This statement does not apply to relaxation-controlled swelling processes and polymers which deviate from it also deviate from Fujita's free-volume theory. The Fokker-Planck equation reduces to this in homogenous systems. The man who discovered this relation later formulated a principle used in physiology to measure cardiac output. The Stokes-Einstein relation can be used to determine one parameter and if concentration does not change with time, one reduces to a Laplace equation. This statement actually encompasses two 
This statement does not apply to relaxation-controlled swelling processes and polymers which deviate from it also deviate from Fujita's free-volume theory. The Fokker-Planck equation reduces to this in homogenous systems. The man who discovered this relation later formulated a principle used in physiology to measure cardiac output. The Stokes-Einstein relation can be used to determine one parameter and if concentration does not change with time, one reduces to a Laplace equation. This statement actually encompasses two different relations, one which applies in steady-state conditions and another which applies in cases where concentration gradient changes over time. To determine exchange rates of gases across membranes, it is often paired with Graham's Law. FTP, identify these laws of diffusion named for a German.
This statement does not apply to relaxation-controlled swelling processes and polymers which deviate from it also deviate from Fujita's free-volume theory.
Fick's Law(s) of Diffusion