Journal De Physique I 

About: Journal De Physique I is an academic journal. The journal publishes majorly in the area(s): Phase transition & Spin glass. It has an ISSN identifier of 1155-4304. Over the lifetime, 945 publications have been published receiving 21841 citations.

A cellular automaton model for freeway traffic

Abstract: We introduce a stochastic discrete automaton model to simulate freeway traffic. Monte-Carlo simulations of the model show a transition from laminar traffic flow to start-stop- waves with increasing vehicle density, as is observed in real freeway traffic. For special cases analytical results can be obtained.

Weak ergodicity breaking and aging in disordered systems

Abstract: We present a phenomenological model for the dynamics of disordered (complex) systems. We postulate that the lifetimes of the many metastable states are distributed according to a broad, power law probability distribution. We show that aging occurs in this model when the average lifetime is infmite. A simple hypothesis leads to a new functional fornl for the relaxation which is in remarkable agreement with spin-glass experiments over nearly five decades in time. In spite of fifteen years of dispute, the theory of equilibrium spin-glasses is not yet settled (1, 2, 3). Dynamical effects are, however, likely to be the dominant aspect in experiments. One of the most striking aspects of the dynamics of spin-glasses in their low temperature phase is the aging phenomenon- a rather peculiar and awkward feature from the thermodynamics point of view : the relaxation of a system depends on its history. More precisely, if a system is field-cooled below its spin-glass temperature, the magnetization relaxation depends on the Waiting time t~ between the quench and the switch off of the magnetic field (4, 5, 6). Similar effects are observed on the viscoelastic properties of polymer melts (7), magnetic properties of HTC superconductors (8) and more recently on the relaxation after a heat pulse in Charge Density Wave systems (9). Analytical fits of the magnetization relaxation as a function of time have been proposed. In (6), it is proposed that the initial «stationary» part of the relaxation is a power-law With a small (negative) exponent. For times longer than the Waiting time, relaxation is Well fitted by a « stretched » exponential decay, provided that an effective time is introduced (6). In (4, 5), however, a stretched exponential of the «real» time was found for relatively short times. Many phenomenological theories have been devised to account for the stretched exponential decay lo-14), and for the slow part and aging (6, 15-18). We however feel that the basic mechanism underlying aging has not been fully appreciated (see however (17)) although it is, in our opinion, one of the constitutive properties of spin-glasses. The aim of this note is to suggest that aging is related to ergodicity breaking which has, in these systems, a peculiar and perhaps unexpected meaning. We find on some simple models that- according to our definition, see below « Weak » ergodicity breaking occurs in the spin-glass phase, defined as the phase Where the Edwards-Anderson parameter is non-zero. We see however no reason Why the two should be linked in general, and suggest that the appearance of aging could be

Force Schemes in Simulations of Granular Materials

Abstract: In computer simulations of granular flow, one widely used technique is classical soft-sphere Molecular Dynamics, where the equations of motion of the particles are numerically integrated. This requires specification of the forces acting between grains. In this paper, we systematically study the properties of the force laws most commonly used and compare them with recent experiments on the impact of spheres. We point out possible problems and give criteria for the right choice of parameters. Finally, two generic problems of soft-sphere simulations are discussed.

Continuum models of crystal growth from atomic beams with and without desorption

Abstract: Continuum equations appropriate to describe crystal growth from atom beams are derived in various cases. When desorption is important, the growth is described on very long lengthscales by the Kardar-Parisi-Zhang equation, but should be corrected for shorter lengthscales where surface diffusion is the dominant mechanism. In the absence of desorption, an important effect at sufficiently low temperature comes from the fact that diffusion of incoming atoms on the surface is anisotropic on long lengthscales becaused it is biased by reflexions against terrace edges. As a result, the growth is described by a pseudo-diffusion equation. In the case of a high symmetry surface, (001) or (ill), an instability arises. Finally,in the absence of diffusion bias, the growth is described by a nonlinear equation of fourth order with respect to 3/3x and 3/3y. The exponents are calculated in a Flory-type approximation. In particular the roughness exponent is found to be x = (5 d)/3 in d dimensions.

Complex Critical Exponents from Renormalization Group Theory of Earthquakes: Implications for Earthquake Predictions

Abstract: Several authors have proposed discrete renormalization group models of earthquakes, viewing them as a kind of dynamical critical phenomena. Here, we propose that the assumed discrete scale invariance stems from the irreversible and intermittent nature of rupture which ensures a breakdown of translational invariance. As a consequence, we show that the renormalization group entails complex critical exponents, describing log-periodic corrections to the leading scaling behavior. We use the mathematical form of this solution to fit the time to failure dependence of the Benioff strain on the approach of large earthquakes. This might provide a new technique for earthquake prediction for which we present preliminary tests on the 1989 Loma Prieta earthquake in northern California and on a recent build-up of seismic activity on a segment of the Aleutian-Island seismic zone. The earthquake phenomenology of precursory phenomena such as the causal sequence of quiescence and foreshocks is captured by the general structure of the mathematical solution of the renormalization group