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arxiv_dataset-100706.1314 | When Did Cosmic Acceleration Start ?
astro-ph gr-qc hep-ph
A precise determination, and comparison, of the epoch of the onset of cosmic
acceleration, at redshift z_acc, and of dark energy domination, at z_eq,
provides an interesting measure with which to parameterize dark energy models.
By combining several cosmological datasets we place constraints on the redshift
and age of cosmological acceleration. For a Lambda-CDM model, we find the
constraint z_acc=0.76\pm0.10 at 95% c.l., occurring 6.7\pm0.4 Gyrs ago.
Allowing a constant equation of state but different from -1 changes the
constraints to z_acc=0.81\pm0.12 (6.9\pm0.5 Gyrs ago) and
z_eq=0.48\pm0.14(4.9\pm0.9 Gyrs ago), while dynamical models markedly increase
the error on the constraints with z_acc=0.81\pm0.30 (6.8\pm1.4 Gyrs ago) and
z_eq=0.44\pm0.20 (4.5\pm1.0 Gyrs ago). Unified dark energy models as Silent
Quartessence yield: z_acc=0.80\pm0.16 (6.8\pm0.6 Gyrs ago).
| arxiv topic:astro-ph gr-qc hep-ph |
arxiv_dataset-101706.1414 | Absence of long-range Ni/Mn ordering in ferromagnetic La2NiMnO6 thin
films
cond-mat.mtrl-sci cond-mat.str-el
Epitaxial La2NiMnO6 thin films have been grown on (001)-oriented SrTiO3 using
the PLD technique. The thin films are semiconducting and FM with a TC close to
270K, a coercive field of 920Oe, and a saturation magnetization of 5muB per
f.u. TEM, conducted at RT, reveals a majority phase having "I-centered"
structure with a=c=1.4asub and b=2asub along with a minority phase-domains
having "P-type" structure (asub being the lattice parameter of the perovskite
structure). A discusion on the presence of Ni/Mn long-range ordering, in light
of recent literature on double perovskites La2NiMnO6 is presented.
| arxiv topic:cond-mat.mtrl-sci cond-mat.str-el |
arxiv_dataset-102706.1514 | Electron and hole spin dynamics and decoherence in quantum dots
cond-mat.mes-hall
In this article we review our work on the dynamics and decoherence of
electron and hole spins in single and double quantum dots. The first part, on
electron spins, focuses on decoherence induced via the hyperfine interaction
while the second part covers decoherence and relaxation of heavy-hole spins due
to spin-orbit interaction as well as the manipulation of heavy-hole spin using
electric dipole spin resonance.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-103706.1614 | Non-Cooperative Scheduling of Multiple Bag-of-Task Applications
cs.DC cs.GT
Multiple applications that execute concurrently on heterogeneous platforms
compete for CPU and network resources. In this paper we analyze the behavior of
$K$ non-cooperative schedulers using the optimal strategy that maximize their
efficiency while fairness is ensured at a system level ignoring applications
characteristics. We limit our study to simple single-level master-worker
platforms and to the case where each scheduler is in charge of a single
application consisting of a large number of independent tasks. The tasks of a
given application all have the same computation and communication requirements,
but these requirements can vary from one application to another. In this
context, we assume that each scheduler aims at maximizing its throughput. We
give closed-form formula of the equilibrium reached by such a system and study
its performance. We characterize the situations where this Nash equilibrium is
optimal (in the Pareto sense) and show that even though no catastrophic
situation (Braess-like paradox) can occur, such an equilibrium can be
arbitrarily bad for any classical performance measure.
| arxiv topic:cs.DC cs.GT |
arxiv_dataset-104706.1714 | Theory of nonlinear particle acceleration at shocks and self-generation
of the magnetic field
astro-ph
We present some recent developments in the theory of particle acceleration at
shock fronts in the presence of dynamical reaction of the accelerated particles
and self-generation of magnetic field due to streaming instability. The spectra
of accelerated particles, the velocity, magnetic field and temperature profiles
can be calculated in this approach anywhere in the precursor and in the
downstream region. The implications for the origin of cosmic rays and for the
phenomenology of supernova remnants will be discussed.
| arxiv topic:astro-ph |
arxiv_dataset-105706.1814 | Study of the structural changes in the Popocatepetl volcano in Mexico
related to microseismicity by applying the lineament analysis to the Aster
(Terra) satellite data
physics.geo-ph
Mexico is one of the most volcanically active regions in North America.
Volcanic activity in central Mexico is associated with the subduction of the
Cocos and Rivera plates beneath the North American plate. Periods of enhanced
microseismic activity, associated with the volcanic activity of the
Popocatepetl volcano is compared with periods, during which the microseismic
activity was low. We detected systematical changes in the number of lineaments,
associated with the microseismic activity due to lineament analysis of a
temporal sequence of high resolution satellite images of the Popocatepetl
volcano, provided by the ASTER/VNIR instrument. The Lineament Extraction and
Stripes Statistic Analysis (LESSA) software package was used for the lineament
extraction. In the future it would allow develop a methodology for detection of
possible elevation of pressure in volcano edifice.
| arxiv topic:physics.geo-ph |
arxiv_dataset-106706.1914 | Approche variationnelle pour le calcul bay\'esien dans les probl\`emes
inverses en imagerie
physics.data-an physics.comp-ph
In a non supervised Bayesian estimation approach for inverse problems in
imaging systems, one tries to estimate jointly the unknown image pixels $\fb$
and the hyperparameters $\thetab$. This is, in general, done through the joint
posterior law $p(\fb,\thetab|\gb)$. The expression of this joint law is often
very complex and its exploration through sampling and computation of the point
estimators such as MAP and posterior means need either optimization of non
convex criteria or int\'egration of non Gaussian and multi variate probability
laws. In any of these cases, we need to do approximations. We had explored
before the possibilities of Laplace approximation and sampling by MCMC. In this
paper, we explore the possibility of approximating this joint law by a
separable one in $\fb$ and in $\thetab$. This gives the possibility of
developing iterative algorithms with more reasonable computational cost, in
particular, if the approximating laws are choosed in the exponential conjugate
families. The main objective of this paper is to give details of different
algorithms we obtain with different choices of these families.
| arxiv topic:physics.data-an physics.comp-ph |
arxiv_dataset-107706.2014 | Fourier analysis of active-region plage
astro-ph
We study the dynamical interaction of the solar chromosphere with the
transition region in mossy and non-mossy active-region plage. We carefully
align image sequences taken with the Transition Region And Coronal Explorer
(TRACE) in the ultraviolet passbands around 1550, 1600, and 1700 A and the
extreme ultraviolet passbands at 171 and 195 A. We compute Fourier
phase-difference spectra that are spatially averaged separately over mossy and
non-mossy plage to study temporal modulations as a function of temporal
frequency. The 1550 versus 171 A comparison shows zero phase difference in
non-mossy plage. In mossy plage, the phase differences between all UV and EUV
passbands show pronounced upward trends with increasing frequency, which
abruptly changes into zero phase difference beyond 4-6 mHz. The phase
difference between the 171 and 195 A sequences exhibits a shallow dip below 3
mHz and then also turns to zero phase difference beyond this value. We
attribute the various similarities between the UV and EUV diagnostics that are
evident in the phase-difference diagrams to the contribution of the C IV
resonance lines in the 1550 and 1600 A passbands. The strong upward trend at
the lower frequencies indicates the presence of upward-traveling disturbances.
It points to correspondence between the lower chromosphere and the upper
transition region, perhaps by slow-mode magnetosonic disturbances, or by a
connection between chromospheric and coronal heating mechanisms. The transition
from this upward trend to zero phase difference at higher frequencies is due to
the intermittent obscuration by fibrils that occult the foot points of hot
loops, which are bright in the EUV and C IV lines, in oscillatory manner.
| arxiv topic:astro-ph |
arxiv_dataset-108706.2114 | Rigid Limit in N=2 Supergravity and Weak-Gravity Conjecture
hep-th
We analyze the coupled N=2 supergravity and Yang-Mills system using
holomorphy, near the rigid limit where the former decouples from the latter. We
find that there appears generically a new mass scale around g M_{pl} where g is
the gauge coupling constant and M_{pl} is the Planck scale. This is in accord
with the weak-gravity conjecture proposed recently. We also study the scale
dependence of the gauge theory prepotential from its embedding into
supergravity.
| arxiv topic:hep-th |
arxiv_dataset-109706.2214 | Nanorheology of viscoelastic shells: Applications to viral capsids
cond-mat.soft q-bio.SC
We study the microrheology of nanoparticle shells [Dinsmore et al. Science
298, 1006 (2002)] and viral capsids [Ivanovska et al. PNAS 101, 7600 (2004)] by
computing the mechanical response function and thermal fluctuation spectrum of
a viscoelastic spherical shell that is permeable to the surrounding solvent. We
determine analytically the damped dynamics of the shear, bend, and compression
modes of the shell coupled to the solvent both inside and outside the sphere in
the zero Reynolds number limit. We identify fundamental length and time scales
in the system, and compute the thermal correlation function of displacements of
antipodal points on the sphere and the mechanical response to pinching forces
applied at these points. We describe how such a frequency-dependent antipodal
correlation and/or response function, which should be measurable in new
AFM-based microrheology experiments, can probe the viscoelasticity of these
synthetic and biological shells constructed of nanoparticles.
| arxiv topic:cond-mat.soft q-bio.SC |
arxiv_dataset-110706.2314 | Hypersurfaces in H^{n+1} and conformally invariant equations: the
generalized Christoffel and Nirenberg problems
math.DG math.AP
Our first objective in this paper is to give a natural formulation of the
Christoffel problem for hypersurfaces in $H^{n+1}$, by means of the hyperbolic
Gauss map and the notion of hyperbolic curvature radii for hypersurfaces. Our
second objective is to provide an explicit equivalence of this Christoffel
problem with the famous problem of prescribing scalar curvature on $\S^n$ for
conformal metrics, posed by Nirenberg and Kazdan-Warner. This construction lets
us translate into the hyperbolic setting the known results for the scalar
curvature problem, and also provides a hypersurface theory interpretation of
such an intrinsic problem from conformal geometry. Our third objective is to
place the above result into a more general framework. Specifically, we will
show how the problem of prescribing the hyperbolic Gauss map and a given
function of the hyperbolic curvature radii in $H^{n+1}$ is strongly related to
some important problems on conformally invariant PDEs in terms of the Schouten
tensor. This provides a bridge between the theory of conformal metrics on
$\S^n$ and the theory of hypersurfaces with prescribed hyperbolic Gauss map in
$\H^{n+1}$. The fourth objective is to use the above correspondence to prove
that for a wide family of Weingarten functionals $W(\k_1,..., \k_n)$, the only
compact immersed hypersurfaces in $H^{n+1}$ on which $W$ is constant are round
spheres.
| arxiv topic:math.DG math.AP |
arxiv_dataset-111706.2414 | Maxwell Equations with Accounting of Tensor Properties of Time
physics.optics
The Maxwell equations with accounting for tensors properties of time have
been considered. The effects that follow from such consideration are described.
