Entender a relação entre riqueza de espécies e diversidade de nichos ecológicos pode auxiliar a compreensão dos diferentes processos que governam a coexistência de espécies. Caracterizar o nicho de diversas espécies não é trivial, e o nicho é frequentemente estudado a partir de características morfológicas. A massa corpórea está relacionada com características metabólicas, fisiológicas, comportamentais e ecológicas das espécies e então é ideal para estudos ecológicos que envolvem muitas espécies e localidades. Em teoria, um aumento na riqueza de espécies poderia ocorrer tanto pela expansão do espaço de nicho total, quanto pelo empacotamento de nicho, ou mesmo por uma combinação de ambos. Neste trabalho utilizamos massa corpórea de mamíferos terrestres para investigar a ocupação do morfoespaço e a relação dessa ocupação com a riqueza de espécies tanto em assembleias locais, quanto em biotas continentais. No primeiro capítulo desta dissertação, investigamos a variação espacial da disparidade morfológica de mamíferos terrestres e sua relação com a riqueza de espécies. Utilizamos os dados de distribuição geográfica de 4146 espécies para determinar a composição de assembléias locais em um grid com células com 1º de lado. Para cada assembleia, calculamos quatro medidas de disparidade morfológica utilizando massa corpórea como um descritor da morfologia de mamíferos. Comparamos as medidas de disparidade de cada célula com o que seria esperado de acordo com dois modelos nulos (um global e outro regional) que diferem em relação ao pool utilizado para reamostragem. No segundo capítulo, investigamos o efeito da extinção da megafauna e os possíveis efeitos das extinções atuais na distribuição de massa de mamíferos terrestres. De acordo com trabalhos anteriores a distribuição de massa de mamíferos tornou-se bimodal 40 milhões de anos atrás e assim se manteve até o final do Pleistoceno, quando foi modificada pela extinção da megafauna, tornando-se unimodal. Ajustamos dois modelos concorrentes (bimodal e unimodal assimétrico) às distribuições de massa corpórea dos mamíferos de todo o globo e de cada continente separadamente em três momentos de tempo: Final do Pleistoceno, Holoceno e Antropoceno. Os resultados obtidos nos dois capítulos, apesar de observados em escalas muito distintas, sugerem um padrão de empacotamento de nichos nos Neotrópicos. Esse padrão não é influenciado pela extinção da megafauna, e se deve à diversificação de grupos específicos no continente sul americano. Grande parte das espécies dos grupos endêmicos são arborícolas sugerindo a importância das florestas tropicais na diversificação de mamíferos desse continente. Nossos resultados também sugerem que a perda das espécies ameaçadas de extinção no Antropoceno irão resultar em mudanças significativas na África e na Eurásia, dois continentes menos afetados pelas extinções do Pleistoceno / Understand the relation between species richness and ecological niche diversity might help to understand processes behind species coexistence. However, to quantify species niche is not easy and a ecomorfological approach is often used instead. Body mass is related to several life history traits such as metabolism, physiology, behaviour and ecology, thus being the ideal trait for studies comparing many different species and localities. In theory, increases in species richness could be attained by an expansion of total niche space or by niche packing, or even by a combination of both. Here we use terrestrial mammals body mass to investigate morphospace occupation and its relation to species richness in both local assemblages and continental biotas. In the first chapter, we investigate the spatial variation of morphological disparity of terrestrial mammals and its relation to species richness. We used species distributions of 4146 species to determine the composition of local assemblages in a grid of 1º cells. For each assemblage we measured four morphological disparity metrics using body mass as a surrogate of mammalian morphology. We compared the observed disparity measures for each cell with the expected distribution given by two null models (one global and other regional) that differ for the species pool used to perform resamples. In the second chapter we investigated the effect of megafauna extinctions and possible effects of ongoing extinctions on the body mass distribution of terrestrial mammals. Previous studies suggest that the body mass distribution of mammals became bimodal 40 million years ago and so remained until the end of the Pleistocene, when it was modified by megafauna extinction and became unimodal. We fitted two concurring models (a bimodal and a skewed unimodal) to the body mass distribution of global mammals and of each continent separately in tree time frames: Late Pleistocene, Holocene and Anthropocene. The results from both chapters, although from observation in different scales, suggest a pattern of niche packing on the Neotropics. This pattern is not biased by the recent megafauna extinction, but is due to the diversification of clades specific to the South American continent during its period of isolation. A high proportion of the species in these endemic groups is arboreal suggesting the importance of tropical forests in the diversification of mammals in this continent. Our results also suggest that the possible loss of endangered species in the Anthropocene will result in meaningful changes in Africa and Eurasia, two continents that where less affected by Pleistocene extinctions

