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Tran, Ich tach. "Vérification de la validité du concept de surface somme par une approche statistique du contact élastique entre deux surfaces rugueuses." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2015. http://www.theses.fr/2015ECAP0010/document.
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Les propriétés de surface, particulièrement microgéométriques, jouent un rôle essentiel dans tous les systèmes tribologiques. L’analyse de la répartition des efforts de contact dans l’interface entre surfaces rugueuses est indispensable à la prédiction du frottement, de l'usure, de l'adhérence, des résistances de contact électrique et thermique… De nombreux modèles ont été proposés ces dernières décennies pour prédire les efforts entre aspérités de surfaces rugueuses. Parmi ces modèles, les modèles statistiques sont majoritairement développés en considérant le contact ente une surface rugueuse équivalente, la surface somme - qui tient compte des microgéométries des deux surfaces en contact ainsi que de leur matériau - et un plan lisse. Cependant la validité de cette modélisation n’a pas été clairement démontrée. L’objectif de notre étude a été de développer un modèle statistique de contact entre deux surfaces rugueuses isotropes aléatoires puis de comparer les résultats obtenus pour ces deux surfaces avec ceux obtenus en considérant la surface somme définie classiquement à partir des deux surfaces rugueuses et un plan lisse. Les différences entre les résultats nous ont amenés à proposer une nouvelle modélisation de la surface sommeSurface properties, particularly micro-geometry, play a key role in all tribological systems. The analysis of the distribution of contact forces in the interface between rough surfaces is essential for the prediction of friction, wear, adhesion, electrical and thermal contact resistance... Many models have been proposed during the last decades to predict the forces between asperities of rough surfaces. Among these models, statistical models are mainly based on the contact between an equivalent rough surface, the sum surface - which combines micro-geometry of the two surfaces in contact and their material - and a smooth plane. However, the validity of this model has not been clearly demonstrated. The aim of our study was to develop a statistical model of the contact between two random isotropic rough surfaces and then compare the results with those obtained by considering the classical sum surface. The differences between the results have led us to propose a new definition for the sum surface
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Gascoin, Simon. "Etude des paramétrisations hydrologiques d'un modèle de surface continentale : importance des aquifères et des premiers centimètres du sol." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00399672.
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Les modèles de surface continentale (Land Surface Models, LSM) ont été développés pour calculer les bilans d'eau et d'énergie à la surface des continents dans les modèles de climat, ou modèles de circulation générale. Depuis le simple « bucket » de Manabe (1969), la représentation des processus hydrologiques dans les LSM n'a cessé d'évoluer, si bien que les LSM de dernière génération sont employés comme des modèles hydrologiques à part entière. Le travail effectué au cours de cette thèse vise à évaluer les paramétrisations hydrologiques d'un LSM de ce type, le Catchment LSM (CLSM), qui utilise l'information topographique pour calculer le ruissellement de surface et le flux souterrain, ainsi que la variabilité sous-maille de l'humidité du sol. Pour cela, nous présentons trois applications de CLSM :– une application au bassin de la Somme (France) qui a permis d'améliorer la prise en compte des écoulements souterrains,
– une application à la moraine du Glacier Zongo (Bolivie) pour analyser la relation entre l'albedo et l'humidité du sol nu,
– une application dans le cadre du projet ALMIP (Afrique de l'Ouest) pour l'intercomparaison régionale de LSM.
La diversité de ces contextes jette un éclairage varié sur les forces et les faiblesses de CLSM, et offre la possibilité de mieux appréhender les interactions complexes qui gouvernent les échanges d'eau et d'énergie à la surface des continents. On montre l'importance de considérer l'intégralité du domaine souterrain, depuis les premiers centimètres du sol jusqu'aux aquifères.
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Dalstein, Laetitia. "Etude par spectroscopie optique non linéaire du couplage entre plasmon de surface de nanoparticules métalliques et excitation vibrationnelle de molécules adsorbées à leur surface." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS222/document.
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Les propriétés optiques des nanoparticules métalliques, caractérisées par l'existence d'une résonance plasmon de surface (SPR) dans le domaine visible, sont aujourd'hui couramment utilisées afin de détecter et de caractériser des espèces chimiques, en solution ou déposées sur des substrats (dans les capteurs par exemple). Dans ce travail, j'ai optimisé la réalisation puis la caractérisation physico-chimique et optique d'interfaces composées de nanoparticules d'or d'environ 15 nm de diamètre sur des substrats de silicium et de verre fonctionnalisés par des silanes, à l'aide de méthodes d'optique linéaire et non linéaire. La spectroscopie UV-visible en réflexion et transmission, couplée aux microscopies électronique et à force atomique, et aidée par la modélisation, m'a permis de corréler les propriétés optiques des particules à leur densité locale sur la surface. La spectroscopie optique non linéaire par génération de fréquence somme (SFG) permet de sonder la chimie de surface des particules et du substrat ainsi que de tirer parti de l'amplification locale des processus optiques par excitation de la SPR. Après avoir montré qu'elle amplifie effectivement des signaux SFG moléculaires peu intenses de la couche de silanes, j'ai révélé la présence dans la couche organique de greffage de groupements méthyles résultant d'une réaction de silanisation incomplète, démontré le lien entre la stabilité temporelle chimique et plasmonique des interfaces et l'irradiation laser, caractérisé finement la qualité de fonctionnalisation des particules par des thiols et montré la relation de proportionnalité entre réponses optiques linéaire et non linéaire en surface. Finalement, j'ai étudié directement le processus d'amplification de la SFG par le couplage à la SPR en réalisant une spectroscopie à deux dimensions infrarouge et visible. J'ai montré que ce couplage est mesurable même sur de petites particules déposées, et qu'il se produit dans la zone spectrale d'existence du plasmon de surface (du vert au rouge). La comparaison avec une surface plane de platine et d'or m'a permis d'extraire de façon fine des facteurs d'amplification, qui correspondent à ce que prédit une modélisation simple de la plasmonique en jeu dans ces interfacesOptical properties of metallic nanoparticles, exhibiting a surface plasmon resonance (SPR) in the visible range, are nowadays extensively used to detect and characterize chemical entities, either in solution or deposited on substrates (e.g. sensors). In this work, I have optimized the creation of interfaces composed of 15nm in diameter gold nanoparticles on silicon and glass substrates after functionnalization by silanes, and their chemical and optical characterization by linear and nonlinear optical methods. I have used UV-visible spectroscopy in reflexion and transmission geometries, coupled to electronic and atomic force microscopies, with the help of optical simulations, to correlate the optical properties of the particles to their local density at the surface. Nonlinear sum frequency generation spectroscopy is able to probe the surface chemistry of both the particles and the substrate, through a local amplification of optical processes due to the excitation of the SPR. After showing that the latter does indeed amplify the low intensity molecular SFG signals from the silane layer, I have revealed the presence, in the organic layer, of unreacted methyl groups arising from an incomplete silanization, evidenced the link between plasmonic and chemical stability in time and laser irradiation, finely assessed the quality of surface functionnalization of the particles by thiols, and established the linear relationship between linear and nonlinear optical responses at the surface. Finally, I have directly studied the amplification process itself by coupling to the SPR through two dimension spectroscopic studies in the visible and infrared ranges. I have shown that the coupling is indeed measurable, even on small deposited particles, and that it happens in the spectral zone where the surface plasmon exists (from green to red). A comparison to flat platinum and gold surfaces leads to a fine estimation of amplification factors, which correspond to the predictions of a simple model for the plasmonic processes at stake at such interfaces
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Chauvet, Nicolas. "De la génération de somme de fréquence à la fluorescence paramétrique dans des nanostructures plasmoniques hybrides." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY011/document.
