Made available in DSpace on 2014-08-20T14:38:50Z (GMT). No. of bitstreams: 1 Dissertacao_Carolina_Boschini.pdf: 903597 bytes, checksum: 9c67bbb615d36cec975435c06e8ceb28 (MD5) Previous issue date: 2011-02-24 / This study aimed to investigate the effects of a product containing a combination of antioxidants (CA) and different levels of vitamin E on performance, carcass traits and meat quality of broilers. A total of 840 Cobb male broilers were fed experimental diets from 1 to 35 days. A completely randomized experimental design was used. Dietary treatments consisted of T1- 200ppm CA, T2- 200ppm CA + Vitamin E (20 ppm), T3- 200ppm CA + Vitamin E (40ppm), T4- 200ppm CA + vitamin E (60ppm), T5- 200ppm CA + vitamin E (80ppm), T6- vitamin E (80ppm). A basal corn-soybean meal diet was formulated according to requirements established by Cobb. Performance was not affected by dietary treatments. Carcass yield and cut-ups were not signifi-cantly influenced, but a numerical improvement of breast and thigh was observed in birds fed T3. Meat colorimetry was significantly affected, finding the best results to L* (T5), a* (T1 and T5) and b* (T6), but results did not differ from T2, T3, T4 and T5. A lowest TBARs index was observed in birds fed T5, indicating lower meat lipidic pe-roxidation. These results indicate that the CA with any level of vitamin E did not change the broiler performance and efficiency factor. The CA improved carcass yield and cut-ups, color and decreases meat lipid peroxidation. / Este estudo teve como objetivo investigar os efeitos de um produto com uma combinação de antioxidantes (CA) e diferentes níveis de vitamina E no desempenho, características de carcaça e qualidade da carne de frangos de corte. Um total de 840 frangos de corte Cobb machos foram alimentados com dietas experimentais de 1 a 35 dias. O delineamento experimental utilizado foi o completamente casualizado. As dietas experimentais consistiram de T1- CA-200ppm, T2-200ppm CA + Vitamina E (20 ppm), T3-200ppm CA + Vitamina E (40ppm), T4-200ppm CA + vitamina E (60ppm), T5-200ppm CA vitamina E + (80ppm) E e T6-vitamina E (80ppm). A dieta base de milho e soja foi formulada de acordo com os requisitos estabelecidos pela Cobb. O desempenho não foi afetado pelos tratamentos. O rendimento de carcaça e corte não foram significativamente influenciados, mas uma melhora numérica do peito e coxa foi observada nas aves alimentadas com T3. Colorimetria da carne foi afetada significativamente, encontrando melhores resultados de L * para o T5, a * (T1 e T5) e b * (T6) não diferindo de T2, T3, T4 e T5. Um menor índice de TBARS foi observado nas aves alimentadas T5, indicando menor peroxidação lipídica na carne. Estes resultados indicam que a CA com qualquer nível de vitamina E não alterou o desempenho de frangos de corte. A CA melhorou o rendimento de carcaça e corte, cor e diminuiu a peroxidação lipídica da carne.

