Este trabalho teve como principal objetivo o estudo sistemático da obtenção da fase beta-BaB204 (beta-BBO) a partir de uma fase vítrea do sistema BaO-B2O3-TiO2. Foram estudadas amostras contendo entre 4 e 16% de TiO2. A avaliação das propriedades térmicas, estruturais e microestruturais das amostras foi realizada empregando as técnicas de Analise Térmica Diferencial (DTA), Difração de Raios-X (DRX), Microscopia óptica (MO), Microscopia Eletrônica de Varredura (MEV), Espectroscopia Raman, Absorção e Transmissão óptica no Infravermelho, Espectroscopia de Absorção de Raios-X (XAS) e Ressonância Magnética Nuclear (RMN). O coeficiente de Geração de Segundo Harmônico (GSH) foi obtido através das medidas do loci de casamento de fase e da Franja de Maker. O estudo do processo de cristalização revelou que em todas as amostras prevaleceu o mecanismo de cristalização superficial. Nas amostras contendo 4 e 8% de TiO2 foi observada a cristalização da fase beta-BBO enquanto que nas amostras contendo 15 e 16% de TiO2, foi observado que o processo de cristalização se inicia pela fase BaTi(BO3)2 e que somente após longos tempos de tratamento, a fase beta-BBO se toma a fase predominante. A identificação da fase BaTi(BO3) somente foi possível com a utilização da técnica de Espectroscopia Raman. O estudo da estrutura local através das técnicas de XAS e RMN mostrou que a estrutura local ao redor dos átomos de titânio, bário e boro nas amostras cristalizadas é pouco afetada quando a quantidade de TiO2 passa de 4 para 16%. A análise dos resultados da medida de geração de segundo harmônico mostrou que nas amostras contendo uma camada da superfície cristalizada, o valor do coeficiente de geração de segundo harmônico (deff) é equivalente ao do quartzo monocristalino e na amostra contendo 16% de TiO2, corresponde a 70% do valor observado na fase beta-BBO em sua forma monocristalina / This work consists of a systematic study of the beta-BaB2O4 (beta-BBO) crystalline phase obtained from the BaO-B2O3-TiO2 glass system containing amounts of titanium varying from 4 to 16 mol%. The thermal, structural and microstructural properties of the samples were evaluated by the following techniques: Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Raman Spectroscopy, Infrared Optical Absorption Spectroscopy, X-Ray Absorption Spectroscopy (XAS) and Nuclear Magnetic Resonance (NMR). The Second Harmonic Generation (SHG) coefficient (def) was obtained from the phase matching Loci and Maker fringe curves. A study of the crystallization process revealed that the surface crystallization mechanism predominated in each of the samples. Only the beta-BBO phase was observed in the samples containing 4 and 8 mol% of TiO2. However, in the samples containing 15 and 16 mol% of TiO2, crystallization of the BaTi(BO3)2 occurred first and was followed by crystallization of the P-BBO phase, which subsequently became the main phase as the period of heat treatment increased. The identification of the BaTi(BO3)2 phase in the early stage of the crystallization process was only possible by using the Raman spectroscopy technique. Based on the results obtained from the XAS and NMR techniques, it was found that the increasing the titanium concentration does not affect significantly the short-range order around Ti, Ba and B atoms. An analysis of the SHG data obtained from the crystallized surface of the glassy samples indicated that the SHG coefficient, def, was comparable to that of the z-quartz monocrystalline sample and, in the sample containing 16 mol% of TiO2, it corresponded to 70% of the value observed for the monocrystalline beta-BBO sample

Este trabalho teve como principal objetivo o estudo sistemático da obtenção da fase beta-BaB204 (beta-BBO) a partir de uma fase vítrea do sistema BaO-B2O3-TiO2. Foram estudadas amostras contendo entre 4 e 16% de TiO2. A avaliação das propriedades térmicas, estruturais e microestruturais das amostras foi realizada empregando as técnicas de Analise Térmica Diferencial (DTA), Difração de Raios-X (DRX), Microscopia óptica (MO), Microscopia Eletrônica de Varredura (MEV), Espectroscopia Raman, Absorção e Transmissão óptica no Infravermelho, Espectroscopia de Absorção de Raios-X (XAS) e Ressonância Magnética Nuclear (RMN). O coeficiente de Geração de Segundo Harmônico (GSH) foi obtido através das medidas do loci de casamento de fase e da Franja de Maker. O estudo do processo de cristalização revelou que em todas as amostras prevaleceu o mecanismo de cristalização superficial. Nas amostras contendo 4 e 8% de TiO2 foi observada a cristalização da fase beta-BBO enquanto que nas amostras contendo 15 e 16% de TiO2, foi observado que o processo de cristalização se inicia pela fase BaTi(BO3)2 e que somente após longos tempos de tratamento, a fase beta-BBO se toma a fase predominante. A identificação da fase BaTi(BO3) somente foi possível com a utilização da técnica de Espectroscopia Raman. O estudo da estrutura local através das técnicas de XAS e RMN