375 research outputs found
Spinodal decomposition during the hadronization stage at RHIC?
The expansion of strongly interacting matter formed in high-energy nuclear
collisions drives the system through the region of phase coexistence. The
present study examines the associated spinodal instability and finds that the
degree of amplification may be sufficient to raise the prospect of using the
spinodal pattern formation as a diagnostic tool for probing the hadronization
phase transition.Comment: 4 pages, 4 eps figure
Collaboration Engineering Methodology: Horizontal Extension to Accommodate Project and Program Concerns
A Collaboration Engineering Methodology (CEM) comprises a set of defined, standardized, documented, and discoverable objectives, deliverables, key actions, tools/templates, principles and policies for establishing effective, efficient, satisfying collaborative work practices for high-value organizational tasks. First-generation CEMs address design and development CE solutions. Existing CEMs, though, focus on the design/build phase, but lack the pre-design and post-build elements that are common to methodologies for adjacent disciplines. We use Design Science Research to situate existing design/build CEMs in the larger context of CE programs and projects. We develop and validate an extended CEM in four phases: 1) Opportunity Assessment, 2) Development, 3) Deployment, and 4) Improvement (ODDI). Phase 1 concerns CE portfolio management and CE project planning; Phase 2 encapsulates existing design/build CEMs; Phase 3 concerns roll-out planning, change management, and implementation; Phase 4 concerns continuous optimization of a deployed work practice. The ODDI model advances CE another step towards becoming a fully realized professional practice, but more research is still required to derive a complete a design theory for CE
Dileptons from Disoriented Chiral Condensates
Disoriented chiral condensates or 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, both in a quantal mean-field treatment and in a semi-classical
approximation. We then illustrate the basic features of the dilepton spectrum
in a schematic model. We find that 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.Comment: 22 pages, 8 figures, uses epsf-styl
Dynamical simulation of DCC formation in Bjorken rods
Using a semi-classical treatment of the linear sigma model, we simulate the
dynamical evolution of an initially hot cylindrical rod endowed with a
longitudinal Bjorken scaling expansion (a ``Bjorken rod''). The field equation
is propagated until full decoupling has occurred and the asymptotic many-body
state of free pions is then obtained by a suitable Fourier decomposition of the
field and a subsequent stochastic determination of the number of quanta in each
elementary mode. The resulting transverse pion spectrum exhibits visible
enhancements below 200 MeV due to the parametric amplification caused by the
oscillatory relaxation of the chiral order parameter. Ensembles of such final
states are subjected to various event-by-event analyses. The factorial moments
of the multiplicity distribution suggest that the soft pions are
non-statistical. Furthermore, their emission patterns exhibit azimuthal
correlations that have a bearing on the domain size in the source. Finally, the
distribution of the neutral pion fraction shows a significant broadening for
the soft pions which grows steadily as the number of azimuthal segments is
increased. All of these features are indicative of disoriented chiral
condensates and it may be interesting to apply similar analyses to actual data
from high-energy nuclear collision experiments.Comment: 38 pages total, incl 26 ps figures ([email protected]
Inhomogeneous isospin distribution in the reactions of 28Si + 112Sn and 124Sn at 30 and 50 MeV/nucleon
We have created quasiprojectiles of varying isospin via peripheral reactions
of 28Si + 112Sn and 124Sn at 30 and 50 MeV/nucleon. The quasiprojectiles have
been reconstructed from completely isotopically identified fragments. The
difference in N/Z of the reconstructed quasiprojectiles allows the
investigation of the disassembly as a function of the isospin of the
fragmenting system. The isobaric yield ratio 3H/3He depends strongly on N/Z
ratio of quasiprojectiles. The dependences of mean fragment multiplicity and
mean N/Z ratio of the fragments on N/Z ratio of the quasiprojectile are
different for light charged particles and intermediate mass fragments.
