In recent years, the emergence and development of crowd-sourced geospatial data has provided challenges and opportunities to national mapping agencies as well as commercial mapping organisations. Crowd-sourced data involves non-specialists in data collection, sharing and maintenance. Compared to authoritative geospatial data, which is collected by surveyors or other geodata professionals, crowd-sourced data is less accurate and less structured, but often provides richer user-based information and reflects real world changes more quickly at a much lower cost. In order to maximize the synergistic use of authoritative and crowd-sourced geospatial data, this research investigates the problem of how to establish and validate correspondences (matches) between spatial features from disparate geospatial datasets. To reason about and validate matches between spatial features, a series of new qualitative spatial logics was developed. Their soundness, completeness, decidability and complexity theorems were proved for models based on a metric space. A software tool `MatchMaps' was developed, which generates matches using location and lexical information, and verifies consistency of matches using reasoning in description logic and qualitative spatial logic. MatchMaps was evaluated by the author and experts from Ordnance Survey, the national mapping agency of Great Britain. In experiments, it achieved high precision and recall, as well as reduced human effort. The methodology developed and implemented in MatchMaps has a wider application than matching authoritative and crowd-sourced data and could be applied wherever it is necessary to match two geospatial datasets of vector data.

The provision of free basic water for domestic uses and a more equal distribution of water for productive uses are seen as important instruments to redress inequities from the past and eradicate poverty in South Africa (SA). Although the government committed itself to providing free basic water for all, this result is still far to be reached, particularly in rural areas. Financing of multiple use water services was identified as an important ingredient to insure improved access to water for rural poor in SA and at the same time allow productive uses and broaden livelihood options. Recent evidence indicated the potential contribution that productive uses of domestic water might make to food security and poverty reduction in rural areas of SA. Following the principles of integrated water resource management (IWRM), efficient, equitable and sustainable investment in improved water services should be demand driven, that is, it should be based on a thorough understanding of effective demand by consumers for multiple use water services. The assessment of demand for improved water services provides the basis for micro level analysis of consumer benefits from multiple water uses. Such studies are not common in SA’s rural areas, where most of the economic analyses focus on either domestic or irrigation water demand. This study attempts to fill this gap by assessing the household demand for multiple use water services in Sekororo-Letsoalo area in the Limpopo Province. Choice modelling is the approach used to identify the attributes determining demand for water services and quantify their respective importance. Households are presented with alternative sets of water services, corresponding to different levels of the attributes. In this study, the following attributes were used: water quantity, water quality, frequency of water supply, price of water, productive uses of water, and source of water. Choice modelling allows estimating the relative importance of these attributes for various strata of the studied population, and ultimately provides a measure of the willingness to pay for different aspects of water demand (attributes), including productive water uses. Results show that households in rural areas are willing to pay for water services improvements. Due to the poor quality of present water services in the area, users are primarily concerned with basic domestic uses and demand for non domestic water uses is low. Only households already relatively well served are interested in engaging in multiple water uses. / Dissertation (MSc(Agric))--University of Pretoria, 2009. / Agricultural Economics, Extension and Rural Development / unrestricted

The thesis is focused on the study of properties of GaN nanocrystals and Ga structures on the surface of silicon and graphene substrate. In the theoretical part of this thesis, the basic properties of Ga/GaN and graphene are described, as well as their applications or connection of both structures together in different devices. The ability of metal nanoparticles to enhance not only photoluminescence, due to the interaction of the material with surface plasmons, is also shown in several examples. The experimental part of the work first deals with the production and characterization of graphene sheets prepared by Chemical Vapor Deposition. Ga/GaN growth on both types of substrates was performed in a UHV chamber using an effusion cell for Ga deposition and an atomic ion source for nitridation. Prepared structures were characterized using various methods (XPS, SEM, AFM, Raman spectroscopy or photoluminescence). In the last step, GaN nanocrystals were coated with Ga islands to study the photoluminescence enhancement.

