The characterization of work functions and field emission stability for molybdenum and iridium oxide coatings was examined. Single emission tips and flat samples of molybdenum and iridium oxide were prepared for characterization. The flat samples were characterized using X-ray Photoelectron Spectroscopy and X-ray diffraction to determine elemental composition, chemical shift, and crystal structure. Flat coatings of iridium oxide were also scanned by Atomic Force Microscopy to examine topography. Work functions were characterized by Ultraviolet Photoelectron Spectroscopy from the flat samples and by Field Emission Electron Distributions from the field emission tips. Field emission characterization was conducted in a custom build analytical chamber capable of measuring Field Emission Electron Distribution and Fowler-Nordheim I-V plots simultaneously to independently evaluate geometric and work function changes. Scanning Electron Microscope pictures were taken of the emission tips before and after field emission characterization to confirm geometric changes. Measurement of emission stability and work functions were the emphasis of this research. In addition, use of iridium oxide coatings to enhance emission stability was evaluated. Molybdenum and iridium oxide, IrO2, were characterized and found to have a work function of 4.6 eV and 4.2 eV by both characterization techniques, with the molybdenum value in agreement with previous research. The analytic chamber used in the field emission analysis demonstrated the ability to independently determine the value and changes in work function and emitter geometry by simultaneous measurement of the Field Emission Energy Distribution and Fowler-Nordheim I-V plots from single emitters. Iridium oxide coating was found to enhance the stability of molybdenum emission tips with a relatively low work function of 4.2 eV and inhibited the formation of high work function molybdenum oxides. However, the method of deposition of iridium and annealing in oxygen to form iridium oxide on molybdenum emitters left rather severe cracking in the protective oxide coating exposing the molybdenum substrate.

No description available.

Improved fracture toughness at a given strength level is one of the most important properties of cemented carbides. Large number of different testing methods (both theoretical and experimental) has been proposed to determine fracture toughness of cemented carbides and it has been always a topic of interest to relate fracture toughness with mechanical properties. In this report method such as Palmqvist toughness, chevron notch, toughness determination through Hertzian indentation and different theoretical toughness models have been utilized in order to investigate fracture characteristics and is also compared with other mechanical properties by varying cobalt content and grain size. This study has provided some new and interesting results as well as new information about hardmetals in different loading conditions.

Saudi Arabia is highly accessible to marine water, receives year-round availability of sunlight and generates a high annual carbon dioxide emission, all of which are justifications that merits the deployment of cyanobacterial cell factories. However, industrial cyanobacterial strains capable of thriving in conditions of the Arabian Peninsula are currently lacking. Given the fact that native cyanobacteria from the Red Sea are adapted to the local conditions, they are therefore good cell factory candidates where their inherent attributes can be harnessed. In this dissertation, an isolation and screening pipeline was developed to specifically identify physiologically robust cyanobacterial strains from the central Red Sea. Seventeen unicellular cyanobacterial strains were extensively cataloged through a series of physiological characterization and their evolutionary relationships were ascertained through phylogenetic analyses. Arising from this survey work, a high light, thermo- and halo-tolerant Synechococcus sp. RSCCF101 was selected for metabolic analysis under various growth conditions to assess its suitability as a platform for cell factory development. Significant metabolic changes were observed in cells subjected to different light regimes. High phycocyanin and chlorophyll a content were obtained under the low-light growth (50 μmol photons.m-2.s-1) while high biomass was accumulated, along with an increase external nitrate demand, under the high light growth (200 μmol photons.m-2.s-1). A genomic and transcriptomic approach was undertaken to elucidate the molecular signatures of Synechococcus sp. RSCCF101. Synechococcus sp. RSCCF101 contains a small genome (3 Mbp) that is rich in guanine cytosine content (68%) and harbors genes that encode for compatible solutes biosynthetic pathway and phycobilisome subunits which may account for its halo-tolerant and phycocyanin rich phenotype. Upon high-light treatment, the light harvesting machineries of Synechococcus sp. RSCCF101 was downregulated while the photosystem protection and carbon fixation capacity were upregulated. Taken together, the findings of this research will facilitate in the development of a new model system for industrial applications in high-light, high temperature and high salinity environments in general and Saudi Arabia in particular.

