Table of contents

A method for the exact treatment of the differential equation governing the potential function associated with the two-dimensional induction velometry problem is explained. The velocity and the magnetic induction are considered non-uniform.

The oscillation of an ammonia beam maser is switched by applying a voltage pulse to an electrode mounted within the resonant cavity. The oscillation amplitude transient so produced has a modulation frequency in the region of 8 kHz and a duration of the order of 300 μs.

An ammonia beam maser has been operated with an electret focuser which provides semi-permanent state separation of molecules, thus permitting operation of the maser in the absence of an EHT supply. Conversely, the use of a neutral molecular beam under high-vacuum conditions permits detailed studies to be made of the relaxation properties of electrets without electrical or mechanical disturbance.

Preliminary observations on the non-stationary aspects of the conduction process in n-hexane indicate that two distinct types of pulse activity occur. Lowamplitude pulses (of about 5 fC) are always present, but at stresses above 400 kV cm⁻¹ they are accompanied by intermittent bursts of much larger pulses (of about 1 pC) which often culminate in breakdown. By means of an audio-visual technique a relationship between the low-level pulse activity and the particle motion in the electrode gap has been established. Typical non-stationarities in a sequence of pulses are illustrated by a plot of pulse rate and mean charge against time.

Contrary to previous observations, it has been found that certain fluorides will undergo an electroforming process at low voltage, in air at atmospheric pressure, when sandwiched between particular metal electrodes. CaF₂, LiF and LaF₃ exhibit forming behaviour with copper or silver electrodes, but only CaF₂ could be formed using gold. It was further observed that the conductivity of formed devices could be altered by simply varying the background pressure of the gaseous environment.

A simple model is developed for the cooling and freezing prior to substrate impact of droplets generated by rotary atomization. Application of the model accounts for Busk's observation in 1960 that droplets below a certain size were solid on impact with the 6 m diameter chamber walls of his apparatus. Application to smaller-scale apparatus indicates negligible cooling or freezing prior to impact. Calculations indicate that termination of flattening after impact could not have resulted from freezing. However, an alternative mechanism of conversion of kinetic to viscous energy predicts too small a terminal thickness by a factor of at least five. The implied restraint in viscous deformation might have arisen from oxide film formation on the droplet surfaces.

To make twist proportional to length, corrections must be applied to the free specimen length between the clamps. These corrections are determined experimentally by clamping a specimen of polymeric material over various lengths and extrapolating the torsion angle to zero length.

For cylinders with ring-shaped clamps, a two-sided correction was found of 0·235 of the diameter.

For rectangular specimens with flat-plate clamping at the ends, the correction varies between 0·20 (square cross section) and −0·55 (very slender cross section) of the greatest width.

Results only partly correspond with theoretical predictions, since theoretical and experimental conditions are not identical.

On the assumption that inelastic electron scattering in a specimen is localized and gives rise to an incoherent beam, an estimate is made of the effect of chromatic aberration on an electron microscope image.

A model specimen of an unstained biological material with a variation in mass thickness is used to calculate the incoherent inelastic image; the aberration function is applied to this image to give an image with spherical and chromatic aberration defects. From this procedure, an estimate is made of the loss in resolution for the inelastic image due to chromatic aberration for two specimens of very different mass thickness (40 and 200 mg m⁻2 of carbonaceous materials) and for objective aperture sizes corresponding to semi-angles of 0·0025, 0·005 and 0·01 rad (incident electron energy 100 keV). It is concluded that chromatic aberration results in a loss in resolution on a 5-10 Å scale within the approximations of this work. The deterioration in resolution due to chromatic aberration is not very dependent on the size of the objective aperture.

The conclusions of the present work are consistent with recent experimental work on the effect of chromatic aberration on the electron microscope image.

Far-field intensity distribution has been plotted for a circular aperture suffering from spherical aberration and illuminated by quasi-monochromatic partially space-coherent light. Gaussian and besinc forms of correlation have been assumed. It is shown that higher values of coefficient of aberration can be tolerated as the value of number of correlation intervals contained in the aperture increases.

Computers have been used to follow the trajectory of Kr ions striking a simulated tungsten single crystal. The crystal faces chosen were the (100) and (110) and the effect of the second plane of atoms below the surface was included. From a study of the ion trajectories, probability of ion penetration into the surface was determined and values are compared with experimental data.

