260 research outputs found
Collective dynamics of two-mode stochastic oscillators
We study a system of two-mode stochastic oscillators coupled through their
collective output. As a function of a relevant parameter four qualitatively
distinct regimes of collective behavior are observed. In an extended region of
the parameter space the periodicity of the collective output is enhanced by the
considered coupling. This system can be used as a new model to describe
synchronization-like phenomena in systems of units with two or more oscillation
modes. The model can also explain how periodic dynamics can be generated by
coupling largely stochastic units. Similar systems could be responsible for the
emergence of rhythmic behavior in complex biological or sociological systems.Comment: 4 pages, RevTex, 5 figure
Coherence Resonance and Noise-Induced Synchronization in Globally Coupled Hodgkin-Huxley Neurons
The coherence resonance (CR) of globally coupled Hodgkin-Huxley neurons is
studied. When the neurons are set in the subthreshold regime near the firing
threshold, the additive noise induces limit cycles. The coherence of the system
is optimized by the noise. A bell-shaped curve is found for the peak height of
power spectra of the spike train, being significantly different from a
monotonic behavior for the single neuron. The coupling of the network can
enhance CR in two different ways. In particular, when the coupling is strong
enough, the synchronization of the system is induced and optimized by the
noise. This synchronization leads to a high and wide plateau in the local
measure of coherence curve. The local-noise-induced limit cycle can evolve to a
refined spatiotemporal order through the dynamical optimization among the
autonomous oscillation of an individual neuron, the coupling of the network,
and the local noise.Comment: five pages, five figure
Memory functions and Correlations in Additive Binary Markov Chains
A theory of additive Markov chains with long-range memory, proposed earlier
in Phys. Rev. E 68, 06117 (2003), is developed and used to describe statistical
properties of long-range correlated systems. The convenient characteristics of
such systems, a memory function, and its relation to the correlation properties
of the systems are examined. Various methods for finding the memory function
via the correlation function are proposed. The inverse problem (calculation of
the correlation function by means of the prescribed memory function) is also
solved. This is demonstrated for the analytically solvable model of the system
with a step-wise memory function.Comment: 11 pages, 5 figure
An Analytical Study of Coupled Two-State Stochastic Resonators
The two-state model of stochastic resonance is extended to a chain of coupled
two-state elements governed by the dynamics of Glauber's stochastic Ising
model. Appropriate assumptions on the model parameters turn the chain into a
prototype system of coupled stochastic resonators. In a weak-signal limit
analytical expressions are derived for the spectral power amplification and the
signal-to-noise ratio of a two-state element embedded into the chain. The
effect of the coupling between the elements on both quantities is analysed and
array-enhanced stochastic resonance is established for pure as well as noisy
periodic signals. The coupling-induced improvement of the SNR compared to an
uncoupled element is shown to be limited by a factor four which is only reached
for vanishing input noise.Comment: 29 pages, 5 figure
System size resonance in coupled noisy systems and in the Ising model
We consider an ensemble of coupled nonlinear noisy oscillators demonstrating
in the thermodynamic limit an Ising-type transition. In the ordered phase and
for finite ensembles stochastic flips of the mean field are observed with the
rate depending on the ensemble size. When a small periodic force acts on the
ensemble, the linear response of the system has a maximum at a certain system
size, similar to the stochastic resonance phenomenon. We demonstrate this
effect of system size resonance for different types of noisy oscillators and
for different ensembles -- lattices with nearest neighbors coupling and
globally coupled populations. The Ising model is also shown to demonstrate the
system size resonance.Comment: 4 page
Nonstationary Stochastic Resonance in a Single Neuron-Like System
Stochastic resonance holds much promise for the detection of weak signals in
the presence of relatively loud noise. Following the discovery of nondynamical
and of aperiodic stochastic resonance, it was recently shown that the
phenomenon can manifest itself even in the presence of nonstationary signals.
