Environmental noise and nonlinear relaxation in biological systems

We investigate the role of the environmental noise in three biological systems: (i) an ecosystem described by a Verhulst model with a multiplicative Lévy noise; (ii) polymer translocation, and (ii) individuals of Nezara viridula. Specifically the transient dynamics of the Verhulst model perturbed by arbitrary non-Gaussian white noise is investigated as a first biological system. For Cauchy stable noise, exact results for the probability distribution of the population density and nonlinear relaxation are derived. We find a transition induced by the multiplicative Lévy noise, from a trimodal probability distribution to a bimodal probability distribution in asymptotics, and a nonmonotonic beha…

Dynamics of a quantum particle interacting with a thermal bath and subject to an oscillating asymmetric bistable potential

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…

Dynamics of a FitzHugh-Nagumo system driven by a periodic signal in the presence of colored noise

We analyze the dynamics of a FitzHugh-Naguno system, driven by a periodic signal, in the presence of coloured noise. We consider the effects of the fluctuations by inserting in the deterministic FitzHugh-Nagumo model a term of additive Gaussian noise. We study the system in two different cases: the fluctuations affect the dynamics of the membrane potential (CASE I), the recovery variable is subjected to noise (CASE II). We review briefly the effects of the white noise, responsible for the appearance of resonant activation (RA) and noise enhanced stability (NES) phenomena. Afterwards we study the two cases in the presence of a coloured noise with correlation time tau. We investigate the effe…

Acceleration of diffusion in switching periodic sawtooth potential

Stochastic Resonance in Magnetic Systems described by Preisach Hysteresis Model

Noise-induced phenomena in transient dynamics of short and long Josephson junctions

The investigation of nonlinear properties of Josephson junctions (JJs) is very important due to their broad applications in logic devices. Currently, all Josephson junctions are manufactured with the use of optical and electronic lithography, and they can always be considered as distributed. Moreover great interest recently has attracted, from theoretical and experimentally point of view, the investigation of the influence of thermal fluctuations in macroscopic quantum phenomena of short and long Josephson junctions. Particularly the role of the noise on the life time of the superconductive state has been subject of many investigations. In fact for some devices, as the rapid single flux qua…

Transient Dynamics of a Driven Quantum Bistable System

We study the transient dynamics and the asymptotic behaviour of a multilevel system in the strong dissipation regime. The system is modeled as a periodically driven quantum particle in an asymmetric double well potential, interacting with the bosonic heat bath of the Caldeira-Leggett model. The analytical approach used is non- perturbative in the particle-bath coupling and is based on a space-discretized path integral expression for the particle’s reduced density matrix. By a suitable approximation on the Feynman-Vernon influence functional a Markov-approximated master equation is obtained for the populations in the Discrete Variable Representation (DVR).

Stochastic resonance effect on the vibratory signals of stink bugs

In this work we investigate the role of the environmental noise in the sexual communication between individuals of the Sicilian green stink bug Nezara Viridula. Our goal is to analyze the spectral features of several types of songs emitted by these insects and to find the amplitude threshold value. Below this value the signal is so weak that no neuronal activation occurs in Nezara Viridula. The presence of activation is revealed by performing directionality tests and observing the behavioral response of the insect in localizing the source of vibratory signals. Afterwards experiments are performed by using a sub-threshold signal added to a white Gaussian noise. The response of the test insec…

Transient Dynamics of Short Josephson Junctions under the influence of non-Gaussian Noise

We investigate the effects of non-Gaussian white noise source on the transient dynamics of short Josephson junctions. The noise signal is simulated generating standard stable random variables with characteristic function described by Lévy index alpha and asymmetry parameter beta. We study the lifetime of the superconductive state as a function both of the frequency of the external driving bias current and the noise intensity for different values of index alpha. We compare our results with those obtained in the presence of Gaussian white noise. We find the presence of noise induced effects such as resonant activation and noise enhanced stability.

Dynamics of a Lotka-Volterra system in the presence of non-Gaussian noise sources

We consider a Lotka-Volterra system of two competing species subject to multiplicative α-stable Lévy noise. The interaction parameter between the species is a random process which obeys a stochastic differential equation with a generalized bistable potential in the presence both of a periodic driving term and an additive alpha-stable Lévy noise. We study the species dynamics, which is characterized by two different dynamical regimes, exclusion of one species and coexistence of both ones, analyzing the role of the Lévy noise sources.

Risonanza stocastica non dinamica in una popolazione di Nezara Viridula (L.)

In questo lavoro viene studiato l’effetto del rumore sul comportamento, durante il periodo di accoppiamento, di individui di Nezara viridula (L.). Analizzando la risposta di insetti maschi a segnali sotto soglia, prodotti da individui di sesso femminile, si osserva, in presenza di una sorgente esterna di rumore bianco Gaussiano, un’attivazione “comportamentale”, con un andamento non monotono in funzione dell’intensit`a di rumore, chiara indicazione della presenza di risonanza stocastica non dinamica. Lo studio `e ripetuto utilizzando una sorgente di rumore colorato. Infine, i risultati sperimentali vengono riprodotti attraverso un modello a soglia “morbida”, in cui la funzione di cross-corr…