2009 , twenty two sequential patients with progressive multiple sclerosis ( ms ) courses were treated with autologous bone marrow mononuclear stem cells ( bm - mnscs ) . the cells were given both intravenously and intrathecally . using the expanded disability status scale ( edss ) score for evaluation , our data indicates that the majority of the patients benefited on the average one point on the scale . this paper adds to the body of evidence suggesting the safety and efficacy of autologous bm - mnscs in the treatment of ms and awaits validation through larger , randomized studies .

<s>[INST]ms is primarily an autoimmune disease involving several arms of the cellular and humoral immune systems resulting ultimately in axonal degeneration . the disease prevalence has been on the rise in several areas around the world including the middle east ( 1 , 2 ) . the diagnosis requires proof of the disease activity on sequential examinations and central nervous system magnetic resonance imaging ( mri ) . genetic , viral along with environmental factors are possible candidate etiologies of the disease ( 3 , 4 ) . the effector cells include different categories of the t - lymphocytes , b - lymphocytes , natural killer cells , and the oligodendrocytes . the deregulated immune inflammatory mediators include ifn- , tumor necrosis factor ( tnf ) , and several interleukins . this unusual combination of abnormally acting cells and factors interact in a very complex schema to produce the clinical manifestations of ms ( 47 ) . the myelin generating , supporting and feeding cells , the oligodendrocytes , are attacked by this immune army , leading to thinning and disappearance of the myelin sheath . the degradation of myelin gradually leads to electrical instability , poor axonal conduction and functional aberrations along the whole neuron ( 4 ) . depending on the location and degree of damage , the lesions show up along the white matter and its tracts in the cns in order of frequency along the basal and lateral ganglia , brain stem , spinal cord , and optic nerves . muscle spasms , visual problems ( nystagmus , diplopia ) , chronic pain , dizziness , headaches , dysarthria , dysphagia , urinary and bowel incontinence are some of those manifestations ( 4 , 7 ) . the patterns and severity of the symptoms are grouped into four subtypes ( 8) : the relapsing remitting ms ( rrms ) : affects almost 80% of the patients with a course of flare - ups alternating with improvements . the symptoms are dynamic and sometimes abrupt with differing degrees of recovery and periods of stability or slow progression . secondary progressive ms ( spms ) : progressive course of symptoms after an initial course of a relapsing remitting pattern with or without periods of regression or stability . the treatments of multiple sclerosis , which can be effective at relieving the symptoms , usually have no or little effect on the actual demyelination and immune disturbances . interferons , natalizumab , fingolimod , glatiramer actetate and others may allow to hit one or more of the abnormalities found in ms rather than restore the normal immune balance and that explains the lack of full remissions or cure with all these medications carrying the price tags of several thousands of dollars yearly ( 911 ) . other strategies involve attacking the leukocyte specific adhesion molecules , tipping the balance to producing immune suppressors like il-4 , il-10 and tgf - beta , inhibiting il-2 , blocking certain specific molecules like cd20 and cd52 have been shown to control ms at least for a period of time ( 913 ) . the bm - mnscs are progenitor cells with regenerative and immune modulatory and growth stimulating properties . they may induce angiogenesis and differentiate into different types of cells of the nervous system . the bm - mnscs include the hematopoietic and mesenchymal cells found in the bone marrow in small numbers ( 1416 ) . the bm - mnscs have been found in several studies to be well tolerated and to have the ability to generate neurons , counteract fibrosis and oxidation . they are easy to handle technically and to inject using sterile methods ( 1619 ) . stem cell therapies have given the ms and neuro - regenerative fields a breath of hope with the promise of regenerating and immune modulating properties . the stem cell immune modulator properties make them capable of breaking the process that leads to ms . stem cells have several useful properties including their ability to self - renew , remodeling , differentiation , immune modulation , and immune balance restoration . mesenchymal stem cells are also known to be immune modulators , a property that may be of utmost importance ( 20 , 21 ) . to quantify , monitor and evaluate the ms patients receiving this therapy we resorted to the edss which is a validated , reproducible tool that quantifies disability in eight functional systems and allows to quantitatively assign a functional system score in each case ( 22 ) . there has been a lot of data but a scarcity of randomized studies . in 2011 , connick et al . administered intravenous autologous bone - marrow - derived mesenchymal stem cells at a mean dose was 1.610 cells per kg to secondary progressive ms patients in an open - label study . they noted improvement after treatment in visual acuity and visual evoked response latency with an increase in the optic nerve area . starting in 2009 , patients with ms were enrolled sequentially on this study using bone marrow derived stem cells . the study was reviewed and approved by the scientific committee and institutional review board at the hospital . the patients had to have confirmed disease by 2 neurologists based on the clinical picture , the mri showing progression on two occasions , and the presence of change over time correlating with the mri findings . the patients had also to have progressive disease despite treatment using at least 2 standard lines of therapy and have adequate renal , hepatic , pulmonary and cardiac functions . all patients signed an informed consent and received full explanation of the protocol , expected outcomes and adverse events . the patients were given 3 days of granulocyte - colony stimulating factor at 10 mg / kg divided in 2 equal doses prior to bone marrow collection . on the day of the procedure , the bone marrow was collected under sterile conditions under local or general anesthesia and adequate sedation . about three milliliters per kg of marrow were collected from the posterior iliac crests bilaterally . the marrow was aspirated using a gauge 8 jamshidi needle into a syringe containing heparin sodium at 10% concentration . the collected bm - mnscs were separated using density gradient centrifugation before counting the cells using a neubauer chamber . the resulting cells were re - suspended to prepare 5~10 ml bm - mnscs to be injected intrathecally . the intrathecally injected cells were adjusted to about 0.5 million mononuclear cells per kilogram of body weight at the l4~l5 level under sterile conditions and the rest of the cells were given intravenously . 22 sequential patients , 10 males and 12 females aged 22 to 56 years were accrued . seven patients were classified as having the spms type , eight as ppms , and seven as rrms . pretreatment edss scores ranged between 1 and 8.5 with an average of 5.5 ( table 1 ) . the patients tolerated the procedures well in general with manageable pain at the site of bone marrow aspiration in most patients . headaches due to sterile meningitis and fever occurred in 12 of the 22 patients ( 54% ) but were easily treated with steroids and pain medications . one patient had nausea and vomiting that lasted for few hours and was easily controlled . 1 shows an interesting phenomenon we observed on the mris demonstrating a significant decrease in the number and intensity of some of the demyelinated areas after the treatment . 16 of the 20 evaluable patients improved as assessed by their edss score ( 80% ) . it meant being able to ambulate or eat independently when they needed much more help in the past and that resulted in significant subjective quality of life improvement . there were no other long term effects noted to prevent repeating the procedure where it was found to be useful . there were also no issues to prevent the use of other therapies especially the newer agents where the neurologist felt the necessity . the response seems to vary from one patient to another as reported in other studies ( 16 , 19 ) although it was our impression that the lesser the symptoms and their duration , the better the response in general ( table 2 ) . the pathobiology of the disease makes it a logical conclusion given the fact that the inflammatory process is at least partially reversible up to the point of neuronal death where it becomes permanent . when comparing the pre and post edss scores , we found a trend towards improvement of the patients functional capacity but the p value did not reach statistical significance probably due to our sample size and the study design as a phase ii rather than a randomized trial . however , comparing the expected edss scores to the post treatment values , the p value and statistical significance improved significantly to a two - tailed p value of 0.04 . one has to keep in mind that the patients progression can be unpredictable and does not usually follow a clear pattern . the 95% confidence interval was 1.003 to 2.653 with a mean of 5.3 before treatment and 4.475 after therapy . the standard deviation widened from 2.5 to 3.2 post treatment indicating the difference in responses seen among patients . even when the expected worsening is accounted for , the improvement shows a wide standard deviation again reflecting the variations among the patients responses . when comparing the pre and post edss scores , we found a trend towards improvement of the patients functional capacity but the p value did not reach statistical significance probably due to our sample size and the study design as a phase ii rather than a randomized trial . however , comparing the expected edss scores to the post treatment values , the p value and statistical significance improved significantly to a two - tailed p value of 0.04 . one has to keep in mind that the patients progression can be unpredictable and does not usually follow a clear pattern . the 95% confidence interval was 1.003 to 2.653 with a mean of 5.3 before treatment and 4.475 after therapy . the standard deviation widened from 2.5 to 3.2 post treatment indicating the difference in responses seen among patients . even when the expected worsening is accounted for , the improvement shows a wide standard deviation again reflecting the variations among the patients responses . the available treatments for ms usually aim at providing symptom relief with no or little effect on the intricate pathobiology of the disease , effector cells and intermediary molecules . there is no available cure but rather calming treatments to maintain function for as long as possible . due to the presence of a big gap in the treatment of ms and the major permanent disability that results , we felt the need to look for alternative ways and new approaches to treat this disease . to assess the patients , we used a validated assessment tool which is the edss score . several growth factors like g - csf , stem cell factor ( scf ) , the fibroblast growth factor ( fgf ) and others may help reduce the ischemia and enhance the migration and proliferation of the stem cells . there is evidence that the growth factors like the ones released from the stem cells may help improve neuronal regeneration ( 24 ) . the transplanted bone marrow cells infiltrate the brain and may help regenerate new elements or combat the neurodegenerative process , fibrosis and oxidative insults . several studies reported significant improvement among patients with neurodegenerative conditions with no significant adverse events . in this study , we report a significant improvement in 80% of the patients treated for progressive ms with minor adverse events and great tolerability as reported by other groups ( 16 , 19 , 25 ) . others used bm - mnscs to treat cerebral palsey , giving five intrathecal injections , they reported significant clinical improvement with no safety issues ( 16 , 26 ) . the bone marrow contains several types of progenitors including the hematopoietic and mesenchymal stem cells in addition to mature differentiated cells . the bm - mnscs seem to concentrate in injured areas and act through paracrine effects to reduce the inflammatory process . the bm - mnscs also contribute to vascular repair and stimulate endogenous stem cells to proliferate and contribute to the repair process . the bm - mnscs may generate neurons ; counteract fibrosis and oxidation ( 2729 ) . there are several auto - immune conditions that reportedly showed a good response to stem cell therapy using different methods . these conditions include crohn s disease , graft versus host disease ( gvhd ) , lupus , and others ( 30 ) . in this report , we summarized the course of 22 patients treated with bone marrow derived stem cells . the cells were given using intravenous and intrathecal routes . our list of patients adds to the current evidence that the bm - mnscs are safe and partially effective in many patients with ms . those cells can be combined with other immunotherapeutic approaches as well as growth factors in the future and tested extensively in phase iii studies to demonstrate and prove their efficacy beyond doubt . the injections could be repeated theoretically to sustain the improvement or add to it over time should the patient benefit from this approach . it is not clear at this time what is the best number of injections , the injection schedule , or whether it is beneficial to add growth factors to maximize this effect . it is also important for the regulatory agencies to keep up with the progress being made in the stem cell science and assist in its proper implementation and benefit . a very large number of hurdles remain but we have to keep in mind the special aspects of this line of therapy requiring new methodologies to keep abiding by the scientific methods and medical ethics . the very concept of cellular therapy entails a fundamental new look at our concepts of pharmacodynamics and pharmacokinetics along with new roles for using new differentiation growth factors and special in vivo microenvironments reaching a re - definition of the different phases of the clinical studies . cell therapy may be the future pathway to solve a large number of debilitating and disabling situations if we can channel this effort into the correct paths .[/INST]stem cell therapy , an evolving , progressive field of therapeutics has shown several successes in areas where classic treatments failed to prevent or stop disability . starting in 2009 , twenty two sequential patients with progressive multiple sclerosis ( ms ) courses were treated with autologous bone marrow mononuclear stem cells ( bm - mnscs ) . the cells were given both intravenously and intrathecally . using the expanded disability status scale ( edss ) score for evaluation , our data indicates that the majority of the patients benefited on the average one point on the scale . this paper adds to the body of evidence suggesting the safety and efficacy of autologous bm - mnscs in the treatment of ms and awaits validation through larger , randomized studies .</s>

gemcitabine has been the standard drug for the treatment of pancreatic cancer as a first - line therapy since 1997.1 in the us , erlotinib was approved for the treatment of advanced pancreatic cancer in 2005 based on a phase iii trial that indicated statistically superior overall survival for gemcitabine plus erlotinib compared to gemcitabine alone.2 in the phase iii study , erlotinib plus gemcitabine was associated with significantly longer progression - free survival than gemcitabine alone ( median , 3.75 vs. 3.55 months ) . objective response rates were not significantly different between the arms ( 8.6% vs. 8.0% ) ; however , a higher incidence of some adverse events was observed with erlotinib plus gemcitabine.2 in japan , erlotinib was approved in 2011 . however , 8.5% of japanese patients subsequently developed interstitial pneumonia,3 which can be fatal , and the survival benefit , which was only 0.33 months improvement in overall survival , was small.2 thus , the overall risk benefit assessment of this drug remains controversial . in addition , erlotinib is relatively expensive , and thus the increase in health care costs is also an issue . in the review report4 of the pharmaceuticals and medical devices agency ( pmda ) , the reviewing authority for drug approval in japan , specialists discussed the risks and benefits of this drug , and their evaluation was controversial . given the risk of severe adverse effects , such as interstitial pneumonia , some specialists claimed that the survival benefit of this drug is too small . thus , decisions related to its use may often be personalized according to the patient s background , including factors such as economic or social conditions . however , no previous reports have investigated the decision - making processes used by patients and physicians . the case of a patient in good general condition who chose gemcitabine monotherapy after refusing combination therapy with gemcitabine plus erlotinib is presented . based on this case , factors in addition to the patient s physical condition that affected the choice of treatment were investigated . to the best of our knowledge , this is the first report to focus on the decision - making process of a patient while taking their social situation into account . a 72-year - old asian man with a past history of cerebral infarction , hypertension , diabetes mellitus , and hepatitis b visited a hospital for treatment of prostate cancer ( stage i ) . he was found to have jaundice on physical examination , and obstructive jaundice due to cancer of the head of the pancreas was diagnosed . after choledochojejunostomy and gastrojejunostomy , chemotherapy was planned . with respect to the patient s social situation , he was retired and lived alone with his wife . his hobby was drawing pictures , which he did every day along with his wife . written , informed consent to report his information was obtained in accordance with the requirements of the institutional review board in yamagata prefectural central hospital . it was explained to both the patient and his wife that he had unresectable and incurable cancer . several treatment options were suggested , including gemcitabine plus erlotinib , gemcitabine monotherapy , and s-1 ( tegafur , gimeracil , and oteracil potassium in a molar ratio of 1:0.4:1 ) . brochures detailing the adverse events and the efficacy of these chemotherapies were also provided , along with information concerning the cost of erlotinib and assistance available for high - cost medical care through the public health insurance system . this information had also been provided by caseworkers in the hospital , while information about the support system for high - cost medical care had been provided at the local city hall . gemcitabine plus erlotinib was recommended because this regimen showed evidence of longer overall survival of about 2 weeks compared to gemcitabine alone , even though the risk of interstitial pneumonia was higher in japanese patients . he did not have the symptoms of cerebral infarction , and his diabetes was controlled with oral medicine . he had no liver dysfunction and hbv - dna was negative ; entecavir was necessary for prevention , according to the guidelines . because his performance status was 1 , he was considered able to tolerate combination therapy using gemcitabine plus erlotinib . the patient and his wife chose gemcitabine monotherapy , primarily because the prolongation of survival with gemcitabine plus erlotinib was only expected to be about 2 weeks . he lived for drawing and did not wish to suffer any debilitating side effects ; therefore , he rejected the combination therapy . the only side effect was grade 1 fatigue , and his performance status was 1 during chemotherapy . three months after the start of the chemotherapy , he was found to have small nodules in both lungs . because these nodules were very small , it was uncertain whether they were lung metastases or inflammatory nodules . he remained at stable disease for 1 year , and none of the nodules increased in size . the patient received gemcitabine monotherapy for 14 months ; however , disease progression was seen . he then received chemotherapy with s-1 for 3 months , but new bone metastases developed . no change was observed in his prostate cancer during the chemotherapy . because of cancer - related pain from the bone metastases , he received radiation therapy to the vertebra . to the best of our knowledge , this is the first known report of the decision - making process of a patient eligible to receive targeted therapy . although this patient s performance status was good , he did not choose targeted therapy . physicians generally recommend chemotherapy regimens based on the evidence and the patient s general condition . although decision making about treatment in clinical practice is usually led by physicians , the number of cases in which patients take the initiative in decision making is increasing . patients decisions are often influenced by factors such as alopecia , costs , or survival benefit.5,6 even with the same type of cancer , staging , age , or sex , patients treatment choices vary based on the factors such as income and family structure . profiles of adverse events in targeted therapies differ from those of cytotoxic therapies . some targeted drugs have specific adverse effects ; for example , erlotinib and cetuximab are associated with skin toxicity , while trastuzumab is associated with heart failure . moreover , drug costs of targeted therapies are obviously higher than those of cytotoxic therapies ( table 1 ) . this case report revealed that the treatment strategy , that is , the decision either to use or not to use targeted therapy , must be personalized . the high cost of erlotinib therapy is also problematic.7 nevertheless , the cost of the drugs did not appear to affect this patient s choice of treatment . in general , japan s health insurance system is financed through social insurance , similar to germany or the netherlands . in this system , patients pay a fixed proportion , which is limited , of the total treatment cost . meanwhile , the health insurance system of the united kingdom is financed through taxes and thus requires no payment from the patient . on the other hand , the system in the united states is based on private insurance , and thus medical costs vary based on the insurance company and the terms of the contract . expensive drugs are available at a fixed cost in japan because of national health insurance and assistance for high - cost medical care that it provides . cost is not so important for patients aged 70 years or over , who pay reduced rates for medical care ; however , patients under 70 years of age may be faced with medical bills up to 80,000 yen ( 825 us dollars ) per month , which is the limit set for monthly expenditures by the social insurance system . if patients are unable to work due to disease , medical bills become a major problem . however , cost is not a factor discussed during the drug approval review process of the pmda . in the review report of erlotinib , as the patient s cost burden is fixed , it is easy for patients and physicians to use high cost molecular - targeted drugs in countries with a universal insurance system ; however , if these drugs are used , the national cost of medical care consequently increases . therefore , the use of expensive molecular - targeted drugs accelerates the increase in cost of medical care while only providing a small benefit to patients . in summary , the factors that affect use of molecular - targeted drugs should be personalized . to facilitate optimal decision making for patients , close communication based on the patient s background , including socioeconomic factors , comorbidities , and decision - making preferences a survey of molecular - targeted drug usage among physicians is currently being conducted , and a questionnaire survey of patients on the use of molecular - targeted drugs is planned for the future .

erlotinib is an approved drug for the treatment of advanced pancreatic cancer ; however , its survival benefit is small and its cost is high , and the decision to use the drug may often be personalized according to the patient s background . a 72-year - old asian man in good general condition chose gemcitabine monotherapy over combination therapy with gemcitabine plus erlotinib because the survival benefit of the latter was small . the cost of the drug did not appear to affect this decision . this report details the process of decision making with respect to whether a patient receives targeted therapy , and suggests that the use of molecular - targeted drugs must be personalized from many perspectives , including the patient s social situation .

<s>[INST]gemcitabine has been the standard drug for the treatment of pancreatic cancer as a first - line therapy since 1997.1 in the us , erlotinib was approved for the treatment of advanced pancreatic cancer in 2005 based on a phase iii trial that indicated statistically superior overall survival for gemcitabine plus erlotinib compared to gemcitabine alone.2 in the phase iii study , erlotinib plus gemcitabine was associated with significantly longer progression - free survival than gemcitabine alone ( median , 3.75 vs. 3.55 months ) . objective response rates were not significantly different between the arms ( 8.6% vs. 8.0% ) ; however , a higher incidence of some adverse events was observed with erlotinib plus gemcitabine.2 in japan , erlotinib was approved in 2011 . however , 8.5% of japanese patients subsequently developed interstitial pneumonia,3 which can be fatal , and the survival benefit , which was only 0.33 months improvement in overall survival , was small.2 thus , the overall risk benefit assessment of this drug remains controversial . in addition , erlotinib is relatively expensive , and thus the increase in health care costs is also an issue . in the review report4 of the pharmaceuticals and medical devices agency ( pmda ) , the reviewing authority for drug approval in japan , specialists discussed the risks and benefits of this drug , and their evaluation was controversial . given the risk of severe adverse effects , such as interstitial pneumonia , some specialists claimed that the survival benefit of this drug is too small . thus , decisions related to its use may often be personalized according to the patient s background , including factors such as economic or social conditions . however , no previous reports have investigated the decision - making processes used by patients and physicians . the case of a patient in good general condition who chose gemcitabine monotherapy after refusing combination therapy with gemcitabine plus erlotinib is presented . based on this case , factors in addition to the patient s physical condition that affected the choice of treatment were investigated . to the best of our knowledge , this is the first report to focus on the decision - making process of a patient while taking their social situation into account . a 72-year - old asian man with a past history of cerebral infarction , hypertension , diabetes mellitus , and hepatitis b visited a hospital for treatment of prostate cancer ( stage i ) . he was found to have jaundice on physical examination , and obstructive jaundice due to cancer of the head of the pancreas was diagnosed . after choledochojejunostomy and gastrojejunostomy , chemotherapy was planned . with respect to the patient s social situation , he was retired and lived alone with his wife . his hobby was drawing pictures , which he did every day along with his wife . written , informed consent to report his information was obtained in accordance with the requirements of the institutional review board in yamagata prefectural central hospital . it was explained to both the patient and his wife that he had unresectable and incurable cancer . several treatment options were suggested , including gemcitabine plus erlotinib , gemcitabine monotherapy , and s-1 ( tegafur , gimeracil , and oteracil potassium in a molar ratio of 1:0.4:1 ) . brochures detailing the adverse events and the efficacy of these chemotherapies were also provided , along with information concerning the cost of erlotinib and assistance available for high - cost medical care through the public health insurance system . this information had also been provided by caseworkers in the hospital , while information about the support system for high - cost medical care had been provided at the local city hall . gemcitabine plus erlotinib was recommended because this regimen showed evidence of longer overall survival of about 2 weeks compared to gemcitabine alone , even though the risk of interstitial pneumonia was higher in japanese patients . he did not have the symptoms of cerebral infarction , and his diabetes was controlled with oral medicine . he had no liver dysfunction and hbv - dna was negative ; entecavir was necessary for prevention , according to the guidelines . because his performance status was 1 , he was considered able to tolerate combination therapy using gemcitabine plus erlotinib . the patient and his wife chose gemcitabine monotherapy , primarily because the prolongation of survival with gemcitabine plus erlotinib was only expected to be about 2 weeks . he lived for drawing and did not wish to suffer any debilitating side effects ; therefore , he rejected the combination therapy . the only side effect was grade 1 fatigue , and his performance status was 1 during chemotherapy . three months after the start of the chemotherapy , he was found to have small nodules in both lungs . because these nodules were very small , it was uncertain whether they were lung metastases or inflammatory nodules . he remained at stable disease for 1 year , and none of the nodules increased in size . the patient received gemcitabine monotherapy for 14 months ; however , disease progression was seen . he then received chemotherapy with s-1 for 3 months , but new bone metastases developed . no change was observed in his prostate cancer during the chemotherapy . because of cancer - related pain from the bone metastases , he received radiation therapy to the vertebra . to the best of our knowledge , this is the first known report of the decision - making process of a patient eligible to receive targeted therapy . although this patient s performance status was good , he did not choose targeted therapy . physicians generally recommend chemotherapy regimens based on the evidence and the patient s general condition . although decision making about treatment in clinical practice is usually led by physicians , the number of cases in which patients take the initiative in decision making is increasing . patients decisions are often influenced by factors such as alopecia , costs , or survival benefit.5,6 even with the same type of cancer , staging , age , or sex , patients treatment choices vary based on the factors such as income and family structure . profiles of adverse events in targeted therapies differ from those of cytotoxic therapies . some targeted drugs have specific adverse effects ; for example , erlotinib and cetuximab are associated with skin toxicity , while trastuzumab is associated with heart failure . moreover , drug costs of targeted therapies are obviously higher than those of cytotoxic therapies ( table 1 ) . this case report revealed that the treatment strategy , that is , the decision either to use or not to use targeted therapy , must be personalized . the high cost of erlotinib therapy is also problematic.7 nevertheless , the cost of the drugs did not appear to affect this patient s choice of treatment . in general , japan s health insurance system is financed through social insurance , similar to germany or the netherlands . in this system , patients pay a fixed proportion , which is limited , of the total treatment cost . meanwhile , the health insurance system of the united kingdom is financed through taxes and thus requires no payment from the patient . on the other hand , the system in the united states is based on private insurance , and thus medical costs vary based on the insurance company and the terms of the contract . expensive drugs are available at a fixed cost in japan because of national health insurance and assistance for high - cost medical care that it provides . cost is not so important for patients aged 70 years or over , who pay reduced rates for medical care ; however , patients under 70 years of age may be faced with medical bills up to 80,000 yen ( 825 us dollars ) per month , which is the limit set for monthly expenditures by the social insurance system . if patients are unable to work due to disease , medical bills become a major problem . however , cost is not a factor discussed during the drug approval review process of the pmda . in the review report of erlotinib , as the patient s cost burden is fixed , it is easy for patients and physicians to use high cost molecular - targeted drugs in countries with a universal insurance system ; however , if these drugs are used , the national cost of medical care consequently increases . therefore , the use of expensive molecular - targeted drugs accelerates the increase in cost of medical care while only providing a small benefit to patients . in summary , the factors that affect use of molecular - targeted drugs should be personalized . to facilitate optimal decision making for patients , close communication based on the patient s background , including socioeconomic factors , comorbidities , and decision - making preferences a survey of molecular - targeted drug usage among physicians is currently being conducted , and a questionnaire survey of patients on the use of molecular - targeted drugs is planned for the future .[/INST]erlotinib is an approved drug for the treatment of advanced pancreatic cancer ; however , its survival benefit is small and its cost is high , and the decision to use the drug may often be personalized according to the patient s background . a 72-year - old asian man in good general condition chose gemcitabine monotherapy over combination therapy with gemcitabine plus erlotinib because the survival benefit of the latter was small . the cost of the drug did not appear to affect this decision . this report details the process of decision making with respect to whether a patient receives targeted therapy , and suggests that the use of molecular - targeted drugs must be personalized from many perspectives , including the patient s social situation .</s>

phosphorus and nitrogen are the most critical bioelements that limit haricot bean production in ethiopia [ 13 ] . phosphorus ( p ) is one of the most indispensable macronutrients next to nitrogen for the growth and development of plants [ 4 , 5 ] . a greater part of soil phosphorus , approximately 9599% , is present in insoluble form complexed with cations like iron , aluminum , and calcium that can not be utilized by the plants . the use of natural phosphate - bearing materials such as rock phosphate ( rp ) as fertilizer for p - deficient soils has received due attention in recent years since substantial deposits of cheaper and low grade rp are locally available in many countries of the world . however , its solubilization rarely occurs in nonacidic soils with a ph greater than 5.5 to 6.0 . conventionally , rp is chemically processed by reacting with sulphuric acid or phosphoric acid to produce partially acidulated rp . a much cheaper and convenient alternative is reclamation of exhausted soil through use of p - solubilizing microorganisms that have opened the possibility for solubilization of rp in soils . thus , soil microorganisms play a critical role in natural phosphorus cycle and recently microbial - based approaches have been proposed to improve the agronomic value of rp . this could be another approach for higher cost of manufacturing phosphate fertilizer in industry and also reduces environment pollution posed by a traditional chemical process . according to ouahmane et al . , utilization of microbial mediated rp has several advantages over conventional chemical fertilizers for agricultural purposes . these advantages are as follows : ( 1 ) microbial products are considered safer than many of the chemical fertilizers now in use ; ( 2 ) neither toxic substances nor microbes themselves will be accumulated in the food chain ; and ( 3 ) self - replication of microbes circumvents the need for repeated application . thus , inoculation with phosphate solubilizing microorganisms along with rock phosphate could be another strategy to improve the physicochemical and biological properties of soil and help in improving crop production . the beneficial plant - microbes interactions in the rhizosphere are determinants of plant health and soil fertility . among the rhizosphere microbes , the important genera of p - solubilizing bacteria include rhizobium , bacillus , and pseudomonas [ 14 , 15 ] . they are widely used as producers of organic acid . aspergillus niger and some penicillium species have been tested for solubilization of rp and other biotechnological importance such as biocontrol , biodegradation , and phosphate mobilization [ 10 , 17 , 18 ] . in ethiopia , effects of plant growth promoting rhizobacteria ( pgpr ) on growth and yield of tef were evaluated by woyessa and assefa . furthermore , the effect of phosphate solubilizing fungus on growth and yield of tef was studied by hailemariam . however , information on the diversity of phosphate solubilizing fungi inhabiting various rhizospheres in this region is limited . the present study was therefore designed to isolate and characterize the phosphate solubilizing fungi isolated from various rhizospheric soils . the study was carried out in jimma university , jimma town , located at 353 km to the southwest of addis ababa . the total area of jimma zone is 18415 km and located between latitudes 718n and 856n and longitudes 3552e and 3737e . manna district is one of the woredas in jimma zone , which is located at 368 km southwest of addis ababa . the major soil types of the area are nitosol and combsols and the area receives an average annual rainfall of 1,467 mm per year . a total of one hundred fifty rhizosphere soil samples were collected from 30 plant samples of cabbage ( brassica integrifolia ) , faba bean ( vicia faba l. ) , haricot bean ( phaseolus vulgaris l. ) , sugar cane ( saccharum officinarum l. ) , and tomato ( lycopersicon esculentum mill . ) . the rhizosphere soil samples were collected from selected kebeles of jimma town ( becho bore , ginjo guduru , and awetu mendera ) and mana district ( sombo mana , hunda toli , kemise waraba , buture , and gudeta bula ) farmlands of different sites . the kebeles were purposively selected based on the preliminary survey made to identify potential growing areas for the crop . the samples were randomly collected from agricultural fields within 1 to 2 km interval between the same samples . roots with adhering soils of healthy plants were collected and transferred to sterile plastic bags and transported to the postgraduate and research laboratory , department of biology , jimma university , and stored at 4c for further analysis . collected rhizosphere soil samples were used for the isolation of phosphate solubilizing fungi on pikovskaya 's ( pkv ) agar medium , containing the following ( g / l ) : 0.5 g ( nh4)2so4 , 0.1 g mgso47h2o , 0.02 g nacl , 0.02 g kcl , 0.003 g feso47h2o , 0.003 g mnso4h2o , 5 g ca3 ( po4)2 , 10.0 g glucose , 0.5 g yeast extract , 15.0 g agar , and 1000 ml distilled water . the medium was autoclaved at 121c for 15 minutes ; about 20 ml of the sterilized molten agar medium was poured into each petri dish and supplemented with 25 g / ml chloramphenicol to inhibit bacterial growth and allowed to solidify before inoculation . for each sample , the loosely adherent soils were removed by agitating the roots strongly ; the root samples with their adhering soil were cut into pieces ( 1 - 2 cm ) by sterile scissors and used for isolation . ten grams of each plant root fragment was aseptically weighed and transferred to 250 ml erlenmeyer flask containing 90 ml of 0.85% saline solution . the suspension was shaken on 110 rpm for 25 minutes on a rotary shaker and then allowed to settle for 10 min . aliquots of 1 ml of the supernatant from the sample was transferred to 9 ml of sterile normal saline solution dispensed into test tubes and serially diluted to 10 , 10 , 10 , 10 , 10 , and 10 . from each serially diluted soil suspension , 0.1 ml aliquots were transferred and spread plated on pikovskaya 's agar plates and incubated at 25c28c for 27 days . after incubation , fungal colonies showing clear zones around the colonies were further purified by transferring into pikovskaya 's agar medium . the pure cultures were preserved on potato dextrose agar ( pda ) slant at 4c for further investigation . pda was used to accelerate the growth rate and the production of enough conidia as reported by diba et al . . the characteristics of fresh cultures were compared with mycological identification keys and taxonomic description to identify the isolated fungi to the genus level . identification was based on colony characteristics and microscopic features , among the colonial characteristics such as surface appearance , texture , and colour of the colonies both from upper and lower side . in addition , conidia , conidiophores , arrangement of spores , and vegetative structures were determined with microscopy . the identified fungi were maintained on potato dextrose agar ( pda ) slant at ( + 4c ) for further investigation . slide culture was prepared in order to identify spores and mycelia of pure fungal isolates . accordingly , the morphology of spores and mycelia of fungal isolates was examined and identified by lacto phenol cotton blue staining using microscope and identified after growing them on slide according to stevens . the fungal isolates obtained from rhizospheric soils were evaluated on agar plates and liquid culture media containing sparingly soluble phosphates for their activity in mobilizing phosphate from insoluble sources ( tricalcium and rock phosphates ) . all the isolates were screened under in vitro condition for their phosphate solubilization activity following the method described by iman on pikovskaya 's agar medium . a spot inoculation of fungal isolates was made onto the plates in triplicate under aseptic condition and incubated at 2528c for 7 days . comparative solubilization index measurement was carried out on day seven of incubation by measuring clear zone and colony diameters in centimeter . phosphate solubilization index was determined by using the following formula : ratio of the total diameter ( colony + halo zone ) and the colony diameter . ( 1)solubilization indexsi = colony diameter+halo zone diametercolony diameter . based on solubilization index on solid medium , out of all fungal isolates , nine isolates having code numbers jufbf58 , jutof166 , jucaf37 , jutof167 , juhbf94 , jufbf59 , jufbf60 , juhbf95 , and jucaf38 were selected and further characterized for their efficiency on pkv broth using tcp and rp as inorganic phosphate sources . accordingly , quantitative estimation of phosphate solubilization activities was carried out in pvk medium amended with tricalcium / rock phosphate for duration of 20 days . rock phosphate ( rp ) was kindly obtained from western wolega zone , gimbi woreda , and bikilal kebele specifically from the area of tulu guda gute . sporulated pure fungal cultures prepared on pvk agar medium were selected for the preparation of spore suspensions from each fungal isolate following the standard procedures of . a total volume of 20 ml sterile water was spread in aliquots on a culture plate from 10-day - old culture and the fungal colony surface was lightly scraped using a sterile glass rod . the cultures were filtered through whatman number 42 filter paper into a sterile glass bottle . spore count was done by using a haemocytometer and the suspension of the isolates was adjusted to approximately 10 spores ml using sterilized distilled water . quantitative estimation of phosphate solubilization was carried out using erlenmeyer flasks containing 100 ml pvk liquid medium supplemented with 0.5% tricalcium phosphate ( tcp ) in amounts equivalent to p 997 g / ml . for the comparative study of the ability of rp mobilization , a second medium was prepared replacing 0.5% tricalcium phosphate ( tcp ) of pvk medium with 0.25% ( w / v ) rock phosphate in 100 ml equivalent to p 500 g / ml with other conditions the same as for tcp solubilization . after sterilization , the medium in each flask was inoculated with the spore suspension of 10% ( v / v ) of a particular fungal isolate containing 10 spores ml . ten milliliters of sterile distilled water inoculated sample was treated as the control . incubation was done at 2528c in an incubator shaker ( sanco , india ) at 150 rpm for 20 days . the amount of pi released and ph in the broth flasks were estimated at different times ( day 5 , day 10 , day 15 , and day 20 ) in the presence of tcp and rp . an aliquot of 5 ml culture supernatant was aseptically withdrawn periodically from each culture flask at 5-day interval . the samples were spun using the centrifuge ( sigma , germany ) at 5,000 rpm for 25 min to remove any suspended solids and mycelial fragments and supernatant of each culture was analyzed for ph and phosphate concentration . the cultures were filtered through whatman number 1 filter paper and the filtrates were used for estimation of pi released . the amount of p - solubilized in culture supernatant was estimated using chlorostannous acid reduced molybdophosphoric blue colour method of jackson and expressed as equivalent phosphate ( gml ) . in this study , a total of 359 fungal isolates were obtained from 150 rhizosphere soil samples from different plants such as cabbage , faba bean , haricot bean , sugar cane , and tomato collected from two districts of jimma zone , jimma town and mana woreda farmlands ( table 1 ) . out of the isolated fungi , a total of 167 phosphate solubilizing fungal cultures having potential of phosphate solubilization were isolated ( table 1 ) . of the isolates , the highest numbers of psf ( 28.14% ) were recovered from tomato and the least ( 13.17% ) was obtained from faba bean ( table 1 ) . the fungal isolates were characterized and identified as aspergillus , penicillium , and fusarium spp . out of 167 psf isolated from the rhizosphere soil samples in the present study , 93 ( 55.69% ) species belonged to the genus aspergillus alone followed by penicillium spp . 39 ( 23.35% ) ( table 3 ) . of all identified , fusarium spp . were the least dominant 16 ( 9.58% ) and the rest 19 ( 11.38% ) fungal colonies were unidentified ( table 3 ) . were detected only in the soil samples from rhizosphere of tomato plant , while other identified isolates were common in cabbage , faba bean , haricot bean , sugar cane , and tomato plant root rhizosphere ( table 3 ) . the solubilization index ( si ) of the isolated phosphate solubilizing fungi ranged from 1.10 to 3.05 at seven days of incubation at 2528c ( table 4 ) . results on ( table 4 ) revealed that , among the screened 167 psf isolates , jucaf38 ( aspergillus sp . ) was the most efficient phosphate solubilizer on pv plates with si = 3.05 followed by juhbf95 ( aspergillus sp . ) with si = 2.87 and jufbf59 ( penicillium sp . ) with si = 2.39 , whereas the smallest si of 1.10 was detected from the isolate juhbpsf61 . the amount of phosphates solubilized by all fungal isolates was showed to be significantly ( p < 0.05 ) higher over uninoculated control ( figure 4 ) . the minimum p - solubilized from tcp containing broth was on day 5 , afterwards the solubilized p increased up to day 15 of incubation . accordingly , the mobilized phosphate values in the medium ranged between ( 92.09778.77 g ml ) with variations ( p < 0.05 ) among different fungal isolates during 20 days of incubation time . the highest amount of solubilized phosphate ( 778.77 g ml ) was recorded from juhbf95 ( aspergillus sp . ) inoculated culture filtrates followed by ( aspergillus sp . ) jufbf60 ( 615.40 g ml ) , ( aspergillus sp . ) jucaf37 ( 553.06 g ml ) , and ( penicillium sp . ) jufbf59 ( 472.20 g ml ) . the minimum concentration of soluble - p ( 225.50 g ml ) was recorded in the cultures of ( aspergillus sp . ) jufbf58 during 15 days of incubation time ( figure 4 ) . in further incubation ( at day 20 ) , decline in the mobilized phosphate was recorded in all cases of the test fungal isolates that reached up to 172.36 g ml ( minimum value ) in case of jufbf58 and 511.22 g ml ( maximum value ) in case of the isolate juhbf95 inoculated culture filtrates ( figure 4 ) . all the nine isolates showed a decrease in the ph significantly ( p < 0.05 ) over control in the liquid culture supernatants during the 20 days of incubation ( figure 5 ) . the ph values decreased to variable levels in the tcp medium during the initial days depending on the culture and later became increased or remained at the same level ( figure 5 ) . the highest drop in ph was recorded in the isolates juhbf95 and jufbf60 from initial ph of 7.0 to 3.08 and 3.31 , respectively , after 15 days of incubation time . the ph values at 5 , 10 , 15 , and 20 days of incubation in pvk liquid medium containing rp were summarized in ( figure 6 ) . a highly significant ( p < 0.05 ) variation of solubilized p concentrations was recorded among the fungal isolates in 20 days of incubation . the minimum p - solubilized value from rp culture medium during 20 days of rp solubilizing experiments was obtained on day 5 ( figure 6 ) . the results also showed that when the medium was supplemented with rock phosphate , the content of soluble phosphate released by the isolates in culture medium increased up to 10th day in all nine fungal isolates ( figure 6 ) . the highest mobilized phosphate value ( 363 g / ml ) was recorded from isolate juhbf95 ( aspergillus sp . ) whereas the minimum concentration of soluble - p ( 96.20 g / ml ) was observed in the cultures of jutof167 ( aspergillus sp . ) on day 10 of incubation ( figure 6 ) . mobilized phosphate values began to decline in all inoculated culture filtrates that reached up to 58.17 g l ( minimum value ) in juhbf94 inoculated culture and 178.12 g / ml ( maximum value ) in case of juhbf95 on day 20 of incubation time ( figure 6 ) . there were significant ( p < 0.05 ) drops of ph in the liquid culture medium amended with rp for all the nine test fungal isolates compared to the control during 20 days of incubation ( figure 7 ) . the maximum ph decrease was recorded from the 5th and 10th days of incubations by most fungal isolates but was later increased or nearly constant in all culture filtrates ( figure 7 ) . among the nine isolates the largest reduction of ph in culture medium was from an initial value of 7.0 to ph values 4.00 , 4.05 , 4.13 , and 4.23 for the isolates juhbf60 , jucaf37 , juhbf95 , and jufbf59 , respectively , after 10 days of incubation ( figure 7 ) . however , no decrement was found in ph medium over the last 1520 days of incubation in all test culture filtrates . from nine efficient phosphate solubilizing fungal isolates , two isolates , namely , juhbf95 ( aspergillus spp . ) and jufbf59 ( penicillium spp . ) resulted in the highest mean phosphate solubilization and mean ph drop from pkv broth containing tricalcium phosphate and rock phosphate , respectively . the present study revealed that the rhizosphere of different plants collected from jimma town and mana district farmlands supports a diverse group of p - solubilizing fungi . the most dominant genera belong to aspergillus and penicillium spp . similarly , chuang et al . , oniya et al . , and verma and ekka also isolated p - solubilizing fungi such as aspergillus niger and penicillium spp . from various rhizospheric soil samples . in the case of tomato plant besides , effective phosphate solubilizing fungi were isolated with higher proportion from tomato plants . in another study , the effectiveness of p - solubilizing fungi in the present study could be probably because of sufficient root exudates since phosphate solubilizing microorganisms are mainly dependent on carbon rich sources from plant root for active production of organic acids that are utilized for solubilizing soil - bound phosphate . in the present study , aspergillus spp . ( 55.69% ) were the most frequently occurring p - solubilizing fungi of the three identified genera . the current result is in agreement with the earlier findings of several workers [ 17 , 31 , 35 ] , who observed predominant occurrence of p - solubilizing fungi belonging to genus aspergillus followed by penicillium spp . in the rhizosphere of different crop plants . in this study , a total of 19 psf isolates were reported as unidentified due to overlapping morphological and colonial features . although morphological and colonial properties are commonly used for identification , molecular , biochemical , and physiological methods are important for the correct identification of fungal species . the variable potential of phosphate solubilization based on si on agar plate in the present study may be because of the varying type , amount , and diffusion rates of diverse organic acids secreted by fungal isolates as previously reported by yadav et al . . iman reported that the solubilization indices ( si ) of the test phosphate solubilizing fungal strains ( penicillium italicum and aspergillus niger ) were 2.42 and 3.15 , respectively . conversely , mahamuni et al . reported si for different fungal strains isolated from sugarcane and sugar beet which ranged from 1.13 to 1.59 . alam et al . also reported si that ranged from 1.53 to 1.80 for the fungal cultures isolated from maize rhizosphere . fungal isolates that have shown higher si on solid agar medium did not show similar trend in liquid broth medium , which is in agreement with the findings of alam et al . who reported that some isolates with little clear zone on solid agar medium exhibited higher efficiency for dissolving insoluble phosphates in liquid medium . some fungal isolates showed larger clear zones on agar but low phosphate solubilization in liquid medium . this shows that production of higher si on solid medium does not necessarily show solubilization efficiency in liquid medium . thus , the plate technique is insufficient to screen the best p solubilizers and to detect all phosphate solubilizers as commented by nautiyal . in the present study , periodical estimates of p in broth media revealed the potential of the isolates in releasing p from insoluble phosphate sources . the fungal isolates solubilized the insoluble phosphate sources such as tcp and rp with gradual increase in the middle of incubation period . , who have also demonstrated a gradual increase in mobilized p by fungal isolate f1 in liquid cultures . decrease in phosphate solubilization was observed at the end of incubation time which is in agreement with the findings of mahamuni et al . . kim et al . reported that this could be attributed to the availability of soluble phosphate , which had an inhibitory effect on further tcp or rp solubilization , or the depletion of carbon source that limited both the production of organic acids and microbial activity . another possibility for reduction of mobilized p could be due to the formation of an organo - p compound induced by released organic metabolites , which in turn reduces the amount of available p . muleta also stated that mobilized p is utilized by fungal cells for their growth and development during this period . the test fungal isolates solubilized maximum amount of phosphate from tcp on day 15 and from rp on day 10 but gradually decreased afterwards . these results are in conformity with the findings of pandey et al . , who observed maximum solubilization of phosphate occurring at day 15 of incubation for tcp under controlled conditions . other studies on rock phosphate solubilization indicated that the maximum soluble phosphorus release was on tenth day of incubation by the psf isolates in liquid culture medium while vyas et al . reported maximum solubilization of rp from nine to twelve days after incubation . the isolates juhbf95 and jufbf60 showed the highest mobilized p values ( 778.77 g ml and 615.40 g ml , resp . ) when the medium was supplemented with tricalcium phosphate which could be linked to its inherent self - solubility . these fungal isolates were also able to release considerable amount of p when the medium was supplemented with rock phosphate . this indicates the potential of these fungal isolates in solubilization of insoluble phosphates which gives new avenue for development of fungal biofertilizers after carrying out the necessary qualifying tests . in line with these findings , chakraborty et al . reported that aspergillus niger ( isolate rs / p-14 ) solubilized maximum amount of tricalcium phosphate ( 799 g ml ) and from rock phosphate ( 385 g ml ) in pvk broth at 15 days of incubation . similarly , pandey et al . recorded mobilized phosphate between 320 g ml ( p. oxalicum ) and 500 g ml ( p. citrinum and p. purpurogenum ) from tcp at 15 days of incubation . this finding is similar to the earlier studies of premono et al . and mahamuni et al . who recorded lesser p solubilization in rp than tcp . these authors remarked that the poor solubilization of rock phosphate may be attributed to the complex mineral composition and particle size in the medium as remarked by pradhan and sukla and mahamuni et al . in addition to the presence of strong apatite bond in the rp , which reduced phosphate solubilization . acidification by organic acid has been reported to be the main solubilization mechanism of inorganic p by microorganisms . decrease in ph values was recorded in all fungal isolates differently in the culture media . this might be due to production of diverse organic acids from the available nutrient ( glucose ) as commented by several investigators [ 18 , 37 ] . the ph drop in cultures has been repeatedly reported by a number of research findings [ 18 , 37 , 40 , 47 ] . the ph values decreased to variable levels depending on the culture type and later became nearly constant or increased with reduction in mobilized phosphate . this observation might be attributed to low glucose concentration in pkv broth which is essential for production of organic acids . in this respect , the present findings are in agreement with nenwani et al . who reported increase in ph value and decrease in solubilized phosphate at the end of incubation time . the results of this study have shown that the rhizosphere soils of cabbage , haricot bean , faba bean , sugar cane , and tomato of different sites of jimma town and mana woreda farmlands support a diverse group of naturally occurring potential phosphate solubilizing fungi ( psf ) . the efficiency of phosphate solubilization is significantly higher in pikovskaya medium containing tcp than in the medium containing rp .

phosphorus ( p ) is one of the major bioelements limiting agricultural production . phosphate solubilizing fungi play a noteworthy role in increasing the bioavailability of soil phosphates for plants . the present study was aimed at isolating and characterizing phosphate solubilizing fungi from different rhizospheres using both solid and liquid pikovskaya ( pvk ) medium . a total of 359 fungal isolates were obtained from 150 rhizosphere soil samples of haricot bean , faba bean , cabbage , tomato , and sugarcane . among the isolates , 167 ( 46.52% ) solubilized inorganic phosphate . the isolated phosphate solubilizing fungi belonged to genera of aspergillus ( 55.69% ) , penicillium spp . ( 23.35% ) , and fusarium ( 9.58% ) . solubilization index ( si ) ranged from 1.10 to 3.05 . isolates designated as juhbf95 ( aspergillus sp . ) and jufbf59 ( penicillium sp . ) solubilized maximum amount of p 728.77 gml1 and 514.44 g ml1 , respectively , from tcp ( tricalcium phosphate ) after 15 days of incubation . the highest ( 363 g ml1 ) soluble - p was released from rp with the inoculation of juhbf95 in the pvk broth after 10 days of incubation . the present study indicated the presence of diverse plant associated p - solubilizing fungi that may serve as potential biofertilizers .

<s>[INST]phosphorus and nitrogen are the most critical bioelements that limit haricot bean production in ethiopia [ 13 ] . phosphorus ( p ) is one of the most indispensable macronutrients next to nitrogen for the growth and development of plants [ 4 , 5 ] . a greater part of soil phosphorus , approximately 9599% , is present in insoluble form complexed with cations like iron , aluminum , and calcium that can not be utilized by the plants . the use of natural phosphate - bearing materials such as rock phosphate ( rp ) as fertilizer for p - deficient soils has received due attention in recent years since substantial deposits of cheaper and low grade rp are locally available in many countries of the world . however , its solubilization rarely occurs in nonacidic soils with a ph greater than 5.5 to 6.0 . conventionally , rp is chemically processed by reacting with sulphuric acid or phosphoric acid to produce partially acidulated rp . a much cheaper and convenient alternative is reclamation of exhausted soil through use of p - solubilizing microorganisms that have opened the possibility for solubilization of rp in soils . thus , soil microorganisms play a critical role in natural phosphorus cycle and recently microbial - based approaches have been proposed to improve the agronomic value of rp . this could be another approach for higher cost of manufacturing phosphate fertilizer in industry and also reduces environment pollution posed by a traditional chemical process . according to ouahmane et al . , utilization of microbial mediated rp has several advantages over conventional chemical fertilizers for agricultural purposes . these advantages are as follows : ( 1 ) microbial products are considered safer than many of the chemical fertilizers now in use ; ( 2 ) neither toxic substances nor microbes themselves will be accumulated in the food chain ; and ( 3 ) self - replication of microbes circumvents the need for repeated application . thus , inoculation with phosphate solubilizing microorganisms along with rock phosphate could be another strategy to improve the physicochemical and biological properties of soil and help in improving crop production . the beneficial plant - microbes interactions in the rhizosphere are determinants of plant health and soil fertility . among the rhizosphere microbes , the important genera of p - solubilizing bacteria include rhizobium , bacillus , and pseudomonas [ 14 , 15 ] . they are widely used as producers of organic acid . aspergillus niger and some penicillium species have been tested for solubilization of rp and other biotechnological importance such as biocontrol , biodegradation , and phosphate mobilization [ 10 , 17 , 18 ] . in ethiopia , effects of plant growth promoting rhizobacteria ( pgpr ) on growth and yield of tef were evaluated by woyessa and assefa . furthermore , the effect of phosphate solubilizing fungus on growth and yield of tef was studied by hailemariam . however , information on the diversity of phosphate solubilizing fungi inhabiting various rhizospheres in this region is limited . the present study was therefore designed to isolate and characterize the phosphate solubilizing fungi isolated from various rhizospheric soils . the study was carried out in jimma university , jimma town , located at 353 km to the southwest of addis ababa . the total area of jimma zone is 18415 km and located between latitudes 718n and 856n and longitudes 3552e and 3737e . manna district is one of the woredas in jimma zone , which is located at 368 km southwest of addis ababa . the major soil types of the area are nitosol and combsols and the area receives an average annual rainfall of 1,467 mm per year . a total of one hundred fifty rhizosphere soil samples were collected from 30 plant samples of cabbage ( brassica integrifolia ) , faba bean ( vicia faba l. ) , haricot bean ( phaseolus vulgaris l. ) , sugar cane ( saccharum officinarum l. ) , and tomato ( lycopersicon esculentum mill . ) . the rhizosphere soil samples were collected from selected kebeles of jimma town ( becho bore , ginjo guduru , and awetu mendera ) and mana district ( sombo mana , hunda toli , kemise waraba , buture , and gudeta bula ) farmlands of different sites . the kebeles were purposively selected based on the preliminary survey made to identify potential growing areas for the crop . the samples were randomly collected from agricultural fields within 1 to 2 km interval between the same samples . roots with adhering soils of healthy plants were collected and transferred to sterile plastic bags and transported to the postgraduate and research laboratory , department of biology , jimma university , and stored at 4c for further analysis . collected rhizosphere soil samples were used for the isolation of phosphate solubilizing fungi on pikovskaya 's ( pkv ) agar medium , containing the following ( g / l ) : 0.5 g ( nh4)2so4 , 0.1 g mgso47h2o , 0.02 g nacl , 0.02 g kcl , 0.003 g feso47h2o , 0.003 g mnso4h2o , 5 g ca3 ( po4)2 , 10.0 g glucose , 0.5 g yeast extract , 15.0 g agar , and 1000 ml distilled water . the medium was autoclaved at 121c for 15 minutes ; about 20 ml of the sterilized molten agar medium was poured into each petri dish and supplemented with 25 g / ml chloramphenicol to inhibit bacterial growth and allowed to solidify before inoculation . for each sample , the loosely adherent soils were removed by agitating the roots strongly ; the root samples with their adhering soil were cut into pieces ( 1 - 2 cm ) by sterile scissors and used for isolation . ten grams of each plant root fragment was aseptically weighed and transferred to 250 ml erlenmeyer flask containing 90 ml of 0.85% saline solution . the suspension was shaken on 110 rpm for 25 minutes on a rotary shaker and then allowed to settle for 10 min . aliquots of 1 ml of the supernatant from the sample was transferred to 9 ml of sterile normal saline solution dispensed into test tubes and serially diluted to 10 , 10 , 10 , 10 , 10 , and 10 . from each serially diluted soil suspension , 0.1 ml aliquots were transferred and spread plated on pikovskaya 's agar plates and incubated at 25c28c for 27 days . after incubation , fungal colonies showing clear zones around the colonies were further purified by transferring into pikovskaya 's agar medium . the pure cultures were preserved on potato dextrose agar ( pda ) slant at 4c for further investigation . pda was used to accelerate the growth rate and the production of enough conidia as reported by diba et al . . the characteristics of fresh cultures were compared with mycological identification keys and taxonomic description to identify the isolated fungi to the genus level . identification was based on colony characteristics and microscopic features , among the colonial characteristics such as surface appearance , texture , and colour of the colonies both from upper and lower side . in addition , conidia , conidiophores , arrangement of spores , and vegetative structures were determined with microscopy . the identified fungi were maintained on potato dextrose agar ( pda ) slant at ( + 4c ) for further investigation . slide culture was prepared in order to identify spores and mycelia of pure fungal isolates . accordingly , the morphology of spores and mycelia of fungal isolates was examined and identified by lacto phenol cotton blue staining using microscope and identified after growing them on slide according to stevens . the fungal isolates obtained from rhizospheric soils were evaluated on agar plates and liquid culture media containing sparingly soluble phosphates for their activity in mobilizing phosphate from insoluble sources ( tricalcium and rock phosphates ) . all the isolates were screened under in vitro condition for their phosphate solubilization activity following the method described by iman on pikovskaya 's agar medium . a spot inoculation of fungal isolates was made onto the plates in triplicate under aseptic condition and incubated at 2528c for 7 days . comparative solubilization index measurement was carried out on day seven of incubation by measuring clear zone and colony diameters in centimeter . phosphate solubilization index was determined by using the following formula : ratio of the total diameter ( colony + halo zone ) and the colony diameter . ( 1)solubilization indexsi = colony diameter+halo zone diametercolony diameter . based on solubilization index on solid medium , out of all fungal isolates , nine isolates having code numbers jufbf58 , jutof166 , jucaf37 , jutof167 , juhbf94 , jufbf59 , jufbf60 , juhbf95 , and jucaf38 were selected and further characterized for their efficiency on pkv broth using tcp and rp as inorganic phosphate sources . accordingly , quantitative estimation of phosphate solubilization activities was carried out in pvk medium amended with tricalcium / rock phosphate for duration of 20 days . rock phosphate ( rp ) was kindly obtained from western wolega zone , gimbi woreda , and bikilal kebele specifically from the area of tulu guda gute . sporulated pure fungal cultures prepared on pvk agar medium were selected for the preparation of spore suspensions from each fungal isolate following the standard procedures of . a total volume of 20 ml sterile water was spread in aliquots on a culture plate from 10-day - old culture and the fungal colony surface was lightly scraped using a sterile glass rod . the cultures were filtered through whatman number 42 filter paper into a sterile glass bottle . spore count was done by using a haemocytometer and the suspension of the isolates was adjusted to approximately 10 spores ml using sterilized distilled water . quantitative estimation of phosphate solubilization was carried out using erlenmeyer flasks containing 100 ml pvk liquid medium supplemented with 0.5% tricalcium phosphate ( tcp ) in amounts equivalent to p 997 g / ml . for the comparative study of the ability of rp mobilization , a second medium was prepared replacing 0.5% tricalcium phosphate ( tcp ) of pvk medium with 0.25% ( w / v ) rock phosphate in 100 ml equivalent to p 500 g / ml with other conditions the same as for tcp solubilization . after sterilization , the medium in each flask was inoculated with the spore suspension of 10% ( v / v ) of a particular fungal isolate containing 10 spores ml . ten milliliters of sterile distilled water inoculated sample was treated as the control . incubation was done at 2528c in an incubator shaker ( sanco , india ) at 150 rpm for 20 days . the amount of pi released and ph in the broth flasks were estimated at different times ( day 5 , day 10 , day 15 , and day 20 ) in the presence of tcp and rp . an aliquot of 5 ml culture supernatant was aseptically withdrawn periodically from each culture flask at 5-day interval . the samples were spun using the centrifuge ( sigma , germany ) at 5,000 rpm for 25 min to remove any suspended solids and mycelial fragments and supernatant of each culture was analyzed for ph and phosphate concentration . the cultures were filtered through whatman number 1 filter paper and the filtrates were used for estimation of pi released . the amount of p - solubilized in culture supernatant was estimated using chlorostannous acid reduced molybdophosphoric blue colour method of jackson and expressed as equivalent phosphate ( gml ) . in this study , a total of 359 fungal isolates were obtained from 150 rhizosphere soil samples from different plants such as cabbage , faba bean , haricot bean , sugar cane , and tomato collected from two districts of jimma zone , jimma town and mana woreda farmlands ( table 1 ) . out of the isolated fungi , a total of 167 phosphate solubilizing fungal cultures having potential of phosphate solubilization were isolated ( table 1 ) . of the isolates , the highest numbers of psf ( 28.14% ) were recovered from tomato and the least ( 13.17% ) was obtained from faba bean ( table 1 ) . the fungal isolates were characterized and identified as aspergillus , penicillium , and fusarium spp . out of 167 psf isolated from the rhizosphere soil samples in the present study , 93 ( 55.69% ) species belonged to the genus aspergillus alone followed by penicillium spp . 39 ( 23.35% ) ( table 3 ) . of all identified , fusarium spp . were the least dominant 16 ( 9.58% ) and the rest 19 ( 11.38% ) fungal colonies were unidentified ( table 3 ) . were detected only in the soil samples from rhizosphere of tomato plant , while other identified isolates were common in cabbage , faba bean , haricot bean , sugar cane , and tomato plant root rhizosphere ( table 3 ) . the solubilization index ( si ) of the isolated phosphate solubilizing fungi ranged from 1.10 to 3.05 at seven days of incubation at 2528c ( table 4 ) . results on ( table 4 ) revealed that , among the screened 167 psf isolates , jucaf38 ( aspergillus sp . ) was the most efficient phosphate solubilizer on pv plates with si = 3.05 followed by juhbf95 ( aspergillus sp . ) with si = 2.87 and jufbf59 ( penicillium sp . ) with si = 2.39 , whereas the smallest si of 1.10 was detected from the isolate juhbpsf61 . the amount of phosphates solubilized by all fungal isolates was showed to be significantly ( p < 0.05 ) higher over uninoculated control ( figure 4 ) . the minimum p - solubilized from tcp containing broth was on day 5 , afterwards the solubilized p increased up to day 15 of incubation . accordingly , the mobilized phosphate values in the medium ranged between ( 92.09778.77 g ml ) with variations ( p < 0.05 ) among different fungal isolates during 20 days of incubation time . the highest amount of solubilized phosphate ( 778.77 g ml ) was recorded from juhbf95 ( aspergillus sp . ) inoculated culture filtrates followed by ( aspergillus sp . ) jufbf60 ( 615.40 g ml ) , ( aspergillus sp . ) jucaf37 ( 553.06 g ml ) , and ( penicillium sp . ) jufbf59 ( 472.20 g ml ) . the minimum concentration of soluble - p ( 225.50 g ml ) was recorded in the cultures of ( aspergillus sp . ) jufbf58 during 15 days of incubation time ( figure 4 ) . in further incubation ( at day 20 ) , decline in the mobilized phosphate was recorded in all cases of the test fungal isolates that reached up to 172.36 g ml ( minimum value ) in case of jufbf58 and 511.22 g ml ( maximum value ) in case of the isolate juhbf95 inoculated culture filtrates ( figure 4 ) . all the nine isolates showed a decrease in the ph significantly ( p < 0.05 ) over control in the liquid culture supernatants during the 20 days of incubation ( figure 5 ) . the ph values decreased to variable levels in the tcp medium during the initial days depending on the culture and later became increased or remained at the same level ( figure 5 ) . the highest drop in ph was recorded in the isolates juhbf95 and jufbf60 from initial ph of 7.0 to 3.08 and 3.31 , respectively , after 15 days of incubation time . the ph values at 5 , 10 , 15 , and 20 days of incubation in pvk liquid medium containing rp were summarized in ( figure 6 ) . a highly significant ( p < 0.05 ) variation of solubilized p concentrations was recorded among the fungal isolates in 20 days of incubation . the minimum p - solubilized value from rp culture medium during 20 days of rp solubilizing experiments was obtained on day 5 ( figure 6 ) . the results also showed that when the medium was supplemented with rock phosphate , the content of soluble phosphate released by the isolates in culture medium increased up to 10th day in all nine fungal isolates ( figure 6 ) . the highest mobilized phosphate value ( 363 g / ml ) was recorded from isolate juhbf95 ( aspergillus sp . ) whereas the minimum concentration of soluble - p ( 96.20 g / ml ) was observed in the cultures of jutof167 ( aspergillus sp . ) on day 10 of incubation ( figure 6 ) . mobilized phosphate values began to decline in all inoculated culture filtrates that reached up to 58.17 g l ( minimum value ) in juhbf94 inoculated culture and 178.12 g / ml ( maximum value ) in case of juhbf95 on day 20 of incubation time ( figure 6 ) . there were significant ( p < 0.05 ) drops of ph in the liquid culture medium amended with rp for all the nine test fungal isolates compared to the control during 20 days of incubation ( figure 7 ) . the maximum ph decrease was recorded from the 5th and 10th days of incubations by most fungal isolates but was later increased or nearly constant in all culture filtrates ( figure 7 ) . among the nine isolates the largest reduction of ph in culture medium was from an initial value of 7.0 to ph values 4.00 , 4.05 , 4.13 , and 4.23 for the isolates juhbf60 , jucaf37 , juhbf95 , and jufbf59 , respectively , after 10 days of incubation ( figure 7 ) . however , no decrement was found in ph medium over the last 1520 days of incubation in all test culture filtrates . from nine efficient phosphate solubilizing fungal isolates , two isolates , namely , juhbf95 ( aspergillus spp . ) and jufbf59 ( penicillium spp . ) resulted in the highest mean phosphate solubilization and mean ph drop from pkv broth containing tricalcium phosphate and rock phosphate , respectively . the present study revealed that the rhizosphere of different plants collected from jimma town and mana district farmlands supports a diverse group of p - solubilizing fungi . the most dominant genera belong to aspergillus and penicillium spp . similarly , chuang et al . , oniya et al . , and verma and ekka also isolated p - solubilizing fungi such as aspergillus niger and penicillium spp . from various rhizospheric soil samples . in the case of tomato plant besides , effective phosphate solubilizing fungi were isolated with higher proportion from tomato plants . in another study , the effectiveness of p - solubilizing fungi in the present study could be probably because of sufficient root exudates since phosphate solubilizing microorganisms are mainly dependent on carbon rich sources from plant root for active production of organic acids that are utilized for solubilizing soil - bound phosphate . in the present study , aspergillus spp . ( 55.69% ) were the most frequently occurring p - solubilizing fungi of the three identified genera . the current result is in agreement with the earlier findings of several workers [ 17 , 31 , 35 ] , who observed predominant occurrence of p - solubilizing fungi belonging to genus aspergillus followed by penicillium spp . in the rhizosphere of different crop plants . in this study , a total of 19 psf isolates were reported as unidentified due to overlapping morphological and colonial features . although morphological and colonial properties are commonly used for identification , molecular , biochemical , and physiological methods are important for the correct identification of fungal species . the variable potential of phosphate solubilization based on si on agar plate in the present study may be because of the varying type , amount , and diffusion rates of diverse organic acids secreted by fungal isolates as previously reported by yadav et al . . iman reported that the solubilization indices ( si ) of the test phosphate solubilizing fungal strains ( penicillium italicum and aspergillus niger ) were 2.42 and 3.15 , respectively . conversely , mahamuni et al . reported si for different fungal strains isolated from sugarcane and sugar beet which ranged from 1.13 to 1.59 . alam et al . also reported si that ranged from 1.53 to 1.80 for the fungal cultures isolated from maize rhizosphere . fungal isolates that have shown higher si on solid agar medium did not show similar trend in liquid broth medium , which is in agreement with the findings of alam et al . who reported that some isolates with little clear zone on solid agar medium exhibited higher efficiency for dissolving insoluble phosphates in liquid medium . some fungal isolates showed larger clear zones on agar but low phosphate solubilization in liquid medium . this shows that production of higher si on solid medium does not necessarily show solubilization efficiency in liquid medium . thus , the plate technique is insufficient to screen the best p solubilizers and to detect all phosphate solubilizers as commented by nautiyal . in the present study , periodical estimates of p in broth media revealed the potential of the isolates in releasing p from insoluble phosphate sources . the fungal isolates solubilized the insoluble phosphate sources such as tcp and rp with gradual increase in the middle of incubation period . , who have also demonstrated a gradual increase in mobilized p by fungal isolate f1 in liquid cultures . decrease in phosphate solubilization was observed at the end of incubation time which is in agreement with the findings of mahamuni et al . . kim et al . reported that this could be attributed to the availability of soluble phosphate , which had an inhibitory effect on further tcp or rp solubilization , or the depletion of carbon source that limited both the production of organic acids and microbial activity . another possibility for reduction of mobilized p could be due to the formation of an organo - p compound induced by released organic metabolites , which in turn reduces the amount of available p . muleta also stated that mobilized p is utilized by fungal cells for their growth and development during this period . the test fungal isolates solubilized maximum amount of phosphate from tcp on day 15 and from rp on day 10 but gradually decreased afterwards . these results are in conformity with the findings of pandey et al . , who observed maximum solubilization of phosphate occurring at day 15 of incubation for tcp under controlled conditions . other studies on rock phosphate solubilization indicated that the maximum soluble phosphorus release was on tenth day of incubation by the psf isolates in liquid culture medium while vyas et al . reported maximum solubilization of rp from nine to twelve days after incubation . the isolates juhbf95 and jufbf60 showed the highest mobilized p values ( 778.77 g ml and 615.40 g ml , resp . ) when the medium was supplemented with tricalcium phosphate which could be linked to its inherent self - solubility . these fungal isolates were also able to release considerable amount of p when the medium was supplemented with rock phosphate . this indicates the potential of these fungal isolates in solubilization of insoluble phosphates which gives new avenue for development of fungal biofertilizers after carrying out the necessary qualifying tests . in line with these findings , chakraborty et al . reported that aspergillus niger ( isolate rs / p-14 ) solubilized maximum amount of tricalcium phosphate ( 799 g ml ) and from rock phosphate ( 385 g ml ) in pvk broth at 15 days of incubation . similarly , pandey et al . recorded mobilized phosphate between 320 g ml ( p. oxalicum ) and 500 g ml ( p. citrinum and p. purpurogenum ) from tcp at 15 days of incubation . this finding is similar to the earlier studies of premono et al . and mahamuni et al . who recorded lesser p solubilization in rp than tcp . these authors remarked that the poor solubilization of rock phosphate may be attributed to the complex mineral composition and particle size in the medium as remarked by pradhan and sukla and mahamuni et al . in addition to the presence of strong apatite bond in the rp , which reduced phosphate solubilization . acidification by organic acid has been reported to be the main solubilization mechanism of inorganic p by microorganisms . decrease in ph values was recorded in all fungal isolates differently in the culture media . this might be due to production of diverse organic acids from the available nutrient ( glucose ) as commented by several investigators [ 18 , 37 ] . the ph drop in cultures has been repeatedly reported by a number of research findings [ 18 , 37 , 40 , 47 ] . the ph values decreased to variable levels depending on the culture type and later became nearly constant or increased with reduction in mobilized phosphate . this observation might be attributed to low glucose concentration in pkv broth which is essential for production of organic acids . in this respect , the present findings are in agreement with nenwani et al . who reported increase in ph value and decrease in solubilized phosphate at the end of incubation time . the results of this study have shown that the rhizosphere soils of cabbage , haricot bean , faba bean , sugar cane , and tomato of different sites of jimma town and mana woreda farmlands support a diverse group of naturally occurring potential phosphate solubilizing fungi ( psf ) . the efficiency of phosphate solubilization is significantly higher in pikovskaya medium containing tcp than in the medium containing rp .[/INST]phosphorus ( p ) is one of the major bioelements limiting agricultural production . phosphate solubilizing fungi play a noteworthy role in increasing the bioavailability of soil phosphates for plants . the present study was aimed at isolating and characterizing phosphate solubilizing fungi from different rhizospheres using both solid and liquid pikovskaya ( pvk ) medium . a total of 359 fungal isolates were obtained from 150 rhizosphere soil samples of haricot bean , faba bean , cabbage , tomato , and sugarcane . among the isolates , 167 ( 46.52% ) solubilized inorganic phosphate . the isolated phosphate solubilizing fungi belonged to genera of aspergillus ( 55.69% ) , penicillium spp . ( 23.35% ) , and fusarium ( 9.58% ) . solubilization index ( si ) ranged from 1.10 to 3.05 . isolates designated as juhbf95 ( aspergillus sp . ) and jufbf59 ( penicillium sp . ) solubilized maximum amount of p 728.77 gml1 and 514.44 g ml1 , respectively , from tcp ( tricalcium phosphate ) after 15 days of incubation . the highest ( 363 g ml1 ) soluble - p was released from rp with the inoculation of juhbf95 in the pvk broth after 10 days of incubation . the present study indicated the presence of diverse plant associated p - solubilizing fungi that may serve as potential biofertilizers .</s>

SECTION 1. FINDINGS. Congress finds the following: (1) The South China Sea contains vital commercial shipping lanes and points of access between the Indian Ocean and Pacific Ocean and provides a maritime lifeline to Taiwan, Japan, and the Korean peninsula. (2) China, Vietnam, the Philippines, Taiwan, Malaysia, and Brunei have disputed territorial claims over the Spratly Islands, and China, Taiwan, and Vietnam have disputed territorial claims over the Paracel Islands. (3) In 2009, the Government of the People's Republic of China introduced the 9-dotted line (also known as the Cow Tongue line) to officially claim most of the 648,000 square miles of the South China Sea, more than any other nation involved in these territorial disputes. (4) Although not a party to these disputes, the United States has a national economic and security interest in maintaining peace, stability and prosperity in East Asia and ensuring that no party threatens or uses force unilaterally to assert maritime territorial claims in East Asia, including in the South China Sea, the East China Sea, or the Yellow Sea. (5) The Association of Southeast Asian Nations (ASEAN) has promoted multilateral talks in disputed areas without settling the issue of sovereignty. (6) In 2002, ASEAN and China signed a Declaration on the Conduct of Parties in the South China Sea. That declaration committed all parties to those territorial disputes to ``reaffirm their respect for and commitment to the freedom of navigation in and overflight above the South China Sea as provided for by the universally recognized principles of international law'', and to ``resolve their territorial and jurisdictional disputes by peaceful means, without resorting to the threat or use of force''. Yet, in September 2010, tensions were raised in the East China Sea off of the Senkaku (Diaoyutai) Islands, a territory under the legal administration of Japan, when a Chinese fishing vessel deliberately rammed Japanese Coast Guard patrol boats. (7) The Government of the People's Republic of China deliberately heightened these tensions by making a series of diplomatic protests, including on one occasion summoning the Japanese Ambassador after midnight, by threatening ``further repercussions'' if Japan did not immediately release the Chinese ship captain involved in the collisions, and by encouraging anti-Japanese demonstrations in Chinese cities. (8) On February 25, 2011, a frigate from China's navy fired shots at 3 fishing boats from the Philippines. (9) On March 2, 2011, the Government of the Philippines reported that two patrol boats from China attempted to ram one of its surveillance ships. (10) On May 26, 2011, a maritime security vessel from China cut the cables of an exploration ship from Vietnam, the Binh Minh, in the South China Sea in waters near Cam Ranh Bay in the exclusive economic zone of Vietnam. (11) On May 31, 2011, three Chinese military vessels used guns to threaten the crews of four Vietnamese fishing boats while they were fishing in the waters of the Truong Sa (Spratly) archipelago. (12) On June 3, 2011, Vietnam's Foreign Ministry released a statement that ``Vietnam is resolutely opposed to these acts by China that seriously violated the sovereign and jurisdiction rights of Viet Nam to its continental shelf and Exclusive Economic Zone (EEZ).''. (13) On June 9, 2011, three vessels from China, including one fishing vessel and two maritime security vessels, ran into and disabled the cables of another exploration ship from Vietnam, the Viking 2, in the exclusive economic zone of Vietnam. (14) On June 13-14, 2011, the Government of Vietnam held a live-fire military exercise on the uninhabited island of Hon Ong, 25 miles off the coast of Vietnam in the South China Sea. (15) On June 25, 2011, Chinese Peoples' Liberation Army Major General (Ret.) Peng Guangqian stated in a television interview that ``China once taught Vietnam a lesson. If Vietnam is not sincere, it will receive a bigger lesson'', adding that ``If Vietnam continues to act tough, play with the knife, sooner or later it will get cut.''. (16) On June 26, 2011, the Chinese news agency Xinhua announced that China and Vietnam had agreed to hold talks on how to resolve conflicts arising from a sovereignty dispute over the South China Sea after a June 25 meeting in Beijing between Dai Bingguo, the senior Chinese official in charge of foreign affairs, and Vietnamese Vice Foreign Minister and Special Envoy Ho Xuan Son. (17) It was reported, on June 17, 2011, that the Philippines removed a string of wooden markers that Manila determined was placed by China in disputed areas of the South China Sea amid growing regional tensions. (18) On June 23, 2011, Secretary of State Hillary Rodham Clinton told visiting Philippines Foreign Secretary Albert del Rosario that ``We are determined and committed to supporting the defense of the Philippines.''. (19) Philippines Foreign Secretary del Rosario stated that the Philippines is a small country, but is ``prepared to do what is necessary to stand up to any aggressive action in our backyard''. (20) The United States, on June 23, 2011, stated that it was ready to provide hardware to modernize the military of the Philippines. (21) The United States and the Philippines conducted combined naval exercises in the Sulu Sea, near the South China Sea, from June 28 to July 8, 2011. (22) On June 17, 2011, China dispatched one of its largest patrol ships, the Haixun 31, on a voyage through disputed areas of the South China Sea in a deliberate show of force en route to a port of call in Singapore. (23) China's official media stated that the sailing route of the Haixun 31 in the South China Sea was determined to protect its ``rights and sovereignty''. (24) A spokesperson for Singapore's Ministry of Foreign Affairs pointed out, on June 20, 2011, that ``as a major trading nation, Singapore has a critical interest in anything affecting freedom of navigation in all international sea lanes, including those in the South China Sea''. (25) Singapore further urged China to clarify its claims in the South China Sea with more precision as the current ambiguity as to their extent has caused serious concerns in the international maritime community. (26) The actions of the Government of the People's Republic of China in the South China Sea have also affected United States military and maritime vessels transiting through international air space and waters, including the collision of a fighter plane of China with a United States surveillance plane in 2001, the harassment of the USNS Impeccable in March 2009, and the collision of a Chinese submarine with the sonar cable of the USS John McCain in June 2009. (27) In July 2010, People's Daily, the official newspaper of the Chinese Communist Party, reported that General Ma Xiaotian, deputy chief of the general staff of the People's Liberation Army, said that China ``strongly opposed'' combined naval exercises to be conducted in the West (Yellow) Sea by the United States and the Republic of Korea. (28) These exercises were to be conducted in international waters, as well as Republic of Korea territorial waters, in the vicinity of the site of the March 2010 North Korean torpedo attack on the South Korean military vessel Cheonan, which resulted in 46 deaths. (29) These exercises were to include participation by the USS George Washington aircraft carrier group. (30) In July 2010, Chinese Major General Luo Yuan, a researcher at the Chinese Academy of Military Sciences, in an interview with a Hong Kong TV station, stressed the importance of the Yellow Sea as ``a gateway to China's capital region'' and said that ``if a U.S. aircraft carrier enters the Yellow Sea, it will become a living target''. (31) On July 23, 2010, Secretary of State Hillary Rodham Clinton stated at the Association of Southeast Asian Nations Regional Forum that ``the United States, like every nation, has a national interest in freedom of navigation, open access to Asia's maritime commons, and respect for international law in the South China Sea''. (32) Secretary Clinton further expressed the support of the United States for the Declaration by the Association of Southeast Asian Nations and China in 2002 on the Conduct of Parties in the South China Sea, and stated, ``The United States supports a collaborative diplomatic process by all claimants for resolving the various territorial disputes without coercion.''. (33) On October 12, 2010, former Secretary of Defense Robert Gates stated at the ASEAN Defense Ministers Meeting- Plus, ``The U.S. position on maritime security remains clear: we have a national interest in freedom of navigation; in unimpeded economic development and commerce; and in respect for international law.''. Former Secretary Gates further maintained ``The United States has always exercised our rights and supported the rights of others to transit through, and operate in, international waters.''. (34) On June 4, 2011, at the Shangri-La Dialogue in Singapore, former Secretary Gates stated that ``maritime security remains an issue of particular importance for the region, with questions about territorial claims and the appropriate use of the maritime domain presenting on-going challenges to regional stability and prosperity''. (35) On June 5, 2011, at the Shangri-La Dialogue, Liang Guanglie, the Defense Minister from China, said, ``China is committed to maintaining peace and stability in the South China Sea.''. (36) On June 14, 2011, Hong Lei, the spokesman for the Chinese Foreign Ministry, stated that ``China always upholds and has been committed to a proper resolution of differences and disputes over the South China Sea in a peaceful manner through bilateral direct negotiation and friendly consultation with relevant countries.''. (37) On June 22, 2011, Chinese Vice Foreign Minister Cui Tiankai told reporters, in reference to the South China Sea disputes, that ``I believe the individual countries are actually playing with fire, and I hope the fire will not be drawn to the United States.''. (38) On June 29, 2011, the Defense Ministry of the People's Republic of China stated that ``Recent drills by the Chinese navy are routine and not connected to the situation in the South China Sea'', further calling for people to view the exercises in a ``rational'' way. (39) On April 8, 2012, a Philippine plane spotted eight Chinese fishing boats in the vicinity of the Scarborough Shoal, which both countries claim. (40) A Philippine coast guard cutter and two Chinese maritime surveillance craft began a tense 10-day standoff, with the Philippine vessel, citing the upcoming typhoon season, withdrawing but the Chinese ships remained in the area. Moreover, China constructed barriers to prevent Philippine vessels from entering the Scarborough Shoal where it was reported that Chinese flags were raised. (41) A Chinese foreign ministry spokesman condemned a long- planned joint military exercise between the U.S. and the Philippines in April, saying ``The major trend of the times in this region is peace and development. Military exercise does not represent the major call of the times.''. (42) In June of 2012, Vietnam passed a law claiming sovereignty over the Paracel and Spratly Islands and called for mutual respect for international law. (43) China quickly criticized the law, with a foreign ministry statement calling it a ``serious violation of China's territorial sovereignty'' and that China expressed its ``resolute and vehement opposition''. (44) In June of 2012, China's cabinet, the State Council, approved the establishment of a prefecture-level government in the city of Sansha to oversee the areas claimed by China in the South China Sea. (45) On June 23, 2012, the China National Offshore Oil Corporation invited bids for oil exploration in areas within 200 nautical miles of the continental shelf and exclusive economic zone of Vietnam. (46) On June 28, 2012, the Chinese Defense Ministry announced that military authorities were considering establishing a military presence in the prefecture capitol of Sansha. (47) Also on June 28, Chinese military press spokesman Senior Colonel Geng Yansheng announced that the PLA had begun ``regular, combat-ready patrols'' in the South China Sea. (48) On July 11, 2012, Chinese patrol ships were spotted near the disputed Senkaku (Diaoyutai) Islands in the East China Sea. (49) When the Japanese coast guard told the Chinese ships to leave, the crew told them, ``We are conducting official duty in Chinese waters. Do not interfere. Leave China's territorial waters.''. (50) Japan's Vice Foreign Minister Kenichrio Sasae called the exchange ``extremely serious'' and ``unacceptable,'' and a government spokesperson was quoted as saying, ``It is clear that historically and legally Senkaku is an inherent territory of Japan.''. (51) At the July 2012 ASEAN Regional Forum (ARF), Secretary Clinton said, ``We believe the nations of the region should work collaboratively and diplomatically to resolve disputes without coercion, without intimidation, without threats, and without the use of force.''. (52) Although ASEAN has agreed on the elements of the Code of Conduct (COC), China stated that it would enter negotiations with ASEAN on the COC ``when the time is ripe''. (53) A day following the conclusion of the ARF meeting on July 14, 2012, a Chinese naval warship ran aground while on patrol about 60 miles from the province of Palawan in the Philippines on Half Moon Shoal in the disputed Spratlys. (54) While the grounded warship was in the process of removing itself from the Half Moon Shoal a day later, Xinhua announced that 30 Chinese fishing boats, guarded by an official government ship, had set sail for the South China Sea. (55) On July 19, 2012, the Chinese Central Military Commission approved the establishment of the ``military defense and watch zone of Sansha'' at the division level. (56) On July 26, 2012, China then appointed a Chief Commander and a Political Commissar of ``the military defense and watch zone of Sansha''. (57) On July 23, 2012, Philippine President Benigno Aquino III announced in his state of the nation address that the Philippines had purchased more than 40 military aircraft, including attack helicopters and two refurbished C-130 cargo planes, as well as a second former U.S. Coast Guard cutter. (58) In the nationally televised address before Congress, President Aquino stressed that he would not back down to Chinese pressure, saying ``I do not think it excessive to ask that our rights be respected, just as we respect their rights as a fellow nation in a world we need to share.''. (59) A day earlier, on July 22, China's Central Military Commission approved the deployment of a garrison of soldiers to guard Chinese claims in the Spratlys, the Paracels and the Macclesfield Bank. (60) On July 24, 2012, China declared a new municipality on Yongxing, or Woody Island, where the previously announced military garrison will be stationed. (61) A State Department spokeswoman said that the United States is concerned about such ``unilateral moves'' and wants to see ``all of these issues resolved at the table''. SEC. 2. SENSE OF CONGRESS. It is the sense of Congress that, in light of the congressional finding described in section 1, the Secretary of State should-- (1) reaffirm the strong support of the United States for the peaceful resolution of maritime territorial disputes in the South China Sea, the Taiwan Strait, the East China Sea, and the Yellow Sea and pledge continued efforts to facilitate a collaborative, peaceful proves to resolve these disputes; (2) condemn the use of threat or force by naval, maritime security, and fishing vessels from China in the South China Sea and the East China Sea as well as the use of force by China's North Korean ally in the Yellow Sea; (3) note that overt threats and gun boat diplomacy are not constructive means for settling these outstanding maritime disputes; (4) call on all parties to these territorial disputes to refrain from threatening force or using force to assert territorial claims; (5) welcome the diplomatic efforts of Association of Southeast Asian Nations (ASEAN) and the United States allies and partners in Taiwan, Japan, and the Republic of Korea to amiably and fairly resolve these outstanding disputes; and (6) support the continuation of operations by the United States Armed Forces in support of freedom of navigation rights in international waters and air space in the South China Sea, the East China Sea, the Taiwan Strait, and the Yellow Sea.

Expresses the sense of Congress that the Secretary of State should: (1) reaffirm U.S. support for the peaceful resolution of maritime territorial disputes in the South China Sea, the East China Sea, the Taiwan Strait, and the Yellow Sea; (2) condemn the use of force by China in the South China and East China Seas and by China's North Korean ally in the Yellow Sea; (3) call on all parties to these territorial disputes to refrain from threatening force or using force to assert territorial claims; (4) welcome the diplomatic efforts of Association of Southeast Asian Nations (ASEAN) and U.S. allies and partners in Taiwan, Japan, and the Republic of Korea to resolve these outstanding disputes; and (5) support U.S. Armed Forces operations in support of freedom of navigation rights in international waters and air space in the South China Sea, the East China Sea, the Taiwan Strait, and the Yellow Sea.

<s>[INST]SECTION 1. FINDINGS. Congress finds the following: (1) The South China Sea contains vital commercial shipping lanes and points of access between the Indian Ocean and Pacific Ocean and provides a maritime lifeline to Taiwan, Japan, and the Korean peninsula. (2) China, Vietnam, the Philippines, Taiwan, Malaysia, and Brunei have disputed territorial claims over the Spratly Islands, and China, Taiwan, and Vietnam have disputed territorial claims over the Paracel Islands. (3) In 2009, the Government of the People's Republic of China introduced the 9-dotted line (also known as the Cow Tongue line) to officially claim most of the 648,000 square miles of the South China Sea, more than any other nation involved in these territorial disputes. (4) Although not a party to these disputes, the United States has a national economic and security interest in maintaining peace, stability and prosperity in East Asia and ensuring that no party threatens or uses force unilaterally to assert maritime territorial claims in East Asia, including in the South China Sea, the East China Sea, or the Yellow Sea. (5) The Association of Southeast Asian Nations (ASEAN) has promoted multilateral talks in disputed areas without settling the issue of sovereignty. (6) In 2002, ASEAN and China signed a Declaration on the Conduct of Parties in the South China Sea. That declaration committed all parties to those territorial disputes to ``reaffirm their respect for and commitment to the freedom of navigation in and overflight above the South China Sea as provided for by the universally recognized principles of international law'', and to ``resolve their territorial and jurisdictional disputes by peaceful means, without resorting to the threat or use of force''. Yet, in September 2010, tensions were raised in the East China Sea off of the Senkaku (Diaoyutai) Islands, a territory under the legal administration of Japan, when a Chinese fishing vessel deliberately rammed Japanese Coast Guard patrol boats. (7) The Government of the People's Republic of China deliberately heightened these tensions by making a series of diplomatic protests, including on one occasion summoning the Japanese Ambassador after midnight, by threatening ``further repercussions'' if Japan did not immediately release the Chinese ship captain involved in the collisions, and by encouraging anti-Japanese demonstrations in Chinese cities. (8) On February 25, 2011, a frigate from China's navy fired shots at 3 fishing boats from the Philippines. (9) On March 2, 2011, the Government of the Philippines reported that two patrol boats from China attempted to ram one of its surveillance ships. (10) On May 26, 2011, a maritime security vessel from China cut the cables of an exploration ship from Vietnam, the Binh Minh, in the South China Sea in waters near Cam Ranh Bay in the exclusive economic zone of Vietnam. (11) On May 31, 2011, three Chinese military vessels used guns to threaten the crews of four Vietnamese fishing boats while they were fishing in the waters of the Truong Sa (Spratly) archipelago. (12) On June 3, 2011, Vietnam's Foreign Ministry released a statement that ``Vietnam is resolutely opposed to these acts by China that seriously violated the sovereign and jurisdiction rights of Viet Nam to its continental shelf and Exclusive Economic Zone (EEZ).''. (13) On June 9, 2011, three vessels from China, including one fishing vessel and two maritime security vessels, ran into and disabled the cables of another exploration ship from Vietnam, the Viking 2, in the exclusive economic zone of Vietnam. (14) On June 13-14, 2011, the Government of Vietnam held a live-fire military exercise on the uninhabited island of Hon Ong, 25 miles off the coast of Vietnam in the South China Sea. (15) On June 25, 2011, Chinese Peoples' Liberation Army Major General (Ret.) Peng Guangqian stated in a television interview that ``China once taught Vietnam a lesson. If Vietnam is not sincere, it will receive a bigger lesson'', adding that ``If Vietnam continues to act tough, play with the knife, sooner or later it will get cut.''. (16) On June 26, 2011, the Chinese news agency Xinhua announced that China and Vietnam had agreed to hold talks on how to resolve conflicts arising from a sovereignty dispute over the South China Sea after a June 25 meeting in Beijing between Dai Bingguo, the senior Chinese official in charge of foreign affairs, and Vietnamese Vice Foreign Minister and Special Envoy Ho Xuan Son. (17) It was reported, on June 17, 2011, that the Philippines removed a string of wooden markers that Manila determined was placed by China in disputed areas of the South China Sea amid growing regional tensions. (18) On June 23, 2011, Secretary of State Hillary Rodham Clinton told visiting Philippines Foreign Secretary Albert del Rosario that ``We are determined and committed to supporting the defense of the Philippines.''. (19) Philippines Foreign Secretary del Rosario stated that the Philippines is a small country, but is ``prepared to do what is necessary to stand up to any aggressive action in our backyard''. (20) The United States, on June 23, 2011, stated that it was ready to provide hardware to modernize the military of the Philippines. (21) The United States and the Philippines conducted combined naval exercises in the Sulu Sea, near the South China Sea, from June 28 to July 8, 2011. (22) On June 17, 2011, China dispatched one of its largest patrol ships, the Haixun 31, on a voyage through disputed areas of the South China Sea in a deliberate show of force en route to a port of call in Singapore. (23) China's official media stated that the sailing route of the Haixun 31 in the South China Sea was determined to protect its ``rights and sovereignty''. (24) A spokesperson for Singapore's Ministry of Foreign Affairs pointed out, on June 20, 2011, that ``as a major trading nation, Singapore has a critical interest in anything affecting freedom of navigation in all international sea lanes, including those in the South China Sea''. (25) Singapore further urged China to clarify its claims in the South China Sea with more precision as the current ambiguity as to their extent has caused serious concerns in the international maritime community. (26) The actions of the Government of the People's Republic of China in the South China Sea have also affected United States military and maritime vessels transiting through international air space and waters, including the collision of a fighter plane of China with a United States surveillance plane in 2001, the harassment of the USNS Impeccable in March 2009, and the collision of a Chinese submarine with the sonar cable of the USS John McCain in June 2009. (27) In July 2010, People's Daily, the official newspaper of the Chinese Communist Party, reported that General Ma Xiaotian, deputy chief of the general staff of the People's Liberation Army, said that China ``strongly opposed'' combined naval exercises to be conducted in the West (Yellow) Sea by the United States and the Republic of Korea. (28) These exercises were to be conducted in international waters, as well as Republic of Korea territorial waters, in the vicinity of the site of the March 2010 North Korean torpedo attack on the South Korean military vessel Cheonan, which resulted in 46 deaths. (29) These exercises were to include participation by the USS George Washington aircraft carrier group. (30) In July 2010, Chinese Major General Luo Yuan, a researcher at the Chinese Academy of Military Sciences, in an interview with a Hong Kong TV station, stressed the importance of the Yellow Sea as ``a gateway to China's capital region'' and said that ``if a U.S. aircraft carrier enters the Yellow Sea, it will become a living target''. (31) On July 23, 2010, Secretary of State Hillary Rodham Clinton stated at the Association of Southeast Asian Nations Regional Forum that ``the United States, like every nation, has a national interest in freedom of navigation, open access to Asia's maritime commons, and respect for international law in the South China Sea''. (32) Secretary Clinton further expressed the support of the United States for the Declaration by the Association of Southeast Asian Nations and China in 2002 on the Conduct of Parties in the South China Sea, and stated, ``The United States supports a collaborative diplomatic process by all claimants for resolving the various territorial disputes without coercion.''. (33) On October 12, 2010, former Secretary of Defense Robert Gates stated at the ASEAN Defense Ministers Meeting- Plus, ``The U.S. position on maritime security remains clear: we have a national interest in freedom of navigation; in unimpeded economic development and commerce; and in respect for international law.''. Former Secretary Gates further maintained ``The United States has always exercised our rights and supported the rights of others to transit through, and operate in, international waters.''. (34) On June 4, 2011, at the Shangri-La Dialogue in Singapore, former Secretary Gates stated that ``maritime security remains an issue of particular importance for the region, with questions about territorial claims and the appropriate use of the maritime domain presenting on-going challenges to regional stability and prosperity''. (35) On June 5, 2011, at the Shangri-La Dialogue, Liang Guanglie, the Defense Minister from China, said, ``China is committed to maintaining peace and stability in the South China Sea.''. (36) On June 14, 2011, Hong Lei, the spokesman for the Chinese Foreign Ministry, stated that ``China always upholds and has been committed to a proper resolution of differences and disputes over the South China Sea in a peaceful manner through bilateral direct negotiation and friendly consultation with relevant countries.''. (37) On June 22, 2011, Chinese Vice Foreign Minister Cui Tiankai told reporters, in reference to the South China Sea disputes, that ``I believe the individual countries are actually playing with fire, and I hope the fire will not be drawn to the United States.''. (38) On June 29, 2011, the Defense Ministry of the People's Republic of China stated that ``Recent drills by the Chinese navy are routine and not connected to the situation in the South China Sea'', further calling for people to view the exercises in a ``rational'' way. (39) On April 8, 2012, a Philippine plane spotted eight Chinese fishing boats in the vicinity of the Scarborough Shoal, which both countries claim. (40) A Philippine coast guard cutter and two Chinese maritime surveillance craft began a tense 10-day standoff, with the Philippine vessel, citing the upcoming typhoon season, withdrawing but the Chinese ships remained in the area. Moreover, China constructed barriers to prevent Philippine vessels from entering the Scarborough Shoal where it was reported that Chinese flags were raised. (41) A Chinese foreign ministry spokesman condemned a long- planned joint military exercise between the U.S. and the Philippines in April, saying ``The major trend of the times in this region is peace and development. Military exercise does not represent the major call of the times.''. (42) In June of 2012, Vietnam passed a law claiming sovereignty over the Paracel and Spratly Islands and called for mutual respect for international law. (43) China quickly criticized the law, with a foreign ministry statement calling it a ``serious violation of China's territorial sovereignty'' and that China expressed its ``resolute and vehement opposition''. (44) In June of 2012, China's cabinet, the State Council, approved the establishment of a prefecture-level government in the city of Sansha to oversee the areas claimed by China in the South China Sea. (45) On June 23, 2012, the China National Offshore Oil Corporation invited bids for oil exploration in areas within 200 nautical miles of the continental shelf and exclusive economic zone of Vietnam. (46) On June 28, 2012, the Chinese Defense Ministry announced that military authorities were considering establishing a military presence in the prefecture capitol of Sansha. (47) Also on June 28, Chinese military press spokesman Senior Colonel Geng Yansheng announced that the PLA had begun ``regular, combat-ready patrols'' in the South China Sea. (48) On July 11, 2012, Chinese patrol ships were spotted near the disputed Senkaku (Diaoyutai) Islands in the East China Sea. (49) When the Japanese coast guard told the Chinese ships to leave, the crew told them, ``We are conducting official duty in Chinese waters. Do not interfere. Leave China's territorial waters.''. (50) Japan's Vice Foreign Minister Kenichrio Sasae called the exchange ``extremely serious'' and ``unacceptable,'' and a government spokesperson was quoted as saying, ``It is clear that historically and legally Senkaku is an inherent territory of Japan.''. (51) At the July 2012 ASEAN Regional Forum (ARF), Secretary Clinton said, ``We believe the nations of the region should work collaboratively and diplomatically to resolve disputes without coercion, without intimidation, without threats, and without the use of force.''. (52) Although ASEAN has agreed on the elements of the Code of Conduct (COC), China stated that it would enter negotiations with ASEAN on the COC ``when the time is ripe''. (53) A day following the conclusion of the ARF meeting on July 14, 2012, a Chinese naval warship ran aground while on patrol about 60 miles from the province of Palawan in the Philippines on Half Moon Shoal in the disputed Spratlys. (54) While the grounded warship was in the process of removing itself from the Half Moon Shoal a day later, Xinhua announced that 30 Chinese fishing boats, guarded by an official government ship, had set sail for the South China Sea. (55) On July 19, 2012, the Chinese Central Military Commission approved the establishment of the ``military defense and watch zone of Sansha'' at the division level. (56) On July 26, 2012, China then appointed a Chief Commander and a Political Commissar of ``the military defense and watch zone of Sansha''. (57) On July 23, 2012, Philippine President Benigno Aquino III announced in his state of the nation address that the Philippines had purchased more than 40 military aircraft, including attack helicopters and two refurbished C-130 cargo planes, as well as a second former U.S. Coast Guard cutter. (58) In the nationally televised address before Congress, President Aquino stressed that he would not back down to Chinese pressure, saying ``I do not think it excessive to ask that our rights be respected, just as we respect their rights as a fellow nation in a world we need to share.''. (59) A day earlier, on July 22, China's Central Military Commission approved the deployment of a garrison of soldiers to guard Chinese claims in the Spratlys, the Paracels and the Macclesfield Bank. (60) On July 24, 2012, China declared a new municipality on Yongxing, or Woody Island, where the previously announced military garrison will be stationed. (61) A State Department spokeswoman said that the United States is concerned about such ``unilateral moves'' and wants to see ``all of these issues resolved at the table''. SEC. 2. SENSE OF CONGRESS. It is the sense of Congress that, in light of the congressional finding described in section 1, the Secretary of State should-- (1) reaffirm the strong support of the United States for the peaceful resolution of maritime territorial disputes in the South China Sea, the Taiwan Strait, the East China Sea, and the Yellow Sea and pledge continued efforts to facilitate a collaborative, peaceful proves to resolve these disputes; (2) condemn the use of threat or force by naval, maritime security, and fishing vessels from China in the South China Sea and the East China Sea as well as the use of force by China's North Korean ally in the Yellow Sea; (3) note that overt threats and gun boat diplomacy are not constructive means for settling these outstanding maritime disputes; (4) call on all parties to these territorial disputes to refrain from threatening force or using force to assert territorial claims; (5) welcome the diplomatic efforts of Association of Southeast Asian Nations (ASEAN) and the United States allies and partners in Taiwan, Japan, and the Republic of Korea to amiably and fairly resolve these outstanding disputes; and (6) support the continuation of operations by the United States Armed Forces in support of freedom of navigation rights in international waters and air space in the South China Sea, the East China Sea, the Taiwan Strait, and the Yellow Sea.[/INST]Expresses the sense of Congress that the Secretary of State should: (1) reaffirm U.S. support for the peaceful resolution of maritime territorial disputes in the South China Sea, the East China Sea, the Taiwan Strait, and the Yellow Sea; (2) condemn the use of force by China in the South China and East China Seas and by China's North Korean ally in the Yellow Sea; (3) call on all parties to these territorial disputes to refrain from threatening force or using force to assert territorial claims; (4) welcome the diplomatic efforts of Association of Southeast Asian Nations (ASEAN) and U.S. allies and partners in Taiwan, Japan, and the Republic of Korea to resolve these outstanding disputes; and (5) support U.S. Armed Forces operations in support of freedom of navigation rights in international waters and air space in the South China Sea, the East China Sea, the Taiwan Strait, and the Yellow Sea.</s>

the study was approved by the university of arkansas for medical sciences institutional review board . elbw infants born at the university of arkansas for medical sciences between january 2006 and may 2007 were eligible for this study if they received mechanical ventilation for respiratory distress syndrome , had umbilical arterial and venous catheters placed during newborn stabilization , developed hypotension on the first day of life , and were already involved in a physiological study evaluating cerebral autoregulation capacity . infants with major congenital anomalies , obvious hypovolemia , early - onset sepsis , or air leaks and infants who received fluid boluses , vasopressors , or hydrocortisone ( before study procedures ) were excluded . when an elbw infant became hypotensive , at any time ( including the middle of the night ) of any day ( including weekends and holidays ) , one of two research assistants initiated continuous monitoring of bp , cbfv , and pco2 . the monitoring sessions often lasted 23 hrs , beginning with a ~15 min baseline period ( before dopamine treatment ) . the dopamine infusion was begun at 5 g / kg / min ( in d5w at 0.2 ml / hr ) and increased stepwise by 2.5 g / kg / min ( 0.1 ml / hr ) increments ( 7.5 , 10 , 12.5 , 15 , 17.5 , and 20 ) every 20 min until mabp was optimized . the dopamine was always infused with maintenance intravenous fluids through the umbilical venous catheter using specialized infusion pumps ( baxter as50 , baxter healthcare corporation , deerfield , il ) . paul , mn ; or argyle / tyco healthcare / kendall , mansfield , ma ) attached to a bp transducer ( transpac iv , abbott critical care systems , north chicago , il ) . cbfv in the right middle cerebral artery was continuously monitored using transcranial doppler ultrasound ( nicolet biomedical pioneer , madison , wi ) . a lightweight 2-mhz pulsed - wave button transducer was placed transtemporally , anterior to the ear and above the zygomatic arch , and held in place by an appropriately sized crocheted hat ( courtesy of the arkansas homemakers extension council ) . a depth of 1622 mm was used to study the proximal portion of the middle cerebral artery . a 100-hz low - pass filter was used to dampen noise from the vessel wall . to obtain reliable cbfv measurements , the transducer was placed with the minimum angle of insonation , accomplished when the highest intensity acoustic signal was perceived and the highest intensity doppler spectrum was visualized . cbfv tracings were consistent with minimal to no drift in signal intensity , as the transducer did not move or need replacement during the monitoring periods . continuous pco2 monitoring was performed with a neotrend system ( diametrics medical ltd . , st . paul , mn ) or a transcutaneous blood gas monitor ( microgas 7650 rapid , radiometer , westlake , oh ) . neotrend was a system that continuously monitored arterial blood gases and temperatures , using fiber optic technology , without the need for blood withdrawal ; it is no longer being produced . briefly , for transcutaneous pco2 monitoring , the skin on either side of the chest was prepped with a small amount of aquaphor emollient ointment ( beiersdorf , norwalk , ct ) . a double - sided adhesive ring of tape was applied to the skin , and one drop of an electrolyte solution ( radiometer ) was placed into the center of the adhesive ring . after 5 min of continuous monitoring ( by either system ) , an arterial blood gas measurement was obtained from the umbilical arterial catheter and processed by the nicu laboratory . the neotrend and/or transcutaneous blood gas monitor was then calibrated with the pco2 laboratory result ( the change was rarely > 3 mm hg ) . analog signals from the bp monitor ( 112 hz ) , transcranial doppler ( 100 hz ) , and the blood gas monitors ( 1 hz ) were simultaneously collected with a data acquisition system ( powerlab 8 channel , adinstruments , mountain view , ca ) . cyclic waveform analyses were performed to calculate mabp ( average amplitude of the bp waveform over one cycle ) and systolic and diastolic bps ( maximum and minimum values of the bp cycle , respectively ) . fast fourier analysis was performed on the cbfv signal to determine the systolic , diastolic , and mean cbf velocities . for each infant , time and date of birth , whether or not their mother received antenatal steroids , birth weight , gestational age , race , gender , apgar scores at 1 and 5 min , presence of severe ivh , survival to hospital discharge , and postnatal age at the time of physiological monitoring was obtained from the research database . gestational age was estimated based on obstetrical criteria and neonatal criteria ; the neonatal estimate was used if the two estimates differed by > 2 weeks . severe ( grades iii and iv ) ivh was determined using the staging criteria of papile et al , based on any cranial ultrasound during the hospitalization . hypotension was defined as mabp in mm hg < gestational age in weeks for 30 min . optimal bp was defined as mabp in mm hg 15% above gestational age in weeks for 30 min . briefly , cbfv reactivity is expressed as the percent change of cbfv that varies per mm hg change in mabp during some time period . when the 95% confidence interval ( ci ) for mean cbfv reactivity includes 0 , i.e. , no statistically significant change in cbfv compared to changes in mabp , intact cerebral autoregulation is implied . in contrast , if the mean percent change in cbfv / mm hg change in mabp > 0 , and the 95% ci does not include 0 , then this implies impaired cerebral autoregulation . resistive index ( ri ) was defined as : ( [ systolic cbfv - diastolic cbfv]/systolic cbfv)100 . physiological variables for the hypotensive infants were analyzed before and after treatment with dopamine ( table ii ) . baseline values for mabp , mean cbfv , pco2 , and ri were determined from ~15 min of continuous monitoring that preceded treatment with dopamine . after optimal mabp was reached , mabp , mean cbfv , pco2 , and ri were again determined . comparisons of physiological variables before and after dopamine were performed by paired t - test . cbf reactivity was determined for each infant by comparing baseline and optimal mabp values after dopamine for mean cbfv and mabp , respectively , and then determined for the group of hypotensive infants . elbw infants born at the university of arkansas for medical sciences between january 2006 and may 2007 were eligible for this study if they received mechanical ventilation for respiratory distress syndrome , had umbilical arterial and venous catheters placed during newborn stabilization , developed hypotension on the first day of life , and were already involved in a physiological study evaluating cerebral autoregulation capacity . infants with major congenital anomalies , obvious hypovolemia , early - onset sepsis , or air leaks and infants who received fluid boluses , vasopressors , or hydrocortisone ( before study procedures ) were excluded . when an elbw infant became hypotensive , at any time ( including the middle of the night ) of any day ( including weekends and holidays ) , one of two research assistants initiated continuous monitoring of bp , cbfv , and pco2 . the monitoring sessions often lasted 23 hrs , beginning with a ~15 min baseline period ( before dopamine treatment ) . the dopamine infusion was begun at 5 g / kg / min ( in d5w at 0.2 ml / hr ) and increased stepwise by 2.5 g / kg / min ( 0.1 ml / hr ) increments ( 7.5 , 10 , 12.5 , 15 , 17.5 , and 20 ) every 20 min until mabp was optimized . the dopamine was always infused with maintenance intravenous fluids through the umbilical venous catheter using specialized infusion pumps ( baxter as50 , baxter healthcare corporation , deerfield , il ) . paul , mn ; or argyle / tyco healthcare / kendall , mansfield , ma ) attached to a bp transducer ( transpac iv , abbott critical care systems , north chicago , il ) . cbfv in the right middle cerebral artery was continuously monitored using transcranial doppler ultrasound ( nicolet biomedical pioneer , madison , wi ) . a lightweight 2-mhz pulsed - wave button transducer was placed transtemporally , anterior to the ear and above the zygomatic arch , and held in place by an appropriately sized crocheted hat ( courtesy of the arkansas homemakers extension council ) . a depth of 1622 mm was used to study the proximal portion of the middle cerebral artery . a 100-hz low - pass filter was used to dampen noise from the vessel wall . to obtain reliable cbfv measurements , the transducer was placed with the minimum angle of insonation , accomplished when the highest intensity acoustic signal was perceived and the highest intensity doppler spectrum was visualized . cbfv tracings were consistent with minimal to no drift in signal intensity , as the transducer did not move or need replacement during the monitoring periods . continuous pco2 monitoring was performed with a neotrend system ( diametrics medical ltd . , st . paul , mn ) or a transcutaneous blood gas monitor ( microgas 7650 rapid , radiometer , westlake , oh ) . neotrend was a system that continuously monitored arterial blood gases and temperatures , using fiber optic technology , without the need for blood withdrawal ; it is no longer being produced . briefly , for transcutaneous pco2 monitoring , the skin on either side of the chest was prepped with a small amount of aquaphor emollient ointment ( beiersdorf , norwalk , ct ) . a double - sided adhesive ring of tape was applied to the skin , and one drop of an electrolyte solution ( radiometer ) was placed into the center of the adhesive ring . after 5 min of continuous monitoring ( by either system ) , an arterial blood gas measurement was obtained from the umbilical arterial catheter and processed by the nicu laboratory . the neotrend and/or transcutaneous blood gas monitor was then calibrated with the pco2 laboratory result ( the change was rarely > 3 mm hg ) . analog signals from the bp monitor ( 112 hz ) , transcranial doppler ( 100 hz ) , and the blood gas monitors ( 1 hz ) were simultaneously collected with a data acquisition system ( powerlab 8 channel , adinstruments , mountain view , ca ) . cyclic waveform analyses were performed to calculate mabp ( average amplitude of the bp waveform over one cycle ) and systolic and diastolic bps ( maximum and minimum values of the bp cycle , respectively ) . fast fourier analysis was performed on the cbfv signal to determine the systolic , diastolic , and mean cbf velocities . for each infant , time and date of birth , whether or not their mother received antenatal steroids , birth weight , gestational age , race , gender , apgar scores at 1 and 5 min , presence of severe ivh , survival to hospital discharge , and postnatal age at the time of physiological monitoring was obtained from the research database . gestational age was estimated based on obstetrical criteria and neonatal criteria ; the neonatal estimate was used if the two estimates differed by > 2 weeks . severe ( grades iii and iv ) ivh was determined using the staging criteria of papile et al , based on any cranial ultrasound during the hospitalization . hypotension was defined as mabp in mm hg < gestational age in weeks for 30 min . optimal bp was defined as mabp in mm hg 15% above gestational age in weeks for 30 min . briefly , cbfv reactivity is expressed as the percent change of cbfv that varies per mm hg change in mabp during some time period . when the 95% confidence interval ( ci ) for mean cbfv reactivity includes 0 , i.e. , no statistically significant change in cbfv compared to changes in mabp , intact cerebral autoregulation is implied . in contrast , if the mean percent change in cbfv / mm hg change in mabp > 0 , and the 95% ci does not include 0 , then this implies impaired cerebral autoregulation . resistive index ( ri ) was defined as : ( [ systolic cbfv - diastolic cbfv]/systolic cbfv)100 . physiological variables for the hypotensive infants were analyzed before and after treatment with dopamine ( table ii ) . baseline values for mabp , mean cbfv , pco2 , and ri were determined from ~15 min of continuous monitoring that preceded treatment with dopamine . after optimal mabp was reached , mabp , mean cbfv , pco2 , and ri were again determined . comparisons of physiological variables before and after dopamine were performed by paired t - test . cbf reactivity was determined for each infant by comparing baseline and optimal mabp values after dopamine for mean cbfv and mabp , respectively , and then determined for the group of hypotensive infants . fifteen hypotensive elbw infants ( 625 174 g , 24 ( 23 to 24.8 weeks ) were studied . eight infants died ( 5 had severe ivh ; 3 died before having a cranial ultrasound ) . other characteristics of the study population are shown in table i. there were significant increases in mabp after treatment with dopamine ( p<0.001 ) , which was expected ( table 2 ) . with the exception of one infant who died secondary to complications from unremitting bilateral pneumothoraces none of the infants received fluid boluses , other vasopressors , or hydrocortisone before dopamine treatment . the increased mabp was accompanied by significant increases in mean cbfv ( 10.9 3.7 at baseline vs 15.7 5.7 cm / s after optimal mabp was reached ; p=0.001 ) . dopamine - treated infants also displayed significant decreases in ri after optimal mabp was reached , from 74.4% to 59.7% ( p=0.001 ) . the mean cbf reactivity ( 95% ci ) was 3.9 ( 1.6 to 6.2 ) % mm hg . the median ( 25 , 75 percentile ) dose of dopamine was 10 ( 7.5 , 14.4 ) g / kg / min to get to the optimal mabp . the dose of dopamine to obtain the optimal mabp was 5 ( n = 1 ) , 7.5 ( n = 4 ) , 10 ( n = 3 ) , 12.5 ( n = 2 ) , 15 ( n = 2 ) , and 17.5 g / kg / min ( n = 2 ) , respectively . one infant did not reach optimal mabp , and did not have dopamine increased beyond 5 g / kg / min . an example of the effects of dopamine treatment on mean cbfv , paco2 , and mabp from a hypotensive premature infant is shown in the figure . dopamine treatment ( 5 g / kg / min ) was initiated 20 min after beginning monitoring . mabp and mean cbfv suddenly and simultaneously surged soon after dopamine administration , possibly due to the infant s response to dopamine once the drug traversed through the medication tubing reaching the infant . mabp and mean cbfv subsequently returned to baseline , and dopamine was increased to 7.5 g / kg / min ( at about 40 min ) . the dopamine was increased to 10 g / kg / min ( at 66 min ) , with a resultant smaller surge in mabp that was again mirrored by a simultaneous surge in cbfv . mabp then returned to the hypotensive baseline , and dopamine was increased to 12.5 g / kg / min ( at 83 min ) . at this point , there was an abrupt , prolonged increase in mabp , reaching hypertensive levels ; this was mirrored by increases in mean cbfv above the 90 percentile . due to the hypertension , dopamine the major aim of our study was to examine cerebral hemodynamics during dopamine infusion in hypotensive ventilated elbw infants on the first day of life . we observed a simultaneous significant increase in mean cbfv as mabp increased to an optimal level during dopamine infusion . the increase in mean cbfv could be because the cerebral vasculature remained pressure - passive , or that the increased mabp was above the upper limit of autoregulation , or alternatively because dopamine could have changed cerebral vessel diameter . mean cbf reactivity for these infants was consistent with ~2 to 4%mm hg previously reported for hypotensive vlbw infants and in premature infants with severe intracranial hemorrhage . since the 95% ci for mean cbf reactivity did not include 0 , we inferred that these elbw infants had a pressure - passive cerebral circulation and impaired cerebral autoregulation during dopamine infusion . although determination of vascular resistance from changes in ris are controversial , significant decreases in ri were noted after optimal mabp was reached ; our findings are consistent with previous studies . thus , hypotensive elbw infants who have their bp optimized during dopamine treatment likely have impaired cerebral autoregulation and increased cbf . in all , 9 infants died and/or developed severe ivh . we recognize that the rates of mortality and morbidity observed in our study are quite high . perhaps these hypotensive infants represented a sicker population of elbw premature infants who were inherently at higher risk for ivh and death . treated hypotension has previously been reported to be associated with poor outcomes , however , it is not clear whether hypotension , the treatment for hypotension , or some other unrecognized variables were to blame for the adverse outcomes . our observations are consistent with previous reports showing that increasing mabp in hypotensive premature infants does not restore intact cerebral autoregulation . in the first comparable study of dopamine s effects on cerebral hemodynamics in 5 hypotensive premature infants on the first day of life ( 6 weeks more mature and more than double the birth weight of our infants ) , cbfv increased but returned to baseline by 5090 min after mabp was increased with dopamine . thus , it was concluded that while cerebral autoregulation was impaired during dopamine treatment , it was not totally ineffective . the next study included a heterogeneous sample of 11 hypotensive infants ( birth weight 5402100 g and gestational age 2432 weeks ) monitored at 13 hrs of age . they concluded that dopamine treatment for hypotension did not restore intact autoregulation ; however , since treatment included fluid boluses , dopamine , and dobutamine , it is unclear exactly how the results relate directly to dopamine s effect on cerebral hemodynamics . in a subsequent study using higher initial and maximum dopamine doses than ours , it was observed that 12 hypotensive elbw infants on the first day of life had impaired cerebral autoregulation because cbf correlated with mabp before and after dopamine ( 1030 g / kg / min ) treatment . since cerebral autoregulation remained impaired after increasing mabp with dopamine into an adequate range , the authors concluded that careful physiological monitoring was necessary during dopamine infusions . in a later study , 28 hypotensive vlbw infants treated with dopamine to an optimal mabp had changes in cerebral intravascular oxygenation ( hbd , reflecting cerebral perfusion changes ) that were significantly correlated with increases in mabp , i.e. , they had impaired cerebral autoregulation . lastly , it was observed in 17 hypotensive premature infants ( < 32 weeks gestation ) with patent ductus arteriosus on day of life 5 ( range 125 days ) that ri decreased significantly after dopamine treatment . alternatively , one dopamine - cerebral hemodynamic study , however , failed to find a simultaneous increase in cbfv in hypotensive vlbw infants when mabp was raised to a normal range . the discrepancy between this study and the others is unclear , but could be due to the use of intermittent cbfv monitoring where an increase could have been missed . first , this is an observational study evaluating cbfv in hypotensive elbw infants during treatment using dopamine , with a somewhat small sample size . while it is quite difficult to accrue and enroll sufficient numbers of hypotensive elbw infants into studies , as shown by the similar low sample sizes in other studies ( that mostly included more mature and heavier infants ) , we evaluated cerebral hemodynamics during dopamine therapy in the largest number of hypotensive elbw infants on the first day of life ever studied . in addition , we used transcranial doppler ultrasound measurements of cbfv instead of more direct measures of cbf . despite concerns that cbfv measurements may not be a reliable proxy for cbf due to possible vessel diameter changes , good correlations have been observed between relative changes of cbfv and near - infrared spectroscopy measures of cerebral hemodynamics . thirdly , the first - line treatment for non - hypovolemic and non - septic hypotensive elbw infants in our neonatal intensive care unit ( nicu ) was dopamine infusions beginning at 5 g / kg / min and incrementally increasing the dose by 2.5 g / kg / min to get to an optimal mabp . many clinicians , however , use fluid boluses first , and thus our observations may not be generalizable to other nicus . it is also possible that our stepwise doses of dopamine were too high and may have contributed to excessively high cbfv in some infants . it may be prudent , for example , to start dopamine at 5 g / kg / min and increase by 1 g / kg / min increments to prevent overshooting of cbfv . further , while it would have been illuminating to determine autoregulatory capacity during hypotension ( prior to receiving dopamine ) , individual mabp varied little during baseline periods making the calculation of cbfv reactivity unfeasible . we also did not assess whether there was a patent ductus arteriosus , or the degree and direction of blood flow through the patent ductus arteriosus , or how a patent ductus arteriosus would affect ri . bouissou et al observed that infants with a significant pda had a similar decrease in cerebral arterial ri following dopamine therapy , and presumably , most elbw infants have a patent ductus arteriosus on the first day . a final limitation is that we did not evaluate the effects of hypotension on other organs , such as the kidneys or heart . while hemodynamics to other organs will be important for future studies , we focused on the brain because disturbances of cbfv have been associated with brain injuries in premature infants . in conclusion , in hypotensive elbw infants on the first day of life with baseline gestational age - appropriate cbfv and ri , cbfv increased pressure - passively as mabp was optimized during treatment with dopamine . it is plausible that increasing bp in this manner with the use of dopamine in elbw infants could potentially place them at risk for brain injury . further research is needed to evaluate the appropriate indications for the use of dopamine in hypotensive elbw infants , and investigations comparing permissive hypotension vs treated hypotension in elbw infants are warranted .

objectiveto evaluate cerebral hemodynamics during dopamine treatment in hypotensive ( mean arterial blood pressure [ mabp ] < gestational age ) elbw infants.study designcontinuous monitoring of cerebral blood flow velocity ( cbfv ) , mabp , and pco2 was performed in hypotensive elbw infants on the first day of life , beginning with ~15 min baseline reading and continued during advancing dopamine infusion until mabp was optimized . physiologic variables and cbfv reactivity were compared before and after mabp was optimized.resultfifteen hypotensive elbw infants ( 625 174 g ; 24 [ 23 to 24.8 ] weeks ) were studied . mean cbfv increased from 10.9 3.7 to 15.7 5.7 cm / s ( p=0.001 ) simultaneously as mabp increased from 22.3 2.8 to 35.2 9.7 mm hg ( p<0.001 ) . mean cbfv reactivity ( 95% ci ) was 3.9 ( 1.6 to 6.2 ) % mm hg1 . nine infants died and/or developed severe intraventricular hemorrhage ( ivh).conclusionmean cbfv increased pressure - passively as mabp was optimized by dopamine treatment in very sick hypotensive elbw infants on the first day of life .

<s>[INST]the study was approved by the university of arkansas for medical sciences institutional review board . elbw infants born at the university of arkansas for medical sciences between january 2006 and may 2007 were eligible for this study if they received mechanical ventilation for respiratory distress syndrome , had umbilical arterial and venous catheters placed during newborn stabilization , developed hypotension on the first day of life , and were already involved in a physiological study evaluating cerebral autoregulation capacity . infants with major congenital anomalies , obvious hypovolemia , early - onset sepsis , or air leaks and infants who received fluid boluses , vasopressors , or hydrocortisone ( before study procedures ) were excluded . when an elbw infant became hypotensive , at any time ( including the middle of the night ) of any day ( including weekends and holidays ) , one of two research assistants initiated continuous monitoring of bp , cbfv , and pco2 . the monitoring sessions often lasted 23 hrs , beginning with a ~15 min baseline period ( before dopamine treatment ) . the dopamine infusion was begun at 5 g / kg / min ( in d5w at 0.2 ml / hr ) and increased stepwise by 2.5 g / kg / min ( 0.1 ml / hr ) increments ( 7.5 , 10 , 12.5 , 15 , 17.5 , and 20 ) every 20 min until mabp was optimized . the dopamine was always infused with maintenance intravenous fluids through the umbilical venous catheter using specialized infusion pumps ( baxter as50 , baxter healthcare corporation , deerfield , il ) . paul , mn ; or argyle / tyco healthcare / kendall , mansfield , ma ) attached to a bp transducer ( transpac iv , abbott critical care systems , north chicago , il ) . cbfv in the right middle cerebral artery was continuously monitored using transcranial doppler ultrasound ( nicolet biomedical pioneer , madison , wi ) . a lightweight 2-mhz pulsed - wave button transducer was placed transtemporally , anterior to the ear and above the zygomatic arch , and held in place by an appropriately sized crocheted hat ( courtesy of the arkansas homemakers extension council ) . a depth of 1622 mm was used to study the proximal portion of the middle cerebral artery . a 100-hz low - pass filter was used to dampen noise from the vessel wall . to obtain reliable cbfv measurements , the transducer was placed with the minimum angle of insonation , accomplished when the highest intensity acoustic signal was perceived and the highest intensity doppler spectrum was visualized . cbfv tracings were consistent with minimal to no drift in signal intensity , as the transducer did not move or need replacement during the monitoring periods . continuous pco2 monitoring was performed with a neotrend system ( diametrics medical ltd . , st . paul , mn ) or a transcutaneous blood gas monitor ( microgas 7650 rapid , radiometer , westlake , oh ) . neotrend was a system that continuously monitored arterial blood gases and temperatures , using fiber optic technology , without the need for blood withdrawal ; it is no longer being produced . briefly , for transcutaneous pco2 monitoring , the skin on either side of the chest was prepped with a small amount of aquaphor emollient ointment ( beiersdorf , norwalk , ct ) . a double - sided adhesive ring of tape was applied to the skin , and one drop of an electrolyte solution ( radiometer ) was placed into the center of the adhesive ring . after 5 min of continuous monitoring ( by either system ) , an arterial blood gas measurement was obtained from the umbilical arterial catheter and processed by the nicu laboratory . the neotrend and/or transcutaneous blood gas monitor was then calibrated with the pco2 laboratory result ( the change was rarely > 3 mm hg ) . analog signals from the bp monitor ( 112 hz ) , transcranial doppler ( 100 hz ) , and the blood gas monitors ( 1 hz ) were simultaneously collected with a data acquisition system ( powerlab 8 channel , adinstruments , mountain view , ca ) . cyclic waveform analyses were performed to calculate mabp ( average amplitude of the bp waveform over one cycle ) and systolic and diastolic bps ( maximum and minimum values of the bp cycle , respectively ) . fast fourier analysis was performed on the cbfv signal to determine the systolic , diastolic , and mean cbf velocities . for each infant , time and date of birth , whether or not their mother received antenatal steroids , birth weight , gestational age , race , gender , apgar scores at 1 and 5 min , presence of severe ivh , survival to hospital discharge , and postnatal age at the time of physiological monitoring was obtained from the research database . gestational age was estimated based on obstetrical criteria and neonatal criteria ; the neonatal estimate was used if the two estimates differed by > 2 weeks . severe ( grades iii and iv ) ivh was determined using the staging criteria of papile et al , based on any cranial ultrasound during the hospitalization . hypotension was defined as mabp in mm hg < gestational age in weeks for 30 min . optimal bp was defined as mabp in mm hg 15% above gestational age in weeks for 30 min . briefly , cbfv reactivity is expressed as the percent change of cbfv that varies per mm hg change in mabp during some time period . when the 95% confidence interval ( ci ) for mean cbfv reactivity includes 0 , i.e. , no statistically significant change in cbfv compared to changes in mabp , intact cerebral autoregulation is implied . in contrast , if the mean percent change in cbfv / mm hg change in mabp > 0 , and the 95% ci does not include 0 , then this implies impaired cerebral autoregulation . resistive index ( ri ) was defined as : ( [ systolic cbfv - diastolic cbfv]/systolic cbfv)100 . physiological variables for the hypotensive infants were analyzed before and after treatment with dopamine ( table ii ) . baseline values for mabp , mean cbfv , pco2 , and ri were determined from ~15 min of continuous monitoring that preceded treatment with dopamine . after optimal mabp was reached , mabp , mean cbfv , pco2 , and ri were again determined . comparisons of physiological variables before and after dopamine were performed by paired t - test . cbf reactivity was determined for each infant by comparing baseline and optimal mabp values after dopamine for mean cbfv and mabp , respectively , and then determined for the group of hypotensive infants . elbw infants born at the university of arkansas for medical sciences between january 2006 and may 2007 were eligible for this study if they received mechanical ventilation for respiratory distress syndrome , had umbilical arterial and venous catheters placed during newborn stabilization , developed hypotension on the first day of life , and were already involved in a physiological study evaluating cerebral autoregulation capacity . infants with major congenital anomalies , obvious hypovolemia , early - onset sepsis , or air leaks and infants who received fluid boluses , vasopressors , or hydrocortisone ( before study procedures ) were excluded . when an elbw infant became hypotensive , at any time ( including the middle of the night ) of any day ( including weekends and holidays ) , one of two research assistants initiated continuous monitoring of bp , cbfv , and pco2 . the monitoring sessions often lasted 23 hrs , beginning with a ~15 min baseline period ( before dopamine treatment ) . the dopamine infusion was begun at 5 g / kg / min ( in d5w at 0.2 ml / hr ) and increased stepwise by 2.5 g / kg / min ( 0.1 ml / hr ) increments ( 7.5 , 10 , 12.5 , 15 , 17.5 , and 20 ) every 20 min until mabp was optimized . the dopamine was always infused with maintenance intravenous fluids through the umbilical venous catheter using specialized infusion pumps ( baxter as50 , baxter healthcare corporation , deerfield , il ) . paul , mn ; or argyle / tyco healthcare / kendall , mansfield , ma ) attached to a bp transducer ( transpac iv , abbott critical care systems , north chicago , il ) . cbfv in the right middle cerebral artery was continuously monitored using transcranial doppler ultrasound ( nicolet biomedical pioneer , madison , wi ) . a lightweight 2-mhz pulsed - wave button transducer was placed transtemporally , anterior to the ear and above the zygomatic arch , and held in place by an appropriately sized crocheted hat ( courtesy of the arkansas homemakers extension council ) . a depth of 1622 mm was used to study the proximal portion of the middle cerebral artery . a 100-hz low - pass filter was used to dampen noise from the vessel wall . to obtain reliable cbfv measurements , the transducer was placed with the minimum angle of insonation , accomplished when the highest intensity acoustic signal was perceived and the highest intensity doppler spectrum was visualized . cbfv tracings were consistent with minimal to no drift in signal intensity , as the transducer did not move or need replacement during the monitoring periods . continuous pco2 monitoring was performed with a neotrend system ( diametrics medical ltd . , st . paul , mn ) or a transcutaneous blood gas monitor ( microgas 7650 rapid , radiometer , westlake , oh ) . neotrend was a system that continuously monitored arterial blood gases and temperatures , using fiber optic technology , without the need for blood withdrawal ; it is no longer being produced . briefly , for transcutaneous pco2 monitoring , the skin on either side of the chest was prepped with a small amount of aquaphor emollient ointment ( beiersdorf , norwalk , ct ) . a double - sided adhesive ring of tape was applied to the skin , and one drop of an electrolyte solution ( radiometer ) was placed into the center of the adhesive ring . after 5 min of continuous monitoring ( by either system ) , an arterial blood gas measurement was obtained from the umbilical arterial catheter and processed by the nicu laboratory . the neotrend and/or transcutaneous blood gas monitor was then calibrated with the pco2 laboratory result ( the change was rarely > 3 mm hg ) . analog signals from the bp monitor ( 112 hz ) , transcranial doppler ( 100 hz ) , and the blood gas monitors ( 1 hz ) were simultaneously collected with a data acquisition system ( powerlab 8 channel , adinstruments , mountain view , ca ) . cyclic waveform analyses were performed to calculate mabp ( average amplitude of the bp waveform over one cycle ) and systolic and diastolic bps ( maximum and minimum values of the bp cycle , respectively ) . fast fourier analysis was performed on the cbfv signal to determine the systolic , diastolic , and mean cbf velocities . for each infant , time and date of birth , whether or not their mother received antenatal steroids , birth weight , gestational age , race , gender , apgar scores at 1 and 5 min , presence of severe ivh , survival to hospital discharge , and postnatal age at the time of physiological monitoring was obtained from the research database . gestational age was estimated based on obstetrical criteria and neonatal criteria ; the neonatal estimate was used if the two estimates differed by > 2 weeks . severe ( grades iii and iv ) ivh was determined using the staging criteria of papile et al , based on any cranial ultrasound during the hospitalization . hypotension was defined as mabp in mm hg < gestational age in weeks for 30 min . optimal bp was defined as mabp in mm hg 15% above gestational age in weeks for 30 min . briefly , cbfv reactivity is expressed as the percent change of cbfv that varies per mm hg change in mabp during some time period . when the 95% confidence interval ( ci ) for mean cbfv reactivity includes 0 , i.e. , no statistically significant change in cbfv compared to changes in mabp , intact cerebral autoregulation is implied . in contrast , if the mean percent change in cbfv / mm hg change in mabp > 0 , and the 95% ci does not include 0 , then this implies impaired cerebral autoregulation . resistive index ( ri ) was defined as : ( [ systolic cbfv - diastolic cbfv]/systolic cbfv)100 . physiological variables for the hypotensive infants were analyzed before and after treatment with dopamine ( table ii ) . baseline values for mabp , mean cbfv , pco2 , and ri were determined from ~15 min of continuous monitoring that preceded treatment with dopamine . after optimal mabp was reached , mabp , mean cbfv , pco2 , and ri were again determined . comparisons of physiological variables before and after dopamine were performed by paired t - test . cbf reactivity was determined for each infant by comparing baseline and optimal mabp values after dopamine for mean cbfv and mabp , respectively , and then determined for the group of hypotensive infants . fifteen hypotensive elbw infants ( 625 174 g , 24 ( 23 to 24.8 weeks ) were studied . eight infants died ( 5 had severe ivh ; 3 died before having a cranial ultrasound ) . other characteristics of the study population are shown in table i. there were significant increases in mabp after treatment with dopamine ( p<0.001 ) , which was expected ( table 2 ) . with the exception of one infant who died secondary to complications from unremitting bilateral pneumothoraces none of the infants received fluid boluses , other vasopressors , or hydrocortisone before dopamine treatment . the increased mabp was accompanied by significant increases in mean cbfv ( 10.9 3.7 at baseline vs 15.7 5.7 cm / s after optimal mabp was reached ; p=0.001 ) . dopamine - treated infants also displayed significant decreases in ri after optimal mabp was reached , from 74.4% to 59.7% ( p=0.001 ) . the mean cbf reactivity ( 95% ci ) was 3.9 ( 1.6 to 6.2 ) % mm hg . the median ( 25 , 75 percentile ) dose of dopamine was 10 ( 7.5 , 14.4 ) g / kg / min to get to the optimal mabp . the dose of dopamine to obtain the optimal mabp was 5 ( n = 1 ) , 7.5 ( n = 4 ) , 10 ( n = 3 ) , 12.5 ( n = 2 ) , 15 ( n = 2 ) , and 17.5 g / kg / min ( n = 2 ) , respectively . one infant did not reach optimal mabp , and did not have dopamine increased beyond 5 g / kg / min . an example of the effects of dopamine treatment on mean cbfv , paco2 , and mabp from a hypotensive premature infant is shown in the figure . dopamine treatment ( 5 g / kg / min ) was initiated 20 min after beginning monitoring . mabp and mean cbfv suddenly and simultaneously surged soon after dopamine administration , possibly due to the infant s response to dopamine once the drug traversed through the medication tubing reaching the infant . mabp and mean cbfv subsequently returned to baseline , and dopamine was increased to 7.5 g / kg / min ( at about 40 min ) . the dopamine was increased to 10 g / kg / min ( at 66 min ) , with a resultant smaller surge in mabp that was again mirrored by a simultaneous surge in cbfv . mabp then returned to the hypotensive baseline , and dopamine was increased to 12.5 g / kg / min ( at 83 min ) . at this point , there was an abrupt , prolonged increase in mabp , reaching hypertensive levels ; this was mirrored by increases in mean cbfv above the 90 percentile . due to the hypertension , dopamine the major aim of our study was to examine cerebral hemodynamics during dopamine infusion in hypotensive ventilated elbw infants on the first day of life . we observed a simultaneous significant increase in mean cbfv as mabp increased to an optimal level during dopamine infusion . the increase in mean cbfv could be because the cerebral vasculature remained pressure - passive , or that the increased mabp was above the upper limit of autoregulation , or alternatively because dopamine could have changed cerebral vessel diameter . mean cbf reactivity for these infants was consistent with ~2 to 4%mm hg previously reported for hypotensive vlbw infants and in premature infants with severe intracranial hemorrhage . since the 95% ci for mean cbf reactivity did not include 0 , we inferred that these elbw infants had a pressure - passive cerebral circulation and impaired cerebral autoregulation during dopamine infusion . although determination of vascular resistance from changes in ris are controversial , significant decreases in ri were noted after optimal mabp was reached ; our findings are consistent with previous studies . thus , hypotensive elbw infants who have their bp optimized during dopamine treatment likely have impaired cerebral autoregulation and increased cbf . in all , 9 infants died and/or developed severe ivh . we recognize that the rates of mortality and morbidity observed in our study are quite high . perhaps these hypotensive infants represented a sicker population of elbw premature infants who were inherently at higher risk for ivh and death . treated hypotension has previously been reported to be associated with poor outcomes , however , it is not clear whether hypotension , the treatment for hypotension , or some other unrecognized variables were to blame for the adverse outcomes . our observations are consistent with previous reports showing that increasing mabp in hypotensive premature infants does not restore intact cerebral autoregulation . in the first comparable study of dopamine s effects on cerebral hemodynamics in 5 hypotensive premature infants on the first day of life ( 6 weeks more mature and more than double the birth weight of our infants ) , cbfv increased but returned to baseline by 5090 min after mabp was increased with dopamine . thus , it was concluded that while cerebral autoregulation was impaired during dopamine treatment , it was not totally ineffective . the next study included a heterogeneous sample of 11 hypotensive infants ( birth weight 5402100 g and gestational age 2432 weeks ) monitored at 13 hrs of age . they concluded that dopamine treatment for hypotension did not restore intact autoregulation ; however , since treatment included fluid boluses , dopamine , and dobutamine , it is unclear exactly how the results relate directly to dopamine s effect on cerebral hemodynamics . in a subsequent study using higher initial and maximum dopamine doses than ours , it was observed that 12 hypotensive elbw infants on the first day of life had impaired cerebral autoregulation because cbf correlated with mabp before and after dopamine ( 1030 g / kg / min ) treatment . since cerebral autoregulation remained impaired after increasing mabp with dopamine into an adequate range , the authors concluded that careful physiological monitoring was necessary during dopamine infusions . in a later study , 28 hypotensive vlbw infants treated with dopamine to an optimal mabp had changes in cerebral intravascular oxygenation ( hbd , reflecting cerebral perfusion changes ) that were significantly correlated with increases in mabp , i.e. , they had impaired cerebral autoregulation . lastly , it was observed in 17 hypotensive premature infants ( < 32 weeks gestation ) with patent ductus arteriosus on day of life 5 ( range 125 days ) that ri decreased significantly after dopamine treatment . alternatively , one dopamine - cerebral hemodynamic study , however , failed to find a simultaneous increase in cbfv in hypotensive vlbw infants when mabp was raised to a normal range . the discrepancy between this study and the others is unclear , but could be due to the use of intermittent cbfv monitoring where an increase could have been missed . first , this is an observational study evaluating cbfv in hypotensive elbw infants during treatment using dopamine , with a somewhat small sample size . while it is quite difficult to accrue and enroll sufficient numbers of hypotensive elbw infants into studies , as shown by the similar low sample sizes in other studies ( that mostly included more mature and heavier infants ) , we evaluated cerebral hemodynamics during dopamine therapy in the largest number of hypotensive elbw infants on the first day of life ever studied . in addition , we used transcranial doppler ultrasound measurements of cbfv instead of more direct measures of cbf . despite concerns that cbfv measurements may not be a reliable proxy for cbf due to possible vessel diameter changes , good correlations have been observed between relative changes of cbfv and near - infrared spectroscopy measures of cerebral hemodynamics . thirdly , the first - line treatment for non - hypovolemic and non - septic hypotensive elbw infants in our neonatal intensive care unit ( nicu ) was dopamine infusions beginning at 5 g / kg / min and incrementally increasing the dose by 2.5 g / kg / min to get to an optimal mabp . many clinicians , however , use fluid boluses first , and thus our observations may not be generalizable to other nicus . it is also possible that our stepwise doses of dopamine were too high and may have contributed to excessively high cbfv in some infants . it may be prudent , for example , to start dopamine at 5 g / kg / min and increase by 1 g / kg / min increments to prevent overshooting of cbfv . further , while it would have been illuminating to determine autoregulatory capacity during hypotension ( prior to receiving dopamine ) , individual mabp varied little during baseline periods making the calculation of cbfv reactivity unfeasible . we also did not assess whether there was a patent ductus arteriosus , or the degree and direction of blood flow through the patent ductus arteriosus , or how a patent ductus arteriosus would affect ri . bouissou et al observed that infants with a significant pda had a similar decrease in cerebral arterial ri following dopamine therapy , and presumably , most elbw infants have a patent ductus arteriosus on the first day . a final limitation is that we did not evaluate the effects of hypotension on other organs , such as the kidneys or heart . while hemodynamics to other organs will be important for future studies , we focused on the brain because disturbances of cbfv have been associated with brain injuries in premature infants . in conclusion , in hypotensive elbw infants on the first day of life with baseline gestational age - appropriate cbfv and ri , cbfv increased pressure - passively as mabp was optimized during treatment with dopamine . it is plausible that increasing bp in this manner with the use of dopamine in elbw infants could potentially place them at risk for brain injury . further research is needed to evaluate the appropriate indications for the use of dopamine in hypotensive elbw infants , and investigations comparing permissive hypotension vs treated hypotension in elbw infants are warranted .[/INST]objectiveto evaluate cerebral hemodynamics during dopamine treatment in hypotensive ( mean arterial blood pressure [ mabp ] < gestational age ) elbw infants.study designcontinuous monitoring of cerebral blood flow velocity ( cbfv ) , mabp , and pco2 was performed in hypotensive elbw infants on the first day of life , beginning with ~15 min baseline reading and continued during advancing dopamine infusion until mabp was optimized . physiologic variables and cbfv reactivity were compared before and after mabp was optimized.resultfifteen hypotensive elbw infants ( 625 174 g ; 24 [ 23 to 24.8 ] weeks ) were studied . mean cbfv increased from 10.9 3.7 to 15.7 5.7 cm / s ( p=0.001 ) simultaneously as mabp increased from 22.3 2.8 to 35.2 9.7 mm hg ( p<0.001 ) . mean cbfv reactivity ( 95% ci ) was 3.9 ( 1.6 to 6.2 ) % mm hg1 . nine infants died and/or developed severe intraventricular hemorrhage ( ivh).conclusionmean cbfv increased pressure - passively as mabp was optimized by dopamine treatment in very sick hypotensive elbw infants on the first day of life .</s>

SECTION 1. SHORT TITLE; TABLE OF CONTENTS. (a) Short Title.--This Act may be cited as the ``Nevada Native Nations Land Act''. (b) Table of Contents.--The table of contents for this Act is as follows: Sec. 1. Short title; table of contents. Sec. 2. Definition of Secretary. TITLE I--ELKO MOTOCROSS LAND CONVEYANCE Sec. 101. Definitions. Sec. 102. Conveyance of land to county. TITLE II--CONVEYANCE OF LAND TO INDIAN TRIBES Sec. 201. Conveyance of land to be held in trust for certain Indian tribes. Sec. 202. Administration. SEC. 2. DEFINITION OF SECRETARY. In this Act, the term ``Secretary'' means the Secretary of the Interior. TITLE I--ELKO MOTOCROSS LAND CONVEYANCE SEC. 101. DEFINITIONS. In this title: (1) City.--The term ``city'' means the city of Elko, Nevada. (2) County.--The term ``county'' means the county of Elko, Nevada. (3) Map.--The term ``map'' means the map entitled ``Elko Motocross Park'' and dated January 9, 2010. SEC. 102. CONVEYANCE OF LAND TO COUNTY. (a) In General.--As soon as practicable after the date of enactment of this Act, subject to valid existing rights and such terms and conditions as the Secretary determines to be necessary and after agreement from the county, the Secretary shall convey to the county, without consideration, all right, title, and interest of the United States in and to the land described in subsection (b). (b) Description of Land.--The land referred to in subsection (a) consists of approximately 275 acres of land managed by the Bureau of Land Management, Elko District, Nevada, as generally depicted on the map as ``Elko Motocross Park''. (c) Map and Legal Description.-- (1) In general.--As soon as practicable after the date of enactment of this Act, the Secretary shall finalize the legal description of the parcel to be conveyed under this section. (2) Minor errors.--The Secretary may correct any minor error in-- (A) the map; or (B) the legal description. (3) Availability.--The map and legal description shall be on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (d) Use of Conveyed Land.--The land conveyed under this section shall be used only as a motocross, bicycle, off-highway vehicle, or stock car racing area, or for any other public purpose consistent with uses allowed under the Act of June 14, 1926 (commonly known as the ``Recreation and Public Purposes Act'') (43 U.S.C. 869 et seq.). (e) Administrative Costs.--The Secretary shall require the county to pay all survey costs and other administrative costs necessary for the preparation and completion of any patents for, and transfers of title to, the land described in subsection (b). (f) Reversion.--If the land conveyed under this section ceases to be used for a public purpose in accordance with subsection (d), the land shall, at the discretion of the Secretary, revert to the United States. TITLE II--CONVEYANCE OF LAND TO INDIAN TRIBES SEC. 201. CONVEYANCE OF LAND TO BE HELD IN TRUST FOR CERTAIN INDIAN TRIBES. (a) Te-Moak Tribe of Western Shoshone Indians of Nevada (Elko Band).-- (1) Definition of map.--In this subsection, the term ``map'' means the map entitled ``Te-moak Tribal Land Expansion'', dated September 30, 2008, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Te-Moak Tribe of Western Shoshone Indians of Nevada (Elko Band); and (B) shall be part of the reservation of the Te-Moak Tribe of Western Shoshone Indians of Nevada (Elko Band). (3) Description of land.--The land referred to in paragraph (2) is the approximately 373 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``Lands to be Held in Trust''. (b) Conveyance of Land to Be Held in Trust for the Fort McDermitt Paiute and Shoshone Tribe.-- (1) Definition of map.--In this subsection, the term ``map'' means the map entitled ``Fort McDermitt Indian Reservation Expansion Act'', dated February 21, 2013, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Fort McDermitt Paiute and Shoshone Tribe; and (B) shall be part of the reservation of the Fort McDermitt Paiute and Shoshone Tribe. (3) Description of land.--The land referred to in paragraph (2) is the approximately 19,094 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``Reservation Expansion Lands''. (c) Conveyance of Land to Be Held in Trust for the Shoshone Paiute Tribes.-- (1) Definition of map.--In this subsection, the term ``map'' means the map entitled ``Mountain City Administrative Site Proposed Acquisition'', dated July 29, 2013, and on file and available for public inspection in the appropriate offices of the Forest Service. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Shoshone Paiute Tribes of the Duck Valley Indian Reservation; and (B) shall be part of the reservation of the Shoshone Paiute Tribes of the Duck Valley Indian Reservation. (3) Description of land.--The land referred to in paragraph (2) is the approximately 82 acres of land administered by the Forest Service as generally depicted on the map as ``Proposed Acquisition Site''. (d) Transfer of Land to Be Held in Trust for the Summit Lake Paiute Tribe.-- (1) Definition of map.--In this section, the term ``map'' means the map entitled ``Summit Lake Indian Reservation Conveyance'', dated February 28, 2013, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Summit Lake Paiute Tribe; and (B) shall be part of the reservation of the Summit Lake Paiute Tribe. (3) Description of land.--The land referred to in paragraph (2) is the approximately 941 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``Reservation Conveyance Lands''. (e) Transfer of Land to Be Held in Trust for the Reno-Sparks Indian Colony Land.-- (1) Definition of map.--In this subsection, the term ``map'' means the map entitled ``Reno-Sparks Indian Colony Expansion'', dated June 11, 2014, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Reno-Sparks Indian Colony; and (B) shall be part of the reservation of the Reno- Sparks Indian Colony. (3) Description of land.--The land referred to in paragraph (2) is the approximately 13,434 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``RSIC Amended Boundary''. (f) Transfer of Land to Be Held in Trust for the Pyramid Lake Paiute Tribe.-- (1) Map.--In this subsection, the term ``map'' means the map entitled ``Pyramid Lake Indian Reservation Expansion'', dated July 26, 2014, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (1)-- (A) is held in trust by the United States for the benefit of the Pyramid Lake Paiute Tribe; and (B) shall be part of the reservation of the Pyramid Lake Paiute Tribe. (3) Description of land.--The land referred to in paragraph (2) is the approximately 11,719 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``Reservation Expansion Lands''. SEC. 202. ADMINISTRATION. (a) Survey.--Not later than 180 days after the date of enactment of this Act, the Secretary shall complete a survey of the boundary lines to establish the boundaries of the land taken into trust for each Indian tribe under section 201. (b) Use of Trust Land.-- (1) Gaming.--Land taken into trust under section 201 shall not be eligible, or considered to have been taken into trust, for class II gaming or class III gaming (as those terms are defined in section 4 of the Indian Gaming Regulatory Act (25 U.S.C. 2703)). (2) Thinning; landscape restoration.--With respect to the land taken into trust under section 201, the Secretary, in consultation and coordination with the applicable Indian tribe, may carry out any fuel reduction and other landscape restoration activities, including restoration of sage grouse habitat, on the land that is beneficial to the Indian tribe and the Bureau of Land Management. Passed the House of Representatives December 1, 2014. Attest: KAREN L. HAAS, Clerk.

Nevada Native Nations Land Act - Title I: Elko Motocross Land Conveyance - (Sec. 102) Directs the Department of the Interior to convey to Elko County, Nevada, without consideration, approximately 275 acres of land managed by the Bureau of Land Management (BLM), Elko District, Nevada, for use as a motocross, bicycle, off-highway vehicle, or stock car racing area or for other public purpose consistent with the Recreation and Public Purposes Act. Reverts the conveyed land to the United States if it ceases being used for a public purpose. Title II: Conveyance of Land To Indian Tribes - (Sec. 201) Declares that the United States holds approximately 373 acres of BLM administered land in trust for the Te-moak Tribe of Western Shoshone Indians of Nevada. Makes such land part of the Tribe's reservation. Declares further that the United States holds approximately 19,094 acres of BLM-administered land in trust for the Fort McDermitt Paiute and Shoshone Tribe. Makes such land part of that Tribe's reservation. Declares that the United States also holds in trust the following lands: for the Shoshone Paiute Tribes, approximately 82 acres of land administered by the Forest Service depicted as the &quot;Proposed Acquisition Site&quot; on a Mountain City Administrative Site Proposed Acquisition map; for the Summit Lake Paiute Tribe, approximately 941 acres of BLM-administered land depicted as &quot;Reservation Conveyance Lands&quot; on a Summit Lake Indian Reservation Conveyance map; for the Reno-Sparks Indian Colony, approximately 13,434 acres of BLM-administered land depicted as &quot;RSIC Amended Boundary&quot; on a Reno-Sparks Indian Colony Expansion map; and for the Pyramid Lake Paiute Tribe, approximately 11,719 acres of BLM-administered land depicted as &quot;Reservation Expansion Lands &quot; on a Pyramid Lake Indian Reservation Expansion map. (Sec. 202) Prohibits certain gaming on the lands taken into trust under this Act. Authorizes the Secretary of the Interior, with respect to such lands, to carry out any fuel reduction and other landscape restoration activities on the land, including restoration of sage grouse habitat, beneficial to the Indian tribe and the BLM.

<s>[INST]SECTION 1. SHORT TITLE; TABLE OF CONTENTS. (a) Short Title.--This Act may be cited as the ``Nevada Native Nations Land Act''. (b) Table of Contents.--The table of contents for this Act is as follows: Sec. 1. Short title; table of contents. Sec. 2. Definition of Secretary. TITLE I--ELKO MOTOCROSS LAND CONVEYANCE Sec. 101. Definitions. Sec. 102. Conveyance of land to county. TITLE II--CONVEYANCE OF LAND TO INDIAN TRIBES Sec. 201. Conveyance of land to be held in trust for certain Indian tribes. Sec. 202. Administration. SEC. 2. DEFINITION OF SECRETARY. In this Act, the term ``Secretary'' means the Secretary of the Interior. TITLE I--ELKO MOTOCROSS LAND CONVEYANCE SEC. 101. DEFINITIONS. In this title: (1) City.--The term ``city'' means the city of Elko, Nevada. (2) County.--The term ``county'' means the county of Elko, Nevada. (3) Map.--The term ``map'' means the map entitled ``Elko Motocross Park'' and dated January 9, 2010. SEC. 102. CONVEYANCE OF LAND TO COUNTY. (a) In General.--As soon as practicable after the date of enactment of this Act, subject to valid existing rights and such terms and conditions as the Secretary determines to be necessary and after agreement from the county, the Secretary shall convey to the county, without consideration, all right, title, and interest of the United States in and to the land described in subsection (b). (b) Description of Land.--The land referred to in subsection (a) consists of approximately 275 acres of land managed by the Bureau of Land Management, Elko District, Nevada, as generally depicted on the map as ``Elko Motocross Park''. (c) Map and Legal Description.-- (1) In general.--As soon as practicable after the date of enactment of this Act, the Secretary shall finalize the legal description of the parcel to be conveyed under this section. (2) Minor errors.--The Secretary may correct any minor error in-- (A) the map; or (B) the legal description. (3) Availability.--The map and legal description shall be on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (d) Use of Conveyed Land.--The land conveyed under this section shall be used only as a motocross, bicycle, off-highway vehicle, or stock car racing area, or for any other public purpose consistent with uses allowed under the Act of June 14, 1926 (commonly known as the ``Recreation and Public Purposes Act'') (43 U.S.C. 869 et seq.). (e) Administrative Costs.--The Secretary shall require the county to pay all survey costs and other administrative costs necessary for the preparation and completion of any patents for, and transfers of title to, the land described in subsection (b). (f) Reversion.--If the land conveyed under this section ceases to be used for a public purpose in accordance with subsection (d), the land shall, at the discretion of the Secretary, revert to the United States. TITLE II--CONVEYANCE OF LAND TO INDIAN TRIBES SEC. 201. CONVEYANCE OF LAND TO BE HELD IN TRUST FOR CERTAIN INDIAN TRIBES. (a) Te-Moak Tribe of Western Shoshone Indians of Nevada (Elko Band).-- (1) Definition of map.--In this subsection, the term ``map'' means the map entitled ``Te-moak Tribal Land Expansion'', dated September 30, 2008, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Te-Moak Tribe of Western Shoshone Indians of Nevada (Elko Band); and (B) shall be part of the reservation of the Te-Moak Tribe of Western Shoshone Indians of Nevada (Elko Band). (3) Description of land.--The land referred to in paragraph (2) is the approximately 373 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``Lands to be Held in Trust''. (b) Conveyance of Land to Be Held in Trust for the Fort McDermitt Paiute and Shoshone Tribe.-- (1) Definition of map.--In this subsection, the term ``map'' means the map entitled ``Fort McDermitt Indian Reservation Expansion Act'', dated February 21, 2013, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Fort McDermitt Paiute and Shoshone Tribe; and (B) shall be part of the reservation of the Fort McDermitt Paiute and Shoshone Tribe. (3) Description of land.--The land referred to in paragraph (2) is the approximately 19,094 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``Reservation Expansion Lands''. (c) Conveyance of Land to Be Held in Trust for the Shoshone Paiute Tribes.-- (1) Definition of map.--In this subsection, the term ``map'' means the map entitled ``Mountain City Administrative Site Proposed Acquisition'', dated July 29, 2013, and on file and available for public inspection in the appropriate offices of the Forest Service. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Shoshone Paiute Tribes of the Duck Valley Indian Reservation; and (B) shall be part of the reservation of the Shoshone Paiute Tribes of the Duck Valley Indian Reservation. (3) Description of land.--The land referred to in paragraph (2) is the approximately 82 acres of land administered by the Forest Service as generally depicted on the map as ``Proposed Acquisition Site''. (d) Transfer of Land to Be Held in Trust for the Summit Lake Paiute Tribe.-- (1) Definition of map.--In this section, the term ``map'' means the map entitled ``Summit Lake Indian Reservation Conveyance'', dated February 28, 2013, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Summit Lake Paiute Tribe; and (B) shall be part of the reservation of the Summit Lake Paiute Tribe. (3) Description of land.--The land referred to in paragraph (2) is the approximately 941 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``Reservation Conveyance Lands''. (e) Transfer of Land to Be Held in Trust for the Reno-Sparks Indian Colony Land.-- (1) Definition of map.--In this subsection, the term ``map'' means the map entitled ``Reno-Sparks Indian Colony Expansion'', dated June 11, 2014, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (3)-- (A) is held in trust by the United States for the benefit of the Reno-Sparks Indian Colony; and (B) shall be part of the reservation of the Reno- Sparks Indian Colony. (3) Description of land.--The land referred to in paragraph (2) is the approximately 13,434 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``RSIC Amended Boundary''. (f) Transfer of Land to Be Held in Trust for the Pyramid Lake Paiute Tribe.-- (1) Map.--In this subsection, the term ``map'' means the map entitled ``Pyramid Lake Indian Reservation Expansion'', dated July 26, 2014, and on file and available for public inspection in the appropriate offices of the Bureau of Land Management. (2) Conveyance of land.--Subject to valid existing rights, all right, title, and interest of the United States in and to the land described in paragraph (1)-- (A) is held in trust by the United States for the benefit of the Pyramid Lake Paiute Tribe; and (B) shall be part of the reservation of the Pyramid Lake Paiute Tribe. (3) Description of land.--The land referred to in paragraph (2) is the approximately 11,719 acres of land administered by the Bureau of Land Management as generally depicted on the map as ``Reservation Expansion Lands''. SEC. 202. ADMINISTRATION. (a) Survey.--Not later than 180 days after the date of enactment of this Act, the Secretary shall complete a survey of the boundary lines to establish the boundaries of the land taken into trust for each Indian tribe under section 201. (b) Use of Trust Land.-- (1) Gaming.--Land taken into trust under section 201 shall not be eligible, or considered to have been taken into trust, for class II gaming or class III gaming (as those terms are defined in section 4 of the Indian Gaming Regulatory Act (25 U.S.C. 2703)). (2) Thinning; landscape restoration.--With respect to the land taken into trust under section 201, the Secretary, in consultation and coordination with the applicable Indian tribe, may carry out any fuel reduction and other landscape restoration activities, including restoration of sage grouse habitat, on the land that is beneficial to the Indian tribe and the Bureau of Land Management. Passed the House of Representatives December 1, 2014. Attest: KAREN L. HAAS, Clerk.[/INST]Nevada Native Nations Land Act - Title I: Elko Motocross Land Conveyance - (Sec. 102) Directs the Department of the Interior to convey to Elko County, Nevada, without consideration, approximately 275 acres of land managed by the Bureau of Land Management (BLM), Elko District, Nevada, for use as a motocross, bicycle, off-highway vehicle, or stock car racing area or for other public purpose consistent with the Recreation and Public Purposes Act. Reverts the conveyed land to the United States if it ceases being used for a public purpose. Title II: Conveyance of Land To Indian Tribes - (Sec. 201) Declares that the United States holds approximately 373 acres of BLM administered land in trust for the Te-moak Tribe of Western Shoshone Indians of Nevada. Makes such land part of the Tribe's reservation. Declares further that the United States holds approximately 19,094 acres of BLM-administered land in trust for the Fort McDermitt Paiute and Shoshone Tribe. Makes such land part of that Tribe's reservation. Declares that the United States also holds in trust the following lands: for the Shoshone Paiute Tribes, approximately 82 acres of land administered by the Forest Service depicted as the &quot;Proposed Acquisition Site&quot; on a Mountain City Administrative Site Proposed Acquisition map; for the Summit Lake Paiute Tribe, approximately 941 acres of BLM-administered land depicted as &quot;Reservation Conveyance Lands&quot; on a Summit Lake Indian Reservation Conveyance map; for the Reno-Sparks Indian Colony, approximately 13,434 acres of BLM-administered land depicted as &quot;RSIC Amended Boundary&quot; on a Reno-Sparks Indian Colony Expansion map; and for the Pyramid Lake Paiute Tribe, approximately 11,719 acres of BLM-administered land depicted as &quot;Reservation Expansion Lands &quot; on a Pyramid Lake Indian Reservation Expansion map. (Sec. 202) Prohibits certain gaming on the lands taken into trust under this Act. Authorizes the Secretary of the Interior, with respect to such lands, to carry out any fuel reduction and other landscape restoration activities on the land, including restoration of sage grouse habitat, beneficial to the Indian tribe and the BLM.</s>

molecular anions play an important role in the chemistry of the interstellar medium@xcite , of carbon stars@xcite , and the earth s ionosphere@xcite . as pointed out in ref.@xcite , the presence of anions in the interstellar medium may have profound consequences for our understanding of the interstellar processing of the biogenic elements ( see e.g. ref.@xcite and references therein ) . yet as judged from the number of entries in the compilations of huber and herzberg@xcite ( for diatomics ) and of jacox@xcite ( for polyatomics ) , high- or even medium - resolution spectroscopic data for anions are relatively scarce compared to the amount of data available for neutral or even cationic species : in the 1992 review of hirota@xcite on spectroscopy of ions , only 13 molecular anions were listed in table vii , compared to 4 1/2 pages worth of entries for cations . ( early reviews of anion spectroscopy are found in refs.@xcite , while ab initio studies of structure and spectroscopy of anions were reviewed fairly recently by botschwina and coworkers@xcite . ) some of the reasons for this paucity are discussed in the introductions to refs.@xcite . one such species is the hydroxyl anion , oh@xmath5 . by means of velocity modulation spectroscopy@xcite , high - resolution fundamentals were obtained@xcite for three isotopomers , namely @xmath6oh@xmath5 , @xmath6od@xmath5 , and @xmath7oh@xmath5 ; in addition , some pure rotational transitions have been observed@xcite . lineberger and coworkers@xcite earlier obtained some rotational data in the course of an electron photodetachment study , and obtained precise electron affinities ( eas ) of 14741.03(17 ) and 14723.92(30 ) @xmath2 , respectively , for oh and od . very recently , the same group re - measured@xcite ea(oh ) and obtained essentially the same value but with a higher precision , 14741.02(3 ) @xmath2 . the spectroscopic constants of oh@xmath5 were previously the subject of ab initio studies , notably by werner et al.@xcite using multireference configuration interaction ( mrci ) methods , and recently by lee and dateo ( ld)@xcite using coupled cluster theory with basis sets as large as @xmath8 $ ] . the ld paper is particularly relevant here . the ccsd(t ) ( coupled cluster with all single and double substitutions@xcite and a quasiperturbative treatment for triple excitations@xcite ) method , in combination with basis sets of at least @xmath9 quality and including an account for inner - shell correlation , can routinely predict vibrational band origins of small polyatomic molecules with a mean absolute error on the order of a few @xmath2 ( e.g. for c@xmath10h@xmath10@xcite , so@xmath10@xcite ) . yet while ld found very good agreement between their computed ccsd(t)/[6s5p4d3f2g/5s4p3d2f ] spectroscopic constants and available experimental data , consideration of further basis set expansion and of inner - shell correlation effects leads to a predicted fundamental @xmath11 at the ccsd(t ) basis set limit of 3566.2@xmath121 @xmath2 , about 11 @xmath2 higher than the experimental results@xcite of 3555.6057(22 ) @xmath2 , where the uncertainty in parentheses represents two standard deviations . in a recent benchmark study@xcite on the ground - state potential curves of the first - row diatomic hydrides using both ccsd(t ) and fci ( full configuration interaction ) methods , the author found that ccsd(t ) has a systematic tendency to overestimate harmonic frequencies of a h stretching frequencies by on the order of 6 @xmath2 . even so , the discrepancy seen by ld is a bit out of the ordinary , and the question arises as to what level of theory is required to obtain ` the right result for the right reason ' in this case . in the present work , we shall show that the discrepancy between the ccsd(t ) basis set limit and nature is mostly due to two factors : ( a ) neglect of the effect of connected quadruple excitations , and ( b ) neglect of scalar relativistic effects . when these are properly accounted for , the available vibrational transitions can be reproduced to within a fraction of a @xmath2 from the computed potential curve . in the context of the present special issue , this will also serve as an illustrative example of the type of accuracy that can be achieved for small systems with the present state of the art . predicted band origins for higher vibrational levels ( and ` hot bands ' ) may assist future experimental work on this system . finally , as by - products of our analysis , we will show that the electron affinity of oh can be reproduced to very high accuracy , and tentatively propose a slight upward revision of the dissociation energy of neutral hydroxyl radical , oh . the coupled cluster , multireference averaged coupled pair functional ( acpf)@xcite , and full ci calculations were carried out using molpro 98.1@xcite running on dec / compaq alpha workstations in our laboratory , and on the sgi origin 2000 of the faculty of chemistry . full ccsdt ( coupled cluster theory with all connected single , double and triple excitations@xcite ) and ccsd(tq ) ( ccsd with quasiperturbative corrections for triple and quadruple excitations@xcite ) calculations were carried out using aces ii@xcite on a dec alpha workstation . correlation consistent basis sets due to dunning and coworkers@xcite were used throughout . since the system under consideration is anionic , the regular cc - pv@xmath13z ( correlation consistent polarized valence @xmath13-tuple zeta , or v@xmath13z for short ) basis sets will be inadequate . we have considered both the aug - cc - pv@xmath13z ( augmented correlation consistent , or av@xmath13z for short ) basis sets@xcite in which one low - exponent function of each angular momentum is added to both the oxygen and hydrogen basis sets , as well as the aug@xmath14-cc - pv@xmath13z basis sets@xcite in which the addition is not made to the hydrogen basis set . in addition we consider both uncontracted versions of the same basis sets ( denoted by the suffix `` uc '' ) and the aug - cc - pcv@xmath13z basis sets@xcite ( acv@xmath13z ) which include added core - valence correlation functions . the largest basis sets considered in this work , aug - cc - pv6z and aug - cc - pcv5z , are of [ 8s7p6d5f4g3h2i/7s6p5d4f3g2h ] and [ 11s10p8d6f4g2h/6s5p4d3f2 g ] quality , respectively . the multireference acpf calculations were carried out from a casscf ( complete active space scf ) reference wave function with an active space consisting of the valence @xmath15 orbitals as well as the @xmath16 rydberg orbitals : this is denoted cas(8/7)-acpf ( i , e , 8 electrons in 7 orbitals ) . while the inclusion of the @xmath16 orbitals is essential ( see below ) , the inclusion of the @xmath17 rydberg orbital ( i.e. , cas(8/8)-acpf ) was considered and found to affect computed properties negligibly . in addition , some exploratory cas - aqcc ( averaged quadratic coupled cluster@xcite ) calculations were also carried out . scalar relativistic effects were computed as expectation values of the one - electron darwin and mass - velocity operators@xcite for the acpf wave functions . the energy was evaluated at 21 points around @xmath18 , with a spacing of 0.01 . ( all energies were converged to 10@xmath19 hartree , or wherever possible to 10@xmath20 hartree . ) a polynomial in @xmath21 of degree 8 or 9 ( the latter if an f - test revealed an acceptable statistical significance for the nonic term ) was fitted to the energies . using the procedure detailed in ref.@xcite , the dunham series@xcite thus obtained was transformed by derivative matching into a variable - beta morse ( vbm ) potential@xcite @xmath22\right)^2\ ] ] in which @xmath23 , @xmath24 is the ( computed or observed ) dissociation energy , and @xmath25 is an adjustable parameter related to that in the morse function . analysis of this function was then carried out in two different manners : ( a ) analytic differentiation with respect to @xmath21 up to the 12th derivative followed by a 12th - order dunham analysis using an adaptation of the acet program of ogilvie@xcite ; and ( b ) numerical integration of the one - dimensional schrdinger equation using the algorithm of balint - kurti et al.@xcite , on a grid of 512 points over the interval 0.5@xmath265@xmath26 . as expected , differences between vibrational energies obtained using both methods are negligible up to the seventh vibrational quantum , and still no larger than 0.4 @xmath2 for the tenth vibrational quantum . the largest basis set in which we were able to obtain a full ci potential curve was cc - pvdz+sp(o ) , which means the standard cc - pvdz basis set with the diffuse @xmath27 and @xmath28 function from aug - cc - pvdz added to oxygen . a comparison of computed properties for oh@xmath5 with different electron correlation methods is given in table [ npart ] , while their errors in the total energy relative to full ci are plotted in figure 1 . it is immediately seen that ccsd(t ) exaggerates the curvature of the potential surface , overestimating @xmath1 by 10 @xmath2 . in addition , it underestimates the bond length by about 0.0006 . these are slightly more pronounced variations on trends previously seen@xcite for the oh radical . the problem does not reside in ccsd(t ) s quasiperturbative treatment of triple excitations : performing a full ccsdt calculation instead lowers @xmath1 by only 1.7 @xmath2 and lengthens the bond by less than 0.0001 . quasiperturbative inclusion of connected quadruple excitations , however , using the ccsd(tq ) method , lowers @xmath1 by 8.5 @xmath2 relative to ccsd(t ) , and slightly lengthens the bond , by 0.00025 . ( essentially the same result was obtained by means of the ccsd+tq * method@xcite , which differs from ccsd(tq ) in a small sixth - order term @xmath29 . ) no ccsdt(q ) code was available to the author : approximating the ccsdt(q ) energy by the expression @xmath30\approx e[ccsdt]+ e[ccsd(tq ) ] - e[cc5sd(t ) ] = e[ccsdt ] + e_{5qq } + e_{5qt}$ ] , we obtain a potential curve in fairly good agreement with full ci . what is the source of the importance of connected quadruple excitations in this case ? analysis of the fci wave function reveals prominent contributions to the wave function from @xmath31 double excitations ; while the @xmath16 orbitals are lumo+2 and lumo+3 rather than lumo , a large portion of them sits in the same spatial region as the occupied @xmath32 orbitals . in any proper multireference treatment , the aforementioned excitations would be in the zero - order wave function : obviously , the space of all double excitations therefrom would also entail quadruple excitations with respect to the hartree - fock reference , including a connected component . since the basis set sizes for which we can hope to perform ccsdt(q ) or similar calculations on this system are quite limited , we considered multireference methods , specifically acpf from a @xmath33 ^ 8 $ ] reference space ( denoted acpf(8/7 ) further on ) . as might be expected , the computed properties are in very close agreement with fci , except for @xmath1 being 1.5 @xmath2 too high . aqcc(8/7 ) does not appear to represent a further improvement , and adding the @xmath17 orbital to the acpf reference space ( i.e. acpf(8/8 ) ) affects properties only marginally . all relevant results are collected in table [ 1part ] . basis set convergence in this system was previously studied in some detail by ld at the ccsd(t ) level . among other things , they noted that @xmath1 still changes by 4 @xmath2 upon expanding the basis set from aug - cc - pvqz to aug - cc - pv5z . they suggested that @xmath1 then should be converged to about 1 @xmath2 ; this statement is corroborated by the ccsd(t)/aug - cc - pv6z results . since the negative charge resides almost exclusively on the oxygen , the temptation exists to use aug@xmath14-cc - pv@xmath13z basis sets , i.e. to apply aug - cc - pv@xmath13z only to the oxygen atom but use a regular cc - pv@xmath13z basis set on hydrogen . for @xmath13=t , this results in fact in a difference of 10 @xmath2 on @xmath1 , but the gap narrows as @xmath13 increases . yet extrapolation suggests convergence of the computed fundamental to a value about 1 @xmath2 higher than the aug - cc - pv@xmath13z curve . for the av@xmath13z and av@xmath13z basis sets ( @xmath13=t , q ) , the cas(8/7)-acpf approach systematically lowers harmonic frequencies by about 8 @xmath2 compared to ccsd(t ) ; for the fundamental the difference is even slightly larger ( 9.5 @xmath2 ) . interestingly , this difference decreases for @xmath13=5 . it was noted previously@xcite that the higher anharmonicity constants exhibit rather greater basis set dependence than one might reasonably have expected , and that this sensitivity is greatly reduced if uncontracted basis sets are employed ( which have greater radial flexibility ) . the same phenomenon is seen here . in agreement with previous observations by ld , inner - shell correlation reduces the bond lengthen slightly , and increases @xmath1 by 56 @xmath2 . this occurs both at the ccsd(t ) and the cas(8/7)-acpf levels . at our highest level of theory so far , namely cas(8/7)-acpf(all)/acv5z , @xmath11 is predicted to be 3559.3 @xmath2 , still several @xmath2 higher than experiment . the effects of further basis set improvement can be gauged from the difference between ccsd(t)/av6z and ccsd(t)/av5z results : one notices an increase of + 1.0 @xmath2 in @xmath1 and a decrease of 0.00006 in @xmath18 . we also performed some calculations with a doubly augmented cc - pv5z basis set ( i.e. d - av5z ) , and found the results to be essentially indistinguishable from those with the singly augmented basis set . residual imperfections in the electron correlation method can be gauged from the cas(8/7)-acpf @xmath34 fci difference with our smallest basis set , and appear to consist principally of a contraction of @xmath18 by 0.00004 and a decrease in @xmath1 by 1.5 @xmath2 . adding the two sets of differences to obtain a ` best nonrelativistic ' set of spectroscopic constants , we obtain @xmath11=3558.6 @xmath2 , still 3 @xmath2 above experiment . in both cases , changes in the anharmonicity constants from the best directly computed results are essentially nil . scalar relativistic corrections were computed at the cas(8/7)-acpf level with and without the @xmath35-like electrons correlated , and with a variety of basis sets . all results are fairly consistent with those obtained at the highest level considered , cas(8/7)-acpf(all)/acvqz , namely an expansion of @xmath18 by about 0.0001 and most importantly for our purposes a decrease of @xmath1 by about 3 @xmath2 . effects on the anharmonicity constants are essentially nonexistent . upon adding these corrections to our best nonrelativistic spectroscopic constants , we obtain our final best estimates . these lead to @xmath11=3555.44 @xmath2 for @xmath6oh@xmath5 , in excellent agreement with the experimental result@xcite 3555.6057(22 ) @xmath2 . the discrepancy between computed ( 3544.30 @xmath2 ) and observed@xcite ( 3544.4551(28 ) @xmath2 ) values for @xmath7oh@xmath5 is quite similar . for @xmath6od@xmath5 , we obtain @xmath11=2625.31 @xmath2 , which agrees to better than 0.1 @xmath2 with the experimental value@xcite 2625.332(3 ) @xmath2 . our computed bond length is slightly shorter than the observed one@xcite for oh@xmath5 , but within the error bar of that for od@xmath5@xcite . if we assume an inverse mass dependence for the experimental diabatic bond distance and extrapolate to infinite mass , we obtain an experimentally derived born - oppenheimer bond distance of 0.96416(16 ) @xmath2 , in perfect agreement with our calculations . while until recently it was generally assumed that scalar relativistic corrections are not important for first - and second - row systems , it has now been shown repeatedly ( e.g.@xcite ) that for kj / mol accuracy on computed bonding energies , scalar relativistic corrections are indispensable . very recently , csaszar et al.@xcite considered the effect of scalar relativistic corrections on the ab initio water surface , and found corrections on the same order of magnitude as seen for the hydroxyl anion here . finally , bauschlicher@xcite compared first - order darwin and mass - velocity corrections to energetics ( for single - reference acpf wave functions ) with more rigorous relativistic methods ( specifically , douglas - kroll@xcite ) , and found that for first - and second - row systems , the two approaches yield essentially identical results , lending additional credence to the results of both csaszar et al . and from the present work . ( the same author found@xcite more significant deviations for third - row main group systems . ) is the relativistic effect seen here in oh@xmath0 unique to it , or does it occur in the neutral first - row diatomic hydrides as well ? some results obtained for bh , ch , nh , oh , and hf in their respective ground states , and using the same method as for oh@xmath0 , are collected in table [ rel ] . in general , @xmath36 is slightly lowered , and @xmath37 very slightly stretched these tendencies becoming more pronounced as one moves from left to right in the periodic table . the effect for oh@xmath0 appears to be stronger than for the isoelectronic neutral hydride hf , and definitely compared to neutral oh . the excellent agreement ( @xmath38 @xmath2 on vibrational quanta ) previously seen@xcite for the first - row diatomic hydrides between experiment and ccsd(t)/acv5z potential curves with an fci correction is at least in part due to a cancellation between the effects of further basis set extension on the one hand , and scalar relativistic effects ( neglected in ref.@xcite ) on the other hand . the shape of the relativistic contribution to the potential curve is easily understood qualitatively : on average , electrons are somewhat further away from the nucleus in a molecule than in the separated atoms ( hence the scalar relativistic contribution to the total energy will be slightly smaller in absolute value at @xmath37 than in the dissociation limit ) : as one approaches the united atom limit , however , the contribution will obviously increase again . the final result is a slight reduction in both the dissociation energy and on @xmath36 . in order to assist future experimental studies on oh@xmath5 and its isomers , predicted vibrational quanta @xmath39 are given in table [ gn ] for various isotopic species , together with some key spectroscopic constants . the vbm parameters of the potential are given in table [ vbm ] . the vbm expansion generally converges quite rapidly@xcite and , as found previously for oh , parameters @xmath40 and @xmath41 are found to be statistically not significant and were omitted . the vbm expansion requires the insertion of a dissociation energy : we have opted , rather than an experimental value , to use our best calculated value ( see next paragraph ) . agreement between computed and observed fundamental frequencies speaks for itself , as does that between computed and observed rotational constants . at first sight agreement for the rotation - vibration coupling constants @xmath42 is somewhat disappointing . however , for @xmath6oh@xmath5 and @xmath7oh@xmath5 , the experimentally derived ` @xmath42 ' actually corresponds to @xmath43 , i.e. to @xmath44 . if we compare the observed @xmath43 with the computed @xmath45 instead , excellent agreement is found . in the case of @xmath6od@xmath5 , the experimentally derived @xmath42 given is actually extrapolated from neutral @xmath6od : again , agreement between computed and observed @xmath43 is rather more satisfying . we also note that our calculations validate the conclusion by lee and dateo that the experimentally derived @xmath1 and @xmath46 for @xmath6oh should be revised upward . this was obtained in the following manner , which is a variant on w2 theory@xcite : ( a ) the casscf(8/7 ) dissociation energy using acvtz , acvqz , and acv5z basis sets was extrapolated geometrically using the geometric formula @xmath47 first proposed by feller@xcite ; ( b ) the dynamical correlation component ( defined at cas(8/7)-acpf(all ) @xmath34 casscf(8/7 ) ) of the dissociation energy was extrapolated to infinite maximum angular momentum in the basis set , @xmath48 from the acvqz ( @xmath49=4 ) and acv5z ( @xmath49=5 ) results using the formula@xcite @xmath50 ; ( c ) the scalar relativistic contribution obtained at the cas(8/7)-acpf level was added to the total , as was the spin - orbit splitting@xcite for o@xmath5(@xmath51 ) . our final result , @xmath4=4.7796 ev , is about 0.02 ev higher than the experimental one@xcite ; interestingly enough , the same is true for the oh radical ( computed @xmath4=4.4124 ev , observed 4.392 ev ) . in combination with either the experimental electron affinity of oxygen atom , ea(o)=1.461122(3 ) ev@xcite or the best computed ea(o)=1.46075 ev@xcite , this leads to electron affinities of oh , ea(oh)=1.8283 ev and 1.8280 ev , respectively , which agree to three decimal places with the experimental value@xcite 1.827611(4 ) ev . we note that the experimental @xmath24(oh@xmath5 ) is derived from @xmath24(oh)@xmath52ea(oh)@xmath34ea(o ) , and that a previous calibration study on the atomization energies of the first - row hydrides@xcite suggested that the experimental @xmath24(oh ) may be too low . while a systematic error in the electronic structure treatment that cancels almost exactly between oh and oh@xmath5 can not entirely be ruled out , the excellent agreement obtained for the electron affinity does lend support to the computed @xmath24 values . we have been able to obtain a fully ab initio radial function of spectroscopic quality for the hydroxyl anion . in order to obtain accurate results for this system , inclusion of connected quadruple excitations ( in a coupled cluster expansion ) is imperative , as is an account for scalar relativistic effects . basis set expansion effects beyond @xmath53 take a distant third place in importance . while consideration of connected quadruple excitation effects and of basis set expansion effects beyond @xmath53 would at present be prohibitively expensive for studies of larger anions , no such impediment would appear to exist for inclusion of the scalar relativistic effects ( at least for one - electron darwin and mass - velocity terms ) . our best computed ea(oh ) , 1.828 ev , agrees to three decimal places with the best available experimental value . our best computed dissociation energies , @xmath4(oh@xmath5)=4.7796 ev and @xmath4(oh)=4.4124 ev , suggest that the experimental @xmath4(oh)=4.392 ev ( from which the experimental @xmath4(oh@xmath5 ) was derived by a thermodynamic cycle ) may possibly be about 0.02 ev too low . one of the purposes of the paper by lee and dateo@xcite was to point out to the scientific community , and in particular the experimental community , that state - of - the art ab initio methods now have the capability to predict the spectroscopic constants of molecular anions with sufficient reliability to permit assignment of a congested spectrum from an uncontrolled environment such as an astronomical observation on the basis of the theoretical calculations alone . the present work would appear to support this assertion beyond any doubt . jm is the incumbent of the helen and milton a. kimmelman career development chair . research at the weizmann institute was supported by the minerva foundation , munich , germany , and by the _ tashtiyot _ program of the ministry of science ( israel ) . m. s. vardya and k. s. krishnaswamy , chem . phys . lett . 73(1980)616 ; g. wallerstein , astron . 105(1982)219 b. d. rehfuss , d .- j . liu , b. m. dinelli , m .- f . jagod , w. c. ho , m. w. crofton , and t. oka , j. chem . 89(1988)129 l. allamandola , m. p. bernstein , and s. a. sanford , in c. b. cosmovici , s. bowyer , d. wertheimer ( eds . ) , _ astronomical and biochemical origins and the search for life in the universe _ , editrice compositori , bologna , 1997 , pp . 2347 . n. h. rosenbaum , j. c. owrutsky , l. m. tack , and r. j. saykally , j. chem . 84(1986)5308 ; see also preliminary communication , j. c. owrutsky , n. h. rosenbaum , l. m. tack , and r. j. saykally , j. chem . 83(1985)5338 . molpro is a package of ab initio programs written by h .- j . werner and p. j. knowles , with contributions from j. almlf , r. d. amos , a. berning , d. l. cooper , m. j. o. deegan , a. j. dobbyn , f. eckert , s. t. elbert , c. hampel , r. lindh , a. w. lloyd , w. meyer , a. nicklass , k. peterson , r. pitzer , a. j. stone , p. r. taylor , m. e. mura , p. pulay , m. schtz , h. stoll , and t. thorsteinsson . j. f. stanton , j. gauss , j. d. watts , w. lauderdale , and r. j. bartlett , ( 1996 ) aces ii , an ab initio program system , incorporating the molecule vectorized molecular integral program by j. almlf and p. r. taylor , and a modified version of the abacus integral derivative package by t. helgaker , h. j. aa . jensen , p. jrgensen , j. olsen , and p. r. taylor . dunning , jr . peterson , and d.e . woon , `` correlation consistent basis sets for molecular calculations '' , in _ encyclopedia of computational chemistry _ , ed . p. von ragu schleyer , ( wiley & sons , chichester , 1998 ) . j. a. coxon , j. mol . 152(1992)274 and references therein . the vbm function with the exponent truncated at the @xmath54 term was originally proposed ( under the name ` generalized morse function ' ) by p. j. kuntz and a. c. roach , j. chem . faraday trans . ii 68(1972)259 c. e. moore , _ atomic energy levels _ , natl . ( us ) circ . * 467_. d. m. neumark , k. r. lykke , t. andersen , and w. c. lineberger , phys . a 32(1985)1890 a recent review proposes a minor revision to 1.4611107(17 ) ev : c. blondel , phys . t58(1995)31 ldddddd & @xmath55 & @xmath18 & @xmath1 & @xmath46 & @xmath56 & @xmath57 + fci & -75.623457 & 0.97503 & 3701.7 & 96.65 & 0.454 & -0.024 + ccsd & -75.616478 & 0.97209 & 3747.1 & 95.28 & 0.537 & -0.010 + ccsd(t ) & -75.622380 & 0.97442 & 3711.6 & 96.45 & 0.401 & -0.031 + cc5sd(t ) & -75.621379 & 0.97428 & 3709.5 & 97.74 & 0.367 & -0.025 + ccsdt & -75.622656 & 0.97449 & 3709.9 & 96.37 & 0.465 & -0.023 + ccsd(tq ) & -75.621660 & 0.97467 & 3703.1 & 98.17 & 0.352 & -0.024 + ccsd+tq * & -75.621473 & 0.97463 & 3702.8 & 98.48 & 0.337 & -0.023 + approx . ccsdt(q ) & -75.622937 & 0.97488 & 3703.5 & 96.78 & 0.452 & -0.022 + approx . ccsdt+q * & -75.622750 & 0.97484 & 3703.2 & 97.10 & 0.438 & -0.020 + cas(8/7)-acpf & -75.623089 & 0.97499 & 3703.2 & 96.60 & 0.455 & -0.023 + cas(8/7)-aqcc & -75.622147 & 0.97500 & 3702.9 & 96.54 & 0.456 & -0.029 + cas(8/8)-acpf & -75.623084 & 0.97501 & 3703.0 & 96.66 & 0.444 & -0.024 + cas(8/8)-aqcc & -75.622669 & 0.97493 & 3704.2 & 96.59 & 0.443 & -0.024 + lllddddddd corr . method & basis set & 1s corr ? & @xmath18 & @xmath1 & @xmath46 & @xmath56 & @xmath57 & @xmath58 & @xmath11 + cas(8/7)-acpf & aug-cc - pvtz & no & 0.96776 & 3725.01 & 92.738 & 0.3623 & -0.0566 & -0.37 & 3540.07 + cas(8/7)-acpf & aug-cc - pvqz & no & 0.96517 & 3742.24 & 93.610 & 0.3855 & -0.0068 & -0.24 & 3556.00 + cas(8/7)-acpf & aug-cc - pvqz & no+rel & 0.96528 & 3739.00 & 93.564 & 0.3881 & -0.0066 & -0.24 & 3552.86 + cas(8/7)-acpf & aug-cc - pv5z & no & 0.96476 & 3745.58 & 93.856 & 0.4968 & -0.0192 & -0.14 & 3559.24 + ccsd(t ) & aug-cc - pvtz & no & 0.96741 & 3733.55 & 91.987 & 0.3284 & -0.0524 & -0.40 & 3549.99 + ccsd(t ) & aug-cc - pvqz & no & 0.96486 & 3750.37 & 92.948 & 0.3474 & -0.0121 & -0.27 & 3565.28 + ccsd(t ) & aug-cc - pv5z & no & 0.96456 & 3751.56 & 93.183 & 0.4643 & -0.0227 & -0.17 & 3566.42 + cas(8/7)-acpf & avtz & no & 0.96809 & 3716.44 & 92.083 & 0.2144 & -0.0133 & -0.42 & 3532.49 + cas(8/7)-acpf & avqz & no & 0.96551 & 3737.30 & 93.868 & 0.4277 & -0.0034 & -0.19 & 3550.75 + cas(8/7)-acpf & av5z & no & 0.96488 & 3744.47 & 93.816 & 0.5236 & -0.0157 & -0.13 & 3558.33 + ccsd(t ) & avtz & no & 0.96781 & 3723.56 & 91.345 & 0.1745 & -0.0188 & -0.46 & 3540.88 + ccsd(t ) & avqz & no & 0.96520 & 3745.61 & 93.159 & 0.3900 & -0.0107 & -0.22 & 3560.29 + ccsd(t ) & av5z & no & 0.96472 & 3749.39 & 93.193 & 0.4966 & -0.0291 & -0.15 & 3564.32 + ccsd(t ) & d - av5z & no & 0.96476 & 3749.31 & 93.079 & 0.4900 & -0.0283 & -0.16 & 3564.45 + ccsd(t ) & av6z & no & 0.96466 & 3750.41 & 93.237 & 0.4839 & -0.0214 & -0.14 & 3565.26 + ccsd(t ) & avtzuc & no & 0.96734 & 3724.84 & 92.600 & 0.4875 & -0.0734 & -0.39 & 3540.46 + ccsd(t ) & avqzuc & no & 0.96522 & 3744.72 & 93.044 & 0.4081 & -0.0219 & -0.27 & 3559.58 + ccsd(t ) & av5zuc & no & 0.96473 & 3749.21 & 93.243 & 0.4435 & -0.0103 & -0.16 & 3563.95 + cas(8/7)-acpf & acvtz & no & 0.96789 & 3713.45 & 91.642 & 0.2137 & 0.0000 & -0.41 & 3530.45 + cas(8/7)-acpf & acvqz & no & 0.96558 & 3735.72 & 93.894 & 0.4219 & -0.0130 & -0.23 & 3549.01 + cas(8/7)-acpf & acv5z & no & 0.96501 & 3740.66 & 94.081 & 0.4691 & -0.0005 & -0.14 & 3553.87 + ccsd(t ) & acvtz & no & 0.96768 & 3718.89 & 91.145 & 0.1639 & -0.0044 & -0.45 & 3536.66 + ccsd(t ) & acvqz & no & 0.96525 & 3744.90 & 93.038 & 0.3867 & -0.0191 & -0.26 & 3559.73 + ccsd(t ) & acv5z & no & 0.96472 & 3749.22 & 93.225 & 0.4361 & -0.0101 & -0.17 & 3563.96 + cas(8/7)-acpf & acvtz & yes & 0.96725 & 3714.74 & 92.017 & 0.1855 & -0.0035 & -0.43 & 3530.86 + cas(8/7)-acpf & acvqz & yes & 0.96468 & 3741.86 & 94.110 & 0.4205 & -0.0129 & -0.23 & 3554.71 + cas(8/7)-acpf & acv5z & yes & 0.96410 & 3746.51 & 94.317 & 0.4682 & 0.0009 & -0.14 & 3559.26 + ccsd(t ) & acvtz & yes & 0.96688 & 3725.04 & 91.122 & 0.1509 & -0.0022 & -0.46 & 3542.81 + ccsd(t ) & acvqz & yes & 0.96435 & 3751.76 & 93.151 & 0.3929 & -0.0202 & -0.26 & 3566.37 + ccsd(t ) & acv5z & yes & 0.96378 & 3756.27 & 93.347 & 0.4427 & -0.0088 & -0.17 & 3570.80 + cas(8/7)-acpf & acvqz all & yes+rel & 0.96478 & 3738.69 & 94.098 & 0.4193 & -0.0102 & -0.24 & 3551.57 + @xmath59rel & & & 0.00010 & -3.17 & -0.012 & -0.0012 & 0.0027 & -0.01 & -3.14 + best calc . & & & 0.96417 & 3742.87 & 94.404 & 0.4527 & 0.0100 & -0.14 & 3555.44 +

a benchmark study has been carried out on the ground - state potential curve of the hydroxyl anion , oh@xmath0 , including detailed calibration of both the 1-particle and n - particle basis sets . the ccsd(t ) basis set limit overestimates @xmath1 by about 10 @xmath2 , which is only remedied by inclusion of connected quadruple excitations in the coupled cluster expansion or , equivalently , the inclusion of the @xmath3 orbitals in the active space of a multireference calculation . upon inclusion of scalar relativistic effects ( -3 @xmath2 on @xmath1 ) , a potential curve of spectroscopic quality ( sub-@xmath2 accuracy ) is obtained . our best computed ea(oh ) , 1.828 ev , agrees to three decimal places with the best available experimental value . our best computed dissociation energies , @xmath4(oh@xmath5)=4.7796 ev and @xmath4(oh)=4.4124 ev , suggest that the experimental @xmath4(oh)=4.392 ev may possibly be about 0.02 ev too low . = 6.5 in = 9.26 in

<s>[INST]molecular anions play an important role in the chemistry of the interstellar medium@xcite , of carbon stars@xcite , and the earth s ionosphere@xcite . as pointed out in ref.@xcite , the presence of anions in the interstellar medium may have profound consequences for our understanding of the interstellar processing of the biogenic elements ( see e.g. ref.@xcite and references therein ) . yet as judged from the number of entries in the compilations of huber and herzberg@xcite ( for diatomics ) and of jacox@xcite ( for polyatomics ) , high- or even medium - resolution spectroscopic data for anions are relatively scarce compared to the amount of data available for neutral or even cationic species : in the 1992 review of hirota@xcite on spectroscopy of ions , only 13 molecular anions were listed in table vii , compared to 4 1/2 pages worth of entries for cations . ( early reviews of anion spectroscopy are found in refs.@xcite , while ab initio studies of structure and spectroscopy of anions were reviewed fairly recently by botschwina and coworkers@xcite . ) some of the reasons for this paucity are discussed in the introductions to refs.@xcite . one such species is the hydroxyl anion , oh@xmath5 . by means of velocity modulation spectroscopy@xcite , high - resolution fundamentals were obtained@xcite for three isotopomers , namely @xmath6oh@xmath5 , @xmath6od@xmath5 , and @xmath7oh@xmath5 ; in addition , some pure rotational transitions have been observed@xcite . lineberger and coworkers@xcite earlier obtained some rotational data in the course of an electron photodetachment study , and obtained precise electron affinities ( eas ) of 14741.03(17 ) and 14723.92(30 ) @xmath2 , respectively , for oh and od . very recently , the same group re - measured@xcite ea(oh ) and obtained essentially the same value but with a higher precision , 14741.02(3 ) @xmath2 . the spectroscopic constants of oh@xmath5 were previously the subject of ab initio studies , notably by werner et al.@xcite using multireference configuration interaction ( mrci ) methods , and recently by lee and dateo ( ld)@xcite using coupled cluster theory with basis sets as large as @xmath8 $ ] . the ld paper is particularly relevant here . the ccsd(t ) ( coupled cluster with all single and double substitutions@xcite and a quasiperturbative treatment for triple excitations@xcite ) method , in combination with basis sets of at least @xmath9 quality and including an account for inner - shell correlation , can routinely predict vibrational band origins of small polyatomic molecules with a mean absolute error on the order of a few @xmath2 ( e.g. for c@xmath10h@xmath10@xcite , so@xmath10@xcite ) . yet while ld found very good agreement between their computed ccsd(t)/[6s5p4d3f2g/5s4p3d2f ] spectroscopic constants and available experimental data , consideration of further basis set expansion and of inner - shell correlation effects leads to a predicted fundamental @xmath11 at the ccsd(t ) basis set limit of 3566.2@xmath121 @xmath2 , about 11 @xmath2 higher than the experimental results@xcite of 3555.6057(22 ) @xmath2 , where the uncertainty in parentheses represents two standard deviations . in a recent benchmark study@xcite on the ground - state potential curves of the first - row diatomic hydrides using both ccsd(t ) and fci ( full configuration interaction ) methods , the author found that ccsd(t ) has a systematic tendency to overestimate harmonic frequencies of a h stretching frequencies by on the order of 6 @xmath2 . even so , the discrepancy seen by ld is a bit out of the ordinary , and the question arises as to what level of theory is required to obtain ` the right result for the right reason ' in this case . in the present work , we shall show that the discrepancy between the ccsd(t ) basis set limit and nature is mostly due to two factors : ( a ) neglect of the effect of connected quadruple excitations , and ( b ) neglect of scalar relativistic effects . when these are properly accounted for , the available vibrational transitions can be reproduced to within a fraction of a @xmath2 from the computed potential curve . in the context of the present special issue , this will also serve as an illustrative example of the type of accuracy that can be achieved for small systems with the present state of the art . predicted band origins for higher vibrational levels ( and ` hot bands ' ) may assist future experimental work on this system . finally , as by - products of our analysis , we will show that the electron affinity of oh can be reproduced to very high accuracy , and tentatively propose a slight upward revision of the dissociation energy of neutral hydroxyl radical , oh . the coupled cluster , multireference averaged coupled pair functional ( acpf)@xcite , and full ci calculations were carried out using molpro 98.1@xcite running on dec / compaq alpha workstations in our laboratory , and on the sgi origin 2000 of the faculty of chemistry . full ccsdt ( coupled cluster theory with all connected single , double and triple excitations@xcite ) and ccsd(tq ) ( ccsd with quasiperturbative corrections for triple and quadruple excitations@xcite ) calculations were carried out using aces ii@xcite on a dec alpha workstation . correlation consistent basis sets due to dunning and coworkers@xcite were used throughout . since the system under consideration is anionic , the regular cc - pv@xmath13z ( correlation consistent polarized valence @xmath13-tuple zeta , or v@xmath13z for short ) basis sets will be inadequate . we have considered both the aug - cc - pv@xmath13z ( augmented correlation consistent , or av@xmath13z for short ) basis sets@xcite in which one low - exponent function of each angular momentum is added to both the oxygen and hydrogen basis sets , as well as the aug@xmath14-cc - pv@xmath13z basis sets@xcite in which the addition is not made to the hydrogen basis set . in addition we consider both uncontracted versions of the same basis sets ( denoted by the suffix `` uc '' ) and the aug - cc - pcv@xmath13z basis sets@xcite ( acv@xmath13z ) which include added core - valence correlation functions . the largest basis sets considered in this work , aug - cc - pv6z and aug - cc - pcv5z , are of [ 8s7p6d5f4g3h2i/7s6p5d4f3g2h ] and [ 11s10p8d6f4g2h/6s5p4d3f2 g ] quality , respectively . the multireference acpf calculations were carried out from a casscf ( complete active space scf ) reference wave function with an active space consisting of the valence @xmath15 orbitals as well as the @xmath16 rydberg orbitals : this is denoted cas(8/7)-acpf ( i , e , 8 electrons in 7 orbitals ) . while the inclusion of the @xmath16 orbitals is essential ( see below ) , the inclusion of the @xmath17 rydberg orbital ( i.e. , cas(8/8)-acpf ) was considered and found to affect computed properties negligibly . in addition , some exploratory cas - aqcc ( averaged quadratic coupled cluster@xcite ) calculations were also carried out . scalar relativistic effects were computed as expectation values of the one - electron darwin and mass - velocity operators@xcite for the acpf wave functions . the energy was evaluated at 21 points around @xmath18 , with a spacing of 0.01 . ( all energies were converged to 10@xmath19 hartree , or wherever possible to 10@xmath20 hartree . ) a polynomial in @xmath21 of degree 8 or 9 ( the latter if an f - test revealed an acceptable statistical significance for the nonic term ) was fitted to the energies . using the procedure detailed in ref.@xcite , the dunham series@xcite thus obtained was transformed by derivative matching into a variable - beta morse ( vbm ) potential@xcite @xmath22\right)^2\ ] ] in which @xmath23 , @xmath24 is the ( computed or observed ) dissociation energy , and @xmath25 is an adjustable parameter related to that in the morse function . analysis of this function was then carried out in two different manners : ( a ) analytic differentiation with respect to @xmath21 up to the 12th derivative followed by a 12th - order dunham analysis using an adaptation of the acet program of ogilvie@xcite ; and ( b ) numerical integration of the one - dimensional schrdinger equation using the algorithm of balint - kurti et al.@xcite , on a grid of 512 points over the interval 0.5@xmath265@xmath26 . as expected , differences between vibrational energies obtained using both methods are negligible up to the seventh vibrational quantum , and still no larger than 0.4 @xmath2 for the tenth vibrational quantum . the largest basis set in which we were able to obtain a full ci potential curve was cc - pvdz+sp(o ) , which means the standard cc - pvdz basis set with the diffuse @xmath27 and @xmath28 function from aug - cc - pvdz added to oxygen . a comparison of computed properties for oh@xmath5 with different electron correlation methods is given in table [ npart ] , while their errors in the total energy relative to full ci are plotted in figure 1 . it is immediately seen that ccsd(t ) exaggerates the curvature of the potential surface , overestimating @xmath1 by 10 @xmath2 . in addition , it underestimates the bond length by about 0.0006 . these are slightly more pronounced variations on trends previously seen@xcite for the oh radical . the problem does not reside in ccsd(t ) s quasiperturbative treatment of triple excitations : performing a full ccsdt calculation instead lowers @xmath1 by only 1.7 @xmath2 and lengthens the bond by less than 0.0001 . quasiperturbative inclusion of connected quadruple excitations , however , using the ccsd(tq ) method , lowers @xmath1 by 8.5 @xmath2 relative to ccsd(t ) , and slightly lengthens the bond , by 0.00025 . ( essentially the same result was obtained by means of the ccsd+tq * method@xcite , which differs from ccsd(tq ) in a small sixth - order term @xmath29 . ) no ccsdt(q ) code was available to the author : approximating the ccsdt(q ) energy by the expression @xmath30\approx e[ccsdt]+ e[ccsd(tq ) ] - e[cc5sd(t ) ] = e[ccsdt ] + e_{5qq } + e_{5qt}$ ] , we obtain a potential curve in fairly good agreement with full ci . what is the source of the importance of connected quadruple excitations in this case ? analysis of the fci wave function reveals prominent contributions to the wave function from @xmath31 double excitations ; while the @xmath16 orbitals are lumo+2 and lumo+3 rather than lumo , a large portion of them sits in the same spatial region as the occupied @xmath32 orbitals . in any proper multireference treatment , the aforementioned excitations would be in the zero - order wave function : obviously , the space of all double excitations therefrom would also entail quadruple excitations with respect to the hartree - fock reference , including a connected component . since the basis set sizes for which we can hope to perform ccsdt(q ) or similar calculations on this system are quite limited , we considered multireference methods , specifically acpf from a @xmath33 ^ 8 $ ] reference space ( denoted acpf(8/7 ) further on ) . as might be expected , the computed properties are in very close agreement with fci , except for @xmath1 being 1.5 @xmath2 too high . aqcc(8/7 ) does not appear to represent a further improvement , and adding the @xmath17 orbital to the acpf reference space ( i.e. acpf(8/8 ) ) affects properties only marginally . all relevant results are collected in table [ 1part ] . basis set convergence in this system was previously studied in some detail by ld at the ccsd(t ) level . among other things , they noted that @xmath1 still changes by 4 @xmath2 upon expanding the basis set from aug - cc - pvqz to aug - cc - pv5z . they suggested that @xmath1 then should be converged to about 1 @xmath2 ; this statement is corroborated by the ccsd(t)/aug - cc - pv6z results . since the negative charge resides almost exclusively on the oxygen , the temptation exists to use aug@xmath14-cc - pv@xmath13z basis sets , i.e. to apply aug - cc - pv@xmath13z only to the oxygen atom but use a regular cc - pv@xmath13z basis set on hydrogen . for @xmath13=t , this results in fact in a difference of 10 @xmath2 on @xmath1 , but the gap narrows as @xmath13 increases . yet extrapolation suggests convergence of the computed fundamental to a value about 1 @xmath2 higher than the aug - cc - pv@xmath13z curve . for the av@xmath13z and av@xmath13z basis sets ( @xmath13=t , q ) , the cas(8/7)-acpf approach systematically lowers harmonic frequencies by about 8 @xmath2 compared to ccsd(t ) ; for the fundamental the difference is even slightly larger ( 9.5 @xmath2 ) . interestingly , this difference decreases for @xmath13=5 . it was noted previously@xcite that the higher anharmonicity constants exhibit rather greater basis set dependence than one might reasonably have expected , and that this sensitivity is greatly reduced if uncontracted basis sets are employed ( which have greater radial flexibility ) . the same phenomenon is seen here . in agreement with previous observations by ld , inner - shell correlation reduces the bond lengthen slightly , and increases @xmath1 by 56 @xmath2 . this occurs both at the ccsd(t ) and the cas(8/7)-acpf levels . at our highest level of theory so far , namely cas(8/7)-acpf(all)/acv5z , @xmath11 is predicted to be 3559.3 @xmath2 , still several @xmath2 higher than experiment . the effects of further basis set improvement can be gauged from the difference between ccsd(t)/av6z and ccsd(t)/av5z results : one notices an increase of + 1.0 @xmath2 in @xmath1 and a decrease of 0.00006 in @xmath18 . we also performed some calculations with a doubly augmented cc - pv5z basis set ( i.e. d - av5z ) , and found the results to be essentially indistinguishable from those with the singly augmented basis set . residual imperfections in the electron correlation method can be gauged from the cas(8/7)-acpf @xmath34 fci difference with our smallest basis set , and appear to consist principally of a contraction of @xmath18 by 0.00004 and a decrease in @xmath1 by 1.5 @xmath2 . adding the two sets of differences to obtain a ` best nonrelativistic ' set of spectroscopic constants , we obtain @xmath11=3558.6 @xmath2 , still 3 @xmath2 above experiment . in both cases , changes in the anharmonicity constants from the best directly computed results are essentially nil . scalar relativistic corrections were computed at the cas(8/7)-acpf level with and without the @xmath35-like electrons correlated , and with a variety of basis sets . all results are fairly consistent with those obtained at the highest level considered , cas(8/7)-acpf(all)/acvqz , namely an expansion of @xmath18 by about 0.0001 and most importantly for our purposes a decrease of @xmath1 by about 3 @xmath2 . effects on the anharmonicity constants are essentially nonexistent . upon adding these corrections to our best nonrelativistic spectroscopic constants , we obtain our final best estimates . these lead to @xmath11=3555.44 @xmath2 for @xmath6oh@xmath5 , in excellent agreement with the experimental result@xcite 3555.6057(22 ) @xmath2 . the discrepancy between computed ( 3544.30 @xmath2 ) and observed@xcite ( 3544.4551(28 ) @xmath2 ) values for @xmath7oh@xmath5 is quite similar . for @xmath6od@xmath5 , we obtain @xmath11=2625.31 @xmath2 , which agrees to better than 0.1 @xmath2 with the experimental value@xcite 2625.332(3 ) @xmath2 . our computed bond length is slightly shorter than the observed one@xcite for oh@xmath5 , but within the error bar of that for od@xmath5@xcite . if we assume an inverse mass dependence for the experimental diabatic bond distance and extrapolate to infinite mass , we obtain an experimentally derived born - oppenheimer bond distance of 0.96416(16 ) @xmath2 , in perfect agreement with our calculations . while until recently it was generally assumed that scalar relativistic corrections are not important for first - and second - row systems , it has now been shown repeatedly ( e.g.@xcite ) that for kj / mol accuracy on computed bonding energies , scalar relativistic corrections are indispensable . very recently , csaszar et al.@xcite considered the effect of scalar relativistic corrections on the ab initio water surface , and found corrections on the same order of magnitude as seen for the hydroxyl anion here . finally , bauschlicher@xcite compared first - order darwin and mass - velocity corrections to energetics ( for single - reference acpf wave functions ) with more rigorous relativistic methods ( specifically , douglas - kroll@xcite ) , and found that for first - and second - row systems , the two approaches yield essentially identical results , lending additional credence to the results of both csaszar et al . and from the present work . ( the same author found@xcite more significant deviations for third - row main group systems . ) is the relativistic effect seen here in oh@xmath0 unique to it , or does it occur in the neutral first - row diatomic hydrides as well ? some results obtained for bh , ch , nh , oh , and hf in their respective ground states , and using the same method as for oh@xmath0 , are collected in table [ rel ] . in general , @xmath36 is slightly lowered , and @xmath37 very slightly stretched these tendencies becoming more pronounced as one moves from left to right in the periodic table . the effect for oh@xmath0 appears to be stronger than for the isoelectronic neutral hydride hf , and definitely compared to neutral oh . the excellent agreement ( @xmath38 @xmath2 on vibrational quanta ) previously seen@xcite for the first - row diatomic hydrides between experiment and ccsd(t)/acv5z potential curves with an fci correction is at least in part due to a cancellation between the effects of further basis set extension on the one hand , and scalar relativistic effects ( neglected in ref.@xcite ) on the other hand . the shape of the relativistic contribution to the potential curve is easily understood qualitatively : on average , electrons are somewhat further away from the nucleus in a molecule than in the separated atoms ( hence the scalar relativistic contribution to the total energy will be slightly smaller in absolute value at @xmath37 than in the dissociation limit ) : as one approaches the united atom limit , however , the contribution will obviously increase again . the final result is a slight reduction in both the dissociation energy and on @xmath36 . in order to assist future experimental studies on oh@xmath5 and its isomers , predicted vibrational quanta @xmath39 are given in table [ gn ] for various isotopic species , together with some key spectroscopic constants . the vbm parameters of the potential are given in table [ vbm ] . the vbm expansion generally converges quite rapidly@xcite and , as found previously for oh , parameters @xmath40 and @xmath41 are found to be statistically not significant and were omitted . the vbm expansion requires the insertion of a dissociation energy : we have opted , rather than an experimental value , to use our best calculated value ( see next paragraph ) . agreement between computed and observed fundamental frequencies speaks for itself , as does that between computed and observed rotational constants . at first sight agreement for the rotation - vibration coupling constants @xmath42 is somewhat disappointing . however , for @xmath6oh@xmath5 and @xmath7oh@xmath5 , the experimentally derived ` @xmath42 ' actually corresponds to @xmath43 , i.e. to @xmath44 . if we compare the observed @xmath43 with the computed @xmath45 instead , excellent agreement is found . in the case of @xmath6od@xmath5 , the experimentally derived @xmath42 given is actually extrapolated from neutral @xmath6od : again , agreement between computed and observed @xmath43 is rather more satisfying . we also note that our calculations validate the conclusion by lee and dateo that the experimentally derived @xmath1 and @xmath46 for @xmath6oh should be revised upward . this was obtained in the following manner , which is a variant on w2 theory@xcite : ( a ) the casscf(8/7 ) dissociation energy using acvtz , acvqz , and acv5z basis sets was extrapolated geometrically using the geometric formula @xmath47 first proposed by feller@xcite ; ( b ) the dynamical correlation component ( defined at cas(8/7)-acpf(all ) @xmath34 casscf(8/7 ) ) of the dissociation energy was extrapolated to infinite maximum angular momentum in the basis set , @xmath48 from the acvqz ( @xmath49=4 ) and acv5z ( @xmath49=5 ) results using the formula@xcite @xmath50 ; ( c ) the scalar relativistic contribution obtained at the cas(8/7)-acpf level was added to the total , as was the spin - orbit splitting@xcite for o@xmath5(@xmath51 ) . our final result , @xmath4=4.7796 ev , is about 0.02 ev higher than the experimental one@xcite ; interestingly enough , the same is true for the oh radical ( computed @xmath4=4.4124 ev , observed 4.392 ev ) . in combination with either the experimental electron affinity of oxygen atom , ea(o)=1.461122(3 ) ev@xcite or the best computed ea(o)=1.46075 ev@xcite , this leads to electron affinities of oh , ea(oh)=1.8283 ev and 1.8280 ev , respectively , which agree to three decimal places with the experimental value@xcite 1.827611(4 ) ev . we note that the experimental @xmath24(oh@xmath5 ) is derived from @xmath24(oh)@xmath52ea(oh)@xmath34ea(o ) , and that a previous calibration study on the atomization energies of the first - row hydrides@xcite suggested that the experimental @xmath24(oh ) may be too low . while a systematic error in the electronic structure treatment that cancels almost exactly between oh and oh@xmath5 can not entirely be ruled out , the excellent agreement obtained for the electron affinity does lend support to the computed @xmath24 values . we have been able to obtain a fully ab initio radial function of spectroscopic quality for the hydroxyl anion . in order to obtain accurate results for this system , inclusion of connected quadruple excitations ( in a coupled cluster expansion ) is imperative , as is an account for scalar relativistic effects . basis set expansion effects beyond @xmath53 take a distant third place in importance . while consideration of connected quadruple excitation effects and of basis set expansion effects beyond @xmath53 would at present be prohibitively expensive for studies of larger anions , no such impediment would appear to exist for inclusion of the scalar relativistic effects ( at least for one - electron darwin and mass - velocity terms ) . our best computed ea(oh ) , 1.828 ev , agrees to three decimal places with the best available experimental value . our best computed dissociation energies , @xmath4(oh@xmath5)=4.7796 ev and @xmath4(oh)=4.4124 ev , suggest that the experimental @xmath4(oh)=4.392 ev ( from which the experimental @xmath4(oh@xmath5 ) was derived by a thermodynamic cycle ) may possibly be about 0.02 ev too low . one of the purposes of the paper by lee and dateo@xcite was to point out to the scientific community , and in particular the experimental community , that state - of - the art ab initio methods now have the capability to predict the spectroscopic constants of molecular anions with sufficient reliability to permit assignment of a congested spectrum from an uncontrolled environment such as an astronomical observation on the basis of the theoretical calculations alone . the present work would appear to support this assertion beyond any doubt . jm is the incumbent of the helen and milton a. kimmelman career development chair . research at the weizmann institute was supported by the minerva foundation , munich , germany , and by the _ tashtiyot _ program of the ministry of science ( israel ) . m. s. vardya and k. s. krishnaswamy , chem . phys . lett . 73(1980)616 ; g. wallerstein , astron . 105(1982)219 b. d. rehfuss , d .- j . liu , b. m. dinelli , m .- f . jagod , w. c. ho , m. w. crofton , and t. oka , j. chem . 89(1988)129 l. allamandola , m. p. bernstein , and s. a. sanford , in c. b. cosmovici , s. bowyer , d. wertheimer ( eds . ) , _ astronomical and biochemical origins and the search for life in the universe _ , editrice compositori , bologna , 1997 , pp . 2347 . n. h. rosenbaum , j. c. owrutsky , l. m. tack , and r. j. saykally , j. chem . 84(1986)5308 ; see also preliminary communication , j. c. owrutsky , n. h. rosenbaum , l. m. tack , and r. j. saykally , j. chem . 83(1985)5338 . molpro is a package of ab initio programs written by h .- j . werner and p. j. knowles , with contributions from j. almlf , r. d. amos , a. berning , d. l. cooper , m. j. o. deegan , a. j. dobbyn , f. eckert , s. t. elbert , c. hampel , r. lindh , a. w. lloyd , w. meyer , a. nicklass , k. peterson , r. pitzer , a. j. stone , p. r. taylor , m. e. mura , p. pulay , m. schtz , h. stoll , and t. thorsteinsson . j. f. stanton , j. gauss , j. d. watts , w. lauderdale , and r. j. bartlett , ( 1996 ) aces ii , an ab initio program system , incorporating the molecule vectorized molecular integral program by j. almlf and p. r. taylor , and a modified version of the abacus integral derivative package by t. helgaker , h. j. aa . jensen , p. jrgensen , j. olsen , and p. r. taylor . dunning , jr . peterson , and d.e . woon , `` correlation consistent basis sets for molecular calculations '' , in _ encyclopedia of computational chemistry _ , ed . p. von ragu schleyer , ( wiley & sons , chichester , 1998 ) . j. a. coxon , j. mol . 152(1992)274 and references therein . the vbm function with the exponent truncated at the @xmath54 term was originally proposed ( under the name ` generalized morse function ' ) by p. j. kuntz and a. c. roach , j. chem . faraday trans . ii 68(1972)259 c. e. moore , _ atomic energy levels _ , natl . ( us ) circ . * 467_. d. m. neumark , k. r. lykke , t. andersen , and w. c. lineberger , phys . a 32(1985)1890 a recent review proposes a minor revision to 1.4611107(17 ) ev : c. blondel , phys . t58(1995)31 ldddddd & @xmath55 & @xmath18 & @xmath1 & @xmath46 & @xmath56 & @xmath57 + fci & -75.623457 & 0.97503 & 3701.7 & 96.65 & 0.454 & -0.024 + ccsd & -75.616478 & 0.97209 & 3747.1 & 95.28 & 0.537 & -0.010 + ccsd(t ) & -75.622380 & 0.97442 & 3711.6 & 96.45 & 0.401 & -0.031 + cc5sd(t ) & -75.621379 & 0.97428 & 3709.5 & 97.74 & 0.367 & -0.025 + ccsdt & -75.622656 & 0.97449 & 3709.9 & 96.37 & 0.465 & -0.023 + ccsd(tq ) & -75.621660 & 0.97467 & 3703.1 & 98.17 & 0.352 & -0.024 + ccsd+tq * & -75.621473 & 0.97463 & 3702.8 & 98.48 & 0.337 & -0.023 + approx . ccsdt(q ) & -75.622937 & 0.97488 & 3703.5 & 96.78 & 0.452 & -0.022 + approx . ccsdt+q * & -75.622750 & 0.97484 & 3703.2 & 97.10 & 0.438 & -0.020 + cas(8/7)-acpf & -75.623089 & 0.97499 & 3703.2 & 96.60 & 0.455 & -0.023 + cas(8/7)-aqcc & -75.622147 & 0.97500 & 3702.9 & 96.54 & 0.456 & -0.029 + cas(8/8)-acpf & -75.623084 & 0.97501 & 3703.0 & 96.66 & 0.444 & -0.024 + cas(8/8)-aqcc & -75.622669 & 0.97493 & 3704.2 & 96.59 & 0.443 & -0.024 + lllddddddd corr . method & basis set & 1s corr ? & @xmath18 & @xmath1 & @xmath46 & @xmath56 & @xmath57 & @xmath58 & @xmath11 + cas(8/7)-acpf & aug-cc - pvtz & no & 0.96776 & 3725.01 & 92.738 & 0.3623 & -0.0566 & -0.37 & 3540.07 + cas(8/7)-acpf & aug-cc - pvqz & no & 0.96517 & 3742.24 & 93.610 & 0.3855 & -0.0068 & -0.24 & 3556.00 + cas(8/7)-acpf & aug-cc - pvqz & no+rel & 0.96528 & 3739.00 & 93.564 & 0.3881 & -0.0066 & -0.24 & 3552.86 + cas(8/7)-acpf & aug-cc - pv5z & no & 0.96476 & 3745.58 & 93.856 & 0.4968 & -0.0192 & -0.14 & 3559.24 + ccsd(t ) & aug-cc - pvtz & no & 0.96741 & 3733.55 & 91.987 & 0.3284 & -0.0524 & -0.40 & 3549.99 + ccsd(t ) & aug-cc - pvqz & no & 0.96486 & 3750.37 & 92.948 & 0.3474 & -0.0121 & -0.27 & 3565.28 + ccsd(t ) & aug-cc - pv5z & no & 0.96456 & 3751.56 & 93.183 & 0.4643 & -0.0227 & -0.17 & 3566.42 + cas(8/7)-acpf & avtz & no & 0.96809 & 3716.44 & 92.083 & 0.2144 & -0.0133 & -0.42 & 3532.49 + cas(8/7)-acpf & avqz & no & 0.96551 & 3737.30 & 93.868 & 0.4277 & -0.0034 & -0.19 & 3550.75 + cas(8/7)-acpf & av5z & no & 0.96488 & 3744.47 & 93.816 & 0.5236 & -0.0157 & -0.13 & 3558.33 + ccsd(t ) & avtz & no & 0.96781 & 3723.56 & 91.345 & 0.1745 & -0.0188 & -0.46 & 3540.88 + ccsd(t ) & avqz & no & 0.96520 & 3745.61 & 93.159 & 0.3900 & -0.0107 & -0.22 & 3560.29 + ccsd(t ) & av5z & no & 0.96472 & 3749.39 & 93.193 & 0.4966 & -0.0291 & -0.15 & 3564.32 + ccsd(t ) & d - av5z & no & 0.96476 & 3749.31 & 93.079 & 0.4900 & -0.0283 & -0.16 & 3564.45 + ccsd(t ) & av6z & no & 0.96466 & 3750.41 & 93.237 & 0.4839 & -0.0214 & -0.14 & 3565.26 + ccsd(t ) & avtzuc & no & 0.96734 & 3724.84 & 92.600 & 0.4875 & -0.0734 & -0.39 & 3540.46 + ccsd(t ) & avqzuc & no & 0.96522 & 3744.72 & 93.044 & 0.4081 & -0.0219 & -0.27 & 3559.58 + ccsd(t ) & av5zuc & no & 0.96473 & 3749.21 & 93.243 & 0.4435 & -0.0103 & -0.16 & 3563.95 + cas(8/7)-acpf & acvtz & no & 0.96789 & 3713.45 & 91.642 & 0.2137 & 0.0000 & -0.41 & 3530.45 + cas(8/7)-acpf & acvqz & no & 0.96558 & 3735.72 & 93.894 & 0.4219 & -0.0130 & -0.23 & 3549.01 + cas(8/7)-acpf & acv5z & no & 0.96501 & 3740.66 & 94.081 & 0.4691 & -0.0005 & -0.14 & 3553.87 + ccsd(t ) & acvtz & no & 0.96768 & 3718.89 & 91.145 & 0.1639 & -0.0044 & -0.45 & 3536.66 + ccsd(t ) & acvqz & no & 0.96525 & 3744.90 & 93.038 & 0.3867 & -0.0191 & -0.26 & 3559.73 + ccsd(t ) & acv5z & no & 0.96472 & 3749.22 & 93.225 & 0.4361 & -0.0101 & -0.17 & 3563.96 + cas(8/7)-acpf & acvtz & yes & 0.96725 & 3714.74 & 92.017 & 0.1855 & -0.0035 & -0.43 & 3530.86 + cas(8/7)-acpf & acvqz & yes & 0.96468 & 3741.86 & 94.110 & 0.4205 & -0.0129 & -0.23 & 3554.71 + cas(8/7)-acpf & acv5z & yes & 0.96410 & 3746.51 & 94.317 & 0.4682 & 0.0009 & -0.14 & 3559.26 + ccsd(t ) & acvtz & yes & 0.96688 & 3725.04 & 91.122 & 0.1509 & -0.0022 & -0.46 & 3542.81 + ccsd(t ) & acvqz & yes & 0.96435 & 3751.76 & 93.151 & 0.3929 & -0.0202 & -0.26 & 3566.37 + ccsd(t ) & acv5z & yes & 0.96378 & 3756.27 & 93.347 & 0.4427 & -0.0088 & -0.17 & 3570.80 + cas(8/7)-acpf & acvqz all & yes+rel & 0.96478 & 3738.69 & 94.098 & 0.4193 & -0.0102 & -0.24 & 3551.57 + @xmath59rel & & & 0.00010 & -3.17 & -0.012 & -0.0012 & 0.0027 & -0.01 & -3.14 + best calc . & & & 0.96417 & 3742.87 & 94.404 & 0.4527 & 0.0100 & -0.14 & 3555.44 +[/INST] a benchmark study has been carried out on the ground - state potential curve of the hydroxyl anion , oh@xmath0 , including detailed calibration of both the 1-particle and n - particle basis sets . the ccsd(t ) basis set limit overestimates @xmath1 by about 10 @xmath2 , which is only remedied by inclusion of connected quadruple excitations in the coupled cluster expansion or , equivalently , the inclusion of the @xmath3 orbitals in the active space of a multireference calculation . upon inclusion of scalar relativistic effects ( -3 @xmath2 on @xmath1 ) , a potential curve of spectroscopic quality ( sub-@xmath2 accuracy ) is obtained . our best computed ea(oh ) , 1.828 ev , agrees to three decimal places with the best available experimental value . our best computed dissociation energies , @xmath4(oh@xmath5)=4.7796 ev and @xmath4(oh)=4.4124 ev , suggest that the experimental @xmath4(oh)=4.392 ev may possibly be about 0.02 ev too low . = 6.5 in = 9.26 in </s>

SECTION 1. SHORT TITLE. This Act may be cited as the ``Raise the Wage Act''. SEC. 2. MINIMUM WAGE INCREASES. (a) In General.--Section 6(a)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(a)(1)) is amended to read as follows: ``(1) except as otherwise provided in this section, not less than-- ``(A) $9.25 an hour, beginning on the effective date under section 7 of the Raise the Wage Act; ``(B) $10.10 an hour, beginning 1 year after such effective date; ``(C) $11.00 an hour, beginning 2 years after such effective date; ``(D) $12.00 an hour, beginning 3 years after such effective date; ``(E) $13.00 an hour, beginning 4 years after such effective date; ``(F) $13.50 an hour, beginning 5 years after such effective date; ``(G) $14.25 an hour, beginning 6 years after such effective date; ``(H) $15.00 an hour, beginning 7 years after such effective date; and ``(I) beginning on the date that is 8 years after such effective date, and annually thereafter, the amount determined by the Secretary under subsection (h);''. (b) Determination Based on Increase in the Median Hourly Wage of All Employees.--Section 6 of the Fair Labor Standards Act of 1938 (29 U.S.C. 206) is amended by adding at the end the following: ``(h)(1) Not later than each date that is 90 days before a new minimum wage determined under subsection (a)(1)(I) is to take effect, the Secretary shall determine the minimum wage to be in effect under this subsection for each period described in subsection (a)(1)(I). The wage determined under this subsection for a year shall be-- ``(A) not less than the amount in effect under subsection (a)(1) on the date of such determination; ``(B) increased from such amount by the annual percentage increase, if any, in the median hourly wage of all employees as determined by the Bureau of Labor Statistics; and ``(C) rounded to the nearest multiple of $0.05. ``(2) In calculating the annual percentage increase in the median hourly wage of all employees for purposes of paragraph (1)(B), the Secretary, through the Bureau of Labor Statistics, shall compile data on the hourly wages of all employees to determine such a median hourly wage and compare such median hourly wage for the most recent year for which data are available with the median hourly wage determined for the preceding year.''. SEC. 3. TIPPED EMPLOYEES. (a) Base Minimum Wage for Tipped Employees.--Section 3(m)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 203(m)(1)) is amended to read as follows: ``(1) the cash wage paid such employee, which for purposes of such determination shall be not less than-- ``(A) for the 1-year period beginning on the effective date under section 7 of the Raise the Wage Act, $4.15 an hour; ``(B) for each succeeding 1-year period until the hourly wage under this paragraph equals the wage in effect under section 6(a)(1) for such period, an hourly wage equal to the amount determined under this paragraph for the preceding year, increased by the lesser of-- ``(i) $1.15; or ``(ii) the amount necessary for the wage in effect under this paragraph to equal the wage in effect under section 6(a)(1) for such period, rounded to the nearest multiple of $0.05; and ``(C) for each succeeding 1-year period after the increase made pursuant to subparagraph (B)(ii), the minimum wage in effect under section 6(a)(1); and''. (b) Tips Retained by Employees.--Section 3(m) of the Fair Labor Standards Act of 1938 (29 U.S.C. 203(m)) is amended-- (1) in the second sentence of the matter following paragraph (2), by striking ``of this subsection, and all tips received by such employee have been retained by the employee'' and inserting ``of this subsection. Any employee shall have the right to retain any tips received by such employee''; and (2) by adding at the end the following: ``An employer shall inform each employee of the right and exception provided under the preceding sentence.''. (c) Scheduled Repeal of Separate Minimum Wage for Tipped Employees.-- (1) Tipped employees.--Section 3(m) of the Fair Labor Standards Act of 1938 (29 U.S.C. 203(m)), as amended by subsections (a) and (b), is further amended by striking the sentence beginning with ``In determining the wage an employer is required to pay a tipped employee,'' and all that follows through ``of this subsection.'' and inserting ``The wage required to be paid to a tipped employee shall be the wage set forth in section 6(a)(1).''. (2) Publication of notice.--Section 6(i) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(i)), as added by section 5, is amended by striking ``or in accordance with subparagraph (B) or (C) of section 3(m)(1) (as applicable),''. (3) Effective date.--The amendments made by paragraphs (1) and (2) shall take effect on the date that is one day after the date on which the hourly wage under section 3(m)(1)(C) of the Fair Labor Standards Act of 1938 (29 U.S.C. 203(m)(1)(C)), as amended by subsection (a), takes effect. SEC. 4. NEWLY HIRED EMPLOYEES WHO ARE LESS THAN 20 YEARS OLD. (a) Base Minimum Wage for Newly Hired Employees Who Are Less Than 20 Years Old.--Section 6(g)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(g)(1)) is amended by striking ``a wage which is not less than $4.25 an hour.'' and inserting the following: ``a wage at a rate that is not less than-- ``(A) for the 1-year period beginning on the effective date under section 7 of the Raise the Wage Act, $5.00 an hour; ``(B) for each succeeding 1-year period until the hourly wage under this paragraph equals the wage in effect under section 6(a)(1) for such period, an hourly wage equal to the amount determined under this paragraph for the preceding year, increased by the lesser of-- ``(i) $1.05; or ``(ii) the amount necessary for the wage in effect under this paragraph to equal the wage in effect under section 6(a)(1) for such period, rounded to the nearest multiple of $0.05; and ``(C) for each succeeding 1-year period after the increase made pursuant to subparagraph (B)(ii), the minimum wage in effect under section 6(a)(1).''. (b) Scheduled Repeal of Separate Minimum Wage for Newly Hired Employees Who Are Less Than 20 Years Old.-- (1) In general.--Section 6(g)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(g)(1)), as amended by subsection (a), shall be repealed effective on the date provided in paragraph (3). (2) Publication of notice.--Section 6(i) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(i)), as amended by section 3(c)(2), is further amended by striking ``or subparagraph (B) or (C) of section 6(g)(1) (as applicable),''. (3) Effective date.--The repeal and amendment made by paragraphs (1) and (2), respectively, shall take effect on the date that is one day after the date on which the hourly wage under section 6(g)(1)(C) of the Fair Labor Standards Act, as amended by subsection (a), takes effect. SEC. 5. PUBLICATION OF NOTICE. Section 6 of the Fair Labor Standards Act of 1938 (29 U.S.C. 206), as amended by the preceding sections, is further amended by adding at the end the following: ``(i) Not later than 60 days prior to the effective date of any increase in the required wage determined under subsection (h), or in accordance with subparagraph (B) or (C) of section 3(m)(1) (as applicable), section 14(c)(1)(A) (as applicable), or subparagraph (B) or (C) of section 6(g)(1) (as applicable), the Secretary shall publish in the Federal Register and on the website of the Department of Labor a notice announcing each increase in such required wage.''. SEC. 6. PROMOTING ECONOMIC SELF-SUFFICIENCY FOR INDIVIDUALS WITH DISABILITIES. (a) Wages.-- (1) Transition to fair wages for individuals with disabilities.--Subparagraph (A) of section 14(c)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 214(c)(1)) is amended to read as follows: ``(A) at a rate that equals, or exceeds, the greater of-- ``(i)(I) $4.25 an hour, beginning 1 year after the date the wage rate specified in section 6(a)(1)(A) takes effect; ``(II) $6.25 an hour, beginning 2 years after such date; ``(III) $8.25 an hour, beginning 3 years after such date; ``(IV) $10.25 an hour, beginning 4 years after such date; ``(V) $12.25 an hour, beginning 5 years after such date; and ``(VI) the wage rate in effect under section 6(a)(1), on the date that is 6 years after the date the wage specified in section 6(a)(1)(A) takes effect; or ``(ii) if applicable, the wage rate in effect on the day before the date of enactment of the Raise the Wage Act for the employment, under a special certificate issued under this paragraph, of the individual for whom the wage rate is being determined under this subparagraph,''. (2) Prohibition on new special certificates; sunset.-- Section 14(c) of the Fair Labor Standards Act of 1938 (29 U.S.C. 214(c)) (as amended by paragraph (1)) is further amended by adding at the end the following: ``(6) Prohibition on new special certificates.-- Notwithstanding paragraph (1), the Secretary shall not issue a special certificate under this subsection to an employer that was not issued a special certificate under this subsection before the date of enactment of the Raise the Wage Act. ``(7) Sunset.--Beginning on the day after the date on which the wage rate described in paragraph (1)(A)(i)(VI) takes effect, the authority to issue special certificates under paragraph (1) shall expire, and no special certificates issued under paragraph (1) shall have any legal effect. ``(8) Transition assistance.--Upon request, the Secretary shall provide-- ``(A) technical assistance and information to employers issued a special certificate under this subsection for the purposes of-- ``(i) transitioning the practices of such employers to comply with this subsection, as amended by the Raise the Wage Act; and ``(ii) ensuring continuing employment opportunities for individuals with disabilities receiving a special minimum wage rate under this subsection; and ``(B) information to individuals employed at a special minimum wage rate under this subsection, which may include referrals to other Federal or State entities with expertise in competitive integrated employment.''. (3) Effective date.--The amendments made by this subsection shall take effect on the date of enactment of this Act. (b) Publication of Notice.-- (1) Amendment.--Section 6(i) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(i)), as amended by section 4(b)(2), is further amended by striking ``section 14(c)(1)(A) (as applicable),''. (2) Effective date.--The amendment made by paragraph (1) shall take effect on the day after the date on which the wage rate described in paragraph (1)(A)(i)(VI) of section 14(c) of the Fair Labor Standards Act of 1938 (29 U.S.C. 214(c)), as amended by subsection (a)(1), takes effect. SEC. 7. GENERAL EFFECTIVE DATE. Except as otherwise provided in this Act or the amendments made by this Act, this Act and the amendments made by this Act shall take effect on the first day of the third month that begins after the date of enactment of this Act.

Raise the Wage Act This bill amends the Fair Labor Standards Act of 1938 to increase the federal minimum wage for regular employees over a 7-year period, for tipped employees, and for newly hired employees who are less than 20 years old. The bill sets forth a schedule of annual increases in the federal minimum wage for individuals with disabilities. The Department of Labor shall no longer issue special certificates for the payment of subminimum wages to such individuals after the final wage increase under this bill for such individuals takes effect. Labor shall provide, upon request, technical assistance and information to employers to: (1) help them transition their practices to comply with wage increases and other requirements under this bill for individuals with disabilities, and (2) ensure continuing employment opportunities for such individuals. The bill eliminates the separate minimum wage requirements for tipped, newly hired, and disabled employees. After a specified period, these employees shall be paid the same minimum wage as regular employees. Labor must publish any increase in the minimum wage in the Federal Register and on its website 60 days before it takes effect.

<s>[INST]SECTION 1. SHORT TITLE. This Act may be cited as the ``Raise the Wage Act''. SEC. 2. MINIMUM WAGE INCREASES. (a) In General.--Section 6(a)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(a)(1)) is amended to read as follows: ``(1) except as otherwise provided in this section, not less than-- ``(A) $9.25 an hour, beginning on the effective date under section 7 of the Raise the Wage Act; ``(B) $10.10 an hour, beginning 1 year after such effective date; ``(C) $11.00 an hour, beginning 2 years after such effective date; ``(D) $12.00 an hour, beginning 3 years after such effective date; ``(E) $13.00 an hour, beginning 4 years after such effective date; ``(F) $13.50 an hour, beginning 5 years after such effective date; ``(G) $14.25 an hour, beginning 6 years after such effective date; ``(H) $15.00 an hour, beginning 7 years after such effective date; and ``(I) beginning on the date that is 8 years after such effective date, and annually thereafter, the amount determined by the Secretary under subsection (h);''. (b) Determination Based on Increase in the Median Hourly Wage of All Employees.--Section 6 of the Fair Labor Standards Act of 1938 (29 U.S.C. 206) is amended by adding at the end the following: ``(h)(1) Not later than each date that is 90 days before a new minimum wage determined under subsection (a)(1)(I) is to take effect, the Secretary shall determine the minimum wage to be in effect under this subsection for each period described in subsection (a)(1)(I). The wage determined under this subsection for a year shall be-- ``(A) not less than the amount in effect under subsection (a)(1) on the date of such determination; ``(B) increased from such amount by the annual percentage increase, if any, in the median hourly wage of all employees as determined by the Bureau of Labor Statistics; and ``(C) rounded to the nearest multiple of $0.05. ``(2) In calculating the annual percentage increase in the median hourly wage of all employees for purposes of paragraph (1)(B), the Secretary, through the Bureau of Labor Statistics, shall compile data on the hourly wages of all employees to determine such a median hourly wage and compare such median hourly wage for the most recent year for which data are available with the median hourly wage determined for the preceding year.''. SEC. 3. TIPPED EMPLOYEES. (a) Base Minimum Wage for Tipped Employees.--Section 3(m)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 203(m)(1)) is amended to read as follows: ``(1) the cash wage paid such employee, which for purposes of such determination shall be not less than-- ``(A) for the 1-year period beginning on the effective date under section 7 of the Raise the Wage Act, $4.15 an hour; ``(B) for each succeeding 1-year period until the hourly wage under this paragraph equals the wage in effect under section 6(a)(1) for such period, an hourly wage equal to the amount determined under this paragraph for the preceding year, increased by the lesser of-- ``(i) $1.15; or ``(ii) the amount necessary for the wage in effect under this paragraph to equal the wage in effect under section 6(a)(1) for such period, rounded to the nearest multiple of $0.05; and ``(C) for each succeeding 1-year period after the increase made pursuant to subparagraph (B)(ii), the minimum wage in effect under section 6(a)(1); and''. (b) Tips Retained by Employees.--Section 3(m) of the Fair Labor Standards Act of 1938 (29 U.S.C. 203(m)) is amended-- (1) in the second sentence of the matter following paragraph (2), by striking ``of this subsection, and all tips received by such employee have been retained by the employee'' and inserting ``of this subsection. Any employee shall have the right to retain any tips received by such employee''; and (2) by adding at the end the following: ``An employer shall inform each employee of the right and exception provided under the preceding sentence.''. (c) Scheduled Repeal of Separate Minimum Wage for Tipped Employees.-- (1) Tipped employees.--Section 3(m) of the Fair Labor Standards Act of 1938 (29 U.S.C. 203(m)), as amended by subsections (a) and (b), is further amended by striking the sentence beginning with ``In determining the wage an employer is required to pay a tipped employee,'' and all that follows through ``of this subsection.'' and inserting ``The wage required to be paid to a tipped employee shall be the wage set forth in section 6(a)(1).''. (2) Publication of notice.--Section 6(i) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(i)), as added by section 5, is amended by striking ``or in accordance with subparagraph (B) or (C) of section 3(m)(1) (as applicable),''. (3) Effective date.--The amendments made by paragraphs (1) and (2) shall take effect on the date that is one day after the date on which the hourly wage under section 3(m)(1)(C) of the Fair Labor Standards Act of 1938 (29 U.S.C. 203(m)(1)(C)), as amended by subsection (a), takes effect. SEC. 4. NEWLY HIRED EMPLOYEES WHO ARE LESS THAN 20 YEARS OLD. (a) Base Minimum Wage for Newly Hired Employees Who Are Less Than 20 Years Old.--Section 6(g)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(g)(1)) is amended by striking ``a wage which is not less than $4.25 an hour.'' and inserting the following: ``a wage at a rate that is not less than-- ``(A) for the 1-year period beginning on the effective date under section 7 of the Raise the Wage Act, $5.00 an hour; ``(B) for each succeeding 1-year period until the hourly wage under this paragraph equals the wage in effect under section 6(a)(1) for such period, an hourly wage equal to the amount determined under this paragraph for the preceding year, increased by the lesser of-- ``(i) $1.05; or ``(ii) the amount necessary for the wage in effect under this paragraph to equal the wage in effect under section 6(a)(1) for such period, rounded to the nearest multiple of $0.05; and ``(C) for each succeeding 1-year period after the increase made pursuant to subparagraph (B)(ii), the minimum wage in effect under section 6(a)(1).''. (b) Scheduled Repeal of Separate Minimum Wage for Newly Hired Employees Who Are Less Than 20 Years Old.-- (1) In general.--Section 6(g)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(g)(1)), as amended by subsection (a), shall be repealed effective on the date provided in paragraph (3). (2) Publication of notice.--Section 6(i) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(i)), as amended by section 3(c)(2), is further amended by striking ``or subparagraph (B) or (C) of section 6(g)(1) (as applicable),''. (3) Effective date.--The repeal and amendment made by paragraphs (1) and (2), respectively, shall take effect on the date that is one day after the date on which the hourly wage under section 6(g)(1)(C) of the Fair Labor Standards Act, as amended by subsection (a), takes effect. SEC. 5. PUBLICATION OF NOTICE. Section 6 of the Fair Labor Standards Act of 1938 (29 U.S.C. 206), as amended by the preceding sections, is further amended by adding at the end the following: ``(i) Not later than 60 days prior to the effective date of any increase in the required wage determined under subsection (h), or in accordance with subparagraph (B) or (C) of section 3(m)(1) (as applicable), section 14(c)(1)(A) (as applicable), or subparagraph (B) or (C) of section 6(g)(1) (as applicable), the Secretary shall publish in the Federal Register and on the website of the Department of Labor a notice announcing each increase in such required wage.''. SEC. 6. PROMOTING ECONOMIC SELF-SUFFICIENCY FOR INDIVIDUALS WITH DISABILITIES. (a) Wages.-- (1) Transition to fair wages for individuals with disabilities.--Subparagraph (A) of section 14(c)(1) of the Fair Labor Standards Act of 1938 (29 U.S.C. 214(c)(1)) is amended to read as follows: ``(A) at a rate that equals, or exceeds, the greater of-- ``(i)(I) $4.25 an hour, beginning 1 year after the date the wage rate specified in section 6(a)(1)(A) takes effect; ``(II) $6.25 an hour, beginning 2 years after such date; ``(III) $8.25 an hour, beginning 3 years after such date; ``(IV) $10.25 an hour, beginning 4 years after such date; ``(V) $12.25 an hour, beginning 5 years after such date; and ``(VI) the wage rate in effect under section 6(a)(1), on the date that is 6 years after the date the wage specified in section 6(a)(1)(A) takes effect; or ``(ii) if applicable, the wage rate in effect on the day before the date of enactment of the Raise the Wage Act for the employment, under a special certificate issued under this paragraph, of the individual for whom the wage rate is being determined under this subparagraph,''. (2) Prohibition on new special certificates; sunset.-- Section 14(c) of the Fair Labor Standards Act of 1938 (29 U.S.C. 214(c)) (as amended by paragraph (1)) is further amended by adding at the end the following: ``(6) Prohibition on new special certificates.-- Notwithstanding paragraph (1), the Secretary shall not issue a special certificate under this subsection to an employer that was not issued a special certificate under this subsection before the date of enactment of the Raise the Wage Act. ``(7) Sunset.--Beginning on the day after the date on which the wage rate described in paragraph (1)(A)(i)(VI) takes effect, the authority to issue special certificates under paragraph (1) shall expire, and no special certificates issued under paragraph (1) shall have any legal effect. ``(8) Transition assistance.--Upon request, the Secretary shall provide-- ``(A) technical assistance and information to employers issued a special certificate under this subsection for the purposes of-- ``(i) transitioning the practices of such employers to comply with this subsection, as amended by the Raise the Wage Act; and ``(ii) ensuring continuing employment opportunities for individuals with disabilities receiving a special minimum wage rate under this subsection; and ``(B) information to individuals employed at a special minimum wage rate under this subsection, which may include referrals to other Federal or State entities with expertise in competitive integrated employment.''. (3) Effective date.--The amendments made by this subsection shall take effect on the date of enactment of this Act. (b) Publication of Notice.-- (1) Amendment.--Section 6(i) of the Fair Labor Standards Act of 1938 (29 U.S.C. 206(i)), as amended by section 4(b)(2), is further amended by striking ``section 14(c)(1)(A) (as applicable),''. (2) Effective date.--The amendment made by paragraph (1) shall take effect on the day after the date on which the wage rate described in paragraph (1)(A)(i)(VI) of section 14(c) of the Fair Labor Standards Act of 1938 (29 U.S.C. 214(c)), as amended by subsection (a)(1), takes effect. SEC. 7. GENERAL EFFECTIVE DATE. Except as otherwise provided in this Act or the amendments made by this Act, this Act and the amendments made by this Act shall take effect on the first day of the third month that begins after the date of enactment of this Act.[/INST]Raise the Wage Act This bill amends the Fair Labor Standards Act of 1938 to increase the federal minimum wage for regular employees over a 7-year period, for tipped employees, and for newly hired employees who are less than 20 years old. The bill sets forth a schedule of annual increases in the federal minimum wage for individuals with disabilities. The Department of Labor shall no longer issue special certificates for the payment of subminimum wages to such individuals after the final wage increase under this bill for such individuals takes effect. Labor shall provide, upon request, technical assistance and information to employers to: (1) help them transition their practices to comply with wage increases and other requirements under this bill for individuals with disabilities, and (2) ensure continuing employment opportunities for such individuals. The bill eliminates the separate minimum wage requirements for tipped, newly hired, and disabled employees. After a specified period, these employees shall be paid the same minimum wage as regular employees. Labor must publish any increase in the minimum wage in the Federal Register and on its website 60 days before it takes effect.</s>

SECTION 1. SHORT TITLE; TABLE OF CONTENTS. (a) Short Title.--This Act may be cited as the ``Medicare Rural Ambulance Service Improvement Act of 2001''. (b) Table of Contents.--The table of contents of this Act is as follows: Sec. 1. Short title; table of contents. Sec. 2. Payment increases for rural ambulance services. Sec. 3. Basing rural areas on population density by postal zip codes. Sec. 4. Requiring use of recent data for calculation of budget neutrality adjustment. Sec. 5. Exemption of ambulance suppliers from certain provider designation rules. Sec. 6. Calculation of separate rates for ground and air ambulance services. SEC. 2. PAYMENT INCREASES FOR RURAL AMBULANCE SERVICES. (a) 20 Percent Increase.--Section 1834(l) of the Social Security Act (42 U.S.C. 1395m(l)), as amended by sections 205(a) and 221(a) of the Medicare, Medicaid, and SCHIP Benefits Improvement and Protection Act of 2000 (114 Stat. 2763A-482, 486), as enacted into law by section 1(a)(6) of Public Law 106-554, is amended-- (1) by redesignating paragraph (8), as added by such section 221(a), as paragraph (9), and (2) by inserting after that paragraph the following new paragraph: ``(10) Increase for rural ambulance services.--Effective for ambulance services furnished on or after January 1, 2002, for which the transportation originates in a rural area or tract to which paragraph (9) applies, notwithstanding the previous provisions of this subsection, the Secretary shall provide for an additional payment for such services equal to 20 percent of the payment amount otherwise made under this section for such services.''. (b) Increase in Mileage Rates for First 50 Miles.--Paragraph (9) of that section, as so redesignated under subsection (a)(1), is amended-- (1) in the heading, by striking ``Transitional assistance'' and inserting ``Mileage assistance''; (2) by striking ``furnished on or after July 1, 2001, and before January 1, 2004,''; (3) by striking ``that,'' and inserting ``that--''; (4) by designating the remaining text of paragraph (9) that follows ``that--'' a new subparagraph (B) and indenting such subparagraph 2 ems to the right; (5) in such subparagraph (B), by striking ``with respect to the payment rate for mileage for a trip above 17 miles, and up to 50 miles, the rate otherwise established shall be increased'' and inserting ``for ambulance services furnished on or after July 1, 2001, the payment rate otherwise established for mileage for a trip above 17 miles, and up to 50 miles, shall be increased''; and (6) by inserting before such subparagraph (B) the following new subparagraph: ``(A) for ambulance services furnished on or after January 1, 2002, the payment rate otherwise established for mileage for the first 17 miles of a trip transporting a patient shall be increased by $7.50 per mile; and''. (c) Nonapplication of Initial Budget Neutrality Provisions.--The provisions of section 1834(l)(3)(A) of the Social Security Act (42 U.S.C. 1395m(l)(3)(A)) do not apply with respect to the amendments made by this section. SEC. 3. BASING RURAL AREAS ON POPULATION DENSITY BY POSTAL ZIP CODES. (a) In General.--Section 1834(l) of the Social Security Act (42 U.S.C. 1395m(l)) is amended in paragraph (9), as so redesignated by section 2(a)(1), by striking ``(as defined in section 1886(d)(2)(D))'' and all that follows through ``(57 Fed. Reg. 6725))'' and inserting ``(as determined under an area classification system established by the Secretary that is based on population density within postal zip code areas)''. (b) Effective Date.--The Secretary of Health and Human Services shall establish the classification system described in the amendment made by subsection (a) by not later than 1 year after the date of the enactment of this Act. Such amendment shall apply to services furnished on or after such date, not later than 30 days after the establishment of such system, as the Secretary shall provide by regulation. SEC. 4. REQUIRING USE OF RECENT DATA FOR CALCULATION OF BUDGET NEUTRALITY ADJUSTMENT. (a) In General.--Section 1834(l)(3) of the Social Security Act (42 U.S.C. 1395m(l)(3)) is amended-- (1) by striking ``and'' at the end of subparagraph (A); (2) by redesignating subparagraph (B) as subparagraph (C); and (3) by inserting after subparagraph (A) the following new subparagraph: ``(B) in making the determination under subparagraph (A), use data from the most recent year for which such data are available, but may not use data from a year that preceded the two-year period ending on the date of the implementation of the fee schedule under this subsection; and''. (b) Effective Date.--The amendments made by subsection (a) shall apply to ambulance services furnished on or after January 1, 2003. SEC. 5. EXEMPTION OF AMBULANCE SUPPLIERS FROM CERTAIN PROVIDER DESIGNATION RULES. In applying the regulation for requirements for determination that a facility or organization has provider-based status under section 413.65 of title 42 of the Code of Federal Regulations, the Secretary of Health and Human Services shall not apply the regulation with respect to ambulance services. SEC. 6. CALCULATION OF SEPARATE RATES FOR GROUND AND AIR AMBULANCE SERVICES. (a) In General.--Section 1861(v)(1)(U) of the Social Security Act (42 U.S.C. 1395x(v)(1)(U)) is amended by adding at the end the following: ``In carrying out the first sentence, upon request of a hospital, the Secretary shall determine and apply separately the reasonable costs of ground and air ambulance services.''. (b) Effective Date.--The amendment made by subsection (a) shall apply to ambulance services furnished on or after the date of the enactment of this Act.

Medicare Rural Ambulance Service Improvement Act of 2001 - Amends title XVIII (Medicare) of the Social Security Act (SSA), as amended by the Medicare, Medicaid, and SCHIP Benefits Improvement and Protection Act of 2000, to direct the Secretary of Health and Human Services to increase by 20 percent the payment under Medicare for rural ambulance services. Increases by $7.50 per mile the payment rate for the first 17 miles of an ambulance trip transporting a patient.Provides for determination of rural areas based on population density by postal zip codes.Requires the use of recent data for calculation of budget neutrality adjustments to payments for ambulance services.Exempts ambulance suppliers from certain provider designation rules.Directs the Secretary to determine and apply separately the reasonable costs of ground and air ambulance services.

<s>[INST]SECTION 1. SHORT TITLE; TABLE OF CONTENTS. (a) Short Title.--This Act may be cited as the ``Medicare Rural Ambulance Service Improvement Act of 2001''. (b) Table of Contents.--The table of contents of this Act is as follows: Sec. 1. Short title; table of contents. Sec. 2. Payment increases for rural ambulance services. Sec. 3. Basing rural areas on population density by postal zip codes. Sec. 4. Requiring use of recent data for calculation of budget neutrality adjustment. Sec. 5. Exemption of ambulance suppliers from certain provider designation rules. Sec. 6. Calculation of separate rates for ground and air ambulance services. SEC. 2. PAYMENT INCREASES FOR RURAL AMBULANCE SERVICES. (a) 20 Percent Increase.--Section 1834(l) of the Social Security Act (42 U.S.C. 1395m(l)), as amended by sections 205(a) and 221(a) of the Medicare, Medicaid, and SCHIP Benefits Improvement and Protection Act of 2000 (114 Stat. 2763A-482, 486), as enacted into law by section 1(a)(6) of Public Law 106-554, is amended-- (1) by redesignating paragraph (8), as added by such section 221(a), as paragraph (9), and (2) by inserting after that paragraph the following new paragraph: ``(10) Increase for rural ambulance services.--Effective for ambulance services furnished on or after January 1, 2002, for which the transportation originates in a rural area or tract to which paragraph (9) applies, notwithstanding the previous provisions of this subsection, the Secretary shall provide for an additional payment for such services equal to 20 percent of the payment amount otherwise made under this section for such services.''. (b) Increase in Mileage Rates for First 50 Miles.--Paragraph (9) of that section, as so redesignated under subsection (a)(1), is amended-- (1) in the heading, by striking ``Transitional assistance'' and inserting ``Mileage assistance''; (2) by striking ``furnished on or after July 1, 2001, and before January 1, 2004,''; (3) by striking ``that,'' and inserting ``that--''; (4) by designating the remaining text of paragraph (9) that follows ``that--'' a new subparagraph (B) and indenting such subparagraph 2 ems to the right; (5) in such subparagraph (B), by striking ``with respect to the payment rate for mileage for a trip above 17 miles, and up to 50 miles, the rate otherwise established shall be increased'' and inserting ``for ambulance services furnished on or after July 1, 2001, the payment rate otherwise established for mileage for a trip above 17 miles, and up to 50 miles, shall be increased''; and (6) by inserting before such subparagraph (B) the following new subparagraph: ``(A) for ambulance services furnished on or after January 1, 2002, the payment rate otherwise established for mileage for the first 17 miles of a trip transporting a patient shall be increased by $7.50 per mile; and''. (c) Nonapplication of Initial Budget Neutrality Provisions.--The provisions of section 1834(l)(3)(A) of the Social Security Act (42 U.S.C. 1395m(l)(3)(A)) do not apply with respect to the amendments made by this section. SEC. 3. BASING RURAL AREAS ON POPULATION DENSITY BY POSTAL ZIP CODES. (a) In General.--Section 1834(l) of the Social Security Act (42 U.S.C. 1395m(l)) is amended in paragraph (9), as so redesignated by section 2(a)(1), by striking ``(as defined in section 1886(d)(2)(D))'' and all that follows through ``(57 Fed. Reg. 6725))'' and inserting ``(as determined under an area classification system established by the Secretary that is based on population density within postal zip code areas)''. (b) Effective Date.--The Secretary of Health and Human Services shall establish the classification system described in the amendment made by subsection (a) by not later than 1 year after the date of the enactment of this Act. Such amendment shall apply to services furnished on or after such date, not later than 30 days after the establishment of such system, as the Secretary shall provide by regulation. SEC. 4. REQUIRING USE OF RECENT DATA FOR CALCULATION OF BUDGET NEUTRALITY ADJUSTMENT. (a) In General.--Section 1834(l)(3) of the Social Security Act (42 U.S.C. 1395m(l)(3)) is amended-- (1) by striking ``and'' at the end of subparagraph (A); (2) by redesignating subparagraph (B) as subparagraph (C); and (3) by inserting after subparagraph (A) the following new subparagraph: ``(B) in making the determination under subparagraph (A), use data from the most recent year for which such data are available, but may not use data from a year that preceded the two-year period ending on the date of the implementation of the fee schedule under this subsection; and''. (b) Effective Date.--The amendments made by subsection (a) shall apply to ambulance services furnished on or after January 1, 2003. SEC. 5. EXEMPTION OF AMBULANCE SUPPLIERS FROM CERTAIN PROVIDER DESIGNATION RULES. In applying the regulation for requirements for determination that a facility or organization has provider-based status under section 413.65 of title 42 of the Code of Federal Regulations, the Secretary of Health and Human Services shall not apply the regulation with respect to ambulance services. SEC. 6. CALCULATION OF SEPARATE RATES FOR GROUND AND AIR AMBULANCE SERVICES. (a) In General.--Section 1861(v)(1)(U) of the Social Security Act (42 U.S.C. 1395x(v)(1)(U)) is amended by adding at the end the following: ``In carrying out the first sentence, upon request of a hospital, the Secretary shall determine and apply separately the reasonable costs of ground and air ambulance services.''. (b) Effective Date.--The amendment made by subsection (a) shall apply to ambulance services furnished on or after the date of the enactment of this Act.[/INST]Medicare Rural Ambulance Service Improvement Act of 2001 - Amends title XVIII (Medicare) of the Social Security Act (SSA), as amended by the Medicare, Medicaid, and SCHIP Benefits Improvement and Protection Act of 2000, to direct the Secretary of Health and Human Services to increase by 20 percent the payment under Medicare for rural ambulance services. Increases by $7.50 per mile the payment rate for the first 17 miles of an ambulance trip transporting a patient.Provides for determination of rural areas based on population density by postal zip codes.Requires the use of recent data for calculation of budget neutrality adjustments to payments for ambulance services.Exempts ambulance suppliers from certain provider designation rules.Directs the Secretary to determine and apply separately the reasonable costs of ground and air ambulance services.</s>

in the last decade or so physicists have begun to do academic research in economics in a newly emerging field often called `` econophysics '' . perhaps a hundred people are now actively involved , with two new journals and frequent conferences . at least ten books have been written on econophysics in general or specific subtopics ( we are restricted by citation limits here , but an extensive bibliography of the books and archived articles is maintained on the econophysics website , http://www.unifr.ch/econophysics ) . theses are being granted by physics departments for research in economics , and in europe there are several professors in physics departments specializing in econophysics . there is even a new annual research prize , titled the `` young scientist award for social and econophysics '' . is this just a fad , or is there something more substantial here ? if physicists want to do research in economics , why do nt they just get degrees in economics in the first place ? why do nt the econophysicists retool , find jobs in economics departments and publish in traditional economics journals ? perhaps this is just a temporary phenomenon , driven by a generation of physicists who made a bad career choice . is there any reason why research in economics should be done in physics departments as an on - going activity , or why economics departments should pay heed to the methods of physics ? what advantage , if any , is conferred by a background in physics ? and most important , how does econophysics differ from economics , and what unique contribution can it make , if any ? one is naturally suspicious that the emergence of econophysics is just a reflection of a depressed job market . it is certainly true that during the last two decades a large number of physicists have been lured to wall st , and that this has been an important stimulus . but this is not the main focus . econophysics is primarily an academic endeavor , whose participants are employed by universities . it offers no special advantages in the job market in fact , quite the opposite : it is even more competitive than mainstream fields of physics . no permanent positions in econophysics have ever been offered in an american university . papers submitted to physical review letters require special justification concerning their relevance to physics . while the situation in europe is a little better than in the u. s. , jobs are still very scarce . the tenuous existence of econophysics relies on senior professors who have redirected their interests from other areas , as well as a few bold students and postdocs . the involvement of physicists in social science has a long history , going back at least to daniel bernoulli , who in 1738 introduced the idea of utility to describe people s preferences . in his _ essai philosophique sur les probabilites _ ( 1812 ) , laplace pointed out that events that might seem random and unpredictable , such as the number of letters that end up in the paris dead - letter office , can in fact be quite predictable and can be shown to obey simple laws . these ideas were further amplified by quetelet , a student of fourier , who in 1835 coined the term `` social physics '' , and studied the existence of patterns in data sets ranging from the frequency of different methods for committing murder to the chest size of scottish men . analogies to physics played an important role in the development of economic theory through the nineteenth century , and some of the founders of neoclassical economic theory , such as irving fisher , a student of willard gibbs , were originally trained as physicists . ettore majorana in 1938 presciently outlined both the opportunities and pitfalls in applying statistical physics methods to the social sciences . the range of topics that have been addressed spans many different areas of economics . finance is particularly well represented ; sample topics include the empirical observation of regularities in market data , the dynamics of price formation , the understanding of bubbles and panics , methods for pricing derivatives such as options , the construction of optimal portfolios , and many other subjects . broader topics in economics include the distribution of income , theories of how money emerges , and implications of symmetry and scaling to the functioning of markets . despite their long history of association , we see the substantial contributions of physics to economics as still in an early stage , and find it fanciful to forecast what will ultimately be accomplished . almost certainly , `` physical '' aspects of theories of social order will _ not _ simply recapitulate existing theories in physics , though already there appear to be overlaps . the development of societies and economies is potentially contingent on accidents of history , and at every turn hinges on complex aspects of human behavior . nonetheless , striking empirical regularities such as those we survey below suggest that at least some social order is not historically contingent , and perhaps is predictable from first principles . the role of markets as mediators of communication and distributed computation , and the emergence of the social institutions that support them , are quintessentially economic phenomena . yet the notions of their computational or communication capacity , and how these account for their stability and historical succession , may naturally be parts of the physical world as it includes human social dynamics . in the context of human desires , markets and other economic institutions bring with them notions of efficiency or optimality in satisfying those desires . while intuitively appealing , such notions have proven hard to formalize , and the examples below show some progress in this area . as with most new areas of physical inquiry , we expect that the ultimate goals of a `` physical economics '' will be declared with hindsight , from successes in identifying , measuring , modeling and in some cases predicting empirical regularities . economists are typically better trained in statistical analysis than physicists , so this might seem to be an area where physicists have little to contribute . however , differences in goals and philosophy are important . physics is driven by the quest for universal laws . in part , because of the extreme complexity of phenomena in society , in the postmodern world where relativist philosophies of science enjoy disturbingly widespread acceptance , this quest has been largely abandoned . modern work in social science is largely focused on documenting differences . although this trend is much less obvious in economics , a typical paper in financial economics , for example , might study the difference between the nyse and the nasdaq stock exchanges , or the effect of changing the tick size of prices ( the unit of the smallest possible price change ) . physicists have ( perhaps naively ) entered with fresh eyes and new hypotheses , and have looked at economic data with the goal of finding pervasive regularities , emphasizing what might be common to all markets rather than what might make them different . this work has been opportunistically motivated by the the existence of large data sets such as the complete transaction histories of major exchanges over timespans of years , which in some cases contain hundreds of millions of events . much of the work by physicists in economics concerns power laws . a power law is an asymptotic relation of the form @xmath0 , where @xmath1 is a variable and @xmath2 is a constant . in many important cases @xmath3 is a probability distribution . power laws have received considerable attention in physics because they indicate scale free behavior and they are characteristic of critical or nonequilibrium phenomena . in fact , the first power law distribution ( in any field ) was observed in economics ( see box [ box : income_dist ] ) , and the existence of power laws in economics has been a matter of debate ever since . in 1963 benoit mandelbrot @xcite observed that the distribution of cotton price fluctuations follows a power law . further observations of power laws in price changes were subsequently noted by rosario mantegna and eugene stanley @xcite , who coined the term `` econophysics '' . [ fig : power_law_fig ] shows the striking fidelity often found in economic power laws . the existence of power laws in price changes is interesting from a practical point of view because of its implications for the risk of financial investments , and from a theoretical point of view because it suggests scale independence and possible analogies to nonequilibrium behavior in the processes that generate financial returns . since then many other power laws have been discovered by physicists . these include the variance in the growth rates of companies as a function of their size @xcite , the distribution function for the number of shares in a transaction , the distribution for the number of trading orders submitted at a price @xmath1 away from the best price offered , the size of the price response to a trade as a function of the size @xmath4 of the company being traded , and many other examples . the question of why power laws are so ubiquitous in financial markets has stimulated a great deal of theoretical work . one of the most famous and most used models of prices is the random walk . the random walk was originally introduced for prices in 1900 by louis bachelier , a student of poincar , five years before einstein introduced it to describe brownian motion . this forms the basis for the black - scholes theory of option pricing @xcite , which won a nobel prize in economics in 1997 ( see box [ box : option_pricing ] ) . one of the interesting and surprising properties of the random walk of real prices is that its diffusion rate is not constant . the size of price changes is strongly positively autocorrelated in time , a phenomenon called _ _ clustered volatility _ _ is defined as @xmath5 , where @xmath6 , @xmath7 denotes a time average and @xmath8 the standard deviation . `` volatility '' is the term used in finance to refer to the variance or size of price shifts . ] . the autocorrelation of the size of price changes decays as a power law of the form @xmath9 . since @xmath10 , this is a long - memory process . long - memory processes display anomalous diffusion and very slow convergence of statistical averages . physicists have recently discovered that volatility is just one of several long - memory - processes in markets . one of the most surprising concerns fluctuations in supply and demand @xcite . if one assigns @xmath11 to an order to buy and @xmath12 to an order to sell , the resulting series of numbers has a positive autocorrelation function that decays as a power law with an exponent @xmath13 , which persists at statistically significant levels across tens of thousands of orders , for periods of time lasting for weeks . this implies that changes in supply and demand obey a long - memory process . this has interesting implications . one of the most fundamental principles in financial economics is called _ market efficiency_. this principle takes many forms : a market is informationally efficient if prices reflect all available information ; it is arbitrage efficient if it is impossible for investors to make `` excess profits '' , and it is allocationally efficient if prices are set so that they in some sense maximize everyone s welfare . one of the consequences of informational efficiency is that prices should not be predictable . in reality this is not a bad approximation ; even the best trading strategies exploit only very weak levels of predictability . the coexistence of the long - memory of supply and demand with market efficiency creates an interesting and as yet unresolved puzzle . long - memory processes are highly predictable using a simple linear algorithm . since the entrance of new buyers tends to drive the price up , and the entrance of new sellers tends to drive it down , this naively suggests that price changes should also be long - memory , which would violate market efficiency . to prevent this from happening , the agents in the market must somehow collectively adjust their behavior to offset this , for example by creating an asymmetric response of prices , so that when there is an excess of new buyers the price response to new buy orders is smaller than it is to new sell orders . how this comes about , and why it comes about , remains a mystery . this may be related to the cause of clustered volatility . there is a great deal of other empirical work using methods and analogies from physics that we do not have the space to describe in any detail . for example , random matrix theory @xcite ( developed in nuclear physics ) and the use of ultrametric correlations have proved useful for understanding the correlation between the movement of prices of different companies . an analogy to the omori law for seismic activity after major earthquakes has proved to be useful for understanding the aftermath of large crashes in stock markets , and other analogies from geophysics has led to a controversial hypothesis about why markets crash @xcite . the statistics of price movements have been noted to bear a striking resemblance to those of turbulent fluids , which has led to what may now be the best empirical models available for predicting clustered volatility . such examples speak to the universality of mathematics in its applications to the world . the most fundamental difference between a physical system and an economy is that economies are inhabited by people , who have strategic interactions . because people think , plan , and make decisions based on their plans , they are much more complicated to understand than atoms this is a problem that physics has never coped with , and it has caused the mathematical techniques and modeling philosophy in economics to diverge from those in physics . while this is clearly necessary , many physicists would argue that the gap is wider than it should be . the central approach to the problem of strategic interactions in neoclassical economics is the theory of rational choice . the economists stylized version of individual rationality is to maximize some measure of one s personal ( usually material ) welfare , having perfect knowledge of the world and of other agents goals and abilities , and the ability to perform computations of any complexity . when agent a considers any strategy , agent b knows that a is considering that strategy , and a knows that b knows that a knows , and so on . this infinite regress appears very complicated . however , a key simplifying result is that in any game there exists at least one nash equilibrium , which is a set of strategies with the property that each is the optimal response to all of the others . the nash equilibrium is a fixed point in the space of strategies , which circumvents the infinite regress problem by imposing self - consistency as a defining criterion . subject to several caveats , rational players who are not cooperating with each other will choose a nash strategy . this is the operational meaning of rational choice . the assumption that decisions of real human beings can be approximated in this way dominated economic thinking about individual choices ( called _ microeconomics _ ) from 1950 until the mid-1980s , though it is clearly implausible for all but the simplest cognitive tasks . it also leaves unaddressed the problem of aggregation of individual choices and the behavior of large populations ( called _ macroeconomics _ ) . in the last twenty years economics has begun to challenge the assumptions of rational choice and perfect markets by modeling imperfections such as asymmetric information , incomplete market structure , and bounded rationality . several new schools of thought have emerged . the behavioral economists attempt to take human psychology into account by studying people s actual choices in idealized economic settings . another school uses idealizations of problem solving and learning ranging from standard statistical methods to artificial intelligence to address the problem of bounded rationality . agent - based modeling makes computer simulations based on idealizations of human behaviors and focuses on the complexity of economic interactions . yet another approach assumes that some agents ( called noise traders ) have extremely limited reasoning capabilities while others are perfectly rational . physicists have joined with many economists in seeking new theories of non - fully - rational choice , bringing new perspectives to bear on the problem . an early effort using both agent based modeling and artificial intelligence is called the santa fe stock market . this grew out of a conference in 1986 organized by ken arrow , phil anderson and david pines @xcite that brought together physicists and economists . presaging the modern move toward behavioral economics , the physicists all expressed disbelief in theories of rational choice and suggested that the economists should take human psychology and learning more into account . the santa fe stock market was a collaboration between economists , physicists and a computer scientist that grew out of this conference . it replaced the rational agents in an idealized market setting with an artificial intelligence model @xcite . it showed that this leads to qualitative modifications of the statistics of prices , such as fat tailed distributions of price change and clustered volatility , and suggested that non - rational behavior plays an important part in generating these phenomena . the problem with this approach is that it is complicated , and while it captures some qualitative features of markets , the path to more quantitative theories is not clear . agent based models tend to require ad hoc assumptions that are difficult to validate . the hypothesis of rational choice , in contrast , has the great virtue that it is parsimonious , making strong predictions from simple hypotheses . from this point of view it is more like theories in physics . this perspective has inspired the search for other simple parsimonious alternatives . one such approach is often called _ zero intelligence_. this amounts to the assumption that agents behave more or less randomly , subject to constraints such as their budget . zero intelligence models can be used to study the properties of market institutions , and to determine which properties of a market depend on intentionality and which do nt . this provides a benchmark to avoid getting lost in the large space of realistic human behaviors . once a zero intelligence model has be made , it can be modified by incorporating more realistic assumptions , adding a little intelligence based on empirical observations or models of learning . where rational choice enters the wilderness of bounded rationality from the top , zero intelligence enters it from the bottom . the zero intelligence approach can be traced back to the work of herbert simon , a nobel laureate in economics and pioneer in artificial intelligence . its main champions in recent years have been physicists , who have used analogies to statistical mechanics to develop new models of markets . a good example is the work of per bak , maya paczuski , and martin shubik ( two physicists and an economist ) , who studied the impact of random trading orders on prices within an idealized model of price formation . they assumed that traders simply place orders to buy or sell at random above or below the prices of the most recent transactions . they then modify their orders from time to time , moving them toward the middle until they generate a transaction . the result is mathematically analogous to a reaction diffusion model for the reaction @xmath14 that was developed by the physicist john cardy . while this model is highly unrealistic , with a few modifications it produces some qualitative features , such as heavy tailed price distributions , that resemble their counterparts in real markets . many variations of the bps model have now been explored . one variation simply assumes that agents place and cancel trading orders at random . after performing a dimensional analysis based on prices , shares and time , the resulting model can be shown to obey simple scaling laws that relate statistical properties of trading order placement to statistical properties of prices . these laws are restrictions on state variables similar to the ideal gas law , but in this case the variables on one side are properties of trading orders , such as the rates for order placement and cancellation , and the variables on the other side are statistical properties of prices , such as the diffusion rate in bachelier s random walk model . these scaling laws have been tested on data from the london stock exchange and have been shown to be in surprisingly good agreement with it @xcite . the model also gives insight into the shape of supply and demand curves , as shown in fig [ fig : impact_collapse ] . another alternative approach is to develop highly simplified models of strategic interaction that do a better job of capturing the essence of the collective behavior in a financial market . brian arthur s el farol bar problem provides an alternative to conventional game theory . the name el farol comes from a bar in santa fe that is often crowded . each day agents decide whether or not to go hear music ; if there is room in the bar they are happy , and if it is too crowded they are disappointed . by definition only a minority of the people can be happy , which leads to a phenomenon analogous to _ frustration _ - some desires are necessarily unsatisfiable and as a result an astronomically large number of equilibria can emerge . the el farol model was simplified and abstracted by challet and zhang as the minority game @xcite , in which an odd number @xmath15 of agents repeatedly choose between two alternatives , which can be labeled @xmath16 or @xmath17 . their decisions are made independently and simultaneously . agents whose choice is the minority value are rewarded ( awarded `` payoffs '' , in game - theoretic terminology ) . typically agents are capable of remembering the outcomes of @xmath18 prior rounds of play , and maintain an inventory of @xmath19 strategies ( random lookup tables ) dictating a next move for each history . for example , for @xmath20 a possible lookup table would be @xmath21 , @xmath22 , @xmath23 , @xmath24 , meaning in the first case , if the previous majority choices were @xmath16 in both previous rounds of the game , choose @xmath17 on the next round " . the strategy chosen is that with the best cumulative performance . minority games exhibit phase transitions for @xmath25 , in the ratio @xmath26 , of the number of resolvable pasts to the number of agents , as shown in fig . [ fig : mg_phases ] . . for @xmath27 the variance is high , indicating that the game is highly inefficient in the sense that the minority group is much smaller than it needs to be . the variance reaches a minimum at @xmath28 , and when @xmath29 is large it approaches the value it would have if all agents make random choices ( from savit et al . - see reference @xcite ) . ] for @xmath27 a critical value , the population is in a symmetric phase , where the outcome of the next move is unpredictable from the history of play . for @xmath30 , in contrast , @xmath15 agents sparsely sample the space of strategies , the next outcome is predictable , and the population is in a symmetry - broken phase that can be understood analytically with replica methods . the variance in the number of winners about the optimum , @xmath31 , measures the failure of `` allocative efficiency '' , and is minimized at @xmath32 . the minority game is readily extended to incorporate more features of real financial markets , such as payoffs that increase as the size of the winning group gets smaller ( much as buyers or sellers of stocks can reap larger profits when they are providing the more scarce of supply or demand ) , or the `` grand canonical '' version in which players are permitted to enter and leave . with these enhancements the game self - organizes around the critical point @xmath32 , the payoff series exhibits fluctuations that display clustered volatility , and they have a distribution with a power law tail , reminiscent of a real market . the minority game provides a fascinating example of how a very simple game can display a rich set of properties as soon as one moves away from the rational choice paradigm . finance is not the only area of economics where physicists are active . in economics as in physics it is traditional to distinguish open from closed systems , which give rise to different notions of equilibrium . markets considered merely as conduits for goods produced or consumed elsewhere are described with theories of `` partial equilibrium '' , largely specified by open - system boundary conditions . financial markets are open in this sense . economists also try to determine the `` general equilibria '' of whole societies , taking into account not only trade , but production , consumption , and to some extent regulation by government . the understanding of relaxation to equilibrium , including when equilibria are possible and whether they are unique , has grown in economics and in physics together . in both fields mechanical models were used first , followed by statistical explanations @xcite . some recent work @xcite has shown which subset of economic decision problems have an identical structure to that of classical thermodynamics , including the emergence of a phenomenological principle equivalent to entropy maximization , while the more general equilibration problems usually considered by economists correspond to physical problems with many equilibria , such as granular , glassy , or hysteretic relaxation . the idea that equilibria correspond to statistically most - probable sets of configurations has led to attempts to define price formation in statistical terms . a related observation , that income distribution seems consistent with various forms of entropy maximization , recasts the problem of understanding income inequality , and interpreting how much it really tells about the social forces affecting incomes ( see box [ box : income_dist ] ) . we expect that maximum - ignorance principles will grow into a conceptual foundation in economics as they have in physics , and that with this change , the roles of symmetry , conservation laws , and scaling will become increasingly important @xcite . efforts to explain which aspects of market function or regulatory structure converge on predictable forms , relatively free of historical contingency , are likely to require characterization in these more basic terms . within the next few years we expect that in some physics and economics departments a basic course teaching the essential elements of both physics and economics will be designed ( much as in biophysics ; see physics today march 2005 ) . we believe physics will continue to contribute to economics in a variety of different directions , ranging from macroeconomics to market microstructure , and that such work will have increasing implications for economic policy making . one area of opportunity , where the applicability of physics might not be at all obvious a priori , concerns the construction of economic indices , such as the consumer price index or the dow jones industrial average . though these indices provide only crude one dimensional summaries of very complex phenomena , they play an important role in economic decision making . for example , pension and wage payments are referenced to the cpi . such indices are currently constructed using essentially _ ad hoc _ methods . we believe that the accuracy of such indices could be improved by careful thinking in terms of dimensional analysis , combined with better data analysis correlating prices and other factors to the phenomena , such as wages and pensions , for which the indices are designed . this is ultimately related to the question of why the economy exhibits so many scale free behaviors , such as the distribution of wealth or the size of firms . to shed light on this we need a better understanding of the natural dimensions of economic life , and the use of systematic dimensional analysis is likely to be very useful in revealing this . dimensional and scaling methods were a cornerstone in the understanding of complex phenomena like turbulence in fluids , and all the constituents that make fluid flow complex long time correlations , nonlinearity , and chaos are likely to be even greater factors in the economy . at the other end of the spectrum , ideas from statistical mechanics could make practical contributions to problems in market microstructure . for market design , for example , some physics - style models suggest that changing the rules to create incentives for patient trading orders vs. those that demand immediate transactions could lower the volatility of prices . a related practical problem concerns the optimal strategy for market makers , i.e. agents that simultaneously buy and sell , and make a profit by taking the difference . though markets are increasingly electronic , the design of automated market makers is still done in a more or less ad hoc manner . the opportunity is ripe to create a theory for market making based on methods from statistical mechanics . this could result in lowering transaction costs and generally making markets more efficient . we are reminded that several key ideas in physics are actually of economic origin . a prejudice that the books should balance was likely responsible for joule s accounting for the energy content of heat before it was well - supported by data . the concept of a `` currency '' , which we still think of primarily in economic metaphor , guides our understanding of the role of energy in complex systems and particularly in biochemistry . understanding the dynamics and statistical mechanics of agency promises similarly to expand the conceptual scope of physics . the first identification of a power law distribution in any field was made by vilfredo pareto in 1897 for the distribution of income among the highest earning few percent of inhabitants of the uk , and all income distributions asymptotically of this form are known in economics as `` pareto distributions '' . subsequent studies by pareto for prussia , saxony , paris , and few italian cities confirmed these results , which continue to hold up very well ( see fig . [ fig : pareto_incomes ] ) . more recent studies @xcite have shown that not only is the income of the wealthy regular , but so is the income of the majority of wage earners , and the two groups follow different distributions . the low- and medium - income body of the distribution is either exponential or lognormal ( variable among data sets ) , with a transition to the pareto law for large incomes , at a level that varies with time , tax laws , and other factors , as yet unknown . as striking as the fact that the large - income distribution is scale free , is the fact that the overall distribution is so featureless , being described by four ( or five ) parameters : mean income , pareto exponent , transition point between low- and high - income ranges , and the exponential constant ( or mean and variance of the lognormal ) in the low range . pareto , lognormal , and exponential distributions are all limiting distributions of simple random processes , and can also be derived as maximum - entropy distributions for either income or its logarithm , subject to appropriate boundary conditions on the ( arithmetic or geometric ) mean income @xcite . income distribution is a hot topic economically and politically , because it lies at the heart of a society s notions of egalitarianism , opportunity , or social insurance . not surprisingly , causes of income inequality are asserted , such as distinctions between capital ownership and wage labor , with major policy implications . maximum - entropy interpretations of income distribution place conceptual as well as quantitative bounds on these arguments . they suggest that the many detailed features of a society that could in principle affect incomes somehow average so that their individual characteristic scales are not imprinted on the aggregate distribution ; the ultimate constraints may be conservation laws or boundary conditions reflected in at most a few parameters . such featureless averaging , like the scaling relations we have noted above , may suggest that a form of universality classification is fundamental to understanding economics , as it has been to thermodynamics and field theory . bachelier s random walk was a triumph of quantitative finance , and became the basis of modern portfolio analysis , and later the black - scholes model for option pricing @xcite . the @xmath33 and @xmath34 coefficients published in every security analysis are mean and covariance coefficients from fits to a random walk . however , the heavy tails of real price fluctuations , under - predicted by the gaussian distribution resulting from accumulation of an uncorrelated random walk , can lead to disastrous mis - estimates of risk . this has been an important problem in financial mathematics which has received a great deal of attention . more recent work by physicists extends analytic methods for pricing options to take the heavy tails and volatility bursts of real prices into account . inspired by the work of constantino tsallis on non - extensive statistical mechanics @xcite , ( see fig . [ fig : student_returns ] ) lisa borland @xcite has developed a new pricing formula that corrects the standard black - scholes model . for three decades option - pricing practitioners have recognized that random - walk estimates were too conservative , and compensated by altering the parameters of the black - scholes model depending on the strike price of the option . the `` implied volatility '' assigned in this way makes a well - known `` smile '' when plotted versus the strike prices ( see fig . [ fig : vol_smile ] ) . the borland option - pricing formula provides a rational basis for pricing of rare events , and nicely reproduces the volatility smile . while there are a large number of other generalizations of the black - scholes theory that address the problem of the smile , borland s has the significant advantage that it gives a closed form solution . the self - consistency condition on which all rational option pricing is based arbitrage - free hedging of risk is a classically reductionist principle relating derivatives to their underlying assets . it is noteworthy that economic practice has chosen to adhere to the specific black - scholes formula based on an empirically invalid model of the underlying , and to introduce the phenomenological curve of `` implied volatility '' to bring the formula in line with data . the borland construction avoids such mixing of reductionism and phenomenology ; its single additional parameter describes the observed fluctuations in the underlying asset price , separating the problem of explaining these from that of pricing their derivatives . , where @xmath35 is the transaction price and @xmath36 is one minute , and are normalized by the sample standard deviation . also shown is the student distribution ( solid line ) which provides a good fit to the data ( from ref . @xcite ) . ] gabaix , xavier , parameswaran gopikrishnan , vasiliki plerou , h. eugene stanley `` a theory of power law distributions in financial market fluctuations '' , nature , 2003 , vol . 423 , p. 267 - 70 . m. h. r. stanley , l. a. n. amaral , s. v. buldyrev , s. havlin , h. leschhorn , p. maass , m. a. salinger , and h. e. stanley , `` scaling behavior in the growth of companies , '' nature 379 , 804 - 806 ( 1996 ) . bouchaud , y. gefen , m. potters , and m. wyart , fluctuations and response in financial markets : the subtle nature of random `` price changes '' , _ quantitative finance _ 4(2 ) : 176 - 190 ( 2004 ) ; f. lillo and j. d. farmer , the long memory of the efficient market " , _ studies in nonlinear dynamics and econometrics _ 8 ( 3 ) , article 1(2004 ) . w. b. arthur , j. h. holland , b. lebaron , r. palmer , and p. tayler . asset pricing under endogenous expectations in an artificial stock market . in w. b. arthur , s. n. durlauf , and d. h. lane , editors , _ the economy as an evolving complex system ii _ , pages 1544 . addison - wesley , redwood city , 1997 . j. d. farmer , p. patelli , and ilija zovko . the predictive power of zero intelligence in financial markets . _ proceedings of the national academy of sciences of the united states of america _ , 102(6):22542259 , 2005 . damien challet , matteo marsili , and yi - cheng zhang . minority games_. oxford university press , oxford , 2005 ; ( if we have to discard one it should be the following ) n. f. johnson , p. jeffries , and p. m. hui . _ financial market complexity_. oxford university press , oxford , 2003 . e. smith and m. shubik `` strategic freedom , constraint , and symmetry in one - period markets with cash and credit payment '' , economic theory * 25 * , 513 - 551 ( 2005 ) ; m. shubik and e. smith , `` the physics of time and dimension in the economics of financial control '' , physica a * 340 * , 656 - 667 ( 2004 ) . m. nirei and w. souma , `` income distribution and stochastic multiplicative process with reset events '' , in gallegati , kirman , marsili eds , the complex dynamics of economic interaction , springer , 2003 ; figure from m. nirei and w. souma , `` two factor model of income distribution dynamics '' , sfi preprint # 04 - 10 - 029 .

we review an emerging body of work by physicists addressing questions of economic organization and function . we suggest that , beyond simply employing models familiar from physics to economic observables , remarkable regularities in economic data may suggest parts of social order that can usefully be incorporated into , and in turn can broaden , the conceptual structure of physics .

<s>[INST]in the last decade or so physicists have begun to do academic research in economics in a newly emerging field often called `` econophysics '' . perhaps a hundred people are now actively involved , with two new journals and frequent conferences . at least ten books have been written on econophysics in general or specific subtopics ( we are restricted by citation limits here , but an extensive bibliography of the books and archived articles is maintained on the econophysics website , http://www.unifr.ch/econophysics ) . theses are being granted by physics departments for research in economics , and in europe there are several professors in physics departments specializing in econophysics . there is even a new annual research prize , titled the `` young scientist award for social and econophysics '' . is this just a fad , or is there something more substantial here ? if physicists want to do research in economics , why do nt they just get degrees in economics in the first place ? why do nt the econophysicists retool , find jobs in economics departments and publish in traditional economics journals ? perhaps this is just a temporary phenomenon , driven by a generation of physicists who made a bad career choice . is there any reason why research in economics should be done in physics departments as an on - going activity , or why economics departments should pay heed to the methods of physics ? what advantage , if any , is conferred by a background in physics ? and most important , how does econophysics differ from economics , and what unique contribution can it make , if any ? one is naturally suspicious that the emergence of econophysics is just a reflection of a depressed job market . it is certainly true that during the last two decades a large number of physicists have been lured to wall st , and that this has been an important stimulus . but this is not the main focus . econophysics is primarily an academic endeavor , whose participants are employed by universities . it offers no special advantages in the job market in fact , quite the opposite : it is even more competitive than mainstream fields of physics . no permanent positions in econophysics have ever been offered in an american university . papers submitted to physical review letters require special justification concerning their relevance to physics . while the situation in europe is a little better than in the u. s. , jobs are still very scarce . the tenuous existence of econophysics relies on senior professors who have redirected their interests from other areas , as well as a few bold students and postdocs . the involvement of physicists in social science has a long history , going back at least to daniel bernoulli , who in 1738 introduced the idea of utility to describe people s preferences . in his _ essai philosophique sur les probabilites _ ( 1812 ) , laplace pointed out that events that might seem random and unpredictable , such as the number of letters that end up in the paris dead - letter office , can in fact be quite predictable and can be shown to obey simple laws . these ideas were further amplified by quetelet , a student of fourier , who in 1835 coined the term `` social physics '' , and studied the existence of patterns in data sets ranging from the frequency of different methods for committing murder to the chest size of scottish men . analogies to physics played an important role in the development of economic theory through the nineteenth century , and some of the founders of neoclassical economic theory , such as irving fisher , a student of willard gibbs , were originally trained as physicists . ettore majorana in 1938 presciently outlined both the opportunities and pitfalls in applying statistical physics methods to the social sciences . the range of topics that have been addressed spans many different areas of economics . finance is particularly well represented ; sample topics include the empirical observation of regularities in market data , the dynamics of price formation , the understanding of bubbles and panics , methods for pricing derivatives such as options , the construction of optimal portfolios , and many other subjects . broader topics in economics include the distribution of income , theories of how money emerges , and implications of symmetry and scaling to the functioning of markets . despite their long history of association , we see the substantial contributions of physics to economics as still in an early stage , and find it fanciful to forecast what will ultimately be accomplished . almost certainly , `` physical '' aspects of theories of social order will _ not _ simply recapitulate existing theories in physics , though already there appear to be overlaps . the development of societies and economies is potentially contingent on accidents of history , and at every turn hinges on complex aspects of human behavior . nonetheless , striking empirical regularities such as those we survey below suggest that at least some social order is not historically contingent , and perhaps is predictable from first principles . the role of markets as mediators of communication and distributed computation , and the emergence of the social institutions that support them , are quintessentially economic phenomena . yet the notions of their computational or communication capacity , and how these account for their stability and historical succession , may naturally be parts of the physical world as it includes human social dynamics . in the context of human desires , markets and other economic institutions bring with them notions of efficiency or optimality in satisfying those desires . while intuitively appealing , such notions have proven hard to formalize , and the examples below show some progress in this area . as with most new areas of physical inquiry , we expect that the ultimate goals of a `` physical economics '' will be declared with hindsight , from successes in identifying , measuring , modeling and in some cases predicting empirical regularities . economists are typically better trained in statistical analysis than physicists , so this might seem to be an area where physicists have little to contribute . however , differences in goals and philosophy are important . physics is driven by the quest for universal laws . in part , because of the extreme complexity of phenomena in society , in the postmodern world where relativist philosophies of science enjoy disturbingly widespread acceptance , this quest has been largely abandoned . modern work in social science is largely focused on documenting differences . although this trend is much less obvious in economics , a typical paper in financial economics , for example , might study the difference between the nyse and the nasdaq stock exchanges , or the effect of changing the tick size of prices ( the unit of the smallest possible price change ) . physicists have ( perhaps naively ) entered with fresh eyes and new hypotheses , and have looked at economic data with the goal of finding pervasive regularities , emphasizing what might be common to all markets rather than what might make them different . this work has been opportunistically motivated by the the existence of large data sets such as the complete transaction histories of major exchanges over timespans of years , which in some cases contain hundreds of millions of events . much of the work by physicists in economics concerns power laws . a power law is an asymptotic relation of the form @xmath0 , where @xmath1 is a variable and @xmath2 is a constant . in many important cases @xmath3 is a probability distribution . power laws have received considerable attention in physics because they indicate scale free behavior and they are characteristic of critical or nonequilibrium phenomena . in fact , the first power law distribution ( in any field ) was observed in economics ( see box [ box : income_dist ] ) , and the existence of power laws in economics has been a matter of debate ever since . in 1963 benoit mandelbrot @xcite observed that the distribution of cotton price fluctuations follows a power law . further observations of power laws in price changes were subsequently noted by rosario mantegna and eugene stanley @xcite , who coined the term `` econophysics '' . [ fig : power_law_fig ] shows the striking fidelity often found in economic power laws . the existence of power laws in price changes is interesting from a practical point of view because of its implications for the risk of financial investments , and from a theoretical point of view because it suggests scale independence and possible analogies to nonequilibrium behavior in the processes that generate financial returns . since then many other power laws have been discovered by physicists . these include the variance in the growth rates of companies as a function of their size @xcite , the distribution function for the number of shares in a transaction , the distribution for the number of trading orders submitted at a price @xmath1 away from the best price offered , the size of the price response to a trade as a function of the size @xmath4 of the company being traded , and many other examples . the question of why power laws are so ubiquitous in financial markets has stimulated a great deal of theoretical work . one of the most famous and most used models of prices is the random walk . the random walk was originally introduced for prices in 1900 by louis bachelier , a student of poincar , five years before einstein introduced it to describe brownian motion . this forms the basis for the black - scholes theory of option pricing @xcite , which won a nobel prize in economics in 1997 ( see box [ box : option_pricing ] ) . one of the interesting and surprising properties of the random walk of real prices is that its diffusion rate is not constant . the size of price changes is strongly positively autocorrelated in time , a phenomenon called _ _ clustered volatility _ _ is defined as @xmath5 , where @xmath6 , @xmath7 denotes a time average and @xmath8 the standard deviation . `` volatility '' is the term used in finance to refer to the variance or size of price shifts . ] . the autocorrelation of the size of price changes decays as a power law of the form @xmath9 . since @xmath10 , this is a long - memory process . long - memory processes display anomalous diffusion and very slow convergence of statistical averages . physicists have recently discovered that volatility is just one of several long - memory - processes in markets . one of the most surprising concerns fluctuations in supply and demand @xcite . if one assigns @xmath11 to an order to buy and @xmath12 to an order to sell , the resulting series of numbers has a positive autocorrelation function that decays as a power law with an exponent @xmath13 , which persists at statistically significant levels across tens of thousands of orders , for periods of time lasting for weeks . this implies that changes in supply and demand obey a long - memory process . this has interesting implications . one of the most fundamental principles in financial economics is called _ market efficiency_. this principle takes many forms : a market is informationally efficient if prices reflect all available information ; it is arbitrage efficient if it is impossible for investors to make `` excess profits '' , and it is allocationally efficient if prices are set so that they in some sense maximize everyone s welfare . one of the consequences of informational efficiency is that prices should not be predictable . in reality this is not a bad approximation ; even the best trading strategies exploit only very weak levels of predictability . the coexistence of the long - memory of supply and demand with market efficiency creates an interesting and as yet unresolved puzzle . long - memory processes are highly predictable using a simple linear algorithm . since the entrance of new buyers tends to drive the price up , and the entrance of new sellers tends to drive it down , this naively suggests that price changes should also be long - memory , which would violate market efficiency . to prevent this from happening , the agents in the market must somehow collectively adjust their behavior to offset this , for example by creating an asymmetric response of prices , so that when there is an excess of new buyers the price response to new buy orders is smaller than it is to new sell orders . how this comes about , and why it comes about , remains a mystery . this may be related to the cause of clustered volatility . there is a great deal of other empirical work using methods and analogies from physics that we do not have the space to describe in any detail . for example , random matrix theory @xcite ( developed in nuclear physics ) and the use of ultrametric correlations have proved useful for understanding the correlation between the movement of prices of different companies . an analogy to the omori law for seismic activity after major earthquakes has proved to be useful for understanding the aftermath of large crashes in stock markets , and other analogies from geophysics has led to a controversial hypothesis about why markets crash @xcite . the statistics of price movements have been noted to bear a striking resemblance to those of turbulent fluids , which has led to what may now be the best empirical models available for predicting clustered volatility . such examples speak to the universality of mathematics in its applications to the world . the most fundamental difference between a physical system and an economy is that economies are inhabited by people , who have strategic interactions . because people think , plan , and make decisions based on their plans , they are much more complicated to understand than atoms this is a problem that physics has never coped with , and it has caused the mathematical techniques and modeling philosophy in economics to diverge from those in physics . while this is clearly necessary , many physicists would argue that the gap is wider than it should be . the central approach to the problem of strategic interactions in neoclassical economics is the theory of rational choice . the economists stylized version of individual rationality is to maximize some measure of one s personal ( usually material ) welfare , having perfect knowledge of the world and of other agents goals and abilities , and the ability to perform computations of any complexity . when agent a considers any strategy , agent b knows that a is considering that strategy , and a knows that b knows that a knows , and so on . this infinite regress appears very complicated . however , a key simplifying result is that in any game there exists at least one nash equilibrium , which is a set of strategies with the property that each is the optimal response to all of the others . the nash equilibrium is a fixed point in the space of strategies , which circumvents the infinite regress problem by imposing self - consistency as a defining criterion . subject to several caveats , rational players who are not cooperating with each other will choose a nash strategy . this is the operational meaning of rational choice . the assumption that decisions of real human beings can be approximated in this way dominated economic thinking about individual choices ( called _ microeconomics _ ) from 1950 until the mid-1980s , though it is clearly implausible for all but the simplest cognitive tasks . it also leaves unaddressed the problem of aggregation of individual choices and the behavior of large populations ( called _ macroeconomics _ ) . in the last twenty years economics has begun to challenge the assumptions of rational choice and perfect markets by modeling imperfections such as asymmetric information , incomplete market structure , and bounded rationality . several new schools of thought have emerged . the behavioral economists attempt to take human psychology into account by studying people s actual choices in idealized economic settings . another school uses idealizations of problem solving and learning ranging from standard statistical methods to artificial intelligence to address the problem of bounded rationality . agent - based modeling makes computer simulations based on idealizations of human behaviors and focuses on the complexity of economic interactions . yet another approach assumes that some agents ( called noise traders ) have extremely limited reasoning capabilities while others are perfectly rational . physicists have joined with many economists in seeking new theories of non - fully - rational choice , bringing new perspectives to bear on the problem . an early effort using both agent based modeling and artificial intelligence is called the santa fe stock market . this grew out of a conference in 1986 organized by ken arrow , phil anderson and david pines @xcite that brought together physicists and economists . presaging the modern move toward behavioral economics , the physicists all expressed disbelief in theories of rational choice and suggested that the economists should take human psychology and learning more into account . the santa fe stock market was a collaboration between economists , physicists and a computer scientist that grew out of this conference . it replaced the rational agents in an idealized market setting with an artificial intelligence model @xcite . it showed that this leads to qualitative modifications of the statistics of prices , such as fat tailed distributions of price change and clustered volatility , and suggested that non - rational behavior plays an important part in generating these phenomena . the problem with this approach is that it is complicated , and while it captures some qualitative features of markets , the path to more quantitative theories is not clear . agent based models tend to require ad hoc assumptions that are difficult to validate . the hypothesis of rational choice , in contrast , has the great virtue that it is parsimonious , making strong predictions from simple hypotheses . from this point of view it is more like theories in physics . this perspective has inspired the search for other simple parsimonious alternatives . one such approach is often called _ zero intelligence_. this amounts to the assumption that agents behave more or less randomly , subject to constraints such as their budget . zero intelligence models can be used to study the properties of market institutions , and to determine which properties of a market depend on intentionality and which do nt . this provides a benchmark to avoid getting lost in the large space of realistic human behaviors . once a zero intelligence model has be made , it can be modified by incorporating more realistic assumptions , adding a little intelligence based on empirical observations or models of learning . where rational choice enters the wilderness of bounded rationality from the top , zero intelligence enters it from the bottom . the zero intelligence approach can be traced back to the work of herbert simon , a nobel laureate in economics and pioneer in artificial intelligence . its main champions in recent years have been physicists , who have used analogies to statistical mechanics to develop new models of markets . a good example is the work of per bak , maya paczuski , and martin shubik ( two physicists and an economist ) , who studied the impact of random trading orders on prices within an idealized model of price formation . they assumed that traders simply place orders to buy or sell at random above or below the prices of the most recent transactions . they then modify their orders from time to time , moving them toward the middle until they generate a transaction . the result is mathematically analogous to a reaction diffusion model for the reaction @xmath14 that was developed by the physicist john cardy . while this model is highly unrealistic , with a few modifications it produces some qualitative features , such as heavy tailed price distributions , that resemble their counterparts in real markets . many variations of the bps model have now been explored . one variation simply assumes that agents place and cancel trading orders at random . after performing a dimensional analysis based on prices , shares and time , the resulting model can be shown to obey simple scaling laws that relate statistical properties of trading order placement to statistical properties of prices . these laws are restrictions on state variables similar to the ideal gas law , but in this case the variables on one side are properties of trading orders , such as the rates for order placement and cancellation , and the variables on the other side are statistical properties of prices , such as the diffusion rate in bachelier s random walk model . these scaling laws have been tested on data from the london stock exchange and have been shown to be in surprisingly good agreement with it @xcite . the model also gives insight into the shape of supply and demand curves , as shown in fig [ fig : impact_collapse ] . another alternative approach is to develop highly simplified models of strategic interaction that do a better job of capturing the essence of the collective behavior in a financial market . brian arthur s el farol bar problem provides an alternative to conventional game theory . the name el farol comes from a bar in santa fe that is often crowded . each day agents decide whether or not to go hear music ; if there is room in the bar they are happy , and if it is too crowded they are disappointed . by definition only a minority of the people can be happy , which leads to a phenomenon analogous to _ frustration _ - some desires are necessarily unsatisfiable and as a result an astronomically large number of equilibria can emerge . the el farol model was simplified and abstracted by challet and zhang as the minority game @xcite , in which an odd number @xmath15 of agents repeatedly choose between two alternatives , which can be labeled @xmath16 or @xmath17 . their decisions are made independently and simultaneously . agents whose choice is the minority value are rewarded ( awarded `` payoffs '' , in game - theoretic terminology ) . typically agents are capable of remembering the outcomes of @xmath18 prior rounds of play , and maintain an inventory of @xmath19 strategies ( random lookup tables ) dictating a next move for each history . for example , for @xmath20 a possible lookup table would be @xmath21 , @xmath22 , @xmath23 , @xmath24 , meaning in the first case , if the previous majority choices were @xmath16 in both previous rounds of the game , choose @xmath17 on the next round " . the strategy chosen is that with the best cumulative performance . minority games exhibit phase transitions for @xmath25 , in the ratio @xmath26 , of the number of resolvable pasts to the number of agents , as shown in fig . [ fig : mg_phases ] . . for @xmath27 the variance is high , indicating that the game is highly inefficient in the sense that the minority group is much smaller than it needs to be . the variance reaches a minimum at @xmath28 , and when @xmath29 is large it approaches the value it would have if all agents make random choices ( from savit et al . - see reference @xcite ) . ] for @xmath27 a critical value , the population is in a symmetric phase , where the outcome of the next move is unpredictable from the history of play . for @xmath30 , in contrast , @xmath15 agents sparsely sample the space of strategies , the next outcome is predictable , and the population is in a symmetry - broken phase that can be understood analytically with replica methods . the variance in the number of winners about the optimum , @xmath31 , measures the failure of `` allocative efficiency '' , and is minimized at @xmath32 . the minority game is readily extended to incorporate more features of real financial markets , such as payoffs that increase as the size of the winning group gets smaller ( much as buyers or sellers of stocks can reap larger profits when they are providing the more scarce of supply or demand ) , or the `` grand canonical '' version in which players are permitted to enter and leave . with these enhancements the game self - organizes around the critical point @xmath32 , the payoff series exhibits fluctuations that display clustered volatility , and they have a distribution with a power law tail , reminiscent of a real market . the minority game provides a fascinating example of how a very simple game can display a rich set of properties as soon as one moves away from the rational choice paradigm . finance is not the only area of economics where physicists are active . in economics as in physics it is traditional to distinguish open from closed systems , which give rise to different notions of equilibrium . markets considered merely as conduits for goods produced or consumed elsewhere are described with theories of `` partial equilibrium '' , largely specified by open - system boundary conditions . financial markets are open in this sense . economists also try to determine the `` general equilibria '' of whole societies , taking into account not only trade , but production , consumption , and to some extent regulation by government . the understanding of relaxation to equilibrium , including when equilibria are possible and whether they are unique , has grown in economics and in physics together . in both fields mechanical models were used first , followed by statistical explanations @xcite . some recent work @xcite has shown which subset of economic decision problems have an identical structure to that of classical thermodynamics , including the emergence of a phenomenological principle equivalent to entropy maximization , while the more general equilibration problems usually considered by economists correspond to physical problems with many equilibria , such as granular , glassy , or hysteretic relaxation . the idea that equilibria correspond to statistically most - probable sets of configurations has led to attempts to define price formation in statistical terms . a related observation , that income distribution seems consistent with various forms of entropy maximization , recasts the problem of understanding income inequality , and interpreting how much it really tells about the social forces affecting incomes ( see box [ box : income_dist ] ) . we expect that maximum - ignorance principles will grow into a conceptual foundation in economics as they have in physics , and that with this change , the roles of symmetry , conservation laws , and scaling will become increasingly important @xcite . efforts to explain which aspects of market function or regulatory structure converge on predictable forms , relatively free of historical contingency , are likely to require characterization in these more basic terms . within the next few years we expect that in some physics and economics departments a basic course teaching the essential elements of both physics and economics will be designed ( much as in biophysics ; see physics today march 2005 ) . we believe physics will continue to contribute to economics in a variety of different directions , ranging from macroeconomics to market microstructure , and that such work will have increasing implications for economic policy making . one area of opportunity , where the applicability of physics might not be at all obvious a priori , concerns the construction of economic indices , such as the consumer price index or the dow jones industrial average . though these indices provide only crude one dimensional summaries of very complex phenomena , they play an important role in economic decision making . for example , pension and wage payments are referenced to the cpi . such indices are currently constructed using essentially _ ad hoc _ methods . we believe that the accuracy of such indices could be improved by careful thinking in terms of dimensional analysis , combined with better data analysis correlating prices and other factors to the phenomena , such as wages and pensions , for which the indices are designed . this is ultimately related to the question of why the economy exhibits so many scale free behaviors , such as the distribution of wealth or the size of firms . to shed light on this we need a better understanding of the natural dimensions of economic life , and the use of systematic dimensional analysis is likely to be very useful in revealing this . dimensional and scaling methods were a cornerstone in the understanding of complex phenomena like turbulence in fluids , and all the constituents that make fluid flow complex long time correlations , nonlinearity , and chaos are likely to be even greater factors in the economy . at the other end of the spectrum , ideas from statistical mechanics could make practical contributions to problems in market microstructure . for market design , for example , some physics - style models suggest that changing the rules to create incentives for patient trading orders vs. those that demand immediate transactions could lower the volatility of prices . a related practical problem concerns the optimal strategy for market makers , i.e. agents that simultaneously buy and sell , and make a profit by taking the difference . though markets are increasingly electronic , the design of automated market makers is still done in a more or less ad hoc manner . the opportunity is ripe to create a theory for market making based on methods from statistical mechanics . this could result in lowering transaction costs and generally making markets more efficient . we are reminded that several key ideas in physics are actually of economic origin . a prejudice that the books should balance was likely responsible for joule s accounting for the energy content of heat before it was well - supported by data . the concept of a `` currency '' , which we still think of primarily in economic metaphor , guides our understanding of the role of energy in complex systems and particularly in biochemistry . understanding the dynamics and statistical mechanics of agency promises similarly to expand the conceptual scope of physics . the first identification of a power law distribution in any field was made by vilfredo pareto in 1897 for the distribution of income among the highest earning few percent of inhabitants of the uk , and all income distributions asymptotically of this form are known in economics as `` pareto distributions '' . subsequent studies by pareto for prussia , saxony , paris , and few italian cities confirmed these results , which continue to hold up very well ( see fig . [ fig : pareto_incomes ] ) . more recent studies @xcite have shown that not only is the income of the wealthy regular , but so is the income of the majority of wage earners , and the two groups follow different distributions . the low- and medium - income body of the distribution is either exponential or lognormal ( variable among data sets ) , with a transition to the pareto law for large incomes , at a level that varies with time , tax laws , and other factors , as yet unknown . as striking as the fact that the large - income distribution is scale free , is the fact that the overall distribution is so featureless , being described by four ( or five ) parameters : mean income , pareto exponent , transition point between low- and high - income ranges , and the exponential constant ( or mean and variance of the lognormal ) in the low range . pareto , lognormal , and exponential distributions are all limiting distributions of simple random processes , and can also be derived as maximum - entropy distributions for either income or its logarithm , subject to appropriate boundary conditions on the ( arithmetic or geometric ) mean income @xcite . income distribution is a hot topic economically and politically , because it lies at the heart of a society s notions of egalitarianism , opportunity , or social insurance . not surprisingly , causes of income inequality are asserted , such as distinctions between capital ownership and wage labor , with major policy implications . maximum - entropy interpretations of income distribution place conceptual as well as quantitative bounds on these arguments . they suggest that the many detailed features of a society that could in principle affect incomes somehow average so that their individual characteristic scales are not imprinted on the aggregate distribution ; the ultimate constraints may be conservation laws or boundary conditions reflected in at most a few parameters . such featureless averaging , like the scaling relations we have noted above , may suggest that a form of universality classification is fundamental to understanding economics , as it has been to thermodynamics and field theory . bachelier s random walk was a triumph of quantitative finance , and became the basis of modern portfolio analysis , and later the black - scholes model for option pricing @xcite . the @xmath33 and @xmath34 coefficients published in every security analysis are mean and covariance coefficients from fits to a random walk . however , the heavy tails of real price fluctuations , under - predicted by the gaussian distribution resulting from accumulation of an uncorrelated random walk , can lead to disastrous mis - estimates of risk . this has been an important problem in financial mathematics which has received a great deal of attention . more recent work by physicists extends analytic methods for pricing options to take the heavy tails and volatility bursts of real prices into account . inspired by the work of constantino tsallis on non - extensive statistical mechanics @xcite , ( see fig . [ fig : student_returns ] ) lisa borland @xcite has developed a new pricing formula that corrects the standard black - scholes model . for three decades option - pricing practitioners have recognized that random - walk estimates were too conservative , and compensated by altering the parameters of the black - scholes model depending on the strike price of the option . the `` implied volatility '' assigned in this way makes a well - known `` smile '' when plotted versus the strike prices ( see fig . [ fig : vol_smile ] ) . the borland option - pricing formula provides a rational basis for pricing of rare events , and nicely reproduces the volatility smile . while there are a large number of other generalizations of the black - scholes theory that address the problem of the smile , borland s has the significant advantage that it gives a closed form solution . the self - consistency condition on which all rational option pricing is based arbitrage - free hedging of risk is a classically reductionist principle relating derivatives to their underlying assets . it is noteworthy that economic practice has chosen to adhere to the specific black - scholes formula based on an empirically invalid model of the underlying , and to introduce the phenomenological curve of `` implied volatility '' to bring the formula in line with data . the borland construction avoids such mixing of reductionism and phenomenology ; its single additional parameter describes the observed fluctuations in the underlying asset price , separating the problem of explaining these from that of pricing their derivatives . , where @xmath35 is the transaction price and @xmath36 is one minute , and are normalized by the sample standard deviation . also shown is the student distribution ( solid line ) which provides a good fit to the data ( from ref . @xcite ) . ] gabaix , xavier , parameswaran gopikrishnan , vasiliki plerou , h. eugene stanley `` a theory of power law distributions in financial market fluctuations '' , nature , 2003 , vol . 423 , p. 267 - 70 . m. h. r. stanley , l. a. n. amaral , s. v. buldyrev , s. havlin , h. leschhorn , p. maass , m. a. salinger , and h. e. stanley , `` scaling behavior in the growth of companies , '' nature 379 , 804 - 806 ( 1996 ) . bouchaud , y. gefen , m. potters , and m. wyart , fluctuations and response in financial markets : the subtle nature of random `` price changes '' , _ quantitative finance _ 4(2 ) : 176 - 190 ( 2004 ) ; f. lillo and j. d. farmer , the long memory of the efficient market " , _ studies in nonlinear dynamics and econometrics _ 8 ( 3 ) , article 1(2004 ) . w. b. arthur , j. h. holland , b. lebaron , r. palmer , and p. tayler . asset pricing under endogenous expectations in an artificial stock market . in w. b. arthur , s. n. durlauf , and d. h. lane , editors , _ the economy as an evolving complex system ii _ , pages 1544 . addison - wesley , redwood city , 1997 . j. d. farmer , p. patelli , and ilija zovko . the predictive power of zero intelligence in financial markets . _ proceedings of the national academy of sciences of the united states of america _ , 102(6):22542259 , 2005 . damien challet , matteo marsili , and yi - cheng zhang . minority games_. oxford university press , oxford , 2005 ; ( if we have to discard one it should be the following ) n. f. johnson , p. jeffries , and p. m. hui . _ financial market complexity_. oxford university press , oxford , 2003 . e. smith and m. shubik `` strategic freedom , constraint , and symmetry in one - period markets with cash and credit payment '' , economic theory * 25 * , 513 - 551 ( 2005 ) ; m. shubik and e. smith , `` the physics of time and dimension in the economics of financial control '' , physica a * 340 * , 656 - 667 ( 2004 ) . m. nirei and w. souma , `` income distribution and stochastic multiplicative process with reset events '' , in gallegati , kirman , marsili eds , the complex dynamics of economic interaction , springer , 2003 ; figure from m. nirei and w. souma , `` two factor model of income distribution dynamics '' , sfi preprint # 04 - 10 - 029 .[/INST] we review an emerging body of work by physicists addressing questions of economic organization and function . we suggest that , beyond simply employing models familiar from physics to economic observables , remarkable regularities in economic data may suggest parts of social order that can usefully be incorporated into , and in turn can broaden , the conceptual structure of physics . </s>

There is no reason for these massive, deadly and costly forest fires in California except that forest management is so poor. Billions of dollars are given each year, with so many lives lost, all because of gross mismanagement of the forests. Remedy now, or no more Fed payments! ||||| President Donald Trump looks at a map as he visits with first responders and local officials at an operations center responding to the wildfires, Saturday, Nov. 17, 2018, in Chico, Calif. House Majority... (Associated Press) PARADISE, Calif. (AP) — From the ashes of a mobile home and RV park, President Donald Trump said Saturday he came to the heart of California's killer wildfire to fully grasp the scale of the desolation wrought on the landscape. "We're going to have to work quickly. ... Hopefully this is going to be the last of these because this was a really, really bad one," said the president, standing amid the crumpled foundations of homes and twisted steel of melted cars. "I think everybody's seen the light and I don't think we'll have this again to this extent," Trump said in Paradise, the town largely destroyed by a wildfire ignited Nov. 8 that he called "this monster." With that bold and perhaps unlikely prediction, Trump pledged that improved forest management practices will diminish future risks. The declaration evoked his initial tweeted reaction to the fire, the worst in the state's history, in which he seemed to blame local officials and threatened to take away federal funding. When asked if seeing the historic devastation, which stretched for miles and left neighborhoods destroyed and fields scorched, altered his opinion on climate change, Trump answered, "No." The president has long voiced skepticism about man's impact on the climate and has been reluctant to assign blame to a warming earth for the increase in the frequency and intensity of natural disasters. At least 71 people died across Northern California, and authorities are trying to locate more than 1,000 people, though not all are believed missing. More than 5,500 fire personnel were battling the blaze that covered 228 square miles (590 square kilometers) and was about 50 percent contained, officials said. For Trump, it was a day to comfort a state grieving from twin tragedies, wildfires in both Northern and Southern California as well as a mass shooting at a popular college bar north of Los Angeles. Wearing a camouflage "USA" hat, Trump gazed solemnly at the devastation in Paradise. Several burned-out buses and cars were nearby. Trees were burned, their branches bare and twisted. Homes were totally gone; some foundations remained, as did a chimney and, in front of one house, a Mickey Mouse lawn ornament. The fire was reported to have moved through the area at 80 mph. "It's going to work out well, but right now we want to take of the people that are so badly hurt," Trump said visiting what remained of the Skyway Villa Mobile Home and RV Park. He noted "there are areas you can't even get to them yet" and the sheer number of people unaccounted for. "I think people have to see this really to understand it," Trump said. The president later toured an operation centers, met with response commanders and praised the work of firefighters, law enforcement and representatives of the Federal Emergency Management Agency. "We've never seen anything like this in California," he said. "It's total devastation." Trump took a helicopter tour en route to Chico before he toured Paradise. A full cover of haze and the smell of smoke greeted the president upon his arrival at Beale Air Force Base near Sacramento. "They're out there fighting and they're fighting like hell," Trump said of the first responders. He pledged that Washington would do its part by coming to the Golden State's aid and urged the House's Republican leader, Rep. Kevin McCarthy of California, a Trump ally and frequent White House visitor, to "come to the office" to help secure the needed funding. Trump, who left Washington early Saturday and didn't expect to return to the White House until well past midnight, planned to travel several hundred miles south to visit with victims of a recent country music bar shooting. A gunman killed a dozen people at the Borderline Bar & Grill in Thousand Oaks on Nov. 7 before committing suicide. Trump long has struggled to convey empathy to victims of national disasters and tragedies. His first reaction to the fires came in a tweet last week that drew criticism as unnecessarily critical and tone-deaf given the devastation: "There is no reason for these massive, deadly and costly forest fires in California except that forest management is so poor. Billions of dollars are given each year, with so many lives lost, all because of gross mismanagement of the forests." Nature and humans share blame for the wildfires, but fire scientists are divided as to whether forest management played a major role. Nature provides the dangerous winds that have whipped the fires, the state has been in a drought and human-caused climate change over the long haul is killing and drying the shrubs and trees that provide the fuel. He stuck to that theme in his remarks just before departing on Saturday when he outlined what he planned to discuss with Gov. Jerry Brown and Gov-elect Gavin Newsom, both Democrats: "We will be talking about forest management. ... The one thing is that everybody now knows that this is what we have to be doing and there's no question about it. It should have been done many years ago, but I think everybody's on the right side." Trump, who has long feuded with the political leaders of heavily Democratic California over issues such as immigration and voting, also has threatened to withhold federal payments to the state. After being criticized for his response, Trump has shifted gears, expressing words of encouragement to first responders and those of sympathy for hit victims. But when he was asked by Fox News in an interview set to air Sunday whether climate change played a role in the number of serious fires, he said "maybe it contributes a little bit. The big problem we have is management." Brown and Newsom welcomed the president's visit, with the governor suggesting they set aside political differences since it "now is a time to pull together for the people of California." Brown, a fierce advocate of addressing climate change, did not respond to Trump's statement that he has not changed his mind on the matter but pointed to several causes and they need to deal with them. "If you really look at the facts, from a really open point of view, there are a lot of elements to be considered," Brown said after Trump spoke. "The president came, he saw and I'm looking forward over the next months and beyond to really understand this threat of fire, the whole matter of drought and all the rest of it. It's not one thing, it's a lot of things and I think that if we just open our minds and look at things we'll get more stuff done." ___ Follow Lemire on Twitter at http://twitter.com/@JonLemire

– From the ashes of a mobile home and RV park, President Donald Trump said Saturday he came to the heart of California's killer wildfire to fully grasp the scale of the desolation wrought on the landscape, the AP reports. "We're going to have to work quickly. ... Hopefully this is going to be the last of these because this was a really, really bad one," says the president, standing amid the crumpled foundations of homes and twisted steel of melted cars. "I think everybody's seen the light and I don't think we'll have this again to this extent," Trump says in Paradise, the town largely destroyed by a wildfire ignited Nov. 8 that he called "this monster." With that bold and perhaps unlikely prediction, Trump pledges that improved forest management practices will diminish future risks. The declaration evoked his initial tweeted reaction to the fire, the worst in the state's history, in which he seemed to blame local officials and threatened to take away federal funding. When asked if seeing the historic devastation, which stretched for miles and left neighborhoods destroyed and fields scorched, altered his opinion on climate change, Trump answered, "No." The president has long voiced skepticism about man's impact on the climate and has been reluctant to assign blame to a warming earth for the increase in the frequency and intensity of natural disasters. At least 71 people died across Northern California, and authorities are trying to locate more than 1,000 people, though not all are believed missing. (See what scientists are saying about the California wildfires.)

