Search results for " Random processes"

showing 10 items of 37 documents

Noise-induced enhancement of stability in a metastable system with damping

2010

5 páginas, 5 figuras.-- PACS number(s): 05.40.-a, 02.50.-r

PhysicsFluctuation phenomena random processes noise and Brownian motionCondensed matter physicsProbability theory stochastic processes and statisticFunction (mathematics)Stability (probability)Settore FIS/03 - Fisica Della MateriaProbability theory stochastic processes and statistics; Fluctuation phenomena random processes noise and Brownian motionColors of noiseMetastabilityQuantum mechanicsParticleFirst-hitting-time modelNoise (radio)Brownian motion
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TRANSIENT DYNAMICS AND ASYMPTOTIC POPULATIONS IN A DRIVEN METASTABLE QUANTUM SYSTEM

2013

The transient dynamics of a periodically driven metastable quantum system, interacting with a heat bath, is investigated. The time evolution of the populations, within the framework of the Feynman–Vernon influ- ence functional and in the discrete variable representation, is analyzed by varying the parameters of the external driving. The results display strong non-monotonic behaviour of the populations with respect to the driving frequency.

PhysicsFluctuation phenomena random processes noise and Brownian motionDynamics (mechanics)quantum statistical methodGeneral Physics and AstronomyRELAXATIONDecoherenceSettore FIS/03 - Fisica Della MateriaNOISEQuantum systems with finite Hilbert spaceClassical mechanicsRELAXATION; NOISEMetastabilityQuantum systemTransient (oscillation)open system
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Noise effects in two different biological systems

2009

We investigate the role of the colored noise in two biological systems: (i) adults of Nezara viridula (L.) (Heteroptera: Pentatomidae), and (ii) polymer translocation. In the first system we analyze, by directionality tests, the response of N. viridula individuals to subthreshold signals plus noise in their mating behaviour. The percentage of insects that react to the subthreshold signal shows a nonmonotonic behaviour, characterized by the presence of a maximum, as a function of the noise intensity. This is the signature of the non-dynamical stochastic resonance phenomenon. By using a “soft” threshold model we find that the maximum of the input-output cross correlation occurs in the same ra…

PhysicsFluctuation phenomena random processes noise and Brownian motionQuantitative Biology::BiomoleculesCondensed matter physicsBistabilityStochastic resonanceStochastic processMolecular dynamics Brownian dynamicThermal fluctuationsMolecular interactionWhite noiseNoise in biological systemCondensed Matter PhysicsMolecular physicsSettore FIS/07 - Fisica Applicata(Beni Culturali Ambientali Biol.e Medicin)Electronic Optical and Magnetic MaterialsColors of noiseBrownian dynamicsPolymermembrane-protein interactionsNoise (radio)Biophysical mechanisms of interaction
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Dynamics of a FitzHugh-Nagumo system subjected to autocorrelated noise

2008

We analyze the dynamics of the FitzHugh-Nagumo (FHN) model in the presence of colored noise and a periodic signal. Two cases are considered: (i) the dynamics of the membrane potential is affected by the noise, (ii) the slow dynamics of the recovery variable is subject to noise. We investigate the role of the colored noise on the neuron dynamics by the mean response time (MRT) of the neuron. We find meaningful modifications of the resonant activation (RA) and noise enhanced stability (NES) phenomena due to the correlation time of the noise. For strongly correlated noise we observe suppression of NES effect and persistence of RA phenomenon, with an efficiency enhancement of the neuronal respo…

PhysicsFluctuation phenomena random processes noise and Brownian motionSettore FIS/02 - Fisica Teorica Modelli E Metodi MatematiciAutocorrelationDynamics (mechanics)Mean and predicted responseModels of single neurons and networks; Noise in the nervous system; Fluctuation phenomena random processes noise and Brownian motion; Nonlinear dynamics and chaosFOS: Physical sciencesNoise in the nervous systemModels of single neurons and networkCondensed Matter PhysicsFitzhugh nagumoNonlinear dynamics and chaosStability (probability)Electronic Optical and Magnetic MaterialsPeriodic functionNoiseColors of noiseBiological Physics (physics.bio-ph)Statistical physicsPhysics - Biological Physics
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Moment Equations for a Spatially Extended System of Two Competing Species

2005

The dynamics of a spatially extended system of two competing species in the presence of two noise sources is studied. A correlated dichotomous noise acts on the interaction parameter and a multiplicative white noise affects directly the dynamics of the two species. To describe the spatial distribution of the species we use a model based on Lotka-Volterra (LV) equations. By writing them in a mean field form, the corresponding moment equations for the species concentrations are obtained in Gaussian approximation. In this formalism the system dynamics is analyzed for different values of the multiplicative noise intensity. Finally by comparing these results with those obtained by direct simulat…

PhysicsFluctuation phenomena random processes noise and Brownian motionSettore FIS/02 - Fisica Teorica Modelli E Metodi MatematiciStatistical Mechanics (cond-mat.stat-mech)Multiplicative white noiseFOS: Physical sciencesFluctuation phenomena random processes noise and Brownian motion; Nonlinear dynamics and nonlinear dynamical systems; Population dynamics and ecological pattern formationCondensed Matter PhysicsSpatial distributionMultiplicative noiseElectronic Optical and Magnetic MaterialsSystem dynamicsMean field theorySpatial ecologyQuantitative Biology::Populations and EvolutionStatistical physicsNonlinear dynamics and nonlinear dynamical systemCondensed Matter - Statistical MechanicsMoment equationsCoupled map latticePopulation dynamics and ecological pattern formation
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STOCHASTIC DYNAMICS OF TWO PICOPHYTOPLANKTON POPULATIONS IN A REAL MARINE ECOSYSTEM

