Tesis para optar al grado de Magíster en Ciencias, Mención Geología / Memoria para optar al título de Geólogo / El Volcán Villarrica es uno de los más activos de los Andes (ciclos de reposo de ~5.3 años), eruptando productos de composiciones basálticas a andesíticas basálticas, con estilos desde hawaiiano a estromboliano vigoroso. Estas características lo hacen un lugar destacado para determinar los parámetros pre-eruptivos y los procesos involucrados en sus erupciones. En esta tesis se compara la geoquímica de roca total y las abundancias, texturas y composiciones minerales de las lavas más relevantes del siglo XX, que fueron eruptadas en 1921, 1948 y 1971. Las lavas analizadas muestran un rango restringido en las composiciones de roca total (51.7-52.4 wt. % SiO2), sin embargo, presentan la siguiente tendencia creciente del contenido de MgO: ~5.3 wt % MgO (1921), ~6.0 wt % MgO (1971) and ~7.0 wt. % MgO (1948). Dos grupos de composiciones de plagioclasas se observan en todas las lavas: pobres en anortita (~An60) y ricas en anortita (~An80). Las composiciones pobres en anortita son las más abundantes en todas las lavas y fueron comúnmente formadas en las etapas tempranas (núcleos) y en las últimas etapas (bordes externos y fenocristales pequeños y casi no zonados) de cristalización de plagioclasa, mientras que las plagioclasas ricas en anortita se formaron alrededor de núcleos pobres en anortita o como cristales aislados durante etapas intermedias. Las temperaturas de equilibrio de plagioclasa-olivino-clinopiroxeno son de aproximadamente 1090 °C y fueron obtenidas en clots de cristales de las tres lavas. Los cálculos termométricos obtenidos con simulaciones de MELTS de formación de plagioclasa indican un calentamiento (thermal mixing) del reservorio a ~0.5 kbar de unos 100 °C con respecto a las temperaturas de los clots cristalinos. La incorporación de pequeñas cantidades de magma máfico más rico en volátiles y más caliente, de composición similar (cryptic mixing), en el reservorio del Villarrica, podría también calentarlo, probablemente, de una manera más eficiente que con la sola conducción de calor. Una interacción más larga del magma máfico caliente con el reservorio podría provocar cristalización de plagioclasa rica en anortita, disolución de plagioclasa pobre en anortita (es decir, un aumento de la razón modal de rica en An/pobre en An) y una modificación composicional hacia composiciones más ricas en MgO y volátiles, que últimamente resultarían en una mayor intensidad de la erupción.

L'étude porte sur une couche de mélange plane horizontale générée par la rencontre de deux écoulements parallèles à vitesse et température différentes. Le mélange turbulent est analysé pour différentes conditions initiales en termes de gradients de vitesse et de température. On distingue en particulier des configurations en régime de stratification stable et instable sous l'effet des forces de flottabilité. L'analyse des corrélations entre les fluctuations de vitesse et de température s'appuie sur la technique expérimentale d'anémométrie à température de fil variable (PCTA), qui permet la mesure instantanée de la vitesse et de la température en un même point grâce à la variation périodique et par palier du coefficient de surchauffe du fil chaud utilisé. Un premier travail a consisté à étendre la technique PCTA à l'utilisation de fils croisés pour la mesure simultanée de la température et de deux composantes de la vitesse. Dans un premier temps, les statistiques en un point permettent d'identifier les caractéristiques de l'écoulement dans la région de similitude et d'y établir les équations de bilan pour l'énergie cinétique turbulente, l'intensité des fluctuations de température et les flux de quantité de mouvement et de chaleur. Il apparaît, vu les faibles nombres de Richardson en jeu (Rif<0,03), que les forces de flottabilité sont quasi-négligeables devant les moteurs principaux du mouvement. Pourtant, ce forçage thermique peu énergétique est suffisant, en configuration instable, pour augmenter significativement le taux d'expansion et la contrainte de cisaillement, ce qui correspond de fait à une augmentation de la production de turbulence. L'analyse des densités de probabilité jointes permet ensuite de mettre en évidence les mécanismes et évènements qui contribuent significativement aux flux transversaux de quantité de mouvement et de chaleur. Ces différentes contributions sont différenciées et quantifiées par une analyse en quadrants qui fait ressortir la prépondérance des mouvements d'entraînement et d'éjection. On examine enfin les statistiques en deux points associées aux incréments de vitesse et de température. Le comportement de ces incréments est étudié à travers leurs densités de probabilité et leurs coefficients de dissymétrie et d'aplatissement. Les exposants des fonctions de structure confirment l'intermittence plus grande de la température par rapport à celle de la vitesse. Les différents termes des équations de Kolmogorov et de Yaglom sont mesurés. L'équilibre de ces bilans par échelle permet de