<s>[INST]There is no reason for these massive, deadly and costly forest fires in California except that forest management is so poor. Billions of dollars are given each year, with so many lives lost, all because of gross mismanagement of the forests. Remedy now, or no more Fed payments! ||||| President Donald Trump looks at a map as he visits with first responders and local officials at an operations center responding to the wildfires, Saturday, Nov. 17, 2018, in Chico, Calif. House Majority... (Associated Press) PARADISE, Calif. (AP) — From the ashes of a mobile home and RV park, President Donald Trump said Saturday he came to the heart of California's killer wildfire to fully grasp the scale of the desolation wrought on the landscape. "We're going to have to work quickly. ... Hopefully this is going to be the last of these because this was a really, really bad one," said the president, standing amid the crumpled foundations of homes and twisted steel of melted cars. "I think everybody's seen the light and I don't think we'll have this again to this extent," Trump said in Paradise, the town largely destroyed by a wildfire ignited Nov. 8 that he called "this monster." With that bold and perhaps unlikely prediction, Trump pledged that improved forest management practices will diminish future risks. The declaration evoked his initial tweeted reaction to the fire, the worst in the state's history, in which he seemed to blame local officials and threatened to take away federal funding. When asked if seeing the historic devastation, which stretched for miles and left neighborhoods destroyed and fields scorched, altered his opinion on climate change, Trump answered, "No." The president has long voiced skepticism about man's impact on the climate and has been reluctant to assign blame to a warming earth for the increase in the frequency and intensity of natural disasters. At least 71 people died across Northern California, and authorities are trying to locate more than 1,000 people, though not all are believed missing. More than 5,500 fire personnel were battling the blaze that covered 228 square miles (590 square kilometers) and was about 50 percent contained, officials said. For Trump, it was a day to comfort a state grieving from twin tragedies, wildfires in both Northern and Southern California as well as a mass shooting at a popular college bar north of Los Angeles. Wearing a camouflage "USA" hat, Trump gazed solemnly at the devastation in Paradise. Several burned-out buses and cars were nearby. Trees were burned, their branches bare and twisted. Homes were totally gone; some foundations remained, as did a chimney and, in front of one house, a Mickey Mouse lawn ornament. The fire was reported to have moved through the area at 80 mph. "It's going to work out well, but right now we want to take of the people that are so badly hurt," Trump said visiting what remained of the Skyway Villa Mobile Home and RV Park. He noted "there are areas you can't even get to them yet" and the sheer number of people unaccounted for. "I think people have to see this really to understand it," Trump said. The president later toured an operation centers, met with response commanders and praised the work of firefighters, law enforcement and representatives of the Federal Emergency Management Agency. "We've never seen anything like this in California," he said. "It's total devastation." Trump took a helicopter tour en route to Chico before he toured Paradise. A full cover of haze and the smell of smoke greeted the president upon his arrival at Beale Air Force Base near Sacramento. "They're out there fighting and they're fighting like hell," Trump said of the first responders. He pledged that Washington would do its part by coming to the Golden State's aid and urged the House's Republican leader, Rep. Kevin McCarthy of California, a Trump ally and frequent White House visitor, to "come to the office" to help secure the needed funding. Trump, who left Washington early Saturday and didn't expect to return to the White House until well past midnight, planned to travel several hundred miles south to visit with victims of a recent country music bar shooting. A gunman killed a dozen people at the Borderline Bar & Grill in Thousand Oaks on Nov. 7 before committing suicide. Trump long has struggled to convey empathy to victims of national disasters and tragedies. His first reaction to the fires came in a tweet last week that drew criticism as unnecessarily critical and tone-deaf given the devastation: "There is no reason for these massive, deadly and costly forest fires in California except that forest management is so poor. Billions of dollars are given each year, with so many lives lost, all because of gross mismanagement of the forests." Nature and humans share blame for the wildfires, but fire scientists are divided as to whether forest management played a major role. Nature provides the dangerous winds that have whipped the fires, the state has been in a drought and human-caused climate change over the long haul is killing and drying the shrubs and trees that provide the fuel. He stuck to that theme in his remarks just before departing on Saturday when he outlined what he planned to discuss with Gov. Jerry Brown and Gov-elect Gavin Newsom, both Democrats: "We will be talking about forest management. ... The one thing is that everybody now knows that this is what we have to be doing and there's no question about it. It should have been done many years ago, but I think everybody's on the right side." Trump, who has long feuded with the political leaders of heavily Democratic California over issues such as immigration and voting, also has threatened to withhold federal payments to the state. After being criticized for his response, Trump has shifted gears, expressing words of encouragement to first responders and those of sympathy for hit victims. But when he was asked by Fox News in an interview set to air Sunday whether climate change played a role in the number of serious fires, he said "maybe it contributes a little bit. The big problem we have is management." Brown and Newsom welcomed the president's visit, with the governor suggesting they set aside political differences since it "now is a time to pull together for the people of California." Brown, a fierce advocate of addressing climate change, did not respond to Trump's statement that he has not changed his mind on the matter but pointed to several causes and they need to deal with them. "If you really look at the facts, from a really open point of view, there are a lot of elements to be considered," Brown said after Trump spoke. "The president came, he saw and I'm looking forward over the next months and beyond to really understand this threat of fire, the whole matter of drought and all the rest of it. It's not one thing, it's a lot of things and I think that if we just open our minds and look at things we'll get more stuff done." ___ Follow Lemire on Twitter at http://twitter.com/@JonLemire[/INST]– From the ashes of a mobile home and RV park, President Donald Trump said Saturday he came to the heart of California's killer wildfire to fully grasp the scale of the desolation wrought on the landscape, the AP reports. "We're going to have to work quickly. ... Hopefully this is going to be the last of these because this was a really, really bad one," says the president, standing amid the crumpled foundations of homes and twisted steel of melted cars. "I think everybody's seen the light and I don't think we'll have this again to this extent," Trump says in Paradise, the town largely destroyed by a wildfire ignited Nov. 8 that he called "this monster." With that bold and perhaps unlikely prediction, Trump pledges that improved forest management practices will diminish future risks. The declaration evoked his initial tweeted reaction to the fire, the worst in the state's history, in which he seemed to blame local officials and threatened to take away federal funding. When asked if seeing the historic devastation, which stretched for miles and left neighborhoods destroyed and fields scorched, altered his opinion on climate change, Trump answered, "No." The president has long voiced skepticism about man's impact on the climate and has been reluctant to assign blame to a warming earth for the increase in the frequency and intensity of natural disasters. At least 71 people died across Northern California, and authorities are trying to locate more than 1,000 people, though not all are believed missing. (See what scientists are saying about the California wildfires.)</s>

continued advances in computing power and availability have led to an increasingly important role for numerical simulations in understanding hydrodynamical phenomena , and astrophysics provides a particular range of interesting applications . high - resolution , multidimensional studies frequently include an ambitious amount of physics in order to reproduce the dynamics of a system with sufficient accuracy . however , numerical artefacts and limitations are necessarily present and must be understood as fully as possible to appreciate the actual physics in the systems being represented . non - physical features enter _ ab initio _ into all hydrodynamic simulations simply because of the discretisation of a ` continuous ' fluid ( which is itself discrete , of course , but on very small scales ) . the two types of method developed for this task have very different structures : lagrangian methods follow moving fluid elements , while eulerian methods compute flow properties on a grid of points ; additionally , there are ` hybrid ' approaches , the so - called ale ( arbitrary lagrangian - eulerian ) schemes , e.g. the bethe - hydro code @xcite . in this paper , we focus on the lagrangian smoothed particle hydrodynamics ( sph ) method , which has been widely used for modelling astrophysical phenomena @xcite . sph has both advantages and disadvantages with respect to other numerical techniques . one main advantage is that it automatically adapts to following dynamic flows and arbitrary geometries , without the need for mesh refinement or other readjustment techniques required with eulerian - based codes . furthermore , the energy equation is solved in the local comoving frame of each fluid element , giving a direct implementation of the first law of thermodynamics . in modelling fluids by means of sph particles , most sph codes have included an artificial viscosity term , both for making the ensemble of discrete particles behave more like a continuum ( in continuous regions of the flow ) and for handling shock discontinuities which may arise during the course of a simulation . methods for shock - handling with riemann solvers have also been implemented in sph @xcite ; these approaches have both advantages and disadvantages . here , we focus on the artificial viscosity methods as used in standard sph formulations . as well as having beneficial effects , artificial viscosity can also introduce unwanted numerical artefacts , among which spurious shearing torques in rotating flows are particularly troublesome ( see , for example , @xcite ) . techniques such as the balsara correction ( described in the next section ) have been developed for counteracting this . typically , sph prescriptions for artificial viscosity are a composite of both bulk and shear viscosity components , but act as a source of dissipation primarily related to shear when modelling rotating fluid flows . it is important to have some quantitative measure of how large the effects of this are , whether one is dealing with problems having no intrinsic shear viscosity or whether there is also a real , physical shear viscosity ; in either case , any numerical viscosity should be suitably negligible ( unless one is trying to use an artificial viscosity to actually model a physical viscosity , see e.g. , @xcite ) . we focus here on two standard artificial viscosity prescriptions , with and without the balsara correction . the main objective of this paper is to advocate monitoring local entropy generation as a means for quantifying the residual effects of artificial viscosity in regular flows not involving shocks . our method is completely general , but we test it out by applying it to frequently - used idealized test problems involving isothermal discs and compare its performance on these with that of other alternative methods . two main types of approach have been used previously , both of which measure the kinematic effect of the artificial viscosity and relate it to an effective viscosity coefficient , @xmath0 . firstly , there are the empirical ` ring - spreading ' tests @xcite . these are based on the analytic relations for the kinematic contribution of the artificial viscosity to disc - averaged behaviour , with assumptions of an isothermal equation of state and a small viscosity ( so as not to generate large radial flow ) that is constant across the disc . in practice , these tests can only be performed in two dimensions , as the thermal pressure of the fluid is zeroed to isolate the viscosity term in the equations of motion . these methods also require post - simulation fitting of averaged results . secondly , analytic approximations have been developed relating @xmath0 to sph and disc parameters @xcite . these relations are generally derived for specific formulations of sph artificial viscosity with the quadratic term set to zero . various additional assumptions include having constant smoothing lengths ( in the continuum limit ) and particular sph particle kernel shapes , as well as considerations that the viscosity is active for both receding and approaching particles . both of these kinds of existing approach involve restrictive assumptions and neither may be applied to artificial viscosity prescriptions that include often - used ` corrective ' terms , such as the balsara method or time - dependent approaches ( discussed below ) , which aim to reduce ` excess ' shearing . the technique presented here involves evaluating the effect of artificial viscosity in rotating flows directly from local entropy production ( i.e. using the energy equation rather than the equation of motion ) . it does not assume any particular equation of state or rotation profile and also does not assume constancy of @xmath0 or of smoothing lengths , or any particular artificial viscosity prescription . moreover , it requires no special simulation setup and is directly calculable from standard sph particle quantities . impetus for this approach arises from the nature of the sph method itself and its direct application of the first law of thermodynamics , noting that a clear understanding of entropy production is of great importance in numerical simulations . the technique is simple and quick to implement , and it allows a detailed characterization of the effects of the artificial viscosity as a function of position . several advantages of this method over existing ones are discussed , including its ease in evaluation , its direct interpretation , its greater accuracy and its broad applicability , e.g. , to arbitary rotation profiles and equations of state . for all of the simulations described here , we have utilised the public - release version of the gadget-2 code @xcite . while several artificial viscosity formulations of varying sophistication have been developed over the years , in this paper we focus mainly on the _ method _ of estimating the effects of this viscosity and therefore utilize only the relatively simple form that is standard in gadget-2 ( with and without the balsara treatment , described below ) . however , the method itself is independent of viscosity prescription , and our aim is to apply it to a comparison of several other formulations in a forthcoming paper . here , we begin by briefly reviewing in [ sec : newtonhydro ] the form of sph equations used and considerations concerning the artificial viscosity ; in [ sec : rotflowartvisc ] , the ring - spreading test is described ; in [ sec : motiv ] , both the motivation for and the general formulation of our local criterion for measuring the effective viscosity in rotating flows are described ; in [ sec : general_spec ] , example applications of our method in thin discs are given , and various simulations performed , for which the results of the local measures of viscosity are compared with those of the ring - spreading tests and existing analytic formulations ; these results are then discussed in [ sec : discuss ] . additionally , in appendix [ appendixa ] , we discuss the sph particle setup used for our initial conditions , which is presented as a simple improvement to aid in reducing numerical effects and increasing the efficiency of convergence . in sph a continuous fluid is sampled at a finite number of points , and discretised versions of the standard hydrodynamic equations of continuity , momentum ( euler ) and the first law of thermodynamics ( energy equation ) are evolved , given respectively in their simplest form as : @xmath1 written with lagrangian derivatives , @xmath2 , and with mass density , @xmath3 ; velocity , @xmath4 ; thermal pressure , @xmath5 ; and specific internal energy , @xmath6 . the exact form of sph implementations has continued to be refined over the decades ; in this work , we have used the publicly - available sph code , gadget-2 , the formulation of which is derived from a fluid lagrangian and , importantly , directly conserves linear and angular momentum , entropy and energy @xcite . the gadget-2 sph equations are presented here , with emphasis on the necessity for including extra , purely numerical terms in the implementation of the continuum equations above . for further details , we refer the reader to much more comprehensive discussions elsewhere , e.g. @xcite . the fluid is taken to have a polytropic equation of state ( eos ) , @xmath7 where @xmath8 is the specific entropy . following standard usage ( e.g. , @xcite ) , a polytropic gas is defined as having constant specific heats , and therefore the related adiabatic index , @xmath9 , is constant . while some authors restrict @xmath10 to being constant as well ( and refer to it as the polytropic constant ) , here it is allowed to vary , and in the following @xmath10 is referred to as the entropic function . in gadget-2 , this @xmath10 is evolved rather than @xmath6 , giving the strict conservation properties of both energy and entropy mentioned above @xcite . in the following , the subscripts @xmath11 will be used only to distinguish individual fluid elements , represented in sph as finite volume pseudo - particles , and not to signify vector components . first , the mass density at the location of a given particle labelled as ` @xmath12 ' and with spatial coordinate vector , @xmath13 , is calculated at each timestep by direct summation using @xmath14 the summation is performed over @xmath15 ` nearest neighbour ' particles labelled as ` @xmath16 ' ( typically @xmath17 @xcite ) , each with mass , @xmath18 , and contained within a radius given by the smoothing length , @xmath19 . the kernel , @xmath20 , is strongly peaked and differentiable ( a cubic spline , in gadget-2 ) and with @xmath21 . the smoothing length is calculated at each timestep such that the kernel volume of a particle contains a constant mass ( for numerical stability ) , according to the following relation : @xmath22 where @xmath23 is the average particle mass . within the fluid , the resolution is essentially determined by the magnitude of @xmath19 , over which discontinuities are smoothed . to evolve the particle velocity , the non - viscous euler equation , including a gravitational potential , @xmath24 , is represented as : @xmath25 where @xmath26 the factors , @xmath27 , arise from the lagrangian derivation and the set of constraints on coordinates provided by eq . [ sph_hsml ] ; they account directly for the variation in smoothing lengths in the system @xcite . self - gravity among particles is calculated efficiently using a tree algorithm ( a hierarchical multipole expansion ) @xcite . additionally , in some cases we include the acceleration due to a ( newtonian ) central object located at the origin of the simulation s coordinates , @xmath28 . gadget-2 uses an artificial viscosity of the form @xmath29 $ 0 $ & \mbox{for $ { \bf v}_{ab}\cdot{\bf r}_{ab}\geq 0 $ } , \end{tabular}\right.\ ] ] with @xmath30 and @xmath31 being the relative velocity between particles in vector and scalar form , respectively ; @xmath32 , the average density ; @xmath33 , the local soundspeed , with average @xmath34 ; and @xmath35 , a free parameter for the strength of the viscosity . in practice , @xmath36 acts similarly to a pressure term in the euler equation , and the related acceleration is : @xmath37 where @xmath38 . the @xmath36 formulation possesses two terms to mimic naturally - occuring , dissipative processes . the first ( linear in @xmath39 ) provides both the bulk and shear viscosity of the converging particles , and the second ( quadratic in @xmath39 ) functions as a von neumann - richtmyer artificial viscosity for shock handling and for spreading shock discontinuities over the smoothing length of supersonic particles . the quadratric term also prevents interparticle penetration . it should be noted that this single artificial viscosity provides both shear and bulk viscosities , which would be given by separate terms in the physical , navier - stokes description ( direct implementations of the latter are discussed briefly below ) . in many sph prescriptions the linear and quadratic terms are scaled by separate free parameters , @xmath40 and @xmath41 , respectively , each with a range of ` typical ' values , but we here follow the practice of setting @xmath42 ( unless otherwise stated ) . an in - depth discussion of the relative scaling of the linear and quadratic terms is provided by @xcite . the entropic function , @xmath10 ( defined in eq . [ polytr_eos ] ) , changes , in general , in the presence of viscosity : @xmath43 cooling in optically thin material may be included in a straightforward manner by subtracting the appropriate entropy loss at the end of a timestep . the inclusion of accurate radiative transport in optically thick material is a separate ( and highly non - trivial ) task , which we do not consider here . finally , to limit spurious angular momentum transfer which arises in shear flow due to the form of the artificial viscosity , the simple balsara correction is commonly utilised @xcite . the aim of this factor is to remove the effect of the artificial viscosity when there is a pure shearing motion and to have it acting only when there is a compression . an estimate of the relative amount of local shear is made from the curl and divergence of the particle velocities : @xmath44 where the third term in the denominator prevents the quantity from diverging . the average value of this quantity for two interacting particles is used as a multiplicative factor in front of @xmath36 , producing the modified form @xmath45 , which is then used instead of @xmath36 in eqs . [ sph_eul_visc ] and [ sph_energ ] . in the following , we examine the effect of the artificial viscosity both with and without the balsara correction ( the former case being the default ) . [ sph_cont ] , [ sph_euler ] and [ sph_energ ] , together with the eos and the smoothing length condition in eq . [ sph_hsml ] , form a complete set of equations for evolving the physical , hydrodynamic quantities in numerical simulations . however , as part of the process of discretisation , a number of additional variables and parameters have been included ( @xmath46 , @xmath47 , etc . ) . while these are used to model realistic properties of the discretised system , such as continuity and shocks , they also introduce purely numerical features by controlling resolution , the ` spread ' of shocks and the stability of interpolations and summations . in the past decades , much work has been done to determine reliable values and forms for these parameters and to reduce associated numerical artefacts . generally , a number of standard problems , in various dimensions and geometries , are used to test the behaviour of a given code and the associated parameters . another purely numerical consideration in using sph is the initial placement of the particles representing points in the flow @xcite . for instance , regularities in particle configurations may lead to the propagation of artificial structures in the simulation along preferred directions , and even randomised placements may produce numerical features , e.g. , due to local overdensities . for each simulation presented here , the initial particle setup was created using an algorithm which maps a non - regular but constant number density profile of ( equal - mass ) particles into the arbitrary number - density ( and trivially , mass - density ) profile of the desired model . this method has also been applied in other simulations @xcite and is described in appendix [ appendixa ] . the standard ring - spreading test starts from an initial @xmath48-function ring of matter in circular keplerian motion around a gravitating point mass @xcite . if shear viscosity is present , this ring will proceed to spread out into a disc , with the rate of spreading dependent on the magnitude of the viscosity . the matter is taken here to behave isothermally , with the temperature and viscosity being sufficiently small so that the spreading is slow and the thin disc is essentially keplerian ( with its height , @xmath49 , being small compared with the radial coordinate , @xmath50 , at any point ) . with certain additional simplifying assumptions ( negligible self - gravity for the disc material and constant viscosity coefficient , @xmath0 ) , an analytic solution can be obtained for the ring - spreading @xcite . the exact analytic results provide a means for comparison for an sph simulation of an equivalent configuration with no viscosity apart from that of the numerical scheme , @xmath51 . from the analytic results , an effective value for the shear component of the artificial viscosity can then be estimated , if one assumes that @xmath51 is roughly constant throughout the disc ( a somewhat doubtful assumption ) and that the corresponding bulk component has negligible effect ( a very good assumption under the circumstances envisaged ) . the value obtained can then be translated into an effective shakura - sunyaev @xmath52 coefficient [ 25 ] , which represents the viscosity according to @xmath53 where @xmath49 is the disc height , and @xmath54 is the sound speed . the analytic solution gives an expression for the surface density of the ring , @xmath55 , as a function of position and time . for the conditions mentioned above , the radial velocity @xmath56 ( positive for ` outer ' material and negative for ` inner ' material ) is always small , with @xmath57 by scaling arguments @xcite . the surface density is then given by @xmath58 where @xmath50 is the radius in the equatorial plane ( with @xmath59 initially ) ; @xmath60 is a time parameter ( @xmath61 ) ; @xmath0 is the kinematic shear viscosity coefficient ; @xmath62 is the disc mass ( taken as the mass unit , i.e. @xmath63 ) , and @xmath64 is a modified bessel function . a detailed derivation of this formula is given by , e.g. , @xcite . in our work reported below , the corresponding numerical simulations begin a short time after the axisymmetric ring has spread to a finite thickness ( at @xmath65 ) using the analytic formula eq . [ sigmathin ] to provide the initial surface density profile . this same formula is also used for matching against the simulation properties at subsequent times ( doing so has been justified in previous numerical studies by the general proximity of the surface density evolution to this expression ) . self - gravity of the sph particles is included in simulations , although it is assumed that the acceleration due to the central point mass dominates ( we take @xmath66 ) . sph particles are removed from the system at an inner boundary with small radius , @xmath67 . as mentioned above , in addition to the ring - spreading test there are also some approximate analytic formulations for estimating the effective shear viscosity of the disc from kinematic considerations : that of @xcite is @xmath68 while that of @xcite is @xmath69 these relations are generated essentially by reversing the summation form of sph equations which involve artificial viscosity back to continuum limits . further details are given in the respective papers . note that the gadget-2 definition of smoothing length has been used in each case . an artificial viscosity term ( @xmath70 ) appears in both the momentum and energy hydrodynamic equations . each of these roles affects the evolution and structure of the system , as the trajectories of fluid elements are modified and as kinetic energy is transformed into heat . the standard form of the ( isothermal ) ring - spreading test has been used essentially to analyse the effective viscosity via the euler equation , with the spreading being caused by the combined action of the viscous and several other additive terms , but it seems better to use , instead , the energy equation , where the effect of viscosity in generating entropy can be clearly singled out . internal energy in fluid systems can be produced both by viscosity and by non - viscous compression . this is expressed in the first law of thermodynamics , as applied to a co - moving fluid element with unit mass : @xmath71 where @xmath72 is the temperature and @xmath8 is the specific entropy . the specific internal energy produced by viscosity , @xmath73 , corresponds to the first term on the right hand side , and its time derivative is simply @xmath74 this quantity can be calculated directly from the sph expressions in all cases , whatever the flow geometry or equation of state , giving a direct local measure of the effects of viscosity . the only caveat is that there should be no other sources of entropy production to contaminate the interpretation . for the particular case of the ( widely used ) class of polytropic equations of state implemented by gadget-2 , the derivative of eq . [ polytr_eos ] gives the following expression for @xmath75 : @xmath76 where the relations @xmath77 and @xmath78 have been used in arriving at the form of the second line . matching terms with the first law in eq . [ firsttherm ] and referring to eq . [ visc_en_entr ] leads to the following set of formulae linking @xmath79 , @xmath80 and @xmath81 : @xmath82 within gadget-2 , computation of the evolution of @xmath83 is very similar to that for the entropic function , @xmath10 ( cf . [ sph_energ ] , [ visc_en_entr ] and [ visc_entr_entr ] ) : @xmath84 and this can be evaluated straightforwardly for each fluid element . note that in the further specialisation to an isothermal equation of state with @xmath85 ( which we will be using below for making comparison with the ring - spreading test ) , then the entropic function , @xmath10 , becomes a constant , but the true entropy , @xmath8 , continues to change under the action of viscosity , as does @xmath83 . importantly , @xmath86 is determined from the contribution of only a single term which contains @xmath36 . in quantifying the effect of any sph artificial viscosity prescription on a disc system , this isolation greatly simplifies analysis ( and interpretation ) . in general , entropy can be produced by shearing , normal compression and shock compression , the totality of which are accounted for when measuring @xmath86 , due to its general relation to specific entropy . in contrast , only the shearing is important under the assumptions of the ring - spreading test ( or the analytic approximations ) . monitoring @xmath86 already provides a suitable way of demonstrating the local effects of artificial viscosity , and one could stop at that point . however , if one wants to calculate an effective shear viscosity coefficient ( for circumstances involving shear and no significant compression ) , one needs to write an expression for @xmath86 in terms of @xmath0 and the shearing velocity field ( see , e.g. , appendix b of @xcite ) and then to invert it to give an expression for @xmath0 . for general planar rotational motion , one finds the following expression for specific internal energy creation @xcite : @xmath87 + \nu \left(r \frac{\partial\omega}{\partial r } \right)^2\,,\ ] ] using cylindrical polar coordinates ( @xmath88 ) here and after . this form may be inverted easily for an expression of the effective viscosity : @xmath89^{-1}.\ ] ] each term on the right hand side is composed of variables which are directly obtainable from the sph particles . as discussed above , the viscous heating is a direct measure of entropy creation due to viscosity , and the gradient terms may be estimated , e.g. , within sph particle kernels or from averaged ring values . in this study , we describe and utilise an expression which includes solely the term involving @xmath90 . this facilitates comparisons with existing approximations and , as shown below , leads to particularly simple expressions of @xmath91 ( though , it must be emphasised , that the preceding expression is by no means prohibitively complicated ) . the surface area of a narrow , axisymmetric ring of width , @xmath92 ( centred around @xmath50 ) , is @xmath93 , and the mass of the ring is therefore @xmath94 . taking the matter to be moving on basically circular orbits , the viscous torque exerted on the ring can be written as @xcite : @xmath95 the work done by this torque leads to local heating in the rotating flow . the specific heating rate due to viscosity is @xmath96 which is recognized as the final term in eq . [ szmil ] . after trivial rearrangement , the expression for the viscosity is given in terms of easily known quantities as : @xmath97 compared to existing methods for evaluating effective viscosity in rotating flows , this expression is particularly general , having made no assumptions of rotation profile , equation of state , constancy of @xmath0 or artificial viscosity prescription . moreover , as a function of radius , this expression provides a more detailed and useful description of viscous behaviour throughout the simulation . as noted above , more general viscous stresses may be applied as well , such as that of eq . [ szmil ] . in the following examples , we implement eq . [ general_visc ] with different disc stuctures and using different artificial viscosity prescriptions . in the examples below , we apply the expression for the effective local viscosity in eq . [ general_visc ] to test scenarios of ring - spreading and thin disc cases . using assumptions of axisymmetry and circular , keplerian orbits , the viscosity expression is @xmath98 presuming vertical equilibrium with some thin disc scale height , @xmath49 , the shakura - sunyaev @xmath52 is then given as @xmath99 in the case of polytropic , nonisothermal equations of state , these expressions for viscosity and the shakura - sunyaev @xmath52 may be written in terms of the entropic function as : @xmath100 respectively . these last forms are particularly relevant to gadget-2 , where the entropic function is directly evolved , and they are used in obtaining the results presented below . finally , it is interesting to note that , for the specific case of an isothermal eos , eq . [ newvisccrit1 ] may be expressed neatly as : @xmath101 using the expression for the scale height given in eq . [ thinstruc ] , below . physically , in this latter form , @xmath52 directly relates the local dynamical timescale ( @xmath102 ) and the viscous thermal timescale ( @xmath103 ) , as it should from accretion disc theory ( e.g. , ) . we now briefly describe the structure equations for the two varieties of thin isothermal discs used in this study ( in dimensionless units ) . each disc is taken to be in vertical , hydrostatic equilibrium with respect to the gradient of the gravitational potential of the massive central object . the density distribution , scale height and central density ( in the equatorial plane ) are , respectively : @xmath104,\nonumber \\ h(r ) & = & \left[\frac{r^3c^2_{\rm{s}}}{gm_{\rm{c}}}\right]^{1/2}= \frac{\,c_{\rm{s}}}{\omega_{\rm{k}}}\,,\nonumber \\ \rho_{\rm{c}}(r ) & = & \frac{\sigma(r)}{[2\pi]^{1/2}h(r)}\ , . \end{aligned}\ ] ] since this gaussian density profile only asymptotically approaches zero in the vertical direction , an arbitrary disc height for the boundary of sph particles above / below the equatorial plane at any radius must be designated , and we set this to be three times the scale height in order to incorporate @xmath105 of the mass of the theoretical distribution into the simulation ( though , the non - arbitrary scale height , @xmath49 , is used everywhere else in the analytic relations and discussion ) . the vertical velocity is taken to be uniformly zero , and the profile of the azimuthal velocity is very nearly keplerian , i.e. , @xmath106 . the global sound speed , @xmath54 , is a parameter restricted in accordance with the thinness condition , @xmath107 , or @xmath108 , where @xmath109 is essentially the mach number of the ( very supersonic ) azimuthal flow . using both the height from eq . [ thinstruc ] and the definition of the viscosity parametrisation in eq . [ shaksuny ] , the global disc viscosity can be related to the shakura - sunyaev @xmath52 as a function of @xmath109 and the keplerian specific angular momentum , @xmath110 : @xmath111 finally , the initial surface density of the flows must be supplied for use in eqs . [ thinstruc ] . the formulation of the spreading ring , @xmath112 , has been given in eq . [ sigmathin ] . we have also calculated a more disc - like system ( of similar mass and surface density ) , with radial span at @xmath113 of @xmath114 . here , the arbitrary surface density profile has been chosen to be flat in this region initially , @xmath115 , and the resulting disc mass was @xmath116 . this is considered solely as a separate test case and not as a representation of a specific , physical system ( e.g. , the initial boundaries are too discontinuous for an equilibrium system ) . here , we first present results for ring - spreading tests with the balsara correction included for various values of the parameter , @xmath117 , where @xmath118 is the radius of the initial midpoint of the ring ( and using units in which @xmath119 ) . first , the viscous properties are determined kinematically by using the global evolution of the surface density and fits to the theoretical progression given by the analytic formulation . then , local values of @xmath0 and @xmath52 are calculated from @xmath86 using eqs . [ newnucrit]-[newvisccrit1 ] . unless stated otherwise , @xmath120 in all of the presented simulations ( and , in the notation of [ sec : newtonhydro ] , the quadratic term coefficient , @xmath121 ) . as an additional example of sar results , fig . [ fig : ring_init ] shows images of particle locations for an evolving sar ring simulation ( the same system as in the left panel of fig . [ fig : ringsp_cs60 ] ) , projected onto the equatorial plane . over time , the particle distribution within system retains its good qualitative properties of smoothness and randomness . note the absence of any temporary artificial spirals , clumps or sub - structures , such as often appear in sph simulations , even at very early times . both the efficiency of modelling and the relative ease of formulation ( the computation requires only a few simple loops through @xmath122 particles ) , in addition to a reduction of numerical artefacts , make the sar initial conditions very beneficial for use in sph simulations . importantly , the sar particle method is effective because the quasi - continuous mapping retains the relative spacing between particles from the initial glass . the new density profile is obtained smoothly and accurately , without the presence of fluctuations or numerical artefacts . how smoothly a density profile is reproduced is principally determined by the size of the incremental volume element . the sar method does result in a small amount of localised asymmetry in the particle distribution , as volume elements are not generally scaled uniformly in all directions , but for small elements this did not appear to produce spurious artefacts during simulations . improvements to the method are currently being considered .

a commonly cited drawback of sph is the introduction of spurious shear viscosity by the artificial viscosity term in situations involving rotation . existing approaches for quantifying its effect include approximate analytic formulae and disc - averaged behaviour in specific ring - spreading simulations , based on the kinematic effects produced by the artificial viscosity . these methods have disadvantages , in that they typically are applicable to a very small range of physical scenarios , have a large number of simplifying assumptions , and often are tied to specific sph formulations which do not include corrective ( e.g. , balsara ) or time - dependent artificial viscosity terms . in this study we have developed a simple , generally applicable and practical technique for evaluating the local effect of artificial viscosity directly from the creation of specific entropy for each sph particle . this local approach is simple and quick to implement , and it allows a detailed characterization of viscous effects as a function of position . several advantages of this method are discussed , including its ease in evaluation , its greater accuracy and its broad applicability . in order to compare this new method with existing ones , simple disc flow examples are used . even in these basic cases , the very roughly approximate nature of the previous methods is shown . our local method provides a detailed description of the effects of the artificial viscosity throughout the disc , even for extended examples which implement balsara corrections . as a further use of this approach , explicit dependencies of the effective viscosity in terms of sph and flow parameters are estimated from the example cases . in an appendix , a method for the initial placement of sph particles is discussed which is very effective in reducing numerical fluctuations . [ firstpage ] hydrodynamic models viscosity accretion and accretion discs

<s>[INST]continued advances in computing power and availability have led to an increasingly important role for numerical simulations in understanding hydrodynamical phenomena , and astrophysics provides a particular range of interesting applications . high - resolution , multidimensional studies frequently include an ambitious amount of physics in order to reproduce the dynamics of a system with sufficient accuracy . however , numerical artefacts and limitations are necessarily present and must be understood as fully as possible to appreciate the actual physics in the systems being represented . non - physical features enter _ ab initio _ into all hydrodynamic simulations simply because of the discretisation of a ` continuous ' fluid ( which is itself discrete , of course , but on very small scales ) . the two types of method developed for this task have very different structures : lagrangian methods follow moving fluid elements , while eulerian methods compute flow properties on a grid of points ; additionally , there are ` hybrid ' approaches , the so - called ale ( arbitrary lagrangian - eulerian ) schemes , e.g. the bethe - hydro code @xcite . in this paper , we focus on the lagrangian smoothed particle hydrodynamics ( sph ) method , which has been widely used for modelling astrophysical phenomena @xcite . sph has both advantages and disadvantages with respect to other numerical techniques . one main advantage is that it automatically adapts to following dynamic flows and arbitrary geometries , without the need for mesh refinement or other readjustment techniques required with eulerian - based codes . furthermore , the energy equation is solved in the local comoving frame of each fluid element , giving a direct implementation of the first law of thermodynamics . in modelling fluids by means of sph particles , most sph codes have included an artificial viscosity term , both for making the ensemble of discrete particles behave more like a continuum ( in continuous regions of the flow ) and for handling shock discontinuities which may arise during the course of a simulation . methods for shock - handling with riemann solvers have also been implemented in sph @xcite ; these approaches have both advantages and disadvantages . here , we focus on the artificial viscosity methods as used in standard sph formulations . as well as having beneficial effects , artificial viscosity can also introduce unwanted numerical artefacts , among which spurious shearing torques in rotating flows are particularly troublesome ( see , for example , @xcite ) . techniques such as the balsara correction ( described in the next section ) have been developed for counteracting this . typically , sph prescriptions for artificial viscosity are a composite of both bulk and shear viscosity components , but act as a source of dissipation primarily related to shear when modelling rotating fluid flows . it is important to have some quantitative measure of how large the effects of this are , whether one is dealing with problems having no intrinsic shear viscosity or whether there is also a real , physical shear viscosity ; in either case , any numerical viscosity should be suitably negligible ( unless one is trying to use an artificial viscosity to actually model a physical viscosity , see e.g. , @xcite ) . we focus here on two standard artificial viscosity prescriptions , with and without the balsara correction . the main objective of this paper is to advocate monitoring local entropy generation as a means for quantifying the residual effects of artificial viscosity in regular flows not involving shocks . our method is completely general , but we test it out by applying it to frequently - used idealized test problems involving isothermal discs and compare its performance on these with that of other alternative methods . two main types of approach have been used previously , both of which measure the kinematic effect of the artificial viscosity and relate it to an effective viscosity coefficient , @xmath0 . firstly , there are the empirical ` ring - spreading ' tests @xcite . these are based on the analytic relations for the kinematic contribution of the artificial viscosity to disc - averaged behaviour , with assumptions of an isothermal equation of state and a small viscosity ( so as not to generate large radial flow ) that is constant across the disc . in practice , these tests can only be performed in two dimensions , as the thermal pressure of the fluid is zeroed to isolate the viscosity term in the equations of motion . these methods also require post - simulation fitting of averaged results . secondly , analytic approximations have been developed relating @xmath0 to sph and disc parameters @xcite . these relations are generally derived for specific formulations of sph artificial viscosity with the quadratic term set to zero . various additional assumptions include having constant smoothing lengths ( in the continuum limit ) and particular sph particle kernel shapes , as well as considerations that the viscosity is active for both receding and approaching particles . both of these kinds of existing approach involve restrictive assumptions and neither may be applied to artificial viscosity prescriptions that include often - used ` corrective ' terms , such as the balsara method or time - dependent approaches ( discussed below ) , which aim to reduce ` excess ' shearing . the technique presented here involves evaluating the effect of artificial viscosity in rotating flows directly from local entropy production ( i.e. using the energy equation rather than the equation of motion ) . it does not assume any particular equation of state or rotation profile and also does not assume constancy of @xmath0 or of smoothing lengths , or any particular artificial viscosity prescription . moreover , it requires no special simulation setup and is directly calculable from standard sph particle quantities . impetus for this approach arises from the nature of the sph method itself and its direct application of the first law of thermodynamics , noting that a clear understanding of entropy production is of great importance in numerical simulations . the technique is simple and quick to implement , and it allows a detailed characterization of the effects of the artificial viscosity as a function of position . several advantages of this method over existing ones are discussed , including its ease in evaluation , its direct interpretation , its greater accuracy and its broad applicability , e.g. , to arbitary rotation profiles and equations of state . for all of the simulations described here , we have utilised the public - release version of the gadget-2 code @xcite . while several artificial viscosity formulations of varying sophistication have been developed over the years , in this paper we focus mainly on the _ method _ of estimating the effects of this viscosity and therefore utilize only the relatively simple form that is standard in gadget-2 ( with and without the balsara treatment , described below ) . however , the method itself is independent of viscosity prescription , and our aim is to apply it to a comparison of several other formulations in a forthcoming paper . here , we begin by briefly reviewing in [ sec : newtonhydro ] the form of sph equations used and considerations concerning the artificial viscosity ; in [ sec : rotflowartvisc ] , the ring - spreading test is described ; in [ sec : motiv ] , both the motivation for and the general formulation of our local criterion for measuring the effective viscosity in rotating flows are described ; in [ sec : general_spec ] , example applications of our method in thin discs are given , and various simulations performed , for which the results of the local measures of viscosity are compared with those of the ring - spreading tests and existing analytic formulations ; these results are then discussed in [ sec : discuss ] . additionally , in appendix [ appendixa ] , we discuss the sph particle setup used for our initial conditions , which is presented as a simple improvement to aid in reducing numerical effects and increasing the efficiency of convergence . in sph a continuous fluid is sampled at a finite number of points , and discretised versions of the standard hydrodynamic equations of continuity , momentum ( euler ) and the first law of thermodynamics ( energy equation ) are evolved , given respectively in their simplest form as : @xmath1 written with lagrangian derivatives , @xmath2 , and with mass density , @xmath3 ; velocity , @xmath4 ; thermal pressure , @xmath5 ; and specific internal energy , @xmath6 . the exact form of sph implementations has continued to be refined over the decades ; in this work , we have used the publicly - available sph code , gadget-2 , the formulation of which is derived from a fluid lagrangian and , importantly , directly conserves linear and angular momentum , entropy and energy @xcite . the gadget-2 sph equations are presented here , with emphasis on the necessity for including extra , purely numerical terms in the implementation of the continuum equations above . for further details , we refer the reader to much more comprehensive discussions elsewhere , e.g. @xcite . the fluid is taken to have a polytropic equation of state ( eos ) , @xmath7 where @xmath8 is the specific entropy . following standard usage ( e.g. , @xcite ) , a polytropic gas is defined as having constant specific heats , and therefore the related adiabatic index , @xmath9 , is constant . while some authors restrict @xmath10 to being constant as well ( and refer to it as the polytropic constant ) , here it is allowed to vary , and in the following @xmath10 is referred to as the entropic function . in gadget-2 , this @xmath10 is evolved rather than @xmath6 , giving the strict conservation properties of both energy and entropy mentioned above @xcite . in the following , the subscripts @xmath11 will be used only to distinguish individual fluid elements , represented in sph as finite volume pseudo - particles , and not to signify vector components . first , the mass density at the location of a given particle labelled as ` @xmath12 ' and with spatial coordinate vector , @xmath13 , is calculated at each timestep by direct summation using @xmath14 the summation is performed over @xmath15 ` nearest neighbour ' particles labelled as ` @xmath16 ' ( typically @xmath17 @xcite ) , each with mass , @xmath18 , and contained within a radius given by the smoothing length , @xmath19 . the kernel , @xmath20 , is strongly peaked and differentiable ( a cubic spline , in gadget-2 ) and with @xmath21 . the smoothing length is calculated at each timestep such that the kernel volume of a particle contains a constant mass ( for numerical stability ) , according to the following relation : @xmath22 where @xmath23 is the average particle mass . within the fluid , the resolution is essentially determined by the magnitude of @xmath19 , over which discontinuities are smoothed . to evolve the particle velocity , the non - viscous euler equation , including a gravitational potential , @xmath24 , is represented as : @xmath25 where @xmath26 the factors , @xmath27 , arise from the lagrangian derivation and the set of constraints on coordinates provided by eq . [ sph_hsml ] ; they account directly for the variation in smoothing lengths in the system @xcite . self - gravity among particles is calculated efficiently using a tree algorithm ( a hierarchical multipole expansion ) @xcite . additionally , in some cases we include the acceleration due to a ( newtonian ) central object located at the origin of the simulation s coordinates , @xmath28 . gadget-2 uses an artificial viscosity of the form @xmath29 $ 0 $ & \mbox{for $ { \bf v}_{ab}\cdot{\bf r}_{ab}\geq 0 $ } , \end{tabular}\right.\ ] ] with @xmath30 and @xmath31 being the relative velocity between particles in vector and scalar form , respectively ; @xmath32 , the average density ; @xmath33 , the local soundspeed , with average @xmath34 ; and @xmath35 , a free parameter for the strength of the viscosity . in practice , @xmath36 acts similarly to a pressure term in the euler equation , and the related acceleration is : @xmath37 where @xmath38 . the @xmath36 formulation possesses two terms to mimic naturally - occuring , dissipative processes . the first ( linear in @xmath39 ) provides both the bulk and shear viscosity of the converging particles , and the second ( quadratic in @xmath39 ) functions as a von neumann - richtmyer artificial viscosity for shock handling and for spreading shock discontinuities over the smoothing length of supersonic particles . the quadratric term also prevents interparticle penetration . it should be noted that this single artificial viscosity provides both shear and bulk viscosities , which would be given by separate terms in the physical , navier - stokes description ( direct implementations of the latter are discussed briefly below ) . in many sph prescriptions the linear and quadratic terms are scaled by separate free parameters , @xmath40 and @xmath41 , respectively , each with a range of ` typical ' values , but we here follow the practice of setting @xmath42 ( unless otherwise stated ) . an in - depth discussion of the relative scaling of the linear and quadratic terms is provided by @xcite . the entropic function , @xmath10 ( defined in eq . [ polytr_eos ] ) , changes , in general , in the presence of viscosity : @xmath43 cooling in optically thin material may be included in a straightforward manner by subtracting the appropriate entropy loss at the end of a timestep . the inclusion of accurate radiative transport in optically thick material is a separate ( and highly non - trivial ) task , which we do not consider here . finally , to limit spurious angular momentum transfer which arises in shear flow due to the form of the artificial viscosity , the simple balsara correction is commonly utilised @xcite . the aim of this factor is to remove the effect of the artificial viscosity when there is a pure shearing motion and to have it acting only when there is a compression . an estimate of the relative amount of local shear is made from the curl and divergence of the particle velocities : @xmath44 where the third term in the denominator prevents the quantity from diverging . the average value of this quantity for two interacting particles is used as a multiplicative factor in front of @xmath36 , producing the modified form @xmath45 , which is then used instead of @xmath36 in eqs . [ sph_eul_visc ] and [ sph_energ ] . in the following , we examine the effect of the artificial viscosity both with and without the balsara correction ( the former case being the default ) . [ sph_cont ] , [ sph_euler ] and [ sph_energ ] , together with the eos and the smoothing length condition in eq . [ sph_hsml ] , form a complete set of equations for evolving the physical , hydrodynamic quantities in numerical simulations . however , as part of the process of discretisation , a number of additional variables and parameters have been included ( @xmath46 , @xmath47 , etc . ) . while these are used to model realistic properties of the discretised system , such as continuity and shocks , they also introduce purely numerical features by controlling resolution , the ` spread ' of shocks and the stability of interpolations and summations . in the past decades , much work has been done to determine reliable values and forms for these parameters and to reduce associated numerical artefacts . generally , a number of standard problems , in various dimensions and geometries , are used to test the behaviour of a given code and the associated parameters . another purely numerical consideration in using sph is the initial placement of the particles representing points in the flow @xcite . for instance , regularities in particle configurations may lead to the propagation of artificial structures in the simulation along preferred directions , and even randomised placements may produce numerical features , e.g. , due to local overdensities . for each simulation presented here , the initial particle setup was created using an algorithm which maps a non - regular but constant number density profile of ( equal - mass ) particles into the arbitrary number - density ( and trivially , mass - density ) profile of the desired model . this method has also been applied in other simulations @xcite and is described in appendix [ appendixa ] . the standard ring - spreading test starts from an initial @xmath48-function ring of matter in circular keplerian motion around a gravitating point mass @xcite . if shear viscosity is present , this ring will proceed to spread out into a disc , with the rate of spreading dependent on the magnitude of the viscosity . the matter is taken here to behave isothermally , with the temperature and viscosity being sufficiently small so that the spreading is slow and the thin disc is essentially keplerian ( with its height , @xmath49 , being small compared with the radial coordinate , @xmath50 , at any point ) . with certain additional simplifying assumptions ( negligible self - gravity for the disc material and constant viscosity coefficient , @xmath0 ) , an analytic solution can be obtained for the ring - spreading @xcite . the exact analytic results provide a means for comparison for an sph simulation of an equivalent configuration with no viscosity apart from that of the numerical scheme , @xmath51 . from the analytic results , an effective value for the shear component of the artificial viscosity can then be estimated , if one assumes that @xmath51 is roughly constant throughout the disc ( a somewhat doubtful assumption ) and that the corresponding bulk component has negligible effect ( a very good assumption under the circumstances envisaged ) . the value obtained can then be translated into an effective shakura - sunyaev @xmath52 coefficient [ 25 ] , which represents the viscosity according to @xmath53 where @xmath49 is the disc height , and @xmath54 is the sound speed . the analytic solution gives an expression for the surface density of the ring , @xmath55 , as a function of position and time . for the conditions mentioned above , the radial velocity @xmath56 ( positive for ` outer ' material and negative for ` inner ' material ) is always small , with @xmath57 by scaling arguments @xcite . the surface density is then given by @xmath58 where @xmath50 is the radius in the equatorial plane ( with @xmath59 initially ) ; @xmath60 is a time parameter ( @xmath61 ) ; @xmath0 is the kinematic shear viscosity coefficient ; @xmath62 is the disc mass ( taken as the mass unit , i.e. @xmath63 ) , and @xmath64 is a modified bessel function . a detailed derivation of this formula is given by , e.g. , @xcite . in our work reported below , the corresponding numerical simulations begin a short time after the axisymmetric ring has spread to a finite thickness ( at @xmath65 ) using the analytic formula eq . [ sigmathin ] to provide the initial surface density profile . this same formula is also used for matching against the simulation properties at subsequent times ( doing so has been justified in previous numerical studies by the general proximity of the surface density evolution to this expression ) . self - gravity of the sph particles is included in simulations , although it is assumed that the acceleration due to the central point mass dominates ( we take @xmath66 ) . sph particles are removed from the system at an inner boundary with small radius , @xmath67 . as mentioned above , in addition to the ring - spreading test there are also some approximate analytic formulations for estimating the effective shear viscosity of the disc from kinematic considerations : that of @xcite is @xmath68 while that of @xcite is @xmath69 these relations are generated essentially by reversing the summation form of sph equations which involve artificial viscosity back to continuum limits . further details are given in the respective papers . note that the gadget-2 definition of smoothing length has been used in each case . an artificial viscosity term ( @xmath70 ) appears in both the momentum and energy hydrodynamic equations . each of these roles affects the evolution and structure of the system , as the trajectories of fluid elements are modified and as kinetic energy is transformed into heat . the standard form of the ( isothermal ) ring - spreading test has been used essentially to analyse the effective viscosity via the euler equation , with the spreading being caused by the combined action of the viscous and several other additive terms , but it seems better to use , instead , the energy equation , where the effect of viscosity in generating entropy can be clearly singled out . internal energy in fluid systems can be produced both by viscosity and by non - viscous compression . this is expressed in the first law of thermodynamics , as applied to a co - moving fluid element with unit mass : @xmath71 where @xmath72 is the temperature and @xmath8 is the specific entropy . the specific internal energy produced by viscosity , @xmath73 , corresponds to the first term on the right hand side , and its time derivative is simply @xmath74 this quantity can be calculated directly from the sph expressions in all cases , whatever the flow geometry or equation of state , giving a direct local measure of the effects of viscosity . the only caveat is that there should be no other sources of entropy production to contaminate the interpretation . for the particular case of the ( widely used ) class of polytropic equations of state implemented by gadget-2 , the derivative of eq . [ polytr_eos ] gives the following expression for @xmath75 : @xmath76 where the relations @xmath77 and @xmath78 have been used in arriving at the form of the second line . matching terms with the first law in eq . [ firsttherm ] and referring to eq . [ visc_en_entr ] leads to the following set of formulae linking @xmath79 , @xmath80 and @xmath81 : @xmath82 within gadget-2 , computation of the evolution of @xmath83 is very similar to that for the entropic function , @xmath10 ( cf . [ sph_energ ] , [ visc_en_entr ] and [ visc_entr_entr ] ) : @xmath84 and this can be evaluated straightforwardly for each fluid element . note that in the further specialisation to an isothermal equation of state with @xmath85 ( which we will be using below for making comparison with the ring - spreading test ) , then the entropic function , @xmath10 , becomes a constant , but the true entropy , @xmath8 , continues to change under the action of viscosity , as does @xmath83 . importantly , @xmath86 is determined from the contribution of only a single term which contains @xmath36 . in quantifying the effect of any sph artificial viscosity prescription on a disc system , this isolation greatly simplifies analysis ( and interpretation ) . in general , entropy can be produced by shearing , normal compression and shock compression , the totality of which are accounted for when measuring @xmath86 , due to its general relation to specific entropy . in contrast , only the shearing is important under the assumptions of the ring - spreading test ( or the analytic approximations ) . monitoring @xmath86 already provides a suitable way of demonstrating the local effects of artificial viscosity , and one could stop at that point . however , if one wants to calculate an effective shear viscosity coefficient ( for circumstances involving shear and no significant compression ) , one needs to write an expression for @xmath86 in terms of @xmath0 and the shearing velocity field ( see , e.g. , appendix b of @xcite ) and then to invert it to give an expression for @xmath0 . for general planar rotational motion , one finds the following expression for specific internal energy creation @xcite : @xmath87 + \nu \left(r \frac{\partial\omega}{\partial r } \right)^2\,,\ ] ] using cylindrical polar coordinates ( @xmath88 ) here and after . this form may be inverted easily for an expression of the effective viscosity : @xmath89^{-1}.\ ] ] each term on the right hand side is composed of variables which are directly obtainable from the sph particles . as discussed above , the viscous heating is a direct measure of entropy creation due to viscosity , and the gradient terms may be estimated , e.g. , within sph particle kernels or from averaged ring values . in this study , we describe and utilise an expression which includes solely the term involving @xmath90 . this facilitates comparisons with existing approximations and , as shown below , leads to particularly simple expressions of @xmath91 ( though , it must be emphasised , that the preceding expression is by no means prohibitively complicated ) . the surface area of a narrow , axisymmetric ring of width , @xmath92 ( centred around @xmath50 ) , is @xmath93 , and the mass of the ring is therefore @xmath94 . taking the matter to be moving on basically circular orbits , the viscous torque exerted on the ring can be written as @xcite : @xmath95 the work done by this torque leads to local heating in the rotating flow . the specific heating rate due to viscosity is @xmath96 which is recognized as the final term in eq . [ szmil ] . after trivial rearrangement , the expression for the viscosity is given in terms of easily known quantities as : @xmath97 compared to existing methods for evaluating effective viscosity in rotating flows , this expression is particularly general , having made no assumptions of rotation profile , equation of state , constancy of @xmath0 or artificial viscosity prescription . moreover , as a function of radius , this expression provides a more detailed and useful description of viscous behaviour throughout the simulation . as noted above , more general viscous stresses may be applied as well , such as that of eq . [ szmil ] . in the following examples , we implement eq . [ general_visc ] with different disc stuctures and using different artificial viscosity prescriptions . in the examples below , we apply the expression for the effective local viscosity in eq . [ general_visc ] to test scenarios of ring - spreading and thin disc cases . using assumptions of axisymmetry and circular , keplerian orbits , the viscosity expression is @xmath98 presuming vertical equilibrium with some thin disc scale height , @xmath49 , the shakura - sunyaev @xmath52 is then given as @xmath99 in the case of polytropic , nonisothermal equations of state , these expressions for viscosity and the shakura - sunyaev @xmath52 may be written in terms of the entropic function as : @xmath100 respectively . these last forms are particularly relevant to gadget-2 , where the entropic function is directly evolved , and they are used in obtaining the results presented below . finally , it is interesting to note that , for the specific case of an isothermal eos , eq . [ newvisccrit1 ] may be expressed neatly as : @xmath101 using the expression for the scale height given in eq . [ thinstruc ] , below . physically , in this latter form , @xmath52 directly relates the local dynamical timescale ( @xmath102 ) and the viscous thermal timescale ( @xmath103 ) , as it should from accretion disc theory ( e.g. , ) . we now briefly describe the structure equations for the two varieties of thin isothermal discs used in this study ( in dimensionless units ) . each disc is taken to be in vertical , hydrostatic equilibrium with respect to the gradient of the gravitational potential of the massive central object . the density distribution , scale height and central density ( in the equatorial plane ) are , respectively : @xmath104,\nonumber \\ h(r ) & = & \left[\frac{r^3c^2_{\rm{s}}}{gm_{\rm{c}}}\right]^{1/2}= \frac{\,c_{\rm{s}}}{\omega_{\rm{k}}}\,,\nonumber \\ \rho_{\rm{c}}(r ) & = & \frac{\sigma(r)}{[2\pi]^{1/2}h(r)}\ , . \end{aligned}\ ] ] since this gaussian density profile only asymptotically approaches zero in the vertical direction , an arbitrary disc height for the boundary of sph particles above / below the equatorial plane at any radius must be designated , and we set this to be three times the scale height in order to incorporate @xmath105 of the mass of the theoretical distribution into the simulation ( though , the non - arbitrary scale height , @xmath49 , is used everywhere else in the analytic relations and discussion ) . the vertical velocity is taken to be uniformly zero , and the profile of the azimuthal velocity is very nearly keplerian , i.e. , @xmath106 . the global sound speed , @xmath54 , is a parameter restricted in accordance with the thinness condition , @xmath107 , or @xmath108 , where @xmath109 is essentially the mach number of the ( very supersonic ) azimuthal flow . using both the height from eq . [ thinstruc ] and the definition of the viscosity parametrisation in eq . [ shaksuny ] , the global disc viscosity can be related to the shakura - sunyaev @xmath52 as a function of @xmath109 and the keplerian specific angular momentum , @xmath110 : @xmath111 finally , the initial surface density of the flows must be supplied for use in eqs . [ thinstruc ] . the formulation of the spreading ring , @xmath112 , has been given in eq . [ sigmathin ] . we have also calculated a more disc - like system ( of similar mass and surface density ) , with radial span at @xmath113 of @xmath114 . here , the arbitrary surface density profile has been chosen to be flat in this region initially , @xmath115 , and the resulting disc mass was @xmath116 . this is considered solely as a separate test case and not as a representation of a specific , physical system ( e.g. , the initial boundaries are too discontinuous for an equilibrium system ) . here , we first present results for ring - spreading tests with the balsara correction included for various values of the parameter , @xmath117 , where @xmath118 is the radius of the initial midpoint of the ring ( and using units in which @xmath119 ) . first , the viscous properties are determined kinematically by using the global evolution of the surface density and fits to the theoretical progression given by the analytic formulation . then , local values of @xmath0 and @xmath52 are calculated from @xmath86 using eqs . [ newnucrit]-[newvisccrit1 ] . unless stated otherwise , @xmath120 in all of the presented simulations ( and , in the notation of [ sec : newtonhydro ] , the quadratic term coefficient , @xmath121 ) . as an additional example of sar results , fig . [ fig : ring_init ] shows images of particle locations for an evolving sar ring simulation ( the same system as in the left panel of fig . [ fig : ringsp_cs60 ] ) , projected onto the equatorial plane . over time , the particle distribution within system retains its good qualitative properties of smoothness and randomness . note the absence of any temporary artificial spirals , clumps or sub - structures , such as often appear in sph simulations , even at very early times . both the efficiency of modelling and the relative ease of formulation ( the computation requires only a few simple loops through @xmath122 particles ) , in addition to a reduction of numerical artefacts , make the sar initial conditions very beneficial for use in sph simulations . importantly , the sar particle method is effective because the quasi - continuous mapping retains the relative spacing between particles from the initial glass . the new density profile is obtained smoothly and accurately , without the presence of fluctuations or numerical artefacts . how smoothly a density profile is reproduced is principally determined by the size of the incremental volume element . the sar method does result in a small amount of localised asymmetry in the particle distribution , as volume elements are not generally scaled uniformly in all directions , but for small elements this did not appear to produce spurious artefacts during simulations . improvements to the method are currently being considered .[/INST] a commonly cited drawback of sph is the introduction of spurious shear viscosity by the artificial viscosity term in situations involving rotation . existing approaches for quantifying its effect include approximate analytic formulae and disc - averaged behaviour in specific ring - spreading simulations , based on the kinematic effects produced by the artificial viscosity . these methods have disadvantages , in that they typically are applicable to a very small range of physical scenarios , have a large number of simplifying assumptions , and often are tied to specific sph formulations which do not include corrective ( e.g. , balsara ) or time - dependent artificial viscosity terms . in this study we have developed a simple , generally applicable and practical technique for evaluating the local effect of artificial viscosity directly from the creation of specific entropy for each sph particle . this local approach is simple and quick to implement , and it allows a detailed characterization of viscous effects as a function of position . several advantages of this method are discussed , including its ease in evaluation , its greater accuracy and its broad applicability . in order to compare this new method with existing ones , simple disc flow examples are used . even in these basic cases , the very roughly approximate nature of the previous methods is shown . our local method provides a detailed description of the effects of the artificial viscosity throughout the disc , even for extended examples which implement balsara corrections . as a further use of this approach , explicit dependencies of the effective viscosity in terms of sph and flow parameters are estimated from the example cases . in an appendix , a method for the initial placement of sph particles is discussed which is very effective in reducing numerical fluctuations . [ firstpage ] hydrodynamic models viscosity accretion and accretion discs </s>

The seed for this crawl was a list of every host in the Wayback Machine This crawl was run at a level 1 (URLs including their embeds, plus the URLs of all outbound links including their embeds) The WARC files associated with this crawl are not currently available to the general public. ||||| Loveland theater accidentally starts R-rated movie in place of kids' flick This image released by Paramount Pictures and Nickelodeon Movies shows characters, from left, Squidward Tentacles, SpongeBob SquarePants, Sandy Cheeks, and Mr. Krabs in a scene from "The Spongebob Movie: Sponge Out of Water." ( Paramount Pictures and Nickelodeon Movies via Associated Press ) WATCH DPTV: Molly Hughes with today's top stories "SpongeBob GreyPants." Or maybe "Fifty Shades of SpongeBob." Joe Jaramillo of Johnstown sat in the MetroLux 14 theater Monday morning with his granddaughter waiting for "The SpongeBob Movie: Sponge Out of Water" film to start. He noticed that the previews all seemed to have a romantic flavor but didn't think much of it until the movie started and the words "Fifty Shades of Grey" appeared on screen. "People ran out of there," Jaramillo said with a laugh. "You could hear little kids going, 'SpongeBob! SpongeBob!' as the parents were dragging them out." He said after a few seconds, the screen abruptly went blank. Then new trailers started rolling, this time with children's themes. While "SpongeBob SquarePants" is about an underwater sea creature and all his silly antics, "Fifty Shades of Grey" is an R-rated erotic romance movie based on a book by the same name. Jaramillo said he was thankful that from what he has heard, the adult themes in "Fifty Shades" don't begin until later in the movie. "What was interesting is they have the policy you can't take a kid into an R-rated movie," Jaramillo said. "Some of the trailers were coming up R-rated." David Corwin, president of Metropolitan Theatres, said that there was a chip problem with the server and somehow the wrong movie started playing. Advertisement "It stopped pretty quickly. Someone came out to tell the staff and they stopped it," Corwin said. "Fortunately, the beginning (of 'Fifty Shades') is pretty scenic. It was obviously not intended." He said that both movies are played in that auditorium at different times; "SpongeBob" during the day and "50 Shades" at night, which means the films are on the same computer server. Digital theaters project digital files onto a screen, unlike older film projectors. Corwin added that the theater managers handle every situation differently. In this case, no free passes were issued because the situation was resolved quickly and without undue harm to the children. Jessica Benes: 970-669-5050 ext. 530, [email protected] or twitter.com/jessicabenes

– Human beings can only see around 30 shades of gray, according to a bit of trivia Popular Science says it found in a research paper and has decided to share "for no particular reason whatsoever." The exact number of shades of gray we can distinguish will vary a little depending on things like lighting conditions, the magazine says. Meanwhile, in Fifty Shades of Grey news, a theater in Loveland, Colo., accidentally showed the beginning of the erotic thriller to an audience expecting the SpongeBob SquarePants movie earlier this week. "People ran out of there," a moviegoer tells the Denver Post. "You could hear little kids going, 'SpongeBob! SpongeBob!' as the parents were dragging them out."

<s>[INST]The seed for this crawl was a list of every host in the Wayback Machine This crawl was run at a level 1 (URLs including their embeds, plus the URLs of all outbound links including their embeds) The WARC files associated with this crawl are not currently available to the general public. ||||| Loveland theater accidentally starts R-rated movie in place of kids' flick This image released by Paramount Pictures and Nickelodeon Movies shows characters, from left, Squidward Tentacles, SpongeBob SquarePants, Sandy Cheeks, and Mr. Krabs in a scene from "The Spongebob Movie: Sponge Out of Water." ( Paramount Pictures and Nickelodeon Movies via Associated Press ) WATCH DPTV: Molly Hughes with today's top stories "SpongeBob GreyPants." Or maybe "Fifty Shades of SpongeBob." Joe Jaramillo of Johnstown sat in the MetroLux 14 theater Monday morning with his granddaughter waiting for "The SpongeBob Movie: Sponge Out of Water" film to start. He noticed that the previews all seemed to have a romantic flavor but didn't think much of it until the movie started and the words "Fifty Shades of Grey" appeared on screen. "People ran out of there," Jaramillo said with a laugh. "You could hear little kids going, 'SpongeBob! SpongeBob!' as the parents were dragging them out." He said after a few seconds, the screen abruptly went blank. Then new trailers started rolling, this time with children's themes. While "SpongeBob SquarePants" is about an underwater sea creature and all his silly antics, "Fifty Shades of Grey" is an R-rated erotic romance movie based on a book by the same name. Jaramillo said he was thankful that from what he has heard, the adult themes in "Fifty Shades" don't begin until later in the movie. "What was interesting is they have the policy you can't take a kid into an R-rated movie," Jaramillo said. "Some of the trailers were coming up R-rated." David Corwin, president of Metropolitan Theatres, said that there was a chip problem with the server and somehow the wrong movie started playing. Advertisement "It stopped pretty quickly. Someone came out to tell the staff and they stopped it," Corwin said. "Fortunately, the beginning (of 'Fifty Shades') is pretty scenic. It was obviously not intended." He said that both movies are played in that auditorium at different times; "SpongeBob" during the day and "50 Shades" at night, which means the films are on the same computer server. Digital theaters project digital files onto a screen, unlike older film projectors. Corwin added that the theater managers handle every situation differently. In this case, no free passes were issued because the situation was resolved quickly and without undue harm to the children. Jessica Benes: 970-669-5050 ext. 530, [email protected] or twitter.com/jessicabenes[/INST]– Human beings can only see around 30 shades of gray, according to a bit of trivia Popular Science says it found in a research paper and has decided to share "for no particular reason whatsoever." The exact number of shades of gray we can distinguish will vary a little depending on things like lighting conditions, the magazine says. Meanwhile, in Fifty Shades of Grey news, a theater in Loveland, Colo., accidentally showed the beginning of the erotic thriller to an audience expecting the SpongeBob SquarePants movie earlier this week. "People ran out of there," a moviegoer tells the Denver Post. "You could hear little kids going, 'SpongeBob! SpongeBob!' as the parents were dragging them out."</s>

throughout , @xmath0 is a polish space and @xmath13 a sequence of @xmath0-valued random variables on the probability space @xmath14 . we let @xmath15 denote the borel @xmath7-field on @xmath0 and @xmath16 the set of probability measures on @xmath15 . a random probability measure on @xmath0 is a map @xmath17 such that @xmath18 , where @xmath19 is the @xmath7-field on @xmath20 generated by @xmath21 for all @xmath22 . for each @xmath9 , let @xmath23 be the @xmath24th _ predictive measure_. thus , @xmath23 is a random probability measure on @xmath0 , and @xmath25 is a version of @xmath26 for all @xmath27 . define also @xmath28 . if @xmath29 is _ exchangeable _ , as assumed in this section , there is a random probability measure @xmath3 on @xmath0 such that @xmath30 such an @xmath3 can also be viewed as @xmath31 where @xmath32 is the empirical measure . further , @xmath3 grants the usual representation @xmath33 where @xmath34 . let @xmath6 be a @xmath7-finite measure on @xmath15 . our _ first problem _ is to give conditions for @xmath35 the conditions should concern the finite dimensional distributions @xmath36 , @xmath9 , only . while investigating ( [ goal ] ) , one meets another problem , of possible independent interest . let @xmath11 denote total variation norm on @xmath37 . our _ second problem _ is to give conditions for @xmath38 again , let @xmath39 be exchangeable . reasonable conditions for ( [ goal ] ) look of theoretical interest . they are of practical interest as well thanks to bayesian nonparametrics . in this framework , the starting point is a prior @xmath40 on @xmath16 . since @xmath41 , condition ( [ goal ] ) is equivalent to @xmath42 this is a basic information for the subsequent statistical analysis . roughly speaking , it means that the `` underlying statistical model '' consists of absolutely continuous laws . notwithstanding the significance of ( [ goal ] ) , however , there is a growing literature which gets around the first problem of this paper . indeed , in a plenty of bayesian nonparametric problems , condition ( [ goal ] ) is just a crude _ assumption _ and the prior @xmath40 is directly assessed on a set of densities ( with respect to @xmath6 ) . see , for example , @xcite and references therein . instead , it seems reasonable to get ( [ goal ] ) as a consequence of explicit assumptions on the finite dimensional distributions @xmath43 , . from a foundational point of view , in fact , only assumptions on observable facts make sense . this attitude is strongly supported by de finetti , among others . when dealing with the sequence @xmath29 , the observable facts are events of the type @xmath44 for some @xmath9 and @xmath45 . this is why , in this paper , the conditions for ( [ goal ] ) are requested to concern @xmath43 , @xmath9 , only . some references related to the above remarks are @xcite and @xcite . in particular , in @xcite and @xcite , diaconis and freedman have an exchangeable sequence of indicators and give conditions for the mixing measure ( i.e. , the prior @xmath40 ) to be absolutely continuous with respect to lebesgue measure . the present paper is much in the spirit of @xcite and @xcite . the main difference is that we give conditions for the mixands @xmath46 , and not for the mixing measure @xmath40 , to be absolutely continuous . next , a necessary condition for ( [ goal ] ) is @xmath47 where @xmath48 . condition ( [ nec ] ) clearly involves the finite dimensional distributions only . thus , a ( natural ) question is whether ( [ nec ] ) suffices for ( [ goal ] ) as well . the answer is yes provided @xmath3 can be approximated by the predictive measures @xmath23 in some stronger sense . in fact , condition ( [ nec ] ) can be written as @xmath49 hence , if ( [ nec ] ) holds and @xmath50 , the set @xmath51 has probability 1 . and , for each @xmath52 , one obtains @xmath53 therefore , ( [ goal ] ) follows from ( [ nec ] ) and @xmath54 . in addition , a martingale argument implies the converse implication , that is , @xmath55 see theorem [ p09nh5 t ] . thus , our first problem turns into the second one . the question of whether @xmath56 is of independent interest . among other things , it is connected to bayesian consistency . surprisingly , however , this question seems not answered so far . to the best of our knowledge , @xmath54 in every example known so far . and in fact , for some time , we conjectured that @xmath54 under condition ( [ nec ] ) . but this is not true . as shown in example [ mainexamp ] , when @xmath57 and @xmath58 lebesgue measure , it may be that @xmath59 for all @xmath24 , and yet @xmath3 is singular continuous a.s . indeed , the ( topological ) support of @xmath60 has hausdorff dimension 0 for almost all @xmath61 . thus , ( [ nec ] ) does not suffice for ( [ goal ] ) . to get ( [ goal ] ) , in addition to ( [ nec ] ) , one needs some growth conditions on the conditional densities . we refer to forthcoming theorem [ rfg76yu8 ] for such conditions . here , we mention a result on the second problem . actually , for @xmath50 , it suffices that @xmath62 where @xmath63 denotes the continuous part of @xmath64 ; see theorem [ gt67fc4 ] . finally , most results mentioned above do not need exchangeability of @xmath29 , but the weaker assumption @xmath65 those sequences @xmath29 satisfying the above condition , investigated in @xcite , are called _ conditionally identically distributed _ ( c.i.d . ) . in this section , @xmath66 , @xmath67 for @xmath9 and @xmath68 . if @xmath69 is a random probability measure on @xmath0 , we write @xmath70 to denote the real random variable @xmath71 , @xmath27 . similarly , if @xmath72 is a borel function , integrable with respect to @xmath73 for almost all @xmath61 , we write @xmath74 to denote @xmath75 . let @xmath39 be c.i.d . , as defined in section [ mot ] . since @xmath29 needs not be exchangeable , the representation @xmath76 can fail for any @xmath77 . however , there is a random probability measure @xmath3 on @xmath0 such that @xmath78 for all @xmath27 . in particular , @xmath4 a.s . also , letting @xmath79 be the empirical measure , one obtains @xmath80 a.s . such an @xmath3 is of interest for one more reason . there is an exchangeable sequence @xmath81 of @xmath0-valued random variables on @xmath14 such that @xmath82 see @xcite for details . we next recall some known facts about vector - valued martingales ; see @xcite . let @xmath83 be a separable banach space . also , let @xmath84 be a filtration and @xmath85 a sequence of @xmath86-valued random variables on @xmath87 such that @xmath88 for all @xmath24 . then , @xmath85 is an @xmath89-martingale in case @xmath90 is an @xmath89-martingale for each linear continuous functional @xmath91 . if @xmath85 is an @xmath92-martingale , @xmath93 is a real - valued @xmath92-submartingale . so , doob s maximal inequality yields @xmath94 the following martingale convergence theorem is available as well . let @xmath95 be @xmath96-measurable and such that @xmath97 , where @xmath98 . then , @xmath99 provided @xmath100 a.s . for all @xmath24 and all linear continuous functionals @xmath101 . in the sequel , @xmath6 is a @xmath7-finite measure on @xmath15 . when @xmath57 , it may be natural to think of @xmath6 as the lebesgue measure , but this is only a particular case . indeed , @xmath6 could be singular continuous or concentrated on any borel subset . in addition , @xmath29 is c.i.d . ( in particular , exchangeable ) , and @xmath3 is a random probability measure on @xmath0 such that @xmath4 a.s . equivalently , @xmath3 can be obtained as @xmath102 a.s . it can ( and will ) be assumed @xmath103 . let @xmath109 be such that @xmath110 for all @xmath61 . since @xmath15 is countably generated , @xmath111 can be taken to be @xmath112-measurable ( see @xcite , v.5.58 , page 52 ) so that @xmath113 thus , given @xmath114 , @xmath115 is well defined for @xmath6-almost all @xmath116 . since @xmath29 is c.i.d . , condition ( [ cideq23vg ] ) also implies @xmath117 since @xmath15 is countably generated , the previous equality yields @xmath118 this proves that @xmath59 for all @xmath24 . in particular , up to modifying @xmath23 on a @xmath119-null set , it can be assumed @xmath120 for all @xmath114 , all @xmath61 , and suitable functions @xmath121 . regard @xmath122 as @xmath123-valued random variables . then , @xmath124 is @xmath125-measurable for @xmath126 is @xmath127-measurable for all @xmath128 . clearly , @xmath129 for all @xmath24 and @xmath130 . finally , @xmath29 c.i.d . implies @xmath131 by the martingale convergence theorem ( see section [ prel ] ) @xmath132 in the space @xmath123 , that is , @xmath133 in the exchangeable case , the argument of the previous proof yields a little bit more . indeed , if @xmath29 is exchangeable and @xmath5 a.s . , then @xmath134 where @xmath135 is any integer and @xmath136 . the next result deals with the second problem of section [ intro ] . for each @xmath137 , let @xmath138 and @xmath139 denote the continuous and discrete parts of @xmath140 , that is , @xmath141 for all @xmath27 and @xmath142 . [ gt67fc4 ] suppose @xmath39 is c.i.d . and @xmath143 . then , @xmath144 if and only if @xmath145 ( recall that @xmath146 denotes the basic @xmath7-field on @xmath147 ) . moreover , condition ( [ mo87xqml9 ] ) is automatically true if @xmath29 is exchangeable , so that @xmath148 provided @xmath29 is exchangeable and @xmath149 a.s . the `` only if '' part is trivial . suppose condition ( [ mo87xqml9 ] ) holds . for each @xmath114 , take functions @xmath150 and @xmath151 on @xmath20 such that @xmath152 and @xmath153 are measures on @xmath15 for all @xmath61 and @xmath154 for all @xmath27 . since @xmath29 is c.i.d . , condition ( [ cideq23vg ] ) yields @xmath155 a.s . we first prove @xmath156 . it can be assumed @xmath157 for all @xmath158 , so that @xmath159 for all @xmath61 and some function @xmath160 . for fixed @xmath27 , arguing as in the proof of theorem [ p09nh5 t ] , one has @xmath161 by standard arguments , it follows that @xmath162 a.s . again , it can be assumed @xmath163 for all @xmath61 and some function @xmath164 . define @xmath165 and regard @xmath166 as @xmath123-valued random variables . by the same martingale argument used for theorem [ p09nh5 t ] , one obtains @xmath132 in the space @xmath123 . that is , @xmath167 . we next prove @xmath168 . take @xmath169 as in condition ( [ mo87xqml9 ] ) , and define @xmath170 then , @xmath171 and @xmath172 for all @xmath173 and @xmath116 . define also @xmath174 since @xmath175 , then @xmath176 . fix @xmath52 and let @xmath177 . then @xmath178 since @xmath179 is countable and @xmath180 for all @xmath181 . further , @xmath182 therefore , @xmath183 is an immediate consequence of @xmath184 finally , suppose @xmath29 is exchangeable . we have to prove condition ( [ mo87xqml9 ] ) . if @xmath0 is countable , condition ( [ mo87xqml9 ] ) is trivial for @xmath185 for fixed @xmath27 . if @xmath57 , the glivenko cantelli theorem yields @xmath186 , where @xmath187 $ ] and @xmath188 is the empirical measure hence , ( [ mo87xqml9 ] ) follows from @xmath189 see corollary 3.2 of @xcite . if @xmath0 is any uncountable polish space , take a borel isomorphism @xmath190 . ( thus @xmath191 is bijective with @xmath191 and @xmath192 borel measurable ) . then @xmath193 is an exchangeable sequence of real random variables , and condition ( [ mo87xqml9 ] ) is a straightforward consequence of @xmath194 for each borel set @xmath195 . this concludes the proof . let @xmath85 and @xmath197 be independent sequences of independent real random variables such that @xmath198 and @xmath199 , where @xmath200 and @xmath201 . as shown in example 1.2 of @xcite , @xmath202 is c.i.d . and @xmath203 for some real random variable @xmath204 . since @xmath205 a.s . , then @xmath206 and @xmath207 a.s . ( in fact , @xmath208 a.s . ) . however , condition ( [ mo87xqml9 ] ) fails . in fact , @xmath59 for all @xmath24 , where @xmath6 is lebesgue measure . hence , @xmath209 while @xmath210 for all @xmath24 and almost all @xmath158 . we now turn to the first problem of section [ intro ] . recall that condition ( [ nec ] ) amounts to @xmath211 a.s . for all @xmath114 . therefore , up to modifying @xmath23 on a @xmath119-null set , under condition ( [ nec ] ) one can write @xmath212 for each @xmath61 , each @xmath114 and some function @xmath121 . we also let @xmath213 [ rfg76yu8 ] suppose @xmath39 is c.i.d . and @xmath214 for all @xmath24 . then @xmath5 a.s . if and only if , for each @xmath215 , @xmath216 in particular , @xmath5 a.s . provided , for each @xmath217 , there is @xmath218 such that @xmath219 moreover , for condition ( [ mer45vk01q ] ) to be true , it suffices that @xmath220 if @xmath5 a.s . , theorem [ p09nh5 t ] yields @xmath221 . thus , @xmath222 converges in @xmath223 , for almost all @xmath61 , and this implies condition ( [ serre123 ] ) . conversely , we now prove that @xmath5 a.s . under condition ( [ serre123 ] ) . fix a nondecreasing sequence @xmath224 such that @xmath225 , @xmath226 , and @xmath227 . since @xmath228 and @xmath0 is polish , there is @xmath229 satisfying @xmath230 and @xmath231 . by induction , for each @xmath232 , there is @xmath233 such that @xmath234 and @xmath235 . since @xmath29 is c.i.d . , condition ( [ cideq23vg ] ) implies @xmath236 define @xmath237 and @xmath238 . if @xmath239 , then @xmath240 moreover , @xmath241 . in fact , @xmath242 and @xmath243 a.s . for all @xmath24 , so that @xmath244 thus , to prove @xmath5 a.s . , it suffices to see that @xmath245 a.s . for all @xmath246 . suppose ( [ serre123 ] ) holds . fix @xmath247 , define @xmath248 and take a set @xmath249 such that @xmath176 and , for each @xmath52 , @xmath250 let @xmath52 . since @xmath251 and @xmath252 is uniformly integrable under @xmath253 , there is a subsequence @xmath254 and a function @xmath255 such that @xmath256 in the weak - topology of @xmath257 . this means that @xmath258 therefore , @xmath259 by standard arguments , the previous two relations yield @xmath260 thus , @xmath261 . this proves that condition ( [ serre123 ] ) implies @xmath5 a.s . fix @xmath27 , @xmath218 , and suppose @xmath264 . let @xmath265 for all @xmath266 . it can be assumed @xmath267 for all @xmath61 and @xmath9 . thus , each @xmath268 can be seen as an @xmath269-valued random variable such that @xmath270 further , @xmath271 is @xmath272-measurable for all @xmath273 , where @xmath274 . since @xmath29 is c.i.d . , condition ( [ cideq23vg ] ) also implies @xmath275 hence , @xmath276 is a @xmath277-martingale . by doob s maximal inequality , @xmath278 in particular , @xmath279 a.s . , and this completes the proof . third , suppose @xmath29 exchangeable , and fix _ any _ random probability measure @xmath285 on @xmath0 such that @xmath286 . then @xmath287 a.s . under the assumptions of theorem [ rfg76yu8 ] . in fact , @xmath3 and @xmath285 have the same probability distribution , when regarded as @xmath288-valued random variables . [ mainexamp ] let @xmath57 and @xmath58 lebesgue measure . all random variables are defined on the probability space @xmath289 . we now exhibit an exchangeable sequence @xmath29 such that @xmath59 for all @xmath9 and yet @xmath290 . in fact , the support of @xmath60 has hausdorff dimension 0 for almost all @xmath61 . two known facts are to be recalled . first , if @xmath291 and @xmath292 are independent @xmath293-valued random variables , then @xmath294 where @xmath45 and @xmath295 is the distribution of @xmath292 . hence , @xmath296 provided @xmath297 . the second fact is the following : define @xmath309 and @xmath310 then , @xmath39 is conditionally i.i.d . given @xmath311 . precisely , for @xmath61 and @xmath22 , define @xmath312 then , @xmath313 is a version of @xmath314 and @xmath315 . in particular , @xmath29 is exchangeable . moreover , @xmath80 a.s . for @xmath316 the ( topological ) support of @xmath60 has hausdorff dimension 0 for almost all @xmath61 . define in fact @xmath317 and @xmath318 . by theorem [ omygod47 ] , it suffices to verify that @xmath319 and condition ( [ m78yuhg5 ] ) follows immediately from @xmath320 we finally prove that @xmath59 for all @xmath9 . given the array @xmath321 , with @xmath322 for all @xmath323 , define @xmath324 fix @xmath9 and denote @xmath325 the @xmath326 identity matrix . if @xmath327 satisfies @xmath328 then @xmath329 in this case , since @xmath330 , then @xmath331 . hence , letting @xmath332 , the conditional distribution of @xmath333 given @xmath334 is absolutely continuous with respect to @xmath283 as far as @xmath327 satisfies ( [ uffa34ed5 t ] ) . to complete the proof , it suffices to note that @xmath335

let @xmath0 be a polish space and @xmath1 an exchangeable sequence of @xmath0-valued random variables . let @xmath2 be the predictive measure and @xmath3 a random probability measure on @xmath0 such that @xmath4 a.s . two ( related ) problems are addressed . one is to give conditions for @xmath5 a.s . , where @xmath6 is a ( nonrandom ) @xmath7-finite borel measure on @xmath0 . such conditions should concern the finite dimensional distributions @xmath8 , @xmath9 , only . the other problem is to investigate whether @xmath10 , where @xmath11 is total variation norm . various results are obtained . some of them do not require exchangeability , but hold under the weaker assumption that @xmath12 is conditionally identically distributed , in the sense of [ _ ann . probab . _ * 32 * ( 2004 ) 20292052 ] . ,

<s>[INST]throughout , @xmath0 is a polish space and @xmath13 a sequence of @xmath0-valued random variables on the probability space @xmath14 . we let @xmath15 denote the borel @xmath7-field on @xmath0 and @xmath16 the set of probability measures on @xmath15 . a random probability measure on @xmath0 is a map @xmath17 such that @xmath18 , where @xmath19 is the @xmath7-field on @xmath20 generated by @xmath21 for all @xmath22 . for each @xmath9 , let @xmath23 be the @xmath24th _ predictive measure_. thus , @xmath23 is a random probability measure on @xmath0 , and @xmath25 is a version of @xmath26 for all @xmath27 . define also @xmath28 . if @xmath29 is _ exchangeable _ , as assumed in this section , there is a random probability measure @xmath3 on @xmath0 such that @xmath30 such an @xmath3 can also be viewed as @xmath31 where @xmath32 is the empirical measure . further , @xmath3 grants the usual representation @xmath33 where @xmath34 . let @xmath6 be a @xmath7-finite measure on @xmath15 . our _ first problem _ is to give conditions for @xmath35 the conditions should concern the finite dimensional distributions @xmath36 , @xmath9 , only . while investigating ( [ goal ] ) , one meets another problem , of possible independent interest . let @xmath11 denote total variation norm on @xmath37 . our _ second problem _ is to give conditions for @xmath38 again , let @xmath39 be exchangeable . reasonable conditions for ( [ goal ] ) look of theoretical interest . they are of practical interest as well thanks to bayesian nonparametrics . in this framework , the starting point is a prior @xmath40 on @xmath16 . since @xmath41 , condition ( [ goal ] ) is equivalent to @xmath42 this is a basic information for the subsequent statistical analysis . roughly speaking , it means that the `` underlying statistical model '' consists of absolutely continuous laws . notwithstanding the significance of ( [ goal ] ) , however , there is a growing literature which gets around the first problem of this paper . indeed , in a plenty of bayesian nonparametric problems , condition ( [ goal ] ) is just a crude _ assumption _ and the prior @xmath40 is directly assessed on a set of densities ( with respect to @xmath6 ) . see , for example , @xcite and references therein . instead , it seems reasonable to get ( [ goal ] ) as a consequence of explicit assumptions on the finite dimensional distributions @xmath43 , . from a foundational point of view , in fact , only assumptions on observable facts make sense . this attitude is strongly supported by de finetti , among others . when dealing with the sequence @xmath29 , the observable facts are events of the type @xmath44 for some @xmath9 and @xmath45 . this is why , in this paper , the conditions for ( [ goal ] ) are requested to concern @xmath43 , @xmath9 , only . some references related to the above remarks are @xcite and @xcite . in particular , in @xcite and @xcite , diaconis and freedman have an exchangeable sequence of indicators and give conditions for the mixing measure ( i.e. , the prior @xmath40 ) to be absolutely continuous with respect to lebesgue measure . the present paper is much in the spirit of @xcite and @xcite . the main difference is that we give conditions for the mixands @xmath46 , and not for the mixing measure @xmath40 , to be absolutely continuous . next , a necessary condition for ( [ goal ] ) is @xmath47 where @xmath48 . condition ( [ nec ] ) clearly involves the finite dimensional distributions only . thus , a ( natural ) question is whether ( [ nec ] ) suffices for ( [ goal ] ) as well . the answer is yes provided @xmath3 can be approximated by the predictive measures @xmath23 in some stronger sense . in fact , condition ( [ nec ] ) can be written as @xmath49 hence , if ( [ nec ] ) holds and @xmath50 , the set @xmath51 has probability 1 . and , for each @xmath52 , one obtains @xmath53 therefore , ( [ goal ] ) follows from ( [ nec ] ) and @xmath54 . in addition , a martingale argument implies the converse implication , that is , @xmath55 see theorem [ p09nh5 t ] . thus , our first problem turns into the second one . the question of whether @xmath56 is of independent interest . among other things , it is connected to bayesian consistency . surprisingly , however , this question seems not answered so far . to the best of our knowledge , @xmath54 in every example known so far . and in fact , for some time , we conjectured that @xmath54 under condition ( [ nec ] ) . but this is not true . as shown in example [ mainexamp ] , when @xmath57 and @xmath58 lebesgue measure , it may be that @xmath59 for all @xmath24 , and yet @xmath3 is singular continuous a.s . indeed , the ( topological ) support of @xmath60 has hausdorff dimension 0 for almost all @xmath61 . thus , ( [ nec ] ) does not suffice for ( [ goal ] ) . to get ( [ goal ] ) , in addition to ( [ nec ] ) , one needs some growth conditions on the conditional densities . we refer to forthcoming theorem [ rfg76yu8 ] for such conditions . here , we mention a result on the second problem . actually , for @xmath50 , it suffices that @xmath62 where @xmath63 denotes the continuous part of @xmath64 ; see theorem [ gt67fc4 ] . finally , most results mentioned above do not need exchangeability of @xmath29 , but the weaker assumption @xmath65 those sequences @xmath29 satisfying the above condition , investigated in @xcite , are called _ conditionally identically distributed _ ( c.i.d . ) . in this section , @xmath66 , @xmath67 for @xmath9 and @xmath68 . if @xmath69 is a random probability measure on @xmath0 , we write @xmath70 to denote the real random variable @xmath71 , @xmath27 . similarly , if @xmath72 is a borel function , integrable with respect to @xmath73 for almost all @xmath61 , we write @xmath74 to denote @xmath75 . let @xmath39 be c.i.d . , as defined in section [ mot ] . since @xmath29 needs not be exchangeable , the representation @xmath76 can fail for any @xmath77 . however , there is a random probability measure @xmath3 on @xmath0 such that @xmath78 for all @xmath27 . in particular , @xmath4 a.s . also , letting @xmath79 be the empirical measure , one obtains @xmath80 a.s . such an @xmath3 is of interest for one more reason . there is an exchangeable sequence @xmath81 of @xmath0-valued random variables on @xmath14 such that @xmath82 see @xcite for details . we next recall some known facts about vector - valued martingales ; see @xcite . let @xmath83 be a separable banach space . also , let @xmath84 be a filtration and @xmath85 a sequence of @xmath86-valued random variables on @xmath87 such that @xmath88 for all @xmath24 . then , @xmath85 is an @xmath89-martingale in case @xmath90 is an @xmath89-martingale for each linear continuous functional @xmath91 . if @xmath85 is an @xmath92-martingale , @xmath93 is a real - valued @xmath92-submartingale . so , doob s maximal inequality yields @xmath94 the following martingale convergence theorem is available as well . let @xmath95 be @xmath96-measurable and such that @xmath97 , where @xmath98 . then , @xmath99 provided @xmath100 a.s . for all @xmath24 and all linear continuous functionals @xmath101 . in the sequel , @xmath6 is a @xmath7-finite measure on @xmath15 . when @xmath57 , it may be natural to think of @xmath6 as the lebesgue measure , but this is only a particular case . indeed , @xmath6 could be singular continuous or concentrated on any borel subset . in addition , @xmath29 is c.i.d . ( in particular , exchangeable ) , and @xmath3 is a random probability measure on @xmath0 such that @xmath4 a.s . equivalently , @xmath3 can be obtained as @xmath102 a.s . it can ( and will ) be assumed @xmath103 . let @xmath109 be such that @xmath110 for all @xmath61 . since @xmath15 is countably generated , @xmath111 can be taken to be @xmath112-measurable ( see @xcite , v.5.58 , page 52 ) so that @xmath113 thus , given @xmath114 , @xmath115 is well defined for @xmath6-almost all @xmath116 . since @xmath29 is c.i.d . , condition ( [ cideq23vg ] ) also implies @xmath117 since @xmath15 is countably generated , the previous equality yields @xmath118 this proves that @xmath59 for all @xmath24 . in particular , up to modifying @xmath23 on a @xmath119-null set , it can be assumed @xmath120 for all @xmath114 , all @xmath61 , and suitable functions @xmath121 . regard @xmath122 as @xmath123-valued random variables . then , @xmath124 is @xmath125-measurable for @xmath126 is @xmath127-measurable for all @xmath128 . clearly , @xmath129 for all @xmath24 and @xmath130 . finally , @xmath29 c.i.d . implies @xmath131 by the martingale convergence theorem ( see section [ prel ] ) @xmath132 in the space @xmath123 , that is , @xmath133 in the exchangeable case , the argument of the previous proof yields a little bit more . indeed , if @xmath29 is exchangeable and @xmath5 a.s . , then @xmath134 where @xmath135 is any integer and @xmath136 . the next result deals with the second problem of section [ intro ] . for each @xmath137 , let @xmath138 and @xmath139 denote the continuous and discrete parts of @xmath140 , that is , @xmath141 for all @xmath27 and @xmath142 . [ gt67fc4 ] suppose @xmath39 is c.i.d . and @xmath143 . then , @xmath144 if and only if @xmath145 ( recall that @xmath146 denotes the basic @xmath7-field on @xmath147 ) . moreover , condition ( [ mo87xqml9 ] ) is automatically true if @xmath29 is exchangeable , so that @xmath148 provided @xmath29 is exchangeable and @xmath149 a.s . the `` only if '' part is trivial . suppose condition ( [ mo87xqml9 ] ) holds . for each @xmath114 , take functions @xmath150 and @xmath151 on @xmath20 such that @xmath152 and @xmath153 are measures on @xmath15 for all @xmath61 and @xmath154 for all @xmath27 . since @xmath29 is c.i.d . , condition ( [ cideq23vg ] ) yields @xmath155 a.s . we first prove @xmath156 . it can be assumed @xmath157 for all @xmath158 , so that @xmath159 for all @xmath61 and some function @xmath160 . for fixed @xmath27 , arguing as in the proof of theorem [ p09nh5 t ] , one has @xmath161 by standard arguments , it follows that @xmath162 a.s . again , it can be assumed @xmath163 for all @xmath61 and some function @xmath164 . define @xmath165 and regard @xmath166 as @xmath123-valued random variables . by the same martingale argument used for theorem [ p09nh5 t ] , one obtains @xmath132 in the space @xmath123 . that is , @xmath167 . we next prove @xmath168 . take @xmath169 as in condition ( [ mo87xqml9 ] ) , and define @xmath170 then , @xmath171 and @xmath172 for all @xmath173 and @xmath116 . define also @xmath174 since @xmath175 , then @xmath176 . fix @xmath52 and let @xmath177 . then @xmath178 since @xmath179 is countable and @xmath180 for all @xmath181 . further , @xmath182 therefore , @xmath183 is an immediate consequence of @xmath184 finally , suppose @xmath29 is exchangeable . we have to prove condition ( [ mo87xqml9 ] ) . if @xmath0 is countable , condition ( [ mo87xqml9 ] ) is trivial for @xmath185 for fixed @xmath27 . if @xmath57 , the glivenko cantelli theorem yields @xmath186 , where @xmath187 $ ] and @xmath188 is the empirical measure hence , ( [ mo87xqml9 ] ) follows from @xmath189 see corollary 3.2 of @xcite . if @xmath0 is any uncountable polish space , take a borel isomorphism @xmath190 . ( thus @xmath191 is bijective with @xmath191 and @xmath192 borel measurable ) . then @xmath193 is an exchangeable sequence of real random variables , and condition ( [ mo87xqml9 ] ) is a straightforward consequence of @xmath194 for each borel set @xmath195 . this concludes the proof . let @xmath85 and @xmath197 be independent sequences of independent real random variables such that @xmath198 and @xmath199 , where @xmath200 and @xmath201 . as shown in example 1.2 of @xcite , @xmath202 is c.i.d . and @xmath203 for some real random variable @xmath204 . since @xmath205 a.s . , then @xmath206 and @xmath207 a.s . ( in fact , @xmath208 a.s . ) . however , condition ( [ mo87xqml9 ] ) fails . in fact , @xmath59 for all @xmath24 , where @xmath6 is lebesgue measure . hence , @xmath209 while @xmath210 for all @xmath24 and almost all @xmath158 . we now turn to the first problem of section [ intro ] . recall that condition ( [ nec ] ) amounts to @xmath211 a.s . for all @xmath114 . therefore , up to modifying @xmath23 on a @xmath119-null set , under condition ( [ nec ] ) one can write @xmath212 for each @xmath61 , each @xmath114 and some function @xmath121 . we also let @xmath213 [ rfg76yu8 ] suppose @xmath39 is c.i.d . and @xmath214 for all @xmath24 . then @xmath5 a.s . if and only if , for each @xmath215 , @xmath216 in particular , @xmath5 a.s . provided , for each @xmath217 , there is @xmath218 such that @xmath219 moreover , for condition ( [ mer45vk01q ] ) to be true , it suffices that @xmath220 if @xmath5 a.s . , theorem [ p09nh5 t ] yields @xmath221 . thus , @xmath222 converges in @xmath223 , for almost all @xmath61 , and this implies condition ( [ serre123 ] ) . conversely , we now prove that @xmath5 a.s . under condition ( [ serre123 ] ) . fix a nondecreasing sequence @xmath224 such that @xmath225 , @xmath226 , and @xmath227 . since @xmath228 and @xmath0 is polish , there is @xmath229 satisfying @xmath230 and @xmath231 . by induction , for each @xmath232 , there is @xmath233 such that @xmath234 and @xmath235 . since @xmath29 is c.i.d . , condition ( [ cideq23vg ] ) implies @xmath236 define @xmath237 and @xmath238 . if @xmath239 , then @xmath240 moreover , @xmath241 . in fact , @xmath242 and @xmath243 a.s . for all @xmath24 , so that @xmath244 thus , to prove @xmath5 a.s . , it suffices to see that @xmath245 a.s . for all @xmath246 . suppose ( [ serre123 ] ) holds . fix @xmath247 , define @xmath248 and take a set @xmath249 such that @xmath176 and , for each @xmath52 , @xmath250 let @xmath52 . since @xmath251 and @xmath252 is uniformly integrable under @xmath253 , there is a subsequence @xmath254 and a function @xmath255 such that @xmath256 in the weak - topology of @xmath257 . this means that @xmath258 therefore , @xmath259 by standard arguments , the previous two relations yield @xmath260 thus , @xmath261 . this proves that condition ( [ serre123 ] ) implies @xmath5 a.s . fix @xmath27 , @xmath218 , and suppose @xmath264 . let @xmath265 for all @xmath266 . it can be assumed @xmath267 for all @xmath61 and @xmath9 . thus , each @xmath268 can be seen as an @xmath269-valued random variable such that @xmath270 further , @xmath271 is @xmath272-measurable for all @xmath273 , where @xmath274 . since @xmath29 is c.i.d . , condition ( [ cideq23vg ] ) also implies @xmath275 hence , @xmath276 is a @xmath277-martingale . by doob s maximal inequality , @xmath278 in particular , @xmath279 a.s . , and this completes the proof . third , suppose @xmath29 exchangeable , and fix _ any _ random probability measure @xmath285 on @xmath0 such that @xmath286 . then @xmath287 a.s . under the assumptions of theorem [ rfg76yu8 ] . in fact , @xmath3 and @xmath285 have the same probability distribution , when regarded as @xmath288-valued random variables . [ mainexamp ] let @xmath57 and @xmath58 lebesgue measure . all random variables are defined on the probability space @xmath289 . we now exhibit an exchangeable sequence @xmath29 such that @xmath59 for all @xmath9 and yet @xmath290 . in fact , the support of @xmath60 has hausdorff dimension 0 for almost all @xmath61 . two known facts are to be recalled . first , if @xmath291 and @xmath292 are independent @xmath293-valued random variables , then @xmath294 where @xmath45 and @xmath295 is the distribution of @xmath292 . hence , @xmath296 provided @xmath297 . the second fact is the following : define @xmath309 and @xmath310 then , @xmath39 is conditionally i.i.d . given @xmath311 . precisely , for @xmath61 and @xmath22 , define @xmath312 then , @xmath313 is a version of @xmath314 and @xmath315 . in particular , @xmath29 is exchangeable . moreover , @xmath80 a.s . for @xmath316 the ( topological ) support of @xmath60 has hausdorff dimension 0 for almost all @xmath61 . define in fact @xmath317 and @xmath318 . by theorem [ omygod47 ] , it suffices to verify that @xmath319 and condition ( [ m78yuhg5 ] ) follows immediately from @xmath320 we finally prove that @xmath59 for all @xmath9 . given the array @xmath321 , with @xmath322 for all @xmath323 , define @xmath324 fix @xmath9 and denote @xmath325 the @xmath326 identity matrix . if @xmath327 satisfies @xmath328 then @xmath329 in this case , since @xmath330 , then @xmath331 . hence , letting @xmath332 , the conditional distribution of @xmath333 given @xmath334 is absolutely continuous with respect to @xmath283 as far as @xmath327 satisfies ( [ uffa34ed5 t ] ) . to complete the proof , it suffices to note that @xmath335[/INST] let @xmath0 be a polish space and @xmath1 an exchangeable sequence of @xmath0-valued random variables . let @xmath2 be the predictive measure and @xmath3 a random probability measure on @xmath0 such that @xmath4 a.s . two ( related ) problems are addressed . one is to give conditions for @xmath5 a.s . , where @xmath6 is a ( nonrandom ) @xmath7-finite borel measure on @xmath0 . such conditions should concern the finite dimensional distributions @xmath8 , @xmath9 , only . the other problem is to investigate whether @xmath10 , where @xmath11 is total variation norm . various results are obtained . some of them do not require exchangeability , but hold under the weaker assumption that @xmath12 is conditionally identically distributed , in the sense of [ _ ann . probab . _ * 32 * ( 2004 ) 20292052 ] . , </s>

the dynamics of conduction electrons in open nanostructures modulated by time - dependent signals is an outstanding problem in quantum transport theory . extensive experimental and theoretical work has been done especially on quantum pumping @xcite ( a detailed bibliography can be found in the recent review @xcite ) and photon - assisted tunneling ( see ref . and references therein ) . in these phenomena one is interested in measuring or computing the current response of a mesoscopic system driven by time - dependent _ periodic _ signals applied either on the system or on the attached leads . in particular , an unbiased system subjected to two periodic potentials differing by a phase lag generates a nonvanishing pumped current , provided one averages over the relevant period . @xcite if the signal frequency is small the pumping is adiabatic and can be described by a frozen scattering matrix as is rigorously shown in ref . . a photon - assisted tunneling implies instead high frequencies and the measured current displays satellite peaks due to the additional side - bands . @xcite from the theoretical point of view , any calculation of the current starts from defining the initial equilibrium state of the system and the perturbation that drives it . one way is to start with the connected system in the absence of the bias , and then to apply the bias adiabatically performing linear response calculations for the steady state current . an alternative picture was proposed by caroli @xcite that takes as the equilibrium state the state of the decoupled system with the bias already imposed on the leads . the perturbation here is instead the coupling to the leads that is usually adiabatically switched in the remote past and eventually reaches its full magnitude at @xmath0 . if one assumes that a steady state is achieved , the green functions depend only on time differences and the keldsyh formalism gives the corresponding current in terms of fourier transformed quantities . both pictures were shown to be useful in capturing and explaining important effects . as for an ac signal , it can be included in the green - keldysh approach as a time - dependent global shift of the spectrum of the leads . @xcite note that the occupation probability ( i.e. the fermi function ) of the leads stays time - independent . therefore this procedure assumes somehow that an ac signal is applied as well adiabatically . in the quantum pumping calculations the pumping potential is applied to the system in a steady - state , be it subjected to a finite bias or not . finally the current ( transient , time - averaged or steady - state ) is computed from the keldysh - green function formalism . @xcite here we aim to get some insight into a related topic : the calculation of the transient current through a quantum dot ( qd ) whose coupling to the leads is time dependent while the bias applied on the leads is constant . there are considerably fewer theoretical results on this issue ( see the references below ) and we were motivated also by recent increasing interest in using suitable electric pulses to investigate relaxation processes in quantum dots by using pump and probe measurements or transient current spectroscopy . @xcite as in the well known case of a turnstile pump @xcite these techniques imply oscillating tunnel barriers so that the transport formalism should deal with the nonlocal time - dependent coupling between the leads and the system . the problem we want to look at is defined as follows : i ) the system is disconnected at any time @xmath1 , and the leads are submitted to a constant bias which is included through the difference between the chemical potentials of the leads . ii ) at @xmath0 the leads are _ suddenly _ plugged to the system . physically this means that the tunneling barriers between the leads and the system are set to be very high at @xmath1 and drop suddenly at @xmath0 to an intermediate value that allows charge transfer across the system . the simplest case of a constant barrier height at any @xmath2 opens already the problem of the existence of non - equilibrium steady - states in the long time limit . in general and at a rigorous level , one can prove the existence of such states when @xmath3 @xcite and moreover , a landauer formula was shown to hold for the steady - state current . @xcite the method we developed is able to check the passage from transient behavior to steady state regime for specific systems , like many - level one- and two - dimensional quantum dots . as we shall see , the onset of the steady state for a given system depends on the its structure ( number of levels ) , on the measurement setup ( the strength of the coupling to the leads and the location of the contacts ) , and also on external parameters like gate potentials . although , in the present work the numerical simulations are restricted to the step - like coupling to the leads , our model allows the consideration of more general time - dependent potentials between the leads and the central region . in particular we can investigate the response of a system to _ nonlocal _ time - dependent perturbations that can be switched on and off individually . recently there have been several theoretical approaches to the transient regime . in ref . the time - dependent density functional was used to compute the transient current in a one - dimensional system submitted to a finite bias applied on the leads . the coupling term does not depend on time and the system is in an equilibrium state in the absence of the bias . starting from this state the kohn - sham equation is used to calculate the response of the system to the external bias . the same techniques allow the calculation of time - averaged current in one - dimensional quantum pumps . @xcite on the other hand , maciejko _ et al . _ @xcite have computed within the keldysh framework the response of a single - site dot for a step - like or periodic signal applied to the _ leads _ , beyond the wide band limit . in their approach the computation of the time - dependent green functions of the perturbed system uses steady - state green functions of the coupled and biased system that have to be provided from density functional theory . we believe that theoretical results regarding the transient regime induced by time - dependent couplings of many - level systems would complement these results . the content of the paper is organized as follows : section ii presents the model and the theoretical tools we use to compute the transient current . we rely essentially on the non - equilibrium green - keldysh formalism . however , in contrast to most of the previous studies we allow a complex structure for the central region coupled to leads ( i.e. there is more than one single localized level and the system can be as complicated as we want : a single dot , a double dot or an aharanov - bohm interferometer ) . also we go beyond the wide - band limit approximation and we solve exactly the integral dyson equation for the retarded green function of the _ coupled _ central region by a suitable numerical procedure . in doing so we take into account _ all _ the scattering processes between the leads and the sample . although the electron - electron interaction could presumably play an important role in the transient behavior and the formalism we use allows the inclusion of coulomb terms in the hamiltonian , we do not take it into account in this work . as is well known , the problem of the coulomb interaction in the keldysh approach is mainly technical and implies suitable approximation schemes for the interaction self - energy . we postpone this issue for future work . iii gives extensive discussion of the numerical simulations for single and double dots . section iv concludes the paper . the systems we study in this work have a typical transport configuration : a central region ( @xmath4 ) coupled to two semiinfinite leads ( @xmath5 and @xmath6 ) via a tunneling term ( see fig.1 for a schematical representation ) . we shall use a tight - binding ( tb ) description of the hamiltonian which has the following form : @xmath7 where @xmath8 describes the system , @xmath9 the semiinfinite leads and @xmath10 is the time - dependent tunneling term : @xmath11 at @xmath0.,scaledwidth=45.0% ] here @xmath12 and @xmath13 denote the annihilation / creation operators on the @xmath14-th site of the lead @xmath15 . similarly @xmath16 and @xmath17 is the pair of operators corresponding to the @xmath18-th site from the central region @xmath4 . @xmath19 is the time - dependent hopping coefficient between the @xmath14-th site of the lead @xmath15 and the @xmath18-th site of the central region . we take here a nearest - neighbor coupling so the double sums in the above expression contain only pairs of sites from the leads endpoint and the corresponding contact region from the central system : @xmath20 in this work we consider a steplike potential , i.e. @xmath21 if @xmath2 and zero otherwise . @xmath8 has a usual tight - binding form @xmath22 here @xmath23 are hopping terms , @xmath24 denotes nearest - neighbor summation over the system sites . @xmath25 is the on - site energy and the diagonal term @xmath26 simulates a plunger gate potential applied on the system . @xmath27 is the number of sites in the central region . the spectral width of the tight - binding lead is as usual @xmath28 $ ] , where @xmath29 is the hopping energy on leads ( we take the same hopping constant on every lead ) . in the numerical calculation we choose @xmath29 such that it covers entirely the spectrum of the central region but we do _ not _ assume it to be infinite , as it is done in the wide - band limit approximation . the central problem in electronic transport is to compute the statistical average of the time - dependent current operator in a given lead ( say @xmath5 ) @xmath30 using the statistical operator @xmath31 . notice that the time - dependence of the current operator appears only because of the time - dependent coupling . denoting by @xmath32 the endpoint sites of the lead @xmath5 which are coupled to the sites @xmath33 of the central region and by @xmath34 the number of sites in the transverse direction of the lead , the current operator @xmath35 has the form ( we take the electron charge as @xmath36 and @xmath37 ) : @xmath38 since the statistical operator @xmath31 of the coupled system is not easy to compute it is useful to move the time - dependence entirely to the current operator by writing @xmath31 in terms of the equilibrium statistical operator @xmath39 of the disconnected system . in general , the coupling to the leads is established at a given instant @xmath40 so that @xmath41 for @xmath42 . then using the unitary evolution @xmath43 of the full hamiltonian in the interaction picture w.r.t . the unperturbed one the solution of the quantum liouville equation is given by @xmath44 then it can be shown ( see e.g. ref . ) that : @xmath45 where @xmath46 is the ordering operator on the schwinger - keldysh contour @xmath47 that runs from @xmath40 to @xmath48 and back to @xmath40 . we remind the reader that in the case of adiabatic coupling the statistical operator becomes time - independent only in the remote past @xmath49 . both the coupling and current operators are written in the interaction picture . using the definitions of the lesser green functions in terms of the heisenberg operators : @xmath50 it follows that the current is given by a simpler relation : @xmath51 at this point the standard keldysh formalism requires the application of the so called langreth rules @xcite in order to express the lesser green function @xmath52 in terms of the green functions of the central region in the presence of the leads @xmath53 and the green functions of the isolated semiinfinite lead @xmath54 . the latter can be analytically computed : @xmath55 in the above equations @xmath56 is the energy of the transverse channel @xmath57 . these channels appear due to the width of the leads which in the tight - binding description is given by the number of the sites @xmath34 in the transverse direction . more exactly , the many channel lead is constructed by taking @xmath34 semiinfinite 1d leads and by coupling them through nearest neighbor hopping constants . then @xmath58 is the transversal eigenfunction associated to @xmath59 , and @xmath60 is the density of states at the endpoint of a semiinfinite one - dimensional lead : @xmath61 finally , @xmath62 is the fermi function in the lead @xmath5 . the bias is included in our approach as the difference between the two chemical potentials of the leads @xmath63 . plugging all these elements in the current formula one gets the main expression that will be numerically implemented in the next section : @xmath64 we have introduced the energy and time - dependent quantity @xmath65 that takes also into account the @xmath34 channels in the lead : @xmath66 a similar formula can be written down for the current @xmath67 and therefore one defines as well the net current @xmath68 it is important to observe that in contrast to the simple case of a single - site system the expressions for the two currents imply the green functions at different contacts . the retarded and the lesser green functions are then to be computed from the dyson and keldysh equations @xcite : @xmath69 where @xmath70 are the retarded and advanced green functions of the isolated central region and @xmath71 are the retarded and lesser self - energies . @xmath72 has a simple expression in terms of the discrete spectrum @xmath73 of the central region and its localized eigenfunctions @xmath74 ( clearly @xmath75 ) : @xmath76 we emphasize the lower integration limit @xmath0 in equations ( [ dyson ] ) and ( [ keldysh ] ) . this is due to the fact that there is no coupling for @xmath1 . in the adiabatic setup the coupling is established in the remote past and one should set a lower cutoff in the numerical implementation . however , the dyson equation still contains two coupled integrals . the two self - energies above contain the information from the leads and are finite rank matrices in the hilbert space of the central region @xmath4 ( @xmath77 ) : @xmath78 we stress that the indices of the leads green function are unambiguously determined as the neighbor sites of the contact surface @xmath79 . in the single channel case @xmath80 one recovers simpler expressions . in particular the retarded green function of the lead can be expressed through the bessel function of the first kind : @xmath81 we point out the difference between the exact form of the retarded self - energy and the simple wide - band limit expression ( which simplifies to @xmath82 up to some constants ) . note that the retarded green function gives the leads self - energy and is a highly oscillating functions . it will turn out in section iii that this behavior has crucial effects on the transient current . another difficulty of eq.([dyson ] ) comes from the quadratic dependence of the self - energies on the time - dependent coupling . clearly this prevents any partial fourier transform trick . given these , our strategy in solving the integral dyson equation relies in transforming it into an algebraic equation of the form @xmath83 where @xmath84 are generalized complex matrices depending on both spatial and time arguments . to this end we first plug the retarded self energy from eq.([sigmar ] ) in the dyson equation ( [ dyson ] ) and discretize the time arguments . note that the variable @xmath85 is defined on a denser grid than the one used for @xmath86 . the inner time integral is evaluated by a repeated 4-point gauss method , which turned out to be accurate enough for the numerical results to be stable when increasing the number of integration steps . this procedure allows us to write the double integral as a matrix @xmath87 , where @xmath88 is actually a product of @xmath89 and some diagonal matrices containing the gauss weights needed in the integration procedure . then the adjoint of the generalized retarded green function @xmath90 is simply the solution of the algebraic equation @xmath91 . the true green function is recovered by turning back the mixed indices of @xmath90 . we stress that by solving the equation for @xmath92 the dyson equation is solved exactly . moreover , no matrix inversion is required . this is certainly an advantage in the numerical simulations since it is known that matrix inversion is both memory and time - consuming . the advanced green function is computed using the identity @xmath93 and the lesser green function is derived from the keldysh equation . also , the time - dependent occupation number can be computed as : @xmath94 the current in the right lead @xmath67 has a similar expression . we note that for a system with many sites one has to deal with different contact green functions besides replacing only the fermi function in the first term in the current formula . moreover , in the transient regime the current conservation does not imply the usual identity @xmath95 . we shall discuss this feature below . in the keldysh approach to time - dependent transport the problem is to extract physical information from the two contributions in eq.([current ] ) . in the simplest case of a single - site and within the wide - band limit it was shown that the _ average _ current obeys a landauer - like formula . the effects of a step - like or harmonic time - dependent potentials applied adiabatically on leads were studied both in the wbl @xcite and beyond @xcite . however , to our best knowledge no transient current calculation for a many - level structure beyond the wide - band limit has been performed within the keldysh formalism . in all the plots the bias , the energy , the hopping constants on the leads , the coupling strengths and the gate potentials will be expressed in terms of the hopping energy of the central region @xmath96 which is chosen as energy unit . the current is therefore given in units of @xmath97 and the time expressed in units of @xmath98 . since the spectrum of the two - dimensional discrete laplacian covers the range @xmath99 $ ] we shall take @xmath100 in order to match it to the spectral width of the one - dimensional lead @xmath101 $ ] . we take also @xmath102 . the current given by eq.([current ] ) can be written as a sum of two contributions @xmath103 the @xmath104 and @xmath105 labelling emphasizing that the corresponding term contains the lesser and retarded green functions . we shall consider for simplicity only single channel leads . and of the bias @xmath106 . ( b ) the effect of the coupling amplitude @xmath107 on the occupation number . the bias is fixed to @xmath108 , and @xmath109.,title="fig:",scaledwidth=45.0% ] and of the bias @xmath106 . ( b ) the effect of the coupling amplitude @xmath107 on the occupation number . the bias is fixed to @xmath108 , and @xmath109.,title="fig:",scaledwidth=45.0% ] we start this section by discussing the case of a single site dot which allows qualitative discussion on the transient regime and on the transition towards the steady - state . the site is coupled to single - channel leads ( i.e. @xmath110 ) . both leads are coupled suddenly to the system with the same strength @xmath107 , i.e @xmath111 . the bias is applied symmetrically on leads , i.e. @xmath112 , @xmath113 being the chemical potential of the unbiased leads . we observe that for @xmath114 the single eigenvalue of the isolated system @xmath115 is located in the middle of the bias window @xmath116 $ ] . as we shall see later on , the position of the eigenvalues of the system within the bias window has important implications on the transient current . the free retarded green function of the single site system is simply @xmath117 but the full retarded green function is still given by the _ integral _ dyson equation and an analytic solution is not at hand . fig.2(a ) gives the transient current for different values of the bias @xmath106 and of the coupling amplitude @xmath107 and reveals that the parameter that controls the shape and the amplitude of the oscillation is the coupling strength @xmath107 . at moderate coupling @xmath118 the steady state ( ss ) is achieved fast but an oscillatory behavior is observed at @xmath119 . the case @xmath120 is beyond the perturbative regime and the steady - state is not achieved in the selected time - range . as the bias increases the current saturates for values of @xmath106 that exceed the spectrum of the leads ( i.e. for @xmath121 ) , emphasizing the non linear transport regime . in turn , the bias neither affects the amplitude nor the period of the oscillations . this is due to the fact that in our model , as in all approaches based on the keldysh formalism , there is no term in the hamiltonian to describe the voltage drop across the sample , the bias being included only via the fermi functions of the leads . is always positive while the lesser contribution @xmath122 is negative . the chosen values for the coupling strength @xmath107 are given in the figure . the bias @xmath108 , and @xmath109.,scaledwidth=45.0% ] in fig.2(b ) we plot the occupation number of the resonant site @xmath123 for the same parameters as in fig.1(a ) . the behavior w.r.t . @xmath107 is similar . few more things worth to be noticed : i ) in the steady state regime the occupation of the site is 1/2 ; ii ) as @xmath107 increases while the bias stays constant the occupation number reaches its maximum value faster and the value corresponding to the steady state decreases ; iii ) comparing fig.2(a ) and 2(b ) it can be seen that there is no clear relation between the principal maximum of the current and the one of the occupation number ; in fact the electrons are accumulating in the system even after the current starts to decrease towards the steady state . fig.3 shows the two contributions to the current @xmath124 and @xmath125 for @xmath108 and several coupling constants considered in fig.2 . a physical significance of these two currents was proposed in ref . for the single site case . although both green functions at the contacts appearing in the current formula are dressed by the leads self - energy one could view @xmath124 as the current flowing towards the sample and @xmath122 as the current from to sample to the lead @xmath5 . one notices that the currents have opposite signs . another observation is that the lesser contribution is responsible for the total current oscillations since @xmath124 saturates quickly . however at small times @xmath124 grows faster than @xmath125 , leading thus to the fast increase of the transient . in order to understand the nature of the oscillations in the transient current and their dependence on the coupling strength @xmath107 it is useful to rewrite the current formula eq.([current ] ) in a more useful form ( since we consider a single site system there is only one contact site and the indices of the green functions can be omitted ) : @xmath126 where @xmath127 are two oscillating integrals : @xmath128 one can easily observe that actually @xmath129 can be expressed through bessel function of the first kind : @xmath130 for fixed @xmath48 , @xmath131 is an oscillating function of @xmath132 whose oscillation amplitudes increase with @xmath132 . @xmath133 does not have a simple analitical expression but it has a similar behavior . the oscillatory behavior of the current is clearly decided by the convolution in eq.([partial ] ) . besides the oscillations of @xmath133 ans @xmath131 one expects as well a complex behavior of the green functions . we recall that the dyson equation counts the infinite back - and - forth tunneling processes involving the leads and that the amplitudes of these events are even powers of @xmath107 . now , the higher order terms in the dyson equation contain multiple integrals of products of the leads self - energy which is highly oscillating ( see ( [ gmic ] ) ) therefore if @xmath134 there will be only few low - order significant contributions from the complicated lead - sample scattering . the critical value @xmath135 corresponds to the onset of the nonperturbative regime , and the method we use for solving the dyson equation captures as well this situation , taken into account all contributions . and the coupling strength @xmath136 . the oscillations seen along the diagonal in ( b ) corresponding to almost equal times are responsible for the oscillations of the occupation number.,title="fig:",scaledwidth=45.0% ] + and the coupling strength @xmath136 . the oscillations seen along the diagonal in ( b ) corresponding to almost equal times are responsible for the oscillations of the occupation number.,title="fig:",scaledwidth=45.0% ] we give in fig.4 the 3d plots of the imaginary parts for the retarded and lesser green functions at coupling strength @xmath137 , which leads to oscillations of the transient . these are the relevant quantities in the current formula since it turns out that the real part of @xmath138 and of @xmath131 are vanishingly small ( not shown ) . ( a ) and strong coupling @xmath136 ( b ) . ( c ) the real part of the oscillating function @xmath131 . the bias @xmath108.,title="fig:",scaledwidth=45.0% ] + ( a ) and strong coupling @xmath136 ( b ) . ( c ) the real part of the oscillating function @xmath131 . the bias @xmath108.,title="fig:",scaledwidth=45.0% ] ( a ) and strong coupling @xmath136 ( b ) . ( c ) the real part of the oscillating function @xmath131 . the bias @xmath108.,title="fig:",scaledwidth=45.0% ] for different sizes of the 1d central region . the number of sites @xmath27 is indicated in the figure . in ( a ) the coupling to the leads is @xmath118 and in ( b ) @xmath139 . by decreasing @xmath107 the shoulders in ( a ) turn to clear steps in ( b ) . the bias is fixed to @xmath140 , and @xmath109.,title="fig:",scaledwidth=45.0% ] for different sizes of the 1d central region . the number of sites @xmath27 is indicated in the figure . in ( a ) the coupling to the leads is @xmath118 and in ( b ) @xmath139 . by decreasing @xmath107 the shoulders in ( a ) turn to clear steps in ( b ) . the bias is fixed to @xmath140 , and @xmath109.,title="fig:",scaledwidth=45.0% ] one observes that @xmath141 for @xmath142 and , more interestingly , that @xmath143 and @xmath144 exhibit pronounced oscillations as time varies and reach a limit value as @xmath132 approaches @xmath48 . in the case of the retarded green function this limit is _ constant _ and equals @xmath145 , which is simply the value of the unperturbed retarded green function . this feature is easy to understand by looking at the dyson equation and noticing that when @xmath146 the integration range of the inner integral shrinks considerably so that at almost equal times the perturbed green function resembles the unperturbed one . this argument is not restricted to the single site case we are discussing . also , since the spectrum of the discrete laplacian is symmetric , the unperturbed retarded green function will always be real and therefore the real part of the full green function will always be vanishingly small , as we shall check numerically in the many site case . in contrast , the limit of @xmath147 as @xmath146 is _ not _ a constant w.r.t . @xmath48 but shows oscillations that disappear as @xmath48 increases . in the particular single - site case the limit value of @xmath148 is clearly the occupation number of the site , whose oscillations were shown already in fig.2(b ) . figs.5 ( a ) and ( b ) show 3d maps of the imaginary part of the lesser green function and emphasize the role of the coupling strength on the transient . at moderate coupling @xmath118 one observe small amplitude oscillations except for @xmath149 , in clear contrast to the case @xmath137 where pronounced oscillations exist even for large time differences . inspecting the real part of the function @xmath131 given in fig.5 ( c ) we see that it does not depend on @xmath48 when @xmath149 and that this gives the main contribution to the integral ( [ partial ] ) . it is now clear from figs.5 ( a ) and ( c ) that the corresponding current will be nearly stationary once the sample is charged ( i.e. for @xmath150 ) , because by increasing @xmath48 the off - diagonal contributions are very small ( some cancelations being possible as well ) . when @xmath107 increases the integral will collect instead nonnegligible contributions from the entire range @xmath151 and therefore the current will oscillate . these observations lead to the following statement : the steady state will be achieved at instant @xmath152 if for any @xmath153 there are no contributions for long - time differences , i.e. when both contact green functions @xmath143 and @xmath144 vanish for @xmath154 . it is easy to observe that this condition implies the well known criteria for the steady state @xmath155 . at different couplings @xmath107 . at small coupling @xmath156 resembles the retarded green function of the isolated system ( the curve corresponding to @xmath157).,title="fig:",scaledwidth=45.0% ] at different couplings @xmath107 . at small coupling @xmath156 resembles the retarded green function of the isolated system ( the curve corresponding to @xmath157).,title="fig:",scaledwidth=45.0% ] we consider now the more interesting case where the central region has more than one level . fig.6(a ) emphasizes the qualitative differences between the transients of 1d systems with @xmath158 sites . a general feature is that as the size increases the transient develops a shoulder which is not met in the single site case . for @xmath159 a second smaller slope of decrease is noticed for @xmath160 $ ] . for @xmath161 the system experiences few very different regimes before reaching the steady state . it first decreases faster up to @xmath162 . for a short time a small hill develops around @xmath163 then the decrease continues but clearly at a smaller rate . finally , for @xmath164 the current approaches the steady state very slowly . a similar behavior is observed for @xmath165 and @xmath166 , the main difference being that the shoulder is longer and the intermediate slope is smaller . the patterns described above suggest that there are some intermediate regimes , some of them being characterized by a rather stable current . fig.6(b ) emphasizes that at lower coupling @xmath139 the transient is even smoother and for @xmath167 and 8 one notices the formation of clear steps . when the coupling strength @xmath107 is increased the transient shows oscillations but they are fewer than in the single site ( not shown ) . since the two oscillatory integrals over energy in the current formula and both self - energies do not depend on the number of sites in the system the above size effects should be explained only by the behavior of the contact green functions . we show in fig.7(a ) and ( b ) the imaginary parts of the the contact green functions @xmath168 of the 4 site system for a strong coupling @xmath169 ( it turns out again that the real part of @xmath170 is vanishingly small ) . comparing with fig.4 it is obvious that for the 4 site dot the green functions have a more regular behavior and in particular the occupation number of the contact site 1 shows milder oscillations than the occupation number of the single site . fig.7(c ) gives the @xmath171 as a function of @xmath85 for different couplings and reveals that at weak coupling to the leads the full retarded green function is close to the unperturbed one and the electron dynamics inside the system must resemble the one of the isolated sample . indeed , the curve at @xmath169 follows the oscillations of the free green function which is also given in the figure ( the curve corresponding to @xmath157 ) . we plot the imaginary part since it turns out again that the real part is vanishingly small so it does not contribute considerably to the retarded current . as @xmath107 increases the green function changes and shows clear oscillations imposed by the leads self - energy . the analysis performed so far was focused on the behavior of the transient current as the intrinsic parameters of the system ( i.e. its size and the height of the tunneling barriers at the contacts are varied . nevertheless , in a typical transport experiment these parameters are fixed and one usually measures the current by varying the bias or a plunger gate voltage . from steady - state current measurements it is well known that the role of such a gate potential is to bring one or more levels of the quantum dot within the bias window ( bw ) . we show in what follows that at fixed bias and given coupling strength to the leads one can tune the transient current with a gate potential . moreover , by inspecting the transient behavior as the gate potential is varied , it is possible to extract some information about the number of states within the bias window or above it . we will make the discussion for the 4 site dot . the gate potential is simulated by the diagonal term @xmath26 added to the on - site energy of the system . we fix the bias window to w=2.0 and for convenience we set @xmath172 . fig.8(a ) give a families of transients for coupling strength @xmath118 and various values of @xmath26 specified in the figures . fig.8(b ) shows the four levels of the isolated quantum dot as the gate potential scans the range @xmath173 $ ] . the @xmath26 values chosen in fig.8(a ) corresponds to different location of the levels w.r.t . to bw . the bottom curve is irregular and settles down to a vanishing current because in this case there is no level within the bw . we note however that a nonvanishing transient current still develops shortly after the coupling is established . at @xmath174 the highest level is located in the bw and the transient is smooth and already shows the additional shoulder noticed previously . the same thing happens when two states lie in the bw ( at @xmath175 ) , the difference being that the steady state current increases considerably . for @xmath176 it is clear from the structure of the spectrum that one can not have more than two states in the bw and that the levels pass gradually above it . we found interesting to look at the transient currents for those gate potentials that still allow two states in the transmission range while pushing one or two states above bw . one notices that for @xmath177 the steady state currents do not distinguish the different spectral structure involved in transport , while the transient current is very sensitive to it . in the case of the six site qd the shoulder in fig.4 is more pronounced because at @xmath175 there are exactly three states inside the bias window . we want to point out that since we have neglected the coulomb interaction our simulations can not capture the transport through excited states of the quantum dot . tunneling processes involving such states would lead to a minipeak structure of the current maxima . we can consider however our results should describe qualitatively the transport involving more levels because for small dots the bias required to cover the ground state of @xmath27 electrons is much higher that the excitation energies . . ( b ) the spectrum of the system as function of the gate potential . it can be checked that the additional shoulders observed in ( a ) develop when there is at least one state of the qd in the bias window and no state above it . other parameters : @xmath178 , and @xmath109 . note that the bias is applied asymmetrically , that is @xmath179.,title="fig:",scaledwidth=45.0% ] . ( b ) the spectrum of the system as function of the gate potential . it can be checked that the additional shoulders observed in ( a ) develop when there is at least one state of the qd in the bias window and no state above it . other parameters : @xmath178 , and @xmath109 . note that the bias is applied asymmetrically , that is @xmath179.,title="fig:",scaledwidth=45.0% ] for the @xmath180 system and for the @xmath181 system in the two configurations of the leads as mentioned in the text . ( b ) - 1d system , ( c ) - symmetric configuration , ( d ) - asymmetric the occupation numbers @xmath182 of the @xmath14-th site for the three cases considered in fig.8(a ) . other parameters : @xmath118 , @xmath140 , and @xmath109.,title="fig:",scaledwidth=42.0% ] for the @xmath180 system and for the @xmath181 system in the two configurations of the leads as mentioned in the text . ( b ) - 1d system , ( c ) - symmetric configuration , ( d ) - asymmetric the occupation numbers @xmath182 of the @xmath14-th site for the three cases considered in fig.8(a ) . other parameters : @xmath118 , @xmath140 , and @xmath109.,title="fig:",scaledwidth=42.0% ] for the @xmath180 system and for the @xmath181 system in the two configurations of the leads as mentioned in the text . ( b ) - 1d system , ( c ) - symmetric configuration , ( d ) - asymmetric the occupation numbers @xmath182 of the @xmath14-th site for the three cases considered in fig.8(a ) . other parameters : @xmath118 , @xmath140 , and @xmath109.,title="fig:",scaledwidth=42.0% ] for the @xmath180 system and for the @xmath181 system in the two configurations of the leads as mentioned in the text . ( b ) - 1d system , ( c ) - symmetric configuration , ( d ) - asymmetric the occupation numbers @xmath182 of the @xmath14-th site for the three cases considered in fig.8(a ) . other parameters : @xmath118 , @xmath140 , and @xmath109.,title="fig:",scaledwidth=42.0% ] , @xmath178 , @xmath109.,scaledwidth=45.0% ] now we investigate two more features of the transient regime : the time - dependent charge filling of the central region and possible effects due to different shapes of the system or of the various ways in which one can couple the leads . besides the 4 site 1d system discussed so far we consider also a @xmath181 quantum dot . both systems are submitted to the same bias and have equal coupling to the leads . however , in the case of the 2d quantum dot one can use different contacts for plugging the leads . we discuss two situations : i ) a symmetric configuration in which the leads are attached to the opposite corners of the system , namely at the sites 1 and 4 and ii ) an asymmetric coupling when we use the 1st and 3th sites as contacts . fig.9(a ) reveals the changes induced in the transient curves in each case . the remaining subfigures show the occupation number @xmath182 of each site @xmath183 for the 1d system and the two configurations considered . inspecting fig.9(a ) and ( b ) we see : i ) the contact sites 1 and 4 are the first to be populated due to their proximity to leads ; ii ) since @xmath184 the right contact site ( the 4-th ) gains less charge at a lower rate than the left contact ( the first ) . both @xmath185 and @xmath186 show a step - like behavior for a short period ( around @xmath187 ) . this coincides with the increased occupation number on the middle sites . we note also that the step in the occupation of the contact site @xmath185 ends when it is equaled by @xmath188 . all the sites are then continuously filled up to the steady - state value . the occupation number on the right contact is smaller than the other ones which attain roughly the same value @xmath189 . iii ) the step - like behavior of the transient currents in the range @xmath190 $ ] corresponds to the almost constant population of the contact sites in the same interval . the symmetric configurations is still characterized by a smooth transient but we notice that the step appears now later that in the 1d case . fig.9(c ) confirms again that this stable regime is assigned to a constant flow in the contact site . also it reflects that the charge is equally distributed in the sites 2 and 3 which are located symmetrically w. r.t . the leads . in the asymmetric geometry the transient is rather similar to the one of the 1d system up to @xmath191 but then drops to a lower steady state value . the occupation numbers show that the fourth site carries more charge than the contact sites in the steady state . this means in our opinion that part of this charge simply accumulates and is not participating in transport . more interestingly , we note that in contrast to the symmetric geometry @xmath188 and @xmath192 are different in the transient regime but reach the same value in the steady state . we mention that time - dependent simulations were performed recently in the case of an aharonov - bohm ring starting from the schrdinger equationi.@xcite we discuss now briefly the total current @xmath193 which is given in fig.10 along with its two components ( the @xmath194 sign is due to the fact that the current @xmath67 represents the current from the lead @xmath6 to the system and therefore has opposite sign ) . as already mentioned , only in the steady state the current conservation reads as @xmath95 . consequently , the net current @xmath193 vanishes . however , in the transient regime the two currents , although having similar shape differ significantly . site qd as a function of time and gate potential @xmath26 . the maxima are related to the spectrum of the isolated system given in ( c ) . ( b ) the 3d map of the transient current for @xmath181 the double dot @xmath195 other parameters : @xmath108 , @xmath139 , @xmath109 . ( c ) the spectra of the two systems as a function of the gate potential . the lines mark the bias window . , title="fig:",scaledwidth=45.0% ] site qd as a function of time and gate potential @xmath26 . the maxima are related to the spectrum of the isolated system given in ( c ) . ( b ) the 3d map of the transient current for @xmath181 the double dot @xmath195 other parameters : @xmath108 , @xmath139 , @xmath109 . ( c ) the spectra of the two systems as a function of the gate potential . the lines mark the bias window . , title="fig:",scaledwidth=45.0% ] site qd as a function of time and gate potential @xmath26 . the maxima are related to the spectrum of the isolated system given in ( c ) . ( b ) the 3d map of the transient current for @xmath181 the double dot @xmath195 other parameters : @xmath108 , @xmath139 , @xmath109 . ( c ) the spectra of the two systems as a function of the gate potential . the lines mark the bias window . , title="fig:",scaledwidth=45.0% ] 0.5 cm to substantiate further the previous analysis we present in fig.11(a ) the contour plot of the current as function of time and gate potential for the @xmath181 site quantum dot coupled to the leads in the symmetrical configuration . fig.11(c ) gives the spectrum of the system as the gate potential varies . the middle eigenvalue is doubly degenerated . when the levels are either below or above the bias window ( @xmath196 starting from @xmath172 ) the transient oscillates for quite a long time before passing to the steady state . we also observe that in these two extreme limits the transient oscillations are qualitatively different . for @xmath197 the current shows decreasing oscillations towards the steady state . in contrast , for @xmath198 one remarks faster oscillations and more importantly , negative values of the transient . since in this regime all the levels are above the bias window and there is no way to pass electrons to the right lead it is clear that the negative current in the left lead is just the reflected one . we underline that this effect is due to the fact that we have considered a finite spectral width of the leads and that similar features were reported for the single site case @xcite . as expected , as the system approaches the stationary regime the current shows three maxima associated to the passage of the localized levels through the bias window . actually the levels turn to resonances when coupling the leads to the system but since one has to deal with a time - dependent hamiltonian it is difficult to characterize the location and width of these resonances in the transient regime . this is why in the 3d plot one can not distinguish between different resonances at times @xmath199 . fig.11(b ) presents the transient current for the same @xmath181 system except that the hopping parameters @xmath200 and @xmath201 are reduced to 0.5 . in this case one can view the system as a double dot , each dot composed of two sites . as the spectrum from fig.11(b ) shows , the degeneracy is lifted and the level spacing diminishes . as a consequence in the long time regime one gets two broader peaks , since the four levels are now grouped into pairs . all the features presented above emphasize that the transient regime of the many - level structures is quite different from the single - level system . we have performed transient current calculations for a many - level finite system coupled suddenly to semiinfinite biased leads . our method is based on the nonequilibrium green - keldysh machinery . we find numerically an exact solution of the integral dyson equation which is solved as an algebraic equation . by analyzing the behavior of the retarded and lesser green functions we explain qualitatively the shape of the transient current and the passage to the steady state . the amplitude of the coupling to the leads controls essentially the convergence to a steady state . we have identified non - trivial effects of the many - level structure of the system and presented an intuitive picture of the charge filling by studying the occupation number inside the system . by increasing the system size the shape of the transient current and the evolution towards the steady state differs significantly from the single - site oscillatory behavior and depends crucially on the number of electronic states available in the bias window . we predict that a step - like structure could be observed in transient current measurements by applying a gate potential on the system that tunes the higher levels within the bias window . different transients are expected to appear as well when different coupling geometries of the leads are used . the present method can be used for studying the response of mesoscopic systems to more complicated time - 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we investigate the nonstationary electronic transport in noninteracting nanostructures driven by a finite bias and time - dependent signals applied at their contacts to the leads . the systems are modelled by a tight - binding hamiltonian and the transient currents are computed from the non - equilibrium green - keldysh formalism . the numerical implementation is not restricted to weak coupling to the leads and does not imply the wide - band limit assumption for the spectral width of the leads . as an application of the method we study in detail the transient behavior and the charge dynamics in single and double quantum dots connected to leads by a step - like potential , but the method allows as well the consideration of non - periodic potentials or short pulses . we show that when the higher energy levels of the isolated system are located within the bias window of the leads the transient current approaches the steady state in a non - oscillatory smooth fashion . at moderate coupling to the leads and fixed bias the transient acquires a step - like structure , the length of the steps increasing with the system size . the number of levels inside a finite bias window can be tuned by a constant gate potential . we find also that the transient behavior depends on the specific way of coupling the leads to the mesoscopic system .

<s>[INST]the dynamics of conduction electrons in open nanostructures modulated by time - dependent signals is an outstanding problem in quantum transport theory . extensive experimental and theoretical work has been done especially on quantum pumping @xcite ( a detailed bibliography can be found in the recent review @xcite ) and photon - assisted tunneling ( see ref . and references therein ) . in these phenomena one is interested in measuring or computing the current response of a mesoscopic system driven by time - dependent _ periodic _ signals applied either on the system or on the attached leads . in particular , an unbiased system subjected to two periodic potentials differing by a phase lag generates a nonvanishing pumped current , provided one averages over the relevant period . @xcite if the signal frequency is small the pumping is adiabatic and can be described by a frozen scattering matrix as is rigorously shown in ref . . a photon - assisted tunneling implies instead high frequencies and the measured current displays satellite peaks due to the additional side - bands . @xcite from the theoretical point of view , any calculation of the current starts from defining the initial equilibrium state of the system and the perturbation that drives it . one way is to start with the connected system in the absence of the bias , and then to apply the bias adiabatically performing linear response calculations for the steady state current . an alternative picture was proposed by caroli @xcite that takes as the equilibrium state the state of the decoupled system with the bias already imposed on the leads . the perturbation here is instead the coupling to the leads that is usually adiabatically switched in the remote past and eventually reaches its full magnitude at @xmath0 . if one assumes that a steady state is achieved , the green functions depend only on time differences and the keldsyh formalism gives the corresponding current in terms of fourier transformed quantities . both pictures were shown to be useful in capturing and explaining important effects . as for an ac signal , it can be included in the green - keldysh approach as a time - dependent global shift of the spectrum of the leads . @xcite note that the occupation probability ( i.e. the fermi function ) of the leads stays time - independent . therefore this procedure assumes somehow that an ac signal is applied as well adiabatically . in the quantum pumping calculations the pumping potential is applied to the system in a steady - state , be it subjected to a finite bias or not . finally the current ( transient , time - averaged or steady - state ) is computed from the keldysh - green function formalism . @xcite here we aim to get some insight into a related topic : the calculation of the transient current through a quantum dot ( qd ) whose coupling to the leads is time dependent while the bias applied on the leads is constant . there are considerably fewer theoretical results on this issue ( see the references below ) and we were motivated also by recent increasing interest in using suitable electric pulses to investigate relaxation processes in quantum dots by using pump and probe measurements or transient current spectroscopy . @xcite as in the well known case of a turnstile pump @xcite these techniques imply oscillating tunnel barriers so that the transport formalism should deal with the nonlocal time - dependent coupling between the leads and the system . the problem we want to look at is defined as follows : i ) the system is disconnected at any time @xmath1 , and the leads are submitted to a constant bias which is included through the difference between the chemical potentials of the leads . ii ) at @xmath0 the leads are _ suddenly _ plugged to the system . physically this means that the tunneling barriers between the leads and the system are set to be very high at @xmath1 and drop suddenly at @xmath0 to an intermediate value that allows charge transfer across the system . the simplest case of a constant barrier height at any @xmath2 opens already the problem of the existence of non - equilibrium steady - states in the long time limit . in general and at a rigorous level , one can prove the existence of such states when @xmath3 @xcite and moreover , a landauer formula was shown to hold for the steady - state current . @xcite the method we developed is able to check the passage from transient behavior to steady state regime for specific systems , like many - level one- and two - dimensional quantum dots . as we shall see , the onset of the steady state for a given system depends on the its structure ( number of levels ) , on the measurement setup ( the strength of the coupling to the leads and the location of the contacts ) , and also on external parameters like gate potentials . although , in the present work the numerical simulations are restricted to the step - like coupling to the leads , our model allows the consideration of more general time - dependent potentials between the leads and the central region . in particular we can investigate the response of a system to _ nonlocal _ time - dependent perturbations that can be switched on and off individually . recently there have been several theoretical approaches to the transient regime . in ref . the time - dependent density functional was used to compute the transient current in a one - dimensional system submitted to a finite bias applied on the leads . the coupling term does not depend on time and the system is in an equilibrium state in the absence of the bias . starting from this state the kohn - sham equation is used to calculate the response of the system to the external bias . the same techniques allow the calculation of time - averaged current in one - dimensional quantum pumps . @xcite on the other hand , maciejko _ et al . _ @xcite have computed within the keldysh framework the response of a single - site dot for a step - like or periodic signal applied to the _ leads _ , beyond the wide band limit . in their approach the computation of the time - dependent green functions of the perturbed system uses steady - state green functions of the coupled and biased system that have to be provided from density functional theory . we believe that theoretical results regarding the transient regime induced by time - dependent couplings of many - level systems would complement these results . the content of the paper is organized as follows : section ii presents the model and the theoretical tools we use to compute the transient current . we rely essentially on the non - equilibrium green - keldysh formalism . however , in contrast to most of the previous studies we allow a complex structure for the central region coupled to leads ( i.e. there is more than one single localized level and the system can be as complicated as we want : a single dot , a double dot or an aharanov - bohm interferometer ) . also we go beyond the wide - band limit approximation and we solve exactly the integral dyson equation for the retarded green function of the _ coupled _ central region by a suitable numerical procedure . in doing so we take into account _ all _ the scattering processes between the leads and the sample . although the electron - electron interaction could presumably play an important role in the transient behavior and the formalism we use allows the inclusion of coulomb terms in the hamiltonian , we do not take it into account in this work . as is well known , the problem of the coulomb interaction in the keldysh approach is mainly technical and implies suitable approximation schemes for the interaction self - energy . we postpone this issue for future work . iii gives extensive discussion of the numerical simulations for single and double dots . section iv concludes the paper . the systems we study in this work have a typical transport configuration : a central region ( @xmath4 ) coupled to two semiinfinite leads ( @xmath5 and @xmath6 ) via a tunneling term ( see fig.1 for a schematical representation ) . we shall use a tight - binding ( tb ) description of the hamiltonian which has the following form : @xmath7 where @xmath8 describes the system , @xmath9 the semiinfinite leads and @xmath10 is the time - dependent tunneling term : @xmath11 at @xmath0.,scaledwidth=45.0% ] here @xmath12 and @xmath13 denote the annihilation / creation operators on the @xmath14-th site of the lead @xmath15 . similarly @xmath16 and @xmath17 is the pair of operators corresponding to the @xmath18-th site from the central region @xmath4 . @xmath19 is the time - dependent hopping coefficient between the @xmath14-th site of the lead @xmath15 and the @xmath18-th site of the central region . we take here a nearest - neighbor coupling so the double sums in the above expression contain only pairs of sites from the leads endpoint and the corresponding contact region from the central system : @xmath20 in this work we consider a steplike potential , i.e. @xmath21 if @xmath2 and zero otherwise . @xmath8 has a usual tight - binding form @xmath22 here @xmath23 are hopping terms , @xmath24 denotes nearest - neighbor summation over the system sites . @xmath25 is the on - site energy and the diagonal term @xmath26 simulates a plunger gate potential applied on the system . @xmath27 is the number of sites in the central region . the spectral width of the tight - binding lead is as usual @xmath28 $ ] , where @xmath29 is the hopping energy on leads ( we take the same hopping constant on every lead ) . in the numerical calculation we choose @xmath29 such that it covers entirely the spectrum of the central region but we do _ not _ assume it to be infinite , as it is done in the wide - band limit approximation . the central problem in electronic transport is to compute the statistical average of the time - dependent current operator in a given lead ( say @xmath5 ) @xmath30 using the statistical operator @xmath31 . notice that the time - dependence of the current operator appears only because of the time - dependent coupling . denoting by @xmath32 the endpoint sites of the lead @xmath5 which are coupled to the sites @xmath33 of the central region and by @xmath34 the number of sites in the transverse direction of the lead , the current operator @xmath35 has the form ( we take the electron charge as @xmath36 and @xmath37 ) : @xmath38 since the statistical operator @xmath31 of the coupled system is not easy to compute it is useful to move the time - dependence entirely to the current operator by writing @xmath31 in terms of the equilibrium statistical operator @xmath39 of the disconnected system . in general , the coupling to the leads is established at a given instant @xmath40 so that @xmath41 for @xmath42 . then using the unitary evolution @xmath43 of the full hamiltonian in the interaction picture w.r.t . the unperturbed one the solution of the quantum liouville equation is given by @xmath44 then it can be shown ( see e.g. ref . ) that : @xmath45 where @xmath46 is the ordering operator on the schwinger - keldysh contour @xmath47 that runs from @xmath40 to @xmath48 and back to @xmath40 . we remind the reader that in the case of adiabatic coupling the statistical operator becomes time - independent only in the remote past @xmath49 . both the coupling and current operators are written in the interaction picture . using the definitions of the lesser green functions in terms of the heisenberg operators : @xmath50 it follows that the current is given by a simpler relation : @xmath51 at this point the standard keldysh formalism requires the application of the so called langreth rules @xcite in order to express the lesser green function @xmath52 in terms of the green functions of the central region in the presence of the leads @xmath53 and the green functions of the isolated semiinfinite lead @xmath54 . the latter can be analytically computed : @xmath55 in the above equations @xmath56 is the energy of the transverse channel @xmath57 . these channels appear due to the width of the leads which in the tight - binding description is given by the number of the sites @xmath34 in the transverse direction . more exactly , the many channel lead is constructed by taking @xmath34 semiinfinite 1d leads and by coupling them through nearest neighbor hopping constants . then @xmath58 is the transversal eigenfunction associated to @xmath59 , and @xmath60 is the density of states at the endpoint of a semiinfinite one - dimensional lead : @xmath61 finally , @xmath62 is the fermi function in the lead @xmath5 . the bias is included in our approach as the difference between the two chemical potentials of the leads @xmath63 . plugging all these elements in the current formula one gets the main expression that will be numerically implemented in the next section : @xmath64 we have introduced the energy and time - dependent quantity @xmath65 that takes also into account the @xmath34 channels in the lead : @xmath66 a similar formula can be written down for the current @xmath67 and therefore one defines as well the net current @xmath68 it is important to observe that in contrast to the simple case of a single - site system the expressions for the two currents imply the green functions at different contacts . the retarded and the lesser green functions are then to be computed from the dyson and keldysh equations @xcite : @xmath69 where @xmath70 are the retarded and advanced green functions of the isolated central region and @xmath71 are the retarded and lesser self - energies . @xmath72 has a simple expression in terms of the discrete spectrum @xmath73 of the central region and its localized eigenfunctions @xmath74 ( clearly @xmath75 ) : @xmath76 we emphasize the lower integration limit @xmath0 in equations ( [ dyson ] ) and ( [ keldysh ] ) . this is due to the fact that there is no coupling for @xmath1 . in the adiabatic setup the coupling is established in the remote past and one should set a lower cutoff in the numerical implementation . however , the dyson equation still contains two coupled integrals . the two self - energies above contain the information from the leads and are finite rank matrices in the hilbert space of the central region @xmath4 ( @xmath77 ) : @xmath78 we stress that the indices of the leads green function are unambiguously determined as the neighbor sites of the contact surface @xmath79 . in the single channel case @xmath80 one recovers simpler expressions . in particular the retarded green function of the lead can be expressed through the bessel function of the first kind : @xmath81 we point out the difference between the exact form of the retarded self - energy and the simple wide - band limit expression ( which simplifies to @xmath82 up to some constants ) . note that the retarded green function gives the leads self - energy and is a highly oscillating functions . it will turn out in section iii that this behavior has crucial effects on the transient current . another difficulty of eq.([dyson ] ) comes from the quadratic dependence of the self - energies on the time - dependent coupling . clearly this prevents any partial fourier transform trick . given these , our strategy in solving the integral dyson equation relies in transforming it into an algebraic equation of the form @xmath83 where @xmath84 are generalized complex matrices depending on both spatial and time arguments . to this end we first plug the retarded self energy from eq.([sigmar ] ) in the dyson equation ( [ dyson ] ) and discretize the time arguments . note that the variable @xmath85 is defined on a denser grid than the one used for @xmath86 . the inner time integral is evaluated by a repeated 4-point gauss method , which turned out to be accurate enough for the numerical results to be stable when increasing the number of integration steps . this procedure allows us to write the double integral as a matrix @xmath87 , where @xmath88 is actually a product of @xmath89 and some diagonal matrices containing the gauss weights needed in the integration procedure . then the adjoint of the generalized retarded green function @xmath90 is simply the solution of the algebraic equation @xmath91 . the true green function is recovered by turning back the mixed indices of @xmath90 . we stress that by solving the equation for @xmath92 the dyson equation is solved exactly . moreover , no matrix inversion is required . this is certainly an advantage in the numerical simulations since it is known that matrix inversion is both memory and time - consuming . the advanced green function is computed using the identity @xmath93 and the lesser green function is derived from the keldysh equation . also , the time - dependent occupation number can be computed as : @xmath94 the current in the right lead @xmath67 has a similar expression . we note that for a system with many sites one has to deal with different contact green functions besides replacing only the fermi function in the first term in the current formula . moreover , in the transient regime the current conservation does not imply the usual identity @xmath95 . we shall discuss this feature below . in the keldysh approach to time - dependent transport the problem is to extract physical information from the two contributions in eq.([current ] ) . in the simplest case of a single - site and within the wide - band limit it was shown that the _ average _ current obeys a landauer - like formula . the effects of a step - like or harmonic time - dependent potentials applied adiabatically on leads were studied both in the wbl @xcite and beyond @xcite . however , to our best knowledge no transient current calculation for a many - level structure beyond the wide - band limit has been performed within the keldysh formalism . in all the plots the bias , the energy , the hopping constants on the leads , the coupling strengths and the gate potentials will be expressed in terms of the hopping energy of the central region @xmath96 which is chosen as energy unit . the current is therefore given in units of @xmath97 and the time expressed in units of @xmath98 . since the spectrum of the two - dimensional discrete laplacian covers the range @xmath99 $ ] we shall take @xmath100 in order to match it to the spectral width of the one - dimensional lead @xmath101 $ ] . we take also @xmath102 . the current given by eq.([current ] ) can be written as a sum of two contributions @xmath103 the @xmath104 and @xmath105 labelling emphasizing that the corresponding term contains the lesser and retarded green functions . we shall consider for simplicity only single channel leads . and of the bias @xmath106 . ( b ) the effect of the coupling amplitude @xmath107 on the occupation number . the bias is fixed to @xmath108 , and @xmath109.,title="fig:",scaledwidth=45.0% ] and of the bias @xmath106 . ( b ) the effect of the coupling amplitude @xmath107 on the occupation number . the bias is fixed to @xmath108 , and @xmath109.,title="fig:",scaledwidth=45.0% ] we start this section by discussing the case of a single site dot which allows qualitative discussion on the transient regime and on the transition towards the steady - state . the site is coupled to single - channel leads ( i.e. @xmath110 ) . both leads are coupled suddenly to the system with the same strength @xmath107 , i.e @xmath111 . the bias is applied symmetrically on leads , i.e. @xmath112 , @xmath113 being the chemical potential of the unbiased leads . we observe that for @xmath114 the single eigenvalue of the isolated system @xmath115 is located in the middle of the bias window @xmath116 $ ] . as we shall see later on , the position of the eigenvalues of the system within the bias window has important implications on the transient current . the free retarded green function of the single site system is simply @xmath117 but the full retarded green function is still given by the _ integral _ dyson equation and an analytic solution is not at hand . fig.2(a ) gives the transient current for different values of the bias @xmath106 and of the coupling amplitude @xmath107 and reveals that the parameter that controls the shape and the amplitude of the oscillation is the coupling strength @xmath107 . at moderate coupling @xmath118 the steady state ( ss ) is achieved fast but an oscillatory behavior is observed at @xmath119 . the case @xmath120 is beyond the perturbative regime and the steady - state is not achieved in the selected time - range . as the bias increases the current saturates for values of @xmath106 that exceed the spectrum of the leads ( i.e. for @xmath121 ) , emphasizing the non linear transport regime . in turn , the bias neither affects the amplitude nor the period of the oscillations . this is due to the fact that in our model , as in all approaches based on the keldysh formalism , there is no term in the hamiltonian to describe the voltage drop across the sample , the bias being included only via the fermi functions of the leads . is always positive while the lesser contribution @xmath122 is negative . the chosen values for the coupling strength @xmath107 are given in the figure . the bias @xmath108 , and @xmath109.,scaledwidth=45.0% ] in fig.2(b ) we plot the occupation number of the resonant site @xmath123 for the same parameters as in fig.1(a ) . the behavior w.r.t . @xmath107 is similar . few more things worth to be noticed : i ) in the steady state regime the occupation of the site is 1/2 ; ii ) as @xmath107 increases while the bias stays constant the occupation number reaches its maximum value faster and the value corresponding to the steady state decreases ; iii ) comparing fig.2(a ) and 2(b ) it can be seen that there is no clear relation between the principal maximum of the current and the one of the occupation number ; in fact the electrons are accumulating in the system even after the current starts to decrease towards the steady state . fig.3 shows the two contributions to the current @xmath124 and @xmath125 for @xmath108 and several coupling constants considered in fig.2 . a physical significance of these two currents was proposed in ref . for the single site case . although both green functions at the contacts appearing in the current formula are dressed by the leads self - energy one could view @xmath124 as the current flowing towards the sample and @xmath122 as the current from to sample to the lead @xmath5 . one notices that the currents have opposite signs . another observation is that the lesser contribution is responsible for the total current oscillations since @xmath124 saturates quickly . however at small times @xmath124 grows faster than @xmath125 , leading thus to the fast increase of the transient . in order to understand the nature of the oscillations in the transient current and their dependence on the coupling strength @xmath107 it is useful to rewrite the current formula eq.([current ] ) in a more useful form ( since we consider a single site system there is only one contact site and the indices of the green functions can be omitted ) : @xmath126 where @xmath127 are two oscillating integrals : @xmath128 one can easily observe that actually @xmath129 can be expressed through bessel function of the first kind : @xmath130 for fixed @xmath48 , @xmath131 is an oscillating function of @xmath132 whose oscillation amplitudes increase with @xmath132 . @xmath133 does not have a simple analitical expression but it has a similar behavior . the oscillatory behavior of the current is clearly decided by the convolution in eq.([partial ] ) . besides the oscillations of @xmath133 ans @xmath131 one expects as well a complex behavior of the green functions . we recall that the dyson equation counts the infinite back - and - forth tunneling processes involving the leads and that the amplitudes of these events are even powers of @xmath107 . now , the higher order terms in the dyson equation contain multiple integrals of products of the leads self - energy which is highly oscillating ( see ( [ gmic ] ) ) therefore if @xmath134 there will be only few low - order significant contributions from the complicated lead - sample scattering . the critical value @xmath135 corresponds to the onset of the nonperturbative regime , and the method we use for solving the dyson equation captures as well this situation , taken into account all contributions . and the coupling strength @xmath136 . the oscillations seen along the diagonal in ( b ) corresponding to almost equal times are responsible for the oscillations of the occupation number.,title="fig:",scaledwidth=45.0% ] + and the coupling strength @xmath136 . the oscillations seen along the diagonal in ( b ) corresponding to almost equal times are responsible for the oscillations of the occupation number.,title="fig:",scaledwidth=45.0% ] we give in fig.4 the 3d plots of the imaginary parts for the retarded and lesser green functions at coupling strength @xmath137 , which leads to oscillations of the transient . these are the relevant quantities in the current formula since it turns out that the real part of @xmath138 and of @xmath131 are vanishingly small ( not shown ) . ( a ) and strong coupling @xmath136 ( b ) . ( c ) the real part of the oscillating function @xmath131 . the bias @xmath108.,title="fig:",scaledwidth=45.0% ] + ( a ) and strong coupling @xmath136 ( b ) . ( c ) the real part of the oscillating function @xmath131 . the bias @xmath108.,title="fig:",scaledwidth=45.0% ] ( a ) and strong coupling @xmath136 ( b ) . ( c ) the real part of the oscillating function @xmath131 . the bias @xmath108.,title="fig:",scaledwidth=45.0% ] for different sizes of the 1d central region . the number of sites @xmath27 is indicated in the figure . in ( a ) the coupling to the leads is @xmath118 and in ( b ) @xmath139 . by decreasing @xmath107 the shoulders in ( a ) turn to clear steps in ( b ) . the bias is fixed to @xmath140 , and @xmath109.,title="fig:",scaledwidth=45.0% ] for different sizes of the 1d central region . the number of sites @xmath27 is indicated in the figure . in ( a ) the coupling to the leads is @xmath118 and in ( b ) @xmath139 . by decreasing @xmath107 the shoulders in ( a ) turn to clear steps in ( b ) . the bias is fixed to @xmath140 , and @xmath109.,title="fig:",scaledwidth=45.0% ] one observes that @xmath141 for @xmath142 and , more interestingly , that @xmath143 and @xmath144 exhibit pronounced oscillations as time varies and reach a limit value as @xmath132 approaches @xmath48 . in the case of the retarded green function this limit is _ constant _ and equals @xmath145 , which is simply the value of the unperturbed retarded green function . this feature is easy to understand by looking at the dyson equation and noticing that when @xmath146 the integration range of the inner integral shrinks considerably so that at almost equal times the perturbed green function resembles the unperturbed one . this argument is not restricted to the single site case we are discussing . also , since the spectrum of the discrete laplacian is symmetric , the unperturbed retarded green function will always be real and therefore the real part of the full green function will always be vanishingly small , as we shall check numerically in the many site case . in contrast , the limit of @xmath147 as @xmath146 is _ not _ a constant w.r.t . @xmath48 but shows oscillations that disappear as @xmath48 increases . in the particular single - site case the limit value of @xmath148 is clearly the occupation number of the site , whose oscillations were shown already in fig.2(b ) . figs.5 ( a ) and ( b ) show 3d maps of the imaginary part of the lesser green function and emphasize the role of the coupling strength on the transient . at moderate coupling @xmath118 one observe small amplitude oscillations except for @xmath149 , in clear contrast to the case @xmath137 where pronounced oscillations exist even for large time differences . inspecting the real part of the function @xmath131 given in fig.5 ( c ) we see that it does not depend on @xmath48 when @xmath149 and that this gives the main contribution to the integral ( [ partial ] ) . it is now clear from figs.5 ( a ) and ( c ) that the corresponding current will be nearly stationary once the sample is charged ( i.e. for @xmath150 ) , because by increasing @xmath48 the off - diagonal contributions are very small ( some cancelations being possible as well ) . when @xmath107 increases the integral will collect instead nonnegligible contributions from the entire range @xmath151 and therefore the current will oscillate . these observations lead to the following statement : the steady state will be achieved at instant @xmath152 if for any @xmath153 there are no contributions for long - time differences , i.e. when both contact green functions @xmath143 and @xmath144 vanish for @xmath154 . it is easy to observe that this condition implies the well known criteria for the steady state @xmath155 . at different couplings @xmath107 . at small coupling @xmath156 resembles the retarded green function of the isolated system ( the curve corresponding to @xmath157).,title="fig:",scaledwidth=45.0% ] at different couplings @xmath107 . at small coupling @xmath156 resembles the retarded green function of the isolated system ( the curve corresponding to @xmath157).,title="fig:",scaledwidth=45.0% ] we consider now the more interesting case where the central region has more than one level . fig.6(a ) emphasizes the qualitative differences between the transients of 1d systems with @xmath158 sites . a general feature is that as the size increases the transient develops a shoulder which is not met in the single site case . for @xmath159 a second smaller slope of decrease is noticed for @xmath160 $ ] . for @xmath161 the system experiences few very different regimes before reaching the steady state . it first decreases faster up to @xmath162 . for a short time a small hill develops around @xmath163 then the decrease continues but clearly at a smaller rate . finally , for @xmath164 the current approaches the steady state very slowly . a similar behavior is observed for @xmath165 and @xmath166 , the main difference being that the shoulder is longer and the intermediate slope is smaller . the patterns described above suggest that there are some intermediate regimes , some of them being characterized by a rather stable current . fig.6(b ) emphasizes that at lower coupling @xmath139 the transient is even smoother and for @xmath167 and 8 one notices the formation of clear steps . when the coupling strength @xmath107 is increased the transient shows oscillations but they are fewer than in the single site ( not shown ) . since the two oscillatory integrals over energy in the current formula and both self - energies do not depend on the number of sites in the system the above size effects should be explained only by the behavior of the contact green functions . we show in fig.7(a ) and ( b ) the imaginary parts of the the contact green functions @xmath168 of the 4 site system for a strong coupling @xmath169 ( it turns out again that the real part of @xmath170 is vanishingly small ) . comparing with fig.4 it is obvious that for the 4 site dot the green functions have a more regular behavior and in particular the occupation number of the contact site 1 shows milder oscillations than the occupation number of the single site . fig.7(c ) gives the @xmath171 as a function of @xmath85 for different couplings and reveals that at weak coupling to the leads the full retarded green function is close to the unperturbed one and the electron dynamics inside the system must resemble the one of the isolated sample . indeed , the curve at @xmath169 follows the oscillations of the free green function which is also given in the figure ( the curve corresponding to @xmath157 ) . we plot the imaginary part since it turns out again that the real part is vanishingly small so it does not contribute considerably to the retarded current . as @xmath107 increases the green function changes and shows clear oscillations imposed by the leads self - energy . the analysis performed so far was focused on the behavior of the transient current as the intrinsic parameters of the system ( i.e. its size and the height of the tunneling barriers at the contacts are varied . nevertheless , in a typical transport experiment these parameters are fixed and one usually measures the current by varying the bias or a plunger gate voltage . from steady - state current measurements it is well known that the role of such a gate potential is to bring one or more levels of the quantum dot within the bias window ( bw ) . we show in what follows that at fixed bias and given coupling strength to the leads one can tune the transient current with a gate potential . moreover , by inspecting the transient behavior as the gate potential is varied , it is possible to extract some information about the number of states within the bias window or above it . we will make the discussion for the 4 site dot . the gate potential is simulated by the diagonal term @xmath26 added to the on - site energy of the system . we fix the bias window to w=2.0 and for convenience we set @xmath172 . fig.8(a ) give a families of transients for coupling strength @xmath118 and various values of @xmath26 specified in the figures . fig.8(b ) shows the four levels of the isolated quantum dot as the gate potential scans the range @xmath173 $ ] . the @xmath26 values chosen in fig.8(a ) corresponds to different location of the levels w.r.t . to bw . the bottom curve is irregular and settles down to a vanishing current because in this case there is no level within the bw . we note however that a nonvanishing transient current still develops shortly after the coupling is established . at @xmath174 the highest level is located in the bw and the transient is smooth and already shows the additional shoulder noticed previously . the same thing happens when two states lie in the bw ( at @xmath175 ) , the difference being that the steady state current increases considerably . for @xmath176 it is clear from the structure of the spectrum that one can not have more than two states in the bw and that the levels pass gradually above it . we found interesting to look at the transient currents for those gate potentials that still allow two states in the transmission range while pushing one or two states above bw . one notices that for @xmath177 the steady state currents do not distinguish the different spectral structure involved in transport , while the transient current is very sensitive to it . in the case of the six site qd the shoulder in fig.4 is more pronounced because at @xmath175 there are exactly three states inside the bias window . we want to point out that since we have neglected the coulomb interaction our simulations can not capture the transport through excited states of the quantum dot . tunneling processes involving such states would lead to a minipeak structure of the current maxima . we can consider however our results should describe qualitatively the transport involving more levels because for small dots the bias required to cover the ground state of @xmath27 electrons is much higher that the excitation energies . . ( b ) the spectrum of the system as function of the gate potential . it can be checked that the additional shoulders observed in ( a ) develop when there is at least one state of the qd in the bias window and no state above it . other parameters : @xmath178 , and @xmath109 . note that the bias is applied asymmetrically , that is @xmath179.,title="fig:",scaledwidth=45.0% ] . ( b ) the spectrum of the system as function of the gate potential . it can be checked that the additional shoulders observed in ( a ) develop when there is at least one state of the qd in the bias window and no state above it . other parameters : @xmath178 , and @xmath109 . note that the bias is applied asymmetrically , that is @xmath179.,title="fig:",scaledwidth=45.0% ] for the @xmath180 system and for the @xmath181 system in the two configurations of the leads as mentioned in the text . ( b ) - 1d system , ( c ) - symmetric configuration , ( d ) - asymmetric the occupation numbers @xmath182 of the @xmath14-th site for the three cases considered in fig.8(a ) . other parameters : @xmath118 , @xmath140 , and @xmath109.,title="fig:",scaledwidth=42.0% ] for the @xmath180 system and for the @xmath181 system in the two configurations of the leads as mentioned in the text . ( b ) - 1d system , ( c ) - symmetric configuration , ( d ) - asymmetric the occupation numbers @xmath182 of the @xmath14-th site for the three cases considered in fig.8(a ) . other parameters : @xmath118 , @xmath140 , and @xmath109.,title="fig:",scaledwidth=42.0% ] for the @xmath180 system and for the @xmath181 system in the two configurations of the leads as mentioned in the text . ( b ) - 1d system , ( c ) - symmetric configuration , ( d ) - asymmetric the occupation numbers @xmath182 of the @xmath14-th site for the three cases considered in fig.8(a ) . other parameters : @xmath118 , @xmath140 , and @xmath109.,title="fig:",scaledwidth=42.0% ] for the @xmath180 system and for the @xmath181 system in the two configurations of the leads as mentioned in the text . ( b ) - 1d system , ( c ) - symmetric configuration , ( d ) - asymmetric the occupation numbers @xmath182 of the @xmath14-th site for the three cases considered in fig.8(a ) . other parameters : @xmath118 , @xmath140 , and @xmath109.,title="fig:",scaledwidth=42.0% ] , @xmath178 , @xmath109.,scaledwidth=45.0% ] now we investigate two more features of the transient regime : the time - dependent charge filling of the central region and possible effects due to different shapes of the system or of the various ways in which one can couple the leads . besides the 4 site 1d system discussed so far we consider also a @xmath181 quantum dot . both systems are submitted to the same bias and have equal coupling to the leads . however , in the case of the 2d quantum dot one can use different contacts for plugging the leads . we discuss two situations : i ) a symmetric configuration in which the leads are attached to the opposite corners of the system , namely at the sites 1 and 4 and ii ) an asymmetric coupling when we use the 1st and 3th sites as contacts . fig.9(a ) reveals the changes induced in the transient curves in each case . the remaining subfigures show the occupation number @xmath182 of each site @xmath183 for the 1d system and the two configurations considered . inspecting fig.9(a ) and ( b ) we see : i ) the contact sites 1 and 4 are the first to be populated due to their proximity to leads ; ii ) since @xmath184 the right contact site ( the 4-th ) gains less charge at a lower rate than the left contact ( the first ) . both @xmath185 and @xmath186 show a step - like behavior for a short period ( around @xmath187 ) . this coincides with the increased occupation number on the middle sites . we note also that the step in the occupation of the contact site @xmath185 ends when it is equaled by @xmath188 . all the sites are then continuously filled up to the steady - state value . the occupation number on the right contact is smaller than the other ones which attain roughly the same value @xmath189 . iii ) the step - like behavior of the transient currents in the range @xmath190 $ ] corresponds to the almost constant population of the contact sites in the same interval . the symmetric configurations is still characterized by a smooth transient but we notice that the step appears now later that in the 1d case . fig.9(c ) confirms again that this stable regime is assigned to a constant flow in the contact site . also it reflects that the charge is equally distributed in the sites 2 and 3 which are located symmetrically w. r.t . the leads . in the asymmetric geometry the transient is rather similar to the one of the 1d system up to @xmath191 but then drops to a lower steady state value . the occupation numbers show that the fourth site carries more charge than the contact sites in the steady state . this means in our opinion that part of this charge simply accumulates and is not participating in transport . more interestingly , we note that in contrast to the symmetric geometry @xmath188 and @xmath192 are different in the transient regime but reach the same value in the steady state . we mention that time - dependent simulations were performed recently in the case of an aharonov - bohm ring starting from the schrdinger equationi.@xcite we discuss now briefly the total current @xmath193 which is given in fig.10 along with its two components ( the @xmath194 sign is due to the fact that the current @xmath67 represents the current from the lead @xmath6 to the system and therefore has opposite sign ) . as already mentioned , only in the steady state the current conservation reads as @xmath95 . consequently , the net current @xmath193 vanishes . however , in the transient regime the two currents , although having similar shape differ significantly . site qd as a function of time and gate potential @xmath26 . the maxima are related to the spectrum of the isolated system given in ( c ) . ( b ) the 3d map of the transient current for @xmath181 the double dot @xmath195 other parameters : @xmath108 , @xmath139 , @xmath109 . ( c ) the spectra of the two systems as a function of the gate potential . the lines mark the bias window . , title="fig:",scaledwidth=45.0% ] site qd as a function of time and gate potential @xmath26 . the maxima are related to the spectrum of the isolated system given in ( c ) . ( b ) the 3d map of the transient current for @xmath181 the double dot @xmath195 other parameters : @xmath108 , @xmath139 , @xmath109 . ( c ) the spectra of the two systems as a function of the gate potential . the lines mark the bias window . , title="fig:",scaledwidth=45.0% ] site qd as a function of time and gate potential @xmath26 . the maxima are related to the spectrum of the isolated system given in ( c ) . ( b ) the 3d map of the transient current for @xmath181 the double dot @xmath195 other parameters : @xmath108 , @xmath139 , @xmath109 . ( c ) the spectra of the two systems as a function of the gate potential . the lines mark the bias window . , title="fig:",scaledwidth=45.0% ] 0.5 cm to substantiate further the previous analysis we present in fig.11(a ) the contour plot of the current as function of time and gate potential for the @xmath181 site quantum dot coupled to the leads in the symmetrical configuration . fig.11(c ) gives the spectrum of the system as the gate potential varies . the middle eigenvalue is doubly degenerated . when the levels are either below or above the bias window ( @xmath196 starting from @xmath172 ) the transient oscillates for quite a long time before passing to the steady state . we also observe that in these two extreme limits the transient oscillations are qualitatively different . for @xmath197 the current shows decreasing oscillations towards the steady state . in contrast , for @xmath198 one remarks faster oscillations and more importantly , negative values of the transient . since in this regime all the levels are above the bias window and there is no way to pass electrons to the right lead it is clear that the negative current in the left lead is just the reflected one . we underline that this effect is due to the fact that we have considered a finite spectral width of the leads and that similar features were reported for the single site case @xcite . as expected , as the system approaches the stationary regime the current shows three maxima associated to the passage of the localized levels through the bias window . actually the levels turn to resonances when coupling the leads to the system but since one has to deal with a time - dependent hamiltonian it is difficult to characterize the location and width of these resonances in the transient regime . this is why in the 3d plot one can not distinguish between different resonances at times @xmath199 . fig.11(b ) presents the transient current for the same @xmath181 system except that the hopping parameters @xmath200 and @xmath201 are reduced to 0.5 . in this case one can view the system as a double dot , each dot composed of two sites . as the spectrum from fig.11(b ) shows , the degeneracy is lifted and the level spacing diminishes . as a consequence in the long time regime one gets two broader peaks , since the four levels are now grouped into pairs . all the features presented above emphasize that the transient regime of the many - level structures is quite different from the single - level system . we have performed transient current calculations for a many - level finite system coupled suddenly to semiinfinite biased leads . our method is based on the nonequilibrium green - keldysh machinery . we find numerically an exact solution of the integral dyson equation which is solved as an algebraic equation . by analyzing the behavior of the retarded and lesser green functions we explain qualitatively the shape of the transient current and the passage to the steady state . the amplitude of the coupling to the leads controls essentially the convergence to a steady state . we have identified non - trivial effects of the many - level structure of the system and presented an intuitive picture of the charge filling by studying the occupation number inside the system . by increasing the system size the shape of the transient current and the evolution towards the steady state differs significantly from the single - site oscillatory behavior and depends crucially on the number of electronic states available in the bias window . we predict that a step - like structure could be observed in transient current measurements by applying a gate potential on the system that tunes the higher levels within the bias window . different transients are expected to appear as well when different coupling geometries of the leads are used . the present method can be used for studying the response of mesoscopic systems to more complicated time - dependent couplings to the leads : pulses having different lengths and decaying rates , and non - periodic signals . m. switkes , c. m. marcus , k. campman , and a. c. gossard , science 283 , 1905 ( 1999 ) . l. j. geerligs , v. f. anderegg , p. a. m. holweg , j. e. mooij , h. pothier , d. esteve , c. urbina and m. h. devoret , phys . 64 , 2691 ( 1990 ) . p. w. brouwer , phys . b * 58 * , r10135 ( 1998 ) . o. entin - wohlman , a. aharony , and y. levinson , phys . rev . b * 65 * , 195411 ( 2002 ) . m. moskalets and m. bttiker , phys . b * 66 * , 205320 ( 2002 ) . l. arrachea , phys . b * 72 * , 125349 ( 2005 ) . l. arrachea , m. moskalets , phys . rev . b 74 , 245322 ( 2006 ) . g. platero and r. aguado , physics reports 395 , 1 ( 2004 ) . avron , a. elgart , g.m . graf , and l. sadun , comm . pure and appl . mathematics lvii , 0538 ( 2004 ) . van der wiel , t.h . oosterkamp , s. de franceschi , c.j.p.m . harmans , and l.p . strongly correlated fermions and bosons in low - dimensional disordered systems , eds . lerner et al . , pp.43 - 68 ( 2002 ) , kluwer academic publishers . c. caroli , r. combescot , p. nozieres , and d. saint - james , j. phys . * c * 4 , 916 ( 1971 ) . a .- jauho , n. s. wingreen , and y. meir , phys . b * 50 * , 5528 ( 1994 ) . h. haug , a .- p . jauho , quantum kinetics in transport and optics of semiconductors ( springer , berlin , 1996 ) . t fujisawa , d g austing , y tokura , y hirayama and s tarucha , j. phys . matt . * 15 * r1395 ( 2003 ) . l. p. kouwenhoven , a. t. johnson , n. c. van der vaart , c. j. p. m. harmans , and c. t. foxon , phys . lett . * 67 * , 1626 ( 1991 ) . w. aschbacher , v. jaksic , yan pautrat c - a . pillet , lecture notes in mathematics 1882/2006 springer berlin . g. nenciu , http://xxx.lanl.gov math - ph/0610074 , to appear in j. math . y. zhu , j. maciejko , t. ji , h. guo , and j. wang , phys . rev . b * 71 * , 075317 ( 2005 ) , j. maciejko , j. wang , and h. guo , phys . rev . b * 74 * , 085324 ( 2006 ) . s. kurth , g. stefanucci , c .- o . almbladh , a. rubio , and e. k. u. gross , phys . b * 72 * , 035308 ( 2005 ) , g. stefanucci , c .- o . almbladh phys . b * 69 * , 195318 ( 2004 ) . g. stefanucci , s. kurth , a. rubio , e. k. u. gross , cond - mat/0701279 . b. szafran and f. m. peeters phys . b * 72 * , 165301 ( 2005 ) . j. rammer , h. smith , rev . mod.phys * 58 * , 323 ( 1986 ) .[/INST] we investigate the nonstationary electronic transport in noninteracting nanostructures driven by a finite bias and time - dependent signals applied at their contacts to the leads . the systems are modelled by a tight - binding hamiltonian and the transient currents are computed from the non - equilibrium green - keldysh formalism . the numerical implementation is not restricted to weak coupling to the leads and does not imply the wide - band limit assumption for the spectral width of the leads . as an application of the method we study in detail the transient behavior and the charge dynamics in single and double quantum dots connected to leads by a step - like potential , but the method allows as well the consideration of non - periodic potentials or short pulses . we show that when the higher energy levels of the isolated system are located within the bias window of the leads the transient current approaches the steady state in a non - oscillatory smooth fashion . at moderate coupling to the leads and fixed bias the transient acquires a step - like structure , the length of the steps increasing with the system size . the number of levels inside a finite bias window can be tuned by a constant gate potential . we find also that the transient behavior depends on the specific way of coupling the leads to the mesoscopic system . </s>

papaver somniferum l. is known as opium poppy , which has been used as a medicinal remedy for its sedative , anesthetic , analgesic , and antidierrheal effects for thousands of years . there are ancient documents mentioning about the medicinal properties of opium poppy such as the de materia medica written in a.c . 65 by pedanius dioscorides . by the more recent studies , it is known that the medicinal properties of opium poppy come from its high concentration alkaloid content . morphine , codeine , thebaine , papaverine , and noscapine are important and effective alkaloids in opium poppy for medicinal usage . besides their medicinal properties , these alkaloids are highly addictive and thus they have forensic importance . therefore , appropriate analysis of alkaloid content of opium poppy for screening and effective extraction is of great importance . furthermore , the alkaloid contents present in opium poppy make it an asset for the researchers . so we hope these findings will be helpful and directive for us and/or other scientists in the future research of papaver species . conventional extraction methods require more solvent , higher temperatures , and longer periods when high efficiency is desired . nowadays , extraction techniques which can be applied in lower temperatures requiring less amount of solvent and time are looking for by the researcher . the ultrasonic extraction technique ( uae ) , using ultrasound waves disrupt open the cellular walls , accomplishes mass transfer successfully [ 4 , 5 ] . by efficiently accomplishing mass transfer , ultrasound assisted extraction proves itself to be an efficient way for extraction . when compared to another extraction techniques such as microwave and supercritical extraction uae is cheaper and simpler [ 5 , 6 ] . recently , uae has become a popular technique among most researchers who try to extract flavonoids , polysaccharides , polyphenols , and oil from different matrices [ 5 , 7 ] . however , not only the extraction method but also the other parameters such as preliminary preparations , particle size of the extracted material , solvent type , solvent concentration , and solvent / solid ratio , extraction temperature , extraction pressure , extraction time , and ph affect the extraction process . to obtain the optimal operating conditions for an extraction method is necessary for commercial applications of the process . in the literature , there are two optimization method in order to optimize the process . one of them is one - factor - at - a - time approach ; and the other one is response surface methodology . one factor at a time is classical method , time consuming , and expensive method . moreover , by ignoring possible interactions among other operating parameters , this approach may result in misleading conclusions . in fact , the response of a process occurs by the interactions of different variables which affect the operation . response surface methodology ( rsm ) considers the probable interactions among operating parameters . in order to simplify this process and maximize utilization of data , design of experiments ( doe ) approach can be used and then the response surface methodology ( rsm ) can be applied for the experimental results [ 5 , 8 ] . utilization of doe and rsm enables us to reduce the number of experiments needed and accurately estimate the optimal conditions from the experimental data . about the poppy straw : the various reported morphine extraction methods from poppy straw have been reported in the literature . these reported methods include various steps involving water , organic solvent , and ph adjustments . the simplest methods are the following ones covering the sonication : even these simplest methods contain some more purification and organic solvent stage . individual alkaloids ( morphine , codeine , papaverine , noscapine , thebaine , oripavine , reticuline , and narceine ) were quantitatively determined in the different samples by a validated capillary electrophoresis method . depending on the plant structure , cultivar , and harvesting time , the composition of morphine is changeable . therefore , a common extraction procedure for all plant species can not exist and for poppy straw . particle size of the extracted material , solvent type , solvent composition , the solvent / solid ratio , extraction temperature , extraction pressure , extraction time , and ph of the solvent are the parameters affecting the industrial processes which are applied for extraction . in order to optimize the process , rsm is an aggregate of statistical and mathematical techniques used for developing , improving , and optimizing the processes [ 5 , 10 ] . sonication has been applied for the extraction of polycyclic aromatic hydrocarbons , pharmaceutically active compounds , and flavonoids from different matrices [ 5 , 11 , 12 ] . the aim of this study is to determine the effect of applied parameters on poppy straw by using ultrasound extraction method with rsm . papaver somniferum was collected from fields of opium alkaloids factory on the harvesting period in july of 2012 ( turkey ) . capsules of the plant were dried at room temperature after the seeds within the plant had been removed . all chemicals used in experiments were of analytical grade and all chemicals used for analysis were of hplc grade . 0.45 m membranes ( millipore , bedford , ma , usa ) was used for filtering the buffer solutions . morphine sulfate number 1448005 ) was obtained from the turkish grain board ( afyonkarahisar , turkey ) , which is the only legal supplier of narcotics in turkey . number 1448005 ) : molecular formula of morphine sulfate is ( c17h19no3)2h2so45h2o . molecular weight of morphine sulfate is 758.83 . 132.93 mg of morphine sulfate pentahydrate is equivalent to 100 mg of anhydrous morphine base 132.93 mg of morphine sulfate pentahydrate is equivalent to 100 mg of anhydrous morphine base . ultrasound assistant extraction was carried out using bandelin sonorex brand ultrasonic bath with 50 khz frequency . ph levels of the solutions were controlled by mettler toledo seven easy ph meter . for the standard ultrasonic conditions , solvent level in the erlenmeyer flask and water level in the ultrasonic bath were kept the same . in order to adjust ph levels to 1 or 13 after the extraction process had been completed , mixture was filtered with whatman filter paper in order to prevent capillary blockage first and was then filtered with 0.45 micron membrane filter ( millipore , bedford , ma , usa ) . identification and quantitative determination of morphine was established by agilent 1260 chromatographic system equipped with autosampler , quaternary pump , column compartment , and a multiwavelength detector . final quantification was performed on a 250 mm 4.6 mm i d , 5 m particle size , zorbax extend c-18 column ( agilent technologies ) . the eluents were a solution of 0.1% tfa in water and ph adjusted to 9.6 with tea ( solvent a ) and methanol ( solvent b ) , both filtered through 0.45 m millipore filters . elution was performed with the gradient : 02 min 45% solvent b ; 210 min from 45 to 70% solvent b ; 1020 min from 70 to 85% solvent b ; 2020.1 min from 85 to 45% solvent b ; 20.130 min 45% solvent b. the flow rate was 1.5 ml / min and the injection volume was 20 l . the column temperature was maintained at 30c , and detection was carried out at 280 nm . the method has been validated according to ich guidelines , taking into account the recommendations of other appropriate guidelines . results obtained from testing different parameters during validation of the analytical method were given in table 1 . the method recommended by the european pharmacopoeia for the quality assessment of the opium dry extract has been standardized ( ph . eur . 7.0 : 01/2008 : 1839 ) . in addition to morphine , codeine , oripavine , thebaine , papaverine , and noscapine were analyzed by this method . despite the retention time of last noscapine peak this is because the organic phase content of mobile phase increases with the analysis progresses . then , concentration of mobile phase will return to the initial conditions after 20 minutes . calibration curve was created to determine the concentration of morphine by comparing the peak areas with standard solutions which consist of morphine in the range of 100500 g / ml . morphine standard solution was prepared by dissolving its salt in purified water . morphine , codeine , thebaine , and noscapine were analyzed and optimized in poppy capsules ; however optimization of other alkaloids were not included in this paper . these designs require only three levels , coded as 1 , 0 , and + 1 . box and behnken created this design by combining two - level factorial designs with incomplete block designs . this procedure creates designs with desirable statistical properties , but , most importantly , with only a fraction of the experiments needed for a full three - level factorial . these designs offer limited blocking options , except for the three - factor version . in this design , while two of the factors are constant at level 0 , the remaining factors are iterated within the levels + 1 and 1 ; then this process is repeated for different groups [ 14 , 15 ] . in this study , box - behnken design was performed with four parameters to explore the effect of them on the responses ( table 2 ) . these were x1 ( solvent / solid ratio , ml/500 mg ) , x2 ( ph ) , x3 ( time , min ) , and x4 ( temperature , c ) . design - expert 8.0.7.1 ( trial version ) software was used in order to apply the box - behnken design model . twenty - nine experiments were performed with three replications at the center values to evaluate the pure error sum of squares . the proposed quadratic model is shown as follows:(1)y=0+i=14ixi+i=14iixi2+i=14j = i+14ijxixj+e , where y is the response , 0 is the constant coefficient which is often described as intercept , x i ( i = 1 4 ) is the noncoded variable , i is the linear , and ii is the quadratic , and ( i and j = 4 ) ij are the second order interaction coefficients [ 5 , 16 ] . statistical analysis on the means of triplicate experiments was performed out using the variance analysis ( anova ) procedure of the instat software version 3.0 . variance analysis were applied to identify the interaction between the variables and the response using design - expert program . variance analysis were applied for identifying the interaction between the variables and the response by using design - expert program . experimental conditions of box - behnken design runs designed with design expert 8.0.7.1 are shown in table 3 . table 3 also displays the effects of ph , solvent / solid ratio , time and temperature on the extraction efficiency obtained by uae . figures 2 , 3 , 4 , 5 , 6 , and 7 display response surface plots for process variables . the solvent / solid ratio is a crucial factor and was also studied to optimize extraction efficiency . large solvent volumes could make the procedure difficult and lead to unnecessary waste , while small volumes may lead to incomplete extraction . a series of experiments were carried out with different solvent / solid ratios ( 10/500 , 15/500 , 20/500 v / w ) to evaluate the effect of the solvent / solid ratio . the increase of the yield with the increase of solvent quantity is consistent with mass transfer principles , since the concentration gradient which is driving force is supposed to be higher when a lower solvent to solid ratio is used , leading to higher diffusion . the influence of the solvent ph on the extraction efficiency of morphine was examined over a range of 113 and the results are shown in table 3 . it can be clearly seen that extraction efficiency was the maximum at ph : 1 . when the solvent ph was increased from 1 to 7 then the extraction efficiency increased gradually , while the solvent ph was increased from 7 to 13 . this might be explained by the fact that an acidic environment helps in the release of morphine into the solvent . the influence of the time ultrasound on the extraction efficiency of morphine was examined over a range of 3060 min and the results are shown in table 3 . they show that when the extraction time was increased from 30 min to 60 min , the extraction efficiency was low during the first 40 min of ultrasonication indicating that more time was needed for ultrasound to disrupt the cell walls and aid the release of morphine into the solvent . extractions of poppy straw were performed over temperatures ranging from 30 to 50c , since extraction at high temperatures is not economical . expectedly , extraction efficiency of morphine increased steadily as a function of temperature until 45c , since mass transfer increase by temperature . but in general , extractions at higher temperatures increase mass transfer and extraction performance because of enhanced solute desorption from the active sites of plant matrix . individual effects of process variables , which are also known as one - factor - at - at - ime approach , were applied in previous section . this classical approach ignores the possible interactions of process variables with each other , which may result in misleading conclusions table 2 shows the four parameters ( ph , solvent / solid ratio , time , and temperature ) including minimum , centre , and maximum points . twenty - nine experiments were run and chosen randomly by the design expert software , and the responses were recorded ( table 3 ) . using response surface methodology owing to the software , a quadratic model applying not only forward stepwise but also backward elimination regressions for ey was obtained . using responce surface methodology from the software , a quadratic model given below was derived:(2)m=3.0002800.040567x10.172330x2 0.035744x3 + 0.038358x40.005500x1x2 0.000933x1x3 + 0.003200x1x4 0.001167x2x3 + 0.000708x2x4 + 0.000783x3x4 + 0.00104x12 + 0.021387x22 + 0.000311x320.001713x42 . in table 4 , x3 , x1x3 , x2x3 , x2x4 , x3x4 , x1 , and x3 are not significant effects for the model . after excluding their regression coefficients , new model may be given for better explanation of new condition:(3)m=3.0002800.040567x10.172330x2 + 0.038358x40.005500x1x2 + 0.003200x1x4 + 0.021387x220.001713x42 . the optimal extraction conditions were found by using optimization choice in design expert software to maximize the response . this value was measured at 1.10 of ph , 60 min of extraction time , 42.36c of extraction temperature , and 19.99 ml to 500 mg solvent / solid ratio . the maximum response was found as 3.38 mg morphine/500 mg dried capsules under these operating conditions . after finding optimal conditions , real sample extraction experiments were repeated 6 times and then average with relative standard deviation was calculated . the results of variance analysis were given in table 4 . in order to obtain the most suitable set of variables , variables are tested and evaluated within the given alpha levels ( 0.1 ) using both backward and forward techniques . backward techniques cover all the variables to estimate parameters and then any variables with a nonsignificant parameter at alpha levels are removed from the equation . similar to backward technique , forward technique also evaluates the given variables within the given alpha levels . unlike backward technique the significant variable with the highest value of standardized beta ( p < 0.05 ) will be added to the equation . then the next variable with the highest standardized beta value is assessed . variance analysis for the quadratic equations of design expert 8.0.7.1 for the response were given in table 4 . ( x1 ) , ( x2 ) , ( x4 ) , ( x1x2 ) , ( x1x4 ) , ( x2 ) , and ( x4 ) are significant model terms in the confidence interval ( table 4 ) . the closer and higher multiple coefficients ( r - squared , adj r - squared , and pred r - squared ) point out to the higher accuracy of the model . adj r - squared also shows a high degree of correlation between actual and predicted data . as seen in table 4 solvent / solid ratio ( x1 ) f - value of lack of fit ( 6.15 ) shows that the lack of fit is significant . in our study , r - squared ( 0.96 ) , adj r - squared ( 0.92 ) , and pred r - squared ( 0.78 ) values for ey display good accuracy of the derived model . also , the coefficient value of variation ( c.v . the lower coefficient of variation value indicates a higher precision and reliability of the experimental results . hereby , the responce surface modeling can be accomplished sufficiently to predict ey from poppy straw with uae . the lower value of coefficient of variation indicates a higher precision and reliability of the experimental results [ 19 , 20 ] . figure 8 exhibits the corelation between the experimental and predicted data calculated from ( 3 ) concerning the ey of poppy straw extracts obtained by uae . it can be seen that the predicted date calculated from the model is in good agreement with the experimental data in the range of operating conditions . a potential source of morphine , poppy straw ( papaver somniferum capsules ) , was used as the research material in this study . the capsules were extracted by uae , which is an environmental and economical alternative to conventional extraction methods , requiring more time and solvent consumption . the results of the study suggests that 1.10 of ph , 42.36c of extraction temperature , 59.94 min of extraction time , and 19.99 ml to 500 mg solvent / solid ratio should be employed as optimal operating conditions for the best ey ( 3.38 mg morphine/500 mg dried capsules ) . linear coefficient of solvent to solid ratio , ph and extraction time , and square coefficient of solvent to solid ratio , ph , and extraction time have the most significant effect on the ey obtained by uae . after finding optimal conditions , real sample extraction experiments were repeated 6 times and then average with relative standard deviation was calculated .

in this study , amount of morphine from poppy capsules ( papaver somniferum ) was investigated using ultrasonic assisted extraction ( uae ) . response surface methodology was used to estimate effective experimental conditions on the content extraction of poppy capsules . for this purpose , solvent / solid ratio ( 1020 ml/500 mg sample ) , ph ( 113 ) , time ( 3060 min ) , and temperature ( 3050c ) were chosen as experimental variables . the affected response is extraction recovery values for morphine from poppy straw . for interpreting the relationship between experimental factors and response , a design table was established with combinations of three different concentrations levels of this compound in 29 trials . the second order quadratic model gave a satisfactory description of the experimental data . in our study , r - squared ( 0.96 ) , adj - r - squared ( 0.92 ) , and pred r - squared ( 0.78 ) values for extraction yield display good accuracy of the derived model . the predicted optimal conditions for the highest morphine level ( 3.38 mg morphine/500 mg - sample ) were found at 19.99 ml solvent/500 mg solid ratio , 59.94 min extraction time , 1.10 ph , and 42.36c temperature . in the optimal extraction conditions , the experimental values are very close to the predicted values . consequently , the response surface modeling can be achieved sufficiently to predict extraction yield from poppy straw by ultrasound assisted extraction .

<s>[INST]papaver somniferum l. is known as opium poppy , which has been used as a medicinal remedy for its sedative , anesthetic , analgesic , and antidierrheal effects for thousands of years . there are ancient documents mentioning about the medicinal properties of opium poppy such as the de materia medica written in a.c . 65 by pedanius dioscorides . by the more recent studies , it is known that the medicinal properties of opium poppy come from its high concentration alkaloid content . morphine , codeine , thebaine , papaverine , and noscapine are important and effective alkaloids in opium poppy for medicinal usage . besides their medicinal properties , these alkaloids are highly addictive and thus they have forensic importance . therefore , appropriate analysis of alkaloid content of opium poppy for screening and effective extraction is of great importance . furthermore , the alkaloid contents present in opium poppy make it an asset for the researchers . so we hope these findings will be helpful and directive for us and/or other scientists in the future research of papaver species . conventional extraction methods require more solvent , higher temperatures , and longer periods when high efficiency is desired . nowadays , extraction techniques which can be applied in lower temperatures requiring less amount of solvent and time are looking for by the researcher . the ultrasonic extraction technique ( uae ) , using ultrasound waves disrupt open the cellular walls , accomplishes mass transfer successfully [ 4 , 5 ] . by efficiently accomplishing mass transfer , ultrasound assisted extraction proves itself to be an efficient way for extraction . when compared to another extraction techniques such as microwave and supercritical extraction uae is cheaper and simpler [ 5 , 6 ] . recently , uae has become a popular technique among most researchers who try to extract flavonoids , polysaccharides , polyphenols , and oil from different matrices [ 5 , 7 ] . however , not only the extraction method but also the other parameters such as preliminary preparations , particle size of the extracted material , solvent type , solvent concentration , and solvent / solid ratio , extraction temperature , extraction pressure , extraction time , and ph affect the extraction process . to obtain the optimal operating conditions for an extraction method is necessary for commercial applications of the process . in the literature , there are two optimization method in order to optimize the process . one of them is one - factor - at - a - time approach ; and the other one is response surface methodology . one factor at a time is classical method , time consuming , and expensive method . moreover , by ignoring possible interactions among other operating parameters , this approach may result in misleading conclusions . in fact , the response of a process occurs by the interactions of different variables which affect the operation . response surface methodology ( rsm ) considers the probable interactions among operating parameters . in order to simplify this process and maximize utilization of data , design of experiments ( doe ) approach can be used and then the response surface methodology ( rsm ) can be applied for the experimental results [ 5 , 8 ] . utilization of doe and rsm enables us to reduce the number of experiments needed and accurately estimate the optimal conditions from the experimental data . about the poppy straw : the various reported morphine extraction methods from poppy straw have been reported in the literature . these reported methods include various steps involving water , organic solvent , and ph adjustments . the simplest methods are the following ones covering the sonication : even these simplest methods contain some more purification and organic solvent stage . individual alkaloids ( morphine , codeine , papaverine , noscapine , thebaine , oripavine , reticuline , and narceine ) were quantitatively determined in the different samples by a validated capillary electrophoresis method . depending on the plant structure , cultivar , and harvesting time , the composition of morphine is changeable . therefore , a common extraction procedure for all plant species can not exist and for poppy straw . particle size of the extracted material , solvent type , solvent composition , the solvent / solid ratio , extraction temperature , extraction pressure , extraction time , and ph of the solvent are the parameters affecting the industrial processes which are applied for extraction . in order to optimize the process , rsm is an aggregate of statistical and mathematical techniques used for developing , improving , and optimizing the processes [ 5 , 10 ] . sonication has been applied for the extraction of polycyclic aromatic hydrocarbons , pharmaceutically active compounds , and flavonoids from different matrices [ 5 , 11 , 12 ] . the aim of this study is to determine the effect of applied parameters on poppy straw by using ultrasound extraction method with rsm . papaver somniferum was collected from fields of opium alkaloids factory on the harvesting period in july of 2012 ( turkey ) . capsules of the plant were dried at room temperature after the seeds within the plant had been removed . all chemicals used in experiments were of analytical grade and all chemicals used for analysis were of hplc grade . 0.45 m membranes ( millipore , bedford , ma , usa ) was used for filtering the buffer solutions . morphine sulfate number 1448005 ) was obtained from the turkish grain board ( afyonkarahisar , turkey ) , which is the only legal supplier of narcotics in turkey . number 1448005 ) : molecular formula of morphine sulfate is ( c17h19no3)2h2so45h2o . molecular weight of morphine sulfate is 758.83 . 132.93 mg of morphine sulfate pentahydrate is equivalent to 100 mg of anhydrous morphine base 132.93 mg of morphine sulfate pentahydrate is equivalent to 100 mg of anhydrous morphine base . ultrasound assistant extraction was carried out using bandelin sonorex brand ultrasonic bath with 50 khz frequency . ph levels of the solutions were controlled by mettler toledo seven easy ph meter . for the standard ultrasonic conditions , solvent level in the erlenmeyer flask and water level in the ultrasonic bath were kept the same . in order to adjust ph levels to 1 or 13 after the extraction process had been completed , mixture was filtered with whatman filter paper in order to prevent capillary blockage first and was then filtered with 0.45 micron membrane filter ( millipore , bedford , ma , usa ) . identification and quantitative determination of morphine was established by agilent 1260 chromatographic system equipped with autosampler , quaternary pump , column compartment , and a multiwavelength detector . final quantification was performed on a 250 mm 4.6 mm i d , 5 m particle size , zorbax extend c-18 column ( agilent technologies ) . the eluents were a solution of 0.1% tfa in water and ph adjusted to 9.6 with tea ( solvent a ) and methanol ( solvent b ) , both filtered through 0.45 m millipore filters . elution was performed with the gradient : 02 min 45% solvent b ; 210 min from 45 to 70% solvent b ; 1020 min from 70 to 85% solvent b ; 2020.1 min from 85 to 45% solvent b ; 20.130 min 45% solvent b. the flow rate was 1.5 ml / min and the injection volume was 20 l . the column temperature was maintained at 30c , and detection was carried out at 280 nm . the method has been validated according to ich guidelines , taking into account the recommendations of other appropriate guidelines . results obtained from testing different parameters during validation of the analytical method were given in table 1 . the method recommended by the european pharmacopoeia for the quality assessment of the opium dry extract has been standardized ( ph . eur . 7.0 : 01/2008 : 1839 ) . in addition to morphine , codeine , oripavine , thebaine , papaverine , and noscapine were analyzed by this method . despite the retention time of last noscapine peak this is because the organic phase content of mobile phase increases with the analysis progresses . then , concentration of mobile phase will return to the initial conditions after 20 minutes . calibration curve was created to determine the concentration of morphine by comparing the peak areas with standard solutions which consist of morphine in the range of 100500 g / ml . morphine standard solution was prepared by dissolving its salt in purified water . morphine , codeine , thebaine , and noscapine were analyzed and optimized in poppy capsules ; however optimization of other alkaloids were not included in this paper . these designs require only three levels , coded as 1 , 0 , and + 1 . box and behnken created this design by combining two - level factorial designs with incomplete block designs . this procedure creates designs with desirable statistical properties , but , most importantly , with only a fraction of the experiments needed for a full three - level factorial . these designs offer limited blocking options , except for the three - factor version . in this design , while two of the factors are constant at level 0 , the remaining factors are iterated within the levels + 1 and 1 ; then this process is repeated for different groups [ 14 , 15 ] . in this study , box - behnken design was performed with four parameters to explore the effect of them on the responses ( table 2 ) . these were x1 ( solvent / solid ratio , ml/500 mg ) , x2 ( ph ) , x3 ( time , min ) , and x4 ( temperature , c ) . design - expert 8.0.7.1 ( trial version ) software was used in order to apply the box - behnken design model . twenty - nine experiments were performed with three replications at the center values to evaluate the pure error sum of squares . the proposed quadratic model is shown as follows:(1)y=0+i=14ixi+i=14iixi2+i=14j = i+14ijxixj+e , where y is the response , 0 is the constant coefficient which is often described as intercept , x i ( i = 1 4 ) is the noncoded variable , i is the linear , and ii is the quadratic , and ( i and j = 4 ) ij are the second order interaction coefficients [ 5 , 16 ] . statistical analysis on the means of triplicate experiments was performed out using the variance analysis ( anova ) procedure of the instat software version 3.0 . variance analysis were applied to identify the interaction between the variables and the response using design - expert program . variance analysis were applied for identifying the interaction between the variables and the response by using design - expert program . experimental conditions of box - behnken design runs designed with design expert 8.0.7.1 are shown in table 3 . table 3 also displays the effects of ph , solvent / solid ratio , time and temperature on the extraction efficiency obtained by uae . figures 2 , 3 , 4 , 5 , 6 , and 7 display response surface plots for process variables . the solvent / solid ratio is a crucial factor and was also studied to optimize extraction efficiency . large solvent volumes could make the procedure difficult and lead to unnecessary waste , while small volumes may lead to incomplete extraction . a series of experiments were carried out with different solvent / solid ratios ( 10/500 , 15/500 , 20/500 v / w ) to evaluate the effect of the solvent / solid ratio . the increase of the yield with the increase of solvent quantity is consistent with mass transfer principles , since the concentration gradient which is driving force is supposed to be higher when a lower solvent to solid ratio is used , leading to higher diffusion . the influence of the solvent ph on the extraction efficiency of morphine was examined over a range of 113 and the results are shown in table 3 . it can be clearly seen that extraction efficiency was the maximum at ph : 1 . when the solvent ph was increased from 1 to 7 then the extraction efficiency increased gradually , while the solvent ph was increased from 7 to 13 . this might be explained by the fact that an acidic environment helps in the release of morphine into the solvent . the influence of the time ultrasound on the extraction efficiency of morphine was examined over a range of 3060 min and the results are shown in table 3 . they show that when the extraction time was increased from 30 min to 60 min , the extraction efficiency was low during the first 40 min of ultrasonication indicating that more time was needed for ultrasound to disrupt the cell walls and aid the release of morphine into the solvent . extractions of poppy straw were performed over temperatures ranging from 30 to 50c , since extraction at high temperatures is not economical . expectedly , extraction efficiency of morphine increased steadily as a function of temperature until 45c , since mass transfer increase by temperature . but in general , extractions at higher temperatures increase mass transfer and extraction performance because of enhanced solute desorption from the active sites of plant matrix . individual effects of process variables , which are also known as one - factor - at - at - ime approach , were applied in previous section . this classical approach ignores the possible interactions of process variables with each other , which may result in misleading conclusions table 2 shows the four parameters ( ph , solvent / solid ratio , time , and temperature ) including minimum , centre , and maximum points . twenty - nine experiments were run and chosen randomly by the design expert software , and the responses were recorded ( table 3 ) . using response surface methodology owing to the software , a quadratic model applying not only forward stepwise but also backward elimination regressions for ey was obtained . using responce surface methodology from the software , a quadratic model given below was derived:(2)m=3.0002800.040567x10.172330x2 0.035744x3 + 0.038358x40.005500x1x2 0.000933x1x3 + 0.003200x1x4 0.001167x2x3 + 0.000708x2x4 + 0.000783x3x4 + 0.00104x12 + 0.021387x22 + 0.000311x320.001713x42 . in table 4 , x3 , x1x3 , x2x3 , x2x4 , x3x4 , x1 , and x3 are not significant effects for the model . after excluding their regression coefficients , new model may be given for better explanation of new condition:(3)m=3.0002800.040567x10.172330x2 + 0.038358x40.005500x1x2 + 0.003200x1x4 + 0.021387x220.001713x42 . the optimal extraction conditions were found by using optimization choice in design expert software to maximize the response . this value was measured at 1.10 of ph , 60 min of extraction time , 42.36c of extraction temperature , and 19.99 ml to 500 mg solvent / solid ratio . the maximum response was found as 3.38 mg morphine/500 mg dried capsules under these operating conditions . after finding optimal conditions , real sample extraction experiments were repeated 6 times and then average with relative standard deviation was calculated . the results of variance analysis were given in table 4 . in order to obtain the most suitable set of variables , variables are tested and evaluated within the given alpha levels ( 0.1 ) using both backward and forward techniques . backward techniques cover all the variables to estimate parameters and then any variables with a nonsignificant parameter at alpha levels are removed from the equation . similar to backward technique , forward technique also evaluates the given variables within the given alpha levels . unlike backward technique the significant variable with the highest value of standardized beta ( p < 0.05 ) will be added to the equation . then the next variable with the highest standardized beta value is assessed . variance analysis for the quadratic equations of design expert 8.0.7.1 for the response were given in table 4 . ( x1 ) , ( x2 ) , ( x4 ) , ( x1x2 ) , ( x1x4 ) , ( x2 ) , and ( x4 ) are significant model terms in the confidence interval ( table 4 ) . the closer and higher multiple coefficients ( r - squared , adj r - squared , and pred r - squared ) point out to the higher accuracy of the model . adj r - squared also shows a high degree of correlation between actual and predicted data . as seen in table 4 solvent / solid ratio ( x1 ) f - value of lack of fit ( 6.15 ) shows that the lack of fit is significant . in our study , r - squared ( 0.96 ) , adj r - squared ( 0.92 ) , and pred r - squared ( 0.78 ) values for ey display good accuracy of the derived model . also , the coefficient value of variation ( c.v . the lower coefficient of variation value indicates a higher precision and reliability of the experimental results . hereby , the responce surface modeling can be accomplished sufficiently to predict ey from poppy straw with uae . the lower value of coefficient of variation indicates a higher precision and reliability of the experimental results [ 19 , 20 ] . figure 8 exhibits the corelation between the experimental and predicted data calculated from ( 3 ) concerning the ey of poppy straw extracts obtained by uae . it can be seen that the predicted date calculated from the model is in good agreement with the experimental data in the range of operating conditions . a potential source of morphine , poppy straw ( papaver somniferum capsules ) , was used as the research material in this study . the capsules were extracted by uae , which is an environmental and economical alternative to conventional extraction methods , requiring more time and solvent consumption . the results of the study suggests that 1.10 of ph , 42.36c of extraction temperature , 59.94 min of extraction time , and 19.99 ml to 500 mg solvent / solid ratio should be employed as optimal operating conditions for the best ey ( 3.38 mg morphine/500 mg dried capsules ) . linear coefficient of solvent to solid ratio , ph and extraction time , and square coefficient of solvent to solid ratio , ph , and extraction time have the most significant effect on the ey obtained by uae . after finding optimal conditions , real sample extraction experiments were repeated 6 times and then average with relative standard deviation was calculated .[/INST]in this study , amount of morphine from poppy capsules ( papaver somniferum ) was investigated using ultrasonic assisted extraction ( uae ) . response surface methodology was used to estimate effective experimental conditions on the content extraction of poppy capsules . for this purpose , solvent / solid ratio ( 1020 ml/500 mg sample ) , ph ( 113 ) , time ( 3060 min ) , and temperature ( 3050c ) were chosen as experimental variables . the affected response is extraction recovery values for morphine from poppy straw . for interpreting the relationship between experimental factors and response , a design table was established with combinations of three different concentrations levels of this compound in 29 trials . the second order quadratic model gave a satisfactory description of the experimental data . in our study , r - squared ( 0.96 ) , adj - r - squared ( 0.92 ) , and pred r - squared ( 0.78 ) values for extraction yield display good accuracy of the derived model . the predicted optimal conditions for the highest morphine level ( 3.38 mg morphine/500 mg - sample ) were found at 19.99 ml solvent/500 mg solid ratio , 59.94 min extraction time , 1.10 ph , and 42.36c temperature . in the optimal extraction conditions , the experimental values are very close to the predicted values . consequently , the response surface modeling can be achieved sufficiently to predict extraction yield from poppy straw by ultrasound assisted extraction .</s>

The seed for this crawl was a list of every host in the Wayback Machine This crawl was run at a level 1 (URLs including their embeds, plus the URLs of all outbound links including their embeds) The WARC files associated with this crawl are not currently available to the general public. ||||| JUNEAU - UPDATE: The Department of Fish and Game has reconsidered its decision to kill the five bears that frequent Government Hill, officials wrote in a press release, Saturday evening. "After receiving waves of requests from the public to spare the sow and her four yearling cubs, Gov. Bill Walker and the department made a collective decision today to instead relocate the bears," officials wrote. According to the release, relocating bears has not always been a good option. A trash-eating bear that was killed last year on the University of Alaska Anchorage campus, had previously been relocated to a remote area near Eklutna, though she returned to Anchorage with her cubs, shortly after. ORIGINAL STORY: A family of trash-eating bears that made headlines as they traipsed around Government Hill is getting a stay of execution from Alaska’s governor. Department of Fish and Game officials said earlier this week there was no choice but to kill the five black bears that have been wandering around the Anchorage neighborhood due to the cost involved with relocation, potential diseases that may result, and the complexities of finding a welcoming home. However, Gov. Bill Walker said Saturday from the Capitol — amid the frenetic close to the 90-day lawmaking session — that he found a minute to contact Fish and Game Commissioner Sam Cotten to instruct them to take another approach. Walker said he was concerned when he saw news reports that the bears could be put down. “I've been following it, watching it,” he said. “I just think this is the season that we can give them another try elsewhere. I really didn’t think the bears had done anything wrong.” Grace Jang, the governor’s spokeswoman, said the department will make another attempt to relocate the animals but will keep public safety as the top priority. Fish and Game officials previously said the city needs to deal with its garbage problem to prevent future incidents where bears are put down due to public safety concerns. Residential areas known to be frequented by bears often have no bear-proof trash cans: “If we can deal with the bear garbage attraction situation properly, they’ll still be around but you won’t see them as much,” said Sean Farley, a research biologist. WATCH: Gov. Bill Walker talks about his decision outside of his Juneau office

– A female black bear and four yearling cubs who have been making a living Dumpster diving in Anchorage will get a new home—and not that great trout stream in the sky, thanks in part to the actions of Alaska Gov. Bill Walker. As the Alaska Dispatch News reports, Walker yesterday intervened to plead for the lives of the quintet, which were set to be euthanized, by asking the state Fish and Game commissioner if there was another solution. "I’m sure there will be plenty of criticism about the governor getting involved in this," Walker said. "But I’m a person too. I have a soft spot for individuals in circumstances not of their own making." The bears will now likely be trapped and transported about 60 miles away, so as to inhibit their return. "I'm here in Juneau being inundated with budget issues and having to say no to all these programs," Walker continues. "I felt these bears had done nothing wrong and just thought it was the right thing to do." Speaking of those budget issues, the Fish and Game chief says it won't be too pricey to move the bears—but don't expect relocation to replace euthanasia as the norm. "There are a lot of bears so it would be expensive if you had somebody doing it full time," he says. Both men underscore that it was a request from Walker that resulted in "a collective decision," per KTUU, not an order.

<s>[INST]The seed for this crawl was a list of every host in the Wayback Machine This crawl was run at a level 1 (URLs including their embeds, plus the URLs of all outbound links including their embeds) The WARC files associated with this crawl are not currently available to the general public. ||||| JUNEAU - UPDATE: The Department of Fish and Game has reconsidered its decision to kill the five bears that frequent Government Hill, officials wrote in a press release, Saturday evening. "After receiving waves of requests from the public to spare the sow and her four yearling cubs, Gov. Bill Walker and the department made a collective decision today to instead relocate the bears," officials wrote. According to the release, relocating bears has not always been a good option. A trash-eating bear that was killed last year on the University of Alaska Anchorage campus, had previously been relocated to a remote area near Eklutna, though she returned to Anchorage with her cubs, shortly after. ORIGINAL STORY: A family of trash-eating bears that made headlines as they traipsed around Government Hill is getting a stay of execution from Alaska’s governor. Department of Fish and Game officials said earlier this week there was no choice but to kill the five black bears that have been wandering around the Anchorage neighborhood due to the cost involved with relocation, potential diseases that may result, and the complexities of finding a welcoming home. However, Gov. Bill Walker said Saturday from the Capitol — amid the frenetic close to the 90-day lawmaking session — that he found a minute to contact Fish and Game Commissioner Sam Cotten to instruct them to take another approach. Walker said he was concerned when he saw news reports that the bears could be put down. “I've been following it, watching it,” he said. “I just think this is the season that we can give them another try elsewhere. I really didn’t think the bears had done anything wrong.” Grace Jang, the governor’s spokeswoman, said the department will make another attempt to relocate the animals but will keep public safety as the top priority. Fish and Game officials previously said the city needs to deal with its garbage problem to prevent future incidents where bears are put down due to public safety concerns. Residential areas known to be frequented by bears often have no bear-proof trash cans: “If we can deal with the bear garbage attraction situation properly, they’ll still be around but you won’t see them as much,” said Sean Farley, a research biologist. WATCH: Gov. Bill Walker talks about his decision outside of his Juneau office[/INST]– A female black bear and four yearling cubs who have been making a living Dumpster diving in Anchorage will get a new home—and not that great trout stream in the sky, thanks in part to the actions of Alaska Gov. Bill Walker. As the Alaska Dispatch News reports, Walker yesterday intervened to plead for the lives of the quintet, which were set to be euthanized, by asking the state Fish and Game commissioner if there was another solution. "I’m sure there will be plenty of criticism about the governor getting involved in this," Walker said. "But I’m a person too. I have a soft spot for individuals in circumstances not of their own making." The bears will now likely be trapped and transported about 60 miles away, so as to inhibit their return. "I'm here in Juneau being inundated with budget issues and having to say no to all these programs," Walker continues. "I felt these bears had done nothing wrong and just thought it was the right thing to do." Speaking of those budget issues, the Fish and Game chief says it won't be too pricey to move the bears—but don't expect relocation to replace euthanasia as the norm. "There are a lot of bears so it would be expensive if you had somebody doing it full time," he says. Both men underscore that it was a request from Walker that resulted in "a collective decision," per KTUU, not an order.</s>

SECTION 1. NATIONAL MILITARY FAMILY RELIEF FUND TO ASSIST FAMILIES OF MEMBERS OF THE ARMED FORCES WHO ARE SERVING IN, OR HAVE SERVED IN, IRAQ OR AFGHANISTAN. (a) In General.--Subchapter I of chapter 88 of title 10, United States Code, is amended by inserting after section 1781b the following new section: ``Sec. 1781c. National Military Family Relief Fund to assist military families ``(a) Establishment.--There is established in the Treasury a fund, which shall be known as the `National Military Family Relief Fund' (in this section referred to as the `Fund'). ``(b) Credits to Fund.--There are hereby appropriated to the Fund in each fiscal year an amount equal to the amounts designated for deposit in the Fund under section 6098 of the Internal Revenue Code of 1986 in the taxable year ending in that fiscal year. ``(c) Use of Fund.--The Secretary of Defense shall use amounts in the Fund, without further specific authorization in law, to make grants to members of the Armed Forces who are serving in, or have served in, Iraq or Afghanistan to assist the families of such members. ``(d) Grant Criteria.--The Secretary of Defense shall prescribe the criteria under which grant applications will be solicited and grants will be made and the purposes for which grants may be used.''. (b) Clerical Amendment.--The table of sections at the beginning of such subchapter is amended by inserting after the item relating to section 1781b the following new item: ``1781c. National Military Family Relief Fund to assist military families.''. SEC. 2. DESIGNATION OF INCOME TAX PAYMENTS TO NATIONAL MILITARY FAMILY RELIEF FUND. (a) In General.--Subchapter A of chapter 61 of the Internal Revenue Code of 1986 (relating to information and returns) is amended by adding at the end the following new part: ``PART IX--DESIGNATION OF INCOME TAX PAYMENTS TO NATIONAL MILITARY FAMILY RELIEF FUND ``Sec. 6098. Designation to National Military Family Relief Fund. ``SEC. 6098. DESIGNATION TO NATIONAL MILITARY FAMILY RELIEF FUND. ``(a) In General.--Every individual (other than a nonresident alien), with respect to each taxpayer's return for the taxable year of the tax imposed by chapter 1-- ``(1) whose adjusted income tax liability for the taxable year is $1 or more may designate that a specified portion (not less than $1) of any overpayment of tax shall be paid over to, and ``(2) in addition to any payment of income tax liability, may make a contribution of an additional amount which shall be paid over to, the National Military Family Relief Fund, established under section 1781c of title 10, United States Code. ``(b) Adjusted Income Tax Liability.--For purposes of subsection (a), the term `adjusted income tax liability' means, for any individual for any taxable year, the excess (if any) of-- ``(1) the income tax liability (as defined in section 6096(b)) of the individual for the taxable year, over ``(2) any amount designated by the individual (and, in the case of a joint return, any amount designated by the individual's spouse) under section 6096(a) for such taxable year. ``(c) Manner and Time of Designation and Contribution.--A designation and contribution under subsection (a) may be made with respect to any taxable year-- ``(1) at the time of filing the return of the tax imposed by chapter 1 for such taxable year, or ``(2) at any other time (after the time of filing the return of the tax imposed by chapter 1 for such taxable year) specified in regulations prescribed by the Secretary. Such designation shall be made in such manner as the Secretary prescribes by regulations except that, if such designation is made at the time of filing the return of the tax imposed by chapter 1 for such taxable year, such designation shall be made either on the first page of the return or on the page bearing the taxpayer's signature. ``(d) Overpayments Treated as Refunded.--For purposes of this title, any portion of an overpayment of tax designated under subsection (a) shall be treated as-- ``(1) being refunded to the taxpayer as of the last date prescribed for filing the return of tax imposed by chapter 1 (determined without regard to extensions) or, if later, the date the return is filed, and ``(2) a contribution made by such taxpayer on such date to the United States.''. (b) Clerical Amendment.--The table of parts for subchapter A of chapter 61 of such Code is amended by adding at the end the following new item: ``Part IX--Designation of Income Tax Payments to National Military Family Relief Fund ``Sec. 6098. Designation to National Military Family Relief Fund.''. (c) Effective Date.--The amendments made by this section shall apply to taxable years beginning after the date of the enactment of this Act.

Establishes in the Treasury the National Military Family Relief Fund to make grants to Armed Forces members who are serving, or have served, in Iraq or Afghanistan to assist the families of such members. Amends the Internal Revenue Code to: (1) allow every individual taxpayer to designate $1 or more of any overpayment to be paid to the Fund; and (2) in addition to any payment of income tax liability, make a contribution of an additional amount which shall be paid over to the Fund.

<s>[INST]SECTION 1. NATIONAL MILITARY FAMILY RELIEF FUND TO ASSIST FAMILIES OF MEMBERS OF THE ARMED FORCES WHO ARE SERVING IN, OR HAVE SERVED IN, IRAQ OR AFGHANISTAN. (a) In General.--Subchapter I of chapter 88 of title 10, United States Code, is amended by inserting after section 1781b the following new section: ``Sec. 1781c. National Military Family Relief Fund to assist military families ``(a) Establishment.--There is established in the Treasury a fund, which shall be known as the `National Military Family Relief Fund' (in this section referred to as the `Fund'). ``(b) Credits to Fund.--There are hereby appropriated to the Fund in each fiscal year an amount equal to the amounts designated for deposit in the Fund under section 6098 of the Internal Revenue Code of 1986 in the taxable year ending in that fiscal year. ``(c) Use of Fund.--The Secretary of Defense shall use amounts in the Fund, without further specific authorization in law, to make grants to members of the Armed Forces who are serving in, or have served in, Iraq or Afghanistan to assist the families of such members. ``(d) Grant Criteria.--The Secretary of Defense shall prescribe the criteria under which grant applications will be solicited and grants will be made and the purposes for which grants may be used.''. (b) Clerical Amendment.--The table of sections at the beginning of such subchapter is amended by inserting after the item relating to section 1781b the following new item: ``1781c. National Military Family Relief Fund to assist military families.''. SEC. 2. DESIGNATION OF INCOME TAX PAYMENTS TO NATIONAL MILITARY FAMILY RELIEF FUND. (a) In General.--Subchapter A of chapter 61 of the Internal Revenue Code of 1986 (relating to information and returns) is amended by adding at the end the following new part: ``PART IX--DESIGNATION OF INCOME TAX PAYMENTS TO NATIONAL MILITARY FAMILY RELIEF FUND ``Sec. 6098. Designation to National Military Family Relief Fund. ``SEC. 6098. DESIGNATION TO NATIONAL MILITARY FAMILY RELIEF FUND. ``(a) In General.--Every individual (other than a nonresident alien), with respect to each taxpayer's return for the taxable year of the tax imposed by chapter 1-- ``(1) whose adjusted income tax liability for the taxable year is $1 or more may designate that a specified portion (not less than $1) of any overpayment of tax shall be paid over to, and ``(2) in addition to any payment of income tax liability, may make a contribution of an additional amount which shall be paid over to, the National Military Family Relief Fund, established under section 1781c of title 10, United States Code. ``(b) Adjusted Income Tax Liability.--For purposes of subsection (a), the term `adjusted income tax liability' means, for any individual for any taxable year, the excess (if any) of-- ``(1) the income tax liability (as defined in section 6096(b)) of the individual for the taxable year, over ``(2) any amount designated by the individual (and, in the case of a joint return, any amount designated by the individual's spouse) under section 6096(a) for such taxable year. ``(c) Manner and Time of Designation and Contribution.--A designation and contribution under subsection (a) may be made with respect to any taxable year-- ``(1) at the time of filing the return of the tax imposed by chapter 1 for such taxable year, or ``(2) at any other time (after the time of filing the return of the tax imposed by chapter 1 for such taxable year) specified in regulations prescribed by the Secretary. Such designation shall be made in such manner as the Secretary prescribes by regulations except that, if such designation is made at the time of filing the return of the tax imposed by chapter 1 for such taxable year, such designation shall be made either on the first page of the return or on the page bearing the taxpayer's signature. ``(d) Overpayments Treated as Refunded.--For purposes of this title, any portion of an overpayment of tax designated under subsection (a) shall be treated as-- ``(1) being refunded to the taxpayer as of the last date prescribed for filing the return of tax imposed by chapter 1 (determined without regard to extensions) or, if later, the date the return is filed, and ``(2) a contribution made by such taxpayer on such date to the United States.''. (b) Clerical Amendment.--The table of parts for subchapter A of chapter 61 of such Code is amended by adding at the end the following new item: ``Part IX--Designation of Income Tax Payments to National Military Family Relief Fund ``Sec. 6098. Designation to National Military Family Relief Fund.''. (c) Effective Date.--The amendments made by this section shall apply to taxable years beginning after the date of the enactment of this Act.[/INST]Establishes in the Treasury the National Military Family Relief Fund to make grants to Armed Forces members who are serving, or have served, in Iraq or Afghanistan to assist the families of such members. Amends the Internal Revenue Code to: (1) allow every individual taxpayer to designate $1 or more of any overpayment to be paid to the Fund; and (2) in addition to any payment of income tax liability, make a contribution of an additional amount which shall be paid over to the Fund.</s>

Tuam historian Catherine Corless said the Bon Secours order should pay the full cost of the exhumation, identification and proper burial of the remains at the Tuam Mother and Baby Home. She told RTÉ’s Morning Ireland that the order’s offer of €2.5million is “a meagre offering” given that the order “has private hospitals all over the place”. “The least they can do to help the healing is cover the cost of the whole thing. The fact that the Bon Secours sisters are paying out shows they feel responsible. “The correct thing is being done, these babies are being given dignity. The important message to the survivors is that the Government care enough to do this.” Minister for Children Katherine Zappone said yesterday that the cost of the exhumation will be between €6 million and €13 million. The Bon Secours Sisters have contributed €2.5 million. However, the excavation cannot happen without specific legislation first being passed by the Dáil, the Minister explained yesterday. The process is unlikely to begin until next year at the earliest. The events at the Tuam Mother and Baby home were first brought to public attention by Ms Corless who found death certificates for 796 infants. Earlier today on Newstalk Breakfast Ms Zappone said the legislation required is a “complicated process” and that the work is just beginning. It has to be done properly as it could be required as a template if further sites are identified. The Minister acknowledged it is possible that even with the best approach and methodology all the remains will not be identified. “This is unchartered territory. We will take a staged approach, and we will learn as we go. That is the most effective way.” The Special Rapporteur on Child Protection, Dr Geoffrey Shannon, told Morning Ireland that there is a duty to bury the remains with “decency and respect”, and he warmly welcomed the Government’s decision. It is important there has been a contribution from the religious order, he said, adding the phased approach is the right decision. “Every reasonable approach must be made to locate remains as the right to dignity after death exists. Ireland’s reputation is in the spotlight,” Dr Shannon said. “Tuam was a particular example. The image of a child on a sewer undermines dignity after death.” He said there could be other sites and they will have to be examined on a case-by-case basis. ||||| DUBLIN — The remains of children buried in the old septic system of a mother and baby home in Ireland will be exhumed and identified if possible, the government said Tuesday. Officials said they would search the grounds of a home run for almost four decades in Tuam, where as many as hundreds of fetuses and babies may be buried. “I understand that this is a hugely important decision for all connected to the site in Tuam, most especially those who believe they may have a loved one buried there and those now living close to the site,” said the Irish minister for children, Katherine Zappone. “I am committed to ensuring that all the children interred at this site can have a dignified and respectful burial. It is a landmark development in a scandal that emerged in 2014 when a local amateur historian, Catherine Corless, said she had found death certificates for 796 children who died in the home from 1925 to 1961 — but whose burial places were not officially recorded. ||||| In this photo taken on Tuesday, Oct. 23, 2018, Children's Minister Katherine Zappone announces the forensic excavation of the site of a former mother and baby's home in Tuam, at Government Buildings in... (Associated Press) In this photo taken on Tuesday, Oct. 23, 2018, Children's Minister Katherine Zappone announces the forensic excavation of the site of a former mother and baby's home in Tuam, at Government Buildings in Dublin. Ireland's government has approved a forensic excavation of a Catholic-run orphanage where... (Associated Press) In this photo taken on Tuesday, Oct. 23, 2018, Children's Minister Katherine Zappone announces the forensic excavation of the site of a former mother and baby's home in Tuam, at Government Buildings in Dublin. Ireland's government has approved a forensic excavation of a Catholic-run orphanage where... (Associated Press) In this photo taken on Tuesday, Oct. 23, 2018, Children's Minister Katherine Zappone announces the forensic excavation of the site of a former mother and baby's home in Tuam, at Government Buildings in... (Associated Press) LONDON (AP) — Ireland's government has approved a forensic excavation of a Catholic-run orphanage where a mass grave containing the remains of hundreds of children was discovered. Children's Minister Katherine Zappone announced Tuesday the excavation and recovery of remains. There will be a respectful burial where possible, she said. The excavation, which will begin after legislation is passed, follows a report from a judge-led commission that confirmed last year that the former Bon Secours Mother and Baby Home in Tuam, County Galway, had an underground sewage structure divided into 20 chambers containing "significant quantities of human remains." Church-run homes in Ireland housed orphans, unmarried pregnant women and their babies for most of the 20th century. The institutions have been subject to intense public scrutiny since a local historian in 2014 tracked down death certificates for nearly 800 children who had died as residents of the facility — but could find a burial record for only one child. Investigators later found a mass grave containing remains of babies and young children from 35 weeks to 3-years-old on the grounds of the home, which closed in 1961. Zappone raised the mass grave scandal with Pope Francis when he visited Ireland in August, calling it a "shameful chapter of recent Irish history." The pope urged the Irish church to make reparations to the home's survivors for its role. ||||| Media playback is unsupported on your device Media caption Tuam babies excavation will be forensic, says minister The remains of children buried in unmarked graves at a former mother and baby home in the Republic of Ireland are to be exhumed, identified and reburied. The announcement was made by Minister for Children Katherine Zappone. The site in Tuam, County Galway, will be excavated in a bid to recover the remains. Forensic tests will be carried out to identify each child before "respectful" reburials. The Catholic-run institution housed unmarried mothers and babies from 1925 to 1961 and had high infant mortality. There was an outcry last year when tests revealed "significant quantities" of human remains had been buried in "underground chambers" at the site. Announcing the phased forensic excavation, Minister Zappone said: "I understand that this is a hugely important decision for all connected to the site in Tuam, most especially those who believe they may have a loved one buried there and those now living close to the site." "I am committed to ensuring that all the children interred at this site can have a dignified and respectful burial." The minister said operation would not be straightforward and said it presented "unprecedented technical and legal issues". But she added: "It is only by taking the right actions now can we truly demonstrate our compassion and commitment to work towards justice, truth and healing for what happened in our past and, most especially, for those who were previously abandoned." Missing records The controversy emerged in 2014, when an amateur historian raised questions about the fate of almost 800 children who died at the home during its 36 years in operation. Catherine Corless spent years trying to find out what happened to the remains of hundreds of children who died in the Tuam home. Ms Corless established that although there were death certificates for 796 infants, no burial records existed, which raised fears of a mass grave. It is thought that the children died of natural causes or malnutrition but the secretive, undignified manner of their burials caused widespread outrage in Ireland and beyond. Image copyright Reuters Image caption Catherine Corless collated hundreds of death certificates for the infants who died in the home The Irish government set up a public inquiry in 2015 to investigate the Tuam burials and to conduct a wider examination of how mother and baby homes were run. The inquiry - known as the Mother and Baby Homes Commission of Investigation - began test excavations at the site in October 2016. In March 2017, the commission confirmed that "significant quantities" of human remains have been discovered in at least 17 underground chambers. Test results showed the remains included premature babies and toddlers up to the age of three, who are believed to have died during the 1950s. Media playback is unsupported on your device Media caption Journalist Alison O Reilly and author of a book about Tuam spoke to BBC Radio 4's PM programme At that time sex outside marriage was considered taboo and many single mothers were disowned by their families and sent to institutions. The Tuam home was one of several Irish institutions in which about 35,000 unmarried pregnant women are thought to have been sent. Malnutrition and high infant mortality were common features of the homes and a child died nearly every two weeks at the Tuam home between the mid-1920s and 1960s. Image copyright PA Image caption Protesters held up placards of the names of babies buried at Tuam during the Pope's visit to Ireland in August The home, which has since been demolished, was run by congregation of Catholic nuns - the Sisters of Bon Secours. Protests were held at the site in August, organised to coincide with Pope Francis' visit to Ireland. Minister Zappone also raised the issue during a meeting with the pontiff in Dubin. "I hope the Church will make reparation for its part in this shameful chapter," she told the Pope.

– In 2016, test excavations at the site of a former Catholic orphanage confirmed "significant quantities of human remains" were present in the old septic system of the Catholic-run Bon Secours Mother and Baby Home in Tuam, Ireland. The probe for such remains followed a bombshell 2014 report by a local historian that suggested some 796 children had died in the home for unwed mothers and babies over a nearly 40-year period beginning in 1925 but had no recorded burial place. The New York Times reports the government was given options on how to proceed following the identification of the remains of babies and young children, from easier and cheaper courses like erecting a memorial to the onerous and expensive task of performing a forensic excavation of the entire area. The country on Tuesday announced it has opted for the latter course. The Times notes legislation will need to be passed before the exhumation can begin. The AP reports the underground sewage structure was found to be divided into 20 chambers, with the remains found within. Children's Minister Katherine Zappone says she is "committed to ensuring that all the children interred at this site can have a dignified and respectful burial," though the Times notes the challenges ahead: The remains found during the test excavations were reportedly intermixed to a degree that identifying individuals prior to their reburial will be no small feat. The Irish Times reports the effort could cost as much as $15 million; the Bon Secours sisters have pledged to pay about $3 million of that. The BBC notes the home itself had previously been razed. (Read one US woman's harrowing story of life in an orphanage.)

<s>[INST]Tuam historian Catherine Corless said the Bon Secours order should pay the full cost of the exhumation, identification and proper burial of the remains at the Tuam Mother and Baby Home. She told RTÉ’s Morning Ireland that the order’s offer of €2.5million is “a meagre offering” given that the order “has private hospitals all over the place”. “The least they can do to help the healing is cover the cost of the whole thing. The fact that the Bon Secours sisters are paying out shows they feel responsible. “The correct thing is being done, these babies are being given dignity. The important message to the survivors is that the Government care enough to do this.” Minister for Children Katherine Zappone said yesterday that the cost of the exhumation will be between €6 million and €13 million. The Bon Secours Sisters have contributed €2.5 million. However, the excavation cannot happen without specific legislation first being passed by the Dáil, the Minister explained yesterday. The process is unlikely to begin until next year at the earliest. The events at the Tuam Mother and Baby home were first brought to public attention by Ms Corless who found death certificates for 796 infants. Earlier today on Newstalk Breakfast Ms Zappone said the legislation required is a “complicated process” and that the work is just beginning. It has to be done properly as it could be required as a template if further sites are identified. The Minister acknowledged it is possible that even with the best approach and methodology all the remains will not be identified. “This is unchartered territory. We will take a staged approach, and we will learn as we go. That is the most effective way.” The Special Rapporteur on Child Protection, Dr Geoffrey Shannon, told Morning Ireland that there is a duty to bury the remains with “decency and respect”, and he warmly welcomed the Government’s decision. It is important there has been a contribution from the religious order, he said, adding the phased approach is the right decision. “Every reasonable approach must be made to locate remains as the right to dignity after death exists. Ireland’s reputation is in the spotlight,” Dr Shannon said. “Tuam was a particular example. The image of a child on a sewer undermines dignity after death.” He said there could be other sites and they will have to be examined on a case-by-case basis. ||||| DUBLIN — The remains of children buried in the old septic system of a mother and baby home in Ireland will be exhumed and identified if possible, the government said Tuesday. Officials said they would search the grounds of a home run for almost four decades in Tuam, where as many as hundreds of fetuses and babies may be buried. “I understand that this is a hugely important decision for all connected to the site in Tuam, most especially those who believe they may have a loved one buried there and those now living close to the site,” said the Irish minister for children, Katherine Zappone. “I am committed to ensuring that all the children interred at this site can have a dignified and respectful burial. It is a landmark development in a scandal that emerged in 2014 when a local amateur historian, Catherine Corless, said she had found death certificates for 796 children who died in the home from 1925 to 1961 — but whose burial places were not officially recorded. ||||| In this photo taken on Tuesday, Oct. 23, 2018, Children's Minister Katherine Zappone announces the forensic excavation of the site of a former mother and baby's home in Tuam, at Government Buildings in... (Associated Press) In this photo taken on Tuesday, Oct. 23, 2018, Children's Minister Katherine Zappone announces the forensic excavation of the site of a former mother and baby's home in Tuam, at Government Buildings in Dublin. Ireland's government has approved a forensic excavation of a Catholic-run orphanage where... (Associated Press) In this photo taken on Tuesday, Oct. 23, 2018, Children's Minister Katherine Zappone announces the forensic excavation of the site of a former mother and baby's home in Tuam, at Government Buildings in Dublin. Ireland's government has approved a forensic excavation of a Catholic-run orphanage where... (Associated Press) In this photo taken on Tuesday, Oct. 23, 2018, Children's Minister Katherine Zappone announces the forensic excavation of the site of a former mother and baby's home in Tuam, at Government Buildings in... (Associated Press) LONDON (AP) — Ireland's government has approved a forensic excavation of a Catholic-run orphanage where a mass grave containing the remains of hundreds of children was discovered. Children's Minister Katherine Zappone announced Tuesday the excavation and recovery of remains. There will be a respectful burial where possible, she said. The excavation, which will begin after legislation is passed, follows a report from a judge-led commission that confirmed last year that the former Bon Secours Mother and Baby Home in Tuam, County Galway, had an underground sewage structure divided into 20 chambers containing "significant quantities of human remains." Church-run homes in Ireland housed orphans, unmarried pregnant women and their babies for most of the 20th century. The institutions have been subject to intense public scrutiny since a local historian in 2014 tracked down death certificates for nearly 800 children who had died as residents of the facility — but could find a burial record for only one child. Investigators later found a mass grave containing remains of babies and young children from 35 weeks to 3-years-old on the grounds of the home, which closed in 1961. Zappone raised the mass grave scandal with Pope Francis when he visited Ireland in August, calling it a "shameful chapter of recent Irish history." The pope urged the Irish church to make reparations to the home's survivors for its role. ||||| Media playback is unsupported on your device Media caption Tuam babies excavation will be forensic, says minister The remains of children buried in unmarked graves at a former mother and baby home in the Republic of Ireland are to be exhumed, identified and reburied. The announcement was made by Minister for Children Katherine Zappone. The site in Tuam, County Galway, will be excavated in a bid to recover the remains. Forensic tests will be carried out to identify each child before "respectful" reburials. The Catholic-run institution housed unmarried mothers and babies from 1925 to 1961 and had high infant mortality. There was an outcry last year when tests revealed "significant quantities" of human remains had been buried in "underground chambers" at the site. Announcing the phased forensic excavation, Minister Zappone said: "I understand that this is a hugely important decision for all connected to the site in Tuam, most especially those who believe they may have a loved one buried there and those now living close to the site." "I am committed to ensuring that all the children interred at this site can have a dignified and respectful burial." The minister said operation would not be straightforward and said it presented "unprecedented technical and legal issues". But she added: "It is only by taking the right actions now can we truly demonstrate our compassion and commitment to work towards justice, truth and healing for what happened in our past and, most especially, for those who were previously abandoned." Missing records The controversy emerged in 2014, when an amateur historian raised questions about the fate of almost 800 children who died at the home during its 36 years in operation. Catherine Corless spent years trying to find out what happened to the remains of hundreds of children who died in the Tuam home. Ms Corless established that although there were death certificates for 796 infants, no burial records existed, which raised fears of a mass grave. It is thought that the children died of natural causes or malnutrition but the secretive, undignified manner of their burials caused widespread outrage in Ireland and beyond. Image copyright Reuters Image caption Catherine Corless collated hundreds of death certificates for the infants who died in the home The Irish government set up a public inquiry in 2015 to investigate the Tuam burials and to conduct a wider examination of how mother and baby homes were run. The inquiry - known as the Mother and Baby Homes Commission of Investigation - began test excavations at the site in October 2016. In March 2017, the commission confirmed that "significant quantities" of human remains have been discovered in at least 17 underground chambers. Test results showed the remains included premature babies and toddlers up to the age of three, who are believed to have died during the 1950s. Media playback is unsupported on your device Media caption Journalist Alison O Reilly and author of a book about Tuam spoke to BBC Radio 4's PM programme At that time sex outside marriage was considered taboo and many single mothers were disowned by their families and sent to institutions. The Tuam home was one of several Irish institutions in which about 35,000 unmarried pregnant women are thought to have been sent. Malnutrition and high infant mortality were common features of the homes and a child died nearly every two weeks at the Tuam home between the mid-1920s and 1960s. Image copyright PA Image caption Protesters held up placards of the names of babies buried at Tuam during the Pope's visit to Ireland in August The home, which has since been demolished, was run by congregation of Catholic nuns - the Sisters of Bon Secours. Protests were held at the site in August, organised to coincide with Pope Francis' visit to Ireland. Minister Zappone also raised the issue during a meeting with the pontiff in Dubin. "I hope the Church will make reparation for its part in this shameful chapter," she told the Pope.[/INST]– In 2016, test excavations at the site of a former Catholic orphanage confirmed "significant quantities of human remains" were present in the old septic system of the Catholic-run Bon Secours Mother and Baby Home in Tuam, Ireland. The probe for such remains followed a bombshell 2014 report by a local historian that suggested some 796 children had died in the home for unwed mothers and babies over a nearly 40-year period beginning in 1925 but had no recorded burial place. The New York Times reports the government was given options on how to proceed following the identification of the remains of babies and young children, from easier and cheaper courses like erecting a memorial to the onerous and expensive task of performing a forensic excavation of the entire area. The country on Tuesday announced it has opted for the latter course. The Times notes legislation will need to be passed before the exhumation can begin. The AP reports the underground sewage structure was found to be divided into 20 chambers, with the remains found within. Children's Minister Katherine Zappone says she is "committed to ensuring that all the children interred at this site can have a dignified and respectful burial," though the Times notes the challenges ahead: The remains found during the test excavations were reportedly intermixed to a degree that identifying individuals prior to their reburial will be no small feat. The Irish Times reports the effort could cost as much as $15 million; the Bon Secours sisters have pledged to pay about $3 million of that. The BBC notes the home itself had previously been razed. (Read one US woman's harrowing story of life in an orphanage.)</s>

Shenzhen is rolling out a high-tech initiative to shame jaywalkers out of their bad habits by displaying their faces on large screens. The new device, dubbed the ‘Electronic Police,’ was installed at a zebra crossing at the intersection of Xinzhou Road and Lianhua Road in Shenzhen, one of China’s wealthiest cities, north of Hong Kong. “The term ‘Chinese Style Road Crossing’ was created by a Chinese netizen in 2012, stating that when a large crowd of pedestrians try to cross a road together, there is no need to obey the traffic rules. It is based on an underlying assumption that law enforcement officers would not punish a large number of offenders all at once,” State University of New York at Albany graduate, Zhong Zheng, explained on safekids.org in autumn 2016. The ‘Smart System for Collecting Evidence of Jaywalking’ captures the image of the offender and projects their photo onto a big screen. “People might be ashamed of running on the red light by seeing their names on the public screens. However, the technology of face detecting has to be 100% accurate,” a passerby told Ruptly news agency. The technology is being tested on that one crossing before the city decides to roll it out across the whole of Shenzhen. As with drivers, pedestrians caught on camera will also be fined 100 yuan ($14). READ MORE: Smart traffic: China introduces lane-changing robots to ease infamous gridlock Motorists can also fall prey to the new system due to its sonar technology, which can capture any honking sound. Horn honking is banned in downtown Shenzhen, resulting in a fine of 500 yuan, China Daily reports. ||||| Pedestrians wait for the light to change in Beijing, but people not obeying the rules of the road in other parts of China might find their faces flashed on a huge screen with facial recognition technology being used to catch jaywalkers Chinese cities are cracking down on jaywalkers by installing facial recognition kits at intersections to identify and shame them by posting their photo on public screens, state media said Tuesday. It is the latest use of the technology in China, where it has been used by fast-food chain KFC to predict orders and in public restrooms to foil toilet paper thefts. This time, cities in four provinces are using the hardware to keep pedestrians from crossing at red lights, according to the official Xinhua news agency. The technology has detected more than 6,000 instances of people crossing red lights since it was installed in early May in Jinan, capital of eastern Shandong province. The facial recognition equipment takes photos and a 15-second video of jaywalkers, whose images instantly appear on a screen, showing them that they've been caught, Xinhua said. The photos are matched with images in a provincial police database. "Within 20 minutes, the offender's photograph and personal information such as their ID number and home address are displayed on the screen at the crossroad," Xinhua said. Traffic police give the offenders the choice between paying a $3 fine, taking a half-hour course on traffic rules or spending 20 minutes helping a traffic officer. Jinan traffic police department may also publish the offender's information on its Weibo social media account. "Since the new technology has been adopted, the cases of jaywalking have been reduced from 200 to 20 each day at the major intersection of Jingshi and Shungeng roads," Jinan police officer Li Yong was quoted as saying by Xinhua. The Xinhua report comes after a video appeared on social media earlier this month showing a woman being hit by a taxi on a crosswalk and then run over by a car. She later died. The footage sparked outrage at the indifference of other pedestrians and drivers who did not stop to help her. Explore further: Chinese police probe endangered pangolin banquet ||||| Not that you shouldn't already think twice before jaywalking, but now, you have yet another reason to wait for your light. Cities in four Chinese provinces are shaming jaywalkers by posting their personal information on public screens, according to state-owned Xinhua. SEE ALSO: How a university campus is using facial recognition to keep its dorms safe The system's been installed at cities in Shandong and Jiangsu in east China, as well as Fujian and Guangdong in south China, and it uses facial recognition to trace the identities of jaywalkers. Cameras take several snapshots of errant pedestrians, as well as a 15-second video which is then displayed on a large screen: A system in Yancheng, eastern China. Image: Weibo A similar system in Shenzhen. Image: Weibo Facial recognition software matches the faces of errant offenders with those in a provincial police database. A police officer then checks them for their accuracy, and if they pass muster, the offender's photograph and personal information (like portions of their ID number and home address) gets displayed. In some cities, like Jinan, Shandong, traffic police post the identities of errant offenders on social media: The man got a 20 yuan ($2.93) fine. Image: Jinan Traffic Police/Weibo The public shaming has very visible effects — Jinan police told The Paper that being publicly shamed could impact a person's credit rating, as well as their insurance and pension premiums. Offenders get to choose between three forms of punishment — a 20 yuan ($2.93) fine, a 30-minute long traffic safety course and or 20 minutes of assisting police in traffic control. Repeat offenders could be fined up to 100 yuan ($14.64). Police could also inform errant pedestrians' employers and residential communities, said Xinhua. The system in place in Yancheng Image: Weibo The system in place in Jinan Image: The Paper/Tencent Video The public shaming's been naturally effective. Jinan police have caught over 6,200 jaywalkers in the city since the system was set up in May this year, according to The Paper. The number of errant pedestrians has also fallen from 200 per day, to 20 per day, the city's traffic police told Xinhua. "I'll take note and remind myself the next time I cross the road," one resident told The Paper. "After all, it's not a good thing to cross the road while the light is still red." Jinan wants to install the system at 50 more major intersections by the end of June. Each unit will cost the city 100,000 yuan ($14,637). Image: Weibo This isn't the first time China's taken, uh, slightly unusual steps to stop jaywalking before. In April, turnstiles were installed in Wuhan, central China, to stop pedestrians from dashing across the road. The country's also deployed dancing aunties to promote road safety at crosswalks, and in January, a robot police officer was deployed at a traffic junction in Xiangyang, central China to stop errant pedestrians, and tell them off.

– Jaywalkers take heed: If you do it in parts of China, you could be in for the shaming of your life. Authorities have installed a new device called the "Electronic Police" at intersections in cities in four provinces. Not only does it detect when people are jaywalking, but it snaps photos of the offenders and uses facial recognition tech to pull up their images in the provincial police database, reports RT. Once police confirm a match, the person isn't just flagged for the offense (they can choose whether to pay a fine, take a safety class, or volunteer with traffic police). Their photo and personal details, including parts of their ID number and home address, are displayed on a large screen for all passersby to see. Facial recognition has already been used in China to catch toilet paper thieves in public restrooms and to predict orders at the fast food chain KFC, reports the AFP. But the use of public shaming takes things to a whole new level—one that local police say is proving effective. They say public shaming can go so far as to impact insurance and pension premiums, and police in the city of Jinan say they've caught more than 6,200 people crossing at red lights since installing the system in early May (yes, that's less than two months), with the number of incidents dropping ten-fold from 200 per day to 20. Jinan is looking to install the system at 50 other major intersections by the end of June, each costing the city roughly $15,000, reports Mashable. (Texting pedestrians are hit with fines in parts of New Jersey.)

<s>[INST]Shenzhen is rolling out a high-tech initiative to shame jaywalkers out of their bad habits by displaying their faces on large screens. The new device, dubbed the ‘Electronic Police,’ was installed at a zebra crossing at the intersection of Xinzhou Road and Lianhua Road in Shenzhen, one of China’s wealthiest cities, north of Hong Kong. “The term ‘Chinese Style Road Crossing’ was created by a Chinese netizen in 2012, stating that when a large crowd of pedestrians try to cross a road together, there is no need to obey the traffic rules. It is based on an underlying assumption that law enforcement officers would not punish a large number of offenders all at once,” State University of New York at Albany graduate, Zhong Zheng, explained on safekids.org in autumn 2016. The ‘Smart System for Collecting Evidence of Jaywalking’ captures the image of the offender and projects their photo onto a big screen. “People might be ashamed of running on the red light by seeing their names on the public screens. However, the technology of face detecting has to be 100% accurate,” a passerby told Ruptly news agency. The technology is being tested on that one crossing before the city decides to roll it out across the whole of Shenzhen. As with drivers, pedestrians caught on camera will also be fined 100 yuan ($14). READ MORE: Smart traffic: China introduces lane-changing robots to ease infamous gridlock Motorists can also fall prey to the new system due to its sonar technology, which can capture any honking sound. Horn honking is banned in downtown Shenzhen, resulting in a fine of 500 yuan, China Daily reports. ||||| Pedestrians wait for the light to change in Beijing, but people not obeying the rules of the road in other parts of China might find their faces flashed on a huge screen with facial recognition technology being used to catch jaywalkers Chinese cities are cracking down on jaywalkers by installing facial recognition kits at intersections to identify and shame them by posting their photo on public screens, state media said Tuesday. It is the latest use of the technology in China, where it has been used by fast-food chain KFC to predict orders and in public restrooms to foil toilet paper thefts. This time, cities in four provinces are using the hardware to keep pedestrians from crossing at red lights, according to the official Xinhua news agency. The technology has detected more than 6,000 instances of people crossing red lights since it was installed in early May in Jinan, capital of eastern Shandong province. The facial recognition equipment takes photos and a 15-second video of jaywalkers, whose images instantly appear on a screen, showing them that they've been caught, Xinhua said. The photos are matched with images in a provincial police database. "Within 20 minutes, the offender's photograph and personal information such as their ID number and home address are displayed on the screen at the crossroad," Xinhua said. Traffic police give the offenders the choice between paying a $3 fine, taking a half-hour course on traffic rules or spending 20 minutes helping a traffic officer. Jinan traffic police department may also publish the offender's information on its Weibo social media account. "Since the new technology has been adopted, the cases of jaywalking have been reduced from 200 to 20 each day at the major intersection of Jingshi and Shungeng roads," Jinan police officer Li Yong was quoted as saying by Xinhua. The Xinhua report comes after a video appeared on social media earlier this month showing a woman being hit by a taxi on a crosswalk and then run over by a car. She later died. The footage sparked outrage at the indifference of other pedestrians and drivers who did not stop to help her. Explore further: Chinese police probe endangered pangolin banquet ||||| Not that you shouldn't already think twice before jaywalking, but now, you have yet another reason to wait for your light. Cities in four Chinese provinces are shaming jaywalkers by posting their personal information on public screens, according to state-owned Xinhua. SEE ALSO: How a university campus is using facial recognition to keep its dorms safe The system's been installed at cities in Shandong and Jiangsu in east China, as well as Fujian and Guangdong in south China, and it uses facial recognition to trace the identities of jaywalkers. Cameras take several snapshots of errant pedestrians, as well as a 15-second video which is then displayed on a large screen: A system in Yancheng, eastern China. Image: Weibo A similar system in Shenzhen. Image: Weibo Facial recognition software matches the faces of errant offenders with those in a provincial police database. A police officer then checks them for their accuracy, and if they pass muster, the offender's photograph and personal information (like portions of their ID number and home address) gets displayed. In some cities, like Jinan, Shandong, traffic police post the identities of errant offenders on social media: The man got a 20 yuan ($2.93) fine. Image: Jinan Traffic Police/Weibo The public shaming has very visible effects — Jinan police told The Paper that being publicly shamed could impact a person's credit rating, as well as their insurance and pension premiums. Offenders get to choose between three forms of punishment — a 20 yuan ($2.93) fine, a 30-minute long traffic safety course and or 20 minutes of assisting police in traffic control. Repeat offenders could be fined up to 100 yuan ($14.64). Police could also inform errant pedestrians' employers and residential communities, said Xinhua. The system in place in Yancheng Image: Weibo The system in place in Jinan Image: The Paper/Tencent Video The public shaming's been naturally effective. Jinan police have caught over 6,200 jaywalkers in the city since the system was set up in May this year, according to The Paper. The number of errant pedestrians has also fallen from 200 per day, to 20 per day, the city's traffic police told Xinhua. "I'll take note and remind myself the next time I cross the road," one resident told The Paper. "After all, it's not a good thing to cross the road while the light is still red." Jinan wants to install the system at 50 more major intersections by the end of June. Each unit will cost the city 100,000 yuan ($14,637). Image: Weibo This isn't the first time China's taken, uh, slightly unusual steps to stop jaywalking before. In April, turnstiles were installed in Wuhan, central China, to stop pedestrians from dashing across the road. The country's also deployed dancing aunties to promote road safety at crosswalks, and in January, a robot police officer was deployed at a traffic junction in Xiangyang, central China to stop errant pedestrians, and tell them off.[/INST]– Jaywalkers take heed: If you do it in parts of China, you could be in for the shaming of your life. Authorities have installed a new device called the "Electronic Police" at intersections in cities in four provinces. Not only does it detect when people are jaywalking, but it snaps photos of the offenders and uses facial recognition tech to pull up their images in the provincial police database, reports RT. Once police confirm a match, the person isn't just flagged for the offense (they can choose whether to pay a fine, take a safety class, or volunteer with traffic police). Their photo and personal details, including parts of their ID number and home address, are displayed on a large screen for all passersby to see. Facial recognition has already been used in China to catch toilet paper thieves in public restrooms and to predict orders at the fast food chain KFC, reports the AFP. But the use of public shaming takes things to a whole new level—one that local police say is proving effective. They say public shaming can go so far as to impact insurance and pension premiums, and police in the city of Jinan say they've caught more than 6,200 people crossing at red lights since installing the system in early May (yes, that's less than two months), with the number of incidents dropping ten-fold from 200 per day to 20. Jinan is looking to install the system at 50 other major intersections by the end of June, each costing the city roughly $15,000, reports Mashable. (Texting pedestrians are hit with fines in parts of New Jersey.)</s>

a 62-year - old , weight 50 kg , height 158 cm woman was scheduled for microdisckectomy for herniated nucleus pulposus at l5s1 . she had a 5-year and 3-year history of type 2 diabetes mellitus ( dm ) and hypertension respectively . her past surgical history was left total knee replacement due to osteoarthritis two years ago . her laboratory examination showed normal fasting serum glucose at 109 mg / dl , platelet 234 10/l , prothrombin time 9.8 sec , activated partial prothrombin time 20.0 sec except rheumatoid factor positive and protein 6.1 g / dl . the patient was taken to a standard american standards association monitor upon arrival in the operating room . anesthetic induction was performed using fentanyl 50 g , lidocaine 40 mg , propofol 100 mg , rocuronium 30 mg and anesthesia was maintained by 2 vol% sevoflurane - o2 2 l / min - n2o 2 l / min . post - induction , a rash was noted on her left arm during inflation of bp cuff , which diminished immediately . the cause of the rash was an initially thought to be due to increased venous pressure , and a transient phenomenon without serious consequences . the patient 's bp stabilized in the prone position , and her arm was covered by a sterilized sheet to prevent a fall in body temperature . during the operation , the patient showed severe bp fluctuations , ranging from 80 - 140/55 - 85 mmhg . for the purpose of maintaining a stable bp and postoperative pain control , we set up patient - controlled analgesia using fentanyl 1,000 g , ketorolac 120 mg and ondansetron 8 mg 20 min before the end of the operation . when the sterilized sheet was removed from the patient at the end of the operation , a severe rash with petechiae on the left arm was noted associated with facial flushing in the supine position ( fig . the patient 's facial flushing diminished in the recovery room . once recovered from anesthesia , the patient did not complain about pain in the affected extremity . petechiae under the bp cuff , even over a short operating duration , are commonly observed . the rumpel - leede ( rl ) phenomenon is the appearance of petechiae in an area following application of pressure on vessels , such as by a tourniquet , for 10 min or less . this technique was used in the past to assess thrombocytopenia and capillary fragility secondary to diabetic microangiopathy . it can be seen in intravenous drug users , and in infectious diseases such as rocky mountain spotted fever , meningococcemia , disseminated intravascular coagulopathy , idiopathic thrombocytopenic purpura , thrombotic thrombocytopenic purpura , fat embolism , dm and in elderly patients . the first and the most likely cause is vascular fragility . the patient could have had microangiopathy caused by dm and steroid use for 6 years for osteoarthritis . facial flushing could also be due to microangiopathy , skin thinning by negative collagen formation in chronic steroid use and vascular stasis by prone position . the second is increased venous pressure during cycling of the bp cuff in a hypertensive state . she did not complain of pain due to postoperative patient - controlled analgesia , but complained of a prolonged rash with petechiae on her left arm . reported a similar case of the rl phenomenon that occurred on the left arm after difficult intubation and uncontrolled high bp . immediately following surgery nibp cuff was moved to the right arm , and a thin cotton roll was placed between the arm and the nibp cuff . after careful nibp monitoring and bp control , no injury occurred to the right arm . devbhandari et al . suggested proper use of the nibp device , as follows : 1 ) avoid wrapping the cuff tightly , 2 ) avoid applying the cuff across a joint , bony prominence or superficial nerve , 3 ) periodically inspect and alternated the cuff site , 4 ) carefully control bp , 5 ) select the maximum cycle time with satisfactory monitoring , 6 ) keep device alarms enabled , 7 ) consider the possibility of a device malfunction and 8) consider use of a thin layer of padding between the bp cuff and the skin . a thin cotton layer significantly reduced cuff - related trauma and there was no significant effect on systolic , mean and diastolic arterial bp . , anesthesiologists should be aware that acute dermal capillary rupture , although rare , can occur in patients with long standing dm , hypertension and chronic steroid use .

we report a case of rumpel - leede ( rl ) phenomenon , - acute dermis capillary rupture , secondary to noninvasive blood pressure ( nibp ) monitoring in a patient with type 2 diabetes mellitus ( dm ) and hypertension . the first most likely cause is vascular fragility in microangiopathy as a result of dm and chronic steroid use . the second is the increased venous pressure during cycling of the blood pressure cuff in a hypertensive state . anesthesiologists need to be aware that acute dermal capillary rupture , although rare , can occur in patients with long - standing dm , hypertension and chronic steroid use .

<s>[INST]a 62-year - old , weight 50 kg , height 158 cm woman was scheduled for microdisckectomy for herniated nucleus pulposus at l5s1 . she had a 5-year and 3-year history of type 2 diabetes mellitus ( dm ) and hypertension respectively . her past surgical history was left total knee replacement due to osteoarthritis two years ago . her laboratory examination showed normal fasting serum glucose at 109 mg / dl , platelet 234 10/l , prothrombin time 9.8 sec , activated partial prothrombin time 20.0 sec except rheumatoid factor positive and protein 6.1 g / dl . the patient was taken to a standard american standards association monitor upon arrival in the operating room . anesthetic induction was performed using fentanyl 50 g , lidocaine 40 mg , propofol 100 mg , rocuronium 30 mg and anesthesia was maintained by 2 vol% sevoflurane - o2 2 l / min - n2o 2 l / min . post - induction , a rash was noted on her left arm during inflation of bp cuff , which diminished immediately . the cause of the rash was an initially thought to be due to increased venous pressure , and a transient phenomenon without serious consequences . the patient 's bp stabilized in the prone position , and her arm was covered by a sterilized sheet to prevent a fall in body temperature . during the operation , the patient showed severe bp fluctuations , ranging from 80 - 140/55 - 85 mmhg . for the purpose of maintaining a stable bp and postoperative pain control , we set up patient - controlled analgesia using fentanyl 1,000 g , ketorolac 120 mg and ondansetron 8 mg 20 min before the end of the operation . when the sterilized sheet was removed from the patient at the end of the operation , a severe rash with petechiae on the left arm was noted associated with facial flushing in the supine position ( fig . the patient 's facial flushing diminished in the recovery room . once recovered from anesthesia , the patient did not complain about pain in the affected extremity . petechiae under the bp cuff , even over a short operating duration , are commonly observed . the rumpel - leede ( rl ) phenomenon is the appearance of petechiae in an area following application of pressure on vessels , such as by a tourniquet , for 10 min or less . this technique was used in the past to assess thrombocytopenia and capillary fragility secondary to diabetic microangiopathy . it can be seen in intravenous drug users , and in infectious diseases such as rocky mountain spotted fever , meningococcemia , disseminated intravascular coagulopathy , idiopathic thrombocytopenic purpura , thrombotic thrombocytopenic purpura , fat embolism , dm and in elderly patients . the first and the most likely cause is vascular fragility . the patient could have had microangiopathy caused by dm and steroid use for 6 years for osteoarthritis . facial flushing could also be due to microangiopathy , skin thinning by negative collagen formation in chronic steroid use and vascular stasis by prone position . the second is increased venous pressure during cycling of the bp cuff in a hypertensive state . she did not complain of pain due to postoperative patient - controlled analgesia , but complained of a prolonged rash with petechiae on her left arm . reported a similar case of the rl phenomenon that occurred on the left arm after difficult intubation and uncontrolled high bp . immediately following surgery nibp cuff was moved to the right arm , and a thin cotton roll was placed between the arm and the nibp cuff . after careful nibp monitoring and bp control , no injury occurred to the right arm . devbhandari et al . suggested proper use of the nibp device , as follows : 1 ) avoid wrapping the cuff tightly , 2 ) avoid applying the cuff across a joint , bony prominence or superficial nerve , 3 ) periodically inspect and alternated the cuff site , 4 ) carefully control bp , 5 ) select the maximum cycle time with satisfactory monitoring , 6 ) keep device alarms enabled , 7 ) consider the possibility of a device malfunction and 8) consider use of a thin layer of padding between the bp cuff and the skin . a thin cotton layer significantly reduced cuff - related trauma and there was no significant effect on systolic , mean and diastolic arterial bp . , anesthesiologists should be aware that acute dermal capillary rupture , although rare , can occur in patients with long standing dm , hypertension and chronic steroid use .[/INST]we report a case of rumpel - leede ( rl ) phenomenon , - acute dermis capillary rupture , secondary to noninvasive blood pressure ( nibp ) monitoring in a patient with type 2 diabetes mellitus ( dm ) and hypertension . the first most likely cause is vascular fragility in microangiopathy as a result of dm and chronic steroid use . the second is the increased venous pressure during cycling of the blood pressure cuff in a hypertensive state . anesthesiologists need to be aware that acute dermal capillary rupture , although rare , can occur in patients with long - standing dm , hypertension and chronic steroid use .</s>

many older people are at risk of cognitive impairment , one of the most disturbing aspects of aging . when these changes in cognitive function are first clinically recognizable , they are often referred to as mild cognitive impairment ( mci ) . mci is considered to be the transitional phase between normal aging and dementia and is recognized as the prodromal stage of alzheimer 's disease ( ad ) . thus , mci is a putative target for the prevention of neurodegenerative disease . the identification of individuals with mci who will progress to ad is a critical issue . longitudinal studies have reported that brain volume decreases by 0.2 - 0.5% each year . among older people experiencing cognitive decline such as mci , the rate of brain volume loss ( notably gray matter volume loss ) is higher than that among healthy older people . numerous studies have demonstrated that mci - related regional gray matter volume loss is most significant in the medial temporal and frontal cortex , including the prefrontal cortex . assessment of gray matter volume may allow early detection of mci and subsequent neurodegenerative disease . scanning mris are not suitable as primary clinical screening to assess gray matter volume since they require money and time , and the assessment of cognitive functioning using neuropsychological tests is more useful in clinical settings . it is well known that the prefrontal cortex plays a crucial role in cognitive functioning and executive functioning in particular . further , there is substantial evidence that different areas of the prefrontal cortex exert different roles in executive control . however , the association between gray matter volume and cognitive dysfunction in patients with mci remains unclear . an understanding of the association between gray matter volume and executive functioning could provide strategies to reduce dementia risk in high - risk populations . the present study examined associations between cognitive performance , specifically executive functioning , and gray matter volume in older people with mci . the sample for this cross - sectional study consisted of 83 community - dwelling older people with mci ( mean age 75.4 years ; 49.4% females ) who consented and completed the baseline assessment of a randomized controlled trial ( rct ; trial registration umin - ctr umin000003662 ) evaluating the effects of multicomponent exercise on cognitive functioning . the ethics committee of the national center for geriatrics and gerontology approved the study protocol . participants enrolled in the rct were aged 65 years and over , community dwelling , and not suffering from dementia . participants who had either a clinical dementia rating of 0 ; a clinical dementia rating of 1 - 3 along with a history of neurological , psychiatric , or cardiac disorders , or other severe health issues ; used donepezil ; showed impairment in basic activities of daily living ; or participated in other research projects were excluded from the rct study . a total of 100 subjects participated in the rct and completed baseline neuropsychological assessments . in the present cross - sectional imaging analysis , mris were performed with a 1.5-tesla system ( magnetom avanto , siemens , germany ) . three - dimensional volumetric acquisition with a t1-weighted gradient echo sequence was then used to produce a gapless series of thin sagittal sections using a magnetization preparation , rapid - acquisition gradient - echo sequence ( repetition time , 1,700 ms ; echo time , 4.0 ms ; flip angle , 15 ; acquisition matrix , 256 256 , and 1.3-mm slice thickness ) . brain tissue volume , normalized for subject head size , was estimated with sienax , which is part of fsl ( fmrib software library , version 5.0 ) . sienax first extracted brain and skull images from the single whole - head input data . the brain image was then affine - registered to mni152 space ( using the skull image to determine the registration scaling ) ; this was done primarily in order to obtain the volumetric scaling factor to be used in normalizing head size . next , tissue type segmentation with partial volume estimation was completed in order to calculate the total volume of brain tissue ( including separate estimates for the volume of gray matter , white matter , peripheral gray matter , and ventricular cerebrospinal fluid ) . we interviewed all participants about their age , gender , body mass index ( bmi ) , and education . in addition , the timed up and go ( tug ) test was used as a mobility assessment . the tug test involves the participant rising from a standard armchair , walking a distance of 3 m at a normal and safe pace , turning around , walking back to the chair , and sitting down again . tug is measured in seconds using a stopwatch . the time taken to complete the tug test was measured twice , and the best - timed trial was used for each participant 's score . global cognition was assessed using the mini - mental state examination ( mmse ) administered by licensed and well - trained clinical speech therapists . the mmse consisted of 11 tasks including the assessment of memory , comprehension , orientation to time and place , praxis , and attention . we assessed three key executive functions , including ( 1 ) set shifting ; ( 2 ) working memory , and ( 3 ) selective attention and conflict resolution . the trail making test ( tmt , parts a and b ) was used to assess set shifting . in tmt part a , participants are asked to draw lines to connect 25 circles numbered from 1 to 25 as quickly as possible . in tmt part b , participants are asked to connect circles containing numbers ( from 1 to 13 ) or letters ( from a to l ) in an alternating numeric , alphabetical order ( 1-a-2-b-3-c- -13-l ) . errors must be corrected immediately and the sequence reestablished . in the japanese version of tmt part b , the amount of time ( in seconds ) it took to complete each task was recorded . we administered forward and backward digit span tests from the wechsler adult intelligence scale - iv in order to assess working memory . both conditions required participants to repeat sequences of verbally presented digits of increasing length ( in either forward or backward order ) . the examiner pronounces a list of digits at a rate of approximately one digit per second , and subjects are required to immediately repeat the list in the same order . if subjects are successful on the second list , a list one digit longer is given , as before . however , if subjects also fail on the second list , the test is ended . the length of the digit sequences gradually increases , starting with a sequence of three numbers ( e.g. , 5 , 8 , 2 ) to a sequence of maximum 9 items ( e.g. , 7 , 1 , 3 , 9 , 4 , 2 , 5 , 6 , 8) . the same procedure is used for the digit span backward task , except that in this case , subjects have to reproduce the sequence of digits in the reverse order and the longest list consists of 8 items . the difference between the forward and backward scores was used as an index of the central executive component of working memory ( ds ) . we used the color- and picture - word stroop test to assess selective attention and conflict resolution . first , participants were instructed to read words printed in black ink out loud ( e.g. , blue ) . finally , they were shown a page with color words printed in incongruently colored ink ( e.g. , the word participants were asked to name the color in which the words were printed ( while ignoring the word itself ) . we recorded the time participants took to complete each condition . the ability to selectively attend and control response output pearson 's correlation coefficients were used to quantify the bivariate associations between gray matter volume and age , bmi , education level , mobility , global cognition , and executive functions . multiple linear regression models were constructed to determine the independent association between executive functioning and gray matter volume . covariates included in the first model were age , gender , bmi , education , and global cognition ( mmse ) . the executive functioning variable(s ) that were significantly related to gray matter volume in the results of pearson 's correlation coefficients were then entered into the second model . the statistical analyses were completed using spss for windows version 17.0 ( spss , chicago , ill . the sample for this cross - sectional study consisted of 83 community - dwelling older people with mci ( mean age 75.4 years ; 49.4% females ) who consented and completed the baseline assessment of a randomized controlled trial ( rct ; trial registration umin - ctr umin000003662 ) evaluating the effects of multicomponent exercise on cognitive functioning . the ethics committee of the national center for geriatrics and gerontology approved the study protocol . participants enrolled in the rct were aged 65 years and over , community dwelling , and not suffering from dementia . participants who had either a clinical dementia rating of 0 ; a clinical dementia rating of 1 - 3 along with a history of neurological , psychiatric , or cardiac disorders , or other severe health issues ; used donepezil ; showed impairment in basic activities of daily living ; or participated in other research projects were excluded from the rct study . a total of 100 subjects participated in the rct and completed baseline neuropsychological assessments . in the present cross - sectional imaging analysis , mris were performed with a 1.5-tesla system ( magnetom avanto , siemens , germany ) . three - dimensional volumetric acquisition with a t1-weighted gradient echo sequence was then used to produce a gapless series of thin sagittal sections using a magnetization preparation , rapid - acquisition gradient - echo sequence ( repetition time , 1,700 ms ; echo time , 4.0 ms ; flip angle , 15 ; acquisition matrix , 256 256 , and 1.3-mm slice thickness ) . brain tissue volume , normalized for subject head size , was estimated with sienax , which is part of fsl ( fmrib software library , version 5.0 ) . sienax first extracted brain and skull images from the single whole - head input data . the brain image was then affine - registered to mni152 space ( using the skull image to determine the registration scaling ) ; this was done primarily in order to obtain the volumetric scaling factor to be used in normalizing head size . next , tissue type segmentation with partial volume estimation was completed in order to calculate the total volume of brain tissue ( including separate estimates for the volume of gray matter , white matter , peripheral gray matter , and ventricular cerebrospinal fluid ) . we interviewed all participants about their age , gender , body mass index ( bmi ) , and education . in addition , the timed up and go ( tug ) test was used as a mobility assessment . the tug test involves the participant rising from a standard armchair , walking a distance of 3 m at a normal and safe pace , turning around , walking back to the chair , and sitting down again . tug is measured in seconds using a stopwatch . the time taken to complete the tug test was measured twice , and the best - timed trial was used for each participant 's score . global cognition was assessed using the mini - mental state examination ( mmse ) administered by licensed and well - trained clinical speech therapists . the mmse consisted of 11 tasks including the assessment of memory , comprehension , orientation to time and place , praxis , and attention . we assessed three key executive functions , including ( 1 ) set shifting ; ( 2 ) working memory , and ( 3 ) selective attention and conflict resolution . these measures are distinct , but moderately correlate with one another . the trail making test ( tmt , parts a and b ) was used to assess set shifting . in tmt part a , participants are asked to draw lines to connect 25 circles numbered from 1 to 25 as quickly as possible . in tmt part b , participants are asked to connect circles containing numbers ( from 1 to 13 ) or letters ( from a to l ) in an alternating numeric , alphabetical order ( 1-a-2-b-3-c- -13-l ) . errors must be corrected immediately and the sequence reestablished . in the japanese version of tmt part b , the amount of time ( in seconds ) it took to complete each task was recorded . we administered forward and backward digit span tests from the wechsler adult intelligence scale - iv in order to assess working memory . both conditions required participants to repeat sequences of verbally presented digits of increasing length ( in either forward or backward order ) . the examiner pronounces a list of digits at a rate of approximately one digit per second , and subjects are required to immediately repeat the list in the same order . if they succeed , a list one digit longer is presented . if they fail , a second list of the same length is presented . if subjects are successful on the second list , a list one digit longer is given , as before . however , if subjects also fail on the second list , the test is ended . the length of the digit sequences gradually increases , starting with a sequence of three numbers ( e.g. , 5 , 8 , 2 ) to a sequence of maximum 9 items ( e.g. , 7 , 1 , 3 , 9 , 4 , 2 , 5 , 6 , 8) . the same procedure is used for the digit span backward task , except that in this case , subjects have to reproduce the sequence of digits in the reverse order and the longest list consists of 8 items . the difference between the forward and backward scores was used as an index of the central executive component of working memory ( ds ) . we used the color- and picture - word stroop test to assess selective attention and conflict resolution . first , participants were instructed to read words printed in black ink out loud ( e.g. , blue ) . finally , they were shown a page with color words printed in incongruently colored ink ( e.g. , the word participants were asked to name the color in which the words were printed ( while ignoring the word itself ) . we recorded the time participants took to complete each condition . the ability to selectively attend and control response output we interviewed all participants about their age , gender , body mass index ( bmi ) , and education . in addition , the timed up and go ( tug ) test was used as a mobility assessment . the tug test involves the participant rising from a standard armchair , walking a distance of 3 m at a normal and safe pace , turning around , walking back to the chair , and sitting down again . tug is measured in seconds using a stopwatch . the time taken to complete the tug test was measured twice , and the best - timed trial was used for each participant 's score . global cognition was assessed using the mini - mental state examination ( mmse ) administered by licensed and well - trained clinical speech therapists . the mmse consisted of 11 tasks including the assessment of memory , comprehension , orientation to time and place , praxis , and attention . we assessed three key executive functions , including ( 1 ) set shifting ; ( 2 ) working memory , and ( 3 ) selective attention and conflict resolution . the trail making test ( tmt , parts a and b ) was used to assess set shifting . in tmt part a , participants are asked to draw lines to connect 25 circles numbered from 1 to 25 as quickly as possible . in tmt part b , participants are asked to connect circles containing numbers ( from 1 to 13 ) or letters ( from a to l ) in an alternating numeric , alphabetical order ( 1-a-2-b-3-c- -13-l ) . errors must be corrected immediately and the sequence reestablished . in the japanese version of tmt part b , the amount of time ( in seconds ) it took to complete each task was recorded . we administered forward and backward digit span tests from the wechsler adult intelligence scale - iv in order to assess working memory . both conditions required participants to repeat sequences of verbally presented digits of increasing length ( in either forward or backward order ) . the examiner pronounces a list of digits at a rate of approximately one digit per second , and subjects are required to immediately repeat the list in the same order . if they succeed , a list one digit longer is presented . if they fail , a second list of the same length is presented . if subjects are successful on the second list , a list one digit longer is given , as before . however , if subjects also fail on the second list , the test is ended . the length of the digit sequences gradually increases , starting with a sequence of three numbers ( e.g. , 5 , 8 , 2 ) to a sequence of maximum 9 items ( e.g. , 7 , 1 , 3 , 9 , 4 , 2 , 5 , 6 , 8) . the same procedure is used for the digit span backward task , except that in this case , subjects have to reproduce the sequence of digits in the reverse order and the longest list consists of 8 items . the difference between the forward and backward scores was used as an index of the central executive component of working memory ( ds ) . we used the color- and picture - word stroop test to assess selective attention and conflict resolution . first , participants were instructed to read words printed in black ink out loud ( e.g. , blue ) . finally , they were shown a page with color words printed in incongruently colored ink ( e.g. , the word participants were asked to name the color in which the words were printed ( while ignoring the word itself ) . we recorded the time participants took to complete each condition . the ability to selectively attend and control response output pearson 's correlation coefficients were used to quantify the bivariate associations between gray matter volume and age , bmi , education level , mobility , global cognition , and executive functions . multiple linear regression models were constructed to determine the independent association between executive functioning and gray matter volume . covariates included in the first model were age , gender , bmi , education , and global cognition ( mmse ) . the executive functioning variable(s ) that were significantly related to gray matter volume in the results of pearson 's correlation coefficients were then entered into the second model . the statistical analyses were completed using spss for windows version 17.0 ( spss , chicago , ill . the results of the correlation coefficient matrix for gray matter volume are given in figure 1 . gray matter volume showed a significantly negative correlation with age ( r = 0.348 , p = 0.001 ) . we found a modest but statistically significant negative correlation with set - shifting performance ( r = 0.414 , p < 0.001 ) . worse performance ( larger tmt ) predicted less gray matter volume . in the multiple linear regression analyses ( table 2 ) , after accounting for covariates including age , gender , bmi , education , and mmse , set - shifting performance ( tmt ) was independently associated with gray matter volume ( standardized = 0.376 , p = 0.001 ) . gray matter volume correlated significantly with set - shifting ability ( less gray matter was associated with worse performance ) . however , we did not find significant correlations with working memory or selective attention and conflict resolution in older people with mci . set shifting requires high - level cognitive ability that includes shifting attention or response patterns based on different rules . performance on set - shifting tests ( such as the tmt ) has been shown to be impaired in patients with frontal lobe lesions , frontal lobe epilepsy , frontal - striatal dysfunction due to basal ganglia lesions , parkinson 's disease , and huntington 's disease . reported that older people with mci and greater annualized atrophy ( e.g. , > 3% per year ) were at much higher risk of ad . thus , brain volume , including gray matter volume , may be a viable sign identifying the risk of progression to ad in older people with mci . in primary health care settings , we recommend set - shifting assessment to reflect gray matter volume ; this assessment may be useful in predicting the risk of dementia in aging populations . higher levels of cognitive functioning such as set shifting could be mediated by a predominantly frontal neural network . set shifting not only relies on brain regions important for cognitive control , but also on brain regions that mediate other fundamental skills critical to good performance , such as visual scanning or motor speed . in the present study , we used tmt to assess the set - shifting ability among older people with mci . previously , tmt has been useful to assess not only set shifting , but also to discriminate individuals destined to convert from mci to ad . . indicated that the ad conversion prediction accuracy of tmt part b reached 64.6% in a longitudinal study . in addition , carlson et al . reported that the decline in executive functioning ( tmt scores ) preceded memory declines associated with progression to ad . according to these previous studies and our findings , tmt to assess set - shifting ability may help in the early detection of those patients with progression to ad . we were therefore unable to investigate causal relationships between gray matter volume and executive functioning . second , we analyzed the gross volume of gray matter rather than a region of interest . cognitive functions ( including executive functioning ) are typically defined by functional localization ; thus , it will be important to further clarify the association between specific cognitive functions and regions of interest in the brain . therefore , additional studies including participants with varying cognitive health will be needed to clarify the relationship between gray matter volume and executive functioning and to characterize dementia - related pathology . finally , we did not investigate the association between gray matter volume and executive functioning according to mci subtypes . the degree of decline in cognitive function varies in nature by mci subtypes ( amnestic vs. non - amnestic , and multiple domain vs. single domain ) . thus , the association between gray matter volume and executive functioning should be investigated in consideration of mci subtypes . our findings suggest that set - shifting performance is positively associated with gray matter volume in older people with mci . set - shifting ability could be more strongly associated with age - related structural brain changes compared to other aspects of executive processes , such as working memory and selective attention and conflict resolution . therefore , we recommend set - shifting assessment to reflect gray matter volume in primary health care settings . there are no financial or personal relationships with other people or organizations that may lead to a conflict of interest .

background / aimsan understanding of the association between gray matter volume and executive functioning could provide strategies to reduce dementia risk in older people with mild cognitive impairment ( mci).methodsin a cross - sectional analysis , we assessed executive functioning in 83 older people with mci using three standard neuropsychological tests : set shifting ( difference between trail making test parts b and a ) , working memory ( difference between digit span forward and backward from the wechsler adult intelligence scale - iv ) , and selective attention / response inhibition ( difference between the second and third conditions of the color- and picture - word stroop test ) . gray matter volume was computed from brain mris and sienax from fsl software.resultsgray matter volume was significantly associated with set - shifting performance after accounting for age , gender , body mass index , education , and global cognition ( standardized = 0.376 , p = 0.001 ) , but not with working memory or selective attention / response inhibition.conclusionthe executive function of set - shifting ability was correlated with gray matter volume in older people with mci .

<s>[INST]many older people are at risk of cognitive impairment , one of the most disturbing aspects of aging . when these changes in cognitive function are first clinically recognizable , they are often referred to as mild cognitive impairment ( mci ) . mci is considered to be the transitional phase between normal aging and dementia and is recognized as the prodromal stage of alzheimer 's disease ( ad ) . thus , mci is a putative target for the prevention of neurodegenerative disease . the identification of individuals with mci who will progress to ad is a critical issue . longitudinal studies have reported that brain volume decreases by 0.2 - 0.5% each year . among older people experiencing cognitive decline such as mci , the rate of brain volume loss ( notably gray matter volume loss ) is higher than that among healthy older people . numerous studies have demonstrated that mci - related regional gray matter volume loss is most significant in the medial temporal and frontal cortex , including the prefrontal cortex . assessment of gray matter volume may allow early detection of mci and subsequent neurodegenerative disease . scanning mris are not suitable as primary clinical screening to assess gray matter volume since they require money and time , and the assessment of cognitive functioning using neuropsychological tests is more useful in clinical settings . it is well known that the prefrontal cortex plays a crucial role in cognitive functioning and executive functioning in particular . further , there is substantial evidence that different areas of the prefrontal cortex exert different roles in executive control . however , the association between gray matter volume and cognitive dysfunction in patients with mci remains unclear . an understanding of the association between gray matter volume and executive functioning could provide strategies to reduce dementia risk in high - risk populations . the present study examined associations between cognitive performance , specifically executive functioning , and gray matter volume in older people with mci . the sample for this cross - sectional study consisted of 83 community - dwelling older people with mci ( mean age 75.4 years ; 49.4% females ) who consented and completed the baseline assessment of a randomized controlled trial ( rct ; trial registration umin - ctr umin000003662 ) evaluating the effects of multicomponent exercise on cognitive functioning . the ethics committee of the national center for geriatrics and gerontology approved the study protocol . participants enrolled in the rct were aged 65 years and over , community dwelling , and not suffering from dementia . participants who had either a clinical dementia rating of 0 ; a clinical dementia rating of 1 - 3 along with a history of neurological , psychiatric , or cardiac disorders , or other severe health issues ; used donepezil ; showed impairment in basic activities of daily living ; or participated in other research projects were excluded from the rct study . a total of 100 subjects participated in the rct and completed baseline neuropsychological assessments . in the present cross - sectional imaging analysis , mris were performed with a 1.5-tesla system ( magnetom avanto , siemens , germany ) . three - dimensional volumetric acquisition with a t1-weighted gradient echo sequence was then used to produce a gapless series of thin sagittal sections using a magnetization preparation , rapid - acquisition gradient - echo sequence ( repetition time , 1,700 ms ; echo time , 4.0 ms ; flip angle , 15 ; acquisition matrix , 256 256 , and 1.3-mm slice thickness ) . brain tissue volume , normalized for subject head size , was estimated with sienax , which is part of fsl ( fmrib software library , version 5.0 ) . sienax first extracted brain and skull images from the single whole - head input data . the brain image was then affine - registered to mni152 space ( using the skull image to determine the registration scaling ) ; this was done primarily in order to obtain the volumetric scaling factor to be used in normalizing head size . next , tissue type segmentation with partial volume estimation was completed in order to calculate the total volume of brain tissue ( including separate estimates for the volume of gray matter , white matter , peripheral gray matter , and ventricular cerebrospinal fluid ) . we interviewed all participants about their age , gender , body mass index ( bmi ) , and education . in addition , the timed up and go ( tug ) test was used as a mobility assessment . the tug test involves the participant rising from a standard armchair , walking a distance of 3 m at a normal and safe pace , turning around , walking back to the chair , and sitting down again . tug is measured in seconds using a stopwatch . the time taken to complete the tug test was measured twice , and the best - timed trial was used for each participant 's score . global cognition was assessed using the mini - mental state examination ( mmse ) administered by licensed and well - trained clinical speech therapists . the mmse consisted of 11 tasks including the assessment of memory , comprehension , orientation to time and place , praxis , and attention . we assessed three key executive functions , including ( 1 ) set shifting ; ( 2 ) working memory , and ( 3 ) selective attention and conflict resolution . the trail making test ( tmt , parts a and b ) was used to assess set shifting . in tmt part a , participants are asked to draw lines to connect 25 circles numbered from 1 to 25 as quickly as possible . in tmt part b , participants are asked to connect circles containing numbers ( from 1 to 13 ) or letters ( from a to l ) in an alternating numeric , alphabetical order ( 1-a-2-b-3-c- -13-l ) . errors must be corrected immediately and the sequence reestablished . in the japanese version of tmt part b , the amount of time ( in seconds ) it took to complete each task was recorded . we administered forward and backward digit span tests from the wechsler adult intelligence scale - iv in order to assess working memory . both conditions required participants to repeat sequences of verbally presented digits of increasing length ( in either forward or backward order ) . the examiner pronounces a list of digits at a rate of approximately one digit per second , and subjects are required to immediately repeat the list in the same order . if subjects are successful on the second list , a list one digit longer is given , as before . however , if subjects also fail on the second list , the test is ended . the length of the digit sequences gradually increases , starting with a sequence of three numbers ( e.g. , 5 , 8 , 2 ) to a sequence of maximum 9 items ( e.g. , 7 , 1 , 3 , 9 , 4 , 2 , 5 , 6 , 8) . the same procedure is used for the digit span backward task , except that in this case , subjects have to reproduce the sequence of digits in the reverse order and the longest list consists of 8 items . the difference between the forward and backward scores was used as an index of the central executive component of working memory ( ds ) . we used the color- and picture - word stroop test to assess selective attention and conflict resolution . first , participants were instructed to read words printed in black ink out loud ( e.g. , blue ) . finally , they were shown a page with color words printed in incongruently colored ink ( e.g. , the word participants were asked to name the color in which the words were printed ( while ignoring the word itself ) . we recorded the time participants took to complete each condition . the ability to selectively attend and control response output pearson 's correlation coefficients were used to quantify the bivariate associations between gray matter volume and age , bmi , education level , mobility , global cognition , and executive functions . multiple linear regression models were constructed to determine the independent association between executive functioning and gray matter volume . covariates included in the first model were age , gender , bmi , education , and global cognition ( mmse ) . the executive functioning variable(s ) that were significantly related to gray matter volume in the results of pearson 's correlation coefficients were then entered into the second model . the statistical analyses were completed using spss for windows version 17.0 ( spss , chicago , ill . the sample for this cross - sectional study consisted of 83 community - dwelling older people with mci ( mean age 75.4 years ; 49.4% females ) who consented and completed the baseline assessment of a randomized controlled trial ( rct ; trial registration umin - ctr umin000003662 ) evaluating the effects of multicomponent exercise on cognitive functioning . the ethics committee of the national center for geriatrics and gerontology approved the study protocol . participants enrolled in the rct were aged 65 years and over , community dwelling , and not suffering from dementia . participants who had either a clinical dementia rating of 0 ; a clinical dementia rating of 1 - 3 along with a history of neurological , psychiatric , or cardiac disorders , or other severe health issues ; used donepezil ; showed impairment in basic activities of daily living ; or participated in other research projects were excluded from the rct study . a total of 100 subjects participated in the rct and completed baseline neuropsychological assessments . in the present cross - sectional imaging analysis , mris were performed with a 1.5-tesla system ( magnetom avanto , siemens , germany ) . three - dimensional volumetric acquisition with a t1-weighted gradient echo sequence was then used to produce a gapless series of thin sagittal sections using a magnetization preparation , rapid - acquisition gradient - echo sequence ( repetition time , 1,700 ms ; echo time , 4.0 ms ; flip angle , 15 ; acquisition matrix , 256 256 , and 1.3-mm slice thickness ) . brain tissue volume , normalized for subject head size , was estimated with sienax , which is part of fsl ( fmrib software library , version 5.0 ) . sienax first extracted brain and skull images from the single whole - head input data . the brain image was then affine - registered to mni152 space ( using the skull image to determine the registration scaling ) ; this was done primarily in order to obtain the volumetric scaling factor to be used in normalizing head size . next , tissue type segmentation with partial volume estimation was completed in order to calculate the total volume of brain tissue ( including separate estimates for the volume of gray matter , white matter , peripheral gray matter , and ventricular cerebrospinal fluid ) . we interviewed all participants about their age , gender , body mass index ( bmi ) , and education . in addition , the timed up and go ( tug ) test was used as a mobility assessment . the tug test involves the participant rising from a standard armchair , walking a distance of 3 m at a normal and safe pace , turning around , walking back to the chair , and sitting down again . tug is measured in seconds using a stopwatch . the time taken to complete the tug test was measured twice , and the best - timed trial was used for each participant 's score . global cognition was assessed using the mini - mental state examination ( mmse ) administered by licensed and well - trained clinical speech therapists . the mmse consisted of 11 tasks including the assessment of memory , comprehension , orientation to time and place , praxis , and attention . we assessed three key executive functions , including ( 1 ) set shifting ; ( 2 ) working memory , and ( 3 ) selective attention and conflict resolution . these measures are distinct , but moderately correlate with one another . the trail making test ( tmt , parts a and b ) was used to assess set shifting . in tmt part a , participants are asked to draw lines to connect 25 circles numbered from 1 to 25 as quickly as possible . in tmt part b , participants are asked to connect circles containing numbers ( from 1 to 13 ) or letters ( from a to l ) in an alternating numeric , alphabetical order ( 1-a-2-b-3-c- -13-l ) . errors must be corrected immediately and the sequence reestablished . in the japanese version of tmt part b , the amount of time ( in seconds ) it took to complete each task was recorded . we administered forward and backward digit span tests from the wechsler adult intelligence scale - iv in order to assess working memory . both conditions required participants to repeat sequences of verbally presented digits of increasing length ( in either forward or backward order ) . the examiner pronounces a list of digits at a rate of approximately one digit per second , and subjects are required to immediately repeat the list in the same order . if they succeed , a list one digit longer is presented . if they fail , a second list of the same length is presented . if subjects are successful on the second list , a list one digit longer is given , as before . however , if subjects also fail on the second list , the test is ended . the length of the digit sequences gradually increases , starting with a sequence of three numbers ( e.g. , 5 , 8 , 2 ) to a sequence of maximum 9 items ( e.g. , 7 , 1 , 3 , 9 , 4 , 2 , 5 , 6 , 8) . the same procedure is used for the digit span backward task , except that in this case , subjects have to reproduce the sequence of digits in the reverse order and the longest list consists of 8 items . the difference between the forward and backward scores was used as an index of the central executive component of working memory ( ds ) . we used the color- and picture - word stroop test to assess selective attention and conflict resolution . first , participants were instructed to read words printed in black ink out loud ( e.g. , blue ) . finally , they were shown a page with color words printed in incongruently colored ink ( e.g. , the word participants were asked to name the color in which the words were printed ( while ignoring the word itself ) . we recorded the time participants took to complete each condition . the ability to selectively attend and control response output we interviewed all participants about their age , gender , body mass index ( bmi ) , and education . in addition , the timed up and go ( tug ) test was used as a mobility assessment . the tug test involves the participant rising from a standard armchair , walking a distance of 3 m at a normal and safe pace , turning around , walking back to the chair , and sitting down again . tug is measured in seconds using a stopwatch . the time taken to complete the tug test was measured twice , and the best - timed trial was used for each participant 's score . global cognition was assessed using the mini - mental state examination ( mmse ) administered by licensed and well - trained clinical speech therapists . the mmse consisted of 11 tasks including the assessment of memory , comprehension , orientation to time and place , praxis , and attention . we assessed three key executive functions , including ( 1 ) set shifting ; ( 2 ) working memory , and ( 3 ) selective attention and conflict resolution . the trail making test ( tmt , parts a and b ) was used to assess set shifting . in tmt part a , participants are asked to draw lines to connect 25 circles numbered from 1 to 25 as quickly as possible . in tmt part b , participants are asked to connect circles containing numbers ( from 1 to 13 ) or letters ( from a to l ) in an alternating numeric , alphabetical order ( 1-a-2-b-3-c- -13-l ) . errors must be corrected immediately and the sequence reestablished . in the japanese version of tmt part b , the amount of time ( in seconds ) it took to complete each task was recorded . we administered forward and backward digit span tests from the wechsler adult intelligence scale - iv in order to assess working memory . both conditions required participants to repeat sequences of verbally presented digits of increasing length ( in either forward or backward order ) . the examiner pronounces a list of digits at a rate of approximately one digit per second , and subjects are required to immediately repeat the list in the same order . if they succeed , a list one digit longer is presented . if they fail , a second list of the same length is presented . if subjects are successful on the second list , a list one digit longer is given , as before . however , if subjects also fail on the second list , the test is ended . the length of the digit sequences gradually increases , starting with a sequence of three numbers ( e.g. , 5 , 8 , 2 ) to a sequence of maximum 9 items ( e.g. , 7 , 1 , 3 , 9 , 4 , 2 , 5 , 6 , 8) . the same procedure is used for the digit span backward task , except that in this case , subjects have to reproduce the sequence of digits in the reverse order and the longest list consists of 8 items . the difference between the forward and backward scores was used as an index of the central executive component of working memory ( ds ) . we used the color- and picture - word stroop test to assess selective attention and conflict resolution . first , participants were instructed to read words printed in black ink out loud ( e.g. , blue ) . finally , they were shown a page with color words printed in incongruently colored ink ( e.g. , the word participants were asked to name the color in which the words were printed ( while ignoring the word itself ) . we recorded the time participants took to complete each condition . the ability to selectively attend and control response output pearson 's correlation coefficients were used to quantify the bivariate associations between gray matter volume and age , bmi , education level , mobility , global cognition , and executive functions . multiple linear regression models were constructed to determine the independent association between executive functioning and gray matter volume . covariates included in the first model were age , gender , bmi , education , and global cognition ( mmse ) . the executive functioning variable(s ) that were significantly related to gray matter volume in the results of pearson 's correlation coefficients were then entered into the second model . the statistical analyses were completed using spss for windows version 17.0 ( spss , chicago , ill . the results of the correlation coefficient matrix for gray matter volume are given in figure 1 . gray matter volume showed a significantly negative correlation with age ( r = 0.348 , p = 0.001 ) . we found a modest but statistically significant negative correlation with set - shifting performance ( r = 0.414 , p < 0.001 ) . worse performance ( larger tmt ) predicted less gray matter volume . in the multiple linear regression analyses ( table 2 ) , after accounting for covariates including age , gender , bmi , education , and mmse , set - shifting performance ( tmt ) was independently associated with gray matter volume ( standardized = 0.376 , p = 0.001 ) . gray matter volume correlated significantly with set - shifting ability ( less gray matter was associated with worse performance ) . however , we did not find significant correlations with working memory or selective attention and conflict resolution in older people with mci . set shifting requires high - level cognitive ability that includes shifting attention or response patterns based on different rules . performance on set - shifting tests ( such as the tmt ) has been shown to be impaired in patients with frontal lobe lesions , frontal lobe epilepsy , frontal - striatal dysfunction due to basal ganglia lesions , parkinson 's disease , and huntington 's disease . reported that older people with mci and greater annualized atrophy ( e.g. , > 3% per year ) were at much higher risk of ad . thus , brain volume , including gray matter volume , may be a viable sign identifying the risk of progression to ad in older people with mci . in primary health care settings , we recommend set - shifting assessment to reflect gray matter volume ; this assessment may be useful in predicting the risk of dementia in aging populations . higher levels of cognitive functioning such as set shifting could be mediated by a predominantly frontal neural network . set shifting not only relies on brain regions important for cognitive control , but also on brain regions that mediate other fundamental skills critical to good performance , such as visual scanning or motor speed . in the present study , we used tmt to assess the set - shifting ability among older people with mci . previously , tmt has been useful to assess not only set shifting , but also to discriminate individuals destined to convert from mci to ad . . indicated that the ad conversion prediction accuracy of tmt part b reached 64.6% in a longitudinal study . in addition , carlson et al . reported that the decline in executive functioning ( tmt scores ) preceded memory declines associated with progression to ad . according to these previous studies and our findings , tmt to assess set - shifting ability may help in the early detection of those patients with progression to ad . we were therefore unable to investigate causal relationships between gray matter volume and executive functioning . second , we analyzed the gross volume of gray matter rather than a region of interest . cognitive functions ( including executive functioning ) are typically defined by functional localization ; thus , it will be important to further clarify the association between specific cognitive functions and regions of interest in the brain . therefore , additional studies including participants with varying cognitive health will be needed to clarify the relationship between gray matter volume and executive functioning and to characterize dementia - related pathology . finally , we did not investigate the association between gray matter volume and executive functioning according to mci subtypes . the degree of decline in cognitive function varies in nature by mci subtypes ( amnestic vs. non - amnestic , and multiple domain vs. single domain ) . thus , the association between gray matter volume and executive functioning should be investigated in consideration of mci subtypes . our findings suggest that set - shifting performance is positively associated with gray matter volume in older people with mci . set - shifting ability could be more strongly associated with age - related structural brain changes compared to other aspects of executive processes , such as working memory and selective attention and conflict resolution . therefore , we recommend set - shifting assessment to reflect gray matter volume in primary health care settings . there are no financial or personal relationships with other people or organizations that may lead to a conflict of interest .[/INST]background / aimsan understanding of the association between gray matter volume and executive functioning could provide strategies to reduce dementia risk in older people with mild cognitive impairment ( mci).methodsin a cross - sectional analysis , we assessed executive functioning in 83 older people with mci using three standard neuropsychological tests : set shifting ( difference between trail making test parts b and a ) , working memory ( difference between digit span forward and backward from the wechsler adult intelligence scale - iv ) , and selective attention / response inhibition ( difference between the second and third conditions of the color- and picture - word stroop test ) . gray matter volume was computed from brain mris and sienax from fsl software.resultsgray matter volume was significantly associated with set - shifting performance after accounting for age , gender , body mass index , education , and global cognition ( standardized = 0.376 , p = 0.001 ) , but not with working memory or selective attention / response inhibition.conclusionthe executive function of set - shifting ability was correlated with gray matter volume in older people with mci .</s>

posterior reversible encephalopathy syndrome ( pres ) is a clinicoradiologic entity which manifests with headache , seizure , altered sensorium . though guillain - barre syndrome ( gbs ) with pres following the intravenous immunoglobulin therapy ( ivig ) had been mentioned , however concurrent occurrences of gbs with pres are rarely reported . here a 63-year - old non - diabetic and non - hypertensive male patient came with complaints of difficulty in walking of five days , inability to do activities of daily living with upper limbs of four days , dysarthria , dysphagia of two days duration , for which he was admitted in the local hospital . on the day of admission he had four generalized tonic - clonic seizures over the interval of 12 h. after the last seizure he did not regain consciousness and was referred to us . history was negative for fever , headache , vomiting , rashes , chronic drug intake or addictions . on examination , for first three days the patient was stuporous with high blood pressure of 192/94 mmhg , flaccid limbs and bilateral plantar extensor . on fourth day , the patient regained consciousness and examination revealed bilateral lower motor neuron type of facial and bulbar weakness , hypotonic limbs with power of 1/5 in muscles of the shoulder , arm , hip , thigh and 2/5 in forearm and leg ( according to mrc grading ) along with the weakness of small muscles of the hand . hemogram , serology , routine biochemistry , chest x - ray , electrocardiogram , echocardiography and abdominal sonography were normal and did not reveal any cause for hypertension . cerebrospinal fluid analysis showed albuminocytological dissociation with 4-lympocytes , 176 mg / dl - of protein and normal sugar . mri brain showed bilateral cortical and subcortical altered signal intensities involving the parieto - occipital areas . they were hypointense on - t1w images , hyperintense on - t2w and flair images with no diffusion restriction suggestive of pres [ figures 1 and 2 ] . nerve conduction studies showed prolonged latencies , reduced conduction velocity and absent f waves with reduction in the amplitude of compound muscle action potentials with normal sensory potentials suggestive of demyelinating type neuropathy according to ho et al . criteria . mri brain axial section flair image showing bilateral parietoccipital hyperintense signals mri brain coronal section flair image showing bilateral parietoccipital hyperintense signals the patient was treated with antihypertensives and antiepileptics initially to control his blood pressure and seizures . after resolution of encephalopathy , ivig was given and his weakness improved over two months . now after 6-months , the patient is ambulatory and is independent in his daily activities . sometimes severe respiratory paralysis may lead to hypoxic brain injury leading to altered sensorium / seizures . in our case , the patient did not have respiratory involvement but still had cluster of seizures with loss of consciousness and imaging was classical of pres . it is the rare combination of gbs with pres before initiation of therapy with ivig may be secondary to dysautonomia . the review of literature shows that the incidence of gbs is 0.75 - 2 cases per-100000 and the incidence of pres is even lower than that . there are few case reports of gbs developing pres , many of them follow after ivig therapy . but , pres developing prior to ivig therapy are very few . with our case report this condition has been designated by a variety of names but pres is now the accepted term . pres can manifest with headache , nausea / vomiting , seizures , altered sensorium , visual abnormalities , and focal neurological deficits . common causes include preeclampsia / eclampsia , septicemia , acute hypertension , exposure to chemotherapeutic drugs and autoimmune disorders like systemic lupus erythematosus , systemic sclerosis , polyarteritis nodosa , wegener 's granulomatosis etc . rarer causes are guillain - barre syndrome , hypomagnesemia , hypercalcemia , tumor - lysis syndrome , porphyria , pheochromocytoma , and cushing syndrome . however regardless of the underlying cause , the main abnormality is cerebral vasogenic edema , the pathogenesis of which is still under debate . one involves impaired cerebral autoregulation responsible for an increase in cerebral blood flow secondary to acute raise in the blood pressure seen in conditions like preeclampsia , eclampsia and autonomic dysfunction , as in our case . whereas the other involves endothelial dysfunction with cerebral hypoperfusion . this hypoperfusion hypothesis may be most relevant to cases of pres associated with cytotoxic therapy . under both hypotheses , the result of the cerebral blood perfusion abnormalities is blood brain barrier dysfunction with cerebral vasogenic edema . the treatment strategy includes general measures , antihypertensives with correction of the underlying cause of pres . permanent neurological deficits can be there but are rare depending on the severity of illness . proposed mechanisms leading to pres in patients of gbs are dysautonomia leading to acute raise in the blood pressure , activation of sympathetic nervous system secondary to pain , ivig therapy and renal decompensation . in our patient , autonomic dysfunction might explain the cause . pres can follow or precede the weakness in the patients of gbs , which followed in our case . there are studies to prove that elevated urinary catecholamines correlate with clinical dysautonomia in gbs and can be used as a biological marker , which was not done in our case . there are no consensus between ivig and plasmapheresis in the patients of gbs developing pres prior to therapy . our case supports the fact that gbs can be considered as an independent risk factor of pres secondary to dysautonomia . failure to recognize or delay the treatment can lead to cerebral infarction or even death . physicians should be aware of such rare coexistence so that early treatment can reduce the mortality and morbidity .

posterior reversible encephalopathy syndrome ( pres ) is a clinicoradiologic entity commonly associated with eclampsia , septicemia , chemotherapeutic drugs etc . concurrent occurrence of guillain - barre syndrome ( gbs ) with pres is a rare entity . dysautonomia is a proposed mechanism for such occurrence . here we present a non - diabetic , non - hypertensive 63-year - old male patient , who came with acute onset flaccid quadriparesis , developing generalized seizures , altered sensorium and raised blood pressure on fifth day of illness . magnetic resonance imaging ( mri ) of brain showed altered signal intensities involving the parieto - occipital areas suggestive of posterior reversible encephalopathy . cerebrospinal fluid analysis showed albuminocytological dissociation , nerve conduction studies revealed demyelinating type of polyneuropathy . the patient was treated with antihypertensives and antiepileptics . after resolution of the encephalopathy , intravenous immunoglobulin ( ivig ) was given . the patient recovered gradually over few months . our case concludes gbs as independent risk factor , for pres may be secondary to dysautonomia and physicians should be aware of such rare coexistence so that early treatment can be done to reduce the mortality and morbidity .

<s>[INST]posterior reversible encephalopathy syndrome ( pres ) is a clinicoradiologic entity which manifests with headache , seizure , altered sensorium . though guillain - barre syndrome ( gbs ) with pres following the intravenous immunoglobulin therapy ( ivig ) had been mentioned , however concurrent occurrences of gbs with pres are rarely reported . here a 63-year - old non - diabetic and non - hypertensive male patient came with complaints of difficulty in walking of five days , inability to do activities of daily living with upper limbs of four days , dysarthria , dysphagia of two days duration , for which he was admitted in the local hospital . on the day of admission he had four generalized tonic - clonic seizures over the interval of 12 h. after the last seizure he did not regain consciousness and was referred to us . history was negative for fever , headache , vomiting , rashes , chronic drug intake or addictions . on examination , for first three days the patient was stuporous with high blood pressure of 192/94 mmhg , flaccid limbs and bilateral plantar extensor . on fourth day , the patient regained consciousness and examination revealed bilateral lower motor neuron type of facial and bulbar weakness , hypotonic limbs with power of 1/5 in muscles of the shoulder , arm , hip , thigh and 2/5 in forearm and leg ( according to mrc grading ) along with the weakness of small muscles of the hand . hemogram , serology , routine biochemistry , chest x - ray , electrocardiogram , echocardiography and abdominal sonography were normal and did not reveal any cause for hypertension . cerebrospinal fluid analysis showed albuminocytological dissociation with 4-lympocytes , 176 mg / dl - of protein and normal sugar . mri brain showed bilateral cortical and subcortical altered signal intensities involving the parieto - occipital areas . they were hypointense on - t1w images , hyperintense on - t2w and flair images with no diffusion restriction suggestive of pres [ figures 1 and 2 ] . nerve conduction studies showed prolonged latencies , reduced conduction velocity and absent f waves with reduction in the amplitude of compound muscle action potentials with normal sensory potentials suggestive of demyelinating type neuropathy according to ho et al . criteria . mri brain axial section flair image showing bilateral parietoccipital hyperintense signals mri brain coronal section flair image showing bilateral parietoccipital hyperintense signals the patient was treated with antihypertensives and antiepileptics initially to control his blood pressure and seizures . after resolution of encephalopathy , ivig was given and his weakness improved over two months . now after 6-months , the patient is ambulatory and is independent in his daily activities . sometimes severe respiratory paralysis may lead to hypoxic brain injury leading to altered sensorium / seizures . in our case , the patient did not have respiratory involvement but still had cluster of seizures with loss of consciousness and imaging was classical of pres . it is the rare combination of gbs with pres before initiation of therapy with ivig may be secondary to dysautonomia . the review of literature shows that the incidence of gbs is 0.75 - 2 cases per-100000 and the incidence of pres is even lower than that . there are few case reports of gbs developing pres , many of them follow after ivig therapy . but , pres developing prior to ivig therapy are very few . with our case report this condition has been designated by a variety of names but pres is now the accepted term . pres can manifest with headache , nausea / vomiting , seizures , altered sensorium , visual abnormalities , and focal neurological deficits . common causes include preeclampsia / eclampsia , septicemia , acute hypertension , exposure to chemotherapeutic drugs and autoimmune disorders like systemic lupus erythematosus , systemic sclerosis , polyarteritis nodosa , wegener 's granulomatosis etc . rarer causes are guillain - barre syndrome , hypomagnesemia , hypercalcemia , tumor - lysis syndrome , porphyria , pheochromocytoma , and cushing syndrome . however regardless of the underlying cause , the main abnormality is cerebral vasogenic edema , the pathogenesis of which is still under debate . one involves impaired cerebral autoregulation responsible for an increase in cerebral blood flow secondary to acute raise in the blood pressure seen in conditions like preeclampsia , eclampsia and autonomic dysfunction , as in our case . whereas the other involves endothelial dysfunction with cerebral hypoperfusion . this hypoperfusion hypothesis may be most relevant to cases of pres associated with cytotoxic therapy . under both hypotheses , the result of the cerebral blood perfusion abnormalities is blood brain barrier dysfunction with cerebral vasogenic edema . the treatment strategy includes general measures , antihypertensives with correction of the underlying cause of pres . permanent neurological deficits can be there but are rare depending on the severity of illness . proposed mechanisms leading to pres in patients of gbs are dysautonomia leading to acute raise in the blood pressure , activation of sympathetic nervous system secondary to pain , ivig therapy and renal decompensation . in our patient , autonomic dysfunction might explain the cause . pres can follow or precede the weakness in the patients of gbs , which followed in our case . there are studies to prove that elevated urinary catecholamines correlate with clinical dysautonomia in gbs and can be used as a biological marker , which was not done in our case . there are no consensus between ivig and plasmapheresis in the patients of gbs developing pres prior to therapy . our case supports the fact that gbs can be considered as an independent risk factor of pres secondary to dysautonomia . failure to recognize or delay the treatment can lead to cerebral infarction or even death . physicians should be aware of such rare coexistence so that early treatment can reduce the mortality and morbidity .[/INST]posterior reversible encephalopathy syndrome ( pres ) is a clinicoradiologic entity commonly associated with eclampsia , septicemia , chemotherapeutic drugs etc . concurrent occurrence of guillain - barre syndrome ( gbs ) with pres is a rare entity . dysautonomia is a proposed mechanism for such occurrence . here we present a non - diabetic , non - hypertensive 63-year - old male patient , who came with acute onset flaccid quadriparesis , developing generalized seizures , altered sensorium and raised blood pressure on fifth day of illness . magnetic resonance imaging ( mri ) of brain showed altered signal intensities involving the parieto - occipital areas suggestive of posterior reversible encephalopathy . cerebrospinal fluid analysis showed albuminocytological dissociation , nerve conduction studies revealed demyelinating type of polyneuropathy . the patient was treated with antihypertensives and antiepileptics . after resolution of the encephalopathy , intravenous immunoglobulin ( ivig ) was given . the patient recovered gradually over few months . our case concludes gbs as independent risk factor , for pres may be secondary to dysautonomia and physicians should be aware of such rare coexistence so that early treatment can be done to reduce the mortality and morbidity .</s>

in its strongest form , gravitational lensing produces unmistakably distorted , amplified , and multiplied images of distant astronomical objects . it is therefore not surprising that the majority of known galaxy - scale gravitational lens systems have been discovered through imaging observations . however , a small number of lenses have been discovered spectroscopically , with the spectrum of a targeted galaxy showing evidence of emission from a background source and follow - up imaging revealing lensing morphology . the three most secure examples are the lensed quasars 2237 + 0305 @xcite and sdss j0903 + 5028 @xcite and the lensed lyman-@xmath0 emitting galaxy 0047@xmath12808 @xcite . several authors have made predictions for the frequency of lensed quasar discoveries in galaxy redshift surveys @xcite . others , inspired by the discovery of 0047@xmath12808 , have undertaken spectroscopic searches for lensed lyman-@xmath0-bright galaxies @xcite . the idea behind such searches is that a massive foreground galaxy should act as an effective gravitational lens of _ any _ object positioned sufficiently far behind it and at small enough impact parameter , and any emission features from such lensed objects should be detectable in the spectra of the foreground galaxy . therefore a search for discrepant emission features in galaxy spectra can potentially lead to a sample of gravitational lens systems that would not be discovered in broadband imaging searches due to faintness of source relative to lens . this `` lenses - looking - for - sources '' approach is complementary to lens searches such as the recently completed cosmic lens all - sky survey ( class ; * ? ? ? * ; * ? ? ? * ) which proceed by targeting sources and looking for evidence of an intervening lens . with its massive scale and quality of data , the spectroscopic component of the sloan digital sky survey ( sdss ) provides an unprecedented opportunity for spectroscopic galaxy - galaxy gravitational lens discovery . this paper presents the first results of such a search within a sample of @xmath251,000 sdss luminous red galaxy ( lrg ) spectra ( * ? ? ? * hereafter e01 ) : a catalog of candidate lensed star - forming galaxies at intermediate redshift . the lens candidates presented in this paper were detected by the presence of not one but ( at least ) three emission lines in the lrg spectra identified as nebular emission from a single background redshift : and two out of the three of h@xmath3 @xmath4 , , and ( all emission - line wavelengths in this paper are vacuum values , in angstroms ) . this implies a maximum redshift of @xmath5 for any candidate lensed galaxies : at higher redshifts , [ o iii ] emission moves off the red end of the sdss spectrograph . the lensing cross section of a particular foreground galaxy is lower for intermediate - redshift sources than high - redshift sources , and in this sense the lens search we describe here is at a disadvantage relative to searches for lensed high - redshift lyman-@xmath0 emitters however , the identities of the emission lines in the sample we present here are absolutely unambiguous . this can not be said for spectroscopic lyman-@xmath0 lens candidates , which are typically detected as single discrepant emission lines and are difficult to distinguish from lower - redshift emission or ( in the case of a huge survey such as the sdss ) non - astrophysical spectral artifacts . ( a forthcoming paper will present sdss single - line [ o ii ] and lyman-@xmath0 lens candidates . ) our spectroscopic lens search based on multiple - line detection has further advantages . first , the source redshift of any lensed galaxies will be known from the outset . second , for a given limiting line flux , star - forming galaxies at intermediate redshift are more numerous on the sky than lyman-@xmath0 emitters at high redshift ( see * ? ? ? * ; * ? ? ? * ) , and hence strong lensing events could be more frequent despite decreased lensing cross sections . the non - lensed source population should thus be more amenable to study and characterization ( * ? ? ? * for example ) , facilitating lens statistical analysis . finally , intermediate - redshift lensed galaxies would probe the mass distribution of the lens population in a systematically different manner than do high - redshift sources . the search for new lens systems is motivated by the unique power of gravitational lensing to constrain the mass distribution of the lensing galaxy . @xcite argued that strong galaxy - galaxy gravitational lenses in the optical band should be both ubiquitous and of great scientific interest , but their detection has proved difficult . in addition to the optical einstein ring 0047@xmath12808 mentioned above , @xcite have published one more spectroscopic galaxy - lens candidate . _ hubble space telescope _ ( _ hst _ ) imaging has also had some success in detecting lensed galaxies , as described by @xcite , @xcite , and @xcite , but spectroscopic confirmation remains a challenge in most cases . lensed galaxies are especially useful for investigating the mass distribution of the lensing galaxy because unlike lensed quasars they are spatially resolved sources which provide more detailed constraints ( * ? ? ? * for example ) . as with lensed quasars , the relative angular deflections between multiple images can constrain the total deflecting lens mass . but the relative distortions of multiple images can provide constraints as well , probing the slope of the radial mass profile and allowing more detailed connection with theories of galaxy formation and cold dark matter ( cdm ) . the promise of our candidate sample is enhanced by the fact that lens _ and _ source redshifts for any confirmed lens systems will be known from the outset with great precision ; this is generally not the case for lenses discovered in optical imaging or radio data . the lack of sufficient lensing constraints on the radial slope of the galaxy mass profile in lensed quasar systems is the greatest source of uncertainty in the hubble constant ( @xmath6 ) values derived from the time delays between images @xcite , which remain systematically low compared to the current best @xmath6 values from the distance ladder @xcite and cosmic microwave background @xcite ; @xcite highlights the importance of resolving this discrepancy . any galaxy - galaxy lenses confirmed within our current list of candidates would help to solve this problem by expanding the sample for ensemble lensing studies of early - type galaxy mass profiles like that of @xcite and allowing for the inclusion of distortion information as mentioned above . the generally lower lens and source redshifts of our candidate systems as compared to known lens systems are also of particular interest because the images of any strong lenses within our sample will tend to form at smaller _ physical _ radii within the lens galaxy than in current lens systems ( see * ? ? ? * table 1 ) , thus probing elliptical galaxy mass profiles in a systematically different manner1231 , has @xmath7 @xcite . ] . a large enough sample of strongly lensed star - forming galaxies could even be monitored directly for supernovae . multiple images of the same supernova would give time delays and @xmath6 measurements , as numerous authors have envisioned @xcite . if we assume one supernova per galaxy per century as an order - of - magnitude estimate @xcite , a program to monitor @xmath8 lensed galaxies for several years would have a good chance of success . numerous studies have addressed the inability of standard macroscopic galaxy mass models to predict the flux ratios observed between images of strongly lensed quasars . some authors have suggested that this phenomenon may be due to the effects of substructure in the lensing galaxy on the scale of either cdm sub - halos @xcite or stars @xcite , while others have invoked macroscopically modified lens models as a possible explanation @xcite . a sizeable sample of strongly lensed galaxies would provide valuable insight into this problem : by virtue of the arcsecond - scale intrinsic angular size of the source , galaxy - galaxy lenses will be immune to the lensing effects of any substructure with lensing deflection angles on the scale of microarcseconds ( stars ) or milliarcseconds ( sub - halos ) . if the suppressed saddle point image fluxes seen in many quasar lenses are indeed due to macroscopic inadequacies in the standard lens models , similar effects should be seen in galaxy - galaxy lenses . if on the other hand these effects are due to micro / millilensing by substructure , they should be absent from lensed galaxy systems . the sloan digital sky survey is a project to image roughly one - quarter of the sky in five optical bands and obtain spectroscopic follow - up observations of @xmath9 galaxies and @xmath10 quasars . @xcite provide a technical summary of the survey , @xcite describe the sdss camera , @xcite , @xcite , and @xcite discuss the photometric system and calibration , @xcite discuss sdss astrometry , @xcite present the spectroscopic plate tiling algorithm , and @xcite and @xcite describe the survey data products . approximately 12% of the galaxy spectroscopic fibers are allocated to the lrg sample ( e01 ) , selected to consist of very luminous ( @xmath11)and hence massive early - type galaxies at higher redshift than the galaxies of the main sample @xcite . we expect these lrgs to be particularly effective gravitational lenses of any objects positioned suitably behind them , and we concentrate our spectroscopic lens search on them . we also note that lrgs should have little dust and therefore any lensed background galaxies should suffer minimal extinction . the sample for our current study consists of 50996 spectra taken between 5 march 2000 and 27 may 2003 of sdss imaging objects flagged as galaxy_red by the photometric pipeline @xcite for passing either of the lrg cuts described by e01 , reduced by the sdss spectroscopic pipeline ( j. frieman et al . , in preparation ) , and selected to have redshifts between 0.15 and 0.65 as determined by the specbs redshift - finding software ( d. j. schlegel et al . , in preparation ) . the low - redshift cutoff is needed because less massive galaxies start to pass the photometric cuts below @xmath12 and pollute the volume - limited lrg sample ; see the discussion in e01 and the bimodal lrg sample redshift histogram in ( * ? ? ? in addition to being much more massive than the average galaxy , lrgs have another property that makes them well suited to a spectroscopic lens survey : their spectra are extremely regular and well - characterized ( see * ? ? ? * ) . to determine the spectroscopic redshift of an sdss target galaxy with observed specific flux @xmath13 and one - sigma sky@xmath14source noise spectrum @xmath15 , the specbs program employs a small set of galaxy eigenspectra ( four in the reductions for this study ) derived from a rest - frame principal - component analysis ( pca ) of 480 galaxy spectra taken on sdss plate 306 , mjd 51690 this eigenbasis is incrementally redshifted , and a model spectrum is generated from the best - fit linear combination to the observed spectrum at each trial redshift , with the final redshift assignment given by the trial value that yields the overall minimum @xmath16 . although redshift is the primary output of this procedure , a byproduct of specbs is the best - fit model spectrum itself , @xmath17 . in the case of lrgs , @xmath17 typically provides a very detailed and accurate fit to @xmath13 , with a reduced @xmath16 of order unity over almost 4000 spectral pixels ( roughly 1600 spectral resolution elements ) attained with only 8 free parameters : a redshift , the four eigen - galaxy coefficients , and the three terms of a quadratic polynomial to fit out spectrophotometric errors and extinction effects , both of which exist at the few - percent level . this extremely regular spectral behavior allows us to form residual lrg spectra @xmath18 that are in principle realizations of @xmath15 . nebular emission lines from galaxies along the line of sight other than the target lrg will not be modeled by specbs and should appear as significant features localized in wavelength within these residual spectra . figure [ noise_spec ] shows the median 1-@xmath19 line flux sensitivity within our lrg residual spectrum sample as a function of wavelength . the ( 20th , 50th , 80th)-percentile lrg spectra themselves have a median signal - to - noise per pixel of ( 3.3 , 5.1 , 9.6 ) at the sdss resolution of @xmath20 . this section describes our candidate selection routine in detail . briefly stated , we select as initial candidates those spectra that show _ both _ blended at @xmath21 _ and _ two out of the three lines h@xmath3 @xmath4 , , and at @xmath22 , then cull the candidate list by applying cuts based on more detailed fits to the presumed emission features , and finally remove any obviously spurious detections . this selection process yields a substantial number of promising systems without an excess of obvious false positives . the key element in the first step of our lens candidate selection ( described fully in [ select ] below ) is a straightforward matched - filtering procedure to search for significant emission features by fitting a gaussian line profile at each point in the residual spectrum @xcite . we describe our implementation here so as to be explicit . let @xmath23 be the residual flux in pixel @xmath24 and @xmath25 be the statistical variance of @xmath23 . s@xmath26 @xmath26 to units of ergs @xmath27 s@xmath26 pixel@xmath26 is made using the re - binned sdss spectroscopic pixel scale relation @xmath28 . ] also let @xmath29 describe a gaussian kernel , centered on @xmath30 , with @xmath31 running from @xmath32 to @xmath33 , and normalized such that @xmath34 . the maximum - likelihood estimator @xmath35 for the line flux @xmath36 of any @xmath29-shaped residual emission feature centered on pixel @xmath24 is that which minimizes @xmath37 differentiating ( [ chi2 ] ) with respect to @xmath36 , setting the resulting expression to zero , and solving yields @xmath38 where we have defined the convolutions @xmath39 the variance of @xmath35 ( under the assumption of uncorrelated gaussian errors in @xmath23 as described by @xmath25 ) is given by @xmath40 the signal - to - noise ratio for a fitted gaussian profile centered on pixel @xmath24 is therefore @xmath41 our null hypothesis is an absence of emission features in the residual spectra that should manifest as the @xmath42 being gaussian - distributed about zero with unit variance : this should hold at most wavelengths in most spectra . we approach the initial search for emission lines in the residual spectra as a search for significance peaks with @xmath43 greater than some threshold value . although insensitive to goodness - of - fit , this convolution - based detection scheme executes quickly and is therefore well suited to the initial search for residual emission features within our large spectral sample . appendix [ noisemodel ] describes a noise - rescaling process that we employ to control the incidence of false - positive emission - feature detections ( due primarily to imperfect sky subtraction ) without masking regions of the spectrum . multiple emission features at the same redshift will have redshift - independent wavelength ratios . the fully reduced sdss spectra have been re - binned at a constant - velocity pixel scale of 69 km s@xmath26 , giving a redshift - independent pixel offset between features . our operational scheme is thus to search for coincident @xmath43 peaks between multiple copies of a single filtered residual spectrum that have been shifted relative to one another . for detection , we filter each residual spectrum with a @xmath44-pixel gaussian kernel ( matched to the typical width of blended emission seen in sdss starburst galaxies ) . we take copies of the same residual spectrum `` blueshifted '' by integer pixel amounts so as to place h@xmath45 @xmath46 , h@xmath47 @xmath48 , h@xmath3 @xmath4 , , , @xmath49 , h@xmath0 @xmath50 , @xmath51 , @xmath52 , and @xmath53 as close as possible to 3728.48 , the geometric - mean wavelength of the doublet . these shifted spectra are filtered with a @xmath54-pixel gaussian kernel ( matched to the typical width of sdss starburst emission ) , with the sub - pixel part of the line offset relative to 3728.48 incorporated by offsetting the kernel . any pixel in the filtered @xmath55 spectra with value greater than 3 for and value greater than 2.5 for two out of h@xmath3 @xmath4 , , and is tagged as a `` hit '' . a group of adjacent `` hit '' pixels is reduced to the single pixel with the greatest quadrature - sum @xmath55 for lines detected above the threshold ( in effect , the pixel most inconsistent with the null hypothesis ) . spectra with more than one isolated hit are rejected . the spectra are only searched in regions that would correspond to emission from @xmath56 km s@xmath26 behind the targeted lrg . the preceding selection leads to 163 hits within our 51,000 spectra . for each hit , we explore a grid of redshift and intrinsic emission - line - width values for the background galaxy to find a best - fit model . at each grid point we fit a gaussian profile to any emission line initially detected above a 2.0-@xmath55 threshold , with the line center determined by the trial redshift and line - width given by the quadrature sum of the trial intrinsic line - width and the measured spectrograph resolution at the observed wavelength of each line . is fit with a double gaussian profile . we adopt as best values for background redshift @xmath57 and ( gaussian-@xmath19 ) intrinsic line - width @xmath58 those that give the minimum @xmath16 over all detected lines . the @xmath57 extent of our grid corresponds to @xmath592 pixels , and the explored @xmath58 range runs from 0 to 2 pixels ( 0 to 138 km s@xmath26 ) . following these fits , we subject the candidate sample to several cuts . first , we reject any system where no convergent ( minimum @xmath16 ) value for @xmath57 is found within the explored @xmath592-pixel range : real background emission systems should have convergent best - fit redshifts roughly coincident with their convolution - based @xmath55 peaks . similarly , we cut systems with no convergent @xmath58 between 0 and 2 pixels : the features of real systems should neither be narrower than the spectrograph resolution nor wider than a reasonable upper limit for emission features of faint star - forming galaxies . finally , we compute a total signal - to - noise ratio for the fit , defined as the total best - fit flux in and all other lines initially detected at @xmath60 divided by the quadrature - sum of the 1-@xmath19 noise from those line fits , and impose a cut in the total-@xmath55@xmath61 plane ( @xmath61 being the @xmath16 per degree of freedom in the fit ) . we cut any system with a total @xmath55 less than the greater of 6 and @xmath62 . this removes both low-@xmath55 candidates and candidates whose @xmath61 values are too high to be explained by high-@xmath55 emission features showing significant non - gaussian structure . ( these cuts were designed to be a quantitative expression of our own judgements about which candidate systems look real upon spectrum inspection and which do not ; the justifications are somewhat _ a posteriori_. ) this cutting procedure reduces the 163 hits to 61 candidate systems . finally , we prune 12 candidates from the list that survive the automated culling but are clearly explained by either over - fit lrg stellar absorption , under - modeled lrg line emission , exceptionally poor data quality , or a generally flawed template fit , leaving the 49 good candidate systems that we present . this search for background galaxy emission lines digs rather deep into the noise of our spectroscopic sample . to gauge the incidence of false positives in our final candidate list , we make a parallel run of the detection , fitting , and automated rejection procedure with the following rest - wavelength perturbations : h@xmath3 @xmath4 @xmath63 4833 , @xmath63 4945 , and @xmath63 5023 . these perturbations alter all of the redshift - independent wavelength ratios among these lines and between all of them and ; this modified detection procedure no longer selects for real multi - line emission , but only for noise features . the `` false candidates '' that result from this perturbed procedure are randomly shuffled along with the candidates from the original procedure , and all are examined together when making the final pruning judgements . the perturbed procedure yields 88 hits and 7 post - cut candidates ; all 7 are pruned upon inspection without knowledge of their intrinsic falseness . this implies that the vast majority of our candidates are indeed background galaxies and not simply noise features . lcccccccclc & 0390 - 51900 - 589 & y & [email protected] & 0.3979 & 286@xmath5919 & 0.5952 & 1.39 & 20 @xmath59 2 & d , e & 11.6 + & 0689 - 52262 - 632 & n & [email protected] & 0.2017 & 176@xmath5921 & 0.2708 & 0.43 & 19 @xmath59 3 & c , e , g , h , i & 10.8 + & 0655 - 52162 - 392 & y & [email protected] & 0.1955 & 279@xmath5910 & 0.6322 & 2.94 & 23 @xmath59 4 & a , c , d , e & 16.0 + & 0422 - 51811 - 508 & y & [email protected] & 0.2939 & 251@xmath5919 & 0.5248 & 1.47 & 19 @xmath59 3 & c , d , e & 10.2 + & 0694 - 52209 - 076 & n & [email protected] & 0.4516 & 86@xmath5925 & 0.5011 & 0.04 & 19 @xmath59 2 & c , e & 11.6 + & 0668 - 52162 - 428 & y & [email protected] & 0.3317 & 333@xmath5923 & 0.5235 & 2.13 & 25 @xmath59 4 & c , d & 8.7 + & 0414 - 51869 - 244 & y & [email protected] & 0.4453 & 267@xmath5935 & 0.6240 & 1.03 & 22 @xmath59 2 & b , c , d , e & 16.5 + & 0541 - 51959 - 145 & n & [email protected] & 0.3223 & 338@xmath5916 & 0.5812 & 2.67 & 62 @xmath59 5 & a , b , c , d , e & 24.7 + & 0860 - 52319 - 452 & n & [email protected] & 0.3200 & 334@xmath5917 & 0.3809 & 0.94 & 54 @xmath59 4 & c , e , g , h & 17.0 + & 0468 - 51912 - 362 & y & [email protected] & 0.4114 & 251@xmath5941 & 0.5672 & 0.88 & 12 @xmath59 4 & d , e & 6.2 + & 0472 - 51955 - 429 & y & [email protected] & 0.1642 & 326@xmath5912 & 0.3240 & 2.90 & 26 @xmath59 4 & b , c , e , g & 11.5 + & 0870 - 52325 - 465 & n & [email protected] & 0.2908 & 198@xmath5924 & 0.4538 & 0.75 & 29 @xmath59 4 & d , e & 9.4 + & 0476 - 52314 - 177 & n & [email protected] & 0.3475 & 396@xmath5935 & 0.4670 & 2.10 & 15 @xmath59 3 & c , e & 8.8 + & 0902 - 52409 - 068 & n & [email protected] & 0.2405 & 334@xmath5915 & 0.4700 & 2.94 & 31 @xmath59 3 & c , e & 11.5 + & 0996 - 52641 - 106 & n & [email protected] & 0.3475 & 183@xmath5922 & 0.4797 & 0.48 & 18 @xmath59 3 & c , e & 7.9 + & 0272 - 51941 - 151 & y & [email protected] & 0.1589 & 264@xmath5911 & 0.2764 & 1.64 & 18 @xmath59 3 & d , e , g , i & 14.6 + & 0772 - 52375 - 140 & n & [email protected] & 0.1574 & 228@xmath5914 & 0.2512 & 1.08 & 31 @xmath59 5 & c , e , f , g , h , i & 18.7 + & 1002 - 52646 - 504 & n & [email protected] & 0.2058 & 217@xmath5917 & 0.5809 & 1.65 & 52 @xmath59 11 & c , e & 6.1 + & 0951 - 52398 - 036 & n & [email protected] & 0.3809 & 223@xmath5928 & 0.5466 & 0.78 & 29 @xmath59 4 & c , d , e & 11.2 + & 0328 - 52282 - 350 & n & [email protected] & 0.3936 & 321@xmath5927 & 0.4646 & 0.81 & 9 @xmath59 3 & c , d , e & 8.9 + & 0598 - 52316 - 477 & n & [email protected] & 0.3804 & 260@xmath5927 & 0.5435 & 1.05 & 14 @xmath59 3 & c , e & 6.5 + & 0777 - 52320 - 501 & n & [email protected] & 0.3751 & 303@xmath5934 & 0.6690 & 2.08 & 16 @xmath59 4 & d , e & 7.5 + & 0494 - 51915 - 074 & y & [email protected] & 0.2312 & 238@xmath5910 & 0.4446 & 1.47 & 16 @xmath59 2 & c , e & 10.5 + & 0783 - 52325 - 279 & n & [email protected] & 0.2334 & 253@xmath5916 & 0.4488 & 1.67 & 23 @xmath59 3 & c , e & 10.6 + & 0602 - 52072 - 332 & y & [email protected] & 0.3050 & 300@xmath5924 & 0.3300 & 0.36 & 16 @xmath59 3 & c , e , g , j & 12.0 + & 0784 - 52327 - 350 & n & [email protected] & 0.1984 & 226@xmath5912 & 0.5141 & 1.71 & 16 @xmath59 5 & c , e & 6.6 + & 0298 - 51955 - 001 & y & [email protected] & 0.3496 & 111@xmath5912 & 0.4425 & 0.14 & 18 @xmath59 3 & d , e & 8.4 + & 0605 - 52353 - 503 & n & [email protected] & 0.2046 & 267@xmath5917 & 0.4814 & 2.23 & 10 @xmath59 3 & d , e & 9.6 + & 0606 - 52365 - 315 & n & [email protected] & 0.2971 & 428@xmath5921 & 0.3556 & 1.60 & 17 @xmath59 3 & c , e , g , h , j & 13.9 + & 1045 - 52725 - 464 & n & [email protected] & 0.2987 & 240@xmath5925 & 0.8115 & 1.92 & 26 @xmath59 2 & c , d & 7.7 + & 0307 - 51663 - 065 & y & [email protected] & 0.3717 & 349@xmath5928 & 0.4404 & 0.99 & 40 @xmath59 3 & c , d , e & 15.8 + & 0615 - 52347 - 311 & y & [email protected] & 0.2042 & 174@xmath5916 & 0.4857 & 0.96 & 30 @xmath59 4 & c , e & 12.1 + & 0315 - 51663 - 143 & y & [email protected] & 0.2992 & 300@xmath5935 & 0.4317 & 1.46 & 19 @xmath59 3 & b , c , e & 9.9 + & 0617 - 52072 - 561 & y & [email protected] & 0.1883 & 254@xmath5912 & 0.3956 & 1.85 & 27 @xmath59 4 & c , e , g , h & 8.5 + & 0618 - 52049 - 123 & y & [email protected] & 0.4564 & 345@xmath5952 & 0.5388 & 0.92 & 8 @xmath59 2 & c , e & 6.8 + & 0364 - 52000 - 084 & y & [email protected] & 0.2076 & 290@xmath5914 & 0.5241 & 2.76 & 29 @xmath59 3 & c , e & 12.5 + & 0626 - 52057 - 518 & y & [email protected] & 0.2479 & 276@xmath5916 & 0.7933 & 2.81 & 21 @xmath59 3 & d , e & 10.1 + & 0973 - 52426 - 464 & n & [email protected] & 0.1785 & 256@xmath5914 & 0.4357 & 2.12 & 23 @xmath59 5 & d , e & 9.2 + & 0353 - 51703 - 121 & y & [email protected] & 0.2437 & 78@xmath5920 & 0.3776 & 0.12 & 9 @xmath59 2 & c , e , g & 8.5 + & 0635 - 52145 - 290 & y & [email protected] & 0.2677 & 264@xmath5928 & 0.6672 & 2.23 & 10 @xmath59 3 & c , d & 6.0 + & 0982 - 52466 - 602 & n & [email protected] & 0.2107 & 320@xmath5917 & 0.4635 & 3.04 & 10 @xmath59 2 & c , d & 6.5 + & 0731 - 52460 - 165 & n & [email protected] & 0.2290 & 224@xmath5914 & 0.3964 & 1.14 & 14 @xmath59 3 & c , d , e , g & 15.3 + & 0641 - 52199 - 021 & y & [email protected] & 0.3090 & 201@xmath5921 & 0.6306 & 1.08 & 11 @xmath59 2 & d , e & 7.9 + & 0371 - 52078 - 307 & n & [email protected] & 0.4892 & 379@xmath5936 & 0.6029 & 1.35 & 12 @xmath59 2 & a , c , e & 8.3 + & 0724 - 52254 - 277 & n & [email protected] & 0.4719 & 414@xmath5947 & 0.6238 & 2.09 & 14 @xmath59 2 & c , e & 9.7 + & 0677 - 52606 - 520 & n & [email protected] & 0.2285 & 279@xmath5917 & 0.4635 & 2.13 & 19 @xmath59 3 & c , e & 9.5 + & 0743 - 52262 - 304 & n & [email protected] & 0.1553 & 255@xmath5916 & 0.5170 & 2.51 & 13 @xmath59 3 & c , e & 8.1 + & 0385 - 51877 - 596 & y & [email protected] & 0.1858 & 229@xmath5914 & 0.2718 & 0.91 & 53 @xmath59 4 & d , e , g , h , i , j & 16.6 + & 0684 - 52523 - 311 & n & [email protected] & 0.4169 & 404@xmath5959 & 0.7146 & 3.47 & 30 @xmath59 3 & c , e & 12.7 + [ galtable ] in this section we present our catalog of 49 candidate lensed star - forming galaxies selected to have emission at @xmath55 of 3 or higher and emission from two out of the three of h@xmath3 @xmath4 , , and each at @xmath55 of 2.5 or higher , at a redshift significantly greater than that of the primary target lrg . table [ galtable ] lists various properties of the candidate lens systems . lrg @xmath64 de vaucouleurs model magnitudes are determined from sdss imaging and photometric reduction . lrg redshifts and velocity dispersions are as provided by specbs ; the software fits for velocity dispersions @xmath65 using a set of 24 stellar eigenspectra derived from a pca of the elodie spectral library @xcite . we report all @xmath65 values from the database , although some are likely unreliable ; see the notes of table [ galtable ] . we also report emission - line redshifts of the detected background galaxies . using the observed lrg and background redshifts and the observed lrg @xmath65 , and assuming a singular isothermal sphere ( sis ) lrg luminous@xmath14dark matter distribution , we calculate a `` best guess '' for the angular scale of any lensing that might be present in these systems as @xmath66 . ( @xmath67 and @xmath68 are angular - diameter distances from lens to source and from observer to source and a hubble constant @xmath6 of 70 km s@xmath26 mpc@xmath26 . since @xmath69 is proportional to a distance ratio , it is independent of @xmath6 . ] ) . this is the separation between the two images of a strongly lensed object in the sis model ; it is also the radius of the strong - lensing region of the image plane , and twice the radius of ring images of compact sources directly behind the lens ( * ? ? ? * for example ) . finally , for each candidate system we report the detected background line flux from the best - fit double gaussian profile , a list of other lines detected at @xmath22 , and the total @xmath55 of the background galaxy emission - line fit as defined in [ select ] . the reported background line fluxes should be viewed with suspicion : the spatial alignments of the background galaxies are unknown , and the spectroscopic fibers will not necessarily have captured all of their light . in addition , most of the reduced candidate lrg spectra have been rescaled based on smear exposures that attempt to account for lrg flux falling outside the @xmath70 fiber @xcite ; we have removed this correction from the tabulated line fluxes , as it has no physical relation to the background emission - line galaxies . figure [ spectra ] shows the sdss discovery spectra and best - fit model spectra , along with close - up views of the residual ( data @xmath1 model ) spectra in the wavelength ranges corresponding to redshifted background , h@xmath3 @xmath4 , , and . smear corrections have not been removed from these plots . although we detect line emission clearly , evidence of background galaxy _ continuum _ in the residual spectra of our candidate systems is scarce . this is not surprising , for three reasons . one , the lrg sample was selected for particular broadband color and luminosity , and significant background continuum would likely perturb an lrg out of the sample . two , any faint background continuum present in an lrg spectrum will largely project onto the lrg - redshift eigenspectrum set and low - order polynomial fit used by specbs , and will be subtracted along with the lrg model when forming the residual spectrum . three , these background galaxies are likely to be high - equivalent - width star - forming systems , and since their line fluxes are detected just above the noise threshold , the associated continuum will typically be lost in the noise . nevertheless , we may obtain a higher signal - to - noise picture of the background galaxies that we detect by constructing a median spectrum as follows . first we transform the residual spectra of our candidate systems into units of erg @xmath27 s@xmath26 pixel@xmath26 , which is a redshift - independent quantity since the sdss pixels are of constant velocity width . we then shift these residual spectra into the rest frame of the background galaxy , rounded to the nearest whole pixel , and transform back to erg @xmath27 s@xmath26 @xmath26 . next we renormalize the spectra by dividing each one by its best - fit -flux value . we then take the median value at each pixel , and restore physical normalization by multiplying this median spectrum by the sample - median best - fit -flux value . the resulting median spectrum is shown in figure [ medspec ] . although there is no discernible continuum in the individual residual spectra , we can see a 4000-continuum break in the median spectrum ; we also see h@xmath47 , h@xmath0 , [ n ii ] and [ s ii ] emission lines in addition to the lines for which we select . this gives further evidence that we have successfully detected and identified background emission features . we have with certainty detected emission from galaxies behind foreground lrgs . for a system to be a strong gravitational lens , the background galaxy must be located at sufficiently small impact parameter relative to the lrg center . the true incidence of lensing within our sample can best be determined and studied with either narrow - band imaging or integral - field spectroscopy . such observations could spectrally isolate the background line flux and resolve it spatially to reveal any lensing morphology . sdss broadband imaging offers some hope for answering the lensing question , but in general sloan images do not detect late - type galaxies at redshift @xmath71 at very high @xmath55 . figure [ ims ] shows @xmath72 sdss @xmath64 postage - stamp images centered on the candidate systems , with linear gray - scaling from @xmath73-@xmath19 sky noise to peak lrg surface brightness . evidence of significantly offset neighboring broadband emission is seen in some images , but it would be difficult to rule out many systems as definite non - lenses based on sdss - quality images . in the spirit of a purely spectroscopic survey , we present as candidates all systems selected spectroscopically . furthermore , we note that many of these lrgs live in high - density group / cluster environments , and neighboring images may be at the lrg redshift and not the source of the background emission that we detect . in preparation for integral - field spectroscopic follow - up , we have obtained broadband reconnaissance images of 14 of our candidate systems ( as indicated in table [ galtable ] ) using the magellan consortium s 6.5-m clay telescope at las campanas observatory . these short @xmath74- and @xmath31-band exposures ( 120s each ) were taken on the nights of 2003 august 1 and 2 with the magellan instant camera ( magic ) ccd imager and active telescope optics @xcite . conditions were similar on both nights : non - photometric due to cirrus clouds , and with @xmath75 median fwhm seeing . for the majority of these systems , the images present no significant evidence for or against the presence of strong lensing ; we describe the exceptions here . one system , sdssj0035 , is almost certainly not a strong lens : a relatively @xmath74-bright galaxy can be seen clearly in the images , approximately @xmath76 offset from the lrg . this far exceeds the anticipated lensing scale of about @xmath77 reported in table [ galtable ] . the images of sdssj2147 reveal a bluer galaxy approximately @xmath78 to the south , about at the limit of the estimated lensing scale . we see no particular evidence for strong lensing , but deeper observation of this system could be of interest . two systems , sdssj0037 and sdssj0216 , show evidence of multiple imaging . figure [ diffims ] shows @xmath74-band images of these two systems , along with difference images created by smoothing aligned @xmath31-band images with a gaussian kernel in order to suppress noise and match the slightly worse @xmath74-band seeing , then fitting this smoothed @xmath31-band lrg image to the @xmath74-band image and subtracting it . the difference images are then smoothed with a gaussian kernel of fwhm @xmath79 in order to bring out coherent features ; they show strong evidence of multiply imaged , relatively blue sources . sdssj0037 seems likely to be a double - image lens . it is tempting to identify quadruple - image morphology in the sdssj0216 difference image , but the level of noise recommends caution . narrow - band imaging or integral - field spectroscopy should permit quantitative study of these systems and of those for which broadband imaging is inconclusive . _ hst _ imaging of any confirmed lenses using the narrow - band ramp filter set of the _ advanced camera for surveys _ could also be pursued to obtain a highly resolved picture of lensed line - emitting regions and permit even more detailed study of the lensing mass distributions . the degree of lensing that will be present in a particular system will depend on the impact parameter ( angular offset ) of the background galaxy in the source plane relative to the center of the lrg : the smaller the impact parameter , the more lensing will be seen . to obtain a rough estimate of the number of lenses within our sample , we can guess at the unlensed surface brightness distribution of our background galaxies , compute lensed images under an assumed lens model , smear to account for seeing , and integrate over the @xmath70-diameter sdss spectroscopic fiber , then compare to the [ o ii ] line flux values that we have observed . to interpret the results in terms of lensing probabilities we must also invoke an luminosity function ( lf ) . appendix [ lensprob ] describes the details of a lensing probability calculation of this nature that we have carried out . the results suggest that a total of 19 out of 49 systems are likely to be strong lenses that is , we expect approximately 19 systems to have source - galaxy impact parameters less than the critical value for multiple imaging . it is important to recognize , though , that the `` lenses - or - not '' question does not have as straightforward an answer for extended sources as it does for point sources . different regions of our background galaxies will be lensed by different amounts , and in general some but not all of the galaxy can be multiply imaged . it is more appropriate to ask _ how much _ lensing is present in any given system . there is a sense in which the unknown degree of lensing in our systems may prove to be of scientific interest . @xcite raises the concern that current strong - lensing evidence for massive dark - matter halos in elliptical galaxies may reflect a selection bias . we quote directly : `` even if only a minority of ellipticals have massive dark halos , nearly all the observed lenses will belong to that minority . '' our lrg sample , in contrast , has not been selected for lensing , but rather for back - lighting . the true incidence of lensing within our sample will thus constitute a test of whether or not the dark halos in currently known lenses are in fact generic to early - type galaxies . we present a comparison between our lens candidate lrgs and the full 51,000 lrg spectroscopic sample in figure [ lrgdist ] . the lens candidate lrgs seem somewhat skewed towards brighter magnitudes . the conservative interpretation is that the broadband selection properties of fainter lrgs are more easily perturbed by background galaxies , but it may also reflect a lensing signal , with more massive galaxies providing more magnification . if the logarithmic slope of the underlying [ o ii ] lf is steeper than @xmath80 at the luminosities probed by our survey , then magnified lines of sight should show a statistically enhanced number of [ o ii ] emitters @xcite . @xcite find the logarithmic [ o ii ] lf slope to be steeper than @xmath80 for line luminosities @xmath81 ergs s@xmath26 , whereas the median observed [ o ii ] luminosity in our sample is of order @xmath82 ergs s@xmath26 ( again , we have taken @xmath83 km s@xmath26 mpc@xmath26 ) . these numbers suggest that magnification bias is not the explanation for the observed brightness of our lens candidates relative to the full lrg sample , but a more definite statement must await follow - up observations that capture the total background line flux . most known gravitational lens systems have been selected on the basis of some combination of source properties and lens cross section , whereas the sdss lrg sample is selected based on colors and magnitude . it is therefore of interest to compare known early - type lens galaxies to our candidate lenses , although this is difficult since we do not currently have truly comparable observations of the two samples . figure [ colormagvdispz ] presents our best attempt at such a comparison for lens velocity dispersions and apparent magnitudes as a function of redshift corrections . ] , with _ hst _ known - lens data taken from @xcite . the known - lens velocity dispersions are estimated from lensed image separations in the manner described by @xcite ; they may be systematic overestimates if these lenses are superimposed on the `` mass sheet '' of a high - density environment @xcite . magnitude comparison is made by transforming sdss @xmath74- and @xmath64-band magnitudes to johnson - morgan @xmath84-band using the observed transformation of @xcite . we see that our lrg lens candidates are in general of greater velocity dispersion than known lenses , and in the redshift range where the two samples overlap , the lrgs are more luminous . the brightness of the lrgs combined with the relative faintness of the background galaxies in our sample suggests that any confirmed lrg lenses would be well suited to the type of detailed lens stellar - dynamical studies described by @xcite and @xcite . we have presented a catalog of candidate strong galaxy - galaxy gravitational lens systems detected spectroscopically within the sloan digital sky survey . these systems have known foreground _ and _ background redshifts ; only the detailed spatial alignment of foreground and background galaxies remains unknown . we plan to conduct integral - field spectrographic follow - up observations of these systems , which will allow us to resolve the spatial distribution of the background nebular line emission that we have detected . these observations should confirm a substantial number of lenses within our candidate sample , with many lensed galaxies at lower redshift than any other currently known lensed extra - galactic optical sources . any lenses confirmed within our sample will be of considerable interest for the study of early - type galaxy mass distributions , and could have implications for lens - time - delay @xmath6 measurements and anomalous quasar - lens flux ratios . our sample demonstrates the feasibility of the emission - line - based spectroscopic lens search technique within the sdss and other redshift surveys , and we plan to extend the search to higher source redshifts in the near future . we have also developed and applied a method for abating the influence of night sky emission - line residuals in the 70009000- range that allows us to detect [ o iii ] and h@xmath3 emission over the redshift range @xmath85 0.40.8 without an excess of false - positive detections . funding for the creation and distribution of the sdss archive has been provided by the alfred p. sloan foundation , the participating institutions , the national aeronautics and space administration , the national science foundation , the u.s . department of energy , the japanese monbukagakusho , and the max planck society . the sdss web site is http://www.sdss.org/. the sdss is managed by the astrophysical research consortium ( arc ) for the participating institutions . the participating institutions are the university of chicago , fermilab , the institute for advanced study , the japan participation group , the johns hopkins university , los alamos national laboratory , the max - planck - institute for astronomy ( mpia ) , the max - planck - institute for astrophysics ( mpa ) , new mexico state university , university of pittsburgh , princeton university , the united states naval observatory , and the university of washington . the authors thank paul hewett for his constructive referee report . asb thanks paul schechter and hsiao - wen chen for valuable discussion and consultation . if the model of a purely gaussian noise spectrum described by @xmath15 were correct , then the distribution of scaled residual specific fluxes @xmath86 across all spectra would be gaussian with unit variance for all wavelengths @xmath87 . this is unfortunately not the case in our sample . imperfect night - sky emission - line subtraction and other miscellaneous effects give rise to an excess of `` high - significance '' outliers beyond the predictions of a gaussian model , leading to a deluge of false - positive astronomical emission - line candidates when the procedure described in [ initial ] is applied , particularly in the 70009000- region of the spectrum where the line at redshifts @xmath880.8 appears . the most drastic solution is simply to mask all sky - afflicted wavelengths . rather than concede such vast spectral coverage ( which would drastically reduce our survey volume ) , we describe the observed distribution of scaled residual specific fluxes @xmath89 within the lrg sample with a more detailed empirical noise model . the generally gaussian behavior of scaled residuals at low significance combined with the excess of high - significance residuals is well described by a mixture of gaussian and laplace distributions , expressed parametrically as @xmath90 \ , dx\ ] ] ( for history and applications of the laplace distribution , see * ? ? ? * ) the parameters of this distribution are wavelength - dependent , but we suppress this dependence in out notation . the values of @xmath91 and @xmath92 are related by normalization : @xmath93 we also fix the following relations between parameters , based on strong correlations observed in free - parameter fits to the distribution at each wavelength : @xmath94 the result is a one - parameter noise model to fit to the distribution of @xmath89 across the sample at each wavelength . ( the numerical values 0.38 and 0.09 are fixed by minimizing the sum of binned @xmath16 values for fits across all wavelengths . ) we relax conditions ( [ cond1 ] ) and ( [ cond2 ] ) and fit freely for @xmath58 and @xmath92 at a few isolated locations in the spectrum , where the effects of sky - subtraction residuals are especially strong and the correlations that suggest ( [ cond1 ] ) and ( [ cond2 ] ) break down regions near 5577 , 5894 , 6305 , and 6366 . additionally , some regions of some spectra are characterized by extreme and correlated excess variance , so for each spectrum we convolve @xmath95 capped at 5 ( to limit the influence of single pixels ) with a 100-pixel boxcar filter and exclude from the noise - modeling sample any pixels within a boxcar whose value exceeds 1.25 . we use our fitted noise model to re - scale the reported @xmath15 values such that the new distribution @xmath96 of scaled residual flux values at each wavelength becomes gaussian , while preserving the position of individual @xmath97-values within the cumulative distribution , then proceed as described in [ initial ] . both the reported noise @xmath15 _ and _ the measured residual flux values @xmath98 contain information about the actual error in the presence of imperfect subtraction , so it is sensible to base an effective noise rescaling on their ratio @xmath89 in this manner . by fitting the noise distribution parameters independently at each wavelength , we also capture the localized effects of individual night - sky lines . our strategy for assessing lensing probabilities in our sample centers on the construction of an approximated probability density @xmath99 for the unknown impact parameter @xmath92 of the background galaxy in each system . the following observed quantities are input to the calculation : the lrg and background redshifts , the lrg velocity dispersion , the background line flux received by the @xmath100-diameter spectroscopic fiber , and the median seeing for the spectroscopic plate under consideration . we also make use of the [ o ii ] line luminosity function ( lf ) reported by @xcite . we adopt the same sis model for the lrg mass distribution as was used to obtain the @xmath69 values in table [ galtable ] , and we model the background galaxies as exponential disks with a half - light radius of approximately 3 kpc ( fixed to @xmath101 at @xmath102 ) . for each system , we explore a range of impact parameters @xmath92 from 0 to @xmath103 . at each @xmath92-value , we generate a lensed image of the model background galaxy , then convolve it with a gaussian point - spread function corresponding to the median seeing reported in the spectroscopic plate header . we then integrate the image over a @xmath100-diameter circular fiber aperture centered on the model lens . the result is a tabulated function @xmath104 giving the fraction of the intrinsic flux received by the fiber ; that is , if the total galaxy line flux were @xmath105 in the absence of lensing and limited fiber sampling , the [ o ii ] line flux received by the spectroscopic fiber from a background galaxy with a source - plane offset @xmath92 would be @xmath106 . in general @xmath104 may be greater or less than one due to the competing effects of lens magnification and incomplete sampling by the fiber . next we adopt the [ o ii]-emitter lf reported by @xcite by fitting a schechter function to their figure 6 . after converting from logarithmic units , the number of [ o ii ] emitters per unit volume in an interval @xmath107 at line luminosity @xmath108 is well approximated by @xmath109 with @xmath110 and @xmath111 ergs s@xmath26 ( the overall normalization is unimportant for our purposes ) . we make a crude conversion from their assumed @xmath112 universe to our cosmology by scaling their reported luminosities up by a factor of 1.2 : the ratio of squared luminosity distances in our cosmology to theirs ranges from 1.16 at @xmath113 to 1.27 at @xmath114 , and the bulk of galaxies in their study fall within this range . assuming the form of the lf does not evolve , it corresponds to an intrinsic flux function at any redshift @xmath115 for the number of galaxies per unit redshift per unit solid angle within some intrinsic flux range @xmath116 about @xmath105 : @xmath117 with the same @xmath0 as the lf and @xmath118 $ ] , where @xmath119 is the luminosity distance to redshift @xmath115 . @xmath120 is a flux- and redshift - dependent normalization , the form of which will prove unimportant . we can now derive a joint probability density function ( pdf ) for the observation of an [ o ii]-emitting galaxy behind a given lrg at impact parameter @xmath92 , redshift @xmath115 , and with line flux @xmath121 in the fiber by setting the differential probability proportional to the corresponding expected differential number count and making use of the known relationship of @xmath121 to intrinsic flux @xmath105 through @xmath104 : @xmath122 \ , ( 2 \pi b \ , db ) \ , dz \ , [ d s_{\mathrm{fib } } / f(b ) ] ~~.\end{aligned}\ ] ] the term @xmath123 represents the solid angle in the source plane of an annulus of radius @xmath92 and thickness @xmath124 . the _ observed _ quantities @xmath125 and @xmath126 for the system are equal to the system s true @xmath121- and @xmath115-values plus some observational noise that is independent of @xmath92 , so assuming the noise is small relative to the scale on which the joint pdf varies , we may reinterpret the joint pdf as an approximate conditional pdf on @xmath92 given @xmath126 and @xmath125 : @xmath127^{-1 } \ , \psi[z_{\mathrm{obs } } , s_{\mathrm{obs } } / f(b ) ] \ , db ~~.\ ] ] the normalization @xmath128 need not be derived explicitly , since we can simply compute the right - hand side without it for the relevant range of @xmath92-values and normalize afterwards . with this pdf in hand , we can finally assign a `` lensing probability '' to the system as the integrated probability for impact parameters less than the critical value for multiple imaging in the sis model the `` einstein radius '' , equal to one - half the @xmath69 value given in table [ galtable ] . summing this probability over all systems gives the estimate quoted in [ lensornot ] of 19 strong lenses out of 49 candidates . abazajian , k. , et al . 2003 , , 126 , 2081 binney , j. 2003 , in iau symp . 220 , dark matter in galaxies , ed . s. ryder , d. j. pisano , m. walker , & k. freeman ( san francisco : asp ) , in press ; 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we present a catalog of 49 spectroscopic strong gravitational lens candidates selected from a sloan digital sky survey sample of 50996 luminous red galaxies . potentially lensed star - forming galaxies are detected through the presence of background oxygen and hydrogen nebular emission lines in the spectra of these massive foreground galaxies . this multiline selection eliminates the ambiguity of single - line identification and provides a very promising sample of candidate galaxy - galaxy lens systems at low to intermediate redshift , with foreground redshifts ranging from 0.16 to 0.49 and background redshifts from 0.25 to 0.81 . any lenses confirmed within our sample would be important new probes of early - type galaxy mass distributions , providing complementary constraints to those obtained from currently known lensed high - redshift quasars .

