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Universality in Anomalous Transport Processes

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Statistical Physics".

Deadline for manuscript submissions: closed (30 August 2022) | Viewed by 4702

Special Issue Editor


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Guest Editor
Institute for complex systems - National research council of Italy (CNR-ISC), via dei Taurini 19, 00185 Roma, Italy
Interests: complex systems; fractal growth; stochastic processes; anomalous diffusion; fractional operators; polymer physics; soft matter; biophysics; theory of elasticity; thermally activated cracks; nuclear magnetic resonance; artificial intelligence

Special Issue Information

Dear Colleagues,

Since its introduction in 1960, the concept of universality has been constantly gaining broader usage in many domains of science. Systems usually display universality in a scaling limit, where a certain number of physical observables exhibit identical properties, irrespective of the details of the microscopical dynamics. In the past two decades, universal scaling has prominently emerged as a key feature of physical processes exhibiting anomalous transport. A typical example is the scale-invariant form of the probability density function of the system’s relevant observable or, when such density is unknown or not self-similar, universal features shine through the asymptotic behavior of the density moments in time, or through the scaling expression of the correlation functions. In systems exhibiting glassy or localization transition, anomalous diffusion is accompanied by universal scaling laws, concomitant with a power-law growth of the correlation length. Yet, anomalous transport often characterizes interacting many-particle systems confined to low dimensionality, in the realms of both quantum and classical models, integrable and non-integrable Hamiltonian systems, in and out of equilibrium:  here, universality classes define the divergence of the coefficients of heat conduction, current–current or density–density time correlation functions decay, Green–Kubo relations, as well as spin dynamical correlations in 1D spin systems.       

Importantly, a unique aspect that seems to characterize anomalous transport systems is that universality emerges as a natural element of the passage from the microscopic level to the macroscopic level of description: the infinite many ‘‘degrees of freedom’’ allowed on the microscopic level collapse to few relevant ‘‘degrees of freedom’’ allowed on the macroscopic level. Remarkably, these relevant variables are governed by equations whose mathematical forms appear to be universal.

On the other hand, universality may not to be “that universal”. Different scalings can determine the bulk and the tail of the probability distributions, as well as the time behavior of the correlation functions, depending crucially on the characteristic scales involved. Moreover, the sensitivity of the asymptotic dynamics on the microscopic details observed in some systems leads one to question the bedrock of universality.

This Special Issue aims to provide a collection of the recent progress toward the systematic comprehension of anomalous transport phenomena, through the identification of universal features. In particular, this Special Issue will collect new ideas and describe numerical and analytical methods for the detection and evaluation of universal scalings.

Dr. Alessandro Taloni
Guest Editor

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Keywords

  • universality classes
  • anomalous transport
  • scaling relations
  • fractional equations
  • low-dimensional systems
  • quantum anomalous transport
  • glassy transition
  • localization transition
  • random walk

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Published Papers (2 papers)

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Research

16 pages, 561 KiB  
Article
Universal and Non-Universal Features in the Random Shear Model
by Fabio Cecconi and Alessandro Taloni
Entropy 2022, 24(10), 1350; https://doi.org/10.3390/e24101350 - 24 Sep 2022
Viewed by 1348
Abstract
The stochastic transport of particles in a disordered two-dimensional layered medium, driven by correlated y-dependent random velocity fields is usually referred to as random shear model. This model exhibits a superdiffusive behavior in the x direction ascribable to the statistical properties [...] Read more.
The stochastic transport of particles in a disordered two-dimensional layered medium, driven by correlated y-dependent random velocity fields is usually referred to as random shear model. This model exhibits a superdiffusive behavior in the x direction ascribable to the statistical properties of the disorder advection field. By introducing layered random amplitude with a power-law discrete spectrum, the analytical expressions for the space and time velocity correlation functions, together with those of the position moments, are derived by means of two distinct averaging procedures. In the case of quenched disorder, the average is performed over an ensemble of uniformly spaced initial conditions: albeit the strong sample-to-sample fluctuations, and universality appears in the time scaling of the even moments. Such universality is exhibited in the scaling of the moments averaged over the disorder configurations. The non-universal scaling form of the no-disorder symmetric or asymmetric advection fields is also derived. Full article
(This article belongs to the Special Issue Universality in Anomalous Transport Processes)
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25 pages, 988 KiB  
Article
Spectral Properties of Stochastic Processes Possessing Finite Propagation Velocity
by Massimiliano Giona, Andrea Cairoli, Davide Cocco and Rainer Klages
Entropy 2022, 24(2), 201; https://doi.org/10.3390/e24020201 - 28 Jan 2022
Cited by 2 | Viewed by 2756
Abstract
This article investigates the spectral structure of the evolution operators associated with the statistical description of stochastic processes possessing finite propagation velocity. Generalized Poisson–Kac processes and Lévy walks are explicitly considered as paradigmatic examples of regular and anomalous dynamics. A generic spectral feature [...] Read more.
This article investigates the spectral structure of the evolution operators associated with the statistical description of stochastic processes possessing finite propagation velocity. Generalized Poisson–Kac processes and Lévy walks are explicitly considered as paradigmatic examples of regular and anomalous dynamics. A generic spectral feature of these processes is the lower boundedness of the real part of the eigenvalue spectrum that corresponds to an upper limit of the spectral dispersion curve, physically expressing the relaxation rate of a disturbance as a function of the wave vector. We also analyze Generalized Poisson–Kac processes possessing a continuum of stochastic states parametrized with respect to the velocity. In this case, there is a critical value for the wave vector, above which the point spectrum ceases to exist, and the relaxation dynamics becomes controlled by the essential part of the spectrum. This model can be extended to the quantum case, and in fact, it represents a simple and clear example of a sub-quantum dynamics with hidden variables. Full article
(This article belongs to the Special Issue Universality in Anomalous Transport Processes)
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