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arxiv_dataset-17001001.4712 | Tunneling and transmission resonances of a Dirac particle by a double
barrier
quant-ph
We calculate the tunneling process of a Dirac particle across two square
barriers separated a distance $d$, as well as the scattering by a double cusp
barrier where the centers of the cusps are separated a distance larger than
their screening lengths. Using the scattering matrix formalism, we obtain the
transmission and reflection amplitudes for the scattering processes of both
configurations. We show that, the presence of transmission resonances modifies
the Lorentizian shape of the energy resonances and induces the appearance of
additional maxima in the transmission coefficient in the range of energies
where transmission resonances occur. We calculate the Wigner time-delay and
show how their maxima depend on the position of the transmission resonance.
| arxiv topic:quant-ph |
arxiv_dataset-17011001.4812 | Inflation in Wess--Zumino Models
hep-ph
We show that a class of Wess--Zumino models lead to inflation in
supersymmetry and supergravity. This is due to the existence of a classically
flat direction generic to these models. The pseudomodulus that parametrizes
this flat direction is the inflaton and obtains a small mass due to either
one--loop or supergravity corrections giving rise to slow--roll inflation. At
the end of inflation, the fields roll to a supersymmetric vacuum that arises
from explicit R symmetry breaking.
| arxiv topic:hep-ph |
arxiv_dataset-17021001.4912 | Enriques manifolds
math.AG
Using the theory of hyperkahler manifolds, we generalize the notion of
Enriques surfaces to higher dimensions and construct several examples using
group actions on Hilbert schemes of points or moduli spaces of stable sheaves.
| arxiv topic:math.AG |
arxiv_dataset-17031001.5012 | Cross-Correlating Probes of Primordial Gravitational Waves
astro-ph.CO
One of the most promising ways of detecting primordial gravitational waves
generated during inflation is to observe B-modes of polarization, generated by
Thomson scattering after reionization, in the cosmic microwave background
(CMB). Large scale foregrounds though are expected to be a major systematic
issue, so -- in the event of a tentative detection -- an independent
confirmation of large scale gravitational waves would be most welcome. Previous
authors have suggested searching for the analogous mode of cosmic shear in weak
lensing surveys but have shown that the signal to noise of this mode is
marginal at best. This argument is reconsidered here, accounting for the
cross-correlations of the polarization and lensing B-modes. A lensing survey
can potentially strengthen the argument for a detection of primordial
gravitational waves, although it is unlikely to help constrain the amplitude of
the signal.
| arxiv topic:astro-ph.CO |
arxiv_dataset-17041001.5112 | Mixed Motives over $k[t]/{(t^{m+1})}$
math.AG
For a perfect field $k$, we construct a triangulated category of mixed
motives over $k[t]/{(t^{m+1})}$. The ext groups in this category are given by
higher Chow groups, and additive higher Chow groups.
| arxiv topic:math.AG |
arxiv_dataset-17051001.5212 | Spontaneous Symmetry Breaking and Nambu-Goldstone Bosons in Quantum
Many-Body Systems
hep-th cond-mat.quant-gas cond-mat.str-el hep-ph nucl-th
Spontaneous symmetry breaking is a general principle, that constitutes the
underlying concept of a vast number of physical phenomena ranging from
ferromagnetism and superconductivity in condensed matter physics to the Higgs
mechanism in the standard model of elementary particles. I focus on
manifestations of spontaneously broken symmetries in systems that are not
Lorentz invariant, which include both, nonrelativistic systems as well as
relativistic systems at nonzero density, providing a self-contained review of
the properties of spontaneously broken symmetries specific to such theories.
Topics covered include: (i) Introduction to the mathematics of spontaneous
symmetry breaking and the Goldstone theorem. (ii) Minimization of Higgs-type
potentials for higher-dimensional representations. (iii) Counting rules for
Nambu-Goldstone bosons and their dispersion relations. (iv) Construction of
effective Lagrangians. Specific examples in both relativistic and
nonrelativistic physics are worked out in detail.
| arxiv topic:hep-th cond-mat.quant-gas cond-mat.str-el hep-ph nucl-th |
arxiv_dataset-17061001.5312 | Period differential equations for families of K3 surfaces derived from
some 3 dimensional reflexive polytopes
math.CV
We study period maps for families of $K3$ surfaces those are given by anti
canonical divisors of toric varieties coming from reflexive polytopes $P_2,
P_4, P_5$ and $P_r$. We obtain systems of period differential equations for
these families. Moreover, in the case $P_4$, we determine the projective
monodromy group of the period map. This group is explicitly related with the
Hilbert modular group for $\mathbb{Q}(\sqrt{5})$.
| arxiv topic:math.CV |
arxiv_dataset-17071001.5412 | A near-infrared study of AGB and red giant stars in the Leo I dSph
galaxy
astro-ph.CO astro-ph.GA
A near-infrared imaging study of the evolved stellar populations in the dwarf
spheroidal galaxy Leo I is presented. Based on JHK observations obtained with
the WFCAM wide-field array at the UKIRT telescope, we build a near-infrared
photometric catalogue of red giant branch (RGB) and asymptotic giant branch
(AGB) stars in Leo I over a 13.5 arcmin square area. The V-K colours of RGB
stars, obtained by combining the new data with existing optical observations,
allow us to derive a distribution of global metallicity [M/H] with average
[M/H] = -1.51 (uncorrected) or [M/H] = -1.24 +/- 0.05 (int) +/- 0.15 (syst)
after correction for the mean age of Leo I stars. This is consistent with the
results from spectroscopy once stellar ages are taken into account. Using a
near-infrared two-colour diagram, we discriminate between carbon- and
oxygen-rich AGB stars and obtain a clean separation from Milky Way foreground
stars. We reveal a concentration of C-type AGB stars relative to the red giant
stars in the inner region of the galaxy, which implies a radial gradient in the
intermediate-age (1-3 Gyr) stellar populations. The numbers and luminosities of
the observed carbon- and oxygen-rich AGB stars are compared with those
predicted by evolutionary models including the thermally-pulsing AGB phase, to
provide new constraints to the models for low-metallicity stars. We find an
excess in the predicted number of C stars fainter than the RGB tip, associated
to a paucity of brighter ones. The number of O-rich AGB stars is roughly
consistent with the models, yet their predicted luminosity function is extended
to brighter luminosity. It appears likely that the adopted evolutionary models
overestimate the C star lifetime and underestimate their K-band luminosity.
| arxiv topic:astro-ph.CO astro-ph.GA |
arxiv_dataset-17081002.0041 | Optically Isotropic and Monoclinic Ferroelectric Phases in PZT Single
Crystals near Morphotropic Phase Boundary
cond-mat.mtrl-sci
We report the finding of unusual scale-dependent symmetry below the
ferroelectric Curie temperature in the perovskite Pb(Zr1-xTix)O3 single
crystals of morphotropic phase boundary compositions. The crystals of
tetragonal symmetry (from x-ray diffraction experiments) on sub-micrometer
scale exhibit a macroscopic (optically determined) cubic symmetry. This
peculiar optical isotropy is explained by the anomalously small size of
tetragonal ferroelectric domains. Upon further cooling the crystals transform
to the phase consisting of micrometer-sized domains of monoclinic Cm symmetry.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-17091002.0141 | Minimally almost periodic group topology on countable torsion Abelian
groups
math.GR math.GN
For any countable torsion subgroup $H$ of an unbounded Abelian group $G$
there is a complete Hausdorff group topology $\tau$ such that $H$ is the von
Neumann radical of $(G,\tau)$. In particular, any unbounded torsion countable
Abelian group admits a complete Hausdorff minimally almost periodic (MinAP)
group topology. If $G$ is a bounded torsion countably infinite Abelian group,
then it admits a MinAP group topology if and only if all its leading
Ulm-Kaplansky invariants are infinite. In such a case, a MinAP group topology
can be chosen to be complete.
| arxiv topic:math.GR math.GN |
arxiv_dataset-17101002.0241 | A Relativistic Approach on 1-Jet Spaces of the Rheonomic Berwald-Moor
Metric
math.DG
The aim of this paper is to develop on the 1-jet space J^1(R,M^4) the
Finsler-like geometry (in the sense of d-connection, d-torsions and
d-curvatures) of the rheonomic Berwald-Moor metric. A natural geometrical
gravitational field theory produced by the rheonomic Berwald-Moor metric is
also constructed.
| arxiv topic:math.DG |
arxiv_dataset-17111002.0341 | A close look at the Centaurus A group of galaxies: I. Metallicity
distribution functions and population gradients in early-type dwarfs
astro-ph.CO
We study dwarf galaxies in the Centaurus A group to investigate their
metallicity and possible environmental effects. The Centaurus A group (at ~4
Mpc from the Milky Way) contains about 50 known dwarf companions of different
morphologies and stellar contents, thus making it a very interesting target to
study how these galaxies evolve. Here we present results for the early-type
dwarf galaxy population in this group. We use archival HST/ACS data to study
the resolved stellar content of 6 galaxies, together with isochrones from the
Dartmouth stellar evolutionary models. We derive photometric metallicity
distribution functions of stars on the upper red giant branch via isochrone
interpolation. The 6 galaxies are moderately metal-poor (<[Fe/H]>=-1.56 to
-1.08), and metallicity spreads are observed (internal dispersions of
sigma_[Fe/H]=0.10 to 0.41 dex). We also investigate the possible presence of
intermediate-age stars, and discuss how these affect our results. The dwarfs
exhibit flat to weak radial metallicity gradients. For the two most luminous,
most metal-rich galaxies, we find statistically significant evidence for at
least two stellar subpopulations: the more metal-rich stars are found in the
center of the galaxies, while the metal-poor ones are more broadly distributed
within the galaxies. We find no clear trend of the derived physical properties
as a function of (present-day) galaxy position in the group, which may be due
to the small sample we investigate. We compare our results to the early-type
dwarf population of the Local Group, and find no outstanding differences,
despite the fact that the Centaurus A group is a denser environment that is
possibly in a more advanced dynamical stage.
| arxiv topic:astro-ph.CO |
arxiv_dataset-17121002.0441 | Spin-resolved scattering through spin-orbit nanostructures in graphene
cond-mat.mes-hall cond-mat.other
We address the problem of spin-resolved scattering through spin-orbit
nanostructures in graphene, i.e., regions of inhomogeneous spin-orbit coupling
on the nanometer scale. We discuss the phenomenon of spin-double refraction and
its consequences on the spin polarization. Specifically, we study the
transmission properties of a single and a double interface between a normal
region and a region with finite spin-orbit coupling, and analyze the
polarization properties of these systems. Moreover, for the case of a single
interface, we determine the spectrum of edge states localized at the boundary
between the two regions and study their properties.
