5,593 research outputs found
Parton cascade description of relativistic heavy-ion collisions at CERN SPS energies ?
We examine Pb+Pb collisions at CERN SPS energy 158 A GeV, by employing the
earlier developed and recently refined parton-cascade/cluster-hadronization
model and its Monte Carlo implementation. This space-time model involves the
dynamical interplay of perturbative QCD parton production and evolution, with
non-perturbative parton-cluster formation and hadron production through cluster
decays. Using computer simulations, we are able to follow the entwined
time-evolution of parton and hadron degrees of freedom in both position and
momentum space, from the instant of nuclear overlap to the final yield of
particles. We present and discuss results for the multiplicity distributions,
which agree well with the measured data from the CERN SPS, including those for
K mesons. The transverse momentum distributions of the produced hadrons are
also found to be in good agreement with the preliminary data measured by the
NA49 and the WA98 collaboration for the collision of lead nuclei at the CERN
SPS. The analysis of the time evolution of transverse energy deposited in the
collision zone and the energy density suggests an existence of partonic matter
for a time of more than 5 fm.Comment: 16 pages including 7 postscript figure
Advanced recovery systems wind tunnel test report
Pioneer Aerospace Corporation (PAC) conducted parafoil wind tunnel testing in the NASA-Ames 80 by 120 test sections of the National Full-Scale Aerodynamic Complex, Moffett Field, CA. The investigation was conducted to determine the aerodynamic characteristics of two scale ram air wings in support of air drop testing and full scale development of Advanced Recovery Systems for the Next Generation Space Transportation System. Two models were tested during this investigation. Both the primary test article, a 1/9 geometric scale model with wing area of 1200 square feet and secondary test article, a 1/36 geometric scale model with wing area of 300 square feet, had an aspect ratio of 3. The test results show that both models were statically stable about a model reference point at angles of attack from 2 to 10 degrees. The maximum lift-drag ratio varied between 2.9 and 2.4 for increasing wing loading
Analysis of reaction dynamics at RHIC in a combined parton/hadron transport approach
We introduce a transport approach which combines partonic and hadronic
degrees of freedom on an equal footing and discuss the resulting reaction
dynamics. The initial parton dynamics is modeled in the framework of the parton
cascade model, hadronization is performed via a cluster hadronization model and
configuration space coalescence, and the hadronic phase is described by a
microscopic hadronic transport approach. The resulting reaction dynamics
indicates a strong influence of hadronic rescattering on the space-time pattern
of hadronic freeze-out and on the shape of transverse mass spectra. Freeze-out
times and transverse radii increase by factors of 2 - 3 depending on the hadron
species.Comment: 10 pages, 4 eps figures include
Inclusive Particle Spectra at RHIC
A simulation is performed of the recently reported data from PHOBOS at
energies of 56 and 130 A GeV using the relativistic heavy ion cascade LUCIFER
which had previously given a good description of the NA49 inclusive spectra at
E=17.2 A GeV. The results compare well with these early measurements at RHIC.Comment: 4 pages, 2 figure
Out of Equilibrium Non-perturbative Quantum Field Dynamics in Homogeneous External Fields
The quantum dynamics of the symmetry broken lambda (Phi^2)^2 scalar field
theory in the presence of an homogeneous external field is investigated in the
large N limit. We choose as initial state the ground state for a constant
external field J .The sign of the external field is suddenly flipped from
J to - J at a given time and the subsequent quantum dynamics calculated.
Spinodal instabilities and parametric resonances produce large quantum
fluctuations in the field components transverse to the external field. This
allows the order parameter to turn around the maximum of the potential for
intermediate times. Subsequently, the order parameter starts to oscillate near
the global minimum for external field - J, entering a novel quasi-periodic
regime.Comment: LaTex, 30 pages, 12 .ps figures, improved version to appear in Phys
Rev
Thermal and Chemical Equilibration in Relativistic Heavy Ion Collisions
We investigate the thermalization and the chemical equilibration of a parton
plasma created from Au+Au collision at LHC and RHIC energies starting from the
early moment when the particle momentum distributions in the central region
become for the first time isotropic due to longitudinal cooling. Using the
relaxation time approximation for the collision terms in the Boltzmann
equations for gluons and for quarks and the real collision terms constructed
from the simplest QCD interactions, we show that the collision times have the
right behaviour for equilibration. The magnitude of the quark (antiquark)
collision time remains bigger than the gluon collision time throughout the
lifetime of the plasma so that gluons are equilibrating faster than quarks both
chemically and kinetically. That is we have a two-stage equilibration scenario
as has been pointed out already by Shuryak sometimes ago. Full kinetic
equilibration is however slow and chemical equilibration cannot be completed
before the onset of the deconfinement phase transition assumed to be at
MeV. By comparing the collision entropy density rates of the
different processes, we show explicitly that inelastic processes, and
\emph{not} elastic processes as is commonly assumed, are dominant in the
equilibration of the plasma and that gluon branching leads the other processes
in entropy generation. We also show that, within perturbative QCD, processes
with higher power in \alpha_s need not be less important for the purpose of
equilibration than those with lower power. The state of equilibration of the
system has also a role to play. We compare our results with those of the parton
cascade model.Comment: 17 pages, revtex+psfig style with 14 embedded postscript figures, to
appear in Phys. Rev.
Soft Electromagnetic Radiations From Equilibrating Quark-Gluon Plasma
We evaluate the bremsstrahlung production of low mass dileptons and soft
photons from equilibrating and transversely expanding quark gluon plasma which
may be created in the wake of relativistic heavy ion collisions. We use initial
conditions obtained from the self screened parton cascade model. We consider a
boost invariant longitudinal and cylindrically symmetric transverse expansion
of the parton plasma and find that for low mass dileptons ( GeV)
and soft photons ( GeV), the bremsstrahlung contribution is
rather large compared to annihilation process at both RHIC and LHC energies. We
also find an increase by a factor of 15-20 in the low mass dileptons and soft
photons yield as one goes from RHIC to LHC energies.Comment: 8 pages, including 7 figures To appear in Phys. Rev.
Examining the Personal and Institutional Determinants of Research Productivity in Hospitality and Tourism Management
The transition toward a post-capitalist knowledge-oriented economy has resulted in an increasingly competitive academic environment, where the success of faculty is dependent on their research productivity. This study examines the personal and institutional determinants of the quantity and quality of the research productivity of hospitality and tourism management faculty in US institutions. A survey of 98 faculty found that a different set of determinants impact the quantity and quality aspects of research productivity. Also, institutional determinants were found to play a larger role, indicating the need for administrators to strive for a culture that is supportive of and an infrastructure that is conducive to their faculty’s research success. The authors use the field of hospitality and tourism management as a case study to develop a holistic and cohesive framework for knowledge worker productivity that can guide the evaluation, hiring, and development of researchers
- …