Sudden rock failure in the form of rockbursting has long been a problem in underground mines. The basic mechanism of this phenomenon is still unresolved. This thesis describes the research work on this problem conducted by the doctoral candidate Daihua Zou in the Department of Mining and Mineral Process Engineering at The University of British Columbia, under the supervision of Professor Hamish D.S. Miller. This research project was undertaken in order to investigate the process of violent rock failure and was achieved by examining various aspects of the rock failure mechanism. The assumption that acoustic emission can be used as a reliable means of predicting rock failure was investigated, as well as the possibility that violent rock failure could occur in any mine rock. As part of the research, a rock failure mechanism was postulated. A process analogous to shearing is postulated to be important at the post-failure stage. The stick-slip phenomenon has been analyzed using a numerical model under a variety of conditions. The conditions which could give rise to possible violent rock failure were determined. At the same time, acoustic emissions were tested from rock specimens under different loading conditions. The experimental results obtained show a correlation with field measurements made in a mine. In order to verify the testing results from limited experiments, a numerical acoustic model was developed, which is unique in that it is entirely based on the stick-slip process not on any acoustic theory. This model allows rock tests and their associated acoustic emission to be realistically simulated. With this model, acoustic emissions were simulated under various loading conditions for different kinds of rocks. The case of a hard or a soft intercalation was also modelled. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

The electron emission characteristics of aluminum, molybdenum and carbon nanotubes were studied. The experiments were setup to study the emission behavior as a function of temperature and exposure to oxygen. Changes in the surface work function as a result of thermal annealing were monitored with low energy ultra-violet photoelectron spectroscopy for flat samples while field emission energy distributions were used on tip samples. The change in the field emission from fabricated single tips exposed to oxygen while in operation was measured using simultaneous Fowler-Nordheim plots and electron energy distributions. From the results a mechanism for the degradation in the emission was concluded. Thermal experiments on molybdenum and aluminum showed that these two materials can be reduced at elevated temperatures, while carbon nanotubes on the other hand show effects of oxidation. To purely reduce molybdenum a temperature in excess of 750 ºC is required. This temperature exceeds that allowed by current display device technology. Aluminum on the other hand shows reduction at a much lower temperature of at least 125 ºC; however, its extreme reactivity towards oxygen containing species produces re-oxidation. It is believed that this reduction is due to the outward diffusion of aluminum atoms through the oxide. Carbon nanotubes on the other hand show signs of oxidation as they are heated above 700 ºC. In this case the elevated temperatures cause the opening of the end caps allowing the uptake of water. Oxygen exposure experiments indicate that degradation in field emission is two-fold and is ultimately dependent on the emission current at which the tip is operated. At low emission currents the degradation is exclusively due to oxidation. At high emission currents ion bombardment results in the degradation of the emitter. In between the two extremes, molybdenum tips are capable of stable emission.

