Entropy production and rectification efficiency in colloids transport along a pulsating channel

We study the current rectification of particles moving in a pulsating channel under the in uence of an applied force. We have shown the existence of diferent rectification scenarios in which entropic and energetic effects compete. The effect can be quantified by means of a rectification coefficient that is analyzed in terms of the force, the frequency and the diffusion coefficient. The energetic cost of the motion of the particles expressed in terms of the entropy production depends on the importance of the entropic contribution to the total force. Rectification is more important at low values of the applied force when entropic effects become dominant. In this regime, the entropy production is not invariant under reversal of the applied force. The phenomenon observed could be used to optimize transport in microfluidic devices or in biological channels

Geometrically-tuned channel permeability

We characterize the motion of charged as well as neutral tracers, in an electrolyte embedded in a varying section channel. We exploit a set of systematic approximations that allows us to simplify the problem, yet capturing the essential of the interplay between the geometrical confinement provided by the corrugated channel walls and the electrolyte properties. Our simplified approach allows us to characterize the transport properties of corrugated channels when a net flux of tracers is obtained by keeping the extrema of the channel at different chemical potentials. For highly diluted tracer suspensions, we have characterized tracers currents and we have estimated the net electric current which occurs when both positively and negatively charged tracers are considered.Comment: Fixed reference

Driving an electrolyte through a corrugated nanopore

We characterize the dynamics of a $z-z$ electrolyte embedded in a varying-section channel. In the linear response regime, by means of suitable approximations, we derive the Onsager matrix associated to externally enforced gradients in electrostatic potential, chemical potential, and pressure, for both dielectric and conducting channel walls. We show here that the linear transport coefficients are particularly sensitive to the geometry and the conductive properties of the channel walls when the Debye length is comparable to the channel width. In this regime, we found that one pair of off-diagonal Onsager matrix elements increases with the corrugation of the channel transport, in contrast to all other elements which are either unaffected by or decrease with increasing corrugation. Our results have a possible impact on the design of blue-energy devices as well as on the understanding of biological ion channels through membrane

Nonequilibrium Stefan-Boltzmann law

We study thermal radiation outside equilibrium. The situation considered consists of two bodies emitting photons at two different temperatures. We show that the system evolves to a stationary state characterized by an energy current which satisfies a Stefan-Boltzmann-like law expressing it as the difference of the temperatures to the fourth power of the emitters . The results obtained show how the classical laws governing the thermal radiation at equlibrium can be generalized away from equilibrium situations.Comment: 9 pages, 1 figure. To be published in J. Noneq. Ther

Radiative heat shuttling

We demonstrate the existence of a shuttling effect for the radiative heat flux exchanged between two bodies separated by a vacuum gap when the chemical potential of photons or the temperature difference is modulated. We show that this modulation typically gives rise to a supplementary flux which superimposes to the flux produced by the mean gradient, enhancing the heat exchange. When the system displays a negative differential thermal resistance, however, the radiative shuttling contributes to insulate the two bodies from each other. These results pave the way for a novel strategy for an active management of radiative heat exchanges in nonequilibrium systems