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

Thermodynamics of a minimal collective heat engine: Comparison between engine designs

Collective effects have attracted remarkable recent interest, not only for their presence in several systems in nature but also for the possibility of being used for the construction of efficient engine setups. Notwithstanding, little is known about the influence of the engine design and most studies are restricted to the simplest cases (e.g. simultaneous contact with two thermal baths), not necessarily constituting a realistic setup implementation. Aimed at partially filling this gap, we introduce the collisional/sequential description for a minimal model for collective effects, composed of two interacting nanomachines placed in contact with a distinct thermal reservoir and nonequilibrium worksource at each stage/stroke. Thermodynamic quantities are exactly obtained irrespectively the model details. Distinct kinds of engines are investigated and the influence of the interaction, temperature, period, and time asymmetry have been undertaken. Results show that a careful design of interaction provides a superior performance than the interactionless case, including optimal power outputs and efficiencies at maximum power greater than known bounds or even the system presenting efficiencies close to the ideal (Carnot) limit. We also show that the case of the system simultaneously placed in contact with two thermal reservoirs constitutes a particular case of our framework.Comment: 12 pages, 9 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