Temos utilizado o método de Hartree-Fock-Roothaan, seguido da teoria de perturbação de segunda ordem, para a determinação das propriedades estruturais e eletrônicas dos aglornerados GaAs, G2As, GaAs2, Ga3As, Ga2As2, GaAs3, G4As, Ga3As2, Ga2As4, GaAs4, Ga3As3, G4Asa, Ga3As4, Ga4As4 e seus íons positivos e negativos. A estrutura de equilíbrio de cada um destes aglomerados foi determinada através de cálculos de otimização de geometria sem a imposição de vínculos espaciais de simetria sobre a função de onda. Uma vez determinadas as estruturas dos estados fundamentais destes aglomerados, obtivemos os valores de diversas propriedades eletrônicas e energéticas, como o potencial de ionização, a afinidade eletrônica, 0 bond-order, populações orbitais de Mulliken, carga sobre os átomos, natureza dos HOMO-LUMO, etc. Com estas informações, pudemos então descrever de forma detalhada cada um destes aglomerados e comparar nossos resultados com os existentes na literatura. Realizando uma analise conjunta dos resultados obtidos, deduzimos um padrão estrutural a ser seguido por estes pequenos aglomerados de GaAs, onde as formas embrionárias destes aglomerados têm SUM estruturas geométrica e eletrônica baseadas em configurações altamente simétricas, formadas pelos átomos de As. Os átomos adicionais de Ga entram em posições que favorecem um padrão de hibridização e ordenamento químico que tende ao padrão apresentado pelo cristal de GaAs. A passagem para uma estrutura em camadas e observada ocorrer ja no aglomerado estequiométrico com oito átomos. Utilizando o princípio de hard and soft acids and bases, estudamos a reatividade química do aglomerado Ga2As2 e da superfície GaAs[ll0], quando em interação com átomos externos. / Using the Hartree-Fock-Roothaan method, followed by second-order perturbation theory we determined the structural and electronic properties of the GaAs, Ga2As, GaAs2, Ga3As, Ga2As2, GaAs3, Ga4As, Ga3As2, Ga2As3, GaAs4, Ga3As3, Ga4As3, Ga4As4, Ga4As4 clusters and its positive and negative ions. The equilibrium structure for each of these clusters was determined throgh geometry optimization calculations, without spatial symmetry constraint on the wave function. Once we have determined the ground state structures of these clusters, the values of different electronic and structural properties were evaluated. This includes the ionization potential, electron affinity, bond-order, Mulliken populations, the nature of the HOMO-LUMO orbitals, etc. With these informations we described in detail each one of the clusters, and we compared our results with the experimental and theoretical published results. Analysing the assembly of the obtained results, we can deduce a structural pattern to be followed by these small clusters of GaAs, where the embrionary forms of these clusters have the geometric and electronic structures based on highly symmetrical configurations formed by the As atoms. The Ga aditional atoms enter in positions that enhance a hybridization and chemical ordering which tends to that presented by the bulk. The change for a layer structure is observed occur yet in the eight atoms stechiometric cluster. Using the hard and soft acids and bases principle, we have studied chemical reactivity of the Ga2As2 cluster and the GaAs[ll0] surface when in interaction with atoms.

Blue stragglers are enigmatic stars which appear to have undergone some form of rejuvenation, bringing them near the zero-age main sequence of the cluster in which they reside. The most likely explanation for the existence of these stars is that they have formed recently, through the merger of two stars, either through a direct stellar collision, or through binary mass-transfer and coalescence. This thesis presents models of the remnants of these processes, and a comparison of the predictions of these models with observed blue stragglers in several clusters. The predictions of smoothed particle hydrodynamic simulations of colliding stars have been used to create models appropriate for input into a stellar evolution code. Since these models develop only thin, short-lived, convective envelopes, angular momentum loss via a magnetically driven stellar wind is unlikely to be a viable mechanism for slowing the rapidly rotating blue stragglers predicted by the collisional scenario. Angular momentum transfer to either a circumstellar disk (possibly collisional ejecta) or a nearby companion remain plausible mechanisms for explaining the low rotation velocities observed for most blue stragglers. In addition to these models of collisional mergers, simplistic models of the remnants of binary coalescence and mass-transfer were also developed. The predictions of both sets of models were compared with the observed blue straggler populations of six globular clusters (NGC 104, NGC 2419, NGC 5024, NGC 6809, NGC 7099). While most of the clusters' blue stragglers appear to be well matched by the predictions of the collisional mergers, the blue stragglers in the cluster with the highest central density, NGC 7099, appear to be a hybrid population of both collisional and binary mergers. The blue stragglers of NGC 2419—the least dense of the clusters studied here—are well matched solely by the predictions of the collisional mergers of equal mass stars. However, due to the low density of this cluster, it is likely that some fraction of these blue stragglers are being formed via binary mergers and that the mergers and that the simple models of binary mergers used here are inadequate. / Graduate

