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1fcc58eb-fadb-471f-94a0-eee3f0f6ac47 | 1fcc58eb-fadb-471f-94a0-eee3f0f6ac47 | 1fcc58eb-fadb-471f-94a0-eee3f0f6ac47 | human | null | null | none | abstracts | Electronic structure of kinetic energy driven superconductors in the
presence of bilayer splitting | null | Within the framework of the kinetic energy driven superconductivity, the
electronic structure of bilayer cuprate superconductors in the superconducting
state is studied. It is shown that the electron spectrum of bilayer cuprate
superconductors is split into the bonding and antibonding components by the
bilayer splitting, then the observed peak-dip-hump structure around the
$[\pi,0]$ point is mainly caused by this bilayer splitting, with the
superconducting peak being related to the antibonding component, and the hump
being formed by the bonding component. The spectral weight increases with
increasing the doping concentration. In analogy to the normal state case, both
electron antibonding peak and bonding hump have the weak dispersions around the
$[\pi,0]$ point.
|
59245298-3f7f-4f11-8775-79d5054aa83d | 59245298-3f7f-4f11-8775-79d5054aa83d | 59245298-3f7f-4f11-8775-79d5054aa83d | human | null | null | none | abstracts | 9.7 micrometer Silicate Absorption in a Damped Lyman-alpha Absorber at
z=0.52 | null | We report a detection of the 9.7 micrometer silicate absorption feature in a
damped Lyman-alpha (DLA) system at z_{abs} = 0.524 toward AO0235+164, using the
Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The feature
shows a broad shallow profile over about 8-12 micrometers in the absorber rest
frame and appears to be > 15 sigma significant in equivalent width. The feature
is fit reasonably well by the silicate absorption profiles for laboratory
amorphous olivine or diffuse Galactic interstellar clouds. To our knowledge,
this is the first indication of 9.7 micrometer silicate absorption in a DLA. We
discuss potential implications of this finding for the nature of the dust in
quasar absorbers. Although the feature is relatively shallow (tau_{9.7} =
0.08-0.09), it is about 2 times deeper than expected from extrapolation of the
tau_{9.7} vs. E(B-V) relation known for diffuse Galactic interstellar clouds.
Further studies of the 9.7 micrometer silicate feature in quasar absorbers will
open a new window on the dust in distant galaxies.
|
0d771502-a06e-487b-903c-7c8a901eb7c8 | 0d771502-a06e-487b-903c-7c8a901eb7c8 | 0d771502-a06e-487b-903c-7c8a901eb7c8 | human | null | null | none | abstracts | On packet lengths and overhead for random linear coding over the erasure
channel | null | We assess the practicality of random network coding by illuminating the issue
of overhead and considering it in conjunction with increasingly long packets
sent over the erasure channel. We show that the transmission of increasingly
long packets, consisting of either of an increasing number of symbols per
packet or an increasing symbol alphabet size, results in a data rate
approaching zero over the erasure channel. This result is due to an erasure
probability that increases with packet length. Numerical results for a
particular modulation scheme demonstrate a data rate of approximately zero for
a large, but finite-length packet. Our results suggest a reduction in the
performance gains offered by random network coding.
|
b9f5493c-091e-4c04-9b70-9b882a55b19b | b9f5493c-091e-4c04-9b70-9b882a55b19b | b9f5493c-091e-4c04-9b70-9b882a55b19b | human | null | null | none | abstracts | Terrestrial and Habitable Planet Formation in Binary and Multi-star
Systems | null | One of the most surprising discoveries of extrasolar planets is the detection
of planets in moderately close binary star systems. The Jovian-type planets in
the two binaries of Gamma Cephei and GJ 86 have brought to the forefront
questions on the formation of giant planets and the possibility of the
existence of smaller bodies in such dynamically complex environments. The
diverse dynamical characteristics of these objects have made scientists wonder
to what extent the current theories of planet formation can be applied to
binaries and multiple star systems. At present, the sensitivity of the
detection techniques does not allow routine discovery of Earth-sized bodies in
binary systems. However, with the advancement of new techniques, and with the
recent launch of CoRoT and the launch of Kepler in late 2008, the detection of
more planets (possibly terrestrial-class objects) in such systems is on the
horizon. Theoretical studies and numerical modeling of terrestrial and
habitable planet formation are, therefore, necessary to gain fundamental
insights into the prospects for life in such systems and have great strategic
impact on NASA science and missions.
|
9c6224f0-a870-4bad-9c46-97f1d665c3b0 | 9c6224f0-a870-4bad-9c46-97f1d665c3b0 | 9c6224f0-a870-4bad-9c46-97f1d665c3b0 | human | null | null | none | abstracts | P-adic arithmetic coding | null | A new incremental algorithm for data compression is presented. For a sequence
of input symbols algorithm incrementally constructs a p-adic integer number as
an output. Decoding process starts with less significant part of a p-adic
integer and incrementally reconstructs a sequence of input symbols. Algorithm
is based on certain features of p-adic numbers and p-adic norm. p-adic coding
algorithm may be considered as of generalization a popular compression
technique - arithmetic coding algorithms. It is shown that for p = 2 the
algorithm works as integer variant of arithmetic coding; for a special class of
models it gives exactly the same codes as Huffman's algorithm, for another
special model and a specific alphabet it gives Golomb-Rice codes.
|
be992496-f91b-4ffd-a913-785bb1451e33 | be992496-f91b-4ffd-a913-785bb1451e33 | be992496-f91b-4ffd-a913-785bb1451e33 | human | null | null | none | abstracts | Compton X-ray and Gamma-ray Emission from Extended Radio Galaxies | null | The extended lobes of radio galaxies are examined as sources of X-ray and
gamma-ray emission via inverse Compton scattering of 3K background photons. The
Compton spectra of two exemplary examples, Fornax A and Centaurus A, are
estimated using available radio measurements in the ~10's MHz - 10's GHz range.
For average lobe magnetic fields of >~0.3-1 micro-G, the lobe spectra are
predicted to extend into the soft gamma-rays making them likely detectable with
the GLAST LAT. If detected, their large angular extents (~1 deg and 8 deg) will
make it possible to ``image'' the radio lobes in gamma-rays. Similarly, this
process operates in more distant radio galaxies and the possibility that such
systems will be detected as unresolved gamma-ray sources with GLAST is briefly
considered.
|
161887f6-d762-45d9-b94f-3c65742aced2 | 161887f6-d762-45d9-b94f-3c65742aced2 | 161887f6-d762-45d9-b94f-3c65742aced2 | human | null | null | none | abstracts | A matroid-friendly basis for the quasisymmetric functions | null | A new Z-basis for the space of quasisymmetric functions (QSym, for short) is
presented. It is shown to have nonnegative structure constants, and several
interesting properties relative to the space of quasisymmetric functions
associated to matroids by the Hopf algebra morphism (F) of Billera, Jia, and
Reiner. In particular, for loopless matroids, this basis reflects the grading
by matroid rank, as well as by the size of the ground set. It is shown that the
morphism F is injective on the set of rank two matroids, and that
decomposability of the quasisymmetric function of a rank two matroid mirrors
the decomposability of its base polytope. An affirmative answer is given to the
Hilbert basis question raised by Billera, Jia, and Reiner.
|
321b3a42-8b92-44f1-a71f-dc15c699e334 | 321b3a42-8b92-44f1-a71f-dc15c699e334 | 321b3a42-8b92-44f1-a71f-dc15c699e334 | human | null | null | none | abstracts | Universal Source Coding for Monotonic and Fast Decaying Monotonic
Distributions | null | We study universal compression of sequences generated by monotonic
distributions. We show that for a monotonic distribution over an alphabet of
size $k$, each probability parameter costs essentially $0.5 \log (n/k^3)$ bits,
where $n$ is the coded sequence length, as long as $k = o(n^{1/3})$. Otherwise,
for $k = O(n)$, the total average sequence redundancy is $O(n^{1/3+\epsilon})$
bits overall. We then show that there exists a sub-class of monotonic
distributions over infinite alphabets for which redundancy of
$O(n^{1/3+\epsilon})$ bits overall is still achievable. This class contains
fast decaying distributions, including many distributions over the integers and
geometric distributions. For some slower decays, including other distributions
over the integers, redundancy of $o(n)$ bits overall is achievable, where a
method to compute specific redundancy rates for such distributions is derived.
The results are specifically true for finite entropy monotonic distributions.
Finally, we study individual sequence redundancy behavior assuming a sequence
is governed by a monotonic distribution. We show that for sequences whose
empirical distributions are monotonic, individual redundancy bounds similar to
those in the average case can be obtained. However, even if the monotonicity in
the empirical distribution is violated, diminishing per symbol individual
sequence redundancies with respect to the monotonic maximum likelihood
description length may still be achievable.
|
9bbc639e-a78b-4515-a8be-134b777274d5 | 9bbc639e-a78b-4515-a8be-134b777274d5 | 9bbc639e-a78b-4515-a8be-134b777274d5 | human | null | null | none | abstracts | Difermion condensates in vacuum in 2-4D four-fermion interaction models | null | Theoretical analysis of interplay between the condensates $<\bar{q}q>$ and
$<qq>$ in vacuum is generally made by relativistic effective potentials in the
mean field approximation in 2D, 3D and 4D models with two flavor and $N_c$
color massless fermions. It is found that in ground states of these models,
interplay between the two condensates mainly depend on the ratio $G_S/H_S$ for
2D and 4D case or $G_S/H_P$ for 3D case, where $G_S$, $H_S$ and $H_P$ are
respectively the coupling constants in a scalar $(\bar{q}q)$, a scalar $(qq)$
and a pseudoscalar $(qq)$ channel. In ground states of all the models, only
pure $<\bar{q}q>$ condensates could exist if $G_S/H_S$ or $G_S/H_P$ is bigger
than the critical value $2/N_c$, the ratio of the color numbers of the fermions
entering into the condensates $<qq>$ and $<\bar{q}q>$. As $G_S/H_S$ or
$G_S/H_P$ decreases to the region below $2/N_c$, differences of the models will
manifest themselves. Depending on different models, and also on $N_c$ in 3D
model, one will have or have no the coexistence phase of the two condensates,
besides the pure $<qq>$ condensate phase. The $G_S-H_S$ (or $G_S-H_P$) phase
diagrams in these models are given. The results also implicate a real
constraint on two-flavor QCD-analogous NJL model.
|
017cca8d-9b9a-4b49-bd26-62e2e5b6d05a | 017cca8d-9b9a-4b49-bd26-62e2e5b6d05a | 017cca8d-9b9a-4b49-bd26-62e2e5b6d05a | human | null | null | none | abstracts | Oscillation bands of condensates on a ring: Beyond the mean field theory | null | The Hamiltonian of a N-boson system confined on a ring with zero spin and
repulsive interaction is diagonalized. The excitation of a pair of
p-wave-particles rotating reversely appears to be a basic mode. The fluctuation
of many of these excited pairs provides a mechanism of oscillation, the states
can be thereby classified into oscillation bands. The particle correlation is
studied intuitively via the two-body densities. Bose-clustering originating
from the symmetrization of wave functions is found, which leads to the
appearance of 1-, 2-, and 3-cluster structures. The motion is divided into
being collective and relative, this leads to the establishment of a relation
between the very high vortex states and the low-lying states.
|
263c9a79-fd5e-4f48-9018-7ffc3163aef7 | 263c9a79-fd5e-4f48-9018-7ffc3163aef7 | 263c9a79-fd5e-4f48-9018-7ffc3163aef7 | human | null | null | none | abstracts | Information entropic superconducting microcooler | null | We consider a design for a cyclic microrefrigerator using a superconducting
flux qubit. Adiabatic modulation of the flux combined with thermalization can
be used to transfer energy from a lower temperature normal metal thin film
resistor to another one at higher temperature. The frequency selectivity of
photonic heat conduction is achieved by including the hot resistor as part of a
high frequency LC resonator and the cold one as part of a low-frequency
oscillator while keeping both circuits in the underdamped regime. We discuss
the performance of the device in an experimentally realistic setting. This
device illustrates the complementarity of information and thermodynamic entropy
as the erasure of the quantum bit directly relates to the cooling of the
resistor.
|
b94d3df4-3fa5-4ad9-9eb2-f630f06ab513 | b94d3df4-3fa5-4ad9-9eb2-f630f06ab513 | b94d3df4-3fa5-4ad9-9eb2-f630f06ab513 | human | null | null | none | abstracts | Density matrix elements and entanglement entropy for the spin-1/2 XXZ
chain at $\Delta$=1/2 | null | We have analytically obtained all the density matrix elements up to six
lattice sites for the spin-1/2 Heisenberg XXZ chain at $\Delta=1/2$. We use the
multiple integral formula of the correlation function for the massless XXZ
chain derived by Jimbo and Miwa. As for the spin-spin correlation functions, we
have newly obtained the fourth- and fifth-neighbour transverse correlation
functions. We have calculated all the eigenvalues of the density matrix and
analyze the eigenvalue-distribution. Using these results the exact values of
the entanglement entropy for the reduced density matrix up six lattice sites
have been obtained. We observe that our exact results agree quite well with the
asymptotic formula predicted by the conformal field theory.
|
9d7beeb5-254b-4f8d-915d-33d2507a8739 | 9d7beeb5-254b-4f8d-915d-33d2507a8739 | 9d7beeb5-254b-4f8d-915d-33d2507a8739 | human | null | null | none | abstracts | Extrasolar scale change in Newton's Law from 5D `plain' R^2-gravity | null | Galactic rotation curves and lack of direct observations of Dark Matter may
indicate that General Relativity is not valid (on galactic scale) and should be
replaced with another theory. There is the only variant of Absolute Parallelism
which solutions are free of arising singularities, if D=5 (there is no room for
changes). This variant does not have a Lagrangian, nor match GR: an equation of
`plain' R^2-gravity (ie without R-term) is in sight instead. Arranging an
expanding O_4-symmetrical solution as the basis of 5D cosmological model, and
probing a universal_function of mass distribution (along very-very long the
extra dimension) to place into bi-Laplace equation (R^2 gravity), one can
derive the Law of Gravitation: 1/r^2 transforms to 1/r with distance (not with
acceleration).
|
95431e26-691a-41e0-9510-b9d7660f8aa7 | 95431e26-691a-41e0-9510-b9d7660f8aa7 | 95431e26-691a-41e0-9510-b9d7660f8aa7 | human | null | null | none | abstracts | Availability assessment of SunOS/Solaris Unix Systems based on Syslogd
and wtmpx logfiles : a case study | null | This paper presents a measurement-based availability assessment study using
field data collected during a 4-year period from 373 SunOS/Solaris Unix
workstations and servers interconnected through a local area network. We focus
on the estimation of machine uptimes, downtimes and availability based on the
identification of failures that caused total service loss. Data corresponds to
syslogd event logs that contain a large amount of information about the normal
activity of the studied systems as well as their behavior in the presence of
failures. It is widely recognized that the information contained in such event
logs might be incomplete or imperfect. The solution investigated in this paper
to address this problem is based on the use of auxiliary sources of data
obtained from wtmpx files maintained by the SunOS/Solaris Unix operating
system. The results obtained suggest that the combined use of wtmpx and syslogd
log files provides more complete information on the state of the target systems
that is useful to provide availability estimations that better reflect reality.
|
8b68bc50-3ae0-4f9a-937b-2a1af779a80c | 8b68bc50-3ae0-4f9a-937b-2a1af779a80c | 8b68bc50-3ae0-4f9a-937b-2a1af779a80c | human | null | null | none | abstracts | The Low CO Content of the Extremely Metal Poor Galaxy I Zw 18 | null | We present sensitive molecular line observations of the metal-poor blue
compact dwarf I Zw 18 obtained with the IRAM Plateau de Bure interferometer.
