Cette thèse a pour but d'étudier les effets quantiques apparaissant pour des agrégats métalliques de très petite taille en raison de l'augmentation du ratio surface/volume et de la discrétisation de la structure électronique. Mettre en avant ces effets demande une très grande qualité de fabrication des nanoparticules étudiées, monodisperse dans le cas idéal. Nous fabriquons des nanostructures en encapsulant des agrégats d'argent générés par une source magnétron dans des matrices solides, comme la silice ou l'alumine. Cette technique nous permet de contrôler indépendamment la composition des particules, leur taille, et leur concentration. Un spectre de masse quadripolaire a été mis en place et utilisé comme un filtre en taille pour obtenir une distribution plus étroite et précise.Les échantillons ont été caractérisés par deux techniques complémentaires : par spectroscopie optique à transmission avec des mesures sur des ensembles de particules, et par spectroscopie de perte d'énergie des électrons (EELS) sur des particules uniques, réalisée dans un microscope électronique à balayage par transmission. Bien qu'utilisant deux outils conceptuellement différents, ces deux méthodes mesurent les résonances plasmoniques des particules. Ce travail a donc pour objectif de relier théoriquement et expérimentalement ces deux méthodes dans le but de comprendre comment les propriétés physiques de ces petits agrégats de métaux nobles sont affectées par les effets quantiques / The aim of this thesis is to study quantum effects appearing in very small metallic clusters caused by the increasing surface/volume ratio and the discretization of the electronic structure. Investigating effects such as size dependencies demand a very high quality of the studied nanoparticles, monodisperse in the ideal case. We fabricate nanostructures by embedding silver clusters generated in a magnetron source in solid matrices, such as silica or alumina. This technique gives us full and independent control over the particle composition, size and concentration. A quadrupole mass spectrometer is used as a size filter to obtain a more precise and narrow distribution.Samples have been characterized with two complementary methods: optical transmission spectroscopy of ensembles of particles and electron energy loss spectroscopy (EELS) on single particles using a scanning transmission electron microscope. Although these two tools are conceptually different, they both measure the plasmonic resonances of metal nanoparticles. The objective of this work is to link theory and experiment in these two methods in order to understand how the physical properties of these small noble metal clusters are affected by quantum effects

Ce mémoire est consacré au développement et à l'application d'une méthode permettant de caractériser finement les propriétés physiques (densité d'hélium, pression, diamètre, morphologie) de bulles d'hélium de taille nanométrique pour in fine améliorer la compréhension du comportement de ces nano-systèmes. L'approche que nous avons choisie est basée sur la spectroscopie de pertes d'énergie des électrons et l'acquisition de spectres images en microscopie électronique en transmission filtrée en énergie. Les différentes étapes d'acquisition, de correction des aberrations, et de traitement des spectres sont détaillées. L'erreur sur la mesure est estimée, et des améliorations potentielles de la méthode sont discutées. Nous montrons de plus que cette approche permet non seulement de dépasser les limites imposées par la microscopie électronique en transmission à balayage habituellement utilisée, mais aussi d'aller au-delà, en terme de statistique notamment. Nous appliquons ensuite notre méthode pour déterminer les propriétés physiques de bulles d'hélium dans le silicium, lors de recuits thermiques in situ dans le microscope. L'évolution des caractéristiques morphologiques des bulles est mise en rapport avec la variation de la densité d'hélium qu'elles contiennent suite à ces recuits. Les valeurs de densité et de pression obtenues sont comparées aux valeurs disponibles dans la littérature par des méthodes expérimentales ou numériques. Enfin, le transfert de notre méthode pour l'étude de bulles dans d'autres matrices (germanium, carbure de silicium, euxénite) est discuté. / This thesis is dedicated to the development and application of a method allowing for the fine characterization of the physical properties (density, diameter, pressure and morphology) of helium bubbles at the nanometric scale, to eventually improve the understanding of the behavior of these nano-systems. The chosen approach is based on electron energy loss spectroscopy and the acquisition of spectral images by energy-filtered transmission electron microscopy. The acquisition, aberration correction, and data analysis steps are detailed. The measurement error is estimated, and potential improvements are discussed. We additionally show that this method is not only able to overcome the limits imposed by commonly used scanning transmission electron microscopy, but also to go further, notably in a statistical way. We then apply our method to determine the physical properties of helium bubbles in silicon, during in situ thermal annealing in the microscope. The evolution of the morphological characteristics of the bubbles is put in relation with the variation of the density of the helium contained following these annealings. The density and pressure values are compared to those available in the litterature through experimental and numerical methods. Finally, the translation of this method towards the study of bubbles in other matrices (germanium, silicon carbide, euxenite) is discussed.