mostrou que a estrutura local ao redor dos átomos de titânio, bário e boro nas amostras cristalizadas é pouco afetada quando a quantidade de TiO2 passa de 4 para 16%. A análise dos resultados da medida de geração de segundo harmônico mostrou que nas amostras contendo uma camada da superfície cristalizada, o valor do coeficiente de geração de segundo harmônico (deff) é equivalente ao do quartzo monocristalino e na amostra contendo 16% de TiO2, corresponde a 70% do valor observado na fase beta-BBO em sua forma monocristalina / This work consists of a systematic study of the beta-BaB2O4 (beta-BBO) crystalline phase obtained from the BaO-B2O3-TiO2 glass system containing amounts of titanium varying from 4 to 16 mol%. The thermal, structural and microstructural properties of the samples were evaluated by the following techniques: Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Raman Spectroscopy, Infrared Optical Absorption Spectroscopy, X-Ray Absorption Spectroscopy (XAS) and Nuclear Magnetic Resonance (NMR). The Second Harmonic Generation (SHG) coefficient (def) was obtained from the phase matching Loci and Maker fringe curves. A study of the crystallization process revealed that the surface crystallization mechanism predominated in each of the samples. Only the beta-BBO phase was observed in the samples containing 4 and 8 mol% of TiO2. However, in the samples containing 15 and 16 mol% of TiO2, crystallization of the BaTi(BO3)2 occurred first and was followed by crystallization of the P-BBO phase, which subsequently became the main phase as the period of heat treatment increased. The identification of the BaTi(BO3)2 phase in the early stage of the crystallization process was only possible by using the Raman spectroscopy technique. Based on the results obtained from the XAS and NMR techniques, it was found that the increasing the titanium concentration does not affect significantly the short-range order around Ti, Ba and B atoms. An analysis of the SHG data obtained from the crystallized surface of the glassy samples indicated that the SHG coefficient, def, was comparable to that of the z-quartz monocrystalline sample and, in the sample containing 16 mol% of TiO2, it corresponded to 70% of the value observed for the monocrystalline beta-BBO sample

Este trabalho teve como objetivo a síntese e a caracterização de pós e filmes finos da fase ß-BaB2O4 (ß-BBO) a partir do sistema temário BaO-B2O3-TiO2. A preparação destas amostras foi baseada na utilização de dois métodos de síntese: o método dos precursores poliméricos e o método de deposição por evaporação utilizando um feixe de elétrons. O estudo das amostras na forma de pós mostrou que a adição de TiO2 ao sistema BaO-B2O3 acelera o processo de decomposição térmica e reduz a temperatura de cristalização e de fusão da fase ß-BBO. No que concerne a obtenção da fase ß-BBO, a composição mais adequada é a que contém 4% de TiO2 e cristalizada a 700°C durante 2 horas. As propriedades estruturais, microestruturais e ópticas dos filmes também foram influenciadas pela quantidade de TiO2. Os filmes finos contendo 4% de TiO2 e cristalizados a 650°C apresentam somente a fase ß-BBO com um alto grau de orientação preferencial quando depositados sobre substratos de quartzo amorfo, silício e quartzo monocristalinos. Filmes finos cristalinos depositados pelo método de evaporação por feixe de elétrons contendo a fase ß-BBO somente foram obtidos \"in-situ\" quando os substratos foram aquecidos a 650°C. Os filmes cristalinos obtidos por ambos os métodos apresentaram o efeito de geração de segundo harmônico (\"SHG\"). / The main objective of this work was the synthesis and the characterization of the ß-BaB2O4 (ß-BBO) phase in a powder and thin film form from the BaO-B2O3-TiO2 ternary system. The powder and thin film samples were obtained using two different methods, the polymeric precursor method and the electron beam evaporation method. The study of the powder samples showed that the addition of titanium oxide to the BaO-B2O3 system accelerate the decomposition process, reduces the crystallization temperature and the ß-BBO melting point. The ß-BBO phase was obtained as the main phase for the sample containing 4% of titanium and heat-treated at 700°C for 2h. Structural, microstructural and optical properties of the thin films were also influenced by addition of TiO2. Thin films with 4% of TiO2 and crystallized at 650°C shown only ß-BBO phase with a higher degree of preferred orientation when coated on fused silica, silicon and quartz substrates. The microstructural and the optical properties of these thin films were affected by the type of the substrate and by crystallization temperature and by the heating rate. For the thin film deposited by electron beam evaporation the crystallization of ß-BBO phase \"in-situ\" was only possible when the substrates was heated at 650°C during the deposition. Thin films prepared by both methods presents the effect of Second Harmonic Generation (SHG).

