Crank, J.: The mathematics of diffusion. 2nd Edn. Oxford: Clarendon Press 1979
Blender, R., Dieterich, W., Frisch, H.L.: Phys. Rev. B (to be published)
Dieterich, W., Fulde, P., Pesche, I.: Adv. Phys.29, 527 (1980)
Blender, R., Dieterich, W.: Solid State Ionics (in press)
Widder, D.V.: The heat equation. New York: Academic Press 1975
Richards, P.M.: Phys. Rev. B16, 16 (1977)