1. Apsel, D. (1981).Gen. Rel. Grav.,13, 605.
2. Yovanovitch, D. D. (1960).Phys. Rev.,117, 1580.
3. Lederman, L. M., and Weinrich, M. (1956). In CERN Symposium on High Energy Accelerators and Pion Physics, Geneva, p. 427.
4. Culligan, G., Hartling, D., Lipman, N. H., and Tibell, G. (1961). In International Conference on Elementary Particles, Aix, France, p. 143.
5. Huff, R. W. (1961).Ann. Phys. (N.Y.),16, 288.