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b0c50edf-cf99-4c7b-a773-b93d9cf488f1 | b0c50edf-cf99-4c7b-a773-b93d9cf488f1 | b0c50edf-cf99-4c7b-a773-b93d9cf488f1 | human | null | null | none | abstracts | Parametric Learning and Monte Carlo Optimization | null | This paper uncovers and explores the close relationship between Monte Carlo
Optimization of a parametrized integral (MCO), Parametric machine-Learning
(PL), and `blackbox' or `oracle'-based optimization (BO). We make four
contributions. First, we prove that MCO is mathematically identical to a broad
class of PL problems. This identity potentially provides a new application
domain for all broadly applicable PL techniques: MCO. Second, we introduce
immediate sampling, a new version of the Probability Collectives (PC) algorithm
for blackbox optimization. Immediate sampling transforms the original BO
problem into an MCO problem. Accordingly, by combining these first two
contributions, we can apply all PL techniques to BO. In our third contribution
we validate this way of improving BO by demonstrating that cross-validation and
bagging improve immediate sampling. Finally, conventional MC and MCO procedures
ignore the relationship between the sample point locations and the associated
values of the integrand; only the values of the integrand at those locations
are considered. We demonstrate that one can exploit the sample location
information using PL techniques, for example by forming a fit of the sample
locations to the associated values of the integrand. This provides an
additional way to apply PL techniques to improve MCO.
|
68a98a65-5297-4591-9ada-3a56714062dc | 68a98a65-5297-4591-9ada-3a56714062dc | 68a98a65-5297-4591-9ada-3a56714062dc | human | null | null | none | abstracts | SDSS J102146.44+234926.3: New WZ Sge-type dwarf nova | null | We report CCD photometry and spectroscopy during 2006 outburst of the dwarf
nova SDSS J102146.44+234926.3 (SDSS J1021). The photographic plates from the
MAO, SAI and CrAO plate archives, which cover the position of the SDSS J1021,
were inspected for the presence of previous outbursts. We also present the
BVRcIc photometric calibration of 52 stars in SDSS J1021 vicinity, which have
V-magnitude in the range of 11.21-17.23m and can serve as comparison stars. The
large amplitude of the SDSS J1021 outburst of 7m, superhumps with a period
below the ''period gap'', rebrightening during the declining stage of
superoutburst, rarity of outbursts and obtained spectrum allow to classify this
object as a WZ Sge type dwarf nova.
|
feeb89d1-b7ee-4cd1-b951-f7bd6a9faeb5 | feeb89d1-b7ee-4cd1-b951-f7bd6a9faeb5 | feeb89d1-b7ee-4cd1-b951-f7bd6a9faeb5 | human | null | null | none | abstracts | The Galactic Center | null | In the past decade high resolution measurements in the infrared employing
adaptive optics imaging on 10m telescopes have allowed determining the three
dimensional orbits stars within ten light hours of the compact radio source at
the center of the Milky Way. These observations show the presence of a three
million solar mass black hole in Sagittarius A* beyond any reasonable doubt.
The Galactic Center thus constitutes the best astrophysical evidence for the
existence of black holes which have long been postulated, and is also an ideal
`lab' for studying the physics in the vicinity of such an object. Remarkably,
young massive stars are present there and probably have formed in the innermost
stellar cusp. Variable infrared and X-ray emission from Sagittarius A* are a
new probe of the physical processes and space-time curvature just outside the
event horizon.
|
fe38de29-96d2-4dfb-aacd-36d49ec735be | fe38de29-96d2-4dfb-aacd-36d49ec735be | fe38de29-96d2-4dfb-aacd-36d49ec735be | human | null | null | none | abstracts | Realizable Hamiltonians for Universal Adiabatic Quantum Computers | null | It has been established that local lattice spin Hamiltonians can be used for
universal adiabatic quantum computation. However, the 2-local model
Hamiltonians used in these proofs are general and hence do not limit the types
of interactions required between spins. To address this concern, the present
paper provides two simple model Hamiltonians that are of practical interest to
experimentalists working towards the realization of a universal adiabatic
quantum computer. The model Hamiltonians presented are the simplest known
QMA-complete 2-local Hamiltonians. The 2-local Ising model with 1-local
transverse field which has been realized using an array of technologies, is
perhaps the simplest quantum spin model but is unlikely to be universal for
adiabatic quantum computation. We demonstrate that this model can be rendered
universal and QMA-complete by adding a tunable 2-local transverse XX coupling.
We also show the universality and QMA-completeness of spin models with only
1-local Z and X fields and 2-local ZX interactions.
|
7953fa49-55b7-46bf-b322-439899ac2a1f | 7953fa49-55b7-46bf-b322-439899ac2a1f | 7953fa49-55b7-46bf-b322-439899ac2a1f | human | null | null | none | abstracts | Quantitative size-dependent structure and strain determination of CdSe
nanoparticles using atomic pair distribution function analysis | null | The size-dependent structure of CdSe nanoparticles, with diameters ranging
from 2 to 4 nm, has been studied using the atomic pair distribution function
(PDF) method. The core structure of the measured CdSe nanoparticles can be
described in terms of the wurtzite atomic structure with extensive stacking
faults. The density of faults in the nanoparticles ~50% . The diameter of the
core region was extracted directly from the PDF data and is in good agreement
with the diameter obtained from standard characterization methods suggesting
that there is little surface amorphous region. A compressive strain was
measured in the Cd-Se bond length that increases with decreasing particle size
being 0.5% with respect to bulk CdSe for the 2 nm diameter particles. This
study demonstrates the size-dependent quantitative structural information that
can be obtained even from very small nanoparticles using the PDF approach.
|
04b6c424-4f10-4f7a-9af2-3e449220204c | 04b6c424-4f10-4f7a-9af2-3e449220204c | 04b6c424-4f10-4f7a-9af2-3e449220204c | human | null | null | none | abstracts | Brane-world Quantum Gravity | null | The Arnowitt-Deser-Misner canonical formulation of general relativity is
extended to the covariant brane-world theory in arbitrary dimensions. The
exclusive probing of the extra dimensions makes a substantial difference,
allowing for the construction of a non-constrained canonical theory. The
quantum states of the brane-world geometry are defined by the
Tomonaga-Schwinger equation, whose integrability conditions are determined by
the classical perturbations of submanifolds contained in the Nash's
differentiable embedding theorem. In principle, quantum brane-world theory can
be tested by current experiments in astrophysics and by near future laboratory
experiments at Tev energy. The implications to the black-hole information loss
problem, to the accelerating cosmology, and to a quantum mathematical theory of
four-sub manifolds are briefly commented.
|
d095fb49-a499-4383-a8ae-8177d300ef74 | d095fb49-a499-4383-a8ae-8177d300ef74 | d095fb49-a499-4383-a8ae-8177d300ef74 | human | null | null | none | abstracts | Isospin diffusion in thermal AdS/CFT with flavor | null | We study the gauge/gravity dual of a finite temperature field theory at
finite isospin chemical potential by considering a probe of two coincident
D7-branes embedded in the AdS-Schwarzschild black hole background. The isospin
chemical potential is obtained by giving a vev to the time component of the
non-Abelian gauge field on the brane. The fluctuations of the non-Abelian gauge
field on the brane are dual to the SU(2) flavor current in the field theory.
For the embedding corresponding to vanishing quark mass, we calculate all Green
functions corresponding to the components of the flavor current correlator. We
discuss the physical properties of these Green functions, which go beyond
linear response theory. In particular, we show that the isospin chemical
potential leads to a frequency-dependent isospin diffusion coefficient.
|
ed35fc93-eb43-4234-a33f-b7126ba2373c | ed35fc93-eb43-4234-a33f-b7126ba2373c | ed35fc93-eb43-4234-a33f-b7126ba2373c | human | null | null | none | abstracts | Projective Hilbert space structures at exceptional points | null | A non-Hermitian complex symmetric 2x2 matrix toy model is used to study
projective Hilbert space structures in the vicinity of exceptional points
(EPs). The bi-orthogonal eigenvectors of a diagonalizable matrix are
Puiseux-expanded in terms of the root vectors at the EP. It is shown that the
apparent contradiction between the two incompatible normalization conditions
with finite and singular behavior in the EP-limit can be resolved by
projectively extending the original Hilbert space. The complementary
normalization conditions correspond then to two different affine charts of this
enlarged projective Hilbert space. Geometric phase and phase jump behavior are
analyzed and the usefulness of the phase rigidity as measure for the distance
to EP configurations is demonstrated. Finally, EP-related aspects of
PT-symmetrically extended Quantum Mechanics are discussed and a conjecture
concerning the quantum brachistochrone problem is formulated.
|
9c585760-6031-4297-b79d-3b22289fdc67 | 9c585760-6031-4297-b79d-3b22289fdc67 | 9c585760-6031-4297-b79d-3b22289fdc67 | human | null | null | none | abstracts | A Disciplined Approach to Adopting Agile Practices: The Agile Adoption
Framework | null | Many organizations aspire to adopt agile processes to take advantage of the
numerous benefits that it offers to an organization. Those benefits include,
but are not limited to, quicker return on investment, better software quality,
and higher customer satisfaction. To date however, there is no structured
process (at least in the public domain) that guides organizations in adopting
agile practices. To address this problem we present the Agile Adoption
Framework. The framework consists of two components: an agile measurement
index, and a 4-Stage process, that together guide and assist the agile adoption
efforts of organizations. More specifically, the agile measurement index is
used to identify the agile potential of projects and organizations. The 4-Stage
process, on the other hand, helps determine (a) whether or not organizations
are ready for agile adoption, and (b) guided by their potential, what set of
agile practices can and should be introduced.
|
6b15d7af-e499-46a3-aaa4-512fc0150b68 | 6b15d7af-e499-46a3-aaa4-512fc0150b68 | 6b15d7af-e499-46a3-aaa4-512fc0150b68 | human | null | null | none | abstracts | Photometry of the SW Sex-type nova-like BH Lyncis in high state | null | Aims: We present a photometric study of the deeply eclipsing SW Sex-type
nova-like cataclysmic variable star BH Lyn
Methods: Time-resolved V-band CCD photometry was obtained for seven nights
between 1999 and 2004.
Results: We determined 11 new eclipse timings of BH Lyn and derived a refined
orbital ephemeris with an orbital period of 0.155875577(14) day. During the
observations, BH Lyn was in high-state with V~15.5 mag. The star presents ~1.5
mag deep eclipses with mean full-width at half-flux of 0.0683(+/-0.0054)P_orb.
The eclipse shape is highly variable, even changing form cycle to cycle. This
is most likely due to accretion disc surface brightness distribution
variations, most probably caused by strong flickering. Time-dependent accretion
disc self-occultation or variations of the hot spot(s) intensity are also
possible explanations. Negative superhumps with period of ~0.145 day are
detected in two long runs in 2000. A possible connection between SW Sex and
negative superhump phenomena through the presence of tilted accretion disc is
discussed, and a way to observationally test this is suggested.
|
0065677e-36f7-43ec-a8e8-3b4fb7c62061 | 0065677e-36f7-43ec-a8e8-3b4fb7c62061 | 0065677e-36f7-43ec-a8e8-3b4fb7c62061 | human | null | null | none | abstracts | The Reverse Shock of SNR 1987A | null | The reverse shock of supernova remnant (SNR) 1987A emits in H-alpha and
Ly-alpha, and comes in two flavors: surface and interior. The former is due to
direct, impact excitation of hydrogen atoms crossing the shock, while the
latter is the result of charge transfer reactions between these atoms and
slower, post-shock ions. Interior and surface emission are analogous to the
broad- and narrow-line components observed in Balmer-dominated SNRs. I
summarize a formalism to derive line intensities and ratios in these SNRs, as
well as a study of the transition zone in supernova shocks; I include an
appendix where I derive in detail the ratio of broad to narrow H-alpha
emission. Further study of the reverse shock emission from SNR 1987A will allow
us to predict when it will vanish and further investigate the origins of the
interior emission.
|
9de95615-f4cd-4de2-bc56-ce4124ce553f | 9de95615-f4cd-4de2-bc56-ce4124ce553f | 9de95615-f4cd-4de2-bc56-ce4124ce553f | human | null | null | none | abstracts | 3.8-Micron Photometry During the Secondary Eclipse of the Extrasolar
Planet HD 209458b | null | We report infrared photometry of the extrasolar planet HD 209458b during the
time of secondary eclipse (planet passing behind the star). Observations were
acquired during two secondary eclipses at the NASA Infrared Telescope Facility
(IRTF) in September 2003. We used a circular variable filter (1.5-percent
bandpass) centered at 3.8 microns to isolate the predicted flux peak of the
planet at this wavelength. Residual telluric absorption and instrument
variations were removed by offsetting the telescope to nearby bright comparison
stars at a high temporal cadence. Our results give a secondary eclipse depth of
0.0013 +/- 0.0011, not yet sufficient precision to detect the eclipse, whose
expected depth is approximately 0.002 - 0.003. We here elucidate the current
observational limitations to this technique, and discuss the approach needed to
achieve detections of hot Jupiter secondary eclipses at 3.8 microns from the
ground.
|
10977dce-f8b1-4580-a28c-d2441223a069 | 10977dce-f8b1-4580-a28c-d2441223a069 | 10977dce-f8b1-4580-a28c-d2441223a069 | human | null | null | none | abstracts | Antenna Combining for the MIMO Downlink Channel | null | A multiple antenna downlink channel where limited channel feedback is
available to the transmitter is considered. In a vector downlink channel
(single antenna at each receiver), the transmit antenna array can be used to
transmit separate data streams to multiple receivers only if the transmitter
has very accurate channel knowledge, i.e., if there is high-rate channel
feedback from each receiver. In this work it is shown that channel feedback
requirements can be significantly reduced if each receiver has a small number
of antennas and appropriately combines its antenna outputs. A combining method
that minimizes channel quantization error at each receiver, and thereby
minimizes multi-user interference, is proposed and analyzed. This technique is
shown to outperform traditional techniques such as maximum-ratio combining
because minimization of interference power is more critical than maximization
of signal power in the multiple antenna downlink. Analysis is provided to
quantify the feedback savings, and the technique is seen to work well with user
selection and is also robust to receiver estimation error.
|
7ad6c049-53e5-4e0b-a415-126704fb70f1 | 7ad6c049-53e5-4e0b-a415-126704fb70f1 | 7ad6c049-53e5-4e0b-a415-126704fb70f1 | human | null | null | none | abstracts | Hitting probabilities for systems of non-linear stochastic heat
equations with multiplicative noise | null | We consider a system of d non-linear stochastic heat equations in spatial
dimension 1 driven by d-dimensional space-time white noise. The non-linearities
appear both as additive drift terms and as multipliers of the noise. Using
techniques of Malliavin calculus, we establish upper and lower bounds on the
one-point density of the solution u(t,x), and upper bounds of Gaussian-type on
the two-point density of (u(s,y),u(t,x)). In particular, this estimate
quantifies how this density degenerates as (s,y) converges to (t,x). From these
results, we deduce upper and lower bounds on hitting probabilities of the
process {u(t,x)}_{t \in \mathbb{R}_+, x \in [0,1]}, in terms of respectively
Hausdorff measure and Newtonian capacity. These estimates make it possible to
show that points are polar when d >6 and are not polar when d<6. We also show
that the Hausdorff dimension of the range of the process is 6 when d>6, and
give analogous results for the processes t \mapsto u(t,x) and x \mapsto u(t,x).