Ce travail de thèse est consacré à l'élaboration de membrane photocatalytique à partir de nanoparticules de TiO2 obtenues par voie sol-gel (système TTIP-eau). Les sols sont préparés dans un réacteur à micro-mélange rapide (turbulent). L'effet de l'hydrodynamique au sein de différents mélangeurs (T simple, T chicanes, T rétrécissement) sur la morphologie et l'activité photocatalytique de nanoparticules déposées sur des plaques d'α-alumine a été étudié. Les dépôts de TiO2 ont été réalisés durant la période d'induction de la réaction sol-gel. Le mélange des réactifs a été simulé en utilisant un logiciel de modélisation numérique (modèle k-ε), Les différences hydrodynamiques au sein du micro-mélange a seulement un impact significatif sur le temps de stabilité des nanoparticules (période d'induction). Des couches minces et des membranes photo-actives ont été réalisées en vue du couplage membrane et réaction photocatalytique. Ces membranes ont été caractérisées et testées en photocatalyse. Elles ont montrées de bonnes photo-activités. Des tests de couplage direct séparation/photodégradation ont été réalisés sur des solutions aqueuses d'acide orange 7. Ce dispositif expérimental a permis de mettre en évidence une augmentation de flux de perméation significative avec de l'eau et en présence de colorant en solution. L'effet de la concentration et du pH de la solution a été évalué sur les flux de perméat et sur la photodégradation. / This PhD work is devoted to the elaboration of photocatalytic membranes using TiO2 nanoparticles synthetized by sol-gel process (titanium tetra-isopropoxyde precursor – water). Sols are prepared in sol-gel reactor with rapid turbulent micro-mixing. The effect of hydrodynamic using 3 T mixers (T simple, T with 3 baffles and T with narrow) during the mixing was studied with k-ε modeling Computational fluid Dynamics (CFD), as well as the morphology and the photo-activity of thin layers deposited on alumina support during induction period. Differences on hydrodynamic during micro-mixing have only impact on the time of nanoparticles stability (induction period). Photo-active thin layers and membranes are synthesized for coupling membrane separation and photocatalytic reaction. Photocatalytic activities of thin layers and membranes are performed with an aqueous solution of acid orange 7. Significant increases of permeate flux are observed during the filtration of water and solution containing dye. Effects of concentration and pH are evaluated on permeation flux and photodegradation.

El objetivo del presente trabajo de investigación consiste en evaluar la calidad de la carpeta asfáltica mediante el análisis de la rueda cargada de Hamburgo, usando el Método Marshall en la rehabilitación de la carretera de Imperial Pampas. El método de la investigación es de tipo cualitativo-cuantitativo. El problema consistió en determinar de qué manera el análisis de la rueda cargada de Hamburgo permite comprobar si la carpeta asfáltica usada en la rehabilitación de la carretera Imperial Pampas cumple con los estándares de calidad de acuerdo al método de Marshall. La hipótesis planteada es que la Rueda de Hamburgo permite comprobar que la carpeta asfáltica usada en la rehabilitación de la carretera Imperial pampas cumple con los estándares de calidad de acuerdo al método Marshall. Llegando a la conclusión que el método Marshall mostró buen performance en condiciones extremas, por cuanto se obtuvo en el umbral de aprobación. The research objective of this study is to assess the quality of the asphalt by analyzing the wheel loaded Hamburg using the Marshall method in the rehabilitation of the road from Imperial Pampas. The research method is qualitative - quantitative The problem was to determine how the analysis of Hamburg loaded wheel lets you check whether the asphalt used in road rehabilitation Imperial Pampas meets quality standards according to the Marshall method. The hypothesis is that the Hamburg Wheel lets you check that the asphalt used in road rehabilitation Imperial pampas meet the quality standards according to the Marshall method. I came to the conclusion that the Marshall method showed good performance in extreme conditions was obtained because the threshold of approval.