These are the appearance of vacuum polarization, anisotropy of electromagnetic
wave velocity in vacuum, anisotropy of the vacuum dielectric permittivity,
rotation of light polarization plane, as well as the existence of longitudinal
components of electromagnetic wave and the rotational (non-potential) component
of electric field caused by electric charges.
| arxiv topic:physics.optics |
arxiv_dataset-112706.2514 | Simple proof of gauge invariance for the S-matrix element of
strong-field photoionization
physics.atom-ph
The relationship between the length gauge (LG) and the velocity gauge (VG)
exact forms of the photoionization probability amplitude is considered. Our
motivation for this paper comes from applications of the Keldysh-Faisal-Reiss
(KFR) theory, which describes atoms (or ions) in a strong laser field (in the
nonrelativistic approach, in the dipole approximation). On the faith of a
certain widely-accepted assumption, we present a simple proof that the
well-known LG form of the exact photoionization (or photodetachment)
probability amplitude is indeed the gauge-invariant result. In contrast, to
obtain the VG form of this probability amplitude, one has to either (i) neglect
the well-known Goeppert-Mayer exponential factor (which assures gauge
invariance) during all the time evolution of the ionized electron or (ii) put
some conditions on the vector potential of the laser field.
| arxiv topic:physics.atom-ph |
arxiv_dataset-113706.2614 | Dust crystallinity in protoplanetary disks: the effect of
diffusion/viscosity ratio
astro-ph
The process of turbulent radial mixing in protoplanetary disks has strong
relevance to the analysis of the spatial distribution of crystalline dust
species in disks around young stars and to studies of the composition of
meteorites and comets in our own solar system.
A debate has gone on in the recent literature on the ratio of the effective
viscosity coefficient $\nu$ (responsible for accretion) to the turbulent
diffusion coefficient $D$ (responsible for mixing). Numerical
magneto-hydrodynamic simulations have yielded values between $\nu/D\simeq 10$
(Carballido, Stone & Pringle, 2005) and $\nu/D\simeq 0.85$ (Johansen & Klahr,
2005}). Here we present two analytic arguments for the ratio $\nu/D=1/3$ which
are based on elegant, though strongly simplified assumptions. We argue that
whichever of these numbers comes closest to reality may be determined {\em
observationally} by using spatially resolved mid-infrared measurements of
protoplanetary disks around Herbig stars. If meridional flows are present in
the disk, then we expect less abundance of crystalline dust in the surface
layers, a prediction which can likewise be observationally tested with
mid-infrared interferometers.
| arxiv topic:astro-ph |
arxiv_dataset-114706.2714 | A Proof of Solomon's Rule
math.CO
We put forward a proof of Solomon's rule, in terms of matrices, for
multiplication in the descent algebra of the symmetric group. Our proof
exploits the graphs that we can obtain from all the subsets of the set of
transpositions, $\{(i,i+1)\}_{i=1}^{n-1}$.
| arxiv topic:math.CO |
arxiv_dataset-115706.2814 | On the tautological ring of a Jacobian modulo rational equivalence
math.AG
We consider the Chow ring with rational coefficients of the Jacobian of a
curve. Assume D is a divisor in a base point free g^r_d of the curve such that
the canonical divisor K is a multiple of the divisor D. We find relations
between tautological cycles. We give applications for curves having a degree d
covering of P^1 whose ramification points are all of order d, and then for
hyperelliptic curves.
| arxiv topic:math.AG |
arxiv_dataset-116706.2914 | Comment on "Infrared freezing of Euclidean QCD observables"
hep-ph
Recently, P. M. Brooks and C.J. Maxwell [Phys. Rev. D{\bf 74} 065012 (2006)]
claimed that the Landau pole of the one-loop coupling at $Q^2=\Lambda^2$ is
absent from the leading one-chain term in a skeleton expansion of the Euclidean
Adler ${\cal D}$ function. Moreover, in this approximation one has continuity
along the Euclidean axis and a smooth infrared freezing, properties known to be
satisfied by the "true" Adler function. We show that crucial in the derivation
of these results is the use of a modified Borel summation, which leads
simultaneously to the loss of another fundamental property of the true Adler
function: the analyticity implied by the K\"allen-Lehmann representation.
| arxiv topic:hep-ph |
arxiv_dataset-117706.3014 | Bayesian Calibrated Significance Levels Applied to the Spectral Tilt and
Hemispherical Asymmetry
astro-ph gr-qc hep-ph hep-th
Bayesian model selection provides a formal method of determining the level of
support for new parameters in a model. However, if there is not a specific
enough underlying physical motivation for the new parameters it can be hard to
assign them meaningful priors, an essential ingredient of Bayesian model
selection. Here we look at methods maximizing the prior so as to work out what
is the maximum support the data could give for the new parameters. If the
maximum support is not high enough then one can confidently conclude that the
new parameters are unnecessary without needing to worry that some other prior
may make them significant. We discuss a computationally efficient means of
doing this which involves mapping p-values onto upper bounds of the Bayes
factor (or odds) for the new parameters. A p-value of 0.05 ($1.96\sigma$)
corresponds to odds less than or equal to 5:2 which is below the `weak' support
at best threshold. A p-value of 0.0003 ($3.6\sigma$) corresponds to odds of
less than or equal to 150:1 which is the `strong' support at best threshold.
Applying this method we find that the odds on the scalar spectral index being
different from one are 49:1 at best. We also find that the odds that there is
primordial hemispherical asymmetry in the cosmic microwave background are 9:1
at best.
| arxiv topic:astro-ph gr-qc hep-ph hep-th |
arxiv_dataset-118706.3114 | Polynomial rate convergence to an invariant measure for the continuum
time limit of the Minority Game
math.PR
In this paper we show that the continuum time version of the Minority Game
satisfies the criteria for the application of a theorem on the existence of an
invariant measure. We consider the special case of a game with "sufficiently"
asymmetric initial condition where the number of possible choices for each
individual is S=2 and $\Gamma<+\infty$. An upper bound for the asymptotic
behavior, as the number of agents grows to infinity, of the waiting time for
reaching the stationary state is then obtained.
| arxiv topic:math.PR |
arxiv_dataset-119706.3214 | Reheating a multi-throat universe by brane motion
hep-th astro-ph gr-qc hep-ph
We propose a mechanism of reheating after inflation in multi-throat scenarios
of warped extra dimensions. Validity of an effective field theory on the
standard model (SM) brane requires that the position of the SM brane during
inflation be different from the position after inflation. The latter is
supposed to be near the tip of the SM throat but the former is not. After
inflation, when the Hubble expansion rate becomes sufficiently low, the SM
brane starts moving towards the tip and eventually oscillates. The SM fields
are excited by the brane motion and the universe is reheated. Since interaction
between the brane position modulus and the SM fields is suppressed only by the
local string scale, the modulus effectively decays into the SM fields.
| arxiv topic:hep-th astro-ph gr-qc hep-ph |
arxiv_dataset-120706.3314 | Structure of W3(OH) from Very High Spectral Resolution Observations of 5
Centimeter OH Masers
astro-ph
Recent studies of methanol and ground-state OH masers at very high spectral
resolution have shed new light on small-scale maser processes. The nearby
source W3(OH), which contains numerous bright masers in several different
transitions, provides an excellent laboratory for high spectral resolution
techniques. We present a model of W3(OH) based on EVN observations of the
rotationally-excited 6030 and 6035 MHz OH masers taken at 0.024 km/s spectral
resolution. The 6.0 GHz masers are becoming brighter with time and show
evidence for tangential proper motions. We confirm the existence of a region of
magnetic field oriented toward the observer to the southeast and find another
such region to the northeast in W3(OH), near the champagne flow. The 6.0 GHz
masers trace the inner edge of a counterclockwise rotating torus feature.
Masers at 6030 MHz are usually a factor of a few weaker than at 6035 MHz but
trace the same material. Velocity gradients of nearby Zeeman components are
much more closely correlated than in the ground state, likely due to the
smaller spatial separation between Zeeman components. Hydroxyl maser peaks at
very long baseline interferometric resolution appear to have structure on
scales both smaller than that resolvable as well as on larger scales.
| arxiv topic:astro-ph |
arxiv_dataset-121706.3414 | Direct measurement of the intermolecular forces confining a single
molecule in an entangled polymer solution
cond-mat.soft
We use optical tweezers to directly measure the intermolecular forces acting
on a single polymer imposed by surrounding entangled polymers (115 kbp DNA, 1
mg/ml). A tube-like confining field was measured in accord with the key
assumption of reptation models. A time-dependent harmonic potential opposed
transverse displacement, in accord with recent simulation findings. A tube
radius of 0.8 microns was determined, close to the predicted value (0.5
microns). Three relaxation modes (~0.4, 5 and 30 s) were measured following
transverse displacement, consistent with predicted relaxation mechanisms.
| arxiv topic:cond-mat.soft |
arxiv_dataset-122706.3514 | Charge Inversion of Divalent Ionic Solutions in Silica Channels
cond-mat.mtrl-sci
Recent experiments (F.H.J. Van Der Heyden et al., PRL 96, 224502 (2006)) of
streaming currents in silica nanochannels with divalent ions report charge
inversion, i.e. interfacial charges attracting counterions in excess of their
own nominal charge, in conflict with existing theoretical and simulation
results. We reveal the mechanism of charge inversion by using all-atomic
molecular dynamics simulations. Our results show excellent agreement with
experiments, both qualitatively and quantitatively. We further discuss the
implications of our study for the general problem of ionic correlations in
solutions as well as in regards of the properties of silica-water interfaces.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-123706.3614 | Nuclear vector polarizability correction to hyperfine splitting
physics.atom-ph nucl-th
The interaction of orbital electrons with the charge and magnetic moment of
the nucleus polarizes it, and the detailed description requires a careful
treatment of the nuclear vector polarizability. We present a complete and
closed form expression for the resulting contribution to hyperfine splitting in
light atomic systems.
| arxiv topic:physics.atom-ph nucl-th |
arxiv_dataset-124706.3714 | No phase transition for Gaussian fields with bounded spins
math.PR math-ph math.MP
Let a<b, \Omega=[a,b]^{\Z^d} and H be the (formal) Hamiltonian defined on
\Omega by
H(\eta) = \frac12 \sum_{x,y\in\Z^d} J(x-y) (\eta(x)-\eta(y))^2 where
J:\Z^d\to\R is any summable non-negative symmetric function (J(x)\ge 0 for all
x\in\Z^d, \sum_x J(x)<\infty and J(x)=J(-x)). We prove that there is a unique
Gibbs measure on \Omega associated to H. The result is a consequence of the
fact that the corresponding Gibbs sampler is attractive and has a unique
invariant measure.
| arxiv topic:math.PR math-ph math.MP |
arxiv_dataset-125706.3814 | The effect of dwarf galaxies disruption in semi-analytic models
astro-ph
We present results for a galaxy formation model that includes a simple
treatment for the disruption of dwarf galaxies by gravitational forces and
galaxy encounters within galaxy clusters. This is implemented a posteriori in a
semi-analytic model by considering the stability of cluster dark matter
sub-haloes at z=0. We assume that a galaxy whose dark matter substructure has
been disrupted will itself disperse, while its stars become part of the
population of intracluster stars responsible for the observed intracluster
light. Despite the simplicity of this assumption, our results show a
substantial improvement over previous models and indicate that the inclusion of
galaxy disruption is indeed a necessary ingredient of galaxy formation models.
