During the quasar era (redshifts between 1 and 3) Radio Galaxies (RGs) have been claimed to have substantially influenced the growth and evolution of large scale structures in the universe. In this dissertation I test the robustness of these exciting claims. In order to probe the impacts in more detail, good theoretical models for such RG systems are required. With this motivation, I seek to develop an essentially analytical model for the evolution of Fanaroff-Riley Class II radio galaxies both as they age individually and as their numbers vary with cosmological epoch. To do so, I first compare three sophisticated semi-analytical models for the dynamical and radio lobe power evolution of FR II galaxies, those given by Kaiser, Dennett-Thorpe & Alexander (1997, KDA), Blundell, Rawlings, & Willott (1999, BRW) and Manolakou & Kirk (2002, MK). I perform multi-dimensional Monte Carlo simulations leading to virtual radio surveys. The predictions of each model for redshift, radio power (at 151 MHz), linear size and spectral index are then compared with data. The observational samples are the low frequency radio surveys, 3CRR, 6CE and 7CRS, which are flux-limited and redshift complete. I next perform extensive statistical tests to compare the distributions of model radio source parameters and those of the observational samples. The statistics used are the 1-Dimensional and 2-Dimensional Kolmogorov-Smirnov (K-S) tests and the 4-variable Spearman partial rank correlation coefficient. I search for and describe the "best" parameters for each model. I then produced modifications to each of the three original models, and extensively compare the original and the modified model performances in fitting the data. The key result of my dissertation is that using the Radio Luminosity Function of Willott et al. (2001) as the redshift birth function of radio sources, the KDA and MK models perform better than the BRW models in fitting the 3CRR, 6CE and 7CRS survey data when using K-S based statistical tests, and the KDA model provides the best fits to the correlation coefficients. However, no pre-existing or modified model can provide adequate fits for the spectral indices. I also calculate the volume fraction of the relevant universe filled by the generations of radio galaxies over the quasar era. This volume filling factor is not as large as estimated earlier. Nonetheless, the allowed ranges of various model parameters produce a rather wide range of astrophysically interesting relevant volume fraction values. I conclude that the expanding RGs born during the quasar era may still play significant roles in the cosmological history of the universe.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Submitted by Aelson Maciera (aelsoncm@terra.com.br) on 2017-10-06T19:48:50Z No. of bitstreams: 1 TeseRFP.pdf: 32637155 bytes, checksum: d3cc624aead32f85bad14acdb9612054 (MD5) / Approved for entry into archive by Ronildo Prado (producaointelectual.bco@ufscar.br) on 2017-10-10T19:37:58Z (GMT) No. of bitstreams: 1 TeseRFP.pdf: 32637155 bytes, checksum: d3cc624aead32f85bad14acdb9612054 (MD5) / Approved for entry into archive by Ronildo Prado (producaointelectual.bco@ufscar.br) on 2017-10-10T19:38:10Z (GMT) No. of bitstreams: 1 TeseRFP.pdf: 32637155 bytes, checksum: d3cc624aead32f85bad14acdb9612054 (MD5) / Made available in DSpace on 2017-10-10T19:42:50Z (GMT). No. of bitstreams: 1 TeseRFP.pdf: 32637155 bytes, checksum: d3cc624aead32f85bad14acdb9612054 (MD5) Previous issue date: 2017-06-06 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Ecological studies were carried out in twenty-five natural temporary aquatic environments, located in the cities of Urucuia, Lagoa Grande and Pirapora, in the north and northwest of the state of Minas Gerais, Brazil. In each environment, collections were carried out in April 2015, May 2016 and January 2017, during which limnological variables were measured and samples from the phytoplankton (qualitative) and zooplankton (qualitative and quantitative) communities, as well as from sediment, were collected. Experiments were also carried out in the laboratory to evaluate the effects of different temperatures and