Les bactéries sont exposées aux perturbations externes causées par les changements environnementaux ou la présence d’agents antibactériens nocifs. L’enveloppe bactérienne forme une barrière entre le milieu externe et l’intérieur de la cellule et se trouve donc potentiellement exposée aux dommages causées par les perturbations et forme la première ligne de défense pour les bactéries. Pour survivre à ces conditions, les bactéries ont développé des systèmes à deux composantes (TCS) qui détectent et permettent la réponse à ces stress.Bien qu’ils soient associés à la protéine périplasmique ZraP, ZraSR constitue un de ces TCS. La présence de cette protéine accessoire associé au système ZraSR montre une homologie avec le système CpxPAR qui capte un grand nombre de stress d’enveloppe. Le système Zra est activé en présence de zinc et cause l’expression de zraP, zraS et zraR. Les protéines ZraP et ZraR ont été étudiées mais aucun travail n’a encore impliqué l’étude de la protéine membranaire ZraS et son mécanisme d’activation. En effet, l’étude des senseurs de TCS s’est beaucoup focalisée sur la compréhension de la partie cytoplasmique mais très peu sur le domaine périplasmique. Dans le cas du système Zra, il y a encore des interrogations sur l’activation ainsi que la régulation de ce système. Lors de ma thèse j’ai concentré mes recherches sur le domaine périplasmique de ZraS. Nous avons d’abord voulu comprendre comment le zinc active le système Zra mais aussi par quel moyen la protéine ZraP influe sur cette activation par le zinc. Pour cela, la caractérisation biochimique du domaine périplasmique de ZraS a été effectué et l’effet du zinc sur ce domaine a été observé. De ce fait, nous avons aussi tenté de déterminer quels sont les résidus de ce domaine qui permettent la liaison du zinc. Par une approche in vivo et in vitro, nous avons voulu comprendre le rôle régulateur de ZraP sur le système Zra. Ce travail s’inscrit dans l’objectif de mieux comprendre les différents mécanismes d’activation des différents ESR. / Bacteria are exposed to external perturbations due to environmental changes or to the presence of noxious agents. Because the bacterial cell envelope forms the barrier between the inside and the outside of the cell it is highly susceptible to be damaged by these perturbations but it is also the first line of defense. To survive gram-negative bacteria have developed two component systems (TCS) that detect and respond to these envelope stresses.ZraSR is one of these TCS, although it is atypical because associated with ZraP, a periplasmic protein. The presence of an accessory protein associated with ZraSR system shows that it is functionally homologous to the CpxPAR system, a sensor of a variety of envelope stress signals. In presence of zinc, Zra system is activated and allows the expression of zraP, zraS and zraR. The periplasmic protein ZraP and the response regulator ZraR have been studied but the activation of the membrane histidine kinase by zinc has not been studied yet. Indeed, studying of TCS sensors was focused on the understanding of the cytoplasmic domain and less on the periplasmic part.During my thesis, I tried to concentrate my study on the periplasmic domain of ZraS. We first tried to understand how the zinc is activating the Zra system but also how ZraP is regulating this activation. For that purpose, we characterized ZraS periplasmic domain and analyzed the effect of zinc binding on it. Hence, we also tried to identify all of ZraS residues that are coordinating the zinc. By combining in vitro and in vivo assays, we tried to determine ZraP role in the regulation of Zra system. This study could help for the understanding of the mechanisms important for the activation of bacterial stress response systems.