These data constrain the CO J=1-0 luminosity within our 300 pc (FWHM) beam to
be L_CO < 1 \times 10^5 K km s^-1 pc^2 (I_CO < 1 K km s^-1), an order of
magnitude lower than previous limits. Although I Zw 18 is starbursting, it has
a CO luminosity similar to or less than nearby low-mass irregulars (e.g. NGC
1569, the SMC, and NGC 6822). There is less CO in I Zw 18 relative to its
B-band luminosity, HI mass, or star formation rate than in spiral or dwarf
starburst galaxies (including the nearby dwarf starburst IC 10). Comparing the
star formation rate to our CO upper limit reveals that unless molecular gas
forms stars much more efficiently in I Zw 18 than in our own galaxy, it must
have a very low CO-to-H_2 ratio, \sim 10^-2 times the Galactic value. We detect
3mm continuum emission, presumably due to thermal dust and free-free emission,
towards the radio peak.
|
edf1996c-bd46-465f-a0a8-903cb5e7995f | edf1996c-bd46-465f-a0a8-903cb5e7995f | edf1996c-bd46-465f-a0a8-903cb5e7995f | human | null | null | none | abstracts | A binary model for the UV-upturn of elliptical galaxies (MNRAS version) | null | The discovery of a flux excess in the far-ultraviolet (UV) spectrum of
elliptical galaxies was a major surprise in 1969. While it is now clear that
this UV excess is caused by an old population of hot helium-burning stars
without large hydrogen-rich envelopes, rather than young stars, their origin
has remained a mystery. Here we show that these stars most likely lost their
envelopes because of binary interactions, similar to the hot subdwarf
population in our own Galaxy. We have developed an evolutionary population
synthesis model for the far-UV excess of elliptical galaxies based on the
binary model developed by Han et al (2002, 2003) for the formation of hot
subdwarfs in our Galaxy. Despite its simplicity, it successfully reproduces
most of the properties of elliptical galaxies with a UV excess: the range of
observed UV excesses, both in $(1550-V)$ and $(2000-V)$, and their evolution
with redshift. We also present colour-colour diagrams for use as diagnostic
tools in the study of elliptical galaxies. The model has major implications for
understanding the evolution of the UV excess and of elliptical galaxies in
general. In particular, it implies that the UV excess is not a sign of age, as
had been postulated previously, and predicts that it should not be strongly
dependent on the metallicity of the population, but exists universally from
dwarf ellipticals to giant ellipticals.
|
4f187b81-b7f8-4971-a0b6-84965005f83b | 4f187b81-b7f8-4971-a0b6-84965005f83b | 4f187b81-b7f8-4971-a0b6-84965005f83b | human | null | null | none | abstracts | Redshifts of the Long Gamma-Ray Bursts | null | The low energy spectra of some gamma-ray bursts' show excess components
beside the power-law dependence. The consequences of such a feature allows to
estimate the gamma photometric redshift of the long gamma-ray bursts in the
BATSE Catalog. There is good correlation between the measured optical and the
estimated gamma photometric redshifts. The estimated redshift values for the
long bright gamma-ray bursts are up to z=4, while for the the faint long bursts
- which should be up to z=20 - the redshifts cannot be determined unambiguously
with this method. The redshift distribution of all the gamma-ray bursts with
known optical redshift agrees quite well with the BATSE based gamma photometric
redshift distribution.
|
7f3b293e-7f56-467d-aefd-27250bc6da66 | 7f3b293e-7f56-467d-aefd-27250bc6da66 | 7f3b293e-7f56-467d-aefd-27250bc6da66 | human | null | null | none | abstracts | An architecture-based dependability modeling framework using AADL | null | For efficiency reasons, the software system designers' will is to use an
integrated set of methods and tools to describe specifications and designs, and
also to perform analyses such as dependability, schedulability and performance.
AADL (Architecture Analysis and Design Language) has proved to be efficient for
software architecture modeling. In addition, AADL was designed to accommodate
several types of analyses. This paper presents an iterative dependency-driven
approach for dependability modeling using AADL. It is illustrated on a small
example. This approach is part of a complete framework that allows the
generation of dependability analysis and evaluation models from AADL models to
support the analysis of software and system architectures, in critical
application domains.
|
c42bd3f9-b98a-4d0b-a1e8-9ffc71d95c72 | c42bd3f9-b98a-4d0b-a1e8-9ffc71d95c72 | c42bd3f9-b98a-4d0b-a1e8-9ffc71d95c72 | human | null | null | none | abstracts | A priori estimates for weak solutions of complex Monge-Amp\`ere
equations | null | Let $X$ be a compact K\"ahler manifold and $\om$ a smooth closed form of
bidegree $(1,1)$ which is nonnegative and big. We study the classes ${\mathcal
E}_{\chi}(X,\om)$ of $\om$-plurisubharmonic functions of finite weighted
Monge-Amp\`ere energy. When the weight $\chi$ has fast growth at infinity, the
corresponding functions are close to be bounded.
We show that if a positive Radon measure is suitably dominated by the
Monge-Amp\`ere capacity, then it belongs to the range of the Monge-Amp\`ere
operator on some class ${\mathcal E}_{\chi}(X,\om)$. This is done by
establishing a priori estimates on the capacity of sublevel sets of the
solutions.
Our result extends U.Cegrell's and S.Kolodziej's results and puts them into a
unifying frame. It also gives a simple proof of S.T.Yau's celebrated a priori
${\mathcal C}^0$-estimate.
|
5103f159-3882-4067-9e7d-9d01e2968a08 | 5103f159-3882-4067-9e7d-9d01e2968a08 | 5103f159-3882-4067-9e7d-9d01e2968a08 | human | null | null | none | abstracts | Effect of electron-electron interaction on the phonon-mediated spin
relaxation in quantum dots | null | We estimate the spin relaxation rate due to spin-orbit coupling and acoustic
phonon scattering in weakly-confined quantum dots with up to five interacting
electrons. The Full Configuration Interaction approach is used to account for
the inter-electron repulsion, and Rashba and Dresselhaus spin-orbit couplings
are exactly diagonalized. We show that electron-electron interaction strongly
affects spin-orbit admixture in the sample. Consequently, relaxation rates
strongly depend on the number of carriers confined in the dot. We identify the
mechanisms which may lead to improved spin stability in few electron (>2)
quantum dots as compared to the usual one and two electron devices. Finally, we
discuss recent experiments on triplet-singlet transitions in GaAs dots subject
to external magnetic fields. Our simulations are in good agreement with the
experimental findings, and support the interpretation of the observed spin
relaxation as being due to spin-orbit coupling assisted by acoustic phonon
emission.
|
b49928a3-10dc-459e-87b2-69635709ee2d | b49928a3-10dc-459e-87b2-69635709ee2d | b49928a3-10dc-459e-87b2-69635709ee2d | human | null | null | none | abstracts | Higher ramification and varieties of secant divisors on the generic
curve | null | For a smooth projective curve, the cycles of e-secant k-planes are among the
most studied objects in classical enumerative geometry and there are well-known
formulas due to Castelnuovo, Cayley and MacDonald concerning them. Despite
various attempts, surprisingly little is known about the enumerative validity
of such formulas. The aim of this paper is to completely clarify this problem
in the case of the generic curve C of given genus. Using degeneration
techniques and a few facts about the birational geometry of moduli spaces of
stable pointed curves we determine precisely under which conditions the cycle
of e-secant k-planes in non-empty and we compute its dimension. We also
precisely determine the dimension of the variety of linear series on C carrying
e-secant k-planes. In a different direction, in the last part of the paper we
study the distribution of ramification points of the powers of a line bundle on
C having prescribed ramification at a given point.
|
b453db3c-ded9-45d4-8ca9-1650d476d821 | b453db3c-ded9-45d4-8ca9-1650d476d821 | b453db3c-ded9-45d4-8ca9-1650d476d821 | human | null | null | none | abstracts | The bimodality of type Ia Supernovae | null | We comment on the presence of a bimodality in the distribution of delay time
between the formation of the progenitors and their explosion as type Ia SNe.
Two "flavors" of such bimodality are present in the literature: a "weak"
bimodality, in which type Ia SNe must explode from both young and old
progenitors, and a "strong" bimodality, in which about half of the systems
explode within 10^8 years from formation. The "weak" bimodality is
observationally based on the dependence of the rates with the host galaxy SFR,
while the "strong" one on the different rates in radio-loud and radio-quiet
early-type galaxies. We review the evidence for these bimodalities. Finally, we
estimate the fraction of SNe which are missed by optical and near-IR searches
because of dust extinction in massive starbursts.
|
c1a42b76-3661-4452-b6f8-834fb2697ac4 | c1a42b76-3661-4452-b6f8-834fb2697ac4 | c1a42b76-3661-4452-b6f8-834fb2697ac4 | human | null | null | none | abstracts | Structural relaxation around substitutional Cr3+ in MgAl2O4 | null | The structural environment of substitutional Cr3+ ion in MgAl2O4 spinel has
been investigated by Cr K-edge Extended X-ray Absorption Fine Structure (EXAFS)
and X-ray Absorption Near Edge Structure (XANES) spectroscopies.
First-principles computations of the structural relaxation and of the XANES
spectrum have been performed, with a good agreement to the experiment. The Cr-O
distance is close to that in MgCr2O4, indicating a full relaxation of the first
neighbors, and the second shell of Al atoms relaxes partially. These
observations demonstrate that Vegard's law is not obeyed in the MgAl2O4-MgCr2O4
solid solution. Despite some angular site distortion, the local D3d symmetry of
the B-site of the spinel structure is retained during the substitution of Cr
for Al. Here, we show that the relaxation is accomodated by strain-induced bond
buckling, with angular tilts of the Mg-centred tetrahedra around the Cr-centred
octahedron. By contrast, there is no significant alteration of the angles
between the edge-sharing octahedra, which build chains aligned along the three
four-fold axes of the cubic structure.
|
82bfd112-7b53-48d1-af83-edc4415a4266 | 82bfd112-7b53-48d1-af83-edc4415a4266 | 82bfd112-7b53-48d1-af83-edc4415a4266 | human | null | null | none | abstracts | A Hierarchical Approach for Dependability Analysis of a Commercial
Cache-Based RAID Storage Architecture | null | We present a hierarchical simulation approach for the dependability analysis
and evaluation of a highly available commercial cache-based RAID storage
system. The archi-tecture is complex and includes several layers of
overlap-ping error detection and recovery mechanisms. Three ab-straction levels
have been developed to model the cache architecture, cache operations, and
error detection and recovery mechanism. The impact of faults and errors
oc-curring in the cache and in the disks is analyzed at each level of the
hierarchy. A simulation submodel is associated with each abstraction level. The
models have been devel-oped using DEPEND, a simulation-based environment for
system-level dependability analysis, which provides facili-ties to inject
faults into a functional behavior model, to simulate error detection and
recovery mechanisms, and to evaluate quantitative measures. Several fault
models are defined for each submodel to simulate cache component failures, disk
failures, transmission errors, and data errors in the cache memory and in the
disks. Some of the parame-ters characterizing fault injection in a given
submodel cor-respond to probabilities evaluated from the simulation of the
lower-level submodel. Based on the proposed method-ology, we evaluate and
analyze 1) the system behavior un-der a real workload and high error rate
(focusing on error bursts), 2) the coverage of the error detection mechanisms
implemented in the system and the error latency distribu-tions, and 3) the
accumulation of errors in the cache and in the disks.
|
2a176a01-cc35-4c60-8e2d-4bf3d347e312 | 2a176a01-cc35-4c60-8e2d-4bf3d347e312 | 2a176a01-cc35-4c60-8e2d-4bf3d347e312 | human | null | null | none | abstracts | Stochastic action principle and maximum entropy | null | A stochastic action principle for stochastic dynamics is revisited. We
present first numerical diffusion experiments showing that the diffusion path
probability depend exponentially on average Lagrangian action. This result is
then used to derive an uncertainty measure defined in a way mimicking the heat
or entropy in the first law of thermodynamics. It is shown that the path
uncertainty (or path entropy) can be measured by the Shannon information and
that the maximum entropy principle and the least action principle of classical
mechanics can be unified into a concise form. It is argued that this action
principle, hence the maximum entropy principle, is simply a consequence of the
mechanical equilibrium condition extended to the case of stochastic dynamics.
|
ec307f33-931f-4897-afb4-d1a7e399691f | ec307f33-931f-4897-afb4-d1a7e399691f | ec307f33-931f-4897-afb4-d1a7e399691f | human | null | null | none | abstracts | A Dark Energy model combining DGP gravity and Chaplygin gas | null | The expansion of the Universe is accelerating, as testified by observations
of supernovae of type Ia as a function of redshift. Explanations are of two
types: modifications of Einstein gravity or new forms of energy, coined dark
energy.The accelerated expansion is explained here by a combination of
Dvali-Gabadadze-Porrati (DGP) model gravity and Chaplygin gas dark energy. Both
models are characterized by a length scale L which may be the same. The
continuity equation for the combined model is derived in flat geometry, and
solved by numerical methods. The solution is shown to have the expected
properties: at very small scales (a<<L) the energy density behaves as
pressureless dust, at very large scales (a>>L) as a cosmological constant. The
modifications to the DGP model and the Chaplygin gas model occur for values of
a L. The results show an increase in the present dark energy density relative
to the plain DGP model.
|
c69baa48-c587-4b5e-8ad0-ec117274bada | c69baa48-c587-4b5e-8ad0-ec117274bada | c69baa48-c587-4b5e-8ad0-ec117274bada | human | null | null | none | abstracts | Lower bounds for the conductivities of correlated quantum systems | null | We show how one can obtain a lower bound for the electrical, spin or heat
conductivity of correlated quantum systems described by Hamiltonians of the
form H = H0 + g H1. Here H0 is an interacting Hamiltonian characterized by
conservation laws which lead to an infinite conductivity for g=0. The small
perturbation g H1, however, renders the conductivity finite at finite
temperatures. For example, H0 could be a continuum field theory, where momentum
is conserved, or an integrable one-dimensional model while H1 might describe
the effects of weak disorder. In the limit g to 0, we derive lower bounds for
the relevant conductivities and show how they can be improved systematically
using the memory matrix formalism. Furthermore, we discuss various applications
and investigate under what conditions our lower bound may become exact.