Observation of a different N/Z ratio of light charged particles and
intermediate mass fragments is consistent with an inhomogeneous distribution of
isospin in the fragmenting system.Comment: 5 pages, 4 Postscript figures, RevTe
Dissipation, noise and DCC domain formation
We investigate the effect of friction on domain formation in disoriented
chiral condensate. We solve the equation of motion of the linear sigma model,
in the Hartree approximation, including a friction and a white noise term. For
quenched initial condition, we find that even in presence of noise and
dissipation domain like structure emerges after a few fermi of evolution.
Domain size as large as 5 fm can be formed.Comment: 7 pages, 3 figure
Near-threshold Production in Heavy-ion Collisions
Within a hadronic transport model we study in detail contributions to kaon
yields and momentum spectra from various baryon (resonance)-baryon (resonance)
and interactions in heavy-ion collisions at beam energies near the
free-space kaon production threshold. It is found that the finite lifetime of
baryon resonances affects significantly the shape of kaon spectra, and the high
energy parts of the kaon spectra are dominated by kaons from processes. resonances are found to contribute
about 10\% to the kaon yield. Effects of boosting the Fermi momentum
distributions of the two colliding nuclei into their center of mass frame,
centrality of the reaction as well as the nuclear equation of state on kaon
yields and spectra are also discussed. Model calculations on ,
and spectra for the reaction of Au+Au at GeV are
compared with the experimental data from the KaoS collaboration.Comment: 18 pages, 11 figures available upon request. TAMU preprint #940403
Effect of nucleon exchange on projectile multifragmentation in the reactions of 28Si + 112Sn and 124Sn at 30 and 50 MeV/nucleon
Multifragmentation of quasiprojectiles was studied in reactions of 28Si beam
with 112Sn and 124Sn targets at projectile energies 30 and 50 MeV/nucleon. The
quasiprojectile observables were reconstructed using isotopically identified
charged particles with Z_f <= 5 detected at forward angles. The nucleon
exchange between projectile and target was investigated using isospin and
excitation energy of reconstructed quasiprojectile. For events with total
reconstructed charge equal to the charge of the beam (Z_tot = 14) the influence
of beam energy and target isospin on neutron transfer was studied in detail.
Simulations employing subsequently model of deep inelastic transfer,
statistical model of multifragmentation and software replica of FAUST detector
array were carried out. A concept of deep inelastic transfer provides good
description of production of highly excited quasiprojectiles. The isospin and
excitation energy of quasiprojectile were described with good overall
agreement. The fragment multiplicity, charge and isospin were reproduced
satisfactorily. The range of contributing impact parameters was determined
using backtracing procedure.Comment: 11 pages, 8 Postscript figures, LaTeX, to appear in Phys. Rev. C (
Dec 2000
Modeling the impact of white-plague coral disease in climate change scenarios
Coral reefs are in global decline, with coral diseases increasing both in prevalence and in space, a situation that is expected only to worsen as future thermal stressors increase. Through intense surveillance, we have collected a unique and highly resolved dataset from the coral reef of Eilat (Israel, Red Sea), that documents the spatiotemporal dynamics of a White Plague Disease (WPD) outbreak over the course of a full season. Based on modern statistical methodologies, we develop a novel spatial epidemiological model that uses a maximum-likelihood procedure to fit the data and assess the transmission pattern of WPD. We link the model to sea surface temperature (SST) and test the possible effect of increasing temperatures on disease dynamics. Our results reveal that the likelihood of a susceptible coral to become infected is governed both by SST and by its spatial location relative to nearby infected corals. The model shows that the magnitude of WPD epidemics strongly depends on demographic circumstances; under one extreme, when recruitment is free-space regulated and coral density remains relatively constant, even an increase of only 0.5 degrees C in SST can cause epidemics to double in magnitude. In reality, however, the spatial nature of transmission can effectively protect the community, restricting the magnitude of annual epidemics. This is because the probability of susceptible corals to become infected is negatively associated with coral density. Based on our findings, we expect that infectious diseases having a significant spatial component, such as Red-Sea WPD, will never lead to a complete destruction of the coral community under increased thermal stress
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