1. J. M. Parpia, D. J. Sandiford, J. E. Berthold, and J. D. Reppy,Phys. Rev. Lett. 40, 565 (1978).
2. C. N. Archie, Thesis, Cornell University (1979), unpublished.
3. J. M. Parpia, Thesis, Cornell University (1979), unpublished.
4. Y. A. Ono, inPhysics at Ultralow Temperatures (Proceedings of the Hakone International Symposium, 1977), T. Sugawara, ed. (Phys. Soc. Japan, Tokyo, 1978).
5. M. J. Rice,Phys. Rev. 165, 288 (1968).