KOLMOGOROV-SINAI ENTROPY, LYAPUNOV EXPONENTS, AND MEAN FREE TIME IN BILLIARD SYSTEMS

We perform new experiments on the Kolmogorov-Sinai entropy, Lyapunov e xponents, and the mean free time in billiards. We study their dependen ce on the geometry of the scatterers made up of two interpenetrating s quare lattices, each one with circular scatterers with different radiu s. We find, in particular, that the above quantities are continuous fu nctions of the ratio of the scatterer radius. However, it seems that t heir derivative is discontinuous around the radius ratio which separat es the diffusive and nondiffusive types of geometries.