| arxiv topic:cond-mat.mes-hall cond-mat.other |
arxiv_dataset-17131002.0541 | Gravity with de Sitter and Unitary Tangent Groups
hep-th
Einstein Gravity can be formulated as a gauge theory with the tangent space
respecting the Lorentz symmetry. In this paper we show that the dimension of
the tangent space can be larger than the dimension of the manifold and by
requiring the invariance of the theory with respect to 5d Lorentz group (de
Sitter group) Einstein theory is reproduced unambiguously. The other
possibility is to have unitary symmetry on a complex tangent space of the same
dimension as the manifold. In this case the resultant theory is
Einstein-Strauss Hermitian gravity. The tangent group is important for matter
couplings. We show that in the de Sitter case the 4 dimensional space time
vector and scalar are naturally unified by a hidden symmetry being components
of a 5d vector in the tangent space. With a de Sitter tangent group spinors can
exist only when they are made complex or taken in doublets in a way similar to
N=2 supersymmetry.
| arxiv topic:hep-th |
arxiv_dataset-17141002.0641 | Boson Stars under Deconstruction
gr-qc
We study solutions for boson stars in multiscalar theory. We start with
simple models with N scalar theories. Our purpose is to study the models in
which the mass matrix of scalars and the scalar couplings are given by an
extended method of dimensional deconstruction. The properties of the boson
stars are investigated by the Newtonian approximation with the large coupling
limit.
| arxiv topic:gr-qc |
arxiv_dataset-17151002.0741 | Astrophysical S-factors for fusion reactions involving C, O, Ne and Mg
isotopes
astro-ph.SR nucl-th
Using the Sao Paulo potential and the barrier penetration formalism we have
calculated the astrophysical factor S(E) for 946 fusion reactions involving
stable and neutron-rich isotopes of C, O, Ne, and Mg for center-of-mass
energies E varying from 2 MeV to 18-30 MeV (covering the range below and above
the Coulomb barrier). We have parameterized the energy dependence S(E) by an
accurate universal 9-parameter analytic expression and present tables of fit
parameters for all the reactions. We also discuss the reduced 3-parameter
version of our fit which is highly accurate at energies below the Coulomb
barrier, and outline the procedure for calculating the reaction rates. The
results can be easily converted to thermonuclear or pycnonuclear reaction rates
to simulate various nuclear burning phenomena, in particular, stellar burning
at high temperatures and nucleosynthesis in high density environments.
| arxiv topic:astro-ph.SR nucl-th |
arxiv_dataset-17161002.0841 | On thermodynamics of N=6 superconformal Chern-Simons theory
hep-th
We study thermodynamics of N=6 superconformal Chern-Simons theory by
computing quantum corrections to the free energy. We find that in weakly
coupled ABJM theory on R(2) x S(1), the leading correction is non-analytic in
the 't Hooft coupling lambda, and is approximately of order lambda^2
log(lambda)^3. The free energy is expressed in terms of the scalar thermal mass
m, which is generated by screening effects. We show that this mass vanishes to
1-loop order. We then go on to 2-loop order where we find a finite and positive
mass squared m^2. We discuss differences in the calculation between Coulomb and
Lorentz gauge. Our results indicate that the free energy is a monotonic
function in lambda which interpolates smoothly to the N^(3/2) behaviour at
strong coupling.
| arxiv topic:hep-th |
arxiv_dataset-17171002.0941 | Description of polygonal regions by polynomials of bounded degree
math.MG math.AG
We show that every (possibly unbounded) convex polygon $P$ in $R^2$ with $m$
edges can be represented by inequalities $p_1 \ge 0,...,p_n \ge 0,$ where the
$p_i$'s are products of at most $k$ affine functions each vanishing on an edge
of $P$ and $n=n(m,k)$ satisfies $s(m,k) \le n(m,k) \le (1+\epsilon_m) s(m,k)$
with $s(m,k):=\max \{m/k,\log_2 m\}$ and $\epsilon_m \to 0$ as $m \to \infty$.
This choice of $n$ is asymptotically best possible. An analogous result on
representing the interior of $P$ in the form $p_1 > 0,..., p_n > 0$ is also
given. For $k \le m/\log_2 m$ these statements remain valid for representations
with arbitrary polynomials of degree not exceeding $k$.
| arxiv topic:math.MG math.AG |
arxiv_dataset-17181002.1041 | On $px^2 + q^{2n}= y^p$ and related Diophantine equations
math.NT
The title equation, where $p>3$ is a prime number $\not\equiv 7 \pmod 8$, $q$
is an odd prime number and $x,y,n$ are positive integers with $x,y$ relatively
prime, is studied. When $p\equiv 3\pmod 8$, we prove (Theorem 2.3) that there
are no solutions. For $p\not\equiv 3\pmod 8$ the treatment of the equation
turns out to be a difficult task. We focus our attention to $p=5$, by reason of
an article by F. Abu Muriefah, published in this journal, vol. 128 (2008),
1670-1675. Our main result concerning this special equation is Theorem 1.1,
whose proof is based on results around the Diophantine equation $5x^2-4=y^n$
(integer solutions), interesting in themselves, which are exposed in Sections 3
and 4. These last results are obtained by using tools such as Linear Forms in
Two Logarithms and Hypergeometric Series.
| arxiv topic:math.NT |
arxiv_dataset-17191002.1141 | Phantom boundary crossing and anomalous growth index of fluctuations in
viable f(R) models of cosmic acceleration
astro-ph.CO gr-qc hep-th
Evolution of a background space-time metric and sub-horizon matter density
perturbations in the Universe is numerically analyzed in viable $f(R)$ models
of present dark energy and cosmic acceleration. It is found that viable models
generically exhibit recent crossing of the phantom boundary $w_{\rm DE}=-1$.
Furthermore, it is shown that, as a consequence of the anomalous growth of
density perturbations during the end of the matter-dominated stage, their
growth index evolves non-monotonically with time and may even become negative
temporarily.
| arxiv topic:astro-ph.CO gr-qc hep-th |
arxiv_dataset-17201002.1241 | Diode laser welding of ABS: Experiments and process modeling
physics.optics
The laser beam weldability of acrylonitrile/butadiene/styrene (ABS) plates is
determined by combining both experimental and theoretical aspects. In modeling
the process, an optical model is used to determine how the laser beam is
attenuated by the first material and to obtain the laser beam profile at the
interface. Using this information as the input data to a thermal model, the
evolution of the temperature field within the two components can be estimated.
The thermal model is based on the first principles of heat transfer and
utilizes the temperature variation laws of material properties. Corroborating
the numerical results with the experimental results, some important insights
concerning the fundamental phenomena that govern the process could be
extracted. This approach proved to be an efficient tool in determining the
weldability of polimeric materials and assures a significant reduction of time
and costs with the experimental exploration.
| arxiv topic:physics.optics |
arxiv_dataset-17211002.1341 | In-plane transport and enhanced thermoelectric performance in thin films
of the topological insulators Bi_2Te_3 and Bi_2Se_3
cond-mat.mes-hall
Several small-bandgap semiconductors are now known to have protected metallic
surface states as a consequence of the topology of the bulk electron
wavefunctions. The known "topological insulators" with this behavior include
the important thermoelectric materials Bi_2Te_3 and Bi_2Se_3, whose surfaces
are observed in photoemission experiments to have an unusual electronic
structure with a single Dirac cone. We study in-plane (i.e., horizontal)
transport in thin films made of these materials. The surface states from top
and bottom surfaces hybridize, and conventional diffusive transport predicts
that the tunable hybridization-induced band gap leads to increased
thermoelectric performance at low temperatures. Beyond simple diffusive
transport, the conductivity shows a crossover from the spin-orbit induced
anti-localization at a single surface to ordinary localization.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-17221002.1441 | Time-Dependent Transport Through Molecular Junctions
cond-mat.mes-hall cond-mat.mtrl-sci
We investigate transport properties of molecular junctions under two types of
bias--a short time pulse or an AC bias--by combining a solution for the Green
functions in the time domain with electronic structure information coming from
ab initio density functional calculations. We find that the short time response
depends on lead structure, bias voltage, and barrier heights both at the
molecule-lead contacts and within molecules. Under a low frequency AC bias, the
electron flow either tracks or leads the bias signal (capacitive or resistive
response) depending on whether the junction is perfectly conducting or not. For
high frequency, the current lags the bias signal due to the kinetic inductance.
The transition frequency is an intrinsic property of the junctions.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-17231002.1541 | Shape derivatives of boundary integral operators in electromagnetic
scattering
math.NA
We develop the shape derivative analysis of solutions to the problem of
scattering of time-harmonic electromagnetic waves by a bounded penetrable
obstacle. Since boundary integral equations are a classical tool to solve
electromagnetic scattering problems, we study the shape differentiability
properties of the standard electromagnetic boundary integral operators. Using
Helmholtz decomposition, we can base their analysis on the study of scalar
integral operators in standard Sobolev spaces, but we then have to study the
G\^ateaux differentiability of surface differential operators. We prove that
the electromagnetic boundary integral operators are infinitely differentiable
without loss of regularity and that the solutions of the scattering problem are
infinitely shape differentiable away from the boundary of the obstacle, whereas
their derivatives lose regularity on the boundary. We also give a
characterization of the first shape derivative as a solution of a new
electromagnetic scattering problem.
| arxiv topic:math.NA |
arxiv_dataset-17241002.1641 | Longitudinal scaling property of the charge balance function in Au + Au
collisions at 200 GeV
nucl-ex
We present measurements of the charge balance function, from the charged
particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au
collisions at 200 GeV using the STAR detector at RHIC. We observe that the
balance function is boost-invariant within the pseudorapidity coverage [-1.3,
1.3]. The balance function properly scaled by the width of the observed
pseudorapidity window does not depend on the position or size of the
pseudorapidity window. This scaling property also holds for particles in
different transverse momentum ranges. In addition, we find that the width of
the balance function decreases monotonically with increasing transverse
momentum for all centrality classes.
| arxiv topic:nucl-ex |
arxiv_dataset-17251002.1741 | An Adiabatic Theorem for Resonances
math-ph math.MP quant-ph
We prove a robust extension of the quantum adiabatic theorem. The theorem
applies to systems that have resonances instead of bound states, and to systems
for which just an approximation to a bound state is known. To demonstrate the
theorem's usefulness in a concrete situation, we apply it to shape resonances.
