27 research outputs found
Transport Coherence in Frictional Ratchets
We study the phenomena of noise induced transport in frictional ratchet
systems. For this we consider a Brownian particle moving in a space dependent
frictional medium in the presence of external white noise fluctuations. To get
the directed transport, unlike in other ratchet models like flashing or rocking
ratchets etc., we do not require the potential experienced by the particle to
be asymmetric nor do we require the external fluctuations to be correlated. We
have obtained analytical expressions for current and the diffusion coefficient.
We show that the frictional ratchet do not exhibit a pronounced coherence in
the transport in that the diffusion spread overshadows the accompanying
directed transport in system with finite spatial extensions.Comment: Based on the poster presentation (by RK) at the Condensed Matter Days
- 2003 held at Jadavpur University, Kolkata, India from 27-29 August 2003.
Minor corrections have been don
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.Comment: 4 pages, latex/revtex, 4 eps figures. Proceedings of CMDAYS2K, held
at Guru Ghasidas University, Bilaspur, Chattisgarh, India, Aug 29-31, 2
Giant diffusion and coherent transport in tilted periodic inhomogeneous systems
We investigate the dynamics of an overdamped Brownian particle moving in a washboard potential with space dependent friction coefficient. Analytical expressions have been obtained for current and diffusion coefficient. We show that the effective diffusion coefficient can be enhanced or suppressed compared to that of the uniform friction case. The diffusion coefficient is maximum near the critical threshold (Fc), which is sensitive to temperature and the frictional profile. In some parameter regime, we observe that increase in noise (temperature) decreases the diffusion, which is counterintuitive. This leads to coherent transport with large mean velocity accompanied by small diffusion. This is shown explicitly by analysis of Peclet number, which has been introduced to study coherent or optimal transport. This phenomenon is complementary to giant diffusion
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
A biologically inspired ratchet model of two coupled Brownian motors
A ratchet model for coupled Brownian motors, inspired by the motion of individual two-headed molecular motors on cytoskeletal filaments, is proposed. Such motors are modeled as two elastically coupled Brownian particles, each of which moves in a flashing ratchet potential. The ratchet potentials felt by the individual particles are anti-correlated, modeling the successive binding and unbinding of the two motor heads to the filament. We obtain, via Langevin simulations, steady-state currents as functions of noise strength, the equilibrium separation of the particles and the rate of switching between potential states. We observe an enhanced current due to coupling, noise-induced stability and phase-locked behaviour in the deterministic regime. A qualitative understanding of these features is provided
Ultrashort pulse generation in modeless laser cavity
We demonstrate experimentally that random phase modulation of an erbium-doped
fiber ring-laser by an intra-cavity electro-optic phase modulator did not
inhibit ultra-short pulse operation (so-called mode-locking). Stable and
self-starting operation was achieved even when the phase modulator was driven
with random sequences sufficiently fast and strong to render the laser cavity
modeless, as determined by heterodyne measurements. No significant change in
the pulse characteristics was observed. The insensitivity to the random phase
modulation is expected, given the lack of phase-sensitive elements in the
cavity.Comment: Manuscript submitted to Optics Express. Final Manuscript Decisio
Stochastic Resonance in Washboard Potentials
We study the mobility of an overdamped particle in a periodic potential
tilted by a constant force. The mobility exhibits a stochastic resonance in
inhomogeneous systems with space dependent friction coefficient. The result
indicates that the presence of oscillating external field is not essential for
the observability of stochastic resonance, at least in the inhomogenous medium.Comment: 10 pages, 3 figure
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