1,721,018 research outputs found
Microscopic dynamics, chaos and transport in nonequilibrium processes
No full textThis EPJ - Special Topics issue is a collection of contributions on theory and the recent developments in nonequilibrium statistical mechanics, fluctuations theory and dynamical systems. The various articles report results on the role of microscopic dynamics in giving rise to complex patterns observed at the macroscopic scale in a variety of physical phenomena
Toward a Quantitative Reduction of the SIR Epidemiological Model
No full textMotivated by our intention to use SIR-type epidemiological models in the context of dynamic networks, we investigate in this framework possibilities to reduce the classical SIR model to a representative evolution model for a suitably chosen observable. For selected scenarios, we provide practical a priori error bounds between the approximate and the original observables. Finally, we illustrate numerically the behavior of the reduced models compared to the original ones. As a long-term goal, we would like to apply such techniques in the context of large-scale highly interacting inhomogeneous human crowds
Equilibrium, fluctuation relations and transport for irreversible deterministic dynamics
No full textIn a recent paper [M. Colangeli et al., J. Stat. Mech. P04021, (2011)] it was argued that the Fluctuation Relation for the phase space contraction rate A could suitably be extended to non-reversible dissipative systems. We strengthen here those arguments, providing analytical and numerical evidence based on the properties of a simple irreversible nonequilibrium baker model. We also consider the problem of response, showing that the transport coefficients are not affected by the irreversibility of the microscopic dynamics. In addition, we prove that a form of detailed balance, hence of equilibrium, holds in the space of relevant variables, despite the irreversibility of the phase space dynamics. This corroborates the idea that the same stochastic description, which arises from a projection onto a subspace of relevant coordinates, is compatible with quite different underlying deterministic dynamics. In other words, the details of the microscopic dynamics are largely irrelevant, for what concerns properties such as those concerning the Fluctuation Relations, the equilibrium behavior and the response to perturbations. (C) 2011 Elsevier B.V. All rights reserved
Transport in quantum multi-barrier systems as random walks on a lattice
No full textA quantum finite multi-barrier system, with a periodic potential, is considered and exact expressions for its plane wave amplitudes are obtained using the Transfer Matrix method (Colangeli et al. in J Stat Mech Theor Exp 6:P06006, 2015). This quantum model is then associated with a stochastic process of independent random walks on a lattice, by properly relating the wave amplitudes with the hopping probabilities of the particles moving on the lattice and with the injection rates from external particle reservoirs. Analytical and numerical results prove that the stationary density profile of the particle system overlaps with the quantum mass density profile of the stationary Schrodinger equation, when the parameters of the two models are suitably matched. The equivalence between the quantum model and a stochastic particle system would mainly be fruitful in a disordered setup. Indeed, we also show, here, that this connection, analytically proven to hold for periodic barriers, holds even when the width of the barriers and the distance between barriers are randomly chosen
Mid -term results of an expandable “non invasive” prosthesis in children with distal femur bone sarcomas”
No full textMid -term results of an expandable “non invasive” prosthesis in children with distal femur bone sarcoma
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Particle transport and finite-size effects in Lorentz channels with finite horizons
No full textParticle transport is investigated in a finite-size realization of the classical Lorentz gas model. We consider point particles moving at constant speed in a 2D rectangular strip of finite length, filled with circular scatterers sitting at the vertices of a triangular lattice. Particles are injected at the left boundary with a prescribed rate, undergo specular reflections when colliding with the scatterers and the horizontal boundaries of the channel, and are finally absorbed at the left or the right boundary. Thanks to the equivalence with give Correlated Random Walks, in the finite horizon case, we show that the inverse probability that a particle exits through the right boundary depends linearly on the number of cells in the channel. A non-monotonic behavior of such probability as a function of the density of scatterers is also discussed and traced back analytically to the geometric features of a single trap. This way, we do not refer to asymptotic quantities and we accurately quantify the finite size effects. Our deterministic model provides a microscopic support for a variety of phenomenological laws, e.g. the Darcy's law for porous media and the Ohm's law in electronic transport
Uniqueness and stability with respect to parameters of solutions to a fluid-like driven system for active-passive pedestrian dynamics
Full text linkWe study a system of parabolic equations consisting of a double nonlinear parabolic equation of Forchheimer type coupled with a semilinear parabolic equation. The system describes a fluid-like driven system for active-passive pedestrian dynamics. The structure of the nonlinearity of the coupling allows us to prove the uniqueness of solutions. We provide also the stability estimate of solutions with respect to selected parameters
Trapping in bottlenecks : Interplay between microscopic dynamics and large scale effects
Full text linkWe investigate the appearance of trapping states in pedestrian flows through bottlenecks as a result of the interplay between the geometry of the system and the microscopic stochastic dynamics. We model the flow through a bottleneck via a Zero Range Process on a one-dimensional periodic lattice. Particle are removed from the lattice sites with rates proportional to the local occupation numbers. The bottleneck is modeled by a particular site of the lattice whose updating rate saturates to a constant value as soon as the local occupation number exceeds a fixed threshold. We show that for any finite value of the threshold the stationary particle current saturates to the limiting bottleneck rate when the total particle density in the system exceeds a critical value corresponding to the bottleneck rate itself.Fulltexten är den inskickade versionen och har inte genomgått peer-review.</p
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