We find that galaxy disruption suppresses the number density of dwarf galaxies
by about a factor of two. This makes the slope of the faint end of the galaxy
luminosity function shallower, in agreement with observations. In particular,
the abundance of faint, red galaxies is strongly suppressed. As a result, the
luminosity function of red galaxies and the distinction between the red and the
blue galaxy populations in colour-magnitude relationships are correctly
predicted. Finally, we estimate a fraction of intracluster light comparable to
that found in clusters of galaxies.
| arxiv topic:astro-ph |
arxiv_dataset-126706.3914 | Asymptotic behavior of the entropy of chains placed on stripes
cond-mat.stat-mech
By using the transfer matrix approach, we investigate the asymptotic behavior
of the entropy of flexible chains with $M$ monomers each placed on stripes. In
the limit of high density of monomers, we study the behavior of the entropy as
a function of the density of monomers and the width of the stripe, inspired by
recent analytical studies of this problem for the particular case of dimers
(M=2). We obtain the entropy in the asymptotic regime of high densities for
chains with $M=2,..,9$ monomers, as well as for the special case of polymers,
where $M\to\infty$, and find that the results show a regular behavior similar
to the one found analytically for dimers. We also verify that in the
low-density limit the mean-field expression for the entropy is followed by the
results from our transfer matrix calculations.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-127706.4014 | The Disturbed 17 keV Cluster Associated with the Radio Galaxy 3C 438
astro-ph
We present results from a {\em Chandra} observation of the cluster gas
associated with the FR II radio galaxy 3C 438. This radio galaxy is embedded
within a massive cluster with gas temperature $\sim$17 keV and bolometric
luminosity of 6$\times10^{45}$ ergs s$^{-1}$. It is unclear if this high
temperature represents the gravitational mass of the cluster, or if this is an
already high ($\sim$ 11 keV) temperature cluster that has been heated
transiently. We detect a surface brightness discontinuity in the gas that
extends $\sim$600 kpc through the cluster. The radio galaxy 3C 438 is too small
($\sim$110 kpc across) and too weak to have created this large disturbance in
the gas. The discontinuity must be the result of either an extremely powerful
nuclear outburst or the major merger of two massive clusters. If the observed
features are the result of a nuclear outburst, it must be from an earlier epoch
of unusually energetic nuclear activity. However, the energy required
($\sim10^{63}$ ergs) to move the gas on the observed spatial scales strongly
supports the merger hypothesis. In either scenario, this is one of the most
extreme events in the local Universe.
| arxiv topic:astro-ph |
arxiv_dataset-128706.4114 | Searches for New Physics at HERA
hep-ex
The high energy programme of the HERA collider ended in March 2007. During
the whole HERA programme, a combined total integrated luminosity of 1 fb$^{-1}$
was collected by the H1 and ZEUS experiments. In this context, an overview of
the most recent results of both experiments concerning searches for new physics
is presented. The topics covered are searches for contact interactions,
leptoquarks and excited leptons, as well as studies of the isolated lepton and
multi-lepton topologies, and a general signature based search.
| arxiv topic:hep-ex |
arxiv_dataset-129706.4214 | Dynamical Systems On Three Manifolds Part II: 3-Manifolds,Heegaard
Splittings and Three-Dimensional Systems
math.DS
The global behaviour of nonlinear systems is extremely important in control
and systems theory since the usual local theories will only give information
about a system in some neighbourhood of an operating point. Away from that
point, the system may have totally different behaviour and so the theory
developed for the local system will be useless for the global one.
In this paper we shall consider the analytical and topological structure of
systems on 2- and 3- manifolds and show that it is possible to obtain systems
with 'arbitrarily strange' behaviour, i.e., arbitrary numbers of chaotic
regimes which are knotted and linked in arbitrary ways. We shall do this by
considering Heegaard Splittings of these manifolds and the resulting systems
defined on the boundaries.
| arxiv topic:math.DS |
arxiv_dataset-130706.4314 | Domain growth morphology in curvature driven two dimensional coarsening
cond-mat.stat-mech
We study the distribution of domain areas, areas enclosed by domain
boundaries (''hulls''), and perimeters for curvature-driven two-dimensional
coarsening, employing a combination of exact analysis and numerical studies,
for various initial conditions. We show that the number of hulls per unit area,
$n_h(A,t) dA$, with enclosed area in the interval $(A,A+dA)$, is described, for
a disordered initial condition, by the scaling function $n_h(A,t) = 2c_h/(A +
\lambda_h t)^2$, where $c_h=1/8\pi\sqrt{3} \approx 0.023$ is a universal
constant and $\lambda_h$ is a material parameter. For a critical initial
condition, the same form is obtained, with the same $\lambda_h$ but with $c_h$
replaced by $c_h/2$. For the distribution of domain areas, we argue that the
corresponding scaling function has, for random initial conditions, the form
$n_d(A,t) = 2c_d (\lambda_d t)^{\tau'-2}/(A + \lambda_d t)^{\tau'}$, where
$c_d=c_h + {\cal O}(c_h^2)$, $\lambda_d=\lambda_h + {\cal O}(c_h)$, and $\tau'
= 187/91 \approx 2.055$. For critical initial conditions, one replaces $c_d$ by
$c_d/2$ (possibly with corrections of ${\cal O}(c_h^2)$) and the exponent is
$\tau = 379/187 \approx 2.027$. These results are extended to describe the
number density of the length of hulls and domain walls surrounding connected
clusters of aligned spins. These predictions are supported by extensive
numerical simulations. We also study numerically the geometric properties of
the boundaries and areas.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-131706.4414 | Decay modes of $^{10}$C nuclei unbound state
nucl-ex
Unbound states of $^{10}$C nuclei produced as quasi-projectiles in
$^{12}$C+$^{24}$Mg collisions at E/A = 53 and 95 MeV are studied with the Indra
detector array. Multi-particle correlation function analyses provide
experimental evidence of sequential de-excitation mechanisms through the
production of intermediate $^{9}$B, $^{6}$Be and $^{8}$Be unbound nuclei. The
relative contributions of different decay sequences to the total decay width of
the explored states is estimated semi-quantitatively. The obtained results show
that heavy-ion collisions can be used as a tool to access spectroscopic
information about exotic nuclei.
| arxiv topic:nucl-ex |
arxiv_dataset-132707.003 | Mass Determination in SUSY-like Events with Missing Energy
hep-ph astro-ph hep-ex
We describe a kinematic method which is capable of determining the overall
mass scale in SUSY-like events at a hadron collider with two missing (dark
matter) particles. We focus on the kinematic topology in which a pair of
identical particles is produced with each decaying to two leptons and an
invisible particle (schematically, $pp\to YY+jets$ followed by each $Y$
decaying via $Y\to \ell X\to \ell\ell'N$ where $N$ is invisible). This topology
arises in many SUSY processes such as squark and gluino production and decay,
not to mention $t\anti t$ di-lepton decays. In the example where the final
state leptons are all muons, our errors on the masses of the particles $Y$, $X$
and $N$ in the decay chain range from 4 GeV for 2000 events after cuts to 13
GeV for 400 events after cuts. Errors for mass differences are much smaller.
Our ability to determine masses comes from considering all the kinematic
information in the event, including the missing momentum, in conjunction with
the quadratic constraints that arise from the $Y$, $X$ and $N$ mass-shell
conditions. Realistic missing momentum and lepton momenta uncertainties are
included in the analysis.
| arxiv topic:hep-ph astro-ph hep-ex |
arxiv_dataset-133707.013 | Incompressible, quasi-rigid deformations of 2-dimensional domains
math.AP math.DS
his paper proposes a sensible definition of a deformation metric between
2-dimensional surfaces obtained from each other by an area preserving
(incompressible) mapping, and an algorithm for obtaining this metric, as well
as the optimal deformation.
| arxiv topic:math.AP math.DS |
arxiv_dataset-134707.023 | Positive Forms and Stability of Linear Time-Delay Systems
math.DS math.OC
We consider the problem of constructing Lyapunov functions for linear
differential equations with delays. For such systems it is known that
exponential stability implies the existence of a positive Lyapunov function
which is quadratic on the space of continuous functions. We give an explicit
parametrization of a sequence of finite-dimensional subsets of the cone of
positive Lyapunov functions using positive semidefinite matrices. This allows
stability analysis of linear time-delay systems to be formulated as a
semidefinite program.
| arxiv topic:math.DS math.OC |
arxiv_dataset-135707.033 | An Algebra of Quantum Processes
quant-ph
We introduce an algebra qCCS of pure quantum processes in which no classical
data is involved, communications by moving quantum states physically are
allowed, and computations is modeled by super-operators. An operational
semantics of qCCS is presented in terms of (non-probabilistic) labeled
transition systems. Strong bisimulation between processes modeled in qCCS is
defined, and its fundamental algebraic properties are established, including
uniqueness of the solutions of recursive equations. To model sequential
computation in qCCS, a reduction relation between processes is defined. By
combining reduction relation and strong bisimulation we introduce the notion of
strong reduction-bisimulation, which is a device for observing interaction of
computation and communication in quantum systems. Finally, a notion of strong
approximate bisimulation (equivalently, strong bisimulation distance) and its
reduction counterpart are introduced. It is proved that both approximate
bisimilarity and approximate reduction-bisimilarity are preserved by various
constructors of quantum processes. This provides us with a formal tool for
observing robustness of quantum processes against inaccuracy in the
implementation of its elementary gates.
| arxiv topic:quant-ph |
arxiv_dataset-136707.043 | Assisted Problem Solving and Decompositions of Finite Automata
cs.CC
A study of assisted problem solving formalized via decompositions of
deterministic finite automata is initiated. The landscape of new types of
decompositions of finite automata this study uncovered is presented. Languages
with various degrees of decomposability between undecomposable and perfectly
decomposable are shown to exist.
| arxiv topic:cs.CC |
arxiv_dataset-137707.053 | Self-similar cosmological solutions with dark energy. II: black holes,
naked singularities and wormholes
gr-qc astro-ph hep-th
We use a combination of numerical and analytical methods, exploiting the
equations derived in a preceding paper, to classify all spherically symmetric
self-similar solutions which are asymptotically Friedmann at large distances
and contain a perfect fluid with equation of state $p=(\gamma -1)\mu$ with
$0<\gamma<2/3$. The expansion of the Friedmann universe is accelerated in this
case. We find a one-parameter family of self-similar solutions representing a
black hole embedded in a Friedmann background. This suggests that, in contrast
to the positive pressure case, black holes in a universe with dark energy can
grow as fast as the Hubble horizon if they are not too large. There are also
self-similar solutions which contain a central naked singularity with negative
mass and solutions which represent a Friedmann universe connected to either
another Friedmann universe or some other cosmological model. The latter are
interpreted as self-similar cosmological white hole or wormhole solutions. The
throats of these wormholes are defined as two-dimensional spheres with minimal
area on a spacelike hypersurface and they are all non-traversable because of
the absence of a past null infinity.
| arxiv topic:gr-qc astro-ph hep-th |
arxiv_dataset-138707.063 | Demonstration of 3-port grating phase relations
physics.optics
We experimentally demonstrate the phase relations of 3-port gratings by
investigating 3-port coupled Fabry-Perot cavities. Two different gratings which
have the same 1st order diffraction efficiency but differ substantially in
their 2nd order diffraction efficiency have been designed and manufactured.
