Question $3(45$ pts$).$ The flow and migration of human polymorphonuclear leukocytes on prosthetic material surfaces can be solved by the diffusion$-$convection equation:

$\frac{\text{d}\text{e}\text{l}\text{C}}{\text{d}\text{e}\text{l}\text{t}}={}_D\frac{de{l}^{2}C}{del{z}^2}-v_{\text{e}\text{f}\text{f}}\frac{\text{d}\text{e}\text{l}\text{C}}{\text{d}\text{e}\text{l}\text{z}}$

Assume that the value of the directional migratory velocity of cells is insignificant, i$.$e$.,$

$($