本研究主要目的是想要探討台灣地區民眾對於維持公共電視的營運與發展之願付價格。資料來自於中央研究院人文社會科學研究中心調查研究專題中心所進行的一項公共電視願付價格調查，其中關於願付價格的部分是透過條件評估法的方式取得，受訪者隨機分配至兩個題組之一，其中A題組為考慮公共電視帶給家人的好處，而B題組為考慮公共電視帶給全國民眾及社會的好處。 建模時我們採用一或二要素混成模型，這是一個可以將不理性受訪者分離，僅針對理性受訪者的願付價格進行估計的一個模型。分析結果顯示考慮到公共電視帶給家人的好處時，年齡50歲以上的受訪者中存在著一群無論什麼價格都不願意支付或Ney-sayers的人，估計的比例大約為21.13%；而考慮到公共電視帶給全國民眾及社會的好處時，很少看文化教育節目的受訪者中也存在著一群無論什麼價格都不願意支付或Ney-sayers的人，估計比例大約為13.53%。 針對願意支付合理價格的受訪者配適加速失敗模型時，我們不僅就位置參數引進解釋變數，同時也引進解釋變數至尺度參數。分析結果顯示願意支付合理價格的受訪者，在考慮公共電視帶給家人的好處時，每年願意支付價格之平均值為1477元；而考慮到公共電視帶給全國民眾及社會的好處時，每年願意支付價格之平均值為1663元。顯示受訪者在考慮到全國民眾及社會的好處，願意付出較高的價錢。 / This study aimed to explore people’s willingness to pay (WTP) for maintaining the operation of Public Television Service (PTS) in Taiwan. The survey using contingent valuation method was conducted by the Center for Survey Research, Academia Sinica. The survey sample was split into two groups, A and B. Each group was presented with the same scenario but different scope of benefits. Group A considered the benefits that PTS might bring to one’s family, while Group B considered the benefits that PTS might bring to the whole society. The model used in this study was a one/two-component hybrid model, a model that is able to separate those who are willing to pay a reasonable price from these who are not, and obtain their mean WTP estimate. Multinomial logistic part of the model, indicated that for Group A, among those who were 50 years of age or older, about 24.48% were not willing to pay any price or Ney-sayers. And for Group B, among those who seldom watched cultural or educational programs, about 12.91% were not willing to pay any price or Ney-sayers. Appling accelerated failure time model to those who were willing to pay for reasonable prices enabled us to evaluate the WTP. We not only introduced explanatory variables in the location parameter but also the scale parameter. The estimated mean WTP for Group A was found to be NT$1477 per year, while the mean WTP for Group B was NT$1663 per year.

Les souches d’Escherichia coli pathogènes aviaires (APEC) sont responsables d’infections respiratoires et de septicémies chez la volaille. Le régulon Pho est contrôlé conjointement par le système à deux composantes PhoBR et par le système de transport spécifique du phosphate (Pst). Afin de déterminer l’implication de PhoBR et du système Pst dans la pathogenèse de la souche APEC O78 χ7122, différentes souche mutantes phoBR et pst ont été testées pour divers traits de virulence in vivo et in vitro. Les mutations menant à l’activation constitutive du régulon Pho rendaient les souches plus sensibles au peroxyde d’hydrogène et au sérum de lapin comparativement à la souche sauvage. De plus, l’expression des fimbriae de type 1 était affectée chez ces souches. L’ensemble des mutants Pho-constitutifs étaient aussi significativement moins virulents que la souche sauvage dans un modèle de coinfection de poulet, incluant les souches avec un système Pst fonctionnel. De plus, l’inactivation du régulateur PhoB chez un mutant Pst restaure la virulence. Par ailleurs, l’inactivation de PhoB n’affecte pas la virulence de la souche χ7122 dans notre modèle. De manière intéressante, le degré d’atténuation des souches mutantes corrèle directement avec le niveau d’activation du régulon Pho. Globalement, les résultats indiquent que l’activation du régulon Pho plutôt que le transport du phosphate via le système Pst joue un rôle majeur dans l’atténuation des APEC. / Avian pathogenic Escherichia coli (APEC) strains are associated with respiratory infections and septicemia in poultry. The Pho regulon is jointly controlled by the two-component regulatory system PhoBR and by the phosphate-specific transport (Pst) system. To determine the involvement of the PhoBR regulon and the Pst system in the pathogenesis of the APEC O78 strain χ7122, different phoBR and pst mutant strains were tested for in vivo and in vitro virulence traits. Mutations resulting in constitutive activation of the Pho regulon rendered strains more sensitive than the wild-type to hydrogen peroxide and to the bactericidal effects of rabbit serum. In addition, production of type 1 fimbriae was also impaired in these strains. Using a chicken competitive infection model, all PhoB constitutive mutants were out-competed by the wild-type parent, including strains containing a functional Pst system. In addition, cumulative inactivation of the Pst system and the PhoB regulator resulted in a restoration of virulence. Loss of the PhoB regulator alone did not affect virulence in the chicken infection model. Interestingly, the level of attenuation of the mutant strains correlated directly with the level of activation of the Pho regulon. Overall, results indicate that activation of the Pho regulon rather than phosphate transport by the Pst system plays a major role in the attenuation of APEC.