Using the gratings as couplers to Fabry-Perot cavities we could validate the
results of an earlier theoretical description of the phases at a three port
grating.
| arxiv topic:physics.optics |
arxiv_dataset-139707.073 | Herbig-Haro Objects - Tracers of the Formation of Low-mass Stars and
Sub-stellar Objects
astro-ph
Herbig-Haro objects (HHOs) are caused by outflows from young objects. Since
the outflow relies on mass accretion from a circumstellar disk, it indicates
ongoing growth. Recent results of infrared observations yielded evidence for
disks around brown dwarfs. This suggests that at least a certain fraction of
brown dwarfs forms like stars. Thus, young sub-stellar objects might cause HHOs
as well. We present selected results of a general survey for HHOs based on
DSS-II plates and CCD images taken with the Tautenburg Schmidt telescope.
Numerous young objects could be identified due to their association with newly
detected HHOs. In some cases the luminosity is consistent with very low-mass
stars or close to sub-stellar values. This holds for L1415-IRS and a few
infrared sources embedded in other dark clouds (e.g., GF9, BHR111). The
question on the minimum mass for outflow activity is addressed.
| arxiv topic:astro-ph |
arxiv_dataset-140707.083 | A New Look at Mode Conversion in a Stratified Isothermal Atmosphere
astro-ph
Recent numerical investigations of wave propagation near coronal magnetic
null points (McLaughlin and Hood: Astron. Astrophys. 459, 641,2006) have
indicated how a fast MHD wave partially converts into a slow MHD wave as the
disturbance passes from a low-beta plasma to a high-beta plasma. This is a
complex process and a clear understanding of the conversion mechanism requires
the detailed investigation of a simpler model. An investigation of mode
conversion in a stratified, isothermal atmosphere, with a uniform, vertical
magnetic field is carried out, both numerically and analytically. In contrast
to previous investigations of upward-propagating waves (Zhugzhda and Dzhalilov:
Astron. Astrophys. 112, 16, 1982a; Cally: Astrophys. J. 548, 473, 2001), this
paper studies the downward propagation of waves from a low-beta to high-beta
environment. A simple expression for the amplitude of the transmitted wave is
compared with the numerical solution.
| arxiv topic:astro-ph |
arxiv_dataset-141707.093 | Bayesian Learning of Neural Networks for Signal/Background
Discrimination in Particle Physics
physics.data-an
Neural networks are used extensively in classification problems in particle
physics research. Since the training of neural networks can be viewed as a
problem of inference, Bayesian learning of neural networks can provide more
optimal and robust results than conventional learning methods. We have
investigated the use of Bayesian neural networks for signal/background
discrimination in the search for second generation leptoquarks at the Tevatron,
as an example. We present a comparison of the results obtained from the
conventional training of feedforward neural networks and networks trained with
Bayesian methods.
| arxiv topic:physics.data-an |
arxiv_dataset-142707.103 | The multiverse and the origin of our universe
astro-ph
The multiverse is a hierarchy in the number of universes, increasing stepwise
towards infinity. It is an evolutionary system, in which universes survive only
near critical mass. That mass is actually a factor of 1.94 less than the
critical mass, and this is found to be consistent with the baryon density
inferred from nucleosynthesis in our universe; it is also precisely verified as
a cosmological effect. That factor seems to have originated in the multiverse
for causing intersecting expansions of its universes, such that mixing occurs
of debris from aging galaxies (over proton-decaying time scales). It follows
that there is an inter-universal medium (IUM), probably having the demand of
new universes in balance with the supply of dark radiation and sub-atomic
particles from the decaying galaxies. The mixing causes the universes to have
the same quantum, relativity, gravity, and particle physics as our universe.
The making of a universe from the radiation and sub-atomic particles occurs
through re-vitalizing the protons, and other particles as well, by
gravitational energy obtained in accretion of the IUM. This process therefore
begins wherever the IUM space density reaches proton density, near 10 E18 kg m
E-3. The process continues quietly as the sweeping-up and gravitational
accretion proceeds, until the near-critical mass is reached. Some of the IUM
debris must also be pervading our present universe, steadily or in partially
accreted lumps. The model therefore predicts that the IUM sub-atomic particles
appear as our dark matter, and its radiation component as our dark energy, both
near 0 K temperatures. The dark energy may cause expansion phenomena, in
addition to the above non-flatness expansion, from an accretion lump that
arrived at our universe at age near 9 x 10 E9 y.
| arxiv topic:astro-ph |
arxiv_dataset-143707.113 | Khovanov-Rozansky homology and the braid index of a knot
math.GT
We prove the existence of a knot whose braid index the Morton-Franks-Williams
inequality fails to detect but a related inequality (KR-MFW inequality), which
uses new information of Khovanov-Rozansky homology, detects. We also prove, by
examples, that there exists infinitely many knots for which the KR-MFW
inequality fails to detect the braid indices.
| arxiv topic:math.GT |
arxiv_dataset-144707.123 | Exploring the Protein G Helix Free Energy Surface by Solute Tempering
Metadynamics
q-bio.BM
The free-energy landscape of the alpha-helix of protein G is studied by means
of metadynamics coupled with a solute tempering algorithm. Metadynamics allows
to overcome large energy barriers, whereas solute tempering improves the
sampling with an affordable computational effort. From the sampled free-energy
surface we are able to reproduce a number of experimental observations, such as
the fact that the lowest minimum corresponds to a globular conformation
displaying some degree of beta-structure, that the helical state is metastable
and involves only 65% of the chain. The calculations also show that the system
populates consistently a pi-helix state and that the hydrophobic staple motif
is present only in the free-energy minimum associated with the helices, and
contributes to their stabilization. The use of metadynamics coupled with solute
tempering results then particularly suitable to provide the thermodynamics of a
short peptide, and its computational efficiency is promising to deal with
larger proteins.
| arxiv topic:q-bio.BM |
arxiv_dataset-145707.133 | Proving the triviality of rational points on Atkin-Lehner quotients of
Shimura curves
math.NT
In this paper we give a method for studying global rational points on certain
quotients of Shimura curves by Atkin-Lehner involutions. We obtain explicit
conditions on such quotients for rational points to be ``trivial'' (coming from
CM points only) and exhibit an explicit infinite family of such quotients
satisfying these conditions.
| arxiv topic:math.NT |
arxiv_dataset-146707.143 | On the Derivatives of Central Loops
math.GM
The right(left) derivative, $a^{-1},e-$ and $e,a^{-1}-$ isotopes of a C-loop
are shown to be C-loops. Furthermore, for a central loop $(L,F)$, it is shown
that $\big\{F,F^{a^{-1}},F_{a^{-1},e}\big\}$ and
$\big\{F,F_{a^{-1}},F_{e,a^{-1}}\big\}$ are systems of isotopic C-loops that
obey a form of generalized distributive law. Quasigroup isotopes $(L,\otimes)$
and $(L,\ominus)$ of a loop $(L,\theta)$ and its parastrophe $(L,\theta ^*)$
respectively are proved to be isotopic if either $(L,\otimes)$ or $(L,\ominus
)$ is commutative. If $(L,\theta)$ is a C-loop, then it is shown that
$\big\{(L,\theta),(L,\theta ^*),(L,\otimes),(L,\oplus)\big\}$ is a system of
isotopic C-quasigroup under the above mentioned condition. It is shown that
C-loops are isotopic to some finite indecomposable groups of the classes ${\cal
D}_i,i=1,2,3,4,5$ and that the center of such C-loops have a rank of 1,2 or 3.
| arxiv topic:math.GM |
arxiv_dataset-147707.153 | Pseudospin Magnetism in Graphene
cond-mat.str-el
We predict that neutral graphene bilayers are pseudospin magnets in which the
charge density-contribution from each valley and spin spontaneously shifts to
one of the two layers. The band structure of this system is characterized by a
momentum-space vortex which is responsible for unusual competition between band
and kinetic energies leading to symmetry breaking in the vortex core. We
discuss the possibility of realizing a pseudospin version of ferromagnetic
metal spintronics in graphene bilayers based on hysteresis associated with this
broken symmetry.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-148707.163 | Direct link between low temperature magnetism and high temperature
sodium order in NaxCoO2
cond-mat.str-el cond-mat.mtrl-sci
We prove the direct link between low temperature magnetism and high
temperature sodium ordering in NaxCoO2 using the example of a heretofore
unreported magnetic transition at 8 K which involves a weak ferromagnetic
moment. The 8 K feature is characterized in detail and its dependence on a
diffusive sodium rearrangement around 200 K is demonstrated. Applying muons as
local probes this process is shown to result in a reversible phase separation
into distinct magnetic phases that can be controlled by specific cooling
protocols. Thus the impact of ordered sodium Coulomb potential on the CoO2
physics is evidenced opening new ways to experimentally revisit the NaxCoO2
phase diagram.
| arxiv topic:cond-mat.str-el cond-mat.mtrl-sci |
arxiv_dataset-149707.173 | Can Strong Gravitational Lensing Constrain Dark Energy?
astro-ph
We discuss the ratio of the angular diameter distances from the source to the
lens, $D_{ds}$, and to the observer at present, $D_{s}$, for various dark
energy models. It is well known that the difference of $D_s$s between the
models is apparent and this quantity is used for the analysis of Type Ia
supernovae. However we investigate the difference between the ratio of the
angular diameter distances for a cosmological constant,
$(D_{ds}/D_{s})^{\Lambda}$ and that for other dark energy models,
$(D_{ds}/D_{s})^{\rm{other}}$ in this paper. It has been known that there is
lens model degeneracy in using strong gravitational lensing. Thus, we
investigate the model independent observable quantity, Einstein radius
($\theta_E$), which is proportional to both $D_{ds}/D_s$ and velocity
dispersion squared, $\sigma_v^2$. $D_{ds}/D_s$ values depend on the parameters
of each dark energy model individually. However, $(D_{ds}/D_s)^{\Lambda} -
(D_{ds}/D_{s})^{\rm{other}}$ for the various dark energy models, is well within
the error of $\sigma_v$ for most of the parameter spaces of the dark energy
models. Thus, a single strong gravitational lensing by use of the Einstein
radius may not be a proper method to investigate the property of dark energy.