<s>[INST]in its strongest form , gravitational lensing produces unmistakably distorted , amplified , and multiplied images of distant astronomical objects . it is therefore not surprising that the majority of known galaxy - scale gravitational lens systems have been discovered through imaging observations . however , a small number of lenses have been discovered spectroscopically , with the spectrum of a targeted galaxy showing evidence of emission from a background source and follow - up imaging revealing lensing morphology . the three most secure examples are the lensed quasars 2237 + 0305 @xcite and sdss j0903 + 5028 @xcite and the lensed lyman-@xmath0 emitting galaxy 0047@xmath12808 @xcite . several authors have made predictions for the frequency of lensed quasar discoveries in galaxy redshift surveys @xcite . others , inspired by the discovery of 0047@xmath12808 , have undertaken spectroscopic searches for lensed lyman-@xmath0-bright galaxies @xcite . the idea behind such searches is that a massive foreground galaxy should act as an effective gravitational lens of _ any _ object positioned sufficiently far behind it and at small enough impact parameter , and any emission features from such lensed objects should be detectable in the spectra of the foreground galaxy . therefore a search for discrepant emission features in galaxy spectra can potentially lead to a sample of gravitational lens systems that would not be discovered in broadband imaging searches due to faintness of source relative to lens . this `` lenses - looking - for - sources '' approach is complementary to lens searches such as the recently completed cosmic lens all - sky survey ( class ; * ? ? ? * ; * ? ? ? * ) which proceed by targeting sources and looking for evidence of an intervening lens . with its massive scale and quality of data , the spectroscopic component of the sloan digital sky survey ( sdss ) provides an unprecedented opportunity for spectroscopic galaxy - galaxy gravitational lens discovery . this paper presents the first results of such a search within a sample of @xmath251,000 sdss luminous red galaxy ( lrg ) spectra ( * ? ? ? * hereafter e01 ) : a catalog of candidate lensed star - forming galaxies at intermediate redshift . the lens candidates presented in this paper were detected by the presence of not one but ( at least ) three emission lines in the lrg spectra identified as nebular emission from a single background redshift : and two out of the three of h@xmath3 @xmath4 , , and ( all emission - line wavelengths in this paper are vacuum values , in angstroms ) . this implies a maximum redshift of @xmath5 for any candidate lensed galaxies : at higher redshifts , [ o iii ] emission moves off the red end of the sdss spectrograph . the lensing cross section of a particular foreground galaxy is lower for intermediate - redshift sources than high - redshift sources , and in this sense the lens search we describe here is at a disadvantage relative to searches for lensed high - redshift lyman-@xmath0 emitters however , the identities of the emission lines in the sample we present here are absolutely unambiguous . this can not be said for spectroscopic lyman-@xmath0 lens candidates , which are typically detected as single discrepant emission lines and are difficult to distinguish from lower - redshift emission or ( in the case of a huge survey such as the sdss ) non - astrophysical spectral artifacts . ( a forthcoming paper will present sdss single - line [ o ii ] and lyman-@xmath0 lens candidates . ) our spectroscopic lens search based on multiple - line detection has further advantages . first , the source redshift of any lensed galaxies will be known from the outset . second , for a given limiting line flux , star - forming galaxies at intermediate redshift are more numerous on the sky than lyman-@xmath0 emitters at high redshift ( see * ? ? ? * ; * ? ? ? * ) , and hence strong lensing events could be more frequent despite decreased lensing cross sections . the non - lensed source population should thus be more amenable to study and characterization ( * ? ? ? * for example ) , facilitating lens statistical analysis . finally , intermediate - redshift lensed galaxies would probe the mass distribution of the lens population in a systematically different manner than do high - redshift sources . the search for new lens systems is motivated by the unique power of gravitational lensing to constrain the mass distribution of the lensing galaxy . @xcite argued that strong galaxy - galaxy gravitational lenses in the optical band should be both ubiquitous and of great scientific interest , but their detection has proved difficult . in addition to the optical einstein ring 0047@xmath12808 mentioned above , @xcite have published one more spectroscopic galaxy - lens candidate . _ hubble space telescope _ ( _ hst _ ) imaging has also had some success in detecting lensed galaxies , as described by @xcite , @xcite , and @xcite , but spectroscopic confirmation remains a challenge in most cases . lensed galaxies are especially useful for investigating the mass distribution of the lensing galaxy because unlike lensed quasars they are spatially resolved sources which provide more detailed constraints ( * ? ? ? * for example ) . as with lensed quasars , the relative angular deflections between multiple images can constrain the total deflecting lens mass . but the relative distortions of multiple images can provide constraints as well , probing the slope of the radial mass profile and allowing more detailed connection with theories of galaxy formation and cold dark matter ( cdm ) . the promise of our candidate sample is enhanced by the fact that lens _ and _ source redshifts for any confirmed lens systems will be known from the outset with great precision ; this is generally not the case for lenses discovered in optical imaging or radio data . the lack of sufficient lensing constraints on the radial slope of the galaxy mass profile in lensed quasar systems is the greatest source of uncertainty in the hubble constant ( @xmath6 ) values derived from the time delays between images @xcite , which remain systematically low compared to the current best @xmath6 values from the distance ladder @xcite and cosmic microwave background @xcite ; @xcite highlights the importance of resolving this discrepancy . any galaxy - galaxy lenses confirmed within our current list of candidates would help to solve this problem by expanding the sample for ensemble lensing studies of early - type galaxy mass profiles like that of @xcite and allowing for the inclusion of distortion information as mentioned above . the generally lower lens and source redshifts of our candidate systems as compared to known lens systems are also of particular interest because the images of any strong lenses within our sample will tend to form at smaller _ physical _ radii within the lens galaxy than in current lens systems ( see * ? ? ? * table 1 ) , thus probing elliptical galaxy mass profiles in a systematically different manner1231 , has @xmath7 @xcite . ] . a large enough sample of strongly lensed star - forming galaxies could even be monitored directly for supernovae . multiple images of the same supernova would give time delays and @xmath6 measurements , as numerous authors have envisioned @xcite . if we assume one supernova per galaxy per century as an order - of - magnitude estimate @xcite , a program to monitor @xmath8 lensed galaxies for several years would have a good chance of success . numerous studies have addressed the inability of standard macroscopic galaxy mass models to predict the flux ratios observed between images of strongly lensed quasars . some authors have suggested that this phenomenon may be due to the effects of substructure in the lensing galaxy on the scale of either cdm sub - halos @xcite or stars @xcite , while others have invoked macroscopically modified lens models as a possible explanation @xcite . a sizeable sample of strongly lensed galaxies would provide valuable insight into this problem : by virtue of the arcsecond - scale intrinsic angular size of the source , galaxy - galaxy lenses will be immune to the lensing effects of any substructure with lensing deflection angles on the scale of microarcseconds ( stars ) or milliarcseconds ( sub - halos ) . if the suppressed saddle point image fluxes seen in many quasar lenses are indeed due to macroscopic inadequacies in the standard lens models , similar effects should be seen in galaxy - galaxy lenses . if on the other hand these effects are due to micro / millilensing by substructure , they should be absent from lensed galaxy systems . the sloan digital sky survey is a project to image roughly one - quarter of the sky in five optical bands and obtain spectroscopic follow - up observations of @xmath9 galaxies and @xmath10 quasars . @xcite provide a technical summary of the survey , @xcite describe the sdss camera , @xcite , @xcite , and @xcite discuss the photometric system and calibration , @xcite discuss sdss astrometry , @xcite present the spectroscopic plate tiling algorithm , and @xcite and @xcite describe the survey data products . approximately 12% of the galaxy spectroscopic fibers are allocated to the lrg sample ( e01 ) , selected to consist of very luminous ( @xmath11)and hence massive early - type galaxies at higher redshift than the galaxies of the main sample @xcite . we expect these lrgs to be particularly effective gravitational lenses of any objects positioned suitably behind them , and we concentrate our spectroscopic lens search on them . we also note that lrgs should have little dust and therefore any lensed background galaxies should suffer minimal extinction . the sample for our current study consists of 50996 spectra taken between 5 march 2000 and 27 may 2003 of sdss imaging objects flagged as galaxy_red by the photometric pipeline @xcite for passing either of the lrg cuts described by e01 , reduced by the sdss spectroscopic pipeline ( j. frieman et al . , in preparation ) , and selected to have redshifts between 0.15 and 0.65 as determined by the specbs redshift - finding software ( d. j. schlegel et al . , in preparation ) . the low - redshift cutoff is needed because less massive galaxies start to pass the photometric cuts below @xmath12 and pollute the volume - limited lrg sample ; see the discussion in e01 and the bimodal lrg sample redshift histogram in ( * ? ? ? in addition to being much more massive than the average galaxy , lrgs have another property that makes them well suited to a spectroscopic lens survey : their spectra are extremely regular and well - characterized ( see * ? ? ? * ) . to determine the spectroscopic redshift of an sdss target galaxy with observed specific flux @xmath13 and one - sigma sky@xmath14source noise spectrum @xmath15 , the specbs program employs a small set of galaxy eigenspectra ( four in the reductions for this study ) derived from a rest - frame principal - component analysis ( pca ) of 480 galaxy spectra taken on sdss plate 306 , mjd 51690 this eigenbasis is incrementally redshifted , and a model spectrum is generated from the best - fit linear combination to the observed spectrum at each trial redshift , with the final redshift assignment given by the trial value that yields the overall minimum @xmath16 . although redshift is the primary output of this procedure , a byproduct of specbs is the best - fit model spectrum itself , @xmath17 . in the case of lrgs , @xmath17 typically provides a very detailed and accurate fit to @xmath13 , with a reduced @xmath16 of order unity over almost 4000 spectral pixels ( roughly 1600 spectral resolution elements ) attained with only 8 free parameters : a redshift , the four eigen - galaxy coefficients , and the three terms of a quadratic polynomial to fit out spectrophotometric errors and extinction effects , both of which exist at the few - percent level . this extremely regular spectral behavior allows us to form residual lrg spectra @xmath18 that are in principle realizations of @xmath15 . nebular emission lines from galaxies along the line of sight other than the target lrg will not be modeled by specbs and should appear as significant features localized in wavelength within these residual spectra . figure [ noise_spec ] shows the median 1-@xmath19 line flux sensitivity within our lrg residual spectrum sample as a function of wavelength . the ( 20th , 50th , 80th)-percentile lrg spectra themselves have a median signal - to - noise per pixel of ( 3.3 , 5.1 , 9.6 ) at the sdss resolution of @xmath20 . this section describes our candidate selection routine in detail . briefly stated , we select as initial candidates those spectra that show _ both _ blended at @xmath21 _ and _ two out of the three lines h@xmath3 @xmath4 , , and at @xmath22 , then cull the candidate list by applying cuts based on more detailed fits to the presumed emission features , and finally remove any obviously spurious detections . this selection process yields a substantial number of promising systems without an excess of obvious false positives . the key element in the first step of our lens candidate selection ( described fully in [ select ] below ) is a straightforward matched - filtering procedure to search for significant emission features by fitting a gaussian line profile at each point in the residual spectrum @xcite . we describe our implementation here so as to be explicit . let @xmath23 be the residual flux in pixel @xmath24 and @xmath25 be the statistical variance of @xmath23 . s@xmath26 @xmath26 to units of ergs @xmath27 s@xmath26 pixel@xmath26 is made using the re - binned sdss spectroscopic pixel scale relation @xmath28 . ] also let @xmath29 describe a gaussian kernel , centered on @xmath30 , with @xmath31 running from @xmath32 to @xmath33 , and normalized such that @xmath34 . the maximum - likelihood estimator @xmath35 for the line flux @xmath36 of any @xmath29-shaped residual emission feature centered on pixel @xmath24 is that which minimizes @xmath37 differentiating ( [ chi2 ] ) with respect to @xmath36 , setting the resulting expression to zero , and solving yields @xmath38 where we have defined the convolutions @xmath39 the variance of @xmath35 ( under the assumption of uncorrelated gaussian errors in @xmath23 as described by @xmath25 ) is given by @xmath40 the signal - to - noise ratio for a fitted gaussian profile centered on pixel @xmath24 is therefore @xmath41 our null hypothesis is an absence of emission features in the residual spectra that should manifest as the @xmath42 being gaussian - distributed about zero with unit variance : this should hold at most wavelengths in most spectra . we approach the initial search for emission lines in the residual spectra as a search for significance peaks with @xmath43 greater than some threshold value . although insensitive to goodness - of - fit , this convolution - based detection scheme executes quickly and is therefore well suited to the initial search for residual emission features within our large spectral sample . appendix [ noisemodel ] describes a noise - rescaling process that we employ to control the incidence of false - positive emission - feature detections ( due primarily to imperfect sky subtraction ) without masking regions of the spectrum . multiple emission features at the same redshift will have redshift - independent wavelength ratios . the fully reduced sdss spectra have been re - binned at a constant - velocity pixel scale of 69 km s@xmath26 , giving a redshift - independent pixel offset between features . our operational scheme is thus to search for coincident @xmath43 peaks between multiple copies of a single filtered residual spectrum that have been shifted relative to one another . for detection , we filter each residual spectrum with a @xmath44-pixel gaussian kernel ( matched to the typical width of blended emission seen in sdss starburst galaxies ) . we take copies of the same residual spectrum `` blueshifted '' by integer pixel amounts so as to place h@xmath45 @xmath46 , h@xmath47 @xmath48 , h@xmath3 @xmath4 , , , @xmath49 , h@xmath0 @xmath50 , @xmath51 , @xmath52 , and @xmath53 as close as possible to 3728.48 , the geometric - mean wavelength of the doublet . these shifted spectra are filtered with a @xmath54-pixel gaussian kernel ( matched to the typical width of sdss starburst emission ) , with the sub - pixel part of the line offset relative to 3728.48 incorporated by offsetting the kernel . any pixel in the filtered @xmath55 spectra with value greater than 3 for and value greater than 2.5 for two out of h@xmath3 @xmath4 , , and is tagged as a `` hit '' . a group of adjacent `` hit '' pixels is reduced to the single pixel with the greatest quadrature - sum @xmath55 for lines detected above the threshold ( in effect , the pixel most inconsistent with the null hypothesis ) . spectra with more than one isolated hit are rejected . the spectra are only searched in regions that would correspond to emission from @xmath56 km s@xmath26 behind the targeted lrg . the preceding selection leads to 163 hits within our 51,000 spectra . for each hit , we explore a grid of redshift and intrinsic emission - line - width values for the background galaxy to find a best - fit model . at each grid point we fit a gaussian profile to any emission line initially detected above a 2.0-@xmath55 threshold , with the line center determined by the trial redshift and line - width given by the quadrature sum of the trial intrinsic line - width and the measured spectrograph resolution at the observed wavelength of each line . is fit with a double gaussian profile . we adopt as best values for background redshift @xmath57 and ( gaussian-@xmath19 ) intrinsic line - width @xmath58 those that give the minimum @xmath16 over all detected lines . the @xmath57 extent of our grid corresponds to @xmath592 pixels , and the explored @xmath58 range runs from 0 to 2 pixels ( 0 to 138 km s@xmath26 ) . following these fits , we subject the candidate sample to several cuts . first , we reject any system where no convergent ( minimum @xmath16 ) value for @xmath57 is found within the explored @xmath592-pixel range : real background emission systems should have convergent best - fit redshifts roughly coincident with their convolution - based @xmath55 peaks . similarly , we cut systems with no convergent @xmath58 between 0 and 2 pixels : the features of real systems should neither be narrower than the spectrograph resolution nor wider than a reasonable upper limit for emission features of faint star - forming galaxies . finally , we compute a total signal - to - noise ratio for the fit , defined as the total best - fit flux in and all other lines initially detected at @xmath60 divided by the quadrature - sum of the 1-@xmath19 noise from those line fits , and impose a cut in the total-@xmath55@xmath61 plane ( @xmath61 being the @xmath16 per degree of freedom in the fit ) . we cut any system with a total @xmath55 less than the greater of 6 and @xmath62 . this removes both low-@xmath55 candidates and candidates whose @xmath61 values are too high to be explained by high-@xmath55 emission features showing significant non - gaussian structure . ( these cuts were designed to be a quantitative expression of our own judgements about which candidate systems look real upon spectrum inspection and which do not ; the justifications are somewhat _ a posteriori_. ) this cutting procedure reduces the 163 hits to 61 candidate systems . finally , we prune 12 candidates from the list that survive the automated culling but are clearly explained by either over - fit lrg stellar absorption , under - modeled lrg line emission , exceptionally poor data quality , or a generally flawed template fit , leaving the 49 good candidate systems that we present . this search for background galaxy emission lines digs rather deep into the noise of our spectroscopic sample . to gauge the incidence of false positives in our final candidate list , we make a parallel run of the detection , fitting , and automated rejection procedure with the following rest - wavelength perturbations : h@xmath3 @xmath4 @xmath63 4833 , @xmath63 4945 , and @xmath63 5023 . these perturbations alter all of the redshift - independent wavelength ratios among these lines and between all of them and ; this modified detection procedure no longer selects for real multi - line emission , but only for noise features . the `` false candidates '' that result from this perturbed procedure are randomly shuffled along with the candidates from the original procedure , and all are examined together when making the final pruning judgements . the perturbed procedure yields 88 hits and 7 post - cut candidates ; all 7 are pruned upon inspection without knowledge of their intrinsic falseness . this implies that the vast majority of our candidates are indeed background galaxies and not simply noise features . lcccccccclc & 0390 - 51900 - 589 & y & [email protected] & 0.3979 & 286@xmath5919 & 0.5952 & 1.39 & 20 @xmath59 2 & d , e & 11.6 + & 0689 - 52262 - 632 & n & [email protected] & 0.2017 & 176@xmath5921 & 0.2708 & 0.43 & 19 @xmath59 3 & c , e , g , h , i & 10.8 + & 0655 - 52162 - 392 & y & [email protected] & 0.1955 & 279@xmath5910 & 0.6322 & 2.94 & 23 @xmath59 4 & a , c , d , e & 16.0 + & 0422 - 51811 - 508 & y & [email protected] & 0.2939 & 251@xmath5919 & 0.5248 & 1.47 & 19 @xmath59 3 & c , d , e & 10.2 + & 0694 - 52209 - 076 & n & [email protected] & 0.4516 & 86@xmath5925 & 0.5011 & 0.04 & 19 @xmath59 2 & c , e & 11.6 + & 0668 - 52162 - 428 & y & [email protected] & 0.3317 & 333@xmath5923 & 0.5235 & 2.13 & 25 @xmath59 4 & c , d & 8.7 + & 0414 - 51869 - 244 & y & [email protected] & 0.4453 & 267@xmath5935 & 0.6240 & 1.03 & 22 @xmath59 2 & b , c , d , e & 16.5 + & 0541 - 51959 - 145 & n & [email protected] & 0.3223 & 338@xmath5916 & 0.5812 & 2.67 & 62 @xmath59 5 & a , b , c , d , e & 24.7 + & 0860 - 52319 - 452 & n & [email protected] & 0.3200 & 334@xmath5917 & 0.3809 & 0.94 & 54 @xmath59 4 & c , e , g , h & 17.0 + & 0468 - 51912 - 362 & y & [email protected] & 0.4114 & 251@xmath5941 & 0.5672 & 0.88 & 12 @xmath59 4 & d , e & 6.2 + & 0472 - 51955 - 429 & y & [email protected] & 0.1642 & 326@xmath5912 & 0.3240 & 2.90 & 26 @xmath59 4 & b , c , e , g & 11.5 + & 0870 - 52325 - 465 & n & [email protected] & 0.2908 & 198@xmath5924 & 0.4538 & 0.75 & 29 @xmath59 4 & d , e & 9.4 + & 0476 - 52314 - 177 & n & [email protected] & 0.3475 & 396@xmath5935 & 0.4670 & 2.10 & 15 @xmath59 3 & c , e & 8.8 + & 0902 - 52409 - 068 & n & [email protected] & 0.2405 & 334@xmath5915 & 0.4700 & 2.94 & 31 @xmath59 3 & c , e & 11.5 + & 0996 - 52641 - 106 & n & [email protected] & 0.3475 & 183@xmath5922 & 0.4797 & 0.48 & 18 @xmath59 3 & c , e & 7.9 + & 0272 - 51941 - 151 & y & [email protected] & 0.1589 & 264@xmath5911 & 0.2764 & 1.64 & 18 @xmath59 3 & d , e , g , i & 14.6 + & 0772 - 52375 - 140 & n & [email protected] & 0.1574 & 228@xmath5914 & 0.2512 & 1.08 & 31 @xmath59 5 & c , e , f , g , h , i & 18.7 + & 1002 - 52646 - 504 & n & [email protected] & 0.2058 & 217@xmath5917 & 0.5809 & 1.65 & 52 @xmath59 11 & c , e & 6.1 + & 0951 - 52398 - 036 & n & [email protected] & 0.3809 & 223@xmath5928 & 0.5466 & 0.78 & 29 @xmath59 4 & c , d , e & 11.2 + & 0328 - 52282 - 350 & n & [email protected] & 0.3936 & 321@xmath5927 & 0.4646 & 0.81 & 9 @xmath59 3 & c , d , e & 8.9 + & 0598 - 52316 - 477 & n & [email protected] & 0.3804 & 260@xmath5927 & 0.5435 & 1.05 & 14 @xmath59 3 & c , e & 6.5 + & 0777 - 52320 - 501 & n & [email protected] & 0.3751 & 303@xmath5934 & 0.6690 & 2.08 & 16 @xmath59 4 & d , e & 7.5 + & 0494 - 51915 - 074 & y & [email protected] & 0.2312 & 238@xmath5910 & 0.4446 & 1.47 & 16 @xmath59 2 & c , e & 10.5 + & 0783 - 52325 - 279 & n & [email protected] & 0.2334 & 253@xmath5916 & 0.4488 & 1.67 & 23 @xmath59 3 & c , e & 10.6 + & 0602 - 52072 - 332 & y & [email protected] & 0.3050 & 300@xmath5924 & 0.3300 & 0.36 & 16 @xmath59 3 & c , e , g , j & 12.0 + & 0784 - 52327 - 350 & n & [email protected] & 0.1984 & 226@xmath5912 & 0.5141 & 1.71 & 16 @xmath59 5 & c , e & 6.6 + & 0298 - 51955 - 001 & y & [email protected] & 0.3496 & 111@xmath5912 & 0.4425 & 0.14 & 18 @xmath59 3 & d , e & 8.4 + & 0605 - 52353 - 503 & n & [email protected] & 0.2046 & 267@xmath5917 & 0.4814 & 2.23 & 10 @xmath59 3 & d , e & 9.6 + & 0606 - 52365 - 315 & n & [email protected] & 0.2971 & 428@xmath5921 & 0.3556 & 1.60 & 17 @xmath59 3 & c , e , g , h , j & 13.9 + & 1045 - 52725 - 464 & n & [email protected] & 0.2987 & 240@xmath5925 & 0.8115 & 1.92 & 26 @xmath59 2 & c , d & 7.7 + & 0307 - 51663 - 065 & y & [email protected] & 0.3717 & 349@xmath5928 & 0.4404 & 0.99 & 40 @xmath59 3 & c , d , e & 15.8 + & 0615 - 52347 - 311 & y & [email protected] & 0.2042 & 174@xmath5916 & 0.4857 & 0.96 & 30 @xmath59 4 & c , e & 12.1 + & 0315 - 51663 - 143 & y & [email protected] & 0.2992 & 300@xmath5935 & 0.4317 & 1.46 & 19 @xmath59 3 & b , c , e & 9.9 + & 0617 - 52072 - 561 & y & [email protected] & 0.1883 & 254@xmath5912 & 0.3956 & 1.85 & 27 @xmath59 4 & c , e , g , h & 8.5 + & 0618 - 52049 - 123 & y & [email protected] & 0.4564 & 345@xmath5952 & 0.5388 & 0.92 & 8 @xmath59 2 & c , e & 6.8 + & 0364 - 52000 - 084 & y & [email protected] & 0.2076 & 290@xmath5914 & 0.5241 & 2.76 & 29 @xmath59 3 & c , e & 12.5 + & 0626 - 52057 - 518 & y & [email protected] & 0.2479 & 276@xmath5916 & 0.7933 & 2.81 & 21 @xmath59 3 & d , e & 10.1 + & 0973 - 52426 - 464 & n & [email protected] & 0.1785 & 256@xmath5914 & 0.4357 & 2.12 & 23 @xmath59 5 & d , e & 9.2 + & 0353 - 51703 - 121 & y & [email protected] & 0.2437 & 78@xmath5920 & 0.3776 & 0.12 & 9 @xmath59 2 & c , e , g & 8.5 + & 0635 - 52145 - 290 & y & [email protected] & 0.2677 & 264@xmath5928 & 0.6672 & 2.23 & 10 @xmath59 3 & c , d & 6.0 + & 0982 - 52466 - 602 & n & [email protected] & 0.2107 & 320@xmath5917 & 0.4635 & 3.04 & 10 @xmath59 2 & c , d & 6.5 + & 0731 - 52460 - 165 & n & [email protected] & 0.2290 & 224@xmath5914 & 0.3964 & 1.14 & 14 @xmath59 3 & c , d , e , g & 15.3 + & 0641 - 52199 - 021 & y & [email protected] & 0.3090 & 201@xmath5921 & 0.6306 & 1.08 & 11 @xmath59 2 & d , e & 7.9 + & 0371 - 52078 - 307 & n & [email protected] & 0.4892 & 379@xmath5936 & 0.6029 & 1.35 & 12 @xmath59 2 & a , c , e & 8.3 + & 0724 - 52254 - 277 & n & [email protected] & 0.4719 & 414@xmath5947 & 0.6238 & 2.09 & 14 @xmath59 2 & c , e & 9.7 + & 0677 - 52606 - 520 & n & [email protected] & 0.2285 & 279@xmath5917 & 0.4635 & 2.13 & 19 @xmath59 3 & c , e & 9.5 + & 0743 - 52262 - 304 & n & [email protected] & 0.1553 & 255@xmath5916 & 0.5170 & 2.51 & 13 @xmath59 3 & c , e & 8.1 + & 0385 - 51877 - 596 & y & [email protected] & 0.1858 & 229@xmath5914 & 0.2718 & 0.91 & 53 @xmath59 4 & d , e , g , h , i , j & 16.6 + & 0684 - 52523 - 311 & n & [email protected] & 0.4169 & 404@xmath5959 & 0.7146 & 3.47 & 30 @xmath59 3 & c , e & 12.7 + [ galtable ] in this section we present our catalog of 49 candidate lensed star - forming galaxies selected to have emission at @xmath55 of 3 or higher and emission from two out of the three of h@xmath3 @xmath4 , , and each at @xmath55 of 2.5 or higher , at a redshift significantly greater than that of the primary target lrg . table [ galtable ] lists various properties of the candidate lens systems . lrg @xmath64 de vaucouleurs model magnitudes are determined from sdss imaging and photometric reduction . lrg redshifts and velocity dispersions are as provided by specbs ; the software fits for velocity dispersions @xmath65 using a set of 24 stellar eigenspectra derived from a pca of the elodie spectral library @xcite . we report all @xmath65 values from the database , although some are likely unreliable ; see the notes of table [ galtable ] . we also report emission - line redshifts of the detected background galaxies . using the observed lrg and background redshifts and the observed lrg @xmath65 , and assuming a singular isothermal sphere ( sis ) lrg luminous@xmath14dark matter distribution , we calculate a `` best guess '' for the angular scale of any lensing that might be present in these systems as @xmath66 . ( @xmath67 and @xmath68 are angular - diameter distances from lens to source and from observer to source and a hubble constant @xmath6 of 70 km s@xmath26 mpc@xmath26 . since @xmath69 is proportional to a distance ratio , it is independent of @xmath6 . ] ) . this is the separation between the two images of a strongly lensed object in the sis model ; it is also the radius of the strong - lensing region of the image plane , and twice the radius of ring images of compact sources directly behind the lens ( * ? ? ? * for example ) . finally , for each candidate system we report the detected background line flux from the best - fit double gaussian profile , a list of other lines detected at @xmath22 , and the total @xmath55 of the background galaxy emission - line fit as defined in [ select ] . the reported background line fluxes should be viewed with suspicion : the spatial alignments of the background galaxies are unknown , and the spectroscopic fibers will not necessarily have captured all of their light . in addition , most of the reduced candidate lrg spectra have been rescaled based on smear exposures that attempt to account for lrg flux falling outside the @xmath70 fiber @xcite ; we have removed this correction from the tabulated line fluxes , as it has no physical relation to the background emission - line galaxies . figure [ spectra ] shows the sdss discovery spectra and best - fit model spectra , along with close - up views of the residual ( data @xmath1 model ) spectra in the wavelength ranges corresponding to redshifted background , h@xmath3 @xmath4 , , and . smear corrections have not been removed from these plots . although we detect line emission clearly , evidence of background galaxy _ continuum _ in the residual spectra of our candidate systems is scarce . this is not surprising , for three reasons . one , the lrg sample was selected for particular broadband color and luminosity , and significant background continuum would likely perturb an lrg out of the sample . two , any faint background continuum present in an lrg spectrum will largely project onto the lrg - redshift eigenspectrum set and low - order polynomial fit used by specbs , and will be subtracted along with the lrg model when forming the residual spectrum . three , these background galaxies are likely to be high - equivalent - width star - forming systems , and since their line fluxes are detected just above the noise threshold , the associated continuum will typically be lost in the noise . nevertheless , we may obtain a higher signal - to - noise picture of the background galaxies that we detect by constructing a median spectrum as follows . first we transform the residual spectra of our candidate systems into units of erg @xmath27 s@xmath26 pixel@xmath26 , which is a redshift - independent quantity since the sdss pixels are of constant velocity width . we then shift these residual spectra into the rest frame of the background galaxy , rounded to the nearest whole pixel , and transform back to erg @xmath27 s@xmath26 @xmath26 . next we renormalize the spectra by dividing each one by its best - fit -flux value . we then take the median value at each pixel , and restore physical normalization by multiplying this median spectrum by the sample - median best - fit -flux value . the resulting median spectrum is shown in figure [ medspec ] . although there is no discernible continuum in the individual residual spectra , we can see a 4000-continuum break in the median spectrum ; we also see h@xmath47 , h@xmath0 , [ n ii ] and [ s ii ] emission lines in addition to the lines for which we select . this gives further evidence that we have successfully detected and identified background emission features . we have with certainty detected emission from galaxies behind foreground lrgs . for a system to be a strong gravitational lens , the background galaxy must be located at sufficiently small impact parameter relative to the lrg center . the true incidence of lensing within our sample can best be determined and studied with either narrow - band imaging or integral - field spectroscopy . such observations could spectrally isolate the background line flux and resolve it spatially to reveal any lensing morphology . sdss broadband imaging offers some hope for answering the lensing question , but in general sloan images do not detect late - type galaxies at redshift @xmath71 at very high @xmath55 . figure [ ims ] shows @xmath72 sdss @xmath64 postage - stamp images centered on the candidate systems , with linear gray - scaling from @xmath73-@xmath19 sky noise to peak lrg surface brightness . evidence of significantly offset neighboring broadband emission is seen in some images , but it would be difficult to rule out many systems as definite non - lenses based on sdss - quality images . in the spirit of a purely spectroscopic survey , we present as candidates all systems selected spectroscopically . furthermore , we note that many of these lrgs live in high - density group / cluster environments , and neighboring images may be at the lrg redshift and not the source of the background emission that we detect . in preparation for integral - field spectroscopic follow - up , we have obtained broadband reconnaissance images of 14 of our candidate systems ( as indicated in table [ galtable ] ) using the magellan consortium s 6.5-m clay telescope at las campanas observatory . these short @xmath74- and @xmath31-band exposures ( 120s each ) were taken on the nights of 2003 august 1 and 2 with the magellan instant camera ( magic ) ccd imager and active telescope optics @xcite . conditions were similar on both nights : non - photometric due to cirrus clouds , and with @xmath75 median fwhm seeing . for the majority of these systems , the images present no significant evidence for or against the presence of strong lensing ; we describe the exceptions here . one system , sdssj0035 , is almost certainly not a strong lens : a relatively @xmath74-bright galaxy can be seen clearly in the images , approximately @xmath76 offset from the lrg . this far exceeds the anticipated lensing scale of about @xmath77 reported in table [ galtable ] . the images of sdssj2147 reveal a bluer galaxy approximately @xmath78 to the south , about at the limit of the estimated lensing scale . we see no particular evidence for strong lensing , but deeper observation of this system could be of interest . two systems , sdssj0037 and sdssj0216 , show evidence of multiple imaging . figure [ diffims ] shows @xmath74-band images of these two systems , along with difference images created by smoothing aligned @xmath31-band images with a gaussian kernel in order to suppress noise and match the slightly worse @xmath74-band seeing , then fitting this smoothed @xmath31-band lrg image to the @xmath74-band image and subtracting it . the difference images are then smoothed with a gaussian kernel of fwhm @xmath79 in order to bring out coherent features ; they show strong evidence of multiply imaged , relatively blue sources . sdssj0037 seems likely to be a double - image lens . it is tempting to identify quadruple - image morphology in the sdssj0216 difference image , but the level of noise recommends caution . narrow - band imaging or integral - field spectroscopy should permit quantitative study of these systems and of those for which broadband imaging is inconclusive . _ hst _ imaging of any confirmed lenses using the narrow - band ramp filter set of the _ advanced camera for surveys _ could also be pursued to obtain a highly resolved picture of lensed line - emitting regions and permit even more detailed study of the lensing mass distributions . the degree of lensing that will be present in a particular system will depend on the impact parameter ( angular offset ) of the background galaxy in the source plane relative to the center of the lrg : the smaller the impact parameter , the more lensing will be seen . to obtain a rough estimate of the number of lenses within our sample , we can guess at the unlensed surface brightness distribution of our background galaxies , compute lensed images under an assumed lens model , smear to account for seeing , and integrate over the @xmath70-diameter sdss spectroscopic fiber , then compare to the [ o ii ] line flux values that we have observed . to interpret the results in terms of lensing probabilities we must also invoke an luminosity function ( lf ) . appendix [ lensprob ] describes the details of a lensing probability calculation of this nature that we have carried out . the results suggest that a total of 19 out of 49 systems are likely to be strong lenses that is , we expect approximately 19 systems to have source - galaxy impact parameters less than the critical value for multiple imaging . it is important to recognize , though , that the `` lenses - or - not '' question does not have as straightforward an answer for extended sources as it does for point sources . different regions of our background galaxies will be lensed by different amounts , and in general some but not all of the galaxy can be multiply imaged . it is more appropriate to ask _ how much _ lensing is present in any given system . there is a sense in which the unknown degree of lensing in our systems may prove to be of scientific interest . @xcite raises the concern that current strong - lensing evidence for massive dark - matter halos in elliptical galaxies may reflect a selection bias . we quote directly : `` even if only a minority of ellipticals have massive dark halos , nearly all the observed lenses will belong to that minority . '' our lrg sample , in contrast , has not been selected for lensing , but rather for back - lighting . the true incidence of lensing within our sample will thus constitute a test of whether or not the dark halos in currently known lenses are in fact generic to early - type galaxies . we present a comparison between our lens candidate lrgs and the full 51,000 lrg spectroscopic sample in figure [ lrgdist ] . the lens candidate lrgs seem somewhat skewed towards brighter magnitudes . the conservative interpretation is that the broadband selection properties of fainter lrgs are more easily perturbed by background galaxies , but it may also reflect a lensing signal , with more massive galaxies providing more magnification . if the logarithmic slope of the underlying [ o ii ] lf is steeper than @xmath80 at the luminosities probed by our survey , then magnified lines of sight should show a statistically enhanced number of [ o ii ] emitters @xcite . @xcite find the logarithmic [ o ii ] lf slope to be steeper than @xmath80 for line luminosities @xmath81 ergs s@xmath26 , whereas the median observed [ o ii ] luminosity in our sample is of order @xmath82 ergs s@xmath26 ( again , we have taken @xmath83 km s@xmath26 mpc@xmath26 ) . these numbers suggest that magnification bias is not the explanation for the observed brightness of our lens candidates relative to the full lrg sample , but a more definite statement must await follow - up observations that capture the total background line flux . most known gravitational lens systems have been selected on the basis of some combination of source properties and lens cross section , whereas the sdss lrg sample is selected based on colors and magnitude . it is therefore of interest to compare known early - type lens galaxies to our candidate lenses , although this is difficult since we do not currently have truly comparable observations of the two samples . figure [ colormagvdispz ] presents our best attempt at such a comparison for lens velocity dispersions and apparent magnitudes as a function of redshift corrections . ] , with _ hst _ known - lens data taken from @xcite . the known - lens velocity dispersions are estimated from lensed image separations in the manner described by @xcite ; they may be systematic overestimates if these lenses are superimposed on the `` mass sheet '' of a high - density environment @xcite . magnitude comparison is made by transforming sdss @xmath74- and @xmath64-band magnitudes to johnson - morgan @xmath84-band using the observed transformation of @xcite . we see that our lrg lens candidates are in general of greater velocity dispersion than known lenses , and in the redshift range where the two samples overlap , the lrgs are more luminous . the brightness of the lrgs combined with the relative faintness of the background galaxies in our sample suggests that any confirmed lrg lenses would be well suited to the type of detailed lens stellar - dynamical studies described by @xcite and @xcite . we have presented a catalog of candidate strong galaxy - galaxy gravitational lens systems detected spectroscopically within the sloan digital sky survey . these systems have known foreground _ and _ background redshifts ; only the detailed spatial alignment of foreground and background galaxies remains unknown . we plan to conduct integral - field spectrographic follow - up observations of these systems , which will allow us to resolve the spatial distribution of the background nebular line emission that we have detected . these observations should confirm a substantial number of lenses within our candidate sample , with many lensed galaxies at lower redshift than any other currently known lensed extra - galactic optical sources . any lenses confirmed within our sample will be of considerable interest for the study of early - type galaxy mass distributions , and could have implications for lens - time - delay @xmath6 measurements and anomalous quasar - lens flux ratios . our sample demonstrates the feasibility of the emission - line - based spectroscopic lens search technique within the sdss and other redshift surveys , and we plan to extend the search to higher source redshifts in the near future . we have also developed and applied a method for abating the influence of night sky emission - line residuals in the 70009000- range that allows us to detect [ o iii ] and h@xmath3 emission over the redshift range @xmath85 0.40.8 without an excess of false - positive detections . funding for the creation and distribution of the sdss archive has been provided by the alfred p. sloan foundation , the participating institutions , the national aeronautics and space administration , the national science foundation , the u.s . department of energy , the japanese monbukagakusho , and the max planck society . the sdss web site is http://www.sdss.org/. the sdss is managed by the astrophysical research consortium ( arc ) for the participating institutions . the participating institutions are the university of chicago , fermilab , the institute for advanced study , the japan participation group , the johns hopkins university , los alamos national laboratory , the max - planck - institute for astronomy ( mpia ) , the max - planck - institute for astrophysics ( mpa ) , new mexico state university , university of pittsburgh , princeton university , the united states naval observatory , and the university of washington . the authors thank paul hewett for his constructive referee report . asb thanks paul schechter and hsiao - wen chen for valuable discussion and consultation . if the model of a purely gaussian noise spectrum described by @xmath15 were correct , then the distribution of scaled residual specific fluxes @xmath86 across all spectra would be gaussian with unit variance for all wavelengths @xmath87 . this is unfortunately not the case in our sample . imperfect night - sky emission - line subtraction and other miscellaneous effects give rise to an excess of `` high - significance '' outliers beyond the predictions of a gaussian model , leading to a deluge of false - positive astronomical emission - line candidates when the procedure described in [ initial ] is applied , particularly in the 70009000- region of the spectrum where the line at redshifts @xmath880.8 appears . the most drastic solution is simply to mask all sky - afflicted wavelengths . rather than concede such vast spectral coverage ( which would drastically reduce our survey volume ) , we describe the observed distribution of scaled residual specific fluxes @xmath89 within the lrg sample with a more detailed empirical noise model . the generally gaussian behavior of scaled residuals at low significance combined with the excess of high - significance residuals is well described by a mixture of gaussian and laplace distributions , expressed parametrically as @xmath90 \ , dx\ ] ] ( for history and applications of the laplace distribution , see * ? ? ? * ) the parameters of this distribution are wavelength - dependent , but we suppress this dependence in out notation . the values of @xmath91 and @xmath92 are related by normalization : @xmath93 we also fix the following relations between parameters , based on strong correlations observed in free - parameter fits to the distribution at each wavelength : @xmath94 the result is a one - parameter noise model to fit to the distribution of @xmath89 across the sample at each wavelength . ( the numerical values 0.38 and 0.09 are fixed by minimizing the sum of binned @xmath16 values for fits across all wavelengths . ) we relax conditions ( [ cond1 ] ) and ( [ cond2 ] ) and fit freely for @xmath58 and @xmath92 at a few isolated locations in the spectrum , where the effects of sky - subtraction residuals are especially strong and the correlations that suggest ( [ cond1 ] ) and ( [ cond2 ] ) break down regions near 5577 , 5894 , 6305 , and 6366 . additionally , some regions of some spectra are characterized by extreme and correlated excess variance , so for each spectrum we convolve @xmath95 capped at 5 ( to limit the influence of single pixels ) with a 100-pixel boxcar filter and exclude from the noise - modeling sample any pixels within a boxcar whose value exceeds 1.25 . we use our fitted noise model to re - scale the reported @xmath15 values such that the new distribution @xmath96 of scaled residual flux values at each wavelength becomes gaussian , while preserving the position of individual @xmath97-values within the cumulative distribution , then proceed as described in [ initial ] . both the reported noise @xmath15 _ and _ the measured residual flux values @xmath98 contain information about the actual error in the presence of imperfect subtraction , so it is sensible to base an effective noise rescaling on their ratio @xmath89 in this manner . by fitting the noise distribution parameters independently at each wavelength , we also capture the localized effects of individual night - sky lines . our strategy for assessing lensing probabilities in our sample centers on the construction of an approximated probability density @xmath99 for the unknown impact parameter @xmath92 of the background galaxy in each system . the following observed quantities are input to the calculation : the lrg and background redshifts , the lrg velocity dispersion , the background line flux received by the @xmath100-diameter spectroscopic fiber , and the median seeing for the spectroscopic plate under consideration . we also make use of the [ o ii ] line luminosity function ( lf ) reported by @xcite . we adopt the same sis model for the lrg mass distribution as was used to obtain the @xmath69 values in table [ galtable ] , and we model the background galaxies as exponential disks with a half - light radius of approximately 3 kpc ( fixed to @xmath101 at @xmath102 ) . for each system , we explore a range of impact parameters @xmath92 from 0 to @xmath103 . at each @xmath92-value , we generate a lensed image of the model background galaxy , then convolve it with a gaussian point - spread function corresponding to the median seeing reported in the spectroscopic plate header . we then integrate the image over a @xmath100-diameter circular fiber aperture centered on the model lens . the result is a tabulated function @xmath104 giving the fraction of the intrinsic flux received by the fiber ; that is , if the total galaxy line flux were @xmath105 in the absence of lensing and limited fiber sampling , the [ o ii ] line flux received by the spectroscopic fiber from a background galaxy with a source - plane offset @xmath92 would be @xmath106 . in general @xmath104 may be greater or less than one due to the competing effects of lens magnification and incomplete sampling by the fiber . next we adopt the [ o ii]-emitter lf reported by @xcite by fitting a schechter function to their figure 6 . after converting from logarithmic units , the number of [ o ii ] emitters per unit volume in an interval @xmath107 at line luminosity @xmath108 is well approximated by @xmath109 with @xmath110 and @xmath111 ergs s@xmath26 ( the overall normalization is unimportant for our purposes ) . we make a crude conversion from their assumed @xmath112 universe to our cosmology by scaling their reported luminosities up by a factor of 1.2 : the ratio of squared luminosity distances in our cosmology to theirs ranges from 1.16 at @xmath113 to 1.27 at @xmath114 , and the bulk of galaxies in their study fall within this range . assuming the form of the lf does not evolve , it corresponds to an intrinsic flux function at any redshift @xmath115 for the number of galaxies per unit redshift per unit solid angle within some intrinsic flux range @xmath116 about @xmath105 : @xmath117 with the same @xmath0 as the lf and @xmath118 $ ] , where @xmath119 is the luminosity distance to redshift @xmath115 . @xmath120 is a flux- and redshift - dependent normalization , the form of which will prove unimportant . we can now derive a joint probability density function ( pdf ) for the observation of an [ o ii]-emitting galaxy behind a given lrg at impact parameter @xmath92 , redshift @xmath115 , and with line flux @xmath121 in the fiber by setting the differential probability proportional to the corresponding expected differential number count and making use of the known relationship of @xmath121 to intrinsic flux @xmath105 through @xmath104 : @xmath122 \ , ( 2 \pi b \ , db ) \ , dz \ , [ d s_{\mathrm{fib } } / f(b ) ] ~~.\end{aligned}\ ] ] the term @xmath123 represents the solid angle in the source plane of an annulus of radius @xmath92 and thickness @xmath124 . the _ observed _ quantities @xmath125 and @xmath126 for the system are equal to the system s true @xmath121- and @xmath115-values plus some observational noise that is independent of @xmath92 , so assuming the noise is small relative to the scale on which the joint pdf varies , we may reinterpret the joint pdf as an approximate conditional pdf on @xmath92 given @xmath126 and @xmath125 : @xmath127^{-1 } \ , \psi[z_{\mathrm{obs } } , s_{\mathrm{obs } } / f(b ) ] \ , db ~~.\ ] ] the normalization @xmath128 need not be derived explicitly , since we can simply compute the right - hand side without it for the relevant range of @xmath92-values and normalize afterwards . with this pdf in hand , we can finally assign a `` lensing probability '' to the system as the integrated probability for impact parameters less than the critical value for multiple imaging in the sis model the `` einstein radius '' , equal to one - half the @xmath69 value given in table [ galtable ] . summing this probability over all systems gives the estimate quoted in [ lensornot ] of 19 strong lenses out of 49 candidates . abazajian , k. , et al . 2003 , , 126 , 2081 binney , j. 2003 , in iau symp . 220 , dark matter in galaxies , ed . s. ryder , d. j. pisano , m. walker , & k. freeman ( san francisco : asp ) , in press ; 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also preprint ( astro - ph/0009048 ) schechter , p. l. , & wambsganss , j. 2002 , , 580 , 685 schechter , p. l. , burley , g. s. , hull , c. l. , johns , m. , martin , h. m. , schaller , s. , schectman , s. a. , & west , s. c. 2003 , in proc . spie 4837 , large ground - based telescopes , ed . j. m. oschmann & l. m. stepp ( spie ) , 619 ; also preprint ( astro - ph/0207250 ) schlegel , d. j. , finkbeiner , d. p. , & davis , m. 1998 , , 500 , 525 sluse , d. , et al . 2003 , , 406 , l43 smith , j. a. , et al . 2002 , , 123 , 2121 spergel , d. n. , et al . 2003 , , 148 , 175 stoughton , c. , et al . 2002 , , 123 , 485 strauss , m. a. , et al . 2002 , , 124 , 1810 treu , t. , & koopmans , l. v. e. 2002 , , 575 , 87 turner , e. l. , ostriker , j. p. , & gott , j. r. 1984 , , 284 , 1 warren , s. j. , hewett , p. c. , lewis , g. f. , mller , p. , iovino , a. , & shaver , p. a. 1996 , , 278 , 139 warren , s. j. , iovino , a. , hewett , p. c. , & shaver , p. a. 1998 , , 299 , 1215 warren , s. j. , lewis , g. f. , hewett , p. c. , mller , p. , shaver , p. a. , & iovino , a. 1999 , , 343 , l35 willis , j. p. , hewett , p. c. , warren , s. j. , & lewis , g. f. 2000 , in proceedings of the xxth moriond meeting : cosmological physics with gravitational lensing , ed . j. tran thanh van , y. mellier , & m. moniez ( les ulis : edp sciences ) ; also preprint ( astro - ph/0008068 ) witt , h. j , mao , s. , & schechter , p. l. 195 , , 443 , 18 york , d. , et al . 2000 , , 120 , 1579[/INST] we present a catalog of 49 spectroscopic strong gravitational lens candidates selected from a sloan digital sky survey sample of 50996 luminous red galaxies . potentially lensed star - forming galaxies are detected through the presence of background oxygen and hydrogen nebular emission lines in the spectra of these massive foreground galaxies . this multiline selection eliminates the ambiguity of single - line identification and provides a very promising sample of candidate galaxy - galaxy lens systems at low to intermediate redshift , with foreground redshifts ranging from 0.16 to 0.49 and background redshifts from 0.25 to 0.81 . any lenses confirmed within our sample would be important new probes of early - type galaxy mass distributions , providing complementary constraints to those obtained from currently known lensed high - redshift quasars . </s>

to understand the nature of star formation processes , it is crucial to measure the fundamental physical parameters of molecular cores during their evolution . density structure is one of the most important parameters which can provide critical information to test theoretical models . the simplest model for a pre - collapsing core is a bonnor - ebert sphere ( hereafter bes ; bonnor 1956 and ebert 1955 ) , which describes an isothermal , non - magnetized , non - rotating , hydrostatic core bounded by external pressure . for a collapsing core , the standard model is inside - out collapse model which predicts the density @xmath5 before the gravitational collapse sets in and @xmath6 in the inner free fall region ( shu 1977 ) . vorobyov and basu ( 2005 ) find the power - law index of density profile becomes much steeper than @xmath5 in the outer region of the core if the core has finite mass reservoir . two methods have been commonly used to map the density structure of cores . one is to measure the thermal dust emission at millimeter or submillimeter wavelengths using single dishes or interferometers , and the other is to measure the extinction of the background stars at near infrared ( nir ) wavelengths . large surveys of core density structure can be conducted relatively easily using single dishes , but the resolutions are often limited and the density profile can depend on observing wavelength ( shirley et al . 2000 ; kauffmann et al . interferometers can be used to achieve high resolution in the inner - most region , but the overall structure are often resolved out ( harvey et al . given enough background stars and integration time , nir extinction observations have the best potential to achieve both high resolution and large scale mapping of the core density structure ( alves et al . previous studies have shown that bes or power - law density profiles are good descriptions for density profiles of molecular cores . kandori et al . ( 2005 ) found that bok globlules can be described as either gravitationally stable or unstable bess with nir extinction observations . shirley et al . ( 2000 ) found that the density profiles of 21 low - mass cores from starless to class i stages can be fitted with power laws @xmath6 to @xmath7 in the resolved regions with assumed dust temperature @xmath8 . it is unclear , however , whether or not the variations in the observed density structure are due to evolutionary effects . in this study , we focus on investigating the evolutionary trend of core density profiles with nir extinction observations . the observations and data reduction processes are described in 2 . the derived visual extinction ( @xmath9 ) distribution and the radial density profiles are presented in 3 . we discuss the implications from our results in 4 . we observed five isolated cores ( cb68 , l483 , cb188 , l158 and b59 ) and two fields in serpens molecular cloud in the h and ks bands using the wide - field infrared camera ( wircam ) on canada - france - hawaii telescope ( cfht ) in 2008 april and may . these fields are located in low galactic latitude and hence they have abundant background stars . the isolated cores and the selected dense cores in two serpens fields have relatively round shape and contains only a protostar ( class 0 or i ) , except for b59 . b59 is a cluster forming core and is chosen for the comparison between single star and cluster formation . for each observing field , we performed in total a 17.5 minute integration ( 5 sets of 21 dithered images ) in h band and a 3.5 minute integration ( one set of 21 dithered images ) in ks band . standard bias subtraction , flat - fielding , bad pixel masking , and sky background subtraction were performed using iiwi system , the wircam pipeline . the sky background of each image was subtracted based on the co - moving averaged frame with length of 15 minutes . we combined all images of each observing field and used sextractor package ( bertin and arnouts 1996 ) for the source extraction and photometry except for the extremly crowded cb188 field for which we used daophot package ( stetson 1987 ) . the photometry results from both methods were calibrated using the point sources with 2mass detections between 13 to 15 magnitude . the typical limiting magnitudes with 3 @xmath10 detection are about 20.7 and 19.5 in h and ks band . the @xmath9 value is determined from near - infrared color excess @xmath11 of stars in the h and ks bands ( nice method , lada et al . 1994 ) , i.e. , @xmath12 . @xmath13 is given by a dust reddening law and @xmath11 is evaluated from @xmath14 . we use @xmath15 as derived from the rv=5.5 model in weingartner and draine ( 2001 , wd ) . recent studies suggest that the reddening law in dense cores is better described with wd s rv=5.5 model rather than their rv=3.1 model which fits the reddening law derived from more diffused regions ( indebetouw et al . 2005 ; chapman et al . @xmath11 can be obtained from observations once @xmath16 of the star is known . we adopt @xmath17 mag ( lada et al . 1994 ) and assume it is a constant for all observed fields . the detected point sources in our fields are not necessary stars ; they could be young stellar objects or distant galaxies . we can not perform the standard @xmath18 color - color diagram to select stars since we did not observe our target sources in j band to save observation time . we can however take advantage of the existing catalogs from the spitzer c2d legacy project ( evans et al . 2003 ) to select bona - fide stars detected in our fields . the c2d project has developed a sophisticated source classification procedure based on the 2mass and spitzer data ( harvey et al . if the point sources are not contained in c2d catalog , we assume them to be stars . the derived extinction maps are shown in figure 1 . we assume the three dimensional shape of our observing cores are spheres and derive their density profiles . we first determine the center , radius , and background extinction of the cores ( table 1 ) , then annularly average the derived extinction to produce the extinction profile ( figure 2 ) . the centers of the four cores with each a single embedded star ( cb68 , l483 , cb188 and serp - bolo20 ) are set to be the position of their associated protostar since the protostar and the peak of @xmath9 distribution almost coincide . the center of the four starless cores ( l158 , serp - bolo1 , serp - bolo5 and serp - bolo19 ) and the cluster forming core , b59 , is set at the peak of their @xmath9 distribution . we set the annular averaging step as @xmath19 and ensure that each step contains at least five detections to obtain properly the average @xmath9 . foreground star contamination may affect the derived extinction . we expect , however , the foreground star fraction is small since all the selected regions are nearby ( @xmath20 pc ) . if foreground stars contaminate the data in @xmath19 , the derived @xmath9 of foreground stars will deviate from the median of the data . therefore , to remove the possible bias from foreground stars , we compute the median ( @xmath21 ) and the standard deviation ( @xmath22 ) of @xmath9 distribution in each annulus and remove the sources with @xmath9 larger than @xmath23 @xmath22 or smaller than @xmath24 @xmath25 . then we annularly average @xmath9 in each @xmath19 . at a certain distance from the center , the @xmath9 approaches nearly a constant value which is defined as the background @xmath9 . we calculate the average background @xmath9 ( bg ) and the standard deviation ( sd ) in the background region . the radius of the cores is defined as the distance from center to the position where the @xmath9 exceeds @xmath26 and the @xmath9 profiles are obtained by subtracting bg . the relationship between the @xmath9 and @xmath27 column density are derived from @xmath28 @xmath29 mag@xmath30 ( bohlin et al . 1978 ) . assuming all hydrogen in the dense cores is in @xmath31 form and adopting the @xmath32=5.5 reddening law ( where @xmath33 ) , we obtain @xmath34 @xmath29 mag@xmath30 . the observed column density profiles can be modeled with various functions that represent different inherent physical conditions . bonnor - ebert spheres are commonly used for presumed hydrostatic cores with flat density profiles in the center and are truncated at radius @xmath35 . on the other hand , the solutions from different collapsing models could be as simple as a single power - law function or as complex as non - analytic functions . in general , these solutions can have approximate forms described by a power - law function with different power - law indices at different positions from the center . in this work , we model the density structure of dense cores with a single power - law profile as the first approach and further examine the power - law index variation within the density profile in @xmath36 . assuming the volume density @xmath37 , the observed column density @xmath38 at the projected radius @xmath39 in the plane of the sky is @xmath40 the best fit power - law index @xmath41 in @xmath42 is obtained by minimizing the @xmath43 between derived density profile and power - law density model . we adopt the bootstrap test to determine the uncertainty in @xmath41 ( see astronomical application in wallin et al . 2007 and `` numerical recipes '' by press et al . 1993 ) . the main idea of the bootstrap test is to find the uncertainty of any operation as the dispersion of the results from the same operation on a large number of simulated data sets . we produce 100 sets of simulated density profiles for each core , where each data point in the simulated profiles is generated from a gaussian random number generator with the mean and standard deviation of the probability distribution equal to the mean and the uncertainty of the observed data . we therefore obtain the uncertainty in @xmath41 from performing our fitting procedure on each simulated data set and measuring the standard deviation of the fitting results for each core . the best - fit results are listed in table 1 . figure 2 shows the best - fit results overploted on the observed data . most of our samples have data in the range of @xmath2 except for serp - bolo1 ( @xmath44 ) and cb188 ( @xmath45 ) . to compare fairly the average power - law index of each core with the same fitting range , we further fit all samples in @xmath46 and fit cb188 in @xmath2 and @xmath46 . figure 3 shows the original best - fit results and the results obtained with the fitting range in @xmath2 and @xmath46 . the normalized @xmath47 square , @xmath48 , of the fitting results are all smaller than one because the dispersion of the data in the same radius are in general larger than the fitting uncertainty . it is common to use the measurement uncertainty as the weighting in fitting processes in many works ( e.g. harvey et al . we use however the dispersion of annularly averaged data as the error bar here to include the uncertainty in assuming spherical structure . this assumption reduces the fitting @xmath48 , but increases the uncertainty in @xmath41 . we investigate the power - law index variation of the density structure at different evolutionary stages . to increase the size of our sample , we include the results from several similar infrared extinction studies , including l694 - 2 ( harvey et al . 2003b ) , b335 ( harvey et al . 2001 ) , thumbprint nebula and dc303.8 ( kainulainen et al . 2007 ) . in these works , the extinction values are all determined from h - k color excess and the density profiles are all fitted with single power law , which is the same as our approach . although the computer codes used to do the fitting may not be identical , we expect that these differences will not be significant . the six starless cores in this sample show two different types of density structure . serp - bolo19 and l694 - 2 have the best - fit power - law index @xmath1 -2.5 ( hereafter `` steep type '' ) , while other four cores ( serp - bolo5 , serp - bolo1 , l158 and thumbprint nebula ) have the power - law index @xmath1 -1.0 to -1.4 ( hereafter `` shallow type '' ) . this index range in shallow type reduces to @xmath1 -1.0 to -1.2 if we reduce the fitting range to @xmath49 . the difference between these two types is significant even after considering the uncertainty of best - fit results and it is obtained under fair comparison with similar fitting range . on the other hand , the power - law indices of class 0 samples do not have clear two different types as starless cores but a range about -1.9 to -2.6 . the two samples in class i stage show two different power - law indices again ( -2.7 in serp - bolo20 and -1.2 in cb188 ) . this discrepancy may result from different fitting ranges . indeed , their best - fit results become similar to class 0 sources after considering only a fixed fitting range within @xmath50 ( figure 3 ) . for the starless cores , the @xmath9 difference between the center and the edge also show a dichotomous nature . the shallow type starless cores have much smaller @xmath9 difference ( @xmath1 22 mag ) compared to the steep type starless and protostellar cores ( @xmath1 45 mag ) . if all starless cores in our sample eventually evolve into protostellar cores , our results suggest that the starless cores with shallower density structure will evolve into steeper ones via certain core - forming processes and their density structure have a averaged @xmath51 during the formation of the protostars . one way to examine if the starless cores will evolve into the protostellar cores is to probe their kinematic structure . lee et al . ( 2004 ) shows that both l158 ( shallow type ) and l694 - 2 ( steep type ) have infall signatures in the molecular spectra , which are consistent with our suggestions that some shallow type starless cores will evolve to the steep type during the formation of protostars . some core collapsing models predict a power - law index variation within the density profile . for example , a discontinuity in power - law indices of the density profile separates the interior infalling region from the exterior static region , and the discontinuity will propagate outward with sound speed during collapse ( e.g. shu 1977 , fatuzzo et al . 2004 ) . since the crossing time of the discontinuity ( @xmath52 yr , estimated with @xmath53 , @xmath54 @xmath55 and @xmath56 @xmath57 ) is comparable to the statistical lifetime of class 0 and class i stages ( @xmath58 yr and @xmath52 yr , andre et al . 2000 ) , we should be able to see the discontinuity in the observed density profiles in class 0 or class i stages . the best - fit results with fitting range of @xmath46 showed in figure 3 are in general steeper than fitting range of @xmath2 , suggesting the power - law index may vary within core density profile and specifically , it may become steeper near the edge . we examine this trend by modified fitting processes . considering the simplest case , a core has a two power - law volume density profile with the discontinuity at @xmath59 . its column density profile within projected radius @xmath60 will be an integration of the volume density over regions with both power - law indices along the line of sight while the column density outside of @xmath60 will only reflect the power - law index in the outer region . therefore , we can obtain the best - fit power - law index @xmath61 in the region @xmath62 and then use @xmath61 as a known parameter to determine the best - fit power - law index @xmath63 in the @xmath64 region . @xmath60 is the radius chosen where the single power - law fitting in the region of @xmath65 reaches minimum @xmath48 . the feasibility of the above procedures , however , is limited due to the large uncertainty of annularly averaged data . when we vary @xmath60 from outer region toward inner region , we may not be able to find obvious minimum @xmath48 and the best fit @xmath61 may vary significantly . if we set the criteria for variation of best - fit @xmath61 smaller than @xmath66 ( i.e. , the typical uncertainty in best - fit single power - law profile ) , l483 is the only possible candidate that shows deviation from a single power - law profile . in l483 , the @xmath48 of the two power - law model are @xmath1 six times smaller than the @xmath48 of single power - law profile . this difference , however , is not significant since the best fit results of two models are both obtained with @xmath67 . the best - fit two power - law profile of l483 has the steep power index @xmath68 at @xmath69 @xmath70 and @xmath71 at @xmath72 . this result shows the possible power - law index variation in a class 0 sample , the power - law index @xmath73 in inner region is consistent with the power - law index in the infall region of inside - out collapsing scenario . the power - law index , however , becomes steeper than @xmath74 at @xmath75 suggesting other effects ( e.g. see the discussions in 4.3 ) besides inside - out collapse should be considered in outer parts of the core . our results show that the density profiles evolve from a shallower one with @xmath76 to a steeper one with @xmath51 in the epoch of core formation and the steepened density profile is sustained during the formation of protostar . furthermore , the procedures for investigating the power - law index variation within a core suggest a steep index may present in the outside part of the core . one explanation for these results is that a core has to form a finite mass object before the inside - out collapse sets in . vorobyov and basu ( 2005 , vb05 ) considered the effect of a finite mass reservoir during the core - forming and collapse phases . they found that an equivalent `` rarefaction wave '' is generated at the core boundary and propagates inward , which rapidly reduces the infall rate and steepens the density profile to @xmath77 ( figure 1 in vb05 ) . our results show a similar evolutionary trend with a steep power - law index seen in the outer region of our samples , as described in vb05 . in addition , the vb05 model predicts that the infall velocity increases toward the center and then decreases when the velocity reaches a peak at @xmath78 to @xmath79 km s@xmath30 . a recent study on the velocity field of two starless cores show results consistent with the vb05 model ( figure 2 in lee et al . 2007 ) . the physical reason for the `` finite mass effect '' could originate from the boundary of supercritical and subcritical region . for example , tassis and mouschovias ( 2007 , tm07 ) show that during core formation via ambipolar diffusion , the magnetically supported mass can not replenish the inner supercritical infall mass , resulting in a steep power - law index in the outer parts of the core ( figure 2d in tm07 ) . therefore , we may still see the cores smoothly blend in with the background but not confined by sharp edges as the literal meaning of finite mass . the origin of the `` finite mass effect '' and how significant is it for the star formation needs further investigation via observations on the density structure and also velocity structure of the cores at various evolutionary stages . we thank shantanu basu and fred c. adams for their insightful discussion on the first draft of this paper . this work is based on observations obtained at the canada - france - hawaii telescope ( cfht ) which is operated by the national research council of canada , the institut national des sciences de lunivers of the centre national de la recherche scientifique of france , and the university of hawaii . access to the cfht was made possible by the institute of astronomy and astrophysics , academia sinica , taiwan . clh and spl are supported by national science council of taiwan under grant nsc 96 - 2112-m-007 - 019-my2 and nsc 98 - 2112-m-007 - 007-my3 . harvey , d. w. a. , wilner , d. j. , lada , c. j. , myers , p. c. , alves , j. f. , & chen , h. 2001 , , 563 , 903 harvey , d. w. a. , wilner , d. j. , myers , p. c. , & tafalla , m. 2003 , , 596 , 383 harvey , d. w. a. , wilner , d. j. , lada , c. j. , myers , p. c. , & alves , j. f. 2003 , , 598 , 1112 harvey , p. , mern , b. , huard , t. l. , rebull , l. m. , chapman , n. , evans , n. j. , ii , & myers , p. c. 2007 , , 663 , 1149 indebetouw , r. , et al . 2005 , , 619 , 931 kainulainen , j. , lehtinen , k. , visnen , p. , bronfman , l. , & knude , j. 2007 , , 463 , 1029 kandori , r. , et al . 2005 , , 130 , 2166 kauffmann , j. , bertoldi , f. , bourke , t. l. , evans , n. j. , ii , & lee , c. w. 2008 , , 487 , 993 lada , c. j. , lada , e. a. , clemens , d. p. , & bally , j. 1994 , , 429 , 694 lee , c. w. , myers , p. c. , & plume , r. 2004 , , 153 , 523 lee , s. h. , park , y .- s . , sohn , j. , lee , c. w. , & lee , h. m. 2007 , , 660 , 1326 shirley , y. l. , evans , n. j. , ii , rawlings , j. m. c. , & gregersen , e. m. 2000 , , 131 , 249 shu , f. h. 1977 , , 214 , 488 stetson , p. b. 1987 , , 99 , 191 tafalla , m. , myers , p. c. , mardones , d. , & bachiller , r. 2000 , , 359 , 967 tassis , k. , & mouschovias , t. c. 2007 , , 660 , 388 lllccccccccc name & & & & & & & & & & + & & & & & & & & & & & + l158&16 47 22.2 & @xmath8013 59 23&@xmath81&starless&@xmath82&@xmath83&@xmath84&@xmath85&@xmath86&@xmath87 & + serp - bolo1&18 28 23.1 & @xmath8800 26 34&@xmath89&starless & @xmath90&@xmath91&@xmath92&@xmath93&@xmath94&@xmath95 & + serp - bolo5&18 28 48.3 & @xmath8800 14 51&@xmath89&starless&@xmath96&@xmath97&@xmath98&@xmath99&@xmath100&@xmath101 & + serp - bolo19&18 29 31.5 & @xmath8800 26 49&@xmath89&starless&@xmath102&@xmath103&@xmath104&@xmath105&@xmath106&@xmath107 & + cb68&16 57 29.6 & @xmath8016 09 23&@xmath108&class 0&@xmath109&@xmath83&@xmath84&@xmath110&@xmath111&@xmath112 & + l483&18 17 30.0 & @xmath8004 39 40&@xmath113&class 0&@xmath114&@xmath83&@xmath115&@xmath116&@xmath117&@xmath118 & + serp - bolo20&18 29 31.9 & @xmath8801 19 01&@xmath89&class i & @xmath119&@xmath103&@xmath120&@xmath121&@xmath122&@xmath107 & + cb188&19 20 15.8 & @xmath8811 35 53&@xmath123&class i&@xmath124&@xmath103&@xmath125&@xmath126&@xmath127&@xmath128 & + b59&17 11 23.8 & @xmath8027 26 03&@xmath81&cluster&@xmath129&@xmath130&@xmath131&@xmath132&@xmath133&@xmath134 & + thumbprint&12 44 55.6 & @xmath8078 48 16&@xmath81 & starless&@xmath80&@xmath80&@xmath80&@xmath80&@xmath135&@xmath136&a + l694 - 2&19 41 04.4 & @xmath8810 57 01&@xmath81 & starless&@xmath80&@xmath80&@xmath80&@xmath80&@xmath137&@xmath138&b + dc303.8 - 14.2&13 07 38.0 & @xmath8077 00 21&@xmath81 & class 0&@xmath80&@xmath80&@xmath80&@xmath80&@xmath139&@xmath140&a + b335&19 37 00.9 & @xmath8807 34 10&@xmath81 & class 0&@xmath80&@xmath80&@xmath80&@xmath80&@xmath141&@xmath142&c +

we present a near - infrared extinction study of nine dense cores at evolutionary stages between starless to class i. our results show that the density structure of all but one observed cores can be modeled with a single power law @xmath0 between @xmath1 @xmath2 of the cores . the starless cores in our sample show two different types of density structures , one follows @xmath3 and the other follows @xmath4 , while the protostellar cores all have @xmath4 . the similarity between the prestellar cores with @xmath4 and protostellar cores implies that those prestellar cores could be evolving towards the protostellar stage . the slope of @xmath4 is steeper than that of an singular isothermal sphere , which may be interpreted with the evolutionary model of cores with finite mass .

<s>[INST]to understand the nature of star formation processes , it is crucial to measure the fundamental physical parameters of molecular cores during their evolution . density structure is one of the most important parameters which can provide critical information to test theoretical models . the simplest model for a pre - collapsing core is a bonnor - ebert sphere ( hereafter bes ; bonnor 1956 and ebert 1955 ) , which describes an isothermal , non - magnetized , non - rotating , hydrostatic core bounded by external pressure . for a collapsing core , the standard model is inside - out collapse model which predicts the density @xmath5 before the gravitational collapse sets in and @xmath6 in the inner free fall region ( shu 1977 ) . vorobyov and basu ( 2005 ) find the power - law index of density profile becomes much steeper than @xmath5 in the outer region of the core if the core has finite mass reservoir . two methods have been commonly used to map the density structure of cores . one is to measure the thermal dust emission at millimeter or submillimeter wavelengths using single dishes or interferometers , and the other is to measure the extinction of the background stars at near infrared ( nir ) wavelengths . large surveys of core density structure can be conducted relatively easily using single dishes , but the resolutions are often limited and the density profile can depend on observing wavelength ( shirley et al . 2000 ; kauffmann et al . interferometers can be used to achieve high resolution in the inner - most region , but the overall structure are often resolved out ( harvey et al . given enough background stars and integration time , nir extinction observations have the best potential to achieve both high resolution and large scale mapping of the core density structure ( alves et al . previous studies have shown that bes or power - law density profiles are good descriptions for density profiles of molecular cores . kandori et al . ( 2005 ) found that bok globlules can be described as either gravitationally stable or unstable bess with nir extinction observations . shirley et al . ( 2000 ) found that the density profiles of 21 low - mass cores from starless to class i stages can be fitted with power laws @xmath6 to @xmath7 in the resolved regions with assumed dust temperature @xmath8 . it is unclear , however , whether or not the variations in the observed density structure are due to evolutionary effects . in this study , we focus on investigating the evolutionary trend of core density profiles with nir extinction observations . the observations and data reduction processes are described in 2 . the derived visual extinction ( @xmath9 ) distribution and the radial density profiles are presented in 3 . we discuss the implications from our results in 4 . we observed five isolated cores ( cb68 , l483 , cb188 , l158 and b59 ) and two fields in serpens molecular cloud in the h and ks bands using the wide - field infrared camera ( wircam ) on canada - france - hawaii telescope ( cfht ) in 2008 april and may . these fields are located in low galactic latitude and hence they have abundant background stars . the isolated cores and the selected dense cores in two serpens fields have relatively round shape and contains only a protostar ( class 0 or i ) , except for b59 . b59 is a cluster forming core and is chosen for the comparison between single star and cluster formation . for each observing field , we performed in total a 17.5 minute integration ( 5 sets of 21 dithered images ) in h band and a 3.5 minute integration ( one set of 21 dithered images ) in ks band . standard bias subtraction , flat - fielding , bad pixel masking , and sky background subtraction were performed using iiwi system , the wircam pipeline . the sky background of each image was subtracted based on the co - moving averaged frame with length of 15 minutes . we combined all images of each observing field and used sextractor package ( bertin and arnouts 1996 ) for the source extraction and photometry except for the extremly crowded cb188 field for which we used daophot package ( stetson 1987 ) . the photometry results from both methods were calibrated using the point sources with 2mass detections between 13 to 15 magnitude . the typical limiting magnitudes with 3 @xmath10 detection are about 20.7 and 19.5 in h and ks band . the @xmath9 value is determined from near - infrared color excess @xmath11 of stars in the h and ks bands ( nice method , lada et al . 1994 ) , i.e. , @xmath12 . @xmath13 is given by a dust reddening law and @xmath11 is evaluated from @xmath14 . we use @xmath15 as derived from the rv=5.5 model in weingartner and draine ( 2001 , wd ) . recent studies suggest that the reddening law in dense cores is better described with wd s rv=5.5 model rather than their rv=3.1 model which fits the reddening law derived from more diffused regions ( indebetouw et al . 2005 ; chapman et al . @xmath11 can be obtained from observations once @xmath16 of the star is known . we adopt @xmath17 mag ( lada et al . 1994 ) and assume it is a constant for all observed fields . the detected point sources in our fields are not necessary stars ; they could be young stellar objects or distant galaxies . we can not perform the standard @xmath18 color - color diagram to select stars since we did not observe our target sources in j band to save observation time . we can however take advantage of the existing catalogs from the spitzer c2d legacy project ( evans et al . 2003 ) to select bona - fide stars detected in our fields . the c2d project has developed a sophisticated source classification procedure based on the 2mass and spitzer data ( harvey et al . if the point sources are not contained in c2d catalog , we assume them to be stars . the derived extinction maps are shown in figure 1 . we assume the three dimensional shape of our observing cores are spheres and derive their density profiles . we first determine the center , radius , and background extinction of the cores ( table 1 ) , then annularly average the derived extinction to produce the extinction profile ( figure 2 ) . the centers of the four cores with each a single embedded star ( cb68 , l483 , cb188 and serp - bolo20 ) are set to be the position of their associated protostar since the protostar and the peak of @xmath9 distribution almost coincide . the center of the four starless cores ( l158 , serp - bolo1 , serp - bolo5 and serp - bolo19 ) and the cluster forming core , b59 , is set at the peak of their @xmath9 distribution . we set the annular averaging step as @xmath19 and ensure that each step contains at least five detections to obtain properly the average @xmath9 . foreground star contamination may affect the derived extinction . we expect , however , the foreground star fraction is small since all the selected regions are nearby ( @xmath20 pc ) . if foreground stars contaminate the data in @xmath19 , the derived @xmath9 of foreground stars will deviate from the median of the data . therefore , to remove the possible bias from foreground stars , we compute the median ( @xmath21 ) and the standard deviation ( @xmath22 ) of @xmath9 distribution in each annulus and remove the sources with @xmath9 larger than @xmath23 @xmath22 or smaller than @xmath24 @xmath25 . then we annularly average @xmath9 in each @xmath19 . at a certain distance from the center , the @xmath9 approaches nearly a constant value which is defined as the background @xmath9 . we calculate the average background @xmath9 ( bg ) and the standard deviation ( sd ) in the background region . the radius of the cores is defined as the distance from center to the position where the @xmath9 exceeds @xmath26 and the @xmath9 profiles are obtained by subtracting bg . the relationship between the @xmath9 and @xmath27 column density are derived from @xmath28 @xmath29 mag@xmath30 ( bohlin et al . 1978 ) . assuming all hydrogen in the dense cores is in @xmath31 form and adopting the @xmath32=5.5 reddening law ( where @xmath33 ) , we obtain @xmath34 @xmath29 mag@xmath30 . the observed column density profiles can be modeled with various functions that represent different inherent physical conditions . bonnor - ebert spheres are commonly used for presumed hydrostatic cores with flat density profiles in the center and are truncated at radius @xmath35 . on the other hand , the solutions from different collapsing models could be as simple as a single power - law function or as complex as non - analytic functions . in general , these solutions can have approximate forms described by a power - law function with different power - law indices at different positions from the center . in this work , we model the density structure of dense cores with a single power - law profile as the first approach and further examine the power - law index variation within the density profile in @xmath36 . assuming the volume density @xmath37 , the observed column density @xmath38 at the projected radius @xmath39 in the plane of the sky is @xmath40 the best fit power - law index @xmath41 in @xmath42 is obtained by minimizing the @xmath43 between derived density profile and power - law density model . we adopt the bootstrap test to determine the uncertainty in @xmath41 ( see astronomical application in wallin et al . 2007 and `` numerical recipes '' by press et al . 1993 ) . the main idea of the bootstrap test is to find the uncertainty of any operation as the dispersion of the results from the same operation on a large number of simulated data sets . we produce 100 sets of simulated density profiles for each core , where each data point in the simulated profiles is generated from a gaussian random number generator with the mean and standard deviation of the probability distribution equal to the mean and the uncertainty of the observed data . we therefore obtain the uncertainty in @xmath41 from performing our fitting procedure on each simulated data set and measuring the standard deviation of the fitting results for each core . the best - fit results are listed in table 1 . figure 2 shows the best - fit results overploted on the observed data . most of our samples have data in the range of @xmath2 except for serp - bolo1 ( @xmath44 ) and cb188 ( @xmath45 ) . to compare fairly the average power - law index of each core with the same fitting range , we further fit all samples in @xmath46 and fit cb188 in @xmath2 and @xmath46 . figure 3 shows the original best - fit results and the results obtained with the fitting range in @xmath2 and @xmath46 . the normalized @xmath47 square , @xmath48 , of the fitting results are all smaller than one because the dispersion of the data in the same radius are in general larger than the fitting uncertainty . it is common to use the measurement uncertainty as the weighting in fitting processes in many works ( e.g. harvey et al . we use however the dispersion of annularly averaged data as the error bar here to include the uncertainty in assuming spherical structure . this assumption reduces the fitting @xmath48 , but increases the uncertainty in @xmath41 . we investigate the power - law index variation of the density structure at different evolutionary stages . to increase the size of our sample , we include the results from several similar infrared extinction studies , including l694 - 2 ( harvey et al . 2003b ) , b335 ( harvey et al . 2001 ) , thumbprint nebula and dc303.8 ( kainulainen et al . 2007 ) . in these works , the extinction values are all determined from h - k color excess and the density profiles are all fitted with single power law , which is the same as our approach . although the computer codes used to do the fitting may not be identical , we expect that these differences will not be significant . the six starless cores in this sample show two different types of density structure . serp - bolo19 and l694 - 2 have the best - fit power - law index @xmath1 -2.5 ( hereafter `` steep type '' ) , while other four cores ( serp - bolo5 , serp - bolo1 , l158 and thumbprint nebula ) have the power - law index @xmath1 -1.0 to -1.4 ( hereafter `` shallow type '' ) . this index range in shallow type reduces to @xmath1 -1.0 to -1.2 if we reduce the fitting range to @xmath49 . the difference between these two types is significant even after considering the uncertainty of best - fit results and it is obtained under fair comparison with similar fitting range . on the other hand , the power - law indices of class 0 samples do not have clear two different types as starless cores but a range about -1.9 to -2.6 . the two samples in class i stage show two different power - law indices again ( -2.7 in serp - bolo20 and -1.2 in cb188 ) . this discrepancy may result from different fitting ranges . indeed , their best - fit results become similar to class 0 sources after considering only a fixed fitting range within @xmath50 ( figure 3 ) . for the starless cores , the @xmath9 difference between the center and the edge also show a dichotomous nature . the shallow type starless cores have much smaller @xmath9 difference ( @xmath1 22 mag ) compared to the steep type starless and protostellar cores ( @xmath1 45 mag ) . if all starless cores in our sample eventually evolve into protostellar cores , our results suggest that the starless cores with shallower density structure will evolve into steeper ones via certain core - forming processes and their density structure have a averaged @xmath51 during the formation of the protostars . one way to examine if the starless cores will evolve into the protostellar cores is to probe their kinematic structure . lee et al . ( 2004 ) shows that both l158 ( shallow type ) and l694 - 2 ( steep type ) have infall signatures in the molecular spectra , which are consistent with our suggestions that some shallow type starless cores will evolve to the steep type during the formation of protostars . some core collapsing models predict a power - law index variation within the density profile . for example , a discontinuity in power - law indices of the density profile separates the interior infalling region from the exterior static region , and the discontinuity will propagate outward with sound speed during collapse ( e.g. shu 1977 , fatuzzo et al . 2004 ) . since the crossing time of the discontinuity ( @xmath52 yr , estimated with @xmath53 , @xmath54 @xmath55 and @xmath56 @xmath57 ) is comparable to the statistical lifetime of class 0 and class i stages ( @xmath58 yr and @xmath52 yr , andre et al . 2000 ) , we should be able to see the discontinuity in the observed density profiles in class 0 or class i stages . the best - fit results with fitting range of @xmath46 showed in figure 3 are in general steeper than fitting range of @xmath2 , suggesting the power - law index may vary within core density profile and specifically , it may become steeper near the edge . we examine this trend by modified fitting processes . considering the simplest case , a core has a two power - law volume density profile with the discontinuity at @xmath59 . its column density profile within projected radius @xmath60 will be an integration of the volume density over regions with both power - law indices along the line of sight while the column density outside of @xmath60 will only reflect the power - law index in the outer region . therefore , we can obtain the best - fit power - law index @xmath61 in the region @xmath62 and then use @xmath61 as a known parameter to determine the best - fit power - law index @xmath63 in the @xmath64 region . @xmath60 is the radius chosen where the single power - law fitting in the region of @xmath65 reaches minimum @xmath48 . the feasibility of the above procedures , however , is limited due to the large uncertainty of annularly averaged data . when we vary @xmath60 from outer region toward inner region , we may not be able to find obvious minimum @xmath48 and the best fit @xmath61 may vary significantly . if we set the criteria for variation of best - fit @xmath61 smaller than @xmath66 ( i.e. , the typical uncertainty in best - fit single power - law profile ) , l483 is the only possible candidate that shows deviation from a single power - law profile . in l483 , the @xmath48 of the two power - law model are @xmath1 six times smaller than the @xmath48 of single power - law profile . this difference , however , is not significant since the best fit results of two models are both obtained with @xmath67 . the best - fit two power - law profile of l483 has the steep power index @xmath68 at @xmath69 @xmath70 and @xmath71 at @xmath72 . this result shows the possible power - law index variation in a class 0 sample , the power - law index @xmath73 in inner region is consistent with the power - law index in the infall region of inside - out collapsing scenario . the power - law index , however , becomes steeper than @xmath74 at @xmath75 suggesting other effects ( e.g. see the discussions in 4.3 ) besides inside - out collapse should be considered in outer parts of the core . our results show that the density profiles evolve from a shallower one with @xmath76 to a steeper one with @xmath51 in the epoch of core formation and the steepened density profile is sustained during the formation of protostar . furthermore , the procedures for investigating the power - law index variation within a core suggest a steep index may present in the outside part of the core . one explanation for these results is that a core has to form a finite mass object before the inside - out collapse sets in . vorobyov and basu ( 2005 , vb05 ) considered the effect of a finite mass reservoir during the core - forming and collapse phases . they found that an equivalent `` rarefaction wave '' is generated at the core boundary and propagates inward , which rapidly reduces the infall rate and steepens the density profile to @xmath77 ( figure 1 in vb05 ) . our results show a similar evolutionary trend with a steep power - law index seen in the outer region of our samples , as described in vb05 . in addition , the vb05 model predicts that the infall velocity increases toward the center and then decreases when the velocity reaches a peak at @xmath78 to @xmath79 km s@xmath30 . a recent study on the velocity field of two starless cores show results consistent with the vb05 model ( figure 2 in lee et al . 2007 ) . the physical reason for the `` finite mass effect '' could originate from the boundary of supercritical and subcritical region . for example , tassis and mouschovias ( 2007 , tm07 ) show that during core formation via ambipolar diffusion , the magnetically supported mass can not replenish the inner supercritical infall mass , resulting in a steep power - law index in the outer parts of the core ( figure 2d in tm07 ) . therefore , we may still see the cores smoothly blend in with the background but not confined by sharp edges as the literal meaning of finite mass . the origin of the `` finite mass effect '' and how significant is it for the star formation needs further investigation via observations on the density structure and also velocity structure of the cores at various evolutionary stages . we thank shantanu basu and fred c. adams for their insightful discussion on the first draft of this paper . this work is based on observations obtained at the canada - france - hawaii telescope ( cfht ) which is operated by the national research council of canada , the institut national des sciences de lunivers of the centre national de la recherche scientifique of france , and the university of hawaii . access to the cfht was made possible by the institute of astronomy and astrophysics , academia sinica , taiwan . clh and spl are supported by national science council of taiwan under grant nsc 96 - 2112-m-007 - 019-my2 and nsc 98 - 2112-m-007 - 007-my3 . harvey , d. w. a. , wilner , d. j. , lada , c. j. , myers , p. c. , alves , j. f. , & chen , h. 2001 , , 563 , 903 harvey , d. w. a. , wilner , d. j. , myers , p. c. , & tafalla , m. 2003 , , 596 , 383 harvey , d. w. a. , wilner , d. j. , lada , c. j. , myers , p. c. , & alves , j. f. 2003 , , 598 , 1112 harvey , p. , mern , b. , huard , t. l. , rebull , l. m. , chapman , n. , evans , n. j. , ii , & myers , p. c. 2007 , , 663 , 1149 indebetouw , r. , et al . 2005 , , 619 , 931 kainulainen , j. , lehtinen , k. , visnen , p. , bronfman , l. , & knude , j. 2007 , , 463 , 1029 kandori , r. , et al . 2005 , , 130 , 2166 kauffmann , j. , bertoldi , f. , bourke , t. l. , evans , n. j. , ii , & lee , c. w. 2008 , , 487 , 993 lada , c. j. , lada , e. a. , clemens , d. p. , & bally , j. 1994 , , 429 , 694 lee , c. w. , myers , p. c. , & plume , r. 2004 , , 153 , 523 lee , s. h. , park , y .- s . , sohn , j. , lee , c. w. , & lee , h. m. 2007 , , 660 , 1326 shirley , y. l. , evans , n. j. , ii , rawlings , j. m. c. , & gregersen , e. m. 2000 , , 131 , 249 shu , f. h. 1977 , , 214 , 488 stetson , p. b. 1987 , , 99 , 191 tafalla , m. , myers , p. c. , mardones , d. , & bachiller , r. 2000 , , 359 , 967 tassis , k. , & mouschovias , t. c. 2007 , , 660 , 388 lllccccccccc name & & & & & & & & & & + & & & & & & & & & & & + l158&16 47 22.2 & @xmath8013 59 23&@xmath81&starless&@xmath82&@xmath83&@xmath84&@xmath85&@xmath86&@xmath87 & + serp - bolo1&18 28 23.1 & @xmath8800 26 34&@xmath89&starless & @xmath90&@xmath91&@xmath92&@xmath93&@xmath94&@xmath95 & + serp - bolo5&18 28 48.3 & @xmath8800 14 51&@xmath89&starless&@xmath96&@xmath97&@xmath98&@xmath99&@xmath100&@xmath101 & + serp - bolo19&18 29 31.5 & @xmath8800 26 49&@xmath89&starless&@xmath102&@xmath103&@xmath104&@xmath105&@xmath106&@xmath107 & + cb68&16 57 29.6 & @xmath8016 09 23&@xmath108&class 0&@xmath109&@xmath83&@xmath84&@xmath110&@xmath111&@xmath112 & + l483&18 17 30.0 & @xmath8004 39 40&@xmath113&class 0&@xmath114&@xmath83&@xmath115&@xmath116&@xmath117&@xmath118 & + serp - bolo20&18 29 31.9 & @xmath8801 19 01&@xmath89&class i & @xmath119&@xmath103&@xmath120&@xmath121&@xmath122&@xmath107 & + cb188&19 20 15.8 & @xmath8811 35 53&@xmath123&class i&@xmath124&@xmath103&@xmath125&@xmath126&@xmath127&@xmath128 & + b59&17 11 23.8 & @xmath8027 26 03&@xmath81&cluster&@xmath129&@xmath130&@xmath131&@xmath132&@xmath133&@xmath134 & + thumbprint&12 44 55.6 & @xmath8078 48 16&@xmath81 & starless&@xmath80&@xmath80&@xmath80&@xmath80&@xmath135&@xmath136&a + l694 - 2&19 41 04.4 & @xmath8810 57 01&@xmath81 & starless&@xmath80&@xmath80&@xmath80&@xmath80&@xmath137&@xmath138&b + dc303.8 - 14.2&13 07 38.0 & @xmath8077 00 21&@xmath81 & class 0&@xmath80&@xmath80&@xmath80&@xmath80&@xmath139&@xmath140&a + b335&19 37 00.9 & @xmath8807 34 10&@xmath81 & class 0&@xmath80&@xmath80&@xmath80&@xmath80&@xmath141&@xmath142&c +[/INST] we present a near - infrared extinction study of nine dense cores at evolutionary stages between starless to class i. our results show that the density structure of all but one observed cores can be modeled with a single power law @xmath0 between @xmath1 @xmath2 of the cores . the starless cores in our sample show two different types of density structures , one follows @xmath3 and the other follows @xmath4 , while the protostellar cores all have @xmath4 . the similarity between the prestellar cores with @xmath4 and protostellar cores implies that those prestellar cores could be evolving towards the protostellar stage . the slope of @xmath4 is steeper than that of an singular isothermal sphere , which may be interpreted with the evolutionary model of cores with finite mass . </s>

rotator cuff tear is a common disease . according to general population surveys , the prevalence of rotator cuff tear is 25 % in those older than 50 years of age and 20 % in those older than 20 years of age . the interesting thing is that only 1/3 of the tears cause pain and 2/3 are without pain . only 20 % of those who have shoulder pain come to the clinic , whereas the rest go to bone setters or chiropractors , buy pain killers , or just leave it alone . this means that only 1/15 of those with rotator cuff tears come to see us at the clinic . in other words , when we see one patient at our clinic with a symptomatic rotator cuff tear , there are 4 more patients with a symptomatic tear and 10 more patients with an asymptomatic tear in the background . we evaluated the symptoms of patients with rotator cuff tears when they first come to see us . there were 157 patients who visited us : 138 patients ( 87.9 % ) came to us because of pain ; 17 ( 10.8 % ) came to us because of pain and muscle weakness less than manual muscle testing ( mmt ) grade 3 ( fair ) ; 2 patients ( 1.3 % ) came to us because of muscle weakness less than mmt grade 3 without pain . almost 99 % of patients with rotator cuff tears come to the clinic because of pain . we often experience that an injection of local anesthetics into the subacromial bursa decreases shoulder pain and increases shoulder strength . reported that the uptake of radioisotopes on bone scintigraphy increased in shoulders with a symptomatic tear compared to the contralateral intact shoulders . inflammation seems to be one of the major causes of pain in shoulders with a rotator cuff tear . in fact , oral medication of anti - inflammatory non - steroidal drugs ( nsaids ) or intra - articular injection of corticosteroid is known to be effective in reducing the pain . although the conservative treatment does not promote the healing of a tear , it is effective in most of the cases because the major symptom is pain , which is often controllable by the conservative treatment . physical examination starts with inspection . it is easy to detect muscle atrophy of the infraspinatus viewing from the back of the patient because the infraspinatus is located just under the skin , whereas the supraspinatus is covered by the trapezius ( fig . 1 ) . atrophy of the shoulder muscles is a common finding in patients with rotator cuff tears . if the parascapular muscles do not function well , the scapula is protracted and located away from the spinous processes . next , the scapular motion on the thorax is examined from the back of the patient . this smooth movement of the scapula on the thorax may have deteriorated because of subacromial impingement , and as a result , the medial boarder of the scapula may be prominent during arm depression in order to avoid the passing of the rotator cuff tendon underneath the acromion ( fig . 2 ) . the tip of the finger is placed just anterior to the acromion to palpate the defect of the cuff tendon ( fig . a tendon defect may be felt just anterior to the acromion with the shoulder in extension , and it disappears under the acromion with the shoulder in flexion . according to wolf and agrawal , the sensitivity and specificity of this palpating of the cuff tendon defect for the diagnosis of full - thickness rotator cuff tears were 96 and 97 % , respectively , which were equivalent to the sensitivity and specificity of magnetic resonance imaging ( mri ) or ultrasonography.fig . the right infraspinatus muscle is atrophic , and the infraspinous fossa is dented ( arrow)fig . the medial boarder of the right scapula ( arrows ) is prominent because of subacromial impingementfig . a delle or defect of the tendon may be palpated just anterior to the anterior margin of the acromion atrophy of the shoulder musculature . the right infraspinatus muscle is atrophic , and the infraspinous fossa is dented ( arrow ) winging of the scapula . the medial boarder of the right scapula ( arrows ) is prominent because of subacromial impingement palpation of a delle ( defect ) of the cuff tendon . a delle or defect of the tendon may be palpated just anterior to the anterior margin of the acromion during active or passive arm elevation , patients may feel shoulder pain because of subacromial impingement . it is called painful arc if the pain appears during active arm elevation or depression . the pain appears between 90 and 120 during arm elevation , and it appears between 90 and 30 during arm depression . on the other hand , if the pain appears during passive arm motion , it is called a positive impingement sign . two types of impingement sign are well known : the neer ( fig . 4 ) and the hawkins and kennedy ( fig . modifications of these signs are also possible ( figs . 6 , 7).fig . 4neer impingement sign . while holding the scapula with one hand to avoid scapular rotation , apply elevation force to the arm that is in internal rotation . this procedure causes pain if there is a subacromial impingementfig . 5hawkins impingement sign . with the arm in flexion , apply internal rotation force , which causes pain if there is a subacromial impingementfig . 6modified neer sign . applying elevation force with the arm in external rotation is a modification of original neer signfig . apply internal rotation force , which causes pain neer impingement sign . while holding the scapula with one hand to avoid scapular rotation , this procedure causes pain if there is a subacromial impingement hawkins impingement sign . with the arm in flexion , apply internal rotation force , which causes pain if there is a subacromial impingement modified neer sign . applying elevation force with the arm in external rotation is a modification of original neer sign modified hawkins sign . keeping the arm in abduction , apply internal rotation force , which causes pain for the purpose of identifying which tendon is ruptured , various location - specific physical examinations have been reported . a tear of the supraspinatus tendon can be detected by the empty - can test ( fig . the accuracy of the tests was the greatest when muscle weakness was interpreted as indicating a torn supraspinatus tendon in both the full - can test ( 75 % accurate ) and the empty - can test ( 70 % accurate ) .fig . 8supraspinatus test ( empty - can test ) . apply downward force to the arm in 90 scaption and in internal rotation ( thumb down ) . if there is a supraspinatus tear , the patient can not resist this force because of muscle weaknessfig . apply downward force with the arm in 90 scaption and in external rotation ( thumb up ) . if there is a supraspinatus tear , the patient can not resist this force and the arm will be depressed supraspinatus test ( empty - can test ) . apply downward force to the arm in 90 scaption and in internal rotation ( thumb down ) . if there is a supraspinatus tear , the patient can not resist this force because of muscle weakness supraspinatus test ( full - can test ) . apply downward force with the arm in 90 scaption and in external rotation ( thumb up ) . if there is a supraspinatus tear , the patient can not resist this force and the arm will be depressed the major external rotators of the shoulder are the infraspinatus and teres minor . measuring the isometric strength of external rotation with the arm at the side a patient can not keep the arm in external rotation at the side when a tear involves the major portion of the infraspinatus tendon . as a result , the forearm drops to the neutral rotation position , and this is called the dropping sign , described by neer ( fig . hertel et al . introduced an external rotation lag sign , which is similar to the dropping sign . if a tear is more extensive and involves the teres minor , the external rotation strength decreases with the arm in abduction , which leads to a positive hornblower s sign ( fig . reported that the hornblower s sign had a sensitivity of 100 % and a specificity of 93 % for the presence of stage 3 or stage 4 fatty degeneration of teres minor on the ct scan . on the other hand , the dropping sign had a 100 % sensitivity and specificity for the presence of stage 3 or stage 4 fatty degeneration of the infraspinatus.fig . on the intact side ( a ) , the patient can keep the arm in external rotation position when the examiner lets the arm go . on the involved side ( b ) , the patient can not keep the arm in external rotation , and the arm comes back to the neutral rotation after the examiner lets the arm gofig . he can do it , but only with the elbow in a high position and the wrist in extension on the affected side ( right arm ) . on the intact side ( left arm ) , the patient can reach the mouth without bringing the elbow high dropping sign or external rotation lag sign . the patient is asked to keep the arm in external rotation . on the intact side ( a ) , the patient can keep the arm in external rotation position when the examiner lets the arm go . on the involved side ( b ) , the patient can not keep the arm in external rotation , and the arm comes back to the neutral rotation after the examiner lets the arm go hornblower s sign . he can do it , but only with the elbow in a high position and the wrist in extension on the affected side ( right arm ) . on the intact side ( left arm ) , the patient can reach the mouth without bringing the elbow high with a tear of the subscapularis , the internal rotation strength theoretically decreases , but because of the other internal rotators such as the teres major , latissimus dorsi , and pectoralis major , it is difficult to evaluate a decrease in the internal rotation strength with the arm in neutral rotation using the manual muscle test . the lift - off test to detect a subscapularis tear was introduced by gerber and krushell ( fig . placing the hand behind the back at the lumbar level , the shoulder is almost in full internal rotation , and the only internal rotator that functions in this position is the subscapularis . the patient is instructed to raise the hand off the back , performing a further internal rotation of the shoulder . inability to hold the hand off the back is indicative of subscapularis tearing . in cases with limited motion of internal rotation , the belly press test a patient can lift off the hand from the back at the lumbar level with the intact subscapularis ( a ) . if it is torn , the patient can not lift off the hand from the back ( b)fig . , a patient can press the belly with the hand , wrist , and elbow straight ( a ) . if the subscapularis is torn , the patient can not keep the hand , wrist , and elbow straight to press the belly ( b ) . due to weakness , the patient flexes the wrist and brings the elbow backward in order to press the belly lift - off test . a patient can lift off the hand from the back at the lumbar level with the intact subscapularis ( a ) . if it is torn , the patient can not lift off the hand from the back ( b ) belly - press test . with the intact subscapularis , a patient can press the belly with the hand , wrist , and elbow straight ( a ) . if the subscapularis is torn , the patient can not keep the hand , wrist , and elbow straight to press the belly ( b ) . due to weakness , the patient flexes the wrist and brings the elbow backward in order to press the belly for the purpose of eliminating pain , we use oral nsaid medication , steroids or hyaluronic acid injections into the glenohumeral joint or subacromial bursa depending upon the site of the tear . physical therapy such as heat , stretching , passive and active range of motion exercises , and muscle strengthening exercises are prescribed . if there is any dyskinesis of the scapulothoracic motion ( scapular protraction ) , it needs to be corrected by physical therapy . the success rate of conservative treatment ranges from 33 % to 82 % in the literature . in our first study , we retrospectively reviewed 62 shoulders of 54 patients with full - thickness tears who were followed up without surgery . the follow - up period averaged 3.4 years . according to modified criteria of wolfgang , 51 shoulders in 45 patients ( 82 % ) were rated as satisfactory ( excellent or good ) . the patients with satisfactory results and unsatisfactory results among those observed more than 5 years were compared . the only significant differences in the initial findings between the two groups were the active abduction angle and the abduction strength : the patients with satisfactory results retained a good range of motion and strength , whereas those with unsatisfactory results had a limited range and muscle weakness on initial examination . conservative treatment affords satisfactory results when given to the patients with well - preserved motion and strength . the limitation of this study was that all surgical cases were excluded . in order to evaluate the efficacy of conservative treatment , those who failed to respond to conservative treatment and eventually underwent surgical treatment should be included as failure cases of conservative treatment . in our next study , we prospectively treated 107 shoulders of 105 consecutive patients with full - thickness tears of the rotator cuff . if the shoulder symptoms remained but the patients did not want to undergo surgery , conservative treatment was continued . if the patients were not happy with their shoulder because of remaining symptoms after 6 months of conservative treatment , they underwent surgical treatment with informed consent . the average age of the patients was 64 years ( range 4480 years ) . these three patients were evaluated as failure cases of conservative treatment . at the time of follow - up , one patient was dead as the result of a cause other than the shoulder and one patient was missing . in total , we followed 102 shoulders of 100 patients with an average follow - up period of 32 ( 1248 ) months . at the time of follow - up , 50 % of them were totally pain free , and 40 % had mild pain not requiring pain killers . regarding activities of daily living , 75 % of the patients said they felt no limitations in daily activities . in total , 75/100 ( 75 % ) had good or excellent results according to the shoulder rating score of the japanese orthopaedic association . adding three surgical cases as failure cases , the success rate was 73 % ( 75/103 ) . as of may 2010 , 396 patients with full thickness rotator cuff tears have been enrolled . they began a physical therapy program with or without an intraarticular injection depending upon the severity of symptoms . , they could choose one of three outcomes : ( 1 ) cured ( no follow - up scheduled ) , ( 2 ) improved ( continued therapy with scheduled reassessment in 6 weeks ) , or ( 3 ) not better ( arthroscopic cuff repair scheduled ) . overall , 10 % of the patients chose surgery after 6 weeks and another 10 % chose surgery within 2 years . this made the success rate of conservative treatment 90 % at 6 weeks and 80 % at 2 years . considering these studies , conservative treatment is thought to be effective in 7380 % of cases with full - thickness tears of the rotator cuff . a systematic review has shown that exercise has statistically and clinically significant effects on pain reduction and improving function , but not on the range of motion or strength . when we perform conservative treatment , we should pay attention to two things : ( 1 ) the responsiveness of patients to conservative treatment and ( 2 ) recurrence of symptoms . if we know who will respond well to conservative treatment and who will not before initiating the treatment , it would be beneficial for both the doctors and patients because we would not have to waste non - responders ' time . also , the present symptom might go away after conservative treatment , but could recur in the future . if the symptoms disappear after the initial treatment but come back repeatedly , the patient will not be happy . if we knew who had a good chance of recurrence , we could advise surgery for them . we performed a study to determine the physical and mri findings characteristic of responders on the initial examination by comparing those who responded well and those who responded poorly to conservative treatment . this study included 123 shoulders of 118 patients with full - thickness rotator cuff tears diagnosed by mri . clinical symptoms improved in 65 shoulders of 62 patients with conservative treatment ( responders ) , but remained unchanged or aggravated in 58 shoulders of 56 patients who eventually underwent surgical repair ( non - responders ) . the following parameters showed significant differences : ( 1 ) impingement sign ( positive in 30.7 % in the responders and 79.3 % in the non - responders ) ; ( 2 ) active external rotation angle on physical examination ( 52.2 in the responders and 35.0 in the non - responders ) ; ( 3 ) integrity of the intramuscular tendon of the supraspinatus on mri ( 58.4 % in the responders and 24.1 % in the non - responders showed an intact intramuscular tendon ) ; ( 4 ) presence of supraspinatus muscle atrophy on mri ( occupancy ratio was 78.0 % in the responders and 69.8 % in the non - responders ) . the success rate of conservative treatment was 92 % in patients with all of these four factors and 5.2 % in those with none of these factors . these four factors seem to be useful in separating responders from non - responders before initiating treatment . after an average of 2.8 years , 51 % of them became symptomatic . they found that there was a strong association between symptom appearances and tear size expansion . mall et al . prospectively monitored 195 patients with asymptomatic tears for pain development . with pain development , the size of a full - thickness tear increased significantly , with 18 % of the full - thickness tears showing an increase of more than 5 mm , and 40 % of the partial - thickness tears progressed to a full - thickness tear . they concluded that pain development in shoulders with an asymptomatic tear was associated with an increase in tear size . safran et al . evaluated 61 full - thickness tears equal to or larger than 5 mm in 51 patients using ultrasonography . at an average follow - up period of 29 months , there was a significant correlation between the existence of pain and increase in tear size . these reports tell us that the remnant or recurrent pain is related to an increase in tear size . , there were no correlations between the change in tear size and age of the patients , sex , existence of a prior trauma , initial size of the tear , and bilateral tears . on the other hand , maman et al . reported that factors that were associated with progression of a rotator cuff tear were an age of more than 60 years , a full - thickness tear , and fatty infiltration of the rotator cuff muscles . we evaluated the relationship between the tear size and the degree of labor in 195 patients with rotator cuff tears ( unpublished data ) . the tear size was significantly greater in heavy laborers ( 8.2 1.7 cm ) than in medium ( 4.9 1.1 cm ) or sedentary laborers ( 4.2 1.5 cm ) ( p = 0.0020 ) . vigorous use of the shoulder or traumatic event on the shoulder seems to be related to tear expansion . smoking is known to be related to tear size : the greater the smoking index , the larger the tear [ 30 , 31 ] .

rotator cuff tear is one of the most common shoulder diseases . it is interesting that some rotator cuff tears are symptomatic , whereas others are asymptomatic . pain is the most common symptom of patients with a tear . even in patients with an asymptomatic tear , it may become symptomatic with an increase in tear size . physical examination is extremely important to evaluate the presence , location , and extent of a tear . it also helps us to understand the mechanism of pain . conservative treatment often works . patients with well - preserved function of the supraspinatus and infraspinatus are the best candidates for conservative treatment . after a successful conservative treatment , the symptom once disappeared may come back again . this recurrence of symptoms is related to tear expansion . those with high risk of tear expansion and those with less functional rotator cuff muscles are less likely to respond to conservative treatment . they may need a surgical treatment .

<s>[INST]rotator cuff tear is a common disease . according to general population surveys , the prevalence of rotator cuff tear is 25 % in those older than 50 years of age and 20 % in those older than 20 years of age . the interesting thing is that only 1/3 of the tears cause pain and 2/3 are without pain . only 20 % of those who have shoulder pain come to the clinic , whereas the rest go to bone setters or chiropractors , buy pain killers , or just leave it alone . this means that only 1/15 of those with rotator cuff tears come to see us at the clinic . in other words , when we see one patient at our clinic with a symptomatic rotator cuff tear , there are 4 more patients with a symptomatic tear and 10 more patients with an asymptomatic tear in the background . we evaluated the symptoms of patients with rotator cuff tears when they first come to see us . there were 157 patients who visited us : 138 patients ( 87.9 % ) came to us because of pain ; 17 ( 10.8 % ) came to us because of pain and muscle weakness less than manual muscle testing ( mmt ) grade 3 ( fair ) ; 2 patients ( 1.3 % ) came to us because of muscle weakness less than mmt grade 3 without pain . almost 99 % of patients with rotator cuff tears come to the clinic because of pain . we often experience that an injection of local anesthetics into the subacromial bursa decreases shoulder pain and increases shoulder strength . reported that the uptake of radioisotopes on bone scintigraphy increased in shoulders with a symptomatic tear compared to the contralateral intact shoulders . inflammation seems to be one of the major causes of pain in shoulders with a rotator cuff tear . in fact , oral medication of anti - inflammatory non - steroidal drugs ( nsaids ) or intra - articular injection of corticosteroid is known to be effective in reducing the pain . although the conservative treatment does not promote the healing of a tear , it is effective in most of the cases because the major symptom is pain , which is often controllable by the conservative treatment . physical examination starts with inspection . it is easy to detect muscle atrophy of the infraspinatus viewing from the back of the patient because the infraspinatus is located just under the skin , whereas the supraspinatus is covered by the trapezius ( fig . 1 ) . atrophy of the shoulder muscles is a common finding in patients with rotator cuff tears . if the parascapular muscles do not function well , the scapula is protracted and located away from the spinous processes . next , the scapular motion on the thorax is examined from the back of the patient . this smooth movement of the scapula on the thorax may have deteriorated because of subacromial impingement , and as a result , the medial boarder of the scapula may be prominent during arm depression in order to avoid the passing of the rotator cuff tendon underneath the acromion ( fig . 2 ) . the tip of the finger is placed just anterior to the acromion to palpate the defect of the cuff tendon ( fig . a tendon defect may be felt just anterior to the acromion with the shoulder in extension , and it disappears under the acromion with the shoulder in flexion . according to wolf and agrawal , the sensitivity and specificity of this palpating of the cuff tendon defect for the diagnosis of full - thickness rotator cuff tears were 96 and 97 % , respectively , which were equivalent to the sensitivity and specificity of magnetic resonance imaging ( mri ) or ultrasonography.fig . the right infraspinatus muscle is atrophic , and the infraspinous fossa is dented ( arrow)fig . the medial boarder of the right scapula ( arrows ) is prominent because of subacromial impingementfig . a delle or defect of the tendon may be palpated just anterior to the anterior margin of the acromion atrophy of the shoulder musculature . the right infraspinatus muscle is atrophic , and the infraspinous fossa is dented ( arrow ) winging of the scapula . the medial boarder of the right scapula ( arrows ) is prominent because of subacromial impingement palpation of a delle ( defect ) of the cuff tendon . a delle or defect of the tendon may be palpated just anterior to the anterior margin of the acromion during active or passive arm elevation , patients may feel shoulder pain because of subacromial impingement . it is called painful arc if the pain appears during active arm elevation or depression . the pain appears between 90 and 120 during arm elevation , and it appears between 90 and 30 during arm depression . on the other hand , if the pain appears during passive arm motion , it is called a positive impingement sign . two types of impingement sign are well known : the neer ( fig . 4 ) and the hawkins and kennedy ( fig . modifications of these signs are also possible ( figs . 6 , 7).fig . 4neer impingement sign . while holding the scapula with one hand to avoid scapular rotation , apply elevation force to the arm that is in internal rotation . this procedure causes pain if there is a subacromial impingementfig . 5hawkins impingement sign . with the arm in flexion , apply internal rotation force , which causes pain if there is a subacromial impingementfig . 6modified neer sign . applying elevation force with the arm in external rotation is a modification of original neer signfig . apply internal rotation force , which causes pain neer impingement sign . while holding the scapula with one hand to avoid scapular rotation , this procedure causes pain if there is a subacromial impingement hawkins impingement sign . with the arm in flexion , apply internal rotation force , which causes pain if there is a subacromial impingement modified neer sign . applying elevation force with the arm in external rotation is a modification of original neer sign modified hawkins sign . keeping the arm in abduction , apply internal rotation force , which causes pain for the purpose of identifying which tendon is ruptured , various location - specific physical examinations have been reported . a tear of the supraspinatus tendon can be detected by the empty - can test ( fig . the accuracy of the tests was the greatest when muscle weakness was interpreted as indicating a torn supraspinatus tendon in both the full - can test ( 75 % accurate ) and the empty - can test ( 70 % accurate ) .fig . 8supraspinatus test ( empty - can test ) . apply downward force to the arm in 90 scaption and in internal rotation ( thumb down ) . if there is a supraspinatus tear , the patient can not resist this force because of muscle weaknessfig . apply downward force with the arm in 90 scaption and in external rotation ( thumb up ) . if there is a supraspinatus tear , the patient can not resist this force and the arm will be depressed supraspinatus test ( empty - can test ) . apply downward force to the arm in 90 scaption and in internal rotation ( thumb down ) . if there is a supraspinatus tear , the patient can not resist this force because of muscle weakness supraspinatus test ( full - can test ) . apply downward force with the arm in 90 scaption and in external rotation ( thumb up ) . if there is a supraspinatus tear , the patient can not resist this force and the arm will be depressed the major external rotators of the shoulder are the infraspinatus and teres minor . measuring the isometric strength of external rotation with the arm at the side a patient can not keep the arm in external rotation at the side when a tear involves the major portion of the infraspinatus tendon . as a result , the forearm drops to the neutral rotation position , and this is called the dropping sign , described by neer ( fig . hertel et al . introduced an external rotation lag sign , which is similar to the dropping sign . if a tear is more extensive and involves the teres minor , the external rotation strength decreases with the arm in abduction , which leads to a positive hornblower s sign ( fig . reported that the hornblower s sign had a sensitivity of 100 % and a specificity of 93 % for the presence of stage 3 or stage 4 fatty degeneration of teres minor on the ct scan . on the other hand , the dropping sign had a 100 % sensitivity and specificity for the presence of stage 3 or stage 4 fatty degeneration of the infraspinatus.fig . on the intact side ( a ) , the patient can keep the arm in external rotation position when the examiner lets the arm go . on the involved side ( b ) , the patient can not keep the arm in external rotation , and the arm comes back to the neutral rotation after the examiner lets the arm gofig . he can do it , but only with the elbow in a high position and the wrist in extension on the affected side ( right arm ) . on the intact side ( left arm ) , the patient can reach the mouth without bringing the elbow high dropping sign or external rotation lag sign . the patient is asked to keep the arm in external rotation . on the intact side ( a ) , the patient can keep the arm in external rotation position when the examiner lets the arm go . on the involved side ( b ) , the patient can not keep the arm in external rotation , and the arm comes back to the neutral rotation after the examiner lets the arm go hornblower s sign . he can do it , but only with the elbow in a high position and the wrist in extension on the affected side ( right arm ) . on the intact side ( left arm ) , the patient can reach the mouth without bringing the elbow high with a tear of the subscapularis , the internal rotation strength theoretically decreases , but because of the other internal rotators such as the teres major , latissimus dorsi , and pectoralis major , it is difficult to evaluate a decrease in the internal rotation strength with the arm in neutral rotation using the manual muscle test . the lift - off test to detect a subscapularis tear was introduced by gerber and krushell ( fig . placing the hand behind the back at the lumbar level , the shoulder is almost in full internal rotation , and the only internal rotator that functions in this position is the subscapularis . the patient is instructed to raise the hand off the back , performing a further internal rotation of the shoulder . inability to hold the hand off the back is indicative of subscapularis tearing . in cases with limited motion of internal rotation , the belly press test a patient can lift off the hand from the back at the lumbar level with the intact subscapularis ( a ) . if it is torn , the patient can not lift off the hand from the back ( b)fig . , a patient can press the belly with the hand , wrist , and elbow straight ( a ) . if the subscapularis is torn , the patient can not keep the hand , wrist , and elbow straight to press the belly ( b ) . due to weakness , the patient flexes the wrist and brings the elbow backward in order to press the belly lift - off test . a patient can lift off the hand from the back at the lumbar level with the intact subscapularis ( a ) . if it is torn , the patient can not lift off the hand from the back ( b ) belly - press test . with the intact subscapularis , a patient can press the belly with the hand , wrist , and elbow straight ( a ) . if the subscapularis is torn , the patient can not keep the hand , wrist , and elbow straight to press the belly ( b ) . due to weakness , the patient flexes the wrist and brings the elbow backward in order to press the belly for the purpose of eliminating pain , we use oral nsaid medication , steroids or hyaluronic acid injections into the glenohumeral joint or subacromial bursa depending upon the site of the tear . physical therapy such as heat , stretching , passive and active range of motion exercises , and muscle strengthening exercises are prescribed . if there is any dyskinesis of the scapulothoracic motion ( scapular protraction ) , it needs to be corrected by physical therapy . the success rate of conservative treatment ranges from 33 % to 82 % in the literature . in our first study , we retrospectively reviewed 62 shoulders of 54 patients with full - thickness tears who were followed up without surgery . the follow - up period averaged 3.4 years . according to modified criteria of wolfgang , 51 shoulders in 45 patients ( 82 % ) were rated as satisfactory ( excellent or good ) . the patients with satisfactory results and unsatisfactory results among those observed more than 5 years were compared . the only significant differences in the initial findings between the two groups were the active abduction angle and the abduction strength : the patients with satisfactory results retained a good range of motion and strength , whereas those with unsatisfactory results had a limited range and muscle weakness on initial examination . conservative treatment affords satisfactory results when given to the patients with well - preserved motion and strength . the limitation of this study was that all surgical cases were excluded . in order to evaluate the efficacy of conservative treatment , those who failed to respond to conservative treatment and eventually underwent surgical treatment should be included as failure cases of conservative treatment . in our next study , we prospectively treated 107 shoulders of 105 consecutive patients with full - thickness tears of the rotator cuff . if the shoulder symptoms remained but the patients did not want to undergo surgery , conservative treatment was continued . if the patients were not happy with their shoulder because of remaining symptoms after 6 months of conservative treatment , they underwent surgical treatment with informed consent . the average age of the patients was 64 years ( range 4480 years ) . these three patients were evaluated as failure cases of conservative treatment . at the time of follow - up , one patient was dead as the result of a cause other than the shoulder and one patient was missing . in total , we followed 102 shoulders of 100 patients with an average follow - up period of 32 ( 1248 ) months . at the time of follow - up , 50 % of them were totally pain free , and 40 % had mild pain not requiring pain killers . regarding activities of daily living , 75 % of the patients said they felt no limitations in daily activities . in total , 75/100 ( 75 % ) had good or excellent results according to the shoulder rating score of the japanese orthopaedic association . adding three surgical cases as failure cases , the success rate was 73 % ( 75/103 ) . as of may 2010 , 396 patients with full thickness rotator cuff tears have been enrolled . they began a physical therapy program with or without an intraarticular injection depending upon the severity of symptoms . , they could choose one of three outcomes : ( 1 ) cured ( no follow - up scheduled ) , ( 2 ) improved ( continued therapy with scheduled reassessment in 6 weeks ) , or ( 3 ) not better ( arthroscopic cuff repair scheduled ) . overall , 10 % of the patients chose surgery after 6 weeks and another 10 % chose surgery within 2 years . this made the success rate of conservative treatment 90 % at 6 weeks and 80 % at 2 years . considering these studies , conservative treatment is thought to be effective in 7380 % of cases with full - thickness tears of the rotator cuff . a systematic review has shown that exercise has statistically and clinically significant effects on pain reduction and improving function , but not on the range of motion or strength . when we perform conservative treatment , we should pay attention to two things : ( 1 ) the responsiveness of patients to conservative treatment and ( 2 ) recurrence of symptoms . if we know who will respond well to conservative treatment and who will not before initiating the treatment , it would be beneficial for both the doctors and patients because we would not have to waste non - responders ' time . also , the present symptom might go away after conservative treatment , but could recur in the future . if the symptoms disappear after the initial treatment but come back repeatedly , the patient will not be happy . if we knew who had a good chance of recurrence , we could advise surgery for them . we performed a study to determine the physical and mri findings characteristic of responders on the initial examination by comparing those who responded well and those who responded poorly to conservative treatment . this study included 123 shoulders of 118 patients with full - thickness rotator cuff tears diagnosed by mri . clinical symptoms improved in 65 shoulders of 62 patients with conservative treatment ( responders ) , but remained unchanged or aggravated in 58 shoulders of 56 patients who eventually underwent surgical repair ( non - responders ) . the following parameters showed significant differences : ( 1 ) impingement sign ( positive in 30.7 % in the responders and 79.3 % in the non - responders ) ; ( 2 ) active external rotation angle on physical examination ( 52.2 in the responders and 35.0 in the non - responders ) ; ( 3 ) integrity of the intramuscular tendon of the supraspinatus on mri ( 58.4 % in the responders and 24.1 % in the non - responders showed an intact intramuscular tendon ) ; ( 4 ) presence of supraspinatus muscle atrophy on mri ( occupancy ratio was 78.0 % in the responders and 69.8 % in the non - responders ) . the success rate of conservative treatment was 92 % in patients with all of these four factors and 5.2 % in those with none of these factors . these four factors seem to be useful in separating responders from non - responders before initiating treatment . after an average of 2.8 years , 51 % of them became symptomatic . they found that there was a strong association between symptom appearances and tear size expansion . mall et al . prospectively monitored 195 patients with asymptomatic tears for pain development . with pain development , the size of a full - thickness tear increased significantly , with 18 % of the full - thickness tears showing an increase of more than 5 mm , and 40 % of the partial - thickness tears progressed to a full - thickness tear . they concluded that pain development in shoulders with an asymptomatic tear was associated with an increase in tear size . safran et al . evaluated 61 full - thickness tears equal to or larger than 5 mm in 51 patients using ultrasonography . at an average follow - up period of 29 months , there was a significant correlation between the existence of pain and increase in tear size . these reports tell us that the remnant or recurrent pain is related to an increase in tear size . , there were no correlations between the change in tear size and age of the patients , sex , existence of a prior trauma , initial size of the tear , and bilateral tears . on the other hand , maman et al . reported that factors that were associated with progression of a rotator cuff tear were an age of more than 60 years , a full - thickness tear , and fatty infiltration of the rotator cuff muscles . we evaluated the relationship between the tear size and the degree of labor in 195 patients with rotator cuff tears ( unpublished data ) . the tear size was significantly greater in heavy laborers ( 8.2 1.7 cm ) than in medium ( 4.9 1.1 cm ) or sedentary laborers ( 4.2 1.5 cm ) ( p = 0.0020 ) . vigorous use of the shoulder or traumatic event on the shoulder seems to be related to tear expansion . smoking is known to be related to tear size : the greater the smoking index , the larger the tear [ 30 , 31 ] .[/INST]rotator cuff tear is one of the most common shoulder diseases . it is interesting that some rotator cuff tears are symptomatic , whereas others are asymptomatic . pain is the most common symptom of patients with a tear . even in patients with an asymptomatic tear , it may become symptomatic with an increase in tear size . physical examination is extremely important to evaluate the presence , location , and extent of a tear . it also helps us to understand the mechanism of pain . conservative treatment often works . patients with well - preserved function of the supraspinatus and infraspinatus are the best candidates for conservative treatment . after a successful conservative treatment , the symptom once disappeared may come back again . this recurrence of symptoms is related to tear expansion . those with high risk of tear expansion and those with less functional rotator cuff muscles are less likely to respond to conservative treatment . they may need a surgical treatment .</s>

absorbing states , i.e. , states which systems may fall into but never escape from , and phase transitions into them are expected to be ubiquitous in nature . for instance , spreading or contamination processes like fires or epidemics exhibit such transitions when the propagation rate changes : initially active ( infected ) regions eventually disappear forever at low rates , i.e. , the absorbing state is reached , while they can be sustained ( pandemic regime ) for fast - enough propagation . examples abound far beyond : hundreds of numerical models , describing , e.g. , catalytic reactions , granular flows , and calcium dynamics in living cells , to name but a few , have been shown to exhibit such absorbing phase transitions @xcite . such phase transitions also naturally arise from general problems such as synchronization @xcite , self - organized criticality @xcite , spatiotemporal intermittency @xcite , and depinning @xcite . the vast majority of these transitions share the same critical behavior , that of the `` directed percolation '' ( dp ) class @xcite , as long as they are continuous . deep theoretical issues underpin this situation . whereas universality is well understood for systems in thermodynamic equilibrium , this is still not the case for systems driven out of equilibrium , where even the relevant ingredients determining the class are not well understood . in this context , absorbing phase transitions are central because of their genuine nonequilibrium character , since absorbing states directly imply violation of the detailed balance . janssen and grassberger @xcite conjectured that the dp universality class contains all continuous transitions into a single effective absorbing state in the absence of any extra symmetry or conservation law . the dp class thus appears as the simplest , and most common case , as testified by overwhelming numerical evidence . however , the situation has been quite different in experiments . over the last twenty years and more , a number of experiments have been performed in situations where dp - class transitions would be theoretically expected , but they have always yielded mixed and/or partial results with limited accuracy @xcite ( table [ tbl : earlierexperiments ] ) . this lack of fully convincing experimental realizations , in contrast with the wealth of numerical results , has been found surprising and a matter of concern in the literature @xcite . recently , though , studying a spatiotemporal intermittency regime occurring in turbulent liquid crystals , we found a transition whose complete set of static critical exponents match those of the dp class @xcite . the goal of the present paper is to provide a comprehensive report on this transition including not only a more complete description of experiments designed to investigate the static critical behavior , but also new experiments giving access to dynamic critical behavior . lllllllll ( 1 + 1)d system & size & @xmath0 & @xmath1 & @xmath2 & @xmath3 & @xmath4 & refs . + annular rayleigh - bnard & @xmath5 & & @xmath6 & & @xmath7 & @xmath8 & @xcite + annular rayleigh - bnard & @xmath9 & & @xmath6 & @xmath6 & @xmath10 & @xmath11 & @xcite + linear rayleigh - bnard & @xmath12 & @xmath13 & @xmath14 & @xmath14 & @xmath15 & @xmath16 & @xcite + interface roughening & & & & & & @xcite + viscous fingering & @xmath17 & @xmath18 & & & @xmath19 & @xmath20 & @xcite + vortices of fluid & @xmath21 & @xmath6 & & & & @xmath22 & @xcite + taylor - deen & @xmath23 & @xmath24 & @xmath25 & @xmath26 & @xmath27 & @xmath28 & @xcite + taylor - couette & @xmath29 & @xmath30 & @xmath31 & & @xmath32-@xmath33 & & @xcite + granular flow & & & & & & @xcite + torsional couette & & @xmath34 & @xmath35 & & & & @xcite + ferrofluidic spikes & @xmath36 & @xmath13 & @xmath37 & @xmath38 & @xmath39 & @xmath40 & @xcite + lateral heat convection in annulus & @xmath41 & @xmath42 & @xmath43 & @xmath44 & & & @xcite + dp & & @xmath45 & @xmath46 & @xmath47 & @xmath48 & @xmath49 & @xcite + & & & & & + ( 2 + 1)d system & size & @xmath0 & @xmath1 & @xmath2 & @xmath3 & @xmath4 & refs . + liquid columns & @xmath50 & @xmath51 & & & & & @xcite + dsm1-dsm2 ( present paper ) & @xmath52 & @xmath53 & @xmath54 & @xmath55 & @xmath56 & @xmath57 & + dp & & @xmath58 & @xmath59 & @xmath60 & @xmath61 & @xmath62 & @xcite + the paper is organized as follows . we first illustrate the coarse - grained dynamics of the turbulent regime of electroconvection studied and our basic experimental setup ( sec . [ sec : setup ] ) , with further details on image analysis given in the appendix . to characterize the critical behavior , we perform three series of experiments : ( a ) steady - state experiment under constant applied voltages ( sec . [ sec : steadystate ] ) , ( b ) critical - quench experiment starting from fully active initial conditions ( sec . [ sec : criticalquench ] ) , and ( c ) critical - spreading experiment starting from a single active seed , prepared with a novel experimental technique using pulse laser , developed in this work ( sec . [ sec : criticalspreading ] ) . in sec . [ sec : summary ] , our results are summarized and we discuss why clear dp - class critical behavior is observed rather easily in our system , contrary to many other experiments performed in the past in this context . we work on the electrohydrodynamic convection of nematic liquid crystals , which occurs when a thin layer of liquid crystal is subjected to an external voltage strong enough to trigger the carr - helfrich instability @xcite . this is _ a priori _ a suitable system to study critical behavior thanks to its possibly large aspect ratio , fast response time , and easy controllability . we focus on the transition between two turbulent regimes , called dynamic scattering modes 1 and 2 ( dsm1 and dsm2 ) , observed successively upon increasing the root - mean - square amplitude of the voltage @xmath63 at relatively low frequencies @xcite . the difference between dsm1 and dsm2 lies in their density of topological defects in the director field [ fig . [ fig : dsm1dsm2](a ) ] . in the dsm2 state , a large quantity of these defects , called disclinations , are present @xcite . they elongate and split constantly under the shear due to the fluctuating turbulent flow around . in dsm1 , on the other hand , disclinations are present but kept smaller than the critical size and disappear immediately . their density thus remains very low . the many disclinations in dsm2 lead to the loss of macroscopic nematic anisotropy and to a lower light transmittance than in dsm1 . our basic experimental setup is shown in fig . [ fig : setup ] . the sample cell is made of two parallel glass plates spaced by a polyester film of thickness @xmath64 . both inner surfaces are covered with transparent electrodes of size @xmath65 , coated with polyvinyl alcohol and then rubbed in order that molecules are planarly aligned in the @xmath66 direction , defined thereby . the cell is filled with @xmath67-(4-methoxybenzylidene)-4-butylaniline ( mbba ; purity @xmath68 , tokyo chemical industry ) doped with 0.01 wt.% of tetra-@xmath69-butylammonium bromide . the temperature of the cell is kept constant carefully by a handmade thermocontroller , composed of heating wires and peltier elements controlled by a proportional - integral - derivative feedback loop with a lock - in amplifier [ fig . [ fig : setup](b ) ] . windows of the thermocontroller are made of sapphire in order to improve the spatial homogeneity of the temperature . throughout each series of experiments , the cell temperature is maintained at @xmath70 with fluctuations typically of a few @xmath71 , unless otherwise stipulated , measured by three thermistors placed at different positions close to the cell . we observe the electroconvection through the transmitted light from a handmade stabilized light source made of light - emitting diodes , recorded by a charge - coupled device camera . the observed region is a central rectangle of size @xmath72 ( fig . [ fig : setup ] , inset ) . since there is a minimum linear size of dsm2 domains , @xmath73 @xcite , we can roughly estimate the number of effective degrees of freedom at @xmath74 for the convection area and @xmath75 for the observation area . note that the meaningful figure is that of the total system size , which is at least four orders of magnitude larger than in earlier experimental studies ( table [ tbl : earlierexperiments ] ) . in the following , we vary @xmath63 and fix the frequency at @xmath76 , at roughly one third of the cutoff frequency @xmath77 which separates the conducting and the dielectric regimes of electroconvection @xcite . disclinations being topological defects , the spontaneous nucleation of dsm2 in a dsm1 domain is in principle forbidden . it is indeed an essentially unobservable rare event , except along the edges of the electrode and for very high voltages , far from the range investigated in the present paper . therefore , the fully dsm1 state serves as an absorbing state . on the other hand , dsm2 domains introduced externally , or present initially in the system can remain sustained in the bulk for large enough voltages , but eventually disappear for voltages lower than a certain threshold @xmath78 . closely above @xmath78 , a regime of spatiotemporal intermittency ( sti ) is observed , with dsm2 patches moving around on a dsm1 background [ fig . [ fig : dsm1dsm2](b ) , and movie s1 of ref . the basic dynamics of the observed sti is illustrated in fig . [ fig : dsm1dsm2](d ) : active dsm2 patches evolve in space - time essentially by contamination of neighboring inactive ( absorbing ) dsm1 regions and by relaxation into the dsm1 state . this suggests an absorbing phase transition induced by change in rates of both elementary processes @xcite , which are functions of the applied voltage here . the order parameter @xmath79 is then simply the ratio of the surface occupied by active dsm2 regions to the whole area . prior to any analysis , we must distinguish dsm2 domains from dsm1 . this binary reduction can be easily performed by our eyes , so we automated it , based on the facts that dsm2 domains have lower transmittance , longer time correlations , and have a minimum area of @xmath80 @xcite ( see appendix for details ) . a typical result is shown in fig . [ fig : dsm1dsm2](c ) , and in movie s2 of ref . figure [ fig : dsm1dsm2](e ) displays spatiotemporal diagrams obtained this way , showing how dsm2 patches evolve in the steady state . this supports the qualitative dynamics illustrated in fig . [ fig : dsm1dsm2](d ) and indeed looks like the directed percolation of , say , water in a porous medium under gravitational field . we first observe sti in the steady state under constant voltage @xmath63 , in the range of @xmath81 . the voltage for the onset of steady roll convection ( williams domain ) is @xmath82 . spatiotemporal distributions of dsm2 patches are recorded over the period @xmath83 , which is longer than @xmath84 correlation times defined from the fluctuations of the order parameter @xmath85 . as a function of @xmath63 in the steady state . inset : same data in logarithmic scales . errorbars indicate the standard deviation of fluctuations in @xmath85 and @xmath63 . blue dashed lines are fitting curves . ] figure [ fig : steadystaterho ] shows the time - averaged order parameter @xmath86 , i.e. , the average fraction of dsm2 . it shows that the transition is continuous and that @xmath86 scales algebraically near the critical point . fitting these data with the usual scaling form @xcite @xmath87 the critical voltage @xmath78 and the critical exponent @xmath0 are found to be @xmath88 where the numbers in parentheses indicate the range of errors in the last digits @xcite . our estimate @xmath89 is in good agreement with the value for @xmath90-dimensional dp , @xmath91 @xcite . we then measure the distributions of the sizes @xmath92 and durations @xmath93 of inactive ( dsm1 ) regions , or intervals between two neighboring active ( dsm2 ) patches . histograms are made separately for each spatial direction , @xmath94 and @xmath95 , to take account of the anisotropy of dsm1 @xcite . care is also taken to compensate missing intervals due to the finite observation window : since an interval of size @xmath92 may not be captured within a frame of size @xmath96 , i.e. , either edge of the interval may not be in the frame , with probability @xmath97 , the unbiased distributions @xmath98 are estimated from the observed ones by @xmath99 @xcite . the results are shown in fig . [ fig : steadystatedsm1dist ] . we find that the dsm1 distributions decay algebraically within the observed length / time scale for voltages very close to criticality , while for higher voltages they start to decay exponentially from certain characteristic length / time scales , as expected for continuous absorbing phase transitions @xcite . the observed power - law decays are fitted as @xmath100 and @xmath101 with @xmath102 where @xmath103 and @xmath104 indicate the exponent @xmath3 measured in the @xmath66 and @xmath105 direction , respectively . these exponents are directly connected to the fractal dimensions @xmath106 of the dsm2 clusters measured in the corresponding direction as @xmath107 . the critical exponents @xmath3 and @xmath4 for dp can be estimated using scaling relations with the order parameter exponent @xmath0 and the correlation length / time exponents @xmath1 and @xmath2 , namely @xcite , @xmath108 they give @xmath109 and @xmath110 for @xmath90 dimensions @xcite . although the existence of slight discrepancies of order @xmath111 in eq . is suggested from numerical studies @xcite , our estimates in eq . agree with values expected for the dp class at any rate . moreover , the dsm1 distributions allow estimating correlation length and time scales , @xmath112 and @xmath113 , respectively , from their exponential tails shown in fig . [ fig : steadystatedsm1dist](d - f ) . fitting distributions with an empirical form @xcite @xmath114 with powers @xmath3 and @xmath4 fixed at the estimates in eq . , we obtain the results shown in fig . [ fig : steadystatenu ] . both @xmath112 and @xmath113 show algebraic divergence @xmath115 near criticality as expected , except for the first two points in fig . [ fig : steadystatenu](c ) , which deviate from the power law presumably due to finite length of movies ( @xmath116 ) used to count the distributions . fitting eq . to the data in scaling regions ( the first five points for @xmath117 and all the points except the first two for @xmath113 ) , we obtain @xmath118 they are in good agreement with the dp values @xmath119 and @xmath120 @xcite . in addition , the facts that no significant anisotropy is found between @xmath121 and @xmath122 and that they can be even shorter than the cell depth @xmath64 [ fig . [ fig : steadystatenu](a , b ) ] suggest that distributions of dsm2 patches are practically not influenced by the anisotropy of dsm1 @xcite and by the existence of coherent roll structure of width roughly @xmath123 behind dsm1 @xcite . on the other hand , distributions of sizes of active ( dsm2 ) patches do not show any long range correlations even close to criticality [ fig . [ fig : steadystatedsm2dist](a , b ) ] . it implies that the local recession of dsm2 into dsm1 sketched in fig . [ fig : dsm1dsm2](d ) is indeed always present . the effective relaxation rate can be directly estimated , just as an inverse of the characteristic time @xmath124 from the exponential tail of the temporal dsm2 distribution , shown in fig . [ fig : steadystatedsm2dist](c ) . the characteristic time @xmath124 increases linearly with @xmath63 except for high voltages , where it is not simply determined from the dynamics of individual patches because of the saturation of the dsm2 fraction ( fig . [ fig : steadystaterho ] ) . in particular , it exhibits no sign of criticality . all these observations are consistent with , e.g. , the dynamics of the so - called contact process @xcite ( depicted in fig . [ fig : dsm1dsm2](d ) ) , a prototypical model showing a dp - class transition @xcite , indicating that such process indeed governs the coarse - grained dynamics of our sti regime in liquid crystal turbulence . similarly , the spatial distributions of dsm2 sizes yield characteristic length scales @xmath125 and @xmath126 [ fig . [ fig : steadystatedsm2dist](c ) ] . although they appear to be also dominated by the relaxation process , as suggested from an effectively constant ratio @xmath127 [ inset of fig . [ fig : steadystatedsm2dist](c ) ] , they clearly show anisotropy [ fig . [ fig : steadystatedsm2dist](c ) ] , as opposed to the correlation lengths @xmath121 and @xmath122 estimated from dsm1-size distributions [ fig . [ fig : steadystatenu](a , b ) ] . this implies that the contamination process of dsm2 is indeed driven by the anisotropic , fluctuating shear flow of surrounding dsm1 . the larger effective contamination rate in @xmath66 is in line with the fact that the turbulent structure of dsm1 remains mainly in the @xmath66-@xmath128 plane @xcite , but at odds with the global elliptic shape of growing dsm2 nuclei , longer in @xmath105 , observed for higher voltages @xcite . both would be explained if we assume that turbulent flow behind is faster and more correlated in the @xmath105 direction , but further studies are necessary on this point . a typical experiment performed usually on numerical models showing absorbing phase transitions is the critical decay of active patches from fully active initial conditions @xcite . in such critical - quench experiments , correlation length and time grow in time , and , as long as they remain much smaller than the system size , scaling estimates are free from finite - size effects . experiments are performed as follows : we first apply @xmath129 to the cell and wait until it is entirely invaded by dsm2 domains . we then suddenly decrease the applied voltage to a value in the range of @xmath130 , i.e. , near @xmath78 , and observe the time decay of activity for @xmath131 . we repeat this @xmath132 times for each @xmath63 and average the results over this ensemble . on critical quenching . ( a ) @xmath85 versus @xmath133 , for @xmath134 , @xmath135 , @xmath136 , @xmath137 from bottom left to top right . the curve for @xmath138 ( showing the longest power - law regime ) is indicated by a thick line . ( b ) same data with rescaled axes @xmath139 and @xmath140 , showing data collapsing . for @xmath78 , @xmath141 , and @xmath2 , we use values measured in the experiment [ eqs . and ] , but a collapse of similar quality is obtained also with dp - class exponent values . the dashed curve indicates the dp universal scaling function @xmath142 obtained numerically from the contact process . ] we first measure the decay of the order parameter @xmath85 after the quench [ fig . [ fig : criticalquenchrho](a ) ] . as expected , @xmath85 decays exponentially with a certain characteristic time for lower voltages , converges to a finite value for higher voltages , and in - between at @xmath143 , it decays algebraically over the whole observation time . a simple scaling ansatz implies the following functional form for @xmath85 in this case : @xmath144 where @xmath145 is the deviation from criticality and @xmath146 is a universal scaling function . from the slopes of the algebraic regimes for the three @xmath63 values closest to the threshold , we estimate @xmath147 note that @xmath78 measured here is slightly higher than in the steady - state experiments . in fact , the roll convection onset @xmath148 was also higher . we believe this is because of possible slight shift in the controlled temperature , and also of the ageing of our sample , a well known property of mbba , during the days which separated the two sets of experiments . on the other hand , no measurable shift of @xmath78 was detected during a given set of experiments . we also confirmed that @xmath78 here is consistent with a threshold roughly estimated from steady state just before the critical - quench experiments . our estimate of the critical exponent @xmath141 is again in good agreement with the dp value @xmath149 @xcite . furthermore , the scaling form of eq . implies that the time series @xmath85 for different voltages collapse on a single curve @xmath146 when @xmath140 is plotted as a function of @xmath139 . our data do collapse reasonably well [ fig . [ fig : criticalquenchrho](b ) ] , where the upper and lower branches correspond to @xmath150 and @xmath151 , respectively . it is compared and found in good agreement with the universal scaling function @xmath146 of the dp class [ dashed curve in fig . [ fig : criticalquenchrho](b ) ] , calculated numerically from the @xmath90-dimensional contact process . it shows that the decay of dsm2 patches is governed by this dp universal function , except for the very early stage where it is influenced by microscopic features of the liquid crystal , as expected . at @xmath152 , measured in the critical - quench experiments . raw data in the inset are collapsed with rescaled axes @xmath153 and @xmath154 . dashed line shows the estimated asymptotic algebraic decay . ] we also measure the autocorrelation function @xmath155 , defined as @xmath156 where @xmath157 denotes average in space and over ensembles . during the critical decaying process , @xmath155 is not a function of @xmath158 ( inset of fig . [ fig : criticalquenchageing ] ) but scaled rather by @xmath153 , a feature sometimes referred to as `` ageing '' in the literature @xcite . our data can be collapsed ( fig . [ fig : criticalquenchageing ] ) using the expected scaling form @xmath159 with @xmath160 both are in agreement with dp values @xmath161 and @xmath162 , estimated from the scaling relations @xcite @xmath163 where @xmath164 is the spatial dimension . the dynamic aspect of critical behavior can also be characterized using first - passage quantities @xcite . one of these is the local persistence probability @xmath165 , defined as the probability that the local state at a given point in space has not changed until time @xmath133 , which typically shows a power - law decay @xmath166 . the non - trivial local persistence exponent @xmath167 is known to be in general independent of usual critical exponents such as @xmath168 , and far less is known about its universality , mainly due to the fact that persistence is a quantity involving an infinite - point correlation function . in the context of dp , local persistence is measured from the probability that initially inactive `` sites '' do not become active up to time @xmath133 . ( the persistence of activity is always dominated by the local relaxation into the inactive state and shows only exponential decay , similarly to fig . [ fig : steadystatedsm2dist ] . ) initial conditions are typically set to be random in numerical studies @xcite , which is , however , impossible in this experiment at present . we therefore consider , as `` initial condition '' for the local persistence , configurations chosen at some moment @xmath169 during the critical quench and measure the persistence probability @xmath170 . in the critical - quench experiments . the initial time is @xmath171 for the main panel and @xmath172 for the inset . the applied voltages are in ascending order from top to bottom . dashed lines are guides to eye with the same slope . ] the scaling regime for the order parameter decay observed in fig . [ fig : criticalquenchrho ] starting only after times of typically @xmath30-@xmath173 , we further limit ourselves to @xmath169 values larger than this microscopic , non - universal time . typical results are shown for @xmath171 in fig . [ fig : criticalquenchpersistence ] . the local persistence probability @xmath165 is found to converge to a finite constant for @xmath174 and to decay exponentially for @xmath175 , as expected from numerical studies of absorbing phase transitions @xcite . at criticality , @xmath165 decays algebraically ( again beyond some time of the order of @xmath169 ) with @xmath176 the value of @xmath167 for @xmath90-dimensional dp is still a matter of debate , with different estimates in past numerical studies : @xmath177 @xcite , @xmath178 @xcite , and very recently @xmath179 , found with an improved algorithm @xcite . our value , which is rather robust with respect to changing the initial conditions and the initial time ( fig . [ fig : criticalquenchpersistence ] ) , is in agreement with all numerical estimates to our accuracy . in order to complete the characterization of the dynamic critical behavior of the dsm1-dsm2 transition , we performed critical spreading experiments , which start from a single seed of active , dsm2 region . this allows to measure other critical exponents , such as the one governing the scaling of the probability @xmath180 that a cluster starting from a single active seed survives forever : @xmath181 , known to serve as another order parameter characterizing absorbing phase transitions @xcite . the two exponents @xmath0 and @xmath182 are known to be equal to each other for the dp class , thanks to an extra symmetry linked to time - reversal , the so - called rapidity symmetry @xcite . this symmetry also implies that @xmath183 where @xmath184 is defined from the time decay of the survival probability at threshold , @xmath185 . we stress , however , that the rapidity symmetry and the resulting scaling relations do not hold generically in absorbing phase transitions . although a value of @xmath182 consistent with dp was suggested from the critical scaling of hysteresis loops in the dsm1-dsm2 transition @xcite , it remains important to assess all spreading exponents as accurately and independently as possible , in order to complete our characterization of dp - class critical behavior and check directly the rapidity symmetry . in contrast to numerical simulations , it is not easy , in experiments , to prepare an initial , single , localized seed of dsm2 in an otherwise homogeneous dsm1 system . we developed an experimental technique for nucleating a dsm2 patch artificially , using a pulse laser . of the molecules ( squares and circles , respectively ) . error bars denote the @xmath186 confidence intervals assuming the binomial distribution . ( inset ) typical spatiotemporal diagram of nucleated dsm2 cluster for @xmath187 . scales are @xmath188 in space and @xmath189 in time . ] the experimental setup for the critical - spreading experiments is schematically shown in fig . [ fig : expsetupspreading ] . we emit @xmath190-@xmath191 pulses of nd : yag laser ( minilase ii 20hz , new wave research ) , focused by an objective lens ( @xmath192 , na @xmath193 , uplanfln , olympus ) , into the cell . using its third harmonic at @xmath194 , around which mbba has a broad absorption band @xcite , and reducing its energy to roughly @xmath195 at the cell , we can indeed nucleate dsm2 from the absorbing dsm1 state ( inset of fig . [ fig : dsm2nucleation ] ) without any observable damage to the sample . figure [ fig : dsm2nucleation ] shows the probability of the dsm2 nucleation induced by emitting five successive laser pulses at @xmath196 . the nucleation probability increases with voltage and is significantly higher for laser polarized along the mean director field . this confirms that nucleation is indeed brought about by the laser absorption of mbba , since its absorbance is higher along the long axis of the molecule @xcite . moreover , the electronic structure of mbba reveals that the ultraviolet absorption band stems from the c n and c c bonds between the aniline and benzyliden rings and is strongly coupled with twist angles there @xcite . we therefore speculate that absorption of ultraviolet laser pulses might lead to a sudden conformation change in the molecular structure , creating a topological defect and thus triggering a dsm2 nucleation . we perform the critical - spreading experiments with the technique above . for each measurement we emit ten successive pulses polarized along the molecules ( in the @xmath66 direction ) , with which dsm2 is always nucleated for voltages of interest . in order to make reliable statistics for the survival probability , it is necessary to repeat experiments at least hundreds of times for each voltage . this led us to improve further the temperature control of the cell , both in short and long time scales . this is achieved by placing the thermocontroller in a thermally - insulated chamber ( fig . [ fig : expsetupspreading ] ) , made of plastic foam stage , wall , and ceiling , whose temperature inside is kept constant by circulating constant - temperature water . the cell temperature is finally stabilized at @xmath197 with fluctuations at most @xmath198 over two weeks . this allows us to repeat the experiment @xmath199-@xmath200 times for each voltage in the range of @xmath201 . the roll convection onset and the critical voltage roughly measured in steady state were @xmath202 and @xmath203 , respectively . we measure not only the survival probability @xmath204 but also the volume @xmath205 and the mean square radius @xmath206 of dsm2 clusters , averaged over all the repetitions , even if the cluster dies before time @xmath133 . the following relations are then expected from the scaling ansatz @xcite : @xmath207 where @xmath208 are universal scaling functions . the experimental results are shown in fig . [ fig : criticalspreadingresults ] . except for @xmath206 where all the data are almost overlapping , which is also typically the case in simulations of dp - class models , the data show opposite curvatures below and above a certain voltage . seeking for the curve with the longest algebraic regime in @xmath205 , which is statistically most reliable , we locate the critical voltage @xmath78 at @xmath209 we then measure the three critical exponents @xmath210 from the algebraic regime for three voltages around @xmath78 , yielding @xmath211 all of them are in good agreement with the dp exponents , @xmath212 , and @xmath213 @xcite . this confirms the scaling relations expressing the rapidity symmetry . it is further confirmed by plotting the ratio of the survival probability @xmath204 to the dsm2 fraction @xmath85 in the critical - quench experiments [ inset of fig . [ fig : criticalspreadingresults](a ) ] , which shows that the two order parameters become asymptotically proportional to each other @xmath214 with the coefficient @xmath215 . we also tested data collapse [ fig . [ fig : criticalspreadingresults](d - f ) ] , which provides reasonable results given the limited statistical accuracy of the data . the obtained scaling functions coincide satisfactorily with those of the @xmath90-dimensional contact process [ dashed curves in fig . [ fig : criticalspreadingresults](d - f ) ] . as in the data collapse of @xmath85 [ fig . [ fig : criticalquenchrho](b ) ] , the collapsed data show typical time scales above which the corresponding quantities are governed by the dp scaling functions . we have performed three series of experiments , namely , steady - state experiments , critical - quench experiments , and critical - spreading experiments , to characterize the critical behavior of the dsm1-dsm2 transition in liquid crystal turbulence . table [ tbl : summaryexponents ] summarizes the main results . we have measured in total 12 critical exponents with reasonable accuracy , typically over a few orders of magnitude of power - law regimes . all of the measured exponent values agree within a few percent with those defining the dp universality class . given that most of them are theoretically linked through scaling relations , we can equivalently say that we have experimentally confirmed those scaling relations , 8 in total , that connect the measured exponents ( table [ tbl : summaryscalingrelations ] ) . among them , we have confirmed in particular the rapidity symmetry @xmath183 , providing also the asymptotic amplitude of the ratio between the two order parameters , @xmath215 . moreover , we have also tested the expected scaling forms of eqs . , , - through data collapse , and found them in good agreement with numerically - obtained dp universal scaling functions . based on all these results , we conclude that the dsm1-dsm2 transition constitutes an unambiguous experimental realization of an absorbing phase transition in the dp universality class . ? = ? .summary of the measured critical exponents [ cols="<,<,<,<,<",options="header " , ] we now return to our initial remark concerning the surprising scarcity of experimental realizations of dp - class transitions ( table [ tbl : earlierexperiments ] ) . one central difficulty lies in the necessity to avoid , as much as possible , quenched disorder , which is known to be relevant . it is theoretically known that such disorder does affect dp criticality and even destroys it for strong disorder @xcite . recent theoretical and numerical studies show that even weak disorder changes the asymptotic critical behavior @xcite , but the characteristic length / time scale separating dp and disordered , so - called `` activated '' critical behavior grows fast with decreasing strength of disorder @xcite . it is therefore important to work with systems made of macroscopic units , where quenched disorder is expected to be negligible . we consider that the quenched disorder in our system , which may take the form of inhomogeneities in the electrodes or impurities in the sample , is also sufficiently weak . still , our dsm1-dsm2 transition seems to be the only fully convincing one . three factors explain , in our view , why our experiments provided such clear dp scaling laws . \(a ) _ large system size and fast response_. as already mentioned , one great advantage to work with electroconvection is that very large aspect ratios can easily be realized . the number of effective degrees of freedom of our cell is @xmath52 , which is orders of magnitude larger than any earlier experiment ( table [ tbl : earlierexperiments ] ) . this considerably suppresses finite - size effects and allows to observe scaling on several orders of magnitude . similarly , the typical microscopic timescales of liquid crystals are very short ( of the order of @xmath216 ) , providing accurate statistics in reasonable laboratory time . \(b ) _ almost perfectly absorbing state_. the condition for being an absorbing state , i.e. , that the system can _ never _ escape once it entered , appears to be somewhat too strict from the experimental point of view . indeed , spontaneous nucleation of the active state seems to have been present at least in some of the past experiments @xcite , which blurs the critical behavior beyond some finite scales . on the other hand , our active state , dsm2 , consists of topological defects , whose spontaneous formation is in principle forbidden . of course this may occur in practice , as suggested from the observation of vanishing hysteresis at the dsm1-dsm2 transition @xcite , but the nucleation rate remains so low that we can not directly observe it , constituting an almost perfectly absorbing state . ( c ) _ fluctuating absorbing state_. in most earlier experiments and numerical studies , the absorbing state has been essentially fluctuation - free , or laminar . this is indeed a natural choice suggested from the minimal theory of dp , and causes of course no problem in numerical studies . in experiments , however , such absorbing states may typically cause long - range effects through the rigidity of their laminar pattern and/or the propagation of soliton - like objects , which may further reduce the effective system size and even break dp scaling @xcite . in contrast , our absorbing state , dsm1 , is itself a fluctuating , turbulent state . long - range interactions are then likely to be killed by the local turbulent fluctuations of dsm1 , which may have led to the observation of clean dp critical behavior . it is noteworthy to remark that the chat - manneville coupled map lattice @xcite , a deterministic numerical model for absorbing phase transitions with a non - chaotic ( laminar ) absorbing state , exhibits non - dp critical behavior probably due to soliton - like objects propagating through laminar regions . interestingly , an elementary modification to render its absorbing state itself chaotic does lead to dp scaling @xcite . in conclusion , we have experimentally found that the dsm1-dsm2 transition in the electroconvection of nematic liquid crystals , showing an absorbing transition into spatiotemporal intermittency , clearly belongs to the dp universality class . both static and dynamic critical behavior has been investigated with the help of the newly developed experimental technique to create a seed of dsm2 , confirming a total of 12 critical exponents , 5 scaling functions , 8 scaling relations , and in particular the rapidity symmetry , in full agreement with those characterizing the dp class in @xmath217 dimensions . we hope that this first clear and comprehensive experimental realization of a dp - class transition will trigger further studies of absorbing phase transitions and of related situations with genuinely non - equilibrium critical properties . in this respect the recent works of cort _ et al . _ @xcite and of mangan _ et al . _ @xcite are especially encouraging , concerning experiments and realistic situations , respectively , for absorbing transitions with a conserved field . the authors are grateful to i. dornic , f. ginelli , j. a. hoyos , s. kai , and n. oikawa for fruitful discussions . we would also like to thank m. henkel and g. i. menon for drawing our attention to ageing and ref . @xcite and to local persistence , respectively . this work is supported in part by grant - in - aid for scientific research ( 18068005 ) and for jsps fellows . every analysis presented in the paper is performed using binarized images , where dsm2 domains are distinguished from the absorbing dsm1 background . we give here a detailed description of the binarizing algorithm we used . the binarization is carried out in the following manner : ( a ) we prepare three successive images taken at 15 frames per second , and remove the inhomogeneity of the incident light intensity . ( b ) we then normalize the obtained intensity @xmath218 of the three images with respect to mean @xmath219 and standard deviation @xmath220 of the dsm1 intensity at a given voltage , namely @xmath221 . note that we can separately measure the intensity of the fully dsm1 state even above the threshold @xmath78 , since dsm1 always appears first when the voltage is applied . ( c ) since dsm2 domains have lower transmittance than dsm1 , we extract the regions where the normalized intensity is less than a certain threshold @xmath222 . here we chose @xmath223 , determined so as to obtain a good agreement with direct visual observations , particularly in movies . ( d ) taking into consideration that dsm2 domains move much slower than the local intensity fluctuations in dsm1 ( recall that dsm1 is itself a turbulent state ) and that the minimum dsm2 area is @xmath80 @xcite , where @xmath123 is the depth of the cell , we take the logical intersection ( `` and '' operator ) of the three successive images , and then remove clusters with area smaller than @xmath80 . clusters are screened out in this way , and their binarized images in the middle frame are used as final images . in other words , the intersection is used only for comparison with the minimum area . ( e ) finally , we cut off the periphery of the image of width @xmath224 , since this region is biased in the step ( d ) . the size of the binarized images reduces to @xmath225 , which roughly corresponds to @xmath226 effective degrees of freedom . we confirmed that the chosen threshold ( @xmath223 ) works well all over the range of voltages we investigate , and that no dsm2 region is falsely detected when binarizing images of the fully dsm1 phase . typical results of the binarization are shown in fig . [ fig : dsm1dsm2](c ) and ( e ) , and movie s2 of ref . @xcite , where we can confirm that dsm2 domains are precisely detected . for the critical - spreading experiments presented in sec . [ sec : criticalspreading ] , we have slightly modified the binarization algorithm in order to detect dsm2 patches originating only from the prepared seed , and not to miss them . to this end , we have reduced the intensity threshold @xmath227 to @xmath228 , and instead , binarized only within a target region , defined from positions of dsm2 patches in previous images ( position of the seed for the first image ) and assumed maximal displacement of dsm2 , which is chosen to be much larger than the actual displacement , namely , @xmath123 during successive two images taken at @xmath229 fps and extrapolated diffusively . we again confirmed that binarized images from a single set of parameters closely follow the actual evolution of dsm2 patches for all the voltages of interest . a typical result is shown in the inset of fig . [ fig : dsm2nucleation ] . the deviation from criticality is measured in terms of @xmath230 instead of @xmath63 by convention , since the dielectric torque that drives the electroconvection is proportional to @xmath230 @xcite . the results do not change if @xmath231 is used . confidence intervals of the critical exponents given in the present paper are determined as follows . ( a ) for values estimated from a finite number of independent data points [ eqs . and ] , @xmath186 confidence intervals in the sense of student s t are provided . ( b ) for values estimated from a continuous curve [ eqs . , , , , ] , range of fitting is varied within reasonable regions , and both the dependence on fitting regions and the confidence interval from each fitting are incorporated in the final estimate of error . when the threshold is simultaneously determined [ eqs . and ] , uncertainty in the estimate of the threshold is also considered . ( c ) for values determined from data collapsing [ eq . ] , we provide the range of values of the exponent with which no systematic shift in data collapsing is seen . ( d ) for values derived from an equation , the range of error is estimated by the law of propagation of error . ( e ) for values cited from literature , we simply borrow the range of errors provided by the corresponding authors . this correction was not made in ref . although algebraic decays in the distributions are not much influenced , this correction is significant to have exponential decays in sufficiently large scales to estimate the correlation length and time .

this is a comprehensive report on the phase transition between two turbulent states of electroconvection in nematic liquid crystals , which was recently found by the authors to be in the directed percolation ( dp ) universality class [ k. a. takeuchi _ et al . _ , phys . rev . lett . * 99 * , 234503 ( 2007 ) ] . we further investigate both static and dynamic critical behavior of this phase transition , measuring a total of 12 critical exponents , 5 scaling functions , and 8 scaling relations , all in full agreement with those characterizing the dp class in 2 + 1 dimensions . developing an experimental technique to create a seed of topological - defect turbulence by pulse laser , we confirm in particular the rapidity symmetry , which is a basic but nontrivial consequence of the field - theoretic approach to dp . this provides the first clear experimental realization of this outstanding , truly out - of - equilibrium universality class , dominating most phase transitions into an absorbing state .

<s>[INST]absorbing states , i.e. , states which systems may fall into but never escape from , and phase transitions into them are expected to be ubiquitous in nature . for instance , spreading or contamination processes like fires or epidemics exhibit such transitions when the propagation rate changes : initially active ( infected ) regions eventually disappear forever at low rates , i.e. , the absorbing state is reached , while they can be sustained ( pandemic regime ) for fast - enough propagation . examples abound far beyond : hundreds of numerical models , describing , e.g. , catalytic reactions , granular flows , and calcium dynamics in living cells , to name but a few , have been shown to exhibit such absorbing phase transitions @xcite . such phase transitions also naturally arise from general problems such as synchronization @xcite , self - organized criticality @xcite , spatiotemporal intermittency @xcite , and depinning @xcite . the vast majority of these transitions share the same critical behavior , that of the `` directed percolation '' ( dp ) class @xcite , as long as they are continuous . deep theoretical issues underpin this situation . whereas universality is well understood for systems in thermodynamic equilibrium , this is still not the case for systems driven out of equilibrium , where even the relevant ingredients determining the class are not well understood . in this context , absorbing phase transitions are central because of their genuine nonequilibrium character , since absorbing states directly imply violation of the detailed balance . janssen and grassberger @xcite conjectured that the dp universality class contains all continuous transitions into a single effective absorbing state in the absence of any extra symmetry or conservation law . the dp class thus appears as the simplest , and most common case , as testified by overwhelming numerical evidence . however , the situation has been quite different in experiments . over the last twenty years and more , a number of experiments have been performed in situations where dp - class transitions would be theoretically expected , but they have always yielded mixed and/or partial results with limited accuracy @xcite ( table [ tbl : earlierexperiments ] ) . this lack of fully convincing experimental realizations , in contrast with the wealth of numerical results , has been found surprising and a matter of concern in the literature @xcite . recently , though , studying a spatiotemporal intermittency regime occurring in turbulent liquid crystals , we found a transition whose complete set of static critical exponents match those of the dp class @xcite . the goal of the present paper is to provide a comprehensive report on this transition including not only a more complete description of experiments designed to investigate the static critical behavior , but also new experiments giving access to dynamic critical behavior . lllllllll ( 1 + 1)d system & size & @xmath0 & @xmath1 & @xmath2 & @xmath3 & @xmath4 & refs . + annular rayleigh - bnard & @xmath5 & & @xmath6 & & @xmath7 & @xmath8 & @xcite + annular rayleigh - bnard & @xmath9 & & @xmath6 & @xmath6 & @xmath10 & @xmath11 & @xcite + linear rayleigh - bnard & @xmath12 & @xmath13 & @xmath14 & @xmath14 & @xmath15 & @xmath16 & @xcite + interface roughening & & & & & & @xcite + viscous fingering & @xmath17 & @xmath18 & & & @xmath19 & @xmath20 & @xcite + vortices of fluid & @xmath21 & @xmath6 & & & & @xmath22 & @xcite + taylor - deen & @xmath23 & @xmath24 & @xmath25 & @xmath26 & @xmath27 & @xmath28 & @xcite + taylor - couette & @xmath29 & @xmath30 & @xmath31 & & @xmath32-@xmath33 & & @xcite + granular flow & & & & & & @xcite + torsional couette & & @xmath34 & @xmath35 & & & & @xcite + ferrofluidic spikes & @xmath36 & @xmath13 & @xmath37 & @xmath38 & @xmath39 & @xmath40 & @xcite + lateral heat convection in annulus & @xmath41 & @xmath42 & @xmath43 & @xmath44 & & & @xcite + dp & & @xmath45 & @xmath46 & @xmath47 & @xmath48 & @xmath49 & @xcite + & & & & & + ( 2 + 1)d system & size & @xmath0 & @xmath1 & @xmath2 & @xmath3 & @xmath4 & refs . + liquid columns & @xmath50 & @xmath51 & & & & & @xcite + dsm1-dsm2 ( present paper ) & @xmath52 & @xmath53 & @xmath54 & @xmath55 & @xmath56 & @xmath57 & + dp & & @xmath58 & @xmath59 & @xmath60 & @xmath61 & @xmath62 & @xcite + the paper is organized as follows . we first illustrate the coarse - grained dynamics of the turbulent regime of electroconvection studied and our basic experimental setup ( sec . [ sec : setup ] ) , with further details on image analysis given in the appendix . to characterize the critical behavior , we perform three series of experiments : ( a ) steady - state experiment under constant applied voltages ( sec . [ sec : steadystate ] ) , ( b ) critical - quench experiment starting from fully active initial conditions ( sec . [ sec : criticalquench ] ) , and ( c ) critical - spreading experiment starting from a single active seed , prepared with a novel experimental technique using pulse laser , developed in this work ( sec . [ sec : criticalspreading ] ) . in sec . [ sec : summary ] , our results are summarized and we discuss why clear dp - class critical behavior is observed rather easily in our system , contrary to many other experiments performed in the past in this context . we work on the electrohydrodynamic convection of nematic liquid crystals , which occurs when a thin layer of liquid crystal is subjected to an external voltage strong enough to trigger the carr - helfrich instability @xcite . this is _ a priori _ a suitable system to study critical behavior thanks to its possibly large aspect ratio , fast response time , and easy controllability . we focus on the transition between two turbulent regimes , called dynamic scattering modes 1 and 2 ( dsm1 and dsm2 ) , observed successively upon increasing the root - mean - square amplitude of the voltage @xmath63 at relatively low frequencies @xcite . the difference between dsm1 and dsm2 lies in their density of topological defects in the director field [ fig . [ fig : dsm1dsm2](a ) ] . in the dsm2 state , a large quantity of these defects , called disclinations , are present @xcite . they elongate and split constantly under the shear due to the fluctuating turbulent flow around . in dsm1 , on the other hand , disclinations are present but kept smaller than the critical size and disappear immediately . their density thus remains very low . the many disclinations in dsm2 lead to the loss of macroscopic nematic anisotropy and to a lower light transmittance than in dsm1 . our basic experimental setup is shown in fig . [ fig : setup ] . the sample cell is made of two parallel glass plates spaced by a polyester film of thickness @xmath64 . both inner surfaces are covered with transparent electrodes of size @xmath65 , coated with polyvinyl alcohol and then rubbed in order that molecules are planarly aligned in the @xmath66 direction , defined thereby . the cell is filled with @xmath67-(4-methoxybenzylidene)-4-butylaniline ( mbba ; purity @xmath68 , tokyo chemical industry ) doped with 0.01 wt.% of tetra-@xmath69-butylammonium bromide . the temperature of the cell is kept constant carefully by a handmade thermocontroller , composed of heating wires and peltier elements controlled by a proportional - integral - derivative feedback loop with a lock - in amplifier [ fig . [ fig : setup](b ) ] . windows of the thermocontroller are made of sapphire in order to improve the spatial homogeneity of the temperature . throughout each series of experiments , the cell temperature is maintained at @xmath70 with fluctuations typically of a few @xmath71 , unless otherwise stipulated , measured by three thermistors placed at different positions close to the cell . we observe the electroconvection through the transmitted light from a handmade stabilized light source made of light - emitting diodes , recorded by a charge - coupled device camera . the observed region is a central rectangle of size @xmath72 ( fig . [ fig : setup ] , inset ) . since there is a minimum linear size of dsm2 domains , @xmath73 @xcite , we can roughly estimate the number of effective degrees of freedom at @xmath74 for the convection area and @xmath75 for the observation area . note that the meaningful figure is that of the total system size , which is at least four orders of magnitude larger than in earlier experimental studies ( table [ tbl : earlierexperiments ] ) . in the following , we vary @xmath63 and fix the frequency at @xmath76 , at roughly one third of the cutoff frequency @xmath77 which separates the conducting and the dielectric regimes of electroconvection @xcite . disclinations being topological defects , the spontaneous nucleation of dsm2 in a dsm1 domain is in principle forbidden . it is indeed an essentially unobservable rare event , except along the edges of the electrode and for very high voltages , far from the range investigated in the present paper . therefore , the fully dsm1 state serves as an absorbing state . on the other hand , dsm2 domains introduced externally , or present initially in the system can remain sustained in the bulk for large enough voltages , but eventually disappear for voltages lower than a certain threshold @xmath78 . closely above @xmath78 , a regime of spatiotemporal intermittency ( sti ) is observed , with dsm2 patches moving around on a dsm1 background [ fig . [ fig : dsm1dsm2](b ) , and movie s1 of ref . the basic dynamics of the observed sti is illustrated in fig . [ fig : dsm1dsm2](d ) : active dsm2 patches evolve in space - time essentially by contamination of neighboring inactive ( absorbing ) dsm1 regions and by relaxation into the dsm1 state . this suggests an absorbing phase transition induced by change in rates of both elementary processes @xcite , which are functions of the applied voltage here . the order parameter @xmath79 is then simply the ratio of the surface occupied by active dsm2 regions to the whole area . prior to any analysis , we must distinguish dsm2 domains from dsm1 . this binary reduction can be easily performed by our eyes , so we automated it , based on the facts that dsm2 domains have lower transmittance , longer time correlations , and have a minimum area of @xmath80 @xcite ( see appendix for details ) . a typical result is shown in fig . [ fig : dsm1dsm2](c ) , and in movie s2 of ref . figure [ fig : dsm1dsm2](e ) displays spatiotemporal diagrams obtained this way , showing how dsm2 patches evolve in the steady state . this supports the qualitative dynamics illustrated in fig . [ fig : dsm1dsm2](d ) and indeed looks like the directed percolation of , say , water in a porous medium under gravitational field . we first observe sti in the steady state under constant voltage @xmath63 , in the range of @xmath81 . the voltage for the onset of steady roll convection ( williams domain ) is @xmath82 . spatiotemporal distributions of dsm2 patches are recorded over the period @xmath83 , which is longer than @xmath84 correlation times defined from the fluctuations of the order parameter @xmath85 . as a function of @xmath63 in the steady state . inset : same data in logarithmic scales . errorbars indicate the standard deviation of fluctuations in @xmath85 and @xmath63 . blue dashed lines are fitting curves . ] figure [ fig : steadystaterho ] shows the time - averaged order parameter @xmath86 , i.e. , the average fraction of dsm2 . it shows that the transition is continuous and that @xmath86 scales algebraically near the critical point . fitting these data with the usual scaling form @xcite @xmath87 the critical voltage @xmath78 and the critical exponent @xmath0 are found to be @xmath88 where the numbers in parentheses indicate the range of errors in the last digits @xcite . our estimate @xmath89 is in good agreement with the value for @xmath90-dimensional dp , @xmath91 @xcite . we then measure the distributions of the sizes @xmath92 and durations @xmath93 of inactive ( dsm1 ) regions , or intervals between two neighboring active ( dsm2 ) patches . histograms are made separately for each spatial direction , @xmath94 and @xmath95 , to take account of the anisotropy of dsm1 @xcite . care is also taken to compensate missing intervals due to the finite observation window : since an interval of size @xmath92 may not be captured within a frame of size @xmath96 , i.e. , either edge of the interval may not be in the frame , with probability @xmath97 , the unbiased distributions @xmath98 are estimated from the observed ones by @xmath99 @xcite . the results are shown in fig . [ fig : steadystatedsm1dist ] . we find that the dsm1 distributions decay algebraically within the observed length / time scale for voltages very close to criticality , while for higher voltages they start to decay exponentially from certain characteristic length / time scales , as expected for continuous absorbing phase transitions @xcite . the observed power - law decays are fitted as @xmath100 and @xmath101 with @xmath102 where @xmath103 and @xmath104 indicate the exponent @xmath3 measured in the @xmath66 and @xmath105 direction , respectively . these exponents are directly connected to the fractal dimensions @xmath106 of the dsm2 clusters measured in the corresponding direction as @xmath107 . the critical exponents @xmath3 and @xmath4 for dp can be estimated using scaling relations with the order parameter exponent @xmath0 and the correlation length / time exponents @xmath1 and @xmath2 , namely @xcite , @xmath108 they give @xmath109 and @xmath110 for @xmath90 dimensions @xcite . although the existence of slight discrepancies of order @xmath111 in eq . is suggested from numerical studies @xcite , our estimates in eq . agree with values expected for the dp class at any rate . moreover , the dsm1 distributions allow estimating correlation length and time scales , @xmath112 and @xmath113 , respectively , from their exponential tails shown in fig . [ fig : steadystatedsm1dist](d - f ) . fitting distributions with an empirical form @xcite @xmath114 with powers @xmath3 and @xmath4 fixed at the estimates in eq . , we obtain the results shown in fig . [ fig : steadystatenu ] . both @xmath112 and @xmath113 show algebraic divergence @xmath115 near criticality as expected , except for the first two points in fig . [ fig : steadystatenu](c ) , which deviate from the power law presumably due to finite length of movies ( @xmath116 ) used to count the distributions . fitting eq . to the data in scaling regions ( the first five points for @xmath117 and all the points except the first two for @xmath113 ) , we obtain @xmath118 they are in good agreement with the dp values @xmath119 and @xmath120 @xcite . in addition , the facts that no significant anisotropy is found between @xmath121 and @xmath122 and that they can be even shorter than the cell depth @xmath64 [ fig . [ fig : steadystatenu](a , b ) ] suggest that distributions of dsm2 patches are practically not influenced by the anisotropy of dsm1 @xcite and by the existence of coherent roll structure of width roughly @xmath123 behind dsm1 @xcite . on the other hand , distributions of sizes of active ( dsm2 ) patches do not show any long range correlations even close to criticality [ fig . [ fig : steadystatedsm2dist](a , b ) ] . it implies that the local recession of dsm2 into dsm1 sketched in fig . [ fig : dsm1dsm2](d ) is indeed always present . the effective relaxation rate can be directly estimated , just as an inverse of the characteristic time @xmath124 from the exponential tail of the temporal dsm2 distribution , shown in fig . [ fig : steadystatedsm2dist](c ) . the characteristic time @xmath124 increases linearly with @xmath63 except for high voltages , where it is not simply determined from the dynamics of individual patches because of the saturation of the dsm2 fraction ( fig . [ fig : steadystaterho ] ) . in particular , it exhibits no sign of criticality . all these observations are consistent with , e.g. , the dynamics of the so - called contact process @xcite ( depicted in fig . [ fig : dsm1dsm2](d ) ) , a prototypical model showing a dp - class transition @xcite , indicating that such process indeed governs the coarse - grained dynamics of our sti regime in liquid crystal turbulence . similarly , the spatial distributions of dsm2 sizes yield characteristic length scales @xmath125 and @xmath126 [ fig . [ fig : steadystatedsm2dist](c ) ] . although they appear to be also dominated by the relaxation process , as suggested from an effectively constant ratio @xmath127 [ inset of fig . [ fig : steadystatedsm2dist](c ) ] , they clearly show anisotropy [ fig . [ fig : steadystatedsm2dist](c ) ] , as opposed to the correlation lengths @xmath121 and @xmath122 estimated from dsm1-size distributions [ fig . [ fig : steadystatenu](a , b ) ] . this implies that the contamination process of dsm2 is indeed driven by the anisotropic , fluctuating shear flow of surrounding dsm1 . the larger effective contamination rate in @xmath66 is in line with the fact that the turbulent structure of dsm1 remains mainly in the @xmath66-@xmath128 plane @xcite , but at odds with the global elliptic shape of growing dsm2 nuclei , longer in @xmath105 , observed for higher voltages @xcite . both would be explained if we assume that turbulent flow behind is faster and more correlated in the @xmath105 direction , but further studies are necessary on this point . a typical experiment performed usually on numerical models showing absorbing phase transitions is the critical decay of active patches from fully active initial conditions @xcite . in such critical - quench experiments , correlation length and time grow in time , and , as long as they remain much smaller than the system size , scaling estimates are free from finite - size effects . experiments are performed as follows : we first apply @xmath129 to the cell and wait until it is entirely invaded by dsm2 domains . we then suddenly decrease the applied voltage to a value in the range of @xmath130 , i.e. , near @xmath78 , and observe the time decay of activity for @xmath131 . we repeat this @xmath132 times for each @xmath63 and average the results over this ensemble . on critical quenching . ( a ) @xmath85 versus @xmath133 , for @xmath134 , @xmath135 , @xmath136 , @xmath137 from bottom left to top right . the curve for @xmath138 ( showing the longest power - law regime ) is indicated by a thick line . ( b ) same data with rescaled axes @xmath139 and @xmath140 , showing data collapsing . for @xmath78 , @xmath141 , and @xmath2 , we use values measured in the experiment [ eqs . and ] , but a collapse of similar quality is obtained also with dp - class exponent values . the dashed curve indicates the dp universal scaling function @xmath142 obtained numerically from the contact process . ] we first measure the decay of the order parameter @xmath85 after the quench [ fig . [ fig : criticalquenchrho](a ) ] . as expected , @xmath85 decays exponentially with a certain characteristic time for lower voltages , converges to a finite value for higher voltages , and in - between at @xmath143 , it decays algebraically over the whole observation time . a simple scaling ansatz implies the following functional form for @xmath85 in this case : @xmath144 where @xmath145 is the deviation from criticality and @xmath146 is a universal scaling function . from the slopes of the algebraic regimes for the three @xmath63 values closest to the threshold , we estimate @xmath147 note that @xmath78 measured here is slightly higher than in the steady - state experiments . in fact , the roll convection onset @xmath148 was also higher . we believe this is because of possible slight shift in the controlled temperature , and also of the ageing of our sample , a well known property of mbba , during the days which separated the two sets of experiments . on the other hand , no measurable shift of @xmath78 was detected during a given set of experiments . we also confirmed that @xmath78 here is consistent with a threshold roughly estimated from steady state just before the critical - quench experiments . our estimate of the critical exponent @xmath141 is again in good agreement with the dp value @xmath149 @xcite . furthermore , the scaling form of eq . implies that the time series @xmath85 for different voltages collapse on a single curve @xmath146 when @xmath140 is plotted as a function of @xmath139 . our data do collapse reasonably well [ fig . [ fig : criticalquenchrho](b ) ] , where the upper and lower branches correspond to @xmath150 and @xmath151 , respectively . it is compared and found in good agreement with the universal scaling function @xmath146 of the dp class [ dashed curve in fig . [ fig : criticalquenchrho](b ) ] , calculated numerically from the @xmath90-dimensional contact process . it shows that the decay of dsm2 patches is governed by this dp universal function , except for the very early stage where it is influenced by microscopic features of the liquid crystal , as expected . at @xmath152 , measured in the critical - quench experiments . raw data in the inset are collapsed with rescaled axes @xmath153 and @xmath154 . dashed line shows the estimated asymptotic algebraic decay . ] we also measure the autocorrelation function @xmath155 , defined as @xmath156 where @xmath157 denotes average in space and over ensembles . during the critical decaying process , @xmath155 is not a function of @xmath158 ( inset of fig . [ fig : criticalquenchageing ] ) but scaled rather by @xmath153 , a feature sometimes referred to as `` ageing '' in the literature @xcite . our data can be collapsed ( fig . [ fig : criticalquenchageing ] ) using the expected scaling form @xmath159 with @xmath160 both are in agreement with dp values @xmath161 and @xmath162 , estimated from the scaling relations @xcite @xmath163 where @xmath164 is the spatial dimension . the dynamic aspect of critical behavior can also be characterized using first - passage quantities @xcite . one of these is the local persistence probability @xmath165 , defined as the probability that the local state at a given point in space has not changed until time @xmath133 , which typically shows a power - law decay @xmath166 . the non - trivial local persistence exponent @xmath167 is known to be in general independent of usual critical exponents such as @xmath168 , and far less is known about its universality , mainly due to the fact that persistence is a quantity involving an infinite - point correlation function . in the context of dp , local persistence is measured from the probability that initially inactive `` sites '' do not become active up to time @xmath133 . ( the persistence of activity is always dominated by the local relaxation into the inactive state and shows only exponential decay , similarly to fig . [ fig : steadystatedsm2dist ] . ) initial conditions are typically set to be random in numerical studies @xcite , which is , however , impossible in this experiment at present . we therefore consider , as `` initial condition '' for the local persistence , configurations chosen at some moment @xmath169 during the critical quench and measure the persistence probability @xmath170 . in the critical - quench experiments . the initial time is @xmath171 for the main panel and @xmath172 for the inset . the applied voltages are in ascending order from top to bottom . dashed lines are guides to eye with the same slope . ] the scaling regime for the order parameter decay observed in fig . [ fig : criticalquenchrho ] starting only after times of typically @xmath30-@xmath173 , we further limit ourselves to @xmath169 values larger than this microscopic , non - universal time . typical results are shown for @xmath171 in fig . [ fig : criticalquenchpersistence ] . the local persistence probability @xmath165 is found to converge to a finite constant for @xmath174 and to decay exponentially for @xmath175 , as expected from numerical studies of absorbing phase transitions @xcite . at criticality , @xmath165 decays algebraically ( again beyond some time of the order of @xmath169 ) with @xmath176 the value of @xmath167 for @xmath90-dimensional dp is still a matter of debate , with different estimates in past numerical studies : @xmath177 @xcite , @xmath178 @xcite , and very recently @xmath179 , found with an improved algorithm @xcite . our value , which is rather robust with respect to changing the initial conditions and the initial time ( fig . [ fig : criticalquenchpersistence ] ) , is in agreement with all numerical estimates to our accuracy . in order to complete the characterization of the dynamic critical behavior of the dsm1-dsm2 transition , we performed critical spreading experiments , which start from a single seed of active , dsm2 region . this allows to measure other critical exponents , such as the one governing the scaling of the probability @xmath180 that a cluster starting from a single active seed survives forever : @xmath181 , known to serve as another order parameter characterizing absorbing phase transitions @xcite . the two exponents @xmath0 and @xmath182 are known to be equal to each other for the dp class , thanks to an extra symmetry linked to time - reversal , the so - called rapidity symmetry @xcite . this symmetry also implies that @xmath183 where @xmath184 is defined from the time decay of the survival probability at threshold , @xmath185 . we stress , however , that the rapidity symmetry and the resulting scaling relations do not hold generically in absorbing phase transitions . although a value of @xmath182 consistent with dp was suggested from the critical scaling of hysteresis loops in the dsm1-dsm2 transition @xcite , it remains important to assess all spreading exponents as accurately and independently as possible , in order to complete our characterization of dp - class critical behavior and check directly the rapidity symmetry . in contrast to numerical simulations , it is not easy , in experiments , to prepare an initial , single , localized seed of dsm2 in an otherwise homogeneous dsm1 system . we developed an experimental technique for nucleating a dsm2 patch artificially , using a pulse laser . of the molecules ( squares and circles , respectively ) . error bars denote the @xmath186 confidence intervals assuming the binomial distribution . ( inset ) typical spatiotemporal diagram of nucleated dsm2 cluster for @xmath187 . scales are @xmath188 in space and @xmath189 in time . ] the experimental setup for the critical - spreading experiments is schematically shown in fig . [ fig : expsetupspreading ] . we emit @xmath190-@xmath191 pulses of nd : yag laser ( minilase ii 20hz , new wave research ) , focused by an objective lens ( @xmath192 , na @xmath193 , uplanfln , olympus ) , into the cell . using its third harmonic at @xmath194 , around which mbba has a broad absorption band @xcite , and reducing its energy to roughly @xmath195 at the cell , we can indeed nucleate dsm2 from the absorbing dsm1 state ( inset of fig . [ fig : dsm2nucleation ] ) without any observable damage to the sample . figure [ fig : dsm2nucleation ] shows the probability of the dsm2 nucleation induced by emitting five successive laser pulses at @xmath196 . the nucleation probability increases with voltage and is significantly higher for laser polarized along the mean director field . this confirms that nucleation is indeed brought about by the laser absorption of mbba , since its absorbance is higher along the long axis of the molecule @xcite . moreover , the electronic structure of mbba reveals that the ultraviolet absorption band stems from the c n and c c bonds between the aniline and benzyliden rings and is strongly coupled with twist angles there @xcite . we therefore speculate that absorption of ultraviolet laser pulses might lead to a sudden conformation change in the molecular structure , creating a topological defect and thus triggering a dsm2 nucleation . we perform the critical - spreading experiments with the technique above . for each measurement we emit ten successive pulses polarized along the molecules ( in the @xmath66 direction ) , with which dsm2 is always nucleated for voltages of interest . in order to make reliable statistics for the survival probability , it is necessary to repeat experiments at least hundreds of times for each voltage . this led us to improve further the temperature control of the cell , both in short and long time scales . this is achieved by placing the thermocontroller in a thermally - insulated chamber ( fig . [ fig : expsetupspreading ] ) , made of plastic foam stage , wall , and ceiling , whose temperature inside is kept constant by circulating constant - temperature water . the cell temperature is finally stabilized at @xmath197 with fluctuations at most @xmath198 over two weeks . this allows us to repeat the experiment @xmath199-@xmath200 times for each voltage in the range of @xmath201 . the roll convection onset and the critical voltage roughly measured in steady state were @xmath202 and @xmath203 , respectively . we measure not only the survival probability @xmath204 but also the volume @xmath205 and the mean square radius @xmath206 of dsm2 clusters , averaged over all the repetitions , even if the cluster dies before time @xmath133 . the following relations are then expected from the scaling ansatz @xcite : @xmath207 where @xmath208 are universal scaling functions . the experimental results are shown in fig . [ fig : criticalspreadingresults ] . except for @xmath206 where all the data are almost overlapping , which is also typically the case in simulations of dp - class models , the data show opposite curvatures below and above a certain voltage . seeking for the curve with the longest algebraic regime in @xmath205 , which is statistically most reliable , we locate the critical voltage @xmath78 at @xmath209 we then measure the three critical exponents @xmath210 from the algebraic regime for three voltages around @xmath78 , yielding @xmath211 all of them are in good agreement with the dp exponents , @xmath212 , and @xmath213 @xcite . this confirms the scaling relations expressing the rapidity symmetry . it is further confirmed by plotting the ratio of the survival probability @xmath204 to the dsm2 fraction @xmath85 in the critical - quench experiments [ inset of fig . [ fig : criticalspreadingresults](a ) ] , which shows that the two order parameters become asymptotically proportional to each other @xmath214 with the coefficient @xmath215 . we also tested data collapse [ fig . [ fig : criticalspreadingresults](d - f ) ] , which provides reasonable results given the limited statistical accuracy of the data . the obtained scaling functions coincide satisfactorily with those of the @xmath90-dimensional contact process [ dashed curves in fig . [ fig : criticalspreadingresults](d - f ) ] . as in the data collapse of @xmath85 [ fig . [ fig : criticalquenchrho](b ) ] , the collapsed data show typical time scales above which the corresponding quantities are governed by the dp scaling functions . we have performed three series of experiments , namely , steady - state experiments , critical - quench experiments , and critical - spreading experiments , to characterize the critical behavior of the dsm1-dsm2 transition in liquid crystal turbulence . table [ tbl : summaryexponents ] summarizes the main results . we have measured in total 12 critical exponents with reasonable accuracy , typically over a few orders of magnitude of power - law regimes . all of the measured exponent values agree within a few percent with those defining the dp universality class . given that most of them are theoretically linked through scaling relations , we can equivalently say that we have experimentally confirmed those scaling relations , 8 in total , that connect the measured exponents ( table [ tbl : summaryscalingrelations ] ) . among them , we have confirmed in particular the rapidity symmetry @xmath183 , providing also the asymptotic amplitude of the ratio between the two order parameters , @xmath215 . moreover , we have also tested the expected scaling forms of eqs . , , - through data collapse , and found them in good agreement with numerically - obtained dp universal scaling functions . based on all these results , we conclude that the dsm1-dsm2 transition constitutes an unambiguous experimental realization of an absorbing phase transition in the dp universality class . ? = ? .summary of the measured critical exponents [ cols="<,<,<,<,<",options="header " , ] we now return to our initial remark concerning the surprising scarcity of experimental realizations of dp - class transitions ( table [ tbl : earlierexperiments ] ) . one central difficulty lies in the necessity to avoid , as much as possible , quenched disorder , which is known to be relevant . it is theoretically known that such disorder does affect dp criticality and even destroys it for strong disorder @xcite . recent theoretical and numerical studies show that even weak disorder changes the asymptotic critical behavior @xcite , but the characteristic length / time scale separating dp and disordered , so - called `` activated '' critical behavior grows fast with decreasing strength of disorder @xcite . it is therefore important to work with systems made of macroscopic units , where quenched disorder is expected to be negligible . we consider that the quenched disorder in our system , which may take the form of inhomogeneities in the electrodes or impurities in the sample , is also sufficiently weak . still , our dsm1-dsm2 transition seems to be the only fully convincing one . three factors explain , in our view , why our experiments provided such clear dp scaling laws . \(a ) _ large system size and fast response_. as already mentioned , one great advantage to work with electroconvection is that very large aspect ratios can easily be realized . the number of effective degrees of freedom of our cell is @xmath52 , which is orders of magnitude larger than any earlier experiment ( table [ tbl : earlierexperiments ] ) . this considerably suppresses finite - size effects and allows to observe scaling on several orders of magnitude . similarly , the typical microscopic timescales of liquid crystals are very short ( of the order of @xmath216 ) , providing accurate statistics in reasonable laboratory time . \(b ) _ almost perfectly absorbing state_. the condition for being an absorbing state , i.e. , that the system can _ never _ escape once it entered , appears to be somewhat too strict from the experimental point of view . indeed , spontaneous nucleation of the active state seems to have been present at least in some of the past experiments @xcite , which blurs the critical behavior beyond some finite scales . on the other hand , our active state , dsm2 , consists of topological defects , whose spontaneous formation is in principle forbidden . of course this may occur in practice , as suggested from the observation of vanishing hysteresis at the dsm1-dsm2 transition @xcite , but the nucleation rate remains so low that we can not directly observe it , constituting an almost perfectly absorbing state . ( c ) _ fluctuating absorbing state_. in most earlier experiments and numerical studies , the absorbing state has been essentially fluctuation - free , or laminar . this is indeed a natural choice suggested from the minimal theory of dp , and causes of course no problem in numerical studies . in experiments , however , such absorbing states may typically cause long - range effects through the rigidity of their laminar pattern and/or the propagation of soliton - like objects , which may further reduce the effective system size and even break dp scaling @xcite . in contrast , our absorbing state , dsm1 , is itself a fluctuating , turbulent state . long - range interactions are then likely to be killed by the local turbulent fluctuations of dsm1 , which may have led to the observation of clean dp critical behavior . it is noteworthy to remark that the chat - manneville coupled map lattice @xcite , a deterministic numerical model for absorbing phase transitions with a non - chaotic ( laminar ) absorbing state , exhibits non - dp critical behavior probably due to soliton - like objects propagating through laminar regions . interestingly , an elementary modification to render its absorbing state itself chaotic does lead to dp scaling @xcite . in conclusion , we have experimentally found that the dsm1-dsm2 transition in the electroconvection of nematic liquid crystals , showing an absorbing transition into spatiotemporal intermittency , clearly belongs to the dp universality class . both static and dynamic critical behavior has been investigated with the help of the newly developed experimental technique to create a seed of dsm2 , confirming a total of 12 critical exponents , 5 scaling functions , 8 scaling relations , and in particular the rapidity symmetry , in full agreement with those characterizing the dp class in @xmath217 dimensions . we hope that this first clear and comprehensive experimental realization of a dp - class transition will trigger further studies of absorbing phase transitions and of related situations with genuinely non - equilibrium critical properties . in this respect the recent works of cort _ et al . _ @xcite and of mangan _ et al . _ @xcite are especially encouraging , concerning experiments and realistic situations , respectively , for absorbing transitions with a conserved field . the authors are grateful to i. dornic , f. ginelli , j. a. hoyos , s. kai , and n. oikawa for fruitful discussions . we would also like to thank m. henkel and g. i. menon for drawing our attention to ageing and ref . @xcite and to local persistence , respectively . this work is supported in part by grant - in - aid for scientific research ( 18068005 ) and for jsps fellows . every analysis presented in the paper is performed using binarized images , where dsm2 domains are distinguished from the absorbing dsm1 background . we give here a detailed description of the binarizing algorithm we used . the binarization is carried out in the following manner : ( a ) we prepare three successive images taken at 15 frames per second , and remove the inhomogeneity of the incident light intensity . ( b ) we then normalize the obtained intensity @xmath218 of the three images with respect to mean @xmath219 and standard deviation @xmath220 of the dsm1 intensity at a given voltage , namely @xmath221 . note that we can separately measure the intensity of the fully dsm1 state even above the threshold @xmath78 , since dsm1 always appears first when the voltage is applied . ( c ) since dsm2 domains have lower transmittance than dsm1 , we extract the regions where the normalized intensity is less than a certain threshold @xmath222 . here we chose @xmath223 , determined so as to obtain a good agreement with direct visual observations , particularly in movies . ( d ) taking into consideration that dsm2 domains move much slower than the local intensity fluctuations in dsm1 ( recall that dsm1 is itself a turbulent state ) and that the minimum dsm2 area is @xmath80 @xcite , where @xmath123 is the depth of the cell , we take the logical intersection ( `` and '' operator ) of the three successive images , and then remove clusters with area smaller than @xmath80 . clusters are screened out in this way , and their binarized images in the middle frame are used as final images . in other words , the intersection is used only for comparison with the minimum area . ( e ) finally , we cut off the periphery of the image of width @xmath224 , since this region is biased in the step ( d ) . the size of the binarized images reduces to @xmath225 , which roughly corresponds to @xmath226 effective degrees of freedom . we confirmed that the chosen threshold ( @xmath223 ) works well all over the range of voltages we investigate , and that no dsm2 region is falsely detected when binarizing images of the fully dsm1 phase . typical results of the binarization are shown in fig . [ fig : dsm1dsm2](c ) and ( e ) , and movie s2 of ref . @xcite , where we can confirm that dsm2 domains are precisely detected . for the critical - spreading experiments presented in sec . [ sec : criticalspreading ] , we have slightly modified the binarization algorithm in order to detect dsm2 patches originating only from the prepared seed , and not to miss them . to this end , we have reduced the intensity threshold @xmath227 to @xmath228 , and instead , binarized only within a target region , defined from positions of dsm2 patches in previous images ( position of the seed for the first image ) and assumed maximal displacement of dsm2 , which is chosen to be much larger than the actual displacement , namely , @xmath123 during successive two images taken at @xmath229 fps and extrapolated diffusively . we again confirmed that binarized images from a single set of parameters closely follow the actual evolution of dsm2 patches for all the voltages of interest . a typical result is shown in the inset of fig . [ fig : dsm2nucleation ] . the deviation from criticality is measured in terms of @xmath230 instead of @xmath63 by convention , since the dielectric torque that drives the electroconvection is proportional to @xmath230 @xcite . the results do not change if @xmath231 is used . confidence intervals of the critical exponents given in the present paper are determined as follows . ( a ) for values estimated from a finite number of independent data points [ eqs . and ] , @xmath186 confidence intervals in the sense of student s t are provided . ( b ) for values estimated from a continuous curve [ eqs . , , , , ] , range of fitting is varied within reasonable regions , and both the dependence on fitting regions and the confidence interval from each fitting are incorporated in the final estimate of error . when the threshold is simultaneously determined [ eqs . and ] , uncertainty in the estimate of the threshold is also considered . ( c ) for values determined from data collapsing [ eq . ] , we provide the range of values of the exponent with which no systematic shift in data collapsing is seen . ( d ) for values derived from an equation , the range of error is estimated by the law of propagation of error . ( e ) for values cited from literature , we simply borrow the range of errors provided by the corresponding authors . this correction was not made in ref . although algebraic decays in the distributions are not much influenced , this correction is significant to have exponential decays in sufficiently large scales to estimate the correlation length and time .[/INST] this is a comprehensive report on the phase transition between two turbulent states of electroconvection in nematic liquid crystals , which was recently found by the authors to be in the directed percolation ( dp ) universality class [ k. a. takeuchi _ et al . _ , phys . rev . lett . * 99 * , 234503 ( 2007 ) ] . we further investigate both static and dynamic critical behavior of this phase transition , measuring a total of 12 critical exponents , 5 scaling functions , and 8 scaling relations , all in full agreement with those characterizing the dp class in 2 + 1 dimensions . developing an experimental technique to create a seed of topological - defect turbulence by pulse laser , we confirm in particular the rapidity symmetry , which is a basic but nontrivial consequence of the field - theoretic approach to dp . this provides the first clear experimental realization of this outstanding , truly out - of - equilibrium universality class , dominating most phase transitions into an absorbing state . </s>

this paper reports the results of a study of the properties of the hadronic final state in positron - proton deep inelastic scattering ( dis ) . the event kinematics of dis are determined by the negative square of the four - momentum transfer of the virtual exchanged boson , @xmath4 , and the bjorken scaling variable , @xmath5 , where @xmath6 is the four - momentum of the proton . in the quark parton model ( qpm ) , the interacting quark from the proton carries four - momentum @xmath7 the variable @xmath8 , the fractional energy transfer to the proton in its rest frame , is related to @xmath1 and @xmath0 by @xmath9 , where @xmath10 is the positron - proton centre of mass energy . a natural frame in which to study the dynamics of the hadronic final state in dis is the breit frame @xcite . in this frame the exchanged virtual boson is completely space - like and has a four - momentum @xmath11 , where @xmath12 is the momentum of the proton in the breit frame . the particles produced in the interaction can be assigned to one of two regions : the current region if their @xmath13-momentum in the breit frame is negative , and the target region if their @xmath13-momentum is positive . the advantage of this frame is that it gives a maximal separation of the incoming and outgoing partons in the qpm . in this model the maximum momentum a particle can have in the current region is @xmath14 the current region in the breit frame is analogous to a single hemisphere of @xmath2 annihilation . in @xmath15 annihilation the two quarks are produced with equal and opposite momenta , @xmath16 the fragmentation of these quarks can be compared with that of the quark struck from the proton which has outgoing momentum @xmath17 in the breit frame . in the direction of this struck quark the scaled momentum spectra of the particles , expressed in terms of @xmath18 are expected to have a dependence on @xmath19 similar to that observed in annihilation @xcite at energy @xmath20 within the modified leading log approximation ( mlla ) there are predictions of how the higher order moments of the parton momentum spectra should evolve with energy scale @xcite . the parton level predictions depend on two free parameters , a running strong coupling , governed by a qcd scale @xmath21 and an energy cut - off , @xmath22 below which the parton evolution is truncated . the hypothesis of local parton hadron duality ( lphd ) @xcite , which relates the observed hadron distributions to the calculated parton distributions via a constant of proportionality , is used in conjunction with the predictions of the mlla allowing the calculation to be directly compared with data . the moments of the distributions have been investigated up to the 4th order ; the mean @xmath23 width @xmath24 skewness @xmath25 and kurtosis @xmath26 were extracted from the distribution by fitting a distorted gaussian of the following form : @xmath27 where @xmath28 over a range of 3 units ( @xmath29 ) or 4 ( @xmath30 ) units in @xmath31 around the mean . the equation was motivated by the expression used for the mlla predictions of the spectra in ref . @xcite . figure [ fig : qevol ] shows the skewness of the @xmath31 spectra as a function of @xmath32 it is evident that the skewness decreases with increasing @xmath33 similar fits performed on data shows a reasonable agreement with our results at high @xmath34 consistent with the universality of fragmentation for this distribution . the ariadne monte carlo model @xcite gives a reasonable description of the data . the data are compared with the mlla predictions of ref . @xcite , using a value of @xmath35 for different values of @xmath36 the mlla calculations predict a negative skewness which decreases towards zero with increasing @xmath19 in the case of the limiting spectra ( @xmath37 ) . this is contrary to the measurements . a reasonable description of the behaviour of the skewness with @xmath19 can be achieved for a truncated cascade ( @xmath38 ) , but a consistent description of the mean , width , skewness and kurtosis can not be achieved @xcite . a range of @xmath39 values were investigated and none gave a good description of all the moments . we conclude that the mlla predictions , assuming lphd , do not describe the data . it should be noted though that a moments analysis has been performed @xcite , taking into account the limitations of the massless assumptions of the mlla predictions , where good agreement was found between the limiting case of the mlla and @xmath40 data over a large range of energy , @xmath41 charged particle distributions have been studied in the current region of the breit frame in dis . the moments of the @xmath31 spectra in the current region at high @xmath0 exhibit the same energy scale behaviour as that observed in @xmath2 data . the moments can not be described by the mlla calculations together with lphd .

the production of charged particles has been measured in deep inelastic scattering ( dis ) with the zeus detector . the evolution of the moments of the scaled momenta distributions in @xmath0 and @xmath1 has been investigated in the current fragmentation region of the breit frame . the results in the current region are compared to @xmath2 data and qcd analytical calculations . the results are consistent with the universality of single - particle spectra in dis and @xmath2 annihilation at high @xmath3 the results at low @xmath0 disagree with analytical calculations based on the modified leading log approximation ( mlla ) and local parton hadron duality ( lphd ) . glas - ppe/199901january 1999

<s>[INST]this paper reports the results of a study of the properties of the hadronic final state in positron - proton deep inelastic scattering ( dis ) . the event kinematics of dis are determined by the negative square of the four - momentum transfer of the virtual exchanged boson , @xmath4 , and the bjorken scaling variable , @xmath5 , where @xmath6 is the four - momentum of the proton . in the quark parton model ( qpm ) , the interacting quark from the proton carries four - momentum @xmath7 the variable @xmath8 , the fractional energy transfer to the proton in its rest frame , is related to @xmath1 and @xmath0 by @xmath9 , where @xmath10 is the positron - proton centre of mass energy . a natural frame in which to study the dynamics of the hadronic final state in dis is the breit frame @xcite . in this frame the exchanged virtual boson is completely space - like and has a four - momentum @xmath11 , where @xmath12 is the momentum of the proton in the breit frame . the particles produced in the interaction can be assigned to one of two regions : the current region if their @xmath13-momentum in the breit frame is negative , and the target region if their @xmath13-momentum is positive . the advantage of this frame is that it gives a maximal separation of the incoming and outgoing partons in the qpm . in this model the maximum momentum a particle can have in the current region is @xmath14 the current region in the breit frame is analogous to a single hemisphere of @xmath2 annihilation . in @xmath15 annihilation the two quarks are produced with equal and opposite momenta , @xmath16 the fragmentation of these quarks can be compared with that of the quark struck from the proton which has outgoing momentum @xmath17 in the breit frame . in the direction of this struck quark the scaled momentum spectra of the particles , expressed in terms of @xmath18 are expected to have a dependence on @xmath19 similar to that observed in annihilation @xcite at energy @xmath20 within the modified leading log approximation ( mlla ) there are predictions of how the higher order moments of the parton momentum spectra should evolve with energy scale @xcite . the parton level predictions depend on two free parameters , a running strong coupling , governed by a qcd scale @xmath21 and an energy cut - off , @xmath22 below which the parton evolution is truncated . the hypothesis of local parton hadron duality ( lphd ) @xcite , which relates the observed hadron distributions to the calculated parton distributions via a constant of proportionality , is used in conjunction with the predictions of the mlla allowing the calculation to be directly compared with data . the moments of the distributions have been investigated up to the 4th order ; the mean @xmath23 width @xmath24 skewness @xmath25 and kurtosis @xmath26 were extracted from the distribution by fitting a distorted gaussian of the following form : @xmath27 where @xmath28 over a range of 3 units ( @xmath29 ) or 4 ( @xmath30 ) units in @xmath31 around the mean . the equation was motivated by the expression used for the mlla predictions of the spectra in ref . @xcite . figure [ fig : qevol ] shows the skewness of the @xmath31 spectra as a function of @xmath32 it is evident that the skewness decreases with increasing @xmath33 similar fits performed on data shows a reasonable agreement with our results at high @xmath34 consistent with the universality of fragmentation for this distribution . the ariadne monte carlo model @xcite gives a reasonable description of the data . the data are compared with the mlla predictions of ref . @xcite , using a value of @xmath35 for different values of @xmath36 the mlla calculations predict a negative skewness which decreases towards zero with increasing @xmath19 in the case of the limiting spectra ( @xmath37 ) . this is contrary to the measurements . a reasonable description of the behaviour of the skewness with @xmath19 can be achieved for a truncated cascade ( @xmath38 ) , but a consistent description of the mean , width , skewness and kurtosis can not be achieved @xcite . a range of @xmath39 values were investigated and none gave a good description of all the moments . we conclude that the mlla predictions , assuming lphd , do not describe the data . it should be noted though that a moments analysis has been performed @xcite , taking into account the limitations of the massless assumptions of the mlla predictions , where good agreement was found between the limiting case of the mlla and @xmath40 data over a large range of energy , @xmath41 charged particle distributions have been studied in the current region of the breit frame in dis . the moments of the @xmath31 spectra in the current region at high @xmath0 exhibit the same energy scale behaviour as that observed in @xmath2 data . the moments can not be described by the mlla calculations together with lphd .[/INST] the production of charged particles has been measured in deep inelastic scattering ( dis ) with the zeus detector . the evolution of the moments of the scaled momenta distributions in @xmath0 and @xmath1 has been investigated in the current fragmentation region of the breit frame . the results in the current region are compared to @xmath2 data and qcd analytical calculations . the results are consistent with the universality of single - particle spectra in dis and @xmath2 annihilation at high @xmath3 the results at low @xmath0 disagree with analytical calculations based on the modified leading log approximation ( mlla ) and local parton hadron duality ( lphd ) . glas - ppe/199901january 1999 </s>

SECTION 1. SHORT TITLE. This Act may be cited as the ``Federal Communications Commission Consolidated Reporting Act of 2011''. SEC. 2. COMMUNICATIONS MARKETPLACE REPORT. Title I of the Communications Act of 1934 (47 U.S.C. 151 et seq.) is amended by adding at the end the following: ``SEC. 13. COMMUNICATIONS MARKETPLACE REPORT. ``(a) In General.--In the last quarter of every even-numbered year, the Commission shall publish on its Web site and submit to the Committee on Energy and Commerce of the House of Representatives and the Committee on Commerce, Science, and Transportation of the Senate a report on the state of the communications marketplace. ``(b) Contents.--Each report required by subsection (a) shall-- ``(1) assess the state of competition in the communications marketplace, including competition to deliver voice, video, and data services among providers of telecommunications, providers of commercial mobile service (as defined in section 332), multichannel video programming distributors (as defined in section 602), broadcast stations, providers of satellite communications, Internet service providers, and other providers of communications services; ``(2) assess the state of deployment of communications capabilities, including advanced telecommunications capability (as defined in section 706 of the Telecommunications Act of 1996 (47 U.S.C. 1302)), regardless of the technology used for such deployment, including whether advanced telecommunications capability is being deployed to all Americans in a reasonable and timely fashion; ``(3) assess whether laws, regulations, or regulatory practices (whether those of the Federal Government, States, political subdivisions of States, Indian tribes or tribal organizations (as such terms are defined in section 4 of the Indian Self-Determination and Education Assistance Act (25 U.S.C. 450b)), or foreign governments) pose a barrier to competitive entry into the communications marketplace or to the competitive expansion of existing providers of communications services; ``(4) describe the agenda of the Commission for the next 2- year period for addressing the challenges and opportunities in the communications marketplace that were identified through the assessments under paragraphs (1) through (3); and ``(5) describe the actions that the Commission has taken in pursuit of the agenda described pursuant to paragraph (4) in the previous report submitted under this section. ``(c) Special Requirements.-- ``(1) Assessing competition.--In assessing the state of competition under subsection (b)(1), the Commission shall consider the effect of intermodal competition, facilities-based competition, and competition from new and emergent communications services, including the provision of content and communications using the Internet. ``(2) Assessing deployment.--In assessing the state of deployment under subsection (b)(2), the Commission shall compile a list of geographical areas that are not served by any provider of advanced telecommunications capability. ``(3) International comparisons and demographic information.--The Commission may use readily available data to draw appropriate comparisons between the United States communications marketplace and the international communications marketplace and to correlate its assessments with demographic information.''. SEC. 3. CONSOLIDATION OF REDUNDANT REPORTS; CONFORMING AMENDMENTS. (a) ORBIT Act Report.--Section 646 of the Communications Satellite Act of 1962 (47 U.S.C. 765e; 114 Stat. 57) is repealed. (b) Satellite Competition Report.--Section 4 of Public Law 109-34 (47 U.S.C. 703) is repealed. (c) International Broadband Data Report.--Section 103 of the Broadband Data Improvement Act (47 U.S.C. 1303) is amended-- (1) by striking subsection (b); and (2) by redesignating subsections (c) through (e) as subsections (b) through (d), respectively. (d) Status of Competition in the Market for the Delivery of Video Programming Report.--Section 628 of the Communications Act of 1934 (47 U.S.C. 548) is amended-- (1) by striking subsection (g); and (2) by redesignating subsection (j) as subsection (g). (e) Report on Cable Industry Prices.-- (1) In general.--Section 623 of the Communications Act of 1934 (47 U.S.C. 543) is amended-- (A) by striking subsection (k); and (B) by redesignating subsections (l) through (n) as subsections (k) through (m), respectively. (2) Conforming amendment.--Section 613(a)(3) of the Communications Act of 1934 (47 U.S.C. 533(a)(3)) is amended by striking ``623(l)'' and inserting ``623(k)''. (f) Triennial Report Identifying and Eliminating Market Entry Barriers for Entrepreneurs and Other Small Businesses.--Section 257 of the Communications Act of 1934 (47 U.S.C. 257) is amended by striking subsection (c). (g) Section 706 Report.--Section 706 of the Telecommunications Act of 1996 (47 U.S.C. 1302) is amended-- (1) in subsection (b)-- (A) in the last sentence, by striking ``If the Commission's determination is negative, it'' and inserting ``If the Commission determines in its report under section 13 of the Communications Act of 1934 that advanced telecommunications capability is not being deployed to all Americans in a reasonable and timely fashion, the Commission''; and (B) by striking the first and second sentences; (2) by striking subsection (c); (3) in subsection (d), by striking ``this subsection'' and inserting ``this section''; and (4) by redesignating subsection (d) as subsection (c). (h) State of Competitive Market Conditions With Respect to Commercial Mobile Radio Services.--Section 332(c)(1)(C) of the Communications Act of 1934 (47 U.S.C. 332(c)(1)(C)) is amended by striking the first and second sentences. (i) Previously Eliminated Annual Report.-- (1) In general.--Section 4 of the Communications Act of 1934 (47 U.S.C. 154) is amended-- (A) by striking subsection (k); and (B) by redesignating subsections (l) through (o) as subsections (k) through (n), respectively. (2) Conforming amendments.--The Communications Act of 1934 is amended-- (A) in section 9(i), by striking ``In the Commission's annual report, the Commission shall prepare an analysis of its progress in developing such systems and'' and inserting ``The Commission''; and (B) in section 309(j)(8)(B), by striking the last sentence. (j) Additional Outdated Reports.--The Communications Act of 1934 is amended-- (1) in section 4-- (A) in subsection (b)(2)(B)-- (i) in clause (i), by striking ``(i) The Commission'' and inserting ``The Commission''; and (ii) by striking clause (ii); and (B) in subsection (g), by striking paragraph (2); (2) in section 215-- (A) by striking subsection (b); and (B) by redesignating subsection (c) as subsection (b); (3) in section 227(e), by striking paragraph (4); (4) in section 309(j)-- (A) by striking paragraph (12); and (B) in paragraph (15)(C), by striking clause (iv); (5) in section 331(b), by striking the last sentence; (6) in section 336(e), by amending paragraph (4) to read as follows: ``(4) Report.--The Commission shall annually advise the Congress on the amounts collected pursuant to the program required by this subsection.''; (7) in section 339(c), by striking paragraph (1); (8) in section 396-- (A) by striking subsection (i); (B) in subsection (k)-- (i) in paragraph (1), by striking subparagraph (F); and (ii) in paragraph (3)(B)(iii), by striking subclause (V); (C) in subsection (l)(1)(B), by striking ``shall be included'' and all that follows through ``The audit report''; and (D) by striking subsection (m); (9) in section 398(b)(4), by striking the third sentence; (10) in section 624A(b)(1)-- (A) by striking ``Report; regulations'' and inserting ``Regulations''; (B) by striking ``Within 1 year after'' and all that follows through ``on means of assuring'' and inserting ``The Commission shall issue such regulations as are necessary to assure''; and (C) by striking ``Within 180 days after'' and all that follows through ``to assure such compatibility.''; and (11) in section 713, by striking subsection (a). SEC. 4. EFFECT ON AUTHORITY. Nothing in this Act or the amendments made by this Act shall be construed to expand or contract the authority of the Federal Communications Commission.

Federal Communications Commission Consolidated Reporting Act of 2011 - Amends the Communications Act of 1934 to require the Federal Communications Commission (FCC) to publish on its website and submit to Congress a biennial report on the state of the communications marketplace assessing: (1) competition, including intermodal, facilities-based, and new and emergent services competition and addressing the provision of content and communications using the Internet; (2) deployment of communications capabilities, including whether advanced telecommunications capability is being deployed to all Americans in a reasonable and timely fashion; and (3) whether laws, regulations, or regulatory practices pose a barrier to competitive entry or expansion of existing providers of communications services. Requires the FCC to compile a list of geographic areas that are not served by any provider of advanced telecommunications capability. Repeals and consolidates various FCC reports including reports on satellite competition, international broadband, video programming, cable industry prices, small business entry barriers, commercial mobile radio, and several other existing reports under such Act.

<s>[INST]SECTION 1. SHORT TITLE. This Act may be cited as the ``Federal Communications Commission Consolidated Reporting Act of 2011''. SEC. 2. COMMUNICATIONS MARKETPLACE REPORT. Title I of the Communications Act of 1934 (47 U.S.C. 151 et seq.) is amended by adding at the end the following: ``SEC. 13. COMMUNICATIONS MARKETPLACE REPORT. ``(a) In General.--In the last quarter of every even-numbered year, the Commission shall publish on its Web site and submit to the Committee on Energy and Commerce of the House of Representatives and the Committee on Commerce, Science, and Transportation of the Senate a report on the state of the communications marketplace. ``(b) Contents.--Each report required by subsection (a) shall-- ``(1) assess the state of competition in the communications marketplace, including competition to deliver voice, video, and data services among providers of telecommunications, providers of commercial mobile service (as defined in section 332), multichannel video programming distributors (as defined in section 602), broadcast stations, providers of satellite communications, Internet service providers, and other providers of communications services; ``(2) assess the state of deployment of communications capabilities, including advanced telecommunications capability (as defined in section 706 of the Telecommunications Act of 1996 (47 U.S.C. 1302)), regardless of the technology used for such deployment, including whether advanced telecommunications capability is being deployed to all Americans in a reasonable and timely fashion; ``(3) assess whether laws, regulations, or regulatory practices (whether those of the Federal Government, States, political subdivisions of States, Indian tribes or tribal organizations (as such terms are defined in section 4 of the Indian Self-Determination and Education Assistance Act (25 U.S.C. 450b)), or foreign governments) pose a barrier to competitive entry into the communications marketplace or to the competitive expansion of existing providers of communications services; ``(4) describe the agenda of the Commission for the next 2- year period for addressing the challenges and opportunities in the communications marketplace that were identified through the assessments under paragraphs (1) through (3); and ``(5) describe the actions that the Commission has taken in pursuit of the agenda described pursuant to paragraph (4) in the previous report submitted under this section. ``(c) Special Requirements.-- ``(1) Assessing competition.--In assessing the state of competition under subsection (b)(1), the Commission shall consider the effect of intermodal competition, facilities-based competition, and competition from new and emergent communications services, including the provision of content and communications using the Internet. ``(2) Assessing deployment.--In assessing the state of deployment under subsection (b)(2), the Commission shall compile a list of geographical areas that are not served by any provider of advanced telecommunications capability. ``(3) International comparisons and demographic information.--The Commission may use readily available data to draw appropriate comparisons between the United States communications marketplace and the international communications marketplace and to correlate its assessments with demographic information.''. SEC. 3. CONSOLIDATION OF REDUNDANT REPORTS; CONFORMING AMENDMENTS. (a) ORBIT Act Report.--Section 646 of the Communications Satellite Act of 1962 (47 U.S.C. 765e; 114 Stat. 57) is repealed. (b) Satellite Competition Report.--Section 4 of Public Law 109-34 (47 U.S.C. 703) is repealed. (c) International Broadband Data Report.--Section 103 of the Broadband Data Improvement Act (47 U.S.C. 1303) is amended-- (1) by striking subsection (b); and (2) by redesignating subsections (c) through (e) as subsections (b) through (d), respectively. (d) Status of Competition in the Market for the Delivery of Video Programming Report.--Section 628 of the Communications Act of 1934 (47 U.S.C. 548) is amended-- (1) by striking subsection (g); and (2) by redesignating subsection (j) as subsection (g). (e) Report on Cable Industry Prices.-- (1) In general.--Section 623 of the Communications Act of 1934 (47 U.S.C. 543) is amended-- (A) by striking subsection (k); and (B) by redesignating subsections (l) through (n) as subsections (k) through (m), respectively. (2) Conforming amendment.--Section 613(a)(3) of the Communications Act of 1934 (47 U.S.C. 533(a)(3)) is amended by striking ``623(l)'' and inserting ``623(k)''. (f) Triennial Report Identifying and Eliminating Market Entry Barriers for Entrepreneurs and Other Small Businesses.--Section 257 of the Communications Act of 1934 (47 U.S.C. 257) is amended by striking subsection (c). (g) Section 706 Report.--Section 706 of the Telecommunications Act of 1996 (47 U.S.C. 1302) is amended-- (1) in subsection (b)-- (A) in the last sentence, by striking ``If the Commission's determination is negative, it'' and inserting ``If the Commission determines in its report under section 13 of the Communications Act of 1934 that advanced telecommunications capability is not being deployed to all Americans in a reasonable and timely fashion, the Commission''; and (B) by striking the first and second sentences; (2) by striking subsection (c); (3) in subsection (d), by striking ``this subsection'' and inserting ``this section''; and (4) by redesignating subsection (d) as subsection (c). (h) State of Competitive Market Conditions With Respect to Commercial Mobile Radio Services.--Section 332(c)(1)(C) of the Communications Act of 1934 (47 U.S.C. 332(c)(1)(C)) is amended by striking the first and second sentences. (i) Previously Eliminated Annual Report.-- (1) In general.--Section 4 of the Communications Act of 1934 (47 U.S.C. 154) is amended-- (A) by striking subsection (k); and (B) by redesignating subsections (l) through (o) as subsections (k) through (n), respectively. (2) Conforming amendments.--The Communications Act of 1934 is amended-- (A) in section 9(i), by striking ``In the Commission's annual report, the Commission shall prepare an analysis of its progress in developing such systems and'' and inserting ``The Commission''; and (B) in section 309(j)(8)(B), by striking the last sentence. (j) Additional Outdated Reports.--The Communications Act of 1934 is amended-- (1) in section 4-- (A) in subsection (b)(2)(B)-- (i) in clause (i), by striking ``(i) The Commission'' and inserting ``The Commission''; and (ii) by striking clause (ii); and (B) in subsection (g), by striking paragraph (2); (2) in section 215-- (A) by striking subsection (b); and (B) by redesignating subsection (c) as subsection (b); (3) in section 227(e), by striking paragraph (4); (4) in section 309(j)-- (A) by striking paragraph (12); and (B) in paragraph (15)(C), by striking clause (iv); (5) in section 331(b), by striking the last sentence; (6) in section 336(e), by amending paragraph (4) to read as follows: ``(4) Report.--The Commission shall annually advise the Congress on the amounts collected pursuant to the program required by this subsection.''; (7) in section 339(c), by striking paragraph (1); (8) in section 396-- (A) by striking subsection (i); (B) in subsection (k)-- (i) in paragraph (1), by striking subparagraph (F); and (ii) in paragraph (3)(B)(iii), by striking subclause (V); (C) in subsection (l)(1)(B), by striking ``shall be included'' and all that follows through ``The audit report''; and (D) by striking subsection (m); (9) in section 398(b)(4), by striking the third sentence; (10) in section 624A(b)(1)-- (A) by striking ``Report; regulations'' and inserting ``Regulations''; (B) by striking ``Within 1 year after'' and all that follows through ``on means of assuring'' and inserting ``The Commission shall issue such regulations as are necessary to assure''; and (C) by striking ``Within 180 days after'' and all that follows through ``to assure such compatibility.''; and (11) in section 713, by striking subsection (a). SEC. 4. EFFECT ON AUTHORITY. Nothing in this Act or the amendments made by this Act shall be construed to expand or contract the authority of the Federal Communications Commission.[/INST]Federal Communications Commission Consolidated Reporting Act of 2011 - Amends the Communications Act of 1934 to require the Federal Communications Commission (FCC) to publish on its website and submit to Congress a biennial report on the state of the communications marketplace assessing: (1) competition, including intermodal, facilities-based, and new and emergent services competition and addressing the provision of content and communications using the Internet; (2) deployment of communications capabilities, including whether advanced telecommunications capability is being deployed to all Americans in a reasonable and timely fashion; and (3) whether laws, regulations, or regulatory practices pose a barrier to competitive entry or expansion of existing providers of communications services. Requires the FCC to compile a list of geographic areas that are not served by any provider of advanced telecommunications capability. Repeals and consolidates various FCC reports including reports on satellite competition, international broadband, video programming, cable industry prices, small business entry barriers, commercial mobile radio, and several other existing reports under such Act.</s>

SECTION 1. SHORT TITLE. This Act may be cited as the ``Bipartisan Commission on Social Security Reform Act of 2001''. SEC. 2. FINDINGS. The Congress finds the following: (1) The 2000 Report of the Social Security Board of Trustees projects that the receipts financing the Social Security trust funds will fall below its outgo in 2015 and the trust funds will be depleted in 2037. At that time only 72 percent of Social Security benefits would be payable then with incoming receipts. (2) The primary reason is demographic: the post-World War II baby boomers will begin retiring in less than a decade and life expectancy is rising. By 2025 the number of people age 65 and older is predicted to grow by 75 percent. In contrast, the number of workers supporting the system would grow by 13 percent. (3) If there are no other surplus governmental receipts, policymakers would have 3 choices: raise taxes or other income, cut spending, or borrow the money. Mirroring this adverse outlook are public opinion polls showing that fewer than 50 percent of respondents are confident that Social Security can meet its long-term commitments. There also is a widespread perception that Social Security may not be as good a value in the future as it is today. (4) While it is accepted that Social Security reform is needed without undue delay, there clearly is no consensus on how this should be accomplished. This was evident by the Report of the 1994-1996 Social Security Advisory Council, which provided 3 very different plans but none of which received a majority's endorsement. It also is reflected by the many bills introduced in the 105th Congress and the 106th Congress and proposals by the administration that represent a diversity of approaches to Social Security reform. As a result of differences within Congress and with the administration, there has been no movement on Social Security reform. (5) This state of affairs shows the need to develop consensus legislation between Congress and the administration that can be enacted into law without undue delay. To accomplish this there is to be established a Bipartisan Commission on Social Security Reform charged with developing a unified proposal to ensure the long-term retirement security of Americans. SEC. 3. ESTABLISHMENT OF COMMISSION. There is established in the legislative branch a Bipartisan Commission on Social Security Reform (in this Act referred to as the ``Commission''). SEC. 4. DUTIES OF THE COMMISSION. The Commission shall design a single set of legislative and administrative recommendations for long-range reforms for restoring the solvency of the Social Security system, and maintaining retirement income security in the United States. SEC. 5. COMPOSITION OF THE COMMISSION. (a) Number and Appointment.--The Commission shall be composed of 17 members, of whom-- (1) 3 members shall be selected by the Speaker of the House of Representatives, 1 from among Members of the House, and 2 from among private citizens; (2) 3 members shall be selected by the majority leader of the Senate, 1 from among Members of the Senate, and 2 from among private citizens; (3) 3 members shall be selected by the minority leader of the House of Representatives, 1 from among Members of the House, and 2 from among private citizens; (4) 3 members shall be selected by the minority leader of the Senate, 1 from among Members of the Senate, and 2 from among private citizens; and (5) 5 members shall be selected by the President, 2 from among officers of the executive branch of the United States Government, and 3 from among private citizens. The Commissioner of Social Security shall be an ex officio, nonvoting member of the Commission. (b) Qualifications.--The members of the Commission shall consist of individuals who are of recognized standing and distinction who can represent the multiple generations who have a stake in the viability of the Social Security system, and who possess a demonstrated capacity to discharge the duties imposed on the Commission. At least 1 of the members shall be appointed from individuals representing the interests of employees, and at least 1 of the members shall be appointed from individuals representing the interests of employers. (c) Chair.--The officials referred to in paragraphs (1) through (5) of subsection (a) shall designate a member of the Commission to serve as Chair of the Commission (or 2 of the members of the Commission to serve as Co-Chairs of the Commission) who shall chair (or jointly chair) the Commission, determine its duties, and supervise its staff. (d) Terms of Appointment.--The members of the Commission shall be appointed not more than 30 days after the date of the enactment of this Act. The members of the Commission shall serve for the life of the Commission. (e) Vacancies.--A vacancy in the Commission shall not affect the power of the remaining members to execute the duties of the Commission but any such vacancy shall be filled in the same manner in which the original appointment was made. SEC. 6. PROCEDURES. (a) Meetings.--The Commission shall meet at the call of its Chair (or Co-Chairs) or a majority of its members. If after 30 days after the date of the enactment of this Act, 9 or more members of the Commission have been appointed, members who have been appointed may meet and select the Chair (or Co-Chairs) who thereafter shall have the authority to begin the operations of the Commission, including the hiring of staff. (b) Quorum.--A quorum shall consist of nine members of the Commission, except that a lesser number may conduct a hearing under subsection (c). (c) Hearings and Other Activities.--For the purpose of carrying out its duties, the Commission may hold such hearings and undertake such other activities as the Commission determines necessary to carry out its duties. (d) Obtaining Information.--Upon request of the Commission, the Commissioner of Social Security and the head of any other agency or instrumentality of the Federal Government shall furnish information deemed necessary by the panel to enable it to carry out its duties. SEC. 7. ADMINISTRATION. (a) Compensation.--Except as provided in subsection (b), members of the Commission shall receive no additional pay, allowances, or benefits by reason of their service on the Commission. (b) Travel Expenses and Per Diem.--Each member of the Commission who is not a present Member of the Congress and who is not otherwise an officer or employee of the Federal Government shall receive travel expenses and per diem in lieu of subsistence in accordance with sections 5702 and 5703 of title 5, United States Code. (c) Staff and Support Services.-- (1) Staff director.-- (A) Appointment.--The Chair (or Co-Chairs) in accordance with the rules agreed upon by the Commission shall appoint a staff director for the Commission. (B) Compensation.--The staff director shall be paid at a rate not to exceed the rate established for level V of the Executive Schedule under section 5315 of title 5, United States Code. (2) Staff.--The Chair (or Co-Chairs) in accordance with the rules agreed upon by the Commission shall appoint such additional personnel as the Commission determines to be necessary. (3) Applicability of civil service laws.--The staff director and other members of the staff of the Commission shall be appointed without regard to the provisions of title 5, United States Code, governing appointments in the competitive service, and shall be paid without regard to the provisions of chapter 51 and subchapter III of chapter 53 of such title relating to classification and General Schedule pay rates. (4) Experts and consultants.--With the approval of the Commission, the staff director may procure temporary and intermittent services under section 3109(b) of title 5, United States Code. (d) Physical Facilities.--The Architect of the Capitol, in consultation with the appropriate entities in the legislative branch, shall locate and provide suitable office space for the operation of the Commission on a nonreimbursable basis. The facilities shall serve as the headquarters of the Commission and shall include all necessary equipment and incidentals required for the proper functioning of the Commission. (e) Administrative Support Services and Other Assistance.-- (1) Upon the request of the Commission, the Architect of the Capitol, the Commissioner of Social Security, and the Administrator of General Services shall provide to the Commission on a nonreimbursable basis such administrative support services as the Commission may request. (2) In addition to the assistance set forth in paragraphs (1) and (2), departments and agencies of the United States may provide the Commission such services, funds, facilities, staff, and other support services as the Commission may deem advisable and as may be authorized by law. (g) Use of Mails.--The Commission may use the United States mails in the same manner and under the same conditions as Federal agencies and shall, for purposes of the frank, be considered a commission of Congress as described in section 3215 of title 39, United States Code. (h) Printing.--For purposes of costs relating to printing and binding, including the cost of personnel detailed from the Government Printing Office, the Commission shall be deemed to be a committee of the Congress. SEC. 8. REPORT. Not later than 6 months after the date of the first meeting of the Commission, the Commission shall submit to the Committee on Ways and Means of the House of Representatives and the Committee on Finance of the Senate a report which shall contain a detailed statement of the findings and conclusions of the Commission, including the set of recommendations required under section 4. The report shall be approved by at least nine members of the Commission. SEC. 9. TERMINATION. The Commission shall terminate 30 days after submitting its final report. SEC. 10. AUTHORIZATION OF APPROPRIATIONS. There are authorized to be appropriated such sums as may be necessary for the activities of the Commission. Until such time as funds are otherwise specifically appropriated for such activities, $2,000,000 shall be available for the activities of the Commission from funds otherwise currently appropriated for administrative expenses of the Social Security Administration pursuant to section 201(g)(1)(A) of the Social Security Act.

Bipartisan Commission on Social Security Reform Act of 2001 - Establishes in the legislative branch a Bipartisan Commission on Social Security Reform to design a single set of legislative and administrative recommendations for long-range reforms for: (1) restoring the solvency of the Social Security system; and (2) maintaining retirement income security in the United States.

<s>[INST]SECTION 1. SHORT TITLE. This Act may be cited as the ``Bipartisan Commission on Social Security Reform Act of 2001''. SEC. 2. FINDINGS. The Congress finds the following: (1) The 2000 Report of the Social Security Board of Trustees projects that the receipts financing the Social Security trust funds will fall below its outgo in 2015 and the trust funds will be depleted in 2037. At that time only 72 percent of Social Security benefits would be payable then with incoming receipts. (2) The primary reason is demographic: the post-World War II baby boomers will begin retiring in less than a decade and life expectancy is rising. By 2025 the number of people age 65 and older is predicted to grow by 75 percent. In contrast, the number of workers supporting the system would grow by 13 percent. (3) If there are no other surplus governmental receipts, policymakers would have 3 choices: raise taxes or other income, cut spending, or borrow the money. Mirroring this adverse outlook are public opinion polls showing that fewer than 50 percent of respondents are confident that Social Security can meet its long-term commitments. There also is a widespread perception that Social Security may not be as good a value in the future as it is today. (4) While it is accepted that Social Security reform is needed without undue delay, there clearly is no consensus on how this should be accomplished. This was evident by the Report of the 1994-1996 Social Security Advisory Council, which provided 3 very different plans but none of which received a majority's endorsement. It also is reflected by the many bills introduced in the 105th Congress and the 106th Congress and proposals by the administration that represent a diversity of approaches to Social Security reform. As a result of differences within Congress and with the administration, there has been no movement on Social Security reform. (5) This state of affairs shows the need to develop consensus legislation between Congress and the administration that can be enacted into law without undue delay. To accomplish this there is to be established a Bipartisan Commission on Social Security Reform charged with developing a unified proposal to ensure the long-term retirement security of Americans. SEC. 3. ESTABLISHMENT OF COMMISSION. There is established in the legislative branch a Bipartisan Commission on Social Security Reform (in this Act referred to as the ``Commission''). SEC. 4. DUTIES OF THE COMMISSION. The Commission shall design a single set of legislative and administrative recommendations for long-range reforms for restoring the solvency of the Social Security system, and maintaining retirement income security in the United States. SEC. 5. COMPOSITION OF THE COMMISSION. (a) Number and Appointment.--The Commission shall be composed of 17 members, of whom-- (1) 3 members shall be selected by the Speaker of the House of Representatives, 1 from among Members of the House, and 2 from among private citizens; (2) 3 members shall be selected by the majority leader of the Senate, 1 from among Members of the Senate, and 2 from among private citizens; (3) 3 members shall be selected by the minority leader of the House of Representatives, 1 from among Members of the House, and 2 from among private citizens; (4) 3 members shall be selected by the minority leader of the Senate, 1 from among Members of the Senate, and 2 from among private citizens; and (5) 5 members shall be selected by the President, 2 from among officers of the executive branch of the United States Government, and 3 from among private citizens. The Commissioner of Social Security shall be an ex officio, nonvoting member of the Commission. (b) Qualifications.--The members of the Commission shall consist of individuals who are of recognized standing and distinction who can represent the multiple generations who have a stake in the viability of the Social Security system, and who possess a demonstrated capacity to discharge the duties imposed on the Commission. At least 1 of the members shall be appointed from individuals representing the interests of employees, and at least 1 of the members shall be appointed from individuals representing the interests of employers. (c) Chair.--The officials referred to in paragraphs (1) through (5) of subsection (a) shall designate a member of the Commission to serve as Chair of the Commission (or 2 of the members of the Commission to serve as Co-Chairs of the Commission) who shall chair (or jointly chair) the Commission, determine its duties, and supervise its staff. (d) Terms of Appointment.--The members of the Commission shall be appointed not more than 30 days after the date of the enactment of this Act. The members of the Commission shall serve for the life of the Commission. (e) Vacancies.--A vacancy in the Commission shall not affect the power of the remaining members to execute the duties of the Commission but any such vacancy shall be filled in the same manner in which the original appointment was made. SEC. 6. PROCEDURES. (a) Meetings.--The Commission shall meet at the call of its Chair (or Co-Chairs) or a majority of its members. If after 30 days after the date of the enactment of this Act, 9 or more members of the Commission have been appointed, members who have been appointed may meet and select the Chair (or Co-Chairs) who thereafter shall have the authority to begin the operations of the Commission, including the hiring of staff. (b) Quorum.--A quorum shall consist of nine members of the Commission, except that a lesser number may conduct a hearing under subsection (c). (c) Hearings and Other Activities.--For the purpose of carrying out its duties, the Commission may hold such hearings and undertake such other activities as the Commission determines necessary to carry out its duties. (d) Obtaining Information.--Upon request of the Commission, the Commissioner of Social Security and the head of any other agency or instrumentality of the Federal Government shall furnish information deemed necessary by the panel to enable it to carry out its duties. SEC. 7. ADMINISTRATION. (a) Compensation.--Except as provided in subsection (b), members of the Commission shall receive no additional pay, allowances, or benefits by reason of their service on the Commission. (b) Travel Expenses and Per Diem.--Each member of the Commission who is not a present Member of the Congress and who is not otherwise an officer or employee of the Federal Government shall receive travel expenses and per diem in lieu of subsistence in accordance with sections 5702 and 5703 of title 5, United States Code. (c) Staff and Support Services.-- (1) Staff director.-- (A) Appointment.--The Chair (or Co-Chairs) in accordance with the rules agreed upon by the Commission shall appoint a staff director for the Commission. (B) Compensation.--The staff director shall be paid at a rate not to exceed the rate established for level V of the Executive Schedule under section 5315 of title 5, United States Code. (2) Staff.--The Chair (or Co-Chairs) in accordance with the rules agreed upon by the Commission shall appoint such additional personnel as the Commission determines to be necessary. (3) Applicability of civil service laws.--The staff director and other members of the staff of the Commission shall be appointed without regard to the provisions of title 5, United States Code, governing appointments in the competitive service, and shall be paid without regard to the provisions of chapter 51 and subchapter III of chapter 53 of such title relating to classification and General Schedule pay rates. (4) Experts and consultants.--With the approval of the Commission, the staff director may procure temporary and intermittent services under section 3109(b) of title 5, United States Code. (d) Physical Facilities.--The Architect of the Capitol, in consultation with the appropriate entities in the legislative branch, shall locate and provide suitable office space for the operation of the Commission on a nonreimbursable basis. The facilities shall serve as the headquarters of the Commission and shall include all necessary equipment and incidentals required for the proper functioning of the Commission. (e) Administrative Support Services and Other Assistance.-- (1) Upon the request of the Commission, the Architect of the Capitol, the Commissioner of Social Security, and the Administrator of General Services shall provide to the Commission on a nonreimbursable basis such administrative support services as the Commission may request. (2) In addition to the assistance set forth in paragraphs (1) and (2), departments and agencies of the United States may provide the Commission such services, funds, facilities, staff, and other support services as the Commission may deem advisable and as may be authorized by law. (g) Use of Mails.--The Commission may use the United States mails in the same manner and under the same conditions as Federal agencies and shall, for purposes of the frank, be considered a commission of Congress as described in section 3215 of title 39, United States Code. (h) Printing.--For purposes of costs relating to printing and binding, including the cost of personnel detailed from the Government Printing Office, the Commission shall be deemed to be a committee of the Congress. SEC. 8. REPORT. Not later than 6 months after the date of the first meeting of the Commission, the Commission shall submit to the Committee on Ways and Means of the House of Representatives and the Committee on Finance of the Senate a report which shall contain a detailed statement of the findings and conclusions of the Commission, including the set of recommendations required under section 4. The report shall be approved by at least nine members of the Commission. SEC. 9. TERMINATION. The Commission shall terminate 30 days after submitting its final report. SEC. 10. AUTHORIZATION OF APPROPRIATIONS. There are authorized to be appropriated such sums as may be necessary for the activities of the Commission. Until such time as funds are otherwise specifically appropriated for such activities, $2,000,000 shall be available for the activities of the Commission from funds otherwise currently appropriated for administrative expenses of the Social Security Administration pursuant to section 201(g)(1)(A) of the Social Security Act.[/INST]Bipartisan Commission on Social Security Reform Act of 2001 - Establishes in the legislative branch a Bipartisan Commission on Social Security Reform to design a single set of legislative and administrative recommendations for long-range reforms for: (1) restoring the solvency of the Social Security system; and (2) maintaining retirement income security in the United States.</s>

chemical adsorption of sulfur atoms on gold surface allows a stable bond between gold tips and thiol groups of molecules . this has been exploited for measuring the conductance and the current - voltage characteristics of gold - molecule - gold junctions @xcite . repeated measurements even with the same sample , however , reveal small but noticeable differences which possibly stem from environmental fluctuations that impact upon the effective molecule parameters . moreover , the particular form of the gold tip can have a significant influence on the transport properties @xcite . a present line of experimental research is the measurement of molecular conductance when the electrons are excited by electromagnetic waves . there one expects various phenomena ranging from photo - assisted transport @xcite to ratchet or non - adiabatic pump effects , i.e. the induction of dc currents by ac fields even in the absence of any voltage bias @xcite . moreover , it has been predicted that properly taylored laser pulses can give rise to short current pulses @xcite . since a dc current flows into one particular direction , a ratchet effect can occur only in `` sufficiently asymmetric '' systems @xcite . in that respect , a static disorder is sufficient to break the reflection symmetry of an individual realization and , thus , may support a ratchet effect . the quantitative prediction of the current through a molecule is still a great challenge despite the significant progress achieved in recent years @xcite . for a more qualitative understanding of the mechanisms involved in molecular transport , it is thus advantageous to employ for the molecule a rather generic tight - binding model @xcite . then a flexible method for the computation of transport properties is provided by master equations of the bloch - redfield type which allow one to include electron - electron and electron - phonon interactions , as well as time - dependent fields @xcite . similar methods have also been used for describing incoherent transport @xcite . here , we explore the role of slow fluctuations or static disorder for molecular conductance . thereby we will assume that the relevant environmental fluctuations are so slow that they can be described as static disorder which defines an ensemble of wire hamiltonians . then a natural quantity of interest is the corresponding distribution of stationary currents . a setup for which this current distribution is also directly relevant is an array of molecular junctions that conduct in parallel . we employ a tight - binding model for the molecule and treat it with the floquet master equation formalism derived in ref . @xcite which we review briefly in section [ sec : model ] . in section [ sec : static ] , we present results for a static model with a large voltage bias , while in section [ sec : driven ] , we investigate pumping effects caused by an interplay of ac driving fields and disorder . the analytical derivation of the current distribution for a wire with two sites is deferred to the appendix . sites with internal tunnelling matrix elements @xmath0 and effective wire - lead coupling strengths @xmath1 . ] the system of the driven molecular wire , the leads , and the coupling between the molecule and the leads , as sketched in fig . [ fig : wire_model ] , is described by the hamiltonian @xmath2 the wire is modelled by @xmath3 tight - binding orbitals @xmath4 , @xmath5 , such that @xmath6 with the tunnel matrix element @xmath0 and the capacitive energy @xmath7 . each onsite energy @xmath8 contains a random contribution @xmath9 that subsumes the influence of environmental fluctuations . we assume that these fluctuations are gaussian distributed and so slow that we can treat them as static disorder . thus , the probability that the onsite energy of orbital @xmath10 lies in an interval of size @xmath11 around @xmath8 reads @xmath12 where the variance @xmath13 is assumed to be position - independent . this implies that the energy fluctuations are spatially uncorrelated , such that @xmath14 . the onsite energies @xmath15 are modulated by a harmonically time - dependent dipole force , where @xmath16 denotes the electrical field amplitude multiplied by the electron charge and the distance between neighbouring sites , with @xmath17 the scaled position of site @xmath18 . our goal will be to compute for many realizations of the wire hamiltonian the resulting dc current which provides the current distribution @xmath19 . the last term in eq . captures the electron - electron interaction within a capacitor model and the operator @xmath20 describes the number of excess electrons residing on the molecule . below we shall assume that @xmath7 is so large that only states with zero or one excess electron play a role . the first and the last site of the molecule , @xmath21 and @xmath22 , couple via the tunnelling hamiltonian @xmath23 to the respective lead . the operator @xmath24 ( @xmath25 ) creates an electron in the left ( right ) lead in state @xmath26 which is orthogonal to all wire states . the influence of the tunnelling hamiltonian is fully characterised by the spectral density @xmath27 . if the lead states are dense and located at the centre of the conduction band , the spectral densities can be replaced by a constant , i.e. we assume @xmath28 for both leads . the leads are modelled as ideal fermi gases @xmath29 which are initially at thermal equilibrium with the chemical potential @xmath30 and , thus , are described by the density operator @xmath31},$ ] where @xmath32 is the electron number operator for lead @xmath33 . since a typical metal screens all electric fields with a frequency below the plasma frequency , we assume that the bulk properties of the leads are not affected by the laser irradiation . the derivation of a master equation starts from the liouville - von neumann equation @xmath34 $ ] for the total density operator @xmath35 for which one obtains by standard techniques the approximate equation of motion @xcite @xmath36 -\frac{1}{\hbar^2}\int_0^\infty { \mathrm{d}}\tau [ h_\mathrm{wire - leads},[\widetilde h_\mathrm{wire - leads}(t-\tau , t),\rho(t ) ] ] . \nonumber\ ] ] here the first term corresponds to the coherent dynamics of both the wire electrons and the lead electrons , while the second term describes resonant electron tunnelling between the leads and the wire . the tilde denotes operators in the interaction picture with respect to the molecule and the lead hamiltonian without the molecule - lead coupling , @xmath37 , where @xmath38 is the propagator without the coupling . the net ( incoming minus outgoing ) electrical current through the left contact is given by minus the time - derivative of the electron number in the left lead multiplied by the electron charge @xmath39 . from eq . follows for the current in the wide - band limit the expression @xmath40 \nonumber = & -e\frac{\gamma_{\mathrm{l}}}{\pi\hbar}\mathop{\mathrm{re}}\int_0^\infty { \mathrm{d}}\tau \int{\mathrm{d}}\epsilon\ , \e^{{\mathrm{i}}\epsilon \tau/\hbar } \label{current - general}\nonumber \\ & \times \big\ { \langle c^\dagger_1 \tilde{c}_1^{\vphantom{\dagger } } ( t , t-\tau)\rangle \bar{f}_{\mathrm{l}}(\epsilon ) - \langle \tilde{c}_1^{\vphantom{\dagger}}(t , t-\tau)c_1^\dagger \rangle f_{\mathrm{l}}(\epsilon)\big\ } , \end{aligned}\ ] ] where @xmath41 is the fermi function of the respective lead and @xmath42 . furthermore , @xmath43 denotes the expectation value with respect to the wire density operator . we emphasise that the expectation values in eq . depend directly on the dynamics of the isolated wire and are thus influenced by the driving . an important feature of the current formula is its dependence on solely the wire operators while all lead operators have been eliminated . therefore it is sufficient to consider the reduced density operator @xmath44 of the wire electrons . the effort necessary to calculate @xmath45 can be reduced significantly by exploiting the fact that the master equation inherited from the total hamiltonian @xmath46 a periodic time - dependence , which opens the way for a floquet treatment . one possibility for such a treatment is to use the floquet states of the central system , i.e. the driven wire , as a basis . thereby we also use the fact that in the wire hamiltonian , the single - particle contribution commutes with the interaction term and , thus , these two hamiltonians possess a complete set of common eigenstates . in analogy to the quasimomenta in bloch theory for spatially periodic potentials , the quasienergies @xmath47 come in classes @xmath48 of which all members represent the same physical solution of the schrdinger equation . thus we can restrict ourselves to states within one brillouin zone like for example @xmath49 . for the computation of the current it is convenient to have an explicit expression for the interaction picture representation of the wire operators . it can be obtained from the ( fermionic ) floquet creation and annihilation operators defined via the transformation @xmath50 which reads in the interaction picture @xmath51 with the important feature that the time difference @xmath52 enters only via the exponential prefactor @xcite . in the following , we assume the interaction @xmath7 to be the dominant energy scale in the system , therefore we can restrict the wire hilbert space to the @xmath53 dimensional subspace of states with zero and one electron , such that a basis for the decomposition of the reduced operator is @xmath54 , where @xmath55 denotes the wire state in the absence of excess electrons . moreover , it can be shown @xcite that at large times , the density operator of the wire becomes diagonal in the electron number @xmath56 . therefore a proper ansatz reads @xmath57 note that we keep terms with @xmath58 , which means that we work beyond a rotating - wave approximation . following our evaluation of the master equation @xcite , we arrive at a set of @xmath59 coupled equations of motion for @xmath60 which in fourier representation read @xmath61 in an analogous manner we obtain for the dc current the expression @xmath62 the results of this section allow us to numerically compute the dc current through a driven conductor as well as studying the undriven limit . the current distributions discussed below are obtained by computing the dc current for typically @xmath63 realizations of the wire hamiltonian . then these values are taken for a histogram with 150 bins which finally will be scaled such that we obtain a normalised probability density . we first address an undriven wire in the configuration sketched in fig . [ fig : wire_model ] where the distribution of all wire levels is centred at energy @xmath64 . the transport voltage is so large that all eigenenergies lie well within the voltage window and , consequently , the transport is unidirectional . then in the absence of onsite energy fluctuations ( @xmath65 ) , the current can be evaluated analytically within a rotating - wave approximation and reads @xmath66 , i.e.it decays with increasing wire length @xcite . the index `` max '' refers to the fact that any modification of the onsite energies can only reduce the current which is confirmed by our simulations . the physical reason for this is that for equal onsite energies , solely the kinetic energy determines the eigenstates which , consequently , are delocalised . different onsite energies , by contrast , tend to `` localise '' the eigenstates . thus in the limit of small disorder , the current distribution @xmath19 is expect to possess a clear peak at @xmath67 and some minor contribution for lower values of @xmath68 . figure [ fig : static ] shows the simulated current distributions for two different variances . for a small variance ( panel a ) , the distributions for short wires show the expected behaviour . with an increasing wire length , the peak at @xmath67 disappears and is eventually replaced by an apparently parabolic distribution . this length dependence can be understood in the following way : for a short wire , the probability that a level is out of resonance is rather low and , thus , most realizations of the wire hamiltonian will allow resonant inter - site tunnelling . with an increasing number of levels , however , the probability for having at least one misaligned level increases and a current significantly smaller than @xmath69 becomes more likely . the precise values will depend on the details and , consequently , we expect a broad distribution . this means that whenever a large number of levels plays a role , the transport through a molecule is extremely sensitive to even small disorder induced by environmental fluctuations . sites in the limit of a large bias voltage . the standard deviation of the onsite energies is @xmath70 ( a ) and @xmath71 ( b ) , while the wire - lead coupling is @xmath72 . the distributions have been obtained by computing the current for @xmath73 realizations of the wire hamiltonian . the black dotted lines mark the analytical results for @xmath74 sites . ] with a larger variance , this scenario becomes even more pronounced as can be seen in fig . [ fig : static]b : then the peak at @xmath69 is rather small and noticeable only for 2 and 3 sites . the most likely realization is a completely disordered wire with an accordingly low conductance . for @xmath75 , the distributions even possesse a significant peak at @xmath76 which corresponds to isolating behaviour . a closer inspection of the numerical data reveals that the crossover between conducting and isolating behaviour occurs when the effective disorder @xmath77 exceeds the tunnel matrix element @xmath0 . interestingly enough , for @xmath78 the distribution turns out to be even non - monotonic , which means that most one most likely finds either a current close to the theoretical maximum or a significantly smaller lower value . the non - monotonic behaviour for @xmath74 can also be found analytically . the derivation of the corresponding current distribution can be found in the appendix . the excellent agreement of this analytical solution and the simulated distributions emphasis that the simulation with approximately @xmath63 realisations ensures good convergence . in order to investigate the influence of an ac driving , we employ the same model as above , but now with an additional dipole driving modelled by time - dependent onsite energies @xmath79 as discussed in sect . [ sec : model ] . the driving frequency @xmath80 is chosen such that it matches the average splitting of the wire energies , while the amplitude @xmath81 corresponds to intermediately strong driving . the solid line in fig . [ fig : driven_system ] shows the current distribution in the absence of a voltage bias , @xmath82 . the reflection symmetry of the ensemble relates to the symmetric shape of the distribution , which implies that the current vanishes in the ensemble average . an individual realization of the wire , however , generally does not possess reflection symmetry because the random energy shifts are spatially uncorrelated . this asymmetry in combination with the non - adiabatic driving induces a coherent ratchet current , i.e. a dc current even in the absence of any net voltage bias . in the present case , the ratchet current is of the order of 1020 percent of the current observed above in the large bias limit . this order of magnitude is typical when the driving frequency or a multiple of the driving frequency lies close to an internal resonance , while the intensity is moderate @xcite . in addition to the broad distribution of ratchet currents , @xmath19 exhibits a peak at @xmath76 . this stems from realizations for which the driving is well out of resonance . sites for various bias voltages . the fluctuations of the onsite energies are characterised by the standard deviation @xmath70 , the driving frequency and amplitude are @xmath81 and @xmath83 , respectively . all the other parameters are as in fig . [ fig : static ] . ] for a bias voltage @xmath84 , the ensemble no longer possesses reflection symmetry and the current distribution is shifted towards positive values ( see fig . [ fig : driven_system ] ) . for sufficiently small voltages @xmath85 , non - adiabatic pumping against the voltage bias is still possible . rather surprisingly , the peak at zero current remains . it now corresponds to realizations for which on the one hand , the driving is off - resonant while on the other hand , both levels lie outside the voltage window . with an increasing bias voltage , the second condition is less frequently fulfilled , and eventually the distribution assumes a form similar to that found for a large voltage in the absence of driving . already for @xmath86 , the distribution is hardly distinguishable from the one shown in fig . [ fig : static]a for a wire with @xmath74 sites in the absence of driving . we have investigated the current through a molecular wire with disordered onsite energies . such a disorder can stem from the interaction with slow fluctuations of background charges in the substrate . in particular , we computed the resulting current distribution for two typical cases , namely an `` open transport channel '' and a driven molecular wire for which random energy shifts break reflection symmetry and , thus , the driving can induce a ratchet current . the open transport channel is characterised by tight - binding levels with equal onsite energies , such that any misalignment stems from the disorder . its main consequence is that as soon as the standard deviation of the onsite energies exceeds the tunnel matrix elements , the current distribution no longer peaks only at a finite value , but also at zero . for longer wires , only the peak at zero current remains . this isolating behaviour resembles anderson localisation which is found for electrons in a one - dimensional disordered lattice @xcite . note however , that we here considered short wires far from the scaling limit in which anderson localisation is usually studied . since the random energy shifts break reflection symmetry , driving the molecular wire with a laser field induces ratchet currents for which we found a relatively broad distribution . if the driving frequency is far from any molecular excitation energy , the ratchet current will be rather small , and we indeed found that this is the case for very many wire realizations . it has the consequence that the corresponding distribution possesses a spike at zero current . this means that non - adiabatic pumping of electrons against a voltage bias becomes generally impossible whenever the relevant wire energy levels lie well within the voltage window . in conclusion , our results reveal that slow fluctuations or a static disorder can have a significant effect on molecular conduction . in various cases , the current distribution emerges to be rather flat , which means that even the magnitude of the current depends sensitively on environmental influences . financial support of the german excellence initiative via the `` nanosystems initiative munich ( nim ) '' and of the elite network of bavaria via the international doctorate program `` nanobiotechnology '' is gratefully acknowledged . this work has been supported by deutsche forschungsgemeinschaft through sfb 484 and spp 1243 . a wire model with @xmath74 sites represents an analytically solvable case for which one observes a non - monotonic current distribution and which can serve as test case for numerical implementations . here we consider a two - level system with on - site energies @xmath87 , i.e.with a bias @xmath88 . since the random energy shifts @xmath9 are gaussian distributed with variance @xmath13 , the bias @xmath89 is also gaussian distributed but with variance @xmath90 , i.e. its distribution function reads @xmath91 . for the computation of the current , we restrict ourselves to the limit of a large transport voltage such that both eigenenergies of the two - level system lie within the voltage window . then , the fermi functions of the left and the right lead effectively become @xmath92 and @xmath93 . in this case , transport can be described within rotating - wave approximation ( rwa ) which practically means that the reduced density operator of the wire is diagonal in energy representation @xcite . within rwa thus follows from the master equation the occupation probability @xmath94 and , thus , @xmath95 . the coefficients @xmath96 and the localised state @xmath18 ( note that in the undriven case , all non - vanishing contributions have sideband index @xmath97 , such that here the sideband index @xmath98 can be omitted ) . inserting this solution into the current formula , we obtain @xmath99 . the remaining task is now to diagonalise the single - particle hamiltonian which provides the coefficients @xmath100 . for bias @xmath89 and tunnelling matrix element @xmath0 , the hamiltonian in pseudo - spin notation reads @xmath101 and possesses the eigenenergies @xmath102 . the corresponding eigenvectors @xmath103 are proportional to @xmath104 and @xmath105 , respectively , such that @xmath106 . then we obtain for the current the expression @xmath107 which assumes its maximum @xmath108 in the unbiased limit @xmath109 . the probability distribution for the current relates to @xmath110 via @xmath111 where the summation considers all values of @xmath112 that fulfil the condition @xmath113 . after some straightforward algebra , we obtain by evaluating expression the current distribution @xmath114 which is defined and normalised on the interval @xmath115 $ ] .

we investigate transport through molecular wires whose energy levels are affected by environmental fluctuations . we assume that the relevant fluctuations are so slow that they , within a tight - binding description , can be described by disordered , gaussian distributed onsite energies . for long wires , we find that the corresponding current distribution can be rather broad even for a small energy variance . moreover , we analyse with a floquet master equation the interplay of laser excitations and static disorder . then the disorder leads to spatial asymmetries such that the laser diving can induce a ratchet current .

<s>[INST]chemical adsorption of sulfur atoms on gold surface allows a stable bond between gold tips and thiol groups of molecules . this has been exploited for measuring the conductance and the current - voltage characteristics of gold - molecule - gold junctions @xcite . repeated measurements even with the same sample , however , reveal small but noticeable differences which possibly stem from environmental fluctuations that impact upon the effective molecule parameters . moreover , the particular form of the gold tip can have a significant influence on the transport properties @xcite . a present line of experimental research is the measurement of molecular conductance when the electrons are excited by electromagnetic waves . there one expects various phenomena ranging from photo - assisted transport @xcite to ratchet or non - adiabatic pump effects , i.e. the induction of dc currents by ac fields even in the absence of any voltage bias @xcite . moreover , it has been predicted that properly taylored laser pulses can give rise to short current pulses @xcite . since a dc current flows into one particular direction , a ratchet effect can occur only in `` sufficiently asymmetric '' systems @xcite . in that respect , a static disorder is sufficient to break the reflection symmetry of an individual realization and , thus , may support a ratchet effect . the quantitative prediction of the current through a molecule is still a great challenge despite the significant progress achieved in recent years @xcite . for a more qualitative understanding of the mechanisms involved in molecular transport , it is thus advantageous to employ for the molecule a rather generic tight - binding model @xcite . then a flexible method for the computation of transport properties is provided by master equations of the bloch - redfield type which allow one to include electron - electron and electron - phonon interactions , as well as time - dependent fields @xcite . similar methods have also been used for describing incoherent transport @xcite . here , we explore the role of slow fluctuations or static disorder for molecular conductance . thereby we will assume that the relevant environmental fluctuations are so slow that they can be described as static disorder which defines an ensemble of wire hamiltonians . then a natural quantity of interest is the corresponding distribution of stationary currents . a setup for which this current distribution is also directly relevant is an array of molecular junctions that conduct in parallel . we employ a tight - binding model for the molecule and treat it with the floquet master equation formalism derived in ref . @xcite which we review briefly in section [ sec : model ] . in section [ sec : static ] , we present results for a static model with a large voltage bias , while in section [ sec : driven ] , we investigate pumping effects caused by an interplay of ac driving fields and disorder . the analytical derivation of the current distribution for a wire with two sites is deferred to the appendix . sites with internal tunnelling matrix elements @xmath0 and effective wire - lead coupling strengths @xmath1 . ] the system of the driven molecular wire , the leads , and the coupling between the molecule and the leads , as sketched in fig . [ fig : wire_model ] , is described by the hamiltonian @xmath2 the wire is modelled by @xmath3 tight - binding orbitals @xmath4 , @xmath5 , such that @xmath6 with the tunnel matrix element @xmath0 and the capacitive energy @xmath7 . each onsite energy @xmath8 contains a random contribution @xmath9 that subsumes the influence of environmental fluctuations . we assume that these fluctuations are gaussian distributed and so slow that we can treat them as static disorder . thus , the probability that the onsite energy of orbital @xmath10 lies in an interval of size @xmath11 around @xmath8 reads @xmath12 where the variance @xmath13 is assumed to be position - independent . this implies that the energy fluctuations are spatially uncorrelated , such that @xmath14 . the onsite energies @xmath15 are modulated by a harmonically time - dependent dipole force , where @xmath16 denotes the electrical field amplitude multiplied by the electron charge and the distance between neighbouring sites , with @xmath17 the scaled position of site @xmath18 . our goal will be to compute for many realizations of the wire hamiltonian the resulting dc current which provides the current distribution @xmath19 . the last term in eq . captures the electron - electron interaction within a capacitor model and the operator @xmath20 describes the number of excess electrons residing on the molecule . below we shall assume that @xmath7 is so large that only states with zero or one excess electron play a role . the first and the last site of the molecule , @xmath21 and @xmath22 , couple via the tunnelling hamiltonian @xmath23 to the respective lead . the operator @xmath24 ( @xmath25 ) creates an electron in the left ( right ) lead in state @xmath26 which is orthogonal to all wire states . the influence of the tunnelling hamiltonian is fully characterised by the spectral density @xmath27 . if the lead states are dense and located at the centre of the conduction band , the spectral densities can be replaced by a constant , i.e. we assume @xmath28 for both leads . the leads are modelled as ideal fermi gases @xmath29 which are initially at thermal equilibrium with the chemical potential @xmath30 and , thus , are described by the density operator @xmath31},$ ] where @xmath32 is the electron number operator for lead @xmath33 . since a typical metal screens all electric fields with a frequency below the plasma frequency , we assume that the bulk properties of the leads are not affected by the laser irradiation . the derivation of a master equation starts from the liouville - von neumann equation @xmath34 $ ] for the total density operator @xmath35 for which one obtains by standard techniques the approximate equation of motion @xcite @xmath36 -\frac{1}{\hbar^2}\int_0^\infty { \mathrm{d}}\tau [ h_\mathrm{wire - leads},[\widetilde h_\mathrm{wire - leads}(t-\tau , t),\rho(t ) ] ] . \nonumber\ ] ] here the first term corresponds to the coherent dynamics of both the wire electrons and the lead electrons , while the second term describes resonant electron tunnelling between the leads and the wire . the tilde denotes operators in the interaction picture with respect to the molecule and the lead hamiltonian without the molecule - lead coupling , @xmath37 , where @xmath38 is the propagator without the coupling . the net ( incoming minus outgoing ) electrical current through the left contact is given by minus the time - derivative of the electron number in the left lead multiplied by the electron charge @xmath39 . from eq . follows for the current in the wide - band limit the expression @xmath40 \nonumber = & -e\frac{\gamma_{\mathrm{l}}}{\pi\hbar}\mathop{\mathrm{re}}\int_0^\infty { \mathrm{d}}\tau \int{\mathrm{d}}\epsilon\ , \e^{{\mathrm{i}}\epsilon \tau/\hbar } \label{current - general}\nonumber \\ & \times \big\ { \langle c^\dagger_1 \tilde{c}_1^{\vphantom{\dagger } } ( t , t-\tau)\rangle \bar{f}_{\mathrm{l}}(\epsilon ) - \langle \tilde{c}_1^{\vphantom{\dagger}}(t , t-\tau)c_1^\dagger \rangle f_{\mathrm{l}}(\epsilon)\big\ } , \end{aligned}\ ] ] where @xmath41 is the fermi function of the respective lead and @xmath42 . furthermore , @xmath43 denotes the expectation value with respect to the wire density operator . we emphasise that the expectation values in eq . depend directly on the dynamics of the isolated wire and are thus influenced by the driving . an important feature of the current formula is its dependence on solely the wire operators while all lead operators have been eliminated . therefore it is sufficient to consider the reduced density operator @xmath44 of the wire electrons . the effort necessary to calculate @xmath45 can be reduced significantly by exploiting the fact that the master equation inherited from the total hamiltonian @xmath46 a periodic time - dependence , which opens the way for a floquet treatment . one possibility for such a treatment is to use the floquet states of the central system , i.e. the driven wire , as a basis . thereby we also use the fact that in the wire hamiltonian , the single - particle contribution commutes with the interaction term and , thus , these two hamiltonians possess a complete set of common eigenstates . in analogy to the quasimomenta in bloch theory for spatially periodic potentials , the quasienergies @xmath47 come in classes @xmath48 of which all members represent the same physical solution of the schrdinger equation . thus we can restrict ourselves to states within one brillouin zone like for example @xmath49 . for the computation of the current it is convenient to have an explicit expression for the interaction picture representation of the wire operators . it can be obtained from the ( fermionic ) floquet creation and annihilation operators defined via the transformation @xmath50 which reads in the interaction picture @xmath51 with the important feature that the time difference @xmath52 enters only via the exponential prefactor @xcite . in the following , we assume the interaction @xmath7 to be the dominant energy scale in the system , therefore we can restrict the wire hilbert space to the @xmath53 dimensional subspace of states with zero and one electron , such that a basis for the decomposition of the reduced operator is @xmath54 , where @xmath55 denotes the wire state in the absence of excess electrons . moreover , it can be shown @xcite that at large times , the density operator of the wire becomes diagonal in the electron number @xmath56 . therefore a proper ansatz reads @xmath57 note that we keep terms with @xmath58 , which means that we work beyond a rotating - wave approximation . following our evaluation of the master equation @xcite , we arrive at a set of @xmath59 coupled equations of motion for @xmath60 which in fourier representation read @xmath61 in an analogous manner we obtain for the dc current the expression @xmath62 the results of this section allow us to numerically compute the dc current through a driven conductor as well as studying the undriven limit . the current distributions discussed below are obtained by computing the dc current for typically @xmath63 realizations of the wire hamiltonian . then these values are taken for a histogram with 150 bins which finally will be scaled such that we obtain a normalised probability density . we first address an undriven wire in the configuration sketched in fig . [ fig : wire_model ] where the distribution of all wire levels is centred at energy @xmath64 . the transport voltage is so large that all eigenenergies lie well within the voltage window and , consequently , the transport is unidirectional . then in the absence of onsite energy fluctuations ( @xmath65 ) , the current can be evaluated analytically within a rotating - wave approximation and reads @xmath66 , i.e.it decays with increasing wire length @xcite . the index `` max '' refers to the fact that any modification of the onsite energies can only reduce the current which is confirmed by our simulations . the physical reason for this is that for equal onsite energies , solely the kinetic energy determines the eigenstates which , consequently , are delocalised . different onsite energies , by contrast , tend to `` localise '' the eigenstates . thus in the limit of small disorder , the current distribution @xmath19 is expect to possess a clear peak at @xmath67 and some minor contribution for lower values of @xmath68 . figure [ fig : static ] shows the simulated current distributions for two different variances . for a small variance ( panel a ) , the distributions for short wires show the expected behaviour . with an increasing wire length , the peak at @xmath67 disappears and is eventually replaced by an apparently parabolic distribution . this length dependence can be understood in the following way : for a short wire , the probability that a level is out of resonance is rather low and , thus , most realizations of the wire hamiltonian will allow resonant inter - site tunnelling . with an increasing number of levels , however , the probability for having at least one misaligned level increases and a current significantly smaller than @xmath69 becomes more likely . the precise values will depend on the details and , consequently , we expect a broad distribution . this means that whenever a large number of levels plays a role , the transport through a molecule is extremely sensitive to even small disorder induced by environmental fluctuations . sites in the limit of a large bias voltage . the standard deviation of the onsite energies is @xmath70 ( a ) and @xmath71 ( b ) , while the wire - lead coupling is @xmath72 . the distributions have been obtained by computing the current for @xmath73 realizations of the wire hamiltonian . the black dotted lines mark the analytical results for @xmath74 sites . ] with a larger variance , this scenario becomes even more pronounced as can be seen in fig . [ fig : static]b : then the peak at @xmath69 is rather small and noticeable only for 2 and 3 sites . the most likely realization is a completely disordered wire with an accordingly low conductance . for @xmath75 , the distributions even possesse a significant peak at @xmath76 which corresponds to isolating behaviour . a closer inspection of the numerical data reveals that the crossover between conducting and isolating behaviour occurs when the effective disorder @xmath77 exceeds the tunnel matrix element @xmath0 . interestingly enough , for @xmath78 the distribution turns out to be even non - monotonic , which means that most one most likely finds either a current close to the theoretical maximum or a significantly smaller lower value . the non - monotonic behaviour for @xmath74 can also be found analytically . the derivation of the corresponding current distribution can be found in the appendix . the excellent agreement of this analytical solution and the simulated distributions emphasis that the simulation with approximately @xmath63 realisations ensures good convergence . in order to investigate the influence of an ac driving , we employ the same model as above , but now with an additional dipole driving modelled by time - dependent onsite energies @xmath79 as discussed in sect . [ sec : model ] . the driving frequency @xmath80 is chosen such that it matches the average splitting of the wire energies , while the amplitude @xmath81 corresponds to intermediately strong driving . the solid line in fig . [ fig : driven_system ] shows the current distribution in the absence of a voltage bias , @xmath82 . the reflection symmetry of the ensemble relates to the symmetric shape of the distribution , which implies that the current vanishes in the ensemble average . an individual realization of the wire , however , generally does not possess reflection symmetry because the random energy shifts are spatially uncorrelated . this asymmetry in combination with the non - adiabatic driving induces a coherent ratchet current , i.e. a dc current even in the absence of any net voltage bias . in the present case , the ratchet current is of the order of 1020 percent of the current observed above in the large bias limit . this order of magnitude is typical when the driving frequency or a multiple of the driving frequency lies close to an internal resonance , while the intensity is moderate @xcite . in addition to the broad distribution of ratchet currents , @xmath19 exhibits a peak at @xmath76 . this stems from realizations for which the driving is well out of resonance . sites for various bias voltages . the fluctuations of the onsite energies are characterised by the standard deviation @xmath70 , the driving frequency and amplitude are @xmath81 and @xmath83 , respectively . all the other parameters are as in fig . [ fig : static ] . ] for a bias voltage @xmath84 , the ensemble no longer possesses reflection symmetry and the current distribution is shifted towards positive values ( see fig . [ fig : driven_system ] ) . for sufficiently small voltages @xmath85 , non - adiabatic pumping against the voltage bias is still possible . rather surprisingly , the peak at zero current remains . it now corresponds to realizations for which on the one hand , the driving is off - resonant while on the other hand , both levels lie outside the voltage window . with an increasing bias voltage , the second condition is less frequently fulfilled , and eventually the distribution assumes a form similar to that found for a large voltage in the absence of driving . already for @xmath86 , the distribution is hardly distinguishable from the one shown in fig . [ fig : static]a for a wire with @xmath74 sites in the absence of driving . we have investigated the current through a molecular wire with disordered onsite energies . such a disorder can stem from the interaction with slow fluctuations of background charges in the substrate . in particular , we computed the resulting current distribution for two typical cases , namely an `` open transport channel '' and a driven molecular wire for which random energy shifts break reflection symmetry and , thus , the driving can induce a ratchet current . the open transport channel is characterised by tight - binding levels with equal onsite energies , such that any misalignment stems from the disorder . its main consequence is that as soon as the standard deviation of the onsite energies exceeds the tunnel matrix elements , the current distribution no longer peaks only at a finite value , but also at zero . for longer wires , only the peak at zero current remains . this isolating behaviour resembles anderson localisation which is found for electrons in a one - dimensional disordered lattice @xcite . note however , that we here considered short wires far from the scaling limit in which anderson localisation is usually studied . since the random energy shifts break reflection symmetry , driving the molecular wire with a laser field induces ratchet currents for which we found a relatively broad distribution . if the driving frequency is far from any molecular excitation energy , the ratchet current will be rather small , and we indeed found that this is the case for very many wire realizations . it has the consequence that the corresponding distribution possesses a spike at zero current . this means that non - adiabatic pumping of electrons against a voltage bias becomes generally impossible whenever the relevant wire energy levels lie well within the voltage window . in conclusion , our results reveal that slow fluctuations or a static disorder can have a significant effect on molecular conduction . in various cases , the current distribution emerges to be rather flat , which means that even the magnitude of the current depends sensitively on environmental influences . financial support of the german excellence initiative via the `` nanosystems initiative munich ( nim ) '' and of the elite network of bavaria via the international doctorate program `` nanobiotechnology '' is gratefully acknowledged . this work has been supported by deutsche forschungsgemeinschaft through sfb 484 and spp 1243 . a wire model with @xmath74 sites represents an analytically solvable case for which one observes a non - monotonic current distribution and which can serve as test case for numerical implementations . here we consider a two - level system with on - site energies @xmath87 , i.e.with a bias @xmath88 . since the random energy shifts @xmath9 are gaussian distributed with variance @xmath13 , the bias @xmath89 is also gaussian distributed but with variance @xmath90 , i.e. its distribution function reads @xmath91 . for the computation of the current , we restrict ourselves to the limit of a large transport voltage such that both eigenenergies of the two - level system lie within the voltage window . then , the fermi functions of the left and the right lead effectively become @xmath92 and @xmath93 . in this case , transport can be described within rotating - wave approximation ( rwa ) which practically means that the reduced density operator of the wire is diagonal in energy representation @xcite . within rwa thus follows from the master equation the occupation probability @xmath94 and , thus , @xmath95 . the coefficients @xmath96 and the localised state @xmath18 ( note that in the undriven case , all non - vanishing contributions have sideband index @xmath97 , such that here the sideband index @xmath98 can be omitted ) . inserting this solution into the current formula , we obtain @xmath99 . the remaining task is now to diagonalise the single - particle hamiltonian which provides the coefficients @xmath100 . for bias @xmath89 and tunnelling matrix element @xmath0 , the hamiltonian in pseudo - spin notation reads @xmath101 and possesses the eigenenergies @xmath102 . the corresponding eigenvectors @xmath103 are proportional to @xmath104 and @xmath105 , respectively , such that @xmath106 . then we obtain for the current the expression @xmath107 which assumes its maximum @xmath108 in the unbiased limit @xmath109 . the probability distribution for the current relates to @xmath110 via @xmath111 where the summation considers all values of @xmath112 that fulfil the condition @xmath113 . after some straightforward algebra , we obtain by evaluating expression the current distribution @xmath114 which is defined and normalised on the interval @xmath115 $ ] .[/INST] we investigate transport through molecular wires whose energy levels are affected by environmental fluctuations . we assume that the relevant fluctuations are so slow that they , within a tight - binding description , can be described by disordered , gaussian distributed onsite energies . for long wires , we find that the corresponding current distribution can be rather broad even for a small energy variance . moreover , we analyse with a floquet master equation the interplay of laser excitations and static disorder . then the disorder leads to spatial asymmetries such that the laser diving can induce a ratchet current . </s>

the experimental determination of the optical properties of bulk semiconductors can now be obtained with high precision @xcite , yet our theoretical understanding is far from complete . the static dielectric constant , which can be obtained from a functional derivative of the electron density with respect to the total kohn - sham potential evaluated at the ground state , hence a ground state property , is over estimated by the local - density approximation ( lda ) calculation @xcite . the inclusion of the gradient correction to the pseudopotential lda reduces slightly the discrepancy in the case of silicon @xcite . the underestimation of the @xmath3 peak and the overestimation of the @xmath4 peak of the imaginary part of the dielectric function , @xmath5 , by one - electron band theory have generated theoretical work for almost two decades to account for these discrepancies . it was clear from the beginning that including excitonic effects , which have been detected experimentally @xcite , could remove some of the disagreement with experiment @xcite . however , the model calculations used to correct @xmath6 have produced only a qualitative understanding of the problem . in particular , the latest model by hanke , mattausch and strinati based on the time - dependent screened hartree - fock approximation and including both the local field and the excitonic effects , described correctly the @xmath3 peak but underestimated significantly the @xmath4 peak of si . the reason for the underestimation of @xmath4 was attributed to a bad representation of the band structure of si by their slater - koster parameterization @xcite . del castello - mussot and sham @xcite based their latest calculation on a @xmath7 model around the l point ( where @xmath3 originates ) and a multiple plane - wave model around the x points ( where @xmath4 originates ) , and solved the bethe - salpeter equation containing the excitonic effect . their model is an improvement over the non - interacting approximation : the @xmath3 peak becomes stronger and the @xmath4 peak weaker . this model is very promising , but , being based on a @xmath7 approximation to the band structure , it provided only a qualitative correction to the intensities of the @xmath3 and @xmath4 structures . calculations ignoring excitonic effects , but including the local - field effect , underestimated both @xmath3 and @xmath4 peaks @xcite . one way to make theoretical progress in this field is to determine the correct contribution of the one - electron theory to the optical properties of semiconductors . this allows us to define precisely the size of the many body corrections to the one electron theory . however , a common belief these days is that the eigenvalues and vectors of the kohn - sham ( ks ) equations @xcite have no direct physical meaning and hence should not be used to calculate optical spectra of materials . only ground state properties derived from the total energy as a function of the electron density have in principle a direct physical meaning . while lda was indeed intended to calculate ground state properties it could also be viewed as a simplified quasi - particle ( qp ) theory where the self - energy is local and static ( @xmath8 , here @xmath9 is the local exchange and correlation potential as , for example , parameterized by von barth and hedin @xcite . the ks eigenvalues are then qp energies and could be compared to experimental data . this argument is supported by calculations using the gw approximation of hedin@xcite . these calculations showed that the valence qp energies of semiconductors are in good agreement with lda and the conduction qp energies differ by approximately a rigid energy shift @xcite . in the literature this shift is often called `` scissors - operator '' shift ( sos ) @xcite . first - principles local density approximation calculations started more than two decades ago , but the major problem of lda , beside the well understood energy band gap problem@xcite , is the numerical difficulty to determine selfconsistent electronic structure and optical matrix elements using a complete basis - set . the early ab - initio calculation of the optical properties of semiconductors by wang and klein , using a selfconsistent linear combination of gaussian orbitals produced static dielectric functions in good agreement with experiment@xcite . but this agreement is fortuitous because the band gaps produced by this method are much larger than the lda band gaps . the recent calculations of 18 semiconductors by huang and ching using an orthogonalized linear combination of atomic orbitals method produced lda static dielectric functions which are in general smaller than experiment despite the fact that their band gaps are much larger than the all - electron or pseudopotential lda band gaps @xcite . those underestimated static dielectric constants are most likely due to the incompleteness of the basis - set used in their calculations . most of the theoretical studies of the optical properties of semiconductors in the literature use several approximations within the lda , ranging from the use of spherical potentials @xcite to the use of pseudopotentials @xcite instead of all electron lda potentials . in this paper we report precise calculations of the optical properties of bulk semiconductors si , ge , and gaas under hydrostatic pressure using an all electron lda linear muffin - tin orbital basis - set@xcite , in which no shape approximation is made for either the potential or the charge density @xcite . the semi - core @xmath1 of ga and ge are included in a fully hybridizing valence basis set , and the rest of the core states are allowed to relax selfconsistently . the effect of spin - orbit coupling is also investigated . a systematic check of the @xmath10-sum rule is performed for all the calculations . we hope that this accurate lda calculation will provide an excellent starting point for the determination of the local field and the excitonic effects in the optical spectra of semiconductors @xcite . we have found that the static dielectric function , @xmath2 , which is a ground state property , is overestimated by lda over all pressure range , and that an excellent agreement with the experimental results of goi and coworkers @xcite for @xmath2 of gaas and ge under hydrostatic pressure is achieved only when the so - called scissors - operator shift is used to account for the correct band gap at @xmath0 . the inclusion of the @xmath1 semi - core states of ge and gaas in the interband transition has almost no significant effects in @xmath2 ; however , the @xmath1 interband transitions contribute significantly to the magnitude of @xmath11 above 25 ev for ge , and above 12 ev for gaas . the spin - orbit coupling increases the lda values by about few percents . the rest of the paper is organized as follows . in section ii , we describe the method of calculation of electronic structure and the macroscopic dielectric function based on our all - electron full - potential lmto basis - set . in section iii we present the electronic properties of si , ge , and gaas and compare them to existing theoretical results . the calculated dielectric functions and a discussion about including the semi - core states and the spin - orbit coupling will be presented in section iv . in the same section we also compare our static dielectric function under hydrostatic pressure with the experimental results of goi _ et al . the conclusion is given in sec . the full - potential linear muffin - tin orbital method in its scalar - relativistic and full - relativistic forms @xcite is used here to calculate the electronic structure and the optical properties of si , ge , and gaas under hydrostatic pressure . the kohn - sham @xcite equations are solved for a general potential without any shape approximation @xcite . in this subsection we describe the bloch wave function inside the so - called muffin - tin spheres and the interstititial region . a correct determination of the crystal wave function is necessary for the accurate determination of the optical matrix elements . as for the cellular methods , the space is divided into non - overlapping muffin - tin spheres surrounding atomic sites where the schrdinger or the dirac equation for each principle quantum number @xmath12 and momentum channel @xmath13 is solved for a fixed energy @xmath14 . in these muffin - tin spheres the trial wave function is linearized in terms of the solution of schrdinger equation @xmath15 and its energy derivative @xmath16 for the energy @xmath14 , and for an atom of type @xmath17 and momentum channel @xmath13 @xcite . it can be shown that the bloch wave function of site @xmath17 calculated at site @xmath18 in the unit cell of the crystal at @xmath19 is given by @xcite : @xmath20 where @xmath21 and @xmath22 are renormalized structure constants obtained from the crystal structure constants @xmath23 to ensure that the bloch wave function is continuous and differentiable at the boundary of each muffin - tin sphere . in the interstitial region , the muffin - tin orbitals are spherical wave solutions @xmath24 to the helmholtz equation with non - zero kinetic energy ; these bases are hankel functions for negative kinetic energies or neumann functions for positive kinetic energies @xmath25 . such that each partial wave inside the muffin - tin sphere is allowed to have different kinetic energy , @xmath26 , in the interstitial region . in this region the bloch wave function is given by : @xmath27 the interstitial - region bloch function is expressed in plane waves over the reciprocal lattice using fourier transform : @xmath28 where @xmath29 , here the parameter @xmath30 is the linearization energy of the wave function in the muffin - tin sphere for the @xmath13 momentum channel , @xmath31 is the azumutal quantum number , and @xmath32 is the variational parameter whose square is the kinetic energy in the interstitial region . the fourier coefficients , @xmath33 , are obtained from a pseudo - wave function that is equal to the crystal wave function in the interstitial region and represented by a smooth function inside the muffin - tin spheres . the exact shape of these pseudo - functions inside the muffin - tin spheres is not important . the only requirement is that they are continuous and differentiable at the sphere boundary and have zero slop at the origin of each sphere . the plane wave expansion is multiplied by a three dimensional step function so that the wave function is kept only in the interstitial region . the knowledge of the bloch wave function in the whole unit cell allows us to calculate the hamiltonian and overlap matrix elements in order to solve the effective one electron schrdinger equation . three different kinetic energies were used for each subset of _ s _ and _ p _ derived bases in the basis set ; two kinetic energies were used for bases derived from orbital parameters @xmath34 . the basis sets used in calculating total energies and structural properties were for si : 3(3_s_3_p _ ) , 2(3_d _ ) , for ge : 2(3_d _ ) , 3(4_s_4_p _ ) , 2(4_d _ ) , and for gaas : 2(ga 3_d _ ) , 3(ga 4_s_4_p _ ) , 2(ga 4_d _ ) , 3(as 4_s_4_p _ ) , 2(as 4_d _ ) ; the pre - multiplicities in this notation refer to the number kinetic energies used in this basis subset . the basis functions for each material comprised a single , fully hybridizing basis set . note the presence of both 3_d _ and 4_d _ derived bases on ga and ge . a useful feature of the method used in these calculations is the ability to incorporate basis functions derived from the same orbital atomic quantum numbers but different principal atomic quantum numbers in a single fully hybridizing basis set . this feature entails the use of multiple sets of radial functions to represent bases with different principle atomic quantum numbers . this capability was particularly useful in calculating the high - lying energy bands which were used to obtain the dielectric functions to high energy ; the basis sets employed for this purpose are given in table i. seven to eight kinetic energies were used in the basis sets . accurate resolution of the bands to high energy was necessary to converge the calculation of the real part of the dielectric function , which was obtained from the imaginary part through the kramers - kronig relation . an interesting consequence of the relaxation of the ga 3_d _ states as valence states is a significant decrease in the calculated band gap @xcite . for the core charge density , the dirac equation is solved selfconsistently , e.g. , no frozen core approximation is used . the exchange and correlation potential is treated within the von barth and hedin parameterization @xcite . to account for the relativistic effects in the dielectric function , the full - selfconsistent relativistic band structure is produced by including the spin - orbit coupling to the hamiltonian . in table i we show the orbitals used to describe the electronic states of si , ge , and gaas . this large number of orbitals is necessary to calculate accurately the eigenvalues and eigenvectors up to 5 ry above the highest valence states . these electronic states will be needed to determine the dynamical dielectric function and the converged static dielectric function through the use of kramers - kronig relations . the completeness of basis - set , with different variational @xmath32 values for each partial wave in the interstitial region together with the fourier representation allows the method to treat open structures like the zinc - blende structure studied here without having to resort to the so - called empty spheres @xcite . the high energy states are also determined more accurately due to the use of many @xmath32 values . as a test we show in table ii the eigenvalues of si at high symmetry points of the brillouin zone compared with some recent results from first principle calculations based on ab - initio pseudopotential and gaussian orbital methods @xcite . the agreement of our calculation with the previous calculations is excellent . [ sec : method ] here we give a concise review of the determination of the dielectric function of a semiconductor crystal due to the application of an electric field . we also determine the approximations used to obtain numerical results for si , ge , and gaas under hydrostatic pressure with or without scissors - operator shift . a perturbative electromagnetic field of frequency @xmath35 , and a wave vector @xmath36 on a crystal produces a response of frequency @xmath35 and a wave vector @xmath37 ( @xmath38 and @xmath39 being reciprocal lattice vectors ) . the microscopic field of wave vector @xmath40 is produced by the umklapp processes as a result of the applied field @xmath41 @xmath42 where @xmath43 is the total field which produces the non - diagonal elements in the microscopic dielectric function @xmath44 . in the random phase approximation the microscopic dielectric function is given by @xcite : @xmath45 here @xmath46 and @xmath47 are the band indexes , @xmath48 is the zero temperature fermi distribution , and @xmath49 is the cell volume . the energies @xmath50 and the the crystal wave function @xmath51 are produced for each band index @xmath46 and for each wave vector @xmath52 in the brillouin zone . the macroscopic dielectric function in the infinite wave length limit is given by the inversion of the microscopic dielectric function : @xmath53_{\bf 0,0 } } \\ \nonumber & = \epsilon_{0,0}(\omega ) - \lim_{{\bf q } \to { \bf 0 } } \sum_{{\bf g , g^\prime \ne 0 } } \epsilon_{0,\bf g}({\bf q } , \omega ) t^{-1}_{\bf g , g^\prime } ( { \bf q } , \omega ) \epsilon_{\bf g^\prime,0}({\bf q } , \omega ) \ ; \label{localfield}\end{aligned}\ ] ] where @xmath54 is the inverse matrix of @xmath55 containing the elements @xmath56 with @xmath57 and @xmath58 . the first term of this equation is the interband contribution to the macroscopic dielectric function and the second term represent the local - field correction to @xmath59 . the most recent ab - initio pseudopotentials calculation found that the local - field effect reduces the static dielectric function by at most 5% @xcite . previous calculations with the same method have also found a decrease of @xmath60 by about the same percentage @xcite . we are looking at the effect of the local field using our all - electron basis - set ; it should be of interest to compare all electron results with these obtained using the pseudopotential method . for insulators the dipole approximation of the imaginary part of the first term of equation ( [ localfield ] ) is given by @xcite : @xmath61 here @xmath62 is the velocity operator , and in the lda @xmath63 ( @xmath64 being the momentum operator ) , and where @xmath65 . the matrix elements @xmath66 are calculated for each projection @xmath67 , @xmath68 or @xmath69 and @xmath70 , with the wave function @xmath71 expressed in terms of the full - potential lmto crystal wave function described by equations ( [ wavemuffin ] ) and ( [ planewave ] ) . the * k*-space integration is performed using the tetrahedron method @xcite with 480 irreducible * k * points the whole brillouin zone . the irreducible * k*-points are obtained from a shifted * k*-space grid from the high symmetry planes and @xmath0 point by a half step in each of the @xmath72 , @xmath73 , and @xmath74 directions . this scheme produces highly accurate integration in the brillouin zone by avoiding high symmetry points . to calculate these matrix elements we first defined a tensor operator of order one out of the momentum operator @xmath75 . the muffin - tin part of the momentum matrix elements is calculated using the commutator @xmath76=2 \nabla_{\mu } $ ] so that : @xmath77 where @xmath78 are the usual gaunt coefficients , and @xmath79 is the radius of the muffin - tin sphere of atom @xmath17 . in the interstitial region the plane - wave representation of the wave function ( see equation [ planewave ] ) makes the calculation straightforward , but a special care has to be taken for the removal of the extra contribution in the muffin - tin spheres . however , we find it much easier and faster to transform the interstitial matrix elements as an integral over the surface of the muffin - tin spheres using the commutation relation of the momentum operator and the hamiltonian in the interstitial region . the calculation of the interstitial momentum matrix elements is then similar to the calculation of the interstitial overlap matrix elements@xcite . the @xmath80 case has been already derived by chen using the korringa , kohn and rostoker greens - function method @xcite . we have tested that both the plane - wave summation and the surface integration provide the same results . equation ( [ ehrenreich ] ) can not be used directly to determine the optical properties of semiconductors , when the gw approximation or the scissors operator is used to determine the electronic structure . the velocity operator should be obtained from the effective momentum operator @xmath81 which is calculated using the self - energy operator , @xmath82 , of the system @xcite : @xmath83 gw calculations show that the quasiparticle wave function is almost equals to the lda wave function @xcite . based on this assumption , del sole and girlanda show that the effective momentum operator @xmath84 can be written in terms of the momentum operator @xmath85 as follows @xcite : @xmath86 where @xmath87 is the difference between the quasiparticle energy @xmath88 of the unoccupied state @xmath89 and the occupied state @xmath90 . by substituting equation [ pqp ] into equation [ ehrenreich ] , it can be easily shown @xcite that in the case of the scissors operator , where all the empty states are shifted rigidly by a constant energy @xmath91 , the imaginary part of the dielectric function is a simple energy shift of the lda dielectric function towards the high energies by an amount @xmath91 , i.e. , @xmath92 . the real part of the dielectric function is then obtained from the shifted @xmath93 using kramers - kronig relations . the expression of @xmath94 is given by : @xmath95 @xmath96 is very similar to @xmath97 except that one of the interband gap @xmath98 is substituted by the qp interband gap @xmath99 . to test for the accuracy of the calculation within the lda the f - sum rule : @xmath100 where @xmath101 is the number of valence bands , is checked in all the calculations , and it is satisfied to within a few percent . it is easily seen that the dielectric function @xmath102 calculated using the scissors - operator shift does not satisfy the sum rule ( @xmath103 is the free - electron plasmon frequency ) : @xmath104 because ( i ) @xmath105 satisfies this rule , and ( ii ) @xmath102 is obtained by a simple shift of @xmath105 by the scissors - operator @xmath91 towards higher energies . using the expression of the quasiparticle dielectric function in the scissors - operator shift approximation we show that @xmath102 satisfy the following integral sum rule : @xmath106 where @xmath107 . we recover the usual sum rule when @xmath108 is equal to zero . the non simultaneous satisfaction of both the f - sum rule and the integral sum rule given by eq . 13 within the scissors approximation shows the limitation of this approximation . while the scissors operator approximation describes nicely the low lying excited states , which is seen in the good determination of the static dielectric function and the low energy structures , i.e. @xmath3 and @xmath4 , in the imaginary part of the dielectric function , it seems to fail for the description of the higher excited states . this is not surprising because the higher excited states which are free electrons like are most probably well described by lda and need no scissors operator shift . this is supported by the fact that the the energy - loss function , -im@xmath109 , within the lda has it maximum roughly at the free electron plasmon frequency whereas within the scissors approximation its maximum is shifted to higher energies as given by equation ( [ intsumruleqp ] ) . [ energyloss ] show the energy - loss function of gaas calculated within lda ( full curve ) and within the scissors approximation ( dashed curve ) . it is clearly seen that the maximum of the lda curve has a maximum which is closer to the free valence electron plasma frequency of 15.5 ev . it is of general interest to see whether the calculated dielectric function within the gw approximation satisfies the integral sum rule . for our purpose the scissors - operator shift remains a good approximation for the description of the low - lying excited states of semiconductors and their optical properties . the electronic structure of si , ge , and gaas are obtained by solving the lda equations by means of a full - potential lmto basis - set as described above . table i shows the orbitals used to describe the valence and conduction bands during the selfconsistency . the large number of orbitals used is found necessary to obtain converged excited states up to 5 ry above the top of the valence states . however the total energy is insensitive to these high energy orbitals , but the presence of the 3@xmath110-core states of ge and gaas are important @xcite . table ii compares our band structure of si for some high symmetry points with some recent results from first - principles calculations based on pseudopotential and gaussian orbitals methods @xcite . we found a good agreement between our results and these calculations . this reflects the high accuracy of our unoccupied states which are used to determine the dynamical dielectric function . table iii shows the calculated equilibrium structural parameters , i.e. , the electronic pressure and the bulk modulus at the experimental unit cell volume , @xmath111 , and calculated cell volume , @xmath112 . the calculated equilibrium volume @xmath112 is at the most 2% smaller than the experimental value which correspond to a less than 0.5% deviation from the experimental lattice parameter . however the bulk modulus which is very sensitive to the slop of the total energy versus the unit cell volume deviates at the most by 10% in the case of ge , and when calculated at the experimental unit cell volume . but only by 5% when calculated at the theoretical equilibrium volume . our calculation of the bulk modulus is in excellent agreement with other calculation @xcite . figure [ bandgap ] shows the lda underestimated ( a ) direct band and ( b ) minimal gaps of si , ge , and gaas compared with the ge , and gaas experimental results of goi et al . @xcite . for gaas a cross over from direct band gap to indirect band gap takes palace between @xmath0 and @xmath113 at approximately 8 gpa . for ge this cross over occurs along @xmath114 at a lower pressure of 3 gpa . the direct band gap increases linearly with pressure and is in good agreement with the experimental results for both gaas and ge . there is no experimental data for si under hydrostatic pressure . table iv present the first and second order coefficients describing the dependence of the direct band gap at @xmath0 under hydrostatic pressure , @xmath115 , compared to the experimental results of goi et al.@xcite . apart for the underestimation of the band gap , the first and second coefficients of the pressure dependence of the band gap are in good agreement with the experimental results . this suggest that the scissors - operator shift is a good approximation for the description of the band gap under hydrostatic pressure . figure [ eps2si ] and [ eps2gegaas ] present the imaginary part of the macroscopic dielectric function of si , ge , and gaas obtained at the experimental ground state lattice parameters except for ge where we have compressed the lattice parameter by about 1% . the compression is done because within lda and at the experimental lattice parameter ge is a semi - metal . the lda @xmath93 is shifted towards higher energy by the scissors - operator shift in order that the optical band gap agrees with experiment . the comparison to experimental results of aspnes and studna @xcite shows that all the features in the experimental spectra are reproduced by the calculation . it is interesting to notice that the calculated lda @xmath6 of si exhibit the largest underestimation of the @xmath3 peak ( about 50% in intensity ) whereas , in ge and gaas the underestimation of the @xmath3 peak is only about 12% . the @xmath4 peak is overestimated by lda by about 34% for si , 50% for ge , and 60% for gaas . this overestimation of the @xmath4 peak by lda is due to a strong van hove singularity near the x points of the brillouin zone where parallel bands occur over a large plateau @xcite . this overestimation can be reduced substantially by including the life - time broadening of the quasiparticles through a self - energy calculation . the effect of interband electronic transitions due to the @xmath1 semi - core states , without scissors operator shift , is presented in fig . [ eps2high]a and refeps2highb for ge , and gaas respectively . for ge the onset of transitions begun at photon energy of about 25 ev , and the intensity is very similar to the @xmath116-density of states of the empty states of ge . this is because the @xmath1 states of ge are very narrow , and the dipole selection rules allow transitions only to the empty @xmath116 states of ge , the f - states in this energy range are absent . whereas for gaas , the onset of transitions begun at 12 ev , and the intensity @xmath93 spectrum above 12 ev is very different from the empty @xmath116 states of ga . this is because of the relatively large dispersion of the @xmath1 semi - core states of ga . it should be of interest to confirm experimentally these theoretical predictions . the real part @xmath117 of the dielectric function of si , ge , and gaas calculated by kramers - kronig transform of the imaginary part @xmath6 are presented in fig . [ eps1gegaas ] together with the experimental results of aspnes and studna @xcite . in the same figure we have also presented the scissors - operator shift @xmath118 and the high frequency asymptotic limit @xmath119 , where @xmath103 is the free - electron plasmon frequency . we notice that the analytic asymptotic limit matches nicely the calculated lda @xmath120 , which is an indication of the quality of the calculation . for the @xmath121 we need to use a different plasmon frequency as described in equation ( [ intsumruleqp ] ) due to the poor description of the higher excited states by the scissors approximation . in conclusion , we believe that the excitonic effects may be important for the dielectric function of si but less for those of ge , and gaas . a qp calculation of the dielectric function including the dynamical screening of the coulomb interaction , like in the gw approximation of hedin @xcite , would certainly improve the intensity of at least the @xmath4 peak by introducing a life - time broadening of the quasi - particles . figure [ staticlda ] and [ staticsos ] presents the hydrostatic pressure dependence of the static dielectric function , @xmath2 , of si , ge , and gaas calculated within the lda without and with the scissors - operator shift ( sos ) , respectively . our data are compared to the experimental results of goi _ et al . _ @xcite and to the pseudopotential calculations of si and ge of levine and allan @xcite . our calculation and the pseudopotential theory of ref . @xcite suggest that lda is overestimating the static dielectric function of si , ge , and gaas over the whole range of hydrostatic pressure , and that the use of a unique value of the scissors - operator shift for the correction of the band gap at @xmath0 produces a nice agreement with the experimental results @xcite . the static dielectric function decreases almost linearly with the pressure due to the increase of the direct band gap . however , for si @xmath2 is almost constant with the pressure and this is because the increase of the direct band gap is almost compensated by a decrease of the indirect band gap ( see figure [ bandgap ] ) . table v , vi , and vii present the calculated pressure band gaps , static dielectric function and f - sum rule for si , ge , and gaas , with a comparison to the experimental results of ref . the agreement with the experimental results is excellent when the scissors - operator shift is used . the f - sum rule deviates at most by 5.2% from unity in the case of ge which reflect the high precision of the calculation of the optical matrix elements . the fact that the f - sum rule is not quite exhausted for ge and gaas ( deviation of about 5% ) as compared to si ( deviation of about 1% ) is not due to a possible incompleteness of our basis set@xcite but rather to our use of all electron electronic structure . when the valence states are very well isolated from the core states , like in the case of si where the core states lie about 80 ev below the valence bands , the sum rule should be exhausted however , for ge and gaas where the semi - core @xmath1-states are very close to the valence states and greatly affect the optical properties , the f - sum rule could deviate markedly from unity , i.e. , the average effective number of electrons per atom contributing to the optical transitions is much larger than 4 electrons per atom @xcite . in pseudopotential theory , since the core states are absent , the f - sum rule is exhausted for all semiconductors @xcite . the details of the contribution of the @xmath1 semi - core states to the oscillator strength and the study of the effective number of electrons contributing to the optical transitions are out of the scope of this paper and will be addressed elsewhere . the first and second - order coefficients describing the pressure dependence of the static dielectric function @xmath2 are presented in table viii . the results are compared to the experimental results of goi et al . @xcite , and the pseudopotential calculation of ref . the overall agreement with experiment and the pseudopotential calculation is excellent . in table ix we present our calculation for the static dielectric function of si , ge , and gaas including the spin - orbit coupling effect at the variational level , and the effect of the 3@xmath110 states in the interband transitions . the calculated potential includes always the @xmath1 states , and only the dielectric function is calculated with or without the @xmath1 interband transitions . we have obtained that the inclusion of the @xmath1 interband transitions increases slightly the static dielectric function , whereas the spin - orbit coupling increases it by 2.1% and 3.2% for ge and gaas , respectively . the @xmath2 of si is insensitive to the spin - orbit coupling . the calculated scissors - operator shift @xmath2 including the spin - orbit coupling effect decreases by about 3.3% and 4.1% for ge and gaas , respectively . this is because the band gaps of ge and gaas are further reduced in presence of spin - orbit coupling which resulted in a larger scissors - operator shift for the determination of @xmath122 . the macroscopic dielectric function in the random - phase - approximation without local field effect has been implemented using the local density approximation with an all electron , full - potential linear muffin - tin orbital orbital basis - set . the method is used to calculate the optical properties of the semiconductors , si , ge , and gaas , under hydrostatic pressure . we have found that the lda overestimation the static dielectric function over all the pressure range from 0 to 12 gpa , and that a single value of the so called scissors - operator shift which account for the correct band gap at @xmath0 produced a good agreement with the experimental data of goi and coworkers @xcite . this makes us conclude that because lda underestimates the band gap it is incapable of producing the correct static dielectric function even though @xmath2 is a ground state property . since ( i ) the kohn - sham ( ks ) density functional ( df ) without the local density approximation should in principle produce the correct @xmath2 , and ( ii ) since the lda calculation with the scissors - operator shift also produces the correct @xmath2 , we are tempted to conclude that the ks - df theory should produce the correct band gap for semiconductors . this conclusion is not confirmed by a non - selfconsistent gw calculations which suggest that the true ks - df theory also underestimates the band gap @xcite . our analysis of the dielectric function , the sum rules and the energy - loss function shows that while the scissors - operator shift is a good approximation for the low lying excited states it appears as bad approximation for the high energy excited states . this is because the high energy states are free electron like hence well described within lda . our calculation of the dynamical dielectric function shows that the @xmath3 peak intensity is underestimated for si by about 50% , and for ge and gaas by only 12% . these results imply that the excitonic effects may be important for the dielectric function of si , but less for those for ge , and gaas . we have also shown that including the @xmath1 semi - core states in the interband transitions hardly changes the static dielectric function , @xmath2 , however their contribution to the intensity of dynamical dielectric function for higher photon energies is substantial , and could be checked experimentally . we have also found that the spin - orbit coupling has a significant effect on @xmath2 of ge and gaas , but not of si . we thank j. w. wilkins for interesting discussions . this research was supported in part by the u.s . department of energy basic energy sciences , division of materials sciences and by nsf , grant number dmr-9520319 . supercomputer time was provided by the ohio state supercomputer center . a. r. goi , k. syassen , and m. cardona , phys . b * 41 * , 10104 ( 1990 ) . l. via , s. logothetidis , and m. cardona , phys . b * 30 * , 1979 ( 1984 ) . d. e. aspnes and a. a. studna , phys . b * 27 * , 985 ( 1983 ) . s. baroni and r. resta , phys . b * 33 * , 7017 ( 1986 ) . m. alouani , l. brey , and n. e. christensen , phys . b * 38 * , 1138 ( 1987 ) . levine and d. allan , phys . b * 43 * , 4187 ( 1991 ) ; phys . rev . lett . * 66 * , 41 ( 1991 ) . a. dal corso , s. baroni , and r. resta , phys . b * 49 * , 5323 ( 1994 ) . m. chandrapal and f. h. pollak , solid state comm . * 18 * , 1263 ( 1976 ) , and phys . rev . b * 15 * 2127 ( 1977 ) . w. r. hanke and l. j. sham , phys . * 33 * , 582 ( 1974 ) ; phys . b * 21 * , 4656 ( 1980 ) . l. j. sham , in _ proceeding of the fifteenth international conference on the physics of semiconductors _ , kyoto , 1980 ( j. phys . a * 49 * , 69 ( 1980 ) ) . w. hanke , h. j. mattausch , and g. strinati , in _ electron correlations in solids , molecules , and atoms _ , edited by j. t. devreese and f. brosens ( plenum publishing corporation , 1983 ) . m. del castello - mussot and l. j. sham , phys . b * 31 * , 2092 ( 1985 ) . s. g. louie , j. r. chelikowsky , and m. l. cohen , phys . lett . * 34 * , 155 ( 1975 ) . p. hehenberg et w. kohn , phys . rev . * 136 * , b864 ( 1964 ) ; w. kohn et l. j. sham , phys . 140 * , 1133 ( 1965 ) . u. von barth and l hedin , j. phys . c * 5 * , 1629 ( 1972 ) . l. hedin , phys . rev . * 139 * , a796 ( 1965 ) . m. s. hybertsen and s. g. louie , phys . b * 34 * , 5390 ( 1986 ) . r. w. godby , m. schlter , and l. j. sham , phys . b * 37 * , 10159 ( 1988 ) . j. p. perdew and m. levy , phys . lett . * 51 * , 1884 ( 1983 ) ; r. w. godby , m. schlter , and l. j. sham , phys . * 56 * , 2415 ( 1986 ) . c. s. wang and b. m. klein , phys . b * 24 * , 3417 ( 1981 ) . m. huang and w. y. ching , phys . b * 47 * , 9449 ( 1993 ) . o. k. andersen , phys . b * 12 * , 3060 ( 1975 ) . j. m. wills , unpublished . here the principal quantum number @xmath12 and the spin channel @xmath123 are ignored for simplicity , however our numerical code has the spin polarization capability , and the use of the different @xmath12 with the same momentum channel in the basis set . we use also only one @xmath32 variational parameter per orbital ( see definition in the text ) in all formulas to avoid using it as an obvious index to the wave function and extra summation in the bloch wave function . g. b. bachelet and n. e. christensen , phys . b * 31 * , 879 ( 1985 ) . n. e. christensen , phys . rev . b * 30 * , 5753 ( 1984 ) . c. t. chan , d. vanderbilt , and s. g. louie , phys . rev . b * 33 * , 2455 ( 1986 ) . m. rohlfing , p krger , and j. pollmann , phys . b * 48 * , 17791 ( 1993 ) . s. l. adler , phys . rev . * 126 * , 413 ( 1962 ) ; n. wiser , phys . rev . * 129 * , 62 ( 1963 ) . h. ehrenreich and m. l. cohen , phys . rev . * 115 * , 786 ( 1959 ) . o. jepsen et o. k. andersen , solid state commun . * 9 * , 1763 ( 1971 ) ; g. lehmann et m. taut , phys . * 54 * , 469 ( 1972 ) . a. b. chen , phys . b * 14 * , 2384 ( 1976 ) . r. del sole and r. girlanda , phys . b * 48 * , 11789 ( 1993 ) . m. methfessel , phys . b * 38 * , 1537 ( 1988 ) . j. r. chelikowsky and m. l. cohen , phys . rev . lett . * 31 * , 1582 ( 1973 ) . we have checked carefully the basis set by increasing the number of hankel functions for negative kinetic energies and neumann functions for positive kinetic energies @xmath26 and have not been able to improve on the f - sum rule . our basis - set indicates that all physical properties quantities have been converged , including the total energy which is converged at the tenth of the mry level . for more information see h. r. philipp and h. ehrenreich , phys . rev . * 129 * , 1550 ( 1963 ) . w. a. harrison , _ electronic strcuture and the properties of solids _ , ( freeman , san fransisco , 1980 ) . h. h. li , j. chem . data * 9 * , 561 ( 1980 ) . . basis - sets used for the calculation of the excited states of si , ge and gaas . each orbital has different kinetic energy @xmath26 in its the interstitial region . for example , the @xmath124 orbital of si is used three times , each of the @xmath124 wave function has a different kinetic energy in the interstitial region . [ cols="^,^ " , ]

the macroscopic dielectric function in the random - phase - approximation without local field effect has been implemented using the local density approximation with an all electron , full - potential linear muffin - tin orbital basis - set . this method is used to investigate the optical properties of the semiconductors si , ge , and gaas under hydrostatic pressure . the pressure dependence of the effective dielectric function is compared to the experimental data of goi and coworkers , and an excellent agreement is found when the so called `` scissors - operator '' shift ( sos ) is used to account for the correct band gap at @xmath0 . the effect of the @xmath1 semi - core states in the interband transitions hardly changes the static dielectric function , @xmath2 ; however , their contribution to the intensity of absorption for higher photon energies is substantial . the spin - orbit coupling has a significant effect on @xmath2 of ge and gaas , but not of si . the @xmath3 peak in the dynamical dielectric function is strongly underestimated for si , but only slightly for ge and gaas , suggesting that excitonic effects might be important only for si . = 10000

<s>[INST]the experimental determination of the optical properties of bulk semiconductors can now be obtained with high precision @xcite , yet our theoretical understanding is far from complete . the static dielectric constant , which can be obtained from a functional derivative of the electron density with respect to the total kohn - sham potential evaluated at the ground state , hence a ground state property , is over estimated by the local - density approximation ( lda ) calculation @xcite . the inclusion of the gradient correction to the pseudopotential lda reduces slightly the discrepancy in the case of silicon @xcite . the underestimation of the @xmath3 peak and the overestimation of the @xmath4 peak of the imaginary part of the dielectric function , @xmath5 , by one - electron band theory have generated theoretical work for almost two decades to account for these discrepancies . it was clear from the beginning that including excitonic effects , which have been detected experimentally @xcite , could remove some of the disagreement with experiment @xcite . however , the model calculations used to correct @xmath6 have produced only a qualitative understanding of the problem . in particular , the latest model by hanke , mattausch and strinati based on the time - dependent screened hartree - fock approximation and including both the local field and the excitonic effects , described correctly the @xmath3 peak but underestimated significantly the @xmath4 peak of si . the reason for the underestimation of @xmath4 was attributed to a bad representation of the band structure of si by their slater - koster parameterization @xcite . del castello - mussot and sham @xcite based their latest calculation on a @xmath7 model around the l point ( where @xmath3 originates ) and a multiple plane - wave model around the x points ( where @xmath4 originates ) , and solved the bethe - salpeter equation containing the excitonic effect . their model is an improvement over the non - interacting approximation : the @xmath3 peak becomes stronger and the @xmath4 peak weaker . this model is very promising , but , being based on a @xmath7 approximation to the band structure , it provided only a qualitative correction to the intensities of the @xmath3 and @xmath4 structures . calculations ignoring excitonic effects , but including the local - field effect , underestimated both @xmath3 and @xmath4 peaks @xcite . one way to make theoretical progress in this field is to determine the correct contribution of the one - electron theory to the optical properties of semiconductors . this allows us to define precisely the size of the many body corrections to the one electron theory . however , a common belief these days is that the eigenvalues and vectors of the kohn - sham ( ks ) equations @xcite have no direct physical meaning and hence should not be used to calculate optical spectra of materials . only ground state properties derived from the total energy as a function of the electron density have in principle a direct physical meaning . while lda was indeed intended to calculate ground state properties it could also be viewed as a simplified quasi - particle ( qp ) theory where the self - energy is local and static ( @xmath8 , here @xmath9 is the local exchange and correlation potential as , for example , parameterized by von barth and hedin @xcite . the ks eigenvalues are then qp energies and could be compared to experimental data . this argument is supported by calculations using the gw approximation of hedin@xcite . these calculations showed that the valence qp energies of semiconductors are in good agreement with lda and the conduction qp energies differ by approximately a rigid energy shift @xcite . in the literature this shift is often called `` scissors - operator '' shift ( sos ) @xcite . first - principles local density approximation calculations started more than two decades ago , but the major problem of lda , beside the well understood energy band gap problem@xcite , is the numerical difficulty to determine selfconsistent electronic structure and optical matrix elements using a complete basis - set . the early ab - initio calculation of the optical properties of semiconductors by wang and klein , using a selfconsistent linear combination of gaussian orbitals produced static dielectric functions in good agreement with experiment@xcite . but this agreement is fortuitous because the band gaps produced by this method are much larger than the lda band gaps . the recent calculations of 18 semiconductors by huang and ching using an orthogonalized linear combination of atomic orbitals method produced lda static dielectric functions which are in general smaller than experiment despite the fact that their band gaps are much larger than the all - electron or pseudopotential lda band gaps @xcite . those underestimated static dielectric constants are most likely due to the incompleteness of the basis - set used in their calculations . most of the theoretical studies of the optical properties of semiconductors in the literature use several approximations within the lda , ranging from the use of spherical potentials @xcite to the use of pseudopotentials @xcite instead of all electron lda potentials . in this paper we report precise calculations of the optical properties of bulk semiconductors si , ge , and gaas under hydrostatic pressure using an all electron lda linear muffin - tin orbital basis - set@xcite , in which no shape approximation is made for either the potential or the charge density @xcite . the semi - core @xmath1 of ga and ge are included in a fully hybridizing valence basis set , and the rest of the core states are allowed to relax selfconsistently . the effect of spin - orbit coupling is also investigated . a systematic check of the @xmath10-sum rule is performed for all the calculations . we hope that this accurate lda calculation will provide an excellent starting point for the determination of the local field and the excitonic effects in the optical spectra of semiconductors @xcite . we have found that the static dielectric function , @xmath2 , which is a ground state property , is overestimated by lda over all pressure range , and that an excellent agreement with the experimental results of goi and coworkers @xcite for @xmath2 of gaas and ge under hydrostatic pressure is achieved only when the so - called scissors - operator shift is used to account for the correct band gap at @xmath0 . the inclusion of the @xmath1 semi - core states of ge and gaas in the interband transition has almost no significant effects in @xmath2 ; however , the @xmath1 interband transitions contribute significantly to the magnitude of @xmath11 above 25 ev for ge , and above 12 ev for gaas . the spin - orbit coupling increases the lda values by about few percents . the rest of the paper is organized as follows . in section ii , we describe the method of calculation of electronic structure and the macroscopic dielectric function based on our all - electron full - potential lmto basis - set . in section iii we present the electronic properties of si , ge , and gaas and compare them to existing theoretical results . the calculated dielectric functions and a discussion about including the semi - core states and the spin - orbit coupling will be presented in section iv . in the same section we also compare our static dielectric function under hydrostatic pressure with the experimental results of goi _ et al . the conclusion is given in sec . the full - potential linear muffin - tin orbital method in its scalar - relativistic and full - relativistic forms @xcite is used here to calculate the electronic structure and the optical properties of si , ge , and gaas under hydrostatic pressure . the kohn - sham @xcite equations are solved for a general potential without any shape approximation @xcite . in this subsection we describe the bloch wave function inside the so - called muffin - tin spheres and the interstititial region . a correct determination of the crystal wave function is necessary for the accurate determination of the optical matrix elements . as for the cellular methods , the space is divided into non - overlapping muffin - tin spheres surrounding atomic sites where the schrdinger or the dirac equation for each principle quantum number @xmath12 and momentum channel @xmath13 is solved for a fixed energy @xmath14 . in these muffin - tin spheres the trial wave function is linearized in terms of the solution of schrdinger equation @xmath15 and its energy derivative @xmath16 for the energy @xmath14 , and for an atom of type @xmath17 and momentum channel @xmath13 @xcite . it can be shown that the bloch wave function of site @xmath17 calculated at site @xmath18 in the unit cell of the crystal at @xmath19 is given by @xcite : @xmath20 where @xmath21 and @xmath22 are renormalized structure constants obtained from the crystal structure constants @xmath23 to ensure that the bloch wave function is continuous and differentiable at the boundary of each muffin - tin sphere . in the interstitial region , the muffin - tin orbitals are spherical wave solutions @xmath24 to the helmholtz equation with non - zero kinetic energy ; these bases are hankel functions for negative kinetic energies or neumann functions for positive kinetic energies @xmath25 . such that each partial wave inside the muffin - tin sphere is allowed to have different kinetic energy , @xmath26 , in the interstitial region . in this region the bloch wave function is given by : @xmath27 the interstitial - region bloch function is expressed in plane waves over the reciprocal lattice using fourier transform : @xmath28 where @xmath29 , here the parameter @xmath30 is the linearization energy of the wave function in the muffin - tin sphere for the @xmath13 momentum channel , @xmath31 is the azumutal quantum number , and @xmath32 is the variational parameter whose square is the kinetic energy in the interstitial region . the fourier coefficients , @xmath33 , are obtained from a pseudo - wave function that is equal to the crystal wave function in the interstitial region and represented by a smooth function inside the muffin - tin spheres . the exact shape of these pseudo - functions inside the muffin - tin spheres is not important . the only requirement is that they are continuous and differentiable at the sphere boundary and have zero slop at the origin of each sphere . the plane wave expansion is multiplied by a three dimensional step function so that the wave function is kept only in the interstitial region . the knowledge of the bloch wave function in the whole unit cell allows us to calculate the hamiltonian and overlap matrix elements in order to solve the effective one electron schrdinger equation . three different kinetic energies were used for each subset of _ s _ and _ p _ derived bases in the basis set ; two kinetic energies were used for bases derived from orbital parameters @xmath34 . the basis sets used in calculating total energies and structural properties were for si : 3(3_s_3_p _ ) , 2(3_d _ ) , for ge : 2(3_d _ ) , 3(4_s_4_p _ ) , 2(4_d _ ) , and for gaas : 2(ga 3_d _ ) , 3(ga 4_s_4_p _ ) , 2(ga 4_d _ ) , 3(as 4_s_4_p _ ) , 2(as 4_d _ ) ; the pre - multiplicities in this notation refer to the number kinetic energies used in this basis subset . the basis functions for each material comprised a single , fully hybridizing basis set . note the presence of both 3_d _ and 4_d _ derived bases on ga and ge . a useful feature of the method used in these calculations is the ability to incorporate basis functions derived from the same orbital atomic quantum numbers but different principal atomic quantum numbers in a single fully hybridizing basis set . this feature entails the use of multiple sets of radial functions to represent bases with different principle atomic quantum numbers . this capability was particularly useful in calculating the high - lying energy bands which were used to obtain the dielectric functions to high energy ; the basis sets employed for this purpose are given in table i. seven to eight kinetic energies were used in the basis sets . accurate resolution of the bands to high energy was necessary to converge the calculation of the real part of the dielectric function , which was obtained from the imaginary part through the kramers - kronig relation . an interesting consequence of the relaxation of the ga 3_d _ states as valence states is a significant decrease in the calculated band gap @xcite . for the core charge density , the dirac equation is solved selfconsistently , e.g. , no frozen core approximation is used . the exchange and correlation potential is treated within the von barth and hedin parameterization @xcite . to account for the relativistic effects in the dielectric function , the full - selfconsistent relativistic band structure is produced by including the spin - orbit coupling to the hamiltonian . in table i we show the orbitals used to describe the electronic states of si , ge , and gaas . this large number of orbitals is necessary to calculate accurately the eigenvalues and eigenvectors up to 5 ry above the highest valence states . these electronic states will be needed to determine the dynamical dielectric function and the converged static dielectric function through the use of kramers - kronig relations . the completeness of basis - set , with different variational @xmath32 values for each partial wave in the interstitial region together with the fourier representation allows the method to treat open structures like the zinc - blende structure studied here without having to resort to the so - called empty spheres @xcite . the high energy states are also determined more accurately due to the use of many @xmath32 values . as a test we show in table ii the eigenvalues of si at high symmetry points of the brillouin zone compared with some recent results from first principle calculations based on ab - initio pseudopotential and gaussian orbital methods @xcite . the agreement of our calculation with the previous calculations is excellent . [ sec : method ] here we give a concise review of the determination of the dielectric function of a semiconductor crystal due to the application of an electric field . we also determine the approximations used to obtain numerical results for si , ge , and gaas under hydrostatic pressure with or without scissors - operator shift . a perturbative electromagnetic field of frequency @xmath35 , and a wave vector @xmath36 on a crystal produces a response of frequency @xmath35 and a wave vector @xmath37 ( @xmath38 and @xmath39 being reciprocal lattice vectors ) . the microscopic field of wave vector @xmath40 is produced by the umklapp processes as a result of the applied field @xmath41 @xmath42 where @xmath43 is the total field which produces the non - diagonal elements in the microscopic dielectric function @xmath44 . in the random phase approximation the microscopic dielectric function is given by @xcite : @xmath45 here @xmath46 and @xmath47 are the band indexes , @xmath48 is the zero temperature fermi distribution , and @xmath49 is the cell volume . the energies @xmath50 and the the crystal wave function @xmath51 are produced for each band index @xmath46 and for each wave vector @xmath52 in the brillouin zone . the macroscopic dielectric function in the infinite wave length limit is given by the inversion of the microscopic dielectric function : @xmath53_{\bf 0,0 } } \\ \nonumber & = \epsilon_{0,0}(\omega ) - \lim_{{\bf q } \to { \bf 0 } } \sum_{{\bf g , g^\prime \ne 0 } } \epsilon_{0,\bf g}({\bf q } , \omega ) t^{-1}_{\bf g , g^\prime } ( { \bf q } , \omega ) \epsilon_{\bf g^\prime,0}({\bf q } , \omega ) \ ; \label{localfield}\end{aligned}\ ] ] where @xmath54 is the inverse matrix of @xmath55 containing the elements @xmath56 with @xmath57 and @xmath58 . the first term of this equation is the interband contribution to the macroscopic dielectric function and the second term represent the local - field correction to @xmath59 . the most recent ab - initio pseudopotentials calculation found that the local - field effect reduces the static dielectric function by at most 5% @xcite . previous calculations with the same method have also found a decrease of @xmath60 by about the same percentage @xcite . we are looking at the effect of the local field using our all - electron basis - set ; it should be of interest to compare all electron results with these obtained using the pseudopotential method . for insulators the dipole approximation of the imaginary part of the first term of equation ( [ localfield ] ) is given by @xcite : @xmath61 here @xmath62 is the velocity operator , and in the lda @xmath63 ( @xmath64 being the momentum operator ) , and where @xmath65 . the matrix elements @xmath66 are calculated for each projection @xmath67 , @xmath68 or @xmath69 and @xmath70 , with the wave function @xmath71 expressed in terms of the full - potential lmto crystal wave function described by equations ( [ wavemuffin ] ) and ( [ planewave ] ) . the * k*-space integration is performed using the tetrahedron method @xcite with 480 irreducible * k * points the whole brillouin zone . the irreducible * k*-points are obtained from a shifted * k*-space grid from the high symmetry planes and @xmath0 point by a half step in each of the @xmath72 , @xmath73 , and @xmath74 directions . this scheme produces highly accurate integration in the brillouin zone by avoiding high symmetry points . to calculate these matrix elements we first defined a tensor operator of order one out of the momentum operator @xmath75 . the muffin - tin part of the momentum matrix elements is calculated using the commutator @xmath76=2 \nabla_{\mu } $ ] so that : @xmath77 where @xmath78 are the usual gaunt coefficients , and @xmath79 is the radius of the muffin - tin sphere of atom @xmath17 . in the interstitial region the plane - wave representation of the wave function ( see equation [ planewave ] ) makes the calculation straightforward , but a special care has to be taken for the removal of the extra contribution in the muffin - tin spheres . however , we find it much easier and faster to transform the interstitial matrix elements as an integral over the surface of the muffin - tin spheres using the commutation relation of the momentum operator and the hamiltonian in the interstitial region . the calculation of the interstitial momentum matrix elements is then similar to the calculation of the interstitial overlap matrix elements@xcite . the @xmath80 case has been already derived by chen using the korringa , kohn and rostoker greens - function method @xcite . we have tested that both the plane - wave summation and the surface integration provide the same results . equation ( [ ehrenreich ] ) can not be used directly to determine the optical properties of semiconductors , when the gw approximation or the scissors operator is used to determine the electronic structure . the velocity operator should be obtained from the effective momentum operator @xmath81 which is calculated using the self - energy operator , @xmath82 , of the system @xcite : @xmath83 gw calculations show that the quasiparticle wave function is almost equals to the lda wave function @xcite . based on this assumption , del sole and girlanda show that the effective momentum operator @xmath84 can be written in terms of the momentum operator @xmath85 as follows @xcite : @xmath86 where @xmath87 is the difference between the quasiparticle energy @xmath88 of the unoccupied state @xmath89 and the occupied state @xmath90 . by substituting equation [ pqp ] into equation [ ehrenreich ] , it can be easily shown @xcite that in the case of the scissors operator , where all the empty states are shifted rigidly by a constant energy @xmath91 , the imaginary part of the dielectric function is a simple energy shift of the lda dielectric function towards the high energies by an amount @xmath91 , i.e. , @xmath92 . the real part of the dielectric function is then obtained from the shifted @xmath93 using kramers - kronig relations . the expression of @xmath94 is given by : @xmath95 @xmath96 is very similar to @xmath97 except that one of the interband gap @xmath98 is substituted by the qp interband gap @xmath99 . to test for the accuracy of the calculation within the lda the f - sum rule : @xmath100 where @xmath101 is the number of valence bands , is checked in all the calculations , and it is satisfied to within a few percent . it is easily seen that the dielectric function @xmath102 calculated using the scissors - operator shift does not satisfy the sum rule ( @xmath103 is the free - electron plasmon frequency ) : @xmath104 because ( i ) @xmath105 satisfies this rule , and ( ii ) @xmath102 is obtained by a simple shift of @xmath105 by the scissors - operator @xmath91 towards higher energies . using the expression of the quasiparticle dielectric function in the scissors - operator shift approximation we show that @xmath102 satisfy the following integral sum rule : @xmath106 where @xmath107 . we recover the usual sum rule when @xmath108 is equal to zero . the non simultaneous satisfaction of both the f - sum rule and the integral sum rule given by eq . 13 within the scissors approximation shows the limitation of this approximation . while the scissors operator approximation describes nicely the low lying excited states , which is seen in the good determination of the static dielectric function and the low energy structures , i.e. @xmath3 and @xmath4 , in the imaginary part of the dielectric function , it seems to fail for the description of the higher excited states . this is not surprising because the higher excited states which are free electrons like are most probably well described by lda and need no scissors operator shift . this is supported by the fact that the the energy - loss function , -im@xmath109 , within the lda has it maximum roughly at the free electron plasmon frequency whereas within the scissors approximation its maximum is shifted to higher energies as given by equation ( [ intsumruleqp ] ) . [ energyloss ] show the energy - loss function of gaas calculated within lda ( full curve ) and within the scissors approximation ( dashed curve ) . it is clearly seen that the maximum of the lda curve has a maximum which is closer to the free valence electron plasma frequency of 15.5 ev . it is of general interest to see whether the calculated dielectric function within the gw approximation satisfies the integral sum rule . for our purpose the scissors - operator shift remains a good approximation for the description of the low - lying excited states of semiconductors and their optical properties . the electronic structure of si , ge , and gaas are obtained by solving the lda equations by means of a full - potential lmto basis - set as described above . table i shows the orbitals used to describe the valence and conduction bands during the selfconsistency . the large number of orbitals used is found necessary to obtain converged excited states up to 5 ry above the top of the valence states . however the total energy is insensitive to these high energy orbitals , but the presence of the 3@xmath110-core states of ge and gaas are important @xcite . table ii compares our band structure of si for some high symmetry points with some recent results from first - principles calculations based on pseudopotential and gaussian orbitals methods @xcite . we found a good agreement between our results and these calculations . this reflects the high accuracy of our unoccupied states which are used to determine the dynamical dielectric function . table iii shows the calculated equilibrium structural parameters , i.e. , the electronic pressure and the bulk modulus at the experimental unit cell volume , @xmath111 , and calculated cell volume , @xmath112 . the calculated equilibrium volume @xmath112 is at the most 2% smaller than the experimental value which correspond to a less than 0.5% deviation from the experimental lattice parameter . however the bulk modulus which is very sensitive to the slop of the total energy versus the unit cell volume deviates at the most by 10% in the case of ge , and when calculated at the experimental unit cell volume . but only by 5% when calculated at the theoretical equilibrium volume . our calculation of the bulk modulus is in excellent agreement with other calculation @xcite . figure [ bandgap ] shows the lda underestimated ( a ) direct band and ( b ) minimal gaps of si , ge , and gaas compared with the ge , and gaas experimental results of goi et al . @xcite . for gaas a cross over from direct band gap to indirect band gap takes palace between @xmath0 and @xmath113 at approximately 8 gpa . for ge this cross over occurs along @xmath114 at a lower pressure of 3 gpa . the direct band gap increases linearly with pressure and is in good agreement with the experimental results for both gaas and ge . there is no experimental data for si under hydrostatic pressure . table iv present the first and second order coefficients describing the dependence of the direct band gap at @xmath0 under hydrostatic pressure , @xmath115 , compared to the experimental results of goi et al.@xcite . apart for the underestimation of the band gap , the first and second coefficients of the pressure dependence of the band gap are in good agreement with the experimental results . this suggest that the scissors - operator shift is a good approximation for the description of the band gap under hydrostatic pressure . figure [ eps2si ] and [ eps2gegaas ] present the imaginary part of the macroscopic dielectric function of si , ge , and gaas obtained at the experimental ground state lattice parameters except for ge where we have compressed the lattice parameter by about 1% . the compression is done because within lda and at the experimental lattice parameter ge is a semi - metal . the lda @xmath93 is shifted towards higher energy by the scissors - operator shift in order that the optical band gap agrees with experiment . the comparison to experimental results of aspnes and studna @xcite shows that all the features in the experimental spectra are reproduced by the calculation . it is interesting to notice that the calculated lda @xmath6 of si exhibit the largest underestimation of the @xmath3 peak ( about 50% in intensity ) whereas , in ge and gaas the underestimation of the @xmath3 peak is only about 12% . the @xmath4 peak is overestimated by lda by about 34% for si , 50% for ge , and 60% for gaas . this overestimation of the @xmath4 peak by lda is due to a strong van hove singularity near the x points of the brillouin zone where parallel bands occur over a large plateau @xcite . this overestimation can be reduced substantially by including the life - time broadening of the quasiparticles through a self - energy calculation . the effect of interband electronic transitions due to the @xmath1 semi - core states , without scissors operator shift , is presented in fig . [ eps2high]a and refeps2highb for ge , and gaas respectively . for ge the onset of transitions begun at photon energy of about 25 ev , and the intensity is very similar to the @xmath116-density of states of the empty states of ge . this is because the @xmath1 states of ge are very narrow , and the dipole selection rules allow transitions only to the empty @xmath116 states of ge , the f - states in this energy range are absent . whereas for gaas , the onset of transitions begun at 12 ev , and the intensity @xmath93 spectrum above 12 ev is very different from the empty @xmath116 states of ga . this is because of the relatively large dispersion of the @xmath1 semi - core states of ga . it should be of interest to confirm experimentally these theoretical predictions . the real part @xmath117 of the dielectric function of si , ge , and gaas calculated by kramers - kronig transform of the imaginary part @xmath6 are presented in fig . [ eps1gegaas ] together with the experimental results of aspnes and studna @xcite . in the same figure we have also presented the scissors - operator shift @xmath118 and the high frequency asymptotic limit @xmath119 , where @xmath103 is the free - electron plasmon frequency . we notice that the analytic asymptotic limit matches nicely the calculated lda @xmath120 , which is an indication of the quality of the calculation . for the @xmath121 we need to use a different plasmon frequency as described in equation ( [ intsumruleqp ] ) due to the poor description of the higher excited states by the scissors approximation . in conclusion , we believe that the excitonic effects may be important for the dielectric function of si but less for those of ge , and gaas . a qp calculation of the dielectric function including the dynamical screening of the coulomb interaction , like in the gw approximation of hedin @xcite , would certainly improve the intensity of at least the @xmath4 peak by introducing a life - time broadening of the quasi - particles . figure [ staticlda ] and [ staticsos ] presents the hydrostatic pressure dependence of the static dielectric function , @xmath2 , of si , ge , and gaas calculated within the lda without and with the scissors - operator shift ( sos ) , respectively . our data are compared to the experimental results of goi _ et al . _ @xcite and to the pseudopotential calculations of si and ge of levine and allan @xcite . our calculation and the pseudopotential theory of ref . @xcite suggest that lda is overestimating the static dielectric function of si , ge , and gaas over the whole range of hydrostatic pressure , and that the use of a unique value of the scissors - operator shift for the correction of the band gap at @xmath0 produces a nice agreement with the experimental results @xcite . the static dielectric function decreases almost linearly with the pressure due to the increase of the direct band gap . however , for si @xmath2 is almost constant with the pressure and this is because the increase of the direct band gap is almost compensated by a decrease of the indirect band gap ( see figure [ bandgap ] ) . table v , vi , and vii present the calculated pressure band gaps , static dielectric function and f - sum rule for si , ge , and gaas , with a comparison to the experimental results of ref . the agreement with the experimental results is excellent when the scissors - operator shift is used . the f - sum rule deviates at most by 5.2% from unity in the case of ge which reflect the high precision of the calculation of the optical matrix elements . the fact that the f - sum rule is not quite exhausted for ge and gaas ( deviation of about 5% ) as compared to si ( deviation of about 1% ) is not due to a possible incompleteness of our basis set@xcite but rather to our use of all electron electronic structure . when the valence states are very well isolated from the core states , like in the case of si where the core states lie about 80 ev below the valence bands , the sum rule should be exhausted however , for ge and gaas where the semi - core @xmath1-states are very close to the valence states and greatly affect the optical properties , the f - sum rule could deviate markedly from unity , i.e. , the average effective number of electrons per atom contributing to the optical transitions is much larger than 4 electrons per atom @xcite . in pseudopotential theory , since the core states are absent , the f - sum rule is exhausted for all semiconductors @xcite . the details of the contribution of the @xmath1 semi - core states to the oscillator strength and the study of the effective number of electrons contributing to the optical transitions are out of the scope of this paper and will be addressed elsewhere . the first and second - order coefficients describing the pressure dependence of the static dielectric function @xmath2 are presented in table viii . the results are compared to the experimental results of goi et al . @xcite , and the pseudopotential calculation of ref . the overall agreement with experiment and the pseudopotential calculation is excellent . in table ix we present our calculation for the static dielectric function of si , ge , and gaas including the spin - orbit coupling effect at the variational level , and the effect of the 3@xmath110 states in the interband transitions . the calculated potential includes always the @xmath1 states , and only the dielectric function is calculated with or without the @xmath1 interband transitions . we have obtained that the inclusion of the @xmath1 interband transitions increases slightly the static dielectric function , whereas the spin - orbit coupling increases it by 2.1% and 3.2% for ge and gaas , respectively . the @xmath2 of si is insensitive to the spin - orbit coupling . the calculated scissors - operator shift @xmath2 including the spin - orbit coupling effect decreases by about 3.3% and 4.1% for ge and gaas , respectively . this is because the band gaps of ge and gaas are further reduced in presence of spin - orbit coupling which resulted in a larger scissors - operator shift for the determination of @xmath122 . the macroscopic dielectric function in the random - phase - approximation without local field effect has been implemented using the local density approximation with an all electron , full - potential linear muffin - tin orbital orbital basis - set . the method is used to calculate the optical properties of the semiconductors , si , ge , and gaas , under hydrostatic pressure . we have found that the lda overestimation the static dielectric function over all the pressure range from 0 to 12 gpa , and that a single value of the so called scissors - operator shift which account for the correct band gap at @xmath0 produced a good agreement with the experimental data of goi and coworkers @xcite . this makes us conclude that because lda underestimates the band gap it is incapable of producing the correct static dielectric function even though @xmath2 is a ground state property . since ( i ) the kohn - sham ( ks ) density functional ( df ) without the local density approximation should in principle produce the correct @xmath2 , and ( ii ) since the lda calculation with the scissors - operator shift also produces the correct @xmath2 , we are tempted to conclude that the ks - df theory should produce the correct band gap for semiconductors . this conclusion is not confirmed by a non - selfconsistent gw calculations which suggest that the true ks - df theory also underestimates the band gap @xcite . our analysis of the dielectric function , the sum rules and the energy - loss function shows that while the scissors - operator shift is a good approximation for the low lying excited states it appears as bad approximation for the high energy excited states . this is because the high energy states are free electron like hence well described within lda . our calculation of the dynamical dielectric function shows that the @xmath3 peak intensity is underestimated for si by about 50% , and for ge and gaas by only 12% . these results imply that the excitonic effects may be important for the dielectric function of si , but less for those for ge , and gaas . we have also shown that including the @xmath1 semi - core states in the interband transitions hardly changes the static dielectric function , @xmath2 , however their contribution to the intensity of dynamical dielectric function for higher photon energies is substantial , and could be checked experimentally . we have also found that the spin - orbit coupling has a significant effect on @xmath2 of ge and gaas , but not of si . we thank j. w. wilkins for interesting discussions . this research was supported in part by the u.s . department of energy basic energy sciences , division of materials sciences and by nsf , grant number dmr-9520319 . supercomputer time was provided by the ohio state supercomputer center . a. r. goi , k. syassen , and m. cardona , phys . b * 41 * , 10104 ( 1990 ) . l. via , s. logothetidis , and m. cardona , phys . b * 30 * , 1979 ( 1984 ) . d. e. aspnes and a. a. studna , phys . b * 27 * , 985 ( 1983 ) . s. baroni and r. resta , phys . b * 33 * , 7017 ( 1986 ) . m. alouani , l. brey , and n. e. christensen , phys . b * 38 * , 1138 ( 1987 ) . levine and d. allan , phys . b * 43 * , 4187 ( 1991 ) ; phys . rev . lett . * 66 * , 41 ( 1991 ) . a. dal corso , s. baroni , and r. resta , phys . b * 49 * , 5323 ( 1994 ) . m. chandrapal and f. h. pollak , solid state comm . * 18 * , 1263 ( 1976 ) , and phys . rev . b * 15 * 2127 ( 1977 ) . w. r. hanke and l. j. sham , phys . * 33 * , 582 ( 1974 ) ; phys . b * 21 * , 4656 ( 1980 ) . l. j. sham , in _ proceeding of the fifteenth international conference on the physics of semiconductors _ , kyoto , 1980 ( j. phys . a * 49 * , 69 ( 1980 ) ) . w. hanke , h. j. mattausch , and g. strinati , in _ electron correlations in solids , molecules , and atoms _ , edited by j. t. devreese and f. brosens ( plenum publishing corporation , 1983 ) . m. del castello - mussot and l. j. sham , phys . b * 31 * , 2092 ( 1985 ) . s. g. louie , j. r. chelikowsky , and m. l. cohen , phys . lett . * 34 * , 155 ( 1975 ) . p. hehenberg et w. kohn , phys . rev . * 136 * , b864 ( 1964 ) ; w. kohn et l. j. sham , phys . 140 * , 1133 ( 1965 ) . u. von barth and l hedin , j. phys . c * 5 * , 1629 ( 1972 ) . l. hedin , phys . rev . * 139 * , a796 ( 1965 ) . m. s. hybertsen and s. g. louie , phys . b * 34 * , 5390 ( 1986 ) . r. w. godby , m. schlter , and l. j. sham , phys . b * 37 * , 10159 ( 1988 ) . j. p. perdew and m. levy , phys . lett . * 51 * , 1884 ( 1983 ) ; r. w. godby , m. schlter , and l. j. sham , phys . * 56 * , 2415 ( 1986 ) . c. s. wang and b. m. klein , phys . b * 24 * , 3417 ( 1981 ) . m. huang and w. y. ching , phys . b * 47 * , 9449 ( 1993 ) . o. k. andersen , phys . b * 12 * , 3060 ( 1975 ) . j. m. wills , unpublished . here the principal quantum number @xmath12 and the spin channel @xmath123 are ignored for simplicity , however our numerical code has the spin polarization capability , and the use of the different @xmath12 with the same momentum channel in the basis set . we use also only one @xmath32 variational parameter per orbital ( see definition in the text ) in all formulas to avoid using it as an obvious index to the wave function and extra summation in the bloch wave function . g. b. bachelet and n. e. christensen , phys . b * 31 * , 879 ( 1985 ) . n. e. christensen , phys . rev . b * 30 * , 5753 ( 1984 ) . c. t. chan , d. vanderbilt , and s. g. louie , phys . rev . b * 33 * , 2455 ( 1986 ) . m. rohlfing , p krger , and j. pollmann , phys . b * 48 * , 17791 ( 1993 ) . s. l. adler , phys . rev . * 126 * , 413 ( 1962 ) ; n. wiser , phys . rev . * 129 * , 62 ( 1963 ) . h. ehrenreich and m. l. cohen , phys . rev . * 115 * , 786 ( 1959 ) . o. jepsen et o. k. andersen , solid state commun . * 9 * , 1763 ( 1971 ) ; g. lehmann et m. taut , phys . * 54 * , 469 ( 1972 ) . a. b. chen , phys . b * 14 * , 2384 ( 1976 ) . r. del sole and r. girlanda , phys . b * 48 * , 11789 ( 1993 ) . m. methfessel , phys . b * 38 * , 1537 ( 1988 ) . j. r. chelikowsky and m. l. cohen , phys . rev . lett . * 31 * , 1582 ( 1973 ) . we have checked carefully the basis set by increasing the number of hankel functions for negative kinetic energies and neumann functions for positive kinetic energies @xmath26 and have not been able to improve on the f - sum rule . our basis - set indicates that all physical properties quantities have been converged , including the total energy which is converged at the tenth of the mry level . for more information see h. r. philipp and h. ehrenreich , phys . rev . * 129 * , 1550 ( 1963 ) . w. a. harrison , _ electronic strcuture and the properties of solids _ , ( freeman , san fransisco , 1980 ) . h. h. li , j. chem . data * 9 * , 561 ( 1980 ) . . basis - sets used for the calculation of the excited states of si , ge and gaas . each orbital has different kinetic energy @xmath26 in its the interstitial region . for example , the @xmath124 orbital of si is used three times , each of the @xmath124 wave function has a different kinetic energy in the interstitial region . [ cols="^,^ " , ][/INST] the macroscopic dielectric function in the random - phase - approximation without local field effect has been implemented using the local density approximation with an all electron , full - potential linear muffin - tin orbital basis - set . this method is used to investigate the optical properties of the semiconductors si , ge , and gaas under hydrostatic pressure . the pressure dependence of the effective dielectric function is compared to the experimental data of goi and coworkers , and an excellent agreement is found when the so called `` scissors - operator '' shift ( sos ) is used to account for the correct band gap at @xmath0 . the effect of the @xmath1 semi - core states in the interband transitions hardly changes the static dielectric function , @xmath2 ; however , their contribution to the intensity of absorption for higher photon energies is substantial . the spin - orbit coupling has a significant effect on @xmath2 of ge and gaas , but not of si . the @xmath3 peak in the dynamical dielectric function is strongly underestimated for si , but only slightly for ge and gaas , suggesting that excitonic effects might be important only for si . = 10000 </s>

channeling and blocking effects in crystals refer to the orientation dependence of charged ion penetration in crystals . in the channeling effect " ions incident upon a crystal along symmetry axes and planes suffer a series of small - angle scatterings that maintain them in the open channels " between the rows or planes of lattice atoms and thus penetrate much further into the crystal than in other directions . channeled incoming ions do not get close to lattice sites , where they would be deflected at large angles . the blocking effect " consists in a reduction of the flux of ions originating in lattice sites along symmetry axes and planes , creating what is called a blocking dip " in the flux of ions exiting from a thin enough crystal as a function of the angle with respect to a symmetry axis or plane . these effects were first observed in the 1960 s and are used in crystallography , in the study of lattice disorder , ion implantation , surfaces , interfaces and epitaxial layers , in measurements of short nuclear lifetimes etc . in particular , avoiding channeling is essential in the manufacturing of semiconductor devices , since ion implantation at a controlled depth is the primary technique . ion channeling in nai ( tl ) was first observed in 1973 by altman _ et al . _ they observed that channeled ions produce more scintillation light because they lose most of their energy via electronic stopping rather than nuclear stopping . the potential importance of the channeling effect for direct dark matter detection was first pointed out by sekiya _ et al . _ @xcite and subsequently for nai ( tl ) by drobyshevski @xcite and by the dama collaboration @xcite . when na or i ions recoiling after a collision with a dark matter wimp ( weakly interacting massive particle ) move along crystal axes and planes , their quenching factor is approximately @xmath0 instead of @xmath1 and @xmath2 , since they give their energy to electrons . ion channeling in crystals could give rise to a daily modulation due to the preferred direction of the dark matter flux arriving on the earth . earth s daily rotation naturally changes the direction of the `` wimp wind '' with respect to the crystal axes , which produces a daily modulation in the measured recoil energy ( equivalent to a modulation of the factor @xmath3 ) . et al . _ @xcite pointed this out for stilbene crystals , and avignone , creswick , and nussinov @xcite for nai ( tl ) crystals , although the available estimates of the strength of these daily modulations are somewhat simplistic . my collaborators , graciela gelmini and paolo gondolo , and i @xcite present here our analytic calculations of the channeling fraction in nai ( tl ) , si and ge crystals . our calculation is based on the classical analytic models developed in the 1960 s and 70 s , in particular by lindhard @xcite . we use the continuum string and plane model , in which the screened thomas - fermi potential is averaged over a direction parallel to a row or a plane . this averaged potential @xmath4 is considered to be uniformly smeared along the row or plane of atoms , which is a good approximation if the propagating ion interacts with many lattice atoms in the row or plane by a correlated series of many consecutive glancing collisions with lattice atoms . just one row or plane is considered in this model . lindhard proved that for an ion propagating with kinetic energy @xmath5 , and for small angle @xmath6 between the ion s trajectory and the atomic row ( or plane ) in the direction perpendicular to the row ( or plane ) , the so called transverse energy " , @xmath7 is conserved . the conservation of the transverse energy provides a definition of the minimum distance of approach to the string ( or plane ) of atoms , @xmath8 , at which the trajectory of the ion makes a zero angle with the string ( or plane ) , and also of the angle @xmath9 at which the ion exits from the string ( or plane ) , i.e. far away from it where @xmath10 . in reality the furthest position from a string or plane of atoms is the middle of the channel , whose width we call @xmath11 . thus , @xmath12 channeling requires that @xmath13 , where @xmath14 is the smallest possible minimum distance of approach of the propagating ion with the row ( or plane ) for a given energy @xmath5 . since the potential @xmath15 decreases monotonically with increasing @xmath16 , @xmath17 . using eq . [ eq : consetrans ] , this can be further translated into an upper bound on @xmath18 and on @xmath9 , the angle the ion makes with the string far away from it , @xmath19 @xmath20 is the maximum angle the ion can make with the string far away from it ( i.e. in the middle of the channel ) if the ion is channeled . at low enough @xmath5 , @xmath14 becomes close to @xmath21 , and the critical angle @xmath20 goes to zero . this means that there is a minimum energy below which channeling can not happen , even for ions moving initially in the middle of the channel . so far we have been considering static strings and planes , but the atoms in a crystal are actually vibrating . we use the debye model , and take into account thermal effects in the crystal through a modification of the critical distances which was found originally by morgan and van vliet @xcite and later by hobler @xcite to provide good agreement with simulations and data . it consists of taking the temperature corrected critical distance @xmath22 to be , @xmath23 ^ 2 } , \label{rcoft}\ ] ] where @xmath24 is the one dimensional rms vibration amplitude of the atoms in a crystal , and the factor @xmath25 in different references is a number between 1 and 2 @xcite . as shown in fig . [ compare - data ] , with this formalism and using @xmath26 we fit relatively well the critical angles measured at room temperature for b and p ions in a si crystal in several channels , for energies between 20 kev and 600 kev that hobler @xcite extracted from thermal wave measurements . ) and measured critical angles extracted from thermal wave measurements @xcite ( green , or gray if color not available , dots , joined by straight lines to guide the eye ) as a function of the energy of ( a ) b ions and ( b ) p ions propagating in a si crystal at t=20 @xmath27c , for the indicated axial and planar channels.,title="fig : " ] ) and measured critical angles extracted from thermal wave measurements @xcite ( green , or gray if color not available , dots , joined by straight lines to guide the eye ) as a function of the energy of ( a ) b ions and ( b ) p ions propagating in a si crystal at t=20 @xmath27c , for the indicated axial and planar channels.,title="fig : " ] + as an example , the static ( @xmath28 ) axial and planar critical distances are presented in fig . [ rc - psic - mv-100](a ) for the 100 channel in nai crystal , together with the amplitude of thermal vibration @xmath24 at 20 @xmath29c , and the thomas - fermi screening distances for na and i ions . [ rc - psic - mv-100](b ) shows the temperature corrected axial and planar critical angles at 20 @xmath29c ( with @xmath30 ) for the same channel as functions of energy of the traveling na and i ions . at 20 @xmath29c and ( b ) critical channeling angles at 20 @xmath29c with @xmath30 as a function of the energy of propagating na ( green / gray ) and i ( black ) ions in the @xmath31100@xmath32 axial and \{100 } planar channels . the screening radii shown as vertical lines are @xmath33 nm and @xmath34 nm @xcite.,title="fig : " ] at 20 @xmath29c and ( b ) critical channeling angles at 20 @xmath29c with @xmath30 as a function of the energy of propagating na ( green / gray ) and i ( black ) ions in the @xmath31100@xmath32 axial and \{100 } planar channels . the screening radii shown as vertical lines are @xmath33 nm and @xmath34 nm @xcite.,title="fig : " ] + the channeling of ions in a crystal depends not only on the angle their initial trajectory makes with strings or planes in the crystal , but also on their initial position . ions which start their motion close to the center of a channel , far from a string or plane , where they make an angle @xmath9 , are channeled if the angle is smaller than a critical angle ( as explain earlier ) and are not channeled otherwise . particles which start their motion in the middle of a channel ( as opposed to a lattice site ) must be incident upon the crystal . no data or simulations of na and i ions propagating in a nai crystal is available at low energies . we show that to a good approximation we can use analytic calculations and reproduce the channeling fraction in nai presented in ref . temperature corrections are neglected and we use a static lattice ( similar to the approach of ref . @xcite ) . for an incident angle @xmath9 with respect to each of the channels and an ion energy @xmath5 , the fraction @xmath35 of channeled incident ions for axial and planar channels is @xmath36 if @xmath9 is smaller than the critical angle for the corresponding channel and zero otherwise . with the static lattice without ( dot dashed lines ) and with ( solid lines ) dechanneling due to interactions with tl impurities . the results of dama are also included ( dashed lines).,title="fig : " ] with the static lattice without ( dot dashed lines ) and with ( solid lines ) dechanneling due to interactions with tl impurities . the results of dama are also included ( dashed lines).,title="fig : " ] to find the total fraction of channeled incident nuclei , we average @xmath37 over the incident direction . the integrals can not be solved analytically , so we integrated numerically by performing a riemann sum once the sphere of directions has been divided using the hierarchical equal area iso - latitude pixelization ( healpix ) method @xcite . the healpix method uses an algorithm to deal with the pixelization of data on a sphere , and it is useful to compute integrals over direction by dividing the surface of a sphere into many pixels , computing the integrand at each pixel ( i.e. each direction , see fig . [ dama](a ) ) , and finally summing up the values of all pixels over the sphere . a channeled ion can be pushed out of a channel by an interaction with an impurity such as the atoms of tl in nai ( tl ) . here we will simply assume that if a channeled ion interacts with a tl atom it becomes dechanneled and thus it does not contribute to the fully channeled fraction any longer . we thus neglect the possibility that after the interaction the ion may reenter into a channel , either the same or another . [ dama](a ) shows the axial and planar channels of the nai crystal for incoming na ions with an energy of 50 kev . we include here only the channels with lower crystallographic indices 100 , 110 and 111 . the fraction of channeled incoming na and i ions after including dechanneling in the way just described is shown in fig . [ dama](b ) . our results agree well with those published by the dama collaboration @xcite , also included in the figure . the recoiling nuclei start initially from lattice sites ( or very close to them ) , thus blocking effects are important . in fact , as argued originally by lindhard @xcite , in a perfect lattice and in the absence of energy - loss processes the probability that a particle starting from a lattice site is channeled would be zero . the argument uses statistical mechanics in which the probability of particle paths related by time - reversal is the same . thus the probability of an incoming ion to have a particular path within the crystal is the same as the probability of the same ion to move backwards along the same path @xcite . this is what lindhard called the rule of reversibility " . using this rule , since the probability of an incoming channeled ion to get very close to a lattice site is zero , the probability of the same ion to move in the time - reversed path , starting at a nuclear site and ending inside a channel , is zero too . however , any departure of the actual lattice from a perfect lattice , for example due to vibrations of the atoms in the lattice , would violate the conditions of this argument and allow for some of the recoiling lattice nuclei to be channeled , as already understood in the 70 s @xcite . we now estimate the effect using the formalism presented so far . for axial channels , the probability distribution function @xmath38 of the perpendicular distance to the row of the colliding atom due to thermal vibrations can be represented by a two - dimensional gaussian . the channeled fraction of nuclei with recoil energy @xmath5 making an initial angle @xmath6 with respect to the axis is given by the fraction of nuclei which can be found at a distance @xmath39 larger than minimum distance @xmath40 from the row at the moment of collision , @xmath41 figure [ fracnai - final ] shows what we consider to be our main predictions for the range expected as an upper limit to the channeling fraction in nai ( tl ) at 239 k for two different assumptions for the effect of thermal vibrations in the lattice , which depend on the value of the parameter @xmath25 used in the temperature corrected critical distances of approach . dechanneling is ignored in fig . [ fracnai - final](a ) and taken into account in fig . [ fracnai - final](b ) . ( black ) and @xmath26 ( green / gray ) cases ( a ) without and ( b ) with dechanneling included.,title="fig : " ] ( black ) and @xmath26 ( green / gray ) cases ( a ) without and ( b ) with dechanneling included.,title="fig : " ] + our results for the geometric total channeling fraction for si ions propagating in a si crystal and ge ions propagating in a ge crystal at different temperatures are shown in figs . [ fracsig - difft - c1 ] and [ fracsig - difft - c2 ] for the two cases of @xmath30 and @xmath26 , respectively . please note that we have not considered the possibility of dechanneling of initially channeled ions , due to imperfections in si and ge crystals . any mechanism of dechanneling will decrease the fractions obtained here for si and ge . c ( orange or medium gray ) , t=600 @xmath29c ( green or light gray ) , 293 k ( black ) , and 44 mk ( blue or dark gray ) in the approximation of @xmath30.,title="fig : " ] c ( orange or medium gray ) , t=600 @xmath29c ( green or light gray ) , 293 k ( black ) , and 44 mk ( blue or dark gray ) in the approximation of @xmath30.,title="fig : " ] + but for @xmath26.,title="fig : " ] but for @xmath26.,title="fig : " ] + we have studied the channeling of ions recoiling after collisions with wimps within nai ( tl ) , si and ge crystals . channeled ions move within the crystal along symmetry axes and planes and suffer a series of small - angle scatterings that maintain them in the open channels " between the rows or planes of lattice atoms and thus penetrate much further into the crystal than in other directions . ions which start their motion close to the center of a channel , at an initial angle @xmath9 , are channeled if the initial angle is smaller than the critical angle in eq . [ psicritaxial ] , and are not channeled otherwise . we have found that the channeling of lattice ions recoiling after a collision with a wimp is very different from the case of incident ions , and that the channeling fraction is smaller . as argued originally by lindhard @xcite , in a perfect lattice and in the absence of energy - loss processes , the probability that a particle starting from a lattice site is channeled would be zero . however , due to vibrations in the crystal , the atom that interacts with a wimp may be displaced from its position in a perfect lattice , and there is a non - zero probability of channeling ( as given in eq . [ chiaxial ] ) . as we see in fig . [ fracnai - final](a ) for nai , without including dechanneling , the channeling fraction is never larger than 5% and the maximum happens at 100 s of kev . this maximum occurs because the critical distances decrease with the ion energy @xmath5 , making channeling more probable , and the critical angles also decrease with @xmath5 , making channeling less probable . the simple extreme model of dechanneling we used for nai predicts much smaller fractions , at most in the 0.1% level , with the maximum shifted to small energies , less than 10 kev ( see fig . [ fracnai - final](b ) ) . this reduction may eventually prove to be too extreme and at present we do not have a better formalism to model dechanneling . with the simple model of dechanneling we used for nai , we could reproduce the channeling fractions computed by the dama collaboration ( which , however , apply to ions which start their motion close to the middle of a channel and not to the case of wimp direct detection ) . if the values found by hobler @xcite , and also by us above ( see fig . [ compare - data ] ) , to reproduce measured channeling angles in b and p propagating in si apply also to the propagation of si ions in si , then the case of @xmath26 should be chosen and the channeling fractions would never be larger than 0.3% . moreover , increasing the temperature of a crystal usually increases the fraction of channeled recoiling ions ( see fig . [ fracsig - difft - c1 ] ) , but not always . sometimes the opposite happens ( see fig . [ fracsig - difft - c2 ] ) . the @xmath30 choice leads to channeling fractions close to 1% for si and ge . the analytical approach used here can successfully describe qualitative features of the channeling and blocking effects , but should be complemented by data fitting of parameters and by simulations to obtain a good quantitative description too . thus our results should in the last instance be checked by using some of the many sophisticated monte carlo simulation programs . n.b . and graciela gelmini were supported in part by the us department of energy grant de - fg03 - 91er40662 , task c. paolo gondolo was supported in part by the nfs grant phy-0456825 at the university of utah . we would like to thank s. nussinov and f. avignone for several important discussions about their work , and j. u andersen , d. s. gemmell , d. v. morgan , g. hobler , and kai nordlund for some exchange of information . we also thank p. belli for several conversations .

the channeling of the ion recoiling after a collision with a wimp changes the ionization signal in direct detection experiments , producing a larger signal than otherwise expected . we give estimates of the fraction of channeled recoiling ions in nai ( tl ) , si and ge crystals using analytic models produced since the 1960 s and 70 s to describe channeling and blocking effects . we find that the channeling fraction of recoiling lattice nuclei is smaller than that of ions that are injected into the crystal and that it is strongly temperature dependent . address = department of physics and astronomy , ucla , 475 portola plaza , los angeles , ca 90095 , usa , [email protected]

<s>[INST]channeling and blocking effects in crystals refer to the orientation dependence of charged ion penetration in crystals . in the channeling effect " ions incident upon a crystal along symmetry axes and planes suffer a series of small - angle scatterings that maintain them in the open channels " between the rows or planes of lattice atoms and thus penetrate much further into the crystal than in other directions . channeled incoming ions do not get close to lattice sites , where they would be deflected at large angles . the blocking effect " consists in a reduction of the flux of ions originating in lattice sites along symmetry axes and planes , creating what is called a blocking dip " in the flux of ions exiting from a thin enough crystal as a function of the angle with respect to a symmetry axis or plane . these effects were first observed in the 1960 s and are used in crystallography , in the study of lattice disorder , ion implantation , surfaces , interfaces and epitaxial layers , in measurements of short nuclear lifetimes etc . in particular , avoiding channeling is essential in the manufacturing of semiconductor devices , since ion implantation at a controlled depth is the primary technique . ion channeling in nai ( tl ) was first observed in 1973 by altman _ et al . _ they observed that channeled ions produce more scintillation light because they lose most of their energy via electronic stopping rather than nuclear stopping . the potential importance of the channeling effect for direct dark matter detection was first pointed out by sekiya _ et al . _ @xcite and subsequently for nai ( tl ) by drobyshevski @xcite and by the dama collaboration @xcite . when na or i ions recoiling after a collision with a dark matter wimp ( weakly interacting massive particle ) move along crystal axes and planes , their quenching factor is approximately @xmath0 instead of @xmath1 and @xmath2 , since they give their energy to electrons . ion channeling in crystals could give rise to a daily modulation due to the preferred direction of the dark matter flux arriving on the earth . earth s daily rotation naturally changes the direction of the `` wimp wind '' with respect to the crystal axes , which produces a daily modulation in the measured recoil energy ( equivalent to a modulation of the factor @xmath3 ) . et al . _ @xcite pointed this out for stilbene crystals , and avignone , creswick , and nussinov @xcite for nai ( tl ) crystals , although the available estimates of the strength of these daily modulations are somewhat simplistic . my collaborators , graciela gelmini and paolo gondolo , and i @xcite present here our analytic calculations of the channeling fraction in nai ( tl ) , si and ge crystals . our calculation is based on the classical analytic models developed in the 1960 s and 70 s , in particular by lindhard @xcite . we use the continuum string and plane model , in which the screened thomas - fermi potential is averaged over a direction parallel to a row or a plane . this averaged potential @xmath4 is considered to be uniformly smeared along the row or plane of atoms , which is a good approximation if the propagating ion interacts with many lattice atoms in the row or plane by a correlated series of many consecutive glancing collisions with lattice atoms . just one row or plane is considered in this model . lindhard proved that for an ion propagating with kinetic energy @xmath5 , and for small angle @xmath6 between the ion s trajectory and the atomic row ( or plane ) in the direction perpendicular to the row ( or plane ) , the so called transverse energy " , @xmath7 is conserved . the conservation of the transverse energy provides a definition of the minimum distance of approach to the string ( or plane ) of atoms , @xmath8 , at which the trajectory of the ion makes a zero angle with the string ( or plane ) , and also of the angle @xmath9 at which the ion exits from the string ( or plane ) , i.e. far away from it where @xmath10 . in reality the furthest position from a string or plane of atoms is the middle of the channel , whose width we call @xmath11 . thus , @xmath12 channeling requires that @xmath13 , where @xmath14 is the smallest possible minimum distance of approach of the propagating ion with the row ( or plane ) for a given energy @xmath5 . since the potential @xmath15 decreases monotonically with increasing @xmath16 , @xmath17 . using eq . [ eq : consetrans ] , this can be further translated into an upper bound on @xmath18 and on @xmath9 , the angle the ion makes with the string far away from it , @xmath19 @xmath20 is the maximum angle the ion can make with the string far away from it ( i.e. in the middle of the channel ) if the ion is channeled . at low enough @xmath5 , @xmath14 becomes close to @xmath21 , and the critical angle @xmath20 goes to zero . this means that there is a minimum energy below which channeling can not happen , even for ions moving initially in the middle of the channel . so far we have been considering static strings and planes , but the atoms in a crystal are actually vibrating . we use the debye model , and take into account thermal effects in the crystal through a modification of the critical distances which was found originally by morgan and van vliet @xcite and later by hobler @xcite to provide good agreement with simulations and data . it consists of taking the temperature corrected critical distance @xmath22 to be , @xmath23 ^ 2 } , \label{rcoft}\ ] ] where @xmath24 is the one dimensional rms vibration amplitude of the atoms in a crystal , and the factor @xmath25 in different references is a number between 1 and 2 @xcite . as shown in fig . [ compare - data ] , with this formalism and using @xmath26 we fit relatively well the critical angles measured at room temperature for b and p ions in a si crystal in several channels , for energies between 20 kev and 600 kev that hobler @xcite extracted from thermal wave measurements . ) and measured critical angles extracted from thermal wave measurements @xcite ( green , or gray if color not available , dots , joined by straight lines to guide the eye ) as a function of the energy of ( a ) b ions and ( b ) p ions propagating in a si crystal at t=20 @xmath27c , for the indicated axial and planar channels.,title="fig : " ] ) and measured critical angles extracted from thermal wave measurements @xcite ( green , or gray if color not available , dots , joined by straight lines to guide the eye ) as a function of the energy of ( a ) b ions and ( b ) p ions propagating in a si crystal at t=20 @xmath27c , for the indicated axial and planar channels.,title="fig : " ] + as an example , the static ( @xmath28 ) axial and planar critical distances are presented in fig . [ rc - psic - mv-100](a ) for the 100 channel in nai crystal , together with the amplitude of thermal vibration @xmath24 at 20 @xmath29c , and the thomas - fermi screening distances for na and i ions . [ rc - psic - mv-100](b ) shows the temperature corrected axial and planar critical angles at 20 @xmath29c ( with @xmath30 ) for the same channel as functions of energy of the traveling na and i ions . at 20 @xmath29c and ( b ) critical channeling angles at 20 @xmath29c with @xmath30 as a function of the energy of propagating na ( green / gray ) and i ( black ) ions in the @xmath31100@xmath32 axial and \{100 } planar channels . the screening radii shown as vertical lines are @xmath33 nm and @xmath34 nm @xcite.,title="fig : " ] at 20 @xmath29c and ( b ) critical channeling angles at 20 @xmath29c with @xmath30 as a function of the energy of propagating na ( green / gray ) and i ( black ) ions in the @xmath31100@xmath32 axial and \{100 } planar channels . the screening radii shown as vertical lines are @xmath33 nm and @xmath34 nm @xcite.,title="fig : " ] + the channeling of ions in a crystal depends not only on the angle their initial trajectory makes with strings or planes in the crystal , but also on their initial position . ions which start their motion close to the center of a channel , far from a string or plane , where they make an angle @xmath9 , are channeled if the angle is smaller than a critical angle ( as explain earlier ) and are not channeled otherwise . particles which start their motion in the middle of a channel ( as opposed to a lattice site ) must be incident upon the crystal . no data or simulations of na and i ions propagating in a nai crystal is available at low energies . we show that to a good approximation we can use analytic calculations and reproduce the channeling fraction in nai presented in ref . temperature corrections are neglected and we use a static lattice ( similar to the approach of ref . @xcite ) . for an incident angle @xmath9 with respect to each of the channels and an ion energy @xmath5 , the fraction @xmath35 of channeled incident ions for axial and planar channels is @xmath36 if @xmath9 is smaller than the critical angle for the corresponding channel and zero otherwise . with the static lattice without ( dot dashed lines ) and with ( solid lines ) dechanneling due to interactions with tl impurities . the results of dama are also included ( dashed lines).,title="fig : " ] with the static lattice without ( dot dashed lines ) and with ( solid lines ) dechanneling due to interactions with tl impurities . the results of dama are also included ( dashed lines).,title="fig : " ] to find the total fraction of channeled incident nuclei , we average @xmath37 over the incident direction . the integrals can not be solved analytically , so we integrated numerically by performing a riemann sum once the sphere of directions has been divided using the hierarchical equal area iso - latitude pixelization ( healpix ) method @xcite . the healpix method uses an algorithm to deal with the pixelization of data on a sphere , and it is useful to compute integrals over direction by dividing the surface of a sphere into many pixels , computing the integrand at each pixel ( i.e. each direction , see fig . [ dama](a ) ) , and finally summing up the values of all pixels over the sphere . a channeled ion can be pushed out of a channel by an interaction with an impurity such as the atoms of tl in nai ( tl ) . here we will simply assume that if a channeled ion interacts with a tl atom it becomes dechanneled and thus it does not contribute to the fully channeled fraction any longer . we thus neglect the possibility that after the interaction the ion may reenter into a channel , either the same or another . [ dama](a ) shows the axial and planar channels of the nai crystal for incoming na ions with an energy of 50 kev . we include here only the channels with lower crystallographic indices 100 , 110 and 111 . the fraction of channeled incoming na and i ions after including dechanneling in the way just described is shown in fig . [ dama](b ) . our results agree well with those published by the dama collaboration @xcite , also included in the figure . the recoiling nuclei start initially from lattice sites ( or very close to them ) , thus blocking effects are important . in fact , as argued originally by lindhard @xcite , in a perfect lattice and in the absence of energy - loss processes the probability that a particle starting from a lattice site is channeled would be zero . the argument uses statistical mechanics in which the probability of particle paths related by time - reversal is the same . thus the probability of an incoming ion to have a particular path within the crystal is the same as the probability of the same ion to move backwards along the same path @xcite . this is what lindhard called the rule of reversibility " . using this rule , since the probability of an incoming channeled ion to get very close to a lattice site is zero , the probability of the same ion to move in the time - reversed path , starting at a nuclear site and ending inside a channel , is zero too . however , any departure of the actual lattice from a perfect lattice , for example due to vibrations of the atoms in the lattice , would violate the conditions of this argument and allow for some of the recoiling lattice nuclei to be channeled , as already understood in the 70 s @xcite . we now estimate the effect using the formalism presented so far . for axial channels , the probability distribution function @xmath38 of the perpendicular distance to the row of the colliding atom due to thermal vibrations can be represented by a two - dimensional gaussian . the channeled fraction of nuclei with recoil energy @xmath5 making an initial angle @xmath6 with respect to the axis is given by the fraction of nuclei which can be found at a distance @xmath39 larger than minimum distance @xmath40 from the row at the moment of collision , @xmath41 figure [ fracnai - final ] shows what we consider to be our main predictions for the range expected as an upper limit to the channeling fraction in nai ( tl ) at 239 k for two different assumptions for the effect of thermal vibrations in the lattice , which depend on the value of the parameter @xmath25 used in the temperature corrected critical distances of approach . dechanneling is ignored in fig . [ fracnai - final](a ) and taken into account in fig . [ fracnai - final](b ) . ( black ) and @xmath26 ( green / gray ) cases ( a ) without and ( b ) with dechanneling included.,title="fig : " ] ( black ) and @xmath26 ( green / gray ) cases ( a ) without and ( b ) with dechanneling included.,title="fig : " ] + our results for the geometric total channeling fraction for si ions propagating in a si crystal and ge ions propagating in a ge crystal at different temperatures are shown in figs . [ fracsig - difft - c1 ] and [ fracsig - difft - c2 ] for the two cases of @xmath30 and @xmath26 , respectively . please note that we have not considered the possibility of dechanneling of initially channeled ions , due to imperfections in si and ge crystals . any mechanism of dechanneling will decrease the fractions obtained here for si and ge . c ( orange or medium gray ) , t=600 @xmath29c ( green or light gray ) , 293 k ( black ) , and 44 mk ( blue or dark gray ) in the approximation of @xmath30.,title="fig : " ] c ( orange or medium gray ) , t=600 @xmath29c ( green or light gray ) , 293 k ( black ) , and 44 mk ( blue or dark gray ) in the approximation of @xmath30.,title="fig : " ] + but for @xmath26.,title="fig : " ] but for @xmath26.,title="fig : " ] + we have studied the channeling of ions recoiling after collisions with wimps within nai ( tl ) , si and ge crystals . channeled ions move within the crystal along symmetry axes and planes and suffer a series of small - angle scatterings that maintain them in the open channels " between the rows or planes of lattice atoms and thus penetrate much further into the crystal than in other directions . ions which start their motion close to the center of a channel , at an initial angle @xmath9 , are channeled if the initial angle is smaller than the critical angle in eq . [ psicritaxial ] , and are not channeled otherwise . we have found that the channeling of lattice ions recoiling after a collision with a wimp is very different from the case of incident ions , and that the channeling fraction is smaller . as argued originally by lindhard @xcite , in a perfect lattice and in the absence of energy - loss processes , the probability that a particle starting from a lattice site is channeled would be zero . however , due to vibrations in the crystal , the atom that interacts with a wimp may be displaced from its position in a perfect lattice , and there is a non - zero probability of channeling ( as given in eq . [ chiaxial ] ) . as we see in fig . [ fracnai - final](a ) for nai , without including dechanneling , the channeling fraction is never larger than 5% and the maximum happens at 100 s of kev . this maximum occurs because the critical distances decrease with the ion energy @xmath5 , making channeling more probable , and the critical angles also decrease with @xmath5 , making channeling less probable . the simple extreme model of dechanneling we used for nai predicts much smaller fractions , at most in the 0.1% level , with the maximum shifted to small energies , less than 10 kev ( see fig . [ fracnai - final](b ) ) . this reduction may eventually prove to be too extreme and at present we do not have a better formalism to model dechanneling . with the simple model of dechanneling we used for nai , we could reproduce the channeling fractions computed by the dama collaboration ( which , however , apply to ions which start their motion close to the middle of a channel and not to the case of wimp direct detection ) . if the values found by hobler @xcite , and also by us above ( see fig . [ compare - data ] ) , to reproduce measured channeling angles in b and p propagating in si apply also to the propagation of si ions in si , then the case of @xmath26 should be chosen and the channeling fractions would never be larger than 0.3% . moreover , increasing the temperature of a crystal usually increases the fraction of channeled recoiling ions ( see fig . [ fracsig - difft - c1 ] ) , but not always . sometimes the opposite happens ( see fig . [ fracsig - difft - c2 ] ) . the @xmath30 choice leads to channeling fractions close to 1% for si and ge . the analytical approach used here can successfully describe qualitative features of the channeling and blocking effects , but should be complemented by data fitting of parameters and by simulations to obtain a good quantitative description too . thus our results should in the last instance be checked by using some of the many sophisticated monte carlo simulation programs . n.b . and graciela gelmini were supported in part by the us department of energy grant de - fg03 - 91er40662 , task c. paolo gondolo was supported in part by the nfs grant phy-0456825 at the university of utah . we would like to thank s. nussinov and f. avignone for several important discussions about their work , and j. u andersen , d. s. gemmell , d. v. morgan , g. hobler , and kai nordlund for some exchange of information . we also thank p. belli for several conversations .[/INST] the channeling of the ion recoiling after a collision with a wimp changes the ionization signal in direct detection experiments , producing a larger signal than otherwise expected . we give estimates of the fraction of channeled recoiling ions in nai ( tl ) , si and ge crystals using analytic models produced since the 1960 s and 70 s to describe channeling and blocking effects . we find that the channeling fraction of recoiling lattice nuclei is smaller than that of ions that are injected into the crystal and that it is strongly temperature dependent . address = department of physics and astronomy , ucla , 475 portola plaza , los angeles , ca 90095 , usa , [email protected] </s>

the study of strongly interacting matter at extreme energy densities as produced in ultrarelativistic heavy ion collisions is the aim of the alice detector @xcite at the large hadron collider ( lhc ) at cern . quantum chromodynamics ( qcd ) @xcite predicts that at sufficiently high energy density , of the order of 0.5 gev/@xmath3 @xcite , a deconfined state of quarks and gluons is produced , the so - called quark gluon plasma ( qgp ) . many different observables are used to find experimental evidence and subsequently study the properties of the qgp . in this contribution we will focus on the measurement of event by event net charge fluctuations and charge balance functions . the analyses use the data taken in pb pb collisions at @xmath2 tev and make use of the excellent tracking capabilities of the alice time projection chamber ( tpc ) . insight into the possible existence of a qgp can be gained by determining the relevant degrees of freedom for the electric charge of the system produced in a heavy ion collision @xcite . in a hadron ( resonance ) gas these are mesons and baryons , while in the qgp phase these would be quarks in the simplest case ( neglecting more complex bound states ) . a significant difference between the two phases is expected in measuring event by event net charge fluctuations per charged degree of freedom : @xmath4 with @xmath5 the variance of the net charge @xmath6 and @xmath7 the average number of all measured charged particles per event . the variable d is close to 1 for the case of a qgp , and is predicted to be close to 3 for a hadron ( resonance ) gas @xcite . in the experiment , charge fluctuations are best studied by calculating the quantity @xmath8 , which is strongly connected to the variable d via the relationship shown in eq . [ equ : d ] and is defined as : @xmath9 taking into account global charge conservation and finite acceptance , one obtains the corrected value of @xmath10 : @xmath11 where @xmath12 is the average total number of charged particles produced over the full phase space . in the left panel of fig . [ fig : chargefluc : nudyn ] the values of @xmath13 are shown for pp and pb pb collisions as a function of the mean number of participating nucleons @xmath14 in two pseudorapidity windows @xmath15 and @xmath16 . the shaded bands indicate the predictions for a hadron resonance gas ( hg ) and the qgp @xcite . the data points show a monotonic decreasing dependence with @xmath14 and lie clearly below the hg , but above the qgp expectation . on the other hand , the results from the hijing event generator for both pseudorapidity windows do not show any dependence on @xmath17 and are in the vicinity of the hg band . the observed pseudorapidity dependence , as shown in the right panel of fig . [ fig : chargefluc : nudyn ] , hints to a dilution of the primordial fluctuations during the evolution of the system from hadronization to kinetic freeze out because of the diffusion of charged hadrons in rapidity @xcite . it can be parametrized with @xmath18 with @xmath19 being a measure for the diffusion . it was proposed to measure the creation time of particles via the correlations between positive and negatively charged pairs as a function of rapidity @xcite . assuming these pairs being created at the same space time point and correlated in momentum space due to a strong collective expansion , their separation in pseudorapidity @xmath0 depends not only on the initial momentum difference but also on the length of the rescattering phase . furthermore , it was shown that the balance function for the relative azimuthal angle of the charge anticharge pair can probe the collective motion of the produced system and in particular its radial flow @xcite . the definition of the balance function ( e.g. for the pseudorapidity difference @xmath0 ) reads : @xmath20 \label{eq : bfdefinitionineta}\ ] ] with @xmath21 the number of @xmath22 particle pairs and @xmath23 the number of positive ( negative ) particles in the analyzed phase space . in fig . [ fig : bf ] the balance functions are shown for the 5% most central and for more peripheral ( 6070% ) pb pb collisions as a function of @xmath0 and @xmath1 @xcite . furthermore , a comparison to results from different mc event generators is shown . hijing @xcite produces charges early in the collision history , mainly via string fragmentation , and includes no collective motion , e.g. radial flow . it is not able to match the data points for @xmath24 and @xmath25 for central collisions . only in the most peripheral events the hijing results for @xmath24 are consistent with the alice data , which shows a strong centrality dependence , that is not observed in hijing . ampt ( string melting ) @xcite , on the other hand , with parameters tuned to reproduce the measured elliptic flow values of non identified particles at the lhc , shows an agreement in @xmath25 , not only in the most central bin but for the whole centrality dependence . this can be understood as collective flow being the determining source of balancing charge correlation in @xmath1 . for @xmath24 the balance functions are similar to hijing . in summary , dynamical net charge fluctuations were presented as a function of centrality and pseudorapidity and have a value below the expectation for a hadron resonance gas and above that of the qgp . the balance functions for charged particles show a strong narrowing with increasing centrality , which can be reproduced in @xmath1 with a model including collective effects , e.g. flow , but not in @xmath0 . the analysis of net charge fluctuations will be extended to higher moments and balance functions will be studied for identified particles and regarding their transverse momentum and event plane dependence .

the measurement of event by event fluctuations and charge dependent particle correlations are used to study properties of nuclear matter at high temperatures as produced in ultrarelativistic heavy ion collisions . we present results for event by event net charge fluctuations and charge balance functions in @xmath0 and @xmath1 in pb pb collisions at @xmath2 tev .

