arXiv subjects

Mangal C. Mahato

Publications and source records attributed to Mangal C. Mahato.

32 records · Page 2Linked to original sources

arXiv2001

Enhancement of mobility by periodically modulating the slanting slope of a washboard potential

Average mobility of very feebly damped particles in tilted periodic potentials is considered. Under the combined action of thermal fluctuations and small temporal modulation of the tilt of the potential the particles, in the small tilt range, become more mobile than without modulation. The enhancement of mobility depends (nonmonotonically) on the frequency of modulation. For small modulations the enhancement shows a peak as a function of frequency. This has an obvious implication on the measured voltage across a Josephson junction driven by a small amplitude alternating current of suitable frequency.

cond-mat.stat-mech↗

arXiv2001

AC driven thermal ratchets

We consider the motion of a overdamped Brownian particle in periodic asymmetric potential with space dependent friction coefficient. In the presence of external time periodic forcing, the system shows multiple current reversals on varying the amplitude of the external forcing and the temperature of the thermal bath. In the adiabatic regime we find a single reversal of current as a function of noise strength which can only be accounted due to the presence of space dependent friction coefficient. For very large forcing term, the current does not go to zero, instead it asymptotically tends to a limiting value depending on the phase shift between the potential and the friction. This fact plays an important role in obtaining multiple current reversals.

cond-mat.stat-mech↗

arXiv2000

Multiple current reversals in forced inhomogeneous ratchets

Transport properties of overdamped Brownian paricles in a rocked thermal ratchet with space dependent friction coefficient is studied. By tuning the parameters, the direction of current exhibit multiple reversals, both as a function of the thermal noise strength as well as the amplitude of rocking force. Current reversals also occur under deterministic conditions and exhibits intriguing structure. All these features arise due to mutual interplay between potential asymmetry,noise, driving frequency and inhomogeneous friction.

cond-mat.stat-mech↗

arXiv2000

Motion in a rocked ratchet with spatially periodic friction

We present a detailed study of the transport and energetics of a Brownian particle moving in a periodic potential in the presence of an adiabatic external periodic drive. The particle is considered to move in a medium with periodic space dependent friction with the same periodicity as that of the potential but with a phase lag. We obtain several results, most of them arising due to the medium being inhomogeneous and are sensitive to the phase lag. When the potential is symmetric we show that efficiency of energy transduction can be maximised as a function of noise strength or temperature. However, in the case of asymmtertic potential the temperature may or may not facilitate the energy conversion but current reversals can be obtained as a function of temperature and the amplitude of the periodic drive. The reentrant behaviour of current can also be seen as a function of phase lag.

cond-mat.stat-mech↗

arXiv1999

Efficiency and current reversals in spatially inhomogeneous ratchets

Efficiency of generation of net unidirectional current in an adiabatically driven symmetric periodic potential system is studied. The efficiency shows a maximum, in the case of an inhomogeneous system with spatially varying periodic friction coefficient, as a function of temperature. The ratchet is not most efficient when it gives maximum current. The direction of current may also be reversed as a function of noise strength when, instead, an asymmetric periodic potential is considered.

cond-mat.soft↗

arXiv1999

Mobility and stochastic resonance in spatially inhomogeneous system

The mobility of an overdamped particle, in a periodic potential tilted by a constant external field and moving in a medium with periodic friction coefficient is examined. When the potential and the friction coefficient have the same periodicity but have a phase difference, the mobility shows many interesting features as a function of the applied force, the temperature, etc. The mobility shows stochastic resonance even for constant applied force, an issue of much recent interest. The mobility also exhibits a resonance like phenomenon as a function of the field strength and noise induced slowing down of the particle in an appropriate parameter regime.

cond-mat.stat-mech↗

arXiv1997

Some stochastic phenomena in a driven double-well system

We study the overdamped motion of a Brownian particle in a driven double-well system to understand various physical phenomena observed experimentally. These phenomena include hysteresis, stochastic resonance, and net unidirectional motion in a symmetric periodic system. We argue that the area of the hysteresis loop so defined is a good measure of synchronization (with respect to the applied field) of passages between the two wells. We find that stochastic resonance may be relevant even in case of large amplitude driving field due to a recently discovered phenomena of noise induced stability of unstable states. We try to find relation between some of these apparently different phenomena.

cond-mat↗

arXiv1997

Asymmetric motion in a double-well under the action of zero-mean Gaussian white noise and periodic forcing

