Physical/thermal activation process temperature coefficients

The use of the same exponent, s, for both coefficients is a simplification this could be refined by considering two separate exponents, S and S2-Finally, we consider the temperature dependence. The coefficients Dy describe the interaction between two different species, and it is physically plausible to assume that the interaction becomes weaker with temperature. We will also adopt an Arrhenius law behaviour as is typical of thermally activated interaction processes. As a first approximation, we assume that all three interaction coefficients vary in the same way, so that their temperature dependence is given through the temperature dependence of the coefficient D 2, which we write as... 

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