No description available.

An experimental investigation has been carried out to study the heat transfer in a two-phase two-component mixture flowing upward inside a 1" double pipe heat exchanger. The heat transfer coefficient was measured using either air to lift the liquid (air-lift system) or a mechanical pump. The heat transfer coefficient results have been extensively studied and compared with other workers' results. An attempt was made to correlate the present heat transfer data in dimensionless correlations. Possible factors affecting the two-phase heat transfer coefficient have been studied with special attention being given to the fluid properties, particularly the liquid viscosity. Experiments were also carried out to investigate the effect of solid particles added to a liquid flow on the measured heat transfer coefficient. The present investigation was carried out using air as the gas-phase ranging from 2x 10-5 up to 80 x 10-5 m3/s. Liquids used were water and glycerol solutions with viscosity ranging from 0.75 up to 5.0 C. P. and flowrates between 4x 10-5 and 25 x 10-5 m3/s. Void fraction and pressure drop were also measured during the heat transfer process. Flow pattern in gas-liquid mixture was investigated in a perspex tube of identical dimensions to the heat exchanger tube.

The problem of determining whether or not a theoretical model is an accurate representation of an empirically observed phenomenon is one of the most challenging in the empirical scientific investigation. The following study explores the problem of stochastic model validation. Special attention is devoted to the unusual two-peaked shape of the empirically observed distributions of the conditional on realised volatility financial returns. The application of statistical hypothesis testing and simulation techniques leads to the conclusion that the conditional on realised volatility returns are distributed with a specific previously undocumented distribution. The probability density that represents this distribution is derived, characterised and applied for validation of the financial model.

Chez les bactéries en contact direct avec leur milieu, la transcription des gènes et la synthèse des protéines sont régulées de manière efficace à chaque changement des paramètres environnementaux afin de permettre la survie cellulaire. Dans le cas des bactéries commensales de l’intestin, ces régulations doivent aussi permettre les interactions symbiotiques et la colonisation dont les mécanismes moléculaires, encore peu connus, sont probablement liés, entre autres, à la surface des bactéries (molécules exposées et sécrétées…). Lactobacillus casei, bactérie commensale, possède environ 330 gènes prédits comme intervenant dans la composition et la fonctionnalité de la surface cellulaire. Afin d’avoir une vue globale de la totalité des gènes qui interviennent dans l’établissement de L. casei dans l’intestin, une approche de génétique inverse a été réalisée. Pour cela, une banque de mutants aléatoires étiquetés de L. casei par « Signature-Tagged Mutagenesis » a été créée puis annotée et réorganisée grâce au séquençage des régions d’insertion du transposon. Les mutants ont été criblés quant à leur capacité à s’établir dans l’anse iléale ligaturée de lapin et quantifiés par qPCR. Parmi les 47 gènes identifiés comme étant impliqués dans l’établissement in vivo, trois gènes en opéron codant pour un système à deux composants et une « penicillin-binding protein » ont été caractérisés. Ces trois gènes sont impliqués dans la modulation de la surface cellulaire et plus particulièrement dans la régulation des hydrolases du peptidoglycane qui sont nécessaires à la protection de la bactérie dans l’environnement intestinal. / In bacteria which are in direct contact with their environment, genes transcription and proteins synthesis are efficiently regulated at each change of environmental parameters to allow cell survival. For intestinal commensal bacteria, these regulations must also allow symbiotic interactions and colonization whose molecular mechanisms, so far little known, are probably related, among others, to the bacteria surface (molecules exposed and secreted…). Lactobacillus casei, a commensal bacterium, has about 330 predicted genes involved in the composition and functionality of the cell surface. To have a global view of the whole genes involved in the establishment of L. casei in the gut, a reverse genetics approach was performed. For that, a library of L. casei random labeled-mutants by Signature-Tagged Mutagenesis was generated then annotated and reassembled thanks to the sequencing of transposon insertion sites. Mutants were screened for their ability to establish themselves in the rabbit ligated ileal loop and quantified by qPCR. Among the 47 genes identified as involved in the in vivo establishment, three genes in an operon encoding a two-component system and a penicillin-binding protein were characterized. These three genes are involved in the cell surface modulation and particularly in the regulation of peptidoglycan hydrolases which are required for the bacteria protection in the intestinal environment.