|
fb71c984-e87e-4eac-81cc-ce87c0636515 | fb71c984-e87e-4eac-81cc-ce87c0636515 | fb71c984-e87e-4eac-81cc-ce87c0636515 | human | null | null | none | abstracts | NMR evidence for a strong modulation of the Bose-Einstein Condensate in
BaCuSi$_2$O$_6$ | null | We present a $^{63,65}$Cu and $^{29}$Si NMR study of the quasi-2D coupled
spin 1/2 dimer compound BaCuSi$_2$O$_6$ in the magnetic field range 13-26 T and
at temperatures as low as 50 mK. NMR data in the gapped phase reveal that below
90 K different intra-dimer exchange couplings and different gaps
($\Delta_{\rm{B}}/\Delta_{\rm{A}}$ = 1.16) exist in every second plane along
the c-axis, in addition to a planar incommensurate (IC) modulation. $^{29}$Si
spectra in the field induced magnetic ordered phase reveal that close to the
quantum critical point at $H_{\rm{c1}}$ = 23.35 T the average boson density
$\bar{n}$ of the Bose-Einstein condensate is strongly modulated along the
c-axis with a density ratio for every second plane
$\bar{n}_{\rm{A}}/\bar{n}_{\rm{B}} \simeq 5$. An IC modulation of the local
density is also present in each plane. This adds new constraints for the
understanding of the 2D value $\phi$ = 1 of the critical exponent describing
the phase boundary.
|
3ebb5590-c4e4-4a64-8f1c-ccd9676f6e60 | 3ebb5590-c4e4-4a64-8f1c-ccd9676f6e60 | 3ebb5590-c4e4-4a64-8f1c-ccd9676f6e60 | human | null | null | none | abstracts | On the Origin of Asymmetries in Bilateral Supernova Remnants | null | AIMS: We investigate whether the morphology of bilateral supernova remnants
(BSNRs) observed in the radio band is determined mainly either by a non-uniform
interstellar medium (ISM) or by a non-uniform ambient magnetic field.
METHODS: We perform 3-D MHD simulations of a spherical SNR shock propagating
through a magnetized ISM. Two cases of shock propagation are considered: 1)
through a gradient of ambient density with a uniform ambient magnetic field; 2)
through a homogeneous medium with a gradient of ambient magnetic field
strength. From the simulations, we synthesize the synchrotron radio emission,
making different assumptions about the details of acceleration and injection of
relativistic electrons.
RESULTS: We find that asymmetric BSNRs are produced if the line-of-sight is
not aligned with the gradient of ambient plasma density or with the gradient of
ambient magnetic field strength. We derive useful parameters to quantify the
degree of asymmetry of the remnants that may provide a powerful diagnostic of
the microphysics of strong shock waves through the comparison between models
and observations.
CONCLUSIONS: BSNRs with two radio limbs of different brightness can be
explained if a gradient of ambient density or, most likely, of ambient magnetic
field strength is perpendicular to the radio limbs. BSNRs with converging
similar radio arcs can be explained if the gradient runs between the two arcs.
|
7dce7109-6077-4603-8837-cc3e920a8583 | 7dce7109-6077-4603-8837-cc3e920a8583 | 7dce7109-6077-4603-8837-cc3e920a8583 | human | null | null | none | abstracts | Nonstationary pattern in unsynchronizable complex networks | null | Pattern formation and evolution in unsynchronizable complex networks are
investigated. Due to the asymmetric topology, the synchronous patterns formed
in complex networks are irregular and nonstationary. For coupling strength
immediately out of the synchronizable region, the typical phenomenon is the
on-off intermittency of the system dynamics. The patterns appeared in this
process are signatured by the coexistence of a giant cluster, which comprises
most of the nodes, and a few number of small clusters. The pattern evolution is
characterized by the giant cluster irregularly absorbs or emits the small
clusters. As the coupling strength leaves away from the synchronization
bifurcation point, the giant cluster is gradually dissolved into a number of
small clusters, and the system dynamics is characterized by the integration and
separation of the small clusters. Dynamical mechanisms and statistical
properties of the nonstationary pattern evolution are analyzed and conducted,
and some scalings are newly revealed. Remarkably, it is found that the few
active nodes, which escape from the giant cluster with a high frequency, are
independent of the coupling strength while are sensitive to the bifurcation
types. We hope our findings about nonstationary pattern could give additional
understandings to the dynamics of complex systems and have implications to some
real problems where systems maintain their normal functions only in the
unsynchronizable state.
|
1aa9fa9f-a80e-46f6-8daf-6a5e84a28f21 | 1aa9fa9f-a80e-46f6-8daf-6a5e84a28f21 | 1aa9fa9f-a80e-46f6-8daf-6a5e84a28f21 | human | null | null | none | abstracts | The Solar Neighborhood. XIX. Discovery and Characterization of 33 New
Nearby White Dwarf Systems | null | We present spectra for 33 previously unclassified white dwarf systems
brighter than V = 17 primarily in the southern hemisphere. Of these new
systems, 26 are DA, 4 are DC, 2 are DZ, and 1 is DQ. We suspect three of these
systems are unresolved double degenerates. We obtained VRI photometry for these
33 objects as well as for 23 known white dwarf systems without trigonometric
parallaxes, also primarily in the southern hemisphere. For the 56 objects, we
converted the photometry values to fluxes and fit them to a spectral energy
distribution using the spectroscopy to determine which model to use (i.e. pure
hydrogen, pure helium, or metal-rich helium), resulting in estimates of
effective temperature and distance. Eight of the new and 12 known systems are
estimated to be within the NStars and Catalogue of Nearby Stars (CNS) horizons
of 25 pc, constituting a potential 18% increase in the nearby white dwarf
sample. Trigonometric parallax determinations are underway via CTIOPI for these
20 systems.
One of the DCs is cool so that it displays absorption in the near infrared.
Using the distance determined via trigonometric parallax, we are able to
constrain the model-dependent physical parameters and find that this object is
most likely a mixed H/He atmosphere white dwarf similar to other cool white
dwarfs identified in recent years with significant absorption in the infrared
due to collision-induced absorptions by molecular hydrogen.
|
660e7d3a-4af7-4cc4-a6f4-04bbbdcff952 | 660e7d3a-4af7-4cc4-a6f4-04bbbdcff952 | 660e7d3a-4af7-4cc4-a6f4-04bbbdcff952 | human | null | null | none | abstracts | Model C critical dynamics of random anisotropy magnets | null | We study the relaxational critical dynamics of the three-dimensional random
anisotropy magnets with the non-conserved n-component order parameter coupled
to a conserved scalar density. In the random anisotropy magnets the structural
disorder is present in a form of local quenched anisotropy axes of random
orientation. When the anisotropy axes are randomly distributed along the edges
of the n-dimensional hypercube, asymptotical dynamical critical properties
coincide with those of the random-site Ising model. However structural disorder
gives rise to considerable effects for non-asymptotic critical dynamics. We
investigate this phenomenon by a field-theoretical renormalization group
analysis in the two-loop order. We study critical slowing down and obtain
quantitative estimates for the effective and asymptotic critical exponents of
the order parameter and scalar density. The results predict complex scenarios
for the effective critical exponent approaching an asymptotic regime.
|
eb70a861-8c3e-4afb-aed9-2e7665838a2b | eb70a861-8c3e-4afb-aed9-2e7665838a2b | eb70a861-8c3e-4afb-aed9-2e7665838a2b | human | null | null | none | abstracts | The density of critical percolation clusters touching the boundaries of
strips and squares | null | We consider the density of two-dimensional critical percolation clusters,
constrained to touch one or both boundaries, in infinite strips, half-infinite
strips, and squares, as well as several related quantities for the infinite
strip. Our theoretical results follow from conformal field theory, and are
compared with high-precision numerical simulation. For example, we show that
the density of clusters touching both boundaries of an infinite strip of unit
width (i.e. crossing clusters) is proportional to $(\sin \pi
y)^{-5/48}\{[\cos(\pi y/2)]^{1/3} +[\sin (\pi y/2)]^{1/3}-1\}$.
We also determine numerically contours for the density of clusters crossing
squares and long rectangles with open boundaries on the sides, and compare with
theory for the density along an edge.
|
6b35c3b9-b4ba-4af2-854e-7fa279c21e83 | 6b35c3b9-b4ba-4af2-854e-7fa279c21e83 | 6b35c3b9-b4ba-4af2-854e-7fa279c21e83 | human | null | null | none | abstracts | Effective band-structure in the insulating phase versus strong dynamical
correlations in metallic VO2 | null | Using a general analytical continuation scheme for cluster dynamical mean
field calculations, we analyze real-frequency self-energies, momentum-resolved
spectral functions, and one-particle excitations of the metallic and insulating
phases of VO2. While for the former dynamical correlations and lifetime effects
prevent a description in terms of quasi-particles, the excitations of the
latter allow for an effective band-structure. We construct an
orbital-dependent, but static one-particle potential that reproduces the full
many-body spectrum. Yet, the ground state is well beyond a static one-particle
description. The emerging picture gives a non-trivial answer to the decade-old
question of the nature of the insulator, which we characterize as a ``many-body
Peierls'' state.
|
57d4b2ea-1f8f-4cd8-afb6-d993093268d3 | 57d4b2ea-1f8f-4cd8-afb6-d993093268d3 | 57d4b2ea-1f8f-4cd8-afb6-d993093268d3 | human | null | null | none | abstracts | New possible properties of atomic nuclei investigated by non linear
methods: Fractal and recurrence quantification analysis | null | For the first time we apply the methodologies of nonlinear analysis to
investigate atomic matter. We use these methods in the analysis of Atomic
Weights and of Mass Number of atomic nuclei. Using the AutoCorrelation Function
and Mutual Information we establish the presence of nonlinear effects in the
mechanism of increasing mass of atomic nuclei considered as a function of the
atomic number. We find that increasing mass is divergent, possibly chaotic. We
also investigate the possible existence of a Power Law for atomic nuclei and,
using also the technique of the variogram, we conclude that a fractal regime
could superintend to the mechanism of increasing mass for nuclei. Finally,
using the Hurst exponent, evidence is obtained that the mechanism of increasing
mass in atomic nuclei is in the fractional Brownian regime. The most
interesting results are obtained by using Recurrence Quantification Analysis
(RQA). New recurrences, psudoperiodicities, self-resemblance and class of
self-similarities are identified with values of determinism showing oscillating
values indicating the presence of more or less stability during the process of
increasing mass of atomic nuclei. In brief, new regimes of regularities are
identified for atomic nuclei that deserve to be studied by future researches.
In particular an accurate analysis of binding energy values by nonlinear
methods is further required.
|
785ed309-54c6-4133-bb62-bdc4a3129e27 | 785ed309-54c6-4133-bb62-bdc4a3129e27 | 785ed309-54c6-4133-bb62-bdc4a3129e27 | human | null | null | none | abstracts | The Use of Weighting in Periodicity Searches in All-Sky Monitor Data:
Applications to the GLAST LAT | null | The light curves produced by all-sky monitors, such as the Rossi X-ray Timing
Explorer All-Sky Monitor and the Swift Burst Alert Telescope (BAT), generally
have non-uniform error bars. In searching for periodic modulation in this type
of data using power spectra it can be important to use appropriate weighting of
data points to achieve the best sensitivity. It was recently demonstrated that
for Swift BAT data a simple weighting scheme can actually sometimes reduce the
sensitivity of the power spectrum depending on source brightness. Instead, a
modified weighting scheme, based on the Cochran semi-weighted mean, gives
improved results independent of source brightness. We investigate the benefits
of weighting power spectra in period searches using simulated GLAST LAT
observations of gamma-ray binaries.
|
f0238b69-2bd8-4dca-a5ff-b6ae2468635d | f0238b69-2bd8-4dca-a5ff-b6ae2468635d | f0238b69-2bd8-4dca-a5ff-b6ae2468635d | human | null | null | none | abstracts | Metropolis algorithm and equienergy sampling for two mean field spin
systems | null | In this paper we study the Metropolis algorithm in connection with two
mean--field spin systems, the so called mean--field Ising model and the
Blume--Emery--Griffiths model. In both this examples the naive choice of
proposal chain gives rise, for some parameters, to a slowly mixing Metropolis
chain, that is a chain whose spectral gap decreases exponentially fast (in the
dimension $N$ of the problem). Here we show how a slight variant in the
proposal chain can avoid this problem, keeping the mean computational cost
similar to the cost of the usual Metropolis. More precisely we prove that, with
a suitable variant in the proposal, the Metropolis chain has a spectral gap
which decreases polynomially in 1/N. Using some symmetry structure of the
energy, the method rests on allowing appropriate jumps within the energy level
of the starting state.
|
db056972-86cd-435a-bd90-4ad2b8a126c5 | db056972-86cd-435a-bd90-4ad2b8a126c5 | db056972-86cd-435a-bd90-4ad2b8a126c5 | human | null | null | none | abstracts | Extragalactic Radio Sources and the WMAP Cold Spot | null | We detect a dip of 20-45% in the surface brightness and number counts of NVSS
sources smoothed to a few degrees at the location of the WMAP cold spot. The
dip has structure on scales of approximately 1-10 degrees. Together with
independent all-sky wavelet analyses, our results suggest that the dip in
extragalactic brightness and number counts and the WMAP cold spot are
physically related, i.e., that the coincidence is neither a statistical anomaly
nor a WMAP foreground correction problem. If the cold spot does originate from
structures at modest redshifts, as we suggest, then there is no remaining need
for non-Gaussian processes at the last scattering surface of the CMB to explain
the cold spot. The late integrated Sachs-Wolfe effect, already seen
statistically for NVSS source counts, can now be seen to operate on a single
region. To create the magnitude and angular size of the WMAP cold spot requires
a ~140 Mpc radius completely empty void at z<=1 along this line of sight. This
is far outside the current expectations of the concordance cosmology, and adds
to the anomalies seen in the CMB.
|
b7100bbb-2d8c-4fe3-96d2-58b180974624 | b7100bbb-2d8c-4fe3-96d2-58b180974624 | b7100bbb-2d8c-4fe3-96d2-58b180974624 | human | null | null | none | abstracts | On the Nonexistence of Nontrivial Involutive n-Homomorphisms of
C*-algebras | null | An n-homomorphism between algebras is a linear map $\phi : A \to B$ such that
$\phi(a_1 ... a_n) = \phi(a_1)... \phi(a_n)$ for all elements $a_1, >..., a_n
\in A.$ Every homomorphism is an n-homomorphism, for all n >= 2, but the
converse is false, in general. Hejazian et al. [7] ask: Is every *-preserving
n-homomorphism between C*-algebras continuous? We answer their question in the
affirmative, but the even and odd n arguments are surprisingly disjoint. We
then use these results to prove stronger ones: If n >2 is even, then $\phi$ is
just an ordinary *-homomorphism. If n >= 3 is odd, then $\phi$ is a difference
of two orthogonal *-homomorphisms. Thus, there are no nontrivial *-linear
n-homomorphisms between C*-algebras.
|
8e8ef6d6-e20f-417a-9550-cd8c3e0cb50b | 8e8ef6d6-e20f-417a-9550-cd8c3e0cb50b | 8e8ef6d6-e20f-417a-9550-cd8c3e0cb50b | human | null | null | none | abstracts | Smooth and Starburst Tidal Tails in the GEMS and GOODS Fields | null | GEMS and GOODS fields were examined to z~1.4 for galaxy interactions and
mergers. The basic morphologies are familiar: antennae with long tidal tails,
tidal dwarfs, and merged cores; M51-type galaxies with disk spirals and tidal
arm companions; early-type galaxies with diffuse plumes; equal-mass
grazing-collisions; and thick J-shaped tails beaded with star formation and
double cores. One type is not common locally and is apparently a loose
assemblage of smaller galaxies. Photometric measurements were made of the tails
and clumps, and physical sizes were determined assuming photometric redshifts.