Finally, we obtain the values of the Hausdorff dimensions of the level sets of
these processes.
|
5ae899c0-ca50-43d2-bc73-db82e3606664 | 5ae899c0-ca50-43d2-bc73-db82e3606664 | 5ae899c0-ca50-43d2-bc73-db82e3606664 | human | null | null | none | abstracts | Physisorption of Nucleobases on Graphene | null | We report the results of our first-principles investigation on the
interaction of the nucleobases adenine (A), cytosine (C), guanine (G), thymine
(T), and uracil (U) with graphene, carried out within the density functional
theory framework, with additional calculations utilizing Hartree--Fock plus
second-order Moeller-Plesset perturbation theory. The calculated binding energy
of the nucleobases shows the following hierarchy: G > T ~ C ~ A > U, with the
equilibrium configuration being very similar for all five of them. Our results
clearly demonstrate that the nucleobases exhibit significantly different
interaction strengths when physisorbed on graphene. The stabilizing factor in
the interaction between the base molecule and graphene sheet is dominated by
the molecular polarizability that allows a weakly attractive dispersion force
to be induced between them. The present study represents a significant step
towards a first-principles understanding of how the base sequence of DNA can
affect its interaction with carbon nanotubes, as observed experimentally.
|
f54433d5-de46-485f-bef1-5877e65d92c6 | f54433d5-de46-485f-bef1-5877e65d92c6 | f54433d5-de46-485f-bef1-5877e65d92c6 | human | null | null | none | abstracts | The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy
formation in action | null | We present a deep photometric survey of M31, conducted with the CFHT and INT,
covering the inner 50 kpc of the galaxy, the Southern quadrant out to 150 kpc,
and extending to M33. This is the first systematic panoramic study of this very
outermost region of galaxies. We detect several streams and other large-scale
structures, and two new dwarf galaxies: And XV and XVI. The discovery of
substructure on the minor axis, together with the fact that the light profile
between 0.5 < R < 1.3 follows the exponential ``extended disk'', is
particularly important in shedding light on the mixed and sometimes conflicting
results reported in previous studies. Underlying the substructures lies a
faint, metal-poor, smooth and extremely extended halo, reaching out to at least
150 kpc. The smooth halo component in M31 has a profile that can be fit with a
Hernquist model of immense scale radius ~55 kpc, almost a factor of 4 larger
than theoretical predictions. Alternatively a power-law with exponent -1.91 +/-
0.11 can be fit to the profile. The total luminosity of this structure is
similar to that of the halo of the Milky Way. This vast, smooth, underlying
halo is reminiscent of a classical monolithic model and completely unexpected
from modern galaxy formation models. M33 is also found to have an extended
metal-poor halo component, which can be fit with a Hernquist model also of
scale radius ~55 kpc. These extended slowly-decreasing halos will provide a
challenge and strong constraints for further modeling. [Abridged]
|
9a952fbc-b828-4ce4-af21-365199578feb | 9a952fbc-b828-4ce4-af21-365199578feb | 9a952fbc-b828-4ce4-af21-365199578feb | human | null | null | none | abstracts | Using conceptual metaphor and functional grammar to explore how language
used in physics affects student learning | null | This paper introduces a theory about the role of language in learning
physics. The theory is developed in the context of physics students' and
physicists' talking and writing about the subject of quantum mechanics. We
found that physicists' language encodes different varieties of analogical
models through the use of grammar and conceptual metaphor. We hypothesize that
students categorize concepts into ontological categories based on the
grammatical structure of physicists' language. We also hypothesize that
students over-extend and misapply conceptual metaphors in physicists' speech
and writing. Using our theory, we will show how, in some cases, we can explain
student difficulties in quantum mechanics as difficulties with language.
|
1d9cebf5-5c36-4945-90df-48249b1f5491 | 1d9cebf5-5c36-4945-90df-48249b1f5491 | 1d9cebf5-5c36-4945-90df-48249b1f5491 | human | null | null | none | abstracts | Supersymmetry versus Gauge Symmetry on the Heterotic Landscape | null | One of the goals of the landscape program in string theory is to extract
information about the space of string vacua in the form of statistical
correlations between phenomenological features that are otherwise uncorrelated
in field theory. Such correlations would thus represent predictions of string
theory that hold independently of a vacuum-selection principle. In this paper,
we study statistical correlations between two features which are likely to be
central to any potential description of nature at high energy scales: gauge
symmetries and spacetime supersymmetry. We analyze correlations between these
two kinds of symmetry within the context of perturbative heterotic string
vacua, and find a number of striking features. We find, for example, that the
degree of spacetime supersymmetry is strongly correlated with the probabilities
of realizing certain gauge groups, with unbroken supersymmetry at the string
scale tending to favor gauge-group factors with larger rank. We also find that
nearly half of the heterotic landscape is non-supersymmetric and yet
tachyon-free at tree level; indeed, less than a quarter of the tree-level
heterotic landscape exhibits any supersymmetry at all at the string scale.
|
42bdf3bd-5dad-436a-be0c-e326dc7b3537 | 42bdf3bd-5dad-436a-be0c-e326dc7b3537 | 42bdf3bd-5dad-436a-be0c-e326dc7b3537 | human | null | null | none | abstracts | Instabilities in the time-dependent neutrino disc in Gamma-Ray Bursts | null | We investigate the properties and evolution of accretion tori formed after
the coalescence of two compact objects. At these extreme densities and
temperatures, the accreting torus is cooled mainly by neutrino emission
produced primarily by electron and positron capture on nucleons (beta
reactions). We solve for the disc structure and its time evolution by
introducing a detailed treatment of the equation of state which includes
photodisintegration of helium, the condition of beta-equilibrium, and neutrino
opacities. We self-consistently calculate the chemical equilibrium in the gas
consisting of helium, free protons, neutrons and electron-positron pairs and
compute the chemical potentials of the species, as well as the electron
fraction throughout the disc. We find that, for sufficiently large accretion
rates (> 10 solar masses per second), the inner regions of the disk become
opaque and develop a viscous and thermal instability. The identification of
this instability might be relevant for GRB observations.
|
c638e434-4cb4-4e75-84c5-7a3cd79f334c | c638e434-4cb4-4e75-84c5-7a3cd79f334c | c638e434-4cb4-4e75-84c5-7a3cd79f334c | human | null | null | none | abstracts | Developing the Galactic diffuse emission model for the GLAST Large Area
Telescope | null | Diffuse emission is produced in energetic cosmic ray (CR) interactions,
mainly protons and electrons, with the interstellar gas and radiation field and
contains the information about particle spectra in distant regions of the
Galaxy. It may also contain information about exotic processes such as dark
matter annihilation, black hole evaporation etc. A model of the diffuse
emission is important for determination of the source positions and spectra.
Calculation of the Galactic diffuse continuum gamma-ray emission requires a
model for CR propagation as the first step. Such a model is based on theory of
particle transport in the interstellar medium as well as on many kinds of data
provided by different experiments in Astrophysics and Particle and Nuclear
Physics. Such data include: secondary particle and isotopic production cross
sections, total interaction nuclear cross sections and lifetimes of radioactive
species, gas mass calibrations and gas distribution in the Galaxy (H_2, H I, H
II), interstellar radiation field, CR source distribution and particle spectra
at the sources, magnetic field, energy losses, gamma-ray and synchrotron
production mechanisms, and many other issues. We are continuously improving the
GALPROP model and the code to keep up with a flow of new data. Improvement in
any field may affect the Galactic diffuse continuum gamma-ray emission model
used as a background model by the GLAST LAT instrument. Here we report about
the latest improvements of the GALPROP and the diffuse emission model.
|
994de64b-5b33-4557-ab4f-175650e1bb72 | 994de64b-5b33-4557-ab4f-175650e1bb72 | 994de64b-5b33-4557-ab4f-175650e1bb72 | human | null | null | none | abstracts | Prompt Emission of High Energy Photons from Gamma Ray Bursts | null | Within the internal shock scenario we consider different mechanisms of high
energy ($>1$ MeV) photon production inside a Gamma Ray Burst (GRB) fireball and
derive the expected high energy photon spectra from individual GRBs during the
prompt phase. The photon spectra of leptonic and hadronic origins are compared
within different sets of parameter regimes. Our results suggest that the high
energy emission is dominated by the leptonic component if fraction of shock
energy carried by electrons is not very small (e.g. $\epsilon_e > 10^{-3}$).
For very small values of $\epsilon_e$ the hadronic emission component could be
comparable to or even exceed the leptonic component in the GeV-TeV regime.
However, in this case a much larger energy budget of the fireball is required
to account for the same level of the observed sub-MeV spectrum. The fireballs
are therefore extremely inefficient in radiation. For a canonical fireball bulk
Lorentz factor (e.g. $\Gamma=400$), emissions above $\sim 10$ GeV are
attenuated by two-photon pair production processes. For a fireball with an even
higher Lorentz factor, the cutoff energy is higher, and emissions of 10 TeV -
PeV due to $\pi^0$-decay can also escape from the internal shocks. The flux
level is however too low to be detected by current TeV detectors, and these
photons also suffer attenuation by external soft photons.
|
139c7048-dd66-453c-801d-2101a1ead14c | 139c7048-dd66-453c-801d-2101a1ead14c | 139c7048-dd66-453c-801d-2101a1ead14c | human | null | null | none | abstracts | On the reductive Borel-Serre compactification: $L^p$-cohomology of
arithmetic groups (for large $p$) | null | The $L^2$-cohomology of a locally symmetric variety is known to have the
topological interpretation as the intersection homology of its Baily-Borel
Satake compactification. In this article, we observe that even without the
Hermitian hypothesis, the $L^p$-cohomology of an arithmetic quotient, for $p$
finite and sufficiently large, is isomorphic to the ordinary cohomology of its
reductive Borel-Serre compactification. We use this to generalize a theorem of
Mumford concerning homogeneous vector bundles, their invariant Chern forms and
the canonical extensions of the bundles; here, though, we are referring to
canonical extensions to the reductive Borel-Serre compactification of any
arithmetic quotient. To achieve that, we give a systematic discussion of vector
bundles and Chern classes on stratified
|
392837bb-17e0-4001-b5df-02bd60bf98fd | 392837bb-17e0-4001-b5df-02bd60bf98fd | 392837bb-17e0-4001-b5df-02bd60bf98fd | human | null | null | none | abstracts | The $^4$He total photo-absorption cross section with two- plus
three-nucleon interactions from chiral effective field theory | null | The total photo-absorption cross section of $^4$He is evaluated
microscopically using two- (NN) and three-nucleon (NNN) interactions based upon
chiral effective field theory ($\chi$EFT). The calculation is performed using
the Lorentz integral transform method along with the {\em ab initio} no-core
shell model approach. An important feature of the present study is the
consistency of the NN and NNN interactions and also, through the Siegert
theorem, of the two- and three-body current operators. This is due to the
application of the $\chi$EFT framework. The inclusion of the NNN interaction
produces a suppression of the low-energy peak and enhancement of the
high-energy tail of the cross section. We compare to calculations obtained
using other interactions and to representative experiments. The rather confused
experimental situation in the giant resonance region prevents discrimination
among different interaction models.
|
7238599d-da23-44fb-b601-f55184edc7a2 | 7238599d-da23-44fb-b601-f55184edc7a2 | 7238599d-da23-44fb-b601-f55184edc7a2 | human | null | null | none | abstracts | Comment on "Mass and Width of the Lowest Resonance in QCD" | null | I. Caprini's, G. Colangelo's, and H. Leutwyler's (CCL) article "Mass and
Width of the Lowest Resonance in QCD", Phys. Rev. Lett. 96, 132001 (2006)
[hep-ph/0512364], is critically reviewed. The present comment is devoted to
complement a recent experimental discussion (D.V. Bugg, J. Phys. G 34, 151
(2007) [hep-ph/0608081]) of short-comings in the CCL analysis, by presenting
theoretical arguments pointing at a serious flaw in the theoretical formalism
used by CCL, and also at the unlikeliness of their tiny error bars in the
sigma-meson mass and width. The criticism made in the comment applies
analogously to the analysis on the kappa-meson mass performed in the article
"The K0*(800) scalar resonance from Roy-Steiner representations of pi K
scattering" published as S. Descotes-Genon and B. Moussallam, Eur. Phys. J. C
48, 553 (2006) [hep-ph/0607133].
|
c942a7b7-92c0-437b-8d94-126e25c0cf7f | c942a7b7-92c0-437b-8d94-126e25c0cf7f | c942a7b7-92c0-437b-8d94-126e25c0cf7f | human | null | null | none | abstracts | Resummation Effects in the Search of SM Higgs Boson at Hadron Colliders | null | We examine the soft-gluon resummation effects, including the exact spin
correlations among the final state particles, in the search of the Standard
Model Higgs boson, via the process $gg\to H\to WW/ZZ \to 4 leptons, at the
Tevatron and the LHC. A comparison between the resummation and the
Next-to-Leading order (NLO) calculation is performed after imposing various
kinematics cuts suggested in the literature for the Higgs boson search. For the
$H\to ZZ$ mode, the resummation effects increase the acceptance of the signal
events by about 25%, as compared to the NLO prediction, and dramatically alter
various kinematics distributions of the final state leptons. For the $H\to WW$
mode, the acceptance rates of the signal events predicted by the resummation
and NLO calculations are almost the same, but some of the predicted kinematical
distributions are quite different. Thus, to precisely determine the properties
of the Higgs boson at hadron colliders, the soft-gluon resummation effects have
to be taken into account.
|
36f6bb9d-ed3c-4d08-8557-8121d7799880 | 36f6bb9d-ed3c-4d08-8557-8121d7799880 | 36f6bb9d-ed3c-4d08-8557-8121d7799880 | human | null | null | none | abstracts | Prediction of future fifteen solar cycles | null | In the previous study (Hiremath 2006a), the solar cycle is modeled as a
forced and damped harmonic oscillator and from all the 22 cycles (1755-1996),
long-term amplitudes, frequencies, phases and decay factor are obtained. Using
these physical parameters of the previous 22 solar cycles and by an {\em
autoregressive model}, we predict the amplitude and period of the future
fifteen solar cycles. Predicted amplitude of the present solar cycle (23)
matches very well with the observations. The period of the present cycle is
found to be 11.73 years. With these encouraging results, we also predict the
profiles of future 15 solar cycles. Important predictions are : (i) the period
and amplitude of the cycle 24 are 9.34 years and 110 ($\pm 11$), (ii) the
period and amplitude of the cycle 25 are 12.49 years and 110 ($\pm$ 11), (iii)
during the cycles 26 (2030-2042 AD), 27 (2042-2054 AD), 34 (2118-2127 AD), 37
(2152-2163 AD) and 38 (2163-2176 AD), the sun might experience a very high
sunspot activity, (iv) the sun might also experience a very low (around 60)
sunspot activity during cycle 31 (2089-2100 AD) and, (v) length of the solar
cycles vary from 8.65 yrs for the cycle 33 to maximum of 13.07 yrs for the
cycle 35.
|
8c6378d7-890c-48d1-9b2c-cd1c08d7a0ee | 8c6378d7-890c-48d1-9b2c-cd1c08d7a0ee | 8c6378d7-890c-48d1-9b2c-cd1c08d7a0ee | human | null | null | none | abstracts | Lowest Landau Level of Relativistic Field Theories in a Strong
Background Field | null | We consider gauge theories in a strong external magnetic like field. This
situation can appear either in conventional four-dimensional theories, but also
naturally in extra-dimensional theories and especially in brane world models.