| arxiv topic:math-ph math.MP quant-ph |
arxiv_dataset-17261002.1841 | Recurrent Activity in Active Galactic Nuclei
astro-ph.CO
There has been a growing body of evidence to suggest that AGN activity, which
is powered by mass accretion on to a supermasive black hole, could be episodic,
although the range of time scales involved needs to be explored further. The
structure and spectra of radio emission from radio galaxies, whose sizes range
up to $\sim$5 Mpc, contain information on the history of AGN activity in the
source. They thus provide a unique opportunity to study the time scales of
recurrent AGN activity. The most striking examples of recurrent activity in
radio galaxies and quasars are the double-double or triple-double radio sources
which contain two or three pairs of distinct lobes on opposite sides of the
parent optical object. Spectral and dynamical ages of these lobes could be used
to constrain time scales of episodic activity. Inverse-Compton scattered cosmic
microwave background radiation could in principle probe lower Lorentz-factor
particles than radio observations of synchrotron emission, and thereby reveal
an older population. We review briefly the radio continuum as well as molecular
and atomic gas properties of radio sources which exhibit recurrent or episodic
activity, and present a few cases of quasars which require further observations
to confirm their episodic nature. We also illustrate evidence of episodic AGN
activity in radio sources in clusters of galaxies.
| arxiv topic:astro-ph.CO |
arxiv_dataset-17271002.1941 | AFT Gravitational Model - Unity of All Elementary Particles in Sp(12,C)
physics.gen-ph
A new unifying theory was recently proposed by the author in the publication
"Arrangement field theory - beyond strings and loop gravity -". Such theory
describes all fields (gravitational, gauge and matter fields) as entries in a
matricial superfield which transforms in the adjoint representation of
Sp(12,C). In this paper we show how this superfield is built and we introduce a
new mechanism of symmetry breaking which doesn't need Higgs bosons.
| arxiv topic:physics.gen-ph |
arxiv_dataset-17281002.2041 | Gravitational Lensing in Spherically Symmetric Spacetimes
gr-qc astro-ph.CO
We present a framework for studying gravitational lensing in spherically
symmetric spacetimes using 1+1+2 covariant methods. A general formula for the
deflection angle is derived and we show how this can be used to recover the
standard result for the Schwarzschild spacetime.
| arxiv topic:gr-qc astro-ph.CO |
arxiv_dataset-17291002.2141 | Advance and prospects in constraining the Yukawa-type corrections to
Newtonian gravity from the Casimir effect
hep-th quant-ph
We report stronger constraints on the parameters of Yukawa-type corrections
to Newtonian gravity from measurements of the lateral Casimir force between
sinusoidally corrugated surfaces of a sphere and a plate. In the interaction
range from 1.6 to 14 nm the strengthening of previously known high confidence
constraints up to a factor of $2.4\times 10^7$ is achieved using these
measurements. It is shown that the replacement of a plane plate with a
corrugated one in the measurements of the normal Casimir force by means of an
atomic force microscope would result in the strengthening of respective high
confidence constraints on the Yukawa-type interaction by a factor of $1.1\times
10^{12}$. The use of a corrugated plate instead of a plane plate in the
experiment by means of a micromachined oscillator also leads to strengthening
of the obtained constraints. We further obtain constraints on the parameters of
Yukawa-type interaction from the data of experiments measuring the gradient of
the Casimir pressure between two parallel plates and the gradient of the
Casimir-Polder force between an atom and a plate. The obtained results are
compared with the previously known constraints. The possibilities of how to
further strengthen the constraints on non-Newtonian gravity are discussed.
| arxiv topic:hep-th quant-ph |
arxiv_dataset-17301002.2241 | Convective-reactive proton-C12 combustion in Sakurai's object (V4334
Sagittarii) and implications for the evolution and yields from the first
generations of stars
astro-ph.SR
Depending on mass and metallicity as well as evolutionary phase, stars
occasionally experience convective-reactive nucleosynthesis episodes. We
specifically investigate the situation when nucleosynthetically unprocessed,
H-rich material is convectively mixed with a He-burning zone, for example in
convectively unstable shell on top of electron-degenerate cores in AGB stars,
young white dwarfs or X-ray bursting neutron stars. Such episodes are
frequently encountered in stellar evolution models of stars of extremely low or
zero metal content [...] We focus on the convective-reactive episode in the
very-late thermal pulse star Sakurai's object (V4334 Sagittarii). Asplund etal.
(1999) determined the abundances of 28 elements, many of which are highly
non-solar, ranging from H, He and Li all the way to Ba and La, plus the C
isotopic ratio. Our simulations show that the mixing evolution according to
standard, one-dimensional stellar evolution models implies neutron densities in
the He that are too low to obtain a significant neutron capture nucleosynthesis
on the heavy elements. We have carried out 3D hydrodynamic He-shell flash
convection [...] we assume that the ingestion process of H into the He-shell
convection zone leads only after some delay time to a sufficient entropy
barrier that splits the convection zone [...] we obtain significantly higher
neutron densities (~few 10^15 1/cm^3) and reproduce the key observed abundance
trends found in Sakurai's object. These include an overproduction of Rb, Sr and
Y by about 2 orders of magnitude higher than the overproduction of Ba and La.
Such a peculiar nucleosynthesis signature is impossible to obtain with the
mixing predictions in our one-dimensional stellar evolution models. [...] We
determine how our results depend on uncertainties of nuclear reaction rates,
for example for the C13(\alpha, n)O16 reaction.
| arxiv topic:astro-ph.SR |
arxiv_dataset-17311002.2341 | Geometric ergodicity for families of homogeneous Markov chains
math.PR math.ST stat.TH
In this paper we find nonasymptotic exponential upper bounds for the
deviation in the ergodic theorem for families of homogeneous Markov processes.
We find some sufficient conditions for geometric ergodicity uniformly over a
parametric family. We apply this property to the nonasymptotic nonparametric
estimation problem for ergodic diffusion processes.
| arxiv topic:math.PR math.ST stat.TH |
arxiv_dataset-17321002.2441 | Flavor sensitivity to theta_13 and the mass hierarchy for neutrinos from
solar WIMP annihilation
hep-ph
The effect of the higher-energy 2nd resonance and the associated
adiabatic-to-nonadiabatic transition on neutrino propagation in solar matter is
presented. For WIMP-annihilation neutrinos injected with energies in the "sweet
region" between 300 MeV and 10 GeV at the Sun's center, a significant and
revealing dependence on the neutrino mass hierarchy and the mixing angle
theta_13 down to 0.5 degrees is found in the flavor ratios arriving at Earth.
In addition, the amplification of flavor ratios in the sweet region allows a
better discrimination among possible annihilation modes of the solar dark
matter. Under mild assumptions on WIMP properties, it is estimated that 200
neutrino events in the sweet region would be required for inferences of
theta_13, the mass hierarchy, and the dominant WIMP annihilation mode. Future
large-volume, low-energy neutrino detectors are likely needed if the
measurement is to be made.
| arxiv topic:hep-ph |
arxiv_dataset-17331002.2541 | Strong electric fields induced on a sharp stellar boundary
astro-ph.SR
Due to a first order phase transition, a compact star may have a
discontinuous distribution of baryon as well as electric charge densities, as
e.g. at the surface of a strange quark star. The induced separation of positive
and negative charges may lead to generation of supercritical electric fields in
the vicinity of such a discontinuity. We study this effect within a
relativistic Thomas-Fermi approximation and demonstrate that the strength of
the electric field depends strongly on the degree of sharpness of the surface.
The influence of strong electric fields on the stability of compact stars is
discussed. It is demonstrated that stable configurations appear only when the
counter-pressure of degenerate fermions is taken into consideration.
| arxiv topic:astro-ph.SR |
arxiv_dataset-17341002.2641 | String scattering in flat space and a scaling limit of Yang-Mills
correlators
hep-th
We use the flat space limit of the AdS/CFT correspondence to derive a simple
relation between the 2 to 2 scattering amplitude of massless string states in
type IIB superstring theory on ten-dimensional Minkowski space and a scaling
limit of the N=4 super Yang-Mills four point functions. We conjecture that this
relation holds non-perturbatively and at arbitrarily high energy.
| arxiv topic:hep-th |
arxiv_dataset-17351002.2741 | Free Lunch
q-fin.GN
The concept of absence of opportunities for free lunches is one of the
pillars in the economic theory of financial markets. This natural assumption
has proved very fruitful and has lead to great mathematical, as well as
economical, insights in Quantitative Finance. Formulating rigorously the exact
definition of absence of opportunities for riskless profit turned out to be a
highly non-trivial fact that troubled mathematicians and economists for at
least two decades. The purpose of this note is to give a quick (and,
necessarily, incomplete) account of the recent work aimed at providing a simple
and intuitive no-free-lunch assumption that would suffice in formulating a
version of the celebrated Fundamental Theorem of Asset Pricing.
| arxiv topic:q-fin.GN |
arxiv_dataset-17361002.2841 | Spin-torque driven magnetic vortex self-oscillations in perpendicular
magnetic fields
cond-mat.mes-hall cond-mat.other
We have employed complete micromagnetic simulations to analyze dc current
driven self-oscillations of a vortex core in a spin-valve nanopillar in a
perpendicular field by including the coupled effect of the spin-torque and the
magnetostatic field computed self-consistently for the entire spin-valve. The
vortex in the thicker nanomagnet moves along a quasi-elliptical trajectory that
expands with applied current, resulting in blue-shifting of the frequency,
while the magnetization of the thinner nanomagnet is non-uniform due to the
bias current. The simulations explain the experimental magnetoresistance-field
hysteresis loop and yield good agreement with the measured frequency vs.
current behavior of this spin-torque vortex oscillator.
| arxiv topic:cond-mat.mes-hall cond-mat.other |
arxiv_dataset-17371002.2941 | Thermodynamic Bethe Ansatz Equations for Minimal Surfaces in AdS_3
hep-th
We study classical open string solutions with a null polygonal boundary in
AdS_3 in relation to gluon scattering amplitudes in N=4 super Yang-Mills at
strong coupling. We derive in full detail the set of integral equations
governing the decagonal and the dodecagonal solutions and identify them with
the thermodynamic Bethe ansatz equations of the homogeneous sine-Gordon models.
