Antibiotic-associated diarrhoea (AAD) and colitis, with the causative agent being the Gram-positive anaerobe, Clostridium difficile, are some of the most important hospital-acquired infections and significant burdens to healthcare services worldwide. Treatment of the infection is often ineffective and currently no vaccine is available against C. difficile infection (CDI). Research to identify novel virulence factors potentially leads to the development of new therapeutic and prophylactic drugs. As lipoproteins have been shown to play key roles in the virulence of several pathogens, the aim of this project was to investigate whether lipoproteins are involved in the virulence of C. difficile. Lipoproteins are anchored to the extracellular side of the cytoplasmic membrane in Gram-positive bacteria. Two enzymes are involved in the biosynthesis of lipoproteins: lipoprotein diacylglycerol transferase (Lgt) attaches lipoproteins to the membrane, and lipoprotein signal peptidase (Lsp) cleaves the signal peptide from the amino-terminus of lipoproteins. In order to study lipoprotein processing in C. difficile, lgt and lsp mutants of the C. difficie 630Δerm strain were generated using the ClosTron system. Antibody reactivity of 14 C. difficile lipoproteins was also investigated. It was shown in this study that lgt mutation caused changes in the lipoproteome of C. difficile. Therefore, inactivation of the lgt gene allowed investigation of the global contribution of lipoproteins to bacterial processes. The physiology and virulence of the lgt mutant was studied in vitro and in vivo. Surprisingly, many of the assayed phenotypes were not significantly affected by disruption of the lgt gene. Nevertheless, the ability of the lgt mutant to adhere to Caco-2 cells was markedly reduced. In addition, the phenotype of the lgt mutant observed in mice suggests that the faecal shedding of C. difficile is affected by Lgt inactivation. In further studies, the CD0873 lipoprotein as a potential adhesin of C. difficile was identified by in silico approach. Contribution of the CD0873 lipoprotein to the adherence of C. difficle was investigated by several different assays and the results strongly suggest that the CD0873 lipoprotein is directly involved in adhesion

Piezoelectric materials are well known for their applications in surface (SAW) and bulk acoustic wave (BAW) devices such as oscillators, resonators and sensors. Quartz has been the main material used in such applications. Ternary calcium gallium germanate (CGG) structure-type materials, so-called langasites, recently emerged as very promising because of their piezoelectric properties superior to quartz. This thesis discusses the growth of langasite-type La3Ga5.5Ta0.5O14 (LGT) films by liquid phase epitaxy (LPE) technique and their chemical and structural characterization. In addition, the different techniques suitable for the growth of LGT are discussed and compared. To adjust the materials properties for given applications, doping by selected ions can be used. However, the dopants must be homogeneously distributed. In the current study, Al, Ti, Cr and Ca were investigated as dopants. In an earlier study, Al and Ti had been chosen because of their ability to substitute the octahedral site of LGT, normally occupied by Ga (CN=VI) with a segregation coefficient near unity in Czochralski growth. Doping with Ca and Cr has never been reported before, and therefore, the segregation behavior was unknown. In this study, Al, Ti and co-doping with Cr and Ca has been investigated for both X and Y-oriented films. The dopant distribution in the films was quantitatively evaluated by Secondary Ion Mass Spectroscopy (SIMS), using ion-implanted LGT substrates as standards. The drop of dopant concentration, in the SIMS profile, allows for the identification of the film-substrate interface and to accurately measure the thickness of the films. The film thickness is found to be typically of the order 0.5 to 2µm, depending on growth conditions. The solvent was found a reliable choice, as solvent ions were not incorporated in the films above the detection limits of the characterization techniques. A lead oxide solvent system is used as a solvent for the growth of LGT LPE films with different orientations. Extensive structural characterization was performed. The crystallinity of substrates and films grown with different orientations was compared by X-ray diffraction (XRD). The films show a very high structural perfection, with typically FWHM values of 0.035 for the (004) reflection of the XRD rocking curve. The films were also characterized by TEM. The optical transmittance of the films was characterized by Varian optical spectrophotometer, and the value obtained of approximately 80% is comparable with the transmittance value of the Czochralski grown polished substrate.

