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Jing-Dong Bao

Publications and source records attributed to Jing-Dong Bao.

11 recordsLinked to original sources
PubMed2006

Time-dependent barrier passage of a non-Ohmic damping system.

We consider a particle passing over the saddle point of an inverse harmonic potential, which is described by a generalized Langevin equation with a non-Ohmic damping of power exponent delta. The time-dependent passing probability and transmission coefficient are obtained analytically by using the reaction flux method. It is shown that the overshooting phenomenon for the passing probability appears in the regime 0<delta<1 and the backflow recrossing over the saddle point is observed, where a nonmonotonous time dependence of the passage probability is detected. The long memory aspect of friction is at the origin of this behavior. Thus the steady transmission coefficient is also a nonmonotonous function of delta.

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PubMed2006

Kramers escape rate in nonlinear diffusive media.

In this paper, we study nonlinear Kramers problem by investigating overdamped systems ruled by the one-dimensional nonlinear Fokker-Planck equation. We obtain an analytic expression for the Kramers escape rate under quasistationary conditions by employing a metastable potential and its predictions are in excellent agreement with numerical simulations. The results exhibit the anomalies due to the nonlinearity in W that the escape rate grows with D and drops as mu becomes large at a fixed D. Indeed, particles in the subdiffusive media (mu>1) can escape over the barrier only when D is above a critical value, while this confinement does not exist in the superdiffusive media (mu<1).

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PubMed2005

Non-Markovian Brownian dynamics and nonergodicity.

We report the breaking of ergodicity for a class of generalized, Brownian motion obeying a non-Markovian dynamics being driven by a generalized Langevin equation (GLE). This very feature originates from a vanishing of the effective friction. A novel quantity b (being uniquely determined from the corresponding memory friction kernel gamma(t)of the GLE) is introduced as a parameter that is capable of measuring the strength of ergodicity breaking. The ergodicity breaking is accompanied by a nonunique stationary probability density for the corresponding embedded Markovian dynamics. Differing physical situations for a Brownian, non-Markovian particle dynamics occurring either in free Brownian motion, in a periodic potential, or in a confining potential are elucidated.

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PubMed2005

Classical and quantum diffusion in the presence of velocity-dependent coupling.

A generalized system-plus-reservoir model is introduced, which includes four kinds of couplings between the coordinates and velocities of a system and its environment. It is found that the velocity-dependent coupling is not equivalent to a coordinate coupling due to the different power spectra of thermal noise. Harmonic velocity and acceleration noises are proposed which correspond to the coordinate-velocities and velocity-velocities couplings, respectively, if the environmental oscillators are assumed to have a harmonic spectral distribution. Indeed, the velocity-dependent coupling can induce ballistic diffusion of a force-free particle and the mean square velocity depends on the initial preparation. Quantum ballistic diffusion is also presented and its velocity correlation function is found to be unstable at any time. One of real examples of velocity-coordinates coupling is a one-electron atom interacting with the radiation field. A particle moving in a periodic potential shows a nonergodic behavior.

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PubMed2005

Numerical simulation of generalized Langevin equation with arbitrary correlated noise.

A generalized Langevin equation with arbitrary correlated noise and associated frequency-dependent friction is simulated, which can lead to anomalous diffusion. The algorithm is realized by using the Fourier transform technique to generate noise and the stochastic Runge-Kutta method to solve the whole equation. Application to an acoustic phonon model, initial preparation-dependent ballistic diffusion, is shown.

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PubMed2005

Cancellation phenomenon of barrier escape driven by a non-Gaussian noise.

The Lévy noise, with a long-tail distribution induced particle escape from a metastable potential, is shown to display a feature called a cancellation phenomenon, as compared to the Brownian motion case. As a consequence, the escape rate is found to be a nonmonotonous function of the Lévy index mu and the Arrhenius law is not obeyed. We have also derived a rate expression using the reactive flux method, which supports our numerical findings, namely, with the decrease of mu, a large positive flow is allowed to establish at the barrier, however, the probability passing over the saddle point decreases. This implies that the particles outside the barrier come back to the inside and cancel with themselves.

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PubMed2005

Harmonic velocity noise: non-Markovian features of noise-driven systems at long times.

We propose a harmonic velocity noise with a broadband feature, which is the time derivative of the harmonic noise. If this noise is regarded as a thermal one, the system has a vanishing effective friction and it should induce ballistic diffusion of a free particle at long times. The effective temperature of the system coupled to such a structured heat bath represented by the harmonic velocity noise is introduced. This means that any initial preparation will approach asymptotically a preparation-dependent variance and mean value for velocity variable. Thus the fluctuation-dissipation theorem does not hold as there is no unique stationary state being connected with a breakdown of ergodicity. This noise can show greenness when it is taken as an external noise source to drive a correlation ratchet.

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PubMed2005

Anomalous dissipation: strong non-Markovian effect and its dynamical origin.

We report the effects of anomalous dissipation with a vanishing effective friction, which can induce ballistic diffusion and dissipative acceleration, where the fluctuation-dissipation theorem is fulfilled. An influence factor is introduced in order to describe the role of non-Markovian friction and the force-folded effect on the long-time results. The velocity-dependent coupling and force might be a dynamical origin of this dissipation. The steady acceleration of a particle moving in periodic and magnetic-force potentials are calculated.

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PubMed2004

Anomalous transport in unbound and ratchet potentials.

A non-Markovian Langevin equation with a broadband noise is proposed to describe anomalous transport of a particle passing over a potential saddle or moving in a ratchet potential. In the presence of thermal broadband noise, the asymptotic mean square displacement of a free particle is proportional to the square of time; this is called ballistic diffusion. The passing probability of a particle driven by this broadband noise over the saddle of an inverted harmonic potential is obtained analytically. It is shown that the passing probability increases with the kinetic energy, which is slower than that of normal case. The mechanisms of ballistic diffusion and mobility are also applied to the rocking (a square-wave driving force acting on the potential) and flashing (the potential fluctuating between on and off) ratchets. Phenomena such as acceleration and double-peak mean velocity are observed.

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PubMed2003

Ballistic diffusion induced by a thermal broadband noise.

We present a thermal broadband noise from the difference between two Ornstein-Uhlenbeck noises, which can induce a ballistic diffusion, i.e., long-time mean square displacement of a free particle driven by this noise reads proportional to t(2). We apply this noise to a flashing ratchet and the mean velocity of the particle is calculated via Langevin simulation. The results show that a double peak of the mean velocity and flux reversal appears for the ratchet with large and small asymmetries, respectively; the inertia effect induces a large mean velocity and multireversal of flux. These rich and interesting phenomena are explained.

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