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L'optique non-linéaire étudie des phénomènes capables de modifier la fréquence de la lumière incidente en s'appuyant sur la symétrie intrinsèque de certains matériaux. Le défi actuel de la miniaturisation des composants va de paire avec une perte d'efficacité à l'échelle sub-micrométrique. Pour résoudre ce problème, l'idée explorée au cours de cette thèse consiste à utiliser un phénomène d'oscillation collective des électrons libres d'une nanostructure en métal, appelé résonance plasmon de surface localisé. Cet effet est associé à une exaltation du champ au voisinage immédiat d'une structure plasmonique, une propriété adaptée pour augmenter l'efficacité non-linéaire d'un matériau placé non loin. Les objectifs principaux de ma thèse consistaient à fabriquer ces objets hybrides, à développer une plate-forme expérimentale polyvalente capable de réaliser différents types d'observation à l'échelle de la particule unique, puis à analyser leur génération de second harmonique (SHG). Ces travaux ont abouti à l'obtention de structures hybrides non-linéaires efficaces, dont l'intensité SHG atteint jusqu'à 100 fois celle d'une antenne plasmonique isolée et jusqu'à plus de 1000 fois celle d'un nanocristal non-linéaire unique, confirmant l'intérêt de ces structures. Nous avons aussi tenté d'observer de la fluorescence paramétrique (SPDC) dans une nanostructure individuelle, une prouesse encore inachevée dans le monde; si nos études n'ont pas davantage abouti, elles esquissent des pistes d'amélioration pour y parvenir, et un modèle numérique innovant développé dans l'équipe annonce un rendement compatible avec des observations. Enfin, une source de photons intriqués a été développée dans le cadre d'une collaboration sur l'intelligence artificielle dans des systèmes physiques et constitue une perspective envisageable d'application pour les travaux précédents. Ces résultats ouvrent potentiellement la voie à l'amélioration de l'éfficacité et de la fiabilité des algorithmes IA actuelsNonlinear optics study phenomena able to modify the frequency of incoming light by using intrinsic symmetry properties of some materials. The current challenge of component miniaturization goes with an efficiency drop at the sub-micrometer scale. To solve this issue, the idea we have explored during my PhD consists in using a collective oscillation phenomenon from free electrons in a metal structure called localized surface plasmon resonance. This effect is indeed linked to an enhancement of the electromagnetic field near a plasmonic structure, a property well suited to increase the nonlinear efficiency of a material placed beside. The main objectives of my PhD consisted in fabricating these hybrid objects, developing a versatile experimental platform able to make different kinds of observations at the single particle level, and finally analyzing their second harmonic generation (SHG). This work has managed to produce efficient nonlinear hybrid structures, whose SHG intensity is up to 100 times that of an isolated plasmonic antenna and up to 1000 times that of a single nonlinear nanocrystal, confirming the potential of this type of structures. We have also tried to detect spontaneous parametric down conversion (SPDC) in a single nanostructure, a never-achieved feat that has yet to be done; although our study wasn't successful, it gives hints to improve experiments, even more since a cutting edge numerical model developed in our team has predicted intensities compatible with observations. Finally, an entangled photon source has been developed in the framework of a collaboration on artificial intelligence in physical systems and is a reachable perspective for potential applications of our work. These results pave the way to improving efficiency and liability of current AI algorithms
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Fernandes, Gomes Janaina. "Etude de l'adsorption et électro-oxydation de l'éthanol sur électrodes de platine par spectroscopie de génération de la fréquence somme." Paris 11, 2007. http://www.theses.fr/2007PA112222.
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L'application de l’éthanol comme combustible pour les piles à combustible directes d’alcool continue à motiver la recherche sur les mécanismes de l’électro-oxydation de l’éthanol. Dans ce travail, l’interface éthanol-platine en milieu acide est étudiée par la spectroscopie SFG infrarouge–visible afin de documenter les intermédiaires de l’électro-oxydation de l’éthanol. De nouvelles évidences sur les intermédiaires adsorbés de l’oxydation de l’éthanol sur le platine, jamais observés auparavant avec la spectroscopie infrarouge, sont rapportées. Nos résultats montrent qu’un dérivé de l’éthanol secondaire, précédemment suggéré, mais jamais documenté précédemment, et des espèces acétate mono et bidentée, eta2-acetaldehyde, acétyle et un dérivé d’acide acétique moléculaire sont les intermédiaires actifs de l’oxydation de l’éthanol en milieu acide. De plus, nous rapportons de nouvelles évidences pour la présence d’un intermédiaire d’ethoxy. Les résultats obtenus confirment également la présence des intermédiaires précédemment observées de l’oxydation de l’éthanol: CO adsorbé et un dérivé d’éthanol tertiaire. D’autre part, nous avons exploité les effets de la structure atomique de l’électrode, de la concentration de l’alcool et du potentiel de l’électrode sur le mécanisme de l’adsorption et de l’électro-oxydation de l’éthanol sur le platine. Ces effets sont analysés par les spectres vibrationnels des intermédiaires adsorbés. La comparaison avec l’adsorption d’autres réactifs simples (méthanol, acétaldéhyde, acide acétique) en milieu acide indique que, même à bas potentiel, la surface de platine est très réactive, produisant des intermédiaires semblables pour tous les réactifsThe possible application of ethanol as a fuel for direct alcohol fuel cells continues to motivate research on the mechanisms of electro-oxidation of ethanol. In this work, the ethanol-platinum interface in acidic medium is investigated using infrared-visible SFG spectroscopy in order to document the intermediates present during the electro-oxidation of ethanol. New evidences of adsorbed intermediates of ethanol oxidation on platinum, never before observed with conventional IR spectroscopy, are reported. Our results show that a secondary ethanol derivative, previously suggested, but never before unambiguously documented, and mono and bidentate acetate, eta2-acetaldehyde, acetyl and a molecular acetic acid derivative are active intermediates of ethanol oxidation in acidic medium. In addition, we report new evidences for the presence of an ethoxy intermediate. The results obtained here also confirm the presence of previously observed ethanol oxidation intermediates: adsorbed CO and a tertiary ethanol derivative. Moreover, we explored the effects of the atomic surface structure of the electrode, alcohol concentration and electrode potential on the mechanism of the adsorption and electro-oxidation of ethanol on platinum. These effects are analyzed through the vibrational spectra of interfacial adsorbed intermediates. Comparison with the adsorption of other simple reactants (methanol, acetaldehyde and acetic acid) in acid medium indicate that even at low potential the platinum surface is highly reactive, producing similar intermediates for all reactants
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Jouve, Florent. "Sommes exponentielles, crible, et variétés sur les corps finis." Bordeaux 1, 2007. http://www.theses.fr/2007BOR13531.
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Dans la première partie de cette thèse, on s'attache à donner une interprétation géométrique pour certaines sommes de caractères sur un corps fini. On donne deux exemples dans lesquels on montre que la valeur du moment d'ordre trois de telles sommes est explicitement reliée au nombre de points à coordonnées dans le corps de base d'une surface algébrique définie sur ce corps. Les propriétés géométriques des surfaces obtenues permettent de déduire des formules explicites donnant la valeur des sommes étudiées. La seconde partie traîte d'applications du grand crible dans le cadre proposé récemment par E. Kowalski. La généralité avec laquelle cette méthode est présentée permet l'attaque de problèmes arithmétiques de différentes natures. On s'intéresse notamment à la probabilité avec laquelle une marche aléatoire sur une classe à gauche d'un groupe arithmétique modulo un sous-groupe donné conduit, après un grand nombre de pas, à une matrice vérifiant certaines propriétés typiques. On s'intéresse également au problème plus géométrique de l'irréductibilité en moyenne de la fonction L d'une courbe elliptique sur un corps de fonctions sur un corps fini, lorsque cette courbe varie à l'intérieur d'une certaine famille algébriqueIn the first part of this Thesis, we give a geometric interpretation for a certain type of character sums over finite fields. We work out two examples in which we show that the third moment of such sums is explicitely related to the number of rational points on an algebraic surface over the base field. The geometric properties of the surfaces arising enable us to obtain explicit formulae for the sums studied. The second part deals with applications of large sieve tehniques as recently formulated by E. Kowalski. Thanks to the great generality in which that method is written, we can investigate different kinds of arithmetical problems. As a first application, we are interested in the probability with which a random walk on a left coset of an arithmetic group modulo a fixed subgroup leads, after sufficiently many steps, to a matrix satisfying typical properties. Then we study the more geometric problem of the generic irreducibility of the L function of an elliptic curve over a function field over a finite field when the curve varies among an algebraic family
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Le, Boudec Pierre. "Répartition des points rationnels sur certaines surfaces de del Pezzo." Paris 7, 2012. http://www.theses.fr/2012PA077138.