Les budgets alloués aux réparations des ouvrages et du patrimoine bâti ont atteint un niveau important. Une démarche scientifique est donc réfléchie pour réduire ces budgets par la mise en place d’outils visant à optimiser et fiabiliser le diagnostic structural des ouvrages. Les méthodes de contrôle non destructif (CND) constituent l’une des voies adaptées. Ces techniques reposent sur des principes physiques bien connus et les sociétés de service en proposent aujourd’hui un emploi courant, mais de nombreux verrous subsistent. Les deux besoins majeurs des gestionnaires d’ouvrages sont celui de l’optimisation de la stratégie de reconnaissance (où mesurer ? en combien de points ? avec quelle(s) techniques(s) et quelle précision ?) et celui de la quantification des propriétés mécaniques des matériaux ou des indicateurs de durabilité telles que la résistance à la compression, l’épaisseur carbonatée, le taux d’humidité. La question est comment déduire ces propriétés et ces indicateurs des mesures faites ? Et quelles sont la précision et la fiabilité de l’évaluation ?Cette thèse s’inscrit dans le cadre de deux projets nationaux de recherche : le projet ACDC-C2D2 et le projet ANR EvaDéOS. L’objectif principal est d’analyser la variabilité issue du CND pour ensuite remonter à la variabilité spatiale des bétons en conditions réelles. Les techniques de CND considérées sont choisies parmi les plus complémentaires : radar, résistivité électrique, ultrasons et rebond (scléromètre). Les résultats sont obtenus à partir d’une large campagne expérimentale effectuée sur des dalles d’un site test et sur deux ouvrages. L’analyse de la variabilité des CND a permis d’évaluer le nombre minimal de mesures nécessaire pour un niveau de confiance souhaité. D’autre part, la corrélation spatiale des données a été modélisée par l’analyse variographique. Les résultats montrent que, dans certain cas, les mesures de CND ne sont pas spatialement indépendantes. Les longueurs de corrélation identifiées dépendent de la propriété mesurée ainsi que du béton de l’ouvrage ausculté. La connaissance de ces longueurs de corrélation est un résultat nouveau qui permettra d’une part de mieux estimer la variabilité spatiale des bétons et d’autre part d’alimenter de manière plus réaliste les calculs fiabilistes des ouvrages. Elle permet également d’identifier un pas d’échantillonnage optimal sur ouvrage dans le cadre du suivi temporel ou pour effectuer des analyses complémentaires (ex. carottage, CND complémentaire ou plus fiable) et de représenter au mieux la cartographie spatiale des propriétés du béton.Dans le cadre du projet de recherche ANR EvaDéOS, les effets de la carbonatation et des gradients de teneur en eau (gradient d’humidité) sur les techniques CND ont été étudiés. Ce travail a pour objectifs d’étudier la sensibilité des techniques de CND à évaluer ces deux indicateurs de durabilité ainsi que leur impact sur la variabilité des mesures de CND. En laboratoire, des campagnes expérimentales ont été réalisées sur corps d’épreuve ayant différentes profondeurs de carbonatation ou des gradients d’humidité. L’effet de la carbonatation a été quantifié pour certains observables : résistivité électrique, vitesse ultrasonore et rebond. En ce qui concerne la variabilité des mesures de CND, l’effet de la carbonatation est seulement notable dans le cas du béton saturé, en particulier pour la variabilité locale de la résistivité électrique et du rebond. Cet effet reste faible par rapport à l’effet du degré de saturation. Les premiers résultats montrent également que les mesures de la résistivité électrique permettraient de suivre des gradients d’humidité dans le béton. / The budgets assigned to the repair of structures and built heritage have reached an alarming level. A scientific approach is needed to reduce these budgets by implementing tools for a more reliable and optimal assessment of existing structures. Non-destructive testing (NDT) techniques constitute one of approaches adapted to real conditions. These techniques are based on well-known physical principles. Many companies offer their services in NDT domain today but many challenges remain. The two particular needs of structure managers are the optimization of the assessment strategy (where to measure? how many testing points? what technique(s) and what precision?) and the quantification of mechanical properties of materials or durability indicators such as the compressive strength, the carbonation depth, the moisture content. The questions are how to estimate these properties from measurements performed, and what are the accuracy and reliability of the evaluation?This thesis is part of two French research projects: ACDC-C2D2 and ANR EVaDéOS. The main objective is to analyze the variability of non-destructive testing (NDT) measurements for assessing the spatial variability of concrete in real conditions. NDT techniques considered are chosen as being complementary: radar, electrical resistivity, ultrasonic, rebound hammer. The results are obtained from a wide campaign of measurements, which was performed on concrete slabs of a testing site and on two existing structures. The analysis of the NDT variability makes it possible to assess the necessary minimum number of measurements for a desired level of confidence. Furthermore, the spatial correlation of the data was modeled using the