Ce travail de thèse se sépare en deux volets. Le premier volet concerne l'étude de l'homogénéité de l'univers, et le second une mesure de l'échelle BAO, qui constitue une règle standard permettant de mesurer l'évolution du taux d'expansion de l'univers. Ces deux analyses reposent sur l'étude de la structuration (ou clustering) des quasars des relevés BOSS et eBOSS, qui couvrent la gamme en redshift 0,9 < z < 2,8. Les mesures des observables caractérisant la structuration de l'univers aux grandes échelles sont très sensibles aux effets systématiques, nous avons donc étudiés ces effets en profondeur. Nous avons mis en évidence que les sélections de cibles quasars BOSS et eBOSS ne sont pas parfaitement homogènes, et corrigé cet effet. Au final, la mesure de la fonction de corrélation des quasars nous a permis de mesurer le biais des quasars sur la gamme en redshift 0,9 < z < 2,8. Nous obtenons la mesure actuelle la plus précise du biais, b = 3,85 ± 0,11 dans la gamme 2,2 < z < 2,8 pour le relevé BOSS, et b = 2,44 ± 0,04 dans la gamme 0,9 < z < 2,2 pour le relevé eBOSS. Le Principe Cosmologique stipule que notre univers est isotrope et homogène à grande échelle. Il s'agit d'un des postulats de base de la cosmologie moderne. En étudiant la structuration à très grande échelle des quasars, nous avons prouvé l'isotropie spatiale de l'univers dans la gamme 0,9 < z < 2,8, indépendamment de toute hypothèse et cosmologie fiducielle. L'isotropie spatiale stipule que l'univers est isotrope dans chaque couche de redshift. En la combinant au principe de Copernic, qui stipule que nous ne nous situons pas à une position particulière dans l'univers, permet de prouver que notre univers est homogène aux grandes échelles. Nous avons effectué une mesure de la dimension de corrélation fractale de l'univers, D₂(r), en utilisant un nouvel estimateur, inspiré de l'estimateur de Landy-Szalay pour la fonction de corrélation. En corrigeant notre estimateur du biais des quasars, nous avons mesuré (3 - D₂(r)) = (6,0 ± 2,1) x 10⁻⁵ entre 250 h⁻¹ Mpc et 1200 h⁻¹ Mpc pour le relevé eBOSS, dans la gamme 0,9 < z < 2,2. Pour le relevé BOSS, nous obtenons (3 - D₂(r)) = (3,9 ± 2,1) x 10⁻⁵, dans la gamme 2,2 < z < 2,8. De plus, nous montrons que le modèle Lambda-CDM décrit très bien la transition d'un régime structuré vers un régime homogène. D’autre part, nous avons mesuré la position du pic BAO dans les fonctions de corrélation des quasars BOSS et eBOSS, détecté à 2,5 sigma dans les deux relevés. Si nous mesurons le paramètre α, qui correspond au rapport entre la position du pic mesuré et la position prédite par une cosmologie fiducielle (en utilisant les paramètres Planck 2013), nous mesurons α = 1,074 pour le relevé BOSS, et α = 1,009 pour le relevé eBOSS. Ces mesures, combinées uniquement à la mesure locale de H₀, nous permettent de contraindre l'espace des paramètres de modèles au-delà du Lambda-CDM. / This work consists in two parts. The first one is a study of cosmic homogeneity, and the second one a measurement of the BAO scale, which provides a standard ruler that allows for a direct measurement of the expansion rate of the universe. These two analyses rely on the study of quasar clustering in the BOSS and eBOSS quasar samples, which cover the redshift range 0.9 < z < 2.8. On large scales, the measurement of statistical observables is very sensitive to systematic effects, so we deeply studied these effects. We found evidences that the target selections of BOSS and eBOSS quasars are not perfectly homogeneous, and we have corrected this effect. The measurement of the quasar correlation function provides the quasar bias in the redshift range 0.9 < z < 2.8. We obtain the most precise measurement of the quasar bias at high redshift, b = 3.85 ± 0.11, in the range 2.2 < z < 2.8 for the BOSS survey, and b = 2.44 ± 0.04 in the range 0.9 < z < 2.2 for the eBOSS survey. The Cosmological Principle states that the universe is homogeneous and isotropic on large scales. It is one of the basic assumptions of modern cosmology. By studying quasar clustering on large scales, we have proved ''spatial isotropy'', i.e. the fact that the universe is isotropic in each redshift bins. This has been done in the range 0.9 < z < 2.8 without any assumption or fiducial cosmology. If we combine spatial isotropy with the Copernican Principle, which states that we do not occupy a peculiar place in the universe, it is proved that the universe is homogeneous on large scales. We provide a measurement of the fractal correlation dimension of the universe, D₂(r), which is 3 for an homogeneous distribution, and we used a new estimator inspired from the Landy-Szalay estimator for the correlation function. If we correct our measurement for quasar bias, we obtain (3 - D₂(r)) = (6.0 ± 2.1) x 10⁻⁵ between 250 h⁻¹ Mpc and 1200 h⁻¹ Mpc for eBOSS, in the range 0.9 < z < 2.2. For BOSS, we obtain (3 - D₂(r)) = (3.9 ± 2.1) x 10⁻⁵, in the range 2.2 < z < 2.8. Moreover, we have shown that the Lambda-CDM model provide a very nice description of the transition from structures to homogeneity. We have also measured the position of the BAO peak in the BOSS and eBOSS quasar correlation functions, which yield a 2,5 sigma detection in both surveys. If we measure the α parameter, which corresponds to the ratio of the measured position of the peak to the predicted position in a fiducial cosmology (here Planck 2013), we measure α = 1.074 for BOSS, and α = 1.009 for eBOSS. These measurements, combined only with the local measurement of H₀, allows for constraints in parameter space for models beyond Lambda-CDM.

La propagation des ondes acoustiques dans le plasma primordial a laissé son empreinte sous la forme d'un pic dans la fonction de corrélation à deux points de la densité de matière. Ce pic d'oscillations acoustiques de baryons (BAO) constitue une échelle standard permettant de déterminer certains paramètres des différents modèles cosmologiques.Dans ce manuscrit de thèse, nous présentons une mise à jour de la mesure de BAO à un redshift z=2.40, à l'aide de la fonction de corrélation croisée entre deux traceurs des fluctuations primordiales de densité de matière: les quasars de SDSS-III (BOSS) et leurs fluctuations d'absorption du flux des forêts Lyman-α. Ces fluctuations tracent la distribution d'hydrogène neutre dans le milieu intergalactique (IGM).Cette étude constitue le premier développement d'un ajustement entièrement physique de la fonction de corrélation croisée; il prend notamment en compte la physique des quasars et la présence d'éléments plus lourds que l'hydrogène dans l'IGM. Nous y présentons également les premières simulations de notre analyse. Celles-ci nous permettent de valider l'ensemble de la procédure de mesure de l'échelle BAO.Cette étude mesure la distance de Hubble et la distance de diamètre angulaire avec respectivement une précision de 2% et 3% (intervalle à 1 σ). Nous combinons nos résultats avec d'autres mesures de BAO à des redshifts plus faibles et trouvons la densité de matière noire et d'énergie noire dans le cadre de deux différents modèles cosmologiques: ΛCDM et oΛCDM. / The acoustic wave propagation in the primordial plasma left its imprint in the two-point correlation function of the matter density field. This baryonic acoustic oscillation (BAO) peak builds up a standard ladder allowing us to infer some parameters of the different cosmological models.In this thesis manuscript we present an update of the BAO measurement at a redshift z=2.40, from the cross-correlation function between two tracers of the primordial matter density fluctuations: quasars of SDSS-III (BOSS) and their Lyman-α-forest absorption fluctuations. These fluctuations trace the neutral hydrogen distribution in the intergalactic medium (IGM).This study gives the first developpment of the full physical fit of the cross-correlation. Among other effects, it takes into account quasar physics and the distribution of IGM elements heavier than hydrogen. We also present the first simulations of our analysis. They allow us to validate the overall data analysis leading to the BAO measurement.This study measures the Hubble distance and the angular diameter distance at the 2%$ and 3%$ precision level respectivelly (1 σ interval). We combine our results with other BAO measurements at lower redshifts and find the dark matter density and dark energy density in the framework of two different cosmological models: ΛCDM et oΛCDM.

