15,376 research outputs found
Spherical collapse with heat flow and without horizon
We present a class of solutions for a heat conducting fluid sphere, which
radiates energy during collapse without the appearance of horizon at the
boundary at any stage of the collapse. A simple model shows that there is no
accumulation of energy due to collapse since it radiates out at the same rate
as it is being generated.Comment: RevTeX, 3 page
Stabilizing Hadron Resonance Gas Models against Future Discoveries
We examine the stability of hadron resonance gas models by extending them to
take care of undiscovered resonances through the Hagedorn formula. We find that
the influence of unknown resonances on thermodynamics is large but bounded.
Hadron resonance gases are internally consistent up to a temperature higher
than the cross over temperature in QCD; but by examining quark number
susceptibilities we find that their region of applicability seems to end even
below the QCD cross over. We model the decays of resonances and investigate the
ratios of particle yields in heavy-ion collisions. We find that observables
such as hydrodynamics and hadron yield ratios change little upon extending the
model. As a result, heavy-ion collisions at RHIC and LHC are insensitive to a
possible exponential rise in the hadronic density of states, thus increasing
the stability of the predictions of hadron resonance gas models
Noise sustained propagation: Local versus global noise
We expand on prior results on noise supported signal propagation in arrays of
coupled bistable elements. We present and compare experimental and numerical
results for kink propagation under the influence of local and global
fluctuations. As demonstrated previously for local noise, an optimum range of
global noise power exists for which the medium acts as a reliable transmission
``channel''. We discuss implications for propagation failure in a model of
cardiac tissue and present a general theoretical framework based on discrete
kink statistics. Valid for generic bistable chains, the theory captures the
essential features ob served in our experiments and numerical simulations.Comment: 1 latex file 20 pages, 9 figures. Accepted for publication in
Physical Review
Computer aided synthesis: a game theoretic approach
In this invited contribution, we propose a comprehensive introduction to game
theory applied in computer aided synthesis. In this context, we give some
classical results on two-player zero-sum games and then on multi-player non
zero-sum games. The simple case of one-player games is strongly related to
automata theory on infinite words. All along the article, we focus on general
approaches to solve the studied problems, and we provide several illustrative
examples as well as intuitions on the proofs.Comment: Invitation contribution for conference "Developments in Language
Theory" (DLT 2017
Chromosomal basis of dosage compensation in Drosophila. X. Assessment of hyperactivity of the male X in situ
The results of examination of the template activity of the fixed polytene chromosomes of Drosophila hydei, monitored by 3H-UTP, under in situ assay conditions, upon the use of endogenous Drosophila polymerase, exogenous Escherichia coli RNA polymerase (holoenzyme) and exogenous Drosophila RNA polymerase II (or B) have been presented. Analysis of the data reveals that the transcription patterns with the 3 enzymes are not strictly comparable with the pattern obtained under in vivo conditions. Yet, with each of the 3 conditions of assay, there is a reasonable concordance between the template activity on the single X chromosome of the male and the paired Xs of the female, as observed under in vivo. There is also, in every case, a high positive correlation between the 3H-UMP incorporation into the X chromosome and that into a specific autosome. A site-wise analysis of 3H-UMP labelling under the 3 assay conditions also reveals that for most of the regions, the sites which are highly active in vivo also show high labelling in situ,'and the proportionality is maintained in both sexes. These results have been interpreted to have suggested that the hyperactivity of the male X vis-a-vis dosage compensation in Drosophila is primarily a property of the inherent organization of the X chromosome itself and is achieved through modulation in the organization, rather than exclusively through autosomal factoids), although a secondary level of autosomal regulation has not yet been ruled out
Decidability Results for Multi-objective Stochastic Games
We study stochastic two-player turn-based games in which the objective of one
player is to ensure several infinite-horizon total reward objectives, while the
other player attempts to spoil at least one of the objectives. The games have
previously been shown not to be determined, and an approximation algorithm for
