Enhanced transport through desorption-mediated diffusion

We present a master equation approach to the study of the bulk-mediated surface diffusion mechanism in a three-dimensional confined domain. The proposed scheme allowed us to evaluate analytically a number of magnitudes that were used to characterize the efficiency of the bulk-mediated surface transport mechanism, for instance, the mean escape time from the domain, and the mean number of distinct visited sites on the confined domain boundary.Fil: Rojo, Félix. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Budde, Carlos Esteban. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Wio, Horacio Sergio. Universidad de Cantabria; España. Consejo Superior de Investigaciones Cientificas; España. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Budde, Carlos Ernesto. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin

Fluctuation theorems and large-deviation functions in systems not featuring a steady state

Motivated by the time behavior of the functional arising in the variational approach to the KPZ equation, we have adapted a path-integral scheme to deal with unstable systems. In a simple mesoscopic model and under two scenarios, we define a suitable mean value of (the exponential of) the entropy production between arbitrary initial and final states. This definition leads naturally to an integral fluctuation theorem (FT)-and on the way, to detailed and Crooks' FT. We also find the general form of a large-deviation function, as well as its particular form for a particle submitted to a constant force.Fil: Wio, Horacio Sergio. Universitat de les Illes Balears-CSIC; IFISC (Instituto de Física Interdisciplinar y Sistemas Complejos); Palma de Mallorca; España. Comision Nacional de Energia Atomica. Gerencia D/area Invest y Aplicaciones No Nucleares. Gerencia de Física (cab). Div.física Teórica; ArgentinaFil: Deza, Roberto Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Físicas de Mar del Plata; ArgentinaFil: Revelli, Jorge Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Nonequilibrium phase transitions induced by multiplicative noise: effects of self-correlation

A recently introduced lattice model, describing an extended system which exhibits a reentrant (symmetry-breaking, second-order) noise-induced nonequilibrium phase transition, is studied under the assumption that the multiplicative noise leading to the transition is colored. Within an effective Markovian approximation and a mean-field scheme it is found that when the self-correlation time of the noise is different from zero, the transition is also reentrant with respect to the spatial coupling D. In other words, at variance with what one expects for equilibrium phase transitions, a large enough value of D favors disorder. Moreover, except for a small region in the parameter subspace determined by the noise intensity and D, an increase in the self-correlation time usually preventsthe formation of an ordered state. These effects are supported by numerical simulations.Comment: 15 pages. 9 figures. To appear in Phys.Rev.

Coupled Brownian Motors: anomalous-to-normal hysteresis transition and noise-induced limit cycle

8 pages, 4 figures.-- Published in: Proc. SPIE's First International Symposium on Fluctuations and Noise, Conference: "Noise in Complex Systems and Stochastic Dynamics" (Santa Fe, NM, USA, Jun 2, 2003).We study a model consisting of N nonlinear oscillators with "global periodic" coupling and "local multiplicative" and additive noises. The model was shown to undergo a non-equilibrium phase transition towards a broken-symmetry phase exhibiting noise-induced "ratchet" behavior. Here we review some aspects leading to an "anomalous-to-normal" transition in the ratchet's hysteretic behavior and also show -as suggested by the absence of stable solutions when the load force is beyond a critical value- the existence of a limit cycle induced by both: multiplicative noise and "global periodic" coupling.HSW acknowledges the partial support from CONICET and ANPCyT, both Argentine agencies, and thanks the MECyD, Spain, for an award within the Programa de Sabáticos para Profesores Visitantes, and the Universitat de les Illes Balears for the kind hospitality extended to him.Peer reviewe

Nonequilibrium phase transitions induced by multiplicative noise: Effects of self-correlation

A recently introduced lattice model, describing an extended system which exhibits a reentrant (symmetry-breaking, second-order) noise-induced nonequilibrium phase transition, is studied under the assumption that the multiplicative noise leading to the transition is colored. Within an effective Markovian approximation and a mean-field scheme it is found that when the self-correlation time τ of the noise is different from zero, the transition is also reentrant with respect to the spatial coupling D. In other words, at variance with what one expects for equilibrium phase transitions, a large enough value of D favors disorder. Moreover, except for a small region in the parameter subspace determined by the noise intensity σ and D, an increase in τ usually prevents the formation of an ordered state. These effects are supported by numerical simulations.R. T. acknowledges financial support from DGICyT, project numbers PB94-1167 and PB97- 0141-C02-01. H. S. W, R. R. D. and S. E. M. acknowledge financial support from CONICET, project number PIP-4953/96, and from ANPCyT, project number .Peer Reviewe

Waves of seed propagation induced by delayed animal dispersion

We study a model of seed dispersal that considers the inclusion of an animal disperser moving diffusively, feeding on fruits and transporting the seeds, which are later deposited and capable of germination. The dynamics depends on several population parameters of growth, decay, harvesting, transport, digestion and germination. In particular, the deposition of transported seeds at places away from their collection sites produces a delay in the dynamics, whose effects are the focus of this work. Analytical and numerical solutions of different simplified scenarios show the existence of travelling waves. The effect of zoochory is apparent in the increase of the velocity of these waves. The results support the hypothesis of the relevance of animal mediated seed dispersion when trying to understand the origin of the high rates of vegetable invasion observed in real systems.Fil: Kazimierski, Laila Daniela. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kuperman, Marcelo Nestor. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Wio, Horacio Sergio. Universidad de Cantabria; España. Universidad de las Islas Baleares; España. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Abramson, Guillermo. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Nonequilibrium phase transitions induced by multiplicative noise: Effects of self-correlation,” Phys

A recently introduced lattice model, describing an extended system which exhibits a reentrant �symmetrybreaking, second-order � noise-induced nonequilibrium phase transition, is studied under the assumption that the multiplicative noise leading to the transition is colored. Within an effective Markovian approximation and a mean-field scheme it is found that when the self-correlation time � of the noise is different from zero, the transition is also reentrant with respect to the spatial coupling D. In other words, at variance with what one expects for equilibrium phase transitions, a large enough value of D favors disorder. Moreover, except for a small region in the parameter subspace determined by the noise intensity � and D, an increase in � usually prevents the formation of an ordered state. These effects are supported by numerical simulations. PACS number�s�: 05.40.�a, 47.20.Ky, 47.20.Hw I

Interplay between social debate and propaganda in an opinion formation model

We introduce a simple model of opinion dynamics in which a two-state agent modified Sznajd model evolves due to the simultaneous action of stochastic driving and a periodic signal. The stochastic effect mimics a social temperature, so the agents may adopt decisions in support for or against some opinion or position, according to a modified Sznajd rule with a varying probability. The external force represents a simplified picture by which society feels the influence of the external effects of propaganda. By means of Monte Carlo simulations we have shown the dynamical interplay between the social condition or mood and the external influence, finding a stochastic resonance-like phenomenon when we depict the noise-to-signal ratio as a function of the social temperature. In addition, we have also studied the effects of the system size and the external signal strength on the opinion formation dynamics.Fil: Gimenez, Maria Cecilia. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Revelli, Jorge Alberto. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: de La Lama, M. S.. Max-Planck-Institute for Dynamics and Self-Organization; AlemaniaFil: Lopez, J. M.. Universidad de Cantabria; EspañaFil: Wio, Horacio Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Cantabria; Españ