Numerous studies have identified the west coast of Canada as an attractive place for the development of wave energy projects. To evaluate the viability of these projects, an accurate description of the wave resource is crucial. Most of the previous efforts to characterize the wave climate in B.C. at shallower waters, where wave energy converters (WECs) are most likely to be deployed, lack the necessary nearshore spatial resolution, and were driven by overly simplistic wave boundary conditions. In addition, none of the previous studies have included the effect of tidal currents, which have been proven to be significant in wave resource characterizations in other locations. This work increased the fidelity of the wave resource characterization and developed an understanding of the impact of tidal currents on the wave conditions in this region by generating two most accurate, long-term (14 years, 2004 to 2017), high resolution (in space and time) datasets of the wave resource for the west coast of Canada. The two datasets were generated using nearly identical SWAN wave models, which their only difference was that one of them (V5), did not incorporate the effect of currents, while the other (V6) included tidal currents as forcing. Thus, the pure influence of the tidal currents on the wave characteristics was able to be identified when comparing the two wave model results. This study developed simple, robust, and objective metrics to support the calibration process and to evaluate the performance of the models. Utilizing these metrics, the V5 and V6 models presented substantial improvements in reproducing the wave conditions of about 18% and 20%, respectively and in relation to the previous most complete and accurate wave model of the region (V4). Their better performance was largely achieved by a significant increment in their ability to reproduce the significant wave height (H_m0) and energy period (T_e). The inclusion of tidal currents in the wave model increased the accuracy of the wave resource characterization, mainly by improving the model’s ability in simulating T_e by 5.1%. The most sensitive wave parameter to the tidal currents was the peakedness of the wave spectrum (Q_p), which was consistently and significantly reduced by values even larger than 2.5. In some regions, directions characterized by the mean wave direction (D_m) and the directional spreading (D_spr) were also noticeably very sensitive to the currents, which even deflected D_m to its opposite direction and drove changes in D_spr that reached values of up to 40°. However, these significant transformations were less frequent and reduced in magnitude at exposed (to swell-waves) sites, where strong currents have affected waves in a reduced part of their trajectory. Typically, tidal currents had the effect of reducing the wave power density (P), but in a relatively small amount, however, during rare events, tidal currents were able to induce changes in this parameter ranging -140 kW/m to 75 kW/m. At these extreme events, it was observed that the peak of the wave spectra became flatter, with some of its wave height variance redistributed to near increasing and decreasing frequencies and directions, regardless to the magnitude and direction of the local tidal currents. Impacts of the tidal currents on P were largely attributed to the induced changes in H_m0 and T_e. Although D_spr and Q_p were greatly transformed by the action the tidal currents, they account very little in explaining the variations in P. These four wave parameters together, and how they are transformed under the presence of currents, can explain a large part of the changes in P, however, other transformations of the wave spectrum due to the currents, not investigated in this study, must account for a considerable part of the changes in P. / Graduate

