Table of contents

Charge transfer between two insulators, or between a metal and an insulator, is not influenced by previous identical contacts. Since it has recently been shown that material transfer occurs to a large extent on the first contact and to a much smaller extent on subsequent contacts, it can be concluded that material transfer is not the primary mechanism of contact electrification.

The useful usable time delay range between the preionizing and main discharges in a TEA CO₂ laser, for reliable, arc-free operation, has been observed to be greatly reduced by the presence of small (<1 %) amounts of O₂ in the laser gas mixture. Three-body attachment of thermal electrons to O₂ molecules provides a loss mechanism for preionizing electrons to explain the observed results.

The use of the internal reflection modulator has been extended to the XDP class of crystals and proposals are given for which are suitable for this modulator to be used as an internal laser cavity switch. Experimental results obtained using the modulator are included.

The ohmic contact stability with evaporated Al was found to improve considerably by annealing in an argon atmosphere.

It is shown that the intensity of the electronic current backscattered from the surface is the convolution product of the total reflection coefficient by the energy distribution of the incident beam. A deconvolution method has been used to obtain this coefficient and this method is based on a rigorous inversion of the convolution integral operator. Numerical tests show that this method is not very sensitive to the experimental random noise. Results are given for W(100), Cu(100), and O/Cu(100) surfaces, and these are correlated with earlier measurements.

The adjoint Boltzmann equation is used to develop a formalism for calculating energy deposition in moderators. Examples of the technique are given and include a point source of fast neutrons in an infinite medium and a uniform source in a sphere of finite radius. Using elastic scattering to describe the slowing down process, the heat rates in moderators with mass numbers 1, 2, 3, 4, 5, 10, 16 and 50 are calculated. The results are compared with some recent Monte Carlo calculations on compressed pellets of deuterium and tritium and good agreement is found.

The authors have studied the self-focusing/defocusing of transverse Gaussian (TEM₀₀ mode) and TEM₁₀ laser beams in a non-linear dielectric in the extraparaxial region. It has been found that at points near the axis, the lowest-order Gaussian mode exhibits self-focusing whereas for points away from the axis, self-defocusing occurs. The reverse effect has been found for the TEM₁₀ mode.

The calibrated piston source technique of measuring the absolute light output from a luminous volume contained within a cylindrical glass tube is compared with the technique of light path computation. The comparison is made by considering the light flux falling on a small axial aperture, placed outside a cylindrical tube, as a result of radiation from a uniform luminous disc placed within the tube. The light flux at the aperture is directly measured, as a function of the position on the tube axis of the diffusing disc of a piston source, and this experimental data is compared with data calculated by taking into account all direct and reflected light paths from disc to aperture. Careful examination of the results of the comparison leads to the conclusion that a calibrated piston source provides a more precise technique for absolute light measurement than light path computation.

Experimental work is described on the propagation of marginal detonation waves in propane-oxygen and hydrogen-oxygen systems diluted with oxygen, nitrogen and argon. The detonation tube was of rectangular section, with internal dimensions 2.3*1.0 cm, and overall length of 30 m. A continuous monitor of the wavefront velocity was achieved using a 3 cm wavelength microwave Doppler system. A cyclic wave phenomenon which is characterized by a normal and a slow velocity regime, is observed to be present near the limits of detonability in all except the hydrogen-oxygen-argon system. The relative durations of these regimes varies from one system to another and appears to be governed by the structural regularity of the detonation front. Schlieren records show that in the low-velocity regime the shock front and reaction zone are dissociated, with a separation varying between 1 and 10 cm, and that a weak transverse wave effect appears to be present at the lead shock which is non-planar.

The thermal conductivity of air treated as a binary mixture has been calculated by way of an unmodified and a modified Wassiljewa equation using recent data on lambda , eta and D for O₂ and N₂. The two expressions are found to yield results in overall agreement with experimental data in the temperature range 400-1600K. The unmodified expression due to Mason and Saxena (1958) perhaps gives more accurate results and may be thus more suitable for predicting the conductivity of other gas mixtures.

The kinetics of growth of KDP crystals from aqueous solution has been examined at various supersaturations and temperatures, when stable supersaturated solutions have been injected with KDP seed crystals. The growth rate has been determined from measurements of the increase in the weight of a crystal. In the unagitated system, the growth rate of KDP follows a parabolic equation with respect to very low supersaturations, and a first-order equation with respect to higher degrees of supersaturation. The activation energy for growth in the temperature range 30-50 degrees C is calculated as 3.8+or-0.04 kcal mole^-1.

Discusses a factor beta _r which contributes to the damping coefficient for domain wall movement in tape-wound 3% Si-Fe and Supermalloy cores. The factor is a constant independent of the domain wall geometry and the dimension of tape. It is similar to the spin relaxation damping but far larger. The study on the eddy current loss equation including beta _r shows that the loss caused by beta _r becomes comparable with that based on the macroscopic eddy current in tape thickness as great as 50 mu m in 3 % Si-Fe. The result will help to clarify anomalous eddy current loss in thin-sheet materials.

The dielectric constant ( epsilon ') and loss ( epsilon ") of three dyes, methylene blue, brilliant green and echtblau saltz, have been investigated as a function of temperature in the frequency range 10² to 10⁵ Hz. The activation energies have been evaluated from the AC conductivity. The dielectric behaviour is discussed in relation to the molecular structure of the dyes.