Le différentiel d'eau est défini comme le flux d'eau net descendant qui traverse l'interface pulpe-écume dans une colonne de flottation. Par ce fait même, il est capable de remplacer l'eau d'alimentation entourant les bulles d'air qui arrivent à l'écume et par conséquent il est relié à l'action nettoyante de l'eau de lavage dans cette zone. Les méthodes utilisées jusqu'à ce moment pour la mesure de cette variable présentent quelques limitations: une grande erreur d'estimation dans le cas du bilan massique d'eau, mesures en état stationnaire dans celle utilisant la règle d'additivité, et la nécessité d'une grande quantité des tests pour entraîner et valider le modèle utilisé par le capteur employant un réseau neuromimétique. Ce travail propose une nouvelle méthode pour mesurer le différentiel d'eau de façon directe et dynamique dans un système à deux phases (eau-air). Cette méthode est basée sur l'équation de Maxwell pour des mélanges de phases et utilise des mesures de conductivité du débit d'alimentation et d'eau de lavage et de la zone de collecte immédiatement audessous de l'interface eau-écume; des valeurs de conductivité utilisées pour la mesure du taux de rétention d'air sont aussi nécessaires. Toutes les expériences réalisées dans ce travail ont été faites dans une colonne automatisée de flottation à l'échelle de laboratoire, de 5.7cm de diamètre et 7 mètres d'hauteur. Dans ce travail un modèle linéaire reliant le différentiel d'eau (Jb) avec la fraction volumique d'eau dé lavage se retrouvant juste au-dessous de l'interface pulpe-écume de la colonne de flottation a été développé. Cette relation a été validée expérimentalement avec un coefficient de corrélation de 0.94. On montre aussi la réponse dynamique de lb face à des changements du débit d'eau de lavage, du débit d'air et ce à différents valeurs de la profondeur d'écume. L'influence de ces variables sur la valeur de Jb est aussi démontrée.

L’insecte phytophage Riptortus pedestris, appartenant au sous-ordre des Hétéroptères, est un ravageur notoire de cultures agricoles en Asie du sud-est qui se nourrit préférentiellement de plants de soja. Cette punaise est associée à une bactérie symbiotique du genre Burkholderia nommée Burkholderia insecticola, localisée dans une région spécifique de l’intestin de l’insecte appelée la région M4. Cette région M4, organisée en cryptes, constitue l’organe symbiotique dans lequel le symbiote prolifère de manière extracellulaire. Cette interaction favorise la croissance et le développement de la punaise. Récemment, il a été montré que Riptortus produit des peptides antimicrobiens au sein des cryptes, appelés “crypt-specific cysteine-rich peptides” ou peptides CCR pour lesquels le symbiote est particulièrement résistant. Il a été proposé que les peptides antimicrobiens de l’hôte,incluant les peptides CCR, participent à la colonisation spécifique de l’organe symbiotique par B. insecticola. Dans ce travail, une approche Tn-seq a été utilisée pour identifier les gènes bactériens impliqués dans la résistance aux peptides antimicrobiens et dans la symbiose. Dans un premier temps, la robustesse de la méthode Tn-seq a été évaluée en identifiant le génome essentiel de B. insecticola. Puis dans un second temps, les facteurs bactériens impliqués dans la résistance aux peptides antimicrobiens ont été caractérisés via une approche gènes-candidats et l’approche Tn-seq. Dans une dernière partie, une expérience de Tn-seq in vivo a permis d’évaluer l’ampleur du goulot d’étranglement sur la population symbiotique lors de l’infection de l’organe symbiotique et d’identifier les facteurs symbiotiques impliqués dans la colonisation de R. pedestris. / The phytophagous insect Riptortus pedestris, belonging to the Heteroptera suborder, is a notorious crop pest in South-Eastern Asia which feeds preferentially on soybean plants. This bean bug is associated with a bacterial symbiont, a specific Burkholderia species named Burkholderia insecticola, located in the M4 region of the insect’s midgut. This M4 region is organized in crypts and constitutes the symbiotic organ where the symbiont proliferates extracellularly. This interaction promotes the growth and the development of the bean bug. Recently, it was demonstrated that Riptortus produces antimicrobial peptides in the midgut crypts called crypt-specific cysteine-rich peptides (CCR) for which the bacterial symbiont demonstrates a high resistance profile. It was proposed that host antimicrobial peptides, including the CCR peptides, contribute to the specific colonization of the symbiotic organ by B. insecticola. In this work, a Tn-seq approach was used to find bacterial fitness genes involved in antimicrobial peptide resistance and symbiosis. First, the robustness of the Tn-seq method was assessed by identifying the essential genome of B. insecticola. Second, the bacterial factors for antimicrobial peptide resistance were characterized, based on both a candidate-gene and the Tn-seq approach. Finally, a Tn-seq in vivo experiment was performed to reveal the infection bottleneck effect on the symbiotic population and to identify the bacterial symbiosis factors for the colonization of R. pedestris.

