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2. W.J. Briscoe, D.H. Fitzgerald, B.M.K. Nefkens, B.H. Silverman, A. Boudard, G. Bruge, P. Couvert and C. Glashausser, to be published.
3. X. Maruyama, private communication.
4. Proc. Third Int. Cryogenics Engineering Conf.;Buhler,1971