4,641 research outputs found
Deconfinement of Constituent Quarks and the Hagedorn Temperature
The double phase transition of hadronic matter, , first, to the gas of
deconfined constituent quarks (for brevity called {\it valons}), , and then,
secondly, the phase transition from to quark-gluon plasma, , is
considered within bag model ideology. In distinction from previous double phase
transition investigations, it is not supposed that at zero chemical potential
(~~) transition temperatures (for ) and
(for , chiral restoration) coincide. Then for
plausible range of chosen bag constants, for and for the
phase transition can proceed {\it only via the
phase} (at least at not too much ). For small the gap,
, is quite essential, up to MeV. The physical
meaning of the transition temperature, , coincide
with that of the Hagedorn temperature, .Comment: 9 pages, 11 Postscript figure
Conformal anomaly as a source of soft photons in heavy ion collisions
We introduce a novel photon production mechanism stemming from the conformal
anomaly of QCDxQED and the existence of strong (electro)magnetic fields in
heavy ion collisions. Using the hydrodynamical description of the bulk modes of
QCD plasma, we show that this mechanism leads to the photon production yield
that is comparable to the yield from conventional sources. This mechanism also
provides a significant positive contribution to the azimuthal anisotropy of
photons, , as well as to the radial "flow". We compare our results to the
data from the PHENIX Collaboration.Comment: 5 pages, 3 figures; version accepted to Phys. Rev. Let
Azimuthal Asymmetry of Direct Photons in High Energy Nuclear Collisions
We show that a sizeable azimuthal asymmetry, characterized by a coefficient
v_2, is to be expected for direct photons produced in non-central high energy
nuclear collisions. This signal is generated by photons radiated by jets
interacting with the surrounding hot plasma. The anisotropy is out of phase by
an angle with respect to that associated with the elliptic anisotropy
of hadrons, leading to negative values of v_2. Such an asymmetry, if observed,
could be a signature for the presence of a quark gluon plasma and would
establish the importance of jet-plasma interactions as a source of
electromagnetic radiation.Comment: New title. Final versio
Impact of ERTS-1 images on management of New Jersey's coastal zone
The thrust of New Jersey's ERTS investigation is development of procedures for operational use of ERTS-1 data by the Department of Environmental Protection in the management of the State's coastal zone. Four major areas of concern were investigated: detection of land use changes in the coastal zone; monitoring of offshore waste disposal; siting of ocean outfalls; and allocation of funds for shore protection. ERTS imagery was not useful for shore protection purposes; it was of limited practical value in the evaluation of offshore waste disposal and ocean outfall siting. However, ERTS imagery shows great promise for operational detection of land use changes in the coastal zone. Some constraints for practical change detection have been identified
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
Scaling and Universality of the Complexity of Analog Computation
We apply a probabilistic approach to study the computational complexity of
analog computers which solve linear programming problems. We analyze
numerically various ensembles of linear programming problems and obtain, for
each of these ensembles, the probability distribution functions of certain
quantities which measure the computational complexity, known as the convergence
rate, the barrier and the computation time. We find that in the limit of very
large problems these probability distributions are universal scaling functions.
In other words, the probability distribution function for each of these three
quantities becomes, in the limit of large problem size, a function of a single
scaling variable, which is a certain composition of the quantity in question
and the size of the system. Moreover, various ensembles studied seem to lead
essentially to the same scaling functions, which depend only on the variance of
the ensemble. These results extend analytical and numerical results obtained
recently for the Gaussian ensemble, and support the conjecture that these
scaling functions are universal.Comment: 22 pages, latex, 12 eps fig
"Free" Constituent Quarks and Dilepton Production in Heavy Ion Collisions
An approach is suggested, invoking vitally the notion of constituent massive
quarks (valons) which can survive and propagate rather than hadrons (except of
pions) within the hot and dense matter formed below the chiral transition
temperature in course of the heavy ion collisions at high energies. This
approach is shown to be quite good for description of the experimentally
observed excess in dilepton yield at masses 250 MeV < M < 700 MeV over the
prompt resonance decay mechanism (CERES cocktail) predictions. In certain
aspects, it looks to be even more successful, than the conventional approaches:
it seems to match the data somewhat better at dilepton masses before the
two-pion threshold and before the rho-meson peak as well as at higher dilepton
masses (beyond the phi-meson one). The approach implies no specific assumptions
on the equation of state (EOS) or peculiarities of phase transitions in the
expanding nuclear matter.Comment: 13 pages, 3 PNG figures. submitted to Sov. Nucl. Phy
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