228 research outputs found
Effect of time delay on feedback control of a flashing ratchet
It was recently shown that the use of feedback control can improve the
performance of a flashing ratchet. We investigate the effect of a time delay in
the implementation of feedback control in a closed-loop collective flashing
ratchet, using Langevin dynamics simulations. Surprisingly, for a large
ensemble, a well-chosen delay time improves the ratchet performance by allowing
the system to synchronize into a quasi-periodic stable mode of oscillation that
reproduces the optimal average velocity for a periodically flashing ratchet.
For a small ensemble, on the other hand, finite delay times significantly
reduce the benefit of feedback control for the time-averaged velocity, because
the relevance of information decays on a time scale set by the diffusion time
of the particles. Based on these results, we establish that experimental use of
feedback control is realistic.Comment: 6 pages, 6 figures, to appear in Europhysics Letter
Extracting work optimally with imprecise measurements
Measurement and feedback allows an external agent to extract work from a
system in contact with a single thermal bath. The maximum amount of work that
can be extracted in a single measurement and the corresponding feedback loop is
given by the information acquired via the measurement, a result that manifests
the close relation between information theory and stochastic thermodynamics. In
this paper we show how to reversibly confine a Brownian particle in an optical
tweezer potential and then extract the corresponding increase of the free
energy as work. By repeatedly tracking the position of the particle and
modifying the potential accordingly, we can extract work optimally even with a
high degree of inaccuracy in the measurements.Comment: 13 pages, 6 figures. Published in Entropy (open access
Closed-loop control strategy with improved current for a flashing ratchet
We show how to switch on and off the ratchet potential of a collective
Brownian motor, depending only on the position of the particles, in order to
attain a current higher than or at least equal to that induced by any periodic
flashing. Maximization of instant velocity turns out to be the optimal protocol
for one particle but is nevertheless defeated by a periodic switching when a
sufficiently large ensemble of particles is considered. The protocol presented
in this article, although not the optimal one, yields approximately the same
current as the optimal protocol for one particle and as the optimal periodic
switching for an infinite number of them.Comment: 4 pages, 4 figure
Efficiency of Brownian Motors
The efficiency of different types of Brownian motors is calculated
analytically and numerically. We find that motors based on flashing ratchets
present a low efficiency and an unavoidable entropy production. On the other
hand, a certain class of motors based on adiabatically changing potentials,
named reversible ratchets, exhibit a higher efficiency and the entropy
production can be arbitrarily reduced.Comment: LaTeX 209, 6 pages, 7 postscript figures, uses psfi
Deterministic ratchet from stationary light fields
Ratchets are dynamic systems where particle transport is induced by
zero-average forces due to the interplay between nonlinearity and asymmetry.
Generally, they rely on the effect of a strong external driving. We show that
stationary optical lattices can be designed to generate particle flow in one
direction while requiring neither noise nor driving. Such optical fields must
be arranged to yield a combination of conservative (dipole) and nonconservative
(radiation pressure) forces. Under strong friction all paths converge to a
discrete set of limit periodic trajectories flowing in the same direction.Comment: 6 pages, 4 figure
Nonequilibrium potential and fluctuation theorems for quantum maps
© 2015 American Physical Society. We derive a general fluctuation theorem for quantum maps. The theorem applies to a broad class of quantum dynamics, such as unitary evolution, decoherence, thermalization, and other types of evolution for quantum open systems. The theorem reproduces well-known fluctuation theorems in a single and simplified framework and extends the Hatano-Sasa theorem to quantum nonequilibrium processes. Moreover, it helps to elucidate the physical nature of the environment that induces a given dynamics in an open quantum system.This work has been supported by grants ENFASIS (Grant No. FIS2011-22644) and TerMic (Grant No. FIS2014-52486-R) from the Spanish Government. G.M.P. acknowledges Grant No. BES-2012-054025. This work also benefited from the COST Action MP1209.Peer Reviewe
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