Three traverses across the exhumed trace of the Punchbowl fault zone in the 11 Pelona Schist, southern California, were examined at the millimeter to kilometer scales to determine the morphology, deformation mechanisms, and geochemistry of the fault zone in schistose rocks. The Pelona Schist is predominantly a quartz-albite-muscovite-actinolite schist with associated minor metabasalts. The Punchbowl fault zone, which is exhumed 2-4 km, has 44 km of right lateral slip, and is composed of a fault core enveloped by a damaged zone. The fault core is a region of extreme slip localization that records most fault displacement. Deformation in the fault core is dominated by grain-size reduction accompanied by fluid-dominated alteration, in contrast to the damage zone, where deformation is dominated by brittle and semi-brittle fracturing, cataclasis, and slip. Portions of the Punchbowl fault have multiple fault cores, with each fault core less than 10 cm thick. The thickness of a fault depends upon the type of deformation measured and the scale of observation. Mesoscopic fractures begin 50 m from the fault core, whereas the onset of fault-related microfractures occurs at approximately 40 m from the fault core . A geochemical signature based on whole-rock geochemistry suggests a fault thickness of less than 10 m. Grain-size reduction occurs over a 10 m thick region and mineralogic changes occur over a region 20-30 m thick. Reorientation of preexisting foliation occurs over a zone 30 m thick. Fault-core morphology and textures are similar to those in the Punchbowl fault to the northwest, where it displaces sedimentary rocks, and the San Gabriel fault, which formed in crystalline rocks. This suggests that the processes that form foliated, finegrained, cataclasite-dominated fault cores of large displacement faults are similar for diverse lithologies. The composition of the fault core is variable along strike, with little geochemical or mineralogical homogenization. Whereas processes that form fault cores are similar, localized interaction of fluids caused compositional variability within the core. Changes in fault composition and fluid-rock interactions may result in different fault properties and behaviors.

We examine the structural complexities of a 28-km long part of the Clark fault of the San Jacinto fault zone in southern California in order to better document its lateral extent and the style of deformation of its southeast end. Changes in structural style are observed as the Clark fault’s damage zone widens from ~ 1-2 km in crystalline rocks of the Peninsular Ranges southeastward to ~ 18 km in the sedimentary rocks of the San Felipe-Borrego subbasin of the Salton Trough. The Clark fault extends into the San Felipe-Borrego subbasin as the Arroyo Salada segment for ~ 11-12 km to a newly defined northeast-trending structural boundary. This structural boundary, referred to herein as the Pumpkin Crossing block, is a ~ 3-km wide and ~ 8-km long fault zone dominated by northeast-striking sinistral-normal strike-slip faults. Southeast of the Pumpkin Crossing block the newly defined San Felipe Hills segment extends the Clark fault another ~12-13 km southeast to its intersection with the Extra fault zone. The Clark fault may have nearly 14.5-18 km of right separation represented in the surface deformation of the Arroyo Salada and San Felipe Hills segments, but the total amount of strain is masked by the wide diffuse fault zone with its complex deformation patterns and geometries. The lateral change observed in microseismicity patterns across the Arroyo Salada and San Felipe Hills segment boundary supports our structural interpretations about the existence, location, and structure of this boundary. Vertical patterns in the microseismicity suggest that the Clark fault zone narrows at depth, dips steeply northeast in the subsurface, and must interact with at least one weak decollement layer(s) beneath and/or with the sedimentary basin. Structural deformation within the late Miocene to Holocene silty- and clay-rich sedimentary basin of the Salton Trough includes features characteristic of strike-slip faults, such as stepovers, conjugate faults, folds, flower structures, and fault bends, as well as many unique structures that include pooch structures, ramp-flat geometries of strike-slip faults, complex en echelon fault zones with localized shear distributed across a high frequency network of faults, and heterogeneous kinematic indicators within individual fault zones.