<s>[INST]the study of strongly interacting matter at extreme energy densities as produced in ultrarelativistic heavy ion collisions is the aim of the alice detector @xcite at the large hadron collider ( lhc ) at cern . quantum chromodynamics ( qcd ) @xcite predicts that at sufficiently high energy density , of the order of 0.5 gev/@xmath3 @xcite , a deconfined state of quarks and gluons is produced , the so - called quark gluon plasma ( qgp ) . many different observables are used to find experimental evidence and subsequently study the properties of the qgp . in this contribution we will focus on the measurement of event by event net charge fluctuations and charge balance functions . the analyses use the data taken in pb pb collisions at @xmath2 tev and make use of the excellent tracking capabilities of the alice time projection chamber ( tpc ) . insight into the possible existence of a qgp can be gained by determining the relevant degrees of freedom for the electric charge of the system produced in a heavy ion collision @xcite . in a hadron ( resonance ) gas these are mesons and baryons , while in the qgp phase these would be quarks in the simplest case ( neglecting more complex bound states ) . a significant difference between the two phases is expected in measuring event by event net charge fluctuations per charged degree of freedom : @xmath4 with @xmath5 the variance of the net charge @xmath6 and @xmath7 the average number of all measured charged particles per event . the variable d is close to 1 for the case of a qgp , and is predicted to be close to 3 for a hadron ( resonance ) gas @xcite . in the experiment , charge fluctuations are best studied by calculating the quantity @xmath8 , which is strongly connected to the variable d via the relationship shown in eq . [ equ : d ] and is defined as : @xmath9 taking into account global charge conservation and finite acceptance , one obtains the corrected value of @xmath10 : @xmath11 where @xmath12 is the average total number of charged particles produced over the full phase space . in the left panel of fig . [ fig : chargefluc : nudyn ] the values of @xmath13 are shown for pp and pb pb collisions as a function of the mean number of participating nucleons @xmath14 in two pseudorapidity windows @xmath15 and @xmath16 . the shaded bands indicate the predictions for a hadron resonance gas ( hg ) and the qgp @xcite . the data points show a monotonic decreasing dependence with @xmath14 and lie clearly below the hg , but above the qgp expectation . on the other hand , the results from the hijing event generator for both pseudorapidity windows do not show any dependence on @xmath17 and are in the vicinity of the hg band . the observed pseudorapidity dependence , as shown in the right panel of fig . [ fig : chargefluc : nudyn ] , hints to a dilution of the primordial fluctuations during the evolution of the system from hadronization to kinetic freeze out because of the diffusion of charged hadrons in rapidity @xcite . it can be parametrized with @xmath18 with @xmath19 being a measure for the diffusion . it was proposed to measure the creation time of particles via the correlations between positive and negatively charged pairs as a function of rapidity @xcite . assuming these pairs being created at the same space time point and correlated in momentum space due to a strong collective expansion , their separation in pseudorapidity @xmath0 depends not only on the initial momentum difference but also on the length of the rescattering phase . furthermore , it was shown that the balance function for the relative azimuthal angle of the charge anticharge pair can probe the collective motion of the produced system and in particular its radial flow @xcite . the definition of the balance function ( e.g. for the pseudorapidity difference @xmath0 ) reads : @xmath20 \label{eq : bfdefinitionineta}\ ] ] with @xmath21 the number of @xmath22 particle pairs and @xmath23 the number of positive ( negative ) particles in the analyzed phase space . in fig . [ fig : bf ] the balance functions are shown for the 5% most central and for more peripheral ( 6070% ) pb pb collisions as a function of @xmath0 and @xmath1 @xcite . furthermore , a comparison to results from different mc event generators is shown . hijing @xcite produces charges early in the collision history , mainly via string fragmentation , and includes no collective motion , e.g. radial flow . it is not able to match the data points for @xmath24 and @xmath25 for central collisions . only in the most peripheral events the hijing results for @xmath24 are consistent with the alice data , which shows a strong centrality dependence , that is not observed in hijing . ampt ( string melting ) @xcite , on the other hand , with parameters tuned to reproduce the measured elliptic flow values of non identified particles at the lhc , shows an agreement in @xmath25 , not only in the most central bin but for the whole centrality dependence . this can be understood as collective flow being the determining source of balancing charge correlation in @xmath1 . for @xmath24 the balance functions are similar to hijing . in summary , dynamical net charge fluctuations were presented as a function of centrality and pseudorapidity and have a value below the expectation for a hadron resonance gas and above that of the qgp . the balance functions for charged particles show a strong narrowing with increasing centrality , which can be reproduced in @xmath1 with a model including collective effects , e.g. flow , but not in @xmath0 . the analysis of net charge fluctuations will be extended to higher moments and balance functions will be studied for identified particles and regarding their transverse momentum and event plane dependence .[/INST] the measurement of event by event fluctuations and charge dependent particle correlations are used to study properties of nuclear matter at high temperatures as produced in ultrarelativistic heavy ion collisions . we present results for event by event net charge fluctuations and charge balance functions in @xmath0 and @xmath1 in pb pb collisions at @xmath2 tev . </s>

Some of the area being searched for two adults and four children missing in Nevada's Pershing County is shown Monday, Dec. 9, 2013. Rescue teams racing against the clock and the bitter cold are working... (Associated Press) Rescue teams racing against the clock and the bitter cold worked into the night and were hoping to resume an aerial search Tuesday for a couple and four children who have been missing since Sunday when they went to play in the snow in the remote mountains of northwest Nevada. The temperature was expected to drop below zero again early Tuesday after plunging to minus-16 degrees the day before in Lovelock in the rugged area where the group was believed to be, about 100 miles northeast of Reno. "It's got to be brutal out there," said Mark Turney, a spokesman for the U.S. Bureau of Land Management. "Let's hope they are found quick." Pershing County deputies said aircraft and crews on the ground were searching for James Glanton, 34, his girlfriend Christina McIntee, 25, and the four children: a 10-year-old, two 4-year-olds and a 3-year-old. Two of the kids are the adults' children, while one is a niece and one is a nephew, according to the Pershing County sheriff's office, which identified them as Evan Glanton, Chloe Glanton, Shelby Fitzpatrick and Tate McIntee. The family has not had any communication with others since they went missing, according to Sheila Reitz of the sheriff's office. They went to the Seven Troughs area on isolated federal land about noon on Sunday in a silver Jeep with a black top, authorities said. It was unclear what supplies they might have been carrying. "I'm hoping they all huddled together and stayed in the Jeep," said Nevada Highway Patrol Trooper Chuck Allen, who added that the area has spotty cellular coverage. "That would be a best-case scenario." The search for the group began Sunday evening. A Navy search-and-rescue team and the Civil Air Patrol, an all-volunteer auxiliary of the U.S. Air Force, were assisting the sheriff's office by searching a concentrated area where the group is thought to be. Two planes scoured the area Monday and three could go out Tuesday if the group isn't found, Maj. Thomas Cooper said. Several inches of snow was on the ground in the area, but the black top on the silver 2005 Jeep should help make it easier to spot from the air, authorities said. While the cold made for dangerous conditions, the clear weather was working in the pilots' favor. The forecast called for mostly sunny again on Tuesday with clouds moving in Tuesday night. The cold "is not a big issue," Cooper said. "We're concerned about stuff coming out of the sky." The area is on land managed by the BLM. "It is a beautiful area out there. Parts of it are extremely remote," said Turney, who was there three weeks ago. He said that other than one main road, most of the roads are dirt and more easily traveled by ATVs or other off-road vehicles. "The roads are basically improved two-tracks out there," Turney said. The Seven Troughs area is named after a series of seven parallel canyons below Seven Trough Peak _ elevation 7,474 feet _ in the Kamma Mountains stretching north across the Pershing-Humboldt county line. It's about 20 miles northwest of where Lovelock sits on Interstate 80 and about 20 miles southeast of the Black Rock Desert, where the annual Burning Man counterculture festival is held. "It's remote, and it's rocky," Nevada Department of Wildlife spokesman Chris Healy said. "There are good dirt roads into the place, but they are dirt roads, and it is cold and snow so it's not ideal." Healy said Seven Troughs is a popular area for hunting chukars, a pheasant-sized winter game bird. "So it's not the kind of area where there would be nobody around," he said Monday. "But most chukar hunters are smart enough not to go out in the weather we have now." ___ Rindels reported from Las Vegas. ||||| Cathleen Allison / AP Two adults and four children arrive at Pershing General Hospital on Tuesday after being lost for two days in the frigid mountains near Lovelock, Nev. By Elisha Fieldstadt and Erin McClam, NBC News A couple and four children who survived two days in the sub-zero Nevada mountains, apparently because one of them built a fire and heated rocks to load into their rolled-over Jeep, expressed thanks Wednesday for “care and love from our community and the nation.” In a statement released by the hospital where they are recovering, the six called their rescuers “valiant” and asked for privacy. One of the children, a 10-year-old girl, signed her name in blue ink in big, careful, cursive letters. The statement offered no new details on the group’s harrowing two days in the frigid cold of the mountain range. The six — James Glanton, his girlfriend, Christina McIntee, their two children and McIntee’s niece and nephew — were found in fairly good shape Tuesday after a rescuer spotted the Jeep. The children range in age from 3 to 10. The rescuer, Chris Montes, said that Glanton built a fire inside a spare tire, used brush and wood from nearby for kindling, and heated rocks to take back to the Jeep. His ingenuity was hailed as the difference between life and death. The temperature on the range was 21 degrees below zero Sunday night, and below zero again Monday night. A family of six is recovering in a hospital after being stranded in subzero conditions for three days and two nights after their Jeep overturned. NBC's Miguel Almaguer reports. Authorities called the group’s survival miraculous and suggested that at least one of them might have died had they tried to walk to safety rather than holing up in the car to stay warm. “It’s a miracle. It really is,” said Richard Machado, the Pershing County sheriff. The ordeal began after the couple and children failed to return Sunday from a trip to play in the snow near their hometown of Lovelock, in Nevada’s high desert, about 100 miles northeast of Reno. The Jeep had been seen Sunday “doing wheelies or doughnuts” at a mining camp in Seven Troughs, a dispatch supervisor said. Officials said the couple had not taken food or water with them. The sheriff’s office got word shortly late Tuesday morning that the Jeep had been found, rolled on its roof, with the group inside, “down off a little slope,” said Leslie Steward, a police dispatcher. The Associated Press reported that Montes first saw what looked to be children’s footprints in the snow before spotting tire tracks that led into a remote canyon but not back out. The Reno Gazette-Journal newspaper reported that Montes and another searcher, Salvador Paredes, hiked to the spot. Paredes went to find cellphone service while Montes approached Glanton. Glanton was startled at first, Montes told the newspaper. “And he reached out and caught me, and he probably thought I was his wife first,” he said. “He looked up and saw my face, and it surprised him a little bit.” Cathleen Allison / AP Marty Happy, holding his son Ryder, 2, hugs David Mosier after they received word that a group of six people had been found alive after being stranded for two days in the frigid mountains near Lovelock, Nev., on Tuesday. Mosier's 10-year-old cousin was among the group who were treated at a local hospital Tuesday. “I think everybody was thinking the worst for a little bit,” said Montes, a longtime friend of Glanton’s who hunts in the area. U.S. Civil Air Patrol and a search-and-rescue team started looking for the couple and children when they were reported missing Monday. Nevada wing Civil Air Patrol Col. Timothy F. Hahn said that the family was found “four miles from civilization.” Hahn said the search team focused on areas without cellphone reception because the last indication of the group’s cellphone activity was early Sunday night. The CEO of the hospital said that the couple and children had not suffered frostbite but had “some exposure issues and dehydration.” “I’m relieved that God answered our prayers,” a cousin, David Mosier, told NBC affiliate KRNV. “They just told me that they found them and that’s all I wanted to hear.” The Associated Press contributed to this report. This story was originally published on

– A Nevada couple and four children went to "play in the snow" Sunday and never returned, according to the Pershing County Sheriff. James Glanton, 34, and Christina MacIntee, 25, took their two children, 3 and 4, and a 10-year old niece and 4-year-old nephew into the remote Seven Troughs area in northwest Nevada, about 20 miles southeast of the Black Rock Desert, where Burning Man is held each year. Family members reported the group missing Sunday night; they haven't been heard from since they left, the AP reports. Their silver Jeep was last seen "doing wheelies or donuts" at a mining camp, a dispatch supervisor tells NBC News. Temperatures in the mountains were "minus 21" Sunday night, she adds, and have been "brutal" since, according to a US Bureau of Land Management spokesperson. The search effort includes a Navy helicopter, planes, a search and rescue team, and a volunteer arm of the Air Force. "I'm hoping they all huddled together and stayed in the Jeep," says a Nevada Highway Patrol Trooper. "That would be a best-case scenario." Three planes could be dispatched to search for them today, and while several inches of snow have fallen, authorities hope the black top on their silver 2005 Jeep will help make it easier to spot from the air.

<s>[INST]Some of the area being searched for two adults and four children missing in Nevada's Pershing County is shown Monday, Dec. 9, 2013. Rescue teams racing against the clock and the bitter cold are working... (Associated Press) Rescue teams racing against the clock and the bitter cold worked into the night and were hoping to resume an aerial search Tuesday for a couple and four children who have been missing since Sunday when they went to play in the snow in the remote mountains of northwest Nevada. The temperature was expected to drop below zero again early Tuesday after plunging to minus-16 degrees the day before in Lovelock in the rugged area where the group was believed to be, about 100 miles northeast of Reno. "It's got to be brutal out there," said Mark Turney, a spokesman for the U.S. Bureau of Land Management. "Let's hope they are found quick." Pershing County deputies said aircraft and crews on the ground were searching for James Glanton, 34, his girlfriend Christina McIntee, 25, and the four children: a 10-year-old, two 4-year-olds and a 3-year-old. Two of the kids are the adults' children, while one is a niece and one is a nephew, according to the Pershing County sheriff's office, which identified them as Evan Glanton, Chloe Glanton, Shelby Fitzpatrick and Tate McIntee. The family has not had any communication with others since they went missing, according to Sheila Reitz of the sheriff's office. They went to the Seven Troughs area on isolated federal land about noon on Sunday in a silver Jeep with a black top, authorities said. It was unclear what supplies they might have been carrying. "I'm hoping they all huddled together and stayed in the Jeep," said Nevada Highway Patrol Trooper Chuck Allen, who added that the area has spotty cellular coverage. "That would be a best-case scenario." The search for the group began Sunday evening. A Navy search-and-rescue team and the Civil Air Patrol, an all-volunteer auxiliary of the U.S. Air Force, were assisting the sheriff's office by searching a concentrated area where the group is thought to be. Two planes scoured the area Monday and three could go out Tuesday if the group isn't found, Maj. Thomas Cooper said. Several inches of snow was on the ground in the area, but the black top on the silver 2005 Jeep should help make it easier to spot from the air, authorities said. While the cold made for dangerous conditions, the clear weather was working in the pilots' favor. The forecast called for mostly sunny again on Tuesday with clouds moving in Tuesday night. The cold "is not a big issue," Cooper said. "We're concerned about stuff coming out of the sky." The area is on land managed by the BLM. "It is a beautiful area out there. Parts of it are extremely remote," said Turney, who was there three weeks ago. He said that other than one main road, most of the roads are dirt and more easily traveled by ATVs or other off-road vehicles. "The roads are basically improved two-tracks out there," Turney said. The Seven Troughs area is named after a series of seven parallel canyons below Seven Trough Peak _ elevation 7,474 feet _ in the Kamma Mountains stretching north across the Pershing-Humboldt county line. It's about 20 miles northwest of where Lovelock sits on Interstate 80 and about 20 miles southeast of the Black Rock Desert, where the annual Burning Man counterculture festival is held. "It's remote, and it's rocky," Nevada Department of Wildlife spokesman Chris Healy said. "There are good dirt roads into the place, but they are dirt roads, and it is cold and snow so it's not ideal." Healy said Seven Troughs is a popular area for hunting chukars, a pheasant-sized winter game bird. "So it's not the kind of area where there would be nobody around," he said Monday. "But most chukar hunters are smart enough not to go out in the weather we have now." ___ Rindels reported from Las Vegas. ||||| Cathleen Allison / AP Two adults and four children arrive at Pershing General Hospital on Tuesday after being lost for two days in the frigid mountains near Lovelock, Nev. By Elisha Fieldstadt and Erin McClam, NBC News A couple and four children who survived two days in the sub-zero Nevada mountains, apparently because one of them built a fire and heated rocks to load into their rolled-over Jeep, expressed thanks Wednesday for “care and love from our community and the nation.” In a statement released by the hospital where they are recovering, the six called their rescuers “valiant” and asked for privacy. One of the children, a 10-year-old girl, signed her name in blue ink in big, careful, cursive letters. The statement offered no new details on the group’s harrowing two days in the frigid cold of the mountain range. The six — James Glanton, his girlfriend, Christina McIntee, their two children and McIntee’s niece and nephew — were found in fairly good shape Tuesday after a rescuer spotted the Jeep. The children range in age from 3 to 10. The rescuer, Chris Montes, said that Glanton built a fire inside a spare tire, used brush and wood from nearby for kindling, and heated rocks to take back to the Jeep. His ingenuity was hailed as the difference between life and death. The temperature on the range was 21 degrees below zero Sunday night, and below zero again Monday night. A family of six is recovering in a hospital after being stranded in subzero conditions for three days and two nights after their Jeep overturned. NBC's Miguel Almaguer reports. Authorities called the group’s survival miraculous and suggested that at least one of them might have died had they tried to walk to safety rather than holing up in the car to stay warm. “It’s a miracle. It really is,” said Richard Machado, the Pershing County sheriff. The ordeal began after the couple and children failed to return Sunday from a trip to play in the snow near their hometown of Lovelock, in Nevada’s high desert, about 100 miles northeast of Reno. The Jeep had been seen Sunday “doing wheelies or doughnuts” at a mining camp in Seven Troughs, a dispatch supervisor said. Officials said the couple had not taken food or water with them. The sheriff’s office got word shortly late Tuesday morning that the Jeep had been found, rolled on its roof, with the group inside, “down off a little slope,” said Leslie Steward, a police dispatcher. The Associated Press reported that Montes first saw what looked to be children’s footprints in the snow before spotting tire tracks that led into a remote canyon but not back out. The Reno Gazette-Journal newspaper reported that Montes and another searcher, Salvador Paredes, hiked to the spot. Paredes went to find cellphone service while Montes approached Glanton. Glanton was startled at first, Montes told the newspaper. “And he reached out and caught me, and he probably thought I was his wife first,” he said. “He looked up and saw my face, and it surprised him a little bit.” Cathleen Allison / AP Marty Happy, holding his son Ryder, 2, hugs David Mosier after they received word that a group of six people had been found alive after being stranded for two days in the frigid mountains near Lovelock, Nev., on Tuesday. Mosier's 10-year-old cousin was among the group who were treated at a local hospital Tuesday. “I think everybody was thinking the worst for a little bit,” said Montes, a longtime friend of Glanton’s who hunts in the area. U.S. Civil Air Patrol and a search-and-rescue team started looking for the couple and children when they were reported missing Monday. Nevada wing Civil Air Patrol Col. Timothy F. Hahn said that the family was found “four miles from civilization.” Hahn said the search team focused on areas without cellphone reception because the last indication of the group’s cellphone activity was early Sunday night. The CEO of the hospital said that the couple and children had not suffered frostbite but had “some exposure issues and dehydration.” “I’m relieved that God answered our prayers,” a cousin, David Mosier, told NBC affiliate KRNV. “They just told me that they found them and that’s all I wanted to hear.” The Associated Press contributed to this report. This story was originally published on[/INST]– A Nevada couple and four children went to "play in the snow" Sunday and never returned, according to the Pershing County Sheriff. James Glanton, 34, and Christina MacIntee, 25, took their two children, 3 and 4, and a 10-year old niece and 4-year-old nephew into the remote Seven Troughs area in northwest Nevada, about 20 miles southeast of the Black Rock Desert, where Burning Man is held each year. Family members reported the group missing Sunday night; they haven't been heard from since they left, the AP reports. Their silver Jeep was last seen "doing wheelies or donuts" at a mining camp, a dispatch supervisor tells NBC News. Temperatures in the mountains were "minus 21" Sunday night, she adds, and have been "brutal" since, according to a US Bureau of Land Management spokesperson. The search effort includes a Navy helicopter, planes, a search and rescue team, and a volunteer arm of the Air Force. "I'm hoping they all huddled together and stayed in the Jeep," says a Nevada Highway Patrol Trooper. "That would be a best-case scenario." Three planes could be dispatched to search for them today, and while several inches of snow have fallen, authorities hope the black top on their silver 2005 Jeep will help make it easier to spot from the air.</s>

at @xmath0 , a large fraction of all high mass stars form in dusty galaxies @xcite . most of the intrinsic uv emission from newly formed stars in these galaxies is obscured , or absorbed by dust grains that subsequently heat up and radiate at ir wavelengths . the ir luminosity resulting from this obscuration is usually much greater than the emergent uv luminosity . for galaxies in which the intrinsic uv emission from newly formed stars is less obscured , the ir luminosity is still greater than the emergent uv luminosity , but to a lesser degree @xcite . the relation between the ir and emergent uv emission from a @xmath0 galaxy depends on the interplay between star formation and dust obscuration . one of the many ways to select dusty galaxies at @xmath0 , without redshift determinations from spectroscopy , is to use the ratio of observed 24 to 0.65@xmath1 ( @xmath4-band ) flux densities @xcite . sources satisfying @xmath5 have been termed `` dust - obscured galaxies '' , or dogs ; their redshift distribution is approximately a gaussian that peaks at @xmath6 with @xmath7 @xcite . in the redshift range @xmath8 , 0.65@xmath1 observations are sensitive to rest - frame uv emission from newly formed massive stars , and 24@xmath1 observations are sensitive to mid - ir emission from hot dust and polycyclic aromatic hydrocarbons ( pahs ) . the dog criterion is thus unique in that it selects galaxies in a specific redshift range , that also exhibit extreme ratios between their rest - frame mid - ir and uv flux densities . we have yet to understand the physical mechanism driving the span of ratios exhibited by dusty galaxies at @xmath0 . the ir luminosities of dogs with @xmath9 are dominated by emission from active galactic nuclei ( agn ; @xcite ) . the dominant sources of the ir luminosities of less luminous dogs is a topic of debate . @xcite and @xcite conclude that the ir luminosities of many dogs with @xmath10 originate from agn , while @xcite conclude that many such dogs are powered by newly formed stars . in this paper , we pose the question `` what makes a dog a dog ? '' the primary goal of our study is determining why dogs have an extreme ratio between their rest - frame mid - ir and uv flux densities when compared to other dusty galaxies . unfortunately , the simple and singular selection criterion can not distinguish between a dog that is : * abnormally bright at rest - frame @xmath11 for its far - ir flux density , indicating its mid - ir luminosity may be dominated by agn emission , or abnormally strong emission from polycyclic aromatic hydrocarbons ( pahs ) ; * or , abnormally faint in the rest - frame uv for its optical flux density , indicating that dust more completely obscures the newly formed stars in the galaxy . we use _ herschel _ @xcite data in the great observatories origins deep survey - north ( goods - n ) region @xcite to show that , on average , dogs with @xmath12 are not abnormally bright at @xmath11 , but are more uv faint than other galaxies with similar ir luminosities . the ratio between rest - frame ir and uv flux densities is set by the amount of obscuration , which can vary with either : 1 ) the degree of alignment between the spatial distributions of dust and massive stars , or 2 ) the total dust content . this paper is organized as follows . we present the data and sample selection in [ sec : data ] ; in [ sec : results ] , we show the results . we discuss the implications of these results in [ sec : discuss ] , and conclude in [ sec : conclude ] . we assume a cosmology with @xmath13 km s@xmath14 mpc @xmath14 , @xmath15 , and @xmath16 . our study uses observations of the goods - n region , which is roughly 10 arcmin @xmath17 16.5 arcmin in extent . we cull the sample of dogs from a catalog of 24@xmath1 sources produced for the _ spitzer_/mips survey of the goods - n region ( m. dickinson , pi ; @xcite ) . a 24@xmath1 source is defined as a @xmath18 flux density measurement from psf fitting to _ 3.6@xmath1 source priors . the catalog is 99% complete at @xmath19jy , and contains 1603 sources . the 2.2@xmath1 ( @xmath20-band ) image we use to identify counterparts for the 24@xmath1 sources comes from observations using the canada - france - hawaii telescope ( cfht ) . the data are presented in @xcite ; we use our own reductions @xcite . the 0.65@xmath1 ( @xmath4-band ) subaru image we use to define the dog sample comes from @xcite . the 5@xmath21 depth of the 2.2@xmath1 image is @xmath220.60@xmath23jy ( 24.5 ab mag ) ; the 3@xmath21 depth of the 0.65@xmath1 image is @xmath220.05@xmath23jy ( 27.2 ab mag ) . to extract flux densities , we follow a modified version of the procedure used by @xcite . using sextractor @xcite , we place 3@xmath24 diameter apertures at the positions of sources detected ( @xmath25 ) in the 2.2@xmath1 image . if the 2.2@xmath1 flux density is detected with s / n @xmath25 but the 0.65@xmath1 flux density is not detected with s / n @xmath26 , we use a 3@xmath21 limit for the latter flux density . to determine rest - frame uv continuum power - law indices , we extract flux densities at 0.45 , 0.55 , 0.80 , and 0.90@xmath1 ( the @xmath27- , @xmath28- , @xmath29- , and @xmath30-bands ) from subaru images @xcite , using the same procedure . we use the 3.6 , 4.5 , 5.8 , and 8@xmath1 flux densities already associated with the 24@xmath1 sources to determine whether or not their spectral energy distributions ( seds ) at these wavelengths behave as power laws ; these flux densities come from a catalog produced for the _ spitzer_/irac survey of the goods - n region , and will be included in catalogs accompanying the goods-_herschel _ public data release . for the optical / near - ir photometry , we calculate aperture corrections , defined as the ratios of total flux density to flux density in a 3@xmath24 diameter aperture for point sources ( non - saturated stars ) . we take the sextractor parameter ` flux_auto ` as the total flux density . the corrections are factors of 1.086 , 1.225 , 1.247 , 1.057 , 1.086 , and 1.057 at 0.45 , 0.55 , 0.65 , 0.80 , 0.90 , and 2.2@xmath1 , respectively . to maintain the signal - to - noise ratios given by sextractor , both the flux densities and their uncertainties are multiplied by these factors . we associate each 24@xmath1 source with a 2.2@xmath1 source and its extracted optical flux densities if the 2.2@xmath1 source is a unique match within 0.76@xmath24 of the position of the 3.6@xmath1 prior . the match radius is chosen by maximizing the number of unique matches while minimizing the number of multiple matches . of the 1603 24@xmath1 sources , 87 either do not have a @xmath25 2.2@xmath1 counterpart within the match radius ( 85 of 87 ) or have multiple counterparts ( 2 of 87 ) . the far - ir flux densities come from a catalog produced for the goods-_herschel _ survey @xcite . we only use 100 and 160@xmath1 flux densities measured with pacs @xcite , and 250@xmath1 flux densities measured with spire @xcite , to avoid the complications of measuring flux densities for 24@xmath1 sources in the 350 and 500@xmath1 spire images that are affected by severe source confusion . we consider a @xmath18 measurement at 100 or 160@xmath1 to be a detection ; at 250@xmath31 , we require a @xmath25 measurement . we impose additional constraints on the 250@xmath1 flux densities ( and @xmath32 limits ) , similar to those defining the `` clean index '' @xcite . the 250@xmath33 flux densities of clean sources ( and @xmath32 limits of clean non - detections ) should not be affected by severe source confusion . we do not impose additional constraints on the 100 and 160@xmath1 flux densities because the 100@xmath1 images are not deep enough to be affected by source confusion , and the 160@xmath1 images are only deep enough to be moderately affected . the 3@xmath21 depths of the 100 and 160@xmath1 images are @xmath221100@xmath23jy and @xmath222700@xmath23jy , respectively ; the 5@xmath21 depth of the 250@xmath1 image is @xmath225700@xmath23jy . we attempt to match each 24@xmath1 source to a source with a spectroscopic redshift from the catalogs of ( * ? ? ? * which includes redshifts compiled from the literature ) and stern et al . ( in preparation ) . we find spectroscopic redshifts for 910 ( 57% ) of the 24@xmath1 sources . if no coincident sources with spectroscopic redshifts are found , we resort to the photometric redshift source catalog of pannella et al . ( in preparation ) to find a source match . we exclude sources with photometric redshifts derived from ill - fitting templates ( those with reduced @xmath34 ) . for an additional 510 ( 32% ) of the 24@xmath1 sources we have photometric redshift estimates . there are no redshift estimates for 183 ( 11% ) of the 24@xmath1 sources , and these sources are excluded from our samples . using the multi - wavelength information and redshifts , we define 2 samples from the superset of all 24@xmath1 sources with @xmath19jy : * _ dog sample _ : all 24@xmath1 sources with 2.2@xmath1 counterparts and @xmath35 ( fig . [ fig : sample ] ) . the 24@xmath1 flux density of the faintest dog is 53@xmath23jy , justifying our @xmath19jy cut for the control sample . the limiting quantity is the depth of the 0.65@xmath1 image ( 3@xmath21 = 0.05@xmath23jy * ? ? ? the redshift distribution of our sample of dogs is shown in fig . [ fig : z_dist ] , also motivating our @xmath8 cut for the control sample . six ( of 61 ; 10% ) dogs have spectroscopic redshifts . in the following analysis , we include only dogs with @xmath8 . our conclusions do not change if we include dogs without redshift estimates in the sample . * _ control sample _ : all @xmath19jy 24@xmath1 sources with 2.2@xmath1 counterparts that are at @xmath8 , and that do not satisfy the dog selection criterion . seventy four ( of 268 ; 28% ) control galaxies have spectroscopic redshifts . for each sample , table [ table : numbers ] characterizes the subset of sources with flux densities detected at 0.65 , 100 , 160 , and 250@xmath1 . more than 70% of these galaxies are undetected in optical spectra ( or are unobserved ) because their observed - frame optical flux densities are so faint . our sample contains dogs with fainter 24@xmath1 emission than does the @xcite sample . their sample is selected from the shallower _ spitzer_/mips survey of the botes region ; their limit is @xmath36jy . however , the goods - n region is much smaller than the botes region , so we have few dogs with @xmath36jy . @xcite also study a sample of dogs in goods - n . the main differences between the @xcite sample and ours are that : 1 ) they limit their sample to @xmath37jy ; and 2 ) they estimate a redshift for each dog using irac and mips photometry , whereas we match dogs to sources in a near - ir / optical catalog , with redshift estimates based on @xmath38 , 3.6 , and 4.5@xmath1 photometry . the fractions of 24@xmath1 sources at @xmath8 that meet the dog criterion increase with increasing 24@xmath1 flux density ( fig . [ fig : sample ] ) . of the sources with @xmath39jy , 4% are dogs . of the sources with @xmath37jy , 25% are dogs . @xcite find similar fractions ; they also find that of their sources with @xmath36jy , 60% are dogs . lccccccc dogs & 61 & 2.1 & 161 & 47 ( 77% ) & 29 ( 48% ) & 24 ( 39% ) & 9 ( 15% ) + control & 268 & 2.0 & 102 & 268 ( 100% ) & 81 ( 30% ) & 52 ( 19% ) & 15 ( 6% ) flux density vs. 0.65@xmath1 flux density for galaxies in the two samples . the dog sample is defined by @xmath40 . [ fig : sample ] ] sources ( before we impose redshift limits ) . for the analysis , we limit all samples to the redshift range @xmath8 ( the area between the vertical lines).[fig : z_dist ] ] several quantities are useful in analyzing the relation between ir and emergent uv emission from galaxies . in this section , we detail how we estimate the total ir and uv luminosities , uv continuum power - law indices , star formation rates , and stellar masses for the galaxies in our samples . we estimate a total ir luminosity ( 81000@xmath1 ; @xmath41 ) for each galaxy with detected emission at 100@xmath1 . we redshift the @xcite template spectral energy distributions ( seds ) to the distance of each galaxy , find the sed that most closely matches the observed 100@xmath1 flux density , and multiply the ir luminosity of that sed by the ratio between actual and predicted flux densities to get @xmath41 . we prefer this approach over estimating the ir luminosity directly , by summing several far - ir flux densities , because the latter procedure requires detected emission at 160 and 250@xmath1 . the goods-_herschel _ image at 160@xmath1 is moderately affected by blending due to source confusion , while the image at 250@xmath1 is so deep that blending is problematic . the drawback to our chosen approach is that all statements we make regarding ir luminosities assume that the low - redshift template seds accurately represent the seds of galaxies at @xmath0 . @xcite show that this assumption is valid when template matching is done to 100@xmath1 flux densities . for galaxies with uv emission from newly formed massive stars , the uv continuum can be approximated as a power law with an index @xmath42 : @xmath43 we use @xmath18 flux densities at 0.45 , 0.55 , 0.65 , 0.80 , and 0.90@xmath1 ( i.e. , in the @xmath27- , @xmath28- , @xmath4- , @xmath29- , and @xmath30-bands ) to fit for @xmath42 and the constant factor @xmath44 for each galaxy which has an estimate of @xmath41 . if only two flux densities have s / n @xmath18 , we calculate @xmath42 analytically . if only one flux density has s / n @xmath18 , we use an upper limit for the 0.45@xmath1 flux density to calculate a lower limit to @xmath42 . we estimate a uv luminosity @xmath45 at rest - frame 0.16@xmath1 for each galaxy using its redshift estimate and the power - law fit to the rest - frame uv flux densities . to estimate a stellar mass for each galaxy , we fit stellar population synthesis models to its @xmath38 , 3.6 , and 4.5@xmath1 flux densities @xcite . full details are in 4.2 of @xcite . we assume the stellar initial mass function in @xcite from 0.1 to 100 @xmath46 , as well as the dust attenuation law in @xcite . we use the equation in @xcite to calculate a star formation rate ( sfr ) , based on the ir luminosity , for each galaxy with detected 100@xmath1 emission . we make no correction for the emergent uv luminosity , since it is negligible for all galaxies in the dog and control samples ( see [ sec : discuss ] ) . in using the @xcite equation , we assume that the observed 100@xmath1 emission is due to star formation and not agn activity , and that the star formation episode lasts for @xmath47 years . @xcite find that the former assumption is valid for most agn with detected x - ray emission at @xmath48 . seventy six percent of the @xmath0 galaxies with detected 100@xmath1 emission have @xmath3 ( fig . [ fig : lir ] ) . the distributions of ir luminosities for the dogs and the control galaxies are statistically indistinguishable ( @xmath49 that the two samples are drawn from the same parent population , using a k - s test ) . . the two distributions are statistically indistinguishable . [ fig : lir ] ] fig . [ fig : mass_z ] shows the stellar masses for dogs and control galaxies with detected emission at 100@xmath1 . the distributions are not strongly different ( @xmath50 , using a k - s test ) , though some control galaxies have lower stellar masses than do the dogs . 17 ( of 72 ; 24% ) control galaxies have stellar masses @xmath51 , while only 1 ( of 25 ; 4% ) dog has a stellar mass below this threshold . . the distribution of stellar masses for dogs is not strongly different from that for control galaxies , though some control galaxies have lower stellar masses than do the dogs . twenty four percent of the control sample has @xmath52 , as opposed to 4% of the dog sample.[fig : mass_z ] ] the infrared seds of most low redshift dusty galaxies peak between rest - frame @xmath53 and 100@xmath1 . the rest - frame @xmath11 luminosity is only a fraction of the total ir luminosity in these galaxies . to address whether or not dogs are abnormally bright at rest - frame @xmath11 , we require a comparison of the rest - frame far - ir and @xmath11 flux densities between dogs and the control galaxies [ fig:100over24_z ] shows that dogs are statistically indistinguishable from the control galaxies when looking at the observed flux density ratio @xmath54 ( @xmath55 , using a k - s test ) . in this figure , we do not show the galaxies with limits for @xmath56 . we perform the gehan and logrank tests , which are conceptually similar to the two sample k - s test , but also allow for the inclusion of galaxies with limits at 100@xmath1 in the two samples . we find no statistically significant difference between the dogs and the control galaxies ( @xmath57 that both samples are drawn from the same parent population , from both tests ) . our conclusions are the same using @xmath58 ( not shown ; @xmath59 from both tests ) . if dogs were abnormally luminous at rest - frame @xmath11 for their far - ir luminosities , then we would expect them to have low values of observed @xmath54 and/or @xmath58 compared to those of the control galaxies ; they do not . however , 100 and 160@xmath1 observations are sensitive to rest - frame 33 and 53@xmath1 emission from galaxies at @xmath6 . these rest - frame wavelengths are still short of the presumed wavelength of the peak of the infrared sed ; the rest - frame luminosities are still only a fraction of the total ir luminosity in these galaxies . 250@xmath1 observations are sensitive to rest - frame @xmath60 emission from galaxies at @xmath6 . this rest - frame wavelength is generally close to the wavelength of the peak of the ir sed . [ fig:250over24_z ] shows that dogs are statistically indistinguishable from the control galaxies when looking at the observed flux density ratio @xmath61 . we reach the same conclusion when including galaxies with limits at 250@xmath1 in statistical tests ( @xmath62 that both samples are drawn from the same parent population , from both a gehan and logrank test ) . vs. redshift for galaxies in the two samples . galaxies with limits at 100@xmath1 are not shown in this figure , but we do include them in our statistical tests . dogs are statistically indistinguishable from the control galaxies in @xmath54 . [ fig:100over24_z ] ] vs. redshift for galaxies in the two samples . galaxies with limits at 250@xmath1 are not shown in this figure , but we do include them in our statistical tests . as in fig . [ fig:100over24_z ] , dogs span the same range of flux density ratios as do the control galaxies ; this leads us to conclude that the dog criterion does not select dusty galaxies that are abnormally bright at rest - frame @xmath11 . [ fig:250over24_z ] ] the dog criterion does not select galaxies that are abnormally bright at rest - frame @xmath11 for their far - ir flux densities . what makes a dog a dog must be that the galaxy s rest - frame uv emission is suppressed , compared to the uv emission from a control galaxy . therefore we expect a clear separation between dogs and control galaxies when looking at the ratios of rest - frame optical to uv flux densities . indeed , fig . [ fig : roverk_z ] shows that 92% of dogs have an observed @xmath63 , while 78% of control galaxies have @xmath64 . the gehan and logrank tests report a statistical difference between the dogs and control galaxies ( @xmath65 that both samples are drawn from the same parent population , from both tests ) . galaxies with @xmath66 are also known as `` extremely red objects '' , or eros ( @xcite ; @xcite ; @xcite ; @xcite ) . we note that even though a galaxy with detected 24@xmath1 emission may meet the ero criterion , it may not meet the dog criterion ( and vice versa , rarely ) . vs. redshift for galaxies in the two samples . a dog is distinguishable from a random galaxy with detected 24@xmath1 emission because it is abnormally faint in the rest - frame uv . [ fig : roverk_z ] ] the statistical difference between the dogs and control galaxies for @xmath67 , and the lack thereof for @xmath54 , is robust against photometric redshift errors . we offset photometric redshifts for the superset of all galaxies with detected 24@xmath1 emission , assuming the offsets obey a gaussian distribution with @xmath68 = 0.1 . we then select new dog and control samples . the differences in @xmath67 are always statistically significant , and the differences in @xmath54 are very rarely statistically significant ( from k - s tests ) . we have shown that the 100 , 160 , and 250 to 24@xmath1 flux density ratios for dogs with moderate ir luminosities ( @xmath69 ) are statistically indistinguishable from those flux density ratios for galaxies with detected 24@xmath23 m emission that lie at similar redshifts and have similar ir luminosities , but that do not meet the dog selection criterion . most dogs have higher 2.2 to 0.65@xmath1 flux density ratios than do the control galaxies . thus it seems clear that dogs occupy the tail of a distribution of uv obscuration in ir - luminous galaxies at @xmath0 . we select a sample of dogs using deep images of the goods - n region . these dogs have lower ir luminosities than do dogs selected using shallower images of wider regions . for example , the @xcite sample in the wide botes region contains many dogs with @xmath70 . our sample contains very few galaxies with @xmath70 , and our conclusions regarding obscuration may not apply to dogs with such high luminosities . at low redshift , agn emission dominates the ir luminosity for most galaxies with @xmath70 @xcite . @xcite find that many dogs at @xmath0 with @xmath70 have featureless seds from observed - frame 3.6 to 8@xmath1 , indicating the presence of agn - heated dust . several studies @xcite find that , for these dogs , the seds at rest - frame mid- and far - ir wavelengths are similar to those of low redshift galaxies with ir luminosities dominated by agn emission , such as markarian 231 . only 2 ( of 59 ; 3% ) dogs , and 8 ( of 253 ; 3% ) control galaxies , have seds that increase ( in @xmath71 ) from observed - frame 3.6 to 8@xmath1 , and indeed both are among the dogs with the highest @xmath41 ( at @xmath72 and @xmath73 ) . two galaxies are not enough to allow us to rule out the possibility that dogs with @xmath74 differ in their 100 or 250 to 24@xmath1 flux density ratios from control galaxies with similar luminosities . most galaxies in our sample have @xmath69 . whether their ir luminosities are dominated by emission from agn or newly formed stars is not clear . @xcite and @xcite find that the average dog in this @xmath41 range has an x - ray spectrum with a power - law index they interpret as indicative of heavily obscured agn emission . an obscured agn would presumably contribute to the ir luminosity as well . @xcite find the same average x - ray index for a similar sample of dogs , but also find pah emission in the mid - infrared spectra of the dogs ; they conclude that heavily obscured agn emission can not coexist with pah emission . @xcite attribute the x - ray emission of the dogs to x - ray binaries rather than agn . in our sample , 5 ( of 61 ; 8% ) dogs and 31 ( of 268 ; 12% ) control galaxies have detected x - ray emission @xcite . for galaxies with @xmath75 , we do not find any evidence that agn emission at rest - frame mid - ir wavelengths is more or less common in dogs than in the control galaxies : the fractions of dogs and control galaxies with increasing seds between observed - frame 3.6@xmath1 and 8@xmath1 are similar , as are the fractions with detected x - ray emission . no matter what powers their ir luminosities , dogs in this @xmath41 range are abnormally uv faint , and are probably the most obscured galaxies . we have shown that the brightness of the emergent uv emission in @xmath0 dusty galaxies can vary considerably from galaxy to galaxy , even though the emergent uv emission is only a fraction of the ir emission . in a dusty galaxy at either low or high redshift , most of the intrinsic uv emission from newly formed stars and/or agn is absorbed by dust grains , which emit at ir wavelengths . we now ask : `` are the uv - emitting regions that we see from a dog or a control galaxy spatially coincident with the ir - emitting regions ? '' if yes , the variation in emergent uv emission is due to uv obscuration . if no , the emergent uv emission may come from stars in a `` normal '' galactic disk , whereas the newly formed stars ultimately responsible for the ir emission are completely obscured , perhaps in a compact , nuclear star - forming region . in this scenario , the variation in the rest - frame optical to uv flux density ratios might be due as much to differences in the stellar populations from galaxy to galaxy as to differences in obscuration @xcite . we can not yet efficiently spatially resolve the ir - emitting regions for large samples of high redshift dusty galaxies . two pieces of circumstantial evidence support the statement that the uv- and ir - emitting regions in these dusty galaxies are spatially coincident : 1 ) a minority of dogs and control galaxies deviate from the median specific sfr for galaxies at @xmath0 ; and 2 ) dogs and control galaxies define a continuous relation between their median ir to uv luminosity ratios and median uv continuum power - law indices . the specific star formation rate of a galaxy is the ratio of its sfr to its stellar mass . most star - forming galaxies at the same redshift fall on a tight relation between sfr and stellar mass ; this relation is referred to as the `` main sequence '' @xcite . @xcite find that sfr and stellar mass are directly proportional at all redshifts , and present the evolution of the median specific sfr for galaxies at @xmath76 . @xcite also isolate the minority of galaxies with specific sfrs much higher than the median values ( `` starbursts '' ) . here , we define starbursts as galaxies with specific sfrs higher than 3 times the median value at their redshift . a minority of dogs ( 5 of 25 ; 20% ) and control galaxies ( 18 of 72 ; 25% ) are starbursts ( fig . [ fig : mainseq ] ) . @xcite find that individual low redshift starbursts have compact uv - emitting regions ; the correspondence between deviation from the median specific sfr and the compact size of the uv - emitting region also holds for the average @xmath0 starburst . if this correspondence holds for individual @xmath0 galaxies , few dogs and control galaxies would have concentrated uv - emitting regions . these regions in the typical dog or control galaxy would be more widely distributed , and it would be less plausible that the uv - emitting regions occupy parts of the galaxy not occupied by ir - emitting regions . that radio - emitting regions in high redshift galaxies are widely distributed indirectly supports this idea @xcite . emission . the solid line is the median specific sfr for star - forming galaxies , as a function of redshift @xcite . the dotted line is three times the median value , which we use as a threshold for identifying starbursts . 20% of dogs and 25% of control galaxies are starbursts . dogs deviate from the median specific sfr no more frequently than do the control galaxies . [ fig : mainseq ] ] for starburst galaxies at low redshift , @xcite ( @xcite , and more recently * ? ? ? * ) find a relation between the ratio of ir to uv luminosities ( denoted irx ) and the power - law index of the sed in the uv ( denoted @xmath42 ) . ( @xcite refer to low redshift galaxies with bright uv - emitting regions as `` starbursts '' ; the term does not necessarily refer to galaxies that deviate from the main sequence . ) this relation is generally interpreted to mean that the ir emission originates as uv emission from newly formed stars , which is partially absorbed by dust . the dependence between the emergent uv emission , the dust emission in the ir , and @xmath42 , in the local irx-@xmath42 relation is consistent with the dependence of dust absorption on @xmath42 in the @xcite dust attenuation law . in other words , we think that galaxies that lie on this relation are thought to have spatially coincident uv- and ir - emitting regions . @xcite show that most lyman break galaxies ( lbg ) at @xmath0 lie on the local irx-@xmath42 relation . however , both @xmath0 lbgs and the low redshift starbursts in @xcite are much less dusty than dogs . some sub - classes of dusty galaxies deviate from the local relation , perhaps because their ir emission is unrelated to their emergent uv emission @xcite . [ fig : irxbeta ] shows the local irx-@xmath42 relation from @xcite and the relevant quantities for the @xmath0 dusty galaxies in our samples . individual galaxies , in both the dog and control samples , are found on either side of the relation . because dogs are so faint in the uv , it is difficult to precisely determine the power - law indices of their uv seds ; the large uncertainties on @xmath42 values preclude us from reaching firm conclusions about individual galaxies . the median @xmath42 values for the dog and control samples tend to lie to the left of the local irx-@xmath42 relation ; dogs do not appear to deviate more strongly from the relation than do control galaxies . these @xmath0 dusty galaxies define their own irx-@xmath42 relation . as noted earlier , specific sub - populations of dusty galaxies deviate from the local relation , but the trend that we find between the averages for a broader @xmath0 population has not been discussed . because the median @xmath42 value increases with increasing irx , from the lbgs to the dogs , the ir emission is not completely independent of the emergent uv emission in these galaxies . this reinforces our initial conclusion that @xmath0 dusty galaxies populate a continuum of uv obscuration , and that dogs are simply the most heavily obscured galaxies . over 0.16@xmath1 luminosity ( irx ) vs. uv continuum power - law index ( @xmath42 ) for galaxies with detected 100@xmath1 emission . we only show errors on the uv power - law indices . filled hourglasses and circles show the median @xmath42 values , in bins of irx ; the vertical bars show the range of irx over which the @xmath42 values are binned . the `` average lbg '' black asterisk is from @xcite , and shows a mean and its dispersion . the solid line is the local irx-@xmath42 relation from @xcite . [ fig : irxbeta ] ] dogs in the luminosity range spanned by our sample are more obscured than the control galaxies for a reason unrelated to their far - ir luminosity , because the @xmath41 distributions of the two samples are statistically indistinguishable . in galaxies with dust heated by uv emission from newly formed stars , the amount of obscuration affecting that uv emission can vary due to either : 1 ) differences in the degree of alignment between the spatial distributions of dust and newly formed massive stars ; or 2 ) differences in the total dust content . @xcite derive the local irx-@xmath42 relation by assuming a uniform screen of dust in the line of sight between us and the newly formed stars ( see figure 8 in @xcite for an illustration ) . @xcite show that this assumption can be recovered when the dust is instead distributed in clumps around star - forming regions . thus , dogs might be more obscured than the control galaxies because dogs have more dust clumps surrounding star - forming regions . variations in uv obscuration might also be caused by differences in the physical properties responsible for the shape of the sub - millimeter sed . for example , increases in the mass of cold dust can result in greater uv obscuration . increases in the cold dust mass can also result in increases in sub - millimeter emission . since the sub - millimeter luminosity is usually a small fraction of the total ir luminosity , the increase in total ir luminosity due to a higher cold dust mass would not be easily measurable between 100 and 250@xmath1 . we can not fully test this hypothesis without sub - millimeter luminosities for galaxies in our samples . the sensitivities of current sub - millimeter facilities limit comparisons of the dust content between dogs and control galaxies to the most luminous ( @xmath70 ) galaxies @xcite . currently available data do not allow us to discriminate between any hypotheses for the physical mechanisms responsible for either the differences in the degree of alignment between dust and stars or differences in the dust content . for instance , two plausible hypotheses are that : 1 ) galaxy inclination might be responsible for the patchiness of dust in the line - of - sight , and 2 ) many dogs are merging galaxies , and some aspect of the merging process creates differences in the degree of alignment . to falsify either we require high resolution rest - frame optical images ; the cosmic assembly near - infrared deep extragalactic legacy survey ( candels ) will obtain such images using _ hst_/wfc3 in the near future @xcite . we note that @xcite and @xcite examine rest - frame optical images of dogs in goods - s and conclude that most are undisturbed disk galaxies . furthermore , @xcite simulate isolated galaxies that meet the dog selection criterion , so dogs are not necessarily merging galaxies on the basis of their extreme rest - frame mid - ir to uv flux density ratios . finally , uv obscuration is affected by the prominence of the `` dust bump '' at rest - frame 2175 in a galaxy s attenuation curve . at @xmath0 , rest - frame 2175 is redshifted into the @xmath4-band filter . the presence of this feature in the attenuation curves of high redshift galaxies has been controversial ; the bump is found , though , in the attenuation curves for several samples of galaxies at @xmath77 @xcite . however , doubling the amplitude of the average bump leads to a reduction in the 0.65@xmath1 flux density by a factor of 1.3 . this is not large enough to explain the spread of @xmath67 in fig . [ fig : roverk_z ] . 1 . we cull a sample of dust - obscured galaxies ( dogs ) , or galaxies with @xmath35 that are at @xmath8 , in the goods - n region . we use deep goods-_herschel _ data to compare the emission from dogs with that from other @xmath0 galaxies with detected 24@xmath1 emission . the dogs in our sample span @xmath3 . dogs and control galaxies , with detected 100@xmath1 emission , have similar distributions of ir luminosities and stellar masses . we compare the rest - frame far - ir and optical flux densities of dogs with those of the control galaxies . dogs have extreme ratios of @xmath78 not because they are abnormally bright at rest - frame @xmath11 for their far - ir flux densities , but because they are abnormally faint in the rest - frame uv . 4 . dogs and the control galaxies scatter around the median specific sfr established by @xmath0 galaxies falling on the `` main sequence '' ; 20% of dogs have specific sfrs greater than 3 times the median value , and are thus starbursts . if uv - emitting regions in high - redshift starbursts are distributed as they are in low - redshift starbursts , few dogs have compact uv - emitting regions . 5 . for both the dog and control samples , the median rest - frame uv continuum power - law index ( @xmath42 ) at a given ir to uv luminosity ratio ( irx ) is lower than the index predicted by the local irx-@xmath42 relation . dogs do not appear to deviate more from this relation than do the control galaxies . over more than a factor of 100 in irx , the median @xmath42 value for these galaxies systematically increases with increasing irx . these pieces of evidence suggest that , for most of these galaxies , the uv- and ir - emitting regions are spatially coincident . thus , the range in rest - frame mid - ir to uv flux density ratios spanned by dusty galaxies at @xmath0 is due to differing amounts of uv obscuration . dogs are the most heavily obscured galaxies . differences in the amount of obscuration between dogs and other dusty galaxies at @xmath0 can be due to : 1 ) differences in the degree of alignment between the spatial distributions of dust and massive stars , or 2 ) differences in the total dust content . our samples do not have many galaxies with @xmath9 . in dogs with these ir luminosities , where agn emission may be the dominant source of dust heating , our conclusions about obscuration may not be valid . further information about the nature of obscuration in these galaxies can come from measurements that spatially resolve uv- and ir - emitting regions . for instance , the h@xmath79 to h@xmath42 line ratio varies with the amount of dust absorption , so its variation across a galaxy traces the spatial dust distribution . @xcite measure the galaxy - wide balmer decrement for several very luminous dogs ( those most likely to have ir luminosities dominated by agn emission ) ; @xcite present spatially resolved h@xmath79 maps , but h@xmath42 is outside their spectral window . _ hst _ can resolve the rest - frame uv and optical emission from these galaxies @xcite , and alma will resolve the ir emission and allow us to measure sub - millimeter luminosities we need to determine cold dust mass . studies using such data will clearly establish the degree to which the spatial distributions of dust and massive stars align . this work is based on observations made with _ , a european space agency cornerstone mission with significant participation by nasa . support for this work was provided by nasa through an award issued by jpl / caltech . the research activities of m.d . and a.d . are supported by noao , which is operated by the association of universities for research in astronomy under a cooperative agreement with the national science foundation . we are grateful to n. drory for sharing the sed - fitting code we use to estimate galaxy stellar masses .

dusty galaxies at @xmath0 span a wide range of relative brightness between rest - frame mid - infrared ( 8@xmath1 ) and ultraviolet wavelengths . we attempt to determine the physical mechanism responsible for this diversity . dust - obscured galaxies ( dogs ) , which have rest - frame mid - ir to uv flux density ratios @xmath2 , might be abnormally bright in the mid - ir , perhaps due to prominent agn and/or pah emission , or abnormally faint in the uv . we use far - infrared data from the goods-_herschel _ survey to show that most dogs with @xmath3 are not abnormally bright in the mid - ir when compared to other dusty galaxies with similar ir ( 81000@xmath1 ) luminosities . we observe a relation between the median ir to uv luminosity ratios and the median uv continuum power - law indices for these galaxies , and we find that only 24% have specific star formation rates which indicate the dominance of compact star - forming regions . this circumstantial evidence supports the idea that the uv- and ir - emitting regions in these galaxies are spatially coincident , which implies a connection between the abnormal uv faintness of dogs and dust obscuration . we conclude that the range in rest - frame mid - ir to uv flux density ratios spanned by dusty galaxies at @xmath0 is due to differing amounts of uv obscuration . of galaxies with these ir luminosities , dogs are the most obscured . we attribute differences in uv obscuration to either : 1 ) differences in the degree of alignment between the spatial distributions of dust and massive stars , or 2 ) differences in the total dust content .

<s>[INST]at @xmath0 , a large fraction of all high mass stars form in dusty galaxies @xcite . most of the intrinsic uv emission from newly formed stars in these galaxies is obscured , or absorbed by dust grains that subsequently heat up and radiate at ir wavelengths . the ir luminosity resulting from this obscuration is usually much greater than the emergent uv luminosity . for galaxies in which the intrinsic uv emission from newly formed stars is less obscured , the ir luminosity is still greater than the emergent uv luminosity , but to a lesser degree @xcite . the relation between the ir and emergent uv emission from a @xmath0 galaxy depends on the interplay between star formation and dust obscuration . one of the many ways to select dusty galaxies at @xmath0 , without redshift determinations from spectroscopy , is to use the ratio of observed 24 to 0.65@xmath1 ( @xmath4-band ) flux densities @xcite . sources satisfying @xmath5 have been termed `` dust - obscured galaxies '' , or dogs ; their redshift distribution is approximately a gaussian that peaks at @xmath6 with @xmath7 @xcite . in the redshift range @xmath8 , 0.65@xmath1 observations are sensitive to rest - frame uv emission from newly formed massive stars , and 24@xmath1 observations are sensitive to mid - ir emission from hot dust and polycyclic aromatic hydrocarbons ( pahs ) . the dog criterion is thus unique in that it selects galaxies in a specific redshift range , that also exhibit extreme ratios between their rest - frame mid - ir and uv flux densities . we have yet to understand the physical mechanism driving the span of ratios exhibited by dusty galaxies at @xmath0 . the ir luminosities of dogs with @xmath9 are dominated by emission from active galactic nuclei ( agn ; @xcite ) . the dominant sources of the ir luminosities of less luminous dogs is a topic of debate . @xcite and @xcite conclude that the ir luminosities of many dogs with @xmath10 originate from agn , while @xcite conclude that many such dogs are powered by newly formed stars . in this paper , we pose the question `` what makes a dog a dog ? '' the primary goal of our study is determining why dogs have an extreme ratio between their rest - frame mid - ir and uv flux densities when compared to other dusty galaxies . unfortunately , the simple and singular selection criterion can not distinguish between a dog that is : * abnormally bright at rest - frame @xmath11 for its far - ir flux density , indicating its mid - ir luminosity may be dominated by agn emission , or abnormally strong emission from polycyclic aromatic hydrocarbons ( pahs ) ; * or , abnormally faint in the rest - frame uv for its optical flux density , indicating that dust more completely obscures the newly formed stars in the galaxy . we use _ herschel _ @xcite data in the great observatories origins deep survey - north ( goods - n ) region @xcite to show that , on average , dogs with @xmath12 are not abnormally bright at @xmath11 , but are more uv faint than other galaxies with similar ir luminosities . the ratio between rest - frame ir and uv flux densities is set by the amount of obscuration , which can vary with either : 1 ) the degree of alignment between the spatial distributions of dust and massive stars , or 2 ) the total dust content . this paper is organized as follows . we present the data and sample selection in [ sec : data ] ; in [ sec : results ] , we show the results . we discuss the implications of these results in [ sec : discuss ] , and conclude in [ sec : conclude ] . we assume a cosmology with @xmath13 km s@xmath14 mpc @xmath14 , @xmath15 , and @xmath16 . our study uses observations of the goods - n region , which is roughly 10 arcmin @xmath17 16.5 arcmin in extent . we cull the sample of dogs from a catalog of 24@xmath1 sources produced for the _ spitzer_/mips survey of the goods - n region ( m. dickinson , pi ; @xcite ) . a 24@xmath1 source is defined as a @xmath18 flux density measurement from psf fitting to _ 3.6@xmath1 source priors . the catalog is 99% complete at @xmath19jy , and contains 1603 sources . the 2.2@xmath1 ( @xmath20-band ) image we use to identify counterparts for the 24@xmath1 sources comes from observations using the canada - france - hawaii telescope ( cfht ) . the data are presented in @xcite ; we use our own reductions @xcite . the 0.65@xmath1 ( @xmath4-band ) subaru image we use to define the dog sample comes from @xcite . the 5@xmath21 depth of the 2.2@xmath1 image is @xmath220.60@xmath23jy ( 24.5 ab mag ) ; the 3@xmath21 depth of the 0.65@xmath1 image is @xmath220.05@xmath23jy ( 27.2 ab mag ) . to extract flux densities , we follow a modified version of the procedure used by @xcite . using sextractor @xcite , we place 3@xmath24 diameter apertures at the positions of sources detected ( @xmath25 ) in the 2.2@xmath1 image . if the 2.2@xmath1 flux density is detected with s / n @xmath25 but the 0.65@xmath1 flux density is not detected with s / n @xmath26 , we use a 3@xmath21 limit for the latter flux density . to determine rest - frame uv continuum power - law indices , we extract flux densities at 0.45 , 0.55 , 0.80 , and 0.90@xmath1 ( the @xmath27- , @xmath28- , @xmath29- , and @xmath30-bands ) from subaru images @xcite , using the same procedure . we use the 3.6 , 4.5 , 5.8 , and 8@xmath1 flux densities already associated with the 24@xmath1 sources to determine whether or not their spectral energy distributions ( seds ) at these wavelengths behave as power laws ; these flux densities come from a catalog produced for the _ spitzer_/irac survey of the goods - n region , and will be included in catalogs accompanying the goods-_herschel _ public data release . for the optical / near - ir photometry , we calculate aperture corrections , defined as the ratios of total flux density to flux density in a 3@xmath24 diameter aperture for point sources ( non - saturated stars ) . we take the sextractor parameter ` flux_auto ` as the total flux density . the corrections are factors of 1.086 , 1.225 , 1.247 , 1.057 , 1.086 , and 1.057 at 0.45 , 0.55 , 0.65 , 0.80 , 0.90 , and 2.2@xmath1 , respectively . to maintain the signal - to - noise ratios given by sextractor , both the flux densities and their uncertainties are multiplied by these factors . we associate each 24@xmath1 source with a 2.2@xmath1 source and its extracted optical flux densities if the 2.2@xmath1 source is a unique match within 0.76@xmath24 of the position of the 3.6@xmath1 prior . the match radius is chosen by maximizing the number of unique matches while minimizing the number of multiple matches . of the 1603 24@xmath1 sources , 87 either do not have a @xmath25 2.2@xmath1 counterpart within the match radius ( 85 of 87 ) or have multiple counterparts ( 2 of 87 ) . the far - ir flux densities come from a catalog produced for the goods-_herschel _ survey @xcite . we only use 100 and 160@xmath1 flux densities measured with pacs @xcite , and 250@xmath1 flux densities measured with spire @xcite , to avoid the complications of measuring flux densities for 24@xmath1 sources in the 350 and 500@xmath1 spire images that are affected by severe source confusion . we consider a @xmath18 measurement at 100 or 160@xmath1 to be a detection ; at 250@xmath31 , we require a @xmath25 measurement . we impose additional constraints on the 250@xmath1 flux densities ( and @xmath32 limits ) , similar to those defining the `` clean index '' @xcite . the 250@xmath33 flux densities of clean sources ( and @xmath32 limits of clean non - detections ) should not be affected by severe source confusion . we do not impose additional constraints on the 100 and 160@xmath1 flux densities because the 100@xmath1 images are not deep enough to be affected by source confusion , and the 160@xmath1 images are only deep enough to be moderately affected . the 3@xmath21 depths of the 100 and 160@xmath1 images are @xmath221100@xmath23jy and @xmath222700@xmath23jy , respectively ; the 5@xmath21 depth of the 250@xmath1 image is @xmath225700@xmath23jy . we attempt to match each 24@xmath1 source to a source with a spectroscopic redshift from the catalogs of ( * ? ? ? * which includes redshifts compiled from the literature ) and stern et al . ( in preparation ) . we find spectroscopic redshifts for 910 ( 57% ) of the 24@xmath1 sources . if no coincident sources with spectroscopic redshifts are found , we resort to the photometric redshift source catalog of pannella et al . ( in preparation ) to find a source match . we exclude sources with photometric redshifts derived from ill - fitting templates ( those with reduced @xmath34 ) . for an additional 510 ( 32% ) of the 24@xmath1 sources we have photometric redshift estimates . there are no redshift estimates for 183 ( 11% ) of the 24@xmath1 sources , and these sources are excluded from our samples . using the multi - wavelength information and redshifts , we define 2 samples from the superset of all 24@xmath1 sources with @xmath19jy : * _ dog sample _ : all 24@xmath1 sources with 2.2@xmath1 counterparts and @xmath35 ( fig . [ fig : sample ] ) . the 24@xmath1 flux density of the faintest dog is 53@xmath23jy , justifying our @xmath19jy cut for the control sample . the limiting quantity is the depth of the 0.65@xmath1 image ( 3@xmath21 = 0.05@xmath23jy * ? ? ? the redshift distribution of our sample of dogs is shown in fig . [ fig : z_dist ] , also motivating our @xmath8 cut for the control sample . six ( of 61 ; 10% ) dogs have spectroscopic redshifts . in the following analysis , we include only dogs with @xmath8 . our conclusions do not change if we include dogs without redshift estimates in the sample . * _ control sample _ : all @xmath19jy 24@xmath1 sources with 2.2@xmath1 counterparts that are at @xmath8 , and that do not satisfy the dog selection criterion . seventy four ( of 268 ; 28% ) control galaxies have spectroscopic redshifts . for each sample , table [ table : numbers ] characterizes the subset of sources with flux densities detected at 0.65 , 100 , 160 , and 250@xmath1 . more than 70% of these galaxies are undetected in optical spectra ( or are unobserved ) because their observed - frame optical flux densities are so faint . our sample contains dogs with fainter 24@xmath1 emission than does the @xcite sample . their sample is selected from the shallower _ spitzer_/mips survey of the botes region ; their limit is @xmath36jy . however , the goods - n region is much smaller than the botes region , so we have few dogs with @xmath36jy . @xcite also study a sample of dogs in goods - n . the main differences between the @xcite sample and ours are that : 1 ) they limit their sample to @xmath37jy ; and 2 ) they estimate a redshift for each dog using irac and mips photometry , whereas we match dogs to sources in a near - ir / optical catalog , with redshift estimates based on @xmath38 , 3.6 , and 4.5@xmath1 photometry . the fractions of 24@xmath1 sources at @xmath8 that meet the dog criterion increase with increasing 24@xmath1 flux density ( fig . [ fig : sample ] ) . of the sources with @xmath39jy , 4% are dogs . of the sources with @xmath37jy , 25% are dogs . @xcite find similar fractions ; they also find that of their sources with @xmath36jy , 60% are dogs . lccccccc dogs & 61 & 2.1 & 161 & 47 ( 77% ) & 29 ( 48% ) & 24 ( 39% ) & 9 ( 15% ) + control & 268 & 2.0 & 102 & 268 ( 100% ) & 81 ( 30% ) & 52 ( 19% ) & 15 ( 6% ) flux density vs. 0.65@xmath1 flux density for galaxies in the two samples . the dog sample is defined by @xmath40 . [ fig : sample ] ] sources ( before we impose redshift limits ) . for the analysis , we limit all samples to the redshift range @xmath8 ( the area between the vertical lines).[fig : z_dist ] ] several quantities are useful in analyzing the relation between ir and emergent uv emission from galaxies . in this section , we detail how we estimate the total ir and uv luminosities , uv continuum power - law indices , star formation rates , and stellar masses for the galaxies in our samples . we estimate a total ir luminosity ( 81000@xmath1 ; @xmath41 ) for each galaxy with detected emission at 100@xmath1 . we redshift the @xcite template spectral energy distributions ( seds ) to the distance of each galaxy , find the sed that most closely matches the observed 100@xmath1 flux density , and multiply the ir luminosity of that sed by the ratio between actual and predicted flux densities to get @xmath41 . we prefer this approach over estimating the ir luminosity directly , by summing several far - ir flux densities , because the latter procedure requires detected emission at 160 and 250@xmath1 . the goods-_herschel _ image at 160@xmath1 is moderately affected by blending due to source confusion , while the image at 250@xmath1 is so deep that blending is problematic . the drawback to our chosen approach is that all statements we make regarding ir luminosities assume that the low - redshift template seds accurately represent the seds of galaxies at @xmath0 . @xcite show that this assumption is valid when template matching is done to 100@xmath1 flux densities . for galaxies with uv emission from newly formed massive stars , the uv continuum can be approximated as a power law with an index @xmath42 : @xmath43 we use @xmath18 flux densities at 0.45 , 0.55 , 0.65 , 0.80 , and 0.90@xmath1 ( i.e. , in the @xmath27- , @xmath28- , @xmath4- , @xmath29- , and @xmath30-bands ) to fit for @xmath42 and the constant factor @xmath44 for each galaxy which has an estimate of @xmath41 . if only two flux densities have s / n @xmath18 , we calculate @xmath42 analytically . if only one flux density has s / n @xmath18 , we use an upper limit for the 0.45@xmath1 flux density to calculate a lower limit to @xmath42 . we estimate a uv luminosity @xmath45 at rest - frame 0.16@xmath1 for each galaxy using its redshift estimate and the power - law fit to the rest - frame uv flux densities . to estimate a stellar mass for each galaxy , we fit stellar population synthesis models to its @xmath38 , 3.6 , and 4.5@xmath1 flux densities @xcite . full details are in 4.2 of @xcite . we assume the stellar initial mass function in @xcite from 0.1 to 100 @xmath46 , as well as the dust attenuation law in @xcite . we use the equation in @xcite to calculate a star formation rate ( sfr ) , based on the ir luminosity , for each galaxy with detected 100@xmath1 emission . we make no correction for the emergent uv luminosity , since it is negligible for all galaxies in the dog and control samples ( see [ sec : discuss ] ) . in using the @xcite equation , we assume that the observed 100@xmath1 emission is due to star formation and not agn activity , and that the star formation episode lasts for @xmath47 years . @xcite find that the former assumption is valid for most agn with detected x - ray emission at @xmath48 . seventy six percent of the @xmath0 galaxies with detected 100@xmath1 emission have @xmath3 ( fig . [ fig : lir ] ) . the distributions of ir luminosities for the dogs and the control galaxies are statistically indistinguishable ( @xmath49 that the two samples are drawn from the same parent population , using a k - s test ) . . the two distributions are statistically indistinguishable . [ fig : lir ] ] fig . [ fig : mass_z ] shows the stellar masses for dogs and control galaxies with detected emission at 100@xmath1 . the distributions are not strongly different ( @xmath50 , using a k - s test ) , though some control galaxies have lower stellar masses than do the dogs . 17 ( of 72 ; 24% ) control galaxies have stellar masses @xmath51 , while only 1 ( of 25 ; 4% ) dog has a stellar mass below this threshold . . the distribution of stellar masses for dogs is not strongly different from that for control galaxies , though some control galaxies have lower stellar masses than do the dogs . twenty four percent of the control sample has @xmath52 , as opposed to 4% of the dog sample.[fig : mass_z ] ] the infrared seds of most low redshift dusty galaxies peak between rest - frame @xmath53 and 100@xmath1 . the rest - frame @xmath11 luminosity is only a fraction of the total ir luminosity in these galaxies . to address whether or not dogs are abnormally bright at rest - frame @xmath11 , we require a comparison of the rest - frame far - ir and @xmath11 flux densities between dogs and the control galaxies [ fig:100over24_z ] shows that dogs are statistically indistinguishable from the control galaxies when looking at the observed flux density ratio @xmath54 ( @xmath55 , using a k - s test ) . in this figure , we do not show the galaxies with limits for @xmath56 . we perform the gehan and logrank tests , which are conceptually similar to the two sample k - s test , but also allow for the inclusion of galaxies with limits at 100@xmath1 in the two samples . we find no statistically significant difference between the dogs and the control galaxies ( @xmath57 that both samples are drawn from the same parent population , from both tests ) . our conclusions are the same using @xmath58 ( not shown ; @xmath59 from both tests ) . if dogs were abnormally luminous at rest - frame @xmath11 for their far - ir luminosities , then we would expect them to have low values of observed @xmath54 and/or @xmath58 compared to those of the control galaxies ; they do not . however , 100 and 160@xmath1 observations are sensitive to rest - frame 33 and 53@xmath1 emission from galaxies at @xmath6 . these rest - frame wavelengths are still short of the presumed wavelength of the peak of the infrared sed ; the rest - frame luminosities are still only a fraction of the total ir luminosity in these galaxies . 250@xmath1 observations are sensitive to rest - frame @xmath60 emission from galaxies at @xmath6 . this rest - frame wavelength is generally close to the wavelength of the peak of the ir sed . [ fig:250over24_z ] shows that dogs are statistically indistinguishable from the control galaxies when looking at the observed flux density ratio @xmath61 . we reach the same conclusion when including galaxies with limits at 250@xmath1 in statistical tests ( @xmath62 that both samples are drawn from the same parent population , from both a gehan and logrank test ) . vs. redshift for galaxies in the two samples . galaxies with limits at 100@xmath1 are not shown in this figure , but we do include them in our statistical tests . dogs are statistically indistinguishable from the control galaxies in @xmath54 . [ fig:100over24_z ] ] vs. redshift for galaxies in the two samples . galaxies with limits at 250@xmath1 are not shown in this figure , but we do include them in our statistical tests . as in fig . [ fig:100over24_z ] , dogs span the same range of flux density ratios as do the control galaxies ; this leads us to conclude that the dog criterion does not select dusty galaxies that are abnormally bright at rest - frame @xmath11 . [ fig:250over24_z ] ] the dog criterion does not select galaxies that are abnormally bright at rest - frame @xmath11 for their far - ir flux densities . what makes a dog a dog must be that the galaxy s rest - frame uv emission is suppressed , compared to the uv emission from a control galaxy . therefore we expect a clear separation between dogs and control galaxies when looking at the ratios of rest - frame optical to uv flux densities . indeed , fig . [ fig : roverk_z ] shows that 92% of dogs have an observed @xmath63 , while 78% of control galaxies have @xmath64 . the gehan and logrank tests report a statistical difference between the dogs and control galaxies ( @xmath65 that both samples are drawn from the same parent population , from both tests ) . galaxies with @xmath66 are also known as `` extremely red objects '' , or eros ( @xcite ; @xcite ; @xcite ; @xcite ) . we note that even though a galaxy with detected 24@xmath1 emission may meet the ero criterion , it may not meet the dog criterion ( and vice versa , rarely ) . vs. redshift for galaxies in the two samples . a dog is distinguishable from a random galaxy with detected 24@xmath1 emission because it is abnormally faint in the rest - frame uv . [ fig : roverk_z ] ] the statistical difference between the dogs and control galaxies for @xmath67 , and the lack thereof for @xmath54 , is robust against photometric redshift errors . we offset photometric redshifts for the superset of all galaxies with detected 24@xmath1 emission , assuming the offsets obey a gaussian distribution with @xmath68 = 0.1 . we then select new dog and control samples . the differences in @xmath67 are always statistically significant , and the differences in @xmath54 are very rarely statistically significant ( from k - s tests ) . we have shown that the 100 , 160 , and 250 to 24@xmath1 flux density ratios for dogs with moderate ir luminosities ( @xmath69 ) are statistically indistinguishable from those flux density ratios for galaxies with detected 24@xmath23 m emission that lie at similar redshifts and have similar ir luminosities , but that do not meet the dog selection criterion . most dogs have higher 2.2 to 0.65@xmath1 flux density ratios than do the control galaxies . thus it seems clear that dogs occupy the tail of a distribution of uv obscuration in ir - luminous galaxies at @xmath0 . we select a sample of dogs using deep images of the goods - n region . these dogs have lower ir luminosities than do dogs selected using shallower images of wider regions . for example , the @xcite sample in the wide botes region contains many dogs with @xmath70 . our sample contains very few galaxies with @xmath70 , and our conclusions regarding obscuration may not apply to dogs with such high luminosities . at low redshift , agn emission dominates the ir luminosity for most galaxies with @xmath70 @xcite . @xcite find that many dogs at @xmath0 with @xmath70 have featureless seds from observed - frame 3.6 to 8@xmath1 , indicating the presence of agn - heated dust . several studies @xcite find that , for these dogs , the seds at rest - frame mid- and far - ir wavelengths are similar to those of low redshift galaxies with ir luminosities dominated by agn emission , such as markarian 231 . only 2 ( of 59 ; 3% ) dogs , and 8 ( of 253 ; 3% ) control galaxies , have seds that increase ( in @xmath71 ) from observed - frame 3.6 to 8@xmath1 , and indeed both are among the dogs with the highest @xmath41 ( at @xmath72 and @xmath73 ) . two galaxies are not enough to allow us to rule out the possibility that dogs with @xmath74 differ in their 100 or 250 to 24@xmath1 flux density ratios from control galaxies with similar luminosities . most galaxies in our sample have @xmath69 . whether their ir luminosities are dominated by emission from agn or newly formed stars is not clear . @xcite and @xcite find that the average dog in this @xmath41 range has an x - ray spectrum with a power - law index they interpret as indicative of heavily obscured agn emission . an obscured agn would presumably contribute to the ir luminosity as well . @xcite find the same average x - ray index for a similar sample of dogs , but also find pah emission in the mid - infrared spectra of the dogs ; they conclude that heavily obscured agn emission can not coexist with pah emission . @xcite attribute the x - ray emission of the dogs to x - ray binaries rather than agn . in our sample , 5 ( of 61 ; 8% ) dogs and 31 ( of 268 ; 12% ) control galaxies have detected x - ray emission @xcite . for galaxies with @xmath75 , we do not find any evidence that agn emission at rest - frame mid - ir wavelengths is more or less common in dogs than in the control galaxies : the fractions of dogs and control galaxies with increasing seds between observed - frame 3.6@xmath1 and 8@xmath1 are similar , as are the fractions with detected x - ray emission . no matter what powers their ir luminosities , dogs in this @xmath41 range are abnormally uv faint , and are probably the most obscured galaxies . we have shown that the brightness of the emergent uv emission in @xmath0 dusty galaxies can vary considerably from galaxy to galaxy , even though the emergent uv emission is only a fraction of the ir emission . in a dusty galaxy at either low or high redshift , most of the intrinsic uv emission from newly formed stars and/or agn is absorbed by dust grains , which emit at ir wavelengths . we now ask : `` are the uv - emitting regions that we see from a dog or a control galaxy spatially coincident with the ir - emitting regions ? '' if yes , the variation in emergent uv emission is due to uv obscuration . if no , the emergent uv emission may come from stars in a `` normal '' galactic disk , whereas the newly formed stars ultimately responsible for the ir emission are completely obscured , perhaps in a compact , nuclear star - forming region . in this scenario , the variation in the rest - frame optical to uv flux density ratios might be due as much to differences in the stellar populations from galaxy to galaxy as to differences in obscuration @xcite . we can not yet efficiently spatially resolve the ir - emitting regions for large samples of high redshift dusty galaxies . two pieces of circumstantial evidence support the statement that the uv- and ir - emitting regions in these dusty galaxies are spatially coincident : 1 ) a minority of dogs and control galaxies deviate from the median specific sfr for galaxies at @xmath0 ; and 2 ) dogs and control galaxies define a continuous relation between their median ir to uv luminosity ratios and median uv continuum power - law indices . the specific star formation rate of a galaxy is the ratio of its sfr to its stellar mass . most star - forming galaxies at the same redshift fall on a tight relation between sfr and stellar mass ; this relation is referred to as the `` main sequence '' @xcite . @xcite find that sfr and stellar mass are directly proportional at all redshifts , and present the evolution of the median specific sfr for galaxies at @xmath76 . @xcite also isolate the minority of galaxies with specific sfrs much higher than the median values ( `` starbursts '' ) . here , we define starbursts as galaxies with specific sfrs higher than 3 times the median value at their redshift . a minority of dogs ( 5 of 25 ; 20% ) and control galaxies ( 18 of 72 ; 25% ) are starbursts ( fig . [ fig : mainseq ] ) . @xcite find that individual low redshift starbursts have compact uv - emitting regions ; the correspondence between deviation from the median specific sfr and the compact size of the uv - emitting region also holds for the average @xmath0 starburst . if this correspondence holds for individual @xmath0 galaxies , few dogs and control galaxies would have concentrated uv - emitting regions . these regions in the typical dog or control galaxy would be more widely distributed , and it would be less plausible that the uv - emitting regions occupy parts of the galaxy not occupied by ir - emitting regions . that radio - emitting regions in high redshift galaxies are widely distributed indirectly supports this idea @xcite . emission . the solid line is the median specific sfr for star - forming galaxies , as a function of redshift @xcite . the dotted line is three times the median value , which we use as a threshold for identifying starbursts . 20% of dogs and 25% of control galaxies are starbursts . dogs deviate from the median specific sfr no more frequently than do the control galaxies . [ fig : mainseq ] ] for starburst galaxies at low redshift , @xcite ( @xcite , and more recently * ? ? ? * ) find a relation between the ratio of ir to uv luminosities ( denoted irx ) and the power - law index of the sed in the uv ( denoted @xmath42 ) . ( @xcite refer to low redshift galaxies with bright uv - emitting regions as `` starbursts '' ; the term does not necessarily refer to galaxies that deviate from the main sequence . ) this relation is generally interpreted to mean that the ir emission originates as uv emission from newly formed stars , which is partially absorbed by dust . the dependence between the emergent uv emission , the dust emission in the ir , and @xmath42 , in the local irx-@xmath42 relation is consistent with the dependence of dust absorption on @xmath42 in the @xcite dust attenuation law . in other words , we think that galaxies that lie on this relation are thought to have spatially coincident uv- and ir - emitting regions . @xcite show that most lyman break galaxies ( lbg ) at @xmath0 lie on the local irx-@xmath42 relation . however , both @xmath0 lbgs and the low redshift starbursts in @xcite are much less dusty than dogs . some sub - classes of dusty galaxies deviate from the local relation , perhaps because their ir emission is unrelated to their emergent uv emission @xcite . [ fig : irxbeta ] shows the local irx-@xmath42 relation from @xcite and the relevant quantities for the @xmath0 dusty galaxies in our samples . individual galaxies , in both the dog and control samples , are found on either side of the relation . because dogs are so faint in the uv , it is difficult to precisely determine the power - law indices of their uv seds ; the large uncertainties on @xmath42 values preclude us from reaching firm conclusions about individual galaxies . the median @xmath42 values for the dog and control samples tend to lie to the left of the local irx-@xmath42 relation ; dogs do not appear to deviate more strongly from the relation than do control galaxies . these @xmath0 dusty galaxies define their own irx-@xmath42 relation . as noted earlier , specific sub - populations of dusty galaxies deviate from the local relation , but the trend that we find between the averages for a broader @xmath0 population has not been discussed . because the median @xmath42 value increases with increasing irx , from the lbgs to the dogs , the ir emission is not completely independent of the emergent uv emission in these galaxies . this reinforces our initial conclusion that @xmath0 dusty galaxies populate a continuum of uv obscuration , and that dogs are simply the most heavily obscured galaxies . over 0.16@xmath1 luminosity ( irx ) vs. uv continuum power - law index ( @xmath42 ) for galaxies with detected 100@xmath1 emission . we only show errors on the uv power - law indices . filled hourglasses and circles show the median @xmath42 values , in bins of irx ; the vertical bars show the range of irx over which the @xmath42 values are binned . the `` average lbg '' black asterisk is from @xcite , and shows a mean and its dispersion . the solid line is the local irx-@xmath42 relation from @xcite . [ fig : irxbeta ] ] dogs in the luminosity range spanned by our sample are more obscured than the control galaxies for a reason unrelated to their far - ir luminosity , because the @xmath41 distributions of the two samples are statistically indistinguishable . in galaxies with dust heated by uv emission from newly formed stars , the amount of obscuration affecting that uv emission can vary due to either : 1 ) differences in the degree of alignment between the spatial distributions of dust and newly formed massive stars ; or 2 ) differences in the total dust content . @xcite derive the local irx-@xmath42 relation by assuming a uniform screen of dust in the line of sight between us and the newly formed stars ( see figure 8 in @xcite for an illustration ) . @xcite show that this assumption can be recovered when the dust is instead distributed in clumps around star - forming regions . thus , dogs might be more obscured than the control galaxies because dogs have more dust clumps surrounding star - forming regions . variations in uv obscuration might also be caused by differences in the physical properties responsible for the shape of the sub - millimeter sed . for example , increases in the mass of cold dust can result in greater uv obscuration . increases in the cold dust mass can also result in increases in sub - millimeter emission . since the sub - millimeter luminosity is usually a small fraction of the total ir luminosity , the increase in total ir luminosity due to a higher cold dust mass would not be easily measurable between 100 and 250@xmath1 . we can not fully test this hypothesis without sub - millimeter luminosities for galaxies in our samples . the sensitivities of current sub - millimeter facilities limit comparisons of the dust content between dogs and control galaxies to the most luminous ( @xmath70 ) galaxies @xcite . currently available data do not allow us to discriminate between any hypotheses for the physical mechanisms responsible for either the differences in the degree of alignment between dust and stars or differences in the dust content . for instance , two plausible hypotheses are that : 1 ) galaxy inclination might be responsible for the patchiness of dust in the line - of - sight , and 2 ) many dogs are merging galaxies , and some aspect of the merging process creates differences in the degree of alignment . to falsify either we require high resolution rest - frame optical images ; the cosmic assembly near - infrared deep extragalactic legacy survey ( candels ) will obtain such images using _ hst_/wfc3 in the near future @xcite . we note that @xcite and @xcite examine rest - frame optical images of dogs in goods - s and conclude that most are undisturbed disk galaxies . furthermore , @xcite simulate isolated galaxies that meet the dog selection criterion , so dogs are not necessarily merging galaxies on the basis of their extreme rest - frame mid - ir to uv flux density ratios . finally , uv obscuration is affected by the prominence of the `` dust bump '' at rest - frame 2175 in a galaxy s attenuation curve . at @xmath0 , rest - frame 2175 is redshifted into the @xmath4-band filter . the presence of this feature in the attenuation curves of high redshift galaxies has been controversial ; the bump is found , though , in the attenuation curves for several samples of galaxies at @xmath77 @xcite . however , doubling the amplitude of the average bump leads to a reduction in the 0.65@xmath1 flux density by a factor of 1.3 . this is not large enough to explain the spread of @xmath67 in fig . [ fig : roverk_z ] . 1 . we cull a sample of dust - obscured galaxies ( dogs ) , or galaxies with @xmath35 that are at @xmath8 , in the goods - n region . we use deep goods-_herschel _ data to compare the emission from dogs with that from other @xmath0 galaxies with detected 24@xmath1 emission . the dogs in our sample span @xmath3 . dogs and control galaxies , with detected 100@xmath1 emission , have similar distributions of ir luminosities and stellar masses . we compare the rest - frame far - ir and optical flux densities of dogs with those of the control galaxies . dogs have extreme ratios of @xmath78 not because they are abnormally bright at rest - frame @xmath11 for their far - ir flux densities , but because they are abnormally faint in the rest - frame uv . 4 . dogs and the control galaxies scatter around the median specific sfr established by @xmath0 galaxies falling on the `` main sequence '' ; 20% of dogs have specific sfrs greater than 3 times the median value , and are thus starbursts . if uv - emitting regions in high - redshift starbursts are distributed as they are in low - redshift starbursts , few dogs have compact uv - emitting regions . 5 . for both the dog and control samples , the median rest - frame uv continuum power - law index ( @xmath42 ) at a given ir to uv luminosity ratio ( irx ) is lower than the index predicted by the local irx-@xmath42 relation . dogs do not appear to deviate more from this relation than do the control galaxies . over more than a factor of 100 in irx , the median @xmath42 value for these galaxies systematically increases with increasing irx . these pieces of evidence suggest that , for most of these galaxies , the uv- and ir - emitting regions are spatially coincident . thus , the range in rest - frame mid - ir to uv flux density ratios spanned by dusty galaxies at @xmath0 is due to differing amounts of uv obscuration . dogs are the most heavily obscured galaxies . differences in the amount of obscuration between dogs and other dusty galaxies at @xmath0 can be due to : 1 ) differences in the degree of alignment between the spatial distributions of dust and massive stars , or 2 ) differences in the total dust content . our samples do not have many galaxies with @xmath9 . in dogs with these ir luminosities , where agn emission may be the dominant source of dust heating , our conclusions about obscuration may not be valid . further information about the nature of obscuration in these galaxies can come from measurements that spatially resolve uv- and ir - emitting regions . for instance , the h@xmath79 to h@xmath42 line ratio varies with the amount of dust absorption , so its variation across a galaxy traces the spatial dust distribution . @xcite measure the galaxy - wide balmer decrement for several very luminous dogs ( those most likely to have ir luminosities dominated by agn emission ) ; @xcite present spatially resolved h@xmath79 maps , but h@xmath42 is outside their spectral window . _ hst _ can resolve the rest - frame uv and optical emission from these galaxies @xcite , and alma will resolve the ir emission and allow us to measure sub - millimeter luminosities we need to determine cold dust mass . studies using such data will clearly establish the degree to which the spatial distributions of dust and massive stars align . this work is based on observations made with _ , a european space agency cornerstone mission with significant participation by nasa . support for this work was provided by nasa through an award issued by jpl / caltech . the research activities of m.d . and a.d . are supported by noao , which is operated by the association of universities for research in astronomy under a cooperative agreement with the national science foundation . we are grateful to n. drory for sharing the sed - fitting code we use to estimate galaxy stellar masses .[/INST] dusty galaxies at @xmath0 span a wide range of relative brightness between rest - frame mid - infrared ( 8@xmath1 ) and ultraviolet wavelengths . we attempt to determine the physical mechanism responsible for this diversity . dust - obscured galaxies ( dogs ) , which have rest - frame mid - ir to uv flux density ratios @xmath2 , might be abnormally bright in the mid - ir , perhaps due to prominent agn and/or pah emission , or abnormally faint in the uv . we use far - infrared data from the goods-_herschel _ survey to show that most dogs with @xmath3 are not abnormally bright in the mid - ir when compared to other dusty galaxies with similar ir ( 81000@xmath1 ) luminosities . we observe a relation between the median ir to uv luminosity ratios and the median uv continuum power - law indices for these galaxies , and we find that only 24% have specific star formation rates which indicate the dominance of compact star - forming regions . this circumstantial evidence supports the idea that the uv- and ir - emitting regions in these galaxies are spatially coincident , which implies a connection between the abnormal uv faintness of dogs and dust obscuration . we conclude that the range in rest - frame mid - ir to uv flux density ratios spanned by dusty galaxies at @xmath0 is due to differing amounts of uv obscuration . of galaxies with these ir luminosities , dogs are the most obscured . we attribute differences in uv obscuration to either : 1 ) differences in the degree of alignment between the spatial distributions of dust and massive stars , or 2 ) differences in the total dust content . </s>

extensive research has implicated a number of genetic , epigenetic , nutritional , and lifestyle factors . furthermore , the composition of the gut microbiome has also been implicated in the development of obesity . irrespective of the specific causes leading to obesity , it is a strong risk factor for the development of cardiometabolic diseases , including insulin resistance , type 2 diabetes , and hypertension . the clinical consequences of obesity extend further to include a spectrum of other diseases such as malignancies , osteoarthritis , and obstructive sleep apnoea [ 1 , 2 ] . moreover , obesity exerts a heavy toll in terms of social and economic consequences [ 3 , 4 ] . the rising prevalence of both childhood and adult obesity is strongly linked to caloric excess and the sedentary urban lifestyle typical of westernised countries . there is , however , growing evidence for a robust physiological process that restricts the voluntary mechanisms to reduce body weight by drastic changes in lifestyle . in this respect , obesity is increasingly recognised as a disease rather than as a wilful choice [ 6 , 7 ] . viral infection has been implicated as a contributing factor in the aetiology of obesity in both animal and human studies . in addition , the gastrointestinal tract is home to over 10 bacteria that collectively form the intestinal microbiome , with a joint genetic repertoire that is larger than the human genome . these symbiotic bacteria establish and maintain the gut immune system and contribute to the breakdown of complex nondigestible plant - derived polysaccharides [ 10 , 11 ] . the aim of this review is to present the epidemiological evidence for the association between microbes and obesity , and discuss the cellular and molecular mechanisms underpinning the inflammatory response that is central to adipocyte dysfunction in obesity pathobiology . increased circulating levels of triglycerides and glucose perturb metabolic homeostasis and stimulate compensatory adipocyte hypertrophy and hyperplasia . persistently elevated triglyceride and glucose levels overwhelm the physiological response such that decompensation ( so - called adipocyte stress response ) arises , and thus adipocyte dysfunction ensues [ 1416 ] . adipocyte dysfunction is epitomised by a low grade chronic inflammatory response , which is an integral feature of obesity [ 20 , 21 ] . adipose tissue is infiltrated with bone marrow - derived macrophages , and the density of these adipose tissue macrophages ( atms ) is dependent on the degree of obesity . atms in lean nonobese individuals are anti - inflammatory ( m2 macrophages ) as opposed to atms in obese individuals that express proinflammatory genes ( m1 classically - activated macrophages ) . in nonobese , the obesity - induced changes in adipocyte gene expression trigger release of proinflammatory cytokines ( tnf- , mcp1 ) that lead to recruitment and activation of macrophages . the activated m1 macrophages produce and secrete other proinflammatory mediators , including il-6 , tnf- , il-1 , and resistin . cytokines such as tnf , il-6 , and il-1 exert paracrine effects to activate inflammatory pathways . this leads to activation of jun n - terminal kinase ( jnk ) , inhibitor of b kinase ( ikk ) , and other serine kinases , which activate transcription factor targets ( c - fos / c - jun ) and nuclear factor - kb ( nf - kb ) that stimulate transcription of inflammatory pathway genes [ 24 , 25 ] . primarily , il-6 triggers subclinical inflammation by instituting a vicious cycle that includes the downregulation of lipoprotein transport to peripheral tissues . the result is development of overt hypertriglyceridemia and hyperlipidaemia , which serves to perpetuate the obesity phenotype by presenting a constitutive signal for adipocyte hypertrophy and hyperplasia . it has also been shown that il-6 expression is more pronounced in metabolically active visceral rather than peripheral adipocytes . the expression of proinflammatory proteins , particularly tnf- , may lead to a reduction in anti - inflammatory adipokines , such as adiponectin which plays a pivotal anti - inflammatory role . despite the extensive research on adipose tissue inflammation , the direct causal link between the events that trigger chronic inflammation and the final metabolic outcome is still not clearly determined . this review will focus on presenting the evidence linking microbes to adipose tissue dysfunction in the setting of obesity . the first association between viruses and obesity in animals was reported by lyons et al . mice infected with canine distemper virus ( cdv ) demonstrated adipocyte hypertrophy and hyperplasia in the absence of cns pathology . cdv does not infect humans but is antigenically related to the paramyxoviridae family that includes the measles virus . subsequently other investigators had demonstrated that the virus targets specific hypothalamic regions and is associated with alteration of various neuropeptide - signalling pathways , including leptin , neuropeptide y , and melanin - concentrating hormone [ 3033 ] . rous - associated virus 7 ( rav-7 ) has also been associated with a syndrome of obesity , stunted growth , hypercholesterolaemia , fatty liver , and thyroid dysfunction in chickens . this rna virus causes a lymphomonocytic inflammation of the hypothalamus , pancreatic islet cell hyperplasia , and elevations of serum glucose and triglyceride levels [ 35 , 36 ] . seroepidemiological studies have implicated bdv in neuropsychiatric diseases including schizophrenia and depression in some populations , though the associations have not been consistent [ 3739 ] . another animal model of virus - induced obesity implicated the smam-1 avian adenovirus in chickens . subsequently , dhurandhar et al . demonstrated that body weight and bmi were higher in human subjects positive for anti - smam-1 antibodies compared to those negative for anti - smam-1 antibodies . kim et al . showed that inoculation of mice with the me7 strain of scrapie results in obesity that is dependent on the hypothalamic - pituitary - adrenal axis . the few associations between viral infection and animal obesity described above are clearly limited in translational terms , yet are still crucial in demonstrating a strong association between viral infection and obesity . human adenovirus 36 ( ad-36 ) is a common human pathogen that has been linked to human obesity and adipocyte function through different mechanisms and is discussed next . the adenoviruses are an important group of widely prevalent human pathogens that have been extensively studied . they are non - enveloped icosahedral dna viruses with a linear double stranded genome that can infect a wide range of species and tissues . their structural biology , genome , evolution , and host cell immune response has been reviewed elsewhere [ 4345 ] . clinically , they are responsible for a wide array of self - limiting infections , primarily of the respiratory and gastrointestinal tracts . furthermore , they are effective vectors for gene - based immunotherapy and gene replacement strategies . genomic characterisation of the virus revealed several unique features compared to other human adenoviruses that could possibly account for its unique tissue tropism . the first reported link between ad-36 and obesity was described in the year 2000 in animal models , where chicken and mice inoculated with ad-36 demonstrated increased adipose tissue and decreased cholesterol and triglyceride levels in the absence of cns histopathological changes . ad-36 dna was detected in adipose tissue but not in skeletal muscle of the inoculated animals . subsequently , other studies reproduced the adiposity - promoting effects of ad-36 in two non - human primate models . it was also shown that horizontal transmission of ad-36 from infected to control animals produces adiposity and is accompanied by a paradoxical reduction in serum lipids . rats infected with ad-36 demonstrate an increase in weight and insulin sensitivity , visceral adipose tissue expression of glycerol 3-phosphate dehydrogenase , and peroxisome proliferator - activated receptor gamma ( ppar- ) . ccaat / enhancer - binding protein ( c / ebp ) alpha and beta were greater in infected animals compared to controls . kapila et al . reported that in a hamster model ad-36 infection altered lipoprotein metabolism to produce a more atherogenic profile , with diminished hdl - c and increased ldl - c . viral dna as a result of acute ad-36 infection is detected in multiple tissues early following inoculation . the authors demonstrated that viral infection in 3t3-l1 murine preadipocytes induces differentiation and an increase in total cell lipid content . subsequently , rathod et al . showed that transient ad-36 mrna expression , but not viral dna replication , is required for preadipocyte differentiation . the increased expression of ppar- and c / ebp reported in animal studies is related to the proadipogenic effects observed in vitro , as these genes are key transcription factors that regulate adipocyte differentiation [ 52 , 57 ] . a detailed analysis of the cellular pathways involved in ad-36-induced adipogenesis showed that the viral e4 orf-1 gene stimulates proadipogenic differentiation in both 3t3-l1 and human adipose stem cells . e4 orf-1 modulates insulin sensitivity via activation of the phosphatidylinositol 3-kinase ( pi3 k ) pathway . studies also showed that ad-36 suppresses the expression of leptin mrna and improves glucose uptake in adipocytes . the role of ad-36 in human adipose tissue was further reinforced by studies that demonstrated that the virus induces commitment , differentiation , and lipid accumulation in human adipose - derived stem cells . adipocyte differentiation and lipid accumulation were observed in the absence of inducers of adipogenesis and in osteogenic culture media . they were accompanied by expression of the adipocyte - specific transcription factors ppar- and c / ebp. wang et al . also demonstrated that ad-36 significantly reduced fatty acid oxidation and increased de novo lipogenesis in cultured human muscle cells . further demonstrated in vitro that incubating preadipocytes and adipocytes with adenovirus ( subtypes 2 and 36 ) , amongst other viruses , was responsible for increased production of il-6 which might contribute to chronic low grade inflammation . a number of investigators have studied the epidemiologic association between ad-36 infection and human obesity . these investigations were carried out in different age groups and population ethnicities and utilised various methodologies for viral detection . the salient findings of these human seroepidemiologic studies have been recently described by ponterio and gnessi . the unique genomic and proteomic structure of ad-36 limits antibody cross reactivity in serum neutralization assays and further strengthens the reported associations between ad-36 and human obesity . the majority , though not all studies , showed greater seropositivity for ad-36 in obesity , with extensive variation in seroprevalence rates between countries . three meta - analyses also showed an association between ad-36 infection and obesity in both adults and children and are summarized in table 1 . the role of bacteria and their associated products in the pathogenesis of obesity has recently attracted considerable interest . moreover , it has been proposed that the composition of the gut microbiome may contribute to obesity through their effects on the gut barrier and beyond . the relatively recent technological advances in genomics have revolutionized the study of the intestinal microbiome . it is now possible to sequence mixed microbial genetic material directly extracted from environmental samples without prior laboratory culture of individual species . this emerging field , known as metagenomics , enables a survey of the different microorganisms present in a specific environment . several large - scale projects such as the human microbiome project have characterised microbial genomes from hundreds of isolated human symbionts and have shed light on the complex interplay between the human host and its microbial populace . the implications of compositional changes in health and disease have also been elucidated ( http://hmpdacc.org/ ) . butyrate along with propionate and acetate are short - chain fatty acids ( scfas ) derived from the bacterial degradation of complex polysaccharides in the gut . they have important metabolic roles with butyrate acting as a metabolic substrate for colonic epithelial cells . the functions mediated by butyrate that are pertinent to the pathogenesis of obesity include its role in the maintenance of intestinal epithelial integrity , thereby preventing the translocation of endotoxins produced by intestinal gram - negative bacteria across the gut barrier . maintaining the integrity of the gut barrier is critical in preventing contact between materials originating from the nonsterile external environment ( gut lumen ) with the sterile systemic circulation . immunoprotection is conferred by means of the gut - associated lymphoid tissue ( galt ) that is present on the mucosal surface and contains antigen presenting cells capable of processing and presenting exogenous antigens . the purpose of antigen presentation is primarily to activate adaptive immunity . the gut barrier is composed primarily of enterocytes which adhere to one another by means of tight junctions , desmosomes , and adherens junctions this is important in order for discriminative transport of material to occur effectively between the gut lumen and the systemic circulation . moreover , the gut barrier 's role as a physical barrier to infection is key in preventing dissemination of bacteria and their associated products from the lumen into the systemic circulation . the integral membrane proteins claudins and occludin , along with cytoskeletal adaptor proteins zo-1 , zo-2 , and zo-3 , have been demonstrated to facilitate paracellular transport between enterocytes . disruption of the gut barrier at any of these points results in indiscriminate dysregulated paracellular transport [ 67 , 71 ] . furthermore , it has been suggested that the integrity of the tight junction barrier is under strict regulation of proinflammatory and anti - inflammatory signalling . proinflammatory cytokines implicated in promoting tight junction leakage include tnf- and ifn-. contrarily , anti - inflammatory cytokines including tgf- and il-10 have been suggested to maintain the integrity of tight junctions by downregulating proinflammatory signalling [ 7276 ] . failure to maintain a robust gut barrier , termed gut barrier dysfunction , may lead to an altered microbiome composition , resulting in microbiome imbalance . the underlying causes of dysbiosis are diverse , and a high fat diet poor in prebiotic - containing nutrients has also been highlighted as a leading cause . a high fat diet has been shown to increase the ratio of obesity - promoting bacteria in the microbiome . in vivo studies widely used models include the obesity mouse model ob / ob ( leptin deficient ) and the db / db ( leptin receptor mutant ) mouse . in a study conducted by turnbaugh et al . it was shown that transfecting sterile laboratory mice with microbiota from ob / ob resulted in the expression of the obesity phenotype akin to ob / ob mice . moreover , sequencing studies performed by ley et al . compared the microbiome of ob / ob mice and lean wild type mice . firmicutes levels were found to be increased in comparison to bacteriodetes in ob / ob mice . extended their study to human subjects who adopted either a low - carbohydrate or a low - fat diet for weight control purposes , during a one - year period . follow - up during this period demonstrated that a change in bacteriodetes and firmicutes levels had occurred in study subjects compared to controls . the change was such that from an initial elevated baseline firmicutes : bacteriodetes ratio , the ratio had normalised in those subjects who lost weight and maintained a lean body weight after a year , matching that of controls . furthermore , faecal microbiome studies in lean and obese monozygotic and dizygotic twins established that the microbiome is shared between relatives , though bacterial lineages were individual - specific . a single dominant bacterial species was not identified and it was concluded that the core microbiome is shared in terms of genetic similarity rather than at a dominant organismal level . certain studies in humans have revealed beneficial commensal bacteria that strive to maintain the integrity of enterocytes and thus the gut barrier . these include akkermansia muciniphila found in the mucosal mucus coating as well as faecalibacterium prausnitzii [ 84 , 85 ] . in dysbiosis such beneficial organisms are lost , and this is coupled with endotoxin secretion by other harmful bacteria that promote gut barrier breakdown , precipitating metabolic endotoxaemia . central to the paradigm of bacteria as contributors to the pathogenesis of obesity is the concept of metabolic endotoxaemia . put simply , this is increased plasma bacterial lipopolysaccharide ( lps ) levels which are believed to originate from gram - negative gut microbiome that spill into the systemic circulation as a direct result of gut barrier dysfunction [ 67 , 77 , 78 ] . a number of systems have been implicated in mediating the gut - to - adipocyte axis signalling , a term that we have coined to describe the communication between the gut microbiome and their associated endotoxins with adipocytes . some systems have been proposed to function as gatekeepers and others as mediators of toxin spillage in the setting of gut barrier dysfunction . these systems include the endocannabinoid system , the apelinergic system , and the enteroendocrine system [ 78 , 86 ] . the endocannabinoid system is a key mediator of molecular signalling between lps ( chiefly originating from gram - negative organisms ) and adipocytes [ 78 , 87 ] . the two most studied bioactive lipids are n - arachidonoylethanolamine ( aea ) and 2-arachidonoylglycerol ( 2-ag ) which activate the g protein - coupled receptors cb1 and cb2 . though the expression of cb1 and cb2 was traditionally believed to be limited to the central nervous system , recent evidence suggests that gastrointestinal expression also occurs . in vivo and ex vivo studies the exact molecular signalling pathway that mediates metabolic endotoxaemia has not yet been elucidated [ 88 , 90 ] . however , cb1 receptor activation has been shown to modulate ion channels and activate different mitogen - activated protein kinase ( mapk ) pathways ( p42/p44 mapk , p38 mapk , and c - jun n - terminal kinase ) . it has also been implicated in the inhibition of adenylyl cyclase in tissues and cells . the aforementioned actions have been attributed to gi / o proteins . in the case of mapk pathways , aside from gi / o proteins , pi3 k also mediates cb1 receptor activation . similarly , l - type voltage - gated calcium channel activity was also shown to be targeted by cb1 receptor activation in cat cerebral arterial muscle and neonatal rat nucleus tractus solitarius . the effects here were primarily inhibitory [ 93 , 94 ] . among the wide array of physiological effects mediated by the endocannabinoid system , the one most pertinent to obesity is mainly increased energy intake and storage [ 95 , 96 ] . interestingly , the administration of the cb1 antagonist sr141716 in humans is accompanied by decreased body weight and anorexigenic effects . furthermore , to investigate the manner in which cb1 receptor agonist treatment or lps treatment gives rise to the metabolic features of diet - induced obesity , mice were chronically treated with low - dose lps before and during a high fat challenge . the plasma lps levels were significantly increased ( metabolic endotoxaemia ) as well as mrna levels of the macrophage markers f4/80 and cd11c in adipose tissue . this study clearly demonstrates a cause and effect relationship between lps inoculation and mediators of inflammation . it is therefore believed that one of the manners by which endotoxaemia promotes obesity is through the upregulation of the endocannabinoid system , thereby indirectly promoting adipogenesis . endotoxaemia has also been implicated in setting up chronic low grade inflammation in obesity , which is in keeping with experimental evidence in animal models . apelin is a peptide involved in the regulation of the central nervous , gastrointestinal , cardiovascular , and immune systems . it is also an adipokine secreted by mature adipocytes in mice and humans and mediates its effects via the apj receptor . it has been suggested as a negative regulator of obesity , though its precise mechanisms in this capacity are yet to be unravelled . a myriad of signalling cascades are triggered upon activation of apj receptor , the endpoint of which is the activation or repression of a number of transcription factors . coupling of the apj receptor to gq/11 stimulates plc- signalling and subsequent hydrolysis of phosphatidylinositol 4,5-bisphosphate ( pip2 ) to ip3 and diacylglycerol ( dag ) . an alternative signalling pathway also exists , where the apj receptor is coupled to gi / o . this pathway activates the mapk cascade via pkc and it can also activate pi3k , which in turn activates akt and mammalian target of rapamycin ( mtor ) . in addition , adenylate cyclase is inhibited by gi / o , whereas gs increases cyclic amp synthesis from atp and activates the pka pathway . a hyperactive endocannabinoid system in the pathogenic setting of obesity , along with low grade chronic inflammation , has been suggested as the culprits for the augmentation in apelin levels observed in obese animal models and humans . intraperitoneal administration of apelin in obese and normal mice over a 14-day period induced weight loss independent of food intake . in addition , it was demonstrated in db / db mice that apelin and apj mrna levels showed twofold and threefold respective increase . possibly , a hyperactive endocannabinoid system and low grade inflammation may directly or indirectly trigger activation of the apelinergic system as a homeostatic mechanism to counteract obesity . the l - cells of the enteroendocrine system are neuroendocrine cells expressed from the duodenum to the rectum and produce glucagon - like peptides 1 and 2 ( glp-1 and glp-2 ) [ 101 , 102 ] . glp-1 is an incretin hormone known for its role in glucose homeostasis and energy balance . glp-1 may be implicated in antagonising the effects of metabolic endotoxaemia by regulating epithelial cell proliferation , thus sustaining the gut barrier . in order to determine the mechanisms through which intestinal proliferation is promoted by glp-1 , c57bl/6 wt mice were treated with the glp-1 receptor agonist exenatide ( ex-4 : exendin-4 ) for a period of one week . increased weight , length , and weight per unit length of small bowel and large were noted . these effects were also observed with chronic ( 1 month ) treatment of c57bl/6 wt mice . however , this effect was not evident in glp1r mice who were subjected to the same treatment over the same period of time . a conditional deletion of the igf1r gene from intestinal epithelial cells and subsequent liraglutide and exenatide administration increased both small bowel and colon weight and length . activation of glp-1 receptor signalling in fgf7 mice failed to increase small bowel and colon mass in the absence of fgf7 . it was therefore deduced that glp-1 receptor agonists activate components of igf-1 and erbb signalling pathways and that the proliferative actions of glp-1 receptor agonists are selectively mediated through mechanisms requiring fgf7 . the cells were subcultured in the presence or absence of glp-2 as well as different kinase antagonist concentrations . these included genistein ( global tyrosine kinase inhibitor ) , ly294002 ( pi3k ) inhibitor , and pd 098059 ( mitogen - activated / extracellular signal - regulated kinase ( mek ) inhibitor ) . cells which were administered glp-2 exhibited more than 10-fold increase in proliferation , a response which was blunted by genistein , ly294002 , and pd 098059 in a dose - dependent fashion . such a response was attributed at least in part to both the pi 3-kinase and the mapk pathways . further studies in humans are warranted in order to elucidate the underlying mechanisms pertinent in gut proliferation mediated by both glp-1 and glp-2 . however , the experimental models provide clear evidence of the involvement of the enteroendocrine system in intestinal proliferation . in light of the previously discussed viral infection and bacterial endotoxaemia , the conventional perspective of adipocyte dysfunction in the pathogenesis of obesity clearly exhibits a number of limitations in substantially explaining adipocyte inflammation as a feature of obesity pathogenesis . firstly , the trigger for inflammatory cell recruitment and secretion of inflammatory cytokines in adipose tissue is poorly accounted for , with no experimental evidence in existence to the best of our knowledge [ 105107 ] . no consideration has therefore been given to the contributory role of microbes or microbial endotoxins such as bacterial lps in initiating and perpetuating chronic low grade inflammation . the physiological goal of inflammation is primarily to eliminate an insult which the body deems alien and noxious . this is often employed via the innate and subsequently the adaptive immune responses should the insult persist . the acute inflammatory response is therefore converted to chronic inflammation in the setting of a persistent insult . it is therefore not unreasonable to propose that viral infection and metabolic endotoxaemia may serve as triggers of inflammation that underpin adipocyte dysfunction . mechanistically , we have subdivided possible triggers of inflammation into transient and persistent factors on the basis of chronicity . in the case of viral infection , it is plausible to suggest that acute repetitive infections may serve as a transient factor that regularly initiates acute inflammation . the infective situation may be described as a repetitive acute - on - chronic scenario . repetitive infections may be explained by the fact that obesity is associated with an increased susceptibility to infection due to impaired systemic immune function . the chronic nature of dysbiosis and subsequent metabolic endotoxaemia is in keeping with the chronicity of inflammation observed in obesity and may qualify as persistent factors . this may therefore suggest a critical role for dysbiosis and endotoxaemia in initiating and perpetuating chronic inflammation via the persistent presence of bacterial lps in the systemic circulation . the repetitive acute - on - chronic viral infections along with chronic dysbiosis and metabolic endotoxaemia may therefore possibly act in a concerted manner to promote chronic inflammation . the characteristically low grade subclinical the resident gut microflora is an essential component of gastrointestinal physiology and its myriad role is beyond the scope of this review . a degree of immunological tolerance is exerted so as not to instigate an immune response against them , in order to preserve their critical function [ 109 , 110 ] . it has been suggested that the gut microbiome regulates not only local intestinal immunity but also systemic immunity . it is therefore logical to suggest that the impaired systemic immune function that occurs in obesity may at least in part be attributed to dysbiosis and metabolic endotoxaemia , therefore resulting in subclinical inflammation . it has been demonstrated that immature haematopoietic stem cells are present in adipocytes , and mature adipocytes express membrane - bound nadph oxidase similar to that of phagocytic neutrophils . it has also been suggested that the fact that adipocytes and their progenitors share a common embryonic origin with cells of the immune system rationalises the adipogenic response to endotoxaemia ( i.e. , adipocyte expansion ) . it is therefore plausible to propose that adipocyte hypertrophy and hyperplasia ( i.e. , the obesity response ) are akin to an immune response mounted against an exogenous antigen , in terms of immune cell replication and phagocytosis . therefore , perhaps the effects of the often recommended healthy diet and exercise extend far beyond lipolysis and weight loss . the beneficial effects of such measures may in addition restore a healthy microbiome and thus eliminate dysbiosis and endotoxaemia as triggers of obesity . exercise - induced hyperaemia and angiogenesis may serve to increase circulatory transport of repair factors to regions of gut barrier damage , promoting repair and resolution . the microbial hypothesis attempts to address the limitations of the classical hypothesis in explaining the trigger of inflammation in adipocyte dysfunction , and the possible role that microbes and microbial endotoxins may play in the process . rather than it does so in terms of filling in the missing link in the chain of events , taking into account the aforementioned recent experimental data that have undoubtedly suggested a critical role for microbes and microbial products in obesity pathobiology . taken together , there is undoubtedly an association between viral infection and metabolic endotoxaemia in the pathogenesis of obesity . however , proof of association , no matter how appealing or robust , does not necessarily imply causation . since the obesity epidemic is recognised as being multifactorial in origin , a multifaceted approach to management is therefore warranted . infection treatment and prevention do not formally feature in clinical practice guidelines given the fact that basic science research in infectobesity is still at its infancy , yet very promising . however , one should make no mistake to undermine the overwhelming evidence in both animal models and humans that suggest an important role for infection and endotoxaemia in the development of obesity . in fact , this is gaining prominence so much so that massachusetts general hospital is sponsoring the faecal microbiota transplant for obesity and metabolism clinical trial , the first clinical trial to study the impact of gut bacteria on weight ( https://clinicaltrials.gov/ct2/show/nct02530385 ) . the results of this trial are awaited anxiously by the scientific community , as it could possibly cause a paradigm shift in our understanding of obesity and alter the management course of this epidemic .

the global obesity epidemic , dubbed globesity by the world health organisation , is a pressing public health issue . the aetiology of obesity is multifactorial incorporating both genetic and environmental factors . recently , epidemiological studies have observed an association between microbes and obesity . obesity - promoting microbiome and resultant gut barrier disintegration have been implicated as key factors facilitating metabolic endotoxaemia . this is an influx of bacterial endotoxins into the systemic circulation , believed to underpin obesity pathogenesis . adipocyte dysfunction and subsequent adipokine secretion characterised by low grade inflammation , were conventionally attributed to persistent hyperlipidaemia . they were thought of as pivotal in perpetuating obesity . it is now debated whether infection and endotoxaemia are also implicated in initiating and perpetuating low grade inflammation . the fact that obesity has a prevalence of over 600 million and serves as a risk factor for chronic diseases including cardiovascular disease and type 2 diabetes mellitus is testament to the importance of exploring the role of microbes in obesity pathobiology . it is on this basis that massachusetts general hospital is sponsoring the faecal microbiota transplant for obesity and metabolism clinical trial , to study the impact of microbiome composition on weight . the association of microbes with obesity , namely , adenovirus infection and metabolic endotoxaemia , is reviewed .

<s>[INST]extensive research has implicated a number of genetic , epigenetic , nutritional , and lifestyle factors . furthermore , the composition of the gut microbiome has also been implicated in the development of obesity . irrespective of the specific causes leading to obesity , it is a strong risk factor for the development of cardiometabolic diseases , including insulin resistance , type 2 diabetes , and hypertension . the clinical consequences of obesity extend further to include a spectrum of other diseases such as malignancies , osteoarthritis , and obstructive sleep apnoea [ 1 , 2 ] . moreover , obesity exerts a heavy toll in terms of social and economic consequences [ 3 , 4 ] . the rising prevalence of both childhood and adult obesity is strongly linked to caloric excess and the sedentary urban lifestyle typical of westernised countries . there is , however , growing evidence for a robust physiological process that restricts the voluntary mechanisms to reduce body weight by drastic changes in lifestyle . in this respect , obesity is increasingly recognised as a disease rather than as a wilful choice [ 6 , 7 ] . viral infection has been implicated as a contributing factor in the aetiology of obesity in both animal and human studies . in addition , the gastrointestinal tract is home to over 10 bacteria that collectively form the intestinal microbiome , with a joint genetic repertoire that is larger than the human genome . these symbiotic bacteria establish and maintain the gut immune system and contribute to the breakdown of complex nondigestible plant - derived polysaccharides [ 10 , 11 ] . the aim of this review is to present the epidemiological evidence for the association between microbes and obesity , and discuss the cellular and molecular mechanisms underpinning the inflammatory response that is central to adipocyte dysfunction in obesity pathobiology . increased circulating levels of triglycerides and glucose perturb metabolic homeostasis and stimulate compensatory adipocyte hypertrophy and hyperplasia . persistently elevated triglyceride and glucose levels overwhelm the physiological response such that decompensation ( so - called adipocyte stress response ) arises , and thus adipocyte dysfunction ensues [ 1416 ] . adipocyte dysfunction is epitomised by a low grade chronic inflammatory response , which is an integral feature of obesity [ 20 , 21 ] . adipose tissue is infiltrated with bone marrow - derived macrophages , and the density of these adipose tissue macrophages ( atms ) is dependent on the degree of obesity . atms in lean nonobese individuals are anti - inflammatory ( m2 macrophages ) as opposed to atms in obese individuals that express proinflammatory genes ( m1 classically - activated macrophages ) . in nonobese , the obesity - induced changes in adipocyte gene expression trigger release of proinflammatory cytokines ( tnf- , mcp1 ) that lead to recruitment and activation of macrophages . the activated m1 macrophages produce and secrete other proinflammatory mediators , including il-6 , tnf- , il-1 , and resistin . cytokines such as tnf , il-6 , and il-1 exert paracrine effects to activate inflammatory pathways . this leads to activation of jun n - terminal kinase ( jnk ) , inhibitor of b kinase ( ikk ) , and other serine kinases , which activate transcription factor targets ( c - fos / c - jun ) and nuclear factor - kb ( nf - kb ) that stimulate transcription of inflammatory pathway genes [ 24 , 25 ] . primarily , il-6 triggers subclinical inflammation by instituting a vicious cycle that includes the downregulation of lipoprotein transport to peripheral tissues . the result is development of overt hypertriglyceridemia and hyperlipidaemia , which serves to perpetuate the obesity phenotype by presenting a constitutive signal for adipocyte hypertrophy and hyperplasia . it has also been shown that il-6 expression is more pronounced in metabolically active visceral rather than peripheral adipocytes . the expression of proinflammatory proteins , particularly tnf- , may lead to a reduction in anti - inflammatory adipokines , such as adiponectin which plays a pivotal anti - inflammatory role . despite the extensive research on adipose tissue inflammation , the direct causal link between the events that trigger chronic inflammation and the final metabolic outcome is still not clearly determined . this review will focus on presenting the evidence linking microbes to adipose tissue dysfunction in the setting of obesity . the first association between viruses and obesity in animals was reported by lyons et al . mice infected with canine distemper virus ( cdv ) demonstrated adipocyte hypertrophy and hyperplasia in the absence of cns pathology . cdv does not infect humans but is antigenically related to the paramyxoviridae family that includes the measles virus . subsequently other investigators had demonstrated that the virus targets specific hypothalamic regions and is associated with alteration of various neuropeptide - signalling pathways , including leptin , neuropeptide y , and melanin - concentrating hormone [ 3033 ] . rous - associated virus 7 ( rav-7 ) has also been associated with a syndrome of obesity , stunted growth , hypercholesterolaemia , fatty liver , and thyroid dysfunction in chickens . this rna virus causes a lymphomonocytic inflammation of the hypothalamus , pancreatic islet cell hyperplasia , and elevations of serum glucose and triglyceride levels [ 35 , 36 ] . seroepidemiological studies have implicated bdv in neuropsychiatric diseases including schizophrenia and depression in some populations , though the associations have not been consistent [ 3739 ] . another animal model of virus - induced obesity implicated the smam-1 avian adenovirus in chickens . subsequently , dhurandhar et al . demonstrated that body weight and bmi were higher in human subjects positive for anti - smam-1 antibodies compared to those negative for anti - smam-1 antibodies . kim et al . showed that inoculation of mice with the me7 strain of scrapie results in obesity that is dependent on the hypothalamic - pituitary - adrenal axis . the few associations between viral infection and animal obesity described above are clearly limited in translational terms , yet are still crucial in demonstrating a strong association between viral infection and obesity . human adenovirus 36 ( ad-36 ) is a common human pathogen that has been linked to human obesity and adipocyte function through different mechanisms and is discussed next . the adenoviruses are an important group of widely prevalent human pathogens that have been extensively studied . they are non - enveloped icosahedral dna viruses with a linear double stranded genome that can infect a wide range of species and tissues . their structural biology , genome , evolution , and host cell immune response has been reviewed elsewhere [ 4345 ] . clinically , they are responsible for a wide array of self - limiting infections , primarily of the respiratory and gastrointestinal tracts . furthermore , they are effective vectors for gene - based immunotherapy and gene replacement strategies . genomic characterisation of the virus revealed several unique features compared to other human adenoviruses that could possibly account for its unique tissue tropism . the first reported link between ad-36 and obesity was described in the year 2000 in animal models , where chicken and mice inoculated with ad-36 demonstrated increased adipose tissue and decreased cholesterol and triglyceride levels in the absence of cns histopathological changes . ad-36 dna was detected in adipose tissue but not in skeletal muscle of the inoculated animals . subsequently , other studies reproduced the adiposity - promoting effects of ad-36 in two non - human primate models . it was also shown that horizontal transmission of ad-36 from infected to control animals produces adiposity and is accompanied by a paradoxical reduction in serum lipids . rats infected with ad-36 demonstrate an increase in weight and insulin sensitivity , visceral adipose tissue expression of glycerol 3-phosphate dehydrogenase , and peroxisome proliferator - activated receptor gamma ( ppar- ) . ccaat / enhancer - binding protein ( c / ebp ) alpha and beta were greater in infected animals compared to controls . kapila et al . reported that in a hamster model ad-36 infection altered lipoprotein metabolism to produce a more atherogenic profile , with diminished hdl - c and increased ldl - c . viral dna as a result of acute ad-36 infection is detected in multiple tissues early following inoculation . the authors demonstrated that viral infection in 3t3-l1 murine preadipocytes induces differentiation and an increase in total cell lipid content . subsequently , rathod et al . showed that transient ad-36 mrna expression , but not viral dna replication , is required for preadipocyte differentiation . the increased expression of ppar- and c / ebp reported in animal studies is related to the proadipogenic effects observed in vitro , as these genes are key transcription factors that regulate adipocyte differentiation [ 52 , 57 ] . a detailed analysis of the cellular pathways involved in ad-36-induced adipogenesis showed that the viral e4 orf-1 gene stimulates proadipogenic differentiation in both 3t3-l1 and human adipose stem cells . e4 orf-1 modulates insulin sensitivity via activation of the phosphatidylinositol 3-kinase ( pi3 k ) pathway . studies also showed that ad-36 suppresses the expression of leptin mrna and improves glucose uptake in adipocytes . the role of ad-36 in human adipose tissue was further reinforced by studies that demonstrated that the virus induces commitment , differentiation , and lipid accumulation in human adipose - derived stem cells . adipocyte differentiation and lipid accumulation were observed in the absence of inducers of adipogenesis and in osteogenic culture media . they were accompanied by expression of the adipocyte - specific transcription factors ppar- and c / ebp. wang et al . also demonstrated that ad-36 significantly reduced fatty acid oxidation and increased de novo lipogenesis in cultured human muscle cells . further demonstrated in vitro that incubating preadipocytes and adipocytes with adenovirus ( subtypes 2 and 36 ) , amongst other viruses , was responsible for increased production of il-6 which might contribute to chronic low grade inflammation . a number of investigators have studied the epidemiologic association between ad-36 infection and human obesity . these investigations were carried out in different age groups and population ethnicities and utilised various methodologies for viral detection . the salient findings of these human seroepidemiologic studies have been recently described by ponterio and gnessi . the unique genomic and proteomic structure of ad-36 limits antibody cross reactivity in serum neutralization assays and further strengthens the reported associations between ad-36 and human obesity . the majority , though not all studies , showed greater seropositivity for ad-36 in obesity , with extensive variation in seroprevalence rates between countries . three meta - analyses also showed an association between ad-36 infection and obesity in both adults and children and are summarized in table 1 . the role of bacteria and their associated products in the pathogenesis of obesity has recently attracted considerable interest . moreover , it has been proposed that the composition of the gut microbiome may contribute to obesity through their effects on the gut barrier and beyond . the relatively recent technological advances in genomics have revolutionized the study of the intestinal microbiome . it is now possible to sequence mixed microbial genetic material directly extracted from environmental samples without prior laboratory culture of individual species . this emerging field , known as metagenomics , enables a survey of the different microorganisms present in a specific environment . several large - scale projects such as the human microbiome project have characterised microbial genomes from hundreds of isolated human symbionts and have shed light on the complex interplay between the human host and its microbial populace . the implications of compositional changes in health and disease have also been elucidated ( http://hmpdacc.org/ ) . butyrate along with propionate and acetate are short - chain fatty acids ( scfas ) derived from the bacterial degradation of complex polysaccharides in the gut . they have important metabolic roles with butyrate acting as a metabolic substrate for colonic epithelial cells . the functions mediated by butyrate that are pertinent to the pathogenesis of obesity include its role in the maintenance of intestinal epithelial integrity , thereby preventing the translocation of endotoxins produced by intestinal gram - negative bacteria across the gut barrier . maintaining the integrity of the gut barrier is critical in preventing contact between materials originating from the nonsterile external environment ( gut lumen ) with the sterile systemic circulation . immunoprotection is conferred by means of the gut - associated lymphoid tissue ( galt ) that is present on the mucosal surface and contains antigen presenting cells capable of processing and presenting exogenous antigens . the purpose of antigen presentation is primarily to activate adaptive immunity . the gut barrier is composed primarily of enterocytes which adhere to one another by means of tight junctions , desmosomes , and adherens junctions this is important in order for discriminative transport of material to occur effectively between the gut lumen and the systemic circulation . moreover , the gut barrier 's role as a physical barrier to infection is key in preventing dissemination of bacteria and their associated products from the lumen into the systemic circulation . the integral membrane proteins claudins and occludin , along with cytoskeletal adaptor proteins zo-1 , zo-2 , and zo-3 , have been demonstrated to facilitate paracellular transport between enterocytes . disruption of the gut barrier at any of these points results in indiscriminate dysregulated paracellular transport [ 67 , 71 ] . furthermore , it has been suggested that the integrity of the tight junction barrier is under strict regulation of proinflammatory and anti - inflammatory signalling . proinflammatory cytokines implicated in promoting tight junction leakage include tnf- and ifn-. contrarily , anti - inflammatory cytokines including tgf- and il-10 have been suggested to maintain the integrity of tight junctions by downregulating proinflammatory signalling [ 7276 ] . failure to maintain a robust gut barrier , termed gut barrier dysfunction , may lead to an altered microbiome composition , resulting in microbiome imbalance . the underlying causes of dysbiosis are diverse , and a high fat diet poor in prebiotic - containing nutrients has also been highlighted as a leading cause . a high fat diet has been shown to increase the ratio of obesity - promoting bacteria in the microbiome . in vivo studies widely used models include the obesity mouse model ob / ob ( leptin deficient ) and the db / db ( leptin receptor mutant ) mouse . in a study conducted by turnbaugh et al . it was shown that transfecting sterile laboratory mice with microbiota from ob / ob resulted in the expression of the obesity phenotype akin to ob / ob mice . moreover , sequencing studies performed by ley et al . compared the microbiome of ob / ob mice and lean wild type mice . firmicutes levels were found to be increased in comparison to bacteriodetes in ob / ob mice . extended their study to human subjects who adopted either a low - carbohydrate or a low - fat diet for weight control purposes , during a one - year period . follow - up during this period demonstrated that a change in bacteriodetes and firmicutes levels had occurred in study subjects compared to controls . the change was such that from an initial elevated baseline firmicutes : bacteriodetes ratio , the ratio had normalised in those subjects who lost weight and maintained a lean body weight after a year , matching that of controls . furthermore , faecal microbiome studies in lean and obese monozygotic and dizygotic twins established that the microbiome is shared between relatives , though bacterial lineages were individual - specific . a single dominant bacterial species was not identified and it was concluded that the core microbiome is shared in terms of genetic similarity rather than at a dominant organismal level . certain studies in humans have revealed beneficial commensal bacteria that strive to maintain the integrity of enterocytes and thus the gut barrier . these include akkermansia muciniphila found in the mucosal mucus coating as well as faecalibacterium prausnitzii [ 84 , 85 ] . in dysbiosis such beneficial organisms are lost , and this is coupled with endotoxin secretion by other harmful bacteria that promote gut barrier breakdown , precipitating metabolic endotoxaemia . central to the paradigm of bacteria as contributors to the pathogenesis of obesity is the concept of metabolic endotoxaemia . put simply , this is increased plasma bacterial lipopolysaccharide ( lps ) levels which are believed to originate from gram - negative gut microbiome that spill into the systemic circulation as a direct result of gut barrier dysfunction [ 67 , 77 , 78 ] . a number of systems have been implicated in mediating the gut - to - adipocyte axis signalling , a term that we have coined to describe the communication between the gut microbiome and their associated endotoxins with adipocytes . some systems have been proposed to function as gatekeepers and others as mediators of toxin spillage in the setting of gut barrier dysfunction . these systems include the endocannabinoid system , the apelinergic system , and the enteroendocrine system [ 78 , 86 ] . the endocannabinoid system is a key mediator of molecular signalling between lps ( chiefly originating from gram - negative organisms ) and adipocytes [ 78 , 87 ] . the two most studied bioactive lipids are n - arachidonoylethanolamine ( aea ) and 2-arachidonoylglycerol ( 2-ag ) which activate the g protein - coupled receptors cb1 and cb2 . though the expression of cb1 and cb2 was traditionally believed to be limited to the central nervous system , recent evidence suggests that gastrointestinal expression also occurs . in vivo and ex vivo studies the exact molecular signalling pathway that mediates metabolic endotoxaemia has not yet been elucidated [ 88 , 90 ] . however , cb1 receptor activation has been shown to modulate ion channels and activate different mitogen - activated protein kinase ( mapk ) pathways ( p42/p44 mapk , p38 mapk , and c - jun n - terminal kinase ) . it has also been implicated in the inhibition of adenylyl cyclase in tissues and cells . the aforementioned actions have been attributed to gi / o proteins . in the case of mapk pathways , aside from gi / o proteins , pi3 k also mediates cb1 receptor activation . similarly , l - type voltage - gated calcium channel activity was also shown to be targeted by cb1 receptor activation in cat cerebral arterial muscle and neonatal rat nucleus tractus solitarius . the effects here were primarily inhibitory [ 93 , 94 ] . among the wide array of physiological effects mediated by the endocannabinoid system , the one most pertinent to obesity is mainly increased energy intake and storage [ 95 , 96 ] . interestingly , the administration of the cb1 antagonist sr141716 in humans is accompanied by decreased body weight and anorexigenic effects . furthermore , to investigate the manner in which cb1 receptor agonist treatment or lps treatment gives rise to the metabolic features of diet - induced obesity , mice were chronically treated with low - dose lps before and during a high fat challenge . the plasma lps levels were significantly increased ( metabolic endotoxaemia ) as well as mrna levels of the macrophage markers f4/80 and cd11c in adipose tissue . this study clearly demonstrates a cause and effect relationship between lps inoculation and mediators of inflammation . it is therefore believed that one of the manners by which endotoxaemia promotes obesity is through the upregulation of the endocannabinoid system , thereby indirectly promoting adipogenesis . endotoxaemia has also been implicated in setting up chronic low grade inflammation in obesity , which is in keeping with experimental evidence in animal models . apelin is a peptide involved in the regulation of the central nervous , gastrointestinal , cardiovascular , and immune systems . it is also an adipokine secreted by mature adipocytes in mice and humans and mediates its effects via the apj receptor . it has been suggested as a negative regulator of obesity , though its precise mechanisms in this capacity are yet to be unravelled . a myriad of signalling cascades are triggered upon activation of apj receptor , the endpoint of which is the activation or repression of a number of transcription factors . coupling of the apj receptor to gq/11 stimulates plc- signalling and subsequent hydrolysis of phosphatidylinositol 4,5-bisphosphate ( pip2 ) to ip3 and diacylglycerol ( dag ) . an alternative signalling pathway also exists , where the apj receptor is coupled to gi / o . this pathway activates the mapk cascade via pkc and it can also activate pi3k , which in turn activates akt and mammalian target of rapamycin ( mtor ) . in addition , adenylate cyclase is inhibited by gi / o , whereas gs increases cyclic amp synthesis from atp and activates the pka pathway . a hyperactive endocannabinoid system in the pathogenic setting of obesity , along with low grade chronic inflammation , has been suggested as the culprits for the augmentation in apelin levels observed in obese animal models and humans . intraperitoneal administration of apelin in obese and normal mice over a 14-day period induced weight loss independent of food intake . in addition , it was demonstrated in db / db mice that apelin and apj mrna levels showed twofold and threefold respective increase . possibly , a hyperactive endocannabinoid system and low grade inflammation may directly or indirectly trigger activation of the apelinergic system as a homeostatic mechanism to counteract obesity . the l - cells of the enteroendocrine system are neuroendocrine cells expressed from the duodenum to the rectum and produce glucagon - like peptides 1 and 2 ( glp-1 and glp-2 ) [ 101 , 102 ] . glp-1 is an incretin hormone known for its role in glucose homeostasis and energy balance . glp-1 may be implicated in antagonising the effects of metabolic endotoxaemia by regulating epithelial cell proliferation , thus sustaining the gut barrier . in order to determine the mechanisms through which intestinal proliferation is promoted by glp-1 , c57bl/6 wt mice were treated with the glp-1 receptor agonist exenatide ( ex-4 : exendin-4 ) for a period of one week . increased weight , length , and weight per unit length of small bowel and large were noted . these effects were also observed with chronic ( 1 month ) treatment of c57bl/6 wt mice . however , this effect was not evident in glp1r mice who were subjected to the same treatment over the same period of time . a conditional deletion of the igf1r gene from intestinal epithelial cells and subsequent liraglutide and exenatide administration increased both small bowel and colon weight and length . activation of glp-1 receptor signalling in fgf7 mice failed to increase small bowel and colon mass in the absence of fgf7 . it was therefore deduced that glp-1 receptor agonists activate components of igf-1 and erbb signalling pathways and that the proliferative actions of glp-1 receptor agonists are selectively mediated through mechanisms requiring fgf7 . the cells were subcultured in the presence or absence of glp-2 as well as different kinase antagonist concentrations . these included genistein ( global tyrosine kinase inhibitor ) , ly294002 ( pi3k ) inhibitor , and pd 098059 ( mitogen - activated / extracellular signal - regulated kinase ( mek ) inhibitor ) . cells which were administered glp-2 exhibited more than 10-fold increase in proliferation , a response which was blunted by genistein , ly294002 , and pd 098059 in a dose - dependent fashion . such a response was attributed at least in part to both the pi 3-kinase and the mapk pathways . further studies in humans are warranted in order to elucidate the underlying mechanisms pertinent in gut proliferation mediated by both glp-1 and glp-2 . however , the experimental models provide clear evidence of the involvement of the enteroendocrine system in intestinal proliferation . in light of the previously discussed viral infection and bacterial endotoxaemia , the conventional perspective of adipocyte dysfunction in the pathogenesis of obesity clearly exhibits a number of limitations in substantially explaining adipocyte inflammation as a feature of obesity pathogenesis . firstly , the trigger for inflammatory cell recruitment and secretion of inflammatory cytokines in adipose tissue is poorly accounted for , with no experimental evidence in existence to the best of our knowledge [ 105107 ] . no consideration has therefore been given to the contributory role of microbes or microbial endotoxins such as bacterial lps in initiating and perpetuating chronic low grade inflammation . the physiological goal of inflammation is primarily to eliminate an insult which the body deems alien and noxious . this is often employed via the innate and subsequently the adaptive immune responses should the insult persist . the acute inflammatory response is therefore converted to chronic inflammation in the setting of a persistent insult . it is therefore not unreasonable to propose that viral infection and metabolic endotoxaemia may serve as triggers of inflammation that underpin adipocyte dysfunction . mechanistically , we have subdivided possible triggers of inflammation into transient and persistent factors on the basis of chronicity . in the case of viral infection , it is plausible to suggest that acute repetitive infections may serve as a transient factor that regularly initiates acute inflammation . the infective situation may be described as a repetitive acute - on - chronic scenario . repetitive infections may be explained by the fact that obesity is associated with an increased susceptibility to infection due to impaired systemic immune function . the chronic nature of dysbiosis and subsequent metabolic endotoxaemia is in keeping with the chronicity of inflammation observed in obesity and may qualify as persistent factors . this may therefore suggest a critical role for dysbiosis and endotoxaemia in initiating and perpetuating chronic inflammation via the persistent presence of bacterial lps in the systemic circulation . the repetitive acute - on - chronic viral infections along with chronic dysbiosis and metabolic endotoxaemia may therefore possibly act in a concerted manner to promote chronic inflammation . the characteristically low grade subclinical the resident gut microflora is an essential component of gastrointestinal physiology and its myriad role is beyond the scope of this review . a degree of immunological tolerance is exerted so as not to instigate an immune response against them , in order to preserve their critical function [ 109 , 110 ] . it has been suggested that the gut microbiome regulates not only local intestinal immunity but also systemic immunity . it is therefore logical to suggest that the impaired systemic immune function that occurs in obesity may at least in part be attributed to dysbiosis and metabolic endotoxaemia , therefore resulting in subclinical inflammation . it has been demonstrated that immature haematopoietic stem cells are present in adipocytes , and mature adipocytes express membrane - bound nadph oxidase similar to that of phagocytic neutrophils . it has also been suggested that the fact that adipocytes and their progenitors share a common embryonic origin with cells of the immune system rationalises the adipogenic response to endotoxaemia ( i.e. , adipocyte expansion ) . it is therefore plausible to propose that adipocyte hypertrophy and hyperplasia ( i.e. , the obesity response ) are akin to an immune response mounted against an exogenous antigen , in terms of immune cell replication and phagocytosis . therefore , perhaps the effects of the often recommended healthy diet and exercise extend far beyond lipolysis and weight loss . the beneficial effects of such measures may in addition restore a healthy microbiome and thus eliminate dysbiosis and endotoxaemia as triggers of obesity . exercise - induced hyperaemia and angiogenesis may serve to increase circulatory transport of repair factors to regions of gut barrier damage , promoting repair and resolution . the microbial hypothesis attempts to address the limitations of the classical hypothesis in explaining the trigger of inflammation in adipocyte dysfunction , and the possible role that microbes and microbial endotoxins may play in the process . rather than it does so in terms of filling in the missing link in the chain of events , taking into account the aforementioned recent experimental data that have undoubtedly suggested a critical role for microbes and microbial products in obesity pathobiology . taken together , there is undoubtedly an association between viral infection and metabolic endotoxaemia in the pathogenesis of obesity . however , proof of association , no matter how appealing or robust , does not necessarily imply causation . since the obesity epidemic is recognised as being multifactorial in origin , a multifaceted approach to management is therefore warranted . infection treatment and prevention do not formally feature in clinical practice guidelines given the fact that basic science research in infectobesity is still at its infancy , yet very promising . however , one should make no mistake to undermine the overwhelming evidence in both animal models and humans that suggest an important role for infection and endotoxaemia in the development of obesity . in fact , this is gaining prominence so much so that massachusetts general hospital is sponsoring the faecal microbiota transplant for obesity and metabolism clinical trial , the first clinical trial to study the impact of gut bacteria on weight ( https://clinicaltrials.gov/ct2/show/nct02530385 ) . the results of this trial are awaited anxiously by the scientific community , as it could possibly cause a paradigm shift in our understanding of obesity and alter the management course of this epidemic .[/INST]the global obesity epidemic , dubbed globesity by the world health organisation , is a pressing public health issue . the aetiology of obesity is multifactorial incorporating both genetic and environmental factors . recently , epidemiological studies have observed an association between microbes and obesity . obesity - promoting microbiome and resultant gut barrier disintegration have been implicated as key factors facilitating metabolic endotoxaemia . this is an influx of bacterial endotoxins into the systemic circulation , believed to underpin obesity pathogenesis . adipocyte dysfunction and subsequent adipokine secretion characterised by low grade inflammation , were conventionally attributed to persistent hyperlipidaemia . they were thought of as pivotal in perpetuating obesity . it is now debated whether infection and endotoxaemia are also implicated in initiating and perpetuating low grade inflammation . the fact that obesity has a prevalence of over 600 million and serves as a risk factor for chronic diseases including cardiovascular disease and type 2 diabetes mellitus is testament to the importance of exploring the role of microbes in obesity pathobiology . it is on this basis that massachusetts general hospital is sponsoring the faecal microbiota transplant for obesity and metabolism clinical trial , to study the impact of microbiome composition on weight . the association of microbes with obesity , namely , adenovirus infection and metabolic endotoxaemia , is reviewed .</s>

the year 2008 marks the 27th anniversary of the first case report of a new disease today known as acquired immunodeficiency syndrome ( aids ) , whose etiological agent is human immunodeficiency virus type 1 ( hiv-1 ) ( 1 ) . an estimated 38.6 million people are now living with hiv or aids worldwide , and nearly 11 000 people are infected by hiv daily ( joint united nations programme on hiv / aids / world health organization ) . since the documentation of the first aids case , numerous efforts have focused on vaccine and antiviral drug discovery and development , on identifying measures to prevent hiv transmission , on understanding hiv pathogenesis and the associated host immune responses , and on defining the interactions of hiv-1 proteins with human host cell proteins . the latter is crucial to understanding the individual steps of hiv-1 replication and pathogenesis , and provides an essential foundation for the development of safe and effective therapeutic and prevention strategies to combat aids . as a result of these efforts , thousands of published articles have addressed the interaction of hiv-1 proteins with human host proteins . however , each individual publication addresses only one or a few hiv protein host protein interactions making it cumbersome to collect information on all interactions for one particular hiv or cellular protein . the division of acquired immunodeficiency syndrome ( daids ) of the national institute of allergy and infectious diseases ( niaid ) recognized the need for a searchable platform to catalog the interactions of individual hiv proteins with host cell proteins . therefore , the development of an hiv-1 , human protein interaction database was initiated in collaboration with southern research institute and the national center for biotechnology information ( ncbi ) . development of the hiv-1 , human protein interaction database from the peer - reviewed scientific literature available in pubmed was a 7-year effort starting in 2000 . a short communication detailing the development of the database and including a visualization of the hiv-1 , human protein interaction network has been published recently ( 2 ) . briefly , more than 100 000 journal abstracts and publications were identified and screened for original research describing interactions between hiv-1 and human host proteins . in addition , new literature is routinely reviewed to identify interactions described in current publications . review of publications by scientific curator staff is organized by individual hiv-1 proteins and catalogued into an access database by extracting the interaction information from the continuous text . as review of individual interactions is completed , data are provided to ncbi incrementally as a set of comprehensive tab - delimited text files and loaded to a ms sql server 2005 database . validated interaction data are integrated into appropriate records in entrez gene and provided as custom reports and downloads per hiv-1 protein through the reports and downloads tools at http://www.ncbi.nlm.nih.gov / projects / refseq / hivinteractions/. the complete dataset is also available for ftp ( ftp://ftp.ncbi.nih.gov/gene/generif/hiv_interactions.gz ) . an update to the database released on 13 november 2007 , which included the interaction data set for the hiv-1 env proteins , marked the milestone of completion of the comprehensive hiv-1 , human protein interaction database based on original research articles published since 1984 . updates to the database based on interactions described in new scientific reports will be released on a recurring basis . the goal in developing this database was to provide scientists in the field of hiv / aids research a concise , yet detailed , summary of all known interactions between hiv-1 and host cell proteins and it has therefore been designed to track the following information for each protein protein interaction identified in the literature : ncbi reference sequence ( refseq ) protein accession numbers;ncbi entrez gene i d numbers;brief description of the protein protein interaction;keywords to support searching for interactions;national library of medicine ( nlm ) pubmed identification numbers ( pmids ) for all journal articles describing the interaction . ncbi reference sequence ( refseq ) protein accession numbers ; ncbi entrez gene i d numbers ; brief description of the protein protein interaction ; keywords to support searching for interactions ; national library of medicine ( nlm ) pubmed identification numbers ( pmids ) for all journal articles describing the interaction . the purpose of the database is to serve as a central interactive interface for viewing an ensemble of the known interactions between individual hiv-1 proteins and human proteins . the hiv-1 , human protein interaction database home page ( http://www.ncbi.nlm.nih.gov/refseq/hivinteractions/ ) enables users to simultaneously view and download a variety of reports detailing interactions for each hiv-1 protein . the database is structured by initial searches for the nine hiv proteins ( e.g. gag , pol , env , tat , rev , nef , vif , vpr and vpu ) , listed in the top right panel of the home page . an alphabetical report of all interacting human proteins is accessed by following the link for any of the hiv-1 proteins . the hiv-1 proteins can also be searched based on their components , for example hiv-1 envelope can be searched either for the entire protein gp160 , or separately for the gp120 surface glycoprotein or the gp41 transmembrane protein , which result from proteolytic cleavage of gp160 . the hiv - to - human protein interactions are categorized by 43 interaction keywords ( e.g. activates , associates with , binds , cleaves , complexes with , deglycosylates , inhibits , modulates , upregulates , etc . ) . a query interface allows for searching of the database to identify cellular proteins that have a specific type of interaction with a viral protein based on these keywords . the report can be customized to categories of interest by selecting a specific hiv protein and interaction keywords from the drop down menus . reports can be viewed as a web page , or downloaded as a text file for later use . in addition , to help facilitate the retrieval of related data , links to other database resources , such as the database of interacting proteins ( dip ; 3 ) , the molecular interaction database ( mint ; 4 ) , the binding database ( 5 ) and the los alamos national laboratories ( lanl ) hiv databases ( 6 ) , are provided on the home page . figure 1 depicts the report and search interface page for the hiv-1 gag polyprotein and its cleavage products . as mentioned earlier , the drop down menus ( figure 1a ) allow for the selection of data related to the individual gag cleavage products ( e.g. matrix , capsid , nucleocapsid , p1 and p6 ) and also facilitate searching by specific keywords ( e.g. associates with , binds and inhibits ) that represent the relationship between the viral proteins and the interacting human proteins ( figure 1b ) . reports can either be viewed online or downloaded in ascii format and contain the hiv-1 tax i d , hiv-1 gene i d , hiv-1 protein accession number , hiv-1 protein name , the interaction keyword , the human tax i d , human gene i d , human protein accession number , human protein name , the pmid(s ) , the modification date and the interaction description . ( a ) all or part of the interaction data available for an hiv-1 protein can be accessed using the drop down menus . ( b ) the interacting relationship between hiv-1 and human proteins is reported below the menus . the figure illustrates a query section to display all interactions catalogued for the hiv-1 pr55 ( gag ) protein . for example , the first two interactions shown are : ( i ) pr55 ( gag ) protein associates with atp - binding cassette , sub - family e , member 1 ; and ( ii ) pr55 ( gag ) protein binds to adaptor - related protein complex 2 , alpha 1 subunit isoform 1 . ( c ) further down , the display shows the association of hiv-1 matrix and p6 with the mitogen - activated protein kinase 1 ( mapk1 ) . ( d ) the arrow points to the link for the entrez gene reports ( the green g icon ) . ( a ) all or part of the interaction data available for an hiv-1 protein can be accessed using the drop down menus . ( b ) the interacting relationship between hiv-1 and human proteins is reported below the menus . the figure illustrates a query section to display all interactions catalogued for the hiv-1 pr55 ( gag ) protein . for example , the first two interactions shown are : ( i ) pr55 ( gag ) protein associates with atp - binding cassette , sub - family e , member 1 ; and ( ii ) pr55 ( gag ) protein binds to adaptor - related protein complex 2 , alpha 1 subunit isoform 1 . ( c ) further down , the display shows the association of hiv-1 matrix and p6 with the mitogen - activated protein kinase 1 ( mapk1 ) . ( d ) the arrow points to the link for the entrez gene reports ( the green g icon ) . currently , the database is composed of 1434 human genes encoding 1448 proteins that directly ( e.g. bind , inhibit ) or indirectly ( e.g. upregulate , modify ) interact with hiv-1 proteins . it was found that the majority of the interactions reported are indirect ( 68% ) , whereas the rest are direct ( 2 ) . in addition , the database comprises 2589 unique hiv-1 to human protein interactions and 5135 brief descriptions of the interactions , with a total of 14 312 pmid references to the original articles that reported the interactions . a network of links to supporting literature and cross - references allows users to navigate concomitantly between this database and other resources at ncbi ( 7 ) , such as entrez gene ( 8) , refseq ( 9 ) and pubmed . reports in entrez gene that contain hiv-1 interaction data can be retrieved with the query navigation to a target human protein interaction can be accomplished via one of two primary routes : an hiv-1 , human protein interaction database search or an entrez gene text query . for illustration purposes , two search scenarios for the signaling protein mitogen - activated protein kinase 1 ( mapk1 ) , which displays a high magnitude of interactions with ten different hiv-1 proteins , are provided subsequently . hiv-1 , human protein interaction database search . to view interactions between mapk1 and gag or its cleavage products , users may select gag in the horizontal selection bar on the top right panel of the database home page ( http://www.ncbi.nlm.nih.gov/refseq/hivinteractions/ ) , which makes a direct link to the illustration as shown in figure 1 . using the scroll down mouse menu , mapk1 can be identified since interacting proteins reported in each interaction session ( e.g. associates with and binds in figure 1b ) are alphabetic . as a searching result , mapk1 is involved in the process of matrix and p6 phosphorylation ( figure 1c ) . users may click on links to entrez gene ( the green g icon ; figure 1d ) to view the mapk1 full report . users may begin with the following query : mitogen - activated protein kinase 1[title ] and homo sapiens [ organism ] . the entries ( e.g. mapk1 and mapk1ip1l ) identified with the query are displayed on the entrez gene results page . adding and hiv1interactions[prop] to the query restricts the results to only those entries that have hiv-1 interaction data , and in this example returns a single match to the mapk1 gene report shown in figure 2 . protein interactions associated with mapk1 are listed on the entrez gene report page in the hiv-1 protein interactions section ( figure 2 ) ; a link to this section is included in the right column table of contents provided on the full report display ( figure 2a ) . individual hiv-1 proteins ( e.g. envelope surface glycoprotein gp120 ) that interact with mapk1 are listed ( figure 2b ) along with brief descriptions of the interactions ( figure 2c ) and links to the supporting literature in pubmed ( figure 2d ) . ( d ) the interactions and descriptions are linked to the supporting literature in pubmed . ( d ) the interactions and descriptions are linked to the supporting literature in pubmed . by integrating the hiv-1 interaction data into the entrez gene database , researchers benefit from the additional computation ncbi hiv-1 , human protein interaction database home page , there are automatic queries provided to pubmed and the ncbi sequence databases for recent records of interest . via entrez gene , information can be easily obtained about genomic context , pathway membership and protein domain structure . the representative entrez gene search strategies summarized in the following table demonstrate the strength of the data integration and provide examples of how specific subsets of data can be retrieved : query to enter in entrez geneexplanationhiv1interactions[prop ] and human[organism ] and 5[chr ] and 1000000:12000000[base position]genes for which products interact with hiv-1 proteins , based on chromosome location . the value before [ chr ] gives the chromosome , and the range separated by : gives the location in base pairs on that chromosome.hiv1interactions[prop ] and human[organism ] and cytoplasm*[go]genes for which products interact with hiv-1 proteins , and are coded by the go consortium with at least one term starting with cytoplasm.hiv1interactions[prop ] and human[organism ] and immunoglobulin[domain name]genes for which products interact with hiv-1 proteins , and are calculated by ncbi 's conserved domain database group as having an immunoglobulin domain.hiv1interactions[prop ] and human[organism ] and ( kegg or reactome)genes for which products interact with hiv-1 proteins and for which pathways data are available from the kegg or reactome groups . data visualization can be accomplished in multiple ways utilizing the information stored in this database . figure 3 shows an example of data visualization using biological process gene ontology ( go ) terms ( 10 , http://www.geneontology.org ) and individual hiv-1 proteins . this bar chart also demonstrates that a large portion of interactions catalogued in the database are associated with the hiv envelope surface ( gp120 ) and tat proteins . the human cellular proteins interacting with hiv span a wide variety of functional categories , ( e.g. signal transduction , protein metabolism , development , etc . ) with an overrepresentation of interactions between tat and cellular proteins involved in transcription . in addition , envelope and tat proteins also have a high number of interactions with proteins representing multiple biological processes . figure 3.distribution of interactions based on biological process gene ontology ( go ) terms and individual hiv-1 proteins . the x - axis shows the individual hiv-1 structural proteins gag , pol and env and their cleavage products , and the regulatory and accessory hiv-1 proteins , tat , rev , nef , vpu , vpr and vif . distribution of interactions based on biological process gene ontology ( go ) terms and individual hiv-1 proteins . the x - axis shows the individual hiv-1 structural proteins gag , pol and env and their cleavage products , and the regulatory and accessory hiv-1 proteins , tat , rev , nef , vpu , vpr and vif . the hiv-1 , human protein interaction database represents an important step towards a more detailed understanding of hiv-1 replication and pathogenesis . a recent example of the value of the database includes the work of brass et al . ( 11,12 ) , who used the database as a tool to help analyze and categorize human proteins required for hiv-1 replication . similarly , in order to support their analysis of human pathogen protein protein interactions , dyer et al . ( 13 ) were able to use a subset of the hiv-1 interaction data that has been incorporated into the biomolecular interaction network database ( bind ; 14 ) . pathogen protein protein interactions has recently been studied in detail and such maps have revealed global and local networks that relate to known biological properties . studies have indicated that both viral and bacterial proteins tend to interact with hubs ( proteins with many interacting partners ) and bottlenecks ( proteins that are central to many pathways in the network ) in human pathogen protein protein interaction networks ( 13,1517 ) . development of such global and local pathway networks by utilizing the information provided in the hiv-1 , human protein interaction database will provide additional insights into hiv-1 replication and disease mechanisms at a systems biology level . these networks may reconfirm and extend known pathways , as well as uncover previously unknown pathway components . in addition , these networks may serve as a starting point for a systems biology modeling of the development of effective therapeutic and prophylactic interventions . hiv-1 , human protein interaction database will be continuously updated to keep the database populated with interactions newly reported in the literature . current efforts are also focused on incorporating these data into canada 's biomolecular object network database ( bond ) ( http://bond.unleashedinformatics.com ; successor to bind ; 14 ) , a database cataloguing the interactions between all known cellular proteins . hiv-1 , human protein interaction database , or any data contained therein can be provided by using the write to the help desk link at the bottom of the database and entrez gene web pages . national institutes of health , national institute of allergy and infectious diseases , division of aids ( n01-ai-05415 and n01-ai-70042 to w.f . , b.e.s .- b . and r.g.p . ) ; intramural research program of the national institutes of health , national library of medicine ( to k.s.k .

the human immunodeficiency virus type 1 ( hiv-1 ) , human protein interaction database , available through the national library of medicine at www.ncbi.nlm.nih.gov/refseq/hivinteractions , was created to catalog all interactions between hiv-1 and human proteins published in the peer - reviewed literature . the database serves the scientific community exploring the discovery of novel hiv vaccine candidates and therapeutic targets . to facilitate this discovery approach , the following information for each hiv-1 human protein interaction is provided and can be retrieved without restriction by web - based downloads and ftp protocols : reference sequence ( refseq ) protein accession numbers , entrez gene identification numbers , brief descriptions of the interactions , searchable keywords for interactions and pubmed identification numbers ( pmids ) of journal articles describing the interactions . currently , 2589 unique hiv-1 to human protein interactions and 5135 brief descriptions of the interactions , with a total of 14 312 pmid references to the original articles reporting the interactions , are stored in this growing database . in addition , all protein protein interactions documented in the database are integrated into entrez gene records and listed in the hiv-1 protein interactions section of entrez gene reports . the database is also tightly linked to other databases through entrez gene , enabling users to search for an abundance of information related to hiv pathogenesis and replication .

<s>[INST]the year 2008 marks the 27th anniversary of the first case report of a new disease today known as acquired immunodeficiency syndrome ( aids ) , whose etiological agent is human immunodeficiency virus type 1 ( hiv-1 ) ( 1 ) . an estimated 38.6 million people are now living with hiv or aids worldwide , and nearly 11 000 people are infected by hiv daily ( joint united nations programme on hiv / aids / world health organization ) . since the documentation of the first aids case , numerous efforts have focused on vaccine and antiviral drug discovery and development , on identifying measures to prevent hiv transmission , on understanding hiv pathogenesis and the associated host immune responses , and on defining the interactions of hiv-1 proteins with human host cell proteins . the latter is crucial to understanding the individual steps of hiv-1 replication and pathogenesis , and provides an essential foundation for the development of safe and effective therapeutic and prevention strategies to combat aids . as a result of these efforts , thousands of published articles have addressed the interaction of hiv-1 proteins with human host proteins . however , each individual publication addresses only one or a few hiv protein host protein interactions making it cumbersome to collect information on all interactions for one particular hiv or cellular protein . the division of acquired immunodeficiency syndrome ( daids ) of the national institute of allergy and infectious diseases ( niaid ) recognized the need for a searchable platform to catalog the interactions of individual hiv proteins with host cell proteins . therefore , the development of an hiv-1 , human protein interaction database was initiated in collaboration with southern research institute and the national center for biotechnology information ( ncbi ) . development of the hiv-1 , human protein interaction database from the peer - reviewed scientific literature available in pubmed was a 7-year effort starting in 2000 . a short communication detailing the development of the database and including a visualization of the hiv-1 , human protein interaction network has been published recently ( 2 ) . briefly , more than 100 000 journal abstracts and publications were identified and screened for original research describing interactions between hiv-1 and human host proteins . in addition , new literature is routinely reviewed to identify interactions described in current publications . review of publications by scientific curator staff is organized by individual hiv-1 proteins and catalogued into an access database by extracting the interaction information from the continuous text . as review of individual interactions is completed , data are provided to ncbi incrementally as a set of comprehensive tab - delimited text files and loaded to a ms sql server 2005 database . validated interaction data are integrated into appropriate records in entrez gene and provided as custom reports and downloads per hiv-1 protein through the reports and downloads tools at http://www.ncbi.nlm.nih.gov / projects / refseq / hivinteractions/. the complete dataset is also available for ftp ( ftp://ftp.ncbi.nih.gov/gene/generif/hiv_interactions.gz ) . an update to the database released on 13 november 2007 , which included the interaction data set for the hiv-1 env proteins , marked the milestone of completion of the comprehensive hiv-1 , human protein interaction database based on original research articles published since 1984 . updates to the database based on interactions described in new scientific reports will be released on a recurring basis . the goal in developing this database was to provide scientists in the field of hiv / aids research a concise , yet detailed , summary of all known interactions between hiv-1 and host cell proteins and it has therefore been designed to track the following information for each protein protein interaction identified in the literature : ncbi reference sequence ( refseq ) protein accession numbers;ncbi entrez gene i d numbers;brief description of the protein protein interaction;keywords to support searching for interactions;national library of medicine ( nlm ) pubmed identification numbers ( pmids ) for all journal articles describing the interaction . ncbi reference sequence ( refseq ) protein accession numbers ; ncbi entrez gene i d numbers ; brief description of the protein protein interaction ; keywords to support searching for interactions ; national library of medicine ( nlm ) pubmed identification numbers ( pmids ) for all journal articles describing the interaction . the purpose of the database is to serve as a central interactive interface for viewing an ensemble of the known interactions between individual hiv-1 proteins and human proteins . the hiv-1 , human protein interaction database home page ( http://www.ncbi.nlm.nih.gov/refseq/hivinteractions/ ) enables users to simultaneously view and download a variety of reports detailing interactions for each hiv-1 protein . the database is structured by initial searches for the nine hiv proteins ( e.g. gag , pol , env , tat , rev , nef , vif , vpr and vpu ) , listed in the top right panel of the home page . an alphabetical report of all interacting human proteins is accessed by following the link for any of the hiv-1 proteins . the hiv-1 proteins can also be searched based on their components , for example hiv-1 envelope can be searched either for the entire protein gp160 , or separately for the gp120 surface glycoprotein or the gp41 transmembrane protein , which result from proteolytic cleavage of gp160 . the hiv - to - human protein interactions are categorized by 43 interaction keywords ( e.g. activates , associates with , binds , cleaves , complexes with , deglycosylates , inhibits , modulates , upregulates , etc . ) . a query interface allows for searching of the database to identify cellular proteins that have a specific type of interaction with a viral protein based on these keywords . the report can be customized to categories of interest by selecting a specific hiv protein and interaction keywords from the drop down menus . reports can be viewed as a web page , or downloaded as a text file for later use . in addition , to help facilitate the retrieval of related data , links to other database resources , such as the database of interacting proteins ( dip ; 3 ) , the molecular interaction database ( mint ; 4 ) , the binding database ( 5 ) and the los alamos national laboratories ( lanl ) hiv databases ( 6 ) , are provided on the home page . figure 1 depicts the report and search interface page for the hiv-1 gag polyprotein and its cleavage products . as mentioned earlier , the drop down menus ( figure 1a ) allow for the selection of data related to the individual gag cleavage products ( e.g. matrix , capsid , nucleocapsid , p1 and p6 ) and also facilitate searching by specific keywords ( e.g. associates with , binds and inhibits ) that represent the relationship between the viral proteins and the interacting human proteins ( figure 1b ) . reports can either be viewed online or downloaded in ascii format and contain the hiv-1 tax i d , hiv-1 gene i d , hiv-1 protein accession number , hiv-1 protein name , the interaction keyword , the human tax i d , human gene i d , human protein accession number , human protein name , the pmid(s ) , the modification date and the interaction description . ( a ) all or part of the interaction data available for an hiv-1 protein can be accessed using the drop down menus . ( b ) the interacting relationship between hiv-1 and human proteins is reported below the menus . the figure illustrates a query section to display all interactions catalogued for the hiv-1 pr55 ( gag ) protein . for example , the first two interactions shown are : ( i ) pr55 ( gag ) protein associates with atp - binding cassette , sub - family e , member 1 ; and ( ii ) pr55 ( gag ) protein binds to adaptor - related protein complex 2 , alpha 1 subunit isoform 1 . ( c ) further down , the display shows the association of hiv-1 matrix and p6 with the mitogen - activated protein kinase 1 ( mapk1 ) . ( d ) the arrow points to the link for the entrez gene reports ( the green g icon ) . ( a ) all or part of the interaction data available for an hiv-1 protein can be accessed using the drop down menus . ( b ) the interacting relationship between hiv-1 and human proteins is reported below the menus . the figure illustrates a query section to display all interactions catalogued for the hiv-1 pr55 ( gag ) protein . for example , the first two interactions shown are : ( i ) pr55 ( gag ) protein associates with atp - binding cassette , sub - family e , member 1 ; and ( ii ) pr55 ( gag ) protein binds to adaptor - related protein complex 2 , alpha 1 subunit isoform 1 . ( c ) further down , the display shows the association of hiv-1 matrix and p6 with the mitogen - activated protein kinase 1 ( mapk1 ) . ( d ) the arrow points to the link for the entrez gene reports ( the green g icon ) . currently , the database is composed of 1434 human genes encoding 1448 proteins that directly ( e.g. bind , inhibit ) or indirectly ( e.g. upregulate , modify ) interact with hiv-1 proteins . it was found that the majority of the interactions reported are indirect ( 68% ) , whereas the rest are direct ( 2 ) . in addition , the database comprises 2589 unique hiv-1 to human protein interactions and 5135 brief descriptions of the interactions , with a total of 14 312 pmid references to the original articles that reported the interactions . a network of links to supporting literature and cross - references allows users to navigate concomitantly between this database and other resources at ncbi ( 7 ) , such as entrez gene ( 8) , refseq ( 9 ) and pubmed . reports in entrez gene that contain hiv-1 interaction data can be retrieved with the query navigation to a target human protein interaction can be accomplished via one of two primary routes : an hiv-1 , human protein interaction database search or an entrez gene text query . for illustration purposes , two search scenarios for the signaling protein mitogen - activated protein kinase 1 ( mapk1 ) , which displays a high magnitude of interactions with ten different hiv-1 proteins , are provided subsequently . hiv-1 , human protein interaction database search . to view interactions between mapk1 and gag or its cleavage products , users may select gag in the horizontal selection bar on the top right panel of the database home page ( http://www.ncbi.nlm.nih.gov/refseq/hivinteractions/ ) , which makes a direct link to the illustration as shown in figure 1 . using the scroll down mouse menu , mapk1 can be identified since interacting proteins reported in each interaction session ( e.g. associates with and binds in figure 1b ) are alphabetic . as a searching result , mapk1 is involved in the process of matrix and p6 phosphorylation ( figure 1c ) . users may click on links to entrez gene ( the green g icon ; figure 1d ) to view the mapk1 full report . users may begin with the following query : mitogen - activated protein kinase 1[title ] and homo sapiens [ organism ] . the entries ( e.g. mapk1 and mapk1ip1l ) identified with the query are displayed on the entrez gene results page . adding and hiv1interactions[prop] to the query restricts the results to only those entries that have hiv-1 interaction data , and in this example returns a single match to the mapk1 gene report shown in figure 2 . protein interactions associated with mapk1 are listed on the entrez gene report page in the hiv-1 protein interactions section ( figure 2 ) ; a link to this section is included in the right column table of contents provided on the full report display ( figure 2a ) . individual hiv-1 proteins ( e.g. envelope surface glycoprotein gp120 ) that interact with mapk1 are listed ( figure 2b ) along with brief descriptions of the interactions ( figure 2c ) and links to the supporting literature in pubmed ( figure 2d ) . ( d ) the interactions and descriptions are linked to the supporting literature in pubmed . ( d ) the interactions and descriptions are linked to the supporting literature in pubmed . by integrating the hiv-1 interaction data into the entrez gene database , researchers benefit from the additional computation ncbi hiv-1 , human protein interaction database home page , there are automatic queries provided to pubmed and the ncbi sequence databases for recent records of interest . via entrez gene , information can be easily obtained about genomic context , pathway membership and protein domain structure . the representative entrez gene search strategies summarized in the following table demonstrate the strength of the data integration and provide examples of how specific subsets of data can be retrieved : query to enter in entrez geneexplanationhiv1interactions[prop ] and human[organism ] and 5[chr ] and 1000000:12000000[base position]genes for which products interact with hiv-1 proteins , based on chromosome location . the value before [ chr ] gives the chromosome , and the range separated by : gives the location in base pairs on that chromosome.hiv1interactions[prop ] and human[organism ] and cytoplasm*[go]genes for which products interact with hiv-1 proteins , and are coded by the go consortium with at least one term starting with cytoplasm.hiv1interactions[prop ] and human[organism ] and immunoglobulin[domain name]genes for which products interact with hiv-1 proteins , and are calculated by ncbi 's conserved domain database group as having an immunoglobulin domain.hiv1interactions[prop ] and human[organism ] and ( kegg or reactome)genes for which products interact with hiv-1 proteins and for which pathways data are available from the kegg or reactome groups . data visualization can be accomplished in multiple ways utilizing the information stored in this database . figure 3 shows an example of data visualization using biological process gene ontology ( go ) terms ( 10 , http://www.geneontology.org ) and individual hiv-1 proteins . this bar chart also demonstrates that a large portion of interactions catalogued in the database are associated with the hiv envelope surface ( gp120 ) and tat proteins . the human cellular proteins interacting with hiv span a wide variety of functional categories , ( e.g. signal transduction , protein metabolism , development , etc . ) with an overrepresentation of interactions between tat and cellular proteins involved in transcription . in addition , envelope and tat proteins also have a high number of interactions with proteins representing multiple biological processes . figure 3.distribution of interactions based on biological process gene ontology ( go ) terms and individual hiv-1 proteins . the x - axis shows the individual hiv-1 structural proteins gag , pol and env and their cleavage products , and the regulatory and accessory hiv-1 proteins , tat , rev , nef , vpu , vpr and vif . distribution of interactions based on biological process gene ontology ( go ) terms and individual hiv-1 proteins . the x - axis shows the individual hiv-1 structural proteins gag , pol and env and their cleavage products , and the regulatory and accessory hiv-1 proteins , tat , rev , nef , vpu , vpr and vif . the hiv-1 , human protein interaction database represents an important step towards a more detailed understanding of hiv-1 replication and pathogenesis . a recent example of the value of the database includes the work of brass et al . ( 11,12 ) , who used the database as a tool to help analyze and categorize human proteins required for hiv-1 replication . similarly , in order to support their analysis of human pathogen protein protein interactions , dyer et al . ( 13 ) were able to use a subset of the hiv-1 interaction data that has been incorporated into the biomolecular interaction network database ( bind ; 14 ) . pathogen protein protein interactions has recently been studied in detail and such maps have revealed global and local networks that relate to known biological properties . studies have indicated that both viral and bacterial proteins tend to interact with hubs ( proteins with many interacting partners ) and bottlenecks ( proteins that are central to many pathways in the network ) in human pathogen protein protein interaction networks ( 13,1517 ) . development of such global and local pathway networks by utilizing the information provided in the hiv-1 , human protein interaction database will provide additional insights into hiv-1 replication and disease mechanisms at a systems biology level . these networks may reconfirm and extend known pathways , as well as uncover previously unknown pathway components . in addition , these networks may serve as a starting point for a systems biology modeling of the development of effective therapeutic and prophylactic interventions . hiv-1 , human protein interaction database will be continuously updated to keep the database populated with interactions newly reported in the literature . current efforts are also focused on incorporating these data into canada 's biomolecular object network database ( bond ) ( http://bond.unleashedinformatics.com ; successor to bind ; 14 ) , a database cataloguing the interactions between all known cellular proteins . hiv-1 , human protein interaction database , or any data contained therein can be provided by using the write to the help desk link at the bottom of the database and entrez gene web pages . national institutes of health , national institute of allergy and infectious diseases , division of aids ( n01-ai-05415 and n01-ai-70042 to w.f . , b.e.s .- b . and r.g.p . ) ; intramural research program of the national institutes of health , national library of medicine ( to k.s.k .[/INST]the human immunodeficiency virus type 1 ( hiv-1 ) , human protein interaction database , available through the national library of medicine at www.ncbi.nlm.nih.gov/refseq/hivinteractions , was created to catalog all interactions between hiv-1 and human proteins published in the peer - reviewed literature . the database serves the scientific community exploring the discovery of novel hiv vaccine candidates and therapeutic targets . to facilitate this discovery approach , the following information for each hiv-1 human protein interaction is provided and can be retrieved without restriction by web - based downloads and ftp protocols : reference sequence ( refseq ) protein accession numbers , entrez gene identification numbers , brief descriptions of the interactions , searchable keywords for interactions and pubmed identification numbers ( pmids ) of journal articles describing the interactions . currently , 2589 unique hiv-1 to human protein interactions and 5135 brief descriptions of the interactions , with a total of 14 312 pmid references to the original articles reporting the interactions , are stored in this growing database . in addition , all protein protein interactions documented in the database are integrated into entrez gene records and listed in the hiv-1 protein interactions section of entrez gene reports . the database is also tightly linked to other databases through entrez gene , enabling users to search for an abundance of information related to hiv pathogenesis and replication .</s>

low - frequency observations are very important for the study of the statistical signatures of extragalactic sources , in particular source counts in the low - frequency sky , which until recently have been only characterized at the very highest end of the flux scale . the number of steep - spectrum sources increases rapidly as the sample selection frequency is lowered @xcite , because these sources become too faint to be detected at high frequencies leading to an expectation that low - frequency sky surveys will uncover this population in greater numbers than current cm - wavelength studies . as it is not trivial to infer the low - frequency ( @xmath5 300 mhz ) sky from higher frequency data , deep source counts at the same frequency as eor observations are required for accurate foreground modeling and subtraction . better understanding of the statistical properties and behavior of radio sources is required and motivated by a number of science goals , such as the foreground modeling and subtraction in the detection of the eor . over the last 30 years , a large and ever increasing number of surveys and targeted observations have been performed at low frequencies commencing with the 6th cambridge ( 6c ) survey of radio sources @xcite , which covered the entire northern sky above 30 degrees at 151 mhz . since then a number of other surveys have been completed such as the 7th and 8th cambridge survey of radio sources ( 7c , and 8c : @xcite ) , the targeted survey on the culgoora circular array @xcite in which the flux densities of 1800 high - frequency - selected radio sources were measured at 80 and 160 mhz , the 74 mhz vla low - frequency sky survey ( vlss : @xcite ) above -30 degrees , the murchison widefield array commissioning survey ( mwacs : @xcite ) covering 6,100 @xmath6 between 104 and 196 mhz , and the precision array for probing the epoch of reionization ( paper ; @xcite ) low resolution survey of the southern sky at 145 mhz . current low frequency radio interferometers , such as lofar @xcite , gmrt @xcite , lwa @xcite , mwa @xcite and paper @xcite have made a considerable advance in our understanding of the population of extragalactic radio sources at frequencies below 300 mhz with all - sky low frequency surveys(@xcite ) . the upcoming square kilometre array ( ska ) is expected to continue to push the boundaries of low - frequency astronomy , observing the radio sky at much higher sensitivity and resolution . recently , @xcite determined the 154mhz source counts with mwa observation of the so - called eor0 field ( which is centered at j2000 @xmath7 ) and compared these with the 7c counts at 151mhz @xcite , as well as the gmrt source counts at 153mhz @xcite finding good agreement to a limiting flux density of @xmath840 mjy . using lofar , @xcite examined source counts at 34 , 46 and 62 mhz , a wavelength regime not explored since the 8c observations at 38 mhz 25 years earlier . the lofar observations are the deepest images ever obtained at these frequencies and reach noise levels of the order of a few mjy , being nearly 2 orders of magnitude deeper than the 8c survey . @xcite confirmed the previously known result that the average spectral index of radio galaxies flattens towards lower frequencies , as is expected from synchrotron losses @xcite . in addition to understanding the properties of the low frequency radio population to study the population itself , it is of great importance to properly characterize the population if we are to fully exploit these instruments to detect the eor as a precise sky model is vital for subtracting foreground sources @xcite . thus , source count studies of the low frequency sky are strongly motivated by a number of complementary science goals . the north celestial pole ( ncp ) region is covered at low - frequencies by the wsrt @xcite and lofar @xcite , it is also the sky region targeted by the 21 centimeter array ( 21cma ) . the key science goal for the 21cma is to statistically measure the redshifted 21 cm signal of neutral hydrogen from the eor . determining the radio source counts and understanding the spectral properties of the radio sources are important for removing the foreground sources and extracting the faint eor signal . in this paper , we present targeted observations centered on the ncp and extending 5 degrees in radius using the 21cma . we determine the source counts using eight sub - band images between 75 mhz and 175 mhz with flux densities down to @xmath9 jy . we also investigate the spectral properties of catalog sources and compare our source counts with the recent surveys . the outline of the paper is as follows . section 2 describes the 21cma telescope , the observation and data reduction pipeline . section 3 presents the source extraction process and resultant source catalog and properties including number counts , spectral indices , completeness and errors . discussion and concluding remarks are given in section 4 . the 21cma is a ground based radio interferometer dedicated to detection of the eor . the array , sited in the ulastai valley of western china , consists of 81 pods or stations , with a total of 10287 log - periodic antennas are deployed in two perpendicular arms along an east - west ( 6.1 km ) ( figure [ fig : baseline ] ) and north - south ( 4 km ) direction , respectively . spacing of these 81 pods is chosen such that a sufficiently large number of redundant baselines and a good uniform uv coverage can both be guaranteed . each antenna element has 16 pairs of dipoles with lengths varying from 0.242 m to 0.829 m , optimized to cover a frequency range of 50 - 200 mhz , which gives rise to an angular resolution of @xmath10 at 200 mhz . all the antennas are fixed on the ground and point at the ncp for the sake of simplicity and economy , which allows us to observe the same patch of sky for 24 hours a day through the whole year . therefore , we can reach a higher sensitivity in a region of a few ten square degrees around the ncp in a relatively short time . phase delayed coaxial cables are used to combine the signal from each antenna for each pod , and the output signal is digitized at a sampling rate of 400 mhz with 8 bit precision to accommodate the bandwidth of 200 mhz , although signal below 50 mhz is actually filtered out . fast fourier transforms ( fft ) and correlations are performed in software by a cluster of 83 , dual - core intel(r ) xeon(tm ) servers , equipped with gigabit ethernet networks ( pci - e 10-gbps 4x ) and a high speed network ( infiniband ) switch ( cisco sfs-7008p ) . the 200 mhz bandwidth is divided into 8192 channels , giving rise to a frequency resolution of 24.4 khz . data in each channel are integrated for about 3 seconds in memory before they are output to a disk array of 32 terabytes . hard disks are transported to the headquarters of the national astronomical observatories of china in beijing for analysis . [ fig : baseline ] construction of the 21cma was completed in 2006 , and a significant upgrade was made in 2009 by installing a new type of low noise amplifier ( 40 k ) on each antenna and 40 sets of gpus in a new data acquisition cluster . the former considerably suppresses thermal noise from the phased delayed cables , while the later provides a very efficient way to speed up correlation computation processing . we have used software instead of hardware or fpgas to perform the fft and correlations . after this upgrade we also decided to run the e - w baseline only to maintain a higher efficiency ( @xmath11 ) of data acquisition by reducing the computing demands for cross - correlations . furthermore , this allows us to work with a relatively simple interferometric imaging algorithm without the concern of the so - called `` w '' term . in the early commissioning observations between 2005 - 2009 , many efforts were made to understand the performance of the 21cma system including antennas , receivers , data acquisition process , and even the power supply . we have developed all software packages and techniques such as identification and mitigation of radio frequency interference ( rfi ) , calibration , deconvolution , wide - field imaging , etc . necessary for full data processing of 21cma data . since july of 2010 after its upgrade , the 21cma has routinely observed the low frequency sky round the ncp , delivering about 2 terabits of visibility data per day for offline analysis . while the primary goal of the 21cma is to accumulate a deep observation for eor detection , even with relatively short integrations we can characterize the extra - galactic source population . on one hand , these bright extragalactic sources , a byproduct of our eor experiment , can be of great interest for exploration of their astrophysical properties . on the other hand , these radio sources constitute one of the major contamination components for our eor detection , and therefore should be perfectly imaged and subsequently subtracted . in the current work we present the point radio sources observed with the 40 pods of the 21cma e - w baselines for an integration of 12 hours made on 2013 april 13 . an extra deep sample with a higher sensitivity from a longer integration time of up to years will be published later . although the radio environment of the 21cma site , ulastai , is exceptionally quiet at low frequency and comparable to sites such as the murchison radio observatory ( @xcite ) , rfi is still a prominent concern for doing the eor experiment . figure [ fig : spectrum ] displays the average spectrum of cross - correlation between two pods over 12 hours with a frequency resolution of @xmath12 khz , which reveals the rfi at the site more clearly than the self - correlation of the same pod because thermal noises from different pods are not correlated . the overall shape reflects the decreasing sky noise at high frequencies and the decreasing efficiency of the antennas at low frequencies with a turnover at roughly 85 mhz . the strongest rfi sources are identified as low orbiting satellites at 137 mhz , local train communications at 150 mhz , civil aviation aircraft around 130 mhz and at 119 mhz , fm radio broadcasting at 88 - 108 mhz scattered by meteor tails and aircraft , and am radio broadcasting around 70 mhz , and several other contaminators @xcite . all these sources of rfi are highly time variable , and can be easily flagged for blanking during the editing process . after the mitigation of strong , time variable rfi , we apply a second statistical algorithm for further removal of other possible rfi using the fact that the sampling of visibilities should exhibit a gaussian distribution for a given frequency , a scheme often adopted in data analysis of recent low frequency experiments ( e.g. @xcite ) . in the second stage of rfi mitigation we excluded all the data points beyond @xmath13 deviation from gaussian statistics . this operation is applied to the real and imaginary parts separately , and the visibility data are edited out if either of the parts fail to reach the @xmath13 restrictions . this still allows us to use the bulk ( about 97% ) of the data except for some of the most noisy channels around 137 mhz and 150 mhz . the reader is referred to @xcite for a detail description of our rfi identification and mitigation processing . low - frequency radio interferometric observations are often affected by ionospheric turbulence , resulting in fluctuations of both source positions and flux densities . we run two algorithms to correct the phase error in the visibilities due primarily to ionospheric effects : self - calibration and the closure relation . software developed in - house is used for self - calibration , in which a time interval of 1 hour is used for the present study . we have tested shorter intervals of down to 10 minutes , and found that the changes are only minor when longer baselines of @xmath14 m are excluded ( see below ) . we have already improved our self - calibration algorithm by combining conventional self - calibration and redundant calibration , we will apply it for all baselines using a short time interval in the future data reduction ( zheng et al . in preparation ) . the ncp sky at 50 - 200 mhz is actually dominated by two bright sources : a central bright quasar ( nvss j011732 + 892848 ) and a galaxy 3c61.1 . 3c61.1 is a very bright giant galaxy with a flux density of 33 jy at 150 mhz , which also shows a complex structure . we select 10 radio sources including these two bright sources ( table [ table : calibrators ] ) to correct the phase errors with self - calibration . following this , we use the closure phase relation to check , and modify if necessary , the results . lllll nvss j011732 + 892848 & 0.52 & [email protected] & [email protected] & point source + nvss j062205 + 871948 & 2.67 & [email protected] & [email protected]&point source + nvss j133218 + 865005 & 3.17 & [email protected] & [email protected] & point source + nvss j092016 + 862845 & 3.52 & [email protected] & [email protected] & point source + 3c061.1 & 3.71 & [email protected] & [email protected] & resolved + nvss j122518 + 860839 & 3.86 & [email protected] & [email protected] & point source + nvss j1013.7 + 8553 & 4.12 & [email protected] & [email protected] & point source + nvss j190350 + 853648 & 4.39 & [email protected] & [email protected] & point source + nvss j194136 + 850138 & 4.97 & [email protected] & [email protected] & point source + nvss j212926 + 845326 & 5.11 & [email protected] & [email protected] & point source to reduce further the ionospheric effect on our interferometric imaging and improve image quality , we exclude both longer baselines of @xmath14 m and the shorter ones of @xmath16 m in the present analysis . we perform a fast fourier transform of the uv map using a uniform weighting with @xmath17 grids , sampled by different baselines and snapshots for each frequency channel , to generate the dirty maps . this yields a total of 6144 images over 50 - 200 mhz frequency bands with a frequency resolution of 24.4 khz . then , each dirty image is deconvolved using the conventional hgbom clean algorithm @xcite with a loop - gain of 0.05 . we terminate the clean process when the fractional change in the total cleaned flux density is less than @xmath18 in the iteration . employment of a smaller threshold does not alter the result significantly . after the deconvolution we adopt a larger frequency bin of 1.56 mhz to combine the 6144 images into 96 mosaics , and concentrate on only the central field of view of @xmath19 pixels , corresponding to a @xmath20 degree square area . note that this gives rise to an angular resolution of @xmath21 arcmin per pixel while the best resolution of the array is only @xmath22 arcmin at 200 mhz . directivity and gain of the 21cma antenna element , the log - periodic antenna , has been precisely measured in laboratory , which indeed allows us to compute the primary beam and gain of the 21cma pod according to the pattern multiplication theorem . however , in situ calibration has to be made to account for the possible effect of crosstalk between the antennas themselves and the antennas and the ground . for a 12 hour ( or more ) observation of the 21cma centered on the ncp , the primary beam of a pod has circular symmetry . moreover , in terms of our laboratory measurement of the spatial response of the 21cma log - periodic antenna and theoretical prediction based on the pattern multiplication theorem , the primary beam pattern of a 21cma pod is nicely approximated by a gaussian profile characterized by the standard deviation @xmath23 . guided by our knowledge and experience , we adopt a modulated gaussian function parametrized by @xmath24 for the primary beam and gain of the 21cma pod , where g is the system gain which varies with frequency @xmath25 , @xmath26 measures the radial distance from the ncp , @xmath27 denotes the standard deviation of the gaussian distribution , and a and b are the coefficients in the polynomial of degree 2 . unfortunately , there are no standard radio sources in the ncp region that can be used for calibration purposes . thus we use the same sources selected in the self - calibration ( table [ table : calibrators ] ) as our flux calibrators . we collect the flux density measurements of these sources made at different frequencies ranging from a few ten mhz to a few ghz from the literature and obtain the spectral index , @xmath28 , for each source by fitting the observed flux densities to a power law , @xmath29 . except for the flat - spectrum sources , the fitting errors in amplitude @xmath30 and spectral index @xmath28 are typically @xmath31 and @xmath32 , respectively . errors in these calibrators will be included in fitting of gain and spatial response function of the telescope . we then use the total flux density within a frequency bin of 1.56 mhz to accommodate our cleaned images over the same frequency band . however , the primary beam is frequency - dependent , and varies roughly as an exponential profile characterized by @xmath27 for the 21cma . this reduces further the number of the bright radio sources that can be used for calibration in the higher frequency bands . as a result , only the inner 4 sources within @xmath33 can be used for the 32 higher frequency bands with @xmath34 mhz , for which uncertainties in the determination of gain and spatial response might be large . we start with a gaussian profile of @xmath35 , and find the best - fit parameters @xmath36 and @xmath27 in each frequency channel . by fixing @xmath36 and @xmath27 , we then use the same calibrators to find the modification parameters @xmath37 and @xmath38 to the gaussian distribution . it turns out that the gaussian profile provides rather a good description for the 12-hour averaged primary beam , and the modification parameters a and b are actually around zero ( see figures [ fig : theta ] and [ fig : poly ] ) . moreover , the best - fit gaussian beam of @xmath39 is in good agreement with our theoretical prediction . figure [ fig : g ] shows the resultant system gain against frequency . the design of the 21cma antenna is such that the effective area remains roughly constant over a wide frequency range , which yields a frequency dependent gain of @xmath40 . the steeper profile of the fitted gain factor also reflects the compensation for signal attenuation of the phased - delayed coaxial cable used for signal combination . [ fig : theta ] [ fig : poly ] [ fig : g ] [ fig : noise ] lll 81.25 & 28.9 & 6.78 + 93.75 & 22.5 & 5.93 + 106.25 & 17.8 & 5.28 + 118.75 & 10.7 & 4.75 + 131.25 & 7.7 & 4.32 + 143.75 & 5.3 & 3.96 + 156.25 & 4.1 & 3.65 + 168.75 & 3.3 & 3.39 the cleaned image in each of the 96 frequency channels is corrected for beam response and flux gain . then the images are stacked into 12 sky maps with a bandwidth of 12.5 mhz . to reduce further the possible roll - off effect of the bandpass filters used in the 21cma receivers , we will not use the data at the two frequency ends , 50 - 75 mhz and 175 - 200 mhz , in the present paper . this yields a total of 8 sky maps centered at 81.25 , 93.75 , 106.25 , 118.75 , 131.25 , 143.75 , 156.25 and 168.75 mhz , respectively , with a varying image noise from @xmath41 mjy at lower frequency end to @xmath42 mjy higher frequency one . figure [ fig : noise ] illustrates an example of the cleaned image and corresponding noise map in the 131.25 mhz subband . the noise and beam size in each 12.5 mhz subband image are summarized in table [ table : noise ] . we calculate the dynamical range of each sky map to provide a quantitative estimate of the image quality , which we defined here as the ratio of the peak brightness @xmath43 of the image to the rms noise @xmath44 , and the result is shown in figure [ fig : ston ] for the 8 sky maps . it appears that the ratio of @xmath45 reaches a value of @xmath46 and shows an increase trend with frequency . such a variation is simply the combined effect of the system sensitivity , which is dominated by the milky way ( e.g. @xcite ) @xmath47 , and the power - law behavior of the background radio source flux density , @xmath48 with @xmath49 . as a consequence , the dynamical range of the sky map varies with frequency roughly as @xmath50 . yet , the current dynamical range is still one order of magnitude below the eor detection requirement ( see @xcite ; @xcite ; @xcite for review ) , and we will address the possible reasons in the sub - section on noise analysis ( section 3.5 ) below . we have also made a full band 75 - 175 mhz image by mosaicing the 8 sub - band images together after convolving to a common resolution of @xmath51 arcmin ( figure [ fig : dirtymap ] and figure [ fig : wideband ] ) . this combined image will be used to remove spurious sources ( see below ) . [ fig : ston ] the field of view ( fov ) depends on the observing frequency , such that fov@xmath52 . as a result , we can only extract full spectral information for radio sources within a radius of @xmath53 around the ncp . nonetheless , we also count the sources between @xmath54 to expand our radio source catalog , for which spectral measurements are based on only the four lower frequency channels , 81.25 , 93.75 , 106.25 and 118.75 mhz . we note that , many more sources have been found beyond @xmath55 at the lower frequency end , but we will not include them in the present catalog . source candidates are first selected in the full - band image covering 75 - 175 mhz , using a method similar to duchamp @xcite , in which a threshold of @xmath13 is adopted to identify source candidates . the position of the peak flux of each candidate in the full - band image is tagged and then used for selection of source candidate in other sub - bands in a procedure similar to that described in @xcite . the source candidates will be removed from the list if their counterparts are missing in one of the frequency bands . this allows us to identify and thus remove all the spurious sources that result from the sidelobes of the brightest radio source , 3c061.1 ( see figure [ fig : dirtymap ] and figure [ fig : wideband ] ) . indeed , we are still unable to perfectly clean the sidelobes of the brightest radio galaxy , 3c061.1 , located at @xmath56 degrees from ncp . the complex structure of this source @xcite is marginally resolved with 21cma . even with a better angular resolution and a multi - directional calibration using sagecal @xcite , lofar imaging of the same source also contains significant errors @xcite . our current experiment towards the detection of the eor is thus largely limited by the presence of this very bright , complex radio galaxy in the ncp field . a gaussian profile is used to fit the `` surface brightness '' of a radio source in each of the sub - bands and the corresponding flux density can be computed straightforwardly . when two sources show an overlap due to poor resolutions , a two - component gaussian profile is adopted to fit the images simultaneously . yet , even this double gaussian models may fail to fit two sources with significant overlap especially at low frequencies . in this case , we will not provide the flux density information for the two sources but still treat them as separate sources . we calculate the spectral index for each source using the measured flux densities in all the available bands , up to 8 bands for sources within @xmath57 and up to 4 bands for the ones in the annulus of @xmath54 . [ fig : dirtymap ] is shown , with an annulus of 1 degree in radial distance . the deconvolution is performed through the hgbom clean algorithm with a loop gain of 0.05 . the brightest source ( lower right ) , 3c061.1 , is located at a distance of @xmath58 from the ncp , and deconvolution noise around 3c061.1 , which arises mainly from grating lobes and inaccurate calibration , is clearly visible . note that we have enhanced the image contract to display the noise field which is actually four orders of magnitude fainter than the typical bright sources in the field.,width=340 ] [ fig : wideband ] our method of source identification is indeed reliable for mitigation of artificial sources . however , the fainter sources below our threshold at least in one of the eight sub - bands can not be included with the current criterion of source selection . in addition , the threshold varies with frequency channels , and therefore , we may have missed a significant fraction of faint sources . we have thus tested two other methods by relaxing the above criterion for source selection . the first is to work with an extreme case : all the candidates with peak fluxes above @xmath13 in any sub - band are selected . this provides an overestimate of source population because image artifacts , due to imperfect cleaning of sidelobes of bright sources , especially 3c061.1 , have contaminated our observing field . we demonstrate in section 3.3 an example of the completeness estimate from such a source selection method for the highest angular resolution sub - band at 168.75 mhz . it turns out that the contamination of spurious sources is indeed very serious . the second test is to select sources based on adjacent frequency channels instead of full bands . to deal with the sidelobes from the bright sources , source candidates should be removed from the list once their counterparts are missing only in one of the adjacent channels , using the frequency - dependence properties of sidelobes ( figure [ fig : sourceselection ] ) . this allows us to identify more faint sources yet leaves the following two drawbacks : ( 1 ) the position variations of the sidelobes - induced `` sources '' become indistinguishable at low frequencies because of poor angular resolution , and ( 2 ) the spectral index can not be estimated reliably if a source shows up only in two frequency bands . while we adopt our conservative way to select sources and construct our source catalog in this work , we will compare the completeness and source counts among the three selection methods below and will improve our source selection algorithm in our future work . [ fig : sourceselection ] ccccccccccc 9.49 & 89.68 & @xmath59 & @xmath60 & @xmath61 & @xmath62 & @xmath63 & @xmath64 & @xmath65 & @xmath66 & @xmath67 + 5.23 & 89.65 & @xmath68 & @xmath69 & @xmath70 & @xmath71 & @xmath72 & @xmath73 & @xmath74 & @xmath75 & @xmath76 + 7.59 & 89.63 & & @xmath77 & @xmath78 & @xmath61 & @xmath79 & @xmath80 & @xmath81 & @xmath82 & @xmath83 + 0.29 & 89.58 & & @xmath84 & @xmath85 & @xmath86 & @xmath87 & @xmath88 & @xmath89 & @xmath90 & @xmath91 + 12.30 & 89.57 & & & & @xmath92 & @xmath93 & @xmath94 & @xmath95 & @xmath96 & @xmath97 + 16.55 & 89.55 & @xmath98 & @xmath99 & @xmath100 & @xmath101 & @xmath102 & @xmath103 & @xmath104 & @xmath105 & @xmath106 + 1.29 & 89.47 & & & & & @xmath107 & @xmath108 & @xmath109 & @xmath110 & @xmath111 + 9.52 & 89.47 & & & @xmath112 & @xmath113 & @xmath114 & @xmath115 & @xmath116 & @xmath117 & @xmath118 + 6.31 & 89.45 & @xmath119 & @xmath120 & @xmath121 & @xmath122 & @xmath123 & @xmath124 & @xmath125 & @xmath126 & @xmath127 + 10.86 & 89.40 & @xmath128 & @xmath129 & @xmath130 & @xmath131 & @xmath132 & @xmath133 & @xmath134 & @xmath135 & @xmath136 a total of 624 radio sources are found around the ncp region , and their positions , integrated fluxes and spectral indices are listed in table [ table : list ] . note that for sources within @xmath57 we fit integrated fluxes in eight subbands to a power - law to estimate their spectral indices . while for sources in annulus of @xmath54 we only use the integrated fluxes measured in 4 lower frequency subbands . moreover , data points in some of the subbands have not been taken if the integrated fluxes of images can not be precisely measured due to poor resolution and/or significant overlap . of the 624 sources , 322 sources lie between 3 and 5 deg from the field center ncp which are selected using the four lower frequency subbands ( 81.25 , 93.75 , 106.25 and 118.75 mhz ) . an immediate cross - check with the existing the 6c catalog at 151 mhz reveals 490 counterparts . the missing sources are the fainter ones below the detection limit of 0.1 jy in the 6c survey . namely , about 134 new sources are detected around and below 0.1 jy at 151 mhz . figure [ fig:21cma-6c ] compares the flux densities of these 490 sources at 151 mhz listed in both 6c catalog and our new catalog , and two measurements above 0.1 jy show rather a good agreement . [ fig:21cma-6c ] figure [ fig : alpha1 ] illustrates the histogram of the spectral indices of the 624 sources presented here . while the distribution peaks at approximately @xmath49 , consistent with what is expected for the overall population of cosmic radio sources , the asymmetrical behavior indicates that more sources tend to have a steeper spectral index . this could arise as the radio sources with steeper indices are more easily detected at low frequencies . in other words , low - frequency observations would probably miss some of the flat - spectrum sources if they are not bright enough . yet , recent observations have argued a spectral flattening towards both lower frequencies and fluxes ( e.g. @xcite ; @xcite ; @xcite ) . to investigate if similar behavior is evident in our radio source catalog , we restrict the sources within 3 degrees and compare in figure [ fig : alpha2 ] the spectral indices between the 4 lower frequency subbands and the 4 higher frequency subbands . it turns out that there is a significant excess of steep - spectrum sources in the higher frequency subbands . this can be further quantified by considering the means , medians and their ratios ( means / medians ) of the two distributions , yielding ( -1.25,-1.15,1.09 ) and ( -0.86,-0.87,0.99 ) for the higher and lower frequency subbands , respectively . we have also compared the low - frequency sources in the inner radius of 3 degrees and the ones in the outer annulus of @xmath54 , and found that their spectral indices are essentially similar ( figure [ fig : alpha3 ] ) . while the absence of bias in spectral index between the sources within the central region ( @xmath137 ) and the ones in the outer region ( @xmath54 ) simply reflects the uniformity of cosmic radio sources , it also indicates that our beam model is correct . it turns out that our analysis does support a flattening trend toward lower frequencies . if confirmed , this may add a further difficulty for low - frequency observations to detect faint , flat - spectrum sources . [ fig : alpha1 ] [ fig : alpha2 ] [ fig : alpha3 ] before we perform monte - carlo simulations to estimate the completeness of our source selections , we compare our source counts with the deep low - frequency observations of the noao botes field down to 6 mjy made with gmrt at 153 mhz @xcite . this allows us to make a quick yet rough judgment on the incompleteness of our source counts at different fluxes . of course , an extrapolation based on a spectral index conversion should be made for source counts at other frequencies for the `` control '' field . we notice that the reliability of such an extrapolation is probably questionable , as argued recently by @xcite . taking the differential source count by @xcite at 153 mhz , @xmath138 , we calculate the ratios of our observed sources @xmath139 to what are expected in terms of this single power law , and plot the results for the 168.75 mhz frequency channel in figure [ fraction-3methods ] . it appears that the incompleteness for our standard method of source selection occurs around 0.1 jy , where the ratio drops to @xmath140 . namely , a significant fraction of the fainter sources may be missed below 0.1 jy when sources are required to be visible in all subbands to guarantee that the artificial sources from sidelobes be clearly discriminated and perfectly removed . we have also shown the completeness estimates for the other two selection methods : the extreme approach that treats all the peaks above @xmath13 as `` sources '' gives rise to an apparent over - estimate of true sources even down to @xmath141 jy , indicating that the contamination is rather significant . sources that are selected in terms of their locations at adjacent frequency channels seem to be complete until @xmath1 jy , and their completeness drops to @xmath142 at 0.01 jy . while the latter provides a `` better '' completeness of source selection , the poor angular resolution at lower frequencies may be inefficient for discrimination of position shifts of the artificial sources due to sidelobes , as was pointed out above . we now perform a monte - carlo simulation to quantify the completeness of the source sample . we generate 20 fields with a radius of @xmath57 , each of which contains 1600 point sources with positions randomly distributed . the fluxes of these artificial sources are assumed to follow a power - law of @xmath143 and are further restricted within @xmath144 mjy @xmath145 jy , for which a spectral index of @xmath146 is assumed . we include the beam smearing effect by convolving the image with a gaussian function characterized by the true beam at each frequency band . we add noise to the simulated map at each channel using the true residual map from our deconvolution after point sources are peeled out . furthermore , the radial variation in sensitivity around the ncp is taken into account by the spatial response of the telescope described by eq.(2 ) . now , we adopt the same mechanism , the so - called standard method , to extract sources at the same eight frequency channels , using the image flux and position information over the frequency bands . figure [ fraction ] shows the mean fraction of simulated sources recovered against total flux density for each of the eight channels , respectively , in which the error bars represent the standard statistical deviations . as expected , the turning points of completeness exhibit a weak increasing tread towards higher frequencies . unfortunately , the completeness decreases rapidly to zero beyond @xmath147 jy , although we can still detect some sources down to @xmath148 jy for all the 8 frequency bands . our estimated completeness will be used for correcting the incompleteness of source counts below . [ fraction-3methods ] are randomly distributed over a circular field with a radius of 3 degrees , and noise and beam smearing are added in terms of the true measurements on the ncp field . the same source selection method as we adopted for the ncp field is applied to the simulation . error bars at each frequency represent the standard deviation from 20 realizations . , width=340 ] [ fraction ] we plot in figure [ numbercount ] the differential source counts @xmath149 of our sample over the central field of radius @xmath57 for each of the 8 frequency bands , in which both the raw data and completeness - corrected data in terms of the above monte - carlo simulation are displayed . for data points with completeness of @xmath11 or above , which corresponds to the brighter sources with fluxes greater than @xmath1 jy , a single power law fits nicely the completeness - corrected data : @xmath150 if we adopt a lower completeness of @xmath151 to include more fainter sources , though the data points below @xmath11 already become unreliable , @xmath149 would follow the the well - known two power laws for cosmic radio population at low frequencies @xcite . @xmath152 where @xmath153 indicates the turnover flux . the best - fit parameters for the 8 frequency subbands are summarized in tables [ table : ncounta ] and [ table : ncountb ] for the @xmath11 and @xmath151 completeness data , respectively . it appears that for the bright population with @xmath154 , our best - fit indices vary between 2.10 and 2.55 , which are both consistent with each other within error bars , and are also close to 2.5 which is expected for a euclidean cosmology . for the fainter radio sources below @xmath153 , we find a weak dependence of @xmath155 on frequency , with a flattening source count towards lower frequencies . we note that a power - law fit at @xmath156 jy to the gmrt counts from williams , intema & rottgering ( 2013 ) , intema et al . ( 2011 ) and ghosh et al . ( 2012 ) gives @xmath157 at 154 mhz @xcite and the gmrt targeted survey at 153 mhz finds essentially similar results , @xmath158 ( @xcite , see also @xcite ) . our best - fit power indices at the two closest bands , 143.75 and 156.25 mhz , are @xmath159 and @xmath160 , respectively , which are slightly higher than these results due to the lack of fainter sources in our samples . for each of the eight frequency subbands . filled and open circles represent the raw data and completeness - corrected data , respectively . the two vertical dashed lines indicate the @xmath151 ( black ) completeness and @xmath11 ( red ) completeness , respectively . the best - fit two power laws for the @xmath151 completeness limit are shown by the black solid lines , while the results for the @xmath11 completeness data are illustrated by the red solid lines . , width=302 ] [ numbercount ] lll 81.25 & 2896@xmath15898 & [email protected] + 93.75 & 3044@xmath15737 & [email protected] + 106.25 & 2879@xmath15635 & [email protected] + 118.75 & 3062@xmath15979 & [email protected] + 131.25 & 3007@xmath15679 & [email protected] + 143.75 & 2974@xmath15789 & [email protected] + 156.25 & 2911@xmath15757 & [email protected] + 168.75 & 2812@xmath15464 & [email protected] llllll 81.25 & 0.95 & 5318@xmath151384 & [email protected] & 5038@xmath151180 & [email protected] + 93.75 & 0.95 & 4850@xmath15928 & [email protected] & 4658@xmath15615 & [email protected] + 106.25 & 0.8 & 4136@xmath15520 & [email protected] & 3708@xmath15355 & [email protected] + 118.75 & 0.8 & 3664@xmath15441 & [email protected] & 3447@xmath15327 & [email protected] + 131.25 & 0.65 & 4432@xmath15444 & [email protected] & 3594@xmath15276 & [email protected] + 143.75 & 0.65 & 3917@xmath15455 & [email protected] & 3327@xmath15240 & [email protected] + 156.25 & 0.5 & 3747@xmath15613 & [email protected] & 3112@xmath15341 & [email protected] + 168.75 & 0.5 & 4269@xmath151167 & [email protected] & 3170@xmath15344 & [email protected] to compare our results with other deep surveys at low frequencies , we derive the euclidean - normalized differential source counts , @xmath161 , for which uncertianties are represented by the poisson errors calculated from the number of sources detected in each flux density bin . we take the source counts from two recent surveys at frequencies in the range of 151 - 154 mhz with gmrt @xcite and mwa @xcite . we choose our results in the 156.25 mhz band to compare with @xmath161 given at 151 - 154 mhz with the gmrt and mwa by scaling the observing frequencies with a single power - law of @xmath162 to 154 mhz ( figure [ fig:154mhz - compare ] ) . within the error bars , our source counts are in good agreement with these recent surveys . in table [ nor - counts81 - 118 ] and table [ nor - counts131 - 168 ] we have provided the tabulated normalized differential source counts for the lower ( 81.25 , 93.75 , 106.25 and 118.75 mhz ) and higher ( 131.25 , 143.75 , 156.25 and 168.75 mhz ) bands , respectively , and the results are also displayed in figure [ fig : sdnds - low ] and figure [ fig : sdnds - high ] , respectively . [ fig:154mhz - compare ] [ fig : sdnds - low ] [ fig : sdnds - high ] lllll 81.25 mhz + 0.367 & 0.527 & 22 & 2910@xmath15620 & 1.3 + 0.527 & 0.755 & 23 & 4841@xmath151009 & 1.2 + 0.755 & 1.083 & 13 & 4462@xmath151237 & 1.1 + 1.083 & 1.554 & 10 & 5587@xmath151767 & 1.0 + 1.554 & 2.228 & 8 & 6964@xmath152462 & 1.0 + 2.228 & 3.196 & 7 & 10172@xmath153844 & 1.0 + 4.584 & 6.575 & 4 & 17150@xmath158575 & 1.0 + 6.575 & 9.430 & 2 & 14730@xmath1510415 & 1.0 + 93.75 mhz + 0.327 & 0.470 & 28 & 3198@xmath15604 & 1.3 + 0.470 & 0.674 & 20 & 3553@xmath15794 & 1.2 + 0.674 & 0.966 & 17 & 4830@xmath151171 & 1.1 + 0.966 & 1.386 & 9 & 4030@xmath151343 & 1.0 + 1.386 & 1.987 & 9 & 6453@xmath152151 & 1.0 + 1.987 & 2.850 & 7 & 8567@xmath153238 & 1.0 + 2.850 & 4.088 & 2 & 4204@xmath152973 & 1.0 + 4.088 & 5.863 & 3 & 10833@xmath156254 & 1.0 + 5.863 & 8.410 & 2 & 12405@xmath158772 & 1.0 + 106.25 mhz + 0.207 & 0.296 & 32 & 2513@xmath15444 & 1.9 + 0.296 & 0.425 & 31 & 2183@xmath15392 & 1.0 + 0.425 & 0.609 & 19 & 2299@xmath15527 & 1.0 + 0.609 & 0.874 & 21 & 4364@xmath15952 & 1.0 + 0.874 & 1.254 & 10 & 3570@xmath151129 & 1.0 + 1.254 & 1.798 & 7 & 4292@xmath151622 & 1.0 + 1.798 & 2.579 & 9 & 9479@xmath153160 & 1.0 + 2.579 & 3.699 & 2 & 3618@xmath152558 & 1.0 + 3.699 & 5.305 & 3 & 9322@xmath155382 & 1.0 + 5.305 & 7.608 & 2 & 10675@xmath157459 & 1.0 + 118.75 mhz + 0.189 & 0.271 & 32 & 2075@xmath15367 & 1.8 + 0.271 & 0.389 & 37 & 2280@xmath15375 & 1.0 + 0.389 & 0.557 & 29 & 3070@xmath15570 & 1.0 + 0.557 & 0.800 & 15 & 2728@xmath15704 & 1.0 + 0.800 & 1.147 & 13 & 4061@xmath151126 & 1.0 + 1.147 & 1.645 & 7 & 3756@xmath151420 & 1.0 + 1.645 & 2.359 & 8 & 7373@xmath152606 & 1.0 + 2.359 & 3.384 & 2 & 3166@xmath152239 & 1.0 + 3.384 & 4.853 & 3 & 8158@xmath154710 & 1.0 + 4.853 & 6.961 & 2 & 9341@xmath156605 & 1.0 lllll 131.25 mhz + 0.174 & 0.250 & 24 & 1266@xmath15258 & 1.6 + 0.250 & 0.359 & 47 & 2569@xmath15375 & 1.0 + 0.359 & 0.515 & 21 & 1972@xmath15430 & 1.0 + 0.515 & 0.738 & 21 & 3387@xmath15739 & 1.0 + 0.738 & 1.059 & 12 & 3324@xmath15960 & 1.0 + 1.059 & 1.518 & 7 & 3331@xmath151259 & 1.0 + 1.518 & 2.178 & 8 & 6538@xmath152312 & 1.0 + 2.178 & 3.123 & 2 & 2807@xmath151985 & 1.0 + 3.123 & 4.480 & 2 & 4823@xmath153410 & 1.0 + 4.480 & 6.425 & 3 & 12427@xmath157174 & 1.0 + 143.75 mhz + 0.162 & 0.233 & 33 & 1489@xmath15259 & 1.5 + 0.233 & 0.334 & 34 & 1666@xmath15286 & 1.0 + 0.334 & 0.478 & 28 & 2357@xmath15445 & 1.0 + 0.478 & 0.686 & 16 & 2313@xmath15578 & 1.0 + 0.686 & 0.984 & 10 & 2484@xmath15785 & 1.0 + 0.984 & 1.411 & 9 & 3839@xmath151279 & 1.0 + 1.412 & 2.025 & 7 & 5129@xmath151939 & 1.0 + 2.025 & 2.904 & 2 & 2517@xmath151780 & 1.0 + 2.904 & 4.165 & 3 & 6486@xmath153745 & 1.0 + 4.165 & 5.974 & 2 & 7428@xmath155252 & 1.0 + 156.25 mhz + 0.152 & 0.218 & 36 & 1624@xmath15271 & 1.7 + 0.218 & 0.312 & 35 & 1551@xmath15262 & 1.0 + 0.312 & 0.448 & 23 & 1752@xmath15365 & 1.0 + 0.448 & 0.642 & 13 & 1701@xmath15472 & 1.0 + 0.642 & 0.921 & 11 & 2472@xmath15745 & 1.0 + 0.921 & 1.321 & 8 & 3088@xmath151092 & 1.0 + 1.321 & 1.894 & 7 & 4641@xmath151754 & 1.0 + 1.894 & 2.717 & 2 & 2278@xmath151611 & 1.0 + 2.717 & 3.896 & 3 & 5869@xmath153388 & 1.0 + 3.896 & 5.589 & 2 & 6720@xmath154752 & 1.0 + 168.75 mhz + 0.142 & 0.205 & 38 & 1653@xmath15268 & 1.8 + 0.205 & 0.293 & 28 & 1132@xmath15214 & 1.0 + 0.293 & 0.421 & 25 & 1736@xmath15347 & 1.0 + 0.421 & 0.604 & 14 & 1670@xmath15446 & 1.0 + 0.603 & 0.866 & 10 & 2049@xmath15648 & 1.0 + 0.866 & 1.242 & 9 & 3167@xmath151056 & 1.0 + 1.242 & 1.781 & 7 & 4232@xmath151599 & 1.0 + 2.554 & 3.664 & 4 & 7135@xmath153567 & 1.0 + 3.664 & 5.255 & 2 & 6128@xmath154333 & 1.0 we now analyze the noise in our interferometric imaging towards the ncp region , which comprises primarily four contributors : thermal noise , confusion noise , calibration error and deconvolution error . the thermal noise for a radio interferometer like 21cma with an effective area @xmath163 and system temperature @xmath164 can be estimated simply from @xmath165 where @xmath166 is boltzmann s constant , @xmath167 , @xmath168 and @xmath169 are the frequency bandwidth , observation duration , and efficiency factor , respectively . @xmath170 is composed of the telescope temperature ( 50k for the 21cma ) and the sky ( the milky way ) temperature described approximately by @xmath171 ( e.g. @xcite ) . for the observation made in this work , we have only used 559 baselines among 780 along the e - w arm after the shorter and longer baselines are taken out . this reduces the total effective area to @xmath172 , in which @xmath173 is the effective area of a single pod which remains roughly constant over our observing frequency range in terms of our antenna design . we also adopt the current efficiency of @xmath174 for 21cma to provide the numerical estimation . confusion noise @xmath175 from the position uncertainties of unresolved , faint radio sources below a flux threshold @xmath176 with finite synthesis beam @xmath177 can be estimated through ( e.g. @xcite ; @xcite ) @xmath178 in principle , we could take a simple extrapolation of our current differential source counts @xmath149 to lower fluxes beyond @xmath176 by considering a lower completeness of our catalog especially at lower frequencies . here we would rather choose the deeper gmrt observations at 153 mhz @xcite and extrapolate their differential number counts to @xmath179 mjy , two orders of magnitude fainter than their flux limit . yet , uncertainty in this extrapolation to very low flux remains unclear . moreover , it seems that the steep power law for the number count may flatten towards lower flux below a few mjy ( see @xcite for a recent compilation ) . figure [ fig : confusion ] plots the theoretically predicted thermal noise and confusion noise , together with the image noise measured across all eight bands . we have set @xmath180 in the estimate of confusion limit in each of the subbands . thermal noise for 12 hour observations and a bandwidth of 12.5 mhz has already become smaller than the image noise , indicating that the key factor influencing the sensitivity of low - frequency interferometric imaging is no longer the system noise . indeed , the confusion limit arising mainly from the unresolved faint sources especially at lower frequencies has actually made a significant contribution to the noise level . unlike the thermal noise which decreases as @xmath181 , the confusion noise is very insensitive to observing time @xmath182 . instead , the upper limit of integral in eq.(6 ) , @xmath176 , now determines the variation trend in confusion limit . one of our primary tasks in low - frequency interferometric imaging is to suppress the low flux limit @xmath176 to allow more fainter sources to be identified and resolved . in fact , @xmath176 is controlled by both calibration error and deconvolution error , in addition to telescope resolution . here the current imaging algorithm has not taken ionospheric effects into account , though self - calibration may partially correct the effect if a timestep is chosen to be within a few minutes or only short baselines are used . performing calibration on a timescale of a few minutes turns out to be very time consuming since the correction should also be made at each frequency channel . moreover , the grating lobes due to numerous redundant baselines of the 21cma generate very prominent , equally spaced rings round bright sources such as b004713 + 891245 and 3c061.1 . complete removals of these ring - like structures in deconvolution processing is still difficult at present . first , an accurate sky model containing both bright point and extended sources should be constructed in the calibration processing . significant uncertainties arise from the inaccurate models of ( marginally ) resolved extended sources , in which surface brightness , spectral index and position of each component of the sources should be determined by other radio observations or left as free parameters in the sky model . the brightest radio galaxy , 3c061.1 , in the ncp field is a typical example of this kind , and its residuals after deconvolution are very prominent . actually , 3c061.1 is the dominant source of both calibration and deconvolution errors for our imaging towards the ncp region . note that calibration error is also present even if a more sophisticated model for 3c061.1 is adopted for lofar data @xcite . second , the deconvolution should be made over a sky map with the field - of - view much larger than the primary beam so that the leakage of sidelobes from off - field strong radio sources can be corrected for . for the 21cma field , the two brightest radio sources , cas a and cygnus a , are visible on the sky map of @xmath183 ( @xcite ) , and their grating lobes have already entered into the central ncp field at certain frequencies . at present the imaging has not included and corrected the sidelobes from these two sources , although they have already contributed to the deconvolution noise . in summary , it appears that with time integration the thermal noise dominated by the milky way can be well controlled to below the confusion noise in current low - frequency interferometric imaging . however , to beat down the confusion noise , one needs to deal with not only the unresolved , faint radio sources , but also the calibration and deconvolution errors . in particular , calibration errors from both ionospheric effects and bright , extended sources are difficult to handle at present . these errors can propagate to the deconvolution processing and affect the lower threshold of identifying the faint radio sources through @xmath176 . as a result , the conventional confusion limit , which is determined by unresolved sources and synthesized beam , is actually affected by the extension of accuracy and reliability of calibration and deconvolution . in fact , the major source of errors in our current imaging arises from the calibration and deconvolution processing . the former is related to both ionospheric effects and modeling of extended , bright radio sources in the field , and the latter is involved with the removals of grating lobes and sidelobes of strong radio sources , both within and outside of the field . and @xmath13 noise levels , respectively , measured at eight sub - bands over the ncp field . the black dashed line represents the theoretically estimated confusion limit due to the unresolved fainter sources below @xmath176 , for which we have taken @xmath180 . , width=302 ] [ fig : confusion ] we have analyzed 12 hours of data taken from the 21cma observations centered on the ncp . to reduce the complexity of interferometric image processing and the influence of ionospheric perturbation , we have used all 40 pods along the east - west arm but restricted our analysis to within a maximum baseline of 1500 m. we have calibrated the gain and primary beam of our telescope using the bright radio sources in the ncp field . following conventional self - calibration and deconvolution methods , we have detected a total of 624 radio sources over the central field within @xmath57 in frequency range of 75 - 175 mhz and the outer annulus of @xmath54 in the 75 - 125 mhz bands . by performing a monte - carlo simulation we have estimated a completeness of @xmath11 at @xmath184 jy . we have compared our source counts with the deep low - frequency observations made recently with gmrt and mwa , and the completeness - corrected source counts show a good agreement with these recent surveys at the corresponding frequency bands . while we are able to detect the fainter sources down to 10 mjy , the detection fraction has dropped to @xmath31 , making a ultra deep observation rather difficult and even impossible with current imaging algorithms . this is primarily caused by errors in sidelobes , calibration , and deconvolution as well as the confusion limit of the array . spacings between the 21cma pods are the integral multiples of 20 m. the original design of such configuration is for the purpose of redundant calibration and statistical measurement of the eor power spectrum ( e.g. @xcite ) . however , this layout also generates the grating lobes evident in our images ( @xcite ) . these equally spaced rings around the bright sources in the field have their brightness almost comparable to the central sources , and therefore should be accurately removed in the deconvolution processing otherwise , their residuals may be the major sources of contaminations for our imaging . indeed , our image quality is largely limited by the presence of imperfectly subtracted grating lobes of the brightest source in the ncp field , 3c061.1 . although this arises partially from the inaccurate calibration , the main reason is the poor modeling of 3c061.1 in our self - calibration processing . 3c061.1 is marginally resolved with 21cma , and its modeling should take the structured components with different surface brightness and spectral index into account ( e.g. @xcite ) . our next step is to improve our sky model by using a sophisticated model for 3c061.1 and even for very bright , far field sources such as cas a and cygnus a. finally , the theoretically expected thermal noise ( @xmath3 mjy ) is well below the confusion limit due to the unresolved , fainter sources , indicating that the dominated factor of influencing the sensitivity for low - frequency interferometric imaging is no longer the system noise but the cosmic sources in the sky . several methods to improve our imaging algorithm including an accurate calibration ( e.g. sky modeling and redundant calibration ) , application of the w - term correction , and `` peeling '' sources @xcite are currently under investigation , with our ultimate goal towards detecting the eor power spectrum . our experience with the 21cma operation and data analysis may provide a useful guide to the design of next generation low - frequency radio array such as the ska . indeed , employment of numerous redundant baselines helps to improve the precision of calibration . however , it brings about very prominent grating lobes from bright sources both in - beam and in the far - field . this not only requires a more careful and accurate calibration of visibilities but also adds an extra difficulty to deconvolution processing . in particular , the grating lobes of the bright , structured sources like giant radio galaxies with jets are hard to model and thus subtract . in this sense , both random antenna element and station layouts should preferentially be chosen for low - frequency radio interferometers to suppress the grating lobes and sidelobes of bright sources . we note that an extensive study on this topic has recently been carried out by @xcite . to summarize , with current layout of the 21cma and conventional imaging algorithm , we have reached a sensitivity of a few mjy and a dynamical range of @xmath185 . we may have to improve our imaging quality by an order of magnitude in order to see statistically the eor signature . we thank judd bownman for useful discussions and heinz andernach for constructive comments . we gratefully acknowledge the constructive suggestions by an anonymous referee that greatly improved the presentation of this work . technical support was provided by the 21cma collaboration . this work was partially supported by the national science foundation of china under grant no . qz and mj - 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we present a catalog of 624 radio sources detected around the north celestial pole ( ncp ) with the 21 centimeter array ( 21cma ) , a radio interferometer dedicated to the statistical measurement of the epoch of reionization ( eor ) . the data are taken from a 12 h observation made on 2013 april 13 , with a frequency coverage from 75 to 175 mhz and an angular resolution of @xmath0 . the catalog includes flux densities at eight sub - bands across the 21cma bandwidth and provides the in - band spectral indices for the detected sources . to reduce the complexity of interferometric imaging from the so - called `` w '' term and ionospheric effects , the present analysis are restricted to the east - west baselines within 1500 m only . the 624 radio sources are found within 5 degrees around the ncp down to @xmath1 jy . our source counts are compared , and also exhibit a good agreement , with deep low - frequency observations made recently with the gmrt and mwa . in particular , for fainter radio sources below @xmath2 jy , we find a flattening trend of source counts towards lower frequencies . while the thermal noise ( @xmath3 mjy ) is well controlled to below the confusion limit , the dynamical range ( @xmath4 ) and sensitivity of current 21cma imaging is largely limited by calibration and deconvolution errors , especially the grating lobes of very bright sources , such as 3c061.1 , in the ncp field which result from the regular spacings of the 21cma . we note that particular attention should be paid to the extended sources , and their modeling and removals may constitute a large technical challenge for current eor experiments . our analysis may serve as a useful guide to design of next generation low - frequency interferometers like the square kilometre array .

<s>[INST]low - frequency observations are very important for the study of the statistical signatures of extragalactic sources , in particular source counts in the low - frequency sky , which until recently have been only characterized at the very highest end of the flux scale . the number of steep - spectrum sources increases rapidly as the sample selection frequency is lowered @xcite , because these sources become too faint to be detected at high frequencies leading to an expectation that low - frequency sky surveys will uncover this population in greater numbers than current cm - wavelength studies . as it is not trivial to infer the low - frequency ( @xmath5 300 mhz ) sky from higher frequency data , deep source counts at the same frequency as eor observations are required for accurate foreground modeling and subtraction . better understanding of the statistical properties and behavior of radio sources is required and motivated by a number of science goals , such as the foreground modeling and subtraction in the detection of the eor . over the last 30 years , a large and ever increasing number of surveys and targeted observations have been performed at low frequencies commencing with the 6th cambridge ( 6c ) survey of radio sources @xcite , which covered the entire northern sky above 30 degrees at 151 mhz . since then a number of other surveys have been completed such as the 7th and 8th cambridge survey of radio sources ( 7c , and 8c : @xcite ) , the targeted survey on the culgoora circular array @xcite in which the flux densities of 1800 high - frequency - selected radio sources were measured at 80 and 160 mhz , the 74 mhz vla low - frequency sky survey ( vlss : @xcite ) above -30 degrees , the murchison widefield array commissioning survey ( mwacs : @xcite ) covering 6,100 @xmath6 between 104 and 196 mhz , and the precision array for probing the epoch of reionization ( paper ; @xcite ) low resolution survey of the southern sky at 145 mhz . current low frequency radio interferometers , such as lofar @xcite , gmrt @xcite , lwa @xcite , mwa @xcite and paper @xcite have made a considerable advance in our understanding of the population of extragalactic radio sources at frequencies below 300 mhz with all - sky low frequency surveys(@xcite ) . the upcoming square kilometre array ( ska ) is expected to continue to push the boundaries of low - frequency astronomy , observing the radio sky at much higher sensitivity and resolution . recently , @xcite determined the 154mhz source counts with mwa observation of the so - called eor0 field ( which is centered at j2000 @xmath7 ) and compared these with the 7c counts at 151mhz @xcite , as well as the gmrt source counts at 153mhz @xcite finding good agreement to a limiting flux density of @xmath840 mjy . using lofar , @xcite examined source counts at 34 , 46 and 62 mhz , a wavelength regime not explored since the 8c observations at 38 mhz 25 years earlier . the lofar observations are the deepest images ever obtained at these frequencies and reach noise levels of the order of a few mjy , being nearly 2 orders of magnitude deeper than the 8c survey . @xcite confirmed the previously known result that the average spectral index of radio galaxies flattens towards lower frequencies , as is expected from synchrotron losses @xcite . in addition to understanding the properties of the low frequency radio population to study the population itself , it is of great importance to properly characterize the population if we are to fully exploit these instruments to detect the eor as a precise sky model is vital for subtracting foreground sources @xcite . thus , source count studies of the low frequency sky are strongly motivated by a number of complementary science goals . the north celestial pole ( ncp ) region is covered at low - frequencies by the wsrt @xcite and lofar @xcite , it is also the sky region targeted by the 21 centimeter array ( 21cma ) . the key science goal for the 21cma is to statistically measure the redshifted 21 cm signal of neutral hydrogen from the eor . determining the radio source counts and understanding the spectral properties of the radio sources are important for removing the foreground sources and extracting the faint eor signal . in this paper , we present targeted observations centered on the ncp and extending 5 degrees in radius using the 21cma . we determine the source counts using eight sub - band images between 75 mhz and 175 mhz with flux densities down to @xmath9 jy . we also investigate the spectral properties of catalog sources and compare our source counts with the recent surveys . the outline of the paper is as follows . section 2 describes the 21cma telescope , the observation and data reduction pipeline . section 3 presents the source extraction process and resultant source catalog and properties including number counts , spectral indices , completeness and errors . discussion and concluding remarks are given in section 4 . the 21cma is a ground based radio interferometer dedicated to detection of the eor . the array , sited in the ulastai valley of western china , consists of 81 pods or stations , with a total of 10287 log - periodic antennas are deployed in two perpendicular arms along an east - west ( 6.1 km ) ( figure [ fig : baseline ] ) and north - south ( 4 km ) direction , respectively . spacing of these 81 pods is chosen such that a sufficiently large number of redundant baselines and a good uniform uv coverage can both be guaranteed . each antenna element has 16 pairs of dipoles with lengths varying from 0.242 m to 0.829 m , optimized to cover a frequency range of 50 - 200 mhz , which gives rise to an angular resolution of @xmath10 at 200 mhz . all the antennas are fixed on the ground and point at the ncp for the sake of simplicity and economy , which allows us to observe the same patch of sky for 24 hours a day through the whole year . therefore , we can reach a higher sensitivity in a region of a few ten square degrees around the ncp in a relatively short time . phase delayed coaxial cables are used to combine the signal from each antenna for each pod , and the output signal is digitized at a sampling rate of 400 mhz with 8 bit precision to accommodate the bandwidth of 200 mhz , although signal below 50 mhz is actually filtered out . fast fourier transforms ( fft ) and correlations are performed in software by a cluster of 83 , dual - core intel(r ) xeon(tm ) servers , equipped with gigabit ethernet networks ( pci - e 10-gbps 4x ) and a high speed network ( infiniband ) switch ( cisco sfs-7008p ) . the 200 mhz bandwidth is divided into 8192 channels , giving rise to a frequency resolution of 24.4 khz . data in each channel are integrated for about 3 seconds in memory before they are output to a disk array of 32 terabytes . hard disks are transported to the headquarters of the national astronomical observatories of china in beijing for analysis . [ fig : baseline ] construction of the 21cma was completed in 2006 , and a significant upgrade was made in 2009 by installing a new type of low noise amplifier ( 40 k ) on each antenna and 40 sets of gpus in a new data acquisition cluster . the former considerably suppresses thermal noise from the phased delayed cables , while the later provides a very efficient way to speed up correlation computation processing . we have used software instead of hardware or fpgas to perform the fft and correlations . after this upgrade we also decided to run the e - w baseline only to maintain a higher efficiency ( @xmath11 ) of data acquisition by reducing the computing demands for cross - correlations . furthermore , this allows us to work with a relatively simple interferometric imaging algorithm without the concern of the so - called `` w '' term . in the early commissioning observations between 2005 - 2009 , many efforts were made to understand the performance of the 21cma system including antennas , receivers , data acquisition process , and even the power supply . we have developed all software packages and techniques such as identification and mitigation of radio frequency interference ( rfi ) , calibration , deconvolution , wide - field imaging , etc . necessary for full data processing of 21cma data . since july of 2010 after its upgrade , the 21cma has routinely observed the low frequency sky round the ncp , delivering about 2 terabits of visibility data per day for offline analysis . while the primary goal of the 21cma is to accumulate a deep observation for eor detection , even with relatively short integrations we can characterize the extra - galactic source population . on one hand , these bright extragalactic sources , a byproduct of our eor experiment , can be of great interest for exploration of their astrophysical properties . on the other hand , these radio sources constitute one of the major contamination components for our eor detection , and therefore should be perfectly imaged and subsequently subtracted . in the current work we present the point radio sources observed with the 40 pods of the 21cma e - w baselines for an integration of 12 hours made on 2013 april 13 . an extra deep sample with a higher sensitivity from a longer integration time of up to years will be published later . although the radio environment of the 21cma site , ulastai , is exceptionally quiet at low frequency and comparable to sites such as the murchison radio observatory ( @xcite ) , rfi is still a prominent concern for doing the eor experiment . figure [ fig : spectrum ] displays the average spectrum of cross - correlation between two pods over 12 hours with a frequency resolution of @xmath12 khz , which reveals the rfi at the site more clearly than the self - correlation of the same pod because thermal noises from different pods are not correlated . the overall shape reflects the decreasing sky noise at high frequencies and the decreasing efficiency of the antennas at low frequencies with a turnover at roughly 85 mhz . the strongest rfi sources are identified as low orbiting satellites at 137 mhz , local train communications at 150 mhz , civil aviation aircraft around 130 mhz and at 119 mhz , fm radio broadcasting at 88 - 108 mhz scattered by meteor tails and aircraft , and am radio broadcasting around 70 mhz , and several other contaminators @xcite . all these sources of rfi are highly time variable , and can be easily flagged for blanking during the editing process . after the mitigation of strong , time variable rfi , we apply a second statistical algorithm for further removal of other possible rfi using the fact that the sampling of visibilities should exhibit a gaussian distribution for a given frequency , a scheme often adopted in data analysis of recent low frequency experiments ( e.g. @xcite ) . in the second stage of rfi mitigation we excluded all the data points beyond @xmath13 deviation from gaussian statistics . this operation is applied to the real and imaginary parts separately , and the visibility data are edited out if either of the parts fail to reach the @xmath13 restrictions . this still allows us to use the bulk ( about 97% ) of the data except for some of the most noisy channels around 137 mhz and 150 mhz . the reader is referred to @xcite for a detail description of our rfi identification and mitigation processing . low - frequency radio interferometric observations are often affected by ionospheric turbulence , resulting in fluctuations of both source positions and flux densities . we run two algorithms to correct the phase error in the visibilities due primarily to ionospheric effects : self - calibration and the closure relation . software developed in - house is used for self - calibration , in which a time interval of 1 hour is used for the present study . we have tested shorter intervals of down to 10 minutes , and found that the changes are only minor when longer baselines of @xmath14 m are excluded ( see below ) . we have already improved our self - calibration algorithm by combining conventional self - calibration and redundant calibration , we will apply it for all baselines using a short time interval in the future data reduction ( zheng et al . in preparation ) . the ncp sky at 50 - 200 mhz is actually dominated by two bright sources : a central bright quasar ( nvss j011732 + 892848 ) and a galaxy 3c61.1 . 3c61.1 is a very bright giant galaxy with a flux density of 33 jy at 150 mhz , which also shows a complex structure . we select 10 radio sources including these two bright sources ( table [ table : calibrators ] ) to correct the phase errors with self - calibration . following this , we use the closure phase relation to check , and modify if necessary , the results . lllll nvss j011732 + 892848 & 0.52 & [email protected] & [email protected] & point source + nvss j062205 + 871948 & 2.67 & [email protected] & [email protected]&point source + nvss j133218 + 865005 & 3.17 & [email protected] & [email protected] & point source + nvss j092016 + 862845 & 3.52 & [email protected] & [email protected] & point source + 3c061.1 & 3.71 & [email protected] & [email protected] & resolved + nvss j122518 + 860839 & 3.86 & [email protected] & [email protected] & point source + nvss j1013.7 + 8553 & 4.12 & [email protected] & [email protected] & point source + nvss j190350 + 853648 & 4.39 & [email protected] & [email protected] & point source + nvss j194136 + 850138 & 4.97 & [email protected] & [email protected] & point source + nvss j212926 + 845326 & 5.11 & [email protected] & [email protected] & point source to reduce further the ionospheric effect on our interferometric imaging and improve image quality , we exclude both longer baselines of @xmath14 m and the shorter ones of @xmath16 m in the present analysis . we perform a fast fourier transform of the uv map using a uniform weighting with @xmath17 grids , sampled by different baselines and snapshots for each frequency channel , to generate the dirty maps . this yields a total of 6144 images over 50 - 200 mhz frequency bands with a frequency resolution of 24.4 khz . then , each dirty image is deconvolved using the conventional hgbom clean algorithm @xcite with a loop - gain of 0.05 . we terminate the clean process when the fractional change in the total cleaned flux density is less than @xmath18 in the iteration . employment of a smaller threshold does not alter the result significantly . after the deconvolution we adopt a larger frequency bin of 1.56 mhz to combine the 6144 images into 96 mosaics , and concentrate on only the central field of view of @xmath19 pixels , corresponding to a @xmath20 degree square area . note that this gives rise to an angular resolution of @xmath21 arcmin per pixel while the best resolution of the array is only @xmath22 arcmin at 200 mhz . directivity and gain of the 21cma antenna element , the log - periodic antenna , has been precisely measured in laboratory , which indeed allows us to compute the primary beam and gain of the 21cma pod according to the pattern multiplication theorem . however , in situ calibration has to be made to account for the possible effect of crosstalk between the antennas themselves and the antennas and the ground . for a 12 hour ( or more ) observation of the 21cma centered on the ncp , the primary beam of a pod has circular symmetry . moreover , in terms of our laboratory measurement of the spatial response of the 21cma log - periodic antenna and theoretical prediction based on the pattern multiplication theorem , the primary beam pattern of a 21cma pod is nicely approximated by a gaussian profile characterized by the standard deviation @xmath23 . guided by our knowledge and experience , we adopt a modulated gaussian function parametrized by @xmath24 for the primary beam and gain of the 21cma pod , where g is the system gain which varies with frequency @xmath25 , @xmath26 measures the radial distance from the ncp , @xmath27 denotes the standard deviation of the gaussian distribution , and a and b are the coefficients in the polynomial of degree 2 . unfortunately , there are no standard radio sources in the ncp region that can be used for calibration purposes . thus we use the same sources selected in the self - calibration ( table [ table : calibrators ] ) as our flux calibrators . we collect the flux density measurements of these sources made at different frequencies ranging from a few ten mhz to a few ghz from the literature and obtain the spectral index , @xmath28 , for each source by fitting the observed flux densities to a power law , @xmath29 . except for the flat - spectrum sources , the fitting errors in amplitude @xmath30 and spectral index @xmath28 are typically @xmath31 and @xmath32 , respectively . errors in these calibrators will be included in fitting of gain and spatial response function of the telescope . we then use the total flux density within a frequency bin of 1.56 mhz to accommodate our cleaned images over the same frequency band . however , the primary beam is frequency - dependent , and varies roughly as an exponential profile characterized by @xmath27 for the 21cma . this reduces further the number of the bright radio sources that can be used for calibration in the higher frequency bands . as a result , only the inner 4 sources within @xmath33 can be used for the 32 higher frequency bands with @xmath34 mhz , for which uncertainties in the determination of gain and spatial response might be large . we start with a gaussian profile of @xmath35 , and find the best - fit parameters @xmath36 and @xmath27 in each frequency channel . by fixing @xmath36 and @xmath27 , we then use the same calibrators to find the modification parameters @xmath37 and @xmath38 to the gaussian distribution . it turns out that the gaussian profile provides rather a good description for the 12-hour averaged primary beam , and the modification parameters a and b are actually around zero ( see figures [ fig : theta ] and [ fig : poly ] ) . moreover , the best - fit gaussian beam of @xmath39 is in good agreement with our theoretical prediction . figure [ fig : g ] shows the resultant system gain against frequency . the design of the 21cma antenna is such that the effective area remains roughly constant over a wide frequency range , which yields a frequency dependent gain of @xmath40 . the steeper profile of the fitted gain factor also reflects the compensation for signal attenuation of the phased - delayed coaxial cable used for signal combination . [ fig : theta ] [ fig : poly ] [ fig : g ] [ fig : noise ] lll 81.25 & 28.9 & 6.78 + 93.75 & 22.5 & 5.93 + 106.25 & 17.8 & 5.28 + 118.75 & 10.7 & 4.75 + 131.25 & 7.7 & 4.32 + 143.75 & 5.3 & 3.96 + 156.25 & 4.1 & 3.65 + 168.75 & 3.3 & 3.39 the cleaned image in each of the 96 frequency channels is corrected for beam response and flux gain . then the images are stacked into 12 sky maps with a bandwidth of 12.5 mhz . to reduce further the possible roll - off effect of the bandpass filters used in the 21cma receivers , we will not use the data at the two frequency ends , 50 - 75 mhz and 175 - 200 mhz , in the present paper . this yields a total of 8 sky maps centered at 81.25 , 93.75 , 106.25 , 118.75 , 131.25 , 143.75 , 156.25 and 168.75 mhz , respectively , with a varying image noise from @xmath41 mjy at lower frequency end to @xmath42 mjy higher frequency one . figure [ fig : noise ] illustrates an example of the cleaned image and corresponding noise map in the 131.25 mhz subband . the noise and beam size in each 12.5 mhz subband image are summarized in table [ table : noise ] . we calculate the dynamical range of each sky map to provide a quantitative estimate of the image quality , which we defined here as the ratio of the peak brightness @xmath43 of the image to the rms noise @xmath44 , and the result is shown in figure [ fig : ston ] for the 8 sky maps . it appears that the ratio of @xmath45 reaches a value of @xmath46 and shows an increase trend with frequency . such a variation is simply the combined effect of the system sensitivity , which is dominated by the milky way ( e.g. @xcite ) @xmath47 , and the power - law behavior of the background radio source flux density , @xmath48 with @xmath49 . as a consequence , the dynamical range of the sky map varies with frequency roughly as @xmath50 . yet , the current dynamical range is still one order of magnitude below the eor detection requirement ( see @xcite ; @xcite ; @xcite for review ) , and we will address the possible reasons in the sub - section on noise analysis ( section 3.5 ) below . we have also made a full band 75 - 175 mhz image by mosaicing the 8 sub - band images together after convolving to a common resolution of @xmath51 arcmin ( figure [ fig : dirtymap ] and figure [ fig : wideband ] ) . this combined image will be used to remove spurious sources ( see below ) . [ fig : ston ] the field of view ( fov ) depends on the observing frequency , such that fov@xmath52 . as a result , we can only extract full spectral information for radio sources within a radius of @xmath53 around the ncp . nonetheless , we also count the sources between @xmath54 to expand our radio source catalog , for which spectral measurements are based on only the four lower frequency channels , 81.25 , 93.75 , 106.25 and 118.75 mhz . we note that , many more sources have been found beyond @xmath55 at the lower frequency end , but we will not include them in the present catalog . source candidates are first selected in the full - band image covering 75 - 175 mhz , using a method similar to duchamp @xcite , in which a threshold of @xmath13 is adopted to identify source candidates . the position of the peak flux of each candidate in the full - band image is tagged and then used for selection of source candidate in other sub - bands in a procedure similar to that described in @xcite . the source candidates will be removed from the list if their counterparts are missing in one of the frequency bands . this allows us to identify and thus remove all the spurious sources that result from the sidelobes of the brightest radio source , 3c061.1 ( see figure [ fig : dirtymap ] and figure [ fig : wideband ] ) . indeed , we are still unable to perfectly clean the sidelobes of the brightest radio galaxy , 3c061.1 , located at @xmath56 degrees from ncp . the complex structure of this source @xcite is marginally resolved with 21cma . even with a better angular resolution and a multi - directional calibration using sagecal @xcite , lofar imaging of the same source also contains significant errors @xcite . our current experiment towards the detection of the eor is thus largely limited by the presence of this very bright , complex radio galaxy in the ncp field . a gaussian profile is used to fit the `` surface brightness '' of a radio source in each of the sub - bands and the corresponding flux density can be computed straightforwardly . when two sources show an overlap due to poor resolutions , a two - component gaussian profile is adopted to fit the images simultaneously . yet , even this double gaussian models may fail to fit two sources with significant overlap especially at low frequencies . in this case , we will not provide the flux density information for the two sources but still treat them as separate sources . we calculate the spectral index for each source using the measured flux densities in all the available bands , up to 8 bands for sources within @xmath57 and up to 4 bands for the ones in the annulus of @xmath54 . [ fig : dirtymap ] is shown , with an annulus of 1 degree in radial distance . the deconvolution is performed through the hgbom clean algorithm with a loop gain of 0.05 . the brightest source ( lower right ) , 3c061.1 , is located at a distance of @xmath58 from the ncp , and deconvolution noise around 3c061.1 , which arises mainly from grating lobes and inaccurate calibration , is clearly visible . note that we have enhanced the image contract to display the noise field which is actually four orders of magnitude fainter than the typical bright sources in the field.,width=340 ] [ fig : wideband ] our method of source identification is indeed reliable for mitigation of artificial sources . however , the fainter sources below our threshold at least in one of the eight sub - bands can not be included with the current criterion of source selection . in addition , the threshold varies with frequency channels , and therefore , we may have missed a significant fraction of faint sources . we have thus tested two other methods by relaxing the above criterion for source selection . the first is to work with an extreme case : all the candidates with peak fluxes above @xmath13 in any sub - band are selected . this provides an overestimate of source population because image artifacts , due to imperfect cleaning of sidelobes of bright sources , especially 3c061.1 , have contaminated our observing field . we demonstrate in section 3.3 an example of the completeness estimate from such a source selection method for the highest angular resolution sub - band at 168.75 mhz . it turns out that the contamination of spurious sources is indeed very serious . the second test is to select sources based on adjacent frequency channels instead of full bands . to deal with the sidelobes from the bright sources , source candidates should be removed from the list once their counterparts are missing only in one of the adjacent channels , using the frequency - dependence properties of sidelobes ( figure [ fig : sourceselection ] ) . this allows us to identify more faint sources yet leaves the following two drawbacks : ( 1 ) the position variations of the sidelobes - induced `` sources '' become indistinguishable at low frequencies because of poor angular resolution , and ( 2 ) the spectral index can not be estimated reliably if a source shows up only in two frequency bands . while we adopt our conservative way to select sources and construct our source catalog in this work , we will compare the completeness and source counts among the three selection methods below and will improve our source selection algorithm in our future work . [ fig : sourceselection ] ccccccccccc 9.49 & 89.68 & @xmath59 & @xmath60 & @xmath61 & @xmath62 & @xmath63 & @xmath64 & @xmath65 & @xmath66 & @xmath67 + 5.23 & 89.65 & @xmath68 & @xmath69 & @xmath70 & @xmath71 & @xmath72 & @xmath73 & @xmath74 & @xmath75 & @xmath76 + 7.59 & 89.63 & & @xmath77 & @xmath78 & @xmath61 & @xmath79 & @xmath80 & @xmath81 & @xmath82 & @xmath83 + 0.29 & 89.58 & & @xmath84 & @xmath85 & @xmath86 & @xmath87 & @xmath88 & @xmath89 & @xmath90 & @xmath91 + 12.30 & 89.57 & & & & @xmath92 & @xmath93 & @xmath94 & @xmath95 & @xmath96 & @xmath97 + 16.55 & 89.55 & @xmath98 & @xmath99 & @xmath100 & @xmath101 & @xmath102 & @xmath103 & @xmath104 & @xmath105 & @xmath106 + 1.29 & 89.47 & & & & & @xmath107 & @xmath108 & @xmath109 & @xmath110 & @xmath111 + 9.52 & 89.47 & & & @xmath112 & @xmath113 & @xmath114 & @xmath115 & @xmath116 & @xmath117 & @xmath118 + 6.31 & 89.45 & @xmath119 & @xmath120 & @xmath121 & @xmath122 & @xmath123 & @xmath124 & @xmath125 & @xmath126 & @xmath127 + 10.86 & 89.40 & @xmath128 & @xmath129 & @xmath130 & @xmath131 & @xmath132 & @xmath133 & @xmath134 & @xmath135 & @xmath136 a total of 624 radio sources are found around the ncp region , and their positions , integrated fluxes and spectral indices are listed in table [ table : list ] . note that for sources within @xmath57 we fit integrated fluxes in eight subbands to a power - law to estimate their spectral indices . while for sources in annulus of @xmath54 we only use the integrated fluxes measured in 4 lower frequency subbands . moreover , data points in some of the subbands have not been taken if the integrated fluxes of images can not be precisely measured due to poor resolution and/or significant overlap . of the 624 sources , 322 sources lie between 3 and 5 deg from the field center ncp which are selected using the four lower frequency subbands ( 81.25 , 93.75 , 106.25 and 118.75 mhz ) . an immediate cross - check with the existing the 6c catalog at 151 mhz reveals 490 counterparts . the missing sources are the fainter ones below the detection limit of 0.1 jy in the 6c survey . namely , about 134 new sources are detected around and below 0.1 jy at 151 mhz . figure [ fig:21cma-6c ] compares the flux densities of these 490 sources at 151 mhz listed in both 6c catalog and our new catalog , and two measurements above 0.1 jy show rather a good agreement . [ fig:21cma-6c ] figure [ fig : alpha1 ] illustrates the histogram of the spectral indices of the 624 sources presented here . while the distribution peaks at approximately @xmath49 , consistent with what is expected for the overall population of cosmic radio sources , the asymmetrical behavior indicates that more sources tend to have a steeper spectral index . this could arise as the radio sources with steeper indices are more easily detected at low frequencies . in other words , low - frequency observations would probably miss some of the flat - spectrum sources if they are not bright enough . yet , recent observations have argued a spectral flattening towards both lower frequencies and fluxes ( e.g. @xcite ; @xcite ; @xcite ) . to investigate if similar behavior is evident in our radio source catalog , we restrict the sources within 3 degrees and compare in figure [ fig : alpha2 ] the spectral indices between the 4 lower frequency subbands and the 4 higher frequency subbands . it turns out that there is a significant excess of steep - spectrum sources in the higher frequency subbands . this can be further quantified by considering the means , medians and their ratios ( means / medians ) of the two distributions , yielding ( -1.25,-1.15,1.09 ) and ( -0.86,-0.87,0.99 ) for the higher and lower frequency subbands , respectively . we have also compared the low - frequency sources in the inner radius of 3 degrees and the ones in the outer annulus of @xmath54 , and found that their spectral indices are essentially similar ( figure [ fig : alpha3 ] ) . while the absence of bias in spectral index between the sources within the central region ( @xmath137 ) and the ones in the outer region ( @xmath54 ) simply reflects the uniformity of cosmic radio sources , it also indicates that our beam model is correct . it turns out that our analysis does support a flattening trend toward lower frequencies . if confirmed , this may add a further difficulty for low - frequency observations to detect faint , flat - spectrum sources . [ fig : alpha1 ] [ fig : alpha2 ] [ fig : alpha3 ] before we perform monte - carlo simulations to estimate the completeness of our source selections , we compare our source counts with the deep low - frequency observations of the noao botes field down to 6 mjy made with gmrt at 153 mhz @xcite . this allows us to make a quick yet rough judgment on the incompleteness of our source counts at different fluxes . of course , an extrapolation based on a spectral index conversion should be made for source counts at other frequencies for the `` control '' field . we notice that the reliability of such an extrapolation is probably questionable , as argued recently by @xcite . taking the differential source count by @xcite at 153 mhz , @xmath138 , we calculate the ratios of our observed sources @xmath139 to what are expected in terms of this single power law , and plot the results for the 168.75 mhz frequency channel in figure [ fraction-3methods ] . it appears that the incompleteness for our standard method of source selection occurs around 0.1 jy , where the ratio drops to @xmath140 . namely , a significant fraction of the fainter sources may be missed below 0.1 jy when sources are required to be visible in all subbands to guarantee that the artificial sources from sidelobes be clearly discriminated and perfectly removed . we have also shown the completeness estimates for the other two selection methods : the extreme approach that treats all the peaks above @xmath13 as `` sources '' gives rise to an apparent over - estimate of true sources even down to @xmath141 jy , indicating that the contamination is rather significant . sources that are selected in terms of their locations at adjacent frequency channels seem to be complete until @xmath1 jy , and their completeness drops to @xmath142 at 0.01 jy . while the latter provides a `` better '' completeness of source selection , the poor angular resolution at lower frequencies may be inefficient for discrimination of position shifts of the artificial sources due to sidelobes , as was pointed out above . we now perform a monte - carlo simulation to quantify the completeness of the source sample . we generate 20 fields with a radius of @xmath57 , each of which contains 1600 point sources with positions randomly distributed . the fluxes of these artificial sources are assumed to follow a power - law of @xmath143 and are further restricted within @xmath144 mjy @xmath145 jy , for which a spectral index of @xmath146 is assumed . we include the beam smearing effect by convolving the image with a gaussian function characterized by the true beam at each frequency band . we add noise to the simulated map at each channel using the true residual map from our deconvolution after point sources are peeled out . furthermore , the radial variation in sensitivity around the ncp is taken into account by the spatial response of the telescope described by eq.(2 ) . now , we adopt the same mechanism , the so - called standard method , to extract sources at the same eight frequency channels , using the image flux and position information over the frequency bands . figure [ fraction ] shows the mean fraction of simulated sources recovered against total flux density for each of the eight channels , respectively , in which the error bars represent the standard statistical deviations . as expected , the turning points of completeness exhibit a weak increasing tread towards higher frequencies . unfortunately , the completeness decreases rapidly to zero beyond @xmath147 jy , although we can still detect some sources down to @xmath148 jy for all the 8 frequency bands . our estimated completeness will be used for correcting the incompleteness of source counts below . [ fraction-3methods ] are randomly distributed over a circular field with a radius of 3 degrees , and noise and beam smearing are added in terms of the true measurements on the ncp field . the same source selection method as we adopted for the ncp field is applied to the simulation . error bars at each frequency represent the standard deviation from 20 realizations . , width=340 ] [ fraction ] we plot in figure [ numbercount ] the differential source counts @xmath149 of our sample over the central field of radius @xmath57 for each of the 8 frequency bands , in which both the raw data and completeness - corrected data in terms of the above monte - carlo simulation are displayed . for data points with completeness of @xmath11 or above , which corresponds to the brighter sources with fluxes greater than @xmath1 jy , a single power law fits nicely the completeness - corrected data : @xmath150 if we adopt a lower completeness of @xmath151 to include more fainter sources , though the data points below @xmath11 already become unreliable , @xmath149 would follow the the well - known two power laws for cosmic radio population at low frequencies @xcite . @xmath152 where @xmath153 indicates the turnover flux . the best - fit parameters for the 8 frequency subbands are summarized in tables [ table : ncounta ] and [ table : ncountb ] for the @xmath11 and @xmath151 completeness data , respectively . it appears that for the bright population with @xmath154 , our best - fit indices vary between 2.10 and 2.55 , which are both consistent with each other within error bars , and are also close to 2.5 which is expected for a euclidean cosmology . for the fainter radio sources below @xmath153 , we find a weak dependence of @xmath155 on frequency , with a flattening source count towards lower frequencies . we note that a power - law fit at @xmath156 jy to the gmrt counts from williams , intema & rottgering ( 2013 ) , intema et al . ( 2011 ) and ghosh et al . ( 2012 ) gives @xmath157 at 154 mhz @xcite and the gmrt targeted survey at 153 mhz finds essentially similar results , @xmath158 ( @xcite , see also @xcite ) . our best - fit power indices at the two closest bands , 143.75 and 156.25 mhz , are @xmath159 and @xmath160 , respectively , which are slightly higher than these results due to the lack of fainter sources in our samples . for each of the eight frequency subbands . filled and open circles represent the raw data and completeness - corrected data , respectively . the two vertical dashed lines indicate the @xmath151 ( black ) completeness and @xmath11 ( red ) completeness , respectively . the best - fit two power laws for the @xmath151 completeness limit are shown by the black solid lines , while the results for the @xmath11 completeness data are illustrated by the red solid lines . , width=302 ] [ numbercount ] lll 81.25 & 2896@xmath15898 & [email protected] + 93.75 & 3044@xmath15737 & [email protected] + 106.25 & 2879@xmath15635 & [email protected] + 118.75 & 3062@xmath15979 & [email protected] + 131.25 & 3007@xmath15679 & [email protected] + 143.75 & 2974@xmath15789 & [email protected] + 156.25 & 2911@xmath15757 & [email protected] + 168.75 & 2812@xmath15464 & [email protected] llllll 81.25 & 0.95 & 5318@xmath151384 & [email protected] & 5038@xmath151180 & [email protected] + 93.75 & 0.95 & 4850@xmath15928 & [email protected] & 4658@xmath15615 & [email protected] + 106.25 & 0.8 & 4136@xmath15520 & [email protected] & 3708@xmath15355 & [email protected] + 118.75 & 0.8 & 3664@xmath15441 & [email protected] & 3447@xmath15327 & [email protected] + 131.25 & 0.65 & 4432@xmath15444 & [email protected] & 3594@xmath15276 & [email protected] + 143.75 & 0.65 & 3917@xmath15455 & [email protected] & 3327@xmath15240 & [email protected] + 156.25 & 0.5 & 3747@xmath15613 & [email protected] & 3112@xmath15341 & [email protected] + 168.75 & 0.5 & 4269@xmath151167 & [email protected] & 3170@xmath15344 & [email protected] to compare our results with other deep surveys at low frequencies , we derive the euclidean - normalized differential source counts , @xmath161 , for which uncertianties are represented by the poisson errors calculated from the number of sources detected in each flux density bin . we take the source counts from two recent surveys at frequencies in the range of 151 - 154 mhz with gmrt @xcite and mwa @xcite . we choose our results in the 156.25 mhz band to compare with @xmath161 given at 151 - 154 mhz with the gmrt and mwa by scaling the observing frequencies with a single power - law of @xmath162 to 154 mhz ( figure [ fig:154mhz - compare ] ) . within the error bars , our source counts are in good agreement with these recent surveys . in table [ nor - counts81 - 118 ] and table [ nor - counts131 - 168 ] we have provided the tabulated normalized differential source counts for the lower ( 81.25 , 93.75 , 106.25 and 118.75 mhz ) and higher ( 131.25 , 143.75 , 156.25 and 168.75 mhz ) bands , respectively , and the results are also displayed in figure [ fig : sdnds - low ] and figure [ fig : sdnds - high ] , respectively . [ fig:154mhz - compare ] [ fig : sdnds - low ] [ fig : sdnds - high ] lllll 81.25 mhz + 0.367 & 0.527 & 22 & 2910@xmath15620 & 1.3 + 0.527 & 0.755 & 23 & 4841@xmath151009 & 1.2 + 0.755 & 1.083 & 13 & 4462@xmath151237 & 1.1 + 1.083 & 1.554 & 10 & 5587@xmath151767 & 1.0 + 1.554 & 2.228 & 8 & 6964@xmath152462 & 1.0 + 2.228 & 3.196 & 7 & 10172@xmath153844 & 1.0 + 4.584 & 6.575 & 4 & 17150@xmath158575 & 1.0 + 6.575 & 9.430 & 2 & 14730@xmath1510415 & 1.0 + 93.75 mhz + 0.327 & 0.470 & 28 & 3198@xmath15604 & 1.3 + 0.470 & 0.674 & 20 & 3553@xmath15794 & 1.2 + 0.674 & 0.966 & 17 & 4830@xmath151171 & 1.1 + 0.966 & 1.386 & 9 & 4030@xmath151343 & 1.0 + 1.386 & 1.987 & 9 & 6453@xmath152151 & 1.0 + 1.987 & 2.850 & 7 & 8567@xmath153238 & 1.0 + 2.850 & 4.088 & 2 & 4204@xmath152973 & 1.0 + 4.088 & 5.863 & 3 & 10833@xmath156254 & 1.0 + 5.863 & 8.410 & 2 & 12405@xmath158772 & 1.0 + 106.25 mhz + 0.207 & 0.296 & 32 & 2513@xmath15444 & 1.9 + 0.296 & 0.425 & 31 & 2183@xmath15392 & 1.0 + 0.425 & 0.609 & 19 & 2299@xmath15527 & 1.0 + 0.609 & 0.874 & 21 & 4364@xmath15952 & 1.0 + 0.874 & 1.254 & 10 & 3570@xmath151129 & 1.0 + 1.254 & 1.798 & 7 & 4292@xmath151622 & 1.0 + 1.798 & 2.579 & 9 & 9479@xmath153160 & 1.0 + 2.579 & 3.699 & 2 & 3618@xmath152558 & 1.0 + 3.699 & 5.305 & 3 & 9322@xmath155382 & 1.0 + 5.305 & 7.608 & 2 & 10675@xmath157459 & 1.0 + 118.75 mhz + 0.189 & 0.271 & 32 & 2075@xmath15367 & 1.8 + 0.271 & 0.389 & 37 & 2280@xmath15375 & 1.0 + 0.389 & 0.557 & 29 & 3070@xmath15570 & 1.0 + 0.557 & 0.800 & 15 & 2728@xmath15704 & 1.0 + 0.800 & 1.147 & 13 & 4061@xmath151126 & 1.0 + 1.147 & 1.645 & 7 & 3756@xmath151420 & 1.0 + 1.645 & 2.359 & 8 & 7373@xmath152606 & 1.0 + 2.359 & 3.384 & 2 & 3166@xmath152239 & 1.0 + 3.384 & 4.853 & 3 & 8158@xmath154710 & 1.0 + 4.853 & 6.961 & 2 & 9341@xmath156605 & 1.0 lllll 131.25 mhz + 0.174 & 0.250 & 24 & 1266@xmath15258 & 1.6 + 0.250 & 0.359 & 47 & 2569@xmath15375 & 1.0 + 0.359 & 0.515 & 21 & 1972@xmath15430 & 1.0 + 0.515 & 0.738 & 21 & 3387@xmath15739 & 1.0 + 0.738 & 1.059 & 12 & 3324@xmath15960 & 1.0 + 1.059 & 1.518 & 7 & 3331@xmath151259 & 1.0 + 1.518 & 2.178 & 8 & 6538@xmath152312 & 1.0 + 2.178 & 3.123 & 2 & 2807@xmath151985 & 1.0 + 3.123 & 4.480 & 2 & 4823@xmath153410 & 1.0 + 4.480 & 6.425 & 3 & 12427@xmath157174 & 1.0 + 143.75 mhz + 0.162 & 0.233 & 33 & 1489@xmath15259 & 1.5 + 0.233 & 0.334 & 34 & 1666@xmath15286 & 1.0 + 0.334 & 0.478 & 28 & 2357@xmath15445 & 1.0 + 0.478 & 0.686 & 16 & 2313@xmath15578 & 1.0 + 0.686 & 0.984 & 10 & 2484@xmath15785 & 1.0 + 0.984 & 1.411 & 9 & 3839@xmath151279 & 1.0 + 1.412 & 2.025 & 7 & 5129@xmath151939 & 1.0 + 2.025 & 2.904 & 2 & 2517@xmath151780 & 1.0 + 2.904 & 4.165 & 3 & 6486@xmath153745 & 1.0 + 4.165 & 5.974 & 2 & 7428@xmath155252 & 1.0 + 156.25 mhz + 0.152 & 0.218 & 36 & 1624@xmath15271 & 1.7 + 0.218 & 0.312 & 35 & 1551@xmath15262 & 1.0 + 0.312 & 0.448 & 23 & 1752@xmath15365 & 1.0 + 0.448 & 0.642 & 13 & 1701@xmath15472 & 1.0 + 0.642 & 0.921 & 11 & 2472@xmath15745 & 1.0 + 0.921 & 1.321 & 8 & 3088@xmath151092 & 1.0 + 1.321 & 1.894 & 7 & 4641@xmath151754 & 1.0 + 1.894 & 2.717 & 2 & 2278@xmath151611 & 1.0 + 2.717 & 3.896 & 3 & 5869@xmath153388 & 1.0 + 3.896 & 5.589 & 2 & 6720@xmath154752 & 1.0 + 168.75 mhz + 0.142 & 0.205 & 38 & 1653@xmath15268 & 1.8 + 0.205 & 0.293 & 28 & 1132@xmath15214 & 1.0 + 0.293 & 0.421 & 25 & 1736@xmath15347 & 1.0 + 0.421 & 0.604 & 14 & 1670@xmath15446 & 1.0 + 0.603 & 0.866 & 10 & 2049@xmath15648 & 1.0 + 0.866 & 1.242 & 9 & 3167@xmath151056 & 1.0 + 1.242 & 1.781 & 7 & 4232@xmath151599 & 1.0 + 2.554 & 3.664 & 4 & 7135@xmath153567 & 1.0 + 3.664 & 5.255 & 2 & 6128@xmath154333 & 1.0 we now analyze the noise in our interferometric imaging towards the ncp region , which comprises primarily four contributors : thermal noise , confusion noise , calibration error and deconvolution error . the thermal noise for a radio interferometer like 21cma with an effective area @xmath163 and system temperature @xmath164 can be estimated simply from @xmath165 where @xmath166 is boltzmann s constant , @xmath167 , @xmath168 and @xmath169 are the frequency bandwidth , observation duration , and efficiency factor , respectively . @xmath170 is composed of the telescope temperature ( 50k for the 21cma ) and the sky ( the milky way ) temperature described approximately by @xmath171 ( e.g. @xcite ) . for the observation made in this work , we have only used 559 baselines among 780 along the e - w arm after the shorter and longer baselines are taken out . this reduces the total effective area to @xmath172 , in which @xmath173 is the effective area of a single pod which remains roughly constant over our observing frequency range in terms of our antenna design . we also adopt the current efficiency of @xmath174 for 21cma to provide the numerical estimation . confusion noise @xmath175 from the position uncertainties of unresolved , faint radio sources below a flux threshold @xmath176 with finite synthesis beam @xmath177 can be estimated through ( e.g. @xcite ; @xcite ) @xmath178 in principle , we could take a simple extrapolation of our current differential source counts @xmath149 to lower fluxes beyond @xmath176 by considering a lower completeness of our catalog especially at lower frequencies . here we would rather choose the deeper gmrt observations at 153 mhz @xcite and extrapolate their differential number counts to @xmath179 mjy , two orders of magnitude fainter than their flux limit . yet , uncertainty in this extrapolation to very low flux remains unclear . moreover , it seems that the steep power law for the number count may flatten towards lower flux below a few mjy ( see @xcite for a recent compilation ) . figure [ fig : confusion ] plots the theoretically predicted thermal noise and confusion noise , together with the image noise measured across all eight bands . we have set @xmath180 in the estimate of confusion limit in each of the subbands . thermal noise for 12 hour observations and a bandwidth of 12.5 mhz has already become smaller than the image noise , indicating that the key factor influencing the sensitivity of low - frequency interferometric imaging is no longer the system noise . indeed , the confusion limit arising mainly from the unresolved faint sources especially at lower frequencies has actually made a significant contribution to the noise level . unlike the thermal noise which decreases as @xmath181 , the confusion noise is very insensitive to observing time @xmath182 . instead , the upper limit of integral in eq.(6 ) , @xmath176 , now determines the variation trend in confusion limit . one of our primary tasks in low - frequency interferometric imaging is to suppress the low flux limit @xmath176 to allow more fainter sources to be identified and resolved . in fact , @xmath176 is controlled by both calibration error and deconvolution error , in addition to telescope resolution . here the current imaging algorithm has not taken ionospheric effects into account , though self - calibration may partially correct the effect if a timestep is chosen to be within a few minutes or only short baselines are used . performing calibration on a timescale of a few minutes turns out to be very time consuming since the correction should also be made at each frequency channel . moreover , the grating lobes due to numerous redundant baselines of the 21cma generate very prominent , equally spaced rings round bright sources such as b004713 + 891245 and 3c061.1 . complete removals of these ring - like structures in deconvolution processing is still difficult at present . first , an accurate sky model containing both bright point and extended sources should be constructed in the calibration processing . significant uncertainties arise from the inaccurate models of ( marginally ) resolved extended sources , in which surface brightness , spectral index and position of each component of the sources should be determined by other radio observations or left as free parameters in the sky model . the brightest radio galaxy , 3c061.1 , in the ncp field is a typical example of this kind , and its residuals after deconvolution are very prominent . actually , 3c061.1 is the dominant source of both calibration and deconvolution errors for our imaging towards the ncp region . note that calibration error is also present even if a more sophisticated model for 3c061.1 is adopted for lofar data @xcite . second , the deconvolution should be made over a sky map with the field - of - view much larger than the primary beam so that the leakage of sidelobes from off - field strong radio sources can be corrected for . for the 21cma field , the two brightest radio sources , cas a and cygnus a , are visible on the sky map of @xmath183 ( @xcite ) , and their grating lobes have already entered into the central ncp field at certain frequencies . at present the imaging has not included and corrected the sidelobes from these two sources , although they have already contributed to the deconvolution noise . in summary , it appears that with time integration the thermal noise dominated by the milky way can be well controlled to below the confusion noise in current low - frequency interferometric imaging . however , to beat down the confusion noise , one needs to deal with not only the unresolved , faint radio sources , but also the calibration and deconvolution errors . in particular , calibration errors from both ionospheric effects and bright , extended sources are difficult to handle at present . these errors can propagate to the deconvolution processing and affect the lower threshold of identifying the faint radio sources through @xmath176 . as a result , the conventional confusion limit , which is determined by unresolved sources and synthesized beam , is actually affected by the extension of accuracy and reliability of calibration and deconvolution . in fact , the major source of errors in our current imaging arises from the calibration and deconvolution processing . the former is related to both ionospheric effects and modeling of extended , bright radio sources in the field , and the latter is involved with the removals of grating lobes and sidelobes of strong radio sources , both within and outside of the field . and @xmath13 noise levels , respectively , measured at eight sub - bands over the ncp field . the black dashed line represents the theoretically estimated confusion limit due to the unresolved fainter sources below @xmath176 , for which we have taken @xmath180 . , width=302 ] [ fig : confusion ] we have analyzed 12 hours of data taken from the 21cma observations centered on the ncp . to reduce the complexity of interferometric image processing and the influence of ionospheric perturbation , we have used all 40 pods along the east - west arm but restricted our analysis to within a maximum baseline of 1500 m. we have calibrated the gain and primary beam of our telescope using the bright radio sources in the ncp field . following conventional self - calibration and deconvolution methods , we have detected a total of 624 radio sources over the central field within @xmath57 in frequency range of 75 - 175 mhz and the outer annulus of @xmath54 in the 75 - 125 mhz bands . by performing a monte - carlo simulation we have estimated a completeness of @xmath11 at @xmath184 jy . we have compared our source counts with the deep low - frequency observations made recently with gmrt and mwa , and the completeness - corrected source counts show a good agreement with these recent surveys at the corresponding frequency bands . while we are able to detect the fainter sources down to 10 mjy , the detection fraction has dropped to @xmath31 , making a ultra deep observation rather difficult and even impossible with current imaging algorithms . this is primarily caused by errors in sidelobes , calibration , and deconvolution as well as the confusion limit of the array . spacings between the 21cma pods are the integral multiples of 20 m. the original design of such configuration is for the purpose of redundant calibration and statistical measurement of the eor power spectrum ( e.g. @xcite ) . however , this layout also generates the grating lobes evident in our images ( @xcite ) . these equally spaced rings around the bright sources in the field have their brightness almost comparable to the central sources , and therefore should be accurately removed in the deconvolution processing otherwise , their residuals may be the major sources of contaminations for our imaging . indeed , our image quality is largely limited by the presence of imperfectly subtracted grating lobes of the brightest source in the ncp field , 3c061.1 . although this arises partially from the inaccurate calibration , the main reason is the poor modeling of 3c061.1 in our self - calibration processing . 3c061.1 is marginally resolved with 21cma , and its modeling should take the structured components with different surface brightness and spectral index into account ( e.g. @xcite ) . our next step is to improve our sky model by using a sophisticated model for 3c061.1 and even for very bright , far field sources such as cas a and cygnus a. finally , the theoretically expected thermal noise ( @xmath3 mjy ) is well below the confusion limit due to the unresolved , fainter sources , indicating that the dominated factor of influencing the sensitivity for low - frequency interferometric imaging is no longer the system noise but the cosmic sources in the sky . several methods to improve our imaging algorithm including an accurate calibration ( e.g. sky modeling and redundant calibration ) , application of the w - term correction , and `` peeling '' sources @xcite are currently under investigation , with our ultimate goal towards detecting the eor power spectrum . our experience with the 21cma operation and data analysis may provide a useful guide to the design of next generation low - frequency radio array such as the ska . indeed , employment of numerous redundant baselines helps to improve the precision of calibration . however , it brings about very prominent grating lobes from bright sources both in - beam and in the far - field . this not only requires a more careful and accurate calibration of visibilities but also adds an extra difficulty to deconvolution processing . in particular , the grating lobes of the bright , structured sources like giant radio galaxies with jets are hard to model and thus subtract . in this sense , both random antenna element and station layouts should preferentially be chosen for low - frequency radio interferometers to suppress the grating lobes and sidelobes of bright sources . we note that an extensive study on this topic has recently been carried out by @xcite . to summarize , with current layout of the 21cma and conventional imaging algorithm , we have reached a sensitivity of a few mjy and a dynamical range of @xmath185 . we may have to improve our imaging quality by an order of magnitude in order to see statistically the eor signature . we thank judd bownman for useful discussions and heinz andernach for constructive comments . we gratefully acknowledge the constructive suggestions by an anonymous referee that greatly improved the presentation of this work . technical support was provided by the 21cma collaboration . this work was partially supported by the national science foundation of china under grant no . qz and mj - 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bands across the 21cma bandwidth and provides the in - band spectral indices for the detected sources . to reduce the complexity of interferometric imaging from the so - called `` w '' term and ionospheric effects , the present analysis are restricted to the east - west baselines within 1500 m only . the 624 radio sources are found within 5 degrees around the ncp down to @xmath1 jy . our source counts are compared , and also exhibit a good agreement , with deep low - frequency observations made recently with the gmrt and mwa . in particular , for fainter radio sources below @xmath2 jy , we find a flattening trend of source counts towards lower frequencies . while the thermal noise ( @xmath3 mjy ) is well controlled to below the confusion limit , the dynamical range ( @xmath4 ) and sensitivity of current 21cma imaging is largely limited by calibration and deconvolution errors , especially the grating lobes of very bright sources , such as 3c061.1 , in the ncp field which result from the regular spacings of the 21cma . we note that particular attention should be paid to the extended sources , and their modeling and removals may constitute a large technical challenge for current eor experiments . our analysis may serve as a useful guide to design of next generation low - frequency interferometers like the square kilometre array . </s>

the undergoing microlensing surveys ( ogle , eros , macho ) are currently providing us with an enormous amount of images of dense crowded stellar fields . this contribution of new data stimulated software development . several successful implementations based on the dophot software ( udalski _ et al . _ 1993 bennet _ et al . _ 1992 ) have been used so far to extract the stellar magnitudes from the images . other software , like peida , which has been developed by the eros group ( ansari _ et al . _ 1996 ) has also been used with some success . however , all these packages use the same basic profile fitting method to estimate the magnitudes of the stars present in the image . this kind of method is not optimal in the case of microlensing surveys , as our aim is to detect and measure variations only . purely differential methods , like the image subtraction technique should give better results . the recent release by the ogle collaboration ( wozniak & szymanski 1998 ) of a collection of small images centered on each ogle microlensing candidate , and the corresponding light curves , offers a nice opportunity to test this assumption . we will analyze these images with the method recently developed by alard & lupton ( 1998 ) . this method is designed to give optimal results , and it is well suited for small images , as all the pixels can be used to derived the best kernel solution . we will compare the image subtraction light curves with the light curves obtained by wozniak & szymanski ( 1998 ) using the dophot software ( schechter , mateo , & saha , 1993 ) . we have a few hundred 101x101 images for each ogle candidate . these ogle i images show a mean quality that seems to be well below the quality of the ogle ii images ( udalski _ et al . we remind that a subsample of the ogle ii images has already been already processed with the image subtraction method ( alard & lupton 1998 ) . as it has been already described in alard and lupton ( 1998 ) , we register the images by fitting the positions of the brightest stars . for these small images , we used a polynomial transform of order 1 . each image is then transformed to the astrometric system of a reference image by using a bicubic spline interpolation . this procedure provides us with a collection of images that have the same sampling but different seeings . we found that better results are obtained if we could derive a high quality and almost noise free reference image . we approach this requirement by stacking between 10 and 20 of our best seeing ( interpolated ) images . using this image we also compute a `` masked '' image in which all obvious defects like saturated stars , or bad ccd regions are masked by putting the relevant pixels in the reference frame to zero . the image subtraction program will use this masked image to derive the list of pixels that should not be fitted in order to derive the kernel solution . as it has been already described in alard & lupton ( 1998 ) , the core of the problem is to seek for a convolution kernel that will transform our reference frame to exactly the same seeing as another frame . to find the best kernel solution we have to solve a set of linear least - square equations . we keep the same general kernel decomposition that we already used for the ogle ii data . however , this time we have to modify the code in order to take into account the defects in the reference image . if we did not take this precaution , the convolution with the kernel would spread the defects and pollute the fit . to solve this problem the linear least square matrix is built by convolving the reference image with each of the vectors we use for the kernel decomposition . we do not wish to calculate the convolution at the pixels we have masked . but the problem will occur just at the border of the masked areas . to compute the convolution at a given position we need the values of the pixels all around this position , within some limiting radius . if some area around our position falls within the masked area we can not get any reasonable value for the relevant pixels . but we can find a straightforward solution to this problem by not using these pixels to calculate the convolution , and to compensate just by re - normalizing the filter . we adopt the sum of the filter to be one , and we re - normalize the filter so that its sum over all the pixels we have not discarded is again one . there are however some convolution filters that have a zero sum . we solve this difficulty by splitting the filter into 2 different filters that do not have a zero sum . we processed the frames for all the ogle candidates with this method , and we found that the treatment of the defects was very satisfactory . for some of the subtracted images we get residuals that are consistent with the poisson fluctuations . however for a large number of frames we found some systematic residual patterns which seems to be related to the behavior of some of the ccd columns . it also appeared that the residuals associated with most of the bright stars were very satisfactory , showing that we reached a good kernel solution , but some showed systematics for one of the bright stars ( somewhat in excess of the poisson fluctuation ) . as a consequence of these defects the photon noise limit which we easily reached with ogle ii data ( alard & lupton 1998 ) is not as clearly reached in the case of these ogle i data . the same image subtraction software has also been used for eros data ( afonso _ et al . _ 1998 ) , and as in the case of ogle ii the residuals were in good agreement with the photon noise . in the first paper concerning this image subtraction method , we used an easy and straightforward way to estimate the flux in each subtracted image . our aim was not to produce the best quality light curves , but just to show the consistency with the photon noise . we estimated the total flux by taking all the flux in a large aperture radius . this is of course not optimal . a better way to proceed is to make aperture photometry in a small radius only , and to compute an aperture correction . it is also possible to use a generic profile fitting technique , by assuming that the profile is a bi - dimensional gaussian that we fit for each image . however , some experiments show that the result is not better than with corrected aperture photometry . it is also important to point out that in the case of profile fitting photometry small biases are introduced by the fact that the analytical model for the profile never matches perfectly the real psf . we make a differential correction of this bias by comparing the flux of bright stars calculated by profile fitting in the image to the flux we estimated in the reference image using the same method . the correction factor we derive this way is about a few percent . to improve the photometry we need to derive a very accurate psf model this is not an easy task in very crowded fields . this time we do not derive an analytical model for the psf . actually all we need to know is the psf at the position of the star we want measure , i.e. the variable . we select a few bright stars in the image . around each of these bright stars , we extract sub - images . we also extract a sub - image around the star to measure . we then re - center the bright stars , so that their exact position in their sub - images is the same as the position of the measured star in its sub - image . for this re - centering we use bicubic splines . we emphasize that in order to get an unbiased position for the variable object ( not the position of the nearest star ) , we stack all the subtracted images for which we find a significant signal at the location of the candidate . this way we build a high signal to noise image of the differential variations . we then use this image to estimate the center of the microlensing candidate . we also normalize each bright star sub - image by using a cross - product with a gaussian . we then do a median stacking of all sub - images , in order to get a numerical psf bitmap . we use this psf bitmap to estimate the flux in the relevant subtracted image . of course , as we have already explained , we systematically apply the differential fitting correction , in order to get rid of small discrepancies in our psf model ; although this time the discrepancy is very small . this procedure gives the best results . we found a mean gain of about 20 to 30 % in the accuracy of the photometry in comparison to the corrected aperture photometry . it certainly indicates that most of the psf s have very complicated shapes . in order to make a comparison between the light curves obtained with dophot ( wozniak & szymanski , 1998 ) and the image subtraction method , we fitted theoretical microlensing light curves to both sets of data . in the fitted parameters we include the blending parameter , as blending of these faint sources is likely . to make a comparison as accurate as possible , we selected the data points that were both in the dophot and the image subtraction light curves . some images were defective and they were not in the dophot light curve . in the case of image subtraction almost all the frames were treated . we could not estimate the flux with this method only in some rare cases ( for instance when a saturation spike originating from a bright star came across the star image ) . we had no problem to process very bad seeings with the image subtraction method . to make comparison of dophot versus image subtraction errors , we re - scaled each data set by dividing by the amplitude . we estimate this amplitude as the difference between the base line value and the value of the fitted curve at the location of the data point that shows the maximum magnification . we have also analyzed the consistency of the image subtraction errors with the poisson noise . for this particular task we calculated the chi - square of the distribution , by summing the square of the errors weighted with the poisson ( or photon noise ) deviation . the poisson deviation is estimated by calculating the variance of our magnitude estimator . in this calculation we assume that the poisson distribution is well approximated by a gaussian distribution with @xmath0 ( @xmath1 is the conversion from adu to electrons ) . the results obtained are summarized in table 1 . we see that the mean improvement we get with the image subtraction method is about a factor of 2 in comparison to dophot . it seems we gain even a little bit more if we compare the residuals during the magnification . thus it is clear that a dramatic improvement is performed by using the image subtraction method . additionally , most of the time we get errors that are only 10 % to 40 % in excess of the photon noise expectation . some candidate events have errors considerably larger than the rest , and they introduce some biase in the mean value of the improvement ; we will discuss this issue later . to illustrate the improvement that we get by using the image subtraction method we present 3 different cases . first we present an event with mean improvement , for which the residuals are smaller by a factor of 2 ( ogle # 1 , fig . 1 ) . in the second figure we present the data for a case of a modest improvement ( ogle # 2 ) , the residuals are smaller by only 37 % for the baseline and by 87 % during the magnification . however , looking at the light curve , we see that the improvement is very significant . in particular , there are 2 bad seeing points at the top of the light curve that deviate a lot in the dophot , but have much smaller errors in the image subtraction light curve . this does illustrates very well the ability of the method to deal with large seeing variations . concerning the residuals along the baseline , it is important to note that at least one point has a very large deviation , and it is not consistent with poisson statistics . we must emphasize again that the ccd used during the ogle i project had lot of defects and that might contribute to the errors . to conclude we present the examples of a large improvement ( ogle # 4 ) , and a very large improvement ( ogle # 5 , fig . 3 ) . in the case of ogle # 4 the residuals are reduced by a factor 2.65 during the baseline and 3.4 during the magnification . it is important to note that this result has been obtained despite especially bad image quality for this event , and yet we get a chi - square that is very close to the photon noise expectation . for ogle # 5 , the residuals are reduced by a factor 7.5 during the magnification . this shows than the image subtraction method can lead to very dramatic improvement . this huge improvement can probably be explained by the fact that ogle # 5 is a case of unresolved ( highly blended ) source ( alard 1997 ) . the largest value of the chi - square is for the ogle # 3 event . it is good to note that ogle # 3 is also the brightest of the candidates , and that it might indicate that with the ogle i data we have some trouble in reaching the photon noise limit for bright stars . considering that a typical photometric error is only @xmath2 , any errors in the flat fielding may contribute to the global error budget . it may also be related to the quality of the ccd chip , and in particular to the stability of the psf to the level of 1 % . the analysis of subtracted images shows residuals with different shapes even for the bright stars that are quite close to each other . these differences can not be explained by the seeing variations as the exposure time ( 10 min ) is relatively long . we did not found such problems in our analysis of ogle ii data ( alard & lupton 1998 ) . to conclude the discussion on ogle # 3 it is important to emphasize that even if the image subtraction is a bit far from the photon noise deviation expected from our profile fitting method , it is about 2 times better than dophot . + + there are some faint stars that show large baseline residuals . these are : ogle # 2 , ogle , # 11 , ogle # 12 , ogle # 14 . in the case of ogle # 2 we get a bad chi - square for both baseline and magnification data . the case of ogle # 11 and ogle # 12 is different , since chi - square is bad during the baseline only . finally , ogle # 14 is the most peculiar since it shows a very bad chi - square during the magnification only . + + it was not possible to find any reason for the bad chi - square obtained for ogle # 2 . the residuals do not show any systematics , and no periodic signal could be identified . it appears that ogle # 2 is quite different from the other ogle events , since it lies close to the edge of the ccd . considering the poor quality of this ccd this situation might lead to additional errors , especially in the flat fields . + + the cases of ogle # 11 and ogle # 12 appear to be completely different since we can observe systematic patterns in the residuals ( fig . 4 and 5 . ) . in the case of ogle # 12 , it is clear that a systematic trend of the baseline magnitude is observed . a similar trend is also visible in the dophot light curve , although it is less clear ; it is also less reliable , as the image subtraction is purely differential and free of systematics . for ogle # 11 we also observe a systematic deviation of a clump of points near the date 1200 . it seems to indicate that these 2 candidates have long term variations which resemble the variations observed for the ogle # 10 candidate ( cf . fig . + + the ogle # 14 candidate does not show too much deviations during the baseline , but it presents very significant deviations from the best fit during the magnification . in particular , a group of points near the tip of the descending branch shows large systematic deviations . there is also a point which shows large deviations both , in the image subtraction and dophot light curves . however the image corresponding to this data point does not show any particular defect , and seems to have a general good quality . we conclude that the most likely explanation is that ogle # 14 could be a variable star , possibly a cataclysmic star , since we do not have a point on the rising branch that could discard this type of a variable . another possibility would be that ogle # 14 be a case of lensing by a binary source , or lensing of a binary source . however with the current data set it seems difficult to study this possibility . + + these 4 microlensing candidates are also those which show the smallest improvements with the image subtraction method . this is not surprising , since it seems that in this case there is some additional error or intrinsic variability that the image subtraction ca nt improve . there is another case where the improvement due to image subtraction is rather small , this is the candidate ogle # 9 . however , the dophot light curve and the image subtraction light curve are very different ( see fig . 8) , and we wonder if the dophot and the image subtraction measured exactly the same object . looking at the composite reference image , we see that in the region occupied by ogle # 9 there are many very faint unresolved objects , and that some confusion is likely . sometimes dophot may find 1 or 2 objects , depending on the seeing . + + to conclude this discussion , we present the mean of the residual ratios and the chi - square when the 4 previous ogle candidates are rejected . as it seems that for these 4 candidates additional ( uncontrolled ) errors or variations are present , it is difficult to derive a reliable statistics from them ( see table 1 ) . in these crowded fields blending of the source with fainter stars is likely ( classical blending ) , and this possibility needs to be investigated . however another kind of blending is also possible : the source is very faint , it is unresolved and it is seen only during the magnification ( alard 1997 , han 1997 ) . this kind of microlensing events is likely to give an important contribution to the optical depth , and it is important to try to detect them . the task should be easer than in the case of classical blending , as the blending of the source is very large and it should make a more noticeable modifications of the light curve . to investigate the blending issue we need to get the baseline magnitude of the star associated with the variations . for this particular task , we used the median psf model that we derived previously to fit the magnitude of the star on the reference image . for this psf fitting we used the coordinates that were found for the variable by stacking the subtracted images . to investigate the possibility of blending of the source , a solution without blending parameter , and with blending parameter has been fitted to the image subtraction data , for each of the ogle candidate . to compare the chi - square s to the fit of the unblended and blended model , the f - test was performed , in order to estimate the significance to add a blending parameter to the model . the result is presented in table 2 . it appears immediately that ogle # 5 and ogle # 6 are blended microlensing events . considering the flux ratio of the source to the flux of the resolved source , it is also very likely that these 2 events result from a large magnification of a faint unresolved star . ogle # 5 had already be identified as a lensing of an unresolved star with the previous ogle data ( alard 1997 ) , but the detection of ogle # 6 as a very blended event is new . we emphasize that the confidence of detection the blended nature of ogle # 5 has been greatly improved with the image subtraction method . there is also some weak evidence that ogle # 18 could belong to the same category as ogle # 5 and ogle # 6 . in this paragraph we shall make a comparison with the analysis of astrometric shifts of the ogle microlensing candidates performed by goldberg & wozniak ( 1998 ) . the two very blended events , ogle # 5 and ogle # 6 , both show very large astrometric shifts . it confirms the prediction by han ( 1998 ) and goldberg ( 1998 ) that lensing of very faint highly blended objects should result in the observation of large astrometric shifts . on the other hand , some large astrometric shifts can be detected without any photometric evidence for them if the separation between the components is large and the amplified star is not much fainter than the other blend component . when the separation between the blend components is small and the source is faint compared to the other component , then photometric analysis is a good way to detect blending . this shows that the two techniques are complementary . this re - analysis of the ogle images clearly demonstrates , with overwhelming evidences , the usefulness of the image subtraction method . on the average , we noticed an improvement by a factor of 2 in the photometric accuracy in comparison to dophot . an improvement of @xmath3 was found for the data points taken during the magnification . this makes it possible to refine the interpretation of the ogle microlensing candidates . the case of the strongly blended ogle # 5 is especially important . ogle # 9 is also very interesting , as it shows a light curve that is completely different from the dophot light curve . it is a good illustration of the large biases that might be present in data processed with dophot . however , it was also found that small amplitude long term variations were present in the ogle # 12 and ogle # 11 baseline magnitudes . it is difficult to state if these variations make these 2 candidates inconsistent with microlensing . further investigation should be conducted in order to estimate the likelihood of such variations in similar stars , which either solar type or subgiants . + + the case of ogle # 14 is more problematic since we have very significant evidence that the shape of the light magnification differ from the point - source microlensing . since we have no data point on the rising branch , it is difficult to prove that this candidate is related to cataclysmic variables . it would be valuable to obtain a spectrum of the star in order to search for specific emission lines . + + a refined analysis of the other candidates shows that ogle # 5 and ogle # 6 are highly blended microlensing events . they result from the magnification of very faint sources which would have been undetectable without the microlensing magnification . + + it is important to emphasize that the improvement provided by the image subtraction method should not be considered only in the case of producing individual light curves of some selected objects . this method is well suited for global processing of all the microlensing data . due to the fact that the whole linear least - square matrix has to be built only once for the reference image , the computing time of the method is very reasonable and should compete with dophot . to conclude , we would like to emphasize that the improvement that has been found in the quality of the light curves is not in any sense specific to ogle . this testing has been conducted with ogle data , as ogle has been the first to provide massive release of images . however such similar improvements , have already been noticed for the light curves of 2 microlensing candidates obtained with eros data ( e.g. afonso _ et al . _ , 1998 ) , and it will certainly be seen for other microlensing data - set , as all these projects use dophot or dophot like softwares . it is also important to add that some small photometric effects which were not found with dophot ( see ogle # 12 for instance ) , will probably be seen as well when large data - sets from the other microlensing experiments will be analyzed with the image subtraction method . + + the light curves of all ogle microlensing events can be accessed with anonymous ftp at : ftp.iap.fr , directory : pub / from_users / alard / ogle . llllllll candidate & d / s ( b ) & d / s ( a ) & chi2 ( b ) & chi2 ( a ) & mag & % ( b ) & % ( a ) + ogle # 1 & 2.17 & 2.38 & 1.15 & 1.09 & 18.7 & 2.7 & 1.9 + ogle # 2 & 1.37 & 1.87 & 1.55 & 2.03 & 19.1 & 4.9 & 4.1 + ogle # 3 & 2.58 & 1.82 & 1.62 & 2.17 & 15.9 & 0.4 & 0.5 + ogle # 4 & 2.65 & 3.39 & 1.15 & 1.08 & 19.2 & 2.2 & 2.3 + ogle # 5 & 2.71 & 7.57 & 1.33 & 1.89 & 18.0 & 1.1 & 1.1 + ogle # 6 & 13.3 & 19.1 & 1.56 & 1.57 & 18.1 & 2.1 & 2.4 + ogle # 8 & 1.73 & 1.34 & 1.29 & 1.37 & 17.8 & 1.1 & 1.1 + ogle # 9 & 1.48 & 1.47 & 1.32 & 0.99 & 19.2 & 4.8 & 3.1 + ogle # 11 & 1.09 & 1.45 & 1.60 & 1.47 & 18.1 & 2.4 & 1.9 + ogle # 12 & 1.21 & 1.52 & 1.92 & 1.29 & 18.6 & 4.1 & 2.5 + ogle # 14 & 1.76 & 1.46 & 1.40 & 3.11 & 19.0 & 2.9 & 4.4 + ogle # 15 & 2.93 & 3.17 & 1.23 & 1.69 & 18.3 & 3.4 & 2.8 + ogle # 16 & 1.71 & 1.36 & 1.19 & 1.46 & 18.4 & 1.0 & 1.0 + ogle # 17 & 1.74 & 1.92 & 1.26 & 1.55 & 18.7 & 3.0 & 2.2 + ogle # 18 & 1.61 & 2.14 & 1.40 & 1.37 & 18.6 & 2.5 & 1.8 + ogle # 19 & 1.72 & 2.99 & 1.48 & 0.92 & 19.7 & 4.9 & 2.7 + mean & 1.96 & 2.5 & 1.4 & 1.56 & 18.5 & 2.7 & 2.2 + mean * & 2.15 & 2.84 & 1.35 & 1.51 & 18.4 & 2.4 & 1.9 + llll candidate & probability & blending ratio & mag ( i band ) + ogle # 1 & 0.530 & 1.7 & 21.9 + ogle # 2 & 0.511 & 1.3 & 19.5 + ogle # 3 & 0.500 & 1.0 & 15.9 + ogle # 4 & 0.568 & 1.7 & 19.9 + ogle # 5 & 1.000 & 49.9 & 22.3 + ogle # 6 & 0.994 & 16.6 & 21.2 + ogle # 8 & 0.509 & 1.3 & 18.2 + ogle # 9 & 0.500 & 1.0 & 19.2 + ogle # 11 & 0.500 & 1.5 & 18.6 + ogle # 12 & 0.506 & 2.1 & 19.5 + ogle # 14 & 0.500 & 1.0 & 19.0 + ogle # 15 & 0.500 & 1.0 & 18.3 + ogle # 16 & 0.526 & 5.5 & 20.3 + ogle # 17 & 0.500 & 1.0 & 18.7 + ogle # 18 & 0.779 & 16.6 & 21.7 + ogle # 19 & 0.534 & 2.7 & 20.9 + the author would like to thank all the ogle team for public release of the image data - set . without this unique opportunity , accurate testing of the new image subtraction method , and comparison with previous method would have been impossible . the author is especially indebted to b. paczyski for his kind help and comments . it is a pleasure to thank a. udalski , p. wozniak , e. aubourg , and d. goldberg for their comments . afonso , _ et al . _ , 1998 , a&a , in press ( astro - ph/9806380 ) alard , c. , & lupton , r.h . , 1998 , apj in press ( astro - ph/9712287 ) alard , c. , 1997 , a&a , 326 , p. 1 ansari , r. , 1996 , vistas in astronomy , v. 40 , p. 519 - 53 bennett , d. , 1992 , texas / pasco , international conference , berkeley , ca , 13 - 18 dec . 1992 goldberg , d. m. , 1998 , apj , 498 , 156 goldberg , d. m. , & wozniak , p. , 1997 , aca , 48 , p. 19 ( astro - ph/9712262 ) han , c. , 1997 , apj , 490 , p.51 han , c. , 1998 , astro - ph/9804272 schechter , p. , mateo , m. , & saha , a. , 1993 , pasp , 105 , p. 1342 udalski , a. , kubiak , m. , & szymanski , m. , 1997 , aca , 47 , p. 319 ( astro - ph/9710091 ) udalski , a. , 1993 , _ _ aca , 43 , p. 69 wozniak , p. , & szymanski , m. , 1998 , astro - ph/9804193

the light curves of the ogle microlensing candidates have been reconstructed using the image subtraction method . a large improvement of the photometric accuracy has been found in comparison with previous processing of the data with dophot . on the mean , the residuals to the fit of a microlensing light curve are improved by a factor of 2 for baseline data points , and by a factor of 2.5 during magnification . the largest improvement was found for the ogle # 5 event , where we get an accuracy 7.5 times better than with dophot . despite some defects in the old ccd used during the ogle i experiment we obtain most of the time errors that are only 30 % to 40 % in excess of the photon noise . previous experiment showed that with modern ccd chips ( ogle ii ) , residuals much closer to the photon noise were obtained . the better photometric quality enabled us to find a low amplitude , long term variability in the ogle # 12 and ogle # 11 baseline magnitude . we also found that the shape of the ogle # 14 candidate light curve is fairly inconsistent with microlensing of a point source by a point lens . a dramatic change in the light curve of the ogle # 9 candidate was also found , which indicates that very large biases can be present in data processed with dophot . to conclude we made a detailed analysis of the blending issue . it is found that ogle # 5 and ogle # 6 are very likely highly blended microlensing events . these events result from the magnification of a faint star that would have been undetectable without microlensing .

<s>[INST]the undergoing microlensing surveys ( ogle , eros , macho ) are currently providing us with an enormous amount of images of dense crowded stellar fields . this contribution of new data stimulated software development . several successful implementations based on the dophot software ( udalski _ et al . _ 1993 bennet _ et al . _ 1992 ) have been used so far to extract the stellar magnitudes from the images . other software , like peida , which has been developed by the eros group ( ansari _ et al . _ 1996 ) has also been used with some success . however , all these packages use the same basic profile fitting method to estimate the magnitudes of the stars present in the image . this kind of method is not optimal in the case of microlensing surveys , as our aim is to detect and measure variations only . purely differential methods , like the image subtraction technique should give better results . the recent release by the ogle collaboration ( wozniak & szymanski 1998 ) of a collection of small images centered on each ogle microlensing candidate , and the corresponding light curves , offers a nice opportunity to test this assumption . we will analyze these images with the method recently developed by alard & lupton ( 1998 ) . this method is designed to give optimal results , and it is well suited for small images , as all the pixels can be used to derived the best kernel solution . we will compare the image subtraction light curves with the light curves obtained by wozniak & szymanski ( 1998 ) using the dophot software ( schechter , mateo , & saha , 1993 ) . we have a few hundred 101x101 images for each ogle candidate . these ogle i images show a mean quality that seems to be well below the quality of the ogle ii images ( udalski _ et al . we remind that a subsample of the ogle ii images has already been already processed with the image subtraction method ( alard & lupton 1998 ) . as it has been already described in alard and lupton ( 1998 ) , we register the images by fitting the positions of the brightest stars . for these small images , we used a polynomial transform of order 1 . each image is then transformed to the astrometric system of a reference image by using a bicubic spline interpolation . this procedure provides us with a collection of images that have the same sampling but different seeings . we found that better results are obtained if we could derive a high quality and almost noise free reference image . we approach this requirement by stacking between 10 and 20 of our best seeing ( interpolated ) images . using this image we also compute a `` masked '' image in which all obvious defects like saturated stars , or bad ccd regions are masked by putting the relevant pixels in the reference frame to zero . the image subtraction program will use this masked image to derive the list of pixels that should not be fitted in order to derive the kernel solution . as it has been already described in alard & lupton ( 1998 ) , the core of the problem is to seek for a convolution kernel that will transform our reference frame to exactly the same seeing as another frame . to find the best kernel solution we have to solve a set of linear least - square equations . we keep the same general kernel decomposition that we already used for the ogle ii data . however , this time we have to modify the code in order to take into account the defects in the reference image . if we did not take this precaution , the convolution with the kernel would spread the defects and pollute the fit . to solve this problem the linear least square matrix is built by convolving the reference image with each of the vectors we use for the kernel decomposition . we do not wish to calculate the convolution at the pixels we have masked . but the problem will occur just at the border of the masked areas . to compute the convolution at a given position we need the values of the pixels all around this position , within some limiting radius . if some area around our position falls within the masked area we can not get any reasonable value for the relevant pixels . but we can find a straightforward solution to this problem by not using these pixels to calculate the convolution , and to compensate just by re - normalizing the filter . we adopt the sum of the filter to be one , and we re - normalize the filter so that its sum over all the pixels we have not discarded is again one . there are however some convolution filters that have a zero sum . we solve this difficulty by splitting the filter into 2 different filters that do not have a zero sum . we processed the frames for all the ogle candidates with this method , and we found that the treatment of the defects was very satisfactory . for some of the subtracted images we get residuals that are consistent with the poisson fluctuations . however for a large number of frames we found some systematic residual patterns which seems to be related to the behavior of some of the ccd columns . it also appeared that the residuals associated with most of the bright stars were very satisfactory , showing that we reached a good kernel solution , but some showed systematics for one of the bright stars ( somewhat in excess of the poisson fluctuation ) . as a consequence of these defects the photon noise limit which we easily reached with ogle ii data ( alard & lupton 1998 ) is not as clearly reached in the case of these ogle i data . the same image subtraction software has also been used for eros data ( afonso _ et al . _ 1998 ) , and as in the case of ogle ii the residuals were in good agreement with the photon noise . in the first paper concerning this image subtraction method , we used an easy and straightforward way to estimate the flux in each subtracted image . our aim was not to produce the best quality light curves , but just to show the consistency with the photon noise . we estimated the total flux by taking all the flux in a large aperture radius . this is of course not optimal . a better way to proceed is to make aperture photometry in a small radius only , and to compute an aperture correction . it is also possible to use a generic profile fitting technique , by assuming that the profile is a bi - dimensional gaussian that we fit for each image . however , some experiments show that the result is not better than with corrected aperture photometry . it is also important to point out that in the case of profile fitting photometry small biases are introduced by the fact that the analytical model for the profile never matches perfectly the real psf . we make a differential correction of this bias by comparing the flux of bright stars calculated by profile fitting in the image to the flux we estimated in the reference image using the same method . the correction factor we derive this way is about a few percent . to improve the photometry we need to derive a very accurate psf model this is not an easy task in very crowded fields . this time we do not derive an analytical model for the psf . actually all we need to know is the psf at the position of the star we want measure , i.e. the variable . we select a few bright stars in the image . around each of these bright stars , we extract sub - images . we also extract a sub - image around the star to measure . we then re - center the bright stars , so that their exact position in their sub - images is the same as the position of the measured star in its sub - image . for this re - centering we use bicubic splines . we emphasize that in order to get an unbiased position for the variable object ( not the position of the nearest star ) , we stack all the subtracted images for which we find a significant signal at the location of the candidate . this way we build a high signal to noise image of the differential variations . we then use this image to estimate the center of the microlensing candidate . we also normalize each bright star sub - image by using a cross - product with a gaussian . we then do a median stacking of all sub - images , in order to get a numerical psf bitmap . we use this psf bitmap to estimate the flux in the relevant subtracted image . of course , as we have already explained , we systematically apply the differential fitting correction , in order to get rid of small discrepancies in our psf model ; although this time the discrepancy is very small . this procedure gives the best results . we found a mean gain of about 20 to 30 % in the accuracy of the photometry in comparison to the corrected aperture photometry . it certainly indicates that most of the psf s have very complicated shapes . in order to make a comparison between the light curves obtained with dophot ( wozniak & szymanski , 1998 ) and the image subtraction method , we fitted theoretical microlensing light curves to both sets of data . in the fitted parameters we include the blending parameter , as blending of these faint sources is likely . to make a comparison as accurate as possible , we selected the data points that were both in the dophot and the image subtraction light curves . some images were defective and they were not in the dophot light curve . in the case of image subtraction almost all the frames were treated . we could not estimate the flux with this method only in some rare cases ( for instance when a saturation spike originating from a bright star came across the star image ) . we had no problem to process very bad seeings with the image subtraction method . to make comparison of dophot versus image subtraction errors , we re - scaled each data set by dividing by the amplitude . we estimate this amplitude as the difference between the base line value and the value of the fitted curve at the location of the data point that shows the maximum magnification . we have also analyzed the consistency of the image subtraction errors with the poisson noise . for this particular task we calculated the chi - square of the distribution , by summing the square of the errors weighted with the poisson ( or photon noise ) deviation . the poisson deviation is estimated by calculating the variance of our magnitude estimator . in this calculation we assume that the poisson distribution is well approximated by a gaussian distribution with @xmath0 ( @xmath1 is the conversion from adu to electrons ) . the results obtained are summarized in table 1 . we see that the mean improvement we get with the image subtraction method is about a factor of 2 in comparison to dophot . it seems we gain even a little bit more if we compare the residuals during the magnification . thus it is clear that a dramatic improvement is performed by using the image subtraction method . additionally , most of the time we get errors that are only 10 % to 40 % in excess of the photon noise expectation . some candidate events have errors considerably larger than the rest , and they introduce some biase in the mean value of the improvement ; we will discuss this issue later . to illustrate the improvement that we get by using the image subtraction method we present 3 different cases . first we present an event with mean improvement , for which the residuals are smaller by a factor of 2 ( ogle # 1 , fig . 1 ) . in the second figure we present the data for a case of a modest improvement ( ogle # 2 ) , the residuals are smaller by only 37 % for the baseline and by 87 % during the magnification . however , looking at the light curve , we see that the improvement is very significant . in particular , there are 2 bad seeing points at the top of the light curve that deviate a lot in the dophot , but have much smaller errors in the image subtraction light curve . this does illustrates very well the ability of the method to deal with large seeing variations . concerning the residuals along the baseline , it is important to note that at least one point has a very large deviation , and it is not consistent with poisson statistics . we must emphasize again that the ccd used during the ogle i project had lot of defects and that might contribute to the errors . to conclude we present the examples of a large improvement ( ogle # 4 ) , and a very large improvement ( ogle # 5 , fig . 3 ) . in the case of ogle # 4 the residuals are reduced by a factor 2.65 during the baseline and 3.4 during the magnification . it is important to note that this result has been obtained despite especially bad image quality for this event , and yet we get a chi - square that is very close to the photon noise expectation . for ogle # 5 , the residuals are reduced by a factor 7.5 during the magnification . this shows than the image subtraction method can lead to very dramatic improvement . this huge improvement can probably be explained by the fact that ogle # 5 is a case of unresolved ( highly blended ) source ( alard 1997 ) . the largest value of the chi - square is for the ogle # 3 event . it is good to note that ogle # 3 is also the brightest of the candidates , and that it might indicate that with the ogle i data we have some trouble in reaching the photon noise limit for bright stars . considering that a typical photometric error is only @xmath2 , any errors in the flat fielding may contribute to the global error budget . it may also be related to the quality of the ccd chip , and in particular to the stability of the psf to the level of 1 % . the analysis of subtracted images shows residuals with different shapes even for the bright stars that are quite close to each other . these differences can not be explained by the seeing variations as the exposure time ( 10 min ) is relatively long . we did not found such problems in our analysis of ogle ii data ( alard & lupton 1998 ) . to conclude the discussion on ogle # 3 it is important to emphasize that even if the image subtraction is a bit far from the photon noise deviation expected from our profile fitting method , it is about 2 times better than dophot . + + there are some faint stars that show large baseline residuals . these are : ogle # 2 , ogle , # 11 , ogle # 12 , ogle # 14 . in the case of ogle # 2 we get a bad chi - square for both baseline and magnification data . the case of ogle # 11 and ogle # 12 is different , since chi - square is bad during the baseline only . finally , ogle # 14 is the most peculiar since it shows a very bad chi - square during the magnification only . + + it was not possible to find any reason for the bad chi - square obtained for ogle # 2 . the residuals do not show any systematics , and no periodic signal could be identified . it appears that ogle # 2 is quite different from the other ogle events , since it lies close to the edge of the ccd . considering the poor quality of this ccd this situation might lead to additional errors , especially in the flat fields . + + the cases of ogle # 11 and ogle # 12 appear to be completely different since we can observe systematic patterns in the residuals ( fig . 4 and 5 . ) . in the case of ogle # 12 , it is clear that a systematic trend of the baseline magnitude is observed . a similar trend is also visible in the dophot light curve , although it is less clear ; it is also less reliable , as the image subtraction is purely differential and free of systematics . for ogle # 11 we also observe a systematic deviation of a clump of points near the date 1200 . it seems to indicate that these 2 candidates have long term variations which resemble the variations observed for the ogle # 10 candidate ( cf . fig . + + the ogle # 14 candidate does not show too much deviations during the baseline , but it presents very significant deviations from the best fit during the magnification . in particular , a group of points near the tip of the descending branch shows large systematic deviations . there is also a point which shows large deviations both , in the image subtraction and dophot light curves . however the image corresponding to this data point does not show any particular defect , and seems to have a general good quality . we conclude that the most likely explanation is that ogle # 14 could be a variable star , possibly a cataclysmic star , since we do not have a point on the rising branch that could discard this type of a variable . another possibility would be that ogle # 14 be a case of lensing by a binary source , or lensing of a binary source . however with the current data set it seems difficult to study this possibility . + + these 4 microlensing candidates are also those which show the smallest improvements with the image subtraction method . this is not surprising , since it seems that in this case there is some additional error or intrinsic variability that the image subtraction ca nt improve . there is another case where the improvement due to image subtraction is rather small , this is the candidate ogle # 9 . however , the dophot light curve and the image subtraction light curve are very different ( see fig . 8) , and we wonder if the dophot and the image subtraction measured exactly the same object . looking at the composite reference image , we see that in the region occupied by ogle # 9 there are many very faint unresolved objects , and that some confusion is likely . sometimes dophot may find 1 or 2 objects , depending on the seeing . + + to conclude this discussion , we present the mean of the residual ratios and the chi - square when the 4 previous ogle candidates are rejected . as it seems that for these 4 candidates additional ( uncontrolled ) errors or variations are present , it is difficult to derive a reliable statistics from them ( see table 1 ) . in these crowded fields blending of the source with fainter stars is likely ( classical blending ) , and this possibility needs to be investigated . however another kind of blending is also possible : the source is very faint , it is unresolved and it is seen only during the magnification ( alard 1997 , han 1997 ) . this kind of microlensing events is likely to give an important contribution to the optical depth , and it is important to try to detect them . the task should be easer than in the case of classical blending , as the blending of the source is very large and it should make a more noticeable modifications of the light curve . to investigate the blending issue we need to get the baseline magnitude of the star associated with the variations . for this particular task , we used the median psf model that we derived previously to fit the magnitude of the star on the reference image . for this psf fitting we used the coordinates that were found for the variable by stacking the subtracted images . to investigate the possibility of blending of the source , a solution without blending parameter , and with blending parameter has been fitted to the image subtraction data , for each of the ogle candidate . to compare the chi - square s to the fit of the unblended and blended model , the f - test was performed , in order to estimate the significance to add a blending parameter to the model . the result is presented in table 2 . it appears immediately that ogle # 5 and ogle # 6 are blended microlensing events . considering the flux ratio of the source to the flux of the resolved source , it is also very likely that these 2 events result from a large magnification of a faint unresolved star . ogle # 5 had already be identified as a lensing of an unresolved star with the previous ogle data ( alard 1997 ) , but the detection of ogle # 6 as a very blended event is new . we emphasize that the confidence of detection the blended nature of ogle # 5 has been greatly improved with the image subtraction method . there is also some weak evidence that ogle # 18 could belong to the same category as ogle # 5 and ogle # 6 . in this paragraph we shall make a comparison with the analysis of astrometric shifts of the ogle microlensing candidates performed by goldberg & wozniak ( 1998 ) . the two very blended events , ogle # 5 and ogle # 6 , both show very large astrometric shifts . it confirms the prediction by han ( 1998 ) and goldberg ( 1998 ) that lensing of very faint highly blended objects should result in the observation of large astrometric shifts . on the other hand , some large astrometric shifts can be detected without any photometric evidence for them if the separation between the components is large and the amplified star is not much fainter than the other blend component . when the separation between the blend components is small and the source is faint compared to the other component , then photometric analysis is a good way to detect blending . this shows that the two techniques are complementary . this re - analysis of the ogle images clearly demonstrates , with overwhelming evidences , the usefulness of the image subtraction method . on the average , we noticed an improvement by a factor of 2 in the photometric accuracy in comparison to dophot . an improvement of @xmath3 was found for the data points taken during the magnification . this makes it possible to refine the interpretation of the ogle microlensing candidates . the case of the strongly blended ogle # 5 is especially important . ogle # 9 is also very interesting , as it shows a light curve that is completely different from the dophot light curve . it is a good illustration of the large biases that might be present in data processed with dophot . however , it was also found that small amplitude long term variations were present in the ogle # 12 and ogle # 11 baseline magnitudes . it is difficult to state if these variations make these 2 candidates inconsistent with microlensing . further investigation should be conducted in order to estimate the likelihood of such variations in similar stars , which either solar type or subgiants . + + the case of ogle # 14 is more problematic since we have very significant evidence that the shape of the light magnification differ from the point - source microlensing . since we have no data point on the rising branch , it is difficult to prove that this candidate is related to cataclysmic variables . it would be valuable to obtain a spectrum of the star in order to search for specific emission lines . + + a refined analysis of the other candidates shows that ogle # 5 and ogle # 6 are highly blended microlensing events . they result from the magnification of very faint sources which would have been undetectable without the microlensing magnification . + + it is important to emphasize that the improvement provided by the image subtraction method should not be considered only in the case of producing individual light curves of some selected objects . this method is well suited for global processing of all the microlensing data . due to the fact that the whole linear least - square matrix has to be built only once for the reference image , the computing time of the method is very reasonable and should compete with dophot . to conclude , we would like to emphasize that the improvement that has been found in the quality of the light curves is not in any sense specific to ogle . this testing has been conducted with ogle data , as ogle has been the first to provide massive release of images . however such similar improvements , have already been noticed for the light curves of 2 microlensing candidates obtained with eros data ( e.g. afonso _ et al . _ , 1998 ) , and it will certainly be seen for other microlensing data - set , as all these projects use dophot or dophot like softwares . it is also important to add that some small photometric effects which were not found with dophot ( see ogle # 12 for instance ) , will probably be seen as well when large data - sets from the other microlensing experiments will be analyzed with the image subtraction method . + + the light curves of all ogle microlensing events can be accessed with anonymous ftp at : ftp.iap.fr , directory : pub / from_users / alard / ogle . llllllll candidate & d / s ( b ) & d / s ( a ) & chi2 ( b ) & chi2 ( a ) & mag & % ( b ) & % ( a ) + ogle # 1 & 2.17 & 2.38 & 1.15 & 1.09 & 18.7 & 2.7 & 1.9 + ogle # 2 & 1.37 & 1.87 & 1.55 & 2.03 & 19.1 & 4.9 & 4.1 + ogle # 3 & 2.58 & 1.82 & 1.62 & 2.17 & 15.9 & 0.4 & 0.5 + ogle # 4 & 2.65 & 3.39 & 1.15 & 1.08 & 19.2 & 2.2 & 2.3 + ogle # 5 & 2.71 & 7.57 & 1.33 & 1.89 & 18.0 & 1.1 & 1.1 + ogle # 6 & 13.3 & 19.1 & 1.56 & 1.57 & 18.1 & 2.1 & 2.4 + ogle # 8 & 1.73 & 1.34 & 1.29 & 1.37 & 17.8 & 1.1 & 1.1 + ogle # 9 & 1.48 & 1.47 & 1.32 & 0.99 & 19.2 & 4.8 & 3.1 + ogle # 11 & 1.09 & 1.45 & 1.60 & 1.47 & 18.1 & 2.4 & 1.9 + ogle # 12 & 1.21 & 1.52 & 1.92 & 1.29 & 18.6 & 4.1 & 2.5 + ogle # 14 & 1.76 & 1.46 & 1.40 & 3.11 & 19.0 & 2.9 & 4.4 + ogle # 15 & 2.93 & 3.17 & 1.23 & 1.69 & 18.3 & 3.4 & 2.8 + ogle # 16 & 1.71 & 1.36 & 1.19 & 1.46 & 18.4 & 1.0 & 1.0 + ogle # 17 & 1.74 & 1.92 & 1.26 & 1.55 & 18.7 & 3.0 & 2.2 + ogle # 18 & 1.61 & 2.14 & 1.40 & 1.37 & 18.6 & 2.5 & 1.8 + ogle # 19 & 1.72 & 2.99 & 1.48 & 0.92 & 19.7 & 4.9 & 2.7 + mean & 1.96 & 2.5 & 1.4 & 1.56 & 18.5 & 2.7 & 2.2 + mean * & 2.15 & 2.84 & 1.35 & 1.51 & 18.4 & 2.4 & 1.9 + llll candidate & probability & blending ratio & mag ( i band ) + ogle # 1 & 0.530 & 1.7 & 21.9 + ogle # 2 & 0.511 & 1.3 & 19.5 + ogle # 3 & 0.500 & 1.0 & 15.9 + ogle # 4 & 0.568 & 1.7 & 19.9 + ogle # 5 & 1.000 & 49.9 & 22.3 + ogle # 6 & 0.994 & 16.6 & 21.2 + ogle # 8 & 0.509 & 1.3 & 18.2 + ogle # 9 & 0.500 & 1.0 & 19.2 + ogle # 11 & 0.500 & 1.5 & 18.6 + ogle # 12 & 0.506 & 2.1 & 19.5 + ogle # 14 & 0.500 & 1.0 & 19.0 + ogle # 15 & 0.500 & 1.0 & 18.3 + ogle # 16 & 0.526 & 5.5 & 20.3 + ogle # 17 & 0.500 & 1.0 & 18.7 + ogle # 18 & 0.779 & 16.6 & 21.7 + ogle # 19 & 0.534 & 2.7 & 20.9 + the author would like to thank all the ogle team for public release of the image data - set . without this unique opportunity , accurate testing of the new image subtraction method , and comparison with previous method would have been impossible . the author is especially indebted to b. paczyski for his kind help and comments . it is a pleasure to thank a. udalski , p. wozniak , e. aubourg , and d. goldberg for their comments . afonso , _ et al . _ , 1998 , a&a , in press ( astro - ph/9806380 ) alard , c. , & lupton , r.h . , 1998 , apj in press ( astro - ph/9712287 ) alard , c. , 1997 , a&a , 326 , p. 1 ansari , r. , 1996 , vistas in astronomy , v. 40 , p. 519 - 53 bennett , d. , 1992 , texas / pasco , international conference , berkeley , ca , 13 - 18 dec . 1992 goldberg , d. m. , 1998 , apj , 498 , 156 goldberg , d. m. , & wozniak , p. , 1997 , aca , 48 , p. 19 ( astro - ph/9712262 ) han , c. , 1997 , apj , 490 , p.51 han , c. , 1998 , astro - ph/9804272 schechter , p. , mateo , m. , & saha , a. , 1993 , pasp , 105 , p. 1342 udalski , a. , kubiak , m. , & szymanski , m. , 1997 , aca , 47 , p. 319 ( astro - ph/9710091 ) udalski , a. , 1993 , _ _ aca , 43 , p. 69 wozniak , p. , & szymanski , m. , 1998 , astro - ph/9804193[/INST] the light curves of the ogle microlensing candidates have been reconstructed using the image subtraction method . a large improvement of the photometric accuracy has been found in comparison with previous processing of the data with dophot . on the mean , the residuals to the fit of a microlensing light curve are improved by a factor of 2 for baseline data points , and by a factor of 2.5 during magnification . the largest improvement was found for the ogle # 5 event , where we get an accuracy 7.5 times better than with dophot . despite some defects in the old ccd used during the ogle i experiment we obtain most of the time errors that are only 30 % to 40 % in excess of the photon noise . previous experiment showed that with modern ccd chips ( ogle ii ) , residuals much closer to the photon noise were obtained . the better photometric quality enabled us to find a low amplitude , long term variability in the ogle # 12 and ogle # 11 baseline magnitude . we also found that the shape of the ogle # 14 candidate light curve is fairly inconsistent with microlensing of a point source by a point lens . a dramatic change in the light curve of the ogle # 9 candidate was also found , which indicates that very large biases can be present in data processed with dophot . to conclude we made a detailed analysis of the blending issue . it is found that ogle # 5 and ogle # 6 are very likely highly blended microlensing events . these events result from the magnification of a faint star that would have been undetectable without microlensing . </s>

Harvard Medical School is cited for mistreatment of lab animals In less than two years, four monkeys have died in labs at Harvard Medical School, including one that was left in a cage as the cage went through a mechanical washer. The most recent death occurred this spring, when a cotton-top tamarin monkey died of thirst for lack of a water bottle. In addition, 41 deer mice died in April at a Harvard facility after their water source was cut off. The Department of Agriculture has given the medical school an official warning for violating the U.S. Animal Welfare Act. “When you see multiple incidents at the same facility over a period of time, that’s when you realize that this is indicative of a system-wide problem,” said Michael Budkie, executive director of Stop Animal Exploitation Now! Harvard University made the nonprofit group’s top-10 list of animal-welfare violators for the first half of 2012, along with Harvard Medical School. The two institutions have separate licenses from the USDA to use animals for research and testing. The Animal Welfare Act, enforced by the USDA’s Animal and Plant Health Inspection Service, or APHIS, requires labs to handle research animals as carefully as possible to prevent trauma, overheating, physical harm, behavioral stress or unnecessary discomfort. APHIS also is investigating the death of five monkeys at the Harvard-affiliated New England Primate Research Center, said USDA spokesman David Sacks. The center’s interim director, Frederick Wang, stepped down in March after the death of the tamarin monkey. In March, Harvard Medical School Dean Jeffrey S. Flier ordered an independent review panel to evaluate the management and care of animals used in experiments. The panel’s recommendations included the appointment of a veterinarian and biosafety officer to oversee the primate center and the development of “new approaches” to its oversight process. ||||| Harvard Medical School logged its latest lab-monkey death this past spring when a cotton-top tamarin monkey died of thirst for lack of a water bottle. Then 41 deer mice died in April at a Harvard facility after their water source got cut off. As with the monkey, the U.S. Department of Agriculture gave the country’s oldest institution of higher learning an official warning. In less than two years, four monkeys have died in Harvard labs, including one left in a cage as it went through a mechanical washer. “When you see multiple incidents at the same facility over a period of time, that’s when you realize that this is indicative of a system-wide problem,” said Michael Budkie, executive director of the nonprofit Stop Animal Exploitation Now!, in a phone interview. The Milford, Ohio-based SAEN has placed Harvard on its top- 10 list of animal-welfare violators for the first half of 2012. The existence of enough violators to glean a top 10 helps indicate the scope of lab-animal abuse nationally. The Animal Welfare Act, enforced by the USDA’s Animal and Plant Health Inspection Service, requires labs to handle research animals as “carefully” as possible to prevent “trauma,” overheating, physical harm, “behavioral stress or unnecessary discomfort.” Two Gerbils TRS Labs Inc., based in Athens, Georgia, ranked first on SAEN’s list with 23 violations affecting about 70 animals, Budkie said. TRS was cited for housing cats in a room that was 88 to 89 degrees. It also failed to separate two gerbils that had been fighting in a cage and to protect dogs from suffering injuries, according to a USDA report. Several calls to TRS executives seeking comment weren’t returned. Santa Cruz Biotechnology Inc. in California, which researches antibodies and animal health-care products, ranked second on the SAEN list with 11 citations affecting 85 animals. In April, an Aphis inspector found a goat with a broken leg whose cast had come off, according to the USDA report. The attending veterinarian said she didn’t have “time to attend to the goat” because of her work load. “This facility was basically understaffed and it couldn’t offer good care,” Budkie said. Santa Cruz Biotechnology officials didn’t respond to a request for comment. Along with vigilance and public exposure, animal-welfare activists are trying to end the use of animals in research projects. Flying Monkeys Last month, the Washington-based People for the Ethical Treatment of Animals persuaded Air China Ltd. (601111) to join Delta Air Lines Inc. and American Airlines Inc. in agreeing to end shipments of monkeys into the U.S. “If you stop the pipeline into the U.S., that will curtail the number of monkeys used for research,” said Justin Goodman, associate director of PETA’s laboratory investigations department. Harvard University ranks third on SAEN’s list, followed by Harvard Medical School at No. 4. The two institutions have separate licenses from the USDA to use animals for research and testing. Aphis also is investigating the death of five monkeys at the Harvard-affiliated New England Primate Research Center, said USDA spokesman David Sacks. The center’s interim director, Frederick Wang, stepped down in March after the death of the tamarin monkey. Too Big “Harvard thinks it’s too big to fail, and it thinks all it has to do is provide information, and they’ll just get a tap on the wrist,” said John Pippin, director of academic affairs for the Washington-based Physicians Committee for Responsible Medicine. “There is no such thing as humane animal research.” In March, Harvard Medical School Dean Jeffrey S. Flier ordered an independent review panel to evaluate the management and care of animals used in experiments. The panel’s recommendations included the appointment of a veterinarian and biosafety officer to oversee the primate center and the development of “new approaches” to its oversight process. “We will be unwavering in our efforts to ensure that our administrative and managerial practices are on par with our scientific standards of excellence,” Flier said in a statement issued this month. Other labs on SAEN’s list include Tuskegee University in Alabama in fifth place with 13 citations, followed by the University of Texas Medical Branch at Galveston; the Harvard- affiliated Massachusetts Eye and Ear Infirmary; Indiana University School of Medicine; University of Puerto Rico; and Methodist Research Institute in Indiana. Muse highlights include Rich Jaroslovsky on technology and Lance Esplund on art. To contact the writer on this story: Patrick Cole in New York at [email protected]. To contact the editor responsible for this story: Manuela Hoelterhoff in New York at [email protected].

– The USDA has issued an official citation against the Harvard Medical School for repeated incidents of cruelty to its lab animals. Four of the school's monkeys have died in less than two years, including one that was still in its cage when it was put through a mechanical washer, Bloomberg reports. Another died of thirst, as did 41 deer mice who had their water supply cut off in April. "When you see multiple incidents at the same facility over a period of time, that's when you realize that this is indicative of a system-wide problem," says one animal rights activist with Stop Animal Exploitation Now. Harvard University recently landed at No. 3 on SAEN's top 10 animal welfare violators list, with its medical school occupying the No. 4 slot. Topping the list: TRS Labs in Athens, Georgia, which received 23 citations affecting around 70 animals.

<s>[INST]Harvard Medical School is cited for mistreatment of lab animals In less than two years, four monkeys have died in labs at Harvard Medical School, including one that was left in a cage as the cage went through a mechanical washer. The most recent death occurred this spring, when a cotton-top tamarin monkey died of thirst for lack of a water bottle. In addition, 41 deer mice died in April at a Harvard facility after their water source was cut off. The Department of Agriculture has given the medical school an official warning for violating the U.S. Animal Welfare Act. “When you see multiple incidents at the same facility over a period of time, that’s when you realize that this is indicative of a system-wide problem,” said Michael Budkie, executive director of Stop Animal Exploitation Now! Harvard University made the nonprofit group’s top-10 list of animal-welfare violators for the first half of 2012, along with Harvard Medical School. The two institutions have separate licenses from the USDA to use animals for research and testing. The Animal Welfare Act, enforced by the USDA’s Animal and Plant Health Inspection Service, or APHIS, requires labs to handle research animals as carefully as possible to prevent trauma, overheating, physical harm, behavioral stress or unnecessary discomfort. APHIS also is investigating the death of five monkeys at the Harvard-affiliated New England Primate Research Center, said USDA spokesman David Sacks. The center’s interim director, Frederick Wang, stepped down in March after the death of the tamarin monkey. In March, Harvard Medical School Dean Jeffrey S. Flier ordered an independent review panel to evaluate the management and care of animals used in experiments. The panel’s recommendations included the appointment of a veterinarian and biosafety officer to oversee the primate center and the development of “new approaches” to its oversight process. ||||| Harvard Medical School logged its latest lab-monkey death this past spring when a cotton-top tamarin monkey died of thirst for lack of a water bottle. Then 41 deer mice died in April at a Harvard facility after their water source got cut off. As with the monkey, the U.S. Department of Agriculture gave the country’s oldest institution of higher learning an official warning. In less than two years, four monkeys have died in Harvard labs, including one left in a cage as it went through a mechanical washer. “When you see multiple incidents at the same facility over a period of time, that’s when you realize that this is indicative of a system-wide problem,” said Michael Budkie, executive director of the nonprofit Stop Animal Exploitation Now!, in a phone interview. The Milford, Ohio-based SAEN has placed Harvard on its top- 10 list of animal-welfare violators for the first half of 2012. The existence of enough violators to glean a top 10 helps indicate the scope of lab-animal abuse nationally. The Animal Welfare Act, enforced by the USDA’s Animal and Plant Health Inspection Service, requires labs to handle research animals as “carefully” as possible to prevent “trauma,” overheating, physical harm, “behavioral stress or unnecessary discomfort.” Two Gerbils TRS Labs Inc., based in Athens, Georgia, ranked first on SAEN’s list with 23 violations affecting about 70 animals, Budkie said. TRS was cited for housing cats in a room that was 88 to 89 degrees. It also failed to separate two gerbils that had been fighting in a cage and to protect dogs from suffering injuries, according to a USDA report. Several calls to TRS executives seeking comment weren’t returned. Santa Cruz Biotechnology Inc. in California, which researches antibodies and animal health-care products, ranked second on the SAEN list with 11 citations affecting 85 animals. In April, an Aphis inspector found a goat with a broken leg whose cast had come off, according to the USDA report. The attending veterinarian said she didn’t have “time to attend to the goat” because of her work load. “This facility was basically understaffed and it couldn’t offer good care,” Budkie said. Santa Cruz Biotechnology officials didn’t respond to a request for comment. Along with vigilance and public exposure, animal-welfare activists are trying to end the use of animals in research projects. Flying Monkeys Last month, the Washington-based People for the Ethical Treatment of Animals persuaded Air China Ltd. (601111) to join Delta Air Lines Inc. and American Airlines Inc. in agreeing to end shipments of monkeys into the U.S. “If you stop the pipeline into the U.S., that will curtail the number of monkeys used for research,” said Justin Goodman, associate director of PETA’s laboratory investigations department. Harvard University ranks third on SAEN’s list, followed by Harvard Medical School at No. 4. The two institutions have separate licenses from the USDA to use animals for research and testing. Aphis also is investigating the death of five monkeys at the Harvard-affiliated New England Primate Research Center, said USDA spokesman David Sacks. The center’s interim director, Frederick Wang, stepped down in March after the death of the tamarin monkey. Too Big “Harvard thinks it’s too big to fail, and it thinks all it has to do is provide information, and they’ll just get a tap on the wrist,” said John Pippin, director of academic affairs for the Washington-based Physicians Committee for Responsible Medicine. “There is no such thing as humane animal research.” In March, Harvard Medical School Dean Jeffrey S. Flier ordered an independent review panel to evaluate the management and care of animals used in experiments. The panel’s recommendations included the appointment of a veterinarian and biosafety officer to oversee the primate center and the development of “new approaches” to its oversight process. “We will be unwavering in our efforts to ensure that our administrative and managerial practices are on par with our scientific standards of excellence,” Flier said in a statement issued this month. Other labs on SAEN’s list include Tuskegee University in Alabama in fifth place with 13 citations, followed by the University of Texas Medical Branch at Galveston; the Harvard- affiliated Massachusetts Eye and Ear Infirmary; Indiana University School of Medicine; University of Puerto Rico; and Methodist Research Institute in Indiana. Muse highlights include Rich Jaroslovsky on technology and Lance Esplund on art. To contact the writer on this story: Patrick Cole in New York at [email protected]. To contact the editor responsible for this story: Manuela Hoelterhoff in New York at [email protected].[/INST]– The USDA has issued an official citation against the Harvard Medical School for repeated incidents of cruelty to its lab animals. Four of the school's monkeys have died in less than two years, including one that was still in its cage when it was put through a mechanical washer, Bloomberg reports. Another died of thirst, as did 41 deer mice who had their water supply cut off in April. "When you see multiple incidents at the same facility over a period of time, that's when you realize that this is indicative of a system-wide problem," says one animal rights activist with Stop Animal Exploitation Now. Harvard University recently landed at No. 3 on SAEN's top 10 animal welfare violators list, with its medical school occupying the No. 4 slot. Topping the list: TRS Labs in Athens, Georgia, which received 23 citations affecting around 70 animals.</s>

“We realize that Rodriguez Aguilera is an unusual candidate.” So conceded a Miami Herald editorial endorsing a candidate who once claimed that majestic, blond extraterrestrial beings kidnapped her when she was 7. Years before Bettina Rodriguez Aguilera announced her bid to replace one of the most influential Cuban Americans in Congress, she appeared on Spanish-language television programs and talked about her alien experience. She saw three beings — two women and a man — she said. They were tall and full-figured. They spoke to her telepathically. They took her on board the spaceship, and inside, she saw round seats. But editorial page editor Nancy Ancrum said she does not believe that Rodriguez Aguilera’s beliefs or past experiences have influenced her ability to become an effective public servant. Rodriguez Aguilera, who is running in the Republican primary for a South Florida congressional district, has the heftiest résumé of all the candidates in that race the editorial board interviewed, Ancrum said. “Here’s why we chose her: She’s not crazy,” Ancrum told The Washington Post, adding later: “We chose not to see her as a two-dimensional figure. And we chose not to make that an overriding concern. We’re more thoughtful than that.” The endorsement does add another layer of weirdness to a state already known for its penchant for oddballs. Take, for example, Melissa Howard, a state House hopeful who is now infamous for touting a fake college diploma and has since dropped out of the race. In its editorial published Sunday, nine days before the primary election, the board said it agreed with Rodriguez Aguilera that her past comments about extraterrestrial beings are a “non-issue.” She is a “strong candidate” with “plausible conservative ideas” who has a solid background as a former city official and a business executive, the board wrote. “The daughter of a Cuban political prisoner, Rodriguez Aguilera became an activist, volunteering with the Cuban American National Foundation,” the board wrote. [She claimed tall, blond aliens kidnapped her as a child. Now she's running for Congress.] Rodriguez Aguilera said she’s happy with the Herald’s endorsement. She said the board asked her about her previous comments about extraterrestrial beings. Her response was that they are not important, and the board agreed, she said. “What people care about is a candidate that can bring jobs … and that’s what I have proven that I have been able to do for the past 40 years, and that will continue throughout my life,” Rodriguez Aguilera, who’s running on a promise to help South Florida’s working class, told The Post. Rodriguez Aguilera is running to replace Rep. Ileana Ros-Lehtinen (R), the first Hispanic woman and Cuban American elected to Congress. Ros-Lehtinen, who represents much of Miami and Miami Beach, announced in April 2017 that she will retire, giving Democrats a chance to flip a South Florida congressional district that Hillary Clinton carried in the 2016 presidential election. According to the Herald, Rodriguez Aguilera is one of three best-known candidates in the crowded Republican primary, though she’s not viewed as the front-runner. The other two, Spanish-language television star Maria Elvira Salazar and former Miami-Dade Commissioner Bruno Barreiro, declined to participate in the Herald’s interview process Ancrum said Barreiro’s campaign told the board that he is not seeking an endorsement, and Salazar’s schedule is booked until Aug. 28, which is Election Day. That left the board with a choice between Rodriguez Aguilera and four other lesser-known candidates. “We have to look at each candidate in the context of who else is running in the race,” Ancrum said, adding that the board did not believe the other four candidates were quite ready for a seat in Congress. Rodriguez Aguilera, however, has raised only about $80,000, compared with Salazar’s $682,000 and Barreiro’s $576,000, according to federal campaign reports. She first entered politics as a council member from Doral, Fla., from 2012 to 2014. The city’s mayor nominated her to replace the vice mayor in 2013. She sponsored a human-trafficking ordinance in 2014 after two massage parlors were shut down for prostitution. She said she helped boost Doral’s economic and population growth during her time as the city’s economic development coordinator, a position she held for four years. She also previously worked as a social worker for Miami-Dade County and later as an ombudsman at the county manager’s office, according to her campaign website. [Florida candidate tried to prove she’s a college graduate. The school says her diploma is fake.] Rodriguez Aguilera announced her candidacy for Florida’s 27th Congressional District in August 2017. A few months later, the Miami Herald unearthed old television interviews in which she talked about extraterrestrials. In one video that was uploaded to YouTube long before the Herald highlighted it, Rodriguez Aguilera talked about boarding the aliens' spaceship. “God is a universal energy, not a person,” the aliens told her, according to Rodriguez Aguilera. “It’s in everything. God talks to people, and they understand it in different ways, but there’s only one religion.” In another interview, she said that the beings, with their arms wide open, reminded her of Jesus Christ, and that she saw them again during her teenage years. She said the aliens also talked about Isis, an Egyptian goddess. (It’s also an acronym for the Islamic State militant group, which did not exist at the time of Rodriguez Aguilera’s interviews). She made several other claims: Africa is the center of energy. There are 30,000 nonhuman skulls in a subterranean cave on the island of Malta in the Mediterranean. Coral Castle, a limestone structure in South Florida, is an ancient pyramid. Rodriguez Aguilera told The Post earlier that she merely described experiences she had and that they have “nothing to do” with who she is and with her work in public service. She also accused the Herald of negatively portraying her interviews, calling an article published in October an “attack piece.” Now, the Herald’s editorial board, which is separate from the paper’s news section, is placing its support behind Rodriguez Aguilera, whose “boots-on-the-ground ideas and experience” set her apart from the two front-runners, the board said. Rodriguez Aguilera has outlined what she calls a “working-class agenda,” and has proposed reforming the Fair Credit Act to change the credit score system, making student loan payments more affordable, and creating hardship rental insurance to reduce homelessness. “I think she would serve this district well . . . I don’t think we went off the rails here,” Ancrum said. “People just have to look at it in context.” Read more: Florida candidate who was caught touting a fake college diploma drops out of race Former state GOP leader kills mother’s dog, claims he’s ‘the second coming of Christ,’ police say A black lawmaker was canvassing door to door in her district. A constituent called 911. ||||| DEMOCRATIC PRIMARY A wealth of candidates, bringing new names, unexpected faces and diverse talents, signed up to be the Democrat who would replace Rep. Ileana Ros-Lehtinen in Congress. When Donna Shalala, former University of Miami president, joined in, bearing a healthy war chest, a well-known name and a CV of singular accomplishments, the field thinned somewhat. Still, with Shalala’s presence, the wealth of talent in this race only got more abundant. Matt Haggman, who spent 10 years as Miami Herald reporter and most recently was program director for the Knight Foundation. He’s is rightly credited with nurturing Greater Miami’s transformation into a technology hub. Michael Hepburn, a former academic adviser at UM’s School of Business; Rep. David Richardson, who has served in the Florida House since 2012 and has taken on Florida’s broken prison system; and Kristen Rosen Gonzalez, a Miami Beach Commissioner since 2015. She proposes, among other things, a bullet tax, whose proceeds would go to retrofit schools to protect students from mass shootings. Be the first to know. No one covers what is happening in our community better than we do. And with a digital subscription, you'll never miss a local story. SIGN ME UP! In recommending David Richardson, the Editorial Board is following voters’ lead. Political brand names have fallen — from county commission races to the White House. Our recommendation is no slight to the stature and ccomplishments of frontrunner Shalala, who has led two major universities to national prominence and confidently walked the halls of power in Washington, D.C. as secretary of the U.S. Department of Health and Human Services under President Bill Clinton. She knows how to “win friends and influence people” — and raise money. All vital skills. The $1 billion she raised for UM as president is evidence of her pull, as are the many ways she leveraged the university to benefit the broader community, from establishing its medical center to subsidizing transportation for students to get cars off clogged streets. David Richardson’s accomplishments may not appear as grand, but are significant: As a state legislator, Richardson took on the task of reforming Florida’s broken prison system. It wasn’t glamorous, there was little publicity, but it was the right thing to do. Richardson made an impact. That was one of his achievements that persuaded us that he is a true public servant who will make the most of a seat in Congress. Let’s face it, felons are not a constituency that anyone loves. However, Richardson knew that Florida’s prisons, including those run for profit, were hellish places, where corrections officers and other staffers were meting out violence, and even death, while being paid by taxpayers. He also recognized that most felons become former felons, and how they’re treated in prison will impact society at large — for better or worse. Richardson got one prison closed and reforms pushed through. All this as a Democrat outnumbered in the Republican-majority state House. In fact, he sought to sponsor a bill to help gay kids in foster care. When he realized its chances would be better as a rider on a GOP bill, he relinquished getting credit in favor of securing the bill’s passage. This alone speaks to his ability to find common ground and work effectively across the aisle. Richardson also convinced reluctant GOP colleagues in the Legislature to ban bump stocks, which let semiautomatic weapons fire even faster. It’s now Florida law. Richardson, a forensic accountant, is a relatively new — but not newbie — elected leader. He is poised to energize both voters and prospective voters, many of whom believe they have been taken for granted by the establishment political machine. And Shalala cannot claim distance from that machine — from her tight bond with long-time friend Hillary Clinton, whose sometimes maligned foundation hired Shalala after she left UM, to her prior corporate board seats. They speak of a well-connected insider, where perhaps fresher relationships are warranted. All of the candidates who agreed to sit down with the Editorial Board — Hepburn did not — express practical, progressives views. They diverge somewhat on how to provide healthcare for all, but are adamant that it must happen. And no one in the group equivocates on sea-level rise: It’s real, and must be confronted. We think the state representative has shown the potential to be an enduring advocate for his district, his state, and the nation. The Herald recommends DAVID RICHARDSON in the Democratic primary of Congressional District 27. REPUBLICAN PRIMARY “This congressional seat has been a pulpit for veteran Miami Republican Ileana Ros-Lehtinen since she won it in 1989. But Ros-Lehtinen is now retiring. Can the Republicans hold on to her seat? It’s one of the biggest political questions in South Florida this election season. A slew of Republican candidates is vying to face the winner of the Democratic primary in November and protect against flipping of the seat from red to blue. But the overcrowded race might be a sign that Republicans have given up the seat, since the district now has shifted closer to the Democrats’ favor. Among the best-known candidates are Spanish-language television star Maria Elvira Salazar, who has wide name recognition; former Miami-Dade Commissioner Bruno Barreiro, whose wife just lost a bid to keep his commission seat in the family, and Bettina Rodriguez Aguilera, a former Doral councilwoman. There are other, lesser known candidates in the race: Elizabeth Adadi, Angie Chirino, who is a daughter of singer Willy Chirino, Stephen Marks, Michael Ohevzion, Maria Peiro and Gina Sosa. Two candidates in the race, Salazar and Barreiro, who are viewed as the front-runners, declined to take part in the Miami Herald’s candidate interview process. Barreiro’s campaign said that he was not seeking our endorsement; Salazar’s campaign said that her schedule was booked until Aug. 28 — Election Day. The Editorial Board was most impressed by Rodriguez Aguilera, now a business consultant. We realize that Rodriguez Aguilera is an unusual candidate. Last year, she told the Miami Herald — and several Spanish-language media outlets — that she believes in extra-terrestrials. She says when she was 7, she was taken aboard a spaceship and, throughout her life, she has communicated telepathically with the beings, which remind her of the concrete Christ in Brazil. There you have it. “This is a non-issue,” she told the Board. We agree. Her bona fides as a former elected official, and now a businesswoman who spends time in other countries training women to run for office are solid. Rodriguez Aguilera is a strong candidate in the race with plausible conservative ideas. The daughter of a Cuban political prisoner, Rodriguez Aguilera became an activist, volunteering with the Cuban American National Foundation. She said that she was coached by its former leader, Jorge Mas Canosa, who taught her that, “If you don’t have a solution to a problem, don’t raise your hand to complain.” Rodriguez Aguilera started her career in the public sector as a social worker for Miami-Dade, and later as an ombudsman at the county manager’s office. She eventually parlayed that government experience — helping residents, companies and start-ups navigate county red tape — into a successful private business. She eventually entered politics and ran for Doral councilwoman, becoming deputy mayor, but these were turbulent times in Doral. In 2013, she was accused of violating Florida’s homestead-exemption rules. The matter was resolved, and there were indications that the accusation was levied by political enemies. Unlike other candidates in the race, she has a “Working Class Agenda.” with proposed solutions that include: reforming the Fair Credit Act to change the credit score system; reducing student loan payments to make them more affordable; cutting taxes and red tape that, she says, paralyze progress; and creating a hardship rental insurance to reduce homelessness. Salazar’s platform has been low key because she has made few public appearances as part of her primary bid. And Barreiro is now running without the power of incumbency. Likely to be an issue in the race is the fact that Barreiro was the commission chairman when the unpopular Miami Marlins Stadium deal was voted on. Many Miami-Dade taxpayers see him as having helped usher the process along — one of the most despised deals ever. While Barreiro and Salazar appear to be saving their ammunition for the general election, for her boots-on-the-ground ideas and experience, the Herald recommends BETTINA RODRIGUEZ AGUILERA in the Republican primary for Congressional District 27. SHARE COPY LINK Miami congressional candidate, Bettina Rodriguez Aguilera, speaks in 2009 about her relationships with extraterrestrial beings in an Américan Tevé program. Read our full list of recommendations for the Aug. 28 primary here. ||||| The Miami Herald newspaper endorsed a Republican House candidate for her "working class agenda," but who also believes she was abducted by aliens. The Herald's editorial board "was most impressed" by former Doral councilwoman Bettina Rodriguez Aguilera in her Congressional District 27 race to take over the seat of longtime incumbent GOP member, Ileana Ros-Lehtinen, who is not seeking re-election this year. While the newspaper acknowledged she is an "unusual candidate" for endorsement, both she and the editors agreed her abduction is a "non-issue" in the upcoming election. Screenshot | Bettina For Congress In 2017, business consultant Rodriguez Aguilera told several Spanish-language news outlets and the Herald she was taken aboard an alien spaceship when she was seven years old. She described the aliens as three blond, big-bodied extraterrestrial beings who have communicated telepathically with her on several occasions in her life. The now 60-year-old GOP candidate recounted "going up" into the spaceship and said some of the alien beings reminded her of Rio de Janeiro's mountaintop Christ the Redeemer statue, in which Jesus poses with his outstretched arms. Among the tidbits of information she gleaned from her alien abduction, Rodriguez Aguilera learned that Africa is the world's "energy center" and the Coral Castle tourist attraction in South Miami-Dade is actually an ancient Egyptian pyramid. But the newspaper's editorial board is unconcerned with the alien allegations and has instead focused on the GOP candidate's other accomplishments, including spending time in other countries training women to run for public office. They touted her career start as a social worker before becoming an ombudsman in the county manager's office. She ultimately turned her government experience into a succesful private business practice. The newspaper said Rodriguez Aguilera has a "Working Class Agenda" to reduce student loan payments, reforming the Fair Credit Act and reducing homelessness. Keep up with this story and more by subscribing now Two of the predicted Republican primary front-runners in the election, Spanish-language TV star Maria Elvira Salazar and former Miami-Dade Commissioner Bruno Barreiro, both declined to participate in any interviews with the newspaper, listed in the Top 40 of largest U.S. reader circulations. The Miami Herald conceded Rodriguez Aguilera was commission chairman when the "most despised deal ever" was made over the Miami Marlins Stadium. Finally, the paper endorsed her "boots-on-the-ground ideas and experience" to defeat her Republican opponents in the August 28 Republican primary.

