Table of contents

If a random assembly of different sized spheres is cut through in such a way that the spheres are not moved then the sections through the spheres are discs. By measuring the probability distribution of disc radii on the cross-section, the probability distribution of sphere radii in the bulk can be deduced.

The friction of copper on copper (a) freshly prepared, and (b) boundary-lubricated with a thin film of an organic polymer, low density polyethylene, has been studied. The results indicate that the organic polymer is not as good a lubricant as some fatty acids and that in the case of the 'freshly prepared' specimens, the friction results are only meaningful when the amount of oxide formed on the surface is known.

Measurement of the relation between polarisation and electric field for ferroelectric trissarcosine calcium chloride was made in the pressure range up to 6 kbar. The pressure dependence of the spontaneous polarisation and the coercive field were obtained, and the existence of a new pressure-induced phase and the paraelectric-ferroelectric-new phase triple point were found.

A theory of the thermally stimulated current (TSC) transport peak, developed recently (Jeszka et al. 1979 and Plans et al. 1980), predicts thickness dependence of the maximum temperature of the peak. The experimental observation of this effect, found for the high-temperature TSC peak in poly(N-vinylcarbazole) is presented and discussed in terms of dispersive transport.

The problem is discussed of assigning a single effective time constant for thermal, diffusion and other relaxation processes in which the time dependence departs markedly from a simple exponential form. The practical advantages of a 'first-moment' definition are pointed out and illustrated by examples from thermal conduction and the preferential sputtering of binary alloys.

Charge-exchange mass spectrometry (CEMS) is a new technique, based on the phenomenon of charge-exchange, for probing molecular structures in the gas phase. A large number of primary positive ions, 40 to 50, of known ionisation potential, (eV_i)_X, are made to collide in succession with a target gas at low relative kinetic energy. The absolute charge-exchange cross-sections, Q, for the target gas parent ion and its ionic fragments are determined mass-spectromically and plotted versus (eV_i)_X. Optically forbidden transitions may be observed and the appearance potentials of not just the target molecule parent ion but also its fragmentation products are determined. The technique is explained and discussed and examples of the results obtained are given.

The Rayleigh-Taylor stability of a multiple-shell ICF target is investigated using a linear perturbation technique. The zero-order solution is provided by a one-dimensional, three-temperature computer code. The results are compared with a full two-dimensional calculation and the agreement is found to be very good. A simple estimate based on integration of the interface acceleration is shown to be surprisingly accurate in some respects but inadequate in others. The instability associated with the hydrodynamic implosion of the inner shell is shown to be capable of seriously degrading the gain of the target.

Experimental range-energy relations are presented for alpha particles in methyl alcohol, propyl alcohol, dichloromethane, chloroform and carbon tetrachloride in both the liquid and vapour phases. Stopping power values for these materials and for oxygen gas over the energy range 1.0-8.0 MeV are also given. Stopping powers have been derived for the -CH₂- group and for -Cl occurring in chemical combination in the liquid and vapour phases. The molecular stopping power in the vapour phase is shown to exceed that in the liquid phase by 2-6% below 2 MeV, reducing to negligible differences at about 5 MeV for the materials directly investigated and for the -Cl atom.

The theory of a cylindrical, pulsed optoacoustic cell is extended to include off-axis beam excitation and calculation of the resulting pressure at an arbitrary point. The theory is restricted to nearly transparent fluids, thus making a two-dimensional analysis adequate. Calculations based on the theory predict the initial pulse response for various beam excitation positions and provide a comparison with experiment. The dependence of subsequent pulse reflections on beam position is also computed.

The results are presented of an analysis of amplitude and phase fluctuations occurring in acoustic waves propagating in media with inhomogeneities in the form of density and compressibility variations which are large compared to the wavelength. Simplification of the results is achieved for extreme values of the wave parameter and for specific forms of the correlation functions. The results have applications to those systems in which the effect of the density variations cannot be neglected compared to that of variations in the acoustic velocity, as assumed in Chernow's analysis (1960).

