22 research outputs found
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
Stochastic Resonance in Ion Channels Characterized by Information Theory
We identify a unifying measure for stochastic resonance (SR) in voltage
dependent ion channels which comprises periodic (conventional), aperiodic and
nonstationary SR. Within a simplest setting, the gating dynamics is governed by
two-state conductance fluctuations, which switch at random time points between
two values. The corresponding continuous time point process is analyzed by
virtue of information theory. In pursuing this goal we evaluate for our
dynamics the tau-information, the mutual information and the rate of
information gain. As a main result we find an analytical formula for the rate
of information gain that solely involves the probability of the two channel
states and their noise averaged rates. For small voltage signals it simplifies
to a handy expression. Our findings are applied to study SR in a potassium
channel. We find that SR occurs only when the closed state is predominantly
dwelled. Upon increasing the probability for the open channel state the
application of an extra dose of noise monotonically deteriorates the rate of
information gain, i.e., no SR behavior occurs.Comment: 10 pages, 2 figures, to appear in Phys. Rev.
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
Evidence of stochastic resonance in the mating behavior of Nezara viridula (L.)
We investigate the role of the noise in the mating behavior between
individuals of Nezara viridula (L.), by analyzing the temporal and spectral
features of the non-pulsed type female calling song emitted by single
individuals. We have measured the threshold level for the signal detection, by
performing experiments with the calling signal at different intensities and
analyzing the insect response by directionality tests performed on a group of
male individuals. By using a sub-threshold signal and an acoustic Gaussian
noise source, we have investigated the insect response for different levels of
noise, finding behavioral activation for suitable noise intensities. In
particular, the percentage of insects which react to the sub-threshold signal,
shows a non-monotonic behavior, characterized by the presence of a maximum, for
increasing levels of the noise intensity. This constructive interplay between
external noise and calling signal is the signature of the non-dynamical
stochastic resonance phenomenon. Finally, we describe the behavioral activation
statistics by a soft threshold model which shows stochastic resonance. We find
that the maximum of the ensemble average of the input-output cross-correlation
occurs at a value of the noise intensity very close to that for which the
behavioral response has a maximum.Comment: 6 pages, 4 figures, to appear in EPJ B (2008
Ecological Complex Systems
Main aim of this topical issue is to report recent advances in noisy
nonequilibrium processes useful to describe the dynamics of ecological systems
and to address the mechanisms of spatio-temporal pattern formation in ecology
both from the experimental and theoretical points of view. This is in order to
understand the dynamical behaviour of ecological complex systems through the
interplay between nonlinearity, noise, random and periodic environmental
interactions. Discovering the microscopic rules and the local interactions
which lead to the emergence of specific global patterns or global dynamical
behaviour and the noises role in the nonlinear dynamics is an important, key
aspect to understand and then to model ecological complex systems.Comment: 13 pages, Editorial of a topical issue on Ecological Complex System
to appear in EPJ B, Vol. 65 (2008
Post-capitalist property
When writing about property and property rights in his imagined post-capitalist society of the future, Marx seemed to envisage âindividual propertyâ co-existing with âsocialized propertyâ in the means of production. As the social and political consequences of faltering growth and increasing inequality, debt and insecurity gradually manifest themselves, and with automation and artificial intelligence lurking in the wings, the future of capitalism, at least in its current form, looks increasingly uncertain. With this, the question of what property and property rights might look like in the future, in a potentially post-capitalist society, is becoming ever more pertinent. Is the choice simply between private property and markets, and public (state-owned) property and planning? Or can individual and social property in the (same) means of production co-exist, as Marx suggested? This paper explores ways in which they might, through an examination of the Chinese household responsibility system (HRS) and the âfuzzyâ and seemingly confusing regime of land ownership that it instituted. It examines the HRS against the backdrop of Marxâs ideas about property and subsequent (post-Marx) theorizing about the legal nature of property in which property has come widely to be conceptualized not as a single, unitary âownershipâ right to a thing (or, indeed, as the thing itself) but as a âbundle of rightsâ. The bundle-of-rights idea of property, it suggests, enables us to see not only that âindividualâ and âsocializedâ propertyâ in the (same) means of production might indeed co-exist, but that the range of institutional possibility is far greater than that between capitalism and socialism/communism as traditionally conceived