A study was conducted to investigate a novel route to low cost processing of alumina/calcium-hexaluminate (A/CA6) composites. The objectives of this study were to: (a) develop A/CA6 and ß-spodumene modified A/CA6 composites using an in-situ reaction sintering method and functionally-graded A/CA6 using an infiltration technique, and (b) evaluate the effects of CA6 platelets on the ensuing physical and mechanical properties. The study has revealed that the processing procedures played an important role in the microstructural development of A/CA6 composites. The microstructure-property relationships of these materials were found to be strongly influenced by the presence of CA6 phase.The A/CA6 composites were synthesised by in-situ reaction sintering of alumina powder and (0, 5, 15, 30, 50 and 100 wt%) CA6 precursor. The phase relations and development of this system were monitored using quantitative x-ray diffraction (XRD) and neutron diffraction (ND). Rietveld analysis which showed the CA6 content to increase in proportion with the increase of CA6 precursor added. The XRD study revealed that the CA and CA2 phases started to develop at approximately 1000 and 1100°C and transformed to CA6 phase at 1400T. Similarly, the dynamic high temperature ND study showed that the corresponding calcium aluminates phases commenced to develop at 1000°C and 1200°C and then eventually transformed to CA6 at 1400°C.The presence of the plate-like CA6 grains in the system was revealed by the back-scattered SEM imaging and confirmed by the Ca x-ray map. Although the presence of CA6 caused the reduction of hardness, the fracture toughness of A/CA6 composites were improved when compared with alumina. It was found that the presence of CA6 hindered the processes of sintering and densification in alumina matrix.The use of ß -spodumene had been investigated as a liquid-phase-sintering aid for ++ / the densification of A/CA6 composites. XRD, ND, differential thermal analysis (DTA), scanning electron microscopy (SEM) and Vickers indentation were used to characterise the effects of ß -spodumene on the phase relations, densification, microstructure and mechanical properties. The results showed that the presence of ß -spodumene had a profound influence on the phase relations, densification and microstructure of A/CA6 composites. Quantitative XRD and ND Rietveld analysis showed that the addition of > 2.5 wt% ß -spodumene caused the reduction of CA6 content due to the formation of ß -quartz solid solution. The reduction of porosity in the presence of ß -spodumene suggests that it may be used as an effective sintering aid for improving the densification of A/CA6 composites. However improvements in hardness and fracture toughness were not achieved probably due to the presence of large spherical pores as well as the formation of recrystallised ß -spodumene and ß -quartz solid solution.A functionally-graded alumina/calcium-hexaluminate (A/CA6) composite was successfully synthesised through infiltration of porous alumina preform with a solution containing calcium-acetate. The infiltration kinetics of liquid into porous alumina preform had also been investigated. It was found that the infiltration rate equation proposed by Washburn is most suitable for describing the effects of preform sintering temperature, viscosity and multiple infiltrations on the infiltration characteristics. The influence of applied pressure is consistent with the model proposed by Darcy, where the applied pressure enhances the infiltration rate behaviour. Key parameters for the optimum processing conditions of preforms for subsequent infiltration have also been identified.The graded composition character of the functionally-graded A/CA6 composites were characterised by XRD and synchrotron ++ / diffraction (SRD). Depth-profiling of compositions with XRD and SRD Rietveld refinement showed that the concentration of CA6 decreased with depth, while that of A1203 increased with depth. Both XRD and SRD results showed that CA and CA2 phases formed initially at 1000°C and 1300°C, respectively, but remained stable even at 1400°C, before eventually transformed to CA6 at 1650°C. These results are consistent with those of dynamic high temperature ND data.The graded microstructure was revealed by SEM back-scattered imaging whereby the content of CA6 platelets was most abundant near the surface and decreased with increasing depth towards the bulk. The presence of CA6 phase in the composite fire at 1400°C was also confirmed by the transmission electron microscopy (TEM) observation in conjunction with energy dispersive spectroscopy (EDS). The hardness results of the graded material showed that the graded-region was softer than the non-graded region as a result of the presence of softer CA6 phase in the former. However, the fracture toughness in the graded region was found to be higher than the non-graded region which might be attributed to the display of toughening processes such as crack deflection and grain bridging.