Le phytopathogène Agrobacterium tumefaciens est l'agent causal de la maladie appelée galle du collet, et est capable d'infecter plus de 90 familles de plantes dicotylédones. Cette ∝-protéobactérie appartient à la famille Rhizobiaceae. A. tumefaciens est un complexe de différentes espèces regroupées en 10 génomovars (G1 à G8 et G13). A. tumefaciens C58 appartient au groupe du G8. Son génome est constitué de 4 réplicons : 1 chromosome circulaire, 1 chromosome linéaire et des 2 plasmides dispensables : pAt (pour A.tumefaciens) et pTi (pour Tumor inducing, qui est requis pour la virulence). Pour explorer de nouveaux aspects du mode de vie d’A. tumefaciens, et en particulier l'interaction entre la bactérie et sa plante hôte, deux approches différentes ont été utilisées pour identifier, caractériser et analyser les gènes qui pourraient jouer un rôle dans l'adaptation des bactéries à la tumeur. Une expérience de l'évolution par des passages en série de trois souches différentes de l'agent pathogène sur la plante hôte Solanum lycopersicum a été effectuée afin de clarifier la dynamique évolutive du génome au cours de l'infection. Parallèlement, une étude de différents transcriptomes (in planta et in vitro) a été réalisée et étudiée pour élucider des gènes bactériens candidats impliqués dans l'interaction de la bactérie avec la plante et divers composés produits dans la tumeur. Ce travail tente de donner une vue plus générale du processus d'adaptation de la bactérie à la niche écologique qui est la tumeur. / Agrobacterium tumefaciens is the causal agent of the plant disease called crowngall, and it’s able to infect more than 90 families of dicotyledonous plants. It is an α-Proteobacterium and belongs to the Rhizobiaceae family. A. tumefaciens is a complex of different species grouped in 10 genomovars (G1 to G8, and G13). A. tumefaciens C58 belongs to the G8 group. Its genome consists in 4 replicons: 1 chromosome circular, 1 chromosome linear and 2 dispensable plasmids: pAt (for A. tumefaciens) and pTi (for Tumor inducing), which is required for virulence. To explore new aspects of the A. tumefaciens lifestyle, and in particular the interaction between the bacteria and its plant host, two different approaches have been used to identify, characterize and analyze genes that could play a role in the adaptation of the bacteria to tumor lifestyle. An evolution experiment by serial passages of three different strains of thepathogen on the host plant Solanum lycopersicum has been carried out to clarify the evolutionary dynamics of the genome during the course of infection. In parallel, a study of different transcriptomes (in planta and in vitro) was performed and studied to elucidate bacterial candidate genes involved in the interaction of the bacteria with the plant and various compounds produced in the tumor. This work attempts to give a more general view of the process of adaptation of the bacteria to the ecological niche that is the tumor.

This thesis aims to describe the ultra-rapid synthesis of a number of important transition metal carbides as well as investigating their reaction mechanisms. 4 binary systems are discussed; Nb-C, Mo-C, Ta-C and W-C, and work carried out on the ternary system, Nb-Ta-C, is also evaluated. Carbide production was investigated from both the oxide and elemental precursors. Ultra-rapid synthesis has been achieved through the development of a reproducible experimental technique and the investigation into a plethora of reaction variables as well as microwave applicators and powers. This resulted in, specifically within the single mode cavity, the completion of the majority of reactions within 20 s. Further development was then built upon the direct relationship observed between phase fraction results (obtained from Powder X-ray Diffraction (PXD) data), in-situ temperature and ex-situ dielectric property measurements; allowing reaction profiles of the various carbides to be mapped, as well as a crucial understanding of the effects of microwave energy on materials at various temperatures. Powder Neutron Diffraction (PND) was also used to evaluate product purity and the C occupancy of the final products, revealing non-stoichiometry which relates directly to the Tc onset observed for the superconducting transition metal carbides. This, in turn, allowed the trends observed for the ternary carbides to be explained, a linear trend does not exist between Tc and C occupancy. In an effort to develop on the understanding of solid state microwave heating, in-situ reaction monitoring techniques were investigated. Through the use of thermal imaging and high speed photography, the W-C system was observed during the crucial initial stages of the reaction process. The information obtained both corroborated previously collected data and allowed a possible reaction mechanism to be alluded to. The observation of localised heating, prior to the beginning of carbide formation, suggests possible high temperatures far exceeding those observed by optical pyrometry. This could well explain the rapid reaction times as well as suggest an interaction mechanism between carbon, an efficient microwave absorber, and tungsten, a low dielectric loss metal.

