Conditions for the usual form of one-electron relativistic virial theorem to be satisfied are derived and illustrated. These can be applied to generate quality basic spinors for solving a one-electron Dirac equation.

A dielectric response approach to the dynamic image potential of a charged particle approaching a planar metal surface is formulated. A self-consistent scheme for calculating the instantaneous speed of the particle, and its image potential is also derived. It is shown that the scheme does not rely on the actual approximations made while describing the response of the metal with surface. Various approximations are discussed and the corresponding numerical results compared. The effect of self-consistency and inclusion of dispersion in metal is noticeable.

Optical absorption of Er³⁺ ion in Er(NO₃)₃·5H₂O, NH₄NO₃, Mg(NO₃)₂·6H₂O, KNO₃ and NaNO₃ complexes has been studied. The second derivative spectra of these Er³⁺ complexes exhibited splittings in the⁴I_9/2,⁴F_9/2,⁴F_7/2,⁴F_5/2 and²H_9/2 levels. These splittings have been tentatively explained as due to a cubic crystalline field. The partial derivatives for Er³⁺ ion have been calculated in terms of Racah (E^k) parameters. The results of a least squares fit of the energy levels and oscillator strengths of the bands are reported in terms of interaction parameters and Judd-Ofelt parameters. Radiative transition probabilities for various fluorescence levels are theoretically estimated. The lifetime of the⁴G_11/2 level is found to be lowest in all nitrate complexes.

The⁷⁹Br quadrupole resonance in cadmium, strontium, barium, zinc, magnesium and nickel bromates is studied in the range 77 to 305 K. The temperature dependence of the resonance frequencies in these systems has been analysed on the basis of the torsional motion of the BrO₃⁻ groups. The torsional frequency and its temperature behaviour have been analysed.

Expressions for thermal properties such as thermal expansion, specific heat and melting point are obtained by employing the usual quadratic-quartic form of the potential energy. Computed results for nineteen cubic metals are presented and compared with the experimental values. The model describes the broad features observed in the thermal properties and an estimate of the anharmonicity in cubic metals.

Ultrasonic velocities, elastic constants and internal friction are studied in Sn-In alloys in the concentration range of 0 to 30 wt% of In using composite oscillator technique. Anomalies observed in the vicinity of the phase transitions of these alloys at fourteen concentrations are interpreted in the light of the phase changes in the phase diagram.

The energy spectra of the even-parity (K^π = 2⁺, 3⁺) and odd-parity (K^π = 3⁻, 4⁻) side-bands in the doubly even nucleus¹⁷⁰Yb are studied in the framework of the microscopic method of variation after angular momentum projection with nucleon number conservation in each projected state. The calculated energy spectra of the ground band and the four side bands in¹⁷⁰Yb are in good agreement with the corresponding experimental results.

A mathematical procedure to calculate the contribution to the reaction cross-section from a shell of radiusr and thickness Δ around the scattering centre within the frame work of a nuclear optical model is presented. The method is illustrated by describing graphically the regionwise absorption in nucleon-nucleus and nucleus-nucleus optical scattering. It is demonstrated that unlike in nucleon-nucleus scattering, in the nucleus-nucleus scattering volume absorptive optical potential, in general, does not imply that absorption is taking place in the entire nuclear volume; it is confined to mostly the surface region.

Measurements of the dependence of track etch rate on the energy-loss of different ions have been presented. In this method,₁₈⁴⁰Ar,₁₀²²Ne,₈¹⁶O and₆¹²C-ions of different energies are used as energetic heavy ions for track formation in the detectors. The bulk etch rate and track etch rate are measured for different temperatures and hence the activation energies are determined. The variation ofV =V_t/V_b along the trajectory of the track has been shown for different temperatures. The maximum etched track length is compared with the theoretical range as well as with the range reported earlier. The experimental results indicate the absence of a well-defined threshold in the plastics studied.

For a large class of phenomenological potential models motivated by quantum chromodynamics, we have studied the behaviour of bound state masses as the constituent mass is increased and found that the mass of a quark-antiquark bound state increases when a constituent mass is increased. It appears, for these potentials, thatd quark is heavier thanu quark.

A review of some recent papers on gauge theories of weak and strong gravity is presented. For weak gravity, SL(2, C) gauge theory along with tetrad formulation is described which yields massless spin-2 gauge fields (quanta gravitons). Next a unified SL(2n,C) model is discussed along with Higgs fields. Its internal symmetry is SU(n). The free field solutions after symmetry breaking yield massless spin-1 (photons) and spin-2 (gravitons) gauge fields and also massive spin-1 and spin-2 bosons. The massive spin-2 gauge fields are responsible for short range superstrong gravity.

Higgs-fermion interaction can lead to baryon and lepton number non-conservation. The relationship of strong gravity with other forces is also briefly considered.

The photoacoustic spectra of Rhodamine 6G (Rh6G), Rhodamine B (RhB) dyes and their mixtures were recorded at different concentrations. It is observed that in the mixture the photoacoustic signal increases due to excitation transfer from Rh6G to RhB in the wavelength region 480–530 nm. The excitation transfer rate estimated from these data show that resonance is dominant rather than the collisional transfer process.

Feasibility of nonresonant third harmonic generation in thallium is investigated. The third order susceptibility, for driving frequencies in the visible region, is calculated and the phase matching with Ar as buffer gas is investigated. Other related quantities like coherence length, minimum pulse lengths required to get phase matching and power input requirements to achieve 50% conversion are also calculated.

Dielectric studies in dilute solutions of cyclohexane and benzene have been carried out in the temperature range 294–318°K. The observed data have been utilized to evaluate the relaxation times and thermodynamic parameters of these molecules. The high values ofα for 2-acetyl pyridine indicate the occurrence of more than one relaxation time. In the remaining systems, the observed lowα values indicate their rigid behaviour. The variation in the dielectric relaxation time is mostly correlated with the change in the heterocyclic configuration of the system.

The drift velocities of positrons in rare gases, He, Ne and Ar have been calculated at various temperatures. The drift velocity depends quite sensitively on the strength of the electric field and temperature.

A modified version of vacuum vibrator ion source is designed, fabricated and used to obtain phosphorous and boron ions. Its main features (i) controlled amplitude of vibrations at the spark position and (ii) small quantity requirements of materials. Pure powders of boron and red phosphorous were used respectively to get boron and phosphorous ions and in each case the ion current obtained was of the order of 1µA. The results obtained from silver electrodes are compared with those obtained from other metal electrodes. Silver is found to be a suitable electrode material for production of phosphorous and boron ions.

The design of a simple inexpensive instrument which can be used along with a simple laboratory microscope to measure microhardness of crystals is described. The design is based on the fact that the lengths of arms of indentation dislocation rosette (idr) are related to the hardness. By controlled indentation and subsequent etching of two similar crystals, the microhardness of one can be estimated in terms of that of the other from measurements of the arms ofidr.

Electrical resistivityρ(T) of spin glasses within the framework of Mookerjee and Chowdhury’s percolation model where there is a distribution of relaxation times (drt) is calculated.ρ(T) thus calculated is in better qualitative agreement with experimental results than that in the single relaxation time model.

The tight binding cluster Bethe lattice model formulated earlier for treating chemisorption systems has been used to study a specific system, namely, hydrogen chemisorption on Ni(100) surface. The hydrogen atom occupies the centre hollow position in agreement with the experimental results.