Measurements of the ion current to a circular flat stagnation probe have been performed in a laboratory flame of known ionization density. The measurements were performed over an ionization density range from 10¹⁵ to 10¹⁸ m⁻³, probe bias voltages from 5 to 400 V and probe/flame velocities from 3 to 19 m s⁻¹. The measurements show good agreement with the calculated sheath/convection currents: I=(VR)^0·8 (n_eeuinfinity)^0·6π(6₀μ)^0·4 (mks) for the case where the sheath is thick compared with the probe, and I=(72R⁸n_e³e³uinfinity³V²μ₀πa⁻³)^0·25 (mks) for the case where the sheath is thin compared with the probe. Here R is the radius of the flat conduction face of the probe, n_e the ionization density, e the electronic charge, μ the ion mobility, uinfinity the plasma flow velocity relative to the probe, far from the probe, V the probe bias voltage, ₀ the permittivity of free space, and α the radius of the insulator surrounding the conducting face of the probe.

Plasma density measurements are reported which were taken simultaneously on a plasma column by three different techniques. The diagnostic methods used were a double-probe method, a resonant microwave cavity technique and an upper hybrid frequency method. The density range covered was 10⁹-10¹¹ cm⁻³, and the plasmas employed were rf discharges in the lower density range and the positive column of arc discharges in the higher density range, each running in hydrogen, helium, neon or argon gas.

It is shown that if sufficient care is taken and corrections are applied reliable results can be obtained. Further, reasonably good agreement (±25%) can be achieved between the three methods under these circumstances.

The flow of a weakly ionized gas past a planar probe is considered. In order to assess the errors incurred using the standard uniform-electron-temperature models, calculations are made of the electron temperature in the boundary layer under conditions of subsonic low-temperature plasma flow typical of flames. It is found that for the usual experimental case of small currents the electrotemperature is only uniform if the parameter α/aless, similar0·2, and is equal to the wall temperature if α/agreater, similar10. The parameter α² is equal to the ratio of the gas flow time past the probe to the characteristic electron cooling time, and a is the reduced gas temperature gradient at the wall.

In studying electrically augmented flames it has been found that the fuel flow to a burner can be reduced to zero, leaving an electrical discharge stabilized in axially flowing air at atmospheric pressure. An electrode configuration of axial anode and cylindrical cathode stabilized the discharge under conditions where it would be unstable in quiescent air. No ionizable seed material was necessary in the air to maintain the discharge once initiated. In addition to stabilization in air, similar discharges have been maintained in nitrogen and argon. Voltages of between 40 and 400 V and currents from 2 to 10 A sustained discharges across electrode gaps of 3 to 15 cm with gas flowrates varying between 10 and 2500 cm³ s⁻¹. The variation of the discharge voltage with these parameters has been correlated with a modified Grotrian expression for long arcs in air. The spectral lines of both copper and carbon (depending upon the electrode material used) were identified using a medium quartz spectrograph, and temperature estimations of 5400 K in the discharge were made by comparing spectral line intensities. High-speed photography has also revealed interesting features of the system.

DC electrode current measurements with liquid benzyl alcohol flowing between the electrodes require an explanation differing from that used for highly insulating liquids such as benzene. In this article a theory is developed which accounts for the decrease of the current with time. It is supported by the agreement between the experimental and theoretical values for the initial charge carrier density n₀ and the time constant τ of the current decay.

Measurements of the diffusion constant and segregation coefficient have been made for silicon dioxide films on silicon, using six different methods of preparing the oxide films. The results show that the thermally grown oxides give the best masking properties against the diffusion of boron, but that other oxides, notably reactively sputtered oxide and oxide formed by decomposition of tetraethoxysilane, can be almost as good. It is also shown that the exact method of preparation of the latter two oxides is important; for example, an argon-oxygen mixture gives much better oxide than pure oxygen.

By the use of Eulerian angles, expressions are given for the directionality of the sets of eighty-one compliance and stiffness constants in cubic materials. These expressions are trigonometric series in nθ (n=1, 2, 4), where θ is the angle of rotation in a given plane. Coefficients of the series are listed for planes in the standard triangle and a procedure is presented to extend the analysis to all planes of the same form.

Efficiency factors are proposed describing the effectiveness of utilization of fibre stiffness and strength when a random distribution of extensible fibres is incorporated in a brittle matrix.

A length efficiency factor for strength calculation is derived, which includes the effect of sliding friction during fibre pull-out; this reduces to the two previously applied efficiency factors in the limits.

