839 research outputs found
Multifractal characterization of stochastic resonance
We use a multifractal formalism to study the effect of stochastic resonance
in a noisy bistable system driven by various input signals. To characterize the
response of a stochastic bistable system we introduce a new measure based on
the calculation of a singularity spectrum for a return time sequence. We use
wavelet transform modulus maxima method for the singularity spectrum
computations. It is shown that the degree of multifractality defined as a width
of singularity spectrum can be successfully used as a measure of complexity
both in the case of periodic and aperiodic (stochastic or chaotic) input
signals. We show that in the case of periodic driving force singularity
spectrum can change its structure qualitatively becoming monofractal in the
regime of stochastic synchronization. This fact allows us to consider the
degree of multifractality as a new measure of stochastic synchronization also.
Moreover, our calculations have shown that the effect of stochastic resonance
can be catched by this measure even from a very short return time sequence. We
use also the proposed approach to characterize the noise-enhanced dynamics of a
coupled stochastic neurons model.Comment: 10 pages, 21 EPS-figures, RevTe
Relativistic Hydrodynamics with General Anomalous Charges
We consider the hydrodynamic regime of gauge theories with general triangle
anomalies, where the participating currents may be global or gauged, abelian or
non-abelian. We generalize the argument of arXiv:0906.5044, and construct at
the viscous order the stress-energy tensor, the charge currents and the entropy
current.Comment: 13 pages, Revte
Noise Induced Complexity: From Subthreshold Oscillations to Spiking in Coupled Excitable Systems
We study stochastic dynamics of an ensemble of N globally coupled excitable
elements. Each element is modeled by a FitzHugh-Nagumo oscillator and is
disturbed by independent Gaussian noise. In simulations of the Langevin
dynamics we characterize the collective behavior of the ensemble in terms of
its mean field and show that with the increase of noise the mean field displays
a transition from a steady equilibrium to global oscillations and then, for
sufficiently large noise, back to another equilibrium. Diverse regimes of
collective dynamics ranging from periodic subthreshold oscillations to
large-amplitude oscillations and chaos are observed in the course of this
transition. In order to understand details and mechanisms of noise-induced
dynamics we consider a thermodynamic limit of the ensemble, and
derive the cumulant expansion describing temporal evolution of the mean field
fluctuations. In the Gaussian approximation this allows us to perform the
bifurcation analysis; its results are in good agreement with dynamical
scenarios observed in the stochastic simulations of large ensembles
Anomalies in Superfluids and a Chiral Electric Effect
We analyze the chiral transport terms in relativistic superfluid
hydrodynamics. In addition to the spontaneously broken symmetry current, we
consider an arbitrary number of unbroken symmetries and extend the results of
arXiv:1105.3733. We suggest an interpretation of some of the new transport
coefficients in terms of chiral and gravitational anomalies. In particular, we
show that with unbroken gauged charges in the system, one can observe a chiral
electric conductivity - a current in a perpendicular direction to the applied
electric field. We present a motivated proposal for the value of the associated
transport coefficient, linking it to the triangle anomaly. Along the way we
present new arguments regarding the interpretation of the anomalous transport
coefficients in normal fluids. We propose a natural generalization of the
chiral transport terms to the case of an arbitrary number of spontaneously
broken symmetry currents.Comment: 30 pages; v2: Onsager-relations argument corrected, references added;
v3: fixed missing line in eq. (38
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
The problem of shot selection in basketball
In basketball, every time the offense produces a shot opportunity the player
with the ball must decide whether the shot is worth taking. In this paper, I
explore the question of when a team should shoot and when they should pass up
the shot by considering a simple theoretical model of the shot selection
process, in which the quality of shot opportunities generated by the offense is
assumed to fall randomly within a uniform distribution. I derive an answer to
the question "how likely must the shot be to go in before the player should
take it?", and show that this "lower cutoff" for shot quality depends
crucially on the number of shot opportunities remaining (say, before the
shot clock expires), with larger demanding that only higher-quality shots
should be taken. The function is also derived in the presence of a
finite turnover rate and used to predict the shooting rate of an
optimal-shooting team as a function of time. This prediction is compared to
observed shooting rates from the National Basketball Association (NBA), and the
comparison suggests that NBA players tend to wait too long before shooting and
undervalue the probability of committing a turnover.Comment: 7 pages, 2 figures; comparison to NBA data adde
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
Wave nucleation rate in excitable systems in the low noise limit
Motivated by recent experiments on intracellular calcium dynamics, we study
the general issue of fluctuation-induced nucleation of waves in excitable
media. We utilize a stochastic Fitzhugh-Nagumo model for this study, a
spatially-extended non-potential pair of equations driven by thermal (i.e.
white) noise. The nucleation rate is determined by finding the most probable
escape path via minimization of an action related to the deviation of the
fields from their deterministic trajectories. Our results pave the way both for
studies of more realistic models of calcium dynamics as well as of nucleation
phenomena in other non-equilibrium pattern-forming processes
Interannual Variations in Aerosol Sources and Their Impact on Orographic Precipitation Over California's Central Sierra Nevada
Aerosols that serve as cloud condensation nuclei (CCN) and ice nuclei (IN) have the potential to profoundly influence precipitation processes. Furthermore, changes in orographic precipitation have broad implications for reservoir storage and flood risks. As part of the CalWater I field campaign (2009-2011), the impacts of aerosol sources on precipitation were investigated in the California Sierra Nevada. In 2009, the precipitation collected on the ground was influenced by both local biomass burning (up to 79% of the insoluble residues found in precipitation) and long-range transported dust and biological particles (up to 80% combined), while in 2010, by mostly local sources of biomass burning and pollution (30-79% combined), and in 2011 by mostly long-range transport from distant sources (up to 100% dust and biological). Although vast differences in the source of residues was observed from year-to-year, dust and biological residues were omnipresent (on average, 55% of the total residues combined) and were associated with storms consisting of deep convective cloud systems and larger quantities of precipitation initiated in the ice phase. Further, biological residues were dominant during storms with relatively warm cloud temperatures (up to -15 C), suggesting these particles were more efficient IN compared to mineral dust. On the other hand, lower percentages of residues from local biomass burning and pollution were observed (on average 31% and 9%, respectively), yet these residues potentially served as CCN at the base of shallow cloud systems when precipitation quantities were low. The direct connection of the source of aerosols within clouds and precipitation type and quantity can be used in models to better assess how local emissions versus long-range transported dust and biological aerosols play a role in impacting regional weather and climate, ultimately with the goal of more accurate predictive weather forecast models and water resource management
Autonomous stochastic resonance in fully frustrated Josephson-junction ladders
We investigate autonomous stochastic resonance in fully frustrated
Josephson-junction ladders, which are driven by uniform constant currents. At
zero temperature large currents induce oscillations between the two ground
states, while for small currents the lattice potential forces the system to
remain in one of the two states. At finite temperatures, on the other hand,
oscillations between the two states develop even below the critical current;
the signal-to-noise ratio is found to display array-enhanced stochastic
resonance. It is suggested that such behavior may be observed experimentally
through the measurement of the staggered voltage.Comment: 6 pages, 11 figures, to be published in Phys. Rev.
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