1. W. E. Gifford and H. O. McMahon, “A New Refrigeration Process,” Proceedings of the Tenth International Congress of Refrigeration, Copenhagen, Denmark (August, 1959).
2. W. E. Gifford and H. O. McMahon, “A New Low-Temperature Gas-Expansion Cycle” (Parts I and II), Advances in Cryogenic Engineering, Vol. 5, K.D. Timmerhaus (ed.), Plenum Press, Inc., New York (1960).