In a recent paper, Parker and van Genuchten [1984] follow Brigham [1974] and Kreft and Zuber [1978] by introducing two concepts of concentration to dispersive flow. It seems that some comments on that paper may clarify certain points.In a flowing fluid the concentration of a solute may be defined in two ways, depending on the definitions of the representative elementary volume of the fluid. where C(x, s) is the Laplace transform of C(x, t) and ['/n is the nth normalized moment about the origin. Similarly, the change of moments A/• n between two observation points Xl and x2 can be found by using the following formula'
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