arXiv subjects

Mangal C. Mahato

Publications and source records attributed to Mangal C. Mahato.

At least 19 recordsLinked to original sources

arXiv2019

An analog simulation experiment to study free oscillations of a damped simple pendulum

The characteristics of drive-free oscillations of a damped simple pendulum under sinusoidal potential force field differ from those of the damped harmonic oscillations. The frequency of oscillation of a large amplitude simple pendulum decreases with increasing amplitude. Many prototype mechanical simple pendulum have been fabricated with precision and studied earlier in view of introducing them in undergraduate physics laboratories. However, fabrication and maintenance of such mechanical pendulum require special skill. In this work, we set up an analog electronic simulation experiment to serve the purpose of studying the force-free oscillations of a damped simple pendulum. We present the details of the setup and some typical results of our experiment. The experiment is simple enough to implement in undergraduate physics laboratories.

physics.class-ph↗

arXiv2018

Stochastic resonance in a sinusoidal potential system: An analog simulation experiment

Recently, stochastic resonance was obtained numerically in an underdamped periodic potential system driven by a periodic force and a Gaussian white noise. In that numerical work, the occurrence of stochastic resonance was explained in terms of the existence of two dynamical states having different amplitude and phase lag. At zero temperature these two initial condition dependent dynamical states are stable. However, at elevated temperatures, these two states make transitions from one to the other at a mean rate. In the present work, we setup an analog simulation experiment to show the existence of the two dynamical states in a sinusoidal potential system as well as to verify the occurrence of stochastic resonance in the same system. The experimental procedure includes setting the initial conditions for the experiment.

nlin.CD↗

arXiv2018

Experimental investigation of water jets under gravity

The Plateau-Rayleigh theory essentially explains the breakup of liquid jets as due to growing perturbations along the length of the jet. The essential idea is supported by several experiments carried out in the past. Recently, the existence of a feedback mechanism in the form of recoil capillary waves was proposed to enhance the effect of the perturbations. We experimentally verify the existence of such recoil capillary waves. Using our experimental setup we further show that the wavy nature of the jet surface appears almost right after the emergence of the jet from the nozzle irrespective of the recoil capillary wave feedback. Moreover, our experimental results indicate existence of a sharp boundary, along the length of the continuous jet, beyond which gravitational effect dominates over the surface tension.

physics.flu-dyn↗

arXiv2017

Resonance oscillation of a damped driven simple pendulum

The resonance characteristics of a driven damped harmonic oscillator are well known. Unlike harmonic oscillators which are guided by parabolic potentials, a simple pendulum oscillates under sinusoidal potentials. The problem of an undamped pendulum has been investigated to a great extent. However, the resonance characteristics of a driven damped pendulum have not been re- ported so far due to the difficulty in solving the problem analytically. In the present work we report the resonance characteristics of a driven damped pendulum calculated numerically. The results are compared with the resonance characteristics of a damped driven harmonic oscillator. The work can be of pedagogic interest too as it reveals the richness of driven damped motion of a simple pendulum in comparison to and how strikingly it differs from the motion of a driven damped harmonic oscillator. We confine our work only to the nonchaotic regime of pendulum motion.

physics.class-ph↗

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

Study of Instability of Liquid Jets Under Gravity

Breakup of water jets under gravity is a common-place phenomenon. The role of surface tension in the instability of water jets was recognized by Rayleigh and the theory propounded goes by the name of Plateau-Rayleigh theory. The necks and bulges down along the jet-length that are created by perturbation waves of wavelengths larger than a certain value keep growing with time and ultimately cause the jet to breakup into drops. The effect of perturbation waves have been investigated experimentally and found to confirm the essentials of the theory. However, there is no unanimity about the origin of these perturbation waves. Recently, the idea of recoil capillary waves as an important source of the perturbation waves has been emphasized. The recoil of the end point of the remaining continuous jet at its breakup point is considered to travel upward as a recoil capillary wave which gets reflected at the mouth of the nozzle from which the jet originates. The reflected capillary wave travels along the jet downward with its Doppler shifted wavelength as a perturbation wave. We set up an experiment to directly verify the existence and effect of the recoil capillary waves and present some preliminary results of our experiment.

physics.flu-dyn↗

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↗

arXiv2011

Stochastic Resonance in Periodic Potentials

The phenomenon of stochastic resonance (SR) is known to occur mostly in bistable systems. However, the question of occurrence of SR in periodic potential systems is not conclusively resolved. Our present numerical work shows that the periodic potential system indeed exhibits SR in the high frequency regime, where the linear response theory yields maximum frequency dependent mobility as a function of noise strength. The existence of two (and only two) distinct dynamical states of trajectories in this moderately feebly-damped periodically driven noisy periodic potential system plays an important role in the occurrence of SR.

