1,669 research outputs found
Analysis of dilepton production in Au+Au collisions at sqrt(s_NN)=200 GeV within the Parton-Hadron-String Dynamics (PHSD) transport approach
We address dilepton production in Au+Au collisions at sqrt(s_NN)=200 GeV by
employing the parton-hadron-string dynamics (PHSD) off-shell transport
approach. Within the PHSD one goes beyond the quasiparticle approximation by
solving generalized transport equations on the basis of the off-shell
Kadanoff-Baym equations for the Green's functions in the phase-space
representation. The approach consistently describes the full evolution of a
relativistic heavy-ion collision from the initial hard scatterings and string
formation through the dynamical deconfinement phase transition to the
quark-gluon plasma (QGP) as well as hadronization and to the subsequent
interactions in the hadronic phase. {With partons described in the PHSD by the
dynamical quasiparticle model (DQPM) - matched to reproduce lattice QCD results
in thermodynamic equilibrium} - we calculate, in particular, the dilepton
radiation from partonic interactions through the reactions q+qbar->gamma^*,
q+qbar->gamma^*+g and q+g->gamma^*+q (qbar+g->gamma^*+qbar) in the early stage
of relativistic heavy-ion collisions. By comparing our results to the data from
the PHENIX Collaboration, we study the relative importance of different
dilepton production mechanisms and point out the regions in phase space where
partonic channels are dominant. Furthermore, explicit predictions are presented
for dileptons within the acceptance of the STAR detector system and compared to
the preliminary data.Comment: 11 pages, 10 figures. arXiv admin note: substantial text overlap with
arXiv:1107.340
The pulsating hot subdwarf Balloon 090100001: results of the 2005 multisite campaign
We present the results of a multisite photometric campaign on the pulsating
sdB star Balloon 090100001. The star is one of the two known hybrid hot
subdwarfs with both long- and short-period oscillations. The campaign involved
eight telescopes with three obtaining UBVR data, four B-band data, and one
Stromgren uvby photometry. The campaign covered 48 nights, providing a temporal
resolution of 0.36microHz with a detection threshold of about 0.2mmag in
B-filter data.
Balloon 090100001 has the richest pulsation spectrum of any known pulsating
subdwarf B star and our analysis detected 114 frequencies including 97
independent and 17 combination ones. The strongest mode (f_1) in the 2.8mHz
region is most likely radial while the remaining ones in this region form two
nearly symmetric multiplets: a triplet and quintuplet, attributed to
rotationally split \ell=1 and 2 modes, respectively. We find clear increases of
splitting in both multiplets between the 2004 and 2005 observing campaigns,
amounting to 15% on average. The observed splittings imply that the rotational
rate in Bal09 depends on stellar latitude and is the fastest on the equator. We
use a small grid of models to constrain the main mode (f_1), which most likely
represents the radial fundamental pulsation. The groups of p-mode frequencies
appear to lie in the vicinity of consecutive radial overtones, up to the third
one. Despite the large number of g-mode frequencies observed, we failed to
identify them, most likely because of the disruption of asymptotic behaviour by
mode trapping. The observed frequencies were not, however, fully exploited in
terms of seismic analysis which should be done in the future with a larger grid
of reliable evolutionary models of hot subdwarfs.Comment: accepted for publication in MNRA
DEFICIENCIES IN THE REQUIREMENT GENERATION PHASE THAT DELAY THE LEAD TIME OF ARMY CONTRACT ACTIONS
The purpose of this mixed-methodology study is to identify opportunities to reduce administrative requirements lead time for contracting actions at Army Contracting Command (ACC) organizations, at CONUS installation level, for future implementation across ACC units. An analysis of FY19–21 reveals issues in the training resources available to operational contract support personnel that degrade critical contract elements, increasing the procurement action lead time for service requirements. The findings show service contracts have a longer requirements generation phase than supply contracts. The longer requirements generation phase is associated with the level of complexity and required documentation for each contract action. As complexity decreases, requirements lead time also decreases. The research further reveals an inverse relationship between the use of standardized resource tools and requirements lead time; the lead time decreased as utilization rates increased. The results of the research indicate that policy implementation and consolidation of standardized resource tools would have a reductive effect on lead time for contract actions within the ACC. Additionally, the research recommends modifying the training curriculum to focus on the requirements generation phase. Furthermore, the research recommends changing table of organization and equipment (TOE) positions to require the additional skill identifier 3C for all S4s/G4s and supply sergeants at every echelon.Major, United States ArmyMajor, United States ArmyMajor, United States ArmyMajor, United States ArmyMajor, United States ArmyApproved for public release. Distribution is unlimited
Effect of isovector-scalar meson on neutron star matter in strong magnetic fields
We study the effects of isovector-scalar meson on the equation of
state (EOS) of neutron star matter in strong magnetic fields. The EOS of
neutron-star matter and nucleon effective masses are calculated in the
framework of Lagrangian field theory, which is solved within the mean-field
approximation. From the numerical results one can find that the -field
