The Rayleigh-Sommerfeld diffraction theory is used to derive expressions for (1) the spectral irradiance on the surface of a hemisphere covering the aperture and (2) the spectral radiant intensity. For a uniform, noncoherent source-aperture, both calculations predict a cosθ angular variation, as is known to be the case of Lambertian sources. A cosine-fourth dependence of the spectral irradiance on a plane parallel to the aperture plane is also indicated.

The charged particle orbits in electromagnetic fields on Kerr background as viewed from a locally non-rotating frame do not exhibit non-gyrating bound orbits, which was an essential feature in the earlier study of Prasanna and Vishveshwara, thus showing the non gyration to be due to the effect of dragging of inertial frames produced by the rotating black hole.

Quantum chromodynamics corrections to orderα_s (the running coupling constant), using the quark-parton approach are calculated for the spin-dependent structure functions in deep-inelastic polarised electron-nucleon scattering. Consequences of these corrections for the Bjorken sum rule and the asymmetry in the case of longitudinally polarised (with respect to the beam) nucleons is discussed which could provide possible tests of quantum chromodynamics. Comparison of our results with the moments of the flavour non-singlet contribution to the structure functions obtained using operator product expansion is also given.

From optical absorption studies at room and liquid air temperatures and from Mössbauer spectrum, the absorption bands of spessartine garnet are attributed to Mn²⁺ and Fe²⁺ ions. The energy matrices ofd⁵ andd⁶ configurations are solved and the experimental data of Mn²⁺ and Fe²⁺ bands are fitted with the calculated values to solve for the Racah and crystal field parameters.

Calcium sulphate phosphors activated with samarium as an impurity with various percentage composition have been prepared and their fluorescence rise and phosphorescence decay behaviours have been studied. The growth curve is investigated to study the density of traps. The process of filling of traps during x-ray excitation is revealed. The decay curves are analysed to study the distribution of traps, the nature of decay and kinetics involved in the luminescence process. The concentration dependence of fluorescence emission of the phosphors is also discussed.

The electric field dependence of the complex dielectric constant in an anharmonic defect ferroelectric crystal is calculated in its paraelectric phase from the Silverman-Joseph-Hamiltonian augmented with fourth-order phonon coordinates using double-time Green’s functions. The field and impurity dependence of the shift in the Curie temperature is discussed. An expression is obtained for the electric field dependence of dielectric loss at microwave frequencies in defect ferroelectrics.

Pressure variation of maximumF-band absorption energies in the halides of lithium, sodium and potassium has been investigated employing the extended-ion approximation for the calculation of theF-electron energy eigenvalues and using values of local compressibility in the neighbourhood of theF-centres which include the effect of vacancy and pressure. The results obtained agree with the experimental results.

A new peak at about 650°C has been observed in the thermoluminescence emission of gamma irradiated natural fluorites containing significant quantities of lanthanide rare-earth (RE) elements as impurities. Thermal activation energy of the corresponding trap has been evaluated to be 2·99 eV with a frequency factor of 10¹⁶ sec⁻¹. The optical activation energy, as deduced from photo-transfer-induced-TL from this trap, is 5·36 eV. Many types of natural fluorites as well as synthetically grown CaF₂ crystals doped with single and pairs of rare earth elements have been studied and the results indicate that the high temperature peak is associated with Sm impurity coexisting with Y, La or Ce in CaF₂. There are indications that this newly observed TL peak can be gainfully employed in ultraviolet dosimetry and geological dating of fluorite deposits.