Entender a relação entre riqueza de espécies e diversidade de nichos ecológicos pode auxiliar a compreensão dos diferentes processos que governam a coexistência de espécies. Caracterizar o nicho de diversas espécies não é trivial, e o nicho é frequentemente estudado a partir de características morfológicas. A massa corpórea está relacionada com características metabólicas, fisiológicas, comportamentais e ecológicas das espécies e então é ideal para estudos ecológicos que envolvem muitas espécies e localidades. Em teoria, um aumento na riqueza de espécies poderia ocorrer tanto pela expansão do espaço de nicho total, quanto pelo empacotamento de nicho, ou mesmo por uma combinação de ambos. Neste trabalho utilizamos massa corpórea de mamíferos terrestres para investigar a ocupação do morfoespaço e a relação dessa ocupação com a riqueza de espécies tanto em assembleias locais, quanto em biotas continentais. No primeiro capítulo desta dissertação, investigamos a variação espacial da disparidade morfológica de mamíferos terrestres e sua relação com a riqueza de espécies. Utilizamos os dados de distribuição geográfica de 4146 espécies para determinar a composição de assembléias locais em um grid com células com 1º de lado. Para cada assembleia, calculamos quatro medidas de disparidade morfológica utilizando massa corpórea como um descritor da morfologia de mamíferos. Comparamos as medidas de disparidade de cada célula com o que seria esperado de acordo com dois modelos nulos (um global e outro regional) que diferem em relação ao pool utilizado para reamostragem. No segundo capítulo, investigamos o efeito da extinção da megafauna e os possíveis efeitos das extinções atuais na distribuição de massa de mamíferos terrestres. De acordo com trabalhos anteriores a distribuição de massa de mamíferos tornou-se bimodal 40 milhões de anos atrás e assim se manteve até o final do Pleistoceno, quando foi modificada pela extinção da megafauna, tornando-se unimodal. Ajustamos dois modelos concorrentes (bimodal e unimodal assimétrico) às distribuições de massa corpórea dos mamíferos de todo o globo e de cada continente separadamente em três momentos de tempo: Final do Pleistoceno, Holoceno e Antropoceno. Os resultados obtidos nos dois capítulos, apesar de observados em escalas muito distintas, sugerem um padrão de empacotamento de nichos nos Neotrópicos. Esse padrão não é influenciado pela extinção da megafauna, e se deve à diversificação de grupos específicos no continente sul americano. Grande parte das espécies dos grupos endêmicos são arborícolas sugerindo a importância das florestas tropicais na diversificação de mamíferos desse continente. Nossos resultados também sugerem que a perda das espécies ameaçadas de extinção no Antropoceno irão resultar em mudanças significativas na África e na Eurásia, dois continentes menos afetados pelas extinções do Pleistoceno / Understand the relation between species richness and ecological niche diversity might help to understand processes behind species coexistence. However, to quantify species niche is not easy and a ecomorfological approach is often used instead. Body mass is related to several life history traits such as metabolism, physiology, behaviour and ecology, thus being the ideal trait for studies comparing many different species and localities. In theory, increases in species richness could be attained by an expansion of total niche space or by niche packing, or even by a combination of both. Here we use terrestrial mammals body mass to investigate morphospace occupation and its relation to species richness in both local assemblages and continental biotas. In the first chapter, we investigate the spatial variation of morphological disparity of terrestrial mammals and its relation to species richness. We used species distributions of 4146 species to determine the composition of local assemblages in a grid of 1º cells. For each assemblage we measured four morphological disparity metrics using body mass as a surrogate of mammalian morphology. We compared the observed disparity measures for each cell with the expected distribution given by two null models (one global and other regional) that differ for the species pool used to perform resamples. In the second chapter we investigated the effect of megafauna extinctions and possible effects of ongoing extinctions on the body mass distribution of terrestrial mammals. Previous studies suggest that the body mass distribution of mammals became bimodal 40 million years ago and so remained until the end of the Pleistocene, when it was modified by megafauna extinction and became unimodal. We fitted two concurring models (a bimodal and a skewed unimodal) to the body mass distribution of global mammals and of each continent separately in tree time frames: Late Pleistocene, Holocene and Anthropocene. The results from both chapters, although from observation in different scales, suggest a pattern of niche packing on the Neotropics. This pattern is not biased by the recent megafauna extinction, but is due to the diversification of clades specific to the South American continent during its period of isolation. A high proportion of the species in these endemic groups is arboreal suggesting the importance of tropical forests in the diversification of mammals in this continent. Our results also suggest that the possible loss of endangered species in the Anthropocene will result in meaningful changes in Africa and Eurasia, two continents that where less affected by Pleistocene extinctions