quantifier le terme qui intègre les différents forçages proposés dans la littérature. / The turbulent mixing is studied in a plane mixing layer for a range of initial conditions applied in terms of velocity and temperature gradients between the two parallel inlet flows. A particular attention is paid to the effect of buoyancy forces, especially in the difference between the so-called stable and unstable configurations, in relation to the sign of the vertical temperature gradient applied. In this study, the novel experimental technique called PCTA, for Parameterizable Constant Temperature Anemometry, is used to enable the analysis of correlations between the velocity and temperature fluctuations. In a preliminary work, the PCTA technique, based on the implementation of repetitive multiple-overheat patterns to a hot wire, is extended and adapted for the instantaneous measurement of temperature and two components of velocity with X-wire probes. In a first stage, one point statistics are analysed. They provide a description of the flow features in the similarity region, where the balance equations for turbulent kinetic energy, temperature variance and the momentum and heat fluxes are established. Considering the low Richardson numbers at stake (Rif <0.03), the buoyancy forces appear logically to be quantitatively negligible compared to the main driving forces, but such a low energy forcing mechanism is in fact sufficient, in unstable configuration, to significantly increase the shear stress and the expansion rate of the mixing layer, both phenomena being associated to an enhanced production of turbulence. In a second stage, a joint probability density function analysis highlights the mechanisms and events that significantly contribute to the transverse momentum and heat fluxes. These contributions are differentiated and quantified through a quadrant analysis which emphasizes the dominance of the local movements of entrainment and ejection associated to the Kelvin-Helmholtz structures. Finally, the study focuses on the two points statistics associated with velocity and temperature increments. The behaviour of these increments is studied through their probability densities, examined along with the skewness and kurtosis coefficients. The structure function exponents confirm the stronger intermittency of temperature compared to that of the velocity. The different terms of the Kolmogorov and Yaglom equations are estimated. The balance of these scale budgets allows the quantification of the forcing term that has been introduced in the literature.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21764号 / 工博第4581号 / 新制||工||1714(附属図書館) / 京都大学大学院工学研究科原子核工学専攻 / (主査)教授 功刀 資彰, 教授 横峯 健彦, 教授 村上 定義 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Des méthodes numériques sont présentées qui permettent la simulation de jets chauds débouchants dans un écoulement transverse aux grands nombres de Reynolds et aux rapports des vitesses faibles. Différentes approches pour la modélisation de turbulence, c'est-à-dire URANS, SAS, DDES et ELES, sont validées par comparaison à des données expérimentales pour une configuration générique, soulignant la nécessité de résoudre les différentes échelles turbulentes pour une prévision correcte du mélange thermique. L'analyse de la solution instationnaire permet l'identification de processus dynamiques intrinsèques ainsi que des phénomènes de mélange et l'application de l'analyse en composantes principales révèle l'ondulation latérale du sillage de jet. Du fait du caractère multi-échelles qui se manifeste dans la simulation d'un jet débouchant sur une configuration avion, l'approche séquentielle basée sur le modèle SAS est mise en place. Comme les résultats pour la sortie d'un système de dégivrage de nacelle sont en bon accord avec les données d'essai en vol, cette approche est finalement appliquée à la sortie complexe d'un système de pre-cooler, mettant en valeur sa capacité à être appliquée dans un processus industriel. / Numerical methods for the simulation of hot jets in cross flow at high Reynolds numbers and small momentum ratios are presented. Different turbulence modeling strategies, i.e. URANS, SAS, DDES and ELES, are validated against experimental data on a generic configuration, highlighting the necessity of scale-resolution for a correct prediction ofthermal mixing. The analysis of transient flow simulations allows the identification of inherent flow dynamics as well as mixing phenomena and the application of the Proper Orthogonal Decomposition revealed the lateral wake meandering as being one of them. Due to the multi-scale problem which arises when simulating jets in cross flow on real aircraft configurations, the sequential approach based on the SAS turbulence model is introduced. As results for the exhaust of a nacelle anti-icing system comprising multiple jets in cross flow agree well with flight test data, the approach is applied in a last step to the complex exhaust of a pre-cooling system, emphasizing the capabilities of this methodology in an industrial environment.

