The dissertation focuses on the analysis of the extended defects present in as-grown and proton bombarded β-SiC (annealed and unannealed) grown by chemical vapour deposition (CVD) on (001) Si. The proton irradiation was done to a dose of 2.8 × 1016 protons/cm2 and the annealing took place at 1300°C and 1600°C for 1hr. The main techniques used for the analysis were transmission electron microscopy (TEM) and high resolution TEM (HRTEM). From the diffraction study of the material the phase of the SiC was confirmed to be the cubic beta phase with the zinc-blende structure. The main defects found in the β- SiC were stacking faults (SFs) with their associated partial dislocations and microtwins. The SFs were uniformly distributed throughout the foil. The SFs were identified as having a fault vector of the type 1/3 <111> with bonding partial dislocations of the type 1/6 <121> by using image simulation. The SFs were also found to be predominantly extrinsic in nature by using HRTEM analysis of SFs viewed edge-on. Also both bright and dar-field images of SFs on inclined planes exhibited symmetrical and complementary fringe contrast images. This is a result of the anomalous absorption ratio of SiC lying between that of Si and diamond. The analysis of the annealed and unannealed irradiated β-SiC yielded no evidence of radiation damage or change in the crystal structure of the β-SiC. This confirmed that β-SiC is a radiation resistant material. The critical proton dose for the creation of small dislocation loops seems to be higher than for other compound semiconductors with the zinc-blende structure.

The advance in transparent electronics requires high-performance transparent conducting oxide materials. The microscopic properties of these materials are sensitive to the presence of defects and interfaces and thus fundamental understanding is required for materials engineering. In this thesis, first principles density functional theory is used to investigate the possibility of tuning the structural, electronic and magnetic properties of tin oxide by means of defects and interfaces. Our aim is to reveal unique properties and the parameters to control them as well as to explain the origin of unique phenomena in oxide materials. The stability of native defect in tin monoxide (SnO) under strain is investigated using formation energy calculations. We find that the conductivity (which is controlled by native defects) can be switched from p-type to either n-type or undoped semiconducting by means of applied pressure. We then target inducing magnetism in SnO by 3d transition metal doping. We propose that V doping is efficient to realize spin polarization at high temperature. We discuss different tin oxide interfaces. Metallic states are found to form at the SnO/SnO2 interface with electronic properties that depend on the interface terminations. The origin of these states is explained in terms of charge transfer caused by chemical bonding and band alignment. For the SnO/SnO2 heterostructure, we observe the formation of a two dimensional hole gas at the interface, which is surprising as it cannot be explained by the standard polar catastrophe model. Thus, we propose a charge density discontinuity model to explain our results. The model can be generalized to other polar-polar interfaces. Motivated by technological applications, the electronic and structural properties of the MgO (100)/SnO2 (110) interface are investigated. Depending on the interface termination, we observe the formation of a two dimensional electron gas or spin polarized hole gas. Aiming to identify further key parameters, we examine O deficient LaAlO3/SrTiO3 (110) and (001) superlattices under hydrostatic pressure. Presence of O vacancies results in formation of a two-dimensional electron gas, for which we observe a distinct spatial pattern of carrier density that depends strongly on the amount of applied pressure.

In the production of parts for direct industrial application and for developing research purposes, it is of utmost importance to understand the defects associated with the material system. In this work, the microstructural and mechanical properties of 316L Stainless Steel deposits and cast Aluminum A356 and Magnesium AZ91 alloys are investigated. The study first examines the design of efficient gating systems utilizing the Electromagnetic Pump Green Sand system to produce vertically cast A356 plates. A series of numerical simulations were developed for each of the four gating designs in order to compare modeling results with actual castings. The method of four-point bend (FPB) testing was used to obtain information about the effect of oxide entrainment on the mechanical properties of the parts, and from this data, a two-parameter Weibull statistical analysis was performed in order to quantify specimen failure rate for each of the configurations. Metallographic analysis was carried out using optical microscopy, and fractography using Scanning Electron Microscopy (SEM). In keeping with light alloys focus, the determination of superior casting processes for AZ91 alloys is also studied. Passenger car control arms were cast by Indirect Squeeze Cast, Low Pressure Permanent Mold, T-Mag, and Ablation processes. The microstructure, grain size, porosity distribution, and defect analyses were obtained with optical microscopy and the ImageAnalyzer program. The mechanical behavior was characterized from the FPB and tensile tests. The four casting processes were evaluated in terms of reliability again using a Weibull analysis of the ultimate bending strength determined from the FPB test samples. Metallographic analysis was performed on these samples, revealing noticeable microstructural differences between them, with some even showing possible evidence of oxide films. Lastly, the study of process parameters such as beam and laser current, translation speed, and wire feed and deposition rate associated with 316L stainless steel deposits produced by both Laser Engineered Net Shaping and Electron Beam Freeform Fabrication becomes the research objective. Tensile tests, optical microscopy, and SEM were used to determine mechanical properties, characterize solidification grain structure, porosity, secondary dendrite arm spacing, and possible modes of failure.

