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  • 1995-1999  (1)
  • 1970-1974  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 739-746 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The maximum-entropy method (MEM) for structure determination is applied on the plastically crystalline phases of KOH and KOD characterized by delocalized H+ or D+ ions in a simple rock salt structure. The structure factors measured by neutron diffraction already give a consistent picture of the hydrogen distribution by conventional Fourier and modelling methods, which helps to understand the merit of the MEM. Owing to the negative sign of the scattering length of hydrogen, the MEM can, in a limited sense `model free', separate off the hydrogen density distribution. It is found, however, that the MEM cannot be applied naively for these compounds and reasons are given why the uniform density as a priori information has to be given up in the present case. The a priori information procedure to be used is discussed. In addition, and perhaps unexpectedly, the deuterium density is also obtained.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 230 (1970), S. 99-107 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An expression for the free energy of thes-d-exchange Hamiltonian for the caseS=1/2 is derived using Tomonaga's model for the description of the free electrons. Thereby a formal equivalence can be established to the thermodynamics of a classical gas of charged particles distributed on a ring with alternating charges interacting via a log sin-potential. Although we are unable to calculate the free energy in a closed form, the result clearly indicates that as the exchange interaction changes sign the behavior of the free energy is changed significantly for low temperatures.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 235 (1970), S. 155-165 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The free energy expression of the full Anderson model is derived in a similar way as has been done before for the Kondo model. Use is made of the “asymptotic time approximation” first invented to study the x-ray threshold singularity. Again the procedure leads to a classical Coulomb gas on a ring. The magnetic field is included and plays the role of an electric field for the Coulomb gas. Further it turns out that the “symmetric” Anderson model (2ε d =−U) is identical to the antiferromagnetic Kondo model. The method and the results suggest the construction of a “polaron” model which in the approximation used is equivalent to the Kondo model as well as the Anderson model. From this a new picture of the “Kondo effect” in terms of spin fluctuations is developed.
    Type of Medium: Electronic Resource
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