Modified Fürth Equation. The left panel shows a plot of Eq. 2, the modified Fürth equation with the axes in nondimensional units, for different values of the excess diffusion coefficient S. The black dashed line corresponds to the original Fürth equation, with S = 0. For S > 0 (colored solid lines), the short-time diffusive interval increases with S. The right panel shows the modified Fürth equation with S = 0.1. We distinguish the three different regimes characterized by Dfast, veff, and Dslow. To see this figure in color, go online.