Reliable and inexpensive methods of in-situ stress measurement have been sought for more than 40 years. A number of non-destructive core-based methods of in-situ stress determination are currently available, among which Deformation Rate Analysis ' DRA ' and Acoustic Emissions ' AE ' method have the most promising potential due to their ability to measure stress as opposed to strain, which is measured by strain recovery techniques. The DRA and AE method are similar in their utilisation of a phenomenon termed Kaiser effect in the case of AE and deformation memory effect in the case of DRA. The KE/DME is defined as a recollection of a maximum stress a rock core had been subjected prior to its retrieval from the in-situ environment. The physical nature of this phenomenon has not however been universally established. In this study, interaction of microcracks as the most probable cause of the KE/DME, was investigated. To reproduce the damage that occurs to rock at the micro level, a discrete element modelling code was required, which enabled dynamic failure propagation to be modelled. Commercially available code PFC [ superscript 2D ] was found to be suitable for this purpose due to its ability to explicitly model mechanical damage in rocks. The numerical model was based on a real prototype - a sandstone rock core, which had also been previously subjected to the DRA. Although the bulk of the numerical tests were conducted on intact rock models, it was found that changes in the lithology and introduction of discontinuities did not have significant effect on the DME. Influence of the confining stress on the DME was confirmed. It was assumed that only the highest historical stress could be determined reliably using the DRA technique. The ability of the numerical model to reproduce the DME was validated. The link between the DME and development of microcracks was established. The results of the study encourage further use of the code for understanding the micromechanical behaviour of rocks under loading. / Thesis (M.Eng.Sc.)--Australian School of Petroleum, 2004.

La détermination de la tenue mécanique de points soudés est un enjeu industriel important, eten particulier dans le cas d'aciers à Très Haute Résistance. Actuellement, l'essai de tractionen croix est l'essai mécanique le plus répandu caractérisant la tenue des points soudés.Toutefois, l'étude de l'influence des différentes zones constituant le point soudé sur la tenueest difficile en se basant sur cet essai.Un essai d'enfoncement de coin a été développé afin de caractériser les ruptures interfacialesdes points soudés. Une section transverse d'un point soudé est observée tandis qu'un coin estinséré entre les deux tôles soudés. Une caméra CCD enregistre l'observation de lapropagation de la fissure.Le pliage limité des tôles durant la fissuration rend efficace la classification des différentspoints soudés par l'énergie totale dissipée par unité de surface rompue. De plus, la mesure insitu de l'angle d'ouverture de fissure caractérise la fissuration stable de la zone fondue. Dessimulations par éléments finis de l'essai sont conduites afin d'estimer un lien entre cesmesures et la rupture du matériau, modélisée par des zones cohésives.La rupture interfaciale de points soudés d'aciers DP et TRIP a été étudiée. Les mesuresexpérimentales permettent d'estimer les paramètres de modèles cohésifs représentatifs de larupture de la zone fondue, constituant des données fiables susceptibles d'être utilisées danstoute simulation numérique du comportement du point soudé.

Graduation date: 1998

In situ bioremediation of pentachlorophenol-contaminated ground water in a sequential anaerobic-aerobic down borehole permeable barrier reactor requires a non-toxic primary substrate for dichlorophenol cometabolism. Serum bottle tests comparing the effectiveness of eight primary substrates for aerobic dichlorophenol degradation showed phenol to be the most effective followed by imitation vanilla flavoring, guaiacol, sodium benzoate, molasses, acetic acid, propylene glycol and ethyl vanillin in propylene glycol. As phenol is a pollutant, imitation vanilla flavoring is the recommended primary substrate for field use. In a second bottle test, 3,4,5-trichlorophenol was not sufficiently biotransformed, emphasizing the need for biotransformation to occur in the anaerobic zone of the reactor. / Graduation date: 1996

This thesis investigates different material systems and processing technology for high temperature compatible laser diodes used in volume applications within the 1.3-μm telecom wavelength window. Laser diodes built from such materials are much desired in order to eleminate the need for active temperature control needed in current systems, which significantly increases both complexity, size and cost. The structures were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) and the evaluation of materials was performed using different characterization methods such as High-Resolution X-Ray Diffraction (HR-XRD), Photoluminescence (PL), Time-Resolved Photoluminescence (TR-PL). Fabrication and evaluation of Fabry-Perot lasers with different geometries was used to check the material quality and temperature performance. A novel in-situ etching technique was developed for the use i future more advanced, buried hetrostructure lasers. The first studied materials system was AlGaInAsP/InGaAsP/InP. To handle a 5-element material with the precision required, modelling of the materials and heterostructure properties was performed. The addition of Al to the InGaAsP barrier allows better electron confinement with little change in valence band properties. The optimum aluminium content was found to be about 12%. Although the effect of Al could be identified, it was not sufficient with T0 of only 90 K only up to 60 °C. A second materials system InGaP/InAsP/ InP initially looked quite promising from a materials and quantum well design point of view but encountered severe problems with the device integration and further work was discontinued. The main effort was therefore was devoted to a third materials system: AlGaInAs/AlGaInAs/InP. This material system is not unknown but has hitherto not found a widespread application for fibre optic applications. In this work, the MOCVD growth of 1.3 μ;m quantum well laser structures was optimized and ridge waveguide laser devices with excellent temperature performance was fabricated (T0 = 97 K at 85 °C). A ridge waveguide laser was identified as suitable structure since it requires only a single epitaxial growth, thus avoiding the main problem of oxidation of Al based buried structures. The dynamic performance was excellent up to 110 °C and the device fabrication is highly reliable (lifetime >7000 h). This high yield uncooled ridge Fabry-Perot laser process has now been transferred to production and is applied in short length 10 Gb/s multimode links. In order to further improve the usefulness of the Al-containing materials in even higher performance devices needed in future applications developments towards fully buried heterostructure device geometry were also pursued. To overcome difficulty of oxidation of Al containing layers at the mesa walls an in-situ etching technique was implemented. Different chemistry approaches were investigated and the first results of lasers devices were reported. / QC 20100930

