1. Pekarek, L., Proc. Sixth Intern. Conf. Ionization Phenomena in Gases, Paris, 1963 (edit. by P. Hubert), 2, 133 (SERMA, Paris, 1964).
2. Lee, D. A., Bletzinger, P., and Garscadden, A., J. App. Phys., 37, 377 (1966).
3. Gentle, K. W., Phys. Fluids, 9, 2212 (1966).
4. Boyd, R. L. F., and Twiddy, N. D., Proc. Roy. Soc., A, 259, 145 (1960).