Antennae tails are a factor of ~3 smaller in GEMS and GOODS systems compared to
local antennae; their disks are a factor of ~2 smaller than locally. Collisions
among early type galaxies generally show no fine structure in their tails,
indicating that stellar debris is usually not unstable. One exception has a
5x10**9 Msun smooth red clump that could be a pure stellar condensation. Most
tidal dwarfs are blue and probably form by gravitational instabilities in the
gas. One tidal dwarf looks like it existed previously and was incorporated into
the arm tip by tidal forces. The star-forming regions in tidal arms are 10 to
1000 times more massive than star complexes in local galaxies, although their
separations are about the same. If they all form by gravitational
instabilities, then the gaseous velocity dispersions in interacting galaxies
have to be larger than in local galaxies by a factor of ~5 or more; the gas
column densities have to be larger by the square of this factor.
|
38aecf58-c9aa-4270-9fff-847ec3abb07b | 38aecf58-c9aa-4270-9fff-847ec3abb07b | 38aecf58-c9aa-4270-9fff-847ec3abb07b | human | null | null | none | abstracts | Nuclear Spin Effects in Optical Lattice Clocks | null | We present a detailed experimental and theoretical study of the effect of
nuclear spin on the performance of optical lattice clocks. With a state-mixing
theory including spin-orbit and hyperfine interactions, we describe the origin
of the $^1S_0$-$^3P_0$ clock transition and the differential g-factor between
the two clock states for alkaline-earth(-like) atoms, using $^{87}$Sr as an
example. Clock frequency shifts due to magnetic and optical fields are
discussed with an emphasis on those relating to nuclear structure. An
experimental determination of the differential g-factor in $^{87}$Sr is
performed and is in good agreement with theory. The magnitude of the tensor
light shift on the clock states is also explored experimentally. State specific
measurements with controlled nuclear spin polarization are discussed as a
method to reduce the nuclear spin-related systematic effects to below
10$^{-17}$ in lattice clocks.
|
ee5dd676-3bfb-408b-8dc0-8c47e4104b64 | ee5dd676-3bfb-408b-8dc0-8c47e4104b64 | ee5dd676-3bfb-408b-8dc0-8c47e4104b64 | human | null | null | none | abstracts | Domain wall switching: optimizing the energy landscape | null | It has recently been suggested that exchange spring media offer a way to
increase media density without causing thermal instability
(superparamagnetism), by using a hard and a soft layer coupled by exchange.
Victora has suggested a figure of merit xi = 2 E_b/mu_0 m_s H_sw, the ratio of
the energy barrier to that of a Stoner-Wohlfarth system with the same switching
field, which is 1 for a Stoner-Wohlfarth (coherently switching) particle and 2
for an optimal two-layer composite medium. A number of theoretical approaches
have been used for this problem (e.g., various numbers of coupled
Stoner-Wohlfarth layers and continuum micromagnetics). In this paper we show
that many of these approaches can be regarded as special cases or
approximations to a variational formulation of the problem, in which the energy
is minimized for fixed magnetization. The results can be easily visualized in
terms of a plot of the energy as a function of magnetic moment m_z, in which
both the switching field [the maximum slope of E(m_z)] and the stability
(determined by the energy barrier E_b) are geometrically visible. In this
formulation we can prove a rigorous limit on the figure of merit xi, which can
be no higher than 4. We also show that a quadratic anistropy suggested by Suess
et al comes very close to this limit.
|
d2fd7016-de8c-41ec-bd72-ef62b3968dfe | d2fd7016-de8c-41ec-bd72-ef62b3968dfe | d2fd7016-de8c-41ec-bd72-ef62b3968dfe | human | null | null | none | abstracts | Electromagnetic wormholes via handlebody constructions | null | Cloaking devices are prescriptions of electrostatic, optical or
electromagnetic parameter fields (conductivity $\sigma(x)$, index of refraction
$n(x)$, or electric permittivity $\epsilon(x)$ and magnetic permeability
$\mu(x)$) which are piecewise smooth on $\mathbb R^3$ and singular on a
hypersurface $\Sigma$, and such that objects in the region enclosed by $\Sigma$
are not detectable to external observation by waves. Here, we give related
constructions of invisible tunnels, which allow electromagnetic waves to pass
between possibly distant points, but with only the ends of the tunnels visible
to electromagnetic imaging. Effectively, these change the topology of space
with respect to solutions of Maxwell's equations, corresponding to attaching a
handlebody to $\mathbb R^3$. The resulting devices thus function as
electromagnetic wormholes.
|
27e6679d-d2d4-4389-92a0-4703606b4ac0 | 27e6679d-d2d4-4389-92a0-4703606b4ac0 | 27e6679d-d2d4-4389-92a0-4703606b4ac0 | human | null | null | none | abstracts | The HARPS search for southern extra-solar planets. IX. Exoplanets
orbiting HD 100777, HD 190647, and HD 221287 | null | The HARPS high-resolution high-accuracy spectrograph is offered to the
astronomical community since the second half of 2003. Since then, we have been
using this instrument for monitoring radial velocities of a large sample of
Solar-type stars (~1400 stars) in order to search for their possible low-mass
companions. Amongst the goals of our survey, one is to significantly increase
the number of detected extra-solar planets in a volume-limited sample to
improve our knowledge of their orbital elements distributions and thus obtain
better constraints for planet-formation models.
In this paper, we present the HARPS radial-velocity data and orbital
solutions for 3 Solar-type stars: HD 100777, HD 190647, and HD 221287. The
radial-velocity data of HD 100777 is best explained by the presence of a 1.1
M_Jup planetary companion on a 384--day eccentric orbit (e=0.36). The orbital
fit obtained for the slightly evolved star HD 190647 reveals the presence of a
long-period (P=1038 d) 1.9 M_Jup planetary companion on a moderately eccentric
orbit (e=0.18). HD 221287 is hosting a 3.1 M_Jup planet on a 456--day orbit.
The shape of this orbit is not very well constrained because of our non-optimal
temporal coverage and because of the presence of abnormally large residuals. We
find clues for these large residuals to result from spectral line profile
variations probably induced by stellar activity related processes.
|
1f120fff-1a2a-4613-b9b9-83c7d8dc0d7f | 1f120fff-1a2a-4613-b9b9-83c7d8dc0d7f | 1f120fff-1a2a-4613-b9b9-83c7d8dc0d7f | human | null | null | none | abstracts | Algebraic geometry of Gaussian Bayesian networks | null | Conditional independence models in the Gaussian case are algebraic varieties
in the cone of positive definite covariance matrices. We study these varieties
in the case of Bayesian networks, with a view towards generalizing the
recursive factorization theorem to situations with hidden variables. In the
case when the underlying graph is a tree, we show that the vanishing ideal of
the model is generated by the conditional independence statements implied by
graph. We also show that the ideal of any Bayesian network is homogeneous with
respect to a multigrading induced by a collection of upstream random variables.
This has a number of important consequences for hidden variable models.
Finally, we relate the ideals of Bayesian networks to a number of classical
constructions in algebraic geometry including toric degenerations of the
Grassmannian, matrix Schubert varieties, and secant varieties.
|
47a2e27a-3686-4554-9a3d-951f45ff911c | 47a2e27a-3686-4554-9a3d-951f45ff911c | 47a2e27a-3686-4554-9a3d-951f45ff911c | human | null | null | none | abstracts | Interactions, superconducting $T_c$, and fluctuation magnetization for
two coupled dots in the crossover between the Gaussian Orthogonal and Unitary
ensembles | null | We study a system of two quantum dots connected by a hopping bridge. Both the
dots and connecting region are assumed to be in universal crossover regimes
between Gaussian Orthogonal and Unitary ensembles. Using a diagrammatic
approach appropriate for energy separations much larger than the level spacing
we obtain the ensemble-averaged one- and two-particle Green's functions. It
turns out that the diffuson and cooperon parts of the two-particle Green's
function can be described by separate scaling functions. We then use this
information to investigate a model interacting system in which one dot has an
attractive s-wave reduced Bardeen-Cooper-Schrieffer interaction, while the
other is noninteracting but subject to an orbital magnetic field. We find that
the critical temperature is {\it nonmonotonic} in the flux through the second
dot in a certain regime of interdot coupling. Likewise, the fluctuation
magnetization above the critical temperature is also nonmonotonic in this
regime, can be either diamagnetic or paramagnetic, and can be deduced from the
cooperon scaling function.
|
28c62904-3666-4e71-a999-088c0c83c96e | 28c62904-3666-4e71-a999-088c0c83c96e | 28c62904-3666-4e71-a999-088c0c83c96e | human | null | null | none | abstracts | Z^0 \to 2\gamma and the Twisted Coproduct of the Poincar\'{e} Group | null | Yang's theorem forbids the process $Z^0 \to 2\gamma$ in any Poincar\'{e}
invariant theory if photons are bosons and their two-particle states transform
under the Poincar\'{e} group in the standard way (under the standard coproduct
of the Poincar\'{e} group). This is an important result as it does not depend
on the assumptions of quantum field theory. Recent work on noncommutative
geometry requires deforming the above coproduct by the Drinfel'd twist. We
prove that $Z^0 \to 2\gamma$ is forbidden for the twisted coproduct as well.
This result is also independent of the assumptions of quantum field theory. As
an illustration of the use of our general formulae, we further show that $Z^0
\to \nu + \nu$ is forbidden for the standard or twisted coproduct of the
Poincar\'{e} group if the neutrino is massless, even if lepton number is not
conserved. This is a special case of our general result that a massive particle
of spin $j$ cannot decay into two identical massless particles of the same
helicity if $j$ is odd, regardless of the coproduct used.
|
9f0d24c9-cb35-4f61-980c-1e8501ee8044 | 9f0d24c9-cb35-4f61-980c-1e8501ee8044 | 9f0d24c9-cb35-4f61-980c-1e8501ee8044 | human | null | null | none | abstracts | A Symplectic Test of the L-Functions Ratios Conjecture | null | Recently Conrey, Farmer and Zirnbauer conjectured formulas for the averages
over a family of ratios of products of shifted L-functions. Their L-functions
Ratios Conjecture predicts both the main and lower order terms for many
problems, ranging from n-level correlations and densities to mollifiers and
moments to vanishing at the central point. There are now many results showing
agreement between the main terms of number theory and random matrix theory;
however, there are very few families where the lower order terms are known.
These terms often depend on subtle arithmetic properties of the family, and
provide a way to break the universality of behavior. The L-functions Ratios
Conjecture provides a powerful and tractable way to predict these terms. We
test a specific case here, that of the 1-level density for the symplectic
family of quadratic Dirichlet characters arising from even fundamental
discriminants d \le X. For test functions supported in (-1/3, 1/3) we calculate
all the lower order terms up to size O(X^{-1/2+epsilon}) and observe perfect
agreement with the conjecture (for test functions supported in (-1, 1) we show
agreement up to errors of size O(X^{-epsilon}) for any epsilon). Thus for this
family and suitably restricted test functions, we completely verify the Ratios
Conjecture's prediction for the 1-level density.
|
b36d9931-b482-4030-85df-fc09ca29d351 | b36d9931-b482-4030-85df-fc09ca29d351 | b36d9931-b482-4030-85df-fc09ca29d351 | human | null | null | none | abstracts | Cosmology from String Theory | null | We explore the cosmological content of Salam-Sezgin six dimensional
supergravity, and find a solution to the field equations in qualitative
agreement with observation of distant supernovae, primordial nucleosynthesis
abundances, and recent measurements of the cosmic microwave background. The
carrier of the acceleration in the present de Sitter epoch is a quintessence
field slowly rolling down its exponential potential. Intrinsic to this model is
a second modulus which is automatically stabilized and acts as a source of cold
dark matter with a mass proportional to an exponential function of the
quintessence field (hence realizing VAMP models within a String context).