The physical explanation for the existence of the galactic warp is one of the major research areas in Astronomy. People have proposed various theories but nobody has yet given a convincing explanation. Most of the spiral galaxies are observed to be warped which reveals that the galactic warp is a stable characteristic. In the theory of kinematic bending wave, warp is considered as a wave that is propagated through the galactic disk with a speed called pattern speed. If the pattern initially had straight line of nodes, according to bending wave theory, the warp would tend to wind up rapidly in the gravitational field of galactic disk. But still we observe warped galaxies in the sky. In the literature, it has been claimed that the winding problem of galactic warp may be solved by incorporating the effect of gravitational field of the dark matter halo in which the galactic disk is embedded. Recently some works on the dynamics of galactic disk claim that the shape of the dark matter halo is pro late spheroid. In this thesis, the effect of the gravitational field of a prolate spheroidal dark matter halo with varying eccentricity to the galactic warp is calculated and discussed. Chapter1 gives the general introduction of the topics discussed in the following chapters. The structure of the spiral galaxy, their classifications, and the disk dynamics are discussed in the first few sections. One of the revolutionary concepts that emerged in the previous century was the existence of the dark matter. Presently tracing the mass distribution and the constituent particles of dark matter is one of the major research areas in theoretical and experimental physics. In this thesis, the effect of a particular type of mass distribution in dark matter halo on the warp is discussed in detail. In the next few sections, the following topics are discussed namely; how the concept of dark matter came into astrophysics, how to measure the total mass inside a given radius and what are the different distributions used for various purposes. A new theory called Modified Newtonian Mechanism was also proposed in the previous century as an alternative to the dark matter concept which is also discussed briefly. Kinematic bending wave theory and the winding problem of the galactic warp is also discussed in detail. In the last section a relation between the pattern speed of the warp and the shape of the dark matter halo is obtained. The calculation of the potential of a prolate spheroidal mass distribution with varying eccentricity is not done in any literature as we know. The calculation of the potential and the patten speed of prolate spheroidal mass distributions and of the galactic disk are described in chapter 2. The calculations of oblate spheroidal mass distribution are also discussed in this chapter but that is out of main theme. In chapter 3 we apply the equations obtained in the Chapter 2 to one simple toy model and to the Galaxy. The rotation curve and the pattern speed of a warp in the gravitational field of prolate spheroidal mass distribution of varying eccentricity are described. Usually the Milky Way disk is treated as an in infinitesimally thin disk but for our calculations the three dimensional but thin disk is used. The usually people use some approximation to calculate the potential due to galactic infinitesimal thin disk. The difference of the work from earlier works done by different people(with the approximation mentioned in above line) is also discussed in this Chapter. Chapter 4 discusses the summary of the entire work.

La cellulose est un biopolymère naturel et très abondant. Selon son origine et son mode d’extraction, elle présente des propriétés de cristallinité et de longueur de chaînes variables. Les interactions hydrogène entre les chaînes de cellulose sont en grande partie responsables de son organisation et forment un réseau très dense qui limite sa solubilité. Sa dissolution, complète et non-dégradante, est donc compliquée et dépend de la capacité du solvant à rompre ces liaisonshydrogène intermoléculaires. L’analyse de la cellulose par chromatographie d’exclusion stérique (SEC) pour suivre l’évolution des distributions de masses molaires (DMM) au cours des procédés de transformation est donc toujours problématique. Le système de solvant le plus commun estactuellement le chlorure de lithium/N,N-diméthylacétamide (LiCl/DMAc) qui est extrêmement toxique. L’objectif de ce travail est le développement d’une méthode d’analyse des DMM de la cellulose dans des conditions moins toxiques et adaptée à tous les types de cellulose. Parmi les nombreux systèmes de solvant décrits dans la littérature, 3 systèmes, plus verts et nondérivatisants, ont été sélectionnés afin d’identifier un système de solvant permettant la dissolution,sans dégradation, d‘échantillons de cellulose de cristallinité et de masse molaire moyenne variables afin de remplacer LiCl/DMAc. Les analyses thermogravimétriques et les mesures viscosimétriques ont permis d’évaluer et de comparer les modifications de 4 échantillons de cellulose dissous dans ces 3 systèmes et dans le LiCl/DMAc. LiCl/DMAc dégrade les celluloses de plus haute masse molaire (-cellulose et Vitacel), réduisant de 50 % les longueurs de chaîne après dissolution. Le système tétrabutylammonium/diméthylsulfoxide (TBAF/DMSO) permet une dissolution rapide des 4 échantillons de cellulose