54 research outputs found
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
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
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
The Role of Interdiffusion and Spatial Confinement in the Formation of Resonant Raman Spectra of Ge/Si(100) Heterostructures with Quantum-Dot Arrays
The phonon modes of self-assembled Ge/Si quantum dots grown by molecular-beam
epitaxy in an apparatus integrated with a chamber of the scanning tunneling
microscope into a single high-vacuum system are investigated using Raman
spectroscopy. It is revealed that the Ge-Ge and Si-Ge vibrational modes are
considerably enhanced upon excitation of excitons between the valence band
and the conduction band (the E1 and E1 +
transitions). This makes it possible to observe the Raman spectrum of very
small amounts of germanium, such as one layer of quantum dots with a germanium
layer thickness of 10 \r{A}. The enhancement of these modes suggests a strong
electron-phonon interaction of the vibrational modes with the E1 and E1 +
excitons in the quantum dot. It is demonstrated that the frequency
of the Ge-Ge mode decreases by 10 cm^-1 with a decrease in the thickness of the
Ge layer from 10 to 6 \r{A} due to the spatial-confinement effect. The optimum
thickness of the Ge layer, for which the size dispersion of quantum dots is
minimum, is determined.Comment: 14 pages, 9 figure
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
1+1 Dimensional Hydrodynamics for High-energy Heavy-ion Collisions
A 1+1 dimensional hydrodynamical model in the light-cone coordinates is used
to describe central heavy-ion collisions at ultrarelativistic bombarding
energies. Deviations from Bjorken's scaling are taken into account by choosing
finite-size profiles for the initial energy density. The sensitivity of fluid
dynamical evolution to the equation of state and the parameters of initial
state is investigated. Experimental constraints on the total energy of produced
particles are used to reduce the number of model parameters. Spectra of
secondary particles are calculated assuming that the transition from the
hydrodynamical stage to the collisionless expansion of matter occurs at a
certain freeze-out temperature. An important role of resonances in the
formation of observed hadronic spectra is demonstrated. The calculated rapidity
distributions of pions, kaons and antiprotons in central Au+Au collisions at
the c.m. energy 200 GeV per NN pair are compared with experimental data of the
BRAHMS Collaboration. Parameters of the initial state are reconstructed for
different choices of the equation of state. The best fit of these data is
obtained for a soft equation of state and Gaussian-like initial profiles of the
energy density, intermediate between the Landau and Bjorken limits.Comment: 43 pages, 27 figure
Nanostructured Silver Substrates With Stable and Universal SERS Properties: Application to Organic Molecules and Semiconductor Nanoparticles
Nanostructured silver films have been prepared by thermal deposition on silicon, and their properties as SERS substrates investigated. The optimal conditions of the post-growth annealing of the substrates were established. Atomic force microscopy study revealed that the silver films with relatively dense and homogeneous arrays of 60â80-nm high pyramidal nanoislands are the most efficient for SERS of both organic dye and inorganic nanoparticles analytes. The noticeable enhancement of the Raman signal from colloidal nanoparticles with the help of silver island films is reported for the first time
Strange Meson Enhancement in PbPb Collisions
The NA44 Collaboration has measured yields and differential distributions of
K+, K-, pi+, pi- in transverse kinetic energy and rapidity, around the
center-of-mass rapidity in 158 A GeV/c Pb+Pb collisions at the CERN SPS. A
considerable enhancement of K+ production per pi is observed, as compared to
p+p collisions at this energy. To illustrate the importance of secondary hadron
rescattering as an enhancement mechanism, we compare strangeness production at
the SPS and AGS with predictions of the transport model RQMD.Comment: 11 pages, including 4 figures, LATE
Miniband-related 1.4â1.8 ÎŒm luminescence of Ge/Si quantum dot superlattices
The luminescence properties of highly strained, Sb-doped Ge/Si multi-layer heterostructures with incorporated Ge quantum dots (QDs) are studied. Calculations of the electronic band structure and luminescence measurements prove the existence of an electron miniband within the columns of the QDs. Miniband formation results in a conversion of the indirect to a quasi-direct excitons takes place. The optical transitions between electron states within the miniband and hole states within QDs are responsible for an intense luminescence in the 1.4â1.8 ”m range, which is maintained up to room temperature. At 300 K, a light emitting diode based on such Ge/Si QD superlattices demonstrates an external quantum efficiency of 0.04% at a wavelength of 1.55 ”m
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