By evaluating the free energy in the conformal limit we compute the central
charges, from which we observe general correspondence between the polygonal
solutions in AdS_n and generalized parafermions.
| arxiv topic:hep-th |
arxiv_dataset-17381002.3041 | A relation between the Barbero-Immirzi parameter and the standard model
gr-qc hep-th
It has been shown that Sakharov's induced, from the fields entering the
standard model, Barbero-Immirzi parameter assumes, in the framework of
euclidean formalism, the UV cutoff-independent value, 1/9. The calculus uses
the Schwinger's proper-time formalism, the Seeley-DeWitt heat-kernel expansion,
and it is akin to the derivation of the ABJ chiral anomaly in space-time with
torsion.
| arxiv topic:gr-qc hep-th |
arxiv_dataset-17391002.3141 | On indecomposable trees in the boundary of Outer space
math.GR math.GT
Let $T$ be an $\mathbb{R}$-tree, equipped with a very small action of the
rank $n$ free group $F_n$, and let $H \leq F_n$ be finitely generated. We
consider the case where the action $F_n \curvearrowright T$ is
indecomposable--this is a strong mixing property introduced by Guirardel. In
this case, we show that the action of $H$ on its minimal invarinat subtree
$T_H$ has dense orbits if and only if $H$ is finite index in $F_n$. There is an
interesting application to dual algebraic laminations; we show that for $T$
free and indecomposable and for $H \leq F_n$ finitely generated, $H$ carries a
leaf of the dual lamination of $T$ if and only if $H$ is finite index in $F_n$.
This generalizes a result of Bestvina-Feighn-Handel regarding stable trees of
fully irreducible automorphisms.
| arxiv topic:math.GR math.GT |
arxiv_dataset-17401002.3241 | Coarse-grained modeling of multiscale diffusions: the p-variation
estimates
math.ST math.PR stat.ME stat.TH
We study the problem of estimating parameters of the limiting equation of a
multiscale diffusion in the case of averaging and homogenization, given data
from the corresponding multiscale system. First, we review some recent results
that make use of the maximum likelihood of the limiting equation. In
particular, it has been shown that in the averaging case, the MLE will be
asymptotically consistent in the limit while in the homogenization case, the
MLE will be asymptotically consistent only if we subsample the data. Then, we
focus on the problem of estimating the diffusion coefficient. We suggest a
novel approach that makes use of the total $p$-variation, as defined in the
theory of rough paths and avoids the subsampling step. The method is applied to
a multiscale OU process.
| arxiv topic:math.ST math.PR stat.ME stat.TH |
arxiv_dataset-17411002.3341 | Pinpointing Cosmic Ray Propagation With The AMS-02 Experiment
astro-ph.HE
The Alpha Magnetic Spectrometer (AMS-02), which is scheduled to be deployed
onboard the International Space Station later this year, will be capable of
measuring the composition and spectra of GeV-TeV cosmic rays with unprecedented
precision. In this paper, we study how the projected measurements from AMS-02
of stable secondary-to-primary and unstable ratios (such as boron-to-carbon and
beryllium-10-to-beryllium-9) can constrain the models used to describe the
propagation of cosmic rays throughout the Milky Way. We find that within the
context of fairly simple propagation models, all of the model parameters can be
determined with high precision from the projected AMS-02 data. Such
measurements are less constraining in more complex scenarios, however, which
allow for departures from a power-law form for the diffusion coefficient, for
example, or for inhomogeneity or stochasticity in the distribution and chemical
abundances of cosmic ray sources.
| arxiv topic:astro-ph.HE |
arxiv_dataset-17421002.3441 | Topological representation of matroids from diagrams of spaces
math.CO math.AT
Swartz proved that any matroid can be realized as the intersection lattice of
an arrangement of codimension one homotopy spheres on a sphere. This was an
unexpected extension from the oriented matroid case, but unfortunately the
construction is not explicit. Anderson later provided an explicit construction,
but had to use cell complexes of high dimensions that are homotopy equivalent
to lower dimensional spheres.
Using diagrams of spaces we give an explicit construction of arrangements in
the right dimensions. Swartz asked if it is possible to arrange spheres of
codimension two, and we provide a construction for any codimension. We also
show that all matroids, and not only tropical oriented matroids, have a
pseudo-tropical representation.
We determine the homotopy type of all the constructed arrangements.
| arxiv topic:math.CO math.AT |
arxiv_dataset-17431002.3541 | Finite Volume Spaces and Sparsification
cs.DS cs.DM
We introduce and study finite $d$-volumes - the high dimensional
generalization of finite metric spaces. Having developed a suitable
combinatorial machinery, we define $\ell_1$-volumes and show that they contain
Euclidean volumes and hypertree volumes. We show that they can approximate any
$d$-volume with $O(n^d)$ multiplicative distortion. On the other hand, contrary
to Bourgain's theorem for $d=1$, there exists a $2$-volume that on $n$ vertices
that cannot be approximated by any $\ell_1$-volume with distortion smaller than
$\tilde{\Omega}(n^{1/5})$.
We further address the problem of $\ell_1$-dimension reduction in the context
of $\ell_1$ volumes, and show that this phenomenon does occur, although not to
the same striking degree as it does for Euclidean metrics and volumes. In
particular, we show that any $\ell_1$ metric on $n$ points can be $(1+
\epsilon)$-approximated by a sum of $O(n/\epsilon^2)$ cut metrics, improving
over the best previously known bound of $O(n \log n)$ due to Schechtman.
In order to deal with dimension reduction, we extend the techniques and ideas
introduced by Karger and Bencz{\'u}r, and Spielman et al.~in the context of
graph Sparsification, and develop general methods with a wide range of
applications.
| arxiv topic:cs.DS cs.DM |
arxiv_dataset-17441002.3641 | Near-linear Dynamics for Shallow Water Waves
physics.flu-dyn
It is shown that spatially periodic one-dimensional surface waves in shallow
water behave almost linearly, provided large part of the energy is contained in
sufficiently high frequencies. The amplitude is not required to be small (apart
from the shallow water approximation assumption) and the near-linear behavior
occurs on a much longer time scale than might be anticipated based on the
amplitude size. Heuristically speaking, this effect is due to the nonlinearity
getting averaged by the dispersive action.
This result is obtained by an averaging procedure, which is briefly outlined,
and is also confirmed by numerical simulations.
| arxiv topic:physics.flu-dyn |
arxiv_dataset-17451002.3741 | New dissipated energy for nonnegative weak solution of unstable
thin-film equations
math.AP math-ph math.MP
The fluid thin film equation $h_t = - (h^n h_{xxx})_x - a_1\,(h^m h_x)_x$ is
known to conserve mass $\int\,h \, dx$, and in the case of $a_1 \leq 0$, to
dissipate entropy $\int\,h^{3/2 - n}\,dx$ (see [8]) and the $L^2$-norm of the
gradient $\int\,h_x^2\,dx$ (see [3]). For the special case of $a_1 = 0$ a new
dissipated quantity $\int\, h^{\alpha}\,h_x^2\,dx $ was recently discovered for
positive classical solutions by Laugesen (see [15]). We extend it in two ways.
First, we prove that Laugesen's functional dissipates strong nonnegative
generalized solutions. Second, we prove the full $\alpha$-energy
$\int\,\bigl(\frac{1}{2} \,h^\alpha \, h_x^2\, - \frac{a_1\,h^{\alpha + m - n +
2}}{(\alpha + m - n + 1)(\alpha + m - n + 2)} \bigr)\, dx $ dissipation for
strong nonnegative generalized solutions in the case of the unstable porous
media perturbation $a_1> 0$ and the critical exponent $m = n+2$.
| arxiv topic:math.AP math-ph math.MP |
arxiv_dataset-17461002.3841 | Band-limited localized Parseval frames and Besov spaces on compact
homogeneous manifolds
math.FA math.CA math.SP
In the last decade, methods based on various kinds of spherical wavelet bases
have found applications in virtually all areas where analysis of spherical data
is required, including cosmology, weather prediction, and geodesy. In
particular, the so-called needlets (=band-limited Parseval frames) have become
an important tool for the analysis of Cosmic Microwave Background (CMB)
temperature data. The goal of the present paper is to construct band-limited
and highly localized Parseval frames on general compact homogeneous manifolds.
Our construction can be considered as an analogue of the well-known
phi-transform on Euclidean spaces.
| arxiv topic:math.FA math.CA math.SP |
arxiv_dataset-17471002.3941 | Modeling of gas adsorption on graphene nanoribbons
cond-mat.mes-hall
We present a theory to study gas molecules adsorption on armchair graphene
nanoribbons (AGNRs) by applying the results of \emph{ab} \emph{initio}
calculations to the single-band tight-binding approximation. In addition, the
effect of edge states on the electronic properties of AGNR is included in the
calculations. Under the assumption that the gas molecules adsorb on the ribbon
sites with uniform probability distribution, the applicability of the method is
examined for finite concentrations of adsorption of several simple gas
molecules (CO, NO, CO$_2$, NH$_3$) on 10-AGNR. We show that the states
contributed by the adsorbed CO and NO molecules are quite localized near the
center of original band gap and suggest that the charge transport in such
systems cannot be enhanced considerably, while CO$_2$ and NH$_3$ molecules
adsorption acts as acceptor and donor, respectively. The results of this theory
at low gas concentration are in good agreement with those obtained by
density-functional theory calculations.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-17481002.4041 | Improving Term Extraction Using Particle Swarm Optimization Techniques
cs.IR
Term extraction is one of the layers in the ontology development process
which has the task to extract all the terms contained in the input document
automatically. The purpose of this process is to generate list of terms that
are relevant to the domain of the input document. In the literature there are
many approaches, techniques and algorithms used for term extraction. In this
paper we propose a new approach using particle swarm optimization techniques in
order to improve the accuracy of term extraction results. We choose five
features to represent the term score. The approach has been applied to the
domain of religious document. We compare our term extraction method precision
with TFIDF, Weirdness, GlossaryExtraction and TermExtractor. The experimental
results show that our propose approach achieve better precision than those four
algorithm.
| arxiv topic:cs.IR |
arxiv_dataset-17491002.4141 | Holomorphic discs and surgery exact triangles
math.GT
We show a connection between a surgery exact sequence in knot Floer homology
and the sequence derived in [18]. As a consequence of this relationship we see
that the exact sequence in [18] also works with coherent orientations and
admits refinements with respect to spinc-structures. As an application of this
discussion, we prove that the ranks of the image and kernel of certain
cobordism maps between knot Floer homologies can be computed combinatorially by
relating them to a count of certain moduli spaces of holomorphic disks.
| arxiv topic:math.GT |
arxiv_dataset-17501002.4241 | A-models in three and four dimensions
hep-th
We introduce and study a new 3d Topological Field Theory which can be
associated to any compact real manifold X. This TFT is analogous to the 2d
A-model and reduces to it upon compactification on an interval with suitable
boundary conditions. It plays a role in 3d mirror symmetry as well as in the
physical approach to the geometric Langlands duality. A similar TFT can be
defined in four dimensions.