– The Miami Herald over the weekend made its endorsements in a local congressional race, an otherwise routine development that is making headlines for an odd reason: The candidate endorsed by the newspaper in the Republican primary not only believes in aliens, she claims to have been abducted by them, reports Newsweek. The Herald does not try to dodge the issue in backing Bettina Rodriguez Aguilera for the 27th District. "We realize that Rodriguez Aguilera is an unusual candidate," the editors write. "Last year, she told the Miami Herald—and several Spanish-language media outlets—that she believes in extra-terrestrials. She says when she was 7, she was taken aboard a spaceship and, throughout her life, she has communicated telepathically with the beings, which remind her of the concrete Christ in Brazil. There you have it." However, the newspaper agrees with Rodriguez Aguilera that this is a "non-issue" and irrelevant to the race. The Herald instead praises her political and business background, along with her "Working Class Agenda." Rodriguez Aguilera tells the Washington Post that "what people care about is a candidate that can bring jobs," not anything she might have to say about extra-terrestrials. One footnote on the latter issue: Rodriguez Aguilera says she learned from the aliens that Coral Castle, a limestone tourist attraction in South Miami-Dade, is, in fact, an ancient pyramid. (A Mississippi man is speaking out about his own supposed alien abduction decades ago.)

<s>[INST]“We realize that Rodriguez Aguilera is an unusual candidate.” So conceded a Miami Herald editorial endorsing a candidate who once claimed that majestic, blond extraterrestrial beings kidnapped her when she was 7. Years before Bettina Rodriguez Aguilera announced her bid to replace one of the most influential Cuban Americans in Congress, she appeared on Spanish-language television programs and talked about her alien experience. She saw three beings — two women and a man — she said. They were tall and full-figured. They spoke to her telepathically. They took her on board the spaceship, and inside, she saw round seats. But editorial page editor Nancy Ancrum said she does not believe that Rodriguez Aguilera’s beliefs or past experiences have influenced her ability to become an effective public servant. Rodriguez Aguilera, who is running in the Republican primary for a South Florida congressional district, has the heftiest résumé of all the candidates in that race the editorial board interviewed, Ancrum said. “Here’s why we chose her: She’s not crazy,” Ancrum told The Washington Post, adding later: “We chose not to see her as a two-dimensional figure. And we chose not to make that an overriding concern. We’re more thoughtful than that.” The endorsement does add another layer of weirdness to a state already known for its penchant for oddballs. Take, for example, Melissa Howard, a state House hopeful who is now infamous for touting a fake college diploma and has since dropped out of the race. In its editorial published Sunday, nine days before the primary election, the board said it agreed with Rodriguez Aguilera that her past comments about extraterrestrial beings are a “non-issue.” She is a “strong candidate” with “plausible conservative ideas” who has a solid background as a former city official and a business executive, the board wrote. “The daughter of a Cuban political prisoner, Rodriguez Aguilera became an activist, volunteering with the Cuban American National Foundation,” the board wrote. [She claimed tall, blond aliens kidnapped her as a child. Now she's running for Congress.] Rodriguez Aguilera said she’s happy with the Herald’s endorsement. She said the board asked her about her previous comments about extraterrestrial beings. Her response was that they are not important, and the board agreed, she said. “What people care about is a candidate that can bring jobs … and that’s what I have proven that I have been able to do for the past 40 years, and that will continue throughout my life,” Rodriguez Aguilera, who’s running on a promise to help South Florida’s working class, told The Post. Rodriguez Aguilera is running to replace Rep. Ileana Ros-Lehtinen (R), the first Hispanic woman and Cuban American elected to Congress. Ros-Lehtinen, who represents much of Miami and Miami Beach, announced in April 2017 that she will retire, giving Democrats a chance to flip a South Florida congressional district that Hillary Clinton carried in the 2016 presidential election. According to the Herald, Rodriguez Aguilera is one of three best-known candidates in the crowded Republican primary, though she’s not viewed as the front-runner. The other two, Spanish-language television star Maria Elvira Salazar and former Miami-Dade Commissioner Bruno Barreiro, declined to participate in the Herald’s interview process Ancrum said Barreiro’s campaign told the board that he is not seeking an endorsement, and Salazar’s schedule is booked until Aug. 28, which is Election Day. That left the board with a choice between Rodriguez Aguilera and four other lesser-known candidates. “We have to look at each candidate in the context of who else is running in the race,” Ancrum said, adding that the board did not believe the other four candidates were quite ready for a seat in Congress. Rodriguez Aguilera, however, has raised only about $80,000, compared with Salazar’s $682,000 and Barreiro’s $576,000, according to federal campaign reports. She first entered politics as a council member from Doral, Fla., from 2012 to 2014. The city’s mayor nominated her to replace the vice mayor in 2013. She sponsored a human-trafficking ordinance in 2014 after two massage parlors were shut down for prostitution. She said she helped boost Doral’s economic and population growth during her time as the city’s economic development coordinator, a position she held for four years. She also previously worked as a social worker for Miami-Dade County and later as an ombudsman at the county manager’s office, according to her campaign website. [Florida candidate tried to prove she’s a college graduate. The school says her diploma is fake.] Rodriguez Aguilera announced her candidacy for Florida’s 27th Congressional District in August 2017. A few months later, the Miami Herald unearthed old television interviews in which she talked about extraterrestrials. In one video that was uploaded to YouTube long before the Herald highlighted it, Rodriguez Aguilera talked about boarding the aliens' spaceship. “God is a universal energy, not a person,” the aliens told her, according to Rodriguez Aguilera. “It’s in everything. God talks to people, and they understand it in different ways, but there’s only one religion.” In another interview, she said that the beings, with their arms wide open, reminded her of Jesus Christ, and that she saw them again during her teenage years. She said the aliens also talked about Isis, an Egyptian goddess. (It’s also an acronym for the Islamic State militant group, which did not exist at the time of Rodriguez Aguilera’s interviews). She made several other claims: Africa is the center of energy. There are 30,000 nonhuman skulls in a subterranean cave on the island of Malta in the Mediterranean. Coral Castle, a limestone structure in South Florida, is an ancient pyramid. Rodriguez Aguilera told The Post earlier that she merely described experiences she had and that they have “nothing to do” with who she is and with her work in public service. She also accused the Herald of negatively portraying her interviews, calling an article published in October an “attack piece.” Now, the Herald’s editorial board, which is separate from the paper’s news section, is placing its support behind Rodriguez Aguilera, whose “boots-on-the-ground ideas and experience” set her apart from the two front-runners, the board said. Rodriguez Aguilera has outlined what she calls a “working-class agenda,” and has proposed reforming the Fair Credit Act to change the credit score system, making student loan payments more affordable, and creating hardship rental insurance to reduce homelessness. “I think she would serve this district well . . . I don’t think we went off the rails here,” Ancrum said. “People just have to look at it in context.” Read more: Florida candidate who was caught touting a fake college diploma drops out of race Former state GOP leader kills mother’s dog, claims he’s ‘the second coming of Christ,’ police say A black lawmaker was canvassing door to door in her district. A constituent called 911. ||||| DEMOCRATIC PRIMARY A wealth of candidates, bringing new names, unexpected faces and diverse talents, signed up to be the Democrat who would replace Rep. Ileana Ros-Lehtinen in Congress. When Donna Shalala, former University of Miami president, joined in, bearing a healthy war chest, a well-known name and a CV of singular accomplishments, the field thinned somewhat. Still, with Shalala’s presence, the wealth of talent in this race only got more abundant. Matt Haggman, who spent 10 years as Miami Herald reporter and most recently was program director for the Knight Foundation. He’s is rightly credited with nurturing Greater Miami’s transformation into a technology hub. Michael Hepburn, a former academic adviser at UM’s School of Business; Rep. David Richardson, who has served in the Florida House since 2012 and has taken on Florida’s broken prison system; and Kristen Rosen Gonzalez, a Miami Beach Commissioner since 2015. She proposes, among other things, a bullet tax, whose proceeds would go to retrofit schools to protect students from mass shootings. Be the first to know. No one covers what is happening in our community better than we do. And with a digital subscription, you'll never miss a local story. SIGN ME UP! In recommending David Richardson, the Editorial Board is following voters’ lead. Political brand names have fallen — from county commission races to the White House. Our recommendation is no slight to the stature and ccomplishments of frontrunner Shalala, who has led two major universities to national prominence and confidently walked the halls of power in Washington, D.C. as secretary of the U.S. Department of Health and Human Services under President Bill Clinton. She knows how to “win friends and influence people” — and raise money. All vital skills. The $1 billion she raised for UM as president is evidence of her pull, as are the many ways she leveraged the university to benefit the broader community, from establishing its medical center to subsidizing transportation for students to get cars off clogged streets. David Richardson’s accomplishments may not appear as grand, but are significant: As a state legislator, Richardson took on the task of reforming Florida’s broken prison system. It wasn’t glamorous, there was little publicity, but it was the right thing to do. Richardson made an impact. That was one of his achievements that persuaded us that he is a true public servant who will make the most of a seat in Congress. Let’s face it, felons are not a constituency that anyone loves. However, Richardson knew that Florida’s prisons, including those run for profit, were hellish places, where corrections officers and other staffers were meting out violence, and even death, while being paid by taxpayers. He also recognized that most felons become former felons, and how they’re treated in prison will impact society at large — for better or worse. Richardson got one prison closed and reforms pushed through. All this as a Democrat outnumbered in the Republican-majority state House. In fact, he sought to sponsor a bill to help gay kids in foster care. When he realized its chances would be better as a rider on a GOP bill, he relinquished getting credit in favor of securing the bill’s passage. This alone speaks to his ability to find common ground and work effectively across the aisle. Richardson also convinced reluctant GOP colleagues in the Legislature to ban bump stocks, which let semiautomatic weapons fire even faster. It’s now Florida law. Richardson, a forensic accountant, is a relatively new — but not newbie — elected leader. He is poised to energize both voters and prospective voters, many of whom believe they have been taken for granted by the establishment political machine. And Shalala cannot claim distance from that machine — from her tight bond with long-time friend Hillary Clinton, whose sometimes maligned foundation hired Shalala after she left UM, to her prior corporate board seats. They speak of a well-connected insider, where perhaps fresher relationships are warranted. All of the candidates who agreed to sit down with the Editorial Board — Hepburn did not — express practical, progressives views. They diverge somewhat on how to provide healthcare for all, but are adamant that it must happen. And no one in the group equivocates on sea-level rise: It’s real, and must be confronted. We think the state representative has shown the potential to be an enduring advocate for his district, his state, and the nation. The Herald recommends DAVID RICHARDSON in the Democratic primary of Congressional District 27. REPUBLICAN PRIMARY “This congressional seat has been a pulpit for veteran Miami Republican Ileana Ros-Lehtinen since she won it in 1989. But Ros-Lehtinen is now retiring. Can the Republicans hold on to her seat? It’s one of the biggest political questions in South Florida this election season. A slew of Republican candidates is vying to face the winner of the Democratic primary in November and protect against flipping of the seat from red to blue. But the overcrowded race might be a sign that Republicans have given up the seat, since the district now has shifted closer to the Democrats’ favor. Among the best-known candidates are Spanish-language television star Maria Elvira Salazar, who has wide name recognition; former Miami-Dade Commissioner Bruno Barreiro, whose wife just lost a bid to keep his commission seat in the family, and Bettina Rodriguez Aguilera, a former Doral councilwoman. There are other, lesser known candidates in the race: Elizabeth Adadi, Angie Chirino, who is a daughter of singer Willy Chirino, Stephen Marks, Michael Ohevzion, Maria Peiro and Gina Sosa. Two candidates in the race, Salazar and Barreiro, who are viewed as the front-runners, declined to take part in the Miami Herald’s candidate interview process. Barreiro’s campaign said that he was not seeking our endorsement; Salazar’s campaign said that her schedule was booked until Aug. 28 — Election Day. The Editorial Board was most impressed by Rodriguez Aguilera, now a business consultant. We realize that Rodriguez Aguilera is an unusual candidate. Last year, she told the Miami Herald — and several Spanish-language media outlets — that she believes in extra-terrestrials. She says when she was 7, she was taken aboard a spaceship and, throughout her life, she has communicated telepathically with the beings, which remind her of the concrete Christ in Brazil. There you have it. “This is a non-issue,” she told the Board. We agree. Her bona fides as a former elected official, and now a businesswoman who spends time in other countries training women to run for office are solid. Rodriguez Aguilera is a strong candidate in the race with plausible conservative ideas. The daughter of a Cuban political prisoner, Rodriguez Aguilera became an activist, volunteering with the Cuban American National Foundation. She said that she was coached by its former leader, Jorge Mas Canosa, who taught her that, “If you don’t have a solution to a problem, don’t raise your hand to complain.” Rodriguez Aguilera started her career in the public sector as a social worker for Miami-Dade, and later as an ombudsman at the county manager’s office. She eventually parlayed that government experience — helping residents, companies and start-ups navigate county red tape — into a successful private business. She eventually entered politics and ran for Doral councilwoman, becoming deputy mayor, but these were turbulent times in Doral. In 2013, she was accused of violating Florida’s homestead-exemption rules. The matter was resolved, and there were indications that the accusation was levied by political enemies. Unlike other candidates in the race, she has a “Working Class Agenda.” with proposed solutions that include: reforming the Fair Credit Act to change the credit score system; reducing student loan payments to make them more affordable; cutting taxes and red tape that, she says, paralyze progress; and creating a hardship rental insurance to reduce homelessness. Salazar’s platform has been low key because she has made few public appearances as part of her primary bid. And Barreiro is now running without the power of incumbency. Likely to be an issue in the race is the fact that Barreiro was the commission chairman when the unpopular Miami Marlins Stadium deal was voted on. Many Miami-Dade taxpayers see him as having helped usher the process along — one of the most despised deals ever. While Barreiro and Salazar appear to be saving their ammunition for the general election, for her boots-on-the-ground ideas and experience, the Herald recommends BETTINA RODRIGUEZ AGUILERA in the Republican primary for Congressional District 27. SHARE COPY LINK Miami congressional candidate, Bettina Rodriguez Aguilera, speaks in 2009 about her relationships with extraterrestrial beings in an Américan Tevé program. Read our full list of recommendations for the Aug. 28 primary here. ||||| The Miami Herald newspaper endorsed a Republican House candidate for her "working class agenda," but who also believes she was abducted by aliens. The Herald's editorial board "was most impressed" by former Doral councilwoman Bettina Rodriguez Aguilera in her Congressional District 27 race to take over the seat of longtime incumbent GOP member, Ileana Ros-Lehtinen, who is not seeking re-election this year. While the newspaper acknowledged she is an "unusual candidate" for endorsement, both she and the editors agreed her abduction is a "non-issue" in the upcoming election. Screenshot | Bettina For Congress In 2017, business consultant Rodriguez Aguilera told several Spanish-language news outlets and the Herald she was taken aboard an alien spaceship when she was seven years old. She described the aliens as three blond, big-bodied extraterrestrial beings who have communicated telepathically with her on several occasions in her life. The now 60-year-old GOP candidate recounted "going up" into the spaceship and said some of the alien beings reminded her of Rio de Janeiro's mountaintop Christ the Redeemer statue, in which Jesus poses with his outstretched arms. Among the tidbits of information she gleaned from her alien abduction, Rodriguez Aguilera learned that Africa is the world's "energy center" and the Coral Castle tourist attraction in South Miami-Dade is actually an ancient Egyptian pyramid. But the newspaper's editorial board is unconcerned with the alien allegations and has instead focused on the GOP candidate's other accomplishments, including spending time in other countries training women to run for public office. They touted her career start as a social worker before becoming an ombudsman in the county manager's office. She ultimately turned her government experience into a succesful private business practice. The newspaper said Rodriguez Aguilera has a "Working Class Agenda" to reduce student loan payments, reforming the Fair Credit Act and reducing homelessness. Keep up with this story and more by subscribing now Two of the predicted Republican primary front-runners in the election, Spanish-language TV star Maria Elvira Salazar and former Miami-Dade Commissioner Bruno Barreiro, both declined to participate in any interviews with the newspaper, listed in the Top 40 of largest U.S. reader circulations. The Miami Herald conceded Rodriguez Aguilera was commission chairman when the "most despised deal ever" was made over the Miami Marlins Stadium. Finally, the paper endorsed her "boots-on-the-ground ideas and experience" to defeat her Republican opponents in the August 28 Republican primary.[/INST]– The Miami Herald over the weekend made its endorsements in a local congressional race, an otherwise routine development that is making headlines for an odd reason: The candidate endorsed by the newspaper in the Republican primary not only believes in aliens, she claims to have been abducted by them, reports Newsweek. The Herald does not try to dodge the issue in backing Bettina Rodriguez Aguilera for the 27th District. "We realize that Rodriguez Aguilera is an unusual candidate," the editors write. "Last year, she told the Miami Herald—and several Spanish-language media outlets—that she believes in extra-terrestrials. She says when she was 7, she was taken aboard a spaceship and, throughout her life, she has communicated telepathically with the beings, which remind her of the concrete Christ in Brazil. There you have it." However, the newspaper agrees with Rodriguez Aguilera that this is a "non-issue" and irrelevant to the race. The Herald instead praises her political and business background, along with her "Working Class Agenda." Rodriguez Aguilera tells the Washington Post that "what people care about is a candidate that can bring jobs," not anything she might have to say about extra-terrestrials. One footnote on the latter issue: Rodriguez Aguilera says she learned from the aliens that Coral Castle, a limestone tourist attraction in South Miami-Dade, is, in fact, an ancient pyramid. (A Mississippi man is speaking out about his own supposed alien abduction decades ago.)</s>

SECTION 1. SHORT TITLE. This Act may be cited as the ``Education Savings Assistance Act of 1994''. SEC. 2. TAX TREATMENT OF STATE EDUCATION SAVINGS ACCOUNTS. (a) In General.--Part III of subchapter B of chapter 1 of the Internal Revenue Code of 1986 (relating to items specifically excluded from gross income) is amended by redesignating section 137 as section 138 and by adding after section 136 the following new section: ``SEC. 137. EDUCATION SAVINGS ACCOUNTS. ``(a) General Rule.--Gross income shall not include any qualified education savings account distribution. ``(b) Qualified Education Savings Account Distribution.--For purposes of this section-- ``(1) In general.--The term `qualified education savings account distribution' means any amount paid or distributed out of an education savings account which would otherwise be includible in gross income to the extent such payment or distribution is used exclusively to pay qualified higher education expenses incurred by the designated beneficiary of the account. ``(2) Rollovers.--The term `qualified education savings account distribution' includes any transfer from an education savings account of one designated beneficiary to another such account of such beneficiary or to such an account of another designated beneficiary. ``(3) Special rules.--The determination under paragraph (1) as to whether an amount is otherwise includible in gross income shall be made in the manner described in section 72, except that-- ``(A) all education savings accounts shall be treated as one contract, ``(B) all distributions during any taxable year shall be treated as one distribution, ``(C) contributions to an account described in subsection (c)(4)(B)(i) shall not be included in the basis of the account, and ``(D) the value of the contract, income on the contract, and investment in the contract shall be computed as of the close of the calendar year in which the taxable year begins. ``(c) Education Savings Account.--For purposes of this section-- ``(1) In general.--The term `education savings account' means a trust created or organized in the United States-- ``(A) pursuant to a qualified State educational savings plan, and ``(B) exclusively for the purpose of paying the qualified higher education expenses of the designated beneficiary of the account. ``(2) Qualified state educational savings plan.--The term `qualified State educational savings plan' means a plan established and maintained by a State or instrumentality thereof under which-- ``(A) participants may save to meet qualified higher education expenses of designated beneficiaries, ``(B) planning and financial information is provided to participants about current and projected qualified higher education expenses, ``(C) education savings account statements are provided to participants at least quarterly, and ``(D) an audited financial statement is provided to participants at least annually. ``(3) Qualified higher education expenses.--The term `qualified higher education expenses' means the cost of attendance (as defined in section 472 of the Higher Education Act of 1965). ``(4) Limitations.--A trust shall not be treated as an education savings account unless the following requirements are met: ``(A) No contribution will be accepted unless it is in cash, stocks, bonds, or other securities which are readily tradable on an established securities market. ``(B) Contributions will not be accepted for any taxable year in excess of the applicable limit. The preceding sentence shall not apply to-- ``(i) contributions to the qualified State educational savings plan which are allocated to all education savings accounts within the class for which the contribution was made, or ``(ii) rollover contributions described in subsection (b)(2). ``(C) The trust may not be established for the benefit of more than one individual. ``(D) The trustee is the qualified State educational savings plan or person designated by it. ``(E) The assets of the trust may be invested only in accordance with the qualified State educational savings plan. ``(5) Applicable limit.--For purposes of paragraph (4)(B)-- ``(A) In general.--The applicable limit is $3,000. ``(B) Indexing.--In the case of taxable years beginning after December 31, 1994, the $3,000 amount under subparagraph (A) shall be increased by the education cost-of-living adjustment for the calendar year in which the taxable year begins. ``(C) Education cost-of-living adjustment.--For purposes of subparagraph (B), the education cost-of- living adjustment for any calendar year is the percentage (if any) by which-- ``(i) the higher education cost index for the preceding calendar year, exceeds ``(ii) such index for 1993. ``(D) Higher education cost index.--For purposes of subparagraph (C), the higher education cost index for any calendar year is the average qualified higher education expenses for undergraduate students at both private and public institutions of higher education for the 12-month period ending on August 31 of the calendar year. The Secretary of Education shall provide for the computation and publication of the higher education cost index. ``(d) Tax Treatment of Accounts and State Plans.-- ``(1) Exemption from tax.--An education savings account shall be exempt from taxation under this subtitle. Notwithstanding the preceding sentence, any such account or plan shall be subject to the taxes imposed by section 511 (relating to imposition of tax on unrelated business income of charitable, etc. organizations). ``(2) Loss of exemption of account where individual engages in prohibited transaction.-- ``(A) In general.--If the designated beneficiary of an education savings account is established or any individual who contributes to such account engages in any transaction prohibited by section 4975 with respect to the account, the account shall cease to be an education savings account as of the first day of the taxable year (of the individual so engaging in such transaction) during which such transaction occurs. ``(B) Account treated as distributing all its assets.--In any case in which any account ceases to be an education savings account by reason of subparagraph (A) as of the first day of any taxable year, an amount equal to the fair market value of all assets in the account shall be treated as having been distributed on such first day. ``(3) Effect of pledging account as security.--If, during any taxable year, the individual for whose benefit an education savings account is established, or any individual who contributes to such account, uses the account or any portion thereof as security for a loan, the portion so used shall be treated as distributed to the individual so using such portion. ``(e) Reports.--The Secretary may require the trustee of an education savings account to make reports regarding such account to the Secretary, to the individual who has established the account, and to the designated beneficiary of the account with respect to contributions, distributions, and such other matters as the Secretary may require. The reports required by this subsection shall be filed at such time and in such manner and furnished to such individuals at such time and in such manner as may be required by those regulations.'' (b) Tax Treatment of Qualified State Educational Savings Plan.-- (1) Treatment as section 501(c)(3) organization.--Section 501(c)(3) of such Code is amended by inserting ``or which is a qualified State education savings plan (as defined in section 137(c)(2)),'' after ``animals,''. (2) Charitable contributions.-- (A) Subparagraph (B) of section 170(c)(2) of such Code is amended by inserting ``, or which is a qualified State education savings plan (as defined in section 137(c)(2)),'' after ``animals''. (B) Section 170(b)(1)(A) of such Code is amended by striking ``or'' at the end of clause (vii), by inserting ``or'' at the end of clause (viii) and by inserting after clause (viii) the following new clause: ``(ix) a qualified State educational savings plan (as defined in section 137(c)(2)).'' (c) Contribution Not Subject to Gift Tax.--Section 2503 of such Code (relating to taxable gifts) is amended by adding at the end thereof the following new subsection: ``(h) Education Savings Accounts.--Any contribution made by an individual to an education savings account described in section 137 shall not be treated as a transfer of property by gift for purposes of this chapter.'' (d) Tax on Prohibited Transactions.--Section 4975 of such Code (relating to prohibited transactions) is amended-- (1) by adding at the end of subsection (c) the following new paragraph: ``(4) Special rule for education savings accounts.--An individual for whose benefit an education savings account is established and any contributor to such account shall be exempt from the tax imposed by this section with respect to any transaction concerning such account (which would otherwise be taxable under this section) if, with respect to such transaction, the account ceases to be an education savings account by reason of the application of section 137(d)(2)(A) to such account.'', and (2) by inserting ``, an education savings account described in section 137(c),'' in subsection (e)(1) after ``described in section 408(a)''. (e) Failure To Provide Reports on Education Savings Accounts.-- Section 6693 of such Code (relating to failure to provide reports on individual retirement accounts or annuities) is amended-- (1) by inserting ``or on education savings accounts'' after ``annuities'' in the heading of such section, and (2) by adding at the end of subsection (a) the following new sentence: ``Any person required by section 137(e) to file a report regarding an education savings account who fails to file the report at the time or in the manner required by such section shall pay a penalty of $50 for each failure, unless it is shown that such failure is due to reasonable cause.'' (f) Special Rule for Determining Amounts of Support for Dependent.--Subsection (b) of section 152 of such Code (relating to definition of dependent) is amended by adding at the end the following new paragraph: ``(6) A distribution from an education savings account described in section 137(c) to the individual for whose benefit such account has been established shall not be taken into account in determining support for purposes of this section to the extent such distribution is excluded from gross income of such individual under section 137.'' (g) Clerical Amendments.-- (1) The table of sections for part III of subchapter B of chapter 1 of such Code is amended by striking out the item relating to section 137 and inserting the following new items: ``Sec. 137. Education savings accounts. ``Sec. 138. Cross references to other Acts.'' (2) The table of sections for subchapter B of chapter 68 of such Code is amended by striking out the item relating to section 6693 and inserting the following new item: ``Sec. 6693. Failure to provide reports on individual retirement accounts or annuities or on education savings accounts.'' (h) Effective Date.--The amendments made by this section shall apply to contributions made in taxable years beginning after December 31, 1993.

Education Savings Assistance Act of 1994 - Amends the Internal Revenue Code to exclude from gross income any qualified education savings account. Describes such account as a trust created pursuant to a State educational savings plan and used exclusively to pay the higher education expenses of the designated beneficiary. Treats such State plans as tax-exempt organizations and treats contributions to such plans as charitable contributions. Declares that contributions to such accounts are not subject to the gift tax. Imposes penalty taxes in connection with reporting requirements or prohibited transactions associated with an account. Excludes distributions from such accounts when determining support for dependents.

<s>[INST]SECTION 1. SHORT TITLE. This Act may be cited as the ``Education Savings Assistance Act of 1994''. SEC. 2. TAX TREATMENT OF STATE EDUCATION SAVINGS ACCOUNTS. (a) In General.--Part III of subchapter B of chapter 1 of the Internal Revenue Code of 1986 (relating to items specifically excluded from gross income) is amended by redesignating section 137 as section 138 and by adding after section 136 the following new section: ``SEC. 137. EDUCATION SAVINGS ACCOUNTS. ``(a) General Rule.--Gross income shall not include any qualified education savings account distribution. ``(b) Qualified Education Savings Account Distribution.--For purposes of this section-- ``(1) In general.--The term `qualified education savings account distribution' means any amount paid or distributed out of an education savings account which would otherwise be includible in gross income to the extent such payment or distribution is used exclusively to pay qualified higher education expenses incurred by the designated beneficiary of the account. ``(2) Rollovers.--The term `qualified education savings account distribution' includes any transfer from an education savings account of one designated beneficiary to another such account of such beneficiary or to such an account of another designated beneficiary. ``(3) Special rules.--The determination under paragraph (1) as to whether an amount is otherwise includible in gross income shall be made in the manner described in section 72, except that-- ``(A) all education savings accounts shall be treated as one contract, ``(B) all distributions during any taxable year shall be treated as one distribution, ``(C) contributions to an account described in subsection (c)(4)(B)(i) shall not be included in the basis of the account, and ``(D) the value of the contract, income on the contract, and investment in the contract shall be computed as of the close of the calendar year in which the taxable year begins. ``(c) Education Savings Account.--For purposes of this section-- ``(1) In general.--The term `education savings account' means a trust created or organized in the United States-- ``(A) pursuant to a qualified State educational savings plan, and ``(B) exclusively for the purpose of paying the qualified higher education expenses of the designated beneficiary of the account. ``(2) Qualified state educational savings plan.--The term `qualified State educational savings plan' means a plan established and maintained by a State or instrumentality thereof under which-- ``(A) participants may save to meet qualified higher education expenses of designated beneficiaries, ``(B) planning and financial information is provided to participants about current and projected qualified higher education expenses, ``(C) education savings account statements are provided to participants at least quarterly, and ``(D) an audited financial statement is provided to participants at least annually. ``(3) Qualified higher education expenses.--The term `qualified higher education expenses' means the cost of attendance (as defined in section 472 of the Higher Education Act of 1965). ``(4) Limitations.--A trust shall not be treated as an education savings account unless the following requirements are met: ``(A) No contribution will be accepted unless it is in cash, stocks, bonds, or other securities which are readily tradable on an established securities market. ``(B) Contributions will not be accepted for any taxable year in excess of the applicable limit. The preceding sentence shall not apply to-- ``(i) contributions to the qualified State educational savings plan which are allocated to all education savings accounts within the class for which the contribution was made, or ``(ii) rollover contributions described in subsection (b)(2). ``(C) The trust may not be established for the benefit of more than one individual. ``(D) The trustee is the qualified State educational savings plan or person designated by it. ``(E) The assets of the trust may be invested only in accordance with the qualified State educational savings plan. ``(5) Applicable limit.--For purposes of paragraph (4)(B)-- ``(A) In general.--The applicable limit is $3,000. ``(B) Indexing.--In the case of taxable years beginning after December 31, 1994, the $3,000 amount under subparagraph (A) shall be increased by the education cost-of-living adjustment for the calendar year in which the taxable year begins. ``(C) Education cost-of-living adjustment.--For purposes of subparagraph (B), the education cost-of- living adjustment for any calendar year is the percentage (if any) by which-- ``(i) the higher education cost index for the preceding calendar year, exceeds ``(ii) such index for 1993. ``(D) Higher education cost index.--For purposes of subparagraph (C), the higher education cost index for any calendar year is the average qualified higher education expenses for undergraduate students at both private and public institutions of higher education for the 12-month period ending on August 31 of the calendar year. The Secretary of Education shall provide for the computation and publication of the higher education cost index. ``(d) Tax Treatment of Accounts and State Plans.-- ``(1) Exemption from tax.--An education savings account shall be exempt from taxation under this subtitle. Notwithstanding the preceding sentence, any such account or plan shall be subject to the taxes imposed by section 511 (relating to imposition of tax on unrelated business income of charitable, etc. organizations). ``(2) Loss of exemption of account where individual engages in prohibited transaction.-- ``(A) In general.--If the designated beneficiary of an education savings account is established or any individual who contributes to such account engages in any transaction prohibited by section 4975 with respect to the account, the account shall cease to be an education savings account as of the first day of the taxable year (of the individual so engaging in such transaction) during which such transaction occurs. ``(B) Account treated as distributing all its assets.--In any case in which any account ceases to be an education savings account by reason of subparagraph (A) as of the first day of any taxable year, an amount equal to the fair market value of all assets in the account shall be treated as having been distributed on such first day. ``(3) Effect of pledging account as security.--If, during any taxable year, the individual for whose benefit an education savings account is established, or any individual who contributes to such account, uses the account or any portion thereof as security for a loan, the portion so used shall be treated as distributed to the individual so using such portion. ``(e) Reports.--The Secretary may require the trustee of an education savings account to make reports regarding such account to the Secretary, to the individual who has established the account, and to the designated beneficiary of the account with respect to contributions, distributions, and such other matters as the Secretary may require. The reports required by this subsection shall be filed at such time and in such manner and furnished to such individuals at such time and in such manner as may be required by those regulations.'' (b) Tax Treatment of Qualified State Educational Savings Plan.-- (1) Treatment as section 501(c)(3) organization.--Section 501(c)(3) of such Code is amended by inserting ``or which is a qualified State education savings plan (as defined in section 137(c)(2)),'' after ``animals,''. (2) Charitable contributions.-- (A) Subparagraph (B) of section 170(c)(2) of such Code is amended by inserting ``, or which is a qualified State education savings plan (as defined in section 137(c)(2)),'' after ``animals''. (B) Section 170(b)(1)(A) of such Code is amended by striking ``or'' at the end of clause (vii), by inserting ``or'' at the end of clause (viii) and by inserting after clause (viii) the following new clause: ``(ix) a qualified State educational savings plan (as defined in section 137(c)(2)).'' (c) Contribution Not Subject to Gift Tax.--Section 2503 of such Code (relating to taxable gifts) is amended by adding at the end thereof the following new subsection: ``(h) Education Savings Accounts.--Any contribution made by an individual to an education savings account described in section 137 shall not be treated as a transfer of property by gift for purposes of this chapter.'' (d) Tax on Prohibited Transactions.--Section 4975 of such Code (relating to prohibited transactions) is amended-- (1) by adding at the end of subsection (c) the following new paragraph: ``(4) Special rule for education savings accounts.--An individual for whose benefit an education savings account is established and any contributor to such account shall be exempt from the tax imposed by this section with respect to any transaction concerning such account (which would otherwise be taxable under this section) if, with respect to such transaction, the account ceases to be an education savings account by reason of the application of section 137(d)(2)(A) to such account.'', and (2) by inserting ``, an education savings account described in section 137(c),'' in subsection (e)(1) after ``described in section 408(a)''. (e) Failure To Provide Reports on Education Savings Accounts.-- Section 6693 of such Code (relating to failure to provide reports on individual retirement accounts or annuities) is amended-- (1) by inserting ``or on education savings accounts'' after ``annuities'' in the heading of such section, and (2) by adding at the end of subsection (a) the following new sentence: ``Any person required by section 137(e) to file a report regarding an education savings account who fails to file the report at the time or in the manner required by such section shall pay a penalty of $50 for each failure, unless it is shown that such failure is due to reasonable cause.'' (f) Special Rule for Determining Amounts of Support for Dependent.--Subsection (b) of section 152 of such Code (relating to definition of dependent) is amended by adding at the end the following new paragraph: ``(6) A distribution from an education savings account described in section 137(c) to the individual for whose benefit such account has been established shall not be taken into account in determining support for purposes of this section to the extent such distribution is excluded from gross income of such individual under section 137.'' (g) Clerical Amendments.-- (1) The table of sections for part III of subchapter B of chapter 1 of such Code is amended by striking out the item relating to section 137 and inserting the following new items: ``Sec. 137. Education savings accounts. ``Sec. 138. Cross references to other Acts.'' (2) The table of sections for subchapter B of chapter 68 of such Code is amended by striking out the item relating to section 6693 and inserting the following new item: ``Sec. 6693. Failure to provide reports on individual retirement accounts or annuities or on education savings accounts.'' (h) Effective Date.--The amendments made by this section shall apply to contributions made in taxable years beginning after December 31, 1993.[/INST]Education Savings Assistance Act of 1994 - Amends the Internal Revenue Code to exclude from gross income any qualified education savings account. Describes such account as a trust created pursuant to a State educational savings plan and used exclusively to pay the higher education expenses of the designated beneficiary. Treats such State plans as tax-exempt organizations and treats contributions to such plans as charitable contributions. Declares that contributions to such accounts are not subject to the gift tax. Imposes penalty taxes in connection with reporting requirements or prohibited transactions associated with an account. Excludes distributions from such accounts when determining support for dependents.</s>

SECTION 1. SHORT TITLE. This Act may be cited as the ``Economic Freedom Act of 2010''. SEC. 2. ZERO PERCENT CAPITAL GAINS RATE FOR INDIVIDUALS AND CORPORATIONS. (a) Zero Percent Capital Gains Rate for Individuals.-- (1) In general.--Paragraph (1) of section 1(h) of the Internal Revenue Code of 1986 is amended by striking subparagraph (C), by redesignating subparagraphs (D) and (E) and subparagraphs (C) and (D), respectively, and by amending subparagraph (B) to read as follows: ``(B) 0 percent of the adjusted net capital gain (or, if less, taxable income);''. (2) Alternative minimum tax.--Paragraph (3) of section 55(b) is amended by striking subparagraph (C), by redesignating subparagraph (D) as subparagraph (C), and by amending subparagraph (B) to read as follows: ``(B) 0 percent of the adjusted net capital gain (or, if less, taxable excess), plus''. (3) Repeal of sunset of reduction in capital gains rates for individuals.--Section 303 of the Jobs and Growth Tax Relief Reconciliation Act of 2003 shall not apply to section 301 of such Act. (b) Zero Percent Capital Gains Rate for Corporations.-- (1) In general.--Section 1201 of the Internal Revenue Code of 1986 is amended by redesignating subsection (b) as subsection (c), and by striking subsection (a) and inserting the following new subsections: ``(a) General Rule.--If for any taxable year a corporation has a net capital gain, then, in lieu of the tax imposed by sections 11, 511, 821(a) or (c), and 831(a), there is hereby imposed a tax (if such tax is less than the tax imposed by such sections) which shall consist of the sum of-- ``(1) a tax computed on the taxable income reduced by the amount of the net capital gain, at the rates and in the manner as if this subsection had not been enacted, ``(2) 0 percent of the adjusted net capital gain (or, if less, taxable income), ``(3) 25 percent of the excess (if any) of-- ``(A) the unrecaptured section 1250 gain (or, if less, the net capital gain (determined without regard to subsection (b)(2)), over ``(B) the excess (if any) of-- ``(i) the sum of the amount on which tax is determined under paragraph (1) plus the net capital gain, over ``(ii) taxable income, plus ``(4) 28 percent of the amount of taxable income in excess of the sum of the amounts on which tax is determined under the preceding paragraphs of this subsection. ``(b) Definitions and Special Rules.--For purposes of this section-- ``(1) In general.--The terms `adjusted net capital gain' and `unrecaptured section 1250 gain' shall have the respective meanings given such terms in section 1(h). ``(2) Dividends taxed at net capital gain.--Except as otherwise provided in this section, the term `net capital gain' has the meaning given such term in section 1(h)(11).''. (2) Alternative minimum tax.--Section 55(b) of such Code is amended by adding at the end the following new paragraph: ``(4) Maximum rate of tax on net capital gain of corporations.--The amount determined under paragraph (1)(B)(i) shall not exceed the sum of-- ``(A) the amount determined under such paragraph computed at the rates and in the same manner as if this paragraph had not been enacted on the taxable excess reduced by the net capital gain, plus ``(B) the amount determined under section 1201.''. (3) Technical amendments.-- (A) Section 1202(a) of such Code is amended by striking ``50 percent'' and inserting ``100 percent''. (B) Section 1445(e)(1) of such Code is amended by striking ``35 percent (or, to the extent provided in regulations, 15 percent)'' and inserting ``0 percent''. (C) Section 1445(e)(2) of such Code is amended by striking ``35 percent'' and inserting ``0 percent''. (D) Section 7518(g)(6)(A) of such Code is amended by striking ``15 percent (34 percent in the case of a corporation)'' and inserting ``0 percent''. (E) Section 607(h)(6)(A) of the Merchant Marine Act, 1936 is amended by striking ``15 percent (34 percent in the case of a corporation)'' and inserting ``0 percent''. (c) Effective Date.-- (1) In general.--Except as provided in paragraph (2), the amendments made by this section shall apply to taxable years beginning after December 31, 2009. (2) Withholding.--The amendments made by subparagraphs (A) and (B) of subsection (b)(3) shall take apply to dispositions and distributions after the date of the enactment of this Act. SEC. 3. REDUCTION IN CORPORATE INCOME TAX RATES. (a) In General.--Subsection (b) of section 11 of the Internal Revenue Code of 1986 is amended to read as follows: ``(b) Amount of Tax.--The amount of the tax imposed by subsection (a) shall be 12.5 percent of taxable income.''. (b) Conforming Amendments.-- (1) Section 55(b)(1)(B)(i) of such Code is amended by striking ``20 percent'' and inserting ``12.5 percent''. (2) Section 280C(c)(3)(B)(ii)(II) of such Code is amended by striking ``maximum rate of tax under section 11(b)(1)'' and inserting ``rate of tax under section 11(b)''. (3) Section 832(b)(1) of such Code is amended by striking ``rates provided in section 11(b)'' and inserting ``rate provided in section 11(b)''. (4) Sections 244(a)(2)(B), 247(a)(2)(B), 527(b)(1), 835(e), 852(b)(1), 857(b)(4)(A), 860G(c)(1), 904(b)(3)(E)(ii)(II), and 1375(a) of such Code is amended by striking ``highest rate of tax'' and inserting ``rate of tax''. (5) Sections 860E(e)(2)(B), 860E(e)(6)(A)(ii), 860K(d)(2)(A)(ii), 860K(e)(1)(B)(ii), 1446(b)(2)(B), and 7874(e)(1)(B) of such Code are each amended by striking ``highest rate of tax specified in section 11(b)(1)'' and inserting ``rate of tax specified in section 11(b)''. (6) Section 904(b)(3)(D)(ii) of such Code is amended by striking ``(determined without regard to the last sentence of section 11(b)(1))''. (7) Section 962 of such Code is amended by striking subsection (c) and by redesignating subsection (d) as subsection (c). (8) Section 1201(a) of such Code is amended-- (A) by striking ``35 percent (determined without regard to the last 2 sentences of section 11(b)(1))'' and inserting ``15 percent'', and (B) by striking ``35 percent'' in paragraph (2) and inserting ``15 percent''. (9) Section 1561(a) of such Code is amended-- (A) by striking paragraph (1) and by redesignating paragraphs (2), (3), and (4) as paragraphs (1), (2), and (3), respectively, (B) by striking ``The amounts specified in paragraph (1), the'' and inserting ``The'', (C) by striking ``paragraph (2)'' and inserting ``paragraph (1)'', (D) by striking ``paragraph (3)'' both places it appears and inserting ``paragraph (2)'', (E) by striking ``paragraph (4)'' and inserting ``paragraph (3)'', and (F) by striking the fourth sentence. (10) Subsection (b) of section 1561 of such Code is amended to read as follows: ``(b) Certain Short Taxable Years.--If a corporation has a short taxable year which does not include a December 31 and is a component member of a controlled group of corporations with respect to such taxable year, then for purposes of this subtitle, the amount to be used in computing the accumulated earnings credit under section 535(c)(2) and (3) of such corporation for such taxable year shall be the amount specified in subsection (a)(1) divided by the number of corporations which are component members of such group on the last day of such taxable year. For purposes of the preceding sentence, section 1563(b) shall be applied as if such last day were substituted for December 31.''. (c) Effective Date.--The amendments made by this section shall apply to taxable years beginning after December 31, 2009. SEC. 4. ESTATE TAX REPEAL MADE PERMANENT. Section 901 of the Economic Growth and Tax Relief Reconciliation Act of 2001 shall not apply to title V of such Act. SEC. 5. ELECTION TO EXPENSE BUSINESS ASSETS. (a) In General.--Section 179 of the Internal Revenue Code of 1986 is amended to read as follows: ``SEC. 179. ELECTION TO EXPENSE CERTAIN DEPRECIABLE BUSINESS ASSETS. ``(a) Treatment as Expenses.--A taxpayer may elect to treat the cost of any property to which this section applies as an expense which is not chargeable to capital account. Any cost so treated shall be allowed as a deduction for the taxable year in which such property is placed in service. ``(b) Property to Which Section Applies.-- ``(1) In general.--This section shall apply to property-- ``(A) which is-- ``(i) tangible property (to which section 168 applies), or ``(ii) computer software (as defined in section 197(e)(3)(B)) which is described in section 197(e)(3)(A)(i), to which section 167 applies, ``(B) which is section 1245 property (as defined in section 1245(a)(3)) or 1250 property (as defined in section 1250(c)), and ``(C) which is acquired by purchase for use in the active conduct of a trade or business. Such term shall not include any property described in section 50(b) and shall not include air conditioning or heating units. ``(2) Purchase defined.--For purposes of paragraph (1), the term `purchase' means any acquisition of property, but only if-- ``(A) the property is not acquired from a person whose relationship to the person acquiring it would result in the disallowance of losses under section 267 or 707(b) (but, in applying section 267(b) and (c) for purposes of this section, paragraph (4) of section 267(c) shall be treated as providing that the family of an individual shall include only his spouse, ancestors, and lineal descendants), ``(B) the property is not acquired by one component member of a controlled group from another component member of the same controlled group, and ``(C) the basis of the property in the hands of the person acquiring it is not determined-- ``(i) in whole or in part by reference to the adjusted basis of such property in the hands of the person from whom acquired, or ``(ii) under section 1014(a) (relating to property acquired from a decedent). ``(3) Cost.--For purposes of this section, the cost of property does not include so much of the basis of such property as is determined by reference to the basis of other property held at any time by the person acquiring such property. ``(4) Controlled group defined.--For purposes of this section, the term `controlled group' has the meaning assigned to it by section 1563(a), except that, for such purposes, the phrase `more than 50 percent' shall be substituted for the phrase `at least 80 percent' each place it appears in section 1563(a)(1). ``(5) Coordination with section 38.--No credit shall be allowed under section 38 with respect to any amount for which a deduction is allowed under subsection (a). ``(6) Recapture in certain cases.--The Secretary shall, by regulations, provide for recapturing the benefit under any deduction allowable under subsection (a) with respect to any property which is not used predominantly in a trade or business at any time. ``(c) Election.-- ``(1) In general.--An election under this section for any taxable year shall-- ``(A) specify the items of property to which the election applies, and ``(B) be made on the taxpayer's return of the tax imposed by this chapter for the taxable year. Such election shall be made in such manner as the Secretary may by regulations prescribe. ``(2) Election irrevocable.--Any election made under this section, and any specification contained in any such election, may not be revoked except with the consent of the Secretary.''. (b) Effective Date.--The amendment made by this section shall apply to property placed in service after the date of the enactment of this Act. SEC. 6. PAYROLL TAX DECREASE FOR 2010. (a) Employees.--Section 3101 of the Internal Revenue Code of 1986 is amended by adding at the end the following new subsection: ``(d) Reduction in Tax Rate for 2010.--In the case of wages received during calendar year 2010-- ``(1) subsection (a) shall be applied by substituting `3.1 percent' for `6.2 percent' in the table contained therein, and ``(2) subsection (b) shall be applied by substituting `0.725 percent' for `1.45 percent' in paragraph (6) thereof.''. (b) Employers.--Section 3111 of such Code is amended by adding at the end the following new subsection: ``(d) Reduction in Tax Rate for 2010.--In the case of wages paid during calendar year 2010-- ``(1) subsection (a) shall be applied by substituting `3.1 percent' for `6.2 percent' in the table contained therein, and ``(2) subsection (b) shall be applied by substituting `0.725 percent' for `1.45 percent' in paragraph (6) thereof.''. (c) Self-Employment.--Section 1401 of such Code is amended by adding at the end the following new subsection: ``(d) Reduction in Tax Rate for 2010.--In the case of a taxable year beginning in 2010-- ``(1) subsection (a) shall be applied by substituting `6.2 percent' for `12.4 percent' in the table contained therein, and ``(2) subsection (b) shall be applied by substituting `1.45 percent' for `2.90 percent' in paragraph (6) thereof.''. (d) Effective Date.-- (1) In general.--Except as provided by paragraph (2), the amendments made by this section shall apply with respect to remuneration paid after December 31, 2009. (2) Self-employment.--The amendment made by subsection (c) shall apply to taxable years beginning after December 31, 2009. SEC. 7. RESCISSION AND REPEAL IN ARRA. (a) Rescission.--Of the discretionary appropriations made available in division A of the American Recovery and Reinvestment Act of 2009 (Public Law 111-5), all unobligated balances are rescinded. (b) Repeal.--Subtitles B and C of title II and titles III through VII of division B of the American Recovery and Reinvestment Act of 2009 (Public Law 111-5) are repealed. SEC. 8. TERMINATION OF TARP AUTHORITY. Section 120 of the Emergency Economic Stabilization Act of 2008 (12 U.S.C. 5230) is amended to read as follows: ``SEC. 120. TERMINATION OF AUTHORITY. ``The authorities provided under sections 101(a), excluding section 101(a)(3), and 102 shall terminate on the date of the enactment of the Economic Freedom Act of 2010.''. SEC. 9. REQUIRING THE SALE OF STOCK AND WARRANTS RECEIVED UNDER TARP. Not later than the end of the 1-year period beginning on the date of the enactment of this Act, the Secretary of the Treasury shall sell all stock and warrants acquired by the Secretary under the Troubled Asset Relief Program under title I of the Emergency Economic Stabilization Act of 2008 (12 U.S.C. 5211 et seq.).

Economic Freedom Act of 2010 - Amends the Internal Revenue Code to: (1) eliminate the tax on the capital gains of individuals and corporations; (2) reduce the maximum corporate income tax rate to 12.5%; (3) allow a permanent and unlimited expensing allowance for depreciable business assets; and (4) reduce payroll tax rates for employers, employees, and self-employed individuals in 2010. Makes permanent the repeal of the estate and generation-skipping transfer taxes. Rescinds unobligated balances available in the American Recovery and Reinvestment Act of 2009. Repeals provisions of such Act relating to the Temporary Assistance to Needy Families program, economic recovery payments, premium assistance for COBRA (health insurance continuation benefits) payments, Medicare and Medicaid health information technology, state fiscal relief, broadband technology, and limits on executive compensation. Amends the Emergency Economic Stabilization Act to repeal the authority for the Troubled Asset Relief Program (TARP). Requires the Secretary of the Treasury to sell all stock and warrants acquired by the Secretary under TARP.

<s>[INST]SECTION 1. SHORT TITLE. This Act may be cited as the ``Economic Freedom Act of 2010''. SEC. 2. ZERO PERCENT CAPITAL GAINS RATE FOR INDIVIDUALS AND CORPORATIONS. (a) Zero Percent Capital Gains Rate for Individuals.-- (1) In general.--Paragraph (1) of section 1(h) of the Internal Revenue Code of 1986 is amended by striking subparagraph (C), by redesignating subparagraphs (D) and (E) and subparagraphs (C) and (D), respectively, and by amending subparagraph (B) to read as follows: ``(B) 0 percent of the adjusted net capital gain (or, if less, taxable income);''. (2) Alternative minimum tax.--Paragraph (3) of section 55(b) is amended by striking subparagraph (C), by redesignating subparagraph (D) as subparagraph (C), and by amending subparagraph (B) to read as follows: ``(B) 0 percent of the adjusted net capital gain (or, if less, taxable excess), plus''. (3) Repeal of sunset of reduction in capital gains rates for individuals.--Section 303 of the Jobs and Growth Tax Relief Reconciliation Act of 2003 shall not apply to section 301 of such Act. (b) Zero Percent Capital Gains Rate for Corporations.-- (1) In general.--Section 1201 of the Internal Revenue Code of 1986 is amended by redesignating subsection (b) as subsection (c), and by striking subsection (a) and inserting the following new subsections: ``(a) General Rule.--If for any taxable year a corporation has a net capital gain, then, in lieu of the tax imposed by sections 11, 511, 821(a) or (c), and 831(a), there is hereby imposed a tax (if such tax is less than the tax imposed by such sections) which shall consist of the sum of-- ``(1) a tax computed on the taxable income reduced by the amount of the net capital gain, at the rates and in the manner as if this subsection had not been enacted, ``(2) 0 percent of the adjusted net capital gain (or, if less, taxable income), ``(3) 25 percent of the excess (if any) of-- ``(A) the unrecaptured section 1250 gain (or, if less, the net capital gain (determined without regard to subsection (b)(2)), over ``(B) the excess (if any) of-- ``(i) the sum of the amount on which tax is determined under paragraph (1) plus the net capital gain, over ``(ii) taxable income, plus ``(4) 28 percent of the amount of taxable income in excess of the sum of the amounts on which tax is determined under the preceding paragraphs of this subsection. ``(b) Definitions and Special Rules.--For purposes of this section-- ``(1) In general.--The terms `adjusted net capital gain' and `unrecaptured section 1250 gain' shall have the respective meanings given such terms in section 1(h). ``(2) Dividends taxed at net capital gain.--Except as otherwise provided in this section, the term `net capital gain' has the meaning given such term in section 1(h)(11).''. (2) Alternative minimum tax.--Section 55(b) of such Code is amended by adding at the end the following new paragraph: ``(4) Maximum rate of tax on net capital gain of corporations.--The amount determined under paragraph (1)(B)(i) shall not exceed the sum of-- ``(A) the amount determined under such paragraph computed at the rates and in the same manner as if this paragraph had not been enacted on the taxable excess reduced by the net capital gain, plus ``(B) the amount determined under section 1201.''. (3) Technical amendments.-- (A) Section 1202(a) of such Code is amended by striking ``50 percent'' and inserting ``100 percent''. (B) Section 1445(e)(1) of such Code is amended by striking ``35 percent (or, to the extent provided in regulations, 15 percent)'' and inserting ``0 percent''. (C) Section 1445(e)(2) of such Code is amended by striking ``35 percent'' and inserting ``0 percent''. (D) Section 7518(g)(6)(A) of such Code is amended by striking ``15 percent (34 percent in the case of a corporation)'' and inserting ``0 percent''. (E) Section 607(h)(6)(A) of the Merchant Marine Act, 1936 is amended by striking ``15 percent (34 percent in the case of a corporation)'' and inserting ``0 percent''. (c) Effective Date.-- (1) In general.--Except as provided in paragraph (2), the amendments made by this section shall apply to taxable years beginning after December 31, 2009. (2) Withholding.--The amendments made by subparagraphs (A) and (B) of subsection (b)(3) shall take apply to dispositions and distributions after the date of the enactment of this Act. SEC. 3. REDUCTION IN CORPORATE INCOME TAX RATES. (a) In General.--Subsection (b) of section 11 of the Internal Revenue Code of 1986 is amended to read as follows: ``(b) Amount of Tax.--The amount of the tax imposed by subsection (a) shall be 12.5 percent of taxable income.''. (b) Conforming Amendments.-- (1) Section 55(b)(1)(B)(i) of such Code is amended by striking ``20 percent'' and inserting ``12.5 percent''. (2) Section 280C(c)(3)(B)(ii)(II) of such Code is amended by striking ``maximum rate of tax under section 11(b)(1)'' and inserting ``rate of tax under section 11(b)''. (3) Section 832(b)(1) of such Code is amended by striking ``rates provided in section 11(b)'' and inserting ``rate provided in section 11(b)''. (4) Sections 244(a)(2)(B), 247(a)(2)(B), 527(b)(1), 835(e), 852(b)(1), 857(b)(4)(A), 860G(c)(1), 904(b)(3)(E)(ii)(II), and 1375(a) of such Code is amended by striking ``highest rate of tax'' and inserting ``rate of tax''. (5) Sections 860E(e)(2)(B), 860E(e)(6)(A)(ii), 860K(d)(2)(A)(ii), 860K(e)(1)(B)(ii), 1446(b)(2)(B), and 7874(e)(1)(B) of such Code are each amended by striking ``highest rate of tax specified in section 11(b)(1)'' and inserting ``rate of tax specified in section 11(b)''. (6) Section 904(b)(3)(D)(ii) of such Code is amended by striking ``(determined without regard to the last sentence of section 11(b)(1))''. (7) Section 962 of such Code is amended by striking subsection (c) and by redesignating subsection (d) as subsection (c). (8) Section 1201(a) of such Code is amended-- (A) by striking ``35 percent (determined without regard to the last 2 sentences of section 11(b)(1))'' and inserting ``15 percent'', and (B) by striking ``35 percent'' in paragraph (2) and inserting ``15 percent''. (9) Section 1561(a) of such Code is amended-- (A) by striking paragraph (1) and by redesignating paragraphs (2), (3), and (4) as paragraphs (1), (2), and (3), respectively, (B) by striking ``The amounts specified in paragraph (1), the'' and inserting ``The'', (C) by striking ``paragraph (2)'' and inserting ``paragraph (1)'', (D) by striking ``paragraph (3)'' both places it appears and inserting ``paragraph (2)'', (E) by striking ``paragraph (4)'' and inserting ``paragraph (3)'', and (F) by striking the fourth sentence. (10) Subsection (b) of section 1561 of such Code is amended to read as follows: ``(b) Certain Short Taxable Years.--If a corporation has a short taxable year which does not include a December 31 and is a component member of a controlled group of corporations with respect to such taxable year, then for purposes of this subtitle, the amount to be used in computing the accumulated earnings credit under section 535(c)(2) and (3) of such corporation for such taxable year shall be the amount specified in subsection (a)(1) divided by the number of corporations which are component members of such group on the last day of such taxable year. For purposes of the preceding sentence, section 1563(b) shall be applied as if such last day were substituted for December 31.''. (c) Effective Date.--The amendments made by this section shall apply to taxable years beginning after December 31, 2009. SEC. 4. ESTATE TAX REPEAL MADE PERMANENT. Section 901 of the Economic Growth and Tax Relief Reconciliation Act of 2001 shall not apply to title V of such Act. SEC. 5. ELECTION TO EXPENSE BUSINESS ASSETS. (a) In General.--Section 179 of the Internal Revenue Code of 1986 is amended to read as follows: ``SEC. 179. ELECTION TO EXPENSE CERTAIN DEPRECIABLE BUSINESS ASSETS. ``(a) Treatment as Expenses.--A taxpayer may elect to treat the cost of any property to which this section applies as an expense which is not chargeable to capital account. Any cost so treated shall be allowed as a deduction for the taxable year in which such property is placed in service. ``(b) Property to Which Section Applies.-- ``(1) In general.--This section shall apply to property-- ``(A) which is-- ``(i) tangible property (to which section 168 applies), or ``(ii) computer software (as defined in section 197(e)(3)(B)) which is described in section 197(e)(3)(A)(i), to which section 167 applies, ``(B) which is section 1245 property (as defined in section 1245(a)(3)) or 1250 property (as defined in section 1250(c)), and ``(C) which is acquired by purchase for use in the active conduct of a trade or business. Such term shall not include any property described in section 50(b) and shall not include air conditioning or heating units. ``(2) Purchase defined.--For purposes of paragraph (1), the term `purchase' means any acquisition of property, but only if-- ``(A) the property is not acquired from a person whose relationship to the person acquiring it would result in the disallowance of losses under section 267 or 707(b) (but, in applying section 267(b) and (c) for purposes of this section, paragraph (4) of section 267(c) shall be treated as providing that the family of an individual shall include only his spouse, ancestors, and lineal descendants), ``(B) the property is not acquired by one component member of a controlled group from another component member of the same controlled group, and ``(C) the basis of the property in the hands of the person acquiring it is not determined-- ``(i) in whole or in part by reference to the adjusted basis of such property in the hands of the person from whom acquired, or ``(ii) under section 1014(a) (relating to property acquired from a decedent). ``(3) Cost.--For purposes of this section, the cost of property does not include so much of the basis of such property as is determined by reference to the basis of other property held at any time by the person acquiring such property. ``(4) Controlled group defined.--For purposes of this section, the term `controlled group' has the meaning assigned to it by section 1563(a), except that, for such purposes, the phrase `more than 50 percent' shall be substituted for the phrase `at least 80 percent' each place it appears in section 1563(a)(1). ``(5) Coordination with section 38.--No credit shall be allowed under section 38 with respect to any amount for which a deduction is allowed under subsection (a). ``(6) Recapture in certain cases.--The Secretary shall, by regulations, provide for recapturing the benefit under any deduction allowable under subsection (a) with respect to any property which is not used predominantly in a trade or business at any time. ``(c) Election.-- ``(1) In general.--An election under this section for any taxable year shall-- ``(A) specify the items of property to which the election applies, and ``(B) be made on the taxpayer's return of the tax imposed by this chapter for the taxable year. Such election shall be made in such manner as the Secretary may by regulations prescribe. ``(2) Election irrevocable.--Any election made under this section, and any specification contained in any such election, may not be revoked except with the consent of the Secretary.''. (b) Effective Date.--The amendment made by this section shall apply to property placed in service after the date of the enactment of this Act. SEC. 6. PAYROLL TAX DECREASE FOR 2010. (a) Employees.--Section 3101 of the Internal Revenue Code of 1986 is amended by adding at the end the following new subsection: ``(d) Reduction in Tax Rate for 2010.--In the case of wages received during calendar year 2010-- ``(1) subsection (a) shall be applied by substituting `3.1 percent' for `6.2 percent' in the table contained therein, and ``(2) subsection (b) shall be applied by substituting `0.725 percent' for `1.45 percent' in paragraph (6) thereof.''. (b) Employers.--Section 3111 of such Code is amended by adding at the end the following new subsection: ``(d) Reduction in Tax Rate for 2010.--In the case of wages paid during calendar year 2010-- ``(1) subsection (a) shall be applied by substituting `3.1 percent' for `6.2 percent' in the table contained therein, and ``(2) subsection (b) shall be applied by substituting `0.725 percent' for `1.45 percent' in paragraph (6) thereof.''. (c) Self-Employment.--Section 1401 of such Code is amended by adding at the end the following new subsection: ``(d) Reduction in Tax Rate for 2010.--In the case of a taxable year beginning in 2010-- ``(1) subsection (a) shall be applied by substituting `6.2 percent' for `12.4 percent' in the table contained therein, and ``(2) subsection (b) shall be applied by substituting `1.45 percent' for `2.90 percent' in paragraph (6) thereof.''. (d) Effective Date.-- (1) In general.--Except as provided by paragraph (2), the amendments made by this section shall apply with respect to remuneration paid after December 31, 2009. (2) Self-employment.--The amendment made by subsection (c) shall apply to taxable years beginning after December 31, 2009. SEC. 7. RESCISSION AND REPEAL IN ARRA. (a) Rescission.--Of the discretionary appropriations made available in division A of the American Recovery and Reinvestment Act of 2009 (Public Law 111-5), all unobligated balances are rescinded. (b) Repeal.--Subtitles B and C of title II and titles III through VII of division B of the American Recovery and Reinvestment Act of 2009 (Public Law 111-5) are repealed. SEC. 8. TERMINATION OF TARP AUTHORITY. Section 120 of the Emergency Economic Stabilization Act of 2008 (12 U.S.C. 5230) is amended to read as follows: ``SEC. 120. TERMINATION OF AUTHORITY. ``The authorities provided under sections 101(a), excluding section 101(a)(3), and 102 shall terminate on the date of the enactment of the Economic Freedom Act of 2010.''. SEC. 9. REQUIRING THE SALE OF STOCK AND WARRANTS RECEIVED UNDER TARP. Not later than the end of the 1-year period beginning on the date of the enactment of this Act, the Secretary of the Treasury shall sell all stock and warrants acquired by the Secretary under the Troubled Asset Relief Program under title I of the Emergency Economic Stabilization Act of 2008 (12 U.S.C. 5211 et seq.).[/INST]Economic Freedom Act of 2010 - Amends the Internal Revenue Code to: (1) eliminate the tax on the capital gains of individuals and corporations; (2) reduce the maximum corporate income tax rate to 12.5%; (3) allow a permanent and unlimited expensing allowance for depreciable business assets; and (4) reduce payroll tax rates for employers, employees, and self-employed individuals in 2010. Makes permanent the repeal of the estate and generation-skipping transfer taxes. Rescinds unobligated balances available in the American Recovery and Reinvestment Act of 2009. Repeals provisions of such Act relating to the Temporary Assistance to Needy Families program, economic recovery payments, premium assistance for COBRA (health insurance continuation benefits) payments, Medicare and Medicaid health information technology, state fiscal relief, broadband technology, and limits on executive compensation. Amends the Emergency Economic Stabilization Act to repeal the authority for the Troubled Asset Relief Program (TARP). Requires the Secretary of the Treasury to sell all stock and warrants acquired by the Secretary under TARP.</s>

many nonlinear dissipative systems that are driven sufficiently far away from thermal equilibrium show selforganization out of an unstructured state : a structured one can appear that is characterized by a ( spatially extended ) pattern which retains some of the symmetries of the system @xcite . convection in binary miscible fluids like ethanol - water , @xmath0he @xmath1he , or various gas mixtures is an example of such systems . it shows rich and interesting pattern formation behavior and it is paradigmatic for problems related to instabilities , bifurcations , and selforganization with complex spatiotemporal behavior . compared to convection in one - component fluids like , e.g. , pure water the spatiotemporal properties are far more complex . the reason is that concentration variations which are generated via thermodiffusion , i.e. , the soret effect by externally imposed and by internal temperature gradients influence the buoyancy , i.e. , the driving force for convective flow . the latter in turn mixes by advectively redistributing concentration . this nonlinear advection gets in developed convective flow typically much larger than the smoothening by linear diffusion pclet numbers measuring the strength of advective concentration transport relative to diffusion are easily @xmath2(1000 ) . thus , the concentration balance is strongly nonlinear giving rise to strong variations of the concentration field and to boundary layer behavior . in contrast to that , momentum and heat balances remain weakly nonlinear close to onset as in pure fluids implying only smooth and basically harmonic variations of velocity and temperature fields as of the critical modes . without the thermodiffusive soret coupling between temperature and concentration any initial concentration deviation from the mean diffuses away and influences no longer the balances of the other fields . hence , the feedback interplay between ( _ i _ ) the soret generated concentration variations , ( _ ii _ ) the resulting modified buoyancy , and ( _ iii _ ) the strongly nonlinear advective transport and mixing causes binary mixture convection to be rather complex with respect to its spatiotemporal properties and its bifurcation behavior . take for example the case of negative soret coupling , @xmath3 , between temperature and concentration fields @xcite when the lighter component migrates to the colder regions thereby stabilizing the density stratification in the quiescent , laterally homogeneous conductive fluid state . then the above described feedback interplay generates oscillations . in fact the buoyancy difference in regions with different concentrations was identified already in @xcite as the cause for traveling wave convection . oscillatory convection appears in the form of the transient growth of convection at supercritical heating , in spatially extended nonlinear traveling wave ( tw ) and standing wave solutions that branch in general subcritically out of the conductive state via a common hopf bifurcation , in spatially localized traveling wave ( ltw ) states , and in various types of fronts . tw and ltw convection has been studied experimentally and theoretically for some time @xcite . the transient oscillatory growth of convection was investigated by numerical simulations @xcite . nonlinear standing wave solutions were obtained only recently @xcite . freely propagating convection fronts that connect subcritically bifurcating nonlinear tw convection with the _ stable _ quiescent fluid do not seem to have been investigated in detail beyond some first preliminary results @xcite . here we determine such fronts in quantitative detail and compare their properties with those of ltws . in narrow rectangular and annular channels convection occurs in the form of rolls with axes oriented perpendicular to the long sidewalls @xcite . these stuctures can efficiently be described in the two dimensional vertical @xmath4 cross section in the middle of the channel perpendicular to the roll axes ignoring variations in axis direction . furthermore , these convection structures have relevant phase gradients only in @xmath5-direction thus causing effectively one dimensional patterns @xcite . when comparing experiments with analytical calculations or numerical simulations performed under the above described conditions it is useful to do that on the basis of reduced rayleigh numbers , @xmath6 , with @xmath7 being the critical one for onset of pure fluid convection for the respective experiment , analytical method , or numerical method . this significantly reduces the dependence of , say , the bifurcation diagrams of convective states on the specific geometry of the respective set - up . in laterally unbounded systems the analytical value for @xmath7 is 1707.762 . _ localized traveling waves . _ for weak negative soret coupling one has observed in experiments a competition between homogeneous laterally extended tw convection and so - called dispersive chaos with an irregular repetitive formation and collapse of spatially localized tw pulses @xcite . during the pulse formation their drift velocities can drop abruptly to about a tenth of the initial group velocity @xcite . we consider this to be a characteristic signal that the lateral redistribution of concentration over the pulse @xcite becomes important and that the strongly nonlinear dynamics sets in . for more negative @xmath8 the collapse is in general less dramatic . there , convection is dominated by isolated strongly peaked localized states . eventually , at @xmath9 a regime is reached where stable ltws coexist near onset with extended tws @xcite . increasing the soret coupling strength further to more negative @xmath10 the band ( @xmath11 ) of rayleigh numbers in which stable ltws exist increases monotonically while shifting upwards as a whole @xmath12 grows stronger than @xmath13 . simultaneosly , the lower band limit for the existence of extended tw states @xmath14 , i.e. , the lowest saddle - node of tws increases even steeper so that eventually for @xmath15 the complete ltw band comes to lie below the existence range of tws , @xmath16 @xcite . ltws consist of slowly drifting , spatially confined convective regions that are embedded in the quiescent fluid . these intriguing structures have been investigated in experiments @xcite and numerical simulations @xcite . a discussion of various theoretical models aiming at their explanation is contained in sec . [ sec : ltwmodels ] . roll vortices grow in a ltw structure out of the quiescent fluid at one end , travel with spatially varying phase velocity @xmath17 to the other end , and decay there back into the basic state . the two interfaces to conduction and with it the whole convective region move with constant , uniquely selected drift velocity @xmath18 . the latter is a function of @xmath19 with magnitude much smaller than the phase velocities . also the oscillation frequency of the ltw is uniquely selected ; it is constant in space and time in the frame that is comoving with its drift velocity . and finally , the length @xmath20 of the convective region of stable ltws and their spatial stucture are uniquely selected . this length grows with increasing heating @xmath21 . a central role for the stable existence of ltws plays a large - scale mean concentration current . extending over the whole ltw it redistributes concentration and thereby changes the buoyancy in a decisive way @xcite . this effect can sustain ltws even at low @xmath21 where no extended tws exist @xcite . _ blinking states in rectangular channels . _ the ltw confinement of convection occurring in translationally invariant annular channels is obviously an inherent process of the hydrodynamic balances . but one has also observed end - wall - assisted or at least end - wall - modified confinement of convection close to the ends of rectangular channels . the weakly nonlinear varieties of such a confinement can largely be understood in terms of the convective behavior of tw packets , their reflection properties at the end walls , and the destructive interaction between left and right traveling patterns @xcite . these effects give rise near onset to a wide range of weakly nonlinear and effectively low dimensional spatiotemporal behavior that depends sensitively on the specific experimental set - up like , e.g. , the end - wall boundary conditions and the system length @xcite . while the linear eigenmodes of such sytems ( linear counterpropagating waves or chevrons ) @xcite are laterally symmetric or antisymmetric localization sets in via a temporal amplitude modulation . thereby convection is alternatingly weakened and enhanced in the left and the right part of the system part giving rise to a blinking state @xcite . the so - called chaotic blinking states @xcite seem to be the analogue of the chaotic dispersive pulse formation in annular containers @xcite . also blinking modes with different frequencies at both ends of the channel were observed @xcite . but their possible relation to a large - scale mean concentration variation @xcite produced by nonlinear propagating waves in a finite cell has not been discussed . _ wall - attached structures . _ at larger @xmath21 one has observed wall - attached tw structures with amplitudes confined to the vicinity of one or both end walls . these wall - attached convective patches @xcite are closely related to free ltws @xcite . they are strongly nonlinear as indicated by their low frequency @xcite . moreover , their spatial structure and their region of existence is largely unaffected by the details of the lateral boundaries or by the container length in contrast to the linear and weakly nonlinear behavior described above @xcite . the more extensive wall - attached structures show some similarities with front - like states . note , however , that here the source or the sink of the propagating rolls is pinned near a wall and the interface to the quiescent fluid in the bulk of the channel does not move @xcite . _ our numerical simulations . _ our numerical simulations have been performed in order to elucidate in quantitative detail the properties of relaxed nonlinear tw convection structures that contain an interface ( or two of them ) to the quiescent fluid as an integrated structural element . we compare for a wide range of soret coupling strengths front states and ltw states showing what they have in common and how they differ . we focus our interest to those parameters where the quiescent conductive state of the fluid is stable and where the solutions describing spatially extended , laterally periodic tw convection bifurcate subcritically out of it . the system we have in mind is a binary fluid layer of thickness @xmath22 which is bounded by two solid horizontal plates perpendicular to the gravitational acceleration @xmath23 . the fluid might be a mixture of water with the lighter component ethanol at a mean concentration @xmath24 . it is heated from below . the temperatures at the plates are @xmath25 . the variation of the fluid density @xmath26 due to temperature and concentration variations is governed by the linear thermal and solutal expansion coefficients @xmath27 and @xmath28 , respectively . both are positive for ethanol - water . the solutal diffusivity of the binary mixture is @xmath29 , its thermal diffusivity is @xmath30 , and its viscosity is @xmath31 . length and time is scaled by @xmath22 and @xmath32 , respectively , so that velocity is measured in units of @xmath33 . temperatures are reduced by the vertical temperature difference @xmath34 across the layer and concentrations by @xmath35 . the scale for the pressure is given by @xmath36 . then , the balance equations for mass , momentum , heat , and concentration @xcite read in oberbeck boussinesq approximation @xcite [ eq : baleqs ] @xmath37\label{eq : baleqheat}\\ \partial_t \delta c = - { \mbox{\bf\boldmath $ \nabla$}}\cdot \left [ { { \bf u } } \delta c - l{\mbox{\bf\boldmath $ \nabla$}}\left(\delta c -\psi \delta t\right ) \right]\ . \label{eq : baleqconc } \end{aligned}\ ] ] here , @xmath38 and @xmath39 denote deviations of the temperature and concentration fields , respectively , from their mean @xmath40 and @xmath24 and @xmath41 is the buoyancy . the dufour effect @xcite that provides a coupling of concentration gradients into the heat current and a change of the thermal diffusivity is discarded in ( [ eq : baleqheat ] ) since it is relevant only in few binary gas mixtures @xcite and possibly in liquids near the liquid vapor critical point @xcite . besides the rayleigh number @xmath42 measuring the thermal driving of the fluid three additional numbers enter into the field equations : the prandtl number @xmath43 , the lewis number @xmath44 , and the separation ratio @xmath45 . here @xmath46 is the thermodiffusion coefficient @xcite and @xmath47 the soret coefficient . they measure changes of concentration fluctuations due to temperature gradients in the fluid . @xmath10 characterizes the sign and the strength of the soret effect . negative soret coupling @xmath10 ( i.e. , positive @xmath47 for mixtures like ethanol water with positive @xmath48 and @xmath49 ) induces concentration gradients of the lighter component that are antiparallel to temperature gradients . in this situation , the buoyancy induced by solutal changes in density is opposed to the thermal buoyancy . when the gradient of the total buoyancy exceeds a threshold , convection sets in typically in the form of straight rolls . for sufficiently negative @xmath10 the primary instability is oscillatory . ignoring field variations along the roll axes we describe here 2d convection in an @xmath5@xmath50 plane perpendicular to the roll axes with a velocity field @xmath51 to find the time - dependent solutions of the above partial differential equations subject to realistic horizontal boundary conditions @xcite we performed numerical simulations with a modification of the sola code that is based on the mac method @xcite . this is a finite - difference method of second order in space formulated on staggered grids for the different fields . the poisson equation for the pressure field that results from taking the divergence of ( [ eq : baleqveloc ] ) was solved iteratively with the artificial compressibility method @xcite by incorporating a multi - grid technique . throughout this paper we consider mixtures with @xmath52 , @xmath53 , and various negative values of @xmath10 that are easily accessible with ethanol - water experiments . the paper is organized as follows : in sec . [ sec : fronts ] we first describe our methods for characterizing the various convective states . then we present results for the two different types of tw front states that can arise in laterally homogeneous mirror symmetric systems with either the phase propagating out of the quiescent fluid or into it . also transient two - front structures are discussed . [ sec : ltw ] deals with ltw states and their relation to fronts . the transient dynamics towards the selected ltw , the stabilization via front repulsion , the difference between long and short ltws , and a critical appraisal of ltw models are topics covered here . in sec . [ sec : compare - exp ] we present a comparison with experiments and a discussion . the last section contains a conclusion . here we discuss front solutions where part of the system is occupied by the quiescent fluid while the other one shows fully developed , saturated , strongly nonlinear tw convection with laterally homogeneous amplitude . strictly speaking these two states are realized only in the two opposing limits of @xmath54 . we focus our investigation of fronts on parameters where the quiescent fluid state is stable and where the tw solutions bifurcate subcritically out of the conductive state . then , any _ linear _ growing and spreading of infinitesimal , localized convective perturbations in the quiescent fluid which could possibly dominate the low amplitude behavior of fronts as in the case of an unstable zero amplitude state @xcite is absent . little general is known about pattern forming fronts in real bistable systems @xcite . most of the research activities were centered on fronts in the quintic ginzburg - landau equation @xcite . one can expect that the front properties are fixed by a strongly nonlinear eigenvalue problem describing a heteroclinic orbit between the two involved states . some of these front solutions will be unstable . there might be also multistable coexistence of fronts so that depending on initial conditions and on the history of the ( control ) parameters different fronts could finally be realized . we call a front uniquely selected when our numerical simulations indicated that different formation processes ended in the same front for a fixed parameter combination . fronts can be classified into coherent and incoherent ones @xcite . we focus here on the first kind which in our system are characterized as strictly time periodic states in a frame that is comoving with the front s velocity @xmath55 . such a front state being monochromatic is a global nonlinear mode . its frequency is an eigenvalue , i.e. , a global constant in space and time so that the convection oscillations have everywhere the same period . thus , we do not consider here , e.g. , complex large scale or chaotic spatiotemporal interface behavior . the coherent fronts of the various hydrodynamic fields and quantities in this paper have a smooth and basically monotonous profile which connects the quiescent fluid with the nonlinear saturated extended tw . the transition region between conduction and convection that is characterized by large amplitude variations is quite short and consists typically only of about 3 -4 convection rolls . we call this transition region also the interface between conduction and convection . if the selected front pattern is incompatible with any stable bulk structure there are two possibilities : ( _ i _ ) a perturbation in the unstable convection bulk grows and expands towards the interface . this would destroy front coherence and could lead to more complex large scale variations , perhaps chaotic spatiotemporal behavior . ( _ ii _ ) the interface region is only convectively unstable against perturbations of the bulk nonlinear tw . then initially localized perturbations would be advected out of every finite system and could not reach the unperturbed interface region of the front . we call a front to be of type @xmath56 when its envelope grows at @xmath57 out of the basic quiescent state . otherwise it is a @xmath58front . then the amplitude falls to zero at @xmath59 @xcite . the phase of the convection pattern in a front state of type @xmath56 can either propagate to the left or to the right and similarly for the @xmath58front state . hence , one would have to discuss four front states separately . however , because of the invariance of the system under @xmath60 a @xmath56front state with positive ( negative ) phase velocity @xmath61 is the mirror image of the @xmath58front state with negative ( positive ) @xmath61 . therefore , it suffices to consider only the front states that consist of roll vortices traveling , say , in positive @xmath5-direction and to use the superscript @xmath56 or @xmath58 to identify the properties of the front in question in a unique way . so , the phase velocities of all oscillatory convective structures investigated in this paper are positive . we call the direction of positive @xmath5 into which the phase propagates also downstream and the opposite one upstream. so , to sum up our notation : in a @xmath56front state the quiescent fluid is located upstream and a source of phase with the latter propagating out of the conductive state into convection . in a @xmath58front the quiescent fluid is located in downstream direction and a sink since phase moves out of convection into conduction . fig . [ fig : frontpics ] shows fronts of each type . under the @xmath56front ( left half of fig . [ fig : frontpics ] ) convection rolls grow out of the quiescent fluid and saturate in a downstream bulk tw . on the other hand , a @xmath58front ( right half of fig . [ fig : frontpics ] ) annihilates roll vortices . in this process their phase velocity is accelerated [ cf . the increase in the lateral profile of @xmath17 in fig . [ fig : frontpics](f ) ] and they are stretched horizontally . it is clear from fig . [ fig : frontpics ] that the quiescent ( convecting ) region expands into the convecting ( quiescent ) one when the velocity @xmath62 of the @xmath56front is positive ( negative ) and vice versa for the @xmath58front . in order to monitor how well the fluid is mixed along the front we always determined for the relaxed front states the mixing number @xmath63^{1/2}\ ] ] as a function of lateral position @xmath5 . it basically measures the mean square of the deviations @xmath64 of the concentration field from its global mean : the overbars imply a vertical average and the brackets a temporal average at the specific horizontal location @xmath5 in the frame comoving with the front velocity @xmath55 . the subscript _ cond _ denotes the reference quiescent conductive state with its linear vertical concentation variation . the mixing number is defined such that @xmath65 in a perfectly mixed fluid and @xmath66 in the quiescent state . in laterally extended tws @xmath67 and with it @xmath61 increase when the concentration variations become larger @xcite . in fact , there is a universal scaling relation between @xmath68 and @xmath67 @xcite which shows that @xmath68 and @xmath61 are linearly related to each other . this relation also holds for the bulk part of front states far away from the interface where the convection is tw - like with only slow spatial amplitude variation ( fig . [ fig : frontpics ] ) . the phase shift between the concentration and velocity waves in the tw - like bulk of the front states sustains as in extended tw states a mean lateral concentration current @xmath69 @xcite : @xmath70 where @xmath71 is the velocity field and @xmath38 the temperature deviation from the global mean . again , the brackets imply a temporal average in the frame that is comoving with the front velocity . the lewis number @xmath52 being rather small in our simulations implies that @xmath72 is dominated by the advective contribution except in those boundary regions in which @xmath71 becomes small . the vertical variation of @xmath72 is such that positive ( negative ) @xmath39 is transported in phase direction in the upper ( lower ) half of the layer . this transport causes a large - scale concentration redistribution in a front state between its tw bulk and its interface to the quiescent fluid and it is responsible for the different characteristic structures of the interfaces in a @xmath56 and a @xmath58front as we will see further below . we simulated systems containing up to 160 rolls . the initial state was prepared by filling one half of the sytem with a nonlinear tw that was previously generated with periodic boundaries to have some fixed wavelength @xmath73 . the other half contained the stable temperature and concentration distribution of the pure quiescent basic state . to simulate @xmath56fronts in infinite systems that connect to developed tw convection with some wavelength @xmath73 far away from the interface between conduction and convection we imposed at the downstream boundary @xmath74 of our computation domain the periodicity condition @xmath75 . for the case of @xmath58fronts we found that imposing the analogous condition at the upstream boundary of the developed tw part at @xmath76 typically will introduce perturbations that can grow in downstream direction for example when the tw region is eckhaus unstable . the different aspects of the stability of @xmath56 and @xmath58fronts are discussed further below in the paper . after a relaxation time of typically 100 to 200 vertical thermal diffusion times we then could observe under certain conditions a coherent front state connecting a quiescent region of the system to a tw with asymptotic wavelength @xmath73 . here the fact that the frequency @xmath67 of such a coherent front state is constant in space and time in the frame that is comoving with the front velocity @xmath55 proved to be a good relaxation criterion to effectively determine whether such a state had been obtained . as soon as the growing convection rolls in a @xmath56front have become sufficiently nonlinear , i.e. , when their lateral flow velocity @xmath77 has grown up to about their phase velocity @xmath61 [ e.g. , close to the vertical arrow in fig . [ fig : frontpics](c ) ] they start to alternatingly suck in positive ( blue ) and negative ( red ) @xmath39 from the top and bottom concentration boundary layers , respectively . it is transported away into the well mixing convection bulk and replaced at the interface location by neutral ( yellow / green ) @xmath39 . note that increasing @xmath77 beyond @xmath61 causes the appearence of closed streamlines of the velocity field in the frame comoving with the phase velocity of a traveling roll @xcite . these closed streamlines regions are responsible for the characteristic roll structure of the @xmath78 field in fig . [ fig : frontpics](a ) : positive ( negative ) @xmath39 is collected from the top ( bottom ) boundary layers and transported within the homogeneously mixed closed streamline regions in phase direction while mean concentration , @xmath79 , is advected along the meandering `` green - yellow stripe '' in fig . [ fig : frontpics](a ) to the left @xcite . the mean concentration current @xmath72 resulting from this complicated concentration redistribution is shown in fig . [ fig : frontpics](i ) . all in all , mean concentration is accumulated ( depleted ) at the @xmath56 ( @xmath58 ) front interface . the concentration redistribution reduces at the interface of the @xmath56front the soret - induced solutal stabilization that occurs to the left of it as a result of the large conductive vertical concentration gradient : at the interface one can observe a minimal mixing number [ fig . [ fig : frontpics](e ) ] and with it a buoyancy overshoot [ fig . [ fig : frontpics](g ) ] which is sufficiently large to sustain local convection growth there and cause even invasion of convection into the quiescent region whenever @xmath80 . with the fluid being well mixed there , i.e. , with @xmath68 being small the local phase velocity is also small there in fact the minimum of @xmath17 in fig . [ fig : frontpics](e ) lies close to the one in @xmath68 . since the strongly stable quiescent fluid to the left of the @xmath56front prohibits a well developed advectively mixing front tail the reduction of @xmath39 variations there is driven primarily by diffusion . the latter having a characteristic time scale given by @xmath52 explains why the front velocities are much smaller than the fast phase velocity . when @xmath21 is increased @xmath81 tends to become ( more ) negative : convection to the right of the @xmath56interface can now , with increased heating , better invade the quiescent fluid to the left of it and thus @xmath82 . similarly , when @xmath10 is increased , i.e. , when the convection suppressing soret effect is diminished the expansion of tw convection is favoured and thus @xmath83 . moving along the @xmath56front in fig . [ fig : frontpics ] to the right from the interface towards the asymptotic tw state at large @xmath5 there develops an equilibrium between the @xmath39 feed - in from the boundary layers at the plates and the amount of advective mixing : the concentration contrast between two neighboring rolls increases on the way towards the tw bulk . with it the phase speed @xmath17 , the wavelength @xmath84 , and the lateral concentration current @xmath72 grow monotonously up to their asymptotic tw values . this growth extends laterally over a wide interval which itself increases when the soret coupling becomes stronger . we found that the minimal wavelength in a @xmath56front state is located at the interface and more remarkably that it is about @xmath85 for _ all @xmath21 and @xmath10 _ that we have simulated . we have no real quantitative explanation for this strong universal selection of the local wavelength at the interface . intuitively the growing rolls are squeezed in the region with the negative lateral gradient of @xmath68 . the squeezing is relaxed when the rolls begin to absorb high concentration contrasts from the plate layers which increases @xmath61 again [ arrow in fig . [ fig : frontpics](c ) ] . it is interesting to note that the mean concentration current @xmath72 of tws becomes maximal close to the tw saddle node , i.e. , where the asymptotic tw parts of our front states are located . finally we mention that the front states do not sustain a measurable lateral meanflow ; the quiescent fluid prohibits that . on the other hand , extended tws in laterally periodic systems show in general a reynolds stress - induced meanflow of the order @xmath86 @xcite . but it goes through zero just near the tw saddle node . in figs . [ fig : psi25v+om+k - r ] - [ fig:3dpsi40om - k - r ] we show the bifurcation properties of fronts in comparison with ltws and laterally periodic tw states . we use front velocities and frequencies being temporally and spatially constant as order parameters to characterize all of the aforementioned oscillatory states . in addition we also consider the local wave numbers of front states and of ltws in the bulk spatial regions where @xmath87 has reached a plateau , i.e. , sufficiently away from any interface to conduction . figs . [ fig : psi25v+om+k - r ] and [ fig:3psisv+l+w - r ] show that the front velocities of @xmath56 and @xmath58fronts vary quite differently as a function of @xmath21 . the former decrease linearly with growing @xmath21 and the latter increase , albeit not linearly . thus , there is a crossing at @xmath88 where @xmath81 becomes equal to @xmath89 , so that both fronts move with the same velocity . at this rayleigh number the length @xmath90 of the ltws diverges , i.e. , @xmath91 . there , and strictly speaking only there , this limiting ltw can be seen as a state consisting of two fronts . the frequency and bulk wave number selected by a @xmath56front and of a very long ltw are close to those of the respective , laterally extended saddle - node tw ( figs . [ fig : psi25v+om+k - r ] , [ fig:4psisom+r - k ] , [ fig:3dpsi40om - k - r ] ) . a somewhat hand - waving explanation for the selection of the saddle - node frequency is as follows : with ( _ i _ ) convection growing out of conduction in a @xmath56 front , with ( _ ii _ ) small - amplitude extended tw perturbations of the latter oscillating according to a purely linear balance with the large hopf frequency , and with ( _ iii _ ) the tendency to decrease @xmath67 with growing convection amplitude the saddle - node frequency is the first , i.e. , the largest possible eigenfrequency of the full nonlinear front problem to allow for a stable tw region away from the interface . a stable front state that has a tw bulk part extending laterally to infinity with frequency @xmath67 and wave number @xmath92 can not be realized at @xmath21-values that lie below the saddle - node curve of laterally extended tws , cf . the curve marked @xmath93 in the @xmath94 plane of fig . [ fig:3dpsi40om - k - r ] . thus , the lowest rayleigh number @xmath95 for the existence of fronts is @xmath96 , i.e. , the location of the tip of the nose - shaped tw bifurcation surface like the grey surface in fig . [ fig:3dpsi40om - k - r ] . ahead of this nose one can not realize front states because at such locations there are no tws to which the interface from conduction could connect . the tw bulk parts of our @xmath56fronts are practically saddle - node tws that have bulk wave numbers on the saddle - node curve @xmath97 . furthermore , it is interesting to note that they are on the _ large_-@xmath92 branch of @xmath97 the big plusses in fig . [ fig:3dpsi40om - k - r ] marking the bulk values of the front states lie all above @xmath98 . in fact , in all our simulations we did not find front states with bulk wave numbers smaller than @xmath99 . this value marks for all @xmath10 that we investigated the tip of the nose - shaped tw bifurcation surface like the grey surface in fig . [ fig:3dpsi40om - k - r ] . in contrast to fronts , however , ltws of _ finite _ length @xmath90 can coexist bistably together with the conductive state at @xmath21-values well below @xmath97 : they can sustain over a finite lateral length convection with frequencies and bulk wave numbers ( big bullets in fig . [ fig:3dpsi40om - k - r ] ) ahead of the grey tw surface for reasons that are explained in ref . this also shows that fronts and ltws are quite different states . in the limit @xmath100 the ltw states merge at @xmath101 with a tw whose wave number and frequency is close to the tw saddle - node as shown in figs . [ fig : psi25v+om+k - r ] , [ fig:4psisom+r - k ] , [ fig:3dpsi40om - k - r ] . therefore , @xmath102 increases when the soret coupling becomes more negative but @xmath103 decreases . for @xmath15 it moves towards the tip of the tw nose at @xmath104 . simulations of @xmath56fronts that were done at fixed control parameters @xmath19 with different initial conditions , e.g. , different wave numbers of an initial tw part produced in general a uniquely selected final front state with the same frequency and the same asymptotic bulk tw part . during the formation process initial wave structures with the wrong wave patterns propagated out of the system in the direction of the phase velocity and were substituted by convection that was selected by the front . that also explains why our tw boundary condition @xmath75 at the downstream end has no measurable influence on the @xmath56front state even when @xmath73 differs from the front - selected value . the substitution dynamics is documented in fig . [ fig : frontrelaxation ] . there a tw bulk part was prepared initially at @xmath105 with a wavelength of @xmath106 and phase velocity @xmath107 . the spatial region to the right of the interface to conduction is then invaded by the front - selected tw pattern that has a smaller bulk wavelength of @xmath108 and that propagates with a faster phase velocity of @xmath109 . the wave number is increased via several phase annihilating defects . all our @xmath56interfaces selected bulk tw wave numbers close to the large-@xmath92 branch of the tw saddle - node curve ; cf . [ fig:4psisom+r - k](b ) and [ fig:3dpsi40om - k - r ] for @xmath110 and fig . [ fig : psi25v+om+k - r](c ) for @xmath111 . thus , these wave numbers are too large to be eckhaus stable @xcite . however , these fully developed tws were only convectively unstable @xcite : perturbations could grow but while doing so they were advected sufficiently fast downstream in the direction of the tw phase propagation so that they could not influence the upstream part of the @xmath56front state in a persistent way . in systems with sufficiently long downstream section of the front state the growing fluctuations have sufficient time or are sufficiently fast growing , respectively to reach a critical amplitude at which two neighboring rolls are annihilated @xcite as , e.g. , for the parameters of fig . [ fig : irregularfront ] . because noise can not be prevented in general one observes then such phase defects as in fig . [ fig : irregularfront ] at irregular points in time and space beyond a certain downstream growth length that is related to size of the noise and the growth rate . the associated roll - annihilation events can lead to an effectively reduced mean wave number in the very far downstream region of the convection bulk . thus , the coherent part of the @xmath56front close to the interface to conduction is followed by a second incoherent , chaotic phase front consisting of the erratically occurring phase defects . this phase front connects the smooth primary eckhaus unstable section to a smooth eckhaus stable tw with smaller wave number that is realized at larger downstream distances . for parameters for which the growth rate of perturbations of the primary front - selected tw is lower than the one of fig . [ fig : irregularfront ] one does not observe in short systems the erratically occurring phase defects and even less so the eckhaus stable final downstream tw state . indeed , that was the situation for most of our front states . we finally mention that we could also generate front states with frequencies larger than those of the laterally extended saddle node tws [ dotted lines in fig . [ fig : psi25v+om+k - r](b ) and fig . [ fig:4psisom+r - k](a ) ] , i.e. , with frequencies that lie above the respective dotted line in the respective 3d plot similar to the one of fig . [ fig:3dpsi40om - k - r ] . however , we suppose that in sufficient long systems and after long enough times these unstable tw realizations develop a @xmath58front in the downstream bulk possibly induced by roll annihilating defects @xcite . the right half of fig . [ fig : frontpics](b ) shows a typical @xmath58front . the mean lateral concentration current in the tw bulk part to the left of the @xmath58interface to conduction shuffles positive ( negative ) @xmath39 in the upper ( lower ) part of the layer towards the @xmath58interface . thus , a large vertical concentration gradient is maintained slightly ahead of it that strongly stabilizes the conduction regime to the right of the @xmath58interface : there the mixing number @xmath68 is even larger than 1 . in this way the tw oscillations are damped and the conduction regime is shielded against a rapid invasion of convection . the increase of @xmath112 upon approaching the interface from the convection side causes and is related to a similar increase of @xmath17 and @xmath87 . the rolls disperse with growing phase velocity @xmath17 over a short lateral distance at the interface . the decreasing convection amplitude lowers the mean concentration current and causes @xmath112 to grow further . this in turn enhances @xmath17 and @xmath87 leading to smaller convection amplitude and so on . it is therefore the strongly nonlinear lateral concentration current @xmath72 which is responsible for the rapid self amplified decay process of convection at the @xmath58interface . with increasing @xmath21 the front velocity @xmath89 changes sign , becomes positive and continues to grow [ fig . [ fig : psi25v+om+k - r](a ) and fig . [ fig:3psisv+l+w - r](a ) ] because the quiescent state becomes less stable when increasing @xmath21 . the slope of @xmath113 , i.e. , the increase of the front velocity is considerably steeper for negative @xmath89 than for positive ones : the strongly stabilizing solutal stratification ahead of the interface hinders convection to intrude into the quiescent fluid region but favours the latter to replace the tw part . the upstream lateral distance over which the @xmath58interface to conduction influences the tw to the left of it is definitely smaller than the downstream influence length of the @xmath56interface on the convective bulk . in the former case one can not observe a difference to an extended tw state at an upstream distance of , say , 10 - 15 rolls while in the latter case the downstream convection properties approach the asymptotic bulk tw behavior only over a significantly longer distance . so , in particular the phase dilatation at a @xmath58interface does not propagate upstream into the tw bulk against the fast phase flow . this also explains why in the formation process of a @xmath58front tw properties that were initially present in a developed form are conserved . in fact , we could produce coherent @xmath58fronts for a fixed @xmath21 with different wave numbers of the bulk tw part out of a whole band near the saddle node wave numbers @xmath114 . only for higher @xmath21 and initial wave numbers away from @xmath115 we observed long - time transient incoherent front behavior . here this transition to incoherence may correspond to a transition from a convectively to an absolutely unstable regime concerning the propagation of phase dilatations in upstream direction . we should like to stress again that in contrast to @xmath58fronts which depend on the preparation process the asymptotic downstream tw part of a @xmath56front is uniquely selected as discussed in the previous section . thus , for a particular @xmath21 we have found only a single coherent @xmath56front . for definiteness and for the sake of comparison with @xmath56fronts we show in the figs . of this paper the properties of @xmath58front states that have a bulk tw part which itself was selected by a @xmath56front . this , however , has a slight numerical drawback stemming from the convective eckhaus instability of this tw part : ever present phase noise ( in particular at the boundary of the upstream tw region ) is enhanced on the downstream way towards the @xmath58interface . we think that this effect is responsible for fluctuations in our frequency measurements of @xmath58fronts . these data are therefore not shown in figs . [ fig : psi25v+om+k - r](b ) and fig . [ fig:4psisom+r - k ] . however , in our simulations the upstream part of the @xmath58fronts were too short to allow for the full development of phase slip defects . consider a set - up where a @xmath56front generates a very long tw part that develops back into the quiescent fluid via a coherent @xmath58front . if the convective part is laterally sufficiently long then this structure appears as a two - front structure with the tw part being spatially confined between a @xmath56 and a @xmath58interface to conduction . this structure will in general either expand or shrink laterally . only when the two front velocities @xmath81 and @xmath89 are equal , i.e. , at the crossing points @xmath88 of the curves in figs . [ fig : psi25v+om+k - r](a ) and [ fig:3psisv+l+w - r](a ) one can have a stationary state , namely , a ltw with diverging length @xmath90 . we have simulated such structures at @xmath116 and @xmath117 for rayleigh numbers for which @xmath118 , i.e. , to the right of the crossing in figs . [ fig : psi25v+om+k - r](a ) and [ fig:3psisv+l+w - r](a ) so that these two - front structures expand . their properties are practically identical to those of the respective single - front states . the two - front structures have a technical advantage over the simulation of single fronts : we could use a periodic boundary condition that was located in the quiescent region of the former . this avoids the noise that is induced at the upstream tw boundary of a single @xmath58front state . with this noise source being absent in our two - front structures the frequency fluctuations at the @xmath58 interfaces of single @xmath58front states did not occur . when we reduced @xmath21 then the velocities of the two fronts approached each other along the lines in figs . [ fig : psi25v+om+k - r](a ) and [ fig:3psisv+l+w - r](a ) that were obtained from velocity measurements of single - front states . in that way we could reproduce the unique crossing point at @xmath88 where @xmath119 and where ltws with diverging @xmath90 exist with a drift velocity @xmath18 given by the crossing velocity . in addition to expanding two - front structures we simulated also shrinking ones for a particular parameter combination ( @xmath120 , for which @xmath121 ) that is located in fig . [ fig:3psisv+l+w - r](a ) at @xmath122 . as an example consider the large two - front structure as in fig . [ fig : ltwapproach ] . the @xmath56front selects in the bulk of this initial two - front structure a saddle node tw with wavelength @xmath123 . in the course of time the velocity @xmath89 of the @xmath58front approaches that of the @xmath56front and a stationary ltw forms with length @xmath124 that drifts with the velocity @xmath125 and oscillates with the frequency of the @xmath56front . these values of the @xmath56front remain practically unchanged in the whole process . we produced ltw states with very large length @xmath90 immediately below the rayleigh number @xmath91 . there , @xmath90 diverges thus marking the upper existence boundary of ltw states . and there , the velocities @xmath81 and @xmath89 of the @xmath56 and @xmath58front states , respectively , become equal . see figs . [ fig : psi25v+om+k - r ] and [ fig:3psisv+l+w - r ] for the corresponding results in the range of @xmath126 that we have investigated in this paper . upon decreasing @xmath21 below the threshold @xmath127 one finds uniquely selected ltw states . depending on parameters they can coexist stably with front states , extended tw states , and the quiescent basic state . for completeness we include here in fig . [ fig : phasediagram ] a phase diagram of the @xmath128 plane where all the ltws that we have numerically obtained in the range @xmath129 are shown by vertical bars together with the saddle - node location @xmath130 of extended tws ( full line ) and the oscillatory hopf bifurcation threshold @xmath131 for tws ( dashed line ) . but in this work we focus on the range @xmath126 . we should like to emphasize again that we found ltws for @xmath126 only in the parameter regime below @xmath127 , i.e. , to the left of the crossing points in figs . [ fig : psi25v+om+k - r](a ) and [ fig:3psisv+l+w - r](a ) where the velocities of independent single fronts become equal . thus , ltws exist at these @xmath10 only for parameters for which @xmath132 , i.e. , for which independent fronts would approach each other : eventually any convective region between them would shrink to zero and the quiescent conductive state would result if this interface motion would continue without change . however , the stabilization effects that allow in such a situation a uniquely selected stable and robust ltw are easily understood with the help of the investigations in the following subsections . on the other hand , for @xmath133 the front velocities are such that a two - front structure expands . a typical transient dynamics towards the uniquely selected ltw is shown in fig . [ fig : frontrelaxation ] for @xmath134 . here the initial condition was a very broad two - front structure that was prepared at @xmath135 where it shrinks with @xmath132 [ fig . [ fig:3psisv+l+w - r](a ) ] . in fact , the @xmath58front moves to the left with a speed that is about three times higher than that of the @xmath56front . in the following shrinking process where the @xmath58front closes up to the @xmath56front the latter does not change its velocity at all and the former keeps its velocity as long as the bulk tw part between the two fronts is effectively asymptotic , i.e. , without lateral variation . this behavior reflects the fact that in such broad two - front structures there is practically no interaction between the fronts when their distance is so large that an asymptotic tw part is realized between the interfaces to conduction . however , the situation changes when the convective region between the interfaces becomes less extended since it requires a finite downstream growth length behind a @xmath56interface over which the convection properties still vary with small gradients before the asymptotic tw is reached . the slow lateral variation is best seen in the mixing number @xmath112 in fig . [ fig : frontpics](e ) reflecting the slow variation of the concentration distribution and in the related convective contribution @xmath136 [ fig . [ fig : frontpics](g ) ] to the local buoyancy . when the front separation comes to the order of this length one can not speak any more of a two - front structure with two independent fronts : for the parameters of fig . [ fig : frontrelaxation ] the velocity of the formerly independent @xmath58front changes continuously from @xmath137 to @xmath138 , i.e , to the velocity of the preceeding @xmath56front and a coherent and robust ltw forms which moves with a drift velocity that is determined by the @xmath56front , @xmath139 . during this slowing - down process of the @xmath58interface its structure changes to that of the characteristic decay interface to conduction of a ltw . therein the two interfaces , i.e. , the former @xmath56 and @xmath58fronts , respectively , are in a robust equilibrium with each other at a uniquely selected fixed distance @xmath90 that depends on @xmath140 as shown in fig . [ fig:3psisv+l+w - r](b ) . so the @xmath58interfaces of ltws and front states do not influence significantly the upstream part of these stuctures . hence , the local concentration barrier ahead of the @xmath58interface does not select the drift velocity of ltws as speculated previously @xcite . it is rather the @xmath56interface that is the more important one . note that it is the downstream wake in the concentration field of the preceeding @xmath56front that effectively slows down the @xmath58front : when the latter reaches the region where the mixing number @xmath112 [ fig . [ fig : frontpics](e ) ] starts to decrease towards the preceeding @xmath56front , i.e. , when the convective contribution @xmath136 [ fig . [ fig : frontpics](g ) ] to the local buoyancy starts to increase then the speed of the approaching @xmath58interface has to slow down . this distance over which the @xmath56front influences the @xmath58front in a two - front structure grows when the soret coupling becomes stronger . for example at @xmath141 a separation of about 160 rolls between the two interfaces is not sufficient to ensure independence . the sensitive dependence of the velocity of the @xmath58interface on the concentration - induced buoyancy variation in the wake behind the @xmath56front is the main reason for the robust localization mechanism of ( long ) ltws . the invasion of conduction into the convective region via the trailing @xmath58interface is stopped at just that well defined distance from the @xmath56front where the concentration - induced convective buoyancy @xmath136 has become sufficiently large . the latter increases monotonously towards the well mixed region under the @xmath56interface since this degree of advective mixing decreases gradually in the wake behind the @xmath56interface . see , e.g. , ref . @xcite for an explanation of the associated interplay of diffusion and advection which both reduce concentration gradients and the soret effect which generates them . of course , the effect of stopping the approaching @xmath58interface at a particular distance from the @xmath56interface can be interpreted as an effective repulsive interaction between them . the structural similarity between long ltws and fronts is documented in fig . [ fig : frontpics ] . differences between the full lines ( fronts ) and the dashed ones ( ltw ) are visible only in the case of the @xmath58front in fig . [ fig : frontpics](d , f , h ) . here the bulk asymptotic tw that is realized to the left of the @xmath58front differs slightly from the plateau tw in the ltw . the above mentioned @xmath39 redistribution via @xmath72 enhances the buoyancy at the @xmath56interface and leads there to a self - consistent stabilization of convection against invasion of conduction at the @xmath56front . this mixing effect makes stable ltws possible even for low heating rates @xmath21 where neither extended tw convection nor fronts exist . long ltws are characterized by a wide tw part with a well developed plateau with almost no lateral variation in the convection properties like , e.g. , @xmath17 or @xmath112 @xcite . the tw plateau separates the growth and the decay part of convection at the @xmath56 and @xmath58interface , respectively and it provides a communication mechanism favoring one direction : the first region is shielded from the second one by the fast downstream phase propagation . like in a single @xmath58front state the @xmath58interface of the ltw does not influence the upstream tw ; it only manages the decay transition of the tw vortices into the quiesent fluid . thus , the @xmath56front character at the @xmath56interface is also present in the ltw . and the properties of long ltws are dominated by and similar to those of the single @xmath56front at the same @xmath21 if the latter exists . for example , the drift velocities of long ltws agree with the values of the corresponding @xmath56fronts in figs . [ fig : psi25v+om+k - r ] , [ fig:3psisv+l+w - r ] , [ fig:4psisom+r - k ] , [ fig:3dpsi40om - k - r ] , [ fig : ltwapproach ] , [ fig:4psisom - r ] . furthermore , they continue to show the same linear variation with @xmath21 as the @xmath56fronts even where the latter cease to exist at smaller @xmath21 , cf . , the open circles in fig . [ fig:3psisv+l+w - r](a ) for the cases of @xmath134 and @xmath142 . similarly , the variation @xmath143 of long ltws follows the corresponding one of @xmath56fronts , cf . , open circles and filled triangles in fig . [ fig:4psisom - r ] . a comparison of ltw plateau values with extended tws and front tws is presented in fig . [ fig : psi25v+om+k - r](b , c ) for @xmath116 , in fig . [ fig:3dpsi40om - k - r ] for @xmath142 , and in fig . [ fig:4psisom+r - k ] for for all examined @xmath10 . at @xmath101 ( arrows ) there is no difference between the fronts , the diverging ltws , and the extended saddle tws . for decreasing @xmath21 convection is less stable , the disintegration of the traveling rolls sets in earlier , and the ltw length @xmath90 is therefore reduced , cf . , the inset of fig . [ fig : psi25v+om+k - r ] and fig . [ fig:3psisv+l+w - r](b ) . the smallest plateau wave numbers of ltws are realized for diverging lengths at @xmath127 . with decreasing @xmath21 one finds a slight increase of @xmath144 while the wave number selected by a single @xmath56front remains close to that of the saddle tw . so this is the ltw bifurcation scenario that we found in the range @xmath126 ( for a discussion of the scenario at smaller soret coupling strength cf . [ sec : small - soret ] ) : approaching @xmath145 from below ltws become indistinguishable from front states when @xmath100 . but further below @xmath145 ltws differ more and more in particular with respect to the bulk wave numbers as can be seen in figs . [ fig:4psisom+r - k ] and [ fig:3dpsi40om - k - r ] . however , for long enough ltws with a well developed spatial bulk plateau behavior the frequencies @xmath146 and drift velocities @xmath147 vary like the corresponding quantities of @xmath56fronts . this confirms the fact @xcite that it is the @xmath56front - like growth interface that selects the properties of a long ltw . shorter ltws behave also with respect to the variation of @xmath146 and @xmath147 somewhat differently . reducing @xmath21 one eventually arrives for any @xmath10 at the regime of short ltws that are marked in figs [ fig : psi25v+om+k - r ] , [ fig:3psisv+l+w - r ] , and [ fig:4psisom - r ] by shaded circles and that are located close to the dotted line in fig . [ fig : phasediagram ] . here , the dominant influence of the @xmath56front vanishes eventually in the regime of short ltw pulses . no convection plateau can be identified any more in these structures , cf . the dotted curves in fig . [ fig : frontrelaxation ] . the prototype of a short ltw consists of a growth interface which is followed directly by the decay of convection so that the whole pulse has to be seen now as one integrated structure that no longer contains front - like independent @xmath56 and @xmath58interfaces . hence , short ltws show a strong lateral variation of their properties . the shape of their amplitudes superficially resemble the pulse solutions of the complex ginzburg - landau equation @xcite . like for long ltws the stable existence of short pulses below any heating that is necessary to sustain extended tws is caused by a lateral @xmath39 redistribution over the pulse . also its frequency @xmath67 is constant in the frame that comoves with the drift velocity @xmath18 of the pulse like for a long ltw . however , compared to long ltws short ltws provide a qualitatively new convection structure . they are independent of and can not even be compared with extended tws because there is no characteristic wavelength or phase velocity . the special character of short pulses compared with long ltws or fronts is reflected in the change of the @xmath21-variation of @xmath148 that can be seen in figs . [ fig : psi25v+om+k - r ] , [ fig:3psisv+l+w - r ] , and [ fig:4psisom - r ] by comparing the dashed circles with the open ones and the filled triangles . we observed the shortest possible ltws at the lower end , @xmath149 , of the @xmath21 band of ltws . there they seem to end via a saddle node bifurcation for pulses @xcite . these minimal pulses always contained about 5 convection rolls for all soret couplings @xmath150 that we have investigated . this surprising universality of @xmath151 , i.e. , its insensitivity to the values of the actual heating rate @xmath149 and the soret coupling @xmath10 is still unexplained . approaching the lower band limit of ltws their flow intensity steeply drops [ fig . [ fig:3psisv+l+w - r](c ) ] and consequently their frequency increases [ fig . [ fig:4psisom - r ] ] as the degree of advective mixing of the fluid decreases . several attempts have been made to describe ltws by simple model equations . stable pulse solutions of the complex ginzburg - landau equation ( cgle ) were proposed as a model for confined binary mixture convection @xcite . the nonlinear interaction between the local amplitude and frequency seems to be the essential localization mechanism in this approximation . indeed , one could find localized solutions of increasing length up to the limit of an infinitely long two - front state @xcite . but some basical problems remained : within the cgle all pulses drift with the same velocity . this is the critical linear group velocity @xmath152 if the coefficients are derived from an asymptotic reduction of the full hydrodynamic field equations . but @xmath152 is too fast by a factor of about 20 - 40 compared with the ltw drift velocity in experiments or simulations @xcite . brand and deissler @xcite introduced asymmetry in the pulse properties by adding nonlinear gradient terms to the cgle . a similar extension was given by bestehorn _ @xcite within their framework of order parameter equations . both could produce a very slow drift , even opposite to the phase direction @xcite . but this kind of nonlinear modification of the linear group velocity involves a balance which seems to be too fragile to explain the occurrence of small pulse velocities over a whole range of @xmath10 and @xmath21 @xcite . another problem was mentioned by van saarloos and hohenberg @xcite . according to their model of a quintic cgle nonlinear wide pulses are expected by counting arguments to exist only in a codimension-2 submanifold of the parameter space . provided there are no hidden symmetries this seems to be incompatible with the robust occurrence of ltws in experiments . furthermore , stable pulse solutions seem to exist only in the bistable regime whereas ltws are known to persist well above the linear onset of extended convection for weakly negative @xmath10 @xcite . furthermore , coexisting small stable and wide unstable ltws were never seen in the cgle but found in experiments by kolodner @xcite . instead , stable broad pulse solutions are found in the model to arise in a saddle node bifurcation together with an unstable branch of smaller critical droplets near the basic state @xcite . finally , numerical solutions of the field equations show the existence of stable ltws even below the lowest tw saddle node @xcite . this makes clear that ltws are influenced by a localization mechanism that is not contained in the cgle . inspired by simulation results of barten _ @xcite which showed the important role of the concentration field for a ltw riecke @xcite proposed an extension of the ginzburg - landau equations . within a weakly nonlinear expansion he coupled into the standard cgle as an additional slow variable the amplitude @xmath153 of an advected mean large - scale concentration mode that influences the growth of the critical modes . a similar idea was advanced already by glazier _ the extension can induce an additional amplitude - intability of phase winding solutions to modulated waves . it may be considered as the origin for pulse formation in this ansatz @xcite . riecke showed that the influence of the real @xmath153-mode alone on the local growth rate ( without dispersion ) suffices to generate slowly drifting stable pulse solutions even below a supercritical tw - bifurcation @xcite . in this way he modelled a new localization mechanism to explain the robust occurrence of ltws in binary mixture convection . the amplitude @xmath153 can be interpreted as a measure for the local mixing state or the mean convection - induced deviation of the vertical concentration gradient from the conductive one . in this way his extended complex ginzburg - landau equation ( ecgle ) contains in a sketchy way physical effects like the mixing influence on the growth rate and the large - scale concentration redistribution . riecke characterized within his model short and long ltws as dispersion - dominated pulses @xcite and states of two fronts that are bounded by the @xmath153 dynamics @xcite , respectively . he proposed an explanation for their coexistence in stable and unstable form , respectively , by the competition between dispersion - dominated and @xmath153-dominated localization @xcite . note , however , that in contrast to the model used by riecke our results show stable long ltws that drift either in or opposite to the direction of phase propagation depending on paramters . it would be interesting to check whether adding a term of the form @xmath154 to the @xmath153-equation can stabilize forward drifting long pulses within the model since it models the concentration wake , i.e. , the transport of the local mixing state in phase direction by the traveling rolls of amplitude @xmath155 . numerical and analytical investigations of the ecgle predict a hysteretic transition from slow to fast drifting pulses or the existence of oscillatory moving ones @xcite . but both were never seen in experiments or simulations . thus , despite their capability in elucidating some essential mechanisms cgle type models have the drawback so far that they reproduce only single aspects of ltws in a qualitative manner . their range of validity and their predictive power is not well known . and since a satisfactory relation with the full field equations has not been established these models remain somewhat arbitrary . it appears questionable that weakly nonlinear expansions with spatially slowly varying mode amplitudes are approriate at all in view of the very large pclet numbers , @xmath2(1000 ) , measuring the strength of the nonlinearity in the concentration balance . thus , so far numerical simulations of the full field equations seem to be the appropriate tool besides careful experiments to gather insight into the specific physical mechanisms for ltw formation in binary mixture convection . an inspection of figs . [ fig : psi25v+om+k - r ] , [ fig:3psisv+l+w - r ] , and [ fig : phasediagram ] shows that the lower band limit @xmath149 for the existence of short ltws and the crossing value , @xmath156 , where the velocities of free fronts become equal approach each other when @xmath157 decreases . thus , one can foresee an interval of moderately negative @xmath10 where short and long ltws can be found close to @xmath145 . in this case the upper band limit for the existence of stable ltws should be defined by a backward saddle - node bifurcation at @xmath158 where the branches of stable short and unstable long ltws annihilate each other . hence , we expect that the upper parts of the bifurcation diagrams of @xmath90 versus @xmath21 in the inset of figs . [ fig : psi25v+om+k - r ] and in fig . [ fig:3psisv+l+w - r](b ) curve backwards towards smaller @xmath21 when @xmath157 decreases further below the values of the two figures . in this way the shape of the curve @xmath159 would change continuously from the form shown in fig . [ fig : l - r - scheme](b ) to the one in fig . [ fig : l - r - scheme](a ) . the former shows schematically the bifurcation behavior of @xmath159 that we have determined numerically for @xmath160 . in fact , at @xmath10 slightly larger than -0.25 we expect the appearence of the saddle - node in the curves @xmath159 . [ fig : l - r - scheme](a ) is a schematic representation of experimental results of kolodner @xcite for @xmath161 as presented in his fig . he stabilized by an adaptive heating mechanism long unstable ltws in coexistence with short stable ones . thus , the unstable ltw solution branch [ dashed line in fig . [ fig : l - r - scheme](a ) ] forms for @xmath162 a separatrix between the domains of attraction of expanding two - front structures to the right of the dashed line in fig . [ fig : l - r - scheme](a ) and the domain to the left of the dashed line leading to stable narrow pulses or the basic state . furthermore , small ltws that are prepared at @xmath163 will evolve into expanding two - front structures when @xmath21 is increased above @xmath158 . note that in kolodner s experiment @xcite done at @xmath161 the upper band limit @xmath158 of ltws lies _ above _ the hopf bifurcation threshold @xmath164 for extended tws where perturbations of the quiescent fluid can grow . therefore , one has to address there questions related to linear and nonlinear convective versus absolute instability @xcite , to linearly selected so - called pulled fronts versus nonlinearly selected so - called pushed fronts @xcite , and to the robustness and stability of nonlinear fronts under emission or absorption of tw perturbations that can grow in the region occupied by the quiescent fluid . for stronger negative @xmath10 the measured ltw properties agree qualitatively well with our results . for example , the arbitrary - width confined states found in experiments @xcite for @xmath165 at a single rayleigh number are to be identified as two - front structures . a quantitative comparison is difficult due to the difference in the boundary conditions : we simulated two - dimensional convection assuming translational symmetry in @xmath166-direction while the narrow experimental convection channels impose no - slip conditions at the walls perpendicular to the roll axes . there are three effects that account for the difference beteen experiments and simulations . first , the characteristic rayleigh numbers in the experiments are higher . this is already known from the suppression of oscillatory or steady convection instabilities in narrow channels @xcite . the no - slip conditions at the side - walls generate a nontrivial @xmath166-variation of the velocity field that introduces additional internal friction and that has to be compensated by a higher heating rate @xcite . second , the ltw drift velocities in the experiment have the global tendency to lie below those of the simulations . for example , for @xmath165 the experimental ltws @xcite move opposite to the phase velocity whereas according to our calculations @xmath18 should be around @xmath167 . again , we attribute this difference to the fact that we neglect gradients in @xmath166-direction . they change the concentration redistribution dynamics in particular at the @xmath56interface of the ltw which determines the drift velocity . in this context one has to note that already weak inhomogeneities in a convection cell can slow down and even pin the ltw movement @xcite . finally , the influence of the different boundaries on the frequencies , phase velocities , and wave numbers of confined states are totally unknown . also when comparing quantitatively our results for fronts with experiments one should take into account the above discussed points . extrapolating our results for the front velocities to more negative @xmath10 beyond @xmath142 we see that already at the lowest tw saddle location @xmath168 two - front stuctures would expand with @xmath169 . in other words , the velocity crossing point @xmath88 is no longer above @xmath168 but has virtually moved below the lowest tw saddle location where in fact no fronts exist . on the other hand , ltws still exist in this @xmath21-range with length increasing with @xmath21 . however , @xmath159 does not seem to diverge anymore as for @xmath170 which is compatible with the absence of fronts moving with the same velocity . laterally confined convection patches of traveling rolls were found in the early experiments @xcite that were done in narrow rectangular convection channels in the form of so - called wall - attached confined structures ( wacs ) . they were localized near one of the short end walls closing the channel . these wacs can be understood with our knowledge of fronts and free ltws . for example , for the weakly negative @xmath10 used in the early experiments the phase velocity of the wacs was directed towards the wall to which they were attached . indeed , for such parameters mainly short ltws occur with drift velocities in phase direction so that they would end as wacs of the above described type in finite length channels . furthermore , the measured wacs profiles of phase velocity @xmath17 , of wavelength @xmath87 , and their decrease of frequency with increasing @xmath21 @xcite agree qualitatively with the typical behavior of free short ltws . the connection between wacs and free ltws was more explicitly demonstrated by kolodner @xcite for more negative separation ratios @xmath171 and @xmath172 : he prepared a free ltw pulse with large phase velocity ( a fast confined state in his terminology ) which drifted slowly opposite to the direction of phase propagation towards an end wall of the convection channel and became there a wacs ( a slow confined state in his terminology ) with lower phase velocity being directed away from the wall . in this wacs the phase generating trailing front , i.e. , the analogue of the @xmath56interface is pinned at the wall and therefore without solutal gradients to the quiescent fluid as in a free ltw . the absence of these concentration variations at the @xmath56interface implies and allows a lateral concentration redistribution over the whole state at lower levels of the mixing number @xmath68 in wacs as compared to free ltws . consequently , the phase velocities and frequencies of wacs are smaller than those of the respective free ltws . a less dramatic drop of frequency was observed also between forward drifting ltws and short wacs at @xmath173 @xcite . due to their better mixing capability , i.e. , smaller @xmath68 it is very probable that short wacs can exist for heating rates below the lower band limit @xmath149 of stable ltw pulses at least in the case where the phase velocity is directed away from the wall . it would be very interesting to test this conjecture experimentally , in particular for strongly negative @xmath10 . there @xmath149 itself lies already well below the range of stable tws @xcite and so the wacs would lie even lower . an inportant hint that this conjecture is right is given by ning _ they have performed two - dimensional simulations of a finite - length convection channel with realistic boundary conditions for @xmath174 , and @xmath52 . neglecting the slight difference in @xmath175 their results should be comparable with our work . they found short wacs at @xmath176 which is according to our results far below the tw saddle nodes for this separation ratio and also below the lower band limit @xmath149 of free ltws for @xmath177 . however , these authors claim we think , incorrectly that their wacs lie above the saddle - node location @xmath93 of extended tws . in the previous section we have shown that the @xmath56interface where the convection rolls grow in downstream direction out of the quiescent fluid plays the dominant role for the stability of ltws . while the @xmath58interface where the decaying rolls are advected into the quiescent fluid does not play a decisive role . this is clearly confirmed in pulse collision experiments @xcite . fast tw pulses linear ones with small amplitude as well as nonlinear ones with larger amplitude were completely absorbed by a ltw when the pulses hit the @xmath58interface of the ltw , i.e. , when the pulse velocity is directed opposite to and towards the phase velocity of the ltw . then the collision with the pulse affects only the @xmath58interface itself and perturbations are quickly advected out of the ltw and do not propagate upstream towards the @xmath56interface . for the same reason double - ltw states of two counter propagating waves can persist over a long time @xcite or even be stable @xcite . moreover , a pair of ltws that have their phase propagation directed towards each other and that interact with each other via their decay interfaces is seen to be stable over a substantially wider @xmath21-range than two ltw pulses which are connected at their growth interfaces @xcite . obviously the latter case is more critical for the structural integrity of the involved ltws . a ltw is most likely destroyed when another wave with the same direction of phase propagation infiltrates its phaseflow at the growth region . then , while growing the perturbations can be transmitted into the strongly nonlinear bulk part of the ltw and can destroy its coherence . the different selection and stability properties of the @xmath56 and @xmath58interfaces were already observed in transient convection behavior in various experiments ( see for example @xcite ) , however without further investigation . the fact that ( @xmath178 ) different @xmath58fronts with different bulk tw parts are possible as stable coexisting states and that ( @xmath179 ) a @xmath56front interface is in general stable against downflow perturbations opens the possibility for another kind of stable long confined tws : therein rolls with low wavelength grow out of the quiescent fluid in a normal growth part . in the bulk an incoherent phase front connects this fast wave that is coming from the @xmath56interface with a slow wave of higher wavelength and larger amplitude via spatiotemporal dislocations as , e.g. , in fig . [ fig : irregularfront ] . the transition could take place via one or more intermediate convection states . eventually this slow tw convection undergoes a decay transition into the basic state via a coherent @xmath58interface . such defected confined states are indeed observed in annular containers @xcite and were studied by kolodner @xcite . he found such structures only for @xmath180 . one may speculate that for these separation ratios the bulk tw that is selected by and behind the @xmath56interface is absolutely unstable against the slow wave in the further downstream part . this could explain the existence of persistent roll pair annihilations without the need of fluctuations . we finally mention that the occurrence of phase annihilating dislocations between a growth part and the downstream convection was observed for moderately negative @xmath10 already in narrow rectangular containers @xcite . furthermore , end - wall induced eckhaus instabilities of downstream tw states have been seen in simulations @xcite . for parameters where the conductive quiescent fluid is stable and where spatially extended tw solutions bifurcate subcritically out of it we have investigated in quantitative detail relaxed , strongly nonlinear oscillatory convection structures with one or two interfaces to the quiescent fluid , i.e , fronts and ltws , respectively . they are time - periodic global nonlinear modes : in the frame that is comoving with the respective front velocity @xmath55 or with the ltw drift velocity @xmath18 the oscillations have everywhere the same period . fronts come in two varieties . in a @xmath56front state the quiescent fluid is located upstream , i.e. , phase propagates out of it into convection . in a @xmath58front the quiescent fluid is located in downstream direction and phase moves out of convection into conduction . the lowest rayleigh number for the existence of fronts is the lowest saddle - node location of extended tws , @xmath181 : below it there are no tws to which the interface from conduction can connect . however , ltws of _ finite _ length @xmath90 can coexist bistably together with the conductive state well below the lowest tw saddle when the soret coupling is sufficiently negative , @xmath182 . furthermore , we have arguments that wacs at end walls of rectangular channels can exist even at smaller @xmath21 than ltws . central for understanding fronts and ltws is a large - scale concentration redistribution that influences the buoyancy at the interfaces to conduction in different ways than in the bulk tw parts . for example , at the @xmath56interfaces of fronts and ltws alike there is a buoyancy overshoot which is sufficiently large to sustain local convection growth there and that can cause even invasion of convection into the stable quiescent fluid . at the @xmath58interface the lateral buoyancy variation is such as to induce the decay of the approaching convection rolls into the conductive state . front velocities as well as ltw drift velocities are much smaller than the phase velocities of the carrier waves for reasons that are related to the concentration redistribution dynamics . the velocities of @xmath56fronts decrease with growing @xmath21 while those of @xmath58fronts increase . at some @xmath88 they become equal so that both fronts move with the same velocity . at this rayleigh number the length @xmath90 of the ltws diverges and there , and strictly speaking only there , the limiting ltw can be seen as a state consisting of two fronts . however , @xmath56fronts and long ltws have almost identical propagation velocities and frequencies . furthermore , they select a similar bulk wave number . the selected frequencies and bulk wave numbers are close to those of a saddle - node tw . in fact , it is the @xmath56front - like growth interface that selects the properties of long ltws . small amplitude extended tw perturbations of the conductive state oscillate with the large hopf frequency . but the global - mode oscillation is restrained by the requirement that its frequency has to allow stable developed bulk tw convection . it is interesting to note that the @xmath56interface connecting conduction with convection selects the largest possible frequency eigenvalue that meets this requirement , namely the tw saddle - node frequency . all our @xmath56fronts select bulk tw wave numbers close to the large-@xmath92 branch of the tw saddle - node curve , i.e. , wave numbers that are too large to be eckhaus stable . however , these tws are only convectively unstable : perturbations can grow but while doing so they are advected sufficiently fast downstream in the direction of the tw phase propagation so that they can not influence the upstream part of the @xmath56front state in a persistent way . while @xmath56front states seem to be uniquely selected we could produce for a fixed @xmath21 different coherent @xmath58fronts that were characterized in the bulk part by different wave numbers and frequencies close to the tw saddles . the decay interface adjusts itself to the respective bulk tw part but does not exert an influence in upstream direction on the bulk convection within a coherent @xmath58front . in contrast , the growth under a @xmath56interface induces in downstream direction a long concentration wake that is characteristic for @xmath56fronts and long ltws and of special importance for the latter . here it is interesting to notice that all the interfaces of fronts and ltws consist typically only of about 3 - 4 convection rolls . we furthermore should like to mention that @xmath56interfaces of fronts and ltws always locate a minimal wavelength . its value , @xmath85 , is remarkably universal for _ all @xmath21 and @xmath10 _ that we have simulated . this is unexplained so far . we have also prepared initial two - front stuctures by connecting a @xmath56front and a @xmath58front with a common long bulk tw . when @xmath133 they expand . but at @xmath122 they shrink towards a uniquely selected ltw of fixed length @xmath90 . here the downstream wake in the concentration field of the preceeding @xmath56front exerts an effective repulsion on the approaching @xmath58interface : the invasion of conduction via the latter is stopped at a well defined distance @xmath90 that is determined by the concentration - induced buoyancy levels in the wake of the @xmath56front . ltws shortly below @xmath88 ( where ltw with diverging @xmath90 are possible ) are very long . their drift velocities , frequencies , and many stuctural properties are similar to those of @xmath56fronts . decreasing @xmath21 the ltw length decreases and one eventually arrives for any @xmath10 at the regime of short ltws that lies for strongly negative @xmath10 well below the tw saddle - 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( a , b ) color coded snapshot of concentration deviation @xmath39 from its global mean in a vertical cross section of the layer . the color code is shown at the right end of ( b ) . ( c , d ) instantaneous lateral wave profile at midheight , @xmath187 , of @xmath39 ( green ) , vertical velocity @xmath188 ( blue ) , and its envelope . arrows mark the positions where @xmath188 has grown up to @xmath61 . ( e , f ) mixing number @xmath68 ( green ) , eq . ( [ eq : m(x ) ] ) , and phase velocity @xmath61 ( black ) of the nodes of @xmath188 in the comoving frames . the variation of @xmath84 is the same since the frequency @xmath67 is a _ global _ constant . ( g , h ) time averaged deviations from the conductive state at @xmath189 for concentration ( green ) , temperature ( red ) , and their sum ( @xmath190 ) measuring the convective contribution to the buoyancy . ( i , j ) streamlines of the averaged concentration current @xmath72 ( green ) and velocity field @xmath191 ( blue ) . the latter results from @xmath190 and documents roll shaped contributions of @xmath192 to @xmath72 at the interfaces . thick blue and green arrows indicate @xmath191 and transport of positive @xmath39 ( alcohol surplus ) , respectively . temporal averaging is always performed in the frame comoving with the respective front velocity . dashed lines show the decay part of the long ltw that coexists at the same parameters ( @xmath193 ) with the fronts . differences between the interfaces of the @xmath56front and the corresponding ltw interface are not visible on the scale of the above plots . [ fig : frontpics],width=529 ] for @xmath116 . left and right pointing triangles with triangles denote @xmath56 and @xmath58fronts , respectively . open and shaded circles refer to long and short ltws , respectively . ( a ) front velocities of relaxed single - front states ( thick dashed lines with filled triangles ) , of expanding two - front states ( thin dashed lines with open triangles ) , and drift velocities of ltws ( circles ) . the inset shows the drastic increase of ltw length @xmath90 at @xmath101 where the front velocities of the @xmath56 and @xmath58 single - front states become equal . ( b ) frequencies of front states and of long ltws in comparison with the rest frame frequencies of laterally periodic tws . the saddle - node vicinities of the latter are shown by full lines for several wave numbers @xmath194 . tw states with frequencies above the dotted line of saddle - node tws are unstable . ( c ) wave numbers selected by front states in the bulk part far away from the interface ( triangles ) and in the central part of long ltws ( open circles ) . horizontal lines indicate the laterally periodic tws that are shown in ( b ) by full lines . the continuum of these tw states is bounded in the @xmath195 plane by the dotted line of tw saddle nodes , @xmath114 . here we show only the large-@xmath92 branch of it ( cf . the dotted line marked @xmath93 in fig . [ fig:3dpsi40om - k - r ] for another perspective ) . [ fig : psi25v+om+k - r],width=302 ] . ( a ) front velocities , @xmath55 , of @xmath56fronts ( left pointing triangles ) , of @xmath58 fronts ( right pointing triangles ) , and drift velocities , @xmath18 , of ltws ( circles ) versus @xmath21 . note that short ltws ( shaded circles ) and long ltws ( open circles ) show different @xmath196-behavior . the latter varying linearly with @xmath21 is nearly indistinguishable from @xmath197 . arrows mark the low-@xmath21 existence boundary @xmath168 of laterally periodic tws and with it of front states . ltws exist below this threshold @xcite with drift velocities that show the above mentioned linear variation with @xmath21 as long as the ltws are long enough . to identify an ltw as a long one we required a clearly visible plateau in the spatial properties . ( b ) length @xmath90 of the ltws of ( a ) measured as the distance between the half maximum values of the envelope of the vertical velocity field @xmath188 [ cf . , blue line in fig . [ fig : frontpics](c , d ) ] . ( c ) maximal vertical flow velocities @xmath198 of ltws . [ fig:3psisv+l+w - r],width=321 ] fronts ( dashed lines with triangles ) , long ltws ( circles ) , and laterally extended saddle - node tws ( dotted lines ) for different @xmath10 . the wave numbers of the two former refer to plateau values in the bulk part away from the interface . ( a ) frequency @xmath67 ( for tws in the rest frame and for ltws and fronts in the comoving frame ) versus wave number @xmath92 . ( b ) the same convection structures in the @xmath94 plane . the wave numbers and frequencies of ltws with @xmath100 ( arrows ) coincide at @xmath101 with those of the respective @xmath56 fronts . [ fig:4psisom+r - k ] , width=321 ] front . shown are the extrema positions of the vertical velocity field @xmath188 . the initial condition at time @xmath199 ( not visible ) consisted of an extended tw for @xmath105 with wavelength @xmath106 and phase velocity @xmath107 and quiescent fluid for @xmath200 . boundary conditions are conduction at @xmath201 and @xmath202 that imposes at @xmath203 a wavelength of @xmath106 . first , a pulse that causes a quite regular sequence of roll - pair annihilation events ( lower line of defects ) propagates to the right with velocity greater than @xmath61 . the intermediate wave pattern resulting from this primary sequence of defects is then transformed via further , somewhat erratically occurring phase defects into the fast asymptotic tw with @xmath204 that is favoured by the @xmath56front . the boundary condition at @xmath203 that imposes a wrong wavelength there does not influence the bulk behavior which is selected by the front . parameters are @xmath205 . [ fig : frontrelaxation],width=566 ] . the front selects a bulk tw with wavelength @xmath206 that is strongly eckhaus unstable : while beeing advected downstream phase deformations ( that are caused , e.g. , by computer noise ) grow sufficiently fast to reach a critical amplitude within the system length . then two neighboring rolls are annihilated . that increases the wavelength and decreases the phase velocity towards eckhaus stable values . parameters are @xmath207 . [ fig : irregularfront],width=566 ] ( bottom ) after starting with a very long two - front structure at @xmath208 . the @xmath56front selects in the bulk of the initial two - front structure a saddle - node tw with wavelength @xmath123 . with @xmath209 the @xmath58front approaches the @xmath56front and doing so the velocity of the former goes monotonously towards @xmath81 . this transient process ends in a long ltw ( dashed line ) of constant length @xmath124 with a plateau wavelength of @xmath210 . its drift and frequency is effectively the same as the respective values of the @xmath56front which remain unchanged all the time . for comparison the profiles of a short ltw at the same @xmath10 but smaller @xmath211 are shown with dotted lines . [ fig : ltwapproach],width=321 ] plane . the vertical bars indicate the range of stable existence of those ltws that we have numerically simulated . full and dashed lines refer to the saddle node location @xmath93 of extended tws and to their oscillatory hopf bifurcation threshold @xmath164 , respectively ; both for a wave number @xmath212 . for @xmath213 the upper existence boundary of ltws was determined by the requirement that @xmath90 remained below about 120 in our numerical set - up . the dotted line guides the eye along the lower band limit @xmath149 of ltws . parameters are @xmath214 . [ fig : phasediagram],width=321 ] of @xmath56fronts ( dashed lines with triangles ) and of ltws ( full lines with circles ) in the respective comoving frame versus @xmath21 for different @xmath10 . open and shaded circles refer to long and short ltws , respectively . the frequencies of the former are the same as those of the fronts while short ltws differ . arrows indicate the lower limit of existence of the fronts at @xmath215 . [ fig:4psisom - r],width=321 ] versus @xmath21 . ( a ) experimental results @xcite obtained for @xmath161 with dashed line denoting unstable states ( cf . , text for further explanation ) ; ( b ) numerically obtained bifurcation behavior for @xmath126 . [ fig : l - r - scheme],width=321 ]

nonlinear fronts between spatially extended traveling wave convection ( tw ) and quiescent fluid and spatially localized traveling waves ( ltws ) are investigated in quantitative detail in the bistable regime of binary fluid mixtures heated from below . a finite - difference method is used to solve the full hydrodynamic field equations in a vertical cross section of the layer perpendicular to the convection roll axes . results are presented for ethanol - water parameters with several strongly negative separation ratios where tw solutions bifurcate subcritically . fronts and ltws are compared with each other and similarities and differences are elucidated . phase propagation out of the quiescent fluid into the convective structure entails a unique selection of the latter while fronts and interfaces where the phase moves into the quiescent state behave differently . interpretations of various experimental observations are suggested .

<s>[INST]many nonlinear dissipative systems that are driven sufficiently far away from thermal equilibrium show selforganization out of an unstructured state : a structured one can appear that is characterized by a ( spatially extended ) pattern which retains some of the symmetries of the system @xcite . convection in binary miscible fluids like ethanol - water , @xmath0he @xmath1he , or various gas mixtures is an example of such systems . it shows rich and interesting pattern formation behavior and it is paradigmatic for problems related to instabilities , bifurcations , and selforganization with complex spatiotemporal behavior . compared to convection in one - component fluids like , e.g. , pure water the spatiotemporal properties are far more complex . the reason is that concentration variations which are generated via thermodiffusion , i.e. , the soret effect by externally imposed and by internal temperature gradients influence the buoyancy , i.e. , the driving force for convective flow . the latter in turn mixes by advectively redistributing concentration . this nonlinear advection gets in developed convective flow typically much larger than the smoothening by linear diffusion pclet numbers measuring the strength of advective concentration transport relative to diffusion are easily @xmath2(1000 ) . thus , the concentration balance is strongly nonlinear giving rise to strong variations of the concentration field and to boundary layer behavior . in contrast to that , momentum and heat balances remain weakly nonlinear close to onset as in pure fluids implying only smooth and basically harmonic variations of velocity and temperature fields as of the critical modes . without the thermodiffusive soret coupling between temperature and concentration any initial concentration deviation from the mean diffuses away and influences no longer the balances of the other fields . hence , the feedback interplay between ( _ i _ ) the soret generated concentration variations , ( _ ii _ ) the resulting modified buoyancy , and ( _ iii _ ) the strongly nonlinear advective transport and mixing causes binary mixture convection to be rather complex with respect to its spatiotemporal properties and its bifurcation behavior . take for example the case of negative soret coupling , @xmath3 , between temperature and concentration fields @xcite when the lighter component migrates to the colder regions thereby stabilizing the density stratification in the quiescent , laterally homogeneous conductive fluid state . then the above described feedback interplay generates oscillations . in fact the buoyancy difference in regions with different concentrations was identified already in @xcite as the cause for traveling wave convection . oscillatory convection appears in the form of the transient growth of convection at supercritical heating , in spatially extended nonlinear traveling wave ( tw ) and standing wave solutions that branch in general subcritically out of the conductive state via a common hopf bifurcation , in spatially localized traveling wave ( ltw ) states , and in various types of fronts . tw and ltw convection has been studied experimentally and theoretically for some time @xcite . the transient oscillatory growth of convection was investigated by numerical simulations @xcite . nonlinear standing wave solutions were obtained only recently @xcite . freely propagating convection fronts that connect subcritically bifurcating nonlinear tw convection with the _ stable _ quiescent fluid do not seem to have been investigated in detail beyond some first preliminary results @xcite . here we determine such fronts in quantitative detail and compare their properties with those of ltws . in narrow rectangular and annular channels convection occurs in the form of rolls with axes oriented perpendicular to the long sidewalls @xcite . these stuctures can efficiently be described in the two dimensional vertical @xmath4 cross section in the middle of the channel perpendicular to the roll axes ignoring variations in axis direction . furthermore , these convection structures have relevant phase gradients only in @xmath5-direction thus causing effectively one dimensional patterns @xcite . when comparing experiments with analytical calculations or numerical simulations performed under the above described conditions it is useful to do that on the basis of reduced rayleigh numbers , @xmath6 , with @xmath7 being the critical one for onset of pure fluid convection for the respective experiment , analytical method , or numerical method . this significantly reduces the dependence of , say , the bifurcation diagrams of convective states on the specific geometry of the respective set - up . in laterally unbounded systems the analytical value for @xmath7 is 1707.762 . _ localized traveling waves . _ for weak negative soret coupling one has observed in experiments a competition between homogeneous laterally extended tw convection and so - called dispersive chaos with an irregular repetitive formation and collapse of spatially localized tw pulses @xcite . during the pulse formation their drift velocities can drop abruptly to about a tenth of the initial group velocity @xcite . we consider this to be a characteristic signal that the lateral redistribution of concentration over the pulse @xcite becomes important and that the strongly nonlinear dynamics sets in . for more negative @xmath8 the collapse is in general less dramatic . there , convection is dominated by isolated strongly peaked localized states . eventually , at @xmath9 a regime is reached where stable ltws coexist near onset with extended tws @xcite . increasing the soret coupling strength further to more negative @xmath10 the band ( @xmath11 ) of rayleigh numbers in which stable ltws exist increases monotonically while shifting upwards as a whole @xmath12 grows stronger than @xmath13 . simultaneosly , the lower band limit for the existence of extended tw states @xmath14 , i.e. , the lowest saddle - node of tws increases even steeper so that eventually for @xmath15 the complete ltw band comes to lie below the existence range of tws , @xmath16 @xcite . ltws consist of slowly drifting , spatially confined convective regions that are embedded in the quiescent fluid . these intriguing structures have been investigated in experiments @xcite and numerical simulations @xcite . a discussion of various theoretical models aiming at their explanation is contained in sec . [ sec : ltwmodels ] . roll vortices grow in a ltw structure out of the quiescent fluid at one end , travel with spatially varying phase velocity @xmath17 to the other end , and decay there back into the basic state . the two interfaces to conduction and with it the whole convective region move with constant , uniquely selected drift velocity @xmath18 . the latter is a function of @xmath19 with magnitude much smaller than the phase velocities . also the oscillation frequency of the ltw is uniquely selected ; it is constant in space and time in the frame that is comoving with its drift velocity . and finally , the length @xmath20 of the convective region of stable ltws and their spatial stucture are uniquely selected . this length grows with increasing heating @xmath21 . a central role for the stable existence of ltws plays a large - scale mean concentration current . extending over the whole ltw it redistributes concentration and thereby changes the buoyancy in a decisive way @xcite . this effect can sustain ltws even at low @xmath21 where no extended tws exist @xcite . _ blinking states in rectangular channels . _ the ltw confinement of convection occurring in translationally invariant annular channels is obviously an inherent process of the hydrodynamic balances . but one has also observed end - wall - assisted or at least end - wall - modified confinement of convection close to the ends of rectangular channels . the weakly nonlinear varieties of such a confinement can largely be understood in terms of the convective behavior of tw packets , their reflection properties at the end walls , and the destructive interaction between left and right traveling patterns @xcite . these effects give rise near onset to a wide range of weakly nonlinear and effectively low dimensional spatiotemporal behavior that depends sensitively on the specific experimental set - up like , e.g. , the end - wall boundary conditions and the system length @xcite . while the linear eigenmodes of such sytems ( linear counterpropagating waves or chevrons ) @xcite are laterally symmetric or antisymmetric localization sets in via a temporal amplitude modulation . thereby convection is alternatingly weakened and enhanced in the left and the right part of the system part giving rise to a blinking state @xcite . the so - called chaotic blinking states @xcite seem to be the analogue of the chaotic dispersive pulse formation in annular containers @xcite . also blinking modes with different frequencies at both ends of the channel were observed @xcite . but their possible relation to a large - scale mean concentration variation @xcite produced by nonlinear propagating waves in a finite cell has not been discussed . _ wall - attached structures . _ at larger @xmath21 one has observed wall - attached tw structures with amplitudes confined to the vicinity of one or both end walls . these wall - attached convective patches @xcite are closely related to free ltws @xcite . they are strongly nonlinear as indicated by their low frequency @xcite . moreover , their spatial structure and their region of existence is largely unaffected by the details of the lateral boundaries or by the container length in contrast to the linear and weakly nonlinear behavior described above @xcite . the more extensive wall - attached structures show some similarities with front - like states . note , however , that here the source or the sink of the propagating rolls is pinned near a wall and the interface to the quiescent fluid in the bulk of the channel does not move @xcite . _ our numerical simulations . _ our numerical simulations have been performed in order to elucidate in quantitative detail the properties of relaxed nonlinear tw convection structures that contain an interface ( or two of them ) to the quiescent fluid as an integrated structural element . we compare for a wide range of soret coupling strengths front states and ltw states showing what they have in common and how they differ . we focus our interest to those parameters where the quiescent conductive state of the fluid is stable and where the solutions describing spatially extended , laterally periodic tw convection bifurcate subcritically out of it . the system we have in mind is a binary fluid layer of thickness @xmath22 which is bounded by two solid horizontal plates perpendicular to the gravitational acceleration @xmath23 . the fluid might be a mixture of water with the lighter component ethanol at a mean concentration @xmath24 . it is heated from below . the temperatures at the plates are @xmath25 . the variation of the fluid density @xmath26 due to temperature and concentration variations is governed by the linear thermal and solutal expansion coefficients @xmath27 and @xmath28 , respectively . both are positive for ethanol - water . the solutal diffusivity of the binary mixture is @xmath29 , its thermal diffusivity is @xmath30 , and its viscosity is @xmath31 . length and time is scaled by @xmath22 and @xmath32 , respectively , so that velocity is measured in units of @xmath33 . temperatures are reduced by the vertical temperature difference @xmath34 across the layer and concentrations by @xmath35 . the scale for the pressure is given by @xmath36 . then , the balance equations for mass , momentum , heat , and concentration @xcite read in oberbeck boussinesq approximation @xcite [ eq : baleqs ] @xmath37\label{eq : baleqheat}\\ \partial_t \delta c = - { \mbox{\bf\boldmath $ \nabla$}}\cdot \left [ { { \bf u } } \delta c - l{\mbox{\bf\boldmath $ \nabla$}}\left(\delta c -\psi \delta t\right ) \right]\ . \label{eq : baleqconc } \end{aligned}\ ] ] here , @xmath38 and @xmath39 denote deviations of the temperature and concentration fields , respectively , from their mean @xmath40 and @xmath24 and @xmath41 is the buoyancy . the dufour effect @xcite that provides a coupling of concentration gradients into the heat current and a change of the thermal diffusivity is discarded in ( [ eq : baleqheat ] ) since it is relevant only in few binary gas mixtures @xcite and possibly in liquids near the liquid vapor critical point @xcite . besides the rayleigh number @xmath42 measuring the thermal driving of the fluid three additional numbers enter into the field equations : the prandtl number @xmath43 , the lewis number @xmath44 , and the separation ratio @xmath45 . here @xmath46 is the thermodiffusion coefficient @xcite and @xmath47 the soret coefficient . they measure changes of concentration fluctuations due to temperature gradients in the fluid . @xmath10 characterizes the sign and the strength of the soret effect . negative soret coupling @xmath10 ( i.e. , positive @xmath47 for mixtures like ethanol water with positive @xmath48 and @xmath49 ) induces concentration gradients of the lighter component that are antiparallel to temperature gradients . in this situation , the buoyancy induced by solutal changes in density is opposed to the thermal buoyancy . when the gradient of the total buoyancy exceeds a threshold , convection sets in typically in the form of straight rolls . for sufficiently negative @xmath10 the primary instability is oscillatory . ignoring field variations along the roll axes we describe here 2d convection in an @xmath5@xmath50 plane perpendicular to the roll axes with a velocity field @xmath51 to find the time - dependent solutions of the above partial differential equations subject to realistic horizontal boundary conditions @xcite we performed numerical simulations with a modification of the sola code that is based on the mac method @xcite . this is a finite - difference method of second order in space formulated on staggered grids for the different fields . the poisson equation for the pressure field that results from taking the divergence of ( [ eq : baleqveloc ] ) was solved iteratively with the artificial compressibility method @xcite by incorporating a multi - grid technique . throughout this paper we consider mixtures with @xmath52 , @xmath53 , and various negative values of @xmath10 that are easily accessible with ethanol - water experiments . the paper is organized as follows : in sec . [ sec : fronts ] we first describe our methods for characterizing the various convective states . then we present results for the two different types of tw front states that can arise in laterally homogeneous mirror symmetric systems with either the phase propagating out of the quiescent fluid or into it . also transient two - front structures are discussed . [ sec : ltw ] deals with ltw states and their relation to fronts . the transient dynamics towards the selected ltw , the stabilization via front repulsion , the difference between long and short ltws , and a critical appraisal of ltw models are topics covered here . in sec . [ sec : compare - exp ] we present a comparison with experiments and a discussion . the last section contains a conclusion . here we discuss front solutions where part of the system is occupied by the quiescent fluid while the other one shows fully developed , saturated , strongly nonlinear tw convection with laterally homogeneous amplitude . strictly speaking these two states are realized only in the two opposing limits of @xmath54 . we focus our investigation of fronts on parameters where the quiescent fluid state is stable and where the tw solutions bifurcate subcritically out of the conductive state . then , any _ linear _ growing and spreading of infinitesimal , localized convective perturbations in the quiescent fluid which could possibly dominate the low amplitude behavior of fronts as in the case of an unstable zero amplitude state @xcite is absent . little general is known about pattern forming fronts in real bistable systems @xcite . most of the research activities were centered on fronts in the quintic ginzburg - landau equation @xcite . one can expect that the front properties are fixed by a strongly nonlinear eigenvalue problem describing a heteroclinic orbit between the two involved states . some of these front solutions will be unstable . there might be also multistable coexistence of fronts so that depending on initial conditions and on the history of the ( control ) parameters different fronts could finally be realized . we call a front uniquely selected when our numerical simulations indicated that different formation processes ended in the same front for a fixed parameter combination . fronts can be classified into coherent and incoherent ones @xcite . we focus here on the first kind which in our system are characterized as strictly time periodic states in a frame that is comoving with the front s velocity @xmath55 . such a front state being monochromatic is a global nonlinear mode . its frequency is an eigenvalue , i.e. , a global constant in space and time so that the convection oscillations have everywhere the same period . thus , we do not consider here , e.g. , complex large scale or chaotic spatiotemporal interface behavior . the coherent fronts of the various hydrodynamic fields and quantities in this paper have a smooth and basically monotonous profile which connects the quiescent fluid with the nonlinear saturated extended tw . the transition region between conduction and convection that is characterized by large amplitude variations is quite short and consists typically only of about 3 -4 convection rolls . we call this transition region also the interface between conduction and convection . if the selected front pattern is incompatible with any stable bulk structure there are two possibilities : ( _ i _ ) a perturbation in the unstable convection bulk grows and expands towards the interface . this would destroy front coherence and could lead to more complex large scale variations , perhaps chaotic spatiotemporal behavior . ( _ ii _ ) the interface region is only convectively unstable against perturbations of the bulk nonlinear tw . then initially localized perturbations would be advected out of every finite system and could not reach the unperturbed interface region of the front . we call a front to be of type @xmath56 when its envelope grows at @xmath57 out of the basic quiescent state . otherwise it is a @xmath58front . then the amplitude falls to zero at @xmath59 @xcite . the phase of the convection pattern in a front state of type @xmath56 can either propagate to the left or to the right and similarly for the @xmath58front state . hence , one would have to discuss four front states separately . however , because of the invariance of the system under @xmath60 a @xmath56front state with positive ( negative ) phase velocity @xmath61 is the mirror image of the @xmath58front state with negative ( positive ) @xmath61 . therefore , it suffices to consider only the front states that consist of roll vortices traveling , say , in positive @xmath5-direction and to use the superscript @xmath56 or @xmath58 to identify the properties of the front in question in a unique way . so , the phase velocities of all oscillatory convective structures investigated in this paper are positive . we call the direction of positive @xmath5 into which the phase propagates also downstream and the opposite one upstream. so , to sum up our notation : in a @xmath56front state the quiescent fluid is located upstream and a source of phase with the latter propagating out of the conductive state into convection . in a @xmath58front the quiescent fluid is located in downstream direction and a sink since phase moves out of convection into conduction . fig . [ fig : frontpics ] shows fronts of each type . under the @xmath56front ( left half of fig . [ fig : frontpics ] ) convection rolls grow out of the quiescent fluid and saturate in a downstream bulk tw . on the other hand , a @xmath58front ( right half of fig . [ fig : frontpics ] ) annihilates roll vortices . in this process their phase velocity is accelerated [ cf . the increase in the lateral profile of @xmath17 in fig . [ fig : frontpics](f ) ] and they are stretched horizontally . it is clear from fig . [ fig : frontpics ] that the quiescent ( convecting ) region expands into the convecting ( quiescent ) one when the velocity @xmath62 of the @xmath56front is positive ( negative ) and vice versa for the @xmath58front . in order to monitor how well the fluid is mixed along the front we always determined for the relaxed front states the mixing number @xmath63^{1/2}\ ] ] as a function of lateral position @xmath5 . it basically measures the mean square of the deviations @xmath64 of the concentration field from its global mean : the overbars imply a vertical average and the brackets a temporal average at the specific horizontal location @xmath5 in the frame comoving with the front velocity @xmath55 . the subscript _ cond _ denotes the reference quiescent conductive state with its linear vertical concentation variation . the mixing number is defined such that @xmath65 in a perfectly mixed fluid and @xmath66 in the quiescent state . in laterally extended tws @xmath67 and with it @xmath61 increase when the concentration variations become larger @xcite . in fact , there is a universal scaling relation between @xmath68 and @xmath67 @xcite which shows that @xmath68 and @xmath61 are linearly related to each other . this relation also holds for the bulk part of front states far away from the interface where the convection is tw - like with only slow spatial amplitude variation ( fig . [ fig : frontpics ] ) . the phase shift between the concentration and velocity waves in the tw - like bulk of the front states sustains as in extended tw states a mean lateral concentration current @xmath69 @xcite : @xmath70 where @xmath71 is the velocity field and @xmath38 the temperature deviation from the global mean . again , the brackets imply a temporal average in the frame that is comoving with the front velocity . the lewis number @xmath52 being rather small in our simulations implies that @xmath72 is dominated by the advective contribution except in those boundary regions in which @xmath71 becomes small . the vertical variation of @xmath72 is such that positive ( negative ) @xmath39 is transported in phase direction in the upper ( lower ) half of the layer . this transport causes a large - scale concentration redistribution in a front state between its tw bulk and its interface to the quiescent fluid and it is responsible for the different characteristic structures of the interfaces in a @xmath56 and a @xmath58front as we will see further below . we simulated systems containing up to 160 rolls . the initial state was prepared by filling one half of the sytem with a nonlinear tw that was previously generated with periodic boundaries to have some fixed wavelength @xmath73 . the other half contained the stable temperature and concentration distribution of the pure quiescent basic state . to simulate @xmath56fronts in infinite systems that connect to developed tw convection with some wavelength @xmath73 far away from the interface between conduction and convection we imposed at the downstream boundary @xmath74 of our computation domain the periodicity condition @xmath75 . for the case of @xmath58fronts we found that imposing the analogous condition at the upstream boundary of the developed tw part at @xmath76 typically will introduce perturbations that can grow in downstream direction for example when the tw region is eckhaus unstable . the different aspects of the stability of @xmath56 and @xmath58fronts are discussed further below in the paper . after a relaxation time of typically 100 to 200 vertical thermal diffusion times we then could observe under certain conditions a coherent front state connecting a quiescent region of the system to a tw with asymptotic wavelength @xmath73 . here the fact that the frequency @xmath67 of such a coherent front state is constant in space and time in the frame that is comoving with the front velocity @xmath55 proved to be a good relaxation criterion to effectively determine whether such a state had been obtained . as soon as the growing convection rolls in a @xmath56front have become sufficiently nonlinear , i.e. , when their lateral flow velocity @xmath77 has grown up to about their phase velocity @xmath61 [ e.g. , close to the vertical arrow in fig . [ fig : frontpics](c ) ] they start to alternatingly suck in positive ( blue ) and negative ( red ) @xmath39 from the top and bottom concentration boundary layers , respectively . it is transported away into the well mixing convection bulk and replaced at the interface location by neutral ( yellow / green ) @xmath39 . note that increasing @xmath77 beyond @xmath61 causes the appearence of closed streamlines of the velocity field in the frame comoving with the phase velocity of a traveling roll @xcite . these closed streamlines regions are responsible for the characteristic roll structure of the @xmath78 field in fig . [ fig : frontpics](a ) : positive ( negative ) @xmath39 is collected from the top ( bottom ) boundary layers and transported within the homogeneously mixed closed streamline regions in phase direction while mean concentration , @xmath79 , is advected along the meandering `` green - yellow stripe '' in fig . [ fig : frontpics](a ) to the left @xcite . the mean concentration current @xmath72 resulting from this complicated concentration redistribution is shown in fig . [ fig : frontpics](i ) . all in all , mean concentration is accumulated ( depleted ) at the @xmath56 ( @xmath58 ) front interface . the concentration redistribution reduces at the interface of the @xmath56front the soret - induced solutal stabilization that occurs to the left of it as a result of the large conductive vertical concentration gradient : at the interface one can observe a minimal mixing number [ fig . [ fig : frontpics](e ) ] and with it a buoyancy overshoot [ fig . [ fig : frontpics](g ) ] which is sufficiently large to sustain local convection growth there and cause even invasion of convection into the quiescent region whenever @xmath80 . with the fluid being well mixed there , i.e. , with @xmath68 being small the local phase velocity is also small there in fact the minimum of @xmath17 in fig . [ fig : frontpics](e ) lies close to the one in @xmath68 . since the strongly stable quiescent fluid to the left of the @xmath56front prohibits a well developed advectively mixing front tail the reduction of @xmath39 variations there is driven primarily by diffusion . the latter having a characteristic time scale given by @xmath52 explains why the front velocities are much smaller than the fast phase velocity . when @xmath21 is increased @xmath81 tends to become ( more ) negative : convection to the right of the @xmath56interface can now , with increased heating , better invade the quiescent fluid to the left of it and thus @xmath82 . similarly , when @xmath10 is increased , i.e. , when the convection suppressing soret effect is diminished the expansion of tw convection is favoured and thus @xmath83 . moving along the @xmath56front in fig . [ fig : frontpics ] to the right from the interface towards the asymptotic tw state at large @xmath5 there develops an equilibrium between the @xmath39 feed - in from the boundary layers at the plates and the amount of advective mixing : the concentration contrast between two neighboring rolls increases on the way towards the tw bulk . with it the phase speed @xmath17 , the wavelength @xmath84 , and the lateral concentration current @xmath72 grow monotonously up to their asymptotic tw values . this growth extends laterally over a wide interval which itself increases when the soret coupling becomes stronger . we found that the minimal wavelength in a @xmath56front state is located at the interface and more remarkably that it is about @xmath85 for _ all @xmath21 and @xmath10 _ that we have simulated . we have no real quantitative explanation for this strong universal selection of the local wavelength at the interface . intuitively the growing rolls are squeezed in the region with the negative lateral gradient of @xmath68 . the squeezing is relaxed when the rolls begin to absorb high concentration contrasts from the plate layers which increases @xmath61 again [ arrow in fig . [ fig : frontpics](c ) ] . it is interesting to note that the mean concentration current @xmath72 of tws becomes maximal close to the tw saddle node , i.e. , where the asymptotic tw parts of our front states are located . finally we mention that the front states do not sustain a measurable lateral meanflow ; the quiescent fluid prohibits that . on the other hand , extended tws in laterally periodic systems show in general a reynolds stress - induced meanflow of the order @xmath86 @xcite . but it goes through zero just near the tw saddle node . in figs . [ fig : psi25v+om+k - r ] - [ fig:3dpsi40om - k - r ] we show the bifurcation properties of fronts in comparison with ltws and laterally periodic tw states . we use front velocities and frequencies being temporally and spatially constant as order parameters to characterize all of the aforementioned oscillatory states . in addition we also consider the local wave numbers of front states and of ltws in the bulk spatial regions where @xmath87 has reached a plateau , i.e. , sufficiently away from any interface to conduction . figs . [ fig : psi25v+om+k - r ] and [ fig:3psisv+l+w - r ] show that the front velocities of @xmath56 and @xmath58fronts vary quite differently as a function of @xmath21 . the former decrease linearly with growing @xmath21 and the latter increase , albeit not linearly . thus , there is a crossing at @xmath88 where @xmath81 becomes equal to @xmath89 , so that both fronts move with the same velocity . at this rayleigh number the length @xmath90 of the ltws diverges , i.e. , @xmath91 . there , and strictly speaking only there , this limiting ltw can be seen as a state consisting of two fronts . the frequency and bulk wave number selected by a @xmath56front and of a very long ltw are close to those of the respective , laterally extended saddle - node tw ( figs . [ fig : psi25v+om+k - r ] , [ fig:4psisom+r - k ] , [ fig:3dpsi40om - k - r ] ) . a somewhat hand - waving explanation for the selection of the saddle - node frequency is as follows : with ( _ i _ ) convection growing out of conduction in a @xmath56 front , with ( _ ii _ ) small - amplitude extended tw perturbations of the latter oscillating according to a purely linear balance with the large hopf frequency , and with ( _ iii _ ) the tendency to decrease @xmath67 with growing convection amplitude the saddle - node frequency is the first , i.e. , the largest possible eigenfrequency of the full nonlinear front problem to allow for a stable tw region away from the interface . a stable front state that has a tw bulk part extending laterally to infinity with frequency @xmath67 and wave number @xmath92 can not be realized at @xmath21-values that lie below the saddle - node curve of laterally extended tws , cf . the curve marked @xmath93 in the @xmath94 plane of fig . [ fig:3dpsi40om - k - r ] . thus , the lowest rayleigh number @xmath95 for the existence of fronts is @xmath96 , i.e. , the location of the tip of the nose - shaped tw bifurcation surface like the grey surface in fig . [ fig:3dpsi40om - k - r ] . ahead of this nose one can not realize front states because at such locations there are no tws to which the interface from conduction could connect . the tw bulk parts of our @xmath56fronts are practically saddle - node tws that have bulk wave numbers on the saddle - node curve @xmath97 . furthermore , it is interesting to note that they are on the _ large_-@xmath92 branch of @xmath97 the big plusses in fig . [ fig:3dpsi40om - k - r ] marking the bulk values of the front states lie all above @xmath98 . in fact , in all our simulations we did not find front states with bulk wave numbers smaller than @xmath99 . this value marks for all @xmath10 that we investigated the tip of the nose - shaped tw bifurcation surface like the grey surface in fig . [ fig:3dpsi40om - k - r ] . in contrast to fronts , however , ltws of _ finite _ length @xmath90 can coexist bistably together with the conductive state at @xmath21-values well below @xmath97 : they can sustain over a finite lateral length convection with frequencies and bulk wave numbers ( big bullets in fig . [ fig:3dpsi40om - k - r ] ) ahead of the grey tw surface for reasons that are explained in ref . this also shows that fronts and ltws are quite different states . in the limit @xmath100 the ltw states merge at @xmath101 with a tw whose wave number and frequency is close to the tw saddle - node as shown in figs . [ fig : psi25v+om+k - r ] , [ fig:4psisom+r - k ] , [ fig:3dpsi40om - k - r ] . therefore , @xmath102 increases when the soret coupling becomes more negative but @xmath103 decreases . for @xmath15 it moves towards the tip of the tw nose at @xmath104 . simulations of @xmath56fronts that were done at fixed control parameters @xmath19 with different initial conditions , e.g. , different wave numbers of an initial tw part produced in general a uniquely selected final front state with the same frequency and the same asymptotic bulk tw part . during the formation process initial wave structures with the wrong wave patterns propagated out of the system in the direction of the phase velocity and were substituted by convection that was selected by the front . that also explains why our tw boundary condition @xmath75 at the downstream end has no measurable influence on the @xmath56front state even when @xmath73 differs from the front - selected value . the substitution dynamics is documented in fig . [ fig : frontrelaxation ] . there a tw bulk part was prepared initially at @xmath105 with a wavelength of @xmath106 and phase velocity @xmath107 . the spatial region to the right of the interface to conduction is then invaded by the front - selected tw pattern that has a smaller bulk wavelength of @xmath108 and that propagates with a faster phase velocity of @xmath109 . the wave number is increased via several phase annihilating defects . all our @xmath56interfaces selected bulk tw wave numbers close to the large-@xmath92 branch of the tw saddle - node curve ; cf . [ fig:4psisom+r - k](b ) and [ fig:3dpsi40om - k - r ] for @xmath110 and fig . [ fig : psi25v+om+k - r](c ) for @xmath111 . thus , these wave numbers are too large to be eckhaus stable @xcite . however , these fully developed tws were only convectively unstable @xcite : perturbations could grow but while doing so they were advected sufficiently fast downstream in the direction of the tw phase propagation so that they could not influence the upstream part of the @xmath56front state in a persistent way . in systems with sufficiently long downstream section of the front state the growing fluctuations have sufficient time or are sufficiently fast growing , respectively to reach a critical amplitude at which two neighboring rolls are annihilated @xcite as , e.g. , for the parameters of fig . [ fig : irregularfront ] . because noise can not be prevented in general one observes then such phase defects as in fig . [ fig : irregularfront ] at irregular points in time and space beyond a certain downstream growth length that is related to size of the noise and the growth rate . the associated roll - annihilation events can lead to an effectively reduced mean wave number in the very far downstream region of the convection bulk . thus , the coherent part of the @xmath56front close to the interface to conduction is followed by a second incoherent , chaotic phase front consisting of the erratically occurring phase defects . this phase front connects the smooth primary eckhaus unstable section to a smooth eckhaus stable tw with smaller wave number that is realized at larger downstream distances . for parameters for which the growth rate of perturbations of the primary front - selected tw is lower than the one of fig . [ fig : irregularfront ] one does not observe in short systems the erratically occurring phase defects and even less so the eckhaus stable final downstream tw state . indeed , that was the situation for most of our front states . we finally mention that we could also generate front states with frequencies larger than those of the laterally extended saddle node tws [ dotted lines in fig . [ fig : psi25v+om+k - r](b ) and fig . [ fig:4psisom+r - k](a ) ] , i.e. , with frequencies that lie above the respective dotted line in the respective 3d plot similar to the one of fig . [ fig:3dpsi40om - k - r ] . however , we suppose that in sufficient long systems and after long enough times these unstable tw realizations develop a @xmath58front in the downstream bulk possibly induced by roll annihilating defects @xcite . the right half of fig . [ fig : frontpics](b ) shows a typical @xmath58front . the mean lateral concentration current in the tw bulk part to the left of the @xmath58interface to conduction shuffles positive ( negative ) @xmath39 in the upper ( lower ) part of the layer towards the @xmath58interface . thus , a large vertical concentration gradient is maintained slightly ahead of it that strongly stabilizes the conduction regime to the right of the @xmath58interface : there the mixing number @xmath68 is even larger than 1 . in this way the tw oscillations are damped and the conduction regime is shielded against a rapid invasion of convection . the increase of @xmath112 upon approaching the interface from the convection side causes and is related to a similar increase of @xmath17 and @xmath87 . the rolls disperse with growing phase velocity @xmath17 over a short lateral distance at the interface . the decreasing convection amplitude lowers the mean concentration current and causes @xmath112 to grow further . this in turn enhances @xmath17 and @xmath87 leading to smaller convection amplitude and so on . it is therefore the strongly nonlinear lateral concentration current @xmath72 which is responsible for the rapid self amplified decay process of convection at the @xmath58interface . with increasing @xmath21 the front velocity @xmath89 changes sign , becomes positive and continues to grow [ fig . [ fig : psi25v+om+k - r](a ) and fig . [ fig:3psisv+l+w - r](a ) ] because the quiescent state becomes less stable when increasing @xmath21 . the slope of @xmath113 , i.e. , the increase of the front velocity is considerably steeper for negative @xmath89 than for positive ones : the strongly stabilizing solutal stratification ahead of the interface hinders convection to intrude into the quiescent fluid region but favours the latter to replace the tw part . the upstream lateral distance over which the @xmath58interface to conduction influences the tw to the left of it is definitely smaller than the downstream influence length of the @xmath56interface on the convective bulk . in the former case one can not observe a difference to an extended tw state at an upstream distance of , say , 10 - 15 rolls while in the latter case the downstream convection properties approach the asymptotic bulk tw behavior only over a significantly longer distance . so , in particular the phase dilatation at a @xmath58interface does not propagate upstream into the tw bulk against the fast phase flow . this also explains why in the formation process of a @xmath58front tw properties that were initially present in a developed form are conserved . in fact , we could produce coherent @xmath58fronts for a fixed @xmath21 with different wave numbers of the bulk tw part out of a whole band near the saddle node wave numbers @xmath114 . only for higher @xmath21 and initial wave numbers away from @xmath115 we observed long - time transient incoherent front behavior . here this transition to incoherence may correspond to a transition from a convectively to an absolutely unstable regime concerning the propagation of phase dilatations in upstream direction . we should like to stress again that in contrast to @xmath58fronts which depend on the preparation process the asymptotic downstream tw part of a @xmath56front is uniquely selected as discussed in the previous section . thus , for a particular @xmath21 we have found only a single coherent @xmath56front . for definiteness and for the sake of comparison with @xmath56fronts we show in the figs . of this paper the properties of @xmath58front states that have a bulk tw part which itself was selected by a @xmath56front . this , however , has a slight numerical drawback stemming from the convective eckhaus instability of this tw part : ever present phase noise ( in particular at the boundary of the upstream tw region ) is enhanced on the downstream way towards the @xmath58interface . we think that this effect is responsible for fluctuations in our frequency measurements of @xmath58fronts . these data are therefore not shown in figs . [ fig : psi25v+om+k - r](b ) and fig . [ fig:4psisom+r - k ] . however , in our simulations the upstream part of the @xmath58fronts were too short to allow for the full development of phase slip defects . consider a set - up where a @xmath56front generates a very long tw part that develops back into the quiescent fluid via a coherent @xmath58front . if the convective part is laterally sufficiently long then this structure appears as a two - front structure with the tw part being spatially confined between a @xmath56 and a @xmath58interface to conduction . this structure will in general either expand or shrink laterally . only when the two front velocities @xmath81 and @xmath89 are equal , i.e. , at the crossing points @xmath88 of the curves in figs . [ fig : psi25v+om+k - r](a ) and [ fig:3psisv+l+w - r](a ) one can have a stationary state , namely , a ltw with diverging length @xmath90 . we have simulated such structures at @xmath116 and @xmath117 for rayleigh numbers for which @xmath118 , i.e. , to the right of the crossing in figs . [ fig : psi25v+om+k - r](a ) and [ fig:3psisv+l+w - r](a ) so that these two - front structures expand . their properties are practically identical to those of the respective single - front states . the two - front structures have a technical advantage over the simulation of single fronts : we could use a periodic boundary condition that was located in the quiescent region of the former . this avoids the noise that is induced at the upstream tw boundary of a single @xmath58front state . with this noise source being absent in our two - front structures the frequency fluctuations at the @xmath58 interfaces of single @xmath58front states did not occur . when we reduced @xmath21 then the velocities of the two fronts approached each other along the lines in figs . [ fig : psi25v+om+k - r](a ) and [ fig:3psisv+l+w - r](a ) that were obtained from velocity measurements of single - front states . in that way we could reproduce the unique crossing point at @xmath88 where @xmath119 and where ltws with diverging @xmath90 exist with a drift velocity @xmath18 given by the crossing velocity . in addition to expanding two - front structures we simulated also shrinking ones for a particular parameter combination ( @xmath120 , for which @xmath121 ) that is located in fig . [ fig:3psisv+l+w - r](a ) at @xmath122 . as an example consider the large two - front structure as in fig . [ fig : ltwapproach ] . the @xmath56front selects in the bulk of this initial two - front structure a saddle node tw with wavelength @xmath123 . in the course of time the velocity @xmath89 of the @xmath58front approaches that of the @xmath56front and a stationary ltw forms with length @xmath124 that drifts with the velocity @xmath125 and oscillates with the frequency of the @xmath56front . these values of the @xmath56front remain practically unchanged in the whole process . we produced ltw states with very large length @xmath90 immediately below the rayleigh number @xmath91 . there , @xmath90 diverges thus marking the upper existence boundary of ltw states . and there , the velocities @xmath81 and @xmath89 of the @xmath56 and @xmath58front states , respectively , become equal . see figs . [ fig : psi25v+om+k - r ] and [ fig:3psisv+l+w - r ] for the corresponding results in the range of @xmath126 that we have investigated in this paper . upon decreasing @xmath21 below the threshold @xmath127 one finds uniquely selected ltw states . depending on parameters they can coexist stably with front states , extended tw states , and the quiescent basic state . for completeness we include here in fig . [ fig : phasediagram ] a phase diagram of the @xmath128 plane where all the ltws that we have numerically obtained in the range @xmath129 are shown by vertical bars together with the saddle - node location @xmath130 of extended tws ( full line ) and the oscillatory hopf bifurcation threshold @xmath131 for tws ( dashed line ) . but in this work we focus on the range @xmath126 . we should like to emphasize again that we found ltws for @xmath126 only in the parameter regime below @xmath127 , i.e. , to the left of the crossing points in figs . [ fig : psi25v+om+k - r](a ) and [ fig:3psisv+l+w - r](a ) where the velocities of independent single fronts become equal . thus , ltws exist at these @xmath10 only for parameters for which @xmath132 , i.e. , for which independent fronts would approach each other : eventually any convective region between them would shrink to zero and the quiescent conductive state would result if this interface motion would continue without change . however , the stabilization effects that allow in such a situation a uniquely selected stable and robust ltw are easily understood with the help of the investigations in the following subsections . on the other hand , for @xmath133 the front velocities are such that a two - front structure expands . a typical transient dynamics towards the uniquely selected ltw is shown in fig . [ fig : frontrelaxation ] for @xmath134 . here the initial condition was a very broad two - front structure that was prepared at @xmath135 where it shrinks with @xmath132 [ fig . [ fig:3psisv+l+w - r](a ) ] . in fact , the @xmath58front moves to the left with a speed that is about three times higher than that of the @xmath56front . in the following shrinking process where the @xmath58front closes up to the @xmath56front the latter does not change its velocity at all and the former keeps its velocity as long as the bulk tw part between the two fronts is effectively asymptotic , i.e. , without lateral variation . this behavior reflects the fact that in such broad two - front structures there is practically no interaction between the fronts when their distance is so large that an asymptotic tw part is realized between the interfaces to conduction . however , the situation changes when the convective region between the interfaces becomes less extended since it requires a finite downstream growth length behind a @xmath56interface over which the convection properties still vary with small gradients before the asymptotic tw is reached . the slow lateral variation is best seen in the mixing number @xmath112 in fig . [ fig : frontpics](e ) reflecting the slow variation of the concentration distribution and in the related convective contribution @xmath136 [ fig . [ fig : frontpics](g ) ] to the local buoyancy . when the front separation comes to the order of this length one can not speak any more of a two - front structure with two independent fronts : for the parameters of fig . [ fig : frontrelaxation ] the velocity of the formerly independent @xmath58front changes continuously from @xmath137 to @xmath138 , i.e , to the velocity of the preceeding @xmath56front and a coherent and robust ltw forms which moves with a drift velocity that is determined by the @xmath56front , @xmath139 . during this slowing - down process of the @xmath58interface its structure changes to that of the characteristic decay interface to conduction of a ltw . therein the two interfaces , i.e. , the former @xmath56 and @xmath58fronts , respectively , are in a robust equilibrium with each other at a uniquely selected fixed distance @xmath90 that depends on @xmath140 as shown in fig . [ fig:3psisv+l+w - r](b ) . so the @xmath58interfaces of ltws and front states do not influence significantly the upstream part of these stuctures . hence , the local concentration barrier ahead of the @xmath58interface does not select the drift velocity of ltws as speculated previously @xcite . it is rather the @xmath56interface that is the more important one . note that it is the downstream wake in the concentration field of the preceeding @xmath56front that effectively slows down the @xmath58front : when the latter reaches the region where the mixing number @xmath112 [ fig . [ fig : frontpics](e ) ] starts to decrease towards the preceeding @xmath56front , i.e. , when the convective contribution @xmath136 [ fig . [ fig : frontpics](g ) ] to the local buoyancy starts to increase then the speed of the approaching @xmath58interface has to slow down . this distance over which the @xmath56front influences the @xmath58front in a two - front structure grows when the soret coupling becomes stronger . for example at @xmath141 a separation of about 160 rolls between the two interfaces is not sufficient to ensure independence . the sensitive dependence of the velocity of the @xmath58interface on the concentration - induced buoyancy variation in the wake behind the @xmath56front is the main reason for the robust localization mechanism of ( long ) ltws . the invasion of conduction into the convective region via the trailing @xmath58interface is stopped at just that well defined distance from the @xmath56front where the concentration - induced convective buoyancy @xmath136 has become sufficiently large . the latter increases monotonously towards the well mixed region under the @xmath56interface since this degree of advective mixing decreases gradually in the wake behind the @xmath56interface . see , e.g. , ref . @xcite for an explanation of the associated interplay of diffusion and advection which both reduce concentration gradients and the soret effect which generates them . of course , the effect of stopping the approaching @xmath58interface at a particular distance from the @xmath56interface can be interpreted as an effective repulsive interaction between them . the structural similarity between long ltws and fronts is documented in fig . [ fig : frontpics ] . differences between the full lines ( fronts ) and the dashed ones ( ltw ) are visible only in the case of the @xmath58front in fig . [ fig : frontpics](d , f , h ) . here the bulk asymptotic tw that is realized to the left of the @xmath58front differs slightly from the plateau tw in the ltw . the above mentioned @xmath39 redistribution via @xmath72 enhances the buoyancy at the @xmath56interface and leads there to a self - consistent stabilization of convection against invasion of conduction at the @xmath56front . this mixing effect makes stable ltws possible even for low heating rates @xmath21 where neither extended tw convection nor fronts exist . long ltws are characterized by a wide tw part with a well developed plateau with almost no lateral variation in the convection properties like , e.g. , @xmath17 or @xmath112 @xcite . the tw plateau separates the growth and the decay part of convection at the @xmath56 and @xmath58interface , respectively and it provides a communication mechanism favoring one direction : the first region is shielded from the second one by the fast downstream phase propagation . like in a single @xmath58front state the @xmath58interface of the ltw does not influence the upstream tw ; it only manages the decay transition of the tw vortices into the quiesent fluid . thus , the @xmath56front character at the @xmath56interface is also present in the ltw . and the properties of long ltws are dominated by and similar to those of the single @xmath56front at the same @xmath21 if the latter exists . for example , the drift velocities of long ltws agree with the values of the corresponding @xmath56fronts in figs . [ fig : psi25v+om+k - r ] , [ fig:3psisv+l+w - r ] , [ fig:4psisom+r - k ] , [ fig:3dpsi40om - k - r ] , [ fig : ltwapproach ] , [ fig:4psisom - r ] . furthermore , they continue to show the same linear variation with @xmath21 as the @xmath56fronts even where the latter cease to exist at smaller @xmath21 , cf . , the open circles in fig . [ fig:3psisv+l+w - r](a ) for the cases of @xmath134 and @xmath142 . similarly , the variation @xmath143 of long ltws follows the corresponding one of @xmath56fronts , cf . , open circles and filled triangles in fig . [ fig:4psisom - r ] . a comparison of ltw plateau values with extended tws and front tws is presented in fig . [ fig : psi25v+om+k - r](b , c ) for @xmath116 , in fig . [ fig:3dpsi40om - k - r ] for @xmath142 , and in fig . [ fig:4psisom+r - k ] for for all examined @xmath10 . at @xmath101 ( arrows ) there is no difference between the fronts , the diverging ltws , and the extended saddle tws . for decreasing @xmath21 convection is less stable , the disintegration of the traveling rolls sets in earlier , and the ltw length @xmath90 is therefore reduced , cf . , the inset of fig . [ fig : psi25v+om+k - r ] and fig . [ fig:3psisv+l+w - r](b ) . the smallest plateau wave numbers of ltws are realized for diverging lengths at @xmath127 . with decreasing @xmath21 one finds a slight increase of @xmath144 while the wave number selected by a single @xmath56front remains close to that of the saddle tw . so this is the ltw bifurcation scenario that we found in the range @xmath126 ( for a discussion of the scenario at smaller soret coupling strength cf . [ sec : small - soret ] ) : approaching @xmath145 from below ltws become indistinguishable from front states when @xmath100 . but further below @xmath145 ltws differ more and more in particular with respect to the bulk wave numbers as can be seen in figs . [ fig:4psisom+r - k ] and [ fig:3dpsi40om - k - r ] . however , for long enough ltws with a well developed spatial bulk plateau behavior the frequencies @xmath146 and drift velocities @xmath147 vary like the corresponding quantities of @xmath56fronts . this confirms the fact @xcite that it is the @xmath56front - like growth interface that selects the properties of a long ltw . shorter ltws behave also with respect to the variation of @xmath146 and @xmath147 somewhat differently . reducing @xmath21 one eventually arrives for any @xmath10 at the regime of short ltws that are marked in figs [ fig : psi25v+om+k - r ] , [ fig:3psisv+l+w - r ] , and [ fig:4psisom - r ] by shaded circles and that are located close to the dotted line in fig . [ fig : phasediagram ] . here , the dominant influence of the @xmath56front vanishes eventually in the regime of short ltw pulses . no convection plateau can be identified any more in these structures , cf . the dotted curves in fig . [ fig : frontrelaxation ] . the prototype of a short ltw consists of a growth interface which is followed directly by the decay of convection so that the whole pulse has to be seen now as one integrated structure that no longer contains front - like independent @xmath56 and @xmath58interfaces . hence , short ltws show a strong lateral variation of their properties . the shape of their amplitudes superficially resemble the pulse solutions of the complex ginzburg - landau equation @xcite . like for long ltws the stable existence of short pulses below any heating that is necessary to sustain extended tws is caused by a lateral @xmath39 redistribution over the pulse . also its frequency @xmath67 is constant in the frame that comoves with the drift velocity @xmath18 of the pulse like for a long ltw . however , compared to long ltws short ltws provide a qualitatively new convection structure . they are independent of and can not even be compared with extended tws because there is no characteristic wavelength or phase velocity . the special character of short pulses compared with long ltws or fronts is reflected in the change of the @xmath21-variation of @xmath148 that can be seen in figs . [ fig : psi25v+om+k - r ] , [ fig:3psisv+l+w - r ] , and [ fig:4psisom - r ] by comparing the dashed circles with the open ones and the filled triangles . we observed the shortest possible ltws at the lower end , @xmath149 , of the @xmath21 band of ltws . there they seem to end via a saddle node bifurcation for pulses @xcite . these minimal pulses always contained about 5 convection rolls for all soret couplings @xmath150 that we have investigated . this surprising universality of @xmath151 , i.e. , its insensitivity to the values of the actual heating rate @xmath149 and the soret coupling @xmath10 is still unexplained . approaching the lower band limit of ltws their flow intensity steeply drops [ fig . [ fig:3psisv+l+w - r](c ) ] and consequently their frequency increases [ fig . [ fig:4psisom - r ] ] as the degree of advective mixing of the fluid decreases . several attempts have been made to describe ltws by simple model equations . stable pulse solutions of the complex ginzburg - landau equation ( cgle ) were proposed as a model for confined binary mixture convection @xcite . the nonlinear interaction between the local amplitude and frequency seems to be the essential localization mechanism in this approximation . indeed , one could find localized solutions of increasing length up to the limit of an infinitely long two - front state @xcite . but some basical problems remained : within the cgle all pulses drift with the same velocity . this is the critical linear group velocity @xmath152 if the coefficients are derived from an asymptotic reduction of the full hydrodynamic field equations . but @xmath152 is too fast by a factor of about 20 - 40 compared with the ltw drift velocity in experiments or simulations @xcite . brand and deissler @xcite introduced asymmetry in the pulse properties by adding nonlinear gradient terms to the cgle . a similar extension was given by bestehorn _ @xcite within their framework of order parameter equations . both could produce a very slow drift , even opposite to the phase direction @xcite . but this kind of nonlinear modification of the linear group velocity involves a balance which seems to be too fragile to explain the occurrence of small pulse velocities over a whole range of @xmath10 and @xmath21 @xcite . another problem was mentioned by van saarloos and hohenberg @xcite . according to their model of a quintic cgle nonlinear wide pulses are expected by counting arguments to exist only in a codimension-2 submanifold of the parameter space . provided there are no hidden symmetries this seems to be incompatible with the robust occurrence of ltws in experiments . furthermore , stable pulse solutions seem to exist only in the bistable regime whereas ltws are known to persist well above the linear onset of extended convection for weakly negative @xmath10 @xcite . furthermore , coexisting small stable and wide unstable ltws were never seen in the cgle but found in experiments by kolodner @xcite . instead , stable broad pulse solutions are found in the model to arise in a saddle node bifurcation together with an unstable branch of smaller critical droplets near the basic state @xcite . finally , numerical solutions of the field equations show the existence of stable ltws even below the lowest tw saddle node @xcite . this makes clear that ltws are influenced by a localization mechanism that is not contained in the cgle . inspired by simulation results of barten _ @xcite which showed the important role of the concentration field for a ltw riecke @xcite proposed an extension of the ginzburg - landau equations . within a weakly nonlinear expansion he coupled into the standard cgle as an additional slow variable the amplitude @xmath153 of an advected mean large - scale concentration mode that influences the growth of the critical modes . a similar idea was advanced already by glazier _ the extension can induce an additional amplitude - intability of phase winding solutions to modulated waves . it may be considered as the origin for pulse formation in this ansatz @xcite . riecke showed that the influence of the real @xmath153-mode alone on the local growth rate ( without dispersion ) suffices to generate slowly drifting stable pulse solutions even below a supercritical tw - bifurcation @xcite . in this way he modelled a new localization mechanism to explain the robust occurrence of ltws in binary mixture convection . the amplitude @xmath153 can be interpreted as a measure for the local mixing state or the mean convection - induced deviation of the vertical concentration gradient from the conductive one . in this way his extended complex ginzburg - landau equation ( ecgle ) contains in a sketchy way physical effects like the mixing influence on the growth rate and the large - scale concentration redistribution . riecke characterized within his model short and long ltws as dispersion - dominated pulses @xcite and states of two fronts that are bounded by the @xmath153 dynamics @xcite , respectively . he proposed an explanation for their coexistence in stable and unstable form , respectively , by the competition between dispersion - dominated and @xmath153-dominated localization @xcite . note , however , that in contrast to the model used by riecke our results show stable long ltws that drift either in or opposite to the direction of phase propagation depending on paramters . it would be interesting to check whether adding a term of the form @xmath154 to the @xmath153-equation can stabilize forward drifting long pulses within the model since it models the concentration wake , i.e. , the transport of the local mixing state in phase direction by the traveling rolls of amplitude @xmath155 . numerical and analytical investigations of the ecgle predict a hysteretic transition from slow to fast drifting pulses or the existence of oscillatory moving ones @xcite . but both were never seen in experiments or simulations . thus , despite their capability in elucidating some essential mechanisms cgle type models have the drawback so far that they reproduce only single aspects of ltws in a qualitative manner . their range of validity and their predictive power is not well known . and since a satisfactory relation with the full field equations has not been established these models remain somewhat arbitrary . it appears questionable that weakly nonlinear expansions with spatially slowly varying mode amplitudes are approriate at all in view of the very large pclet numbers , @xmath2(1000 ) , measuring the strength of the nonlinearity in the concentration balance . thus , so far numerical simulations of the full field equations seem to be the appropriate tool besides careful experiments to gather insight into the specific physical mechanisms for ltw formation in binary mixture convection . an inspection of figs . [ fig : psi25v+om+k - r ] , [ fig:3psisv+l+w - r ] , and [ fig : phasediagram ] shows that the lower band limit @xmath149 for the existence of short ltws and the crossing value , @xmath156 , where the velocities of free fronts become equal approach each other when @xmath157 decreases . thus , one can foresee an interval of moderately negative @xmath10 where short and long ltws can be found close to @xmath145 . in this case the upper band limit for the existence of stable ltws should be defined by a backward saddle - node bifurcation at @xmath158 where the branches of stable short and unstable long ltws annihilate each other . hence , we expect that the upper parts of the bifurcation diagrams of @xmath90 versus @xmath21 in the inset of figs . [ fig : psi25v+om+k - r ] and in fig . [ fig:3psisv+l+w - r](b ) curve backwards towards smaller @xmath21 when @xmath157 decreases further below the values of the two figures . in this way the shape of the curve @xmath159 would change continuously from the form shown in fig . [ fig : l - r - scheme](b ) to the one in fig . [ fig : l - r - scheme](a ) . the former shows schematically the bifurcation behavior of @xmath159 that we have determined numerically for @xmath160 . in fact , at @xmath10 slightly larger than -0.25 we expect the appearence of the saddle - node in the curves @xmath159 . [ fig : l - r - scheme](a ) is a schematic representation of experimental results of kolodner @xcite for @xmath161 as presented in his fig . he stabilized by an adaptive heating mechanism long unstable ltws in coexistence with short stable ones . thus , the unstable ltw solution branch [ dashed line in fig . [ fig : l - r - scheme](a ) ] forms for @xmath162 a separatrix between the domains of attraction of expanding two - front structures to the right of the dashed line in fig . [ fig : l - r - scheme](a ) and the domain to the left of the dashed line leading to stable narrow pulses or the basic state . furthermore , small ltws that are prepared at @xmath163 will evolve into expanding two - front structures when @xmath21 is increased above @xmath158 . note that in kolodner s experiment @xcite done at @xmath161 the upper band limit @xmath158 of ltws lies _ above _ the hopf bifurcation threshold @xmath164 for extended tws where perturbations of the quiescent fluid can grow . therefore , one has to address there questions related to linear and nonlinear convective versus absolute instability @xcite , to linearly selected so - called pulled fronts versus nonlinearly selected so - called pushed fronts @xcite , and to the robustness and stability of nonlinear fronts under emission or absorption of tw perturbations that can grow in the region occupied by the quiescent fluid . for stronger negative @xmath10 the measured ltw properties agree qualitatively well with our results . for example , the arbitrary - width confined states found in experiments @xcite for @xmath165 at a single rayleigh number are to be identified as two - front structures . a quantitative comparison is difficult due to the difference in the boundary conditions : we simulated two - dimensional convection assuming translational symmetry in @xmath166-direction while the narrow experimental convection channels impose no - slip conditions at the walls perpendicular to the roll axes . there are three effects that account for the difference beteen experiments and simulations . first , the characteristic rayleigh numbers in the experiments are higher . this is already known from the suppression of oscillatory or steady convection instabilities in narrow channels @xcite . the no - slip conditions at the side - walls generate a nontrivial @xmath166-variation of the velocity field that introduces additional internal friction and that has to be compensated by a higher heating rate @xcite . second , the ltw drift velocities in the experiment have the global tendency to lie below those of the simulations . for example , for @xmath165 the experimental ltws @xcite move opposite to the phase velocity whereas according to our calculations @xmath18 should be around @xmath167 . again , we attribute this difference to the fact that we neglect gradients in @xmath166-direction . they change the concentration redistribution dynamics in particular at the @xmath56interface of the ltw which determines the drift velocity . in this context one has to note that already weak inhomogeneities in a convection cell can slow down and even pin the ltw movement @xcite . finally , the influence of the different boundaries on the frequencies , phase velocities , and wave numbers of confined states are totally unknown . also when comparing quantitatively our results for fronts with experiments one should take into account the above discussed points . extrapolating our results for the front velocities to more negative @xmath10 beyond @xmath142 we see that already at the lowest tw saddle location @xmath168 two - front stuctures would expand with @xmath169 . in other words , the velocity crossing point @xmath88 is no longer above @xmath168 but has virtually moved below the lowest tw saddle location where in fact no fronts exist . on the other hand , ltws still exist in this @xmath21-range with length increasing with @xmath21 . however , @xmath159 does not seem to diverge anymore as for @xmath170 which is compatible with the absence of fronts moving with the same velocity . laterally confined convection patches of traveling rolls were found in the early experiments @xcite that were done in narrow rectangular convection channels in the form of so - called wall - attached confined structures ( wacs ) . they were localized near one of the short end walls closing the channel . these wacs can be understood with our knowledge of fronts and free ltws . for example , for the weakly negative @xmath10 used in the early experiments the phase velocity of the wacs was directed towards the wall to which they were attached . indeed , for such parameters mainly short ltws occur with drift velocities in phase direction so that they would end as wacs of the above described type in finite length channels . furthermore , the measured wacs profiles of phase velocity @xmath17 , of wavelength @xmath87 , and their decrease of frequency with increasing @xmath21 @xcite agree qualitatively with the typical behavior of free short ltws . the connection between wacs and free ltws was more explicitly demonstrated by kolodner @xcite for more negative separation ratios @xmath171 and @xmath172 : he prepared a free ltw pulse with large phase velocity ( a fast confined state in his terminology ) which drifted slowly opposite to the direction of phase propagation towards an end wall of the convection channel and became there a wacs ( a slow confined state in his terminology ) with lower phase velocity being directed away from the wall . in this wacs the phase generating trailing front , i.e. , the analogue of the @xmath56interface is pinned at the wall and therefore without solutal gradients to the quiescent fluid as in a free ltw . the absence of these concentration variations at the @xmath56interface implies and allows a lateral concentration redistribution over the whole state at lower levels of the mixing number @xmath68 in wacs as compared to free ltws . consequently , the phase velocities and frequencies of wacs are smaller than those of the respective free ltws . a less dramatic drop of frequency was observed also between forward drifting ltws and short wacs at @xmath173 @xcite . due to their better mixing capability , i.e. , smaller @xmath68 it is very probable that short wacs can exist for heating rates below the lower band limit @xmath149 of stable ltw pulses at least in the case where the phase velocity is directed away from the wall . it would be very interesting to test this conjecture experimentally , in particular for strongly negative @xmath10 . there @xmath149 itself lies already well below the range of stable tws @xcite and so the wacs would lie even lower . an inportant hint that this conjecture is right is given by ning _ they have performed two - dimensional simulations of a finite - length convection channel with realistic boundary conditions for @xmath174 , and @xmath52 . neglecting the slight difference in @xmath175 their results should be comparable with our work . they found short wacs at @xmath176 which is according to our results far below the tw saddle nodes for this separation ratio and also below the lower band limit @xmath149 of free ltws for @xmath177 . however , these authors claim we think , incorrectly that their wacs lie above the saddle - node location @xmath93 of extended tws . in the previous section we have shown that the @xmath56interface where the convection rolls grow in downstream direction out of the quiescent fluid plays the dominant role for the stability of ltws . while the @xmath58interface where the decaying rolls are advected into the quiescent fluid does not play a decisive role . this is clearly confirmed in pulse collision experiments @xcite . fast tw pulses linear ones with small amplitude as well as nonlinear ones with larger amplitude were completely absorbed by a ltw when the pulses hit the @xmath58interface of the ltw , i.e. , when the pulse velocity is directed opposite to and towards the phase velocity of the ltw . then the collision with the pulse affects only the @xmath58interface itself and perturbations are quickly advected out of the ltw and do not propagate upstream towards the @xmath56interface . for the same reason double - ltw states of two counter propagating waves can persist over a long time @xcite or even be stable @xcite . moreover , a pair of ltws that have their phase propagation directed towards each other and that interact with each other via their decay interfaces is seen to be stable over a substantially wider @xmath21-range than two ltw pulses which are connected at their growth interfaces @xcite . obviously the latter case is more critical for the structural integrity of the involved ltws . a ltw is most likely destroyed when another wave with the same direction of phase propagation infiltrates its phaseflow at the growth region . then , while growing the perturbations can be transmitted into the strongly nonlinear bulk part of the ltw and can destroy its coherence . the different selection and stability properties of the @xmath56 and @xmath58interfaces were already observed in transient convection behavior in various experiments ( see for example @xcite ) , however without further investigation . the fact that ( @xmath178 ) different @xmath58fronts with different bulk tw parts are possible as stable coexisting states and that ( @xmath179 ) a @xmath56front interface is in general stable against downflow perturbations opens the possibility for another kind of stable long confined tws : therein rolls with low wavelength grow out of the quiescent fluid in a normal growth part . in the bulk an incoherent phase front connects this fast wave that is coming from the @xmath56interface with a slow wave of higher wavelength and larger amplitude via spatiotemporal dislocations as , e.g. , in fig . [ fig : irregularfront ] . the transition could take place via one or more intermediate convection states . eventually this slow tw convection undergoes a decay transition into the basic state via a coherent @xmath58interface . such defected confined states are indeed observed in annular containers @xcite and were studied by kolodner @xcite . he found such structures only for @xmath180 . one may speculate that for these separation ratios the bulk tw that is selected by and behind the @xmath56interface is absolutely unstable against the slow wave in the further downstream part . this could explain the existence of persistent roll pair annihilations without the need of fluctuations . we finally mention that the occurrence of phase annihilating dislocations between a growth part and the downstream convection was observed for moderately negative @xmath10 already in narrow rectangular containers @xcite . furthermore , end - wall induced eckhaus instabilities of downstream tw states have been seen in simulations @xcite . for parameters where the conductive quiescent fluid is stable and where spatially extended tw solutions bifurcate subcritically out of it we have investigated in quantitative detail relaxed , strongly nonlinear oscillatory convection structures with one or two interfaces to the quiescent fluid , i.e , fronts and ltws , respectively . they are time - periodic global nonlinear modes : in the frame that is comoving with the respective front velocity @xmath55 or with the ltw drift velocity @xmath18 the oscillations have everywhere the same period . fronts come in two varieties . in a @xmath56front state the quiescent fluid is located upstream , i.e. , phase propagates out of it into convection . in a @xmath58front the quiescent fluid is located in downstream direction and phase moves out of convection into conduction . the lowest rayleigh number for the existence of fronts is the lowest saddle - node location of extended tws , @xmath181 : below it there are no tws to which the interface from conduction can connect . however , ltws of _ finite _ length @xmath90 can coexist bistably together with the conductive state well below the lowest tw saddle when the soret coupling is sufficiently negative , @xmath182 . furthermore , we have arguments that wacs at end walls of rectangular channels can exist even at smaller @xmath21 than ltws . central for understanding fronts and ltws is a large - scale concentration redistribution that influences the buoyancy at the interfaces to conduction in different ways than in the bulk tw parts . for example , at the @xmath56interfaces of fronts and ltws alike there is a buoyancy overshoot which is sufficiently large to sustain local convection growth there and that can cause even invasion of convection into the stable quiescent fluid . at the @xmath58interface the lateral buoyancy variation is such as to induce the decay of the approaching convection rolls into the conductive state . front velocities as well as ltw drift velocities are much smaller than the phase velocities of the carrier waves for reasons that are related to the concentration redistribution dynamics . the velocities of @xmath56fronts decrease with growing @xmath21 while those of @xmath58fronts increase . at some @xmath88 they become equal so that both fronts move with the same velocity . at this rayleigh number the length @xmath90 of the ltws diverges and there , and strictly speaking only there , the limiting ltw can be seen as a state consisting of two fronts . however , @xmath56fronts and long ltws have almost identical propagation velocities and frequencies . furthermore , they select a similar bulk wave number . the selected frequencies and bulk wave numbers are close to those of a saddle - node tw . in fact , it is the @xmath56front - like growth interface that selects the properties of long ltws . small amplitude extended tw perturbations of the conductive state oscillate with the large hopf frequency . but the global - mode oscillation is restrained by the requirement that its frequency has to allow stable developed bulk tw convection . it is interesting to note that the @xmath56interface connecting conduction with convection selects the largest possible frequency eigenvalue that meets this requirement , namely the tw saddle - node frequency . all our @xmath56fronts select bulk tw wave numbers close to the large-@xmath92 branch of the tw saddle - node curve , i.e. , wave numbers that are too large to be eckhaus stable . however , these tws are only convectively unstable : perturbations can grow but while doing so they are advected sufficiently fast downstream in the direction of the tw phase propagation so that they can not influence the upstream part of the @xmath56front state in a persistent way . while @xmath56front states seem to be uniquely selected we could produce for a fixed @xmath21 different coherent @xmath58fronts that were characterized in the bulk part by different wave numbers and frequencies close to the tw saddles . the decay interface adjusts itself to the respective bulk tw part but does not exert an influence in upstream direction on the bulk convection within a coherent @xmath58front . in contrast , the growth under a @xmath56interface induces in downstream direction a long concentration wake that is characteristic for @xmath56fronts and long ltws and of special importance for the latter . here it is interesting to notice that all the interfaces of fronts and ltws consist typically only of about 3 - 4 convection rolls . we furthermore should like to mention that @xmath56interfaces of fronts and ltws always locate a minimal wavelength . its value , @xmath85 , is remarkably universal for _ all @xmath21 and @xmath10 _ that we have simulated . this is unexplained so far . we have also prepared initial two - front stuctures by connecting a @xmath56front and a @xmath58front with a common long bulk tw . when @xmath133 they expand . but at @xmath122 they shrink towards a uniquely selected ltw of fixed length @xmath90 . here the downstream wake in the concentration field of the preceeding @xmath56front exerts an effective repulsion on the approaching @xmath58interface : the invasion of conduction via the latter is stopped at a well defined distance @xmath90 that is determined by the concentration - induced buoyancy levels in the wake of the @xmath56front . ltws shortly below @xmath88 ( where ltw with diverging @xmath90 are possible ) are very long . their drift velocities , frequencies , and many stuctural properties are similar to those of @xmath56fronts . decreasing @xmath21 the ltw length decreases and one eventually arrives for any @xmath10 at the regime of short ltws that lies for strongly negative @xmath10 well below the tw saddle - 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( a , b ) color coded snapshot of concentration deviation @xmath39 from its global mean in a vertical cross section of the layer . the color code is shown at the right end of ( b ) . ( c , d ) instantaneous lateral wave profile at midheight , @xmath187 , of @xmath39 ( green ) , vertical velocity @xmath188 ( blue ) , and its envelope . arrows mark the positions where @xmath188 has grown up to @xmath61 . ( e , f ) mixing number @xmath68 ( green ) , eq . ( [ eq : m(x ) ] ) , and phase velocity @xmath61 ( black ) of the nodes of @xmath188 in the comoving frames . the variation of @xmath84 is the same since the frequency @xmath67 is a _ global _ constant . ( g , h ) time averaged deviations from the conductive state at @xmath189 for concentration ( green ) , temperature ( red ) , and their sum ( @xmath190 ) measuring the convective contribution to the buoyancy . ( i , j ) streamlines of the averaged concentration current @xmath72 ( green ) and velocity field @xmath191 ( blue ) . the latter results from @xmath190 and documents roll shaped contributions of @xmath192 to @xmath72 at the interfaces . thick blue and green arrows indicate @xmath191 and transport of positive @xmath39 ( alcohol surplus ) , respectively . temporal averaging is always performed in the frame comoving with the respective front velocity . dashed lines show the decay part of the long ltw that coexists at the same parameters ( @xmath193 ) with the fronts . differences between the interfaces of the @xmath56front and the corresponding ltw interface are not visible on the scale of the above plots . [ fig : frontpics],width=529 ] for @xmath116 . left and right pointing triangles with triangles denote @xmath56 and @xmath58fronts , respectively . open and shaded circles refer to long and short ltws , respectively . ( a ) front velocities of relaxed single - front states ( thick dashed lines with filled triangles ) , of expanding two - front states ( thin dashed lines with open triangles ) , and drift velocities of ltws ( circles ) . the inset shows the drastic increase of ltw length @xmath90 at @xmath101 where the front velocities of the @xmath56 and @xmath58 single - front states become equal . ( b ) frequencies of front states and of long ltws in comparison with the rest frame frequencies of laterally periodic tws . the saddle - node vicinities of the latter are shown by full lines for several wave numbers @xmath194 . tw states with frequencies above the dotted line of saddle - node tws are unstable . ( c ) wave numbers selected by front states in the bulk part far away from the interface ( triangles ) and in the central part of long ltws ( open circles ) . horizontal lines indicate the laterally periodic tws that are shown in ( b ) by full lines . the continuum of these tw states is bounded in the @xmath195 plane by the dotted line of tw saddle nodes , @xmath114 . here we show only the large-@xmath92 branch of it ( cf . the dotted line marked @xmath93 in fig . [ fig:3dpsi40om - k - r ] for another perspective ) . [ fig : psi25v+om+k - r],width=302 ] . ( a ) front velocities , @xmath55 , of @xmath56fronts ( left pointing triangles ) , of @xmath58 fronts ( right pointing triangles ) , and drift velocities , @xmath18 , of ltws ( circles ) versus @xmath21 . note that short ltws ( shaded circles ) and long ltws ( open circles ) show different @xmath196-behavior . the latter varying linearly with @xmath21 is nearly indistinguishable from @xmath197 . arrows mark the low-@xmath21 existence boundary @xmath168 of laterally periodic tws and with it of front states . ltws exist below this threshold @xcite with drift velocities that show the above mentioned linear variation with @xmath21 as long as the ltws are long enough . to identify an ltw as a long one we required a clearly visible plateau in the spatial properties . ( b ) length @xmath90 of the ltws of ( a ) measured as the distance between the half maximum values of the envelope of the vertical velocity field @xmath188 [ cf . , blue line in fig . [ fig : frontpics](c , d ) ] . ( c ) maximal vertical flow velocities @xmath198 of ltws . [ fig:3psisv+l+w - r],width=321 ] fronts ( dashed lines with triangles ) , long ltws ( circles ) , and laterally extended saddle - node tws ( dotted lines ) for different @xmath10 . the wave numbers of the two former refer to plateau values in the bulk part away from the interface . ( a ) frequency @xmath67 ( for tws in the rest frame and for ltws and fronts in the comoving frame ) versus wave number @xmath92 . ( b ) the same convection structures in the @xmath94 plane . the wave numbers and frequencies of ltws with @xmath100 ( arrows ) coincide at @xmath101 with those of the respective @xmath56 fronts . [ fig:4psisom+r - k ] , width=321 ] front . shown are the extrema positions of the vertical velocity field @xmath188 . the initial condition at time @xmath199 ( not visible ) consisted of an extended tw for @xmath105 with wavelength @xmath106 and phase velocity @xmath107 and quiescent fluid for @xmath200 . boundary conditions are conduction at @xmath201 and @xmath202 that imposes at @xmath203 a wavelength of @xmath106 . first , a pulse that causes a quite regular sequence of roll - pair annihilation events ( lower line of defects ) propagates to the right with velocity greater than @xmath61 . the intermediate wave pattern resulting from this primary sequence of defects is then transformed via further , somewhat erratically occurring phase defects into the fast asymptotic tw with @xmath204 that is favoured by the @xmath56front . the boundary condition at @xmath203 that imposes a wrong wavelength there does not influence the bulk behavior which is selected by the front . parameters are @xmath205 . [ fig : frontrelaxation],width=566 ] . the front selects a bulk tw with wavelength @xmath206 that is strongly eckhaus unstable : while beeing advected downstream phase deformations ( that are caused , e.g. , by computer noise ) grow sufficiently fast to reach a critical amplitude within the system length . then two neighboring rolls are annihilated . that increases the wavelength and decreases the phase velocity towards eckhaus stable values . parameters are @xmath207 . [ fig : irregularfront],width=566 ] ( bottom ) after starting with a very long two - front structure at @xmath208 . the @xmath56front selects in the bulk of the initial two - front structure a saddle - node tw with wavelength @xmath123 . with @xmath209 the @xmath58front approaches the @xmath56front and doing so the velocity of the former goes monotonously towards @xmath81 . this transient process ends in a long ltw ( dashed line ) of constant length @xmath124 with a plateau wavelength of @xmath210 . its drift and frequency is effectively the same as the respective values of the @xmath56front which remain unchanged all the time . for comparison the profiles of a short ltw at the same @xmath10 but smaller @xmath211 are shown with dotted lines . [ fig : ltwapproach],width=321 ] plane . the vertical bars indicate the range of stable existence of those ltws that we have numerically simulated . full and dashed lines refer to the saddle node location @xmath93 of extended tws and to their oscillatory hopf bifurcation threshold @xmath164 , respectively ; both for a wave number @xmath212 . for @xmath213 the upper existence boundary of ltws was determined by the requirement that @xmath90 remained below about 120 in our numerical set - up . the dotted line guides the eye along the lower band limit @xmath149 of ltws . parameters are @xmath214 . [ fig : phasediagram],width=321 ] of @xmath56fronts ( dashed lines with triangles ) and of ltws ( full lines with circles ) in the respective comoving frame versus @xmath21 for different @xmath10 . open and shaded circles refer to long and short ltws , respectively . the frequencies of the former are the same as those of the fronts while short ltws differ . arrows indicate the lower limit of existence of the fronts at @xmath215 . [ fig:4psisom - r],width=321 ] versus @xmath21 . ( a ) experimental results @xcite obtained for @xmath161 with dashed line denoting unstable states ( cf . , text for further explanation ) ; ( b ) numerically obtained bifurcation behavior for @xmath126 . [ fig : l - r - scheme],width=321 ][/INST] nonlinear fronts between spatially extended traveling wave convection ( tw ) and quiescent fluid and spatially localized traveling waves ( ltws ) are investigated in quantitative detail in the bistable regime of binary fluid mixtures heated from below . a finite - difference method is used to solve the full hydrodynamic field equations in a vertical cross section of the layer perpendicular to the convection roll axes . results are presented for ethanol - water parameters with several strongly negative separation ratios where tw solutions bifurcate subcritically . fronts and ltws are compared with each other and similarities and differences are elucidated . phase propagation out of the quiescent fluid into the convective structure entails a unique selection of the latter while fronts and interfaces where the phase moves into the quiescent state behave differently . interpretations of various experimental observations are suggested . </s>

Bradley Manning, the Army private arrested in the biggest leak of classified material in U.S. history, pleaded guilty Thursday to charges that could send him to prison for 20 years, saying he was trying to expose the American military's "bloodlust" and disregard for human life in Iraq and Afghanistan. FILE - In this June 25, 2012 file photo, Army Pfc. Bradley Manning, right, is escorted out of a courthouse in Fort Meade, Md. The Army private charged in the largest leak of classified material in U.S.... (Associated Press) Military prosecutors said they plan to move forward with a court-martial on 12 remaining charges against him, including aiding the enemy, which carries a potential life sentence. "I began to become depressed at the situation we found ourselves mired in year after year. In attempting counterinsurgency operations, we became obsessed with capturing and killing human targets on lists," the 25-year-old former intelligence analyst in Baghdad told a military judge. He added: "I wanted the public to know that not everyone living in Iraq were targets to be neutralized." It was the first time Manning directly admitted leaking the material to the anti-secrecy website WikiLeaks and detailed the frustrations that led him to do it. The slightly built soldier from Crescent, Okla., read from a 35-page statement through his wire-rimmed glasses for more than an hour. He spoke quickly and evenly, showing little emotion even when he described how troubled he was by what he had seen. The judge, Col. Denise Lind, accepted his plea to 10 charges involving illegal possession or distribution of classified material. Manning was allowed to plead guilty under military regulations instead of federal espionage law, which knocked the potential sentence down from 92 years. He will not be sentenced until his court-martial on the other charges is over. Manning admitted sending hundreds of thousands of Iraq and Afghanistan battlefield reports, State Department diplomatic cables, other classified records and two battlefield video clips to WikiLeaks in 2009 and 2010. WikiLeaks posted some of the material, embarrassing the U.S. and its allies. He said he was disturbed by the conduct of the wars in Afghanistan and Iraq and the way American troops treated the populace. He said he did not believe the release of the information he downloaded onto a thumb drive would harm the U.S. "I believed that if the general public, especially the American public, had access to the information ... this could spark a domestic debate on the role of the military and our foreign policy in general," Manning said. Manning said he was appalled by 2007 combat video of an assault by a U.S. helicopter that killed 11 men, including a Reuters news photographer. The Pentagon concluded the troops mistook the camera equipment for weapons. "The most alarming aspect of the video to me was the seemingly delightful bloodlust the aerial weapons team happened to have," Manning said, adding that the soldiers' actions "seemed similar to a child torturing ants with a magnifying glass." As for the State Department cables, he said they "documented backdoor deals and criminality that didn't reflect the so-called leader of the free world." "I thought these cables were a prime example of the need for a more open diplomacy," Manning said. "I believed that these cables would not damage the United States. However, I believed these cables would be embarrassing." The battlefield reports were the first documents Manning decided to leak. He said he sent them to WikiLeaks after contacting The Washington Post and The New York Times. He said he felt a reporter at the Post didn't take him seriously, and a message he left for news tips at the Times was not returned. Times spokeswoman Eileen Murphy said Thursday of the purported phone call: "This is news to us." The Obama administration has said the release of the documents threatened valuable military and diplomatic sources and strained America's relations with other governments. The administration has aggressively pursued people accused of leaking classified material, and Manning's is the highest-profile case. Manning has been embraced by some left-leaning activists as a whistle-blowing hero whose actions exposed war crimes and helped trigger the Middle Eastern pro-democracy uprisings known as the Arab Spring in 2010. He has spent more than 1,000 days in custody. The soldier told the court that he corresponded online with someone he believed to be WikiLeaks founder Julian Assange but never confirmed the person's identity. WikiLeaks has been careful never to confirm or deny Manning was the source of the documents. Reached by telephone in Britain on Thursday, Assange would not say whether he had any dealings with Manning but called him a political prisoner and said his prosecution was part of an effort by the U.S. to clamp down on criticism of its military and foreign policy. Assange himself remains under investigation by the U.S. and has been holed up in the Ecuadorean Embassy in London for the better part of a year to avoid extradition to Sweden on sex-crimes allegations. ___ Associated Press Writer Raphael Satter in London contributed to this report. ___ Follow Ben Nuckols on Twitter at https://twitter.com/APBenNuckols ||||| These crawls are part of an effort to archive pages as they are created and archive the pages that they refer to. That way, as the pages that are referenced are changed or taken from the web, a link to the version that was live when the page was written will be preserved.Then the Internet Archive hopes that references to these archived pages will be put in place of a link that would be otherwise be broken, or a companion link to allow people to see what was originally intended by a page's authors.The goal is to fix all broken links on the web . Crawls of supported "No More 404" sites. ||||| FT. MEADE, Md. – Army Pfc. Bradley Edward Manning pleaded guilty Thursday to 10 charges that he illegally acquired and transferred U.S. government secrets, agreeing to serve 20 years in prison for leaking classified material to WikiLeaks that described U.S. military and diplomatic efforts in Iraq, Afghanistan and around the globe. The 25-year-old soldier, however, pleaded not guilty to 12 more serious charges, including espionage for aiding the enemy, meaning that his criminal case will go forward at a general court-martial in June. If convicted at trial, he risks a sentence of life in prison at Ft. Leavenworth, Kan. A small, thin soldier in Army blues and eyeglasses, Manning admitted that he leaked the video of a helicopter gun battle, State Department cables, an Army field manual and Army documents on Iraq and Afghanistan that detailed the military’s patrol reports there. FULL COVERAGE: Bradley Manning's trial He also admitted that he leaked confidential file assessments of detainees at the U.S. naval base at Guantanamo Bay, Cuba, and five classified records from a U.S. bombing in the Farah Province of Afghanistan, which killed up to 30 civilians. In all, the 5-1/2-year veteran once assigned to Operation Station Hammer near Baghdad in Iraq pleaded guilty to 10 counts, each drawing two years in prison. Asked repeatedly by the judge, Army Col. Denise Lind, if he wanted to go forward with the guilty pleas, Manning answered each time with short, crisp words: “Yes, ma’am,” and “Yes, your honor.” He was arrested in May 2010, and already has spent 1,007 days in jail. Follow Politics Now on Twitter and Facebook [email protected]

– Bradley Manning pleaded not guilty today to the 12 most serious charges against him, including espionage for aiding the enemy. But the US Army private did plead guilty to 10 lesser charges in the WikiLeaks case, the Los Angeles Times reports. Those 10 charges could mean he spends 20 years in prison for leaking classified material. (NBC News puts the sentence at 18 years for nine charges, plus dishonorable discharge.) Because of the not-guilty pleas, Manning's court-martial will begin June 3. If convicted, he faces life in prison. Also at today's hearing, Manning read a statement explaining his motives, saying he was disillusioned with the US wars in Iraq and Afghanistan, reports AP. "I believed that if the general public, especially the American public, had access to the information ... this could spark a domestic debate on the role of the military and our foreign policy in general," he said. Manning added that he went to WikiLeaks after trying unsuccessfully to give the data to the Washington Post and New York Times.

<s>[INST]Bradley Manning, the Army private arrested in the biggest leak of classified material in U.S. history, pleaded guilty Thursday to charges that could send him to prison for 20 years, saying he was trying to expose the American military's "bloodlust" and disregard for human life in Iraq and Afghanistan. FILE - In this June 25, 2012 file photo, Army Pfc. Bradley Manning, right, is escorted out of a courthouse in Fort Meade, Md. The Army private charged in the largest leak of classified material in U.S.... (Associated Press) Military prosecutors said they plan to move forward with a court-martial on 12 remaining charges against him, including aiding the enemy, which carries a potential life sentence. "I began to become depressed at the situation we found ourselves mired in year after year. In attempting counterinsurgency operations, we became obsessed with capturing and killing human targets on lists," the 25-year-old former intelligence analyst in Baghdad told a military judge. He added: "I wanted the public to know that not everyone living in Iraq were targets to be neutralized." It was the first time Manning directly admitted leaking the material to the anti-secrecy website WikiLeaks and detailed the frustrations that led him to do it. The slightly built soldier from Crescent, Okla., read from a 35-page statement through his wire-rimmed glasses for more than an hour. He spoke quickly and evenly, showing little emotion even when he described how troubled he was by what he had seen. The judge, Col. Denise Lind, accepted his plea to 10 charges involving illegal possession or distribution of classified material. Manning was allowed to plead guilty under military regulations instead of federal espionage law, which knocked the potential sentence down from 92 years. He will not be sentenced until his court-martial on the other charges is over. Manning admitted sending hundreds of thousands of Iraq and Afghanistan battlefield reports, State Department diplomatic cables, other classified records and two battlefield video clips to WikiLeaks in 2009 and 2010. WikiLeaks posted some of the material, embarrassing the U.S. and its allies. He said he was disturbed by the conduct of the wars in Afghanistan and Iraq and the way American troops treated the populace. He said he did not believe the release of the information he downloaded onto a thumb drive would harm the U.S. "I believed that if the general public, especially the American public, had access to the information ... this could spark a domestic debate on the role of the military and our foreign policy in general," Manning said. Manning said he was appalled by 2007 combat video of an assault by a U.S. helicopter that killed 11 men, including a Reuters news photographer. The Pentagon concluded the troops mistook the camera equipment for weapons. "The most alarming aspect of the video to me was the seemingly delightful bloodlust the aerial weapons team happened to have," Manning said, adding that the soldiers' actions "seemed similar to a child torturing ants with a magnifying glass." As for the State Department cables, he said they "documented backdoor deals and criminality that didn't reflect the so-called leader of the free world." "I thought these cables were a prime example of the need for a more open diplomacy," Manning said. "I believed that these cables would not damage the United States. However, I believed these cables would be embarrassing." The battlefield reports were the first documents Manning decided to leak. He said he sent them to WikiLeaks after contacting The Washington Post and The New York Times. He said he felt a reporter at the Post didn't take him seriously, and a message he left for news tips at the Times was not returned. Times spokeswoman Eileen Murphy said Thursday of the purported phone call: "This is news to us." The Obama administration has said the release of the documents threatened valuable military and diplomatic sources and strained America's relations with other governments. The administration has aggressively pursued people accused of leaking classified material, and Manning's is the highest-profile case. Manning has been embraced by some left-leaning activists as a whistle-blowing hero whose actions exposed war crimes and helped trigger the Middle Eastern pro-democracy uprisings known as the Arab Spring in 2010. He has spent more than 1,000 days in custody. The soldier told the court that he corresponded online with someone he believed to be WikiLeaks founder Julian Assange but never confirmed the person's identity. WikiLeaks has been careful never to confirm or deny Manning was the source of the documents. Reached by telephone in Britain on Thursday, Assange would not say whether he had any dealings with Manning but called him a political prisoner and said his prosecution was part of an effort by the U.S. to clamp down on criticism of its military and foreign policy. Assange himself remains under investigation by the U.S. and has been holed up in the Ecuadorean Embassy in London for the better part of a year to avoid extradition to Sweden on sex-crimes allegations. ___ Associated Press Writer Raphael Satter in London contributed to this report. ___ Follow Ben Nuckols on Twitter at https://twitter.com/APBenNuckols ||||| These crawls are part of an effort to archive pages as they are created and archive the pages that they refer to. That way, as the pages that are referenced are changed or taken from the web, a link to the version that was live when the page was written will be preserved.Then the Internet Archive hopes that references to these archived pages will be put in place of a link that would be otherwise be broken, or a companion link to allow people to see what was originally intended by a page's authors.The goal is to fix all broken links on the web . Crawls of supported "No More 404" sites. ||||| FT. MEADE, Md. – Army Pfc. Bradley Edward Manning pleaded guilty Thursday to 10 charges that he illegally acquired and transferred U.S. government secrets, agreeing to serve 20 years in prison for leaking classified material to WikiLeaks that described U.S. military and diplomatic efforts in Iraq, Afghanistan and around the globe. The 25-year-old soldier, however, pleaded not guilty to 12 more serious charges, including espionage for aiding the enemy, meaning that his criminal case will go forward at a general court-martial in June. If convicted at trial, he risks a sentence of life in prison at Ft. Leavenworth, Kan. A small, thin soldier in Army blues and eyeglasses, Manning admitted that he leaked the video of a helicopter gun battle, State Department cables, an Army field manual and Army documents on Iraq and Afghanistan that detailed the military’s patrol reports there. FULL COVERAGE: Bradley Manning's trial He also admitted that he leaked confidential file assessments of detainees at the U.S. naval base at Guantanamo Bay, Cuba, and five classified records from a U.S. bombing in the Farah Province of Afghanistan, which killed up to 30 civilians. In all, the 5-1/2-year veteran once assigned to Operation Station Hammer near Baghdad in Iraq pleaded guilty to 10 counts, each drawing two years in prison. Asked repeatedly by the judge, Army Col. Denise Lind, if he wanted to go forward with the guilty pleas, Manning answered each time with short, crisp words: “Yes, ma’am,” and “Yes, your honor.” He was arrested in May 2010, and already has spent 1,007 days in jail. Follow Politics Now on Twitter and Facebook [email protected][/INST]– Bradley Manning pleaded not guilty today to the 12 most serious charges against him, including espionage for aiding the enemy. But the US Army private did plead guilty to 10 lesser charges in the WikiLeaks case, the Los Angeles Times reports. Those 10 charges could mean he spends 20 years in prison for leaking classified material. (NBC News puts the sentence at 18 years for nine charges, plus dishonorable discharge.) Because of the not-guilty pleas, Manning's court-martial will begin June 3. If convicted, he faces life in prison. Also at today's hearing, Manning read a statement explaining his motives, saying he was disillusioned with the US wars in Iraq and Afghanistan, reports AP. "I believed that if the general public, especially the American public, had access to the information ... this could spark a domestic debate on the role of the military and our foreign policy in general," he said. Manning added that he went to WikiLeaks after trying unsuccessfully to give the data to the Washington Post and New York Times.</s>

arthroscopic fixation of tibial spine fracture without damage to the growth plate is very important in patients with open physis . the present article describes a simple and effective technique being used for the first time to treat this condition . a 16-year - old boy sustained avulsion fractures of tibial spine while playing . he was treated arthroscopically with excellent result . arthroscopic fixation of tibial spine fracture in patients with open physis with two cannulated screws perpendicular to each other is a very simple technique which provides strong construct , and allows early mobilization without risk of damage to the growth plate . avulsion fractures of tibial spine leading to discontinuity of anterior cruciate ligament fibers are uncommon but well described in literature in both pediatric and adult population . these injuries are commonly seen in children aged between 8 - 14 years and are usually sports related injuries . in adults , these injuries are commonly related to high energy trauma usually road traffic accidents [ 1 , 2 ] and have high incidence of associated injuries . the cause of increased incidence amongst children is hypothesized as being secondary to relative weakness of incompletely ossified tibial eminence compared to native acl fibres . meyers and mckeever classified these injuries in 1959 as non - displaced ( type i ) , partially displaced or hinged ( type ii ) and completely displaced ( type iii ) fractures . this classification was modified by zaricznyj to include comminuted avulsion fractures ( type iv ) . the patient had severe pain and swelling and was unable to bear weight in the affected knee . x - rays revealed displaced tibial spine fracture [ fig . 1 , 2 ] , and the young boy was treated with cast . however , the patient was uncomfortable with the cast and came to our institute . it was displaced fracture . note the heterogenous palpable mass about 35 28 30 mm in posterolateral aspect of the left lateral malleolus . notice the incision scar of foot shortening operation , the patient underwent at adolescent age . both the portals should be standard or slightly low as higher portal may put the scope above the fractured fragment and one may not be able to see the fracture clearly . it also involved significant portion of medial tibial platue [ fig . 4 , 5 ] . fracture was reduced with help of acl zig and under c- arm guidance provisionally fixed with guide wire from superolateral portal taking care not to cross physis , as it was a large fragment it was not sitting completely from medial side so another wire was used from superomedial portal to fix medial side of fragment perpendicular to lateral wire , again without crossing the physis . two 3.5 mm partially threaded cannulated screws ( zimmer ) were directly used 45 mm from lateral side and 35 mm from medial side [ fig . stability of the fragment was assessed with a probe and was found to be stable [ fig . 6 ] . post - op x - rays showed proper postion of both the screws [ fig . 8 , knee range of motion was allowed from 0 - 90 for 2 weeks than 0 - 120 for next 2 weeks . after one month , he was allowed to walk without knee brace . at 6 months , patients was allowed to run . mri clearly shows the heterogeneous large soft tissue mass lesion on the posterior aspect of left ankle . appearance of the ankle after local recurrence , which lead to dehiscence of surgical area . arthroscopic fixation of displaced tibial spine fracture is a standard procedure [ 8 , 9 ] . commonly , tibial spine is fixed either with cannulated screws or strong non absorbable sutures . in patients with open physis , injury to physis is a serious concern as it may lead to various growth disturbances [ 10 , 11 ] . in patients with open physis , suture fixation is considered safer than cannulated screw fixation but even suture fixation requires drilling through the physis which may cause damage to the physis , incidence of growth disturbances have been reported even with transphyseal suture technique which lead to development of transepiphyseal suture technique . both transphyseal and transepiphyseal suture techniques are quite complex and require more time as compared to screw fixation technique . biomechanical studies on strength of various fixation techniques have produced mixed results [ 5 , 6 , 7 ] . in porcine model , egger & colleagues demonstrated that fiber wire ( arthrex ) suture were superior to ethibond suture ( ethicon ) and 1 or 2 ante grade cannulated screws in single and cyclical loading protocol . in bovine model , mahar and colleagues found no difference between ethibond suture , bioabsorbable nails , single bioabsorbable screw or single metal screw in an ultimate failure test . in cyclical loading test , tsucada and coworkers found a statistically significant difference in displacement favoring cannulated screw over ethibond suture . in cases of comminuted fractures suture technique is preferred as screws are unlikely to provide adequate fixation [ 5 , 6 , 7 ] . in this case as this was large fragment , we used two cannulated screws ( zimmer ) perpendicular to each other holding only in epiphysis for fixation . thus avoiding any risk of physeal damage . these self tapping screws are directly used after provisional fixation with guidewire as no drilling is required . we started full weight bearing mobilization in post knee brace from second post op day . for first two weeks knee rom from 0 - 90 was allowed which was increased to 120 for next two weeks . thus , arthroscopic fixation with two cannulated screws perpendicular to each other is a very simple technique providing a strong construct and thus allows early mobilization . arthroscopic fixation of tibial spine fracture in patients with open physis with two cannulated screws perpendicular to each other is a very simple technique that provides a strong construct and allows early mobilization without any risk of damage to growth plate . arthroscopic fixation of tibial spine fracture in patients with open physis with two cannulated screws perpendicular to each other is very strong construct , allowing early mobilization without risk of damage to growth plate .

introduction : arthroscopic fixation of tibial spine fracture without damage to the growth plate is very important in patients with open physis . the present article describes a simple and effective technique being used for the first time to treat this condition.case report : a 16-year - old boy sustained avulsion fractures of tibial spine while playing . he was treated arthroscopically with excellent result.conclusion:arthroscopic fixation of tibial spine fracture in patients with open physis with two cannulated screws perpendicular to each other is a very simple technique which provides strong construct , and allows early mobilization without risk of damage to the growth plate .

<s>[INST]arthroscopic fixation of tibial spine fracture without damage to the growth plate is very important in patients with open physis . the present article describes a simple and effective technique being used for the first time to treat this condition . a 16-year - old boy sustained avulsion fractures of tibial spine while playing . he was treated arthroscopically with excellent result . arthroscopic fixation of tibial spine fracture in patients with open physis with two cannulated screws perpendicular to each other is a very simple technique which provides strong construct , and allows early mobilization without risk of damage to the growth plate . avulsion fractures of tibial spine leading to discontinuity of anterior cruciate ligament fibers are uncommon but well described in literature in both pediatric and adult population . these injuries are commonly seen in children aged between 8 - 14 years and are usually sports related injuries . in adults , these injuries are commonly related to high energy trauma usually road traffic accidents [ 1 , 2 ] and have high incidence of associated injuries . the cause of increased incidence amongst children is hypothesized as being secondary to relative weakness of incompletely ossified tibial eminence compared to native acl fibres . meyers and mckeever classified these injuries in 1959 as non - displaced ( type i ) , partially displaced or hinged ( type ii ) and completely displaced ( type iii ) fractures . this classification was modified by zaricznyj to include comminuted avulsion fractures ( type iv ) . the patient had severe pain and swelling and was unable to bear weight in the affected knee . x - rays revealed displaced tibial spine fracture [ fig . 1 , 2 ] , and the young boy was treated with cast . however , the patient was uncomfortable with the cast and came to our institute . it was displaced fracture . note the heterogenous palpable mass about 35 28 30 mm in posterolateral aspect of the left lateral malleolus . notice the incision scar of foot shortening operation , the patient underwent at adolescent age . both the portals should be standard or slightly low as higher portal may put the scope above the fractured fragment and one may not be able to see the fracture clearly . it also involved significant portion of medial tibial platue [ fig . 4 , 5 ] . fracture was reduced with help of acl zig and under c- arm guidance provisionally fixed with guide wire from superolateral portal taking care not to cross physis , as it was a large fragment it was not sitting completely from medial side so another wire was used from superomedial portal to fix medial side of fragment perpendicular to lateral wire , again without crossing the physis . two 3.5 mm partially threaded cannulated screws ( zimmer ) were directly used 45 mm from lateral side and 35 mm from medial side [ fig . stability of the fragment was assessed with a probe and was found to be stable [ fig . 6 ] . post - op x - rays showed proper postion of both the screws [ fig . 8 , knee range of motion was allowed from 0 - 90 for 2 weeks than 0 - 120 for next 2 weeks . after one month , he was allowed to walk without knee brace . at 6 months , patients was allowed to run . mri clearly shows the heterogeneous large soft tissue mass lesion on the posterior aspect of left ankle . appearance of the ankle after local recurrence , which lead to dehiscence of surgical area . arthroscopic fixation of displaced tibial spine fracture is a standard procedure [ 8 , 9 ] . commonly , tibial spine is fixed either with cannulated screws or strong non absorbable sutures . in patients with open physis , injury to physis is a serious concern as it may lead to various growth disturbances [ 10 , 11 ] . in patients with open physis , suture fixation is considered safer than cannulated screw fixation but even suture fixation requires drilling through the physis which may cause damage to the physis , incidence of growth disturbances have been reported even with transphyseal suture technique which lead to development of transepiphyseal suture technique . both transphyseal and transepiphyseal suture techniques are quite complex and require more time as compared to screw fixation technique . biomechanical studies on strength of various fixation techniques have produced mixed results [ 5 , 6 , 7 ] . in porcine model , egger & colleagues demonstrated that fiber wire ( arthrex ) suture were superior to ethibond suture ( ethicon ) and 1 or 2 ante grade cannulated screws in single and cyclical loading protocol . in bovine model , mahar and colleagues found no difference between ethibond suture , bioabsorbable nails , single bioabsorbable screw or single metal screw in an ultimate failure test . in cyclical loading test , tsucada and coworkers found a statistically significant difference in displacement favoring cannulated screw over ethibond suture . in cases of comminuted fractures suture technique is preferred as screws are unlikely to provide adequate fixation [ 5 , 6 , 7 ] . in this case as this was large fragment , we used two cannulated screws ( zimmer ) perpendicular to each other holding only in epiphysis for fixation . thus avoiding any risk of physeal damage . these self tapping screws are directly used after provisional fixation with guidewire as no drilling is required . we started full weight bearing mobilization in post knee brace from second post op day . for first two weeks knee rom from 0 - 90 was allowed which was increased to 120 for next two weeks . thus , arthroscopic fixation with two cannulated screws perpendicular to each other is a very simple technique providing a strong construct and thus allows early mobilization . arthroscopic fixation of tibial spine fracture in patients with open physis with two cannulated screws perpendicular to each other is a very simple technique that provides a strong construct and allows early mobilization without any risk of damage to growth plate . arthroscopic fixation of tibial spine fracture in patients with open physis with two cannulated screws perpendicular to each other is very strong construct , allowing early mobilization without risk of damage to growth plate .[/INST]introduction : arthroscopic fixation of tibial spine fracture without damage to the growth plate is very important in patients with open physis . the present article describes a simple and effective technique being used for the first time to treat this condition.case report : a 16-year - old boy sustained avulsion fractures of tibial spine while playing . he was treated arthroscopically with excellent result.conclusion:arthroscopic fixation of tibial spine fracture in patients with open physis with two cannulated screws perpendicular to each other is a very simple technique which provides strong construct , and allows early mobilization without risk of damage to the growth plate .</s>

supersymmetry ( susy ) is one of the best motivated theories beyond the standard model ( sm ) . not only does it provide a natural solution to the gauge hierarchy problem , but also gives a dynamical mechanism for electroweak symmetry breaking and a natural candidate for dark matter . the most recent lower bound on the higgs boson mass has been raised to 114.4 gev @xcite . this in fact puts some stress on the soft susy parameters , known as the little hierarchy problem , on the minimal supersymmetric standard model ( mssm ) . since the higgs boson receives radiative corrections dominated by the top squark loop , the mass bound requires the top squark mass to be heavier than 1 tev . from the renormalization - group ( rg ) equation of @xmath1 , the magnitude of @xmath2 . thus , the parameters in the higgs potential are fine - tuned at a level of a few percent in order to obtain a higgs boson mass of @xmath3 gev . such fine - tuning has motivated a number of solutions to relieve the problem . one of these is to add additional singlet fields to the minimal supersymmetric standard model ( mssm ) . the minimal version of the latter is realized by adding a singlet higgs field to the mssm , and becomes the next - to - minimal supersymmetric standard model ( nmssm ) . it has been shown @xcite that in some corners of the parameter space , the higgs boson can decay into a pair of very light pseudoscalars such that the lep2 limit can be evaded . it has also been demonstrated that the fine - tuning or the little hierarchy problems are relieved @xcite . the nmssm is in fact well motivated as it provides an elegant solution to the @xmath4 problem in susy . the @xmath4 parameter in the term @xmath5 of the superpotential of the mssm naturally has its value at either @xmath6 or zero ( due to a symmetry ) . however , the radiative electroweak symmetry breaking conditions require the @xmath4 parameter to be of the same order as @xmath7 for fine - tuning reasons . such a conflict is coined as the @xmath4 problem @xcite . in the nmssm , the @xmath4 term is generated dynamically through the vacuum - expectation - value ( vev ) , @xmath8 , of the scalar component of the additional higgs field @xmath9 , which is naturally of the order of the susy breaking scale . thus , an effective @xmath4 parameter of the order of the electroweak scale is generated . explicitly , the superpotential of the nmssm is given by @xmath10 it is well - known that that the superpotential has a discrete @xmath11 symmetry , which may induce the harmful domain - wall effect @xcite . one possible way out is to introduce some nonrenormalizable operators at the planck scale that break the @xmath11 symmetry through the harmless tadpoles that they generate @xcite . once the domain wall problem is solved , the nmssm is phenomenologically very interesting . with the additional singlet higgs field , there are one more cp - even and one more cp - odd higgs bosons , and one more neutralino other than those in the mssm . the higgs phenomenology is much richer @xcite , and so does the neutralinos @xcite . one particular feature of the nmssm is the allowable light pseudoscalar boson @xmath12 , which is consistent with existing data . since this @xmath12 mainly comes from the singlet higgs field , it can escape all the experimental constraints when the mixing angle with the mssm higgs fields goes to zero . it was pointed out in ref . @xcite that even in the zero mixing limit , there is always a sm - like higgs boson that decays into a pair of @xmath12 s , which helps the higgs boson to evade the lep bound . the possibility to detect such light pseudoscalar higgs bosons coming from the @xmath13 decay was studied using the two photon mode of the @xmath12 , but the two photons may be too collimated for realistic detection @xcite . another possibility to detect such an almost decoupling case is to search for the four tau - leptons coming from @xmath14 decay @xcite . nevertheless , in the large @xmath15 and large @xmath16 limits , the mixing angle is extremely small and approaching zero , such that the decay of @xmath12 into tau - leptons or heavy quarks is negligible . in this work , we probe another novel signature in the zero - mixing limit . the unique term @xmath0 in the superpotential gives rise to the coupling of @xmath17 , which includes the neutral and charged higgsinos . we study the associated production of a light pseudoscalar higgs boson with a chargino pair in the zero - mixing limit at the lhc and ilc . provided that the pseudoscalar is very light and the mixing angle is less than @xmath18 , the dominant decay mode of @xmath12 is a pair of photons . thus , the novel signature for the production is a pair of charged leptons and a pair of photons plus large missing energy . such a signal can distinguish nmssm from the mssm . we will show the production rates at the lhc and the ilc . one critical issue in identifying the two - photon decay of the light pseudoscalar higgs boson is whether the two photons can be resolved . we will demonstrate the distribution of the opening angle between the two photons , from which one can tell to what extent the experiments can resolve the two photons . the cms detector has a `` preshower '' in the ecal that has the strong capability to resolve the two photons of the neutral pion decay as it is the most important background for the intermediate mass higgs boson search . we can make use of this preshower in the ecal to resolve the two photons of the @xmath12 decay . we will then show the cross section for the associated production after imposing the preshower requirements . once we resolve the two photons in the decay of the pseudoscalar higgs boson , we can differentiate the nmssm from the mssm . the organization is as follows . in the next section , we describe the particular region of parameter space in which the light pseudoscalar higgs boson decouples and decays into a pair of photons . in sec . iii , we calculate the decay branching ratios of the @xmath12 . we then calculate the associated production of the light pseudoscalar higgs boson with a chargino pair in the zero - mixing limit at the lhc and ilc in sec . we also work out the distribution of the opening angle of the photon pair . we conclude in sec . the higgs sector of the nmssm consists of the usual two higgs doublets @xmath19 and @xmath20 and an extra higgs singlet @xmath9 . the extra singlet field is allowed to couple only to the higgs doublets of the model , the supersymmetrization of which is that the singlet field only couples to the higgsino doublets . consequently , the couplings of the singlet @xmath9 to gauge bosons and fermions will only be manifest via their mixing with the doublet higgs fields . after the higgs fields take on the vev s and rotating away the goldstone modes , we are left with a pair charged higgs bosons , 3 real scalar fields , and 2 pseudoscalar fields . in particular , the mass matrix for the two pseudoscalar higgs bosons @xmath21 and @xmath22 is @xmath23 with @xmath24 where @xmath25 and @xmath26 and @xmath27 and @xmath28 . here @xmath21 is the one in mssm while @xmath22 comes from the singlet @xmath9 and from the effects of rotating away the goldstone modes . the pseudoscalar fields are further rotated to the diagonal basis ( @xmath12 , @xmath29 ) through a mixing angle @xcite : @xmath30 where the masses of @xmath31 are arranged such that @xmath32 . at tree - level the mixing angle is given by @xmath33 in the approximation of large @xmath15 and large @xmath34 , which is normally valid in the usual mssm , the tree - level cp - odd masses can be written as @xcite @xmath35 we are interested in the case that @xmath12 is very light . from eq . ( [ small - ma ] ) it can be seen that @xmath36 can be very small if either @xmath37 or @xmath38 is very small , which is made possible by a pecci - quinn ( pq ) symmetry : @xmath39 and @xmath40 . we can achieve a small mixing angle by the cancellation between the two terms in the numerator of eq.([tana ] ) , by setting @xmath41 explicitly , here we give a sample point in the parameter space : @xmath42 then it can give @xmath43 we have the following parameters in the nmssm in addition to those of the mssm : @xmath44 , @xmath37 , @xmath45 , @xmath38 , and @xmath8 ( @xmath46 has been eliminated by one of the tadpole equations in the electroweak symmetry breaking . ) since @xmath47 , we can use @xmath4 and @xmath44 in place of @xmath8 . also from eqs . ( [ ma ] ) , ( [ small - ma ] ) and ( [ tana ] ) we can trade @xmath37 , @xmath45 , and @xmath38 for @xmath48 , @xmath36 and @xmath49 . the small @xmath36 can be achieved by requiring @xmath39 in eq . ( [ small - ma ] ) while keeping @xmath8 and @xmath38 typical . the small mixing angle , on the other hand , is achieved by the condition in eq . ( [ cond ] ) such that the fine - tuned cancellation is possible to give a small value of @xmath50 . we admit that this is a fine tuning requirement . recall in the cp violating supersymmetry a natural mechanism to suppress the contributions from various sources of cp violating phases is to have a cancellation among various sources @xcite . if the measurement of edm continues to push to more stringent limits , more and more fine - tuned cancellations are needed to suppress the susy contributions . a lot of existing constraints on the lightest pseudoscalar higgs boson @xmath12 depend on the mixing angle @xmath49 . when @xmath49 goes to zero , the @xmath12 decouples and behaves like the singlet . this light @xmath12 can be extremely light without violating any existing data . it was pointed out @xcite that it can be produced in the scalar higgs boson decay , @xmath51 , which is due to the term @xmath52 in the superpotential . we found in this work that there is another novel signature for this light @xmath12 from the same term . we calculate the associated production of @xmath12 with a pair of charginos , followed by @xmath53 decay at hadronic and @xmath54 colliders . this is an undebatable signal of the decoupling regime of the nmssm . in the limit of zero mixing , the @xmath12 only couples to a pair of charginos and neutralinos . therefore , the dominant decay mode is @xmath55 via a chargino loop if @xmath36 is very light . when we turn on the small mixing angle , other modes , such as @xmath56 , @xmath57 , and @xmath58 , appear , which will eventually dominate when the mixing angle is larger than @xmath59 . we show a typical decay branching ratio versus the mixing angle for @xmath60 gev in fig . [ fig1 ] . when @xmath36 is as light as 0.1 gev , only the @xmath54 and @xmath55 modes are possible . the @xmath54 mode scales as @xmath61 , and so the @xmath54 mode increases sharply as @xmath49 increases in fig . [ fig1](a ) . as @xmath36 increases other @xmath62 modes open up , such as @xmath63 . as long as @xmath64 the @xmath55 dominates the decay of @xmath12 . the coupling of @xmath31 to charginos comes from the usual higgs - higgsino - gaugino source and , specific to nmssm , from the term @xmath65 in the superpotential . the interaction is given by @xmath66 where @xmath67 where @xmath68 are the chiral projectors . production cross sections for @xmath69 at the ilc with @xmath70 tev . we have chosen @xmath71 , @xmath72 , @xmath73 gev , @xmath74 gev , and @xmath75.,width=336 ] we stress in passing that in the limit of zero mixing , the production of @xmath12 through the drell - yan process @xmath76 is very suppressed . so is the gluon fusion since only quarks can mediate inside the loops . the associated production of @xmath12 with a chargino pair proceeds via the feynman diagrams , in which the @xmath12 radiates off the chargino legs . the radiation off the intermediate @xmath77 is not considered in the very small mixing limit . note that the production is proportional to @xmath78 , which implies a large higgsino component in @xmath79 is necessary for large cross sections . details of the calculation will be given in a future publication . we choose @xmath73 gev and a much larger @xmath80 gev , @xmath81 , which should be of the order of @xmath82 . the size is limited by the perturbativity argument when the yukawa coupling is evolved to the gut scale . we have followed the prescription from other papers . in general , the perturbativity argument is rather loose . there may be some other new physics that appear well below the gut scale . but roughly @xmath83 is the upper limit applied to @xmath44 for the perturbativity reason . ] and @xmath84 in our results . we show the production cross sections at @xmath54 colliders versus @xmath36 for @xmath85 tev in fig . note that the cross section is insensitive to @xmath49 as long as it is less than @xmath86 . also , in this near - zero mixing region , the cross section scales as @xmath87 . with @xmath88 fb@xmath89 yearly luminosity at the ilc , the number of raw events is of the order of @xmath88 . the signature is very spectacular with a pair of charged leptons and a pair of photons with a large missing energy . in contrast to the process of @xmath90 @xcite , the photon pair is less collimated because the @xmath12 radiating off the chargino would not be as energetic as the @xmath12 from higgs decay . almost all sm backgrounds are reducible once the photon pair and the charged lepton pair are identified together with large missing energies . the leptonic branching ratio of the chargino can increase if the slepton or sneutrino mass is relatively light . one can also increase the detection rates by including the hadronic decay of the charginos . therefore , in the final state we can have ( i ) two charged leptons @xmath91 two photons @xmath91 @xmath92 , ( ii ) one charged leptons @xmath91 two jets @xmath91 two photons @xmath91 @xmath92 , or ( iii ) 4 jets @xmath91 two photons @xmath91 @xmath92 . production cross sections for @xmath93 at the lhc . we have chosen @xmath71 , @xmath72 , @xmath73 gev , @xmath74 gev , and @xmath75 . , width=326 ] we show the production cross section for @xmath94 at the lhc in fig . [ fig3 ] , with the same set of parameters as in fig . we obtain a cross section slightly shy of @xmath82 fb . with a yearly luminosity of 100 fb@xmath89 one can have about @xmath95 raw events . it remains possible to detect the pseudoscalar higgs boson and chargino decays . experiments can search for the same final states that we listed for the ilc . almost all sm backgrounds are reducible if the photon pair can be resolved and measured , together with the charged leptons or jets plus missing energies . the critical issue here is whether the lhc experiment can resolve the two photons in the decay of the pseudoscalar higgs boson . we perform a monte carlo study for the production of @xmath96 followed by the decay of @xmath97 . since @xmath12 is a pseudoscalar , it is sufficient to study the @xmath98 phase - space decay of @xmath12 . we impose transverse momentum and rapidity requirements on the photons : @xmath99 which are in accord with the ecal of the cms detector @xcite . the resolution of the `` preshower '' detector quoted in the report is as good as @xmath100 mrad . we shall use 10 mrad as our minimum separation of the two photons that the detector can resolve . we show the distribution of the sine of the opening angle between the two photons for @xmath101 gev in fig . [ angle ] . it is easy to understand that for @xmath12 as light as @xmath102 gev all the cross sections are within the opening angle @xmath103 rad . when @xmath104 increases to 1 gev , more than half of the cross sections are beyond 0.01 rad . for @xmath104 as large as 5 gev almost all cross sections are beyond @xmath105 rad . we show the resultant cross sections for @xmath106 gev with @xmath107 , @xmath108 , and @xmath109 rad in table [ table ] . suppose the lhc can accumulate @xmath110 fb@xmath89 luminosity , so @xmath104 as low as @xmath111 gev are possible to be detected . for a mere @xmath95 fb@xmath89 luminosity , the size of the cross section in table i shows that it is only possible to detect @xmath112 gev . the final issue is the background suppression . we have shown in fig . [ angle ] that for @xmath113 gev , almost all cross section lies below @xmath103 , which is our conservative choice of resolution according to the preshower detector of the cms . however , when @xmath114 gev , more than half of the cross section survives this @xmath105 cut . we can also reconstruct the invariant mass of the photon pair to identify the pseudoscalar higgs boson @xmath12 and separate it from the other sm mesons such as @xmath115 and @xmath116 . photon and lepton isolation cuts are the most useful ones to reject the jet - faking background and other qcd background . the remaining backgrounds are mostly gauge - boson pair and @xmath117 plus photons / jets production with the photons / jets radiating off fermion or gauge boson legs . although they are irreducible , they are of higher order in couplings and should be small . perhaps , the more serious background issue in the lhc environment may be the combinatorial background because of many photons within a jet . again , using strong photon - pair isolation ( that is without hadronic jets around the photon pair ) one should be able to substantially reduce this background . the differential cross section versus the sine of the opening angle between the two photons for @xmath81 and @xmath84 at the lhc . requirements of @xmath118 gev and @xmath108 are imposed . , width=480 ] .[table ] cross sections in fb for associated production of @xmath119 followed by @xmath53 . the cuts applied to the two photons are : @xmath120 gev , @xmath108 , and @xmath121 mrad . [ cols="^,^",options="header " , ] one may ask if a very light pseudoscalar higgs boson is consistent with the muon anomalous magnetic moment ( @xmath122 ) because it can contribute substantially to @xmath122 at both 1-loop and 2-loop levels . however , it was shown that the 2-loop barr - zee type contributions with a light pseudoscalar can be of comparable size as the 1-loop contributions and opposite in sign @xcite . note that the contributions of the light @xmath12 of the nmssm go to zero as @xmath123 . in the nmssm , there could also be a light neutralino @xcite that can contribute to @xmath122 . in addition , there are many parameters in the mssm , such as gaugino and sfermion masses , which the @xmath122 depends on . thus , one can carefully take into account both 1- and 2-loop contributions and by adjusting the nmssm parameters , such that the @xmath122 constraint is satisfied . there are other constraints on a light pseudoscalar from rare @xmath124 and @xmath125 meson decays , such as @xmath126 and @xmath127 , @xmath128 mixing , @xmath129 , and @xmath130 @xcite . however , it is obvious that in these processes the light pseudoscalar interacts via the mixing with the mssm pseudoscalar . thus , in the limit of zero - mixing the constraints on the light @xmath12 can be easily evaded . the major difference between mssm and nmssm is the existence of a singlet field , which gives rise to a scalar , a pseudoscalar , and a neutralino , in addition to the particle contents of the mssm . we have shown that it is possible to have a very light pseudoscalar with a tiny mixing with the mssm pseudoscalar . such a light pseudoscalar boson is consistent with all existing constraints . the discovery mode has been shown @xcite to be @xmath131 , which enjoys a large production cross section . however , the photon pair from the @xmath12 decay may be too collimated . in this paper , we have pointed out another unambiguous signature from the associated production of the light pseudoscalar with a pair of charginos at the lhc and ilc , with a pair of charged leptons and a pair of photons plus large missing energy in the final state . we have also shown that the event rates at the lhc and ilc should be enough to identify such a signature when @xmath104 is larger than @xmath132 gev . r. dermisek and j. f. gunion , arxiv : hep - ph/0502105 . j. e. kim and h. p. nilles , phys . lett . b * 138 * , 150 ( 1984 ) ; y. nir , phys . b * 354 * , 107 ( 1995 ) m. cvetic and p. langacker , phys . d * 54 * , 3570 ( 1996 ) d. a. kirzhnits and a. d. linde , phys . b * 42 * , 471 ( 1972 ) ; y. b. zeldovich et al . jetp * 40 * , 1 ( 1974 ) ; s. a. abel et al . b * 454 * , 663 ( 1995 ) c. panagiotakopoulos and k. tamvakis , phys . lett . b * 446 * , 224 ( 1999 ) phys . b * 469 * , 145 ( 1999 ) r. dermisek and j. f. gunion , arxiv : hep - ph/0510322 . u. ellwanger , j. f. gunion and c. hugonie , jhep * 0502 * , 066 ( 2005 ) u. ellwanger , j. f. gunion and c. hugonie , jhep * 0507 * , 041 ( 2005 ) u. ellwanger , m. rausch de traubenberg and c. a. savoy , nucl . phys . b * 492 * , 21 ( 1997 ) d. j. miller , r. nevzorov and p. m. zerwas , nucl . b * 681 * , 3 ( 2004 ) s. y. choi , d. j. miller and p. m. zerwas , nucl . phys . b * 711 * , 83 ( 2005 ) v. barger , p. langacker and h. s. lee , arxiv : hep - ph/0508027 . j. f. gunion , d. hooper and b. mcelrath , phys . rev . d * 73 * , 015011 ( 2006 ) t. ibrahim and p. nath , the neutron and the lepton edms in mssm , large cp violating phases , and phys . d * 58 * , 111301 ( 1998 ) [ erratum - ibid . d * 60 * , 099902 ( 1999 ) ] [ arxiv : hep - ph/9807501 ] . b. a. dobrescu , g. landsberg and k. t. matchev , phys . d * 63 * , 075003 ( 2001 ) p. w. graham , a. pierce and j. g. wacker , arxiv : hep - ph/0605162 . p. c. schuster and n. toro , arxiv : hep - ph/0512189 . `` cms ecal technical design report '' , cern / lhcc 97 - 33 , december 1997 : http://cmsdoc.cern.ch/cms/tdr/ecal/ecal.html . d. chang , w. f. chang , c. h. chou and w. y. keung , phys . d * 63 * , 091301 ( 2001 ) ; k. cheung , c. h. chou and o. c. w. kong , phys . d * 64 * , 111301 ( 2001 ) . g. hiller , phys . d * 70 * , 034018 ( 2004 ) .

in the next - to - minimal supersymmetric standard model ( nmssm ) , the unique @xmath0 in the superpotential gives rise to a coupling involving the lighter pseudoscalar higgs boson and a pair of charged or neutral higgsinos , even in the limit of zero mixing between the two pseudoscalar higgs bosons . we study the associated production of a very light pseudoscalar higgs boson with a pair of charginos . the novel signature involves a pair of charged leptons from chargino decays and a pair of photons from the pseudoscalar higgs boson decay , plus large missing energy at the lhc and ilc . the signal may help us to distinguish the nmssm from mssm , provided that the experiment can resolve the two photons from the decay of the pseudoscalar higgs boson .

<s>[INST]supersymmetry ( susy ) is one of the best motivated theories beyond the standard model ( sm ) . not only does it provide a natural solution to the gauge hierarchy problem , but also gives a dynamical mechanism for electroweak symmetry breaking and a natural candidate for dark matter . the most recent lower bound on the higgs boson mass has been raised to 114.4 gev @xcite . this in fact puts some stress on the soft susy parameters , known as the little hierarchy problem , on the minimal supersymmetric standard model ( mssm ) . since the higgs boson receives radiative corrections dominated by the top squark loop , the mass bound requires the top squark mass to be heavier than 1 tev . from the renormalization - group ( rg ) equation of @xmath1 , the magnitude of @xmath2 . thus , the parameters in the higgs potential are fine - tuned at a level of a few percent in order to obtain a higgs boson mass of @xmath3 gev . such fine - tuning has motivated a number of solutions to relieve the problem . one of these is to add additional singlet fields to the minimal supersymmetric standard model ( mssm ) . the minimal version of the latter is realized by adding a singlet higgs field to the mssm , and becomes the next - to - minimal supersymmetric standard model ( nmssm ) . it has been shown @xcite that in some corners of the parameter space , the higgs boson can decay into a pair of very light pseudoscalars such that the lep2 limit can be evaded . it has also been demonstrated that the fine - tuning or the little hierarchy problems are relieved @xcite . the nmssm is in fact well motivated as it provides an elegant solution to the @xmath4 problem in susy . the @xmath4 parameter in the term @xmath5 of the superpotential of the mssm naturally has its value at either @xmath6 or zero ( due to a symmetry ) . however , the radiative electroweak symmetry breaking conditions require the @xmath4 parameter to be of the same order as @xmath7 for fine - tuning reasons . such a conflict is coined as the @xmath4 problem @xcite . in the nmssm , the @xmath4 term is generated dynamically through the vacuum - expectation - value ( vev ) , @xmath8 , of the scalar component of the additional higgs field @xmath9 , which is naturally of the order of the susy breaking scale . thus , an effective @xmath4 parameter of the order of the electroweak scale is generated . explicitly , the superpotential of the nmssm is given by @xmath10 it is well - known that that the superpotential has a discrete @xmath11 symmetry , which may induce the harmful domain - wall effect @xcite . one possible way out is to introduce some nonrenormalizable operators at the planck scale that break the @xmath11 symmetry through the harmless tadpoles that they generate @xcite . once the domain wall problem is solved , the nmssm is phenomenologically very interesting . with the additional singlet higgs field , there are one more cp - even and one more cp - odd higgs bosons , and one more neutralino other than those in the mssm . the higgs phenomenology is much richer @xcite , and so does the neutralinos @xcite . one particular feature of the nmssm is the allowable light pseudoscalar boson @xmath12 , which is consistent with existing data . since this @xmath12 mainly comes from the singlet higgs field , it can escape all the experimental constraints when the mixing angle with the mssm higgs fields goes to zero . it was pointed out in ref . @xcite that even in the zero mixing limit , there is always a sm - like higgs boson that decays into a pair of @xmath12 s , which helps the higgs boson to evade the lep bound . the possibility to detect such light pseudoscalar higgs bosons coming from the @xmath13 decay was studied using the two photon mode of the @xmath12 , but the two photons may be too collimated for realistic detection @xcite . another possibility to detect such an almost decoupling case is to search for the four tau - leptons coming from @xmath14 decay @xcite . nevertheless , in the large @xmath15 and large @xmath16 limits , the mixing angle is extremely small and approaching zero , such that the decay of @xmath12 into tau - leptons or heavy quarks is negligible . in this work , we probe another novel signature in the zero - mixing limit . the unique term @xmath0 in the superpotential gives rise to the coupling of @xmath17 , which includes the neutral and charged higgsinos . we study the associated production of a light pseudoscalar higgs boson with a chargino pair in the zero - mixing limit at the lhc and ilc . provided that the pseudoscalar is very light and the mixing angle is less than @xmath18 , the dominant decay mode of @xmath12 is a pair of photons . thus , the novel signature for the production is a pair of charged leptons and a pair of photons plus large missing energy . such a signal can distinguish nmssm from the mssm . we will show the production rates at the lhc and the ilc . one critical issue in identifying the two - photon decay of the light pseudoscalar higgs boson is whether the two photons can be resolved . we will demonstrate the distribution of the opening angle between the two photons , from which one can tell to what extent the experiments can resolve the two photons . the cms detector has a `` preshower '' in the ecal that has the strong capability to resolve the two photons of the neutral pion decay as it is the most important background for the intermediate mass higgs boson search . we can make use of this preshower in the ecal to resolve the two photons of the @xmath12 decay . we will then show the cross section for the associated production after imposing the preshower requirements . once we resolve the two photons in the decay of the pseudoscalar higgs boson , we can differentiate the nmssm from the mssm . the organization is as follows . in the next section , we describe the particular region of parameter space in which the light pseudoscalar higgs boson decouples and decays into a pair of photons . in sec . iii , we calculate the decay branching ratios of the @xmath12 . we then calculate the associated production of the light pseudoscalar higgs boson with a chargino pair in the zero - mixing limit at the lhc and ilc in sec . we also work out the distribution of the opening angle of the photon pair . we conclude in sec . the higgs sector of the nmssm consists of the usual two higgs doublets @xmath19 and @xmath20 and an extra higgs singlet @xmath9 . the extra singlet field is allowed to couple only to the higgs doublets of the model , the supersymmetrization of which is that the singlet field only couples to the higgsino doublets . consequently , the couplings of the singlet @xmath9 to gauge bosons and fermions will only be manifest via their mixing with the doublet higgs fields . after the higgs fields take on the vev s and rotating away the goldstone modes , we are left with a pair charged higgs bosons , 3 real scalar fields , and 2 pseudoscalar fields . in particular , the mass matrix for the two pseudoscalar higgs bosons @xmath21 and @xmath22 is @xmath23 with @xmath24 where @xmath25 and @xmath26 and @xmath27 and @xmath28 . here @xmath21 is the one in mssm while @xmath22 comes from the singlet @xmath9 and from the effects of rotating away the goldstone modes . the pseudoscalar fields are further rotated to the diagonal basis ( @xmath12 , @xmath29 ) through a mixing angle @xcite : @xmath30 where the masses of @xmath31 are arranged such that @xmath32 . at tree - level the mixing angle is given by @xmath33 in the approximation of large @xmath15 and large @xmath34 , which is normally valid in the usual mssm , the tree - level cp - odd masses can be written as @xcite @xmath35 we are interested in the case that @xmath12 is very light . from eq . ( [ small - ma ] ) it can be seen that @xmath36 can be very small if either @xmath37 or @xmath38 is very small , which is made possible by a pecci - quinn ( pq ) symmetry : @xmath39 and @xmath40 . we can achieve a small mixing angle by the cancellation between the two terms in the numerator of eq.([tana ] ) , by setting @xmath41 explicitly , here we give a sample point in the parameter space : @xmath42 then it can give @xmath43 we have the following parameters in the nmssm in addition to those of the mssm : @xmath44 , @xmath37 , @xmath45 , @xmath38 , and @xmath8 ( @xmath46 has been eliminated by one of the tadpole equations in the electroweak symmetry breaking . ) since @xmath47 , we can use @xmath4 and @xmath44 in place of @xmath8 . also from eqs . ( [ ma ] ) , ( [ small - ma ] ) and ( [ tana ] ) we can trade @xmath37 , @xmath45 , and @xmath38 for @xmath48 , @xmath36 and @xmath49 . the small @xmath36 can be achieved by requiring @xmath39 in eq . ( [ small - ma ] ) while keeping @xmath8 and @xmath38 typical . the small mixing angle , on the other hand , is achieved by the condition in eq . ( [ cond ] ) such that the fine - tuned cancellation is possible to give a small value of @xmath50 . we admit that this is a fine tuning requirement . recall in the cp violating supersymmetry a natural mechanism to suppress the contributions from various sources of cp violating phases is to have a cancellation among various sources @xcite . if the measurement of edm continues to push to more stringent limits , more and more fine - tuned cancellations are needed to suppress the susy contributions . a lot of existing constraints on the lightest pseudoscalar higgs boson @xmath12 depend on the mixing angle @xmath49 . when @xmath49 goes to zero , the @xmath12 decouples and behaves like the singlet . this light @xmath12 can be extremely light without violating any existing data . it was pointed out @xcite that it can be produced in the scalar higgs boson decay , @xmath51 , which is due to the term @xmath52 in the superpotential . we found in this work that there is another novel signature for this light @xmath12 from the same term . we calculate the associated production of @xmath12 with a pair of charginos , followed by @xmath53 decay at hadronic and @xmath54 colliders . this is an undebatable signal of the decoupling regime of the nmssm . in the limit of zero mixing , the @xmath12 only couples to a pair of charginos and neutralinos . therefore , the dominant decay mode is @xmath55 via a chargino loop if @xmath36 is very light . when we turn on the small mixing angle , other modes , such as @xmath56 , @xmath57 , and @xmath58 , appear , which will eventually dominate when the mixing angle is larger than @xmath59 . we show a typical decay branching ratio versus the mixing angle for @xmath60 gev in fig . [ fig1 ] . when @xmath36 is as light as 0.1 gev , only the @xmath54 and @xmath55 modes are possible . the @xmath54 mode scales as @xmath61 , and so the @xmath54 mode increases sharply as @xmath49 increases in fig . [ fig1](a ) . as @xmath36 increases other @xmath62 modes open up , such as @xmath63 . as long as @xmath64 the @xmath55 dominates the decay of @xmath12 . the coupling of @xmath31 to charginos comes from the usual higgs - higgsino - gaugino source and , specific to nmssm , from the term @xmath65 in the superpotential . the interaction is given by @xmath66 where @xmath67 where @xmath68 are the chiral projectors . production cross sections for @xmath69 at the ilc with @xmath70 tev . we have chosen @xmath71 , @xmath72 , @xmath73 gev , @xmath74 gev , and @xmath75.,width=336 ] we stress in passing that in the limit of zero mixing , the production of @xmath12 through the drell - yan process @xmath76 is very suppressed . so is the gluon fusion since only quarks can mediate inside the loops . the associated production of @xmath12 with a chargino pair proceeds via the feynman diagrams , in which the @xmath12 radiates off the chargino legs . the radiation off the intermediate @xmath77 is not considered in the very small mixing limit . note that the production is proportional to @xmath78 , which implies a large higgsino component in @xmath79 is necessary for large cross sections . details of the calculation will be given in a future publication . we choose @xmath73 gev and a much larger @xmath80 gev , @xmath81 , which should be of the order of @xmath82 . the size is limited by the perturbativity argument when the yukawa coupling is evolved to the gut scale . we have followed the prescription from other papers . in general , the perturbativity argument is rather loose . there may be some other new physics that appear well below the gut scale . but roughly @xmath83 is the upper limit applied to @xmath44 for the perturbativity reason . ] and @xmath84 in our results . we show the production cross sections at @xmath54 colliders versus @xmath36 for @xmath85 tev in fig . note that the cross section is insensitive to @xmath49 as long as it is less than @xmath86 . also , in this near - zero mixing region , the cross section scales as @xmath87 . with @xmath88 fb@xmath89 yearly luminosity at the ilc , the number of raw events is of the order of @xmath88 . the signature is very spectacular with a pair of charged leptons and a pair of photons with a large missing energy . in contrast to the process of @xmath90 @xcite , the photon pair is less collimated because the @xmath12 radiating off the chargino would not be as energetic as the @xmath12 from higgs decay . almost all sm backgrounds are reducible once the photon pair and the charged lepton pair are identified together with large missing energies . the leptonic branching ratio of the chargino can increase if the slepton or sneutrino mass is relatively light . one can also increase the detection rates by including the hadronic decay of the charginos . therefore , in the final state we can have ( i ) two charged leptons @xmath91 two photons @xmath91 @xmath92 , ( ii ) one charged leptons @xmath91 two jets @xmath91 two photons @xmath91 @xmath92 , or ( iii ) 4 jets @xmath91 two photons @xmath91 @xmath92 . production cross sections for @xmath93 at the lhc . we have chosen @xmath71 , @xmath72 , @xmath73 gev , @xmath74 gev , and @xmath75 . , width=326 ] we show the production cross section for @xmath94 at the lhc in fig . [ fig3 ] , with the same set of parameters as in fig . we obtain a cross section slightly shy of @xmath82 fb . with a yearly luminosity of 100 fb@xmath89 one can have about @xmath95 raw events . it remains possible to detect the pseudoscalar higgs boson and chargino decays . experiments can search for the same final states that we listed for the ilc . almost all sm backgrounds are reducible if the photon pair can be resolved and measured , together with the charged leptons or jets plus missing energies . the critical issue here is whether the lhc experiment can resolve the two photons in the decay of the pseudoscalar higgs boson . we perform a monte carlo study for the production of @xmath96 followed by the decay of @xmath97 . since @xmath12 is a pseudoscalar , it is sufficient to study the @xmath98 phase - space decay of @xmath12 . we impose transverse momentum and rapidity requirements on the photons : @xmath99 which are in accord with the ecal of the cms detector @xcite . the resolution of the `` preshower '' detector quoted in the report is as good as @xmath100 mrad . we shall use 10 mrad as our minimum separation of the two photons that the detector can resolve . we show the distribution of the sine of the opening angle between the two photons for @xmath101 gev in fig . [ angle ] . it is easy to understand that for @xmath12 as light as @xmath102 gev all the cross sections are within the opening angle @xmath103 rad . when @xmath104 increases to 1 gev , more than half of the cross sections are beyond 0.01 rad . for @xmath104 as large as 5 gev almost all cross sections are beyond @xmath105 rad . we show the resultant cross sections for @xmath106 gev with @xmath107 , @xmath108 , and @xmath109 rad in table [ table ] . suppose the lhc can accumulate @xmath110 fb@xmath89 luminosity , so @xmath104 as low as @xmath111 gev are possible to be detected . for a mere @xmath95 fb@xmath89 luminosity , the size of the cross section in table i shows that it is only possible to detect @xmath112 gev . the final issue is the background suppression . we have shown in fig . [ angle ] that for @xmath113 gev , almost all cross section lies below @xmath103 , which is our conservative choice of resolution according to the preshower detector of the cms . however , when @xmath114 gev , more than half of the cross section survives this @xmath105 cut . we can also reconstruct the invariant mass of the photon pair to identify the pseudoscalar higgs boson @xmath12 and separate it from the other sm mesons such as @xmath115 and @xmath116 . photon and lepton isolation cuts are the most useful ones to reject the jet - faking background and other qcd background . the remaining backgrounds are mostly gauge - boson pair and @xmath117 plus photons / jets production with the photons / jets radiating off fermion or gauge boson legs . although they are irreducible , they are of higher order in couplings and should be small . perhaps , the more serious background issue in the lhc environment may be the combinatorial background because of many photons within a jet . again , using strong photon - pair isolation ( that is without hadronic jets around the photon pair ) one should be able to substantially reduce this background . the differential cross section versus the sine of the opening angle between the two photons for @xmath81 and @xmath84 at the lhc . requirements of @xmath118 gev and @xmath108 are imposed . , width=480 ] .[table ] cross sections in fb for associated production of @xmath119 followed by @xmath53 . the cuts applied to the two photons are : @xmath120 gev , @xmath108 , and @xmath121 mrad . [ cols="^,^",options="header " , ] one may ask if a very light pseudoscalar higgs boson is consistent with the muon anomalous magnetic moment ( @xmath122 ) because it can contribute substantially to @xmath122 at both 1-loop and 2-loop levels . however , it was shown that the 2-loop barr - zee type contributions with a light pseudoscalar can be of comparable size as the 1-loop contributions and opposite in sign @xcite . note that the contributions of the light @xmath12 of the nmssm go to zero as @xmath123 . in the nmssm , there could also be a light neutralino @xcite that can contribute to @xmath122 . in addition , there are many parameters in the mssm , such as gaugino and sfermion masses , which the @xmath122 depends on . thus , one can carefully take into account both 1- and 2-loop contributions and by adjusting the nmssm parameters , such that the @xmath122 constraint is satisfied . there are other constraints on a light pseudoscalar from rare @xmath124 and @xmath125 meson decays , such as @xmath126 and @xmath127 , @xmath128 mixing , @xmath129 , and @xmath130 @xcite . however , it is obvious that in these processes the light pseudoscalar interacts via the mixing with the mssm pseudoscalar . thus , in the limit of zero - mixing the constraints on the light @xmath12 can be easily evaded . the major difference between mssm and nmssm is the existence of a singlet field , which gives rise to a scalar , a pseudoscalar , and a neutralino , in addition to the particle contents of the mssm . we have shown that it is possible to have a very light pseudoscalar with a tiny mixing with the mssm pseudoscalar . such a light pseudoscalar boson is consistent with all existing constraints . the discovery mode has been shown @xcite to be @xmath131 , which enjoys a large production cross section . however , the photon pair from the @xmath12 decay may be too collimated . in this paper , we have pointed out another unambiguous signature from the associated production of the light pseudoscalar with a pair of charginos at the lhc and ilc , with a pair of charged leptons and a pair of photons plus large missing energy in the final state . we have also shown that the event rates at the lhc and ilc should be enough to identify such a signature when @xmath104 is larger than @xmath132 gev . r. dermisek and j. f. gunion , arxiv : hep - ph/0502105 . j. e. kim and h. p. nilles , phys . lett . b * 138 * , 150 ( 1984 ) ; y. nir , phys . b * 354 * , 107 ( 1995 ) m. cvetic and p. langacker , phys . d * 54 * , 3570 ( 1996 ) d. a. kirzhnits and a. d. linde , phys . b * 42 * , 471 ( 1972 ) ; y. b. zeldovich et al . jetp * 40 * , 1 ( 1974 ) ; s. a. abel et al . b * 454 * , 663 ( 1995 ) c. panagiotakopoulos and k. tamvakis , phys . lett . b * 446 * , 224 ( 1999 ) phys . b * 469 * , 145 ( 1999 ) r. dermisek and j. f. gunion , arxiv : hep - ph/0510322 . u. ellwanger , j. f. gunion and c. hugonie , jhep * 0502 * , 066 ( 2005 ) u. ellwanger , j. f. gunion and c. hugonie , jhep * 0507 * , 041 ( 2005 ) u. ellwanger , m. rausch de traubenberg and c. a. savoy , nucl . phys . b * 492 * , 21 ( 1997 ) d. j. miller , r. nevzorov and p. m. zerwas , nucl . b * 681 * , 3 ( 2004 ) s. y. choi , d. j. miller and p. m. zerwas , nucl . phys . b * 711 * , 83 ( 2005 ) v. barger , p. langacker and h. s. lee , arxiv : hep - ph/0508027 . j. f. gunion , d. hooper and b. mcelrath , phys . rev . d * 73 * , 015011 ( 2006 ) t. ibrahim and p. nath , the neutron and the lepton edms in mssm , large cp violating phases , and phys . d * 58 * , 111301 ( 1998 ) [ erratum - ibid . d * 60 * , 099902 ( 1999 ) ] [ arxiv : hep - ph/9807501 ] . b. a. dobrescu , g. landsberg and k. t. matchev , phys . d * 63 * , 075003 ( 2001 ) p. w. graham , a. pierce and j. g. wacker , arxiv : hep - ph/0605162 . p. c. schuster and n. toro , arxiv : hep - ph/0512189 . `` cms ecal technical design report '' , cern / lhcc 97 - 33 , december 1997 : http://cmsdoc.cern.ch/cms/tdr/ecal/ecal.html . d. chang , w. f. chang , c. h. chou and w. y. keung , phys . d * 63 * , 091301 ( 2001 ) ; k. cheung , c. h. chou and o. c. w. kong , phys . d * 64 * , 111301 ( 2001 ) . g. hiller , phys . d * 70 * , 034018 ( 2004 ) .[/INST] in the next - to - minimal supersymmetric standard model ( nmssm ) , the unique @xmath0 in the superpotential gives rise to a coupling involving the lighter pseudoscalar higgs boson and a pair of charged or neutral higgsinos , even in the limit of zero mixing between the two pseudoscalar higgs bosons . we study the associated production of a very light pseudoscalar higgs boson with a pair of charginos . the novel signature involves a pair of charged leptons from chargino decays and a pair of photons from the pseudoscalar higgs boson decay , plus large missing energy at the lhc and ilc . the signal may help us to distinguish the nmssm from mssm , provided that the experiment can resolve the two photons from the decay of the pseudoscalar higgs boson . </s>

productivity , as measured by annual patient encounters , is a valuable metric by which to assess the contribution financial and otherwise of members of the health care team as well as utilization of primary care services . productivity measures establish provider value and legitimacy in the health care system , in addition to informing other important practice- and system - level management decisions . the emerging focus on quality and performance indicators , cost - effective care , and optimizing team - based care calls for an effective strategy to holistically evaluate access and productivity in family medicine . in the current health care system , patients struggle to access preventive and primary care services , there is a maldistribution of primary care physicians , and the average cost per patient has steadily risen over the past decade . for physicians , the pressures associated with outcomes - based care lead to new business models other than independent practice . in 2012 , between 50% and 60% of physicians were employed by hospital systems or medical groups , and in 2014 , 64% of recruitment opportunities were for hospital - employed physicians . in response to a national call to disseminate workforce models that incorporate physician assistants ( pas ) and nurse practitioners ( nps ) , this report highlights the contributions of pas and nps in both physician - owned and hospital or integrated delivery system - owned family medicine practices . given the payment differentials based on practice ownership and the need to improve access , incorporating more pas and nps may maximize cost - effective primary health care . here we evaluate ( 1 ) mean total annual patient encounters by provider type and practice ownership and ( 2 ) mean annual compensation by provider type and practice ownership using a robust , national data set . these data inform the discussion on the team - based workforce capacity required for accessible , high - quality primary care in the united states . to evaluate productivity and compensation , the authors used national data from the medical group management association ( mgma ) physician compensation & production survey , 2014 report based on 2013 data . the mgma represents more than 33 000 medical practice administrators and executives in primary and specialty care . the mgma data represent individual providers , family practitioners , pas , or nps , from member physician group practices . in this article , we compared mean total patient encounters and mean annual compensation by provider type , defined as full - time family medicine physicians , pas , and nps without obstetrics . analyses also included mean annual encounters and mean annual compensation within and across practice ownership , defined as physician - owned or hospital or integrated delivery system - owned . all comparisons were made using an unpaired t test , presented in appendices a and b. stata ( statacorp . for overall annual patient encounters in family medicine without obstetrics , physicians and pas reported equivalent annual mean percentage of patient encounters ( 36% ; table 1 ) . for overall annual compensation , physicians reported the highest mean salary ( us$230 884 ) , while pas and nps reported lower but equivalent salaries ( us$99,731 and us$100,981 , respectively ; table 2 ) . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . mean annual compensation , by provider type . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . in physician - owned practices , pas are significantly more productive compared to physicians or nps , based on annual patient encounters . although physicians are compensated significantly more , particularly in physician - owned practices , compensation for pas and nps remains consistent across practice ownership , suggesting improved patient access within a cost - effective compensation structure ( tables 3 and 4 ) . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . mean annual compensation , by practice ownership and provider type , 2013 . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . in 2013 , there was a 34% difference in mean annual patient encounters between physician - owned and hospital or integrated delivery system - owned practices ( 13 040 and 9 729 , respectively ) . in evaluating provider productivity within practice ownership , pas reported significantly more patient encounters compared to both physicians and nps in physician - owned practices . physicians reported more annual patient encounters compared to nps , but the results were not significant ( table 3 and figure 1 ) . within hospital or integrated delivery system - owned practices , physicians reported significantly more patient encounters compared to both nps and pas , and pas reported significantly more patient encounters compared to nps ( table 3 and figure 1 ) . in evaluating productivity across practice ownership , both pas and nps were statistically more productive in physician - owned practices compared to hospital or integrated delivery system - owned ( table 3 and figure 1 ) . however , despite a difference of over 3000 annual encounters between physician - owned and hospital or integrated delivery system - owned practices , physicians were responsible for 41% of the total patient encounters , and pas were responsible for 32% in hospital or integrated delivery system - owned practices ( table 3 ) . in both physician - owned and hospital or integrated delivery system - owned practices , physicians reported significantly higher compensation compared to both nps and pas . there was no significant difference in compensation between nps and pas ( table 4 and figure 2 ) . physicians reported significantly higher compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices , despite no difference in mean annual patient encounters ( table 4 and figure 2 ) . nurse practitioners reported no significant difference in compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices . similarly , pas reported no significant difference in compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices , despite significantly more patient encounters in physician - owned practices compared to both physicians and nps ( table 4 and figure 2 ) . for overall annual patient encounters in family medicine without obstetrics , physicians and pas reported equivalent annual mean percentage of patient encounters ( 36% ; table 1 ) . for overall annual compensation , physicians reported the highest mean salary ( us$230 884 ) , while pas and nps reported lower but equivalent salaries ( us$99,731 and us$100,981 , respectively ; table 2 ) . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . mean annual compensation , by provider type . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . in physician - owned practices , pas are significantly more productive compared to physicians or nps , based on annual patient encounters . although physicians are compensated significantly more , particularly in physician - owned practices , compensation for pas and nps remains consistent across practice ownership , suggesting improved patient access within a cost - effective compensation structure ( tables 3 and 4 ) . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . mean annual compensation , by practice ownership and provider type , 2013 . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . in 2013 , there was a 34% difference in mean annual patient encounters between physician - owned and hospital or integrated delivery system - owned practices ( 13 040 and 9 729 , respectively ) . in evaluating provider productivity within practice ownership , pas reported significantly more patient encounters compared to both physicians and nps in physician - owned practices . physicians reported more annual patient encounters compared to nps , but the results were not significant ( table 3 and figure 1 ) . within hospital or integrated delivery system - owned practices , physicians reported significantly more patient encounters compared to both nps and pas , and pas reported significantly more patient encounters compared to nps ( table 3 and figure 1 ) . mean annual patient encounters , by practice ownership and provider type , 2013 . in evaluating productivity across practice ownership , both pas and nps were statistically more productive in physician - owned practices compared to hospital or integrated delivery system - owned ( table 3 and figure 1 ) . however , despite a difference of over 3000 annual encounters between physician - owned and hospital or integrated delivery system - owned practices , physicians were responsible for 41% of the total patient encounters , and pas were responsible for 32% in hospital or integrated delivery system - owned practices ( table 3 ) . in both physician - owned and hospital or integrated delivery system - owned practices , physicians reported significantly higher compensation compared to both nps and pas . there was no significant difference in compensation between nps and pas ( table 4 and figure 2 ) . physicians reported significantly higher compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices , despite no difference in mean annual patient encounters ( table 4 and figure 2 ) . nurse practitioners reported no significant difference in compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices . similarly , pas reported no significant difference in compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices , despite significantly more patient encounters in physician - owned practices compared to both physicians and nps ( table 4 and figure 2 ) . these data do not sufficiently account for incident to billing methodology that allows claims to be submitted under the physician s national provider identifier for work provided by pas and nps in physician - owned practices . with incident - to - billing practices , the number of patient encounters may be skewed toward the physician in physician - owned practices . in these data , the lack of significance between physician encounters across ownership supports suggests a further , undocumented contribution of pas and nps in physician - owned practices . these results do not control for hours worked , case mix , complexity of patient visits , provider demographics , or collections by provider or practice . further clarity is needed in determining compensation structures in hospital or integrated delivery system - owned practices across provider type , as they seem to deviate from traditional productivity models . finally , here the patient encounters are not weighted , so some of the differences seen may be due to differences in complexity or severity or hours worked in clinical practice . the data presented do not account for management or administrative responsibilities assumed by physicians , team - based visits , time spent outside of the examination room on patient - related care , variability in state provider distribution , or level of delegated practice autonomy . these results are limited to family medicine without obstetrics and do not include primary care , family medicine with obstetrics , internal medicine , or pediatrics . the percentage of distribution of the sample overrepresents physicians in the family medicine workforce and underrepresents nps . finally , the mgma physician compensation & production survey design does not permit temporal comparison between cohorts . although these data do not stratify by patient case mix or complexity , the results have implications for labor costs and workforce distribution in emerging models of primary care delivery . these results also suggest further research using longitudinal data on measures of productivity in clinical medicine to include resource utilization , labor costs , cost - effective care delivery , and models of high - quality , team - based practice . it will be important to consider complexity of cases , comorbidity , and management factors in further studies . additionally , studies incorporating provider compensation and production , gender variances , time devoted to clinical care ( vs administration or practice management ) , geographic distribution , payment mechanism , and specialty practice are needed for workforce planning . this study serves as a benchmark in demonstrating the contributions of pas and nps to the delivery of family medicine in emerging employment settings . although these data provide a 1-year national snapshot of patient encounters and compensation , the results certainly seem supportive of other published reports . these data demonstrate that pas and nps are important and productive primary care team members where they are deployed . of note , it may be important to consider their contributions in rural and underserved communities where physician - owned practices remain the model . additional research is needed to inform both practice organizational and policy decisions for the provision of high - quality , cost - effective , and accessible health care . this is an ambitious but essential goal in order to improve the health of our population .

the increasing focus on high performance , patient - centered , team - based care calls for a strategy to evaluate cost - effective primary care . the trend toward physician practice consolidation further challenges the primary care health care system . productivity measures establish provider value and help inform decision making regarding resource allocation in this evolving health care system . in this national survey of family medicine practices , physician assistant ( pa ) productivity , as defined by mean annual patient encounters , exceeds that of both nurse practitioners ( nps ) and physicians in physician - owned practices and of nps in hospital or integrated delivery system - owned practices . total compensation , defined as salary , bonus , incentives , and honoraria for physicians , is significantly more compared to both pas and nps , regardless of practice ownership or productivity . physician assistants and nps earn equivalent compensation , regardless of practice ownership or productivity . not only do these data support the value and role of pas and nps on the primary care team but also highlight differences in patient encounters between practice settings . rural and underserved community practices , where physician - owned practices persist , also merit further consideration . further research is needed to inform both organizational and policy decisions for the provision of high - quality , cost - effective , and accessible primary health care .

<s>[INST]productivity , as measured by annual patient encounters , is a valuable metric by which to assess the contribution financial and otherwise of members of the health care team as well as utilization of primary care services . productivity measures establish provider value and legitimacy in the health care system , in addition to informing other important practice- and system - level management decisions . the emerging focus on quality and performance indicators , cost - effective care , and optimizing team - based care calls for an effective strategy to holistically evaluate access and productivity in family medicine . in the current health care system , patients struggle to access preventive and primary care services , there is a maldistribution of primary care physicians , and the average cost per patient has steadily risen over the past decade . for physicians , the pressures associated with outcomes - based care lead to new business models other than independent practice . in 2012 , between 50% and 60% of physicians were employed by hospital systems or medical groups , and in 2014 , 64% of recruitment opportunities were for hospital - employed physicians . in response to a national call to disseminate workforce models that incorporate physician assistants ( pas ) and nurse practitioners ( nps ) , this report highlights the contributions of pas and nps in both physician - owned and hospital or integrated delivery system - owned family medicine practices . given the payment differentials based on practice ownership and the need to improve access , incorporating more pas and nps may maximize cost - effective primary health care . here we evaluate ( 1 ) mean total annual patient encounters by provider type and practice ownership and ( 2 ) mean annual compensation by provider type and practice ownership using a robust , national data set . these data inform the discussion on the team - based workforce capacity required for accessible , high - quality primary care in the united states . to evaluate productivity and compensation , the authors used national data from the medical group management association ( mgma ) physician compensation & production survey , 2014 report based on 2013 data . the mgma represents more than 33 000 medical practice administrators and executives in primary and specialty care . the mgma data represent individual providers , family practitioners , pas , or nps , from member physician group practices . in this article , we compared mean total patient encounters and mean annual compensation by provider type , defined as full - time family medicine physicians , pas , and nps without obstetrics . analyses also included mean annual encounters and mean annual compensation within and across practice ownership , defined as physician - owned or hospital or integrated delivery system - owned . all comparisons were made using an unpaired t test , presented in appendices a and b. stata ( statacorp . for overall annual patient encounters in family medicine without obstetrics , physicians and pas reported equivalent annual mean percentage of patient encounters ( 36% ; table 1 ) . for overall annual compensation , physicians reported the highest mean salary ( us$230 884 ) , while pas and nps reported lower but equivalent salaries ( us$99,731 and us$100,981 , respectively ; table 2 ) . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . mean annual compensation , by provider type . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . in physician - owned practices , pas are significantly more productive compared to physicians or nps , based on annual patient encounters . although physicians are compensated significantly more , particularly in physician - owned practices , compensation for pas and nps remains consistent across practice ownership , suggesting improved patient access within a cost - effective compensation structure ( tables 3 and 4 ) . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . mean annual compensation , by practice ownership and provider type , 2013 . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . in 2013 , there was a 34% difference in mean annual patient encounters between physician - owned and hospital or integrated delivery system - owned practices ( 13 040 and 9 729 , respectively ) . in evaluating provider productivity within practice ownership , pas reported significantly more patient encounters compared to both physicians and nps in physician - owned practices . physicians reported more annual patient encounters compared to nps , but the results were not significant ( table 3 and figure 1 ) . within hospital or integrated delivery system - owned practices , physicians reported significantly more patient encounters compared to both nps and pas , and pas reported significantly more patient encounters compared to nps ( table 3 and figure 1 ) . in evaluating productivity across practice ownership , both pas and nps were statistically more productive in physician - owned practices compared to hospital or integrated delivery system - owned ( table 3 and figure 1 ) . however , despite a difference of over 3000 annual encounters between physician - owned and hospital or integrated delivery system - owned practices , physicians were responsible for 41% of the total patient encounters , and pas were responsible for 32% in hospital or integrated delivery system - owned practices ( table 3 ) . in both physician - owned and hospital or integrated delivery system - owned practices , physicians reported significantly higher compensation compared to both nps and pas . there was no significant difference in compensation between nps and pas ( table 4 and figure 2 ) . physicians reported significantly higher compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices , despite no difference in mean annual patient encounters ( table 4 and figure 2 ) . nurse practitioners reported no significant difference in compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices . similarly , pas reported no significant difference in compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices , despite significantly more patient encounters in physician - owned practices compared to both physicians and nps ( table 4 and figure 2 ) . for overall annual patient encounters in family medicine without obstetrics , physicians and pas reported equivalent annual mean percentage of patient encounters ( 36% ; table 1 ) . for overall annual compensation , physicians reported the highest mean salary ( us$230 884 ) , while pas and nps reported lower but equivalent salaries ( us$99,731 and us$100,981 , respectively ; table 2 ) . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . mean annual compensation , by provider type . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . in physician - owned practices , pas are significantly more productive compared to physicians or nps , based on annual patient encounters . although physicians are compensated significantly more , particularly in physician - owned practices , compensation for pas and nps remains consistent across practice ownership , suggesting improved patient access within a cost - effective compensation structure ( tables 3 and 4 ) . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . mean annual compensation , by practice ownership and provider type , 2013 . abbreviation : sd , standard deviation . adapted from authors analyses of the medical group management association physician compensation & production survey , 2014 report based on 2013 data . in 2013 , there was a 34% difference in mean annual patient encounters between physician - owned and hospital or integrated delivery system - owned practices ( 13 040 and 9 729 , respectively ) . in evaluating provider productivity within practice ownership , pas reported significantly more patient encounters compared to both physicians and nps in physician - owned practices . physicians reported more annual patient encounters compared to nps , but the results were not significant ( table 3 and figure 1 ) . within hospital or integrated delivery system - owned practices , physicians reported significantly more patient encounters compared to both nps and pas , and pas reported significantly more patient encounters compared to nps ( table 3 and figure 1 ) . mean annual patient encounters , by practice ownership and provider type , 2013 . in evaluating productivity across practice ownership , both pas and nps were statistically more productive in physician - owned practices compared to hospital or integrated delivery system - owned ( table 3 and figure 1 ) . however , despite a difference of over 3000 annual encounters between physician - owned and hospital or integrated delivery system - owned practices , physicians were responsible for 41% of the total patient encounters , and pas were responsible for 32% in hospital or integrated delivery system - owned practices ( table 3 ) . in both physician - owned and hospital or integrated delivery system - owned practices , physicians reported significantly higher compensation compared to both nps and pas . there was no significant difference in compensation between nps and pas ( table 4 and figure 2 ) . physicians reported significantly higher compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices , despite no difference in mean annual patient encounters ( table 4 and figure 2 ) . nurse practitioners reported no significant difference in compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices . similarly , pas reported no significant difference in compensation in physician - owned practices compared to hospital or integrated delivery system - owned practices , despite significantly more patient encounters in physician - owned practices compared to both physicians and nps ( table 4 and figure 2 ) . these data do not sufficiently account for incident to billing methodology that allows claims to be submitted under the physician s national provider identifier for work provided by pas and nps in physician - owned practices . with incident - to - billing practices , the number of patient encounters may be skewed toward the physician in physician - owned practices . in these data , the lack of significance between physician encounters across ownership supports suggests a further , undocumented contribution of pas and nps in physician - owned practices . these results do not control for hours worked , case mix , complexity of patient visits , provider demographics , or collections by provider or practice . further clarity is needed in determining compensation structures in hospital or integrated delivery system - owned practices across provider type , as they seem to deviate from traditional productivity models . finally , here the patient encounters are not weighted , so some of the differences seen may be due to differences in complexity or severity or hours worked in clinical practice . the data presented do not account for management or administrative responsibilities assumed by physicians , team - based visits , time spent outside of the examination room on patient - related care , variability in state provider distribution , or level of delegated practice autonomy . these results are limited to family medicine without obstetrics and do not include primary care , family medicine with obstetrics , internal medicine , or pediatrics . the percentage of distribution of the sample overrepresents physicians in the family medicine workforce and underrepresents nps . finally , the mgma physician compensation & production survey design does not permit temporal comparison between cohorts . although these data do not stratify by patient case mix or complexity , the results have implications for labor costs and workforce distribution in emerging models of primary care delivery . these results also suggest further research using longitudinal data on measures of productivity in clinical medicine to include resource utilization , labor costs , cost - effective care delivery , and models of high - quality , team - based practice . it will be important to consider complexity of cases , comorbidity , and management factors in further studies . additionally , studies incorporating provider compensation and production , gender variances , time devoted to clinical care ( vs administration or practice management ) , geographic distribution , payment mechanism , and specialty practice are needed for workforce planning . this study serves as a benchmark in demonstrating the contributions of pas and nps to the delivery of family medicine in emerging employment settings . although these data provide a 1-year national snapshot of patient encounters and compensation , the results certainly seem supportive of other published reports . these data demonstrate that pas and nps are important and productive primary care team members where they are deployed . of note , it may be important to consider their contributions in rural and underserved communities where physician - owned practices remain the model . additional research is needed to inform both practice organizational and policy decisions for the provision of high - quality , cost - effective , and accessible health care . this is an ambitious but essential goal in order to improve the health of our population .[/INST]the increasing focus on high performance , patient - centered , team - based care calls for a strategy to evaluate cost - effective primary care . the trend toward physician practice consolidation further challenges the primary care health care system . productivity measures establish provider value and help inform decision making regarding resource allocation in this evolving health care system . in this national survey of family medicine practices , physician assistant ( pa ) productivity , as defined by mean annual patient encounters , exceeds that of both nurse practitioners ( nps ) and physicians in physician - owned practices and of nps in hospital or integrated delivery system - owned practices . total compensation , defined as salary , bonus , incentives , and honoraria for physicians , is significantly more compared to both pas and nps , regardless of practice ownership or productivity . physician assistants and nps earn equivalent compensation , regardless of practice ownership or productivity . not only do these data support the value and role of pas and nps on the primary care team but also highlight differences in patient encounters between practice settings . rural and underserved community practices , where physician - owned practices persist , also merit further consideration . further research is needed to inform both organizational and policy decisions for the provision of high - quality , cost - effective , and accessible primary health care .</s>

let @xmath1 be a riemann surface with a spectral covering @xmath2 for the group @xmath0 . in @xcite we proposed in general terms a reduction process that would construct a versal @xmath3-harmonic map to an @xmath0 pre - building . it was conjectured that if the @xmath3-spectral network @xcite has no bps states then the reduction process should be well - defined . this conjecture would lead to a precise calculation of the wkb exponents for singular perturbations whose spectral curve has no bps states , generalizing the known picture @xcite for quadratic differentials and @xmath4 . the purpose of the present paper is to provide more details on the reduction process , particularly about the combinatorial structure of the singularities that occur and how they are arranged at each reduction step . we will show ( although the proofs are sometimes only sketches ) that the reduction steps are well - defined if there are no bps states . it is left for later to show that the process finishes in finitely many steps . assume @xmath1 is complete and simply connected . for the present one should think of it as being the complex plane with @xmath3 a spectral covering similar to the one considered in our original example @xcite . the case of the universal covering of a compact riemann surface would pose additional problems of non - finiteness of the set of singularities , and the right notion of convergence seems less clear . the process and results will be summed up in [ scholium ] and the reader is referred there . in the remainder of the introduction , we review the motivation for the reduction process considered here . a building @xmath5 for the group @xmath0 is a piecewise linear cell complex that is covered by copies of the standard appartment @xmath6 , and indeed any two points of @xmath5 are contained in a common appartment . one of the main properties characterizing a building is that it is negatively curved . a _ harmonic map _ @xmath7 is a continuous map such that any point @xmath8 , except for a discrete set of singularities , admits a neighborhood @xmath9 such that there is an appartment @xmath10 with @xmath11 being a harmonic map . the differential @xmath12 is naturally a triple of real @xmath13-forms @xmath14 with @xmath15 . these are well - defined up to permutation . now , these real harmonic forms are real parts of holomorphic @xmath13-forms @xmath16 and the collection @xmath17 defines the spectral curve @xmath2 . we say that @xmath18 is a @xmath3-harmonic map . for a given spectral curve we would like to understand the @xmath3-harmonic maps to buildings . we conjectured in @xcite that , under a certain genericity hypothesis , there should be an essentially uniquely defined map @xmath19 depending only on the spectral curve @xmath20 with the following properties : ( 1 ) the pre - building @xmath21 is a negatively curved complex built out of enclosures in @xmath22 @xcite , and ( 2 ) any @xmath3-harmonic map to a building @xmath7 factors through an embedding @xmath23 isometric for the finsler and vector distances . the conjectured genericity hypothesis for existence of @xmath24 is that the spectral network associated to @xmath3 should not have any bps states @xcite . before getting to the proposed method for constructing @xmath21 , let us consider the implications for exponents of wkb problems . there are several different ways of getting harmonic mappings to buildings , such as gromov - schoen s theory @xcite . parreau interpreted boundary points of the character variety as actions on buildings @xcite . in @xcite we extended parreau s theory slightly for the situation of wkb problems , getting a control on the differential . suppose @xmath25 is a singular perturbation of flat connections , for @xmath26 a large parameter . there are two typical ways of getting @xmath27 , the riemann - hilbert situation @xmath28 or by solution of hitchin s equations for the higgs bundle @xmath29 . in either case , there is an associated limiting higgs bundle @xmath30 and we let @xmath3 be its spectral curve . for @xmath31 let @xmath32 denote the transport for @xmath25 . for an ultrafilter @xmath33 on @xmath34 define the _ exponent _ @xmath35 there is a similar _ vector exponent _ @xcite that is a point in the positive weyl chamber of @xmath22 . the groupoid version of parreau s theory @xcite gives a map to a building @xmath36 such that the finsler distance ( resp . vector distance ) between @xmath37 is the exponent @xmath38 ( resp . the vector exponent ) . we showed in @xcite for the riemann - hilbert situation that @xmath39 is a @xmath3-harmonic map . mochizuki @xcite showed this for the hitchin wkb problem . if there exists a @xmath3-harmonic map @xmath24 satisfying the properties ( 1 ) , ( 2 ) above , then it follows that @xmath40 is calculated as the finsler distance between @xmath41 . in particular , it depends only on the spectral curve @xmath3 . indepenence of the choice of ultrafilter means that the ultrafilter limit used to define the exponent is actually a limit , and we obtain a calculation of the wkb exponents for our singular perturbation . turn now to the reduction process for constructing @xmath21 . a conjectural yet detailed picture of this construction was set out in @xcite and readers are referred there for a full explanation . the first step was to make an initial construction . that is essentially what we shall be calling @xmath42 below , although the initial construction for the pre - building has to include additional small parallelogram - shaped regions corresponding to the folded pieces @xmath43 that we ll meet in [ sec - initial ] below . our @xmath42 has these trimmed off . the main problem of the initial construction is that it contains points of positive curvature , referred to as @xmath44-fold points or @xmath45 points below . these have to collapse in some way under any harmonic map to a building @xmath5 since @xmath5 is negatively curved . the construction of the pre - building consists of successively doing such a collapsing operation . unfortunately , the direction of collapsing at a @xmath44-fold point is not well - defined , rather there are two possibilities . for that reason , the notion of _ scaffolding _ was introduced in @xcite . the initial scaffolding formalizes the existence of small neighborhoods @xmath46 that map , in an unfolded way , into appartments of the building . it follows that @xmath46 should not be folded in the map @xmath24 to @xmath21 . the edges gotten by gluing together sectors are , on the other hand , to be folded further , and this collection of data is complete : every edge is either marked as folded or unfolded ( open ) in the scaffolding . the scaffolding tells us which direction to fold at a @xmath45 point . the remaining difficulty is to propagate the information of the scaffolding into the new constructions obtained by collapsing . it was conjectured in @xcite that this should be possible , under the hypothesis of absence of bps states in the original spectral network . the purpose of the present paper is to prove this conjecture on propagation of the scaffolding . we show how to make a series of reduction steps and how to propagate the scaffolding and other required information so that the series of reduction steps is well - defined . the present work does not yet result in a full construction of @xmath21 . notably missing is a convergence statement saying that the process stops in a ( locally ) finite number of steps . some parts of our arguments are also sketches rather than full proofs , and we do nt provide here a justification for the choice of initial construction ( principle [ chooseinitial ] ) . it was observed in @xcite that each step of the reduction process towards the pre - building , could be accompanied by a trimming of the just glued - together parallelograms . if one does that , then the sequence of constructions is a sequence of @xmath47-dimensional surfaces . this point of view will be useful for the program of generalizing bridgeland - smith s work on stability conditions , discussed briefly in [ sec - further ] at the end . also , the combinatorics of the reduction steps are all contained in this sequence of surfaces . therefore , in the present paper we shall include the trimming operation as part of our reduction steps . in order to construct the pre - building @xmath21 one should put back in the pieces that were trimmed off the procedure for doing that was explained in @xcite . start by considering spectral networks in @xmath1 . away from the branch points , the spectral curve @xmath3 consists of three holomorphic @xmath13-forms @xmath48 and setting @xmath49 these define _ foliation lines _ @xmath50 where @xmath51 . assume the ramification of @xmath3 consists of simple branch points . at a branch point , two indices are interchanged , picking out one of the foliations @xmath51 whose singular leaves starting from the branch point are the initial edges of the spectral network . away from the _ caustics _ where the three foliation lines are tangent , the coordinates @xmath52 define a flat structure on @xmath1 by local identification with the standard apartment @xmath53 for buildings of the group @xmath0 . we use this flat structure when speaking of angles . we are going to add some extra singularities , so suppose given a finite subset @xmath54 and for each @xmath55 one of the three foliations @xmath56 . spectral network graph _ is a map from a trivalent graph @xmath57 , that can have endpoints as well as at most one infinite end , to @xmath1 that sends endpoints of @xmath57 to elements of @xmath58 , that sends edges to foliation lines , and that sends trivalent vertices to _ collisions _ @xcite , points where foliation lines @xmath59 meet at @xmath60 angles . we require that an endpoint of the graph going to @xmath55 has adjoining edge going to a foliation line for the given foliation @xmath56 . a foliation line in @xmath1 is an _ sn - line _ if there exists a spectral network graph such that the given foliation line is in the image of an edge of the graph that is either adjacent to an endpoint , or is an infinite end . a _ bps state _ @xcite is a compact spectral network graph . our main hypothesis will be that these do nt exist . we now note how to add singularities while conserving this hypothesis . the original set @xmath61 of singular points is equal to the set of ramification points of the spectral curve , assumed to be simple ramifications . the foliation line @xmath56 at a ramification point is the one determined by the two sheets of the spectral curve that come together at that point . the following proposition will allow us successively to add points to the set of singularities . [ addsn ] suppose given a set of singularities @xmath62 such that the resulting spectral network does nt have bps states . choose a point @xmath63 in general position along the interior of a caustic curve , let @xmath64 be one of the foliation lines at @xmath63 and let @xmath65 . then the spectral network associated to @xmath66 also does nt have any bps states . suppose we are given a spectral network graph @xmath67 that is a bps state for @xmath68 . consider a nearby point @xmath69 obtained by moving it a small distance @xmath70 in one direction along the caustic curve ( the caustic is generically transverse to the foliation lines otherwise it would constitute a bps state itself ) . we may assume that the bps state follows to a nearby one @xmath71 . the foliation lines are defined by differential forms @xmath72 so this gives us a way of measuring transverse distances ; in these terms it makes sense to talk about the distance between one of the foliation lines and an adjacent one for the same foliation . we should choose for each edge of the graph a sign for the form in question . now , label edges of the graph @xmath73 by integers @xmath74 such that the edge @xmath75 moves by @xmath76 . an edge @xmath77 adjoining an endpoint of the graph that goes to a previous singularity @xmath78 has to be labeled with @xmath79 , since @xmath80 does nt move with @xmath70 . there is a balancing condition on the labels at the collision points . the edges that end in @xmath81 from one direction have to be labeled by @xmath82 whereas the edges that end in @xmath81 from the other direction have to be labeled by @xmath83 . however , the balancing condition at the trivalent vertices plus the condition that all the other endpoint labels are zero , means that the number of @xmath82 labels and the number of @xmath83 labels at @xmath81 have to be equal . therefore , we can pair up edges coming in from one direction with edges going out in the other , glueing these edges together pairwise . this results in a new graph @xmath84 that is a bps state for the previous set of singularities @xmath62 . * boundedness*let us mention a boundedness hypothesis that will be useful . suppose that there exists a compact subset @xmath85 whose boundary @xmath86 consists of foliation lines , such that the corners of @xmath86 are convex in the sense that each corner consists of foliation lines separated by two sectors inside @xmath87 . and , we suppose that all ramification points of the spectral curve , and all caustics , are contained in the interior of @xmath87 . since the additional singularities were chosen on caustics , it follows that @xmath88 . with this hypothesis , a spectral network graph has no collisions outside of @xmath87 , and any edge that leaves @xmath87 continues as an infinite end . indeed , all caustics are contained in the interior of @xmath87 , so @xmath89 has a flat structure modeled on the standard appartment @xmath22 . suppose @xmath90 were a collision point , say the first one outside of @xmath87 . then the two incoming edges must exit from @xmath87 , but two distinct foliation lines that exit from @xmath87 and meet , must exit from the same edge because of the convexity hypothesis on the corners . if they exit from the same edge and meet , then they must meet at a @xmath91 angle , contradicting the hypothesis that they form incoming edges of a collision . thus , such a collision can not occur . referring to the reduction steps that will be discussed later , any regions that are to be folded together have to stay inside @xmath87 by the same kind of considerations . therefore , we may follow our compact subset along into the sequence of constructions @xmath92 that will occur ; the compact subset will contain all modifications , and @xmath89 remains untouched as a flat space contained in each of our series of constructions . although we do nt discuss the question of convergence in the present paper , the existence of a series of compact subsets that contain all the modifications means that one could envision an argument using decrease of the area to conclude termination of the reduction process . that would require bounding from below the size of the reduction steps the _ initial construction _ is a construction @xmath42 obtained by a first process of folding together certain regions in @xmath1 and trimming away the resulting pieces . we consider a collection of regions @xmath93 covering the caustics , such that @xmath94 are bounded by foliation lines meeting in two points @xmath95 symmetrical with respect to the caustic . in any @xmath96-harmonic map to a building @xmath7 , @xmath97 and @xmath98 have to map to the same point , and indeed @xmath99 has to factor through a map @xmath100 where @xmath43 is @xmath94 folded in two along the caustic @xcite . here is a picture of the regions @xmath94 in @xmath1 and here is what their images look like in any harmonic map to a building : we assume that the boundaries of the regions @xmath94 are formed by new spectral network lines gotten after adding singularities along the caustics according to proposition [ addsn ] . that will be used for the refracting property in [ sec - refracting ] . let @xmath101 denote the quotient of @xmath1 by the equivalence relation induced by the quotients @xmath102 . now let @xmath103 be the result of trimming off the folded - together pieces , in other words it is the closure in @xmath101 of @xmath104 , or equivalently the image of @xmath105 . the space @xmath106 is a topological surface , and we have cut out the caustics . thus , @xmath103 is provided with a geometric structure locally modeled on the standard appartment @xmath22 ; the three foliation lines at any point correspond to the three standard directions in @xmath22 . in particular @xmath103 has a flat metric . the conformal structure for this flat metric is different from the original structure of riemann surface on @xmath1 . it has singular points of positive and negative curvature , namely @xmath107-fold points of negative curvature whose total angle is @xmath108 and @xmath44-fold points of positive curvature whose total angle is @xmath109 . view @xmath103 as corresponding to a construction , i.e. a presheaf on the site of enclosures as discussed in @xcite . more precisely we have a construction @xmath42 whose usual set of points is @xmath110 . it is provided with a map @xmath111 that sends foliation lines in @xmath1 to segments in @xmath42 . this construction will be the starting point of our reduction process . it is provided with a _ scaffolding _ @xcite : certain edges ( the image of @xmath112 ) are designated as `` fold edges '' while all the other edge germs are designated as `` open '' or `` unfolded '' . if @xmath7 is any @xmath96-harmonic map to a building , then its restriction to @xmath113 factors through a map @xmath114 that respects the scaffolding , in the sense that fold edges are folded and open edges are unfolded . let @xmath92 be a construction . we say that @xmath92 is _ complete _ if the associated metric space is complete . it is _ normal _ if the link at any point is connected . we say that @xmath92 is _ ecarinate _ if , at any edge there are two half - planes . notice that @xmath42 satisfies these conditions , and our reduction process will conserve them , so let us consider only complete normal ecarinate and simply connected constructions @xmath92 . in particular the set of usual points @xmath115 is a complete @xmath47-manifold . if @xmath116 is a point then the link @xmath117 is a connected graph such that each vertex ( corresponding to a germ of edge at @xmath118 ) is contained in two edges ( corresponding to germs of sectors at @xmath118 ) . therefore , the link is a polygon . by the parity property the polygon has an even number of edges . we assume that the number of edges in the link at any point is @xmath44 , @xmath119 or @xmath107 . most points are _ flat _ , meaning that their links are hexagons . the other points are called @xmath44-fold , or @xmath107-fold respectively . the @xmath44-fold points are points of positive curvature , and the @xmath107-fold points are points of negative curvature . a _ scaffolding _ consists of the following structures : ( 1 ) a marking of each edge in @xmath92 as either _ open _ ( o ) or _ folded _ ( f ) , such that the fold edges are those from a discrete collection @xmath120 of straight edges in @xmath92 . ( 2 ) an orientation assigned to each fold edge . ( 3 ) a marking of some subset of the fold edges said to be _ refracting_. our initial construction @xmath42 contains a scaffolding in which all the edges are already marked as refracting , see [ sec - refracting ] below , and our reduction process will preserve the refracting condition so we henceforth consider only fully refracting scaffoldings . we assume that @xmath42 and its scaffolding have the property that there exists a harmonic mapping to a building such that the fold edges are folded and the open edges are unfolded . this constrains the local type of singularities . however , the number of possibilities is still rather large . we describe here a list standard examples that will be sufficient for our reduction process the statement that we remain within this standard list is indeed one of the main conclusions of our treatment in the present paper . the notation will consist of a boldface number saying how many sectors there are , and a subscript saying how many folded lines in the scaffolding there are . arrows in the pictures indicate the orientations of the scaffolding edges . for example , points of type @xmath121 and @xmath122 are respectively @xmath119-fold and @xmath107-fold points with no adjoining fold edges . a point of type @xmath123 is a @xmath119-fold point with a single straight fold edge ( it is nonsingular ) ; a @xmath124 point has three folded edges separated by @xmath60 , and a @xmath125 point is the same with an additional folded edge . these may be pictured as follows : @xmath126 next we picture the @xmath107-fold and @xmath44-fold points . note that the pictures can not be conformally correct for the angles ; all drawn sectors represent sectors of @xmath91 in @xmath92 . the @xmath107-fold points have at most @xmath47 fold edges ; and if there are @xmath47 of them , they are separated by either @xmath13 or @xmath44 sectors . the fold edge orientations go outward , so after the @xmath122 picture there are three possibilities : @xmath127 recall @xcite that at a @xmath44-fold point , at least two of the four edges are folded , and if an edge is folded then so is the opposite one . our standard type is when only two edges are folded , and the edge orientations are inwards towards the singularity , so it has the following picture : @xmath128 [ singdef ] we say that the singularities of the scaffolding are _ initial _ if at any point of @xmath92 the picture is either @xmath121 ( a smooth point not on the scaffolding ) , @xmath123 ( an interior point of an edge of the scaffolding ) , an @xmath107-fold point of the form @xmath129 , or a @xmath44-fold point @xmath45 . we say that the singularities of the scaffolding are _ standard _ if at any point the local picture is one of the ones we have described , namely : @xmath130 shown above . included in the above definitions are compatibility of the orientations of the fold lines with the singularity types as drawn in the pictures . recall that edges are oriented outward at @xmath107-fold points and inward at @xmath44-fold points . for initial scaffoldings we obtain the following characterization : [ postcaustic ] given a scaffolding with initial singularities , the collection of fold lines decomposes into a disjoint union of piecewise linear curves called the _ post - caustics _ , whose endpoints are of type @xmath131 , and along which the @xmath44-fold points alternate with @xmath107-fold points . in particular , the number of @xmath107-fold points on a connected post - caustic is @xmath13 more than the number of @xmath44-fold points . using proposition [ addsn ] to add spectral network lines along the boundaries of the regions @xmath94 used to define the initial construction , will give that the scaffolding of the initial construction @xmath42 is a fully refracting scaffolding . the `` refracting properties '' with respect to the spectral network are : ( r1 ) at singular points of the scaffolding , all unfolded edges are initial edges of the spectral network ; and ( r2 ) when a spectral network line crosses over a fold edge , it can continue on the other side in either one of the two available directions . suppose we are given a construction @xmath92 and a fully refracting scaffolding . spectral network graph for the refracting spectral network _ is a map from a graph @xmath132 satisfying the following properties : edges of @xmath57 go to segments in @xmath92 that are straight except when they cross the fold edges ; edges do not go along fold edges of the scaffolding ; when edges cross over the fold edges they can `` refract '' , that is to say they go out of the fold edge on the other side in either one of the two directions ; trivalent vertices of the graph go to collisions at @xmath121 points i.e. points not on fold edges of the scaffolding ; and endpoints of the graph go to singular points of the scaffolding or @xmath122 points of @xmath92 , with the adjoining edges going outward in any non - fold directions . before choosing the regions @xmath93 that will be folded and trimmed to get @xmath103 , add points to the set of singularities of our spectral network , using proposition [ addsn ] . add these points along the caustic curves at the places where the boundaries of the @xmath94 meet the caustics , so that the boundary curves of the @xmath94 become spectral network curves . notice furthermore that at the corners @xmath95 , all three directions outward to the rest of @xmath1 are spectral network lines , two from continuing the boundary curves and the third by collision of the two boundary curves . our above somewhat heuristic discussion leads to the following principle . [ nobps ] if the original spectral network of @xmath1 had no bps states , then the refracting spectral network of @xmath42 has no bps states . we also need to know something about the arrangement of singularities of the scaffolding for @xmath42 . we state this as another principle : [ chooseinitial ] the initial construction @xmath42 may be chosen to have only initial singularities ( definition [ singdef ] ) . the fold edges of the scaffolding are thus arranged into post - caustics as described in remark [ postcaustic ] . we do nt give here a formal justification for the possibility of choosing the initial construction in this way , but note that it is what happens in the pictures we have considered . for example , see @xcite for a picture leading to an @xmath133 point . this section begins the discussion of a step in the reduction process . the first question is to show the existence of a @xmath45 point about which some collapsing can be done . [ prop - noloops ] suppose given a construction with a refracting scaffolding , such that there are no bps states in the resulting spectral network . suppose that the fold edges of the scaffolding are oriented and the singularities are all from our standard list . make a directed graph using the singularities as vertices , except that we separate a @xmath125 singularity into two vertices . the edges of the graph are the fold edges with their orientations ; at a @xmath125 point the `` spine '' ( consisting of the two fold edges that are opposite ) goes to one of the vertices and the other two edges go to the other one . this directed graph has no directed loops . _ ( sketch)_consider a path parallel to a directed loop , just to one side of it . this will satisfy the collision and refracting conditions , so taken together with the appropriate initial sn lines coming from singularities , it constitutes a bps state . [ existsfourtwo ] if there are no bps states and if the set of fold lines in the scaffolding is nonempty , then there must be a @xmath45 point . in the directed graph described in proposition [ prop - noloops ] , our hypothesis that there are no bps states implies that there are no directed loops . therefore , the orientations of edges make the graph into a poset ; since it is finite it has a minimal vertex . the only type of point on the scaffolding that has all fold edges pointed inward is a @xmath45 point , therefore there exists a @xmath45 point . @xmath134 we now consider an extended collapsing operation at a @xmath45 point @xmath135 . for this , consider two pieces @xmath136 and @xmath137 that match up , and share a common vertex @xmath135 and common edges @xmath138 and @xmath139 . let @xmath140 ( resp . @xmath141 ) denote the endpoint of @xmath138 ( resp . @xmath139 ) different from @xmath135 . the @xmath142 are assumed to be constructions that can be considered as isomorphic to a subset @xmath143 in an abstract parallelogram @xmath144 . let us also label the corresponding vertex @xmath135 and the corresponding edges @xmath145 in @xmath144 . the embeddings @xmath146 preserve @xmath147 . we can now describe the configuration of @xmath143 : the vertex @xmath135 is an obtuse vertex of @xmath144 , and @xmath145 are the full edges of @xmath144 meeting @xmath135 . hence the points also labelled @xmath148 are the two acute vertices . we assume that @xmath143 is a union of finitely many sub - parallelograms @xmath149 ( see the picture below for the numbering ) such that @xmath150 contains @xmath135 as obtuse vertex , that is to say the edges of @xmath150 will be segments in @xmath145 starting at @xmath135 . let @xmath151 denote the vertices of @xmath150 opposite to @xmath135 . we assume that the order @xmath152 is such that @xmath153 is on the same edge of @xmath144 as @xmath140 , and they go in a consecutive sequence until @xmath154 is on the same edge of @xmath144 as @xmath141 . the @xmath155 are the other convex corners of @xmath143 after @xmath156 . let @xmath157 denote the concave corners of @xmath143 in between them , so that @xmath158 lies between @xmath151 and @xmath159 . let @xmath160 be the edge from @xmath140 to @xmath153 and let @xmath161 be the edge from @xmath154 to @xmath141 . let @xmath162 be the edge from @xmath151 to @xmath158 and @xmath163 be the edge from @xmath158 to @xmath159 . thus , @xmath162 and @xmath138 are parallel , and @xmath164 and @xmath139 are parallel . now consider the same points in the regions @xmath142 , indicated as @xmath165 and @xmath166 , with edges @xmath167 . the configuration of this maximal collapsing pair of regions may be pictured as in figure [ mcr ] . we assume that @xmath143 is a maximal such region with corresponding regions @xmath168 , such that the following conditions are satisfied : there are no singularities in the interior of @xmath142 ; the only singularities on the interior of the edges @xmath145 are @xmath125 points where @xmath138 or @xmath139 is the straight fold edge ( spine ) . [ properties ] under the above maximality conditions , we have the following properties : 1 . the vertices @xmath169 are singularities , and furthermore these singularities are not @xmath125 points with edge @xmath138 or @xmath139 on the spine ; 2 . for each @xmath170 there is exactly one of the @xmath171 that is an @xmath107-fold singularity , and the other is nonsingular ; 3 . there are no @xmath107-fold singularities in the interiors of the edges @xmath167 ; 4 . if @xmath172 is a @xmath44-fold or singular @xmath119-fold point on an edge @xmath173 of @xmath136 then the corresponding point @xmath174 on @xmath137 is not a singularity , and vice - versa , and this also applies for corners @xmath166 . notice in general that there ca nt be a fold edge going from a point on one of the edges @xmath167 into @xmath142 in the middle direction between the directions of @xmath138 and @xmath139 ( vertical in figure [ mcr ] ) ; that would have to meet the @xmath44-fold point making it of type @xmath175 , or meet an edge in a @xmath125 point but oriented in the wrong direction . it follows that two corresponding points @xmath176 and @xmath177 ca nt both be singularities , for they are joined by a common foliation line that refracts at an edge @xmath145 ; we have seen that it ca nt be a fold line so it would be an initial sn - line from both singularities resulting in a bps state . we get 4 and part of 2 . for 1 , if @xmath140 ( resp . @xmath141 ) were nonsingular , or a @xmath125 point with edge @xmath138 ( resp . @xmath139 ) along the spine , then one could continue the regions @xmath142 further along the corresponding edge . for 2 , if both points are nonsingular then the regions are not maximal , so one must be singular , say on @xmath136 . however , if it were a @xmath119-fold point then both lines going into @xmath136 parallel to @xmath138 and @xmath139 would be fold lines ; these would have to meet @xmath138 and @xmath139 in @xmath124 or @xmath125 points , resulting in fold lines going back in the opposite direction in @xmath137 . these two would meet in the corresponding point of @xmath137 but that would have to be singular , contradicting the statement above . for 3 , notice that if some segments of one of these edges are folded , then the orientations of the fold segments are all the same ( it follows from the consideration of the first paragraph ) . but if we had an @xmath107-fold point on the interior of one of these edges , it would send out either a fold line or an sn - line , and that would contradict the existence of the @xmath107-fold singularity given in part 2 . we now consider how fold lines , sn lines and singularities can be arranged along a pair of edges @xmath178 . each edge @xmath167 has two endpoints , @xmath179 that is either @xmath180 or @xmath169 , and @xmath181 . [ onesn ] one of the two edges @xmath173 or @xmath182 is an sn line , and has no singularities in its interior ( so @xmath183 ) , or at the endpoint @xmath184 . it points towards the endpoint @xmath185 . one of the two @xmath179 is an @xmath107-fold point . at our admissible possibilities @xmath186 there are never two fold edges separated by three sectors . therefore , at this point either the outgoing edge along @xmath167 , or the edge that goes into @xmath142 in the opposite direction ( that is to say separated by three sectors interior to @xmath142 ) , are sn - lines . if @xmath167 is an sn - line then we obtain the desired conclusion . notably , there are no singular points along this edge otherwise that would create a bps state . in the other case , the sn line reflects at @xmath138 or @xmath139 and comes back in the other region @xmath187 , eventually joining the edge @xmath188 so that edge is an sn line . again in that case it has no singularities . the sn line points away from @xmath179 in both cases , so towards @xmath184 . on the edge @xmath167 not concerned by the above lemma , let @xmath189 denote the singularities in order along the interior of @xmath167 , starting from the nearest to @xmath179 ( recall that was @xmath180 or @xmath169 ) . the internal singularities are @xmath44 or @xmath119-fold points . all the segments @xmath190 are fold lines for @xmath191 . furthermore , for any @xmath192 the singularity @xmath193 is a @xmath125 point with the connecting segments of the edge @xmath194 being its spine . these are oriented in the direction away from @xmath179 . if any of these segments were sn lines that would create a bps state . note that if @xmath179 is not the singular one of the two points @xmath195 , then an sn line from @xmath184 to @xmath179 would continue to one of the edges @xmath145 and reflect and hit the corresponding point @xmath196 on the other piece , that is then a singularity by part 2 of proposition [ properties ] . if @xmath197 then both segments @xmath190 and @xmath198 are fold edges . the only type of singularity with two fold edges separated by three sectors is a @xmath125 point and these edges are the spine . for the orientation , note that all the segments from @xmath179 up to @xmath199 are fold edges , and @xmath200 is oriented outwards from @xmath179 . by the rule for orientations at @xmath125 it follows inductively that all the segments are oriented the same way . when we do our glue and trim operation , the combination of any edge with a folded edge has the same marking as the first edge . so , for the problem of deciding which edges are in the scaffolding , the only indeterminacy is whether the edge @xmath201 is a fold edge or an sn edge . this could mean the entire edge @xmath167 if @xmath183 . the following lemma says that the spectral network or fold lines created in the glued and trimmed construction will satisfy the refracting property . [ newrefract ] if the edge @xmath201 is an sn line , then it points in the direction towards the endpoint @xmath181 . as a corollary , if a spectral network line crosses into @xmath136 from anywhere across the edge @xmath202 , it is reflected from @xmath138 or @xmath139 and creates two sn lines going out from @xmath137 at the corresponding point in both outward directions . same with @xmath203 interchanged . the point @xmath204 is a singularity so all outgoing non - folded edges are initial for the spectral network . let us now proceed with the collapsing operation of glueing together @xmath136 and @xmath137 , and trimming off the resulting piece . after doing this we obtain the new construction @xmath205 . it is again ecarinate , complete , normal and simply connected . let @xmath206 denote the edges in @xmath205 obtained by identifying @xmath207 with @xmath208 . similarly let @xmath209 ( resp . @xmath210 ) denote the points resulting from the identification of @xmath211 and @xmath212 ( resp . @xmath211 and @xmath212 ) . the images of @xmath169 are again denoted @xmath169 . we identify @xmath213 with @xmath214 . a point @xmath209 is obtained by gluing together an @xmath107-fold point and a @xmath119-fold point , having removed @xmath44 sectors from each one . it follows that @xmath209 is a @xmath119-fold point . if say @xmath215 is a @xmath45 then @xmath216 is a @xmath121 point , indeed the edges @xmath173 and @xmath217 must be folded so by lemma [ onesn ] both edges @xmath182 and @xmath218 are sn lines . it follows in this case that @xmath210 is a @xmath121 point . if @xmath219 are both @xmath119-fold points then @xmath210 is an @xmath107-fold point . suppose that an edge say @xmath173 contains some singularities @xmath220 . as we have seen , @xmath221 are @xmath125 points with spine along @xmath222 . one can see that these become @xmath123 points in @xmath205 . the segments of @xmath173 that are folded , become unfolded segments in @xmath205 since the opposite edge @xmath182 is an sn line and a folded segment glued to an unfolded one yields an unfolded segment in the new construction . in order to determine the scaffolding of @xmath205 it remains to see what becomes of the last segment @xmath223 , in case @xmath173 contains some singularities , or of the whole of @xmath206 in case neither side contains singularities in the interior . this depends on the singularities at @xmath224 and on the last singular point @xmath225 if it is there , or else on @xmath180 . one must do an analysis of cases . the conclusion is that the labeling of the resulting segment of @xmath206 as folded or unfolded , is determined by these singularities . in some cases the answer is indeterminate at @xmath226 but determined by the other endpoint . the determinations of fold / unfold coming from the two ends of the segment must be the same , because we are supposing the existence of some harmonic map to a building compatible with the scaffolding . if a segment becomes folded , then it is oriented outwards from the @xmath107-fold point @xmath226 ( if it is a folded segment then we were not in the case where one @xmath224 is a @xmath44-fold point , treated above ) . we have seen in lemma [ newrefract ] that such a folded segment will satisfy the refracting condition for reflection of sn lines . we have determined the scaffolding of @xmath205 , satisfying the refracting condition , and with orientations of edges . notice that the two edges meeting in @xmath210 can not both have singular points in the interior , as that would have meant that there was an intersection of fold lines in the interior of @xmath136 or @xmath137 . what remains to be verified is that the new points @xmath209 , @xmath210 , and the images of the @xmath227 if they are there , fall into the standard list of possible singularities ; that the required spectral network lines emanating from these points exist ; and that the orientations of fold lines are compatible with the allowable orientations at these new singularities . discuss first the compatibilities of orientations of fold lines . an @xmath107-fold point @xmath228 becomes a @xmath119-fold point @xmath209 . any fold lines not on the edges @xmath229 will stay oriented in the outgoing direction . there may be one or two new fold lines on the edges @xmath229 , but these will now orient inwards towards @xmath209 . indeed , this only happens if @xmath206 ( resp . @xmath230 ) has no interior singularities and @xmath226 is an @xmath107-fold point . see table [ s8table ] below for compatibility . consider singularities interior to the edges . suppose say @xmath173 contains a sequence of singular points with last one @xmath225 . let @xmath231 denote its image in @xmath205 . the segment @xmath232 might or might not be folded . if it is folded , it is oriented outward from @xmath226 hence inward towards @xmath231 . we should check that this is compatible with the singularity type of @xmath231 . if @xmath225 is a @xmath44-fold point then so is @xmath231 and this compatibility holds . if our new segment is folded it means that the previous segment @xmath233 had to be unfolded . recall that @xmath234 is folded and oriented towards @xmath225 . the direction into @xmath136 that is parallel to @xmath138 or @xmath139 is folded , and this fold line hits one of the edges @xmath138 or @xmath139 at a @xmath125 point getting reflected back into @xmath137 and eventually forming a fold line that will participate in the local picture at the point @xmath231 . using these facts there are two possibilities . first , @xmath225 could be a @xmath124 point whose fold edge along @xmath173 , the segment @xmath234 , is oriented inwards . the new segment @xmath232 is not folded , and the resulting point @xmath231 is a nonsingular @xmath123 point with compatible orientations of fold edges ( see the middle two lines of table [ q6table ] ) . the other possibility is that @xmath225 be a @xmath125 point . in this case the new segment @xmath232 must be folded , and oriented inwards towards @xmath231 since @xmath226 is an @xmath107-fold point , whereas @xmath235 is unfolded . the resulting point @xmath231 is a @xmath125 point . the inward oriented edge of its spine comes from the inward oriented edge of the spine of @xmath225 reflected into @xmath137 . see the next - to - last line of table [ q6table ] below for the other fold edges and their orientations . this completes the discussion of compatibility of the orientations of new scaffolding edges . we need to verify that the new singular types are all contained in the list that we are using . this will be done by writing down tables of the possibilities . the cases of the points @xmath169 are similar and are left to the reader . let us assume that we have a singular point on @xmath136 . also , for singularities inside edges , we consider edges @xmath173 that are parallel to @xmath138 . the other cases are the same by symmetry . it will be convenient to establish a convention for speaking of directions in @xmath236 at a singularity @xmath237 . number them as follows : @xmath238 corresponds to the direction from our singularity , towards the interior of @xmath142 , not parallel to @xmath138 or @xmath139 ( `` up '' in the picture ) . then @xmath239 are the directions obtained by turning clockwise @xmath240 sectors . on the other side , @xmath241 are the directions obtained by turning counterclockwise that many sectors . these join up : at a @xmath119-fold point @xmath242 while at an @xmath107-fold point @xmath243 . the edge @xmath138 is oriented @xmath244 , and @xmath139 is oriented @xmath245 . in our tables below we will be listing the folded directions at singular points . in this case , a notation @xmath246 means the edge germ emanating from the singularity in the specified direction . with this notation , in the orientation of our scaffolding , the fold edge is said to be oriented outwards . the same edge oriented inwards towards the singularity will be denoted @xmath247 . we now consider a singularity of the form @xmath211 . it is an @xmath107-fold point , and the corresponding @xmath212 is a nonsingular @xmath119-fold point ( either @xmath121 or @xmath123 ) . these glue together to form a point @xmath248 . table [ s8table ] gives the structure of the scaffolding at @xmath209 as a function of the structure at @xmath211 . in order to fill in the table , recall that four sectors are removed from the neighborhood of @xmath211 , as well as from the neighborhood of @xmath212 ; then the remaining two sectors from @xmath212 are glued back in to give the neighborhood of @xmath249 . we make the convention that edge germs at @xmath209 are numbered starting with the middle edge of the two sectors from @xmath212 being @xmath238 ; the two indeterminate lines are @xmath250 , then remaining @xmath251 . these latter correspond to the directions @xmath252 respectively at @xmath211 . we include a column in the table to say what is happening at the point @xmath212 . note that it is a nonsingular @xmath119-fold point , hence either @xmath121 or @xmath123 . if it is @xmath123 then the direction of the fold line comes from the direction of the fold line at @xmath211 that goes in direction either @xmath244 or @xmath245 . this extra column will be most useful in our third table below . we do nt include configurations that are obtained by symmetry ( changing @xmath246 to @xmath253 ) from ones that were already included , and we do nt include configurations ( such as @xmath254 ) that are ruled out . .[s8table ] structure at @xmath209 [ cols="^,^,^,^,^",options="header " , ] in some rows of the table , the answer is not determined by the information local to @xmath219 . in those cases we have included the various possibilities . notice that the marking of edges @xmath255 will be determined from what happens in the two previous tables at the adjacent singularities on these segments . the scaffolding of @xmath205 is well - defined , with orientations of the fold edges . from the tables , the types of local pictures of the scaffolding for @xmath205 are in our standard list @xmath256 . the orientations of the fold edges at these singularities are compatible with the allowable configurations . [ snsubset ] define the refracting spectral network of @xmath205 to be generated by an initial sn line going in every non - fold direction from each of the singularities , and closed under collisions as well as refraction upon crossing fold lines of the new scaffolding . then , any sn - line of this new spectral network , outside of the edges @xmath206 , is contained in the previous spectral network of @xmath92 . sn lines along non - folded segments of the @xmath206 are with reversed orientation with respect to those of @xmath92 . under the assumption that there were no bps states in the refracting spectral network of @xmath92 , then there are no bps states in the refracting spectral network of @xmath205 . _ ( sketch)_we verify in each of the cases contained in the tables , that there are sn lines in @xmath257 corresponding to all non - folded outward directions from singular points . in the case of non - folded edges that are segments of the @xmath206 , there were sn lines in the non - folded segments of @xmath167 going in the opposite direction . switch the directions of these , and when these new sn lines meet a @xmath123 point , notice that it came from a singular point and the refracted directions are among the directions containing sn lines of @xmath92 ( or we continue along the next segment of @xmath206 to the next @xmath123 point ) . at an @xmath107-fold singularity obtained from the third table , the sn lines in all directions are generated by the sn lines along the segments of @xmath167 and @xmath258 , sometimes by using the collision process in @xmath92 . we should check that there are no bps states in the new spectral network . concerning lines not on the edges @xmath206 this comes from the inclusion into the previous spectral network in @xmath213 , and the existence of sn lines going outwards from any new singularities as noted above . we therefore need to consider new sn lines along segments of @xmath206 . for this , let us notice that in table [ s8table ] , whenever a singular @xmath124 or @xmath125 is created , the edges going along @xmath259 and @xmath230 , there denoted @xmath244 and @xmath245 , are folded . furthermore , whenever a @xmath123 is created , one of those two edges is folded so a bps state between the two adjacent @xmath260 is not created . similarly , in [ q6table ] when a @xmath125 or point is created , the segment after it on @xmath206 , denoted there @xmath261 , is folded . this has only been a sketch of proof , a more detailed discussion is needed in order to follow through all possible sn lines that might start with directions along the edges @xmath206 . we now review what has been done ( or sketched ) above . from @xmath1 we created an initial complete normal ecarinate construction @xmath42 and we are assuming that this is done following principles [ nobps ] and [ chooseinitial ] . thus @xmath42 is provided with a fully refracting scaffolding , whose associated spectral network has no bps states . initially the scaffolding has only @xmath262 singularities , so the endpoints of the post - caustics are @xmath131 points , and the @xmath107-fold and @xmath44-fold points alternate . the reduction process will consist of a sequence of reduction steps starting with @xmath42 . let us denote by @xmath92 the construction obtained after a certain number of steps . our goal is to describe the next reduction step . our construction @xmath92 is again complete , ecarinate , normal , and it is provided with a refracting scaffolding with oriented fold edges . our assumptions are as follows : that the refracting spectral network generated by the scaffolding has no bps states ; and that the types of points in the scaffolding are in the standard list of definition [ singdef ] , taking account orientations of edges . suppose that there are some remaining fold edges . by corollary [ existsfourtwo ] , there exists a @xmath45 point . the reduction step will be to collapse a neighborhood of this @xmath45 point in a good way . choose a maximal collapsing pair @xmath236 at this vertex . these regions are arranged with singularities and edges satisfying the properties of proposition [ properties ] and the subsequent discussion . we then glue together @xmath136 and @xmath137 , and trim away the resulting piece ( except for the union of edges @xmath206 ) , to get a new construction @xmath205 . this is the result of a single step of our reduction process . the main point is to verify that @xmath205 is provided with a well - defined refracting scaffolding that still satisfies the required properties . we have seen that the configurations at singularities in @xmath92 determine the fold edges at the new points in @xmath205 . indeed , this is the case at points of the form @xmath209 and @xmath231 , and the only indeterminacy at points @xmath210 is along segments that will be connected either to points @xmath231 or @xmath209 so the fold edges are determined . we have also assigned orientations to the fold edges . specific analysis of each case allows to fill in tables [ s8table ] , [ q6table ] , [ t6table ] . these show that the new singularities are only of the types in our standard list . furthermore , we see here that the types of singularities are compatible with the assigned orientations of the fold edges in the new scaffolding . we noted along the way that the fold edges of the new scaffolding have the required refracting effect on spectral network lines . the sketch of proof of proposition [ snsubset ] shows how the new spectral network is a subset of the previous one , apart from the spectral network lines that might have switched directions along the unfolded segments of the edges @xmath206 , and this spectral network does nt have any bps states . this completes the verification that our new construction @xmath205 has the required structures and satisfies the required properties so it can be used as the starting point in a next step of the reduction process . we have described a single step of the reduction process . the main question will now be to obtain a convergence statement saying that the process ends in finitely many steps with a construction @xmath263 whose scaffolding has an empty set of edges . suppose it does end . the only singularities of @xmath263 are @xmath122 points of negative curvature this reduced construction will be the _ core _ of the pre - building that we are conjecturing to exist in @xcite . in order to get the pre - building , the steps of putting back in the pieces that have been trimmed off , need to be done as described in @xcite . the core @xmath263 has a natural flat structure with geometry modeled on the standard appartment @xmath22 for @xmath0 . this geometric structure carries with it a natural cyclic @xmath265-fold spectral covering with ramification at the @xmath107-fold singular points . the @xmath107-fold singular points are negatively curved conical points for the flat metric , with angles of @xmath108 . the flat metric determines a conformal and hence complex structure ; this is a modification of the complex structure of the original riemann surface @xmath1 , and the cyclic covering corresponds to a cubic differential . this modification looks to be a discrete or possibly `` tropical '' analogue of labourie s result ( * ? ? ? * conjectures 1.6 , 1.7 ) @xcite , replacing a general spectral curve by a cubic differential . the first conjecture is that a minimization process provides a stability condition corresponding to the cubic differential , on the category of sections of the perverse schober with fiber @xmath266 corresponding to the cyclic spectral covering . if we can do that , then a procedure for defining the stability condition for a general @xmath0-spectral curve @xmath3 will be to define the categories @xmath267 of objects of phase @xmath268 , for any @xmath269 by considering the core @xmath270 and using the stability condition given by the conjectured minimization process of the previous paragraph . these @xmath26-structures should each satisfy the required axioms for taking part in a stability condition . therefore , taken together for all phases they should define a stability condition . we are just beginning to work on this program . t. aoki , t. kawai , y. takei . new turning points in the exact wkb analysis for higher - order ordinary differential equations . _ analyse algbrique des perturbations singulires , i ( luminy 1991 ) _ travaux en cours * 47 * , hermann , paris ( 1994 ) , 69 - 84 .

given an @xmath0 spectral curve over a simply connected riemann surface , we describe in detail the reduction steps necessary to construct the core of a pre - building with versal harmonic map whose differential is given by the spectral curve .

<s>[INST]let @xmath1 be a riemann surface with a spectral covering @xmath2 for the group @xmath0 . in @xcite we proposed in general terms a reduction process that would construct a versal @xmath3-harmonic map to an @xmath0 pre - building . it was conjectured that if the @xmath3-spectral network @xcite has no bps states then the reduction process should be well - defined . this conjecture would lead to a precise calculation of the wkb exponents for singular perturbations whose spectral curve has no bps states , generalizing the known picture @xcite for quadratic differentials and @xmath4 . the purpose of the present paper is to provide more details on the reduction process , particularly about the combinatorial structure of the singularities that occur and how they are arranged at each reduction step . we will show ( although the proofs are sometimes only sketches ) that the reduction steps are well - defined if there are no bps states . it is left for later to show that the process finishes in finitely many steps . assume @xmath1 is complete and simply connected . for the present one should think of it as being the complex plane with @xmath3 a spectral covering similar to the one considered in our original example @xcite . the case of the universal covering of a compact riemann surface would pose additional problems of non - finiteness of the set of singularities , and the right notion of convergence seems less clear . the process and results will be summed up in [ scholium ] and the reader is referred there . in the remainder of the introduction , we review the motivation for the reduction process considered here . a building @xmath5 for the group @xmath0 is a piecewise linear cell complex that is covered by copies of the standard appartment @xmath6 , and indeed any two points of @xmath5 are contained in a common appartment . one of the main properties characterizing a building is that it is negatively curved . a _ harmonic map _ @xmath7 is a continuous map such that any point @xmath8 , except for a discrete set of singularities , admits a neighborhood @xmath9 such that there is an appartment @xmath10 with @xmath11 being a harmonic map . the differential @xmath12 is naturally a triple of real @xmath13-forms @xmath14 with @xmath15 . these are well - defined up to permutation . now , these real harmonic forms are real parts of holomorphic @xmath13-forms @xmath16 and the collection @xmath17 defines the spectral curve @xmath2 . we say that @xmath18 is a @xmath3-harmonic map . for a given spectral curve we would like to understand the @xmath3-harmonic maps to buildings . we conjectured in @xcite that , under a certain genericity hypothesis , there should be an essentially uniquely defined map @xmath19 depending only on the spectral curve @xmath20 with the following properties : ( 1 ) the pre - building @xmath21 is a negatively curved complex built out of enclosures in @xmath22 @xcite , and ( 2 ) any @xmath3-harmonic map to a building @xmath7 factors through an embedding @xmath23 isometric for the finsler and vector distances . the conjectured genericity hypothesis for existence of @xmath24 is that the spectral network associated to @xmath3 should not have any bps states @xcite . before getting to the proposed method for constructing @xmath21 , let us consider the implications for exponents of wkb problems . there are several different ways of getting harmonic mappings to buildings , such as gromov - schoen s theory @xcite . parreau interpreted boundary points of the character variety as actions on buildings @xcite . in @xcite we extended parreau s theory slightly for the situation of wkb problems , getting a control on the differential . suppose @xmath25 is a singular perturbation of flat connections , for @xmath26 a large parameter . there are two typical ways of getting @xmath27 , the riemann - hilbert situation @xmath28 or by solution of hitchin s equations for the higgs bundle @xmath29 . in either case , there is an associated limiting higgs bundle @xmath30 and we let @xmath3 be its spectral curve . for @xmath31 let @xmath32 denote the transport for @xmath25 . for an ultrafilter @xmath33 on @xmath34 define the _ exponent _ @xmath35 there is a similar _ vector exponent _ @xcite that is a point in the positive weyl chamber of @xmath22 . the groupoid version of parreau s theory @xcite gives a map to a building @xmath36 such that the finsler distance ( resp . vector distance ) between @xmath37 is the exponent @xmath38 ( resp . the vector exponent ) . we showed in @xcite for the riemann - hilbert situation that @xmath39 is a @xmath3-harmonic map . mochizuki @xcite showed this for the hitchin wkb problem . if there exists a @xmath3-harmonic map @xmath24 satisfying the properties ( 1 ) , ( 2 ) above , then it follows that @xmath40 is calculated as the finsler distance between @xmath41 . in particular , it depends only on the spectral curve @xmath3 . indepenence of the choice of ultrafilter means that the ultrafilter limit used to define the exponent is actually a limit , and we obtain a calculation of the wkb exponents for our singular perturbation . turn now to the reduction process for constructing @xmath21 . a conjectural yet detailed picture of this construction was set out in @xcite and readers are referred there for a full explanation . the first step was to make an initial construction . that is essentially what we shall be calling @xmath42 below , although the initial construction for the pre - building has to include additional small parallelogram - shaped regions corresponding to the folded pieces @xmath43 that we ll meet in [ sec - initial ] below . our @xmath42 has these trimmed off . the main problem of the initial construction is that it contains points of positive curvature , referred to as @xmath44-fold points or @xmath45 points below . these have to collapse in some way under any harmonic map to a building @xmath5 since @xmath5 is negatively curved . the construction of the pre - building consists of successively doing such a collapsing operation . unfortunately , the direction of collapsing at a @xmath44-fold point is not well - defined , rather there are two possibilities . for that reason , the notion of _ scaffolding _ was introduced in @xcite . the initial scaffolding formalizes the existence of small neighborhoods @xmath46 that map , in an unfolded way , into appartments of the building . it follows that @xmath46 should not be folded in the map @xmath24 to @xmath21 . the edges gotten by gluing together sectors are , on the other hand , to be folded further , and this collection of data is complete : every edge is either marked as folded or unfolded ( open ) in the scaffolding . the scaffolding tells us which direction to fold at a @xmath45 point . the remaining difficulty is to propagate the information of the scaffolding into the new constructions obtained by collapsing . it was conjectured in @xcite that this should be possible , under the hypothesis of absence of bps states in the original spectral network . the purpose of the present paper is to prove this conjecture on propagation of the scaffolding . we show how to make a series of reduction steps and how to propagate the scaffolding and other required information so that the series of reduction steps is well - defined . the present work does not yet result in a full construction of @xmath21 . notably missing is a convergence statement saying that the process stops in a ( locally ) finite number of steps . some parts of our arguments are also sketches rather than full proofs , and we do nt provide here a justification for the choice of initial construction ( principle [ chooseinitial ] ) . it was observed in @xcite that each step of the reduction process towards the pre - building , could be accompanied by a trimming of the just glued - together parallelograms . if one does that , then the sequence of constructions is a sequence of @xmath47-dimensional surfaces . this point of view will be useful for the program of generalizing bridgeland - smith s work on stability conditions , discussed briefly in [ sec - further ] at the end . also , the combinatorics of the reduction steps are all contained in this sequence of surfaces . therefore , in the present paper we shall include the trimming operation as part of our reduction steps . in order to construct the pre - building @xmath21 one should put back in the pieces that were trimmed off the procedure for doing that was explained in @xcite . start by considering spectral networks in @xmath1 . away from the branch points , the spectral curve @xmath3 consists of three holomorphic @xmath13-forms @xmath48 and setting @xmath49 these define _ foliation lines _ @xmath50 where @xmath51 . assume the ramification of @xmath3 consists of simple branch points . at a branch point , two indices are interchanged , picking out one of the foliations @xmath51 whose singular leaves starting from the branch point are the initial edges of the spectral network . away from the _ caustics _ where the three foliation lines are tangent , the coordinates @xmath52 define a flat structure on @xmath1 by local identification with the standard apartment @xmath53 for buildings of the group @xmath0 . we use this flat structure when speaking of angles . we are going to add some extra singularities , so suppose given a finite subset @xmath54 and for each @xmath55 one of the three foliations @xmath56 . spectral network graph _ is a map from a trivalent graph @xmath57 , that can have endpoints as well as at most one infinite end , to @xmath1 that sends endpoints of @xmath57 to elements of @xmath58 , that sends edges to foliation lines , and that sends trivalent vertices to _ collisions _ @xcite , points where foliation lines @xmath59 meet at @xmath60 angles . we require that an endpoint of the graph going to @xmath55 has adjoining edge going to a foliation line for the given foliation @xmath56 . a foliation line in @xmath1 is an _ sn - line _ if there exists a spectral network graph such that the given foliation line is in the image of an edge of the graph that is either adjacent to an endpoint , or is an infinite end . a _ bps state _ @xcite is a compact spectral network graph . our main hypothesis will be that these do nt exist . we now note how to add singularities while conserving this hypothesis . the original set @xmath61 of singular points is equal to the set of ramification points of the spectral curve , assumed to be simple ramifications . the foliation line @xmath56 at a ramification point is the one determined by the two sheets of the spectral curve that come together at that point . the following proposition will allow us successively to add points to the set of singularities . [ addsn ] suppose given a set of singularities @xmath62 such that the resulting spectral network does nt have bps states . choose a point @xmath63 in general position along the interior of a caustic curve , let @xmath64 be one of the foliation lines at @xmath63 and let @xmath65 . then the spectral network associated to @xmath66 also does nt have any bps states . suppose we are given a spectral network graph @xmath67 that is a bps state for @xmath68 . consider a nearby point @xmath69 obtained by moving it a small distance @xmath70 in one direction along the caustic curve ( the caustic is generically transverse to the foliation lines otherwise it would constitute a bps state itself ) . we may assume that the bps state follows to a nearby one @xmath71 . the foliation lines are defined by differential forms @xmath72 so this gives us a way of measuring transverse distances ; in these terms it makes sense to talk about the distance between one of the foliation lines and an adjacent one for the same foliation . we should choose for each edge of the graph a sign for the form in question . now , label edges of the graph @xmath73 by integers @xmath74 such that the edge @xmath75 moves by @xmath76 . an edge @xmath77 adjoining an endpoint of the graph that goes to a previous singularity @xmath78 has to be labeled with @xmath79 , since @xmath80 does nt move with @xmath70 . there is a balancing condition on the labels at the collision points . the edges that end in @xmath81 from one direction have to be labeled by @xmath82 whereas the edges that end in @xmath81 from the other direction have to be labeled by @xmath83 . however , the balancing condition at the trivalent vertices plus the condition that all the other endpoint labels are zero , means that the number of @xmath82 labels and the number of @xmath83 labels at @xmath81 have to be equal . therefore , we can pair up edges coming in from one direction with edges going out in the other , glueing these edges together pairwise . this results in a new graph @xmath84 that is a bps state for the previous set of singularities @xmath62 . * boundedness*let us mention a boundedness hypothesis that will be useful . suppose that there exists a compact subset @xmath85 whose boundary @xmath86 consists of foliation lines , such that the corners of @xmath86 are convex in the sense that each corner consists of foliation lines separated by two sectors inside @xmath87 . and , we suppose that all ramification points of the spectral curve , and all caustics , are contained in the interior of @xmath87 . since the additional singularities were chosen on caustics , it follows that @xmath88 . with this hypothesis , a spectral network graph has no collisions outside of @xmath87 , and any edge that leaves @xmath87 continues as an infinite end . indeed , all caustics are contained in the interior of @xmath87 , so @xmath89 has a flat structure modeled on the standard appartment @xmath22 . suppose @xmath90 were a collision point , say the first one outside of @xmath87 . then the two incoming edges must exit from @xmath87 , but two distinct foliation lines that exit from @xmath87 and meet , must exit from the same edge because of the convexity hypothesis on the corners . if they exit from the same edge and meet , then they must meet at a @xmath91 angle , contradicting the hypothesis that they form incoming edges of a collision . thus , such a collision can not occur . referring to the reduction steps that will be discussed later , any regions that are to be folded together have to stay inside @xmath87 by the same kind of considerations . therefore , we may follow our compact subset along into the sequence of constructions @xmath92 that will occur ; the compact subset will contain all modifications , and @xmath89 remains untouched as a flat space contained in each of our series of constructions . although we do nt discuss the question of convergence in the present paper , the existence of a series of compact subsets that contain all the modifications means that one could envision an argument using decrease of the area to conclude termination of the reduction process . that would require bounding from below the size of the reduction steps the _ initial construction _ is a construction @xmath42 obtained by a first process of folding together certain regions in @xmath1 and trimming away the resulting pieces . we consider a collection of regions @xmath93 covering the caustics , such that @xmath94 are bounded by foliation lines meeting in two points @xmath95 symmetrical with respect to the caustic . in any @xmath96-harmonic map to a building @xmath7 , @xmath97 and @xmath98 have to map to the same point , and indeed @xmath99 has to factor through a map @xmath100 where @xmath43 is @xmath94 folded in two along the caustic @xcite . here is a picture of the regions @xmath94 in @xmath1 and here is what their images look like in any harmonic map to a building : we assume that the boundaries of the regions @xmath94 are formed by new spectral network lines gotten after adding singularities along the caustics according to proposition [ addsn ] . that will be used for the refracting property in [ sec - refracting ] . let @xmath101 denote the quotient of @xmath1 by the equivalence relation induced by the quotients @xmath102 . now let @xmath103 be the result of trimming off the folded - together pieces , in other words it is the closure in @xmath101 of @xmath104 , or equivalently the image of @xmath105 . the space @xmath106 is a topological surface , and we have cut out the caustics . thus , @xmath103 is provided with a geometric structure locally modeled on the standard appartment @xmath22 ; the three foliation lines at any point correspond to the three standard directions in @xmath22 . in particular @xmath103 has a flat metric . the conformal structure for this flat metric is different from the original structure of riemann surface on @xmath1 . it has singular points of positive and negative curvature , namely @xmath107-fold points of negative curvature whose total angle is @xmath108 and @xmath44-fold points of positive curvature whose total angle is @xmath109 . view @xmath103 as corresponding to a construction , i.e. a presheaf on the site of enclosures as discussed in @xcite . more precisely we have a construction @xmath42 whose usual set of points is @xmath110 . it is provided with a map @xmath111 that sends foliation lines in @xmath1 to segments in @xmath42 . this construction will be the starting point of our reduction process . it is provided with a _ scaffolding _ @xcite : certain edges ( the image of @xmath112 ) are designated as `` fold edges '' while all the other edge germs are designated as `` open '' or `` unfolded '' . if @xmath7 is any @xmath96-harmonic map to a building , then its restriction to @xmath113 factors through a map @xmath114 that respects the scaffolding , in the sense that fold edges are folded and open edges are unfolded . let @xmath92 be a construction . we say that @xmath92 is _ complete _ if the associated metric space is complete . it is _ normal _ if the link at any point is connected . we say that @xmath92 is _ ecarinate _ if , at any edge there are two half - planes . notice that @xmath42 satisfies these conditions , and our reduction process will conserve them , so let us consider only complete normal ecarinate and simply connected constructions @xmath92 . in particular the set of usual points @xmath115 is a complete @xmath47-manifold . if @xmath116 is a point then the link @xmath117 is a connected graph such that each vertex ( corresponding to a germ of edge at @xmath118 ) is contained in two edges ( corresponding to germs of sectors at @xmath118 ) . therefore , the link is a polygon . by the parity property the polygon has an even number of edges . we assume that the number of edges in the link at any point is @xmath44 , @xmath119 or @xmath107 . most points are _ flat _ , meaning that their links are hexagons . the other points are called @xmath44-fold , or @xmath107-fold respectively . the @xmath44-fold points are points of positive curvature , and the @xmath107-fold points are points of negative curvature . a _ scaffolding _ consists of the following structures : ( 1 ) a marking of each edge in @xmath92 as either _ open _ ( o ) or _ folded _ ( f ) , such that the fold edges are those from a discrete collection @xmath120 of straight edges in @xmath92 . ( 2 ) an orientation assigned to each fold edge . ( 3 ) a marking of some subset of the fold edges said to be _ refracting_. our initial construction @xmath42 contains a scaffolding in which all the edges are already marked as refracting , see [ sec - refracting ] below , and our reduction process will preserve the refracting condition so we henceforth consider only fully refracting scaffoldings . we assume that @xmath42 and its scaffolding have the property that there exists a harmonic mapping to a building such that the fold edges are folded and the open edges are unfolded . this constrains the local type of singularities . however , the number of possibilities is still rather large . we describe here a list standard examples that will be sufficient for our reduction process the statement that we remain within this standard list is indeed one of the main conclusions of our treatment in the present paper . the notation will consist of a boldface number saying how many sectors there are , and a subscript saying how many folded lines in the scaffolding there are . arrows in the pictures indicate the orientations of the scaffolding edges . for example , points of type @xmath121 and @xmath122 are respectively @xmath119-fold and @xmath107-fold points with no adjoining fold edges . a point of type @xmath123 is a @xmath119-fold point with a single straight fold edge ( it is nonsingular ) ; a @xmath124 point has three folded edges separated by @xmath60 , and a @xmath125 point is the same with an additional folded edge . these may be pictured as follows : @xmath126 next we picture the @xmath107-fold and @xmath44-fold points . note that the pictures can not be conformally correct for the angles ; all drawn sectors represent sectors of @xmath91 in @xmath92 . the @xmath107-fold points have at most @xmath47 fold edges ; and if there are @xmath47 of them , they are separated by either @xmath13 or @xmath44 sectors . the fold edge orientations go outward , so after the @xmath122 picture there are three possibilities : @xmath127 recall @xcite that at a @xmath44-fold point , at least two of the four edges are folded , and if an edge is folded then so is the opposite one . our standard type is when only two edges are folded , and the edge orientations are inwards towards the singularity , so it has the following picture : @xmath128 [ singdef ] we say that the singularities of the scaffolding are _ initial _ if at any point of @xmath92 the picture is either @xmath121 ( a smooth point not on the scaffolding ) , @xmath123 ( an interior point of an edge of the scaffolding ) , an @xmath107-fold point of the form @xmath129 , or a @xmath44-fold point @xmath45 . we say that the singularities of the scaffolding are _ standard _ if at any point the local picture is one of the ones we have described , namely : @xmath130 shown above . included in the above definitions are compatibility of the orientations of the fold lines with the singularity types as drawn in the pictures . recall that edges are oriented outward at @xmath107-fold points and inward at @xmath44-fold points . for initial scaffoldings we obtain the following characterization : [ postcaustic ] given a scaffolding with initial singularities , the collection of fold lines decomposes into a disjoint union of piecewise linear curves called the _ post - caustics _ , whose endpoints are of type @xmath131 , and along which the @xmath44-fold points alternate with @xmath107-fold points . in particular , the number of @xmath107-fold points on a connected post - caustic is @xmath13 more than the number of @xmath44-fold points . using proposition [ addsn ] to add spectral network lines along the boundaries of the regions @xmath94 used to define the initial construction , will give that the scaffolding of the initial construction @xmath42 is a fully refracting scaffolding . the `` refracting properties '' with respect to the spectral network are : ( r1 ) at singular points of the scaffolding , all unfolded edges are initial edges of the spectral network ; and ( r2 ) when a spectral network line crosses over a fold edge , it can continue on the other side in either one of the two available directions . suppose we are given a construction @xmath92 and a fully refracting scaffolding . spectral network graph for the refracting spectral network _ is a map from a graph @xmath132 satisfying the following properties : edges of @xmath57 go to segments in @xmath92 that are straight except when they cross the fold edges ; edges do not go along fold edges of the scaffolding ; when edges cross over the fold edges they can `` refract '' , that is to say they go out of the fold edge on the other side in either one of the two directions ; trivalent vertices of the graph go to collisions at @xmath121 points i.e. points not on fold edges of the scaffolding ; and endpoints of the graph go to singular points of the scaffolding or @xmath122 points of @xmath92 , with the adjoining edges going outward in any non - fold directions . before choosing the regions @xmath93 that will be folded and trimmed to get @xmath103 , add points to the set of singularities of our spectral network , using proposition [ addsn ] . add these points along the caustic curves at the places where the boundaries of the @xmath94 meet the caustics , so that the boundary curves of the @xmath94 become spectral network curves . notice furthermore that at the corners @xmath95 , all three directions outward to the rest of @xmath1 are spectral network lines , two from continuing the boundary curves and the third by collision of the two boundary curves . our above somewhat heuristic discussion leads to the following principle . [ nobps ] if the original spectral network of @xmath1 had no bps states , then the refracting spectral network of @xmath42 has no bps states . we also need to know something about the arrangement of singularities of the scaffolding for @xmath42 . we state this as another principle : [ chooseinitial ] the initial construction @xmath42 may be chosen to have only initial singularities ( definition [ singdef ] ) . the fold edges of the scaffolding are thus arranged into post - caustics as described in remark [ postcaustic ] . we do nt give here a formal justification for the possibility of choosing the initial construction in this way , but note that it is what happens in the pictures we have considered . for example , see @xcite for a picture leading to an @xmath133 point . this section begins the discussion of a step in the reduction process . the first question is to show the existence of a @xmath45 point about which some collapsing can be done . [ prop - noloops ] suppose given a construction with a refracting scaffolding , such that there are no bps states in the resulting spectral network . suppose that the fold edges of the scaffolding are oriented and the singularities are all from our standard list . make a directed graph using the singularities as vertices , except that we separate a @xmath125 singularity into two vertices . the edges of the graph are the fold edges with their orientations ; at a @xmath125 point the `` spine '' ( consisting of the two fold edges that are opposite ) goes to one of the vertices and the other two edges go to the other one . this directed graph has no directed loops . _ ( sketch)_consider a path parallel to a directed loop , just to one side of it . this will satisfy the collision and refracting conditions , so taken together with the appropriate initial sn lines coming from singularities , it constitutes a bps state . [ existsfourtwo ] if there are no bps states and if the set of fold lines in the scaffolding is nonempty , then there must be a @xmath45 point . in the directed graph described in proposition [ prop - noloops ] , our hypothesis that there are no bps states implies that there are no directed loops . therefore , the orientations of edges make the graph into a poset ; since it is finite it has a minimal vertex . the only type of point on the scaffolding that has all fold edges pointed inward is a @xmath45 point , therefore there exists a @xmath45 point . @xmath134 we now consider an extended collapsing operation at a @xmath45 point @xmath135 . for this , consider two pieces @xmath136 and @xmath137 that match up , and share a common vertex @xmath135 and common edges @xmath138 and @xmath139 . let @xmath140 ( resp . @xmath141 ) denote the endpoint of @xmath138 ( resp . @xmath139 ) different from @xmath135 . the @xmath142 are assumed to be constructions that can be considered as isomorphic to a subset @xmath143 in an abstract parallelogram @xmath144 . let us also label the corresponding vertex @xmath135 and the corresponding edges @xmath145 in @xmath144 . the embeddings @xmath146 preserve @xmath147 . we can now describe the configuration of @xmath143 : the vertex @xmath135 is an obtuse vertex of @xmath144 , and @xmath145 are the full edges of @xmath144 meeting @xmath135 . hence the points also labelled @xmath148 are the two acute vertices . we assume that @xmath143 is a union of finitely many sub - parallelograms @xmath149 ( see the picture below for the numbering ) such that @xmath150 contains @xmath135 as obtuse vertex , that is to say the edges of @xmath150 will be segments in @xmath145 starting at @xmath135 . let @xmath151 denote the vertices of @xmath150 opposite to @xmath135 . we assume that the order @xmath152 is such that @xmath153 is on the same edge of @xmath144 as @xmath140 , and they go in a consecutive sequence until @xmath154 is on the same edge of @xmath144 as @xmath141 . the @xmath155 are the other convex corners of @xmath143 after @xmath156 . let @xmath157 denote the concave corners of @xmath143 in between them , so that @xmath158 lies between @xmath151 and @xmath159 . let @xmath160 be the edge from @xmath140 to @xmath153 and let @xmath161 be the edge from @xmath154 to @xmath141 . let @xmath162 be the edge from @xmath151 to @xmath158 and @xmath163 be the edge from @xmath158 to @xmath159 . thus , @xmath162 and @xmath138 are parallel , and @xmath164 and @xmath139 are parallel . now consider the same points in the regions @xmath142 , indicated as @xmath165 and @xmath166 , with edges @xmath167 . the configuration of this maximal collapsing pair of regions may be pictured as in figure [ mcr ] . we assume that @xmath143 is a maximal such region with corresponding regions @xmath168 , such that the following conditions are satisfied : there are no singularities in the interior of @xmath142 ; the only singularities on the interior of the edges @xmath145 are @xmath125 points where @xmath138 or @xmath139 is the straight fold edge ( spine ) . [ properties ] under the above maximality conditions , we have the following properties : 1 . the vertices @xmath169 are singularities , and furthermore these singularities are not @xmath125 points with edge @xmath138 or @xmath139 on the spine ; 2 . for each @xmath170 there is exactly one of the @xmath171 that is an @xmath107-fold singularity , and the other is nonsingular ; 3 . there are no @xmath107-fold singularities in the interiors of the edges @xmath167 ; 4 . if @xmath172 is a @xmath44-fold or singular @xmath119-fold point on an edge @xmath173 of @xmath136 then the corresponding point @xmath174 on @xmath137 is not a singularity , and vice - versa , and this also applies for corners @xmath166 . notice in general that there ca nt be a fold edge going from a point on one of the edges @xmath167 into @xmath142 in the middle direction between the directions of @xmath138 and @xmath139 ( vertical in figure [ mcr ] ) ; that would have to meet the @xmath44-fold point making it of type @xmath175 , or meet an edge in a @xmath125 point but oriented in the wrong direction . it follows that two corresponding points @xmath176 and @xmath177 ca nt both be singularities , for they are joined by a common foliation line that refracts at an edge @xmath145 ; we have seen that it ca nt be a fold line so it would be an initial sn - line from both singularities resulting in a bps state . we get 4 and part of 2 . for 1 , if @xmath140 ( resp . @xmath141 ) were nonsingular , or a @xmath125 point with edge @xmath138 ( resp . @xmath139 ) along the spine , then one could continue the regions @xmath142 further along the corresponding edge . for 2 , if both points are nonsingular then the regions are not maximal , so one must be singular , say on @xmath136 . however , if it were a @xmath119-fold point then both lines going into @xmath136 parallel to @xmath138 and @xmath139 would be fold lines ; these would have to meet @xmath138 and @xmath139 in @xmath124 or @xmath125 points , resulting in fold lines going back in the opposite direction in @xmath137 . these two would meet in the corresponding point of @xmath137 but that would have to be singular , contradicting the statement above . for 3 , notice that if some segments of one of these edges are folded , then the orientations of the fold segments are all the same ( it follows from the consideration of the first paragraph ) . but if we had an @xmath107-fold point on the interior of one of these edges , it would send out either a fold line or an sn - line , and that would contradict the existence of the @xmath107-fold singularity given in part 2 . we now consider how fold lines , sn lines and singularities can be arranged along a pair of edges @xmath178 . each edge @xmath167 has two endpoints , @xmath179 that is either @xmath180 or @xmath169 , and @xmath181 . [ onesn ] one of the two edges @xmath173 or @xmath182 is an sn line , and has no singularities in its interior ( so @xmath183 ) , or at the endpoint @xmath184 . it points towards the endpoint @xmath185 . one of the two @xmath179 is an @xmath107-fold point . at our admissible possibilities @xmath186 there are never two fold edges separated by three sectors . therefore , at this point either the outgoing edge along @xmath167 , or the edge that goes into @xmath142 in the opposite direction ( that is to say separated by three sectors interior to @xmath142 ) , are sn - lines . if @xmath167 is an sn - line then we obtain the desired conclusion . notably , there are no singular points along this edge otherwise that would create a bps state . in the other case , the sn line reflects at @xmath138 or @xmath139 and comes back in the other region @xmath187 , eventually joining the edge @xmath188 so that edge is an sn line . again in that case it has no singularities . the sn line points away from @xmath179 in both cases , so towards @xmath184 . on the edge @xmath167 not concerned by the above lemma , let @xmath189 denote the singularities in order along the interior of @xmath167 , starting from the nearest to @xmath179 ( recall that was @xmath180 or @xmath169 ) . the internal singularities are @xmath44 or @xmath119-fold points . all the segments @xmath190 are fold lines for @xmath191 . furthermore , for any @xmath192 the singularity @xmath193 is a @xmath125 point with the connecting segments of the edge @xmath194 being its spine . these are oriented in the direction away from @xmath179 . if any of these segments were sn lines that would create a bps state . note that if @xmath179 is not the singular one of the two points @xmath195 , then an sn line from @xmath184 to @xmath179 would continue to one of the edges @xmath145 and reflect and hit the corresponding point @xmath196 on the other piece , that is then a singularity by part 2 of proposition [ properties ] . if @xmath197 then both segments @xmath190 and @xmath198 are fold edges . the only type of singularity with two fold edges separated by three sectors is a @xmath125 point and these edges are the spine . for the orientation , note that all the segments from @xmath179 up to @xmath199 are fold edges , and @xmath200 is oriented outwards from @xmath179 . by the rule for orientations at @xmath125 it follows inductively that all the segments are oriented the same way . when we do our glue and trim operation , the combination of any edge with a folded edge has the same marking as the first edge . so , for the problem of deciding which edges are in the scaffolding , the only indeterminacy is whether the edge @xmath201 is a fold edge or an sn edge . this could mean the entire edge @xmath167 if @xmath183 . the following lemma says that the spectral network or fold lines created in the glued and trimmed construction will satisfy the refracting property . [ newrefract ] if the edge @xmath201 is an sn line , then it points in the direction towards the endpoint @xmath181 . as a corollary , if a spectral network line crosses into @xmath136 from anywhere across the edge @xmath202 , it is reflected from @xmath138 or @xmath139 and creates two sn lines going out from @xmath137 at the corresponding point in both outward directions . same with @xmath203 interchanged . the point @xmath204 is a singularity so all outgoing non - folded edges are initial for the spectral network . let us now proceed with the collapsing operation of glueing together @xmath136 and @xmath137 , and trimming off the resulting piece . after doing this we obtain the new construction @xmath205 . it is again ecarinate , complete , normal and simply connected . let @xmath206 denote the edges in @xmath205 obtained by identifying @xmath207 with @xmath208 . similarly let @xmath209 ( resp . @xmath210 ) denote the points resulting from the identification of @xmath211 and @xmath212 ( resp . @xmath211 and @xmath212 ) . the images of @xmath169 are again denoted @xmath169 . we identify @xmath213 with @xmath214 . a point @xmath209 is obtained by gluing together an @xmath107-fold point and a @xmath119-fold point , having removed @xmath44 sectors from each one . it follows that @xmath209 is a @xmath119-fold point . if say @xmath215 is a @xmath45 then @xmath216 is a @xmath121 point , indeed the edges @xmath173 and @xmath217 must be folded so by lemma [ onesn ] both edges @xmath182 and @xmath218 are sn lines . it follows in this case that @xmath210 is a @xmath121 point . if @xmath219 are both @xmath119-fold points then @xmath210 is an @xmath107-fold point . suppose that an edge say @xmath173 contains some singularities @xmath220 . as we have seen , @xmath221 are @xmath125 points with spine along @xmath222 . one can see that these become @xmath123 points in @xmath205 . the segments of @xmath173 that are folded , become unfolded segments in @xmath205 since the opposite edge @xmath182 is an sn line and a folded segment glued to an unfolded one yields an unfolded segment in the new construction . in order to determine the scaffolding of @xmath205 it remains to see what becomes of the last segment @xmath223 , in case @xmath173 contains some singularities , or of the whole of @xmath206 in case neither side contains singularities in the interior . this depends on the singularities at @xmath224 and on the last singular point @xmath225 if it is there , or else on @xmath180 . one must do an analysis of cases . the conclusion is that the labeling of the resulting segment of @xmath206 as folded or unfolded , is determined by these singularities . in some cases the answer is indeterminate at @xmath226 but determined by the other endpoint . the determinations of fold / unfold coming from the two ends of the segment must be the same , because we are supposing the existence of some harmonic map to a building compatible with the scaffolding . if a segment becomes folded , then it is oriented outwards from the @xmath107-fold point @xmath226 ( if it is a folded segment then we were not in the case where one @xmath224 is a @xmath44-fold point , treated above ) . we have seen in lemma [ newrefract ] that such a folded segment will satisfy the refracting condition for reflection of sn lines . we have determined the scaffolding of @xmath205 , satisfying the refracting condition , and with orientations of edges . notice that the two edges meeting in @xmath210 can not both have singular points in the interior , as that would have meant that there was an intersection of fold lines in the interior of @xmath136 or @xmath137 . what remains to be verified is that the new points @xmath209 , @xmath210 , and the images of the @xmath227 if they are there , fall into the standard list of possible singularities ; that the required spectral network lines emanating from these points exist ; and that the orientations of fold lines are compatible with the allowable orientations at these new singularities . discuss first the compatibilities of orientations of fold lines . an @xmath107-fold point @xmath228 becomes a @xmath119-fold point @xmath209 . any fold lines not on the edges @xmath229 will stay oriented in the outgoing direction . there may be one or two new fold lines on the edges @xmath229 , but these will now orient inwards towards @xmath209 . indeed , this only happens if @xmath206 ( resp . @xmath230 ) has no interior singularities and @xmath226 is an @xmath107-fold point . see table [ s8table ] below for compatibility . consider singularities interior to the edges . suppose say @xmath173 contains a sequence of singular points with last one @xmath225 . let @xmath231 denote its image in @xmath205 . the segment @xmath232 might or might not be folded . if it is folded , it is oriented outward from @xmath226 hence inward towards @xmath231 . we should check that this is compatible with the singularity type of @xmath231 . if @xmath225 is a @xmath44-fold point then so is @xmath231 and this compatibility holds . if our new segment is folded it means that the previous segment @xmath233 had to be unfolded . recall that @xmath234 is folded and oriented towards @xmath225 . the direction into @xmath136 that is parallel to @xmath138 or @xmath139 is folded , and this fold line hits one of the edges @xmath138 or @xmath139 at a @xmath125 point getting reflected back into @xmath137 and eventually forming a fold line that will participate in the local picture at the point @xmath231 . using these facts there are two possibilities . first , @xmath225 could be a @xmath124 point whose fold edge along @xmath173 , the segment @xmath234 , is oriented inwards . the new segment @xmath232 is not folded , and the resulting point @xmath231 is a nonsingular @xmath123 point with compatible orientations of fold edges ( see the middle two lines of table [ q6table ] ) . the other possibility is that @xmath225 be a @xmath125 point . in this case the new segment @xmath232 must be folded , and oriented inwards towards @xmath231 since @xmath226 is an @xmath107-fold point , whereas @xmath235 is unfolded . the resulting point @xmath231 is a @xmath125 point . the inward oriented edge of its spine comes from the inward oriented edge of the spine of @xmath225 reflected into @xmath137 . see the next - to - last line of table [ q6table ] below for the other fold edges and their orientations . this completes the discussion of compatibility of the orientations of new scaffolding edges . we need to verify that the new singular types are all contained in the list that we are using . this will be done by writing down tables of the possibilities . the cases of the points @xmath169 are similar and are left to the reader . let us assume that we have a singular point on @xmath136 . also , for singularities inside edges , we consider edges @xmath173 that are parallel to @xmath138 . the other cases are the same by symmetry . it will be convenient to establish a convention for speaking of directions in @xmath236 at a singularity @xmath237 . number them as follows : @xmath238 corresponds to the direction from our singularity , towards the interior of @xmath142 , not parallel to @xmath138 or @xmath139 ( `` up '' in the picture ) . then @xmath239 are the directions obtained by turning clockwise @xmath240 sectors . on the other side , @xmath241 are the directions obtained by turning counterclockwise that many sectors . these join up : at a @xmath119-fold point @xmath242 while at an @xmath107-fold point @xmath243 . the edge @xmath138 is oriented @xmath244 , and @xmath139 is oriented @xmath245 . in our tables below we will be listing the folded directions at singular points . in this case , a notation @xmath246 means the edge germ emanating from the singularity in the specified direction . with this notation , in the orientation of our scaffolding , the fold edge is said to be oriented outwards . the same edge oriented inwards towards the singularity will be denoted @xmath247 . we now consider a singularity of the form @xmath211 . it is an @xmath107-fold point , and the corresponding @xmath212 is a nonsingular @xmath119-fold point ( either @xmath121 or @xmath123 ) . these glue together to form a point @xmath248 . table [ s8table ] gives the structure of the scaffolding at @xmath209 as a function of the structure at @xmath211 . in order to fill in the table , recall that four sectors are removed from the neighborhood of @xmath211 , as well as from the neighborhood of @xmath212 ; then the remaining two sectors from @xmath212 are glued back in to give the neighborhood of @xmath249 . we make the convention that edge germs at @xmath209 are numbered starting with the middle edge of the two sectors from @xmath212 being @xmath238 ; the two indeterminate lines are @xmath250 , then remaining @xmath251 . these latter correspond to the directions @xmath252 respectively at @xmath211 . we include a column in the table to say what is happening at the point @xmath212 . note that it is a nonsingular @xmath119-fold point , hence either @xmath121 or @xmath123 . if it is @xmath123 then the direction of the fold line comes from the direction of the fold line at @xmath211 that goes in direction either @xmath244 or @xmath245 . this extra column will be most useful in our third table below . we do nt include configurations that are obtained by symmetry ( changing @xmath246 to @xmath253 ) from ones that were already included , and we do nt include configurations ( such as @xmath254 ) that are ruled out . .[s8table ] structure at @xmath209 [ cols="^,^,^,^,^",options="header " , ] in some rows of the table , the answer is not determined by the information local to @xmath219 . in those cases we have included the various possibilities . notice that the marking of edges @xmath255 will be determined from what happens in the two previous tables at the adjacent singularities on these segments . the scaffolding of @xmath205 is well - defined , with orientations of the fold edges . from the tables , the types of local pictures of the scaffolding for @xmath205 are in our standard list @xmath256 . the orientations of the fold edges at these singularities are compatible with the allowable configurations . [ snsubset ] define the refracting spectral network of @xmath205 to be generated by an initial sn line going in every non - fold direction from each of the singularities , and closed under collisions as well as refraction upon crossing fold lines of the new scaffolding . then , any sn - line of this new spectral network , outside of the edges @xmath206 , is contained in the previous spectral network of @xmath92 . sn lines along non - folded segments of the @xmath206 are with reversed orientation with respect to those of @xmath92 . under the assumption that there were no bps states in the refracting spectral network of @xmath92 , then there are no bps states in the refracting spectral network of @xmath205 . _ ( sketch)_we verify in each of the cases contained in the tables , that there are sn lines in @xmath257 corresponding to all non - folded outward directions from singular points . in the case of non - folded edges that are segments of the @xmath206 , there were sn lines in the non - folded segments of @xmath167 going in the opposite direction . switch the directions of these , and when these new sn lines meet a @xmath123 point , notice that it came from a singular point and the refracted directions are among the directions containing sn lines of @xmath92 ( or we continue along the next segment of @xmath206 to the next @xmath123 point ) . at an @xmath107-fold singularity obtained from the third table , the sn lines in all directions are generated by the sn lines along the segments of @xmath167 and @xmath258 , sometimes by using the collision process in @xmath92 . we should check that there are no bps states in the new spectral network . concerning lines not on the edges @xmath206 this comes from the inclusion into the previous spectral network in @xmath213 , and the existence of sn lines going outwards from any new singularities as noted above . we therefore need to consider new sn lines along segments of @xmath206 . for this , let us notice that in table [ s8table ] , whenever a singular @xmath124 or @xmath125 is created , the edges going along @xmath259 and @xmath230 , there denoted @xmath244 and @xmath245 , are folded . furthermore , whenever a @xmath123 is created , one of those two edges is folded so a bps state between the two adjacent @xmath260 is not created . similarly , in [ q6table ] when a @xmath125 or point is created , the segment after it on @xmath206 , denoted there @xmath261 , is folded . this has only been a sketch of proof , a more detailed discussion is needed in order to follow through all possible sn lines that might start with directions along the edges @xmath206 . we now review what has been done ( or sketched ) above . from @xmath1 we created an initial complete normal ecarinate construction @xmath42 and we are assuming that this is done following principles [ nobps ] and [ chooseinitial ] . thus @xmath42 is provided with a fully refracting scaffolding , whose associated spectral network has no bps states . initially the scaffolding has only @xmath262 singularities , so the endpoints of the post - caustics are @xmath131 points , and the @xmath107-fold and @xmath44-fold points alternate . the reduction process will consist of a sequence of reduction steps starting with @xmath42 . let us denote by @xmath92 the construction obtained after a certain number of steps . our goal is to describe the next reduction step . our construction @xmath92 is again complete , ecarinate , normal , and it is provided with a refracting scaffolding with oriented fold edges . our assumptions are as follows : that the refracting spectral network generated by the scaffolding has no bps states ; and that the types of points in the scaffolding are in the standard list of definition [ singdef ] , taking account orientations of edges . suppose that there are some remaining fold edges . by corollary [ existsfourtwo ] , there exists a @xmath45 point . the reduction step will be to collapse a neighborhood of this @xmath45 point in a good way . choose a maximal collapsing pair @xmath236 at this vertex . these regions are arranged with singularities and edges satisfying the properties of proposition [ properties ] and the subsequent discussion . we then glue together @xmath136 and @xmath137 , and trim away the resulting piece ( except for the union of edges @xmath206 ) , to get a new construction @xmath205 . this is the result of a single step of our reduction process . the main point is to verify that @xmath205 is provided with a well - defined refracting scaffolding that still satisfies the required properties . we have seen that the configurations at singularities in @xmath92 determine the fold edges at the new points in @xmath205 . indeed , this is the case at points of the form @xmath209 and @xmath231 , and the only indeterminacy at points @xmath210 is along segments that will be connected either to points @xmath231 or @xmath209 so the fold edges are determined . we have also assigned orientations to the fold edges . specific analysis of each case allows to fill in tables [ s8table ] , [ q6table ] , [ t6table ] . these show that the new singularities are only of the types in our standard list . furthermore , we see here that the types of singularities are compatible with the assigned orientations of the fold edges in the new scaffolding . we noted along the way that the fold edges of the new scaffolding have the required refracting effect on spectral network lines . the sketch of proof of proposition [ snsubset ] shows how the new spectral network is a subset of the previous one , apart from the spectral network lines that might have switched directions along the unfolded segments of the edges @xmath206 , and this spectral network does nt have any bps states . this completes the verification that our new construction @xmath205 has the required structures and satisfies the required properties so it can be used as the starting point in a next step of the reduction process . we have described a single step of the reduction process . the main question will now be to obtain a convergence statement saying that the process ends in finitely many steps with a construction @xmath263 whose scaffolding has an empty set of edges . suppose it does end . the only singularities of @xmath263 are @xmath122 points of negative curvature this reduced construction will be the _ core _ of the pre - building that we are conjecturing to exist in @xcite . in order to get the pre - building , the steps of putting back in the pieces that have been trimmed off , need to be done as described in @xcite . the core @xmath263 has a natural flat structure with geometry modeled on the standard appartment @xmath22 for @xmath0 . this geometric structure carries with it a natural cyclic @xmath265-fold spectral covering with ramification at the @xmath107-fold singular points . the @xmath107-fold singular points are negatively curved conical points for the flat metric , with angles of @xmath108 . the flat metric determines a conformal and hence complex structure ; this is a modification of the complex structure of the original riemann surface @xmath1 , and the cyclic covering corresponds to a cubic differential . this modification looks to be a discrete or possibly `` tropical '' analogue of labourie s result ( * ? ? ? * conjectures 1.6 , 1.7 ) @xcite , replacing a general spectral curve by a cubic differential . the first conjecture is that a minimization process provides a stability condition corresponding to the cubic differential , on the category of sections of the perverse schober with fiber @xmath266 corresponding to the cyclic spectral covering . if we can do that , then a procedure for defining the stability condition for a general @xmath0-spectral curve @xmath3 will be to define the categories @xmath267 of objects of phase @xmath268 , for any @xmath269 by considering the core @xmath270 and using the stability condition given by the conjectured minimization process of the previous paragraph . these @xmath26-structures should each satisfy the required axioms for taking part in a stability condition . therefore , taken together for all phases they should define a stability condition . we are just beginning to work on this program . t. aoki , t. kawai , y. takei . new turning points in the exact wkb analysis for higher - order ordinary differential equations . _ analyse algbrique des perturbations singulires , i ( luminy 1991 ) _ travaux en cours * 47 * , hermann , paris ( 1994 ) , 69 - 84 .[/INST] given an @xmath0 spectral curve over a simply connected riemann surface , we describe in detail the reduction steps necessary to construct the core of a pre - building with versal harmonic map whose differential is given by the spectral curve . </s>

“Logan” tore into the weekend box office, opening to a massive $85.3 million and proving that moviegoers will show up in force for R-rated comic book movies. The superhero spinoff marks Hugh Jackman’s last turn as Wolverine after 17 years of donning the adamantium claws. As the movie business grows more saturated with stories about costumed vigilantes, studios are trying to find ways to differentiate their own comic book adaptations. Like “Deadpool” before it, “Logan” demonstrates that adults will turn out for tentpole fare that is bloodier and more profane than your average X-Men movie. “Logan” was produced by 20th Century Fox and cost $97 million to make. Set in the near future, it follows Wolverine and an ailing Professor X (Patrick Stewart), who leaving their hiding place on the Mexican border to help a young mutant (Dafne Keen). James Mangold, who previously collaborated with Jackman on 2013’s “The Wolverine,” directed the movie and co-wrote the screenplay. “Logan” takes its inspiration from “Old Man Logan,” an acclaimed 2008 graphic novel that’s long been a fan favorite for its darker take on the hero. “The movie is one of the truest movies to the source material in the comic book universe that’s ever been done,” said Chris Aronson, Fox’s domestic distribution chief. “It’s so real, it’s so emotional, and it’s so visceral.” Critics embraced the film, hailing it as a comic book movie with bite, with Variety’s Owen Gleiberman writing that “Logan” “…brings the saga to a satisfying finish.” The audience for the film was older and male-skewing – men made up 63% of ticket buyers, with 68% of the opening weekend crowd clocking in over the age of 25. Despite “Logan’s” dominance, Blumhouse and Universal’s “Get Out” keeps going strong. The low-budget thriller racked up $26.1 million, bringing its domestic haul to $75.9 million. That’s an impressive return for a film that cost less than $5 million to make. Lionsgate’s “The Shack” took third place, earning a solid $16.1 million in its first weekend in theaters. The faith-based drama stars Oscar-winner Octavia Spencer and cost $26 million to produce. “The Shack” centers on a man (Sam Worthington) whose religious beliefs are tested following a family tragedy. Warner Bros.’ “The Lego Batman Movie” and Open Road’s “Before I Fall” rounded out the top five, earning $11.6 million and $4.9 million, respectively. That pushes the Lego spinoff’s box office total to $148.6 million. “Before I Fall” is a young adult movie about a teenager (Zoey Dutch) who is stuck reliving her last day on earth until she gets it right. Fresh off its best picture win, A24’s “Moonlight” grossed over $2.5 million and crossed the $25 million mark. The indie studio expects the coming-of-age drama to be the highest-grossing film in its history. That said, “Moonlight,” which focuses on a young man growing up gay in Miami, is one of the least widely seen best picture winners, trailing the likes of “Spotlight” ($45 million, domestically ) and “Birdman” ($42.3 million, domestically). It has grossed more than “The Hurt Locker,” the 2009 victor that made just over $17 million stateside. Bleecker Street’s “The Last Word” opened to $35,620 in limited release. The story of an aging businesswoman (Shirley MacLaine) who enlists a writer (Amanda Seyfried) to pen her obituary, screened in four locations last weekend. “Logan’s” success turbocharged the domestic box office, lifting ticket sales up 12% over the prior-year period, when “Zootopia” debuted to $75.1 million. It also gets March off to a hot start. This month sees the openings of “Beauty and the Beast” and “Kong: Skull Island,” both of which are on pace to score big debuts. “This is going to be a banner month,” said Paul Dergarabedian, senior media analyst with ComScore. “It’s going to end up being one of the biggest, if not the biggest March ever.”

– The R-rated X-Men spinoff Logan slashed into the weekend box office, reports the AP, opening with a massive $85.3 million that surpassed expectations and ranks among the top March debuts ever. The 20th Century Fox release features Hugh Jackman in what he has hinted could be his final performance as Wolverine. Word of mouth got a boost from good reviews for the unusually dark and dramatic comic-book movie that—like Deadpool—further proves moviegoers' hunger for less conventional superhero films. "The movie is one of the truest movies to the source material in the comic book universe that’s ever been done," a rep for distributor 20th Century Fox tells Variety. "It’s so real, it’s so emotional, and it’s so visceral." The Oscar best-picture winner Moonlight had its widest release yet, appearing on 1,564 screens. It turned in its biggest weekend, too, with an estimated $2.5 million. Last week's No. 1 film, Jordan Peele's horror sensation Get Out slid remarkably little, dropping to second place with $26.1 million. Rounding out the top five were The Shack with $16.1 million, The Lego Batman Movie with $11.6 million, and Before I Fall with $4.9 million.

<s>[INST]“Logan” tore into the weekend box office, opening to a massive $85.3 million and proving that moviegoers will show up in force for R-rated comic book movies. The superhero spinoff marks Hugh Jackman’s last turn as Wolverine after 17 years of donning the adamantium claws. As the movie business grows more saturated with stories about costumed vigilantes, studios are trying to find ways to differentiate their own comic book adaptations. Like “Deadpool” before it, “Logan” demonstrates that adults will turn out for tentpole fare that is bloodier and more profane than your average X-Men movie. “Logan” was produced by 20th Century Fox and cost $97 million to make. Set in the near future, it follows Wolverine and an ailing Professor X (Patrick Stewart), who leaving their hiding place on the Mexican border to help a young mutant (Dafne Keen). James Mangold, who previously collaborated with Jackman on 2013’s “The Wolverine,” directed the movie and co-wrote the screenplay. “Logan” takes its inspiration from “Old Man Logan,” an acclaimed 2008 graphic novel that’s long been a fan favorite for its darker take on the hero. “The movie is one of the truest movies to the source material in the comic book universe that’s ever been done,” said Chris Aronson, Fox’s domestic distribution chief. “It’s so real, it’s so emotional, and it’s so visceral.” Critics embraced the film, hailing it as a comic book movie with bite, with Variety’s Owen Gleiberman writing that “Logan” “…brings the saga to a satisfying finish.” The audience for the film was older and male-skewing – men made up 63% of ticket buyers, with 68% of the opening weekend crowd clocking in over the age of 25. Despite “Logan’s” dominance, Blumhouse and Universal’s “Get Out” keeps going strong. The low-budget thriller racked up $26.1 million, bringing its domestic haul to $75.9 million. That’s an impressive return for a film that cost less than $5 million to make. Lionsgate’s “The Shack” took third place, earning a solid $16.1 million in its first weekend in theaters. The faith-based drama stars Oscar-winner Octavia Spencer and cost $26 million to produce. “The Shack” centers on a man (Sam Worthington) whose religious beliefs are tested following a family tragedy. Warner Bros.’ “The Lego Batman Movie” and Open Road’s “Before I Fall” rounded out the top five, earning $11.6 million and $4.9 million, respectively. That pushes the Lego spinoff’s box office total to $148.6 million. “Before I Fall” is a young adult movie about a teenager (Zoey Dutch) who is stuck reliving her last day on earth until she gets it right. Fresh off its best picture win, A24’s “Moonlight” grossed over $2.5 million and crossed the $25 million mark. The indie studio expects the coming-of-age drama to be the highest-grossing film in its history. That said, “Moonlight,” which focuses on a young man growing up gay in Miami, is one of the least widely seen best picture winners, trailing the likes of “Spotlight” ($45 million, domestically ) and “Birdman” ($42.3 million, domestically). It has grossed more than “The Hurt Locker,” the 2009 victor that made just over $17 million stateside. Bleecker Street’s “The Last Word” opened to $35,620 in limited release. The story of an aging businesswoman (Shirley MacLaine) who enlists a writer (Amanda Seyfried) to pen her obituary, screened in four locations last weekend. “Logan’s” success turbocharged the domestic box office, lifting ticket sales up 12% over the prior-year period, when “Zootopia” debuted to $75.1 million. It also gets March off to a hot start. This month sees the openings of “Beauty and the Beast” and “Kong: Skull Island,” both of which are on pace to score big debuts. “This is going to be a banner month,” said Paul Dergarabedian, senior media analyst with ComScore. “It’s going to end up being one of the biggest, if not the biggest March ever.”[/INST]– The R-rated X-Men spinoff Logan slashed into the weekend box office, reports the AP, opening with a massive $85.3 million that surpassed expectations and ranks among the top March debuts ever. The 20th Century Fox release features Hugh Jackman in what he has hinted could be his final performance as Wolverine. Word of mouth got a boost from good reviews for the unusually dark and dramatic comic-book movie that—like Deadpool—further proves moviegoers' hunger for less conventional superhero films. "The movie is one of the truest movies to the source material in the comic book universe that’s ever been done," a rep for distributor 20th Century Fox tells Variety. "It’s so real, it’s so emotional, and it’s so visceral." The Oscar best-picture winner Moonlight had its widest release yet, appearing on 1,564 screens. It turned in its biggest weekend, too, with an estimated $2.5 million. Last week's No. 1 film, Jordan Peele's horror sensation Get Out slid remarkably little, dropping to second place with $26.1 million. Rounding out the top five were The Shack with $16.1 million, The Lego Batman Movie with $11.6 million, and Before I Fall with $4.9 million.</s>

These crawls are part of an effort to archive pages as they are created and archive the pages that they refer to. That way, as the pages that are referenced are changed or taken from the web, a link to the version that was live when the page was written will be preserved.Then the Internet Archive hopes that references to these archived pages will be put in place of a link that would be otherwise be broken, or a companion link to allow people to see what was originally intended by a page's authors.The goal is to fix all broken links on the web . Crawls of supported "No More 404" sites. ||||| Many Good Samaritans have come to the aid of Flint, Michigan, during its water crisis, with donations pouring in for bottled water and water filters to deal with the high levels of lead found in the city's municipal water supply. Interested in ? Add as an interest to stay up to date on the latest news, video, and analysis from ABC News. Add Interest One resident in Dearborn, Michigan, about an hour south of Flint, said she couldn't turn a blind eye to Flint's woes. "I had been thinking a lot about Flint at that point," Diana Hussein, 29, told ABC News. "I didn't feel there was anything that I was doing." So, she's helping out by donating a very valuable piece of digital real estate. Hussein said she created the Twitter handle @DietDrPepper in 2009. The drink was sitting on her desk when she was trying to come up with a name for her Twitter account, she said, so she went with it. Over the years, she tried reaching out to the giant multi-product company, Dr Pepper Snapple Group, to see if they would be interested in the username. "I hadn’t expected anything outside of maybe some free pop," Hussein said. Courtesy Diana Hussein Hussein said it was not until January this year that the company started showing interest in the account. She made a post about it on Facebook, where some people encouraged her to negotiate a sale. Hussein said company representatives offered her brand merchandise. Hussein thought about it and decided she would relinquish the name if the soft drink company promised to help Flint. That's it. "She wasn't trying to come after a monetary value," Dr Pepper's public relations manager Brian Bell told ABC News. "Diana was very straightforward. She was very open and honest with us." Courtesy Diana Hussein Hussein, who works as a communications specialist, said she was thinking "maybe I could convince them to do some kind of monetary contribution" to help Flint. "When I found out they owned and distributed [bottles of water], I thought that was a really great opportunity." The Texas-based business was on board, delivering 41,000 bottles of water last month in exchange for the @DietDrPepper Twitter handle. Bell said the company had made previous donations to Flint, but Hussein's request presented another opportunity to do it again. Michigan Gov. Rick Synder declared a state of emergency in January over Flint's water crisis, and has faced criticism and calls to resign. Hussein now tweets under the handle @HeyaDiana. ||||| Flint, Michigan (CNN) An "arsenal" of cases of fresh water stacked in the basement and a graveyard of scattered empty bottles are daily reminders that life in Flint, Michigan, is anything but normal. For Gina Luster, 41, seeing the stacks of bottles angers her. She says she feels like less than a good parent after watching her daughter, 7, and niece, 13, suffer from hair loss and skin rashes. "It makes me feel like the lowest of the low. My self-esteem when it first began was so, so bad," Luster said on the verge of tears in her dining room. "You pull up to a place where you need this water, and the line is a mile long and you're waiting in your car, praying you don't run out of gas waiting, and you've got your kids in the car and they're looking at you like 'What are you going to do about this?'" she said. 151 bottles of water in a day CNN tallied the number of bottles the Luster family uses in a day and sorted how each bottle was used into eight categories. 36 bottles were used for cooking and another 36 were for washing hair. They used 27 bottles for drinking, plus 24 for doing dishes, and the rest were used for washing faces, brushing teeth and more. Each bottle held 16.9 ounces of water. The grand total came to 151 bottles -- that's how much the family of three uses in a day. JUST WATCHED 1 day in Flint, 151 bottles of water Replay More Videos ... MUST WATCH 1 day in Flint, 151 bottles of water 00:22 The average American uses 100 gallons of water a day , according to the U.S. Environmental Protection Agency. That translates to roughly 757 bottles of water, which is way more the 50 water bottles each person in the Luster household is using. The EPA statistics include water used to flush toilets, wash hands, shower and it even accounts for leaks. The family still uses the tap water for washing their hands -- they get tired of having to unscrew a bottle for just about everything. Once or twice a week, they head to Gina's mother's house in nearby Swartz Creek, a suburb of Flint, to shower and do their laundry. 'The taste was like metal' The family didn't know what was going on until each one started exhibiting health problems in summer 2014 -- the city of Flint switched its water source from Lake Huron to the Flint River in spring 2014. "By July I had shriveled down and lost 60 pounds. I was down to a size 4," said Luster, who used to weigh 200 pounds. Gina Luster in her Flint, Michigan home with the total bottles of water it takes to get through a day. Luster, a self-admitted ice chewer, started noticing the taste of the water was different that summer. It tasted like metal or medicine. Things grew worse when Luster collapsed at her job that month. She had been a store manager at a retailer Citi Trends until she was forced to go on medical leave in August 2014. That fall, Luster's medical records indicate doctors found cysts on her ovaries. She had a partial hysterectomy to remove the cysts, but the cause of the cysts was not cited. Unable to return to work, Luster lost her job. She had previously been making $38,000 a year, but now she was relying on odd part-time jobs and the graciousness of her family to make things work. Meanwhile, alarm bells were going off in Luster's head when she started getting calls from school about her daughter, Kennedy. "You're getting calls from the teacher, 'Kennedy was at school today scratching with both hands and she's bleeding.' What? I mean, she scratched until she was raw," Luster said, exasperated. Kennedy, a bright-eyed, spunky student, was also losing chunks of her hair, her mother said. Luster's well-spoken teenage niece, Eeshyia King, who lives with the family, was experiencing breakouts and rashes that drove her to an intense face-washing ritual. They had been drinking the water for a year Fifteen months after the family started seeing adverse changes in their health, they switched to using bottled water in October 2015. The total number of bottles of water the Luster family uses in one day. "For a whole year's span, we were drinking that water. That's finally when they came out and said there was lead in the water," Luster said, wide-eyed with a smile of disbelief. Luster didn't know just how much water they needed until she realized she was going through almost an entire 24-pack of water per day. By night, they'd only have four or five bottles left. After dropping the girls off at school, Luster drove to a water station to pick up a new pack of water. Local fire stations set up "water stations" to distribute water to the families in Flint. She picked up a case of water each day, seven days a week, for four months, she said. With the rashes and hair loss persisting, Luster started using bottled water for more than just drinking. They started washing their hair and faces, brushing teeth and cooking with the precious, fresh water. Kennedy Luster, 7, holds a pot her mother says was ruined by washing it in Flint's water. "It just became like second nature to come in and start unscrewing caps and doing whatever you had to do," she said. To keep up with the family's increasing demand, she started driving to more water stations, acquiring a pack of water from each place. The family would pull off the side of the road, throw the water in the trunk, and go to the next place to get more water, sometimes up to 4 or 5 cases in one excursion. Friends from around the country rallied to send her money so she could purchase a more water and save on gas money. Luster said she feels blessed when she sees the donated pallet of water sitting in her basement, flanked by more packs of water ascending the stairs. A family comes together to survive Since losing her job and taking on whatever random work she can, like cleaning a dialysis center at night, Luster is grateful for the help of her family. "I've tapped out my savings and I'm literally living off my parents," she said. Her sister, Corey Luster, chimed in from the kitchen. "It has forced us to be really reliant on each other for our survival, both economic and the water, period," said the 33-year-old. Beyond her thinning and breaking hair, weight loss, rashes and more, Luster is worried about more than just the physical problems she and her girls are having. "People are forgetting the emotional and mental problems that we're going through now," said Luster. "I'm never going to forget this. My 7-year-old is never going to forget this. My 13-year-old niece is never going to forget this." ||||| CLOSE Skip in Skip x Embed x Share The once quiet city of Flint, Michigan is facing a drinking water crisis that is drawing concern from around the nation. Here's what you need to know about how the public health crisis has evolved. VPC The Dr Pepper Snapple Group donated 24 pallets of water to the residents of Flint. (Photo: Dr Pepper Snapple Group) When Diana Hussein, 29, of Dearborn, chose her Twitter handle seven years ago, she barely gave it a second thought. But the name she picked would end up being very important. Important to her, but even more so to the water-starved residents of Flint who would end up with a truckload of bottled water out of the deal. So what was the Twitter handle? @DietDrPepper. ► Related: Costs of Schuette Flint investigation hit $2.3 million ► Related: Grand jury investigation sought over Snyder legal fees for Flint "I created my handle using what was the nearest thing to me: a can of soda on my desk," Hussein said in an online conversation with the Free Press. Hussein, a communications specialist, has been using the name to tweet about Detroit sports and "a lot about my cats," she said. (Photo: Diana Hussein) When she first picked her handle, it was the early days of Twitter, and companies had barely begun to see the social media platform as an advertising opportunity. "I never expected Twitter to take off in the way it did, where brands would be all over, including sodas with their own accounts," Hussein said. @DietDrPepper would end up being her leverage in an effort to help in Flint, where families continue to struggle to get their hands on clean water after the city water system became contaminated with lead. Reaching out In 2013, Hussein thought she might want to shed the Twitter name and find one that suited her better. So she reached out to the Dr Pepper parent company, Dr Pepper Snapple Group (DPSG), to see if the company was interested in the handle, but got nowhere. It wasn't until mid-January that someone from DPSG started reaching out to her, "pretty aggressively," said Hussein. The company made a proposal: Hand over the @DietDrPepper name in exchange for some official swag. "I wasn't sure what I was going to do at first. Just about everyone I spoke to told me that I shouldn't just give them the handle. Especially not just for 'swag,'" Hussein said. Eventually, Hussein learned that DPSG also owned the DeJa Blue water brand and her idea came to life in the form of a counter offer. In lieu of swag, she asked for the company to donate bottled water to the residents of Flint. Their offer? $5,000 worth of water, equivalent to about 41,000 bottles. On March 3, DeJa Blue sent an entire truckload of bottled water to Flint. "I had been feeling kind of helpless. Still do, really. But I'm glad I had an opportunity like this present itself for me to be able to take advantage," Hussein said. Despite the contribution, Hussein continues her push to find more help for Flint, urging people to donate, if possible. "When you hear about what they're having to do right now," she said, "it doesn't seem like there could be enough water." If you'd like to know how you can help in Flint, whether it's monetary, a water dropoff, or by volunteering your time, visit this link. Hussein can now be found on Twitter as @HeyaDiana. Read or Share this story: http://on.freep.com/1MQCR9r ||||| A Michigan woman was able to get Dr Pepper to donate $5,000 worth of bottled water because she chose a Twitter username seven years ago that the company really wanted. Diana Hussein chose the Twitter handle @DietDrPepper in 2009, the 29-year-old told NBC Chicago on social media. “I literally had a can of Diet Dr Pepper on my desk. It was the closest thing to me when I needed to come up with a name,” Hussein said. She wrote mostly about sports and cats before she offered it to the soda manufacturer in 2013 because she wanted one that suited her better, she told NBC Chicago. When she reached out to Dr Pepper’s parent company, Dr Pepper Snapple Group (DPSG), they gave her an offer – an offer of company swag. When she learned DPSG is behind the DeJa Blue water brand, Hussein instead asked that they donate water bottles to Flint, Michigan, which is currently dealing with a water crisis due to lead contamination in city pipes. The company agreed, and told NBC Chicago in a statement that in early January it made a “sizeable contribution of water through our Flint sales and distribution branch to a number of community organizations.” The company donated $5,000 worth of water, which is about 41,000 bottles, according to Hussein. “Recently Diana Hussein presented us with a fantastic opportunity to help further by providing more water in exchange for the @DietDrPepper Twitter handle and we jumped at this opportunity,” said Dr Pepper Snapple Group spokesperson Brian Bell said in a statement. “Rather than accepting any compensation for this Twitter handle as many might expect, she put the needs of her community first and we were happy to oblige.” You can now follow Diana Hussein on Twitter as @heyadiana.

– For seven years, Diana Hussein has held the @DrDietPepper Twitter handle she created on a whim, tweeting mainly about local sports and her cats and hoping to maybe one day get some money or free swag if the Dr Pepper Snapple Group wanted to barter for it, the Detroit Free Press reports. "I created my handle [at the time] using what was the nearest thing to me: a can of soda on my desk," she recalls. But when the Dearborn, Mich., resident started hearing about the Flint water crisis, the wheels in her head started turning. The soda company had actually extended a proposal earlier this year—her account for a bunch of branded merch—but Hussein counteroffered with a more generous idea: The company could donate water to Flint, ABC News reports. "When I found out they owned and distributed [bottles of water], I thought that was a really great opportunity," she says, and the company agreed, shipping 41,000 bottles (worth about $5,000) to the parched city last month—an amount the New York Daily News notes would provide enough water to 250 families for one day or to a family of three through the end of 2016. "Rather than accepting any compensation for this Twitter handle as many might expect, she put the needs of her community first and we were happy to oblige," a Dr Pepper Snapple Group rep said in a statement, per NBC Chicago. "I had been feeling kind of helpless [about Flint]," she tells the Free Press. "Still do, really. But I'm glad I had an opportunity like this present itself … When you hear about what they're having to do right now, it doesn't seem like there could be enough water." As for Hussein, she's still on Twitter, but now under the more personalized @heyadiana handle. (The crisis has made Flint's property values plummet.)

<s>[INST]These crawls are part of an effort to archive pages as they are created and archive the pages that they refer to. That way, as the pages that are referenced are changed or taken from the web, a link to the version that was live when the page was written will be preserved.Then the Internet Archive hopes that references to these archived pages will be put in place of a link that would be otherwise be broken, or a companion link to allow people to see what was originally intended by a page's authors.The goal is to fix all broken links on the web . Crawls of supported "No More 404" sites. ||||| Many Good Samaritans have come to the aid of Flint, Michigan, during its water crisis, with donations pouring in for bottled water and water filters to deal with the high levels of lead found in the city's municipal water supply. Interested in ? Add as an interest to stay up to date on the latest news, video, and analysis from ABC News. Add Interest One resident in Dearborn, Michigan, about an hour south of Flint, said she couldn't turn a blind eye to Flint's woes. "I had been thinking a lot about Flint at that point," Diana Hussein, 29, told ABC News. "I didn't feel there was anything that I was doing." So, she's helping out by donating a very valuable piece of digital real estate. Hussein said she created the Twitter handle @DietDrPepper in 2009. The drink was sitting on her desk when she was trying to come up with a name for her Twitter account, she said, so she went with it. Over the years, she tried reaching out to the giant multi-product company, Dr Pepper Snapple Group, to see if they would be interested in the username. "I hadn’t expected anything outside of maybe some free pop," Hussein said. Courtesy Diana Hussein Hussein said it was not until January this year that the company started showing interest in the account. She made a post about it on Facebook, where some people encouraged her to negotiate a sale. Hussein said company representatives offered her brand merchandise. Hussein thought about it and decided she would relinquish the name if the soft drink company promised to help Flint. That's it. "She wasn't trying to come after a monetary value," Dr Pepper's public relations manager Brian Bell told ABC News. "Diana was very straightforward. She was very open and honest with us." Courtesy Diana Hussein Hussein, who works as a communications specialist, said she was thinking "maybe I could convince them to do some kind of monetary contribution" to help Flint. "When I found out they owned and distributed [bottles of water], I thought that was a really great opportunity." The Texas-based business was on board, delivering 41,000 bottles of water last month in exchange for the @DietDrPepper Twitter handle. Bell said the company had made previous donations to Flint, but Hussein's request presented another opportunity to do it again. Michigan Gov. Rick Synder declared a state of emergency in January over Flint's water crisis, and has faced criticism and calls to resign. Hussein now tweets under the handle @HeyaDiana. ||||| Flint, Michigan (CNN) An "arsenal" of cases of fresh water stacked in the basement and a graveyard of scattered empty bottles are daily reminders that life in Flint, Michigan, is anything but normal. For Gina Luster, 41, seeing the stacks of bottles angers her. She says she feels like less than a good parent after watching her daughter, 7, and niece, 13, suffer from hair loss and skin rashes. "It makes me feel like the lowest of the low. My self-esteem when it first began was so, so bad," Luster said on the verge of tears in her dining room. "You pull up to a place where you need this water, and the line is a mile long and you're waiting in your car, praying you don't run out of gas waiting, and you've got your kids in the car and they're looking at you like 'What are you going to do about this?'" she said. 151 bottles of water in a day CNN tallied the number of bottles the Luster family uses in a day and sorted how each bottle was used into eight categories. 36 bottles were used for cooking and another 36 were for washing hair. They used 27 bottles for drinking, plus 24 for doing dishes, and the rest were used for washing faces, brushing teeth and more. Each bottle held 16.9 ounces of water. The grand total came to 151 bottles -- that's how much the family of three uses in a day. JUST WATCHED 1 day in Flint, 151 bottles of water Replay More Videos ... MUST WATCH 1 day in Flint, 151 bottles of water 00:22 The average American uses 100 gallons of water a day , according to the U.S. Environmental Protection Agency. That translates to roughly 757 bottles of water, which is way more the 50 water bottles each person in the Luster household is using. The EPA statistics include water used to flush toilets, wash hands, shower and it even accounts for leaks. The family still uses the tap water for washing their hands -- they get tired of having to unscrew a bottle for just about everything. Once or twice a week, they head to Gina's mother's house in nearby Swartz Creek, a suburb of Flint, to shower and do their laundry. 'The taste was like metal' The family didn't know what was going on until each one started exhibiting health problems in summer 2014 -- the city of Flint switched its water source from Lake Huron to the Flint River in spring 2014. "By July I had shriveled down and lost 60 pounds. I was down to a size 4," said Luster, who used to weigh 200 pounds. Gina Luster in her Flint, Michigan home with the total bottles of water it takes to get through a day. Luster, a self-admitted ice chewer, started noticing the taste of the water was different that summer. It tasted like metal or medicine. Things grew worse when Luster collapsed at her job that month. She had been a store manager at a retailer Citi Trends until she was forced to go on medical leave in August 2014. That fall, Luster's medical records indicate doctors found cysts on her ovaries. She had a partial hysterectomy to remove the cysts, but the cause of the cysts was not cited. Unable to return to work, Luster lost her job. She had previously been making $38,000 a year, but now she was relying on odd part-time jobs and the graciousness of her family to make things work. Meanwhile, alarm bells were going off in Luster's head when she started getting calls from school about her daughter, Kennedy. "You're getting calls from the teacher, 'Kennedy was at school today scratching with both hands and she's bleeding.' What? I mean, she scratched until she was raw," Luster said, exasperated. Kennedy, a bright-eyed, spunky student, was also losing chunks of her hair, her mother said. Luster's well-spoken teenage niece, Eeshyia King, who lives with the family, was experiencing breakouts and rashes that drove her to an intense face-washing ritual. They had been drinking the water for a year Fifteen months after the family started seeing adverse changes in their health, they switched to using bottled water in October 2015. The total number of bottles of water the Luster family uses in one day. "For a whole year's span, we were drinking that water. That's finally when they came out and said there was lead in the water," Luster said, wide-eyed with a smile of disbelief. Luster didn't know just how much water they needed until she realized she was going through almost an entire 24-pack of water per day. By night, they'd only have four or five bottles left. After dropping the girls off at school, Luster drove to a water station to pick up a new pack of water. Local fire stations set up "water stations" to distribute water to the families in Flint. She picked up a case of water each day, seven days a week, for four months, she said. With the rashes and hair loss persisting, Luster started using bottled water for more than just drinking. They started washing their hair and faces, brushing teeth and cooking with the precious, fresh water. Kennedy Luster, 7, holds a pot her mother says was ruined by washing it in Flint's water. "It just became like second nature to come in and start unscrewing caps and doing whatever you had to do," she said. To keep up with the family's increasing demand, she started driving to more water stations, acquiring a pack of water from each place. The family would pull off the side of the road, throw the water in the trunk, and go to the next place to get more water, sometimes up to 4 or 5 cases in one excursion. Friends from around the country rallied to send her money so she could purchase a more water and save on gas money. Luster said she feels blessed when she sees the donated pallet of water sitting in her basement, flanked by more packs of water ascending the stairs. A family comes together to survive Since losing her job and taking on whatever random work she can, like cleaning a dialysis center at night, Luster is grateful for the help of her family. "I've tapped out my savings and I'm literally living off my parents," she said. Her sister, Corey Luster, chimed in from the kitchen. "It has forced us to be really reliant on each other for our survival, both economic and the water, period," said the 33-year-old. Beyond her thinning and breaking hair, weight loss, rashes and more, Luster is worried about more than just the physical problems she and her girls are having. "People are forgetting the emotional and mental problems that we're going through now," said Luster. "I'm never going to forget this. My 7-year-old is never going to forget this. My 13-year-old niece is never going to forget this." ||||| CLOSE Skip in Skip x Embed x Share The once quiet city of Flint, Michigan is facing a drinking water crisis that is drawing concern from around the nation. Here's what you need to know about how the public health crisis has evolved. VPC The Dr Pepper Snapple Group donated 24 pallets of water to the residents of Flint. (Photo: Dr Pepper Snapple Group) When Diana Hussein, 29, of Dearborn, chose her Twitter handle seven years ago, she barely gave it a second thought. But the name she picked would end up being very important. Important to her, but even more so to the water-starved residents of Flint who would end up with a truckload of bottled water out of the deal. So what was the Twitter handle? @DietDrPepper. ► Related: Costs of Schuette Flint investigation hit $2.3 million ► Related: Grand jury investigation sought over Snyder legal fees for Flint "I created my handle using what was the nearest thing to me: a can of soda on my desk," Hussein said in an online conversation with the Free Press. Hussein, a communications specialist, has been using the name to tweet about Detroit sports and "a lot about my cats," she said. (Photo: Diana Hussein) When she first picked her handle, it was the early days of Twitter, and companies had barely begun to see the social media platform as an advertising opportunity. "I never expected Twitter to take off in the way it did, where brands would be all over, including sodas with their own accounts," Hussein said. @DietDrPepper would end up being her leverage in an effort to help in Flint, where families continue to struggle to get their hands on clean water after the city water system became contaminated with lead. Reaching out In 2013, Hussein thought she might want to shed the Twitter name and find one that suited her better. So she reached out to the Dr Pepper parent company, Dr Pepper Snapple Group (DPSG), to see if the company was interested in the handle, but got nowhere. It wasn't until mid-January that someone from DPSG started reaching out to her, "pretty aggressively," said Hussein. The company made a proposal: Hand over the @DietDrPepper name in exchange for some official swag. "I wasn't sure what I was going to do at first. Just about everyone I spoke to told me that I shouldn't just give them the handle. Especially not just for 'swag,'" Hussein said. Eventually, Hussein learned that DPSG also owned the DeJa Blue water brand and her idea came to life in the form of a counter offer. In lieu of swag, she asked for the company to donate bottled water to the residents of Flint. Their offer? $5,000 worth of water, equivalent to about 41,000 bottles. On March 3, DeJa Blue sent an entire truckload of bottled water to Flint. "I had been feeling kind of helpless. Still do, really. But I'm glad I had an opportunity like this present itself for me to be able to take advantage," Hussein said. Despite the contribution, Hussein continues her push to find more help for Flint, urging people to donate, if possible. "When you hear about what they're having to do right now," she said, "it doesn't seem like there could be enough water." If you'd like to know how you can help in Flint, whether it's monetary, a water dropoff, or by volunteering your time, visit this link. Hussein can now be found on Twitter as @HeyaDiana. Read or Share this story: http://on.freep.com/1MQCR9r ||||| A Michigan woman was able to get Dr Pepper to donate $5,000 worth of bottled water because she chose a Twitter username seven years ago that the company really wanted. Diana Hussein chose the Twitter handle @DietDrPepper in 2009, the 29-year-old told NBC Chicago on social media. “I literally had a can of Diet Dr Pepper on my desk. It was the closest thing to me when I needed to come up with a name,” Hussein said. She wrote mostly about sports and cats before she offered it to the soda manufacturer in 2013 because she wanted one that suited her better, she told NBC Chicago. When she reached out to Dr Pepper’s parent company, Dr Pepper Snapple Group (DPSG), they gave her an offer – an offer of company swag. When she learned DPSG is behind the DeJa Blue water brand, Hussein instead asked that they donate water bottles to Flint, Michigan, which is currently dealing with a water crisis due to lead contamination in city pipes. The company agreed, and told NBC Chicago in a statement that in early January it made a “sizeable contribution of water through our Flint sales and distribution branch to a number of community organizations.” The company donated $5,000 worth of water, which is about 41,000 bottles, according to Hussein. “Recently Diana Hussein presented us with a fantastic opportunity to help further by providing more water in exchange for the @DietDrPepper Twitter handle and we jumped at this opportunity,” said Dr Pepper Snapple Group spokesperson Brian Bell said in a statement. “Rather than accepting any compensation for this Twitter handle as many might expect, she put the needs of her community first and we were happy to oblige.” You can now follow Diana Hussein on Twitter as @heyadiana.[/INST]– For seven years, Diana Hussein has held the @DrDietPepper Twitter handle she created on a whim, tweeting mainly about local sports and her cats and hoping to maybe one day get some money or free swag if the Dr Pepper Snapple Group wanted to barter for it, the Detroit Free Press reports. "I created my handle [at the time] using what was the nearest thing to me: a can of soda on my desk," she recalls. But when the Dearborn, Mich., resident started hearing about the Flint water crisis, the wheels in her head started turning. The soda company had actually extended a proposal earlier this year—her account for a bunch of branded merch—but Hussein counteroffered with a more generous idea: The company could donate water to Flint, ABC News reports. "When I found out they owned and distributed [bottles of water], I thought that was a really great opportunity," she says, and the company agreed, shipping 41,000 bottles (worth about $5,000) to the parched city last month—an amount the New York Daily News notes would provide enough water to 250 families for one day or to a family of three through the end of 2016. "Rather than accepting any compensation for this Twitter handle as many might expect, she put the needs of her community first and we were happy to oblige," a Dr Pepper Snapple Group rep said in a statement, per NBC Chicago. "I had been feeling kind of helpless [about Flint]," she tells the Free Press. "Still do, really. But I'm glad I had an opportunity like this present itself … When you hear about what they're having to do right now, it doesn't seem like there could be enough water." As for Hussein, she's still on Twitter, but now under the more personalized @heyadiana handle. (The crisis has made Flint's property values plummet.)</s>

an ensemble of coupled phase oscillators provides a simple yet powerful paradigm for studying the collective behaviour of many complex real life systems and has been extensively studied in this context@xcite . under appropriate conditions , phase oscillators can exhibit stable in - phase synchronous or other type of phase - locked solutions @xcite . in a class of discrete networks of oscillators it has been shown that in - phase synchronous behavior can be achieved even in the presence of a fixed signal transmission delay @xcite . more intricate dynamics have been discovered in nonlocally coupled continuous networks , whereby phase - locked and incoherent activity can simultaneously exist at different spatial locations @xcite , giving rise to a spatio - temporal pattern that has been termed as a _ chimera state _ @xcite . in this paper , we discuss the existence and stability of phase - locked solutions in a continuum of nonlocally coupled identical phase oscillators with distance - dependent delays . such delays are a natural consequence of the finite speed of information propagation in space . in similar contexts , distance - dependent delays have been considered in continuum models of neural activity @xcite . in particular , the effects of distributed delays can be very different from fixed delays @xcite , and the analysis is generally more difficult . we consider a continuum of identical phase oscillators , arranged on a circular ring @xmath0 and labeled by @xmath1 $ ] with periodic boundary conditions , whose dynamics is governed by @xmath2dz , \label{pha}\ ] ] where @xmath3 is the phase of the oscillator at location @xmath4 and time @xmath5 , whose intrinsic oscillation frequency is @xmath6 , @xmath7 is the coupling strength and @xmath8\rightarrow\mathbb{r}$ ] is an even function describing the coupling kernel . the quantity @xmath9 denotes the signal propagation speed which gives rise to a time delay of @xmath10 for distance @xmath11 from the locations @xmath4 . as the oscillators are located on a ring with circumference @xmath12 , the distance between any two oscillators is given by the shorter of the euclidean distance between them along the ring . in this configuration , the maximum distance between the coupled oscillators is @xmath13 and thus the maximum time delay would be @xmath14 . if we denote the location of any two oscillators as @xmath4 and @xmath15 then @xmath16 . @xmath17 is a parameter which makes the coupling phase - shifted and has been crucial for observing chimera states . we choose the coupling kernel @xmath18 to have an exponentially decaying nature and its normalized form is taken to be @xmath19 where @xmath20 is the inverse of the interaction scale length and is a measure of the nonlocality of the coupling . the exponential form of @xmath18 and the @xmath21 coupling function are the natural consequences of the reduction of a more general reaction - diffusion system to a phase model under nonlocal and weak coupling limits @xcite . we further make time and space dimensionless in eqs.([pha ] ) and ( [ ker ] ) by the transformations @xmath22 , @xmath23 , @xmath24 , @xmath25 , @xmath26 and @xmath27 and obtain @xmath28dz . \label{phase}\ ] ] @xmath29 we look for phase - locked solutions of eq . ( [ phase ] ) that have the form : @xmath30 these solutions are _ phase - locked _ , in the sense that the difference of the phases at two fixed locations in space does not change in time @xcite . they can describe spatially uniform equilibria ( @xmath31 , spatial patterns ( @xmath32 @xmath33 ) , synchronous oscillations ( @xmath34 , @xmath35 ) , or traveling waves ( @xmath34 , @xmath33 ) . notice that @xmath36needs to be an integer because of periodic boundary conditions , and the value of @xmath37 can be taken to be zero by a translation . it is useful to first look at the undelayed case ( @xmath38 ) . substitution of ( [ sol ] ) into ( [ phase ] ) gives the relation between the temporal frequency @xmath39 and the wave number @xmath40 as@xmath41 where @xmath42 @xmath43 denotes the discrete cosine transform of @xmath44 . note that the role of @xmath45 is simply to shift the value of @xmath39 , so it can be taken to be zero without loss of generality ( we will see later that this is no longer true in the presence of delays ) . when @xmath46 , @xmath39 is identical to the individual oscillator frequency @xmath45 . more generally , for @xmath47 , ( [ nodelay - omega2 ] ) yields a unique @xmath48 for any given @xmath49 . hence there exists a countably infinite set of solutions @xmath50 , @xmath49 , of ( [ phase ] ) . the condition for spatial patterns with wave number @xmath40 is@xmath51 and can only be satisfied if @xmath52 is not too small . generically , however , the value of @xmath39 from ( [ nodelay - omega2 ] ) is nonzero , so the set @xmath53 includes a unique synchronous solution ( @xmath35 ) and the rest correspond to traveling waves ( @xmath33 ) , with wave speed equal to @xmath54 . it turns out that in general only a few of the solutions @xmath55 can be stable . the linear stability is determined by the variational equation @xmath56dz\nonumber\end{aligned}\ ] ] where @xmath57 . with the ansatz @xmath58 , @xmath59 , @xmath60 , we have@xmath61 after some simplification and using the fact that @xmath44 is an even function , one obtains@xmath62 note that the pair @xmath63 is always a solution , corresponding to the rotational symmetry of the solutions ( [ sol ] ) . hence , @xmath55 is linearly asymptotically stable if and only if the right hand side of ( [ nodelay - lambda ] ) is negative for all nonzero integers @xmath64 . for instance , if @xmath65 has a global maximum ( respectively , minimum ) at @xmath40 , then the corresponding solution @xmath55 is stable provided @xmath66 ( resp . , @xmath67 ) . furthermore , if @xmath68 for all @xmath69 , then @xmath55 is the only stable phase - locked solution ( up to a phase shift ) for @xmath66 . in particular , if the coupling kernel is constant ( that is , @xmath70 iff @xmath35 ) or has a predominant constant component ( @xmath71 @xmath72 , @xmath73 @xmath74 ) , then the synchronous solution @xmath75 is the only stable phase - locked solution ( up to a phase shift ) for @xmath66 , which explains the widespread use of globally coupled oscillators in synchronization studies . we now show that the inclusion of propagation delays offers a much richer solution structure . we again seek solutions @xmath55 of the form ( [ sol ] ) when the propagation velocity @xmath9 is finite . the relation ( [ nodelay - omega2 ] ) between the temporal frequency and the wave number now takes the form @xmath76 \,dz,\label{delay - omega}%\ ] ] which is an implicit equation in @xmath39 . note that the right hand side is a bounded and continuous function of @xmath39 ; therefore , ( [ delay - omega ] ) has a solution @xmath39 for each @xmath49 . however , in contrast to the undelayed case , it is now possible to have several solutions @xmath39 for a given wave number @xmath77 ( note , however , that the condition for spatial patterns ( [ pattern - cond ] ) remains identical to the undelayed case . ) furthermore , the linear stability of the phase - locked solutions @xmath55 is determined through a dispersion relation @xmath78 as before , linear stability requires @xmath79 for all solutions @xmath80 of ( [ delay - lambda ] ) for all nonzero integers @xmath64 . the main difference with the undelayed case ( [ nodelay - lambda ] ) is that ( [ delay - lambda ] ) is an implicit equation in @xmath80 , so its solution is not straightforward . furthermore , even for a fixed value of @xmath60 , ( [ delay - lambda ] ) generally has an infinite number of solutions for @xmath80 . for simplicity we take @xmath46 and carry out the integration in equation ( [ delay - omega ] ) for @xmath35 to get an analytical equation for the synchronous solutions @xmath39 as : @xmath81 , \label{eqlbm}\end{aligned}\ ] ] which is an implicit equation in @xmath39 . being a transcendental equation its solution can in principle be multi - valued in @xmath39 for a given set of parameters @xmath82 and @xmath83 and can lead to higher branches of collective frequencies as pointed out by schuster and wagner @xcite for a system of two coupled oscillators . a similar ( much lengthier ) analytical expression can also be obtained for finite values of @xmath40 which we do not write here . we further define a mean delay parameter by @xmath84 which weights the individual delays with the corresponding connection weights . with the exponential connectivity given by eq . ( [ kernel ] ) , this translates into @xmath85 this gives values for the limiting cases : @xmath86 for local ( @xmath87 ) and @xmath88 for global ( @xmath89 ) coupling . 1(a ) and fig 1(b ) show plots of the numerical solutions of the equilibrium relations for @xmath39 as a function of @xmath90 for traveling wave with @xmath91and for synchronous ( @xmath35 ) states respectively . in both cases the value of @xmath83 is taken to be @xmath92 and the plots are obtained for several values of @xmath45 . in these figures as the curves for @xmath93 show , it is possible to have multiple solutions @xmath39 for a given value of @xmath90 . the stability of these higher states will be discussed in later sections of the paper . one also notes that the lowest branch shows frequency suppression as a function of the mean time delay @xmath90 . [ c]cc of the phase - locked solutions given by of eq . ( [ delay - omega ] ) is plotted as a function of the mean time delay @xmath90 for @xmath94 and @xmath95 . the panel ( a ) on the left is for the travelling wave number @xmath91 whereas the panel ( b ) on right is for synchronous solutions with @xmath35 . the different curves correspond to different values of the intrinsic oscillator frequency @xmath45 . the solid portions denote stable states and the dotted ones ( in red ) unstable states in panel ( b).,title="fig:",scaledwidth=50.0% ] & of the phase - locked solutions given by of eq . ( [ delay - omega ] ) is plotted as a function of the mean time delay @xmath90 for @xmath94 and @xmath95 . the panel ( a ) on the left is for the travelling wave number @xmath91 whereas the panel ( b ) on right is for synchronous solutions with @xmath35 . the different curves correspond to different values of the intrinsic oscillator frequency @xmath45 . the solid portions denote stable states and the dotted ones ( in red ) unstable states in panel ( b).,title="fig:",scaledwidth=50.0% ] we now examine the stability of the synchronous solutions @xcite , @xmath96 by using the eigenvalue equation ( [ delay - lambda ] ) obtained in the previous section . writing @xmath97 and separating eq . ( [ delay - lambda ] ) into its real and imaginary parts we get @xmath98dz,\label{lambda_r}\\ \lambda_i & = -\int_{-1}^{1}g(z)\cos\left ( \omega |z|\tau_{m}\right)e^{-\lambda_r|z|\tau_{m}}\sin\left(\lambda_i|z|\tau_{m } + \pi nz\right)dz.\label{lambda_i}\end{aligned}\ ] ] since the perturbations @xmath99 corresponding to @xmath100 again yield synchronous solutions , the linear stability of the synchronous state requires that all solutions of eq . ( [ delay - lambda ] ) have @xmath101 for all non - zero integer values of @xmath64 . the marginal stability curve in the parameter space of @xmath102 is defined by @xmath103 and in principle can be obtained by setting @xmath103 in eq . ( [ lambda_r ] ) , solving it for @xmath104 and substituting it in eq . ( [ lambda_i ] ) . in practice it is not possible to carry out such a procedure analytically for the integral eqs . @xmath105 and one needs to adopt a numerical approach , which is discussed in the next section . to systematically determine the eigenvalues of eq . ( [ delay - lambda ] ) in a given region of the complex plane we use multiple methods in a complementary fashion . first , eq . ( [ eqlbm ] ) is solved for @xmath39 for a given set of values of the parameters @xmath83 , @xmath45 and @xmath106 . following that , we need to determine the complex zeros of the function @xmath107 defined as @xmath108 which is equivalent to finding solutions @xmath80 of ( [ delay - lambda ] ) . to do this we have primarily relied on the numerical technique developed by delves and lyness @xcite based on the cauchy s argument principle . by this principle the number of unstable roots @xmath109 of @xmath107 is given by @xmath110 where the closed contour @xmath0 encloses a domain in the right half of the complex @xmath80 plane with the imaginary axis forming its left boundary . once we get a finite number for @xmath109 we further trace the location of the roots by plotting the zero value contour lines of the real and imaginary parts of the function @xmath107 in a finite region of the complex plane @xmath111 . the intersections of the two sets of contours locate all the eigenvalues of eq . ( [ delay - lambda ] ) in the given region of the complex plane . the computations are done on a fine enough grid ( typically @xmath112 ) to get a good resolution . a systematic scan for unstable roots is made by repeating the above procedure for many values of the perturbation number @xmath64 and by gradually extending the region of the complex plane . we have made extensive use of _ mathematica _ in obtaining the numerical results on the stability of the synchronous states . in fig . [ fig : fig1 ] the solid portion of the curve shows the stable synchronous states of eq . ( [ phase ] ) for @xmath94 and for various values of @xmath45 and @xmath90 . the terminal point on a given solid curve of @xmath39 _ vs _ @xmath90 marks the marginal stability point . the marginal stability point is seen to shift towards larger values of @xmath90 as one moves down to curves with lower values of @xmath45 . ) for the synchronous oscillation frequency for several values of @xmath83 , plotted in terms of @xmath113 versus @xmath114 . note that @xmath115 for the equilibrium solutions ( see eq.([h ] ) ) . in this representation , the different curves of fig.1 corresponding to different values of @xmath45 collapse onto a single curve for a given value of @xmath83 . the solid ( black ) portions of the curves correspond to stable synchronous states and the dotted ones ( red ) to unstable synchronous states.,title="fig:",scaledwidth=80.0% ] .0 cm a more compact representation is obtained if one plots @xmath116 versus @xmath117 , since in this case the solutions corresponding to different values of @xmath45 for a given @xmath83 consolidate onto a single curve , as shown in fig . [ fig : fig2 ] for @xmath118 and @xmath119 respectively . it is seen from both figures that the stability domains of the synchronous solutions are restricted to the lowest branch where the curves are decreasing . this suggests a heuristic necessary ( but not sufficient ) condition for stability of the synchronous solutions : from fig . [ fig : fig1 ] we have that @xmath120 for stable synchronous solutions , and from eq . ( [ eqlbm ] ) we calculate @xmath121 where @xmath122 and @xmath123 since @xmath124 and @xmath125 is bounded , the denominator in eq . ( [ d - omega ] ) is positive for small values of @xmath90 . hence , for positive @xmath39 , the requirement @xmath120 implies the condition @xmath126 , that is , @xmath127 an alternative approach to arrive at the necessary condition ( eq.[nec_cond ] ) would be to make use of the results presented in fig.[fig : fig2 ] . we recast the dispersion relation given by eq.([eqlbm ] ) in the form : @xmath128 where @xmath129 it is seen from fig.[fig : fig2 ] that the stability domain of the synchronous solutions is restricted to the lowest branch where the curves have a negative slope . this again suggests a heuristic necessary condition for stability of the synchronous solutions to be @xmath130 leading to the necessary condition given by eq.([nec_cond ] ) . the prime indicates a derivative of @xmath131 @xmath132 @xmath114 . as we will see later , the marginal stability curve obtained from @xmath133 or @xmath134 does lie above the true marginal stability curve ( see fig . [ fig : fig4 ] ) , confirming that condition ( [ nec_cond ] ) is necessary but not sufficient for the stability of synchronous states . [ cols="^,^ " , ] the points where solid and dotted lines meet in the curves of fig . [ fig : fig2 ] mark the marginal stability point for the respective @xmath83 values . these points are obtained for a range of @xmath83 values and are plotted in ( @xmath135 ) space in fig . [ fig : fig3 ] by filled points . they all lie on a single curve , which is analytically derived below . our numerical results further reveal that for the marginal stability points , the imaginary part of the eigenvalue of the mode is zero in other words the mode loses stability through a saddle - node bifurcation . it can easily be checked by inspection that @xmath136 is one of the solutions of eq . ( [ lambda_i ] ) for any value of @xmath137 ; however , it is not evident analytically that this is the only possible solution for @xmath103 , and our numerical results have helped us confirm that this is indeed the case . hence , putting @xmath138 in eq . ( [ lambda_r ] ) we get the following integral relation between the parameters @xmath139 and @xmath83 . @xmath140dz = 0 \label{marg_stab}\ ] ] further , we have also observed that the most unstable perturbation is the one with the lowest mode number , namely @xmath141 . therefore eq . ( [ marg_stab ] ) with @xmath141 defines the marginal stability curve , so the condition for synchronization takes the form @xmath142dz > 0 \label{marg_stab2}\ ] ] the solid line in fig . [ fig : fig3 ] is the analytical curve of marginal stability defined by setting the left side of eq . ( [ marg_stab2 ] ) to zero , and it can be seen that the numerically calculated marginal values ( represented by points ) fit this curve perfectly . the figure also shows the stability curves obtained for the @xmath143 and @xmath144 perturbations ( dashed and dotted lines , respectively ) and these are seen to lie above the @xmath141 marginal stability curve . we have carried out a numerical check for a whole range of higher @xmath64 numbers and the results are consistent with the above findings . for a system with constant delay @xmath145 ( i.e. if @xmath146 is replaced by @xmath145 in eq . ( [ phase ] ) ) , the @xmath147 term can be taken outside of the integral in ( [ marg_stab2 ] ) and the remaining integrand is nonnegative . hence , the synchronization condition in this case becomes simply @xmath148 this agrees with the results obtained previously for constant - delay systems @xcite.thus our result , as given by eq . ( [ marg_stab ] ) , generalizes the condition ( [ strogatz - cond ] ) to systems with space - dependent delays , and shows a nontrivial relation between the spatial connectivity and delays for the latter case . in order to gain some intuition into the complex interaction between connectivity and delays , we have obtained an approximate expression for the marginal stability curve by a numerical fitting procedure , yielding the relation @xmath149 for the stability of synchronous oscillations . here , the left side involves the temporal scales of the dynamics ( namely , it is the average time delay normalized by the oscillation period of the synchronized solution ) while the right hand side involves the spatial scales of connectivity . in this view , the synchronization condition is a balance between the temporal and spatial scales . for high connectivity ( @xmath89 ) , the system can tolerate higher average delays in maintaining synchrony , and the largest allowable delays decrease roughly exponentially as the spatial connectivity is decreased . in the same figure we have also plotted with dotted curve the approximate condition ( [ nec_cond ] ) , which is found to lie above the marginal stability curve in the entire range of @xmath83 . the disparity between the two curves becomes particularly noticeable at large values of @xmath83 . since the marginal stability curve given by the condition eq . ( [ marg_stab2 ] ) is an analytical one , one can obtain the limiting values of the phase shifts ( @xmath114 ) in the global ( @xmath89 ) as well as in the local limits ( @xmath87 ) . they are given as : @xmath150 in the case of global coupling and @xmath151 in the case of local coupling . similarly one can obtain the limits on the frequency depression for the stability of the corresponding synchronous state in the two limiting cases ( see fig . [ fig : fig2 ] ) . in the case of global coupling the condition becomes : @xmath152 whereas in the case of local coupling the condition is : @xmath153 we note from fig . [ fig : fig2 ] that the disparity between @xmath39 and @xmath45 ( @xmath154 ) increases with delay induced phase shifts ( @xmath114 ) and at some critical point the synchronous state becomes unstable . the value of the disparity at this critical juncture is larger for higher connectivity ( global ) and smaller for lesser connectivity ( local ) as we see from above . we have investigated the existence and stability of the synchronous solutions of a continuum of nonlocally coupled phase oscillators with distance - dependent time delays . our model system is a generalization of the original kuramoto model by the inclusion of naturally occurring propagation delays . the existence regions of the equilibrium synchronous and traveling wave solutions of this system are delineated . the equilibrium solutions of the lowest branch are seen to exhibit frequency suppression as a function of the mean time delay . we have carried out a linear stability analysis of the synchronous solutions and obtained a comprehensive marginal stability curve in the parameter domain of the system . our numerical results show that the synchronous states become unstable via a saddle - node bifurcation process and the most unstable perturbation corresponds to an @xmath141 ( or kink type ) spatial perturbation on the ring of oscillators . these findings allow us to define an analytic relation , given by eq . ( [ marg_stab2 ] ) , as a condition for synchronization . we have also obtained approximate forms for the synchronization condition that provides a convenient means of assessing the stability of synchronous states . our results indicate an intricate relation between synchronization and connectivity in spatially extended systems with time delays . a detailed analysis of the stability of traveling wave solutions is currently in progress and will be reported later . y. kuramoto , in _ international symposium on mathematical problems in theoretical physics _ , lecture notes in physics vol . 39 , edited by h. araki ( springer - verlag , berlin , 1975 ) ; _ chemical oscillations , waves , and turbulence _ ( springer - verlag , berlin , 1984 ) .

we investigate phase - locked solutions of a continuum field of nonlocally coupled identical phase oscillators with distance - dependent propagation delays . equilibrium relations for both synchronous and traveling wave solutions in the parameter space characterizing the non - locality and time delay are delineated . for the synchronous states a comprehensive stability diagram is presented that provides a heuristic synchronization condition as well as an analytic relation for the marginal stability curve . the relation yields simple stability expressions in the limiting cases of local and global coupling of the phase oscillators .

<s>[INST]an ensemble of coupled phase oscillators provides a simple yet powerful paradigm for studying the collective behaviour of many complex real life systems and has been extensively studied in this context@xcite . under appropriate conditions , phase oscillators can exhibit stable in - phase synchronous or other type of phase - locked solutions @xcite . in a class of discrete networks of oscillators it has been shown that in - phase synchronous behavior can be achieved even in the presence of a fixed signal transmission delay @xcite . more intricate dynamics have been discovered in nonlocally coupled continuous networks , whereby phase - locked and incoherent activity can simultaneously exist at different spatial locations @xcite , giving rise to a spatio - temporal pattern that has been termed as a _ chimera state _ @xcite . in this paper , we discuss the existence and stability of phase - locked solutions in a continuum of nonlocally coupled identical phase oscillators with distance - dependent delays . such delays are a natural consequence of the finite speed of information propagation in space . in similar contexts , distance - dependent delays have been considered in continuum models of neural activity @xcite . in particular , the effects of distributed delays can be very different from fixed delays @xcite , and the analysis is generally more difficult . we consider a continuum of identical phase oscillators , arranged on a circular ring @xmath0 and labeled by @xmath1 $ ] with periodic boundary conditions , whose dynamics is governed by @xmath2dz , \label{pha}\ ] ] where @xmath3 is the phase of the oscillator at location @xmath4 and time @xmath5 , whose intrinsic oscillation frequency is @xmath6 , @xmath7 is the coupling strength and @xmath8\rightarrow\mathbb{r}$ ] is an even function describing the coupling kernel . the quantity @xmath9 denotes the signal propagation speed which gives rise to a time delay of @xmath10 for distance @xmath11 from the locations @xmath4 . as the oscillators are located on a ring with circumference @xmath12 , the distance between any two oscillators is given by the shorter of the euclidean distance between them along the ring . in this configuration , the maximum distance between the coupled oscillators is @xmath13 and thus the maximum time delay would be @xmath14 . if we denote the location of any two oscillators as @xmath4 and @xmath15 then @xmath16 . @xmath17 is a parameter which makes the coupling phase - shifted and has been crucial for observing chimera states . we choose the coupling kernel @xmath18 to have an exponentially decaying nature and its normalized form is taken to be @xmath19 where @xmath20 is the inverse of the interaction scale length and is a measure of the nonlocality of the coupling . the exponential form of @xmath18 and the @xmath21 coupling function are the natural consequences of the reduction of a more general reaction - diffusion system to a phase model under nonlocal and weak coupling limits @xcite . we further make time and space dimensionless in eqs.([pha ] ) and ( [ ker ] ) by the transformations @xmath22 , @xmath23 , @xmath24 , @xmath25 , @xmath26 and @xmath27 and obtain @xmath28dz . \label{phase}\ ] ] @xmath29 we look for phase - locked solutions of eq . ( [ phase ] ) that have the form : @xmath30 these solutions are _ phase - locked _ , in the sense that the difference of the phases at two fixed locations in space does not change in time @xcite . they can describe spatially uniform equilibria ( @xmath31 , spatial patterns ( @xmath32 @xmath33 ) , synchronous oscillations ( @xmath34 , @xmath35 ) , or traveling waves ( @xmath34 , @xmath33 ) . notice that @xmath36needs to be an integer because of periodic boundary conditions , and the value of @xmath37 can be taken to be zero by a translation . it is useful to first look at the undelayed case ( @xmath38 ) . substitution of ( [ sol ] ) into ( [ phase ] ) gives the relation between the temporal frequency @xmath39 and the wave number @xmath40 as@xmath41 where @xmath42 @xmath43 denotes the discrete cosine transform of @xmath44 . note that the role of @xmath45 is simply to shift the value of @xmath39 , so it can be taken to be zero without loss of generality ( we will see later that this is no longer true in the presence of delays ) . when @xmath46 , @xmath39 is identical to the individual oscillator frequency @xmath45 . more generally , for @xmath47 , ( [ nodelay - omega2 ] ) yields a unique @xmath48 for any given @xmath49 . hence there exists a countably infinite set of solutions @xmath50 , @xmath49 , of ( [ phase ] ) . the condition for spatial patterns with wave number @xmath40 is@xmath51 and can only be satisfied if @xmath52 is not too small . generically , however , the value of @xmath39 from ( [ nodelay - omega2 ] ) is nonzero , so the set @xmath53 includes a unique synchronous solution ( @xmath35 ) and the rest correspond to traveling waves ( @xmath33 ) , with wave speed equal to @xmath54 . it turns out that in general only a few of the solutions @xmath55 can be stable . the linear stability is determined by the variational equation @xmath56dz\nonumber\end{aligned}\ ] ] where @xmath57 . with the ansatz @xmath58 , @xmath59 , @xmath60 , we have@xmath61 after some simplification and using the fact that @xmath44 is an even function , one obtains@xmath62 note that the pair @xmath63 is always a solution , corresponding to the rotational symmetry of the solutions ( [ sol ] ) . hence , @xmath55 is linearly asymptotically stable if and only if the right hand side of ( [ nodelay - lambda ] ) is negative for all nonzero integers @xmath64 . for instance , if @xmath65 has a global maximum ( respectively , minimum ) at @xmath40 , then the corresponding solution @xmath55 is stable provided @xmath66 ( resp . , @xmath67 ) . furthermore , if @xmath68 for all @xmath69 , then @xmath55 is the only stable phase - locked solution ( up to a phase shift ) for @xmath66 . in particular , if the coupling kernel is constant ( that is , @xmath70 iff @xmath35 ) or has a predominant constant component ( @xmath71 @xmath72 , @xmath73 @xmath74 ) , then the synchronous solution @xmath75 is the only stable phase - locked solution ( up to a phase shift ) for @xmath66 , which explains the widespread use of globally coupled oscillators in synchronization studies . we now show that the inclusion of propagation delays offers a much richer solution structure . we again seek solutions @xmath55 of the form ( [ sol ] ) when the propagation velocity @xmath9 is finite . the relation ( [ nodelay - omega2 ] ) between the temporal frequency and the wave number now takes the form @xmath76 \,dz,\label{delay - omega}%\ ] ] which is an implicit equation in @xmath39 . note that the right hand side is a bounded and continuous function of @xmath39 ; therefore , ( [ delay - omega ] ) has a solution @xmath39 for each @xmath49 . however , in contrast to the undelayed case , it is now possible to have several solutions @xmath39 for a given wave number @xmath77 ( note , however , that the condition for spatial patterns ( [ pattern - cond ] ) remains identical to the undelayed case . ) furthermore , the linear stability of the phase - locked solutions @xmath55 is determined through a dispersion relation @xmath78 as before , linear stability requires @xmath79 for all solutions @xmath80 of ( [ delay - lambda ] ) for all nonzero integers @xmath64 . the main difference with the undelayed case ( [ nodelay - lambda ] ) is that ( [ delay - lambda ] ) is an implicit equation in @xmath80 , so its solution is not straightforward . furthermore , even for a fixed value of @xmath60 , ( [ delay - lambda ] ) generally has an infinite number of solutions for @xmath80 . for simplicity we take @xmath46 and carry out the integration in equation ( [ delay - omega ] ) for @xmath35 to get an analytical equation for the synchronous solutions @xmath39 as : @xmath81 , \label{eqlbm}\end{aligned}\ ] ] which is an implicit equation in @xmath39 . being a transcendental equation its solution can in principle be multi - valued in @xmath39 for a given set of parameters @xmath82 and @xmath83 and can lead to higher branches of collective frequencies as pointed out by schuster and wagner @xcite for a system of two coupled oscillators . a similar ( much lengthier ) analytical expression can also be obtained for finite values of @xmath40 which we do not write here . we further define a mean delay parameter by @xmath84 which weights the individual delays with the corresponding connection weights . with the exponential connectivity given by eq . ( [ kernel ] ) , this translates into @xmath85 this gives values for the limiting cases : @xmath86 for local ( @xmath87 ) and @xmath88 for global ( @xmath89 ) coupling . 1(a ) and fig 1(b ) show plots of the numerical solutions of the equilibrium relations for @xmath39 as a function of @xmath90 for traveling wave with @xmath91and for synchronous ( @xmath35 ) states respectively . in both cases the value of @xmath83 is taken to be @xmath92 and the plots are obtained for several values of @xmath45 . in these figures as the curves for @xmath93 show , it is possible to have multiple solutions @xmath39 for a given value of @xmath90 . the stability of these higher states will be discussed in later sections of the paper . one also notes that the lowest branch shows frequency suppression as a function of the mean time delay @xmath90 . [ c]cc of the phase - locked solutions given by of eq . ( [ delay - omega ] ) is plotted as a function of the mean time delay @xmath90 for @xmath94 and @xmath95 . the panel ( a ) on the left is for the travelling wave number @xmath91 whereas the panel ( b ) on right is for synchronous solutions with @xmath35 . the different curves correspond to different values of the intrinsic oscillator frequency @xmath45 . the solid portions denote stable states and the dotted ones ( in red ) unstable states in panel ( b).,title="fig:",scaledwidth=50.0% ] & of the phase - locked solutions given by of eq . ( [ delay - omega ] ) is plotted as a function of the mean time delay @xmath90 for @xmath94 and @xmath95 . the panel ( a ) on the left is for the travelling wave number @xmath91 whereas the panel ( b ) on right is for synchronous solutions with @xmath35 . the different curves correspond to different values of the intrinsic oscillator frequency @xmath45 . the solid portions denote stable states and the dotted ones ( in red ) unstable states in panel ( b).,title="fig:",scaledwidth=50.0% ] we now examine the stability of the synchronous solutions @xcite , @xmath96 by using the eigenvalue equation ( [ delay - lambda ] ) obtained in the previous section . writing @xmath97 and separating eq . ( [ delay - lambda ] ) into its real and imaginary parts we get @xmath98dz,\label{lambda_r}\\ \lambda_i & = -\int_{-1}^{1}g(z)\cos\left ( \omega |z|\tau_{m}\right)e^{-\lambda_r|z|\tau_{m}}\sin\left(\lambda_i|z|\tau_{m } + \pi nz\right)dz.\label{lambda_i}\end{aligned}\ ] ] since the perturbations @xmath99 corresponding to @xmath100 again yield synchronous solutions , the linear stability of the synchronous state requires that all solutions of eq . ( [ delay - lambda ] ) have @xmath101 for all non - zero integer values of @xmath64 . the marginal stability curve in the parameter space of @xmath102 is defined by @xmath103 and in principle can be obtained by setting @xmath103 in eq . ( [ lambda_r ] ) , solving it for @xmath104 and substituting it in eq . ( [ lambda_i ] ) . in practice it is not possible to carry out such a procedure analytically for the integral eqs . @xmath105 and one needs to adopt a numerical approach , which is discussed in the next section . to systematically determine the eigenvalues of eq . ( [ delay - lambda ] ) in a given region of the complex plane we use multiple methods in a complementary fashion . first , eq . ( [ eqlbm ] ) is solved for @xmath39 for a given set of values of the parameters @xmath83 , @xmath45 and @xmath106 . following that , we need to determine the complex zeros of the function @xmath107 defined as @xmath108 which is equivalent to finding solutions @xmath80 of ( [ delay - lambda ] ) . to do this we have primarily relied on the numerical technique developed by delves and lyness @xcite based on the cauchy s argument principle . by this principle the number of unstable roots @xmath109 of @xmath107 is given by @xmath110 where the closed contour @xmath0 encloses a domain in the right half of the complex @xmath80 plane with the imaginary axis forming its left boundary . once we get a finite number for @xmath109 we further trace the location of the roots by plotting the zero value contour lines of the real and imaginary parts of the function @xmath107 in a finite region of the complex plane @xmath111 . the intersections of the two sets of contours locate all the eigenvalues of eq . ( [ delay - lambda ] ) in the given region of the complex plane . the computations are done on a fine enough grid ( typically @xmath112 ) to get a good resolution . a systematic scan for unstable roots is made by repeating the above procedure for many values of the perturbation number @xmath64 and by gradually extending the region of the complex plane . we have made extensive use of _ mathematica _ in obtaining the numerical results on the stability of the synchronous states . in fig . [ fig : fig1 ] the solid portion of the curve shows the stable synchronous states of eq . ( [ phase ] ) for @xmath94 and for various values of @xmath45 and @xmath90 . the terminal point on a given solid curve of @xmath39 _ vs _ @xmath90 marks the marginal stability point . the marginal stability point is seen to shift towards larger values of @xmath90 as one moves down to curves with lower values of @xmath45 . ) for the synchronous oscillation frequency for several values of @xmath83 , plotted in terms of @xmath113 versus @xmath114 . note that @xmath115 for the equilibrium solutions ( see eq.([h ] ) ) . in this representation , the different curves of fig.1 corresponding to different values of @xmath45 collapse onto a single curve for a given value of @xmath83 . the solid ( black ) portions of the curves correspond to stable synchronous states and the dotted ones ( red ) to unstable synchronous states.,title="fig:",scaledwidth=80.0% ] .0 cm a more compact representation is obtained if one plots @xmath116 versus @xmath117 , since in this case the solutions corresponding to different values of @xmath45 for a given @xmath83 consolidate onto a single curve , as shown in fig . [ fig : fig2 ] for @xmath118 and @xmath119 respectively . it is seen from both figures that the stability domains of the synchronous solutions are restricted to the lowest branch where the curves are decreasing . this suggests a heuristic necessary ( but not sufficient ) condition for stability of the synchronous solutions : from fig . [ fig : fig1 ] we have that @xmath120 for stable synchronous solutions , and from eq . ( [ eqlbm ] ) we calculate @xmath121 where @xmath122 and @xmath123 since @xmath124 and @xmath125 is bounded , the denominator in eq . ( [ d - omega ] ) is positive for small values of @xmath90 . hence , for positive @xmath39 , the requirement @xmath120 implies the condition @xmath126 , that is , @xmath127 an alternative approach to arrive at the necessary condition ( eq.[nec_cond ] ) would be to make use of the results presented in fig.[fig : fig2 ] . we recast the dispersion relation given by eq.([eqlbm ] ) in the form : @xmath128 where @xmath129 it is seen from fig.[fig : fig2 ] that the stability domain of the synchronous solutions is restricted to the lowest branch where the curves have a negative slope . this again suggests a heuristic necessary condition for stability of the synchronous solutions to be @xmath130 leading to the necessary condition given by eq.([nec_cond ] ) . the prime indicates a derivative of @xmath131 @xmath132 @xmath114 . as we will see later , the marginal stability curve obtained from @xmath133 or @xmath134 does lie above the true marginal stability curve ( see fig . [ fig : fig4 ] ) , confirming that condition ( [ nec_cond ] ) is necessary but not sufficient for the stability of synchronous states . [ cols="^,^ " , ] the points where solid and dotted lines meet in the curves of fig . [ fig : fig2 ] mark the marginal stability point for the respective @xmath83 values . these points are obtained for a range of @xmath83 values and are plotted in ( @xmath135 ) space in fig . [ fig : fig3 ] by filled points . they all lie on a single curve , which is analytically derived below . our numerical results further reveal that for the marginal stability points , the imaginary part of the eigenvalue of the mode is zero in other words the mode loses stability through a saddle - node bifurcation . it can easily be checked by inspection that @xmath136 is one of the solutions of eq . ( [ lambda_i ] ) for any value of @xmath137 ; however , it is not evident analytically that this is the only possible solution for @xmath103 , and our numerical results have helped us confirm that this is indeed the case . hence , putting @xmath138 in eq . ( [ lambda_r ] ) we get the following integral relation between the parameters @xmath139 and @xmath83 . @xmath140dz = 0 \label{marg_stab}\ ] ] further , we have also observed that the most unstable perturbation is the one with the lowest mode number , namely @xmath141 . therefore eq . ( [ marg_stab ] ) with @xmath141 defines the marginal stability curve , so the condition for synchronization takes the form @xmath142dz > 0 \label{marg_stab2}\ ] ] the solid line in fig . [ fig : fig3 ] is the analytical curve of marginal stability defined by setting the left side of eq . ( [ marg_stab2 ] ) to zero , and it can be seen that the numerically calculated marginal values ( represented by points ) fit this curve perfectly . the figure also shows the stability curves obtained for the @xmath143 and @xmath144 perturbations ( dashed and dotted lines , respectively ) and these are seen to lie above the @xmath141 marginal stability curve . we have carried out a numerical check for a whole range of higher @xmath64 numbers and the results are consistent with the above findings . for a system with constant delay @xmath145 ( i.e. if @xmath146 is replaced by @xmath145 in eq . ( [ phase ] ) ) , the @xmath147 term can be taken outside of the integral in ( [ marg_stab2 ] ) and the remaining integrand is nonnegative . hence , the synchronization condition in this case becomes simply @xmath148 this agrees with the results obtained previously for constant - delay systems @xcite.thus our result , as given by eq . ( [ marg_stab ] ) , generalizes the condition ( [ strogatz - cond ] ) to systems with space - dependent delays , and shows a nontrivial relation between the spatial connectivity and delays for the latter case . in order to gain some intuition into the complex interaction between connectivity and delays , we have obtained an approximate expression for the marginal stability curve by a numerical fitting procedure , yielding the relation @xmath149 for the stability of synchronous oscillations . here , the left side involves the temporal scales of the dynamics ( namely , it is the average time delay normalized by the oscillation period of the synchronized solution ) while the right hand side involves the spatial scales of connectivity . in this view , the synchronization condition is a balance between the temporal and spatial scales . for high connectivity ( @xmath89 ) , the system can tolerate higher average delays in maintaining synchrony , and the largest allowable delays decrease roughly exponentially as the spatial connectivity is decreased . in the same figure we have also plotted with dotted curve the approximate condition ( [ nec_cond ] ) , which is found to lie above the marginal stability curve in the entire range of @xmath83 . the disparity between the two curves becomes particularly noticeable at large values of @xmath83 . since the marginal stability curve given by the condition eq . ( [ marg_stab2 ] ) is an analytical one , one can obtain the limiting values of the phase shifts ( @xmath114 ) in the global ( @xmath89 ) as well as in the local limits ( @xmath87 ) . they are given as : @xmath150 in the case of global coupling and @xmath151 in the case of local coupling . similarly one can obtain the limits on the frequency depression for the stability of the corresponding synchronous state in the two limiting cases ( see fig . [ fig : fig2 ] ) . in the case of global coupling the condition becomes : @xmath152 whereas in the case of local coupling the condition is : @xmath153 we note from fig . [ fig : fig2 ] that the disparity between @xmath39 and @xmath45 ( @xmath154 ) increases with delay induced phase shifts ( @xmath114 ) and at some critical point the synchronous state becomes unstable . the value of the disparity at this critical juncture is larger for higher connectivity ( global ) and smaller for lesser connectivity ( local ) as we see from above . we have investigated the existence and stability of the synchronous solutions of a continuum of nonlocally coupled phase oscillators with distance - dependent time delays . our model system is a generalization of the original kuramoto model by the inclusion of naturally occurring propagation delays . the existence regions of the equilibrium synchronous and traveling wave solutions of this system are delineated . the equilibrium solutions of the lowest branch are seen to exhibit frequency suppression as a function of the mean time delay . we have carried out a linear stability analysis of the synchronous solutions and obtained a comprehensive marginal stability curve in the parameter domain of the system . our numerical results show that the synchronous states become unstable via a saddle - node bifurcation process and the most unstable perturbation corresponds to an @xmath141 ( or kink type ) spatial perturbation on the ring of oscillators . these findings allow us to define an analytic relation , given by eq . ( [ marg_stab2 ] ) , as a condition for synchronization . we have also obtained approximate forms for the synchronization condition that provides a convenient means of assessing the stability of synchronous states . our results indicate an intricate relation between synchronization and connectivity in spatially extended systems with time delays . a detailed analysis of the stability of traveling wave solutions is currently in progress and will be reported later . y. kuramoto , in _ international symposium on mathematical problems in theoretical physics _ , lecture notes in physics vol . 39 , edited by h. araki ( springer - verlag , berlin , 1975 ) ; _ chemical oscillations , waves , and turbulence _ ( springer - verlag , berlin , 1984 ) .[/INST] we investigate phase - locked solutions of a continuum field of nonlocally coupled identical phase oscillators with distance - dependent propagation delays . equilibrium relations for both synchronous and traveling wave solutions in the parameter space characterizing the non - locality and time delay are delineated . for the synchronous states a comprehensive stability diagram is presented that provides a heuristic synchronization condition as well as an analytic relation for the marginal stability curve . the relation yields simple stability expressions in the limiting cases of local and global coupling of the phase oscillators . </s>

x - linked retinoschisis ( xlrs ) is a bilateral progressive disease of the retina that is likely present at birth and progresses as the child ages . it is associated with a mutation of the xlrs1 gene located on the short arm of the x chromosome , xp22,1 and is clinically characterized by cystoid changes of the fovea arranged in a stellate pattern.2 several publications describing the optical coherence tomography ( oct ) characteristics of xlrs have noted different findings for this condition . splitting in the nerve fiber layer ( nfl ) attributed to mueller cell dysfunction was noted on histological studies3 and was observed in vivo with oct by eriksson et al.4 additionally , groups have described splitting in retinal layers deep to the nfl with oct.57 a 13-year - old african - american boy ( case 1 ) presented for evaluation of decreased vision . the patient s mother reported that the boy had experienced poor vision for many years . his best - corrected visual acuity was 20/200 od and 20/400 os with no improvement on manifest refraction or pinhole testing . the fundus ( figure 1 ) and spectral domain optical coherence tomography ( sd - oct ) ( figure 2 ) exams demonstrated findings consistent with xlrs . the boy s 14-year - old brother ( case 2 ) was examined and found to have a best - corrected visual acuity of 20/400 od and 20/40 os without improvement on manifest refraction or pinhole testing . the mother reported that this sibling had experienced poor vision for the past 7 years and that his sensory exotropia had also existed for approximately the same time . fundus ( figure 3 ) and sd - oct ( figure 4 ) exams demonstrated findings consistent with xlrs . genetic and electrophysiologic testing were offered for these patients ; however , the parents deferred these additional exams . sd - oct is a powerful technology that has several advantages over time - domain oct . although the axial resolution of the two technologies is comparable , the advantage of sd - oct is in the speed of image acquisition . the result is reduced motion artifact and improved image clarity , allowing clinicians to better delineate retinal structures and pathology.810 the imaging of patients was performed using an sd - oct instrument with 6 m axial resolution ( cirrusoct ; carl zeiss meditec , dublin , ca ) with an acquisition speed of approximately 26,000 a - scans per second . images were acquired using a 6 mm 6 mm raster scanning pattern through the macula , centered on the fovea . each of the horizontal scans consisted of 200 a - scans , and 30 m separated each of 200 horizontal scans through the macula . the entire 6 mm 6 mm dataset at a depth of 2 mm was acquired in approximately 1.5 seconds . in addition , the central macula was imaged using five high - density 6 mm horizontal b - scans separated by 250 m , each consisting of 4096 a - scans , which were acquired in approximately 0.6 seconds . the detail from the sd - oct scans was ideal for visualizing the retinal architecture and cystic changes in the eyes with xlrs , thereby allowing for precise identification of the pathologic changes and their location within the structure of the retina.1113 most likely , the retinal cystic changes associated with xlrs begin to occur shortly after birth , enlarge , and coalesce in size over time . in early cases , it may not be evident from the clinical dilated fundus exam that any pathology is present . given the enhanced detail available with sd - oct , the early retinal changes may be visualized and a diagnosis made sooner in patients suspected to have the disease . an earlier diagnosis results in timely referrals to low vision services and genetic counselors for this macular disease . these two cases also highlight the variability of the same genetic disease , even within the same family . furthermore , while the first case had very pronounced findings ( a large central cyst that extended from the nfl to the outer retina and a lamellar macular hole ) , the left eye of the second case had very subtle retinal findings ( figure 3b ) ; and there were no foveal lesions present on exam . however , sd - oct was able to visualize the early cystic changes associated with xlrs ( figure 4 ) . the enhanced retinal detail that is possible with sd - oct is not only beneficial to earlier diagnosis , but may also aid in the previously described classification schemes for xlrs.14

spectral domain optical coherence tomography was used to image the maculae of two brothers who had the diagnosis of x - linked retinoschisis maculopathy . one patient demonstrated a large foveal cyst in one eye and a lamellar macular hole in the fellow eye . the second patient demonstrated small retinal cysts in multiple layers of the retina . spectral domain optical coherence tomography allowed high - resolution imaging and characterization of the features in x - linked retinoschisis in these patients , and it highlighted the variability of the same genetic disease , even in one family .

<s>[INST]x - linked retinoschisis ( xlrs ) is a bilateral progressive disease of the retina that is likely present at birth and progresses as the child ages . it is associated with a mutation of the xlrs1 gene located on the short arm of the x chromosome , xp22,1 and is clinically characterized by cystoid changes of the fovea arranged in a stellate pattern.2 several publications describing the optical coherence tomography ( oct ) characteristics of xlrs have noted different findings for this condition . splitting in the nerve fiber layer ( nfl ) attributed to mueller cell dysfunction was noted on histological studies3 and was observed in vivo with oct by eriksson et al.4 additionally , groups have described splitting in retinal layers deep to the nfl with oct.57 a 13-year - old african - american boy ( case 1 ) presented for evaluation of decreased vision . the patient s mother reported that the boy had experienced poor vision for many years . his best - corrected visual acuity was 20/200 od and 20/400 os with no improvement on manifest refraction or pinhole testing . the fundus ( figure 1 ) and spectral domain optical coherence tomography ( sd - oct ) ( figure 2 ) exams demonstrated findings consistent with xlrs . the boy s 14-year - old brother ( case 2 ) was examined and found to have a best - corrected visual acuity of 20/400 od and 20/40 os without improvement on manifest refraction or pinhole testing . the mother reported that this sibling had experienced poor vision for the past 7 years and that his sensory exotropia had also existed for approximately the same time . fundus ( figure 3 ) and sd - oct ( figure 4 ) exams demonstrated findings consistent with xlrs . genetic and electrophysiologic testing were offered for these patients ; however , the parents deferred these additional exams . sd - oct is a powerful technology that has several advantages over time - domain oct . although the axial resolution of the two technologies is comparable , the advantage of sd - oct is in the speed of image acquisition . the result is reduced motion artifact and improved image clarity , allowing clinicians to better delineate retinal structures and pathology.810 the imaging of patients was performed using an sd - oct instrument with 6 m axial resolution ( cirrusoct ; carl zeiss meditec , dublin , ca ) with an acquisition speed of approximately 26,000 a - scans per second . images were acquired using a 6 mm 6 mm raster scanning pattern through the macula , centered on the fovea . each of the horizontal scans consisted of 200 a - scans , and 30 m separated each of 200 horizontal scans through the macula . the entire 6 mm 6 mm dataset at a depth of 2 mm was acquired in approximately 1.5 seconds . in addition , the central macula was imaged using five high - density 6 mm horizontal b - scans separated by 250 m , each consisting of 4096 a - scans , which were acquired in approximately 0.6 seconds . the detail from the sd - oct scans was ideal for visualizing the retinal architecture and cystic changes in the eyes with xlrs , thereby allowing for precise identification of the pathologic changes and their location within the structure of the retina.1113 most likely , the retinal cystic changes associated with xlrs begin to occur shortly after birth , enlarge , and coalesce in size over time . in early cases , it may not be evident from the clinical dilated fundus exam that any pathology is present . given the enhanced detail available with sd - oct , the early retinal changes may be visualized and a diagnosis made sooner in patients suspected to have the disease . an earlier diagnosis results in timely referrals to low vision services and genetic counselors for this macular disease . these two cases also highlight the variability of the same genetic disease , even within the same family . furthermore , while the first case had very pronounced findings ( a large central cyst that extended from the nfl to the outer retina and a lamellar macular hole ) , the left eye of the second case had very subtle retinal findings ( figure 3b ) ; and there were no foveal lesions present on exam . however , sd - oct was able to visualize the early cystic changes associated with xlrs ( figure 4 ) . the enhanced retinal detail that is possible with sd - oct is not only beneficial to earlier diagnosis , but may also aid in the previously described classification schemes for xlrs.14[/INST]spectral domain optical coherence tomography was used to image the maculae of two brothers who had the diagnosis of x - linked retinoschisis maculopathy . one patient demonstrated a large foveal cyst in one eye and a lamellar macular hole in the fellow eye . the second patient demonstrated small retinal cysts in multiple layers of the retina . spectral domain optical coherence tomography allowed high - resolution imaging and characterization of the features in x - linked retinoschisis in these patients , and it highlighted the variability of the same genetic disease , even in one family .</s>

it has been shown in ref . that there is a unitary transformation that relates the @xmath0 chiral basis , usually represented as @xmath1 , where @xmath4 is the index of the chiral representation ( @xmath5 ) , @xmath6 is the quantum number of isospin , and @xmath7 indicates the total angular momentum of the state with definite parity and charge , and the @xmath8 basis , which regards the spin - orbit angular momentum coupling used in nonrelativistic quantum mechanics . this allows one to write a particular state belonging to a chiral multiplet with quantum numbers @xmath7 , as a superposition of states of the nonrelativistic - inspired @xmath2 classification scheme . a chiral state with definite parity @xmath9 can be decomposed as a superposition of helicity states without definite parity @xmath10 through @xcite @xmath11 and @xmath12 are individual isospin and helicity respectively . coefficients @xmath13 relate the helicity basis to the chiral basis with definite parity in the state . they can be found in refs . . @xmath14 are the usual @xmath3 clebsch - gordan coefficients . two - particle helicity states @xmath15 can be written in terms of vectors in the @xmath2 basis once one knows the expression for the matrix elements @xcite @xmath16 it represents the angular momentum coupling of a two - particle state with individual helicities @xmath17 , @xmath18 ( with @xmath19 ) to a system of total spin @xmath20 and and orbital angular momentum @xmath21 . combining ( [ leonid1 ] ) and ( [ leonid3 ] ) one finds @xmath22 as an example , the @xmath23-like state which belongs to the chiral multiplet @xmath24 and @xmath25 can be represented as @xcite @xmath26 representations are complete for two - particle systems with the quantum numbers @xmath27 , the angular momentum expansion is uniquely determined for each chiral state . chiral symmetry imposes strong restrictions on the spin and angular momentum distribution of a system . the decomposition has been used in ref . to test the chiral symmetry breaking of the @xmath23 meson in the infrared , and at the same time , to reconstruct its spin and orbital angular momentum content in terms of partial waves . this was achieved by using interpolators that transform according to @xmath24 and @xmath28 . if chiral symmetry were not broken there would be only two possible chiral states in the meson , while chiral symmetry breaking would imply a superposition of both . the obtained result in ref . indicates that the @xmath0 component of the @xmath23-meson in the infrared is indeed a superposition of the @xmath24 and @xmath28 chiral states , and therefore chiral symmetry turns out to be broken . by using transformation ( [ rho1 ] ) and ( [ rho2 ] ) the partial wave content can be extracted , obtaining for the particular case of the @xmath23 meson , a nearly pure @xmath29 state @xcite . this is an example of application , see also refs . . in this paper we will not discuss problems in which the chiral basis or its transformation can play a role as was done in refs . or , for instance . the problem we want to address here is more technical and related to the transformation ( [ chiral : to : ls ] ) itself . the unitary transformation ( [ chiral : to : ls ] ) was obtained in the instant form of relativistic quantum mechanics . in this work we investigate the corresponding expression one should use in the context of approaches that use light - front quantization @xcite or front - form relativistic quantum mechanics @xcite . we pose the question whether the transformation ( [ chiral : to : ls ] ) is identical in any other form @xcite or if it is a special feature of those that use canonical spin , such as the instant- or the point - forms . the problem is not trivial since in relativistic composite systems the internal degrees of freedom transform among themselves nontrivially under rotations @xcite . relativity mixes spatial and temporal components , and as a consequence , one is not allowed to treat boosts and angular momentum separately in general . the election of a particular representation matters and in some cases some of the symmetry properties of the poincar group might not be manifest . the front form is of special interest , since rotations do not form a subgroup of the kinematical group and hence , rotational invariance is not manifest . on the other hand , front - form boosts form a subgroup of the poincar group , and as a result , the front - form wigner rotation becomes the identity @xcite . in this article we will show that the unitary transformation derived in ref . in instant form is indeed identical in the front form of relativistic quantum mechanics . the argument resides in the fact that the _ generalized melosh rotation _ that transforms front - form spins to helicity ones , becomes the identity when the mass goes to zero @xcite . due to rotational and translational invariance in nonrelativistic quantum mechanics , the angular momentum coupling of two particles with individual spin and orbital angular momentum @xmath30 and @xmath31 to give a composite system of total spin and orbital angular momentum @xmath32 is easily realized by using the @xmath3 clebsch - gordan coefficients . relativity involves however , a change of representation in which the single - particle momenta and spins are replaced by an overall system momentum and internal angular momentum @xcite . it is customary to use the clebsch - gordan coefficients of the poincar group @xcite . the kind of spin vector can be fully determined through the choice of a certain type of boost . canonical boosts are rotationless . spin vectors defined through canonical boosts have the advantage that in the center of momentum frame they transform under rotations in the same way as in nonrelativistic quantum mechanics , and therefore , for a composite system one can find a direct decomposition in terms of @xmath3 clebsch - gordan coefficients . the reason is that in the canonical case the wigner rotation associated with a pure rotation , turns out to be the rotation itself @xcite . this does not hold in general . in the front form , rotational invariance is not manifest , and an angular momentum decomposition in terms of clebsch - gordan coefficients requires additional transformations . expression ( [ leonid3 ] ) can be achieved in a straightforward manner in non relativistic quantum mechanics , as well as in the instant form of dynamics or in any other form that uses canonical spin . the derivation of ( [ leonid3 ] ) can be found in ref . . we will reproduce it here in a basis of eigenstates of the poincar group in order to be able to refer some steps that concern what will be exposed in the next section . we decompose the spin part of a two - particle state with total canonical angular momentum @xmath33 and @xmath34-component @xmath35 , orbital angular momentum @xmath21 and total spin @xmath36 , in terms of quantum numbers of the constituents in the center of momentum frame ( @xmath37 ) , where the relative momentum is expressed as @xmath38 , @xmath39 where @xmath40 , @xmath41 and @xmath42 are respectively the individual canonical spins and their @xmath34-projections . given a particular direction @xmath43 , where the tensor product state can be written @xmath44 one can write @xmath45|\mathbf k| j ; \mathbf 0\ , m\rangle \nonumber\\ & = & \sum_{m_lm_s}\sum_{\sigma_1\sigma_2}\psi_{s_1\sigma_1}(\mathbf k ) \psi_{s_2\sigma_2}(-\mathbf k ) c^{sm_s}_{s_1\sigma_1 s_2\sigma_2 } y_{lm_l}(\mathbf{\hat{\mathbf k}})\ ; c^{jm}_{lm_lsm_s}.\end{aligned}\ ] ] in order to express it in terms of helicities one needs to transform states with canonical spin to a basis of states with helicity spin . the unitary transformation that provides this is a wigner rotation whose argument corresponds to the angle between the @xmath46-axis and the direction of motion @xmath47 @xmath48 replacing in ( [ landauformel ] ) one gets @xmath49 it is convenient to write the spherical harmonics in terms of wigner @xmath50-functions in the definition of the phase of the spherical function . ] @xmath51 in such a way that one can make use of the relation for the product of wigner @xmath50-functions with the same argument for axially symmetric systems @xcite , @xmath52 with @xmath53 , @xmath54 , and @xmath55 accounting for the euler angles . this leads to @xmath56 the fact that the wigner @xmath50-functions in ( [ helicity : decomp ] ) have the same argument , is a particular feature of the instant form , and it is restricted to the rest frame @xcite . it is easy to identify the needed matrix elements as @xmath57 with @xmath58 and @xmath59 this permits the translation from two - particle helicity states with total angular momentum @xmath33 , to a one - particle state of overall orbital angular momentum @xmath21 and intrinsic spin @xmath20 . the connexion with chirality is immediately given by ( [ leonid1 ] ) . ( [ landauformel ] ) describes the angular momentum decomposition of a representation of canonical spin into a superposition of representations with canonical spin . because on the front - form rotations do not form a subgroup of the kinematical group of the poincar group , the decomposition ( [ landauformel ] ) is not feasible _ a priori_. in order to analyze the coupling of two representations with individual spin to a superposition of representations with total spin for an arbitrary case in relativistic quantum mechanics , it is necessary to use a consistent expression of the clebsch - gordan coefficients of the poincar group @xcite . front - form angular momentum coupling is well known and it has been widely applied to hadron problems in front - form relativistic quantum mechanics . a relation of the type of ( [ chiral : to : ls ] ) , however , has not been established yet in the front form . this is the aim of the present section . in the following we will use the normalization criteria and notation of ref . . the light - front components of the four - momentum are defined by @xmath60 , @xmath61 . @xmath62 represents a single particle state in a front - form basis ( denoted by @xmath63 ) , with @xmath34-spin projection @xmath64 . the expression for the clebsch - gordan coefficients of the poincar group in the front form for an arbitrary frame is given by @xcite @xmath65\,|\mathbf k| j ; \mathbf { \tilde p } \,m\rangle_f \nonumber\\ & = & \delta(\mathbf { \tilde p } - \mathbf { \tilde p}_1- \mathbf { \tilde p}_2 ) \ ; \frac{1}{|\mathbf k|^2 } \delta(\mathbf k ( \mathbf{\tilde p}_1,\mathbf { \tilde p}_2)-\mathbf k ) \left|\frac{\partial ( \mathbf{\tilde p},\mathbf{k})}{\partial(\mathbf{\tilde p}_1,\mathbf{\tilde p}_2)}\right|^{1/2}\nonumber \\ & & \times \sum_{\sigma_1\sigma_2 } d^{(s_1)}_{\mu_1\sigma_1 } [ \text r_{fc}(\mathbf k , \text{m}_1)]d^{(s_2)}_{\mu_2\sigma_2 } [ \text r_{fc}(-\mathbf k,\text{m}_2)]\nonumber \\ & & \times y^l_{m_l}(\hat{\mathbf k})c^{sm_s}_{s_1\sigma_1 s_2 \sigma_2 } c^{jm}_{lm_l sm_s},\end{aligned}\ ] ] where @xmath66 represents a tensor - product state of two particles with individual momenta @xmath67 and @xmath68 and spin @xmath34-projections @xmath69 and @xmath70 respectively . the system of two particles moves with a total light - front momentum @xmath71 and the individual spins couple to give a total angular momentum @xmath33 with orbital and spin contributions @xmath72 $ ] in the rest frame in the canonical form , and total angular momentum projection on the @xmath34-direction , @xmath35 . finally , @xmath38 is used to denote the individual momenta in the rest frame in the canonical form , and @xmath73 and @xmath74 denote the individual constituent masses ( they should not be confused with the spin projections , which appear in italics in equation ( [ d : same : arguments ] ) ) . the arguments of the wigner @xmath50-functions are melosh rotations which transform states with canonical spin to states with front - form spin and vice versa . note that the rotation depends on the mass in general , producing a different effect on each constituent . unless we are dealing with a system of identical constituent masses ( e.g. the chiral case ) , we will not be able to use the properties of the @xmath50-function with the same argument as was done in the instant form . the clebsch - gordan coefficient ( [ ff : clebschgordan ] ) is consistent with the normalization condition for single states @xmath75 and for state vectors of overall momentum @xmath76 @xmath77\,|\mathbf k'|j ' ; \mathbf { \tilde p } ' \,m ' |\ , [ ls]\,|\mathbf k|j ; \mathbf { \tilde p } \,m\rangle_f \nonumber\\ & & \quad \quad= \delta_{m'm}\delta_{j'j}\delta_{l'l}\delta_{s's}\delta(p'^+-p^+ ) \delta^2(\mathbf p'_\perp-\mathbf p_\perp)\frac{1}{|\mathbf k|^2}\delta(\mathbf k-\mathbf k').\end{aligned}\ ] ] the problem now is to couple a state of total front - form angular momentum @xmath33 and spin projection @xmath35 , @xmath78|\mathbf k| , j ; \mathbf { \tilde p } \,m\rangle_f $ ] , to a tensor - product state of two particles with individual spins described in terms of helicities @xmath79 . irreducible representations with different types of spin are related to each other through a unitary transformation @xcite . the unitary transformation that relates helicity spin to front - form spin becomes the identity for massless particles @xcite . this means : @xmath80 where the subindex @xmath81 labels helicity states . front - form spins and helicity spins coincide in the chiral limit , and one is allowed to make use of them without distinction . replacing ( [ h : to : f ] ) in ( [ ff : clebschgordan ] ) , one obtains the clebsch - gordan coefficient that couples two - particle helicity states to an overall state of the front - form basis , @xmath82\,|\mathbf k |j ; \mathbf { \tilde p } \,m\rangle_f \nonumber\\ & = & \delta(\mathbf { \tilde p } - \mathbf { \tilde p}_1- \mathbf { \tilde p}_2 ) \ ; \frac{1}{|\mathbf k|^2}\ ; \delta(\mathbf k ( \mathbf{\tilde p}_1,\mathbf { \tilde p}_2)-\mathbf k ) \left|\frac{\partial ( \mathbf{\tilde p},\mathbf{k})}{\partial(\mathbf{\tilde p}_1,\mathbf{\tilde p}_2)}\right|^{1/2}\nonumber \\ & & \times \sum_{\sigma_1\sigma_2 } d^{(s_1)}_{\lambda_1\sigma_1 } [ \text r_{hc}(\hat{\mathbf k})]d^{(s_2)}_{\lambda_2\sigma_2 } [ \text r_{hc}(-\hat{\mathbf k})]\nonumber \\ & & \times y^l_{m_l}(\hat{\mathbf k})c^{sm_s}_{s_1\sigma_1 s_2\sigma_2}c^{jm}_{lm_ls m_s}. \end{aligned}\ ] ] now the melosh rotations @xmath83 $ ] and @xmath84 $ ] are equivalent to the wigner rotations and they only depend on the direction of @xmath85 . they have exactly the same significance as in ( [ helicity : decomp ] ) : they transform canonical spins into helicity spins . we are in the position to write the expression for the state in which we are interested @xmath86\,|\mathbf k| j ; \mathbf { \tilde p } \,m\rangle_f & = & \sum_{\lambda_1\lambda_2 } \int d^3 \tilde p_1 d^3 \tilde p_2 & & \times _ h\langle \mathbf{\tilde p}_1 \lambda_1 \mathbf { \tilde p}_2 \lambda_2 |\ , [ ls]\,|\mathbf k|,j ; \mathbf { \tilde p } \,m\rangle_f , \nonumber\end{aligned}\ ] ] where @xmath87 has been introduced . reexpresing it in terms of @xmath71 and @xmath85 and setting the center of momentum frame , @xmath88 , @xmath89d^{(s_2)}_{\lambda_2\sigma_2 } [ \text r_{hc}(-\hat{\mathbf k})]\nonumber \\ & & \times y^l_{m_l}(\hat{\mathbf k})c^{sm_s}_{s_1\sigma_1 s_2\sigma_2}c^{jm}_{lm_ls m_s}. \end{aligned}\ ] ] setting now a particular direction of motion @xmath90 , the integral over @xmath91 can be carried out by means of @xmath92 and we have @xmath93\,|\mathbf k|j ; \mathbf { \tilde 0 } \,m\rangle_f \nonumber\\ & = & \sum_{\lambda_1\lambda_2 } \sum_{\sigma_1\sigma_2 } \psi_{s_1\lambda_1 } ( \mathbf k)\psi_{s_2-\lambda_2 } ( \mathbf k ) d^{(s_1)}_{\lambda_1\sigma_1 } [ \text r_{hc}(\hat{\mathbf k})]d^{(s_2)}_{-\lambda_2\sigma_2 } [ \text r_{hc}(\hat{\mathbf k})]\nonumber \\ & & \times y^l_{m_l}(\hat{\mathbf k})c^{sm_s}_{s_1\sigma_1 s_2\sigma_2}c^{jm}_{lm_ls m_s}. \end{aligned}\ ] ] proceeding in the same way as in the previous section in the combination of the spherical harmonic and the wigner @xmath50-functions one obtains @xmath94 and @xmath95 having found ( [ repeated : final ] ) , the validity of decomposition ( [ chiral : to : ls ] ) is demonstrated . unlike in the instant form , the combination of the wigner @xmath50-functions would not have been possible if we had considered particles of different masses . only in the chiral limit , or for equal masses , the eigenstates in the rest frame transform in the same way as in nonrelativistic quantum mechanics . note that in general the coupling ( [ ff : clebschgordan ] ) involves rotations that depend on the masses , namely @xmath96 $ ] and @xmath97 $ ] . this would have prevented the application of ( [ d : same : arguments ] ) , since the @xmath50-functions would not have the same arguments , and the dependence on the masses would have entered the decomposition , making it impossible to write ( [ ff : jlms ] ) in the form of a product of ( [ ff : sincg ] ) and ( [ repeated : final ] ) . moreover , a further rotation would have been necessary in order to transform front - from spins to helicity spins , which in the chiral limit turns out to be trivial by means of ( [ h : to : f ] ) . the result is that decomposition ( [ chiral : to : ls ] ) can be therefore used to expand chiral states as a superposition of vectors of the @xmath98-basis within a front - form framework . it can be expressed as @xmath99 we have derived the unitary transformation that relates the @xmath0 chiral basis to the @xmath2-basis in a front - form framework . the result turns out to be the same as in instant form.@xcite spin vectors belonging to different representations can be related through a unitary transformation @xcite . we have used the feature of the generalized melosh rotation that relates helicity and front - form spins , which becomes the identity for massless particles . this has made it possible to find a simple expression in terms of @xmath3 clebsch - gordan coefficients , by starting from the most general case of the clebsch - gordan coefficients of the poincar group . the limit @xmath100 eliminates the mass - dependence in the wigner @xmath50-functions making it possible to express the product of @xmath50-functions with the same argument through a clebsch - gordan series for axially symmetric systems . to better understand the significance of this calculation let us recall that the purpose of the clebsch - gordan coefficients of the poincar group is to convert any kind of spin to canonical spin in the rest frame , in such a way that they can be added using @xmath3 clebsch - gordan coefficients @xcite . in the system rest frame , the only feature that distinguishes front - form spins from canonical ones is the fact that front - form spins are characterized for being invariant under front - form boosts . this difference is accounted by the melosh rotation ( cf . ( [ ff : clebschgordan ] ) ) . as a last remark , let us also mention that it would have been possible to develop such a decomposition for any type of spin . the clebsch - gordan coefficients of the poincar group for an arbitrary form are given in ref . . proceeding in an analogous way as before , it is possible to see that again the wigner @xmath50-functions do not have the same argument , and it is not possible to bring them together to an overall rotation by means of @xmath3 clebsch - gordan coefficients . only in the chiral limit the rotations are again the same . but unlike in the front form , an additional transformation on such arbitrary spins into helicity spins is necessary to make the relation to chirality possible . i want to thank w. schweiger and l. ya . glozman for many helpful ideas and discussions as well as for their help in the elaboration of this paper . i acknowledge the support of the fond zur frderung der wissenschaftlichen forschung in sterreich(fwf dk w1203-n16 ) . 12 l. y. glozman and a. v. nefediev , phys . d * 76 * , 096004 ( 2007 ) [ arxiv:0704.2673 [ hep - ph ] ] . l. y. glozman , phys . rept . * 444 * , 1 ( 2007 ) [ hep - ph/0701081 ] , and references therein . l. d. landau and e. m. lifshitz , _ quantum electrodynamics_. course of theoretical physics vol . 4 ( pergamon press , new york , 1982 ) , sec . 69 , problem 2 . l. y. glozman , c. b. lang and m. limmer , phys . lett . * 103 * , 121601 ( 2009 ) [ arxiv:0905.0811 [ hep - lat ] ] . l. y. glozman and a. v. nefediev , phys . d * 80 * , 057901 ( 2009 ) [ arxiv:0904.3067 [ hep - ph ] ] . s. j. brodsky , h. -c . pauli and s. s. pinsky , phys . rept . * 301 * , 299 ( 1998 ) [ hep - ph/9705477 ] . l. d. landau and e. m. lifshitz , _ quantum mechanics : non - relativistic theory_. course of theoretical physics vol . 3 ( pergamon press , 1977 ) .

in this article we derive the unitary transformation that relates the @xmath0 chiral basis @xmath1 to the @xmath2-basis in a front - form framework . from the most general expression for the clebsch - gordan coefficients of the poincar group one can see that the chiral limit brings the angular momentum coupling into a simple form that permits the relation in terms of @xmath3 clebsch - gordan coefficients . we demonstrate that such a transformation is identical to the one was obtained for canonical spin in the instant form .

<s>[INST]it has been shown in ref . that there is a unitary transformation that relates the @xmath0 chiral basis , usually represented as @xmath1 , where @xmath4 is the index of the chiral representation ( @xmath5 ) , @xmath6 is the quantum number of isospin , and @xmath7 indicates the total angular momentum of the state with definite parity and charge , and the @xmath8 basis , which regards the spin - orbit angular momentum coupling used in nonrelativistic quantum mechanics . this allows one to write a particular state belonging to a chiral multiplet with quantum numbers @xmath7 , as a superposition of states of the nonrelativistic - inspired @xmath2 classification scheme . a chiral state with definite parity @xmath9 can be decomposed as a superposition of helicity states without definite parity @xmath10 through @xcite @xmath11 and @xmath12 are individual isospin and helicity respectively . coefficients @xmath13 relate the helicity basis to the chiral basis with definite parity in the state . they can be found in refs . . @xmath14 are the usual @xmath3 clebsch - gordan coefficients . two - particle helicity states @xmath15 can be written in terms of vectors in the @xmath2 basis once one knows the expression for the matrix elements @xcite @xmath16 it represents the angular momentum coupling of a two - particle state with individual helicities @xmath17 , @xmath18 ( with @xmath19 ) to a system of total spin @xmath20 and and orbital angular momentum @xmath21 . combining ( [ leonid1 ] ) and ( [ leonid3 ] ) one finds @xmath22 as an example , the @xmath23-like state which belongs to the chiral multiplet @xmath24 and @xmath25 can be represented as @xcite @xmath26 representations are complete for two - particle systems with the quantum numbers @xmath27 , the angular momentum expansion is uniquely determined for each chiral state . chiral symmetry imposes strong restrictions on the spin and angular momentum distribution of a system . the decomposition has been used in ref . to test the chiral symmetry breaking of the @xmath23 meson in the infrared , and at the same time , to reconstruct its spin and orbital angular momentum content in terms of partial waves . this was achieved by using interpolators that transform according to @xmath24 and @xmath28 . if chiral symmetry were not broken there would be only two possible chiral states in the meson , while chiral symmetry breaking would imply a superposition of both . the obtained result in ref . indicates that the @xmath0 component of the @xmath23-meson in the infrared is indeed a superposition of the @xmath24 and @xmath28 chiral states , and therefore chiral symmetry turns out to be broken . by using transformation ( [ rho1 ] ) and ( [ rho2 ] ) the partial wave content can be extracted , obtaining for the particular case of the @xmath23 meson , a nearly pure @xmath29 state @xcite . this is an example of application , see also refs . . in this paper we will not discuss problems in which the chiral basis or its transformation can play a role as was done in refs . or , for instance . the problem we want to address here is more technical and related to the transformation ( [ chiral : to : ls ] ) itself . the unitary transformation ( [ chiral : to : ls ] ) was obtained in the instant form of relativistic quantum mechanics . in this work we investigate the corresponding expression one should use in the context of approaches that use light - front quantization @xcite or front - form relativistic quantum mechanics @xcite . we pose the question whether the transformation ( [ chiral : to : ls ] ) is identical in any other form @xcite or if it is a special feature of those that use canonical spin , such as the instant- or the point - forms . the problem is not trivial since in relativistic composite systems the internal degrees of freedom transform among themselves nontrivially under rotations @xcite . relativity mixes spatial and temporal components , and as a consequence , one is not allowed to treat boosts and angular momentum separately in general . the election of a particular representation matters and in some cases some of the symmetry properties of the poincar group might not be manifest . the front form is of special interest , since rotations do not form a subgroup of the kinematical group and hence , rotational invariance is not manifest . on the other hand , front - form boosts form a subgroup of the poincar group , and as a result , the front - form wigner rotation becomes the identity @xcite . in this article we will show that the unitary transformation derived in ref . in instant form is indeed identical in the front form of relativistic quantum mechanics . the argument resides in the fact that the _ generalized melosh rotation _ that transforms front - form spins to helicity ones , becomes the identity when the mass goes to zero @xcite . due to rotational and translational invariance in nonrelativistic quantum mechanics , the angular momentum coupling of two particles with individual spin and orbital angular momentum @xmath30 and @xmath31 to give a composite system of total spin and orbital angular momentum @xmath32 is easily realized by using the @xmath3 clebsch - gordan coefficients . relativity involves however , a change of representation in which the single - particle momenta and spins are replaced by an overall system momentum and internal angular momentum @xcite . it is customary to use the clebsch - gordan coefficients of the poincar group @xcite . the kind of spin vector can be fully determined through the choice of a certain type of boost . canonical boosts are rotationless . spin vectors defined through canonical boosts have the advantage that in the center of momentum frame they transform under rotations in the same way as in nonrelativistic quantum mechanics , and therefore , for a composite system one can find a direct decomposition in terms of @xmath3 clebsch - gordan coefficients . the reason is that in the canonical case the wigner rotation associated with a pure rotation , turns out to be the rotation itself @xcite . this does not hold in general . in the front form , rotational invariance is not manifest , and an angular momentum decomposition in terms of clebsch - gordan coefficients requires additional transformations . expression ( [ leonid3 ] ) can be achieved in a straightforward manner in non relativistic quantum mechanics , as well as in the instant form of dynamics or in any other form that uses canonical spin . the derivation of ( [ leonid3 ] ) can be found in ref . . we will reproduce it here in a basis of eigenstates of the poincar group in order to be able to refer some steps that concern what will be exposed in the next section . we decompose the spin part of a two - particle state with total canonical angular momentum @xmath33 and @xmath34-component @xmath35 , orbital angular momentum @xmath21 and total spin @xmath36 , in terms of quantum numbers of the constituents in the center of momentum frame ( @xmath37 ) , where the relative momentum is expressed as @xmath38 , @xmath39 where @xmath40 , @xmath41 and @xmath42 are respectively the individual canonical spins and their @xmath34-projections . given a particular direction @xmath43 , where the tensor product state can be written @xmath44 one can write @xmath45|\mathbf k| j ; \mathbf 0\ , m\rangle \nonumber\\ & = & \sum_{m_lm_s}\sum_{\sigma_1\sigma_2}\psi_{s_1\sigma_1}(\mathbf k ) \psi_{s_2\sigma_2}(-\mathbf k ) c^{sm_s}_{s_1\sigma_1 s_2\sigma_2 } y_{lm_l}(\mathbf{\hat{\mathbf k}})\ ; c^{jm}_{lm_lsm_s}.\end{aligned}\ ] ] in order to express it in terms of helicities one needs to transform states with canonical spin to a basis of states with helicity spin . the unitary transformation that provides this is a wigner rotation whose argument corresponds to the angle between the @xmath46-axis and the direction of motion @xmath47 @xmath48 replacing in ( [ landauformel ] ) one gets @xmath49 it is convenient to write the spherical harmonics in terms of wigner @xmath50-functions in the definition of the phase of the spherical function . ] @xmath51 in such a way that one can make use of the relation for the product of wigner @xmath50-functions with the same argument for axially symmetric systems @xcite , @xmath52 with @xmath53 , @xmath54 , and @xmath55 accounting for the euler angles . this leads to @xmath56 the fact that the wigner @xmath50-functions in ( [ helicity : decomp ] ) have the same argument , is a particular feature of the instant form , and it is restricted to the rest frame @xcite . it is easy to identify the needed matrix elements as @xmath57 with @xmath58 and @xmath59 this permits the translation from two - particle helicity states with total angular momentum @xmath33 , to a one - particle state of overall orbital angular momentum @xmath21 and intrinsic spin @xmath20 . the connexion with chirality is immediately given by ( [ leonid1 ] ) . ( [ landauformel ] ) describes the angular momentum decomposition of a representation of canonical spin into a superposition of representations with canonical spin . because on the front - form rotations do not form a subgroup of the kinematical group of the poincar group , the decomposition ( [ landauformel ] ) is not feasible _ a priori_. in order to analyze the coupling of two representations with individual spin to a superposition of representations with total spin for an arbitrary case in relativistic quantum mechanics , it is necessary to use a consistent expression of the clebsch - gordan coefficients of the poincar group @xcite . front - form angular momentum coupling is well known and it has been widely applied to hadron problems in front - form relativistic quantum mechanics . a relation of the type of ( [ chiral : to : ls ] ) , however , has not been established yet in the front form . this is the aim of the present section . in the following we will use the normalization criteria and notation of ref . . the light - front components of the four - momentum are defined by @xmath60 , @xmath61 . @xmath62 represents a single particle state in a front - form basis ( denoted by @xmath63 ) , with @xmath34-spin projection @xmath64 . the expression for the clebsch - gordan coefficients of the poincar group in the front form for an arbitrary frame is given by @xcite @xmath65\,|\mathbf k| j ; \mathbf { \tilde p } \,m\rangle_f \nonumber\\ & = & \delta(\mathbf { \tilde p } - \mathbf { \tilde p}_1- \mathbf { \tilde p}_2 ) \ ; \frac{1}{|\mathbf k|^2 } \delta(\mathbf k ( \mathbf{\tilde p}_1,\mathbf { \tilde p}_2)-\mathbf k ) \left|\frac{\partial ( \mathbf{\tilde p},\mathbf{k})}{\partial(\mathbf{\tilde p}_1,\mathbf{\tilde p}_2)}\right|^{1/2}\nonumber \\ & & \times \sum_{\sigma_1\sigma_2 } d^{(s_1)}_{\mu_1\sigma_1 } [ \text r_{fc}(\mathbf k , \text{m}_1)]d^{(s_2)}_{\mu_2\sigma_2 } [ \text r_{fc}(-\mathbf k,\text{m}_2)]\nonumber \\ & & \times y^l_{m_l}(\hat{\mathbf k})c^{sm_s}_{s_1\sigma_1 s_2 \sigma_2 } c^{jm}_{lm_l sm_s},\end{aligned}\ ] ] where @xmath66 represents a tensor - product state of two particles with individual momenta @xmath67 and @xmath68 and spin @xmath34-projections @xmath69 and @xmath70 respectively . the system of two particles moves with a total light - front momentum @xmath71 and the individual spins couple to give a total angular momentum @xmath33 with orbital and spin contributions @xmath72 $ ] in the rest frame in the canonical form , and total angular momentum projection on the @xmath34-direction , @xmath35 . finally , @xmath38 is used to denote the individual momenta in the rest frame in the canonical form , and @xmath73 and @xmath74 denote the individual constituent masses ( they should not be confused with the spin projections , which appear in italics in equation ( [ d : same : arguments ] ) ) . the arguments of the wigner @xmath50-functions are melosh rotations which transform states with canonical spin to states with front - form spin and vice versa . note that the rotation depends on the mass in general , producing a different effect on each constituent . unless we are dealing with a system of identical constituent masses ( e.g. the chiral case ) , we will not be able to use the properties of the @xmath50-function with the same argument as was done in the instant form . the clebsch - gordan coefficient ( [ ff : clebschgordan ] ) is consistent with the normalization condition for single states @xmath75 and for state vectors of overall momentum @xmath76 @xmath77\,|\mathbf k'|j ' ; \mathbf { \tilde p } ' \,m ' |\ , [ ls]\,|\mathbf k|j ; \mathbf { \tilde p } \,m\rangle_f \nonumber\\ & & \quad \quad= \delta_{m'm}\delta_{j'j}\delta_{l'l}\delta_{s's}\delta(p'^+-p^+ ) \delta^2(\mathbf p'_\perp-\mathbf p_\perp)\frac{1}{|\mathbf k|^2}\delta(\mathbf k-\mathbf k').\end{aligned}\ ] ] the problem now is to couple a state of total front - form angular momentum @xmath33 and spin projection @xmath35 , @xmath78|\mathbf k| , j ; \mathbf { \tilde p } \,m\rangle_f $ ] , to a tensor - product state of two particles with individual spins described in terms of helicities @xmath79 . irreducible representations with different types of spin are related to each other through a unitary transformation @xcite . the unitary transformation that relates helicity spin to front - form spin becomes the identity for massless particles @xcite . this means : @xmath80 where the subindex @xmath81 labels helicity states . front - form spins and helicity spins coincide in the chiral limit , and one is allowed to make use of them without distinction . replacing ( [ h : to : f ] ) in ( [ ff : clebschgordan ] ) , one obtains the clebsch - gordan coefficient that couples two - particle helicity states to an overall state of the front - form basis , @xmath82\,|\mathbf k |j ; \mathbf { \tilde p } \,m\rangle_f \nonumber\\ & = & \delta(\mathbf { \tilde p } - \mathbf { \tilde p}_1- \mathbf { \tilde p}_2 ) \ ; \frac{1}{|\mathbf k|^2}\ ; \delta(\mathbf k ( \mathbf{\tilde p}_1,\mathbf { \tilde p}_2)-\mathbf k ) \left|\frac{\partial ( \mathbf{\tilde p},\mathbf{k})}{\partial(\mathbf{\tilde p}_1,\mathbf{\tilde p}_2)}\right|^{1/2}\nonumber \\ & & \times \sum_{\sigma_1\sigma_2 } d^{(s_1)}_{\lambda_1\sigma_1 } [ \text r_{hc}(\hat{\mathbf k})]d^{(s_2)}_{\lambda_2\sigma_2 } [ \text r_{hc}(-\hat{\mathbf k})]\nonumber \\ & & \times y^l_{m_l}(\hat{\mathbf k})c^{sm_s}_{s_1\sigma_1 s_2\sigma_2}c^{jm}_{lm_ls m_s}. \end{aligned}\ ] ] now the melosh rotations @xmath83 $ ] and @xmath84 $ ] are equivalent to the wigner rotations and they only depend on the direction of @xmath85 . they have exactly the same significance as in ( [ helicity : decomp ] ) : they transform canonical spins into helicity spins . we are in the position to write the expression for the state in which we are interested @xmath86\,|\mathbf k| j ; \mathbf { \tilde p } \,m\rangle_f & = & \sum_{\lambda_1\lambda_2 } \int d^3 \tilde p_1 d^3 \tilde p_2 & & \times _ h\langle \mathbf{\tilde p}_1 \lambda_1 \mathbf { \tilde p}_2 \lambda_2 |\ , [ ls]\,|\mathbf k|,j ; \mathbf { \tilde p } \,m\rangle_f , \nonumber\end{aligned}\ ] ] where @xmath87 has been introduced . reexpresing it in terms of @xmath71 and @xmath85 and setting the center of momentum frame , @xmath88 , @xmath89d^{(s_2)}_{\lambda_2\sigma_2 } [ \text r_{hc}(-\hat{\mathbf k})]\nonumber \\ & & \times y^l_{m_l}(\hat{\mathbf k})c^{sm_s}_{s_1\sigma_1 s_2\sigma_2}c^{jm}_{lm_ls m_s}. \end{aligned}\ ] ] setting now a particular direction of motion @xmath90 , the integral over @xmath91 can be carried out by means of @xmath92 and we have @xmath93\,|\mathbf k|j ; \mathbf { \tilde 0 } \,m\rangle_f \nonumber\\ & = & \sum_{\lambda_1\lambda_2 } \sum_{\sigma_1\sigma_2 } \psi_{s_1\lambda_1 } ( \mathbf k)\psi_{s_2-\lambda_2 } ( \mathbf k ) d^{(s_1)}_{\lambda_1\sigma_1 } [ \text r_{hc}(\hat{\mathbf k})]d^{(s_2)}_{-\lambda_2\sigma_2 } [ \text r_{hc}(\hat{\mathbf k})]\nonumber \\ & & \times y^l_{m_l}(\hat{\mathbf k})c^{sm_s}_{s_1\sigma_1 s_2\sigma_2}c^{jm}_{lm_ls m_s}. \end{aligned}\ ] ] proceeding in the same way as in the previous section in the combination of the spherical harmonic and the wigner @xmath50-functions one obtains @xmath94 and @xmath95 having found ( [ repeated : final ] ) , the validity of decomposition ( [ chiral : to : ls ] ) is demonstrated . unlike in the instant form , the combination of the wigner @xmath50-functions would not have been possible if we had considered particles of different masses . only in the chiral limit , or for equal masses , the eigenstates in the rest frame transform in the same way as in nonrelativistic quantum mechanics . note that in general the coupling ( [ ff : clebschgordan ] ) involves rotations that depend on the masses , namely @xmath96 $ ] and @xmath97 $ ] . this would have prevented the application of ( [ d : same : arguments ] ) , since the @xmath50-functions would not have the same arguments , and the dependence on the masses would have entered the decomposition , making it impossible to write ( [ ff : jlms ] ) in the form of a product of ( [ ff : sincg ] ) and ( [ repeated : final ] ) . moreover , a further rotation would have been necessary in order to transform front - from spins to helicity spins , which in the chiral limit turns out to be trivial by means of ( [ h : to : f ] ) . the result is that decomposition ( [ chiral : to : ls ] ) can be therefore used to expand chiral states as a superposition of vectors of the @xmath98-basis within a front - form framework . it can be expressed as @xmath99 we have derived the unitary transformation that relates the @xmath0 chiral basis to the @xmath2-basis in a front - form framework . the result turns out to be the same as in instant form.@xcite spin vectors belonging to different representations can be related through a unitary transformation @xcite . we have used the feature of the generalized melosh rotation that relates helicity and front - form spins , which becomes the identity for massless particles . this has made it possible to find a simple expression in terms of @xmath3 clebsch - gordan coefficients , by starting from the most general case of the clebsch - gordan coefficients of the poincar group . the limit @xmath100 eliminates the mass - dependence in the wigner @xmath50-functions making it possible to express the product of @xmath50-functions with the same argument through a clebsch - gordan series for axially symmetric systems . to better understand the significance of this calculation let us recall that the purpose of the clebsch - gordan coefficients of the poincar group is to convert any kind of spin to canonical spin in the rest frame , in such a way that they can be added using @xmath3 clebsch - gordan coefficients @xcite . in the system rest frame , the only feature that distinguishes front - form spins from canonical ones is the fact that front - form spins are characterized for being invariant under front - form boosts . this difference is accounted by the melosh rotation ( cf . ( [ ff : clebschgordan ] ) ) . as a last remark , let us also mention that it would have been possible to develop such a decomposition for any type of spin . the clebsch - gordan coefficients of the poincar group for an arbitrary form are given in ref . . proceeding in an analogous way as before , it is possible to see that again the wigner @xmath50-functions do not have the same argument , and it is not possible to bring them together to an overall rotation by means of @xmath3 clebsch - gordan coefficients . only in the chiral limit the rotations are again the same . but unlike in the front form , an additional transformation on such arbitrary spins into helicity spins is necessary to make the relation to chirality possible . i want to thank w. schweiger and l. ya . glozman for many helpful ideas and discussions as well as for their help in the elaboration of this paper . i acknowledge the support of the fond zur frderung der wissenschaftlichen forschung in sterreich(fwf dk w1203-n16 ) . 12 l. y. glozman and a. v. nefediev , phys . d * 76 * , 096004 ( 2007 ) [ arxiv:0704.2673 [ hep - ph ] ] . l. y. glozman , phys . rept . * 444 * , 1 ( 2007 ) [ hep - ph/0701081 ] , and references therein . l. d. landau and e. m. lifshitz , _ quantum electrodynamics_. course of theoretical physics vol . 4 ( pergamon press , new york , 1982 ) , sec . 69 , problem 2 . l. y. glozman , c. b. lang and m. limmer , phys . lett . * 103 * , 121601 ( 2009 ) [ arxiv:0905.0811 [ hep - lat ] ] . l. y. glozman and a. v. nefediev , phys . d * 80 * , 057901 ( 2009 ) [ arxiv:0904.3067 [ hep - ph ] ] . s. j. brodsky , h. -c . pauli and s. s. pinsky , phys . rept . * 301 * , 299 ( 1998 ) [ hep - ph/9705477 ] . l. d. landau and e. m. lifshitz , _ quantum mechanics : non - relativistic theory_. course of theoretical physics vol . 3 ( pergamon press , 1977 ) .[/INST] in this article we derive the unitary transformation that relates the @xmath0 chiral basis @xmath1 to the @xmath2-basis in a front - form framework . from the most general expression for the clebsch - gordan coefficients of the poincar group one can see that the chiral limit brings the angular momentum coupling into a simple form that permits the relation in terms of @xmath3 clebsch - gordan coefficients . we demonstrate that such a transformation is identical to the one was obtained for canonical spin in the instant form . </s>

SECTION 1. TREATMENT OF CERTAIN ENTRIES. (a) Liquidation or Reliquidation of Entries.--Notwithstanding sections 514 and 520 of the Tariff Act of 1930 (19 U.S.C. 1514 and 1520), or any other provision of law, the United States Customs Service shall liquidate or reliquidate those entries made at New York, New York, which are listed in subsection (c), in accordance with the final results of the administrative reviews covering the period from April 1, 1984, through March 31, 1991, undertaken by the International Trade Administration of the Department of Commerce for such entries (case number A-580-008). (b) Payment of Amounts Owed.--Any amounts owed by the United States pursuant to the liquidation or reliquidation of an entry under subsection (a) shall be paid by the Customs Service within 90 days after such liquidation or reliquidation. (c) Entry List.--The entries referred to in subsection (a) are the following: Entry Number Date of Entry 84-915604-7..................... July 6, 1984 84-915604-7..................... July 6, 1984 84-915830-4..................... July 17, 1984 84-916057-0..................... July 19, 1984 84-916057-0..................... July 23, 1984 84-916302-7..................... July 28, 1984 84-916323-4..................... July 28, 1984 84-916302-7..................... July 30, 1984 84-525823-7..................... September 20, 1984 84-525823-7..................... September 25, 1984 84-525971-5..................... September 27, 1984 84-525971-5..................... September 27, 1984 84-525971-5..................... September 27, 1984 84-525971-5..................... October 2, 1984 84-525971-5..................... October 2, 1984 85-279644-9..................... October 4, 1984 85-279654-6..................... October 9, 1984 85-280518-1..................... December 28, 1984 85-280518-1..................... December 28, 1984 85-102631-4..................... November 13, 1984 85-102631-4..................... November 13, 1984 85-401288-5..................... October 8, 1984 84-444821-3..................... August 3, 1984 84-444821-3..................... August 3, 1984 84-422128-4..................... October 2, 1984 85-422162-4..................... October 31, 1984 85-422162-4..................... October 31, 1984 84-215744-1..................... July 6, 1984 84-216018-2..................... August 6, 1984 84-208013-6..................... July 30, 1984 84-208013-6..................... July 30, 1984 84-208511-5..................... July 30, 1984 84-208013-6..................... August 1, 1984 84-208968-7..................... August 7, 1984 84-208968-7..................... August 7, 1984 85-432884-4..................... February 22, 1985 85-432884-4..................... February 22, 1985 85-102272-9..................... October 19, 1984 85-151075-2..................... February 5, 1985 85-210038-1..................... March 27, 1985 84-780372-9..................... August 3, 1984 84-781699-4..................... September 6, 1984 84-781699-4..................... September 6, 1984 84-781699-4..................... September 6, 1984 84-781846-8..................... September 18, 1984 85-944006-0..................... May 3, 1985 85-294383-6..................... August 27, 1985 86-215010-1..................... October 30, 1985 86-215185-4..................... December 2, 1985 86-215310-8..................... December 16, 1985 85-602949-7..................... April 15, 1985 85-602950-7..................... April 19, 1985 85-602966-2..................... April 19, 1985 85-603347-0..................... April 26, 1985 85-603523-2..................... May 8, 1985 85-604545-5..................... May 31, 1985 86-383795-7..................... April 22, 1986 110-1905894-7................... February 23, 1987 86-216530-3..................... April 16, 1986 110-0269614-1................... January 12, 1987 110-0269942-6................... January 19, 1987 110-0269947-5................... January 19, 1987 110-0269942-6................... January 22, 1987 86-476752-1..................... April 10, 1986 86-477371-9..................... August 14, 1986 86-477371-9..................... August 20, 1986 86-477413-2..................... August 22, 1986 86-477413-2..................... August 22, 1986 331-3808023-0................... October 20, 1986 331-3808023-0................... October 20, 1986 86-198869-1..................... September 9, 1986 86-198893-4..................... September 17, 1986 86-198964-5..................... October 14, 1986 331-3807959-6................... October 15, 1986 331-3807959-6................... October 15, 1986 331-3807959-6................... October 15, 1986 331-3807959-6................... October 15, 1986 331-3808023-0................... October 20, 1986 331-3812541-5................... December 26, 1986 331-3812541-5................... December 26, 1986 331-3813766-7................... February 19, 1987 86-477413-2..................... August 22, 1986 86-477413-2..................... August 22, 1986 110-1123057-7................... January 2, 1987 110-1124082-4................... March 26, 1987 110-1272348-9................... November 14, 1986 110-1272348-9................... November 14, 1986 110-1272505-4................... December 10, 1986 110-1272505-4................... December 10, 1986 110-1273532-7................... January 10, 1987 110-1274561-5................... February 20, 1987 110-1274921-1................... March 6, 1987 110-1274921-1................... March 6, 1987 110-1275320-5................... March 23, 1987 110-1275321-3................... March 31, 1987 110-1272505-4................... No Date Available 110-1907947-1................... January 22, 1988 110-1906495-2................... June 5, 1987 110-1906599-1................... June 22, 1987 110-1906599-1................... June 22, 1987 110-1906856-5................... August 2, 1987 110-1907967-9................... January 27, 1988 110-1908198-0................... March 4, 1988 110-1908178-2................... March 10, 1988 110-0294344-8................... May 6, 1987 110-0294344-8................... June 5, 1987 110-1906522-3................... June 6, 1987 110-1124130-1................... April 1, 1987 110-1124130-1................... April 2, 1987 110-1124130-1................... April 2, 1987 110-1125551-7................... July 17, 1987 110-1125551-7................... July 17, 1987 110-1126810-6................... October 27, 1987 110-1127047-4................... November 6, 1987 110-1127620-8................... December 23, 1987 110-1275844-4................... April 16, 1987 110-1278368-1................... July 28, 1987 110-1278958-9................... September 10, 1987 110-1278958-9................... September 10, 1987 110-1279151-0................... September 18, 1987 110-1279825-9................... October 8, 1987 110-1279767-3................... October 16, 1987 110-1280177-2................... October 21, 1987 110-1280206-9................... October 22, 1987 110-1282001-2................... January 12 1988 110-1282566-4................... February 11, 1988 110-1282642-3................... February 11, 1988 110-1286015-8................... February 22, 1988 110-1286165-1................... March 16, 1988 110-1286165-1................... March 16, 1988 110-1286165-1................... March 16, 1988 110-1908453-9................... April 22, 1988 110-1908567-6................... May 11, 1988 110-1908567-6................... May 11, 1988 110-1908928-0................... June 29, 1988 110-1129739-4................... May 13, 1988 110-1131047-8................... August 4, 1988 110-1133675-4................... January 6, 1989 110-1286261-8................... April 7, 1988 110-1286261-8................... April 7, 1988 110-1286492-9................... May 12, 1988 110-1286492-9................... May 12, 1988 110-1286492-9................... May 12, 1988 110-1286677-5................... June 16, 1988 110-1286796-3................... July 7, 1988 110-1286965-4................... August 4, 1988 110-1286965-4................... August 4, 1988 110-1288931-4................... December 8, 1988 110-0301260-3................... May 12, 1989 110-0301272-8................... May 19, 1989 110-0153952-4................... September 3, 1989 110-1135558-0................... May 12, 1989 110-1135558-0................... May 12, 1989 110-1136677-7................... July 11, 1989 110-1139014-0................... November 24, 1989 110-1294013-3................... September 14, 1989 110-1298751-4................... May 15, 1990 110-1274861-9................... March 4, 1987 110-1274863-5................... March 4, 1987 110-1275349-4................... May 12, 1987 110-1285836-8................... August 31, 1988 110-1285994-4................... August 1, 1988 110-1286179-2................... March 25, 1988 110-1286180-0................... March 25, 1988 110-1286181-8................... March 25, 1988 110-1286265-9................... April 5, 1988 110-1286507-4................... May 12, 1988 110-1286580-1................... May 26, 1988 110-1286582-7................... May 26, 1988 110-1286584-3................... May 26, 1988 110-1286634-6................... June 7, 1988 110-1286681-7................... June 18, 1988 110-1286751-8................... June 23, 1988 110-1286763-1................... June 29, 1988 110-1286782-3................... July 7, 1988 110-1286879-7................... July 27, 1988 110-1286881-3................... August 1, 1988 110-1286882-1................... August 10, 1988 110-1286925-8................... July 27, 1988 110-1286927-4................... August 1, 1988 110-1286972-0................... August 11, 1988 110-1286991-0................... August 1, 1988 110-1286993-6................... August 1, 1988 110-1287029-8................... August 15, 1988 110-1287030-6................... August 15, 1988 110-1287031-4................... August 15, 1988 110-1287032-2................... August 15, 1988 110-1287061-1................... August 15, 1988 110-1287062-9................... August 15, 1988 110-1287078-5................... August 17, 1988 110-1287095-9................... August 19, 1988 110-1287147-8................... September 2, 1988 110-1288475-2................... November 23, 1988 110-1288478-8................... November 10, 1988 110-1289801-8................... January 20, 1989 110-1293960-6................... September 11, 1989 110-1296719-3................... February 12, 1990

Directs the United States Customs Service to provide for the liquidation or reliquidation (refund) of certain entries made at New York, New York, in accordance with the results of an administrative review, during the period from April 1, 1984, through March 31, 1991, by the International Trade Administration of the Department of Commerce (case number A-580-008).

<s>[INST]SECTION 1. TREATMENT OF CERTAIN ENTRIES. (a) Liquidation or Reliquidation of Entries.--Notwithstanding sections 514 and 520 of the Tariff Act of 1930 (19 U.S.C. 1514 and 1520), or any other provision of law, the United States Customs Service shall liquidate or reliquidate those entries made at New York, New York, which are listed in subsection (c), in accordance with the final results of the administrative reviews covering the period from April 1, 1984, through March 31, 1991, undertaken by the International Trade Administration of the Department of Commerce for such entries (case number A-580-008). (b) Payment of Amounts Owed.--Any amounts owed by the United States pursuant to the liquidation or reliquidation of an entry under subsection (a) shall be paid by the Customs Service within 90 days after such liquidation or reliquidation. (c) Entry List.--The entries referred to in subsection (a) are the following: Entry Number Date of Entry 84-915604-7..................... July 6, 1984 84-915604-7..................... July 6, 1984 84-915830-4..................... July 17, 1984 84-916057-0..................... July 19, 1984 84-916057-0..................... July 23, 1984 84-916302-7..................... July 28, 1984 84-916323-4..................... July 28, 1984 84-916302-7..................... July 30, 1984 84-525823-7..................... September 20, 1984 84-525823-7..................... September 25, 1984 84-525971-5..................... September 27, 1984 84-525971-5..................... September 27, 1984 84-525971-5..................... September 27, 1984 84-525971-5..................... October 2, 1984 84-525971-5..................... October 2, 1984 85-279644-9..................... October 4, 1984 85-279654-6..................... October 9, 1984 85-280518-1..................... December 28, 1984 85-280518-1..................... December 28, 1984 85-102631-4..................... November 13, 1984 85-102631-4..................... November 13, 1984 85-401288-5..................... October 8, 1984 84-444821-3..................... August 3, 1984 84-444821-3..................... August 3, 1984 84-422128-4..................... October 2, 1984 85-422162-4..................... October 31, 1984 85-422162-4..................... October 31, 1984 84-215744-1..................... July 6, 1984 84-216018-2..................... August 6, 1984 84-208013-6..................... July 30, 1984 84-208013-6..................... July 30, 1984 84-208511-5..................... July 30, 1984 84-208013-6..................... August 1, 1984 84-208968-7..................... August 7, 1984 84-208968-7..................... August 7, 1984 85-432884-4..................... February 22, 1985 85-432884-4..................... February 22, 1985 85-102272-9..................... October 19, 1984 85-151075-2..................... February 5, 1985 85-210038-1..................... March 27, 1985 84-780372-9..................... August 3, 1984 84-781699-4..................... September 6, 1984 84-781699-4..................... September 6, 1984 84-781699-4..................... September 6, 1984 84-781846-8..................... September 18, 1984 85-944006-0..................... May 3, 1985 85-294383-6..................... August 27, 1985 86-215010-1..................... October 30, 1985 86-215185-4..................... December 2, 1985 86-215310-8..................... December 16, 1985 85-602949-7..................... April 15, 1985 85-602950-7..................... April 19, 1985 85-602966-2..................... April 19, 1985 85-603347-0..................... April 26, 1985 85-603523-2..................... May 8, 1985 85-604545-5..................... May 31, 1985 86-383795-7..................... April 22, 1986 110-1905894-7................... February 23, 1987 86-216530-3..................... April 16, 1986 110-0269614-1................... January 12, 1987 110-0269942-6................... January 19, 1987 110-0269947-5................... January 19, 1987 110-0269942-6................... January 22, 1987 86-476752-1..................... April 10, 1986 86-477371-9..................... August 14, 1986 86-477371-9..................... August 20, 1986 86-477413-2..................... August 22, 1986 86-477413-2..................... August 22, 1986 331-3808023-0................... October 20, 1986 331-3808023-0................... October 20, 1986 86-198869-1..................... September 9, 1986 86-198893-4..................... September 17, 1986 86-198964-5..................... October 14, 1986 331-3807959-6................... October 15, 1986 331-3807959-6................... October 15, 1986 331-3807959-6................... October 15, 1986 331-3807959-6................... October 15, 1986 331-3808023-0................... October 20, 1986 331-3812541-5................... December 26, 1986 331-3812541-5................... December 26, 1986 331-3813766-7................... February 19, 1987 86-477413-2..................... August 22, 1986 86-477413-2..................... August 22, 1986 110-1123057-7................... January 2, 1987 110-1124082-4................... March 26, 1987 110-1272348-9................... November 14, 1986 110-1272348-9................... November 14, 1986 110-1272505-4................... December 10, 1986 110-1272505-4................... December 10, 1986 110-1273532-7................... January 10, 1987 110-1274561-5................... February 20, 1987 110-1274921-1................... March 6, 1987 110-1274921-1................... March 6, 1987 110-1275320-5................... March 23, 1987 110-1275321-3................... March 31, 1987 110-1272505-4................... No Date Available 110-1907947-1................... January 22, 1988 110-1906495-2................... June 5, 1987 110-1906599-1................... June 22, 1987 110-1906599-1................... June 22, 1987 110-1906856-5................... August 2, 1987 110-1907967-9................... January 27, 1988 110-1908198-0................... March 4, 1988 110-1908178-2................... March 10, 1988 110-0294344-8................... May 6, 1987 110-0294344-8................... June 5, 1987 110-1906522-3................... June 6, 1987 110-1124130-1................... April 1, 1987 110-1124130-1................... April 2, 1987 110-1124130-1................... April 2, 1987 110-1125551-7................... July 17, 1987 110-1125551-7................... July 17, 1987 110-1126810-6................... October 27, 1987 110-1127047-4................... November 6, 1987 110-1127620-8................... December 23, 1987 110-1275844-4................... April 16, 1987 110-1278368-1................... July 28, 1987 110-1278958-9................... September 10, 1987 110-1278958-9................... September 10, 1987 110-1279151-0................... September 18, 1987 110-1279825-9................... October 8, 1987 110-1279767-3................... October 16, 1987 110-1280177-2................... October 21, 1987 110-1280206-9................... October 22, 1987 110-1282001-2................... January 12 1988 110-1282566-4................... February 11, 1988 110-1282642-3................... February 11, 1988 110-1286015-8................... February 22, 1988 110-1286165-1................... March 16, 1988 110-1286165-1................... March 16, 1988 110-1286165-1................... March 16, 1988 110-1908453-9................... April 22, 1988 110-1908567-6................... May 11, 1988 110-1908567-6................... May 11, 1988 110-1908928-0................... June 29, 1988 110-1129739-4................... May 13, 1988 110-1131047-8................... August 4, 1988 110-1133675-4................... January 6, 1989 110-1286261-8................... April 7, 1988 110-1286261-8................... April 7, 1988 110-1286492-9................... May 12, 1988 110-1286492-9................... May 12, 1988 110-1286492-9................... May 12, 1988 110-1286677-5................... June 16, 1988 110-1286796-3................... July 7, 1988 110-1286965-4................... August 4, 1988 110-1286965-4................... August 4, 1988 110-1288931-4................... December 8, 1988 110-0301260-3................... May 12, 1989 110-0301272-8................... May 19, 1989 110-0153952-4................... September 3, 1989 110-1135558-0................... May 12, 1989 110-1135558-0................... May 12, 1989 110-1136677-7................... July 11, 1989 110-1139014-0................... November 24, 1989 110-1294013-3................... September 14, 1989 110-1298751-4................... May 15, 1990 110-1274861-9................... March 4, 1987 110-1274863-5................... March 4, 1987 110-1275349-4................... May 12, 1987 110-1285836-8................... August 31, 1988 110-1285994-4................... August 1, 1988 110-1286179-2................... March 25, 1988 110-1286180-0................... March 25, 1988 110-1286181-8................... March 25, 1988 110-1286265-9................... April 5, 1988 110-1286507-4................... May 12, 1988 110-1286580-1................... May 26, 1988 110-1286582-7................... May 26, 1988 110-1286584-3................... May 26, 1988 110-1286634-6................... June 7, 1988 110-1286681-7................... June 18, 1988 110-1286751-8................... June 23, 1988 110-1286763-1................... June 29, 1988 110-1286782-3................... July 7, 1988 110-1286879-7................... July 27, 1988 110-1286881-3................... August 1, 1988 110-1286882-1................... August 10, 1988 110-1286925-8................... July 27, 1988 110-1286927-4................... August 1, 1988 110-1286972-0................... August 11, 1988 110-1286991-0................... August 1, 1988 110-1286993-6................... August 1, 1988 110-1287029-8................... August 15, 1988 110-1287030-6................... August 15, 1988 110-1287031-4................... August 15, 1988 110-1287032-2................... August 15, 1988 110-1287061-1................... August 15, 1988 110-1287062-9................... August 15, 1988 110-1287078-5................... August 17, 1988 110-1287095-9................... August 19, 1988 110-1287147-8................... September 2, 1988 110-1288475-2................... November 23, 1988 110-1288478-8................... November 10, 1988 110-1289801-8................... January 20, 1989 110-1293960-6................... September 11, 1989 110-1296719-3................... February 12, 1990[/INST]Directs the United States Customs Service to provide for the liquidation or reliquidation (refund) of certain entries made at New York, New York, in accordance with the results of an administrative review, during the period from April 1, 1984, through March 31, 1991, by the International Trade Administration of the Department of Commerce (case number A-580-008).</s>

BigGovernment.com and BigJournalism.com have reported throughout the morning about the emergence of new details in the Weinergate saga, after a young woman came forward with new information that tends to undermine severely the theory that Rep. Anthony Weiner (D-NY) was the victim of a “prank” or a “hack.” The following photograph, reminiscent of that posted by former Rep. Chris Lee (R-NY) on Craigslist earlier this year, was allegedly sent to the young woman on Friday, May 20, 2011 via a Yahoo! email address that she claims was an alternate alias for Rep. Weiner: The array of images behind the shirtless congressman include several apparently identifying portraits, including a photograph that appears to be of Rep. Weiner with former President Bill Clinton (at above right, behind the left shoulder). A Google search for the email address Rep. Weiner allegedly used on that occasion yields an invisible Yahoo! profile with images that appear to be a repository for some of Rep. Weiner’s personal photographs. The profile automatically provides what appear to be the last three uploaded photographs in thumbnail form. Below is a screen grab taken yesterday from that page: On Wednesday, May 18, 2011, Rep. Weiner sent an email to the young woman from that same Yahoo! email address that included the now-infamous grey underwear photograph (attached to the email as “package.JPG”): Later that same day, apparently after receiving several images from the young woman, Rep. Weiner allegedly sent another photograph to her from the same Yahoo! email address. That photograph (attached to the email as “ready.JPG”) is extremely graphic, and leaves nothing to the imagination. ||||| Earlier this morning, BigGovernment.com and BigJournalism.com revealed that a woman had come forward with what she claims are intimate photographs, chats, and emails that she allegedly exchanged with Rep. Anthony Weiner (D-NY). The following photograph was allegedly sent to the young woman from [email protected] via BlackBerry on Wednesday, May 4, 2011, under the subject, “Me and the pussys” (note cats in background): Keep following BigGovernment.com and BigJournalism.com throughout the day for more photographs and details. ||||| A new woman has come forward with what she claims are photographs, chats, and emails with Rep. Anthony Weiner (D-NY). These appear to undermine severely Rep. Weiner’s explanations that he was the victim of a “prank” or a “hack.” The detailed new information suggests that the Brooklyn- and Queens-based representative and the young woman in question were involved in an online, consensual relationship involving the mutual exchange of intimate photographs. BigGovernment.com and BigJournalism.com were approached regarding this information more than a week prior to the separate, independent event of Friday, May 27, 2011, when a link to the now-infamous “gray underwear” photograph appeared publicly on Rep. Weiner’s Twitter feed. We will be updating BigGovernment.com and BigJournalism.com throughout the day with photographs, timelines, and other clarifying details. However, we will not be releasing all of the material because some of it is of an extreme, graphic nature. ||||| ‘It’s Me’: Rep. Weiner Sends Playful Photo to New Friend Earlier today, BigGovernment.com and BigJournalism.com revealed that a woman had come forward with what she claims are photographs, chats, and emails she exchanged with Rep. Anthony Weiner (D-NY). The following photograph was allegedly emailed to the young woman in question from [email protected] on Thursday, May 5, 2011, via BlackBerry: The woman has indicated that Rep. Weiner allegedly sent the photograph after she asked him to confirm that he was taking photographs contemporaneously, in conjunction with their apparent online communications. Keep following BigGovernment.com and BigJournalism.com throughout the day for more photographs and details.

– Weinergate just keeps getting worse for Anthony Weiner. Andrew Breitbart's BigGovernment.com claims to have a cache of "photographs, chats, and emails" Weiner allegedly sent to a woman—not the one involved in the original scandal—that shows the two had "an online, consensual relationship involving the mutual exchange of intimate photographs." The site says it will reveal portions of the material throughout the day, but won't release all of it because "some of it is of an extreme, graphic nature." The most recent picture released shows a bare torso belonging to, Breitbart theorizes, Weiner (a determination Breitbart based in part on some framed photos that appear in the background). The woman claims Weiner sent her that photo on May 20 from a Yahoo! email address the Congressman was using, and that two days earlier he sent her the now-famous underwear photo from that same address as well as another, much more graphic, photo. Two other pictures the website has released clearly show Weiner's face. In one, allegedly sent May 4 from [email protected], he's posing with cats (or, as he called them in the email he allegedly sent to the woman, "pussys"); in the other, sent the next day, he's holding a sign with the word "me" and an arrow pointing to him. The website claims it was approached by the woman more than a week before the crotch-shot scandal broke.

<s>[INST]BigGovernment.com and BigJournalism.com have reported throughout the morning about the emergence of new details in the Weinergate saga, after a young woman came forward with new information that tends to undermine severely the theory that Rep. Anthony Weiner (D-NY) was the victim of a “prank” or a “hack.” The following photograph, reminiscent of that posted by former Rep. Chris Lee (R-NY) on Craigslist earlier this year, was allegedly sent to the young woman on Friday, May 20, 2011 via a Yahoo! email address that she claims was an alternate alias for Rep. Weiner: The array of images behind the shirtless congressman include several apparently identifying portraits, including a photograph that appears to be of Rep. Weiner with former President Bill Clinton (at above right, behind the left shoulder). A Google search for the email address Rep. Weiner allegedly used on that occasion yields an invisible Yahoo! profile with images that appear to be a repository for some of Rep. Weiner’s personal photographs. The profile automatically provides what appear to be the last three uploaded photographs in thumbnail form. Below is a screen grab taken yesterday from that page: On Wednesday, May 18, 2011, Rep. Weiner sent an email to the young woman from that same Yahoo! email address that included the now-infamous grey underwear photograph (attached to the email as “package.JPG”): Later that same day, apparently after receiving several images from the young woman, Rep. Weiner allegedly sent another photograph to her from the same Yahoo! email address. That photograph (attached to the email as “ready.JPG”) is extremely graphic, and leaves nothing to the imagination. ||||| Earlier this morning, BigGovernment.com and BigJournalism.com revealed that a woman had come forward with what she claims are intimate photographs, chats, and emails that she allegedly exchanged with Rep. Anthony Weiner (D-NY). The following photograph was allegedly sent to the young woman from [email protected] via BlackBerry on Wednesday, May 4, 2011, under the subject, “Me and the pussys” (note cats in background): Keep following BigGovernment.com and BigJournalism.com throughout the day for more photographs and details. ||||| A new woman has come forward with what she claims are photographs, chats, and emails with Rep. Anthony Weiner (D-NY). These appear to undermine severely Rep. Weiner’s explanations that he was the victim of a “prank” or a “hack.” The detailed new information suggests that the Brooklyn- and Queens-based representative and the young woman in question were involved in an online, consensual relationship involving the mutual exchange of intimate photographs. BigGovernment.com and BigJournalism.com were approached regarding this information more than a week prior to the separate, independent event of Friday, May 27, 2011, when a link to the now-infamous “gray underwear” photograph appeared publicly on Rep. Weiner’s Twitter feed. We will be updating BigGovernment.com and BigJournalism.com throughout the day with photographs, timelines, and other clarifying details. However, we will not be releasing all of the material because some of it is of an extreme, graphic nature. ||||| ‘It’s Me’: Rep. Weiner Sends Playful Photo to New Friend Earlier today, BigGovernment.com and BigJournalism.com revealed that a woman had come forward with what she claims are photographs, chats, and emails she exchanged with Rep. Anthony Weiner (D-NY). The following photograph was allegedly emailed to the young woman in question from [email protected] on Thursday, May 5, 2011, via BlackBerry: The woman has indicated that Rep. Weiner allegedly sent the photograph after she asked him to confirm that he was taking photographs contemporaneously, in conjunction with their apparent online communications. Keep following BigGovernment.com and BigJournalism.com throughout the day for more photographs and details.[/INST]– Weinergate just keeps getting worse for Anthony Weiner. Andrew Breitbart's BigGovernment.com claims to have a cache of "photographs, chats, and emails" Weiner allegedly sent to a woman—not the one involved in the original scandal—that shows the two had "an online, consensual relationship involving the mutual exchange of intimate photographs." The site says it will reveal portions of the material throughout the day, but won't release all of it because "some of it is of an extreme, graphic nature." The most recent picture released shows a bare torso belonging to, Breitbart theorizes, Weiner (a determination Breitbart based in part on some framed photos that appear in the background). The woman claims Weiner sent her that photo on May 20 from a Yahoo! email address the Congressman was using, and that two days earlier he sent her the now-famous underwear photo from that same address as well as another, much more graphic, photo. Two other pictures the website has released clearly show Weiner's face. In one, allegedly sent May 4 from [email protected], he's posing with cats (or, as he called them in the email he allegedly sent to the woman, "pussys"); in the other, sent the next day, he's holding a sign with the word "me" and an arrow pointing to him. The website claims it was approached by the woman more than a week before the crotch-shot scandal broke.</s>

lupus panniculitis ( lp ) occurs in 3% of the patients with cutaneous lupus erythematosus . it primarily affects subcutaneous tissues of the face and the proximal areas of the limbs , leading to residual atrophy . lp may lead to major aesthetic sequelae that severely decrease quality of life ( even during good long - term control of the autoimmune processes ) . given the condition 's low prevalence , treatment strategies in lp only 1 case of lipofilling has been reported with a follow - up period limited to 12 months . here , we report on the strikingly good aesthetic outcomes , the long - term quality - of - life benefits , and the safety of lipofilling in 2 patients with lp - associated subcutaneous atrophy . patient 1 ( a 13-year - old boy ) was referred for an ill - defined subcutaneous inflammatory nodule on the chin . a histopathological examination revealed a marked lymphocytic infiltrate ( in superficial and deep tissues ) with juxtafollicular involvement , prompting us to diagnose lp . treatment with hydroxychloroquine for 18 months led to the complete disappearance of inflammatory signs but resulted in a cup - shaped lipoatrophy and facial asymmetry . patient 2 ( a 32-year - old female ) had been monitored over a 6-year period for systemic lupus erythematosus with positive antinuclear and anti - double - stranded dna antibodies . during treatment with hydroxychloroquine , she presented with subcutaneous inflammatory lesions on the thighs and cheeks . a diagnosis of lp was confirmed by histopathological examination of a skin biopsy according to the criteria by peter and su . the initial response to oral prednisone was good , but the patient became steroid dependent . a series of steroid - sparing agents was then administered ( including thalidomide , cyclophosphamide , and azathioprine ) . four weekly intravenous infusions of rituximab ( 375 mg / m ) , which were repeated 1 year later , led to complete remission , although atrophic scarring in malar areas persisted . following a request from both patients for correction of the aesthetic sequelae , we chose to use lipofilling . briefly , 10 ml of fat were collected via a 2-mm incision below the umbilicus . next , fat cells were injected into the submental ( patient 1 ) or malar ( patient 2 ) areas using coleman needles . there were no complications , and the positive aesthetic outcome was maintained 3 years after the procedure with no signs of the recurrence of lp ( fig 1 ) . the dermatology quality of life index decreased from 16 before lipofilling to 0 six months thereafter ( patient 1 ) . lipofilling is a well - established technique widely used in the rejuvenation of the aging face and in iatrogenic lipoatrophy [ 7 , 8 ] . this technique was also used successfully in some cases of linear scleroderma en coup de sabre . most of the common side effects of lipofilling are not severe . nevertheless , it is critical for surgeons to have a firm knowledge of the vascular anatomy because some cases of irreversible blindness have been reported . the good response of patient 2 to rituximab suggests that the efficacy of rituximab as a salvage therapy for treatment - refractory lp should be assessed in prospective trials . along with a previous report , the 2 present cases suggest that lipofilling is effective for treating the atrophic scars that result from permanent alterations of the subcutaneous fatty tissue in lp . moreover , the short- and long - term absence of any signs of lupus relapse or postsurgical complications is encouraging . the lipofilling procedure appears to be very safe when performed in patients with stable disease and thus paves the way for prospective , larger - scale studies in patients with completely controlled autoimmune disorder . these long - term , controlled trials will be able to accurately assess the benefit - risk ratio of lipofilling in lp and other immune - related subcutaneous scarring conditions .

lupus panniculitis is a rare manifestation of cutaneous lupus erythematosus , which may lead to major aesthetic sequelae with a severe impact on patients quality of life . we report 2 cases supporting the short- and long - term efficacy and safety of lipofilling in the treatment of lupus panniculitis - induced atrophy . these observations pave the way for prospective , larger - scale studies in patients with scarring lupus panniculitis , provided that the autoimmune pathogenic process is in complete , stable remission .

<s>[INST]lupus panniculitis ( lp ) occurs in 3% of the patients with cutaneous lupus erythematosus . it primarily affects subcutaneous tissues of the face and the proximal areas of the limbs , leading to residual atrophy . lp may lead to major aesthetic sequelae that severely decrease quality of life ( even during good long - term control of the autoimmune processes ) . given the condition 's low prevalence , treatment strategies in lp only 1 case of lipofilling has been reported with a follow - up period limited to 12 months . here , we report on the strikingly good aesthetic outcomes , the long - term quality - of - life benefits , and the safety of lipofilling in 2 patients with lp - associated subcutaneous atrophy . patient 1 ( a 13-year - old boy ) was referred for an ill - defined subcutaneous inflammatory nodule on the chin . a histopathological examination revealed a marked lymphocytic infiltrate ( in superficial and deep tissues ) with juxtafollicular involvement , prompting us to diagnose lp . treatment with hydroxychloroquine for 18 months led to the complete disappearance of inflammatory signs but resulted in a cup - shaped lipoatrophy and facial asymmetry . patient 2 ( a 32-year - old female ) had been monitored over a 6-year period for systemic lupus erythematosus with positive antinuclear and anti - double - stranded dna antibodies . during treatment with hydroxychloroquine , she presented with subcutaneous inflammatory lesions on the thighs and cheeks . a diagnosis of lp was confirmed by histopathological examination of a skin biopsy according to the criteria by peter and su . the initial response to oral prednisone was good , but the patient became steroid dependent . a series of steroid - sparing agents was then administered ( including thalidomide , cyclophosphamide , and azathioprine ) . four weekly intravenous infusions of rituximab ( 375 mg / m ) , which were repeated 1 year later , led to complete remission , although atrophic scarring in malar areas persisted . following a request from both patients for correction of the aesthetic sequelae , we chose to use lipofilling . briefly , 10 ml of fat were collected via a 2-mm incision below the umbilicus . next , fat cells were injected into the submental ( patient 1 ) or malar ( patient 2 ) areas using coleman needles . there were no complications , and the positive aesthetic outcome was maintained 3 years after the procedure with no signs of the recurrence of lp ( fig 1 ) . the dermatology quality of life index decreased from 16 before lipofilling to 0 six months thereafter ( patient 1 ) . lipofilling is a well - established technique widely used in the rejuvenation of the aging face and in iatrogenic lipoatrophy [ 7 , 8 ] . this technique was also used successfully in some cases of linear scleroderma en coup de sabre . most of the common side effects of lipofilling are not severe . nevertheless , it is critical for surgeons to have a firm knowledge of the vascular anatomy because some cases of irreversible blindness have been reported . the good response of patient 2 to rituximab suggests that the efficacy of rituximab as a salvage therapy for treatment - refractory lp should be assessed in prospective trials . along with a previous report , the 2 present cases suggest that lipofilling is effective for treating the atrophic scars that result from permanent alterations of the subcutaneous fatty tissue in lp . moreover , the short- and long - term absence of any signs of lupus relapse or postsurgical complications is encouraging . the lipofilling procedure appears to be very safe when performed in patients with stable disease and thus paves the way for prospective , larger - scale studies in patients with completely controlled autoimmune disorder . these long - term , controlled trials will be able to accurately assess the benefit - risk ratio of lipofilling in lp and other immune - related subcutaneous scarring conditions . [/INST]lupus panniculitis is a rare manifestation of cutaneous lupus erythematosus , which may lead to major aesthetic sequelae with a severe impact on patients quality of life . we report 2 cases supporting the short- and long - term efficacy and safety of lipofilling in the treatment of lupus panniculitis - induced atrophy . these observations pave the way for prospective , larger - scale studies in patients with scarring lupus panniculitis , provided that the autoimmune pathogenic process is in complete , stable remission .</s>

medical practitioners commonly advice their patients who are on antiplatelet therapy to either stop or alter their medications prior to surgical procedures due to fear of excessive and uncontrolled bleeding . it is a proven fact that aspirin causes increased risk of intraoperative as well as postoperative bleeding and also increased risk of thromboembolic events such as myocardial infraction and cerebrovascular accidents if the drug is continued . thrombotic and thromboembolic occlusion of blood vessels is the main cause of ischemic events in heart , lungs , and brain . in case of blood vessel injury , primary mechanism arrests early bleeding as a result of platelet plug formation . the secondary hemostasis phase is mediated by a complex cascade of clotting factors which helps in the formation of fibrin clot . in recent years , lot of research has been done and progress has been made in the field of antiplatelet agents and anticoagulants . even though a number of antiplatelet and anticoagulant agents have been developed , aspirin and warfarin remain the standard drugs of choice . development of aspirin dates back to 1897 and is considered as one of the safest and cheapest drugs worldwide . a general practitioner lawrence craven prescribed low - dose aspirin ( baby aspirin ) to his 400 patients and none of them developed myocardial infraction . this was probably the first time in medical history where aspirin was used to prevent myocardial infarction . the antithrombotic effect of aspirin is mediated by irreversible inhibition of cyclooxygenase activity in platelets . thromboxane a2 is a potent platelet stimulant which leads to degranulation of platelet and platelet aggregation . aspirin inhibits cyclooxygenase enzyme and decreases the level of platelet stimulant thromboxane a2 , thus increasing the bleeding time . this is the important reason for a medical practitioner to stop aspirin 3 - 7 days prior to any invasive surgery . the purpose of this study was to investigate the influence of aspirin on post - extraction bleeding . patients who were on aspirin therapy , aged between 50 and 65 years , and who had to undergo tooth extraction for endodontic reason with no mobility were selected for the study . patients on warfarin , non - steroidal anti - inflammatory drugs , heparin , steroids , or suffering from blood disorders and diabetes were excluded from the study . informed consent was obtained from the patients and the ethical committee clearance was also obtained . two hundred patients including both males and females whose teeth were indicated for extraction were included in the study . group a patients continued to receive aspirin preoperatively , while group b patients were asked to stop aspirin 7 days prior to extraction after consultation with the physician . bleeding time ( white and lee technique ) and clotting time ( ivy 's technique ) were calculated . after atraumatic extraction ( forceps method ) was performed , the bleeding time was recorded . chi - square test was used to evaluate the relative frequencies of patients in both groups . after applying chi - square test , the mean bleeding time was calculated as 2.1 0.52 min in the patients who discontinued baby aspirin ( group b ) 7 days prior to extraction . bleeding time of group a patients who continued aspirin through the entire study was found to be 3.8 0.75 min . this difference was statistically significant ( p = 0.002 ) [ table 1 and graph 1 ] . although there was significant increase in the bleeding time of group a patients , it should be noted that the bleeding time of both the groups was within normal limits . clotting time of group b patients was 3.8 0.75 min and group a patients was 4.7 0.52 min , which were also within the normal limits ( normal range according to ivy 's method : 3 - 5 min ) . mean bleeding time and mean clotting time ( in minutes ) of group a and group b patients historically , aspirin was used as an anti - inflammatory , analgesic , and antipyretic drug for a short period of disease activity . in 1950 , lawrence craven reported for the first time its long - term use to prevent myocardial infarction . antiplatelet activity of aspirin occurs at doses ranging from as low as 40 mg / day to 320 mg / day . doses above 320 mg / day decrease the effectiveness of aspirin as an antiplatelet agent due to inhibition of prostacyclin production . however , recent clinical trial indicates that 160 mg / day is optimal for antiplatelet action . in emergencies where urgent antithrombotic action is required , a loading dose of 300 mg is advocated . usually , in the united states , daily dose of 81 mg , 160 mg , or 325 mg is prescribed , while in europe and other countries , daily dose of 75 mg , 150 mg , or 300 mg is prescribed . risk of continuing aspirin therapy prior to surgery is that with the alteration of platelet function , longer time period is required to stop bleeding from a surgical site . collet et al . stated that in patients on aspirin , the average risk of bleeding increases 1.5-fold . at the same time , there is a risk of stopping aspirin prior to surgery , which leads to a potential risk of rebound of thromboembolic vascular events . on stopping aspirin , thromboxane a2 activity increases to a greater extent with decrease in fibrinolytic activity . anderson et al . showed the existence of biological platelet rebound phenomenon on interruption of aspirin therapy . approximately 20% of these episodes are fatal and another 40% can lead to permanent disability . practitioners who advocate the stoppage of aspirin have been debating among themselves regarding the time limit to stop aspirin . according to literature the effect lasts for 7 - 10 days which is the life span of platelets . sonksen et al . , in their study comprising 52 healthy individuals , reported that it is not recommended to withdraw aspirin for more than 5 days . wahl et al . advocated that aspirin should be discontinued for 3 days only , as after 3 days of interruption of aspirin , sufficient number of newer platelets would be present in the circulation for hemostasis . some studies have shown that there is always an increased risk of bleeding in patients continuing aspirin . however , if the aspirin therapy is discontinued , there is increased risk of thromboembolic events which can be fatal , but none of these have been reported in dental literature . mentioned in their article that there is scarcity of literature regarding dental surgeries involving patients on aspirin medication . little et al . reported that unless the bleeding time is increased above 20 min , aspirin - affected platelets would not cause significant bleeding complication . canigral et al . conducted a research involving surgical extraction in patients on antithrombotic therapy . in 92% cases , gaspar et al . advocated that ambulatory oral surgical procedures can be performed in patients without discontinuing the use of aspirin . a recent recommendation from the american heart association and american college of cardiology is either continuing aspirin or clopidogrel therapy for minor oral surgical procedures in patients with coronary artery stents or delay the treatment until prescribed regimen is complicated . the present study demonstrated that there was significant increase in the bleeding time in both the groups , but it was not difficult to stop the bleeding in any case . although the bleeding time increased in group a patients , it still remained within the normal range , regardless of whether the patients continued or discontinued their aspirin therapy . conducted a study with 17 patients randomized to aspirin and 19 to placebo and found no differences in the bleeding outcomes for patients on aspirin . this finding suggested that there was no need to discontinue aspirin prior to any ambulatory oral surgical procedure . adchariyapetch compared the postoperative bleeding in subjects who stopped taking aspirin and those who continued taking aspirin for 7 days prior to extraction . matocha concluded in his study that the risk of bleeding after dental extraction is minimal in the patients with aspirin therapy and did not exceed 0.2 - 2.3% murphy et al . concluded in their survey that 86% of the dental practitioners who advised patients to stop taking antiplatelet drugs prior to dental extraction did so with the consultation of the patients physicians , and found that the protocol followed by the physicians and dentists was not based on the current recommendations and guidelines . concluded that the risk of stopping antiplatelet therapy and predisposing the patient to thromboembolic events overweighed the minimal risk of bleeding from dental procedures . wahl reported in his study that of 950 patients receiving anticoagulation therapy , only 12 required ( < 1.3% ) more than local measures to stop the bleeding . he concluded that while discontinuation of anticoagulation therapy has been a common practice , bleeding after dental surgery is rarely life threatening . thus , it can be concluded based on dental and medical literature that if a practitioner wishes to discontinue the aspirin therapy , it should not exceed more than 3 days . risk of stopping antiplatelet therapy and predisposing the patient to thromboembolic events overweighs the minimal risk of bleeding from dental procedures . although there was increase in bleeding time in the present study , it was not beyond the normal range . hence , it can be concluded that low dose of aspirin should not be discontinued prior to dental extractions , as it predisposes the patient to unwanted thromboembolic events .

aim : the aim of the study was to evaluate the influence of aspirin on post - extraction bleeding in a clinical setup.materials and methods : two hundred patients aged between 50 and 65 years who were indicated for dental extraction for endodontic reason were selected from the outpatient department of oral and maxillofacial surgery . the patients were randomly divided into aspirin continuing group ( group a ) and aspirin discontinuing group ( group b ) . after checking all the vital signs , the extractions were carried out . bleeding time and clotting time were recorded for evaluation by chi - square test.results:chi-square test revealed that the bleeding time increased ( 3.8 0.75 ) in group a patients continued with the aspirin therapy where as group b discontinued aspirin . similarly , the clotting time increased in group b patients and decreased in group a patients . but in both the groups , bleeding and clotting time remained within normal limits.conclusion:reviewing most of the dental and medical literature , it can be concluded that there is absolutely no need to discontinue antiplatelet therapy for any ambulatory dental procedure , and even if the practitioner wishes to discontinue , it should not be for more than 3 daaq2ys . this is also stated in the guidelines of the american heart association .

<s>[INST]medical practitioners commonly advice their patients who are on antiplatelet therapy to either stop or alter their medications prior to surgical procedures due to fear of excessive and uncontrolled bleeding . it is a proven fact that aspirin causes increased risk of intraoperative as well as postoperative bleeding and also increased risk of thromboembolic events such as myocardial infraction and cerebrovascular accidents if the drug is continued . thrombotic and thromboembolic occlusion of blood vessels is the main cause of ischemic events in heart , lungs , and brain . in case of blood vessel injury , primary mechanism arrests early bleeding as a result of platelet plug formation . the secondary hemostasis phase is mediated by a complex cascade of clotting factors which helps in the formation of fibrin clot . in recent years , lot of research has been done and progress has been made in the field of antiplatelet agents and anticoagulants . even though a number of antiplatelet and anticoagulant agents have been developed , aspirin and warfarin remain the standard drugs of choice . development of aspirin dates back to 1897 and is considered as one of the safest and cheapest drugs worldwide . a general practitioner lawrence craven prescribed low - dose aspirin ( baby aspirin ) to his 400 patients and none of them developed myocardial infraction . this was probably the first time in medical history where aspirin was used to prevent myocardial infarction . the antithrombotic effect of aspirin is mediated by irreversible inhibition of cyclooxygenase activity in platelets . thromboxane a2 is a potent platelet stimulant which leads to degranulation of platelet and platelet aggregation . aspirin inhibits cyclooxygenase enzyme and decreases the level of platelet stimulant thromboxane a2 , thus increasing the bleeding time . this is the important reason for a medical practitioner to stop aspirin 3 - 7 days prior to any invasive surgery . the purpose of this study was to investigate the influence of aspirin on post - extraction bleeding . patients who were on aspirin therapy , aged between 50 and 65 years , and who had to undergo tooth extraction for endodontic reason with no mobility were selected for the study . patients on warfarin , non - steroidal anti - inflammatory drugs , heparin , steroids , or suffering from blood disorders and diabetes were excluded from the study . informed consent was obtained from the patients and the ethical committee clearance was also obtained . two hundred patients including both males and females whose teeth were indicated for extraction were included in the study . group a patients continued to receive aspirin preoperatively , while group b patients were asked to stop aspirin 7 days prior to extraction after consultation with the physician . bleeding time ( white and lee technique ) and clotting time ( ivy 's technique ) were calculated . after atraumatic extraction ( forceps method ) was performed , the bleeding time was recorded . chi - square test was used to evaluate the relative frequencies of patients in both groups . after applying chi - square test , the mean bleeding time was calculated as 2.1 0.52 min in the patients who discontinued baby aspirin ( group b ) 7 days prior to extraction . bleeding time of group a patients who continued aspirin through the entire study was found to be 3.8 0.75 min . this difference was statistically significant ( p = 0.002 ) [ table 1 and graph 1 ] . although there was significant increase in the bleeding time of group a patients , it should be noted that the bleeding time of both the groups was within normal limits . clotting time of group b patients was 3.8 0.75 min and group a patients was 4.7 0.52 min , which were also within the normal limits ( normal range according to ivy 's method : 3 - 5 min ) . mean bleeding time and mean clotting time ( in minutes ) of group a and group b patients historically , aspirin was used as an anti - inflammatory , analgesic , and antipyretic drug for a short period of disease activity . in 1950 , lawrence craven reported for the first time its long - term use to prevent myocardial infarction . antiplatelet activity of aspirin occurs at doses ranging from as low as 40 mg / day to 320 mg / day . doses above 320 mg / day decrease the effectiveness of aspirin as an antiplatelet agent due to inhibition of prostacyclin production . however , recent clinical trial indicates that 160 mg / day is optimal for antiplatelet action . in emergencies where urgent antithrombotic action is required , a loading dose of 300 mg is advocated . usually , in the united states , daily dose of 81 mg , 160 mg , or 325 mg is prescribed , while in europe and other countries , daily dose of 75 mg , 150 mg , or 300 mg is prescribed . risk of continuing aspirin therapy prior to surgery is that with the alteration of platelet function , longer time period is required to stop bleeding from a surgical site . collet et al . stated that in patients on aspirin , the average risk of bleeding increases 1.5-fold . at the same time , there is a risk of stopping aspirin prior to surgery , which leads to a potential risk of rebound of thromboembolic vascular events . on stopping aspirin , thromboxane a2 activity increases to a greater extent with decrease in fibrinolytic activity . anderson et al . showed the existence of biological platelet rebound phenomenon on interruption of aspirin therapy . approximately 20% of these episodes are fatal and another 40% can lead to permanent disability . practitioners who advocate the stoppage of aspirin have been debating among themselves regarding the time limit to stop aspirin . according to literature the effect lasts for 7 - 10 days which is the life span of platelets . sonksen et al . , in their study comprising 52 healthy individuals , reported that it is not recommended to withdraw aspirin for more than 5 days . wahl et al . advocated that aspirin should be discontinued for 3 days only , as after 3 days of interruption of aspirin , sufficient number of newer platelets would be present in the circulation for hemostasis . some studies have shown that there is always an increased risk of bleeding in patients continuing aspirin . however , if the aspirin therapy is discontinued , there is increased risk of thromboembolic events which can be fatal , but none of these have been reported in dental literature . mentioned in their article that there is scarcity of literature regarding dental surgeries involving patients on aspirin medication . little et al . reported that unless the bleeding time is increased above 20 min , aspirin - affected platelets would not cause significant bleeding complication . canigral et al . conducted a research involving surgical extraction in patients on antithrombotic therapy . in 92% cases , gaspar et al . advocated that ambulatory oral surgical procedures can be performed in patients without discontinuing the use of aspirin . a recent recommendation from the american heart association and american college of cardiology is either continuing aspirin or clopidogrel therapy for minor oral surgical procedures in patients with coronary artery stents or delay the treatment until prescribed regimen is complicated . the present study demonstrated that there was significant increase in the bleeding time in both the groups , but it was not difficult to stop the bleeding in any case . although the bleeding time increased in group a patients , it still remained within the normal range , regardless of whether the patients continued or discontinued their aspirin therapy . conducted a study with 17 patients randomized to aspirin and 19 to placebo and found no differences in the bleeding outcomes for patients on aspirin . this finding suggested that there was no need to discontinue aspirin prior to any ambulatory oral surgical procedure . adchariyapetch compared the postoperative bleeding in subjects who stopped taking aspirin and those who continued taking aspirin for 7 days prior to extraction . matocha concluded in his study that the risk of bleeding after dental extraction is minimal in the patients with aspirin therapy and did not exceed 0.2 - 2.3% murphy et al . concluded in their survey that 86% of the dental practitioners who advised patients to stop taking antiplatelet drugs prior to dental extraction did so with the consultation of the patients physicians , and found that the protocol followed by the physicians and dentists was not based on the current recommendations and guidelines . concluded that the risk of stopping antiplatelet therapy and predisposing the patient to thromboembolic events overweighed the minimal risk of bleeding from dental procedures . wahl reported in his study that of 950 patients receiving anticoagulation therapy , only 12 required ( < 1.3% ) more than local measures to stop the bleeding . he concluded that while discontinuation of anticoagulation therapy has been a common practice , bleeding after dental surgery is rarely life threatening . thus , it can be concluded based on dental and medical literature that if a practitioner wishes to discontinue the aspirin therapy , it should not exceed more than 3 days . risk of stopping antiplatelet therapy and predisposing the patient to thromboembolic events overweighs the minimal risk of bleeding from dental procedures . although there was increase in bleeding time in the present study , it was not beyond the normal range . hence , it can be concluded that low dose of aspirin should not be discontinued prior to dental extractions , as it predisposes the patient to unwanted thromboembolic events .[/INST]aim : the aim of the study was to evaluate the influence of aspirin on post - extraction bleeding in a clinical setup.materials and methods : two hundred patients aged between 50 and 65 years who were indicated for dental extraction for endodontic reason were selected from the outpatient department of oral and maxillofacial surgery . the patients were randomly divided into aspirin continuing group ( group a ) and aspirin discontinuing group ( group b ) . after checking all the vital signs , the extractions were carried out . bleeding time and clotting time were recorded for evaluation by chi - square test.results:chi-square test revealed that the bleeding time increased ( 3.8 0.75 ) in group a patients continued with the aspirin therapy where as group b discontinued aspirin . similarly , the clotting time increased in group b patients and decreased in group a patients . but in both the groups , bleeding and clotting time remained within normal limits.conclusion:reviewing most of the dental and medical literature , it can be concluded that there is absolutely no need to discontinue antiplatelet therapy for any ambulatory dental procedure , and even if the practitioner wishes to discontinue , it should not be for more than 3 daaq2ys . this is also stated in the guidelines of the american heart association .</s>

standard linear response theories for electronic transport are formulated to obtain the conductivity tensor . some models for scattering are needed to get a finite response . the most popular approximation is the elastic scattering approach , despite the fact that it can not compensate the electron acceleration due to the applied electric field . it can only be compensated by a momentum dissipation , which can ensure that the total force acting on electrons vanishes in the steady state . another possibility is to analyze forces acting on electrons in the transport regime . the condition of the vanishing total force is the basic physical condition for the steady state . the application of the linear response approach , limiting the problem to the case of small deviation from the equilibrium , gives the transport coefficients satisfying the steady state condition . this idea will be used to determine the hall resistance of a system of bloch spinless electrons in the case of a weak magnetic field . for the sake of simplicity we limit our consideration to isotropic systems where the energy spectrum is represented by a single electron band . it can be expected that in this case the hall resistance will not depend on the dissipation explicitly , which can simplify the analysis substantially . the hall resistance is standardly measured on the so - called hall bar samples , having the form of a long strip . far from the contacts the current density is parallel to the strip edges , say along @xmath0-direction . if the magnetic field is applied perpendicularly to the strip surface , along @xmath1-direction , the current induced lorentz force is shifting the electron charge distribution . as the result there appears a non - equilibrium charge distribution giving rise the hall voltage . the steady state requires the compensation of the lorentz force by the gradient force . for isotropic systems this condition can be written in the following form @xmath2 where @xmath3 is the current density , @xmath4 denotes the background potential including that given by the electric field along @xmath5 direction , @xmath6 , and @xmath7 stands for electro - chemical potential . angular brackets represent quantum - mechanical and statistical average . the internal pressure @xmath8 represents the force of the electron ensemble acting on the external system per unit area . linear response approximation with respect to the electro - chemical potential gradient leads to the following expression for the hall resistance @xmath9 where @xmath10 is the applied current through the strip of thickness @xmath11 and @xmath12 denotes the voltage drop between strip edges . the gradient force and consequently the pressure are quantities which are generally dependent on the magnetic field strength @xmath13 . in the weak field limit the hall resistance can be supposed a linear function of @xmath13 which implies that the @xmath13-dependent internal pressure can be replaced by its zero field limit . for a free electron gas ( resp . hole gas ) it can be identified with the so - called statistical pressure , and its derivative with respect to @xmath7 is simply equal to the electron concentration @xmath14 ( resp . to the negative value of the hole concentration ) @xcite . considering a single electron band the hall resistance for chemical potentials in the vicinity of band edges is thus quite well understood . since it has opposite signs at opposite band edges it should vanish at the band center . to our knowledge , the only published work in which the transition between electron to hole like character of the hall resistance has been described was based on the application of the kubo formula for the special case of substitutional alloys @xcite . however , no procedure based on force analysis has been presented . a previous publication @xcite made by one of us was unfortunately based on incorrect application of the quasi - classical approach as will be specified later . in crystalline solids the equilibrium electron charge distribution can not be assumed as uniform . it is periodic in real space , having translation symmetry given by the lattice periodicity . non - zero current density gives rise to the lorentz force inducing a shift of the mass - center positions . this shift has to be compensated by the gradient force trying to return it back into the equilibrium distribution . the results generally depend on the experimental set up , particularly the way how the non - zero current density is induced . in the regime we will call as fully dissipative , the current is supposed to be exclusively given by the electric field @xmath15 along strip axis . in other words , if @xmath16 the current vanishes . this assumption requires that dissipation take place within the strip , i.e. that the system can be viewed as a macroscopic system . it can be expected that this fully dissipative regime represents the conditions of the standardly measured hall resistance in the weak field limit for which it can be assumed that the effect of the magnetic field to the energy spectrum is negligible . the opposite limiting case is the purely non - dissipative regime for which the current density is exclusively determined by the electric field @xmath6 across the strip , while @xmath17 . such a situation is observed whenever the fermi energy is located within the conduction gaps , i.e. when the magnetic field is strong enough to induce energy gaps giving rise to a hofstadter type spectrum @xcite . it has already been shown that in such a quantum hall regime the induced hall current is closely related to the static electron polarizability @xcite . the non - dissipative regime , for which the hall current is exclusively determined by the orbital magnetization , can be in principle induced even if the fermi energy is located within the energy band . this regime , in the considered weak field limit , will also be analyzed , although the resulting effect is expected to be small , of the order @xmath18 . the main attention will be devoted to the fully dissipative regime . vanishing of the total shift of the mass - center position will be taken as the steady state condition . it will be shown that it is equivalent to the condition of vanishing acceleration along the direction perpendicular to both the current flow and the magnetic field direction . for the sake of simplicity the outlined idea will be described in detail for a two - dimensional electron system since the extension to three - dimensional systems is straightforward . we will limit our consideration to the case of a single band given by a square array of tight - binding atomic states . this model will be described in section ii . the following section will be devoted to the determination of the mass - center shifts within the quasi - classical approach . the obtained results we will be used to determine properties of macroscopic systems at zero temperature . in section iv the magnetic moment due to the motion of mass - center positions will be analyzed and its main features compared with those well known for the case of a strong magnetic field . in section v explicit expressions for the hall resistance and the statistical pressure will be derived . as an example of three - dimensional system the properties of a body - centered cubic lattice of tight - binding states will be presented . the section vi will be devoted to the non - dissipative regime , which is closely related to the effect of the magnetic field on the static electron polarizability . it will be shown that the polarizability of open systems is modified by the lorentz force giving rise to a non - dissipative hall current exclusively determined by demagnetization currents . in the section vii it will be argued that in standard hall bar measurement the current flow is composed of two contributions , that induced by the electric field along the current flow and that originated in demagnetization currents . the resulting general formula for the hall resistance will be presented and its properties briefly discussed . the paper will be closed with short summary . tight - binding model is the standard approach to model band structure of crystals . if periodic boundary conditions are applied eigenfunctions are of bloch form , characterized by the wave vector @xmath19 . assuming square lattice and non - zero overlaps between atomic functions located at the nearest neighbor atomic sites only , the single - band energy spectrum is @xmath20 \ ; , \ ] ] where @xmath21 and @xmath22 denote lattice constant and overlap integral , respectively . the components of the wave vector @xmath19 along the main crystallographic axes , ( 1,0 ) and ( 0,1 ) , are @xmath23 and @xmath24 , respectively . the position of the band center given by the energy of the atomic orbitals , which can be represented by a confining frequency @xmath25 , has been chosen as the origin of the energy scale . the wave numbers @xmath23 and @xmath24 are not the only choice to characterize the eigenstates . the square lattice has a translation symmetry along ( 1,@xmath26 1 ) crystallographic directions as well . choosing components of the wave vector along these directions to characterize bloch states , @xmath27 and @xmath28 , eigenenergies become @xmath29 where @xmath30 . energy dispersions are shown in fig . [ branches ] . in the inset the used elementary cell in the @xmath31 space , which has been chosen as @xmath32 $ ] and @xmath33 $ ] , is shown . since the second derivatives of the energy with respect of @xmath34 as well as @xmath35 are equivalent , these states represent quasiparticles having isotropic effective mass @xmath36 where @xmath37 denotes the absolute value of the effective mass at band edges , @xmath38 . all quasiparticles of the same energy have the same effective mass . this property simplifies the quasi - classical approach which will be described in the following section . at negative energies , @xmath39 , quasiparticles have electron - like character with positive effective mass while at positive energies , @xmath40 , quasiparticles have hole - like character with negative effective mass the same dispersions are obtained for fixed values of @xmath35 . in the inset equi - energy contours are shown in the @xmath41 space . full and dotted lines correspond to states having electron or hole like character , respectively . the dashed line shows the boundary of the standard first brillouin zone , while the bold line shows the elementary cell we are using.,width=3 ] electronic transport is studied on samples having the form of a long strip with a finite width @xmath42 . it is thus natural to assume periodic boundary conditions along the direction given by the strip axis only . the eigenfuctions thus have bloch - like character along strip axis , while along perpendicular direction they are of limited range . if the strip width can be counted as macroscopic , eigenenergies are practically untouched by the change of the boundary conditions . for isotropic systems , like the considered square lattice , the measured transport coefficient are independent of the strip orientation . we can thus choose the strip axis to be parallel with the ( 1,1 ) crystallographic direction without loss of generality . in this case the eigenfunctions can be approximated by a linear combination of bloch states @xmath43 and @xmath44 . the index @xmath34 can be then viewed as the branch index representing bound modes across the strip . in such the case the only nonzero component of the velocity expectation value is along strip axis @xmath45 in the spirit of the preceding section we consider a strip opened along the @xmath0 direction which coincides with ( 1,1 ) crystallographic direction of the considered square lattice . the applied magnetic field along the @xmath1 direction and the electric field across strip , i.e. along the @xmath5 direction , @xmath6 , give rise to the lorentz force and electric force , respectively . to preserve the bloch character of the wavefunctions along the @xmath0 direction the landau gauge for vector potential is used , @xmath46 . we include it into the hamiltonian by using the so - called peierls substitution @xcite . since the effective mass of quasiparticles is isotropic we can use the following effective hamiltonian @xmath47 where the @xmath48 corresponds to the sign of the effective mass @xmath49 , and @xmath50 denotes the magnetic length , which is related to the cyclotron frequency @xmath51 as @xmath52 the last term of the effective hamiltonian @xmath53 appears to preserve the origin of the energy scale given by the oscillator energy @xmath54 . the energy operator @xmath55 is defined by its taylor expansion in @xmath35 , and in the considered case of the weak field limit only terms up to the second order are preserved . the effective hamiltonian then becomes simply the one of an effective harmonic oscillator @xmath56 ^ 2 + \nonumber \\ - \frac{1}{2 } \ , m_{\beta}^{\ast}(\kappa ) \ , \tilde{\omega}^2 \left [ y_{\beta}(\kappa ) \right]^2 \ , + \ , e_{\beta}^{(0)}(\kappa ) \ , - \ , \frac{\pm 1}{2 } \ , \hbar \omega_0 \ , , \;\end{aligned}\ ] ] where @xmath57 denotes the expectation value of the mass - center position @xmath58 and @xmath59 resulting eigenenergies are @xmath60 ^ 2 .\ ] ] the expectation of the velocity along the strip axis has the following expression @xmath61 which coincides with the well known result for magnetic field corrections to the velocity @xcite . the corrections to the energy , as well as to the velocity , due to the presence of magnetic and electric fields are proportional to square of these fields or their product . in the weak field limit , @xmath62 and @xmath63 , these corrections can thus be neglected and the only effect that will be considered is the change of the quasiparticle dynamics , represented in our description by the change of their mass - center positions . this approach which will be used in the following treatment is in accord with the standard quasi - classical view . to support this let us consider the product @xmath64 representing the quasiparticle acceleration @xmath65 along @xmath5 direction . from eq . ( [ y_eff ] ) we get @xmath66 this relation leads to the conclusion that in crystals the acceleration of quasiparticles is modified by their effective mass which is in agreement with the quasi - classical approach presented e.g. in landau - lifshitz textbook @xcite . note that the quasiparticle acceleration along the @xmath5 direction induced by the electric field @xmath6 originates in their transfer between branches @xmath34 . the presented quasi - classical approach neglects the interference effects induced by the magnetic field which are responsible for modification of the energy spectrum . a number of energy gaps are created and the energy structure is of the hofstadter type @xcite . in weak field limit , the gaps in the energy spectrum becomes extremely small , and it can be expected that theses interferences will be destroyed by dissipative processes always present at finite temperatures . for this reason the presented quasi - classical approach is acceptable . the applied magnetic field along the @xmath1 direction gives rise to the magnetic moment @xmath67 . generally @xmath67 can be divided into two contributions : @xmath68 given by the internal momentum of quasiparticles and @xmath69 due to the motion of their mass - centers . the second contribution can be viewed as the macroscopic one since the trajectories of the mass - center positions are extended along the @xmath0 direction . it can easily be determined within the quasi - classical approximation presented in the preceding section . its expectation value reads @xmath70 where in accord with eq . ( [ y_eff ] ) @xmath71 defining the dimensionless quantity @xmath72 as @xmath73 where @xmath42 is the strip width , the fermi electron contribution per unit area reads @xmath74 the relation between @xmath69 and @xmath72 defined by eq . ( [ sigma_gen ] ) is quite general and for the case of quantizing magnetic fields and weak periodic modulation has already been discussed in detail , where @xmath72 was called the effective topological number @xcite . in the weak field limit , for the square lattice , performing the @xmath35 integration in eq . ( [ sigma_gen ] ) gives @xmath75 where @xmath76 if the positive value of @xmath35 on the fermi surface for a given @xmath34 . using @xmath77 , we finally get @xmath78 where @xmath79 at the band edges the effective quasiparticle concentration @xmath80 approaches the electron or hole concentration @xmath81 with @xmath82 for electrons and @xmath83 for holes . energy dependence of @xmath72 and @xmath80 are shown in fig . [ sigma_e ] . , full line , and the effective quasiparticle number in a unit cell @xmath84 , dashed line.,width=3 ] at negative energies , @xmath85 , for which quasiparticles have electron - like character , the fermi contribution to @xmath69 given by eq . ( [ m_z ] ) is positive , i.e. it represents paramagnetic contribution to the total magnetic moment . it is often interpreted as a contribution given by electrons skipping along sample edges , which fully compensates the diamagnetic moment of electrons in the classical limit . in the presented model it has been equally splited over the local strips of tight - binding atomic orbitals . at positive energies the contribution of fermi particles to @xmath69 has opposite sign revealing electron - hole symmetry . at the band center it vanishes , @xmath86 this is the consequence of the electron - hole symmetry and this feature persists even in the case of strong magnetic fields affecting energy spectra substantially @xcite . similarly , when the energy band is fully occupied , @xmath86 in the weak field limit , as well as in the case of quantizing magnetic fields . the electric field along the strip axis , @xmath15 , accelerates electrons along the @xmath0 direction . this effect can be modelled by including the time dependent vector potential @xmath87 into the hamiltonian . for small values of the electric field and short times the linear response gives the following change of the quasiparticle velocity @xmath88 where corrections to the velocity proportional to @xmath18 , eq . ( [ v_b ] ) , have been neglected . summation over occupied states gives the current density along @xmath0 direction @xmath89 change of the velocities gives rise to the shift of mass - center positions of quasiparticles , eq . ( [ y_b ] ) . summation over occupied states leads to the following expression for mass - center shift @xmath90 of the electron density within the unit cell area @xmath91 evidently this time dependent shift is induced by the lorentz force . the shift of the mass - center position is closely related to the shift of the electron charge distribution with respect of the periodic positive background charge . it gives rise to the coulomb energy . for the system is thus energetically more acceptable to induce electric field along @xmath5 direction , @xmath6 , which would be able to minimize the coulomb energy , i.e. to force shifted electron charge distribution towards its equilibrium one . in the presented model this force is represented by the confining potential of the strength given by the frequency @xmath25 . standard condition to estimate the induced field @xmath6 is the condition of vanishing acceleration given by eq . ( [ acceleration ] ) . it coincides with the condition of vanishing average shift of mass center positions defined by eq . ( [ y_eff ] ) . summation over occupied states gives @xmath92 for the hall resistance we get @xmath93 the energy dependence of the hall resistance is shown on fig . it shows clearly the electron hole symmetry . at band edges , @xmath94 , @xmath80 approaches quasiparticle concentration and the classical result for the hall resistance is recovered . is replaced by the negative value of the electron concentration ( @xmath95 ) or by the hole concentration ( @xmath96).,width=3 ] to approach a steady state an energy dissipation is necessary to eliminate the acceleration induced by @xmath15 . the standard way is to assume exponential decay of momentum characterized by the relaxation time @xmath97 . in other words the time entering expression for the current density , eq . ( [ j_x ] ) , has to be replaced by @xmath97 , which is in general a @xmath7 dependent quantity . although the hall resistance does not explicitly depends on the momentum relaxation it is essential for application of the linear response with respect of @xmath6 to held it sufficiently small . in the considered weak field limit the current is supposed to be fully determined by the electric field along the strip axis . this assumption is applicable if the dissipation take place within the strip area . in the case of a quantizing magnetic field this assumption is not acceptable . whenever the fermi energy is located within an energy gap there might appear magnetic edge states leading to non - dissipative current . in this case the electric field along the current flow vanishes and the current is fully determined by the perpendicular electric field . comparison of the expression for the hall resistance , eq . ( [ rh_2d ] ) , with the more general form given by the eq . ( [ rh_gen ] ) suggests that hall resistance has to be related to a pressure gradient representing the fully dissipative regime . in the quasi - classical approach we are using , the carriers are supposed to be quasiparticles having isotropic effective mass @xmath98 which is defined by their energy , eq . ( [ m_ast ] ) . quasiparticles are allowed to move freely along any direction ( i.e. even along @xmath5 direction by transitions between branches ) . the effect of the periodic background is included via their effective mass and their momentum is given by the product of the effective mass and the velocity . in this case the so - called statistical pressure can be easily evaluated following the standard procedure for gas system @xcite . let us consider quasiparticles located within a finite area separated from outside quasiparticles by walls preventing particle transfer . the total momentum transfered to the wall perpendicular e.g. to @xmath0 direction is equal to @xmath99 . the number of electrons hitting the wall per unit time is given by their velocity , and statistical pressure defined as the force per unit length acting along any direction reads @xmath100 ^ 2 \ , , \ ] ] where the prime indicates that summation is taken over those states for which the velocity is of one particular sign , say the positive one . inserting explicit expressions for the effective mass and velocity , eq . ( [ m_ast ] ) and eq . ( [ v_0 ] ) , respectively , we get @xmath101 contribution of fermi carriers to the statistical pressure is positive for electron - like quasiparticles while for hole - like quasiparticles it is negative since the hole concentration decreases with rising value of the chemical potential @xmath7 . at the band center where the density of states diverges , the statistical pressure diverges as well and consequently the hall resistance vanishes . comparison of eq . ( [ dp_stat / dmu ] ) with eq . ( [ rh_2d ] ) gives for the hall resistance in the fully dissipative regime the relation we have been looking for @xmath102 note that for two - dimensional systems the strip thickness @xmath11 entering the general formula , eq . ( [ rh_gen ] ) , has to be replaced by unity . the above calculation corrects a previous result presented by one of us @xcite , where the effective mass was erroneously identified with the local cyclotron mass . the results presented above can easily be generalized to a three dimensional system . as an example we consider here the body - centered cubic lattice . taking into account the overlap between nearest neighbor atomic sites only , the tight - binding single band spectrum , in the analogy with that for square lattice , can be written in the following form @xmath103 where index @xmath104 represents eigenstate modes along @xmath1 direction . the effective mass is isotropic and all states of the same energy have the same effective mass @xmath105 for negative energies particles have electron - like character while for positive energies they have hole - like character . at the band edges the absolute value of the effective mass is @xmath106 . we can thus proceed as in the preceding section . we get expressions with the same structure , but with an additional summation over the index @xmath104 . for the hall resistance defined by eq . ( [ rh_gen ] ) we get @xmath107 where @xmath108 @xmath109 $ ] . in this case also the condition of vanishing acceleration as well as the independently derived expression for the statistical pressure lead to the same results . at the lower band edge ( @xmath110 ) @xmath111 approaches the electron concentration , while at the upper edge ( @xmath112 ) it approaches the hole concentration . at the band center the hall resistance vanishes as expected . as function of the energy it shows the same qualitative features as that for square lattice presented in fig . it has recently been shown that a strong magnetic field , which leads to magnetic quantization of the electron energy spectra , can significantly affect the static electron polarizability of crystalline solids . this is caused by appearance of the lorentz force . as a result a close relation between the induced hall current and the static electron polarizability of two - dimensional systems open along one direction has been established @xcite . in the weak field limit we consider here , it can be expected that this effect will be nearly negligible since the effect of the magnetic field on the energy spectra is proportional to square of the field strength . nevertheless , the analysis of this effect will allow us to understand the difference between this purely non - dissipative regime and the fully dissipative one . let us consider the same geometry as that used for discussion of the hall resistance in fully dissipative regime , i.e. a strip of the square lattice of tight - binding atomic states opened along @xmath0 direction with electron concentration @xmath14 . to establish the electron polarizability the strip has to be placed between capacitor plates . to model non - dissipative process the charging of the plates has to be slow to allow adiabatic evolution of the electron system within the strip : at any time the electrons are in a quantum eigenstate . no current across strip is allowed , i.e. contrary to fully dissipate regime electron transitions between energy branches are forbidden . the resulting charge density redistribution across the strip , accompanied by an internal electric field @xmath6 , more precisely by the gradient of the electro - chemical potential , can be characterized by the shift of the mass - center positions . although @xmath6 is not uniform across the strip , within the linear response approach the mass - center shift can be split into the local shifts per unit cell induced by an average field @xmath6 . to estimate the static electron polarizability we follow the same procedure as that already used for the case of quantizing magnetic field @xcite . let us first discuss the case of zero magnetic field . for small deviations from the equilibrium allowing linear response approach , the condition of the vanishing total force , defining the shift of the mass - center position within the unit cell area , reads @xmath113 where @xmath114 denotes unit cell area . the force @xmath115 represents harmonic approximation of the gradient force originated in the shift of the electron charge with respect of the background positive charge distribution . the static electron polarizability @xmath116 is defined as the total dipole moment per unit area divided by the electric field @xcite and we get @xmath117 note that the confining frequency @xmath25 corresponds to that determining the energy of atomic states only in the limit of vanishing overlap , @xmath118 . generally it depends on the electron concentration as well as on the overlap strength . it has thus be viewed as the parameter depending on the chemical potential . the same is true for the confining frequency entering effective hamiltonian , eq . ( [ h_eff_0 ] ) . electric field gives rise to a shift of atomic orbitals defined by eq . ( [ dy_0 ] ) , @xmath119 along @xmath5 direction . in the presence of the magnetic field there appears additional effect given by change of the vector potential value at the center of shifted atomic orbitals . it can be estimated by the peierls substitution leading to the shift of the wave number @xmath35 @xmath120 in the weak field limit the expansion up to the second order in the magnetic field strength gives the following shift of the mass - center position @xmath121 for the average mass - center shift @xmath122 of the electron density within the unit cell area induced by the electric field @xmath6 we get @xmath123 the mass - center shifts give rise a current along the @xmath0 direction , the induced hall current . within linear response with respect to the electric field the energy becomes dependent on the mass - center position @xmath124 where @xmath125 is the position of @xmath126-th local strip . the resulting change of the velocity @xmath127 leads to the following expression for the induced hall current density @xmath128 the equality given by eq . ( [ delta_y ] ) is the consequence of the condition of the vanishing total force acting on electrons which reads @xmath129 in comparison with the zero field case ( eq . ( [ dy_0 ] ) ) , the presence of the magnetic field gives rise to another term , the lorentz force . for the static electron polarizability @xmath130 we get @xmath131 where the last equality defines @xmath132 . as in the case of a quantizing magnetic field @xcite , the corrections are due to the existence of macroscopic demagnetization currents responsible for non - zero value of @xmath72 as follows from eq . ( [ m_z ] ) . in contrast to the case of a quantizing magnetic field , the magnetic corrections to the static electron polarizability are practically negligible in the weak field limit since they are proportional to @xmath18 . finally , note that we have analyzed the effect of the magnetic field to the polarizability of a strip opened along @xmath0 direction , which models a strip of finite length with periodic boundary conditions . the results are thus applicable also for corbino samples of large radius , placed between cylindrical capacitor plates , i.e. a system which can be experimentally realized . two origins of the current induced in the open strip have been discussed . first , the current induced by an electric field @xmath15 applied along strip axis , given by eq . ( [ j_x ] ) . in this case , we call as fully dissipative , electric field @xmath6 across the strip has been introduced to fully compensate acceleration of electrons along @xmath5 direction induced by @xmath15 . by another words the field @xmath6 was supposed to return charge distribution across the strip back into its equilibrium one . second , assuming zero electric field along strip axis , the non - dissipative current @xmath133 induced by an electric field @xmath6 across the strip , eq . ( [ j_h ] ) , has been established . this field , @xmath6 , gives rise to the non - equilibrium charge distribution modeled by the shift of the equilibrium distribution . resulting current density @xmath133 originates in the response of macroscopic demagnetization currents to the electric field @xmath6 . however , the condition defining fully dissipative regime is not realistic in principle . electric field @xmath6 can not exists without shift of the charge distribution across the strip which gives rise the non - zero current density @xmath133 . within linear response with respect of electric fields , @xmath15 and @xmath6 , the current density is thus given by the sum of both contributions , @xmath134 . consequently , for the hall resistance we get @xmath135 d } \ , .\ ] ] comparison with its general form , eq . ( [ rh_gen ] ) , and the use of the relation between @xmath72 and macroscopic part of the magnetic moment , eq . ( [ m_z ] ) , give the following expression for the contribution of fermi electrons to the internal pressure @xmath136 in the considered quasi - classical approach the internal pressure is thus composed of two contributions , the statistical pressure and that induced by the magnetic field @xmath137 . in the weak field limit the correction term @xmath138 is proportional to @xmath139 and can thus be neglected . the expression for the hall resistance given by eq . ( [ r_h_tot ] ) is applicable to the case of strong quantizing magnetic fields as well . for two - dimensional systems the single band energy spectrum is split into magnetic subbands for which a quasi - classical approach describing quasiparticle dynamics can be developed . however , the resulting statistical pressure will be a magnetic field dependent quantity . the corresponding non - dissipative currents have already been analyzed in detail and the properties of the effective topological number @xmath72 well understood @xcite . for fully occupied magnetic subbands the derivative of the statistical pressure with respect of the chemical potential vanishes , @xmath72 approaches an integer value , and the quantum hall resistance is recovered @xcite . we have applied a quasi - classical approach to establish the hall resistance of bloch electrons in the weak field limit . the single tight - binding band for a square lattice and for a body centered cubic lattice have been used as model systems . in both cases quasiparticles having an isotropic effective mass can be introduced which simplifies the description significantly . to obtain the hall resistance the forces acting on the quasiparticles have been analyzed . the resulting dependence of the hall resistance on the fermi energy , i.e. on the electron concentration , shows a smooth transition from electron to hole like character . it has zero value at the band center as expected . the role of macroscopic demagnetization currents , often treated as non - dissipative edge currents , has also been analyzed and their effect to the hall resistance established . while in the weak field limit their contribution can be neglected , in quantizing magnetic fields they are responsible for the quantum hall effect . this research was supported by the grant agency of the czech republic under grant no . 202/08/0551 and by the institutional research plan no . p. steda acknowledges support of cpt ( umr6207 of cnrs ) and the universite sud toulon var for their hospitality .

a theory of the weak field hall effect of bloch electrons based on the analysis of the forces acting on electrons is presented . it is argued that the electric current is composed of two contributions , that driven by the electric field along current flow and the non - dissipative contribution originated in demagnetization currents . the hall resistance as a function of the electron concentration for the tight - binding model of a crystal with square lattice and body - centered cubic lattice is described in detail . for comparison the effect of strong magnetic fields is also discussed .

<s>[INST]standard linear response theories for electronic transport are formulated to obtain the conductivity tensor . some models for scattering are needed to get a finite response . the most popular approximation is the elastic scattering approach , despite the fact that it can not compensate the electron acceleration due to the applied electric field . it can only be compensated by a momentum dissipation , which can ensure that the total force acting on electrons vanishes in the steady state . another possibility is to analyze forces acting on electrons in the transport regime . the condition of the vanishing total force is the basic physical condition for the steady state . the application of the linear response approach , limiting the problem to the case of small deviation from the equilibrium , gives the transport coefficients satisfying the steady state condition . this idea will be used to determine the hall resistance of a system of bloch spinless electrons in the case of a weak magnetic field . for the sake of simplicity we limit our consideration to isotropic systems where the energy spectrum is represented by a single electron band . it can be expected that in this case the hall resistance will not depend on the dissipation explicitly , which can simplify the analysis substantially . the hall resistance is standardly measured on the so - called hall bar samples , having the form of a long strip . far from the contacts the current density is parallel to the strip edges , say along @xmath0-direction . if the magnetic field is applied perpendicularly to the strip surface , along @xmath1-direction , the current induced lorentz force is shifting the electron charge distribution . as the result there appears a non - equilibrium charge distribution giving rise the hall voltage . the steady state requires the compensation of the lorentz force by the gradient force . for isotropic systems this condition can be written in the following form @xmath2 where @xmath3 is the current density , @xmath4 denotes the background potential including that given by the electric field along @xmath5 direction , @xmath6 , and @xmath7 stands for electro - chemical potential . angular brackets represent quantum - mechanical and statistical average . the internal pressure @xmath8 represents the force of the electron ensemble acting on the external system per unit area . linear response approximation with respect to the electro - chemical potential gradient leads to the following expression for the hall resistance @xmath9 where @xmath10 is the applied current through the strip of thickness @xmath11 and @xmath12 denotes the voltage drop between strip edges . the gradient force and consequently the pressure are quantities which are generally dependent on the magnetic field strength @xmath13 . in the weak field limit the hall resistance can be supposed a linear function of @xmath13 which implies that the @xmath13-dependent internal pressure can be replaced by its zero field limit . for a free electron gas ( resp . hole gas ) it can be identified with the so - called statistical pressure , and its derivative with respect to @xmath7 is simply equal to the electron concentration @xmath14 ( resp . to the negative value of the hole concentration ) @xcite . considering a single electron band the hall resistance for chemical potentials in the vicinity of band edges is thus quite well understood . since it has opposite signs at opposite band edges it should vanish at the band center . to our knowledge , the only published work in which the transition between electron to hole like character of the hall resistance has been described was based on the application of the kubo formula for the special case of substitutional alloys @xcite . however , no procedure based on force analysis has been presented . a previous publication @xcite made by one of us was unfortunately based on incorrect application of the quasi - classical approach as will be specified later . in crystalline solids the equilibrium electron charge distribution can not be assumed as uniform . it is periodic in real space , having translation symmetry given by the lattice periodicity . non - zero current density gives rise to the lorentz force inducing a shift of the mass - center positions . this shift has to be compensated by the gradient force trying to return it back into the equilibrium distribution . the results generally depend on the experimental set up , particularly the way how the non - zero current density is induced . in the regime we will call as fully dissipative , the current is supposed to be exclusively given by the electric field @xmath15 along strip axis . in other words , if @xmath16 the current vanishes . this assumption requires that dissipation take place within the strip , i.e. that the system can be viewed as a macroscopic system . it can be expected that this fully dissipative regime represents the conditions of the standardly measured hall resistance in the weak field limit for which it can be assumed that the effect of the magnetic field to the energy spectrum is negligible . the opposite limiting case is the purely non - dissipative regime for which the current density is exclusively determined by the electric field @xmath6 across the strip , while @xmath17 . such a situation is observed whenever the fermi energy is located within the conduction gaps , i.e. when the magnetic field is strong enough to induce energy gaps giving rise to a hofstadter type spectrum @xcite . it has already been shown that in such a quantum hall regime the induced hall current is closely related to the static electron polarizability @xcite . the non - dissipative regime , for which the hall current is exclusively determined by the orbital magnetization , can be in principle induced even if the fermi energy is located within the energy band . this regime , in the considered weak field limit , will also be analyzed , although the resulting effect is expected to be small , of the order @xmath18 . the main attention will be devoted to the fully dissipative regime . vanishing of the total shift of the mass - center position will be taken as the steady state condition . it will be shown that it is equivalent to the condition of vanishing acceleration along the direction perpendicular to both the current flow and the magnetic field direction . for the sake of simplicity the outlined idea will be described in detail for a two - dimensional electron system since the extension to three - dimensional systems is straightforward . we will limit our consideration to the case of a single band given by a square array of tight - binding atomic states . this model will be described in section ii . the following section will be devoted to the determination of the mass - center shifts within the quasi - classical approach . the obtained results we will be used to determine properties of macroscopic systems at zero temperature . in section iv the magnetic moment due to the motion of mass - center positions will be analyzed and its main features compared with those well known for the case of a strong magnetic field . in section v explicit expressions for the hall resistance and the statistical pressure will be derived . as an example of three - dimensional system the properties of a body - centered cubic lattice of tight - binding states will be presented . the section vi will be devoted to the non - dissipative regime , which is closely related to the effect of the magnetic field on the static electron polarizability . it will be shown that the polarizability of open systems is modified by the lorentz force giving rise to a non - dissipative hall current exclusively determined by demagnetization currents . in the section vii it will be argued that in standard hall bar measurement the current flow is composed of two contributions , that induced by the electric field along the current flow and that originated in demagnetization currents . the resulting general formula for the hall resistance will be presented and its properties briefly discussed . the paper will be closed with short summary . tight - binding model is the standard approach to model band structure of crystals . if periodic boundary conditions are applied eigenfunctions are of bloch form , characterized by the wave vector @xmath19 . assuming square lattice and non - zero overlaps between atomic functions located at the nearest neighbor atomic sites only , the single - band energy spectrum is @xmath20 \ ; , \ ] ] where @xmath21 and @xmath22 denote lattice constant and overlap integral , respectively . the components of the wave vector @xmath19 along the main crystallographic axes , ( 1,0 ) and ( 0,1 ) , are @xmath23 and @xmath24 , respectively . the position of the band center given by the energy of the atomic orbitals , which can be represented by a confining frequency @xmath25 , has been chosen as the origin of the energy scale . the wave numbers @xmath23 and @xmath24 are not the only choice to characterize the eigenstates . the square lattice has a translation symmetry along ( 1,@xmath26 1 ) crystallographic directions as well . choosing components of the wave vector along these directions to characterize bloch states , @xmath27 and @xmath28 , eigenenergies become @xmath29 where @xmath30 . energy dispersions are shown in fig . [ branches ] . in the inset the used elementary cell in the @xmath31 space , which has been chosen as @xmath32 $ ] and @xmath33 $ ] , is shown . since the second derivatives of the energy with respect of @xmath34 as well as @xmath35 are equivalent , these states represent quasiparticles having isotropic effective mass @xmath36 where @xmath37 denotes the absolute value of the effective mass at band edges , @xmath38 . all quasiparticles of the same energy have the same effective mass . this property simplifies the quasi - classical approach which will be described in the following section . at negative energies , @xmath39 , quasiparticles have electron - like character with positive effective mass while at positive energies , @xmath40 , quasiparticles have hole - like character with negative effective mass the same dispersions are obtained for fixed values of @xmath35 . in the inset equi - energy contours are shown in the @xmath41 space . full and dotted lines correspond to states having electron or hole like character , respectively . the dashed line shows the boundary of the standard first brillouin zone , while the bold line shows the elementary cell we are using.,width=3 ] electronic transport is studied on samples having the form of a long strip with a finite width @xmath42 . it is thus natural to assume periodic boundary conditions along the direction given by the strip axis only . the eigenfuctions thus have bloch - like character along strip axis , while along perpendicular direction they are of limited range . if the strip width can be counted as macroscopic , eigenenergies are practically untouched by the change of the boundary conditions . for isotropic systems , like the considered square lattice , the measured transport coefficient are independent of the strip orientation . we can thus choose the strip axis to be parallel with the ( 1,1 ) crystallographic direction without loss of generality . in this case the eigenfunctions can be approximated by a linear combination of bloch states @xmath43 and @xmath44 . the index @xmath34 can be then viewed as the branch index representing bound modes across the strip . in such the case the only nonzero component of the velocity expectation value is along strip axis @xmath45 in the spirit of the preceding section we consider a strip opened along the @xmath0 direction which coincides with ( 1,1 ) crystallographic direction of the considered square lattice . the applied magnetic field along the @xmath1 direction and the electric field across strip , i.e. along the @xmath5 direction , @xmath6 , give rise to the lorentz force and electric force , respectively . to preserve the bloch character of the wavefunctions along the @xmath0 direction the landau gauge for vector potential is used , @xmath46 . we include it into the hamiltonian by using the so - called peierls substitution @xcite . since the effective mass of quasiparticles is isotropic we can use the following effective hamiltonian @xmath47 where the @xmath48 corresponds to the sign of the effective mass @xmath49 , and @xmath50 denotes the magnetic length , which is related to the cyclotron frequency @xmath51 as @xmath52 the last term of the effective hamiltonian @xmath53 appears to preserve the origin of the energy scale given by the oscillator energy @xmath54 . the energy operator @xmath55 is defined by its taylor expansion in @xmath35 , and in the considered case of the weak field limit only terms up to the second order are preserved . the effective hamiltonian then becomes simply the one of an effective harmonic oscillator @xmath56 ^ 2 + \nonumber \\ - \frac{1}{2 } \ , m_{\beta}^{\ast}(\kappa ) \ , \tilde{\omega}^2 \left [ y_{\beta}(\kappa ) \right]^2 \ , + \ , e_{\beta}^{(0)}(\kappa ) \ , - \ , \frac{\pm 1}{2 } \ , \hbar \omega_0 \ , , \;\end{aligned}\ ] ] where @xmath57 denotes the expectation value of the mass - center position @xmath58 and @xmath59 resulting eigenenergies are @xmath60 ^ 2 .\ ] ] the expectation of the velocity along the strip axis has the following expression @xmath61 which coincides with the well known result for magnetic field corrections to the velocity @xcite . the corrections to the energy , as well as to the velocity , due to the presence of magnetic and electric fields are proportional to square of these fields or their product . in the weak field limit , @xmath62 and @xmath63 , these corrections can thus be neglected and the only effect that will be considered is the change of the quasiparticle dynamics , represented in our description by the change of their mass - center positions . this approach which will be used in the following treatment is in accord with the standard quasi - classical view . to support this let us consider the product @xmath64 representing the quasiparticle acceleration @xmath65 along @xmath5 direction . from eq . ( [ y_eff ] ) we get @xmath66 this relation leads to the conclusion that in crystals the acceleration of quasiparticles is modified by their effective mass which is in agreement with the quasi - classical approach presented e.g. in landau - lifshitz textbook @xcite . note that the quasiparticle acceleration along the @xmath5 direction induced by the electric field @xmath6 originates in their transfer between branches @xmath34 . the presented quasi - classical approach neglects the interference effects induced by the magnetic field which are responsible for modification of the energy spectrum . a number of energy gaps are created and the energy structure is of the hofstadter type @xcite . in weak field limit , the gaps in the energy spectrum becomes extremely small , and it can be expected that theses interferences will be destroyed by dissipative processes always present at finite temperatures . for this reason the presented quasi - classical approach is acceptable . the applied magnetic field along the @xmath1 direction gives rise to the magnetic moment @xmath67 . generally @xmath67 can be divided into two contributions : @xmath68 given by the internal momentum of quasiparticles and @xmath69 due to the motion of their mass - centers . the second contribution can be viewed as the macroscopic one since the trajectories of the mass - center positions are extended along the @xmath0 direction . it can easily be determined within the quasi - classical approximation presented in the preceding section . its expectation value reads @xmath70 where in accord with eq . ( [ y_eff ] ) @xmath71 defining the dimensionless quantity @xmath72 as @xmath73 where @xmath42 is the strip width , the fermi electron contribution per unit area reads @xmath74 the relation between @xmath69 and @xmath72 defined by eq . ( [ sigma_gen ] ) is quite general and for the case of quantizing magnetic fields and weak periodic modulation has already been discussed in detail , where @xmath72 was called the effective topological number @xcite . in the weak field limit , for the square lattice , performing the @xmath35 integration in eq . ( [ sigma_gen ] ) gives @xmath75 where @xmath76 if the positive value of @xmath35 on the fermi surface for a given @xmath34 . using @xmath77 , we finally get @xmath78 where @xmath79 at the band edges the effective quasiparticle concentration @xmath80 approaches the electron or hole concentration @xmath81 with @xmath82 for electrons and @xmath83 for holes . energy dependence of @xmath72 and @xmath80 are shown in fig . [ sigma_e ] . , full line , and the effective quasiparticle number in a unit cell @xmath84 , dashed line.,width=3 ] at negative energies , @xmath85 , for which quasiparticles have electron - like character , the fermi contribution to @xmath69 given by eq . ( [ m_z ] ) is positive , i.e. it represents paramagnetic contribution to the total magnetic moment . it is often interpreted as a contribution given by electrons skipping along sample edges , which fully compensates the diamagnetic moment of electrons in the classical limit . in the presented model it has been equally splited over the local strips of tight - binding atomic orbitals . at positive energies the contribution of fermi particles to @xmath69 has opposite sign revealing electron - hole symmetry . at the band center it vanishes , @xmath86 this is the consequence of the electron - hole symmetry and this feature persists even in the case of strong magnetic fields affecting energy spectra substantially @xcite . similarly , when the energy band is fully occupied , @xmath86 in the weak field limit , as well as in the case of quantizing magnetic fields . the electric field along the strip axis , @xmath15 , accelerates electrons along the @xmath0 direction . this effect can be modelled by including the time dependent vector potential @xmath87 into the hamiltonian . for small values of the electric field and short times the linear response gives the following change of the quasiparticle velocity @xmath88 where corrections to the velocity proportional to @xmath18 , eq . ( [ v_b ] ) , have been neglected . summation over occupied states gives the current density along @xmath0 direction @xmath89 change of the velocities gives rise to the shift of mass - center positions of quasiparticles , eq . ( [ y_b ] ) . summation over occupied states leads to the following expression for mass - center shift @xmath90 of the electron density within the unit cell area @xmath91 evidently this time dependent shift is induced by the lorentz force . the shift of the mass - center position is closely related to the shift of the electron charge distribution with respect of the periodic positive background charge . it gives rise to the coulomb energy . for the system is thus energetically more acceptable to induce electric field along @xmath5 direction , @xmath6 , which would be able to minimize the coulomb energy , i.e. to force shifted electron charge distribution towards its equilibrium one . in the presented model this force is represented by the confining potential of the strength given by the frequency @xmath25 . standard condition to estimate the induced field @xmath6 is the condition of vanishing acceleration given by eq . ( [ acceleration ] ) . it coincides with the condition of vanishing average shift of mass center positions defined by eq . ( [ y_eff ] ) . summation over occupied states gives @xmath92 for the hall resistance we get @xmath93 the energy dependence of the hall resistance is shown on fig . it shows clearly the electron hole symmetry . at band edges , @xmath94 , @xmath80 approaches quasiparticle concentration and the classical result for the hall resistance is recovered . is replaced by the negative value of the electron concentration ( @xmath95 ) or by the hole concentration ( @xmath96).,width=3 ] to approach a steady state an energy dissipation is necessary to eliminate the acceleration induced by @xmath15 . the standard way is to assume exponential decay of momentum characterized by the relaxation time @xmath97 . in other words the time entering expression for the current density , eq . ( [ j_x ] ) , has to be replaced by @xmath97 , which is in general a @xmath7 dependent quantity . although the hall resistance does not explicitly depends on the momentum relaxation it is essential for application of the linear response with respect of @xmath6 to held it sufficiently small . in the considered weak field limit the current is supposed to be fully determined by the electric field along the strip axis . this assumption is applicable if the dissipation take place within the strip area . in the case of a quantizing magnetic field this assumption is not acceptable . whenever the fermi energy is located within an energy gap there might appear magnetic edge states leading to non - dissipative current . in this case the electric field along the current flow vanishes and the current is fully determined by the perpendicular electric field . comparison of the expression for the hall resistance , eq . ( [ rh_2d ] ) , with the more general form given by the eq . ( [ rh_gen ] ) suggests that hall resistance has to be related to a pressure gradient representing the fully dissipative regime . in the quasi - classical approach we are using , the carriers are supposed to be quasiparticles having isotropic effective mass @xmath98 which is defined by their energy , eq . ( [ m_ast ] ) . quasiparticles are allowed to move freely along any direction ( i.e. even along @xmath5 direction by transitions between branches ) . the effect of the periodic background is included via their effective mass and their momentum is given by the product of the effective mass and the velocity . in this case the so - called statistical pressure can be easily evaluated following the standard procedure for gas system @xcite . let us consider quasiparticles located within a finite area separated from outside quasiparticles by walls preventing particle transfer . the total momentum transfered to the wall perpendicular e.g. to @xmath0 direction is equal to @xmath99 . the number of electrons hitting the wall per unit time is given by their velocity , and statistical pressure defined as the force per unit length acting along any direction reads @xmath100 ^ 2 \ , , \ ] ] where the prime indicates that summation is taken over those states for which the velocity is of one particular sign , say the positive one . inserting explicit expressions for the effective mass and velocity , eq . ( [ m_ast ] ) and eq . ( [ v_0 ] ) , respectively , we get @xmath101 contribution of fermi carriers to the statistical pressure is positive for electron - like quasiparticles while for hole - like quasiparticles it is negative since the hole concentration decreases with rising value of the chemical potential @xmath7 . at the band center where the density of states diverges , the statistical pressure diverges as well and consequently the hall resistance vanishes . comparison of eq . ( [ dp_stat / dmu ] ) with eq . ( [ rh_2d ] ) gives for the hall resistance in the fully dissipative regime the relation we have been looking for @xmath102 note that for two - dimensional systems the strip thickness @xmath11 entering the general formula , eq . ( [ rh_gen ] ) , has to be replaced by unity . the above calculation corrects a previous result presented by one of us @xcite , where the effective mass was erroneously identified with the local cyclotron mass . the results presented above can easily be generalized to a three dimensional system . as an example we consider here the body - centered cubic lattice . taking into account the overlap between nearest neighbor atomic sites only , the tight - binding single band spectrum , in the analogy with that for square lattice , can be written in the following form @xmath103 where index @xmath104 represents eigenstate modes along @xmath1 direction . the effective mass is isotropic and all states of the same energy have the same effective mass @xmath105 for negative energies particles have electron - like character while for positive energies they have hole - like character . at the band edges the absolute value of the effective mass is @xmath106 . we can thus proceed as in the preceding section . we get expressions with the same structure , but with an additional summation over the index @xmath104 . for the hall resistance defined by eq . ( [ rh_gen ] ) we get @xmath107 where @xmath108 @xmath109 $ ] . in this case also the condition of vanishing acceleration as well as the independently derived expression for the statistical pressure lead to the same results . at the lower band edge ( @xmath110 ) @xmath111 approaches the electron concentration , while at the upper edge ( @xmath112 ) it approaches the hole concentration . at the band center the hall resistance vanishes as expected . as function of the energy it shows the same qualitative features as that for square lattice presented in fig . it has recently been shown that a strong magnetic field , which leads to magnetic quantization of the electron energy spectra , can significantly affect the static electron polarizability of crystalline solids . this is caused by appearance of the lorentz force . as a result a close relation between the induced hall current and the static electron polarizability of two - dimensional systems open along one direction has been established @xcite . in the weak field limit we consider here , it can be expected that this effect will be nearly negligible since the effect of the magnetic field on the energy spectra is proportional to square of the field strength . nevertheless , the analysis of this effect will allow us to understand the difference between this purely non - dissipative regime and the fully dissipative one . let us consider the same geometry as that used for discussion of the hall resistance in fully dissipative regime , i.e. a strip of the square lattice of tight - binding atomic states opened along @xmath0 direction with electron concentration @xmath14 . to establish the electron polarizability the strip has to be placed between capacitor plates . to model non - dissipative process the charging of the plates has to be slow to allow adiabatic evolution of the electron system within the strip : at any time the electrons are in a quantum eigenstate . no current across strip is allowed , i.e. contrary to fully dissipate regime electron transitions between energy branches are forbidden . the resulting charge density redistribution across the strip , accompanied by an internal electric field @xmath6 , more precisely by the gradient of the electro - chemical potential , can be characterized by the shift of the mass - center positions . although @xmath6 is not uniform across the strip , within the linear response approach the mass - center shift can be split into the local shifts per unit cell induced by an average field @xmath6 . to estimate the static electron polarizability we follow the same procedure as that already used for the case of quantizing magnetic field @xcite . let us first discuss the case of zero magnetic field . for small deviations from the equilibrium allowing linear response approach , the condition of the vanishing total force , defining the shift of the mass - center position within the unit cell area , reads @xmath113 where @xmath114 denotes unit cell area . the force @xmath115 represents harmonic approximation of the gradient force originated in the shift of the electron charge with respect of the background positive charge distribution . the static electron polarizability @xmath116 is defined as the total dipole moment per unit area divided by the electric field @xcite and we get @xmath117 note that the confining frequency @xmath25 corresponds to that determining the energy of atomic states only in the limit of vanishing overlap , @xmath118 . generally it depends on the electron concentration as well as on the overlap strength . it has thus be viewed as the parameter depending on the chemical potential . the same is true for the confining frequency entering effective hamiltonian , eq . ( [ h_eff_0 ] ) . electric field gives rise to a shift of atomic orbitals defined by eq . ( [ dy_0 ] ) , @xmath119 along @xmath5 direction . in the presence of the magnetic field there appears additional effect given by change of the vector potential value at the center of shifted atomic orbitals . it can be estimated by the peierls substitution leading to the shift of the wave number @xmath35 @xmath120 in the weak field limit the expansion up to the second order in the magnetic field strength gives the following shift of the mass - center position @xmath121 for the average mass - center shift @xmath122 of the electron density within the unit cell area induced by the electric field @xmath6 we get @xmath123 the mass - center shifts give rise a current along the @xmath0 direction , the induced hall current . within linear response with respect to the electric field the energy becomes dependent on the mass - center position @xmath124 where @xmath125 is the position of @xmath126-th local strip . the resulting change of the velocity @xmath127 leads to the following expression for the induced hall current density @xmath128 the equality given by eq . ( [ delta_y ] ) is the consequence of the condition of the vanishing total force acting on electrons which reads @xmath129 in comparison with the zero field case ( eq . ( [ dy_0 ] ) ) , the presence of the magnetic field gives rise to another term , the lorentz force . for the static electron polarizability @xmath130 we get @xmath131 where the last equality defines @xmath132 . as in the case of a quantizing magnetic field @xcite , the corrections are due to the existence of macroscopic demagnetization currents responsible for non - zero value of @xmath72 as follows from eq . ( [ m_z ] ) . in contrast to the case of a quantizing magnetic field , the magnetic corrections to the static electron polarizability are practically negligible in the weak field limit since they are proportional to @xmath18 . finally , note that we have analyzed the effect of the magnetic field to the polarizability of a strip opened along @xmath0 direction , which models a strip of finite length with periodic boundary conditions . the results are thus applicable also for corbino samples of large radius , placed between cylindrical capacitor plates , i.e. a system which can be experimentally realized . two origins of the current induced in the open strip have been discussed . first , the current induced by an electric field @xmath15 applied along strip axis , given by eq . ( [ j_x ] ) . in this case , we call as fully dissipative , electric field @xmath6 across the strip has been introduced to fully compensate acceleration of electrons along @xmath5 direction induced by @xmath15 . by another words the field @xmath6 was supposed to return charge distribution across the strip back into its equilibrium one . second , assuming zero electric field along strip axis , the non - dissipative current @xmath133 induced by an electric field @xmath6 across the strip , eq . ( [ j_h ] ) , has been established . this field , @xmath6 , gives rise to the non - equilibrium charge distribution modeled by the shift of the equilibrium distribution . resulting current density @xmath133 originates in the response of macroscopic demagnetization currents to the electric field @xmath6 . however , the condition defining fully dissipative regime is not realistic in principle . electric field @xmath6 can not exists without shift of the charge distribution across the strip which gives rise the non - zero current density @xmath133 . within linear response with respect of electric fields , @xmath15 and @xmath6 , the current density is thus given by the sum of both contributions , @xmath134 . consequently , for the hall resistance we get @xmath135 d } \ , .\ ] ] comparison with its general form , eq . ( [ rh_gen ] ) , and the use of the relation between @xmath72 and macroscopic part of the magnetic moment , eq . ( [ m_z ] ) , give the following expression for the contribution of fermi electrons to the internal pressure @xmath136 in the considered quasi - classical approach the internal pressure is thus composed of two contributions , the statistical pressure and that induced by the magnetic field @xmath137 . in the weak field limit the correction term @xmath138 is proportional to @xmath139 and can thus be neglected . the expression for the hall resistance given by eq . ( [ r_h_tot ] ) is applicable to the case of strong quantizing magnetic fields as well . for two - dimensional systems the single band energy spectrum is split into magnetic subbands for which a quasi - classical approach describing quasiparticle dynamics can be developed . however , the resulting statistical pressure will be a magnetic field dependent quantity . the corresponding non - dissipative currents have already been analyzed in detail and the properties of the effective topological number @xmath72 well understood @xcite . for fully occupied magnetic subbands the derivative of the statistical pressure with respect of the chemical potential vanishes , @xmath72 approaches an integer value , and the quantum hall resistance is recovered @xcite . we have applied a quasi - classical approach to establish the hall resistance of bloch electrons in the weak field limit . the single tight - binding band for a square lattice and for a body centered cubic lattice have been used as model systems . in both cases quasiparticles having an isotropic effective mass can be introduced which simplifies the description significantly . to obtain the hall resistance the forces acting on the quasiparticles have been analyzed . the resulting dependence of the hall resistance on the fermi energy , i.e. on the electron concentration , shows a smooth transition from electron to hole like character . it has zero value at the band center as expected . the role of macroscopic demagnetization currents , often treated as non - dissipative edge currents , has also been analyzed and their effect to the hall resistance established . while in the weak field limit their contribution can be neglected , in quantizing magnetic fields they are responsible for the quantum hall effect . this research was supported by the grant agency of the czech republic under grant no . 202/08/0551 and by the institutional research plan no . p. steda acknowledges support of cpt ( umr6207 of cnrs ) and the universite sud toulon var for their hospitality .[/INST] a theory of the weak field hall effect of bloch electrons based on the analysis of the forces acting on electrons is presented . it is argued that the electric current is composed of two contributions , that driven by the electric field along current flow and the non - dissipative contribution originated in demagnetization currents . the hall resistance as a function of the electron concentration for the tight - binding model of a crystal with square lattice and body - centered cubic lattice is described in detail . for comparison the effect of strong magnetic fields is also discussed . </s>

mechanical switches have attracted the attention of the scientific community for a long time @xcite . one interesting aspect is the non - volatile nature of bits encoded into bistable mechanical systems . this condition could in principle avoid the typical heat production associated with losses due to electric currents . in fact , excess heat production during computation is one of the main limitations that standard cmos technology is presently facing in order to develop next generations of switches . present cmos switches are orders of magnitude far from the theoretical minimum heat required for computing . this fundamental bound , known as landauer limit@xcite , arises for any physical system encoding two logic states , @xmath0 and @xmath1 , and in contact with a heat bath at temperature @xmath2 , when we intend to set the system into one given state , regardless of the knowledge of the initial state . according to the so - called landauer principle , such a reset operation must produce at least @xmath3 of heat ( with @xmath4 boltzmann constant)@xcite . however the landauer limit does not close the door to switch procedures that do not generate heat , once the initial state is known and a proper switch protocol is observed@xcite . in this paper we consider the encoding of a logical bit in a given configuration of a clamped - clamped single - layer graphene ribbon , as depicted in . to achieve two stable states , a compression is applied by bringing closer the extremes of the ribbon in the @xmath5-direction that buckles the structure in the out - of - plane direction . this compression generates an energy barrier separating the two stable states corresponding to the upward and downward buckling . to identify which logic state the ribbon represents at time @xmath6 , we monitor the coordinates of the central atom in the ribbon ( see zoomed image in ) . being @xmath7 the coordinates of the central atom , we indicate with @xmath8 ( @xmath9 ) the set of possible physical microstates with @xmath10 ( @xmath11 ) . if the system is a micro state that belongs to @xmath9 ( @xmath8 ) we say that the ribbon encodes the logical state @xmath0 ( @xmath1 ) . starting from these considerations we present a _ reset protocol _ based on electrostatic forces acting on the graphene ribbon that approaches the landauer limit . the procedure is designed to reach the theoretical thermodynamic bound without altering the compression of the ribbon . we also discuss a similar _ switch protocol _ that realizes the switch process approaching @xmath12 . heat production during protocol execution is evaluated by using molecular dynamics simulations , performed with lammps@xcite . here we consider a simulated ribbon consisting in a @xmath13 suspended structure composed by 240 carbon atoms . carbon - carbon interactions are described through the rebo potential@xcite . the optimized lattice constant is @xmath14 which is in good agreement with both _ ab initio _ calculations and experimental values@xcite . the obtained young modulus , @xmath15 , is also close to the expected value @xcite . all the simulations are performed at temperature @xmath16 . electrostatic forces are applied on the structure by a set of four electrodes , classified by labels _ u ( up ) _ , _ d ( down ) _ , _ l ( left ) _ and _ r ( right ) _ as shown in the top left side of . as the graphene ribbon is considered to be electrically connected to the ground , @xmath17 , the force produced by any of the electrodes is attractive if @xmath18 and zero otherwise . in the reference scheme , ( _ down _ ) electrodes generate positive ( negative ) forces along _ z _ direction . the total energy of the graphene ribbon under the action of electric external fields can be written as @xmath19 where @xmath20 and @xmath21 are the momenta and positions of all carbon atoms respectively . @xmath22 is the total kinetic energy of the ribbon , @xmath23 the interatomic interaction energy and @xmath24 the total interaction energy between atoms and the external electric fields . in the case under consideration we have : @xmath25 \end{aligned}\ ] ] where @xmath26 is the number of atoms , @xmath27 is the clamp - clamp distance , @xmath28 , @xmath29 is the heaviside function , and @xmath30 is the distance between the electrodes and the plane @xmath31 . parameters @xmath32 , @xmath33 , @xmath34 and @xmath35 are relative to the corresponding electrode and their values depend on the voltages applied according to the given protocol . since the system is symmetric with respect to the @xmath36 plane , both @xmath0 and @xmath1 logic states have the same average potential energy . this implies that quasi - static transformations between two logic states are characterized by a zero change in the average total energy : @xmath37 , and consequently @xmath38 . in practice , transformations occurs in finite times , so @xmath39 may be nonzero . since we consider protocol duration much larger than the relaxation time of the system ( @xmath40 ) , we make the assumption that @xmath37 also in practice . under these conditions we can compute the generated heat as the average work performed on the system , via the stratonovich integral@xcite : @xmath41 where @xmath42 denote averages over an ensemble of protocol realizations and @xmath43 and @xmath44 are the starting and ending time of the protocol . in order to provide a visual description of the system dynamics , we focus our attention on the time evolution of the first two normal modes of the ribbon . being @xmath45 and @xmath46 the amplitudes of the first two flexural modes , we can write an effective potential energy of the ribbon @xmath47 in terms of these amplitudes ( ) . the local maximum in the potential landscape , @xmath48 , corresponds to a flat configuration of the ribbon . as function of the first two flexural mode amplitudes @xmath45 and @xmath46 . inset : schematics of the two normal modes and their amplitudes.,scaledwidth=85.0% ] trajectories on the landscape represent the evolution of the system undergoing a physical transformation . in particular we are interested in trajectories that go from one well to the other : they represent the physical realization of the switch between the two logic states . a trajectory that goes directly through the maximum at @xmath48 corresponds to a _ snapping _ of the ribbon . on the other hand trajectories that go around the maximum correspond to a dynamic that implies an intermediate _ s_-shape ribbon configuration . as a matter of fact , snapping trajectories can be hardly associated with a thermodynamically reversible ( i.e. adiabatic ) transformation due to the difficulty to control the velocity of the switch dynamics . on the other hand , _ s_-shape trajectories can be followed with an arbitrarily low velocity and thus result more promising for minimizing the heat production during the switch protocols . due to the presence of fluctuations the trajectories are random paths and are best monitored by computing the time evolution of the probability density function ( pdf ) of @xmath45 and @xmath46 . in the following , we focus our attention on the reset operation . such an operation is generally performed to bring to a known logic state a bistable system that is in an unknown state . this implies that at the beginning the system has @xmath49 of probability of being both in @xmath9 and @xmath8 ; after the reset operation the system ends with @xmath50 of probability in @xmath8 ( or equivalently in @xmath9 ) . in our case , the initial condition is prepared by setting @xmath11 or @xmath10 with @xmath49 of probability , and allowing the system to thermalize near the corresponding energy minimum , similarly to what is done in ref . @xcite . to perform the reset operation we apply the following protocol : a set of electrostatic forces ( that can be expressed using ) acting on each individual atom is applied according to the sequence presented in . applying the reset protocol , the pdf of @xmath45 and @xmath46 change as illustrated in . from time @xmath43 to @xmath51 ( panels 1 to 4 ) the system evolves into a _ s_-shape ( @xmath52 ) . from @xmath51 to @xmath53 ( panels 4 to 7 ) the system goes from a _ s_-shape to a buckled ( @xmath54 ) configuration . at time @xmath55 the system is stable in the final logic state , the forces are removed and it thermalizes toward local equilibrium ( panel 9 ) . and @xmath46 for the reset procedure . panels are numbered from 1 to 9 according with the time evolution indicated by the arrows.,scaledwidth=85.0% ] the total heat produced during the reset is computed by evaluating over the time interval @xmath56 . in the produced heat is represented as function of the total time of the protocol @xmath57 . continuous line represents the fit with @xmath58 . for large values of @xmath57 the total produced heat approaches @xmath59 as prescribed for a total entropy reduction of @xmath60@xcite . it s interesting to note that the trend @xmath58 is empirical and , to be consistent with the literature , must be lower bounded by the limit @xmath61 derived in @xcite . this requires that @xmath62 with equality saturated only if our protocol is proven to be optimal in the sense of @xcite . this study goes beyond the scope of the present paper and will not be discussed here . . the heat produced , obtained from the simulated experiment ( squares ) , is plotted together with a fit to the data ( solid line ) . the dashed line represents the landauer limit . inset : distribution of produced heat for @xmath63.,scaledwidth=85.0% ] we now focus our attention on the switch operation . a switch operation consists in a transformation that brings the system from a known logic state to a known ( and different ) logic state ( e.g. from @xmath9 to @xmath8 or _ vice - versa _ ) . for the sake of discussion , in the following we will consider the transformation from the state @xmath9 to @xmath8 . in this case , at difference with the reset protocol , being the total entropy variation equal to zero , the expected minimum heat produced by the procedure is @xmath64 . the switch protocol relative to is presented in . the system is considered to be initially in local equilibrium in @xmath9 . in the first time frame ( @xmath65 ) it is in the buckled configuration by applying a large electrostatic force ( panel 2 ) . in the following time frames ( @xmath66 ) the ribbon is gently changed in a _ s_-shape configuration ( @xmath52 , panel 3 - 5 ) . subsequently the system evolves into a shape with @xmath67 , confining the system in the destination state ( panel 8) . finally , at time @xmath68 all the forces are removed and the system relaxes at local equilibrium in the final configuration ( panel 9 ) . and @xmath46 for the reset procedure . panels are numbered from 1 to 9 according with the time evolution indicated by the arrows.,scaledwidth=85.0% ] as before , the work done on the system is evaluated according to . results are presented in where the expected value @xmath12 is asymptotically approached as the duration of the protocol increases . the produced heat follows the trend @xmath69 ( solid line ) . for slow protocols , approaching the adiabatic condition , it is interesting to note that , although @xmath70 , the distribution of the generated heat presents negative tails ( inset ) . . produced heat approaches zero by increasing @xmath57 . the heat produced , obtained from the simulated experiment ( squares ) , is plotted together with a fit to the data ( solid line ) . inset : distribution of produced heat for @xmath71 . , scaledwidth=85.0% ] in conclusion , in this article we have studied the minimum energy required by reset and switch protocols for a bit encoded by a compressed clamped - clamped graphene ribbon . we presented two protocols that avoid the costly snapping procedure and are specifically designed to reach the minimum heat produced for these logic operations without the need of a fine control of the compression parameter . we stress that it is usually difficult to achieve a precise control of the compression parameter and thus protocols for reset / switch that are robust against variations of such parameter are of great potential interest for practical applications . victor zhirnov , ralph cavin and luca gammaitoni in minimum energy of computing , fundamental considerations , edited by dr . giorgos fagas , ict - energy - concepts towards zero - power information and communication technology ( 2014 )

heat produced during a reset operation is meant to show a fundamental bound known as landauer limit , while simple switch operations have an expected minimum amount of produced heat equals to zero . however , in both cases , present day technology realizations dissipate far beyond these theoretical limits . in this paper we present a study based on molecular dynamics simulations , where reset and switch protocols are applied on a graphene buckled ribbon , employed here as a nano electromechanical switch working at the thermodynamic limit .

<s>[INST]mechanical switches have attracted the attention of the scientific community for a long time @xcite . one interesting aspect is the non - volatile nature of bits encoded into bistable mechanical systems . this condition could in principle avoid the typical heat production associated with losses due to electric currents . in fact , excess heat production during computation is one of the main limitations that standard cmos technology is presently facing in order to develop next generations of switches . present cmos switches are orders of magnitude far from the theoretical minimum heat required for computing . this fundamental bound , known as landauer limit@xcite , arises for any physical system encoding two logic states , @xmath0 and @xmath1 , and in contact with a heat bath at temperature @xmath2 , when we intend to set the system into one given state , regardless of the knowledge of the initial state . according to the so - called landauer principle , such a reset operation must produce at least @xmath3 of heat ( with @xmath4 boltzmann constant)@xcite . however the landauer limit does not close the door to switch procedures that do not generate heat , once the initial state is known and a proper switch protocol is observed@xcite . in this paper we consider the encoding of a logical bit in a given configuration of a clamped - clamped single - layer graphene ribbon , as depicted in . to achieve two stable states , a compression is applied by bringing closer the extremes of the ribbon in the @xmath5-direction that buckles the structure in the out - of - plane direction . this compression generates an energy barrier separating the two stable states corresponding to the upward and downward buckling . to identify which logic state the ribbon represents at time @xmath6 , we monitor the coordinates of the central atom in the ribbon ( see zoomed image in ) . being @xmath7 the coordinates of the central atom , we indicate with @xmath8 ( @xmath9 ) the set of possible physical microstates with @xmath10 ( @xmath11 ) . if the system is a micro state that belongs to @xmath9 ( @xmath8 ) we say that the ribbon encodes the logical state @xmath0 ( @xmath1 ) . starting from these considerations we present a _ reset protocol _ based on electrostatic forces acting on the graphene ribbon that approaches the landauer limit . the procedure is designed to reach the theoretical thermodynamic bound without altering the compression of the ribbon . we also discuss a similar _ switch protocol _ that realizes the switch process approaching @xmath12 . heat production during protocol execution is evaluated by using molecular dynamics simulations , performed with lammps@xcite . here we consider a simulated ribbon consisting in a @xmath13 suspended structure composed by 240 carbon atoms . carbon - carbon interactions are described through the rebo potential@xcite . the optimized lattice constant is @xmath14 which is in good agreement with both _ ab initio _ calculations and experimental values@xcite . the obtained young modulus , @xmath15 , is also close to the expected value @xcite . all the simulations are performed at temperature @xmath16 . electrostatic forces are applied on the structure by a set of four electrodes , classified by labels _ u ( up ) _ , _ d ( down ) _ , _ l ( left ) _ and _ r ( right ) _ as shown in the top left side of . as the graphene ribbon is considered to be electrically connected to the ground , @xmath17 , the force produced by any of the electrodes is attractive if @xmath18 and zero otherwise . in the reference scheme , ( _ down _ ) electrodes generate positive ( negative ) forces along _ z _ direction . the total energy of the graphene ribbon under the action of electric external fields can be written as @xmath19 where @xmath20 and @xmath21 are the momenta and positions of all carbon atoms respectively . @xmath22 is the total kinetic energy of the ribbon , @xmath23 the interatomic interaction energy and @xmath24 the total interaction energy between atoms and the external electric fields . in the case under consideration we have : @xmath25 \end{aligned}\ ] ] where @xmath26 is the number of atoms , @xmath27 is the clamp - clamp distance , @xmath28 , @xmath29 is the heaviside function , and @xmath30 is the distance between the electrodes and the plane @xmath31 . parameters @xmath32 , @xmath33 , @xmath34 and @xmath35 are relative to the corresponding electrode and their values depend on the voltages applied according to the given protocol . since the system is symmetric with respect to the @xmath36 plane , both @xmath0 and @xmath1 logic states have the same average potential energy . this implies that quasi - static transformations between two logic states are characterized by a zero change in the average total energy : @xmath37 , and consequently @xmath38 . in practice , transformations occurs in finite times , so @xmath39 may be nonzero . since we consider protocol duration much larger than the relaxation time of the system ( @xmath40 ) , we make the assumption that @xmath37 also in practice . under these conditions we can compute the generated heat as the average work performed on the system , via the stratonovich integral@xcite : @xmath41 where @xmath42 denote averages over an ensemble of protocol realizations and @xmath43 and @xmath44 are the starting and ending time of the protocol . in order to provide a visual description of the system dynamics , we focus our attention on the time evolution of the first two normal modes of the ribbon . being @xmath45 and @xmath46 the amplitudes of the first two flexural modes , we can write an effective potential energy of the ribbon @xmath47 in terms of these amplitudes ( ) . the local maximum in the potential landscape , @xmath48 , corresponds to a flat configuration of the ribbon . as function of the first two flexural mode amplitudes @xmath45 and @xmath46 . inset : schematics of the two normal modes and their amplitudes.,scaledwidth=85.0% ] trajectories on the landscape represent the evolution of the system undergoing a physical transformation . in particular we are interested in trajectories that go from one well to the other : they represent the physical realization of the switch between the two logic states . a trajectory that goes directly through the maximum at @xmath48 corresponds to a _ snapping _ of the ribbon . on the other hand trajectories that go around the maximum correspond to a dynamic that implies an intermediate _ s_-shape ribbon configuration . as a matter of fact , snapping trajectories can be hardly associated with a thermodynamically reversible ( i.e. adiabatic ) transformation due to the difficulty to control the velocity of the switch dynamics . on the other hand , _ s_-shape trajectories can be followed with an arbitrarily low velocity and thus result more promising for minimizing the heat production during the switch protocols . due to the presence of fluctuations the trajectories are random paths and are best monitored by computing the time evolution of the probability density function ( pdf ) of @xmath45 and @xmath46 . in the following , we focus our attention on the reset operation . such an operation is generally performed to bring to a known logic state a bistable system that is in an unknown state . this implies that at the beginning the system has @xmath49 of probability of being both in @xmath9 and @xmath8 ; after the reset operation the system ends with @xmath50 of probability in @xmath8 ( or equivalently in @xmath9 ) . in our case , the initial condition is prepared by setting @xmath11 or @xmath10 with @xmath49 of probability , and allowing the system to thermalize near the corresponding energy minimum , similarly to what is done in ref . @xcite . to perform the reset operation we apply the following protocol : a set of electrostatic forces ( that can be expressed using ) acting on each individual atom is applied according to the sequence presented in . applying the reset protocol , the pdf of @xmath45 and @xmath46 change as illustrated in . from time @xmath43 to @xmath51 ( panels 1 to 4 ) the system evolves into a _ s_-shape ( @xmath52 ) . from @xmath51 to @xmath53 ( panels 4 to 7 ) the system goes from a _ s_-shape to a buckled ( @xmath54 ) configuration . at time @xmath55 the system is stable in the final logic state , the forces are removed and it thermalizes toward local equilibrium ( panel 9 ) . and @xmath46 for the reset procedure . panels are numbered from 1 to 9 according with the time evolution indicated by the arrows.,scaledwidth=85.0% ] the total heat produced during the reset is computed by evaluating over the time interval @xmath56 . in the produced heat is represented as function of the total time of the protocol @xmath57 . continuous line represents the fit with @xmath58 . for large values of @xmath57 the total produced heat approaches @xmath59 as prescribed for a total entropy reduction of @xmath60@xcite . it s interesting to note that the trend @xmath58 is empirical and , to be consistent with the literature , must be lower bounded by the limit @xmath61 derived in @xcite . this requires that @xmath62 with equality saturated only if our protocol is proven to be optimal in the sense of @xcite . this study goes beyond the scope of the present paper and will not be discussed here . . the heat produced , obtained from the simulated experiment ( squares ) , is plotted together with a fit to the data ( solid line ) . the dashed line represents the landauer limit . inset : distribution of produced heat for @xmath63.,scaledwidth=85.0% ] we now focus our attention on the switch operation . a switch operation consists in a transformation that brings the system from a known logic state to a known ( and different ) logic state ( e.g. from @xmath9 to @xmath8 or _ vice - versa _ ) . for the sake of discussion , in the following we will consider the transformation from the state @xmath9 to @xmath8 . in this case , at difference with the reset protocol , being the total entropy variation equal to zero , the expected minimum heat produced by the procedure is @xmath64 . the switch protocol relative to is presented in . the system is considered to be initially in local equilibrium in @xmath9 . in the first time frame ( @xmath65 ) it is in the buckled configuration by applying a large electrostatic force ( panel 2 ) . in the following time frames ( @xmath66 ) the ribbon is gently changed in a _ s_-shape configuration ( @xmath52 , panel 3 - 5 ) . subsequently the system evolves into a shape with @xmath67 , confining the system in the destination state ( panel 8) . finally , at time @xmath68 all the forces are removed and the system relaxes at local equilibrium in the final configuration ( panel 9 ) . and @xmath46 for the reset procedure . panels are numbered from 1 to 9 according with the time evolution indicated by the arrows.,scaledwidth=85.0% ] as before , the work done on the system is evaluated according to . results are presented in where the expected value @xmath12 is asymptotically approached as the duration of the protocol increases . the produced heat follows the trend @xmath69 ( solid line ) . for slow protocols , approaching the adiabatic condition , it is interesting to note that , although @xmath70 , the distribution of the generated heat presents negative tails ( inset ) . . produced heat approaches zero by increasing @xmath57 . the heat produced , obtained from the simulated experiment ( squares ) , is plotted together with a fit to the data ( solid line ) . inset : distribution of produced heat for @xmath71 . , scaledwidth=85.0% ] in conclusion , in this article we have studied the minimum energy required by reset and switch protocols for a bit encoded by a compressed clamped - clamped graphene ribbon . we presented two protocols that avoid the costly snapping procedure and are specifically designed to reach the minimum heat produced for these logic operations without the need of a fine control of the compression parameter . we stress that it is usually difficult to achieve a precise control of the compression parameter and thus protocols for reset / switch that are robust against variations of such parameter are of great potential interest for practical applications . victor zhirnov , ralph cavin and luca gammaitoni in minimum energy of computing , fundamental considerations , edited by dr . giorgos fagas , ict - energy - concepts towards zero - power information and communication technology ( 2014 )[/INST] heat produced during a reset operation is meant to show a fundamental bound known as landauer limit , while simple switch operations have an expected minimum amount of produced heat equals to zero . however , in both cases , present day technology realizations dissipate far beyond these theoretical limits . in this paper we present a study based on molecular dynamics simulations , where reset and switch protocols are applied on a graphene buckled ribbon , employed here as a nano electromechanical switch working at the thermodynamic limit . </s>

the production and redistribution of heavy ( non - hydrogen or -helium ) elements within galaxies is an important aspect of galaxy evolution . the amount of heavy elements in the gas phase of galaxies has been a topic of study over the decades since resolved galaxy spectroscopy became commonplace . in particular , emission line spectroscopy of star - forming regions has been of great use in understanding the distribution of chemical elements in nearby , normal galaxies . for more distant galaxies , the mass - metallicity relationship , an important signpost of galaxy chemical evolution , has been used to constrain chemical evolution across a broader range of galaxy types and , increasingly , across cosmic history . intense study of the mass - metallicity ( hereafter , ) relation in recent years has yet to pin down its origin ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) . however , it is apparent from an increasing number of unique studies that part of the scatter in the relation is due to a nuclear underabundance in interacting galaxies , at both low @xcite and high masses @xcite . if one of the progenitor galaxies in an interacting system is a spiral , a radial abundance gradient exists ( e.g. , * ? ? ? * ; * ? ? ? * ) , with lower abundances at larger galactocentric radius . during the interaction , low - metallicity gas from the galaxy outskirts is torqued into the high - metallicity galaxy center @xcite , resulting in gas with a lower average abundance ( as first suggested in @xcite ) . we discussed the quantitative details of this scenario for present - day equal - mass mergers in @xcite . a prediction of this model is that this gas redistribution dramatically flattens the initial radial metallicity gradient very shortly after first pericenter @xcite . @xcite found no oxygen gradient along the tidal tails of the mice , consistent with strong radial mixing of gas . shallow or broken gradients are also present in many nearby barred galaxies , which are undergoing radial redistribution of gas due to bar - induced gas motions @xcite . barred galaxies also show lower central metallicity than galaxies of similar morphological type and luminosity @xcite , as is observed in mergers . numerical models of barred galaxies reproduce this behavior @xcite . in a companion paper @xcite , we showed that eight interacting galaxies which are underabundant with respect to the luminosity - metallicity relation all have gradients that are flatter than the nearby spirals m83 , m101 , and the milky way . this result strongly supports the model of merger - induced metal mixing . in the present paper , we expand on this result by giving a detailed analysis of the systems in @xcite , doubling the sample of interacting galaxies with measured gradients ( to 16 ) , and presenting a comprehensive comparison to isolated spirals and the numerical simulations . the interacting galaxies in this sample are all in the early stages of merging . they are after first passage of the two ( or more ) galaxies , but probably prior to second passage . a future paper will present similar data on galaxies in the later stages of merging ( rupke et al . 2010 , in prep . ) . understanding chemical evolution during a major merger will shed light on galaxy evolution at the peak of cosmic star formation , since the major merger rate , especially involving gas - rich galaxies , was higher in the past @xcite . these major mergers have likely played an important role in the production and growth of massive , red galaxies since @xmath0 ( e.g. , * ? ? ? * ; * ? ? ? simulations suggest that dry mergers ( with no gas ) flatten stellar metallicity gradients in ellipticals @xcite . it may be that wet mergers that form bulge - dominated systems may do the same , if significant star formation occurs after the gas gradient flattens . in short , the metallicity redistribution caused by gas - rich mergers may significantly impact galaxy chemical evolution . in 2 and 3 , we present the observations and our analysis . in 4 we present the metal distributions , and then compare to numerical simulations in 5 . we summarize in 6 . cosmological quantities are computed using @xmath1 , @xmath2 , and @xmath3 , and in the rest frame defined by the cosmic microwave background ( where applicable ) . our sample consists of galaxy pairs undergoing strong interactions in the local universe . the pairs are chosen from both optically - selected @xcite and infrared - selected @xcite catalogs of interacting systems . the primary selection criteria , to ensure that the systems are strongly interacting , are that the projected nuclear separation is small ( @xmath4 30 kpc ) , the galaxy mass ratios are small ( 1:1@xmath51:3 ) , and that the systems are obviously disturbed ( i.e. , after first passage ) . to distinguish from systems in later stages of merging , we have rejected systems with ( 1 ) projected pair separations @xmath615 kpc and/or ( 2 ) compact morphology and faint tidal features that indicate the system is near or after nuclear coalescence . the first criterion may remove some systems very near first or second pericenter , but also securely rules out most systems after second pericenter , since rapid orbital decay in strong , equal - mass interactions leads to small nuclear separations after second pericenter ( e.g. , * ? ? ? * and references therein ) . we have chosen spiral - spiral interactions to maximize the prevalence of regions . in each system in our sample , there is an obviously interacting pair with small projected separation , near - equal masses , and signs of interaction . however , in some cases there is also a third galaxy at large projected separations ( @xmath750 kpc ) from the dominant pair which may or may not be involved in the interaction . given their large distances , we do not further consider these possible third members of the system . basic properties of individual galaxies in our sample are listed in table [ tab : sample ] . our sample of 9 pairs / groups have fairly average properties for nearby galaxies ( figure [ fig : sample ] ) . individual galaxies are evenly distributed around @xmath8 ( @xmath9 mag ; @xcite ) , and have total infrared luminosities near @xmath10 @xcite . as mentioned above , the pair mass ratios ( as traced by @xmath11-band luminosity ) are in the 1:1@xmath51:3 range , with projected nuclear separations of @xmath12 kpc ( except for arp 248 , where the separation of the two primary galaxies is 54.3 kpc ) . table [ tab : sample ] also lists optical diameters , inclinations , and line - of - nodes position angles for the sample . many of these parameters are taken directly from hyperleda @xcite . for the ngc 2207 / ic 2163 system , we used parameters determined from numerical models @xcite . in the cases of a few galaxies , the tidal stretching of the galaxies or general interaction - induced disturbances make determining disk orientations a challenge . in this handful of cases , we have turned where possible to maps to determine the position angles . these cases are listed in the table notes . we have also used this data and inspection of visual images to double - check hyperleda inclinations . the inclinations of two galaxies remain uncertain : arp 248 ned02 and arp 256 ned02 , which are particularly tidally - stretched . in both of these cases , the effect on the gradient is compensated for somewhat by a larger measured . we estimate that the inclinations lie in the range @xmath13 , and compute the deprojection using 30@xmath14 . a control sample of isolated galaxies is a necessary component of this study . in particular , we need to compare our results to a group of galaxies that plausibly represent the galaxies in our sample as they were before a major interaction . we have selected our control sample from published data on nearby , isolated spirals that have data on region emission - line fluxes . in particular , we have focused on mid - to - late - type spirals with a mix of bar strengths @xcite , since mid - to - late types are best represented in the literature . gradients correlate with bar strength in a relationship with significant scatter @xcite , and depend weakly or not at all on spiral type @xcite . our sample should thus be representative of isolated spirals at the level allowed by small number statistics . finally , with only two exceptions , we have picked galaxies from moderate - size , homogeneous studies to minimize systematic uncertainties . ( the two exceptions , ngc 300 and m101 , are well - characterized benchmarks in gradient studies , and so we include them as well . ) the salient properties of our control sample , and the references for the sample properties , are listed in table [ tab : control ] . the interacting and control samples are well - matched in mass , as traced by @xmath11-band luminosity ( fig . [ fig : sample]@xmath15 ; the control sample is only half a magnitude fainter on average ) . they are also well - matched in optical radius , with average ( median ) optical radii of @xmath16 13 ( 12 ) kpc in both samples . however , the interacting galaxies have an average ( median ) infrared luminosity that is boosted a factor of 7 ( 4 ) above the control sample ( fig . [ fig : sample]@xmath17 ) . this is unsurprising , given the expected higher star formation rates in the interacting sample @xcite . rather than use gradient determinations published in the literature , we have used the published line fluxes to measure abundances using the same strong - line diagnostic that we apply to our interacting galaxies sample ( [ sec : spectral - analysis ] ) . we have also performed our own spatial deprojections using published photometric parameters ( see references in table [ tab : control ] ) . the resulting oxygen abundance gradients , in terms of dex / kpc and dex/ , are given in table [ tab : control ] . we used the multiobject spectroscopic capabilities of the keck low - resolution imaging spectrometer ( lris ; @xcite ) to observe regions in the galaxies of interest . the excellent blue sensitivity of lris was important for measuring the emission lines at high s / n ; the doublet is used in our strong - line metallicity diagnostics ( [ sec : data - reduct - analys ] ) . our typical setup was to observe the wavelength range @xmath18 , using the 900 l / mm grating in the red and either the 400 or the 600 l / mm grism in the blue , and the 560 nm dichroic to separate the red and blue spectra . ( for one galaxy , arp 248 , we were forced to use the 300 l / mm grism in the blue to obtain the entire spectrum , because lris - r was inoperable . ) for over half of our data , the lris atmospheric dispersion corrector ( adc ) was in place , mitigating any light loss in the blue . for the other half ( taken prior to mid-2007 ) , slit losses due to atmospheric refraction were generally small . total exposure times per mask were typically an hour . slitmasks were created in most cases using sensitive emission - line images . slits were 1 wide . the images were taken using redshifted narrowband filters at either the vatican advanced technology telescope ( vatt ; e. barton and r. jansen 2005 , private comm . ) or the university of hawaii 88-inch telescope . however , in two cases ( arp 256 and arp 298 ) , the spectroscopic data was taken in the context of a program to observe star clusters ( chien et al . 2010 , in prep . ) . in this case , star clusters were targeted using _ hubble space telescope _ ( @xmath19 ) broadband f435w images . since significant h@xmath20 emission fell in the slits in these cases , we were able to extract useful region spectra for the current work . the lris data were reduced using a pipeline we developed specifically for the current dataset . this pipeline combines image reduction and analysis facility ( iraf ) and interactive data language ( idl ) scripts . for each side of the spectrograph , the steps we took were as follows : bias subtraction ; slit identification and tracing using flatfield exposures ; arc lamp identification ; slit extraction and spatial rectification ( including any atmospheric dispersion correction , if required ) ; a small shift to match dispersion solutions among exposures ; data combination , including noise - threshold cosmic ray rejection ; wavelength calibration ; extraction of spectra ; sky subtraction ; and flux calibration . in the slit identification step , slit edges were detected using a directional filter that computed the first derivative of the flatfield in the spatial direction . we extracted each local peak in h@xmath20 using a 1@xmath211 aperture , and subtracted the sky using off - object spectra free of galaxy continuum and line emission . sky subtraction was generally imperfect due to the change of the lris point spread function across the @xmath22 field - of - view combined with the use of a small number of sky spectra that were typically on the field edges ( to avoid galaxy contamination within the on - source slits ) . blue and red spectra were reduced separately , and then combined near 5600 by multiplicatively matching the continuum fluxes in this region . following the analysis of the spectra , this relative flux calibration was further refined . spectra were mapped to positions on the sky assuming correct alignment of each slitmask during observations along with knowledge of the slit plane to focal plane mapping . ( we used at least four alignment stars per slitmask to ensure correct mask alignment . ) galactocentric radii were then computed using information on the 3-dimensional alignment of each galaxy ( [ sec : sample ] ) . to determine the center of all galaxies except ngc 3994/5 , we used near - infrared positions from 2mass . sloan digital sky survey ( sdss ) centers were used for ngc 3994/5 . though these systems are gravitationally disturbed , the near - infrared is able to probe the central bulge in each galaxy and thus yield a reasonably accurate true gravitational center . we extracted information from the resulting spectra by performing detailed fits to the stellar continuum and line emission . the software fitting package that we wrote for this purpose , uhspecfit , was based on the stellar fitting routines of @xcite , who fit stellar continua using a linear combination of several template spectra . we built on these routines a sophisticated suite of emission - line fitting software that fits all emission lines simultaneously and allows for multiple velocity components , starting with the code framework used in @xcite . to fit these relatively high - resolution data , we used the stellar population synthesis models of @xcite as our stellar continuum templates . we relied on the solar metallicity , geneva isochrone models for our fits . the quality of the fits is not a sensitive function of stellar metallicity ; since our goal was not to constrain the stellar metallicity , but rather to remove the stellar continuum , we used only the solar metallicity models . the stellar fits were performed on the blue half of the spectra ( from @xmath23 in the rest frame ) after removal of wavelength regions near strong emission lines ; the resulting stellar fit was then normalized to fit the red half of the spectra . we subtracted the stellar continuum from the spectra and performed emission - line fits . two example fits are shown in figure [ fig : example_fit ] . one is a high emission line flux case , and the other is a low emission line flux case ( roughly 1@xmath24 , in flux , of the high flux case ) . these are illustrative of the typical high fidelity of the fits , and reveal that fits to the balmer absorption lines in particular are very good . once the fits were complete , a final blue - red relative flux calibration was performed by comparing the measured reddening from the / emission line ratio ( using the extinction law of @xcite ) with that measured from the / ratio . the discrepancy was used to correct the blue emission - line fluxes . this method worked very well for our data ( which showed high signal - to - noise in ) and our choice of spectral fitting ( which permitted robust separation of balmer absorption and emission ) . however , our abundance errors increase with the use of / to determine the reddening ( as opposed to / ) . we corrected the emission line fluxes for reddening @xcite and computed important line ratios . spectra with very uncertain reddening because of poorly - fit or weak and emission lines were ignored . the dereddened line ratios were then used to classify each spectrum as -region , composite , seyfert , or liner @xcite . we calculated abundances only for those regions which are securely of -region origin , without probable contamination from other sources of excitation . we included only those data identified as -region spectra based on the /vs . / diagnostic ( i.e. , regions that fall below the @xcite star formation locus ) and or composite spectra based on the / vs. / diagnostic ( i.e. , regions that fall below the @xcite extreme starburst line ) . for both line ratio cuts , we included data up to 0.1 dex to the right of the diagnostic line to account for possible uncertainties . roughly 25% of our spectra were rejected because of poorly - fit emission , line ratio cuts , or inadequate line fits . spectra rejected due to line ratio cuts are shown as black crosses atop the galaxy images in figure [ fig : results ] . our final sample of regions in early - stage interacting galaxies consists of 332 spectra . these are accompanied by 281 region spectra from the control sample . four nuclei in our sample show either seyfert ( ngc 2207 , ic 2163 , ngc 7469 ) or liner ( ngc 3994 ) spectra based on our data . however , these nuclear ionizing sources have minimal impact on the extra - nuclear regions that are used to compute abundances ; phenomena like ionization cones would in any case be detected and rejected using our line ratio cuts . in this paper , we quote abundances calculated from the /abundance diagnostic ( * ? ? ? * hereafter kd02 ) . of the strong - line diagnostics , this one produces the least root - mean - square ( rms ) dispersion about the mean due to its relative insensitivity to ionization parameter ( kd02 ) . to study possible systematic errors from the use of this diagnostic ( due to , e.g. , improper extinction corrections or improper relative flux calibration of the blue and red lris arms ) , we computed abundances using the ( * ? ? ? * hereafter kk04 ) and ( * ? ? ? * hereafter pp04 ) ( /)/(/ ) diagnostics ( following the guidelines laid out by @xcite ) and then converted these diagnostics into the kd02 calibration using the formulas of @xcite . the results are shown for all of the regions in this paper in figure [ fig : abundcomp ] , and for individual systems in figure [ fig : results ] . it is clear from examining figure [ fig : abundcomp ] that , overall , there are no significant systematic discrepancies introduced by our data reduction and analysis that make our / line ratios suspect . for instance , both kk04 and pp04 are less sensitive to extinction than kd02 , and inaccurate extinction corrections should show up as deviations from equality in these figures . the interacting galaxies sample does in fact show a 0.05 dex offset from equality in the kd02 vs. pp04 diagram . however , the pp04 diagnostic does not correct for ionization parameter variations , which introduces a systematic uncertainty in this diagnostic ; the kd02 diagnostic is insensitive to ionization parameter . furthermore , the offset is well within the expected uncertainties of the diagnostic and conversion formulas , and as a simple offset , will have no impact on relative abundances like gradients . in fact , the rms dispersion about the line of equality in the interacting galaxies sample ( 0.05 dex ) is significantly lower than that in the control sample for the kd02 vs. kk04 diagram , suggesting that our data is highly uniform . in the kd02 vs. pp04 diagram , the rms dispersions are the same for the two samples , but for the interacting sample this is in large part due to the systematic offset to one side of equality . errors in the emission - line fluxes were computed by assigning the error in the peak flux to equal the rms residual within 2@xmath25 of each line center , after subtracting the continuum and line fits from the data . errors were propagated primarily using analytic expressions , but for abundance and gradient errors we employed monte carlo methods . in the following section , we use the calculated abundances and radii for the regions in each galaxy to compute radial abundance gradients , and compare the gradients of the control and interacting samples . with abundances and deprojected radii in hand , we computed radial oxygen gradients for each galaxy in our sample . in two cases ( ic 5283 and ugc 12915 ) , the radial coverage and number of regions available were each too small to yield a reliable estimate of the gradient . in the control sample , we limited the gradient fits to within 1.5 , to match the radii fit in the interacting galaxy sample . we wished to avoid biasing the gradient fit toward particular locations in the galaxy ( e.g. , to high - luminosity regions ) , so we performed unweighted least - squares fits . our fits were computed with radius as the independent variable , and errors in slope and intercept were estimated using monte carlo methods . the resulting gradients and intercepts are given in table [ tab : gradients ] . in figure [ fig : results ] , we present for each system the results of our emission - line analysis : emission line diagnostic diagrams , comparison of different metallicity diagnostics , a two - dimensional projected oxygen abundance map , and a one - dimensional deprojected radial oxygen abundance profile . the measured gradients in these interacting systems are on average significantly flatter than those in the control sample ( figure [ fig : hist - grads ] ) . the control sample exhibits median slopes of [email protected] dex / kpc and [email protected] dex/ , while the interacting systems have median slopes of [email protected] dex / kpc and [email protected] dex/ ( where the errors given are the standard error ) . in short , the interacting systems have gradients that are , on average , less than half as steep as isolated galaxies . in @xcite , we showed that gradients in eight of the systems presented here were shallower than gradients in m83 , m101 , and the milky way . the present data quantify this difference at a high confidence level using large control and interacting samples . taken by themselves , these differences in gradients are a strong confirmation of the model of merger - induced gas inflow leading to metal mixing . surprisingly , the dispersions in the interacting sample gradient distributions are also less than the dispersions in the control sample : the control sample shows standard deviations of 0.03 dex / kpc and 0.17 dex/ , compared to 0.01 dex / kpc and 0.11 dex/. the explanation for the latter effect is unclear , but could result from the origin of the region data in heterogeneous and homogeneous datasets , respectively . no significant correlations are seen between gradients and galaxy near infrared and total infrared luminosities , either in the interacting sample or the control sample ( figure [ fig : grads - vs - gal ] ) . previous work has shown that correlations may exist between optical luminosities and gradients in dex / kpc @xcite ; however , such a trend apparently does not persist in interacting systems ( and is not obvious in our control sample ) . one might expect a correlation of infrared luminosity with gradient in interacting systems , if is assumed to trace star formation rate and star formation is driven by gas inflow . again , no such trend is evident , though we only have upper limits in for much of our sample . no obvious trends are seen when comparing gradients to system properties that may parameterize the stage or strength of the interaction : projected nuclear separation , near - infrared luminosity ratio , or total system infrared luminosity ( figure [ fig : grads - vs - sys ] ) . projected nuclear separation is of course only approximate , since we can not deproject the two galaxies without detailed modeling , and there is a degeneracy in the age of the interaction between galaxies moving apart after first pericenter and returning to second pericenter . furthermore , mass ratios in our sample ( as traced by @xmath11-band luminosity ratio ) are all close to unity , and one might expect little variation among the systems in our sample based on this parameter alone . finally , confusing the matter , simulations also show that although both galaxies in a strongly interacting pair experience a flattening of the gradient very quickly after first pericenter , the relative degree of flattening of the two disks varies depending on the geometry and the distance of first pericenter @xcite . this effect would introduce scatter into any underlying correlation between gradients and system properties . [ sec : gradients - vs .- merger ] for further discussion . some systematic uncertainty arises in our abundance gradients due to our choice of abundance calibration / diagnostic . some calibrations ( including both strong- and weak - line ones ) may yield shallower slopes than we calculate ( e.g. , * ? ? ? * ; * ? ? ? however , @xcite showed that an -based diagnostic yields the same results as the kd02 diagnostic we employ in this paper . more importantly , we rely on the fact that within a particular abundance calibration / diagnostic , _ relative _ abundances are reliably computed and internally consistent @xcite . when using detailed chemodynamical models to constrain parameters of individual systems , measuring the absolute value of the gradient precisely may be important . within the context of the current study , we are concerned only with gradient changes relative to initial conditions . we also emphasize that , were the initial galaxy gradients too shallow ( or completely flat ) , the metal dilution clearly observed in interacting systems would be impossible , and would thus be inconsistent with empirical evidence . nevertheless , as a check on the reliability of our / gradients , figure [ fig : results ] shows , for each system , how the /abundances compare with those computed in the kk04 and pp04 diagnostics ( see [ sec : spectral - analysis ] for more details ) . as is seen in the full sample ( fig . [ fig : abundcomp ] ) , individual systems are largely free of systematic discrepancies . the two exceptions are ngc 2207/ic 2163 and arp 248 , which show discrepancies between the kd02- and pp04-computed metallicities . these anomalies may result from variations in ionization parameter that remain uncorrected in the pp04 diagnostic ( [ sec : spectral - analysis ] ) or reddening uncertainties . further analysis shows that , if we were to use the pp04 abundances ( after being converted into the kd02 system ) , we would measure shallower gradients in arp 248 ned01 and arp 248 ned02 and a steeper gradient in ngc 2207 ( but not ic 2163 ) , in each case by a factor of @xmath272 . with the common exception of the galaxy nuclei , the vast majority of data in our sample are pure regions . ugc 12914/12915 has a significant number of regions indicative of non - photoionized emission . in fact , the north half of ugc 12914 has a significant number of regions with multiple velocity components and shock - like line ratios @xcite . this region overlaps a bridge of gas between the galaxies @xcite . numerical simulations are a powerful tool for investigating the evolution of galaxy mergers . however , most simulations of mergers to date have paid little attention to gas - phase metallicity and its evolution . recently , @xcite discussed metallicity evolution prior to second pericenter in smoothed particle hydrodynamic ( sph ) / n - body simulations of equal - mass mergers with gas mass fractions of 10% ( to match nearby galaxies ) . though they did not include enrichment from ongoing star formation , @xcite reached good agreement with the magnitude of deviations of major mergers from the mass - metallicity relation . they also showed that radial abundance gradients should flatten rapidly after first pericenter , and predict the relationship between gradient flattening and nuclear abundance and the detailed shape of the gradient with time . @xcite presented simulations including star formation that largely agreed with @xcite , but did not address the evolution of gradients . torrey et al . ( 2010 , in prep . ) find similar results to @xcite , but show that preferential consumption of high - metallicity gas by star formation in galaxy nuclei plays a role alongside metal dilution due to inflow . in the following sections , we compare our data on metallicity distributions in interacting galaxies to the simulations of @xcite . these sph / n - body simulations are described in detail in @xcite . in brief , 24576 gas particles were distributed in an exponential disk of scale height equal to 6% of the disk scale length . the stars occupied a bulge and identical disk , with a bulge - to - disk ratio of @xmath28 . eight close - passage mergers were simulated , with all combinations of direct and retrograde considered . the metallicity per gas particle was unchanged during the simulation , and two different initial metallicity gradients were considered ( -0.2 dex/@xmath29 and -0.4 dex/@xmath30 ) . in this work we modified the initial gradients slightly to match our control sample : -0.15 dex/@xmath30 . this number results from the typical gradient in dex / for the control sample ( [ sec : oxygen - gradients ] ) , when converted to dex/@xmath30 using a typical ratio for /@xmath30 ( [ sec : grad - lumin - metall ] ) . our galaxy sample was chosen to represent major mergers somewhere between first and second pericenter . the distribution of observed gradients is shown in figure [ fig : hist - grads ] . for comparison , we construct a predicted gradient distribution from our set of simulated major mergers , assuming that our sample is randomly distributed between first and second pericenter . we also assumed that the simulated galaxies start with a single gradient equal to the mean value in the control sample . the observed and simulated distribution show remarkable agreement ( figure [ fig : hist - grads - sims ] ) . we show in figure [ fig : grads - vs - sys ] that , for the present sample , there is no strong dependence of gradient on merger stage , as parameterized by projected nuclear separation . this is consistent with the predictions of our simulations . figure [ fig : grads - vs - nsep - sims ] reveals that , between first and second pericenter , there is no predicted dependence of the gradients on actual nuclear separation , for the ensemble of simulations as a whole . within particular mergers , a more recognizable dependence of gradient on nuclear separation may emerge , but we must consider our present dataset as random snapshots of an ensemble of different mergers . we do not at present have an accurate understanding of the initial conditions of most or all of the systems in our sample . the motivation for the present work was the observation that interacting galaxies fall below the luminosity - metallicity ( ) and mass - metallicity ( ) relations of star - forming galaxies . do the current data present a consistent picture in this regard , such that the nuclear metallicities of interacting systems with shallow gradients also fall below these relationships ? for a subset of the current sample , we used the @xmath31-band relation in @xcite and found no correlation between gradients and offsets , but were limited by small sample size and the fact that @xmath31-band luminosity is sensitive to ongoing star formation and extinction effects . in this paper , we compare the control and interacting samples to the luminosity - metallicity relation as measured in the near - infrared @xcite , and use simulations to interpret the result . multicolor broadband photometry is not available for our entire sample , so we are unable to measure accurate masses and apply the relation . near - infrared photometry , however , is less sensitive to extinction or contamination from star formation than the optical ; it is also a reasonable tracer of stellar mass within a factor of @xmath272 @xcite . the @xcite abundances are available in several diagnostics . none of these are the / diagnostic that we employ , so we resort to the abundance conversion formulas of @xcite . we start with the -computed abundances from @xcite ; the diagnostic they use is a functional fit of to abundances from modeling of sdss spectra @xcite . we then apply the formula from @xcite . because two transformations are involved , we consider these abundances to be only approximate , and are useful primarily for establishing the slope of the relation . we do not have nuclear abundances measured from long - slit spectra for all of the galaxies in the current sample . we thus estimate abundances by extrapolating our gradient fits , and compute the abundances at a discrete radius of @xmath32 . this roughly matches the extent of the long - slit apertures of the @xcite data , which have @xmath33 . using this method , neither the control nor interacting samples fall on the @xmath11-band relation . this is presumably due to one of two effects : ( 1 ) the @xcite abundances are luminosity - weighted measurements from nuclear spectra , while ours are measured at a fiducial radius using fits to region data ; and/or ( 2 ) the uncertainties introduced by the two transformations involved in computing the abundances of the @xcite sample . the latter effect is not unusual when converting among different metallicity calibrations @xcite . to account for this effect , we apply a constant offset of @xmath50.3 dex to both the control sample and interacting sample metallicities . this offset minimizes the rms deviation of the control sample from the relation . the exact vertical normalization of the data is irrelevant , however ; the important quantities are the _ relative _ nuclear abundances of the control and interacting samples at a given luminosity , which are secure since we use the same abundance diagnostic and compute the nuclear abundances in the same way . the @xcite data simply provide a more accurate slope for the relation than the control sample by itself . the result of this exercise is displayed in figure [ fig : lz-0p1 ] . this figure makes evident that the early - stage interacting galaxies , which have shallower gradients than the control sample , also fall below the relation defined by the control sample and emission line galaxy sample . in fact , the interacting galaxies form a remarkably coherent relationship that is simply offset from that of isolated star - formers by @xmath50.2 dex in abundance . to tie together abundance offsets and gradients , we compare directly to the simulations of @xcite . these simulations predicted that the gradient slope would change quickly after first pericenter , while the nuclear metallicity would change more slowly between first and second pericenter . the simulations yield gradients in units of exponential disk scale length of the gas disk ( dex / r@xmath34 ) , while we express observed gradients in physical units ( dex / kpc ) and optical ( stellar ) isophotal radius ( dex/ ) . for our control sample , we have stellar disk scale lengths as well as optical radii , and the two are related according to @xmath35r@xmath34 , where the uncertainty given is the standard deviation . using this scaling , we compute the gradients in dex / r@xmath34 for our interacting galaxy sample . for the current data set , we measured abundances at a fiducial radius of 0.1 . to match this procedure for the simulations , we computed average abundances within a narrow , 0.1r@xmath34-wide radial bin centered on 0.35r@xmath34 . ( this differs from the method in @xcite , in which we averaged over the entire central disk within 0.5r@xmath34 . ) for the data , we assume that the interacting galaxies started on the relation of the control sample and have had their central metallicity lowered during the merger . it is clear that , given the uncertainties inherent in this procedure ( e.g. , the galaxies did nt necessarily start on the mean relation ) and the simplicity of the simulations ( which do not include ongoing star formation ) , there is remarkable agreement between the data and simulations ( figures [ fig : dz - vs - grad ] and [ fig : dz - vs - grad - lab ] ) . a total of @xmath36 of the interacting galaxies fall directly in the phase space delineated by the simulated evolutionary tracks . furthermore , the region of overlap with the simulations is near the time of first turnaround ( between first and second pericenter ) for many of the simulated pairs , which is consistent with the galaxies in our sample being somewhere between first and second pericenter on average . ( in a random distribution of post - pericenter pairs selected by nuclear separation , half should be pre - turnaround , and half post - turnaround . ) the data are thus quantitatively consistent with the prediction of the simulations of @xcite that the gradient should flatten quickly after first pericenter , and that the nuclear abundance should decrease at a slower rate between first and second pericenter . the scatter of plausible initial conditions , as represented by the control sample , do caution against drawing detailed conclusions from this comparison of data and simulations . in particular , a variety of initial conditions can explain the current position of the interacting galaxies in the metallicity - gradient phase space . the metallicity scatter in the control sample is partly a measurement issue ; e.g. , the scatter in the simulated control relation is larger than in the @xcite sample , and the control sample regions show a larger rms dispersion in abundance than the interacting sample ( fig . [ fig : hist - rms ] ) . to deal with this metallicity scatter , whatever its origin , however , we simply shift the simulations left or right in figure [ fig : dz - vs - grad ] to start at the control sample initial conditions . a shift in offset could in principle resolve any discrepancies between data and simulations for individual galaxies . for example , ngc 2207 is clearly not at a late merger stage , as suggested by its position with respect to the merger models ( it is probably just after first passage ; @xcite ) . however , it could initially have had lower metallicity than predicted by the mean relation and/or a steeper initial gradient , leading to a more favorable comparison with models in figure [ fig : dz - vs - grad ] . if a galaxy were to start with a larger gradient than is assumed in the models , then the changes in gradient and central metallicity are larger @xcite . for instance , if we assume the initial conditions represented by ngc 300 or ngc 2997 , the simulations still overlap the data , due to the more extreme changes that result from a steeper gradient and the same amount of infall ( figure [ fig : dz - vs - grad - steep ] ) . closer inspection rules out this scenario for most systems , however , since ( a ) the overlap of the data and the bulk of the simulations is not as good and ( b ) these initial conditions would require almost all of the observed interacting systems to lie near second pericenter . this is unlikely , due to how we have selected our sample ( [ sec : sample ] ) . the simulation - to - data comparison shown in figure [ fig : dz - vs - grad ] , with half the initial gradient of that in ngc 300 or ngc 2997 , is therefore a more likely scenario for most systems . following standard practice , we have characterized radial metallicity profiles using straight line fits [ i.e. , 12@xmath37log(o / h ) @xmath16 a @xmath37 br ] . however , the predicted metallicity profiles from the simulations of @xcite do show distinctive shapes that are not purely straight lines at all times . individual galaxies in our sample do not have enough data points to accurately characterize the profile shapes beyond straight lines . however , we can compute the average deviation from straightness as a function of radius by subtracting the gradients and binning the data in radius . we do this for both the control and interacting samples , and show the results in figure [ fig : profile ] . these two samples show metallicity profile residuals that are significantly different . the control sample is largely consistent with a straight line . however , the interacting sample shows a clear `` concave up '' shape , in the sense that positive deviations are seen at small and large radius , with negative deviations at middle radii . how does this compare with simulations ? to bin the simulation data , we consider the ensemble of profiles at first and second pericenter and first turnaround . the result , with the interacting galaxies data overplotted , is shown in figure [ fig : profile ] . it is apparent that for the simulations , there is a small upturn at low radius at all times , consistent with the data . though there is not exact quantitative agreement in any of the three stages , the simulations at first turnaround show the same `` concave up '' shape seen in the data . by contrast , the simulations at 1st and 2nd pericenter show a flatter profile outside the nuclear regions . as discussed above , this is consistent with the idea that , on average , our sample is near first turnaround , and otherwise evenly distributed between first and second pericenter . given the complexity and variety of the actual merging systems in this study , it is impressive that there remains such good agreement at this level of comparison between data and simulations , and speaks to the robustness of the dilution model and its predictions . it also suggests that metals produced in star formation initiated by the merger have only a small effect on the gas - phase metallicity distributions prior to second pericenter . this could occur either because most star formation occurs after second pericenter or because of inefficient mixing of the metal - enriched hot phase with the cooler ism . in fact , only a limited fraction of the gas in interacting galaxies can be consumed in star formation prior to merging , in order to leave a significant gas reservoir at late stages @xcite . we have presented here data on the gas - phase oxygen abundance gradients in 9 pairs / groups ( 18 galaxies ) in the early stages of an interaction ( after first pericenter , prior to second ) . we computed radial gradients based on region spectroscopy and the most precise strong - line abundance diagnostic available ( kd02 ) . we find a clear break between the gradient distributions of isolated and interacting systems : interacting systems consistently have gradients about half that in normal , isolated spirals . we compare the data to the simulations of @xcite , and find remarkable statistical agreement at the ensemble level . the simulations accurately reproduce ( 1 ) the gradient distribution , ( 2 ) the lack of gradient dependence on projected nuclear separation , ( 3 ) the relationship between gradients and deviations from the luminosity - metallicity relation , and ( 4 ) metallicity profile deviations from a straight line . these data are clear evidence that models of metal redistribution due to interaction - induced gas inflow @xcite are able to account for the low nuclear abundances observed in interacting galaxies @xcite . now that this mechanism is firmly established , future work should be devoted to understanding how this affects the global evolution of the mass - metallicity relation over cosmic times and the formation of elliptical galaxies . in particular , if mergers or post - mergers dominate samples of galaxies used to determine the @xmath38 relation at high redshift , this bias must be taken into account . furthermore , all massive galaxies have experienced mergers during their lifetime . the re - distribution of metals due to gas inflow will then affect the stellar populations formed at later times at all radii . though we have already found remarkable agreement between the data and simulations at a statistical level , this comparison could be improved upon using simulations that incorporate realistic models of star formation and chemical enrichment ( including a sophisticated model of starburst - driven galactic winds ) . secondly , we have compared to simulations only after binning the data azimuthally ; more detailed comparison of theory to actual projected metallicity distributions would provide a stronger understanding of how and where the dilution occurs . furthermore , we have only looked for agreement at a statistical level . though the current data already provide broad constraints on the simulations , more detailed constraints will require careful modeling of individual systems . the limited merger ages traced by this early - stage sample constrain our ability to trace metal redistribution over the entire course of a merger . in future work ( rupke et al . 2010 , in prep . ) , we will present data on later stage mergers to accomplish this . the authors thank jabran zahid for sharing the software that formed the basis of uhspecfit ; fabio bresolin for data analysis tips , a galaxy deprojection algorithm , and commenting on the manuscript ; margaret geller for commenting on the manuscript ; betsy barton and rolf jansen for providing their h@xmath20 images ; josh barnes for helpful discussion ; and the referee for useful comments regarding content and presentation . the data presented herein were obtained at the w.m . keck observatory , which is operated as a scientific partnership among the california institute of technology , the university of california and the national aeronautics and space administration . the observatory was made possible by the generous financial support of the w.m . keck foundation . the authors also recognize the very significant cultural and spiritual role that the summit of mauna kea has within the indigenous hawaiian community . we are most fortunate to have the opportunity to observe the universe from this mountain . , j. e. 1998 , in saas - fee advanced course 26 : galaxies : interactions and induced star formation , ed . r. c. kennicutt jr . , f. schweizer , j. e. barnes , d. friedli , l. martinet , & d. pfenniger , 275 , http://adsabs.harvard.edu/abs/1998giis.conf..275b[ads ] ugc 12914 & vv254 & 4371 & & -24.23 & 10.36 & 14.69 & 54 & 160 & 2,3,4 + ugc 12915 & vv254 & 4336 & 17.40 & -23.70 & 10.76 & 11.11 & 73 & 135 & 2,3,4 + arp 256 ned02 & arp 256 & 8193 & & -23.11 & & 16.58 & 0@xmath545 & 70 & 1,3,4 + arp 256 ned01 & arp 256 & 8125 & 28.20 & -23.80 & 11.35 & 13.66 & 61 & 80 & 1,3,4 + ugc 312 & hcg 2 & 4364 & & -21.56 & 9.93 & 11.67 & 79 & 8 & 2 + mrk 552 & hcg 2 & 4349 & 21.10 & -22.33 & 10.38 & & & & 2 + ugc 314 & hcg 2 & 4271 & 65.40 & -20.52 & & & & & + ugc 813 & wbl 036 & 5344 & & -22.89 & 10.68 & 11.16 & 72 & 110 & 2 + ugc 816 & wbl 036 & 5188 & 16.50 & -23.01 & 10.68 & 13.33 & 62 & 190 & 2 + cgcg 551 - 011 & wbl 036 & 5373 & 42.60 & -23.27 & & & & & 2 + ngc 2207 & ngc 2207/ic 2163 & 2741 & & -24.54 & 11.00 & 22.11 & 35 & 140 & 3,4 + ic 2163 & ngc 2207/ic 2163 & 2765 & 15.80 & -24.18 & & 9.80 & 35 & 128 & 3,4 + arp 248 ned01 & arp 248 & 5167 & & -22.39 & 10.66 & 13.90 & 66 & 43 & 1 + arp 248 ned02 & arp 248 & 5167 & 54.60 & -23.32 & 10.66 & 13.27 & 0@xmath545 & 109 & 1 + arp 248 ned03 & arp 248 & 5276 & 93.10 & -20.82 & & & & & 1 + ngc 3994 & arp 313 & 3086 & & -23.56 & 10.55 & 6.18 & 58 & 10 & 1,2,3,4 + ngc 3995 & arp 313 & 3254 & 24.70 & -22.64 & 10.42 & 19.40 & 69 & 45 & 1,2,3,4 + ngc 3991 & arp 313 & 3192 & 50.10 & -22.51 & 10.26 & & & & 4 + ngc 7469 & arp 298 & 4892 & & -24.23 & 11.46 & 12.22 & 30 & 127 & 1,3,4 + ic 5283 & arp 298 & 4804 & 23.30 & -23.36 & & 9.90 & 60 & 105 & 1,3,4 + ugc 12545 & wbl 713 & 5754 & & -21.41 & 10.28 & 11.81 & 63 & 85 & 2 + ugc 12546 & wbl 713 & 6055 & 21.90 & -22.69 & 10.28 & 10.64 & 63 & 20 & 2 + ngc 300 & sad & 2.08 & a & -19.43 & 8.43 & 5.90 & 2.26 & b & 40 & 114 & aa & 1 + ngc 628 ( m74 ) & sac & 8.59 & b & -22.48 & 9.82 & 13.08 & 3.57 & a & 7 & 25 & cc & 6,7 + ngc 925 & sabd & 7.38 & e & -20.75 & 9.21 & 12.04 & 2.60 & d & 61 & 107 & aa & 7 + ngc 1232 & sabc & 14.50 & d & -23.08 & 9.91 & 14.59 & 4.51 & c & 33 & 270 & aa , ee & 3,7 + ngc 2403 & sabcd & 3.16 & a & -21.05 & 9.19 & 9.17 & 1.72 & c & 60 & 127 & aa & 4,7 + ngc 2805 & sabd & 28.00 & c & -21.44 & 9.68 & 14.42 & 8.96 & e & 36 & 290 & aa , bb & 7 + ngc 2903 & sabbc & 8.55 & e & -23.56 & 10.22 & 14.95 & 3.09 & e & 56 & 23 & aa & 3,7 + ngc 2997 & sabc & 7.08 & e & -22.61 & 9.82 & 11.55 & 4.84 & f & 41 & 110 & aa & 3 + ngc 3184 & sabcd & 8.70 & c & -22.09 & 9.48 & 9.60 & 2.59 & g & 24 & 135 & aa & 7 + ngc 5236 ( m83 ) & sabc & 4.92 & a & -23.66 & 10.37 & 10.34 & 2.89 & f & 27 & 45 & aa & 2,3 + ngc 5457 ( m101 ) & sabcd & 6.96 & a & -23.26 & 10.23 & 29.19 & 5.19 & e & 37 & 18 & dd & 5 + ngc 300 & 27 & -0.1246 & -0.664 & 8.95 + ngc 628 & 25 & -0.0410 & -0.536 & 9.10 + ngc 925 & 44 & -0.0471 & -0.568 & 8.83 + ngc 1232 & 22 & -0.0310 & -0.451 & 9.10 + ngc 2403 & 25 & -0.0750 & -0.689 & 8.93 + ngc 2805 & 15 & -0.0237 & -0.342 & 8.93 + ngc 2903 & 17 & -0.0239 & -0.357 & 9.08 + ngc 2997 & 14 & -0.0642 & -0.741 & 9.30 + ngc 3184 & 17 & -0.0613 & -0.590 & 9.35 + ngc 5236 & 38 & -0.0413 & -0.427 & 9.29 + ngc 5457 & 25 & -0.0310 & -0.899 & 9.13 + ugc 12914 & 20 & -0.0071@xmath26 0.0033 & -0.104@xmath26 0.048 & 9.13@xmath26 0.02 + arp 256 ned01 & 13 & -0.0142@xmath26 0.0022 & -0.193@xmath26 0.031 & 8.95@xmath26 0.01 + arp 256 ned02 & 25 & -0.0162@xmath26 0.0014 & -0.271@xmath26 0.023 & 9.05@xmath26 0.01 + ugc 312 & 13 & -0.0114@xmath26 0.0070 & -0.133@xmath26 0.081 & 8.84@xmath26 0.05 + ugc 813 & 20 & -0.0210@xmath26 0.0040 & -0.233@xmath26 0.045 & 9.00@xmath26 0.02 + ugc 816 & 21 & -0.0189@xmath26 0.0023 & -0.252@xmath26 0.030 & 9.05@xmath26 0.02 + ngc 2207 & 43 & -0.0124@xmath26 0.0026 & -0.273@xmath26 0.057 & 9.08@xmath26 0.03 + ic 2163 & 19 & -0.0165@xmath26 0.0036 & -0.162@xmath26 0.035 & 9.17@xmath26 0.02 + arp 248 ned01 & 8 & -0.0368@xmath26 0.0040 & -0.512@xmath26 0.056 & 8.85@xmath26 0.02 + arp 248 ned02 & 11 & -0.0144@xmath26 0.0020 & -0.190@xmath26 0.026 & 9.03@xmath26 0.01 + ngc 3994 & 25 & -0.0224@xmath26 0.0072 & -0.139@xmath26 0.045 & 9.08@xmath26 0.02 + ngc 3995 & 41 & -0.0175@xmath26 0.0030 & -0.339@xmath26 0.059 & 8.86@xmath26 0.03 + ngc 7469 & 12 & -0.0146@xmath26 0.0089 & -0.179@xmath26 0.109 & 9.09@xmath26 0.05 + ic 5283 & 12 & -0.0249@xmath26 0.0060 & -0.246@xmath26 0.059 & 9.14@xmath26 0.01 + ugc 12545 & 14 & -0.0323@xmath26 0.0142 & -0.381@xmath26 0.168 & 8.87@xmath26 0.08 + ugc 12546 & 20 & -0.0395@xmath26 0.0082 & -0.421@xmath26 0.087 & 9.10@xmath26 0.03 +

a consensus is emerging that interacting galaxies show depressed nuclear gas metallicities compared to isolated star - forming galaxies . simulations suggest that this nuclear underabundance is caused by interaction - induced inflow of metal - poor gas , and that this inflow concurrently flattens the radial metallicity gradients in strongly interacting galaxies . we present metallicities of over 300 regions in a sample of 16 spirals that are members of strongly interacting galaxy pairs with mass ratio near unity . the deprojected radial gradients in these galaxies are about half of those in a control sample of isolated , late - type spirals . detailed comparison of the gradients with simulations show remarkable agreement in gradient distributions , the relationship between gradients and nuclear underabundances , and the shape of profile deviations from a straight line . taken together , this evidence conclusively demonstrates that strongly interacting galaxies at the present day undergo nuclear metal dilution due to gas inflow , as well as significant flattening of their gas - phase metallicity gradients , and that current simulations can robustly reproduce this behavior at a statistical level .