The interaction of fibre length and orientation is considered, and general efficiency factors describing the effect of both length and orientation on the strength of randomly reinforced short fibre brittle matrices are derived.

The shear stiffness and strength of uniaxial specimens of carbon-fibre-reinforced epoxy resin have been measured by use of a torsional testing machine. Both type I (high stiffness) and type II (high strength) fibres were tested in the range 30-70% fibre by volume and the results compared with those for unreinforced resin. A quantitative study was made of the effect on these properties of the hypochlorite surface treatment designed to promote fibre-resin adhesion.

The results have been analysed in terms of calculated stress concentration factors and the ideas of fracture mechanics. It is concluded that for type II fibres the surface treatment is fully effective in that resin failure is more likely than bond failure, at least for this particular resin. For type I fibres, however, a stronger treatment should be investigated, and possible improvements in the technique of manufacture of materials with high fibre content are indicated.

A comparison has been made of torsional measurements with the results of short-beam interlaminar shear tests. The usefulness and limitations of the latter technique are assessed.

The current-voltage characteristics of gel gelatin were measured so that information could be obtained concerning the behaviour of the charge carriers. The electric characteristics of the specimen were controlled by the addition of NaCl and by the absorption of water.

The current-voltage curves were obtained by the application of dc and pulse voltages. Every specimen exhibited ohmic behaviour in the high-conductance region and also space-charge-limited behaviour in the low-conductance region. These regions correspond to the specimen conduction being that of a soft gelatin and a solid-like gelatin respectively.

As a consequence of theoretical considerations concerning monopolar space-charge-limited phenomena, with and without dissociation and recombination, values for carrier mobility of between 4×10⁻³ and 10×10⁻³ cm² V⁻¹s⁻¹ were obtained for the critical transition condition from the space-charge-limited state to the non-space-charge-limited state, and electrons seemed to be main charge carriers in the solid-like gelatin.

The penetration of magnetic flux and ac losses have been measured at 50 Hz in superconducting niobium films deposited by sputtering on the inside of cylindrical substrates, and the results are compared with other work on ac losses. Flux penetration has been found to be localized at pinholes and similar defects in the films.

The generation of an alternating voltage by varying the velocity with which a conductor cuts a uniform magnetic field should not be accompanied by the production of ac losses. Experiments to check this theory are described for both superconductors and normal conductors. Samples of each type of conductor were rotated at 3000 rpm and then reciprocated at the same frequency, and the losses measured by noting the increase in power ΔP required by the driving motor when the uniform magnetic field was switched on.

Significant values of ΔP were recorded for both the normal and superconducting samples when rotated, even in the lowest flux densities (similar 0·1 T). When reciprocated, however, it was not possible to detect ΔP for either type of sample, even in B=5 T. This means that the copper losses were less than 0·01% and the Nb-Ti losses less than 0·1% of the respective rotational losses under the same electromagnetic conditions; it also implies that the superconductor losses were less than those appropriate to the superficial transport current density (5·5×10⁴ A m⁻¹) that might be used in a large generator employing the reciprocating principle.

The aluminium-germanium contact has been studied in detail, with particular emphasis on (a) the change of barrier height with time after fabrication and (b) the current changes which take place following the application of a constant bias voltage. Three kinds of germanium surface have been used: etched, cleaved in air and cleaved in ultra-high vacuum. The results can be explained in detail by a model involving slow surface states in the oxide by making two assumptions: (i) that changes take place in the oxide film on the germanium surface after metal evaporation; (ii) that the application of a voltage of either polarity causes charge exchange between the slow states and the semiconductor, which leads in turn to a change in the height of the potential barrier for electrons passing from the metal into the semiconductor.

A simple approximate solution is derived for the current and potential distributions around a sphere gap with small separation. The method is based on the fact that the problem has an elementary solution for two equal spheres in contact. Its accuracy is about 1% for ratios of gap/sphere radius not greater than 0·1. Explicit elementary expressions are obtained for the stress distribution, the total conductance for spheres and segments of spheres, the fraction of the total current flowing within a given radius from the axis, and the same fraction within a radius having a specified ratio of stress to maximum stress. The implications of the results are discussed in relation to measurements of the dielectric properties of liquids and solids.

