arXiv subjects

W. L. Reenbohn

Publications and source records attributed to W. L. Reenbohn.

8 recordsLinked to original sources

arXiv2026

Conditional Residence Times and Sequential Transition Dynamics of an Overdamped Dimer

We investigate the completion dynamics of an overdamped dimer moving in a bistable potential under thermal fluctuations and a weak periodic force. Both monomers start in one of the two wells separated by a barrier. The transition is initiated when the monomer closer to the barrier makes a jump across it. The completion dynamics refers to the next part of the dynamics where the second monomer has to wait for some time before it can follow up. We use the Conditional Residence Time (CRT) to study the delay between the successive barrier crossing of the two monomers. The CRT distributions highlight qualitatively different regimes formed by the competition between the escape times of the lagging monomer and the time period of the external drive. The effect is strongest in the weak coupling regime where the delayed completion is spread across multiple forcing cycles. By partitioning this process into three windows, i.e. the immediate, first cycle and later cycles, we show that the probability that the lagging monomer will make a transition in the said cycle is redistributed among these pathways as we change the frequency of the drive. This leads to a non-monotonic dependence of the mean CRT on the frequency of the drive. Our results demonstrate that transition initiation and completion in a coupled system are two separate processes and establish CRT as a useful measure to quantify the sequential barrier crossing dynamics in coupled stochastic systems.

cond-mat.stat-mech↗

arXiv2024

Coupling-Induced Synchronized Motion and Stochastic Resonance in Overdamped Dimers

In this study, we explore an overdamped system of a dimer in a bistable potential immersed in a heat bath. The monomers interact via the combination of the Lennard-Jones potential and the harmonic potential. We have introduced a short-range interaction in our model making it more physical. Such a classical system can be used as a model for stochastic resonance (SR) based energy harvesters where the interplay between the noise, coupling and a periodic perturbation leads to a rich class of dynamical behaviours. A key distinction between observing SR in single and coupled particle studies is that a transition between the two wells is only considered successful if both the particles cross a certain threshold position. Although we observe qualitatively a similar peaking behaviour in different quantifiers of SR (like input energy ($W_p$) and hysteresis loop area (HLA)), the effects of the above-mentioned condition on the dynamics of the system remain unaddressed to the best of our knowledge. We study SR using different measures like the input energy per period of the external forcing, the hysteresis loop area as well as quantities like phase lag between the response and the external forcing and the maximum average amplitude of the response. Additionally, we have defined a new quantity called the successful transition ratio. This ratio helps us understand the effects of the dimer's coupling on the number of successful transitions out of the total attempted transitions. The successful transition ratio is almost unity for strongly coupled dimer suggesting most of the transition attempts end up successfully however few they are in numbers. On the other hand, the ratio shows a peaking behaviour with respect to noise for weak and intermediate couplings. We show that only for the weakly coupled dimer, the ratio is maximum around the temperature where SR takes place.

cond-mat.stat-mech↗

arXiv2017

Inertial frictional ratchets and their load bearing efficiencies

We investigate the performance of an inertial frictional ratchet in a sinusoidal potential driven by a sinusoidal external field. The dependence of the performance on the parameters of the sinusoidally varying friction, such as the mean friction coefficient and its phase difference with the potential, is studied in detail. Interestingly, under certain circumstances, the thermodynamic efficiency of the ratchet against an applied load shows a non-monotonic behavior as a function of the mean friction coefficient. Also, in the large friction ranges, the efficiency is shown to increase with increasing applied load even though the corresponding ratchet current decreases as the applied load increases. These counterintuitive numerical results are explained in the text.

cond-mat.stat-mech↗

arXiv2016

Particle dynamics in a symmetrically driven underdamped inhomogeneous periodic potential system

