1. Lemmon, E.W., McLinden, M., Huber, M.: NIST standard reference database 23, NIST reference fluid thermodynamic and transport properties -REFPROP. U.S. Deptartment of Commerce (2002)
2. Thummes, G., Wang, C., Heiden, C.: Small scale 4He liquefaction using a two-stage 4 K pulse tube cooler. Cryogenics 38(3), 337–342 (1998)
3. Zhu, S.W., Ichikawa, M., Nogawa, M., Inoue, T.: 4K pulse tube refrigerator and excess cooling power. In: Breon, S., DiPirro, M. (eds.) Advances in Cryogenic Engineering, Vol 47, Pts A and B, pp. 633–640. Amer Inst Physics, Madison, Wisconsin, USA (2002)
4. Wang, C.: Helium liquefaction with a 4 K pulse tube cryocooler. Cryogenics 41(7), 491–496 (2001)
5. Cao, Q.: Attainability of the carnot efficiency with real gases in the regenerator of the refrigeration cycle. Appl. Energy 220(15), 705–712 (2018)