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Dans cette thèse, nous nous intéressons à des problèmes de comptage de points rationnels sur certaines variétés algébriques. Une conjecture de Manin prévoit avec précision le comportement asymptotique du nombre de points rationnels de hauteur bornée sur les variétés de Fano. Notre but principal est de prouver la conjecture de Manin pour certains exemples de surfaces de del Pezzo définies sur Q. Pour cela, nous avons recours à des torseurs universels pour paramétrer les points rationnels et nous utilisons ensuite divers résultats de théorie analytique des nombres, tels que par exemple l'équidistribution des valeurs de certaines fonctions diviseur dans les progressions arithmétiques. Tout d'abord, nous traitons dans une première partie les cas de trois surfaces de del Pezzo de degré quatre, dont les types de singularité sont respectivement 3A1, A1+A2 et A3. Ensuite, nous traitons dans une seconde partie les cas de deux surfaces cubiques, dont les types de singularité sont respectivement 2A2+A1 et D4. Cette première est seulement le troisième exemple de surface cubique non-torique pour laquelle la conjecture de Manin est prouvée. Notons par ailleurs que le travail concernant cette dernière améliore un résultat de Browning et répond à un problème initialement posé par Tschinkel. Enfin, dans une annexe, comme autre application des résultats d'équidistribution mentionnés ci-dessus, nous établissons une formule asymptotique pour le nombre de valeurs sans puissance k ème du polynôme en r variables t1⋯tr−1In this thesis, we are interested in counting rational points on certain algebraic varieties. A conjecture of Manin predicts precisely the asymptotic behaviour of the number of rational points of bounded height on Fano varieties. Our main goal is to prove Manin's conjecture for some examples of del Pezzo surfaces defined over Q. For this, we resort to universal torsors to parametrize the rational points and then we make use of various analytic number theory results, such as for instance the equidistribution of the values of certain divisor functions in arithmetic progressions. To begin with, we deal in a first part with the cases of three quartic del Pezzo surfaces, whose singularity types are respectively 3A1, A1+A2 and A3. Afterwards, we deal in a second part with the cases of two cubic surfaces, whose singularity types are respectively 2A2+A1 and D4. The former is only the third example of non-toric cubic surface for which Manin's conjecture is proved. Note in addition that the work about the latter improves on a result of Browning and answers a problem initially posed by Tschinkel. Finally, in an appendix, as another application of the equidistribution results mentioned above, we establish an asymptotic formula for the number of power-free values of the r variables polynomial t1⋯tr−1
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Ong, Wen Eng. "Some Basis Function Methods for Surface Approximation." Thesis, University of Canterbury. Mathematics and Statistics, 2012. http://hdl.handle.net/10092/7776.
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This thesis considers issues in surface reconstruction such as identifying approximation methods that work well for certain applications and developing efficient methods to compute and manipulate these approximations.
The first part of the thesis illustrates a new fast evaluation scheme to efficiently calculate thin-plate splines in two dimensions. In the fast multipole method scheme, exponential expansions/approximations are used as an intermediate step in converting far field series to local polynomial approximations. The contributions here are extending the scheme to the thin-plate spline and a new error analysis. The error analysis covers the practically important case where truncated series are used throughout, and through off line computation of error constants gives sharp error bounds.
In the second part of this thesis, we investigates fitting a surface to an object using blobby models as a coarse level approximation. The aim is to achieve a given quality of approximation with relatively few parameters. This process involves an optimization procedure where a number of blobs (ellipses or ellipsoids) are separately fitted to a cloud of points. Then the optimized blobs are combined to yield an implicit surface approximating the cloud of points. The results for our test cases in 2 and 3 dimensions are very encouraging. For many applications, the coarse level blobby model itself will be sufficient. For example adding texture on top of the blobby surface can give a surprisingly realistic image.
The last part of the thesis describes a method to reconstruct surfaces with known discontinuities. We fit a surface to the data points by performing a scattered data interpolation using compactly supported RBFs with respect to a geodesic distance. Techniques from computational geometry such as the visibility graph are used to compute the shortest Euclidean distance between two points, avoiding any obstacles. Results have shown that discontinuities on the surface were clearly reconstructed, and the
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Hopkins, Ian. "Surface composition profiles in some polymer mixtures." Thesis, Durham University, 1994. http://etheses.dur.ac.uk/5518/.
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The surface composition of selected polymer mixtures has been studied to a depth of circa 4000Å with a resolution of up to l0Å using neutron reflectometry (NR) and nuclear reaction analysis (NRA). The effective interaction parameters, X, of several blends have been measured as a function of both composition and temperature, using Small Angle Neutron Scattering (SANS) and the incompressible random phase approximation, in order to understand the surface segregation behaviour of the polymer blends. No surface segregation was observed in annealed blends of syndiotactic poly (methyl methacrylate) (h-PMMA) with perdeuterated poly (methyl methylacrylate) (d-PMMA), where the h-PMMA was the majority component with a high molecular weight and the d-PMMA had lower molecular weights. Values of X for these blends showed a chain length disparity effect, higher disparity led to a small negative X. Increases in X were observed at low volume fractions of d-PMMA. Surface segregation of perdeuterated poly (ethylene oxide) (d-PEO) to the polymer - silicon oxide interface of an annealed d-PEO/h-PMMA blend was observed, where the bulk volume fraction of the d-PEO was <0.30. The surface composition profile could not be described by current theory. Measured X values were small and negative and there was a change in X on changing the locus of deuteration from PEO to PMMA in a PEO/PMMA blend. These blends exhibited a decrease in X at low volume fractions of PEO. Polymer brushes were found at the air - polymer interface of a blend of low molecular weight polystyrene (h- PS) with perdeuterated polystyrene with a single perfluorohexane end group (d-PS(F)) or two perfluorohexane end groups (d-PS(F2)). These results were in good agreement with a self consistent field theory. Similar blends of high molecular h-PS / d-PS(F) showed enhanced surface segregation, compared to blends with no perfluorohexane end groups. NR data showed that the surface of a blend of polystyrene with perdeuterated dibutyl phthalate (d-DBP) (a model additive) was enriched with d-DBP over a 30Ålength scale. The loss of d-DBP from a thin film (~ 8OO Å thick) was observed using NR and attenuated total reflection (ATR) infra red spectroscopy.
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Bleloch, Andrew Luke. "Some aspects of surface imaging in STEM." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238161.
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Arnould, Maëlis. "Some surface expressions of mantle convective instabilities." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN036/document.