We numerically solve the underdamped Langevin equation to obtain the trajectories of a particle in a sinusoidal potential driven by a temporally sinusoidal force in a medium with coefficient of friction periodic in space as the potential but with a phase difference. With the appropriate choice of system parameters, like the mean friction coefficient and the period of the applied field, only two kinds of periodic trajectories are obtained for all possible initial conditions at low noise strengths: one with a large amplitude and a large phase lag with respect to the applied field and the other with a small amplitude and a small phase lag. Thus, the periodic potential system is effectively mapped dynamically into a bistable system. Though the directional asymmetry, brought about only by the frictional inhomogeneity, is weak we find both the phenomena of stochastic resonance, with ready explanation in terms of the two dynamical states of trajectories, and ratchet effect simultaneously in the same parameter space. We analyse the results in detail attempting to find plausible explanations for each.

cond-mat.stat-mech↗

arXiv2015

Dynamical States, Stochastic Resonance and Ratchet Effect in a Biharmonically Driven Sinusoidal Potential

Two stable dynamical states of trajectories of an underdamped particle, under appropriate conditions, appear naturally in a sinusoidal potential when driven by a low amplitude biharmonic external field. These states are quite stable at low temperatures but make transitions between them as the temperature is raised. The proper choice of the biharmonic drive makes it possible for the system to show, at the same time, {\it{both}} the phenomena of stochastic resonance and ratchet effect. Ratchet effect, in this case, a consequence of the biharmonic drive, is obtained over a large domain of parameter space. However, stochastic resonance can be obtained only over a restricted (sub)domain of parameter space and owes its existence largely to the existence of the two dynamical states.

cond-mat.stat-mech↗

arXiv2012

Stochastic Resonance in Periodic Potentials Revisited

The phenomenon of Stochastic Resonance (SR) has been conclusively demonstrated in bistable potentials. However, SR in sinusoidal potentials have only recently been shown numerically to occur in terms of hysteresis loop area. We show that the occurrence of SR is not specific to sinusoidal potentials and can occur in periodic bistable potential, $U(x)=2/3(\cos x +\cos 2x)$, as well. We further show that SR can occur even in a washboard potential, where hysteresis loops normally do not close because of average drift of particles. Upon correcting for the drift term, the closed hysteresis loop area (input energy loss) shows the usual SR peaking behaviour as also the signal-to-noise ratio in a limited domain in the high drive-frequency range. The occurrence of SR is attributed to the existence of effectively two dynamical states in the driven periodic sinusoidal and periodic bistable potentials. The same explanation holds also when the periodic potentials are tilted by a small constant slope.

cond-mat.stat-mech↗

arXiv2008

Ratchet effect in inhomogeneous inertial systems: I. Adiabatic case

Risken's matrix continued fraction method is used to solve the Fokker-Planck equation to calculate particle current in an inertial symmetric (sinusoidal) periodic potential under the action of a constant force. The particle moves in a medium with friction coefficient also varying periodically in space as the potential but with a finite phase difference $ϕ(\ne nπ, n=0,1,2, ...)$. The algebraic sum of current with applied forces $\pm|F|$ gives the ratchet current in the adiabatic limit. Even though, the effect of frictional inhomogeneity is weak, the ratchet current shows very rich qualitative characteristics. The effects of variation of $F$, the temperature $T$, and the average friction coefficient $γ_0$ on the performance characteristics of the ratchet are presented.

cond-mat.stat-mech↗

arXiv2008

Motional dispersions and ratchet effect in inertial systems

We obtain ratchet effect in inertial structureless systems in symmetric periodic potentials where the asymmetry comes from the nonuniform friction offered by the medium and driven by symmetric periodic forces. In the adiabatic limit the calculations are done by extending the matrix continued fraction method and also by numerically solving the appropriate Langevin equation. For finite frequency field drive the ratchet effect is obtained only numerically. In the transient time scales the system shows dispersionless behaviour as reported earlier when a constant force is applied. In the periodic drive case the dispersion behaviour is more complex. In this brief communication we report some of the results of our work

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