We show that in the lowest Landau level approximation, some of the coordinates
become non-commutative. We find physical reasons to formal problems with
non-commutative gauge theories such as the issue with SU(N) gauge symmetries.
Our construction is applied to a minimal extension of the standard model. It is
shown that the Higgs sector might be non-commutative whereas the remaining
sectors of the standard model remain commutative. Signatures of this model at
the LHC are discussed. We then discuss an application to a dark matter sector
coupled to the Higgs sector of the standard model and show that here again,
dark matter could be non-commutative, the standard model fields remaining
commutative.
|
1beb8785-76cd-4fce-9ac1-d764addecb92 | 1beb8785-76cd-4fce-9ac1-d764addecb92 | 1beb8785-76cd-4fce-9ac1-d764addecb92 | human | null | null | none | abstracts | Mechanical and dielectric relaxation spectra in seven highly viscous
glass formers | null | Published dielectric and shear data of six molecular glass formers and one
polymer are evaluated in terms of a spectrum of thermally activated processes,
with the same barrier density for the retardation spectrum of shear and
dielectrics. The viscosity, an independent parameter of the fit, seems to be
related to the high-barrier cutoff time of the dielectric signal, in accordance
with the idea of a renewal of the relaxing entities after this critical time.
In the five cases where one can fit accurately, the temperature dependence of
the high-barrier cutoff follows the shoving model. The Johari-Goldstein peaks,
seen in four of our seven cases, are describable in terms of gaussians in the
barrier density, superimposed on the high-frequency tail of the
$\alpha$-process. Dielectric and shear measurements of the same substance find
the same peak positions and widths of these gaussians, but in general a
different weight.
|
a51078a3-639c-4559-aad7-8c741c9a8358 | a51078a3-639c-4559-aad7-8c741c9a8358 | a51078a3-639c-4559-aad7-8c741c9a8358 | human | null | null | none | abstracts | Computational and experimental imaging of Mn defects on GaAs (110)
cross-sectional surface | null | We present a combined experimental and computational study of the (110)
cross-sectional surface of Mn $\delta$-doped GaAs samples. We focus our study
on three different selected Mn defect configurations not previously studied in
details, namely surface interstitial Mn, isolated and in pairs, and
substitutional Mn atoms on cationic sites (Mn$_{\rm Ga}$) in the first
subsurface layer. The sensitivity of the STM images to the specific local
environment allows to distinguish between Mn interstitials with nearest
neighbor As atoms (Int$_{\rm As}$) rather than Ga atoms (Int$_{\rm Ga}$), and
to identify the fingerprint of peculiar satellite features around subsurface
substitutional Mn. The simulated STM maps for Int$_{\rm As}$, both isolated and
in pairs, and Mn$_{\rm Ga}$ in the first subsurface layer are consistent with
some experimental images hitherto not fully characterized.
|
eeab8ad8-7ccd-4547-85cb-46baa731a41c | eeab8ad8-7ccd-4547-85cb-46baa731a41c | eeab8ad8-7ccd-4547-85cb-46baa731a41c | human | null | null | none | abstracts | Hamiltonian Quantum Dynamics With Separability Constraints | null | Schroedinger equation on a Hilbert space ${\cal H}$, represents a linear
Hamiltonian dynamical system on the space of quantum pure states, the
projective Hilbert space $P {\cal H}$. Separable states of a bipartite quantum
system form a special submanifold of $P {\cal H}$.
We analyze the Hamiltonian dynamics that corresponds to the quantum system
constrained on the manifold of separable states, using as an important example
the system of two interacting qubits. The constraints introduce nonlinearities
which render the dynamics nontrivial. We show that the qualitative properties
of the constrained dynamics clearly manifest the symmetry of the qubits system.
In particular, if the quantum Hamilton's operator has not enough symmetry, the
constrained dynamics is nonintegrable, and displays the typical features of a
Hamiltonian dynamical system with mixed phase space. Possible physical
realizations of the separability constraints are discussed.
|
64e96a18-1c6e-4ef3-a5cf-8e5fbce521b7 | 64e96a18-1c6e-4ef3-a5cf-8e5fbce521b7 | 64e96a18-1c6e-4ef3-a5cf-8e5fbce521b7 | human | null | null | none | abstracts | Fast recursive filters for simulating nonlinear dynamic systems | null | A fast and accurate computational scheme for simulating nonlinear dynamic
systems is presented. The scheme assumes that the system can be represented by
a combination of components of only two different types: first-order low-pass
filters and static nonlinearities. The parameters of these filters and
nonlinearities may depend on system variables, and the topology of the system
may be complex, including feedback. Several examples taken from neuroscience
are given: phototransduction, photopigment bleaching, and spike generation
according to the Hodgkin-Huxley equations. The scheme uses two slightly
different forms of autoregressive filters, with an implicit delay of zero for
feedforward control and an implicit delay of half a sample distance for
feedback control. On a fairly complex model of the macaque retinal horizontal
cell it computes, for a given level of accuracy, 1-2 orders of magnitude faster
than 4th-order Runge-Kutta. The computational scheme has minimal memory
requirements, and is also suited for computation on a stream processor, such as
a GPU (Graphical Processing Unit).
|
a328fd30-62ee-4425-b856-6fc2de5be1f6 | a328fd30-62ee-4425-b856-6fc2de5be1f6 | a328fd30-62ee-4425-b856-6fc2de5be1f6 | human | null | null | none | abstracts | On families of rational curves in the Hilbert square of a surface (with
an Appendix by Edoardo Sernesi) | null | Under natural hypotheses we give an upper bound on the dimension of families
of singular curves with hyperelliptic normalizations on a surface S with p_g(S)
>0 via the study of the associated families of rational curves in Hilb^2(S).
We use this result to prove the existence of nodal curves of geometric genus
3 with hyperelliptic normalizations, on a general K3 surface, thus obtaining
specific 2-dimensional families of rational curves in its Hilbert square. We
describe two infinite series of examples of general, primitively polarized K3's
such that their Hilbert squares contain a IP^2 or a threefold birational to a
IP^1-bundle over a K3.
We discuss some consequences on the Mori cone of the Hilbert square of a
general K3.
|
8e953edf-08bc-4c46-81d6-fb1f5d853388 | 8e953edf-08bc-4c46-81d6-fb1f5d853388 | 8e953edf-08bc-4c46-81d6-fb1f5d853388 | human | null | null | none | abstracts | Anisotropy and Magnetic Field Effects on the Genuine Multipartite
Entanglement of Multi-Qubit Heisenberg {\it XY} Chains | null | It has been shown that, for the two-qubit Heisenberg XY model, anisotropy and
magnetic field may together be used to produce entanglement for any finite
temperature by adjusting the external magnetic field beyond some finite
critical strength. This interesting result arises from an analysis employing
the Wootters concurrence, a computable measure of entanglement for two-qubit
states. Recently, Mintert {\em et al.} proposed generalizations of Wootters
concurrence for multipartite states. These MKB concurrences possess a
mathematical property that enables one to understand the origin of this
characteristic behavior. Here, we first study the effect of anisotropy and
magnetic field on the multipartite thermal entanglement of a four-qubit
Heisenberg XY chain using the MKB concurrences. We show that this model
exhibits characteristic behavior similar to that of the two-qubit model. In
addition, we show that this can again be understood using the same mathematical
property. Next, we show that the six-qubit Heisenberg XY chain possesses
properties necessary for it to have the characteristic behavior too. Most
importantly, it is possible to directly measure the multipartite MKB
concurrences of pure states. This may provide an experimental verification of
our conjecture that for a Heisenberg XY chain of any even number of qubits, it
is always possible to obtain non-zero genuine multipartite entanglement at any
finite temperature by applying a sufficiently large magnetic field.
|
352225e0-debf-4fd7-83e0-a75cfd2547fd | 352225e0-debf-4fd7-83e0-a75cfd2547fd | 352225e0-debf-4fd7-83e0-a75cfd2547fd | human | null | null | none | abstracts | A Language-Based Approach for Improving the Robustness of Network
Application Protocol Implementations | null | The secure and robust functioning of a network relies on the defect-free
implementation of network applications. As network protocols have become
increasingly complex, however, hand-writing network message processing code has
become increasingly error-prone. In this paper, we present a domain-specific
language, Zebu, for describing protocol message formats and related processing
constraints. From a Zebu specification, a compiler automatically generates
stubs to be used by an application to parse network messages. Zebu is easy to
use, as it builds on notations used in RFCs to describe protocol grammars. Zebu
is also efficient, as the memory usage is tailored to application needs and
message fragments can be specified to be processed on demand. Finally,
Zebu-based applications are robust, as the Zebu compiler automatically checks
specification consistency and generates parsing stubs that include validation
of the message structure. Using a mutation analysis in the context of SIP and
RTSP, we show that Zebu significantly improves application robustness.
|
c5d60547-d846-44b4-b804-0578b0b34473 | c5d60547-d846-44b4-b804-0578b0b34473 | c5d60547-d846-44b4-b804-0578b0b34473 | human | null | null | none | abstracts | Kibble-Zurek mechanism in a quenched ferromagnetic Bose-Einstein
condensate | null | The spin vortices are shown to be created through the Kibble-Zurek (KZ)
mechanism in a quantum phase transition of a spin-1 ferromagnetic Bose-Einstein
condensate, when the applied magnetic field is quenched below a critical value.
It is shown that the magnetic correlation functions have finite correlation
lengths, and magnetizations at widely separated positions grow in random
directions, resulting in spin vortices. We numerically confirm the scaling law
that the winding number of spin vortices is proportional to the square root of
the length of the closed path, and for slow quench, proportional to $\tau_{\rm
Q}^{-1/6}$ with $\tau_{\rm Q}$ being the quench time. The relation between the
spin conservation and the KZ mechanism is discussed.
|
ca3d4cb9-cef7-4546-a0ec-a233621baae7 | ca3d4cb9-cef7-4546-a0ec-a233621baae7 | ca3d4cb9-cef7-4546-a0ec-a233621baae7 | human | null | null | none | abstracts | How far is it to a sudden future singularity of pressure? | null | We discuss the constraints coming from current observations of type Ia
supernovae on cosmological models which allow sudden future singularities of
pressure (with the scale factor and the energy density regular). We show that
such a sudden singularity may happen in the very near future (e.g. within ten
million years) and its prediction at the present moment of cosmic evolution
cannot be distinguished, with current observational data, from the prediction
given by the standard quintessence scenario of future evolution. Fortunately,
sudden future singularities are characterized by a momentary peak of infinite
tidal forces only; there is no geodesic incompletness which means that the
evolution of the universe may eventually be continued throughout until another
``more serious'' singularity such as Big-Crunch or Big-Rip.
|
5c329192-dc96-461f-84cd-15e5d50f2fd3 | 5c329192-dc96-461f-84cd-15e5d50f2fd3 | 5c329192-dc96-461f-84cd-15e5d50f2fd3 | human | null | null | none | abstracts | Decreasing families of dynamically determined intervals in the power-law
family | null | We study the rate of growth of ratios of intervals delimited by the
post-critical orbit of a map in the quasi-quadratic family $x\mapsto
-|x|^\alpha +a.$ The critical order $\alpha$ is an arbitrary real number
$\alpha>1.$ The range of the parameter $a$ is confined to an interval
$(1,a_{\alpha})$ of length depending on the critical order. We prove that in
every power-law family there is a unique parameter $p_{\alpha}$ corresponding
to the kneading sequence $RLRRRLRC.$ Subsequently, we obtain monotonicity
results concerning ratios of all intervals labeled by infinite post-critical
orbit in the case of the kneading sequence $RLRL...$ This extends the results
from \cite{P}, via refinement of the tools based on special properties of
power-law mappings in non-euclidean metric.
|
5dce4f52-1d11-4d3d-8fcb-68475a52d9a8 | 5dce4f52-1d11-4d3d-8fcb-68475a52d9a8 | 5dce4f52-1d11-4d3d-8fcb-68475a52d9a8 | human | null | null | none | abstracts | Why do some intermediate polars show soft X-ray emission? A survey of
XMM-Newton spectra | null | We make a systematic analysis of the XMM-Newton X-ray spectra of intermediate
polars (IPs) and find that, contrary to the traditional picture, most show a
soft blackbody component. We compare the results with those from AM Her stars
and deduce that the blackbody emission arises from reprocessing of hard X-rays,
rather than from the blobby accretion sometimes seen in AM Hers. Whether an IP
shows a blackbody component appears to depend primarily on geometric factors: a
blackbody is not seen in those that have accretion footprints that are always
obscured by accretion curtains or are only visible when foreshortened on the
white-dwarf limb. Thus we argue against previous suggestions that the blackbody
emission characterises a separate sub-group of IPs which are more akin to AM
Hers, and develop a unified picture of the blackbody emission in these stars.
|
52d5ccd8-9820-4676-92ad-8c96feb85ea1 | 52d5ccd8-9820-4676-92ad-8c96feb85ea1 | 52d5ccd8-9820-4676-92ad-8c96feb85ea1 | human | null | null | none | abstracts | A Panchromatic Study of the Globular Cluster NGC 1904. I: The Blue
Straggler Population | null | By combining high-resolution (HST-WFPC2) and wide-field ground based (2.2m
ESO-WFI) and space (GALEX) observations, we have collected a multi-wavelength
photometric data base (ranging from the far UV to the near infrared) of the
galactic globular cluster NGC1904 (M79). The sample covers the entire cluster
extension, from the very central regions up to the tidal radius. In the present
paper such a data set is used to study the BSS population and its radial
distribution. A total number of 39 bright ($m_{218}\le 19.5$) BSS has been
detected, and they have been found to be highly segregated in the cluster core.