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Constituant la couche limite supérieure de la convection mantellique, la lithosphère terrestre est à l'interface entre les enveloppes externes et internes de notre Planète. Les interactions multiples entre celle-ci et le manteau sont à l'origine de déformations latérales (tectonique des plaques) et verticales (topographie dynamique) de la surface terrestre. Comprendre comment la formation et l'évolution d'instabilités convectives mantelliques renouvellent sans-cesse la surface est donc primordial pour améliorer nos interprétations d'un grand nombre d'observations de surface, telles que la formation de bassins sédimentaires, le mouvement des continents, la localisation des points chauds, la formation d'anomalies gravimétriques ou encore les variations du niveau marin.Cette thèse propose de développer des modèles numériques de convection mantellique générant defaçon auto-organisée de la tectonique des plaques en surface an d'étudier la façon dont le développement et la dynamique d'instabilités convectives telles que les panneaux de subduction ou les panaches mantelliques modifient la surface, dans un contexte de tectonique de surface approchant le régime terrestre.Dans une première partie, je m'intéresse à l'influence du couplage des mouvements de convection mantellique et de tectonique des plaques sur le développement de topographie dynamique (i.e. les mouvements verticaux de la lithosphère induits par la convection mantellique) à différentes échelles spatio-temporelles. Mes résultats suggèrent que la surface terrestre peut se déformer à toutes les échelles spatiales, du fait de mouvements convectifs de grande ampleur faisant intervenir le manteau entier (> 104 km) ou encore de convection à petite échelle sub-lithosphérique (< 500 km). Les variations temporelles de topographie dynamique s‘étendent de cinq à plusieurs centaines de millions d'années selon la nature des processus convectifs dont elles dérivent. En particulier, la dynamique d'initiation ou d'arrêt des zones de subduction contrôle l'existence d'échelles intermédiaires de topographie dynamique (longueurs d'onde variant entre 500 et 104 km). Ces résultats montrent donc que les interactions entre la dynamique de la lithosphère et la convection mantellique génèrent des motifs spatio-temporels de topographie dynamique complexes et cohérents par rapport aux observations terrestres.Dans un deuxième temps, cette thèse se focalise sur la dynamique des panaches mantelliques, et leurs interactions avec la surface. Je caractérise d'abord précisement le comportement des panaches générés dans nos modèles de convection à la lumière d'observations de surface. Puis, j'étudie la façon dont leurs interactions avec la tectonique de surface et les différentes échelles convectives modifient leurs mouvements latéraux. Enfin, la compréhension de la signature thermique des interactions entre panaches et rides océaniques me permet de proposer une reconstitution des mouvements relatifs entre le panache des Açores et la ride médio-AtlantiqueEarth's lithosphere, which is the upper boundary layer of mantle convection, represents the interface between the external and internal envelopes of our Planet. The multiple interactions between the mantle and lithosphere generate lateral (plate tectonics) and vertical (dynamic topography) deformations of Earth's surface. Understanding the influence of the dynamics of mantle convective instabilities on the surface is fundamental to improve our interpretations of a large range of surface observations, such as the formation of sedimentary basins, continental motions, the location of hotspots, the presence of gravity anomalies or sea-level variations.This thesis aims at developing numerical models of whole-mantle convection self-generating plate-like tectonics in order to study the impacts of the development and the dynamics of mantle convective instabilities (such as slabs or mantle plumes) on the continuous reshaping of the surface.First, I focus on the influence of the coupling between mantle convective motions and plate tectonics on the development of dynamic topography (i.e. surface vertical deformations induced by mantle convection) at different spatial and temporal scales. The results suggest that Earth's surface can deform over large spatial scales (> 104 km) induced by whole-mantle convection to small-scales (< 500 km) arising from small-scale sub-lithospheric convection. The temporal variations of dynamic topography range between five and several hundreds of millions of years depending on the convective instabilities from which they originate. In particular, subduction initiation and slab break-off events control the existence of intermediate scales of dynamic topography (between 500 and 104 km). This reflects that the interplay between mantle convection and lithosphere dynamics generates complex spatial and temporal patterns of dynamic topography consistent with constraints for Earth.A second aim of this thesis is to understand the dynamics of mantle plumes and their interactionswith surface. I first characterize in detail the behaviour of mantle plumes arising in models ofwhole-mantle convection self-generating plate-like tectonics, in light of surface observations. Then, I study how the interactions between surface plate tectonics and mantle convection affect plume motions. Finally, I use observations of the thermal signature of plume/ridge interactions to propose a reconstruction of the relative motions between the Azores mantle plume and the Mid-Atlantic Ridge
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Lamour, Guillaume. "Influence de la nanostructuration énergétique des substrats dans l'adhésion et la différenciation des cellules neuronales modèles PC12." Phd thesis, Université Paris-Diderot - Paris VII, 2010. http://tel.archives-ouvertes.fr/tel-00523656.
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Les paramètres de surface contrôlent les fonctions des cellules, en coopération avec leurs codes génétiques. Des études récentes soulignent l'impact combiné des signaux chimiques, topographiques et mécaniques des substrats d'adhésion sur les processus de différenciation. Cette étude se focalise sur le paramètre énergétique, et plus spécialement, sur l'influence exercée par la distribution spatiale des énergies de surface sur la différenciation des cellules neuronales. Le modèle étudié est constitué par les cellules de la lignée PC12, capables de se différencier en neurones suite au traitement par le facteur de croissance nerveux (NGF). Les cellules sont cultivées sur des surfaces de verre modifiées par auto-assemblage de monocouches d'alkylsiloxanes ou de biopolymères. La modification de la nature chimique et du degré d'organisation des monocouches module la distribution des composantes dispersives et polaires de l'énergie de surface, à une échelle inférieure au micron. Sur des substrats très homogènes (dotés de terminaisons CH3, NH2, ou OH), l'adhésion des cellules PC12 est modulée par le degré d'affinité chimique, et peu de cellules initient des neurites. Inversement, sur des substrats localement très hétérogènes, les cellules adhèrent quel que soit le couple chimique produisant les hétérogénéités (NH2/OH ou CH3/OH), et elles génèrent un nombre important de neurites en moins de 48 h, sans traitement au NGF. Ce travail démontre que les hétérogénéités chimiques de surface exercent une influence critique sur les processus de régénérescence des cellules nerveuses, en induisant des gradients dans les énergies d'adhésion aux échelles nanométriques.
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Gao, Guangyue. "Some Controllability and Stabilization Problems of Surface Waves on Water with Surface tension." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64377.
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The thesis consists of two parts. The first part discusses the initial value problem of a fifth-order Korteweg-de Vries type of equation
wt + wxxx - wxxxxx - n∑j=1 ajwjwx = 0, w(x, 0) = w0(x)
posed on a periodic domain x ∈ [0, 2π] with boundary conditions wix(0, t) = wix(2π, t), i = 0, 2, 3, 4 and an L2-stabilizing feedback control law wx(2π, t) = αwx(0, t) + (1 - α)wxxx(0; t) where n is a fixed positive integer, aj, j = 1, 2, ... n, α are real constants, and |α| < 1. It is shown that for w0(x) ∈ H1α(0, 2π) with the boundary conditions described above, the problem is locally well-posed for w ∈ C([0, T]; H1α(0, 2π)) with a conserved volume of w, [w] = ∫2π0 w(x, t)dx. Moreover, the solution with small initial condition exists globally and approaches to [w0(x)]/(2π) as t → + ∞. The second part concerns wave motions on water in a rectangular basin with a wave generator mounted on a side wall. The linear governing equations are used and it is assumed that the surface tension on the free surface is not zero. Two types of generators are considered, flexible and rigid. For the flexible case, it is shown that the system is exactly controllable. For the rigid case, the system is not exactly controllable in a finite-time interval. However, it is approximately controllable. The stability problem of the system with the rigid generator controlled by a static feedback is also studied and it is proved that the system is strongly stable for this case.Ph. D.
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Thornton, John M. C. "Some aspects of silicon surface modification and oxide removal." Thesis, Cardiff University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314790.
