95 research outputs found
System Size Stochastic Resonance from the Viewpoint of the Nonequilibrium Potential
We analyze the phenomenon of system size stochastic resonance in a simple
spatially extended system by exploiting the knowledge of the nonequilibrium
potential. We show that through the analysis of that potential, and
particularly its "symmetry", we can obtain a clear physical interpretation of
this phenomenon in a wide class of extended systems, and also analyze, for the
same simple model, the effect of a general class of boundary conditions
(albedo) on this kind of phenomena.Comment: 10 pages, 3 figures, submitted to Phys. Rev. Let
Variational Formulation for the KPZ and Related Kinetic Equations
We present a variational formulation for the Kardar-Parisi-Zhang (KPZ)
equation that leads to a thermodynamic-like potential for the KPZ as well as
for other related kinetic equations. For the KPZ case, with the knowledge of
such a potential we prove some global shift invariance properties previously
conjectured by other authors. We also show a few results about the form of the
stationary probability distribution function for arbitrary dimensions. The
procedure used for KPZ was extended in order to derive more general forms of
such a functional leading to other nonlinear kinetic equations, as well as
cases with density dependent surface tension.Comment: RevTex, 8pgs, double colum
Aspects of stochastic resonance in reaction-diffusion systems: The nonequilibrium-potential approach
We analyze several aspects of the phenomenon of stochastic resonance in
reaction-diffusion systems, exploiting the nonequilibrium potential's
framework. The generalization of this formalism (sketched in the appendix) to
extended systems is first carried out in the context of a simplified scalar
model, for which stationary patterns can be found analytically. We first show
how system-size stochastic resonance arises naturally in this framework, and
then how the phenomenon of array-enhanced stochastic resonance can be further
enhanced by letting the diffusion coefficient depend on the field. A yet less
trivial generalization is exemplified by a stylized version of the
FitzHugh-Nagumo system, a paradigm of the activator-inhibitor class. After
discussing for this system the second aspect enumerated above, we derive from
it -through an adiabatic-like elimination of the inhibitor field- an effective
scalar model that includes a nonlocal contribution. Studying the role played by
the range of the nonlocal kernel and its effect on stochastic resonance, we
find an optimal range that maximizes the system's response.Comment: 16 pages, 15 figures, uses svjour.cls and svepj-spec.clo. Minireview
to appear in The European Physical Journal Special Topics (issue in memory of
Carlos P\'erez-Garc\'{\i}a, edited by H. Mancini
Stochastic resonance in bistable systems: The effect of simultaneous additive and multiplicative correlated noises
We analyze the effect of the simultaneous presence of correlated additive and
multiplicative noises on the stochastic resonance response of a modulated
bistable system. We find that when the correlation parameter is also modulated,
the system's response, measured through the output signal-to-noise ratio,
becomes largely independent of the additive noise intensity.Comment: RevTex, 10 pgs, 3 figure
Noise effects in extended chaotic system: study on the Lorenz'96 model
We investigate the effects of a time-correlated noise on an extended chaotic
system. The chosen model is the Lorenz'96, a kind of toy model used for climate
studies. The system is subjected to both temporal and spatiotemporal
perturbations. Through the analysis of the system's time evolution and its time
correlations, we have obtained numerical evidence for two stochastic
resonance-like behaviors. Such behavior is seen when a generalized
signal-to-noise ratio function are depicted as a function of the external noise
intensity or as function of the system size. The underlying mechanism seems to
be associated to a noise-induced chaos reduction. The possible relevance of
those findings for an optimal climate prediction are discussed, using an
analysis of the noise effects on the evolution of finite perturbations and
errors.Comment: To appear in Statistical Mechanics Research Focus, Special volume
(Nova Science Pub., NY, in press) (LaTex, 16 pgs, 14 figures
Noise-induced phase transitions: Effects of the noises' statistics and spectrum
The local, uncorrelated multiplicative noises driving a second-order, purely
noise-induced, ordering phase transition (NIPT) were assumed to be Gaussian and
white in the model of [Phys. Rev. Lett. \textbf{73}, 3395 (1994)]. The
potential scientific and technological interest of this phenomenon calls for a
study of the effects of the noises' statistics and spectrum. This task is
facilitated if these noises are dynamically generated by means of stochastic
differential equations (SDE) driven by white noises. One such case is that of
Ornstein--Uhlenbeck noises which are stationary, with Gaussian pdf and a
variance reduced by the self-correlation time (\tau), and whose effect on the
NIPT phase diagram has been studied some time ago. Another such case is when
the stationary pdf is a (colored) Tsallis' (q)--\emph{Gaussian} which, being a
\emph{fat-tail} distribution for (q>1) and a \emph{compact-support} one for
(q<1), allows for a controlled exploration of the effects of the departure from
Gaussian statistics. As done before with stochastic resonance and other
phenomena, we now exploit this tool to study--within a simple mean-field
approximation and with an emphasis on the \emph{order parameter} and the
``\emph{susceptibility}''--the combined effect on NIPT of the noises'
statistics and spectrum. Even for relatively small (\tau), it is shown that
whereas fat-tail noise distributions ((q>1)) counteract the effect of
self-correlation, compact-support ones ((q<1)) enhance it. Also, an interesting
effect on the susceptibility is seen in the last case.Comment: 6 pages, 10 figures, uses aipproc.cls, aip-8s.clo and aipxfm.sty. To
appear in AIP Conference Proceedings. Invited talk at MEDYFINOL'06 (XV
Conference on Nonequilibrium Statistical Mechanics and Nonlinear Physics
Diffusion in Fluctuating Media: The Resonant Activation Problem
We present a one-dimensional model for diffusion in a fluctuating lattice;
that is a lattice which can be in two or more states. Transitions between the
lattice states are induced by a combination of two processes: one periodic
deterministic and the other stochastic. We study the dynamics of a system of
particles moving in that medium, and characterize the problem from different
points of view: mean first passage time (MFPT), probability of return to a
given site (), and the total length displacement or number of visited
lattice sites (). We observe a double {\it resonant activation}-like
phenomenon when we plot the MFPT and as functions of the intensity of
the transition rate stochastic component.Comment: RevTex, 15 pgs, 8 figures, submitted to Eur.Phys.J.
Spontaneous emergence of contrarian-like behaviour in an opinion spreading model
We introduce stochastic driving in the Sznajd model of opinion spreading.
This stochastic effect is meant to mimic a social temperature, so that agents
can take random decisions with a varying probability. We show that a stochastic
driving has a tremendous impact on the system dynamics as a whole by inducing
an order-disorder nonequilibrium phase transition. Interestingly, under certain
conditions, this stochastic dynamics can spontaneously lead to agents in the
system who are analogous to Galam's contarians.Comment: 4 eps figs, EuroPhys Lett styl
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