luminosity on the hatching of diapause eggs of zooplankton species present in these environments. In general, the values obtained for the physical and chemical variables of the studied environments were in a favorable range to the development of the phytoplankton community. However the low concentration of chlorophyll a and the low richness of phytoplankton species may be reflections of the low water transparency, and the turbidity may limit the growth of the phytoplankton. Qualitative and quantitative analyzes of the zooplankton community indicated low species richness in these ponds. Although Rotifera presented a greater richness of taxa, Copepoda Cyclopoida was the most abundant and numerically representative group. The presence or absence of the Anostraca Dendrocephalus brasiliensis does not seem to interfere in the composition and density of the zoplanktonic community. Species richness and local diversity should be related to disturbances and environmental dynamics. The results obtained in the experiment of hatching of zooplankton diapause eggs showed that the different ponds have similar hatching values, and low temperatures (20°C) and absence of light have a negative influence on hatching these eggs. In addition, it was observed that higher temperatures (35°C) accelerated the hatching of the diapause eggs during the first days of incubation. Thus we can infer that, in general, zooplankton community present in all the studied temporary aquatic environments behave in a similar way. / Foram realizados estudos ecológicos em vinte e cinco ambientes aquáticos temporários naturais, localizados nos municípios de Urucuia, Lagoa Grande e Pirapora, a norte e noroeste do estado de Minas Gerais, Brasil. Em cada ambiente, foram realizadas coletas em abril de 2015, maio de 2016 e janeiro de 2017, durante as quais foram medidas variáveis limnológicas e tomadas amostras das comunidades fitoplanctônica (qualitativas) e zooplanctônicas (qualitativas e quantitativas), além de amostras do sedimento. Também foram realizados experimentos em laboratório para avaliar os efeitos de diferentes temperaturas e da luminosidade sobre a eclosão de ovos de diapausa de espécies zooplanctônicas presentes nesses ambientes. De modo geral, os valores obtidos para as variáveis físicas e químicas dos ambientes estudados encontraram-se numa faixa favorável ao desenvolvimento da comunidade fitoplanctônica. No entanto, a baixa concentração de clorofila a e a baixa riqueza de espécies fitoplanctônicas podem ser reflexos da baixa transparência da água, sendo que a turbidez pode limitar o crescimento do fitoplâncton. Análises qualitativa e quantitativa da comunidade zooplanctônica indicaram baixa riqueza de espécies nessas lagoas. Embora o grupo Rotifera tenha apresentado maior riqueza de táxons, o grupo Copepoda Cyclopoida foi o mais abundante e representativo numericamente. A presença ou ausência do Anostraca Dendrocephalus brasiliensis parece não interferir na composição e na densidade da comunidade zooplanctônica, sendo que a riqueza de espécie e a diversidade local devem estar relacionadas a perturbações e dinâmica do ambiente. Os resultados obtidos no experimento de eclosão de ovos de diapausa do zooplâncton evidenciaram que as diferentes lagoas têm valores semelhantes de eclosão, sendo que baixas temperaturas (20°C) e ausência de luz têm influência negativa sobre a eclosão desses ovos. Além disso, foi observado que temperaturas mais elevadas (35°C) aceleraram a eclosão dos ovos de diapausa durante os primeiros dias de incubação. Assim, podemos inferir que, no geral, a comunidade zooplanctônica presente em todos os ambientes aquáticos temporários estudados se comporta de maneira semelhante. / CNPq: 141023/2013-9