However, any attempt to saturate the present cold dark matter component in this
manner leads to unacceptable deviations from cosmological data -- a numerical
study reveals that this source can account for up to about 7% of the total cold
dark matter budget. We also show that (1) the model will support a de Sitter
energy in agreement with observation at the expense of a miniscule breaking of
supersymmetry in the compact space; (2) variations in the fine structure
constant are controlled by the stabilized modulus and are negligible; (3)
``fifth''forces are carried by the stabilized modulus and are short range; (4)
the long time behavior of the model in four dimensions is that of a
Robertson-Walker universe with a constant expansion rate (w = -1/3). Finally,
we present a String theory background by lifting our six dimensional
cosmological solution to ten dimensions.
|
6c416ddb-0b92-4b46-8b89-d3b3e741c361 | 6c416ddb-0b92-4b46-8b89-d3b3e741c361 | 6c416ddb-0b92-4b46-8b89-d3b3e741c361 | human | null | null | none | abstracts | Noncommutative Electromagnetism As A Large N Gauge Theory | null | We map noncommutative (NC) U(1) gauge theory on R^d_C X R^{2n}_{NC} to U(N ->
\infty) Yang-Mills theory on R^d_C, where R^d_C is a d-dimensional commutative
spacetime while R^{2n}_{NC} is a 2n-dimensional NC space. The resulting U(N)
Yang-Mills theory on R^d_C is equivalent to that obtained by the dimensional
reduction of (d+2n)-dimensional U(N) Yang-Mills theory onto R^d_C. We show that
the gauge-Higgs system (A_\mu,\Phi^a) in the U(N -> \infty) Yang-Mills theory
on R^d_C leads to an emergent geometry in the (d+2n)-dimensional spacetime
whose metric was determined by Ward a long time ago. In particular, the
10-dimensional gravity for d=4 and n=3 corresponds to the emergent geometry
arising from the 4-dimensional N=4 vector multiplet in the AdS/CFT duality. We
further elucidate the emergent gravity by showing that the gauge-Higgs system
(A_\mu,\Phi^a) in half-BPS configurations describes self-dual Einstein gravity.
|
99c4909e-34f8-4734-b715-f3d788a580cd | 99c4909e-34f8-4734-b715-f3d788a580cd | 99c4909e-34f8-4734-b715-f3d788a580cd | human | null | null | none | abstracts | The Isophotal Structure of Early-Type Galaxies in the SDSS: Dependence
on AGN Activity and Environment | null | We study the dependence of the isophotal shape of early-type galaxies on
their absolute B-band magnitude, their dynamical mass, and their nuclear
activity and environment, using an unprecedented large sample of 847 early-type
galaxies identified in the SDSS by Hao et al (2006). We find that the fraction
of disky galaxies smoothly decreases with increasing luminosity. The large
sample allows us to describe these trends accurately with tight linear
relations that are statistically robust against the uncertainty in the
isophotal shape measurements. There is also a host of significant correlations
between the disky fraction and indicators of nuclear activity (both in the
optical and in the radio) and environment (soft X-rays, group mass, group
hierarchy). Our analysis shows however that these correlations can be
accurately matched by assuming that the disky fraction depends only on galaxy
luminosity or mass. We therefore conclude that neither the level of activity,
nor group mass or group hierarchy help in better predicting the isophotal shape
of early-type galaxies.
|
a3c75396-6ef1-44e6-b05a-852359592b96 | a3c75396-6ef1-44e6-b05a-852359592b96 | a3c75396-6ef1-44e6-b05a-852359592b96 | human | null | null | none | abstracts | Invariants of Triangular Lie Algebras | null | Triangular Lie algebras are the Lie algebras which can be faithfully
represented by triangular matrices of any finite size over the real/complex
number field. In the paper invariants ('generalized Casimir operators') are
found for three classes of Lie algebras, namely those which are either strictly
or non-strictly triangular, and for so-called special upper triangular Lie
algebras. Algebraic algorithm of [J. Phys. A: Math. Gen., 2006, V.39, 5749;
math-ph/0602046], developed further in [J. Phys. A: Math. Theor., 2007, V.40,
113; math-ph/0606045], is used to determine the invariants. A conjecture of [J.
Phys. A: Math. Gen., 2001, V.34, 9085], concerning the number of independent
invariants and their form, is corroborated.
|
9ed0777a-83c5-48ed-b848-3e3fa56906e7 | 9ed0777a-83c5-48ed-b848-3e3fa56906e7 | 9ed0777a-83c5-48ed-b848-3e3fa56906e7 | human | null | null | none | abstracts | Approaching equilibrium and the distribution of clusters | null | We investigate the approach to stable and metastable equilibrium in Ising
models using a cluster representation. The distribution of nucleation times is
determined using the Metropolis algorithm and the corresponding $\phi^{4}$
model using Langevin dynamics. We find that the nucleation rate is suppressed
at early times even after global variables such as the magnetization and energy
have apparently reached their time independent values. The mean number of
clusters whose size is comparable to the size of the nucleating droplet becomes
time independent at about the same time that the nucleation rate reaches its
constant value. We also find subtle structural differences between the
nucleating droplets formed before and after apparent metastable equilibrium has
been established.
|
983d6e33-c292-41dc-a041-5ae29f326c39 | 983d6e33-c292-41dc-a041-5ae29f326c39 | 983d6e33-c292-41dc-a041-5ae29f326c39 | human | null | null | none | abstracts | Recovering galaxy star formation and metallicity histories from spectra
using VESPA | null | We introduce VErsatile SPectral Analysis (VESPA): a new method which aims to
recover robust star formation and metallicity histories from galactic spectra.
VESPA uses the full spectral range to construct a galaxy history from synthetic
models. We investigate the use of an adaptative parametrization grid to recover
reliable star formation histories on a galaxy-by-galaxy basis. Our goal is
robustness as opposed to high resolution histories, and the method is designed
to return high time resolution only where the data demand it. In this paper we
detail the method and we present our findings when we apply VESPA to synthetic
and real Sloan Digital Sky Survey (SDSS) spectroscopic data. We show that the
number of parameters that can be recovered from a spectrum depends strongly on
the signal-to-noise, wavelength coverage and presence or absence of a young
population. For a typical SDSS sample of galaxies, we can normally recover
between 2 to 5 stellar populations. We find very good agreement between VESPA
and our previous analysis of the SDSS sample with MOPED.
|
86b67a61-1aa4-472a-9ecf-6e9f41a791e2 | 86b67a61-1aa4-472a-9ecf-6e9f41a791e2 | 86b67a61-1aa4-472a-9ecf-6e9f41a791e2 | human | null | null | none | abstracts | Axiom A polynomial skew products of C^2 and their postcritical sets | null | A polynomial skew product of C^2 is a map of the form f(z,w) = (p(z),
q(z,w)), where p and q are polynomials, such that f is regular of degree d >=
2. For polynomial maps of C, hyperbolicity is equivalent to the condition that
the closure of the postcritical set is disjoint from the Julia set; further,
critical points either iterate to an attracting cycle or infinity. For
polynomial skew products, Jonsson (Math. Ann., 1999) established that f is
Axiom A if and only if the closure of the postcritical set is disjoint from the
right analog of the Julia set. Here we present the analogous conclusion:
critical orbits either escape to infinity or accumulate on an attracting set.
In addition, we construct new examples of Axiom A maps demonstrating various
postcritical behaviors.
|
2e248860-eee7-4ae1-8b39-02a12b66264c | 2e248860-eee7-4ae1-8b39-02a12b66264c | 2e248860-eee7-4ae1-8b39-02a12b66264c | human | null | null | none | abstracts | Search for gravitational-wave bursts in LIGO data from the fourth
science run | null | The fourth science run of the LIGO and GEO 600 gravitational-wave detectors,
carried out in early 2005, collected data with significantly lower noise than
previous science runs. We report on a search for short-duration
gravitational-wave bursts with arbitrary waveform in the 64-1600 Hz frequency
range appearing in all three LIGO interferometers. Signal consistency tests,
data quality cuts, and auxiliary-channel vetoes are applied to reduce the rate
of spurious triggers. No gravitational-wave signals are detected in 15.5 days
of live observation time; we set a frequentist upper limit of 0.15 per day (at
90% confidence level) on the rate of bursts with large enough amplitudes to be
detected reliably. The amplitude sensitivity of the search, characterized using
Monte Carlo simulations, is several times better than that of previous
searches. We also provide rough estimates of the distances at which
representative supernova and binary black hole merger signals could be detected
with 50% efficiency by this analysis.
|
a0b2de8e-eab1-43e8-810f-62785f143304 | a0b2de8e-eab1-43e8-810f-62785f143304 | a0b2de8e-eab1-43e8-810f-62785f143304 | human | null | null | none | abstracts | Spectroscopy of Nine Cataclysmic Variable Stars | null | We present optical spectroscopy of nine cataclysmic binary stars, mostly
dwarf novae, obtained primarily to determine orbital periods Porb. The stars
and their periods are LX And, 0.1509743(5) d; CZ Aql, 0.2005(6) d; LU Cam,
0.1499686(4) d; GZ Cnc, 0.0881(4) d; V632 Cyg, 0.06377(8) d; V1006 Cyg,
0.09903(9) d; BF Eri, 0.2708804(4) d; BI Ori, 0.1915(5) d; and FO Per, for
which Porb is either 0.1467(4) or 0.1719(5) d.
Several of the stars proved to be especially interesting. In BF Eri, we
detect the absorption spectrum of a secondary star of spectral type K3 +- 1
subclass, which leads to a distance estimate of approximately 1 kpc. However,
BF Eri has a large proper motion (100 mas/yr), and we have a preliminary
parallax measurement that confirms the large proper motion and yields only an
upper limit for the parallax. BF Eri's space velocity is evidently large, and
it appears to belong to the halo population. In CZ Aql, the emission lines have
strong wings that move with large velocity amplitude, suggesting a
magnetically-channeled accretion flow. The orbital period of V1006 Cyg places
it squarely within the 2- to 3-hour "gap" in the distribution of cataclysmic
binary orbital periods.
|
2e666ce0-d6d9-4870-9892-2d48c79545a7 | 2e666ce0-d6d9-4870-9892-2d48c79545a7 | 2e666ce0-d6d9-4870-9892-2d48c79545a7 | human | null | null | none | abstracts | Displacement of the Sun from the Galactic Plane | null | We have carried out a comparative statistical study for the displacement of
the Sun from the Galactic plane (z_\odot) following three different methods.
The study has been done using a sample of 537 young open clusters (YOCs) with
log(Age) < 8.5 lying within a heliocentric distance of 4 kpc and 2030 OB stars
observed up to a distance of 1200 pc, all of them have distance information. We
decompose the Gould Belt's member in a statistical sense before investigating
the variation in the z_\odot estimation with different upper cut-off limits in
the heliocentric distance and distance perpendicular to the Galactic plane. We
found z_\odot varies in a range of ~ 13 - 20 pc from the analys is of YOCs and
~ 6 - 18 pc from the OB stars. A significant scatter in the z_\odot obtained
due to different cut-off values is noticed for the OB stars although no such
deviation is seen for the YOCs. We also determined scale heights of
56.9(+3.8)(-3.4} and 61.4(+2.7)(-2.4) pc for the distribution of YOCs and OB
stars respectively.
|
a6621755-5a92-43f3-afe7-60bc7b182968 | a6621755-5a92-43f3-afe7-60bc7b182968 | a6621755-5a92-43f3-afe7-60bc7b182968 | human | null | null | none | abstracts | Correlation amplitude and entanglement entropy in random spin chains | null | Using strong-disorder renormalization group, numerical exact diagonalization,
and quantum Monte Carlo methods, we revisit the random antiferromagnetic XXZ
spin-1/2 chain focusing on the long-length and ground-state behavior of the
average time-independent spin-spin correlation function C(l)=\upsilon
l^{-\eta}. In addition to the well-known universal (disorder-independent)
power-law exponent \eta=2, we find interesting universal features displayed by
the prefactor \upsilon=\upsilon_o/3, if l is odd, and \upsilon=\upsilon_e/3,
otherwise. Although \upsilon_o and \upsilon_e are nonuniversal (disorder
dependent) and distinct in magnitude, the combination \upsilon_o + \upsilon_e =
-1/4 is universal if C is computed along the symmetric (longitudinal) axis. The
origin of the nonuniversalities of the prefactors is discussed in the
renormalization-group framework where a solvable toy model is considered.
Moreover, we relate the average correlation function with the average
entanglement entropy, whose amplitude has been recently shown to be universal.
The nonuniversalities of the prefactors are shown to contribute only to surface
terms of the entropy. Finally, we discuss the experimental relevance of our
results by computing the structure factor whose scaling properties,
interestingly, depend on the correlation prefactors.
|
798b66e9-488a-4322-a4c1-925889ef3659 | 798b66e9-488a-4322-a4c1-925889ef3659 | 798b66e9-488a-4322-a4c1-925889ef3659 | human | null | null | none | abstracts | SIM PlanetQuest: The Most Promising Near-Term Technique to Detect, Find
Masses, and Determine Three-Dimensional Orbits of Nearby Habitable Planets | null | The past two Decadal Surveys in Astronomy and Astrophysics recommended the
completion of a space-based interferometry mission, known today as SIM
PlanetQuest, for its unique ability to detect and characterize nearby rocky
planets (Bahcall 1991, McKee & Taylor 2001), as well as contributions to a
broad range of problems in astrophysics. Numerous committees of the National
Research Council as well as NASA Roadmaps have similarly highlighted SIM as the
one technology that offers detection and characterization of rocky planets
around nearby stars and which is technically ready. To date, SIM remains the
only program with the capability of detecting and confirming rocky planets in
the habitable zones of nearby solar-type stars. Moreover, SIM measures masses
and three-dimensional orbits of habitable planets around nearby stars (within
25 pc); these are the only stars for which follow-up by other techniques is
feasible, such as space-based spectroscopy, ground-based interferometry, and of
course TPF.
|
0b000c89-9ab5-4747-a4cb-6c71aaca9416 | 0b000c89-9ab5-4747-a4cb-6c71aaca9416 | 0b000c89-9ab5-4747-a4cb-6c71aaca9416 | human | null | null | none | abstracts | IR observations of MS 1054-03: Star Formation and its Evolution in Rich
Galaxy Clusters | null | We study the infrared (IR) properties of galaxies in the cluster MS 1054-03
at z=0.83 by combining MIPS 24 micron data with spectra of more than 400
galaxies and a very deep K-band selected catalog. 19 IR cluster members are
selected spectroscopically, and an additional 15 are selected by their
photometric redshifts. We derive the IR luminosity function of the cluster and
find strong evolution compared to the similar-mass Coma cluster. The best
fitting Schechter function gives L*_{IR}=11.49 +0.30/-0.29 L_sun with a fixed
faint end slope, about one order of magnitude larger than that in Coma. The
rate of evolution of the IR luminosity from Coma to MS 1054-03 is consistent
with that found in field galaxies, and it suggests that some internal
mechanism, e.g., the consumption of the gas fuel, is responsible for the
general decline of the cosmic star formation rate (SFR) in different
environments. The mass-normalized integrated SFR within 0.5R_200 in MS 1054-03
also shows evolution compared with other rich clusters at lower redshifts, but
the trend is less conclusive if the mass selection effect is considered. A
nonnegligible fraction (13%) of cluster members, are forming stars actively and
the overdensity of IR galaxies is about 20 compared to the field. It is
unlikely that clusters only passively accrete star forming galaxies from the
surrounding fields and have their star formation quenched quickly afterward;
instead, many cluster galaxies still have large amounts of gas, and their star
formation may be enhanced by the interaction with the cluster.
|
a7518a2e-6abd-429e-884f-5130aeff7836 | a7518a2e-6abd-429e-884f-5130aeff7836 | a7518a2e-6abd-429e-884f-5130aeff7836 | human | null | null | none | abstracts | Charges from Attractors | null | We describe how to recover the quantum numbers of extremal black holes from
their near horizon geometries. This is achieved by constructing the
gravitational Noether-Wald charges which can be used for non-extremal black
holes as well. These charges are shown to be equivalent to the U(1) charges of
appropriately dimensionally reduced solutions. Explicit derivations are
provided for 10 dimensional type IIB supergravity and 5 dimensional minimal
gauged supergravity, with illustrative examples for various black hole
solutions. We also discuss how to derive the thermodynamic quantities and their
relations explicitly in the extremal limit, from the point of view of the
near-horizon geometry. We relate our results to the entropy function formalism.
