The way in which the network of intramolecular interactions determines the cooperative folding and conformational dynamics of a protein remains poorly understood. High-pressure NMR spectroscopy is uniquely suited to examine this problem because it combines the site-specific resolution of the NMR experiments with the local character of pressure perturbations. Here we report on the temperature dependence of the site-specific volumetric properties of various forms of staphylococcal nuclease (SNase), including three variants with engineered internal cavities, as measured with high-pressure NMR spectroscopy. The strong temperature dependence of pressure-induced unfolding arises from poorly understood differences in thermal expansion between the folded and unfolded states. A significant inverse correlation was observed between the global thermal expansion of the folded proteins and the number of strong intramolecular hydrogen bonds, as determined by the temperature coefficient of the backbone amide chemical shifts. Comparison of the identity of these strong H-bonds with the co-evolution of pairs of residues in the SNase protein family suggests that the architecture of the interactions detected in the NMR experiments could be linked to a functional aspect of the protein. Moreover, the temperature dependence of the residue-specific volume changes of unfolding yielded residue-specific differences in expansivity and revealed how mutations impact intramolecular interaction patterns. These results show that intramolecular interactions in the folded states of proteins impose constraints against thermal expansion and that, hence, knowledge of site-specific thermal expansivity offers insight into the patterns of strong intramolecular interactions and other local determinants of protein stability, cooperativity, and potentially also of function.

La dynamique de particules colloïdales à l'interface entre deux fluides joue un rôle central dans la micro-rhéologie, l'encapsulation, l'émulsification, la formation de biofilms, la décontamination de l'eau. En outre, ce sujet est également stimulant d'un point de vue théorique en raison de la complexité de l'hydrodynamique à l'interface et du rôle de la ligne de contact. Malgré ce grand intérêt, le comportement d'une particule à une interface fluide n'a jamais été caractérisé directement. Dans cette thèse, nous étudions le mouvement brownien de billes micrométriques de silice et de sphéroïdes de polystyrène à une interface eau-air. Nous contrôlons expérimentalement tous les paramètres d'intérêt. L'angle de contact des billes est finement ajusté dans la gamme 30°-140° par des traitements chimiques de surface et mesuré in situ par interférométrie. Le rapport d'aspect de particules sphéroïdales varie dans la gamme 1 -10 par étirage de billes sphériques commerciales. Les dynamiques de translation et de rotation sont suivies par particle tracking. Contre intuitivement et contre tous les modèles hydrodynamiques la diffusion est beaucoup plus lente que prévu. Pour expliquer cette dissipation supplémentaire nous concevons un modèle tenant compte de la contribution des fluctuations thermiques de l'interface à la ligne de contact. Les fluctuations donnent origine à des forces aléatoires qui s'ajoutent à celles dues aux chocs de molécules. Le théorème de fluctuation-dissipation permet d'obtenir la friction supplémentaire associée à ces forces flottantes. La friction totale est discutée en termes d'hétérogénéités de la surface des particules et d'ondes capillaires à l'interface.

Regular bouncing solutions in the framework of a scalar-tensor gravity model were found in a recent work. We reconsider the problem in the Einstein frame (EF) in the present work. Singularities arising at the limit of physical viability of the model in the Jordan frame (JF) are either of the Big Bang or of the Big Crunch type in the EF. As a result we obtain integrable scalar field cosmological models in general relativity (GR) with inverted double-well potentials unbounded from below which possess solutions regular in the future, tending to a de Sitter space, and starting with a Big Bang. The existence of the two fixed points for the field dynamics at late times found earlier in the JF becomes transparent in the EF.

