Diffusion and collective motion of rotlets in 2D space
(a) Average velocity 〈 v 〉 = 〈 |v| 〉 as a function of the area fraction. (b) The velocity auto-correlation function as a function of the elapsed time τ (initial state: random). The inset shows the relaxation time of the velocity auto-correlation function τ0 as a function of the area fraction.