The calculation has been done for orbit-motion-limited conditions, for charged-particle speed ratios S=u/(2kT/m)^1/2 from 0 to 7, and for chi _p=e phi _p/kT_i from 0 to -50, where phi _p is sphere surface potential. Result show that: (i) for the front axial point, the local heat flux may be a non-monotonic function of speed ratio and increases with increasing attracting potential - chi _p; (ii) the non-monotonic dependence of the local heat flux to the speed ratio can also be found up to position theta =90 degrees referred to the front axial point ( theta =0 degrees ); (iii) for the rear axial point, the local heat flux is a continuously decreasing function of speed ratio; (iv) for ion retarding potentials, chi _p>0, the total heat flux decreases with increasing chi _p.

After a justification of correlating permeability and sedimentation equations, the Kozeny-Carman and Richardson-Zaki expressions are related to show how the Kozeny parameter k varies with suspension porosity, under sedimentation conditions. The variation of k with suspension composition is also illustrated; k can be very much greater than the values ( approximately 5) commonly quoted. It is predicted that maximum sedimentation mass-transfer rate will never occur at greater than 25% solids concentration by volume, and experimental data do not appear to contradict this.

The boundary layer form of the conservation equations for supersonic flow of a perfect gas in the inlet region of a smooth circular pipe are solved numerically using the Von Karman-Pohlhausen integral technique. The wall condition is adiabatic, and the thermal and hydrodynamic boundary layers are considered to be of equal thickness. Details of boundary layer development, choking condition, pressure gradient, wall shear stress, and temperature are presented for different inlet Mach number values. The trend of results is in agreement with one-dimensional Fanno line predictions.

A theoretical study has been made of the medium-pressure rare-gas positive-column plasma by taking into account the effects of molecular ion formation, volume recombination and ionisation due to metastable atoms, simultaneously. Calculated values of the electron temperature and the densities of metastable atoms, molecular and atomic ions, at various gas pressures for both He and Ne gases are presented. Numerical results show that in a rare-gas positive-column plasma, molecular ions become dominant in the discharge as the gas pressure increases above approximately 10 Torr. Theoretical values are compared with the experimental data and discussed. A new method to determine the three-body conversion rate coefficient is also proposed.

High current density ( approximately 10⁴ A cm^-2) AC arcs in long confining tubes have been investigated experimentally and theoretically. A uni-dimensional arc model based on simplifying assumptions has been presented. The main energy transfer mechanism is via radiation to the bore surface, resulting in the heating, ablation and ionisation of the (C₅H₈O₂) which becomes the main plasma source. The ablation results in high measured pressures ( approximately 100 bars) in the tube central stagnation zone. It is shown that a two-zone arc develops, namely a hot core and a cooler sheath. Semi-empirical scaling formulae linking current density with field gradient, core temperature, sheath temperature and pressure have been derived. Effects of turbulence on the arc model are discussed.

The measurement of statistical time lags of cold-cathode gas discharge tubes and the application of these measurements to the determination of the quantum efficiencies of metal cathodes in the near-ultraviolet wavelength range are described. It is proposed that a thin layer of contamination on the cathode accounts for the departure at high voltage from the Wijsman theory describing the statistical time lag variation with applied voltage.

325 keV H⁺-ion implantation was done in annealed polycrystalline copper specimens in the fluence range 2.2-8.4*10¹⁸ ions cm^-2 at ambient temperature. SEM examination of the surface topography showed the occurrence of blistering at 5.2*10¹⁸ ions cm^-2. Blisters were observed to grow with increasing dose. At 8.4*10¹⁸ ions cm^-2 severe sponginess localised only to blister skins, in contrast to the porous surface features developed on the whole implanted region by the high temperature (>or approximately=0.5 T_m) implantations, was observed. The present observations are explained in terms of the growth of bubbles contained within the blister skin at its ambient temperature.