Cette thèse porte sur l’interaction lumière-matière au sein de nanostructures placées dansdes cavités optiques à base de semi-conducteurs nitrures. A l’aide d’expériences de microphotoluminescencedans l’ultra-violet, nous étudions les propriétés optiques de boîtes quantiquesGaN/AlN dans des microcavités planaires et celles de puits quantiques GaN/AlN insérés dansdes microdisques AlN. Afin d’améliorer la collection du faible signal de photoluminescence deboîtes quantiques uniques, nous utilisons des microcavités planaires pour modifier le diagrammed’émission d’une boîte quantique. Le dessin des microcavités est optimisé grâce à des simulationsnumériques basées sur la méthode des matrices de transfert en présence d’un émetteur.Nous montrons que, pour une microcavité nitrure à base de miroirs de Bragg AlN/AlGaN, lacollection des photons émis par une boîte quantique peut être théoriquement améliorée d’unordre de grandeur, ce qui est confirmé par nos mesures sur boîtes quantiques uniques, ouvrantainsi la voie à des études avancées de corrélations de photons dans l’UV. La seconde partiedes travaux est dédiée à la réalisation d’un micro-laser opérant dans l’UV profond et à températureambiante. En utilisant des puits quantiques GaN/AlN de 2,8 mono-couches, crûs sursubstrat silicium et insérés dans des microdisques AlN, nous observons une émission laser à275 nm sous pompage optique impulsionnel. Cette démonstration montre le fort potentiel dessemi-conducteurs nitrures pour la nano-photonique UV sur silicium.

This invention relates to agricultural adjuvant compositions,pesticide compositions and methods for using such compositions, and in particular to adjuvant compositions useful in providing anti-drift properties.

Two ways have been explored to impart to nanosize self-assembled colloidal particles the ability to assemble further into clusters: the first one relies on coordination chemistry and the second relies on non-uniform charge distribution. Scattering experiments have been analyzed either in terms of effective potential to determine the amplitude and range the short range attractive contribution, or in terms of aggregation number of the resulting clusters. Mixed surfactant micelles have been functionalized by chelating groups, using specifically designed complexing surfactants. Functionnalizing the micelles in such a way first enhances the repulsive interactions, but those are switched to attractive ones in the presence of coordination centers such as aluminum cations. This is revealed by the strong increase of scattering intensity at low q. A square well potential allows accounting for the structure factor of such systems. The range of attractive interaction depends solely on the molecular size of the complexing surfactant, while the concentration of coordination centers and the pH determine the depth of the well, probably through the condensation state of the polycations. Increassing attraction leads to clusters with aggregation numbers up to 12, before reaching the stability limit of the system.Patchy charged nano-sized particles have been designed by doping initially neutral micro-emulsion droplets by gemini type cationic surfactants. Three-charge and four-charge surfactants with either linear or branched polar backbone have been used as dopants. Bromide specific potentiometry reveals higher counter-ions condensation on patchy charged colloids. The structure factors of these patchy charged micro-emulsions suggest that peculiar distributions of charges induce short range attraction inducing clustering with aggregation number up to 6 with monovalent couter-ions but that could be increase using divalent ones.Both approaches show that supracolloidal colloidal clusters are certainly accessible through assembling strategies at equilibrium, but it certainly requires fine control on the antagonistic interactions involved.

Active colloids are an emerging and promising class of colloidal particles, which are designed to perform autonomous motion as biological microswimmers by transforming chemical or other form of energies into work and propulsion. When the particle size is about a micrometer or smaller, the directional propulsion competes with the translational and rotational Brownian motion. Here we explore the possibility of enhancing the directional motion of self-propelled Janus colloids by slowing down their rotational diffusion.We have investigated the active motion of self-propelled colloids confined at the air-water interface. The two dimensional motion of micron-sized Silica-Platinum Janus colloids has been experimentally measured by particle tracking video-microscopy under increasing concentration of the catalytic fuel, i.e. H2O2. Comparing to the motion in bulk, a dramatic enhancement of both the persistence length of trajectories and the speed has been observed. The interplay of colloid self-propulsion, due to an asymmetric catalytic reaction occurring on the colloid, and interfacial frictions controls the enhancement of the directional movement. The slowing down of the rotational diffusion at the interface, also measured experimentally, plays a pivotal role in the control and enhancement of active motion.