Thesis (PhD.(Department of Chemistry))--University of the Western Cape, 2007. / Includes bibliographical references (leaves 191-221).

Thesis (Ph. D.)--University of Michigan, 1941. / Cover-title. An article, by W.G. Keck and W.F. Colby, reprinted from the journal of applied physics, v. 13, no. 3, March, 1942. Bibliographical foot-notes.

Thesis--University of California, Berkeley, 1959. / Includes bibliographical references (p. 130-133).

Inaug.-diss.--Marburg. / Lebenslauf.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This study was undertaken in order to investigate the possible occurrence of horizontal variations in the electrical conductivity of the Earth’s upper mantle in southwestern Canada, using a series of simultaneous magnetic variograph recordings. Until recently no variation in the conductivity in a horizontal direction had been anticipated nor observed. During the past five years Parkinson in Australia, Rikitake in Japan, Schmucker in Germany and others have observed marked differences in the magnetograms at closely spaced stations. Secondary magnetic fields produced by induction in high conductivity regions in the Earth’s upper mantle have been suggested as the cause of these differences. The profile described in this thesis indicates conductivity inhomogeneities in southwestern British Columbia and southwestern Alberta. The vertical magnetic fields produced by induction in these inhomogeneities for magnetic variations with periods from 10 to 120 minutes have magnitudes of about 30 to 60 percent of the normal horizontal component. The normal vertical component is about 20 percent of the horizontal. These regions appear to be essentially two dimensional with anomalous induction resulting only from that component of the incident magnetic variations which is perpendicular to their strike. This strike and the intensity of the induced field have been estimated at each station. A pronounced difference has also been found between the vertical component of the diurnal geomagnetic variations at a station In the Rocky Mountains and those at the rest of the stations along the profile. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A general analytical method to derive the distributed circuit parameters and mode propagation constants for an n-conductor transmission line is developed. The analysis uses electromagnetic field concepts and the results are interpreted in terms of distributed circuit parameters. The procedure involves transforming the problem of the n-conductor line above a ground with finite conductivity into that of an n-conductor above a ground with infinite conductivity. Correction factors are added to account for the finite conductivity of the ground. The distributed circuit parameters thus calculated are used to calculate the mode propagation constants over a frequency range from 10 Hz to 1 MHz for values of ground conductivity varying between 1 mho/m and 10⁻⁵ mho/m and relative permittivity varying between 10 and 50. Numerical results for the distributed circuit parameters and mode propagation constants for a typical 500 kV single circuit transmission line and various ground conditions are given. The results show that one mode has a higher attenuation and a lower velocity than either of the other two modes, suggesting the zero sequence mode for a completely balanced system. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The critical, currents and magnetic fields required to destroy superconductivity have been measured for thin films of indium and tin in the thickness range of 585 Å to 3600 Å, The measurements were made in the region close to the transition temperature, T[subscript c] . The critical current measurements on a 585 Å thick indium film are the first reported which combine the use of a compensated geometry avoiding the difficulties associated with specimen edges, and fast rising current pulses in which the transition is not obscured by specimen heating. The fast current pulses used had a rise time of 7 nanoseconds. It was found that the temperature dependence of the critical currents in the region near the transition temperature, 0 ⋜ ΔT ⋜ 0.15°K is in. agreement with the Ginzburg-Landau theory. For a number of films the critical currents were measured using pulses having a rise time of 1.2 microseconds. The critical currents have been found to vary linear 1 with the film thickness, in agreement with the G-L theory. Measurements with fast pulses seem to indicate the existence of a transition delay of about 7 nanoseconds, independent of the current amplitudes. The transition from the superconducting to the normal state immediately following the transition delay appears to be very fast. For the critical field data, the temperature dependence is in accordance with the G-L theory in the range 0⋜ΔT ⋜ 0.3°K for both indium and tin films. The effective penetration depth calculated in the manner of Ittner, and Douglass and Blumberg was found to be dependent on the thickness and the mean free path. The critical magnetic fields were found to be inversely proportional to the film thickness in agreement with G-L theory. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis describes an investigation of flow phenomena of liquid helium II associated with temperature and pressure gradients. The experiments were done primarily in the range of heat flow critical with respect to mutual friction and with respect to turbulence in the normal fluid. The results are analysed on a phenomenological basis due to Gorter and Mellink,(12) and are interpreted by making use of the model put forward by Hall and Vinen. (14) This model assumes that the superfluid can develop vortex lines which interact with the thermal excitations of the normal fluid. A conclusion is reached, that a considerable amount of energy is stored in non-thermal motion in this vorticity. Friction in the normal fluid is reviewed in the light of the work of Staas, et al. (8) An experiment to measure the attenuation of secound sound at very low frequencies is described. A few suggestions for further investigation are tendered. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The conductance of a small electric probe has been determined for radial distances (2 - 15 cm) from a recovering spark gap as a function of time after discharge initiation. The times investigated were from 0.2 to 15 ms and the gas pressure was varied from 22 mmHg down to 0.1 mmHg. The voltage applied to the probes was a sawtooth pulse which rose to about 80 volts in 10 μs. It is shown theoretically that the probe conductance should be proportional to the three-halves power of the gas temperature. Prom a known value of the temperature, deduced from recovery measurements, and the known probe conductance the constant of proportionality was deduced. Hence it was possible to determine the temperature from the probe conductance. The probe conductance measurements show that at 200 mmHg pressure the spark channel is only 2 cm in radius and that there is no detectable ionization left 2 ms after the discharge. As the gas pressure decreases the spark channel increases in size and takes longer to deionize, until at 1 mmHg pressure the channel fills the whole spark chamber (spark channel radius is 15 cm) and requires almost 15 ms to deionize. At 1 mmHg gas pressure there is a radial temperature gradient, while at 0.1 mmHg pressure the gas everywhere in the channel recovers at the same rate. In this experiment it is theoretically predicted that volume recombination should be the dominant recovery method and this is experimentally verified. / Science, Faculty of / Physics and Astronomy, Department of / Graduate