Number of particles remaining in the percolation fractal

These results reveal that the same law describes release from both fractal and Euclidean matrices. The release rate is given by the time derivative of (4.14). For early stages of the release, calculating the derivative of (4.14) and performing a Taylor series expansion of the exponential will result in a power law for the 

2The classical kinetics solution is obtained by solving (4.13) in case of g(t) = 1. 

When Fickian diffusion in normal Euclidean space is justified, further verification can be obtained from the analysis of 60% of the release data using the power law in accord with the values of the exponent quoted in Table 4.1. Special attention is given below for the values of b in the range 0.75-1.0, which indicate a combined release mechanism. Simulated pseudodata were used to substantiate this argument assuming that the release obeys exclusively Fickian diffusion up to time t = 90 (arbitrary units), while for I, 90 a Case II transport starts to operate too this scenario can be modeled using 

the following equation was used to simulate concurrent release mechanisms of Fickian diffusion and Case II transport throughout the release process  

In bioerodible drug delivery systems various physicochemical processes take place upon contact of the device with the release medium. Apart from the classical physical mass transport phenomena (water imbibition into the system, drug dissolution, diffusion of the drug, creation of water-filled pores) chemical reactions (polymer degradation, breakdown of the polymeric structure once the system becomes unstable upon erosion) occur during drug release. 

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