| arxiv topic:hep-th |
arxiv_dataset-17511002.4341 | Single photons from coupled quantum modes
cond-mat.mes-hall
Single photon emitters often rely on a strong nonlinearity to make the
behaviour of a quantum mode susceptible to a change in the number of quanta
between one and two. In most systems the strength of nonlinearity is weak, such
that changes at the single quantum level have little effect. Here, we consider
coupled quantum modes and and that they can be strongly sensitive at the single
quantum level, even if nonlinear interactions are modest. As examples, we
consider solid-state implementations based on the tunneling of polaritons
between quantum boxes or their parametric modes in a microcavity. We find that
these systems can act as promising single photon emitters.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-17521002.4441 | Heavy quark(onium) at LHC: the statistical hadronization case
nucl-th
We discuss the production of charmonium in nuclear collisions within the
framework of the statistical hadronization model. We demonstrate that the model
reproduces very well the availble data at RHIC. We provide predictions for the
LHC energy where, dependently on the charm production cross section, a
dramatically different behaviour of charmonium production as a function of
centrality might be expected. We discuss also the case in elementary
collisions, where clearly the statistical model does not reproduce the
measurements.
| arxiv topic:nucl-th |
arxiv_dataset-17531002.4541 | Vibrational Excitations in Weakly Coupled Single-Molecule Junctions: A
Computational Analysis
cond-mat.mes-hall
In bulk systems, molecules are routinely identified by their vibrational
spectrum using Raman or infrared spectroscopy. In recent years, vibrational
excitation lines have been observed in low-temperature conductance measurements
on single molecule junctions and they can provide a similar means of
identification. We present a method to efficiently calculate these excitation
lines in weakly coupled, gateable single-molecule junctions, using a
combination of ab initio density functional theory and rate equations. Our
method takes transitions from excited to excited vibrational state into account
by evaluating the Franck-Condon factors for an arbitrary number of vibrational
quanta, and is therefore able to predict qualitatively different behaviour from
calculations limited to transitions from ground state to excited vibrational
state. We find that the vibrational spectrum is sensitive to the molecular
contact geometry and the charge state, and that it is generally necessary to
take more than one vibrational quantum into account. Quantitative comparison to
previously reported measurements on pi-conjugated molecules reveals that our
method is able to characterize the vibrational excitations and can be used to
identify single molecules in a junction. The method is computationally feasible
on commodity hardware.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-17541002.4641 | Sensitivity of the Performance of a Simple Exchange Model to its
Topology
q-fin.TR
We study a simple exchange model in which price is fixed and the amount of a
good transferred between actors depends only on the actors' respective budgets
and the existence of a link between transacting actors. The model induces a
simply-connected but possibly multi-component bipartite graph. A trading
session on a fixed graph consists of a sequence of exchanges between connected
buyers and sellers until no more exchanges are possible. We deem a trading
session "feasible" if all of the buyers satisfy their respective demands. If
all trading sessions are feasible the graph is deemed "successful", otherwise
the feasibility of a trading session depends on the order of the sequence of
exchanges. We demonstrate that topology is important for the success of trading
sessions on graphs. In particular, for the case that supply equals demand for
each component of the graph, we prove that the graph is successful if and only
if the graph consists of components each of which are complete bipartite. For
the case that supply exceeds demand, we prove that the other topologies also
can be made successful but with finite reserve (i.e., excess supply)
requirements that may grow proportional to the number of buyers. Finally, with
computations for a small instance of the model, we provide an example of the
wide range of performance in which only the connectivity varies. These results
taken together place limits on the improvements in performance that can be
expected from proposals to increase the connectivity of sparse exchange
networks.
| arxiv topic:q-fin.TR |
arxiv_dataset-17551002.4741 | How large can the electron to proton mass ratio be in Particle-In-Cell
simulations of unstable systems?
physics.plasm-ph physics.space-ph
Particle-in-cell (PIC) simulations are widely used as a tool to investigate
instabilities that develop between a collisionless plasma and beams of charged
particles. However, even on contemporary supercomputers, it is not always
possible to resolve the ion dynamics in more than one spatial dimension with
such simulations. The ion mass is thus reduced below 1836 electron masses,
which can affect the plasma dynamics during the initial exponential growth
phase of the instability and during the subsequent nonlinear saturation. The
goal of this article is to assess how far the electron to ion mass ratio can be
increased, without changing qualitatively the physics. It is first demonstrated
that there can be no exact similarity law, which balances a change of the mass
ratio with that of another plasma parameter, leaving the physics unchanged.
Restricting then the analysis to the linear phase, a criterion allowing to
define a maximum ratio is explicated in terms of the hierarchy of the linear
unstable modes. The criterion is applied to the case of a relativistic electron
beam crossing an unmagnetized electron-ion plasma.
| arxiv topic:physics.plasm-ph physics.space-ph |
arxiv_dataset-17561002.4841 | Lattice gas simulations of dynamical geometry in two dimensions
cond-mat.soft cond-mat.other
We present a hydrodynamic lattice gas model for two-dimensional flows on
curved surfaces with dynamical geometry. This model is an extension to two
dimensions of the dynamical geometry lattice gas model previously studied in
one-dimension. We expand upon a variation of the two-dimensional flat space FHP
model created by Frisch, Hasslacher and Pomeau, and independently by Wolfram,
and modified by Boghosian, Love, and Meyer. We define a hydrodynamic lattice
gas model on an arbitrary triangulation, whose flat space limit is the FHP
model. Rules that change the geometry are constructed using the Pachner moves,
which alter the triangulation but not the topology. We present results on the
growth of the number of triangles as a function of time. Simulations show that
the number of triangles lattice grows with time as the cube root of the number
of time steps, in agreement a mean field prediction. We also present
preliminary results on the distribution of curvature over a typical
triangulation for these simulations.
| arxiv topic:cond-mat.soft cond-mat.other |
arxiv_dataset-17571002.4941 | Universal efficiency at optimal work with Bayesian statistics
cond-mat.stat-mech physics.data-an quant-ph
If the work per cycle of a quantum heat engine is averaged over an
appropriate prior distribution for an external parameter $a$, the work becomes
optimal at Curzon-Ahlborn efficiency. More general priors of the form $\Pi(a)
\propto 1/a^{\gamma}$ yield optimal work at an efficiency which stays close to
CA value, in particular near equilibrium the efficiency scales as one-half of
the Carnot value. This feature is analogous to the one recently observed in
literature for certain models of finite-time thermodynamics. Further, the use
of Bayes' theorem implies that the work estimated with posterior probabilities
also bears close analogy with the classical formula. These findings suggest
that the notion of prior information can be used to reveal thermodynamic
features in quantum systems, thus pointing to a new connection between
thermodynamic behavior and the concept of information.
| arxiv topic:cond-mat.stat-mech physics.data-an quant-ph |
arxiv_dataset-17581002.5041 | Arbitrage Opportunities in Misspecified Stochastic volatility Models
q-fin.PR q-fin.GN q-fin.ST
There is vast empirical evidence that given a set of assumptions on the
real-world dynamics of an asset, the European options on this asset are not
efficiently priced in options markets, giving rise to arbitrage opportunities.
We study these opportunities in a generic stochastic volatility model and
exhibit the strategies which maximize the arbitrage profit. In the case when
the misspecified dynamics is a classical Black-Scholes one, we give a new
interpretation of the classical butterfly and risk reversal contracts in terms
of their (near) optimality for arbitrage strategies. Our results are
illustrated by a numerical example including transaction costs.
| arxiv topic:q-fin.PR q-fin.GN q-fin.ST |
arxiv_dataset-17591003.0093 | Joint Subcarrier Pairing and Power Allocation for OFDM Transmission with
Decode-and-Forward Relaying
cs.IT math.IT
In this paper, a point-to-point Orthogonal Frequency Division Multiplexing
(OFDM) system with a decode-and-forward (DF) relay is considered. The
transmission consists of two hops. The source transmits in the first hop, and
the relay transmits in the second hop. Each hop occupies one time slot. The
relay is half-duplex, and capable of decoding the message on a particular
subcarrier in one time slot, and re-encoding and forwarding it on a different
subcarrier in the next time slot. Thus each message is transmitted on a pair of
subcarriers in two hops. It is assumed that the destination is capable of
combining the signals from the source and the relay pertaining to the same
message. The goal is to maximize the weighted sum rate of the system by jointly
optimizing subcarrier pairing and power allocation on each subcarrier in each
hop. The weighting of the rates is to take into account the fact that different
subcarriers may carry signals for different services. Both total and individual
power constraints for the source and the relay are investigated. For the
situations where the relay does not transmit on some subcarriers because doing
so does not improve the weighted sum rate, we further allow the source to
transmit new messages on these idle subcarriers. To the best of our knowledge,
such a joint optimization inclusive of the destination combining has not been
discussed in the literature. The problem is first formulated as a mixed integer
programming problem. It is then transformed to a convex optimization problem by
continuous relaxation, and solved in the dual domain. Based on the optimization
results, algorithms to achieve feasible solutions are also proposed. Simulation
results show that the proposed algorithms almost achieve the optimal weighted
sum rate, and outperform the existing methods in various channel conditions.
| arxiv topic:cs.IT math.IT |
arxiv_dataset-17601003.0193 | Tunable Multifunctional Topological Insulators in Ternary Heusler
Compounds
cond-mat.mtrl-sci cond-mat.dis-nn cond-mat.mes-hall
Recently the Quantum Spin Hall effect (QSH) was theoretically predicted and
experimentally realized in a quantum wells based on binary semiconductor
HgTe[1-3]. QSH state and topological insulators are the new states of quantum
matter interesting both for fundamental condensed matter physics and material
science[1-11]. Many of Heusler compounds with C1b structure are ternary
semiconductors which are structurally and electronically related to the binary
semiconductors. The diversity of Heusler materials opens wide possibilities for
tuning the band gap and setting the desired band inversion by choosing
compounds with appropriate hybridization strength (by lattice parameter) and
the magnitude of spin-orbit coupling (by the atomic charge). Based on the
first-principle calculations we demonstrate that around fifty Heusler compounds
show the band inversion similar to HgTe. The topological state in these
zero-gap semiconductors can be created by applying strain or by designing an
appropriate quantum well structure, similar to the case of HgTe. Many of these
ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the
rare earth element Ln which can realize additional properties ranging from
superconductivity (e. g. LaPtBi[12]) to magnetism (e. g. GdPtBi[13]) and
heavy-fermion behavior (e. g. YbPtBi[14]). These properties can open new
research directions in realizing the quantized anomalous Hall effect and
topological superconductors.