variogram analysis. In some cases, the results show that NDT measurements are not spatially independent. The correlation lengths identified depend on the measured property and the concrete of the structure inspected. They are a new result, which will provide on one hand a better evaluation of spatial variability of concrete and on the other hand a more realistic input of reliability calculations of structures. The correlation length allows also the identification of an optimal sampling distance on existing structure within the monitoring time or the implementation of additional analyses (eg. core, complementary or more reliable NDT) and a better representation of the spatial mapping of concrete properties.Within the framework of the ANR EvaDéOS research project, the effects of carbonation and of moisture gradients on NDT measurements were studied. This work aims to study the sensitivity of NDT techniques for assessing these two durability indicators and their impact on the variability of NDT measurements. In laboratory, the experimental surveys were carried out on testing specimens having different depths of carbonation or moisture gradients. The effect of carbonation was quantified for several parameters: electrical resistivity, ultrasonic pulse velocity and rebound hammer. With respect to the variability of NDT measurements, the effect of carbonation is only significant in the case of saturated concrete, in particular for the local variability of electrical resistivity and rebound hammer. This effect is weak in comparison with the effect of saturation degree. The first results show also that the measurements of electrical resistivity would follow moisture gradients in concrete.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A forecast of future demand for the products is the main variable to be considered in the planning and in production control in organizations. Two methods of time series forecasting often used in the literature are the ARIMA and MLP/RNA models. A practice that began in 1969 and has consolidated for greater accuracy is the combination of individual forecasts from two or more models. Considering the need for organizations by predictive techniques that generate better results, this study aims to predict the future values of a time series of the demand for UHT milk in a dairy industry, through the combination of ARIMA and MLP/RNA models, and to compare the results obtained by the combinations compared to individual models, exemplifying the achievement of combined forecasting in production planning. Accuracy measures to measure the results and to select the best model were the RMSE and MAPE for forecasting. The results showed that the combination of models SARIMA(3,0,1)(1,1,0)12 and DMLP the inverse mean square method provided a performance forecast for the six months ahead, up to 66.5% higher than individual models used, where the combination of the predictions obtained a RMSE of 1.43, and a MAPE of 2.16. In the 12 month ahead prediction for the performance of the combination was up to 56.5% higher compared to individual models, in which case obtained a RMSE of 2.86 and 3.70% MAPE. The combination of time series models enabled a significant increase in performance prediction models, but in order to produce satisfactory absolute results should be used to complement their predictive abilities mutually. / A previsão da demanda futura dos produtos é a principal variável a ser considerada no planejamento e controle da produção nas organizações. As técnicas de previsão de demanda são fundamentais no planejamento da produção de nível tático e operacional, especialmente as séries temporais, pois não requerem do planejador, uma investigação mais aprofundada acerca dos fatores que influenciam a demanda. Dois métodos de previsão de séries temporais frequentemente utilizados na literatura são os modelos ARIMA e os modelos MLP/RNA. Uma prática que surgiu em 1969 e já consolidada para obter maior acurácia é a combinação das previsões individuais de dois ou mais modelos. Considerando a necessidade das organizações por técnicas preditivas que gerem melhores resultados, este estudo tem como objetivo prever os valores futuros de uma série temporal da demanda de leite UHT em uma indústria de lácteos, por meio da combinação dos modelos ARIMA e MLP/RNA, e comparar os resultados obtidos pelas combinações em relação aos modelos individuais, exemplificando a obtenção da previsão combinada no planejamento da produção. As medidas de acurácia para mensurar os resultados obtidos e selecionar o melhor modelo, foram o RMSE e o MAPE de previsão. Os resultados mostraram que a combinação dos modelos SARIMA(3,0,1)(1,1,0)12 e DMLP pelo método inverse mean square forneceu um desempenho na previsão para 6 meses adiante, de até 66,5% superior em relação aos modelos individuais utilizados, onde a combinação das previsões obteve um RMSE de 1,43 e um MAPE de 2,16. Na previsão para 12 meses adiante, o desempenho da combinação foi de até 56,5% superior em relação aos modelos individuais, caso em que obteve um RMSE de 2,86 e um MAPE de 3,70%. A combinação de modelos de séries temporais possibilitou um aumento significativo no desempenho de previsão dos modelos, mas para que se obtenham resultados absolutos satisfatórios, devem-se utilizar modelos previsores que complementem mutuamente a capacidade preditiva.