The first part of this thesis presents a review of colour-magnitude photometry of Galactic globular clusters. A survey has been made of recently-published colourmagnitude photometry of globular clusters, and a self-consistent distance scale established for these data, using the method of subdwarf matching to the observed main sequences. The distances thus derived have been combined with other published colour-magnitude data to infer cluster ages and horizontal branch magnitudes. The relationship between cluster horizontal branch magnitude and metallicity is dicussed. In Chapter 2, a review is made of the photometric applications of charge coupled devices, giving particular attention to the aquisition and analysis of crowded field CCD images within globular clusters. Digital photometric techniques are discussed, including analytic profile fitting to stellar images. The major experimental part of this thesis concerns observations of the globular cluster w Centauri. These observations, their subsequent reduction, and photometric analysis, are discussed in Chapter 3. This chapter also contains a discussion of previous work on this cluster, and highlights its extremely unusual nature. The significant discovery of geometrically varying stellar profiles in the programme CCD images, and the techniques for their analysis, are discussed. The colour-magnitude data from these observations are discussed in Chapter 4. The distance to the cluster is determined, and it is shown that there exists an intrinsic spread in colour upon the cluster main sequence. Theoretical isochrones are employed to show that this spread in colour is consistent with a main sequence metallicity distribution similar to that seen in more highly-evolved stars within the cluster. The age of the cluster is determined as 16 +3 Gyr, by comparison with theoretical isochrones. This result is consistent with recent determinations for other clusters, and supports the theory that the Galactic globular cluster system is essentially coeval. The cluster main sequence luminosity function has been constructed, and is compared with recent observations and theory. In Chapter 5, a preliminary colour-magnitude study of the SMC cluster Lindsay 11 is presented.

No description available.

No description available.

L’aptitude des zéolithes à initier spontanément des séparations de charges durables constitue une de leurs propriétés les plus fascinantes. Dans le cadre de cette étude, l’adsorption de trois amines aromatiques (phénothiazine, tétraméthyl-p-phénylènediamine et diéthylaniline) possédant un potentiel d’ionisation faible (< 7 eV) a été étudiée dans des zéolithes à canaux de types mordénite, ZSM-5 et Ferriérite. Ces échantillons ont été caractérisés par spectroscopie d’absorption UV-visible par réflexion diffuse, spectroscopie de diffusion Raman et résonance paramagnétique électronique. Les effets de la largeur des pores et de la longueur de la chaine alkyle portée par la molécule ont ainsi été testés. L’ensemble des résultats a mis en évidence le rôle essentiel de l’effet du confinement sur le processus d’ionisation et sur la stabilisation des états de charges séparées pendant de longues durées. L’observation d’espèces radicalaires de longues durées de vie s’explique par un éloignement des électrons éjectés par rapport au site d’ionisation de la molécule (compartimentalisation).Le deuxième enjeu de cette thèse est consacré à l’étude d’une nouvelle voie de synthèse de nanoclusters d’argent au sein du réseau poreux des zéolithes. La formation des clusters est initiée par la réduction de cations Ag+ suite à l’ionisation spontanée ou photoinduite d’une molécule aromatique donneuse d’électron préalablement adsorbée dans les canaux. Les premières étapes de formation de ces nanoclusters d’argent ont été identifiées grâce à la spectroscopie d’absorption UV-visible résolue en temps et à l’utilisation de nanoparticules de zéolithes en solution colloïdale. / One of the most intriguing properties of zeolite is their ability to promote spontaneously ionization through mere incorporation of electron donor molecules in their porous framework. In the present work, we describe the sorption of three aromatic amines (phenothiazine, tetramethyl-p-phenylenediamine and diethylaniline) with low ionization potential values (< 7 eV) within the porous void of channel type zeolites. Spectroscopic and modeling results show that molecule incorporation, charge separation and charge recombination differed dramatically among zeolites with respect to channel structure (ferrierite, ZSM-5, mordenite). The ionization rates and ionization yield values demonstrate that a strong synergy exists between the polarization energy of the channel inner space and spatial constraints imposed by the channel topology as well as by molecule steric constraints. The compartmentalization of ejected electron away from the initial site of ionization decreases dramatically the propensity of charge recombination.The second part of this study shows a new way of synthesis for silver nanoclusters into the void space of zeolite. Cluster formation is initiated by Ag+ reduction through spontaneous or laser photolysis ionization of an electron donor molecule previously occluded in the zeolite channel. The first steps of silver cluster formation are identified by using time resolved spectroscopy and zeolite nanoparticles in colloidal solution.

La dialectique territoire - économie est interrogée depuis les métropoles régionales indiennes dans lesquelles s’agglomèrent des activités de services informatiques et de conception logicielle. Les villes de Pune (Maharashtra), Thiruvananthapuram et Kochi (Kerala) constituent de véritables laboratoires d’observation du processus technopolitain. L'objet de la recherche est le système territorial potentiellement innovant saisi à travers ses phases d’apparition, de croissance et d’adaptation. La thèse démontre que la genèse des clusters de haute technologie dans une logique de remontée de filière est soumise à la réalisation simultanée de conditions contextuelles et de jeux d’acteurs favorables. La géographie économique de l’innovation et la géographie urbaine éclairent ce constat, en permettant une lecture multi-échelle et sur le temps long du dynamisme des systèmes. La recherche souligne le rôle moteur des pouvoirs publics centraux et régionaux, tantôt initiateurs tantôt facilitateurs, dans l’accompagnement et le développement d’un secteur informatique à haut contenu technologique et scientifique. Par ailleurs, l’étude des lieux met en évidence l’étroite imbrication de la fabrique urbaine et technopolitaine. La construction de l’attractivité engendre des processus d’enclosure dépassant les activités économiques pour aller toucher les quartiers bénéficiant de la métropolisation. Enfin, la question de l’ancrage des activités numériques dans le tissu urbain met en perspective l’entrepreneur à la fois mondialisé, encastré localement et aux prises avec son implication dans des réseaux sociaux professionnels dont les initiatives contribuent à façonner l’évolution du système. / Dialectic of territory and economy is questioned from regional metropolitan areas located in India, where Information Technology and software activities cluster. Cities of Pune (Maharashtra), Kochi and Thiruvananthapuram (Kerala) represent some interesting labs to observe cumulative effects of the technopolitan process. The main research purpose is to grasp innovative spatial systems within three of its evolution stages: genesis, growth and adjustment capacities. From a perspective of climbing up the value-chain, this thesis aims to demonstrate the making of high-tech clusters is realized by simultaneous favorable actors’ play, stakeholders’ interactions and changing contexts. Economic geography of innovation and urban planning clarify this fact, by providing analyzing tools of multi-scaled and long-term system’s dynamics. Research underlines the leveraging effect of central and regional policies makers - either initiator, either facilitator - by encouraging strong economic, scientific and technological environment to develop software sector. In addition, studying places evidences overlapping of both urban and technopolitan fabric. Beyond the only IT parks, we prove that competitiveness strategies fraction the whole space getting benefits from metropolization. Finally, the examination of IT initiatives’ embeddedness within the city leads us to put forward the entrepreneur, at the same time world linked and localized. Furthermore, their deep involvement in social, scientific and professional networks implements good conditions for the innovative spatial systems evolution.

La compréhension du comportement des actinides dans l’environnement est un enjeu important et très complexe en raison des nombreux phénomènes intervenant dans les processus chimiques. Parmi eux, nous pouvons citer la complexation, notamment via les fonctions carboxylates issues des substances humiques présentes dans les sols. En milieu aqueux, les actinides au degré d’oxydation IV sont très sensibles à l’hydrolyse impactant alors leur mobilité. Au cours de ce travail de thèse, nous avons étudié la réactivité de ces actinides(IV) (Th, U et Np) en présence de ligands organiques de type carboxylate aromatique, afin d’enrichir nos connaissances sur les entités formées. Plus de quarante nouveaux composés à base d’actinides(IV) et d’acides polycarboxyliques ont été synthétisés. Leurs structures cristallographiques ont été déterminées par DRX sur monocristal et leurs descriptions sont rapportées. Le contrôle de l’hydrolyse de ces métaux au sein de nos composés a été effectué par une variation de l’acidité en milieu aqueux ou par ajout contrôlé de quantités d’eau dans des solvants organiques. Certains des composés présentés sont construits autour d’assemblages polynucléaires possédant entre 2 et 38 centres métalliques. Pour ces derniers ({U38} et {Np38}), une nouvelle voie de synthèse a été investiguée. Au cours de l’étude de ces différents composés, nous avons mis en évidence les analogies ou les différences existant entre ces actinides, et avons enrichis notamment nos connaissances sur la cristallochimie du neptunium(IV). Enfin, nous avons montré la capacité de ligands N- et O- donneurs à complexer simultanément l’uranium(IV) avec d’autres métaux di- (Mn) ou trivalent (Ln). / Understanding the behavior of actinides in the environment is an important and very complex issue due to phenomena involved in chemical processes. Among them, one can mention the complexation, via carboxylate functions from the humic substances present in the soils. In an aqueous medium, actinides at the oxidation state IV are very sensitive to the hydrolysis process impacting their mobility. This thesis focuses the reactivity of these actinides (IV) (Th, U and Np) in the presence of organic ligands with aromatic carboxylate functions, in order to improve our knowledge about entities formed and linked to such organic linkers.More than forty new compounds based on actinides (IV) and polycarboxylic acids have been synthesized. Their crystallographic structures were determined by single crystal XRD and their descriptions are reported. The control of the hydrolysis of these metals within our compounds has been managed by varying the acidity in aqueous medium or by addition of controlled amount of water in organic solvents. Some of the compounds presented are built from polynuclear moieties having from 2 to 38 metal centers. For the latter ({U38} and {Np38}), a new synthetic pathway was investigated. During the study of these different compounds, we have demonstrated the analogies or the differences existing between these actinides, and have improved our knowledge on the crystallochemistry of neptunium (IV). Finally, we proved the ability of N- and O-donor ligands to simultaneously complex the uranium (IV) with other di- (Mn) or trivalent (Ln) metals.

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Realistic star cluster simulations that dynamically evolve embedded star clusters require an accurate treatment of the stars, gas and their interaction. We present and validate a novel technique which creates an initial gas density distribution based on observational gas column density data. We consider two approaches to this technique where the first is based on randomly sampling from the original gas density distribution and the second assigns one particle to represent the gas in each observed image pixel. To create a three-dimensional distribution, we consider two estimates of cloud depth where one is a constant value and the second involves variable depths calculated using image processing techniques based on density features seen in the plane of the sky. We apply these methods to evolve the Carina region using initial stellar positions derived from the MYSTiX catalogue and gas data from the Herschel Hi-GAL survey. We evolve the stars using an N-body code and the gas using a smoothed-particle hydrodynamics code which are coupled through the AMUSE framework. We analyzed our results using dendrograms to describe the gas distribution over time and the DBSCAN clustering algorithm to track the clustering of stars over time. We model the gas using an adiabatic ideal gas equation of state and find that increasing the initial gas velocity dispersion prevents gas from accumulating and therefore could hinder future star formation. We also find that the stars, initially in subclusters spatially (not necessarily bound), tend to merge together to form one large cluster regardless of the initial conditions of the gas. It is only after the subclusters have merged that the initial conditions of the gas start to have a noticeable effect on the structure of the star cluster. Of the two approaches to our novel technique, the second approach leads to more accurate and realistic results. The second approach also has a significant effect on the stars as the subclusters merge together approximately 1 Myr earlier compared to the first approach. Therefore the choice of initial gas conditions affects the dynamical evolution of star cluster systems and being able to incorporate observational gas data leads to the increasingly accurate dynamical evolution of such systems. / Thesis / Master of Science (MSc)