1. I. A. Sellin, ed., Topics in Current Physics, Vol. 5 (Springer-Verlag, Berlin, 1978).
2. N. Stolterfoht, in Topics in Current Physics, Vol. 5, ed. by I. A. Sellin (Springer-verlag, Berlin, 1978), p. 155.
3. P. H. Mokier and F. Folkmann, in Topics in Current Physics, Vol. 5, ed. by I. A. Sellin (Springer-Verlag, Berlin, 1978), p. 201.
4. I. A. Sellin, in Topics in Current Physics, Vol. 5, ed. by I. A. Sellin (Springer-Verlag, Berlin, 1978), p. 273.
5. J. S. Briggs and K. Taulbjerg, in Topics in Current Physics, Vol. 5, ed, by I. A. Sellin (Springer-Verlag, Berlin, 1978), p. 105.