−5 −3 −1 1 3 5 l 0 0.2 0.4 P M=36m M=60m M=120m −5 −3 −1 1 3 5 l 10 −4 10 −3 10 −2 10 −1 P M=36m M=60m M=120m FIG. 2: Steady position distribution of the piston P ( l ) in both normal and logarithmic scales. The symbols are from the simulations while the solid lines are Gaussian with unity dispersion. The data correspond to three systems differing in the mass of the piston, as indicated. The coefficient of normal restitution for the particle collisions is α = 0 . 94. The dimensionless length ℓ is defined 9