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Common brown colour in natural diamond forms by plastic deformation during storage in the subcontinental lithospheric mantle (SCLM). Dislocation movement generates vacancies, which aggregate into clusters of perhaps 30–60 vacancies. Positron annihilation lifetime spectroscopy (PALS) and electron energy loss spectroscopy (EELS) support such vacancy clusters as the cause of brown colour. Brief treatment in a high-pressure–high-temperature (HPHT) vessel at 1800–2700 °C can destroy the brown colour. There has been speculation that similar colour removal should occur continuously at depth in the SCLM. Diamonds are stored at 900–1400 °C in the SCLM, according to inclusion thermometry. The effect of temperature on the time required to destroy brown colour has been calculated from published data. The activation energy for the breakup of vacancy clusters is a critical component. The time required to destroy brown colour in the SCLM is significant at the scale of geological time. Brown diamonds should easily maintain their colour for millions of years during cooler mantle storage at or below about 1000 °C. Warmer temperatures toward the base of the lithosphere may be able to reduce or eliminate brown colour within thousands of years. The survival of brown colour in the lithospheric mantle does not require the colour to be formed late in the storage history nor does it require metastable storage in the graphite stability field. Crystal strain is preserved upon loss of brown colour during HPHT treatment. Inhomogeneous crystal strain was measured in 18 natural diamonds using micro-X-ray diffraction (μXRD) χ-dimension peak widths. There is a correlation between strain and depth of brown colour. None of the colourless diamonds examined have high strain, as should be expected for a diamond that has gained and lost brown colour. This suggests that removal of brown colour is not a common natural occurrence. Infrared spectroscopy was used to determine nitrogen concentration and aggregation state in 60 natural diamonds. A loose association was found between brown colour and lower total nitrogen content. Within single diamonds, regions with less nitrogen tend to exhibit more anomalous birefringence due to strain. Colour zoned diamonds tend to have less nitrogen in the darker brown regions. This supports the hypothesis that diamonds with less nitrogen are more susceptible to plastic deformation and the development of brown colour. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2009-09-17 17:10:11.078

This thesis addresses some important issues when designing microfluidic systems for hot pressurized water. The properties and behavior of water at elevated temperatures and in micro scale is briefly reviewed, and opportunities and possible problems of using hot pressurized water in microfluidic devices are brought up. Experimental work was focused on corrosion resistance for commonly used microsystem materials in hot pressurized water, and the microfluidic behavior for hot pressurized water. An experiment system was successfully designed, assembled and used for corrosion resistance experiments in hot pressurized water. Corrosion resistance tests were performed for some common materials used in microfluidic and microsystems (silicon, stainless steel grade 304, silicon carbide, aluminum nitride, aluminum oxide, soda-lime glass and borosilicate glass) in deionized water and in low concentration HCl (0.1 mM) at two different temperatures (180oC and 270oC). All of the tested materials, except soda-lime glass, showed a good overall performance in the low temperature range. In the high temperature range, all materials showed signs of corrosion to some extent. Severe damages and high corrosion rates were observed for silicon and the two glasses, and stainless steel 304 showed signs of pitting corrosion. A microfluidic study identified some major issues needed to be overcome to make future microfluidic studies with hot pressurized water possible. Important observations included the importance of a short traveling distance for a hot micro flow to avoid rapid cooling, and to choose a suitable dye to avoid particles clogging thin capillaries and micro channels.