No significant upturn in the BSS frequency has been observed in the outskirts
of NGC 1904, in contrast to other clusters (M 3, 47 Tuc, NGC 6752, M 5) studied
with the same technique. Such evidences, coupled with the large radius of
avoidance estimated for NGC 1904 ($r_{avoid}\sim 30$ core radii), indicate that
the vast majority of the cluster heavy stars (binaries) has already sunk to the
core. Accordingly, extensive dynamical simulations suggest that BSS formed by
mass transfer activity in primordial binaries evolving in isolation in the
cluster outskirts represent only a negligible (0--10%) fraction of the overall
population.
|
5e13817d-c07b-48b0-9566-84cac9a75dd4 | 5e13817d-c07b-48b0-9566-84cac9a75dd4 | 5e13817d-c07b-48b0-9566-84cac9a75dd4 | human | null | null | none | abstracts | Higgs and Z' Phenomenology in B-L extension of the Standard Model at LHC | null | The phenomenology of the low scale U(1)_{B-L} extension of the standard model
and its implications at LHC is presented. In this model, an extra gauge boson
corresponding to B-L gauge symmetry and an extra SM singlet scalar (heavy
Higgs) are predicted. We show a detailed analysis of both heavy and light
Higgses decay and production in addition to the possible decay channels of the
new gauge boson. We find that the cross sections of the SM-like Higgs
production are reduced by ~ 20%-30%, while its decay branching ratios remain
intact. The extra Higgs has relatively small cross sections and the branching
ratios of Z'-> l^+ l^- are of order ~20% compared to ~ 3% of the SM resuls.
Hence, the search for Z' is accessible via a clean dilepton signal at LHC.
|
fee640b1-9e01-467c-b484-3a1c276d4154 | fee640b1-9e01-467c-b484-3a1c276d4154 | fee640b1-9e01-467c-b484-3a1c276d4154 | human | null | null | none | abstracts | What Can be Learned Studying the Distribution of the Biggest Fragment ? | null | In the canonical formalism of statistical physics, a signature of a first
order phase transition for finite systems is the bimodal distribution of an
order parameter. Previous thermodynamical studies of nuclear sources produced
in heavy-ion collisions provide information which support the existence of a
phase transition in those finite nuclear systems. Some results suggest that the
observable Z1 (charge of the biggest fragment) can be considered as a reliable
order parameter of the transition. This talk will show how from peripheral
collisions studied with the INDRA detector at GSI we can obtain this bimodal
behaviour of Z1. Getting rid of the entrance channel effects and under the
constraint of an equiprobable distribution of excitation energy (E*), we use
the canonical description of a phase transition to link this bimodal behaviour
with the residual convexity of the entropy. Theoretical (with and without phase
transition) and experimental Z1-E* correlations are compared. This comparison
allows us to rule out the case without transition. Moreover that quantitative
comparison provides us with information about the coexistence region in the
Z1-E* plane which is in good agreement with that obtained with the signal of
abnormal uctuations of configurational energy (microcanonical negative heat
capacity).
|
d211de25-585c-4f97-9bf1-97d80643a279 | d211de25-585c-4f97-9bf1-97d80643a279 | d211de25-585c-4f97-9bf1-97d80643a279 | human | null | null | none | abstracts | Reconstructing the Intrinsic Triaxial Shape of the Virgo Cluster | null | To use galaxy clusters as a cosmological probe, it is important to account
for their triaxiality. Assuming that the triaxial shapes of galaxy clusters are
induced by the tidal interaction with the surrounding matter, Lee and Kang
recently developed a reconstruction algorithm for the measurement of the axial
ratio of a triaxial cluster. We examine the validity of this reconstruction
algorithm by performing an observational test of it with the Virgo cluster as a
target. We first modify the LK06 algorithm by incorporating the two dimensional
projection effect. Then, we analyze the 1275 member galaxies from the Virgo
Cluster Catalogue and find the projected direction of the Virgo cluster major
axis by measuring the anisotropy in the spatial distribution of the member
galaxies in the two dimensional projected plane. Applying the modified
reconstruction algorithm to the analyzed data, we find that the axial ratio of
the triaxial Virgo cluster is (1: 0.54 : 0.73). This result is consistent with
the recent observational report from the Virgo Cluster Survey, proving the
robustness of the reconstruction algorithm. It is also found that at the inner
radii the shape tends to be more like prolate. We discuss the possible effect
of the Virgo cluster triaxiality on the mass estimation.
|
b4a49cf7-b417-4ca5-b917-46a88fb457ec | b4a49cf7-b417-4ca5-b917-46a88fb457ec | b4a49cf7-b417-4ca5-b917-46a88fb457ec | human | null | null | none | abstracts | Euclidean analysis of the entropy functional formalism | null | The attractor mechanism implies that the supersymmetric black hole near
horizon solution is defined only in terms of the conserved charges and is
therefore independent of asymptotic moduli. Starting only with the near horizon
geometry, Sen's entropy functional formalism computes the entropy of an extreme
black hole by means of a Legendre transformation where the electric fields are
defined as conjugated variables to the electric charges. However, traditional
Euclidean methods require the knowledge of the full geometry to compute the
black hole thermodynamic quantities. We establish the connection between the
entropy functional formalism and the standard Euclidean formalism taken at zero
temperature. We find that Sen's entropy function 'f' (on-shell) matches the
zero temperature limit of the Euclidean action. Moreover, Sen's near horizon
angular and electric fields agree with the chemical potentials that are defined
from the zero-temperature limit of the Euclidean formalism.
|
0befef55-245e-43c5-8f9b-c5a7557e0c32 | 0befef55-245e-43c5-8f9b-c5a7557e0c32 | 0befef55-245e-43c5-8f9b-c5a7557e0c32 | human | null | null | none | abstracts | First principles theory of chiral dichroism in electron microscopy
applied to 3d ferromagnets | null | Recently it was demonstrated (Schattschneider et al., Nature 441 (2006),
486), that an analogue of the X-ray magnetic circular dichroism (XMCD)
experiment can be performed with the transmission electron microscope (TEM).
The new phenomenon has been named energy-loss magnetic chiral dichroism (EMCD).
In this work we present a detailed ab initio study of the chiral dichroism in
the Fe, Co and Ni transition elements. We discuss the methods used for the
simulations together with the validity and accuracy of the treatment, which
can, in principle, apply to any given crystalline specimen. The dependence of
the dichroic signal on the sample thickness, accuracy of the detector position
and the size of convergence and collection angles is calculated.
|
7400e8f0-e7b2-4149-b7e6-f7bbbdc44e26 | 7400e8f0-e7b2-4149-b7e6-f7bbbdc44e26 | 7400e8f0-e7b2-4149-b7e6-f7bbbdc44e26 | human | null | null | none | abstracts | QCD thermodynamics and confinement from a dynamical quasiparticle point
of view | null | In this study it is demonstrated that a simple picture of the
QCD gluon liquid emerges in the dynamical quasiparticle model that specifies
the active degrees of freedom in the time-like sector and yields a potential
energy density in the space-like sector. By using the time-like gluon density
(or scalar gluon density) as an independent degree of freedom - instead of the
temperature $T$ as a Lagrange parameter - variations of the potential energy
density lead to effective mean-fields for time-like gluons and an effective
gluon-gluon interaction strength at low density. The latter yields a simple
dynamical picture for the gluon fusion to color neutral glueballs when
approaching the phase boundary from a temperature higher than $T_c$ and paves
the way for an off-shell transport theoretical description of the parton
dynamics.
|
5d59df5a-7985-48dd-ad9f-9bd7b3316b87 | 5d59df5a-7985-48dd-ad9f-9bd7b3316b87 | 5d59df5a-7985-48dd-ad9f-9bd7b3316b87 | human | null | null | none | abstracts | Dynamic fracture of icosahedral model quasicrystals: A molecular
dynamics study | null | Ebert et al. [Phys. Rev. Lett. 77, 3827 (1996)] have fractured icosahedral
Al-Mn-Pd single crystals in ultrahigh vacuum and have investigated the cleavage
planes in-situ by scanning tunneling microscopy (STM). Globular patterns in the
STM-images were interpreted as clusters of atoms. These are significant
structural units of quasicrystals. The experiments of Ebert et al. imply that
they are also stable physical entities, a property controversially discussed
currently. For a clarification we performed the first large scale fracture
simulations on three-dimensional complex binary systems. We studied the
propagation of mode I cracks in an icosahedral model quasicrystal by molecular
dynamics techniques at low temperature. In particular we examined how the shape
of the cleavage plane is influenced by the clusters inherent in the model and
how it depends on the plane structure. Brittle fracture with no indication of
dislocation activity is observed. The crack surfaces are rough on the scale of
the clusters, but exhibit constant average heights for orientations
perpendicular to high symmetry axes. From detailed analyses of the fractured
samples we conclude that both, the plane structure and the clusters, strongly
influence dynamic fracture in quasicrystals and that the clusters therefore
have to be regarded as physical entities.
|
5851cfbc-2a0e-434f-90c0-103577749a68 | 5851cfbc-2a0e-434f-90c0-103577749a68 | 5851cfbc-2a0e-434f-90c0-103577749a68 | human | null | null | none | abstracts | Exact distribution of the sample variance from a gamma parent
distribution | null | Several representations of the exact cdf of the sum of squares of n
independent gamma-distributed random variables Xi are given, in particular by a
series of gamma distribution functions. Using a characterization of the gamma
distribution by Laha, an expansion of the exact distribution of the sample
variance is derived by a Taylor series approach with the former distribution as
its leading term. In particular for integer orders alpha some further series
are provided, including a convex combination of gamma distributions for alpha =
1 and nearly of this type for alpha > 1. Furthermore, some representations of
the distribution of the angle Phi between (X1,...,Xn) and (1,...,1) are given
by orthogonal series. All these series are based on the same sequence of easily
computed moments of cos(Phi).
|
02f38caa-a28e-4062-9896-c413fb6fee23 | 02f38caa-a28e-4062-9896-c413fb6fee23 | 02f38caa-a28e-4062-9896-c413fb6fee23 | human | null | null | none | abstracts | Quantitative LEED I-V and ab initio study of the Si(111)-3x2-Sm surface
structure and the missing half order spots in the 3x1 diffraction pattern | null | We have used Low Energy Electron Diffraction (LEED) I-V analysis and ab
initio calculations to quantitatively determine the honeycomb chain model
structure for the Si(111)-3x2-Sm surface. This structure and a similar 3x1
recontruction have been observed for many Alkali-Earth and Rare-Earth metals on
the Si(111) surface. Our ab initio calculations show that there are two almost
degenerate sites for the Sm atom in the unit cell and the LEED I-V analysis
reveals that an admixture of the two in a ratio that slightly favours the site
with the lower energy is the best match to experiment. We show that the I-V
curves are insensitive to the presence of the Sm atom and that this results in
a very low intensity for the half order spots which might explain the
appearance of a 3x1 LEED pattern produced by all of the structures with a 3x2
unit cell.
|
f046431a-cf88-4718-ad04-9aee408f081d | f046431a-cf88-4718-ad04-9aee408f081d | f046431a-cf88-4718-ad04-9aee408f081d | human | null | null | none | abstracts | Momentum distributions in time-dependent density functional theory:
Product phase approximation for non-sequential double ionization in strong
laser fields | null | We investigate the possibility to deduce momentum space properties from
time-dependent density functional calculations. Electron and ion momentum
distributions after double ionization of a model Helium atom in a strong
few-cycle laser pulse are studied. We show that, in this case, the choice of
suitable functionals for the observables is considerably more important than
the choice of the correlation potential in the time-dependent Kohn-Sham
equations. By comparison with the solution of the time-dependent Schroedinger
equation, the insufficiency of functionals neglecting electron correlation is
demonstrated. We construct a functional of the Kohn-Sham orbitals, which in
principle yields the exact momentum distributions of the electrons and the ion.
The product-phase approximation is introduced, which reduces the problem of
approximating this functional significantly.
|
1c76135c-fa43-4279-87dc-6c3e98965ffe | 1c76135c-fa43-4279-87dc-6c3e98965ffe | 1c76135c-fa43-4279-87dc-6c3e98965ffe | human | null | null | none | abstracts | Measurements and analysis of the upper critical field $H_{c2}$ on an
underdoped and overdoped $La_{2-x}Sr_xCuO_4$ compounds | null | The upper critical field $H_{c2}$ is one of the many non conventional
properties of high-$T_c$ cuprates. It is possible that the $H_{c2}(T)$
anomalies are due to the presence of inhomogeneities in the local charge
carrier density $\rho$ of the $CuO_2$ planes. In order to study this point, we
have prepared good quality samples of polycrystalline $La_{2-x}Sr_xCuO_{4}$
using the wet-chemical method, which has demonstrated to produce samples with a
better cation distribution. In particular, we have studied the temperature
dependence of the second critical field, $H_{c2}(T)$, through the magnetization
measurements on two samples with opposite average carrier concentration
($\rho_m=x$) and nearly the same critical temperature, namely $\rho_m = 0.08$
(underdoped) and $\rho_m = 0.25$ (overdoped). The results close to $T_c$ do not
follow the usual Ginzburg-Landau theory and are interpreted by a theory which
takes into account the influence of the inhomogeneities.
|
c05e8460-dbb4-4a2c-8464-f4af70ea2384 | c05e8460-dbb4-4a2c-8464-f4af70ea2384 | c05e8460-dbb4-4a2c-8464-f4af70ea2384 | human | null | null | none | abstracts | A unified projection formalism for the Al-Pd-Mn quasicrystal
Xi-approximants and their metadislocations | null | The approximants xi, xi' and xi'_n of the quasicrystal Al-Mn-Pd display most
interesting plastic properties as for example phason-induced deformation
processes (Klein, H., Audier, M., Boudard, M., de Boissieu, M., Beraha, L., and
Duneau, M., 1996, Phil. Mag. A, 73, 309.) or metadislocations (Klein, H.,
Feuerbacher, M., Schall, P., and Urban, K., 1999, Phys. Rev. Lett., 82, 3468.).