>Magister Scientiae - MSc / Future radio surveys as the Square Kilometer Array (SKA) and its precursor, the "Meer" Karoo Array Telescope (MeerKAT), will map the Neutral Hydrogen (HI) in large areas of the sky using the intensity mapping (IM). HI IM is currently one of the most promising ways of accessing the Large-Scale Structure of the Universe. The distribution of matter in the Universe not only encodes its composition but also how it evolves and its initial conditions. An effect on the matter distribution that will be detected by the SKA on the post re-ionization Universe are the Baryonic Acoustic Oscillations (BAO). While it has been shown that in single dish mode the SKA can measure the BAO peak in the radial 21cm power spectrum at low redshifts, this possibility has not yet been studied in detail for the MeerKAT. In this thesis we construct a set of full sky simulations to test how well MeerKAT will be able to extract the BAO wiggles along the line of sight. These simulations are done for the frequencies corresponding to MeerKAT L-band. The maps combine the cosmological HI signal, systematic noise, cosmological foregrounds and the instrumental telescope beam. A model-independent estimator is used to extract the BAO wiggles by subtracting a smooth polynomial component from the 21cm radial power spectrum. We test with simulations if this estimator is biased and the signal to noise of the extraction. We conclude that we are able to remove contaminants and recover the cosmological HI signal while not risking the recovery of the BAO signal. We investigate the effects of varying the sky area and the observational hours on the signal to noise ratio for the BAO wiggles. We found that for a HI IM experiment using MeerKAT, the optimal sky area to detect the BAO along the line of sight is 50% of the sky. With a signal-to-noise ratio of 3.37. This can be achieved with 2000 hours of exposure time

Pour se renseigner et pour acheter des produits les consommateurs vont sur les pages de marques sur Facebook. Ces utilisateurs font du bouche à oreille au sein de communautés de marques sur Facebook. L’objectif de cette thèse est de proposer une analyse des déterminants au bouche à oreille au sein des communautés de marques sur Facebook. Les principaux déterminants au bouche à oreille que nous présentons dans le cadre de cette thèse sont l’engagement à la marque, les motivations au partage, et la disposition générale au partage. / EWord of Mouth (eWOM) influences consumers who belong to brand communities on Facebook. The aim of this thesis is to analyze the antecedents for eWOM on brand communities on Facebook. The thesis proposes an analysis of eWOM’s antecedents: brand engagement, identification to brand communities, general tendency to share on Facebook.

This paper explores the practical teachings found in the Dunhuang manuscript of the Platform Sutra of the Sixth Patriarch and considers the possibility of practice within a doctrine of sudden enlightenment. Part One outlines how the doctrine of sudden enlightenment can be understood to undermine the purpose for practicing meditation. Part Two first makes a case for the position that practice is presupposed by the text regardless of the doctrine of sudden enlightenment. Next the paper argues for what type of meditation practice the Platform Sutra teaches is consistent with sudden enlightenment. The practice the Platform Sutra teaches is an intentionless, continuous, non-passive non-attachment while in the midst of dharmas that takes as its basis the suchness of things inherent in sentient beings.

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