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Varronia curassavica is a Brazilian native medicinal plant, popularly known as “erva-beleeira”, that belong to the Cordiaceae family, and can be found in the coastal strip from the state of Ceará to the state of Rio Grande do Sul. The objective of this work was to evaluate the influence of the cultivation environment on the anatomical, physiological and essential oil characteristics of V. curassavica accessions. The experimental design was in randomized blocks, in a split plot scheme, testing two cultivation environments (full sun and protected with 50% shade screen) in the plots, and five V. curassavica accessions (VCUR-101, VCUR-102, VCUR-201, VCUR -302 and VCUR-802) in the split plots, with three replications and three plants per replication. At 180 days of cultivation, foliar anatomy, chlorophyll a, b and, total, leaf area, dry weight of plants, and content, yield and chemical composition of the essential oil were evaluated. The thickest palisade parenchyma were registered in VCUR-102 (75.87 μm), in full sun environment, and VCUR-201, in both environments (75.87 and 54.75 μm). The thickest adaxial epidermis were found in the accessions VCUR-102 and VCUR-201 (21.15 and 13.60 μm), in full sun and protected environment with 50% shade screen, respectively. The accession VCUR-802 presented the largest leaf area (18.30 cm2) in the protected environment with 50% shade screen. The essential oil content of the accessions ranged from 1.33 to 3.9% in full sun environment, and from 1.4 to 3.3% in the protected environment with 50% shade screen. The essential oil yield of the accessions ranged from 0.26 to 0.87 mL.plant-1 in full sun environment, and from 0.34 to 0.53 mL.plant-1 in the protected environment with 50% shade screen. The highest contents of trans-caryophyllene (17.9%), α-humulene (5.11%), germacrene D (4.86%) and α-zingiberene (38.04%) were found in plants of accession VCUR-302 cultivated in protected environment with 50% shade screen. Cultivating V. curassavica for 180 days in full sun environment provided bigger development of leaf limb, palisade parenchyma and epidermis of the abaxial and adaxial face in almost all the tested accessions. In general, the full sun environment also favored the higher production of dry mass, and essential oil content and yield. / A Varronia curassavica é uma planta medicinal nativa do Brasil, conhecida popularmente como erva-baleeira, pertencente à família Cordiaceae, que pode ser encontrada na faixa litorânea que vai do Ceará ao Rio Grande do Sul. O objetivo deste trabalho foi avaliar a influência do ambiente de cultivo nas características anatômicas, fisiológicas e no óleo essencial de acessos de V. curassavica. O delineamento experimental foi em blocos casualisados, em esquema de parcelas subdivididas, testando dois ambientes de cultivo (pleno sol e protegido com tela de sombreamento de 50%) nas parcelas, e cinco acessos de V. curassavica (VCUR-101, VCUR-102, VCUR-201, VCUR-302, e VCUR-802) nas subparcelas, com três repetições e três plantas por repetição. Aos 180 dias de cultivo foi avaliada a anatomia foliar, teores de clorofila a, b e total, área foliar, massa seca de plantas, teor, rendimento e composição química do óleo essencial. As maiores espessuras do parênquima paliçádico foram registradas nos acessos VCUR-102 (75,87 μm) a pleno sol e VCUR-201 nos dois ambientes (75,87 e 54,75 μm). As maiores espessuras de epiderme adaxial foram encontradas nos acessos VCUR-102 e VCUR-201 (21,15 e 13,60 μm), nos ambientes pleno sol e protegido com tela de sombreamento de 50%, respectivamente. O acesso VCUR-802 apresentou a maior área foliar (18,30 cm2) no ambiente protegido com tela de sombreamento de 50%. O teor do óleo essencial dos acessos variou de 1,33 a 3,9% no ambiente pleno sol, e de 1,4 a 3,3% no ambiente protegido com tela de sombreamento de 50%. O rendimento do óleo essencial dos acessos variou de 0,26 a 0,87 mL.planta-1 no ambiente pleno sol, e de 0,34 a 0,53 mL.planta-1 no ambiente protegido com tela de sombreamento de 50%. Os maiores teores de trans-cariofileno (17,9%), α-humuleno (5,11%), germacreno D (4,86%) e α-zingibereno (38,04%) foram encontrados em plantas do acesso VCUR-302 cultivadas no ambiente protegido com tela de sombreamento de 50%. Cultivando V. curassavica por 180 dias em ambiente pleno sol proporcionou maior desenvolvimento do limbo foliar, do parênquima paliçádico e das epidermes da face abaxial e adaxial em quase todos os acessos testados. De modo geral, o ambiente pleno sol favoreceu a maior produção de massa seca, teor e rendimento de óleos essências. / São Cristóvão, SE