Here we demonstrate that the phases and their deformed or defected states can
be described by a simple projection formalism in three-dimensional space - not
as usual in four to six dimensions. With the method we can interpret
microstructures observed with electron microscopy as phasonic phase boundaries.
Furthermore we determine the metadislocations of lowest energy and relate them
uniquely to experimentally observed ones. Since moving metadislocations in the
xi'-phase can create new phason-planes, we suggest a dislocation induced phase
transition from xi' to xi'_n. The methods developed in this paper can as well
be used for various other complex metallic alloys.
|
63e880ad-7ec9-4c03-a962-a63924b9931b | 63e880ad-7ec9-4c03-a962-a63924b9931b | 63e880ad-7ec9-4c03-a962-a63924b9931b | human | null | null | none | abstracts | Light stops in the MSSM parameter space | null | We consider the regions of the MSSM parameter space where the top squarks
become light and even may be the LSP. This happens when the triple scalar
coupling A becomes very big compared to m_0. We show that in this case the
requirement that the LSP is neutral imposes noticeable constraint on the
parameter space excluding low m_0 and m_{1/2} similar to constraint from the
Higgs mass limit. In some cases these constraints overlap. This picture takes
place in a wide region of \tan\beta. In a narrow band close to the border line
the stops are long-lived particles and decay into quarks and neutralino
(chargino). The cross-section of their production at LHC via gluon fusion
mechanism in this region may reach a few pb.
|
dc96fce4-fe8c-49fd-ac3c-4b8a0547587b | dc96fce4-fe8c-49fd-ac3c-4b8a0547587b | dc96fce4-fe8c-49fd-ac3c-4b8a0547587b | human | null | null | none | abstracts | The blue plume population in dwarf spheroidal galaxies: genuine blue
stragglers or young stellar population? | null | Abridged... Blue stragglers (BSS) are thought to be the product of either
primordial or collisional binary systems. In the context of dwarf spheroidal
galaxies it is hard to firmly disentangle a genuine BSS population from young
main sequence (MS) stars tracing a ~1-2 Gyr old star forming episode. Assuming
that their blue plume populations are made of BSS, we estimate the BSS
frequency for 8 Local Group non star-forming dwarf galaxies, using a
compilation of ground and space based photometry.
Our results can be summarized as follows: (i) The BSS frequency in dwarf
galaxies, at any given Mv, is always higher than that in globular clusters of
similar luminosities; (ii) the BSS frequency for the lowest luminosity dwarf
galaxies is in excellent agreement with that observed in the Milky Way halo;
and most interestingly (iii) derive a statistically significant
anti-correlation between the BSS frequency and the galaxy Mv.
The low density, almost collision-less, environments of our dwarf galaxy
sample allow us to infer (i) their very low dynamical evolution; (ii) a
negligible production of collisional BSS; and consequently (iii) that their
blue plumes are mainly made of primordial binaries. The dwarf galaxies
anti-correlation can be used as a discriminator: galaxies obeying the
anti-correlation are more likely to possess genuine primordial BSS rather than
young main sequence stars.
|
35915575-4eeb-4749-bbad-72ce7ff64159 | 35915575-4eeb-4749-bbad-72ce7ff64159 | 35915575-4eeb-4749-bbad-72ce7ff64159 | human | null | null | none | abstracts | Rotationally-invariant slave-boson formalism and momentum dependence of
the quasiparticle weight | null | We generalize the rotationally-invariant formulation of the slave-boson
formalism to multiorbital models, with arbitrary interactions, crystal fields,
and multiplet structure. This allows for the study of multiplet effects on the
nature of low-energy quasiparticles. Non-diagonal components of the matrix of
quasiparticle weights can be calculated within this framework. When combined
with cluster extensions of dynamical mean-field theory, this method allows us
to address the effects of spatial correlations, such as the generation of the
superexchange and the momentum dependence of the quasiparticle weight. We
illustrate the method on a two-band Hubbard model, a Hubbard model made of two
coupled layers, and a two-dimensional single-band Hubbard model (within a
two-site cellular dynamical mean-field approximation).
|
99ecc0ed-8bdd-4892-b8a9-a6421396c7c4 | 99ecc0ed-8bdd-4892-b8a9-a6421396c7c4 | 99ecc0ed-8bdd-4892-b8a9-a6421396c7c4 | human | null | null | none | abstracts | Symmetries and the cosmological constant puzzle | null | We outline the evaluation of the cosmological constant in the framework of
the standard field-theoretical treatment of vacuum energy and discuss the
relation between the vacuum energy problem and the gauge-group spontaneous
symmetry breaking. We suggest possible extensions of the 't Hooft-Nobbenhuis
symmetry, in particular, its complexification till duality symmetry and discuss
the compatible implementation on gravity. We propose to use the discrete
time-reflection transform to formulate a framework in which one can eliminate
the huge contributions of vacuum energy into the effective cosmological
constant and suggest that the breaking of time--reflection symmetry could be
responsible for a small observable value of this constant.
|
aa18cc28-a3e2-449d-a4db-0d7592e5b059 | aa18cc28-a3e2-449d-a4db-0d7592e5b059 | aa18cc28-a3e2-449d-a4db-0d7592e5b059 | human | null | null | none | abstracts | The property of kappa-deformed statistics for a relativistic gas in an
electromagnetic field: kappa parameter and kappa-distribution | null | We investigate the physical property of the kappa parameter and the
kappa-distribution in the kappa-deformed statistics, based on Kaniadakis
entropy, for a relativistic gas in an electromagnetic field. We derive two
relations for the relativistic gas in the framework of kappa-deformed
statistics, which describe the physical situation represented by the
relativistic kappa-distribution function, provide a reasonable connection
between the parameter kappa, the temperature four-gradient and the four-vector
potential gradient, and thus present for the case kappa different from zero a
clearly physical meaning. It is shown that such a physical situation is a
meta-equilibrium state of the system, but has a new physical characteristic.
|
6cb3e00d-e655-4069-8662-db79517913ad | 6cb3e00d-e655-4069-8662-db79517913ad | 6cb3e00d-e655-4069-8662-db79517913ad | human | null | null | none | abstracts | Heisenberg antiferromagnet with anisotropic exchange on the Kagome
lattice: Description of the magnetic properties of volborthite | null | We study the properties of the Heisenberg antiferromagnet with spatially
anisotropic nearest-neighbour exchange couplings on the kagome net, i.e. with
coupling J in one lattice direction and couplings J' along the other two
directions. For J/J' > 1, this model is believed to describe the magnetic
properties of the mineral volborthite. In the classical limit, it exhibits two
kinds of ground states: a ferrimagnetic state for J/J' < 1/2 and a large
manifold of canted spin states for J/J' > 1/2. To include quantum effects
self-consistently, we investigate the Sp(N) symmetric generalisation of the
original SU(2) symmetric model in the large-N limit. In addition to the
dependence on the anisotropy, the Sp(N) symmetric model depends on a parameter
kappa that measures the importance of quantum effects. Our numerical
calculations reveal that in the kappa-J/J' plane, the system shows a rich phase
diagram containing a ferrimagnetic phase, an incommensurate phase, and a
decoupled chain phase, the latter two with short- and long-range order. We
corroborate these results by showing that the boundaries between the various
phases and several other features of the Sp(N) phase diagram can be determined
by analytical calculations. Finally, the application of a block-spin
perturbation expansion to the trimerised version of the original spin-1/2 model
leads us to suggest that in the limit of strong anisotropy, J/J' >> 1, the
ground state of the original model is a collinearly ordered antiferromagnet,
which is separated from the incommensurate state by a quantum phase transition.
|
4d8ec366-0778-461d-9e0e-c4e76797dd37 | 4d8ec366-0778-461d-9e0e-c4e76797dd37 | 4d8ec366-0778-461d-9e0e-c4e76797dd37 | human | null | null | none | abstracts | On the Nature of Ultra-Luminous X-ray Sources from Optical/IR
Measurements | null | We present a model for the prediction of the optical/infra-red emission from
ULXs. In the model, ULXs are binary systems with accretion taking place through
Roche lobe overflow. We show that irradiation effects and presence of an
accretion disk significantly modify the optical/infrared flux compared to
single stars, and also that the system orientation is important. We include
additional constraints from the mass transfer rate to constrain the parameters
of the donor star, and to a lesser extent the mass of the BH. We apply the
model to fit photometric data for several ULX counterparts. We find that most
donor stars are of spectral type B and are older and less massive than reported
elsewhere, but that no late-type donors are admissable. The degeneracy of the
acceptable parameter space will be significantly reduced with observations over
a wider spectral range, and if time-resolved data become available.
|
2fc841eb-9be8-4ed4-a52d-69b690ef9b43 | 2fc841eb-9be8-4ed4-a52d-69b690ef9b43 | 2fc841eb-9be8-4ed4-a52d-69b690ef9b43 | human | null | null | none | abstracts | Deformed Wigner crystal in a one-dimensional quantum dot | null | The spatial Fourier spectrum of the electron density distribution in a finite
1D system and the distribution function of electrons over single-particle
states are studied in detail to show that there are two universal features in
their behavior, which characterize the electron ordering and the deformation of
Wigner crystal by boundaries. The distribution function has a $\delta$-like
singularity at the Fermi momentum $k_F$. The Fourier spectrum of the density
has a step-like form at the wavevector $2k_F$, with the harmonics being absent
or vanishing above this threshold. These features are found by calculations
using exact diagonalization method. They are shown to be caused by Wigner
ordering of electrons, affected by the boundaries. However the common Luttinger
liquid model with open boundaries fails to capture these features, because it
overestimates the deformation of the Wigner crystal. An improvement of the
Luttinger liquid model is proposed which allows one to describe the above
features correctly. It is based on the corrected form of the density operator
conserving the particle number.
|
df579248-0b43-4595-90da-d4c07eddb212 | df579248-0b43-4595-90da-d4c07eddb212 | df579248-0b43-4595-90da-d4c07eddb212 | human | null | null | none | abstracts | Structures in the Universe and Origin of Galaxies | null | The analysis of images (of obtained in various ranges of the lengths of
waves) of luminous objects in the Universe by means of a method of multilevel
dynamic contrasting led author to the conclusions: a) the structures of all
observable galaxies represents a complicated constructions which have the
tendency to self-similarity and made of separate (basic) blocks, which are a
coaxially tubular structures and a cartwheel-like structures; b) the majority
of observable objects in the Universe are luminous butt-ends of almost
invisible (of almost completely transparent) of filamentary formations which
structures are seen only near to their luminous butt-ends; c) the result of
analysis of images of cosmic objects show the structure of many pairs of
cooperating galaxies point to opportunity of their formation at butt-ends
generated in a place of break of the similar filament; d) the interacting
galaxies (M 81 and M 82) show they are butt-ends of sawed off of two branches
of a treelike filament and their interaction is coming out through this
filament; e) as our Universe is in dynamics the processes of formation of
stars, galaxies and their congestions can go presently by means of a fracturing
of filaments with a corresponding diameters and of the time for their such
formation is necessary much less, than along existing standard model.
|
f7e5d13c-b8e7-499a-ae9a-b12c8a1f2e54 | f7e5d13c-b8e7-499a-ae9a-b12c8a1f2e54 | f7e5d13c-b8e7-499a-ae9a-b12c8a1f2e54 | human | null | null | none | abstracts | U B V R I Photometry of Stellar Structures throughout the Disk of the
Barred Galaxy NGC 3367 | null | We report new detailed surface U, B, V, R, and I photometry of 81 stellar
structures in the disk of the barred galaxy NGC 3367. The images show many
different structures indicating that star formation is going on in the most
part of the disk. NGC 3367 is known to have a very high concentration of
molecular gas distribution in the central regions of the galaxy and bipolar
synchrotron emission from the nucleus with two lobes (at 6 kpc) forming a
triple structure similar to a radio galaxy. We have determined the U, B, V, R,
and I magnitudes and U - B, B - V, U - V, and V - I colors for the central
region (nucleus), a region which includes supernovae 2003 AA, and 79 star
associations throughout NGC 3367. Estimation of ages of star associations is
very difficult due to several factors, among them: filling factor, metallicity,
spatial distribution of each structure and the fact that we estimated the
magnitudes with a circular aperture of 16 pixels in diameter, equivalent to
$6''.8\sim1.4$ kpc. However, if the colors derived for NGC 3367 were similar to
the colors expected of star clusters with theoretical evolutionary star tracks
developed for the LMC and had a similar metallicity, NGC 3367 show 51 percent
of the observed structures with age type SWB I (few tens of Myrs), with seven
sources outside the bright surface brightness visible disk of NGC 3367.
|
3496499c-fb46-4a50-bb91-5f73f568e50e | 3496499c-fb46-4a50-bb91-5f73f568e50e | 3496499c-fb46-4a50-bb91-5f73f568e50e | human | null | null | none | abstracts | Structure factors of harmonic and anharmonic Fibonacci chains by
molecular dynamics simulations | null | The dynamics of quasicrystals is characterized by the existence of phason
excitations in addition to the usual phonon modes. In order to investigate
their interplay on an elementary level we resort to various one-dimensional
model systems. The main observables are the static, the incoherent, and the
coherent structure factor, which are extracted from molecular dynamics
simulations. For the validation of the algorithms, results for the harmonic
periodic chain are presented. We then study the Fibonacci chain with harmonic
and anharmonic interaction potentials. In the dynamic Fibonacci chain
neighboring atoms interact by double-well potentials allowing for phason flips.