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Tam, Ming Sin. "Some surface deformation algorithms with applications in footwear design /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?IEEM%202003%20TAM.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 93-95). Also available in electronic version. Access restricted to campus users.
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McCaffrey, David Charles. "Differential operators on some surfaces with singularities." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303424.
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Finski, Siarhei. "On some problems of holomorphic analytic torsion." Thesis, Sorbonne Paris Cité, 2019. https://theses.md.univ-paris-diderot.fr/FINSKI_Siarhei_va.pdf.
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Le but de cette thèse est d'étudier la torsion analytique dans deux contextes différents. Dans le premier contexte, on étudie l'asymptotique de la torsion analytique, quand un fibré vectoriel holomorphe hermitien est tordué par une puissance croissant du fibré en droites positif. Dans le deuxième contexte, on généralise la théorie de la torsion analytique pour des surfaces de Riemann avec des pointes hyperboliques. Motivé par des singularités de la métrique complète de courbure scalaire constante -1 sur des surfaces de Riemann stables épointées, on demande que la métrique sur la surface de Riemann soit lisse seulement en dehors d'un nombre fini des points au voisinage auxquelles elle peut avoir des singularités comme la métrique de Poincaré sur un disque épointé. On fixe un fibré vectoriel holomorphe hermitien qui peut avoir au pire des singularités logarithmiques au voisinage des points marqués. Pour ces données, en renormalisant la trace de l'opérateur de la chaleur, on construit la torsion analytique et on étudie ces propriétésIn the first context, we study the asymptotics of the analytic torsion, when a Hermitian holomorphic vector bundle is twisted by an increasing power of a positive line bundle. In the second context, we generalize the theory of analytic torsion for surfaces with hyperbolic cusps. Motivated by singularities appearing in complete metrics of constant scalar curvature -1 on stable Riemann surfaces, we suppose that the metric on the surface is smooth outside a finite number points in the neighborhood of which it can to have singularities like Poincaré metric has on a punctured disc. We fix a Hermitian holomorphic vector bundle which has at worst logarithmic singularities in the neighborhood of the marked points. For these data, by renormalizing the trace of the heat operator, we construct the analytic torsion and study its properties. Then we study the properties of the analytic torsion in family setting: we prove the curvature theorem, we study the behavior of the analytic torsion when the cusps are created by degeneration and we give some applications to the moduli spaces of pointed curves
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Seymour, D. L. "A secondary electron emission investigation of the initial stages of oxidation of some metal surfaces." Thesis, Keele University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328716.
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Dubois, Isabelle E. "Specific surface area of some minerals commonly found in granite." Licentiate thesis, KTH, Industriell ekologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-41259.
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The specific surface area, determined by the BET method, is a parameter often used to scale results of mineral studies of surface reactions in terms of rate and capacity to the field scale. Such extrapolations of results from small-scale laboratory experiments to the field-scale are important within many environmental applications. An example of this is for the prediction of radionuclide retention in the bedrock surrounding a deep repository for radioactive waste, following failure of the engineered barriers, where radionuclides may sorb onto minerals constituting the geological environment. As a first step, the approach used in this work is to study the relationship between specific surface area and the particle size (0.075-8 mm) and to approach the field scale via measurements on large, centimetre-sized pieces, for seven natural minerals commonly found in granite: apatite, biotite, chlorite, K-feldspar, hornblende, labradorite and magnetite. The underlying assumption is that sorption of radionuclides can be related to specific surface area of a particular mineral in a continuation of this project.The results show that the phyllosilicates biotite and chlorite have a specific surface area that is about 10 times larger than the other minerals. Over the range of particle size fractions studied, the specific surface area varies between 0.1 and 1.2 m2g-1 for biotite and chlorite. The other studied minerals have specific surface areas varying between 0.01 m2g-1 for the largest fraction and up to 0.06 - 0.12 m2g-1 for the smallest. Results show linear relationships between the specific surface area and the inverse of the particle size for all studied minerals for small particle sizes, as expected. For some minerals, however, the data seemingly can be divided in two linear trends, where a change in internal surface area, surface roughness and/or particle geometry as the particle size decreases may explain this behaviour. Interestingly, for larger particles, there is a deviation from the linearity observed for small particles. Tentatively, this behaviour is attributed to a disturbed zone, created by the mechanical treatment of the material during particle size reduction, extending throughout small particles, but not altering an undisturbed core of the larger particles. In agreement with this, measurements on large pieces show a surface area 5 to 150 times lower than expected from the linear trends observed for the crushed material, implying an overestimation of the surface area and possibly also of the sorption capacities of the rock material from simple extrapolations of experimental results employing finely crushed material to the field situation.QC 20110929
Äspö Radionuclide sorption
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Bossé, Francis. "Surface properties of some diblock copolymers adsorbed onto solid substrates." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41354.
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Surface and interaction characteristics of poly(styrene-b-4vinylpyridine) (S-4VP) and poly(styrene-b-methacrylic acid) (S-MAA) diblock copolymers were investigated by the method of inverse gas chromatography (IGC). Not surprisingly, the MAA segments were found to be acidic, while the polystyrene (PS) and the 4VP blocks were found to be basic, the 4VP moiety being the stronger base. For the S-4VP diblocks, when adsorbed onto particulates with acidic surfaces, the 4VP block is preferentially oriented to the substrate, leaving an air interphase which is enriched in PS. For the S-MAA diblock, at higher interphase thicknesses, the bulk and surface compositions became similar, and the interphases are non-isotropic with respect to local composition, and molecular conformation. For both diblocks, it was shown that the adsorbed layers form interphases in which the local composition varies with the adsorbed mass and the composition of the copolymer diblock. The effect was more pronounced when the strength of the acid/base interactions at the interface was increased. The experimental finding also permits the calculation of thicknesses for the adsorbed interphases (100-1000 A).Proton nuclear magnetic resonance was used to determine the quantities of S-4VP diblocks in solution. In a selective solvent (toluene), it was found that surface interactions lead to preferential adsorption of the 4VP chain segments onto the particulates. Isotherms show that there is a direct correlation between the normalized equilibrium quantities of adsorbed copolymer diblocks and the length of the 4VP anchor. A linear relationship also was obtained between the equilibrium quantities per unit area of substrate, and the acid/base properties of the particulates. Using a published scaling model, good agreement was found between the experimental and predicted equilibrium quantities of adsorbed material. For these systems, it was demonstrated that the prefactor of the scaling law relation was directly related to the acid/base properties of the substrate, as expressed by the values of the acid/base surface indices obtained by IGC.
Composites based on PS and polychloroethylene were analyzed by dynamic mechanical thermal analysis and differential scanning calorimetry methods. The composites were formulated with four loading levels (2, 5, 20 and 35 wt %) of uncoated and coated (S-4VP modified) particulates. A chain overlap region at the boundary of the particulate was determined. The extent of this region was found to increase in parallel with the PS diblock segments, and with favorable acid/base interactions between the composite constituents.
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Tabbaa, Dima al. "On the classification of some automorphisms of K3 surfaces." Thesis, Poitiers, 2015. http://www.theses.fr/2015POIT2299/document.
