Pressure-temperature diagrams have been studied for two discotic compounds, hexa-n-octyloxytriphenylene and hexa-n-decanoyloxytriphenylene, both of which exhibit the columnar (D) phase at atmospheric pressure. Two interesting results, common to both compounds, have been obtained: (a) in contrast to what is usually observed in liquid crystals of rod-like molecules, the columnar-isotropic (D-I) transition, which is enantiotropic at atmospheric pressure, becomes monotropic at high pressures; (b) dT/dP ≈ 0 for theD-I transition, implying that despite the drastic change in the molecular order at this transition, the associated volume change is extremely small.

A new, non-perturbative, coordinate space method is formulated to calculate the full and partial wave amplitudes for the potentialae^−λr/r withλ=+0. The basic ingredients are a plausible use of the point Coulomb wave function up to moderate distances and a Wronskian identity to take care of the large distance behaviour of integrands.

The design and fabrication of an all-metal cryostat, superconducting magnet and variable temperature sample holder insert for the measurement of magnetoresistance at temperatures in the range 1.5–300 K are described. A field of 50 kilogauss has been achieved at the centre of a one-inch bore superconducting solenoid and has a uniformity of 0.2% over an axial distance of 20 mm around the centre of the solenoid. Also, the design and construction of vapour cooled current leads for the magnet are discussed.

The magnetic moments of charmed baryons are studied in the covariant oscillator quark model including isospin symmetry breaking effect. In the uncharmed sector, the results differ from those obtained using conventional non-relativistic quark model (nrqm). But in the charmed sector the present values are much nearer to thenrqm results than those calculated using models with hadron mass dependence.

The etch pit diameters of soda glass detector samples exposed to₅₄¹³²Xe-ions of different energies are measured for different etching times after etching the detector in a ‘new etchant’ free of the adverse effect of the etch product layer. The dependence of track diameter on the energy and on the energy loss, dE/dx of₅₄¹³²Xe-ion in soda glass has been presented. The energy resolution of soda glass and the critical angle for etching of fission fragment tracks in glass detectors have also been determined. The maximum etched track length of₅₄¹³²Xe-ion in soda glass has been compared with the theoretical range. The effects of different annealing conditions on bulk etch rate of glass detector and on diameters of₅₄¹³²Xe-ion tracks have been presented. Experimental results show that there is a decrease in track etch rate, etching efficiency and etchable range of₅₄¹³²Xe-ions with annealing. The annealing of oblique tracks shows that the vertical tracks are more stable than the oblique tracks.

Geometries of the first triplet and first singletn-π* excited states of benzaldehyde have been optimized using thesindo 1 molecular orbital wave-function (with CI) and the Newton-Raphson method. The triplet excited state geometry of the molecule is found to be appreciably non-planar whereas that of the singlet excited state is planar. A crossing of molecular orbitals occurs in going from the ground state equilibrium geometry to the triplet and singletn-π* excited state equilibrium geometries. Existence of the para-directing effect of the singletn-π* transition for electronic charges found in an earlier work is confirmed by the present work. The tripletn-π* excitation rearranges electronic charges mainly on the CHO group. It is found that the dipole moment of the molecule would appreciably increase following the singletn-π* excitation whereas the same would appreciably decrease following the tripletn-π* excitation.

Study of transport in the boundary layer of tokamak plasma in presence of magnetic divertors is extended to the second order in ion collision frequency. Numerical results for ion and energy losses to the collector plates are presented for toroidal and poloidal divertors. For the toroidal case, the Wiener-Hopf solution for the second order distribution function is obtained. An error occurring in an earlier first order calculation is pointed out and corrected first order fluxes are also given. For the poloidal divertor, asymmetry observed in ion and energy transport is found to persist in the second order result.

Experimental investigations on ablatively accelerated thin plastic foil targets irradiated by a 6J, 5 nsec Nd: glass laser pulse, were conducted using shadowgraphy technique. A 2 nsec, 0.53 µm probe pulse, derived from the main laser was used for recording the foil motion. It was observed that 6 µm plastic foils could be accelerated to a velocity of about 3 × 10⁶ cm/sec for an incident laser intensity of 5 × 10¹³ W/cm² and the corresponding ablation pressure was 0.4 Mbar. Ablation pressure (P) scaling against absorbed laser intensity (I_a) was slower (P ∝I_a^0.4) for a smaller laser focal spot (30 µm) as compared to the scaling (P ∝I_a^0.7) for a larger focal spot (500 µm). This result has been explained considering the loss due to lateral energy transport from the laser plasma interaction region.

The integrated intensities of Bragg reflections have been measured for mixed crystals in the K_xRb_(1−x)Br system with an x-ray powder diffractometer. From the intensities, the mean Debye-Waller factors are determined. The Debye-Waller factors are corrected for static contribution and Debye temperature values are determined for the entire composition range. The x-ray Debye temperatures follow the Kopp-Neumann equation closely.

An experimental program has been started to study polymorphic phase transitions under pressure in organic solids using the Be gasketing technique developed by us. This allows us to obtain x-ray diffraction patterns of low symmetry organic solids with high resolution, employing CuK_α radiation. The first organic solid studied is α-resorcinol. At 0.5 GPa, it transforms to its high temperature and denser modification, β-resorcinol. The transformation mechanism is discussed with the help of molecular packing calculations.

Effects of dielectrophoretic transients on stability ofn-pentane and methyl methacrylate have been experimentally studied. Dielectrophoretic transients have been found to demonstrate anomalous effects in methyl methacrylate. The effects are observed both on the application of electric field and its subsequent turning off to zero and are equal in magnitude and direction during both the operations. Results have been explained on the basis of the body forces acting on the dielectric in presence of a non-uniform electric field and a temperature gradient. Heater surface thermodynamics has been studied under controlled temperature and electric field gradients. A striking feature of the experiment is the application of a high voltage directly on the heater surface making the body force calculations more realistic.

The efficiency of electronic excitation energy transfer from toluene to a dissolved fluorescent indole, is determined experimentally in systems comprising neat toluene, 1:9 mixture of toluene-cyclohexane and 1:9 mixture of toluene-paraffin as a function of temperature in the range 293–353°K (viscosity range 0.6–39 cP). The results are discussed in terms of the influence of temperature, dilution and viscosity of the medium on the energy transfer efficiency in binary organic scintillator systems.

A comprehensive theoretical analysis of optimization of gain in CO₂-N₂ gasdynamic laser employing wedge or conical or hyperbolic nozzles with either H₂O or He as the catalyst is presented. After a review of previous work, the usual governing equations for the steady inviscid quasi-one-dimensional flow in a supersonic nozzle of a gasdynamic laser are used to obtain similar solutions for the various flow quantities, which variables are subsequently used to optimize the small-signal gain on theP(20) line of the (001) → (100) transition of CO₂ at wavelength 10.6µm. The corresponding optimum values like reservoir pressure and temperature and nozzle area ratio also have been predicted and presented in the form of graphs. The analysis predicts that employing of 2D-wedge nozzle results in higher gain values and the CO₂-N₂-H₂O gasdynamic laser employing 2D-wedge nozzle is operationally the best laser system for which the optimum value as high as 3.1 m⁻¹ gain can be obtained.