The difference between the structure factors of the dynamic and the harmonic
Fibonacci chain lies in the temperature dependence of the phonon line width. If
a bias is introduced in the well depth, dispersionless optic phonon bands split
off.
|
6e4d5877-e8fb-4eb0-a31e-412847500ed9 | 6e4d5877-e8fb-4eb0-a31e-412847500ed9 | 6e4d5877-e8fb-4eb0-a31e-412847500ed9 | human | null | null | none | abstracts | Ground-Based Direct Detection of Exoplanets with the Gemini Planet
Imager (GPI) | null | The Gemini Planet (GPI) imager is an "extreme" adaptive optics system being
designed and built for the Gemini Observatory. GPI combines precise and
accurate wavefront control, diffraction suppression, and a speckle-suppressing
science camera with integral field and polarimetry capabilities. GPI's primary
science goal is the direct detection and characterization of young, Jovian-mass
exoplanets. For systems younger than 2 Gyr exoplanets more massive than 6 MJ
and semimajor axes beyond 10 AU are detected with completeness greater than
50%. GPI will also discover faint debris disks, explore icy moons and minor
planets in the solar system, reveal high dynamic range main-sequence binaries,
and study mass loss from evolved stars. This white paper explains the role of
GPI in exoplanet discovery and characterization and summarizes our
recommendations to the NSF-NASA-DOE Astronomy and Astrophysics Advisory
Committee ExoPlanet Task Force.
|
701d4720-8bdf-4392-9020-761fd1050989 | 701d4720-8bdf-4392-9020-761fd1050989 | 701d4720-8bdf-4392-9020-761fd1050989 | human | null | null | none | abstracts | A Better Good-Turing Estimator for Sequence Probabilities | null | We consider the problem of estimating the probability of an observed string
drawn i.i.d. from an unknown distribution. The key feature of our study is that
the length of the observed string is assumed to be of the same order as the
size of the underlying alphabet. In this setting, many letters are unseen and
the empirical distribution tends to overestimate the probability of the
observed letters. To overcome this problem, the traditional approach to
probability estimation is to use the classical Good-Turing estimator. We
introduce a natural scaling model and use it to show that the Good-Turing
sequence probability estimator is not consistent. We then introduce a novel
sequence probability estimator that is indeed consistent under the natural
scaling model.
|
d57cb11d-aba6-48de-bbe0-3ea28227e6ff | d57cb11d-aba6-48de-bbe0-3ea28227e6ff | d57cb11d-aba6-48de-bbe0-3ea28227e6ff | human | null | null | none | abstracts | Chaos and Symmetry in String Cosmology | null | We review the recently discovered interplay between chaos and symmetry in the
general inhomogeneous solution of many string-related Einstein-matter systems
in the vicinity of a cosmological singularity. The
Belinsky-Khalatnikov-Lifshitz-type chaotic behaviour is found, for many
Einstein-matter models (notably those related to the low-energy limit of
superstring theory and M-theory), to be connected with certain
(infinite-dimensional) hyperbolic Kac-Moody algebras. In particular, the
billiard chambers describing the asymptotic cosmological behaviour of pure
Einstein gravity in spacetime dimension d+1, or the metric-three-form system of
11-dimensional supergravity, are found to be identical to the Weyl chambers of
the Lorentzian Kac-Moody algebras AE_d, or E_{10}, respectively. This suggests
that these Kac-Moody algebras are hidden symmetries of the corresponding
models. There even exists some evidence of a hidden equivalence between the
general solution of the Einstein-three-form system and a null geodesic in the
infinite dimensional coset space E_{10} / K(E_{10}), where K(E_{10}) is the
maximal compact subgroup of E_{10}.
|
b294b2d7-cf77-4d40-bc94-42dd6bb1be26 | b294b2d7-cf77-4d40-bc94-42dd6bb1be26 | b294b2d7-cf77-4d40-bc94-42dd6bb1be26 | human | null | null | none | abstracts | Radio Emission from the Intermediate-mass Black Hole in the Globular
Cluster G1 | null | We have used the Very Large Array (VLA) to search for radio emission from the
globular cluster G1 (Mayall-II) in M31. G1 has been reported by Gebhardt et al.
to contain an intermediate-mass black hole (IMBH) with a mass of ~2 x 10^4
solar masses. Radio emission was detected within an arcsecond of the cluster
center with an 8.4 GHz power of 2 x 10^{15} W/Hz. The radio/X-ray ratio of G1
is a few hundred times higher than that expected for a high-mass X-ray binary
in the cluster center, but is consistent with the expected value for accretion
onto an IMBH with the reported mass. A pulsar wind nebula is also a possible
candidate for the radio and X-ray emission from G1; future high-sensitivity
VLBI observations might distinguish between this possibility and an IMBH. If
the radio source is an IMBH, and similar accretion and outflow processes occur
for hypothesized ~ 1000-solar-mass black holes in Milky Way globular clusters,
they are within reach of the current VLA and should be detectable easily by the
Expanded VLA when it comes on line in 2010.
|
1d58b178-d3fb-408c-a951-35a274fc9a78 | 1d58b178-d3fb-408c-a951-35a274fc9a78 | 1d58b178-d3fb-408c-a951-35a274fc9a78 | human | null | null | none | abstracts | Even infinite dimensional real Banach spaces | null | This article is a continuation of a paper of the first author \cite{F} about
complex structures on real Banach spaces. We define a notion of even infinite
dimensional real Banach space, and prove that there exist even spaces,
including HI or unconditional examples from \cite{F} and $C(K)$ examples due to
Plebanek \cite{P}. We extend results of \cite{F} relating the set of complex
structures up to isomorphism on a real space to a group associated to
inessential operators on that space, and give characterizations of even spaces
in terms of this group. We also generalize results of \cite{F} about totally
incomparable complex structures to essentially incomparable complex structures,
while showing that the complex version of a space defined by S. Argyros and A.
Manoussakis \cite{AM} provide examples of essentially incomparable complex
structures which are not totally incomparable.
|
950912c1-80db-4102-be61-423f967f4cd7 | 950912c1-80db-4102-be61-423f967f4cd7 | 950912c1-80db-4102-be61-423f967f4cd7 | human | null | null | none | abstracts | Landau-Lifshitz sigma-models, fermions and the AdS/CFT correspondence | null | We define Landau-Lifshitz sigma models on general coset space $G/H$, with $H$
a maximal stability sub-group of $G$. These are non-relativistic models that
have $G$-valued N\"other charges, local $H$ invariance and are classically
integrable. Using this definition, we construct the $PSU(2,2|4)/PS(U(2|2)^2)$
Landau-Lifshitz sigma-model. This sigma model describes the thermodynamic limit
of the spin-chain Hamiltonian obtained from the complete one-loop dilatation
operator of the N=4 super Yang-Mills (SYM) theory. In the second part of the
paper, we identify a number of consistent truncations of the Type IIB
Green-Schwarz action on $AdS_5\times S^5$ whose field content consists of two
real bosons and 4,8 or 16 real fermions. We show that $\kappa$-symmetry acts
trivially in these sub-sectors. In the context of the large spin limit of the
AdS/CFT correspondence, we map the Lagrangians of these sub-sectors to
corresponding truncations of the $PSU(2,2|4)/PS(U(2|2)^2)$ Landau-Lifshitz
sigma-model.
|
5b3b48e6-27ad-4545-96e9-a1a477af68ad | 5b3b48e6-27ad-4545-96e9-a1a477af68ad | 5b3b48e6-27ad-4545-96e9-a1a477af68ad | human | null | null | none | abstracts | Trajectory of neutron$-$neutron$-^{18}C$ excited three-body state | null | The trajectory of the first excited Efimov state is investigated by using a
renormalized zero-range three-body model for a system with two bound and one
virtual two-body subsystems. The approach is applied to $n-n-^{18}$C, where the
$n-n$ virtual energy and the three-body ground state are kept fixed. It is
shown that such three-body excited state goes from a bound to a virtual state
when the $n-^{18}$C binding energy is increased. Results obtained for the
$n-^{19}$C elastic cross-section at low energies also show dominance of an
$S-$matrix pole corresponding to a bound or virtual Efimov state. It is also
presented a brief discussion of these findings in the context of ultracold atom
physics with tunable scattering lengths.
|
e65e9e88-f7da-489a-9c5d-a33e30aca638 | e65e9e88-f7da-489a-9c5d-a33e30aca638 | e65e9e88-f7da-489a-9c5d-a33e30aca638 | human | null | null | none | abstracts | Distributed quantum information processing with minimal local resources | null | We present a protocol for growing graph states, the resource for one-way
quantum computing, when the available entanglement mechanism is highly
imperfect. The distillation protocol is frugal in its use of ancilla qubits,
requiring only a single ancilla qubit when the noise is dominated by one Pauli
error, and two for a general noise model. The protocol works with such scarce
local resources by never post-selecting on the measurement outcomes of
purification rounds. We find that such a strategy causes fidelity to follow a
biased random walk, and that a target fidelity is likely to be reached more
rapidly than for a comparable post-selecting protocol. An analysis is presented
of how imperfect local operations limit the attainable fidelity. For example, a
single Pauli error rate of 20% can be distilled down to $\sim 10$ times the
imperfection in local operations.
|
6da95514-03a8-4d3d-8116-cd9c6ebcacf0 | 6da95514-03a8-4d3d-8116-cd9c6ebcacf0 | 6da95514-03a8-4d3d-8116-cd9c6ebcacf0 | human | null | null | none | abstracts | X-Raying the MOJAVE Sample of Compact Extragalactic Radio Jets | null | The MOJAVE sample is the first large radio-selected, VLBI-monitored AGN
sample for which complete X-ray spectral information is being gathered. We
report on the status of Swift survey observations which complement the
available archival X-ray data at 0.3-10 keV and in the UV with its XRT and UVOT
instruments. Many of these 133 radio-brightest AGN in the northern sky are now
being observed for the first time at these energies. These and complementary
other multi-wavelength observations provide a large statistical sample of
radio-selected AGN whose spectral energy distributions are measured from radio
to gamma-ray wavelengths, available at the beginning of GLAST operations in
2008. Here, we report the X-ray spectral characteristics of 36 of these
previously unobserved MOJAVE sources. In addition, the number of MOJAVE sources
detected by the BAT instrument in the hard X-ray band is growing: we report the
detection of five new blazars with BAT.
|
3a7f92a6-3d28-41c0-a317-5d7bb1806639 | 3a7f92a6-3d28-41c0-a317-5d7bb1806639 | 3a7f92a6-3d28-41c0-a317-5d7bb1806639 | human | null | null | none | abstracts | Sparse Estimators and the Oracle Property, or the Return of Hodges'
Estimator | null | We point out some pitfalls related to the concept of an oracle property as
used in Fan and Li (2001, 2002, 2004) which are reminiscent of the well-known
pitfalls related to Hodges' estimator. The oracle property is often a
consequence of sparsity of an estimator. We show that any estimator satisfying
a sparsity property has maximal risk that converges to the supremum of the loss
function; in particular, the maximal risk diverges to infinity whenever the
loss function is unbounded. For ease of presentation the result is set in the
framework of a linear regression model, but generalizes far beyond that
setting. In a Monte Carlo study we also assess the extent of the problem in
finite samples for the smoothly clipped absolute deviation (SCAD) estimator
introduced in Fan and Li (2001). We find that this estimator can perform rather
poorly in finite samples and that its worst-case performance relative to
maximum likelihood deteriorates with increasing sample size when the estimator
is tuned to sparsity.
|
7768d431-5e25-456d-8d29-913400ece506 | 7768d431-5e25-456d-8d29-913400ece506 | 7768d431-5e25-456d-8d29-913400ece506 | human | null | null | none | abstracts | Capillary ordering and layering transitions in two-dimensional hard-rod
fluids | null | In this article we calculate the surface phase diagram of a two-dimensional
hard-rod fluid confined between two hard lines. In a first stage we study the
semi-infinite system consisting of an isotropic fluid in contact with a single
hard line. We have found complete wetting by the columnar phase at the
wall-isotropic fluid interface. When the fluid is confined between two hard
walls, capillary columnar ordering occurs via a first-order phase transition.
For higher chemical potentials the system exhibits layering transitions even
for very narrow slits (near the one-dimensional limit). The theoretical model
used was a density-functional theory based on the Fundamental-Measure
Functional applied to a fluid of hard rectangles in the restricted-orientation
approximation (Zwanzig model). The results presented here can be checked
experimentally in two-dimensional granular media made of rods, where vertical
motions induced by an external source and excluded volume interactions between
the grains allow the system to explore those stationary states which
entropically maximize packing configurations. We claim that some of the surface
phenomena found here can be present in two-dimensional granular-media fluids.
|
a03e6ee5-b1b2-49e5-bfe8-9e619ee5691b | a03e6ee5-b1b2-49e5-bfe8-9e619ee5691b | a03e6ee5-b1b2-49e5-bfe8-9e619ee5691b | human | null | null | none | abstracts | Monte Carlo Simulations of Quantum Spin Systems in the Valence Bond
Basis | null | We discuss a projector Monte Carlo method for quantum spin models formulated
in the valence bond basis, using the S=1/2 Heisenberg antiferromagnet as an
example. Its singlet ground state can be projected out of an arbitrary basis
state as the trial state, but a more rapid convergence can be obtained using a
good variational state. As an alternative to first carrying out a time
consuming variational Monte Carlo calculation, we show that a very good trial
state can be generated in an iterative fashion in the course of the simulation
itself. We also show how the properties of the valence bond basis enable
calculations of quantities that are difficult to obtain with the standard basis
of Sz eigenstates. In particular, we discuss quantities involving
finite-momentum states in the triplet sector, such as the dispersion relation
and the spectral weight of the lowest triplet.
|
5d0070ec-fc81-4c61-bd22-db9c4f9f210d | 5d0070ec-fc81-4c61-bd22-db9c4f9f210d | 5d0070ec-fc81-4c61-bd22-db9c4f9f210d | human | null | null | none | abstracts | Emergence of U(1) symmetry in the 3D XY model with Zq anisotropy | null | We study the three-dimensional XY model with a Z_q anisotropic term. At
temperatures T < Tc this dangerously irrelevant perturbation is relevant only
above a length scale Lambda, which diverges as a power of the correlation
length; Lambda ~ xi^a_q. Below Lambda the order parameter is U(1) symmetric. We
derive the full scaling function controlling the emergence of U(1) symmetry and
use Monte Carlo results to extract the exponent a_q for q=4,...,8. We find that
a_q = a_4 (q/4)^2, with a_4 only marginally larger than 1. We discuss these
results in the context of U(1) symmetry at "deconfined" quantum critical points
separating antiferromagnetic and valence-bond-solid states in quantum spin
systems.
|
8274d071-fa11-4c4e-8612-ab6eeaf63f98 | 8274d071-fa11-4c4e-8612-ab6eeaf63f98 | 8274d071-fa11-4c4e-8612-ab6eeaf63f98 | human | null | null | none | abstracts | Fan-shaped and toric textures of mesomorphic oxadiazoles | null | When a family of non symmetrical heterocycled compounds is investigated, a
variety of mesophases can be observed with rather different features. Here we
report the behaviour of seven different members among a family of such
materials, that consists of mesomorphic oxadiazole compounds. In two of these
compounds, the optical microscope investigation shows very interesting
behaviours. In their smectic phases, fan-shaped and toric textures, sometimes
with periodic instability, are observed. Moreover, the nematic phase displays a
texture transition. Texture transitions have been previously observed only
inside the nematic phase of some compounds belonging to the families of the
oxybenzoic and cyclohexane acids. In these two oxadiazole compounds we can
observe what we define as a "toric nematic phase", heating the samples from the
smectic phase. The toric nematic texture disappears as the sample is further
heated, changing into a smooth texture.