sans dégradation ou modification majeure. Le système TBAF/DMSO a, par la suite, été privilégié pour la caractérisation des échantillons en SEC. Du fait d’interactions possibles entre les groupements aromatiques composant la phase stationnaire et les molécules de TBAF, le système complet n’a pas pu être utilisé comme éluant. L’éluant choisi a donc été le DMSO mais qui, seul, ne solubilise pas les échantillons cellulosiques. Les molécules de TBAF sont cependant indispensables au mécanisme de dissolution et laconcentration en TBAF dans le DMSO a dû être adaptée en fonction des échantillons. Pour les échantillons cellulosiques de faible masse molaire, une concentration en TBAF de l’ordre de 1 %(m/v) est suffisante et permet de réaliser une analyse des masses molaires satisfaisantes. Pour les échantillons de plus haut poids moléculaire, cette concentration n’est plus suffisante pour les dissoudre convenablement. Or, avec des concentrations plus élevées, des phénomènesd’agrégation provoque l’élution d’une partie importante des macromolécules dans le volume mort, comme observé avec l’analyse de standards de pullulane. / Cellulose is a very abundant natural biopolymer. According to its origin and to its extraction mode, it presents various cristallinity rate and molar mass. Its organization relies mainly on intermolecular hydrogen bonds that form a strong network and thus limitating cellulose solubility. Complete andnon-degradative dissolution is then complicated and depends on the solvent ability to disrupt these hydrogen bonds. Analysis of the molar mass distribution (MMD) of cellulose by size exclusion chromatography (SEC) of cellulose is consequently problematic while the study of the evolution of cellulose molar mass during transformations could be extremely useful in many processes. The most common solvent used in SEC is lithium chloride/N,N-dimethylacetamide (LiCl/DMAc), which is extremely toxic. The aim of this PhD study is then to develop a new analytical method to characterize cellulose MMD using safer solvents and adapted to all kinds of cellulosic sample. Among the numerous non-derivatizing solvent systems described in the literature, three of themhave been selected. Greener and less toxic than LiCl/DMAc, their ability to dissolve cellulosic sample of various cristallinity and average molar mass without degradation was then tested. Thermogravimetric analyses and viscosimetric studies allowed to evaluate and to compare the modifications involved by the dissolution for four different cellulosic samples. LiCl/DMAc degraded the samples of higher molar mass (-cellulose and Vitacel) decreasing their degree ofpolymerization by 50 % after dissolution. Tetrabutylammonium/dimethylsulfoxide (TBAF/DMSO) system allows rapid dissolution of the 4 cellulose samples, without major degradation or modification. TBAF/DMSO system was then studied as solvent for SEC analysis of these cellulose samples. Due to the interactions between the aromatic groups composing the stationary phase with TBAF molecules, the complete system could not be used as eluant. Chosen eluant was then DMSO alone. However, as the TBAF molecules are mandatory for the dissolution of cellulose, TBAF concentration was adapted according to the cellulose nature for the preparation of the samples. For low molar mass cellulose samples, a TBAF concentration of 1 %(w/v) was sufficient and allowed to performed correctly the chromatographic analysis. For the samples of higher molar mass, this concentration was not high enough to complete the dissolution. Using, higher concentrations caused aggregation phenomena resulting in the elution of a large amount of the macromolecules in the dead volume, as observed with the analysis of pullulan standards.

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2017-09-15T18:57:49Z No. of bitstreams: 1 2014 - Ana Carolina Carvalho de Barros.pdf: 2646968 bytes, checksum: 755045d3111f54dc02cc0c3c6834d0c5 (MD5) / Made available in DSpace on 2017-09-15T18:57:49Z (GMT). No. of bitstreams: 1 2014 - Ana Carolina Carvalho de Barros.pdf: 2646968 bytes, checksum: 755045d3111f54dc02cc0c3c6834d0c5 (MD5) Previous issue date: 2014-09-22 / CAPES / This study was carried out for evaluating the dynamics of the root dry matter stock in Florico grass pastures managed at two light interception levels (90 and 95%) and two post-grazing residue heights (0.2 and 0.3 m) (90IL 0,2m RPP; 90IL 0,3m RPP; 95IL 0,2m RPP; 95IL 0,3m RPP). The lowering of vegetation was performed by the technique "mob grazing", simulating the condition of intermittent grazing. In shoot mass were related (MFF and MF) and the rate of herbage accumulation (TAMFF and TAF) with varying root system, using the technique of digging trenches 0,5x0,4x0,6 me withdraw prism?sticos blocks per monoliths 0,05x0,2x0,1 m up to 0.4 m profundida for root stock and fractional distribution (DF), and the root / shoot ratio, and total biomass (FT). The experiment was performed at PESAGRO-RIO, in Serop?dica municipality, Rio de Janeiro state , from July, 2012 to July, 2013, covering the four seasons. Shoots fresh matter yield was effective for treatment, season, and repeated measures interaction, with total production in the summer of 2013 for the four grazing intensities (908.1 ? 73.8 g/m2), compared to other seasons where treatments were similar. In the season of different days between cycles, shoots fresh matter yield was estimated where the winter, presented the lowest yield (10.8 ? 