leads to a remarkable splitting of proton and neutron effective masses. The
strength of -field decreases with the increasing of the magnetic field
and is little at ultrastrong field. The proton effective mass is highly
influenced by magnetic fields, while the effect of magnetic fields on the
neutron effective mass is negligible. The EOS turns out to be stiffer at G but becomes softer at stronger magnetic field after including the
-field. The AMM terms can affect the system merely at ultrastrong
magnetic field(G). In the range of G -- G the
properties of neutron-star matter are found to be similar with those without
magnetic fields.Comment: 26 pages, 9 figure
Coulomb effects on growth of instabilities in asymmetric nuclear matter
We study the effects of the Coulomb interaction on the growth of unstable
modes in asymmetric nuclear matter. In order to compare with previous
calculations we use a semiclassical approach based on the linearized Vlasov
equation. Moreover, a quantum calculation is performed within the R.P.A.. The
Coulomb effects are a slowing down of the growth and the occurrence of a
minimal wave vector for the onset of the instabilities. The quantum corrections
cause a further decrease of the growth rates.Comment: 10 pages, revtex, 4 ps figures, to appear in Phys. Rev. C e-mail:
[email protected], [email protected]
A phenomenological equation of state for isospin asymmetric nuclear matter
A phenomenological momentum-independent (MID) model is constructed to
describe the equation of state (EOS) for isospin asymmetric nuclear matter,
especially the density dependence of the nuclear symmetry energy
. This model can reasonably describe the general
properties of the EOS for symmetric nuclear matter and the symmetry energy
predicted by both the sophisticated isospin and momentum dependent MDI model
and the Skyrme-Hartree-Fock approach. We find that there exists a nicely linear
correlation between and as well as between and , where and represent, respectively, the
slope and curvature parameters of the symmetry energy at the normal nuclear
density while and are, respectively, the
incompressibility and the third-order derivative parameter of symmetric nuclear
matter at . These correlations together with the empirical
constraints on , and lead to an
estimation of -477 MeV MeV for the
second-order isospin asymmetry expansion coefficient for the incompressibility
of asymmetric nuclear matter at the saturation point.Comment: 9 pages, 4 figures, contribution to Special Topic on Large-Scale
Scientific Facilities (LSSF) in Science in China Series G: Physics, Mechanics
& Astronom
Higher order bulk characteristic parameters of asymmetric nuclear matter
The bulk parameters characterizing the energy of symmetric nuclear matter and
the symmetry energy defined at normal nuclear density provide
important information on the equation of state (EOS) of isospin asymmetric
nuclear matter. While significant progress has been made in determining some
lower order bulk characteristic parameters, such as the energy
and incompressibility of symmetric nuclear matter as well as the symmetry
energy and its slope parameter , yet the higher order bulk
characteristic parameters are still poorly known. Here, we analyze the
correlations between the lower and higher order bulk characteristic parameters
within the framework of Skyrme Hartree-Fock energy density functional and then
estimate the values of some higher order bulk characteristic parameters. In
particular, we obtain MeV and MeV for the
third-order and fourth-order derivative parameters of symmetric nuclear matter
at and MeV, MeV,
MeV for the curvature parameter, third-order and
fourth-order derivative parameters of the symmetry energy at , using
the empirical constraints on , , , , and
the isoscalar and isovector nucleon effective masses. Furthermore, our results
indicate that the three parameters , , and can
reasonably characterize the EOS of symmetric nuclear matter up to
while the symmetry energy up to can be well described by
, , and .Comment: 6 pages, 7 figures. Typos fixed. Contribution to a special issue in
Science China: Physics, Mechanics & Astronom
Space-time analysis of reaction at RHIC
Space-time information about the Au-Au collisions produced at RHIC are key
tools to understand the evolution of the system and especially assess the
presence of collective behaviors. Using a parameterization of the system's
final state relying on collective expansion, we show that pion source radii can
be tied together with transverse mass spectra and elliptic flow within the same
framework. The consistency between these different measures provide a solid
ground to understand the characteristics of collective flow and especially the
possible peculiar behavior of particles such as Xi, Omega or phi. The validity
of the short time scales that are extracted from fits to the pion source size
is also addressed. The wealth of new data that will soon be available from
Au-Au collisions at sqrt{s_{NN}} = 200 GeV, will provide a stringet test of the
space-time analysis framework developped in these proceedings.Comment: Invited talk given at the SQM2003 conference (March 2003), to be
published in Journal of Physics G. 10 pages, 3 figure
Strongly damped nuclear collisions: zero or first sound ?
The relaxation of the collective quadrupole motion in the initial stage of a
central heavy ion collision at beam energies AMeV is studied
within a microscopic kinetic transport model. The damping rate is shown to be a
non-monotonic function of E_{lab} for a given pair of colliding nuclei. This
fact is interpreted as a manifestation of the zero-to-first sound transition in
a finite nuclear system.Comment: 15 pages, 4 figure
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