This thesis deals with deposition of GaN thin films and GaN selective growth utilizing pyrolyzed resist masks. Carbon masks were prepared on silicon substrates by electron-beam litography and resist pyrolysis. As a further step, Ga and GaN were deposited on the masked substrates by Moleculer Beam Epitaxy (MBE) method. A selective growth of Ga droplets was achieved. These results were used for preparation of GaN crystallites by pulse deposition. It is also shown that direct MBE deposition of GaN on the masked substrates leads to a selective growth of GaN thin films with GaN film growing only on the areas which are not covered by the carbon mask. The results are explained by enhanced surface diffusion of gallium atoms on the surface of the carbon mask.

Im binären Mn-Ga-System wurde für Legierungen mit 55 at.% bis 65 at.% Mangan die Phasenbildung der L10-Phase mit Röntgenbeugung und Differenzialkalorimetrie untersucht. Nach der Herstellung der L10-Phase in allen Legierungen erfolgte eine Untersuchung der intrinsischen magnetischen Eigenschaften. Die Mn55Ga45-Legierung zeigte dabei die höchste Sättigungsmagnetisierung mit µ0Ms = 0,81 T. Für diese Legierung erfolgten deshalb Versuche zur Verbesserung der extrinsischen Eigenschaften. Dazu wurden Pulver gemahlen und die Möglichkeit der Ausrichtung im Magnetfeld untersucht. Dabei konnte ein Texturgrad von 0,45 für Pulver mit einer Partikelgröße kleiner 10 µm erreicht und die Koerzitivfeldstärke um das 7-fache gegenüber der Volumenprobe erhöht werden. Weiterhin konnten die Pulverproben durch Heißkompaktieren bei 400 °C erneut zu einer Volumenprobe gepresst werden. Die dabei erhaltene Probe besitzt eine Koerzitivfeldstärke von 0,16 T und eine leicht reduzierte Sättigungsmagnetisierung auf Grund einer Packungsdichte von 83 %. Im ternären Mn-Al-Ga-System wurden Proben der Sollzusammensetzung Mn55Al45-xGax mit 5,625 < x < 22,5 hergestellt. Für Legierungen mit x >= 11,86 erwies sich eine Wärmebehandlung bei 600°C für 24 Stunden als ausreichend die reine L10-Phase zu erzeugen. Bei den Legierungen mit einem geringeren Ga-Anteil war eine zweistufige Wärmebehandlung notwendig, um ausschließlich L10 zu erhalten. Nach der ersten Wärmebehandlung bei 1100 °C entstand ein Phasengemisch aus gamma2 und L10(epsilon). Letzteres wurde aus der epsilon-Hochtemperaturphase gebildet. Durch die anschließende Wärmebehandlung bei 500 °C für 24 Stunden konnte die verbleibende gamma2-Phase in L10(gamma2) umgewandelt werden. Untersuchungen der lokalen Legierungszusammensetzung ergaben einen geringeren Mn-Anteil der L10(gamma2)-Phase im Vergleich zu L10(epsilon). Die Unterschiede in den zwei L10-Phasen konnten weiterhin durch eine Reflexaufspaltung in den Röntgenbeugungsaufnahmen sowie der Existenz zweier Curie-Temperaturen bestätigt werden. Die gemessenen Sättigungsmagnetisierungen ergaben eine Superposition beider Phasen und einen maximalen Wert von µ0Ms = 0,85 T. Untersuchungen der thermischen Stabilität der L10-Phasen bei 700 °C zeigten, dass die L10(gamma2)-Phase thermisch stabil ist und sich die L10(epsilon)-Phase langsam in beta-Mn und gamma2 zersetzt. Bei der Zersetzung war im Vergleich zum binären Mn-Al-System eine starke Steigerung der thermischen Stabilität durch die Substitution geringer Mengen Galliums zu erkennen. Über die zersetzungsbedingte Reduktion der Magnetisierung konnten Abschätzungen der Zersetzungskinetik getroffen werden.