However, better understanding to the mass profile of clusters in the future or
other methods related to arc statistics rather than the distances may be used
for constraints on dark energy.
| arxiv topic:astro-ph |
arxiv_dataset-150707.183 | Nonlinear transport of Bose-Einstein condensates through mesoscopic
waveguides
cond-mat.other
We study the coherent flow of interacting Bose-condensed atoms in mesoscopic
waveguide geometries. Analytical and numerical methods, based on the mean-field
description of the condensate, are developed to study both stationary as well
as time-dependent propagation processes. We apply these methods to the
propagation of a condensate through an atomic quantum dot in a waveguide,
discuss the nonlinear transmission spectrum and show that resonant transport is
generally suppressed due to an interaction-induced bistability phenomenon.
Finally, we establish a link between the nonlinear features of the transmission
spectrum and the self-consistent quasi-bound states of the quantum dot.
| arxiv topic:cond-mat.other |
arxiv_dataset-151707.193 | Improved Simulation of the Mass Charging for ASTROD I
astro-ph
The electrostatic charging of the test mass in ASTROD I (Astrodynamical Space
Test of Relativity using Optical Devices I) mission can affect the quality of
the science data as a result of spurious Coulomb and Lorentz forces. To
estimate the size of the resultant disturbances, credible predictions of
charging rates and the charging noise are required. Using the GEANT4 software
toolkit, we present a detailed Monte Carlo simulation of the ASTROD I test mass
charging due to exposure of the spacecraft to galactic cosmic-ray (GCR) protons
and alpha particles (3He, 4He) in the space environment. A positive charging
rate of 33.3 e+/s at solar minimum is obtained. This figure reduces by 50% at
solar maximum. Based on this charging rate and factoring in the contribution of
minor cosmic-ray components, we calculate the acceleration noise and stiffness
associated with charging. We conclude that the acceleration noise arising from
Coulomb and Lorentz effects are well below the ASTROD I acceleration noise
limit at 0.1 mHz both at solar minimum and maximum. The coherent Fourier
components due to charging are investigated, it needs to be studied carefully
in order to ensure that these do not compromise the quality of science data in
the ASTROD I mission.
| arxiv topic:astro-ph |
arxiv_dataset-152707.203 | On the definition of the \Delta mass and width
hep-ph
In the framework of effective field theory we show that, at two-loop order,
the mass and width of the \Delta resonance defined via the (relativistic)
Breit-Wigner parametrization both depend on the choice of field variables. In
contrast, the complex-valued position of the pole of the propagator is
independent of this choice.
| arxiv topic:hep-ph |
arxiv_dataset-153707.213 | Gagliardo-Nirenberg inequalities on manifolds
math.AP
We prove Gagliardo-Nirenberg inequalities on some classes of manifolds, Lie
groups and graphs.
| arxiv topic:math.AP |
arxiv_dataset-154707.223 | Ab initio relativistic many-body calculation of hyperfine splitting of
^{113}Cd^+
physics.atom-ph physics.comp-ph
This work presents accurate ab initio determination of the hyperfine
splitting for the ground state and few low-lying excited states of 113Cd+;
important candidates for the frequency standard in the microwave region, using
coupled-cluster theory (CC) in the relativistic framework. The calculated
hyperfine splitting are well in agreement with recent experimental results. We
have also carried out the lifetimes of the 5p2P1=2 and 5p2P3=2 states, which
are in well agreement with recent experimental result (Moehring et al., PRA 73
023413, 2006). The roles of different electron correlation effects in the
determination of these quantities are discussed and their contributions are
presented in the CC terms.
| arxiv topic:physics.atom-ph physics.comp-ph |
arxiv_dataset-155707.233 | Hilbert Function and Betti Numbers of Algebras with Lefschetz Property
of Order m
math.AC
The authors T.Harima, J.C.Migliore, U.Nagel and J.Watanabe characterized the
Hilbert function of algbebras with the Lefschetz property. We extend this
characterization to algebras with the Lefschetz property m times. We also give
upper bounds for the Betti numbers of Artinian algebras with a given Hilbert
function and with the Lefschetz property m times and describe the cases in
which these bounds are reached.
| arxiv topic:math.AC |
arxiv_dataset-156707.243 | A study of logarithmic corrections and universal amplitude ratios in the
two-dimensional 4-state Potts model
cond-mat.stat-mech hep-lat hep-th
Monte Carlo (MC) and series expansion (SE) data for the energy, specific
heat, magnetization and susceptibility of the two-dimensional 4-state Potts
model in the vicinity of the critical point are analysed. The role of
logarithmic corrections is discussed and an approach is proposed in order to
account numerically for these corrections in the determination of critical
amplitudes. Accurate estimates of universal amplitude ratios $A_+/A_-$,
$\Gamma_+/\Gamma_-$, $\Gamma_T/\Gamma_-$ and $R_C^\pm$ are given, which arouse
new questions with respect to previous works.
| arxiv topic:cond-mat.stat-mech hep-lat hep-th |
arxiv_dataset-157707.253 | New homogeneous iron abundances of double-mode Cepheids from
high-resolution echelle spectroscopy
astro-ph
Aims: We define the relationship between the double-mode pulsation of
Cepheids and metallicity in a more accurate way, determine the empirical
metallicities of double-mode Cepheids from homogeneous, high-resolution
spectroscopic data, and study of the period-ratio -- metallicity dependence.
Methods: The high S/N echelle spectra obtained with the FEROS spectrograph were
analyzed using a self-developed IRAF script, and the iron abundances were
determined by comparing with synthetic spectra assuming LTE. Results: Accurate
[Fe/H] values of 17 galactic beat Cepheids were determined. All these stars
have solar or slightly subsolar metallicity. Their period ratio P1/P0 shows
strong correlation with their derived [Fe/H] values. The corresponding period
ratio -- metallicity relation has been evaluated.
| arxiv topic:astro-ph |
arxiv_dataset-158707.263 | Multi-physics Extension of OpenFMO Framework
cs.DC physics.comp-ph
OpenFMO framework, an open-source software (OSS) platform for Fragment
Molecular Orbital (FMO) method, is extended to multi-physics simulations (MPS).
After reviewing the several FMO implementations on distributed computer
environments, the subsequent development planning corresponding to MPS is
presented. It is discussed which should be selected as a scientific software,
lightweight and reconfigurable form or large and self-contained form.
| arxiv topic:cs.DC physics.comp-ph |
arxiv_dataset-159707.273 | Attractors with Vanishing Central Charge
hep-th
We consider the Attractor Equations of particular $\mathcal{N}=2$, d=4
supergravity models whose vector multiplets' scalar manifold is endowed with
homogeneous symmetric cubic special K\"{a}hler geometry, namely of the
so-called $st^{2}$ and $stu$ models. In this framework, we derive explicit
expressions for the critical moduli corresponding to non-BPS attractors with
vanishing $\mathcal{N}=2$ central charge. Such formul\ae hold for a generic
black hole charge configuration, and they are obtained without formulating any
\textit{ad hoc} simplifying assumption. We find that such attractors are
related to the 1/2-BPS ones by complex conjugation of some moduli. By uplifting
to $\mathcal{N}=8$, d=4 supergravity, we give an interpretation of such a
relation as an exchange of two of the four eigenvalues of the $\mathcal{N}=8$
central charge matrix $Z_{AB}$. We also consider non-BPS attractors with
non-vanishing $\mathcal{Z}$; for peculiar charge configurations, we derive
solutions violating the Ansatz usually formulated in literature. Finally, by
group-theoretical considerations we relate Cayley's hyperdeterminant (the
invariant of the stu model) to the invariants of the st^{2} and of the
so-called t^{3} model.
| arxiv topic:hep-th |
arxiv_dataset-160707.283 | Characterization of thermalized Fermi-Pasta-Ulam chains
math-ph math.DS math.MP
The Fermi-Pasta-Ulam (FPU) chains of particles in \textit{thermal
equilibrium} are studied from both wave-interaction and particle-interaction
points of view. It is shown that, even in a strongly nonlinear regime, the
chain in thermal equilibrium can be effectively described by a system of weakly
interacting \textit{renormalized} nonlinear waves. These waves possess (i) the
Rayleigh-Jeans distribution and (ii) zero correlations between waves, just as
noninteracting free waves would. This renormalization is achieved through a set
of canonical transformations. The renormalized linear dispersion of these
renormalized waves is obtained and shown to be in excellent agreement with
numerical experiments. Moreover, a dynamical interpretation of the
renormalization of the dispersion relation is provided via a self-consistency,
mean-field argument. It turns out that this renormalization arises mainly from
the trivial resonant wave interactions, i.e., interactions with no momentum
exchange. Furthermore, using a multiple time-scale, statistical averaging
method, we show that the interactions of near-resonant waves give rise to the
broadening of the resonance peaks in the frequency spectrum of renormalized
modes. The theoretical prediction for the resonance width for the thermalized
$\beta$-FPU chain is found to be in very good agreement with its numerically
measured value. Moreover, we show that the dynamical scenario for thermalized
$\beta$-FPU chains is spatially highly localized discrete breathers riding
chaotically on spatially extended, renormalized waves. We present numerical
evidence of existence of discrete breathers in thermal equilibrium.
| arxiv topic:math-ph math.DS math.MP |
arxiv_dataset-161707.293 | Strong saturation absorption imaging of dense clouds of ultracold atoms
physics.optics physics.atom-ph
We report on a far above saturation absorption imaging technique to
investigate the characteristics of dense packets of ultracold atoms. The
transparency of the cloud is controlled by the incident light intensity as a
result of the non-linear response of the atoms to the probe beam. We detail our
experimental procedure to calibrate the imaging system for reliable
quantitative measurements, and demonstrate the use of this technique to extract
the profile and its spatial extent of an optically thick atomic cloud.
| arxiv topic:physics.optics physics.atom-ph |
arxiv_dataset-162707.303 | Optimal Design of Ad Hoc Injection Networks by Using Genetic Algorithms
cs.NE cs.AI cs.NI
This work aims at optimizing injection networks, which consist in adding a
set of long-range links (called bypass links) in mobile multi-hop ad hoc
networks so as to improve connectivity and overcome network partitioning. To
this end, we rely on small-world network properties, that comprise a high
clustering coefficient and a low characteristic path length. We investigate the
use of two genetic algorithms (generational and steady-state) to optimize three
instances of this topology control problem and present results that show
initial evidence of their capacity to solve it.