| arxiv topic:cond-mat.mtrl-sci cond-mat.dis-nn cond-mat.mes-hall |
arxiv_dataset-17611003.0293 | Strong entanglement causes low gate fidelity in inaccurate one-way
quantum computation
quant-ph
We study how entanglement among the register qubits affects the gate fidelity
in the one-way quantum computation if a measurement is inaccurate. We derive an
inequality which shows that the mean gate fidelity is upper bounded by a
decreasing function of the magnitude of the error of the measurement and the
amount of the entanglement between the measured qubit and other register
qubits. The consequence of this inequality is that, for a given amount of
entanglement, which is theoretically calculated once the algorithm is fixed, we
can estimate from this inequality how small the magnitude of the error should
be in order not to make the gate fidelity below a threshold, which is specified
by a technical requirement in a particular experimental setup or by the
threshold theorem of the fault-tolerant quantum computation.
| arxiv topic:quant-ph |
arxiv_dataset-17621003.0393 | Dilaton and gluon condensate in a nucleon medium
nucl-th hep-ph
The gluon condensate as a function of temperature and baryon density in a
nucleon medium is obtained from an effective dilaton Lagrangian. It is shown
that, at a normal nuclear density of nucleons, n_0 = 0.17 fm^{-3} the gluon
condensate decreases by about 10%.
| arxiv topic:nucl-th hep-ph |
arxiv_dataset-17631003.0493 | Possible Frictionless States at Room-Temperature Regime for Many
Fermions in Confined Domain
physics.gen-ph
We investigate the possible frictionless transport of many composite
(condensed) fermions at room temperature regime along an annular tube with
transversely wavy-corrugations by using the verified transition-rate model and
boundary perturbation approach. We found that for certain activation volume and
energy there exist possible frictionless states at room temperature regime.
| arxiv topic:physics.gen-ph |
arxiv_dataset-17641003.0593 | Multiqubit symmetric states with high geometric entanglement
quant-ph
We propose a detailed study of the geometric entanglement properties of pure
symmetric N-qubit states, focusing more particularly on the identification of
symmetric states with a high geometric entanglement and how their entanglement
behaves asymptotically for large N. We show that much higher geometric
entanglement with improved asymptotical behavior can be obtained in comparison
with the highly entangled balanced Dicke states studied previously. We also
derive an upper bound for the geometric measure of entanglement of symmetric
states. The connection with the quantumness of a state is discussed.
| arxiv topic:quant-ph |
arxiv_dataset-17651003.0693 | Large scale outflows from z ~ 0.7 starburst galaxies identified via
ultra-strong MgII quasar absorption lines
astro-ph.CO
(Abridged) Star formation-driven outflows are a critical phenomenon in
theoretical treatments of galaxy evolution, despite the limited ability of
observations to trace them across cosmological timescales. If the strongest
MgII absorption-line systems detected in the spectra of background quasars
arise in such outflows, "ultra-strong" MgII (USMgII) absorbers would identify
significant numbers of galactic winds over a huge baseline in cosmic time, in a
manner independent of the luminous properties of the galaxy. To this end, we
present the first detailed imaging and spectroscopic study of the fields of two
USMgII absorber systems culled from a statistical absorber catalog, with the
goal of understanding the physical processes leading to the large velocity
spreads that define such systems. Each field contains two bright emission-line
galaxies at similar redshift (dv < 300 km/s) to that of the absorption.
Lower-limits on their instantaneous star formation rates (SFR) from the
observed OII and Hb line fluxes, and stellar masses from spectral template
fitting indicate specific SFRs among the highest for their masses at z~0.7.
Additionally, their 4000A break and Balmer absorption strengths imply they have
undergone recent (~0.01 - 1 Gyr) starbursts. The concomitant presence of two
rare phenomena - starbursts and USMgII absorbers - strongly implies a causal
connection. We consider these data and USMgII absorbers in general in the
context of various popular models, and conclude that galactic outflows are
generally necessary to account for the velocity extent of the absorption. We
favour starburst driven outflows over tidally-stripped gas from a major
interaction which triggered the starburst as the energy source for the majority
of systems. Finally, we discuss the implications of these results and speculate
on the overall contribution of such systems to the global SFR density at z~0.7.
| arxiv topic:astro-ph.CO |
arxiv_dataset-17661003.0793 | Boolean delay equations on networks: An application to economic damage
propagation
q-fin.GN nlin.CG
We introduce economic models based on Boolean Delay Equations: this formalism
makes easier to take into account the complexity of the interactions between
firms and is particularly appropriate for studying the propagation of an
initial damage due to a catastrophe. Here we concentrate on simple cases, which
allow to understand the effects of multiple concurrent production paths as well
as the presence of stochasticity in the path time lengths or in the network
structure.
In absence of flexibility, the shortening of production of a single firm in
an isolated network with multiple connections usually ends up by attaining a
finite fraction of the firms or the whole economy, whereas the interactions
with the outside allow a partial recovering of the activity, giving rise to
periodic solutions with waves of damage which propagate across the structure.
The damage propagation speed is strongly dependent upon the topology. The
existence of multiple concurrent production paths does not necessarily imply a
slowing down of the propagation, which can be as fast as the shortest path.
| arxiv topic:q-fin.GN nlin.CG |
arxiv_dataset-17671003.0893 | Spin-active interfaces and unconventional pairing in
half-metal$\mid$superconductor junctions
cond-mat.supr-con
We study the physical properties of a half-metallic
ferromagnet$\mid$superconductor (HM$\mid$S) bilayer, allowing for an arbitrary
bulk pairing symmetry of the superconductor and spin-dependent processes at the
interface. In particular, we study how the possibility of unconventional
pairing such as $p$- and d-wave and a spin-active interface influence the
\textit{(i)} conductance spectra, \textit{(ii)} proximity effect, and
\textit{(iii)} local density of states of such a bilayer. Our calculation is
done both analytically and numerically in the ballistic limit, using both a
continuum- and lattice-model. It is found that the spin-dependent phase-shifts
occuring at the HM$\mid$S interface seriously influence all of the
aforementioned phenomena. We explain our results in terms of Andreev reflection
in the presence of a spin-active interface, allowing for both spin-filtering
and spin-mixing processes. We demonstrate how the surface-bound states induced
by the anisotropy of the superconducting order parameter at the HM$\mid$S
interface are highly sensitive to these spin-dependent processes. Our results
can be directly tested experimentally using STM-measurements and/or
point-contact spectroscopy.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-17681003.0993 | Decision Making: Superiority Degree
math.OC
It is introduced the concept of Superiority Degree one competitive decision
over another. On the basis of this concept the mathematics theoretic structure
is developed, which is part of pairs comparisons branch in modern decision
making theory. It will be useful for practice and interesting for scientific
research.
| arxiv topic:math.OC |
arxiv_dataset-17691003.1093 | Leptonic contribution to the bulk viscosity of nuclear matter
nucl-th
For beta-equilibrated nuclear matter we estimate the contribution to the bulk
viscosity from purely leptonic processes, namely the conversion of electrons to
and from muons. For oscillation frequencies in the kiloHertz range, we find
that this process provides the dominant contribution to the bulk viscosity when
the temperature is well below the critical temperature for superconductivity or
superfluidity of the nuclear matter.
| arxiv topic:nucl-th |
arxiv_dataset-17701003.1193 | A Hybrid Mechanism Forming a 2:1 Librating-Circulating Resonant
Configuration in the Planetary System
astro-ph.EP
A diversity of resonance configurations may be formed under different
migration of two giant planets. And the researchers show that the HD 128311 and
HD 73526 planetary systems are involved in a 2:1 mean motion resonance but not
in apsidal corotation, because one of the resonance argument circulates over
the dynamical evolution. In this paper, we investigate potential mechanisms to
form the 2:1 librating-circulating resonance configuration.
In the late stage of planetary formation, scattering or colliding among
planetesimals and planetary embryos can frequently occur. Hence, in our model,
we consider a planetary configuration of two giants together with few
terrestrial planets. We find that both colliding or scattering events at very
early stage of dynamical evolution can influence the configurations trapped
into resonance. A planet-planet scattering of a moderate terrestrial planet, or
multiple scattering of smaller planets in a crowded planetary system can change
the resonant configuration. In addition, collision or merging can alter the
masses and location of the giant planets, which also play an important role in
shaping the resonant configuration during the dynamical evolution. In this
sense, the librating-circulating resonance configuration is more likely to form
by a hybrid mechanism of scattering and collision.
| arxiv topic:astro-ph.EP |
arxiv_dataset-17711003.1293 | On the conjugacy growth functions of groups
math.GR
To every finitely generated group one can assign the conjugacy growth
function that counts the number of conjugacy classes intersecting a ball of
radius $n$. Results of Ivanov and Osin show that the conjugacy growth function
may be constant even if the (ordinary) growth function is exponential. The aim
of this paper is to provide conjectures, examples and statements that show that
in "normal" cases, groups with exponential growth functions also have
exponential conjugacy growth functions.
| arxiv topic:math.GR |
arxiv_dataset-17721003.1393 | A variational formula for the free energy of an interacting
many-particle system
math.PR math-ph math.MP
We consider $N$ bosons in a box in $\mathbb {R}^d$ with volume $N/\rho$ under
the influence of a mutually repellent pair potential. The particle density
$\rho\in (0,\infty)$ is kept fixed. Our main result is the identification of
the limiting free energy, $f(\beta,\rho)$, at positive temperature $1/\beta$,
in terms of an explicit variational formula, for any fixed $\rho$ if $\beta$ is
sufficiently small, and for any fixed $\beta$ if $\rho$ is sufficiently small.