5.1 g/m2 day 1), when compared to the rainy season (28,7 ? 13.1 g/m2 day 1), as well as, between the treatments, the highest grazing intensity presented the greatest yield (26.6 ? 15.8 g/m2 day 1) while the lowest one presented the smallest yields (13.6 ? 4.1 g/m2 day 1). Shoots dry matter yield indicated high significant effects for treatments, season, and interaction for repeated measurements over time between treatments the 90IL 0,3RPP treatment presented no difference in relation to shoot dry matter among seasons, whereas 95IL 0,3RPP treatment presented greater shoot dry matter quantity in the spring (219.8 g/m2 cycle 1), followed by summer (192.2 g/m2 cycle 1), as well as, in the autumn 90IL 0,3RPP treatment was more productive than 95IL 0,3RPP one. Shoot dry matter yield was lower in all the treatments in the winter when compared to the other seasons, the greatest roots dry matter (RDM) were: 639.3 ? 246.8 and 667.2 ? 225.7 g 400dm3 soil in the spring, for 90IL 0,3RPP and 95IL 0.3 RPP, respectively and 591.8 ? 168.2 and 655.1 ? 252.7g 400 dm3 soil in the summer anol autumn, for 90IL 0.2RPP respectively 647.8 ? 68.4g 400 dm3 soil in the autumn for 95IL 0,2RPP treatment. In regarding to the roots distribution profile there was no difference between RDM stock treatments between grazing intensities evaluated, summer and autumn equations did not differ eithen. In fractional root distribution all the seasons presented significative results, being autumn the single one no differing between treatments on the present study. Total phytomass presented significantive effect for the treatments, where the winter was the season presenting the lowest yield in all the treatments, when compared to other stations. Root:shoot ratio was no effect for treatment and season, as well as, the autumn highlighted with the greatest RDM:SDM ratio in 95IL 0,2RPP treatment, when compared to the other seasons. It might be concluded that The Florico grass was sensitive to variations in weather conditions presenting to the accumulation of forage and root stock, showing the existence of phenotypic plasticity for the evaluated variables. / Objetivou-se avaliar o estoque de massa seca de raiz em pastos de capim Florico manejados sob dois n?veis de intercepta??o luminosa (90 e 95 %) e duas alturas de res?duo p?s-pastejo (0,2 e 0,3 m), os quais deram origem a quatro tratamentos de intensidades de pastejo (90IL 0,2m RPP; 90IL 0,3m RPP; 95IL 0,2m RPP; 95IL 0,3m RPP). O rebaixamento da vegeta??o foi realizado pela t?cnica ?mob grazing?, simulando a condi??o de pastejo intermitente. Na parte a?rea foram relacionados massa (MFF e MF) e a taxa de ac?mulo de forragem (TAMFF e TAF) com vari?veis do sistema radicular, utilizando a t?cnica de escava??o de trincheiras de 0,5x0,4x0,6 m e retirada de blocos prism?sticos por mon?litos de 0,05x0,2x0,1 m, at? a profundida de 0,4 m para o estoque radicular e distribui??o fracional (DF), al?m da rela??o raiz/parte a?rea e fitomassa total (FT). O experimento foi conduzido na PESAGRO-RIO, em Serop?dica, Rio de Janeiro, de julho de 2012 a julho de 2013, durante quatro esta??es do ano. A massa fresca de forragem variou com tratamento, esta??o do ano e com a intera??o entre eles (p<0,01), apresentando maiores valores no ver?o com 908,1 ? 73,8 g m-2 (m?dias dos quatro tratamentos de pastejo), comparado com as demais esta??es que foram semelhantes entre si. Devido a varia??o existente entre os ciclos de pastejos, em dias, foi calculado a taxa de ac?mulo de forragem de massa seca de forragem, com menor valor obtido no inverno (10,8 ? 5,1 g m-2 dia-1), quando comparado ao per?odo chuvoso (28,7 ? 13,1 g m-2 dia-1). Maior taxa de ac?mulo de forragem massa fresca de forragem foi obtida para o tratamento (90IL 0,2m RPP) de maior intensidade de pastejo (26,6 ? 15,8 g m-2 dia-1) e, menor valor, para aquele (95IL 0,3m RPP) de menor intensidade (13,6 ? 4,1 g m-2 dia-1). A massa seca de forragem n?o variou (p>0,05) entre as esta??es para o tratamento 90IL 0,3m RPP, enquanto que, o tratamento 95IL 0,3RPP, na primavera e ver?o, apresentou maior massa, (219,8 e 192,2 g m-2 ciclo-1), enquanto o tratamento 90IL 0,3RPP foi mais produtivo que o 95IL 0,3RPP no outono. A produ??o de massa seca radicular (MSR) do inverno foi inferior aquelas das demais esta??es. Na primavera, os maiores estoques de MSR foi de: 639,3 ? 246,8 e 667,2 ? 225,7 g 400dm3 de solo, respectivamente , para 90IL 0,3m RPP e 95IL 0,3m RPP; enquanto que o tratamento 90IL 0,2m RPP apresentou maiores estoques de MSR: 591,8 ? 168,2 e 655,1 ? 252,7 g 400dm3 de solo-1, respectivamente no ver?o e outono e o tratamento 95IL 0,2m RPP estocou maiores quantidades de MSR no outono (647,8 ? 68,4 g 400dm3 de solo-1). Quanto a distribui??o das ra?zes no perfil, houve diferen?a do estoque de MSR entre tratamentos na primavera e, as equa??es do ver?o e outono n?o diferiram entre si. A distribui??o fracional do sistema radicular variou (p<0,05) entre todas as esta??es, por?m no outono, houve semelhan?a entre os tratamentos. A produ??o de fitomassa total variou (p<0,05) entre os tratamentos, com a menor produ??o no inverno, para os tratamentos. A rela??o raiz: parte a?rea variou (p<0,05) com tratamento e esta??o. Para 95IL 0,2m RPP, maior valor foi obtido no outono. O capim Florico foi sens?vel ?s condi??es clim?ticas apresentando varia??es quanto ao ac?mulo de forragem e estoque radicular, evidenciando a exist?ncia de plasticidade fenot?pica para as vari?veis avaliadas.