The study of defect formation and identification is important to the further application of friction stir welding in industry. To better understand the topic, a systematic study was undertaken to describe material flow effects on the formation of defects, to list the various types of defects encountered across a parameter window, and to identify features in the weld force data that can then be used to recognize defects within the weld without destructive testing. Tracer studies were used to determine the impact of the material flow on defect formation with a determination that proper shoulder contact is necessary to obtain sufficient material flow to fully consolidate the weld. A series of welds across a range of rotational speeds was used to identify mechanisms that led to variations in the mechanical properties of the welded panels. A balance between the x- and yorces on the tool is needed to produce robust welds that were defect free. UMF was shown to identify regions of changing material flow conditions; however, the identification of intermittent defects was not as successful.

No description available.

Automated defect detection methods allow the forest products industry to better utilize its resources by improving yield, reducing labor costs, and allowing minimum lumber grades to be utilized more intelligently. While many methods have been proposed on what sensors and processing methods should be used to detect and classify wood features, there exists a lack of understanding of what parameters are best used to differentiate wood features. The goal of this research is to demonstrate that by having an in depth knowledge of how wood features are represented by color, shape, and density parameters, more accurate classification methods can be developed. This goal was achieved through describing wood features using parameters derived from color and x-ray images and characterizing the variability and interrelationships of these parameters, determining the effect of resolution and species on these relationships, and determining the importance and contribution of each parameter for differentiating between wood features using a statistical prediction model relating feature types to the parameters. Knots, bark pockets, stain and mineral streak, and clearwood were selected as features from red oak, (Quercus rubra), hard maple, (Acer saccharum), and Eastern white pine (Pinus stobus). Color (RGB and HSI), shape (eccentricity and roundness), and density (gray-scale values) parameters were measured. Parameters were measured for each wood feature from images and parameter differences between feature types were tested using analysis of variance techniques (ANOVA) and Tukey's pairwise comparisons with a=0.05. Discriminant classifiers were then developed to demonstrate that an in-depth knowledge of how parameters relate between feature types could be used to develop the best possible classification methods. Classifiers developed using the knowledge of parameter relationships were found to provide higher classification accuracies for all features and species than those which used all parameters and where variable selection procedures had been used< It was determined that differences exist between all feature types and can be characterized and classified based on two color means, one color standard deviation, the mean density, and a shape parameter. A reduction in image resolution was determined not to affect the relationship of parameters. For different species, the intensity of features was to be related to the intensity of clearwood. The ability to explain classification errors using the knowledge gained about feature parameters was demonstrated. This knowledge could be used to reduce future classification errors. It was determined that combining parameters collected using multiple sensors increases classification accuracy of wood features. Shape and density were found not to provide good classification variables for features when used separately, but were found to contribute to classification of features when used with other parameters. The ability to differentiate between the feature types examined in this research was found be equal when using the RGB or HSI colorspace. / Ph. D.

In May of 2006, the Hrubec group suddenly began to observe neural tube defects (NTDs) in embryos of untreated control mice. Unintentional exposure to a teratogenic agent in tap water was identified as the cause. We aimed to identify the contaminant, but first we demonstrated that the NTDs were pathological being present on both gestational day 9 and 10. We also found that a second species, rats, developed NTDs when exposed to tap waters. Disinfection by-products (DBPs) arise when natural organic matter in municipal water sources reacts with disinfectants used in the water treatment process. Purge and trap gas chromatography-mass spectrometry (PT GC-MS) and animal exposure studies were used to determine if the teratogenic contaminant was a DBP. Since the distribution pattern of DBPs did not match the distribution pattern of NTDs, we concluded that a DBP was not likely to be responsible for the observed malformations. Pharmaceuticals and personal care products have emerged as ubiquitous contaminants of ground and surface waters, and have been detected in drinking water. In order to analyze for these compounds, we submitted different water samples to a commercial water analysis lab (AXYS Analytical Services, Sidney, BC, Canada). Several pharmaceuticals were identified in a number of samples, including a known teratogenic drug used to treat mood disorders and seizures: carbamazepine. Further analysis for carbamazepine was conducted in-house. Carbamazepine was found in several ground, surface, and tap waters, at various concentrations. To establish whether or not carbamazepine was responsible for NTDs in our mice, we conducted 2 dosing studies. Carbamazepine was provided to mice at concentrations detected in tap water, as well as approximately 2 x and 1000 x that concentration. Both studies found no significant differences in NTD rates among the dose groups. As no dose effect was observed, we concluded that CBZ was not directly responsible for the malformations. The identity of the teratogenic contaminant is not known at this time, but is unlikely to be a DBP or low concentrations of the pharmaceutical carbamazepine. / Master of Science

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published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy