Institute de Fisica 'Gleb Wataghin,' Universidade Estadual de Campinas, Unicamp, 13083-970 Campinas, Sao Paulo, Brazil

摘要

The dependence of the Lyapunov spectrum on the strength of the external field is studied for small nonequilibrium systems. For the periodic Lorentz gas in two and three dimensions the coefficient of the square of the field is largest in magnitude for the largest exponent, and decreases with each successively smaller exponent. The lowest level periodic orbit expansion approximation for the two-dimensional Lorentz gas, which can be calculated analytically, has the same qualitative behavior as a function of external field. Using periodic orbits of length 2 the dynamical origin of the observed field dependence is investigated.