De nouveaux modèles d'atmosphère sont présentés, incluant les profils de raie d'hélium neutre améliorés de Beauchamp (1995) et le formalisme de probabilité d'occupation pour ce même atome. Ces modèles sont utilisés pour calculer une grille de spectres synthétiques correspondant à des atmosphères riches en hélium et contenant des traces d'hydrogène. Cette grille est utilisée pour déterminer les paramètres atmosphériques principaux des étoiles de notre échantillon, soient la température effective, la gravité de surface et l'abondance d'hydrogène. Notre échantillon contient des spectres visibles de haut rapport signal-sur-bruit pour 102 naines blanches riches en hélium, dont 29 ont été observés au cours de ce projet, ce qui en fait le plus grand échantillon de spectres de qualité de naines blanches riches en hélium. Des spectres synthétiques ont été calculés en utilisant différentes valeurs du paramètre α de la théorie de la longueur de mélange dans le but de calibrer empiriquement la valeur de ce paramètre pour les DB. Afin d'améliorer la précision sur les paramètres atmosphériques de quelques étoiles, nous avons utilisé des spectres couvrant la raie Hα pour mieux déterminer l'abondance d'hydrogène. Finalement, nous avons calculé la distribution de masse de notre échantillon et la fonction de luminosité des DB. La distribution de masse montre une coupure à 0.5 fois la masse solaire qui est prédite par les modèles d'évolution stellaire et dévoile une masse moyenne significativement plus élevée pour les étoiles de type DBA. La masse moyenne de l'ensemble des DB et DBA est très proche de celle des DA. La fonction de luminosité nous permet de calculer que le rapport du nombre de DB sur le nombre de DA vaut environ 25%. / New model atmospheres are presented, including improved neutral helium lines from Beauchamp (1995) and the occupation probability formalism for that atom. These models are used to compute a grid of synthetic spectra for helium rich atmospheres with different hydrogen abundances. This grid is used to determine the principal atmospheric parameters of the stars in our sample, e.g. effective temperature, surface gravity and hydrogen abundance. There are 102 high quality spectra of helium-rich white dwarfs in our sample, making it the largest sample of this kind. 29 of these spectra were observed for this project. Synthetic spectra using different values of the α parameter from the mixing length theory have been calculated in order to determine the correct value of this parameter for DB model atmospheres. Finally, we have computed the mass distribution of our sample and the DB luminosity funtion. The mass distribution shows a clear cutoff at 0.5 solar masses which is predicted by stellar evolution theory and gives a significantly higher mean mass for the DBA stars of the sample. However, the global mean mass of our sample is very close to that of DA stars. With our luminosity function, we found a number ratio of DB stars over DA stars of about 25%.

Neste trabalho apresentamos um estudo das reações de spallation a energias interme- diárias em núcleos actinídeos e pré-actinídeos. Para esta finalidade foi utilizado o modelo de Monte Carlo CRISP (Colaboração Rio-São Paulo), que neste estudo foi importante na reprodução da distribuição de massa de produtos residuais e as seções de choque de fissão e espalação. Estes observáveis são importantes para o estudo de Reatores Hibridos ADS considerado como dispositivos promissores para a transmutação de resíduos nucle- ares. Os modelos físicos necessários para uma correta simulação de dados experimentais foram já implementadas no CRISP, como o modelo de evaporação para emissão de par- tículas descrito por Weisskopf de 1937, e para fissão o clássico modelo de Bohr/Wheeler de 1939. Para a obtenção da distribuição dos fragmentos de massa de fissão o CRISP conta também com um modelo baseado na parametrização multimodal de fissão, que si- mula os processos de fissão simétrica e assimétrica predominantes em altas e baixas ener- gias, respectivamente. Os resultados obtidos do CRISP depois da aplicação dos modelos mencionados, foram os rendimentos de massa dos fragmentos residuais, os quais foram analisadas para o cálculo da seção de choque de fissão e espalação mediante uma fórmula implementada no modelo. Com o resultado se fez o gráfico da distribuição de massa para cada uma das reações analisadas. Uma das reações estudadas foi a reação induzida por fótons de Bremsstrahlung com energias máximas de 50 e 3500 MeV em um alvo de 181 Ta, calculando a distribuição de massa de fissão e espalação, mostrando bons resultados de acordo com os dados experimentais. Nas reações induzidas por prótons foram calcula- das as seções de choque de fissão e espalação assim como sua respectiva distribuição de massa dos produtos residuais. Neste caso estudamos duas reações, sendo: a reação p (1 GeV) + 208 Pb, e a reação de p (660 MeV) + 238 U. Para a primeira reação com chumbo os resultados do CRISP foram comparados com dados experimentais, e também com os resultados obtidos do modelo MCNPX-Bertini do trabalho de Baylac-Domengetroy de 2003, que simulou a mesma reação com chumbo. Obtendo-se melhores resultados com o CRISP mas com uma superestimação de dados no final da distribuição calculada. No caso do urânio, foi necessário usar a chamada fissão superassimétrica porque a distribuição de massa experimental é mais complexa e o modelo multimodal clássico não é suficiente para sua correta simulação. Foi também estudado as reações induzidas por dêuterons usando o modelo CRISP, mostrando os resultados