The dielectric constant prime and dielectric loss double prime in the paraelectric phase of polycrystalline potassium nitrate have been measured at 100 KHz and several microwave frequencies. The measured values of dielectric constant and loss were corrected for the reduced density of the sample. A comparison of prime and double prime values of the polycrystalline sample is made with previously reported values for a single crystal measured along its ferroelectric axis. It is observed that the relaxation behaviour in the paraelectric phase of a polycrystalline sample is similar to that of a single crystal and that both types of sample show a Debye-type dielectric relaxation, with relaxation times τ inversely proportional to (T-T_c), where T_c is the Curie-Weiss temperature.

The permeability and power loss during cyclic magnetization of anisotropic ferromagnetic laminations depend strongly on the angle between the texture axis and the applied field. This paper puts forward a simple macroscopic tensor theory which enables the angular dependence of these and other related magnetic properties to be predicted from measurements made in the symmetry directions alone. The essential feature of the theory is the assumption that, in the absence of any shape anisotropy, magnetization in each of these orthogonal symmetry directions proceeds independently. Experiments designed to test the theory are described. Very good agreement is found in the initial permeability region for Goss-textured (110) [001] silicon iron. The angular dependence of the peak field required for sinusoidal magnetization is also shown to be predicted accurately for inductions up to some 10 kG; losses at these inductions tend to be underestimated by up to 15%. The analysis also reveals the importance of transverse flux closure, via neighbouring laminations, on the behaviour of skew-magnetized grain-oriented silicon iron at flux densities up to 15 kG.

The conditions under which the space-charge-limited current in a solid is enhanced by the Frenkel effect are discussed and the current-voltage relations are calculated analytically.

Hall coefficient measurements are reported on heavily doped n-type and p-type hot-pressed germanium - silicon alloys over the temperature range 300-900 K. The temperature variations of carrier concentration and conductivity mobility are obtained by combining the results with electrical resistivity and Seebeck coefficient data on the same specimens. The results indicate that the carrier concentration in the n-type alloys increases significantly with temperature.

Absorption of photons from a ruby laser (hv=1·78 eV) in a CdS crystal (band gap E_gsimilar, equals2·4 eV) was found to be non-linear with the incident photon fluxes above about 5×10²⁰ photons/s. A second-order transmission equation was fitted to the experimentally observed transmission data and the value of the non-linear absorption constant B was evaluated. The photocurrent in the same crystal for incident photon fluxes above about 5×10²⁰ photons/s was found to have a quadratic relation, indicating a double-photon process of absorption. The double-photon absorption constant due to the non-linear absorption was also calculated from the observed photocurrent. The value lay between 10⁻² and 10⁻³ cm⁻¹ compared with Braunstein's predicted value of about 10⁻⁴ cm⁻¹ for a photon flux of 6×10²² photons/s cm².

Phosphor samples of ZnS(Cu, Mn) powder have been synthesized in an inert atmosphere of pure nitrogen. It has been observed that for low concentrations of manganese (copper concentration being fixed) there is an increase in the luminescence from copper centres. A second peak other than the green emission from copper centres develops at higher concentrations of manganese. The copper centres must be transferring absorbed energy to manganese centres, as is also borne out by the excitation spectra remaining practically the same. The decay characteristics have also been studied. Results tally with the trap depths determined from the thermo-luminescence data.

Faraday rotation measurements have been performed on a number of antimony-doped (111) and (110) oriented n-type germanium crystals using 23·99 GHz microwave radiation at room temperature. The samples studied were thin circular slices having resistivities between 10 and 1 Ω cm. The anisotropy in the Faraday rotation with respect to the magnetic field orientation has been studied by applying B along the [110] and [111] directions. The corrections for the multiple reflections and guided waves have also been included. All the rotation measurements for the [110] direction of B are found to be in good agreement with the anisotropic theory developed by Donovan and Webster, while for the [111] propagation the `isotropic formula' is sufficient. The rotation is found to increase with the magnetic induction as well as with the conductivity of the samples in the above range, as expected.

A light transmission technique has been employed for evaluating the performance of a two-stage electrostatic dust precipitator, using fly-ash as the test dust. Collection efficiency of the second (ie collector) stage of the precipitator was obtained in terms of the surface area of the dust as a function of the applied voltage. Experiments using light of various wavelengths throughout the visible region indicate clearly the limitations of the technique when the mean particle diameter becomes of the same order of magnitude as the wavelength of the light, and some semi-quantitative assessments are made with respect to the behaviour of the particle extinction coefficient in that régime. Finally, some results obtained with white light are compared with some efficiency values obtained in terms of dust weight by isokinetic sampling.