Decay model, discrete-continuum

AD-equation a Peclet number of Pe=10 is used. This gives a spread in the RTD (dispersion) that is within the range of observed values in the field. The standard deviation of the transmissivities of the channels in the network model was chosen such that the RTD of a nonsorbing tracer also has a Pe=10. In the time scale presented there seem not be dramatic differences between the model results for the Network and the AD-models. It should be noted, however, that the early arrival times are of special interest for radionuclides that decay. There the differences are considerable. Similar results were obtained in comparisons of different models using very similar data bases (Selroos et a. 2002). In that comparison a discrete fracture network model, a channel network model and a stochastic continuum model were used. 

In Section 2.2 we show how this appears approximately for a discrete state coupled to a continuum. (See also Ref. [13] for a similar buf more elaborate model.) This energy density has a pole at E = Er - iVjl, giving the exponential decay contribution... 

Using the model of Eq. (15) for phofoionization, Greenland and Lane [115] studied the effect of laser flucfuafions (i.e., fluctuations in discrete to continuum matrix elements). They obtained for the decay rate the usual result, InW-, averaged over the bandwidth and also argued, based on arguments similar to those in Ref. [13], fhat laser fluctuations eliminate the post-exponential region unless the transition is fast on the timescale of the fluctuations. 

---