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The thesis begins with an introduction to transformer theory. The partial core transformer is then introduced and compared with a full core design. A brief introduction to superconductors and high temperature superconductors is then presented. High temperature superconducting fault current limiters are then examined and the advantage of a high temperature superconducting partial core transformer and fault current limiter as a single unit is highlighted. The reverse design model is discussed followed by the model parameters that are used in designing the high temperature superconducting partial core transformer. Partial core transformers with copper windings and high temperature superconductor windings at the University of Canterbury were then tested and the measured results compared with the results calculated from the reverse design model, to validate the model. The high temperature superconducting partial core transformer failed during an endurance run and the investigation of the failure is then presented. The results of the failure investigation prompted an alternative winding insulation design. A model to calculate the time at which the high temperature superconducting winding of the partial core transformer would melt at different currents was then built. The time was calculated to be used in the operation of the quench detection mechanism and it could also be used in choosing a circuit breaker with a known operating time. The design of the high temperature superconducting partial core transformer and fault current limiter is then presented. Design configurations with different core length and winding length are examined. The idea behind choosing the final design for the high temperature superconducting partial core transformer and fault current limiter is then discussed. The final design of the high temperature superconducting partial core transformer and fault current limiter is then presented. A new 7.5 kVA, 230-248 V high temperature superconducting partial core transformer and fault current limiter was designed, built and tested. The windings are layer wound with first generation Bi2223 high temperature superconductor. A series of electrical tests were performed on the new device including open circuit, short circuit, resistive load, overload and fault ride through. These tests were performed to determine the operational characteristics of the new high temperature superconducting partial core transformer and fault current limiter. The measured results from the tests were compared with the calculated results. The fault ride through test results were then compared to a 15 kVA high temperature superconducting partial core transformer that was designed and built at the University of Canterbury. Since the resistive component of the silver matrix in Bi2223 high temperature superconductor plays a very little role in controlling the fault current, the current limited by the leakage reactance is compared between the two devices. The high temperature superconducting partial core transformer and fault current limiter was found to be 99.1% efficient at rated power with 5.7% regulation and fault current limiting ability of 500 % over the 15 kVA high temperature superconductor partial core transformer from University of Canterbury.

<p> This thesis presents a scheme for preparation of trapped molecular ions with a high degree of internal state purity by optical pumping with a broadband pulse-shaped femtosecond laser; the internal structure of SiO⁺ permits fast stepwise pumping through the tens of rotational levels populated in a room-temperature distribution. Two analyses, which guided the experimental implementation, are presented: (1) a novel method of quantifying anharmonicity in the trapping potentials, which limits the number of ions that can be trapped, and (2) a rate-equation simulation of the quantum state evolution during pumping. Experimental implementation of pulse shaping and its characterization are discussed, as is the molecular spectroscopy used to reference this light to the rotational cooling transitions. Internal state analysis can be performed using resonance enhanced multiphoton dissociation.</p>

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No description available.

The utilisation of alternate sources of energy has reached critical levels due to the constantly growing demand for energy and the diminishing of fossil fuels. The production of hydrogen through the Hybrid Sulphur process is a possible alternative that may contribute towards alleviating the pressure on the world's energy resources. The two-step thermochemical cycle for decomposing water into hydrogen and oxygen offers the potential to obtain acceptable thermal efficiencies, while still using common and inexpensive chemicals. The process mainly makes use of two unit process operations: an electrolyser and a chemical decomposition reactor. This research project focuses on the concept design of the decomposition reactor operated adiabatically as a multi-stage reactor system with inter-stage heating, in order to simplify the reactor design. This approach allows for the independent evaluation of the reaction kinetics and the heat transfer mechanism. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

This study investigates the development of a strategy to simulate nuclear graphite oxidation with Computational Fluid Dynamics (CFD) to determine an estimate of graphite lost. The task was achieved by comparing the results of the CFD approach with a number of different experiments. For molecular diffusion, simulated results were compared to analytical solutions. Mass flow rates under conditions of natural convection were sourced from the 2002 NACOK experiment. Experimental data from the KAIST facility were sourced for the basic oxidation of graphite in a controlled environment. Tests included the reactions of carbon with oxygen and with carbon dioxide. Finally, the tests at NACOK from 2004 and 2005 were chosen for comparison for the simulation of oxidation. The 2005 test considered two reacting pebble bed regions at different temperatures. The 2004 test included multiple detailed structural graphite. Comparison of results indicated that the phenomenon of diffusion can be correctly simulated. The general trends of the mass flow rates under conditions of natural convection were obtained. Surface reaction rates were defined with user functions in Fluent. Good comparisons of the simulated and the KAIST experimental results were obtained. For the 2005 NACOK comparison, the pebble bed regions were simulated with a porous medium approach. Results showed that correct trends and areas of oxidation were estimated. The 2004 tests were with a combination of a porous medium and surface reaction approaches. More detailed oxidation experimental data would possibly improve the accuracy of the results. This research has shown that the CFD approach developed in the present study can identify areas of maximum oxidation although the accuracy needs to be improved. Both the porous and detailed surface reaction approaches produced consistent results. The limitations of the approach were discussed. These included transient phenomena which were estimated with steady state simulations, and the effects of change in geometry were not considered. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2010.