Using the continuum theory of linear elasticity, Huang diffuse scattering (HDS) has been calculated from self-interstitials in a general orthorhombic and tetragonal lattice. Various defect configurations are represented according to the point group symmetry of the defect site. The contribution toHDS from all possible equivalent orientations (assumed to be equally populated) of the defect configuration is averaged. The limitations ofHDS in discriminating between defect configurations having the same long-range symmetry are discussed, considering some special cases.

Using the continuum theory of linear elasticity, diffuse x-ray scattering has been calculated in the immediate neighbourhood of Bragg peaks from point defects in a lattice containing more than one atom in the unit cell. General expressions are obtained for the Debye-Waller factor, Huang diffuse scattering and the asymmetric scattering due to the defect. For lattices with one atom per unit cell, these expressions reduce to the well-known formulae of diffuse scattering.

A study is made for the search of superheavy nuclei in Marjalahti, Eagle Station and in other pallasite olivines. The olivine crystals are calibrated for heavy ion track lengths by using heavy ion beams from cyclotrons. The calibration for ultra heavy ions which are presently not available with sufficient energy to produce volume tracks in olivine crystals, is based on Katz and Kobetich model of track formation. The length spectrum of volume tracks, revealed by puncturing them with focussed Nd-glass laser beam, is measured and the abundances of different nuclei groups are calculated. Partial annealing has been used at 430°C for 32 hr which eliminates the interfering tracks due to nuclei of atomic numberS ≤ 50. During the scanning 4 cm³ olivine crystals, about 360 long tracks of uranium group as well as two very long tracks have been found. If these tracks belong to superheavy nuclei, the relative abundance of super heavies is found to be 6 × 10⁻¹¹ in galactic cosmic rays.

Following the work of Arms, Fischer, Marsden and Moncrief, it is proved that the space of solutions of Einstein’s equations coupled with self-gravitating mass-less scalar fields has conical singularities at each spacetime possessing a compact Cauchy surface of constant mean curvature and a nontrivial set of simultaneous Killing fields, either all spacelike or including one (independent) timelike.

Electrical and galvanomagnetic properties of Co_x Sn_1−x Te thin films have been studied. On the basis of small positive temperature coefficient of resistance, small and constant resistivity, low Hall coefficient and negligible magnetoresistance, it was concluded that CoTe-SnTe system is metallic. Discussion employing the Sondheimer’s model further corroborated the metallic nature of the thin films.

The perturbation theory of Weeks, Chandler and Anderson (WCA) has been employed to calculate the free energy and compressibility factor of simple dense fluids characterised by a double Yukawa potential. The structure factor has been calculated in the random phase approximation together with theWCA prescription for the division of the pair potential. The calculated values are in excellent agreement with experimental results.

The radial distribution function (RDF) and thermodynamic properties of a two-dimensional hard-disc mixture are calculated by using the perturbation theory. Numerical results are given for theRDF, pressure and excess-free energy of the binary mixture of both additive and non-additive hard discs. It is found that the thermodynamic properties of the binary mixture of non-additive hard discs increase with Δ, the non-additive parameter.

The weighted geometric mean of resistors considered for determining the effective thermal conductivityK_E of two-phase systems has been optimised. Solutions of the equations lead to a useful set of bounds. When compared with other bounds the present bounds give the better results in estimating the upper and lower values of the effective thermal conductivity of a two-phase system.

A thermodynamic perturbation theory in which all angle-dependent interactions are considered as a perturbation of the central potential is applied to calculate the second and third virial coefficients of a fluid composed of non-axial molecules. The influence of a large number of anisotropic pair- and three-body non-ādditive interactions has been considered. Experimental values have been used for the dipole moment, quadrupole tensor and for anisotropic polarizability. The parameters for the central Lennard-Jones (12-6) potential have been determined from the viscosity data. The relative contribution of each branch of pair and triplet interactions has been evaluated as a function of temperature for molecules possessing both the axial- and non-axial symmetries. It has been shown that the non-axial approximation is an improvement over the axial one. Theoretical results have been compared with the experimental data of CH₃OH.