cond-mat.stat-mech↗

arXiv2010

Deterministic inhomogeneous inertia ratchets

We study the deterministic dynamics of a periodically driven particle in the underdamped case in a spatially symmetric periodic potential. The system is subjected to a space-dependent friction coefficient, which is similarly periodic as the potential but with a phase difference. We observe that frictional inhomogeneity in a symmetric periodic potential mimics most of the qualitative features of deterministic dynamics in a homogeneous system with an asymmetric periodic potential. We point out the need of averaging over the initial phase of the external drive at small frictional inhomogeneity parameter values or analogously low potential asymmetry regimes in obtaining ratchet current. We also show that at low amplitudes of the drive, where ratchet current is not possible in the deterministic case, noise plays a significant role in realizing ratchet current.

cond-mat.stat-mech↗

arXiv2009

Dispersionless motion in a driven periodic potential

Recently, dispersionless (coherent) motion of (noninteracting) massive Brownian particles, at intermediate time scales, was reported in a sinusoidal potential with a constant tilt. The coherent motion persists for a finite length of time before the motion becomes diffusive. We show that such coherent motion can be obtained repeatedly by applying an external zero-mean square-wave drive of appropriate period and amplitude, instead of a constant tilt. Thus, the cumulative duration of coherent motion of particles is prolonged. Moreover, by taking an appropriate combination of periods of the external field, one can postpone the beginning of the coherent motion and can even have coherent motion at a lower value of position dispersion than in the constant tilt case.

cond-mat.stat-mech↗

arXiv2008

Ratchet effect in inhomogeneous inertial systems: II. The square-wave drive case

The underdamped Langevin equation of motion of a particle, in a symmetric periodic potential and subjected to a symmetric periodic forcing with mean zero over a period, with nonuniform friction, is solved numerically. The particle is shown to acquire a steady state mean velocity at asymptotically large time scales. This net particle velocity or the ratchet current is obtained in a range of forcing amplitudes $F_0$ and peaks at some value of $F_0$ within the range depending on the value of the average friction coefficient and temperature of the medium. At these large time scales the position dispersion grows proportionally with time, $t$, allowing for calculating the steady state diffusion coefficient $D$ which, interestingly, shows a peaking behaviour around the same $F_0$. The ratchet current, however, turns out to be largely coherent. At intermediate time scales, which bridge the small time scale behaviour of dispersion$\sim t^2$ to the large time one, the system shows, in some cases, periodic oscillation between dispersionless and steeply growing dispersion depending on the frequency of the forcing. The contribution of these different dispersion regimes to ratchet current is analysed.

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

cond-mat.stat-mech↗

arXiv2008

Stochastic resonance and heat fluctuations in a driven double-well system

We study a periodically driven (symmetric as well as asymmetric)double-well potential system at finite temperature. We show that mean heat loss by the system to the environment(bath) per period of the applied field is a good quantifier of stochastic resonance. It is found that the heat fluctuations over a single period are always larger than the work fluctuations. The observed distributions of work and heat exhibit pronounced asymmetry near resonance. The heat losses over a large number of periods satisfies the conventional steady-state fluctuation theorem, though different relation exists for this quantity.

cond-mat.stat-mech↗

arXiv2006

Supersymmetry and Fokker-Planck dynamics in periodic potentials

Recently, the Fokker-Planck dynamics of particles in periodic potentials $\pm V$, have been investigated by using the matrix continued fraction method. It was found that the two periodic potentials, one being bistable and the other metastable give the same diffusion coefficient in the overdamped limit. We show that this result naturally follows from the fact that the considered potentials in the corresponding Schrödinger equation form supersymmetric partners. We show that these differing potentials ${\pm}V$ also exhibit symmetry in current and diffusion coefficients: $J_{+}(F)=-J_{-}(-F)$ and $D_{+}(F)=D_{-}(-F)$ in the presence of a constant applied force F. Moreover, we show numerically that the transport properties in these potentials are related even in the presence of oscillating drive.

cond-mat.stat-mech↗

arXiv2004

Brownian rectifiers in the presence of temporally asymmetric unbiased forces

The efficiency of energy transduction in a temporally asymmetric rocked ratchet is studied. Time asymmetry favours current in one direction and suppresses it in the opposite direction due to which large efficiency ~ 50% is readily obtained. The spatial asymmetry in the potential together with system inhomogeneity may help in further enhancing the efficiency. Fine tuning of system parameters considered leads to multiple current reversals even in the adiabatic regime.

cond-mat.stat-mech↗