<p> The purpose of this work was to develop a growth pathway for synthesis of high-quality ferromagnetic Ni-Mn-Ga shape memory thin films and to understand their functional properties. </p> <p>Two groups of Ni-Mn-Ga films were prepared using the pulsed laser deposition technique. One group was grown on (100) YSZ ((Zr,Y)O2 with ZrO2:Y2O2=92:8) and was used to study the thermal, magnetic, and magnetocaloric properties. The other group was deposited on (100) MgO. These films were fabricated into free-standing micro-bridges.</p> <p>These Ni-Mn-Ga films were synthesized in a previously unexplored high temperature deposition regime. The temperatures employed encouraged the development of the desired micrometer-size highly twinned martensite grain structure while the general problem of preferential evaporation of the volatile elements at elevated temperatures was solved by using a manganese and gallium enriched target.</p> <p> The films grown on (100) YSZ exhibit a self-reversible, magnetically induced reorientation of the martensite variants (MIR), which is temperature dependent. The mechanism associated with the self-activated reversibility in the MIR effect was established through a detailed characterization of the texture, microstructure, and magnetic domain structure of the films. </p> <p> The synthesized films also show a large magnetocaloric effect (MCE), which is particularly strong at low magnetic fields. The effect is associated with an overlapped ferromagnetic and martensitic phase transition. Detailed characterization of these transitions allow for an understanding of the role each phase transition plays in determining the level of enhancement to a standard MCE governed only by the ferromagnetic phase transition.</p> <p> Ni-Mn-Ga free-standing micro-bridges were fabricated using photolithography followed by wet chemical etching. Microstructural evolution of the martensitic variants resulting from changes to the stress field in the detached areas was studied in the context of potential film applications for micro-actuators.</p> / Thesis / Doctor of Philosophy (PhD)

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No description available.

No description available.

Marine structures must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum satisfies these conditions, and would be a good choice for a sacrificial anode to protect steel structures if it did not passivate. However, various elements can be added to aluminum to prevent this passivation. Currently, Al-Ga alloys are used commercially as sacrificial anodes but their performance is not consistent. In this research, Thermo-Calc software was used to simulate various aspects of the Al-Ga system in an attempt to understand and potentially correct this reliability issue. Simulations showed that gallium segregates to the grain boundaries during solidification and then diffuses back into the grains during cooling to room temperature. Simulations also suggest that faster cooling rates and larger grains cause the potential segregation of gallium at the grain boundaries to remain after cooling. A set of aluminum plus 0.1% weight percent gallium alloy plates were produced with varying cooling rates, along with a control set (cooled slowly in a sand mold). Some samples were later homogenized via annealing. Samples were subjected to a 168 hour long galvanostatic test to assess voltage response. The corrosion performance of samples was found to have both consistent and optimal voltage range when subjected to quick cooling rates followed by annealing. Testing samples at near freezing temperature seems to completely remove optimal corrosion behavior, suggesting that there are multiple causes for the voltage behavior. / Master of Science / Ships must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum has properties which could allow a plate of it to rust instead of a ship it is attached to, thus protecting the ships from rusting. However, because aluminum usually does not rust, gallium can be added to aluminum to allow it to rust. Currently, aluminum-gallium alloys are used commercially to protect ships, but their performance is not consistent. In this research, various aspects of the aluminum-gallium system were simulated in an attempt to understand and potentially correct this reliability issue. Simulations showed that the gallium concentration may not be uniform in the alloy, and various conditions can cause the gallium concentration to be inconsistent. A set of aluminum-gallium alloy plates were cast in molds from liquid aluminum. Some of the plates were cooled quickly, and some cooled slowly. Some samples were later heated in an oven at high temperatures in an attempt to even out the gallium concentration. Samples were subjected to tests to observe corrosion behavior. The corrosion performance of samples was found to be best when subjected to quick cooling rates followed by the oven heating. Testing the samples in cold temperatures seemed to remove the desired corrosion behavior, suggesting that there are multiple reasons for the inconsistent corrosion behavior of aluminum gallium.