1,157 research outputs found
Stability measures in metastable states with Gaussian colored noise
We present a study of the escape time from a metastable state of an
overdamped Brownian particle, in the presence of colored noise generated by
Ornstein-Uhlenbeck process. We analyze the role of the correlation time on the
enhancement of the mean first passage time through a potential barrier and on
the behavior of the mean growth rate coefficient as a function of the noise
intensity. We observe the noise enhanced stability effect for all the initial
unstable states used, and for all values of the correlation time
investigated. We can distinguish two dynamical regimes characterized by weak
and strong correlated noise respectively, depending on the value of
with respect to the relaxation time of the system.Comment: 6 pages, 7 figure
Critical Phenomena and Diffusion in Complex Systems
Editorial of the International Conference on Critical Phenomena and Diffusion
in Complex Systems held on 5--7 December, 2006 in Nizhniy Novgorod State
University, Russia and was dedicated to the memory and 80th anniversary of
Professor Askold N. Malakhov.Comment: 4 pages, to appear in International Journal of Bifurcation and Chao
Switching times in long-overlap Josephson junctions subject to thermal fluctuations and non-Gaussian noise sources
We investigate the superconducting lifetime of long current-biased Josephson
junctions, in the presence of Gaussian and non-Gaussian noise sources. In
particular, we analyze the dynamics of a Josephson junction as a function of
the noise signal intensity, for different values of the parameters of the
system and external driving currents. We find that the mean lifetime of the
superconductive state is characterized by nonmonotonic behavior as a function
of noise intensity, driving frequency and junction length. We observe that
these nonmonotonic behaviours are connected with the dynamics of the junction
phase string during the switching towards the resistive state. An important
role is played by the formation and propagation of solitons, with two different
dynamical regimes characterizing the dynamics of the phase string. Our analysis
allows to evidence the effects of different bias current densities, that is a
simple spatially homogeneous distribution and a more realistic inhomogeneous
distribution with high current values at the junction edges. Stochastic
resonant activation, noise enhanced stability and temporary trapping phenomena
are observed in the system investigated.Comment: 16 pages, 9 figures, Physical Review B, in pres
Uhlmann curvature in dissipative phase transitions
We study the mean Uhlmann curvature in fermionic systems undergoing a
dissipative driven phase transition. We consider a paradigmatic class of
lattice fermion systems in non-equilibrium steady-state of an open system with
local reservoirs, which are characterised by a Gaussian fermionic steady state.
In the thermodynamical limit, in systems with translational invariance we show
that a singular behaviour of the Uhlmann curvature represents a sufficient
criterion for criticalities, in the sense of diverging correlation length, and
it is not otherwise sensitive to the closure of the Liouvillian dissipative
gap. In finite size systems, we show that the scaling behaviour of the mean
Uhlmann curvature maps faithfully the phase diagram, and a relation to the
dissipative gap is put forward. We argue that the mean Uhlmann phase can shade
light upon the nature of non equilibrium steady state criticality in particular
with regard to the role played by quantum vs classical fluctuations.Comment: 5 pages, 3 figures with appendix of 10 pages, 1 figur
Quantum dissipative dynamics of a bistable system in the sub-Ohmic to super-Ohmic regime
We investigate the quantum dynamics of a multilevel bistable system coupled
to a bosonic heat bath beyond the perturbative regime. We consider different
spectral densities of the bath, in the transition from sub-Ohmic to super-Ohmic
dissipation, and different cutoff frequencies. The study is carried out by
using the real-time path integral approach of the Feynman-Vernon influence
functional. We find that, in the crossover dynamical regime characterized by
damped \emph{intrawell} oscillations and incoherent tunneling, the short time
behavior and the time scales of the relaxation starting from a nonequilibrium
initial condition depend nontrivially on the spectral properties of the heat
bath.Comment: 16 pages, 7 figure
Noise Enhanced Stability
The noise can stabilize a fluctuating or a periodically driven metastable
state in such a way that the system remains in this state for a longer time
than in the absence of white noise. This is the noise enhanced stability
phenomenon, observed experimentally and numerically in different physical
systems. After shortly reviewing all the physical systems where the phenomenon
was observed, the theoretical approaches used to explain the effect are
presented. Specifically the conditions to observe the effect: (a) in systems
with periodical driving force, and (b) in random dichotomous driving force, are
discussed. In case (b) we review the analytical results concerning the mean
first passage time and the nonlinear relaxation time as a function of the white
noise intensity, the parameters of the potential barrier, and of the
dichotomous noise.Comment: 18 pages, 6 figures, in press Acta Physica Polonica (2004
Quantum resonant activation
Quantum resonant activation is investigated for the archetype setup of an
externally driven two-state (spin-boson) system subjected to strong dissipation
by means of both analytical and extensive numerical calculations. The
phenomenon of resonant activation emerges in the presence of either randomly
fluctuating or deterministic periodically varying driving fields. Addressing
the incoherent regime, a characteristic minimum emerges in the mean first
passage time to reach an absorbing neighboring state whenever the intrinsic
time scale of the modulation matches the characteristic time scale of the
system dynamics. For the case of deterministic periodic driving, the first
passage time probability density function (pdf) displays a complex,
multi-peaked behavior, which depends crucially on the details of initial phase,
frequency, and strength of the driving. As an interesting feature we find that
the mean first passage time enters the resonant activation regime at a critical
frequency which depends very weakly on the strength of the driving.
Moreover, we provide the relation between the first passage time pdf and the
statistics of residence times.Comment: 14 pages, 13 figure
Effects of L\'evy noise on the dynamics of sine-Gordon solitons in long Josephson junctions
We numerically investigate the generation of solitons in current-biased long
Josephson junctions in relation to the superconducting lifetime and the voltage
drop across the device. The dynamics of the junction is modelled with a
sine-Gordon equation driven by an oscillating field and subject to an external
non-Gaussian noise. A wide range of -stable L\'evy distributions is
considered as noise source, with varying stability index and asymmetry
parameter . In junctions longer than a critical length, the mean
switching time (MST) from superconductive to the resistive state assumes a
values independent of the device length. Here, we demonstrate that such a value
is directly related to the mean density of solitons which move into or from the
washboard potential minimum corresponding to the initial superconductive state.
Moreover, we observe: (i) a connection between the total mean soliton density
and the mean potential difference across the junction; (ii) an inverse behavior
of the mean voltage in comparison with the MST, with varying the junction
length; (iii) evidences of non-monotonic behaviors, such as stochastic resonant
activation and noise enhanced stability, of MST versus the driving frequency
and noise intensity for different values of and ; (iv) finally,
these non-monotonic behaviors are found to be related to the mean density of
solitons formed along the junction.Comment: 24 pages, 8 figures, submitted to J. Stat. Mech.: Theory Exp. arXiv
admin note: text overlap with arXiv:1406.481
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