Rectification of current in ac-driven nonlinear systems and symmetry properties of the Boltzmann equationO. Yevtushenko, S. Flach, Y. Zolotaryuk and A. A. OvchinnikovEurophys. Lett., 54 2 (2001) 141-147DOI: https://doi.org/10.1209/epl/i2001-00287-1