Le projet de maîtrise était axé sur l’utilisation de traitements multivariables afin d’analyser adéquatement des ensembles de données provenant d’imagerie spectrale. Ce mémoire met premièrement en relief la particularité des détecteurs utilisés dans les microscopes, ainsi que les caractéristiques du bruit dans les données acquises. L’analyse en composantes principales est une méthode qui se trouve dans plusieurs méthodologies de traitements de données d’imagerie spectrale. Celle-ci comprend certains désavantages, dont l’impossibilité d’extraire de réels spectres et des distributions de concentrations des composés en présence dans l’échantillon. La résolution multivariée de courbes – moindres carrés alternatifs est une méthodologie qui a été popularisée dans les années 2000. Celle-ci permet de contrer les désavantages de l’analyse en composantes principales en extrayant des spectres physiquement cohérents et en créant des cartes de concentrations associées à ces spectres. Cependant, ce mémoire démontre que cette méthode est inefficace lorsque les données ont un très faible ratio signal sur bruit et que plusieurs composants sont à extraire. Des améliorations à la résolution multivariée de courbes – moindres carrés alternatifs sont donc apportées. Notamment, la caractéristique du bruit des données, connue et documentée à la suite de nombreuses études, est utilisée afin d’améliorer la convergence de l’algorithme vers la bonne solution. Ce mémoire démontre que ces améliorations sont appliquées avec succès sur des ensembles de données d’imagerie spectrale provenant de spectrométrie photoélectronique X, d’analyse dispersive en énergie et de spectroscopie des pertes d’énergie.

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

Concerns regarding the decreasing population of the American eel (reported by Castonguay et al. 1994; Haro et al. 2000) have led to design restrictions for hydropower facilities in the Eastern United States. However, the effects of these restrictions on eel passage and their impacts on power generation have not been fully researched. The goal of this study was to evaluate design parameters for bar racks that have potential to prevent entrainment of silver American eels, but also have minimal impacts on power generation. Hydraulic and biological assessments were used to determine the role of bar spacing, rack angle, and approach velocity on head loss across bar racks and the effects of bar spacing and approach velocity on eel bypass efficiency. The hydraulic assessments included computational fluid dynamics (CFD) analyses and laboratory experiments conducted in a re-circulatory flume at Alden Research Laboratory (Alden) in Holden MA. The flume allowed for determination of head losses across bar racks placed at angles of 45 and 90 degrees to the flow direction, with bar spacings of 0.75, 1.0 and 1.5 inches (19, 25 and 38 mm) and approach velocities of 1.5, 2.0 and 2.5 ft/sec (0.46, 0.61 and 0.76 m/s). Biological assessment, supported by funding from the Electric Power Research Institute (EPRI), used the same flume and included experiments with a 90 degree rack angle, bar spacings of 0.75 and 1.0 inches (19 and 25 mm), and approach velocities of 1.5 and 2.0 ft/sec (0.46 and 0.61 m/s). Bypass efficiencies, defined by the percentage of eels moving through the bypass, were evaluated for eels using three 2-hour replicate trials with nighttime releases of 30 eels per trial. Eel behavior in the vicinity of the racks was observed to the extent possible using a DIDSON acoustic camera. Experiments for the 90 degree configuration showed that the guidance efficiencies for the 0.75 inch (19 mm) spacing were greater than those for the 1.0 inch (25 mm) spacing, while the head losses for the 0.75 inch (19 mm) spacing exceeded the head losses for the 1.0 inch (25 mm) spacing by more than 10 percent. Linear regression analysis indicated that 53 percent of the variations in head width are explained by changes in the length of the eel. Results of the hydraulic evaluations were used to develop a new head loss equation that has a correlation coefficient of 98.6 percent. The results of the hydraulic and biological assessments provide a basis for quantifying the impacts of bar rack design on hydropower operation and downstream passage for American eels.

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No description available.

With 226-343 individual/ha, population density of Chelodina longicollis in the dams of the University of Western Sydney-Hawkesbury Richmond campus were in the range of other studies around Australia. Their size extremes (24.3 -223.3 mm) were within the range of previous studies, and the overall sex ratio was skewed toward males. The annual growth rates varied and were weakly correlated with animal size. Scute shedding occurred between September and April and peaked in December. Turtles were generally in excellent condition, indicating that sufficient food resources were available in local habitats. Only 3.4% of the population were in poor condition and few animals (8.8 %) carried signs of past injury. No gross abnormalities were recorded, however, there has been low levels of recruitment to the population compared with other Australian studies. Despite a maximum distance dams sampled of 2.8 km and ample evidence of interchange between dams, there was a great variation in animal size, cohort structure, sex ratio among dams. There are a range of factors which have the potential to bias sampling results. Turtles were not influenced by a dominance hierarchy or by the presence of eels, however, they appeared to be capable of avoidance behaviour when nets are set at a specific location. Different cohorts were caught differentially and this varied with month, season and year. In addition, catchability varied among cohorts. Juveniles were least likely, and sub-adult males were most likely, to be recaptured. In some dams there was evidence that animals moved at random while in others movement did not conform to this pattern. These results could not be accounted for in terms of dam size, physical structure of the dam or the distribution and abundance of vegetation. / Master of Science (Hons)

The aim of this master thesis was to compare EELS in TEM with TEM-EDS and WDS-EPMA for quantitative analysis of γ-phase in cemented carbide. Especially, the quantification of the light elements nitrogen and carbon in compounds like TiCxN1-x is interesting, since this is problematic. The techniques were compared by acquiring spectra for quantification of two samples of cemented carbide containing γ-phase (Tix,W1-x)(CyN1-y) with different nitrogen and tungsten content. Also, a rigorous evaluation about how EELS spectra best is acquired and processed was performed in order to enable the comparison. Experimental results show that EELS gives satisfying results for TiC0.7N0.3 and that EELS is comparable with WDS-EPMA for quantification of nitrogen, carbon and titanium in (Tix,W1-x)(CyN1-y) when the atomic concentration of nitrogen is around 20%. However, EELS was not used for quantification of tungsten. Concluded is also that EELS and WDS should be considered as complementary rather than competing techniques.

No description available.