A model of this process in multicomponent systems that permits its namesake coefficients to be negative was developed independently by Maxwell and Stefan. An ensemble of photons can be modeled with equations for this process in materials with high optical depth and low mean free path. Two laws of this process give the time 
A model of this process in multicomponent systems that permits its namesake coefficients to be negative was developed independently by Maxwell and Stefan. An ensemble of photons can be modeled with equations for this process in materials with high optical depth and low mean free path. Two laws of this process give the time derivative of the field as k times the second position derivative of the field and give the flux J as negative k times the first position derivative; those are (*) Fick's laws. For 10 points, identify this process referred to as "osmosis" when the substance in question is water, in which molecules move down a gradient from regions of high concentrations to regions of lower concentrations.
A model of this process in multicomponent systems that permits its namesake coefficients to be negative was developed independently by Maxwell and Stefan.
molecular {diffusion} [prompt on {osmosis} before mention]