162,701 research outputs found

### Azimuthal asymmetry in transverse energy flow in nuclear collisions at high energies

The azimuthal pattern of transverse energy flow in nuclear collisions at RHIC
and LHC energies is considered. We show that the probability distribution of
the event-by-event azimuthal disbalance in transverse energy flow is
essentially sensitive to the presence of the semihard minijet component.Comment: 6 pages, 2 figure

### Strangeness Production in Chemically Non-Equilibrated Parton Plasma

Strangeness production was investigated during the equilibration of a gluon
dominated parton plasma produced at RHIC and LHC energies. The time evolution
of parton densities are followed by a set of rate equations in a 1-dimensional
expanding system. The strangeness production will depend on the initial
chemical equilibration level and in our case the parton densities will remain
far from the full equilibrium. We investigate the influence of gluon
fragmentation on final strangeness content.Comment: 12 pages (LaTeX) + 2 postscript figures (tarred, compressed,
uuencoded) included. Review to appear in Proceedings of Strangeness'95,
Tucson, Arizona, Jan. 4--6 1995. (American Institute of Physics

### Where is the jet quenching in Pb+Pb collisions at 158 AGeV?

Because of the rapidly falling particle spectrum at large $p_T$ from jet
fragmentation at the CERN SPS energy, the high-$p_T$ hadron distribution should
be highly sensitive to parton energy loss inside a dense medium as predicted by
recent perturbative QCD (pQCD) studies. A careful analysis of recent data from
CERN SPS experiments via pQCD calculation shows little evidence of energy loss.
This implies that either the life-time of the dense partonic matter is very
short or one has to re-think about the problem of parton energy loss in dense
matter. The hadronic matter does not seem to cause jet quenching in $Pb+Pb$
collisions at the CERN SPS. High-$p_T$ two particle correlation in the
azimuthal angle is proposed to further clarify this issue.Comment: 4 pages with 2 ps figures. Minors changes are made in the text with
updated references. Revised version to appear in Phys. Rev. Letter

### Finite Volume Analysis of Nonlinear Thermo-mechanical Dynamics of Shape Memory Alloys

In this paper, the finite volume method is developed to analyze coupled
dynamic problems of nonlinear thermoelasticity. The major focus is given to the
description of martensitic phase transformations essential in the modelling of
shape memory alloys. Computational experiments are carried out to study the
thermo-mechanical wave interactions in a shape memory alloy rod, and a patch.
Both mechanically and thermally induced phase transformations, as well as
hysteresis effects, in a one-dimensional structure are successfully simulated
with the developed methodology. In the two-dimensional case, the main focus is
given to square-to-rectangular transformations and examples of martensitic
combinations under different mechanical loadings are provided.Comment: Keywords: shape memory alloys, phase transformations, nonlinear
thermo-elasticity, finite volume metho

### Numerical Model For Vibration Damping Resulting From the First Order Phase Transformations

A numerical model is constructed for modelling macroscale damping effects
induced by the first order martensite phase transformations in a shape memory
alloy rod. The model is constructed on the basis of the modified
Landau-Ginzburg theory that couples nonlinear mechanical and thermal fields.
The free energy function for the model is constructed as a double well function
at low temperature, such that the external energy can be absorbed during the
phase transformation and converted into thermal form. The Chebyshev spectral
methods are employed together with backward differentiation for the numerical
analysis of the problem. Computational experiments performed for different
vibration energies demonstrate the importance of taking into account damping
effects induced by phase transformations.Comment: Keywords: martensite transformation, thermo-mechanical coupling,
vibration damping, Ginzburg-Landau theor

### Studying minijets via the $p_T$ dependence of two-particle correlation in azimuthal angle $\phi$

Following my previous proposal that two-particle correlation functions can be
used to resolve the minijet contribution to particle production in minimum
biased events of high energy hadronic interactions, I study the $p_T$ and
energy dependence of the correlation. Using HIJING Monte Carlo model, it is
found that the correlation $c(\phi_1,\phi_2)$ in azimuthal angle $\phi$ between
two particles with $p_T>p_T^{cut}$ resembles much like two back-to-back jets as
$p_T^{cut}$ increases at high colliding energies due to minijet production. It
is shown that $c(0,0)-c(0,\pi)$, which is related to the relative fraction of
particles from minijets, increases with energy. The background of the
correlation for fixed $p_T^{cut}$ also grows with energy due to the increase of
multiple minijet production. Application of this analysis to the study of jet
quenching in ultrarelativistic heavy ion collisions is also discussed.Comment: 11 pages Latex text and 8 ps figures, LBL-3349

### Thermo-Mechanical Wave Propagation In Shape Memory Alloy Rod With Phase Transformations

Many new applications of ferroelastic materials require a better
understanding of their dynamics that often involve phase transformations. In
such cases, an important prerequisite is the understanding of wave propagation
caused by pulse-like loadings. In the present study, a mathematical model is
developed to analyze the wave propagation process in shape memory alloy rods.
The first order martensite transformations and associated thermo-mechanical
coupling effects are accounted for by employing the modified
Ginzburg-Landau-Devonshire theory. The Landau-type free energy function is
employed to characterize different phases, while a Ginzburg term is introduced
to account for energy contributions from phase boundaries. The effect of
internal friction is represented by a Rayleigh dissipation term. The resulted
nonlinear system of PDEs is reduced to a differential-algebraic system, and
Chebyshev's collocation method is employed together with the backward
differentiation method. A series of numerical experiments are performed. Wave
propagations caused by impact loadings are analyzed for different initial
temperatures. It is demonstrated that coupled waves will be induced in the
material. Such waves will be dissipated and dispersed during the propagation
process, and phase transformations in the material will complicate their
propagation patterns. Finally, the influence of internal friction and capillary
effects on the process of wave propagation is analyzed numerically.Comment: Keywords: nonlinear waves, thermo-mechanical coupling, martensite
transformations, Ginzburg-Landau theory, Chebyshev collocation metho

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