111 research outputs found
On an exact hydrodynamic solution for the elliptic flow
Looking for the underlying hydrodynamic mechanisms determining the elliptic
flow we show that for an expanding relativistic perfect fluid the transverse
flow may derive from a solvable hydrodynamic potential, if the entropy is
transversally conserved and the corresponding expansion "quasi-stationary",
that is mainly governed by the temperature cooling. Exact solutions for the
velocity flow coefficients and the temperature dependence of the spatial
and momentum anisotropy are obtained and shown to be in agreement with the
elliptic flow features of heavy-ion collisions.Comment: 10 pages, 4 figure
Particle Freeze-out and Discontinuities in Relativistic Hydrodynamics
Freeze-out of particles in relativistic hydrodynamics is considered across a
3-dimensional space-time hypersurface. The conservation laws for time-like
parts of the freeze-out hypersurface require different values of temperature,
baryonic chemical potential and flow velocity in the fluid and in the final
particle spectra. We analyze this freeze-out discontinuity and its connection
to the shock-wave phenomena in relativistic hydrodynamics.Comment: 6 figure
Equilibrium Relativistic Mass Distribution for Indistinguishable Events
A manifestly covariant relativistic statistical mechanics of the system of
indistinguishable events with motion in space-time parametrized by an
invariant ``historical time'' is considered. The relativistic mass
distribution for such a system is obtained from the equilibrium solution of the
generalized relativistic Boltzmann equation by integration over angular and
hyperbolic angular variables. All the characteristic averages are calculated.
Expressions for the pressure and the density of events are found and the
relativistic equation of state is obtained. The Galilean limit is considered;
the theory is shown to pass over to the usual nonrelativistic statistical
mechanics of indistinguishable particles.Comment: TAUP-2115-9
Nonequilibrium effects in hadronic fireball expansion
We consider a spherical volume of hot and dense hadronic matter (fireball)
expanding into a vacuum. It is assumed that initially the fireball matter is in
local thermal and chemical equilibrium with vanishing collective velocity. The
time evolution of the fireball is studied in parallel within the GiBUU
transport model and an ideal hydrodynamic model. The equation of state of an
ideal hadronic gas is used in the hydrodynamic calculation. The same set of
hadronic species is used in transport and fluid-dynamical simulations. Initial
coordinates and momenta of hadrons in transport simulations have been randomly
generated by using the Fermi and Bose distributions for (anti)baryons and
mesons. The model results for radial profiles of densities and collective
velocities of different hadronic species are compared at different times. We
find that two considered models predict essential differences in time evolution
of hadron abundances, which are especially pronounced for hyperonic species.
This gives an evidence of a strong deviation from chemical equilibrium in
expanding hadronic matter.Comment: 23 pages, 12 figure
Relativistic mass distribution in event-anti-event system and ``realistic'' equation of state for hot hadronic matter
We find the equation of state which gives the value of
the sound velocity in agreement with the ``realistic'' equation of
state for hot hadronic matter suggested by Shuryak, in the framework of a
covariant relativistic statistical mechanics of an event--anti-event system
with small chemical and mass potentials. The relativistic mass distribution for
such a system is obtained and shown to be a good candidate for fitting hadronic
resonances, in agreement with the phenomenological models of Hagedorn, Shuryak,
{\it et al.} This distribution provides a correction to the value of specific
heat 3/2, of the order of 5.5\%, at low temperatures.Comment: 19 pages, report TAUP-2161-9
Resonant Raman Scattering of ZnS, ZnO, and ZnS/ZnO Core/shell quantum dots
Resonant Raman scattering by optical phonon modes as well as their overtones was investigated in ZnS and ZnO quantum dots grown by the Langmuir–Blodgett technique. The in situ formation of ZnS/ZnO core/shell quantum dots was monitored by Raman spectroscopy during laser illumination
Ge/Si Quantum Dots Superlattices Grown at Different Temperatures and Characterized by Raman Spectroscopy and Capacitance Measurements
Ge/Si heterostructures with Ge self-assembled quantum dots (SAQDs) grown at various temperatures by molecular beam epitaxy were investigated using resonant Raman spectroscopy and capacitance measurements. The occurrence of quantum confinement effects was confirmed by both techniques. For the structures grown at low temperatures (300 − 400 • C), the SAQDs optical phonon wavenumbers decrease as the Raman excitation energy is increased; this is an evidence of the scattering sensitivity to the size of the SAQDs and to the inhomogeneity in their sizes. However, the opposite behavior is observed for the SAQDs grown at higher temperatures, as a consequence of the competition between the phonon localization and internal mechanical stress effects. The E 1 electronic transition of the Ge in the SAQDs was found to be shifted towards higher energies as compared to bulk Ge, due to biaxial compressive stress and to the electronic confinement effect present in the structures. The intermixing of Si atoms in the quantum dots was found to be much more significant for the sample grown at higher temperatures. The capacitance measurements, besides confirming the existence of the dots in these structures, showed that the deepest Ge layers lose their 0D signature as the growth temperature increases
On freeze-out problem in relativistic hydrodynamics
A finite unbound system which is equilibrium in one reference frame is in
general nonequilibrium in another frame. This is a consequence of the relative
character of the time synchronization in the relativistic physics. This puzzle
was a prime motivation of the Cooper--Frye approach to the freeze-out in
relativistic hydrodynamics. Solution of the puzzle reveals that the
Cooper--Frye recipe is far not a unique phenomenological method that meets
requirements of energy-momentum conservation. Alternative freeze-out recipes
are considered and discussed.Comment: 6 pages, 2 figures, references are corrected and updated, to be
published in the issue of Phys. Atom. Nucl. dedicated to S.T. Belyaev on the
occasion of his birthda
Studies of multiplicity in relativistic heavy-ion collisions
In this talk I'll review the present status of charged particle multiplicity
measurements from heavy-ion collisions. The characteristic features of
multiplicity distributions obtained in Au+Au collisions will be discussed in
terms of collision centrality and energy and compared to those of p+p
collisions. Multiplicity measurements of d+Au collisions at 200 GeV
nucleon-nucleon center-of-mass energy will also be discussed. The results will
be compared to various theoretical models and simple scaling properties of the
data will be identified.Comment: "Focus on Multiplicity" Internationsl Workshop on Particle
Multiplicity in Relativistic Heavy Ion Collisions, Bari, Italy, June 17-19,
2003, 16 pages, 15 figure
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