Nesta dissertação nós revisamos a teoria básica que descreve a junção Josephson bosônica para uma e duas espécies partindo do modelo de Bose-Hubbard. Em seguida explicamos como é possível gerar campos de calibe artificiais em um sistema de átomos neutros, como é o caso do condensado de Bose-Einstein. Finalmente, utilizando os conhecimentos teóricos desenvolvidos anteriormente nós buscamos os estados estacionários de um sistema de pseudospin 1/2 submetido a um campo de calibre não-Abeliano artificial, que torna a dinâmica da junção muito mais complexa e rica. Nós também exploramos um novo desbalanceamento de população que surge no sistema, devido a presença do campo de calibre, com características similares as do Macroscopic Quantum Self-Trapping. / In this dissertation we review the basic theory that describes the bosonic Josephson junction for one and two species using the Bose-Hubbard model. Afterwards, we explain how it is possible to generate artificial gauge fields for neutral atoms, like a Bose-Einstein condensate. Finally, using this theoretical background we search for stationary states of a pseudospin 1/2 system subject to a non-Abelian artificial gauge field which turns the dynamic of the junction much more complex and rich. We also explore a possible new populational imbalance that appears on the system due to the presence of the gauge field, with similar features as the Macroscopic Quantum Self-Trapping.

Many agricultural fields that have received long-term applications of P often contain levels of P exceeding those required for optimal crop production. Knowledge of the effect of the P remaining in the soil (residual effect) is of great importance for fertilization management. In order to characterize P forms in soils, a wide variety of methods have been proposed. The use of dialysis membrane tubes filled with hydrous ferric oxide (DMT-HFO) has recently been reported as an effective way to characterize P desorption over a long-term in laboratoty studies. However, there is little information on the relationship between kinetics of P release using this new method and plant P uptake. This method consist of a procedure of shaking a sample for a long period of time there by exploiting the whole volume of the soil which is in contrast to the actual plant mode of uptake. This method has also practical limitations in employing it for a routine soil analysis, as it is very expensive and time consuming. The objectives of this study were (i) to study the changes in labile, non-labile and residual P using successive P desorption by DMT-HFO followed by a subsequent fractionation method (combined method) (ii) to assess how the information gained from P desorption kinetic data relates to plant growth at green house and field trials (iii) to investigate the effect of varying shaking time on DMT-HFO extractable P and (iv) to propose a short cut approach to the combined method. The release kinetics of the plots from long term fertilizer trials at the University of Pretoria and Ermelo were studied. P desorption kinetics were described relatively well by a two-component first-order model (R2 = 0.947, 0.918,&0.993 for NPK, MNK,&MNPK treatments respectively). The relative contributions of both the labile pool (SPA) and the less labile pool (SPB) to the total P extracted increased with increased P supply levels. Significant correlations were observed between the rate coefficients and maize grain yield for both soil types. The correlation between the cumulative P extracted and maize yield (r = 0.997**) however was highly significant for Ermelo soils. This method was also used to determine the changes in the different P pools and to relate these P fractions with maize yield. Highly significant correlations were observed between maize grain yield and the different P fractions including total P. In both soil types the contribution of both the labile and non-labile inorganic P fractions in replenishing the solution Pi was significant where as the contributions from the organic fractions were limited. The C/HCl-Pi is the fraction that decreased most in both cases as well. Investigation was carried out to evaluate the effect of varying shaking periods on the extractable DMT-HFO-Pi for UP soils of varying P levels. Four shaking options were applied. Significant difference was observed for the treatment of high P application. Shaking option 2 seemed relatively better than the others since it showed the strongest correlation. Thus for soils with high releasing kinetics and high total P content, provided that the P release from the soil is a rate limiting step, reducing the length of shaking time could shorten the duration one needs to complete the experiment with out influencing the predicting capacity of the methodology. The other objective of this thesis was also to present a short cut method alternative to the combined fractionation method. Comparison of the sum of DMT-HFO-Pi, NaHCO3-Pi, NaOH-Pi, D/HCl-Pi and C/HCl-Pi extracted by a conventional step-by-step method with the sum of DMT-HFO-Pi and a single C/HCl-Pi extraction as a short cut approach for all extraction periods resulted in strong and significant correlations. The C/HCl-Pi fraction extracted by both methods was correlated with maize grain yield and it was found to be highly significant. This study revealed that this short cut approach could be a simplified and economically viable option to study the P dynamics of soils especially for soils where the P pool acting as a source in replenishing the labile portion of P is already identified. The method employed here therefore could act as an analytical tool to approximate successive cropping experiments carried out under green house or field condition. However, data from a wider range of soils is needed to evaluate the universality of this method. More work is also required in relating desorption indices of this method with yield parameters especially at field level. / Thesis (PhD)--University of Pretoria, 2009. / Plant Production and Soil Science / PhD / unrestricted