2013

A stochastic reaction-diffusion-taxis model is analyzed to get the stationary distribution along water column of two species of picophytoplankton, that is picoeukaryotes and Prochlorococcus. The model is valid for weakly mixed waters, typical of the Mediterranean Sea. External random fluctuations are considered by adding a multiplicative Gaussian noise to the dynamical equation of the nutrient concentration. The statistical tests show that shape and magnitude of the theoretical concentration profile exhibit a good agreement with the experimental findings. Finally, we study the effects of seasonal variations on picophytoplankton groups, including an oscillating term in the auxiliary equation…

PhysicsGeneral Physics and AstronomySpatial ecology; Marine ecosystems; Phytoplankton dynamics; Deep chlorophyll maximum; Random processes; Stochastic differential equationsRandom processeSettore FIS/07 - Fisica Applicata(Beni Culturali Ambientali Biol.e Medicin)OceanographyStochastic dynamicsMarine ecosystemStochastic differential equationsSpatial ecologyDeep chlorophyll maximumMarine ecosystemPhytoplankton dynamic
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Suppression of timing errors in short overdamped Josephson junctions

2004

The influence of fluctuations and periodical driving on temporal characteristics of short overdamped Josephson junction is analyzed. We obtain the standard deviation of the switching time in the presence of a dichotomous driving force for arbitrary noise intensity and in the frequency range of practical interest. For sinusoidal driving the resonant activation effect has been observed. The mean switching time and its standard deviation have a minimum as a function of driving frequency. As a consequence the optimization of the system for fast operation will simultaneously lead to minimization of timing errors.

PhysicsJosephson effectSuperconductivityFluctuation phenomena random processes noise and Brownian motionStatistical Mechanics (cond-mat.stat-mech)Numerical analysisCondensed Matter - SuperconductivityGeneral Physics and AstronomyFOS: Physical sciencesStatistical mechanicsFunction (mathematics)Standard deviationSwitching timeSuperconductivity (cond-mat.supr-con)Range (statistics)Statistical physicsStochastic analysis methods Fokker-Planck equation Langevin equationCondensed Matter - Statistical MechanicsSuperconducting device
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Active Brownian Motion Models and Applications to Ratchets

2008

We give an overview over recent studies on the model of Active Brownian Motion (ABM) coupled to reservoirs providing free energy which may be converted into kinetic energy of motion. First, we present an introduction to a general concept of active Brownian particles which are capable to take up energy from the source and transform part of it in order to perform various activities. In the second part of our presentation we consider applications of ABM to ratchet systems with different forms of differentiable potentials. Both analytical and numerical evaluations are discussed for three cases of sinusoidal, staircase-like and Mateos ratchet potentials, also with the additional loads modeled by…

PhysicsStatistical Mechanics (cond-mat.stat-mech)RatchetPerturbation (astronomy)FOS: Physical sciencesFluctuation phenomena random processes noise Brownian motion Nonlinear dynamics and chaosWhite noiseCondensed Matter - Soft Condensed MatterCondensed Matter PhysicsKinetic energyElectronic Optical and Magnetic MaterialsClassical mechanicsPhysics - Data Analysis Statistics and ProbabilityMolecular motorDirectionalitySoft Condensed Matter (cond-mat.soft)Differentiable functionBrownian motionData Analysis Statistics and Probability (physics.data-an)Condensed Matter - Statistical Mechanics
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Stochastic models for phytoplankton dynamics in marine ecosystems

2014

In this thesis, the stochastic advection-reaction-diffusion models are analyzed to obtain the vertical stationary spatial distributions of the main groups of picophytoplankton, which account about for 80% of total chlorophyll on average in Mediterranean Sea. In Chapter 1 we give a short presentation of the experimental and phytoplanktonic data collected during different oceanographic surveys in Mediterranean Sea. In Chapter 2 we introduce the deterministic and stochastic approaches (one-population model) adopted to describe the picoeukaryotes dynamics in Sicily Channel. Moreover, numerical results for the biomass concentration are compared with experimental data by using chi-squared goodnes…

Phytoplankton dynamics Marine ecosystems Spatial ecology Deep chlorophyll maximum Random processes Stochastic differential equationsSettore FIS/03 - Fisica Della Materia
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Dynamics of a quantum particle interacting with a thermal bath and subject to an oscillating asymmetric bistable potential

2012

Exploiting the approach of the Feynman-Vernon influence functional [1] within the framework of the discrete variable representation (DVR) [2], we consider a quantum particle described by the Caldeira-Leggett model [3]. The particle, “moving” in an asymmetric bistable potential and subject to a periodical driving, interacts with a thermal bath of harmonic oscillators. In this conditions we study the dynamics of the particle by analyzing the time evolution of the populations in the DVR. Specifically we focalize on the position eigenstate located in the shallower well, i.e. metastable state, finding a non-monotonic behaviour of the corresponding population as a function of the frequency. Moreo…

Quantum systems with finite Hilbert spaceFluctuation phenomena random processes noise and Brownian motionquantum statistical methodDecoherenceopen systemQuantum systems with finite Hilbert space;Decoherence; open systems; quantum statistical methods;Fluctuation phenomena random processes noise and Brownian motionSettore FIS/03 - Fisica Della Materia
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