A soja é a cultura agrícola com maior extensão de área plantada no Brasil, país que se destaca no cenário mundial como o segundo maior produtor e exportador desta oleaginosa. A ferrugem asiática (FA), causada pelo fungo Phakopsora pachyrhizi, apresenta-se como um dos mais graves problemas fitossanitários da cultura da soja no Brasil, principalmente por não existirem, até o presente momento, cultivares com níveis de resistência satisfatórios. Com o objetivo de melhor se conhecer a biologia de Phakopsora pachyrhizi e alguns fatores relacionados ao processo infeccioso em soja, no presente trabalho foram avaliados: (1) Métodos de preservação de urediniósporos; (2) Influência da descontinuidade do molhamento foliar no processo infeccioso dos urediniósporos; (3) Influência da luminosidade e da superfície foliar no processo infeccioso de urediniósporos de P. pachyrhizi; (4) Influência do estádio fenológico da soja na infecção de P. pachyrhizi. Os resultados obtidos mostraram que a desidratação dos esporos proporcionou maior viabilidade destes ao longo do tempo, para todas as condições de armazenamento testadas. No deep freezer foi possível preservar os esporos por até 231 dias, independente da sua condição de hidratação. No ambiente, os esporos não desidratados e desidratados permaneceram viáveis por 16 e 22 dias, respectivamente. A reversão de dormência dos esporos foi efetiva ao empregar hidratação (24h de câmara úmida) seguida ou não por choque térmico (40°C/5 minutos). Em todos os tratamentos onde se aplicou molhamento foliar descontínuo, a severidade de FA foi sempre inferior quando comparada ao molhamento contínuo, principalmente quando a interrupção do molhamento se deu após 4 horas de câmara úmida inicial. A interrupção temporária do molhamento afetou os esporos que haviam germinado, pois os mesmo não foram aptos a infectar após novo período de molhamento. Com relação à luminosidade, os urediniósporos foram aptos a infectar plantas de soja tanto na luz quanto no escuro. Porém, severidade maior foi observada quando se inoculou a superfície adaxial, com posterior incubação das plantas no escuro. Os experimentos in vitro mostraram que, na ausência de luz, houve maior germinação e maior formação de apressórios. O teor de cera epicuticular e o seu aspecto ultra-estrutural não apresentaram diferenças entre as superfícies adaxial e abaxial no cultivar BRS 154. Os cultivares BRS 154 e BRS 258, no estádio fenológico reprodutivo, R5, apresentaram menor severidade em relação aos estádios V3 e R1. O período latente médio (PLM) da FA foi 8 e 9 dias para os cultivares BRS 154 e BRS 258, respectivamente. O PLM não se diferenciou em função do estádio fenológico para ambos cultivares. Quanto à influência da idade da folha na suscetibilidade à FA, a folha 1, considerando-se o sentido base-ápice da planta, mostrou maior suscetibilidade e freqüência de infecção de P. pachyrhizi . Os resultados apresentados são essenciais, tanto por disponibilizarem informações sobre a biologia e epidemiologia do fungo, quanto por servirem como base para novos estudos, nas mais diversas áreas sobre este importante patossistema. / Soybean is the agricultural crop with the largest planted area in Brazil. The country stands out in the world scenario as the second-largest producer and exporter of this oilseed crop. The Asian rust (AR), caused by the fungus Phakopsora pachyrhizi, is one of the most serious phytosanitary problems of soybean in Brazil, especially because no cultivars exist so far with satisfactory resistance levels. In order to acquire better knowledge about the biology of Phakopsora pachyrhizi and some factors related to its infectious process in soybean, the following were evaluated in the present work: (1) Uredospore preservation methods; (2) Influence of leaf wetness discontinuity on the infectious process of uredospores; (3) Influence of luminosity and leaf surface on the infectious process of P. pachyrhizi uredospores; (4) Influence of phenological stage of soybean on infection by P. pachyrhizi . The results obtained showed that spore dehydration provided greater spore viability with time, in all storage