LAUSR

Grains are vibrated so as to achieve a granular gas, here regarded as an archetype for a dissipative Non Equilibrium Steady State (NESS). We report on two distinct and concordant experimental measures of the system effective temperature. To do so, a blade fastened to the shaft of a small DC-motor, immersed in the grains, behaves as a driven 1D Brownian rotator which is used as both actuator and sensor, simultaneously. On the one hand, the Gallavotti-Cohen Fluctuation Theorem (FT), which involves a measure of the asymmetry of the energy exchanges between the rotator and the NESS reservoir, provides a first effective temperature. On the other hand, the Fluctuation-Dissipation Theorem (FDT), which involves the relation between the spontaneous fluctuations and the response to a weak perturbation, defines a second, independent, effective temperature. Both methods, even though they are based on drastically different ideas, give nicely concordant results.