This thesis contains three essays covering different topics in the field of statistics<p>and econometrics of survey data. Chapters one and two analyse two aspects<p>of the Survey of Professional Forecasters (SPF hereafter) dataset. This survey<p>provides a large information on macroeconomic expectations done by the professional<p>forecasters and offers an opportunity to exploit a rich information set.<p>But it poses a challenge on how to extract the relevant information in a proper<p>way. The last chapter addresses the issue of analyzing the opinions on the euro<p>reported in the Flash Eurobaromenter dataset.<p>The first chapter Measuring Uncertainty and Disagreement in the European<p>Survey of Professional Forecasters proposes a density forecast methodology based<p>on the piecewise linear approximation of the individual’s forecasting histograms,<p>to measure uncertainty and disagreement of the professional forecasters. Since<p>1960 with the introduction of the SPF in the US, it has been clear that they were a<p>useful source of information to address the issue on how to measure disagreement<p>and uncertainty, without relying on macroeconomic or time series models. Direct<p>measures of uncertainty are seldom available, whereas many surveys report point<p>forecasts from a number of individual respondents. There has been a long tradition<p>of using measures of the dispersion of individual respondents’ point forecasts<p>(disagreement or consensus) as proxies for uncertainty. Unlike other surveys, the<p>SPF represents an exception. It directly asks for the point forecast, and for the<p>probability distribution, in the form of histogram, associated with the macro variables<p>of interest. An important issue that should be considered concerns how to<p>approximate individual probability densities and get accurate individual results<p>for disagreement and uncertainty before computing the aggregate measures. In<p>contrast to Zarnowitz and Lambros (1987), and Giordani and Soderlind (2003) we<p>overcome the problem associated with distributional assumptions of probability<p>density forecasts by using a non parametric approach that, instead of assuming<p>a functional form for the individual probability law, approximates the histogram<p>by a piecewise linear function. In addition, and unlike earlier works that focus on<p>US data, we employ European data, considering gross domestic product (GDP),<p>inflation and unemployment.<p>The second chapter Optimal Combination of Survey Forecasts is based on<p>a joint work with Christine De Mol and Domenico Giannone. It proposes an<p>approach to optimally combine survey forecasts, exploiting the whole covariance<p>structure among forecasters. There is a vast literature on forecast combination<p>methods, advocating their usefulness both from the theoretical and empirical<p>points of view (see e.g. the recent review by Timmermann (2006)). Surprisingly,<p>it appears that simple methods tend to outperform more sophisticated ones, as<p>shown for example by Genre et al. (2010) on the combination of the forecasts in<p>the SPF conducted by the European Central Bank (ECB). The main conclusion of<p>several studies is that the simple equal-weighted average constitutes a benchmark<p>that is hard to improve upon. In contrast to a great part of the literature which<p>does not exploit the correlation among forecasters, we take into account the full<p>covariance structure and we determine the optimal weights for the combination<p>of point forecasts as the minimizers of the mean squared forecast error (MSFE),<p>under the constraint that these weights are nonnegative and sum to one. We<p>compare our combination scheme with other methodologies in terms of forecasting<p>performance. Results show that the proposed optimal combination scheme is an<p>appropriate methodology to combine survey forecasts.<p>The literature on point forecast combination has been widely developed, however<p>there are fewer studies analyzing the issue for combination density forecast.<p>We extend our work considering the density forecasts combination. Moving from<p>the main results presented in Hall and Mitchell (2007), we propose an iterative<p>algorithm for computing the density weights which maximize the average logarithmic<p>score over the sample period. The empirical application is made for the<p>European GDP and inflation forecasts. Results suggest that optimal weights,<p>obtained via an iterative algorithm outperform the equal-weighted used by the<p>ECB density combinations.