515 research outputs found
Thermodynamics of Delta resonances
The thermodynamic potential of a system of pions and nucleons is computed
including the piN interactions in the P33 channel. A consistent treatment of
the width of the resonance in this channel, the Delta(1232) resonance, is
explored in detail. In the low-density limit we recover the leading term of the
virial expansion for the thermodynamic potential. An instructive diagrammatic
interpretation of the contributions to the total baryon number is presented.
Furthermore, we examine within a fireball model the consequences for the pion
spectra in heavy-ion collisions at intermediate energies, including the effect
of collective flow. A consistent treatment of the Delta width leads to a
substantial enhancement of the pion yield at low momenta.Comment: 12 pages, 3 Postscript figures, LaTeX, elsart, epsfig, minor changes,
references added, to be published in Physics Letters
Analyzing Correlation Functions with Tesseral and Cartesian Spherical Harmonics
The dependence of inter-particle correlations on the orientation of particle
relative-momentum can yield unique information on the space-time features of
emission in reactions with multiparticle final states. In the present paper,
the benefits of a representation and analysis of the three-dimensional
correlation information in terms of surface spherical harmonics is presented.
The harmonics include the standard complex tesseral harmonics and the real
cartesian harmonics. Mathematical properties of the lesser-known cartesian
harmonics are illuminated. The physical content of different angular harmonic
components in a correlation is described. The resolving power of different
final-state effects with regarding to determining angular features of emission
regions is investigated. The considered final-state effects include identity
interference and strong and Coulomb interactions. The correlation analysis in
terms of spherical harmonics is illustrated with the cases of gaussian and
blast-wave sources for proton-charged meson and baryon-baryon pairs.Comment: 32 pages 10 figure
Probing the isospin dependence of the in-medium nucleon-nucleon cross sections with radioactive beams
Within a transport model we search for potential probes of the isospin
dependence of the in-medium nucleon-nucleon (NN) cross sections. Traditional
measures of the nuclear stopping power are found sensitive to the magnitude but
they are ambiguous for determining the isospin dependence of the in-medium NN
cross sections. It is shown that isospin tracers, such as the neutron/proton
ratio of free nucleons, at backward rapidities/angles in nuclear reactions
induced by radioactive beams in inverse kinematics is a sensitive probe of the
isospin dependence of the in-medium NN cross sections. At forward
rapidities/angles, on the other hand, they are more sensitive to the density
dependence of the symmetry energy. Measurements of the rapidity/angular
dependence of the isospin transport in nuclear reactions will enable a better
understanding of the isospin dependence of in-medium nuclear effective
interactions.Comment: 19 pages including 7 figures, submitted to Phys. Rev.
Experimental and analytical performance investigation of air to air two phase closed thermosyphon based heat exchangers
In recent years, the use of wickless heat pipes (thermosyphons) in heat exchangers has been on the rise, particularly in gas to gas heat recovery applications due to their reliability and the level of contingency they offer compared to conventional heat exchangers. Recent technological advances in the manufacturing processes and production of gravity assisted heat pipes (thermosyphons) have resulted in significant improvements in both quality and cost of industrial heat pipe heat exchangers. This in turn has broadened the potential for their usage in industrial waste heat recovery applications. In this paper, a tool to predict the performance of an air to air thermosyphon based heat exchanger using the ε-NTU method is explored. This tool allows the predetermination of variables such as the overall heat transfer coefficient, effectiveness, pressure drop and heat exchanger duty according to the flow characteristics and the thermosyphons configuration within the heat exchanger. The new tool's predictions were validated experimentally and a good correlation between the theoretical predictions and the experimental data, was observed. © 2014 Elsevier Ltd. All rights reserved
Photoexcited transients in disordered semiconductors: Quantum coherence at very short to intermediate times
We study theoretically electron transients in semiconductor alloys excited by
light pulses shorter than 100 femtoseconds and tuned above the absorption edge
during and shortly after the pulse, when disorder scattering is dominant.
We use non-equilibrium Green functions employing the field-dependent
self-consistent Born approximation. The propagators and the particle
correlation function are obtained by a direct numerical solution of the Dyson
equations in differential form. For the purely elastic scattering in our model
system the solution procedures for the retarded propagator and for the
correlation function can be decoupled.The propagator is used as an input in
calculating the correlation function. Numerical results combined with a
cumulant expansion permit to separate in a consistent fashion the dark and the
induced parts of the self-energy. The dark behavior reduces to propagation of
strongly damped quasi-particles; the field induced self-energy leads to an
additional time non-local coherence. The particle correlation function is
formed by a coherent transient and an incoherent back-scattered component. The
particle number is conserved only if the field induced coherence is fully
incorporated. The transient polarization and the energy balance are also
obtained and interpreted.Comment: Accepted for publication in Phys. Rev. B; 37 pages,17 figure
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