Figure 3. Mean-squared displacement.

(A) Log-log plot of the mean-squared displacement vs time interval τ. (B) Mean-squared displacement divided by τ plotted as a function of τ. Random walk would gives rise to a line with zero slope. Cyan, data from the 3 trajectories showed in Fig. 2; Red, additional 9 trajectories; Blue, average of all 12 trajectories. Yellow, fit of an exponential cross-over from directed to random walk in the interval τ [10∶100] min: 〈δ(τ)²〉 = 2t_pv ²(τ−t_p(1−exp(−τ/t_p))), where v = 5.4±0.1 µm/min is a characteristic speed, and t_p = 8.8±0.1 min is a persistence time.