| arxiv topic:cs.NE cs.AI cs.NI |
arxiv_dataset-163707.313 | Angular momentum projection of cranked Hartree-Fock states: Application
to terminating bands in A~44 nuclei
nucl-th
We present the first systematic calculations based on the angular-momentum
projection of cranked Slater determinants. We propose the Iy --> I scheme, by
which one projects the angular momentum I from the 1D cranked state constrained
to the average spin projection of <I_y>=I. Calculations performed for the
rotational band in 46Ti show that the AMP Iy --> I scheme offers a natural
mechanism for correcting the cranking moment of inertia at low-spins and
shifting the terminating state up by ~2 MeV, in accordance with data. We also
apply this scheme to high-spin states near the band termination in A~44 nuclei,
and compare results thereof with experimental data, shell-model calculations,
and results of the approximate analytical symmetry-restoration method proposed
previously.
| arxiv topic:nucl-th |
arxiv_dataset-164707.323 | Is WMAP3 normalization compatible with the X-Ray cluster abundance?
astro-ph
We present the mass and X-ray temperature functions derived from a sample of
more than 15,000 galaxy clusters of the MareNostrum Universe cosmological SPH
simulations. In these simulations, we follow structure formation in a cubic
volume of 500/h Mpc on a side assuming cosmological parameters consistent with
either the first or third year WMAP data and gaussian initial conditions. We
compare our numerical predictions with the most recent observational estimates
of the cluster X-ray temperature functions and find that the low normalization
cosmological model inferred from the 3 year WMAP data results is barely
compatible with the present epoch X-ray cluster abundances. We can only
reconcile the simulations with the observational data if we assume a
normalization of the Mass-Temperature relation which is a factor of 2.5--3
smaller than our non-radiative simulations predict. This deviation seems to be
too large to be accounted by the effects of star formation or cooling in the
ICM, not taken into account in these simulations.
| arxiv topic:astro-ph |
arxiv_dataset-165707.333 | Extended Air Shower Simulations Based on EPOS
astro-ph hep-ph
We discuss air shower simulations based on the EPOS hadronic interaction
model.
A remarkable feature is the fact that the number of produced muons is
considerably larger compared to other interaction models. We show that this is
due to an improved treatment of baryon-antibaryon production.
| arxiv topic:astro-ph hep-ph |
arxiv_dataset-166707.343 | Commensurability of geometric subgroups of mapping class groups
math.GT math.GR
Let M be a surface (possibly nonorientable) with punctures and/or boundary
components. The paper is a study of ``geometric subgroups'' of the mapping
class group of M, that is subgroups corresponding to inclusions of subsurfaces
(possibly disconnected). We characterise the subsurfaces which lead to
virtually abelian geometric subgroups. We provide algebraic and geometric
conditions under which two geometric subgroups are commensurable. We also
describe the commensurator of a geometric subgroup in terms of the stabiliser
of the underlying subsurface. Finally, we show some applications of our
analysis to the theory of irreducible unitary representations of mapping class
groups.
| arxiv topic:math.GT math.GR |
arxiv_dataset-167707.353 | $A$-dependence of coherent electroproduction of $\rho^{0}$ mesons on
nuclei in forward direction
hep-ph
This article presents the $A$-dependence of the differential cross section
for the coherent electroproduction of vector mesons on nuclei in forward
direction, at fixed values of longitudinal momentum transfer $q_{L}$. It is
shown that such cross section has complicated behavior over the atomic mass
number $A$ with local minimums and maximums. It is also shown that a ratio of
the real to the imaginary parts of the forward coherent amplitude on nuclei
$\alpha_{A} = \Re e{f_{A}} / \Im m{f_{A}}$ has breaking points at some values
of $A$. Comparison of the behaviors of the normalized cross section
$\Big(\frac{d\sigma}{d\Omega}\Big)_{A}\Big/\Big(\frac{d\sigma}{d\Omega}\Big)_{N}$
and $\alpha_{A}$ over $A$ shows that the location of minimums of the cross
section are very close to the breaking points of $\alpha_{A}$.
| arxiv topic:hep-ph |
arxiv_dataset-168707.363 | Molecular production at a wide Feshbach resonance in Fermi-gas of cooled
atoms
cond-mat.other
The problem of molecular production from degenerate gas of fermions at a wide
Feshbach resonance, in a single-mode approximation, is reduced to the linear
Landau-Zener problem for operators. The strong interaction leads to significant
renormalization of the gap between adiabatic levels. In contrast to static
problem the close vicinity of exact resonance does not play substantial role.
Two main physical results of our theory is the high sensitivity of molecular
production to the initial value of magnetic field and generation of a large BCS
condensate distributed over a broad range of momenta in inverse process of the
molecule dissociation.
| arxiv topic:cond-mat.other |
arxiv_dataset-169707.373 | Affine linear and D4 symmetric lattice equations : symmetry analysis and
reductions
nlin.SI
We consider lattice equations on ${\mathds{Z}}^2$ which are autonomous,
affine linear and possess the symmetries of the square. Some basic properties
of equations of this type are derived, as well as a sufficient linearization
condition and a conservation law. A systematic analysis of the Lie point and
the generalized three- and five-point symmetries is presented. It leads to the
generic form of the symmetry generators of all the equations in this class,
which satisfy a certain non-degeneracy condition. Finally, symmetry reductions
of certain lattice equations to discrete analogues of the Painlev\'e equations
are considered.
| arxiv topic:nlin.SI |
arxiv_dataset-170707.383 | On Cosmological Implications of Gravitational Trace Anomaly
gr-qc astro-ph hep-th
We study the infrared effective theory of gravity that stems from the quantum
trace anomaly. Quantum fluctuations of the metric induce running of the
cosmological constant and the Newton constant at cosmological scales. By
imposing the generalized Bianchi identity we obtain a prediction for the scale
dependence of the dark matter and dark energy densities in terms of the
parameters of the underlying conformal theory. For certain values of the model
parameters the dark energy equation of state and the observed spectral index of
the primordial density fluctuations can be simultaneously reproduced.
| arxiv topic:gr-qc astro-ph hep-th |
arxiv_dataset-171707.393 | Superfluid-Insulator and Roughening Transitions in Domain Walls
cond-mat.other cond-mat.stat-mech
We have performed quantum Monte Carlo simulations to investigate the
superfluid behavior of one- and two-dimensional interfaces separating
checkerboard solid domains. The system is described by the hard-core
Bose-Hubbard Hamiltonian with nearest-neighbor interaction. In accordance with
Ref.1, we find that (i) the interface remains superfluid in a wide range of
interaction strength before it undergoes a superfluid-insulator transition;
(ii) in one dimension, the transition is of the Kosterlitz-Thouless type and is
accompanied by the roughening transition, driven by proliferation of charge 1/2
quasiparticles; (iii) in two dimensions, the transition belongs to the 3D U(1)
universality class and the interface remains smooth. Similar phenomena are
expected for domain walls in quantum antiferromagnets.
| arxiv topic:cond-mat.other cond-mat.stat-mech |
arxiv_dataset-172707.403 | Killing spinors on supersymmetric P-branes
hep-th
A class of p-brane solutions for supersymmetric gravity theories with
negative cosmological constant are proposed and analyzed. The solutions are
purely bosonic and contain a worldsheet and a transverse section. The
classification relays on the number of intrinsic Killing spinors on the
worldsheet and the transverse section. A explicit discussion of the
classification is performed for the four dimensional worldsheet case.
| arxiv topic:hep-th |
arxiv_dataset-173707.413 | Study of the process e+e- -> omega p0 with the KLOE detector
hep-ex
Using ~600 pb-1 collected with the KLOE detector at DAPhiNE, we have studied
the production cross section of pi+ pi- pi0 pi0 and p0p0 gamma final states in
e+e- collisions at center of mass energies between 1000 and 1030 MeV. By
fitting the observed interference pattern around Mphi for both final states, we
extract a measurement (preliminary) for the ratio Gamma(omega -> pi0
gamma)/Gamma(omega -> pi+ pi- pi0) = 0.0934 +- 0.0022. Since these two final
states represent the 98% of the omega decay channels, we use unitarity to
derive BR(omega -> pi+pi-pi0)= (89.94 +- 0.23)% and BR(omega -> pi0 gamma) =
(8.40 +- 0.19)%. Moreover, the parameters describing the e+e- -> pi+ pi- pi0
pi0 reaction around Mphi are used to extract the branching fraction for the OZI
and G-parity violating phi -> omega pi0 decay: BR(phi -> omega pi0) = (5.63 +-
0.70) x 10^-5.
| arxiv topic:hep-ex |
arxiv_dataset-174707.423 | The Role of Electron-electron Interactions in Graphene ARPES Spectra
cond-mat.mes-hall
We report on a theoretical study of the influence of electron-electron
interactions on ARPES spectra in graphene that is based on the
random-phase-approximation and on graphene's massless Dirac equation continuum
model. We find that level repulsion between quasiparticle and plasmaron
resonances gives rise to a gap-like feature at small k. ARPES spectra are
sensitive to the electron-electron interaction coupling strength $\alpha_{\rm
gr}$ and might enable an experimental determination of this material parameter.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-175707.433 | Heating and Turbulence Driving by Galaxy Motions in Galaxy Clusters
astro-ph
Using three-dimensional hydrodynamic simulations, we investigate heating and
turbulence driving in an intracluster medium (ICM) by orbital motions of
galaxies in a galaxy cluster. We consider Ng member galaxies on isothermal and
isotropic orbits through an ICM typical of rich clusters. An introduction of
the galaxies immediately produces gravitational wakes, providing perturbations
that can potentially grow via resonant interaction with the background gas.
When Ng^{1/2}Mg_11 < 100, where Mg_11 is each galaxy mass in units of 10^{11}
Msun, the perturbations are in the linear regime and the resonant excitation of
gravity waves is efficient to generate kinetic energy in the ICM, resulting in
the velocity dispersion sigma_v ~ 2.2 Ng^{1/2}Mg_11 km/s. When Ng^{1/2}Mg_11 >
100, on the other hand, nonlinear fluctuations of the background ICM destroy
galaxy wakes and thus render resonant excitation weak or absent. In this case,
the kinetic energy saturates at the level corresponding to sigma_v ~ 220 km/s.
