84 research outputs found
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 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
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