1. J.Kurkijarvi and W.Webb, in Proc.ASC.72,IEEE New York 1973 p.581
2. A.Cavalieri, M.Cerdonio, G.Fontana, G.Jung, R.Mezzenaand S.Vitale, in Proc. of LTEC’90, Inst, of Cryogenics, Southampton 1990 p. 09. 3
3. Cryogenic Cons. Lim., model SQS6
4. A.P. Long, T.D. Clark and R.J. Prance, Rev. Seien. Instrum., 51, 8 (1980)
5. L.D. Jackel and R.A. Buhrman, J. Low Temp. Phys., 19, 201 (1974)