Heat capacity of high-temperature superconductors: Analysis within the framework of the impurity mechanism

The impurity mechanism proposed earlier is used to interpret the heat properties of hightemperature superconductors. The expression for the heat-capacity jump describing its temperature and magnetic field dependences is obtained. An explanation of the dependence of the Sommerfeld constant on the stoichiometric composition is proposed.     

Photoemission spectroscopy of high-T c superconductors: Proofs in favor of the impurity mechanism

A new interpretation of photoemission spectroscopy data is proposed. It is based on the impurity mechanism of high-temperature superconductivity proposed earlier. The band observed near the Fermi level in this interpretation is the impurity band, and the observed large “Fermi surface” is the surface of the mobility edge, different in different directions. Many other details are also explained naturally.     

c-axis phonons and the enhancement of pairing correlations in high-temperature superconductors

We consider the two-dimensional Hubbard model including electron-phonon interaction. Strong local correlations (U limit) are taken into account within the mean-field approximation for auxiliary boson fields. Phonon-assisted transitions between intraand interlayer states are introduced as the source of coupling between two-dimensional CuO₂ layers. This type of processes effectively leads to the nonlinear (quadratic) interaction of intralayer electrons withc-axis phonons. We construct the Eliashberg equations for the resulting Hamiltonian and evaluate the superconducting transition temperatureT _c. Our model calculation demonstrates that a pronounced enhancement ofT _c in thed-wave channel is possible. The largest enhancement ofT _c tends to take place for small hole concentrations. This means that the coupling toc-axis phonons could compete with two-dimensional correlations responsible for the onset of antiferromagnetic order. It is remarkable that the two-dimensional features in the normal state are hardly affected by this specific interlayer interaction. Therefore,c-axis two-phonon-mediated interlayer coupling can cooperate with interlayer pair tunneling and substantially contribute to an increased pairing.     

The influence of API concentration on the roller compaction process: modeling and prediction of the post compacted ribbon,granule and tablet properties using multivariate data analysis

Objective: While previous research has demonstrated roller compaction operating parameters strongly influence the properties of the final product, a greater emphasis might be placed on the raw material attributes of the formulation. There were two main objectives to this study. First, to assess the effects of different process variables on the properties of the obtained ribbons and downstream granules produced from the rolled compacted ribbons. Second, was to establish if models obtained with formulations of one active pharmaceutical ingredient (API) could predict the properties of similar formulations in terms of the excipients used, but with a different API.

Materials and methods: Tolmetin and acetaminophen, chosen for their different compaction properties, were roller compacted on Fitzpatrick roller compactor using the same formulation. Models created using tolmetin and tested using acetaminophen. The physical properties of the blends, ribbon, granule and tablet were characterized. Multivariate analysis using partial least squares was used to analyze all data.

Results: Multivariate models showed that the operating parameters and raw material attributes were essential in the prediction of ribbon porosity and post-milled particle size. The post compacted ribbon and granule attributes also significantly contributed to the prediction of the tablet tensile strength.

Conclusions: Models derived using tolmetin could reasonably predict the ribbon porosity of a second API. After further processing, the post-milled ribbon and granules properties, rather than the physical attributes of the formulation were needed to predict downstream tablet properties. An understanding of the percolation threshold of the formulation significantly improved the predictive ability of the models.     

Analysis of a number of elements in the mechanism of mass entrainment of carbon material within the framework of the complete thermochemical model of its destruction

The results of a numerical solution of the equations constructed for a frozen boundary layer on the surface of a carbon material, with allowance for the complete thermochemical model of the entrainment of its mass, are presented. The results obtained are compared with the data that correspond to the use of the analogy between the processes of heat and mass transfer in a boundary layer and of the simplified model of the mass entrainment of the materials of the class considered. The results of comparison between experimental and calculated-theoretical data on the rate of destruction of the ATJ-grade graphite are also presented. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 127–133, January–February, 2009.