The angle-averaged velocity power spectra of turbulence driven in our models
have slopes in the range of -3.7 to -4.3. With the nonlinear saturation of
resonant excitation, none of the cooling models considered are able to halt
cooling catastrophe, suggesting that the galaxy motions alone are unlikely to
solve the cooling flow problem.
| arxiv topic:astro-ph |
arxiv_dataset-176707.443 | A negative-U interpretation of the femto-second laser pulse induced
crystallographic expansion of a cuprate HTSC material reported recently by
Gedik et al
cond-mat.supr-con cond-mat.str-el
Gedik et al have very recently demonstrated using a pump/probe femto-second
laser technique that the c-axis lattice parameter of LaCuO4+d temporarily
becomes expanded by as much as 2.5% following pulsed laser optical excitation
at 1.55 eV. Access to an out-of-equilibrium metastable excited state is
observed to develop on a time scale of 30 ps. Subsequently the latter state
decays displaying a still longer half-life of just over 300 ps. Observation of
the temperature independence of this laser induced interstate transfer and of
the linear dependence of the production of the metastable population upon the
energy delivered per unit area by the initiating light pulse (beyond a key
threshold fluence) have been interpreted by Gedik et al within the framework of
standard p-to-d, O-to-Cu, charge transfer excitations. By contrast these same
data are reinterpreted here in terms of pumped local pairs, within a negative-U
scenario of cuprate HTSC behaviour long advocated by the current author. The
d8-to-d10 laser-induced augmentation in the negative-U state population
(10CuIII2-) brings marked c-axis expansion by virtue of (i) the local
electrostatic charge imbalance, (ii) the increased antibonding nature of the
electron double-loading d10(p6) configuration created at pair-receptive CuIII
coordination units, and (iii) the layered nature of the cuprate crystal
structure. The new observations are related through to Rohlers striking,
standard crystallographic observations, to the stripe domain formation, and to
previous pump/probe experiments.
| arxiv topic:cond-mat.supr-con cond-mat.str-el |
arxiv_dataset-177707.453 | Stabilization of a Bose-Einstein droplet by hyperfine Rabi oscillations
cond-mat.other
A self-trapped Bose-Einstein condensate is shown to be stabilized in
two-dimensional free space by Rabi oscillations between two hyperfine states
which make an effective interatomic interaction oscillate in time. The
stabilization mechanism is elucidated by using a two-component Gross-Pitaevskii
equation combined with a variational analysis. The parameter regime of
stability is investigated.
| arxiv topic:cond-mat.other |
arxiv_dataset-178707.463 | Ground state properties of a homogeneous 2D system of Bosons with
dipolar interactions
cond-mat.other
The ground-state phase properties of a two-dimensional Bose system with
dipole-dipole interactions is studied by means of quantum Monte Carlo
techniques. Limitations of mean-field theory in a two-dimensional geometry are
discussed. A quantum phase transition from gas to solid is found. Crystal is
tested for existence of a supersolid in the vicinity of the phase transition.
Existence of mesoscopic analogue of the off-diagonal long-range order is shown
in the one-body density matrix in a finite-size crystal. Non-zero superfluid
fraction is found in a finite-size crystal, the signal being dramatically
increased in presence of vacancies.
| arxiv topic:cond-mat.other |
arxiv_dataset-179708.0049 | Near-Field Focusing Plates and Their Design
physics.class-ph
This paper describes the design of near-field focusing plates, which are
grating-like structures that can focus electromagnetic radiation to spots or
lines of arbitrarily small subwavelength dimension. A general procedure is
outlined for designing a near-field plate given a desired image, and its
implementation at microwave frequencies is discussed. Full-wave (method of
moments) simulations clearly demonstrate the near-field plate's ability to
overcome the diffraction limit. Finally, it is shown that the performance of
near-field plates is weakly affected by losses.
| arxiv topic:physics.class-ph |
arxiv_dataset-180708.0149 | Modeling the spectral energy distribution of ULIRGs I: the radio spectra
astro-ph
As a constraint for new starburst/AGN models of IRAS bright galaxies we
determine the radio spectra of 31 luminous and ultraluminous IRAS galaxies
(LIRGs/ULIRGs). We construct the radio spectra using both new and archival
data. From our sample of radio spectra we find that very few have a straight
power-law slope. Although some sources show a flattening of the radio spectral
slope at high frequencies the average spectrum shows a steepening of the radio
spectrum from 1.4 to 22.5 GHz. This is unexpected because in sources with high
rates of star formation we expect flat spectrum, free-free emission to make a
significant contribution to the radio flux at higher radio frequencies. Despite
this trend the radio spectral indices between 8.4 and 22.5 GHz are flatter for
sources with higher values of the FIR-radio flux density ratio q, when this is
calculated at 8.4 GHz. Therefore, sources that are deficient in radio emission
relative to FIR emission (presumably younger sources) have a larger thermal
component to their radio emission. However, we find no correlation between the
radio spectral index between 1.4 and 4.8 GHz and q at 8.4 GHz. Because the low
frequency spectral index is affected by free-free absorption, and this is a
function of source size for a given mass of ionized gas, this is evidence that
the ionized gas in ULIRGs shows a range of densities. The youngest LIRGs and
ULIRGs are characterized by a larger contribution to their high-frequency radio
spectra from free-free emission. However, the youngest sources are not those
that have the greatest free-free absorption at low radio frequencies. The
sources in which the effects of free-free absorption are strongest are instead
the most compact sources. Although these have the warmest FIR colours, they are
not necessarily the youngest sources.
| arxiv topic:astro-ph |
arxiv_dataset-181708.0249 | Classifying the Unclassifiables
math.LO math.RT
In 1955 George Mackey suggested that there is a fundamental dichotomy in the
unitary representation theory of locally compact second countable groups. He
felt that there cannnot be a reasonable classification theory for the unitary
representations of a group G for which the dual is a non-smooth Borel space.
Mackey's precise conjecture regarding when this is the case was subsequently
verified by Glimm. This approach to "classifiability" can be applied in many
other branches of mathematics. Included in this article is a sketch of some of
the exciting new developments that have been made in this direction. Evidence
is given that there should be extensions of Mackey's ideas to such "finitistic"
problems as the classification of the finite p-groups. In a different
direction, Mackey's thoughts about quantization are also briefly discussed.
| arxiv topic:math.LO math.RT |
arxiv_dataset-182708.0349 | Observational Constraints on Agegraphic Dark Energy
astro-ph
In this paper, we use the Type Ia supernova data as well as the CMB and LSS
data to constrain the agegraphic dark energy model recently proposed by Cai.
Due to its peculiar nature, the parameter $n$ of this model cannot be well
constrained by the SNIa data, while the other parameter $\Omega_{m0}$ can be
constrained to be $0.34\pm0.04$. When combined with CMB and LSS data, the range
of $1\sigma$ confidence level for $n$ is greatly narrowed, albeit still very
large. The best fit result is $\Omega_{m0}=0.28\pm0.02$, which is consistent
with most observations like WMAP and SDSS, and $n=3.4$, of which a meaningful
range of confidence level can not be obtained due to the fact that the contours
are not closed. Despite of this result, we conclude that for $n>1$ this model
is consistent with SNIa, CMB and LSS observations. Furthermore, the fitting
results indicate a generalized definition for the agegraphic dark energy.
| arxiv topic:astro-ph |
arxiv_dataset-183708.0449 | Unitary Solution to a Quantum Gravity Information Paradox
quant-ph gr-qc
We consider a toy model of the interaction of a qubit with an exotic
space-time containing a time-like curve. Consistency seems to require that the
global evolution of the qubit be non-unitary. Given that quantum mechanics is
globally unitary, this then is an example of a quantum gravity information
paradox. However, we show that a careful analysis of the problem in the
Heisenberg picture reveals an underlying unitarity, thus resolving the paradox.
| arxiv topic:quant-ph gr-qc |
arxiv_dataset-184708.0549 | Azimuthal decorrelation of forward jets in Deep Inelastic Scattering
hep-ph
We study the azimuthal angle decorrelation of forward jets in Deep Inelastic
Scattering. We make predictions for this observable at HERA describing the high
energy limit of the relevant scattering amplitudes with quasi-multi-Regge
kinematics together with a collinearly improved evolution kernel for
multiparton emissions.
| arxiv topic:hep-ph |
arxiv_dataset-185708.0649 | Quenched Limits for Transient, Ballistic, Sub-Gaussian One-Dimensional
Random Walk in Random Environment
math.PR
We consider a nearest-neighbor, one-dimensional random walk $\{X_n\}_{n\geq
0}$ in a random i.i.d. environment, in the regime where the walk is transient
with speed v_P > 0 and there exists an $s\in(1,2)$ such that the annealed law
of $n^{-1/s} (X_n - n v_P)$ converges to a stable law of parameter s. Under the
quenched law (i.e., conditioned on the environment), we show that no limit laws
are possible. In particular we show that there exist sequences {t_k} and {t_k'}
depending on the environment only, such that a quenched central limit theorem
holds along the subsequence t_k, but the quenched limiting distribution along
the subsequence t_k' is a centered reverse exponential distribution. This
complements the results of a recent paper of Peterson and Zeitouni
(arXiv:0704.1778v1 [math.PR]) which handled the case when the parameter
$s\in(0,1)$.
| arxiv topic:math.PR |
arxiv_dataset-186708.0749 | Nodal free geometric phases: Concept and application to geometric
quantum computation
quant-ph
Nodal free geometric phases are the eigenvalues of the final member of a
parallel transporting family of unitary operators. These phases are gauge
invariant, always well-defined, and can be measured interferometrically. Nodal
free geometric phases can be used to construct various types of quantum phase
gates.
| arxiv topic:quant-ph |
arxiv_dataset-187708.0849 | The mass-critical nonlinear Schr\"odinger equation with radial data in
dimensions three and higher
math.AP
We establish global well-posedness and scattering for solutions to the
mass-critical nonlinear Schr\"odinger equation $iu_t + \Delta u = \pm |u|^{4/d}
u$ for large spherically symmetric L^2_x(R^d) initial data in dimensions $d\geq
3$. In the focusing case we require that the mass is strictly less than that of
the ground state. As a consequence, we obtain that in the focusing case, any
spherically symmetric blowup solution must concentrate at least the mass of the
ground state at the blowup time.
| arxiv topic:math.AP |
arxiv_dataset-188708.0949 | The Evolution of Galaxies
astro-ph
The evolution of galaxies results from a combination of internal and external
processes. The star formation is an internal process transforming cold and
dense cores of molecular clouds to stars. It may be triggered internally by
expanding shells, or externally, e. g. by galaxy collisions. The gas accretion
and galaxy merging events are external contributors to galaxy evolution. They
compete with another internal process of galaxy evolution, which is the secular
evolution redistributing the mass and angular momentum inside of galaxies as a
consequence of bar and spiral arms formation. As a nearby example of gas
accretion we mention the interacting system Milky Way - Large and Small
Magellanic Clouds. Stripping of ISM in galaxy clusters is reviewed as another
example of interaction of galaxies with their environment.
