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published_or_final_version / Electrical Engineering / Master / Master of Science in Engineering

M.Sc. / Aspects of electron-electron correlations have for the past few decades been at the forefront of research in Solid State Physics. More traditional concepts under this topic have been phenomena such as superconductivity, and magnetic ordering in its many forms including long-range ordering and spin-glass freezing. The class of so-called strongly correlated electron systems has been a particularly active field of study, as witnessed by for instance the series of annual international conferences held under this topic since 1992. Compounds and alloys of strong electronic correlations have proved a very rich field of new and anomalous physical behaviours in metallic and semiconducting compounds and alloys of especially 4f- and 5f-electron systems, together with ceramics characterized as the so-called ¡§high-TC¡¨ superconductors. The f-electron systems have revealed a variety of behaviours such as ~ 1000-fold enhanced effective electron masses at low temperature, coexistence of superconductivity and magnetic ordering in systems where the magnetic interactions are far too strong to allow for Cooper-pair formation within the well-established BCS-interpretation, and electron transport and thermodynamic behaviour at low temperatures that completely defy our conventional Fermi-liquid paradigm of understanding the ground states of metals. The series of pseudo-ternary compounds Ce1-xLaxRu4Sn6 that were synthesized and characterized in this work for the first time are formed by substituting La for Ce in CeRu4Sn6, the parent compound. CeRu4Sn6 exhibits a number of properties which have been associated with a special class, the Kondo semiconductors of strongly correlated electron systems. CeRu4Sn6 has very recently been shown [A. M. Strydom et al. (2004)] to comprise an intriguing combination of characteristics that are thus far unique among the Kondo semiconductors: At low temperature (T 10 K) the specific heat proves the development of very strong electronic correlation out of an already low density of charge carriers (as shown by Hall-effect, resistivity, and the Sommerfeld coefficient of the specific heat). Furthermore, the specific heat follows a logarithmic increase as temperature is decreased below ~ 2 K, in a range where thermal transport shows the presence of an energy gap in the electronic density of states. The aim of this work was to investigate the intermediate and higher temperature (4.01 K „T T „T 300 K) behaviour of the electrical resistivity of the Ce1-xLaxRu4Sn6 series of compounds in which the concentration of the 4f-electron magnetic ion Ce is progressively being reduced. A steady but slow decrease of the energy gap with increasing La concentration was found in this work in contrast with what is usually the case in Kondo semiconductors. Both the presence of an energy gap and the low density of charge carriers are found to be connected to the presence of Ce in the unit cell, and are therefore not an artefact of the peculiar filledƒ{cageƒ{like tetragonal crystal structure of these compounds. An interesting strong anisotropy was found in the way in which the tetragonal unit cell expands preferentially within the aƒ{b plane, compared to the elongation along the cƒ{axis, upon moving from CeRu4Sn6 to LaRu4Sn6. / Prof. A.M. Strydom

I. S?mon. / 3697726 RSC / "June 15, 1949." / Bibliography: p. 27. / Army Signals Corps Contract No. W36-039-sc-32037 Project No. 102B. Dept. of the Army Project No. 3-99-10-022.

Thesis (Ph. D.)--University of Hong Kong. / Mimeographed.

Thesis--M. Sc.(Eng.), University of Hong Kong. / Mimeographed.

published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--Brown University, 1926. / Part 1 reprinted from Journal of the American chemical society, v.47, 1925. Part 2 of thesis has title: Liquid mixtures of tellurium and sodium telluride. I. Specific resistance as a function of composition and temperature.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / Tomography is the ability to internally visualise an opaque medium or a body, using different imaging techniques. Electrical Resistance Tomography (ERT) technique is a method commonly used in process tomography. It uses a non-intrusive resistance measurement between a set of electrodes attached on the circumference of a fixed cross-section with a given conductivity and permittivity distribution. ERT appears to be simple, low cost, safe and non-invasive. Despite the advantages of ERT, the reconstruction of the internal conductivity of the pipe still face a crucial challenges such as noise, a relatively low spatial resolution, as well as ill-posedness of the inverse problem when doing the image reconstruction using reconstruction algorithms. Although previous work showed the potential of various algorithms for the reconstruction of ERT tomograms, no full characterisation and comparison of different algorithms could be found for real flow situations. The ERT system was tested in the identification of different objects and fluid beds in a real time situation. The data collected from the measurements were then used for the image reconstruction using an algorithm developed by Time Long (One-step algorithm) and four EIDORS-based algorithms namely: Gauss-Newton algorithm with Laplace Prior (LP) and Gaussian prior (Automatic Hyper Parameter Selection (AHSP)), the Total Variation (TV) algorithm and the Conjugate Gradient (CG) algorithm. The performance of each algorithm was tested in different scenarios. The results obtained were then compared based on the quality and the accuracy of the images as well as the computational time of each algorithm. Firstly, reconstructed images were obtained using objects placed inside the ERT pipe test. Secondly, the algorithm performances were put to test in a level bed setup experiment and finally, the algorithm reconstructions were applied to the real flow situation, where different flow rates were applied. The results obtained were then analysed and compared.

In the summer of 1967, dipole arrays were used to make deep resistivity soundings in the Fraser Valley of British Columbia. The large dipole moment of the input dipole (270 amp x 37 km) allowed input-to-measuring dipole spacings as great as 100 km. Calculations show that Georgia Strait, which is spanned by the input dipole, should have little effect on layered earth potentials for the dipole to dipole spacings used in this survey. A three-layer model with a resistive second layer (transverse resistance approximately 3000 times that of the upper layer) agrees well with the data. A more complicated four-layer model can be devised by using data from deep wells in the area. Interpretation of well and sounding data indicates that 500 m of conductive ocean and ocean sediments overlie 4-5 km of Tertiary and Cretaceous sedimentary rocks and 2 km of granitic rock. A conducting layer underlying the granitic rock may be the result of water saturation of the rocks at these depths. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate