19,147 research outputs found
Baryon number and strangeness: signals of a deconfined antecedent
The correlation between baryon number and strangeness is used to discern the
nature of the deconfined matter produced at vanishing chemical potential in
high-energy nuclear collisions at the BNL RHIC. Comparisons of results of
various phenomenological models with correlations extracted from lattice QCD
calculations suggest that a quasi-particle picture applies. At finite baryon
densities, such as those encountered at the CERN SPS, it is demonstrated that
the presence of a first-order phase transition and the accompanying development
of spinodal decomposition would significantly enhance the number of strangeness
carriers and the associated fluctuations.Comment: 10 pages, 4 figures, latex, to appear in the proceedings of the
Workshop on Correlations and Fluctuations in Relativistic Nuclear collisions,
(MIT, April 21-23,2005
The QCD phase diagram and statistics friendly distributions
The preliminary STAR data for proton cumulants for central collisions at s=7.7GeV component proton multiplicity distribution. We show that this two-component distribution is statistics friendly in that factorial cumulants of surprisingly high orders may be extracted with a relatively small number of events. As a consequence the two-component model can be tested and verified right now with the presently available STAR data from the first phase of the RHIC beam energy scan
Baryon-strangeness correlations: a diagnostic of strongly interacting matter
The correlation between baryon number and strangeness elucidates the nature
of strongly interacting matter, such as that formed transiently in high-energy
nuclear collisions. This diagnostic can be extracted theoretically from lattice
QCD calculations and experimentally from event-by-event fluctuations. The
analysis of present lattice results above the critical temperature severely
limits the presence of q-qbar bound states, thus supporting a picture of
independent (quasi)quarks.Comment: 4 pages, 2 eps figures, Revised: several sign typos have been fixed
(the PRL version is correct
Non-equilibrium dynamics in the dual-wavelength operation of Vertical external-cavity surface-emitting lasers
Microscopic many-body theory coupled to Maxwell's equation is used to
investigate dual-wavelength operation in vertical external-cavity
surface-emitting lasers. The intrinsically dynamic nature of coexisting
emission wavelengths in semiconductor lasers is associated with characteristic
non-equilibrium carrier dynamics which causes significant deformations of the
quasi-equilibrium gain and carrier inversion. Extended numerical simulations
are employed to efficiently investigate the parameter space to identify the
regime for two-wavelength operation. Using a frequency selective intracavity
etalon, two families of modes are stabilized with dynamical interchange of the
strongest emission peaks. For this operation mode, anti-correlated intensity
noise is observed in agreement with the experiment. A method using effective
frequency selective filtering is suggested for stabilization genuine
dual-wavelength output.Comment: 15 pages, 7 figure
Dilepton from Disoriented Chiral Condensates
Disoriented chiral condensates are manifested as long wavelength pionic
oscillations and their interaction with the thermal environment can be a
significant source of dileptons. We calculate the yield of such dilepton
production within the linear sigma model and illustrate the basic features of
the dilepton spectrum in a schematic model. We find that the dilepton yield
with invariant mass near and below due to the soft pion modes can be
up to two orders of magnitude larger than the corresponding equilibrium yield.
We conclude with a discussion on how this enhancement can be detected by
present dilepton experiments.Comment: 15 pages, 9 figs, uses epsf and sprocl style files Contribution to
Proceedings, International Workshop on Astro Hadron Physics `Hadrons in Dense
Matter', APCTP, Seoul, Korea, October 199
A machine learning study to identify spinodal clumping in high energy nuclear collisions
The coordinate and momentum space configurations of the net baryon number in heavy ion collisions that undergo spinodal decomposition, due to a first-order phase transition, are investigated using state-of-the-art machine-learning methods. Coordinate space clumping, which appears in the spinodal decomposition, leaves strong characteristic imprints on the spatial net density distribution in nearly every event which can be detected by modern machine learning techniques. On the other hand, the corresponding features in the momentum distributions cannot clearly be detected, by the same machine learning methods, in individual events. Only a small subset of events can be systematically differ- entiated if only the momentum space information is available. This is due to the strong similarity of the two event classes, with and without spinodal decomposition. In such sce- narios, conventional event-averaged observables like the baryon number cumulants signal a spinodal non-equilibrium phase transition. Indeed the third-order cumulant, the skewness, does exhibit a peak at the beam energy (Elab = 3–4 A GeV), where the transient hot and dense system created in the heavy ion collision reaches the first-order phase transition
Mode-locking in vertical external-cavity surface-emitting lasers with type-II quantum-well configurations
A microscopic study of mode-locked pulse generation is presented for vertical
external-cavity surface-emitting lasers utilizing type-II quantum well
configurations. The coupled Maxwell semiconductor Bloch equations are solved
numerically where the type-II carrier replenishment is modeled via suitably
chosen reservoirs. Conditions for stable mode-locked pulses are identified
allowing for pulses in the \unit[100]{fs} range. Design strategies for type-II
configurations are proposed that avoid potentially unstable pulse dynamics.Comment: Main paper with supplementary material
Highlights of the Beam Energy Scan from STAR
The first part of the beam energy scan (BES) program at RHIC was successfully
completed in the years 2010 and 2011. First STAR results from particle yield
measurements are in good agreement with previously published data from SPS and
AGS experiments whereas other results like azimuthal HBT and
event-by-event fluctuations differ at some energies. In addition, new
observations like the centrality dependence of chemical freeze-out parameters
( and ) or the smoothly increasing difference with
decreasing energy in the elliptic flow between particles and
corresponding anti-particles, are discussed.Comment: CPOD 2011 proceedings, 5 pages, 4 figure
Searching for the QCD Critical Point Using Particle Ratio Fluctuations and Higher Moments of Multiplicity Distributions
Dynamical fluctuations in global conserved quantities such as baryon number,
strangeness, or charge may be observed near a QCD critical point. Results from
new measurements of dynamical , , and ratio fluctuations
are presented. The commencing of a QCD critical point search at RHIC has
extended the reach of possible measurements of dynamical , , and
ratio fluctuations from Au+Au collisions to lower energies. The STAR
experiment has performed a comprehensive study of the energy dependence of
these dynamical fluctuations in Au+Au collisions at the energies
= 7.7, 11.5, 39, 62.4, and 200 GeV. New results are compared to
previous measurements and to theoretical predictions from several models. The
measured dynamical fluctuations are found to be independent of
collision energy, while dynamical and fluctuations have a
negative value that increases toward zero at top RHIC energy. Fluctuations of
the higher moments of conserved quantities (net-proton and net-charge)
distributions, which are predicted to be sensitive to the presence of a
critical point, are also presented.Comment: 4 pages, 2 figures, Proceedings of the 21st International Conference
On Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2011), Annecy,
France, May 23 - May 28, 201
Thermally stable electrolytes for rechargeable lithium batteries, phase 2
During the second year of research under NASA SBIR Contract NAS7-967, Covalent Associates and NASA contract monitors at the Jet Propulsion Laboratory agreed to perform an evaluation of the three best electrolytes developed during Phase 2. Due to the extensive period of time required to collect meaningful cycling data, we realized the study would extend well beyond the original formal end of the Phase 2 program (August 31, 1988). The substitution of this effort in lieu of an earlier proposed 20-cell final deliverable is formally documented in Modification No. 1 of Contract NAS7-967 as task 7. This Addendum contains the results of the cycling studies performed at Covalent Associates. In addition, sealed ampoules of each of these three electrolytes were delivered to the Jet Propulsion Laboratory Electrochemical Power Group. Their concurrent evaluation in a different test vehicle has also been recently concluded and their results are also summarized herein
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