Estimating effective thermal damage process coefficients for the first order kinetic model of damage processes is not difficult when the temperature is held constant for a substantial period. Laser coagulation experiments, however, are of short duration and, because of non uniform beam profiles, exhibit important heat transfer effects: the thermal histories are transient by nature and spatial temperature gradients are significant. An attempt is made to obtain useful estimates of activation energy, E, and collision frequency factor, A, directly from the transient history at the boundary of the zones of white coagulation and red hemorrhagic coagulation in liver in the rat, as identified by histologic studies. The Trial Region Method proves to be effective for transient data, in that a useful estimate of A and E can be obtained even from a single temperature curve. However, the results are very sensitive to small uncertainties in the actual value of Ω for the transient thermal histories to which the method is applied.

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