2,205 research outputs found
Spinodal Decomposition in High Temperature Gauge Theories
After a rapid increase in temperature across the deconfinement temperature , pure gauge theories exhibit unstable long wavelength fluctuations in
the approach to equilibrium. This phenomenon is analogous to spinodal
decomposition observed in condensed matter physics, and also seen in models of
disordered chiral condensate formation. At high temperature, the unstable modes
occur only in the range , where is on the order
of the Debye screening mass . Equilibration always occurs via spinodal
decomposition for at temperatures and for SU(3) for . For SU(3) at temperatures , nucleation may replace
spinodal decomposition as the dominant equilibration mechanism. Monte Carlo
simulations of SU(2) lattice gauge theory exhibit the predicted phenomena. The
observed value of is in reasonable agreement with a value predicted from
previous lattice measurements of .Comment: minor revisions, 16 pages, 6 figures, RevTe
Exonerations in the United States, 1989-2012: Report by the National Registry of Exonerations
This report is about 873 exonerations in the United States, from January 1989 through February 2012. Behind each is a story, and almost all are tragedies. The tragedies are not limited to the exonerated defendants themselves, or to their families and friends. In most cases they were convicted of vicious crimes in which other innocent victims were killed or brutalized. Many of the victims who survived were traumatized all over again, years later, when they learned that the criminal who had attacked them had not been caught and punished after all, and that they themselves may have played a role in condemning an innocent person. In many cases, the real criminals went on to rape or kill other victims, while the innocent defendants remained in prison. Some of the stories have villains; many do not. Few have happy endings
The stability of the spectator, Dirac, and Salpeter equations for mesons
Mesons are made of quark-antiquark pairs held together by the strong force.
The one channel spectator, Dirac, and Salpeter equations can each be used to
model this pairing. We look at cases where the relativistic kernel of these
equations corresponds to a time-like vector exchange, a scalar exchange, or a
linear combination of the two. Since the model used in this paper describes
mesons which cannot decay physically, the equations must describe stable
states. We find that this requirement is not always satisfied, and give a
complete discussion of the conditions under which the various equations give
unphysical, unstable solutions
Cosmological Implications of Lyman-Break Galaxy Clustering
We review our analysis of the clustering properties of ``Lyman-break''
galaxies (LBGs) at redshift z~3, previously discussed in Wechsler et al (1998).
We examine the likelihood of spikes found by Steidel et al (1998) in the
redshift distribution of LBGs, within a suite of models for the evolution of
structure in the Universe. Using high-resolution dissipationless N-body
simulations, we analyze deep pencil-beam surveys from these models in the same
way that they are actually observed, identifying LBGs with the most massive
dark matter halos. We find that all the models (with SCDM as a marginal
exception) have a substantial probability of producing spikes similar to those
observed, because the massive halos are much more clumped than the underlying
matter -- i.e., they are biased. Therefore, the likelihood of such a spike is
not a good discriminator among these models. The LBG correlation functions are
less steep than galaxies today (gamma~1.4), but show similar or slightly longer
correlation lengths. We have extened this analysis and include a preliminary
comparison to the new data presented in Adelberger et al (1998). We also
discuss work in progress, in which we use semi-analytic models to identify
Lyman-break galaxies within dark-matter halos.Comment: 4 pages, 2 figures, Latex, uses aipproc.sty; to appear in the
proceedings of the 9th Annual October Maryland Astrophysics Conference,
"After the Dark Ages: When the Galaxies Were Young (the Universe at 2<z<5)
Performance regression testing of concurrent classes
Developers of thread-safe classes struggle with two oppos-ing goals. The class must be correct, which requires syn-chronizing concurrent accesses, and the class should pro-vide reasonable performance, which is difficult to realize in the presence of unnecessary synchronization. Validating the performance of a thread-safe class is challenging because it requires diverse workloads that use the class, because ex-isting performance analysis techniques focus on individual bottleneck methods, and because reliably measuring the per-formance of concurrent executions is difficult. This paper presents SpeedGun, an automatic performance regression testing technique for thread-safe classes. The key idea is to generate multi-threaded performance tests and to com-pare two versions of a class with each other. The analysis notifies developers when changing a thread-safe class signif-icantly influences the performance of clients of this class. An evaluation with 113 pairs of classes from popular Java projects shows that the analysis effectively identifies 13 per-formance differences, including performance regressions that the respective developers were not aware of
Microcanonical entropy inflection points: Key to systematic understanding of transitions in finite systems
We introduce a systematic classification method for the analogs of phase
transitions in finite systems. This completely general analysis, which is
applicable to any physical system and extends towards the thermodynamic limit,
is based on the microcanonical entropy and its energetic derivative, the
inverse caloric temperature. Inflection points of this quantity signal
cooperative activity and thus serve as distinct indicators of transitions. We
demonstrate the power of this method through application to the long-standing
problem of liquid-solid transitions in elastic, flexible homopolymers.Comment: 4 pages, 3 figure
Stable isochronal synchronization of mutually coupled chaotic lasers
The dynamics of two mutually coupled chaotic diode lasers are investigated
experimentally and numerically. By adding self feedback to each laser, stable
isochronal synchronization is established. This stability, which can be
achieved for symmetric operation, is essential for constructing an optical
public-channel cryptographic system. The experimental results on diode lasers
are well described by rate equations of coupled single mode lasers
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