published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Mathematics / Doctoral / Doctor of Philosophy

This thesis is concerned with determining the orientation of small Unmanned Aerial Vehicles(UAVs). To make commercial use of these aircraft in aerial surveying markets their attitude needs to be determined accurately and precisely throughout a survey flight. Traditionally inertial sensors have been used on larger aircraft to estimate both position and orientation in combination with Global Navigation Satellite Systems (GNSS). High quality inertial sensors have many downsides when used on the small UAV. They are expensive, power hungry and often heavy. Inertial sensors are vulnerable to vibration, high acceleration, high rotation rate and jerk. All of these are present on the small UAV. This thesis identifies GNSS attitude determination as a potentially suitable alternative to inertial techniques. Carrier phase GNSS attitude determination uses three or more GNSS receivers with antennas separated by a short baseline to estimate the orientation of the UAV. This technique offers low cost, high accuracy and drift-free attitude estimates. To be successfully used it requires removal of the biases present in the received GNSS signals and estimation of the integer cycle ambiguity present in the carrier phase measurement. This thesis presents and examines the state of the art techniques for removing these biases and estimating an integer cycle ambiguity using a priori measurement of the interantenna distance. In this work a novel method is developed which uses this a priori baseline measurement to validate estimates of the carrier phase ambiguities. In order to test these methods data has been gathered using low cost, commercially available GNSS receivers and antennas. This is the first work in which modern, low cost, GNSS equipment has been tested for use in attitude determination. It is found that the state of the art carrier phase GNSS attitude determination methods can provide an accurate attitude estimate for every set of measurements from the GNSS receivers. However, a real UAV flight indicates that the low cost GNSS equipment does not track the GNSS signals throughout the flight. Signal outages, cycle slips and half cycle ambiguous carrier phase measurements occur due to rapid UAV manoeuvres. Having identified this problem this work goes on to replicate and quantify it through the use of a GNSS hardware simulator. Algorithms are then devised to increase the availability of the GNSS attitude solution throughout the tracking difficulties. Complete GNSS signal tracking failures are overcome through the innovative use of kinematic and dynamic attitude models. Both types of model give an attitude solution throughout GNSS signal tracking problems without adding significant cost or weight to the system. When tracking of the GNSS carrier phase signal is possible, novel use of the carrier phase triple difference observable allows the attitude rate to be estimated even when the carrier phase measurements are half cycle ambiguous. It is shown that integer and half integer cycle slips can be removed from the measurement through the combination of the modelling and triple difference techniques. The attitude output of both modelling and triple difference methods is used to resolve half cycle ambiguities and make full use of half cycle ambiguous data where previously it could not have been used. Success rates of up to 99.6% have been achieved for half cycle ambiguity resolution. As a result precise and accurate GNSS attitude solutions are available at nearly every epoch for which a carrier phase measurement is output by the GNSS receivers. When no measurement is available the attitude solution gracefully degrades over time. This work makes reliable, accurate, low cost attitude determination possible on mini-UAVs.

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The study aims to discover the strategies and techniques used by community mediators in the People's Republic of China. Previous research argues that mediator legitimacy in China draws on state authorization and the mediator's community standing. In contrast to Western conceptions of the mediator's role as a neutral facilitator of dispute resolution, research suggests that Chinese mediators openly speak on behalf of community norms, calling on disputants to subordinate personal preferences in the interest of maintaining harmonious relationships and governmental policies and legal regulations. The legitimacy of the mediation process depends more on a persuasive articulation of community norms than an impression of mediator neutrality. However, this account of Chinese mediation has been based solely on interview and questionnaire data. How (and whether) this contrast between self-report measures and mediation techniques in practice actually manifests itself in mediator discourse, at what stages, and to what degree has not really been observed or analyzed. This study records and analyzes community mediation cases to better understand what features are prevalent in mediation discourse. Cases were selected in both rural and urban areas. Discourse analysis is applied to transcripts so as to provide direct and detailed picture of how mediation is conducted in reality. Strategies typical of Chinese mediation, relative to American mediation are identified and illustrated with excerpts from the transcripts. Neutrality and power distribution are discussed and compared with their roles in American mediation. Their implications for political, social and cultural aspects are drawn to provide a glimpse of contemporary Chinese society and how resolution is created. Future research directions are pointed out with regard to mediator's gender difference, the location where the mediation happens (urban and rural) and the socio-economic class of disputants (e.g., migrant workers) involved in the mediation.

