Category: Nonequilibrium

Foundations of statistical mechanics for unstable interactions

Post author By R Hilfer
Post date May 27, 2021

R. Hilfer

Physical Review E 105, 024142 (2022)
https://doi.org/10.1103/PhysRevE.105.024142

submitted on
Thursday, May 27, 2021

Traditional Boltzmann-Gibbs statistical mechanics does not apply to systems with unstable interactions, because for such systems the conventional thermodynamic limit does not exist. In unstable systems the ground state energy does not have an additive lower bound, i.e., no lower bound linearly proportional to the number N of particles or degrees of freedom. In this article unstable systems are studied whose ground state energy is bounded below by a regularly varying function of N with index \sigma\geq 1. The index \sigma\geq 1 of regular variation introduces a classification with respect to stability. Stable interactions correspond to σ = 1. A simple example for an unstable system with σ =2 is an ideal gas with a nonvanishing constant two-body potential. The foundations of statistical physics are revisited, and generalized ensembles are introduced for unstable interactions in such a way that the thermodynamic limit exists. The extended ensembles are derived by identifying and postulating three basic properties as extended foundations for statistical mechanics: first, extensivity of thermodynamic systems, second, divisibility of equilibrium states, and third, statistical independence of isolated systems. The traditional Boltzmann-Gibbs postulate, resp. the hypothesis of equal a priori probabilities, is identified as a special case of the extended ensembles. Systems with unstable interactions are found to be thermodynamically normal and extensive. The formalism is applied to ideal gases with constant many-body potentials. The results show that, contrary to claims in the literature, stability of the interaction is not a necessary condition for the existence of a thermodynamic limit. As a second example the formalism is applied to the Curie-Weiss-Ising model with strong coupling. This model has index of stability σ = 2. Its thermodynamic potentials [originally obtained in R. Hilfer, Physica A 320, 429 (2003)] are confirmed up to a trivial energy shift. The strong coupling model shows a thermodynamic phase transition of order 1 representing a novel mean-field universality class. The disordered high temperature phase collapses into the ground state of the system. The metastable extension of the high temperature free energy to low temperatures ends at absolute zero in a phase transition of order 1/2. Between absolute zero and the critical temperature of the first order transition all fluctuations are absent.

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Fractional Time Irreversibility Mathematical Physics Nonequilibrium Theory of Time

Mathematical analysis of time flow

Post author By R Hilfer
Post date July 4, 2015

R. Hilfer

Analysis 36, 49-64 (2016)
https://doi.org/10.1515/anly-2015-5005

submitted on
Saturday, July 4, 2015

The mathematical analysis of time fow in physical many-body systems leads to the study of long-time limits. This article discusses the interdisciplinary problem of local stationarity, how stationary solutions can remain slowly time dependent after a long-time limit. A mathematical defnition of almost invariant and nearly indistinguishable states on C*-algebras is introduced using functions of bounded mean oscillation. Rescaling of time yields generalized time fows of almost invariant and macroscopically indistinguishable states, that are mathematically related to stable convolution semigroups and fractional calculus. The infnitesimal generator is a fractional derivative of order less than or equal to unity. Applications of the analysis are given to irreversibility and to a physical experiment.

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Tags 2016, C*-algebras, Scaling Limit

dielectric relaxation Glasses Nonequilibrium Special Functions

Analytical representations for relaxation functions of glasses

Post author By R Hilfer
Post date April 13, 2001

R. Hilfer

Journal of Non-Crystalline Solids 305, 122 (2002)
https://doi.org/10.1016/S0022-3093(02)01088-8

submitted on
Friday, April 13, 2001

Analytical representations in the time and frequency domains are derived for the most frequently used phenomenological fit functions for non-Debye relaxation processes. In the time domain the relaxation functions corresponding to the complex frequency dependent Cole–Cole, Cole–Davidson and Havriliak–Negami susceptibilities are also rep- resented in terms of H-functions. In the frequency domain the complex frequency dependent susceptibility function corresponding to the time dependent stretched exponential relaxation function is given in terms of H-functions. The new representations are useful for fitting to experiment.

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Lattice Models Nonequilibrium Simulations Stochastic Processes

Statistical Prediction of Corrosion Front Penetration

Post author By R Hilfer
Post date August 18, 1996

T. Johnsen, R. Hilfer

Phys.Rev. E 55, 5433 (1997)
https://doi.org/10.1103/PhysRevE.55.5433

submitted on
Wednesday, September 18, 1996

A statistical method to predict the stochastic evolution of corrosion fronts has been developed. The method is based on recording material loss and maximum front depth. In this paper we introduce the method and test its applicability. In the absence of experimental data we use simulation data from a three-dimensional corrosion model for this test. The corrosion model simulates localized breakdown of a protective oxide layer, hydrolysis of corrosion product and repassivation of the exposed surface. In the long time limit of the model, pits tend to coalesce. For different model parameters the model reproduces corrosion patterns observed in experiment. The statistical prediction method is based in the theory of stochastic processes. It allows the estimation of conditional probability densities for penetration depth, pitting factor, residual lifetimes, and corrosion rates which are of technological interest.

