“…In recent years significant progress in the field of dry refrigerator systems has been made, for instance by Godfrin [1,2], Kirichek [3,4], Uhlig [5,6,7], and Wang [8,9] together with their respective co-workers. In the meantime, some of these and similar systems have become commercially available and are now in use in many laboratories employing low temperatures world-wide.…”