da distribuição de massa para 197 Au e 208 Pb com algumas limitações do modelo para este tipo de reações. / In this work we present a study of the spallation reactions by intermediate energies in actinide and pre-actinide nuclei. For this purpose we used the Monte Carlo model CRISP (Rio-São Paulo Collaboration), for our study was important in the reproduction of the mass distribution of waste products and the total fission and spallation cross secti- ons. These observables are important for the study of Accelerator Driven System Reac- tors (ADS) considered as promising devices for the transmutation of nuclear waste. The physical models needed for a correct simulation of experimental data were already imple- mented in CRISP, such as the evaporation model for emission of particles described by Weisskopf in 1937, and the classical Bohr/Wheeler model in 1939, for fission. To obtain the fragment mass distribution for fission, CRISP has a model based on multimodal fis- sion parameter, which simulates the processes called symmetric and asymmetric fission that are predominant at high and low energies respectively. The CRISP results, obtai- ned after the application of the above mentioned models, were the mass yield of residual fragments, which were analyzed to calculate the fission and spallation cross section using a formula that was implemented in the CRISP model. With these result was obtained the mass distribution for each reaction analyzed. One of the reactions studied was a re- action induced by Bremsstrahlung photons with endpoint energies of 50 MeV and 3500 in a target 181 Ta, calculating the fission and spallation mass distribution, showing good results according the experimental data. In the reactions induced by protons were cal- culated fission and spallation cross sections as well as their respective mass distribution of the residual products. In this case we study two reactions, as follows: p (1 GeV) + 208 , and p (660 MeV) + 238 U. For the first reaction with lead, the results of CRISP were compared with experimental data and with results obtained of MCNPX-Bertini model of Baylac-Domengetroy work in 2003, simulated the same reaction with lead. Obtaining better results with CRISP, but with data-overestimated at the end of calculated distribu- tion. For uranium it was necessary to use the called superasymmetric fission, because the experimental mass distribution is more complicated and the classical model is not suffi- cient for a correct simulation. Has been also studied the reactions induced by deuterons using the CRISP model, showing the mass distribution

De nouveaux modèles d'atmosphère sont présentés, incluant les profils de raie d'hélium neutre améliorés de Beauchamp (1995) et le formalisme de probabilité d'occupation pour ce même atome. Ces modèles sont utilisés pour calculer une grille de spectres synthétiques correspondant à des atmosphères riches en hélium et contenant des traces d'hydrogène. Cette grille est utilisée pour déterminer les paramètres atmosphériques principaux des étoiles de notre échantillon, soient la température effective, la gravité de surface et l'abondance d'hydrogène. Notre échantillon contient des spectres visibles de haut rapport signal-sur-bruit pour 102 naines blanches riches en hélium, dont 29 ont été observés au cours de ce projet, ce qui en fait le plus grand échantillon de spectres de qualité de naines blanches riches en hélium. Des spectres synthétiques ont été calculés en utilisant différentes valeurs du paramètre α de la théorie de la longueur de mélange dans le but de calibrer empiriquement la valeur de ce paramètre pour les DB. Afin d'améliorer la précision sur les paramètres atmosphériques de quelques étoiles, nous avons utilisé des spectres couvrant la raie Hα pour mieux déterminer l'abondance d'hydrogène. Finalement, nous avons calculé la distribution de masse de notre échantillon et la fonction de luminosité des DB. La distribution de masse montre une coupure à 0.5 fois la masse solaire qui est prédite par les modèles d'évolution stellaire et dévoile une masse moyenne significativement plus élevée pour les étoiles de type DBA. La masse moyenne de l'ensemble des DB et DBA est très proche de celle des DA. La fonction de luminosité nous permet de calculer que le rapport du nombre de DB sur le nombre de DA vaut environ 25%. / New model atmospheres are presented, including improved neutral helium lines from Beauchamp (1995) and the occupation probability formalism for that atom. These models are used to compute a grid of synthetic spectra for helium rich atmospheres with different hydrogen abundances. This grid is used to determine the principal atmospheric parameters of the stars in our sample, e.g. effective temperature, surface gravity and hydrogen abundance. There are 102 high quality spectra of helium-rich white dwarfs in our sample, making it the largest sample of this kind. 29 of these spectra were observed for this project. Synthetic spectra using different values of the α parameter from the mixing length theory have been calculated in order to determine the correct value of this parameter for DB model atmospheres. Finally, we have computed the mass distribution of our sample and the DB luminosity funtion. The mass distribution shows a clear cutoff at 0.5 solar masses which is predicted by stellar evolution theory and gives a significantly higher mean mass for the DBA stars of the sample. However, the global mean mass of our sample is very close to that of DA stars. With our luminosity function, we found a number ratio of DB stars over DA stars of about 25%.