Films of magnesium fluoride are found to be under large tensile stress following exposure to water vapour. It is shown that this stress, which varies reversibly in magnitude with the adsorption equilibrium, can be attributed to electrostatic dipole interactions between the adsorbed water molecules. The effect is not confined to magnesium fluoride, but can occur in other materials of an appropriate porous structure. Its relevance to the stability of optical coatings is discussed, together with some other applications.

If a current is passed between two contacts near one end of a conducting bar, a measurable voltage may appear between two contacts near the other end, particularly if the resistivity of the material is much higher for current flow across the bar than along it. Expressions are derived and evaluated for the 'cross-resistance' which describes this effect, for both rectangular and circular bars.

Measurements of charging and discharging currents in polyvinylidene fluoride (PVF₂) were made over a wide range of fields, temperature, and a limited range of sample thickness and electrode materials. Experimental results suggest that dipolar re-orientation and space charge relaxations are dominant mechanisms for the observed current transients. The quasi-steady-state conduction, observed at 10⁵ s at high temperature and fields, may be due to an ionic hopping process.

Measurements of the electrical conductivity of n-octadecane in the liquid and solid phases are reported. The results indicate that ion transport predominates in the liquid phase and may also be important in the solid. An electrolytic purification process has been observed in both phases. The situation in the solid is complicated because defects formed in the solid during solidification from the melt appear to facilitate the transport of ions, causing the conductivity of the solid to be higher than expected.

The currents flowing along two crystal directions, viz. parallel with and perpendicular to the molecular axis, were monitored but an apparent anisotropy in the conduction properties was removed by a voltage conditioning procedure. It is concluded that n-octadecane does not show an intrinsic DC conduction process when pure, defect-free crystals are grown. The voltage step-responses of the crystals do, however, show the logarithmic time dependence which is common to a wide range of insulators and semiconductors. Comparisons are made with results presented previously on liquid and polycrystalline n-octadecane.

The electrical characteristics of GaAs-metal and GaAs-electrolyte Schottky barrier diodes have been studied as a function of applied voltage and of frequency, using conventional Schottky barrier C-V analysis and I-V measurements. For forward voltages approaching the flat-band voltage, i.e. the diffusion voltage, the measured capacitance deviates from a linear C^-2 versus V dependence, i.e. the C^-2 value drops steeply and a 'knee' in the Mott-Schottky plot is observed. This effect is found for the equivalent series capacitance C_s as well as for the equivalent parallel capacitance C_p, but in a different voltage range. The 'knee' in the C_p^-2 versus V and in the C_s^-2 versus V plots is explained. The difference between these two plots is attributed to the forward current.

The growth and evaluation of large single crystals of a new piezoelectric oxide, tellurium (IV) vanadium (V) oxide (Te₂V₂O₉), are described. A full set of the coefficients of the elastic, piezoelectric, dielectric and thermal expansion matrices is presented, together with the first-order temperature coefficients of these quantities, where appropriate. A preliminary theoretical and experimental analysis of the potential of the material for surface acoustic wave substrate applications is given. Te₂V₂O₉ shows low acoustic wave velocities, combined with moderately strong piezoelectric coupling, which could make it interesting for a variety of SAW and bulk-wave applications.

An analysis of the continuum equations of nematic layers subject to large electric or magnetic fields leads to simple extrapolation procedures which allow the infinite field capacitance of the layers to be inferred. For a magnetic aligning field H the reciprocal of the capacitance should be plotted against 1/H, whereas for an aligning electric voltage V the capacitance should be plotted against 1/V except in certain cases where there is a large change in the dielectric permittivities between the frequencies of the aligning and measuring electric fields, when a plot of the reciprocal of the capacitance against 1/V should be used. The optimum experiments for accurate routine measurement of both principal electric permittivities of a small sample of nematic using a single cell are identified and two experimental arrangements described.

The authors describe the emission characteristics of a Cs⁺ ion field-emitter, consisting of a sharply pointed Ni needle (apex radius of curvature approximately 0.1 mu m) wetted with liquid Cs and continuously fed via a capillary reservoir in which the lower part of the needle resides. The experimental results are compared with the predictions of the field-evaporation theory.