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 QQˉ Q \bar {Q} - pairs in Collisions of Heavy Ions at High Energies

The double coherent and non-coherent diffractive production of heavy quark - antiquark pairs ($Q \bar{Q}$) in heavy ion scattering at high energies (LHC) is considered. The total and differential cross sections of these processes with the formation of $c \bar{c}$ and $b \bar{b}$ pairs in $pp$, $CaCa$ and $PbPb$ 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 $c$, $b$ 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 $Q \bar{Q}$pair, M_{Q \bar{Q}} \gsim 100 GeV, in association with a large rapidity gap between diffractive jets $\Delta \eta > 5$.Comment: 22 pages, 5(.eps) figures, 3 tables, LaTe

Розрахунок розмірів газ-динамічного комплексу

In the paper exact and approximation analytical expressions for calculation of the gas-dynamic jets parameters for gas-dynamic complex are obtained. The sizes of gas-dynamic complex for providing of the unmanned aerial vehicle takeoff and landing with help of these expressions be defined. In particular, the relationship between the aerodynamic characteristics of the unmanned aerial vehicle and braking distance in artificial airstream is obtained. The mathematical model of the unmanned aerial vehicle motion in artificial airstream is based on kinematics and flight dynamics equations. Peculiarity of this model is that it is used real function of velocity distribution in a transverse cross-section of axisymmetric flooded.Отримано точні і наближені аналітичні вирази для розрахунку параметрів газодинамічних струменів для газодинамічного комплексу. За допомогою цих виразів визначено розміри газодинамічного комплексу для забезпечення зльоту і посадки безпілотного літального апарату. Зокрема, отримано зв'язок між аеродинамічними характеристиками безпілотного літального апарату і відстанню гальмування в штучному повітряному потоці. Математичну модель руху безпілотного літального апарату в штучному повітряному потоці побудовано на базі рівнянь кінематики і динаміки польоту. Особливість описаної моделі полягає в тому, що вона використовує реальну функцію розподілу швидкості в поперечному перерізі осесиметричного затопленого струменя

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 $N\to\infty$ 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.