Peter G. O. Freund and Enrico Predazzi
Physics Physique Fizika 3, 81 (1967) - Published 1 February, 1967
R. P. Hudson and R. S. Kaeser
Physics Physique Fizika 3, 95 (1967) - Published 1 February, 1967
L. Gunther, M. Revzen, and A. Ron
Physics Physique Fizika 3, 115 (1967) - Published 1 February, 1967