This dissertation presents the findings of a project where, following investigation and assessment, a million tonnes of sand and gravel at a contaminated former US Air Force Base was excavated for use as aggregate. The process required on-site screening for petroleum hydrocarbons of over 7,000 soil samples and provided an opportunity to assess the efficiency of the investigation, assess the application of geophysics of hydrocarbon contaminated sites, and look at the role of aggregate extraction in the contaminated land industry.

This thesis presents research into the binding, extraction and transport of the hexachloroplatinate anion, [PtCl6]2-, by organic receptors in a solvent extraction process. The target anion is produced during the processing of platinum-containing ores and the aim was to develop reagents that can selectively extract [PtCl6]2- to optimise the recovery of platinum. Chapter One outlines reasons for the interest in [PtCI6]2-and provides an overview of the processes and techniques used to refine precious metals. An introduction to anion coordination chemistry relevant to the research project is also presented. Chapter Two discusses the design features incorporated into organic receptors to enable strong and selective binding of [PtCl6]2-. These features include a tertiary amine protonation site, hydrogen-bond donor groups and organic solubilising moieties. The synthesis of a series of functionalised tripodal tris(2-aminoethyl)amine based receptors with sulfonamide, amide, urea, thiourea or pyrrole NH hydrogenbond donor groups are reported. Complexation reactions between the receptors and H2PtCl6 to form [(LH)2PtCl6] ion pairs are discussed. Crystallographic analysis of the [(LH)2PtCl6]complexes with TREN-based sulfonamide, urea and amide receptors confirms the presence of hydrogen-bonds between the NH donor groups and the outer-sphere of [PtCl6]2-. The low organic solubility of the complexes prevented the study of these systems in solvent extractions. Chapter Three describes the variation of terminal substituents of the tripodal receptors with the aim of improving the organic solubility of the extractants and their [PtCl6]2-complexes. In these "second generation" receptors the terminal substituents assessed include 3, 5-dimethylphenyl, 4-iso-propylphenyl, 4-tert-butylphenyl, 3, 5- dimethoxyphenyl, 3, 4 dimethoxypheynl and 3, 4, 5-trimethoxyphenyl. Through reaction of the receptors with H2PtCl6 the solubility of the resultant complexes are assessed. Chapter Four describes the development of an optimised solvent extraction method to study the extractive behaviour receptors. A pH swing mechanism is utilised to control the uptake and release of [PtCl6]2-. The extraction results for trioctylamine and the soluble tripodal urea and amide receptors are compared. Attempts are also made to confirm the stoichiometry of the complex in solution. Chapter Five describes the synthesis of tris(2-aminoethyl)amine based receptors with hydrogen- and halogen-bond donor groups with the aim of increasing the strength of the interaction between a receptor and [PtCI6]2-. Receptors with an extended tripodal scaffold based on a tris(3-aminopropyl)amine with urea and amide moieties are also presented. The results of the complexation reactions and solvent extraction studies with these modified extractants are presented. Chapter Six presents the design and synthesis of bipodal and monopodal receptors in order to assess the role of the number of hydrogen-bond donor functionalised arms. The results of the solvent extraction studies with these receptors are discussed and comparisons made between tripodal, bipodal and monopodal extractants. The crystallographic analysis of the [(LH)2PtCl6] complexes formed between the bipodal urea and amide receptors is described. Chapter Seven highlights the important findings from this work. Conclusions are drawn as to the optimum receptor system developed and this is compared to the extractant system thought to be in current use for the extraction and transport of [PtCl6]2-.