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Un automorphisme non-symplectique d'ordre fini n sur une surface X de type K3 est un automorphisme σ ∈ Aut(X) qui satisfait σ*(ω) = λω où λ est une racine primitive n-ième de l'unité et ω est le générateur de H2,0(X). Dans cette thèse on s’intéresse aux automorphismes non-symplectiques d'ordre 8 et 16 sur les surfaces K3. Dans un premier temps, nous classifionsles automorphismes non-symplectiques σ d'ordre 8 quand le lieu fixe de sa quatrième puissance σ⁴ contient une courbe de genre positif, on montre plus précisément que le genre de la courbe fixée par σ est au plus un. Ensuite nous étudions le cas où le lieu fixe de σ contient au moins une courbe et toutes les courbes fixées par sa quatrième puissance σ⁴ sont rationnelles. Enfin nous étudions le cas où σ et son carré σ² agissent trivialement sur le groupe de Néron-Severi. Nous classifions toutes les possibilités pour le lieu fixe de σ et de son carré σ² dans ces trois cas. Nous obtenons la classification complète pour les automorphismes non-symplectiques d'ordre 8 sur les surfaces K3. Dans la deuxième partie de la thèse, nous classifions les surfaces K3 avec automorphisme non-symplectique d'ordre 16 en toute généralité. Nous montrons que le lieu fixe contient seulement courbes rationnelles et points isolés et nous classifions complètement les sept configurations possibles. Si le groupe de Néron-Severi a rang 6, alors il y a deux possibilités et si son rang est 14, il y a cinq possibilités. En particulier si l'action de l'automorphisme est trivial sur le groupe de Néron-Severi, alors nous montrons que son rang est six. Enfin, nous construisons des exemples qui correspondent à plusieurs cas dans la classification des automorphismes non-symplectiques d'ordre 8 et nous donnons des exemples pour chaque cas dans la classification des automorphismes non-symplectiques d'ordre 16A non-symplectic automorphism of finite order n on a K3 surface X is an automorphism σ ∈ Aut(X) that satisfies σ*(ω) = λω where λ is a primitive n−root of the unity and ω is a generator of H2,0(X). In this thesis we study the non-symplectic automorphisms of order 8 and 16 on K3 surfaces. First we classify the non-symplectic automorphisms σ of order eight when the fixed locus of its fourth power σ⁴ contains a curve of positive genus, we show more precisely that the genus of the fixed curve by σ is at most one. Then we study the case of the fixed locus of σ that contains at least a curve and all the curves fixed by its fourth power σ⁴ are rational. Finally we study the case when σ and its square σ² act trivially on the Néron-Severi group. We classify all the possibilities for the fixed locus of σ and σ² in these three cases. We obtain a complete classifiction for the non-symplectic automorphisms of order 8 on a K3 surfaces.In the second part of the thesis, we classify K3 surfaces with non-symplectic automorphism of order 16 in full generality. We show that the fixed locus contains only rational curves and isolated points and we completely classify the seven possible configurations. If the Néron-Severi group has rank 6, there are two possibilities and if its rank is 14, there are five possibilities. In particular ifthe action of the automorphism is trivial on the Néron-Severi group, then we show that its rank is six.Finally, we construct several examples corresponding to several cases in the classification of the non-symplectic automorphisms of order 8 and we give an example for each case in the classification of the non-symplectic automorphisms of order 16
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Glans, Per-Anders. "Electronic structure of some SiC and Be surfaces /." Linköping : Univ, 2001. http://www.bibl.liu.se/liupubl/disp/disp2001/tek661s.htm.
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Evans, J. D. "Symplectic topology of some Stein and rational surfaces." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598911.
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A symplectic manifold is a 2n-dimensional smooth manifold endowed with a closed, non-degenerate 2-form. This picks out the set of Lagrangian submanifolds, n-dimensional submanifolds on which the 2-form vanishes, and the group of symplectomorphisms, diffeomorphisms which preserve the symplectic form. In this thesis I study the homotopy type of the (compactly-supported) symplectomorphism group and the connectivity of the space of Lagrangian spheres for an array of symplectic 4-manifolds comprising some Stein surfaces and some Del Prezzo surfaces. In part I of the thesis, concerning Stein surfaces, I calculate the homotopy type of the compactly-supported symplectomorphism group for C* x C with its split symplectic form and T*RP2 with its canonical symplectic form. More significantly, I show that the compactly-supported symplectomorphism group of the 4-dimensional An-Milnor fibre {x2 + y2 + zn+1 = 1} is homotopy equivalent to a discrete group which injects naturally into the braid group on n + 1-strands. In part II of the thesis, concerning Del Pezzo surfaces: I show that the isotopy class of a Lagrangian sphere in the monotone 2-, 3- or 4-point blow-up of CP2 is determined by its homology class; I calculate the homotopy type of the symplectomorphism group for the monotone 3-, 4- and 5-point blow-ups of CP2. The calculations of homotopy groups of symplectomorphism groups rely on nothing more than the standard technology of pseudoholomorphic curves and some involved topological arguments to prove the fibration property of various maps between infinite-dimensional spaces. The new idea is the compactification of the Milnor fibres by a configuration of holomorphic spheres which puts the calculation in a context familiar from the world of Lalonde-Pinsonnault and Abreu. The classification of Lagrangian spheres is based on an argument of Richard Hind.
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Pablo, MartiÌn GarciÌa. "Embedding of some finite geometries into Riemann surfaces." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409755.
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Hughes, Ian John. "The scattering of sound from some practical surfaces." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292984.
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Walker, Christopher John. "X-ray diffraction of some technologically important surfaces." Thesis, University of Leicester, 2001. http://hdl.handle.net/2381/30655.
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Surface X-ray diffraction (SXRD) has been used to study the effect of pressure and temperature on the Ni(110)-(2x1)-2CO reconstruction and the effect of temperature on the InSb(001)-c(8x2) reconstruction. The Ni(110)-(2x1)-2CO reconstruction was observed at a carbon monoxide pressure of 2.3 bar and has a structure unchanged from that at 1 x 10 -5 mbar. This structure was found to consist of CO molecules near short bridge sites in agreement with other recent studies in high vacuum conditions. Heating at 1 x 10-5 mbar causes a lifting of the (2x1) reconstruction due to desorption of the CO. In contrast, heating in 2.3 bar of CO leads to a massive rearrangement of the surface and the formation of {111} microfacets. The base of the microfacets is ≈100 A across and their surfaces are disrupted from the bulk terminated (111) surface. This is consistent with an enlargement of the lattice due to the dissolution of carbon in the facets. SXRD and LEED experiments on the c(8x2) reconstruction of InSb (001) show no structural changes on cooling from room temperature to 74K. Key features of the reconstruction are determined which are at variance with the recent model of Jones et al.
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王筠 and Yun Wang. "Some quantum effects in confined low-dimensional systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31214708.
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Wang, Yun. "Some quantum effects in confined low-dimensional systems /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18598444.
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Liu, Dan, and 刘丹. "Some surface treatments for improving the durability of zirconia-based restorations." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206648.
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Zirconia has now been increasingly used in modern dental prosthetic practice due to its high mechanical strength, good esthetics, and excellent biocompatibility. However, the application of zirconia-based dental restorations is still constrained by its chemical inertness and the resultant relatively weak bonding properties, including porcelain to zirconia bonding, and resin to zirconia bonding. Therefore, many investigations have been carried out on the development of an effective method of surface modification on zirconia for improving its bonding ability. The aim of this laboratory study was to evaluate the effects of some new modified surface treatments on the adhesion durability of dental zirconia prosthetic system.
In Part I and Part II, the application of laser surface treatment was examined. Laser energy was utilized and applied on zirconia surface before porcelain veneering procedure. Its influence on porcelain zirconia integration interface was mechanically tested and compared with sandblasting treatment. The changes in porcelain zirconia shear bond strength and mechanical strength values of zirconia with the modulation of output energy were recorded. In Part III and Part IV, several types of coating treatment, such as tribochemical approach, silica powder coating, and zirconium silicate coating, were compared with their effects on resin zirconia bonding. The changes in resin zirconia shear bond strength under different aging conditions were observed. The elemental analysis was also performed for clarifying the chemical composition of zirconia surface.
