IR intensity formulae can be derived in the formI=L′ A; I being square root of intensityI², has sign ambiguity. Equations likeI′ I=A′ LL′ A=A′ GA have been used to solve the sign ambiguity. There is only one equation for each species. This position has now been improved by introducing a new concept about this sign ambiguity and solved for electro-optical parameters taking a pair of molecules CHCl₃ and CDCl₃ for demonstration. This incidentally solves the sign ambiguity problem of polar tensors which are calculated for these molecules.

A new method to calculate the lattice contribution to electric field gradients at a nuclear site in tetragonal crystals is developed. The crystal is regarded as an assembly of positive ions at lattice points embedded in a uniform background of negative charge (point charge model). The method uses Euler-Maclaurin formula and makes the plane-wise summation in the direct crystal space unlike most of the previous methods utilising Fourier transform to reciprocal space. The numerical values obtained using the above approach agree well with previous results.

Electrical conductivity studies in NaNO₂ single crystals with inherent impurities and also in crystals with added Mn²⁺ impurities have been reported. The heating conductivity runs of undoped and doped NaNO₂ crystals have been compared. The decrease in conductivity in cooling following a heating run has been attributed to the oxidation during heating leading to the bulk precipitation of impurities in the host. Above 170°C however the intrinsic defects are responsible for conduction. An anomaly is noticed in both the heating and cooling conductivity runs of the sample at about the Curie temperatures and has been found to show thermal hysteresis.

The first-order Raman spectra ofE_gandA_1g modes in MnF₂ crystal were measured at temperatures from 4.2 to 563 K, and the values of the linewidths obtained. The temperature dependence of the linewidths was analyzed by the phonon dispersion curves based on the rigid ion model, and the result showed that it was caused approximately by the cubic anharmonic term in crystal potential energy.

We prove using the Schwinger-Dyson equations that the factorisation property holds for all gauge-invariant Green’s function in the large-N limit of a Wilson-Polyakov lattice gauge theory.

The nature of wave front of light radiations from a tachyon is studied from the first principles. The elementary approach employed here yields many novel and interesting results. These results, specially the conical envelope of radiation, bear an excellent analogy to the case of Cerenkov radiation. Finally a possible astrophysical method of searching for the existence of tachyonic celestial objects is discussed.

Some errors in a recent article by Zadoo and Sofi are discussed.