Neste trabalho apresentamos um estudo das reações de spallation a energias interme- diárias em núcleos actinídeos e pré-actinídeos. Para esta finalidade foi utilizado o modelo de Monte Carlo CRISP (Colaboração Rio-São Paulo), que neste estudo foi importante na reprodução da distribuição de massa de produtos residuais e as seções de choque de fissão e espalação. Estes observáveis são importantes para o estudo de Reatores Hibridos ADS considerado como dispositivos promissores para a transmutação de resíduos nucle- ares. Os modelos físicos necessários para uma correta simulação de dados experimentais foram já implementadas no CRISP, como o modelo de evaporação para emissão de par- tículas descrito por Weisskopf de 1937, e para fissão o clássico modelo de Bohr/Wheeler de 1939. Para a obtenção da distribuição dos fragmentos de massa de fissão o CRISP conta também com um modelo baseado na parametrização multimodal de fissão, que si- mula os processos de fissão simétrica e assimétrica predominantes em altas e baixas ener- gias, respectivamente. Os resultados obtidos do CRISP depois da aplicação dos modelos mencionados, foram os rendimentos de massa dos fragmentos residuais, os quais foram analisadas para o cálculo da seção de choque de fissão e espalação mediante uma fórmula implementada no modelo. Com o resultado se fez o gráfico da distribuição de massa para cada uma das reações analisadas. Uma das reações estudadas foi a reação induzida por fótons de Bremsstrahlung com energias máximas de 50 e 3500 MeV em um alvo de 181 Ta, calculando a distribuição de massa de fissão e espalação, mostrando bons resultados de acordo com os dados experimentais. Nas reações induzidas por prótons foram calcula- das as seções de choque de fissão e espalação assim como sua respectiva distribuição de massa dos produtos residuais. Neste caso estudamos duas reações, sendo: a reação p (1 GeV) + 208 Pb, e a reação de p (660 MeV) + 238 U. Para a primeira reação com chumbo os resultados do CRISP foram comparados com dados experimentais, e também com os resultados obtidos do modelo MCNPX-Bertini do trabalho de Baylac-Domengetroy de 2003, que simulou a mesma reação com chumbo. Obtendo-se melhores resultados com o CRISP mas com uma superestimação de dados no final da distribuição calculada. No caso do urânio, foi necessário usar a chamada fissão superassimétrica porque a distribuição de massa experimental é mais complexa e o modelo multimodal clássico não é suficiente para sua correta simulação. Foi também estudado as reações induzidas por dêuterons usando o modelo CRISP, mostrando os resultados da distribuição de massa para 197 Au e 208 Pb com algumas limitações do modelo para este tipo de reações. / In this work we present a study of the spallation reactions by intermediate energies in actinide and pre-actinide nuclei. For this purpose we used the Monte Carlo model CRISP (Rio-São Paulo Collaboration), for our study was important in the reproduction of the mass distribution of waste products and the total fission and spallation cross secti- ons. These observables are important for the study of Accelerator Driven System Reac- tors (ADS) considered as promising devices for the transmutation of nuclear waste. The physical models needed for a correct simulation of experimental data were already imple- mented in CRISP, such as the evaporation model for emission of particles described by Weisskopf in 1937, and the classical Bohr/Wheeler model in 1939, for fission. To obtain the fragment mass distribution for fission, CRISP has a model based on multimodal fis- sion parameter, which simulates the processes called symmetric and asymmetric fission that are predominant at high and low energies respectively. The CRISP results, obtai- ned after the application of the above mentioned models, were the mass yield of residual fragments, which were analyzed to calculate the fission and spallation cross section using a formula that was implemented in the CRISP model. With these result was obtained the mass distribution for each reaction analyzed. One of the reactions studied was a re- action induced by Bremsstrahlung photons with endpoint energies of 50 MeV and 3500 in a target 181 Ta, calculating the fission and spallation mass distribution, showing good results according the experimental data. In the reactions induced by protons were cal- culated fission and spallation cross sections as well as their respective mass distribution of the residual products. In this case we study two reactions, as follows: p (1 GeV) + 208 , and p (660 MeV) + 238 U. For the first reaction with lead, the results of CRISP were compared with experimental data and with results obtained of MCNPX-Bertini model of Baylac-Domengetroy work in 2003, simulated the same reaction with lead. Obtaining better results with CRISP, but with data-overestimated at the end of calculated distribu- tion. For uranium it was necessary to use the called superasymmetric fission, because the experimental mass distribution is more complicated and the classical model is not suffi- cient for a correct simulation. Has been also studied the reactions induced by deuterons using the CRISP model, showing the mass distribution

Le but de ce travail est d’étudier le potentiel d’un bitume naturel (BN) extrait en Albanie pour la production des bitumes durs (BD) et des enrobés à module élevé (EME). Pour la production des BD, différentes techniques de raffinage du pétrole existent. Néanmoins, avec certains bruts pétroliers il est impossible de les fabriquer. De plus, les BD de raffinerie comportent souvent des défauts qui limitent leurs applications. Ces raisons, couplées à des questions d’approvisionnement, conduisent à chercher des méthodes de substitution. Dans ce contexte, il est intéressant d’utiliser des BN. Cette étude a montré que le BN d’Albanie donne des BD et des EME en conformité avec la Normalisation Européenne, résistants au vieillissement et performants aux basses températures. Un dosage adéquat permet de formuler des matériaux d’une dureté désirée en réponse des exigences techniques des applications routières visées tout en facilitant la gestion des stocks de bitumes dans les centrales d’enrobages. / The aim of this thesis is to study the potential of a natural bitumen (NB) mined in Albania in the production of hard bitumens (HB) and that of high modulus asphalt concrete (HMAC). Various petroleum refining techniques are available for the production of HB. Nevertheless, this is impossible with some crude oils. In addition, HB from refineries often present shortcomings which limit their applications. These reasons, coupled with practical issues related to HB supply, motivate the research of alternative methods. In this industrial context it is interesting to use NB. This study has shown that the Albanian NB provides HB and HMAC in accordance with European Standards, resistant to aging and relatively performant at low temperatures. The proper dosage of this NB allows the formulation of materials of desired properties, in response to the technical requirements of the considered road applications, facilitating in this way the use of bitumen stocks in asphalt concrete production plants.