On statistics and 1/f noise of Brownian motion in Boltzmann-Grad gas and   finite gas on torus. II. Finite gas
  An attempt is made to compare statistical properties of self-diffusion of particles constituting gases in infinite volume and on torus. In this second part, derivation, from BBGKY equations, of roughened model of self-diffusion is revised as applied to finite $N$-particle gas under micro-canonical ensemble. The model confirms existence of characteristic time $\approx N$, in units of free flight time, for cross-over between non-Gaussian and Gaussian regimes of diffusion, but then loses its legacy. 
Yuriy E. Kuzovlev