|
6afb1ab2-6bb5-4e5c-8262-053a42b5e263 | 6afb1ab2-6bb5-4e5c-8262-053a42b5e263 | 6afb1ab2-6bb5-4e5c-8262-053a42b5e263 | human | null | null | none | abstracts | One-dimensional Brownian particle systems with rank dependent drifts | null | We study interacting systems of linear Brownian motions whose drift vector at
every time point is determined by the relative ranks of the coordinate
processes at that time. Our main objective has been to study the long range
behavior of the spacings between the Brownian motions arranged in increasing
order. For finitely many Brownian motions interacting in this manner, we
characterize drifts for which the family of laws of the vector of spacings is
tight, and show its convergence to a unique stationary joint distribution given
by independent exponential distributions with varying means. We also study one
particular countably infinite system, where only the minimum Brownian particle
gets a constant upward drift, and prove that independent and identically
distributed exponential spacings remain stationary under the dynamics of such a
process. Some related conjectures in this direction have also been discussed.
|
fdb57084-1660-4a18-bb3a-ee0fa874001f | fdb57084-1660-4a18-bb3a-ee0fa874001f | fdb57084-1660-4a18-bb3a-ee0fa874001f | human | null | null | none | abstracts | Generating Squeezed States of Nanomechanical Resonator | null | We propose a scheme for generating squeezed states in solid state circuits
consisting of a nanomechanical resonator (NMR), a superconducting Cooper-pair
box (CPB) and a superconducting transmission line resonator (STLR). The
nonlinear interaction between the NMR and the STLR can be implemented by
setting the external biased flux of the CPB at certain values. The interaction
Hamiltonian between the NMR and the STLR is derived by performing Fr$\rm\ddot
o$hlich transformation on the total Hamiltonian of the combined system. Just by
adiabatically keeping the CPB at the ground state, we get the standard
parametric down-conversion Hamiltonian. The CPB plays the role of ``nonlinear
media", and the squeezed states of the NMR can be easily generated in a manner
similar to the three-wave mixing in quantum optics. This is the three-wave
mixing in a solid-state circuit.
|
7688cd06-d707-4388-a109-30b28abe2a1e | 7688cd06-d707-4388-a109-30b28abe2a1e | 7688cd06-d707-4388-a109-30b28abe2a1e | human | null | null | none | abstracts | On the orbital period of the magnetic Cataclysmic Variable HS 0922+1333 | null | Context: The object HS 0922+1333 was visited briefly in 2002 in a mini survey
of low accretion rate polars (LARPs) in order to test if they undergo high
luminosity states similar to ordinary polars. On the basis of that short
observation the suspicion arose that the object might be an asynchronous polar
(Tovmassian et al. 2004). The disparity between the presumed orbital and spin
period appeared to be quite unusual. Aims: We performed follow-up observations
of the object to resolve the problem. Methods: New simultaneous spectroscopic
and photometric observations spanning several years allowed measurements of
radial velocities of emission and absorption lines from the secondary star and
brightness variations due to synchrotron emission from the primary. Results:
New observations show that the object is actually synchronous and its orbital
and spin period are equal to 4.04 hours. Conclusions: We identify the source of
confusion of previous observations to be a high velocity component of emission
line arousing from the stream of matter leaving L1 point.
|
4118ea7e-d99b-4555-bfca-d2b63105db9b | 4118ea7e-d99b-4555-bfca-d2b63105db9b | 4118ea7e-d99b-4555-bfca-d2b63105db9b | human | null | null | none | abstracts | Nova Geminorum 1912 and the Origin of the Idea of Gravitational Lensing | null | Einstein's early calculations of gravitational lensing, contained in a
scratch notebook and dated to the spring of 1912, are reexamined. A hitherto
unknown letter by Einstein suggests that he entertained the idea of explaining
the phenomenon of new stars by gravitational lensing in the fall of 1915 much
more seriously than was previously assumed. A reexamination of the relevant
calculations by Einstein shows that, indeed, at least some of them most likely
date from early October 1915. But in support of earlier historical
interpretation of Einstein's notes, it is argued that the appearance of Nova
Geminorum 1912 (DN Gem) in March 1912 may, in fact, provide a relevant context
and motivation for Einstein's lensing calculations on the occasion of his first
meeting with Erwin Freundlich during a visit in Berlin in April 1912. We also
comment on the significance of Einstein's consideration of gravitational
lensing in the fall of 1915 for the reconstruction of Einstein's final steps in
his path towards general relativity.
|
8ad1eac1-91a5-42af-b5a4-19c9be3b0221 | 8ad1eac1-91a5-42af-b5a4-19c9be3b0221 | 8ad1eac1-91a5-42af-b5a4-19c9be3b0221 | human | null | null | none | abstracts | Upper bounds on entangling rates of bipartite Hamiltonians | null | We discuss upper bounds on the rate at which unitary evolution governed by a
non-local Hamiltonian can generate entanglement in a bipartite system. Given a
bipartite Hamiltonian H coupling two finite dimensional particles A and B, the
entangling rate is shown to be upper bounded by c*log(d)*norm(H), where d is
the smallest dimension of the interacting particles, norm(H) is the operator
norm of H, and c is a constant close to 1. Under certain restrictions on the
initial state we prove analogous upper bound for the ancilla-assisted
entangling rate with a constant c that does not depend upon dimensions of local
ancillas. The restriction is that the initial state has at most two distinct
Schmidt coefficients (each coefficient may have arbitrarily large
multiplicity). Our proof is based on analysis of a mixing rate -- a functional
measuring how fast entropy can be produced if one mixes a time-independent
state with a state evolving unitarily.
|
fbeabbea-9239-440f-ad71-2fa4f2ea8176 | fbeabbea-9239-440f-ad71-2fa4f2ea8176 | fbeabbea-9239-440f-ad71-2fa4f2ea8176 | human | null | null | none | abstracts | Cluster properties from two-particle angular correlations in p+p
collisions at $\sqrt{s}$ = 200 and 410 GeV | null | We present results on two-particle angular correlations in proton-proton
collisions at center of mass energies of 200 and 410 GeV. The PHOBOS experiment
at the Relativistic Heavy Ion Collider has a uniquely large coverage for
charged particles, giving the opportunity to explore the correlations at both
short- and long-range scales. At both energies, a complex two-dimensional
correlation structure in $\Delta \eta$ and $\Delta \phi$ is observed. In the
context of an independent cluster model of short-range correlations, the
cluster size and its decay width are extracted from the two-particle
pseudorapidity correlation function and compared with previous measurements in
proton-proton and proton-antiproton collisions, as well as PYTHIA and HIJING
predictions.
|
1c3d632d-f38d-4ff2-9543-9e4935a10030 | 1c3d632d-f38d-4ff2-9543-9e4935a10030 | 1c3d632d-f38d-4ff2-9543-9e4935a10030 | human | null | null | none | abstracts | Cross-Layer Optimization of MIMO-Based Mesh Networks with Gaussian
Vector Broadcast Channels | null | MIMO technology is one of the most significant advances in the past decade to
increase channel capacity and has a great potential to improve network capacity
for mesh networks. In a MIMO-based mesh network, the links outgoing from each
node sharing the common communication spectrum can be modeled as a Gaussian
vector broadcast channel. Recently, researchers showed that ``dirty paper
coding'' (DPC) is the optimal transmission strategy for Gaussian vector
broadcast channels. So far, there has been little study on how this fundamental
result will impact the cross-layer design for MIMO-based mesh networks. To fill
this gap, we consider the problem of jointly optimizing DPC power allocation in
the link layer at each node and multihop/multipath routing in a MIMO-based mesh
networks. It turns out that this optimization problem is a very challenging
non-convex problem. To address this difficulty, we transform the original
problem to an equivalent problem by exploiting the channel duality. For the
transformed problem, we develop an efficient solution procedure that integrates
Lagrangian dual decomposition method, conjugate gradient projection method
based on matrix differential calculus, cutting-plane method, and subgradient
method. In our numerical example, it is shown that we can achieve a network
performance gain of 34.4% by using DPC.
|
449e36b0-6293-4f1e-be80-f2bcd4bf074f | 449e36b0-6293-4f1e-be80-f2bcd4bf074f | 449e36b0-6293-4f1e-be80-f2bcd4bf074f | human | null | null | none | abstracts | D0-anti-D0 Mixing and CP Violation in D0 vs anti-D0 to K*(+-) K(-+)
Decays | null | The noteworthy BaBar and Belle evidence for $D^0$-$\bar{D}^0$ mixing
motivates us to study its impact on $D^0\to K^{*\pm} K^\mp$ decays and their
CP-conjugate processes. We show that both the $D^0$-$\bar{D}^0$ mixing
parameters ($x$ and $y$) and the strong phase difference between $\bar{D}^0\to
K^{*\pm}K^\mp$ and $D^0\to K^{*\pm}K^\mp$ transitions ($\delta$) can be
determined or constrained from the time-dependent measurements of these decay
modes. On the $\psi (3770)$ and $\psi (4140)$ resonances at a $\tau$-charm
factory, it is even possible to determine or constrain $x$, $y$ and $\delta$
from the time-independent measurements of coherent $(D^0\bar{D}^0) \to
(K^{*\pm} K^\mp)(K^{*\pm} K^\mp)$ decays. If the CP-violating phase of
$D^0$-$\bar{D}^0$ mixing is significant in a scenario beyond the standard
model, it can also be extracted from the $K^{*\pm} K^\mp$ events.
|
0bdd5d62-6ec3-4ff3-9748-8e99acff89d4 | 0bdd5d62-6ec3-4ff3-9748-8e99acff89d4 | 0bdd5d62-6ec3-4ff3-9748-8e99acff89d4 | human | null | null | none | abstracts | X-ray Timing Observations of PSR J1930+1852 in the Crab-like SNR
G54.1+0.3 | null | We present new X-ray timing and spectral observations of PSR J1930+1852, the
young energetic pulsar at the center of the non-thermal supernova remnant
G54.1+0.3. Using data obtained with the Rossi X-ray Timing Explorer and Chandra
X-ray observatories we have derived an updated timing ephemeris of the 136 ms
pulsar spanning 6 years. During this interval, however, the period evolution
shows significant variability from the best fit constant spin-down rate of
$\dot P = 7.5112(6) \times 10^{-13}$ s s$^{-1}$, suggesting strong timing noise
and/or glitch activity. The X-ray emission is highly pulsed ($71\pm5%$
modulation) and is characterized by an asymmetric, broad profile ($\sim 70%$
duty cycle) which is nearly twice the radio width. The spectrum of the pulsed
emission is well fitted with an absorbed power law of photon index $\Gamma =
1.2\pm0.2$; this is marginally harder than that of the unpulsed component. The
total 2-10 keV flux of the pulsar is $1.7 \times 10^{-12}$ erg cm$^{-2}$
s$^{-1}$. These results confirm PSR J1930+1852 as a typical Crab-like pulsar.
|
56bec242-813a-4ff4-893f-06e972a4a103 | 56bec242-813a-4ff4-893f-06e972a4a103 | 56bec242-813a-4ff4-893f-06e972a4a103 | human | null | null | none | abstracts | A Topological Glass | null | We propose and study a model with glassy behavior. The state space of the
model is given by all triangulations of a sphere with $n$ nodes, half of which
are red and half are blue. Red nodes want to have 5 neighbors while blue ones
want 7. Energies of nodes with different numbers of neighbors are supposed to
be positive. The dynamics is that of flipping the diagonal of two adjacent
triangles, with a temperature dependent probability. We show that this system
has an approach to a steady state which is exponentially slow, and show that
the stationary state is unordered. We also study the local energy landscape and
show that it has the hierarchical structure known from spin glasses. Finally,
we show that the evolution can be described as that of a rarefied gas with
spontaneous generation of particles and annihilating collisions.
|
2bdb8f4e-52aa-4b27-a8a9-92ec312ecaa4 | 2bdb8f4e-52aa-4b27-a8a9-92ec312ecaa4 | 2bdb8f4e-52aa-4b27-a8a9-92ec312ecaa4 | human | null | null | none | abstracts | Anomalous pressure behavior of tangential modes in single-wall carbon
nanotubes | null | Using the molecular dynamics simulations and the force constant model we have
studied the Raman-active tangential modes (TMs) of a (10, 0) single-wall carbon
nanotube (SWNT) under hydrostatic pressure. With increasing pressure, the
atomic motions in the three TMs present obvious diversities. The pressure
derivative of E1g, A1g, and E2g mode frequency shows an increased value (), a
constant value (), and a negative value () above 5.3 GPa, respectively. The
intrinsic characteristics of TMs consumedly help to understand the essence of
the experimental T band of CNT. The anomalous pressure behavior of the TMs
frequencies may be originated from the tube symmetry alteration from D10h to
D2h then to C2h.
|
8c248a04-dd3e-42bd-9218-b9a24ca16e09 | 8c248a04-dd3e-42bd-9218-b9a24ca16e09 | 8c248a04-dd3e-42bd-9218-b9a24ca16e09 | human | null | null | none | abstracts | Distribution of the molecular absorption in front of the quasar
B0218+357 | null | The line of sight to the quasar B0218+357, one of the most studied lensed
systems, intercepts a z=0.68 spiral galaxy, which splits its image into two
main components A and B, separated by ca. 0.3'', and gives rise to molecular
absorption. Although the main absorption component has been shown to arise in
front of image A, it is not established whether some absorption from other
velocity components is also occuring in front of image B. To tackle this
question, we have observed the HCO+(2-1) absorption line during the
commissioning phase of the new very extended configuration of the Plateau de
Bure Interferometer, in order to trace the position of the absorption as a
function of frequency. Visibility fitting of the self-calibrated data allowed
us to achieve position accuracy between ~12 and 80 mas per velocity component.
Our results clearly demonstrate that all the different velocity components of
the HCO+(2-1) absorption arise in front of the south-west image A of the
quasar. We estimate a flux ratio fA/fB = 4.2 (-1.0;+1.8 at 106 GHz.
|
81597f90-e8c6-4625-981f-051095804a8e | 81597f90-e8c6-4625-981f-051095804a8e | 81597f90-e8c6-4625-981f-051095804a8e | human | null | null | none | abstracts | Daemons and DAMA: Their Celestial-Mechanics Interrelations | null | The assumption of the capture by the Solar System of the electrically charged
Planckian DM objects (daemons) from the galactic disk is confirmed not only by
the St.Petersburg (SPb) experiments detecting particles with V<30 km/s. Here
the daemon approach is analyzed considering the positive model independent
result of the DAMA/NaI experiment. We explain the maximum in DAMA signals
observed in the May-June period to be associated with the formation behind the
Sun of a trail of daemons that the Sun captures into elongated orbits as it
moves to the apex. The range of significant 2-6-keV DAMA signals fits well the
iodine nuclei elastically knocked out of the NaI(Tl) scintillator by particles
falling on the Earth with V=30-50 km/s from strongly elongated heliocentric
orbits. The half-year periodicity of the slower daemons observed in SPb
originates from the transfer of particles that are deflected through ~90 deg
into near-Earth orbits each time the particles cross the outer reaches of the
Sun which had captured them. Their multi-loop (cross-like) trajectories
traverse many times the Earth's orbit in March and September, which increases
the probability for the particles to enter near-Earth orbits during this time.