The thermodynamic equilibrium is described by the symmetrized trace of
$e^{-\beta {\mathcal{H}}_N}$, where ${\mathcal{H}}_N$ denotes the corresponding
Hamilton operator. The well-known Feynman--Kac formula reformulates this trace
in terms of $N$ interacting Brownian bridges. Due to the symmetrization, the
bridges are organized in an ensemble of cycles of various lengths. The novelty
of our approach is a description in terms of a marked Poisson point process
whose marks are the cycles. This allows for an asymptotic analysis of the
system via a large-deviations analysis of the stationary empirical field. The
resulting variational formula ranges over random shift-invariant marked point
fields and optimizes the sum of the interaction and the relative entropy with
respect to the reference process. In our proof of the lower bound for the free
energy, we drop all interaction involving "infinitely long" cycles, and their
possible presence is signalled by a loss of mass of the "finitely long" cycles
in the variational formula. In the proof of the upper bound, we only keep the
mass on the "finitely long" cycles. We expect that the precise relationship
between these two bounds lies at the heart of Bose--Einstein condensation and
intend to analyze it further in future.
| arxiv topic:math.PR math-ph math.MP |
arxiv_dataset-17731003.1493 | Integration of Rule Based Expert Systems and Case Based Reasoning in an
Acute Bacterial Meningitis Clinical Decision Support System
cs.AI
This article presents the results of the research carried out on the
development of a medical diagnostic system applied to the Acute Bacterial
Meningitis, using the Case Based Reasoning methodology. The research was
focused on the implementation of the adaptation stage, from the integration of
Case Based Reasoning and Rule Based Expert Systems. In this adaptation stage we
use a higher level RBC that stores and allows reutilizing change experiences,
combined with a classic rule-based inference engine. In order to take into
account the most evident clinical situation, a pre-diagnosis stage is
implemented using a rule engine that, given an evident situation, emits the
corresponding diagnosis and avoids the complete process.
| arxiv topic:cs.AI |
arxiv_dataset-17741003.1593 | Time-resolving intra-atomic two-electron collision dynamics
physics.atom-ph
We generalize the one electron attosecond streaking camera to time-resolve
the correlated two-electron escape dynamics during a collision process
involving a deep core electron. The collision process is triggered by an XUV
attosecond pulse and probed by a weak infrared field. The principle of our
two-electron streak camera is that by placing the maximum of the vector
potential of the probing field at the time of collision we get the maximum
splitting of the inter-electronic angle of escape. We thus identify the time of
collision.
| arxiv topic:physics.atom-ph |
arxiv_dataset-17751003.1693 | Structure of nilpotent Lie algebra by its multiplier
math.RA
For a finite dimensional Lie algebra $L$, it is known that
$s(L)=\f{1}{2}(n-1)(n-2)+1-\mathrm{dim} M(L)$ is non negative. Moreover, the
structure of all finite nilpotent Lie algebras is characterized when $s(L)=0,1$
in \cite{ni,ni4}. In this paper, we intend to characterize all nilpotent Lie
algebra while $s(L)=2.$
| arxiv topic:math.RA |
arxiv_dataset-17761003.1793 | Should recombinations of radical pairs be considered as accompanied by
measurements?
quant-ph physics.chem-ph
The so-called "phenomenological" kinetic equation for one-pair density
operator for spin-selective reactions is defended. We derive this equation from
the kinetic equation for density operator of all pairs which are treated as
singlet and triplet bosons. There presented some reasons for inconsistency of
measurement-like approach to the problem.
| arxiv topic:quant-ph physics.chem-ph |
arxiv_dataset-17771003.1893 | The Infrared Astronomical Characteristics of Roque de los Muchachos
Observatory: precipitable water vapor statistics
astro-ph.IM
The atmospheric water vapor content above the Roque de los Muchachos
Observatory (ORM) obtained from Global Positioning Systems (GPS) is presented.
GPS measurements have been evaluated by comparison with 940nm-radiometer
observations. Statistical analysis of GPS measurements points to ORM as an
observing site with suitable conditions for infrared (IR) observations, with a
median column of precipitable water vapor (PWV) of 3.8 mm. PWV presents a clear
seasonal behavior, being Winter and Spring the best seasons for IR
observations. The percentage of nighttime showing PWV values smaller than 3 mm
is over 60% in February, March and April. We have also estimated the temporal
variability of water vapor content at the ORM. A summary of PWV statistical
results at different astronomical sites is presented, recalling that these
values are not directly comparable as a result of the differences in the
techniques used to recorded the data.
| arxiv topic:astro-ph.IM |
arxiv_dataset-17781003.1993 | A stem-cell ageing hypothesis on the origin of Parkinson's disease
q-bio.CB q-bio.OT
A transcriptome-wide blood expression dataset of Parkinson's disease (PD)
patients and controls was analyzed under the hypothesis-rich mathematical
framework. The analysis pointed towards differential expression in blood cells
in many of the processes known or predicted to be disrupted in PD. We suggest
that circulating blood cells in PD patients can be in a full-blown
PD-expression state. We put forward the hypothesis that sporadic PD can
originate as a case of hematopoietic stem cell/differentiation process
expression program defect and suggest this research direction deserves further
investigation.
| arxiv topic:q-bio.CB q-bio.OT |
arxiv_dataset-17791003.2093 | Thermodynamics of interacting entropy-corrected holographic dark energy
in a non-flat FRW universe
physics.gen-ph hep-th
A so-called "entropy-corrected holographic dark energy" (ECHDE), was recently
proposed to explain the dark energy-dominated universe with the help of quantum
corrections to the entropy-area relation in the setup of loop quantum
cosmology. Using this new definition, we investigate its thermodynamical
features including entropy and energy conservation. We describe the
thermodynamical interpretation of the interaction between ECHDE and dark matter
in a non-flat universe. We obtain a relation between the interaction term of
the dark components and thermal fluctuation. Our study further generalizes the
earlier works [M.R. Setare and E.C. Vagenas, Phys. Lett. B 666 (2008) 111; B.
Wang et al., Phys. Lett. B 662 (2008) 1] in this direction.
| arxiv topic:physics.gen-ph hep-th |
arxiv_dataset-17801003.2193 | Unimpeded tunneling in graphene nanoribbons
cond-mat.mtrl-sci
We studied the Klein paradox in zigzag (ZNR) and anti-zigzag (AZNR) graphene
nanoribbons. Due to the fact that ZNR (the number of lattice sites across the
nanoribbon (N is even) and AZNR (N is odd) configurations are indistinguishable
when treated by the Dirac equation, we supplemented the model with a
pseudo-parity operator whose eigenvalues correctly depend on the sublattice
wavefunctions for the number of carbon atoms across the ribbon, in agreement
with the tight-binding model. We have shown that the Klein tunneling in zigzag
nanoribbons is related to conservation of the pseudo-parity rather than
pseudo-spin in infinite graphene. The perfect transmission in the case of
head-on incidence is replaced by perfect transmission at the center of the
ribbon and the chirality is interpreted as the projection of the pseudo-parity
on momentum at different corners of the Brillouin zone.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-17811003.2293 | On the Chiral Magnetic Effect in Soft-Wall AdS/QCD
hep-ph hep-th
The essence of the chiral magnetic effect is generation of an electric
current along an external magnetic field. Recently it has been studied by
Rebhan et al. within the Sakai--Sugimoto model, where it was shown to be zero.
As an alternative, we calculate the chiral magnetic effect in soft-wall AdS/QCD
and find a non-zero result with the natural boundary conditions. The mechanism
of the dynamical neutralization of the chiral chemical potential via the string
production is discussed in the dual two-form representation.
| arxiv topic:hep-ph hep-th |
arxiv_dataset-17821003.2393 | On the transitional behavior of quantum Gaussian memory channels
quant-ph
We address the question of optimality of entangled input states in quantum
Gaussian memory channels. For a class of such channels, that can be traced back
to the memoryless setting, we state a criterion which relate the optimality of
entangled inputs to the symmetry properties of the channels' action. Several
examples of channel models belonging to this class are discussed.
| arxiv topic:quant-ph |
arxiv_dataset-17831003.2493 | Bivariate Quasi-Tower Sets and Their Associated Lagrange Interpolation
Bases
math.AC math.NA
As we all known, there is still a long way for us to solve arbitrary
multivariate Lagrange interpolation in theory. Nevertheless, it is well
accepted that theories about Lagrange interpolation on special point sets
should cast important lights on the general solution. In this paper, we propose
a new type of bivariate point sets, quasi-tower sets, whose geometry is more
natural than some known point sets such as cartesian sets and tower sets. For
bivariate Lagrange interpolation on quasi-tower sets, we construct the
associated degree reducing interpolation monomial and Newton bases w.r.t.
common monomial orderings theoretically. Moreover, by inputting these bases
into Buchberger-M\"{o}ller algorithm, we obtain the reduced Gr\"{o}bner bases
for vanishing ideals of quasi-tower sets much more efficiently than before.
| arxiv topic:math.AC math.NA |
arxiv_dataset-17841003.2593 | Manipulation of the dynamics of many-body systems via quantum control
methods
quant-ph cond-mat.other
We investigate how dynamical decoupling methods may be used to manipulate the
time evolution of quantum many-body systems. These methods consist of sequences
of external control operations designed to induce a desired dynamics. The
systems considered for the analysis are one-dimensional spin-1/2 models, which,
according to the parameters of the Hamiltonian, may be in the integrable or
non-integrable limits, and in the gapped or gapless phases. We show that an
appropriate control sequence may lead a chaotic chain to evolve as an
integrable chain and a system in the gapless phase to behave as a system in the
gapped phase. A key ingredient for the control schemes developed here is the
possibility to use, in the same sequence, different time intervals between
control operations.
| arxiv topic:quant-ph cond-mat.other |
arxiv_dataset-17851003.2693 | Relativistic quantum Brownian motion
quant-ph cond-mat.stat-mech
A Wigner-Klein-Kramers equation is proposed, which merges relativistic,
quantum and thermo dynamics. The relativistic effect on quantum Brownian motion
is studied via the Breit-Fermi Hamiltonian applied into a dissipative Madelung
hydrodynamics. A new thermo-quantum Smoluchowski equation is derived, which
accounts for the relativistic correction of the Bohm quantum potential.
| arxiv topic:quant-ph cond-mat.stat-mech |
arxiv_dataset-17861003.2793 | KAM for the quantum harmonic oscillator
math.AP
In this paper we prove an abstract KAM theorem for infinite dimensional
Hamiltonians systems. This result extends previous works of S.B. Kuksin and J.
P\"oschel and uses recent techniques of H. Eliasson and S.B. Kuksin. As an
application we show that some 1D nonlinear Schr\"odinger equations with
harmonic potential admits many quasi-periodic solutions. In a second
application we prove the reducibility of the 1D Schr\"odinger equations with
the harmonic potential and a quasi periodic in time potential.
| arxiv topic:math.AP |
arxiv_dataset-17871003.2893 | Investigation of mechanical losses of thin silicon flexures at low
temperatures
cond-mat.mtrl-sci
The investigation of the mechanical loss of different silicon flexures in a
temperature region from 5 to 300 K is presented. The flexures have been
prepared by different fabrication techniques. A lowest mechanical loss of
$3\times10^{-8}$ was observed for a 130 $\mu$m thick flexure at around 10 K.