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Stereochemistry and chirality are arguably two of the most important subjects pertaining to the development of new pharmaceutical drugs. Since enantiomers have the potential to encompass different pharmacological effects in biological systems, both enantiomers have to be tested for pharmacological activity. Not only has obtaining these single enantiomers become crucial, but formulation of the pure enantiomer of a drug also has the potential to contain advantages for both pharmaceutical formulation and therapeutic effect. Epoxide hydrolase is an enzyme commonly found in nature that catalyses the hydrolysis of epoxides, resulting in the formation of the corresponding vicinal diol. Over the last few years a large amount of research has been completed on these enzymes from sources such as mammals, insects, bacteria and fungi. Micro-organisms especially have enjoyed ample attention because of their abundant supply. Recently it was found that certain yeasts contain this enzyme and have the ability to enantioselectively catalyse certain hydrolysis reactions. Styrene oxides are terminal epoxides that are, due to the reactivity of the epoxide ring, useful synthons in the organic synthesis of pharmaceutical products. The first objective of this project was to synthesize three nitro derivatives of styrene oxide namely para-, meta-, and ortho-nitrostyrene oxide. Al three products were obtained from the corresponding nitrophenacyl bromide in yields of 52%, 90% and 57% respectively. The second objective was lo find a suitable yeast slrain containing the epoxide hydrolase enzyme to enantioselectively hydrolyse the synthesised products and unsubstituted styrene oxide. A screening was completed during which 410 yeast strains from more than 44 genera were tested. Epoxide hydrolase activity was found to be widespread throughout the screened yeast domain, while the genera Candida, Debaryomyces, Pichia, Rhodosporidium, Rhodotorula and Trichosporon specifically were very successful in catalysing the hydrolysis of the substrates. Rhodosporidium toruloides UOFS Y-0471 and Rhodotorula glutinis UOFS Y-0653 were chosen for further studies because of their superior enantioselectivity. The final objective was to optimise these reactions in terms of pH, temperature and substrate concentration. It was found that a pH value of 7.2 and a temperature of 45’C yielded optimal enzyme activity. Increased temperatures (45’C), however, lead to a decrease in enantioselectivity and, in the case of R. toruloides together with the substrate puranitrostyrene oxide, reversed enantioselectivity. Lower temperatures (15’C) increased enantioselectivity, resulting in a remarkable improvement from a 10% yield of the single enantiomer (45’C) to a 35% yield. Surprisingly this temperature decrease had a very small affect upon the reaction time. / Thesis (M.Sc. (Pharmaceutical Chemistry)--Potchefstroom University for Christian Higher Education, 2002.

The proliferation of regional trading agreements around the world has changed the landscape of international trade law from a multi-polar system anchored in the nationstate to one where there are groups of closely-knit sovereign nations. They are usually drawn along geographical lines and are conducting trade with one another in a myriad of ways. This craze for trade deals is sure to give rise to disputes that are an inescapable outcome of the bilateral, regional and international agreements that contain the will of these nations to engage in greater co-operation with one another. As such, it has become necessary to design reliable dispute settlement mechanisms for the settlement of trade related disputes for the effective functioning of the trading agreements. Dispute settlement systems have progressed from being unsophisticated and diplomacy oriented as typified by that of the GATT to the highly legalized adjudication based mechanism that is the crowning glory of the WTO. This trend has been followed by other trading organizations that have modified their dispute settlement mechanisms to become more legalistic. CARICOM is a reborn regional trading bloc in the Caribbean and in lock step with the trend of other trading clubs has augmented its dispute settlement mechanism with a long awaited regional court and other non-binding alternative dispute resolution methods to avert legal clashes. This thesis examines the progress of the CARICOM dispute settlement mechanism from its originally diplomatic procedures to its enhanced legalistic system. A standing judicial institution in CARICOM is a coming of age for this region and its jurisprudence now referred to as CARICOM law. These significant legal advances raise many normative questions about the adequacy of the dispute settlement institutions and whether the rules and processes are clearly defined to enable nascent CARICOM law to be the primary tool by which there can be effective regulation of CARICOM integration. In order to answer these questions this thesis reviews the dispute settlement mechanisms of the WTO and the EU as the natural ‘parents’ of the CARICOM dispute settlement system.