<p>The third chapter entitled Opinion surveys on the euro: a multilevel multinomial<p>logistic analysis outlines the multilevel aspects related to public attitudes<p>toward the euro. This work was motivated by the on-going debate whether the<p>perception of the euro among European citizenships after ten years from its introduction<p>was positive or negative. The aim of this work is, therefore, to disentangle<p>the issue of public attitudes considering either individual socio-demographic characteristics<p>and macroeconomic features of each country, counting each of them<p>as two separate levels in a single analysis. Considering a hierarchical structure<p>represents an advantage as it models within-country as well as between-country<p>relations using a single analysis. The multilevel analysis allows the consideration<p>of the existence of dependence between individuals within countries induced by<p>unobserved heterogeneity between countries, i.e. we include in the estimation<p>specific country characteristics not directly observable. In this chapter we empirically<p>investigate which individual characteristics and country specificities are<p>most important and affect the perception of the euro. The attitudes toward the<p>euro vary across individuals and countries, and are driven by personal considerations<p>based on the benefits and costs of using the single currency. Individual<p>features, such as a high level of education or living in a metropolitan area, have<p>a positive impact on the perception of the euro. Moreover, the country-specific<p>economic condition can influence individuals attitudes. / Doctorat en Sciences économiques et de gestion / info:eu-repo/semantics/nonPublished

In a wide range of applications, decisions must be made by combining information from multiple agents with varying levels of trust and expertise. For example, citizen science involves large numbers of human volunteers with differing skills, while disaster management requires aggregating information from multiple people and devices to make timely decisions. This thesis introduces efficient and scalable Bayesian inference for decision combination, allowing us to fuse the responses of multiple agents in large, real-world problems and account for the agents’ unreliability in a principled manner. As the behaviour of individual agents can change significantly, for example if agents move in a physical space or learn to perform an analysis task, this work proposes a novel combination method that accounts for these time variations in a fully Bayesian manner using a dynamic generalised linear model. This approach can also be used to augment agents’ responses with continuous feature data, thus permitting decision-making when agents’ responses are in limited supply. Working with information inferred using the proposed Bayesian techniques, an information-theoretic approach is developed for choosing optimal pairs of tasks and agents. This approach is demonstrated by an algorithm that maintains a trustworthy pool of workers and enables efficient learning by selecting informative tasks. The novel methods developed here are compared theoretically and empirically to a range of existing decision combination methods, using both simulated and real data. The results show that the methodology proposed in this thesis improves accuracy and computational efficiency over alternative approaches, and allows for insights to be determined into the behavioural groupings of agents.

近年來遠程醫療成為中國大陸大力推動的政策，其不僅被賦予催化分級醫療的角色，在照護產業應用上亦被寄予厚望。本研究透過穿戴式裝置的例子，說明遠程醫療的推動仍面臨諸多挑戰。中央政府透過組建醫療聯合體、跨省技術等試點政策，大力推動遠程醫療。地方醫院基於保護醫療收益，對於遠程醫療抱持著不配合的態度，地方政府之間的競爭亦加劇了這樣的發展，推動過程面臨了明顯的瓶頸。與遠程醫療最相近的產品應用，當屬穿戴式裝置，本研究指出在穿戴式裝置依然以地區醫院為母體，鮮少有跨不同事業單位的大規模串聯。從政策與產業兩大領域來看，遠程醫療要全面性推廣仍有一段路要走，然而中國大陸強力推動產業的決心仍值得吾人關注。 / In recent years, policy of telemedicine, proposed by Chinese mainland, played an important role in hierarchical medical system. The care industry has been highly expected. This study research data of the formation of medical treatment combination, interprovincial technology and other pilot policies which were proposed by central government with wearable device to describe the challenge of the promotion in telemedicine industry. In fact, local hospital keep an uncooperative attitude to develop remote medical care in order to protect the medical benefits. Furthermore, competitiveness between local governments made things worse. It is clear that the promotion of telemedicine is facing a bottleneck now. Wearable device, the closest product application in telemedicine industry, is used as keyword to search the data in dilemma of local hospitals. The result show that there is few small units across the large industry chain.From the policy and industry two major areas of view, comprehensive promotion of telemedicine is still a way to go, nonetheless, the Chinese mainland’s determination to promote the industry's is still worthy of my attention.

