There is an understanding of surface photovoltage (SPV) behavior for GaN, yet little is known about the SPV behavior for AlGaN. In this work, a Kelvin probe was used to measure the SPV for p-type AlGaN. Very slow SPV transients were found in AlGaN, which could not be explained with a simple thermionic model. A possible explanation of this behavior is the segregation of impurities to the surface, which causes significant reduction of the depletion region width (down to 2 nm), with carrier tunneling and hopping becoming the dominant mechanisms responsible for the SPV transients. To verify this assumption, the near-surface defective region (about 40 nm) has been removed through the ICP-RIE process. After the etching, the SPV transients became fast and increased in magnitude by about 0.6 eV. By using the thermionic model, band bending was estimated to be -1 eV.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Coal is one of the major energy sources in the world and contains most of the elements from the periodic table. During combustion of coal these elements are released and redistributed. This may lead to environmental problems. Some of these elements are considered to be very dangerous for human and animal health and ecosystems. The knowledge of concentration and speciation of elements in coal is important for the prevention of the adverse environmental phenomena associated with the use of coal. One of the hazardous elements in coal is lead. The purpose of this work is to determine the concentration of lead and its isotopic composition simultaneously with determining the speciation of lead in coal. The ICP-MS method was used to determine the concentration and isotope ratios of lead. A total of 62 samples of subbituminous coal was analyzed. The method of selective extraction analysis BCR was used on 9 samples of subbitumnious coal to identify the speciation of lead in coal. Lead concentrations in coal were measured in the range of 0.25 to 78.84 mg·kg-1 . These concentrations correspond to the average concentrations of lead in most of the coals. Isotope ratio 206 Pb/207 Pb in coal samples ranged from 1.169 to 1.219. Isotopic 208 Pb/206 Pb ratio was measured in the interval 2.047 to 2.093. The isotopic...

Anion-exchange chromatography with inductively coupled plasma - atomic emission spectrometry (ICP-AES) has been used for the speciation of chromium (Cr). Chromium speciation has attracted attention because of the different toxicity, Cr(III) is relatively non-toxic and Cr(VI) has been classified as a human carcinogen. The aim of the present study was to develop simple method for the speciation analysis of Cr (Cr(III) and Cr(VI)) in particulate matter of urban dust. A combination of 2% KOH + 3% Na2CO3 has been chosen as the optimal reagent for the extraction of chromium from particular matter. It was found that there was no conversion of Cr(VI) into Cr(III). The effect of separation parameters such as acidity of mobile phase was also studied. The detection limit for Cr(VI) was about 12 ng.ml-1 . Results for the determination of Cr(VI) were confirmed by the analysis of standard reference material (BCR CRM 545, Cr(VI) in welding dust loaded on a filter) with good agreement between certified (40,16 ± 0,60 μg.g-1 ) and found (37,83 ± 1,14 μg.g-1 ) values.

15 samples of gem opals were analyzed by laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). For this study were selected the most representative samples from Slovakia, Australia, Peru, Ethiopia, Mexico, USA and the Czech Republic. These samples were obtained from private collections. The study focuses on the geochemical relationships between various forms of opal originating from igneous and sedimentary environments based on the results from LA ICP-MS and ICP-MS. The major and trace element compositions are unique for each studied opal locality and important for understanding numerous aspects of opal formation. Major element analysis shows that opals are essentially pure SiO2 (77 - 92 wt. %). Al, Fe, Ca, K, Na and Mg are the main elemental impurities. The concentrations of the trace elements vary strongly depending on the opal locality. Differences were found, e.g., in the concentrations of REE and some refractory elements, which might be indicative for determining the provenance of opals. Many studies have been published explaining the origin of luminescence, microstructures and the thermal properties of opals. However, there are very few comprehensive studies comparing gem opals from the most important historical and...

Magister Scientiae (Medical Bioscience) - MSc(MBS) / Mercury (Hg) is an example of a toxic metal that is not essential for nutrition. It exists in organic and inorganic forms in seafood and vapour from dental amalgam fillings respectively. Elemental mercury (Hg0) from dental amalgam was the focus of this study. Dental amalgam is one of the most commonly used dental filling materials and has been used for over 150 years. It is composed of Hg0 (approximately 50%) combined with other metals such as copper and zinc (Zn). These fillings give off Hg0 vapour throughout their existence, and is further enhanced by activities such as chewing, grinding of teeth and drinking hot liquids. Mercury consumption can lead to Zn loss or deficiency, and is reported to displace Zn and copper. Several European nations have outlawed the use of amalgam as a restorative material due to controversies regarding its safety in children, women of childbearing age and individuals with renal disease. Moreover, various studies have reported correlations between the number of amalgam fillings and Hg concentration in blood plasma, urine, faeces, saliva and different organs. Blood, urine, and hair mercury levels are used to predict possible health effects that may be caused by the different forms of Hg. Urine Hg is used to test exposure to metallic Hg0 vapour and inorganic Hg forms. This study aimed to evaluate the effects of Hg0 from dental amalgam restorations on the status of Zn in the urine. This was done by determining the concentrations of Hg0 in urine, buccal cells and the oral cavity, and its relationship with urinary Zn concentrations in the same individuals. Samples of urine, buccal tissues, chewing gum and completed questionnaires were collected from the participants (women and men) at the dental clinics in Tygerberg Hospital (TBH), Cape Town. Samples were analyzed using inductively coupled plasma mass spectrometer (ICP-MS). Findings from this study show that there was a correlation between levels of urinary Hg0 and urinary Zn (p=0.02). However, urinary Hg0 did not predict the amount of urinary Zn. Also, no relationship was found between levels of Hg0 in buccal swab or the chew test samples and urinary Zn level. There was a significant difference between females and males in the level of urinary Zn, men had higher levels of Zn excreted in the urine than females (p=0.05). However, there was no significant difference in the level of urinary Hg0 between males and females. The number of fillings (4-7) and age of fillings were significantly associated with urinary Hg0 level (p˂0.05), while smoking ˃15 cigarettes/day increased the level of Hg0 in buccal swab samples (p=0.002). We were not able to demonstrate a causal effect of Hg0 leaching on urinary zinc levels.