<s>[INST]the production and redistribution of heavy ( non - hydrogen or -helium ) elements within galaxies is an important aspect of galaxy evolution . the amount of heavy elements in the gas phase of galaxies has been a topic of study over the decades since resolved galaxy spectroscopy became commonplace . in particular , emission line spectroscopy of star - forming regions has been of great use in understanding the distribution of chemical elements in nearby , normal galaxies . for more distant galaxies , the mass - metallicity relationship , an important signpost of galaxy chemical evolution , has been used to constrain chemical evolution across a broader range of galaxy types and , increasingly , across cosmic history . intense study of the mass - metallicity ( hereafter , ) relation in recent years has yet to pin down its origin ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) . however , it is apparent from an increasing number of unique studies that part of the scatter in the relation is due to a nuclear underabundance in interacting galaxies , at both low @xcite and high masses @xcite . if one of the progenitor galaxies in an interacting system is a spiral , a radial abundance gradient exists ( e.g. , * ? ? ? * ; * ? ? ? * ) , with lower abundances at larger galactocentric radius . during the interaction , low - metallicity gas from the galaxy outskirts is torqued into the high - metallicity galaxy center @xcite , resulting in gas with a lower average abundance ( as first suggested in @xcite ) . we discussed the quantitative details of this scenario for present - day equal - mass mergers in @xcite . a prediction of this model is that this gas redistribution dramatically flattens the initial radial metallicity gradient very shortly after first pericenter @xcite . @xcite found no oxygen gradient along the tidal tails of the mice , consistent with strong radial mixing of gas . shallow or broken gradients are also present in many nearby barred galaxies , which are undergoing radial redistribution of gas due to bar - induced gas motions @xcite . barred galaxies also show lower central metallicity than galaxies of similar morphological type and luminosity @xcite , as is observed in mergers . numerical models of barred galaxies reproduce this behavior @xcite . in a companion paper @xcite , we showed that eight interacting galaxies which are underabundant with respect to the luminosity - metallicity relation all have gradients that are flatter than the nearby spirals m83 , m101 , and the milky way . this result strongly supports the model of merger - induced metal mixing . in the present paper , we expand on this result by giving a detailed analysis of the systems in @xcite , doubling the sample of interacting galaxies with measured gradients ( to 16 ) , and presenting a comprehensive comparison to isolated spirals and the numerical simulations . the interacting galaxies in this sample are all in the early stages of merging . they are after first passage of the two ( or more ) galaxies , but probably prior to second passage . a future paper will present similar data on galaxies in the later stages of merging ( rupke et al . 2010 , in prep . ) . understanding chemical evolution during a major merger will shed light on galaxy evolution at the peak of cosmic star formation , since the major merger rate , especially involving gas - rich galaxies , was higher in the past @xcite . these major mergers have likely played an important role in the production and growth of massive , red galaxies since @xmath0 ( e.g. , * ? ? ? * ; * ? ? ? simulations suggest that dry mergers ( with no gas ) flatten stellar metallicity gradients in ellipticals @xcite . it may be that wet mergers that form bulge - dominated systems may do the same , if significant star formation occurs after the gas gradient flattens . in short , the metallicity redistribution caused by gas - rich mergers may significantly impact galaxy chemical evolution . in 2 and 3 , we present the observations and our analysis . in 4 we present the metal distributions , and then compare to numerical simulations in 5 . we summarize in 6 . cosmological quantities are computed using @xmath1 , @xmath2 , and @xmath3 , and in the rest frame defined by the cosmic microwave background ( where applicable ) . our sample consists of galaxy pairs undergoing strong interactions in the local universe . the pairs are chosen from both optically - selected @xcite and infrared - selected @xcite catalogs of interacting systems . the primary selection criteria , to ensure that the systems are strongly interacting , are that the projected nuclear separation is small ( @xmath4 30 kpc ) , the galaxy mass ratios are small ( 1:1@xmath51:3 ) , and that the systems are obviously disturbed ( i.e. , after first passage ) . to distinguish from systems in later stages of merging , we have rejected systems with ( 1 ) projected pair separations @xmath615 kpc and/or ( 2 ) compact morphology and faint tidal features that indicate the system is near or after nuclear coalescence . the first criterion may remove some systems very near first or second pericenter , but also securely rules out most systems after second pericenter , since rapid orbital decay in strong , equal - mass interactions leads to small nuclear separations after second pericenter ( e.g. , * ? ? ? * and references therein ) . we have chosen spiral - spiral interactions to maximize the prevalence of regions . in each system in our sample , there is an obviously interacting pair with small projected separation , near - equal masses , and signs of interaction . however , in some cases there is also a third galaxy at large projected separations ( @xmath750 kpc ) from the dominant pair which may or may not be involved in the interaction . given their large distances , we do not further consider these possible third members of the system . basic properties of individual galaxies in our sample are listed in table [ tab : sample ] . our sample of 9 pairs / groups have fairly average properties for nearby galaxies ( figure [ fig : sample ] ) . individual galaxies are evenly distributed around @xmath8 ( @xmath9 mag ; @xcite ) , and have total infrared luminosities near @xmath10 @xcite . as mentioned above , the pair mass ratios ( as traced by @xmath11-band luminosity ) are in the 1:1@xmath51:3 range , with projected nuclear separations of @xmath12 kpc ( except for arp 248 , where the separation of the two primary galaxies is 54.3 kpc ) . table [ tab : sample ] also lists optical diameters , inclinations , and line - of - nodes position angles for the sample . many of these parameters are taken directly from hyperleda @xcite . for the ngc 2207 / ic 2163 system , we used parameters determined from numerical models @xcite . in the cases of a few galaxies , the tidal stretching of the galaxies or general interaction - induced disturbances make determining disk orientations a challenge . in this handful of cases , we have turned where possible to maps to determine the position angles . these cases are listed in the table notes . we have also used this data and inspection of visual images to double - check hyperleda inclinations . the inclinations of two galaxies remain uncertain : arp 248 ned02 and arp 256 ned02 , which are particularly tidally - stretched . in both of these cases , the effect on the gradient is compensated for somewhat by a larger measured . we estimate that the inclinations lie in the range @xmath13 , and compute the deprojection using 30@xmath14 . a control sample of isolated galaxies is a necessary component of this study . in particular , we need to compare our results to a group of galaxies that plausibly represent the galaxies in our sample as they were before a major interaction . we have selected our control sample from published data on nearby , isolated spirals that have data on region emission - line fluxes . in particular , we have focused on mid - to - late - type spirals with a mix of bar strengths @xcite , since mid - to - late types are best represented in the literature . gradients correlate with bar strength in a relationship with significant scatter @xcite , and depend weakly or not at all on spiral type @xcite . our sample should thus be representative of isolated spirals at the level allowed by small number statistics . finally , with only two exceptions , we have picked galaxies from moderate - size , homogeneous studies to minimize systematic uncertainties . ( the two exceptions , ngc 300 and m101 , are well - characterized benchmarks in gradient studies , and so we include them as well . ) the salient properties of our control sample , and the references for the sample properties , are listed in table [ tab : control ] . the interacting and control samples are well - matched in mass , as traced by @xmath11-band luminosity ( fig . [ fig : sample]@xmath15 ; the control sample is only half a magnitude fainter on average ) . they are also well - matched in optical radius , with average ( median ) optical radii of @xmath16 13 ( 12 ) kpc in both samples . however , the interacting galaxies have an average ( median ) infrared luminosity that is boosted a factor of 7 ( 4 ) above the control sample ( fig . [ fig : sample]@xmath17 ) . this is unsurprising , given the expected higher star formation rates in the interacting sample @xcite . rather than use gradient determinations published in the literature , we have used the published line fluxes to measure abundances using the same strong - line diagnostic that we apply to our interacting galaxies sample ( [ sec : spectral - analysis ] ) . we have also performed our own spatial deprojections using published photometric parameters ( see references in table [ tab : control ] ) . the resulting oxygen abundance gradients , in terms of dex / kpc and dex/ , are given in table [ tab : control ] . we used the multiobject spectroscopic capabilities of the keck low - resolution imaging spectrometer ( lris ; @xcite ) to observe regions in the galaxies of interest . the excellent blue sensitivity of lris was important for measuring the emission lines at high s / n ; the doublet is used in our strong - line metallicity diagnostics ( [ sec : data - reduct - analys ] ) . our typical setup was to observe the wavelength range @xmath18 , using the 900 l / mm grating in the red and either the 400 or the 600 l / mm grism in the blue , and the 560 nm dichroic to separate the red and blue spectra . ( for one galaxy , arp 248 , we were forced to use the 300 l / mm grism in the blue to obtain the entire spectrum , because lris - r was inoperable . ) for over half of our data , the lris atmospheric dispersion corrector ( adc ) was in place , mitigating any light loss in the blue . for the other half ( taken prior to mid-2007 ) , slit losses due to atmospheric refraction were generally small . total exposure times per mask were typically an hour . slitmasks were created in most cases using sensitive emission - line images . slits were 1 wide . the images were taken using redshifted narrowband filters at either the vatican advanced technology telescope ( vatt ; e. barton and r. jansen 2005 , private comm . ) or the university of hawaii 88-inch telescope . however , in two cases ( arp 256 and arp 298 ) , the spectroscopic data was taken in the context of a program to observe star clusters ( chien et al . 2010 , in prep . ) . in this case , star clusters were targeted using _ hubble space telescope _ ( @xmath19 ) broadband f435w images . since significant h@xmath20 emission fell in the slits in these cases , we were able to extract useful region spectra for the current work . the lris data were reduced using a pipeline we developed specifically for the current dataset . this pipeline combines image reduction and analysis facility ( iraf ) and interactive data language ( idl ) scripts . for each side of the spectrograph , the steps we took were as follows : bias subtraction ; slit identification and tracing using flatfield exposures ; arc lamp identification ; slit extraction and spatial rectification ( including any atmospheric dispersion correction , if required ) ; a small shift to match dispersion solutions among exposures ; data combination , including noise - threshold cosmic ray rejection ; wavelength calibration ; extraction of spectra ; sky subtraction ; and flux calibration . in the slit identification step , slit edges were detected using a directional filter that computed the first derivative of the flatfield in the spatial direction . we extracted each local peak in h@xmath20 using a 1@xmath211 aperture , and subtracted the sky using off - object spectra free of galaxy continuum and line emission . sky subtraction was generally imperfect due to the change of the lris point spread function across the @xmath22 field - of - view combined with the use of a small number of sky spectra that were typically on the field edges ( to avoid galaxy contamination within the on - source slits ) . blue and red spectra were reduced separately , and then combined near 5600 by multiplicatively matching the continuum fluxes in this region . following the analysis of the spectra , this relative flux calibration was further refined . spectra were mapped to positions on the sky assuming correct alignment of each slitmask during observations along with knowledge of the slit plane to focal plane mapping . ( we used at least four alignment stars per slitmask to ensure correct mask alignment . ) galactocentric radii were then computed using information on the 3-dimensional alignment of each galaxy ( [ sec : sample ] ) . to determine the center of all galaxies except ngc 3994/5 , we used near - infrared positions from 2mass . sloan digital sky survey ( sdss ) centers were used for ngc 3994/5 . though these systems are gravitationally disturbed , the near - infrared is able to probe the central bulge in each galaxy and thus yield a reasonably accurate true gravitational center . we extracted information from the resulting spectra by performing detailed fits to the stellar continuum and line emission . the software fitting package that we wrote for this purpose , uhspecfit , was based on the stellar fitting routines of @xcite , who fit stellar continua using a linear combination of several template spectra . we built on these routines a sophisticated suite of emission - line fitting software that fits all emission lines simultaneously and allows for multiple velocity components , starting with the code framework used in @xcite . to fit these relatively high - resolution data , we used the stellar population synthesis models of @xcite as our stellar continuum templates . we relied on the solar metallicity , geneva isochrone models for our fits . the quality of the fits is not a sensitive function of stellar metallicity ; since our goal was not to constrain the stellar metallicity , but rather to remove the stellar continuum , we used only the solar metallicity models . the stellar fits were performed on the blue half of the spectra ( from @xmath23 in the rest frame ) after removal of wavelength regions near strong emission lines ; the resulting stellar fit was then normalized to fit the red half of the spectra . we subtracted the stellar continuum from the spectra and performed emission - line fits . two example fits are shown in figure [ fig : example_fit ] . one is a high emission line flux case , and the other is a low emission line flux case ( roughly 1@xmath24 , in flux , of the high flux case ) . these are illustrative of the typical high fidelity of the fits , and reveal that fits to the balmer absorption lines in particular are very good . once the fits were complete , a final blue - red relative flux calibration was performed by comparing the measured reddening from the / emission line ratio ( using the extinction law of @xcite ) with that measured from the / ratio . the discrepancy was used to correct the blue emission - line fluxes . this method worked very well for our data ( which showed high signal - to - noise in ) and our choice of spectral fitting ( which permitted robust separation of balmer absorption and emission ) . however , our abundance errors increase with the use of / to determine the reddening ( as opposed to / ) . we corrected the emission line fluxes for reddening @xcite and computed important line ratios . spectra with very uncertain reddening because of poorly - fit or weak and emission lines were ignored . the dereddened line ratios were then used to classify each spectrum as -region , composite , seyfert , or liner @xcite . we calculated abundances only for those regions which are securely of -region origin , without probable contamination from other sources of excitation . we included only those data identified as -region spectra based on the /vs . / diagnostic ( i.e. , regions that fall below the @xcite star formation locus ) and or composite spectra based on the / vs. / diagnostic ( i.e. , regions that fall below the @xcite extreme starburst line ) . for both line ratio cuts , we included data up to 0.1 dex to the right of the diagnostic line to account for possible uncertainties . roughly 25% of our spectra were rejected because of poorly - fit emission , line ratio cuts , or inadequate line fits . spectra rejected due to line ratio cuts are shown as black crosses atop the galaxy images in figure [ fig : results ] . our final sample of regions in early - stage interacting galaxies consists of 332 spectra . these are accompanied by 281 region spectra from the control sample . four nuclei in our sample show either seyfert ( ngc 2207 , ic 2163 , ngc 7469 ) or liner ( ngc 3994 ) spectra based on our data . however , these nuclear ionizing sources have minimal impact on the extra - nuclear regions that are used to compute abundances ; phenomena like ionization cones would in any case be detected and rejected using our line ratio cuts . in this paper , we quote abundances calculated from the /abundance diagnostic ( * ? ? ? * hereafter kd02 ) . of the strong - line diagnostics , this one produces the least root - mean - square ( rms ) dispersion about the mean due to its relative insensitivity to ionization parameter ( kd02 ) . to study possible systematic errors from the use of this diagnostic ( due to , e.g. , improper extinction corrections or improper relative flux calibration of the blue and red lris arms ) , we computed abundances using the ( * ? ? ? * hereafter kk04 ) and ( * ? ? ? * hereafter pp04 ) ( /)/(/ ) diagnostics ( following the guidelines laid out by @xcite ) and then converted these diagnostics into the kd02 calibration using the formulas of @xcite . the results are shown for all of the regions in this paper in figure [ fig : abundcomp ] , and for individual systems in figure [ fig : results ] . it is clear from examining figure [ fig : abundcomp ] that , overall , there are no significant systematic discrepancies introduced by our data reduction and analysis that make our / line ratios suspect . for instance , both kk04 and pp04 are less sensitive to extinction than kd02 , and inaccurate extinction corrections should show up as deviations from equality in these figures . the interacting galaxies sample does in fact show a 0.05 dex offset from equality in the kd02 vs. pp04 diagram . however , the pp04 diagnostic does not correct for ionization parameter variations , which introduces a systematic uncertainty in this diagnostic ; the kd02 diagnostic is insensitive to ionization parameter . furthermore , the offset is well within the expected uncertainties of the diagnostic and conversion formulas , and as a simple offset , will have no impact on relative abundances like gradients . in fact , the rms dispersion about the line of equality in the interacting galaxies sample ( 0.05 dex ) is significantly lower than that in the control sample for the kd02 vs. kk04 diagram , suggesting that our data is highly uniform . in the kd02 vs. pp04 diagram , the rms dispersions are the same for the two samples , but for the interacting sample this is in large part due to the systematic offset to one side of equality . errors in the emission - line fluxes were computed by assigning the error in the peak flux to equal the rms residual within 2@xmath25 of each line center , after subtracting the continuum and line fits from the data . errors were propagated primarily using analytic expressions , but for abundance and gradient errors we employed monte carlo methods . in the following section , we use the calculated abundances and radii for the regions in each galaxy to compute radial abundance gradients , and compare the gradients of the control and interacting samples . with abundances and deprojected radii in hand , we computed radial oxygen gradients for each galaxy in our sample . in two cases ( ic 5283 and ugc 12915 ) , the radial coverage and number of regions available were each too small to yield a reliable estimate of the gradient . in the control sample , we limited the gradient fits to within 1.5 , to match the radii fit in the interacting galaxy sample . we wished to avoid biasing the gradient fit toward particular locations in the galaxy ( e.g. , to high - luminosity regions ) , so we performed unweighted least - squares fits . our fits were computed with radius as the independent variable , and errors in slope and intercept were estimated using monte carlo methods . the resulting gradients and intercepts are given in table [ tab : gradients ] . in figure [ fig : results ] , we present for each system the results of our emission - line analysis : emission line diagnostic diagrams , comparison of different metallicity diagnostics , a two - dimensional projected oxygen abundance map , and a one - dimensional deprojected radial oxygen abundance profile . the measured gradients in these interacting systems are on average significantly flatter than those in the control sample ( figure [ fig : hist - grads ] ) . the control sample exhibits median slopes of [email protected] dex / kpc and [email protected] dex/ , while the interacting systems have median slopes of [email protected] dex / kpc and [email protected] dex/ ( where the errors given are the standard error ) . in short , the interacting systems have gradients that are , on average , less than half as steep as isolated galaxies . in @xcite , we showed that gradients in eight of the systems presented here were shallower than gradients in m83 , m101 , and the milky way . the present data quantify this difference at a high confidence level using large control and interacting samples . taken by themselves , these differences in gradients are a strong confirmation of the model of merger - induced gas inflow leading to metal mixing . surprisingly , the dispersions in the interacting sample gradient distributions are also less than the dispersions in the control sample : the control sample shows standard deviations of 0.03 dex / kpc and 0.17 dex/ , compared to 0.01 dex / kpc and 0.11 dex/. the explanation for the latter effect is unclear , but could result from the origin of the region data in heterogeneous and homogeneous datasets , respectively . no significant correlations are seen between gradients and galaxy near infrared and total infrared luminosities , either in the interacting sample or the control sample ( figure [ fig : grads - vs - gal ] ) . previous work has shown that correlations may exist between optical luminosities and gradients in dex / kpc @xcite ; however , such a trend apparently does not persist in interacting systems ( and is not obvious in our control sample ) . one might expect a correlation of infrared luminosity with gradient in interacting systems , if is assumed to trace star formation rate and star formation is driven by gas inflow . again , no such trend is evident , though we only have upper limits in for much of our sample . no obvious trends are seen when comparing gradients to system properties that may parameterize the stage or strength of the interaction : projected nuclear separation , near - infrared luminosity ratio , or total system infrared luminosity ( figure [ fig : grads - vs - sys ] ) . projected nuclear separation is of course only approximate , since we can not deproject the two galaxies without detailed modeling , and there is a degeneracy in the age of the interaction between galaxies moving apart after first pericenter and returning to second pericenter . furthermore , mass ratios in our sample ( as traced by @xmath11-band luminosity ratio ) are all close to unity , and one might expect little variation among the systems in our sample based on this parameter alone . finally , confusing the matter , simulations also show that although both galaxies in a strongly interacting pair experience a flattening of the gradient very quickly after first pericenter , the relative degree of flattening of the two disks varies depending on the geometry and the distance of first pericenter @xcite . this effect would introduce scatter into any underlying correlation between gradients and system properties . [ sec : gradients - vs .- merger ] for further discussion . some systematic uncertainty arises in our abundance gradients due to our choice of abundance calibration / diagnostic . some calibrations ( including both strong- and weak - line ones ) may yield shallower slopes than we calculate ( e.g. , * ? ? ? * ; * ? ? ? however , @xcite showed that an -based diagnostic yields the same results as the kd02 diagnostic we employ in this paper . more importantly , we rely on the fact that within a particular abundance calibration / diagnostic , _ relative _ abundances are reliably computed and internally consistent @xcite . when using detailed chemodynamical models to constrain parameters of individual systems , measuring the absolute value of the gradient precisely may be important . within the context of the current study , we are concerned only with gradient changes relative to initial conditions . we also emphasize that , were the initial galaxy gradients too shallow ( or completely flat ) , the metal dilution clearly observed in interacting systems would be impossible , and would thus be inconsistent with empirical evidence . nevertheless , as a check on the reliability of our / gradients , figure [ fig : results ] shows , for each system , how the /abundances compare with those computed in the kk04 and pp04 diagnostics ( see [ sec : spectral - analysis ] for more details ) . as is seen in the full sample ( fig . [ fig : abundcomp ] ) , individual systems are largely free of systematic discrepancies . the two exceptions are ngc 2207/ic 2163 and arp 248 , which show discrepancies between the kd02- and pp04-computed metallicities . these anomalies may result from variations in ionization parameter that remain uncorrected in the pp04 diagnostic ( [ sec : spectral - analysis ] ) or reddening uncertainties . further analysis shows that , if we were to use the pp04 abundances ( after being converted into the kd02 system ) , we would measure shallower gradients in arp 248 ned01 and arp 248 ned02 and a steeper gradient in ngc 2207 ( but not ic 2163 ) , in each case by a factor of @xmath272 . with the common exception of the galaxy nuclei , the vast majority of data in our sample are pure regions . ugc 12914/12915 has a significant number of regions indicative of non - photoionized emission . in fact , the north half of ugc 12914 has a significant number of regions with multiple velocity components and shock - like line ratios @xcite . this region overlaps a bridge of gas between the galaxies @xcite . numerical simulations are a powerful tool for investigating the evolution of galaxy mergers . however , most simulations of mergers to date have paid little attention to gas - phase metallicity and its evolution . recently , @xcite discussed metallicity evolution prior to second pericenter in smoothed particle hydrodynamic ( sph ) / n - body simulations of equal - mass mergers with gas mass fractions of 10% ( to match nearby galaxies ) . though they did not include enrichment from ongoing star formation , @xcite reached good agreement with the magnitude of deviations of major mergers from the mass - metallicity relation . they also showed that radial abundance gradients should flatten rapidly after first pericenter , and predict the relationship between gradient flattening and nuclear abundance and the detailed shape of the gradient with time . @xcite presented simulations including star formation that largely agreed with @xcite , but did not address the evolution of gradients . torrey et al . ( 2010 , in prep . ) find similar results to @xcite , but show that preferential consumption of high - metallicity gas by star formation in galaxy nuclei plays a role alongside metal dilution due to inflow . in the following sections , we compare our data on metallicity distributions in interacting galaxies to the simulations of @xcite . these sph / n - body simulations are described in detail in @xcite . in brief , 24576 gas particles were distributed in an exponential disk of scale height equal to 6% of the disk scale length . the stars occupied a bulge and identical disk , with a bulge - to - disk ratio of @xmath28 . eight close - passage mergers were simulated , with all combinations of direct and retrograde considered . the metallicity per gas particle was unchanged during the simulation , and two different initial metallicity gradients were considered ( -0.2 dex/@xmath29 and -0.4 dex/@xmath30 ) . in this work we modified the initial gradients slightly to match our control sample : -0.15 dex/@xmath30 . this number results from the typical gradient in dex / for the control sample ( [ sec : oxygen - gradients ] ) , when converted to dex/@xmath30 using a typical ratio for /@xmath30 ( [ sec : grad - lumin - metall ] ) . our galaxy sample was chosen to represent major mergers somewhere between first and second pericenter . the distribution of observed gradients is shown in figure [ fig : hist - grads ] . for comparison , we construct a predicted gradient distribution from our set of simulated major mergers , assuming that our sample is randomly distributed between first and second pericenter . we also assumed that the simulated galaxies start with a single gradient equal to the mean value in the control sample . the observed and simulated distribution show remarkable agreement ( figure [ fig : hist - grads - sims ] ) . we show in figure [ fig : grads - vs - sys ] that , for the present sample , there is no strong dependence of gradient on merger stage , as parameterized by projected nuclear separation . this is consistent with the predictions of our simulations . figure [ fig : grads - vs - nsep - sims ] reveals that , between first and second pericenter , there is no predicted dependence of the gradients on actual nuclear separation , for the ensemble of simulations as a whole . within particular mergers , a more recognizable dependence of gradient on nuclear separation may emerge , but we must consider our present dataset as random snapshots of an ensemble of different mergers . we do not at present have an accurate understanding of the initial conditions of most or all of the systems in our sample . the motivation for the present work was the observation that interacting galaxies fall below the luminosity - metallicity ( ) and mass - metallicity ( ) relations of star - forming galaxies . do the current data present a consistent picture in this regard , such that the nuclear metallicities of interacting systems with shallow gradients also fall below these relationships ? for a subset of the current sample , we used the @xmath31-band relation in @xcite and found no correlation between gradients and offsets , but were limited by small sample size and the fact that @xmath31-band luminosity is sensitive to ongoing star formation and extinction effects . in this paper , we compare the control and interacting samples to the luminosity - metallicity relation as measured in the near - infrared @xcite , and use simulations to interpret the result . multicolor broadband photometry is not available for our entire sample , so we are unable to measure accurate masses and apply the relation . near - infrared photometry , however , is less sensitive to extinction or contamination from star formation than the optical ; it is also a reasonable tracer of stellar mass within a factor of @xmath272 @xcite . the @xcite abundances are available in several diagnostics . none of these are the / diagnostic that we employ , so we resort to the abundance conversion formulas of @xcite . we start with the -computed abundances from @xcite ; the diagnostic they use is a functional fit of to abundances from modeling of sdss spectra @xcite . we then apply the formula from @xcite . because two transformations are involved , we consider these abundances to be only approximate , and are useful primarily for establishing the slope of the relation . we do not have nuclear abundances measured from long - slit spectra for all of the galaxies in the current sample . we thus estimate abundances by extrapolating our gradient fits , and compute the abundances at a discrete radius of @xmath32 . this roughly matches the extent of the long - slit apertures of the @xcite data , which have @xmath33 . using this method , neither the control nor interacting samples fall on the @xmath11-band relation . this is presumably due to one of two effects : ( 1 ) the @xcite abundances are luminosity - weighted measurements from nuclear spectra , while ours are measured at a fiducial radius using fits to region data ; and/or ( 2 ) the uncertainties introduced by the two transformations involved in computing the abundances of the @xcite sample . the latter effect is not unusual when converting among different metallicity calibrations @xcite . to account for this effect , we apply a constant offset of @xmath50.3 dex to both the control sample and interacting sample metallicities . this offset minimizes the rms deviation of the control sample from the relation . the exact vertical normalization of the data is irrelevant , however ; the important quantities are the _ relative _ nuclear abundances of the control and interacting samples at a given luminosity , which are secure since we use the same abundance diagnostic and compute the nuclear abundances in the same way . the @xcite data simply provide a more accurate slope for the relation than the control sample by itself . the result of this exercise is displayed in figure [ fig : lz-0p1 ] . this figure makes evident that the early - stage interacting galaxies , which have shallower gradients than the control sample , also fall below the relation defined by the control sample and emission line galaxy sample . in fact , the interacting galaxies form a remarkably coherent relationship that is simply offset from that of isolated star - formers by @xmath50.2 dex in abundance . to tie together abundance offsets and gradients , we compare directly to the simulations of @xcite . these simulations predicted that the gradient slope would change quickly after first pericenter , while the nuclear metallicity would change more slowly between first and second pericenter . the simulations yield gradients in units of exponential disk scale length of the gas disk ( dex / r@xmath34 ) , while we express observed gradients in physical units ( dex / kpc ) and optical ( stellar ) isophotal radius ( dex/ ) . for our control sample , we have stellar disk scale lengths as well as optical radii , and the two are related according to @xmath35r@xmath34 , where the uncertainty given is the standard deviation . using this scaling , we compute the gradients in dex / r@xmath34 for our interacting galaxy sample . for the current data set , we measured abundances at a fiducial radius of 0.1 . to match this procedure for the simulations , we computed average abundances within a narrow , 0.1r@xmath34-wide radial bin centered on 0.35r@xmath34 . ( this differs from the method in @xcite , in which we averaged over the entire central disk within 0.5r@xmath34 . ) for the data , we assume that the interacting galaxies started on the relation of the control sample and have had their central metallicity lowered during the merger . it is clear that , given the uncertainties inherent in this procedure ( e.g. , the galaxies did nt necessarily start on the mean relation ) and the simplicity of the simulations ( which do not include ongoing star formation ) , there is remarkable agreement between the data and simulations ( figures [ fig : dz - vs - grad ] and [ fig : dz - vs - grad - lab ] ) . a total of @xmath36 of the interacting galaxies fall directly in the phase space delineated by the simulated evolutionary tracks . furthermore , the region of overlap with the simulations is near the time of first turnaround ( between first and second pericenter ) for many of the simulated pairs , which is consistent with the galaxies in our sample being somewhere between first and second pericenter on average . ( in a random distribution of post - pericenter pairs selected by nuclear separation , half should be pre - turnaround , and half post - turnaround . ) the data are thus quantitatively consistent with the prediction of the simulations of @xcite that the gradient should flatten quickly after first pericenter , and that the nuclear abundance should decrease at a slower rate between first and second pericenter . the scatter of plausible initial conditions , as represented by the control sample , do caution against drawing detailed conclusions from this comparison of data and simulations . in particular , a variety of initial conditions can explain the current position of the interacting galaxies in the metallicity - gradient phase space . the metallicity scatter in the control sample is partly a measurement issue ; e.g. , the scatter in the simulated control relation is larger than in the @xcite sample , and the control sample regions show a larger rms dispersion in abundance than the interacting sample ( fig . [ fig : hist - rms ] ) . to deal with this metallicity scatter , whatever its origin , however , we simply shift the simulations left or right in figure [ fig : dz - vs - grad ] to start at the control sample initial conditions . a shift in offset could in principle resolve any discrepancies between data and simulations for individual galaxies . for example , ngc 2207 is clearly not at a late merger stage , as suggested by its position with respect to the merger models ( it is probably just after first passage ; @xcite ) . however , it could initially have had lower metallicity than predicted by the mean relation and/or a steeper initial gradient , leading to a more favorable comparison with models in figure [ fig : dz - vs - grad ] . if a galaxy were to start with a larger gradient than is assumed in the models , then the changes in gradient and central metallicity are larger @xcite . for instance , if we assume the initial conditions represented by ngc 300 or ngc 2997 , the simulations still overlap the data , due to the more extreme changes that result from a steeper gradient and the same amount of infall ( figure [ fig : dz - vs - grad - steep ] ) . closer inspection rules out this scenario for most systems , however , since ( a ) the overlap of the data and the bulk of the simulations is not as good and ( b ) these initial conditions would require almost all of the observed interacting systems to lie near second pericenter . this is unlikely , due to how we have selected our sample ( [ sec : sample ] ) . the simulation - to - data comparison shown in figure [ fig : dz - vs - grad ] , with half the initial gradient of that in ngc 300 or ngc 2997 , is therefore a more likely scenario for most systems . following standard practice , we have characterized radial metallicity profiles using straight line fits [ i.e. , 12@xmath37log(o / h ) @xmath16 a @xmath37 br ] . however , the predicted metallicity profiles from the simulations of @xcite do show distinctive shapes that are not purely straight lines at all times . individual galaxies in our sample do not have enough data points to accurately characterize the profile shapes beyond straight lines . however , we can compute the average deviation from straightness as a function of radius by subtracting the gradients and binning the data in radius . we do this for both the control and interacting samples , and show the results in figure [ fig : profile ] . these two samples show metallicity profile residuals that are significantly different . the control sample is largely consistent with a straight line . however , the interacting sample shows a clear `` concave up '' shape , in the sense that positive deviations are seen at small and large radius , with negative deviations at middle radii . how does this compare with simulations ? to bin the simulation data , we consider the ensemble of profiles at first and second pericenter and first turnaround . the result , with the interacting galaxies data overplotted , is shown in figure [ fig : profile ] . it is apparent that for the simulations , there is a small upturn at low radius at all times , consistent with the data . though there is not exact quantitative agreement in any of the three stages , the simulations at first turnaround show the same `` concave up '' shape seen in the data . by contrast , the simulations at 1st and 2nd pericenter show a flatter profile outside the nuclear regions . as discussed above , this is consistent with the idea that , on average , our sample is near first turnaround , and otherwise evenly distributed between first and second pericenter . given the complexity and variety of the actual merging systems in this study , it is impressive that there remains such good agreement at this level of comparison between data and simulations , and speaks to the robustness of the dilution model and its predictions . it also suggests that metals produced in star formation initiated by the merger have only a small effect on the gas - phase metallicity distributions prior to second pericenter . this could occur either because most star formation occurs after second pericenter or because of inefficient mixing of the metal - enriched hot phase with the cooler ism . in fact , only a limited fraction of the gas in interacting galaxies can be consumed in star formation prior to merging , in order to leave a significant gas reservoir at late stages @xcite . we have presented here data on the gas - phase oxygen abundance gradients in 9 pairs / groups ( 18 galaxies ) in the early stages of an interaction ( after first pericenter , prior to second ) . we computed radial gradients based on region spectroscopy and the most precise strong - line abundance diagnostic available ( kd02 ) . we find a clear break between the gradient distributions of isolated and interacting systems : interacting systems consistently have gradients about half that in normal , isolated spirals . we compare the data to the simulations of @xcite , and find remarkable statistical agreement at the ensemble level . the simulations accurately reproduce ( 1 ) the gradient distribution , ( 2 ) the lack of gradient dependence on projected nuclear separation , ( 3 ) the relationship between gradients and deviations from the luminosity - metallicity relation , and ( 4 ) metallicity profile deviations from a straight line . these data are clear evidence that models of metal redistribution due to interaction - induced gas inflow @xcite are able to account for the low nuclear abundances observed in interacting galaxies @xcite . now that this mechanism is firmly established , future work should be devoted to understanding how this affects the global evolution of the mass - metallicity relation over cosmic times and the formation of elliptical galaxies . in particular , if mergers or post - mergers dominate samples of galaxies used to determine the @xmath38 relation at high redshift , this bias must be taken into account . furthermore , all massive galaxies have experienced mergers during their lifetime . the re - distribution of metals due to gas inflow will then affect the stellar populations formed at later times at all radii . though we have already found remarkable agreement between the data and simulations at a statistical level , this comparison could be improved upon using simulations that incorporate realistic models of star formation and chemical enrichment ( including a sophisticated model of starburst - driven galactic winds ) . secondly , we have compared to simulations only after binning the data azimuthally ; more detailed comparison of theory to actual projected metallicity distributions would provide a stronger understanding of how and where the dilution occurs . furthermore , we have only looked for agreement at a statistical level . though the current data already provide broad constraints on the simulations , more detailed constraints will require careful modeling of individual systems . the limited merger ages traced by this early - stage sample constrain our ability to trace metal redistribution over the entire course of a merger . in future work ( rupke et al . 2010 , in prep . ) , we will present data on later stage mergers to accomplish this . the authors thank jabran zahid for sharing the software that formed the basis of uhspecfit ; fabio bresolin for data analysis tips , a galaxy deprojection algorithm , and commenting on the manuscript ; margaret geller for commenting on the manuscript ; betsy barton and rolf jansen for providing their h@xmath20 images ; josh barnes for helpful discussion ; and the referee for useful comments regarding content and presentation . the data presented herein were obtained at the w.m . keck observatory , which is operated as a scientific partnership among the california institute of technology , the university of california and the national aeronautics and space administration . the observatory was made possible by the generous financial support of the w.m . keck foundation . the authors also recognize the very significant cultural and spiritual role that the summit of mauna kea has within the indigenous hawaiian community . we are most fortunate to have the opportunity to observe the universe from this mountain . , j. e. 1998 , in saas - fee advanced course 26 : galaxies : interactions and induced star formation , ed . r. c. kennicutt jr . , f. schweizer , j. e. barnes , d. friedli , l. martinet , & d. pfenniger , 275 , http://adsabs.harvard.edu/abs/1998giis.conf..275b[ads ] ugc 12914 & vv254 & 4371 & & -24.23 & 10.36 & 14.69 & 54 & 160 & 2,3,4 + ugc 12915 & vv254 & 4336 & 17.40 & -23.70 & 10.76 & 11.11 & 73 & 135 & 2,3,4 + arp 256 ned02 & arp 256 & 8193 & & -23.11 & & 16.58 & 0@xmath545 & 70 & 1,3,4 + arp 256 ned01 & arp 256 & 8125 & 28.20 & -23.80 & 11.35 & 13.66 & 61 & 80 & 1,3,4 + ugc 312 & hcg 2 & 4364 & & -21.56 & 9.93 & 11.67 & 79 & 8 & 2 + mrk 552 & hcg 2 & 4349 & 21.10 & -22.33 & 10.38 & & & & 2 + ugc 314 & hcg 2 & 4271 & 65.40 & -20.52 & & & & & + ugc 813 & wbl 036 & 5344 & & -22.89 & 10.68 & 11.16 & 72 & 110 & 2 + ugc 816 & wbl 036 & 5188 & 16.50 & -23.01 & 10.68 & 13.33 & 62 & 190 & 2 + cgcg 551 - 011 & wbl 036 & 5373 & 42.60 & -23.27 & & & & & 2 + ngc 2207 & ngc 2207/ic 2163 & 2741 & & -24.54 & 11.00 & 22.11 & 35 & 140 & 3,4 + ic 2163 & ngc 2207/ic 2163 & 2765 & 15.80 & -24.18 & & 9.80 & 35 & 128 & 3,4 + arp 248 ned01 & arp 248 & 5167 & & -22.39 & 10.66 & 13.90 & 66 & 43 & 1 + arp 248 ned02 & arp 248 & 5167 & 54.60 & -23.32 & 10.66 & 13.27 & 0@xmath545 & 109 & 1 + arp 248 ned03 & arp 248 & 5276 & 93.10 & -20.82 & & & & & 1 + ngc 3994 & arp 313 & 3086 & & -23.56 & 10.55 & 6.18 & 58 & 10 & 1,2,3,4 + ngc 3995 & arp 313 & 3254 & 24.70 & -22.64 & 10.42 & 19.40 & 69 & 45 & 1,2,3,4 + ngc 3991 & arp 313 & 3192 & 50.10 & -22.51 & 10.26 & & & & 4 + ngc 7469 & arp 298 & 4892 & & -24.23 & 11.46 & 12.22 & 30 & 127 & 1,3,4 + ic 5283 & arp 298 & 4804 & 23.30 & -23.36 & & 9.90 & 60 & 105 & 1,3,4 + ugc 12545 & wbl 713 & 5754 & & -21.41 & 10.28 & 11.81 & 63 & 85 & 2 + ugc 12546 & wbl 713 & 6055 & 21.90 & -22.69 & 10.28 & 10.64 & 63 & 20 & 2 + ngc 300 & sad & 2.08 & a & -19.43 & 8.43 & 5.90 & 2.26 & b & 40 & 114 & aa & 1 + ngc 628 ( m74 ) & sac & 8.59 & b & -22.48 & 9.82 & 13.08 & 3.57 & a & 7 & 25 & cc & 6,7 + ngc 925 & sabd & 7.38 & e & -20.75 & 9.21 & 12.04 & 2.60 & d & 61 & 107 & aa & 7 + ngc 1232 & sabc & 14.50 & d & -23.08 & 9.91 & 14.59 & 4.51 & c & 33 & 270 & aa , ee & 3,7 + ngc 2403 & sabcd & 3.16 & a & -21.05 & 9.19 & 9.17 & 1.72 & c & 60 & 127 & aa & 4,7 + ngc 2805 & sabd & 28.00 & c & -21.44 & 9.68 & 14.42 & 8.96 & e & 36 & 290 & aa , bb & 7 + ngc 2903 & sabbc & 8.55 & e & -23.56 & 10.22 & 14.95 & 3.09 & e & 56 & 23 & aa & 3,7 + ngc 2997 & sabc & 7.08 & e & -22.61 & 9.82 & 11.55 & 4.84 & f & 41 & 110 & aa & 3 + ngc 3184 & sabcd & 8.70 & c & -22.09 & 9.48 & 9.60 & 2.59 & g & 24 & 135 & aa & 7 + ngc 5236 ( m83 ) & sabc & 4.92 & a & -23.66 & 10.37 & 10.34 & 2.89 & f & 27 & 45 & aa & 2,3 + ngc 5457 ( m101 ) & sabcd & 6.96 & a & -23.26 & 10.23 & 29.19 & 5.19 & e & 37 & 18 & dd & 5 + ngc 300 & 27 & -0.1246 & -0.664 & 8.95 + ngc 628 & 25 & -0.0410 & -0.536 & 9.10 + ngc 925 & 44 & -0.0471 & -0.568 & 8.83 + ngc 1232 & 22 & -0.0310 & -0.451 & 9.10 + ngc 2403 & 25 & -0.0750 & -0.689 & 8.93 + ngc 2805 & 15 & -0.0237 & -0.342 & 8.93 + ngc 2903 & 17 & -0.0239 & -0.357 & 9.08 + ngc 2997 & 14 & -0.0642 & -0.741 & 9.30 + ngc 3184 & 17 & -0.0613 & -0.590 & 9.35 + ngc 5236 & 38 & -0.0413 & -0.427 & 9.29 + ngc 5457 & 25 & -0.0310 & -0.899 & 9.13 + ugc 12914 & 20 & -0.0071@xmath26 0.0033 & -0.104@xmath26 0.048 & 9.13@xmath26 0.02 + arp 256 ned01 & 13 & -0.0142@xmath26 0.0022 & -0.193@xmath26 0.031 & 8.95@xmath26 0.01 + arp 256 ned02 & 25 & -0.0162@xmath26 0.0014 & -0.271@xmath26 0.023 & 9.05@xmath26 0.01 + ugc 312 & 13 & -0.0114@xmath26 0.0070 & -0.133@xmath26 0.081 & 8.84@xmath26 0.05 + ugc 813 & 20 & -0.0210@xmath26 0.0040 & -0.233@xmath26 0.045 & 9.00@xmath26 0.02 + ugc 816 & 21 & -0.0189@xmath26 0.0023 & -0.252@xmath26 0.030 & 9.05@xmath26 0.02 + ngc 2207 & 43 & -0.0124@xmath26 0.0026 & -0.273@xmath26 0.057 & 9.08@xmath26 0.03 + ic 2163 & 19 & -0.0165@xmath26 0.0036 & -0.162@xmath26 0.035 & 9.17@xmath26 0.02 + arp 248 ned01 & 8 & -0.0368@xmath26 0.0040 & -0.512@xmath26 0.056 & 8.85@xmath26 0.02 + arp 248 ned02 & 11 & -0.0144@xmath26 0.0020 & -0.190@xmath26 0.026 & 9.03@xmath26 0.01 + ngc 3994 & 25 & -0.0224@xmath26 0.0072 & -0.139@xmath26 0.045 & 9.08@xmath26 0.02 + ngc 3995 & 41 & -0.0175@xmath26 0.0030 & -0.339@xmath26 0.059 & 8.86@xmath26 0.03 + ngc 7469 & 12 & -0.0146@xmath26 0.0089 & -0.179@xmath26 0.109 & 9.09@xmath26 0.05 + ic 5283 & 12 & -0.0249@xmath26 0.0060 & -0.246@xmath26 0.059 & 9.14@xmath26 0.01 + ugc 12545 & 14 & -0.0323@xmath26 0.0142 & -0.381@xmath26 0.168 & 8.87@xmath26 0.08 + ugc 12546 & 20 & -0.0395@xmath26 0.0082 & -0.421@xmath26 0.087 & 9.10@xmath26 0.03 +[/INST] a consensus is emerging that interacting galaxies show depressed nuclear gas metallicities compared to isolated star - forming galaxies . simulations suggest that this nuclear underabundance is caused by interaction - induced inflow of metal - poor gas , and that this inflow concurrently flattens the radial metallicity gradients in strongly interacting galaxies . we present metallicities of over 300 regions in a sample of 16 spirals that are members of strongly interacting galaxy pairs with mass ratio near unity . the deprojected radial gradients in these galaxies are about half of those in a control sample of isolated , late - type spirals . detailed comparison of the gradients with simulations show remarkable agreement in gradient distributions , the relationship between gradients and nuclear underabundances , and the shape of profile deviations from a straight line . taken together , this evidence conclusively demonstrates that strongly interacting galaxies at the present day undergo nuclear metal dilution due to gas inflow , as well as significant flattening of their gas - phase metallicity gradients , and that current simulations can robustly reproduce this behavior at a statistical level . </s>

between january 2006 and december 2009 , a total of 50 consecutive patients fulfilling the inclusion criteria were included in a randomized controlled trial ( fig . 1 ) . fully edentulous patients , referred to the department of oral and maxillofacial surgery ( university medical center groningen , the netherlands ) , suffering from lack of retention and stability of the upper denture and lower denture , were considered for inclusion if they fulfilled the following criteria : flow diagram of the study . at least 18 years of age;capable of understanding and giving informed consent;at least 1 year edentulous in the maxilla and mandible;bone dimensions in the region between the bicuspids in the anterior area of the maxilla had to be at least 12 mm in height and at least 5 mm in width to reach initial stability of the implant;sufficient interocclusal space for a barsupported attachment system in this region . at least 18 years of age ; capable of understanding and giving informed consent ; at least 1 year edentulous in the maxilla and mandible ; bone dimensions in the region between the bicuspids in the anterior area of the maxilla had to be at least 12 mm in height and at least 5 mm in width to reach initial stability of the implant ; sufficient interocclusal space for a barsupported attachment system in this region . excluded were patients with american society of anesthesiologists score ( asa score ) iii ( smeets et al . 1998 ) , who were smoking , with a history of radiotherapy in the head and neck region or a history of preprosthetic surgery or previous implant placement . the patients were informed about the study on overdenture treatment with insertion of four or six dental implants in the maxilla and about the extra efforts associated with the study ( questionnaires , evaluation visits ) before they signed an informed consent . the study was approved by the medical ethical committee of the university medical center groningen ( abr nl32503.042.11 ) . rotational panoramic radiographs , lateral cephalograms and posteroanterior oblique radiographs were taken to assess the volume of the maxillary alveolar bone , the dimensions of the maxillary sinus and the anteroposterior relationship of the maxilla to the mandible . in addition , to assess the bone volume of the maxillary processus , a ridgemapping procedure was performed as described by ten bruggenkate et al . a diagnostic setup of the planned overdenture was made to obtain insight into the available dimensions for the barsupported attachment system and overdenture . the treatment and evaluation procedures have been described in detail with the reporting of 1year results of the study by slot et al . four or six dental implants with a length of at least 11 mm and a diameter of 4 mm were inserted in the maxillary anterior region ( osseospeed 4.0 s dental implants , astra tech ab , mlndal , sweden ) . the implants were placed at crestal bone level in predefined positions ( positions 15 , 13 , 11 , 21 , 23 , 25 in the six implants group and positions 13 , 11 , 21 , 23 in the four implants group ) with the help of a surgical template following a submerged healing protocol . in some cases , the most distal implant position may be 16 or 26 ( in the six implants group ) , but it is always without a large sinus floor elevation . small dehiscences or fenestrations were covered with bone harvested from the maxillary tuberosity and organic bovine bone ( biooss ; geistlich pharma ag , wolhusen , switzerland ) and subsequently covered with a resorbable membrane ( biogide ; geistlich pharma ag , wolhusen , switzerland ) . if the most distally placed implants ( usually in the six implants group ) were partially placed in the anterior part of the maxillary sinus , a small sinus floor elevation surgery was performed in that region to prevent a perforation of the sinus membrane by the implant . after a 3month osseointegration period , secondstage surgery was performed and healing abutments ( uni healing abutments , astra tech ab ) were placed . after the secondstage surgery , prosthetic procedures were initiated . healing abutments were replaced by 20 uni abutments ( astra tech ab ) and with impression copings and polyether material ( impregum f ; 3 m espe , st . paul , minn ) , a complete arch impression was made . a composite resin record base ( lightplast base plates ; dreve dentamid gmbh , unna , germany ) with a wax occlusion rim was used to determine the occlusal vertical dimension and to record the maxillomandibular relationship . acrylic resin artificial teeth ( ivoclar sr orthotyp dcl and ivoclar vivodent pe , ivoclar vivadent ag , schaan , liechtenstein ) were selected and arranged on the record base for a trial arrangement . the final superstructure consisted of a milled titanium eggshaped bar with distal extensions , screwretained to abutments , and an overdenture with builtin cobalt chromium reinforcement structure and gold retentive clips attached to it ( slot et al . the design of the overdentures was with full coverage of the alveolar process , but with limited palatal coverage . the patient was instructed in hygiene procedures associated with the dentures and the bars ( fig . 2 ) . fiveyear panoramic radiograph of a patient with four implants connected with a bar in the maxillary anterior region . secondary outcome measures were implant survival , overdenture survival and soft tissue conditions ( plaque index , presence of calculus , gingiva index , sulcus bleeding index and pocket probing depth ) . these parameters were scored at placement of the overdenture , and 1 year and 5 years after loading . patients ' satisfaction was also scored before treatment , and 1 year and 5 years after loading . thereafter , the patients were followed up for routine checkup visits at 2 , 3 and 4 years . if plaque and/or calculus were present at an evaluation period , cleaning was performed with additional hygiene reinstructions . standardized intraoral radiographs were taken according to a longcone paralleling technique with an individualized xray holder as described by meijndert et al . the digital images were analysed using computer software ( biomedical engineering , university medical center groningen , the netherlands ) to perform linear measurements on digital radiographs . the known implant length was used as a reference to transform the linear measurements into mm . reference line for bone level evaluation was the outer border of the neck of the implant . implant survival was defined as the percentage of implants initially placed that was still present and not mobile at followup . survival of maxillary overdentures was defined as the percentage of overdentures initially placed that was still present at followup . remake or adjustment of the maxillary overdenture was scored any time after placement . for presence of plaque , the presence of calculus ( score 1 ) or the absence of calculus ( score 0 ) was scored . to qualify the degree of periimplant inflammation , probing depth was measured at four sites of each implant ( mesial , labial , distal and lingual ) using a manual periodontal probe ( williams colourcoded probe ; hufriedy , chicago , il , usa ) . periimplant mucositis and periimplantitis was calculated at patient level . as definition for periimplant mucositis and periimplantitis , the consensus reached at the vi and vii european workshop on periodontology ( lindhe & meyle 2008 , lang & berglundh 2011 ) and reconfirmed at the viii european workshop on periodontology ( sanz & chapple 2012 has been used , being : periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration andperiimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration and periimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . patients ' satisfaction with their overdenture was assessed using a validated questionnaire ( vervoorn et al . this questionnaire focused on complaints and consisted of 54 items and was divided into six scales : nine items concerning functional problems of the upper denture;eighteen items concerning functional complaints in general;three items concerning facial aesthetics;three items concerning accidental lip , cheek and tongue biting ( neutral space);twelve items concerning aesthetics of the denture . nine items concerning functional problems of the upper denture ; eighteen items concerning functional complaints in general ; three items concerning facial aesthetics ; three items concerning accidental lip , cheek and tongue biting ( neutral space ) ; twelve items concerning aesthetics of the denture . the extent of each specific complaint could be expressed on a fourpoint rating scale ( 0 = no complaints , 1 = little , 2 = moderate , 3 = severe complaints . chewing ability questionnaire ( stellingsma et al . 2005 ) . in this questionnaire , patients gave their opinion about the ability to chew nine different kinds of food on a threepoint rating scale ( 0 = good , 1 = moderate , 2 = bad ) . the items were grouped into three scales , being soft food , tough food and hard food . next to these questionnaires , the patients ' overall denture satisfaction was expressed on a 10point rating scale ( 1 = very bad to 10 = excellent ) . it was assumed that an implantsupported overdenture on four implants was not inferior to an overdenture supported by six implants . sample size calculation of the study and allocation to the groups is described in the study of slot et al . a difference of at least 0.4 mm in bone height ( measured on standardized radiographs , with a standard deviation of 0.5 mm ) between the four implants group and six implants group after 12 months was expected to differentiate between the two groups , based on the findings of a study on maxillary implantsupported overdentures ( raghoebar et al . a ttest given a = 0.05 with a power 80% combined with the expected effect size for two independent means gives a sample size of 21 persons in each group . to deal with withdrawal of individuals in the study , data collection and analysis of the radiographs were done by the same observer . for clinical and radiographical parameters , the implant has been taken as statistical unit ( with multiple scores per implant , the worst score was taken ) . for calculation of percentage of perimucositis and periimplantitis , the patient has been as taken as statistical unit ( worst implant per patient ) . and data were analysed using the statistical package for social sciences ( version 22.0 ; spss inc . , ibm corporation , chicago , il , usa ) . in all tests , a significance level of 0.05 was chosen . to see whether the data were normally distributed , the frequency distribution was plotted in a histogram . to test whether the result from the frequency analyses differed significantly from a normal distribution , kolmogorov the potential effects of imbalances between the study groups on the outcomes of this study were analysed by regression analysis . as no such effects were observed , differences between study groups were tested with an independent student 's ttest and between evaluation periods were tested with a paired student 's ttest . between january 2006 and december 2009 , a total of 50 consecutive patients fulfilling the inclusion criteria were included in a randomized controlled trial ( fig . 1 ) . fully edentulous patients , referred to the department of oral and maxillofacial surgery ( university medical center groningen , the netherlands ) , suffering from lack of retention and stability of the upper denture and lower denture , were considered for inclusion if they fulfilled the following criteria : flow diagram of the study . at least 18 years of age;capable of understanding and giving informed consent;at least 1 year edentulous in the maxilla and mandible;bone dimensions in the region between the bicuspids in the anterior area of the maxilla had to be at least 12 mm in height and at least 5 mm in width to reach initial stability of the implant;sufficient interocclusal space for a barsupported attachment system in this region . at least 18 years of age ; capable of understanding and giving informed consent ; at least 1 year edentulous in the maxilla and mandible ; bone dimensions in the region between the bicuspids in the anterior area of the maxilla had to be at least 12 mm in height and at least 5 mm in width to reach initial stability of the implant ; sufficient interocclusal space for a barsupported attachment system in this region . excluded were patients with american society of anesthesiologists score ( asa score ) iii ( smeets et al . 1998 ) , who were smoking , with a history of radiotherapy in the head and neck region or a history of preprosthetic surgery or previous implant placement . the patients were informed about the study on overdenture treatment with insertion of four or six dental implants in the maxilla and about the extra efforts associated with the study ( questionnaires , evaluation visits ) before they signed an informed consent . the study was approved by the medical ethical committee of the university medical center groningen ( abr nl32503.042.11 ) . rotational panoramic radiographs , lateral cephalograms and posteroanterior oblique radiographs were taken to assess the volume of the maxillary alveolar bone , the dimensions of the maxillary sinus and the anteroposterior relationship of the maxilla to the mandible . in addition , to assess the bone volume of the maxillary processus , a ridgemapping procedure was performed as described by ten bruggenkate et al . a diagnostic setup of the planned overdenture was made to obtain insight into the available dimensions for the barsupported attachment system and overdenture . the treatment and evaluation procedures have been described in detail with the reporting of 1year results of the study by slot et al . four or six dental implants with a length of at least 11 mm and a diameter of 4 mm were inserted in the maxillary anterior region ( osseospeed 4.0 s dental implants , astra tech ab , mlndal , sweden ) . the implants were placed at crestal bone level in predefined positions ( positions 15 , 13 , 11 , 21 , 23 , 25 in the six implants group and positions 13 , 11 , 21 , 23 in the four implants group ) with the help of a surgical template following a submerged healing protocol . in some cases , the most distal implant position may be 16 or 26 ( in the six implants group ) , but it is always without a large sinus floor elevation . small dehiscences or fenestrations were covered with bone harvested from the maxillary tuberosity and organic bovine bone ( biooss ; geistlich pharma ag , wolhusen , switzerland ) and subsequently covered with a resorbable membrane ( biogide ; geistlich pharma ag , wolhusen , switzerland ) . if the most distally placed implants ( usually in the six implants group ) were partially placed in the anterior part of the maxillary sinus , a small sinus floor elevation surgery was performed in that region to prevent a perforation of the sinus membrane by the implant . after a 3month osseointegration period , secondstage surgery was performed and healing abutments ( uni healing abutments , astra tech ab ) were placed . after the secondstage surgery , prosthetic procedures were initiated . healing abutments were replaced by 20 uni abutments ( astra tech ab ) and with impression copings and polyether material ( impregum f ; 3 m espe , st . paul , minn ) , a complete arch impression was made . a composite resin record base ( lightplast base plates ; dreve dentamid gmbh , unna , germany ) with a wax occlusion rim was used to determine the occlusal vertical dimension and to record the maxillomandibular relationship . acrylic resin artificial teeth ( ivoclar sr orthotyp dcl and ivoclar vivodent pe , ivoclar vivadent ag , schaan , liechtenstein ) were selected and arranged on the record base for a trial arrangement . the final superstructure consisted of a milled titanium eggshaped bar with distal extensions , screwretained to abutments , and an overdenture with builtin cobalt chromium reinforcement structure and gold retentive clips attached to it ( slot et al . the design of the overdentures was with full coverage of the alveolar process , but with limited palatal coverage . the patient was instructed in hygiene procedures associated with the dentures and the bars ( fig . 2 ) . fiveyear panoramic radiograph of a patient with four implants connected with a bar in the maxillary anterior region . four or six dental implants with a length of at least 11 mm and a diameter of 4 mm were inserted in the maxillary anterior region ( osseospeed 4.0 s dental implants , astra tech ab , mlndal , sweden ) . the implants were placed at crestal bone level in predefined positions ( positions 15 , 13 , 11 , 21 , 23 , 25 in the six implants group and positions 13 , 11 , 21 , 23 in the four implants group ) with the help of a surgical template following a submerged healing protocol . in some cases , the most distal implant position may be 16 or 26 ( in the six implants group ) , but it is always without a large sinus floor elevation . small dehiscences or fenestrations were covered with bone harvested from the maxillary tuberosity and organic bovine bone ( biooss ; geistlich pharma ag , wolhusen , switzerland ) and subsequently covered with a resorbable membrane ( biogide ; geistlich pharma ag , wolhusen , switzerland ) . if the most distally placed implants ( usually in the six implants group ) were partially placed in the anterior part of the maxillary sinus , a small sinus floor elevation surgery was performed in that region to prevent a perforation of the sinus membrane by the implant . after a 3month osseointegration period , secondstage surgery was performed and healing abutments ( uni healing abutments , astra tech ab ) were placed . healing abutments were replaced by 20 uni abutments ( astra tech ab ) and with impression copings and polyether material ( impregum f ; 3 m espe , st . paul , minn ) , a complete arch impression was made . a composite resin record base ( lightplast base plates ; dreve dentamid gmbh , unna , germany ) with a wax occlusion rim was used to determine the occlusal vertical dimension and to record the maxillomandibular relationship . acrylic resin artificial teeth ( ivoclar sr orthotyp dcl and ivoclar vivodent pe , ivoclar vivadent ag , schaan , liechtenstein ) were selected and arranged on the record base for a trial arrangement . the final superstructure consisted of a milled titanium eggshaped bar with distal extensions , screwretained to abutments , and an overdenture with builtin cobalt chromium reinforcement structure and gold retentive clips attached to it ( slot et al . the design of the overdentures was with full coverage of the alveolar process , but with limited palatal coverage . the patient was instructed in hygiene procedures associated with the dentures and the bars ( fig . 2 ) . fiveyear panoramic radiograph of a patient with four implants connected with a bar in the maxillary anterior region . secondary outcome measures were implant survival , overdenture survival and soft tissue conditions ( plaque index , presence of calculus , gingiva index , sulcus bleeding index and pocket probing depth ) . these parameters were scored at placement of the overdenture , and 1 year and 5 years after loading . patients ' satisfaction was also scored before treatment , and 1 year and 5 years after loading . thereafter , the patients were followed up for routine checkup visits at 2 , 3 and 4 years . if plaque and/or calculus were present at an evaluation period , cleaning was performed with additional hygiene reinstructions . standardized intraoral radiographs were taken according to a longcone paralleling technique with an individualized xray holder as described by meijndert et al . the digital images were analysed using computer software ( biomedical engineering , university medical center groningen , the netherlands ) to perform linear measurements on digital radiographs . the known implant length was used as a reference to transform the linear measurements into mm . reference line for bone level evaluation implant survival was defined as the percentage of implants initially placed that was still present and not mobile at followup . survival of maxillary overdentures was defined as the percentage of overdentures initially placed that was still present at followup . remake or adjustment of the maxillary overdenture was scored any time after placement . for presence of plaque , the index according to mombelli et al . the presence of calculus ( score 1 ) or the absence of calculus ( score 0 ) was scored . to qualify the degree of periimplant inflammation , the modified le and silness index ( 1963 ) was used . for bleeding , the bleeding index according to mombelli et al . probing depth was measured at four sites of each implant ( mesial , labial , distal and lingual ) using a manual periodontal probe ( williams colourcoded probe ; hufriedy , chicago , il , usa ) . periimplant mucositis and periimplantitis was calculated at patient level . as definition for periimplant mucositis and periimplantitis , the consensus reached at the vi and vii european workshop on periodontology ( lindhe & meyle 2008 , lang & berglundh 2011 ) and reconfirmed at the viii european workshop on periodontology ( sanz & chapple 2012 has been used , being : periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration andperiimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration and periimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . patients ' satisfaction with their overdenture was assessed using a validated questionnaire ( vervoorn et al . this questionnaire focused on complaints and consisted of 54 items and was divided into six scales : nine items concerning functional problems of the upper denture;eighteen items concerning functional complaints in general;three items concerning facial aesthetics;three items concerning accidental lip , cheek and tongue biting ( neutral space);twelve items concerning aesthetics of the denture . nine items concerning functional problems of the upper denture ; eighteen items concerning functional complaints in general ; three items concerning facial aesthetics ; three items concerning accidental lip , cheek and tongue biting ( neutral space ) ; twelve items concerning aesthetics of the denture . the extent of each specific complaint could be expressed on a fourpoint rating scale ( 0 = no complaints , 1 = little , 2 = moderate , 3 = severe complaints . chewing ability questionnaire ( stellingsma et al . 2005 ) . in this questionnaire , patients gave their opinion about the ability to chew nine different kinds of food on a threepoint rating scale ( 0 = good , 1 = moderate , 2 = bad ) . the items were grouped into three scales , being soft food , tough food and hard food . next to these questionnaires , the patients ' overall denture satisfaction was expressed on a 10point rating scale ( 1 = very bad to 10 = excellent ) . standardized intraoral radiographs were taken according to a longcone paralleling technique with an individualized xray holder as described by meijndert et al . the digital images were analysed using computer software ( biomedical engineering , university medical center groningen , the netherlands ) to perform linear measurements on digital radiographs . the known implant length was used as a reference to transform the linear measurements into mm . reference line for bone level evaluation implant survival was defined as the percentage of implants initially placed that was still present and not mobile at followup . survival of maxillary overdentures was defined as the percentage of overdentures initially placed that was still present at followup . the presence of calculus ( score 1 ) or the absence of calculus ( score 0 ) was scored . to qualify the degree of periimplant inflammation , the modified le and silness index ( 1963 ) was used . for bleeding , the bleeding index according to mombelli et al . probing depth was measured at four sites of each implant ( mesial , labial , distal and lingual ) using a manual periodontal probe ( williams colourcoded probe ; hufriedy , chicago , il , usa ) . periimplant mucositis and periimplantitis was calculated at patient level . as definition for periimplant mucositis and periimplantitis , the consensus reached at the vi and vii european workshop on periodontology ( lindhe & meyle 2008 , lang & berglundh 2011 ) and reconfirmed at the viii european workshop on periodontology ( sanz & chapple 2012 has been used , being : periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration andperiimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration and periimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . patients ' satisfaction with their overdenture was assessed using a validated questionnaire ( vervoorn et al . this questionnaire focused on complaints and consisted of 54 items and was divided into six scales : nine items concerning functional problems of the upper denture;eighteen items concerning functional complaints in general;three items concerning facial aesthetics;three items concerning accidental lip , cheek and tongue biting ( neutral space);twelve items concerning aesthetics of the denture . nine items concerning functional problems of the upper denture ; eighteen items concerning functional complaints in general ; three items concerning facial aesthetics ; three items concerning accidental lip , cheek and tongue biting ( neutral space ) ; twelve items concerning aesthetics of the denture . the extent of each specific complaint could be expressed on a fourpoint rating scale ( 0 = no complaints , 1 = little , 2 = moderate , 3 = severe complaints . chewing ability questionnaire ( stellingsma et al . 2005 ) . in this questionnaire , patients gave their opinion about the ability to chew nine different kinds of food on a threepoint rating scale ( 0 = good , 1 = moderate , 2 = bad ) . the items were grouped into three scales , being soft food , tough food and hard food . next to these questionnaires , the patients ' overall denture satisfaction was expressed on a 10point rating scale ( 1 = very bad to 10 = excellent ) . study analysis was performed according to a noninferiority design . it was assumed that an implantsupported overdenture on four implants was not inferior to an overdenture supported by six implants . sample size calculation of the study and allocation to the groups is described in the study of slot et al . ( 2013 ) . a difference of at least 0.4 mm in bone height ( measured on standardized radiographs , with a standard deviation of 0.5 mm ) between the four implants group and six implants group after 12 months was expected to differentiate between the two groups , based on the findings of a study on maxillary implantsupported overdentures ( raghoebar et al . 2003 ) . a ttest given a = 0.05 with a power 80% combined with the expected effect size for two independent means gives a sample size of 21 persons in each group . to deal with withdrawal of individuals in the study , data collection and analysis of the radiographs were done by the same observer . for clinical and radiographical parameters , the implant has been taken as statistical unit ( with multiple scores per implant , the worst score was taken ) . for calculation of percentage of perimucositis and periimplantitis , the patient has been as taken as statistical unit ( worst implant per patient ) . and data were analysed using the statistical package for social sciences ( version 22.0 ; spss inc . , ibm corporation , chicago , il , usa ) . in all tests , a significance level of 0.05 was chosen . to see whether the data were normally distributed , the frequency distribution was plotted in a histogram . to test whether the result from the frequency analyses differed significantly from a normal distribution , kolmogorov the potential effects of imbalances between the study groups on the outcomes of this study were analysed by regression analysis . as no such effects were observed , differences between study groups were tested with an independent student 's ttest and between evaluation periods were tested with a paired student 's ttest . two patients died during the followup period ( one patient in the four implants group before the 1year evaluation and one patient in the six implants group between the 1year and 5year evaluation ) . two patients of the six implants group did not attend the 5year evaluation because of severe illness . no implants failed in the four implants group , while one implant in the six implants group was lost during the osseointegration period . because a barsupported overdenture could still be made on the remaining five implants , there was no need to replace the implant . fiveyears ' survival rate of implants was 100% in the four implants group , 99.2% in the six implants group . baseline characteristics ( at placement of overdenture ) of the groups with four implants ( four implants group ) and six implants ( six implants group ) differences between study groups were tested with the independent student 's ttest ( p < 0.05 ) . the mean loss of marginal bone between baseline ( placement of the overdenture ) and the 5year evaluation was 0.50 0.37 mm in the four implants group and 0.52 0.43 mm in the six implants group ( p > 0.05 , table 2 ) . mean scores of the indices for plaque , calculus , gingiva and bleeding were very low at all evaluation periods and did not differ between the groups . also no timedependent significant changes in probing depth were observed between the groups ( p > 0.05 , table 3 ) . patientlevel incidence of periimplant mucositis was 41.7% and 45.5% , and of periimplantitis was 8.3% and 4.5% in the four and six implants groups respectively . mean values and standard deviations of marginal bone loss in mm , and frequency distribution of bone loss 1 and 5 years after placement of the overdenture of the four and six implants groups . mean marginal bone loss did not differ significantly between the groups differences between study groups were tested with the independent student 's ttest ( p < 0.05 ) . mean change from baseline to 1 and 5 years of followup for plaque index , calculus index , gingival index , bleeding index and probing depth . no timedependent significant changes were observed between the groups differences between study groups were tested with the independent student 's ttest ( p < 0.05 ) . in both groups , all scores had improved significantly ( p < 0.05 ) between pretreatment and posttreatment assessments , but the scores did not differ between the groups ( p > 0.05 ) . after 5 years , patients continued to be very satisfied with their overdentures ; the results are rather similar to the 1year data . mean score of 5 scales concerning the denture complaints ( possible range 03 ) , mean scores of chewing ability of soft , tough and hard food ( possible range 02 ) and overall satisfaction score ( possible range 110 ) before , and 1 and 5 years after treatment . no significant differences between the four and six implants group were observed at all evaluation periods differences between study groups were tested with the independent student 's ttest ( p < 0.05 ) . the surgical and prosthetic aftercare during 5 years of followup revealed a small number of events , mostly repair of the denture base or teeth . surgical treatment of periimplantitis was not performed during the 5year followup ( table 5 ) . at the 5year followup evaluation , a number of patients were identified as having periimplant mucositis ( treatment : cleaning and reinstruction ) or periimplantitis ( treatment : cleaning , reinstruction and openflap surgical treatment ) . this study revealed that both four and six dental implants placed in the anterior region of the edentulous maxilla , connected with a bar , form a proper base for the support of an overdenture . in none of the parameters studied , significant differences were observed between the four and six implants group . fiveyears ' survival rate of implants was high in both the four and six implants group . these results are on the high end compared to the implant survival reported in the 5year followup case series of jemt et al . ( 1997 ) and bergendal & engquist ( 1998 ) who used implants with a machined surface ( 5year implants survival 72.479% ) and similar to those reported by mangano et al . the latter studies also used implants with a roughened surface , as in this study . although a study comparing various implant designs was not analysed , apparently implants with a roughened surface perform better than implants with a machined surface in the maxilla . the mean marginal bone loss between baseline ( placement of the overdenture ) and the 5year evaluation was limited in both groups and again comparable to those reported by mangano et al . the very limited marginal bone loss might be due to the neck design of the implants used ( hermann et al . mean indices for plaque , calculus , gingiva and bleeding were very low at the 5year evaluation and probing depth was not deviating . there might be some extra effort in performing hygiene tasks with six implants , but this does not result in worse results . incidence of periimplantitis after 5 years was 8.3% and 4.5% in the four and six implants groups respectively . because there was no significant change in pocket probing depth at an earlier stage , no extra radiographs were made . nevertheless , bone loss as a sign of periimplantitis could not be reliably excluded in some patients before the 5year evaluation period . in a systematic review of de waal et al . ( 2013 ) , it was reported that numbers of prevalence of periimplant mucositis and periimplantitis with standardized threshold levels are missing in studies with fully edentulous patients . in this study , the patientlevel incidence of periimplant mucositis was 41.7% and of periimplantitis was 8.3% in the four implants group . in the six implants group , patientlevel incidence of periimplant mucositis was 45.5% and of periimplantitis was 4.5% . also in fully edentulous patients , but for mandibular overdentures , 51.9% periimplant mucositis and 16.9% periimplantitis was reported after 5 years ( meijer et al . existing studies have demonstrated clearly that edentulism per se is no protection from periimplant disease and that continuous supportive care is essential in maintaining periimplant health . patients ' satisfaction improved significantly when wearing implantsupported maxillary overdentures and results were shown to be favourable at both the 1 and 5year evaluation , again in agreement with data reported by krennmair et al . ( 2008 ) also mentioned in their case series that patients with an overdenture on four or six implants in the anterior maxilla were equally satisfied . in other words , patients ' satisfaction seemed to be irrespective of whether the bar was supported by four or six implants in the anterior maxillary region . the high satisfaction might be due to the fact that the overdenture is supported by a bar , which gives a comparable stability for both treatment options . the idea that six implants gives more stability than four implants , and resulting in more patients ' satisfaction , turned out to be not true . probably because four and six implants are more or less placed in the same area and the fact that the length of the bar is the same in both designs . the high satisfaction with maxillary overdentures , including opinions on speech , resemble the results of heydecke et al . ( 2004 ) in which favourable results of an overdenture were displayed compared with a fixed implant prosthesis . ( 2011 ) reported that the majority of complications were related to the weakness of the anchorage components connecting bar and overdenture . this is in contrast with this study in which no clip repairs were recorded . in this study , an overdenture with builtin cobalt chromium reinforcement structure and gold retentive clips attached to it were used , which probably led to a minimum of prosthetic complications ( slot et al . rotational panoramic radiographs , lateral cephalograms and posteroanterior oblique radiographs were made to assess bone volume and possible pathology . nowadays , in terms of radiation protection and diagnostic possibilities , cone beam computer tomography is preferred . in the study , some studies reveal that periimplant hygiene of solitary attachment systems are superior compared with bar attachment systems ( zou et al . longterm studies on comparison of attachment systems would be advantageous . from this 5year followup study , it was concluded that barconnected maxillary overdentures on four or six implants resulted in a comparable treatment outcome with high implant survival , limited loss of periimplant marginal bone and high patient satisfaction .

abstractobjectiveto compare a four and siximplant maxillary overdenture after an observation period of 5 years.material and methodsfifty subjects with functional problems concerning their maxillary denture , who had ample bone volume in the anterior region to place four or six implants , were included and randomly assigned to either group . implant and overdenture survival , clinical performance , marginal bone loss and patient satisfaction were assessed.resultsfortysix patients completed the 5year followup . one implant failed in the six implants group ( 99.2% survival ) and none in the four implants group ( 100% survival ) . no overdentures had to be replaced during the observation period and the number of complications was limited . clinical function was good , with no difference in clinical parameters between the groups . mean marginal bone resorption was 0.50 0.37 and 0.52 0.43 mm in the four and six implant group respectively.conclusionin patients with functional complaints of their maxillary denture , barsupported overdentures on four implants in the anterior maxillary region were not inferior to overdentures supported by six implants after 5 years of function . implant survival and patient satisfaction were high , clinical parameters favourable , bone loss and complications to the denture were minor in both groups ( clinical trial registration number : ntr2969 ) .

<s>[INST]between january 2006 and december 2009 , a total of 50 consecutive patients fulfilling the inclusion criteria were included in a randomized controlled trial ( fig . 1 ) . fully edentulous patients , referred to the department of oral and maxillofacial surgery ( university medical center groningen , the netherlands ) , suffering from lack of retention and stability of the upper denture and lower denture , were considered for inclusion if they fulfilled the following criteria : flow diagram of the study . at least 18 years of age;capable of understanding and giving informed consent;at least 1 year edentulous in the maxilla and mandible;bone dimensions in the region between the bicuspids in the anterior area of the maxilla had to be at least 12 mm in height and at least 5 mm in width to reach initial stability of the implant;sufficient interocclusal space for a barsupported attachment system in this region . at least 18 years of age ; capable of understanding and giving informed consent ; at least 1 year edentulous in the maxilla and mandible ; bone dimensions in the region between the bicuspids in the anterior area of the maxilla had to be at least 12 mm in height and at least 5 mm in width to reach initial stability of the implant ; sufficient interocclusal space for a barsupported attachment system in this region . excluded were patients with american society of anesthesiologists score ( asa score ) iii ( smeets et al . 1998 ) , who were smoking , with a history of radiotherapy in the head and neck region or a history of preprosthetic surgery or previous implant placement . the patients were informed about the study on overdenture treatment with insertion of four or six dental implants in the maxilla and about the extra efforts associated with the study ( questionnaires , evaluation visits ) before they signed an informed consent . the study was approved by the medical ethical committee of the university medical center groningen ( abr nl32503.042.11 ) . rotational panoramic radiographs , lateral cephalograms and posteroanterior oblique radiographs were taken to assess the volume of the maxillary alveolar bone , the dimensions of the maxillary sinus and the anteroposterior relationship of the maxilla to the mandible . in addition , to assess the bone volume of the maxillary processus , a ridgemapping procedure was performed as described by ten bruggenkate et al . a diagnostic setup of the planned overdenture was made to obtain insight into the available dimensions for the barsupported attachment system and overdenture . the treatment and evaluation procedures have been described in detail with the reporting of 1year results of the study by slot et al . four or six dental implants with a length of at least 11 mm and a diameter of 4 mm were inserted in the maxillary anterior region ( osseospeed 4.0 s dental implants , astra tech ab , mlndal , sweden ) . the implants were placed at crestal bone level in predefined positions ( positions 15 , 13 , 11 , 21 , 23 , 25 in the six implants group and positions 13 , 11 , 21 , 23 in the four implants group ) with the help of a surgical template following a submerged healing protocol . in some cases , the most distal implant position may be 16 or 26 ( in the six implants group ) , but it is always without a large sinus floor elevation . small dehiscences or fenestrations were covered with bone harvested from the maxillary tuberosity and organic bovine bone ( biooss ; geistlich pharma ag , wolhusen , switzerland ) and subsequently covered with a resorbable membrane ( biogide ; geistlich pharma ag , wolhusen , switzerland ) . if the most distally placed implants ( usually in the six implants group ) were partially placed in the anterior part of the maxillary sinus , a small sinus floor elevation surgery was performed in that region to prevent a perforation of the sinus membrane by the implant . after a 3month osseointegration period , secondstage surgery was performed and healing abutments ( uni healing abutments , astra tech ab ) were placed . after the secondstage surgery , prosthetic procedures were initiated . healing abutments were replaced by 20 uni abutments ( astra tech ab ) and with impression copings and polyether material ( impregum f ; 3 m espe , st . paul , minn ) , a complete arch impression was made . a composite resin record base ( lightplast base plates ; dreve dentamid gmbh , unna , germany ) with a wax occlusion rim was used to determine the occlusal vertical dimension and to record the maxillomandibular relationship . acrylic resin artificial teeth ( ivoclar sr orthotyp dcl and ivoclar vivodent pe , ivoclar vivadent ag , schaan , liechtenstein ) were selected and arranged on the record base for a trial arrangement . the final superstructure consisted of a milled titanium eggshaped bar with distal extensions , screwretained to abutments , and an overdenture with builtin cobalt chromium reinforcement structure and gold retentive clips attached to it ( slot et al . the design of the overdentures was with full coverage of the alveolar process , but with limited palatal coverage . the patient was instructed in hygiene procedures associated with the dentures and the bars ( fig . 2 ) . fiveyear panoramic radiograph of a patient with four implants connected with a bar in the maxillary anterior region . secondary outcome measures were implant survival , overdenture survival and soft tissue conditions ( plaque index , presence of calculus , gingiva index , sulcus bleeding index and pocket probing depth ) . these parameters were scored at placement of the overdenture , and 1 year and 5 years after loading . patients ' satisfaction was also scored before treatment , and 1 year and 5 years after loading . thereafter , the patients were followed up for routine checkup visits at 2 , 3 and 4 years . if plaque and/or calculus were present at an evaluation period , cleaning was performed with additional hygiene reinstructions . standardized intraoral radiographs were taken according to a longcone paralleling technique with an individualized xray holder as described by meijndert et al . the digital images were analysed using computer software ( biomedical engineering , university medical center groningen , the netherlands ) to perform linear measurements on digital radiographs . the known implant length was used as a reference to transform the linear measurements into mm . reference line for bone level evaluation was the outer border of the neck of the implant . implant survival was defined as the percentage of implants initially placed that was still present and not mobile at followup . survival of maxillary overdentures was defined as the percentage of overdentures initially placed that was still present at followup . remake or adjustment of the maxillary overdenture was scored any time after placement . for presence of plaque , the presence of calculus ( score 1 ) or the absence of calculus ( score 0 ) was scored . to qualify the degree of periimplant inflammation , probing depth was measured at four sites of each implant ( mesial , labial , distal and lingual ) using a manual periodontal probe ( williams colourcoded probe ; hufriedy , chicago , il , usa ) . periimplant mucositis and periimplantitis was calculated at patient level . as definition for periimplant mucositis and periimplantitis , the consensus reached at the vi and vii european workshop on periodontology ( lindhe & meyle 2008 , lang & berglundh 2011 ) and reconfirmed at the viii european workshop on periodontology ( sanz & chapple 2012 has been used , being : periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration andperiimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration and periimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . patients ' satisfaction with their overdenture was assessed using a validated questionnaire ( vervoorn et al . this questionnaire focused on complaints and consisted of 54 items and was divided into six scales : nine items concerning functional problems of the upper denture;eighteen items concerning functional complaints in general;three items concerning facial aesthetics;three items concerning accidental lip , cheek and tongue biting ( neutral space);twelve items concerning aesthetics of the denture . nine items concerning functional problems of the upper denture ; eighteen items concerning functional complaints in general ; three items concerning facial aesthetics ; three items concerning accidental lip , cheek and tongue biting ( neutral space ) ; twelve items concerning aesthetics of the denture . the extent of each specific complaint could be expressed on a fourpoint rating scale ( 0 = no complaints , 1 = little , 2 = moderate , 3 = severe complaints . chewing ability questionnaire ( stellingsma et al . 2005 ) . in this questionnaire , patients gave their opinion about the ability to chew nine different kinds of food on a threepoint rating scale ( 0 = good , 1 = moderate , 2 = bad ) . the items were grouped into three scales , being soft food , tough food and hard food . next to these questionnaires , the patients ' overall denture satisfaction was expressed on a 10point rating scale ( 1 = very bad to 10 = excellent ) . it was assumed that an implantsupported overdenture on four implants was not inferior to an overdenture supported by six implants . sample size calculation of the study and allocation to the groups is described in the study of slot et al . a difference of at least 0.4 mm in bone height ( measured on standardized radiographs , with a standard deviation of 0.5 mm ) between the four implants group and six implants group after 12 months was expected to differentiate between the two groups , based on the findings of a study on maxillary implantsupported overdentures ( raghoebar et al . a ttest given a = 0.05 with a power 80% combined with the expected effect size for two independent means gives a sample size of 21 persons in each group . to deal with withdrawal of individuals in the study , data collection and analysis of the radiographs were done by the same observer . for clinical and radiographical parameters , the implant has been taken as statistical unit ( with multiple scores per implant , the worst score was taken ) . for calculation of percentage of perimucositis and periimplantitis , the patient has been as taken as statistical unit ( worst implant per patient ) . and data were analysed using the statistical package for social sciences ( version 22.0 ; spss inc . , ibm corporation , chicago , il , usa ) . in all tests , a significance level of 0.05 was chosen . to see whether the data were normally distributed , the frequency distribution was plotted in a histogram . to test whether the result from the frequency analyses differed significantly from a normal distribution , kolmogorov the potential effects of imbalances between the study groups on the outcomes of this study were analysed by regression analysis . as no such effects were observed , differences between study groups were tested with an independent student 's ttest and between evaluation periods were tested with a paired student 's ttest . between january 2006 and december 2009 , a total of 50 consecutive patients fulfilling the inclusion criteria were included in a randomized controlled trial ( fig . 1 ) . fully edentulous patients , referred to the department of oral and maxillofacial surgery ( university medical center groningen , the netherlands ) , suffering from lack of retention and stability of the upper denture and lower denture , were considered for inclusion if they fulfilled the following criteria : flow diagram of the study . at least 18 years of age;capable of understanding and giving informed consent;at least 1 year edentulous in the maxilla and mandible;bone dimensions in the region between the bicuspids in the anterior area of the maxilla had to be at least 12 mm in height and at least 5 mm in width to reach initial stability of the implant;sufficient interocclusal space for a barsupported attachment system in this region . at least 18 years of age ; capable of understanding and giving informed consent ; at least 1 year edentulous in the maxilla and mandible ; bone dimensions in the region between the bicuspids in the anterior area of the maxilla had to be at least 12 mm in height and at least 5 mm in width to reach initial stability of the implant ; sufficient interocclusal space for a barsupported attachment system in this region . excluded were patients with american society of anesthesiologists score ( asa score ) iii ( smeets et al . 1998 ) , who were smoking , with a history of radiotherapy in the head and neck region or a history of preprosthetic surgery or previous implant placement . the patients were informed about the study on overdenture treatment with insertion of four or six dental implants in the maxilla and about the extra efforts associated with the study ( questionnaires , evaluation visits ) before they signed an informed consent . the study was approved by the medical ethical committee of the university medical center groningen ( abr nl32503.042.11 ) . rotational panoramic radiographs , lateral cephalograms and posteroanterior oblique radiographs were taken to assess the volume of the maxillary alveolar bone , the dimensions of the maxillary sinus and the anteroposterior relationship of the maxilla to the mandible . in addition , to assess the bone volume of the maxillary processus , a ridgemapping procedure was performed as described by ten bruggenkate et al . a diagnostic setup of the planned overdenture was made to obtain insight into the available dimensions for the barsupported attachment system and overdenture . the treatment and evaluation procedures have been described in detail with the reporting of 1year results of the study by slot et al . four or six dental implants with a length of at least 11 mm and a diameter of 4 mm were inserted in the maxillary anterior region ( osseospeed 4.0 s dental implants , astra tech ab , mlndal , sweden ) . the implants were placed at crestal bone level in predefined positions ( positions 15 , 13 , 11 , 21 , 23 , 25 in the six implants group and positions 13 , 11 , 21 , 23 in the four implants group ) with the help of a surgical template following a submerged healing protocol . in some cases , the most distal implant position may be 16 or 26 ( in the six implants group ) , but it is always without a large sinus floor elevation . small dehiscences or fenestrations were covered with bone harvested from the maxillary tuberosity and organic bovine bone ( biooss ; geistlich pharma ag , wolhusen , switzerland ) and subsequently covered with a resorbable membrane ( biogide ; geistlich pharma ag , wolhusen , switzerland ) . if the most distally placed implants ( usually in the six implants group ) were partially placed in the anterior part of the maxillary sinus , a small sinus floor elevation surgery was performed in that region to prevent a perforation of the sinus membrane by the implant . after a 3month osseointegration period , secondstage surgery was performed and healing abutments ( uni healing abutments , astra tech ab ) were placed . after the secondstage surgery , prosthetic procedures were initiated . healing abutments were replaced by 20 uni abutments ( astra tech ab ) and with impression copings and polyether material ( impregum f ; 3 m espe , st . paul , minn ) , a complete arch impression was made . a composite resin record base ( lightplast base plates ; dreve dentamid gmbh , unna , germany ) with a wax occlusion rim was used to determine the occlusal vertical dimension and to record the maxillomandibular relationship . acrylic resin artificial teeth ( ivoclar sr orthotyp dcl and ivoclar vivodent pe , ivoclar vivadent ag , schaan , liechtenstein ) were selected and arranged on the record base for a trial arrangement . the final superstructure consisted of a milled titanium eggshaped bar with distal extensions , screwretained to abutments , and an overdenture with builtin cobalt chromium reinforcement structure and gold retentive clips attached to it ( slot et al . the design of the overdentures was with full coverage of the alveolar process , but with limited palatal coverage . the patient was instructed in hygiene procedures associated with the dentures and the bars ( fig . 2 ) . fiveyear panoramic radiograph of a patient with four implants connected with a bar in the maxillary anterior region . four or six dental implants with a length of at least 11 mm and a diameter of 4 mm were inserted in the maxillary anterior region ( osseospeed 4.0 s dental implants , astra tech ab , mlndal , sweden ) . the implants were placed at crestal bone level in predefined positions ( positions 15 , 13 , 11 , 21 , 23 , 25 in the six implants group and positions 13 , 11 , 21 , 23 in the four implants group ) with the help of a surgical template following a submerged healing protocol . in some cases , the most distal implant position may be 16 or 26 ( in the six implants group ) , but it is always without a large sinus floor elevation . small dehiscences or fenestrations were covered with bone harvested from the maxillary tuberosity and organic bovine bone ( biooss ; geistlich pharma ag , wolhusen , switzerland ) and subsequently covered with a resorbable membrane ( biogide ; geistlich pharma ag , wolhusen , switzerland ) . if the most distally placed implants ( usually in the six implants group ) were partially placed in the anterior part of the maxillary sinus , a small sinus floor elevation surgery was performed in that region to prevent a perforation of the sinus membrane by the implant . after a 3month osseointegration period , secondstage surgery was performed and healing abutments ( uni healing abutments , astra tech ab ) were placed . healing abutments were replaced by 20 uni abutments ( astra tech ab ) and with impression copings and polyether material ( impregum f ; 3 m espe , st . paul , minn ) , a complete arch impression was made . a composite resin record base ( lightplast base plates ; dreve dentamid gmbh , unna , germany ) with a wax occlusion rim was used to determine the occlusal vertical dimension and to record the maxillomandibular relationship . acrylic resin artificial teeth ( ivoclar sr orthotyp dcl and ivoclar vivodent pe , ivoclar vivadent ag , schaan , liechtenstein ) were selected and arranged on the record base for a trial arrangement . the final superstructure consisted of a milled titanium eggshaped bar with distal extensions , screwretained to abutments , and an overdenture with builtin cobalt chromium reinforcement structure and gold retentive clips attached to it ( slot et al . the design of the overdentures was with full coverage of the alveolar process , but with limited palatal coverage . the patient was instructed in hygiene procedures associated with the dentures and the bars ( fig . 2 ) . fiveyear panoramic radiograph of a patient with four implants connected with a bar in the maxillary anterior region . secondary outcome measures were implant survival , overdenture survival and soft tissue conditions ( plaque index , presence of calculus , gingiva index , sulcus bleeding index and pocket probing depth ) . these parameters were scored at placement of the overdenture , and 1 year and 5 years after loading . patients ' satisfaction was also scored before treatment , and 1 year and 5 years after loading . thereafter , the patients were followed up for routine checkup visits at 2 , 3 and 4 years . if plaque and/or calculus were present at an evaluation period , cleaning was performed with additional hygiene reinstructions . standardized intraoral radiographs were taken according to a longcone paralleling technique with an individualized xray holder as described by meijndert et al . the digital images were analysed using computer software ( biomedical engineering , university medical center groningen , the netherlands ) to perform linear measurements on digital radiographs . the known implant length was used as a reference to transform the linear measurements into mm . reference line for bone level evaluation implant survival was defined as the percentage of implants initially placed that was still present and not mobile at followup . survival of maxillary overdentures was defined as the percentage of overdentures initially placed that was still present at followup . remake or adjustment of the maxillary overdenture was scored any time after placement . for presence of plaque , the index according to mombelli et al . the presence of calculus ( score 1 ) or the absence of calculus ( score 0 ) was scored . to qualify the degree of periimplant inflammation , the modified le and silness index ( 1963 ) was used . for bleeding , the bleeding index according to mombelli et al . probing depth was measured at four sites of each implant ( mesial , labial , distal and lingual ) using a manual periodontal probe ( williams colourcoded probe ; hufriedy , chicago , il , usa ) . periimplant mucositis and periimplantitis was calculated at patient level . as definition for periimplant mucositis and periimplantitis , the consensus reached at the vi and vii european workshop on periodontology ( lindhe & meyle 2008 , lang & berglundh 2011 ) and reconfirmed at the viii european workshop on periodontology ( sanz & chapple 2012 has been used , being : periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration andperiimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration and periimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . patients ' satisfaction with their overdenture was assessed using a validated questionnaire ( vervoorn et al . this questionnaire focused on complaints and consisted of 54 items and was divided into six scales : nine items concerning functional problems of the upper denture;eighteen items concerning functional complaints in general;three items concerning facial aesthetics;three items concerning accidental lip , cheek and tongue biting ( neutral space);twelve items concerning aesthetics of the denture . nine items concerning functional problems of the upper denture ; eighteen items concerning functional complaints in general ; three items concerning facial aesthetics ; three items concerning accidental lip , cheek and tongue biting ( neutral space ) ; twelve items concerning aesthetics of the denture . the extent of each specific complaint could be expressed on a fourpoint rating scale ( 0 = no complaints , 1 = little , 2 = moderate , 3 = severe complaints . chewing ability questionnaire ( stellingsma et al . 2005 ) . in this questionnaire , patients gave their opinion about the ability to chew nine different kinds of food on a threepoint rating scale ( 0 = good , 1 = moderate , 2 = bad ) . the items were grouped into three scales , being soft food , tough food and hard food . next to these questionnaires , the patients ' overall denture satisfaction was expressed on a 10point rating scale ( 1 = very bad to 10 = excellent ) . standardized intraoral radiographs were taken according to a longcone paralleling technique with an individualized xray holder as described by meijndert et al . the digital images were analysed using computer software ( biomedical engineering , university medical center groningen , the netherlands ) to perform linear measurements on digital radiographs . the known implant length was used as a reference to transform the linear measurements into mm . reference line for bone level evaluation implant survival was defined as the percentage of implants initially placed that was still present and not mobile at followup . survival of maxillary overdentures was defined as the percentage of overdentures initially placed that was still present at followup . the presence of calculus ( score 1 ) or the absence of calculus ( score 0 ) was scored . to qualify the degree of periimplant inflammation , the modified le and silness index ( 1963 ) was used . for bleeding , the bleeding index according to mombelli et al . probing depth was measured at four sites of each implant ( mesial , labial , distal and lingual ) using a manual periodontal probe ( williams colourcoded probe ; hufriedy , chicago , il , usa ) . periimplant mucositis and periimplantitis was calculated at patient level . as definition for periimplant mucositis and periimplantitis , the consensus reached at the vi and vii european workshop on periodontology ( lindhe & meyle 2008 , lang & berglundh 2011 ) and reconfirmed at the viii european workshop on periodontology ( sanz & chapple 2012 has been used , being : periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration andperiimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . periimplant mucositis ( radiographic bone loss < 2 mm ) : bop+ and/or suppuration and periimplantitis : bop+ and/or suppuration in combination with marginal bone loss 2 mm . patients ' satisfaction with their overdenture was assessed using a validated questionnaire ( vervoorn et al . this questionnaire focused on complaints and consisted of 54 items and was divided into six scales : nine items concerning functional problems of the upper denture;eighteen items concerning functional complaints in general;three items concerning facial aesthetics;three items concerning accidental lip , cheek and tongue biting ( neutral space);twelve items concerning aesthetics of the denture . nine items concerning functional problems of the upper denture ; eighteen items concerning functional complaints in general ; three items concerning facial aesthetics ; three items concerning accidental lip , cheek and tongue biting ( neutral space ) ; twelve items concerning aesthetics of the denture . the extent of each specific complaint could be expressed on a fourpoint rating scale ( 0 = no complaints , 1 = little , 2 = moderate , 3 = severe complaints . chewing ability questionnaire ( stellingsma et al . 2005 ) . in this questionnaire , patients gave their opinion about the ability to chew nine different kinds of food on a threepoint rating scale ( 0 = good , 1 = moderate , 2 = bad ) . the items were grouped into three scales , being soft food , tough food and hard food . next to these questionnaires , the patients ' overall denture satisfaction was expressed on a 10point rating scale ( 1 = very bad to 10 = excellent ) . study analysis was performed according to a noninferiority design . it was assumed that an implantsupported overdenture on four implants was not inferior to an overdenture supported by six implants . sample size calculation of the study and allocation to the groups is described in the study of slot et al . ( 2013 ) . a difference of at least 0.4 mm in bone height ( measured on standardized radiographs , with a standard deviation of 0.5 mm ) between the four implants group and six implants group after 12 months was expected to differentiate between the two groups , based on the findings of a study on maxillary implantsupported overdentures ( raghoebar et al . 2003 ) . a ttest given a = 0.05 with a power 80% combined with the expected effect size for two independent means gives a sample size of 21 persons in each group . to deal with withdrawal of individuals in the study , data collection and analysis of the radiographs were done by the same observer . for clinical and radiographical parameters , the implant has been taken as statistical unit ( with multiple scores per implant , the worst score was taken ) . for calculation of percentage of perimucositis and periimplantitis , the patient has been as taken as statistical unit ( worst implant per patient ) . and data were analysed using the statistical package for social sciences ( version 22.0 ; spss inc . , ibm corporation , chicago , il , usa ) . in all tests , a significance level of 0.05 was chosen . to see whether the data were normally distributed , the frequency distribution was plotted in a histogram . to test whether the result from the frequency analyses differed significantly from a normal distribution , kolmogorov the potential effects of imbalances between the study groups on the outcomes of this study were analysed by regression analysis . as no such effects were observed , differences between study groups were tested with an independent student 's ttest and between evaluation periods were tested with a paired student 's ttest . two patients died during the followup period ( one patient in the four implants group before the 1year evaluation and one patient in the six implants group between the 1year and 5year evaluation ) . two patients of the six implants group did not attend the 5year evaluation because of severe illness . no implants failed in the four implants group , while one implant in the six implants group was lost during the osseointegration period . because a barsupported overdenture could still be made on the remaining five implants , there was no need to replace the implant . fiveyears ' survival rate of implants was 100% in the four implants group , 99.2% in the six implants group . baseline characteristics ( at placement of overdenture ) of the groups with four implants ( four implants group ) and six implants ( six implants group ) differences between study groups were tested with the independent student 's ttest ( p < 0.05 ) . the mean loss of marginal bone between baseline ( placement of the overdenture ) and the 5year evaluation was 0.50 0.37 mm in the four implants group and 0.52 0.43 mm in the six implants group ( p > 0.05 , table 2 ) . mean scores of the indices for plaque , calculus , gingiva and bleeding were very low at all evaluation periods and did not differ between the groups . also no timedependent significant changes in probing depth were observed between the groups ( p > 0.05 , table 3 ) . patientlevel incidence of periimplant mucositis was 41.7% and 45.5% , and of periimplantitis was 8.3% and 4.5% in the four and six implants groups respectively . mean values and standard deviations of marginal bone loss in mm , and frequency distribution of bone loss 1 and 5 years after placement of the overdenture of the four and six implants groups . mean marginal bone loss did not differ significantly between the groups differences between study groups were tested with the independent student 's ttest ( p < 0.05 ) . mean change from baseline to 1 and 5 years of followup for plaque index , calculus index , gingival index , bleeding index and probing depth . no timedependent significant changes were observed between the groups differences between study groups were tested with the independent student 's ttest ( p < 0.05 ) . in both groups , all scores had improved significantly ( p < 0.05 ) between pretreatment and posttreatment assessments , but the scores did not differ between the groups ( p > 0.05 ) . after 5 years , patients continued to be very satisfied with their overdentures ; the results are rather similar to the 1year data . mean score of 5 scales concerning the denture complaints ( possible range 03 ) , mean scores of chewing ability of soft , tough and hard food ( possible range 02 ) and overall satisfaction score ( possible range 110 ) before , and 1 and 5 years after treatment . no significant differences between the four and six implants group were observed at all evaluation periods differences between study groups were tested with the independent student 's ttest ( p < 0.05 ) . the surgical and prosthetic aftercare during 5 years of followup revealed a small number of events , mostly repair of the denture base or teeth . surgical treatment of periimplantitis was not performed during the 5year followup ( table 5 ) . at the 5year followup evaluation , a number of patients were identified as having periimplant mucositis ( treatment : cleaning and reinstruction ) or periimplantitis ( treatment : cleaning , reinstruction and openflap surgical treatment ) . this study revealed that both four and six dental implants placed in the anterior region of the edentulous maxilla , connected with a bar , form a proper base for the support of an overdenture . in none of the parameters studied , significant differences were observed between the four and six implants group . fiveyears ' survival rate of implants was high in both the four and six implants group . these results are on the high end compared to the implant survival reported in the 5year followup case series of jemt et al . ( 1997 ) and bergendal & engquist ( 1998 ) who used implants with a machined surface ( 5year implants survival 72.479% ) and similar to those reported by mangano et al . the latter studies also used implants with a roughened surface , as in this study . although a study comparing various implant designs was not analysed , apparently implants with a roughened surface perform better than implants with a machined surface in the maxilla . the mean marginal bone loss between baseline ( placement of the overdenture ) and the 5year evaluation was limited in both groups and again comparable to those reported by mangano et al . the very limited marginal bone loss might be due to the neck design of the implants used ( hermann et al . mean indices for plaque , calculus , gingiva and bleeding were very low at the 5year evaluation and probing depth was not deviating . there might be some extra effort in performing hygiene tasks with six implants , but this does not result in worse results . incidence of periimplantitis after 5 years was 8.3% and 4.5% in the four and six implants groups respectively . because there was no significant change in pocket probing depth at an earlier stage , no extra radiographs were made . nevertheless , bone loss as a sign of periimplantitis could not be reliably excluded in some patients before the 5year evaluation period . in a systematic review of de waal et al . ( 2013 ) , it was reported that numbers of prevalence of periimplant mucositis and periimplantitis with standardized threshold levels are missing in studies with fully edentulous patients . in this study , the patientlevel incidence of periimplant mucositis was 41.7% and of periimplantitis was 8.3% in the four implants group . in the six implants group , patientlevel incidence of periimplant mucositis was 45.5% and of periimplantitis was 4.5% . also in fully edentulous patients , but for mandibular overdentures , 51.9% periimplant mucositis and 16.9% periimplantitis was reported after 5 years ( meijer et al . existing studies have demonstrated clearly that edentulism per se is no protection from periimplant disease and that continuous supportive care is essential in maintaining periimplant health . patients ' satisfaction improved significantly when wearing implantsupported maxillary overdentures and results were shown to be favourable at both the 1 and 5year evaluation , again in agreement with data reported by krennmair et al . ( 2008 ) also mentioned in their case series that patients with an overdenture on four or six implants in the anterior maxilla were equally satisfied . in other words , patients ' satisfaction seemed to be irrespective of whether the bar was supported by four or six implants in the anterior maxillary region . the high satisfaction might be due to the fact that the overdenture is supported by a bar , which gives a comparable stability for both treatment options . the idea that six implants gives more stability than four implants , and resulting in more patients ' satisfaction , turned out to be not true . probably because four and six implants are more or less placed in the same area and the fact that the length of the bar is the same in both designs . the high satisfaction with maxillary overdentures , including opinions on speech , resemble the results of heydecke et al . ( 2004 ) in which favourable results of an overdenture were displayed compared with a fixed implant prosthesis . ( 2011 ) reported that the majority of complications were related to the weakness of the anchorage components connecting bar and overdenture . this is in contrast with this study in which no clip repairs were recorded . in this study , an overdenture with builtin cobalt chromium reinforcement structure and gold retentive clips attached to it were used , which probably led to a minimum of prosthetic complications ( slot et al . rotational panoramic radiographs , lateral cephalograms and posteroanterior oblique radiographs were made to assess bone volume and possible pathology . nowadays , in terms of radiation protection and diagnostic possibilities , cone beam computer tomography is preferred . in the study , some studies reveal that periimplant hygiene of solitary attachment systems are superior compared with bar attachment systems ( zou et al . longterm studies on comparison of attachment systems would be advantageous . from this 5year followup study , it was concluded that barconnected maxillary overdentures on four or six implants resulted in a comparable treatment outcome with high implant survival , limited loss of periimplant marginal bone and high patient satisfaction .[/INST]abstractobjectiveto compare a four and siximplant maxillary overdenture after an observation period of 5 years.material and methodsfifty subjects with functional problems concerning their maxillary denture , who had ample bone volume in the anterior region to place four or six implants , were included and randomly assigned to either group . implant and overdenture survival , clinical performance , marginal bone loss and patient satisfaction were assessed.resultsfortysix patients completed the 5year followup . one implant failed in the six implants group ( 99.2% survival ) and none in the four implants group ( 100% survival ) . no overdentures had to be replaced during the observation period and the number of complications was limited . clinical function was good , with no difference in clinical parameters between the groups . mean marginal bone resorption was 0.50 0.37 and 0.52 0.43 mm in the four and six implant group respectively.conclusionin patients with functional complaints of their maxillary denture , barsupported overdentures on four implants in the anterior maxillary region were not inferior to overdentures supported by six implants after 5 years of function . implant survival and patient satisfaction were high , clinical parameters favourable , bone loss and complications to the denture were minor in both groups ( clinical trial registration number : ntr2969 ) .</s>

resins are the most commonly used material in dentistry due to their satisfactory results.1,2 in human mouth dentures as an indwelling medical device , prepare an optimal environment for adhesion and multiplication of both pathogenic and non - pathogenic organisms . the wide use of removable dentures has caused a sharp increase in denture - related soft tissue infections.3,4 the rate at which deposits accumulate on dentures may vary between individuals and can be affected by factors such as saliva composition , dietary intake , surface texture , and porosity of the denture base material , duration for which the dentures are worn , and the denture - cleansing regimen adopted by the wearer . management of these denture - related infections is challenging , and infected dentures generally need to be cleaned and disinfected . the best disinfectant should fulfill most of the requirements of the ideal agent will not cause any kind of alteration in the structural and mechanical properties the denture.5,6 the combination of mechanical and chemical methods seems to be the best choice for denture cleaning.1,7 - 9 in choosing a disinfectant for dental prostheses , one should be aware of possible adverse effect of the disinfecting material . in the oral cavity , moisture contamination and thermal variation facilitate the absorption of water.9,10 absorbed water can act as a plasticizer and affect the mechanical properties of the material causing reduction in the hardness of the denture.1 hence , the possible effect of water absorption and thermal cycling on the hardness of the acrylic resin surface also must be considered . absorption of water is markedly increased at high temperatures , which causes the acrylic surface to be supersaturated with water during cooling of the specimen . the water absorption and thermal effects may combine to cause the acrylic to form zones with different optical properties . this phenomenon is distinct from crazing of acrylic , where definite cracking occurs.11 it has been shown that when patients use hot water with alkaline peroxide tablets to clean their acrylic dentures , the dentures take on a bleached appearance as these cleansers contain alkaline detergents and oxygen releasing compounds ( such as sodium perborate or percarbonate).12,13 due to an extensive surface degradation of the acrylic , there is a marked reduction in the physical properties like hardness of the acrylic resulting from the plasticizing effect of absorbed water.11 though various studies have proved that denture cleansers cause color changes and alterations in the physical properties of acrylic resins , however , few studies have investigated the influence on mechanical properties of acrylic denture base surfaces . furthermore , there is a lack of literature regarding the long - term effect of denture cleansers used with water at high temperature on the mechanical properties of the acrylic resin . therefore , this in vitro study was undertaken to assess the difference in the hardness of heat - cure acrylic resin immersed in water at different temperatures along with dispersed disinfectant tablet . the present study was undertaken to fulfill the following objectives : to determine and compare the long - term effect of the water bath with alkaline peroxide denture cleanser tablet on the surface hardness of acrylic denture base after thermocycling at two different temperatures.to compare the long - term effect of the water bath with alkaline peroxide denture cleanser on the color changes of acrylic denture base after thermocycling at two different temperatures . to determine and compare the long - term effect of the water bath with alkaline peroxide denture cleanser tablet on the surface hardness of acrylic denture base after thermocycling at two different temperatures . to compare the long - term effect of the water bath with alkaline peroxide denture cleanser on the color changes of acrylic denture base after thermocycling at two different temperatures . the present study was undertaken to fulfill the following objectives : to determine and compare the long - term effect of the water bath with alkaline peroxide denture cleanser tablet on the surface hardness of acrylic denture base after thermocycling at two different temperatures.to compare the long - term effect of the water bath with alkaline peroxide denture cleanser on the color changes of acrylic denture base after thermocycling at two different temperatures . to determine and compare the long - term effect of the water bath with alkaline peroxide denture cleanser tablet on the surface hardness of acrylic denture base after thermocycling at two different temperatures . to compare the long - term effect of the water bath with alkaline peroxide denture cleanser on the color changes of acrylic denture base after thermocycling at two different temperatures . a total of 40 heat cure acrylic ( lucitone 199-dentspl trubyte - newyork ) samples of the dimension 10 mm 10 mm 2.5 mm were fabricated to test the effects of water immersion and heat on surface hardness . all the samples are of a standard thickness of 2.5 mm to mimic the clinical conditions . the standard length and width of 10 mm were kept according to the specifications for testing on the rockwell hardness tester ( model rasn , fuel instruments and engineers pvt . ltd ) . to achieve acrylic samples of standardized dimensions ten customized stainless steel metal dies of dimension 10 mm 10 mm this was done to ensure that all acrylic resin samples had same dimensions ( figure 1 ) . fabrication of stainless steel dies the lower member of the universal dental flask was filled with dental stone , and all the 10 dies were placed on the wet stone maintaining enough distance between each other . after setting of the stone , a thin layer of petroleum jelly was applied all over the set plaster as well as the dies . the counter of the flask was then poured with dental stone under vibration and finally the lid was placed over the counter and the entire assembly was secured using a dental clamp . after the dental stone had set according to manufactures instructions plus 10 - 15 min , the flask was opened , and the dies were gently teased out . the mold spaces thus created were packed with conventional heat - cure acrylic resin lucitone 199 ( dentsply trubyte)using a mixture of monomer and polymer in the ratio of 21 g ( 32 cc)/10 ml by weight . the trial closures were carried out using the hydropress and cellophane sheets until no flash was obtained . india ) using a long curing cycle of 9 h at 73c and a half hour of terminal boiling temperature at 100c . to avoid distortions , then immersed in cool water ( 16 - 27c ) for 15 min before deflasking . after deflasking the samples were recovered , and excess acrylic in all of the samples was trimmed away using a tungsten carbide bur . the samples were then subsequently finished using 200 grit sand papers 79 mounted on a mandrill , with a micromotor at 2000 rpm for 2 min ( figure 2 ) . surface hardness measurements were made for all samples with a digital rockwell hardness tester ( [ model rasn ] , manufactured by fuel instruments and engineers pvt . ltd . ) . rockwell hardness tests consist of forcing an indentor ( ball)into the surface of a test piece with two loads ( figure 3 ) . all the samples were first numbered from 1 to 40 before subjecting them to the hardness test . a inch diameter ball indenter and with a load of 60 kg force was used for testing . 23 indentation hardness number was calculated for each sample , and the values generated were tabulated thus forming the control group . preparation of samples for experimental group a and group b : after the calculation of the rockwell hardness of the 40 samples , they were divided into two groups of 20 samples each . experimental group a : 20 samples ( sample no . 1 to sample no . 20 ) experimental group b : 20 samples ( sample no . 21 to sample no . 40 ) group a samples were immersed in 250 ml of warm deionized distilled water at 40c . alkaline peroxide ( clanden tablet 85 dent aids - new delhi , india ) used for cleaning dentures the water in the bath was changed after every 24 h , and fresh water at 40c was poured in with fresh clanden tablet . group b samples were immersed in 250 ml of hot deionized distilled water at 100c . alkaline peroxide ( clanden tablet 85)used for cleaning dentures the water in the bath was changed after every 24 h , and fresh water at 100c was poured in with fresh clanden tablet . all the samples from group a and b were evaluated for surface hardness after the completion of 30 soak cycles using rock well hardness tester ( modle rasn ) values . the pre and post hardness valve of group a and group b are shown in tables 1 and 2 . pre and post rockwell hardness number for group a. pre and post rockwell hardness number for group b. five samples from the experimental group a ( immersed in warm water ) and five samples from the experimental group b ( immersed in hot water ) were selected randomly and were put side by side and photographed using a camera:(nikon d 40 digital slr camera with attached close - up lenses 1 , 2 , 3 . the lower member of the universal dental flask was filled with dental stone , and all the 10 dies were placed on the wet stone maintaining enough distance between each other . after setting of the stone , a thin layer of petroleum jelly was applied all over the set plaster as well as the dies . the counter of the flask was then poured with dental stone under vibration and finally the lid was placed over the counter and the entire assembly was secured using a dental clamp . after the dental stone had set according to manufactures instructions plus 10 - 15 min , the flask was opened , and the dies were gently teased out . the mold spaces thus created were packed with conventional heat - cure acrylic resin lucitone 199 ( dentsply trubyte)using a mixture of monomer and polymer in the ratio of 21 g ( 32 cc)/10 ml by weight . the trial closures were carried out using the hydropress and cellophane sheets until no flash was obtained . india ) using a long curing cycle of 9 h at 73c and a half hour of terminal boiling temperature at 100c . to avoid distortions , then immersed in cool water ( 16 - 27c ) for 15 min before deflasking . after deflasking the samples were recovered , and excess acrylic in all of the samples was trimmed away using a tungsten carbide bur . the samples were then subsequently finished using 200 grit sand papers 79 mounted on a mandrill , with a micromotor at 2000 rpm for 2 min ( figure 2 ) . surface hardness measurements were made for all samples with a digital rockwell hardness tester ( [ model rasn ] , manufactured by fuel instruments and engineers pvt . ltd . ) . rockwell hardness tests consist of forcing an indentor ( ball)into the surface of a test piece with two loads ( figure 3 ) . all the samples were first numbered from 1 to 40 before subjecting them to the hardness test . a inch diameter ball indenter and with a load of 60 kg force was used for testing . 23 indentation hardness number was calculated for each sample , and the values generated were tabulated thus forming the control group . preparation of samples for experimental group a and group b : after the calculation of the rockwell hardness of the 40 samples , they were divided into two groups of 20 samples each . experimental group a : 20 samples ( sample no . 1 to sample no . 20 ) experimental group b : 20 samples ( sample no . 21 to sample no . 40 ) group a samples were immersed in 250 ml of warm deionized distilled water at 40c . alkaline peroxide ( clanden tablet 85 dent aids - new delhi , india ) used for cleaning dentures was also added to this water bath . the water in the bath was changed after every 24 h , and fresh water at 40c was poured in with fresh clanden tablet . group b samples were immersed in 250 ml of hot deionized distilled water at 100c . alkaline peroxide ( clanden tablet 85)used for cleaning dentures the water in the bath was changed after every 24 h , and fresh water at 100c was poured in with fresh clanden tablet . all the samples from group a and b were evaluated for surface hardness after the completion of 30 soak cycles using rock well hardness tester ( modle rasn ) values . the pre and post hardness valve of group a and group b are shown in tables 1 and 2 . pre and post rockwell hardness number for group a. pre and post rockwell hardness number for group b. five samples from the experimental group a ( immersed in warm water ) and five samples from the experimental group b ( immersed in hot water ) were selected randomly and were put side by side and photographed using a camera:(nikon d 40 digital slr camera with attached close - up lenses 1 , 2 , 3 . % change in mean hardness = mean ( post rhn data) mean ( pre rhn data) 100/mean value ( pre rhn data ) it is observed that the mean reduction in hardness of the acrylic specimens the treatment of samples in warm water ( 40c ) , samples 1 - 20 , on the other hand , showed a slight increase in hardness , which was 0.67% . for the experimental group a , the difference in mean is 7.57 with a t - value of 1.17 . however , since the probability is 0.258 ( > 0.05 ) , the results are not statistically significant . for the experimental group b , during clinical use , denture base resin materials in the oral cavity are exposed to thermal changes and saliva , therefore during denture storage they are soaked in water or an aqueous cleansing solution . as a result of this immersion , water or saliva may be absorbed by the denture base resins.14 acrylic denture bases absorb relatively small amounts of water when placed in an aqueous environment . this water exerts a significant effect on the mechanical and dimensional properties of the polymer . although the absorption is facilitated by the polarity of polymethyl methacrylate molecules , a diffusion mechanism is primarily responsible for the ingress of water . second , water molecules interfere with the entanglement of polymer chains and thereby act as plasticizers.15,16 this water absorption along with the change in temperature of the environment in which the denture base is may cause degradation of the denture polymers.17 mechanical properties of the acrylic resin are affected by the heat and water sorption due to the changes in polymer chains which in turn soften the denture.1,8 on the other hand some studies showed a gradual increase in surface hardness of some denture base resins after water immersion.14 this improvement in the hardness property has been attributed in part to leaching of the residual monomer from the resin as the residual monomer may adversely affect the mechanical properties of denture base resins by having a plasticizing effect.17 this rate of diffusion of monomer out of the resin into water decreases progressively.14 a routine denture cleaning regimen which includes the mechanical and chemical cleansing is also a very important part of the denture use and maintenance to remove and prevent reaccumulation of microbial plaque and also to remove mucin , food debris , calculus , and exogenous discoloration . alkaline peroxides cleansers which are used in this study when dissolved in water converts into hydrogen peroxide reduces the surface tension , and effervescent oxygen helps in mechanical cleaning which are more effective over a long period of immersion . according to some studies , prolonged immersion of heat or chemically cured acrylic resin in peroxide cleansers did not affect the surface of the acrylic resins . according to some studies , prolonged immersion of heat or chemically cured however , when these alkaline are regularly used may change the color of the denture due their bleaching action.12,18 conversely there are some other studies which state that the major factor responsible for whitening is a high temperature of water in which the dentures are soaked , irrespective of the presence of the denture cleaning agent.17,19 previous studies have measured hardness using a variety of shaped indentors ( e.g. , rockwell and vickers hardness measurement systems ) and loading conditions subjecting the acrylic samples to thermal cycling at different temperatures.11,14,20 there have also been a lot of studies regarding the effect of different denture cleansers on the mechanical properties of the acrylic surfaces.3,6,12,21 - 23 in this study it has been observed that when the acrylic samples were repeatedly immersed in hot water at 100c along with alkaline peroxide denture cleanser tablet for a period of 30 days there was a significant reduction of 5.8% in the surface hardness of acrylic and a slight increase of 0.67% in the surface hardness when immersed in warm water at 40c . these results are in correlation with the results of similar studies conducted earlier by devlin and kaushik11 and goiato et al.24 color changes are measured objectively using a spectrophotometer where the standardization can not be achieved . this study concludes that the hot alkaline peroxide solution caused a water supersaturation of the acrylic surface , resulted in a clinically insignificant surface whitening of acrylic . study done by unl et al.12 found that clinically significant whitening effect of regular use of denture cleansers is seen on auto polymerized acrylic resin and not on the heat polymerized resin denture bases . but studies conducted by goiato et al.24 and polyzois et al.25 have found clinically significant changes in the gloss and color of denture base acrylic after long - term immersion in disinfectant . the resemblance between the whitening of acrylic due to long - term water immersion and crazing is , at present , poorly understood . solvents such as chloroform readily cause crazing of acrylic but not whitening or opacity of the surface . high residual monomer content does affect the mechanical properties of acrylic by acting as a plasticizer , but there is no evidence that it contributes to whitening of the acrylic surface.11,26,27 hence , the possible effect of thermal cycling and denture cleansers on the acrylic resins may influence the performance of the acrylic prostheses.1 acrylic samples immersed in hot water showed a small but statistically significant decrease of 5.8% in surface hardness.acrylic samples immersed in warm water showed a slight but statistically insignificant increase of 0.67% in surface hardness.samples immersed in hot water showed clinically insignificant color change when compared to samples immersed in warm water on examination of the photographs . acrylic samples immersed in hot water showed a small but statistically significant decrease of 5.8% in surface hardness . acrylic samples immersed in warm water showed a slight but statistically insignificant increase of 0.67% in surface hardness . samples immersed in hot water showed clinically insignificant color change when compared to samples immersed in warm water on examination of the photographs .

background : use of alkaline peroxide denture cleanser with different temperature of water could cause a change in surface hardness of the acrylic denture and also has a bleaching effect . the purpose of the study was to determine the effect of increased water content during thermal cycling of hot water - treated acrylic on the surface hardness of acrylic denture base when compared to warm water treated acrylic . and to compare the bleaching effect of alkaline peroxide solution on the acrylic denture base on hot water and warm water treated acrylic.materials and methods : forty samples ( 10 mm 10 mm 2.5 mm ) were prepared . after the calculation of the initial hardness 40 samples , each was randomly assigned to two groups . group a : 20 samples were immersed in 250 ml of warm distilled water at 40c with alkaline peroxide tablet . group b : 20 samples were immersed in 250 ml of hot distilled water at 100c with alkaline peroxide tablet . the surface hardness of each test sample was obtained using the digital hardness testing machine recording the rockwell hardness number before the beginning of the soaking cycles and after completion of 30 soak cycles and compared . values were analyzed using paired t - test . five samples from the group a and five samples from group b were put side by side and photographed using a nikon d 40 digital slr camera and the photographs were examined visually to assess the change in color.results:acrylic samples immersed in hot water showed a statistically significant decrease of 5.8% in surface hardness . and those immersed in warm water showed a statistically insignificant increase of 0.67% in surface hardness . samples from the two groups showed clinically insignificant difference in color when compared to each other on examination of the photographs.conclusion:thermocycling of the acrylic resin at different water bath temperature at 40c and 100c showed significant changes in the surface hardness .

<s>[INST]resins are the most commonly used material in dentistry due to their satisfactory results.1,2 in human mouth dentures as an indwelling medical device , prepare an optimal environment for adhesion and multiplication of both pathogenic and non - pathogenic organisms . the wide use of removable dentures has caused a sharp increase in denture - related soft tissue infections.3,4 the rate at which deposits accumulate on dentures may vary between individuals and can be affected by factors such as saliva composition , dietary intake , surface texture , and porosity of the denture base material , duration for which the dentures are worn , and the denture - cleansing regimen adopted by the wearer . management of these denture - related infections is challenging , and infected dentures generally need to be cleaned and disinfected . the best disinfectant should fulfill most of the requirements of the ideal agent will not cause any kind of alteration in the structural and mechanical properties the denture.5,6 the combination of mechanical and chemical methods seems to be the best choice for denture cleaning.1,7 - 9 in choosing a disinfectant for dental prostheses , one should be aware of possible adverse effect of the disinfecting material . in the oral cavity , moisture contamination and thermal variation facilitate the absorption of water.9,10 absorbed water can act as a plasticizer and affect the mechanical properties of the material causing reduction in the hardness of the denture.1 hence , the possible effect of water absorption and thermal cycling on the hardness of the acrylic resin surface also must be considered . absorption of water is markedly increased at high temperatures , which causes the acrylic surface to be supersaturated with water during cooling of the specimen . the water absorption and thermal effects may combine to cause the acrylic to form zones with different optical properties . this phenomenon is distinct from crazing of acrylic , where definite cracking occurs.11 it has been shown that when patients use hot water with alkaline peroxide tablets to clean their acrylic dentures , the dentures take on a bleached appearance as these cleansers contain alkaline detergents and oxygen releasing compounds ( such as sodium perborate or percarbonate).12,13 due to an extensive surface degradation of the acrylic , there is a marked reduction in the physical properties like hardness of the acrylic resulting from the plasticizing effect of absorbed water.11 though various studies have proved that denture cleansers cause color changes and alterations in the physical properties of acrylic resins , however , few studies have investigated the influence on mechanical properties of acrylic denture base surfaces . furthermore , there is a lack of literature regarding the long - term effect of denture cleansers used with water at high temperature on the mechanical properties of the acrylic resin . therefore , this in vitro study was undertaken to assess the difference in the hardness of heat - cure acrylic resin immersed in water at different temperatures along with dispersed disinfectant tablet . the present study was undertaken to fulfill the following objectives : to determine and compare the long - term effect of the water bath with alkaline peroxide denture cleanser tablet on the surface hardness of acrylic denture base after thermocycling at two different temperatures.to compare the long - term effect of the water bath with alkaline peroxide denture cleanser on the color changes of acrylic denture base after thermocycling at two different temperatures . to determine and compare the long - term effect of the water bath with alkaline peroxide denture cleanser tablet on the surface hardness of acrylic denture base after thermocycling at two different temperatures . to compare the long - term effect of the water bath with alkaline peroxide denture cleanser on the color changes of acrylic denture base after thermocycling at two different temperatures . the present study was undertaken to fulfill the following objectives : to determine and compare the long - term effect of the water bath with alkaline peroxide denture cleanser tablet on the surface hardness of acrylic denture base after thermocycling at two different temperatures.to compare the long - term effect of the water bath with alkaline peroxide denture cleanser on the color changes of acrylic denture base after thermocycling at two different temperatures . to determine and compare the long - term effect of the water bath with alkaline peroxide denture cleanser tablet on the surface hardness of acrylic denture base after thermocycling at two different temperatures . to compare the long - term effect of the water bath with alkaline peroxide denture cleanser on the color changes of acrylic denture base after thermocycling at two different temperatures . a total of 40 heat cure acrylic ( lucitone 199-dentspl trubyte - newyork ) samples of the dimension 10 mm 10 mm 2.5 mm were fabricated to test the effects of water immersion and heat on surface hardness . all the samples are of a standard thickness of 2.5 mm to mimic the clinical conditions . the standard length and width of 10 mm were kept according to the specifications for testing on the rockwell hardness tester ( model rasn , fuel instruments and engineers pvt . ltd ) . to achieve acrylic samples of standardized dimensions ten customized stainless steel metal dies of dimension 10 mm 10 mm this was done to ensure that all acrylic resin samples had same dimensions ( figure 1 ) . fabrication of stainless steel dies the lower member of the universal dental flask was filled with dental stone , and all the 10 dies were placed on the wet stone maintaining enough distance between each other . after setting of the stone , a thin layer of petroleum jelly was applied all over the set plaster as well as the dies . the counter of the flask was then poured with dental stone under vibration and finally the lid was placed over the counter and the entire assembly was secured using a dental clamp . after the dental stone had set according to manufactures instructions plus 10 - 15 min , the flask was opened , and the dies were gently teased out . the mold spaces thus created were packed with conventional heat - cure acrylic resin lucitone 199 ( dentsply trubyte)using a mixture of monomer and polymer in the ratio of 21 g ( 32 cc)/10 ml by weight . the trial closures were carried out using the hydropress and cellophane sheets until no flash was obtained . india ) using a long curing cycle of 9 h at 73c and a half hour of terminal boiling temperature at 100c . to avoid distortions , then immersed in cool water ( 16 - 27c ) for 15 min before deflasking . after deflasking the samples were recovered , and excess acrylic in all of the samples was trimmed away using a tungsten carbide bur . the samples were then subsequently finished using 200 grit sand papers 79 mounted on a mandrill , with a micromotor at 2000 rpm for 2 min ( figure 2 ) . surface hardness measurements were made for all samples with a digital rockwell hardness tester ( [ model rasn ] , manufactured by fuel instruments and engineers pvt . ltd . ) . rockwell hardness tests consist of forcing an indentor ( ball)into the surface of a test piece with two loads ( figure 3 ) . all the samples were first numbered from 1 to 40 before subjecting them to the hardness test . a inch diameter ball indenter and with a load of 60 kg force was used for testing . 23 indentation hardness number was calculated for each sample , and the values generated were tabulated thus forming the control group . preparation of samples for experimental group a and group b : after the calculation of the rockwell hardness of the 40 samples , they were divided into two groups of 20 samples each . experimental group a : 20 samples ( sample no . 1 to sample no . 20 ) experimental group b : 20 samples ( sample no . 21 to sample no . 40 ) group a samples were immersed in 250 ml of warm deionized distilled water at 40c . alkaline peroxide ( clanden tablet 85 dent aids - new delhi , india ) used for cleaning dentures the water in the bath was changed after every 24 h , and fresh water at 40c was poured in with fresh clanden tablet . group b samples were immersed in 250 ml of hot deionized distilled water at 100c . alkaline peroxide ( clanden tablet 85)used for cleaning dentures the water in the bath was changed after every 24 h , and fresh water at 100c was poured in with fresh clanden tablet . all the samples from group a and b were evaluated for surface hardness after the completion of 30 soak cycles using rock well hardness tester ( modle rasn ) values . the pre and post hardness valve of group a and group b are shown in tables 1 and 2 . pre and post rockwell hardness number for group a. pre and post rockwell hardness number for group b. five samples from the experimental group a ( immersed in warm water ) and five samples from the experimental group b ( immersed in hot water ) were selected randomly and were put side by side and photographed using a camera:(nikon d 40 digital slr camera with attached close - up lenses 1 , 2 , 3 . the lower member of the universal dental flask was filled with dental stone , and all the 10 dies were placed on the wet stone maintaining enough distance between each other . after setting of the stone , a thin layer of petroleum jelly was applied all over the set plaster as well as the dies . the counter of the flask was then poured with dental stone under vibration and finally the lid was placed over the counter and the entire assembly was secured using a dental clamp . after the dental stone had set according to manufactures instructions plus 10 - 15 min , the flask was opened , and the dies were gently teased out . the mold spaces thus created were packed with conventional heat - cure acrylic resin lucitone 199 ( dentsply trubyte)using a mixture of monomer and polymer in the ratio of 21 g ( 32 cc)/10 ml by weight . the trial closures were carried out using the hydropress and cellophane sheets until no flash was obtained . india ) using a long curing cycle of 9 h at 73c and a half hour of terminal boiling temperature at 100c . to avoid distortions , then immersed in cool water ( 16 - 27c ) for 15 min before deflasking . after deflasking the samples were recovered , and excess acrylic in all of the samples was trimmed away using a tungsten carbide bur . the samples were then subsequently finished using 200 grit sand papers 79 mounted on a mandrill , with a micromotor at 2000 rpm for 2 min ( figure 2 ) . surface hardness measurements were made for all samples with a digital rockwell hardness tester ( [ model rasn ] , manufactured by fuel instruments and engineers pvt . ltd . ) . rockwell hardness tests consist of forcing an indentor ( ball)into the surface of a test piece with two loads ( figure 3 ) . all the samples were first numbered from 1 to 40 before subjecting them to the hardness test . a inch diameter ball indenter and with a load of 60 kg force was used for testing . 23 indentation hardness number was calculated for each sample , and the values generated were tabulated thus forming the control group . preparation of samples for experimental group a and group b : after the calculation of the rockwell hardness of the 40 samples , they were divided into two groups of 20 samples each . experimental group a : 20 samples ( sample no . 1 to sample no . 20 ) experimental group b : 20 samples ( sample no . 21 to sample no . 40 ) group a samples were immersed in 250 ml of warm deionized distilled water at 40c . alkaline peroxide ( clanden tablet 85 dent aids - new delhi , india ) used for cleaning dentures was also added to this water bath . the water in the bath was changed after every 24 h , and fresh water at 40c was poured in with fresh clanden tablet . group b samples were immersed in 250 ml of hot deionized distilled water at 100c . alkaline peroxide ( clanden tablet 85)used for cleaning dentures the water in the bath was changed after every 24 h , and fresh water at 100c was poured in with fresh clanden tablet . all the samples from group a and b were evaluated for surface hardness after the completion of 30 soak cycles using rock well hardness tester ( modle rasn ) values . the pre and post hardness valve of group a and group b are shown in tables 1 and 2 . pre and post rockwell hardness number for group a. pre and post rockwell hardness number for group b. five samples from the experimental group a ( immersed in warm water ) and five samples from the experimental group b ( immersed in hot water ) were selected randomly and were put side by side and photographed using a camera:(nikon d 40 digital slr camera with attached close - up lenses 1 , 2 , 3 . % change in mean hardness = mean ( post rhn data) mean ( pre rhn data) 100/mean value ( pre rhn data ) it is observed that the mean reduction in hardness of the acrylic specimens the treatment of samples in warm water ( 40c ) , samples 1 - 20 , on the other hand , showed a slight increase in hardness , which was 0.67% . for the experimental group a , the difference in mean is 7.57 with a t - value of 1.17 . however , since the probability is 0.258 ( > 0.05 ) , the results are not statistically significant . for the experimental group b , during clinical use , denture base resin materials in the oral cavity are exposed to thermal changes and saliva , therefore during denture storage they are soaked in water or an aqueous cleansing solution . as a result of this immersion , water or saliva may be absorbed by the denture base resins.14 acrylic denture bases absorb relatively small amounts of water when placed in an aqueous environment . this water exerts a significant effect on the mechanical and dimensional properties of the polymer . although the absorption is facilitated by the polarity of polymethyl methacrylate molecules , a diffusion mechanism is primarily responsible for the ingress of water . second , water molecules interfere with the entanglement of polymer chains and thereby act as plasticizers.15,16 this water absorption along with the change in temperature of the environment in which the denture base is may cause degradation of the denture polymers.17 mechanical properties of the acrylic resin are affected by the heat and water sorption due to the changes in polymer chains which in turn soften the denture.1,8 on the other hand some studies showed a gradual increase in surface hardness of some denture base resins after water immersion.14 this improvement in the hardness property has been attributed in part to leaching of the residual monomer from the resin as the residual monomer may adversely affect the mechanical properties of denture base resins by having a plasticizing effect.17 this rate of diffusion of monomer out of the resin into water decreases progressively.14 a routine denture cleaning regimen which includes the mechanical and chemical cleansing is also a very important part of the denture use and maintenance to remove and prevent reaccumulation of microbial plaque and also to remove mucin , food debris , calculus , and exogenous discoloration . alkaline peroxides cleansers which are used in this study when dissolved in water converts into hydrogen peroxide reduces the surface tension , and effervescent oxygen helps in mechanical cleaning which are more effective over a long period of immersion . according to some studies , prolonged immersion of heat or chemically cured acrylic resin in peroxide cleansers did not affect the surface of the acrylic resins . according to some studies , prolonged immersion of heat or chemically cured however , when these alkaline are regularly used may change the color of the denture due their bleaching action.12,18 conversely there are some other studies which state that the major factor responsible for whitening is a high temperature of water in which the dentures are soaked , irrespective of the presence of the denture cleaning agent.17,19 previous studies have measured hardness using a variety of shaped indentors ( e.g. , rockwell and vickers hardness measurement systems ) and loading conditions subjecting the acrylic samples to thermal cycling at different temperatures.11,14,20 there have also been a lot of studies regarding the effect of different denture cleansers on the mechanical properties of the acrylic surfaces.3,6,12,21 - 23 in this study it has been observed that when the acrylic samples were repeatedly immersed in hot water at 100c along with alkaline peroxide denture cleanser tablet for a period of 30 days there was a significant reduction of 5.8% in the surface hardness of acrylic and a slight increase of 0.67% in the surface hardness when immersed in warm water at 40c . these results are in correlation with the results of similar studies conducted earlier by devlin and kaushik11 and goiato et al.24 color changes are measured objectively using a spectrophotometer where the standardization can not be achieved . this study concludes that the hot alkaline peroxide solution caused a water supersaturation of the acrylic surface , resulted in a clinically insignificant surface whitening of acrylic . study done by unl et al.12 found that clinically significant whitening effect of regular use of denture cleansers is seen on auto polymerized acrylic resin and not on the heat polymerized resin denture bases . but studies conducted by goiato et al.24 and polyzois et al.25 have found clinically significant changes in the gloss and color of denture base acrylic after long - term immersion in disinfectant . the resemblance between the whitening of acrylic due to long - term water immersion and crazing is , at present , poorly understood . solvents such as chloroform readily cause crazing of acrylic but not whitening or opacity of the surface . high residual monomer content does affect the mechanical properties of acrylic by acting as a plasticizer , but there is no evidence that it contributes to whitening of the acrylic surface.11,26,27 hence , the possible effect of thermal cycling and denture cleansers on the acrylic resins may influence the performance of the acrylic prostheses.1 acrylic samples immersed in hot water showed a small but statistically significant decrease of 5.8% in surface hardness.acrylic samples immersed in warm water showed a slight but statistically insignificant increase of 0.67% in surface hardness.samples immersed in hot water showed clinically insignificant color change when compared to samples immersed in warm water on examination of the photographs . acrylic samples immersed in hot water showed a small but statistically significant decrease of 5.8% in surface hardness . acrylic samples immersed in warm water showed a slight but statistically insignificant increase of 0.67% in surface hardness . samples immersed in hot water showed clinically insignificant color change when compared to samples immersed in warm water on examination of the photographs .[/INST]background : use of alkaline peroxide denture cleanser with different temperature of water could cause a change in surface hardness of the acrylic denture and also has a bleaching effect . the purpose of the study was to determine the effect of increased water content during thermal cycling of hot water - treated acrylic on the surface hardness of acrylic denture base when compared to warm water treated acrylic . and to compare the bleaching effect of alkaline peroxide solution on the acrylic denture base on hot water and warm water treated acrylic.materials and methods : forty samples ( 10 mm 10 mm 2.5 mm ) were prepared . after the calculation of the initial hardness 40 samples , each was randomly assigned to two groups . group a : 20 samples were immersed in 250 ml of warm distilled water at 40c with alkaline peroxide tablet . group b : 20 samples were immersed in 250 ml of hot distilled water at 100c with alkaline peroxide tablet . the surface hardness of each test sample was obtained using the digital hardness testing machine recording the rockwell hardness number before the beginning of the soaking cycles and after completion of 30 soak cycles and compared . values were analyzed using paired t - test . five samples from the group a and five samples from group b were put side by side and photographed using a nikon d 40 digital slr camera and the photographs were examined visually to assess the change in color.results:acrylic samples immersed in hot water showed a statistically significant decrease of 5.8% in surface hardness . and those immersed in warm water showed a statistically insignificant increase of 0.67% in surface hardness . samples from the two groups showed clinically insignificant difference in color when compared to each other on examination of the photographs.conclusion:thermocycling of the acrylic resin at different water bath temperature at 40c and 100c showed significant changes in the surface hardness .</s>

Miss Colombia Paulina Vega poses after being named a top 5 finalist, on her way to be crowned as Miss Universe, at the 63rd Annual Miss Universe Pageant in Miami, Florida, January 25, 2015. BOGOTA Colombia's Marxist FARC rebels have invited the newly-crowned Miss Universe Paulina Vega, a native of the country's Caribbean coast, to attend their peace negotiations with the government, a bid to end 50 years of fighting. The 22-year-old Vega, a business student and model from the northern city of Barranquilla, was named Miss Universe in late January and has said in interviews that she would be willing to travel to the talks. "We have read with interest your desire to contribute with your good works to reaching peace," the Revolutionary Armed Forces of Colombia, or FARC, said in a statement on their website late on Friday. "We salute your willingness to travel to Havana, at this time we invite you to make a visit," added the FARC, which has been holding negotiations with the government in Cuba since late 2012. The FARC did not say how Vega's visit would help advance the peace talks. She has yet to respond to the invitation. Representatives at the talks have so far reached agreement on three of five agenda points, including land reform, an end to the illegal drugs trade and political participation for ex-guerrillas. (Reporting by Julia Symmes Cobb; Editing by David Gregorio) ||||| International Colombian Rebels Invite Miss Universe To Join Peace Talks i itoggle caption Wilfredo Lee/AP Wilfredo Lee/AP Future beauty pageant contestants might want to be careful with all that loose talk about "world peace," unless they're willing to put up: after Miss Universe Paulina Vega expressed a desire to help end her native Colombia's 50-year civil war, she received an invitation from FARC rebels to join truce talks. Vega, 22, a business student and model from Colombia's coastal city of Barranquilla, was crowned last month. Since then, she's said in interviews that she would be willing to travel to the negotiations in Havana, according to Reuters. On Friday, the peace delegation of the Marxist Revolutionary Armed Forces of Colombia posted this online: "We have read with interest about your desire to contribute with your good offices to peace and reconciliation of the Colombian people," FARC's delegation to the talks wrote. "We welcome your willingness to travel to Havana and we invite you," the statement said. "Be assured that we are willing to address your concerns and consider your views a valuable contribution to peace; we are waiting for your confirmation and your contribution." The invitation didn't say how Vega might be expected to advance the peace efforts. She did not immediately responded to the offer. Reuters adds: "Representatives at the talks have so far reached agreement on three of five agenda points, including land reform, an end to the illegal drugs trade and political participation for ex-guerrillas."

– Last month, Miss Colombia Paulina Vega was crowned Miss Universe. This month, the guerrilla rebels that have been locked in a bloody fight with her nation's government for a half-century said they would like her to sit down at the negotiating table and end the conflict. As Reuters reports, Vega had said she'd like to attend talks between the two parties in Havana, and on Friday the Revolutionary Armed Forces of Colombia invited her to put her money where her mouth is: "We read with interest about your desire to contribute with your good offices to peace and reconciliation of the Colombian people," FARC said in a message posted online. "We welcome your willingness to travel to Havana and we invite you" to the Havana talks. Further, "Be assured that we are willing to address your concerns and consider your views a valuable contribution to peace." There is as yet no response from Vega, notes NPR. Reuters notes that the two sides have already agreed on three of five points.

<s>[INST]Miss Colombia Paulina Vega poses after being named a top 5 finalist, on her way to be crowned as Miss Universe, at the 63rd Annual Miss Universe Pageant in Miami, Florida, January 25, 2015. BOGOTA Colombia's Marxist FARC rebels have invited the newly-crowned Miss Universe Paulina Vega, a native of the country's Caribbean coast, to attend their peace negotiations with the government, a bid to end 50 years of fighting. The 22-year-old Vega, a business student and model from the northern city of Barranquilla, was named Miss Universe in late January and has said in interviews that she would be willing to travel to the talks. "We have read with interest your desire to contribute with your good works to reaching peace," the Revolutionary Armed Forces of Colombia, or FARC, said in a statement on their website late on Friday. "We salute your willingness to travel to Havana, at this time we invite you to make a visit," added the FARC, which has been holding negotiations with the government in Cuba since late 2012. The FARC did not say how Vega's visit would help advance the peace talks. She has yet to respond to the invitation. Representatives at the talks have so far reached agreement on three of five agenda points, including land reform, an end to the illegal drugs trade and political participation for ex-guerrillas. (Reporting by Julia Symmes Cobb; Editing by David Gregorio) ||||| International Colombian Rebels Invite Miss Universe To Join Peace Talks i itoggle caption Wilfredo Lee/AP Wilfredo Lee/AP Future beauty pageant contestants might want to be careful with all that loose talk about "world peace," unless they're willing to put up: after Miss Universe Paulina Vega expressed a desire to help end her native Colombia's 50-year civil war, she received an invitation from FARC rebels to join truce talks. Vega, 22, a business student and model from Colombia's coastal city of Barranquilla, was crowned last month. Since then, she's said in interviews that she would be willing to travel to the negotiations in Havana, according to Reuters. On Friday, the peace delegation of the Marxist Revolutionary Armed Forces of Colombia posted this online: "We have read with interest about your desire to contribute with your good offices to peace and reconciliation of the Colombian people," FARC's delegation to the talks wrote. "We welcome your willingness to travel to Havana and we invite you," the statement said. "Be assured that we are willing to address your concerns and consider your views a valuable contribution to peace; we are waiting for your confirmation and your contribution." The invitation didn't say how Vega might be expected to advance the peace efforts. She did not immediately responded to the offer. Reuters adds: "Representatives at the talks have so far reached agreement on three of five agenda points, including land reform, an end to the illegal drugs trade and political participation for ex-guerrillas."[/INST]– Last month, Miss Colombia Paulina Vega was crowned Miss Universe. This month, the guerrilla rebels that have been locked in a bloody fight with her nation's government for a half-century said they would like her to sit down at the negotiating table and end the conflict. As Reuters reports, Vega had said she'd like to attend talks between the two parties in Havana, and on Friday the Revolutionary Armed Forces of Colombia invited her to put her money where her mouth is: "We read with interest about your desire to contribute with your good offices to peace and reconciliation of the Colombian people," FARC said in a message posted online. "We welcome your willingness to travel to Havana and we invite you" to the Havana talks. Further, "Be assured that we are willing to address your concerns and consider your views a valuable contribution to peace." There is as yet no response from Vega, notes NPR. Reuters notes that the two sides have already agreed on three of five points.</s>

SECTION 1. SHORT TITLE. This Act may be cited as the ``Digital Divide Elimination Act of 2000''. SEC. 2. CREDIT FOR PURCHASE OF COMPUTERS BY LOW-INCOME INDIVIDUALS. (a) In General.--Subpart C of part IV of subchapter A of chapter 1 of the Internal Revenue Code of 1986 (relating to refundable credits) is amended by redesignating section 35 as section 36 and by inserting after section 34 the following new section: ``SEC. 35. PURCHASE OF COMPUTERS BY LOW-INCOME INDIVIDUALS. ``(a) In General.--In the case of an eligible individual, there shall be allowed as a credit against the tax imposed by this subtitle for the taxable year an amount equal to 50 percent of the amount paid by the taxpayer for qualified computer technology or equipment. ``(b) Dollar Limitation.--The credit allowed by subsection (a) for any taxable year shall not exceed $500. ``(c) Definitions.--For purposes of this section-- ``(1) Eligible individual.--The term `eligible individual' means any taxpayer who is allowed a credit under section 32 (relating to earned income credit) for the taxable year. ``(2) Qualified computer technology or equipment.-- ``(A) In general.--Except as provided in subparagraph (B), the term `qualified computer technology or equipment' means any computer technology or equipment (as defined in section 170(e)(6)) acquired by purchase (as defined in section 170(d)(2)). ``(B) Exceptions.-- ``(i) Certain software excluded.--Such term shall not include game software or any other software which is not necessary for-- ``(I) use of the computer for access and use of the Internet (including email), or ``(II) business or educational use. ``(ii) Computer must be capable of internet access.--Such term shall not include any computer which does not have a modem or other equipment capable of supporting Internet access.'' (b) Conforming Amendments.-- (1) Paragraph (2) of section 1324(b) of title 31, United States Code, is amended by inserting before the period ``, or from section 35 of such Code''. (2) The table of sections for subpart C of part IV of subchapter A of chapter 1 of such Code is amended by striking the last item and inserting the following new items: ``Sec. 35. Purchase of computers by low-income individuals. ``Sec. 36. Overpayments of tax.'' (c) Effective Date.--The amendments made by this section shall apply to taxable years beginning after the date of the enactment of this Act. SEC. 3. EXTENSION AND EXPANSION OF ENHANCED DEDUCTION FOR CHARITABLE CONTRIBUTIONS OF COMPUTERS. (a) Extension.--Subparagraph (F) of section 170(e)(6) of the Internal Revenue Code of 1986 (relating to special rule for contributions of computer technology and equipment for elementary or secondary school purposes) is amended by striking ``December 31, 2000'' and inserting ``June 30, 2004''. (b) Expansion.-- (1) In general.--Paragraph (6) of section 170(e) of such Code is amended by redesignating subparagraphs (C), (D), (E), and (F) as subparagraphs (D), (E), (F), and (G), respectively, and by striking all that precedes subparagraph (D) (as so redesignated) and inserting the following: ``(6) Special rule for contributions of computer technology and equipment.-- ``(A) In general.--The amount of any qualified computer contribution which is taken into account under this section shall be the greater of-- ``(i) the amount determined without regard to paragraph (1), or ``(ii) the amount determined with regard to paragraph (1). ``(B) Qualified computer contribution.--For purposes of this paragraph, the term `qualified computer contribution' means a charitable contribution by a corporation of any computer technology or equipment, but only if-- ``(i) the contribution is to a qualified organization, ``(ii) the contribution is made not later than 2 years after the date the taxpayer acquired the property (or in the case of property constructed by the taxpayer, the date the construction of the property is substantially completed), ``(iii) the original use of the property is by the donor or the donee, ``(iv) substantially all of the use of the property by the donee is for use within the United States and, in the case of a qualified educational organization, for educational purposes in any of the grades K-12 that are related to the purpose or function of the organization, ``(v) the property is not transferred by the donee in exchange for money, other property, or services, except for shipping, installation and transfer costs, ``(vi) in the case of a qualified educational organization, the property will fit productively into the entity's education plan, and ``(vii) the entity's use and disposition of the property will be in accordance with the provisions of clauses (iv) and (v). ``(C) Qualified organization.--For purposes of this paragraph-- ``(i) In general.--The term `qualified organization' means-- ``(I) any qualified educational organization, ``(II) any public library located in an area which is an empowerment zone, enterprise community, or a high- poverty area (as determined by the Secretary), ``(III) any technology center located in such an area, and ``(IV) any entity described in section 501(c)(3) and exempt from tax under section 501(a) that is organized primarily for purposes of providing computers without charge to lower income families. ``(ii) Qualified educational organization.--For purposes of clause (i), the term `qualified educational organization' means-- ``(I) an educational organization described in subsection (b)(1)(A)(ii), and ``(II) an entity described in section 501(c)(3) and exempt from tax under section 501(a) (other than an entity described in subclause (I)) that is organized primarily for purposes of supporting elementary and secondary education.'' (2) Conforming amendment.--Subparagraph (D) of section 170(e)(6) of such Code, as redesignated by paragraph (1), is amended by striking ``qualified elementary or secondary educational contribution'' and inserting ``qualified computer contribution''. (c) Effective Date.--The amendments made by this section shall apply to taxable years beginning after the date of the enactment of this Act.

Extends and expands the deduction for charitable computer contributions to elementary and secondary schools.

<s>[INST]SECTION 1. SHORT TITLE. This Act may be cited as the ``Digital Divide Elimination Act of 2000''. SEC. 2. CREDIT FOR PURCHASE OF COMPUTERS BY LOW-INCOME INDIVIDUALS. (a) In General.--Subpart C of part IV of subchapter A of chapter 1 of the Internal Revenue Code of 1986 (relating to refundable credits) is amended by redesignating section 35 as section 36 and by inserting after section 34 the following new section: ``SEC. 35. PURCHASE OF COMPUTERS BY LOW-INCOME INDIVIDUALS. ``(a) In General.--In the case of an eligible individual, there shall be allowed as a credit against the tax imposed by this subtitle for the taxable year an amount equal to 50 percent of the amount paid by the taxpayer for qualified computer technology or equipment. ``(b) Dollar Limitation.--The credit allowed by subsection (a) for any taxable year shall not exceed $500. ``(c) Definitions.--For purposes of this section-- ``(1) Eligible individual.--The term `eligible individual' means any taxpayer who is allowed a credit under section 32 (relating to earned income credit) for the taxable year. ``(2) Qualified computer technology or equipment.-- ``(A) In general.--Except as provided in subparagraph (B), the term `qualified computer technology or equipment' means any computer technology or equipment (as defined in section 170(e)(6)) acquired by purchase (as defined in section 170(d)(2)). ``(B) Exceptions.-- ``(i) Certain software excluded.--Such term shall not include game software or any other software which is not necessary for-- ``(I) use of the computer for access and use of the Internet (including email), or ``(II) business or educational use. ``(ii) Computer must be capable of internet access.--Such term shall not include any computer which does not have a modem or other equipment capable of supporting Internet access.'' (b) Conforming Amendments.-- (1) Paragraph (2) of section 1324(b) of title 31, United States Code, is amended by inserting before the period ``, or from section 35 of such Code''. (2) The table of sections for subpart C of part IV of subchapter A of chapter 1 of such Code is amended by striking the last item and inserting the following new items: ``Sec. 35. Purchase of computers by low-income individuals. ``Sec. 36. Overpayments of tax.'' (c) Effective Date.--The amendments made by this section shall apply to taxable years beginning after the date of the enactment of this Act. SEC. 3. EXTENSION AND EXPANSION OF ENHANCED DEDUCTION FOR CHARITABLE CONTRIBUTIONS OF COMPUTERS. (a) Extension.--Subparagraph (F) of section 170(e)(6) of the Internal Revenue Code of 1986 (relating to special rule for contributions of computer technology and equipment for elementary or secondary school purposes) is amended by striking ``December 31, 2000'' and inserting ``June 30, 2004''. (b) Expansion.-- (1) In general.--Paragraph (6) of section 170(e) of such Code is amended by redesignating subparagraphs (C), (D), (E), and (F) as subparagraphs (D), (E), (F), and (G), respectively, and by striking all that precedes subparagraph (D) (as so redesignated) and inserting the following: ``(6) Special rule for contributions of computer technology and equipment.-- ``(A) In general.--The amount of any qualified computer contribution which is taken into account under this section shall be the greater of-- ``(i) the amount determined without regard to paragraph (1), or ``(ii) the amount determined with regard to paragraph (1). ``(B) Qualified computer contribution.--For purposes of this paragraph, the term `qualified computer contribution' means a charitable contribution by a corporation of any computer technology or equipment, but only if-- ``(i) the contribution is to a qualified organization, ``(ii) the contribution is made not later than 2 years after the date the taxpayer acquired the property (or in the case of property constructed by the taxpayer, the date the construction of the property is substantially completed), ``(iii) the original use of the property is by the donor or the donee, ``(iv) substantially all of the use of the property by the donee is for use within the United States and, in the case of a qualified educational organization, for educational purposes in any of the grades K-12 that are related to the purpose or function of the organization, ``(v) the property is not transferred by the donee in exchange for money, other property, or services, except for shipping, installation and transfer costs, ``(vi) in the case of a qualified educational organization, the property will fit productively into the entity's education plan, and ``(vii) the entity's use and disposition of the property will be in accordance with the provisions of clauses (iv) and (v). ``(C) Qualified organization.--For purposes of this paragraph-- ``(i) In general.--The term `qualified organization' means-- ``(I) any qualified educational organization, ``(II) any public library located in an area which is an empowerment zone, enterprise community, or a high- poverty area (as determined by the Secretary), ``(III) any technology center located in such an area, and ``(IV) any entity described in section 501(c)(3) and exempt from tax under section 501(a) that is organized primarily for purposes of providing computers without charge to lower income families. ``(ii) Qualified educational organization.--For purposes of clause (i), the term `qualified educational organization' means-- ``(I) an educational organization described in subsection (b)(1)(A)(ii), and ``(II) an entity described in section 501(c)(3) and exempt from tax under section 501(a) (other than an entity described in subclause (I)) that is organized primarily for purposes of supporting elementary and secondary education.'' (2) Conforming amendment.--Subparagraph (D) of section 170(e)(6) of such Code, as redesignated by paragraph (1), is amended by striking ``qualified elementary or secondary educational contribution'' and inserting ``qualified computer contribution''. (c) Effective Date.--The amendments made by this section shall apply to taxable years beginning after the date of the enactment of this Act.[/INST]Extends and expands the deduction for charitable computer contributions to elementary and secondary schools.</s>

cell growth is as fundamental for organismal growth as cell division . without cell growth , no organism can grow . yet , compared to cell division , cell growth has been inexplicably neglected by cell biologists . proliferating cells in culture tend to double their mass before each division , but it is not known how cell growth is coordinated with cell - cycle progression to ensure that the cells maintain their size . we have been studying how this coordination is achieved in mammalian cells , using primary rat schwann cells as a model system . yeast cells are thought to coordinate cell - cycle progression with cell growth through the action of cell - size checkpoints in g1 and/or g2 , where the cell cycle can pause until the cell reaches an adequate size before proceeding into s or m phase , respectively . it is still uncertain how such checkpoints work , although there is evidence that the coupling of the threshold levels of certain cell - cycle activators to the general rate of translation plays a part . it is also unknown whether mammalian cells have cell - size checkpoints , although it is widely believed that they do [ 3,7 - 9 ] . for most populations of proliferating eukaryotic cells in culture , including yeast cells and mammalian cells , the mean cell size remains constant over time , even though individual cells vary in size at division . thus , cells that are initially bigger or smaller than the mean after mitosis tend to return to the mean size over time . how is this achieved , and is the mechanism the same for all eukaryotic cells ? for yeast cells , it has been shown , by blocking cell - cycle progression and measuring cell growth rate , that big cells grow faster than small cells . thus , for a population of yeast cells to maintain a constant average cell size and cell - size distribution , it would seem that cell - size checkpoints must be operating . without such checkpoints , yeast cells that are born larger than the mean birth size will grow faster than those that are born smaller , and these larger cells will produce still larger daughters , which will then grow even faster . thus , the spread of sizes in the population would increase over time , which does not happen , presumably because cell - size checkpoints ensure that cells that are larger or smaller than the mean at cell division tend to return toward the mean before dividing again . cells proliferating in nutrient - rich media generally grow at a faster rate and divide at a larger size than cells proliferating in nutrient - poor media . when switched from a nutrient - poor medium to a nutrient - rich medium , the cell cycle arrests and resumes only when the cells have reached the appropriate size for the new condition , which occurs within one cell cycle . thus , the cells can adjust their size threshold rapidly in response to changing external conditions . it is often assumed that animal cells also coordinate cell growth with cell - cycle progression by means of cell - size checkpoints , although the evidence for this is weak . proliferating mammalian cells , like proliferating yeast cells , maintain a constant average cell size and size distribution over time despite differences in the size of cells at division , but this does not necessarily mean that cell - size checkpoints are operating . if large cells do not grow faster than small cells , a cell - size checkpoint is not required to account for this behavior . this is illustrated in figure 1 , where the sizes of two , unequally sized , hypothetical daughter cells are followed through several cell cycles . if the cells and their progeny grow and progress through the cell cycle at the same rates , they will eventually converge to a common mean size ( figure 1 ) . the sizes converge , even in the absence of a cell - size checkpoint , because the larger cells do not double their cell mass each cycle , and the smaller cells more than double their cell mass each cycle . thus , proliferating cells can maintain a constant average size and size distribution without cell - size checkpoints , as long as individual cells grow at the same rate irrespective of their size . without cell - size checkpoints , however , cells that are born larger or smaller than the mean birth size will take longer to attain the mean birth size than if they had cell - size checkpoints . we showed previously that , unlike in yeasts , cell growth is not necessarily rate limiting for cell - cycle progression in primary rat schwann cells . extracellular mitogens that promote cell - cycle progression but not cell growth can shorten the cell cycle in schwann cells . this finding suggested that yeasts and schwann cells might use different strategies to coordinate cell growth and cell - cycle progression . it did not , however , indicate whether schwann cells use cell - size checkpoints for this coordination . here , we show that , unlike yeasts , primary rat schwann cells grow at a rate that is independent of their size , over a large range of sizes . in addition , we demonstrate that , unlike yeast cells , schwann cells do not adjust their size quickly when shifted from a relatively poor to a relatively rich environment ; instead , their mean cell size increases gradually over many divisions . these results suggest that schwann cells , and probably many types of mammalian cells , do not need and do not have cell - size checkpoints . instead , they apparently use extracellular signals to coordinate their growth with cell - cycle progression . we maintained the cells in a proliferative state in ' complete ' medium : dulbecco 's modified eagles ' medium ( dmem ) , supplemented with 3% fetal calf serum ( fcs ) , the neuregulin glial growth factor 2 ( ggf 2 ) , and the adenylyl cyclase stimulator forskolin . we passaged the cells before they reached confluence and measured their size ( volume ) in a coulter counter after removing the cells from the culture dish with trypsin at the time of passage . as expected , the average size of the cells remained unchanged with repeated passaging ( figure 2 ) . to determine if schwann cell growth depends on cell size , we used the dna polymerase inhibitor aphidicolin to arrest the cells in s phase . we then replated them and treated them with aphidicolin and simultaneously stimulated them with complete medium to re - enter the cell cycle and begin to grow . in these conditions , the cells remained arrested in s phase and continued to increase in size for many days . if schwann cell growth were like yeast cell growth , the rate of cell growth would increase over time as the cells enlarged , and the growth curve would be exponential - like . to determine cell - growth rate , we measured the volume of cells in parallel cultures every 24 hours after removing the cells from the culture dish with trypsin . as can be seen in figure 3a , cell growth was linear over a period of 5 days , indicating that the cells added a constant amount of volume each day , independent of their size . to confirm that the increase in cell volume reflected an increase in protein , we measured the amount of protein per cell , with similar results ( figure 3b ) . these findings indicate that large schwann cells do not grow faster than small schwann cells , at least in these conditions . as explained in the background , this means that cell - size checkpoints need not be invoked to explain why these cells maintain a constant average size ( figure 2 ) and cell - size distribution ( not shown ) when proliferating in complete medium . although the experiments were not done with this question in mind , there have been previous reports indicating that other types of mammalian cells grow linearly , independent of their size . hutson and mortimore , for example , starved mice , which causes the liver to shrink rapidly , solely as a result of hepatocyte shrinkage , rather than an increase in cell death or a decrease in cell proliferation . when they re - fed the mice , the liver re - grew rapidly , entirely as a result of hepatocyte growth , which was clearly linear . similarly , when deleu et al . stimulated dog thyrocytes with insulin , the thyrocytes grew but did not proliferate , and the growth was linear . in an experiment to test whether cell - size checkpoints were necessary , brooks and shields separated quiescent 3t3 cells by size and stimulated them to re - enter the cell cycle ; they found that large cells did not grow faster than small cells at the same point in the cycle , consistent with linear growth . we have not found any reports in which big mammalian cells have been observed to grow faster than small cells of the same type and at the same point of the cell cycle . it thus seems likely that most mammalian cells grow linearly , independent of their size , and that they therefore do not require cell - size checkpoints to maintain a constant size distribution as they proliferate . our finding that serum - stimulated , aphidicolin - arrested schwann cells add the same net amount of protein per cell per day , independent of their size , raised the possibility that big schwann cells synthesize protein at the same rate as small schwann cells . to test this possibility we cultured schwann cells in complete medium and aphidicolin and , after 24 , 48 , or 72 hours , added [ s]-methionine and [ s]-cysteine for two hours . as can be seen in figure 4a , the rate of protein synthesis increased as the cells increased in size over time . as the net amount of protein added per day does not increase as the schwann cells get bigger ( figure 3 ) , the rate of protein degradation ( and/or secretion ) must also increase as the cells get bigger . to determine the rate of protein degradation , we cultured the cells in complete medium and aphidicolin and , after various times , added [ s]-methionine and [ s]-cysteine for 2 hours , as before . we then washed the cells and incubated them in non - radioactive medium for a 2 or 6 hour ' chase ' . as can be seen in figure 4b , the rate of decrease in radiolabeled protein increased as the cells increased in size . thus , the rates of both synthesis and degradation of short - lived proteins increase with schwann cell size , and the net accumulation of protein is independent of size . it remains a mystery how mammalian cells maintain a constant difference between protein synthesis and degradation independent of their size , although there is evidence that this tight coupling between protein synthesis and degradation can depend on extracellular signals . we showed previously that schwann cell growth depends on extracellular signals , such as those present in fcs . to determine if cell growth remains linear in different concentrations of such extracellular factors , we cultured quiescent schwann cells in aphidicolin and various concentrations of fcs , and measured cell volume over time . as can be seen in figure 5 , the rate of growth remained linear for up to 9 days ( figure 5a ) but increased with increasing amounts of fcs ( figure 5b ) . even in 50% serum , cell growth remained linear and was faster than in 10% serum ( not shown ) . thus , even at high concentrations of fcs , it seems that the levels of extracellular growth factors , rather than anything inside the cells , limit schwann cell growth . in figure 5c , we show how the spread of cell sizes changed as aphidicolin - arrested schwann cells grew over time . like cell size itself , the spread of sizes increased linearly with time , as expected in a situation where some cells are growing faster and some slower than the mean rate , but all are growing linearly , independent of their size . we have shown that the growth rate of schwann cells is linear , unlike in yeasts , which means that cell - size checkpoints are unnecessary to explain how proliferating schwann cells maintain their size in a particular environment . as discussed in the background , a crucial line of evidence for the existence of cell - size checkpoints in yeasts is that they can rapidly change the size at which they divide , by adjusting their size threshold , when switched to different nutrient conditions . we therefore tested whether proliferating schwann cells behave similarly when shifted from serum - free to serum - containing culture medium . if schwann cells had cell - size checkpoints , one might expect them to adjust their size rapidly to the new condition . if they do not have such checkpoints , one would expect the cells to adjust their size only gradually to the new conditions over a number of cell cycles , much as illustrated for the small cells in figure 1 . we maintained purified schwann cells in a proliferative state on laminin , in dmem supplemented with ggf 2 , forskolin , insulin , and serum - free schwann - cell - conditioned medium , with or without 3% fcs , passaging the cells when they reached near - confluence . in both conditions , the schwann cells maintained their average size over time , when assessed at the time of passage ( figure 6a ) , although the cells in serum were , on average , more than twice the size of cells without serum ( figure 6b ) . in this respect , the cells behave similarly to yeast cells , which grow at a faster rate and divide at a larger size when proliferating in a nutrient - rich medium than in a nutrient - poor medium . we then switched the schwann cells that had been proliferating in serum - free medium to serum - containing medium . we plated these ' switched ' cells and the cells maintained throughout the experiment in serum - containing medium at the same plating density both now in serum - containing medium . we passaged them when they reached about 300,000 cells per well , which was usually every 3 days . we counted cell numbers and measured mean cell volume of the population every day using a coulter counter . the average cell - cycle times of the two populations were approximately the same ( figures 6c , d ) . unlike yeasts , the switched cells took around six divisions and about 10 days before they divided at the characteristic size of schwann cells maintained in serum - containing medium all along ( figure 6e ) . the finding that big schwann cells grow at the same rate as small schwann cells means that they do not require cell - size checkpoints to maintain a constant size distribution as they proliferate . the finding that they take many divisions to adjust to new culture conditions strongly suggests that they do not have such checkpoints , or at least not ones that resemble those operating in yeast cells . in addition , their slow adjustment to a change in culture conditions is the behavior predicted by the hypothetical model illustrated in figure 1 for proliferating cells that grow linearly and do not have cell - size checkpoints . whereas proliferating populations of yeast cells and schwann cells can both maintain a constant size over time , they seem to do so in very different ways . for yeasts , cell - size checkpoints apparently operate to coordinate cell growth and cell - cycle progression . for schwann cells , by contrast , extracellular signals that stimulate cell growth , cell - cycle progression , or both , appear to control the size at which the cells divide . although a population of schwann cells maintained a constant average cell size if passaged frequently ( figure 2 ) , the cells decrease in size if not passaged , even if the medium was replaced every day ( figure 7a ) , although they continue to proliferate ( figure 7b ) . this is presumably because there was increased competition for extracellular growth factors as the cultures got denser . a similar competition for extracellular signals has been shown to regulate the size of lymphocytes in vivo . apparently , signaling for schwann cell growth is more affected by the competition than signaling for cell - cycle progression . we found previously that schwann cells do not maintain a constant size over time when proliferating in insulin - like growth factor i ( igf - i ) and ggf 2 in the absence of fcs or schwann - cell - conditioned medium , presumably because growth stimulation was insufficient to keep up with mitogenic stimulation . we suspect that the size of most proliferating animal cells in vivo is controlled by the levels of extracellular signals in a way that is similar to how schwann cell size is controlled in culture . in the few studies that have analyzed the size of proliferating animal cells during normal development , for example , it seems that cell size can vary significantly for the same cell type . during development of the wing imaginal disc in drosophila , for instance , the size of the disc cells varies throughout development : the cells initially grow without dividing and then proliferate and get progressively smaller . , each yeast cell grows and divides as fast as the nutrient supply allows , and it must quickly adapt to changing extracellular conditions . the growth and division of animal cells , by contrast , must be carefully controlled and coordinated for the good of the animal as a whole , and this control relies mainly on intercellular signaling . thus , whereas yeast cell proliferation is controlled mainly by nutrients , animal cell proliferation is controlled mainly by signals from other cells . as such signals seem usually to be present at limiting , rather than saturating , concentrations , small changes in their levels can powerfully influence cell growth and proliferation . given its importance , it is surprising how little is known about how the levels of such signals are controlled in animals . animal cell proliferation also depends on nutrients , however , and our results do not exclude the possibility that cell - size checkpoints might be revealed by nutrient deprivation experiments . our findings also do not exclude the possibility that animal cells such as lymphocytes , which can proliferate in suspension like yeast cells , might use cell - size checkpoints to coordinate their growth with cell - cycle progression . these will be important avenues to explore in the future , but we shall leave this to others . we maintained the cells in a proliferative state in ' complete ' medium : dulbecco 's modified eagles ' medium ( dmem ) , supplemented with 3% fetal calf serum ( fcs ) , the neuregulin glial growth factor 2 ( ggf 2 ) , and the adenylyl cyclase stimulator forskolin . we passaged the cells before they reached confluence and measured their size ( volume ) in a coulter counter after removing the cells from the culture dish with trypsin at the time of passage . as expected , the average size of the cells remained unchanged with repeated passaging ( figure 2 ) . to determine if schwann cell growth depends on cell size , we used the dna polymerase inhibitor aphidicolin to arrest the cells in s phase . we then replated them and treated them with aphidicolin and simultaneously stimulated them with complete medium to re - enter the cell cycle and begin to grow . in these conditions , the cells remained arrested in s phase and continued to increase in size for many days . if schwann cell growth were like yeast cell growth , the rate of cell growth would increase over time as the cells enlarged , and the growth curve would be exponential - like . to determine cell - growth rate , we measured the volume of cells in parallel cultures every 24 hours after removing the cells from the culture dish with trypsin . as can be seen in figure 3a , cell growth was linear over a period of 5 days , indicating that the cells added a constant amount of volume each day , independent of their size . to confirm that the increase in cell volume reflected an increase in protein , we measured the amount of protein per cell , with similar results ( figure 3b ) . these findings indicate that large schwann cells do not grow faster than small schwann cells , at least in these conditions . as explained in the background , this means that cell - size checkpoints need not be invoked to explain why these cells maintain a constant average size ( figure 2 ) and cell - size distribution ( not shown ) when proliferating in complete medium . although the experiments were not done with this question in mind , there have been previous reports indicating that other types of mammalian cells grow linearly , independent of their size . hutson and mortimore , for example , starved mice , which causes the liver to shrink rapidly , solely as a result of hepatocyte shrinkage , rather than an increase in cell death or a decrease in cell proliferation . when they re - fed the mice , the liver re - grew rapidly , entirely as a result of hepatocyte growth , which was clearly linear . similarly , when deleu et al . stimulated dog thyrocytes with insulin , the thyrocytes grew but did not proliferate , and the growth was linear . in an experiment to test whether cell - size checkpoints were necessary , brooks and shields separated quiescent 3t3 cells by size and stimulated them to re - enter the cell cycle ; they found that large cells did not grow faster than small cells at the same point in the cycle , consistent with linear growth . we have not found any reports in which big mammalian cells have been observed to grow faster than small cells of the same type and at the same point of the cell cycle . it thus seems likely that most mammalian cells grow linearly , independent of their size , and that they therefore do not require cell - size checkpoints to maintain a constant size distribution as they proliferate . our finding that serum - stimulated , aphidicolin - arrested schwann cells add the same net amount of protein per cell per day , independent of their size , raised the possibility that big schwann cells synthesize protein at the same rate as small schwann cells . to test this possibility we cultured schwann cells in complete medium and aphidicolin and , after 24 , 48 , or 72 hours , added [ s]-methionine and [ s]-cysteine for two hours . as can be seen in figure 4a , the rate of protein synthesis increased as the cells increased in size over time . as the net amount of protein added per day does not increase as the schwann cells get bigger ( figure 3 ) , the rate of protein degradation ( and/or secretion ) must also increase as the cells get bigger . to determine the rate of protein degradation , we cultured the cells in complete medium and aphidicolin and , after various times , added [ s]-methionine and [ s]-cysteine for 2 hours , as before . we then washed the cells and incubated them in non - radioactive medium for a 2 or 6 hour ' chase ' . as can be seen in figure 4b , the rate of decrease in radiolabeled protein increased as the cells increased in size . thus , the rates of both synthesis and degradation of short - lived proteins increase with schwann cell size , and the net accumulation of protein is independent of size . it remains a mystery how mammalian cells maintain a constant difference between protein synthesis and degradation independent of their size , although there is evidence that this tight coupling between protein synthesis and degradation can depend on extracellular signals . we showed previously that schwann cell growth depends on extracellular signals , such as those present in fcs . to determine if cell growth remains linear in different concentrations of such extracellular factors , we cultured quiescent schwann cells in aphidicolin and various concentrations of fcs , and measured cell volume over time . as can be seen in figure 5 , the rate of growth remained linear for up to 9 days ( figure 5a ) but increased with increasing amounts of fcs ( figure 5b ) . even in 50% serum , cell growth remained linear and was faster than in 10% serum ( not shown ) . thus , even at high concentrations of fcs , it seems that the levels of extracellular growth factors , rather than anything inside the cells , limit schwann cell growth . in figure 5c , we show how the spread of cell sizes changed as aphidicolin - arrested schwann cells grew over time . like cell size itself , the spread of sizes increased linearly with time , as expected in a situation where some cells are growing faster and some slower than the mean rate , but all are growing linearly , independent of their size . we have shown that the growth rate of schwann cells is linear , unlike in yeasts , which means that cell - size checkpoints are unnecessary to explain how proliferating schwann cells maintain their size in a particular environment . as discussed in the background , a crucial line of evidence for the existence of cell - size checkpoints in yeasts is that they can rapidly change the size at which they divide , by adjusting their size threshold , when switched to different nutrient conditions . we therefore tested whether proliferating schwann cells behave similarly when shifted from serum - free to serum - containing culture medium . if schwann cells had cell - size checkpoints , one might expect them to adjust their size rapidly to the new condition . if they do not have such checkpoints , one would expect the cells to adjust their size only gradually to the new conditions over a number of cell cycles , much as illustrated for the small cells in figure 1 . we maintained purified schwann cells in a proliferative state on laminin , in dmem supplemented with ggf 2 , forskolin , insulin , and serum - free schwann - cell - conditioned medium , with or without 3% fcs , passaging the cells when they reached near - confluence . in both conditions , the schwann cells maintained their average size over time , when assessed at the time of passage ( figure 6a ) , although the cells in serum were , on average , more than twice the size of cells without serum ( figure 6b ) . in this respect , the cells behave similarly to yeast cells , which grow at a faster rate and divide at a larger size when proliferating in a nutrient - rich medium than in a nutrient - poor medium . we then switched the schwann cells that had been proliferating in serum - free medium to serum - containing medium . we plated these ' switched ' cells and the cells maintained throughout the experiment in serum - containing medium at the same plating density both now in serum - containing medium . we passaged them when they reached about 300,000 cells per well , which was usually every 3 days . we counted cell numbers and measured mean cell volume of the population every day using a coulter counter . the average cell - cycle times of the two populations were approximately the same ( figures 6c , d ) . unlike yeasts , the switched cells took around six divisions and about 10 days before they divided at the characteristic size of schwann cells maintained in serum - containing medium all along ( figure 6e ) . the finding that big schwann cells grow at the same rate as small schwann cells means that they do not require cell - size checkpoints to maintain a constant size distribution as they proliferate . the finding that they take many divisions to adjust to new culture conditions strongly suggests that they do not have such checkpoints , or at least not ones that resemble those operating in yeast cells . in addition , their slow adjustment to a change in culture conditions is the behavior predicted by the hypothetical model illustrated in figure 1 for proliferating cells that grow linearly and do not have cell - size checkpoints . whereas proliferating populations of yeast cells and schwann cells can both maintain a constant size over time , they seem to do so in very different ways . for yeasts , cell - size checkpoints apparently operate to coordinate cell growth and cell - cycle progression . for schwann cells , by contrast , extracellular signals that stimulate cell growth , cell - cycle progression , or both , appear to control the size at which the cells divide . although a population of schwann cells maintained a constant average cell size if passaged frequently ( figure 2 ) , the cells decrease in size if not passaged , even if the medium was replaced every day ( figure 7a ) , although they continue to proliferate ( figure 7b ) . this is presumably because there was increased competition for extracellular growth factors as the cultures got denser . a similar competition for extracellular signals has been shown to regulate the size of lymphocytes in vivo . apparently , signaling for schwann cell growth is more affected by the competition than signaling for cell - cycle progression . we found previously that schwann cells do not maintain a constant size over time when proliferating in insulin - like growth factor i ( igf - i ) and ggf 2 in the absence of fcs or schwann - cell - conditioned medium , presumably because growth stimulation was insufficient to keep up with mitogenic stimulation . we suspect that the size of most proliferating animal cells in vivo is controlled by the levels of extracellular signals in a way that is similar to how schwann cell size is controlled in culture . in the few studies that have analyzed the size of proliferating animal cells during normal development , for example , it seems that cell size can vary significantly for the same cell type . during development of the wing imaginal disc in drosophila , for instance , the size of the disc cells varies throughout development : the cells initially grow without dividing and then proliferate and get progressively smaller . the lifestyles of yeasts and animal cells are crucially different . as a unicellular organism , each yeast cell grows and divides as fast as the nutrient supply allows , and it must quickly adapt to changing extracellular conditions . the growth and division of animal cells , by contrast , must be carefully controlled and coordinated for the good of the animal as a whole , and this control relies mainly on intercellular signaling . thus , whereas yeast cell proliferation is controlled mainly by nutrients , animal cell proliferation is controlled mainly by signals from other cells . as such signals seem usually to be present at limiting , rather than saturating , concentrations , small changes in their levels can powerfully influence cell growth and proliferation . given its importance , it is surprising how little is known about how the levels of such signals are controlled in animals . animal cell proliferation also depends on nutrients , however , and our results do not exclude the possibility that cell - size checkpoints might be revealed by nutrient deprivation experiments . our findings also do not exclude the possibility that animal cells such as lymphocytes , which can proliferate in suspension like yeast cells , might use cell - size checkpoints to coordinate their growth with cell - cycle progression . these will be important avenues to explore in the future , but we shall leave this to others . all reagents were from sigma - aldrich ( gillingham , uk ) , unless indicated otherwise . for experiments on growth rate , schwann cells were purified from postnatal day 7 rat sciatic nerve by sequential immunopanning as described previously . the cells were expanded on poly - d - lysine- and fibronectin - coated culture dishes ( falcon ; bd biosciences , oxford , uk ) in ' complete medium ' : dmem ( gibco ; invitrogen ltd , paisley , uk ) supplemented with 3% fcs , 1 m forskolin ( calbiochem ; merck biosciences , nottingham , uk ) and 20 ng / ml recombinant ggf 2 ( a gift from m. marchionni , cambridge neuroscience inc . , cambridge , usa ) . cells were passaged every 3 days and were > 99.9% pure as judged by antigenic markers . for the switch experiments , purified schwann cells were maintained in a proliferative state on poly - d - lysine- and laminin - coated culture dishes , in dmem supplemented with 20 ng / ml ggf 2 , 1 m forskolin , 10 g / ml insulin , serum - free schwann - cell - conditioned medium ( to a final concentration of 20% ) , 100 g / ml transferrrin , 100 g / ml bovine serum albumin , 16 mg / ml putrescine , and 40 ng / ml selenium , either with ( serum - containing sc medium ) or without ( serum - free sf medium ) 3% fcs . cells were plated at a concentration of 100,000 cells per well of a six - well culture plate ( falcon ) and passaged when they reached a concentration of around 300,000 cells per well . for cell - growth experiments , about 4 10 quiescent cells were then plated in each well of a six - well poly - d - lysine- and fibronectin - coated culture dish in dmem containing 1% , 3% , 10% , or 50% fcs and 2 g / ml aphidicolin to arrest the cells in s phase . cell volume and cell number ( to assess cell - cycle time ) were assessed every 24 hours in a coulter counter ( multisizer ii , beckman - coulter , high wycombe , uk ) , using a volumetric analysis , after removing the cells from the culture dish with trypsin - edta ( gibco ) and resuspending them in isoton ii ( beckman - coulter ) . between 1,000 and 5,000 cells were counted per well , and the data were analyzed using coulter multisizer accucomp software ( beckman - coulter ) . about 10quiescent cells were plated in a poly - d - lysine - and fibronectin - coated 15 cm culture dish ( falcon ) in dmem containing 1% , 3% , or 10% fcs and 2 g / ml aphidicolin . the cells were rinsed twice with phosphate - buffered saline ( pbs ) , scraped off the dish , and centrifuged at 3,000 g for 3 minutes . cell number was determined by measuring the concentration of dna in the aliquot and assuming the haploid amount of dna per cell is 6 pg . protein concentration was determined by lysing the cells on ice for 15 minutes in 0.4% triton and 0.2% sodium dodecyl sulfate ( sds ) , in the presence of protease inhibitors ( boehringer mannheim ) and using a micro - bca ( bicinchoninic acid ) assay with a bovine serum albumin ( bsa ) standard . about 10quiescent cells were plated in a poly - d - lysine- and fibronectin - coated 6 cm culture dish in medium containing 3% fcs and 2 g / ml aphidicolin . in one experiment , the protein synthesis rate of proliferating cells in complete medium was determined . at the time point to be investigated , cells were washed twice with cysteine- and methionine - free dmem ( gibco ) . then , 2.5 ml of this dmem was added , together with glutamate , forskolin , 3% fcs , and 100 ci of [ s]-methionine and [ s]-cysteine ( amersham , little chalfont , uk ) for 2 hours at 37c . the amount of radiolabel was saturating , as the amount in the medium did not decrease significantly during the 2-hour incubation . to determine the protein synthesis rate , the cells were then washed , trypsinized , centrifuged at 3,000 g , and resuspended in serum - free medium . aliquots were taken for cell - number analysis in a coulter counter and for protein analysis . then , 100% ice - cold trichloroacetic acid ( tca ) was added to each aliquot to a final concentration of 10% , to precipitate the protein . after 10 minutes on ice , the solutions were centrifuged at 12,000 g to pellet the precipitated protein , and the amount of free radiolabel was assessed by removing three aliquots and counting them in a scintillation counter . the amount of radiolabel incorporated into protein was calculated by subtracting the value of the non - incorporated label from the value of the label in the total cell lysate . to determine the rate of protein degradation , cells were radiolabeled as above , washed three times with complete medium , and then left for either 2 or 6 hours at 37c . the amount of radiolabeled protein still remaining in the cells after the chase was determined as described above . for experiments on growth rate , schwann cells were purified from postnatal day 7 rat sciatic nerve by sequential immunopanning as described previously . the cells were expanded on poly - d - lysine- and fibronectin - coated culture dishes ( falcon ; bd biosciences , oxford , uk ) in ' complete medium ' : dmem ( gibco ; invitrogen ltd , paisley , uk ) supplemented with 3% fcs , 1 m forskolin ( calbiochem ; merck biosciences , nottingham , uk ) and 20 ng / ml recombinant ggf 2 ( a gift from m. marchionni , cambridge neuroscience inc . , cambridge , usa ) . cells were passaged every 3 days and were > 99.9% pure as judged by antigenic markers . for the switch experiments , purified schwann cells were maintained in a proliferative state on poly - d - lysine- and laminin - coated culture dishes , in dmem supplemented with 20 ng / ml ggf 2 , 1 m forskolin , 10 g / ml insulin , serum - free schwann - cell - conditioned medium ( to a final concentration of 20% ) , 100 g / ml transferrrin , 100 g / ml bovine serum albumin , 16 mg / ml putrescine , and 40 ng / ml selenium , either with ( serum - containing sc medium ) or without ( serum - free sf medium ) 3% fcs . cells were plated at a concentration of 100,000 cells per well of a six - well culture plate ( falcon ) and passaged when they reached a concentration of around 300,000 cells per well . for cell - growth experiments , quiescent schwann cells were obtained by culturing them to confluence in complete medium . about 4 10 quiescent cells were then plated in each well of a six - well poly - d - lysine- and fibronectin - coated culture dish in dmem containing 1% , 3% , 10% , or 50% fcs and 2 g / ml aphidicolin to arrest the cells in s phase . cell volume and cell number ( to assess cell - cycle time ) were assessed every 24 hours in a coulter counter ( multisizer ii , beckman - coulter , high wycombe , uk ) , using a volumetric analysis , after removing the cells from the culture dish with trypsin - edta ( gibco ) and resuspending them in isoton ii ( beckman - coulter ) . between 1,000 and 5,000 cells were counted per well , and the data were analyzed using coulter multisizer accucomp software ( beckman - coulter ) . about 10quiescent cells were plated in a poly - d - lysine - and fibronectin - coated 15 cm culture dish ( falcon ) in dmem containing 1% , 3% , or 10% fcs and 2 g / ml aphidicolin . the cells were rinsed twice with phosphate - buffered saline ( pbs ) , scraped off the dish , and centrifuged at 3,000 g for 3 minutes . cell number was determined by measuring the concentration of dna in the aliquot and assuming the haploid amount of dna per cell is 6 pg . protein concentration was determined by lysing the cells on ice for 15 minutes in 0.4% triton and 0.2% sodium dodecyl sulfate ( sds ) , in the presence of protease inhibitors ( boehringer mannheim ) and using a micro - bca ( bicinchoninic acid ) assay with a bovine serum albumin ( bsa ) standard . about 10quiescent cells were plated in a poly - d - lysine- and fibronectin - coated 6 cm culture dish in medium containing 3% fcs and 2 g / ml aphidicolin . in one experiment , the protein synthesis rate of proliferating cells in complete medium was determined . at the time point to be investigated , cells were washed twice with cysteine- and methionine - free dmem ( gibco ) . then , 2.5 ml of this dmem was added , together with glutamate , forskolin , 3% fcs , and 100 ci of [ s]-methionine and [ s]-cysteine ( amersham , little chalfont , uk ) for 2 hours at 37c . the amount of radiolabel was saturating , as the amount in the medium did not decrease significantly during the 2-hour incubation . to determine the protein synthesis rate , the cells were then washed , trypsinized , centrifuged at 3,000 g , and resuspended in serum - free medium . aliquots were taken for cell - number analysis in a coulter counter and for protein analysis . radiolabel incorporation into protein was assessed by lysing the cells in 0.2% triton and then removing three aliquots and counting each in a scintillation counter . then , 100% ice - cold trichloroacetic acid ( tca ) was added to each aliquot to a final concentration of 10% , to precipitate the protein . after 10 minutes on ice , the solutions were centrifuged at 12,000 g to pellet the precipitated protein , and the amount of free radiolabel was assessed by removing three aliquots and counting them in a scintillation counter . the amount of radiolabel incorporated into protein was calculated by subtracting the value of the non - incorporated label from the value of the label in the total cell lysate . to determine the rate of protein degradation , cells were radiolabeled as above , washed three times with complete medium , and then left for either 2 or 6 hours at 37c . the amount of radiolabeled protein still remaining in the cells after the chase was determined as described above . the authors of the second research article in this print issue ( ) have both had close associations with journal of biology , and martin raff continues to do so . neither author was involved in the refereeing of this article , in the decision to publish it , or in the choice of accompanying commentary . this work and the authors were supported by the medical research council of the uk . we are grateful to robert brooks , murdoch mitchison , and paul nurse for helpful discussions . a hypothetical model showing why the progeny of large and small daughter cells eventually return to the mean population size over time if large and small cells grow and progress through the cell cycle at the same rates ( after brooks ) . the initial division is unequal and produces one cell of 10 mass units and one cell of 1 mass unit ; the subsequent eight divisions of the progeny cells are equal . following thus , the initial small daughter cell grows to 6.5 units before it divides to produce two daughters of about 3.2 units each , while the initial large daughter cell grows to 15.5 units before it divides to produce two daughters of about 7.8 units . mean cell volume remains constant as purified schwann cells proliferate in complete medium and are passaged every three days . the growth of aphidicolin - arrested schwann cells is linear over time , indicating that it is independent of cell size . ( a ) quiescent cells were cultured in complete medium with aphidicolin to arrest the cells in s phase . each point represents the mean standard deviation of the results derived from three independent experiments , where , for each experiment , the mode cell volumes of three plates were measured and averaged . ( b ) cells were cultured as in ( a ) , but protein per cell , rather than cell volume , was measured at the time points shown . the results are shown as the mean standard deviation of three cultures in one experiment , in which about 10cells were assayed for each point . the experiments in ( a ) and ( b ) were performed three times with similar results . ( a ) quiescent cells were cultured in 3% fcs , forskolin , and aphidicolin for various times . the rate of protein synthesis was then determined by measuring the amount of incorporation of [ s]-methionine and [ s]-cysteine into cellular protein over 2 hours . the results are shown as the mean standard deviation of nine independent plates of cells . ( b ) quiescent cells were treated as in ( a ) and then either harvested immediately ( 0 hours after pulse ) to assess the rate of total protein synthesis or washed and ' chased ' with medium containing non - radioactive methionine and cysteine for 2 or 6 hours before harvesting to assess the rate of protein degradation . the shallowness of the curve for the 24-hour - arrested cells is likely to be the result of the lower than expected value at 0 hours . the 0 hour result in ( a ) is likely to be more accurate , as it represents the mean of nine independent cultures , instead of three . if one uses the value of 80 , the curve in ( b ) for the 24-hour - arrested cells would be steeper . the experiments in ( a ) and ( b ) were performed three times with similar results . schwann cell growth remains linear for 9 days but increases with increasing concentrations of serum . in ( a ) the cells were cultured in 1% fcs , forskolin , and aphidicolin , while in ( b ) they were cultured in forskolin and aphidicolin and various concentrations of fcs . ( c ) the cells were cultured as in ( a ) , but each point represents the mean standard deviation of cell volumes from one plate of cells . schwann cells adjust their size slowly when shifted from serum - free ( sf ) medium to serum - containing ( sc ) medium . the cells were plated at 100,000 cells per well and were passaged when they reached a density of about 300,000 cells per well . ( a , b ) the mean volume of cells proliferating in either sc or sf medium was measured in a coulter counter at the time of passage . the raw data for each condition are shown in ( a ) , and the mean standard deviation of the mode cell volume at passage is shown in ( b ) . ( c , d ) the cell - cycle time of schwann cells proliferating either in sc medium or in sc medium after a shift from sf medium was measured by determining the rate at which cell number increased . the raw data for each condition are shown in ( c ) , and the mean standard deviation of four population - doubling times is shown in ( d ) . ( e ) the size of cells proliferating in sc medium , in sf medium , or in sc medium after a shift from sf medium ( ' switched ' cells ) was measured every day in a coulter counter . because the cells in sc medium and the switched cells had similar cycle times see ( d ) they were passaged about every 3 days in both cases , when they reached around 300,000 cells per well ; the cells in sf medium cycled more slowly and cells were cultured in serum - containing medium , with or without passaging on day 4 . in both cases , 100,000 cells were plated per well , and the medium was changed every day . mode cell volume ( a ) and cell number ( b )

backgroundit is widely believed that cell - size checkpoints help to coordinate cell growth and cell - cycle progression , so that proliferating eukaryotic cells maintain their size . there is strong evidence for such size checkpoints in yeasts , which maintain a constant cell - size distribution as they proliferate , even though large yeast cells grow faster than small yeast cells . moreover , when yeast cells are shifted to better or worse nutrient conditions , they alter their size threshold within one cell cycle . populations of mammalian cells can also maintain a constant size distribution as they proliferate , but it is not known whether this depends on cell - size checkpoints.resultswe show that proliferating rat schwann cells do not require a cell - size checkpoint to maintain a constant cell - size distribution , as , unlike yeasts , large and small schwann cells grow at the same rate , which depends on the concentration of extracellular growth factors . in addition , when shifted from serum - free to serum - containing medium , schwann cells take many divisions to increase their size to that appropriate to the new condition , suggesting that they do not have cell - size checkpoints similar to those in yeasts.conclusionsproliferating schwann cells and yeast cells seem to use different mechanisms to coordinate their growth with cell - cycle progression . whereas yeast cells use cell - size checkpoints , schwann cells apparently do not . it seems likely that many mammalian cells resemble schwann cells in this respect .

<s>[INST]cell growth is as fundamental for organismal growth as cell division . without cell growth , no organism can grow . yet , compared to cell division , cell growth has been inexplicably neglected by cell biologists . proliferating cells in culture tend to double their mass before each division , but it is not known how cell growth is coordinated with cell - cycle progression to ensure that the cells maintain their size . we have been studying how this coordination is achieved in mammalian cells , using primary rat schwann cells as a model system . yeast cells are thought to coordinate cell - cycle progression with cell growth through the action of cell - size checkpoints in g1 and/or g2 , where the cell cycle can pause until the cell reaches an adequate size before proceeding into s or m phase , respectively . it is still uncertain how such checkpoints work , although there is evidence that the coupling of the threshold levels of certain cell - cycle activators to the general rate of translation plays a part . it is also unknown whether mammalian cells have cell - size checkpoints , although it is widely believed that they do [ 3,7 - 9 ] . for most populations of proliferating eukaryotic cells in culture , including yeast cells and mammalian cells , the mean cell size remains constant over time , even though individual cells vary in size at division . thus , cells that are initially bigger or smaller than the mean after mitosis tend to return to the mean size over time . how is this achieved , and is the mechanism the same for all eukaryotic cells ? for yeast cells , it has been shown , by blocking cell - cycle progression and measuring cell growth rate , that big cells grow faster than small cells . thus , for a population of yeast cells to maintain a constant average cell size and cell - size distribution , it would seem that cell - size checkpoints must be operating . without such checkpoints , yeast cells that are born larger than the mean birth size will grow faster than those that are born smaller , and these larger cells will produce still larger daughters , which will then grow even faster . thus , the spread of sizes in the population would increase over time , which does not happen , presumably because cell - size checkpoints ensure that cells that are larger or smaller than the mean at cell division tend to return toward the mean before dividing again . cells proliferating in nutrient - rich media generally grow at a faster rate and divide at a larger size than cells proliferating in nutrient - poor media . when switched from a nutrient - poor medium to a nutrient - rich medium , the cell cycle arrests and resumes only when the cells have reached the appropriate size for the new condition , which occurs within one cell cycle . thus , the cells can adjust their size threshold rapidly in response to changing external conditions . it is often assumed that animal cells also coordinate cell growth with cell - cycle progression by means of cell - size checkpoints , although the evidence for this is weak . proliferating mammalian cells , like proliferating yeast cells , maintain a constant average cell size and size distribution over time despite differences in the size of cells at division , but this does not necessarily mean that cell - size checkpoints are operating . if large cells do not grow faster than small cells , a cell - size checkpoint is not required to account for this behavior . this is illustrated in figure 1 , where the sizes of two , unequally sized , hypothetical daughter cells are followed through several cell cycles . if the cells and their progeny grow and progress through the cell cycle at the same rates , they will eventually converge to a common mean size ( figure 1 ) . the sizes converge , even in the absence of a cell - size checkpoint , because the larger cells do not double their cell mass each cycle , and the smaller cells more than double their cell mass each cycle . thus , proliferating cells can maintain a constant average size and size distribution without cell - size checkpoints , as long as individual cells grow at the same rate irrespective of their size . without cell - size checkpoints , however , cells that are born larger or smaller than the mean birth size will take longer to attain the mean birth size than if they had cell - size checkpoints . we showed previously that , unlike in yeasts , cell growth is not necessarily rate limiting for cell - cycle progression in primary rat schwann cells . extracellular mitogens that promote cell - cycle progression but not cell growth can shorten the cell cycle in schwann cells . this finding suggested that yeasts and schwann cells might use different strategies to coordinate cell growth and cell - cycle progression . it did not , however , indicate whether schwann cells use cell - size checkpoints for this coordination . here , we show that , unlike yeasts , primary rat schwann cells grow at a rate that is independent of their size , over a large range of sizes . in addition , we demonstrate that , unlike yeast cells , schwann cells do not adjust their size quickly when shifted from a relatively poor to a relatively rich environment ; instead , their mean cell size increases gradually over many divisions . these results suggest that schwann cells , and probably many types of mammalian cells , do not need and do not have cell - size checkpoints . instead , they apparently use extracellular signals to coordinate their growth with cell - cycle progression . we maintained the cells in a proliferative state in ' complete ' medium : dulbecco 's modified eagles ' medium ( dmem ) , supplemented with 3% fetal calf serum ( fcs ) , the neuregulin glial growth factor 2 ( ggf 2 ) , and the adenylyl cyclase stimulator forskolin . we passaged the cells before they reached confluence and measured their size ( volume ) in a coulter counter after removing the cells from the culture dish with trypsin at the time of passage . as expected , the average size of the cells remained unchanged with repeated passaging ( figure 2 ) . to determine if schwann cell growth depends on cell size , we used the dna polymerase inhibitor aphidicolin to arrest the cells in s phase . we then replated them and treated them with aphidicolin and simultaneously stimulated them with complete medium to re - enter the cell cycle and begin to grow . in these conditions , the cells remained arrested in s phase and continued to increase in size for many days . if schwann cell growth were like yeast cell growth , the rate of cell growth would increase over time as the cells enlarged , and the growth curve would be exponential - like . to determine cell - growth rate , we measured the volume of cells in parallel cultures every 24 hours after removing the cells from the culture dish with trypsin . as can be seen in figure 3a , cell growth was linear over a period of 5 days , indicating that the cells added a constant amount of volume each day , independent of their size . to confirm that the increase in cell volume reflected an increase in protein , we measured the amount of protein per cell , with similar results ( figure 3b ) . these findings indicate that large schwann cells do not grow faster than small schwann cells , at least in these conditions . as explained in the background , this means that cell - size checkpoints need not be invoked to explain why these cells maintain a constant average size ( figure 2 ) and cell - size distribution ( not shown ) when proliferating in complete medium . although the experiments were not done with this question in mind , there have been previous reports indicating that other types of mammalian cells grow linearly , independent of their size . hutson and mortimore , for example , starved mice , which causes the liver to shrink rapidly , solely as a result of hepatocyte shrinkage , rather than an increase in cell death or a decrease in cell proliferation . when they re - fed the mice , the liver re - grew rapidly , entirely as a result of hepatocyte growth , which was clearly linear . similarly , when deleu et al . stimulated dog thyrocytes with insulin , the thyrocytes grew but did not proliferate , and the growth was linear . in an experiment to test whether cell - size checkpoints were necessary , brooks and shields separated quiescent 3t3 cells by size and stimulated them to re - enter the cell cycle ; they found that large cells did not grow faster than small cells at the same point in the cycle , consistent with linear growth . we have not found any reports in which big mammalian cells have been observed to grow faster than small cells of the same type and at the same point of the cell cycle . it thus seems likely that most mammalian cells grow linearly , independent of their size , and that they therefore do not require cell - size checkpoints to maintain a constant size distribution as they proliferate . our finding that serum - stimulated , aphidicolin - arrested schwann cells add the same net amount of protein per cell per day , independent of their size , raised the possibility that big schwann cells synthesize protein at the same rate as small schwann cells . to test this possibility we cultured schwann cells in complete medium and aphidicolin and , after 24 , 48 , or 72 hours , added [ s]-methionine and [ s]-cysteine for two hours . as can be seen in figure 4a , the rate of protein synthesis increased as the cells increased in size over time . as the net amount of protein added per day does not increase as the schwann cells get bigger ( figure 3 ) , the rate of protein degradation ( and/or secretion ) must also increase as the cells get bigger . to determine the rate of protein degradation , we cultured the cells in complete medium and aphidicolin and , after various times , added [ s]-methionine and [ s]-cysteine for 2 hours , as before . we then washed the cells and incubated them in non - radioactive medium for a 2 or 6 hour ' chase ' . as can be seen in figure 4b , the rate of decrease in radiolabeled protein increased as the cells increased in size . thus , the rates of both synthesis and degradation of short - lived proteins increase with schwann cell size , and the net accumulation of protein is independent of size . it remains a mystery how mammalian cells maintain a constant difference between protein synthesis and degradation independent of their size , although there is evidence that this tight coupling between protein synthesis and degradation can depend on extracellular signals . we showed previously that schwann cell growth depends on extracellular signals , such as those present in fcs . to determine if cell growth remains linear in different concentrations of such extracellular factors , we cultured quiescent schwann cells in aphidicolin and various concentrations of fcs , and measured cell volume over time . as can be seen in figure 5 , the rate of growth remained linear for up to 9 days ( figure 5a ) but increased with increasing amounts of fcs ( figure 5b ) . even in 50% serum , cell growth remained linear and was faster than in 10% serum ( not shown ) . thus , even at high concentrations of fcs , it seems that the levels of extracellular growth factors , rather than anything inside the cells , limit schwann cell growth . in figure 5c , we show how the spread of cell sizes changed as aphidicolin - arrested schwann cells grew over time . like cell size itself , the spread of sizes increased linearly with time , as expected in a situation where some cells are growing faster and some slower than the mean rate , but all are growing linearly , independent of their size . we have shown that the growth rate of schwann cells is linear , unlike in yeasts , which means that cell - size checkpoints are unnecessary to explain how proliferating schwann cells maintain their size in a particular environment . as discussed in the background , a crucial line of evidence for the existence of cell - size checkpoints in yeasts is that they can rapidly change the size at which they divide , by adjusting their size threshold , when switched to different nutrient conditions . we therefore tested whether proliferating schwann cells behave similarly when shifted from serum - free to serum - containing culture medium . if schwann cells had cell - size checkpoints , one might expect them to adjust their size rapidly to the new condition . if they do not have such checkpoints , one would expect the cells to adjust their size only gradually to the new conditions over a number of cell cycles , much as illustrated for the small cells in figure 1 . we maintained purified schwann cells in a proliferative state on laminin , in dmem supplemented with ggf 2 , forskolin , insulin , and serum - free schwann - cell - conditioned medium , with or without 3% fcs , passaging the cells when they reached near - confluence . in both conditions , the schwann cells maintained their average size over time , when assessed at the time of passage ( figure 6a ) , although the cells in serum were , on average , more than twice the size of cells without serum ( figure 6b ) . in this respect , the cells behave similarly to yeast cells , which grow at a faster rate and divide at a larger size when proliferating in a nutrient - rich medium than in a nutrient - poor medium . we then switched the schwann cells that had been proliferating in serum - free medium to serum - containing medium . we plated these ' switched ' cells and the cells maintained throughout the experiment in serum - containing medium at the same plating density both now in serum - containing medium . we passaged them when they reached about 300,000 cells per well , which was usually every 3 days . we counted cell numbers and measured mean cell volume of the population every day using a coulter counter . the average cell - cycle times of the two populations were approximately the same ( figures 6c , d ) . unlike yeasts , the switched cells took around six divisions and about 10 days before they divided at the characteristic size of schwann cells maintained in serum - containing medium all along ( figure 6e ) . the finding that big schwann cells grow at the same rate as small schwann cells means that they do not require cell - size checkpoints to maintain a constant size distribution as they proliferate . the finding that they take many divisions to adjust to new culture conditions strongly suggests that they do not have such checkpoints , or at least not ones that resemble those operating in yeast cells . in addition , their slow adjustment to a change in culture conditions is the behavior predicted by the hypothetical model illustrated in figure 1 for proliferating cells that grow linearly and do not have cell - size checkpoints . whereas proliferating populations of yeast cells and schwann cells can both maintain a constant size over time , they seem to do so in very different ways . for yeasts , cell - size checkpoints apparently operate to coordinate cell growth and cell - cycle progression . for schwann cells , by contrast , extracellular signals that stimulate cell growth , cell - cycle progression , or both , appear to control the size at which the cells divide . although a population of schwann cells maintained a constant average cell size if passaged frequently ( figure 2 ) , the cells decrease in size if not passaged , even if the medium was replaced every day ( figure 7a ) , although they continue to proliferate ( figure 7b ) . this is presumably because there was increased competition for extracellular growth factors as the cultures got denser . a similar competition for extracellular signals has been shown to regulate the size of lymphocytes in vivo . apparently , signaling for schwann cell growth is more affected by the competition than signaling for cell - cycle progression . we found previously that schwann cells do not maintain a constant size over time when proliferating in insulin - like growth factor i ( igf - i ) and ggf 2 in the absence of fcs or schwann - cell - conditioned medium , presumably because growth stimulation was insufficient to keep up with mitogenic stimulation . we suspect that the size of most proliferating animal cells in vivo is controlled by the levels of extracellular signals in a way that is similar to how schwann cell size is controlled in culture . in the few studies that have analyzed the size of proliferating animal cells during normal development , for example , it seems that cell size can vary significantly for the same cell type . during development of the wing imaginal disc in drosophila , for instance , the size of the disc cells varies throughout development : the cells initially grow without dividing and then proliferate and get progressively smaller . , each yeast cell grows and divides as fast as the nutrient supply allows , and it must quickly adapt to changing extracellular conditions . the growth and division of animal cells , by contrast , must be carefully controlled and coordinated for the good of the animal as a whole , and this control relies mainly on intercellular signaling . thus , whereas yeast cell proliferation is controlled mainly by nutrients , animal cell proliferation is controlled mainly by signals from other cells . as such signals seem usually to be present at limiting , rather than saturating , concentrations , small changes in their levels can powerfully influence cell growth and proliferation . given its importance , it is surprising how little is known about how the levels of such signals are controlled in animals . animal cell proliferation also depends on nutrients , however , and our results do not exclude the possibility that cell - size checkpoints might be revealed by nutrient deprivation experiments . our findings also do not exclude the possibility that animal cells such as lymphocytes , which can proliferate in suspension like yeast cells , might use cell - size checkpoints to coordinate their growth with cell - cycle progression . these will be important avenues to explore in the future , but we shall leave this to others . we maintained the cells in a proliferative state in ' complete ' medium : dulbecco 's modified eagles ' medium ( dmem ) , supplemented with 3% fetal calf serum ( fcs ) , the neuregulin glial growth factor 2 ( ggf 2 ) , and the adenylyl cyclase stimulator forskolin . we passaged the cells before they reached confluence and measured their size ( volume ) in a coulter counter after removing the cells from the culture dish with trypsin at the time of passage . as expected , the average size of the cells remained unchanged with repeated passaging ( figure 2 ) . to determine if schwann cell growth depends on cell size , we used the dna polymerase inhibitor aphidicolin to arrest the cells in s phase . we then replated them and treated them with aphidicolin and simultaneously stimulated them with complete medium to re - enter the cell cycle and begin to grow . in these conditions , the cells remained arrested in s phase and continued to increase in size for many days . if schwann cell growth were like yeast cell growth , the rate of cell growth would increase over time as the cells enlarged , and the growth curve would be exponential - like . to determine cell - growth rate , we measured the volume of cells in parallel cultures every 24 hours after removing the cells from the culture dish with trypsin . as can be seen in figure 3a , cell growth was linear over a period of 5 days , indicating that the cells added a constant amount of volume each day , independent of their size . to confirm that the increase in cell volume reflected an increase in protein , we measured the amount of protein per cell , with similar results ( figure 3b ) . these findings indicate that large schwann cells do not grow faster than small schwann cells , at least in these conditions . as explained in the background , this means that cell - size checkpoints need not be invoked to explain why these cells maintain a constant average size ( figure 2 ) and cell - size distribution ( not shown ) when proliferating in complete medium . although the experiments were not done with this question in mind , there have been previous reports indicating that other types of mammalian cells grow linearly , independent of their size . hutson and mortimore , for example , starved mice , which causes the liver to shrink rapidly , solely as a result of hepatocyte shrinkage , rather than an increase in cell death or a decrease in cell proliferation . when they re - fed the mice , the liver re - grew rapidly , entirely as a result of hepatocyte growth , which was clearly linear . similarly , when deleu et al . stimulated dog thyrocytes with insulin , the thyrocytes grew but did not proliferate , and the growth was linear . in an experiment to test whether cell - size checkpoints were necessary , brooks and shields separated quiescent 3t3 cells by size and stimulated them to re - enter the cell cycle ; they found that large cells did not grow faster than small cells at the same point in the cycle , consistent with linear growth . we have not found any reports in which big mammalian cells have been observed to grow faster than small cells of the same type and at the same point of the cell cycle . it thus seems likely that most mammalian cells grow linearly , independent of their size , and that they therefore do not require cell - size checkpoints to maintain a constant size distribution as they proliferate . our finding that serum - stimulated , aphidicolin - arrested schwann cells add the same net amount of protein per cell per day , independent of their size , raised the possibility that big schwann cells synthesize protein at the same rate as small schwann cells . to test this possibility we cultured schwann cells in complete medium and aphidicolin and , after 24 , 48 , or 72 hours , added [ s]-methionine and [ s]-cysteine for two hours . as can be seen in figure 4a , the rate of protein synthesis increased as the cells increased in size over time . as the net amount of protein added per day does not increase as the schwann cells get bigger ( figure 3 ) , the rate of protein degradation ( and/or secretion ) must also increase as the cells get bigger . to determine the rate of protein degradation , we cultured the cells in complete medium and aphidicolin and , after various times , added [ s]-methionine and [ s]-cysteine for 2 hours , as before . we then washed the cells and incubated them in non - radioactive medium for a 2 or 6 hour ' chase ' . as can be seen in figure 4b , the rate of decrease in radiolabeled protein increased as the cells increased in size . thus , the rates of both synthesis and degradation of short - lived proteins increase with schwann cell size , and the net accumulation of protein is independent of size . it remains a mystery how mammalian cells maintain a constant difference between protein synthesis and degradation independent of their size , although there is evidence that this tight coupling between protein synthesis and degradation can depend on extracellular signals . we showed previously that schwann cell growth depends on extracellular signals , such as those present in fcs . to determine if cell growth remains linear in different concentrations of such extracellular factors , we cultured quiescent schwann cells in aphidicolin and various concentrations of fcs , and measured cell volume over time . as can be seen in figure 5 , the rate of growth remained linear for up to 9 days ( figure 5a ) but increased with increasing amounts of fcs ( figure 5b ) . even in 50% serum , cell growth remained linear and was faster than in 10% serum ( not shown ) . thus , even at high concentrations of fcs , it seems that the levels of extracellular growth factors , rather than anything inside the cells , limit schwann cell growth . in figure 5c , we show how the spread of cell sizes changed as aphidicolin - arrested schwann cells grew over time . like cell size itself , the spread of sizes increased linearly with time , as expected in a situation where some cells are growing faster and some slower than the mean rate , but all are growing linearly , independent of their size . we have shown that the growth rate of schwann cells is linear , unlike in yeasts , which means that cell - size checkpoints are unnecessary to explain how proliferating schwann cells maintain their size in a particular environment . as discussed in the background , a crucial line of evidence for the existence of cell - size checkpoints in yeasts is that they can rapidly change the size at which they divide , by adjusting their size threshold , when switched to different nutrient conditions . we therefore tested whether proliferating schwann cells behave similarly when shifted from serum - free to serum - containing culture medium . if schwann cells had cell - size checkpoints , one might expect them to adjust their size rapidly to the new condition . if they do not have such checkpoints , one would expect the cells to adjust their size only gradually to the new conditions over a number of cell cycles , much as illustrated for the small cells in figure 1 . we maintained purified schwann cells in a proliferative state on laminin , in dmem supplemented with ggf 2 , forskolin , insulin , and serum - free schwann - cell - conditioned medium , with or without 3% fcs , passaging the cells when they reached near - confluence . in both conditions , the schwann cells maintained their average size over time , when assessed at the time of passage ( figure 6a ) , although the cells in serum were , on average , more than twice the size of cells without serum ( figure 6b ) . in this respect , the cells behave similarly to yeast cells , which grow at a faster rate and divide at a larger size when proliferating in a nutrient - rich medium than in a nutrient - poor medium . we then switched the schwann cells that had been proliferating in serum - free medium to serum - containing medium . we plated these ' switched ' cells and the cells maintained throughout the experiment in serum - containing medium at the same plating density both now in serum - containing medium . we passaged them when they reached about 300,000 cells per well , which was usually every 3 days . we counted cell numbers and measured mean cell volume of the population every day using a coulter counter . the average cell - cycle times of the two populations were approximately the same ( figures 6c , d ) . unlike yeasts , the switched cells took around six divisions and about 10 days before they divided at the characteristic size of schwann cells maintained in serum - containing medium all along ( figure 6e ) . the finding that big schwann cells grow at the same rate as small schwann cells means that they do not require cell - size checkpoints to maintain a constant size distribution as they proliferate . the finding that they take many divisions to adjust to new culture conditions strongly suggests that they do not have such checkpoints , or at least not ones that resemble those operating in yeast cells . in addition , their slow adjustment to a change in culture conditions is the behavior predicted by the hypothetical model illustrated in figure 1 for proliferating cells that grow linearly and do not have cell - size checkpoints . whereas proliferating populations of yeast cells and schwann cells can both maintain a constant size over time , they seem to do so in very different ways . for yeasts , cell - size checkpoints apparently operate to coordinate cell growth and cell - cycle progression . for schwann cells , by contrast , extracellular signals that stimulate cell growth , cell - cycle progression , or both , appear to control the size at which the cells divide . although a population of schwann cells maintained a constant average cell size if passaged frequently ( figure 2 ) , the cells decrease in size if not passaged , even if the medium was replaced every day ( figure 7a ) , although they continue to proliferate ( figure 7b ) . this is presumably because there was increased competition for extracellular growth factors as the cultures got denser . a similar competition for extracellular signals has been shown to regulate the size of lymphocytes in vivo . apparently , signaling for schwann cell growth is more affected by the competition than signaling for cell - cycle progression . we found previously that schwann cells do not maintain a constant size over time when proliferating in insulin - like growth factor i ( igf - i ) and ggf 2 in the absence of fcs or schwann - cell - conditioned medium , presumably because growth stimulation was insufficient to keep up with mitogenic stimulation . we suspect that the size of most proliferating animal cells in vivo is controlled by the levels of extracellular signals in a way that is similar to how schwann cell size is controlled in culture . in the few studies that have analyzed the size of proliferating animal cells during normal development , for example , it seems that cell size can vary significantly for the same cell type . during development of the wing imaginal disc in drosophila , for instance , the size of the disc cells varies throughout development : the cells initially grow without dividing and then proliferate and get progressively smaller . the lifestyles of yeasts and animal cells are crucially different . as a unicellular organism , each yeast cell grows and divides as fast as the nutrient supply allows , and it must quickly adapt to changing extracellular conditions . the growth and division of animal cells , by contrast , must be carefully controlled and coordinated for the good of the animal as a whole , and this control relies mainly on intercellular signaling . thus , whereas yeast cell proliferation is controlled mainly by nutrients , animal cell proliferation is controlled mainly by signals from other cells . as such signals seem usually to be present at limiting , rather than saturating , concentrations , small changes in their levels can powerfully influence cell growth and proliferation . given its importance , it is surprising how little is known about how the levels of such signals are controlled in animals . animal cell proliferation also depends on nutrients , however , and our results do not exclude the possibility that cell - size checkpoints might be revealed by nutrient deprivation experiments . our findings also do not exclude the possibility that animal cells such as lymphocytes , which can proliferate in suspension like yeast cells , might use cell - size checkpoints to coordinate their growth with cell - cycle progression . these will be important avenues to explore in the future , but we shall leave this to others . all reagents were from sigma - aldrich ( gillingham , uk ) , unless indicated otherwise . for experiments on growth rate , schwann cells were purified from postnatal day 7 rat sciatic nerve by sequential immunopanning as described previously . the cells were expanded on poly - d - lysine- and fibronectin - coated culture dishes ( falcon ; bd biosciences , oxford , uk ) in ' complete medium ' : dmem ( gibco ; invitrogen ltd , paisley , uk ) supplemented with 3% fcs , 1 m forskolin ( calbiochem ; merck biosciences , nottingham , uk ) and 20 ng / ml recombinant ggf 2 ( a gift from m. marchionni , cambridge neuroscience inc . , cambridge , usa ) . cells were passaged every 3 days and were > 99.9% pure as judged by antigenic markers . for the switch experiments , purified schwann cells were maintained in a proliferative state on poly - d - lysine- and laminin - coated culture dishes , in dmem supplemented with 20 ng / ml ggf 2 , 1 m forskolin , 10 g / ml insulin , serum - free schwann - cell - conditioned medium ( to a final concentration of 20% ) , 100 g / ml transferrrin , 100 g / ml bovine serum albumin , 16 mg / ml putrescine , and 40 ng / ml selenium , either with ( serum - containing sc medium ) or without ( serum - free sf medium ) 3% fcs . cells were plated at a concentration of 100,000 cells per well of a six - well culture plate ( falcon ) and passaged when they reached a concentration of around 300,000 cells per well . for cell - growth experiments , about 4 10 quiescent cells were then plated in each well of a six - well poly - d - lysine- and fibronectin - coated culture dish in dmem containing 1% , 3% , 10% , or 50% fcs and 2 g / ml aphidicolin to arrest the cells in s phase . cell volume and cell number ( to assess cell - cycle time ) were assessed every 24 hours in a coulter counter ( multisizer ii , beckman - coulter , high wycombe , uk ) , using a volumetric analysis , after removing the cells from the culture dish with trypsin - edta ( gibco ) and resuspending them in isoton ii ( beckman - coulter ) . between 1,000 and 5,000 cells were counted per well , and the data were analyzed using coulter multisizer accucomp software ( beckman - coulter ) . about 10quiescent cells were plated in a poly - d - lysine - and fibronectin - coated 15 cm culture dish ( falcon ) in dmem containing 1% , 3% , or 10% fcs and 2 g / ml aphidicolin . the cells were rinsed twice with phosphate - buffered saline ( pbs ) , scraped off the dish , and centrifuged at 3,000 g for 3 minutes . cell number was determined by measuring the concentration of dna in the aliquot and assuming the haploid amount of dna per cell is 6 pg . protein concentration was determined by lysing the cells on ice for 15 minutes in 0.4% triton and 0.2% sodium dodecyl sulfate ( sds ) , in the presence of protease inhibitors ( boehringer mannheim ) and using a micro - bca ( bicinchoninic acid ) assay with a bovine serum albumin ( bsa ) standard . about 10quiescent cells were plated in a poly - d - lysine- and fibronectin - coated 6 cm culture dish in medium containing 3% fcs and 2 g / ml aphidicolin . in one experiment , the protein synthesis rate of proliferating cells in complete medium was determined . at the time point to be investigated , cells were washed twice with cysteine- and methionine - free dmem ( gibco ) . then , 2.5 ml of this dmem was added , together with glutamate , forskolin , 3% fcs , and 100 ci of [ s]-methionine and [ s]-cysteine ( amersham , little chalfont , uk ) for 2 hours at 37c . the amount of radiolabel was saturating , as the amount in the medium did not decrease significantly during the 2-hour incubation . to determine the protein synthesis rate , the cells were then washed , trypsinized , centrifuged at 3,000 g , and resuspended in serum - free medium . aliquots were taken for cell - number analysis in a coulter counter and for protein analysis . then , 100% ice - cold trichloroacetic acid ( tca ) was added to each aliquot to a final concentration of 10% , to precipitate the protein . after 10 minutes on ice , the solutions were centrifuged at 12,000 g to pellet the precipitated protein , and the amount of free radiolabel was assessed by removing three aliquots and counting them in a scintillation counter . the amount of radiolabel incorporated into protein was calculated by subtracting the value of the non - incorporated label from the value of the label in the total cell lysate . to determine the rate of protein degradation , cells were radiolabeled as above , washed three times with complete medium , and then left for either 2 or 6 hours at 37c . the amount of radiolabeled protein still remaining in the cells after the chase was determined as described above . for experiments on growth rate , schwann cells were purified from postnatal day 7 rat sciatic nerve by sequential immunopanning as described previously . the cells were expanded on poly - d - lysine- and fibronectin - coated culture dishes ( falcon ; bd biosciences , oxford , uk ) in ' complete medium ' : dmem ( gibco ; invitrogen ltd , paisley , uk ) supplemented with 3% fcs , 1 m forskolin ( calbiochem ; merck biosciences , nottingham , uk ) and 20 ng / ml recombinant ggf 2 ( a gift from m. marchionni , cambridge neuroscience inc . , cambridge , usa ) . cells were passaged every 3 days and were > 99.9% pure as judged by antigenic markers . for the switch experiments , purified schwann cells were maintained in a proliferative state on poly - d - lysine- and laminin - coated culture dishes , in dmem supplemented with 20 ng / ml ggf 2 , 1 m forskolin , 10 g / ml insulin , serum - free schwann - cell - conditioned medium ( to a final concentration of 20% ) , 100 g / ml transferrrin , 100 g / ml bovine serum albumin , 16 mg / ml putrescine , and 40 ng / ml selenium , either with ( serum - containing sc medium ) or without ( serum - free sf medium ) 3% fcs . cells were plated at a concentration of 100,000 cells per well of a six - well culture plate ( falcon ) and passaged when they reached a concentration of around 300,000 cells per well . for cell - growth experiments , quiescent schwann cells were obtained by culturing them to confluence in complete medium . about 4 10 quiescent cells were then plated in each well of a six - well poly - d - lysine- and fibronectin - coated culture dish in dmem containing 1% , 3% , 10% , or 50% fcs and 2 g / ml aphidicolin to arrest the cells in s phase . cell volume and cell number ( to assess cell - cycle time ) were assessed every 24 hours in a coulter counter ( multisizer ii , beckman - coulter , high wycombe , uk ) , using a volumetric analysis , after removing the cells from the culture dish with trypsin - edta ( gibco ) and resuspending them in isoton ii ( beckman - coulter ) . between 1,000 and 5,000 cells were counted per well , and the data were analyzed using coulter multisizer accucomp software ( beckman - coulter ) . about 10quiescent cells were plated in a poly - d - lysine - and fibronectin - coated 15 cm culture dish ( falcon ) in dmem containing 1% , 3% , or 10% fcs and 2 g / ml aphidicolin . the cells were rinsed twice with phosphate - buffered saline ( pbs ) , scraped off the dish , and centrifuged at 3,000 g for 3 minutes . cell number was determined by measuring the concentration of dna in the aliquot and assuming the haploid amount of dna per cell is 6 pg . protein concentration was determined by lysing the cells on ice for 15 minutes in 0.4% triton and 0.2% sodium dodecyl sulfate ( sds ) , in the presence of protease inhibitors ( boehringer mannheim ) and using a micro - bca ( bicinchoninic acid ) assay with a bovine serum albumin ( bsa ) standard . about 10quiescent cells were plated in a poly - d - lysine- and fibronectin - coated 6 cm culture dish in medium containing 3% fcs and 2 g / ml aphidicolin . in one experiment , the protein synthesis rate of proliferating cells in complete medium was determined . at the time point to be investigated , cells were washed twice with cysteine- and methionine - free dmem ( gibco ) . then , 2.5 ml of this dmem was added , together with glutamate , forskolin , 3% fcs , and 100 ci of [ s]-methionine and [ s]-cysteine ( amersham , little chalfont , uk ) for 2 hours at 37c . the amount of radiolabel was saturating , as the amount in the medium did not decrease significantly during the 2-hour incubation . to determine the protein synthesis rate , the cells were then washed , trypsinized , centrifuged at 3,000 g , and resuspended in serum - free medium . aliquots were taken for cell - number analysis in a coulter counter and for protein analysis . radiolabel incorporation into protein was assessed by lysing the cells in 0.2% triton and then removing three aliquots and counting each in a scintillation counter . then , 100% ice - cold trichloroacetic acid ( tca ) was added to each aliquot to a final concentration of 10% , to precipitate the protein . after 10 minutes on ice , the solutions were centrifuged at 12,000 g to pellet the precipitated protein , and the amount of free radiolabel was assessed by removing three aliquots and counting them in a scintillation counter . the amount of radiolabel incorporated into protein was calculated by subtracting the value of the non - incorporated label from the value of the label in the total cell lysate . to determine the rate of protein degradation , cells were radiolabeled as above , washed three times with complete medium , and then left for either 2 or 6 hours at 37c . the amount of radiolabeled protein still remaining in the cells after the chase was determined as described above . the authors of the second research article in this print issue ( ) have both had close associations with journal of biology , and martin raff continues to do so . neither author was involved in the refereeing of this article , in the decision to publish it , or in the choice of accompanying commentary . this work and the authors were supported by the medical research council of the uk . we are grateful to robert brooks , murdoch mitchison , and paul nurse for helpful discussions . a hypothetical model showing why the progeny of large and small daughter cells eventually return to the mean population size over time if large and small cells grow and progress through the cell cycle at the same rates ( after brooks ) . the initial division is unequal and produces one cell of 10 mass units and one cell of 1 mass unit ; the subsequent eight divisions of the progeny cells are equal . following thus , the initial small daughter cell grows to 6.5 units before it divides to produce two daughters of about 3.2 units each , while the initial large daughter cell grows to 15.5 units before it divides to produce two daughters of about 7.8 units . mean cell volume remains constant as purified schwann cells proliferate in complete medium and are passaged every three days . the growth of aphidicolin - arrested schwann cells is linear over time , indicating that it is independent of cell size . ( a ) quiescent cells were cultured in complete medium with aphidicolin to arrest the cells in s phase . each point represents the mean standard deviation of the results derived from three independent experiments , where , for each experiment , the mode cell volumes of three plates were measured and averaged . ( b ) cells were cultured as in ( a ) , but protein per cell , rather than cell volume , was measured at the time points shown . the results are shown as the mean standard deviation of three cultures in one experiment , in which about 10cells were assayed for each point . the experiments in ( a ) and ( b ) were performed three times with similar results . ( a ) quiescent cells were cultured in 3% fcs , forskolin , and aphidicolin for various times . the rate of protein synthesis was then determined by measuring the amount of incorporation of [ s]-methionine and [ s]-cysteine into cellular protein over 2 hours . the results are shown as the mean standard deviation of nine independent plates of cells . ( b ) quiescent cells were treated as in ( a ) and then either harvested immediately ( 0 hours after pulse ) to assess the rate of total protein synthesis or washed and ' chased ' with medium containing non - radioactive methionine and cysteine for 2 or 6 hours before harvesting to assess the rate of protein degradation . the shallowness of the curve for the 24-hour - arrested cells is likely to be the result of the lower than expected value at 0 hours . the 0 hour result in ( a ) is likely to be more accurate , as it represents the mean of nine independent cultures , instead of three . if one uses the value of 80 , the curve in ( b ) for the 24-hour - arrested cells would be steeper . the experiments in ( a ) and ( b ) were performed three times with similar results . schwann cell growth remains linear for 9 days but increases with increasing concentrations of serum . in ( a ) the cells were cultured in 1% fcs , forskolin , and aphidicolin , while in ( b ) they were cultured in forskolin and aphidicolin and various concentrations of fcs . ( c ) the cells were cultured as in ( a ) , but each point represents the mean standard deviation of cell volumes from one plate of cells . schwann cells adjust their size slowly when shifted from serum - free ( sf ) medium to serum - containing ( sc ) medium . the cells were plated at 100,000 cells per well and were passaged when they reached a density of about 300,000 cells per well . ( a , b ) the mean volume of cells proliferating in either sc or sf medium was measured in a coulter counter at the time of passage . the raw data for each condition are shown in ( a ) , and the mean standard deviation of the mode cell volume at passage is shown in ( b ) . ( c , d ) the cell - cycle time of schwann cells proliferating either in sc medium or in sc medium after a shift from sf medium was measured by determining the rate at which cell number increased . the raw data for each condition are shown in ( c ) , and the mean standard deviation of four population - doubling times is shown in ( d ) . ( e ) the size of cells proliferating in sc medium , in sf medium , or in sc medium after a shift from sf medium ( ' switched ' cells ) was measured every day in a coulter counter . because the cells in sc medium and the switched cells had similar cycle times see ( d ) they were passaged about every 3 days in both cases , when they reached around 300,000 cells per well ; the cells in sf medium cycled more slowly and cells were cultured in serum - containing medium , with or without passaging on day 4 . in both cases , 100,000 cells were plated per well , and the medium was changed every day . mode cell volume ( a ) and cell number ( b )[/INST]backgroundit is widely believed that cell - size checkpoints help to coordinate cell growth and cell - cycle progression , so that proliferating eukaryotic cells maintain their size . there is strong evidence for such size checkpoints in yeasts , which maintain a constant cell - size distribution as they proliferate , even though large yeast cells grow faster than small yeast cells . moreover , when yeast cells are shifted to better or worse nutrient conditions , they alter their size threshold within one cell cycle . populations of mammalian cells can also maintain a constant size distribution as they proliferate , but it is not known whether this depends on cell - size checkpoints.resultswe show that proliferating rat schwann cells do not require a cell - size checkpoint to maintain a constant cell - size distribution , as , unlike yeasts , large and small schwann cells grow at the same rate , which depends on the concentration of extracellular growth factors . in addition , when shifted from serum - free to serum - containing medium , schwann cells take many divisions to increase their size to that appropriate to the new condition , suggesting that they do not have cell - size checkpoints similar to those in yeasts.conclusionsproliferating schwann cells and yeast cells seem to use different mechanisms to coordinate their growth with cell - cycle progression . whereas yeast cells use cell - size checkpoints , schwann cells apparently do not . it seems likely that many mammalian cells resemble schwann cells in this respect .</s>

U.S. Catholics Welcome a Papal Change: In a New York Times/CBS poll, the majority of Catholics said Pope Benedict XVI made the right decision to step down and hope for a more liberally focused leadership. Roman Catholics in the United States say that their church and bishops are out of touch, and that the next pope should lead the church in a more modern direction on issues like birth control and ordaining women and married men as priests, according to the latest New York Times/CBS News poll. Seven out of 10 say Pope Benedict XVI and the Vatican have done a poor job of handling sexual abuse, a significant rise from three years ago. A majority said that the issue had led them to question the Vatican’s authority. The sexual abuse of children by priests is the largest problem facing the church, Catholics in the poll said. Three-fourths of those polled said they thought it was a good idea for Benedict to resign. Most wanted the next pope to be “someone younger, with new ideas.” A majority said they wanted the next pope to make the church’s teachings more liberal. With cardinals now in Rome preparing to elect Benedict’s successor, the poll indicated that the church’s hierarchy had lost the confidence and allegiance of many American Catholics, an intensification of a long-term trend. They like their priests and nuns, but many feel that the bishops and cardinals do not understand their lives. “I don’t think they are in the trenches with people,” said Therese Spender, 51, a homemaker in Fort Wayne, Ind., who said she attended Mass once a week and agreed to answer further questions after the poll. “They go to a lot of meetings, but they are not out in the street.” Even Catholics who frequently attend Mass said they were not following the bishops’ lead on issues that the church had recently invested much energy, money and credibility in fighting — artificial birth control and same-sex marriage. Eric O’Leary, 38, a funeral director in Des Moines who attends Mass weekly, said: “I would like them not to be so quick to condemn people because of their sexual preference or because of abortion, or to refuse priests the right to get married or women to be priests. I don’t think the church should get involved in whether or not people use birth control.” The nationwide telephone poll was conducted on landlines and cellphones from Feb. 23 to 27, when many Catholics were still absorbing news of the first resignation of a pope in 600 years. The margin of sampling error is plus or minus four percentage points for the 580 Catholics, who were oversampled for purposes of analysis in the survey of 1,585 adults. Benedict, a soft-spoken scholar and a church traditionalist, had apparently made little impression on American Catholics in his eight years as pope. Half of those in the poll said they either had no opinion of him or had not heard enough about him. Nevertheless, 4 in 10 had a favorable opinion, and only one in 10 unfavorable. “He’s written three or four books, and his writings are incredible,” said Leonard Lefebvre, 70, a retired economist in Tequesta, Fla. “He’s continued on course, and he’s held the religion to where it’s supposed to be at.” The poll suggested that the papacy no longer occupies the exalted position it once did. Asked whether the pope is infallible when he teaches on matters of morality and faith, 40 percent said yes, 46 percent said no, and 14 percent said they did not know. Nearly 8 in 10 Catholics polled said they would be more likely to follow their conscience on “difficult moral questions” than to follow the pope’s teachings. When asked which “one thing” they would “most like to see the next pope accomplish,” the most common responses that respondents volunteered were, in order: bring people back to church, modernize the church, unify the church, and do something about sexual abuse. A spate of new information about prelates hiding the misdeeds of pedophile priests appeared to have taken a toll. A higher percentage of Catholics said the pope and the Vatican had done a poor job of handling reports of past sexual abuse recently (69 percent) compared with 2010 (55 percent), when the abuse scandal flared in many European countries. This is despite the church’s many reforms in the last 10 years and reports of abuse by priests in the United States declining drastically. Majorities said they wanted to see the next pope maintain the church’s opposition to abortion and the death penalty, even though they themselves were not opposed to them. Three-quarters of Catholics supported abortion under at least some circumstances, and three-fifths favored the death penalty. “I can understand how the Catholic Church stands against it,” said Geri Toni, 57, of abortion. “We are not supposed to kill. That is one of our Ten Commandments.” ||||| Pope Benedict XVI, in failing health, became the first pope in six centuries to retire. Allen Pizzey reports from the Vatican on the pope's final day. Analysis by the CBS News Polling Unit: Sarah Dutton, Jennifer De Pinto, Anthony Salvanto and Fred Backus. As the College of Cardinals descends on Rome this week to select the world's next pope, most U.S. Catholics want the new pope to be younger, to have new ideas, and to liberalize the church's teachings on issues like birth control, ordaining women, and permitting priests to marry, according to a new poll by CBS News/New York Times. When former Pope Benedict XVI ascended to the Papacy after his 78th birthday in 2005, he was known for defending traditional Catholic teachings and values. As he becomes the first pope to retire since the Middle Ages, most Catholics - 66 percent - say they would prefer the next Pope to be younger with new ideas, rather than older with more experience. The poll, conducted among a random sample of 580 Catholic adults from Feb. 23-27, showed a groundswell of support among U.S. Catholics for a more modern church in general: A majority said the Catholic Church is out of touch with the needs of its members. More specifically, over half of Catholics - 54 percent - would like the next pope to espouse more liberal teachings going forward. Only 19 percent hoped for a continuation of Benedict's teachings, and 18 percent cited a desire for someone with more conservative ideas. Foremost among those subjects where most Catholics see room for change is on the question of contraception: 91 percent said the next Pope should favor the use of condoms to help stop HIV, and 71 percent said he should favor artificial methods of birth control. Sixty-nine percent of Catholics said, too, that priests should be able to get married, and the same number said women should be able to become priests. A majority of Catholics (56 percent) think the pope should continue to support the Catholic Church's opposition to the death penalty and legalized abortion, however. Regardless, Catholics don't think it is necessary to agree with the pope on issues like abortion and birth control in order to be a faithful member of the church. Eighty-three percent of Catholics said they think it's possible to disagree with the pope on issues like these and still be a good Catholic, and 78 percent of American Catholics are more likely to follow their own consciences rather than the pope's teachings (13 percent) on difficult moral issues. One challenge for the next pope will be to convince Catholics that the church understands them. Just 39 percent of Catholics say the church is in touch with the needs of Catholics today. Far more - 53 percent -- say it is out of touch. Fewer people now (29 percent) than in 2005 (38 percent) have a great deal of confidence that the next pope will be in touch with their needs. Even so, 74 percent of Catholics say they have at least some confidence that the College of Cardinals will select a Pope who fits this description. Asked what they most want the next pope to accomplish, Catholics cited a desire to see him bring people back to the church (12 percent). Nine percent said they want him to modernize it, eight percent want him to unify it, and another eight percent want to see something done about the sex abuse scandals. Seven percent said they want the new pope to allow priests to marry, and the same number wants him to change the rules on birth control and homosexuality. Nearly half of Catholics say it doesn't matter to them where in the world the next Pope comes from. Fourteen percent think the next pope should come from Latin America, 13 percent think he should come from Europe, four percent think he should come from Africa, and 17 percent say someplace else. Hispanic Catholics (23 percent) are much more likely than Catholics overall (14 percent) to want the next Pope to come from Latin America. no previous page next

– The last pope was installed as a 78-year-old spring chicken who wasn't cool with birth control. This time around, a majority of US Catholics think that should change. A CBS News/New York Times poll finds that 66% of American Catholics want a pope who is "younger with new ideas," compared to 26% who want to stick with someone "older with more experience." And 54% want the new pope to "change to more liberal teachings," compared to 19% who want Benedict's more traditional teachings to be continued and 18% who want someone even more conservative. The poll found that a majority of US Catholics think the church and its bishops and cardinals are out of touch with the modern world and disconnected from modern Catholics. Exactly which issues should the new pope liberalize? A huge number say birth control: 71% think he should OK artificial birth control, and a massive 91% say he should approve of condom use to stop the spread of HIV. Another big number, 69%, say he should allow priests to get married; the same percentage favors allowing women priests; and 62% think gay marriage should be legal. But a majority of respondents still hold traditional views on some matters: 56% think the pope should continue to oppose the death penalty and abortion.

<s>[INST]U.S. Catholics Welcome a Papal Change: In a New York Times/CBS poll, the majority of Catholics said Pope Benedict XVI made the right decision to step down and hope for a more liberally focused leadership. Roman Catholics in the United States say that their church and bishops are out of touch, and that the next pope should lead the church in a more modern direction on issues like birth control and ordaining women and married men as priests, according to the latest New York Times/CBS News poll. Seven out of 10 say Pope Benedict XVI and the Vatican have done a poor job of handling sexual abuse, a significant rise from three years ago. A majority said that the issue had led them to question the Vatican’s authority. The sexual abuse of children by priests is the largest problem facing the church, Catholics in the poll said. Three-fourths of those polled said they thought it was a good idea for Benedict to resign. Most wanted the next pope to be “someone younger, with new ideas.” A majority said they wanted the next pope to make the church’s teachings more liberal. With cardinals now in Rome preparing to elect Benedict’s successor, the poll indicated that the church’s hierarchy had lost the confidence and allegiance of many American Catholics, an intensification of a long-term trend. They like their priests and nuns, but many feel that the bishops and cardinals do not understand their lives. “I don’t think they are in the trenches with people,” said Therese Spender, 51, a homemaker in Fort Wayne, Ind., who said she attended Mass once a week and agreed to answer further questions after the poll. “They go to a lot of meetings, but they are not out in the street.” Even Catholics who frequently attend Mass said they were not following the bishops’ lead on issues that the church had recently invested much energy, money and credibility in fighting — artificial birth control and same-sex marriage. Eric O’Leary, 38, a funeral director in Des Moines who attends Mass weekly, said: “I would like them not to be so quick to condemn people because of their sexual preference or because of abortion, or to refuse priests the right to get married or women to be priests. I don’t think the church should get involved in whether or not people use birth control.” The nationwide telephone poll was conducted on landlines and cellphones from Feb. 23 to 27, when many Catholics were still absorbing news of the first resignation of a pope in 600 years. The margin of sampling error is plus or minus four percentage points for the 580 Catholics, who were oversampled for purposes of analysis in the survey of 1,585 adults. Benedict, a soft-spoken scholar and a church traditionalist, had apparently made little impression on American Catholics in his eight years as pope. Half of those in the poll said they either had no opinion of him or had not heard enough about him. Nevertheless, 4 in 10 had a favorable opinion, and only one in 10 unfavorable. “He’s written three or four books, and his writings are incredible,” said Leonard Lefebvre, 70, a retired economist in Tequesta, Fla. “He’s continued on course, and he’s held the religion to where it’s supposed to be at.” The poll suggested that the papacy no longer occupies the exalted position it once did. Asked whether the pope is infallible when he teaches on matters of morality and faith, 40 percent said yes, 46 percent said no, and 14 percent said they did not know. Nearly 8 in 10 Catholics polled said they would be more likely to follow their conscience on “difficult moral questions” than to follow the pope’s teachings. When asked which “one thing” they would “most like to see the next pope accomplish,” the most common responses that respondents volunteered were, in order: bring people back to church, modernize the church, unify the church, and do something about sexual abuse. A spate of new information about prelates hiding the misdeeds of pedophile priests appeared to have taken a toll. A higher percentage of Catholics said the pope and the Vatican had done a poor job of handling reports of past sexual abuse recently (69 percent) compared with 2010 (55 percent), when the abuse scandal flared in many European countries. This is despite the church’s many reforms in the last 10 years and reports of abuse by priests in the United States declining drastically. Majorities said they wanted to see the next pope maintain the church’s opposition to abortion and the death penalty, even though they themselves were not opposed to them. Three-quarters of Catholics supported abortion under at least some circumstances, and three-fifths favored the death penalty. “I can understand how the Catholic Church stands against it,” said Geri Toni, 57, of abortion. “We are not supposed to kill. That is one of our Ten Commandments.” ||||| Pope Benedict XVI, in failing health, became the first pope in six centuries to retire. Allen Pizzey reports from the Vatican on the pope's final day. Analysis by the CBS News Polling Unit: Sarah Dutton, Jennifer De Pinto, Anthony Salvanto and Fred Backus. As the College of Cardinals descends on Rome this week to select the world's next pope, most U.S. Catholics want the new pope to be younger, to have new ideas, and to liberalize the church's teachings on issues like birth control, ordaining women, and permitting priests to marry, according to a new poll by CBS News/New York Times. When former Pope Benedict XVI ascended to the Papacy after his 78th birthday in 2005, he was known for defending traditional Catholic teachings and values. As he becomes the first pope to retire since the Middle Ages, most Catholics - 66 percent - say they would prefer the next Pope to be younger with new ideas, rather than older with more experience. The poll, conducted among a random sample of 580 Catholic adults from Feb. 23-27, showed a groundswell of support among U.S. Catholics for a more modern church in general: A majority said the Catholic Church is out of touch with the needs of its members. More specifically, over half of Catholics - 54 percent - would like the next pope to espouse more liberal teachings going forward. Only 19 percent hoped for a continuation of Benedict's teachings, and 18 percent cited a desire for someone with more conservative ideas. Foremost among those subjects where most Catholics see room for change is on the question of contraception: 91 percent said the next Pope should favor the use of condoms to help stop HIV, and 71 percent said he should favor artificial methods of birth control. Sixty-nine percent of Catholics said, too, that priests should be able to get married, and the same number said women should be able to become priests. A majority of Catholics (56 percent) think the pope should continue to support the Catholic Church's opposition to the death penalty and legalized abortion, however. Regardless, Catholics don't think it is necessary to agree with the pope on issues like abortion and birth control in order to be a faithful member of the church. Eighty-three percent of Catholics said they think it's possible to disagree with the pope on issues like these and still be a good Catholic, and 78 percent of American Catholics are more likely to follow their own consciences rather than the pope's teachings (13 percent) on difficult moral issues. One challenge for the next pope will be to convince Catholics that the church understands them. Just 39 percent of Catholics say the church is in touch with the needs of Catholics today. Far more - 53 percent -- say it is out of touch. Fewer people now (29 percent) than in 2005 (38 percent) have a great deal of confidence that the next pope will be in touch with their needs. Even so, 74 percent of Catholics say they have at least some confidence that the College of Cardinals will select a Pope who fits this description. Asked what they most want the next pope to accomplish, Catholics cited a desire to see him bring people back to the church (12 percent). Nine percent said they want him to modernize it, eight percent want him to unify it, and another eight percent want to see something done about the sex abuse scandals. Seven percent said they want the new pope to allow priests to marry, and the same number wants him to change the rules on birth control and homosexuality. Nearly half of Catholics say it doesn't matter to them where in the world the next Pope comes from. Fourteen percent think the next pope should come from Latin America, 13 percent think he should come from Europe, four percent think he should come from Africa, and 17 percent say someplace else. Hispanic Catholics (23 percent) are much more likely than Catholics overall (14 percent) to want the next Pope to come from Latin America. no previous page next[/INST]– The last pope was installed as a 78-year-old spring chicken who wasn't cool with birth control. This time around, a majority of US Catholics think that should change. A CBS News/New York Times poll finds that 66% of American Catholics want a pope who is "younger with new ideas," compared to 26% who want to stick with someone "older with more experience." And 54% want the new pope to "change to more liberal teachings," compared to 19% who want Benedict's more traditional teachings to be continued and 18% who want someone even more conservative. The poll found that a majority of US Catholics think the church and its bishops and cardinals are out of touch with the modern world and disconnected from modern Catholics. Exactly which issues should the new pope liberalize? A huge number say birth control: 71% think he should OK artificial birth control, and a massive 91% say he should approve of condom use to stop the spread of HIV. Another big number, 69%, say he should allow priests to get married; the same percentage favors allowing women priests; and 62% think gay marriage should be legal. But a majority of respondents still hold traditional views on some matters: 56% think the pope should continue to oppose the death penalty and abortion.</s>

Image copyright AP Image caption Film director Osman Abu Laban lost four relatives in the disaster Debris and body parts have been found in the Mediterranean Sea by teams searching for a doomed EgyptAir plane, Greek and Egyptian officials say. Flight MS804 was en route from Paris to Cairo with 66 passengers and crew when it crashed early on Thursday. Items including seats and luggage have also been retrieved by Egyptian search crews. The debris was discovered about 290km (180 miles) north of Alexandria, the Egyptian military said. European Space Agency satellites spotted an oil slick in the area where the flight went missing but the organisation said there was no guarantee it was from the plane. The search is now focused on finding the plane's flight recorders, the Associated Press news agency reports. There were smoke alerts from the onboard toilet and the plane's electrics shortly before the signal was lost, according to data published on air industry website the Aviation Herald. However, there has been no independent confirmation. Egyptian President Abdel Fattah al-Sisi has expressed his "utmost sadness and regret" at the crash. Greek, Egyptian, French and UK military units have been taking part in a search operation near Greece's Karpathos island. Greece said radar showed the Airbus A320 had made two sharp turns and dropped more than 25,000ft (7,620m) before plunging into the sea. The focus of the investigation Egypt says the plane was more likely to have been brought down by a terrorist act than a technical fault. However, there has been "absolutely no indication" so far as to why the plane came down, French Foreign Minister Jean-Marc Ayrault said on Friday morning. Three investigators from the French air accident investigation bureau, along with a technical adviser from Airbus, have joined the Egyptian inquiry. The BBC has learned the plane that disappeared was forced to make an emergency landing in 2013 after the pilot noticed the engine overheating, but an official report said the defect had been repaired. In France, the focus is on whether a possible breach of security happened at Paris Charles de Gaulle airport. After last November's Paris attacks, some airport staff had their security clearance revoked over fears of links to Islamic extremists. Eric Moutet, a lawyer for some of those employees, told the BBC that there had been attempts by Islamists to recruit airport staff. "That is clear," he said. "There are people who are being radicalised in some of the trade unions, etc. The authorities have their work cut out with this problem." Media playback is unsupported on your device Media caption Aviation experts give their views on what may have happened to EgyptAir flight MS804 In October, an Airbus A321 operated by Russia's Metrojet blew up over Egypt's Sinai Peninsula, with all 224 people on board killed. Sinai Province, a local affiliate of the Islamic State jihadist group, said it had smuggled a bomb on board. What do we know about what happened? Flight MS804 left Paris at 23:09 local time on Wednesday (21:09 GMT) and was scheduled to arrive in the Egyptian capital soon after 03:15 local time (01:15 GMT) on Thursday. On the plane were 56 passengers, seven crew members and three security personnel. Greek aviation officials say air traffic controllers spoke to the pilot when he entered Greek airspace and everything appeared normal. They tried to contact him again at 02:27 Cairo time, as the plane was set to enter Egyptian airspace, but "despite repeated calls, the aircraft did not respond". Two minutes later it vanished from radar. Philip Baum, the editor of Aviation Security International Magazine, said given smoke was detected on board shortly before the crash it was unlikely to be a hijacking. "It's more likely a fire," he told the BBC. "Now whether that was a technical fire, a short circuit or whether it was because a bomb went off on board, we don't know." Media playback is unsupported on your device Media caption What happened to flight MS804? Richard Westcott examines the evidence so far Who were the victims? EgyptAir flight MS804 Passengers' nationalities 66 people on board - 56 passengers, seven crew members and three security personnel 30 Egyptians 15 French citizens 2 Iraqis 1 from Britain, Canada, Belgium, Kuwait, Saudi Arabia, Algeria, Sudan, Chad and Portugal AP Image copyright Athena Picture Agency Image caption Richard Osman was a father of two and of Egyptian origin The names of some of those who were on board have emerged, but most have not been identified publicly. Those on board included: Richard Osman, a 40-year-old geologist and father-of-two from South Wales; Canadian national Marwa Hamdy, a mother-of-three and an executive with IBM originally from Saskatchewan, but who had relocated to Cairo; Pascal Hess, a photographer from Normandy, France, who had lost his passport last week - only for it to be found in the street, allowing him to catch the flight; An unnamed couple in their 40s from Angers in north-west France, as well as their two children; Ahmed Helal, the Egyptian-born manager of a Procter and Gamble plant in Amiens, northern France Read more on some of the MS804 victims here If anyone is concerned about relatives or friends following the disappearance of the flight, they can call this free number provided by EgyptAir: +202 259 89320 ||||| CAIRO — The EgyptAir red-eye from Paris to Cairo, an Airbus A320 jetliner less than half full, had just entered Egyptian airspace early Thursday on the final part of its journey. Suddenly the twin-engine jetliner jerked hard to the left, then hard to the right, circled and plunged 28,000 feet, disappearing from the radar screens of Greek and Egyptian air traffic controllers. That began a day of emergency rescuers scrambling, officials issuing conflicting information and experts speculating about the fate of EgyptAir Flight 804, which carried at least 66 people from roughly a dozen nations and was presumed to have crashed into the Mediterranean Sea. EgyptAir initially said wreckage of the plane had been found with the help of searchers from Greece, but a senior official of the airline speaking on CNN retracted that assertion hours later. Egyptian officials suggested that terrorism was a more likely cause for the disappearance than mechanical failure, but others cautioned that it was premature to make that judgment. ||||| In this Thursday, May 19, 2016 video image released by the Egyptian Defense Ministry, an Egyptian plane searches in the Mediterranean Sea for the missing EgyptAir flight 804 plane which crashed after... (Associated Press) In this Thursday, May 19, 2016 video image released by the Egyptian Defense Ministry, an Egyptian plane searches in the Mediterranean Sea for the missing EgyptAir flight 804 plane which crashed after disappearing from the radar early Thursday morning while carrying 66 passengers and crew from Paris... (Associated Press) CAIRO (AP) — The Latest on the disappearance of EgyptAir Flight 804 (all times local): 1:15 p.m. Greece's defense minister says Greek authorities have received notification that Egyptian authorities had spotted a body part, two seats and suitcases during their search in the Mediterranean Sea for the crashed EgyptAir Flight 804. Minister Panos Kammenos says Friday that the items were found in the search area slightly to the south of where the aircraft had vanished from radar signals early Thursday. He said the location was slightly north of where some debris had been found on Thursday afternoon but authorities had been unable to identify that as having come from the missing aircraft. The Airbus A320 was carrying 66 passengers and crew from Paris to Cairo when it disappeared. 11:35 p.m. The Egyptian presidency has expressed its "deep sadness and extreme regret" over the deaths of the 66 passengers and crew members aboard EgyptAir Flight 804. The Friday statement is the first official recognition of the tragic crash of the missing plane. It came minutes after the Egyptian army announced for the first time that it located plane debris and passengers' personal belongings some 190 miles (306 kilometers) north of the city of Alexandria in the Mediterranean Sea. The Airbus A320 plane was flying from Paris to Cairo when it disappeared early Thursday over the sea. ___ 11:15 a.m. Egyptian airport officials say that investigators will inspect the plane debris and personal belongings that the Egyptian army says it found 180 miles (290 kilometers) north of the city of Alexandria. The officials said Friday that the chief Egyptian investigator Ayman el-Mokadam will be joined by French and British investigators as well as an expert from Airbus. The Airbus 320 plane operated by EgyptAir was carrying 66 people from Paris to Cairo when it disappeared off radar at around 2.45 a.m. local time in Egypt. The officials spoke on condition of anonymity because they were not authorized to speak to the press. ___ 11:00 a.m. The Egyptian army says it has found wreckage of the missing EgyptAir flight 804, which crashed after disappearing from the radar while carrying 66 passengers and crew from Paris to Cairo. The Egyptian army spokesman, Brig. Gen. Mohammed Samir, says in a statement posted on his Facebook page Friday that Egyptian jets and naval vessels participating in the search for the missing plane have found "personal belongings of the passengers and parts of the plane debris," 180 miles (290 kilometers) north of the city of Alexandria. The Airbus 320 lost contact at 2.45 a.m. local time Thursday morning. ___ 10:15 a.m. Egyptian airport officials say that three French and three British investigators and an Airbus technical expert have arrived in Cairo to join the investigation into what caused EgyptAir flight 804 to crash while carrying 66 people bound for Cairo from Paris. Authorities are continuing to search a wide area to the south of the Greek island of Crete Friday. The plane dropped off the radar while crossing the Mediterranean at around 2.45 a.m. local time Thursday morning. The officials spoke on condition of anonymity because they were not authorized to speak to the press. ___ 8:45 a.m. France's foreign minister and a top transport official say there is still no sign of what brought down a Paris-Cairo EgyptAir flight in the Mediterranean. Foreign Minister Jean-Marc Ayrault said Friday on France-2 television there is "absolutely no indication" of the cause. The junior minister for transport, Alain Vidalies, said on France-Info radio that "no theory is favored" at this stage and urged "the greatest caution." A French military Falcon jet is helping in the search for debris. Vidalies said France could offer undersea search equipment and experts. Amid fears it was an extremist attack, Vidalies defended security at Charles de Gaulle Airport, saying staff badges are revoked if there is the slightest security doubt. ___ 8:15 a.m. The search is continuing for missing EgyptAir flight 804, which disappeared from the radar while carrying 66 passengers and crew from Paris to Cairo. Authorities are scouring a wide area south of the Greek island of Crete on Friday to search for wreckage, over 24 hours after the Airbus 320 lost contact. The Greek Defense Minister Panos Kammenos says that the plane swerved wildly before plummeting into the sea. The Egyptian military says that no distress call was received from the pilot. The country's aviation minister Sherif Fathi says the likelihood the plane was brought down by a terror attack is "higher than the possibility of a technical failure." The distressed relatives of those on board have spent the night in a hotel in Cairo while they await news. ||||| PARIS/CAIRO (Reuters) - The EgyptAir jet which crashed in the Mediterranean on Thursday sent a series of warnings indicating that smoke had been detected on board, shortly before it disappeared off radar screens, French investigators said on Saturday. A spokesman for France’s BEA air accident investigation agency said the signals did not indicate what caused the smoke or fire on board the plane, which plunged into the sea with 66 people on board as it was heading from Paris to Cairo. But they offered the first clues as to what unfolded in the moments before the crash. One aviation source said that a fire on board would likely have generated multiple warning signals, while a sudden explosion may not have generated any - though officials stress that no scenario, including explosion, is being ruled out. Egypt said its navy had found human remains, wreckage and the personal belongings of passengers floating in the Mediterranean about 290 km (180 miles) north of Alexandria. The army published pictures on Saturday on its official Facebook page of the recovered items, which included blue and white debris with EgyptAir markings, seat fabric with designs in the airline’s colors, and a yellow lifejacket. Analysis of the debris and recovery of the plane’s twin flight recorders are likely to be key to determining the cause of the crash - the third blow since October to Egypt’s travel industry, still reeling from political unrest following the 2011 uprising that ousted Hosni Mubarak. A suspected Islamic State bombing brought down a Russian airliner after it took off from Sharm el-Sheikh airport in late October, killing all 224 people on board, and an EgyptAir plane was hijacked in March by a man wearing a fake suicide belt. A message purporting to come from Islamic State urged attacks on the United States and Europe in the Islamic holy month of Ramadan beginning in early June. “Ramadan, the month of conquest. Get prepared...so that you make it a month of calamity on the non-believers anywhere,” said the message posted on Twitter accounts that usually publish Islamic State statements. It made no claim of responsibility for the Egyptair crash. The October crash devastated Egyptian tourism, a main source of foreign exchange for a country of 80 million people, and another similar incident would crush hopes of it recovering. Egypt’s tourism revenue in the first three months of the year plunged by two thirds to $500 million from a year earlier. HUNT FOR BLACK BOXES The signals from the plane “do not allow in any way to say what may have caused smoke or fire on board the aircraft”, said a spokesman for the French BEA agency, which is assisting an official Egyptian investigation. He added that the priority now was to find the two flight recorders, known as black boxes, containing cockpit voice recordings and data readings, from the Airbus A320 which vanished from radar early on Thursday. Recovered debris of the EgyptAir jet that crashed in the Mediterranean Sea is seen in this handout image released May 21, 2016 by Egypt's military. Egyptian Military/Handout via Reuters the head of the Egyptian investigation team was quoted by Egypt’s state-owned Al-Ahram newspaper as saying a preliminary report into the crash would be presented in a month. Civil Aviation Minister Sherif Fathi told reporters an additional challenge in the hunt for the black boxes was the depth of the Mediterranean in the area under search. “What I understand is that it is 3,000 (meters),” he said. That would place the black box locator beacons, which last for 30 days, on the edge of their detectable range from the surface based on the type of acoustic equipment typically used during the first stages of a search, according to a report into the 2009 crash of an Air France jet in the Atlantic. “No important devices from the plane have been retrieved so far,” Fathi said. The flight data transmitted before the crash was sent through an automatic system called the Aircraft Communications Addressing and Reporting System (ACARS), which routinely downloads maintenance and fault data to the airline operator. Aviation Herald, a respected Austria-based website specializing in air accidents, first published a burst of seven messages broadcast over the space of three minutes. These included alarms about smoke in the lavatory as well as the aircraft’s avionics area, which sits under the cockpit. While suggesting a possible fire, the relatively short sequence of data gives no insight into pilot efforts to control the aircraft, nor does it show whether it fell in one piece or disintegrated in mid-air, two aviation safety experts said. The data fragments also included alarms related to cockpit window heating and two flight control computers, both of which have backups. “The question now is whether the fire that caused the smoke was the result of an electrical fault - for example a short-circuit caused by damaged wiring - or whether some form of explosive or incendiary device was used - for example by a terrorist - to generate a fire or other damage,” aviation safety expert David Learmont said. The ACARS data suggested the fire had spread quickly and “that might explain the fact that there was no distress call”, Learmont wrote in a blog. “ALL SCENARIOS” POSSIBLE The aircraft was carrying 56 passengers, including a child and two infants, and 10 crew. They included 30 Egyptian and 15 French nationals, along with citizens of 10 other countries. Egyptair said officials met family members and told them the process of gathering body parts and information would take time, while DNA testing to identify victims would require weeks. French Foreign Minister Jean-Marc Ayrault, who met relatives of crash victims in Paris on Saturday, said there were several possible causes. “At this very moment all scenarios are being examined and none is being given greater emphasis,” he said. France sent a plane and navy ship to help the search, centered on an area just south of where the signal from the plane was lost early on Thursday. Slideshow (17 Images) EgyptAir Chairman Safwat Moslem said the radius of the search zone was 40 nautical miles, but could be expanded. The radius is equivalent to an area of 5,000 square miles (17,000 square km), the same expanse covered in the initial hunt for the Air France jet in 2009. The large area reflects the fact that neither jet could be accounted for in the last few minutes of flying time. A European satellite spotted a 2 km-long oil slick in the Mediterranean, about 40 km (20 nautical miles) southeast of the aircraft’s last known position, the European Space Agency said.

– If EgyptAir Flight 804 was indeed brought down by a terrorist group, that group is apparently not in a big hurry to claim credit for it. The mystery deepened on Friday, at which point more than 24 hours had elapsed since the flight crashed into the Mediterranean Sea with 66 people on board and no one had claimed responsibility, reports Reuters. The latest developments: Egyptian authorities say they've spotted a body part, two seats, and suitcases from the plane, reports AP. Earlier reports on the discovery of wreckage turned out to be inaccurate. Egypt says a terrorist attack is more likely the cause than a mechanical problem, but French Foreign Minister Jean-Marc Ayrault says there is still "absolutely no indication" why the Paris-to-Cairo flight came down, the BBC reports. French investigators are looking at whether security at Paris' Charles de Gaulle Airport could have been breached, although security breaches at airports with looser security are also a strong possibility, the New York Times notes. In the 24 hours before going to Paris, the Airbus A320 flew round trips between Cairo and Asmara, Eritrea, and between Cairo and Tunis. Egyptian President Abdel Fattah al-Sisi expressed his "utmost sadness and regret" in an official statement. Greece's chief air accident investigator tells the Guardian that while the investigation can't fully begin until the black boxes are found, weather can be ruled out as a cause. The three reasons for plane crashes are "meteorological, technical, and human," he says. "The first has now been ruled out because the weather was quite good. Whether a technical factor or human factor, either inside or outside the plane, is to blame remains to be seen. All possibilities are open."

<s>[INST]Image copyright AP Image caption Film director Osman Abu Laban lost four relatives in the disaster Debris and body parts have been found in the Mediterranean Sea by teams searching for a doomed EgyptAir plane, Greek and Egyptian officials say. Flight MS804 was en route from Paris to Cairo with 66 passengers and crew when it crashed early on Thursday. Items including seats and luggage have also been retrieved by Egyptian search crews. The debris was discovered about 290km (180 miles) north of Alexandria, the Egyptian military said. European Space Agency satellites spotted an oil slick in the area where the flight went missing but the organisation said there was no guarantee it was from the plane. The search is now focused on finding the plane's flight recorders, the Associated Press news agency reports. There were smoke alerts from the onboard toilet and the plane's electrics shortly before the signal was lost, according to data published on air industry website the Aviation Herald. However, there has been no independent confirmation. Egyptian President Abdel Fattah al-Sisi has expressed his "utmost sadness and regret" at the crash. Greek, Egyptian, French and UK military units have been taking part in a search operation near Greece's Karpathos island. Greece said radar showed the Airbus A320 had made two sharp turns and dropped more than 25,000ft (7,620m) before plunging into the sea. The focus of the investigation Egypt says the plane was more likely to have been brought down by a terrorist act than a technical fault. However, there has been "absolutely no indication" so far as to why the plane came down, French Foreign Minister Jean-Marc Ayrault said on Friday morning. Three investigators from the French air accident investigation bureau, along with a technical adviser from Airbus, have joined the Egyptian inquiry. The BBC has learned the plane that disappeared was forced to make an emergency landing in 2013 after the pilot noticed the engine overheating, but an official report said the defect had been repaired. In France, the focus is on whether a possible breach of security happened at Paris Charles de Gaulle airport. After last November's Paris attacks, some airport staff had their security clearance revoked over fears of links to Islamic extremists. Eric Moutet, a lawyer for some of those employees, told the BBC that there had been attempts by Islamists to recruit airport staff. "That is clear," he said. "There are people who are being radicalised in some of the trade unions, etc. The authorities have their work cut out with this problem." Media playback is unsupported on your device Media caption Aviation experts give their views on what may have happened to EgyptAir flight MS804 In October, an Airbus A321 operated by Russia's Metrojet blew up over Egypt's Sinai Peninsula, with all 224 people on board killed. Sinai Province, a local affiliate of the Islamic State jihadist group, said it had smuggled a bomb on board. What do we know about what happened? Flight MS804 left Paris at 23:09 local time on Wednesday (21:09 GMT) and was scheduled to arrive in the Egyptian capital soon after 03:15 local time (01:15 GMT) on Thursday. On the plane were 56 passengers, seven crew members and three security personnel. Greek aviation officials say air traffic controllers spoke to the pilot when he entered Greek airspace and everything appeared normal. They tried to contact him again at 02:27 Cairo time, as the plane was set to enter Egyptian airspace, but "despite repeated calls, the aircraft did not respond". Two minutes later it vanished from radar. Philip Baum, the editor of Aviation Security International Magazine, said given smoke was detected on board shortly before the crash it was unlikely to be a hijacking. "It's more likely a fire," he told the BBC. "Now whether that was a technical fire, a short circuit or whether it was because a bomb went off on board, we don't know." Media playback is unsupported on your device Media caption What happened to flight MS804? Richard Westcott examines the evidence so far Who were the victims? EgyptAir flight MS804 Passengers' nationalities 66 people on board - 56 passengers, seven crew members and three security personnel 30 Egyptians 15 French citizens 2 Iraqis 1 from Britain, Canada, Belgium, Kuwait, Saudi Arabia, Algeria, Sudan, Chad and Portugal AP Image copyright Athena Picture Agency Image caption Richard Osman was a father of two and of Egyptian origin The names of some of those who were on board have emerged, but most have not been identified publicly. Those on board included: Richard Osman, a 40-year-old geologist and father-of-two from South Wales; Canadian national Marwa Hamdy, a mother-of-three and an executive with IBM originally from Saskatchewan, but who had relocated to Cairo; Pascal Hess, a photographer from Normandy, France, who had lost his passport last week - only for it to be found in the street, allowing him to catch the flight; An unnamed couple in their 40s from Angers in north-west France, as well as their two children; Ahmed Helal, the Egyptian-born manager of a Procter and Gamble plant in Amiens, northern France Read more on some of the MS804 victims here If anyone is concerned about relatives or friends following the disappearance of the flight, they can call this free number provided by EgyptAir: +202 259 89320 ||||| CAIRO — The EgyptAir red-eye from Paris to Cairo, an Airbus A320 jetliner less than half full, had just entered Egyptian airspace early Thursday on the final part of its journey. Suddenly the twin-engine jetliner jerked hard to the left, then hard to the right, circled and plunged 28,000 feet, disappearing from the radar screens of Greek and Egyptian air traffic controllers. That began a day of emergency rescuers scrambling, officials issuing conflicting information and experts speculating about the fate of EgyptAir Flight 804, which carried at least 66 people from roughly a dozen nations and was presumed to have crashed into the Mediterranean Sea. EgyptAir initially said wreckage of the plane had been found with the help of searchers from Greece, but a senior official of the airline speaking on CNN retracted that assertion hours later. Egyptian officials suggested that terrorism was a more likely cause for the disappearance than mechanical failure, but others cautioned that it was premature to make that judgment. ||||| In this Thursday, May 19, 2016 video image released by the Egyptian Defense Ministry, an Egyptian plane searches in the Mediterranean Sea for the missing EgyptAir flight 804 plane which crashed after... (Associated Press) In this Thursday, May 19, 2016 video image released by the Egyptian Defense Ministry, an Egyptian plane searches in the Mediterranean Sea for the missing EgyptAir flight 804 plane which crashed after disappearing from the radar early Thursday morning while carrying 66 passengers and crew from Paris... (Associated Press) CAIRO (AP) — The Latest on the disappearance of EgyptAir Flight 804 (all times local): 1:15 p.m. Greece's defense minister says Greek authorities have received notification that Egyptian authorities had spotted a body part, two seats and suitcases during their search in the Mediterranean Sea for the crashed EgyptAir Flight 804. Minister Panos Kammenos says Friday that the items were found in the search area slightly to the south of where the aircraft had vanished from radar signals early Thursday. He said the location was slightly north of where some debris had been found on Thursday afternoon but authorities had been unable to identify that as having come from the missing aircraft. The Airbus A320 was carrying 66 passengers and crew from Paris to Cairo when it disappeared. 11:35 p.m. The Egyptian presidency has expressed its "deep sadness and extreme regret" over the deaths of the 66 passengers and crew members aboard EgyptAir Flight 804. The Friday statement is the first official recognition of the tragic crash of the missing plane. It came minutes after the Egyptian army announced for the first time that it located plane debris and passengers' personal belongings some 190 miles (306 kilometers) north of the city of Alexandria in the Mediterranean Sea. The Airbus A320 plane was flying from Paris to Cairo when it disappeared early Thursday over the sea. ___ 11:15 a.m. Egyptian airport officials say that investigators will inspect the plane debris and personal belongings that the Egyptian army says it found 180 miles (290 kilometers) north of the city of Alexandria. The officials said Friday that the chief Egyptian investigator Ayman el-Mokadam will be joined by French and British investigators as well as an expert from Airbus. The Airbus 320 plane operated by EgyptAir was carrying 66 people from Paris to Cairo when it disappeared off radar at around 2.45 a.m. local time in Egypt. The officials spoke on condition of anonymity because they were not authorized to speak to the press. ___ 11:00 a.m. The Egyptian army says it has found wreckage of the missing EgyptAir flight 804, which crashed after disappearing from the radar while carrying 66 passengers and crew from Paris to Cairo. The Egyptian army spokesman, Brig. Gen. Mohammed Samir, says in a statement posted on his Facebook page Friday that Egyptian jets and naval vessels participating in the search for the missing plane have found "personal belongings of the passengers and parts of the plane debris," 180 miles (290 kilometers) north of the city of Alexandria. The Airbus 320 lost contact at 2.45 a.m. local time Thursday morning. ___ 10:15 a.m. Egyptian airport officials say that three French and three British investigators and an Airbus technical expert have arrived in Cairo to join the investigation into what caused EgyptAir flight 804 to crash while carrying 66 people bound for Cairo from Paris. Authorities are continuing to search a wide area to the south of the Greek island of Crete Friday. The plane dropped off the radar while crossing the Mediterranean at around 2.45 a.m. local time Thursday morning. The officials spoke on condition of anonymity because they were not authorized to speak to the press. ___ 8:45 a.m. France's foreign minister and a top transport official say there is still no sign of what brought down a Paris-Cairo EgyptAir flight in the Mediterranean. Foreign Minister Jean-Marc Ayrault said Friday on France-2 television there is "absolutely no indication" of the cause. The junior minister for transport, Alain Vidalies, said on France-Info radio that "no theory is favored" at this stage and urged "the greatest caution." A French military Falcon jet is helping in the search for debris. Vidalies said France could offer undersea search equipment and experts. Amid fears it was an extremist attack, Vidalies defended security at Charles de Gaulle Airport, saying staff badges are revoked if there is the slightest security doubt. ___ 8:15 a.m. The search is continuing for missing EgyptAir flight 804, which disappeared from the radar while carrying 66 passengers and crew from Paris to Cairo. Authorities are scouring a wide area south of the Greek island of Crete on Friday to search for wreckage, over 24 hours after the Airbus 320 lost contact. The Greek Defense Minister Panos Kammenos says that the plane swerved wildly before plummeting into the sea. The Egyptian military says that no distress call was received from the pilot. The country's aviation minister Sherif Fathi says the likelihood the plane was brought down by a terror attack is "higher than the possibility of a technical failure." The distressed relatives of those on board have spent the night in a hotel in Cairo while they await news. ||||| PARIS/CAIRO (Reuters) - The EgyptAir jet which crashed in the Mediterranean on Thursday sent a series of warnings indicating that smoke had been detected on board, shortly before it disappeared off radar screens, French investigators said on Saturday. A spokesman for France’s BEA air accident investigation agency said the signals did not indicate what caused the smoke or fire on board the plane, which plunged into the sea with 66 people on board as it was heading from Paris to Cairo. But they offered the first clues as to what unfolded in the moments before the crash. One aviation source said that a fire on board would likely have generated multiple warning signals, while a sudden explosion may not have generated any - though officials stress that no scenario, including explosion, is being ruled out. Egypt said its navy had found human remains, wreckage and the personal belongings of passengers floating in the Mediterranean about 290 km (180 miles) north of Alexandria. The army published pictures on Saturday on its official Facebook page of the recovered items, which included blue and white debris with EgyptAir markings, seat fabric with designs in the airline’s colors, and a yellow lifejacket. Analysis of the debris and recovery of the plane’s twin flight recorders are likely to be key to determining the cause of the crash - the third blow since October to Egypt’s travel industry, still reeling from political unrest following the 2011 uprising that ousted Hosni Mubarak. A suspected Islamic State bombing brought down a Russian airliner after it took off from Sharm el-Sheikh airport in late October, killing all 224 people on board, and an EgyptAir plane was hijacked in March by a man wearing a fake suicide belt. A message purporting to come from Islamic State urged attacks on the United States and Europe in the Islamic holy month of Ramadan beginning in early June. “Ramadan, the month of conquest. Get prepared...so that you make it a month of calamity on the non-believers anywhere,” said the message posted on Twitter accounts that usually publish Islamic State statements. It made no claim of responsibility for the Egyptair crash. The October crash devastated Egyptian tourism, a main source of foreign exchange for a country of 80 million people, and another similar incident would crush hopes of it recovering. Egypt’s tourism revenue in the first three months of the year plunged by two thirds to $500 million from a year earlier. HUNT FOR BLACK BOXES The signals from the plane “do not allow in any way to say what may have caused smoke or fire on board the aircraft”, said a spokesman for the French BEA agency, which is assisting an official Egyptian investigation. He added that the priority now was to find the two flight recorders, known as black boxes, containing cockpit voice recordings and data readings, from the Airbus A320 which vanished from radar early on Thursday. Recovered debris of the EgyptAir jet that crashed in the Mediterranean Sea is seen in this handout image released May 21, 2016 by Egypt's military. Egyptian Military/Handout via Reuters the head of the Egyptian investigation team was quoted by Egypt’s state-owned Al-Ahram newspaper as saying a preliminary report into the crash would be presented in a month. Civil Aviation Minister Sherif Fathi told reporters an additional challenge in the hunt for the black boxes was the depth of the Mediterranean in the area under search. “What I understand is that it is 3,000 (meters),” he said. That would place the black box locator beacons, which last for 30 days, on the edge of their detectable range from the surface based on the type of acoustic equipment typically used during the first stages of a search, according to a report into the 2009 crash of an Air France jet in the Atlantic. “No important devices from the plane have been retrieved so far,” Fathi said. The flight data transmitted before the crash was sent through an automatic system called the Aircraft Communications Addressing and Reporting System (ACARS), which routinely downloads maintenance and fault data to the airline operator. Aviation Herald, a respected Austria-based website specializing in air accidents, first published a burst of seven messages broadcast over the space of three minutes. These included alarms about smoke in the lavatory as well as the aircraft’s avionics area, which sits under the cockpit. While suggesting a possible fire, the relatively short sequence of data gives no insight into pilot efforts to control the aircraft, nor does it show whether it fell in one piece or disintegrated in mid-air, two aviation safety experts said. The data fragments also included alarms related to cockpit window heating and two flight control computers, both of which have backups. “The question now is whether the fire that caused the smoke was the result of an electrical fault - for example a short-circuit caused by damaged wiring - or whether some form of explosive or incendiary device was used - for example by a terrorist - to generate a fire or other damage,” aviation safety expert David Learmont said. The ACARS data suggested the fire had spread quickly and “that might explain the fact that there was no distress call”, Learmont wrote in a blog. “ALL SCENARIOS” POSSIBLE The aircraft was carrying 56 passengers, including a child and two infants, and 10 crew. They included 30 Egyptian and 15 French nationals, along with citizens of 10 other countries. Egyptair said officials met family members and told them the process of gathering body parts and information would take time, while DNA testing to identify victims would require weeks. French Foreign Minister Jean-Marc Ayrault, who met relatives of crash victims in Paris on Saturday, said there were several possible causes. “At this very moment all scenarios are being examined and none is being given greater emphasis,” he said. France sent a plane and navy ship to help the search, centered on an area just south of where the signal from the plane was lost early on Thursday. Slideshow (17 Images) EgyptAir Chairman Safwat Moslem said the radius of the search zone was 40 nautical miles, but could be expanded. The radius is equivalent to an area of 5,000 square miles (17,000 square km), the same expanse covered in the initial hunt for the Air France jet in 2009. The large area reflects the fact that neither jet could be accounted for in the last few minutes of flying time. A European satellite spotted a 2 km-long oil slick in the Mediterranean, about 40 km (20 nautical miles) southeast of the aircraft’s last known position, the European Space Agency said.[/INST]– If EgyptAir Flight 804 was indeed brought down by a terrorist group, that group is apparently not in a big hurry to claim credit for it. The mystery deepened on Friday, at which point more than 24 hours had elapsed since the flight crashed into the Mediterranean Sea with 66 people on board and no one had claimed responsibility, reports Reuters. The latest developments: Egyptian authorities say they've spotted a body part, two seats, and suitcases from the plane, reports AP. Earlier reports on the discovery of wreckage turned out to be inaccurate. Egypt says a terrorist attack is more likely the cause than a mechanical problem, but French Foreign Minister Jean-Marc Ayrault says there is still "absolutely no indication" why the Paris-to-Cairo flight came down, the BBC reports. French investigators are looking at whether security at Paris' Charles de Gaulle Airport could have been breached, although security breaches at airports with looser security are also a strong possibility, the New York Times notes. In the 24 hours before going to Paris, the Airbus A320 flew round trips between Cairo and Asmara, Eritrea, and between Cairo and Tunis. Egyptian President Abdel Fattah al-Sisi expressed his "utmost sadness and regret" in an official statement. Greece's chief air accident investigator tells the Guardian that while the investigation can't fully begin until the black boxes are found, weather can be ruled out as a cause. The three reasons for plane crashes are "meteorological, technical, and human," he says. "The first has now been ruled out because the weather was quite good. Whether a technical factor or human factor, either inside or outside the plane, is to blame remains to be seen. All possibilities are open."</s>

BEIRUT/GENEVA Syrian government forces killed at least 100 people on Tuesday in assaults on villages and an artillery barrage in the restive city of Homs, activists said, and the Red Cross called for daily ceasefires to allow in urgently needed aid. Washington, which is preparing for a "Friends of Syria" meeting of Western and Arab states opposing President Bashar al-Assad, declined to rule out eventually providing arms to rebels seeking to overthrow him. U.N. chief Ban Ki-moon said he was searching for a candidate to name as a humanitarian coordinator for Syria, whose role could evolve into seeking a political solution to the conflict. Security forces killed at least 100 people in attacks on Homs and raids on villages and towns in the province of Idlib near Turkey, the Local Coordination Committees said. Ten children and three women were among the dead, the opposition activists' organization, which documents what it describes as killings and human rights abuses by security forces, said in a statement. In Damascus, security forces opened fire on demonstrators overnight, wounding at least four, activists said. Violence has hit the capital over the past week, undermining Assad's assertion that the 11-month-old uprising against his rule is limited to the provinces and the work of saboteurs. Activist accounts of the violence could not be confirmed. The government bars most foreign journalists from Syria. The International Committee of the Red Cross said it had asked authorities and rebels to agree daily ceasefires so life-saving aid can reach civilians in hard-hit areas including Homs. "It should last at least two hours every day, so that ICRC staff and Syrian Arab Red Crescent volunteers have enough time to deliver aid and evacuate the wounded and the sick," ICRC President Jakob Kellenberger said. Western and Arab powers that are openly seeking Assad's downfall are preparing for the inaugural meeting of a "Friends of Syria" contact group in Tunisia on Friday. Asked about the prospect of arming the rebels, U.S. State Department spokeswoman Victoria Nuland said: "We don't believe that it makes sense to contribute now to the further militarization of Syria." But she added: "That said... if we can't get Assad to yield to the pressure that we are all bringing to bear, we may have to consider additional measures." Russia and China back Assad's own program for reforms, which includes plans for a referendum on Sunday on a new constitution which would lead to elections in 90 days. Assad says this should satisfy demands for more democracy; his opponents say the proposals are a sham. Russia said it would not attend the "Friends of Syria" meeting because the Syrian government would not be represented. Lebanon, which has tried to distance itself from the turmoil across its border, will also stay away from the Tunis meeting. Russia and China have faced Western and Arab criticism for blocking U.N. action against Syria. A former Syrian Defence Ministry auditor who defected in January told Reuters Moscow's arms sales to Damascus - nearly $1 billion last year - had increased sharply since the start of the uprising. In an interview with Reuters, U.N. chief Ban said he was urgently contacting prospective candidates for the role of U.N. humanitarian coordinator for Syria. The U.N. General Assembly asked Ban last week to name someone for the job. Russia has said it would support a U.N. humanitarian envoy. ARTILLERY ATTACK Activists said government forces launched the artillery attack on Homs after rebel fighters holding the opposition Baba Amro district blocked troops from entering. "Several shells are falling each minute," activist Nader al-Husseini told Reuters from the district. The British-based opposition Syrian Observatory for Human Rights said security forces had stormed villages in Idlib province in the north of the country. Activists in Homs said government forces backed by armour have been closing in on Baba Amro, a mainly Sunni Muslim neighborhood, since the offensive on the city began on Feb 3. Much of the opposition to Assad comes from the Sunni majority, while much of his support comes from minorities including his Alawite sect, raising worries that violence could take on a sectarian slant and draw in neighboring countries. Tanks are deployed in the Inshaat district next to Baba Amro, opposition sources said. The Observatory said a convoy of more than 50 armored vehicles was seen heading from Damascus towards Homs. A city of one million people on the Damascus-Aleppo highway, Homs has been at the heart of the uprising against Assad's 11-year rule. Residents say they are running short of medicine and food, and are massed together in crowded homes to seek shelter. Government curbs on access make it hard to verify details of fighting there but international rights and aid organizations say hundreds of people have been killed in recent weeks in Homs. UNDER FIRE IN DAMASCUS Assad says the revolt is the work of foreign-backed terrorists. Until recently it was limited mainly to the provinces, but anti-government rallies have drawn crowds in Damascus in recent days. On Monday night at least four people were wounded when security forces opened fire, activists said. Elsewhere, an activist group in Kfar Tkharim near the Turkish border said rebel fighters had killed five soldiers and captured two in an ambush on a government column. An activist in al-Qusair, about 32 km (20 miles) southwest of Homs and close to the Lebanese border, said five people were killed and eight wounded when the northern part of the town came under heavy fire from army mortars and T-72 tanks. "People in that area are hiding in their homes, they can't leave. Others are resisting. Those who are farther away are fleeing the town. Some people are so scared they're trying to leave anyway even if they are close to the fire," Abu Ansa told Reuters by telephone. Activists in the western city of Hama said troops, police and militias had set up dozens of roadblocks, cutting neighborhoods off from each other. Ahmad Ramadan, a leader of the opposition Syrian National Council, said Assad loyalists killed his brother Mahmoud when they riddled his car with gunfire in his home city of Aleppo. "The regime has been accusing Mahmoud of sending food and medicine to Homs and he was receiving daily threats. He was hit in the head and neck and died immediately," Ramadan told al-Jazeera Arabic news channel. Western and Arab nations who want Assad to relinquish power are preparing an explicit gesture of support for his opponents. U.S. Secretary of State Hillary Clinton said the Friends of Syria meeting would show that his government was increasingly isolated and offer support for "the brave Syrian people." "We'll send a clear message to Russia, China and others who are still unsure about how to handle the increasing violence but are up until now unfortunately making the wrong choices," Clinton said in Mexico at a meeting of the G20 world powers. One firm ally of Assad is Iran. Iranian television reported on Monday that two Iranian warships had docked in Syria to provide training for Syrian naval forces. Washington said on Tuesday it had no indication that the report was true. (Additional reporting by Dominic Evans and Erika Solomon in Beirut, Shaimaa Fayed in Cairo; Writing by Angus MacSwan in Beirut; Editing by Peter Graff) ||||| Syrian tanks and troops massed Monday outside the resistance stronghold of Homs for a possible ground assault that one activist warned could unleash a new round of fierce and bloody urban combat even as the Red Cross tried to broker a cease-fire to allow emergency aid in. Two of three Syrian injured men who were wounded from the shelling at Baba Amr neighborhood in the Syrian province of Homs, on their hospital beds as they receive treatment, in the eastern town of Chtoura,... (Associated Press) In this Feb. 18, 2012 citizen journalism image provided by the Local Coordination Committees in Syria and accessed on Sunday, Feb. 19, 2012, anti-Syrian regime mourners carry the coffins of three protesters... (Associated Press) In this Feb. 18, 2012 citizen journalism image provided by the Local Coordination Committees in Syria and accessed on Sunday, Feb. 19, 2012, the dead body of anti-Syrian regime protester is seen wrapped... (Associated Press) CORRECTS THE DAY - A Syrian boy chants slogans during a rally demanding UNICEF to protect Syrian children in front of the UNICEF Compound in Amman, Jordan, Monday, Feb. 20, 2012. (AP photo/Mohammad Hannon) (Associated Press) One of three Syrian injured men who were wounded by shelling at Baba Amr neighborhood in the Syrian province of Homs, lies on his hospital bed as he receives treatment, in the eastern town of Chtoura,... (Associated Press) A flood of military reinforcements has been a prelude to previous offensives by President Bashar Assad's regime, which has tried to use its overwhelming firepower to crush an opposition that has been bolstered by defecting soldiers and hardened by 11 months of street battles. "The human loss is going to be huge if they retake Baba Amr," said Rami Abdul-Rahman, who heads the Britain-based activist group Syrian Observatory for Human Rights. Russia's U.N. Ambassador Vitaly Churkin said Russia will put forward a proposal at the U.N. Security Council in the coming days regarding humanitarian aid to Syria, the Itar-Tass news agency reported. Churkin was quoted by the agency as telling Vesti 24 television on Monday that the council "could undertake concrete steps aimed at solving humanitarian issues, relying, among other things, on the fact that Damascus allowed the Red Cross to bring humanitarian aid to some regions." Churkin gave no details about the proposal, his spokesman Anton Uspensky told AP. Russia and China have vetoed two Security Council resolutions backing Arab League plans aimed at ending the conflict and condemning the government crackdown. The central city of Homs _ and in particular the opposition district known as Baba Amr _ has become a critical ground for both sides. The opposition has lionized it as "Syria's Misrata" after the Libyan city where rebels fought off a brutal government siege. Assad's regime wants desperately to erase the embarrassing defiance in Syria's third-largest city after weeks of shelling, including a barrage of mortars that killed up to 200 people earlier this month. At least nine people were killed in shelling Monday, activists said. Another massive death toll would only bring further international isolation on Assad from Western and Arab leaders. "The massacre in Syria goes on," said U.S. Sen. John McCain during a visit to Cairo, where he urged Washington and its allies to find way to help arm and equip Syrian rebels. McCain, a senior member of the Senate Armed Service Committee, said he did not support direct U.S. weapons supplies to Syrian opposition forces, but has suggested the Arab League or others could help bolster the fighting power of the anti-Assad groups. The U.S., he said, could assist with equipment such as medical supplies or global positioning devices. "It is time we gave them the wherewithal to fight back and stop the slaughter," he said. Assad's fall also would be a potentially devastating blow for his close ally Iran, which counts on Syria as its most reliable Arab ally and a pathway for aid to Tehran's patron Hezbollah in Lebanon. But McCain urged for "like-minded" Western and Arab nations also to guard against attempts by al-Qaida or other extremists to exploit a leadership vacuum if the regime crumbles. "For us to sit back and do nothing while people are being slaughtered ... is an affront to everything America stands for and believes in," said McCain, suggesting that the Republicans could seek to make Syria a central campaign issue in this year's U.S. presidential election. But U.S. Secretary of State Hillary Rodham Clinton, on a visit to Mexico on Monday, dodged a question about whether the U.S. could accept Arab countries or others arming the Syrian rebels. We are all working for the planned friends of Syria meeting at the end of this week, which we think will give us a chance to come together and chart a way forward," she said. She said the meeting in Tunisia "will demonstrate the Assad regime is increasingly isolated and that the brave Syrian people need our support and solidarity." But she said that should be expressed through humanitarian help and encouragement to the Syrian opposition to promise that everyone they will be represented in a new Syria. In Cairo, Arab League Secretary-General Nabil Elaraby suggested at a news conference that Russia and China _ two countries that recently supported Damascus by vetoing a U.N. Security Council resolution condemning Assad's regime _ may be shifting their positions. "There are some indications, especially from China and to some degree from Russia that there may be a change in their stance," he said, without elaborating. Syria-based activist Mustafa Osso told The Associated Press that Assad's military should face strong resistance as residents plan to fight until "the last person." He added that Homs is facing "savage shelling that does not differentiate between military or civilians targets." The Baba Amr neighborhood on Homs' southwest edge has become the centerpiece of the city's opposition. Hundreds of army defectors are thought to be taking shelter there, clashing with troops in hit-and-run attacks each day. Amateur videos posted online showed what activists said were shells falling into Baba Amr. Black smoke billowed from residential areas. Phone lines and Internet connections have been cut with the city, making it difficult to get firsthand accounts from Homs residents. In Geneva, a spokeswoman for the International Committee of the Red Cross said the group has been in talks with Syrian authorities and opposition groups to negotiate a cease-fire in some of the most violence-torn areas. "We are currently discussing several possibilities with all those concerned, and it includes a cessation of fighting in the most affected areas," the spokeswoman, Carla Haddad, told the AP. She said the talks weren't aimed at resolving any of the entrenched political differences. "The idea is to be able to facilitate swift access to people in need," Haddad said. Clashes between military rebels and Syrian forces are growing more frequent and the defectors have managed to take control of small pieces of territory in the north as well as parts of Homs province, which is Syria's largest stretching from the border with Lebanon in the west to Iraq and Jordan in the east. Increasingly, Syria appears to be careening toward an all-out civil war. Activists believe Assad may be trying to subdue Homs _ an important stronghold for anti-Assad groups _ before a planned referendum Sunday on a new constitution. The charter would allow a bigger role for political opposition to challenge Assad's Baath Party, which has controlled Syria since a 1963 coup. But the leaders of the uprising have dismissed the referendum as an attempt at superficial reforms that do nothing to crack the regime's hold on power. "We have called for a boycott of the referendum which cannot be held while parts of Syria are a war zone," said Omar Idilbi, a Beirut-based member of the opposition Syrian National Council. The U.N. last gave a death toll for the conflict in January, saying 5,400 had been killed in 2011 alone. But hundreds more have been killed since, according to activist groups. The group Local Coordination Committees says more than 7,300 have been killed since March of last year. There is no way to independently verify the numbers, however, as Syria bans almost all foreign journalists and human rights organizations. In the western Hama province, troops backed by armored personnel carriers and military buses stormed several villages, conducting raids and arrests. A 32-year-old man was killed by gunfire from a security checkpoint in the area, activists said. ___ Associated Press writers Frank Jordans in Geneva, Bradley Klapper in Mexico, Edith M. Lederer at the United Nations, and Sarah El-Deeb in Cairo contributed to this report. ||||| Syria crisis: Red Cross presses for humanitarian truce The Red Cross is the only international aid agency working in Syria The International Committee of the Red Cross says it is in talks with "all those concerned" in Syria's conflict to negotiate a ceasefire. The group says it wants to negotiate a brief truce in the most affected areas to allow it to deliver aid packages. Correspondents say the fact that the ICRC has spoken publicly about the negotiations shows just how concerned it is by the situation in Syria. Thousands have died there in an 11-month uprising against the government. ICRC spokesman Bijan Farnoudi said the group was "discussing several possibilities" to enable humanitarian aid to be delivered. He said the aim of the discussions was "to facilitate swift Syrian Arab Red Crescent and ICRC access to the people in need". "The content of the discussions we are having with the Syrian authorities and all those involved in the fighting remains bilateral and confidential," he added. The Red Cross indicated that any such ceasefire would probably be only for a limited period, possibly only a few hours. Homs has been repeatedly shelled by government forces The ICRC has been delivering food and medicine to civilians in Syria since the start of the uprising against President Bashar al-Assad. It is the only international aid agency operating inside the country, but it has had difficulty reaching the areas badly affected by the conflict. The BBC's Imogen Foulkes in Geneva, where the ICRC is based, says it is very unusual for the organisation to discuss any talks it might be having with participants in an armed conflict. Russian talks Following a visit at the weekend by China's Deputy Foreign Minister Zhai Jun, Mr Assad hosted prominent Russian politician Alexei Pushkov on Monday in Damascus. Continue reading the main story Analysis The ICRC says conditions in Homs and Bludan are deteriorating, and that the sick and wounded are bearing the brunt of the violence. It is likely the Red Cross wants a ceasefire in these areas in order to deliver food and medical supplies, and to evacuate the wounded. A senior official from the Syrian Red Crescent was shot dead last month while travelling in a clearly marked vehicle. The ICRC also says its ambulances have been regularly subjected to harassment and unnecessary delays. It seems that without at least a temporary ceasefire, the ICRC does not believe it can do its job in Syria at all. Syria's Sana state news agency said Mr Assad had thanked Mr Pushkov for Russia's support, repeating his insistence that his country is tackling "armed terrorist groups receiving funding and arms from foreign parties, aiming to destabilise Syria". Mr Pushkov had stressed the need for all parties to "to continue working for a political solution to the crisis based on dialogue between all concerned parties, without foreign intervention", Sana reported. After Mr Zhai's visit, the official newspaper of the Chinese Communist Party accused the West of provoking a civil war in Syria. Russia and China have both refused to join the growing international condemnation of Mr Assad's regime. Both countries vetoed a resolution in the UN Security Council condemning the violence and voted against a similar General Assembly resolution, saying they amounted to forced regime change. However, Arab League Secretary-General Nabil Elaraby said on Monday there were "indications coming from China and to some extent from Russia that there may be a change in position", without giving further details. 'Awaiting death' The London-based Syrian Observatory for Human Rights said 16 people people were killed across the country on Monday. Nine of them - including three children in one family - died in renewed shelling of the city of Homs, they said. Activists say government forces are being reinforced around Homs, and they fear that a ground assault on the city is planned. Hadi Abdallah, an activist in Homs, has called for women and children to flee from the heavily bombarded area of Baba Amr. He told the AFP news agency that residents of the suburb were living in cold and "unsustainable" conditions, and that they were "awaiting death". Another activist told the Associated Press that government forces would face stiff opposition in Homs and the residents would fight until "the last person". Mr Assad is pressing ahead with his plan to hold a referendum on Sunday on a new constitution for Syria. The vote has been dismissed as "farcical" by the US and others. Opposition groups have called on Syrians to boycott the referendum. Omar Idilbi, a Beirut-based member of the main opposition movement the Syrian National Council (SNC), said it "cannot be held while parts of Syria are a war zone". Human rights groups believe more than 7,000 people have been killed since the uprising began. The Syrian government says at least 2,000 members of the security forces have died fighting militants. Syria restricts access to foreign media and it is not possible to verify casualty figures.

– Syrian troops are massing outside the rebellious city of Homs, and human rights groups fear that one of the bloodiest crackdowns of the 11-month uprising is imminent. The district of Baba Amr is an opposition stronghold, and residents aim to fight until "the last person," an activist tells the AP, adding that the city is facing savage shelling that does not "differentiate between military or civilian targets." At least 16 people were killed across the country, nine of them—including three children in one family—by the renewed shelling in Homs, the BBC reports. In Damascus, at least four activists were injured overnight when government troops opened fire on demonstrators, reports Reuters. The Red Cross is urging both sides to declare a ceasefire, even just for a few hours, so humanitarian aid can reach civilians in affected areas. Sens. John McCain and Lindsey Graham say it's time for the US to look at ways of aiding the rebels.

<s>[INST]BEIRUT/GENEVA Syrian government forces killed at least 100 people on Tuesday in assaults on villages and an artillery barrage in the restive city of Homs, activists said, and the Red Cross called for daily ceasefires to allow in urgently needed aid. Washington, which is preparing for a "Friends of Syria" meeting of Western and Arab states opposing President Bashar al-Assad, declined to rule out eventually providing arms to rebels seeking to overthrow him. U.N. chief Ban Ki-moon said he was searching for a candidate to name as a humanitarian coordinator for Syria, whose role could evolve into seeking a political solution to the conflict. Security forces killed at least 100 people in attacks on Homs and raids on villages and towns in the province of Idlib near Turkey, the Local Coordination Committees said. Ten children and three women were among the dead, the opposition activists' organization, which documents what it describes as killings and human rights abuses by security forces, said in a statement. In Damascus, security forces opened fire on demonstrators overnight, wounding at least four, activists said. Violence has hit the capital over the past week, undermining Assad's assertion that the 11-month-old uprising against his rule is limited to the provinces and the work of saboteurs. Activist accounts of the violence could not be confirmed. The government bars most foreign journalists from Syria. The International Committee of the Red Cross said it had asked authorities and rebels to agree daily ceasefires so life-saving aid can reach civilians in hard-hit areas including Homs. "It should last at least two hours every day, so that ICRC staff and Syrian Arab Red Crescent volunteers have enough time to deliver aid and evacuate the wounded and the sick," ICRC President Jakob Kellenberger said. Western and Arab powers that are openly seeking Assad's downfall are preparing for the inaugural meeting of a "Friends of Syria" contact group in Tunisia on Friday. Asked about the prospect of arming the rebels, U.S. State Department spokeswoman Victoria Nuland said: "We don't believe that it makes sense to contribute now to the further militarization of Syria." But she added: "That said... if we can't get Assad to yield to the pressure that we are all bringing to bear, we may have to consider additional measures." Russia and China back Assad's own program for reforms, which includes plans for a referendum on Sunday on a new constitution which would lead to elections in 90 days. Assad says this should satisfy demands for more democracy; his opponents say the proposals are a sham. Russia said it would not attend the "Friends of Syria" meeting because the Syrian government would not be represented. Lebanon, which has tried to distance itself from the turmoil across its border, will also stay away from the Tunis meeting. Russia and China have faced Western and Arab criticism for blocking U.N. action against Syria. A former Syrian Defence Ministry auditor who defected in January told Reuters Moscow's arms sales to Damascus - nearly $1 billion last year - had increased sharply since the start of the uprising. In an interview with Reuters, U.N. chief Ban said he was urgently contacting prospective candidates for the role of U.N. humanitarian coordinator for Syria. The U.N. General Assembly asked Ban last week to name someone for the job. Russia has said it would support a U.N. humanitarian envoy. ARTILLERY ATTACK Activists said government forces launched the artillery attack on Homs after rebel fighters holding the opposition Baba Amro district blocked troops from entering. "Several shells are falling each minute," activist Nader al-Husseini told Reuters from the district. The British-based opposition Syrian Observatory for Human Rights said security forces had stormed villages in Idlib province in the north of the country. Activists in Homs said government forces backed by armour have been closing in on Baba Amro, a mainly Sunni Muslim neighborhood, since the offensive on the city began on Feb 3. Much of the opposition to Assad comes from the Sunni majority, while much of his support comes from minorities including his Alawite sect, raising worries that violence could take on a sectarian slant and draw in neighboring countries. Tanks are deployed in the Inshaat district next to Baba Amro, opposition sources said. The Observatory said a convoy of more than 50 armored vehicles was seen heading from Damascus towards Homs. A city of one million people on the Damascus-Aleppo highway, Homs has been at the heart of the uprising against Assad's 11-year rule. Residents say they are running short of medicine and food, and are massed together in crowded homes to seek shelter. Government curbs on access make it hard to verify details of fighting there but international rights and aid organizations say hundreds of people have been killed in recent weeks in Homs. UNDER FIRE IN DAMASCUS Assad says the revolt is the work of foreign-backed terrorists. Until recently it was limited mainly to the provinces, but anti-government rallies have drawn crowds in Damascus in recent days. On Monday night at least four people were wounded when security forces opened fire, activists said. Elsewhere, an activist group in Kfar Tkharim near the Turkish border said rebel fighters had killed five soldiers and captured two in an ambush on a government column. An activist in al-Qusair, about 32 km (20 miles) southwest of Homs and close to the Lebanese border, said five people were killed and eight wounded when the northern part of the town came under heavy fire from army mortars and T-72 tanks. "People in that area are hiding in their homes, they can't leave. Others are resisting. Those who are farther away are fleeing the town. Some people are so scared they're trying to leave anyway even if they are close to the fire," Abu Ansa told Reuters by telephone. Activists in the western city of Hama said troops, police and militias had set up dozens of roadblocks, cutting neighborhoods off from each other. Ahmad Ramadan, a leader of the opposition Syrian National Council, said Assad loyalists killed his brother Mahmoud when they riddled his car with gunfire in his home city of Aleppo. "The regime has been accusing Mahmoud of sending food and medicine to Homs and he was receiving daily threats. He was hit in the head and neck and died immediately," Ramadan told al-Jazeera Arabic news channel. Western and Arab nations who want Assad to relinquish power are preparing an explicit gesture of support for his opponents. U.S. Secretary of State Hillary Clinton said the Friends of Syria meeting would show that his government was increasingly isolated and offer support for "the brave Syrian people." "We'll send a clear message to Russia, China and others who are still unsure about how to handle the increasing violence but are up until now unfortunately making the wrong choices," Clinton said in Mexico at a meeting of the G20 world powers. One firm ally of Assad is Iran. Iranian television reported on Monday that two Iranian warships had docked in Syria to provide training for Syrian naval forces. Washington said on Tuesday it had no indication that the report was true. (Additional reporting by Dominic Evans and Erika Solomon in Beirut, Shaimaa Fayed in Cairo; Writing by Angus MacSwan in Beirut; Editing by Peter Graff) ||||| Syrian tanks and troops massed Monday outside the resistance stronghold of Homs for a possible ground assault that one activist warned could unleash a new round of fierce and bloody urban combat even as the Red Cross tried to broker a cease-fire to allow emergency aid in. Two of three Syrian injured men who were wounded from the shelling at Baba Amr neighborhood in the Syrian province of Homs, on their hospital beds as they receive treatment, in the eastern town of Chtoura,... (Associated Press) In this Feb. 18, 2012 citizen journalism image provided by the Local Coordination Committees in Syria and accessed on Sunday, Feb. 19, 2012, anti-Syrian regime mourners carry the coffins of three protesters... (Associated Press) In this Feb. 18, 2012 citizen journalism image provided by the Local Coordination Committees in Syria and accessed on Sunday, Feb. 19, 2012, the dead body of anti-Syrian regime protester is seen wrapped... (Associated Press) CORRECTS THE DAY - A Syrian boy chants slogans during a rally demanding UNICEF to protect Syrian children in front of the UNICEF Compound in Amman, Jordan, Monday, Feb. 20, 2012. (AP photo/Mohammad Hannon) (Associated Press) One of three Syrian injured men who were wounded by shelling at Baba Amr neighborhood in the Syrian province of Homs, lies on his hospital bed as he receives treatment, in the eastern town of Chtoura,... (Associated Press) A flood of military reinforcements has been a prelude to previous offensives by President Bashar Assad's regime, which has tried to use its overwhelming firepower to crush an opposition that has been bolstered by defecting soldiers and hardened by 11 months of street battles. "The human loss is going to be huge if they retake Baba Amr," said Rami Abdul-Rahman, who heads the Britain-based activist group Syrian Observatory for Human Rights. Russia's U.N. Ambassador Vitaly Churkin said Russia will put forward a proposal at the U.N. Security Council in the coming days regarding humanitarian aid to Syria, the Itar-Tass news agency reported. Churkin was quoted by the agency as telling Vesti 24 television on Monday that the council "could undertake concrete steps aimed at solving humanitarian issues, relying, among other things, on the fact that Damascus allowed the Red Cross to bring humanitarian aid to some regions." Churkin gave no details about the proposal, his spokesman Anton Uspensky told AP. Russia and China have vetoed two Security Council resolutions backing Arab League plans aimed at ending the conflict and condemning the government crackdown. The central city of Homs _ and in particular the opposition district known as Baba Amr _ has become a critical ground for both sides. The opposition has lionized it as "Syria's Misrata" after the Libyan city where rebels fought off a brutal government siege. Assad's regime wants desperately to erase the embarrassing defiance in Syria's third-largest city after weeks of shelling, including a barrage of mortars that killed up to 200 people earlier this month. At least nine people were killed in shelling Monday, activists said. Another massive death toll would only bring further international isolation on Assad from Western and Arab leaders. "The massacre in Syria goes on," said U.S. Sen. John McCain during a visit to Cairo, where he urged Washington and its allies to find way to help arm and equip Syrian rebels. McCain, a senior member of the Senate Armed Service Committee, said he did not support direct U.S. weapons supplies to Syrian opposition forces, but has suggested the Arab League or others could help bolster the fighting power of the anti-Assad groups. The U.S., he said, could assist with equipment such as medical supplies or global positioning devices. "It is time we gave them the wherewithal to fight back and stop the slaughter," he said. Assad's fall also would be a potentially devastating blow for his close ally Iran, which counts on Syria as its most reliable Arab ally and a pathway for aid to Tehran's patron Hezbollah in Lebanon. But McCain urged for "like-minded" Western and Arab nations also to guard against attempts by al-Qaida or other extremists to exploit a leadership vacuum if the regime crumbles. "For us to sit back and do nothing while people are being slaughtered ... is an affront to everything America stands for and believes in," said McCain, suggesting that the Republicans could seek to make Syria a central campaign issue in this year's U.S. presidential election. But U.S. Secretary of State Hillary Rodham Clinton, on a visit to Mexico on Monday, dodged a question about whether the U.S. could accept Arab countries or others arming the Syrian rebels. We are all working for the planned friends of Syria meeting at the end of this week, which we think will give us a chance to come together and chart a way forward," she said. She said the meeting in Tunisia "will demonstrate the Assad regime is increasingly isolated and that the brave Syrian people need our support and solidarity." But she said that should be expressed through humanitarian help and encouragement to the Syrian opposition to promise that everyone they will be represented in a new Syria. In Cairo, Arab League Secretary-General Nabil Elaraby suggested at a news conference that Russia and China _ two countries that recently supported Damascus by vetoing a U.N. Security Council resolution condemning Assad's regime _ may be shifting their positions. "There are some indications, especially from China and to some degree from Russia that there may be a change in their stance," he said, without elaborating. Syria-based activist Mustafa Osso told The Associated Press that Assad's military should face strong resistance as residents plan to fight until "the last person." He added that Homs is facing "savage shelling that does not differentiate between military or civilians targets." The Baba Amr neighborhood on Homs' southwest edge has become the centerpiece of the city's opposition. Hundreds of army defectors are thought to be taking shelter there, clashing with troops in hit-and-run attacks each day. Amateur videos posted online showed what activists said were shells falling into Baba Amr. Black smoke billowed from residential areas. Phone lines and Internet connections have been cut with the city, making it difficult to get firsthand accounts from Homs residents. In Geneva, a spokeswoman for the International Committee of the Red Cross said the group has been in talks with Syrian authorities and opposition groups to negotiate a cease-fire in some of the most violence-torn areas. "We are currently discussing several possibilities with all those concerned, and it includes a cessation of fighting in the most affected areas," the spokeswoman, Carla Haddad, told the AP. She said the talks weren't aimed at resolving any of the entrenched political differences. "The idea is to be able to facilitate swift access to people in need," Haddad said. Clashes between military rebels and Syrian forces are growing more frequent and the defectors have managed to take control of small pieces of territory in the north as well as parts of Homs province, which is Syria's largest stretching from the border with Lebanon in the west to Iraq and Jordan in the east. Increasingly, Syria appears to be careening toward an all-out civil war. Activists believe Assad may be trying to subdue Homs _ an important stronghold for anti-Assad groups _ before a planned referendum Sunday on a new constitution. The charter would allow a bigger role for political opposition to challenge Assad's Baath Party, which has controlled Syria since a 1963 coup. But the leaders of the uprising have dismissed the referendum as an attempt at superficial reforms that do nothing to crack the regime's hold on power. "We have called for a boycott of the referendum which cannot be held while parts of Syria are a war zone," said Omar Idilbi, a Beirut-based member of the opposition Syrian National Council. The U.N. last gave a death toll for the conflict in January, saying 5,400 had been killed in 2011 alone. But hundreds more have been killed since, according to activist groups. The group Local Coordination Committees says more than 7,300 have been killed since March of last year. There is no way to independently verify the numbers, however, as Syria bans almost all foreign journalists and human rights organizations. In the western Hama province, troops backed by armored personnel carriers and military buses stormed several villages, conducting raids and arrests. A 32-year-old man was killed by gunfire from a security checkpoint in the area, activists said. ___ Associated Press writers Frank Jordans in Geneva, Bradley Klapper in Mexico, Edith M. Lederer at the United Nations, and Sarah El-Deeb in Cairo contributed to this report. ||||| Syria crisis: Red Cross presses for humanitarian truce The Red Cross is the only international aid agency working in Syria The International Committee of the Red Cross says it is in talks with "all those concerned" in Syria's conflict to negotiate a ceasefire. The group says it wants to negotiate a brief truce in the most affected areas to allow it to deliver aid packages. Correspondents say the fact that the ICRC has spoken publicly about the negotiations shows just how concerned it is by the situation in Syria. Thousands have died there in an 11-month uprising against the government. ICRC spokesman Bijan Farnoudi said the group was "discussing several possibilities" to enable humanitarian aid to be delivered. He said the aim of the discussions was "to facilitate swift Syrian Arab Red Crescent and ICRC access to the people in need". "The content of the discussions we are having with the Syrian authorities and all those involved in the fighting remains bilateral and confidential," he added. The Red Cross indicated that any such ceasefire would probably be only for a limited period, possibly only a few hours. Homs has been repeatedly shelled by government forces The ICRC has been delivering food and medicine to civilians in Syria since the start of the uprising against President Bashar al-Assad. It is the only international aid agency operating inside the country, but it has had difficulty reaching the areas badly affected by the conflict. The BBC's Imogen Foulkes in Geneva, where the ICRC is based, says it is very unusual for the organisation to discuss any talks it might be having with participants in an armed conflict. Russian talks Following a visit at the weekend by China's Deputy Foreign Minister Zhai Jun, Mr Assad hosted prominent Russian politician Alexei Pushkov on Monday in Damascus. Continue reading the main story Analysis The ICRC says conditions in Homs and Bludan are deteriorating, and that the sick and wounded are bearing the brunt of the violence. It is likely the Red Cross wants a ceasefire in these areas in order to deliver food and medical supplies, and to evacuate the wounded. A senior official from the Syrian Red Crescent was shot dead last month while travelling in a clearly marked vehicle. The ICRC also says its ambulances have been regularly subjected to harassment and unnecessary delays. It seems that without at least a temporary ceasefire, the ICRC does not believe it can do its job in Syria at all. Syria's Sana state news agency said Mr Assad had thanked Mr Pushkov for Russia's support, repeating his insistence that his country is tackling "armed terrorist groups receiving funding and arms from foreign parties, aiming to destabilise Syria". Mr Pushkov had stressed the need for all parties to "to continue working for a political solution to the crisis based on dialogue between all concerned parties, without foreign intervention", Sana reported. After Mr Zhai's visit, the official newspaper of the Chinese Communist Party accused the West of provoking a civil war in Syria. Russia and China have both refused to join the growing international condemnation of Mr Assad's regime. Both countries vetoed a resolution in the UN Security Council condemning the violence and voted against a similar General Assembly resolution, saying they amounted to forced regime change. However, Arab League Secretary-General Nabil Elaraby said on Monday there were "indications coming from China and to some extent from Russia that there may be a change in position", without giving further details. 'Awaiting death' The London-based Syrian Observatory for Human Rights said 16 people people were killed across the country on Monday. Nine of them - including three children in one family - died in renewed shelling of the city of Homs, they said. Activists say government forces are being reinforced around Homs, and they fear that a ground assault on the city is planned. Hadi Abdallah, an activist in Homs, has called for women and children to flee from the heavily bombarded area of Baba Amr. He told the AFP news agency that residents of the suburb were living in cold and "unsustainable" conditions, and that they were "awaiting death". Another activist told the Associated Press that government forces would face stiff opposition in Homs and the residents would fight until "the last person". Mr Assad is pressing ahead with his plan to hold a referendum on Sunday on a new constitution for Syria. The vote has been dismissed as "farcical" by the US and others. Opposition groups have called on Syrians to boycott the referendum. Omar Idilbi, a Beirut-based member of the main opposition movement the Syrian National Council (SNC), said it "cannot be held while parts of Syria are a war zone". Human rights groups believe more than 7,000 people have been killed since the uprising began. The Syrian government says at least 2,000 members of the security forces have died fighting militants. Syria restricts access to foreign media and it is not possible to verify casualty figures.[/INST]– Syrian troops are massing outside the rebellious city of Homs, and human rights groups fear that one of the bloodiest crackdowns of the 11-month uprising is imminent. The district of Baba Amr is an opposition stronghold, and residents aim to fight until "the last person," an activist tells the AP, adding that the city is facing savage shelling that does not "differentiate between military or civilian targets." At least 16 people were killed across the country, nine of them—including three children in one family—by the renewed shelling in Homs, the BBC reports. In Damascus, at least four activists were injured overnight when government troops opened fire on demonstrators, reports Reuters. The Red Cross is urging both sides to declare a ceasefire, even just for a few hours, so humanitarian aid can reach civilians in affected areas. Sens. John McCain and Lindsey Graham say it's time for the US to look at ways of aiding the rebels.</s>

SECTION 1. SHORT TITLE. This Act may be cited as the ``Simplifying the Application for Student Aid Act''. SEC. 2. USING DATA FROM SECOND PRECEDING YEAR. Section 480(a)(1)(B) of the Higher Education Act of 1965 (20 U.S.C. 1087vv(a)(1)(B)) is amended by striking ``may'' in both places it appears and inserting ``shall''. SEC. 3. CALCULATION OF ANNUAL ADJUSTMENT PERCENTAGE FOR FEDERAL PELL GRANTS. Section 401(b)(7)(C)(iv)(I) of the Higher Education Act of 1965 (20 U.S.C. 1070a(b)(7)(C)(iv)(I)) is amended by striking ``calendar year'' and inserting ``fiscal year''. SEC. 4. FAFSA SIMPLIFICATION. (a) FAFSA Simplification.--Section 483 of the Higher Education Act of 1965 (20 U.S.C. 1090) is amended-- (1) in subsection (a)(3), by adding at the end the following: ``(I) Format.--Not later than 180 days after the date of the enactment of the Simplifying the Application for Student Aid Act, the Secretary shall make the electronic version of the forms under this paragraph available through a technology tool that can be used on mobile devices. Such technology tool shall, at minimum, enable applicants to-- ``(i) save data; and ``(ii) submit their FAFSA to the Secretary through such tool. ``(J) Consumer testing.--In developing and maintaining the electronic version of the forms under this paragraph and the technology tool for mobile devices under subparagraph (I), the Secretary shall conduct consumer testing with appropriate persons to ensure the forms and technology tool are designed to be easily usable and understandable by students and families. Such consumer testing shall include-- ``(i) current and prospective college students, family members of such students, and other individuals with expertise in student financial assistance application processes; ``(ii) dependent students and independent students meeting the requirements under subsection (b) or (c) of section 479; and ``(iii) dependent students and independent students who do not meet the requirements under subsection (b) or (c) of section 479.''; and (2) by amending subsection (f) to read as follows: ``(f) Use of Internal Revenue Service Data Retrieval Tool To Populate FAFSA.-- ``(1) Simplification efforts.--The Secretary shall-- ``(A) make every effort to allow applicants to utilize the current data retrieval tool to transfer data available from the Internal Revenue Service to reduce the amount of original data entry by applicants and strengthen the reliability of data used to calculate expected family contributions, including through the use of technology to-- ``(i) allow an applicant to automatically populate the electronic version of the forms under this paragraph with data available from the Internal Revenue Service; and ``(ii) direct an applicant to appropriate questions on such forms based on the applicant's answers to previous questions; and ``(B) allow single taxpayers, married taxpayers filing jointly, and married taxpayers filing separately to utilize the current data retrieval tool to its full capacity. ``(2) Use of tax return in application process.--The Secretary shall continue to examine whether data provided by the Internal Revenue Service can be used to generate an expected family contribution without additional action on the part of the student and taxpayer. ``(3) Reports on fafsa simplification efforts.--Not less than once every other year, the Secretary shall report to the authorizing committees on the progress of the simplification efforts under this subsection. ``(4) Reports on fafsa access.--Not less than once every 10 years, the Secretary shall report to the authorizing committees on the needs of limited English proficient students using the FAFSA.''. (b) Funding.-- (1) Use of existing funds.--Of the amount authorized to be appropriated to the Department of Education to maintain the Free Application for Federal Student Aid, $3,000,000 shall be available to carry out this Act and the amendments made by this Act. (2) No additional funds authorized.--No funds are authorized by this Act to be appropriated to carry out this Act or the amendments made by this Act. Passed the House of Representatives July 11, 2016. Attest: KAREN L. HAAS, Clerk.

Simplifying the Application for Student Aid Act (Sec. 2) This bill amends title IV (Student Assistance) of the Higher Education Act of 1965 to require the Department of Education (ED) to use tax information from the second preceding tax year (the "prior, prior year") to determine a student's financial aid eligibility. It requires data sharing between ED and the Internal Revenue Service (IRS), pursuant to taxpayer consent. (Sec. 3) The bill revises the annual adjustment percentage calculation used to determine the total maximum Federal Pell Grant award by measuring inflation over the most recent fiscal year instead of calendar year. (Sec. 4) ED must develop and maintain a consumer-tested technology tool to allow a federal financial aid applicant to complete, save, and submit electronic forms (e.g., the Free Application for Federal Student Aid) using a mobile device. Additionally, ED must make every effort to allow applicants to utilize the existing IRS data tool to automatically populate the electronic forms with tax return information. ED must report to Congress on: (1) efforts to simplify the federal financial aid application process, and (2) the needs of limited English proficient students.

<s>[INST]SECTION 1. SHORT TITLE. This Act may be cited as the ``Simplifying the Application for Student Aid Act''. SEC. 2. USING DATA FROM SECOND PRECEDING YEAR. Section 480(a)(1)(B) of the Higher Education Act of 1965 (20 U.S.C. 1087vv(a)(1)(B)) is amended by striking ``may'' in both places it appears and inserting ``shall''. SEC. 3. CALCULATION OF ANNUAL ADJUSTMENT PERCENTAGE FOR FEDERAL PELL GRANTS. Section 401(b)(7)(C)(iv)(I) of the Higher Education Act of 1965 (20 U.S.C. 1070a(b)(7)(C)(iv)(I)) is amended by striking ``calendar year'' and inserting ``fiscal year''. SEC. 4. FAFSA SIMPLIFICATION. (a) FAFSA Simplification.--Section 483 of the Higher Education Act of 1965 (20 U.S.C. 1090) is amended-- (1) in subsection (a)(3), by adding at the end the following: ``(I) Format.--Not later than 180 days after the date of the enactment of the Simplifying the Application for Student Aid Act, the Secretary shall make the electronic version of the forms under this paragraph available through a technology tool that can be used on mobile devices. Such technology tool shall, at minimum, enable applicants to-- ``(i) save data; and ``(ii) submit their FAFSA to the Secretary through such tool. ``(J) Consumer testing.--In developing and maintaining the electronic version of the forms under this paragraph and the technology tool for mobile devices under subparagraph (I), the Secretary shall conduct consumer testing with appropriate persons to ensure the forms and technology tool are designed to be easily usable and understandable by students and families. Such consumer testing shall include-- ``(i) current and prospective college students, family members of such students, and other individuals with expertise in student financial assistance application processes; ``(ii) dependent students and independent students meeting the requirements under subsection (b) or (c) of section 479; and ``(iii) dependent students and independent students who do not meet the requirements under subsection (b) or (c) of section 479.''; and (2) by amending subsection (f) to read as follows: ``(f) Use of Internal Revenue Service Data Retrieval Tool To Populate FAFSA.-- ``(1) Simplification efforts.--The Secretary shall-- ``(A) make every effort to allow applicants to utilize the current data retrieval tool to transfer data available from the Internal Revenue Service to reduce the amount of original data entry by applicants and strengthen the reliability of data used to calculate expected family contributions, including through the use of technology to-- ``(i) allow an applicant to automatically populate the electronic version of the forms under this paragraph with data available from the Internal Revenue Service; and ``(ii) direct an applicant to appropriate questions on such forms based on the applicant's answers to previous questions; and ``(B) allow single taxpayers, married taxpayers filing jointly, and married taxpayers filing separately to utilize the current data retrieval tool to its full capacity. ``(2) Use of tax return in application process.--The Secretary shall continue to examine whether data provided by the Internal Revenue Service can be used to generate an expected family contribution without additional action on the part of the student and taxpayer. ``(3) Reports on fafsa simplification efforts.--Not less than once every other year, the Secretary shall report to the authorizing committees on the progress of the simplification efforts under this subsection. ``(4) Reports on fafsa access.--Not less than once every 10 years, the Secretary shall report to the authorizing committees on the needs of limited English proficient students using the FAFSA.''. (b) Funding.-- (1) Use of existing funds.--Of the amount authorized to be appropriated to the Department of Education to maintain the Free Application for Federal Student Aid, $3,000,000 shall be available to carry out this Act and the amendments made by this Act. (2) No additional funds authorized.--No funds are authorized by this Act to be appropriated to carry out this Act or the amendments made by this Act. Passed the House of Representatives July 11, 2016. Attest: KAREN L. HAAS, Clerk.[/INST]Simplifying the Application for Student Aid Act (Sec. 2) This bill amends title IV (Student Assistance) of the Higher Education Act of 1965 to require the Department of Education (ED) to use tax information from the second preceding tax year (the "prior, prior year") to determine a student's financial aid eligibility. It requires data sharing between ED and the Internal Revenue Service (IRS), pursuant to taxpayer consent. (Sec. 3) The bill revises the annual adjustment percentage calculation used to determine the total maximum Federal Pell Grant award by measuring inflation over the most recent fiscal year instead of calendar year. (Sec. 4) ED must develop and maintain a consumer-tested technology tool to allow a federal financial aid applicant to complete, save, and submit electronic forms (e.g., the Free Application for Federal Student Aid) using a mobile device. Additionally, ED must make every effort to allow applicants to utilize the existing IRS data tool to automatically populate the electronic forms with tax return information. ED must report to Congress on: (1) efforts to simplify the federal financial aid application process, and (2) the needs of limited English proficient students. </s>

Image caption Nicholas Keith Warner had been due to return to the US from his NI honeymoon on Wednesday An American electrical engineer on honeymoon has appeared in court charged with attempting to murder three men in County Antrim. Nicholas Warner, 31, from Summerville in South Carolina, walked into court using crutches having allegedly broken his leg in the incident. He was charged after three men were stabbed in a fight outside a bar in Ballycarry. It happened at about 01:00 BST on Saturday in Main Street. Mr Warner faces six charges, including three attempted murder charges, possessing a knife, assault occasioning actual bodily harm and causing affray. He accepts having a knife and causing the injuries, but will argue he acted in self-defence, his solicitor told Limavady Magistrates' Court. 'Self-defence' The accused, who was accompanied in court by his wife, was in Northern Ireland on honeymoon and had been due to return to the US on Wednesday. He said the case will be contested on the grounds of using "reasonable force". Two of the alleged victims were aged in their 30s and one was in his 60s. Mr Warner was released on bail and ordered to surrender his passport. He is due in court again next month. ||||| Get daily updates directly to your inbox Subscribe Thank you for subscribing See our privacy notice Could not subscribe, try again later Invalid Email An American man on honeymoon in Ireland has appeared in court facing attempted murder charges. The 31-year-old, who together with his new wife arrived in Dublin last week, appeared at Limavady Magistrate’s Court in Derry charged with attempting to murder three men, two of them aged in their 30s and one aged in his 60s. The three men each sustained stabbing injuries in an incident outside a bar at Main Street in the Antrim village of Ballycarry last Saturday night, Belfast Live reports. In court charged was Nicholas Keith Warner, an electrical engineer from Morrow Lane in Summerville, South Carolina. He denies attempting to murder the three men and he also denies assaulting a fourth man. The defendant further denies causing an affray but he admits possessing a knife. The defendant, who sustained a broken leg in the incident, was helped by two police officers as he walked on crutches from a cell van on Main Street, Limavady, into the courthouse for his remand appearance. His wife Kaylee, a nurse also from South Carolina, sat behind her husband as he sat in the dock during the hearing. When asked by the court clerk if he understood the charges, the defendant replied “yes mam”. A detective constable told Deputy District Judge Ted Magill that he believed he could connect the defendant to the charges and he said alcohol was an issue in the case. (Image: Google) Defence solicitor David Jones told the court that bail conditions proposed by the police and by the Public Prosecution Service were acceptable to the defendant. “He accepts he was the individual who caused the injuries. From the moment of his arrest prior to his interviews he accepted he possessed the knife to defend himself," Mr Jones said. “This case will come down to the argument of reasonable force or otherwise and because he is a US citizen I would request that if possible the case could be fast tracked. It is regrettable in that he is here on his honeymoon and his employment as an electrical engineer is now is jeopardy," he added. Mr Warner must also maintain an absolute ban from both possessing and consuming alcohol and he must agree to carrying out a preliminary breath test if asked to do so by the police. An additional bail condition is that the defendant must not enter within the 30mph zone around the village of Ballycarry.

– A South Carolina man honeymooning in Northern Ireland has been charged with three counts of attempted murder following a fight outside of a bar in the village of Ballycarry, DublinLive reports. Nicholas Keith Warner, 31, an electrical engineer who lives in Summerville, allegedly used a knife to stab three men during the altercation last Saturday night. He and his new wife, Kaylee, arrived in Dublin last week. Warner, who suffered a broken leg in the fight, was in court Wednesday (the day he and his wife, a nurse, were due to return home), the BBC reports. He was released on bail after surrendering his passport. Warner admits that he had a knife, according to reports, but denies causing the fight, saying he was acting in self-defense. A detective told the judge that he believes he can make a case against Warner, per DublinLive, adding that alcohol was a contributing factor. While on bail, Warner is prohibited from possessing or drinking alcohol. Two of the alleged victims were in their 30s, according to reports, and the third was in his 60s. Warner is next due to be in court next month.