Sucrose esters have an established use in food industry as emulsifiers. Two novel lactose esters (lactose monodecanoate and lactose monomyristate) were synthesized and studied for their antimicrobial and emulsification properties. Lactose is a byproduct in cheese production and is an inexpensive carbohydrate source. The antimicrobial activity of lactose monodecanoate (LMD) and lactose monomyristate (LMM) was tested against the growth of seven different bacteria. Both esters, when dissolved in dimethoxy sulfoxide (DMSO), proved bactericidal against Bacillus cereus, Mycobacteria KMS and Streptococcus suis. LMM/DMSO was bactericidal against B. cereus at concentrations between 1 and 3 mg/ml. LMM/DMSO was bactericidal against M. KMS and S. suis at concentrations between 3 and 5 mg/ml. LMD/DMSO was bactericidal against B. cereus and S. suis at concentrations between 1 and 3 mg/ml and against M. KMS at concentrations between 0.1 and 1 mg/ml. LMM/DMSO and LMD/DMSO were not effective in inhibiting the growth of Listeria monocyotgenes and Enterococcus faecalis. The antimicrobial effects of LMD on the growth of Listeria monocytogenes and Enterococcus faecalis were found to be solvent dependent. LMD, when dissolved in 30% ethanol, was able to inhibit the growth of L. monocytogenes at concentration between 1 and 3 mg/ml and E. faecalis at concentration between 3 and 5 mg/ml. The growth of Streptococcus mutans and Escherichia coli O157:H7 remained unaltered in the presence of LMD/ETOH, LMD/DMSO and LMM/DMSO up to 5 mg/ml. LMM was also analyzed for its emulsification properties. The destabilization rates and droplet size of the emulsion were determined for five consecutive days. At a concentration of 0.5%, LMM produced 20% oil in water emulsion with destabilization rate of 1.1 mm/day, which can be considered a stable emulsion. The droplet size of the emulsion was also within the range of 0-10 μm. Lower droplet size range signifies the effective work of the LMM as an emulsifier. Also the droplet size of the emulsion was found to be consistent over five days, which is indicative of a stable emulsion.

Recent carbonate sediments from (133-236m) on the northern Jamaican island slope are significantly different from shallower reef zones (l-70m) in grain constituents, textural parameters, and foraminiferal assemblages. The island slope sediment is dominated by coral fragments, calcareous algae, Halimeda plates, and foraminiferal tests. The sediment is characteristically poorly-sorted, nearly-symmetrically skewed, and mesokurtic, with a mean grain size in the fine sand range. Mineralogically, the sediment is predominantly aragonite (66%) and high-Mg calcite (22%), with some calcite (8%), and minor amounts of clays and other insoluble minerals (4%). Q-mode cluster analyses of sediment constituents, textural parameters, and foraminiferal species and larger group abundances were utilized in the delineation of shelf and island slope depositional environments. ineffective for such use. Mineralogy proves No significant differences are observed in sedimentological parameters (textures, constituents, and sedimentation rates) between an island slope traverse located below an area with prominant sill reefs and a traverse below an area lacking well-developed sill reefs. It is suggested that the sill reefs have less effect on off-reef transport than was previously believed. Based on the abundance trends of certain sediment grains and the similarity of sediment grains in island slope and deep fore reef/fore reef slope sediment, it is suggested that the deeper reef zones (>30m) are the source of most sediment transported seaward. Foraminiferal abundances show lateral differences between traverses related to input of shallow water (

