1. I. Pomeranchuk, Zh. Eksp. i Teor. Fiz. (USSR) 20, 919 (1950).
2. There are several elegant and systemattic discussions of the compressional cooling technique. Some especially useful discussions about compressional cooling and crygenic methods in general are contained in the textbooks by Betts and Lounasmaa.
3. Betts, D. S., Refrigeration and Thermometry Below 1K, Sussex University Press, London (1974)
4. O.V. Lounasma, Experimental Principles and Methods Below 1K, Academic Press, NY (1974).
5. L.D. Landau, Zh. Eksp. i Teor. Fiz. (USSR) 30, 1058 (1956).