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  • 1970-1974  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Heat exchange in liquid helium by phonon tunneling through very thin plates (1971)
    Springer
    Journal of low temperature physics 4 (1971), S. 263-271 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Thin plates with a thicknessd smaller than the phonon mean-free path can be used to increase the heat exchange in 3 He- 4 He refrigerators at very low temperatures. The resistanceR for the heat current density of these plates is theoretically investigated. For plates withd still larger than the dominant thermal-phonon wavelength λ T in the plate,R is given by twice the Kapitza resistance. Ford ≈ λ T the resistanceR decreases due to phonon tunneling. Ford ≪ λ T there exists a region whereR varies asT −1, in contrast to theT −3 dependence for thicker plates. Numerical calculations are carried out for copper plates immersed in pure 4 He. The results show that one obtains a large increase of the heat exchange due to phonon tunneling for plates with a thickness of a few microns at temperatures in the millidegree range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00629713
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A quantum mechanical determination of the superfluid density (1972)
    Springer
    The European physical journal 14 (1972), S. 324-335 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The constituting conservation laws for a superfluid are quantum mechanically derived. Using thermodynamic relations the superfluid density is model-independently expressed in terms of reduced-density matrices. The general relation is illustrated for the Bogolubov model, and for two other approximations for the two-particle reduced-density matrix. The resulting relations between the densities of the super component and of the condensate are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02422689
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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