0000000000273113
AUTHOR
D Valenti
Magnetically excited breather modes in an overlap-geometry Josephson tunnel junction
A scheme for the controlled generation of single traveling sine- Gordon breathers in a long Josephson junction is described. In the presence of dissipation, a direct current source, and thermal fluctuations, the theoretical analysis shows that, through the nonlinear supratransmission effect, tailored magnetic pulses at the junction’s edge can effectively yield breather modes only.
Ruolo del rumore ambientale in sistemi complessi di natura biologica
La Fisica dei Sistemi Complessi ha recentemente assunto un ruolo sempre più importante nella descrizione dei sistemi biologici a causa delle interazioni, sia deterministiche sia rumorose o “randomiche”, di tali sistemi con l’ambiente. La presenza del rumore diviene particolarmente rilevante nella trattazione dei sistemi biologici in ambito medico. In questo lavoro vengono presentati due diversi sistemi: i) un modello di dinamica di popolazioni che descrive lo sviluppo delle cellule tumorali responsabili della Leucemia Mieloide Cronica (CML); ii) un modello stocastico che riproduce la crescita di batteri in alimenti di origine animale. Nel primo sistema viene utilizzato un approccio Monte Ca…
Stochastic model for a biological complex system: analysis of the bacterial growth in food products
The Physics of Complex Systems has recently taken a more and more important role in the description of natural systems because of the interactions, both deterministic and noisy, between such systems and the environment. In particular the noise plays a relevant role in biological systems, whose dynamics is strongly influenced by environmental variables subject to random fluctuations. In this work a stochastic model is exploited to reproduce the growth of bacteria in food of animal origin. Specifically the dynamics of a bacterial species, Listeria monocytogenes, is analyzed in the presence of lactic acid bacteria (LAB) during the period of the fermentation of meat products. The model, based o…
Nonlinear relaxation in quantum and mesoscopic systems
The nonlinear relaxation of three mesoscopic and quantum systems are investigated. Specifically we study the nonlinear relaxation in: (i) a long Josephson junction (LJJ) driven by a non-Gaussian Lévy noise current; (ii) a metastable quantum open system driven by an external periodical driving; and (iii) the electron spin relaxation process in n-type GaAs crystals driven by a fluctuating electric field. In the first system the LJJ phase evolution is described by the perturbed sine-Gordon equation. Two well known noise induced effects are found: the noise enhanced stability and resonant activation phenomena. We investigate the mean escape time as a function of the bias current frequency, nois…
A stochastic reaction-diffusion-taxis model for two picophytoplankton populations
In this work, the stationary distributions of two populations of picophytoplankton, i.e. picoeukaryotes and Prochlorococcus, are studied. This two groups account on average for 60% of the total chlorophyll a (chl a) and divinil chlorophyll a (divinil chl a) concentration in Mediterranean Sea. The interaction of these populations with the environment occurs through two factors that limit the growth of the aquatic microorganisms: light intensity and nutrient, i.e. phosphorus. The dynamics of the two picophytoplanktonic groups, distributed at different depth along a water column (one-dimensional spatial domain), is analyzed starting from a deterministic reaction-diffusion-taxis model. This con…