Symmetric Brownian motor

In this paper, we present a model of a symmetric Brownian motor which changes the sign of its velocity when the temperature gradient is inverted. The velocity, external work, and efficiency are studied as a function of the temperatures of the baths and other relevant parameters. The motor shows a current reversal when another parameter (a phase shift) is varied. Analytical predictions and results from numerical simulations are performed and agree very well. Generic properties of this type of motor are discussed.

Heat fluctuations in Brownian transducers

The heat fluctuation probability distribution function in Brownian transducers operating between two heat reservoirs is studied. We find, both analytically and numerically, that the recently proposed fluctuation theorem for heat exchange [C. Jarzynski and D. K. Wojcik, Phys. Rev. Lett. 92, 230602 (2004)] has to be applied carefully when the coupling mechanism between both baths is considered. We also conjecture how to extend such a relation when an external work is present.

Heat transfer between nanoparticles: Thermal conductance for near-field interactions

We analyze the heat transfer between two nanoparticles separated by a distance lying in the near-field domain in which energy interchange is due to the Coulomb interactions. The thermal conductance is computed by assuming that the particles have charge distributions characterized by fluctuating multipole moments in equilibrium with heat baths at two different temperatures. This quantity follows from the fluctuation-dissipation theorem for the fluctuations of the multipolar moments. We compare the behavior of the conductance as a function of the distance between the particles with the result obtained by means of molecular dynamics simulations. The formalism proposed enables us to provide a comprehensive explanation of the marked growth of the conductance when decreasing the distance between the nanoparticles.

En olor de santidad. La actitud del cristianismo hacia la cultura del baño

Los primeros siglos de la historia del cristianismo contemplaron la aparición del ascetismo, un movimiento que propugnaba el abandono de los modos de vida típicamente urbanos que caracterizaron el mundo grecolatino con el que los ascetas deseaban romper. Los hábitos higiénicos simbolizaban en buena medida este mundo del que deseaban alejarse. Así, los relatos de vidas de eremitas están llenos de referencias a esta ruptura con la cultura del baño. Jerónimo, gran defensor del anacoretismo, critica la higiene, en más de una ocasión, con palabras que recuerdan a ciertos pasajes de los Evangelios. La prohibición del baño también se encuentra en las primeras reglas monásticas. Estas posturas extremistas no representaban la opinión oficial de la Iglesia ni la de la gran masa del vulgo que profesaba la religión cristiana, quien continuaba frecuentando las termas. Los obispos de algunas ciudades, incluso, fueron los responsables de que determinadas termas públicas continuaran en uso.