Effect of physicochemical transformations occurring in compacts during heating on the properties of manganese-zinc ferrites

Conclusions The temperature ranges of the physicochemical transformations occurring during heating in compacts from manganese-zinc ferrite powders produced by different methods have been established. The effect of method of preparation of ferrite powders on the character of processes taking place in compacts during heating is demonstrated. The degree of decomposition of the spinel at a given rate of heating is lower in powders produced by the carbonate coprecipitation method than in powders obtained from an oxide mixture. The reason for this is that the structure of carbonate-grade powders has comparatively few defects. Lowering the rate of heating of specimens in the temperature range 550–650C increases the degree of decomposition of the spinel, ensures a better reproducibility of properties, and improves the quality of ferrite parts.Translated from Poroshkovaya Metallurgiya, No. 10(238), pp. 62–66, October, 1982.     

Superconductivity from Repulsion: Ginzburg–Landau Phenomenology of Cuprates

We develop Ginzburg–Landau approach to the problem of superconducting pairing with large momentum under screened Coulomb repulsion (η_K-pairing). Two-component order parameter arising in this scheme can be associated with charge and orbital current degrees of freedom of the relative motion of η_K-pair corresponding to superconducting and orbital antiferromagnetic ordered states, respectively. All basic features of the phase diagram of cuprate superconductors result directly from the η_K-pairing concept. PACS numbers: 74.20.-z, 74.20.De, 74.72.-h.     

Mirror Nesting of the Fermi Contour and Superconducting Pairing from the Repulsive Interaction

We consider the necessary conditions of superconducting pairing at repulsive interaction between particles composing a pair with large total momentum: (1) the existence of, at least, one negative eigenvalue of the repulsion potential and (2) mirror nesting of the Fermi contour. Under these conditions, we represent the solution of the self-consistency equation continuously depending on the momentum of the relative motion of the pair. The corresponding superconducting order parameter changes its sign on a line crossing the Fermi contour inside the domain of definition of the relative motion pair momentum. We argue that repulsive-induced superconducting pairing with large total pair momentum maybe just the case relating to high-temperature superconducting cuprates.     

Methods for calculating the behaviour characteristics of the condition of the model of strength of resistance spot welded joints

The role of the behaviour characteristic in the development of a mathematical model is examined. The maximum compactness method and the least squares method used for determining the characteristics of the behaviour of the mathematical model are compared.