Thesis advisor: Michelle Meyer / The primary bacterial targets for most antibiotics are well known. To survive the stress of an antibiotic a bacterium must decrease the antibiotic to target binding ratio to escape from harmful effects. This can occur through a number of different functions including down-regulation of the target, mutation of the binding site on the target, and decreasing the intake or increasing the efflux of the antibiotic. However, it is becoming more evident that an antibiotic stress response influences more than just the primary target, and that a wave of secondary responses can be triggered throughout the bacterium. As a result resistance mutations may arise in genes that are indirectly affected by the initial interaction between the antibiotic and target. These indirect responses have been found to be associated with metabolism, regulation, cell division, oxidative stress, and other critical pathways. One technique recently developed in our lab, called transposon insertion sequencing (Tn-seq), can be used to further understand the complexity of these indirect responses by profiling growth rates (fitness) of mutants at a genome-wide level. However, Tn-seq is normally performed with large libraries of pooled mutants and thus it remains unclear how this may influence fitness of some independent mutants that may be compensated by others in the population. Additionally, since the original method has only utilized planktonic culture, it is also not clear how higher order bacterial structures, such as biofilms or microcolonies, influence bacterial fitness. To better understand the dynamics of pooled versus individual mutant culture, as well as the effect of community structure in microcolony development on the influence of fitness, we adapted a droplet microfluidics-based technique to encapsulate and culture single mutants. We were able to successfully encapsulate at least 7 different species of bacterial pathogens, including Streptococcus pneumoniae, and culture them planktonically, or as microcolonies, in either monodisperse liquid or agarose droplets. These experiments, however, raised an important challenge: the DNA yield from one encapsulation experiment is insufficient to generate samples for sequencing by means of the traditional Tn-seq method. This led us to develop a novel Tn-seq DNA library preparation method, which is able to generate functional Tn-seq library molecules from picogram amounts of DNA. This method is not ideal yet because fitness data generated through the new method currently does not correlate well with data from traditional Tn-seq library preparation. However, we have identified one major culprit that should be easily solvable. We expect by modifying the binding site of the primer used for linear amplification of transposon ends that the new preparation method will be able recapitulate results from the traditional Illumina preparation method for Tn-seq. This will enable us to prepare robust Tn-seq samples from very small amounts of DNA in order to probe stress responses in single mutants as well as in microcolonies in a high-throughput manner. / Thesis (MS) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

Low temperature plasma surface alloying with nitrogen (nitriding), carbon (carburising) and both (carbonitriding) has been successfully employed in hardening medical grade ASTM F138, ASTM F1586 and ASTM F2581 as well as engineering grade AISI 316 by the formation of a modified layer better known as S-phase or expanded austenite. In this study, systematic plasma treatments and characterisation were performed on medical grade stainless steel in order to establish the optimised treatment conditions, especially temperature, which can maximise the hardened case depth without any detriment in corrosion resistance. The surface of a biomaterial must not adversely affect its biological environment and return the material surface must not be adversely affected by the surrounding host tissue and fluids. Experimental results have shown that this duality of concern can be addressed by creating S-phase. It has been shown that low-temperature nitriding (430°C), carburising (500°C) and carbonitriding (430°C) improved the localised corrosion, corrosion-wear and fretting-wear resistance of these medical grade stainless. Also biocompatibility studies have proved that these hardened surfaces were biocompatible under the realms of the tests conducted in this study therefore the use of hardened medical grade austenitic stainless steel might be suitable in implant applications.

This thesis reports on an environmentally-friendly pultrusion technique for the production of fibre-reinforced composites, termed as “clean pultrusion”. In this new manufacturing technique, the resin bath used in the conventional pultrusion was replaced with a custom-built resin impregnator. The resin impregnator was designed and built to impregnate the rovings using a combination of pin, injection and capillary-based impregnation. An integral aspect of the clean pultrusion process was spreading of the filaments in the rovings, via mechanical means, prior to impregnation. An automated fibre spreading rig was designed and built based on “tension-release” process. The rig-design was optimised using Taguchi method. The physical, mechanical and thermo-mechanical properties of the composites pultruded using the clean and conventional techniques were compared. It was found that the composites manufactured using the clean pultrusion exhibited lower void and better mechanical properties. A life cycle assessment (LCA) was also performed to compare the environmental impact of the clean and conventional pultrusion processes. The LCA demonstrated conclusively that the clean pultrusion technique offers several environmental advantages over the conventional resin-bath pultrusion. The new pultrusion technique was demonstrated as being a viable method to pultrude composites without using a resin bath.

Microstructural analysis and mechanical property assessment have been carried out on hot isostatically pressed (HIPped) and heat treated samples of RR 1000 powder to assess Net Shape HIPping as a process-route for aero engine components. HIPping led to (Hf,Zr)-rich oxides and carbides on prior particle boundaries (PPBs) which could be coarsened, but not eliminated by changing the HIP procedure. HIPping above the γ′ solvus resulted in coarser grains with serrated boundaries and in the formation of irregular-shaped secondary γ′ and fan-type γ-γ′ structures. Factors which influence the growth and morphology of γ′ particles are considered and it is shown that particle impingement dominates in the formation of irregular γ′ during continuous cooling from supersolvus. Solution treatment near the HIPping temperature led to thermally induced pores (TIP) but lower temperatures avoided TIP and changed the γ′ size, distribution and morphology giving a large volume fraction of finer cuboidal secondary γ′ and medium-sized spherical tertiary γ′.