| arxiv topic:astro-ph |
arxiv_dataset-189708.1049 | An Interval Analysis Based Study for the Design and the Comparison of
3-DOF Parallel Kinematic Machines
cs.RO
This paper addresses an interval analysis based study that is applied to the
design and the comparison of 3-DOF parallel kinematic machines. Two design
criteria are used, (i) a regular workspace shape and, (ii) a kinetostatic
performance index that needs to be as homogeneous as possible throughout the
workspace. The interval analysis based method takes these two criteria into
account: on the basis of prescribed kinetostatic performances, the workspace is
analysed to find out the largest regular dextrous workspace enclosed in the
Cartesian workspace. An algorithm describing this method is introduced. Two
3-DOF translational parallel mechanisms designed for machining applications are
compared using this method. The first machine features three fixed linear
joints which are mounted orthogonally and the second one features three linear
joints which are mounted in parallel. In both cases, the mobile platform moves
in the Cartesian x-y-z space with fixed orientation.
| arxiv topic:cs.RO |
arxiv_dataset-190708.1149 | Discovery of Pulsations and a Possible Spectral Feature in the X-ray
Emission from Rotating Radio Transient J1819-1458
astro-ph
PSR J1819-1458 is a rotating radio transient (RRAT) source with an inferred
surface dipole magnetic field strength of 5e13 G and a 4.26-s spin period. We
present XMM-Newton observations of the X-ray counterpart of this source, CXOU
J181939.1-145804, in which we identify pulsations and a possible spectral
feature. The X-ray pulsations are at the period predicted by the radio
ephemeris, providing an unambiguous identification with the radio source and
confirmation of its neutron star nature. The X-ray pulse has a 0.3-5 keV pulsed
fraction of 34% and is aligned with the expected phase of the radio pulse. The
X-ray spectrum is fit well by an absorbed blackbody with kT = 0.14 keV with the
addition of an absorption feature at 1 keV, with total absorbed flux of 1.5e-13
ergs/cm^2/s (0.3-5 keV). This absorption feature is well modeled by a Gaussian
or resonant cyclotron scattering model, but its significance is dependent on
the choice of continuum model. We find no evidence for any X-ray bursts or
aperiodic variability on timescales of 6 ms to the duration of the observation
and can place the most stringent limit to date of < 3e-9 ergs/cm^2/s on the
absorbed 0.3-5 keV flux of any bursts.
| arxiv topic:astro-ph |
arxiv_dataset-191708.1249 | Unstable GRB photospheres and electron-positron annihilation lines
astro-ph
We propose an emission mechanism of prompt gamma-ray bursts (GRBs) that can
reproduce the observed non-thermal spectra with high radiative efficiencies,
>50%. Internal dissipation below a photosphere can create a radiation-dominated
thermal fireball. If electron-positron pairs outnumber protons, radiative
acceleration of pairs drives the two-stream instabilities between pairs and
protons, leading to the ``proton sedimentation'' in the accelerating pair
frame. Pairs are continuously shock heated by proton clumps, scattering the
thermal photons into the broken power-law shape, with the non-thermal energy
that is comparable to the proton kinetic energy, consistent with observations.
Pair photospheres become unstable around the radius of the progenitor star
where strong thermalization occurs, if parameters satisfy the observed spectral
(Yonetoku) relation. Pair annihilation lines are predicted above continua,
which could be verified by GLAST.
| arxiv topic:astro-ph |
arxiv_dataset-192708.1349 | On the formation and the stability of suspended transition metal
monatomic chains
cond-mat.mtrl-sci
We present a Tight-Binding Molecular Dynamics investigation of the stability,
the geometrical and the electronic structure of suspended monatomic transition
metal chains. We show that linear and stable monatomic chains are formed at
temperature equal or smaller than 500 K for Au, 200 K for Ag and 4 K for Cu. We
also evidence that such stability is associated with the persisting sd orbital
hybridization along the chains. The study highlight fundamental limitations of
conductance measurement experiments to detect these chains in the breaking
process of nanowires.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-193708.1449 | Slow beams of massive molecules
quant-ph physics.atm-clus physics.bio-ph physics.chem-ph
Slow beams of neutral molecules are of great interest for a wide range of
applications, from cold chemistry through precision measurements to tests of
the foundations of quantum mechanics. We report on the quantitative observation
of thermal beams of perfluorinated macromolecules with masses up to 6000 amu,
reaching velocities down to 11 m/s. Such slow, heavy and neutral molecular
beams are of importance for a new class of experiments in matter-wave
interferometry and we also discuss the requirements for further manipulation
and cooling schemes with molecules in this unprecedented mass range.
| arxiv topic:quant-ph physics.atm-clus physics.bio-ph physics.chem-ph |
arxiv_dataset-194708.1549 | Improved Measurement of Time-Dependent CP Asymmetries and the CP-Odd
Fraction in the Decay B0->D*+D*-
hep-ex
We present an updated measurement of the CP-odd fraction and the
time-dependent CP asymmetries in the decay B0->D*+D*-using (383 +/- 4) \times
10^{6} BB pairs collected with the Babar detector. We determine the CP-odd
fraction to be $0.143\pm0.034\stat\pm0.008\syst$. The time-dependent CP
asymmetry parameters are determined to be $C_+ = -0.05\pm 0.14\stat \pm
0.02\syst$ and $S_+ = -0.72 \pm 0.19\stat \pm 0.05\syst$. The non-zero value of
the measured $S_+$ indicates the evidence of CP violation at the $3.7 \sigma$
confidence level.
| arxiv topic:hep-ex |
arxiv_dataset-195708.1649 | Scattered Emission from A Relativistic Outflow and Its Application to
Gamma-Ray Bursts
astro-ph
We investigate a scenario of photons scattering by electrons within a
relativistic outflow. The outflow is composed of discrete shells with different
speeds. One shell emits radiation for a short duration. Some of this radiation
is scattered by the shell(s) behind. We calculate in a simple two-shell model
the observed scattered flux density as a function of the observed primary flux
density, the normalized arrival time delay between the two emission components,
the Lorentz factor ratio of the two shells and the scattering shell's optical
depth. Thomson scattering in a cold shell and inverse Compton scattering in a
hot shell are both considered. The results of our calculations are applied to
the Gamma-Ray Bursts and the afterglows. We find that the scattered flux from a
cold slower shell is small and likely to be detected only for those bursts with
very weak afterglows. A hot scattering shell could give rise to a scattered
emission as bright as the X-ray shallow decay component detected in many
bursts, on a condition that the isotropically equivalent total energy carried
by the hot electrons is large, $\sim 10^{52-56}$ erg. The scattered emission
from a faster shell could appear as a late short $\gamma$-ray/MeV flash or
become part of the prompt emission depending on the delay of the ejection of
the shell.
| arxiv topic:astro-ph |
arxiv_dataset-196708.1749 | Efficiency of quantum Monte Carlo impurity solvers for dynamical
mean-field theory
cond-mat.str-el
Since the inception of the dynamical mean-field theory, numerous numerical
studies have relied on the Hirsch-Fye quantum Monte Carlo (HF-QMC) method for
solving the associated impurity problem. Recently developed continuous-time
algorithms (CT-QMC) avoid the Trotter discretization error and allow for faster
configuration updates, which makes them candidates for replacing HF-QMC. We
demonstrate, however, that a state-of-the-art implementation of HF-QMC (with
extrapolation of discretization delta_tau -> 0) is competitive with CT-QMC. A
quantitative analysis of Trotter errors in HF-QMC estimates and of appropriate
delta_tau values is included.
| arxiv topic:cond-mat.str-el |
arxiv_dataset-197708.1849 | Effects of Ox-LDL on Macrophages NAD(P)H Autofluorescence Changes by
Two-photon Microscopy
physics.bio-ph
Ox-LDL uptakes by macrophage play a critical role in the happening of
atherosclerosis. Because of its low damage on observed cells and better
signal-to- background ratio, two-photon excitation fluorescence microscopy is
used to observe NAD(P)H autofluorescence of macrophage under difference
cultured conditions- bare cover glass, coated with fibronectin or
poly-D-lysine. The results show that the optimal condition is fibronectin
coated surface, on which, macrophages profile can be clearly identified on
NAD(P)H autofluorescence images collected by two-photon microscopy. Moreover,
different morphology and intensities of autofluorescence under different
conditions were observed as well. In the future, effects of ox-LDL on
macrophages will be investigated by purposed system to research etiology of
atherosclerosis.
| arxiv topic:physics.bio-ph |
arxiv_dataset-198708.1949 | Cold Dark Matter Substructure and Galactic Disks I: Morphological
Signatures of Hierarchical Satellite Accretion
astro-ph
(Abridged) We conduct a series of high-resolution, dissipationless N-body
simulations to investigate the cumulative effect of substructure mergers onto
thin disk galaxies in the context of the LCDM paradigm of structure formation.
Our simulation campaign is based on a hybrid approach. Substructure properties
are culled directly from cosmological simulations of galaxy-sized cold dark
matter (CDM) halos. In contrast to what can be inferred from statistics of the
present-day substructure populations, accretions of massive subhalos onto the
central regions of host halos, where the galactic disk resides, since z~1
should be common occurrences. One host halo merger history is subsequently used
to seed controlled numerical experiments of repeated satellite impacts on an
initially-thin Milky Way-type disk galaxy. We show that these accretion events
produce several distinctive observational signatures in the stellar disk
including: a ring-like feature in the outskirts; a significant flare; a central
bar; and faint filamentary structures that (spuriously) resemble tidal streams.
The final distribution of disk stars exhibits a complex vertical structure that
is well-described by a standard ``thin-thick'' disk decomposition. We conclude
that satellite-disk encounters of the kind expected in LCDM models can induce
morphological features in galactic disks that are similar to those being
discovered in the Milky Way, M31, and in other disk galaxies. These results
highlight the significant role of CDM substructure in setting the structure of
disk galaxies and driving galaxy evolution. Upcoming galactic structure surveys
and astrometric satellites may be able to distinguish between competing
cosmological models by testing whether the detailed structure of galactic disks
is as excited as predicted by the CDM paradigm.
| arxiv topic:astro-ph |
arxiv_dataset-199708.2049 | Three-dimensional MHD simulation of expanding magnetic flux ropes
physics.plasm-ph physics.flu-dyn
Three-dimensional, time-dependent numerical simulations of the dynamics of
magnetic flux ropes are presented. The simulations are targeted towards an
experiment previously conducted at CalTech (Bellan, P. M. and J. F. Hansen,
Phys. Plasmas, 5, 1991 (1998)) which aimed at simulating Solar prominence
eruptions in the laboratory. The plasma dynamics is described by ideal MHD
using different models for the evolution of the mass density. Key features of
the reported experimental observations like pinching of the current loop, its
expansion and distortion into helical shape are reproduced in the numerical
simulations. Details of the final structure depend on the choice of a specific
model for the mass density.
| arxiv topic:physics.plasm-ph physics.flu-dyn |
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