While the mechanical loss follows the thermoelastic predictions down to 50 K a
difference can be observed at lower temperatures for different surface
treatments. This surface loss will be limiting for all applications using
silicon based oscillators at low temperatures. The extraction of a surface loss
parameter using different results from our measurements and other references is
presented. We focused on structures that are relevant for gravitational wave
detectors. The surface loss parameter $\alpha_s$ = 0.5 pm was obtained. This
reveals that the surface loss of silicon is significantly lower than the
surface loss of fused silica.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-17881003.2993 | On the bound-state spectrum of a nonrelativistic particle in the
background of a short-ranged linear potential
quant-ph
The nonrelativistic problem of a particle immersed in a triangular potential
well, set forth by N.A. Rao and B.A. Kagali, is revised. It is shown that these
researchers misunderstood the full meaning of the potential and obtained a
wrong quantization condition. By exploring the space inversion symmetry, this
work presents the correct solution to this problem with potential applications
in electronics in a simple and transparent way.
| arxiv topic:quant-ph |
arxiv_dataset-17891003.3093 | Relationship between preexponent and distribution over activation
barrier energies for enzymatic reactions
q-bio.BM
A relationship between the preexponent of the rate constant and the
distribution over activation barrier energies for enzymatic/protein reactions
is revealed. We consider an enzyme solution as an ensemble of individual
molecules with different values of the activation barrier energy described by
the distribution. From the solvent viscosity effect on the preexponent we
derive the integral equation for the distribution and find its approximate
solution. Our approach enables us to attain a twofold purpose. On the one hand
it yields a simple interpretation of the solvent viscosity dependence for
enzymatic/protein reactions that requires neither a modification of the
Kramers' theory nor that of the Stokes law. On the other hand our approach
enables us to deduce the form of the distribution over activation barrier
energies. The obtained function has a familiar bell-shaped form and is in
qualitative agreement with the results of single enzyme kinetics measurements.
General formalism is exemplified by the analysis of literature experimental
data.
| arxiv topic:q-bio.BM |
arxiv_dataset-17901003.3193 | The early stages of star formation in Infrared Dark Clouds:
characterizing the core dust properties
astro-ph.SR
Identified as extinction features against the bright Galactic mid-infrared
background, infrared dark clouds (IRDCs) are thought to harbor the very
earliest stages of star and cluster formation. In order to better characterize
the properties of their embedded cores, we have obtained new 24um, 60-100um,
and sub-millimeter continuum data toward a sample of 38 IRDCs. The 24um Spitzer
images reveal that while the IRDCs remain dark, many of the cores are
associated with bright 24um emission sources, which suggests that they contain
one or more embedded protostars. Combining the 24um, 60-100um, and
sub-millimeter continuum data, we have constructed broadband spectral energy
distributions (SEDs) for 157 of the cores within these IRDCs and, using simple
gray-body fits to the SEDs, have estimated their dust temperatures,
emissivities, opacities, bolometric luminosities, masses and densities. Based
on their Spitzer/IRAC 3-8um colors and the presence of 24um point source
emission, we have separated cores that harbor active, high-mass star formation
from cores that are quiescent. The active `protostellar' cores typically have
warmer dust temperatures and higher bolometric luminosities than the more
quiescent, perhaps `pre-protostellar', cores. Because the mass distributions of
the populations are similar, however, we speculate that the active and
quiescent cores may represent different evolutionary stages of the same
underlying population of cores. Although we cannot rule out low-mass
star-formation in the quiescent cores, the most massive of them are excellent
candidates for the `high-mass starless core' phase, the very earliest in the
formation of a high-mass star.
| arxiv topic:astro-ph.SR |
arxiv_dataset-17911003.3293 | Transport properties of the fluid produced at RHIC
nucl-th hep-ph nucl-ex
It is by now well known that the relativistic heavy-ion collisions at RHIC,
BNL have produced a strongly interacting fluid with remarkable properties,
among them the lowest ever observed ratio of the coefficient of shear viscosity
to entropy density. Arguments based on ideas from the String Theory, in
particular the AdS/CFT correspondence, led to the conjecture --- now known to
be violated --- that there is an absolute lower limit $1/4 \pi$ on the value of
this ratio. Causal viscous hydrodynamics calculations together with the RHIC
data have put an upper limit on this ratio, a small multiple of $1/4 \pi$, in
the relevant temperature regime. Less well-determined is the ratio of the
coefficient of bulk viscosity to entropy density. These transport coefficients
have also been studied nonperturbatively in the lattice QCD framework, and
perturbatively in the limit of high-temperature QCD. Another interesting
transport coefficient is the coefficient of diffusion which is also being
studied in this context. I review some of these recent developments and then
discuss the opportunities presented by the anticipated LHC data, for the
general nuclear physics audience.
| arxiv topic:nucl-th hep-ph nucl-ex |
arxiv_dataset-17921003.3393 | Spectral signatures of ultra-rapidly varying objects
astro-ph.HE
The main purpose of this article is to alert spectroscopists, particularly
those involved in surveys, to the fact that rapidly pulsating sources induce
periodic structures in spectra. This would allow the detection of new classes
of objects sending bursts of pulses separated by constant time intervals that
are too short to be detected with conventional techniques. The outstanding
advantage of the technique is that there is no need for specialized instruments
or surveys. One only must incorporate signal-searching algorithms into existing
data analyzing software and use it with standard spectroscopic surveys,
including existing ones. It is a small effort with a potentially huge pay-off
because finding rapidly pulsating objects would be of enormous interest. Even a
lack of detection could be used to eliminate exotic theoretical models.
| arxiv topic:astro-ph.HE |
arxiv_dataset-17931003.3493 | Statistical analysis of the sigma meson considered as two-pion resonance
nucl-th
It was found that the most simple analysis in the linear \sigma- model, where
the sigma meson couples in vacuum to two virtual pions, predicted the most
typical values for the \sigma-mass and total decay width as 486+/-7MeV and
340+/-20MeV respectively. It was demonstrate, via statistical analysis, that
the experimental values reported by the Fermilab (E791) Collaboration
represents approximately 56% of the values predicted by the linear \sigma-
model together with the Breit-Wigner formalism. Additional, it was created the
spectral function, in terms of the \sigma-meson regularized self-energy, which
is consistently with the Breit-Wigner distribution and it reproduces reasonably
well the total width and observable mass given by the Fermilab (E791)
Collaboration and Dalitz plot. The results are a strong evidence that the
\sigma- meson can be considered as a two-pion resonance.
| arxiv topic:nucl-th |
arxiv_dataset-17941003.3593 | The index growth and multiplicity of closed geodesics
math.DG math.DS math.SG
In the recent paper \cite{LoD1}, we classified closed geodesics on Finsler
manifolds into rational and irrational two families, and gave a complete
understanding on the index growth properties of iterates of rational closed
geodesics. This study yields that a rational closed geodesic can not be the
only closed geodesic on every irreversible or reversible (including Riemannian)
Finsler sphere, and that there exist at least two distinct closed geodesics on
every compact simply connected irreversible or reversible (including
Riemannian) Finsler 3-dimensional manifold. In this paper, we study the index
growth properties of irrational closed geodesics on Finsler manifolds. This
study allows us to extend results in \cite{LoD1} on rational and in
\cite{DuL1}, \cite{Rad4} and \cite{Rad5} on completely non-degenerate closed
geodesics on spheres and $\CP^2$ to every compact simply connected Finsler
manifold. Then we prove the existence of at least two distinct closed geodesics
on every compact simply connected irreversible or reversible (including
Riemannian) Finsler 4-dimensional manifold.
| arxiv topic:math.DG math.DS math.SG |
arxiv_dataset-17951003.3693 | Feasibility Study of Lense-Thirring Precession in LS I +61303
astro-ph.HE
Very recent analysis of the radio spectral index and high energy observations
have shown that the two-peak accretion/ejection microquasar model applies for
LSI+61303. The fast variations of the position angle observed with MERLIN and
confirmed by consecutive VLBA images must therefore be explained in the context
of the microquasar scenario. We calculate what could be the precessional period
for the accretion disk in LSI+61303 under tidal forces of the Be star
(P_{tidal-forces}) or under the effect of frame dragging produced by the
rotation of the compact object (P_{Lense-Thirring}). P_{tidal-forces}$ is more
than one year. P_{Lense-Thirring} depends on the truncated radius of the
accretion disk, $R_{tr}$. We determined R_{tr}=300 r_g for observed QPO at 2
Hz. This value is much above the few $r_g$, where the Bardeen-Petterson effect
should align the midplane of the disk. For this truncated radius of the
accretion disk P_{Lense-Thirring} for a slow rotator results in a few days.
Therefore, Lense-Thirring precession induced by a slowly rotating compact
object could be compatible with the daily variations of the ejecta angle
observed in LSI+61303.
| arxiv topic:astro-ph.HE |
arxiv_dataset-17961003.3793 | Anisotropy of the superconducting state parameters and intrinsic pinning
in low-level Pr-doped YBa2Cu3O(7-delta) single crystals
cond-mat.supr-con
The influence of low-level Pr substitution in Y1-xPrxBa2Cu3O(7-delta) single
crystals on the anisotropy of the superconducting state parameters was
investigated by torque magnetometry in magnetic fields of up to 9 T. An
averaged anisotropy parameter, \gamma, of 7.4 was found and no influence of the
Pr ion concentration on \gamma was observed up to a Pr content of 2.4%. A
pronounced maximum at angles between 0.5 and 1 degree out of the ab-plane was
observed in all crystals in the irreversible angular dependence of the torque.
This maximum is attributed to intrinsic pinning associated with kinked
vortices. The variation of the irreversible torque with the substitution level
indicates the influence of the Pr content on pinning within the CuO2 planes,
even though the anisotropy of the superconducting state parameters is not
affected.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-17971003.3893 | Unwinding Conditional Noninterference
cs.CR
Noninterference provides a control over information flow in a system for
ensuring confidentiality and integrity properties. In the literature this
notion has been well studied as transitive noninterference and intransitive
noninterference. In this paper we define a framework on the notion of
conditional noninterference, which allows to specify information flow policies
based on the semantics of action channels. Our new policies subsume the
policies of both transitive and intransitive noninterference, and support
dynamic requirements such as upgrading and downgrading. We also present
unwinding relations that are both sound and complete for the new policies.
| arxiv topic:cs.CR |
arxiv_dataset-17981003.3993 | An improved design of an inductive fault current limiter based on a
superconducting cylinder
cond-mat.supr-con
The paper deals with basic designs of a fault current limiter of the
transformer type which differ each other by the mutual location of a primary
winding and a superconducting short-circuited cylinder. Theoretical study of
the main parameters of the different designs is performed in the framework of
the critical state model and shows that the most effective is a design in which
the primary winding is divided to two sections with equal turn numbers. The
sections are placed inside and outside of the cylinder and connected in series.
Such arrangement of the windings leads to a substantial reduction of AC losses
in the superconducting cylinder, an increase of the activation current and a
decrease of the inductive reactance in the normal regime of a protected
circuit. The experimental results obtained on the laboratory model with a BSSCO
cylinder confirm the theoretical predictions.
| arxiv topic:cond-mat.supr-con |
arxiv_dataset-17991003.4093 | Convergent sequences in discrete groups
math.GR math.FA
We prove that a finitely generated group contains a sequence of non-trivial
elements which converge to the identity in every compact homomorphic image if
and only if the group is not virtually abelian.
| arxiv topic:math.GR math.FA |
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