6,725 research outputs found
Study of non-equilibrium effects and thermal properties of heavy ion collisions using a covariant approach
Non-equilibrium effects are studied using a full Lorentz-invariant formalism.
Our analysis shows that in reactions considered here, no global or local
equilibrium is reached. The heavier masses are found to be equilibrated more
than the lighter systems. The local temperature is extracted using hot Thomas
Fermi formalism generalized for the case of two interpenetrating pieces of
nuclear matter. The temperature is found to vary linearly with bombarding
energy and impact parameter whereas it is nearly independent of the mass of the
colliding nuclei. This indicates that the study of temperature with medium size
nuclei is also reliable. The maximum temperatures obtained in our approach are
in a nice agreement with earlier calculations of other approaches. A simple
parametrization of maximal temperature as a function of the bombarding energy
is also given.Comment: LaTex-file, 17 pages, 8 figures (available upon request), Journal of
Physics G20 (1994) 181
Scaling Behavior of Response Functions in the Coarsening Dynamics of Disordered Ferromagnets
We study coarsening dynamics in the ferromagnetic random bond Ising model in
d = 1; 2. We focus on the validity of super-universality and the scaling
properties of the response functions. In the d = 1 case, we obtain a complete
understanding of the evolution, from pre- asymptotic to asymptotic behavior.
The corresponding response function shows a clear violation of
super-universality. Further, our results for d = 1; 2 settle the controversy
regarding the decay exponent which characterizes the response function
Crossover in Growth Law and Violation of Superuniversality in the Random Field Ising Model
We study the nonconserved phase ordering dynamics of the d = 2, 3 random
field Ising model, quenched to below the critical temperature. Motivated by the
puzzling results of previous work in two and three di- mensions, reporting a
crossover from power-law to logarithmic growth, together with superuniversal
behavior of the correlation function, we have undertaken a careful
investigation of both the domain growth law and the autocorrelation function.
Our main results are as follows: We confirm the crossover to asymptotic
logarithmic behavior in the growth law, but, at variance with previous
findings, the exponent in the preasymptotic power law is disorder-dependent,
rather than being the one of the pure system. Furthermore, we find that the
autocorre- lation function does not display superuniversal behavior. This
restores consistency with previous results for the d = 1 system, and fits
nicely into the unifying scaling scheme we have recently proposed in the study
of the random bond Ising model.Comment: To be published in Physical Review
The multifragmentation of spectator matter
We present the first microscopic calculation of the spectator fragmentation
observed in heavy ion reactions at relativistic energies which reproduces the
slope of the kinetic energy spectra of the fragments as well as their
multiplicity, both measured by the ALADIN collaboration. In the past both have
been explained in thermal models, however with vastly different assumptions
about the excitation energy and the density of the system. We show that both
observables are dominated by dynamical processes and that the system does not
pass a state of thermal equilibrium. These findings question the recent
conjecture that in these collisions a phase transition of first order, similar
to that between water and vapor, can be observed.Comment: 7 page
Domain Growth in Random Magnets
We study the kinetics of domain growth in ferromagnets with random exchange
interactions. We present detailed Monte Carlo results for the nonconserved
random-bond Ising model, which are consistent with power-law growth with a
variable exponent. These results are interpreted in the context of disorder
barriers with a logarithmic dependence on the domain size. Further, we clarify
the implications of logarithmic barriers for both nonconserved and conserved
domain growth.Comment: 7 pages, 4 figure
Sensitivity of the transverse flow towards symmetry energy
We study the sensitivity of transverse flow towards symmetry energy in the
Fermi energy region as well as at high energies. We find that transverse flow
is sensitive to symmetry energy as well as its density dependence in the Fermi
energy region. We also show that the transverse flow can address the symmetry
energy at densities about twice the saturation density, however it shows the
insensitivity towards the symmetry energy at densities 2.
The mechanism for the sensitivity of transverse flow towards symmetry energy as
well as its density dependence is also discussed.Comment: Phys. Rev. C (in press)2011 14 pages, 6 figure
Microscopic approach to the spectator matter fragmentation from 400 to 1000 AMeV
A study of multifragmentation of gold nuclei is reported at incident energies
of 400, 600 and 1000 MeV/nucleon using microscopic theory. The present
calculations are done within the framework of quantum molecular dynamics (QMD)
model. The clusterization is performed with advanced sophisticated algorithm
namely \emph{simulated annealing clusterization algorithm} (SACA) along with
conventional spatial correlation method. A quantitative comparison of mean
multiplicity of intermediate mass fragments with experimental findings of
ALADiN group gives excellent agreement showing the ability of SACA method to
reproduce the fragment yields. It also emphasizes the importance of clustering
criterion in describing the fragmentation process within semi-classical model
Isospin effects in the disappearance of flow as a function of colliding geometry
We study the effect of isospin degree of freedom on the balance energy
(E) as well as its mass dependence throughout the mass range 48-270 for
two sets of isobaric systems with N/Z = 1 and 1.4 at different colliding
geometries ranging from central to peripheral ones. Our findings reveal the
dominance of Coulomb repulsion in isospin effects on E as well as its
mass dependence throughout the range of the colliding geometry. Our results
also indicate that the effect of symmetry energy and nucleon-nucleon cross
section on E is uniform throughout the mass range and throughout the
colliding geometry. We also present the counter balancing of nucleon-nucleon
collisions and mean field by reducing the Coulomb and the counter balancing of
Coulomb and mean filed by removing the nucleon-nucleon collisions.Comment: 15 pages, 5 figure
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