Abstract
The origin of the sublinear frequency dependence of the ac conductivity is discussed using percolation theory. Different physical bases for calculation in different frequency regimes are discussed. Both the crossover frequencies separating the frequency regimes and the different results for the conductivity are given. The appropriate analogies between one- and three-dimensional systems are summarized. Some important comparisons with results from effective-medium theories are given. Results for the ac conductivity in one dimension and three dimensions are summarized in tabular and graphical (schematic) forms.