1. Anders, E.: 1972, in A. Elvius (ed.),Nobel Symp. No. 21, 133, J. Wiley & Sons.
2. Arnold, G. W., Jr.: 1960,J. Phys. Chem. Solids 13, 306.
3. Bishay, A.: 1970,J. Non Cryst. Solids,3, 54.
4. Bloch, M., Chalonge, D., and Dufay, J.: 1964,Ann. Astrophys. 24, 315.
5. Donn, B.: 1976,Liège Symp. No. 75.