|
b142dcae-3b1e-42ee-b930-140f5cf94e32 | b142dcae-3b1e-42ee-b930-140f5cf94e32 | b142dcae-3b1e-42ee-b930-140f5cf94e32 | human | null | null | none | abstracts | TeV-scale gravity in Horava-Witten theory on a compact complex
hyperbolic threefold | null | The field equations and boundary conditions of Horava-Witten theory,
compactified on a smooth compact spin quotient of CH^3, where CH^3 denotes the
hyperbolic cousin of CP^3, are studied in the presence of Casimir energy
density terms. If the Casimir energy densities near one boundary result in a
certain constant of integration taking a value greater than around 10^5 in
units of the d = 11 gravitational length, a form of thick pipe geometry is
found that realizes TeV-scale gravity by the ADD mechanism, with that boundary
becoming the inner surface of the thick pipe, where we live. Three alternative
ways in which the outer surface of the thick pipe might be stabilized
consistent with the observed value of the effective d = 4 cosmological constant
are considered. In the first alternative, the outer surface is stabilized in
the classical region and the constant of integration is fixed at around 10^{13}
in units of the d = 11 gravitational length for consistency with the observed
cosmological constant. In the second alternative, the four observed dimensions
have reduced in size down to the d = 11 gravitational length at the outer
surface, and there are Casimir effects near the outer surface. In the third
alternative, the outer surface is stabilized in the classical region by extra
fluxes of the three-form gauge field, whose four-form field strength wraps
three-cycles of the compact six-manifold times the radial dimension of the
thick pipe. Some problems related to fitting the strong/electroweak Standard
Model are considered.
|
e0a75c54-4d21-4d35-85ff-2b3a90e326dc | e0a75c54-4d21-4d35-85ff-2b3a90e326dc | e0a75c54-4d21-4d35-85ff-2b3a90e326dc | human | null | null | none | abstracts | Balance of forces in simulated bilayers | null | Two kinds of simulated bilayers are described and the results are reported
for lateral tension and for partial contributions of intermolecular forces to
it.Data for a widest possible range of areas per surfactant head, from tunnel
formation through tensionless state, transition to floppy bilayer,to its
disintegration, are reported and discussed. The significance of the tensionless
state, is discussed. Conclusions: (1) the tensionless state is a
coincidence;(2) the transition from extended to floppy bilayer occurs nearby
and has hallmarks of a phase transition (3) there is no theory of that
transition.(4)The lateral tension of the floppy bilayer scales with size; that
of the extended bilayer does not depend on size. (4) The drumhead model not
appropriate for interfaces as these fluctuate via diffusion.(5) The radius of
gyration also! shows a discontinuity.
|
535f5348-e429-41c8-8a00-1199d2e62991 | 535f5348-e429-41c8-8a00-1199d2e62991 | 535f5348-e429-41c8-8a00-1199d2e62991 | human | null | null | none | abstracts | Search for the radiative leptonic decay B+ --> gamma l+ nu | null | We present the results of a search for $B^{+}\to\gamma \ell^{+}\nu_{\ell}$,
where $\ell = e, \mu$. We use a sample of 232 million $B\bar{B}$ pairs recorded
at the $\Upsilon(4S)$ with the BaBar detector at the PEP-II $B$ Factory. We
measure a partial branching fraction $\Delta\mathcal{B}$ in a restricted region
of phase space that reduces the effect of theoretical uncertainties, requiring
the lepton energy to be between 1.875 and 2.850GeV, the photon energy to be
between 0.45 and 2.35GeV, and the cosine of the angle between the lepton and
photon momenta to be less than -0.36, with all quantities computed in the
$\Upsilon(4S)$ center-of-mass frame. We find $\Delta\mathcal{B}(B^{+}\to\gamma
\ell^{+}\nu_{\ell}) = (-0.3^{+1.3}_{-1.5} ({stat}) \pm 0.6 ({syst}) \pm 0.1
({th})) \times 10^{-6}$, assuming lepton universality. Interpreted as a 90%
C.L. Bayesian upper limit, the result corresponds to $1.7\times10^{-6}$ for a
prior flat in amplitude, and $2.3\times10^{-6}$ for a prior flat in branching
fraction.
|
c1db1b16-660c-42c9-a96b-1b8a92fee27d | c1db1b16-660c-42c9-a96b-1b8a92fee27d | c1db1b16-660c-42c9-a96b-1b8a92fee27d | human | null | null | none | abstracts | Magnetic structure of Sm2IrIn8 | null | The magnetic structure of the intermetallic antiferromagnet Sm2IrIn8 was
determined using x-ray resonant magnetic scattering (XRMS). Below TN = 14.2,
Sm2IrIn8 has a commensurate antiferromagnetic structure with a propagation
vector (1/2,0,0). The Sm magnetic moments lie in the ab plane and are rotated
roughly 18 degrees away from the a axis. The magnetic structure of this
compound was obtained by measuring the strong dipolar resonant peak whose
enhancement was of over two orders of magnitude at the L2 edge. At the L3 edge
both quadrupolar and dipolar features were observed in the energy line shape.
The magnetic structure and properties of Sm2IrIn8 are found to be consistent
with the general trend already seen for the Nd-, Tb- and the Ce-based compounds
from the RmMnIn3m+2n family (R = rare earth; M=Rh or Ir, m = 1, 2; n = 0, 1),
where the crystalline electrical field (CEF) effects determine the direction of
magnetic moments and the TN evolution in the series. The measured Neel
temperature for Sm2IrIn8 is slightly suppressed when compared to the TN of the
parent cubic compound SmIn3.
|
53e636e8-eca1-4580-b951-20bc2cc53e8a | 53e636e8-eca1-4580-b951-20bc2cc53e8a | 53e636e8-eca1-4580-b951-20bc2cc53e8a | human | null | null | none | abstracts | TEXES Observations of Pure Rotational H2 Emission From AB Aurigae | null | We present observations of pure rotational molecular hydrogen emission from
the Herbig Ae star, AB Aurigae. Our observations were made using the Texas
Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope
Facility and the Gemini North Observatory. We searched for H2 emission in the
S(1), S(2), and S(4) lines at high spectral resolution and detected all three.
By fitting a simple model for the emission in the three transitions, we derive
T = 670 +/- 40 K and M = 0.52 +/- 0.15 earth masses for the emitting gas. Based
on the 8.5 km/s FWHM of the S(2) line, assuming the emission comes from the
circumstellar disk, and with an inclination estimate of the AB Aur system taken
from the literature, we place the location for the emission near 18 AU.
Comparison of our derived temperature to a disk structure model suggests that
UV and X-ray heating are important in heating the disk atmosphere.
|
1c291100-ea74-444a-b7b3-6dddcf796b52 | 1c291100-ea74-444a-b7b3-6dddcf796b52 | 1c291100-ea74-444a-b7b3-6dddcf796b52 | human | null | null | none | abstracts | Deciphering top flavor violation at the LHC with B factories | null | The LHC will have unprecedented sensitivity to flavor-changing neutral
current (FCNC) top quark decays, whose observation would be a clear sign of
physics beyond the standard model. Although many details of top flavor
violation are model dependent, the standard model gauge symmetries relate top
FCNCs to other processes, which are strongly constrained by existing data. We
study these constraints in a model independent way, using a low energy
effective theory from which the new physics is integrated out. We consider the
most important operators which contribute to top FCNCs and analyze the current
constraints on them. We find that the data rule out top FCNCs at a level
observable at the LHC due to most of the operators comprising left-handed first
or second generation quark fields, while there remains a substantial window for
top decays mediated by operators with right-handed charm or up quarks. If FCNC
top decays are observed at the LHC, such an analysis may help decipher the
underlying physics.
|
870e0d76-44bf-486f-929b-4ee011c64a96 | 870e0d76-44bf-486f-929b-4ee011c64a96 | 870e0d76-44bf-486f-929b-4ee011c64a96 | human | null | null | none | abstracts | Exploring Infrared Properties of Giant Low Surface Brightness Galaxies | null | Abridged: We present analysis of Spitzer Space Telescope observations of the
three low surface brightness (LSB) optical giant galaxies Malin 1, UGC 6614 and
UGC 9024. Mid- and far-infrared morphology, spectral energy distributions, and
integrated colors are used to derive the dust mass, dust-to-gas mass ratio,
total infrared luminosity, and star formation rate (SFR). The 8 micron images
indicate that polycyclic aromatic hydrocarbon molecules are present in the
central regions of all three metal-poor LSB galaxies. The diffuse optical disks
of Malin 1 and UGC 9024 remain undetected at mid- and far-infrared wavelengths.
The dustiest of the three LSB galaxies, UGC 6614, has infrared morphology that
varies significantly with wavelength. The 8 and 24 micron emission is
co-spatial with H\alpha emission previously observed in the outer ring of UGC
6614. The estimated dust-to-gas ratios, from less than 10^{-3} to 10^{-2},
support previous indications that the LSB galaxies are relatively dust poor
compared to the HSB galaxies. The total infrared luminosities are approximately
1/3 to 1/2 the blue band luminosities, suggesting that old stellar populations
are the primary source of dust heating in these LSB objects. The SFR estimated
from the infrared data ranges ~0.01-0.88 M_sun yr^{-1}, consistent with results
from optical studies.
|
d318d31f-4ad3-4bf6-ad96-1755c2eda4f5 | d318d31f-4ad3-4bf6-ad96-1755c2eda4f5 | d318d31f-4ad3-4bf6-ad96-1755c2eda4f5 | human | null | null | none | abstracts | One-time pad booster for Internet | null | One-time pad encrypted files can be sent through Internet channels using
current Internet protocols. However, the need for renewing shared secret keys
make this method unpractical. This work shows how users can use a fast physical
random generator based on fluctuations of a light field and the Internet
channel to directly boost key renewals. The transmitted signals are
deterministic but carries imprinted noise that cannot be eliminated by the
attacker. Thus, a one-time pad for Internet can be made practical. Security is
achieved without third parties and not relying on the difficulty of factoring
numbers in primes. An informational fragility to be avoided is discussed.
Information-theoretic analysis is presented and bounds for secure operation are
determined.
|
a1fb6f78-50ea-4a88-a4e0-03962da35b41 | a1fb6f78-50ea-4a88-a4e0-03962da35b41 | a1fb6f78-50ea-4a88-a4e0-03962da35b41 | human | null | null | none | abstracts | Wavelet frames, Bergman spaces and Fourier transforms of Laguerre
functions | null | The Fourier transforms of Laguerre functions play the same canonical role in
wavelet analysis as do the Hermite functions in Gabor analysis. We will use
them as analyzing wavelets in a similar way the Hermite functions were recently
by K. Groechenig and Y. Lyubarskii in "Gabor frames with Hermite functions, C.
R. Acad. Sci. Paris, Ser. I 344 157-162 (2007)". Building on the work of K.
Seip, "Beurling type density theorems in the unit disc, Invent. Math., 113,
21-39 (1993)", concerning sampling sequences on weighted Bergman spaces, we
find a sufficient density condition for constructing frames by translations and
dilations of the Fourier transform of the nth Laguerre function. As in
Groechenig-Lyubarskii theorem, the density increases with n, and in the special
case of the hyperbolic lattice in the upper half plane it is given by b\log
a<\frac{4\pi}{2n+\alpha}, where alpha is the parameter of the Laguerre
function.
|
b04898fd-79e8-4324-b180-8ac25cd9219a | b04898fd-79e8-4324-b180-8ac25cd9219a | b04898fd-79e8-4324-b180-8ac25cd9219a | human | null | null | none | abstracts | Staggered Heavy Baryon Chiral Perturbation Theory | null | Although taste violations significantly affect the results of staggered
calculations of pseudoscalar and heavy-light mesonic quantities, those entering
staggered calculations of baryonic quantities have not been quantified. Here I
develop staggered chiral perturbation theory in the light-quark baryon sector
by mapping the Symanzik action into heavy baryon chiral perturbation theory.
For 2+1 dynamical quark flavors, the masses of flavor-symmetric nucleons are
calculated to third order in partially quenched and fully dynamical staggered
chiral perturbation theory. To this order the expansion includes the leading
chiral logarithms, which come from loops with virtual decuplet-like states, as
well as terms the order of the cubed pion mass, which come from loops with
virtual octet-like states. Taste violations enter through the meson propagators
in loops and tree-level terms the order of the squared lattice spacing. The
pattern of taste symmetry breaking and the resulting degeneracies and mixings
are discussed in detail. The resulting chiral forms are appropriate to lattice
results obtained with operators already in use and could be used to study the
restoration of taste symmetry in the continuum limit. I assume that the fourth
root of the fermion determinant can be incorporated in staggered chiral
perturbation theory using the replica method.
|
630f5ddf-d3b7-49c1-b468-ce2006d67f8a | 630f5ddf-d3b7-49c1-b468-ce2006d67f8a | 630f5ddf-d3b7-49c1-b468-ce2006d67f8a | human | null | null | none | abstracts | Imaging Magnetic Focusing of Coherent Electron Waves | null | The magnetic focusing of electrons has proven its utility in fundamental
studies of electron transport. Here we report the direct imaging of magnetic
focusing of electron waves, specifically in a two-dimensional electron gas
(2DEG). We see the semicircular trajectories of electrons as they bounce along
a boundary in the 2DEG, as well as fringes showing the coherent nature of the
electron waves. Imaging flow in open systems is made possible by a cooled
scanning probe microscope. Remarkable agreement between experiment and theory
demonstrates our ability to see these trajectories and to use this system as an
interferometer. We image branched electron flow as well as the interference of
electron waves. This technique can visualize the motion of electron waves
between two points in an open system, providing a straightforward way to study
systems that may be useful for quantum information processing and spintronics.
|
cc8d3b93-267c-4aa3-b1ec-07d460faebbe | cc8d3b93-267c-4aa3-b1ec-07d460faebbe | cc8d3b93-267c-4aa3-b1ec-07d460faebbe | human | null | null | none | abstracts | On a {K_4,K_{2,2,2}}-ultrahomogeneous graph | null | The existence of a connected 12-regular $\{K_4,K_{2,2,2}\}$-ultrahomogeneous
graph $G$ is established, (i.e. each isomorphism between two copies of $K_4$ or
$K_{2,2,2}$ in $G$ extends to an automorphism of $G$), with the 42 ordered
lines of the Fano plane taken as vertices. This graph $G$ can be expressed in a
unique way both as the edge-disjoint union of 42 induced copies of $K_4$ and as
the edge-disjoint union of 21 induced copies of $K_{2,2,2}$, with no more
copies of $K_4$ or $K_{2,2,2}$ existing in $G$. Moreover, each edge of $G$ is
shared by exactly one copy of $K_4$ and one of $K_{2,2,2}$. While the line
graphs of $d$-cubes, ($3\le d\in\ZZ$), are $\{K_d, K_{2,2}\}$-ultrahomogeneous,
$G$ is not even line-graphical. In addition, the chordless 6-cycles of $G$ are
seen to play an interesting role and some self-dual configurations associated
to $G$ with 2-arc-transitive, arc-transitive and semisymmetric Levi graphs are
considered.
|
7d47e4cf-c8bd-4d90-871b-dcc753988eba | 7d47e4cf-c8bd-4d90-871b-dcc753988eba | 7d47e4cf-c8bd-4d90-871b-dcc753988eba | human | null | null | none | abstracts | Unconventional approaches to combine optical transparency with
electrical conductivity | null | Combination of electrical conductivity and optical transparency in the same
material -- known to be a prerogative of only a few oxides of post-transition
metals, such as In, Sn, Zn and Cd -- manifests itself in a distinctive band
structure of the transparent conductor host. While the oxides of other elements
with $s^2$ electronic configuration, for example, Mg, Ca, Sc and Al, also
exhibit the desired optical and electronic features, they have not been
considered as candidates for achieving good electrical conductivity because of
the challenges of efficient carrier generation in these wide-bandgap materials.
