A Mössbauer study of cation distribution in systems Co_x Mn_3−x−yFe_yO₄ and Ni_x Mn_3−x−y Fe_yO₄ has been made. It has been found that in both systems all specimens withy<0.6 value exhibit quadrupole doublets corresponding to site symmetries Fe³⁺(I) and Fe³⁺(II) of octahedral site. As more and more cobalt or nickel is introduced into the matrix the intensity of the inner quadrupole doublet increases while on introducing iron that of the outer quadrupole doublet increases. After a certain concentration of iron the inner doublet starts becoming more intense. It is suggested that this arises possibly from the substitution of cations in the second co-ordination sphere of Fe³⁺(I) and Fe³⁺(II) sites. Fory>0.6 the Mössbauer spectra show relaxation effects.

Structural, electrical and Mössbauer studies were carried out for the system Zn_1−xCo_xFe MnO₄. It is observed that forx⩽0.6, the ionic configuration of the system is Zn_1−x²⁺Mn_x²⁺ [Co_x³⁺Mn_1−x³⁺Fe³⁺]O₄²⁻ and forx⩾0.8 Fe³⁺ ions occupy tetrahedral site also. On the basis of electrical and Mössbauer studies a probable valence distribution of CoMnFeO₄ has been suggested. All the compounds showed positive values of thermoelectric coefficient and electrical conduction takes place by a hopping mechanism. Activation energy and thermoelectric coefficient values decreased with decrease in concentration of Zn²⁺ ions. The compounds possess low mobility values varying between 10⁻⁷ and 10⁻⁹ cm²/V sec.

N-m-tolyl phthalimide, C₁₅NO₂H₁₁ crystallizes in the space group Cc with unit cell dimensions,a=8·54(1),b=19·89(2),c = 7·59(1)A, β=114·53(1)° andZ=4.V=1173(2)A³,D_m=1·35(1),D_c = 1·344 mg.m⁻³,M_r=237 λCoK_a=1·7903A. The structure was solved byMULTAN and refined to an R-factor of 0·116 for 632 counter reflections. The molecules are held together by van der Waal’s forces. The angle between the tolyl plane and the plane through the phthalimide group is 53·4(4)°.

The problem of surface sound propagation in the presence of external high frequency dipole electric field is investigated using Vlasov-Poisson equations. The structure of the electric field of these surface waves is also determined. It has been found that the ion sound waves that exist in the presence of external high frequency waves are true surface waves while those without the external field are quasi-surface waves as the former waves decay within one wavelength away from the surface.

The various energy loss mechanisms in ion acoustic wave propagation in a gas discharge plasma have been discussed. The relative characteristic acoustic impedance of the plasma has also been experimentally determined which would help to measure the electron temperature of the plasma.

Absolute electron beam-plasma instability is suggested as a means of energy compression for pellet and liner inertial confinement fusion systems.

The theory for the transient build-up of mode locked pulses in a mode-locked and frequency-doubled laser is presented. The time required for the mode-locked pulsewidth to reach a steady-state value is computed. It is found that steady-state is reached faster in the presence of internal frequency doubling because of the broadening effect of the doubling crystal. The effects of different conversion efficiencies and modulation depths on the mode-locked pulsewidth are investigated and the results are graphically presented.

The interrelation between some basic concepts of information, theory and thermodynamics has been studied on the basis of the statistical measures of entropy and information. The problems studied are the negentropy principle of information, a minimax information principle of thermal equilibrium and the role of information correlation in the derivation of a functional equation characterising the statistical equilibrium of a system.

From the computation of self-avoiding walks on the kagomé lattice, its connectivity constant is found to be 2·569 ± 0·008.

The viscous nature of binary liquid solutions of non-polar solvents,viz. n-heptane, benzene, carbon tetrachloride and paraffin oil has been studied in terms of the deviation from the ideal law. The ideal law is supposed to take the form of (weighted) geometric mean. The viscous behaviour has been observed over a range of temperatures (298–322°K). The relative excess volume and relative excess enthalpy of activation have been evaluated to study the increase in viscosity associated with the shrinkage in mixing of its components.

Radiation damage in polyacrylonitrile (PAN) has been studied in the temperature range 273 to 420 K using thermoluminescence, electron spin resonance and optical absorption techniques. ATL glow peak has been observed with maximum at 362 K. The species responsible for theTL glow peak has been identified to be due to the free radical -CH₂-CH(CN)-ĊH-CH(CN)-CH₂-by correlation with the data obtained by the temperature variation ofESR and optical absorption spectra of thex-irradiated, pre- and post-x-irradiated and thermally-treated samples. A mechanism of formation of network structures accelerated by the free radicals formed on irradiation has been investigated to explain the optical absorption spectra. TheTL glow peak is analysed by various methods and corresponds to an activation energy of 1 eV, following second order kinetics.

The validity of the expression for the Grüneisen parameter of liquids has been tested by obtaining expressions for the heat capacity ratio, isothermal and adiabatic Anderson-Grüneisen parameters,C₁-parameter, Rao’s acoustical parameter, Beyer’s non-linearity parameter, and relate them to the Grüneisen parameter. The calculated values for five liquefied gases comparising of quasi-spherical molecules are reasonably satisfactory and explain the experimental results for the variation of heat capacity ratio, Beyer’s nonlinearity parameter andC₁-parameter with temperature for liquid state. It is shown that the isochoric temperature derivative of the sound speed, specified heat ratio and the compressibility are dominant factors with significant contribution for influencing the thermo-acoustic properties of liquids.