Power injected in dissipative systems and the fluctuation theorem

We consider three examples of dissipative dynamical systems involving many degrees of freedom, driven far from equilibrium by a constant or time depen dent forcing. We study the statistical properties of the injected and dissi pated power as well as the fluctuations of the total energy of these system s. The three systems under consideration are: a shell model of turbulence, a gas of hard spheres colliding inelastically and excited by a vibrating pi ston, and a Burridge-Knopoff spring-block model. Although they involve diff erent types of forcing and dissipation, we show that the statistics of the injected power obey the "fluctuation theorem" demonstrated in the case of t ime reversible dissipative systems maintained at constant total energy, or in the case of some stochastic processes. Although this may be only a conse quence of the theory of large deviations, this allows a possible definition of "temperature" for a dissipative system out of equilibrium. We consider how this "temperature" scales with the energy and the number of degrees of freedom in the different systems under consideration.