Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Thesis (doctoral)--Lunds universitet, Malmö, 1990. / Extra t.p. wih thesis statement inserted. Bibliography: p. 156-170.

Recent work has highlighted unusual effects of vanadium when used in conjunction with other microalloying additions on the hardenability of steels. Positive and negative synergistic effects have been observed, but studies into the mechanisms have been limited. To investigate the effects, vanadium interactions with aluminium, molybdenum, niobium and titanium were studied in low (0.1%) and medium (0.4%) carbon steels, containing normal (0.008%) and enhanced (0.020%) nitrogen. Utilising standard jominy test conditions of 950°C for one hour resulted in classical hardenability responses being obtained, where increasing quantities of microalloying additions in solution increase the hardenability. However, when the jominy test conditions were varied unexpected effects were observed. Extending the austenitising time to eight hours showed that the hardenability was dependent upon kinetic effects such as the rate of solution of the alloy carbides/nitrides and the rate at which the microalloying elements in solution segregated to the austenite grain boundaries. It was also observed that if the austenitising temperature was increased to 1200°C a decrease in hardenability could be obtained by increasing the quantity of vanadium, niobium or titanium. These effects were attributed to a combination of thermal dispersion of microalloying clusters from the austenite grain boundaries, preferrential transformation on large alloy carbides/nitrides and migration of the austenite grain boundaries. Therefore it was considered inadequate to explain hardenablity solely in terms of the carbon concentration, austenite grain size and amount of other alloying elements present. Additional factors such as cluster formation, grain boundary pinning etc., were identified and applied to the results to successfully explain the effects of the alloy interactions on hardenability. Recent studies on vanadium alloyed pearlitic steels showed significant increases in strength could be obtained by precipitation within the pearlitic ferrite. Mechanical property investigations of two steels indicated that a maximum precipitation effect was obtained at an isothermal transformation temperature of 600°C.

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Compression-moulded unplasticised poly(vinylchloride) (uPVC) was swollen with various organic liquids at two temperatures, 60°C and 30°C, both temperatures being below the glass transition temperature of uPVC. Liquids were chosen to give a range of solubility parameters, molecular sizes and ability to form hydrogen bonds. It was hoped to find a PVC–liquid system which behaved similarly to PVC swollen with vinyl chloride monomer (VCM).

The purpose of this thesis is to investigate the operation of GaAs field-effect transistors with particular attention to the existence of negative resistance regions in the current-voltage characteristics, velocity overshoot effects, the role of substrate, and the role of heterojunctions. The approach used is to solve the electron transport equation using the Monte Carlo method which accounts for non-local effects in electron transport. Arguments are presented to support the contention that the negative resistance regions in the current-voltage characteristics observed in some experimental devices and produced by other researchers' computer simulations are attributed, in part, to the negative differential mobility of GaAs. The main reason of the existence of this negative resistance is related to the active layer thickness and it will be explained in terms of the rotation of the velocity vector. Electron velocity overshoot, a consequence of non-local effects, is examined in terms of gate length. The velocity overshoot becomes significant for FET structures with gates less than a micron in length and has many significant effects on the device performance. It is found also that velocity overshoot accounts for the undesirable saturation characteristics of submicron gate length GaAs FET which are observed in practical devices. However, it was also found that the presence of a low-doped n-type GaAs substrate below the active layer removes the negative resistance regions in the current-voltage characteristics. This is attributed to the effect of carrier injection from the active layer into the substrate which leads to the decrease of the effective channel thickness. This then will decrease the transconductance of the device, increase the gate pinchoff voltage and lower the device frequency response. This degradation of device's performance depends entirely on the purity and properties of the substrate. The performance of substrated FETs can be improved by preventing electron penetration into the substrate. This situation can be reached by using AlGaAs substrate whose energy band gap is higher than that of GaAs which then leads to electron confinement in the active layer. The use of AlGaAs in FETs can be in different forms. These will also be demonstrated in this thesis.

Improvement in the mechanical properties of soil by lime (Ca(OH)2) results from the formation and development of cementitious phases. The newly formed phases interlock and bond the soil particles together increasing the strength of the soil and improving its durability. In the present work the engineering properties including plasticity, density, compressive strength, porosity, permeability and frost heave resistance were investigated for cylindrical specimens of a Devonian Red-Marl containing various amounts of lime (2-14 wt%), cured for up to 24 weeks at different temperatures (25, 50 and 75°C) and in different environments (sealed, unsealed, air, nitrogen and carbon dioxide). Mineralogical analysis of Red-Marl as well as montmorillonite, kaolinite and illite and also the reaction products of these materials with lime (10-20wt%) were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy with energy dispersive analysis (TEM/EDAX) and thermogravimetric analysis (TG). The Red-Marl was found to consist of illite/glauconite, quartz and feldspar with minor amounts of chlorite and haematite. It was observed that curing temperature has a dramatic effect on the reaction between soil and lime and on the engineering properties of the cured soil-lime samples. At normal curing temperatures the plasticity index decreases markedly and the strength increases only marginally with increasing lime content and curing time. At elevated temperatures, the strength sharply increases in a moist environment whereas lack of sufficient moisture virtually stops any further reaction. It was observed that carbonation of lime does not contribute to any great extent to the increase in strength and should be minimized. The addition of a small amount of NaCl in conjunction with lime may accelerate the reaction slightly. It was observed that the nature of clay soil alters by adding lime and the cured materials show a greater durability with a significant improvement in properties such as pore structure, permeability, volume stability and frost resistance. The analyses of the newly formed cementitious material shows it to consist of almost amorphous gel forming foil-like membranes and fine filaments which interconnect the soil particles. Morphological development and microstructural analyses of the gel suggest that it is formed as a result of the progressive breakdown of the original clay particles by reaction with lime.