4,727 research outputs found
Suppression of timing errors in short overdamped Josephson junctions
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.Comment: 4 pages, 4 figures, in press in Physical Review Letter
Coherent and Non-Coherent Double Diffractive Production of - pairs in Collisions of Heavy Ions at High Energies
The double coherent and non-coherent diffractive production of heavy quark -
antiquark pairs () in heavy ion scattering at high energies (LHC) is
considered. The total and differential cross sections of these processes with
the formation of and pairs in , and
collisions are evaluated. The contribution of the considered mechanisms is a
few per cent of the number of heavy quark - antiquark pairs obtained in the
processes of hard (QCD) scattering, and it will be taken into account in the
registration of , quarks or, for instance, in the study of the heavy
quarkonia suppression effects in Quark - Gluon Plasma, in the search for
intermediate mass Higgs bosons and so on. It is shown that the cross section of
the coherent scattering process is great enough. This makes it suitable for
studying collective effects in nuclear interactions at high energies. An
example of such effects is given: large values of the invariant mass of a pair, M_{Q \bar{Q}} \gsim 100 GeV, in association with a large
rapidity gap between diffractive jets .Comment: 22 pages, 5(.eps) figures, 3 tables, LaTe
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
Noise delayed decay of unstable states: theory versus numerical simulations
We study the noise delayed decay of unstable nonequilibrium states in
nonlinear dynamical systems within the framework of the overdamped Brownian
motion model. We give the exact expressions for the decay times of unstable
states for polynomial potential profiles and obtain nonmonotonic behavior of
the decay times as a function of the noise intensity for the unstable
nonequilibrium states. The analytical results are compared with numerical
simulations.Comment: 9 pages, 6 figures, in press in J. Phys.
Numerical simulations versus theoretical predictions for a non-Gaussian noise induced escape problem in application to full counting statistics
A theoretical approach for characterizing the influence of asymmetry of noise distribution on the escape rate
of a multistable system is presented. This was carried out via the estimation of an action, which is defined as
an exponential factor in the escape rate, and discussed in the context of full counting statistics paradigm. The
approach takes into account all cumulants of the noise distribution and demonstrates an excellent agreement with
the results of numerical simulations. An approximation of the third-order cumulant was shown to have limitations
on the range of dynamic stochastic system parameters. The applicability of the theoretical approaches developed
so far is discussed for an adequate characterization of the escape rate measured in experiments
Clustering in light nuclei in fragmentation above 1 A GeV
The relativistic invariant approach is applied to analyzing the 3.3 A GeV
Ne fragmentation in a nuclear track emulsion. New results on few-body
dissociations have been obtained from the emulsion exposures to 2.1 A GeV
N and 1.2 A GeV Be nuclei. It can be asserted that the use of the
invariant approach is an effective means of obtaining conclusions about the
behavior of systems involving a few He nuclei at a relative energy close to 1
MeV per nucleon. The first observations of fragmentation of 1.2 A GeV B
and C nuclei in emulsion are described. The presented results allow one
to justify the development of few-body aspects of nuclear astrophysics.Comment: 7 pages, 8 figures, 3 tables, Nuclear Physics in Astrophysics-2,
16-20 May, 2005 (ATOMKI), Debrecen, Hungar
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