Les besoins de villes durables, la réduction de l'effet de serre et la recherche d'un substitut aux énergies fossiles sont autant de raisons qui poussent la recherche et l'industrie à trouver d'autres alternatives. Une de ces solutions est une utilisation plus large de l'énergie électrique. Au fil des années, ce vecteur d'énergie a été largement répandu en utilisant l'électronique de puissance dans des applications dans de nombreux domaines tels que l'automobile, l'aéronautique, ferroviaire, militaire…etc. Les systèmes électroniques de puissance sont composés en partie de composants actifs de puissance tels que des diodes et des transistors. Les applications nécessitant des profils de missions sévères en termes de températures ambiantes, de variations de températures de fortes amplitudes ou de fortes tensions requièrent des composants avec des caractéristiques spécifiques. Pour certaines des applications pour lesquelles les contraintes sont élevées, les composants doivent être à base de matériaux grands gaps comme le carbure de silicium (SiC) ou le nitrure de galium (GaN), le silicium quant à lui présentant certaines limitations. Les atouts et avantages liés à un composant ne sont malgré tout pas suffisants pour sa diffusion dans les applications. Les problèmes de fiabilité sont important et représentent une phase inévitable avant de valider son utilisation. Bien que les composants GaN aient montré de nombreux avantages, la question de leur fiabilité reste posée pour leur utilisation dans des applications. De nombreuses recherches sont en cours pour répondre à cette question. Les travaux menés dans cette thèse participent à cette réponse. L'objectif principal de cette thèse est d'étudier certains éléments de la fiabilité des transistors GaN à haute mobilité électronique (HEMT) pour les applications de puissance. L'étude de la fiabilité des dispositifs à semi-conducteurs nécessite des approches théoriques et expérimentales. Les composants doivent être conformes aux environnements sévères (correspondant à des applications réelles), et doivent également fonctionner de manière cohérente pendant de longues périodes. Parmi ces domaines, côté théorique, on peut citer la physique des semi-conducteurs, la modélisation mathématique et les simulations numériques multi physiques. En revanche, côté expérimental, cela débute par des caractérisations électriques, thermiques et physiques ainsi que des tests expérimentaux de vieillissement. Enfin, il est à noter l'importance de l'analyse des défaillances dans ce processus. Ces champs fournissent les éléments nécessaires pour étudier les modes de dégradation des dispositifs de puissance et réaliser une étude de fiabilité. Dans l'état actuel de la technologie, les transistors GaN souffrent encore d'un phénomène physique réversible appelé "piégeage", ce phénomène représente une source d'instabilité des caractéristiques physiques et électriques du dispositif. Il est un des éléments de fiabilité qu'il reste à résoudre pour les transistors HEMTs à base de GaN dans le domaine de la puissance. La pleine compréhension des effets de ces mécanismes et de leurs évolutions avec le vieillissement n'est pas encore complètement accomplie. Dans cette thèse, nous présentons des travaux théoriques et expérimentaux pour mieux comprendre la fiabilité liée à ce phénomène et l'interaction possible avec le vieillissement dans des conditions de cyclage de puissance. / Seeking green cities, reducing the greenhouse effect and finding a substitute to oil uses are all strong reasons that attract research and industry to find other alternatives. One of these solutions is a broader use of electrical energy. Over the years, this energy vector has been widespread by using power electronics in many automotive, aeronautical and military applications. A power electronics system is mainly composed of power components such as diodes and transistors. Depending on the applications, these components may have specific characteristics to withstand severe operating conditions such as high temperature, high power and high-frequency operations. In order to reach these characteristics, the power devices must be made of specific semiconductor materials. Initially, the most common semiconductor material (Silicon) is used, but it shows some performance limitations for power electronics applications. Over the last two decades, with research and development, there has been new materials that have demonstrated better characteristics than Silicon. Silicon Carbide (SiC) and Gallium Nitride (GaN) have shown many advantages for use in power electronics. They represent the materials estimated to be widely used for power electronics shortly; they have attracted significant interest benefiting from their excellent semiconductor properties. Power components based on these materials have recently attracted much attention. They have presented the fashion in which the scientific community has not ceased to work on it.The presence of advantages for a device is not sufficient before its emergence in real applications. The reliability issue is essential and represents an inevitable phase before validating its use. Although GaN components have shown many advantages, users are wondering: “Are we ready to use these components in real applications?” Much current research is underway to answer this question. In this thesis, we will participate in the answer. The main objective of this thesis is to study some elements of the GaN High Electron Mobility Transistors (HEMT) reliability for power applications. The power transistors reliability study is carried out by a lot of theoretical and experimental works. It can be performed at the semiconductor, packaging or system level. In this thesis, we present theoretical and experimental works carried out only at the semiconductor level.GaN transistors suffer from a reversible physical phenomenon called “trapping”, this phenomenon represents a source of instability of the device physical and electrical characteristics. It has presented an essential element for the reliability works of GaN HEMTs. The full understanding of the effect of this phenomenon and its evolution with ageing is not yet fully accomplished. In this thesis, we present theoretical and experimental works to understand better the reliability linked to this phenomenon and the possible interaction with ageing in power cycling conditions. This work was carried out within the framework of the French MEGaN project, founded by the public investment bank (bpi France). These studies were carried out on two different components; the first one is manufactured and supplied by a project partner CEA-LET, the second one is a commercial power device fabricated by GaN-Systems Inc.