[en] The Mattis spin glass model is described as following from a particular quenched random solid solution picture, and its zero-field properties are discussed. The random field model is reviewed. The application to the spin glass problem is made and the more general scaling theory presented, and the limitations of the model are discussed

[en] Renormalization-group techniques are applied to a model Hamilonian recently proposed by Harris, Plischke, and Zuckerman for the description of amorphous magnets. In this model, a single-ion uniaxial anisotropy, with a random direction of the axis of anisotropy, is introduced. Averaging over this random variable yields an (translationally invariant) effective Hamiltonian, in which the m-component spin variable is replaced by an nm-component vector, and n is finally set equal to zero. Contrary to the result for an isotropic random perturbation, the fixed-point describing the nonrandom m-component critical behavior is unstable with respect to terms Hamiltonian generated by the randomness, the appropriate crossover exponent being given exactly by (2phi/sub m/--2 + α/sub m/), where phi/sub m/ is the Fisher--Pfeuty anisotropic spin crossover exponent and c/sub m/ is the specific-heat exponent. Depending on the distribution function for the random anisotropy directions, there are seven or thirteen other fixed points. Most of these are unstable, and the recursion relations probably yield a ''runaway'' which is interpreted as a smeared transition. Experiments on amorphous TbFe₂ are discussed. (auth)

[en] A Flory approximat for the exponent describing the end-to-end distance of a self-avoiding walk (SAW) on fractals is derived. The approximat involves the fractal dimensionalities of the backbone and of the minimal path, and the exponent describing the resistance of the fractal. The approximant yields values which are very close to those available from exact and numerical calculations

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[en] The necessity of the assumption of time reversal symmetry in the proofs of both the H theorem and the Onsager relations is investigated in relation with the system of neutral kaons. The master equation description of the neutral kaon system, the H theorem, the stationary state and Onsager relations, and the arrows of time. (U.S.)

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[en] The structural phase transition occurring in NbO₂ is analysed using renormalisation group techniques. It is suggested that the observed crossover in the order parameter critical exponent β from β = approximately 0.19 to β = approximately 0.39 may reflect a crossover from Lifshitz to ordinary critical behaviour. This phenomenon is associated with the strongly anisotropic dispersion relation found in this compound. (author)

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