<s>[INST]Image caption Nicholas Keith Warner had been due to return to the US from his NI honeymoon on Wednesday An American electrical engineer on honeymoon has appeared in court charged with attempting to murder three men in County Antrim. Nicholas Warner, 31, from Summerville in South Carolina, walked into court using crutches having allegedly broken his leg in the incident. He was charged after three men were stabbed in a fight outside a bar in Ballycarry. It happened at about 01:00 BST on Saturday in Main Street. Mr Warner faces six charges, including three attempted murder charges, possessing a knife, assault occasioning actual bodily harm and causing affray. He accepts having a knife and causing the injuries, but will argue he acted in self-defence, his solicitor told Limavady Magistrates' Court. 'Self-defence' The accused, who was accompanied in court by his wife, was in Northern Ireland on honeymoon and had been due to return to the US on Wednesday. He said the case will be contested on the grounds of using "reasonable force". Two of the alleged victims were aged in their 30s and one was in his 60s. Mr Warner was released on bail and ordered to surrender his passport. He is due in court again next month. ||||| Get daily updates directly to your inbox Subscribe Thank you for subscribing See our privacy notice Could not subscribe, try again later Invalid Email An American man on honeymoon in Ireland has appeared in court facing attempted murder charges. The 31-year-old, who together with his new wife arrived in Dublin last week, appeared at Limavady Magistrate’s Court in Derry charged with attempting to murder three men, two of them aged in their 30s and one aged in his 60s. The three men each sustained stabbing injuries in an incident outside a bar at Main Street in the Antrim village of Ballycarry last Saturday night, Belfast Live reports. In court charged was Nicholas Keith Warner, an electrical engineer from Morrow Lane in Summerville, South Carolina. He denies attempting to murder the three men and he also denies assaulting a fourth man. The defendant further denies causing an affray but he admits possessing a knife. The defendant, who sustained a broken leg in the incident, was helped by two police officers as he walked on crutches from a cell van on Main Street, Limavady, into the courthouse for his remand appearance. His wife Kaylee, a nurse also from South Carolina, sat behind her husband as he sat in the dock during the hearing. When asked by the court clerk if he understood the charges, the defendant replied “yes mam”. A detective constable told Deputy District Judge Ted Magill that he believed he could connect the defendant to the charges and he said alcohol was an issue in the case. (Image: Google) Defence solicitor David Jones told the court that bail conditions proposed by the police and by the Public Prosecution Service were acceptable to the defendant. “He accepts he was the individual who caused the injuries. From the moment of his arrest prior to his interviews he accepted he possessed the knife to defend himself," Mr Jones said. “This case will come down to the argument of reasonable force or otherwise and because he is a US citizen I would request that if possible the case could be fast tracked. It is regrettable in that he is here on his honeymoon and his employment as an electrical engineer is now is jeopardy," he added. Mr Warner must also maintain an absolute ban from both possessing and consuming alcohol and he must agree to carrying out a preliminary breath test if asked to do so by the police. An additional bail condition is that the defendant must not enter within the 30mph zone around the village of Ballycarry.[/INST]– A South Carolina man honeymooning in Northern Ireland has been charged with three counts of attempted murder following a fight outside of a bar in the village of Ballycarry, DublinLive reports. Nicholas Keith Warner, 31, an electrical engineer who lives in Summerville, allegedly used a knife to stab three men during the altercation last Saturday night. He and his new wife, Kaylee, arrived in Dublin last week. Warner, who suffered a broken leg in the fight, was in court Wednesday (the day he and his wife, a nurse, were due to return home), the BBC reports. He was released on bail after surrendering his passport. Warner admits that he had a knife, according to reports, but denies causing the fight, saying he was acting in self-defense. A detective told the judge that he believes he can make a case against Warner, per DublinLive, adding that alcohol was a contributing factor. While on bail, Warner is prohibited from possessing or drinking alcohol. Two of the alleged victims were in their 30s, according to reports, and the third was in his 60s. Warner is next due to be in court next month.</s>

three - body systems are ubiquitous in astrophysics , appearing in a wide range of configurations and scales , from planet - satellite systems to black holes in dense stellar clusters . although the gravitational three - body problem is in general non - integrable , a hierarchical system ( i.e. , triple configuration consisting of an inner binary orbited by a distant companion ) can be simplified by retaining the lowest orders in the multipole expansion of the interaction potentials . in this case , the triple system is represented by two nested binary systems ( an inner binary " and an outer binary " ) , with the corresponding orbital elements evolving on secular timescales due to mutual interactions . @xcite and @xcite discovered that when the mutual inclination angle between the inner and outer binaries is sufficiently high , the time - averaged tidal gravitational force from the outer companion can induce large - amplitude oscillations in the eccentricity and inclination of the inner binary . in recent years , numerous works have shown that lidov kozai oscillations could play an important role in the formation and evolution of various astrophysical systems . examples include : ( i ) the formation of close stellar binaries , including those containing compact objects ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) ; ( ii ) the excitation of eccentricities of exoplanet systems ( e.g. , * ? ? ? ? * ; * ? ? ? * ) and the formation of hot jupiters through high - eccentricity migration ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? ? * ; * ? ? ? * ) ; ( iii ) the production of type ia supernovae from white - dwarf binary mergers ( e.g. , * ? ? ? * ; * ? ? ? * ) or direct collisions ( e.g. , * ? ? ? * ; * ? ? ? * ) ; ( iv ) the properties of irregular satellites ( particularly their inclination distribution relative to the ecliptic ) of giant planets in the solar system ( e.g. , * ? ? ? * ; * ? ? ? * ) ; ( v ) the formation and merger of ( stellar and supermassive ) black hole binaries at the centers globular clusters or galaxies ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? the simplest lidov kozai mechanism involves a test mass ( `` planet '' ) orbiting a primary body ( `` star '' ) perturbed by an external companion , with the interaction potential truncated to the quadrupole order . in this test - mass , quadrupole approximation , the projected angular momentum ( along the external binary axis ) of the planet is conserved . if the influence of other short - range forces ( srfs ) is negligible , the maximum eccentricity achieved by the inner binary ( for an initially very small eccentricity ) during the lidov kozai oscillation is given by @xmath3 where @xmath4 is the initial inclination angle of the two orbits . thus lidov kozai oscillation requires @xmath4 to lie between @xmath5 and @xmath6 . it has been recognized that the lidov kozai cycles can be suppressed by other short - range effects that induce periapse precession of the inner binary , including the precessions due to general relativity ( gr ) , rotational bulge and tidal distortion ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? the suppression arises because these additional precessions tend to destroy the near @xmath7 resonance between the longitude of the periapse @xmath8 and the longitude of the ascending node @xmath9 required for eccentricity excitation . thus , the maximum eccentricity can be reduced from the `` pure '' lidov kozai value ( equation [ eq : emax ] ) . it has also been recognized that high - order expansion of the interaction potential can lead to a much richer dynamical behaviour of hierarchical triples than the simplest lidov kozai oscillation based on the test - mass , quadrupole approximation . @xcite have derived the orbit - averaged hamiltonian to octupole order and used the resulting equation of motion to explore some aspects of the evolution of triples . unlike the pure quadrupole case , the projected angular momentum of the inner binary ( even in the test - mass limit ) is no longer constant when the octupole potential is included ( the octupole potential is nonzero when the outer binary is eccentric and the components of the inner binary have different masses ) . therefore , the secular dynamics of triples is generally not integrable in the octupole order and may lead to chaos ( e.g. , * ? ? ? * ; * ? ? ? recent works have examined the rich dynamical behaviour of such `` eccentric '' lidov kozai mechanism , either numerically ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) or semi - analytically ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , and explored their implications for the formation of hot jupiters and the resulting spin - orbit misalignments ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? the works cited above have revealed two important consequences of the `` eccentric '' lidov kozai mechanism : ( i ) the eccentricity of the inner binary can be driven to extreme value ( @xmath10 ) even for `` modest '' initial orbital inclinations ; ( ii ) the inner orbit can flip and come retrograde relative to the outer orbit . these two effects are related , as orbital flip is often associated with extreme eccentricity . since the precession of periapse due to short - range forces is strongly dependent on eccentricity , it is not clear to what extent the extreme eccentricity can be realized in realistic situations . while short - range effects were included in some population synthesis calculations for the formation of hot jupiters ( e.g. , * * ; * ? ? ? * ; * ? ? ? * ) , a systematic study of the short - range force effects on eccentric lidov kozai mechanism is currently lacking . in this paper , by running a sequence of numerical integrations , we study how srfs affect the evolution of the inner binary ( with and without the test - mass approximation ) , including the interaction potential up to the octupole order . combining with various analytical considerations , we characterize the parameters space systematically to understand how the maximum eccentricity is modified by the srfs . our paper is organized as follows . in section 2 , we derive the secular equations of motion up to the octupole order using a vectorial formalism . in section 3 , we provide a brief overview of short - range effects , estimating the maximum eccentricity allowed by the presence of various srfs . in section 4 , we describe our numerical integrations , carried out over a range of parameters for triple systems consisting of a star - planet binary and an outer stellar companion . in section 5 , we extend our analysis to triple systems in which all components have comparable masses . we summarize our main results in section 6 . in a hierarchical triple system , two bodies of masses @xmath11 and @xmath12 orbit each other ( with semimajor axis @xmath13 ) while a third body of mass @xmath14 orbits the center mass of the inner bodies ( @xmath11 and @xmath12 ) on a wider orbit ( with semimajor axis @xmath15 ) . the complete hamiltonian of the system can then be written as the sum of the individual hamiltonians of the inner and outer orbits plus an interaction potential @xmath16 ( e.g. , * ? ? ? * ) : @xmath17 where @xmath18 is the instantaneous separation vector between the inner masses @xmath11 and @xmath12 , @xmath19 is the instantaneous separation vector between @xmath14 and center of mass of @xmath11 and @xmath12 , and @xmath20 is the angle between @xmath21 and @xmath22 . in equation ( [ eq : ham ] ) , @xmath23 is the legendre polynomial of degree @xmath24 and @xmath25 is a coefficient that depends on @xmath11 , @xmath12 , @xmath14 and @xmath24 . if @xmath14 is sufficiently distant ( i.e. , @xmath26 ) , only the smallest values of @xmath24 contribute significantly to @xmath16 , and the coupling term is weak such that the inner and outer keplerian orbits change very slowly ( on timescales much longer than their orbital periods ) . in this regime , the secular approximation is valid , meaning that , the system can be adequately described by two slowly evolving keplerian orbits , while the short timescale behaviour of the three individual trajectories is irrelevant ( e.g. , * ? ? ? this perturbative method has been used extensively to study three - body systems up to quadrupole ( @xmath27)(e.g . ? * ; * ? ? ? * ) and octupole ( @xmath28 ) orders ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? most of these studies have used the classical perturbation methods of celestial mechanics , based on an orbital - element formulation of the hamiltonian system . in the following , we present the secular evolution equations to the octupole order using a geometric ( vectorial ) formalism ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , and confirm via angular projections that they are equivalent to hamilton s equations for the orbital elements . in vector form , the instantaneous position @xmath29 of a body in keplerian motion can be written as @xmath30 with @xmath31 , where @xmath32 , @xmath33 and @xmath34 are the semimajor axis , eccentricity and true anomaly , respectively . the orthogonal unit vectors @xmath35 and @xmath36 define the orbital plane , where @xmath35 points in the direction of pericenter ( i.e. , at @xmath37 ) . a third unit vector @xmath38 , pointed in the direction of the orbital angular momentum , completes an orthonormal triad , @xmath39 . alternatively , it is often useful to work in terms of the dimensionless angular momentum vector @xmath40 and the eccentricity vector @xmath41 : @xmath42 where @xmath40 and @xmath41 satisfy @xmath43 and @xmath44 . truncating the interaction potential ( equation [ eq : ham ] ) at the @xmath28 order , we write @xmath45 , where the quadrupole term is @xmath46,\ ] ] and the octupole term is @xmath47~~,\ ] ] and where the position vectors @xmath21 and @xmath22 track two different keplerian orbits ( equation [ eq : keplerian ] ) of orbital elements @xmath13 and @xmath48 ( inner ) and @xmath15 and @xmath49 ( outer ) , which are oriented in space by the triads @xmath50 and @xmath51 , respectively . in terms of the averaged potentials , the equations of motion for the orbital vectors @xmath58 , @xmath59 , @xmath60 and @xmath61 ( defined as in equation [ eq : defineje ] for the inner and outer orbits ) are @xmath62 here , @xmath63 and @xmath64 are @xmath65 where @xmath66 is the reduced mass of the outer orbit @xmath67 . substituting equations ( [ eq : apk ] ) and ( [ eq : apo ] ) into ( [ eq : gj1])([eq : ge2 ] ) , the octupole - level secular evolution equations can be obtained . for the inner orbit , we have @xmath68\\ & -\frac{75\varepsilon_{{\mathrm{oct}}}}{64~t_k}\bigg\ { \bigg[2\big[({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)\\ & + ( { \mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)\big]~{\mathbf{j}}_1 + 2\big[({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)\\ & -7({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)\big]~{\mathbf{e}}_1\bigg]\times{\hat{\mathbf{n}}}_2\\ & + \bigg[2({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\mathbf{j}}_1 + \big[\frac{8}{5}e_1 ^ 2-\frac{1}{5}\\ & -7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\mathbf{e}}_1\bigg ] \times{\hat{\mathbf{u}}}_2\bigg\ } , \end{split}\ ] ] @xmath69\\ & -\frac{75\varepsilon_{{\mathrm{oct}}}}{64~t_k}\bigg\ { \bigg[2({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\mathbf{e}}_1\\ & + \big[\frac{8}{5}e_1 ^ 2-\frac{1}{5}-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\mathbf{j}}_1\bigg]\times{\hat{\mathbf{u}}}_2\\ & + \bigg[2\big[({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)+({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)\big]~{\mathbf{e}}_1\\ & + 2\big[({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)\big]~{\mathbf{j}}_1 \bigg]\times{\hat{\mathbf{n}}}_2\\ & + \frac{16}{5}({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)~{\mathbf{j}}_1\times{\mathbf{e}}_1\bigg\}~~. \end{split}\ ] ] for the outer orbit , we have @xmath70\\ & -\frac{75\varepsilon_{{\mathrm{oct}}}}{64t_k}\frac{l_1}{l_2}\bigg\ { 2\big[({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)~{\hat{\mathbf{n}}}_2\\ & + ( { \mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{n}}}_2+({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{u}}}_2\big]\times{\mathbf{j}}_1\\ & + \bigg[2({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{n}}}_2- 14({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{n}}}_2\\ & + \big[\frac{8}{5}e_1 ^ 2-\frac{1}{5}-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\hat{\mathbf{u}}}_2\frac{}{}\bigg]\times{\mathbf{e}}_1 \bigg\},\\ \end{split}\ ] ] @xmath71{\hat{\mathbf{n}}}_2\times{\mathbf{e}}_2\bigg]\\ & -\frac{75}{64t_k}\frac{\varepsilon_{{\mathrm{oct}}}}{\sqrt{1-e_2 ^ 2}}\frac{l_1}{l_2 } \bigg\{2\big[({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\mathbf{e}}_2)~{\hat{\mathbf{u}}}_2\\ & + ( { \mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{e}}_1\cdot{\mathbf{e}}_2)~{\hat{\mathbf{u}}}_2+\frac{1-e_2 ^ 2}{e_2}({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2 ) ( { \mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{n}}}_2\big]\times{\mathbf{j}}_1\\ & + \bigg[2({\mathbf{j}}_1\cdot{\mathbf{e}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{u}}}_2 -14({\mathbf{e}}_1\cdot{\mathbf{e}}_2)({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{u}}}_2\\ & + \frac{1-e_2 ^ 2}{e_2}\big[\frac{8}{5}e_1 ^ 2-\frac{1}{5}-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\hat{\mathbf{n}}}_2\bigg ] \times{\mathbf{e}}_1\\ & -\bigg[2\left(\frac{1}{5}-\frac{8}{5}e_1 ^ 2\right)({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)~{\mathbf{e}}_2\\ & + 14({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\mathbf{e}}_2 + 7({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)\big[\frac{8}{5}e_1 ^ 2\\ & -\frac{1}{5}-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\mathbf{e}}_2 \bigg]\times{\hat{\mathbf{n}}}_2\bigg\}~~. \end{split}\ ] ] in the above , we have defined the ( quadrupole ) kozai timescale as @xmath72 where @xmath73 is the mean motion of the inner binary . equations ( [ eq : j1vec])([eq : e2vec ] ) describe the long - term evolution of the inner and outer binaries for all mass ratios . our equations are equivalent to those presented in @xcite , although they are in a somewhat different form . often times , the triple system contains a body of much smaller mass than the other two , such as in the case of a planet around one member of a binary . in this case , the planet can be considered to be a particle of effective zero mass to a very good approximation . in this test - particle limit " ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , the outer orbit contains the totality of the angular momentum in the system , and consequently remains fixed in time . to derive the test - particle limit from equations ( [ eq : j1vec])([eq : e2vec ] ) , we take the limit @xmath74 , for which we confirm that @xmath75 . in this case , the triad @xmath76 is fixed in space , thus , for the sake of clarity , we relabel these vectors with lab - frame coordinates @xmath76 in equations ( [ eq : j1vec])([eq : e1vec ] ) and in equations ( [ eq : apk ] ) and ( [ eq : apo ] ) . with these replacements , we recover the expressions of @xcite for the potentials and for @xmath77 and @xmath78 for a test particle . the secular equations for the orbital elements of the inner and outer orbits have been the focus of previous work on hierarchical triple systems @xcite . with the introduction of delaunay variables , conjugate pairs of coordinates and momenta can be defined , the equations of motion of the orbital elements can be directly derived using hamilton s equations ( e.g. * ? ? ? * ) . instead of using hamilton equations , one can convert the vector equations ( equations [ eq : j1vec][eq : e2vec ] ) into the orbital element form by expressing the cartesian components of the vectors @xmath79 , @xmath80 ( with @xmath81 ) in terms of the orbital eccentricity @xmath82 , inclination @xmath83 , argument of periapse @xmath84 and longitude of ascending nodes @xmath85 ( e.g. * ? ? ? * ) : @xmath86 here the angles are defined respect to a fixed coordinate frame in which @xmath87-axis is aligned with the ( conserved ) total angular momentum , while the @xmath88-@xmath89 plane coincides with the so - called invariable plane . thus the relative inclination between the two orbits is @xmath90 . because of angular momentum conservation , the condition @xmath91 is satisfied . by substituting equations ( [ eq : proj ] ) and ( [ eq : proe ] ) into equations ( [ eq : j1vec])([eq : e2vec ] ) , we can solve for @xmath92 , @xmath93 , @xmath94 and @xmath95 ( for @xmath81 ) . since @xmath96 , the system is determined by seven independent differential equations . these equations are listed in appendix [ sec : full ] ( see equations [ eq : fulle1][eq : fullcos ] ) . although different in form , we have checked that these equations are equivalent to those presented by @xcite . for the test mass case ( @xmath97 ) , we take the limit @xmath98 in equations ( [ eq : fulle1])([eq : fullcos ] ) . also , note that in this limit , @xmath99 , @xmath100 , @xmath101 . we choose @xmath102 , @xmath103 , @xmath104 and @xmath105 , where @xmath106 . accordingly , the secular evolution equations become @xmath107 + 2\cos i_1\\ & \times\cos\omega_1\sin\omega_1\big[15(2 + 5\e1)\cos2i_1\\ & + 7(30\e1\cos2\omega_1\sin^2\!i_1 - 2 - 9\e1)\big]\bigg\ } , \end{split}\ ] ] @xmath108\bigg\ } , \end{split}\ ] ] @xmath109\sin\omega_1\sin\omega_1\bigg\ } , \end{split}\ ] ] @xmath110 - 5b\cos i_1\cos\theta\bigg]\\ & -\frac{\sqrt{1-\e1}}{e_1}\big[10\sin\omega_1\sin\omega_1\cos i_1\\ & \times\sin^2\!i_1(1 - 3\e1)+\cos\theta(3a-10\cos^2\!i_1 + 2)\big]\bigg\ } , \end{split}\ ] ] where we have introduced the dimensionless time @xmath111 and @xmath112 when the octupole terms are ignored ( i.e. , @xmath113 ) , equations ( [ eq : testpe])([eq : testpo ] ) reduce to the orbital element equations of motion found in ( * ? ? ? 5 ) for lidov - kozai oscillations in @xcite appears with the term @xmath114 in the numerator instead of the denominator . ] . and eccentricity @xmath48 from numerical integration of equations ( [ eq : testpe])([eq : testpo ] ) for a prograde ( red ) and a retrograde ( blue ) inner binary . the system parameters are @xmath115 , @xmath97 , @xmath116 , @xmath117 , @xmath118 and @xmath119 . we set @xmath120 initially . inclinations are initialized at @xmath121 from @xmath122 . red lines : @xmath123 , @xmath124 , @xmath125 ; blue lines : @xmath126 , @xmath127 , @xmath128 . in the lower panel , the blue and red curves exactly overlap . , title="fig:",width=313 ] and eccentricity @xmath48 from numerical integration of equations ( [ eq : testpe])([eq : testpo ] ) for a prograde ( red ) and a retrograde ( blue ) inner binary . the system parameters are @xmath115 , @xmath97 , @xmath116 , @xmath117 , @xmath118 and @xmath119 . we set @xmath120 initially . inclinations are initialized at @xmath121 from @xmath122 . red lines : @xmath123 , @xmath124 , @xmath125 ; blue lines : @xmath126 , @xmath127 , @xmath128 . in the lower panel , the blue and red curves exactly overlap . , title="fig:",width=313 ] , evolution of inclination @xmath129 and eccentricity @xmath48 from numerical integration of equations ( [ eq : fulle1])([eq : fullcos ] ) for prograde ( red ) and retrograde ( blue ) inner binaries , this time for a general triple with comparable masses . the system parameters are @xmath115 , @xmath130 , @xmath116 , @xmath131 and @xmath118 . eccentricities are initialized as @xmath120 and @xmath132 . red lines : @xmath133 , @xmath134 , @xmath135 , @xmath136 , @xmath137 ; blue lines : @xmath138 , @xmath139 , @xmath140 , @xmath141 , @xmath142 . , title="fig:",width=313 ] , evolution of inclination @xmath129 and eccentricity @xmath48 from numerical integration of equations ( [ eq : fulle1])([eq : fullcos ] ) for prograde ( red ) and retrograde ( blue ) inner binaries , this time for a general triple with comparable masses . the system parameters are @xmath115 , @xmath130 , @xmath116 , @xmath131 and @xmath118 . eccentricities are initialized as @xmath120 and @xmath132 . red lines : @xmath133 , @xmath134 , @xmath135 , @xmath136 , @xmath137 ; blue lines : @xmath138 , @xmath139 , @xmath140 , @xmath141 , @xmath142 . , title="fig:",width=313 ] in the test - particle limit ( @xmath97 ) , the vector equations ( [ eq : j1vec])([eq : e1vec ] ) are symmetric under reflections of the inner binary . if we perform the replacement @xmath143 ( leaving @xmath59 unchanged ) , we find that @xmath144 and @xmath145 , which may be interpreted as reversing the direction of time . in terms of orbital elements , this reflection operation is equivalent to changing @xmath146 , @xmath147 and @xmath148 . performing this replacement in equations ( [ eq : testpe])([eq : testpo ] ) , we obtain @xmath149 , @xmath150 , @xmath151 and @xmath152 , as expected . figure [ fig : stp ] shows the integration of equations ( [ eq : testpe])([eq : testpo ] ) for two configurations differing solely on the orientation of the @xmath58 vector ( this reflection is carried out by changing the initial conditions @xmath153 , @xmath154 and @xmath155 ) . the evolution of eccentricity is indistinguishable between the prograde ( red curves ) and retrograde ( blue curves ) cases , while the inclination angle @xmath129 shows a reflection symmetry around @xmath122 , evolving in an identical manner in both cases except for a phase offset of half of what can be interpreted as an octupole period " @xcite . for the comparable - mass case ( @xmath156 ) , the inner and outer binaries evolve together , exchanging angular momentum . under reflection operation ( @xmath143 ) , we find that @xmath144 , @xmath145 , @xmath157 and @xmath158 , i.e. , the symmetry of the equations is broken . figure [ fig : scm ] shows the numerical integration in the case of general masses , for two configurations with similar reflection operation as in figure [ fig : stp ] . in this case , it is apparent that there is no reflection symmetry between the prograde ( red curves ) and retrograde ( blue curves ) initial conditions . even the octupole periods " are different . the high eccentricity phase of a lidov kozai cycle can be severely modified if the inner binary separation at pericenter is sufficiently small for additional forces to overcome the tidal torque exerted by the outer binary . if the energy associated to these extra forces @xmath159 surpasses the interaction potential @xmath16 of equation ( [ eq : ham ] ) , the lidov kozai mechanism is said to be arrested " ( e.g. * ? ? ? * ) . here we study the effects of short - range forces on the eccentricity evolution of triple system consisting of a jupiter - mass planet orbiting the primary star of a binary . the short range effects we consider include ( 1 ) precession of periapse due to gr , ( 2 ) tidal bulge of the planet induced by the star , and ( 3 ) planet oblateness due to rotation . in the absence of energy dissipation ( e.g. , tidal friction or gravitational wave radiation ) , the energy of the system @xmath160 is conserved , and so is its orbit - averaged version . since the semimajor axes of the inner and outer orbits are constant , we only need to consider the conserved potential @xmath161 where , as before , @xmath162 . the post - newtonian potential associated with periastron advance is ( e.g. , * ? ? ? * ) @xmath163 where we have defined the dimensionless parameter @xmath164 the potential due to the non - dissipative tidal bulge on @xmath12 is @xmath165 where @xmath166 and @xmath167 , @xmath168 are the tidal love number and the radius of @xmath12 , respectively . the potential energy associated with the rotation - induced oblateness of @xmath12 is @xmath169 here , @xmath170 where @xmath171 is the apsidal motion constant and @xmath172 is the spin rate of @xmath12 , and we have assumed that the spin vector of @xmath12 is aligned with the angular momentum vector @xmath58 of the inner orbit . we can rewrite equation ( [ eq : prot0 ] ) as @xmath173 where @xmath174 the three dimensionless parameters @xmath175 , @xmath176 and @xmath177 quantify the relative importance of the short - range potential terms respect to the quadrupole potential @xmath178 . since the three short - range potentials ( equations [ eq : pgr ] , [ eq : ptide ] and [ eq : prot ] ) depend on the orbital vectors solely through @xmath179 , only the evolution equations for @xmath59 is modified ( see equations [ eq : gj1 ] and [ eq : ge1 ] ) . these extra forces induce an additional precession of @xmath59 around @xmath58 : @xmath180 where ( e.g. , * ? ? ? @xmath181 thus , the gr - induced precession rate is : @xmath182 similarly , for the static tide , we have @xmath183 and for the rotation - induced planet oblateness @xmath184 to obtain an estimate of the relative importance of @xmath185 and @xmath186 , we may consider a pseudo - synchronized planet spin , that is , the planet rotation rate @xmath172 is of order the orbital frequency of periapse @xmath187 . in the weak friction theory of equilibrium tides , the pseudo - synchronized rotation rate is given by ( e.g. , * ? ? ? * ; * ? ? ? * ) @xmath188 thus , in equation ( [ eq : omegarot ] ) , we have @xmath189 with @xmath190 comparing with @xmath185 , we have @xmath191 . since @xmath192 , we find @xmath193 for synchronized rotation . thus , in the vast majority of our examples , the effect of tides will dominate over the effect of the rotational bulge . before systematically examining the parameter space in @xmath194 , @xmath195 , @xmath196 and @xmath197 , we consider a few examples to illustrate how srfs affect lidov kozai oscillations . , @xmath198 , @xmath199 @xmath200 and @xmath118 . initial conditions are @xmath201 , @xmath202 , @xmath203 , @xmath204 , @xmath205 , @xmath206 , @xmath207 , @xmath137 and @xmath208 . total integration time is 50 myr@xmath209 . the red lines are from the integration of the pure lidov kozai effect to octupole order , while the blue lines are the results of integration including srfs . orbital flips seem to be entirely suppressed . however , when extending the integration time to @xmath210 myrs @xmath211 , the inner orbit eventually flips to retrograde in the interval of 90130 myr before going back to its original orientation . , title="fig:",width=309 ] , @xmath198 , @xmath199 @xmath200 and @xmath118 . initial conditions are @xmath201 , @xmath202 , @xmath203 , @xmath204 , @xmath205 , @xmath206 , @xmath207 , @xmath137 and @xmath208 . total integration time is 50 myr@xmath209 . the red lines are from the integration of the pure lidov kozai effect to octupole order , while the blue lines are the results of integration including srfs . orbital flips seem to be entirely suppressed . however , when extending the integration time to @xmath210 myrs @xmath211 , the inner orbit eventually flips to retrograde in the interval of 90130 myr before going back to its original orientation . , title="fig:",width=309 ] in figure [ fig : case91 ] , we show the evolution of a triple system with @xmath212 and initial mutual inclination @xmath213 obtained by numerical integration of the equations of motion in orbital elements form ( see appendix [ sec : full ] ) . when srfs are ignored ( red curves ) , the inner orbit evolves into a highly eccentric state over a timescale of order @xmath214 , reaching values as extreme as @xmath215 ( red curves , bottom panel ) . in this example , eccentricity maxima of @xmath216 are always accompanied by orbital flips ( red curves , top panel ) , i.e. , the @xmath87-component of @xmath40 reverses its sign . orbital flips are always tied to eccentricity maxima and correspond to @xmath58 shrinking going through the origin ( @xmath217 ) as @xmath216 ( e.g. , * ? ? ? * ; * ? ? ? * ) . in some cases , it is possible to even derive a closed - form solution of this behaviour over long timescales provided the slowly varying quantity @xmath218 remains positive at all times ( e.g. , * ? ? ? * ; * ? ? ? assuming that the maximum eccentricity of a lidov kozai cycle is reached when @xmath219 crosses zero , @xcite find that the maximum @xmath48 scales with @xmath194 roughly as @xmath220 . if this theoretical maximum can not be reached owing to additional effects such as srfs , then we expect that @xmath221 will be unable to come arbitrarily close to zero , and therefore orbital flips will not be allowed . indeed , when srfs are included ( blue curves ) , the maximum eccentricity is capped down to values such that @xmath222 ( blue curves , bottom panel ) . although still large , this upper limit to the eccentricity is sufficient to introduce a lower limit to @xmath223 ( see section [ sec : max_ecc ] below ) such that @xmath221 can not reverse signs under the criterion introduced by @xcite . as a result , we see no orbital flips in this example ( red curves , top panel ) . surprisingly , however , orbital flips are not prohibited in every case . in figure [ fig : case92 ] , we present an example of a system which exhibits an orbital flip even though the maximum allowed eccentricity has been reduced by srfs . as in the previous example , we integrate a triple system with @xmath212 with and without srfs ( blue and red curves respectively ) . this time , the initial conditions are modified slightly , changing the initial mutual inclination angle from @xmath213 to @xmath224 . over the first half of the integration , the evolution of eccentricity ( bottom panel ) and inclination ( top panel ) in figure [ fig : case92 ] closely resemble of those of figure [ fig : case91 ] . however , after 25 myrs , the two systems start following entirely differently trajectories , despite the very small difference in initial conditions . in addition , the figure shows that this system finds a way to cause an orbital flip ( i.e. @xmath221 crosses zero ) , despite that the eccentricity is not allowed to exceed @xmath225 just as in figure [ fig : case91 ] . from figure [ fig : case92 ] , we conclude that ( 1 ) orbital flips can still take place in presence of sfrs that are strong enough to limit the eccentricity maximum , and ( 2 ) that the inclination of the inner binary may exhibit chaotic behaviour ( e.g. * ? ? ? * ; * ? ? ? * ) , and that conservative srfs modify do not necessarily suppress this erratic evolution . to check whether the example of figure [ fig : case91 ] has entirely suppressed orbital flips or if it is just a matter of time before it finds a channel to cross @xmath226 , we integrate the system for @xmath227 myr @xmath211 . indeed , we confirm that after a very long time @xmath228 , this system also undergoes an orbital flip that lasts for @xmath229 before returning to its original orientation . figure [ fig : case93 ] shows the evolution of @xmath221 and the angle @xmath230 ( see * ? ? ? * ; * ? ? ? * ) for the example of figure [ fig : case92 ] . the red curves show the evolution of the system in the absence of srfs , where a regular oscillation of @xmath221 at earlier times transitions to a different regime after @xmath231 myrs . when srfs are included ( blue curves ) , the evolution of @xmath221 stays bounded between its initial value and zero , without being allowed to change sign , until suddenly a flip takes place . the transition between these two regimes can be seen in the evolution of @xmath232 ( bottom panel ) . at early times , @xmath232 remains bounded between @xmath233 and @xmath234 . however , by the time @xmath221 changes sign , @xmath232 is circulating , sweeping all possible angles . an analogous plot of @xmath232 for the example in figure [ fig : case91 ] shows that @xmath232 never circulates during the entire extent of the integration . , but slightly changing the initial inclination : @xmath224 with @xmath235 and @xmath236 . , title="fig:",width=309 ] , but slightly changing the initial inclination : @xmath224 with @xmath235 and @xmath236 . , title="fig:",width=309 ] and @xmath230 for the case corresponding to figure [ fig : case92 ] . the red lines are from the integration of pure lidov kozai effect in octupole order , while the blue lines are the results of integration including srfs . when srfs limit the maximum eccentricity , flips are suppressed if @xmath232 is bounded , but they become possible once again if @xmath232 is circulating . , title="fig : " ] and @xmath230 for the case corresponding to figure [ fig : case92 ] . the red lines are from the integration of pure lidov kozai effect in octupole order , while the blue lines are the results of integration including srfs . when srfs limit the maximum eccentricity , flips are suppressed if @xmath232 is bounded , but they become possible once again if @xmath232 is circulating . , title="fig : " ] we see in section 3.2 that srfs limit the maximum eccentricity that can be achieved during the lidov kozai cycles ( e.g. , * ? ? ? * ; * ? ? ? in the test - mass approximation ( @xmath97 ) and neglecting the octupole effect , this maximum eccentricity , @xmath237 , can be derived analytically . we shall see in section 4 that the limiting eccentricity , @xmath238 , achieved for the initial inclination @xmath239 , is also applicable when the octupole effect is included and binaries of comparable masses ( @xmath156 ) are considered . in the test - mass approximation ( @xmath97 , which implies @xmath75 ) and at the quadrupole level ( @xmath113 ) , equation ( [ eq : j1vec ] ) implies @xmath240 in addition , the total potential is conserved @xmath241 in terms of the orbital elements of the inner binary , the quadrupole potential ( equation [ eq : apk ] ) can be written as @xmath242,\ ] ] if the system is initialized with @xmath243 , the maximum eccentricity @xmath237 is achieved at @xmath244 or @xmath245 during the lidov kozai cycles . using equations ( [ eq : jconst ] ) ( [ eq : apk2 ] ) , we find that @xmath237 is given by @xmath246 where @xmath247 . in the absence of the srfs ( @xmath248 ) , the above equation yields the well - known maximum eccentricity @xmath249 for pure " lidov kozai oscillation ( e.g. , * ? ? ? * ; * ? ? ? * ) @xmath250 if we neglect the tidal or rotation terms ( @xmath251 ) and assume @xmath252 , equation ( [ eq : ft ] ) results to ( e.g. , * ? ? ? * ) @xmath253\ ] ] figure [ fig : emaxi ] depicts several example of @xmath237 for different values of @xmath254 , @xmath255 , @xmath256 . the physical meaning of equation ( [ eq : ft ] ) can be made clear if we use the expression of @xmath257 equations [ eq : omegagr][eq : omegarot ] ) to re - express it as ( assuming @xmath258 ) @xmath259_{e_1=e_{1,{\mathrm{max}}}}\\ & \approx\frac{9}{8}e_{1,{\mathrm{max}}}^2\frac{j_{1,{\mathrm{min}}}^2 - 5\cos^2\!i_0/3}{j_{1,{\mathrm{min}}}^2}~ , \end{split}\ ] ] where @xmath260 and where we have defined for convenience a characteristic " lidov kozai rate @xmath261 which should not be confused with the precession rate derived from applying the operation in equation [ eq : extraomega ] to @xmath262 . for @xmath239 , the eccentricity attains the limiting value , @xmath263 , given by @xmath264_{e_1=e_{\mathrm{lim}}}=\frac{9}{8}e_{\mathrm{lim}}^2~.\ ] ] for @xmath265 , we have @xmath266 , equation ( [ eq : ftt ] ) becomes @xmath267_{e_1=e_{\mathrm{lim}}}\simeq\frac{9}{8}~.\ ] ] thus , the limiting eccentricity is achieved when the periapse precession rate due to srfs becomes comparable to the lidov kozai rate @xmath268 . in the test - mass limit ( @xmath97 ) , the evolution of the inner binary depends on the dimensionless ratios @xmath194 , @xmath254 , @xmath255 , @xmath256 as well as the initial inclination angle @xmath4 ( we assume @xmath269 ) . in this section , we consider the evolution of jupiter - mass planet ( @xmath270 ) moving around a solar - mass star ( @xmath271 ) . we carry out calculations for different values of @xmath13 , @xmath15 , @xmath14 and @xmath49 . the different orbital configurations and their corresponding values of @xmath194 and @xmath272 are listed in table [ tab : paramspace ] . these conditions of parameters are subject to the stability criterion of @xcite @xmath273 @llrrrrlrlr@ parameter & @xmath57 & @xmath175 & @xmath176 & @xmath274 & @xmath275 & @xmath49 & @xmath276 + case 1 & 0.001 & @xmath277 & @xmath278 & 1 & 200 & 0.2 & 0.5 + + case 2 & 0.002 & @xmath279 & @xmath280 & 1 & 100 & 0.2 & 1 + + case 3a & 0.006 & @xmath281 & @xmath282 & 6 & 200 & 0.2 & 1 + case 3b & 0.006 & @xmath283 & @xmath284 & 1 & 33.33 & 0.2 & 1 + case 3c & 0.006 & @xmath285 & @xmath286 & 1 & 33.33 & 0.2 & 0.1 + + case 4 & 0.011 & @xmath287 & @xmath288 & 1 & 200 & 0.8 & 1 + + case 5 & 0.013 & @xmath289 & @xmath290 & 6 & 100 & 0.2 & 1 + + case 6 & 0.022 & @xmath291 & @xmath292 & 1 & 100 & 0.8 & 1 + + case 7 & 0.033 & @xmath293 & @xmath294 & 5 & 100 & 0.5 & 1 + + case 8 & 0.044 & @xmath295 & @xmath296 & 2 & 100 & 0.8 & 1 + + case 9 & 0.056 & @xmath297 & @xmath298 & 6 & 100 & 0.6 & 0.04 + + case 10a & 0.067 & @xmath299 & @xmath300 & 6 & 200 & 0.8 & 1 + case 10b & 0.067 & @xmath301 & @xmath302 & 1 & 33.33 & 0.8 & 1 + case 10c & 0.067 & @xmath303 & @xmath304 & 1 & 33.33 & 0.8 & 0.1 + + case 11 & 0.133 & @xmath305 & @xmath306 & 6 & 100 & 0.8 & 1 + @llrrrrlrlr@ parameter & @xmath307 & @xmath308 & @xmath309 & @xmath310 & @xmath311 & @xmath312(deg ) & @xmath313(deg ) & @xmath314(deg ) + case 1 & @xmath315 & @xmath316 & @xmath317 & @xmath318 & @xmath319 & 87.7 & @xmath320 & 88.5 + + case 2 & @xmath321 & @xmath322 & @xmath323 & 6.23 & @xmath324 & 86.2 & @xmath320 & 85.4 + + case 3a & @xmath325 & @xmath326 & @xmath327 & 7.29 & @xmath328 & 82.2 & @xmath320 & 87.1 + case 3b & @xmath329 & @xmath330 & @xmath331 & 7.21 & @xmath332 & 82.2 & @xmath320 & 86.8 + case 3c & @xmath333 & @xmath334 & @xmath335 & 6.81 & @xmath336 & 82.2 & @xmath320 & 85.4 + + case 4 & @xmath337 & @xmath338 & @xmath339 & 5.56 & @xmath340 & 80.2 & @xmath320 & 83.9 + + case 5 & @xmath341 & @xmath342 & @xmath343 & 7.32 & @xmath344 & 79.0 & 89.4 & 78.8 + + case 6 & @xmath345 & @xmath346 & @xmath347 & 6.96 & @xmath348 & 69.9 & 89.1 & 71.9 + + case 7 & @xmath349 & @xmath350 & @xmath351 & 7.32 & @xmath352 & 58.7 & 60.4 & 59.3 + + case 8 & @xmath353 & @xmath354 & @xmath355 & 7.27 & @xmath356 & 51.3 & 73.3 & 51.9 + + case 9 & @xmath357 & @xmath358 & @xmath359 & 7.28 & @xmath360 & 47.8 & 56.0 & 49.1 + + case 10a & @xmath361 & @xmath362 & @xmath363 & 7.31 & @xmath352 & 47.3 & 53.9 & 47.8 + case 10b & @xmath364 & @xmath365 & @xmath366 & 7.27 & @xmath367 & 47.3 & 73.1 & 51.9 + case 10c & @xmath368 & @xmath369 & @xmath370 & 7.14 & @xmath371 & 47.3 & 81.1 & 52.1 + + case 11 & @xmath372 & @xmath373 & @xmath374 & 7.32 & @xmath344 & 47.3 & 48.4 & 49.6 + for each combination of @xmath194 and @xmath272 ( table [ tab : paramspace ] ) , we integrate a total of 300 triple systems over a total integration time ranging from @xmath209 to @xmath228 . we setup each system by varying the initial inclination of the inner binary @xmath4 ( @xmath375 when @xmath97 ) between @xmath376 and @xmath122 . we first consider a specific example with @xmath212 ( case 9 in table 1 ) . for each initial inclination angle @xmath4 ( in the range between @xmath376 and @xmath122 ) , we integrate equations ( [ eq : fulle1])-([eq : fullomega2 ] ) for @xmath377 yrs , corresponding to 360.5 @xmath378 for this specific set of parameters . for each of these subsystems , we record the maximum eccentricity @xmath237 and the maximum and minimum of @xmath379 attained during the evolution . the results are shown in figure [ fig : case94 ] . the upper panel in figure [ fig : case94 ] shows the maximum eccentricity of inner orbit as a function of @xmath4 . at the quadrupole level , the pure lidov kozai cycles can give extremely large eccentricity ( @xmath380 ) only for @xmath381 . when the short - range effects are included , the value of @xmath237 at that point is limited to @xmath382 , in accordance with the analytic expression ( equation [ eq : ft ] ) . for the parameters considered in this case ( case 9 ) , the tidal effect plays the dominate role in limiting the maximum eccentricity ( table 2 , when we see that @xmath383 at @xmath384 ; see also equation [ eq : l ] ) . when the octupole term is included , there is a sharp jump of @xmath385 at @xmath386 . without the srfs , @xmath387 becomes very small and varies erratically as @xmath4 increases beyond @xmath388 . this erratic variation is the result of the overlap between the quadrupole and octupole contributions . when the srfs are included , we find that instead of the rapid variation of @xmath387 , the maximum eccentricity becomes approximately a constant , equal to @xmath389 . we define @xmath390 as the the value of @xmath4 when @xmath391 first reaches @xmath389 . for the case considered in fig . 7 , @xmath390 is close to @xmath388 . it is important to note that although @xmath389 is derived in the quadrupole approximation ( see section 3.3 ) , it serves as the maximum eccentricity attainable even when the octupole term is included . the lower panel in figure [ fig : case94 ] shows the maximum and minimum of the orbital inclination attained during the evolution of the inner binary as functions of @xmath4 . at the pure quadrupole level ( without srfs ) , the inclination does not change until @xmath4 reaches @xmath392 , beyond which @xmath393 and @xmath394 . including srfs , @xmath395 is modified for @xmath4 close to @xmath122 as the maximum eccenticity is limited by the srfs . note that @xmath396 . at the octupole level , the angular momentum of the inner binary experiences a flip ( @xmath397 ) at a critical angle @xmath398 . this angle is always greater than @xmath399 ( the onset of quadrupole lidov kozai oscillations ) . when the srfs are included , this critical angle is pushed to a higher value , @xmath400 . at inclinations slightly higher than the angle critical @xmath390 ( demarcated by inverted triangle in figure [ fig : case94 ] , the orbital flips seen in absence of srfs ( red curves ) have now been inhibited . note , however , that at even higher inclinations ( @xmath401 ) , orbital flips are once again allowed . this can occur even though the maximum eccentricity @xmath237 is strongly affected by the srfs ( see figure [ fig : case93 ] and section [ sec : examples ] ) . note also that the individual examples shown in figures [ fig : case92 ] and [ fig : case93 ] ( with @xmath4 of @xmath402 and @xmath403 respectively ) lie within the erratically varying region that starts at @xmath404 . it is possible that the inclination angle in the example with @xmath405 ( figure [ fig : case92 ] ) will eventually flip as well . from this figure we can conclude that srfs have broken the symmetry that existed between the upper and lower panels of figure [ fig : case94 ] ( red curves ) , which showed that both the extreme maximum eccentricity and the orbital flip where achieved above the same critical inclination . the erratic variation of @xmath406 for @xmath407 results from the combined effects of quadrupole , octupole and srfs , and may be associated with the chaotic behaviour of lidov kozai oscillations studied by @xcite . these authors find that configurations with higher inclinations and larger @xmath194 are more chaotic ( with lyapunov times of @xmath408 for the chaotic regions of parameter space ) . it is possible that the complexity of a system with conservative srfs ( three additional frequencies are present and no energy dissipation ) only shift the inclination threshold for chaotic behaviour to larger angles , but have not fundamentally suppressed the chaotic nature of lidov kozai oscillations with octupole - level terms . it is also possible that the characteristic timescale for a flip has been entirely altered by the srfs , and that all systems with @xmath407 will eventually flip ( on timescales much longer than @xmath409 ) . to explore how the extrema in @xmath48 and @xmath129 change with @xmath4 for different values of @xmath194 , we carry out another set of numerical integrations , this time with @xmath411 ( listed as ` case 5 ' in table 1 below ) . the results of this set of integrations are shown in figure [ fig : case5 ] . without srfs ( red curves ) , the @xmath410 and @xmath412 curves exhibit the same overall morphology observed in the case with @xmath212 ( figure [ fig : case94 ] ) . in this case , however , significant deviations from the quadrupole - only calculations are confined to a narrower range in @xmath4 . this is to be expected , since this octupole active " region will gradually shrink as @xmath194 is made smaller , until the quadrupole level solutions ( black and green curves ) are recovered . in the limit @xmath413 , the only angle which allows for @xmath414 is @xmath239 ( equation [ eq : me ] ) . similarly , when @xmath413 only @xmath239 permits @xmath226 . quantitatively , the width along the @xmath4-axis of the octupole - active region or window of influence " for a given value of @xmath194 can be understood using the flip condition " identified by @xcite . from approximate conservation laws , these authors find that , given @xmath415 and @xmath416 , the long term oscillation of @xmath221 owing to octupole terms can only result in a change of sign if and only if @xmath4 is greater than a critical value that depends on @xmath194 . equivalently , given @xmath4 , there is a critical value @xmath417 above which orbits will flip . this flip condition can be approximately expressed as @xmath418 where @xmath419 is a non - monotonic function that is equal to zero at @xmath420 and @xmath421 and peaks at 0.0475 for @xmath422 ( see * ? ? ? * ; * ? ? ? the critical value @xmath417 is a monotonically decreasing function of @xmath4 , meaning that the closer @xmath4 is to @xmath122 , the smaller @xmath423 becomes ( i.e. , the easier it is to flip ) . we illustrate this by overlaying @xmath423 as a function of @xmath4 in the bottom panel of figure [ fig : case5 ] . when @xmath423 becomes smaller than @xmath424 ( at @xmath425 ) , test particle trajectories are allowed to flip orientations . above this critical angle , each orbital flip is accompanied by an extreme increase in eccentricity . following @xcite , we estimate that this limiting eccentricity within the octupole active region is such that @xmath426 , i.e. , @xmath427 , which is in good agreement with the average value of @xmath428 in the region where @xmath429 . when srfs are included , ( blue and green curves in figure [ fig : case5 ] ) , the modifications to the evolution of eccentricity are consistent with what was observed in the @xmath212 example . however , the amplitude of the inclination oscillations is more dramatically affected . on one hand , we find a consistently truncated maximum eccentricity down to a value of @xmath430 , in rough agreement with the value of @xmath431 predicted by equation ( [ eq : ftt ] ) . on the other hand , the orbital flips above @xmath432 are entirely suppressed , in contrast with the behaviour observed in figure [ fig : case94 ] , where only a fraction of the systems have their orbital flips entirely suppressed , while at high inclinations the orbits still manage to reverse their orientations despite the strict limits on the maximum eccentricity . , @xmath433 , @xmath434 ) . system parameters are @xmath115 , @xmath198 , @xmath116 @xmath200 and @xmath435 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath437 years ( @xmath438 ) . , title="fig:",scaledwidth=50.0% ] , @xmath433 , @xmath434 ) . system parameters are @xmath115 , @xmath198 , @xmath116 @xmath200 and @xmath435 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath437 years ( @xmath438 ) . , title="fig:",scaledwidth=50.0% ] , @xmath439 , @xmath440 ) . system parameters are @xmath115 , @xmath198 , @xmath116 @xmath117 and @xmath441 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath442 years ( @xmath443 ) . note that @xmath238 decreases , the critical angles ( @xmath390 and @xmath400 ) are pushed to higher values . , title="fig:",scaledwidth=50.0% ] , @xmath439 , @xmath440 ) . system parameters are @xmath115 , @xmath198 , @xmath116 @xmath117 and @xmath441 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath442 years ( @xmath443 ) . note that @xmath238 decreases , the critical angles ( @xmath390 and @xmath400 ) are pushed to higher values . , title="fig:",scaledwidth=50.0% ] , @xmath444 , @xmath445 ) . system parameters are @xmath115 , @xmath198 , @xmath446 @xmath117 and @xmath441 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath447 years ( @xmath443 ) . the value of @xmath238 becomes smaller than in case 10b and the maximum inclination angle can not reach @xmath448 . , title="fig:",scaledwidth=50.0% ] , @xmath444 , @xmath445 ) . system parameters are @xmath115 , @xmath198 , @xmath446 @xmath117 and @xmath441 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath447 years ( @xmath443 ) . the value of @xmath238 becomes smaller than in case 10b and the maximum inclination angle can not reach @xmath448 . , title="fig:",scaledwidth=50.0% ] we have carried out calculations of the inner binary evolution for various combinations of @xmath449 that yield different values of the parameters @xmath194 , @xmath254 , @xmath255 , @xmath256 ( see table 1 ) . in particular , the dimensionless octupole parameter @xmath194 can be varied by changing the values of @xmath49 and the ratio of @xmath13 to @xmath15 ( see equation [ eq : c ] ) , and we consider @xmath194 ranging from @xmath450 to @xmath451 . for a given @xmath194 , we consider various possible values of @xmath254 , @xmath255 , @xmath256 ( see equations [ eq : r11 ] , [ eq : r12 ] and [ eq : r13 ] ) in order to assess the role of srfs . for each set of parameters and the initial inclination angle @xmath4 , we integrate the binary evolution equations for a few octupole oscillation periods , @xmath452 , and record the maximum of @xmath48 and the extrema of @xmath379 attained during the evolution . table 2 summarizes our key findings . as noted before ( section 4.1 ) , the srfs provide an upper limit to the maximum eccentricity attainable during the binary evolution , even for large @xmath194 . in particular , our numerical result for the maximum eccentricity @xmath453 ( for all @xmath4 s ) is in good agreement with the limiting eccentricity @xmath389 given by equation ( [ eq : ftt ] ) . comparing @xmath454 at @xmath455 , we see that with the exception of case 1 , the tidal effect and the rotational bulge are responsible for limiting the eccentricity growth . the last three columns of table 2 summarize the three critical initial inclination angles introduced in section 4.1 for the different cases . without srfs , the angle @xmath398 ( at which orbital flip occurs due to the octupole potential ) decreases with increasing @xmath194 . when the srfs are included , orbital flips require higher inclinations ( @xmath456 ) , and the critical angle @xmath400 decreases as @xmath194 increases . note that when @xmath457 ( case 1 to case 6 ) , @xmath458 , implying that the octupole potential can not lead to orbit flip . finally , in the presence of the srfs , the critical inclination @xmath390 at which the maximum eccentricity saturates to @xmath459 is roughly equals to @xmath398 . this implies that the excitations of eccentricity and inclination are related . figures [ fig : case10a][fig : case10c ] depict the results for case 10a-10c , corresponding to the same @xmath194 but different srf strength . note that , as @xmath194 is the same for all these examples , the width of the octupole window of influence is unaltered . however , the region in inclination angle for which orbits are allowed to flip changes with @xmath272 . this is quantified by the value of the critical angle @xmath400 , which grows monotonically with @xmath272 , meaning that orbital flips are progressively confined to the neighboring region of @xmath239 . in this section , we extend the analysis of previous sections to the general case of lidov kozai cycles with srfs in systems composed of three comparable masses ( @xmath460 ) , focusing on the long term evolution of eccentricity and inclination of the inner binary . as discussed in section [ sec : symmetry ] , the equations of motion in the test - particle limit are symmetric upon reflections of the @xmath58 vector through the origin . this implies that the lidov kozai cycles with srfs examples in the small mass regime ( @xmath97 ) presented in figures [ fig : case94][fig : case10c ] show even symmetry around @xmath239 in the eccentricity curves ( top panels ) and odd symmetry in the inclination curves ( bottom panels ) . as we have shown in a previous example ( figure [ fig : scm ] ) , this reflection symmetry is removed when @xmath156 . however , there is still an approximate symmetry center for calculations at the quadrupole - level . this can be seen in figure [ fig : case1c ] for a triple system of comparable masses . in a similar fashion to figures [ fig : case94][fig : case10c ] , the black curves in figure [ fig : case1c ] show @xmath237 and @xmath461 as a function of @xmath462 and @xmath463 calculated from the quadrupole - level potential . we have extended the initial inclinations to cover @xmath464,@xmath465 , encompassing the full range of prograde and retrograde orientations . there is a reflection symmetry respect to @xmath466 ( or equivalently , respect to @xmath467 ) . however , this symmetry is erased once octupole - level terms are considered ( red curves ) . this is in contrast to the test - particle limit , for which the reflection symmetry around @xmath468 is valid for the quadrupole - level and octupole - level approximations . @llrrrrlrlr@ parameter & @xmath57 & @xmath175 & @xmath176 & @xmath274 & @xmath275 & @xmath469 & @xmath470 & @xmath276 & @xmath471 + case 1a & 0.022 & @xmath472 & @xmath473 & 10 & 100 & 0.5 & 0.5 & 1 & 0.5 + case 1b & 0.022 & @xmath474 & @xmath475 & 3 & 30 & 0.5 & 0.5 & 1 & 0.5 + case 1c & 0.022 & @xmath476 & @xmath477 & 1 & 10 & 0.5 & 0.5 & 1 & 0.5 + case 1d & 0.022 & @xmath476 & @xmath478 & 1 & 10 & 0.5 & 0.5 & 1 & 2 + case 1e & 0.022 & @xmath476 & @xmath479 & 1 & 10 & 0.5 & 0.5 & 1 & 5 + + case 2a & 0.042 & @xmath480 & @xmath481 & 10 & 120 & 0.6 & 0.3 & 0.8 & 0.3 + case 2b & 0.042 & @xmath482 & @xmath483 & 5 & 60 & 0.6 & 0.3 & 0.8 & 0.3 + case 2c & 0.042 & @xmath484 & @xmath485 & 1 & 12 & 0.6 & 0.3 & 0.8 & 0.3 + case 2d & 0.042 & @xmath484 & @xmath486 & 1 & 12 & 0.6 & 0.3 & 0.8 & 0.6 + case 2e & 0.042 & @xmath484 & @xmath487 & 1 & 12 & 0.6 & 0.3 & 0.8 & 5 + @llrrrrlrlr@ parameter & @xmath307 & @xmath308 & @xmath309 & @xmath310 & @xmath488(deg ) & @xmath489(deg ) + case 1a & @xmath490 & @xmath491 & @xmath492 & 10.12 & 85.5 & 94.5 + case 1b & @xmath493 & @xmath494 & @xmath495 & 10.11 & 85.5 & 94.5 + case 1c & @xmath496 & @xmath497 & @xmath498 & 10.09 & 85.5 & 94.5 + case 1d & @xmath499 & @xmath500 & @xmath501 & 9.98 & 85.5 & 94.5 + case 1e & @xmath502 & @xmath503 & @xmath504 & 9.74 & 85.5 & 94.5 + + case 2a & @xmath505 & @xmath506 & @xmath507 & 10.12 & 86.2 & 93.8 + case 2b & @xmath508 & @xmath509 & @xmath510 & 10.12 & 86.2 & 93.8 + case 2c & @xmath511 & @xmath512 & @xmath513 & 10.10 & 86.2 & 93.8 + case 2d & @xmath514 & @xmath515 & @xmath516 & 10.07 & 86.2 & 93.8 + case 2e & @xmath517 & @xmath518 & @xmath519 & 9.65 & 86.2 & 93.8 + the shift in the symmetry center away from @xmath122 results from the conservation of total angular momentum and the quadrupole - level potential . introducing the total angular momentum @xmath520 , we can write the mutual inclination of the inner and outer orbits as @xcite @xmath521 where @xmath63 and @xmath64 are given by equations ( [ eq : l1])([eq : l2 ] ) . since @xmath522 is conserved , this expression becomes @xmath523 where @xmath463 , @xmath524 and @xmath469 are the initial values for the mutual inclination and for the inner and outer eccentricities , respectively . note that , at the quadrupole level , the eccentricity of the outer orbit @xmath525 constant . next , we rewrite the ( constant ) potential of equation ( [ eq : apk2 ] ) as @xmath526 combining equations ( [ eq : gtot2 ] ) and ( [ eq : apk3 ] ) , we obtain an expression for the maximum eccentricity @xmath237 ( after evaluating at @xmath244 ) : @xmath527=0~. \end{split}\ ] ] equation ( [ eq : meg ] ) generalizes equation ( [ eq : me ] ) for the test - mass case . these two expressions become equivalent in the limit @xmath98 . in the test - particle limit at the quadrupole level , the symmetry center ( at @xmath239 ) coincides with the point of maximal eccentricity " or @xmath528 . similarly , for the general case of comparable masses , we define the angle @xmath489 by setting @xmath528 in equation ( [ eq : meg ] ) : @xmath529 as expected , in the limit @xmath98 we have that @xmath530 . note that the negative sign in equation ( [ eq : isym ] ) implies that @xmath489 is always greater than @xmath122 . this symmetry breaking can also be realized for the inner inclination @xmath129 , which can be obtained from conservation of angular momentum and the law of sines : @xmath531 . this is consistent with the numerical result shown in figure [ fig : case1c ] . figures [ fig : case1c][fig : case2e ] show the dependence of maximum eccentricity and inclination extrema as a function of @xmath532 ( or @xmath463 ) for systems with different masses @xmath115 , @xmath130 and other parameters . as in the examples of section [ sec : paramspace ] , four different calculations shown : ( 1 ) quadrupole - level approximation with no srfs ( black curves ) , ( 2 ) octupole - level approximation with no srfs ( red curves ) , ( 3 ) quadrupole - level approximation with srfs ( green curves ) , and ( 4 ) octupole - level approximation with srfs ( blue curves ) . just as in section [ sec : paramspace ] , we explore the changes in @xmath237 and @xmath461 as we vary @xmath194 and @xmath272 , this time for triple stars of comparable masses . note that in equation ( [ eq : c ] ) , the octupole contribution is exactly zero if the members of inner binary here equal mass , so for similar masses , @xmath194 can not be very large . the orbital separations and other physical parameters of the systems studied in this section are listed in table [ tab : paramspace_general ] . the values of initial inclinations induced both prograde and retrograde orbits in @xmath462 ( i.e. , respect to the total angular momentum vector ) . the range in angles is chosen so as to enclose the lidov kozai active " region . this region is contained between the angles @xmath533 and @xmath534 , which are the two solutions of the quadratic equation obtained from equation ( [ eq : meg ] ) after setting @xmath535 : @xmath536 for all the examples considered here ( table [ tab : paramspace_general ] ) , an inclination interval of @xmath537 is sufficient to capture the entire range of systems that are subject to lidov kozai oscillations . . we extend the test - particle case in section 4 to comparable - mass case . here , the system has an inner binary of @xmath115 , @xmath130 , @xmath117 , @xmath538 and the companion has @xmath116 , @xmath539 . we initially set @xmath201 , @xmath132 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . because there is no reflection symmetry between the prograde and retrograde configurations , we integrate equations ( [ eq : fulle1])-([eq : fullomega2 ] ) with @xmath537 for @xmath540 years ( @xmath541 ) . note that limiting eccentricity holds as well and the flip can not occur with srfs . , title="fig:",width=321 ] . we extend the test - particle case in section 4 to comparable - mass case . here , the system has an inner binary of @xmath115 , @xmath130 , @xmath117 , @xmath538 and the companion has @xmath116 , @xmath539 . we initially set @xmath201 , @xmath132 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . because there is no reflection symmetry between the prograde and retrograde configurations , we integrate equations ( [ eq : fulle1])-([eq : fullomega2 ] ) with @xmath537 for @xmath540 years ( @xmath541 ) . note that limiting eccentricity holds as well and the flip can not occur with srfs . , title="fig:",width=321 ] by changing @xmath117 , @xmath539 and @xmath542 , and keep other quantities the same as case 1c ( see table 3 ) . we integrate the equations and the total integration time is @xmath540 years ( @xmath541 ) . note that @xmath238 become smaller and srfs affect the octupole - level effects significantly . , title="fig:",width=321 ] by changing @xmath117 , @xmath539 and @xmath542 , and keep other quantities the same as case 1c ( see table 3 ) . we integrate the equations and the total integration time is @xmath540 years ( @xmath541 ) . note that @xmath238 become smaller and srfs affect the octupole - level effects significantly . , title="fig:",width=321 ] . the system has an inner binary of @xmath115 , @xmath543 , @xmath117 , @xmath544 and the companion has @xmath545 , @xmath546 . we initially set @xmath201 , @xmath202,@xmath136 , @xmath436 , @xmath137 and @xmath208 . we integrate the equations for @xmath547 years ( @xmath548 ) . due to the stronger octupole potential , the width of the @xmath237 and @xmath549 regions become lager and the flip occur even with srfs . , title="fig:",width=321 ] . the system has an inner binary of @xmath115 , @xmath543 , @xmath117 , @xmath544 and the companion has @xmath545 , @xmath546 . we initially set @xmath201 , @xmath202,@xmath136 , @xmath436 , @xmath137 and @xmath208 . we integrate the equations for @xmath547 years ( @xmath548 ) . due to the stronger octupole potential , the width of the @xmath237 and @xmath549 regions become lager and the flip occur even with srfs . , title="fig:",width=321 ] . the system has an inner binary of @xmath115 , @xmath543 , @xmath117 , @xmath542 and the companion has @xmath545 , @xmath546 . we initially set @xmath201 , @xmath202 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath547 years ( @xmath548 ) . , title="fig:",width=321 ] . the system has an inner binary of @xmath115 , @xmath543 , @xmath117 , @xmath542 and the companion has @xmath545 , @xmath546 . we initially set @xmath201 , @xmath202 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath547 years ( @xmath548 ) . , title="fig:",width=321 ] as discussed in section [ sec : symmetry_general ] above , for finite @xmath12 , the symmetry of the system respect to @xmath550 is shifted to a different value @xmath489 . however , this symmetry center only reflects the behaviour of the system at the quadrupole level . in addition to the significant when the octupole potential is included , figure [ fig : case1c ] ( for @xmath551 ) also shows how the symmetry between prograde and retrograde orbits is broken . figure [ fig : case1c ] shows that at the quadrupole level , the excitation of eccentricity only takes place in the range between @xmath552 and @xmath553 , as given by equation ( [ eq : ist ] ) , and @xmath237 is achieved at @xmath554 ( table 4 ) , as predicted by equation ( [ eq : isym ] ) . when the octupole - level terms are included ( red curve ) , @xmath555 is not the only inclination that allows for such extreme eccentricity ( i.e. , @xmath556 ) . indeed , as in the test - mass case ( figures [ fig : case94][fig : case10c ] ) , the inclusion of octupole terms widens the range on angles for which @xmath557 is possible . in this case however , the widening " takes place to the right of @xmath489 , while the quadrupole - level solution remains valid for @xmath558 down to for @xmath559 . below @xmath560 , deviations from the quadrupole - level solution become significant . these features , which can be compared to what seemed to be minor fluctuations in @xmath237 for the test - particle cases ( see figures [ fig : case94][fig : case10c ] ) , show that moderately high eccentricities can be excited at lower inclinations ( @xmath561 ) than the quadrupole - order calculation would allow . when srfs are included , the quadrupole - level eccentricity maxima are truncated at a global maximum corresponding to @xmath562 . the horizontal line in figure [ fig : case1c ] corresponds to the limiting eccentricity given by equation ( [ eq : ftt ] ) . it is important to note that this limiting eccentricity applies even in the general case of comparable masses . also note that the tides are mainly responsible for the eccentricity suppression ( see table 4 ) . it is not surprising that the analytic estimate of @xmath563 , derived in the test - mass limit ( section [ sec : max_ecc ] ) , remains a good approximation for comparable - mass systems . for @xmath48 very close to unity , the vast majority of the angular momentum resides in the outer binary , forcing the inner binary to behave essentially as a test particle . note that we can use equations ( [ eq : j1vec ] ) , ( [ eq : j2vec ] ) and ( [ eq : e2vec ] ) at the quadrupole level ( @xmath113 ) to write @xmath564 where all the vectors involved are of norm unity . then we find that @xmath565 is very small provided that @xmath566 . therefore , for the high eccentricity phase of lidov kozai cycles , the analysis of section [ sec : max_ecc ] for test particles still applies in the comparable - mass regime . as in the test - mass cases ( section [ sec : paramspace ] ) , the octupole effect expands the range of the initial mutual inclinations capable of reaching maximal eccentricities . as for the eccentricity curves , the inclination curves at the quadrupole level in figure [ fig : case1c ] ( black curves ) are symmetric respect to @xmath488 . in this particular example , srfs do not inflict significant modifications except for the close vicinity of @xmath488 , which sees the amplitude in the inclination oscillations ( the difference between @xmath567 and @xmath568 ) reduced ( green curves ) . at the octupole level ( red curves ) , the asymmetries that arise in the eccentricity curve find their counterpart in the inclination curves . within a narrow range of angles ( rightward of @xmath488 ) , the orbits are allowed to flip from retrograde to prograde . for initial inclinations bellow @xmath569 , although the octupole potential introduces significant changes in @xmath570 and @xmath571 , it is not strong enough to cause orbital flips . in accordance to what is observed in the eccentricity curves , the octupole contributions to the left of @xmath488 are not affected by srf , however , the flips observed for angles @xmath572 is nearly entirely suppressed by the inclusion of these additional effects ( blue curves ) . the example of figure [ fig : case1c ] shows moderate differences in maximum eccentricity and inclination range between the quadrupole and the octupole - level solutions . to explore the behaviour of these variables for larger octupole contributions we integrate systems with @xmath574 varying the magnitude of @xmath272 ( table [ tab : paramspace_general ] ) . some of these examples are shown in figure [ fig : case2c ] and [ fig : case2e ] . the most important difference between the top panels of figure [ fig : case2c ] and figure [ fig : case1c ] is the width of the maximal eccentricity region to the right of @xmath488 ( this was already observed in the examples of section [ sec : paramspace ] ) and the deepening of the high eccentricity region to the left of @xmath488 . as @xmath194 is increased , the asymmetries between the prograde and retrograde regions of the figure become more pronounced . prograde orbits at intermediate inclination see their maximum eccentricities increase , to a point that they become comparable to those seen for the retrograde orbits . it is at this point ( when @xmath575 ) that prograde orbits are allowed to flip orientations . when srfs are considered , the maximum eccentricities ( green and blue curves ) are altered in a similar fashion as the example of figure [ fig : case1c ] . the value of @xmath238 of equation ( [ eq : ftt ] ) is still in agreement with the global maximum of @xmath237 ( see table 4 ) . on the other hand , the growth of @xmath576 is suppressed ( no flip ) in prograde configurations , while @xmath577 appears to vary erratically when @xmath572 ( see figure [ fig : case2c ] ) . figures [ fig : case1e ] and [ fig : case2e ] show examples of increased @xmath272 for the same @xmath194 as in figures [ fig : case1c ] and [ fig : case2c ] . in these cases , @xmath563 is smaller than in case 2c ( figure [ fig : case2c ] ) , which implies that srfs are truncating @xmath237 not only in the vicinity of @xmath489 , but also in the lower inclination region [ @xmath578 , thus affecting the octupole - level effects significantly . despite the significant restrictions on @xmath237 imposed by srfs , the octupole effects can not be neglected for their values of @xmath194 , since they allow for these systems to reach eccentricities with @xmath579 for initial mutual inclinations as low as @xmath580 ( figure [ fig : case2e ] ) while the quadrupole - level calculation would require inclinations beyond @xmath581 to reach similar values . in this paper , we have computed the extent to which energy - conserving short - range effects alter the orbital evolution of planets and stars in hierarchical triple systems undergoing lidov - kozai oscillations . in particular , we have systematically examined how general relativistic precession , tides and oblateness can moderate the extreme values in eccentricity and inclination that can be achieved owing to the octupole terms in the interaction potential . by carrying of a sequence of numerical experiments , we have measured the extrema in eccentricity and inclination for a variety of hierarchical triples , systematically varying the relative strengths of the octupole terms and of the short - range effects in terms of their contributions to the potential energy . the results of our calculations can be summarized into four main findings . \(1 ) the importance of the octupole effects depends on the dimensionless parameter @xmath57 ( see equation [ eq : c ] ) , which measures the relative strength between the octupole and quadrupole potentials . the main contribution of the octupole terms to eccentricity and inclination excitation is limited to a range in initial inclinations or window of influence " , the width of which grows with @xmath57 . as @xmath57 decreases , the window of influence becomes increasingly confined to mutual inclinations close to @xmath122 . for example , at @xmath582 , the octupole terms are important only within a few degrees around @xmath583 ( see tables 1 and 2 ; also see fig . [ fig : case5 ] ) . \(2 ) we find that short range forces can indeed compete with the octupole - level terms in the potential , and that these additional effects impose a strict upper limit on the maximum achievable eccentricity . most importantly , we find that to a very good approximation , this maximum eccentricity can be derived analytically using the quadrupole approximation in the test - particle limit ( see section 3.3 and equation [ eq : ftt ] ) . this analytic limiting eccentricity holds even for a strong octupole contribution as well as in the general case of three comparable masses . \(3 ) our results indicate that , despite the upper limit in eccentricity ( which is independent on the octupole strength ) , the width of the window of influence of the octupole potential ( see point 1 above ) is largely unaffected by the srfs . \(4 ) we find that orbital flips are affected by the srfs . with increasing strength of the srfs ( characterized by the dimensionless parameters ; see equations [ eq : r11 ] , [ eq : r12 ] and [ eq : r13 ] ) , orbital flips are increasingly confined to the region close to @xmath584 ( see figs . 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form equations of motion ( equations [ eq : j1vec][eq : e2vec ] ) . omitting the laborious matrix manipulation , we get : @xmath585\\ & -\frac{15\varepsilon_{{\mathrm{oct}}}}{4}\cos\i\cos\omega_1\big[15(2 + 5\e1)\cos2\i\\ & + 7(30\e1\cos2\omega_1\sin^2\i-2 - 9\e1)\big]\sin\omega_2\frac{}{}\bigg\}~ , \end{split}\ ] ] and @xmath586\\ & \times\sin\omega_2-\cos\i\cos\omega_2\big[5(6+\e1)\cos2\i\\ & + 7(10\e1\cos2\omega_1\sin^2\i-2+\e1)\big]\sin\omega_1\bigg\}~. \end{split}\ ] ] for the inner and outer eccentricities . the time evolution of the inclinations are described by @xmath587\\ & + \frac{5\varepsilon_{{\mathrm{oct}}}}{8}\cos\omega_1\big[26 + 37\e1 - 35\e1\cos2\omega_1\\ & -15\cos2\i(7\e1\cos2\omega_1 - 2 - 5\e1)\big]\sin\i\sin\omega_2\bigg\}~ , \end{split}\ ] ] and @xmath588\\ & + \frac{5\varepsilon_{{\mathrm{oct}}}}{8}\big[26 + 107\e1 + 5(6+\e1)\cos2\i\\ & -35\e1(\cos2\i-5)\cos2\omega_1\big]\cos\omega_2\sin\i\sin\omega_1\bigg\}~. \end{split}\ ] ] we also write the longitudes of ascending nodes as a function of time @xmath589\\ & \times\sin2\i-\frac{5\varepsilon_{{\mathrm{oct}}}e_1}{8}\big[35\e1(1 + 3\cos2\i)\cos2\omega_1\\ & -46 - 17\e1 - 15(6+\e1)\cos2\i\big]\sin\i\sin\omega_1\sin\omega_2\bigg\}~. \end{split}\ ] ] finally , the argument of periapse for the inner and outer binaries evolve according to @xmath590+\frac{l_1\cos\i}{l_2\sqrt{1-e_2 ^ 2}}\big[2+\e1(3\\ & -5\cos2\omega_1)\big]\bigg\}+\frac{15\varepsilon_{{\mathrm{oct}}}}{64~t_k } \bigg\{\left(\frac{l_1}{l_2\sqrt{1-e_2 ^ 2}}+\frac{\cos\i}{\sqrt{1-\e1}}\right)\\ & \times e_1\bigg[\sin\omega_1\sin\omega_2\big[10(3\cos^2\i-1)(1-\e1)+a\big]\\ & -5b\cos\i\cos\theta\bigg]-\frac{\sqrt{1-\e1}}{e_1}\big[10\sin\omega_1\sin\omega_2\cos\i\\ & \times\sin^2\i(1 - 3\e1)+\cos\theta(3a-10\cos^2\i+2)\big]\bigg\}~ , \end{split}\ ] ] and @xmath591\\ & + \frac{l_1}{l_2\sqrt{1-e_2 ^ 2}}\bigg[\frac{}{}4 + 6\e1+(5\cos^2\i-3)\\ & \times\big[\frac{}{}2+\e1(3 - 5\cos2\omega_1)\big]\bigg]\bigg\ } -\frac{15\varepsilon_{{\mathrm{oct}}}e_1}{64~t_k~e_2}\\ & \times\bigg\{\sin\omega_1\sin\omega_2\bigg [ \frac{l_1(4e_2 ^ 2 + 1)}{e_2~l_2\sqrt{1-e_2 ^ 2}}10\cos\i\sin^2\i\\ & \times(1-\e1)-e_2\left(\frac{1}{\sqrt{1-\e1}}+\frac{l_1\cos\i}{l_2\sqrt{1-e_2 ^ 2}}\right)\\ & \times\big[a+10(3\cos^2\i-1)(1-\e1)\big]\bigg]+\cos\theta\\ & \times\bigg[5b\cos\i e_2\left(\frac{1}{\sqrt{1-\e1}}+\frac{l_1\cos\i}{l_2\sqrt{1-e_2 ^ 2}}\right)\\ & + \frac{l_1(4e_2 ^ 2 + 1)}{e_2~l_2\sqrt{1-e_2 ^ 2}}a\bigg]\bigg\}~ , \end{split}\ ] ] where we define @xmath592 and @xmath593

the lidov - kozai ( lk ) mechanism plays an important role in the secular evolution of many hierarchical triple systems . the standard lk mechanism consists of large - amplitude oscillations in eccentricity and inclination of a binary subject to the quadrupole potential from an outer perturber . recent work has shown that when the octupole terms are included in the potential , the inner binary can reach more extreme eccentricities as well as undergo orientation flips . it is known that pericenter precessions due to short - range effects , such as general relativity and tidal and rotational distortions , can limit the growth of eccentricity and even suppress standard ( quadrupolar ) lk oscillations , but their effect on the octupole - level lk mechanism has not been fully explored . in this paper , we systematically study how these short - range forces affect the extreme orbital behaviour found in octupole lk cycles . in general , the influence of the octupole potential is confined to a range of initial mutual inclinations @xmath0 centered around 90@xmath1 ( when the inner binary mass ratio is @xmath2 ) , with this range expanding with increasing octupole strength . we find that , while the short - range forces do not change the width and location of this `` window of influence '' , they impose a strict upper limit on the maximum achievable eccentricity . this limiting eccentricity can be calculated analytically , and its value holds even for strong octupole potential and for the general case of three comparable masses . short - range forces also affect orbital flips , progressively reducing the range of @xmath0 within which flips are possible as the intensity of these forces increases . [ firstpage ] binaries : close planetary system

<s>[INST]three - body systems are ubiquitous in astrophysics , appearing in a wide range of configurations and scales , from planet - satellite systems to black holes in dense stellar clusters . although the gravitational three - body problem is in general non - integrable , a hierarchical system ( i.e. , triple configuration consisting of an inner binary orbited by a distant companion ) can be simplified by retaining the lowest orders in the multipole expansion of the interaction potentials . in this case , the triple system is represented by two nested binary systems ( an inner binary " and an outer binary " ) , with the corresponding orbital elements evolving on secular timescales due to mutual interactions . @xcite and @xcite discovered that when the mutual inclination angle between the inner and outer binaries is sufficiently high , the time - averaged tidal gravitational force from the outer companion can induce large - amplitude oscillations in the eccentricity and inclination of the inner binary . in recent years , numerous works have shown that lidov kozai oscillations could play an important role in the formation and evolution of various astrophysical systems . examples include : ( i ) the formation of close stellar binaries , including those containing compact objects ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) ; ( ii ) the excitation of eccentricities of exoplanet systems ( e.g. , * ? ? ? ? * ; * ? ? ? * ) and the formation of hot jupiters through high - eccentricity migration ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? ? * ; * ? ? ? * ) ; ( iii ) the production of type ia supernovae from white - dwarf binary mergers ( e.g. , * ? ? ? * ; * ? ? ? * ) or direct collisions ( e.g. , * ? ? ? * ; * ? ? ? * ) ; ( iv ) the properties of irregular satellites ( particularly their inclination distribution relative to the ecliptic ) of giant planets in the solar system ( e.g. , * ? ? ? * ; * ? ? ? * ) ; ( v ) the formation and merger of ( stellar and supermassive ) black hole binaries at the centers globular clusters or galaxies ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? the simplest lidov kozai mechanism involves a test mass ( `` planet '' ) orbiting a primary body ( `` star '' ) perturbed by an external companion , with the interaction potential truncated to the quadrupole order . in this test - mass , quadrupole approximation , the projected angular momentum ( along the external binary axis ) of the planet is conserved . if the influence of other short - range forces ( srfs ) is negligible , the maximum eccentricity achieved by the inner binary ( for an initially very small eccentricity ) during the lidov kozai oscillation is given by @xmath3 where @xmath4 is the initial inclination angle of the two orbits . thus lidov kozai oscillation requires @xmath4 to lie between @xmath5 and @xmath6 . it has been recognized that the lidov kozai cycles can be suppressed by other short - range effects that induce periapse precession of the inner binary , including the precessions due to general relativity ( gr ) , rotational bulge and tidal distortion ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? the suppression arises because these additional precessions tend to destroy the near @xmath7 resonance between the longitude of the periapse @xmath8 and the longitude of the ascending node @xmath9 required for eccentricity excitation . thus , the maximum eccentricity can be reduced from the `` pure '' lidov kozai value ( equation [ eq : emax ] ) . it has also been recognized that high - order expansion of the interaction potential can lead to a much richer dynamical behaviour of hierarchical triples than the simplest lidov kozai oscillation based on the test - mass , quadrupole approximation . @xcite have derived the orbit - averaged hamiltonian to octupole order and used the resulting equation of motion to explore some aspects of the evolution of triples . unlike the pure quadrupole case , the projected angular momentum of the inner binary ( even in the test - mass limit ) is no longer constant when the octupole potential is included ( the octupole potential is nonzero when the outer binary is eccentric and the components of the inner binary have different masses ) . therefore , the secular dynamics of triples is generally not integrable in the octupole order and may lead to chaos ( e.g. , * ? ? ? * ; * ? ? ? recent works have examined the rich dynamical behaviour of such `` eccentric '' lidov kozai mechanism , either numerically ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) or semi - analytically ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , and explored their implications for the formation of hot jupiters and the resulting spin - orbit misalignments ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? the works cited above have revealed two important consequences of the `` eccentric '' lidov kozai mechanism : ( i ) the eccentricity of the inner binary can be driven to extreme value ( @xmath10 ) even for `` modest '' initial orbital inclinations ; ( ii ) the inner orbit can flip and come retrograde relative to the outer orbit . these two effects are related , as orbital flip is often associated with extreme eccentricity . since the precession of periapse due to short - range forces is strongly dependent on eccentricity , it is not clear to what extent the extreme eccentricity can be realized in realistic situations . while short - range effects were included in some population synthesis calculations for the formation of hot jupiters ( e.g. , * * ; * ? ? ? * ; * ? ? ? * ) , a systematic study of the short - range force effects on eccentric lidov kozai mechanism is currently lacking . in this paper , by running a sequence of numerical integrations , we study how srfs affect the evolution of the inner binary ( with and without the test - mass approximation ) , including the interaction potential up to the octupole order . combining with various analytical considerations , we characterize the parameters space systematically to understand how the maximum eccentricity is modified by the srfs . our paper is organized as follows . in section 2 , we derive the secular equations of motion up to the octupole order using a vectorial formalism . in section 3 , we provide a brief overview of short - range effects , estimating the maximum eccentricity allowed by the presence of various srfs . in section 4 , we describe our numerical integrations , carried out over a range of parameters for triple systems consisting of a star - planet binary and an outer stellar companion . in section 5 , we extend our analysis to triple systems in which all components have comparable masses . we summarize our main results in section 6 . in a hierarchical triple system , two bodies of masses @xmath11 and @xmath12 orbit each other ( with semimajor axis @xmath13 ) while a third body of mass @xmath14 orbits the center mass of the inner bodies ( @xmath11 and @xmath12 ) on a wider orbit ( with semimajor axis @xmath15 ) . the complete hamiltonian of the system can then be written as the sum of the individual hamiltonians of the inner and outer orbits plus an interaction potential @xmath16 ( e.g. , * ? ? ? * ) : @xmath17 where @xmath18 is the instantaneous separation vector between the inner masses @xmath11 and @xmath12 , @xmath19 is the instantaneous separation vector between @xmath14 and center of mass of @xmath11 and @xmath12 , and @xmath20 is the angle between @xmath21 and @xmath22 . in equation ( [ eq : ham ] ) , @xmath23 is the legendre polynomial of degree @xmath24 and @xmath25 is a coefficient that depends on @xmath11 , @xmath12 , @xmath14 and @xmath24 . if @xmath14 is sufficiently distant ( i.e. , @xmath26 ) , only the smallest values of @xmath24 contribute significantly to @xmath16 , and the coupling term is weak such that the inner and outer keplerian orbits change very slowly ( on timescales much longer than their orbital periods ) . in this regime , the secular approximation is valid , meaning that , the system can be adequately described by two slowly evolving keplerian orbits , while the short timescale behaviour of the three individual trajectories is irrelevant ( e.g. , * ? ? ? this perturbative method has been used extensively to study three - body systems up to quadrupole ( @xmath27)(e.g . ? * ; * ? ? ? * ) and octupole ( @xmath28 ) orders ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? most of these studies have used the classical perturbation methods of celestial mechanics , based on an orbital - element formulation of the hamiltonian system . in the following , we present the secular evolution equations to the octupole order using a geometric ( vectorial ) formalism ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , and confirm via angular projections that they are equivalent to hamilton s equations for the orbital elements . in vector form , the instantaneous position @xmath29 of a body in keplerian motion can be written as @xmath30 with @xmath31 , where @xmath32 , @xmath33 and @xmath34 are the semimajor axis , eccentricity and true anomaly , respectively . the orthogonal unit vectors @xmath35 and @xmath36 define the orbital plane , where @xmath35 points in the direction of pericenter ( i.e. , at @xmath37 ) . a third unit vector @xmath38 , pointed in the direction of the orbital angular momentum , completes an orthonormal triad , @xmath39 . alternatively , it is often useful to work in terms of the dimensionless angular momentum vector @xmath40 and the eccentricity vector @xmath41 : @xmath42 where @xmath40 and @xmath41 satisfy @xmath43 and @xmath44 . truncating the interaction potential ( equation [ eq : ham ] ) at the @xmath28 order , we write @xmath45 , where the quadrupole term is @xmath46,\ ] ] and the octupole term is @xmath47~~,\ ] ] and where the position vectors @xmath21 and @xmath22 track two different keplerian orbits ( equation [ eq : keplerian ] ) of orbital elements @xmath13 and @xmath48 ( inner ) and @xmath15 and @xmath49 ( outer ) , which are oriented in space by the triads @xmath50 and @xmath51 , respectively . in terms of the averaged potentials , the equations of motion for the orbital vectors @xmath58 , @xmath59 , @xmath60 and @xmath61 ( defined as in equation [ eq : defineje ] for the inner and outer orbits ) are @xmath62 here , @xmath63 and @xmath64 are @xmath65 where @xmath66 is the reduced mass of the outer orbit @xmath67 . substituting equations ( [ eq : apk ] ) and ( [ eq : apo ] ) into ( [ eq : gj1])([eq : ge2 ] ) , the octupole - level secular evolution equations can be obtained . for the inner orbit , we have @xmath68\\ & -\frac{75\varepsilon_{{\mathrm{oct}}}}{64~t_k}\bigg\ { \bigg[2\big[({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)\\ & + ( { \mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)\big]~{\mathbf{j}}_1 + 2\big[({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)\\ & -7({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)\big]~{\mathbf{e}}_1\bigg]\times{\hat{\mathbf{n}}}_2\\ & + \bigg[2({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\mathbf{j}}_1 + \big[\frac{8}{5}e_1 ^ 2-\frac{1}{5}\\ & -7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\mathbf{e}}_1\bigg ] \times{\hat{\mathbf{u}}}_2\bigg\ } , \end{split}\ ] ] @xmath69\\ & -\frac{75\varepsilon_{{\mathrm{oct}}}}{64~t_k}\bigg\ { \bigg[2({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\mathbf{e}}_1\\ & + \big[\frac{8}{5}e_1 ^ 2-\frac{1}{5}-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\mathbf{j}}_1\bigg]\times{\hat{\mathbf{u}}}_2\\ & + \bigg[2\big[({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)+({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)\big]~{\mathbf{e}}_1\\ & + 2\big[({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)\big]~{\mathbf{j}}_1 \bigg]\times{\hat{\mathbf{n}}}_2\\ & + \frac{16}{5}({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)~{\mathbf{j}}_1\times{\mathbf{e}}_1\bigg\}~~. \end{split}\ ] ] for the outer orbit , we have @xmath70\\ & -\frac{75\varepsilon_{{\mathrm{oct}}}}{64t_k}\frac{l_1}{l_2}\bigg\ { 2\big[({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)~{\hat{\mathbf{n}}}_2\\ & + ( { \mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{n}}}_2+({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{u}}}_2\big]\times{\mathbf{j}}_1\\ & + \bigg[2({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{n}}}_2- 14({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{n}}}_2\\ & + \big[\frac{8}{5}e_1 ^ 2-\frac{1}{5}-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\hat{\mathbf{u}}}_2\frac{}{}\bigg]\times{\mathbf{e}}_1 \bigg\},\\ \end{split}\ ] ] @xmath71{\hat{\mathbf{n}}}_2\times{\mathbf{e}}_2\bigg]\\ & -\frac{75}{64t_k}\frac{\varepsilon_{{\mathrm{oct}}}}{\sqrt{1-e_2 ^ 2}}\frac{l_1}{l_2 } \bigg\{2\big[({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\mathbf{e}}_2)~{\hat{\mathbf{u}}}_2\\ & + ( { \mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{e}}_1\cdot{\mathbf{e}}_2)~{\hat{\mathbf{u}}}_2+\frac{1-e_2 ^ 2}{e_2}({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2 ) ( { \mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{n}}}_2\big]\times{\mathbf{j}}_1\\ & + \bigg[2({\mathbf{j}}_1\cdot{\mathbf{e}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{u}}}_2 -14({\mathbf{e}}_1\cdot{\mathbf{e}}_2)({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)~{\hat{\mathbf{u}}}_2\\ & + \frac{1-e_2 ^ 2}{e_2}\big[\frac{8}{5}e_1 ^ 2-\frac{1}{5}-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\hat{\mathbf{n}}}_2\bigg ] \times{\mathbf{e}}_1\\ & -\bigg[2\left(\frac{1}{5}-\frac{8}{5}e_1 ^ 2\right)({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)~{\mathbf{e}}_2\\ & + 14({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{u}}}_2)({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)~{\mathbf{e}}_2 + 7({\mathbf{e}}_1\cdot{\hat{\mathbf{u}}}_2)\big[\frac{8}{5}e_1 ^ 2\\ & -\frac{1}{5}-7({\mathbf{e}}_1\cdot{\hat{\mathbf{n}}}_2)^2+({\mathbf{j}}_1\cdot{\hat{\mathbf{n}}}_2)^2\big]~{\mathbf{e}}_2 \bigg]\times{\hat{\mathbf{n}}}_2\bigg\}~~. \end{split}\ ] ] in the above , we have defined the ( quadrupole ) kozai timescale as @xmath72 where @xmath73 is the mean motion of the inner binary . equations ( [ eq : j1vec])([eq : e2vec ] ) describe the long - term evolution of the inner and outer binaries for all mass ratios . our equations are equivalent to those presented in @xcite , although they are in a somewhat different form . often times , the triple system contains a body of much smaller mass than the other two , such as in the case of a planet around one member of a binary . in this case , the planet can be considered to be a particle of effective zero mass to a very good approximation . in this test - particle limit " ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , the outer orbit contains the totality of the angular momentum in the system , and consequently remains fixed in time . to derive the test - particle limit from equations ( [ eq : j1vec])([eq : e2vec ] ) , we take the limit @xmath74 , for which we confirm that @xmath75 . in this case , the triad @xmath76 is fixed in space , thus , for the sake of clarity , we relabel these vectors with lab - frame coordinates @xmath76 in equations ( [ eq : j1vec])([eq : e1vec ] ) and in equations ( [ eq : apk ] ) and ( [ eq : apo ] ) . with these replacements , we recover the expressions of @xcite for the potentials and for @xmath77 and @xmath78 for a test particle . the secular equations for the orbital elements of the inner and outer orbits have been the focus of previous work on hierarchical triple systems @xcite . with the introduction of delaunay variables , conjugate pairs of coordinates and momenta can be defined , the equations of motion of the orbital elements can be directly derived using hamilton s equations ( e.g. * ? ? ? * ) . instead of using hamilton equations , one can convert the vector equations ( equations [ eq : j1vec][eq : e2vec ] ) into the orbital element form by expressing the cartesian components of the vectors @xmath79 , @xmath80 ( with @xmath81 ) in terms of the orbital eccentricity @xmath82 , inclination @xmath83 , argument of periapse @xmath84 and longitude of ascending nodes @xmath85 ( e.g. * ? ? ? * ) : @xmath86 here the angles are defined respect to a fixed coordinate frame in which @xmath87-axis is aligned with the ( conserved ) total angular momentum , while the @xmath88-@xmath89 plane coincides with the so - called invariable plane . thus the relative inclination between the two orbits is @xmath90 . because of angular momentum conservation , the condition @xmath91 is satisfied . by substituting equations ( [ eq : proj ] ) and ( [ eq : proe ] ) into equations ( [ eq : j1vec])([eq : e2vec ] ) , we can solve for @xmath92 , @xmath93 , @xmath94 and @xmath95 ( for @xmath81 ) . since @xmath96 , the system is determined by seven independent differential equations . these equations are listed in appendix [ sec : full ] ( see equations [ eq : fulle1][eq : fullcos ] ) . although different in form , we have checked that these equations are equivalent to those presented by @xcite . for the test mass case ( @xmath97 ) , we take the limit @xmath98 in equations ( [ eq : fulle1])([eq : fullcos ] ) . also , note that in this limit , @xmath99 , @xmath100 , @xmath101 . we choose @xmath102 , @xmath103 , @xmath104 and @xmath105 , where @xmath106 . accordingly , the secular evolution equations become @xmath107 + 2\cos i_1\\ & \times\cos\omega_1\sin\omega_1\big[15(2 + 5\e1)\cos2i_1\\ & + 7(30\e1\cos2\omega_1\sin^2\!i_1 - 2 - 9\e1)\big]\bigg\ } , \end{split}\ ] ] @xmath108\bigg\ } , \end{split}\ ] ] @xmath109\sin\omega_1\sin\omega_1\bigg\ } , \end{split}\ ] ] @xmath110 - 5b\cos i_1\cos\theta\bigg]\\ & -\frac{\sqrt{1-\e1}}{e_1}\big[10\sin\omega_1\sin\omega_1\cos i_1\\ & \times\sin^2\!i_1(1 - 3\e1)+\cos\theta(3a-10\cos^2\!i_1 + 2)\big]\bigg\ } , \end{split}\ ] ] where we have introduced the dimensionless time @xmath111 and @xmath112 when the octupole terms are ignored ( i.e. , @xmath113 ) , equations ( [ eq : testpe])([eq : testpo ] ) reduce to the orbital element equations of motion found in ( * ? ? ? 5 ) for lidov - kozai oscillations in @xcite appears with the term @xmath114 in the numerator instead of the denominator . ] . and eccentricity @xmath48 from numerical integration of equations ( [ eq : testpe])([eq : testpo ] ) for a prograde ( red ) and a retrograde ( blue ) inner binary . the system parameters are @xmath115 , @xmath97 , @xmath116 , @xmath117 , @xmath118 and @xmath119 . we set @xmath120 initially . inclinations are initialized at @xmath121 from @xmath122 . red lines : @xmath123 , @xmath124 , @xmath125 ; blue lines : @xmath126 , @xmath127 , @xmath128 . in the lower panel , the blue and red curves exactly overlap . , title="fig:",width=313 ] and eccentricity @xmath48 from numerical integration of equations ( [ eq : testpe])([eq : testpo ] ) for a prograde ( red ) and a retrograde ( blue ) inner binary . the system parameters are @xmath115 , @xmath97 , @xmath116 , @xmath117 , @xmath118 and @xmath119 . we set @xmath120 initially . inclinations are initialized at @xmath121 from @xmath122 . red lines : @xmath123 , @xmath124 , @xmath125 ; blue lines : @xmath126 , @xmath127 , @xmath128 . in the lower panel , the blue and red curves exactly overlap . , title="fig:",width=313 ] , evolution of inclination @xmath129 and eccentricity @xmath48 from numerical integration of equations ( [ eq : fulle1])([eq : fullcos ] ) for prograde ( red ) and retrograde ( blue ) inner binaries , this time for a general triple with comparable masses . the system parameters are @xmath115 , @xmath130 , @xmath116 , @xmath131 and @xmath118 . eccentricities are initialized as @xmath120 and @xmath132 . red lines : @xmath133 , @xmath134 , @xmath135 , @xmath136 , @xmath137 ; blue lines : @xmath138 , @xmath139 , @xmath140 , @xmath141 , @xmath142 . , title="fig:",width=313 ] , evolution of inclination @xmath129 and eccentricity @xmath48 from numerical integration of equations ( [ eq : fulle1])([eq : fullcos ] ) for prograde ( red ) and retrograde ( blue ) inner binaries , this time for a general triple with comparable masses . the system parameters are @xmath115 , @xmath130 , @xmath116 , @xmath131 and @xmath118 . eccentricities are initialized as @xmath120 and @xmath132 . red lines : @xmath133 , @xmath134 , @xmath135 , @xmath136 , @xmath137 ; blue lines : @xmath138 , @xmath139 , @xmath140 , @xmath141 , @xmath142 . , title="fig:",width=313 ] in the test - particle limit ( @xmath97 ) , the vector equations ( [ eq : j1vec])([eq : e1vec ] ) are symmetric under reflections of the inner binary . if we perform the replacement @xmath143 ( leaving @xmath59 unchanged ) , we find that @xmath144 and @xmath145 , which may be interpreted as reversing the direction of time . in terms of orbital elements , this reflection operation is equivalent to changing @xmath146 , @xmath147 and @xmath148 . performing this replacement in equations ( [ eq : testpe])([eq : testpo ] ) , we obtain @xmath149 , @xmath150 , @xmath151 and @xmath152 , as expected . figure [ fig : stp ] shows the integration of equations ( [ eq : testpe])([eq : testpo ] ) for two configurations differing solely on the orientation of the @xmath58 vector ( this reflection is carried out by changing the initial conditions @xmath153 , @xmath154 and @xmath155 ) . the evolution of eccentricity is indistinguishable between the prograde ( red curves ) and retrograde ( blue curves ) cases , while the inclination angle @xmath129 shows a reflection symmetry around @xmath122 , evolving in an identical manner in both cases except for a phase offset of half of what can be interpreted as an octupole period " @xcite . for the comparable - mass case ( @xmath156 ) , the inner and outer binaries evolve together , exchanging angular momentum . under reflection operation ( @xmath143 ) , we find that @xmath144 , @xmath145 , @xmath157 and @xmath158 , i.e. , the symmetry of the equations is broken . figure [ fig : scm ] shows the numerical integration in the case of general masses , for two configurations with similar reflection operation as in figure [ fig : stp ] . in this case , it is apparent that there is no reflection symmetry between the prograde ( red curves ) and retrograde ( blue curves ) initial conditions . even the octupole periods " are different . the high eccentricity phase of a lidov kozai cycle can be severely modified if the inner binary separation at pericenter is sufficiently small for additional forces to overcome the tidal torque exerted by the outer binary . if the energy associated to these extra forces @xmath159 surpasses the interaction potential @xmath16 of equation ( [ eq : ham ] ) , the lidov kozai mechanism is said to be arrested " ( e.g. * ? ? ? * ) . here we study the effects of short - range forces on the eccentricity evolution of triple system consisting of a jupiter - mass planet orbiting the primary star of a binary . the short range effects we consider include ( 1 ) precession of periapse due to gr , ( 2 ) tidal bulge of the planet induced by the star , and ( 3 ) planet oblateness due to rotation . in the absence of energy dissipation ( e.g. , tidal friction or gravitational wave radiation ) , the energy of the system @xmath160 is conserved , and so is its orbit - averaged version . since the semimajor axes of the inner and outer orbits are constant , we only need to consider the conserved potential @xmath161 where , as before , @xmath162 . the post - newtonian potential associated with periastron advance is ( e.g. , * ? ? ? * ) @xmath163 where we have defined the dimensionless parameter @xmath164 the potential due to the non - dissipative tidal bulge on @xmath12 is @xmath165 where @xmath166 and @xmath167 , @xmath168 are the tidal love number and the radius of @xmath12 , respectively . the potential energy associated with the rotation - induced oblateness of @xmath12 is @xmath169 here , @xmath170 where @xmath171 is the apsidal motion constant and @xmath172 is the spin rate of @xmath12 , and we have assumed that the spin vector of @xmath12 is aligned with the angular momentum vector @xmath58 of the inner orbit . we can rewrite equation ( [ eq : prot0 ] ) as @xmath173 where @xmath174 the three dimensionless parameters @xmath175 , @xmath176 and @xmath177 quantify the relative importance of the short - range potential terms respect to the quadrupole potential @xmath178 . since the three short - range potentials ( equations [ eq : pgr ] , [ eq : ptide ] and [ eq : prot ] ) depend on the orbital vectors solely through @xmath179 , only the evolution equations for @xmath59 is modified ( see equations [ eq : gj1 ] and [ eq : ge1 ] ) . these extra forces induce an additional precession of @xmath59 around @xmath58 : @xmath180 where ( e.g. , * ? ? ? @xmath181 thus , the gr - induced precession rate is : @xmath182 similarly , for the static tide , we have @xmath183 and for the rotation - induced planet oblateness @xmath184 to obtain an estimate of the relative importance of @xmath185 and @xmath186 , we may consider a pseudo - synchronized planet spin , that is , the planet rotation rate @xmath172 is of order the orbital frequency of periapse @xmath187 . in the weak friction theory of equilibrium tides , the pseudo - synchronized rotation rate is given by ( e.g. , * ? ? ? * ; * ? ? ? * ) @xmath188 thus , in equation ( [ eq : omegarot ] ) , we have @xmath189 with @xmath190 comparing with @xmath185 , we have @xmath191 . since @xmath192 , we find @xmath193 for synchronized rotation . thus , in the vast majority of our examples , the effect of tides will dominate over the effect of the rotational bulge . before systematically examining the parameter space in @xmath194 , @xmath195 , @xmath196 and @xmath197 , we consider a few examples to illustrate how srfs affect lidov kozai oscillations . , @xmath198 , @xmath199 @xmath200 and @xmath118 . initial conditions are @xmath201 , @xmath202 , @xmath203 , @xmath204 , @xmath205 , @xmath206 , @xmath207 , @xmath137 and @xmath208 . total integration time is 50 myr@xmath209 . the red lines are from the integration of the pure lidov kozai effect to octupole order , while the blue lines are the results of integration including srfs . orbital flips seem to be entirely suppressed . however , when extending the integration time to @xmath210 myrs @xmath211 , the inner orbit eventually flips to retrograde in the interval of 90130 myr before going back to its original orientation . , title="fig:",width=309 ] , @xmath198 , @xmath199 @xmath200 and @xmath118 . initial conditions are @xmath201 , @xmath202 , @xmath203 , @xmath204 , @xmath205 , @xmath206 , @xmath207 , @xmath137 and @xmath208 . total integration time is 50 myr@xmath209 . the red lines are from the integration of the pure lidov kozai effect to octupole order , while the blue lines are the results of integration including srfs . orbital flips seem to be entirely suppressed . however , when extending the integration time to @xmath210 myrs @xmath211 , the inner orbit eventually flips to retrograde in the interval of 90130 myr before going back to its original orientation . , title="fig:",width=309 ] in figure [ fig : case91 ] , we show the evolution of a triple system with @xmath212 and initial mutual inclination @xmath213 obtained by numerical integration of the equations of motion in orbital elements form ( see appendix [ sec : full ] ) . when srfs are ignored ( red curves ) , the inner orbit evolves into a highly eccentric state over a timescale of order @xmath214 , reaching values as extreme as @xmath215 ( red curves , bottom panel ) . in this example , eccentricity maxima of @xmath216 are always accompanied by orbital flips ( red curves , top panel ) , i.e. , the @xmath87-component of @xmath40 reverses its sign . orbital flips are always tied to eccentricity maxima and correspond to @xmath58 shrinking going through the origin ( @xmath217 ) as @xmath216 ( e.g. , * ? ? ? * ; * ? ? ? * ) . in some cases , it is possible to even derive a closed - form solution of this behaviour over long timescales provided the slowly varying quantity @xmath218 remains positive at all times ( e.g. , * ? ? ? * ; * ? ? ? assuming that the maximum eccentricity of a lidov kozai cycle is reached when @xmath219 crosses zero , @xcite find that the maximum @xmath48 scales with @xmath194 roughly as @xmath220 . if this theoretical maximum can not be reached owing to additional effects such as srfs , then we expect that @xmath221 will be unable to come arbitrarily close to zero , and therefore orbital flips will not be allowed . indeed , when srfs are included ( blue curves ) , the maximum eccentricity is capped down to values such that @xmath222 ( blue curves , bottom panel ) . although still large , this upper limit to the eccentricity is sufficient to introduce a lower limit to @xmath223 ( see section [ sec : max_ecc ] below ) such that @xmath221 can not reverse signs under the criterion introduced by @xcite . as a result , we see no orbital flips in this example ( red curves , top panel ) . surprisingly , however , orbital flips are not prohibited in every case . in figure [ fig : case92 ] , we present an example of a system which exhibits an orbital flip even though the maximum allowed eccentricity has been reduced by srfs . as in the previous example , we integrate a triple system with @xmath212 with and without srfs ( blue and red curves respectively ) . this time , the initial conditions are modified slightly , changing the initial mutual inclination angle from @xmath213 to @xmath224 . over the first half of the integration , the evolution of eccentricity ( bottom panel ) and inclination ( top panel ) in figure [ fig : case92 ] closely resemble of those of figure [ fig : case91 ] . however , after 25 myrs , the two systems start following entirely differently trajectories , despite the very small difference in initial conditions . in addition , the figure shows that this system finds a way to cause an orbital flip ( i.e. @xmath221 crosses zero ) , despite that the eccentricity is not allowed to exceed @xmath225 just as in figure [ fig : case91 ] . from figure [ fig : case92 ] , we conclude that ( 1 ) orbital flips can still take place in presence of sfrs that are strong enough to limit the eccentricity maximum , and ( 2 ) that the inclination of the inner binary may exhibit chaotic behaviour ( e.g. * ? ? ? * ; * ? ? ? * ) , and that conservative srfs modify do not necessarily suppress this erratic evolution . to check whether the example of figure [ fig : case91 ] has entirely suppressed orbital flips or if it is just a matter of time before it finds a channel to cross @xmath226 , we integrate the system for @xmath227 myr @xmath211 . indeed , we confirm that after a very long time @xmath228 , this system also undergoes an orbital flip that lasts for @xmath229 before returning to its original orientation . figure [ fig : case93 ] shows the evolution of @xmath221 and the angle @xmath230 ( see * ? ? ? * ; * ? ? ? * ) for the example of figure [ fig : case92 ] . the red curves show the evolution of the system in the absence of srfs , where a regular oscillation of @xmath221 at earlier times transitions to a different regime after @xmath231 myrs . when srfs are included ( blue curves ) , the evolution of @xmath221 stays bounded between its initial value and zero , without being allowed to change sign , until suddenly a flip takes place . the transition between these two regimes can be seen in the evolution of @xmath232 ( bottom panel ) . at early times , @xmath232 remains bounded between @xmath233 and @xmath234 . however , by the time @xmath221 changes sign , @xmath232 is circulating , sweeping all possible angles . an analogous plot of @xmath232 for the example in figure [ fig : case91 ] shows that @xmath232 never circulates during the entire extent of the integration . , but slightly changing the initial inclination : @xmath224 with @xmath235 and @xmath236 . , title="fig:",width=309 ] , but slightly changing the initial inclination : @xmath224 with @xmath235 and @xmath236 . , title="fig:",width=309 ] and @xmath230 for the case corresponding to figure [ fig : case92 ] . the red lines are from the integration of pure lidov kozai effect in octupole order , while the blue lines are the results of integration including srfs . when srfs limit the maximum eccentricity , flips are suppressed if @xmath232 is bounded , but they become possible once again if @xmath232 is circulating . , title="fig : " ] and @xmath230 for the case corresponding to figure [ fig : case92 ] . the red lines are from the integration of pure lidov kozai effect in octupole order , while the blue lines are the results of integration including srfs . when srfs limit the maximum eccentricity , flips are suppressed if @xmath232 is bounded , but they become possible once again if @xmath232 is circulating . , title="fig : " ] we see in section 3.2 that srfs limit the maximum eccentricity that can be achieved during the lidov kozai cycles ( e.g. , * ? ? ? * ; * ? ? ? in the test - mass approximation ( @xmath97 ) and neglecting the octupole effect , this maximum eccentricity , @xmath237 , can be derived analytically . we shall see in section 4 that the limiting eccentricity , @xmath238 , achieved for the initial inclination @xmath239 , is also applicable when the octupole effect is included and binaries of comparable masses ( @xmath156 ) are considered . in the test - mass approximation ( @xmath97 , which implies @xmath75 ) and at the quadrupole level ( @xmath113 ) , equation ( [ eq : j1vec ] ) implies @xmath240 in addition , the total potential is conserved @xmath241 in terms of the orbital elements of the inner binary , the quadrupole potential ( equation [ eq : apk ] ) can be written as @xmath242,\ ] ] if the system is initialized with @xmath243 , the maximum eccentricity @xmath237 is achieved at @xmath244 or @xmath245 during the lidov kozai cycles . using equations ( [ eq : jconst ] ) ( [ eq : apk2 ] ) , we find that @xmath237 is given by @xmath246 where @xmath247 . in the absence of the srfs ( @xmath248 ) , the above equation yields the well - known maximum eccentricity @xmath249 for pure " lidov kozai oscillation ( e.g. , * ? ? ? * ; * ? ? ? * ) @xmath250 if we neglect the tidal or rotation terms ( @xmath251 ) and assume @xmath252 , equation ( [ eq : ft ] ) results to ( e.g. , * ? ? ? * ) @xmath253\ ] ] figure [ fig : emaxi ] depicts several example of @xmath237 for different values of @xmath254 , @xmath255 , @xmath256 . the physical meaning of equation ( [ eq : ft ] ) can be made clear if we use the expression of @xmath257 equations [ eq : omegagr][eq : omegarot ] ) to re - express it as ( assuming @xmath258 ) @xmath259_{e_1=e_{1,{\mathrm{max}}}}\\ & \approx\frac{9}{8}e_{1,{\mathrm{max}}}^2\frac{j_{1,{\mathrm{min}}}^2 - 5\cos^2\!i_0/3}{j_{1,{\mathrm{min}}}^2}~ , \end{split}\ ] ] where @xmath260 and where we have defined for convenience a characteristic " lidov kozai rate @xmath261 which should not be confused with the precession rate derived from applying the operation in equation [ eq : extraomega ] to @xmath262 . for @xmath239 , the eccentricity attains the limiting value , @xmath263 , given by @xmath264_{e_1=e_{\mathrm{lim}}}=\frac{9}{8}e_{\mathrm{lim}}^2~.\ ] ] for @xmath265 , we have @xmath266 , equation ( [ eq : ftt ] ) becomes @xmath267_{e_1=e_{\mathrm{lim}}}\simeq\frac{9}{8}~.\ ] ] thus , the limiting eccentricity is achieved when the periapse precession rate due to srfs becomes comparable to the lidov kozai rate @xmath268 . in the test - mass limit ( @xmath97 ) , the evolution of the inner binary depends on the dimensionless ratios @xmath194 , @xmath254 , @xmath255 , @xmath256 as well as the initial inclination angle @xmath4 ( we assume @xmath269 ) . in this section , we consider the evolution of jupiter - mass planet ( @xmath270 ) moving around a solar - mass star ( @xmath271 ) . we carry out calculations for different values of @xmath13 , @xmath15 , @xmath14 and @xmath49 . the different orbital configurations and their corresponding values of @xmath194 and @xmath272 are listed in table [ tab : paramspace ] . these conditions of parameters are subject to the stability criterion of @xcite @xmath273 @llrrrrlrlr@ parameter & @xmath57 & @xmath175 & @xmath176 & @xmath274 & @xmath275 & @xmath49 & @xmath276 + case 1 & 0.001 & @xmath277 & @xmath278 & 1 & 200 & 0.2 & 0.5 + + case 2 & 0.002 & @xmath279 & @xmath280 & 1 & 100 & 0.2 & 1 + + case 3a & 0.006 & @xmath281 & @xmath282 & 6 & 200 & 0.2 & 1 + case 3b & 0.006 & @xmath283 & @xmath284 & 1 & 33.33 & 0.2 & 1 + case 3c & 0.006 & @xmath285 & @xmath286 & 1 & 33.33 & 0.2 & 0.1 + + case 4 & 0.011 & @xmath287 & @xmath288 & 1 & 200 & 0.8 & 1 + + case 5 & 0.013 & @xmath289 & @xmath290 & 6 & 100 & 0.2 & 1 + + case 6 & 0.022 & @xmath291 & @xmath292 & 1 & 100 & 0.8 & 1 + + case 7 & 0.033 & @xmath293 & @xmath294 & 5 & 100 & 0.5 & 1 + + case 8 & 0.044 & @xmath295 & @xmath296 & 2 & 100 & 0.8 & 1 + + case 9 & 0.056 & @xmath297 & @xmath298 & 6 & 100 & 0.6 & 0.04 + + case 10a & 0.067 & @xmath299 & @xmath300 & 6 & 200 & 0.8 & 1 + case 10b & 0.067 & @xmath301 & @xmath302 & 1 & 33.33 & 0.8 & 1 + case 10c & 0.067 & @xmath303 & @xmath304 & 1 & 33.33 & 0.8 & 0.1 + + case 11 & 0.133 & @xmath305 & @xmath306 & 6 & 100 & 0.8 & 1 + @llrrrrlrlr@ parameter & @xmath307 & @xmath308 & @xmath309 & @xmath310 & @xmath311 & @xmath312(deg ) & @xmath313(deg ) & @xmath314(deg ) + case 1 & @xmath315 & @xmath316 & @xmath317 & @xmath318 & @xmath319 & 87.7 & @xmath320 & 88.5 + + case 2 & @xmath321 & @xmath322 & @xmath323 & 6.23 & @xmath324 & 86.2 & @xmath320 & 85.4 + + case 3a & @xmath325 & @xmath326 & @xmath327 & 7.29 & @xmath328 & 82.2 & @xmath320 & 87.1 + case 3b & @xmath329 & @xmath330 & @xmath331 & 7.21 & @xmath332 & 82.2 & @xmath320 & 86.8 + case 3c & @xmath333 & @xmath334 & @xmath335 & 6.81 & @xmath336 & 82.2 & @xmath320 & 85.4 + + case 4 & @xmath337 & @xmath338 & @xmath339 & 5.56 & @xmath340 & 80.2 & @xmath320 & 83.9 + + case 5 & @xmath341 & @xmath342 & @xmath343 & 7.32 & @xmath344 & 79.0 & 89.4 & 78.8 + + case 6 & @xmath345 & @xmath346 & @xmath347 & 6.96 & @xmath348 & 69.9 & 89.1 & 71.9 + + case 7 & @xmath349 & @xmath350 & @xmath351 & 7.32 & @xmath352 & 58.7 & 60.4 & 59.3 + + case 8 & @xmath353 & @xmath354 & @xmath355 & 7.27 & @xmath356 & 51.3 & 73.3 & 51.9 + + case 9 & @xmath357 & @xmath358 & @xmath359 & 7.28 & @xmath360 & 47.8 & 56.0 & 49.1 + + case 10a & @xmath361 & @xmath362 & @xmath363 & 7.31 & @xmath352 & 47.3 & 53.9 & 47.8 + case 10b & @xmath364 & @xmath365 & @xmath366 & 7.27 & @xmath367 & 47.3 & 73.1 & 51.9 + case 10c & @xmath368 & @xmath369 & @xmath370 & 7.14 & @xmath371 & 47.3 & 81.1 & 52.1 + + case 11 & @xmath372 & @xmath373 & @xmath374 & 7.32 & @xmath344 & 47.3 & 48.4 & 49.6 + for each combination of @xmath194 and @xmath272 ( table [ tab : paramspace ] ) , we integrate a total of 300 triple systems over a total integration time ranging from @xmath209 to @xmath228 . we setup each system by varying the initial inclination of the inner binary @xmath4 ( @xmath375 when @xmath97 ) between @xmath376 and @xmath122 . we first consider a specific example with @xmath212 ( case 9 in table 1 ) . for each initial inclination angle @xmath4 ( in the range between @xmath376 and @xmath122 ) , we integrate equations ( [ eq : fulle1])-([eq : fullomega2 ] ) for @xmath377 yrs , corresponding to 360.5 @xmath378 for this specific set of parameters . for each of these subsystems , we record the maximum eccentricity @xmath237 and the maximum and minimum of @xmath379 attained during the evolution . the results are shown in figure [ fig : case94 ] . the upper panel in figure [ fig : case94 ] shows the maximum eccentricity of inner orbit as a function of @xmath4 . at the quadrupole level , the pure lidov kozai cycles can give extremely large eccentricity ( @xmath380 ) only for @xmath381 . when the short - range effects are included , the value of @xmath237 at that point is limited to @xmath382 , in accordance with the analytic expression ( equation [ eq : ft ] ) . for the parameters considered in this case ( case 9 ) , the tidal effect plays the dominate role in limiting the maximum eccentricity ( table 2 , when we see that @xmath383 at @xmath384 ; see also equation [ eq : l ] ) . when the octupole term is included , there is a sharp jump of @xmath385 at @xmath386 . without the srfs , @xmath387 becomes very small and varies erratically as @xmath4 increases beyond @xmath388 . this erratic variation is the result of the overlap between the quadrupole and octupole contributions . when the srfs are included , we find that instead of the rapid variation of @xmath387 , the maximum eccentricity becomes approximately a constant , equal to @xmath389 . we define @xmath390 as the the value of @xmath4 when @xmath391 first reaches @xmath389 . for the case considered in fig . 7 , @xmath390 is close to @xmath388 . it is important to note that although @xmath389 is derived in the quadrupole approximation ( see section 3.3 ) , it serves as the maximum eccentricity attainable even when the octupole term is included . the lower panel in figure [ fig : case94 ] shows the maximum and minimum of the orbital inclination attained during the evolution of the inner binary as functions of @xmath4 . at the pure quadrupole level ( without srfs ) , the inclination does not change until @xmath4 reaches @xmath392 , beyond which @xmath393 and @xmath394 . including srfs , @xmath395 is modified for @xmath4 close to @xmath122 as the maximum eccenticity is limited by the srfs . note that @xmath396 . at the octupole level , the angular momentum of the inner binary experiences a flip ( @xmath397 ) at a critical angle @xmath398 . this angle is always greater than @xmath399 ( the onset of quadrupole lidov kozai oscillations ) . when the srfs are included , this critical angle is pushed to a higher value , @xmath400 . at inclinations slightly higher than the angle critical @xmath390 ( demarcated by inverted triangle in figure [ fig : case94 ] , the orbital flips seen in absence of srfs ( red curves ) have now been inhibited . note , however , that at even higher inclinations ( @xmath401 ) , orbital flips are once again allowed . this can occur even though the maximum eccentricity @xmath237 is strongly affected by the srfs ( see figure [ fig : case93 ] and section [ sec : examples ] ) . note also that the individual examples shown in figures [ fig : case92 ] and [ fig : case93 ] ( with @xmath4 of @xmath402 and @xmath403 respectively ) lie within the erratically varying region that starts at @xmath404 . it is possible that the inclination angle in the example with @xmath405 ( figure [ fig : case92 ] ) will eventually flip as well . from this figure we can conclude that srfs have broken the symmetry that existed between the upper and lower panels of figure [ fig : case94 ] ( red curves ) , which showed that both the extreme maximum eccentricity and the orbital flip where achieved above the same critical inclination . the erratic variation of @xmath406 for @xmath407 results from the combined effects of quadrupole , octupole and srfs , and may be associated with the chaotic behaviour of lidov kozai oscillations studied by @xcite . these authors find that configurations with higher inclinations and larger @xmath194 are more chaotic ( with lyapunov times of @xmath408 for the chaotic regions of parameter space ) . it is possible that the complexity of a system with conservative srfs ( three additional frequencies are present and no energy dissipation ) only shift the inclination threshold for chaotic behaviour to larger angles , but have not fundamentally suppressed the chaotic nature of lidov kozai oscillations with octupole - level terms . it is also possible that the characteristic timescale for a flip has been entirely altered by the srfs , and that all systems with @xmath407 will eventually flip ( on timescales much longer than @xmath409 ) . to explore how the extrema in @xmath48 and @xmath129 change with @xmath4 for different values of @xmath194 , we carry out another set of numerical integrations , this time with @xmath411 ( listed as ` case 5 ' in table 1 below ) . the results of this set of integrations are shown in figure [ fig : case5 ] . without srfs ( red curves ) , the @xmath410 and @xmath412 curves exhibit the same overall morphology observed in the case with @xmath212 ( figure [ fig : case94 ] ) . in this case , however , significant deviations from the quadrupole - only calculations are confined to a narrower range in @xmath4 . this is to be expected , since this octupole active " region will gradually shrink as @xmath194 is made smaller , until the quadrupole level solutions ( black and green curves ) are recovered . in the limit @xmath413 , the only angle which allows for @xmath414 is @xmath239 ( equation [ eq : me ] ) . similarly , when @xmath413 only @xmath239 permits @xmath226 . quantitatively , the width along the @xmath4-axis of the octupole - active region or window of influence " for a given value of @xmath194 can be understood using the flip condition " identified by @xcite . from approximate conservation laws , these authors find that , given @xmath415 and @xmath416 , the long term oscillation of @xmath221 owing to octupole terms can only result in a change of sign if and only if @xmath4 is greater than a critical value that depends on @xmath194 . equivalently , given @xmath4 , there is a critical value @xmath417 above which orbits will flip . this flip condition can be approximately expressed as @xmath418 where @xmath419 is a non - monotonic function that is equal to zero at @xmath420 and @xmath421 and peaks at 0.0475 for @xmath422 ( see * ? ? ? * ; * ? ? ? the critical value @xmath417 is a monotonically decreasing function of @xmath4 , meaning that the closer @xmath4 is to @xmath122 , the smaller @xmath423 becomes ( i.e. , the easier it is to flip ) . we illustrate this by overlaying @xmath423 as a function of @xmath4 in the bottom panel of figure [ fig : case5 ] . when @xmath423 becomes smaller than @xmath424 ( at @xmath425 ) , test particle trajectories are allowed to flip orientations . above this critical angle , each orbital flip is accompanied by an extreme increase in eccentricity . following @xcite , we estimate that this limiting eccentricity within the octupole active region is such that @xmath426 , i.e. , @xmath427 , which is in good agreement with the average value of @xmath428 in the region where @xmath429 . when srfs are included , ( blue and green curves in figure [ fig : case5 ] ) , the modifications to the evolution of eccentricity are consistent with what was observed in the @xmath212 example . however , the amplitude of the inclination oscillations is more dramatically affected . on one hand , we find a consistently truncated maximum eccentricity down to a value of @xmath430 , in rough agreement with the value of @xmath431 predicted by equation ( [ eq : ftt ] ) . on the other hand , the orbital flips above @xmath432 are entirely suppressed , in contrast with the behaviour observed in figure [ fig : case94 ] , where only a fraction of the systems have their orbital flips entirely suppressed , while at high inclinations the orbits still manage to reverse their orientations despite the strict limits on the maximum eccentricity . , @xmath433 , @xmath434 ) . system parameters are @xmath115 , @xmath198 , @xmath116 @xmath200 and @xmath435 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath437 years ( @xmath438 ) . , title="fig:",scaledwidth=50.0% ] , @xmath433 , @xmath434 ) . system parameters are @xmath115 , @xmath198 , @xmath116 @xmath200 and @xmath435 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath437 years ( @xmath438 ) . , title="fig:",scaledwidth=50.0% ] , @xmath439 , @xmath440 ) . system parameters are @xmath115 , @xmath198 , @xmath116 @xmath117 and @xmath441 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath442 years ( @xmath443 ) . note that @xmath238 decreases , the critical angles ( @xmath390 and @xmath400 ) are pushed to higher values . , title="fig:",scaledwidth=50.0% ] , @xmath439 , @xmath440 ) . system parameters are @xmath115 , @xmath198 , @xmath116 @xmath117 and @xmath441 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath442 years ( @xmath443 ) . note that @xmath238 decreases , the critical angles ( @xmath390 and @xmath400 ) are pushed to higher values . , title="fig:",scaledwidth=50.0% ] , @xmath444 , @xmath445 ) . system parameters are @xmath115 , @xmath198 , @xmath446 @xmath117 and @xmath441 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath447 years ( @xmath443 ) . the value of @xmath238 becomes smaller than in case 10b and the maximum inclination angle can not reach @xmath448 . , title="fig:",scaledwidth=50.0% ] , @xmath444 , @xmath445 ) . system parameters are @xmath115 , @xmath198 , @xmath446 @xmath117 and @xmath441 . orbits are started with @xmath201 , @xmath119 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath447 years ( @xmath443 ) . the value of @xmath238 becomes smaller than in case 10b and the maximum inclination angle can not reach @xmath448 . , title="fig:",scaledwidth=50.0% ] we have carried out calculations of the inner binary evolution for various combinations of @xmath449 that yield different values of the parameters @xmath194 , @xmath254 , @xmath255 , @xmath256 ( see table 1 ) . in particular , the dimensionless octupole parameter @xmath194 can be varied by changing the values of @xmath49 and the ratio of @xmath13 to @xmath15 ( see equation [ eq : c ] ) , and we consider @xmath194 ranging from @xmath450 to @xmath451 . for a given @xmath194 , we consider various possible values of @xmath254 , @xmath255 , @xmath256 ( see equations [ eq : r11 ] , [ eq : r12 ] and [ eq : r13 ] ) in order to assess the role of srfs . for each set of parameters and the initial inclination angle @xmath4 , we integrate the binary evolution equations for a few octupole oscillation periods , @xmath452 , and record the maximum of @xmath48 and the extrema of @xmath379 attained during the evolution . table 2 summarizes our key findings . as noted before ( section 4.1 ) , the srfs provide an upper limit to the maximum eccentricity attainable during the binary evolution , even for large @xmath194 . in particular , our numerical result for the maximum eccentricity @xmath453 ( for all @xmath4 s ) is in good agreement with the limiting eccentricity @xmath389 given by equation ( [ eq : ftt ] ) . comparing @xmath454 at @xmath455 , we see that with the exception of case 1 , the tidal effect and the rotational bulge are responsible for limiting the eccentricity growth . the last three columns of table 2 summarize the three critical initial inclination angles introduced in section 4.1 for the different cases . without srfs , the angle @xmath398 ( at which orbital flip occurs due to the octupole potential ) decreases with increasing @xmath194 . when the srfs are included , orbital flips require higher inclinations ( @xmath456 ) , and the critical angle @xmath400 decreases as @xmath194 increases . note that when @xmath457 ( case 1 to case 6 ) , @xmath458 , implying that the octupole potential can not lead to orbit flip . finally , in the presence of the srfs , the critical inclination @xmath390 at which the maximum eccentricity saturates to @xmath459 is roughly equals to @xmath398 . this implies that the excitations of eccentricity and inclination are related . figures [ fig : case10a][fig : case10c ] depict the results for case 10a-10c , corresponding to the same @xmath194 but different srf strength . note that , as @xmath194 is the same for all these examples , the width of the octupole window of influence is unaltered . however , the region in inclination angle for which orbits are allowed to flip changes with @xmath272 . this is quantified by the value of the critical angle @xmath400 , which grows monotonically with @xmath272 , meaning that orbital flips are progressively confined to the neighboring region of @xmath239 . in this section , we extend the analysis of previous sections to the general case of lidov kozai cycles with srfs in systems composed of three comparable masses ( @xmath460 ) , focusing on the long term evolution of eccentricity and inclination of the inner binary . as discussed in section [ sec : symmetry ] , the equations of motion in the test - particle limit are symmetric upon reflections of the @xmath58 vector through the origin . this implies that the lidov kozai cycles with srfs examples in the small mass regime ( @xmath97 ) presented in figures [ fig : case94][fig : case10c ] show even symmetry around @xmath239 in the eccentricity curves ( top panels ) and odd symmetry in the inclination curves ( bottom panels ) . as we have shown in a previous example ( figure [ fig : scm ] ) , this reflection symmetry is removed when @xmath156 . however , there is still an approximate symmetry center for calculations at the quadrupole - level . this can be seen in figure [ fig : case1c ] for a triple system of comparable masses . in a similar fashion to figures [ fig : case94][fig : case10c ] , the black curves in figure [ fig : case1c ] show @xmath237 and @xmath461 as a function of @xmath462 and @xmath463 calculated from the quadrupole - level potential . we have extended the initial inclinations to cover @xmath464,@xmath465 , encompassing the full range of prograde and retrograde orientations . there is a reflection symmetry respect to @xmath466 ( or equivalently , respect to @xmath467 ) . however , this symmetry is erased once octupole - level terms are considered ( red curves ) . this is in contrast to the test - particle limit , for which the reflection symmetry around @xmath468 is valid for the quadrupole - level and octupole - level approximations . @llrrrrlrlr@ parameter & @xmath57 & @xmath175 & @xmath176 & @xmath274 & @xmath275 & @xmath469 & @xmath470 & @xmath276 & @xmath471 + case 1a & 0.022 & @xmath472 & @xmath473 & 10 & 100 & 0.5 & 0.5 & 1 & 0.5 + case 1b & 0.022 & @xmath474 & @xmath475 & 3 & 30 & 0.5 & 0.5 & 1 & 0.5 + case 1c & 0.022 & @xmath476 & @xmath477 & 1 & 10 & 0.5 & 0.5 & 1 & 0.5 + case 1d & 0.022 & @xmath476 & @xmath478 & 1 & 10 & 0.5 & 0.5 & 1 & 2 + case 1e & 0.022 & @xmath476 & @xmath479 & 1 & 10 & 0.5 & 0.5 & 1 & 5 + + case 2a & 0.042 & @xmath480 & @xmath481 & 10 & 120 & 0.6 & 0.3 & 0.8 & 0.3 + case 2b & 0.042 & @xmath482 & @xmath483 & 5 & 60 & 0.6 & 0.3 & 0.8 & 0.3 + case 2c & 0.042 & @xmath484 & @xmath485 & 1 & 12 & 0.6 & 0.3 & 0.8 & 0.3 + case 2d & 0.042 & @xmath484 & @xmath486 & 1 & 12 & 0.6 & 0.3 & 0.8 & 0.6 + case 2e & 0.042 & @xmath484 & @xmath487 & 1 & 12 & 0.6 & 0.3 & 0.8 & 5 + @llrrrrlrlr@ parameter & @xmath307 & @xmath308 & @xmath309 & @xmath310 & @xmath488(deg ) & @xmath489(deg ) + case 1a & @xmath490 & @xmath491 & @xmath492 & 10.12 & 85.5 & 94.5 + case 1b & @xmath493 & @xmath494 & @xmath495 & 10.11 & 85.5 & 94.5 + case 1c & @xmath496 & @xmath497 & @xmath498 & 10.09 & 85.5 & 94.5 + case 1d & @xmath499 & @xmath500 & @xmath501 & 9.98 & 85.5 & 94.5 + case 1e & @xmath502 & @xmath503 & @xmath504 & 9.74 & 85.5 & 94.5 + + case 2a & @xmath505 & @xmath506 & @xmath507 & 10.12 & 86.2 & 93.8 + case 2b & @xmath508 & @xmath509 & @xmath510 & 10.12 & 86.2 & 93.8 + case 2c & @xmath511 & @xmath512 & @xmath513 & 10.10 & 86.2 & 93.8 + case 2d & @xmath514 & @xmath515 & @xmath516 & 10.07 & 86.2 & 93.8 + case 2e & @xmath517 & @xmath518 & @xmath519 & 9.65 & 86.2 & 93.8 + the shift in the symmetry center away from @xmath122 results from the conservation of total angular momentum and the quadrupole - level potential . introducing the total angular momentum @xmath520 , we can write the mutual inclination of the inner and outer orbits as @xcite @xmath521 where @xmath63 and @xmath64 are given by equations ( [ eq : l1])([eq : l2 ] ) . since @xmath522 is conserved , this expression becomes @xmath523 where @xmath463 , @xmath524 and @xmath469 are the initial values for the mutual inclination and for the inner and outer eccentricities , respectively . note that , at the quadrupole level , the eccentricity of the outer orbit @xmath525 constant . next , we rewrite the ( constant ) potential of equation ( [ eq : apk2 ] ) as @xmath526 combining equations ( [ eq : gtot2 ] ) and ( [ eq : apk3 ] ) , we obtain an expression for the maximum eccentricity @xmath237 ( after evaluating at @xmath244 ) : @xmath527=0~. \end{split}\ ] ] equation ( [ eq : meg ] ) generalizes equation ( [ eq : me ] ) for the test - mass case . these two expressions become equivalent in the limit @xmath98 . in the test - particle limit at the quadrupole level , the symmetry center ( at @xmath239 ) coincides with the point of maximal eccentricity " or @xmath528 . similarly , for the general case of comparable masses , we define the angle @xmath489 by setting @xmath528 in equation ( [ eq : meg ] ) : @xmath529 as expected , in the limit @xmath98 we have that @xmath530 . note that the negative sign in equation ( [ eq : isym ] ) implies that @xmath489 is always greater than @xmath122 . this symmetry breaking can also be realized for the inner inclination @xmath129 , which can be obtained from conservation of angular momentum and the law of sines : @xmath531 . this is consistent with the numerical result shown in figure [ fig : case1c ] . figures [ fig : case1c][fig : case2e ] show the dependence of maximum eccentricity and inclination extrema as a function of @xmath532 ( or @xmath463 ) for systems with different masses @xmath115 , @xmath130 and other parameters . as in the examples of section [ sec : paramspace ] , four different calculations shown : ( 1 ) quadrupole - level approximation with no srfs ( black curves ) , ( 2 ) octupole - level approximation with no srfs ( red curves ) , ( 3 ) quadrupole - level approximation with srfs ( green curves ) , and ( 4 ) octupole - level approximation with srfs ( blue curves ) . just as in section [ sec : paramspace ] , we explore the changes in @xmath237 and @xmath461 as we vary @xmath194 and @xmath272 , this time for triple stars of comparable masses . note that in equation ( [ eq : c ] ) , the octupole contribution is exactly zero if the members of inner binary here equal mass , so for similar masses , @xmath194 can not be very large . the orbital separations and other physical parameters of the systems studied in this section are listed in table [ tab : paramspace_general ] . the values of initial inclinations induced both prograde and retrograde orbits in @xmath462 ( i.e. , respect to the total angular momentum vector ) . the range in angles is chosen so as to enclose the lidov kozai active " region . this region is contained between the angles @xmath533 and @xmath534 , which are the two solutions of the quadratic equation obtained from equation ( [ eq : meg ] ) after setting @xmath535 : @xmath536 for all the examples considered here ( table [ tab : paramspace_general ] ) , an inclination interval of @xmath537 is sufficient to capture the entire range of systems that are subject to lidov kozai oscillations . . we extend the test - particle case in section 4 to comparable - mass case . here , the system has an inner binary of @xmath115 , @xmath130 , @xmath117 , @xmath538 and the companion has @xmath116 , @xmath539 . we initially set @xmath201 , @xmath132 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . because there is no reflection symmetry between the prograde and retrograde configurations , we integrate equations ( [ eq : fulle1])-([eq : fullomega2 ] ) with @xmath537 for @xmath540 years ( @xmath541 ) . note that limiting eccentricity holds as well and the flip can not occur with srfs . , title="fig:",width=321 ] . we extend the test - particle case in section 4 to comparable - mass case . here , the system has an inner binary of @xmath115 , @xmath130 , @xmath117 , @xmath538 and the companion has @xmath116 , @xmath539 . we initially set @xmath201 , @xmath132 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . because there is no reflection symmetry between the prograde and retrograde configurations , we integrate equations ( [ eq : fulle1])-([eq : fullomega2 ] ) with @xmath537 for @xmath540 years ( @xmath541 ) . note that limiting eccentricity holds as well and the flip can not occur with srfs . , title="fig:",width=321 ] by changing @xmath117 , @xmath539 and @xmath542 , and keep other quantities the same as case 1c ( see table 3 ) . we integrate the equations and the total integration time is @xmath540 years ( @xmath541 ) . note that @xmath238 become smaller and srfs affect the octupole - level effects significantly . , title="fig:",width=321 ] by changing @xmath117 , @xmath539 and @xmath542 , and keep other quantities the same as case 1c ( see table 3 ) . we integrate the equations and the total integration time is @xmath540 years ( @xmath541 ) . note that @xmath238 become smaller and srfs affect the octupole - level effects significantly . , title="fig:",width=321 ] . the system has an inner binary of @xmath115 , @xmath543 , @xmath117 , @xmath544 and the companion has @xmath545 , @xmath546 . we initially set @xmath201 , @xmath202,@xmath136 , @xmath436 , @xmath137 and @xmath208 . we integrate the equations for @xmath547 years ( @xmath548 ) . due to the stronger octupole potential , the width of the @xmath237 and @xmath549 regions become lager and the flip occur even with srfs . , title="fig:",width=321 ] . the system has an inner binary of @xmath115 , @xmath543 , @xmath117 , @xmath544 and the companion has @xmath545 , @xmath546 . we initially set @xmath201 , @xmath202,@xmath136 , @xmath436 , @xmath137 and @xmath208 . we integrate the equations for @xmath547 years ( @xmath548 ) . due to the stronger octupole potential , the width of the @xmath237 and @xmath549 regions become lager and the flip occur even with srfs . , title="fig:",width=321 ] . the system has an inner binary of @xmath115 , @xmath543 , @xmath117 , @xmath542 and the companion has @xmath545 , @xmath546 . we initially set @xmath201 , @xmath202 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath547 years ( @xmath548 ) . , title="fig:",width=321 ] . the system has an inner binary of @xmath115 , @xmath543 , @xmath117 , @xmath542 and the companion has @xmath545 , @xmath546 . we initially set @xmath201 , @xmath202 , @xmath136 , @xmath436 , @xmath137 and @xmath208 . the total integration time is @xmath547 years ( @xmath548 ) . , title="fig:",width=321 ] as discussed in section [ sec : symmetry_general ] above , for finite @xmath12 , the symmetry of the system respect to @xmath550 is shifted to a different value @xmath489 . however , this symmetry center only reflects the behaviour of the system at the quadrupole level . in addition to the significant when the octupole potential is included , figure [ fig : case1c ] ( for @xmath551 ) also shows how the symmetry between prograde and retrograde orbits is broken . figure [ fig : case1c ] shows that at the quadrupole level , the excitation of eccentricity only takes place in the range between @xmath552 and @xmath553 , as given by equation ( [ eq : ist ] ) , and @xmath237 is achieved at @xmath554 ( table 4 ) , as predicted by equation ( [ eq : isym ] ) . when the octupole - level terms are included ( red curve ) , @xmath555 is not the only inclination that allows for such extreme eccentricity ( i.e. , @xmath556 ) . indeed , as in the test - mass case ( figures [ fig : case94][fig : case10c ] ) , the inclusion of octupole terms widens the range on angles for which @xmath557 is possible . in this case however , the widening " takes place to the right of @xmath489 , while the quadrupole - level solution remains valid for @xmath558 down to for @xmath559 . below @xmath560 , deviations from the quadrupole - level solution become significant . these features , which can be compared to what seemed to be minor fluctuations in @xmath237 for the test - particle cases ( see figures [ fig : case94][fig : case10c ] ) , show that moderately high eccentricities can be excited at lower inclinations ( @xmath561 ) than the quadrupole - order calculation would allow . when srfs are included , the quadrupole - level eccentricity maxima are truncated at a global maximum corresponding to @xmath562 . the horizontal line in figure [ fig : case1c ] corresponds to the limiting eccentricity given by equation ( [ eq : ftt ] ) . it is important to note that this limiting eccentricity applies even in the general case of comparable masses . also note that the tides are mainly responsible for the eccentricity suppression ( see table 4 ) . it is not surprising that the analytic estimate of @xmath563 , derived in the test - mass limit ( section [ sec : max_ecc ] ) , remains a good approximation for comparable - mass systems . for @xmath48 very close to unity , the vast majority of the angular momentum resides in the outer binary , forcing the inner binary to behave essentially as a test particle . note that we can use equations ( [ eq : j1vec ] ) , ( [ eq : j2vec ] ) and ( [ eq : e2vec ] ) at the quadrupole level ( @xmath113 ) to write @xmath564 where all the vectors involved are of norm unity . then we find that @xmath565 is very small provided that @xmath566 . therefore , for the high eccentricity phase of lidov kozai cycles , the analysis of section [ sec : max_ecc ] for test particles still applies in the comparable - mass regime . as in the test - mass cases ( section [ sec : paramspace ] ) , the octupole effect expands the range of the initial mutual inclinations capable of reaching maximal eccentricities . as for the eccentricity curves , the inclination curves at the quadrupole level in figure [ fig : case1c ] ( black curves ) are symmetric respect to @xmath488 . in this particular example , srfs do not inflict significant modifications except for the close vicinity of @xmath488 , which sees the amplitude in the inclination oscillations ( the difference between @xmath567 and @xmath568 ) reduced ( green curves ) . at the octupole level ( red curves ) , the asymmetries that arise in the eccentricity curve find their counterpart in the inclination curves . within a narrow range of angles ( rightward of @xmath488 ) , the orbits are allowed to flip from retrograde to prograde . for initial inclinations bellow @xmath569 , although the octupole potential introduces significant changes in @xmath570 and @xmath571 , it is not strong enough to cause orbital flips . in accordance to what is observed in the eccentricity curves , the octupole contributions to the left of @xmath488 are not affected by srf , however , the flips observed for angles @xmath572 is nearly entirely suppressed by the inclusion of these additional effects ( blue curves ) . the example of figure [ fig : case1c ] shows moderate differences in maximum eccentricity and inclination range between the quadrupole and the octupole - level solutions . to explore the behaviour of these variables for larger octupole contributions we integrate systems with @xmath574 varying the magnitude of @xmath272 ( table [ tab : paramspace_general ] ) . some of these examples are shown in figure [ fig : case2c ] and [ fig : case2e ] . the most important difference between the top panels of figure [ fig : case2c ] and figure [ fig : case1c ] is the width of the maximal eccentricity region to the right of @xmath488 ( this was already observed in the examples of section [ sec : paramspace ] ) and the deepening of the high eccentricity region to the left of @xmath488 . as @xmath194 is increased , the asymmetries between the prograde and retrograde regions of the figure become more pronounced . prograde orbits at intermediate inclination see their maximum eccentricities increase , to a point that they become comparable to those seen for the retrograde orbits . it is at this point ( when @xmath575 ) that prograde orbits are allowed to flip orientations . when srfs are considered , the maximum eccentricities ( green and blue curves ) are altered in a similar fashion as the example of figure [ fig : case1c ] . the value of @xmath238 of equation ( [ eq : ftt ] ) is still in agreement with the global maximum of @xmath237 ( see table 4 ) . on the other hand , the growth of @xmath576 is suppressed ( no flip ) in prograde configurations , while @xmath577 appears to vary erratically when @xmath572 ( see figure [ fig : case2c ] ) . figures [ fig : case1e ] and [ fig : case2e ] show examples of increased @xmath272 for the same @xmath194 as in figures [ fig : case1c ] and [ fig : case2c ] . in these cases , @xmath563 is smaller than in case 2c ( figure [ fig : case2c ] ) , which implies that srfs are truncating @xmath237 not only in the vicinity of @xmath489 , but also in the lower inclination region [ @xmath578 , thus affecting the octupole - level effects significantly . despite the significant restrictions on @xmath237 imposed by srfs , the octupole effects can not be neglected for their values of @xmath194 , since they allow for these systems to reach eccentricities with @xmath579 for initial mutual inclinations as low as @xmath580 ( figure [ fig : case2e ] ) while the quadrupole - level calculation would require inclinations beyond @xmath581 to reach similar values . in this paper , we have computed the extent to which energy - conserving short - range effects alter the orbital evolution of planets and stars in hierarchical triple systems undergoing lidov - kozai oscillations . in particular , we have systematically examined how general relativistic precession , tides and oblateness can moderate the extreme values in eccentricity and inclination that can be achieved owing to the octupole terms in the interaction potential . by carrying of a sequence of numerical experiments , we have measured the extrema in eccentricity and inclination for a variety of hierarchical triples , systematically varying the relative strengths of the octupole terms and of the short - range effects in terms of their contributions to the potential energy . the results of our calculations can be summarized into four main findings . \(1 ) the importance of the octupole effects depends on the dimensionless parameter @xmath57 ( see equation [ eq : c ] ) , which measures the relative strength between the octupole and quadrupole potentials . the main contribution of the octupole terms to eccentricity and inclination excitation is limited to a range in initial inclinations or window of influence " , the width of which grows with @xmath57 . as @xmath57 decreases , the window of influence becomes increasingly confined to mutual inclinations close to @xmath122 . for example , at @xmath582 , the octupole terms are important only within a few degrees around @xmath583 ( see tables 1 and 2 ; also see fig . [ fig : case5 ] ) . \(2 ) we find that short range forces can indeed compete with the octupole - level terms in the potential , and that these additional effects impose a strict upper limit on the maximum achievable eccentricity . most importantly , we find that to a very good approximation , this maximum eccentricity can be derived analytically using the quadrupole approximation in the test - particle limit ( see section 3.3 and equation [ eq : ftt ] ) . this analytic limiting eccentricity holds even for a strong octupole contribution as well as in the general case of three comparable masses . \(3 ) our results indicate that , despite the upper limit in eccentricity ( which is independent on the octupole strength ) , the width of the window of influence of the octupole potential ( see point 1 above ) is largely unaffected by the srfs . \(4 ) we find that orbital flips are affected by the srfs . with increasing strength of the srfs ( characterized by the dimensionless parameters ; see equations [ eq : r11 ] , [ eq : r12 ] and [ eq : r13 ] ) , orbital flips are increasingly confined to the region close to @xmath584 ( see figs . 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form equations of motion ( equations [ eq : j1vec][eq : e2vec ] ) . omitting the laborious matrix manipulation , we get : @xmath585\\ & -\frac{15\varepsilon_{{\mathrm{oct}}}}{4}\cos\i\cos\omega_1\big[15(2 + 5\e1)\cos2\i\\ & + 7(30\e1\cos2\omega_1\sin^2\i-2 - 9\e1)\big]\sin\omega_2\frac{}{}\bigg\}~ , \end{split}\ ] ] and @xmath586\\ & \times\sin\omega_2-\cos\i\cos\omega_2\big[5(6+\e1)\cos2\i\\ & + 7(10\e1\cos2\omega_1\sin^2\i-2+\e1)\big]\sin\omega_1\bigg\}~. \end{split}\ ] ] for the inner and outer eccentricities . the time evolution of the inclinations are described by @xmath587\\ & + \frac{5\varepsilon_{{\mathrm{oct}}}}{8}\cos\omega_1\big[26 + 37\e1 - 35\e1\cos2\omega_1\\ & -15\cos2\i(7\e1\cos2\omega_1 - 2 - 5\e1)\big]\sin\i\sin\omega_2\bigg\}~ , \end{split}\ ] ] and @xmath588\\ & + \frac{5\varepsilon_{{\mathrm{oct}}}}{8}\big[26 + 107\e1 + 5(6+\e1)\cos2\i\\ & -35\e1(\cos2\i-5)\cos2\omega_1\big]\cos\omega_2\sin\i\sin\omega_1\bigg\}~. \end{split}\ ] ] we also write the longitudes of ascending nodes as a function of time @xmath589\\ & \times\sin2\i-\frac{5\varepsilon_{{\mathrm{oct}}}e_1}{8}\big[35\e1(1 + 3\cos2\i)\cos2\omega_1\\ & -46 - 17\e1 - 15(6+\e1)\cos2\i\big]\sin\i\sin\omega_1\sin\omega_2\bigg\}~. \end{split}\ ] ] finally , the argument of periapse for the inner and outer binaries evolve according to @xmath590+\frac{l_1\cos\i}{l_2\sqrt{1-e_2 ^ 2}}\big[2+\e1(3\\ & -5\cos2\omega_1)\big]\bigg\}+\frac{15\varepsilon_{{\mathrm{oct}}}}{64~t_k } \bigg\{\left(\frac{l_1}{l_2\sqrt{1-e_2 ^ 2}}+\frac{\cos\i}{\sqrt{1-\e1}}\right)\\ & \times e_1\bigg[\sin\omega_1\sin\omega_2\big[10(3\cos^2\i-1)(1-\e1)+a\big]\\ & -5b\cos\i\cos\theta\bigg]-\frac{\sqrt{1-\e1}}{e_1}\big[10\sin\omega_1\sin\omega_2\cos\i\\ & \times\sin^2\i(1 - 3\e1)+\cos\theta(3a-10\cos^2\i+2)\big]\bigg\}~ , \end{split}\ ] ] and @xmath591\\ & + \frac{l_1}{l_2\sqrt{1-e_2 ^ 2}}\bigg[\frac{}{}4 + 6\e1+(5\cos^2\i-3)\\ & \times\big[\frac{}{}2+\e1(3 - 5\cos2\omega_1)\big]\bigg]\bigg\ } -\frac{15\varepsilon_{{\mathrm{oct}}}e_1}{64~t_k~e_2}\\ & \times\bigg\{\sin\omega_1\sin\omega_2\bigg [ \frac{l_1(4e_2 ^ 2 + 1)}{e_2~l_2\sqrt{1-e_2 ^ 2}}10\cos\i\sin^2\i\\ & \times(1-\e1)-e_2\left(\frac{1}{\sqrt{1-\e1}}+\frac{l_1\cos\i}{l_2\sqrt{1-e_2 ^ 2}}\right)\\ & \times\big[a+10(3\cos^2\i-1)(1-\e1)\big]\bigg]+\cos\theta\\ & \times\bigg[5b\cos\i e_2\left(\frac{1}{\sqrt{1-\e1}}+\frac{l_1\cos\i}{l_2\sqrt{1-e_2 ^ 2}}\right)\\ & + \frac{l_1(4e_2 ^ 2 + 1)}{e_2~l_2\sqrt{1-e_2 ^ 2}}a\bigg]\bigg\}~ , \end{split}\ ] ] where we define @xmath592 and @xmath593[/INST] the lidov - kozai ( lk ) mechanism plays an important role in the secular evolution of many hierarchical triple systems . the standard lk mechanism consists of large - amplitude oscillations in eccentricity and inclination of a binary subject to the quadrupole potential from an outer perturber . recent work has shown that when the octupole terms are included in the potential , the inner binary can reach more extreme eccentricities as well as undergo orientation flips . it is known that pericenter precessions due to short - range effects , such as general relativity and tidal and rotational distortions , can limit the growth of eccentricity and even suppress standard ( quadrupolar ) lk oscillations , but their effect on the octupole - level lk mechanism has not been fully explored . in this paper , we systematically study how these short - range forces affect the extreme orbital behaviour found in octupole lk cycles . in general , the influence of the octupole potential is confined to a range of initial mutual inclinations @xmath0 centered around 90@xmath1 ( when the inner binary mass ratio is @xmath2 ) , with this range expanding with increasing octupole strength . we find that , while the short - range forces do not change the width and location of this `` window of influence '' , they impose a strict upper limit on the maximum achievable eccentricity . this limiting eccentricity can be calculated analytically , and its value holds even for strong octupole potential and for the general case of three comparable masses . short - range forces also affect orbital flips , progressively reducing the range of @xmath0 within which flips are possible as the intensity of these forces increases . [ firstpage ] binaries : close planetary system </s>

esophageal ph monitoring was first used by tuttle and grossman in 1958 ( 1 ) . miller first reported in 1964 the use of an indwelling ph electrode positioned above the lower esophageal sphincter ( les ) to continuously monitor the intraesophageal ph ( 2 ) . this technique overcame many of the weak points of the other tests that had been used to detect gastroesophageal reflux . ambulatory 24-hr esophageal ph monitoring is increasing in popularity as the standard method for measuring esophageal exposure to gastric acid . it provides quantitative data on esophageal acid exposure as well as the temporal correlation between symptoms and actual acid reflux events . since acid reflux into the esophagus is a physiological event even in normal subjects , discrimination between physiological and pathological reflux is often difficult ( 3 ) . good temporal correlation between a distinct pathological event such as chest pain and a ph drop on the recording provides evidence of pathogenicity ( 4 ) . however , if any symptomatic correlation is not present , then only the quantifiable parameters can be used to determine the presence of any abnormality . as this technique has become widely available , questions have been raised regarding the best parameter to use to measure esophageal acid exposure , the optimal thresholds to differentiate normal from abnormal and the influence of gender and age on the measurement ( 5 - 8 ) . most studies concerned with the standard values of esophageal ph monitoring have been done in western countries ( 5 , 6 , 8 - 10 ) . because the genetic and environmental factors are different between western and eastern countries , there might also be a difference in the degree of gastroesophageal reflux between them . actually , the reported ph standards have shown a considerable variability between western countries and even among regions of the same country ( 6 , 7 , 10 , 11 ) . establishing the normal values of esophageal ph monitoring for eastern countries different in many aspects from western countries would be of great benefit for better understanding of gastroesophageal reflux disease ( gerd ) and its proper treatment . there have been a few previous reports about the normal reflux parameters in eastern countries such as china ( 12 , 13 ) . therefore , the aim of this study was to establish the normal values for gastroesophageal acid exposure in healthy koreans . this study was performed at 7 university hospitals in korea from may to october 2007 . each volunteer was carefully interviewed and when appropriate , he or she underwent a physical examination and laboratory studies to exclude systemic disorders that might alter esophageal motility or predispose to gerd . volunteers were excluded if there was any history of heartburn , regurgitation , chest pain , dysphagia for solids or liquids , odynophagia or use of antacids , promotility drugs , histamine-2 receptor blockers or proton pump inhibitors . additionally , none of the volunteers had a history of esophageal or gastric surgery , diabetes mellitus , alcoholism , neurological disorders or collagen vascular disorders . the medication histories were closely reviewed and none of the volunteers were taking any drugs that would influence acid secretion or esophageal function at the time of the study . upper endoscopy was performed on all the volunteers to exclude hiatal hernia , reflux esophagitis or other organic diseases such as peptic ulcer . informed written consent was obtained from each subject prior to the study and this study was approved by the institutional review board at each university hospital . ambulatory 24-hr esophageal ph monitoring was performed immediately after standard esophageal manometry with using a single - use monocrystalline antimony ph probe ( zinetics 24 , medtronic inc . , all the electrodes were initially calibrated in buffer solution of ph 7 and then in buffer solution of ph 1 . the ph catheter was introduced transnasally into the stomach and then it was withdrawn back into the esophagus until the electrode was 5 cm above the proximal margin of the les . the subjects were encouraged to eat regular meals with restrictions for the intake of drink or food with a ph below 4 . all the subjects recorded their meal times ( start and end ) , body position ( supine and upright ) and any symptoms in a diary . the data were collected using a portable data logger ( digitrapper mark iii , synetics medical co. , stockholm , sweden ) with a sampling rate of 4 sec , and the data was then transferred to a computer for analysis with using polygram for windows ( release 2.04 , synetics medical co. ) . a decrease in ph below 4 , which was not induced by eating or drinking , was considered the beginning of a reflux episode , and the following rise to ph above 4 was considered to be the end of such an episode . all the tracings were inspected by one of the authors to confirm the computerized calculations and to assure the quality of the recordings . the six parameters assessed for gastroesophageal reflux were the total percentage of time the ph was < 4 , the percentage of time the ph was < 4 in the supine and upright positions , the number of episodes the ph was < 4 , the number of episodes the ph was < 4 for 5 min , the duration of the longest episode the ph was < 4 and the composite score ( 14 ) . to obtain the composite score , a scoring system based on the standard deviation of the mean of each of the six components was used ( 5 , 10 ) . the simplified formula for scoring each of the six components is : component score = ( patient value - mean / standard deviation ) + 1 then , the composite score was obtained by adding the scores calculated for each of the six components ( 5 , 10 ) . the normal values for each parameter were assessed by calculating the 95th percentile for the subject group . the age of 40 was used to dichotomize the subject sample because visual inspection of the data suggested it would maximize the probability of finding an age effect on the ph variables . the mann - whitney test and the kruskal - wallis test were used to assess the effect of age and gender on each esophageal ph parameter . statistical calculations were performed using the spss version 10.0 for windows software ( spss inc . , chicago , il , u.s.a . ) . this study was performed at 7 university hospitals in korea from may to october 2007 . each volunteer was carefully interviewed and when appropriate , he or she underwent a physical examination and laboratory studies to exclude systemic disorders that might alter esophageal motility or predispose to gerd . volunteers were excluded if there was any history of heartburn , regurgitation , chest pain , dysphagia for solids or liquids , odynophagia or use of antacids , promotility drugs , histamine-2 receptor blockers or proton pump inhibitors . additionally , none of the volunteers had a history of esophageal or gastric surgery , diabetes mellitus , alcoholism , neurological disorders or collagen vascular disorders . the medication histories were closely reviewed and none of the volunteers were taking any drugs that would influence acid secretion or esophageal function at the time of the study . upper endoscopy was performed on all the volunteers to exclude hiatal hernia , reflux esophagitis or other organic diseases such as peptic ulcer . informed written consent was obtained from each subject prior to the study and this study was approved by the institutional review board at each university hospital . ambulatory 24-hr esophageal ph monitoring was performed immediately after standard esophageal manometry with using a single - use monocrystalline antimony ph probe ( zinetics 24 , medtronic inc . , minneapolis , mn , u.s.a . ) . a cutaneous reference electrode placed on the upper chest was also used . all the electrodes were initially calibrated in buffer solution of ph 7 and then in buffer solution of ph 1 . the ph catheter was introduced transnasally into the stomach and then it was withdrawn back into the esophagus until the electrode was 5 cm above the proximal margin of the les . the subjects were encouraged to eat regular meals with restrictions for the intake of drink or food with a ph below 4 . all the subjects recorded their meal times ( start and end ) , body position ( supine and upright ) and any symptoms in a diary . the data were collected using a portable data logger ( digitrapper mark iii , synetics medical co. , stockholm , sweden ) with a sampling rate of 4 sec , and the data was then transferred to a computer for analysis with using polygram for windows ( release 2.04 , synetics medical co. ) . a decrease in ph below 4 , which was not induced by eating or drinking , was considered the beginning of a reflux episode , and the following rise to ph above 4 was considered to be the end of such an episode . all the tracings were inspected by one of the authors to confirm the computerized calculations and to assure the quality of the recordings . the six parameters assessed for gastroesophageal reflux were the total percentage of time the ph was < 4 , the percentage of time the ph was < 4 in the supine and upright positions , the number of episodes the ph was < 4 , the number of episodes the ph was < 4 for 5 min , the duration of the longest episode the ph was < 4 and the composite score ( 14 ) . to obtain the composite score , a scoring system based on the standard deviation of the mean of each of the six components was used ( 5 , 10 ) . the simplified formula for scoring each of the six components is : component score = ( patient value - mean / standard deviation ) + 1 then , the composite score was obtained by adding the scores calculated for each of the six components ( 5 , 10 ) . the data were expressed as median values ( range ) unless otherwise noted . the normal values for each parameter were assessed by calculating the 95th percentile for the subject group . the age of 40 was used to dichotomize the subject sample because visual inspection of the data suggested it would maximize the probability of finding an age effect on the ph variables . the mann - whitney test and the kruskal - wallis test were used to assess the effect of age and gender on each esophageal ph parameter . statistical calculations were performed using the spss version 10.0 for windows software ( spss inc . , chicago , il , u.s.a . ) . fifty healthy volunteers ( 24 males and 26 females ; mean age , 45 yr ; range , 19 - 66 yr ) were recruited for this study . table 1 summarized the demographic data of the 50 volunteers who constituted the study population . the values for the composite score and the six parameters used to express the esophageal acid exposure in the 50 healthy volunteers are shown in table 2 . the median and 95th percentile values for the percent time ph < 4 for the total monitoring period and the composite score were 1.1 , 4.3 , 4.7 , and 14.2 , respectively . there was no difference in all the ph parameters between male volunteers and female volunteers ( table 3 ) . in addition , there was no difference in all the ph parameters between young volunteers and old volunteers ( table 4 ) . the interaction of gender and age did not show any significant difference for all the ph parameters ( table 5 ) . the results of our multicenter study for the amount of physiologic gastroesophageal acid reflux in 50 healthy koreans can be summarized as follows : 1 ) gender does not independently influence the ph parameters ; and 2 ) age also does not influence the ph parameters . men are generally known to secrete more gastric acid than women and this is explained in part by the larger body mass of men ( 15 , 16 ) . in a previous report , male volunteers showed higher median values than women volunteers for all the ph parameters except for the percentage time ph < 4 in the supine position ( 6 ) . in another report , there was no difference in esophageal acid exposure between males and females when the results of 24-hr ph monitoring were expressed as the composite score ( 5 ) . they suggested that using the composite score to determine when a patient had increased esophageal exposure to gastric juice could eliminate the necessity of having separate normal values for men and women . in present study , there was no difference in all the ph parameters between males and females . in one previous prospective study about acid output , gender had no significant effect on the basal output of acid and it had only borderline significant effects on the peak acid output ( 17 ) . this fact could explain our results , even though differences of genetic and environmental factors between koreans and western populations do exist . in the present study , there was no reliable association between the esophageal ph parameters and age . schlesinger et al . first raised the possibility that increasing age had an effect on the esophageal ph parameters ( 7 ) . it was also reported that older subjects showed significantly higher values for the total and upright percentage of time of ph < 4 as well as the total number of reflux episodes > 5 min ( 18 ) . but in that study , the sample size was relatively small and older controls were obtained from a hospitalized veteran population , and this veteran population had a high prevalence of hypertension and diabetes mellitus . on the other hand , the results of a large population study on 110 healthy subjects did not show an independent effect of age on the ph parameters ( 6 ) . thus , for clinical purposes , it seems that age generally does not have an important effect on the physiologic parameters of acid reflux . first , in our study , all the healthy volunteers underwent upper endoscopy to exclude asymptomatic esophagitis and hiatal hernia . in two large western studies concerned with the normal ambulatory esophageal ph values ( 5 , 6 ) therefore , they could not exclude the subjects with asymptomatic esophagitis or hiatal hernia . in the present study , we excluded these subjects by performing endoscopy . second , the distribution of gender and age of the healthy volunteers in our study was uniform ( data not shown ) . first , the number of subjects in this study was not large ; this could raise the possibility of a type-2 error . however , to be included in the study , the volunteers were required not to have any clinical evidence of gerd and they were also without endoscopic documentation of reflux esophagitis and hiatal hernia . these facts reduced the number of subjects for the study , so as to render our healthy volunteers as being appropriate . second , although our study population was carefully screened to be healthy and asymptomatic and we excluded the subjects who had reflux esophagitis or hiatal hernia , many of the subjects might have h. pylori infection with or without chronic atrophic gastritis . there is a higher prevalence of h. pylori infection in koreans than in western populations ( 19 ) . mild h. pylori - associated chronic active superficial gastritis had little effect on gastric acid output , whereas severe chronic active gastritis was associated with a lower gastric acid output ( 17 ) . this fact could also explain the lower values of the reflux parameters in our study as compared to the western studies . finally , because this study was performed at 7 medical centers , there would be bias of the reflux parameters among each center . to lessen the bias , we defined a standard method of ambulatory 24-hr esophageal ph monitoring and then we started this study . in addition , the coefficient of variation for the reflux parameters among each center was less than 40% , except the percentage of time the ph was < 4 in the supine positions . the normal values of the ph parameters , as 95th percentiles in 3 previous western studies ( 5 , 6 , 10 ) and in our study , are shown in table 6 . almost all the parameters except the number of reflux episodes were lower in our study than those in the western studies . many factors , including the differences in the age distribution of the control subjects , the real population differences for gastroesophageal reflux and the different incidence of h. pylori infection , could have contributed to these results . in conclusion , our multi - center data were based on 50 healthy volunteers , and these data provides the normal values for esophageal ph monitoring in koreans . however , no database is perfect because of the well - known variability of acid exposure from day to day and the inherent problems with the ph probe ( i.e. , it may get buried in the esophageal mucosa and so miss reflux episodes ) ( 8 , 20 ) . on the basis of our results , these normal esophageal ph values can provide reference data for future clinical and research studies in korea .

ambulatory 24-hr esophageal ph monitoring is considered the gold standard for diagnosing gastroesophageal reflux disease . the aim of this study was to establish normal values for gastroesophageal acid exposure in healthy koreans . fifty healthy volunteers ( 24 males and 26 females ; mean age , 45 yr ) without reflux symptoms and without reflux esophagitis or hiatal hernia on upper endoscopy underwent ambulatory 24-hr esophageal ph monitoring after esophageal manometry . the 95th percentiles for the reflux parameters were : the percent total time ph < 4 , 3.7% ; the percent upright time ph < 4 , 5.7% ; the percent supine time ph < 4 , 1.0% ; the number of reflux episodes with ph < 4 , 76.5 ; the number of reflux episodes with ph < 4 for > 5 min , 1.5 ; the duration of the longest episode , 12.5 min ; and the composite score , 14.2 . age and gender were not associated with any of the ph parameters . in conclusion , physiological gastroesophageal reflux occurs in healthy koreans . these normal esophageal ph values will provide reference data for clinical and research studies in korea .

<s>[INST]esophageal ph monitoring was first used by tuttle and grossman in 1958 ( 1 ) . miller first reported in 1964 the use of an indwelling ph electrode positioned above the lower esophageal sphincter ( les ) to continuously monitor the intraesophageal ph ( 2 ) . this technique overcame many of the weak points of the other tests that had been used to detect gastroesophageal reflux . ambulatory 24-hr esophageal ph monitoring is increasing in popularity as the standard method for measuring esophageal exposure to gastric acid . it provides quantitative data on esophageal acid exposure as well as the temporal correlation between symptoms and actual acid reflux events . since acid reflux into the esophagus is a physiological event even in normal subjects , discrimination between physiological and pathological reflux is often difficult ( 3 ) . good temporal correlation between a distinct pathological event such as chest pain and a ph drop on the recording provides evidence of pathogenicity ( 4 ) . however , if any symptomatic correlation is not present , then only the quantifiable parameters can be used to determine the presence of any abnormality . as this technique has become widely available , questions have been raised regarding the best parameter to use to measure esophageal acid exposure , the optimal thresholds to differentiate normal from abnormal and the influence of gender and age on the measurement ( 5 - 8 ) . most studies concerned with the standard values of esophageal ph monitoring have been done in western countries ( 5 , 6 , 8 - 10 ) . because the genetic and environmental factors are different between western and eastern countries , there might also be a difference in the degree of gastroesophageal reflux between them . actually , the reported ph standards have shown a considerable variability between western countries and even among regions of the same country ( 6 , 7 , 10 , 11 ) . establishing the normal values of esophageal ph monitoring for eastern countries different in many aspects from western countries would be of great benefit for better understanding of gastroesophageal reflux disease ( gerd ) and its proper treatment . there have been a few previous reports about the normal reflux parameters in eastern countries such as china ( 12 , 13 ) . therefore , the aim of this study was to establish the normal values for gastroesophageal acid exposure in healthy koreans . this study was performed at 7 university hospitals in korea from may to october 2007 . each volunteer was carefully interviewed and when appropriate , he or she underwent a physical examination and laboratory studies to exclude systemic disorders that might alter esophageal motility or predispose to gerd . volunteers were excluded if there was any history of heartburn , regurgitation , chest pain , dysphagia for solids or liquids , odynophagia or use of antacids , promotility drugs , histamine-2 receptor blockers or proton pump inhibitors . additionally , none of the volunteers had a history of esophageal or gastric surgery , diabetes mellitus , alcoholism , neurological disorders or collagen vascular disorders . the medication histories were closely reviewed and none of the volunteers were taking any drugs that would influence acid secretion or esophageal function at the time of the study . upper endoscopy was performed on all the volunteers to exclude hiatal hernia , reflux esophagitis or other organic diseases such as peptic ulcer . informed written consent was obtained from each subject prior to the study and this study was approved by the institutional review board at each university hospital . ambulatory 24-hr esophageal ph monitoring was performed immediately after standard esophageal manometry with using a single - use monocrystalline antimony ph probe ( zinetics 24 , medtronic inc . , all the electrodes were initially calibrated in buffer solution of ph 7 and then in buffer solution of ph 1 . the ph catheter was introduced transnasally into the stomach and then it was withdrawn back into the esophagus until the electrode was 5 cm above the proximal margin of the les . the subjects were encouraged to eat regular meals with restrictions for the intake of drink or food with a ph below 4 . all the subjects recorded their meal times ( start and end ) , body position ( supine and upright ) and any symptoms in a diary . the data were collected using a portable data logger ( digitrapper mark iii , synetics medical co. , stockholm , sweden ) with a sampling rate of 4 sec , and the data was then transferred to a computer for analysis with using polygram for windows ( release 2.04 , synetics medical co. ) . a decrease in ph below 4 , which was not induced by eating or drinking , was considered the beginning of a reflux episode , and the following rise to ph above 4 was considered to be the end of such an episode . all the tracings were inspected by one of the authors to confirm the computerized calculations and to assure the quality of the recordings . the six parameters assessed for gastroesophageal reflux were the total percentage of time the ph was < 4 , the percentage of time the ph was < 4 in the supine and upright positions , the number of episodes the ph was < 4 , the number of episodes the ph was < 4 for 5 min , the duration of the longest episode the ph was < 4 and the composite score ( 14 ) . to obtain the composite score , a scoring system based on the standard deviation of the mean of each of the six components was used ( 5 , 10 ) . the simplified formula for scoring each of the six components is : component score = ( patient value - mean / standard deviation ) + 1 then , the composite score was obtained by adding the scores calculated for each of the six components ( 5 , 10 ) . the normal values for each parameter were assessed by calculating the 95th percentile for the subject group . the age of 40 was used to dichotomize the subject sample because visual inspection of the data suggested it would maximize the probability of finding an age effect on the ph variables . the mann - whitney test and the kruskal - wallis test were used to assess the effect of age and gender on each esophageal ph parameter . statistical calculations were performed using the spss version 10.0 for windows software ( spss inc . , chicago , il , u.s.a . ) . this study was performed at 7 university hospitals in korea from may to october 2007 . each volunteer was carefully interviewed and when appropriate , he or she underwent a physical examination and laboratory studies to exclude systemic disorders that might alter esophageal motility or predispose to gerd . volunteers were excluded if there was any history of heartburn , regurgitation , chest pain , dysphagia for solids or liquids , odynophagia or use of antacids , promotility drugs , histamine-2 receptor blockers or proton pump inhibitors . additionally , none of the volunteers had a history of esophageal or gastric surgery , diabetes mellitus , alcoholism , neurological disorders or collagen vascular disorders . the medication histories were closely reviewed and none of the volunteers were taking any drugs that would influence acid secretion or esophageal function at the time of the study . upper endoscopy was performed on all the volunteers to exclude hiatal hernia , reflux esophagitis or other organic diseases such as peptic ulcer . informed written consent was obtained from each subject prior to the study and this study was approved by the institutional review board at each university hospital . ambulatory 24-hr esophageal ph monitoring was performed immediately after standard esophageal manometry with using a single - use monocrystalline antimony ph probe ( zinetics 24 , medtronic inc . , minneapolis , mn , u.s.a . ) . a cutaneous reference electrode placed on the upper chest was also used . all the electrodes were initially calibrated in buffer solution of ph 7 and then in buffer solution of ph 1 . the ph catheter was introduced transnasally into the stomach and then it was withdrawn back into the esophagus until the electrode was 5 cm above the proximal margin of the les . the subjects were encouraged to eat regular meals with restrictions for the intake of drink or food with a ph below 4 . all the subjects recorded their meal times ( start and end ) , body position ( supine and upright ) and any symptoms in a diary . the data were collected using a portable data logger ( digitrapper mark iii , synetics medical co. , stockholm , sweden ) with a sampling rate of 4 sec , and the data was then transferred to a computer for analysis with using polygram for windows ( release 2.04 , synetics medical co. ) . a decrease in ph below 4 , which was not induced by eating or drinking , was considered the beginning of a reflux episode , and the following rise to ph above 4 was considered to be the end of such an episode . all the tracings were inspected by one of the authors to confirm the computerized calculations and to assure the quality of the recordings . the six parameters assessed for gastroesophageal reflux were the total percentage of time the ph was < 4 , the percentage of time the ph was < 4 in the supine and upright positions , the number of episodes the ph was < 4 , the number of episodes the ph was < 4 for 5 min , the duration of the longest episode the ph was < 4 and the composite score ( 14 ) . to obtain the composite score , a scoring system based on the standard deviation of the mean of each of the six components was used ( 5 , 10 ) . the simplified formula for scoring each of the six components is : component score = ( patient value - mean / standard deviation ) + 1 then , the composite score was obtained by adding the scores calculated for each of the six components ( 5 , 10 ) . the data were expressed as median values ( range ) unless otherwise noted . the normal values for each parameter were assessed by calculating the 95th percentile for the subject group . the age of 40 was used to dichotomize the subject sample because visual inspection of the data suggested it would maximize the probability of finding an age effect on the ph variables . the mann - whitney test and the kruskal - wallis test were used to assess the effect of age and gender on each esophageal ph parameter . statistical calculations were performed using the spss version 10.0 for windows software ( spss inc . , chicago , il , u.s.a . ) . fifty healthy volunteers ( 24 males and 26 females ; mean age , 45 yr ; range , 19 - 66 yr ) were recruited for this study . table 1 summarized the demographic data of the 50 volunteers who constituted the study population . the values for the composite score and the six parameters used to express the esophageal acid exposure in the 50 healthy volunteers are shown in table 2 . the median and 95th percentile values for the percent time ph < 4 for the total monitoring period and the composite score were 1.1 , 4.3 , 4.7 , and 14.2 , respectively . there was no difference in all the ph parameters between male volunteers and female volunteers ( table 3 ) . in addition , there was no difference in all the ph parameters between young volunteers and old volunteers ( table 4 ) . the interaction of gender and age did not show any significant difference for all the ph parameters ( table 5 ) . the results of our multicenter study for the amount of physiologic gastroesophageal acid reflux in 50 healthy koreans can be summarized as follows : 1 ) gender does not independently influence the ph parameters ; and 2 ) age also does not influence the ph parameters . men are generally known to secrete more gastric acid than women and this is explained in part by the larger body mass of men ( 15 , 16 ) . in a previous report , male volunteers showed higher median values than women volunteers for all the ph parameters except for the percentage time ph < 4 in the supine position ( 6 ) . in another report , there was no difference in esophageal acid exposure between males and females when the results of 24-hr ph monitoring were expressed as the composite score ( 5 ) . they suggested that using the composite score to determine when a patient had increased esophageal exposure to gastric juice could eliminate the necessity of having separate normal values for men and women . in present study , there was no difference in all the ph parameters between males and females . in one previous prospective study about acid output , gender had no significant effect on the basal output of acid and it had only borderline significant effects on the peak acid output ( 17 ) . this fact could explain our results , even though differences of genetic and environmental factors between koreans and western populations do exist . in the present study , there was no reliable association between the esophageal ph parameters and age . schlesinger et al . first raised the possibility that increasing age had an effect on the esophageal ph parameters ( 7 ) . it was also reported that older subjects showed significantly higher values for the total and upright percentage of time of ph < 4 as well as the total number of reflux episodes > 5 min ( 18 ) . but in that study , the sample size was relatively small and older controls were obtained from a hospitalized veteran population , and this veteran population had a high prevalence of hypertension and diabetes mellitus . on the other hand , the results of a large population study on 110 healthy subjects did not show an independent effect of age on the ph parameters ( 6 ) . thus , for clinical purposes , it seems that age generally does not have an important effect on the physiologic parameters of acid reflux . first , in our study , all the healthy volunteers underwent upper endoscopy to exclude asymptomatic esophagitis and hiatal hernia . in two large western studies concerned with the normal ambulatory esophageal ph values ( 5 , 6 ) therefore , they could not exclude the subjects with asymptomatic esophagitis or hiatal hernia . in the present study , we excluded these subjects by performing endoscopy . second , the distribution of gender and age of the healthy volunteers in our study was uniform ( data not shown ) . first , the number of subjects in this study was not large ; this could raise the possibility of a type-2 error . however , to be included in the study , the volunteers were required not to have any clinical evidence of gerd and they were also without endoscopic documentation of reflux esophagitis and hiatal hernia . these facts reduced the number of subjects for the study , so as to render our healthy volunteers as being appropriate . second , although our study population was carefully screened to be healthy and asymptomatic and we excluded the subjects who had reflux esophagitis or hiatal hernia , many of the subjects might have h. pylori infection with or without chronic atrophic gastritis . there is a higher prevalence of h. pylori infection in koreans than in western populations ( 19 ) . mild h. pylori - associated chronic active superficial gastritis had little effect on gastric acid output , whereas severe chronic active gastritis was associated with a lower gastric acid output ( 17 ) . this fact could also explain the lower values of the reflux parameters in our study as compared to the western studies . finally , because this study was performed at 7 medical centers , there would be bias of the reflux parameters among each center . to lessen the bias , we defined a standard method of ambulatory 24-hr esophageal ph monitoring and then we started this study . in addition , the coefficient of variation for the reflux parameters among each center was less than 40% , except the percentage of time the ph was < 4 in the supine positions . the normal values of the ph parameters , as 95th percentiles in 3 previous western studies ( 5 , 6 , 10 ) and in our study , are shown in table 6 . almost all the parameters except the number of reflux episodes were lower in our study than those in the western studies . many factors , including the differences in the age distribution of the control subjects , the real population differences for gastroesophageal reflux and the different incidence of h. pylori infection , could have contributed to these results . in conclusion , our multi - center data were based on 50 healthy volunteers , and these data provides the normal values for esophageal ph monitoring in koreans . however , no database is perfect because of the well - known variability of acid exposure from day to day and the inherent problems with the ph probe ( i.e. , it may get buried in the esophageal mucosa and so miss reflux episodes ) ( 8 , 20 ) . on the basis of our results , these normal esophageal ph values can provide reference data for future clinical and research studies in korea .[/INST]ambulatory 24-hr esophageal ph monitoring is considered the gold standard for diagnosing gastroesophageal reflux disease . the aim of this study was to establish normal values for gastroesophageal acid exposure in healthy koreans . fifty healthy volunteers ( 24 males and 26 females ; mean age , 45 yr ) without reflux symptoms and without reflux esophagitis or hiatal hernia on upper endoscopy underwent ambulatory 24-hr esophageal ph monitoring after esophageal manometry . the 95th percentiles for the reflux parameters were : the percent total time ph < 4 , 3.7% ; the percent upright time ph < 4 , 5.7% ; the percent supine time ph < 4 , 1.0% ; the number of reflux episodes with ph < 4 , 76.5 ; the number of reflux episodes with ph < 4 for > 5 min , 1.5 ; the duration of the longest episode , 12.5 min ; and the composite score , 14.2 . age and gender were not associated with any of the ph parameters . in conclusion , physiological gastroesophageal reflux occurs in healthy koreans . these normal esophageal ph values will provide reference data for clinical and research studies in korea .</s>

SECTION 1. SHORT TITLE. This Act may be cited as the ``Helium Privatization Act of 1997''. SEC. 2. AMENDMENT OF HELIUM ACT. Whenever in this Act an amendment or repeal is expressed in terms of an amendment to, or repeal of, a section or other provision, the reference shall be considered to be made to a section or other provision of the Helium Act (50 U.S.C. 167-167n), as amended by the Helium Privatization Act of 1996 (Public Law 104-273). SEC. 3. DISPOSAL OF FACILITIES. Section 4 is amended by-- (1) striking subsection (c); and (2) redesignating subsection (d) as subsection (c). SEC. 4. SALE OF CRUDE HELIUM. Subsection 6(c) is amended by striking ``--'' and all that follows through ``(2)''. SEC. 5. ELIMINATION OF STOCKPILE. Section 8 is amended to read as follows: ``SEC. 8. ELIMINATION OF STOCKPILE. ``(a) Secretary of Defense.-- ``(1) In general.--Half of the helium reserves owned by the United States on the date of the enactment of the Helium Privatization Act of 1997 shall be placed under the authority of the Secretary of Defense, who shall determine and execute the storage, transportation, and use of helium from the reserves. The Federal Government shall forgive any share of debt owed on these reserves. ``(2) Location of reserves.--The Secretary of Defense may maintain the reserves under the authority of the Secretary of Defense at the site on which they are located on the date of enactment of this Act, or transfer the reserves to another site. In a case in which the Secretary of Defense elects to transfer the reserves, the Secretary shall notify the Secretary of the Interior of the transfer not later than the predetermined date agreed to by the Secretary of Defense and Secretary of the Interior. ``(b) Department of the Interior.-- ``(1) In general.--The remaining half of the helium reserves owned by the United States on the date of the enactment of the Helium Privatization Act of 1997 shall remain under the authority of the Secretary of the Interior. ``(2) Disposal of reserves.-- ``(A) Investment administrator.--In order to dispose of the helium reserves under the authority of the Secretary of the Interior, the Secretary of the Interior shall appoint an Investment Administrator to sell-- ``(i) the helium from the helium reserves; and ``(ii) any production, refining, and marketing assets of the reserves, unless the Secretary of Defense determines that such assets are essential to the transportation or storage needs of the Secretary of Defense. The proceeds from any sales shall be paid to the Treasury of the United States. A percentage of the proceeds, as agreed to by the Secretary of the Interior and the Investment Administrator, shall be used to pay the salary of the Investment Administrator. ``(B) Selection criteria for investment administrator.--Any individual interested in the position of Investment Administrator shall, within a time period to be determined by the Secretary of the Interior-- ``(i) submit in writing to the Secretary of the Interior a plan for disposing of the helium reserves under the authority of the Secretary of the Interior (including any unobligated natural gas reserves and real estate at the helium reserves used in helium refinement and production); and ``(ii) make an oral presentation to the Secretary of the Interior on such plan. ``(C) Interim disposal.--The Secretary of the Interior may determine a price in consultation with the helium industry, and sell helium described in paragraph (1) during the period in which an Investment Administrator has not been selected. ``(c) Discovery of Additional Reserves.--The discovery of additional helium reserves shall not affect the duties of the Secretaries to make sales of helium under this section.''. SEC. 6. REPORT ON HELIUM. (a) National Academy of Sciences Report.--Subsection 15(a) is amended by inserting after ``disposal of helium reserves'' the following: ``under the authority of the Secretary of Defense''. (b) Report to Congress.--Subsection 15(b) is amended-- (1) in paragraph (1) by inserting ``and'' after the semicolon; (2) in paragraph (2) by striking ``; and'' and inserting a period; and (3) by striking paragraph (3).

Helium Privatization Act of 1997 - Amends the Helium Act to repeal requirements for disposal of helium facilities. Revises the formula for price determinations for crude helium sales to eliminate all factors but inflation adjustments. Revises stockpile elimination guidelines to mandate that half the Federal helium reserves be placed under the authority of the Secretary of Defense, who shall determine and implement helium storage, transportation, and use. States that the Federal Government shall forgive any debt owed on such reserves. Retains the remaining Federal helium under the authority of the Secretary of the Interior. Instructs such Secretary to appoint an Investment Administrator to sell the helium reserves and their attendant production, refining, and marketing assets unless the Secretary of Defense determines such assets are essential to Department of Defense transportation or storage needs. Mandates payment of helium sales proceeds to the Treasury, with a percentage of such proceeds paid as salary to the Administrator pursuant to an agreement between the Administrator and the Secretary of the Interior. States that such Administrator shall be selected from individuals who submit and make an oral presentation of a written helium disposal plan (including any unobligated natural gas reserves and real estate used in helium refinement and production). Authorizes the Secretary of the Interior to determine a sales price in consultation with the helium industry, and to sell helium during the period in which no Investment Administrator has been selected. Declares that discovery of additional helium reserves shall not affect the duties of the Secretaries to make helium sales. Narrows solely to reserves under the authority of the Secretary of Defense the scope of a currently mandated National Academy of Sciences study on whether disposal of helium reserves will have a substantial adverse effect on U.S. scientific, technical, biomedical, or national security interests. Repeals the mandate that the Secretary of Defense make recommendations to the Congress on how to avoid potential adverse effects upon such U.S. interests by sales of crude helium reserves.

<s>[INST]SECTION 1. SHORT TITLE. This Act may be cited as the ``Helium Privatization Act of 1997''. SEC. 2. AMENDMENT OF HELIUM ACT. Whenever in this Act an amendment or repeal is expressed in terms of an amendment to, or repeal of, a section or other provision, the reference shall be considered to be made to a section or other provision of the Helium Act (50 U.S.C. 167-167n), as amended by the Helium Privatization Act of 1996 (Public Law 104-273). SEC. 3. DISPOSAL OF FACILITIES. Section 4 is amended by-- (1) striking subsection (c); and (2) redesignating subsection (d) as subsection (c). SEC. 4. SALE OF CRUDE HELIUM. Subsection 6(c) is amended by striking ``--'' and all that follows through ``(2)''. SEC. 5. ELIMINATION OF STOCKPILE. Section 8 is amended to read as follows: ``SEC. 8. ELIMINATION OF STOCKPILE. ``(a) Secretary of Defense.-- ``(1) In general.--Half of the helium reserves owned by the United States on the date of the enactment of the Helium Privatization Act of 1997 shall be placed under the authority of the Secretary of Defense, who shall determine and execute the storage, transportation, and use of helium from the reserves. The Federal Government shall forgive any share of debt owed on these reserves. ``(2) Location of reserves.--The Secretary of Defense may maintain the reserves under the authority of the Secretary of Defense at the site on which they are located on the date of enactment of this Act, or transfer the reserves to another site. In a case in which the Secretary of Defense elects to transfer the reserves, the Secretary shall notify the Secretary of the Interior of the transfer not later than the predetermined date agreed to by the Secretary of Defense and Secretary of the Interior. ``(b) Department of the Interior.-- ``(1) In general.--The remaining half of the helium reserves owned by the United States on the date of the enactment of the Helium Privatization Act of 1997 shall remain under the authority of the Secretary of the Interior. ``(2) Disposal of reserves.-- ``(A) Investment administrator.--In order to dispose of the helium reserves under the authority of the Secretary of the Interior, the Secretary of the Interior shall appoint an Investment Administrator to sell-- ``(i) the helium from the helium reserves; and ``(ii) any production, refining, and marketing assets of the reserves, unless the Secretary of Defense determines that such assets are essential to the transportation or storage needs of the Secretary of Defense. The proceeds from any sales shall be paid to the Treasury of the United States. A percentage of the proceeds, as agreed to by the Secretary of the Interior and the Investment Administrator, shall be used to pay the salary of the Investment Administrator. ``(B) Selection criteria for investment administrator.--Any individual interested in the position of Investment Administrator shall, within a time period to be determined by the Secretary of the Interior-- ``(i) submit in writing to the Secretary of the Interior a plan for disposing of the helium reserves under the authority of the Secretary of the Interior (including any unobligated natural gas reserves and real estate at the helium reserves used in helium refinement and production); and ``(ii) make an oral presentation to the Secretary of the Interior on such plan. ``(C) Interim disposal.--The Secretary of the Interior may determine a price in consultation with the helium industry, and sell helium described in paragraph (1) during the period in which an Investment Administrator has not been selected. ``(c) Discovery of Additional Reserves.--The discovery of additional helium reserves shall not affect the duties of the Secretaries to make sales of helium under this section.''. SEC. 6. REPORT ON HELIUM. (a) National Academy of Sciences Report.--Subsection 15(a) is amended by inserting after ``disposal of helium reserves'' the following: ``under the authority of the Secretary of Defense''. (b) Report to Congress.--Subsection 15(b) is amended-- (1) in paragraph (1) by inserting ``and'' after the semicolon; (2) in paragraph (2) by striking ``; and'' and inserting a period; and (3) by striking paragraph (3).[/INST]Helium Privatization Act of 1997 - Amends the Helium Act to repeal requirements for disposal of helium facilities. Revises the formula for price determinations for crude helium sales to eliminate all factors but inflation adjustments. Revises stockpile elimination guidelines to mandate that half the Federal helium reserves be placed under the authority of the Secretary of Defense, who shall determine and implement helium storage, transportation, and use. States that the Federal Government shall forgive any debt owed on such reserves. Retains the remaining Federal helium under the authority of the Secretary of the Interior. Instructs such Secretary to appoint an Investment Administrator to sell the helium reserves and their attendant production, refining, and marketing assets unless the Secretary of Defense determines such assets are essential to Department of Defense transportation or storage needs. Mandates payment of helium sales proceeds to the Treasury, with a percentage of such proceeds paid as salary to the Administrator pursuant to an agreement between the Administrator and the Secretary of the Interior. States that such Administrator shall be selected from individuals who submit and make an oral presentation of a written helium disposal plan (including any unobligated natural gas reserves and real estate used in helium refinement and production). Authorizes the Secretary of the Interior to determine a sales price in consultation with the helium industry, and to sell helium during the period in which no Investment Administrator has been selected. Declares that discovery of additional helium reserves shall not affect the duties of the Secretaries to make helium sales. Narrows solely to reserves under the authority of the Secretary of Defense the scope of a currently mandated National Academy of Sciences study on whether disposal of helium reserves will have a substantial adverse effect on U.S. scientific, technical, biomedical, or national security interests. Repeals the mandate that the Secretary of Defense make recommendations to the Congress on how to avoid potential adverse effects upon such U.S. interests by sales of crude helium reserves.</s>

successful local anesthesia is important for pain control . fear and anxiety associated with endodontic treatment it was found that the anesthesia of mandibular molars with irreversible pulpitis was more difficult than the healthy pulps . the reason for difficulty in pulpal anesthesia of teeth with irreversible pulpitis were described in previous studies . however in mandibular teeth due to the thickness of buccal cortical bone buccal infiltration technique is not as effective as nerve block techniques . pulpal anesthesia of posterior mandibular teeth with irreversible pulpitis is most frequently achieved by the inferior alveolar nerve block ( ianb ) injection technique . the failure rate is between 44% and 81% as was described in various clinical studies . due to the failure rate of ianb when the conventional ianb fails , supplemental injections ( with different techniques and/or types of anesthetic ) are frequently required in patients with irreversible pulpitis to achieve complete anesthesia . supplemental techniques such as the intraosseous , intraligamentary , and infiltration injections technique have been studied to raise the anesthetic success . the intraosseous injection requires special equipment for drilling the cortical bone and injecting the anesthetic solution thus is not a preferred technique . . it would be useful to have results produced by these techniques be achieved with simpler options such as infiltration technique . infiltration injection increases the success of ianb injection and is used very often as the supplemental injection technique . the present systematic review compared and evaluated the anesthetic success rates of ianb injection technique alone or along with supplemental infiltration ( si ) technique when used for pulpal anesthesia of mandibular posterior teeth with irreversible pulpitis . the search was done in pubmed and medline ( twease ) and google search engine . ianb and irreversible pulpitis , infiltration in mandibular teeth and irreversible pulpitis . the search was done till march 2014 . the inclusion and exclusion criteria for selecting the studies for the systematic review were listed in table 1 . the abstract of 159 studies were then assessed depending on the predetermined criteria , to identify 14 relevant studies and 145 studies were excluded . the full texts of the 14 relevant studies were further analyzed and found only 6 studies were eligible , which were meeting the defined specific criteria . the structured question was is there any difference in the anesthetic success rates of ianb injection technique used alone compared with the combination of ianb and si injection technique when used for pulpal anesthesia of mandibular teeth with irreversible pulpitis . the pico analysis was performed where the population was represented by patients with irreversible pulpitis in posterior mandibular teeth . the primary outcome was a percentage of successful pulpal anesthesia in the block alone or along with the si technique with the help of heft parker visual analog scale ( hp - vas ) method while performing the endodontic procedure . hp - vas with a 170-mm line marked with various terms describing the levels of pain was used for this purpose . the millimeter marks were removed from the scale , and the scale was divided into four categories : no pain corresponded to 0 mm ; faint , weak , or mild pain corresponded to 0 - 54 mm ; moderate pain 55 - 114 mm ; and strong , intense , and maximum possible study design of the included studies the list of excluded studies with reason for exclusion was shown in table 3 . studies with reason for exclusion the comparison of percentage of patients with successful anesthesia with ianb alone and si technique ( no pain or weak / mild pain during endodontic access preparation and instrumentation ) was presented in table 4 . the comparison of percentage of patients with successful anesthesia with ianb ( block ) and ianb and si inferior alveolar nerve block alone gave 14 - 39% success rate . the difficulty regarding adequate pain control in the posterior region of the mandible during dental procedures has been reported . the reduced efficacy of ianb has been associated with various factors such as the thickness of cortical bone , overlying soft tissue and accessory innervations . success rate of ianb in an uninflamed pulp was reported to be 70% compared with 30% in patients with irreversible pulpitis . it was also reported that the failure of local anesthesia in patients with irreversible pulpitis was found to be 8 times more with respect to normal patients . thus , the present study was undertaken to compare the success rates of ianb alone or along with the si technique in irreversible pulpitis . first , the inflamed tissue has a lowered ph as a result of which the amount of the base form of the anesthetic required to go through the nerve sheath and membrane has reduced . this leads to decreased ionized form of the anesthetic within the nerve with resultant decreased anesthesia . second , altered resting potentials and lowered thresholds of excitability of the nerves in the inflamed tissue . as a result of lowered threshold of excitability of these nerves , third , there were anesthetic resistant sodium channels and upregulation of sodium channels in pulp with irreversible pulpitis . the patients in the included studies of the review were actively experiencing pain in mandibular posterior teeth and were diagnosed with irreversible pulpitis . the subject was asked to rate the pain before the treatment and during the treatment using a hp - vas . profound lip numbness was the subjective criteria selected for the inclusion of the subjects in all the studies . lip numbness was used as subjective criteria for the inclusion of the subjects in the study . it should be noted that all the patients included in the study had subjective symptoms of lip numbness , but the anesthesia was not successful in all cases . patient 's age , gender , posterior tooth type , initial pain in the included studies were not significantly different between the two groups . furthermore , patients included were not premedicated , had no systemic conditions such as diabetes , heart disease , high blood pressure . therefore , it can be assumed that the results of this study are not affected by these factors as a result of which the two groups can be compared on their respective anesthetic success . in all the selected studies , anesthetic response of the patient was taken 15 min after ianb and 5 min after the si as this time period was previously reported to obtain complete anesthesia . the hp - vas was used in the included studies to rate the pain to measure the degree of pulpal anesthesia . however , two methods have been used to assess the efficacy of local anesthetic injections in previous studies . some investigators have used pulp sensibility tests such as electric pulp tester ( ept ) or the cold test , whereas others have used the hp - vas . hp - vas was selected in the inclusion criteria of the review for measuring pain level . found in their study that 42% of the patient who received anesthesia despite giving a negative response to ept experienced pain during treatment . various methods have been used for assessing pulpal anesthesia bjorn was the first to correlate a negative response to the maximum output of electrical pulp stimulation to painless dental treatment . however , negative response to ept does not produce profound anesthesia . also , lip numbness is not the indication of pulpal anesthesia . therefore , the preparation of access cavity and extirpation of pulp was used to measure effectively the success of pulpal anesthesia using hp - vas . randomization of patients in the two groups and blinding of the anesthetic agent was performed to eliminate any bias . the anesthetic success was clinically evident with si injection technique as compared to ianb injection technique , but was not statistically significant in the studies .

aim : to systematically review the anesthetic success rates of inferior alveolar nerve block ( ianb ) injection technique alone with that of combination of ianb and supplemental infiltration ( si ) technique when used for pulpal anesthesia of mandibular posterior teeth with irreversible pulpitis during endodontic treatment.settings and design : the study follows a longitudinal study design involving original research.materials and methods : electronic databases were systematically searched for randomized controlled clinical studies . studies were selected by predefined inclusion and exclusion criteria.statistical analysis used and result : the statistical analysis used was based on the results of the original research . all the included studies showed that there is the difference in the values comparing the two techniques , but the data are not statistically significantly different.conclusion:based on this review , the better anesthetic efficacy of the si was observed .

<s>[INST]successful local anesthesia is important for pain control . fear and anxiety associated with endodontic treatment it was found that the anesthesia of mandibular molars with irreversible pulpitis was more difficult than the healthy pulps . the reason for difficulty in pulpal anesthesia of teeth with irreversible pulpitis were described in previous studies . however in mandibular teeth due to the thickness of buccal cortical bone buccal infiltration technique is not as effective as nerve block techniques . pulpal anesthesia of posterior mandibular teeth with irreversible pulpitis is most frequently achieved by the inferior alveolar nerve block ( ianb ) injection technique . the failure rate is between 44% and 81% as was described in various clinical studies . due to the failure rate of ianb when the conventional ianb fails , supplemental injections ( with different techniques and/or types of anesthetic ) are frequently required in patients with irreversible pulpitis to achieve complete anesthesia . supplemental techniques such as the intraosseous , intraligamentary , and infiltration injections technique have been studied to raise the anesthetic success . the intraosseous injection requires special equipment for drilling the cortical bone and injecting the anesthetic solution thus is not a preferred technique . . it would be useful to have results produced by these techniques be achieved with simpler options such as infiltration technique . infiltration injection increases the success of ianb injection and is used very often as the supplemental injection technique . the present systematic review compared and evaluated the anesthetic success rates of ianb injection technique alone or along with supplemental infiltration ( si ) technique when used for pulpal anesthesia of mandibular posterior teeth with irreversible pulpitis . the search was done in pubmed and medline ( twease ) and google search engine . ianb and irreversible pulpitis , infiltration in mandibular teeth and irreversible pulpitis . the search was done till march 2014 . the inclusion and exclusion criteria for selecting the studies for the systematic review were listed in table 1 . the abstract of 159 studies were then assessed depending on the predetermined criteria , to identify 14 relevant studies and 145 studies were excluded . the full texts of the 14 relevant studies were further analyzed and found only 6 studies were eligible , which were meeting the defined specific criteria . the structured question was is there any difference in the anesthetic success rates of ianb injection technique used alone compared with the combination of ianb and si injection technique when used for pulpal anesthesia of mandibular teeth with irreversible pulpitis . the pico analysis was performed where the population was represented by patients with irreversible pulpitis in posterior mandibular teeth . the primary outcome was a percentage of successful pulpal anesthesia in the block alone or along with the si technique with the help of heft parker visual analog scale ( hp - vas ) method while performing the endodontic procedure . hp - vas with a 170-mm line marked with various terms describing the levels of pain was used for this purpose . the millimeter marks were removed from the scale , and the scale was divided into four categories : no pain corresponded to 0 mm ; faint , weak , or mild pain corresponded to 0 - 54 mm ; moderate pain 55 - 114 mm ; and strong , intense , and maximum possible study design of the included studies the list of excluded studies with reason for exclusion was shown in table 3 . studies with reason for exclusion the comparison of percentage of patients with successful anesthesia with ianb alone and si technique ( no pain or weak / mild pain during endodontic access preparation and instrumentation ) was presented in table 4 . the comparison of percentage of patients with successful anesthesia with ianb ( block ) and ianb and si inferior alveolar nerve block alone gave 14 - 39% success rate . the difficulty regarding adequate pain control in the posterior region of the mandible during dental procedures has been reported . the reduced efficacy of ianb has been associated with various factors such as the thickness of cortical bone , overlying soft tissue and accessory innervations . success rate of ianb in an uninflamed pulp was reported to be 70% compared with 30% in patients with irreversible pulpitis . it was also reported that the failure of local anesthesia in patients with irreversible pulpitis was found to be 8 times more with respect to normal patients . thus , the present study was undertaken to compare the success rates of ianb alone or along with the si technique in irreversible pulpitis . first , the inflamed tissue has a lowered ph as a result of which the amount of the base form of the anesthetic required to go through the nerve sheath and membrane has reduced . this leads to decreased ionized form of the anesthetic within the nerve with resultant decreased anesthesia . second , altered resting potentials and lowered thresholds of excitability of the nerves in the inflamed tissue . as a result of lowered threshold of excitability of these nerves , third , there were anesthetic resistant sodium channels and upregulation of sodium channels in pulp with irreversible pulpitis . the patients in the included studies of the review were actively experiencing pain in mandibular posterior teeth and were diagnosed with irreversible pulpitis . the subject was asked to rate the pain before the treatment and during the treatment using a hp - vas . profound lip numbness was the subjective criteria selected for the inclusion of the subjects in all the studies . lip numbness was used as subjective criteria for the inclusion of the subjects in the study . it should be noted that all the patients included in the study had subjective symptoms of lip numbness , but the anesthesia was not successful in all cases . patient 's age , gender , posterior tooth type , initial pain in the included studies were not significantly different between the two groups . furthermore , patients included were not premedicated , had no systemic conditions such as diabetes , heart disease , high blood pressure . therefore , it can be assumed that the results of this study are not affected by these factors as a result of which the two groups can be compared on their respective anesthetic success . in all the selected studies , anesthetic response of the patient was taken 15 min after ianb and 5 min after the si as this time period was previously reported to obtain complete anesthesia . the hp - vas was used in the included studies to rate the pain to measure the degree of pulpal anesthesia . however , two methods have been used to assess the efficacy of local anesthetic injections in previous studies . some investigators have used pulp sensibility tests such as electric pulp tester ( ept ) or the cold test , whereas others have used the hp - vas . hp - vas was selected in the inclusion criteria of the review for measuring pain level . found in their study that 42% of the patient who received anesthesia despite giving a negative response to ept experienced pain during treatment . various methods have been used for assessing pulpal anesthesia bjorn was the first to correlate a negative response to the maximum output of electrical pulp stimulation to painless dental treatment . however , negative response to ept does not produce profound anesthesia . also , lip numbness is not the indication of pulpal anesthesia . therefore , the preparation of access cavity and extirpation of pulp was used to measure effectively the success of pulpal anesthesia using hp - vas . randomization of patients in the two groups and blinding of the anesthetic agent was performed to eliminate any bias . the anesthetic success was clinically evident with si injection technique as compared to ianb injection technique , but was not statistically significant in the studies .[/INST]aim : to systematically review the anesthetic success rates of inferior alveolar nerve block ( ianb ) injection technique alone with that of combination of ianb and supplemental infiltration ( si ) technique when used for pulpal anesthesia of mandibular posterior teeth with irreversible pulpitis during endodontic treatment.settings and design : the study follows a longitudinal study design involving original research.materials and methods : electronic databases were systematically searched for randomized controlled clinical studies . studies were selected by predefined inclusion and exclusion criteria.statistical analysis used and result : the statistical analysis used was based on the results of the original research . all the included studies showed that there is the difference in the values comparing the two techniques , but the data are not statistically significantly different.conclusion:based on this review , the better anesthetic efficacy of the si was observed .</s>

SECTION 1. SHORT TITLE; TABLE OF CONTENTS. (a) Short Title.--This Act may be cited as the ``Border Reinforcement and Violence Reduction Act of 2009''. (b) Table of Contents.--The table of contents for this Act is as follows: Sec. 1. Short title; table of contents. TITLE I--BORDER LAW ENFORCEMENT ENHANCEMENT Sec. 101. Short title. Sec. 102. Findings. Sec. 103. Border relief grant program. Sec. 104. Authorization of appropriations. Sec. 105. Enforcement of Federal immigration law. Sec. 106. Regulations. TITLE II--SOUTHWEST BORDER VIOLENCE REDUCTION Sec. 201. Short title. Sec. 202. Project Gunrunner. Sec. 203. Enhanced international cooperation. Sec. 204. Operation Armas Cruzadas. Sec. 205. Vehicle inspections. Sec. 206. Affirmation of Second Amendment. TITLE I--BORDER LAW ENFORCEMENT ENHANCEMENT SECTION 101. SHORT TITLE. This Act may be cited as the ``Border Law Enforcement Enhancement Act of 2009''. SEC. 102. FINDINGS. Congress finds the following: (1) It is the obligation of the Federal Government to adequately secure the borders of the United States and prevent the flow of undocumented persons and illegal drugs into the United States in order to better secure such borders. (2) Border communities continue to incur significant costs due to the lack of adequate border security. A 2001 study by the United States-Mexico Border Counties Coalition found that law enforcement and criminal justice expenses associated with illegal immigration exceed $89,000,000 annually for the Southwest border counties. (3) In August 2005, the States of New Mexico and Arizona declared states of emergency in order to provide local law enforcement immediate assistance in addressing criminal activity along the Southwest border. (4) While the Federal Government provides States and localities assistance in covering costs related to the detention of certain criminal aliens and the prosecution of Federal drug cases, local law enforcement along the border are provided no assistance in covering such expenses and must use their limited resources to combat drug trafficking, human smuggling, kidnappings, the destruction of private property, and other border security related crimes. (5) The United States shares 5,525 miles of border with Canada and 1,989 miles with Mexico. Many of the local law enforcement agencies located along the border are small, rural departments charged with patrolling large areas of land. Counties along the Southwest United States-Mexico border are some of the poorest in the country and lack the financial resources to cover the additional costs associated with border security, narcoterrorism, and other border-related crimes. (6) Federal assistance is required to help local law enforcement operating along the border address the unique challenges that arise as a result of their proximity to an international border and the lack of overall border security in the region. SEC. 103. BORDER RELIEF GRANT PROGRAM. (a) In General.--From amounts made available under section 104, the Secretary of Homeland Security may make border security grants to-- (1) sheriffs' offices of counties any part of which is within 25 miles of the southern border of the United States; and (2) police departments serving a city, town, or other political subdivision in a county any part of which is within 25 miles of the southern border of the United States (including tribal police departments serving a community any part of which is within 25 miles of such border). (b) Use of Funds.-- (1) In general.--Grant funds received under subsection (a) may be used for the following activities: (A) To conduct law enforcement operations to enforce criminal laws, prevent and punish criminal activity, and protect the lives, property, and security of the people within the jurisdiction of the grant recipient. (B) To transfer to appropriate Federal law enforcement officials aliens unlawfully present in the United States who detained or in the custody of the grant recipient. (C) To enforce State and Federal laws relating to securing the border and enforce other State and Federal criminal laws. (2) Payment of costs.--Use of funds under paragraph (1) shall include payment for costs of-- (A) hiring, equipping, training, and otherwise controlling the operations and deployment of law enforcement officials engaged in duties described in paragraph (1), as well as the costs of paying overtime to such officials; and (B) detaining, housing, and transporting aliens who are unlawfully present in the United States and who are taken into custody by the grant recipient, until such aliens are transferred to appropriate Federal law enforcement officials. (3) Detention facilities.--In accordance with paragraph (2)(B), grant funds received under subsection (a) may be used for the construction, maintenance, and operation of detention facilities to detain aliens who are unlawfully present in the United States, except that not more than 20 percent of such funds may be used for the construction or renovation of detention or similar facilities. (c) Application.-- (1) In general.--Each eligible law enforcement agency seeking a grant under this section shall submit to the Secretary of Homeland Security an application at such time, in such manner, and accompanied by such information as the Secretary may require. (2) Contents.--Each application submitted pursuant to paragraph (1) shall-- (A) describe the activities for which assistance under this section is sought; and (B) provide such additional assurances as the Secretary of Homeland Security determines to be essential to ensure compliance with the requirements of this section. SEC. 104. AUTHORIZATION OF APPROPRIATIONS. There is authorized to be appropriated to the Secretary of Homeland Security to carry out this title $150,000,000 for fiscal year 2010 and each succeeding fiscal year. SEC. 105. ENFORCEMENT OF FEDERAL IMMIGRATION LAW. Nothing in this title shall be construed to authorize State or local law enforcement agencies or their officers to exercise Federal immigration law enforcement authority. SEC. 106. REGULATIONS. Not later than 90 days after the date of the enactment of this title, the Secretary of Homeland Security shall issue regulations to carry out this title. TITLE II--SOUTHWEST BORDER VIOLENCE REDUCTION SEC. 201. SHORT TITLE. This Act may be cited as the ``Southwest Border Violence Reduction Act of 2009''. SEC. 202. PROJECT GUNRUNNER. (a) In General.--The Attorney General shall dedicate and expand the resources provided for the Project Gunrunner initiative of the Bureau of Alcohol, Tobacco, Firearms, and Explosives to identify, investigate, and prosecute individuals involved in the trafficking of firearms across the international border between the United States and Mexico. (b) Activities.--In carrying out this section, the Attorney General shall-- (1) assign additional agents of the Bureau of Alcohol, Tobacco, Firearms, and Explosives to the area of the United States adjacent to the international border between the United States and Mexico to support the expansion of Project Gunrunner teams; (2) establish not fewer than 1 Project Gunrunner team in each State along the international border between the United States and Mexico; and (3) coordinate with the heads of other relevant Federal law enforcement agencies and State and local law enforcement agencies to address firearms trafficking in a comprehensive manner. (c) Additional Staff.--The Attorney General may hire Bureau of Alcohol, Tobacco, Firearms, and Explosives agents for, and otherwise expend additional resources needed to adequately support, Project Gunrunner. (d) Authorization of Appropriations.--There is authorized to be appropriated $15,000,000 for each of fiscal years 2010 and 2011 to carry out this section. SEC. 203. ENHANCED INTERNATIONAL COOPERATION. (a) In General.--The Attorney General, in cooperation with the Secretary of State, shall-- (1) assign agents of the Bureau of Alcohol, Tobacco, Firearms, and Explosives to the United States mission in Mexico, to work with Mexican law enforcement agencies in conducting investigations relating to firearms trafficking and other criminal enterprises; (2) provide the equipment and technological resources necessary to support investigations and to trace firearms recovered in Mexico; and (3) support the training of Mexican law enforcement officers in serial number restoration techniques, canine explosive detection, and antitrafficking tactics. (b) Authorization of Appropriations.--There is authorized to be appropriated $9,500,000 for each of fiscal years 2010 and 2011 to carry out this section. SEC. 204. OPERATION ARMAS CRUZADAS. (a) In General.--In accordance with subsection (b), the Secretary of Homeland Security shall dedicate and expand the resources provided for Operation Armas Cruzadas of United States Immigration and Customs Enforcement (ICE) to identify, investigate, and prosecute individuals involved in the trafficking and smuggling of firearms and in other unlawful activities across the international border between the United States and Mexico. (b) Resources.--To achieve the goal described in subsection (a), the Secretary of Homeland Security shall-- (1) increase the number of ICE agents assigned to Operation Armas Cruzadas over the number of such agents who are so assigned as of the date of the enactment of this section; (2) increase the number of Border Enforcement Security Task Force (BEST) teams stationed along the border over the number of such teams so stationed as of the date of the enactment of this section; and (3) coordinate with the heads of other relevant Federal, State, and local law enforcement agencies to address firearms trafficking in a comprehensive manner. (c) Authorization of Appropriations.--There is authorized to be appropriated $15,000,000 for each of fiscal years 2010 and 2011 to carry out this section. SEC. 205. VEHICLE INSPECTIONS. The Secretary of Homeland Security shall coordinate with the heads of other relevant Federal, State, and local law enforcement agencies along the border to develop a comprehensive and strategic plan for the inspection of vehicles heading into Mexico. SEC. 206. AFFIRMATION OF SECOND AMENDMENT. Nothing in this title shall be construed to restrict or limit the use and ownership of legal handguns and firearms by law-abiding gun owners.

Border Reinforcement and Violence Reduction Act of 2009 - Authorizes and directs the Attorney General and the Secretary of Homeland Security to expand resources, make grants, and take other actions to protect U.S. citizens and property and to identify, investigate, and prosecute firearms trafficking and other unlawful activities along the U.S.-Mexican border. Border Law Enforcement Enhancement Act of 2009 - Authorizes the Secretary to make border security grants to local sheriffs' offices and police departments within 25 miles of the southern border of the United States. Allows grant funds to be used to pay for law enforcement operations along the U.S.-Mexican border, the costs of training and equipping law enforcement personnel, transporting illegal aliens to U.S. custody, and building detention facilities. Southwest Border Violence Reduction Act of 2009 - Directs the Attorney General to: (1) to dedicate and expand resources for the Project Gunrunner initiative of the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) to identify, investigate, and prosecute firearms trafficking across the U.S.-Mexican border; and (2) provide ATF agents, equipment, and training to assist Mexican law enforcement officers in combating firearms trafficking and other criminal enterprises. Directs the Secretary to: (1) dedicate and expand resources for the Operation Armas Cruzadas of the U.S. Immigration and Customs Enforcement to identify, investigate, and prosecute firearms trafficking, smuggling, and other unlawful activities across the U.S.-Mexican border; and (2) coordinate with other federal, state, and local law enforcement agencies to develop a comprehensive and strategic plan to inspect vehicles heading into Mexico.

<s>[INST]SECTION 1. SHORT TITLE; TABLE OF CONTENTS. (a) Short Title.--This Act may be cited as the ``Border Reinforcement and Violence Reduction Act of 2009''. (b) Table of Contents.--The table of contents for this Act is as follows: Sec. 1. Short title; table of contents. TITLE I--BORDER LAW ENFORCEMENT ENHANCEMENT Sec. 101. Short title. Sec. 102. Findings. Sec. 103. Border relief grant program. Sec. 104. Authorization of appropriations. Sec. 105. Enforcement of Federal immigration law. Sec. 106. Regulations. TITLE II--SOUTHWEST BORDER VIOLENCE REDUCTION Sec. 201. Short title. Sec. 202. Project Gunrunner. Sec. 203. Enhanced international cooperation. Sec. 204. Operation Armas Cruzadas. Sec. 205. Vehicle inspections. Sec. 206. Affirmation of Second Amendment. TITLE I--BORDER LAW ENFORCEMENT ENHANCEMENT SECTION 101. SHORT TITLE. This Act may be cited as the ``Border Law Enforcement Enhancement Act of 2009''. SEC. 102. FINDINGS. Congress finds the following: (1) It is the obligation of the Federal Government to adequately secure the borders of the United States and prevent the flow of undocumented persons and illegal drugs into the United States in order to better secure such borders. (2) Border communities continue to incur significant costs due to the lack of adequate border security. A 2001 study by the United States-Mexico Border Counties Coalition found that law enforcement and criminal justice expenses associated with illegal immigration exceed $89,000,000 annually for the Southwest border counties. (3) In August 2005, the States of New Mexico and Arizona declared states of emergency in order to provide local law enforcement immediate assistance in addressing criminal activity along the Southwest border. (4) While the Federal Government provides States and localities assistance in covering costs related to the detention of certain criminal aliens and the prosecution of Federal drug cases, local law enforcement along the border are provided no assistance in covering such expenses and must use their limited resources to combat drug trafficking, human smuggling, kidnappings, the destruction of private property, and other border security related crimes. (5) The United States shares 5,525 miles of border with Canada and 1,989 miles with Mexico. Many of the local law enforcement agencies located along the border are small, rural departments charged with patrolling large areas of land. Counties along the Southwest United States-Mexico border are some of the poorest in the country and lack the financial resources to cover the additional costs associated with border security, narcoterrorism, and other border-related crimes. (6) Federal assistance is required to help local law enforcement operating along the border address the unique challenges that arise as a result of their proximity to an international border and the lack of overall border security in the region. SEC. 103. BORDER RELIEF GRANT PROGRAM. (a) In General.--From amounts made available under section 104, the Secretary of Homeland Security may make border security grants to-- (1) sheriffs' offices of counties any part of which is within 25 miles of the southern border of the United States; and (2) police departments serving a city, town, or other political subdivision in a county any part of which is within 25 miles of the southern border of the United States (including tribal police departments serving a community any part of which is within 25 miles of such border). (b) Use of Funds.-- (1) In general.--Grant funds received under subsection (a) may be used for the following activities: (A) To conduct law enforcement operations to enforce criminal laws, prevent and punish criminal activity, and protect the lives, property, and security of the people within the jurisdiction of the grant recipient. (B) To transfer to appropriate Federal law enforcement officials aliens unlawfully present in the United States who detained or in the custody of the grant recipient. (C) To enforce State and Federal laws relating to securing the border and enforce other State and Federal criminal laws. (2) Payment of costs.--Use of funds under paragraph (1) shall include payment for costs of-- (A) hiring, equipping, training, and otherwise controlling the operations and deployment of law enforcement officials engaged in duties described in paragraph (1), as well as the costs of paying overtime to such officials; and (B) detaining, housing, and transporting aliens who are unlawfully present in the United States and who are taken into custody by the grant recipient, until such aliens are transferred to appropriate Federal law enforcement officials. (3) Detention facilities.--In accordance with paragraph (2)(B), grant funds received under subsection (a) may be used for the construction, maintenance, and operation of detention facilities to detain aliens who are unlawfully present in the United States, except that not more than 20 percent of such funds may be used for the construction or renovation of detention or similar facilities. (c) Application.-- (1) In general.--Each eligible law enforcement agency seeking a grant under this section shall submit to the Secretary of Homeland Security an application at such time, in such manner, and accompanied by such information as the Secretary may require. (2) Contents.--Each application submitted pursuant to paragraph (1) shall-- (A) describe the activities for which assistance under this section is sought; and (B) provide such additional assurances as the Secretary of Homeland Security determines to be essential to ensure compliance with the requirements of this section. SEC. 104. AUTHORIZATION OF APPROPRIATIONS. There is authorized to be appropriated to the Secretary of Homeland Security to carry out this title $150,000,000 for fiscal year 2010 and each succeeding fiscal year. SEC. 105. ENFORCEMENT OF FEDERAL IMMIGRATION LAW. Nothing in this title shall be construed to authorize State or local law enforcement agencies or their officers to exercise Federal immigration law enforcement authority. SEC. 106. REGULATIONS. Not later than 90 days after the date of the enactment of this title, the Secretary of Homeland Security shall issue regulations to carry out this title. TITLE II--SOUTHWEST BORDER VIOLENCE REDUCTION SEC. 201. SHORT TITLE. This Act may be cited as the ``Southwest Border Violence Reduction Act of 2009''. SEC. 202. PROJECT GUNRUNNER. (a) In General.--The Attorney General shall dedicate and expand the resources provided for the Project Gunrunner initiative of the Bureau of Alcohol, Tobacco, Firearms, and Explosives to identify, investigate, and prosecute individuals involved in the trafficking of firearms across the international border between the United States and Mexico. (b) Activities.--In carrying out this section, the Attorney General shall-- (1) assign additional agents of the Bureau of Alcohol, Tobacco, Firearms, and Explosives to the area of the United States adjacent to the international border between the United States and Mexico to support the expansion of Project Gunrunner teams; (2) establish not fewer than 1 Project Gunrunner team in each State along the international border between the United States and Mexico; and (3) coordinate with the heads of other relevant Federal law enforcement agencies and State and local law enforcement agencies to address firearms trafficking in a comprehensive manner. (c) Additional Staff.--The Attorney General may hire Bureau of Alcohol, Tobacco, Firearms, and Explosives agents for, and otherwise expend additional resources needed to adequately support, Project Gunrunner. (d) Authorization of Appropriations.--There is authorized to be appropriated $15,000,000 for each of fiscal years 2010 and 2011 to carry out this section. SEC. 203. ENHANCED INTERNATIONAL COOPERATION. (a) In General.--The Attorney General, in cooperation with the Secretary of State, shall-- (1) assign agents of the Bureau of Alcohol, Tobacco, Firearms, and Explosives to the United States mission in Mexico, to work with Mexican law enforcement agencies in conducting investigations relating to firearms trafficking and other criminal enterprises; (2) provide the equipment and technological resources necessary to support investigations and to trace firearms recovered in Mexico; and (3) support the training of Mexican law enforcement officers in serial number restoration techniques, canine explosive detection, and antitrafficking tactics. (b) Authorization of Appropriations.--There is authorized to be appropriated $9,500,000 for each of fiscal years 2010 and 2011 to carry out this section. SEC. 204. OPERATION ARMAS CRUZADAS. (a) In General.--In accordance with subsection (b), the Secretary of Homeland Security shall dedicate and expand the resources provided for Operation Armas Cruzadas of United States Immigration and Customs Enforcement (ICE) to identify, investigate, and prosecute individuals involved in the trafficking and smuggling of firearms and in other unlawful activities across the international border between the United States and Mexico. (b) Resources.--To achieve the goal described in subsection (a), the Secretary of Homeland Security shall-- (1) increase the number of ICE agents assigned to Operation Armas Cruzadas over the number of such agents who are so assigned as of the date of the enactment of this section; (2) increase the number of Border Enforcement Security Task Force (BEST) teams stationed along the border over the number of such teams so stationed as of the date of the enactment of this section; and (3) coordinate with the heads of other relevant Federal, State, and local law enforcement agencies to address firearms trafficking in a comprehensive manner. (c) Authorization of Appropriations.--There is authorized to be appropriated $15,000,000 for each of fiscal years 2010 and 2011 to carry out this section. SEC. 205. VEHICLE INSPECTIONS. The Secretary of Homeland Security shall coordinate with the heads of other relevant Federal, State, and local law enforcement agencies along the border to develop a comprehensive and strategic plan for the inspection of vehicles heading into Mexico. SEC. 206. AFFIRMATION OF SECOND AMENDMENT. Nothing in this title shall be construed to restrict or limit the use and ownership of legal handguns and firearms by law-abiding gun owners.[/INST]Border Reinforcement and Violence Reduction Act of 2009 - Authorizes and directs the Attorney General and the Secretary of Homeland Security to expand resources, make grants, and take other actions to protect U.S. citizens and property and to identify, investigate, and prosecute firearms trafficking and other unlawful activities along the U.S.-Mexican border. Border Law Enforcement Enhancement Act of 2009 - Authorizes the Secretary to make border security grants to local sheriffs' offices and police departments within 25 miles of the southern border of the United States. Allows grant funds to be used to pay for law enforcement operations along the U.S.-Mexican border, the costs of training and equipping law enforcement personnel, transporting illegal aliens to U.S. custody, and building detention facilities. Southwest Border Violence Reduction Act of 2009 - Directs the Attorney General to: (1) to dedicate and expand resources for the Project Gunrunner initiative of the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) to identify, investigate, and prosecute firearms trafficking across the U.S.-Mexican border; and (2) provide ATF agents, equipment, and training to assist Mexican law enforcement officers in combating firearms trafficking and other criminal enterprises. Directs the Secretary to: (1) dedicate and expand resources for the Operation Armas Cruzadas of the U.S. Immigration and Customs Enforcement to identify, investigate, and prosecute firearms trafficking, smuggling, and other unlawful activities across the U.S.-Mexican border; and (2) coordinate with other federal, state, and local law enforcement agencies to develop a comprehensive and strategic plan to inspect vehicles heading into Mexico.</s>

SECTION 1. SHORT TITLE. This Act may be cited as the ``Teach Safe Relationships Act of 2015''. SEC. 2. FUND FOR THE IMPROVEMENT OF EDUCATION. Part D of title V of the Elementary and Secondary Education Act of 1965 (20 U.S.C. 7241 et seq.) is amended by adding at the end the following: ``Subpart 22--Providing Safe Relationship Behavior Education and Training ``SEC. 5621. SHORT TITLE. ``This subpart may be cited as the `Teach Safe Relationships Act of 2015'. ``SEC. 5622. STATEMENT OF PURPOSE. ``It is the purpose of this subpart: ``(1) To help ensure that all students receive evidence- informed safe relationship behavior education and training, including education and training regarding the prevention of teen and adolescent dating violence or relationship abuse, domestic abuse, and sexual violence and harassment. ``(2) To promote safe and healthy relationships between and among students. ``(3) To help students and school faculty and staff to develop healthy and respectful attitudes and insights necessary for students to understand themselves in the context of relationships with others and with society. ``(4) To provide financial assistance to support local educational agencies in meeting the requirements of title IX of the Educational Amendments of 1972. ``SEC. 5623. FINDINGS. ``Congress finds the following: ``(1) Educating students about safe relationship behavior will aid in the prevention of unsafe dating practices, including dating violence, sexual assault, and stalking. ``(2) The Violence Against Women Act of 1994 (42 U.S.C. 13925 et seq.) included programs to develop and implement prevention and intervention policies in middle and high schools, including appropriate responses to, and identification and referral procedures for, students who are experiencing or perpetrating domestic violence, dating violence, sexual assault, sexual harassment, stalking, or sex trafficking. ``(3) Schools can play an important role in providing students with a knowledge base that may allow students to make informed decisions and form a healthy lifestyle. ``(4) According to the Department of Justice, there is an average of 293,066 victims (age 12 or older) of rape and sexual assault each year. ``(5) Young women between the ages of 16 and 24 experience the highest rate of intimate partner violence. According to one national study, 29 percent of the young women surveyed who had ever been in a relationship said they had been pressured to have sex or to engage in sexual activity they did not want. ``(6) From 1997 to 2013, females ages 18 to 24 consistently experienced higher rates of rape and sexual assault than females in other age brackets. ``(7) Partners of all genders and those in same-sex relationships also experience dating violence. A 2013 survey of grade school students found that 43 percent of lesbian, gay, bisexual, and transgender youth reported being victims of physical dating violence, compared to 29 percent of heterosexual youth. ``(8) Experiencing dating violence is associated with an increase in sexual risk-taking behaviors, health risks, and is associated with adolescent and unintended pregnancy. ``(9) Teaching and learning practices in the United States frequently do not address safe relationship behavior education and training, for example-- ``(A) sex education curriculum should address emotional relationship health; ``(B) sexual harassment undermines the ability of schools to provide safe and equitable learning or workplace environments; and ``(C) classroom textbooks and educational materials do not sufficiently reflect the promotion of safe and healthy relationships. ``(10) Efforts to improve the quality of public education must also include efforts to ensure programs for safe relationship behavior training. ``(11) Federal support should address not only research and development of innovative model curricula and teaching and learning strategies to promote healthy behavior, but should also assist schools and local communities with implementing a curriculum that includes sexual assault and teen dating violence. ``SEC. 5624. DEFINITIONS. ``In this subpart: ``(1) Consent.-- ``(A) In general.--The term `consent' means affirmative, unambiguous, and voluntary agreement to engage in a specific sexual activity during a sexual encounter. ``(B) Limitations.--Consent cannot be given by an individual who is-- ``(i) asleep, or mentally or physically incapacitated, either through the effect of drugs or alcohol or for any other reason; ``(ii) under duress or experiencing a threat, coercion, or force; or ``(iii) inferred under circumstances in which consent is not clear, including the absence of language or actions that indicate unwillingness (such as saying `no' or `stop'), or the existence of a prior or current relationship or prior or current sexual activity. ``(2) Safe relationship behavior education.--The term `safe relationship behavior education' means education that-- ``(A) is medically accurate and appropriate for an individual's age, developmental stage, and culture; ``(B) promotes safe relationships and teaches students to recognize and prevent-- ``(i) physical and emotional relationship abuse; and ``(ii) coercion, violence, or abuse, including teen and adolescent dating violence, domestic abuse, and sexual violence and harassment; ``(C) includes education regarding relationship communication skills, emotional health, accountability, and well-being in relationships, and consent; and ``(D) includes education regarding healthy relationships, including the development of healthy attitudes and insights necessary for understanding relationships between oneself, family, partners, others, and society, including skills on healthy self- esteem, and self-efficacy and stress management. ``(3) Sexual assault.--The term `sexual assault' means any nonconsensual sexual act proscribed by Federal, State, or tribal law, including when a victim lacks capacity to consent. ``(4) Sexual harassment.--The term `sexual harassment' means unwelcome conduct of a sexual nature, including unwelcome sexual advances, requests for sexual favors, and other verbal, nonverbal, or physical conduct of a sexual nature. ``(5) Sexual violence.--The term `sexual violence' means physical sexual acts perpetrated against a person's will or when or where a person is incapable of giving consent. ``(6) Teen and adolescent dating violence.--The term `teen and adolescent dating violence' means-- ``(A) violence committed by a person who is or has been in a social relationship of a romantic or intimate nature with the victim; and ``(B) where the existence of such a relationship shall be determined based on a consideration of factors, including-- ``(i) the length of the relationship; ``(ii) the type of relationship; and ``(iii) the frequency of interaction between the persons involved in the relationship. ``SEC. 5625. GRANTS AUTHORIZED. ``(a) Authority.--The Secretary is authorized to award grants to local educational agencies in order to enable such agencies-- ``(1) to provide professional development to school administrators, teachers, and staff in safe relationship behavior education and teaching and learning practices; and ``(2) to provide educational programming and curricula that is age appropriate and developmentally and culturally appropriate for students regarding safe relationship behavior education and training. ``(b) Award Basis.--The Secretary is authorized to award grants under this section-- ``(1) on a competitive basis; and ``(2) in a manner that ensures that such grants are equitably distributed among local educational agencies located in rural, urban, and suburban areas. ``(c) Duration.--Grants awarded under this section shall be for a period of 4 years. ``(d) Policy Dissemination.--The Secretary shall disseminate to local educational agencies any Department policy guidance regarding safe relationship behavior training and the promotion of safe and healthy relationships. ``(e) Use of Funds.--Each local educational agency that receives a grant under this subpart shall use grant funds to develop and implement curricula for students that-- ``(1) incorporate elements of effective and evidence-based or evidence-informed programs that include-- ``(A) safe relationship behavior training, including for the prevention of teen and adolescent dating violence, domestic abuse, and sexual violence and harassment; and ``(B) education about healthy relationships between oneself and family, others, and society; and ``(2) are age appropriate, developmentally appropriate, and culturally and linguistically appropriate, reflecting the diverse circumstance and realities of young people. ``(f) Application.--To be eligible for a grant under this section, a local educational agency shall submit an application to the Secretary at such time, in such manner, and containing such information as the Secretary may require. Each application shall include a description of the local educational agency's-- ``(1) need for funds provided under this subpart; ``(2) plan for implementing the activities described under subsection (e); and ``(3) measurable objectives for, and expected results from, the use of funds provided by the grant under this subpart. ``(g) Selection of Grantees.-- ``(1) In general.--The Secretary shall determine, based on the peer review process described in paragraph (3), which local educational agencies shall receive funding under this subpart, and the amount of the grant funding under this subpart that each selected local educational agency will receive. ``(2) Grant amounts.--In determining the amount of each grant awarded under this subpart, the Secretary shall take into account the total amount of funds available for all grants under this subpart and the types of activities proposed to be carried out by each local educational agency, in order to ensure that all grants are of sufficient size, scope, and quality to be effective. ``(3) Peer review process.--The Secretary shall convene a peer review committee to review applications for grants under this subpart and to make recommendations to the Secretary regarding the selection of grantees.''. SEC. 3. GENERAL PROHIBITION. Section 9526(a)(3) of the Elementary and Secondary Education Act of 1965 (20 U.S.C. 7906(a)(3)) is amended by adding ``and safe relationship behavior education (as defined in section 5624)'' after ``abstinence''.

Teach Safe Relationships Act of 2015 This bill amends the Elementary and Secondary Education Act of 1965 (ESEA) to authorize the Department of Education (ED) to award competitive four-year grants to local educational agencies (LEAs) to provide: (1) professional development to school administrators, teachers, and staff in safe relationship behavior education; and (2) educational programming and curricula for students regarding safe relationship behavior. "Safe relationship behavior education" is&nbsp;education that: is medically accurate and appropriate for an individual's age, developmental stage, and culture; promotes safe relationships and teaches students to recognize and prevent coercion, violence, or abuse, including physical and emotional relationship abuse; includes education regarding communication skills, emotional health, accountability, and well-being in relationships; and includes education regarding healthy relationships and consent. ED must provide LEAs with policy guidance regarding safe relationship behavior training and the promotion of safe and healthy relationships. ESEA funds may not be used for sex or HIV-prevention education in schools if that instruction does not include safe relationship behavior education. (Under current law, sex or HIV-prevention education in schools must be age appropriate and include the health benefits of abstinence.)

<s>[INST]SECTION 1. SHORT TITLE. This Act may be cited as the ``Teach Safe Relationships Act of 2015''. SEC. 2. FUND FOR THE IMPROVEMENT OF EDUCATION. Part D of title V of the Elementary and Secondary Education Act of 1965 (20 U.S.C. 7241 et seq.) is amended by adding at the end the following: ``Subpart 22--Providing Safe Relationship Behavior Education and Training ``SEC. 5621. SHORT TITLE. ``This subpart may be cited as the `Teach Safe Relationships Act of 2015'. ``SEC. 5622. STATEMENT OF PURPOSE. ``It is the purpose of this subpart: ``(1) To help ensure that all students receive evidence- informed safe relationship behavior education and training, including education and training regarding the prevention of teen and adolescent dating violence or relationship abuse, domestic abuse, and sexual violence and harassment. ``(2) To promote safe and healthy relationships between and among students. ``(3) To help students and school faculty and staff to develop healthy and respectful attitudes and insights necessary for students to understand themselves in the context of relationships with others and with society. ``(4) To provide financial assistance to support local educational agencies in meeting the requirements of title IX of the Educational Amendments of 1972. ``SEC. 5623. FINDINGS. ``Congress finds the following: ``(1) Educating students about safe relationship behavior will aid in the prevention of unsafe dating practices, including dating violence, sexual assault, and stalking. ``(2) The Violence Against Women Act of 1994 (42 U.S.C. 13925 et seq.) included programs to develop and implement prevention and intervention policies in middle and high schools, including appropriate responses to, and identification and referral procedures for, students who are experiencing or perpetrating domestic violence, dating violence, sexual assault, sexual harassment, stalking, or sex trafficking. ``(3) Schools can play an important role in providing students with a knowledge base that may allow students to make informed decisions and form a healthy lifestyle. ``(4) According to the Department of Justice, there is an average of 293,066 victims (age 12 or older) of rape and sexual assault each year. ``(5) Young women between the ages of 16 and 24 experience the highest rate of intimate partner violence. According to one national study, 29 percent of the young women surveyed who had ever been in a relationship said they had been pressured to have sex or to engage in sexual activity they did not want. ``(6) From 1997 to 2013, females ages 18 to 24 consistently experienced higher rates of rape and sexual assault than females in other age brackets. ``(7) Partners of all genders and those in same-sex relationships also experience dating violence. A 2013 survey of grade school students found that 43 percent of lesbian, gay, bisexual, and transgender youth reported being victims of physical dating violence, compared to 29 percent of heterosexual youth. ``(8) Experiencing dating violence is associated with an increase in sexual risk-taking behaviors, health risks, and is associated with adolescent and unintended pregnancy. ``(9) Teaching and learning practices in the United States frequently do not address safe relationship behavior education and training, for example-- ``(A) sex education curriculum should address emotional relationship health; ``(B) sexual harassment undermines the ability of schools to provide safe and equitable learning or workplace environments; and ``(C) classroom textbooks and educational materials do not sufficiently reflect the promotion of safe and healthy relationships. ``(10) Efforts to improve the quality of public education must also include efforts to ensure programs for safe relationship behavior training. ``(11) Federal support should address not only research and development of innovative model curricula and teaching and learning strategies to promote healthy behavior, but should also assist schools and local communities with implementing a curriculum that includes sexual assault and teen dating violence. ``SEC. 5624. DEFINITIONS. ``In this subpart: ``(1) Consent.-- ``(A) In general.--The term `consent' means affirmative, unambiguous, and voluntary agreement to engage in a specific sexual activity during a sexual encounter. ``(B) Limitations.--Consent cannot be given by an individual who is-- ``(i) asleep, or mentally or physically incapacitated, either through the effect of drugs or alcohol or for any other reason; ``(ii) under duress or experiencing a threat, coercion, or force; or ``(iii) inferred under circumstances in which consent is not clear, including the absence of language or actions that indicate unwillingness (such as saying `no' or `stop'), or the existence of a prior or current relationship or prior or current sexual activity. ``(2) Safe relationship behavior education.--The term `safe relationship behavior education' means education that-- ``(A) is medically accurate and appropriate for an individual's age, developmental stage, and culture; ``(B) promotes safe relationships and teaches students to recognize and prevent-- ``(i) physical and emotional relationship abuse; and ``(ii) coercion, violence, or abuse, including teen and adolescent dating violence, domestic abuse, and sexual violence and harassment; ``(C) includes education regarding relationship communication skills, emotional health, accountability, and well-being in relationships, and consent; and ``(D) includes education regarding healthy relationships, including the development of healthy attitudes and insights necessary for understanding relationships between oneself, family, partners, others, and society, including skills on healthy self- esteem, and self-efficacy and stress management. ``(3) Sexual assault.--The term `sexual assault' means any nonconsensual sexual act proscribed by Federal, State, or tribal law, including when a victim lacks capacity to consent. ``(4) Sexual harassment.--The term `sexual harassment' means unwelcome conduct of a sexual nature, including unwelcome sexual advances, requests for sexual favors, and other verbal, nonverbal, or physical conduct of a sexual nature. ``(5) Sexual violence.--The term `sexual violence' means physical sexual acts perpetrated against a person's will or when or where a person is incapable of giving consent. ``(6) Teen and adolescent dating violence.--The term `teen and adolescent dating violence' means-- ``(A) violence committed by a person who is or has been in a social relationship of a romantic or intimate nature with the victim; and ``(B) where the existence of such a relationship shall be determined based on a consideration of factors, including-- ``(i) the length of the relationship; ``(ii) the type of relationship; and ``(iii) the frequency of interaction between the persons involved in the relationship. ``SEC. 5625. GRANTS AUTHORIZED. ``(a) Authority.--The Secretary is authorized to award grants to local educational agencies in order to enable such agencies-- ``(1) to provide professional development to school administrators, teachers, and staff in safe relationship behavior education and teaching and learning practices; and ``(2) to provide educational programming and curricula that is age appropriate and developmentally and culturally appropriate for students regarding safe relationship behavior education and training. ``(b) Award Basis.--The Secretary is authorized to award grants under this section-- ``(1) on a competitive basis; and ``(2) in a manner that ensures that such grants are equitably distributed among local educational agencies located in rural, urban, and suburban areas. ``(c) Duration.--Grants awarded under this section shall be for a period of 4 years. ``(d) Policy Dissemination.--The Secretary shall disseminate to local educational agencies any Department policy guidance regarding safe relationship behavior training and the promotion of safe and healthy relationships. ``(e) Use of Funds.--Each local educational agency that receives a grant under this subpart shall use grant funds to develop and implement curricula for students that-- ``(1) incorporate elements of effective and evidence-based or evidence-informed programs that include-- ``(A) safe relationship behavior training, including for the prevention of teen and adolescent dating violence, domestic abuse, and sexual violence and harassment; and ``(B) education about healthy relationships between oneself and family, others, and society; and ``(2) are age appropriate, developmentally appropriate, and culturally and linguistically appropriate, reflecting the diverse circumstance and realities of young people. ``(f) Application.--To be eligible for a grant under this section, a local educational agency shall submit an application to the Secretary at such time, in such manner, and containing such information as the Secretary may require. Each application shall include a description of the local educational agency's-- ``(1) need for funds provided under this subpart; ``(2) plan for implementing the activities described under subsection (e); and ``(3) measurable objectives for, and expected results from, the use of funds provided by the grant under this subpart. ``(g) Selection of Grantees.-- ``(1) In general.--The Secretary shall determine, based on the peer review process described in paragraph (3), which local educational agencies shall receive funding under this subpart, and the amount of the grant funding under this subpart that each selected local educational agency will receive. ``(2) Grant amounts.--In determining the amount of each grant awarded under this subpart, the Secretary shall take into account the total amount of funds available for all grants under this subpart and the types of activities proposed to be carried out by each local educational agency, in order to ensure that all grants are of sufficient size, scope, and quality to be effective. ``(3) Peer review process.--The Secretary shall convene a peer review committee to review applications for grants under this subpart and to make recommendations to the Secretary regarding the selection of grantees.''. SEC. 3. GENERAL PROHIBITION. Section 9526(a)(3) of the Elementary and Secondary Education Act of 1965 (20 U.S.C. 7906(a)(3)) is amended by adding ``and safe relationship behavior education (as defined in section 5624)'' after ``abstinence''.[/INST]Teach Safe Relationships Act of 2015 This bill amends the Elementary and Secondary Education Act of 1965 (ESEA) to authorize the Department of Education (ED) to award competitive four-year grants to local educational agencies (LEAs) to provide: (1) professional development to school administrators, teachers, and staff in safe relationship behavior education; and (2) educational programming and curricula for students regarding safe relationship behavior. "Safe relationship behavior education" is&nbsp;education that: is medically accurate and appropriate for an individual's age, developmental stage, and culture; promotes safe relationships and teaches students to recognize and prevent coercion, violence, or abuse, including physical and emotional relationship abuse; includes education regarding communication skills, emotional health, accountability, and well-being in relationships; and includes education regarding healthy relationships and consent. ED must provide LEAs with policy guidance regarding safe relationship behavior training and the promotion of safe and healthy relationships. ESEA funds may not be used for sex or HIV-prevention education in schools if that instruction does not include safe relationship behavior education. (Under current law, sex or HIV-prevention education in schools must be age appropriate and include the health benefits of abstinence.)</s>

it is estimated that half of the canceric patients undergo radiotherapy as a part of their treatment . skin is prone to radiation damage , because it is a continuously renewing organ containing rapidly proliferating mature cells . radiation burn is defined as a damage to the skin or other biological tissues caused by exposure to radiofrequency energy or ionizing radiation . high exposure to x - rays during repeated diagnostic medical imaging , interventional radiology procedures or radiotherapy can also cause radiation damage . the most common radiation burn is the therapeutic one [ 4 - 6 ] . radiation burn properties include : first , radiation burns have a dose - dependent clinical pattern . third , unpredictable successive inflammatory waves which may occur weeks up to years after radiation exposure . despite all the care , unintentional radiation burns can occur with x - ray or rt machines as a result of mechanical problems , electrical instability , human errors , etc . acute skin reaction is the most common side effect of radiation therapy with statistics between 90 - 95% of patients experiencing some degrees of reaction . skin reactions are graded by severity n a continuum from erythema and dry desquamation to the moist desquamation and in more severe cases , ulceration in which threshold doses for the onset of each of these reactions are listed in table 1 . in general , any chemical / biological agent given prior to or at the time of irradiation to prohibit or improve damage to the normal tissues is called a radioprotector since radiotherapy , occupational and accidental exposure to radiation or space travel and exploration can induce unwilling side effects . ideally , a radioprotector should benefit several properties including ; first , the agent should have protective effects on lots of organs and tissues . fourth , it should be applicable in radiotherapy treatment . finally , to a large extent , radioprotectors should be compatible with lots of other drugs which are prescribed to patients in the process of their treatment . after discovery of cysteine in 1949 , a large number of chemical compounds with radiation protection capabilities have been studied . some of these newly discovered drugs such as mercaptoethylamine ( mea ) , cystamine and wr2721 were considered as the most effective radioprotectors . due to some side effects such as : drowsiness , hypotension , nausea , vomiting and toxicity , these drugs had limited clinical use , and attempts for finding new radioprotectors with low levels of toxicity are on the rise . melatonin was discovered in 1917 as an endogenous agent produced by the pineal gland . during past decades these organs included bile fluid , bone marrow , cerebrospinal fluid , ovary , eye , lymphocytes , gastral mucosa and the skin . melatonin is a highly lipophilic substance which easily penetrates organic membranes and is able to protect important intracellular structures including mitochondria and dna against oxidative stress . its concentration in the body is typically low during daylight hours and high at night ( figure 1 ) . there is clear evidence which supports the claim that melatonin level is conversely proportional to the age in mammals , including man . the levels probably are higher in winter as compared to summer [ 12 - 15 ] . melatonin concentration in proportion with age and time per pg / ml unit in addition , melatonin contributes mainly to hair growth cycles , cutaneous pigmentation and skin physiology and pathology . when examined in fur - producing animals , it was obvious that melatonin could stimulate hair growth , considerably . a clinical trial in women suffering from androgenetic or diffuse alopecia cleared positive effect of melatonin in human hair growth . melatonin receptors are categorized into two major groups including membrane - bond receptors and nuclear receptors . membrane - bond receptors are divided into 3 subgroups including mt1 , mt2 and mt3 . in c57bl/6 mouse skin , mt2 is expressed uniquely , whereas , both receptors are expressed in human skin although with uneven proportion and a bias toward mt1 . in skin cells , receptor - independent melatonin actions might be interceded partly by cytosolic flavoprotein quinone reductase ii ( nqo2 ) , which is specific to skin cells . nuclear receptor rora ( retinoid - related orphan receptor ) is a member of the rzr / ror subfamily which includes at least four splicing variants : rora1 , rora2 , rora3 and rzra ( rora4 ) . rora1 is expressed only in adult dermal fibroblasts , whereas the type rora2 is expressed in immortalized melanocytes and rora4 ( rzra ) is expressed in adult epidermal keratinocytes , hacat keratinocytes , neonatal melanocytes and adult dermal fibroblasts ( figure 2 ) [ 13 - 16 ] . exogenous or endogenously synthesized melatonin can regulate skin - cell phenotype through an interaction with membrane - bound melatonin receptors mt1 and mt2 or with nuclear retinoid - acid orphan receptors ( rora ) . among phenotypic effects of receptor activation , it is worth noting melanin - synthesis inhibition , dna repair and overexpression of antioxidative enzymes . non - receptor actions are mediated through an interaction with intracellular proteins , such as quinone reductase 2 ( nqo2 ) or caldmodulin . melatonin and its metabolites , represented in this figure by n1-acetyl - n2-formyl - methoxykynuramine ( afmk ) , act as direct scavengers of reactive oxygen and nitrogen species ( ros and rns ) and help to maintain mitochondrial homeostasis by interacting with cytochrome c or the electron - transport chain . in the skin , intra- , para- and auto - crine actions direct effects are shown by solid lines and multiple reactions and signaling are shown by broken lines . melatonin can be injected through different routes including oral , sub - mucosal , transdermal , sub - lingual , respiration and intravenously . in order to determine melatonin toxicity potential , physiologic to pharmacologic concentrations doses of melatonin tested in vivo were as follows : 10 - 250 mg / kg in mice , 100 - 200 mg / kg in rats or even 800 mg / kg in mice , rabbits , cats and dogs . however , doses as low as 0.1 mg / kg administered via oral route were believed to be effective and appropriate minimum dose level of melatonin . it has been reported that melatonin ( at a dose as high as 250 mg / kg ) is not considered toxic anymore . as an important note , melatonin use is not illegal in the usa ( i.e. it does not require us fda confirmation ) for treatment of androgenic alopecia and as a component of sunscreens [ 14 - 17 ] . melatonin increases the molecular level of some significant antioxidative enzymes such as superoxide dismotase and glutation - peroxidase and also reduces synthetic activity of nitric oxide . according to tan et al . study , melatonin is more effective than glotatione or manythole in the process of oh free radical scavenging ( respectively 5 , 14 fold ) . melatonin is also a potent free - radical scavenger relative to vitamin c and throlox . ( figure 3 ) [ 13 - 18 ] . presumed actions of melatonin as a direct free radical scavenger and as an indirect antioxidant . in this review only the direct detoxification of reactive oxygen and nitrogen species by melatonin are considered . however , melatonin also has been shown to have indirect antioxidative actions , through the stimulation of several antioxidative enzymes and the stabilization of membrane fluidity . in both in vitro and in vivo studies , melatonin reduced free radical damage to lipids , proteins , and dna . because of the role of oxidative damage in disease processes , antioxidants , including melatonin may help to resist the development of various pathophysiologies . in 1998 , dreher et al . administered vitamin c , vitamin e and melatonin alone or in combination , topically 30 min . prior to ultraviolet - irradiation of the skin . the results showed a mild protective effect of such vitamins when applied alone and a dose - dependent photoprotective effect of melatonin . better protection was reached by using the combination of melatonin with both vitamins . in 2000 , nickle et al . studied the effect of melatonin on human keratinocytes which were exposed to uv radiation . significant protection against uvb - induced decrease in dna synthesis was reported as compared to the irradiated control group without melatonin supplementation . interestingly , no protective effect of melatonin was observed after uva irradiation . in 2001 , kim et al . investigated the effects of x - ray irradiation and melatonin on cytotoxicity , lipid peroxidation and alteration of the cell cycle in cultured skin fibroblast . by pre - incubation with melatonin ( 10 m ) , a significant preventive effect was reported on the increase in the absolute number of surviving cells ( up to 68% of cells survived ) , and the levels of mda considerably reduced . dna flow - cytometry analysis revealed that x radiation increased pre - g1 apoptotic population by 7.6% compared to a very low level ( 1.3% ) of non - irradiated cells . however , by pretreatment with melatonin , this apoptotic population decreased up to 4.5% at 10 m . in 2001 , ryoo et al . studied the effect of melatonin on uvb ( 10 m ) , a significant preventive effect was reported on the increase in the absolute number of surviving cells ( up to 92.5% of cells survived ) , and the levels of mda considerably decreased . uvb limits g1 progression induced pre - g1 arrest leading to apoptotic changes of dermal fibroblast , and those are stopped by melatonin pre - treatment . in 2005 , hussein et al . studied radioprotective effects of melatonin against x - ray - induced skin damages in albino rats ultrastructurally . as compared to non - irradiated skin , xri skin demonstrated signs of cellular damage in the basal , spinous and granular cells . these features included destruction of epidermal cells , reduced irregularity of the basal cell borders , swollen mitochondria , dilated rer , decreased complements of cytoplasmic organelles and shortage of desmosomes . additionally , irradiated cells exhibited early apoptotic changes such as reduction in the cytoplasmic and nuclear areas , extensive cytoplasmic vacuolization , abnormal er , mitochondria and condensation of the nuclear chromatin . results revealed that melatonin could minimize all xri - induced ultrastructural skin damage parameters . in 2006 , fischer et al . dna synthesis experiments showed a strong protective effect by pre - treatment with melatonin at concentrations of 10 m and 10 m. the mechanism of melatonin protective effect ( 10 to 10 m ) consists of inhibition of apoptosis as measured by tunel assay . clonogenic studies demonstrated a significantly higher number of colonies in cultures treated with melatonin compared to controls . pretreatment with melatonin led to significant protection against uvb - induced damage in keratinocytes . in 2009 , izykowska et al . studied the effect of melatonin after its addition to the culture medium for 30 minutes before exposure of melanoma cells to uva or uvb . melatonin added to the medium at concentrations of 10 to 10 m was found to increase the number of melanoma cells as compared to the control after 24 hours . at 10 m melatonin , melanoma cells irradiated by 30 mj / cm uvb increased in number and at 10 m increased the survival of those exposed to 60 mj / cm uvb . the cells exposed to uva ( 15 j / cm ) were protected by melatonin at 10 and 10 m. in 2009 , izykowska et al . evaluated the effect of melatonin added to culture medium 30 minutes before exposure of keratinocytes and fibroblasts to irradiation with uva and uvb . melatonin at 10 m increased the number of surviving keratinocytes and at 10 m increased the number of surviving fibroblasts irradiated by uvb as compared to cells exposed only to radiation . melatonin at 10 m showed a protective effect on both types of cells irradiated with uva . in 2014 , cakir et al . , the histological abnormalities of radiation are shaped to be better protected in skin through pretreatment with melatonin . in 2014 , janjetovic et al . investigated the protective effects of melatonin and its derivatives in human keratinocytes against a range of doses of ultraviolet b radiation . there was significant reduction in the production of reactive oxygen species ( 50 - 60% ) when uvb - exposed keratinocytes were treated with melatonin or its metabolites . similarly , melatonin and its derivatives decreased the nitrite and hydrogen peroxide levels induced by uvb as early as 30 min . in addition , melatonin and its metabolites enhanced the levels of reduced glutathione in keratinocytes within 1 hr . they also observed a dose - dependent increase in viability of uvb - irradiated keratinocytes which were treated with melatonin or its metabolites after 48 hr . mmelatonin and its derivatives enhanced the dna repair capacity of uvb - induced pyrimidine photoproducts or cyclobutane pyrimidine dimers production in human keratinocytes . melatonin and its metabolites further reinforced expression of p53 phosphorylated at ser-15 but not at ser-46 or its non - phosphorylated form . in 2014 , ozguner et al . studied the effect of melatonin on mobile - phone - induced skin tissue changes . in ir group , increased thickness of stratum corneum , atrophy of epidermis , papillamatosis , basal cell proliferation , increased granular cell layer ( hypergranulosis ) in epidermis and capillary proliferation , impairment in collagen tissue distribution and separation of collagen bundles in dermis were all reported compared to the control group . cho et al . performed cdna microarray analysis from keratinocytes that were pre - incubated with melatonin and then irradiated by 100 mj / cm uv irradiation . a great variety of genes related to apoptosis , cancer induction , cyclin - dependent kinase 2-interacting protein , gpx , ubiquitin - conjugating enzyme e2 m enzymes and signal transducer genes ( fibroblast growth factor , tgf-stimulated protein tsc 22 ) were under - expressed by melatonin compared with uv - exposed keratinocytes . this agent has different features such as direct and indirect scavenging of free radicals , the ability to stimulate the activity of antioxidant enzymes and inhibiting the activity of a pro - oxidative enzyme making it a potentially useful radioprotector . there are ample of in - vitro and in - vivo studies which demonstrate its protection against radiation injury . melatonin might be successfully used for the prevention and treatment of radiation - induced skin injury . based on radiobiological models , we can assume that melatonin might delay the saturation of repair enzymes which leads to repairing more radiation - induced damage by repair system and more importantly providing the possibility of administering higher doses of radiation during radiotherapy to get a better therapeutic ratio . we propose that , in the future , melatonin would improve the therapeutic ratio in radiation oncology and ameliorate skin damages more effectively when administered in optimal and non - toxic doses .

normal skin is composed of epidermis and dermis . skin is susceptible to radiation damage because it is a continuously renewing organ containing rapidly proliferating mature cells . radiation burn is a damage to the skin or other biological tissues caused by exposure to radiofrequency energy or ionizing radiation . acute skin reaction is the most frequently occurring side effect of radiation therapy . generally , any chemical / biological agent given before or at the time of irradiation to prevent or ameliorate damage to normal tissues is called a radioprotector . melatonin is a highly lipophilic substance that easily penetrates organic membranes and therefore is able to protect important intracellular structures including mitochondria and dna against oxidative damage directly at the sites where such a kind of damage would occur . melatonin leads to an increase in the molecular level of some important antioxidative enzymes such as superoxide , dismotase and glutation - peroxidase , and also a reduction in synthetic activity of nitric oxide . there is a large body of evidence which proves the efficacy of melatonin in ameliorating uv and x ray - induced skin damage . we propose that , in the future , melatonin would improve the therapeutic ratio in radiation oncology and ameliorate skin damage more effectively when administered in optimal and non - toxic doses .

<s>[INST]it is estimated that half of the canceric patients undergo radiotherapy as a part of their treatment . skin is prone to radiation damage , because it is a continuously renewing organ containing rapidly proliferating mature cells . radiation burn is defined as a damage to the skin or other biological tissues caused by exposure to radiofrequency energy or ionizing radiation . high exposure to x - rays during repeated diagnostic medical imaging , interventional radiology procedures or radiotherapy can also cause radiation damage . the most common radiation burn is the therapeutic one [ 4 - 6 ] . radiation burn properties include : first , radiation burns have a dose - dependent clinical pattern . third , unpredictable successive inflammatory waves which may occur weeks up to years after radiation exposure . despite all the care , unintentional radiation burns can occur with x - ray or rt machines as a result of mechanical problems , electrical instability , human errors , etc . acute skin reaction is the most common side effect of radiation therapy with statistics between 90 - 95% of patients experiencing some degrees of reaction . skin reactions are graded by severity n a continuum from erythema and dry desquamation to the moist desquamation and in more severe cases , ulceration in which threshold doses for the onset of each of these reactions are listed in table 1 . in general , any chemical / biological agent given prior to or at the time of irradiation to prohibit or improve damage to the normal tissues is called a radioprotector since radiotherapy , occupational and accidental exposure to radiation or space travel and exploration can induce unwilling side effects . ideally , a radioprotector should benefit several properties including ; first , the agent should have protective effects on lots of organs and tissues . fourth , it should be applicable in radiotherapy treatment . finally , to a large extent , radioprotectors should be compatible with lots of other drugs which are prescribed to patients in the process of their treatment . after discovery of cysteine in 1949 , a large number of chemical compounds with radiation protection capabilities have been studied . some of these newly discovered drugs such as mercaptoethylamine ( mea ) , cystamine and wr2721 were considered as the most effective radioprotectors . due to some side effects such as : drowsiness , hypotension , nausea , vomiting and toxicity , these drugs had limited clinical use , and attempts for finding new radioprotectors with low levels of toxicity are on the rise . melatonin was discovered in 1917 as an endogenous agent produced by the pineal gland . during past decades these organs included bile fluid , bone marrow , cerebrospinal fluid , ovary , eye , lymphocytes , gastral mucosa and the skin . melatonin is a highly lipophilic substance which easily penetrates organic membranes and is able to protect important intracellular structures including mitochondria and dna against oxidative stress . its concentration in the body is typically low during daylight hours and high at night ( figure 1 ) . there is clear evidence which supports the claim that melatonin level is conversely proportional to the age in mammals , including man . the levels probably are higher in winter as compared to summer [ 12 - 15 ] . melatonin concentration in proportion with age and time per pg / ml unit in addition , melatonin contributes mainly to hair growth cycles , cutaneous pigmentation and skin physiology and pathology . when examined in fur - producing animals , it was obvious that melatonin could stimulate hair growth , considerably . a clinical trial in women suffering from androgenetic or diffuse alopecia cleared positive effect of melatonin in human hair growth . melatonin receptors are categorized into two major groups including membrane - bond receptors and nuclear receptors . membrane - bond receptors are divided into 3 subgroups including mt1 , mt2 and mt3 . in c57bl/6 mouse skin , mt2 is expressed uniquely , whereas , both receptors are expressed in human skin although with uneven proportion and a bias toward mt1 . in skin cells , receptor - independent melatonin actions might be interceded partly by cytosolic flavoprotein quinone reductase ii ( nqo2 ) , which is specific to skin cells . nuclear receptor rora ( retinoid - related orphan receptor ) is a member of the rzr / ror subfamily which includes at least four splicing variants : rora1 , rora2 , rora3 and rzra ( rora4 ) . rora1 is expressed only in adult dermal fibroblasts , whereas the type rora2 is expressed in immortalized melanocytes and rora4 ( rzra ) is expressed in adult epidermal keratinocytes , hacat keratinocytes , neonatal melanocytes and adult dermal fibroblasts ( figure 2 ) [ 13 - 16 ] . exogenous or endogenously synthesized melatonin can regulate skin - cell phenotype through an interaction with membrane - bound melatonin receptors mt1 and mt2 or with nuclear retinoid - acid orphan receptors ( rora ) . among phenotypic effects of receptor activation , it is worth noting melanin - synthesis inhibition , dna repair and overexpression of antioxidative enzymes . non - receptor actions are mediated through an interaction with intracellular proteins , such as quinone reductase 2 ( nqo2 ) or caldmodulin . melatonin and its metabolites , represented in this figure by n1-acetyl - n2-formyl - methoxykynuramine ( afmk ) , act as direct scavengers of reactive oxygen and nitrogen species ( ros and rns ) and help to maintain mitochondrial homeostasis by interacting with cytochrome c or the electron - transport chain . in the skin , intra- , para- and auto - crine actions direct effects are shown by solid lines and multiple reactions and signaling are shown by broken lines . melatonin can be injected through different routes including oral , sub - mucosal , transdermal , sub - lingual , respiration and intravenously . in order to determine melatonin toxicity potential , physiologic to pharmacologic concentrations doses of melatonin tested in vivo were as follows : 10 - 250 mg / kg in mice , 100 - 200 mg / kg in rats or even 800 mg / kg in mice , rabbits , cats and dogs . however , doses as low as 0.1 mg / kg administered via oral route were believed to be effective and appropriate minimum dose level of melatonin . it has been reported that melatonin ( at a dose as high as 250 mg / kg ) is not considered toxic anymore . as an important note , melatonin use is not illegal in the usa ( i.e. it does not require us fda confirmation ) for treatment of androgenic alopecia and as a component of sunscreens [ 14 - 17 ] . melatonin increases the molecular level of some significant antioxidative enzymes such as superoxide dismotase and glutation - peroxidase and also reduces synthetic activity of nitric oxide . according to tan et al . study , melatonin is more effective than glotatione or manythole in the process of oh free radical scavenging ( respectively 5 , 14 fold ) . melatonin is also a potent free - radical scavenger relative to vitamin c and throlox . ( figure 3 ) [ 13 - 18 ] . presumed actions of melatonin as a direct free radical scavenger and as an indirect antioxidant . in this review only the direct detoxification of reactive oxygen and nitrogen species by melatonin are considered . however , melatonin also has been shown to have indirect antioxidative actions , through the stimulation of several antioxidative enzymes and the stabilization of membrane fluidity . in both in vitro and in vivo studies , melatonin reduced free radical damage to lipids , proteins , and dna . because of the role of oxidative damage in disease processes , antioxidants , including melatonin may help to resist the development of various pathophysiologies . in 1998 , dreher et al . administered vitamin c , vitamin e and melatonin alone or in combination , topically 30 min . prior to ultraviolet - irradiation of the skin . the results showed a mild protective effect of such vitamins when applied alone and a dose - dependent photoprotective effect of melatonin . better protection was reached by using the combination of melatonin with both vitamins . in 2000 , nickle et al . studied the effect of melatonin on human keratinocytes which were exposed to uv radiation . significant protection against uvb - induced decrease in dna synthesis was reported as compared to the irradiated control group without melatonin supplementation . interestingly , no protective effect of melatonin was observed after uva irradiation . in 2001 , kim et al . investigated the effects of x - ray irradiation and melatonin on cytotoxicity , lipid peroxidation and alteration of the cell cycle in cultured skin fibroblast . by pre - incubation with melatonin ( 10 m ) , a significant preventive effect was reported on the increase in the absolute number of surviving cells ( up to 68% of cells survived ) , and the levels of mda considerably reduced . dna flow - cytometry analysis revealed that x radiation increased pre - g1 apoptotic population by 7.6% compared to a very low level ( 1.3% ) of non - irradiated cells . however , by pretreatment with melatonin , this apoptotic population decreased up to 4.5% at 10 m . in 2001 , ryoo et al . studied the effect of melatonin on uvb ( 10 m ) , a significant preventive effect was reported on the increase in the absolute number of surviving cells ( up to 92.5% of cells survived ) , and the levels of mda considerably decreased . uvb limits g1 progression induced pre - g1 arrest leading to apoptotic changes of dermal fibroblast , and those are stopped by melatonin pre - treatment . in 2005 , hussein et al . studied radioprotective effects of melatonin against x - ray - induced skin damages in albino rats ultrastructurally . as compared to non - irradiated skin , xri skin demonstrated signs of cellular damage in the basal , spinous and granular cells . these features included destruction of epidermal cells , reduced irregularity of the basal cell borders , swollen mitochondria , dilated rer , decreased complements of cytoplasmic organelles and shortage of desmosomes . additionally , irradiated cells exhibited early apoptotic changes such as reduction in the cytoplasmic and nuclear areas , extensive cytoplasmic vacuolization , abnormal er , mitochondria and condensation of the nuclear chromatin . results revealed that melatonin could minimize all xri - induced ultrastructural skin damage parameters . in 2006 , fischer et al . dna synthesis experiments showed a strong protective effect by pre - treatment with melatonin at concentrations of 10 m and 10 m. the mechanism of melatonin protective effect ( 10 to 10 m ) consists of inhibition of apoptosis as measured by tunel assay . clonogenic studies demonstrated a significantly higher number of colonies in cultures treated with melatonin compared to controls . pretreatment with melatonin led to significant protection against uvb - induced damage in keratinocytes . in 2009 , izykowska et al . studied the effect of melatonin after its addition to the culture medium for 30 minutes before exposure of melanoma cells to uva or uvb . melatonin added to the medium at concentrations of 10 to 10 m was found to increase the number of melanoma cells as compared to the control after 24 hours . at 10 m melatonin , melanoma cells irradiated by 30 mj / cm uvb increased in number and at 10 m increased the survival of those exposed to 60 mj / cm uvb . the cells exposed to uva ( 15 j / cm ) were protected by melatonin at 10 and 10 m. in 2009 , izykowska et al . evaluated the effect of melatonin added to culture medium 30 minutes before exposure of keratinocytes and fibroblasts to irradiation with uva and uvb . melatonin at 10 m increased the number of surviving keratinocytes and at 10 m increased the number of surviving fibroblasts irradiated by uvb as compared to cells exposed only to radiation . melatonin at 10 m showed a protective effect on both types of cells irradiated with uva . in 2014 , cakir et al . , the histological abnormalities of radiation are shaped to be better protected in skin through pretreatment with melatonin . in 2014 , janjetovic et al . investigated the protective effects of melatonin and its derivatives in human keratinocytes against a range of doses of ultraviolet b radiation . there was significant reduction in the production of reactive oxygen species ( 50 - 60% ) when uvb - exposed keratinocytes were treated with melatonin or its metabolites . similarly , melatonin and its derivatives decreased the nitrite and hydrogen peroxide levels induced by uvb as early as 30 min . in addition , melatonin and its metabolites enhanced the levels of reduced glutathione in keratinocytes within 1 hr . they also observed a dose - dependent increase in viability of uvb - irradiated keratinocytes which were treated with melatonin or its metabolites after 48 hr . mmelatonin and its derivatives enhanced the dna repair capacity of uvb - induced pyrimidine photoproducts or cyclobutane pyrimidine dimers production in human keratinocytes . melatonin and its metabolites further reinforced expression of p53 phosphorylated at ser-15 but not at ser-46 or its non - phosphorylated form . in 2014 , ozguner et al . studied the effect of melatonin on mobile - phone - induced skin tissue changes . in ir group , increased thickness of stratum corneum , atrophy of epidermis , papillamatosis , basal cell proliferation , increased granular cell layer ( hypergranulosis ) in epidermis and capillary proliferation , impairment in collagen tissue distribution and separation of collagen bundles in dermis were all reported compared to the control group . cho et al . performed cdna microarray analysis from keratinocytes that were pre - incubated with melatonin and then irradiated by 100 mj / cm uv irradiation . a great variety of genes related to apoptosis , cancer induction , cyclin - dependent kinase 2-interacting protein , gpx , ubiquitin - conjugating enzyme e2 m enzymes and signal transducer genes ( fibroblast growth factor , tgf-stimulated protein tsc 22 ) were under - expressed by melatonin compared with uv - exposed keratinocytes . this agent has different features such as direct and indirect scavenging of free radicals , the ability to stimulate the activity of antioxidant enzymes and inhibiting the activity of a pro - oxidative enzyme making it a potentially useful radioprotector . there are ample of in - vitro and in - vivo studies which demonstrate its protection against radiation injury . melatonin might be successfully used for the prevention and treatment of radiation - induced skin injury . based on radiobiological models , we can assume that melatonin might delay the saturation of repair enzymes which leads to repairing more radiation - induced damage by repair system and more importantly providing the possibility of administering higher doses of radiation during radiotherapy to get a better therapeutic ratio . we propose that , in the future , melatonin would improve the therapeutic ratio in radiation oncology and ameliorate skin damages more effectively when administered in optimal and non - toxic doses .[/INST]normal skin is composed of epidermis and dermis . skin is susceptible to radiation damage because it is a continuously renewing organ containing rapidly proliferating mature cells . radiation burn is a damage to the skin or other biological tissues caused by exposure to radiofrequency energy or ionizing radiation . acute skin reaction is the most frequently occurring side effect of radiation therapy . generally , any chemical / biological agent given before or at the time of irradiation to prevent or ameliorate damage to normal tissues is called a radioprotector . melatonin is a highly lipophilic substance that easily penetrates organic membranes and therefore is able to protect important intracellular structures including mitochondria and dna against oxidative damage directly at the sites where such a kind of damage would occur . melatonin leads to an increase in the molecular level of some important antioxidative enzymes such as superoxide , dismotase and glutation - peroxidase , and also a reduction in synthetic activity of nitric oxide . there is a large body of evidence which proves the efficacy of melatonin in ameliorating uv and x ray - induced skin damage . we propose that , in the future , melatonin would improve the therapeutic ratio in radiation oncology and ameliorate skin damage more effectively when administered in optimal and non - toxic doses .</s>

leaf springs like all other springs serve to absorb , store , and release the energy . in heavy vehicles , leaves are stacked one upon another to ensure rigidity and strength . during its operation , the leaf spring requires that the load rate should vary within limit ( 7% ) and the maximum stress induced should be lower than the maximum design stress . for a given stress range the leaf spring should have maximum fatigue life or as specified . the stress range and the maximum stress induced in the leaf spring play a vital role in deciding the load rate and fatigue life of the leaf spring . the maximum stress induced can be reduced by assembling the leaves with different radii of curvature and establishing a common curvature under no load . the proper distribution of the stress between the leaves can enhance the fatigue life of the leaf springs . evaluated the axial fatigue strength of en45a spring steel specimen experimentally as a function of shot peening in the conditions used . s / n curves of the specimens were correlated with leaf springs curve in vehicles . concluded that the influence of high contact pressure and temperatures resulted in microweld between the two leaf surfaces . the fatigue strength of the leaf springs was studied as a function of shot peening parameters . an experimental leaf springs model was verified by using a leaf springs test rig that could measure vertical static deflection of leaf springs under static loading condition . the results showed a nonlinear relationship between the applied load and the leaf springs deflection for both directions of loading , in form of a hysteresis loop . . studied the origin of premature failure analysis procedures , including examining the leaf spring history . the visual inspection of fractured specimens and simulation tests on real components were also performed . it was concluded that fracture occurred by a mechanism of mechanical fatigue initiated at the region of the central hole , which suffered the highest tensile stress levels . kumar and vijayarangan described static and fatigue analysis of steel leaf springs and composite multileaf springs made up of glass fibre reinforced polymer using life data analysis . the dimensions of an existing conventional steel leaf spring of a light commercial vehicle were taken and verified by design calculations . static analysis of 2d model of conventional leaf springs was also performed using ansys 7.1 , and the results obtained were compared with experimental results . patunkar and dolas worked on nonlinear force displacement of each leaf spring as well as the spring characteristics of a pack consisting of two to four leaves using ansys . the results from ansys were compared with those from the test , which showed a fairly good agreement with each other . the objective of the present work is to determine the effect of assembly stresses on fatigue life reliability of leaf springs . it is available in open literature that with proper combination of stepping and individual leaf camber the stress distribution can be uniform along the leaf . the 65si7 leaf springs design parameter of a light commercial vehicle is taken into consideration for this work . this paper is divided into two parts . in part one , a design procedure for determination of total moment of inertia , number of leaves , and stepping and individual leaf camber is established . the stepping and individual leaf camber is proposed with a view to lower stresses . using sae approach fatigue life of the leaf spring , three leaf springs specimens lots ( four leaf spring assemblies in each lot ) have been manufactured . all the specimens are tested on a full scale leaf spring testing machine for fatigue life of the leaf spring . the theoretical and experimental fatigue life results ( with and without assembly stresses ) are compared for validation . the material is heat - treated at 880c and oil - quench - hardened and it is tempered at 410c for 90 minutes to get tempered martensite structure . a leaf spring is considered as a beam of uniform strength composed of leaves of equal thickness where the fiber stress is the same throughout the length of the beam . this approximation is justified for most of the springs within the accuracy necessary for layout work and with certain correction factors for estimate of required length , overhang , camber , width , thickness , and number of leaves . the calculation of the leaf spring parameters involves certain number of steps . as per sae spring design manual approach , the steps involved in leaf springs design are as follows . consider ( 1)i = kl332esf=34351.7 mm4 , where k = load rate , l = spring span , e = young 's modulus , and sf = stiffening factor . consider ( 2)tmax=8ismaxlpmax=8.20 mm . consider ( 3)i1=n1i1 , where n1 = number of leaves with thickness t1 , i1 = moment of inertia for section t1 = 8 mm , and width b = 70 mm and ( 4)i1=b1t1312 + 3.1428t1464=2846.5 mm4 , where b1 = b t1 = 62 mm and n1 = 11 . consider ( 5)i1=112846.13=31311 mm4i2=n2i2 , where n2 = number of leaves with thickness t2 , i2 = moment of inertia for section t2 = 7 mm , and width b = 70 mm and ( 6)i2=b2t2312 + 3.1428t2464=1918.6 mm4 , where n2 = 1 and b2 = b t2 = 63 mm and ( 7)i2=11918.6=1918.6 mm4itotal=i1+i2=33230 mm4 . n / mm% age variation of k=3.271% ( hence acceptable ) . the seat clamp is taken into consideration for stress calculation between the leaves . the inactive length in the seat for a spring without liners is estimated as distance between the outside edges of the clamp bolts which is 100 mm for this spring . the active length for both front and rear cantilever will be 50 mm less than the distance from centre of the eye to centre of an axle seat . the stress at 50 mm distance from the centre of axle seat can be calculated as the following : ( 10)front cantilever stress , sfa = palat2itrear cantilever stress , srb = pblbt2it . front cantilever ( a ) length = l = l/2 = 575 mm and rear cantilever ( b ) length = l = l/2 = 575 mm . cantilever ratio y = a / b = 1 ( symmetric spring ) and seat length sl = 100 mm . active length of front cantilever la = ( l sl/2 ) = 525 mm . active length of rear cantilever lb = ( l sl/2 ) = 525 mm . design load on front cantilever pa = p/2 = 6479.5 n. design load on rear cantilever pb = p/2 = 6479.5 n. maximum load on front cantilever pamax = pmax/2 = 14005 n. maximum load on rear cantilever pbmax = pmax/2 = 14005 n. as the leaf spring is symmetric cantilever ratio = y = a / b = 1 ; therefore , la = lb , pa = pb ( at design load ) and pamax = pbmax ( at maximum load ) . also sfa = srb = sd ( at design load ) and sfa = srb = sm ( at maximum load ) . front cantilever ( a ) length = l = l/2 = 575 mm and rear cantilever ( b ) length = l = l/2 = 575 mm . cantilever ratio y = a / b = 1 ( symmetric spring ) and seat length sl = 100 mm . active length of front cantilever la = ( l sl/2 ) = 525 mm . active length of rear cantilever lb = ( l sl/2 ) = 525 mm . design load on front cantilever pa = p/2 = 6479.5 n. design load on rear cantilever pb = p/2 = 6479.5 n. maximum load on front cantilever pamax = pmax/2 = 14005 n. maximum load on rear cantilever pbmax = pmax/2 = 14005 n. as the leaf spring is symmetric cantilever ratio = y = a / b = 1 ; therefore , la = lb , pa = pb ( at design load ) and pamax = pbmax ( at maximum load ) . also sfa = srb = sd ( at design load ) and sfa = srb = sm ( at maximum load ) . the total stress induced in the leaf spring is the summation of load stress and assembly stress : ( 11)s = sl+sa . if all the leaves are fitted with the common unassembled curvature , then the assembly stress is zero ; but the leaves are fitted in such a manner that the radius of curvature goes on increasing from the master leaf to the last leaf . with the use of different individual leaf camber , the assembly stress can be added to or deducted from the load stress of the assembled spring to obtain desirable stress pattern in the leaf spring . the assembly stress is arbitrarily chosen except they must be selected in increasing order from the main leaf to shorter leaf such that sat = 0 . a negative assembly stress in the main leaf is required to reduce the maximum stress induced in the master leaf to safe limits as the longitudinal and lateral forces are more in the master leaf . a negative assembly stress is provided in the main leaf so as to reduce the maximum stress to about 866 mpa . the longitudinal and lateral forces imposed on the main leaf and also its greater stress range are the reasons for reducing its bending stress . in view of the condition sa t = 0 , several selections of deducted and added stresses for the individual leaves are analysed before deciding on the best arrangement as shown in table 4 . in almost all leaf springs the unassembled curvatures qn are different in the unassembled leaves . in assembly , a common ( unloaded ) curvature qo is established which is variable along the spring even if the leaves are made of circular arcs . the individual leaf curvature is calculated from common curvature as the folowing : ( 12)qn = qosaey . curvature is called positive in the direction of increasing load and camber is conventionally positive in the opposite direction . camber can be converted into curvature as ( 13)qo = curvature=8camberlength2=0.000574669 mm1 . the relationship between free curvature , assembly curvature , and loaded curvature is given by ( 14)qfree+q = qloaded . for flat leaf , the curvature is zero and it increases in the direction of load application ; and for most of the springs the free curvature is negative . the no load camber requirement for this leaf spring assembly is 95 4 mm . the deflection can be determined as force per unit load rate . for different values of the load the corresponding values of deflection the stresses induced at different loads can be determined by substituting the values of the load in the stress induced formula . the analytical results for load , deflection , and bending stress are shown in table 6 . fatigue life is expressed by the number of deflection cycles a spring will withstand without failure or permanent set . a leaf spring used in a suspension will undergo a large number of cycles of small amplitude near the design load position without failure . under the greater amplitude the number of cycles without failure will be reduced since the maximum stresses as well as the stress range are increased and both are determining factors in fatigue life of the spring . as per sae spring design manual , this criteria is frequently used for determination of approximate fatigue life of the spring ; initial stress ( horizontal scale ) and maximum stress ( vertical scale ) are intersected to estimate the number of cycles the spring will withstand for given loading condition . the fatigue test stroke for leaf spring without considering assembly stress is determined as the following : deflection to design load = 12959/153.1 = 84.6 mm , maximum load = 28 kn , metal - to - metal clearance ( compression stroke ) = 94.6 mm , total deflection to maximum load = 182.9 mm , stress at metal - to - metal position = 969 mpa , stress rate = 969/182.9 = 5.29 mpa / mm , release stroke = 0.5 94.6 = 47.3 mm , fatigue test stoke = 47.3 + 94.6 = 141.9 mm , initial stress = 969 ( 141.9 5.29 ) = 218.3 mpa . deflection to design load = 12959/153.1 = 84.6 mm , maximum load = 28 kn , metal - to - metal clearance ( compression stroke ) = 94.6 mm , total deflection to maximum load = 182.9 mm , stress at metal - to - metal position = 969 mpa , stress rate = 969/182.9 = 5.29 mpa / mm , release stroke = 0.5 94.6 = 47.3 mm , fatigue test stoke = 47.3 + 94.6 = 141.9 mm , initial stress = 969 ( 141.9 5.29 ) = 218.3 mpa . the fatigue test stroke for leaf spring by considering assembly stress is determined as the following : deflection to design load = 12959/153.1 = 84.6 mm , maximum load = 28 kn , metal - to - metal clearance ( compression stroke ) = 94.6 mm , total deflection to maximum load = 182.9 mm , stress at metal - to - metal position = 885 mpa , stress rate = 885/182.9 = 4.83 mpa / mm , release stroke = 0.5 94.6 = 47.3 mm , fatigue test stoke = 47.3 + 94.6 = 141.9 mm , initial stress = 885 ( 141.9 4.83 ) = 199.6 mpa . deflection to design load = 12959/153.1 = 84.6 mm , maximum load = 28 kn , metal - to - metal clearance ( compression stroke ) = 94.6 mm , total deflection to maximum load = 182.9 mm , stress at metal - to - metal position = 885 mpa , stress rate = 885/182.9 = 4.83 mpa / mm , release stroke = 0.5 94.6 = 47.3 mm , fatigue test stoke = 47.3 + 94.6 = 141.9 mm , initial stress = 885 ( 141.9 4.83 ) = 199.6 mpa . for the production of high strength leaf springs , the process is comprised of shearing , punching , heat treatment , hot cambering , shot peening , scragging , and testing for load rate and durability . the processing of the raw material plays a vital role in achieving the required load rate and fatigue life . after punching and shearing , the raw material the structure of the raw material is partial austenite , and after quenching the structure is martensite , but after the tempering process the structure should be tempered martensite . the material is heated in the furnace in the temperature range of 880910c depending upon the cross section thickness and width . the spring steel is having the thickness of 8 mm and width of 70 mm which is heated at 880c to achieve full austenite structure . hot cambering of the spring is done in this state by passing through finger cambering tools followed by quenching in oil at temperature of 80c . tempering is done at a temperature of 410c for 90 min slow cooling till the tempered martensite structure is achieved . the final assembly is done by pulling all the leaf with a centre nut and bolt . the 65si7 leaf springs assembly consists of two full length leaves and ten graduated leaves , four rebound clips of mild steel , four shim pipes with four nut and bolts , four rivets , centre nut and bolt , and bush of bronze . the full scale testing of leaf springs was carried out in an electrohydraulic static component testing system . the laminated leaf springs were placed in a fixture simulating the conditions of a vehicle . the setup consists of a hydraulic power pack to give a hydraulic pressure of 20.6 mpa with a flow rate of 210 liters per minute ( lpm ) , which was sent to a hydraulic actuator to operate at a frequency of 0.3 hz with the displacement specified by the alternating load . this involves applying the axial load on the leaf springs and measuring the deflection and bending stress . the conventional leaf spring was tested under static load condition by using hydraulic static load ram for load application . mounting of the leaf spring was done by keeping it in inverted manner on the test bed . two eye ends were held in the clamping devices and load was applied from the top , at the center of leaf springs . to measure the load dial indicator was used , which was located beside the full scale testing machine and deflection was measured by strain gauges located at the clamping of the test rig . the springs were loaded from unladen load ( i.e. , 7.6 kn ) to maximum load ( i.e. , 28 kn ) . the vertical deflection of the springs at the unladen load , design load , flat load , rubber touching load , and metal - to - metal contact or maximum load was recorded , respectively , as per the standard operating procedure prescribed . the leaf springs were tested on a full scale testing machine under the unladen load , rated load , flat load , rubber touching load , and metal - to - metal load , and the corresponding deflection and stress values observed are shown in table 7 . table 7 depicts the observed values of deflection and stress corresponding to the loads applied on the shorter leaf by a static hydraulic ram . as per the is1135 typically this can be between 0.5 times the rated load and twice the rated load unless otherwise specified by vehicle manufacturer . consider ( 15)oa = ob(ocob)2 , where oa = load / deflection corresponding to rated load . consider ob = load / deflection corresponding to maximum load experienced under actual vehicle conditions typically 2 g , where g is the load shared by springs under the laden condition of the vehicle . for determination of experimental fatigue life , four specimens ( s-1 , s-2 , s-3 , and s-4 per batch ) for three stress ranges ( i.e. , 269896 mpa , 218969 mpa , and 200885 mpa ) are manufactured with proposed parameters . the stress range was considered for first lot of the specimens to be 627 mpa , 1.3 0.7 g. all the four specimens were tested under same stress range and fatigue life was determined . the stress range for second lot of the specimen was 751 mpa based on sae spring design manual approach , without considering assembly stresses ; that is , all the leaves with common curvature were assembled . the stress range for third lot of the specimen was 685 mpa based on sae spring design manual approach , by considering assembly stresses . the spring was clamped in the centre to simulate its installation in the vehicle as shown in figure 3 . as per the requirement specified by the vehicle manufacturer , the leaf springs are to be tested on full scale testing machine as per 1.3 0.7 g. the maximum load will be 2 g and the minimum load will be 0.6 g. here g represents the design load . the material processing for all the twelve specimens is the same , that is , normal rolling , quenching at 880c , tempering at 410c for 90 mins , shot peening at 18 a intensity , bhn 380432 , and scragging at 0.9% of yield stress . for the first lot of the specimens the maximum stress is 896 mpa and minimum stress is 269 mpa as specified by the vehicle manufacturer . the fatigue life for the four specimens is 84212 , 81961 , 82226 , and 85656 number of cycles . the second lot of specimen is assembled by considering common curvature , that is , without assembly stresses . the fatigue life for the four specimens is 66796 , 69320 , 70119 , and 69956 number of cycles . the third lot of specimens is assembled by considering the assembly stresses and leaves with proposed individual leaf camber assembled by pulling against each other to establish common curvature . the fatigue life for the four specimens is 74827 , 76658 , 79010 , and 77229 number of cycles . it is observed that the stress range for first lot , second lot , and third lot is 627 mpa , 751 mpa , and 685 mpa , respectively . the maximum stress for first lot , second lot , and third lot is 896 mpa , 969 mpa , and 885 mpa , respectively . it is observed that the lower the stress range is the higher the fatigue life will be . but for almost same stress range , the fatigue life decreases by increasing the maximum stress . it is also observed that the experimental fatigue life increases by 11.41% by considering assembly stresses . other factors like shape , size , temperature , surface , and so forth also affect the fatigue life of the leaf springs which can be considered for estimation of fatigue life . it is observed from figure 4 that the individual leaf camber is 99 mm , which is decreasing from the main leaf . the individual leaf camber is 84 mm for the second leaf with military wrapper . hence , the individual leaf camber decreases from the main leaf to the last leaf ( almost flat ) . from figure 5 it is observed that the maximum stress induced in the leaf springs without considering the assembly stresses is 969 mpa and the initial stress value is 218 mpa . the intersection of 969 mpa and 218 mpa lies in the zone of 30000 to 50000 cycles . as the point of intersection it is observed that the maximum stress induced in the leaf springs by considering the assembly stresses is 885 mpa and the initial stress value is 200 mpa . the intersection of 885 mpa and 200 mpa lies in the zone of 50000 to 75000 cycles . as the point of intersection therefore , fatigue life of leaf springs without and with considering assembly stresses would be approximately ( 460001.2 ) 55200 cycles and ( 580001.2 ) 69600 cycles , respectively . table 9 shows the fatigue life comparison between the sae spring design manual and experimental testing , by considering and not considering the assembly stresses . it is observed from table 9 that as per sae approach the fatigue life without considering the assembly stresses is 55200 cycles and by considering the assembly stress the fatigue life is 69600 cycles . as per sae the fatigue life is 69047 and 76931 cycles without and by considering the assembly stresses , respectively , in the experimental testing . in experimental testing it is observed that the fatigue life increases by 11.41% due to the reduction in stress range , and maximum stress has reduced from 969 mpa to 885 mpa by considering assembly stress . the theoretical and experimental fatigue life of a light commercial vehicle leaf spring is determined by considering assembly stresses and without considering assembly stresses , and following conclusions are made.the maximum stress induced in the leaf spring reduces and uniform stress distribution is achieved by considering the assembly stresses . the fatigue life increases due to negative assembly stresses , which reduces the maximum stress.it is also concluded that for the same stress range , higher maximum stress reduces the fatigue life of the leaf spring and higher initial stress improves the fatigue life of the leaf springs . the maximum stress induced in the leaf spring reduces and uniform stress distribution is achieved by considering the assembly stresses . the fatigue life increases due to negative assembly stresses , which reduces the maximum stress . it is also concluded that for the same stress range , higher maximum stress reduces the fatigue life of the leaf spring and higher initial stress improves the fatigue life of the leaf springs .

the maximum stress induced plays vital role in fatigue life improvement of leaf springs . to reduce this maximum stress , leaves with different unassembled cambers are assembled by pulling against each other and a common curvature is established . this causes stress concentration or sets assembly stress in the assembled leaf springs which is subtractive from load stress in master leaf while it is additive to load stress for short leaves . by suitable combination of assembly stresses and stepping , it is possible to distribute the stress and improve the fatigue life of the leaf spring . the effect of assembly stresses on fatigue life of the leaf spring of a light commercial vehicle ( lcv ) has been studied . a proper combination of stepping and camber has been proposed by taking the design parameters into consideration , so that the stress in the leaves does not exceed maximum design stress . the theoretical fatigue life of the leaf springs with and without considering the assembly stresses is determined and compared with experimental life . the numbers of specimens are manufactured with proposed parameters and tested for load rate , fatigue life on a full scale leaf springs testing machine . the effect of stress range , maximum stress , and initial stress is also discussed .

<s>[INST]leaf springs like all other springs serve to absorb , store , and release the energy . in heavy vehicles , leaves are stacked one upon another to ensure rigidity and strength . during its operation , the leaf spring requires that the load rate should vary within limit ( 7% ) and the maximum stress induced should be lower than the maximum design stress . for a given stress range the leaf spring should have maximum fatigue life or as specified . the stress range and the maximum stress induced in the leaf spring play a vital role in deciding the load rate and fatigue life of the leaf spring . the maximum stress induced can be reduced by assembling the leaves with different radii of curvature and establishing a common curvature under no load . the proper distribution of the stress between the leaves can enhance the fatigue life of the leaf springs . evaluated the axial fatigue strength of en45a spring steel specimen experimentally as a function of shot peening in the conditions used . s / n curves of the specimens were correlated with leaf springs curve in vehicles . concluded that the influence of high contact pressure and temperatures resulted in microweld between the two leaf surfaces . the fatigue strength of the leaf springs was studied as a function of shot peening parameters . an experimental leaf springs model was verified by using a leaf springs test rig that could measure vertical static deflection of leaf springs under static loading condition . the results showed a nonlinear relationship between the applied load and the leaf springs deflection for both directions of loading , in form of a hysteresis loop . . studied the origin of premature failure analysis procedures , including examining the leaf spring history . the visual inspection of fractured specimens and simulation tests on real components were also performed . it was concluded that fracture occurred by a mechanism of mechanical fatigue initiated at the region of the central hole , which suffered the highest tensile stress levels . kumar and vijayarangan described static and fatigue analysis of steel leaf springs and composite multileaf springs made up of glass fibre reinforced polymer using life data analysis . the dimensions of an existing conventional steel leaf spring of a light commercial vehicle were taken and verified by design calculations . static analysis of 2d model of conventional leaf springs was also performed using ansys 7.1 , and the results obtained were compared with experimental results . patunkar and dolas worked on nonlinear force displacement of each leaf spring as well as the spring characteristics of a pack consisting of two to four leaves using ansys . the results from ansys were compared with those from the test , which showed a fairly good agreement with each other . the objective of the present work is to determine the effect of assembly stresses on fatigue life reliability of leaf springs . it is available in open literature that with proper combination of stepping and individual leaf camber the stress distribution can be uniform along the leaf . the 65si7 leaf springs design parameter of a light commercial vehicle is taken into consideration for this work . this paper is divided into two parts . in part one , a design procedure for determination of total moment of inertia , number of leaves , and stepping and individual leaf camber is established . the stepping and individual leaf camber is proposed with a view to lower stresses . using sae approach fatigue life of the leaf spring , three leaf springs specimens lots ( four leaf spring assemblies in each lot ) have been manufactured . all the specimens are tested on a full scale leaf spring testing machine for fatigue life of the leaf spring . the theoretical and experimental fatigue life results ( with and without assembly stresses ) are compared for validation . the material is heat - treated at 880c and oil - quench - hardened and it is tempered at 410c for 90 minutes to get tempered martensite structure . a leaf spring is considered as a beam of uniform strength composed of leaves of equal thickness where the fiber stress is the same throughout the length of the beam . this approximation is justified for most of the springs within the accuracy necessary for layout work and with certain correction factors for estimate of required length , overhang , camber , width , thickness , and number of leaves . the calculation of the leaf spring parameters involves certain number of steps . as per sae spring design manual approach , the steps involved in leaf springs design are as follows . consider ( 1)i = kl332esf=34351.7 mm4 , where k = load rate , l = spring span , e = young 's modulus , and sf = stiffening factor . consider ( 2)tmax=8ismaxlpmax=8.20 mm . consider ( 3)i1=n1i1 , where n1 = number of leaves with thickness t1 , i1 = moment of inertia for section t1 = 8 mm , and width b = 70 mm and ( 4)i1=b1t1312 + 3.1428t1464=2846.5 mm4 , where b1 = b t1 = 62 mm and n1 = 11 . consider ( 5)i1=112846.13=31311 mm4i2=n2i2 , where n2 = number of leaves with thickness t2 , i2 = moment of inertia for section t2 = 7 mm , and width b = 70 mm and ( 6)i2=b2t2312 + 3.1428t2464=1918.6 mm4 , where n2 = 1 and b2 = b t2 = 63 mm and ( 7)i2=11918.6=1918.6 mm4itotal=i1+i2=33230 mm4 . n / mm% age variation of k=3.271% ( hence acceptable ) . the seat clamp is taken into consideration for stress calculation between the leaves . the inactive length in the seat for a spring without liners is estimated as distance between the outside edges of the clamp bolts which is 100 mm for this spring . the active length for both front and rear cantilever will be 50 mm less than the distance from centre of the eye to centre of an axle seat . the stress at 50 mm distance from the centre of axle seat can be calculated as the following : ( 10)front cantilever stress , sfa = palat2itrear cantilever stress , srb = pblbt2it . front cantilever ( a ) length = l = l/2 = 575 mm and rear cantilever ( b ) length = l = l/2 = 575 mm . cantilever ratio y = a / b = 1 ( symmetric spring ) and seat length sl = 100 mm . active length of front cantilever la = ( l sl/2 ) = 525 mm . active length of rear cantilever lb = ( l sl/2 ) = 525 mm . design load on front cantilever pa = p/2 = 6479.5 n. design load on rear cantilever pb = p/2 = 6479.5 n. maximum load on front cantilever pamax = pmax/2 = 14005 n. maximum load on rear cantilever pbmax = pmax/2 = 14005 n. as the leaf spring is symmetric cantilever ratio = y = a / b = 1 ; therefore , la = lb , pa = pb ( at design load ) and pamax = pbmax ( at maximum load ) . also sfa = srb = sd ( at design load ) and sfa = srb = sm ( at maximum load ) . front cantilever ( a ) length = l = l/2 = 575 mm and rear cantilever ( b ) length = l = l/2 = 575 mm . cantilever ratio y = a / b = 1 ( symmetric spring ) and seat length sl = 100 mm . active length of front cantilever la = ( l sl/2 ) = 525 mm . active length of rear cantilever lb = ( l sl/2 ) = 525 mm . design load on front cantilever pa = p/2 = 6479.5 n. design load on rear cantilever pb = p/2 = 6479.5 n. maximum load on front cantilever pamax = pmax/2 = 14005 n. maximum load on rear cantilever pbmax = pmax/2 = 14005 n. as the leaf spring is symmetric cantilever ratio = y = a / b = 1 ; therefore , la = lb , pa = pb ( at design load ) and pamax = pbmax ( at maximum load ) . also sfa = srb = sd ( at design load ) and sfa = srb = sm ( at maximum load ) . the total stress induced in the leaf spring is the summation of load stress and assembly stress : ( 11)s = sl+sa . if all the leaves are fitted with the common unassembled curvature , then the assembly stress is zero ; but the leaves are fitted in such a manner that the radius of curvature goes on increasing from the master leaf to the last leaf . with the use of different individual leaf camber , the assembly stress can be added to or deducted from the load stress of the assembled spring to obtain desirable stress pattern in the leaf spring . the assembly stress is arbitrarily chosen except they must be selected in increasing order from the main leaf to shorter leaf such that sat = 0 . a negative assembly stress in the main leaf is required to reduce the maximum stress induced in the master leaf to safe limits as the longitudinal and lateral forces are more in the master leaf . a negative assembly stress is provided in the main leaf so as to reduce the maximum stress to about 866 mpa . the longitudinal and lateral forces imposed on the main leaf and also its greater stress range are the reasons for reducing its bending stress . in view of the condition sa t = 0 , several selections of deducted and added stresses for the individual leaves are analysed before deciding on the best arrangement as shown in table 4 . in almost all leaf springs the unassembled curvatures qn are different in the unassembled leaves . in assembly , a common ( unloaded ) curvature qo is established which is variable along the spring even if the leaves are made of circular arcs . the individual leaf curvature is calculated from common curvature as the folowing : ( 12)qn = qosaey . curvature is called positive in the direction of increasing load and camber is conventionally positive in the opposite direction . camber can be converted into curvature as ( 13)qo = curvature=8camberlength2=0.000574669 mm1 . the relationship between free curvature , assembly curvature , and loaded curvature is given by ( 14)qfree+q = qloaded . for flat leaf , the curvature is zero and it increases in the direction of load application ; and for most of the springs the free curvature is negative . the no load camber requirement for this leaf spring assembly is 95 4 mm . the deflection can be determined as force per unit load rate . for different values of the load the corresponding values of deflection the stresses induced at different loads can be determined by substituting the values of the load in the stress induced formula . the analytical results for load , deflection , and bending stress are shown in table 6 . fatigue life is expressed by the number of deflection cycles a spring will withstand without failure or permanent set . a leaf spring used in a suspension will undergo a large number of cycles of small amplitude near the design load position without failure . under the greater amplitude the number of cycles without failure will be reduced since the maximum stresses as well as the stress range are increased and both are determining factors in fatigue life of the spring . as per sae spring design manual , this criteria is frequently used for determination of approximate fatigue life of the spring ; initial stress ( horizontal scale ) and maximum stress ( vertical scale ) are intersected to estimate the number of cycles the spring will withstand for given loading condition . the fatigue test stroke for leaf spring without considering assembly stress is determined as the following : deflection to design load = 12959/153.1 = 84.6 mm , maximum load = 28 kn , metal - to - metal clearance ( compression stroke ) = 94.6 mm , total deflection to maximum load = 182.9 mm , stress at metal - to - metal position = 969 mpa , stress rate = 969/182.9 = 5.29 mpa / mm , release stroke = 0.5 94.6 = 47.3 mm , fatigue test stoke = 47.3 + 94.6 = 141.9 mm , initial stress = 969 ( 141.9 5.29 ) = 218.3 mpa . deflection to design load = 12959/153.1 = 84.6 mm , maximum load = 28 kn , metal - to - metal clearance ( compression stroke ) = 94.6 mm , total deflection to maximum load = 182.9 mm , stress at metal - to - metal position = 969 mpa , stress rate = 969/182.9 = 5.29 mpa / mm , release stroke = 0.5 94.6 = 47.3 mm , fatigue test stoke = 47.3 + 94.6 = 141.9 mm , initial stress = 969 ( 141.9 5.29 ) = 218.3 mpa . the fatigue test stroke for leaf spring by considering assembly stress is determined as the following : deflection to design load = 12959/153.1 = 84.6 mm , maximum load = 28 kn , metal - to - metal clearance ( compression stroke ) = 94.6 mm , total deflection to maximum load = 182.9 mm , stress at metal - to - metal position = 885 mpa , stress rate = 885/182.9 = 4.83 mpa / mm , release stroke = 0.5 94.6 = 47.3 mm , fatigue test stoke = 47.3 + 94.6 = 141.9 mm , initial stress = 885 ( 141.9 4.83 ) = 199.6 mpa . deflection to design load = 12959/153.1 = 84.6 mm , maximum load = 28 kn , metal - to - metal clearance ( compression stroke ) = 94.6 mm , total deflection to maximum load = 182.9 mm , stress at metal - to - metal position = 885 mpa , stress rate = 885/182.9 = 4.83 mpa / mm , release stroke = 0.5 94.6 = 47.3 mm , fatigue test stoke = 47.3 + 94.6 = 141.9 mm , initial stress = 885 ( 141.9 4.83 ) = 199.6 mpa . for the production of high strength leaf springs , the process is comprised of shearing , punching , heat treatment , hot cambering , shot peening , scragging , and testing for load rate and durability . the processing of the raw material plays a vital role in achieving the required load rate and fatigue life . after punching and shearing , the raw material the structure of the raw material is partial austenite , and after quenching the structure is martensite , but after the tempering process the structure should be tempered martensite . the material is heated in the furnace in the temperature range of 880910c depending upon the cross section thickness and width . the spring steel is having the thickness of 8 mm and width of 70 mm which is heated at 880c to achieve full austenite structure . hot cambering of the spring is done in this state by passing through finger cambering tools followed by quenching in oil at temperature of 80c . tempering is done at a temperature of 410c for 90 min slow cooling till the tempered martensite structure is achieved . the final assembly is done by pulling all the leaf with a centre nut and bolt . the 65si7 leaf springs assembly consists of two full length leaves and ten graduated leaves , four rebound clips of mild steel , four shim pipes with four nut and bolts , four rivets , centre nut and bolt , and bush of bronze . the full scale testing of leaf springs was carried out in an electrohydraulic static component testing system . the laminated leaf springs were placed in a fixture simulating the conditions of a vehicle . the setup consists of a hydraulic power pack to give a hydraulic pressure of 20.6 mpa with a flow rate of 210 liters per minute ( lpm ) , which was sent to a hydraulic actuator to operate at a frequency of 0.3 hz with the displacement specified by the alternating load . this involves applying the axial load on the leaf springs and measuring the deflection and bending stress . the conventional leaf spring was tested under static load condition by using hydraulic static load ram for load application . mounting of the leaf spring was done by keeping it in inverted manner on the test bed . two eye ends were held in the clamping devices and load was applied from the top , at the center of leaf springs . to measure the load dial indicator was used , which was located beside the full scale testing machine and deflection was measured by strain gauges located at the clamping of the test rig . the springs were loaded from unladen load ( i.e. , 7.6 kn ) to maximum load ( i.e. , 28 kn ) . the vertical deflection of the springs at the unladen load , design load , flat load , rubber touching load , and metal - to - metal contact or maximum load was recorded , respectively , as per the standard operating procedure prescribed . the leaf springs were tested on a full scale testing machine under the unladen load , rated load , flat load , rubber touching load , and metal - to - metal load , and the corresponding deflection and stress values observed are shown in table 7 . table 7 depicts the observed values of deflection and stress corresponding to the loads applied on the shorter leaf by a static hydraulic ram . as per the is1135 typically this can be between 0.5 times the rated load and twice the rated load unless otherwise specified by vehicle manufacturer . consider ( 15)oa = ob(ocob)2 , where oa = load / deflection corresponding to rated load . consider ob = load / deflection corresponding to maximum load experienced under actual vehicle conditions typically 2 g , where g is the load shared by springs under the laden condition of the vehicle . for determination of experimental fatigue life , four specimens ( s-1 , s-2 , s-3 , and s-4 per batch ) for three stress ranges ( i.e. , 269896 mpa , 218969 mpa , and 200885 mpa ) are manufactured with proposed parameters . the stress range was considered for first lot of the specimens to be 627 mpa , 1.3 0.7 g. all the four specimens were tested under same stress range and fatigue life was determined . the stress range for second lot of the specimen was 751 mpa based on sae spring design manual approach , without considering assembly stresses ; that is , all the leaves with common curvature were assembled . the stress range for third lot of the specimen was 685 mpa based on sae spring design manual approach , by considering assembly stresses . the spring was clamped in the centre to simulate its installation in the vehicle as shown in figure 3 . as per the requirement specified by the vehicle manufacturer , the leaf springs are to be tested on full scale testing machine as per 1.3 0.7 g. the maximum load will be 2 g and the minimum load will be 0.6 g. here g represents the design load . the material processing for all the twelve specimens is the same , that is , normal rolling , quenching at 880c , tempering at 410c for 90 mins , shot peening at 18 a intensity , bhn 380432 , and scragging at 0.9% of yield stress . for the first lot of the specimens the maximum stress is 896 mpa and minimum stress is 269 mpa as specified by the vehicle manufacturer . the fatigue life for the four specimens is 84212 , 81961 , 82226 , and 85656 number of cycles . the second lot of specimen is assembled by considering common curvature , that is , without assembly stresses . the fatigue life for the four specimens is 66796 , 69320 , 70119 , and 69956 number of cycles . the third lot of specimens is assembled by considering the assembly stresses and leaves with proposed individual leaf camber assembled by pulling against each other to establish common curvature . the fatigue life for the four specimens is 74827 , 76658 , 79010 , and 77229 number of cycles . it is observed that the stress range for first lot , second lot , and third lot is 627 mpa , 751 mpa , and 685 mpa , respectively . the maximum stress for first lot , second lot , and third lot is 896 mpa , 969 mpa , and 885 mpa , respectively . it is observed that the lower the stress range is the higher the fatigue life will be . but for almost same stress range , the fatigue life decreases by increasing the maximum stress . it is also observed that the experimental fatigue life increases by 11.41% by considering assembly stresses . other factors like shape , size , temperature , surface , and so forth also affect the fatigue life of the leaf springs which can be considered for estimation of fatigue life . it is observed from figure 4 that the individual leaf camber is 99 mm , which is decreasing from the main leaf . the individual leaf camber is 84 mm for the second leaf with military wrapper . hence , the individual leaf camber decreases from the main leaf to the last leaf ( almost flat ) . from figure 5 it is observed that the maximum stress induced in the leaf springs without considering the assembly stresses is 969 mpa and the initial stress value is 218 mpa . the intersection of 969 mpa and 218 mpa lies in the zone of 30000 to 50000 cycles . as the point of intersection it is observed that the maximum stress induced in the leaf springs by considering the assembly stresses is 885 mpa and the initial stress value is 200 mpa . the intersection of 885 mpa and 200 mpa lies in the zone of 50000 to 75000 cycles . as the point of intersection therefore , fatigue life of leaf springs without and with considering assembly stresses would be approximately ( 460001.2 ) 55200 cycles and ( 580001.2 ) 69600 cycles , respectively . table 9 shows the fatigue life comparison between the sae spring design manual and experimental testing , by considering and not considering the assembly stresses . it is observed from table 9 that as per sae approach the fatigue life without considering the assembly stresses is 55200 cycles and by considering the assembly stress the fatigue life is 69600 cycles . as per sae the fatigue life is 69047 and 76931 cycles without and by considering the assembly stresses , respectively , in the experimental testing . in experimental testing it is observed that the fatigue life increases by 11.41% due to the reduction in stress range , and maximum stress has reduced from 969 mpa to 885 mpa by considering assembly stress . the theoretical and experimental fatigue life of a light commercial vehicle leaf spring is determined by considering assembly stresses and without considering assembly stresses , and following conclusions are made.the maximum stress induced in the leaf spring reduces and uniform stress distribution is achieved by considering the assembly stresses . the fatigue life increases due to negative assembly stresses , which reduces the maximum stress.it is also concluded that for the same stress range , higher maximum stress reduces the fatigue life of the leaf spring and higher initial stress improves the fatigue life of the leaf springs . the maximum stress induced in the leaf spring reduces and uniform stress distribution is achieved by considering the assembly stresses . the fatigue life increases due to negative assembly stresses , which reduces the maximum stress . it is also concluded that for the same stress range , higher maximum stress reduces the fatigue life of the leaf spring and higher initial stress improves the fatigue life of the leaf springs .[/INST]the maximum stress induced plays vital role in fatigue life improvement of leaf springs . to reduce this maximum stress , leaves with different unassembled cambers are assembled by pulling against each other and a common curvature is established . this causes stress concentration or sets assembly stress in the assembled leaf springs which is subtractive from load stress in master leaf while it is additive to load stress for short leaves . by suitable combination of assembly stresses and stepping , it is possible to distribute the stress and improve the fatigue life of the leaf spring . the effect of assembly stresses on fatigue life of the leaf spring of a light commercial vehicle ( lcv ) has been studied . a proper combination of stepping and camber has been proposed by taking the design parameters into consideration , so that the stress in the leaves does not exceed maximum design stress . the theoretical fatigue life of the leaf springs with and without considering the assembly stresses is determined and compared with experimental life . the numbers of specimens are manufactured with proposed parameters and tested for load rate , fatigue life on a full scale leaf springs testing machine . the effect of stress range , maximum stress , and initial stress is also discussed .</s>

macrophages are plastic phagocytic cells that participate in innate and adaptive immunity , with important roles in the response against extra- and intracellular parasites , as well as in tissue homeostasis [ 1 , 2 ] . , macrophages contribute to mounting specific immunological responses for host defense , and the plasticity of macrophage phenotypes is modulated by the cytokine profile . tissue damage during inflammation increases the extracellular levels of otherwise intracellular molecules , resulting in damage - associated molecular patterns ( damps ) recognized by the immune system [ 35 ] . extracellular nucleotides , such as the atp released by dying cells and by activated immune cells during inflammation , are important danger signals involved in immune response , participating in both paracrine and autocrine signaling pathways . in inflammatory processes , high extracellular atp levels generated by tissue damage or secretion are recognized by the immune system as a danger signal , activating purinergic p2 receptors that contribute to a proinflammatory response . purinergic p2 receptors can be classified as ionotropic atp - gated ( p2x ) or g - protein coupled metabotropic ( p2y ) . extracellular atp ( eatp ) induces macrophage - mediated immune responses mainly through the activation of p2x7 receptors . these receptors have a ubiquitous distribution , although the highest levels of receptor expression are observed in immune cells of monocyte / macrophage origin . p2x7 receptor activation induces a myriad of intracellular events , including the production of nitric oxide ( no ) and of reactive oxygen species ( ros ) and the activation of phospholipase - d ( pld ) . these events are important for intracellular parasite killing , for the release of proinflammatory cytokines ( such as il-1 ) , and for inducing apoptosis [ 13 , 14 ] . the expression and function of p2x7 receptors are regulated by both pro- and anti - inflammatory stimuli . initially , p2x7 receptor activation in macrophages opens a plasma membrane cation channel that allows a substantial efflux of k , and influx of ca , with later formation of pores permeable to large molecules [ 16 , 17 ] . p2x receptor activation may also induce caspase-1 activation , interleukin il-1 release , apoptosis , phagolysosomal fusion , and the elimination of intracellular pathogens [ 14 , 18 , 19 ] . in murine macrophages , the mature il-1 secretion by the activation of p2x7 receptors is reduced by the incubation in a free - ca buffer . thus , murine macrophage release of mature il-1 depends on intracellular ca , confirming that ca signaling is essential for this p2x7 receptor function . schistosomiasis is a chronic inflammatory disease caused by schistosoma mansoni and it represents the second most common tropical parasitic disease related to socioeconomical factors . while migrating through the vascular system of infected mammalian hosts , parasites evolve from the schistosomula migratory form into adult worms , causing endothelial cell activation , immunological responses , and tissue damage . the disease starts with a th1-type immune response that gradually changes to a th2 profile [ 2124 ] . previous data suggest that the th2 stage begins four to six weeks after infection and is related to egg deposition by adult worms . macrophages play important roles in both phases of schistosomiasis . in the early phase of the disease , macrophages act as immune system effectors cells killing schistosomula and promoting tissue repair . after egg deposition , the immune response switches to a th2 profile that is involved in the formation of liver and colonic granulomas and fibrosis . the eggs are laid in mesenteric microcirculation and they may reach peritoneal cavity where the granulomas formed contain mainly macrophages . although granulomas are important to limit egg - derived potential cytotoxic products , macrophages isolated , for example , from hepatic granulomas , produce lipids mediators and free radicals that are potentially destructive to host tissues . among cytokines involved in schistosomiasis , transforming growth factor-1 ( tgf-1 ) is of particular interest , since high levels of this cytokine are released by peripheral blood mononuclear cells ( pbmcs ) from s. mansoni - infected mice . tgf- has an important role in immune modulation later during infection , limiting liver inflammation and favoring host survival [ 27 , 28 ] . recently , bhardwaj and skelly showed that s. mansoni expresses p2x7 receptors - like molecules and also enzymes responsible for the clearance of extracellular atp ( ectonucleotidases ) , suggesting that purinergic signaling is conserved in these parasites and is important for the host - parasite interplay . however , the impact of the chronic inflammation trigged by schistosomiasis on macrophage p2x7 receptor function remains unknown . here , we evaluated p2x7 receptor function and expression in macrophage from s. mansoni - infected mice . our data show that peritoneal macrophage p2x7 receptor function is attenuated during schistosomiasis and that this is associated with high peritoneal levels of tgf-1 , the important inflammatory mediator present in the chronic phase of the disease . we also show that tgf-1 downregulates p2x function in vitro , mimicking the effect of s. mansoni infection . the following primary antibodies were used in this work : rabbit polyclonal anti - p2x7 receptors ( apr-004 and apr-008 ; alomone labs , israel ) ; mouse monoclonal anti--actin ( santa cruz biotechnology , usa ) ; rat anti - f4/80 ( biolegend , usa ) ; rat anti - f4/80 fitc ( abd serotec , usa ) . atp , 3-o-(4-benzoyl)-atp ( bzatp ) , pmsf , sodium orthovanadate , aprotinin , leupeptin , bsa , ionomycin , and egta were from sigma chemical co. ( usa ) . fura-2-am was from molecular probes ( usa ) and a740003 was from tocris ( usa ) . rpmi , foetal bovine serum ( fbs ) , and penicillin / streptomycin solutions were from gibco brl ( usa ) . stock solutions were prepared in dmso ( 2.5 mm fura-2-am and 10 mm a740003 ) , water ( 10 mm bzatp ) , rpmi ( 5 ng / ml tgf-1 ) , or a buffered physiological saline solution ( 10 mm atp ) . the highest concentration of solvent used was 0.1% ( v / v ) . swiss , c57bl/6 ( wild type ) , and p2x7 receptor knockout ( p2x7 ko ) male mice were used in all procedures . swiss and c57bl/6 mice were obtained from the animal facility of the paulo de goes microbiology institute ( federal university of rio de janeiro , rio de janeiro , brazil ) . p2x7 ko mice ( originally from the jackson laboratory , usa , stock number 005576 ) were maintained in the transgenic animal house of the federal university of rio de janeiro . all mice were kept under a light / dark cycle of 12/12 h and with access to water and food ad libitum . all experiments were conducted in compliance with the ethical standards of our institution ( ethics committee of the federal university of rio de janeiro ; approved under the licenses dfbc - icb-011 and ibccf 154 ) and following both the guidelines of the national council on experimental animal control ( concea , brazil ) and the committee of care and use of laboratory animals ( national research council , united states ) . all efforts were made to minimize both animals suffering and the number of animals used , on the basis of valid statistical evaluation . in this work , we used the bh strain of s. mansoni , obtained from infected biomphalaria glabrata snails . swiss , c57bl/6 , and p2x7 ko mice ( 7 - 10 days old ) were infected percutaneously with approximately 80 cercariae from both genders , for 8 min , as previously described . animals were used in experiments at least 45 days after infection ( dpi ) to allow for full establishment of the infection . age - matched ( 60 to 80 days old ) uninfected swiss , c57bl/6 , and p2x7 ko mice were used as controls . c57bl/6 and p2x7 ko mice survival the peritoneal cavity was washed with 5 ml of sterile phosphate buffered saline ( pbs : 137 mm nacl , 8.1 mm na2hpo4 , 1.5 mm nah2po4 , and 2.7 mm kcl , ph 7.4 ) , and the peritoneal exudate was collected and centrifuged at 350 g , for 5 min , at 4c . the pellet was resuspended in 1 ml of pbs and used to perform total leukocyte counts ( cell viability , as estimated by trypan blue exclusion , was always 95% ) . for macrophages culture , cells were resuspended in 1 ml of rpmi-1640 medium containing 2 g / l sodium bicarbonate , 1 mm l - glutamine , 100 u / ml penicillin , and 100 g / ml streptomycin and plated in 35 mm petri dishes or on 6-well plates . after 1 h of incubation at 37c with 5% co2 , nonadherent cells were removed by vigorous washing , and rpmi-1640 medium with 10% heat - inactivated fbs was added to the cultures , which were kept at 37c with 5% co2 for 24 h until further use . to investigate macrophage responses to atp , freshly harvested peritoneal macrophages ( 10 cells ) from swiss ( uninfected or s. mansoni - infected ) or c57bl/6 ( wild type or p2x7 ko ) mice were treated with 0.1 , 0.5 , or 1 mm atp and 2.5 m ethidium bromide ( eb ) in pbs ( 15 min ; 37c ) . eb was used as a tracer for p2x7 receptor activation ( i.e. , cell permeabilization ) triggered by atp . after incubation with atp and eb , f4/80 positive cells were analyzed by flow cytometry ( 10,000 events / sample ) using a facscan system ( bd pharmingen , usa ) . , a marker was added based on a gate of the f4/80 positive macrophages population , which limited the basal fluorescence . the specific atp - induced permeabilization threshold was defined by comparison with the baseline profile of control cells not treated with atp ( i.e. , incubated with eb only ) . the specific permeabilization is the percentage of eb positive cells after atp stimulation in the f4/80 positive gated cells . alternatively , peritoneal macrophages were plated on 24-well plates ( 2 10 cells / well ) and , after 24 h , treated with 5 ng / ml tgf-1 or vehicle ( rpmi ) , for 24 h , at 37c and in 5% co2 . macrophages were washed in pbs ( ph 7.4 ) and then incubated with 1 mm atp and 5 m eb in buffer ( 145 mm nacl , 5 mm kcl , 1 mm mgcl2 , 1 mm cacl , and 10 mm hepes , ph 7.4 ) for 15 min at 37c to evaluate the p2x7 receptor activation . the ratio between permeabilized ( i.e. , eb positive ) and total cells was determined by direct counting of cells in five randomly chosen fields , using an axiovert 100 microscope ( karl zeiss , oberkochen , germany ) equipped with an olympus digital camera ( olympus american inc . the specific atp - induced permeabilization value ( in % ) was calculated by subtracting from the total % of permeabilized cells a value corresponding to the % of permeabilized cells in control samples not treated with atp ( i.e. , incubated with eb only ) . measurements of the intracellular ca concentration ( [ ca]i ) using fura-2-am were performed as previously described . briefly , macrophages were plated on glass bottom plates ( mattek , usa ) , at a density of 1 10 cells / plate , and maintained for 24 h at 37c , with 5% co2 . then , the medium was removed and the cells were incubated for 40 min with 2.5 m fura-2-am at room temperature . cells were subjected to alternate cycles of illumination with 340 nm and 380 nm excitation wavelengths , and the emission was measured at 500 nm . cells were washed twice with buffered physiological solution ( in mm : nacl 140 , kcl 5 , mgcl2 1 , cacl2 2 , glucose 5 , and hepes 5 , ph 7.4 ) and then stimulated with 100 m 3-o-(4-benzoyl)-atp ( bzatp ) ( at 37c ) in the absence or in the presence of 50 nm of the p2x7 receptor antagonist a740003 ( preincubated for 45 min , at 37c ) . after the maximum effect had been achieved , cells were treated with ca ionophore ( 10 m ionomycin ) and then with 6 mm egta to determine the molar concentration of ca according to the grynkiewicz equation . the estimation of tgf-1 levels in mouse peritoneal washes was performed using an elisa immunoassay kit ( peprotech , rocky hill , nj , usa ) , according to manufacturer 's instructions . for peritoneal wash collection , mice were euthanized with co2 and the peritoneal cavity was washed with 1 ml of sterile pbs . approximately 60% of the initial volume of pbs was recovered and centrifuged at 350 g for 5 min , at 4c . supernatants were collected and stored in liquid n2 until further use ( to determine tgf-1 content ) . peritoneal macrophages from control and infected mice ( 10 cells / well ) were treated with 5 ng / ml tgf- for 24 h , fixed with 4% paraformaldehyde and 4% sucrose for 10 min in pbs , washed , and incubated for 30 min with 50 mm ammonium chloride ( ph 8.0 ) . after three washes in pbs , samples were blocked in pbs with 10% fbs and 0.1% bsa for 30 min , washed twice in pbs , and incubated overnight with a rabbit polyclonal antibody that recognizes an extracellular epitope of p2x7 receptors ( apr-008 ; alomone labs , israel ; peptide kkgwmdpqskgiqtgrc , corresponding to amino acid residues 136152 of mouse p2x7 receptor ; extracellular loop ) diluted to 1 : 400 in pbs and 0.1% bsa . then , cells were washed and incubated with a rat anti - f4/80 antibody diluted to 1 : 50 in pbs and 0.1% bsa for 4 h , at 4c . samples were then labelled with secondary anti - rabbit - alexa 488 and anti - rat - alexa 546 antibodies diluted to 1 : 500 in pbs and 0.1% bsa for 1 h at 4c . after labelling , cells were mounted on slides using vectashield with dapi ( vector , burlingame , ca , usa ) and examined on a tcs - sp5 aobs confocal microscope ( leica microsystems , germany ) . , imagej , us national institutes of health , bethesda , maryland , usa , http://imagej.nih.gov/ij/ , 19972014 ) . the region of interest ( roi ) was delimited in each cell and the respective mean fluorescence intensity was measured based on the pixel intensity . 10 cells per image were evaluated and the fluorescent values were used for statistical analysis . data were also displayed in an orthogonal slice view that shows the raw pixel intensity values found mutually in each of three perpendicular planes . macrophages adhered to 6-well plates were washed with sterile pbs and lysed with 200 l ripa buffer ( 50 mm tris - hcl , ph 7.4 , containing 1% nonidet p40 , 0.25% sodium deoxycholate , 150 mm nacl , 1 mm edta , 1 mm pmsf , 1 mm sodium orthovanadate , 1 mm naf , 10 g / ml aprotinin , and 10 g / ml leupeptin ) . cell lysates were incubated at 4c for 30 min and centrifuged at 8,100 g , for 10 min , at 4c ; the pellets were discarded and the supernatant had their protein content determined by the lowry method . page gels ( 15 g protein / lane ) and then transferred to nitrocellulose membranes using a semidry transfer system . membranes were blocked for 1 h in tris - buffered saline ( tbs ) with 2% nonfat milk and then incubated overnight with rabbit anti - p2x7 receptors ( apr-004 ; alomone labs , israel ; 1 : 200 ; peptide ( c)kirkefpktqgqysgfkypy , corresponding to amino acid residues 576595 of p2x7 receptor intracellular , c - terminus ) or mouse monoclonal anti--actin ( 1 : 20.000 ) primary antibodies . after 3 washes in tbs - tween , membranes were incubated with hrp - conjugated anti - rabbit or anti - mouse secondary antibody ( 1 : 1.000 ) for 1 h and developed using enhanced chemiluminescence ( ecl ) . ponceau staining and labeling with a monoclonal anti--actin antibody were used as internal controls for protein loading . densitometry of protein bands was performed using the imagej software , and the values for relative amounts of protein were normalized to the -actin loading control . peritoneal macrophages from uninfected swiss mice ( treated with 5 ng / ml tgf-1 or with vehicle , for 24 h ) or from s. mansoni - infected mice were used to isolate total rna using the trizol reagent ( life technologies ) , according to the manufacturer 's instructions . total rna was quantified using an nd-1000 spectrophotometer ( nanodrop ) , and cdna was synthesized from 500 ng of total rna using the high capacity cdna reverse transcription kit with rnase inhibitor ( invitrogen ) . the sybr select master mix ( applied biosystems ) was used for qrt - pcr , to detect double - stranded dna synthesis . reactions were carried out in a final volume of 10 l , using 2 l of diluted cdna ( 1 : 10 ) and 300 nm of each of the reverse and forward primers . the following primers were used for qrt - pcr : for p2rx7 , 5 aatcggtgtgtttcctttgg 3 ( forward ) and 5 ccgggtgactttgtttgtct 3 ( reverse ) ; for actb , 5 tatgccaacacagtgctgtctgg 3 ( forward ) and 5 tactcctgcttgctgatccacat 3 ( reverse ) ; and for gapdh , 5 ggtcatcccagagctgaacg 3 ( forward ) and 5 ttgctgttgaagtcgcagga 3 ( reverse ) . reactions were performed in a 7500 fast real - time system ( applied biosystems ) , using the following pcr conditions : 5 min at 95c , followed by 40 cycles of 15 s at 95c , 35 s at 60c , and 15 s at 72c . at the end of cycling protocol , a melting - curve analysis ( with fluorescence measurements from 60 to 99c ) was performed . relative expression levels were determined using the sequence detection software v.2.0.5 ( applied biosystems ) , and the efficiency per sample was calculated using the linregpcr 11.0 software ( manufacturer).-actin and gapdh were used as internal controls to calculate relative p2rx7 mrna levels , by the comparative threshold cycle ( ct ) method with efficiency correction , using the mean qrt - pcr efficiency for each amplicon , as previously described [ 34 , 35 ] . differences between two or more groups were analyzed by student 's t - test or one - way analysis of variance ( anova ) followed by post hoc newman - keuls test , respectively , considering p < 0.05 . we used several approaches to examine the impact of the chronic inflammation triggered by s. mansoni infection on macrophage p2x7 receptor function . activation of p2x7 receptors by atp opens plasma membrane pores that allow molecules greater than 900 kda ( such as the fluorescent dye eb ) to enter the cells [ 17 , 36 ] . thus , we used atp - induced cell permeabilization ( as evidenced by staining with eb ) as a tool to compare the p2x7 receptor activation in peritoneal macrophage from infected and uninfected swiss mice . incubations with 0.11 mm atp induced cell permeabilization in macrophages from uninfected mice ; however , this effect was reduced in macrophages from infected mice ( figure 1(a ) ) . atp also induced permeabilization in macrophages from c57bl/6 wild type mice but , as expected , not in macrophages from p2x7 ko mice ( figure 1(b ) ) . we also used the potent p2x7 agonist bzatp to verify if p2x7 receptor activation increased the cytosolic ca concentration in macrophages from infected and uninfected swiss mice , since atp - induced ca influx is a hallmark of p2x7 activation . the basal levels of cytosolic ca ( before bzatp addition ) were similar in both groups ( figure 2(a ) ) . after treatment with 100 m bzatp , macrophages from uninfected mice showed a typical p2x7 receptors activation profile at 37c , characterized by a pronounced biphasic increase in intracellular ca levels ( figure 2(a ) ) . however , the p2x7 receptor - mediated ca influx was considerably less pronounced in macrophages from infected mice when compared to that observed in macrophages from uninfected mice ( figures 2(a ) and 2(b ) ) . we also assessed changes in intracellular ca in the presence of the selective p2x7 receptor antagonist a740003 . treatment with 50 nm a740003 did not alter basal intracellular ca levels , but it had a strong negative effect on the bzatp - induced ca influx , and this effect was similar in macrophages from both groups . these results confirmed that the increase in intracellular ca levels after addition of bzatp was due to p2x7 receptor activation . these data are in agreement with the reduction in atp - induced permeabilization observed in macrophages from infected mice ( figure 1(a ) ) and suggest that p2x7 receptor signaling is downregulated during schistosomiasis . moreover , in the chronic phase of schistosomiasis , there is a gradual increase of serum th2 cytokines . indeed , we observed a significant increase in tgf-1 levels in the peritoneal cavity of mice infected with s. mansoni ( figure 3 ) . to investigate if tgf-1 could modulate p2x7 receptor function in peritoneal macrophages similar to that described for monocytes , we harvested peritoneal macrophages from uninfected animals and treated these cells with 5 ng / ml tgf-1 for 24 h before assessing their sensitivity to atp - induced permeabilization ( using eb as a tracer ) . in the absence of atp , tgf-1 treatment did not induce cell permeabilization ; however , tgf-1 reduced the permeabilizing effect of 1 mm atp by approximately 50% , when compared to controls treated with atp only ( figure 4 ) . we also performed the permeabilization after 48 h of tgf- treatment and we observed that , even after 48 h , the p2x7-induced permeabilization was also reduced ( data not shown ) . the analysis of the concentration - response curve using different concentrations of tgf- showed that only the concentrations 5 ng / ml and 10 ng / ml were able to reduce the permeabilization intensity in macrophages ( data not shown ) . to evaluate whether the reduction in p2x7 receptors function observed in schistosomiasis and in tgf-1-treated cells was due , at least in part , to changes in p2x7 receptor expression , we quantified both p2x7 protein expression and the transcription from the p2rx7 locus by western blotting and qrt - pcr , respectively . we detected similar levels of p2x7 protein and mrna in macrophages from uninfected and infected groups ( figures 5(a ) and 5(c ) ) . moreover , the levels of p2x7 protein and mrna in macrophages from uninfected mice were not altered by treatment with 5 ng / ml tgf-1 for 24 h ( figures 5(b ) and 5(c ) ) . p2x7 receptors are targets of posttranslational modifications that regulate their insertion into plasma membrane , and the proinflammatory effects of p2x7 receptors ( including il-1 release and no and ros production ) depend on receptor localization at the cell surface . moreover , prolonged exposure of macrophages to atp may induce p2x7 receptors removal from the cell surface by internalization [ 39 , 40 ] . since the reduction in p2x7 function during s. mansoni infection was not due to decreases in protein or mrna levels , we hypothesized that changes in receptor structure or localization occurred during infection and downregulated receptor function , similar to that described for other p2x receptors . to test this hypothesis , we analyzed p2x7 receptor localization in nonpermeabilized f4/80 ( a common surface marker of mature macrophages ) positive macrophages from uninfected and s. mansoni - infected mice using an antibody that recognizes an extracellular p2x7 epitope . confocal microscopy analysis of anti - p2x7 labeled cells suggested that the levels of cell surface p2x7 receptors were reduced in macrophages from infected mice ( figures 6(a ) and 6(b ) ) . interestingly , there was also a reduction in cell surface p2x7 in macrophages from uninfected mice treated with tgf-1 ( figures 6(a ) and 6(b ) ) . relative quantification of the immunofluorescence data showed that there was a 1.6-fold decrease ( approximately ) in the intensity of cell surface p2x7 fluorescence in macrophages from infected mice , when compared to that observed in uninfected control mice ( figure 6(b ) ) . next , to evaluate the participation of p2x7 receptors during the disease , we infected c57bl/6 wild type and p2x7 ko mice and followed the progression of infection . the survival curves showed that mortality in p2x7 ko infected mice started at 28 dpi and reached 100% at 60 dpi . in contrast , no death was observed in c57bl/6 wild type mice ( figure 7 ) . the latter phenotype is present mainly in macrophages surrounding eggs within liver granulomas and was recently shown to be important in the control of tissue fibrosis . considering that schistosomiasis is a chronic inflammatory disease and that macrophages are involved in schistosomiasis pathogenesis , we sought to evaluate the function of p2x7 receptors in macrophages from mice infected with s. mansoni , since these receptors play an important role in inflammatory processes . here , we used a combination of atp - induced permeabilization and intracellular ca measurement assays to show that , during the chronic phase of schistosomiasis , there is a reduction in the atp - dependent p2x7 receptor function in macrophages ( figures 1 and 2 ) , similar to that observed in mesenteric endothelial cells using the same experimental model . while the function and expression of macrophage p2x7 receptors are positively regulated by proinflammatory cytokines such as ifn- [ 44 , 45 ] , gadeock and coworkers showed that the upregulation of p2x7 receptors in thp-1 monocytes is negatively regulated by tgf-. on the other hand , peripheral blood mononuclear cells ( pbmcs ) from s. mansoni - infected mice produce high levels of tgf- , and this cytokine is important to limit liver inflammation and favor host survival [ 27 , 28 ] . overall , these data are in agreement with our results also showing that the levels of peritoneal tgf-1 are increased in mice infected with s. mansoni ( figure 3 ) and that tgf-1 , in a concentration close to the ones observed in the serum of chronic patients , reduces by approximately 50% the p2x7-dependent macrophage permeabilization triggered by atp ( figure 4 ) , mimicking the attenuated p2x7 response observed during s. mansoni infection ( figure 1(a ) ) . taken together , these results support our hypothesis that the downregulation of p2x7 function observed in schistosomiasis is a result of the increase in tgf-1 levels during infection . regarding tgf- levels , despite the difference between the in vitro treatment concentration ( 5 ng / ml ) and the in vivo peritoneal measurement ( 100 pg / ml ) , we must consider that we injected 1 ml of pbs in the peritoneal cavity of infected animals before removing the body fluid for cytokine determination . therefore the samples were diluted , and , as a consequence , peritoneal tgf- levels in vivo may be higher than the estimation in vitro . moreover , previous data showed that individuals chronically infected with schistosomiasis have tgf- serum levels around 20 ng / ml and the serum level estimated in s. mansoni - infected mice ( 19.98 2.37 ng / ml ) is compatible with the value observed in patients . therefore we conclude that the tgf- concentration used in present work is compatible with the disease , and the peritoneal tgf- concentration in the infected animals is probably higher than estimated . finally , tgf- in the ng / ml range of concentration is able to modulate p2x7r function . western blotting and qrt - pcr data ( using whole cell lysates ) excluded the possibility that the reduction in p2x7 receptor function during s. mansoni infection or after treatment with tgf-1 resulted from decreased levels of p2x7 protein or mrna . in fact , immunofluorescence microscopy analysis of nonpermeabilized macrophages expressing f4/80 on their cell surface revealed that there was a lower density of surface p2x7 receptors in cells from infected mice compared to those from uninfected , control animals ( figure 6 ) . since total p2x7 protein levels were similar in both groups , we propose that there is reduction of p2x7 receptor in plasma membrane of macrophages from infected mice . the disappearance of immunoreactivity from plasma membrane could be related to some conformational changes of the receptor , an interaction with other proteins masking the extracellular epitope recognized by the antibody or the p2x7 receptor internalization . however , tgf- treatment in vitro mimicked both the reduced cell surface receptor expression and function observed in macrophages obtained from infected animals . consequently , a plausible explanation for the reduction in p2x7 function ( without corresponding decreases in total protein or mrna levels ) during chronic schistosomiasis could be related to a reduced cell surface expression of p2x7 receptor . despite the work of gadeock et al . , data investigating the link between tgf-1 and p2x7 receptors function and/or expression are still missing . since control macrophage treatment with tgf-1 mimicked the profile of cell surface p2x7 receptors expression and function observed in live macrophages obtained from infected mice , it is supposed that tgf-1 could be involved in the p2x7 receptors reduced function observed in the disease . to the best of our knowledge , this is the first report that shows a direct effect of tgf-1 on macrophage p2x7 receptor function . however , we do not exclude that other cytokines could contribute to the p2x7 reduced function in macrophages from s. mansoni - infected mice , since in the later phase of the disease beyond the increase of tgf- levels there is also the increase of il-4 , il-5 , il-10 , and il-13 .. moreover , it was shown that il-4 and il-10 also inhibit eb uptake in rat alveolar macrophage . furthermore , previous data showed that tgf- , il-10 , and il-4 inhibit macrophage cytotoxicity which could be an important strategy used by s. mansoni to evade macrophage - mediated immune destruction . patients with schistosomiasis may be more susceptible to secondary infections , and prior infection with schistosoma also increases the severity of secondary infections with leishmania , toxoplasma gondii , and salmonella . in addition , a previous report showed that macrophages from chronically infected mice have reduced phagocytic activity ; however , little is known about the mechanisms underlying this phenomenon . recently , wiley and gu showed that p2x7 receptors on the surface of monocytes / macrophages may act as scavenger receptors for bacteria in the absence of atp . therefore , the reduction of p2x7 receptor function in s. mansoni - infected animals could limit bacterial ( and possibly protozoal ) phagocytosis during schistosomiasis . this phenomenon might explain the increased susceptibility of patients infected with s. mansoni to secondary infections with other parasites and also the higher severity of secondary infections in these patients . kusner and adams showed that atp kills mycobacterium tuberculosis in human macrophages and that this effect depends on p2x7 receptor - mediated pld activation . this mechanism is also important for the atp - mediated killing of chlamydia trachomatis in murine peritoneal macrophages . moreover , our group showed that the acute infection of macrophages with chlamydia psittaci reduces p2x7 receptor - mediated cell permeabilization and ca influx , thus inhibiting macrophage apoptosis . considering that c. psittaci are obligatory intracellular parasites , this phenomenon could be an attempt to limit immunological responses by reducing atp - mediated apoptosis and , consequently , favoring parasite survival . an important new aspect of p2x7 receptors signaling highlighted in the present work is that the function of macrophage p2x7 receptors may also be modulated by the extracellular parasite s. mansoni . altogether , our data suggest that , during schistosomiasis , the function of macrophage p2x7 receptors is reduced and that tgf-1 plays a key putative role in the downregulation of receptor signaling . we hypothesize that macrophage purinergic receptors are differentially modulated during disease progression and that this phenomenon has a key role in the immune response against s. mansoni . in this context , our data show that p2x7 receptor knockout animals ( p2x7 ko ) are much more susceptible to death during s. mansoni infection than wt mice highlighting this p2 purinergic receptor and reinforcing the necessity of future studies exploring in deep its importance in s. mansoni - induced disease . given that purinergic signaling is also found in s. mansoni , understanding the interplay between host and parasite purinergic signaling pathways is now important to clarify if future therapeutic approaches targeting these signaling pathways would be useful against schistosomiasis . altogether , our data show that s. mansoni infection reduced p2x7 function in peritoneal macrophages during the chronic phase of the disease . furthermore , the peritoneal cavity of infected mice had increased levels of tgf-1 , and this cytokine reduced p2x7 receptor function in macrophages from uninfected mice . thus , immunomodulation by tgf-1 could limit p2x7-dependent inflammatory effects in macrophages from s. mansoni patients and may provide an explanation for the increased susceptibility of these patients to infections by others pathogens .

schistosomiasis is a chronic inflammatory disease whose macrophages are involved in immunopathology modulation . although p2x7 receptor signaling plays an important role in inflammatory responses mediated by macrophages , no reports have examined the role of p2x7 receptors in macrophage function during schistosomiasis . thus , we evaluated p2x7 receptor function in peritoneal macrophages during schistosomiasis using an atp - induced permeabilization assay and measurements of the intracellular ca2 + concentration . atp treatment induced significantly less permeabilization in macrophages from s. mansoni - infected mice than in control cells from uninfected animals . furthermore , p2x7-mediated increases in intracellular ca2 + levels were also reduced in macrophages from infected mice . tgf-1 levels were increased in the peritoneal cavity of infected animals , and pretreatment of control macrophages with tgf-1 reduced atp - induced permeabilization , mimicking the effect of s. mansoni infection . western blot and qrt - pcr data showed no difference in p2x7 protein and mrna between uninfected , infected , and tgf-1-treated groups . however , immunofluorescence analysis revealed reduced cell surface localization of p2x7 receptors in macrophages from infected and tgf-1-treated mice compared to controls . therefore , our data suggest that schistosomiasis reduces peritoneal macrophage p2x7 receptor signaling . this effect is likely due to the fact that infected mice have increased levels of tgf-1 , which reduces p2x7 receptor cell surface expression .

<s>[INST]macrophages are plastic phagocytic cells that participate in innate and adaptive immunity , with important roles in the response against extra- and intracellular parasites , as well as in tissue homeostasis [ 1 , 2 ] . , macrophages contribute to mounting specific immunological responses for host defense , and the plasticity of macrophage phenotypes is modulated by the cytokine profile . tissue damage during inflammation increases the extracellular levels of otherwise intracellular molecules , resulting in damage - associated molecular patterns ( damps ) recognized by the immune system [ 35 ] . extracellular nucleotides , such as the atp released by dying cells and by activated immune cells during inflammation , are important danger signals involved in immune response , participating in both paracrine and autocrine signaling pathways . in inflammatory processes , high extracellular atp levels generated by tissue damage or secretion are recognized by the immune system as a danger signal , activating purinergic p2 receptors that contribute to a proinflammatory response . purinergic p2 receptors can be classified as ionotropic atp - gated ( p2x ) or g - protein coupled metabotropic ( p2y ) . extracellular atp ( eatp ) induces macrophage - mediated immune responses mainly through the activation of p2x7 receptors . these receptors have a ubiquitous distribution , although the highest levels of receptor expression are observed in immune cells of monocyte / macrophage origin . p2x7 receptor activation induces a myriad of intracellular events , including the production of nitric oxide ( no ) and of reactive oxygen species ( ros ) and the activation of phospholipase - d ( pld ) . these events are important for intracellular parasite killing , for the release of proinflammatory cytokines ( such as il-1 ) , and for inducing apoptosis [ 13 , 14 ] . the expression and function of p2x7 receptors are regulated by both pro- and anti - inflammatory stimuli . initially , p2x7 receptor activation in macrophages opens a plasma membrane cation channel that allows a substantial efflux of k , and influx of ca , with later formation of pores permeable to large molecules [ 16 , 17 ] . p2x receptor activation may also induce caspase-1 activation , interleukin il-1 release , apoptosis , phagolysosomal fusion , and the elimination of intracellular pathogens [ 14 , 18 , 19 ] . in murine macrophages , the mature il-1 secretion by the activation of p2x7 receptors is reduced by the incubation in a free - ca buffer . thus , murine macrophage release of mature il-1 depends on intracellular ca , confirming that ca signaling is essential for this p2x7 receptor function . schistosomiasis is a chronic inflammatory disease caused by schistosoma mansoni and it represents the second most common tropical parasitic disease related to socioeconomical factors . while migrating through the vascular system of infected mammalian hosts , parasites evolve from the schistosomula migratory form into adult worms , causing endothelial cell activation , immunological responses , and tissue damage . the disease starts with a th1-type immune response that gradually changes to a th2 profile [ 2124 ] . previous data suggest that the th2 stage begins four to six weeks after infection and is related to egg deposition by adult worms . macrophages play important roles in both phases of schistosomiasis . in the early phase of the disease , macrophages act as immune system effectors cells killing schistosomula and promoting tissue repair . after egg deposition , the immune response switches to a th2 profile that is involved in the formation of liver and colonic granulomas and fibrosis . the eggs are laid in mesenteric microcirculation and they may reach peritoneal cavity where the granulomas formed contain mainly macrophages . although granulomas are important to limit egg - derived potential cytotoxic products , macrophages isolated , for example , from hepatic granulomas , produce lipids mediators and free radicals that are potentially destructive to host tissues . among cytokines involved in schistosomiasis , transforming growth factor-1 ( tgf-1 ) is of particular interest , since high levels of this cytokine are released by peripheral blood mononuclear cells ( pbmcs ) from s. mansoni - infected mice . tgf- has an important role in immune modulation later during infection , limiting liver inflammation and favoring host survival [ 27 , 28 ] . recently , bhardwaj and skelly showed that s. mansoni expresses p2x7 receptors - like molecules and also enzymes responsible for the clearance of extracellular atp ( ectonucleotidases ) , suggesting that purinergic signaling is conserved in these parasites and is important for the host - parasite interplay . however , the impact of the chronic inflammation trigged by schistosomiasis on macrophage p2x7 receptor function remains unknown . here , we evaluated p2x7 receptor function and expression in macrophage from s. mansoni - infected mice . our data show that peritoneal macrophage p2x7 receptor function is attenuated during schistosomiasis and that this is associated with high peritoneal levels of tgf-1 , the important inflammatory mediator present in the chronic phase of the disease . we also show that tgf-1 downregulates p2x function in vitro , mimicking the effect of s. mansoni infection . the following primary antibodies were used in this work : rabbit polyclonal anti - p2x7 receptors ( apr-004 and apr-008 ; alomone labs , israel ) ; mouse monoclonal anti--actin ( santa cruz biotechnology , usa ) ; rat anti - f4/80 ( biolegend , usa ) ; rat anti - f4/80 fitc ( abd serotec , usa ) . atp , 3-o-(4-benzoyl)-atp ( bzatp ) , pmsf , sodium orthovanadate , aprotinin , leupeptin , bsa , ionomycin , and egta were from sigma chemical co. ( usa ) . fura-2-am was from molecular probes ( usa ) and a740003 was from tocris ( usa ) . rpmi , foetal bovine serum ( fbs ) , and penicillin / streptomycin solutions were from gibco brl ( usa ) . stock solutions were prepared in dmso ( 2.5 mm fura-2-am and 10 mm a740003 ) , water ( 10 mm bzatp ) , rpmi ( 5 ng / ml tgf-1 ) , or a buffered physiological saline solution ( 10 mm atp ) . the highest concentration of solvent used was 0.1% ( v / v ) . swiss , c57bl/6 ( wild type ) , and p2x7 receptor knockout ( p2x7 ko ) male mice were used in all procedures . swiss and c57bl/6 mice were obtained from the animal facility of the paulo de goes microbiology institute ( federal university of rio de janeiro , rio de janeiro , brazil ) . p2x7 ko mice ( originally from the jackson laboratory , usa , stock number 005576 ) were maintained in the transgenic animal house of the federal university of rio de janeiro . all mice were kept under a light / dark cycle of 12/12 h and with access to water and food ad libitum . all experiments were conducted in compliance with the ethical standards of our institution ( ethics committee of the federal university of rio de janeiro ; approved under the licenses dfbc - icb-011 and ibccf 154 ) and following both the guidelines of the national council on experimental animal control ( concea , brazil ) and the committee of care and use of laboratory animals ( national research council , united states ) . all efforts were made to minimize both animals suffering and the number of animals used , on the basis of valid statistical evaluation . in this work , we used the bh strain of s. mansoni , obtained from infected biomphalaria glabrata snails . swiss , c57bl/6 , and p2x7 ko mice ( 7 - 10 days old ) were infected percutaneously with approximately 80 cercariae from both genders , for 8 min , as previously described . animals were used in experiments at least 45 days after infection ( dpi ) to allow for full establishment of the infection . age - matched ( 60 to 80 days old ) uninfected swiss , c57bl/6 , and p2x7 ko mice were used as controls . c57bl/6 and p2x7 ko mice survival the peritoneal cavity was washed with 5 ml of sterile phosphate buffered saline ( pbs : 137 mm nacl , 8.1 mm na2hpo4 , 1.5 mm nah2po4 , and 2.7 mm kcl , ph 7.4 ) , and the peritoneal exudate was collected and centrifuged at 350 g , for 5 min , at 4c . the pellet was resuspended in 1 ml of pbs and used to perform total leukocyte counts ( cell viability , as estimated by trypan blue exclusion , was always 95% ) . for macrophages culture , cells were resuspended in 1 ml of rpmi-1640 medium containing 2 g / l sodium bicarbonate , 1 mm l - glutamine , 100 u / ml penicillin , and 100 g / ml streptomycin and plated in 35 mm petri dishes or on 6-well plates . after 1 h of incubation at 37c with 5% co2 , nonadherent cells were removed by vigorous washing , and rpmi-1640 medium with 10% heat - inactivated fbs was added to the cultures , which were kept at 37c with 5% co2 for 24 h until further use . to investigate macrophage responses to atp , freshly harvested peritoneal macrophages ( 10 cells ) from swiss ( uninfected or s. mansoni - infected ) or c57bl/6 ( wild type or p2x7 ko ) mice were treated with 0.1 , 0.5 , or 1 mm atp and 2.5 m ethidium bromide ( eb ) in pbs ( 15 min ; 37c ) . eb was used as a tracer for p2x7 receptor activation ( i.e. , cell permeabilization ) triggered by atp . after incubation with atp and eb , f4/80 positive cells were analyzed by flow cytometry ( 10,000 events / sample ) using a facscan system ( bd pharmingen , usa ) . , a marker was added based on a gate of the f4/80 positive macrophages population , which limited the basal fluorescence . the specific atp - induced permeabilization threshold was defined by comparison with the baseline profile of control cells not treated with atp ( i.e. , incubated with eb only ) . the specific permeabilization is the percentage of eb positive cells after atp stimulation in the f4/80 positive gated cells . alternatively , peritoneal macrophages were plated on 24-well plates ( 2 10 cells / well ) and , after 24 h , treated with 5 ng / ml tgf-1 or vehicle ( rpmi ) , for 24 h , at 37c and in 5% co2 . macrophages were washed in pbs ( ph 7.4 ) and then incubated with 1 mm atp and 5 m eb in buffer ( 145 mm nacl , 5 mm kcl , 1 mm mgcl2 , 1 mm cacl , and 10 mm hepes , ph 7.4 ) for 15 min at 37c to evaluate the p2x7 receptor activation . the ratio between permeabilized ( i.e. , eb positive ) and total cells was determined by direct counting of cells in five randomly chosen fields , using an axiovert 100 microscope ( karl zeiss , oberkochen , germany ) equipped with an olympus digital camera ( olympus american inc . the specific atp - induced permeabilization value ( in % ) was calculated by subtracting from the total % of permeabilized cells a value corresponding to the % of permeabilized cells in control samples not treated with atp ( i.e. , incubated with eb only ) . measurements of the intracellular ca concentration ( [ ca]i ) using fura-2-am were performed as previously described . briefly , macrophages were plated on glass bottom plates ( mattek , usa ) , at a density of 1 10 cells / plate , and maintained for 24 h at 37c , with 5% co2 . then , the medium was removed and the cells were incubated for 40 min with 2.5 m fura-2-am at room temperature . cells were subjected to alternate cycles of illumination with 340 nm and 380 nm excitation wavelengths , and the emission was measured at 500 nm . cells were washed twice with buffered physiological solution ( in mm : nacl 140 , kcl 5 , mgcl2 1 , cacl2 2 , glucose 5 , and hepes 5 , ph 7.4 ) and then stimulated with 100 m 3-o-(4-benzoyl)-atp ( bzatp ) ( at 37c ) in the absence or in the presence of 50 nm of the p2x7 receptor antagonist a740003 ( preincubated for 45 min , at 37c ) . after the maximum effect had been achieved , cells were treated with ca ionophore ( 10 m ionomycin ) and then with 6 mm egta to determine the molar concentration of ca according to the grynkiewicz equation . the estimation of tgf-1 levels in mouse peritoneal washes was performed using an elisa immunoassay kit ( peprotech , rocky hill , nj , usa ) , according to manufacturer 's instructions . for peritoneal wash collection , mice were euthanized with co2 and the peritoneal cavity was washed with 1 ml of sterile pbs . approximately 60% of the initial volume of pbs was recovered and centrifuged at 350 g for 5 min , at 4c . supernatants were collected and stored in liquid n2 until further use ( to determine tgf-1 content ) . peritoneal macrophages from control and infected mice ( 10 cells / well ) were treated with 5 ng / ml tgf- for 24 h , fixed with 4% paraformaldehyde and 4% sucrose for 10 min in pbs , washed , and incubated for 30 min with 50 mm ammonium chloride ( ph 8.0 ) . after three washes in pbs , samples were blocked in pbs with 10% fbs and 0.1% bsa for 30 min , washed twice in pbs , and incubated overnight with a rabbit polyclonal antibody that recognizes an extracellular epitope of p2x7 receptors ( apr-008 ; alomone labs , israel ; peptide kkgwmdpqskgiqtgrc , corresponding to amino acid residues 136152 of mouse p2x7 receptor ; extracellular loop ) diluted to 1 : 400 in pbs and 0.1% bsa . then , cells were washed and incubated with a rat anti - f4/80 antibody diluted to 1 : 50 in pbs and 0.1% bsa for 4 h , at 4c . samples were then labelled with secondary anti - rabbit - alexa 488 and anti - rat - alexa 546 antibodies diluted to 1 : 500 in pbs and 0.1% bsa for 1 h at 4c . after labelling , cells were mounted on slides using vectashield with dapi ( vector , burlingame , ca , usa ) and examined on a tcs - sp5 aobs confocal microscope ( leica microsystems , germany ) . , imagej , us national institutes of health , bethesda , maryland , usa , http://imagej.nih.gov/ij/ , 19972014 ) . the region of interest ( roi ) was delimited in each cell and the respective mean fluorescence intensity was measured based on the pixel intensity . 10 cells per image were evaluated and the fluorescent values were used for statistical analysis . data were also displayed in an orthogonal slice view that shows the raw pixel intensity values found mutually in each of three perpendicular planes . macrophages adhered to 6-well plates were washed with sterile pbs and lysed with 200 l ripa buffer ( 50 mm tris - hcl , ph 7.4 , containing 1% nonidet p40 , 0.25% sodium deoxycholate , 150 mm nacl , 1 mm edta , 1 mm pmsf , 1 mm sodium orthovanadate , 1 mm naf , 10 g / ml aprotinin , and 10 g / ml leupeptin ) . cell lysates were incubated at 4c for 30 min and centrifuged at 8,100 g , for 10 min , at 4c ; the pellets were discarded and the supernatant had their protein content determined by the lowry method . page gels ( 15 g protein / lane ) and then transferred to nitrocellulose membranes using a semidry transfer system . membranes were blocked for 1 h in tris - buffered saline ( tbs ) with 2% nonfat milk and then incubated overnight with rabbit anti - p2x7 receptors ( apr-004 ; alomone labs , israel ; 1 : 200 ; peptide ( c)kirkefpktqgqysgfkypy , corresponding to amino acid residues 576595 of p2x7 receptor intracellular , c - terminus ) or mouse monoclonal anti--actin ( 1 : 20.000 ) primary antibodies . after 3 washes in tbs - tween , membranes were incubated with hrp - conjugated anti - rabbit or anti - mouse secondary antibody ( 1 : 1.000 ) for 1 h and developed using enhanced chemiluminescence ( ecl ) . ponceau staining and labeling with a monoclonal anti--actin antibody were used as internal controls for protein loading . densitometry of protein bands was performed using the imagej software , and the values for relative amounts of protein were normalized to the -actin loading control . peritoneal macrophages from uninfected swiss mice ( treated with 5 ng / ml tgf-1 or with vehicle , for 24 h ) or from s. mansoni - infected mice were used to isolate total rna using the trizol reagent ( life technologies ) , according to the manufacturer 's instructions . total rna was quantified using an nd-1000 spectrophotometer ( nanodrop ) , and cdna was synthesized from 500 ng of total rna using the high capacity cdna reverse transcription kit with rnase inhibitor ( invitrogen ) . the sybr select master mix ( applied biosystems ) was used for qrt - pcr , to detect double - stranded dna synthesis . reactions were carried out in a final volume of 10 l , using 2 l of diluted cdna ( 1 : 10 ) and 300 nm of each of the reverse and forward primers . the following primers were used for qrt - pcr : for p2rx7 , 5 aatcggtgtgtttcctttgg 3 ( forward ) and 5 ccgggtgactttgtttgtct 3 ( reverse ) ; for actb , 5 tatgccaacacagtgctgtctgg 3 ( forward ) and 5 tactcctgcttgctgatccacat 3 ( reverse ) ; and for gapdh , 5 ggtcatcccagagctgaacg 3 ( forward ) and 5 ttgctgttgaagtcgcagga 3 ( reverse ) . reactions were performed in a 7500 fast real - time system ( applied biosystems ) , using the following pcr conditions : 5 min at 95c , followed by 40 cycles of 15 s at 95c , 35 s at 60c , and 15 s at 72c . at the end of cycling protocol , a melting - curve analysis ( with fluorescence measurements from 60 to 99c ) was performed . relative expression levels were determined using the sequence detection software v.2.0.5 ( applied biosystems ) , and the efficiency per sample was calculated using the linregpcr 11.0 software ( manufacturer).-actin and gapdh were used as internal controls to calculate relative p2rx7 mrna levels , by the comparative threshold cycle ( ct ) method with efficiency correction , using the mean qrt - pcr efficiency for each amplicon , as previously described [ 34 , 35 ] . differences between two or more groups were analyzed by student 's t - test or one - way analysis of variance ( anova ) followed by post hoc newman - keuls test , respectively , considering p < 0.05 . we used several approaches to examine the impact of the chronic inflammation triggered by s. mansoni infection on macrophage p2x7 receptor function . activation of p2x7 receptors by atp opens plasma membrane pores that allow molecules greater than 900 kda ( such as the fluorescent dye eb ) to enter the cells [ 17 , 36 ] . thus , we used atp - induced cell permeabilization ( as evidenced by staining with eb ) as a tool to compare the p2x7 receptor activation in peritoneal macrophage from infected and uninfected swiss mice . incubations with 0.11 mm atp induced cell permeabilization in macrophages from uninfected mice ; however , this effect was reduced in macrophages from infected mice ( figure 1(a ) ) . atp also induced permeabilization in macrophages from c57bl/6 wild type mice but , as expected , not in macrophages from p2x7 ko mice ( figure 1(b ) ) . we also used the potent p2x7 agonist bzatp to verify if p2x7 receptor activation increased the cytosolic ca concentration in macrophages from infected and uninfected swiss mice , since atp - induced ca influx is a hallmark of p2x7 activation . the basal levels of cytosolic ca ( before bzatp addition ) were similar in both groups ( figure 2(a ) ) . after treatment with 100 m bzatp , macrophages from uninfected mice showed a typical p2x7 receptors activation profile at 37c , characterized by a pronounced biphasic increase in intracellular ca levels ( figure 2(a ) ) . however , the p2x7 receptor - mediated ca influx was considerably less pronounced in macrophages from infected mice when compared to that observed in macrophages from uninfected mice ( figures 2(a ) and 2(b ) ) . we also assessed changes in intracellular ca in the presence of the selective p2x7 receptor antagonist a740003 . treatment with 50 nm a740003 did not alter basal intracellular ca levels , but it had a strong negative effect on the bzatp - induced ca influx , and this effect was similar in macrophages from both groups . these results confirmed that the increase in intracellular ca levels after addition of bzatp was due to p2x7 receptor activation . these data are in agreement with the reduction in atp - induced permeabilization observed in macrophages from infected mice ( figure 1(a ) ) and suggest that p2x7 receptor signaling is downregulated during schistosomiasis . moreover , in the chronic phase of schistosomiasis , there is a gradual increase of serum th2 cytokines . indeed , we observed a significant increase in tgf-1 levels in the peritoneal cavity of mice infected with s. mansoni ( figure 3 ) . to investigate if tgf-1 could modulate p2x7 receptor function in peritoneal macrophages similar to that described for monocytes , we harvested peritoneal macrophages from uninfected animals and treated these cells with 5 ng / ml tgf-1 for 24 h before assessing their sensitivity to atp - induced permeabilization ( using eb as a tracer ) . in the absence of atp , tgf-1 treatment did not induce cell permeabilization ; however , tgf-1 reduced the permeabilizing effect of 1 mm atp by approximately 50% , when compared to controls treated with atp only ( figure 4 ) . we also performed the permeabilization after 48 h of tgf- treatment and we observed that , even after 48 h , the p2x7-induced permeabilization was also reduced ( data not shown ) . the analysis of the concentration - response curve using different concentrations of tgf- showed that only the concentrations 5 ng / ml and 10 ng / ml were able to reduce the permeabilization intensity in macrophages ( data not shown ) . to evaluate whether the reduction in p2x7 receptors function observed in schistosomiasis and in tgf-1-treated cells was due , at least in part , to changes in p2x7 receptor expression , we quantified both p2x7 protein expression and the transcription from the p2rx7 locus by western blotting and qrt - pcr , respectively . we detected similar levels of p2x7 protein and mrna in macrophages from uninfected and infected groups ( figures 5(a ) and 5(c ) ) . moreover , the levels of p2x7 protein and mrna in macrophages from uninfected mice were not altered by treatment with 5 ng / ml tgf-1 for 24 h ( figures 5(b ) and 5(c ) ) . p2x7 receptors are targets of posttranslational modifications that regulate their insertion into plasma membrane , and the proinflammatory effects of p2x7 receptors ( including il-1 release and no and ros production ) depend on receptor localization at the cell surface . moreover , prolonged exposure of macrophages to atp may induce p2x7 receptors removal from the cell surface by internalization [ 39 , 40 ] . since the reduction in p2x7 function during s. mansoni infection was not due to decreases in protein or mrna levels , we hypothesized that changes in receptor structure or localization occurred during infection and downregulated receptor function , similar to that described for other p2x receptors . to test this hypothesis , we analyzed p2x7 receptor localization in nonpermeabilized f4/80 ( a common surface marker of mature macrophages ) positive macrophages from uninfected and s. mansoni - infected mice using an antibody that recognizes an extracellular p2x7 epitope . confocal microscopy analysis of anti - p2x7 labeled cells suggested that the levels of cell surface p2x7 receptors were reduced in macrophages from infected mice ( figures 6(a ) and 6(b ) ) . interestingly , there was also a reduction in cell surface p2x7 in macrophages from uninfected mice treated with tgf-1 ( figures 6(a ) and 6(b ) ) . relative quantification of the immunofluorescence data showed that there was a 1.6-fold decrease ( approximately ) in the intensity of cell surface p2x7 fluorescence in macrophages from infected mice , when compared to that observed in uninfected control mice ( figure 6(b ) ) . next , to evaluate the participation of p2x7 receptors during the disease , we infected c57bl/6 wild type and p2x7 ko mice and followed the progression of infection . the survival curves showed that mortality in p2x7 ko infected mice started at 28 dpi and reached 100% at 60 dpi . in contrast , no death was observed in c57bl/6 wild type mice ( figure 7 ) . the latter phenotype is present mainly in macrophages surrounding eggs within liver granulomas and was recently shown to be important in the control of tissue fibrosis . considering that schistosomiasis is a chronic inflammatory disease and that macrophages are involved in schistosomiasis pathogenesis , we sought to evaluate the function of p2x7 receptors in macrophages from mice infected with s. mansoni , since these receptors play an important role in inflammatory processes . here , we used a combination of atp - induced permeabilization and intracellular ca measurement assays to show that , during the chronic phase of schistosomiasis , there is a reduction in the atp - dependent p2x7 receptor function in macrophages ( figures 1 and 2 ) , similar to that observed in mesenteric endothelial cells using the same experimental model . while the function and expression of macrophage p2x7 receptors are positively regulated by proinflammatory cytokines such as ifn- [ 44 , 45 ] , gadeock and coworkers showed that the upregulation of p2x7 receptors in thp-1 monocytes is negatively regulated by tgf-. on the other hand , peripheral blood mononuclear cells ( pbmcs ) from s. mansoni - infected mice produce high levels of tgf- , and this cytokine is important to limit liver inflammation and favor host survival [ 27 , 28 ] . overall , these data are in agreement with our results also showing that the levels of peritoneal tgf-1 are increased in mice infected with s. mansoni ( figure 3 ) and that tgf-1 , in a concentration close to the ones observed in the serum of chronic patients , reduces by approximately 50% the p2x7-dependent macrophage permeabilization triggered by atp ( figure 4 ) , mimicking the attenuated p2x7 response observed during s. mansoni infection ( figure 1(a ) ) . taken together , these results support our hypothesis that the downregulation of p2x7 function observed in schistosomiasis is a result of the increase in tgf-1 levels during infection . regarding tgf- levels , despite the difference between the in vitro treatment concentration ( 5 ng / ml ) and the in vivo peritoneal measurement ( 100 pg / ml ) , we must consider that we injected 1 ml of pbs in the peritoneal cavity of infected animals before removing the body fluid for cytokine determination . therefore the samples were diluted , and , as a consequence , peritoneal tgf- levels in vivo may be higher than the estimation in vitro . moreover , previous data showed that individuals chronically infected with schistosomiasis have tgf- serum levels around 20 ng / ml and the serum level estimated in s. mansoni - infected mice ( 19.98 2.37 ng / ml ) is compatible with the value observed in patients . therefore we conclude that the tgf- concentration used in present work is compatible with the disease , and the peritoneal tgf- concentration in the infected animals is probably higher than estimated . finally , tgf- in the ng / ml range of concentration is able to modulate p2x7r function . western blotting and qrt - pcr data ( using whole cell lysates ) excluded the possibility that the reduction in p2x7 receptor function during s. mansoni infection or after treatment with tgf-1 resulted from decreased levels of p2x7 protein or mrna . in fact , immunofluorescence microscopy analysis of nonpermeabilized macrophages expressing f4/80 on their cell surface revealed that there was a lower density of surface p2x7 receptors in cells from infected mice compared to those from uninfected , control animals ( figure 6 ) . since total p2x7 protein levels were similar in both groups , we propose that there is reduction of p2x7 receptor in plasma membrane of macrophages from infected mice . the disappearance of immunoreactivity from plasma membrane could be related to some conformational changes of the receptor , an interaction with other proteins masking the extracellular epitope recognized by the antibody or the p2x7 receptor internalization . however , tgf- treatment in vitro mimicked both the reduced cell surface receptor expression and function observed in macrophages obtained from infected animals . consequently , a plausible explanation for the reduction in p2x7 function ( without corresponding decreases in total protein or mrna levels ) during chronic schistosomiasis could be related to a reduced cell surface expression of p2x7 receptor . despite the work of gadeock et al . , data investigating the link between tgf-1 and p2x7 receptors function and/or expression are still missing . since control macrophage treatment with tgf-1 mimicked the profile of cell surface p2x7 receptors expression and function observed in live macrophages obtained from infected mice , it is supposed that tgf-1 could be involved in the p2x7 receptors reduced function observed in the disease . to the best of our knowledge , this is the first report that shows a direct effect of tgf-1 on macrophage p2x7 receptor function . however , we do not exclude that other cytokines could contribute to the p2x7 reduced function in macrophages from s. mansoni - infected mice , since in the later phase of the disease beyond the increase of tgf- levels there is also the increase of il-4 , il-5 , il-10 , and il-13 .. moreover , it was shown that il-4 and il-10 also inhibit eb uptake in rat alveolar macrophage . furthermore , previous data showed that tgf- , il-10 , and il-4 inhibit macrophage cytotoxicity which could be an important strategy used by s. mansoni to evade macrophage - mediated immune destruction . patients with schistosomiasis may be more susceptible to secondary infections , and prior infection with schistosoma also increases the severity of secondary infections with leishmania , toxoplasma gondii , and salmonella . in addition , a previous report showed that macrophages from chronically infected mice have reduced phagocytic activity ; however , little is known about the mechanisms underlying this phenomenon . recently , wiley and gu showed that p2x7 receptors on the surface of monocytes / macrophages may act as scavenger receptors for bacteria in the absence of atp . therefore , the reduction of p2x7 receptor function in s. mansoni - infected animals could limit bacterial ( and possibly protozoal ) phagocytosis during schistosomiasis . this phenomenon might explain the increased susceptibility of patients infected with s. mansoni to secondary infections with other parasites and also the higher severity of secondary infections in these patients . kusner and adams showed that atp kills mycobacterium tuberculosis in human macrophages and that this effect depends on p2x7 receptor - mediated pld activation . this mechanism is also important for the atp - mediated killing of chlamydia trachomatis in murine peritoneal macrophages . moreover , our group showed that the acute infection of macrophages with chlamydia psittaci reduces p2x7 receptor - mediated cell permeabilization and ca influx , thus inhibiting macrophage apoptosis . considering that c. psittaci are obligatory intracellular parasites , this phenomenon could be an attempt to limit immunological responses by reducing atp - mediated apoptosis and , consequently , favoring parasite survival . an important new aspect of p2x7 receptors signaling highlighted in the present work is that the function of macrophage p2x7 receptors may also be modulated by the extracellular parasite s. mansoni . altogether , our data suggest that , during schistosomiasis , the function of macrophage p2x7 receptors is reduced and that tgf-1 plays a key putative role in the downregulation of receptor signaling . we hypothesize that macrophage purinergic receptors are differentially modulated during disease progression and that this phenomenon has a key role in the immune response against s. mansoni . in this context , our data show that p2x7 receptor knockout animals ( p2x7 ko ) are much more susceptible to death during s. mansoni infection than wt mice highlighting this p2 purinergic receptor and reinforcing the necessity of future studies exploring in deep its importance in s. mansoni - induced disease . given that purinergic signaling is also found in s. mansoni , understanding the interplay between host and parasite purinergic signaling pathways is now important to clarify if future therapeutic approaches targeting these signaling pathways would be useful against schistosomiasis . altogether , our data show that s. mansoni infection reduced p2x7 function in peritoneal macrophages during the chronic phase of the disease . furthermore , the peritoneal cavity of infected mice had increased levels of tgf-1 , and this cytokine reduced p2x7 receptor function in macrophages from uninfected mice . thus , immunomodulation by tgf-1 could limit p2x7-dependent inflammatory effects in macrophages from s. mansoni patients and may provide an explanation for the increased susceptibility of these patients to infections by others pathogens .[/INST]schistosomiasis is a chronic inflammatory disease whose macrophages are involved in immunopathology modulation . although p2x7 receptor signaling plays an important role in inflammatory responses mediated by macrophages , no reports have examined the role of p2x7 receptors in macrophage function during schistosomiasis . thus , we evaluated p2x7 receptor function in peritoneal macrophages during schistosomiasis using an atp - induced permeabilization assay and measurements of the intracellular ca2 + concentration . atp treatment induced significantly less permeabilization in macrophages from s. mansoni - infected mice than in control cells from uninfected animals . furthermore , p2x7-mediated increases in intracellular ca2 + levels were also reduced in macrophages from infected mice . tgf-1 levels were increased in the peritoneal cavity of infected animals , and pretreatment of control macrophages with tgf-1 reduced atp - induced permeabilization , mimicking the effect of s. mansoni infection . western blot and qrt - pcr data showed no difference in p2x7 protein and mrna between uninfected , infected , and tgf-1-treated groups . however , immunofluorescence analysis revealed reduced cell surface localization of p2x7 receptors in macrophages from infected and tgf-1-treated mice compared to controls . therefore , our data suggest that schistosomiasis reduces peritoneal macrophage p2x7 receptor signaling . this effect is likely due to the fact that infected mice have increased levels of tgf-1 , which reduces p2x7 receptor cell surface expression .</s>