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  • Articles: DFG German National Licenses  (15)
  • 1985-1989  (9)
  • 1965-1969  (6)
  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 11 (1989), S. 123-139 
    ISSN: 0392-6737
    Keywords: Heat capacities of liquids ; Functional analytic methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si presentano i risultati di una formulazione basata sugli integrali di cammino applicata alla termodinamica di un sistema a due stati accoppiato agli elettroni di conduzione. Si mostra che l'usuale approssimazione di un gas diluito di «bounce» è inadeguata nel caso di debole smorzamento e basse temperature e si presenta pertanto un'appropriata generalizzazione. Il modo di valutare esattamente la funzione di partizione di un sistema a due stati debolmente smorzato è quello di generalizzare un singolo «bounce» a una classe di insiemi irriducibili di «bounce» multipli con interazioni interne e di considerare questi insiemi come un gas diluito. Si ricavano le espressioni per la funzione di partizione e per il calore specifico. Si discute anche il caso di un sistema a due stati in presenza di moderata asimmetria.
    Abstract: Резюме Приводятся результаты применения метода интегрирования по траекториям к термодинамике системы с двумя состояниями, связанной с электронами проводимости. Показывается, что стандартное приближение разжиженного газа не является адекватным для слабого затухания и при низких температурах. Предлагается соотаетствующее обобщение. Для выписления функции распределения для слабо затухающей системы с двумя состояниями необходимо обобщение рассматриваемого приближения для класса неприводимых кластеров с внутренними взвимодействиями, в затем рассматривать эти кластеры, как разжиженный газ. Приводятся количественные выражения для функции распределения и для удельной теплоёмкости. Так же обсуждается случай смещения.
    Notes: Summary The results of a path integral approach to the thermodynamics of a two-state system coupled to conduction electrons are presented. It is shown that the standard dilute bounce gas approximation is inadequate for weak damping and low temperatures and the appropriate generalization is presented. The strategy to evaluate exactly the partition function of a weakly damped two-state system is to generalize a single bounce to a class of irreducible multibounce clusters with internal interactions and to consider these clusters as a dilute gas. Quantitative expressions for the partition function and for the specific heat are presented. The case of a bias is also discussed.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 228 (1969), S. 1-15 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The (e, H) collision problem is treated using the multichannel quasiparticle method recently introduced by Grassberger and Sandhas. We derive single variable integral equations for the singlet and triplet transition amplitudes valid for scattering energies up toE≈8 eV and especially calculate the scattering lengths which are in good agreement with previous results found by variational methods.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 68 (1987), S. 193-199 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The quantum-mechanical decay of a metastable state of a system coupled to a heat bath environment is studied. A functional integral method is presented allowing for the calculation of decay rates at finite temperatures and in the presence of dissipation. Analytical methods for high and intermediate temperatures are combined with an accurate numerical method for low temperatures where the system decays by quantum tunneling. Explicit results are given for a system with a cubic potential and frequency-independent damping.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 68 (1987), S. 213-244 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The dynamics of a quantum particle tunneling through the barrier of an almost symmetric double-well potential is studied. The coherent quantum oscillations characteristic for isolated tunneling systems are shown to be strongly affected by the interaction with a heat bath environment. Attention is focused on the situation where the heat bath causes an Ohmic damping. This case is of potential relevance to the problem of macroscopic quantum coherence in SQUID rings. The range of parameters in which quantum coherence survives is determined and the time evolution of the occupation probabilities in the two wells is calculated.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 31 (1986), S. 147-152 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The motion of a particle in a metallic crystal is studied for low temperatures where transitions between adjacent interstitial sites are caused by quantum tunneling. The influence of electrons and phonons on the hopping rate is taken into account by means of a functional integral method. The electronic influence may effectively be described by Ohmic damping which dominates the low temperature behavior of the defect motion. When subsequent tunneling transitions are statistically independent, the diffusion constant is found to obey a power law, D∼T2K−1, where K depends on the defect-electron interaction. This power law is limited at low temperatures by the effects of phonon excitations. Near the transition between electron and phonon dominated behavior the diffusion constant has a minimum where the precise temperature dependence of the rate depends not only on phonon spectra but also on the processes limiting phonon lifetimes.
    Type of Medium: Electronic Resource
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