Corroboration of celestial mechanics calculations with observations yields
~1e-19 cm2 for the cross section of daemon interaction with the solar matter.
|
d4a42c7c-cb1c-4bb7-848e-bdd87e58841d | d4a42c7c-cb1c-4bb7-848e-bdd87e58841d | d4a42c7c-cb1c-4bb7-848e-bdd87e58841d | human | null | null | none | abstracts | Architecture for Pseudo Acausal Evolvable Embedded Systems | null | Advances in semiconductor technology are contributing to the increasing
complexity in the design of embedded systems. Architectures with novel
techniques such as evolvable nature and autonomous behavior have engrossed lot
of attention. This paper demonstrates conceptually evolvable embedded systems
can be characterized basing on acausal nature. It is noted that in acausal
systems, future input needs to be known, here we make a mechanism such that the
system predicts the future inputs and exhibits pseudo acausal nature. An
embedded system that uses theoretical framework of acausality is proposed. Our
method aims at a novel architecture that features the hardware evolability and
autonomous behavior alongside pseudo acausality. Various aspects of this
architecture are discussed in detail along with the limitations.
|
c5eb1d39-ab24-4540-8cac-8d8ff02e15bd | c5eb1d39-ab24-4540-8cac-8d8ff02e15bd | c5eb1d39-ab24-4540-8cac-8d8ff02e15bd | human | null | null | none | abstracts | On reference frames in spacetime and gravitational energy in freely
falling frames | null | We consider the interpretation of tetrad fields as reference frames in
spacetime. Reference frames may be characterized by an antisymmetric
acceleration tensor, whose components are identified as the inertial
accelerations of the frame (the translational acceleration and the frequency of
rotation of the frame). This tensor is closely related to
gravitoelectromagnetic field quantities. We construct the set of tetrad fields
adapted to observers that are in free fall in the Schwarzschild spacetime, and
show that the gravitational energy-momentum constructed out of this set of
tetrad fields, in the framework of the teleparallel equivalent of general
relatrivity, vanishes. This result is in agreement with the principle of
equivalence, and may be taken as a condition for a viable definition of
gravitational energy.
|
8033f19b-2773-4e5e-87cf-50099d46901d | 8033f19b-2773-4e5e-87cf-50099d46901d | 8033f19b-2773-4e5e-87cf-50099d46901d | human | null | null | none | abstracts | A kind of prediction from string phenomenology: extra matter at low
energy | null | We review the possibility that the Supersymmetric Standard Model arises from
orbifold constructions of the E_8 x E_8 Heterotic Superstring, and the
phenomenological properties that such a model should have. In particular,
trying to solve the discrepancy between the unification scale predicted by the
Heterotic Superstring (g_{GUT}x5.27x10^{17} GeV) and the value deduced from LEP
experiments (2x10^{16} GeV), we will predict the presence at low energies of
three families of Higgses and vector-like colour triplets. Our approach relies
on the Fayet-Iliopoulos breaking, and this is also a crucial ingredient,
together with having three Higgs families, to obtain in these models an
interesting pattern of fermion masses and mixing angles at the renormalizable
lebel. Namely, after the gauge breaking some physical particles appear combined
with other states, and the Yukawa couplings are modified in a well controlled
way. On the other hand, dangerous flavour-changing neutral currents may appear
when fermions of a given charge receive their mass through couplings with
several Higgs doublets. We will address this potential problem, finding that
viable scenarios can be obtained for a reasonable light Higgs spectrum.
|
57f30c79-1f7c-47c5-851a-9e05e44d4acc | 57f30c79-1f7c-47c5-851a-9e05e44d4acc | 57f30c79-1f7c-47c5-851a-9e05e44d4acc | human | null | null | none | abstracts | Dynamics of Size-Selected Gold Nanoparticles Studied by Ultrafast
Electron Nanocrystallography | null | We report the studies of ultrafast electron nanocrystallography on
size-selected Au nanoparticles (2-20 nm) supported on a molecular interface.
Reversible surface melting, melting, and recrystallization were investigated
with dynamical full-profile radial distribution functions determined with
sub-picosecond and picometer accuracies. In an ultrafast photoinduced melting,
the nanoparticles are driven to a non-equilibrium transformation, characterized
by the initial lattice deformations, nonequilibrium electron-phonon coupling,
and upon melting, the collective bonding and debonding, transforming
nanocrystals into shelled nanoliquids. The displasive structural excitation at
premelting and the coherent transformation with crystal/liquid coexistence
during photomelting differ from the reciprocal behavior of recrystallization,
where a hot lattice forms from liquid and then thermally contracts. The degree
of structural change and the thermodynamics of melting are found to depend on
the size of nanoparticle.
|
e9c2350b-ea88-4394-b5d2-943b9f2561fa | e9c2350b-ea88-4394-b5d2-943b9f2561fa | e9c2350b-ea88-4394-b5d2-943b9f2561fa | human | null | null | none | abstracts | Composite Structure and Causality | null | We study the question of whether a composite structure of elementary
particles, with a length scale $1/\Lambda$, can leave observable effects of
non-locality and causality violation at higher energies (but $\lesssim
\Lambda$). We formulate a model-independent approach based on
Bogoliubov-Shirkov formulation of causality. We analyze the relation between
the fundamental theory (of finer constituents) and the derived theory (of
composite particles). We assume that the fundamental theory is causal and
formulate a condition which must be fulfilled for the derived theory to be
causal. We analyze the condition and exhibit possibilities which fulfil and
which violate the condition. We make comments on how causality violating
amplitudes can arise.
|
83a2e41b-f32e-4afe-a690-74dee9b69663 | 83a2e41b-f32e-4afe-a690-74dee9b69663 | 83a2e41b-f32e-4afe-a690-74dee9b69663 | human | null | null | none | abstracts | Brane World Black Rings | null | Five dimensional neutral rotating black rings are described from a
Randall-Sundrum brane world perspective in the bulk black string framework. To
this end we consider a rotating black string extension of a five dimensional
black ring into the bulk of a six dimensional Randall-Sundrum brane world with
a single four brane. The bulk solution intercepts the four brane in a five
dimensional black ring with the usual curvature singularity on the brane. The
bulk geodesics restricted to the plane of rotation of the black ring are
constructed and their projections on the four brane match with the usual black
ring geodesics restricted to the same plane. The asymptotic nature of the bulk
geodesics are elucidated with reference to a bulk singularity at the AdS
horizon. We further discuss the description of a brane world black ring as a
limit of a boosted bulk black 2 brane with periodic identification.
|
cc3b67cb-5081-41d8-b808-9f596de7bb07 | cc3b67cb-5081-41d8-b808-9f596de7bb07 | cc3b67cb-5081-41d8-b808-9f596de7bb07 | human | null | null | none | abstracts | Measurement of D0-D0bar mixing in D0->Ks pi+ pi- decays | null | We report a measurement of D0-D0bar mixing in D0->Ks pi+ pi- decays using a
time-dependent Dalitz plot analysis. We first assume CP conservation and
subsequently allow for CP violation. The results are based on 540 fb$^{-1}$ of
data accumulated with the Belle detector at the KEKB $e^+e^-$ collider.
Assuming negligible CP violation, we measure the mixing parameters
$x=(0.80\pm0.29^{+0.09 +0.10}_{-0.07 -0.14})%$ and $y=(0.33\pm0.24^{+0.08
+0.06}_{-0.12 -0.08})%$, where the errors are statistical, experimental
systematic, and systematic due to the Dalitz decay model, respectively.
Allowing for CP violation, we obtain the $CPV$ parameters $|q/p|=0.86^{+0.30
+0.06}_{-0.29 -0.03}\pm0.08$ and $\arg(q/p)=(-14^{+16 +5 +2}_{-18 -3
-4})^\circ$.
|
9a3ebcf5-43a4-4e54-96ae-b62a815f7a12 | 9a3ebcf5-43a4-4e54-96ae-b62a815f7a12 | 9a3ebcf5-43a4-4e54-96ae-b62a815f7a12 | human | null | null | none | abstracts | Tautological relations in Hodge field theory | null | We propose a Hodge field theory construction that captures algebraic
properties of the reduction of Zwiebach invariants to Gromov-Witten invariants.
It generalizes the Barannikov-Kontsevich construction to the case of higher
genera correlators with gravitational descendants.
We prove the main theorem stating that algebraically defined Hodge field
theory correlators satisfy all tautological relations. From this perspective
the statement that Barannikov-Kontsevich construction provides a solution of
the WDVV equation looks as the simplest particular case of our theorem. Also it
generalizes the particular cases of other low-genera tautological relations
proven in our earlier works; we replace the old technical proofs by a novel
conceptual proof.
|
51998be9-8dd8-45b6-ad29-fc6ab300ab6c | 51998be9-8dd8-45b6-ad29-fc6ab300ab6c | 51998be9-8dd8-45b6-ad29-fc6ab300ab6c | human | null | null | none | abstracts | SBF: multi-wavelength data and models | null | Recent applications have proved that the Surface Brightness Fluctuations
(SBF) technique is a reliable distance indicator in a wide range of distances,
and a promising tool to analyze the physical and chemical properties of
unresolved stellar systems, in terms of their metallicity and age. We present
the preliminary results of a project aimed at studying the evolutionary
properties and distance of the stellar populations in external galaxies based
on the SBF method.
On the observational side, we have succeeded in detecting I-band SBF
gradients in six bright ellipticals imaged with the ACS, for these same objects
we are now presenting also B-band SBF data. These B-band data are the first
fluctuations magnitude measurements for galaxies beyond 10 Mpc.
To analyze the properties of stellar populations from the data, accurate SBF
models are essential. As a part of this project, we have evaluated SBF
magnitudes from Simple Stellar Population (SSP) models specifically optimized
for the purpose. A wide range of chemical compositions and ages, as well as
different choices of the photometric system have been investigated. All models
are available at the Teramo-Stellar Populations Tools web site:
www.oa-teramo.inaf.it/SPoT.
|
6c11c490-520e-4a4b-a90b-8c2f2613300c | 6c11c490-520e-4a4b-a90b-8c2f2613300c | 6c11c490-520e-4a4b-a90b-8c2f2613300c | human | null | null | none | abstracts | Simulating CCD images of elliptical galaxies | null | We introduce a procedure developed by the ``Teramo Stellar Populations
Tools'' group (Teramo-SPoT), specifically optimized to obtain realistic
simulations of CCD images of elliptical galaxies.
Particular attention is devoted to include the Surface Brightness Fluctuation
(SBF) signal observed in ellipticals and to simulate the Globular Cluster (GC)
system in the galaxy, and the distribution of background galaxies present in
real CCD frames. In addition to the physical properties of the simulated
objects - galaxy distance and brightness profile, luminosity function of GC and
background galaxies, etc. - the tool presented allows the user to set some of
the main instrumental properties - FoV, zero point magnitude, exposure time,
etc.
|
df43c86c-b20c-409d-a3f4-a1ab6ebde436 | df43c86c-b20c-409d-a3f4-a1ab6ebde436 | df43c86c-b20c-409d-a3f4-a1ab6ebde436 | human | null | null | none | abstracts | Transient Dynamics of Sparsely Connected Hopfield Neural Networks with
Arbitrary Degree Distributions | null | Using probabilistic approach, the transient dynamics of sparsely connected
Hopfield neural networks is studied for arbitrary degree distributions. A
recursive scheme is developed to determine the time evolution of overlap
parameters. As illustrative examples, the explicit calculations of dynamics for
networks with binomial, power-law, and uniform degree distribution are
performed. The results are good agreement with the extensive numerical
simulations. It indicates that with the same average degree, there is a gradual
improvement of network performance with increasing sharpness of its degree
distribution, and the most efficient degree distribution for global storage of
patterns is the delta function.
|
c9eb8e38-07d4-40f0-bc2d-daf351e63621 | c9eb8e38-07d4-40f0-bc2d-daf351e63621 | c9eb8e38-07d4-40f0-bc2d-daf351e63621 | human | null | null | none | abstracts | Unstable and Stable Galaxy Models | null | To determine the stability and instability of a given steady galaxy
configuration is one of the fundamental problems in the Vlasov theory for
galaxy dynamics. In this article, we study the stability of isotropic spherical
symmetric galaxy models $f_{0}(E)$, for which the distribution function $f_{0}$
depends on the particle energy $E$ only. In the first part of the article, we
derive the first sufficient criterion for linear instability of $f_{0}(E):$
$f_{0}(E)$ is linearly unstable if the second-order operator \[
A_{0}\equiv-\Delta+4\pi\int f_{0}^{\prime}(E)\{I-\mathcal{P}\}dv \] has a
negative direction, where $\mathcal{P}$ is the projection onto the function
space $\{g(E,L)\},$ $L$ being the angular momentum [see the explicit formula
(\ref{A0-radial})]. In the second part of the article, we prove that for the
important King model, the corresponding $A_{0}$ is positive definite. Such a
positivity leads to the nonlinear stability of the King model under all
spherically symmetric perturbations.
|
096fa0e1-6c99-4e81-8298-5d2c9c111ebc | 096fa0e1-6c99-4e81-8298-5d2c9c111ebc | 096fa0e1-6c99-4e81-8298-5d2c9c111ebc | human | null | null | none | abstracts | Phenomenological theory of spin excitations in La- and Y-based cuprates | null | Motivated by recent inelastic neutron scattering (INS) experiments on
La-based cuprates and based on the fermiology theories, we study the spin
susceptibility for La-based (e.g., La$_{2-x}$Sr$_x$CuO$_4$) and Y-based (e.g.,
YBa$_2$Cu$_3$O$_y$) cuprates, respectively. The spin excitation in
YBa$_2$Cu$_3$O$_y$ is dominated by a sharp resonance peak at the frequency 40
meV in the superconducting state. Below and above the resonance frequency, the
incommensurate (IC) peaks develop and the intensity of the peaks decreases
dramatically. In the normal state, the resonant excitation does not occur and
the IC peaks are merged into commensurate ones. The spin excitation of
La$_{2-x}$Sr$_x$CuO$_4$ is significantly different from that of Y-based ones,
namely, the resonance peak does not exist due to the decreasing of the
superconducting gap and the presence of the possible spin-stripe order. The
spectra are only enhanced at the expected resonance frequency (about 18 meV)
while it is still incommensurate. On the other hand, another frequency scale at
the frequency 55 meV is also revealed, namely the spectra are commensurate and
local maximum at this frequency. We elaborate all the results based on the
Fermi surface topology and the d-wave superconductivity, and suggest that the
spin-stripe order be also important in determining the spin excitation of
La-based cuprates. A coherent picture for the spin excitations is presented for
Y-based and La-based cuprates.
|
0d39f525-6e8b-4caf-a84f-aa9c88f3eadd | 0d39f525-6e8b-4caf-a84f-aa9c88f3eadd | 0d39f525-6e8b-4caf-a84f-aa9c88f3eadd | human | null | null | none | abstracts | Magnetic susceptibility and specific heat of the spin-1/2 Heisenberg
model on the kagome lattice and experimental data on ZnCu3(OH)6Cl2 | null | We compute the magnetic susceptibility and specific heat of the spin-1/2
Heisenberg model on the kagome lattice with high-temperature expansions and
exact diagonalizations. We compare the results with the experimental data on
ZnCu3(OH)6Cl2 obtained by Helton et al. [Phys. Rev. Lett. 98, 107204 (2007)].