Residence times of a particle in both the wells of a double-well system, under the action of zero-mean Gaussian white noise and zero-averaged but temporally asymmetric periodic forcings, are recorded in a numerical simulation. The difference between the relative mean residence times in the two wells shows monotonic variation as a function of asymmetry in the periodic forcing and for a given asymmetry the difference becomes largest at an optimum value of the noise strength. Moreover, the passages from one well to the other become less synchronous at small noise strength as the asymmetry parameter (defined below) differs from zero, but at relatively larger noise strengths the passages become more synchronous with asymmetry in the field sweep. We propose that asymmetric periodic forcing (with zero mean) could provide a simple but sensible physical model for unidirectional motion in a symmetric periodic system aided by a symmetric Gaussian white noise.

cond-mat.stat-mech↗

arXiv1997

Two-Well System under Large Amplitude Periodic Forcing: Stochastic Synchronization, Stochastic Resonance and Stability

We study the residence time distributions and explore the possibility of observing stochastic resonance and synchonization of passages in a two-well system driven by a periodic forcing of amplitude larger than a marginal value beyond which one of the two wells become unstable and diasppear. We define and calculate hysteresis loop in the system, the area of which measures the degree of synchronization between the residence time statistics and the input signal, as a function of input noise strength. We analyse the noise induced stability obtained in such a deterministically overall unstable system and within this context discuss the above two phenomena.

cond-mat.stat-mech↗

arXiv1997

Stochastic resonance and nonlinear response in a dissipative quantum two-state system

We study the dynamics of a dissipative two-level, system driven by a monochromatic ac field, starting from the usual spin-boson Hamiltonian. The quantum Langevin equations for the spin variables are obtained. The amplitude of the coherent oscillations in the average position of the particle is studied in the high temperature limit. The system exhibits quantum stochastic resonance in qualitative agreement with earlier numerical results.

cond-mat.stat-mech↗

arXiv1997

Relation between Stochastic Resonance and Synchronization of Passages in a Double-Well System

We calculate, numerically, the residence times (and their distribution) of a Brownian particle in a two-well system under the action of a periodic, saw-tooth type, external field. We define hysteresis in the system. The hysteresis loop area is shown to be a good measure of synchronization of passages from one well to the other. We establish connection between this stochastic synchronization and stochastic resonance in the system.

cond-mat.stat-mech↗

arXiv1996

Enslaving random fluctuations in nonequlibrium systems

Several physical models have recently been proposed to obtain unidirectional motion of an overdamped Brownian particle in a periodic potential system. The asymmetric ratchetlike form of the periodic potential and the presence of correlated nonequilibrium fluctuating forces are considered essential to obtain such a macroscopic motion in homogeneous systems. In the present work, instead, inhomogeneous systems are considered, wherein the friction coefficient and/or temperature could vary in space. We show that unidirectional motion can be obtained even in a symmetric nonratchetlike periodic potential system in the presence of white noise fluctuations. We consider four different cases of system inhomogeneity We argue that all these different models work under the same basic principle of alteration of relative stability of otherwise locally stable states in the presence of temperature inhomogeneity.

cond-mat↗

arXiv1995

Synchronized First-Passages in a Double-Well System

We perform Langevin dynamic numerical simulation on a double-well potential system subjected to an asymmetric saw-tooth type external time varying field and white noise forces. The hysteresis loss calculated from the first-passage time distribution obtained shows asymmetric behaviour with respect to the asymmetry in the field sweep. The hysteresis loss, in our model, being a measure of the synchronized passages from one well to the other, indicates asymmetric "correlated" passages in the two opposing directions when driven by a temporally asymmetric external field in the presence of white noise (fluctuating) forces. The implication of our results on the phenomena of predominantly unidirectional motion of a Brownian particle in a symmetric periodic (nonratchet-like) potential is discussed.

cond-mat↗

arXiv1995

Macroscopic Equation of Motion in Inhomogeneous media

The dynamical evolution of a Brownian particle in an inhomogeneous medium with spatially varying friction and temperature field is important to understand conceptually. It requires to address the basic problem of relative stability of states in nonequilibrium systems which has been a subject of debate for over several decades. The theoretical treatments adopted so far are mostly phenomenological in nature. In this work we give a microscopic treatment of this problem. We derive the Langevin equation of motion and the associated Fokker-Planck equation. The correct reduced description of the Kramers equation in the overdamped limit (Smoluchowski equation) is obtained. Our microscopic treatment may be helpful in understanding the working of thermal ratchets, a problem of much current interest.

cond-mat↗