conditions tested. Spores could be preserved for up to 231 days in the deep freezer, regardless of their hydration condition. At room temperature, non-dehydrated and dehydrated spores remained viable for 16 and 22 days, respectively. Spore dormancy reversion was effective when hydration was used (24h in humid chamber), followed or not by thermal shock (40°C/5 minutes). In all treatments where discontinuous leaf wetting was applied, AR severity was always lower when compared with continuous wetting, especially when wetting was interrupted after 4 hours of initial treatment in the humid chamber. Temporary wetness interruption affected spores that had already germinated, as these were not able to infect after a new wetness period. As to luminosity, uredospores were capable of infecting soybean plants both in the light and in the dark. However, higher severity was observed when the adaxial surface was inoculated, with later incubation of the plants in the dark. The in vitro experiments showed that there was greater germination and greater formation of appressoria in the absence of light. Epicuticular wax content and its ultrastructural aspect did not show differences between the adaxial and abaxial surfaces in cultivar BRS 154. At the R5 reproductive phenological stage, cultivars BRS 154 and BRS 258 showed smaller severity in relation to stages V3 and R1. The AR mean latent period (MLP) was 8 and 9 days for cultivars BRS 154 and BRS 258, respectively. MLP differences due to phenological stage were not detected in any of the cultivars. As to the influence of leaf age on AR susceptibility, leaf 1 showed greater susceptibility and frequency of infection by P. pachyrhizi, considering the plant base-apex direction. The results herein presented are essential, either because they make information available on the biology and epidemiology of the fungus, or because they serve as a foundation for new studies on the most diverse areas about this important pathosystem.

No description available.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The erva-mate (Ilex paraguariensis) is a species broadly cultivated in southern Brazil and neighboring countries, which leaves and fine branches prepared according to the appropriate method, make the mate or chimarrão , the most popular tea consumed in Brazil and exported everywhere. With the increasing planted area, mainly in the last decade, fitossanitary problems caused by pest and diseases have increased in this crop and among them, the root-rot is becoming one of the main ones. The disease is caused by Fusarium spp., besides Pythium sp. and Rhizoctonia sp. and, it causes serious damages to the roots, causing, in most serious cases, death of the plant. With the suspicion that the incidence and disease severity are influenced by cultivation methods and management practices, such as mineral fertilizers application without technical criteria or no fertilizers, lime application and erva-mate cultivation at full sun, experiments were conducted in the Forest Nursery area belonging to Forest Sciences Department of the Federal University Santa Maria with the objective of confirming these assumptions. The first experiment was conducted in a factorial design (4 x 3 x 4) composed by Fusarium spp. inoculation, by lime application and by NPK fertilization. The second experiment was conducted in a factorial design (2 x 5), composed by Fusarium spp. inoculation and by shading levels. The use of commercial bioprotectors containing antagonistic organisms to Fusarium spp. has given satisfactory results in some patossystems. Therefore, in the conduction of a third experiment, in a factorial design (4 x 4), Fusarium spp. inoculation and the efficiency of commercial products for biological control was tested. It was verified that the lime application, combined with large fertilizer doses, compromised the development of the erva-mate plants, besides turning them more susceptible to Fusarium spp. The availability of nutrients also influenced the fungic population of the soil. In the same way, plants submitted to cower shading levels or full sun had its development compromised and were more susceptible to