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Tags corrosion

Disordered Systems electrical conductivity Lattice Models Nonequilibrium Percolation Statistical Physics Transport Processes

Correlated Random Walks in Dynamically Disordered Systems

Post author By R Hilfer
Post date November 22, 1988

R. Hilfer, R. Orbach

in: Dynamical Processes in Condensed Molecular Systems
edited by: J. Klafter and J. Jortner and A. Blumen
World Scientific Publ.Co., Singapore, 175 (1989)
https://doi.org/10.1142/9789814434379_0009
ISBN: 978-981-4434-37-9

submitted on
Tuesday, November 22, 1988

We discuss correlated hopping motion in a dynamically disordered environment. Particles of type A with one hopping rate diffuse in a background of B-particles with a different hopping rate. Double occupancy of sites is forbidden. Without correlations the limit in which the ratio of hopping rates diverges corresponds to diffusion on a percolating network, while the case of equal hopping rates is that of self-diffusion in a lattice gas. We consider also the effect of correlations. In general these will change the transition rate of the A-particle to the previously occupied site as compared to the rate for transitions to all other neighbouring sites. We calculate the frequency dependent conductivity for this model with arbitrary ratio of hopping rates and correlation strength. Results are reported for the two dimensional hexagonal lattice and the three dimensional face centered cubic lattice. We obtain our results from a generalization of the effective medium approximation for frozen percolating networks. We predict the appearance of new features in real and imaginary part of the conductivity as a result of correlations. Crossover behaviour resulting from the combined effect of disorder and correlations leads to apparent power laws over roughly one to two decades in frequency. In addition we find a crossover between a low frequency regime where the response is governed by the rearrangements in the geometry and a high frequency regime where the geometry appears frozen. We calculate the correlation factor for the d.c. limit and check our results against Monte Carlo simulations on the hexagonal and face centered cubic lattices. In all cases we find good agreement.

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Tags conductivity, correlations, dynamic percolation, Superionenleiter

Disordered Systems Nonequilibrium Pattern Formation

Theoretical Aspects of Polycrystalline Pattern Growth in Al/Ge Films

Post author By R Hilfer
Post date July 22, 1988

R. Hilfer

in: Fluctuation Phenomena and Pattern Growth
edited by: H.E. Stanley and N. Ostrowsky
Kluwer Academic Publishing, Dordrecht, 127 (1988)
https://doi.org/10.1007/978-94-009-2653-0_23
ISBN 978-94-009-2653-0, ISBN 978-0-7923-0073-1

submitted on
Friday, July 22, 1988

These notes discuss recent theoretical approaches to polycrystalline fingering during annealing of amorphous Al/Ge thin films, and compare the to experiment.

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Tags growth, nucleation

diffusion fluid flow Nonequilibrium Pattern Formation

Pattern Formation at Liquid Interfaces

Post author By R Hilfer
Post date January 11, 1988

B. Heidel, C. Knobler, R. Hilfer, R. Bruinsma

Physical Review Letters 60, 2492 (1988)
10.1103/PhysRevLett.60.2492

submitted on
Monday, January 11, 1988

Although many examples of pattern formation resulting from chemical reactions at liquid interfaces are known, few have been studied in detail. We report a quantitative study of patterns formed by the photoproduction of Fe++ and its subsequent reaction to form Turnbull’s Blue. The experiment leads to the postulation of a mechanism in which autocatalysis is enhanced by double diffusion. The phase diagram contains a line of phase transitions whose critical behavior is discussed.

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Tags growth

Disordered Systems Fractals Nonequilibrium Pattern Formation

Phase Separation by Coupled Single-Crystal Growth and Polycrystalline Fingering in Al/Ge: Theory

Post author By R Hilfer
Post date May 26, 1987

S. Alexander, R. Bruinsma, R. Hilfer, G. Deutscher, Y. Lereah

Physical Review Letters 60, 1514 (1988)
10.1103/PhysRevLett.60.1514

submitted on
Tuesday, May 26, 1987

We present a theory for a new mode of phase separation discovered recently in thin layers of amorphous Al-Ge alloys. Phase separation and crystallization occurs in colonies developing from Al nuclei. Their growth is controlled by diffusion of atomic Ge inside crystalline Al, and by the nucleation and growth of Ge crystallites on the Al-Ge interface. We find that the growth velocity is constant as a consequence of the interaction between the ramified Al-Ge interface and the smooth boundary of the colony with the amorphous phase. Diffusion occurs only in a narrow strip controlled by a length scale related to the width of the Ge dendrites. Solution of the growth equations leads to a velocity selection mechanism as long as the Ge concentration is above a critical threshold. The basic length scale is argued to be controlled by a competition between nucleation and growth of the Ge crystallites.

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Tags growth, linear stability analysis, nucleation, velocity selection mechanism

Disordered Systems Nonequilibrium Pattern Formation

On Dense Branching Phase Separation

Post author By R Hilfer
Post date March 31, 1987

R. Hilfer, S. Alexander, R. Bruinsma

in: Time Dependent Effects in Disordered Materials
edited by: R.Pynn and T. Riste
Plenum Press, New York, 417 (1987)
https://doi.org/10.1007/978-1-4684-7476-3_43
ISBN 978-1-4684-7478-7, ISBN 978-1-4684-7476-3

submitted on
Tuesday, March 31, 1987

Recently Deutscher and Lareah discovered a new mode of phase separation in thin films of Al/Ge alloys. They observe the growth of circular “colonies” whose densely packed appearance has been called “dense branching morphology”. The colonies consist of a highly branched starlike “island” of polycrystalline Ge inside a “lake” of monocrystalline Al which is only slightly larger than the Ge island. Thus the Al forms a thin but essentially uninterrupted rim around the Ge peninsulas. The whole colony is embedded in the amorphous phase having an overall composition of 40 percent Al and 60 percent Ge. As these colonies grow into the metastable amorphous surrounding they preserve their more or less circular shape. This immediately raises the question why on the one hand the Al/Ge-interface shows an instability, while on the other the Al/amorphous boundary does not. We investigate this question first. We then present the theoretical description of the new growth morphology. We outline the solution of our equations and indicate how a unique growth velocity is selected. We finally compare our results with experiment.

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Tags growth, linear stability analysis, nucleation, velocity selection mechanism