computing a Pareto curve has been given. The major drawback of the existing
algorithm is that it needs to compute Pareto curves for finite horizon
objectives (for increasing length of the horizon), and the size of these Pareto
curves can grow unboundedly, even when the infinite-horizon Pareto curve is
small. By adapting existing results, we first give an algorithm that computes
the Pareto curve for determined games. Then, as the main result of the paper,
we show that for the natural class of stopping games and when there are two
reward objectives, the problem of deciding whether a player can ensure
satisfaction of the objectives with given thresholds is decidable. The result
relies on intricate and novel proof which shows that the Pareto curves contain
only finitely many points. As a consequence, we get that the two-objective
discounted-reward problem for unrestricted class of stochastic games is
decidable.Comment: 35 page
Proper Motions of PSRs B1757-24 and B1951+32: Implications for Ages and Associations
Over the last decade, considerable effort has been made to measure the proper
motions of the pulsars B1757-24 and B1951+32 in order to establish or refute
associations with nearby supernova remnants and to understand better the
complicated geometries of their surrounding nebulae. We present proper motion
measurements of both pulsars with the Very Large Array, increasing the time
baselines of the measurements from 3.9 yr to 6.5 yr and from 12.0 yr to 14.5
yr, respectively, compared to previous observations. We confirm the
non-detection of proper motion of PSR B1757-24, and our measurement of (mu_a,
mu_d) = (-11 +/- 9, -1 +/- 15) mas yr^{-1} confirms that the association of PSR
B1757-24 with SNR G5.4-1.2 is unlikely for the pulsar characteristic age of
15.5 kyr, although an association can not be excluded for a significantly
larger age. For PSR B1951+32, we measure a proper motion of (mu_a, mu_d) =
(-28.8 +/- 0.9, -14.7 +/- 0.9) mas yr^{-1}, reducing the uncertainty in the
proper motion by a factor of two compared to previous results. After correcting
to the local standard of rest, the proper motion indicates a kinetic age of ~51
kyr for the pulsar, assuming it was born near the geometric center of the
supernova remnant. The radio-bright arc of emission along the pulsar proper
motion vector shows time-variable structure, but moves with the pulsar at an
approximately constant separation ~2.5", lending weight to its interpretation
as a shock structure driven by the pulsar.Comment: LaTeX file uses emulateapj.cls; 7 pages, 4 figures, to be published
ApJ February 10, 2008, v674 p271-278. Revision reflects journal formatting;
there are no substantial revision
Condensate fragmentation as a sensitive measure of the quantum many-body behavior of bosons with long-range interactions
The occupation of more than one single-particle state and hence the emergence
of fragmentation is a many-body phenomenon universal to systems of spatially
confined interacting bosons. In the present study, we investigate the effect of
the range of the interparticle interactions on the fragmentation degree of one-
and two-dimensional systems. We solve the full many-body Schr\"odinger equation
of the system using the recursive implementation of the multiconfigurational
time-dependent Hartree for bosons method, R-MCTDHB. The dependence of the
degree of fragmentation on dimensionality, particle number, areal or line
density and interaction strength is assessed. It is found that for contact
interactions, the fragmentation is essentially density independent in two
dimensions. However, fragmentation increasingly depends on density the more
long-ranged the interactions become. The degree of fragmentation is increasing,
keeping the particle number fixed, when the density is decreasing as
expected in one spatial dimension. We demonstrate that this remains,
nontrivially, true also for long-range interactions in two spatial dimensions.
We, finally, find that within our fully self-consistent approach, the
fragmentation degree, to a good approximation, decreases universally as
when only is varied.Comment: 8 pages of RevTex4-1, 5 figure
Nondestructive Evaluation of Flaw Criticality in Graphite-Epoxy Laminates
An analytical and experimental study is conducted to determine criticality of interlaminar disbands by NDE methods. Criticality of such flaws in a shear environment (action of shear near support) is defined in terms of crack propagation and is analyzed by principles and methods of fracture mechanics. Growth of disbands under cyclic loading is also being studied. Fajlure under compressive loading in presence of a disband is defined in terms of buckling and an elastic stability analysis is utilized for assessing criticality. Analytical predictions are compared with experimental results in both cases
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