The two photon pair momentum density and the angular correlation curves for positron annihilation radiation from copper have been obtained by a band structure calculation, employing Hubbard’s approximation scheme. A comparison of the calculated curve for the long slit geometry with the experimental results shows that the theory rather overestimates the contributions in the high momentum region. An angular correlation curve for a point slit geometry is also calculated.

Using a kinetic description for electrons and the usual equation of motion for lattice displacement we have derived a general dispersion relation for acoustic waves in a piezoelectric semiconductor, in the presence of a strong high frequency electric field oscillating near the electron plasma frequency. Earlier hydrodynamic results valid forkλ_e≪1 (wherek is the wave number of the acoustic wave andλ_ethe electron mean free path) are rederived as a special case. Forkλ_e≫1, two instability branches are discovered and magnitudes of the threshold electric field required to drive the acoustic wave unstable in each case, are obtained.

Ultrasonic velocity dispersion in methylcyclohexane was studied in the frequency range of 0.5 to 5.0 MHz at 60°, 65°, 70°, 75° and 80°C using a variable path interferometer. Necessary corrections for the diffraction of the ultrasonic beam were applied. The velocity data were used to evaluate the relaxation parameters pertaining to the interconversion of the axial and equatorial isomers. The value of the difference in enthalpy, difference in entropy and the activation energy are 11.2±4.0 kJ mole⁻¹, 28.0±8.0 J mole⁻¹K⁻¹ and 43.7±4.0 kJ mole⁻¹ respectively. These values are in good agreement with values derived by Piercy and Subrahmanyam from their ultrasonic absorption measurements.

The data on$$\bar N_0 \left( {n\_} \right)$$, the average number of neutrals as a function ofn₋, the number of negatively charged particles produced, is fitted at 69, 205 and 303 GeV/c. The two-component model used for the charged multiplicity distributionP_n, is one which envisages two distinct types of collisions and is the simplest such model consistent with charge conservation. We find that the data on$$\bar N_0 \left( {n\_} \right)$$ can be fitted reasonably well. Further, our results, based on this model forP_n, suggest that at 50 GeV/c,$$\bar N_0 \left( {n\_} \right)$$ should increase linearly withn₋and that neutral-negative correlations should be present in the central component.

The filamentary structure of the magnetic fields as well as the coherent radiations that emanate from a sunspot are explained considering solar burst as a non-equilibrium process. Methods of irreversible statistical mechanics have been applied to the problem of an electron gas in a constant magnetic field to explain the above features. We have obtained the non-equilibrium distribution function in the self-consistent field approximation. The dielectric function, we obtained, is a function of time, besides being a function of frequency and wavevector. We have thus taken the non-linearity of the system as well. This theory explains many features of stria bursts, chain bursts as well as the type III bursts. This also accounts for the bunching of the magnetic field lines as a consequence of quantisation of flux in the Landau sense.

From the radial velocity data for O-B5 stars within 3 kpc of the Sun the variation of the semi-axesΣ₁ andΣ₂ of the velocity ellipsoid in the solar region is estimated. It is found that both the semi-axes as well as their ratioΣ₂/Σ₁ decrease away from the galactic centre. The value ofΣ₂/Σ₁ changes from 1.17 atR=9 kpc to 0.48 atR=11 kpc passing through a value of 0.86 at the solar distance ofR₀=10 kpc. These results are consistent with the usually assumed inverse square law of force in the outer regions of the galaxy.

An analysis has been made of the experimental results of Akimovet al on the inelastic cross sections of proton on proton and carbon targets in the energy range 20 to 600 GeV obtained from artificial earth satellites. It is found that an upper limit of 4% at 95% confidence level can be set on the fraction of deuterons relative to the flux of protons in the primary cosmic radiation at energies in the range 20 to 60 GeV. There is an indication for a rise of (29±7) mb in the inelastic cross section of proton against carbon in the energy range of 200 to 600 GeV over and above what is expected from Glauber’s theory. If this rise has to be interpreted as due to contamination from cosmic ray deuterons, the fraction of deuterons relative to protons needed is (15±4)% in this energy region.

From existing cosmic ray measurements of theinelastic collision cross sections of nucleons on nuclei of carbon, iron and lead in the range of energies 10² to 10⁴ GeV as well as the measurements of cross sections on air nuclei in the extensive air shower (EAS) regions (10⁵ to 10⁸ GeV), we conclude that the Glauber multiple scattering theory is adequate to account for the data. Recent suggestion of Maor and Nussinov to parametrize the nucleon-nucleon total cross section with a component growing proportional to ln²E (E is the incident energy) is at variance with the EAS data. However the data are consistent with a nucleon-nucleon total cross section rising no faster than lnE in these energy regions.