Parmi les plus grandes menaces de la santé publique dans le monde entier, la résistance aux antibiotiques est à la pointe. Ceci en partie est dû à l'augmentation des infections causées par des bactéries pathogènes résistantes aux antibiotiques ainsi que la diminution du nombre actuel de nouveaux antibiotiques. Dans le souci de remédier à cette situation malheureuse, il y a eu récemment la ré-surfaçage des antibiotiques anciens et abandonnés comme les polymyxines. Colistine, un membre des antibiotiques de polymyxine, est maintenant considéré comme un antibiotique de «dernier recours» pour le traitement des infections bactériennes à Gram-négatives graves en raison de son action puissante contre ces agents pathogènes. Cependant, la résistance à la colistine parmi ces agents pathogènes a émergé dans plusieurs pays et est actuellement en augmentation. En raison de la nouvelle réintroduction relative de cet antibiotique, il ya un manque d'information complètes sur ses propriétés pharmacologiques ainsi que des mécanismes par lequel les bactéries développent une résistance contre celle-ci.Afin de combler ce manque d'information en ce qui concerne le mécanisme de résistance, nous avons donc entrepris ce projet. Tout d'abord, pour procéder à une surveillance épidémiologique des bactéries résistantes à la colistine chez les humains et les animaux domestiques et d'autre part, de décrypter les mécanismes moléculaires de résistance à la colistine parmi les bactéries résistantes isolées. / Among one of the greatest threats facing public health worldwide, antibiotic resistance is at the forefront. This is partly due to increase in infections caused by antibiotic-resistant pathogenic bacterial as well as the current dwindling number of new antibiotics. In a way to address this unfortunate situation, there have been recent resuscitation of old and abandoned antibiotics such as polymyxins. Colistin, a member of polymyxin antibiotics, is now regarded as a 'last-resort' antibiotic for the treatment of severe Gram-negative bacterial infections owing to its potent action against these pathogens. However, resistance to colistin among these pathogens has emerged in several countries and is currently on increase. Due to the relatively new reintroduction of this antibiotic, there is a lack of comprehensive information on its pharmacological properties as well as mechanisms by which bacteria develop resistance against it.In order to bridge this information gap in relation to the mechanism of resistance, we therefore undertook this project. First, to carry out an epidemiological surveillance of colistin-resistant bacteria in humans and domesticated animals and secondly, to decipher the molecular mechanisms mediating colistin resistance among the isolated resistant bacteria.