This was found in a composite system of differentiated trigger mechanisms
mounted in parallel, which suggests that it could be realized in some
elementary neural networks or nonlinear electronic circuits. Here, we find that
even an individual trigger system may be able to detect weak nonstationary
signals using stochastic resonance. The very simple modification to the trigger
mechanism that makes this possible is reminiscent of some aspects of actual
neuron physics. Stochastic resonance may thus become relevant to more types of
biological or electronic systems injected with an ever broader class of
realistic signals.Comment: Plain Latex, 7 figure
Synchronous bursts on scale-free neuronal networks with attractive and repulsive coupling
This paper investigates the dependence of synchronization transitions of
bursting oscillations on the information transmission delay over scale-free
neuronal networks with attractive and repulsive coupling. It is shown that for
both types of coupling, the delay always plays a subtle role in either
promoting or impairing synchronization. In particular, depending on the
inherent oscillation period of individual neurons, regions of irregular and
regular propagating excitatory fronts appear intermittently as the delay
increases. These delay-induced synchronization transitions are manifested as
well-expressed minima in the measure for spatiotemporal synchrony. For
attractive coupling, the minima appear at every integer multiple of the average
oscillation period, while for the repulsive coupling, they appear at every odd
multiple of the half of the average oscillation period. The obtained results
are robust to the variations of the dynamics of individual neurons, the system
size, and the neuronal firing type. Hence, they can be used to characterize
attractively or repulsively coupled scale-free neuronal networks with delays.Comment: 15 pages, 9 figures; accepted for publication in PLoS ONE [related
work available at http://arxiv.org/abs/0907.4961 and
http://www.matjazperc.com/
Imaginarios en disputa o sobre la territorialización de un conflicto urbano. El caso de “La Canchita de los Bomberos” (Mar del Plata, Argentina)
Apenas transcurridos tres meses de la creaciĂłn del Programa CrĂ©dito Argentino del Bicentenario para la Vivienda Ăšnica Familiar, el Municipio de General PueyrredĂłn anuncia las tierras disponibles para comprometer en su implementaciĂłn; entre ellas, el predio conocido como Canchita de los Bomberos de la ciudad de Mar del Plata. Frente a ello, se conforma un grupo de vecinos autoconvocados en defensa de su utilizaciĂłn como espacio pĂşblico-verde, llevando a cabo diversas estrategias cuyo objetivo es evitar la construcciĂłn de viviendas en esa zona. Paralelamente, otras personas manifiestan su parecer en relaciĂłn a la ejecuciĂłn del programa y desarrollan prácticas que cuestionan la legitimidad de las demandas sostenidas por aquellos vecinos. El propĂłsito del artĂculo es analizar las formas de apropiaciĂłn simbĂłlica que se refuerzan y/o modifican en funciĂłn de la disputa; lo que MelĂ© (2003) llama el proceso de territorializaciĂłn del conflicto. Se argumenta que, aunque se produce un choque de imaginarios (Hiernaux; 2008a), emerge un imaginario dominante que logra imponerse y legitimar el uso y disfrute del espacio a su favor
Nonstationary Stochastic Resonance
It is by now established that, remarkably, the addition of noise to a
nonlinear system may sometimes facilitate, rather than hamper the detection of
weak signals. This phenomenon, usually referred to as stochastic resonance, was
originally associated with strictly periodic signals, but it was eventually
shown to occur for stationary aperiodic signals as well. However, in several
situations of practical interest, the signal can be markedly nonstationary. We
demonstrate that the phenomenon of stochastic resonance extends to
nonstationary signals as well, and thus could be relevant to a wider class of
biological and electronic applications. Building on both nondynamic and
aperiodic stochastic resonance, our scheme is based on a multilevel trigger
mechanism, which could be realized as a parallel network of differentiated
threshold sensors. We find that optimal detection is reached for a number of
thresholds of order ten, and that little is gained by going much beyond that
number. We raise the question of whether this is related to the fact that
evolution has favored some fixed numbers of precisely this order of magnitude
in certain aspects of sensory perception.Comment: Plain Latex, 6 figure
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