the disease. The use of commercial bioprotectors was not efficient in the conditions of this experiment. / A erva-mate (Ilex paraguariensis) é uma espécie amplamente cultivada no sul do Brasil e países vizinhos, cujas folhas e galhos finos preparados, segundo método apropriado, fornecem o mate ou chimarrão, o mais popular chá consumido no Brasil e exportado para todo o mundo. Com o aumento da área plantada, sobretudo na última década, os problemas fitossanitários causados por pragas e doenças aumentaram e, dentre estes, a podridão-de-raízes vem se tornando um dos principais. A doença é causada por Fusarium spp., além de Pythium sp. e Rhizoctonia sp. e provoca sérios danos decorrentes da destruição do sistema radicular, ocasionando, nos casos mais graves, morte da planta. Suspeita-se que a incidência e a severidade da doença são influenciadas pelos métodos de cultivo e por práticas de manejo do erval, como aplicação de adubos minerais sem critérios técnicos ou ausência de adubação, calagem do solo e cultivo de ervais a pleno sol. Assim, foram instalados experimentos na área do Viveiro Florestal pertencente ao Departamento de Ciências Florestais da Universidade Federal de Santa Maria com o objetivo de confirmar tais hipóteses. O primeiro experimento foi conduzido em um esquema fatorial (4 x 3 x 4) composto pela inoculação de Fusarium spp., pela calagem do solo e pela adubação NPK. O segundo experimento foi conduzido em um esquema fatorial (2 x 5), composto pela inoculação de Fusarium spp. e por níveis de sombreamento. Além disso, a utilização de bioprotetores comerciais contendo organismos antagônicos ao Fusarium spp. tem dado resultados satisfatórios em alguns patossistemas. Portanto, conduziu-se um terceiro experimento, em um esquema fatorial (4 x 4), testando-se a inoculação de Fusarium spp. e a eficiência de produtos comerciais para controle biológico. Verificou-se que a calagem do solo, combinada com maiores doses de adubação, comprometeu o desenvolvimento das plantas de erva-mate, além de torná-las mais suscetíveis ao ataque de Fusarium spp. A disponibilidade de nutrientes também influenciou a população fúngica do solo. Da mesma forma, plantas submetidas aos menores níveis de sombreamento ou a pleno sol tiveram seu desenvolvimento prejudicado e ficaram mais suscetíveis à doença. A utilização de bioprotetores comerciais não foi eficiente nas condições deste experimento.

<p>The future International Linear Collider (ILC) and Compact Linear Collider (CLIC) are intended for precision measurements of phenomena discovered at the Large Hadron Collider (LHC) and also for the discovery of new physics. In order to offer optimal conditions for such experiments, the new colliders must produce very-high-luminosity collisions at energies in the TeV regime.</p><p>Emittance growth caused by imperfections in the main linacs is one of the factors limiting the luminosity of CLIC and ILC. In this thesis, various emittance preservation and luminosity tuning techniques have been tested and developed in order to meet the challenging luminosity requirements.</p><p>Beam-based alignment was shown to be insufficient for reduction of emittance growth. Emittance tuning bumps provide an additional powerful preservation tool. After initial studies of tuning bumps designed to treat certain imperfections, a general strategy for design of optimised bumps was developed. The new bumps are optimal both in terms of emittance reduction performance and convergence speed. They were clearly faster than previous bumps and reduced emittance growth by nearly two orders of magnitude both for CLIC and ILC.</p><p>Time-dependent imperfections such as ground motion and magnet vibrations also limit the performance of the colliders. This type of imperfections was studied in detail, and a new feedback system for optimal reduction of emittance growth was developed and shown to be approximately ten times more efficient than standard trajectory feedbacks.</p><p>The emittance tuning bumps require fast and accurate diagnostics. The possibility of measuring emittance using a wide laserwire was introduced and simulated with promising results. While luminosity cannot be directly measured fast enough, it was shown that a beamstrahlung tuning signal could be used for efficient optimisation of a number of collision parameters using tuning bumps in the Final Focus System.</p><p>Complete simulations of CLIC emittance tuning bumps, including static and dynamic imperfections and realistic tuning and emittance measurement procedures, showed that an emittance growth six times lower than that required may be obtained using these methods.</p>