The application of laser produced a flake-like micro-retentive structure on zirconia surface. Laser irradiation with the output energy higher than 11.3 W/cm2 was effective in increasing porcelain to zirconia bond strength values. The biaxial flexural strength of zirconia was not significantly affected by laser irradiation with the settings in this study. However, most of the laser treatments still demonstrated slightly lower flexural strength values compared with the control group. No changes in crystalline structure were detected after laser treatment with X-ray Diffraction (XRD) technique. Resin to zirconia shear bond strength was significantly increased after surface coatings. Without surface treatment the bonding between resin and zirconia was susceptible to artificial aging effects. Zirconia and silica-coating groups demonstrated the highest resistance to hydrolytic influence. On the other hand, the chemical changes of zirconia surface were still in need of clarification.
It was concluded that porcelain zirconia bonding could be effectively enhanced by applying both sandblasting and a new laser irradiation approach. Laser irradiation might be a potential approach as a surface treatment for improving the quality of porcelain zirconia bonding interface. The strong and reliable resin zirconia integration could not be achieved without appropriate surface pre-treatment. This coating treatment is a promising approach for strengthening resin to zirconia adhesion.published_or_final_version
Dentistry
Doctoral
Doctor of Philosophy
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Psychogyiopoulou, Krystallia. "Synthesis, surface spectroscopy and single molecule conductance measurements of some metalloporphyrins." Thesis, University of Liverpool, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422991.
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Gould, Larissa Anne. "Some factors influencing the effects of surface active agents on membranes." Thesis, King's College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338742.
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Johnson, Andrew David. "Epitaxial growth and surface morphology of some metal and semiconductor structures." Thesis, University of Leicester, 1989. http://hdl.handle.net/2381/35922.
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Forward focussing of medium energy Auger and photoelectrons have been used along with LEED and Auger electron spectroscopy to investigate the initial stages of growth of both Cr and Co on Ag(001). Cr was found to grow epitaxially on Ag in the bcc phase up to ~2ML, in agreement with previous results. Co also grows epitaxially on Ag up to 3ML although it is proposed that the Co lattice is in the FCC phase but no comment can be made as to whether the overlayer is laterally expanded. Polarised Neutron Reflection measurements have been made on Ag/Cr/Ag sandwich structures with varying thicknesses of Cr. It is shown that for Cr thicknesses of 2 and 3.3ML the Cr is ordered non-ferromagnetically and it is proposed that at these thicknesses the Cr has reverted to its bulk antiferromagnetic order. However measurements on samples with Cr thicknesses of 0.33ML indicate ferromagnetic ordering with a greatly enhanced magnetic moment per atom over the bulk Cr value, in partial agreement with previous theoretical predictions. PNR measurements on a Ag/Fe/Ag (001) structure with thickness of Fe of 8ML have yielded an accurate measurement of the magnetic moment per atom for the Fe film of 1.0 +; 0.15microB, indicating a reduced value from that of bulk Fe of 2.22microB. x-ray scattering from a Ge (001) surface has been used to show that the surface undergoes a reversible phase transition at T = 954 +; 7K. It is proposed that the transition occurs due to the formation of vacancy-adatom pairs as some of the surface dimers break with increasing temperature. The data is explained in terms of a three level model used to describe the vacancy-adatom creation. The three level model results are compared with results from a simple Monte-Carlo simulation and an energy of 0.41 +; 0.05eV is deduced as the energy required to break the dimer bonds on the surface of Ge (001). Further X-ray scattering from a miscut Ge (001) surface shows that the surface is made up of regularly spaced steps of double atomic height, in agreement with theoretical and previous experimental studies. It is shown that perpendicular to the steps the reconstructed domains are limited in dimension by the steps, although both orientations of the reconstruction are possible.
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Rose, Simon Robert. "Studies of the high temperature tribological behaviour of some superalloys." Thesis, Northumbria University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324419.
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Van, Opstall Michael A. "Some stable degenerations and applications to moduli /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/5732.
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Berzin, Corinne. "Surfaces aléatoires : approximation du temps local." Paris 11, 1989. http://www.theses.fr/1989PA112337.
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Soit { X(t,ω), t ∈ Rd, ω ∈ Ω }, d ≥2 un processus gaussien stationnaire, à valeurs réelles sur un espace de probabilité ( Ω, Around, P ). Nous étudions le comportement asymptotique d'une intégrale stochastique particulière, par rapport à la mesure géométrique de l'ensemble de niveau u, u ∈ R, du champ régularisé, obtenu par la composition d'une convoluée de X, soit Xɛ, et d'une normalisation matricielle contenant une partie de l'information de la matrice des moments spectraux d'ordre deux de Xɛ. Sous l'hypothèse que la fonction de covariance de X est deux fois continûment différentiable en dehors d'un ensemble de mesure de Lebesgue nulle dans Rd, cette intégrale converge dans L²(Ω ) vers le temps local de X, évalué en u. En outre, une majoration de la vitesse de convergence est proposée, à une constante prèsLet { X(t,ω), t ∈ Rd, ω ∈ Ω }, d ≥2, be a real stationary gaussian field, defined on a probability space ( Ω, Around, P ). We look at the asymptotic behavior of a particular stochastic integral, with respect to the geometric measure of the u-level sets, u ∈ R, of the regularized field, obtained by composition of a convolution of X, say Xɛ, with a matrix normalization which contains part of the information contained in the spectral moments matrix of second order of Xɛ. Under the condition that the covariance function is twice continuously differentiable out of a set of zero Lebesgue's measure, this functional converges in L² (Ω ) to the local time of X at the level u. Furthermore, we give a bound for the speed of convergence
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Rad, M. Goshtasbi. "Electronic structure and reactions at some tetrahedral semiconductor surfaces /." Stockholm : Tekniska högsk, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3069.
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Lu, Hua. "NO and SO₂ reactions on some model catalyst surfaces /." Stockholm, 1998. http://www.lib.kth.se/abs98/lu0227.pdf.
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Farooq, Khadija. "Hecke groups and some properties of their quotient surfaces." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/59697/.
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Pierro, Emilio. "Some calculations on the action of groups on surfaces." Thesis, Birkbeck (University of London), 2015. http://bbktheses.da.ulcc.ac.uk/158/.
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In this thesis we treat a number of topics related to generation of finite groups with motivation from their action on surfaces. The majority of our findings are presented in two chapters which can be read independently. The first deals with Beauville groups which are automorphism groups of the product of two Riemann surfaces with genus g > 1, subject to some further conditions. When these two surfaces are isomorphic and transposed by elements of G we say these groups are mixed, otherwise they are unmixed. We first examine the relationship between when an almost simple group and its socle are unmixed Beauville groups and then go on to determine explicit examples of several infinite families of mixed Beauville groups. In the second we determine the Mobius function of the small Ree groups 2G2(32m+1) = R(32m+1), where m >0, and use this to enumerate various ordered generating n-tuples of these groups. We then apply this to questions of the generation and asymptotic generation of the small Ree groups as well as interpretations in other categories, such as the number of regular coverings of a surface with a given fundamental group and whose covering group is isomorphic to R(32m+1).
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Bilbruck, John. "Some factors affecting bacterial adhesion to polymer monofilaments." Thesis, University of Brighton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292350.
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DRAGNEA, BOGDAN. "Modification de surfaces induites par laser et sondees par reflectivite et somme de frequences." Paris 11, 1997. http://www.theses.fr/1997PA112317.
