Thesis (Ph. D.)--Johns Hopkins University, 1928. / Cover title. Vita. "By J.B. Whitehead and R.H. Marvin." "Report to Engineering foundation of an experimental research conduceted in the Laboratory of electrical engineering of the Johns Hopkins university, Baltimore, MD." Bibliography: p. 15-16.

Thesis (Ph. D.)--John Hopkins University, 1931. / "By J.B. Whitehead and F. Hamburger, jr." Vita. "Presented at the summer convention of A.I.E.E., Asheville, N.C., June 22-26, 1931." Bibliography: p. 11.

Thesis (Ph. D.)--Columbia University, 1934. / Vita. Bibliography: p. 41-42.

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

No description available.

The present methods of ascertaining the probable sludging of transformer oils are laborious. A simple test, comparable to that used in obtaining the dielectric strength, would be of considerable value in reducing test manpower, equipment and expense. Present investigators measure such properties as oxygen absorption, colour change, increase in acidity, carbon dioxide evolved, water formed, the power factor, and the lnterfacial-tension value. Numerous dielectric materials exhibit anomalous dispersions. The attendant rise in dissipation factor encountered at the points of dispersion is helpful in determining the amounts and types of polarization present. Transformer oils, although initially non-polar, are subject to oxidation. This oxidation produces materials of polar molecular structure which govern the power loss in alternating current electric fields. The problem is one of correlating such losses to the state of the oil under test. This thesis deals with the investigations carried out on the above problem. Absorption bands for transformer oils have been found. The present work describes the presence and location of such absorption bands, and illustrates how the dipolar state of the oil affects the position of the loss peaks. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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We are living in an era of digital electronics. The number of robots have already exceeded the human population of the entire earth. An article in the Guardian newspaper dated 30th March 2018 suggests that 10 million UK workers will be jobless within 15 years as they will be replaced by robots. These astonishing facts shed light on the importance of knowledge and how important it is to use it wisely for our benefit without ultimately destroying us. Knowledge in all forms is accessible without going to a library or buying a newspaper. Furthermore to access information, we often use sleek devices such as smart phones, using highly developed multimedia platforms which consume large amounts of power. In 2016, IBM found that humans create 2.5 quintillion bytes of data daily. Since high computing usage is related to large power consumption, the basic building block of electronics i.e. the transistor is required to be more power efficient. This is now possible through spintronics, where the spin of an electron is exploited instead of the charge. A new class of exotic materials called topological insulators are predicted to exhibit efficient spintronic applications. These materials can conduct spin polarised current on their surface while remaining completely insulting from the inside. Moreover, doping topological insulators with magnetic impurities unlocks new avenues for spin memory devices in the form of a single spin polarized dissipationless conduction channel. In topological insulators, there is always a contribution from the inside (bulk) in addition to surface conduction, thereby yielding charge transport rather than spin transport. On this basis, the aim of my PhD was to explore techniques to grow, characterize, fabricate and measure devices on topological Dirac materials, with the hope to experimentally distinguish the bulk from the surface states and also exploit their exotic properties arising from opening of the bulk band gap by intentional magnetic doping. Samples consisted of thin films of Bi2Se3, Sb2Te3, Cr doped Sb2Te3, bilayers of Dy doped Bi2Te3/Cr doped Sb2Te3 and Cd3As2 nanowires. It was found that a seed layer of an undoped topological insulator was a crucial first step to ensure high quality growth by molecular beam epitaxy, followed by the desired stoichiometry. By physically doping Sb2Te3 with Cr, a successful control of the magnetic and electrical properties such as coercivity, anomalous Hall resistance RA xy, Curie temperature Tc, carrier density and mobility were achieved. A substitutional Cr doping ranging from 7.5% to 38% was attained revealing a Tc reaching up to 186 K. Gated electrical measurements displayed a change in RA xy and carrier density by ~ 50% on applicating of just -3 V gate bias in a sample with 29% doping. A comparison between electrical transport, Magneto-optical Kerr effect and terahertz time domain spectroscopy measurements revealed that the mechanism of magnetization was RKKY mediated. Furthermore, the bilayer structure displays a clear exchange bias coupling arising from the proximity of the antiferromagnetic Dy doped Bi2Te3 layer with the ferromagnetic Cr doped Sb2Te3 layer. Electrical transport measurements on Bi2Se3 Hall bars fabricated using Ar+ milling and wet chemical etching were compared. The results showed a more bulk type response in the chemical etched sample even though Ar+ milling was responsible for creating more disorder in the system leading to a higher carrier density and lower mobility. A thickness dependent study on Sb2Te3 thin films revealed a single conducting channel associated with a coupled surface and bulk state for a 12 nm sample, compared to, two conducting channels associated with the top and bottom surfaces for the 25 nm sample. Electrical transport on Dirac semimetal Cd3As2 nanowires reveal an ultra-high mobility of 56884 cm2V-1s-1 at 1.8 K from analysis of Shubnikov-de Haas oscillations. By studying various Dirac materials, new avenues for practical device applications can be explored.

No description available.