358 research outputs found
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
Chance Constrained Optimization for Targeted Internet Advertising
We introduce a chance constrained optimization model for the fulfillment of
guaranteed display Internet advertising campaigns. The proposed formulation for
the allocation of display inventory takes into account the uncertainty of the
supply of Internet viewers. We discuss and present theoretical and
computational features of the model via Monte Carlo sampling and convex
approximations. Theoretical upper and lower bounds are presented along with a
numerical substantiation
Highly synchronized noise-driven oscillatory behavior of a FitzHugh-Nagumo ring with phase-repulsive coupling
We investigate a ring of FitzHugh--Nagumo elements coupled in
\emph{phase-repulsive} fashion and submitted to a (subthreshold) common
oscillatory signal and independent Gaussian white noises. This system can be
regarded as a reduced version of the one studied in [Phys. Rev. E \textbf{64},
041912 (2001)], although externally forced and submitted to noise. The
noise-sustained synchronization of the system with the external signal is
characterized.Comment: 7 pages, 15 figures, uses aipproc.cls, aip-6s.clo and aipxfm.sty.
"Cooperative Behavior in Neural Systems: Ninth Granada Lectures'', edited by
J. Marro, P. L. Garrido, and J. J. Torre
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
Invited review: KPZ. Recent developments via a variational formulation
Recently, a variational approach has been introduced for the paradigmatic
Kardar--Parisi--Zhang (KPZ) equation. Here we review that approach, together
with the functional Taylor expansion that the KPZ nonequilibrium potential
(NEP) admits. Such expansion becomes naturally truncated at third order, giving
rise to a nonlinear stochastic partial differential equation to be regarded as
a gradient-flow counterpart to the KPZ equation. A dynamic renormalization
group analysis at one-loop order of this new mesoscopic model yields the KPZ
scaling relation alpha+z=2, as a consequence of the exact cancelation of the
different contributions to vertex renormalization. This result is quite
remarkable, considering the lower degree of symmetry of this equation, which is
in particular not Galilean invariant. In addition, this scheme is exploited to
inquire about the dynamical behavior of the KPZ equation through a
path-integral approach. Each of these aspects offers novel points of view and
sheds light on particular aspects of the dynamics of the KPZ equation.Comment: 16 pages, 2 figure
Supragaussian-fluctuaction energy harvesting by piezoelectric method, through monostable squarewell-like oscillators: an electronic analogy
Se presenta un análogo electrónico de un oscilador monoestable de tipo pozo cuadrado, propuesto para cosechar energía del ruido mediante transducción piezoeléctrica. Se supone un ruido altamente correlacionado y con estadística supra Gaussiana, que se controla mediante un parámetro q. Éste es sintetizado y enviado a través de un circuito electrónico en el que se utiliza un diodo Zener como análogo del potencial tipo pozo cuadrado, para observar cómo varía la tensión cuadrática media entregada a la carga a medida que el ruido se aleja de uno Gaussiano. Los resultados muestran que al crecer q por encima de 1 (correspondiente a estadística Gaussiana) la tensión cuadrática media se incrementa, de modo que el Zener actúa efectivamente como selector de grandes excursiones.An electronic analog is introduced of a square-well monostable oscillator, proposed for noise energy harvesting using piezoelectric transduction. A highly correlated noise is assumed, whose supra Gaussian statistics is controlled by a parameter q. This is synthesized and sent through an electronic circuit in which a Zener diode is used as an analogue of the square-well potential, to observe how the rms voltage delivered to the load varies as the noise departs from Gaussian. The results show that as q grows above 1 (corresponding to Gaussian statistics) the rms voltage increases, so that the Zener effectively acts as selector of large excursions.Fil: Peña Rosselló, Julián Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata; ArgentinaFil: Deza, J. I.. Universidad Politecnica de Catalunya; EspañaFil: Wio, H. S.. Consejo Superior de Investigaciones Cientificas; EspañaFil: Deza, R. R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata; Argentin
Bell inequalities stronger than the CHSH inequality for 3-level isotropic states
We show that some two-party Bell inequalities with two-valued observables are
stronger than the CHSH inequality for 3 \otimes 3 isotropic states in the sense
that they are violated by some isotropic states in the 3 \otimes 3 system that
do not violate the CHSH inequality. These Bell inequalities are obtained by
applying triangular elimination to the list of known facet inequalities of the
cut polytope on nine points. This gives a partial solution to an open problem
posed by Collins and Gisin. The results of numerical optimization suggest that
they are candidates for being stronger than the I_3322 Bell inequality for 3
\otimes 3 isotropic states. On the other hand, we found no Bell inequalities
stronger than the CHSH inequality for 2 \otimes 2 isotropic states. In
addition, we illustrate an inclusion relation among some Bell inequalities
derived by triangular elimination.Comment: 9 pages, 1 figure. v2: organization improved; less references to the
cut polytope to make the main results clear; references added; typos
corrected; typesetting style change
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