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Ce travail illustre la double potentialite des lasers, comme moyen de modification des surfaces, et comme moyen de sonde des processus photoinduits et de leur dynamique. Les lasers sont appliques ici a la fois a des systemes d'interet en microelectronique (dopage du silicium, formation d'une couche mince de sic sur silicium, gravure du silicium) et a des systemes d'interet en catalyse heterogene (adsorption de co sur un metal ayant des proprietes catalytiques). Dans le premier domaine, notre effort a porte sur l'amelioration de la comprehension des transitoires de reflectivite, qui constituent le meilleur moyen pour mesurer la dynamique de la fusion superficielle photoinduite. En enregistrant ces transitoires en ultra-vide sur le silicium propre, nous avons observe que les proprietes thermiques du silicium solide sont modifiees par la presence d'une densite d'electrons significative dans la bande de conduction due a la photoexcitation, a l'echauffement photoinduit, et au retrecissement du gap du a cet echauffement. L'adsorption controlee d'impuretes en ultra-vide (oxygene, propene, chlore) confirme l'importance des electrons de conduction : l'effet de l'oxygene et du chlore sur les electrons de conduction et sur l'evolution des transitoires de reflectivite et de photoemission par rapport au si nu est conforme a notre interpretation. Les experiences de sfg en ultravide ont permis d'observer co dans des sites tres peu lies, desorbant par un echauffement de quelques dizaines de k seulement. Ceci montre le potentiel de la sfg pour detecter des especes reactives, qui sont en general tres peu liees. La forme particuliere des pics de sfg, par comparaison avec la ftir, a ete simulee en prenant en compte l'effet du couplage entre les reponses sfg du substrat et de l'adsorbat d'une part, et de la vibration de co et des electrons d'autre part.
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Villegas-Jiménez, Adrián. "On the surface chemistry of some rhombohedral carbonate minerals in aqueous solutions." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66755.
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Fundamental aspects of the surface chemistry of calcite, dolomite, magnesite, and gaspeite in aqueous solutions were examined using different lines of investigation including experimental, theoretical, and/or computer-assisted modeling approaches (i.e., ab initio molecular and surface complexation modeling). A Genetic Algorithm (GA) was implemented and tested for the calibration of surface complexation models (SCMs). The GA can successfully optimize numerous adjustable SCM parameters without incurring convergence problems while minimizing numerical instability problems, a notable advantage over conventional deterministic, root-finding, and optimization techniques implemented in codes such as FITEQL. It was routinely used throughout this thesis for the simultaneous calibration of surface complexation parameters (e.g., intrinsic constants, capacitances) at carbonate surfaces. The definition of reactive surface sites at hydrated rhombohedral carbonate mineral surfaces was critically revisited. Using calcite as the model mineral, a single generic charge-neutral surface site scheme was proposed for the formulation of surface equilibria. The resulting molecular representation of surface equilibria is consistent with experimental and theoretical findings and is compatible with assumptions implicit in SCMs. Based upon the one-site scheme, new and simplified SCMs for magnesite and dolomite were formulated. These successfully reproduced published surface charge and electrokinetic data while yielding surface speciation predictions consistent with available spectroscopic data. The acid-base behavior of the gaspeite (NiCO3(s)) surface in NaCl solutions was investigated for the first time by means of conventional titration techniques and micro-electrophoresis. Surface protonation and the electrophoretic mobility of gaspeite are strongly affected by the background electrolyte. Acid-base surface complexation reactions,Des aspects fondamentaux sur la chimie surfacique des minéraux carbonatés dans des solutions aqueuses ont été examinés par des approches expérimentales et théoriques ainsi que par des méthodes d'optimisation numérique et de modélisation moléculaire.Un algorithme génétique (GA, selon son sigle anglais) a été implémenté et testé pour la calibration de modèles de complexation à la surface (SCMs, selon son sigle anglais). Le GA peut optimiser de façon stochastique et simultanée des nombreux paramètres tout en minimisant des problèmes de convergence ou de stabilité numérique. Cet algorithme est très avantageux par rapport aux techniques déterministiques conventionnelles adoptées par des codes d'optimisation de constantes d'équilibre tel que FITEQL. Le GA a donc été utilisé de façon routinière dans cette étude, pour estimer les constantes de formation des espèces chimiques se formant à la surface des minéraux carbonatés. En utilisant la calcite comme modèle, nous avons réévalué de façon critique la définition de sites réactifs à la surface hydratée des minéraux carbonatés rhomboédriques. Ceci nous a permis de définir un site d'adsorption générique neutre pour ce type de minéraux, qui est compatible avec les résultats d'études théoriques et expérimentales ainsi qu'avec des hypothèses associées à la formulation de SCMs. Des nouvelles réactions, basées sur un seul site générique, ont été formulées pour la magnésite et dolomite et calibrées en utilisant des données publiées de charge surfacique et, par la suite, testées avec des données électrocinétiques et spectroscopiques disponibles dans la littérature.Le comportement acide-base à la surface de la gaspéite (NiCO3(s)), dans des solutions de NaCl, à été examiné par des techniques conventionnelles de titrage surfacique et par la micro-électrophorèse. Nous avons trouvé que l'él
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Spence, Stephen John. "Some studies of non-planar porphyrins and reproducible surface-enhancing Raman media." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390856.
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Yan, Song. "Spectroscopic and kinetic studies of the adsorption and coadsorption of some small molecules on Zn(0001) and Ag(111) surfaces." Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303758.
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Miasik, J. J. "Interaction of some organic semi-conductor surfaces with electroactive gases." Thesis, University of Kent, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356852.
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Francis, S. M. "Helium atom diffraction studies of some transition metal (110) surfaces." Thesis, University of Liverpool, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304313.
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Darugar, Qusai A. "Surface effects on the ultrafast electronic relaxation of some semiconductor and metallic nanoparticles." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-06272006-160645/.
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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2007.Zhang, John, Committee Member ; Wang, Zhong, Committee Member ; El-Sayed, Mostafa, Committee Chair ; Orlando, Thomas, Committee Member ; Lyon, Andrew, Committee Member.
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edu, Laurent@math berkeley. "Growth Series and Random Walks on Some Hyperbolic Graphs." ESI preprints, 2001. ftp://ftp.esi.ac.at/pub/Preprints/esi1075.ps.
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Reeson, Karen J. "Microreflectance and ellipsometric studies on the polished surfaces of some minerals." Thesis, London Metropolitan University, 1987. http://repository.londonmet.ac.uk/3148/.
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The optical properties of a series of ore minerals are assessed using microscope photometry and ellipsometry. Results from both methods are compared and any discrepancies in the data are Interpreted within the experimental and instrumental constraints of the two techniques. The errors involved in the calculation of reflectance and the optical constants n and k are also considered. A new type of microphotometric error known as the Standard-Specimen-Reflectance-Difference-Phenomenon (SSRDP) is investigated, its possible causes are discussed and tables evaluated for its correction. The results of this study are compared with those of other workers and differences between the measurements are discussed within the context of electronic, structural and impurity ion considerations. Where possible, spectral maxima are assigned to electronic and/or excitonic transitions and ideas are advanced to rationalise some of the observed reflectance dispersions. The use of spectroscopic ellipsometry in this investigation makes it possible to assess the effects of alr-formed or other contaminant films. The influence of specimen preparation on the optical characteristics is discussed and the importance of using 'real surfaces' in order to make possible the geological and commercial application of this study is emphasised.
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Valli, Giorgio. "Some aspects of the theory of harmonic gauges over Riemann surfaces." Thesis, University of Warwick, 1988. http://wrap.warwick.ac.uk/109833/.
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The main subject of this Thesis is the study of harmonic maps from compact Riemann surfaces into unitary groups, and various generalisations and related subjects. Harmonic maps are critical points of the energy functional. In the case we are considering, the associated Euler-Lagrange equations are particularly simple, because of the conformal invariance of the energy for maps from surfaces, which emphasizes the role of the complex structure, and of the simplicity of the target manifold. Another important feature is that the non-linear equations are representable as O-curvature conditions for families (loops) of connections. This is the elliptic version of a phenomenon which is typical of a class of evolution equations, where it induces soliton behaviour, and complete integrability. ln this elliptic situation, this representation (due to Zakharov et al.) allows us to substitute algebraic geometry to analysis, in the description of the solutions.