Diffusion length x_p2(p) (top) and mean acceleration time ⟨t_acc(p)⟩ (bottom) calculated in the analytical approach (i.e., it is time-independent). The model with x_A = 0.01R, x_B = 0.03R, u_AB = −2u₁ is shown with the orange line; it is calculated with Eqs. (1) and (15). The model with uniform u₂ is shown with the blue line, as from x_p = D₂/u₂ (then simply x_p ∝ p^1/3) and (14) for acceleration time. The green dashed line shows x_p1(p) upstream, and the gray dashed line corresponds to t = 420 yr.