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

Growth Law and Superuniversality in the Coarsening of Disordered Ferromagnets

We present comprehensive numerical results for domain growth in the two-dimensional {\it Random Bond Ising Model} (RBIM) with nonconserved Glauber kinetics. We characterize the evolution via the {\it domain growth law}, and two-time quantities like the {\it autocorrelation function} and {\it autoresponse function}. Our results clearly establish that the growth law shows a crossover from a pre-asymptotic regime with "power-law growth with a disorder-dependent exponent" to an asymptotic regime with "logarithmic growth". We compare this behavior with previous results on one-dimensional disordered systems and we propose a unifying picture in a renormalization group framework. We also study the corresponding crossover in the scaling functions for the two-time quantities. Super-universality is found not to hold. Clear evidence supporting the dimensionality dependence of the scaling exponent of the autoresponse function is obtained.Comment: Thoroughly revised manuscript. The Introduction, Section 2 and Section 4 have been largely rewritten. References added. Final version accepted for publication on Journal of Statistical Mechanics: Theory and Experimen

Amplification of Fluctuations in Unstable Systems with Disorder

We study the early-stage kinetics of thermodynamically unstable systems with quenched disorder. We show analytically that the growth of initial fluctuations is amplified by the presence of disorder. This is confirmed by numerical simulations of morphological phase separation (MPS) in thin liquid films and spinodal decomposition (SD) in binary mixtures. We also discuss the experimental implications of our results.Comment: 15 pages, 4 figure

Executive function in first-episode schizophrenia

BACKGROUND: We tested the hypothesis that schizophrenia is primarily a frontostriatal disorder by examining executive function in first-episode patients. Previous studies have shown either equal decrements in many cognitive domains or specific deficits in memory. Such studies have grouped test results or have used few executive measures, thus, possibly losing information. We, therefore, measured a range of executive ability with tests known to be sensitive to frontal lobe function. METHODS: Thirty first-episode schizophrenic patients and 30 normal volunteers, matched for age and NART IQ, were tested on computerized test of planning, spatial working memory and attentional set shifting from the Cambridge Automated Neuropsychological Test Battery. Computerized and traditional tests of memory were also administered for comparison. RESULTS: Patients were worse on all tests but the profile was non-uniform. A componential analysis indicated that the patients were characterized by a poor ability to think ahead and organize responses but an intact ability to switch attention and inhibit prepotent responses. Patients also demonstrated poor memory, especially for free recall of a story and associate learning of unrelated word pairs. CONCLUSIONS: In contradistinction to previous studies, schizophrenic patients do have profound executive impairments at the beginning of the illness. However, these concern planning and strategy use rather than attentional set shifting, which is generally unimpaired. Previous findings in more chronic patients, of severe attentional set shifting impairment, suggest that executive cognitive deficits are progressive during the course of schizophrenia. The finding of severe mnemonic impairment at first episode suggests that cognitive deficits are not restricted to one cognitive domain

Heavy Ion Collisions and the Density Dependence of the Local Mean Field

We study the effect of the density dependence of the scalar and the vector part of the nucleonic self-energy in Relativistic Quantum Molecular Dynamics (RQMD) on observables like the transversal flow and the rapidity distribution. The stability of nuclei in RQMD is greatly improved if the density dependence is included in the self-energies compared to a calculation assuming always saturation density of nuclear matter. Different approaches are studied: The main results are calculated with self-energies extracted from a Dirac-Br\"uckner-Hartree-Fock G-matrix of a one boson exchange model, i.e. the Bonn potential. These results are compared with those obtained by a generalization of static Skyrme force, with calculations in the simple linear Walecka model and results of the Br\"uckner-Hartree-Fock G-matrix of the Reid soft core potential. The transversal flow is very sensitive to these different approaches. A comparison with the data is given.Comment: LaTex-file, 13 pages, 5 figures (available upon request), submitted to Nuclear Physics

Domain Growth in Ising Systems with Quenched Disorder

We present results from extensive Monte Carlo (MC) simulations of domain growth in ferromagnets and binary mixtures with quenched disorder. These are modeled by the "random-bond Ising model" and the "dilute Ising model" with either nonconserved (Glauber) spin-flip kinetics or conserved (Kawasaki) spin-exchange kinetics. In all cases, our MC results are consistent with power-law growth with an exponent $\theta (T,\epsilon)$ which depends on the quench temperature $T$ and the disorder amplitude $\epsilon$. Such exponents arise naturally when the coarsening domains are trapped by energy barriers which grow logarithmically with the domain size. Our MC results show excellent agreement with the predicted dependence of $\theta (T,\epsilon)$.Comment: 11 pages, 15 figure

Kinetics of Phase Separation in Thin Films: Simulations for the Diffusive Case

We study the diffusion-driven kinetics of phase separation of a symmetric binary mixture (AB), confined in a thin-film geometry between two parallel walls. We consider cases where (a) both walls preferentially attract the same component (A), and (b) one wall attracts A and the other wall attracts B (with the same strength). We focus on the interplay of phase separation and wetting at the walls, which is referred to as {\it surface-directed spinodal decomposition} (SDSD). The formation of SDSD waves at the two surfaces, with wave-vectors oriented perpendicular to them, often results in a metastable layered state (also referred to as ``stratified morphology''). This state is reminiscent of the situation where the thin film is still in the one-phase region but the surfaces are completely wet, and hence coated with thick wetting layers. This metastable state decays by spinodal fluctuations and crosses over to an asymptotic growth regime characterized by the lateral coarsening of pancake-like domains. These pancakes may or may not be coated by precursors of wetting layers. We use Langevin simulations to study this crossover and the growth kinetics in the asymptotic coarsening regime.Comment: 39 pages, 19 figures, submitted to Phys.Rev.