Ce mémoire présente une exploitation additionnelle du catalogue LSPM comportant deux grandes parties, soit la poursuite du relevé des naines blanches à l'intérieur d'un rayon de 40 pc et l'étude de la contrepartie SDSS de ce catalogue. La première consiste à utiliser les critères basés sur des diagrammes de mouvements propres réduits établis dans des travaux antérieurs afin de dresser une liste de candidates naines blanches. Quelques modifications quant à l'ordre de priorité ainsi que le critère basé sur les magnitudes photographiques seront apportées. Une approche de moindres carrés non-linéaire appliquée aux magnitudes observées dans les systèmes photométriques disponibles permet ensuite de déterminer la distance des objets sélectionnés par comparaison avec les plus récents modèles de naines blanches disponibles. Un second critère est appliqué en se basant sur la qualité de l'ajustement résultant de la procédure. Ceci mènera à l'identification de 31 nouvelles naines blanches, dont 11 situées vraisemblablement à moins de 40 pc. Une nouvelle liste de candidates a aussi pu être établie pour la poursuite du relevé. La seconde partie consiste à utiliser tous les objets du 7e relevé du SDSS identifiés dans le catalogue LSPM pour l'étude statistique des naines blanches, essentiellement via la détermination de leur fonction de luminosité. Pour ce faire, un critère basé sur les diagrammes de mouvements propres réduits sera encore une fois utilisé. La distance des objets sélectionnés sera déterminée selon la même procédure, mais cette fois en ne se limitant pas à 40 pc. La méthode de pondération selon le volume observable (1/v_max) est utilisée afin de compenser pour le biais introduit par la sensibilité du catalogue à la magnitude. Cependant, d'autres facteurs viennent influencer la détermination de la fonction de luminosité et une analyse de ceux-ci est finalement présentée. / We present an additional exploitation of the Lépine \& Shara Proper Motion catalog (LSPM) divided in two main parts: a follow up and some improvements on the census or northern white dwarfs within 40 pc of the Sun and a study of the SDSS white dwarfs component in the LSPM survey. The former consists in the use of criteria previously established in order to create a list of white dwarf candidates with an associated priority. The priority order has been enriched and one of the criteria has been slightly modified. We then use a non-linear least square method to the observed magnitudes in each available photometric system simultaneously in order to determine the atmospheric parameters and, in particular, the distance of each white dwarf candidate. This approach allows a second criteria to be applied on our sample based on the goodness of the fit. This will lead us to the identification of 31 new white dwarfs, from which 11 are likely to remain within 40 pc of the Sun. A new list of 340 candidates has also been established for eventual observations. The latter consists in the use of all the objects from the 7th data release of the SDSS that have a counterpart in the LSPM catalog to elaborate a statistical study of white dwarfs, in this case by calculating the white dwarf luminosity function. To do so, one of the same criterion mentioned above will be used to make a first selection of presumed white dwarfs. Afterwards, the distance will be determined by the same least-square method, but without any restriction on the distance. To balance the effect due to the sensibility in magnitude of the survey, we used a ponderation method based on the maximum observable volume (1/v_max). However, other factors come to affect our results and the last part of this work concentrates on their identification.

