82 research outputs found
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
Fluctuation theorem for black-body radiation
The fluctuation theorem is verified for black-body radiation, provided the
bunching of photons is taken into account appropriately.Comment: 4 pages, 3 figure
Comment on "Generalized exclusion processes: Transport coefficients"
In a recent paper Arita et al. [Phys. Rev. E 90, 052108 (2014)] consider the
transport properties of a class of generalized exclusion processes. Analytical
expressions for the transport-diffusion coefficient are derived by ignoring
correlations. It is claimed that these expressions become exact in the
hydrodynamic limit. In this Comment, we point out that (i) the influence of
correlations upon the diffusion does not vanish in the hydrodynamic limit, and
(ii) the expressions for the self- and transport diffusion derived by Arita et
al. are special cases of results derived in [Phys. Rev. Lett. 111, 110601
(2013)].Comment: (citation added, published version
Diffusion of interacting particles in discrete geometries
We evaluate the self-diffusion and transport diffusion of interacting
particles in a discrete geometry consisting of a linear chain of cavities, with
interactions within a cavity described by a free-energy function. Exact
analytical expressions are obtained in the absence of correlations, showing
that the self-diffusion can exceed the transport diffusion if the free-energy
function is concave. The effect of correlations is elucidated by comparison
with numerical results. Quantitative agreement is obtained with recent
experimental data for diffusion in a nanoporous zeolitic imidazolate framework
material, ZIF-8.Comment: 5 pages main text (3 figures); 9 pages supplemental material (2
figures). (minor changes, published version
Adsorption and desorption in confined geometries: a discrete hopping model
We study the adsorption and desorption kinetics of interacting particles
moving on a one-dimensional lattice. Confinement is introduced by limiting the
number of particles on a lattice site. Adsorption and desorption are found to
proceed at different rates, and are strongly influenced by the
concentration-dependent transport diffusion. Analytical solutions for the
transport and self-diffusion are given for systems of length 1 and 2 and for a
zero-range process. In the last situation the self- and transport diffusion can
be calculated analytically for any length.Comment: Published in EPJ ST volume "Brownian Motion in Confined Geometries
Fluctuation theorem for entropy production during effusion of a relativistic ideal gas
The probability distribution of the entropy production for the effusion of a
relativistic ideal gas is calculated explicitly. This result is then extended
to include particle and anti-particle pair production and annihilation. In both
cases, the fluctuation theorem is verified.Comment: 6 pages, no figure
Models of granular ratchets
We study a general model of granular Brownian ratchet consisting of an
asymmetric object moving on a line and surrounded by a two-dimensional granular
gas, which in turn is coupled to an external random driving force. We discuss
the two resulting Boltzmann equations describing the gas and the object in the
dilute limit and obtain a closed system for the first few moments of the system
velocity distributions. Predictions for the net ratchet drift, the variance of
its velocity fluctuations and the transition rates in the Markovian limit, are
compared to numerical simulations and a fair agreement is observed.Comment: 15 pages, 4 figures, to be published on Journal of Statistical
Mechanics: Theory and Experiment
Diffusion of interacting particles in discrete geometries: equilibrium and dynamical properties
We expand on a recent study of a lattice model of interacting particles
[Phys. Rev. Lett. 111, 110601 (2013)]. The adsorption isotherm and equilibrium
fluctuations in particle number are discussed as a function of the interaction.
Their behavior is similar to that of interacting particles in porous materials.
Different expressions for the particle jump rates are derived from transition
state theory. Which expression should be used depends on the strength of the
inter-particle interactions. Analytical expressions for the self- and transport
diffusion are derived when correlations, caused by memory effects in the
environment, are neglected. The diffusive behavior is studied numerically with
kinetic Monte Carlo (kMC) simulations, which reproduces the diffusion including
correlations. The effect of correlations is studied by comparing the analytical
expressions with the kMC simulations. It is found that the Maxwell-Stefan
diffusion can exceed the self-diffusion. To our knowledge, this is the first
time this is observed. The diffusive behavior in one-dimensional and higher
dimensional systems is qualitatively the same, with the effect of correlations
decreasing for increasing dimension. The length dependence of both the self-
and transport diffusion is studied for one-dimensional systems. For long
lengths the self-diffusion shows a one over length dependence. Finally, we
discuss when agreement with experiments and simulations can be expected. The
assumption that particles in different cavities do not interact is expected to
hold quantitatively at low and medium particle concentrations, if the particles
are not strongly interacting.Comment: (18 pages, 16 figures, published version
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