This study is presented in nine chapters as follows: Chapter one reviews the reported literature on the NMR of natural diamond. The NMR signal of diamond consists on a single line at 39 ppm from TMS and two hyperfine lines due to 13C interactions. The reported relaxation times, measured in natural diamond, synthetic diamonds and 13C enriched diamonds, are discussed. The second chapter introduces the apparatus used, which included a Bruker Avance NMR spectrometer, a Bruker ESP380E pulsed EPR spectrometer and a high powersband DNP system. The availability of this excellently equiped laboratory presented a unique opportunity to perform this investigation. Chapter three outlines the experimental techniques used as well as the manner in which the acquired data was processed. The fourth chapter presents an overview of the most common defects found in diamond. Proposed models of these defects are presented and the resulting EPR spectra displayed. The methods developed to determine the paramagnetic impurity concentration from the EPR line width and the spin-spin relaxation times are presented in the fifth chapter. The line width gives the total paramagnetic impurity concentration to about 10 ppm. The spin-spin relaxation time allows the determination of Pl and P2 paramagnetic impurity concentrations individually, to much lower levels from measurements on the central and hyperfine lines. This information was used in the explanation of the relaxation behaviour for the various diamonds investigated. The temperature dependence of the paramagnetic electron relaxation times is reported in the sixth chapter. The results obtained are consistent with the findings in prior work that Pl impurities are typical Jahn Teller centres. Two diamonds, however, display trends that depart from this theory. These diamonds contain N3 defect centres, which appear to be responsible for this behaviour. It was found in these experiments that, bar thermal expansion effects, the spin-spin relaxation time is essentially independent of temperature. The seventh chapter deals with the solid state and thermal mixing effects. The relevant theory, results obtained and a discussion of these results, are presented. The effect of impurity concentration, defect types, microwave power, the exposure time and the offset from resonance on the polarisation rates and the 13C polarisation are investigated in depth. Finally the effect of applying the DNP treatment on the central and hyperfine lines is discussed. The pulsed DNP process is presented in the eighth chapter. The relevant theory, the effects of matching of the Hartmann-Hahn condition, impurity concentrations and types, on the polarisation rate and signal enhancement of JJC nuclei is given. A comparison to the continuous wave techniques is then made. The ninth chapter summarises the achievements and recommendations for further work. / Physics / D. Phil. (Physics)

This study is presented in nine chapters as follows: Chapter one reviews the reported literature on the NMR of natural diamond. The NMR signal of diamond consists on a single line at 39 ppm from TMS and two hyperfine lines due to 13C interactions. The reported relaxation times, measured in natural diamond, synthetic diamonds and 13C enriched diamonds, are discussed. The second chapter introduces the apparatus used, which included a Bruker Avance NMR spectrometer, a Bruker ESP380E pulsed EPR spectrometer and a high powersband DNP system. The availability of this excellently equiped laboratory presented a unique opportunity to perform this investigation. Chapter three outlines the experimental techniques used as well as the manner in which the acquired data was processed. The fourth chapter presents an overview of the most common defects found in diamond. Proposed models of these defects are presented and the resulting EPR spectra displayed. The methods developed to determine the paramagnetic impurity concentration from the EPR line width and the spin-spin