“…Apart from the large number of results which are based on either highly approximated micromodels or ad hoc mixing rules, several approaches based on reasonable physical models have also been established and refined to include the effects of various particle shapes plus imperfect thermal contact between the particle surface and the continuous medium. Such studies include: exact mathematical analysis of dilute systems in which bounds are established on the effective properties, and asymptotic behavior is determined (see, for example, Beasley and Torquato [2], and Thovert and Acrivos [3]); exact mathematical analysis of various regular arrays of particles (see, for example, McKenzie et al [4], Gu and Tao [5], Gu and Liu [6], Torquato and Rintoul [7], and Cheng and Torquato [8]); numerical simulation of Brownian diffusion of pulsed sources through particle arrays (see, for example, Torquato and Kim [9], and Kim and Torquato [10]); the self-consistent field concept for analyzing non-dilute, non-regularly spaced particles (see, for example, Hashin [11], Benveniste and Miloh [12], and Benveniste [13]); and the technique of Ôsuccessive embedding of effective media' to treat multi-coated cylinders or spheres (see, for example, Schulgasser [14], and Milgrom and Shtrikman [15]). …”