Here we demonstrate that alternative approaches to the problem not only allow
attaining the transport and optical properties which compete with those in
currently utilized transparent conducting oxides (TCO), but also significantly
broaden the range of materials with a potential of being developed into novel
functional transparent conductors.
|
4b65c827-37c6-44c1-a7bd-218e8aef24d5 | 4b65c827-37c6-44c1-a7bd-218e8aef24d5 | 4b65c827-37c6-44c1-a7bd-218e8aef24d5 | human | null | null | none | abstracts | Follow-up observations of pulsating subdwarf B stars: Multisite
campaigns on PG 1618+563B and PG 0048+091 | null | We present follow-up observations of pulsating subdwarf B (sdB) stars as part
of our efforts to resolve the pulsation spectra for use in asteroseismological
analyses. This paper reports on multisite campaigns of the pulsating sdB stars
PG 1618+563B and PG 0048+091. Data were obtained from observatories placed
around the globe for coverage from all longitudes. For PG 1618+563B, our
five-site campaign uncovered a dichotomy of pulsation states: Early during the
campaign the amplitudes and phases (and perhaps frequencies) were quite
variable while data obtained late in the campaign were able to fully resolve
five stable pulsation frequencies. For PG 0048+091, our five-site campaign
uncovered a plethora of frequencies with short pulsation lifetimes. We find
them to have observed properties consistent with stochastically excited
oscillations, an unexpected result for subdwarf B stars. We discuss our
findings and their impact on subdwarf B asteroseismology.
|
ddebafd7-dcfd-4e73-ae31-37549913f3f0 | ddebafd7-dcfd-4e73-ae31-37549913f3f0 | ddebafd7-dcfd-4e73-ae31-37549913f3f0 | human | null | null | none | abstracts | DIRBE Minus 2MASS: Confirming the CIRB in 40 New Regions at 2.2 and 3.5
Microns | null | With the release of the 2MASS All-Sky Point Source Catalog, stellar fluxes
from 2MASS are used to remove the contribution due to Galactic stars from the
intensity measured by DIRBE in 40 new regions in the North and South Galactic
polar caps. After subtracting the interplanetary and Galactic foregrounds, a
consistent residual intensity of 14.69 +/- 4.49 kJy/sr at 2.2 microns is found.
Allowing for a constant calibration factor between the DIRBE 3.5 microns and
the 2MASS 2.2 microns fluxes, a similar analysis leaves a residual intensity of
15.62 +/- 3.34 kJy/sr at 3.5 microns. The intercepts of the DIRBE minus 2MASS
correlation at 1.25 microns show more scatter and are a smaller fraction of the
foreground, leading to a still weak limit on the CIRB of 8.88 +/- 6.26 kJy/sr
(1 sigma).
|
4c6a7541-f545-45df-b3c5-397fcbc728ed | 4c6a7541-f545-45df-b3c5-397fcbc728ed | 4c6a7541-f545-45df-b3c5-397fcbc728ed | human | null | null | none | abstracts | Averaging of the electron effective mass in multicomponent transparent
conducting oxides | null | We find that layered materials composed of various oxides of cations with
$s^2$ electronic configuration, $XY_2$O$_4$, $X$=In or Sc, $Y$=Ga, Zn, Al, Cd
and/or Mg, exhibit isotropic electron effective mass which can be obtained via
averaging over those of the corresponding single-cation oxide constituents.
This effect is due to a hybrid nature of the conduction band formed from the
s-states of {\it all} cations and the oxygen p-states. Moreover, the observed
insensitivity of the electron effective mass to the oxygen coordination and to
the distortions in the cation-oxygen chains suggests that similar behavior can
be expected in technologically important amorphous state. These findings
significantly broaden the range of materials as efficient transparent conductor
hosts.
|
6375ef97-70a4-4c18-bb7a-e81799e66765 | 6375ef97-70a4-4c18-bb7a-e81799e66765 | 6375ef97-70a4-4c18-bb7a-e81799e66765 | human | null | null | none | abstracts | A Diagrammatic Category for the Representation Theory of U_q(sl_n) | null | This thesis provides a partial answer to a question posed by Greg Kuperberg
in q-alg/9712003 and again by Justin Roberts as problem 12.18 in "Problems on
invariants of knots and 3-manifolds", math.GT/0406190, essentially: "Can one
describe the category of representations of the quantum group U_q(sl_n)
(thought of as a spherical category) via generators and relations?"
For each n \geq 0, I define a certain tensor category of trivalent graphs,
modulo isotopy, and construct a functor from this category onto (a full
subcategory of) the category of representations of the quantum group U_q(sl_n).
One would like to describe completely the kernel of this functor, by providing
generators. The resulting quotient of the diagrammatic category would then be a
category equivalent to the representation category of U_q(sl_n).
I make significant progress towards this, describing certain generators of
the kernel, and some obstructions to further elements. It remains a conjecture
that these relations generate the kernel. My results extend those of
q-alg/9712003, MR1659228, math.QA/0310143 and math.GT/0506403.
The argument is essentially by constructing a diagrammatic version of the
forgetful functor coming from the inclusion of U_q(sl_{n-1}) in U_q(sl_n}. We
know this functor is faithful, so a diagram is in the kernel for n exactly if
its image under the diagrammatic forgetful functor is in the kernel for n-1.
This allows us to perform inductive calculations, both establishing families of
elements of the kernel, and finding obstructions.
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96bebe41-f0ad-4834-973b-e711cbedeac3 | 96bebe41-f0ad-4834-973b-e711cbedeac3 | 96bebe41-f0ad-4834-973b-e711cbedeac3 | human | null | null | none | abstracts | The Formation of Lake Stars | null | Star patterns, reminiscent of a wide range of diffusively controlled growth
forms from snowflakes to Saffman-Taylor fingers, are ubiquitous features of ice
covered lakes. Despite the commonality and beauty of these ``lake stars'' the
underlying physical processes that produce them have not been explained in a
coherent theoretical framework. Here we describe a simple mathematical model
that captures the principal features of lake-star formation; radial fingers of
(relatively warm) water-rich regions grow from a central source and evolve
through a competition between thermal and porous media flow effects in a
saturated snow layer covering the lake. The number of star arms emerges from a
stability analysis of this competition and the qualitative features of this
meter-scale natural phenomena are captured in laboratory experiments.
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8210868b-831d-4c65-8c3a-7cc0736551cc | 8210868b-831d-4c65-8c3a-7cc0736551cc | 8210868b-831d-4c65-8c3a-7cc0736551cc | human | null | null | none | abstracts | A Higgs-Higgs bound state due to New Physics at a TeV | null | We examine the effects of new physics effecting the Higgs sector of the
standard model, focusing on the effects on the Higgs self couplings. We
demonstrate that a low mass higgs, m_h < 2 m_t, can have a strong effective
self coupling due to the effects of a new interaction at a TeV. We investigate
the possibility that the first evidence of such an interaction could be a
higgs-higgs bound state. To this end, we construct an effective field theory
formalism to examine the physics of such a low mass higgs boson. We explore the
possibility of a non relativistic bound state of the higgs field (Higgsium) at
LHC and construct a non relativistic effective field theory of the higgs sector
that is appropriate for such studies (NRHET).
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b078f636-ba2d-4a60-9e35-801fb059dbb1 | b078f636-ba2d-4a60-9e35-801fb059dbb1 | b078f636-ba2d-4a60-9e35-801fb059dbb1 | human | null | null | none | abstracts | Measuring two-photon orbital angular momentum entanglement | null | We put forward an approach to estimate the amount of bipartite spatial
entanglement of down-converted photon states correlated in orbital angular
momentum and the magnitude of the transverse (radial) wave vectors. Both
degrees of freedom are properly considered in our framework, which only
requires azimuthal local linear optical transformations and mode selection
analysis with two fiber detectors. The coincidence distributions predicted by
our approach give an excellent fit to the distributions measured in a recent
experiment aimed to show the very high-dimensional transverse entanglement of
twin photons from a down-conversion source. Our estimate for the Schmidt number
is substantially lower but still confirms the presence of high-dimensional
entanglement.
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3513ac96-c7d3-4b92-b7a7-34f3165bf6d0 | 3513ac96-c7d3-4b92-b7a7-34f3165bf6d0 | 3513ac96-c7d3-4b92-b7a7-34f3165bf6d0 | human | null | null | none | abstracts | HST/ACS Coronagraphic Observations of the Dust Surrounding HD 100546 | null | We present ACS/HST coronagraphic observations of HD 100546, a B9.5 star, 103
pc away from the sun, taken in the F435W, F606W, and F814W bands. Scattered
light is detected up to 14'' from the star. The observations are consistent
with the presence of an extended flattened nebula with the same inclination as
the inner disk. The well-known ``spiral arms'' are clearly observed and they
trail the rotating disk material. Weaker arms never before reported are also
seen. The inter-arm space becomes brighter, but the structures become more
neutral in color at longer wavelengths, which is not consistent with models
that assume that they are due to the effects of a warped disk. Along the major
disk axis, the colors of the scattered-light relative to the star are \Delta
(F435W-F606W) ~ 0.0--0.2 mags and \Delta (F435W-F814W)~0.5--1 mags. To explain
these colors, we explore the role of asymmetric scattering, reddening, and
large minimum sizes on ISM-like grains. We conclude each of these hypotheses by
itself cannot explain the colors. The disk colors are similar to those derived
for Kuiper Belt objects, suggesting that the same processes responsible for
their colors may be at work here. We argue that we are observing only the
geometrically thick, optically thin envelope of the disk, while the optically
thick disk responsible for the far-IR emission is undetected. The observed
spiral arms are then structures on this envelope. The colors indicate that the
extended nebulosity is not a remnant of the infalling envelope but reprocessed
disk material.
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72fdc62e-b50c-48ec-8510-8f1db2db26e5 | 72fdc62e-b50c-48ec-8510-8f1db2db26e5 | 72fdc62e-b50c-48ec-8510-8f1db2db26e5 | human | null | null | none | abstracts | Anomalous diffusion and stretched exponentials in heterogeneous
glass-forming liquids: Low-temperature behavior | null | We propose a model of a heterogeneous glass forming liquid and compute the
low-temperature behavior of a tagged molecule moving within it. This model
exhibits stretched-exponential decay of the wavenumber-dependent, self
intermediate scattering function in the limit of long times. At temperatures
close to the glass transition, where the heterogeneities are much larger in
extent than the molecular spacing, the time dependence of the scattering
function crosses over from stretched-exponential decay with an index $b=1/2$ at
large wave numbers to normal, diffusive behavior with $b = 1$ at small
wavenumbers. There is a clear separation between early-stage, cage-breaking
$\beta$ relaxation and late-stage $\alpha$ relaxation. The spatial
representation of the scattering function exhibits an anomalously broad
exponential (non-Gaussian) tail for sufficiently large values of the molecular
displacement at all finite times.
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efe91379-0f88-4d6c-bd2b-39c563176687 | efe91379-0f88-4d6c-bd2b-39c563176687 | efe91379-0f88-4d6c-bd2b-39c563176687 | human | null | null | none | abstracts | 3d Numerical Models of the Chromosphere, Transition Region, and Corona | null | A major goal in solar physics has during the last five decades been to find
how energy flux generated in the solar convection zone is transported and
dissipated in the outer solar layers. Progress in this field has been slow and
painstaking. However, advances in computer hardware and numerical methods,
vastly increased observational capabilities and growing physical insight seem
finally to be leading towards understanding. Here we present exploratory
numerical MHD models that span the entire solar atmosphere from the upper
convection zone to the lower corona. These models include non-grey, non-LTE
radiative transport in the photosphere and chromosphere, optically thin
radiative losses as well as magnetic field-aligned heat conduction in the
transition region and corona.
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e8492d61-5b68-4109-b612-5030f4e0f1ab | e8492d61-5b68-4109-b612-5030f4e0f1ab | e8492d61-5b68-4109-b612-5030f4e0f1ab | human | null | null | none | abstracts | Gauge Invariant Factorisation and Canonical Quantisation of
Topologically Massive Gauge Theories in Any Dimension | null | Abelian topologically massive gauge theories (TMGT) provide a topological
mechanism to generate mass for a bosonic p-tensor field in any spacetime
dimension. These theories include the 2+1 dimensional Maxwell-Chern-Simons and
3+1 dimensional Cremmer-Scherk actions as particular cases. Within the
Hamiltonian formulation, the embedded topological field theory (TFT) sector
related to the topological mass term is not manifest in the original phase
space. However through an appropriate canonical transformation, a gauge
invariant factorisation of phase space into two orthogonal sectors is feasible.
The first of these sectors includes canonically conjugate gauge invariant
variables with free massive excitations. The second sector, which decouples
from the total Hamiltonian, is equivalent to the phase space description of the
associated non dynamical pure TFT. Within canonical quantisation, a likewise
factorisation of quantum states thus arises for the full spectrum of TMGT in
any dimension. This new factorisation scheme also enables a definition of the
usual projection from TMGT onto topological quantum field theories in a most
natural and transparent way. None of these results rely on any gauge fixing
procedure whatsoever.
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