176 research outputs found
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
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