A. Gnoli, A. Petri, F. Dalton, G. Gradenigo, G. Pontuale, A. Sarracino, A. Puglisi
The rectification of unbiased fluctuations, also known as ratchet effect, can be obtained under statistical non-equilibrium conditions. Recently, it has been demonstrated that it is possible to rectify the fluctuations of macroscopic mechanical devices, for instance, by suspending an asymmetric probe in a fluidized granular medium. Here we demonstrate experimentally the existence of a ratchet effect entirely originated from the Coulomb friction. Such a friction-induced torque acts in the opposite direction with respect to the net torque provided by inelastic collisions between the ratchet and the granular fluid, resulting in a resonant behaviour and a ratchet velocity inversion point. Our experimental observations are reproduced by simulations and explained by kinetic theory. Our discovery paves the way to the realization of Brownian motors in the realm of micro and sub-micrometer scales purely based upon nano-friction.
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http://arxiv.org/abs/1211.4209
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