In case of a release of radioactive nuclides into the environment it is necessary to  have reliable methods to estimate the potential effect on people and the ecosystem. In this context the total activity deposited, the elemental composition and the depth distribution are of importance. An efficient in situ method to estimate the average contamination over larger areas using high purity germanium (HPGe) detectors has been developed. The method combines simulation of photon transport with measured detector properties. The total activity of 137Cs determined from gamma-ray spectra recorded in situ are compared to results from soil sampling. Another in situ method has been developed to determine the depth distribution of a radionuclide contamination, using an array of small detectors inserted into the ground, as an alternative to the standard procedure of soil sampling. The possibility to use cadmium telluride (CdTe) detectors as well as lanthanum bromide (LaBr3) detectors has been investigated. As a demonstration of the developed method the small-scale variation of the activity distributions in an area covering 350 m2 have been measured and is compared to results obtained by other methods. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.

The presence of coal tars in the subsurface associated with former manufactured gas plants (MGPs) offers a remediation challenge due to their complex chemical composition, dissolution behaviour and recalcitrant characteristics. A former MGP site in Clearwater Beach, Florida was characterized and bench-scale analyses were conducted to assess the potential for in situ chemical oxidation (ISCO) using persulfate to treat MGP residuals. Completion of a conceptual site model identified a homogeneous, silty sand aquifer, with an average hydraulic conductivity of approximately 2.3x10-3 cm/s and a groundwater flow rate of 2 cm/day in the direction of S20°E. Six source zones, three near the water table and three in the deep aquifer were estimated to have a total volume of 108 m3. A multi-level well transect was installed to monitor concentrations of dissolved compounds and to estimate mass discharge downgradient of the source zones over time. On average, the morphology of the aqueous concentrations remained consistent with time. A total mass discharge across the transect of 94 mg/day was estimated for site-specific compounds. Bench-scale tests were conducted on aquifer sediments and groundwater samples. The aquifer was determined to have a low buffering capacity, low chemical oxygen demand, and low natural oxidant interaction (NOI) with persulfate. Aqueous batch experiments identified the potential for iron (II) activated persulfate to reduce concentrations of BTEX and PAHs below method detection limits (MDLs). Unactivated persulfate was able to reduce BTEX concentrations to below MDLs after 14 days; however, the concentration of PAH compounds remained above MDLs after 14 days. Higher iron doses within the system were shown to be more effective in reducing BTEX and PAH compounds. Column experiments designed to mimic site conditions were used to evaluate the feasibility of persulfate treatment on impacted sediments from the Clearwater site. Two sets of column experiments were conducted: one using unactivated persulfate followed by alkaline activated persulfate; and one using iron (II) activated persulfate. On average, unactivated persulfate was able to reduce BTEX and PAH aqueous effluent concentrations by > 75% and 40%, respectively, after a total dose of 60 g/g soil. Two additional doses of alkaline activated persulfate (total persulfate dose of ~80g/g soil) in these columns were able to further reduce effluent BTEX and PAH concentrations by > 90% and > 75%, respectively. Iron (II) activated persulfate reduced effluent BTEX concentrations by > 70% and PAHs by > 65% after a total dose of 35 g/g soil. Average reductions in mass for BTEX and PAH compounds were approximately of 48% and 26% respectively in the iron (II) activated persulfate columns, and 24% and 10%, respectively in the alkaline activated persulfate columns. The potential for the ability to use in situ chemical oxidation using persulfate for the remediation of MGP residuals in the subsurface is evaluated using field measurements and bench-scale experimentation. The reductions observed in aqueous phase compounds in MGP groundwater as observed in the laboratory indicate the potential for reductions in groundwater concentrations at this and other contaminated former MGP sites. However, column experiments, indicating the inability for activated persulfate to reduce all identified compounds in the MGP NAPL suggest source treatment with activated persulfate would not reduce concentrations to below Florida Department of Environmental Protection natural attenuation concentrations.

