Likely presence of superconductivity in layered nickelates of K₂NiF₄ structure is pointed out.

A method is presented for an accurate numerical determination of eigenvalues of real symmetric para-p diagonal matrices. The method takes advantage of the band structure to break up the matrix intop ×p blocks and performing algebraic operations including inversions on these blocks only, no matter what the size of the matrix is. The eigenvalues are determined independently one at a time. Thus any error in the determination of one eigenvalue does not affect the other eigenvalues. The method is ideally suited for the Schrödinger eigen alue problem of the anharmonic potentials, which is taken up in the following paper.

Energy eigenvalues and matrix elements of various anharmonic oscillators are determined to a high accuracy by applying a method for determining the eigenvalues and eigenvectors of real symmetric para-p diagonal matrices (described in the preceding paper). Our results for the 2- and 3-dimensional oscillators are new and complement similar accurate results for the one dimensional oscillators available in the literature.

The Hartree-Fock procedure is used to study the behaviour of the ground state of a system ofM spinless electrons distributed overN equivalent and equidistant sites (M ⩽N) as a function of the strength of the mutual repulsion between the electrons. Below a critical strength, all initial configurations are seen, after repeated iterations, to converge to a unique solution. Above this critical strength, in addition to the initial configurations which lead to a unique solution, there exist configurations which on repeated iterations give rise to stable two-period solutions. Although the number of independent stable two-period solutions depends on the coupling strength, for no value of the coupling are stable solutions of periodicity higher than two seen.

The modified variable-charge Coulomb-projected Born approximation is applied to electron impact excitation of 1¹S–2¹S transition in helium. The results are compared with other theoretical and experimental results.

Elastic differential cross-sections for thee-O₂ ande-O₃ systems are obtained in the independent atom model at high energies (E_i ⩾ 300 eV). The basic atomic scattering amplitudes are obtained in the partial wave method through a sum of static exchange and polarization potentials. Oure-O₂ results agree with experiments except for small angles. No data are available for O₃, for comparison.

A comparative study of the methods for oxygen stoichiometry—direct inert gas fusion method and two indirect iodometric methods—has been carried out. The indirect iodometric method in which Cu(III) is directly estimated, has been found to be more precise. Several samples of YBa₂Cu₃O_x of varyingx, their fluorine-substituted counterparts and also Bi₂Sr₂Ca₁Cu₂O_x and Tl₂Ba₂Ca₁Cu₂O_x have been analysed.

The theory of free-carrier absorption (FCA) is developed, in the extreme quantum limit when the carriers are assumed to populate only the lowest quantized energy level, for quasi-two and one-dimensional semiconducting quantum well structures where the carriers are scattered by ionized impurities. The radiation field is assumed to be polarized in the plane of the layer in the quasi-two-dimensional case and along the length of the wire in the quasi-one-dimensional case. Expressions for FCA are obtained for the cases where the impurities are either in the well (background impurities) or outside the well (remote impurities). Variation of FCA is numerically studied with photon frequency and well width.

Electrical conductivity and thermoelectric power of liquid-quenched Bi-Sb tapes with Sb concentration in the range 8 to 18 at.% are reported between 77K and room temperature. Analysis of the data shows that the total electrical conductivity of these tapes is determined by a temperature-independent component due to band conduction, and a strongly temperature-dependent part due to carrier transport across or through the defect states. These defect states which appear to originate from structural imperfections and disorders due to rapid cooling, are formed close to the mobility edge within a small energy range.