Spatial Patterns Induced Purely by Dichotomous Disorder

We study conditions under which spatially extended systems with coupling a la Swift-Hohenberg exhibit spatial patterns induced purely by the presence of quenched dichotomous disorder. Complementing the theoretical results based on a generalized mean-field approximation, we also present numerical simulations of particular dynamical systems that exhibit the proposed phenomenology

Effects of internal fluctuations on the spreading of Hantavirus

We study the spread of Hantavirus over a host population of deer mice using a population dynamics model. We show that taking into account the internal fluctuations in the mouse population due to its discrete character strongly alters the behaviour of the system. In addition to the familiar transition present in the deterministic model, the inclusion of internal fluctuations leads to the emergence of an additional deterministically hidden transition. We determine parameter values that lead to maximal propagation of the disease, and discuss some implications for disease prevention policies

Comprehensive study of phase transitions in relaxational systems with field-dependent coefficients

We present a comprehensive study of phase transitions in single-field systems that relax to a non-equilibrium global steady state. The mechanism we focus on is not the so-called Stratonovich drift combined with collective effects, but is instead similar to the one associated with noise-induced transitions a la Horsthemke-Lefever in zero-dimensional systems. As a consequence, the noise interpretation (e.g., Ito vs Stratonvich) merely shifts the phase boundaries. With the help of a mean-field approximation, we present a broad qualitative picture of the various phase diagrams that can be found in these systems. To complement the theoretical analysis we present numerical simulations that confirm the findings of the mean-field theory

Análisis comparativo entre un tutor circular y uno monolateral en elongaciones óseas

El presente trabajo compara la funcionalidad de dos tutores externos utilizados para elongación: el del Dr. Ilizarov y el tutor HG, desarrollado en nuestra institución. De 131 pacientes tratados con elongación ósea en 147 huesos largos se seleccionaron al azar 25 huesos por cada aparato anteriormente mencionado. Para objetivar los resultados se registraron estadísticamente variables independientes y dependientes en sus características subjetivas y objetivas, tales como: edad, sexo, tipo de hueso elongado, tolerancia psíquica, sensación de confort, facilidad de higiene y control, las infecciones, las rigideces articulares por retracción músculo tendinosa, y la deformación ósea residual. El objetivo fue comparar y establecer si el cambio en la elección del sistema fue ventajoso para nuestros pacientes. En el intento comparativo se enfrentaron dos variables, que a nuestro criterio eran las más importantes para establecer diferencias: la calidad del callo del hueso sometido a elongación y la presencia de complicaciones tanto transitorias como definitivas.In this work we compare the results obtained with two different external fixation devices in patients undergoing bone lengthening. The devices studied were the Ilizarov type and the HG, an apparatons developed in our institution. Out of 131 patientes treated by bone lengthening in 147 long bones, 25 bones lengthened with each device were selected at random. Different subjective and objective variables were assessed: age, sex, type of bone, psichological tolerance, patients, confort, nursing, infections, joint stiffness due to musculotendinous retractions, and residual bone deformity. The aim of the study was to analyze if the monolateral frame entailed advantages for our patients. Two main factors were more deeply analysed, namely the quality of the bone callus subjected to lengthening and the presence of both transitory and definitive complications

Stationary and Oscillatory Spatial Patterns Induced by Global Periodic Switching

We propose a new mechanism for pattern formation based on the global alternation of two dynamics neither of which exhibits patterns. When driven by either one of the separate dynamics, the system goes to a spatially homogeneous state associated with that dynamics. However, when the two dynamics are globally alternated sufficiently rapidly, the system exhibits stationary spatial patterns. Somewhat slower switching leads to oscillatory patterns. We support our findings by numerical simulations and discuss the results in terms of the symmetries of the system and the ratio of two relevant characteristic times, the switching period and the relaxation time to a homogeneous state in each separate dynamics.Comment: REVTEX preprint: 12 pages including 1 (B&W) + 3 (COLOR) figures (to appear in Physical Review Letters

Driven lattice glass as a ratchet and pawl machine

Boundary-induced transport in particle systems with anomalous diffusion exhibits rectification, negative resistance, and hysteresis phenomena depending on the way the drive acts on the boundary. The solvable case of a 1D system characterized by a power-law diffusion coefficient and coupled to two particles reservoirs at different chemical potential is examined. In particular, it is shown that a microscopic realisation of such a diffusion model is provided by a 3D driven lattice-gas with kinetic constraints, in which energy barriers are absent and the local microscopic reversibility holds.Comment: 12 pages, 4 figures, minor change

Nonequilibrium coupled Brownian phase oscillators

A model of globally coupled phase oscillators under equilibrium (driven by Gaussian white noise) and nonequilibrium (driven by symmetric dichotomic fluctuations) is studied. For the equilibrium system, the mean-field state equation takes a simple form and the stability of its solution is examined in the full space of order parameters. For the nonequilbrium system, various asymptotic regimes are obtained in a closed analytical form. In a general case, the corresponding master equations are solved numerically. Moreover, the Monte-Carlo simulations of the coupled set of Langevin equations of motion is performed. The phase diagram of the nonequilibrium system is presented. For the long time limit, we have found four regimes. Three of them can be obtained from the mean-field theory. One of them, the oscillating regime, cannot be predicted by the mean-field method and has been detected in the Monte-Carlo numerical experiments.Comment: 9 pages 8 figure

Noise-Driven Mechanism for Pattern Formation

We extend the mechanism for noise-induced phase transitions proposed by Ibanes et al. [Phys. Rev. Lett. 87, 020601-1 (2001)] to pattern formation phenomena. In contrast with known mechanisms for pure noise-induced pattern formation, this mechanism is not driven by a short-time instability amplified by collective effects. The phenomenon is analyzed by means of a modulated mean field approximation and numerical simulations

Can two chaotic systems give rise to order?

The recently discovered Parrondo's paradox claims that two losing games can result, under random or periodic alternation of their dynamics, in a winning game: "losing+losing=winning". In this paper we follow Parrondo's philosophy of combining different dynamics and we apply it to the case of one-dimensional quadratic maps. We prove that the periodic mixing of two chaotic dynamics originates an ordered dynamics in certain cases. This provides an explicit example (theoretically and numerically tested) of a different Parrondian paradoxical phenomenon: "chaos+chaos=order"Comment: 22 pages, 9 figures. Please address all correspondence to D. Peralta-Salas. To appear in Physica