Les travaux présentés dans ce mémoire portent sur l'étude de matériaux piézoélectriques de synthèse de la famille des langasite et sur la réalisation de micro-résonateurs basse fréquence dans ces matériaux. La première partie de l'étude se concentre sur la recherche des orientations des coupes compensées en température pour les coupes X de la langasite (LGS) et de la langatate (LGT), pour les modes d'extension selon Y et de flexion autour de X. Un modèle analytique simple et des simulations par éléments finis permettent de déterminer les valeurs théoriques de ces orientations. Des dispositifs de types barreau et diapason sont ensuite réalisés afin d'effectuer des mesures électriques pou confirmer l'existence de ces coupes compensées. La seconde partie de l'étude concerne la fabrication de micro-résonateurs en langasite. Plusieurs méthodes d'usinage (mécanique, DRIE,...) sont envisagées avant que notre choix ne se porte sur l'usinage chimique (solution HCl). Le procédé de fabrication est détaillé puis des mesures de vibration sont menées pour les dispositifs obtenus.

Les travaux présentés dans ce mémoire portent sur l'amélioration des sources ultra-stables de fréquences dans le domaine des temps courts (typiquement inferieurs à une minute). Deux voies d'investigations ont été explorées : <br />- La première concerne l'évaluation des potentialités des matériaux de la famille de la langasite (LGS). Une classification des coefficients de qualité (Q) des matériaux LGS et langatate (LGT) en fonction de leurs provenances a été mise en évidence. Les premiers prototypes de résonateurs à ondes de volume ont été réalisés dans un cristal de LGT à fort Q. A cette occasion un procédé de fabrication spécifique a été mis au point. Une électronique d'oscillateur et un packaging thermique adaptés aux caractéristiques de ces résonateurs ont été développés. Enfin, ces premiers prototypes d'oscillateurs ont été caractérisés en terme de stabilité temporelle et de vieillissement.<br />- La seconde voie exploratoire concerne la mise en place d'un ensemble expérimental permettant la réfrigération d'oscillateurs à résonateurs à ondes de volume à des températures inférieures à celles de l'hélium liquide (4,2K). Pour cela, des résonateurs en quartz de coupe SC et LD, et en LGT de coupe Y, ont été caractérisés à basses températures. Une campagne de mesures systématiques a révélé des coefficients de qualité exceptionnels pour certains modes de vibration. Par ailleurs, différents modèles de transistors ont été testés et l'une des références testées a été modélisée simplement, à température cryogénique. Deux premiers prototypes d'oscillateurs à résonateur à quartz de coupe SC ont été développés puis testés à basses températures. Il en résulte les toutes premières caractérisations en terme de stabilité temporelle.

Tax evasion has been happening for decades, but after the highly publicized cases with two foreign banks, LGT and UBS, the United States (US) is cracking down on tax evaders. The latest addition to the Internal Revenue Service (IRS)’s repertoire of enforcement tools is the Foreign Account Tax Compliance Act, otherwise known as FATCA. The Act was enacted to incentivize tax information release by foreign financial institutions (FFIs) who would otherwise face a 30% withholding tax on any US source income. The question was whether or not the design of the Act and its implementation successfully met this goal. This paper explores the history leading up to FATCA’s creation, beginning from the basic data underlying tax evasion. With the US losing approximately $100 billion a year of tax revenue, the IRS is keen on reducing the money flow out of the US. It will dig deeper into the facts of the LGT and UBS cases which led to Congress’s realization that their other enforcement mechanisms were not sufficient and describe FATCA’s unintended impact. Through researching articles on the predicted impact of FATCA, surveys of FFIs, testimonials from US citizens, this paper will explain how FATCA has unfortunately detrimentally impacted FFIs and US citizens living abroad.