Magister Public Health - MPH / Malaria is a health, social and economic burden in Nigeria and consistently ranks amongst the four most common causes of childhood deaths. Treatment of malaria is usually started at home; care is only sought from the health facility when the treatment is ineffective (McCombie, 1996). Patent medicine vendors (PMVs) have been identified as a widely patronized source for drugs used in the home treatment of malaria (Breiger et al, 2001; Goodman, et al, 2007; Salako et al, 2001). Inadequate or poor knowledge and practices in the use of anti-malaria drugs (AMDs) increases morbidity and mortality, undermines therapeutic efficacy, and promotes the emergence and spread of drugresistant malaria. Aim: The aim of the study was to describe and quantify the knowledge and self-reported practices of PMVs in the use of antimalarials, particularly artemisinin-based combination therapies (ACTs), in a poor urban community in Lagos state, Nigeria. / South Africa

Virgo est un interféromètre de Michelson dont les bras contiennent des cavités Fabry-Perot. Il a été construit pour détecter directement les ondes gravitationnelles. Le projet Advanced Virgo est une amélioration majeure de Virgo pour atteindre une sensibilité encore plus élevée avec laquelle la détection des ondes gravitationnelles deviendra probable. On prévoit un système laser mono-fréquence de 175 Watts de puissance optique présentant des stabilités accrues pour le bruit relatif de puissance et pour le bruit de fréquence. Ce travail de thèse a pour objet la réalisation de ce système laser de haute-puissance et de haute-stabilité basée sur l'utilisation d'amplificateurs à fibre combinés de façon cohérente. Des amplificateurs à fibre disponibles dans le commerce sont caractérisés en termes de qualité de faisceau, de bruit de puissance, de bruit de fréquence, de stabilité de pointé du faisceau, et également en terme de stabilité à long terme sur quelques milliers d'heures. On implémente l'interférométrie de Mach-Zehnder pour la combinaison cohérente de faisceaux. Les techniques de caractérisation de faisceaux laser sont aussi développées en considérant leurs limites ultimes. Hormis un déficit de puissance optique, le système laser développé dans cette étude sur la base de la combinaison cohérente de Master Oscillator Fiber Power Amplifiers, remplit les conditions posées par Advanced Virgo. / Virgo is a cavity-enhanced Michelson interferometer built for the direct detection of gravitational waves. The Advanced Virgo project consists of major upgrades to the Virgo gravitational wave detector for an order of magnitude improvement in differential strain sensitivity, one of which is the tenfold increase in injected laser power to 175 Watts. The use of fiber laser amplifiers and their coherent combination are foreseen to deliver the required high-power low-noise beam. In this thesis work, we review the laser requirements for gravitational wave detectors, introduce the design of the laser system for Advanced Virgo, and develop the means for laser characterization in accordance with the stringent noise specifications. We then present the results to date, notably the quasi-continuous long-term operation of two 40-Watt fiber laser amplifiers over thousands of hours and their coherent combination with Mach-Zehnder interferometry. Although the targeted power for Advanced Virgo is not yet attained, the developed system shows decent noise performance and is promising for further power-scaling efforts.