Diffusion dominated systems, including naturally occurring aquitards and engineered barrier systems, are important components for long-term waste containment. Diffusive transport can be quantified using the effective coefficient of diffusion (De) and the effective porosity (ne). These are empirical parameters that are commonly measured in a laboratory setting. The purpose of this research was to develop a field-based technique to perform <i>in situ</i> measurement of diffusive transport rates. Results from this measurement technique were evaluated by comparison with the results of conventional laboratory testing and back-analysis of a previously determined large-scale field diffusion profile.<p> <i>In situ</i> diffusion testing was performed on two wells completed in diffusion-dominated zone of a till aquitard. Laboratory diffusion cell tests were conducted on core samples obtained from the screened zones of the diffusion wells. Diffusion testing was completed using conservative isotopes of water as tracers.<p>A finite element model was used to back-analyze results of laboratory and field experiments to determine the De values that best describe each system. Comparison of the field results with the laboratory results obtained from this study as well as previous studies indicate the field system is a useful method for measurement of De.<p>Back-analysis of a previously determined large-scale field deuterium profile for this aquitard showed very precise measurement of De is not required for estimation of contaminant transport in thick till aquitard systems. More accurate measurement may be more useful for barrier systems such as clay liners or slurry walls, where the characteristics of the diffusion-dominated zone are easier to define and the transport path is shorter relative to the transport time.

La diversidad del maíz está siendo amenazada por un conjunto de procesos tan diversos como el comercio internacional, la emigración rural, el cambio en los patrones culturales y el desarrollo de modernas tecnologías de producción, por ello es de fundamental importancia para México, país en el que se encuentra el centro de origen y mayor diversidad de maíz en el mundo, conocer cual es el estado que guarda dicha diversidad en el contexto de las comunidades campesinas que lo han desarrollado y lo mantienen.El objetivo fundamental de esta tesis ha sido mostrar que, en el contexto de las comunidades indígenas campesinas de México, hay un conjunto de valores asociados al manejo de la diversidad del maíz, que pueden ser traducidos a un lenguaje científico occidental a través de un método de análisis multicriterial, que estos valores pueden ser ordenados y jerarquizados, y que a partir de estos resultados se pueden plantear propuestas tendientes a establecer programas de conservación in situ de la diversidad del maíz, y con ello contribuir a su conservación.En esta investigación, se abordó el problema de la valoración de la diversidad del maíz bajo un enfoque de sistemas complejos, intentando integrar el análisis de diferentes escalas: la unidad campesina como el sistema mayor, la cuál se caracterizó a través de su estrategia de reproducción, el agroecosistema milpa como subsistema de la unidad campesina que cumple un conjunto de funciones y objetivos al interior de la misma, y la diversidad del maíz que manejan los campesinos como componente fundamental del agroecosistema milpa.Los resultados indican que si bien hay una diversidad de variables asociados al manejo de la diversidad del maíz, son los valores culturales y ambientales los que soportan el manejo de esta diversidad en las comunidades estudiadas, en tanto que los valores económicos y sociales más bien tienden a ejercer un desestímulo a la conservación de esta diversidad.Palabras clave: diversidad del maíz, valoración multicriterial, reproducción campesina, agroecosistema milpa, unidades campesinas. / Maize diversity is being threatened by many different processes such as international trade, rural migration, change in consumption patterns and the impact of new technologies. Because of this threat, it is very important for Mexico, which is center of origin and greatest diversity of maize landraces of the world, to know which is the situation of maize diversity conservation in peasant communities, were this diversity is maintained.The main objective has been to show that, in the context of indigenous peasant communities, there are multiple value dimensions which support the management of maize diversity. This can be translated to a western scientific language through a multicriteria analysis method. These values can be ordered and ranked, and that from this it is possible to make proposals to establish in situ conservation programs for maize diversity.In this research, the valuation of maize diversity has been approached in terms of complex systems, considering different analysis scales: the peasant household as the mayor system, which has been characterized through its reproduction strategy, the milpa agroecosystem as a subsystem of peasant household, and maize diversity as a fundamental component of milpa system. My results show that in peasants contexts, the monetary value of production is not the most important value in maintaining milpa and its diversity, but a group of values cultural, environmental and social values which are combined in many different ways depending on specific circumstances. Key words: maize diversity, multicriteria valuation, peasant reproduction, milpa agroecosystem and peasant units.