Down to k_BT/J~0.2, our calculations reproduce accurately the experimental
susceptibility, with an exchange interaction J~190K and a contribution of 3.7%
of weakly interacting impurity spins. The comparison between our calculations
of the specific heat and the experiments indicate that the low-temperature
entropy (below ~20K) is smaller in ZnCu3(OH)6Cl2 than in the kagome Heisenberg
model, a likely signature of other interactions in the system.
|
111b4c83-3774-4d39-957b-8591b776686a | 111b4c83-3774-4d39-957b-8591b776686a | 111b4c83-3774-4d39-957b-8591b776686a | human | null | null | none | abstracts | Environmental dielectric screening effect on exciton transition energies
in single-walled carbon nanotubes | null | Environmental dielectric screening effects on exciton transition energies in
single-walled carbon nanotubes (SWNTs) have been studied quantitatively in the
range of dielectric constants from 1.0 to 37 by immersing SWNTs bridged over
trenches in various organic solvents by means of photoluminescence and the
excitation spectroscopies. With increasing environmental dielectric constant
($\epsilon_{\rm env}$), both $E_{11}$ and $E_{22}$ exhibited a redshift by
several tens meV and a tendency to saturate at a $\epsilon_{\rm env} \sim 5$
without an indication of significant ($n$,$m$) dependence. The redshifts can be
explained by dielectric screening of the repulsive electron-electron
interaction. The $\epsilon_{\rm env}$ dependence of $E_{11}$ and $E_{22}$ can
be expressed by a simple empirical equation with a power law in $\epsilon_{\rm
env}$, $E_{\rm ii} = E_{\rm ii}^{\infty} + A\epsilon_{\rm env}^{-\alpha}$. We
also immersed a sample in sodium-dodecyl-sulfate (SDS) solution to investigate
the effects of wrapping SWNTs with surfactant. The resultant $E_{11}$ and
$E_{22}$, which agree well with Weisman's data [Nano Lett. {\bf 3}, 1235
(2003)], are close to those of $\epsilon_{\rm env}$ of 2. However, in addition
to the shift due to dielectric screening, another shift was observed so that
the ($2n+m$)-family patterns spread more widely, similar to that of the
uniaxial-stress-induced shift.
|
202eb47a-b071-41b8-9023-6bf03d69ab2c | 202eb47a-b071-41b8-9023-6bf03d69ab2c | 202eb47a-b071-41b8-9023-6bf03d69ab2c | human | null | null | none | abstracts | Cyclic cohomology of certain nuclear Fr\'echet and DF algebras | null | We give explicit formulae for the continuous Hochschild and cyclic homology
and cohomology of certain topological algebras. To this end we show that, for a
continuous morphism $\phi: \X\to \Y$ of complexes of complete nuclear
$DF$-spaces, the isomorphism of cohomology groups $H^n(\phi): H^n(\X) \to
H^n(\Y)$ is automatically topological. The continuous cyclic-type homology and
cohomology are described up to topological isomorphism for the following
classes of biprojective $\hat{\otimes}$-algebras: the tensor algebra $E
\hat{\otimes} F$ generated by the duality $(E, F, < \cdot, \cdot >)$ for
nuclear Fr\'echet spaces $E$ and $F$ or for nuclear $DF$-spaces $E$ and $F$;
nuclear biprojective K\"{o}the algebras $\lambda(P)$ which are Fr\'echet spaces
or $DF$-spaces; the algebra of distributions $\mathcal{E}^*(G)$ on a compact
Lie group $G$.
|
6755ed36-a02d-4771-8f55-fb60599915f5 | 6755ed36-a02d-4771-8f55-fb60599915f5 | 6755ed36-a02d-4771-8f55-fb60599915f5 | human | null | null | none | abstracts | The Effect of Annealing Temperature on Statistical Properties of $WO_3$
Surface | null | We have studied the effect of annealing temperature on the statistical
properties of $WO_3$ surface using atomic force microscopy techniques (AFM). We
have applied both level crossing and structure function methods. Level crossing
analysis indicates an optimum annealing temperature of around 400$^oC$ at which
the effective area of the $WO_3$ thin film is maximum, whereas composition of
the surface remains stoichiometric. The complexity of the height fluctuation of
surfaces was characterized by roughness, roughness exponent and lateral size of
surface features. We have found that there is a phase transition at around
400$^oC$ from one set to two sets of roughness parameters. This happens due to
microstructural changes from amorphous to crystalline structure in the samples
that has been already found experimentally.
|
8aad7dbe-25ba-4175-90d9-9d74e8ea93dc | 8aad7dbe-25ba-4175-90d9-9d74e8ea93dc | 8aad7dbe-25ba-4175-90d9-9d74e8ea93dc | human | null | null | none | abstracts | Determination of Low-Energy Parameters of Neutron--Proton Scattering on
the Basis of Modern Experimental Data from Partial-Wave Analyses | null | The triplet and singlet low-energy parameters in the effective-range
expansion for neutron--proton scattering are determined by using the latest
experimental data on respective phase shifts from the SAID nucleon--nucleon
database. The results differ markedly from the analogous parameters obtained on
the basis of the phase shifts of the Nijmegen group and contradict the
parameter values that are presently used as experimental ones. The values found
with the aid of the phase shifts from the SAID nucleon--nucleon database for
the total cross section for the scattering of zero-energy neutrons by protons,
$\sigma_{0}=20.426 $b, and the neutron--proton coherent scattering length,
$f=-3.755 $fm, agree perfectly with the experimental cross-section values
obtained by Houk, $\sigma_{0}=20.436\pm 0.023 $b, and experimental
scattering-length values obtained by Houk and Wilson, $f=-3.756\pm 0.009 $fm,
but they contradict cross-section values of $\sigma_{0}=20.491\pm 0.014 $b
according to Dilg and coherent-scattering-length values of $f=-3.7409\pm 0.0011
$fm according to Koester and Nistler.
|
f28e98bc-a408-4d16-b7a2-f348086c2673 | f28e98bc-a408-4d16-b7a2-f348086c2673 | f28e98bc-a408-4d16-b7a2-f348086c2673 | human | null | null | none | abstracts | $B_s^0 \to \eta^{(\prime)} \eta^{(\prime)}$ decays in the pQCD approach | null | We calculate the CP averaged branching ratios and CP-violating asymmetries
for $B_s^0 \to \eta \eta, \eta \eta^\prime$ and $\eta^\prime \eta^\prime$
decays in the perturbative QCD (pQCD) approach here. The pQCD predictions for
the CP-averaged branching ratios are $Br(B_s^0 \to \eta \eta) = \left
(14.2^{+18.0}_{-7.5}) \times 10^{-6}$, $Br(B_s^0 \to \eta \eta^\prime)= \left
(12.4 ^{+18.2}_{-7.0}) \times 10^{-6}$, and $Br(B_s^0 \to \eta^{\prime}
\eta^{\prime}) = \left (9.2^{+15.3}_{-4.9}) \times 10^{-6}$, which agree well
with those obtained by employing the QCD factorization approach and also be
consistent with available experimental upper limits. The gluonic contributions
are small in size: less than 7% for $B_s \to \eta \eta$ and $ \eta \eta^\prime$
decays, and around 18% for $B_s \to \eta' \eta'$ decay. The CP-violating
asymmetries for three decays are very small: less than 3% in magnitude.
|
b27bb403-479e-4cec-836a-0202e3e7d022 | b27bb403-479e-4cec-836a-0202e3e7d022 | b27bb403-479e-4cec-836a-0202e3e7d022 | human | null | null | none | abstracts | A neural network approach to ordinal regression | null | Ordinal regression is an important type of learning, which has properties of
both classification and regression. Here we describe a simple and effective
approach to adapt a traditional neural network to learn ordinal categories. Our
approach is a generalization of the perceptron method for ordinal regression.
On several benchmark datasets, our method (NNRank) outperforms a neural network
classification method. Compared with the ordinal regression methods using
Gaussian processes and support vector machines, NNRank achieves comparable
performance. Moreover, NNRank has the advantages of traditional neural
networks: learning in both online and batch modes, handling very large training
datasets, and making rapid predictions. These features make NNRank a useful and
complementary tool for large-scale data processing tasks such as information
retrieval, web page ranking, collaborative filtering, and protein ranking in
Bioinformatics.
|
ac96103a-e088-4701-b46f-b43691766d14 | ac96103a-e088-4701-b46f-b43691766d14 | ac96103a-e088-4701-b46f-b43691766d14 | human | null | null | none | abstracts | Anisotropic brane gravity with a confining potential | null | We consider an anisotropic brane world with Bianchi type I and V geometries
where the mechanism of confining the matter on the brane is through the use of
a confining potential. The resulting equations on the anisotropic brane are
modified by an extra term that may be interpreted as the x-matter, providing a
possible phenomenological explanation for the accelerated expansion of the
universe. We obtain the general solution of the field equations in an exact
parametric form for both Bianchi type I and V space-times. In the special case
of a Bianchi type I the solutions of the field equations are obtained in an
exact analytic form. Finally, we study the behavior of the observationally
important parameters.
|
2fd7fa08-3945-42cf-9761-2baf187205ea | 2fd7fa08-3945-42cf-9761-2baf187205ea | 2fd7fa08-3945-42cf-9761-2baf187205ea | human | null | null | none | abstracts | Maximal ball packings of symplectic-toric manifolds | null | Let M be a symplectic-toric manifold of dimension at least four. This paper
investigates the so called symplectic ball packing problem in the toral
equivariant setting. We show that the set of toric symplectic ball packings of
M admits the structure of a convex polytope. Previous work of the first author
shows that up to equivalence, only CP^1 x CP^1 and CP^2 admit density one
packings when n=2 and only CP^n admits density one packings when n>2. In
contrast, we show that for a fixed n>=2 and each r in (0, 1), there are
uncountably many inequivalent 2n-dimensional symplectic-toric manifolds with a
maximal toric packing of density r. This result follows from a general analysis
of how the densities of maximal packings change while varying a given
symplectic-toric manifold through a family of symplectic-toric manifolds that
are equivariantly diffeomorphic but not equivariantly symplectomorphic.
|
df00fff4-9459-4377-b885-cdc67b361ef6 | df00fff4-9459-4377-b885-cdc67b361ef6 | df00fff4-9459-4377-b885-cdc67b361ef6 | human | null | null | none | abstracts | Controlled collisions of a single atom and ion guided by movable
trapping potentials | null | We consider a system composed of a trapped atom and a trapped ion. The ion
charge induces in the atom an electric dipole moment, which attracts it with an
r^{-4} dependence at large distances. In the regime considered here, the
characteristic range of the atom-ion interaction is comparable or larger than
the characteristic size of the trapping potential, which excludes the
application of the contact pseudopotential. The short-range part of the
interaction is described in the framework of quantum-defect theory, by
introducing some short-range parameters, which can be related to the s-wave
scattering length. When the separation between traps is changed we observe
trap-induced shape resonances between molecular bound states and vibrational
states of the external trapping potential. Our analysis is extended to
quasi-one-dimensional geometries, when the scattering exhibit
confinement-induced resonances, similar to the ones studied before for
short-range interactions. For quasi-one-dimensional systems we investigate the
effects of coupling between the center of mass and relative motion, which
occurs for different trapping frequencies of atom and ion traps. Finally, we
show how the two types of resonances can be employed for quantum state control
and spectroscopy of atom-ion molecules.
|
23ae01ab-8fed-457d-99bd-5d94bb8a89d5 | 23ae01ab-8fed-457d-99bd-5d94bb8a89d5 | 23ae01ab-8fed-457d-99bd-5d94bb8a89d5 | human | null | null | none | abstracts | Counting BPS operators in N=4 SYM | null | The free field partition function for a generic U(N) gauge theory, where the
fundamental fields transform in the adjoint representation, is analysed in
terms of symmetric polynomial techniques. It is shown by these means how this
is related to the cycle polynomial for the symmetric group and how the large N
result may be easily recovered. Higher order corrections for finite N are also
discussed in terms of symmetric group characters. For finite N, the partition
function involving a single bosonic fundamental field is recovered and explicit
counting of multi-trace quarter BPS operators in free \N=4 super Yang Mills
discussed, including a general result for large N. The partition function for
BPS operators in the chiral ring of \N=4 super Yang Mills is analysed in terms
of plane partitions. Asymptotic counting of BPS primary operators with
differing R-symmetry charges is discussed in both free \N=4 super Yang Mills
and in the chiral ring. Also, general and explicit expressions are derived for
SU(2) gauge theory partition functions, when the fundamental fields transform
in the adjoint, for free field theory.
|
4aedfb22-f019-40be-a54c-f73df874f8ac | 4aedfb22-f019-40be-a54c-f73df874f8ac | 4aedfb22-f019-40be-a54c-f73df874f8ac | human | null | null | none | abstracts | On the Kolmogorov-Chaitin Complexity for short sequences | null | A drawback of Kolmogorov-Chaitin complexity (K) as a function from s to the
shortest program producing s is its noncomputability which limits its range of
applicability. Moreover, when strings are short, the dependence of K on a
particular universal Turing machine U can be arbitrary. In practice one can
approximate it by computable compression methods. However, such compression
methods do not always provide meaningful approximations--for strings shorter,
for example, than typical compiler lengths. In this paper we suggest an
empirical approach to overcome this difficulty and to obtain a stable
definition of the Kolmogorov-Chaitin complexity for short sequences.
Additionally, a correlation in terms of distribution frequencies was found
across the output of two models of abstract machines, namely unidimensional
cellular automata and deterministic Turing machine.
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