Electronic processes, such as electronic breakdown and electron emission, in gases and liquids have implications in microplasmas, laser applications, water purification, biomedical applications, geographical mapping, and radiation detection. Electron emission and breakdown mechanisms are heavily researched and characterized in gases. Much of the current research into these mechanisms is focused on unifying breakdown and emission mechanisms. For electron emission, these mechanisms include field emission (FE), space-charge-limited emission (SCLE), thermionic emission (TE), and photoemission (PE), while gas breakdown emission mechanisms include Paschen’s law (PL) and Townsend breakdown (TB)with ion-enhanced FE becoming important at microscale. This research first unified SCLE and FE in vacuum and has been extended to include SCLE with collisions (for a gas at non-vacuum) and TE. This thesis extends this approach in electron emission unification, referred to as “nexus” theory, in two directions. First, we will apply this theory to liquids to examine the transition from FE to SCLE and hypothesize about the implications should there be a phase change. Second, we will incorporate PE, which becomes important with increasing interest in ultrafast laser phenomena at nanoscale and development of solar cells, with SCLE, TE, and FE.<div><br></div><div>Initial nexus theory studies included gas at non-vacuum pressures by including electron mobility in the electron force law. In principle, this behavior should be the same whether the medium is air or liquid. Electron emission and breakdown, which can arise from field emission, are increasingly important in plasma water treatment, pulsed power systems, radiation detection, and even understanding the physics of high electric fields applied to liquid helium for the Spallation Neutron Source. To demonstrate the applicability of nexus theory to liquids, we fit experimental data for electron emission in hydrocarbons to the full theory unifying FE to SCLE with and without collisions. The measured current followed Fowler-Nordheim scaling for FE at lower voltages with space charge beginning to contribute at higher voltages; none of the hydrocarbons study fully transitioned to Mott-Gurney (SCLE with collisions) scaling within the experimentally studied parameter range. Considering a higher mobility representative of a vapor in the theory demonstrates the feasibility of achieving Child-Langmuir (SCLE in vacuum)scaling for the gaps of the size considered experimentally. Thus, this approach may ultimately be applied to model electron emission during both phases changes and transitions between the mechanisms.<br></div><div><br></div><div>We next extended the gas nexus theory to analyze the transitions between PE and the other emission mechanisms. We modified the previous theory that used the generalized thermal-field emission (GTF) theory for electron current to instead use the generalized thermal-field photoemission (GTFP) theory. Using this, we obtained exact solutions for current as a function of applied voltage and demonstrated the asymptotic behavior with regard to the modified Fowler DuBridge (MFD) equation, which models PE. We combined the MFD equation with the other asymptotic solutions to develop state diagrams unifying the various emission mechanisms to provide guidance to the mechanisms and transitions relevant under various conditions of mobility, gap distance, temperature, and laser energy/wavelength/frequency. These diagrams provide guidance on which asymptotic solution or more detailed theory would be necessary to accurately relate current and voltage under various operating conditions.<br></div>

Due to its impact on human health and the nature surrounding us, diesel engine emissions have been significantly reduced over the last two decades. This reduction has been enforced by the legislating organs around the world that gradually have made the manufacturers transform their engines to today’s complex high-tech products. One of the most challenging areas to meet the legislations is transient operation where the inertia in gas-exchange system makes transition from one load to another problematic.   Modern engines have great potential to minimize the problems associated with transient operation. However, their complexity also imposes a great challenge regarding optimization and systematical testing of transient control strategies in an engine test bed could be both expensive and time consuming.   The objective of this project is to facilitate optimization of transient control strategies. This should be done by identifying appropriate measurement methods for evaluation of transients and by providing models that can be used to optimize strategies off-line.   Measurement methods for evaluation of transients have been tested in several experiments, mainly focusing on emission but also regarding e.g. EGR flow. Applicable instruments for transient emission measurements have been identified and used. However, no method to measure soot emissions cycle resolved has yet been found. Other measurements such as EGR flow and temperatures are believed to have significantly decreased accuracy during transients.   A model for prediction of NOx emissions have been used and complemented with a new approach for soot emission predictions that has been developed in this project. The emission models have been shown to be applicable over a wide range of operating conditions with exception for highly premixed combustion. It has also been shown that models developed for steady state conditions can be used for transients operation.

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With their unique photochemical properties, porphyrins have remained a central research topic for decades. Porphyrins can self-assemble into tubular structures at acidic pHs. However, the possibility of the disassembly of the aggregated porphyrin has not been investigated. Furthermore, quantitative understanding of the porphyrin optical activities is complicated by the complex interplay of the photon absorption, scattering, and fluorescence emission that can concurrently occur in porphyrin samples. Using meso- Tetrakis (4-sulfonato phenyl) porphyrin (TPPS) as the model molecule, discussed herein is combined UV-vis extinction, Stokes-shifted fluorescence, and polarized resonance synchronous spectroscopy (PRS2) study of porphyrin assembly and disassembly at acidic solutions. A series of optical constants, including photon absorption, scattering, and fluorescence emission cross-sections as well as its fluorescence and light scattering depolarizations has been quantified. Compared to UV-vis and SSF methods, the PRS2 is significantly more sensitivity in the detection of both concentration- and time-dependent porphyrin aggregation.

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