Les seize détecteurs MPX constituant le réseau ATLAS-MPX ont été placés à différentes positions dans le détecteur ATLAS et sa averne au CERN dans le but de mesurer en emps réel les champs de radiation produits ar des particules primaires (protons des faisceaux) et des particules secondaires (kaons, pions, g, protons) issues des collisions proton-proton. Des films de polyéthylène (PE) et de fluorure de lithium (6LiF) recouvrent les détecteurs afin d’augmenter leur sensibilité aux neutrons produits par les particules primaires et secondaires interagissant avec les matériaux présents dans l’environnement d’ATLAS. La reconnaissance des traces laissées par les particules dans un détecteur ATLAS-MPX se fait à partir des algorithmes du logiciel MAFalda (“Medipix Analysis Framework”) basé sur les librairies et le logiciel d’analyse de données ROOT. Une étude sur le taux d’identifications erronées et le chevauchement d’amas a été faite en reconstruisant les activités des sources 106Ru et 137Cs. L’efficacité de détection des neutrons rapides a été mesurée à l’aide des sources 252Cf et 241AmBe (neutrons d’énergie moyenne de 2.13 et 4.08 MeV respectivement). La moyenne des efficacités de détection mesurées pour les neutrons produits par les sources 252C f et 241AmBe a été calculée pour les convertisseurs 6LiF et PE et donnent (0.8580 ± 0.1490)% et (0.0254 ± 0.0031)% pour LiF et (0.0510 ± 0.0061)% et (0.0591 ± 0.0063)% pour PE à bas et à haut seuil d’énergie respectivement. Une simulation du calcul de l’efficacité de détection des neutrons dans le détecteur MPX a été réalisée avec le logiciel GEANT4. Des données MPX correspondant aux collisions proton-proton à 2.4 TeV et à 7 TeV dans le centre de masse ont été analysées. Les flux détectés d’électrons et de photons sont particulièrement élevés dans les détecteurs MPX01 et MPX14 car ils sont plus près du point de collision. Des flux de neutrons ont été estimés en utilisant les efficacités de détection mesurées. Une corrélation avec la luminosité du LHC a été établie et on prédit que pour les collisions à 14 TeV dans le centre de masse et avec une luminosité de 10^34 cm-1*s-1 il y aura environ 5.1x10^8 ± 1.5x10^7 et 1.6x10^9 ± 6.3x10^7 particules détectées par les détecteurs MPX01 et MPX14 respectivement. / The sixteen detectors forming the ATLAS-MPX network have been placed in different positions inside the ATLAS detector and its cavern at CERN in order to measure, in real time, the radiation fields produced by primary particles (beam protons) and secondary particles (kaons, pions, photons, protons) resulting from the proton-proton collisions. Films of polyethylene (PE) and lithium fluoride (6LiF) cover the detectors so as to increase their sensitivity to neutrons produced by the primary and secondary particles interacting with the materials present in the ATLAS environment. The tracks identification in an ATLAS-MPX detector is obtained with the algorithms of the MAFalda software (Medipix Analysis Framework) based on the libraries and data-analysis software ROOT. A study on the mistag rate and blob overlap was made by reconstructing the activities of 106Ru and 137Cs sources. The fast neutron detection efficiency was measured with the help of 252C f and 241AmBe sources (neutrons with an average energy of 2.13 and 4.08 MeV, respectively). The detection efficiency measured for neutrons produced by 252Cf et 241AmBe sources was calculated for the 6LiF and PE converters. It averaged at low and high energy respectively (0.8580 ± 0.1490)% and (0.0254 ± 0.0031)% for LiF and (0.0510 ± 0.0061)% and (0.0591 ± 0.0063)% for PE. A simulation of the neutron detection efficiency calculation in the MPX detector was carried out with the GEANT4 software. MPX data corresponding to the proton-proton collisions at 2.4 TeV and 7 TeV at the center of mass were analyzed. The detected flux of electrons and photons are particularly high in the MPX01 and MPX14 detectors because they are closer to the point of collision. Fluxes of neutrons were estimated using the measured detection efficiencies. A correlation with the luminosity of the LHC was established. We predict that for 14 TeV collisions at the center of mass, with a luminosity of 1034 cm^2*s^1, the number of particle detected by MPX01 and MPX14 respectively will be about 5.1x10^8 ± 1.5x10^7 and 1.6x10^9 ± 6.3x10^7.