The primary aim of this thesis is to develop image processing algorithms to quantitatively determine the link between traumatic brain injury (TBI) severity and chronic traumatic encephalopathy (CTE) neuropathology, specifically looking into the role of blood-brain barrier disruption following TBI. In order to causally investigate the relationship between the tau protein neurodegenerative disease CTE and TBI, mouse models of blast neurotrauma (BNT) and impact neurotrauma (INT) are investigated. First, a high-speed video tracking algorithm is developed based on K-means clustering, active contours and Kalman filtering to comparatively study the head kinematics in blast and impact experiments. Then, to compare BNT and INT neuropathology, methods for quantitative analysis of macroscopic optical images and fluorescent images are described. The secondary aim of this thesis focuses on developing methods for a novel application of metallomic imaging mass spectrometry (MIMS) to biological tissue. Unlike traditional modalities used to assess neuropathology, that suffer from limited sensitivity and analytical capacity, MIMS uses a mass spectrometer -- an analytical instrument for measuring elements and isotopes with high dynamic range, sensitivity and specificity -- as the imaging sensor to generate spatial maps with spectral (vector-valued) data per pixel. Given the vector nature of MIMS data, a unique end-to-end processing pipeline is designed to support data acquisition, visualization and interpretation. A novel multi-modal and multi-channel image registration (MMMCIR) method using multi-variate mutual information as a similarity metric is developed in order to establish correspondence between two images of arbitrary modality. The MMMCIR method is then used to automatically segment MIMS images of the mouse brain and systematically evaluate the levels of relevant elements and isotopes after experimental closed-head impact injury on the impact side (ipsilateral) and opposing side (contralateral) of the brain. This method quantifiably confirms observed differences in gadolinium levels for a cohort of images. Finally, MIMS images of human lacrimal sac biopsy samples are used for preliminary clinicopathological assessments, supporting the utility of the unique insights MIMS provides by correlating areas of inflammation to areas of elevated toxic metals. The image processing methods developed in this work demonstrate the significant capabilities of MIMS and its role in enhancing our understanding of the underlying pathological mechanisms of TBI and other medical conditions. / 2019-07-09T00:00:00Z

CICYT (PB88-0288 y PTRI91-0029)

No description available.

In 2012, plasma figuring was proven to be an alternative solution for the fabrication of large scale ultra-precise optical surfaces. Indeed, plasma figuring was successfully demonstrated on a metre class glass surface. The process was exceptionally rapid but residual errors were observed. This thesis addresses this issue by proposing an enhanced tool that provides a highly collimated plasma jet. The enhanced tool is characterized by a targeted material removal footprint in the range 1 to 5 mm FWHM. The energy beam is provided by an Inductively Coupled Plasma (ICP) torch equipped with a De-Laval nozzle. This thesis focuses on characterization and optimisation of the bespoke plasma torch and its plasma jet. Two research investigations were carried out using both numerical and experimental approaches. A novel CFD model was created to analyse and understand the behaviour of high temperature gas in the De-Laval nozzle. The numerical approach, that was based on appropriate profiles of temperature and velocity applied to the nozzle inlet, led to a significant reduction of computational resources. This model enabled to investigate the aerodynamic phenomena observed from the nozzle inlet up to the processed surface. Design rules and the effect of changing nozzle parameters were identified. Sensitivity analysis highlighted that the throat diameter is the most critical parameter. A challenging power dissipation analysis of the plasma torch was carried out. Temperature and flow rate in key components of the torch were measured. Experimental results enabled to calculate the power dissipation values for RF power up to 800 W and for the entire series of designed nozzles. This work enabled to scientifically understand the power dissipation mechanism in the bespoke ICP torches. In addition, by comparing the intensity of the power dissipation values, one nozzle was clearly identified as being more capable to provide a highly efficient plasma jet.