1. W. P. Halperin,Proceedings of the 16th International Conference on Low Temperature Physics, Part 3, W. G. Clark, ed. (North-Holland, Amsterdam, 1981), p. 1596.
2. J. B. Ketterson, B. S. Shivaram, M. W. Meisel, B. K. Sarma, and W. P. Halperin,Quantum Fluids and Solids - 1983, E. D. Adams and G. G. Ihas, eds. (American Institute of Physics, New York, 1983), p. 288.
3. P. Hakonen, O. V. Lounasmaa, and J. Simola,Physica B 160, 1 (1989).
4. P. Wölfle and V. E. Koch,J. Low Temp. Phys. 30, 61 (1978).
5. R. Ling, W. Wojtanowski, J. Saunders, and E. R. Dobbs,J. Low Temp. Phys. 78, 187 (1990).