relaxation times are presented in the fifth chapter. The line width gives the total paramagnetic impurity concentration to about 10 ppm. The spin-spin relaxation time allows the determination of Pl and P2 paramagnetic impurity concentrations individually, to much lower levels from measurements on the central and hyperfine lines. This information was used in the explanation of the relaxation behaviour for the various diamonds investigated. The temperature dependence of the paramagnetic electron relaxation times is reported in the sixth chapter. The results obtained are consistent with the findings in prior work that Pl impurities are typical Jahn Teller centres. Two diamonds, however, display trends that depart from this theory. These diamonds contain N3 defect centres, which appear to be responsible for this behaviour. It was found in these experiments that, bar thermal expansion effects, the spin-spin relaxation time is essentially independent of temperature. The seventh chapter deals with the solid state and thermal mixing effects. The relevant theory, results obtained and a discussion of these results, are presented. The effect of impurity concentration, defect types, microwave power, the exposure time and the offset from resonance on the polarisation rates and the 13C polarisation are investigated in depth. Finally the effect of applying the DNP treatment on the central and hyperfine lines is discussed. The pulsed DNP process is presented in the eighth chapter. The relevant theory, the effects of matching of the Hartmann-Hahn condition, impurity concentrations and types, on the polarisation rate and signal enhancement of JJC nuclei is given. A comparison to the continuous wave techniques is then made. The ninth chapter summarises the achievements and recommendations for further work. / Physics / D. Phil. (Physics)

Le travail de cette thèse a consisté à concevoir, réaliser et optimiser un montage expérimental de Polarisation Dynamique Nucléaire multi-échantillons pour des applications biomédicales en Imagerie Spectroscopique par Résonance Magnétique. Ce montage est constitué d'un aimant à fort champ magnétique (3,35T), dans lequel se place un système cryogénique à bain d'hélium (He4) liquide pompé pouvant atteindre des températures inférieures à 1,2K. Un ensemble d'inserts permet d'effectuer les différentes étapes du processus PDN dont l'irradiation des échantillons par un champ micro-onde (f=94GHz et P=50mW) et le suivi de leur polarisation par Résonance Magnétique Nucléaire. Ce système permet de polariser jusqu'à trois échantillons, de volume proche de 1mL, à des taux de polarisation de quelques pourcents. Il présente une forte autonomie supérieure à quatre heures, autorisant ainsi la polarisation de molécules à longues constantes de temps de polarisation. La possibilité de disposer quasi-simultanément, après dissolution, de plusieurs échantillons fortement polarisés ouvre la voie à de nouvelles applications dans le domaine de l'imagerie biomédicale / The aim of this thesis work was to design, build and optimize a large volume multisamples DNP (Dynamic Nuclear Polarization) polarizer dedicated to Magnetic Resonance Spectroscopic Imaging applications. The experimental system is made up of a high magnetic field magnet (3,35T) in which takes place a cryogenic system with a pumped bath of liquid helium (4He) allowing temperatures lower than 1,2K. A set of inserts is used for the different steps of DNP : irradiation of the sample by a microwave field (f=94GHz and P=50mW), polarization measurement by Nuclear Magnetic Resonance. . . With this system, up to three samples of 1mL volume can be polarized to a rate of few percents. The system has a long autonomy of four hours, so it can be used for polarizing molecules with a long time constant of polarization. Finally, the possibility to get quasisimultaneously, after dissolution, several samples with a high rate of polarization opens the way of new applications in biomedical imaging