Made available in DSpace on 2016-08-17T14:52:57Z (GMT). No. of bitstreams: 1 Miriam Dora Chavez Lope.pdf: 1604085 bytes, checksum: 7eec68bb32ad68dca944d6146d4e5c5f (MD5) Previous issue date: 2005-03-14 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / In the whole world, the restructuring of the electrical sector promoted by the deregulation of the electric utilities has brought economical benefits for the society; furthermore there has been an increase of the pertinent interest in the subject of power quality. The competitive environment created by the deregulation forces the electric companies of generation and transmission to redefine their objectives in order to reduce their operation costs and to maximize their profits to guarantee their survival. Some of the measures adopted to reach these objectives, such as the postponement of the maintenance and investments for the expansion in the electric network, have as direct consequence the deterioration on the levels of reliability and quality of the supply. In distribution systems, this situation is more critical due to the monopolist nature of the electrical utilities. In other words, the consumers are subjected to the lucrative interests of these companies and, for that reasons, in several countries, the regulatory entities have been establishing goals for the reliability and quality of the supply aiming to punish the distribution utilities that violate these goals. In this new environment the interest of the electric utilities, consumers and regulatory entities for the quality of energy have been increasing due to the economical impact experienced by them. One of the problems of the quality of energy are the voltage sags effects, which has increased in recent years due to the crescent use of new equipments, which are more sensitive to voltage variations. The aim of this work is to develop a probabilistic methodology to analyse voltage sags in distribution networks. With the proposed methodology, power quality índices associated with voltage sags can be estimated in distribution systems, considering the system s topology and failure data. Due to the stochastic nature of the frequency and duration of fault, the proposed methodology is based on probabilistic models that permit to represent the system´s operation under faults. The proposed methodology is based on the combination of the Monte Carlo Method with the Admittance Summation Method. The Monte Carlo Method with sequential simulation is used to sample the failure scenarios and the Admittance Summation Method to evaluate fault currents. These fault currents are evaluated using a phase coordinate model of the distribution system. This model has been used due to the distribution networks unbalance caused by loads and untransposed overhead lines. Furthermore, voltage sags duration has been estimated using the current×time curves of the protection devices (fuses, breakers, reclosers). The proposed methodology has been tested in a feeder belonging to the Maranhão Electric Utility(CEMAR) and the results indicate that the proposed methodology is a good tool for studies of sags in distribution systems because it permits the evaluation of the system s performance against voltage sags, also estimating the compatibility between the system and the customer equipments. The results are shown through probability distributions of the SARFI%V, SARFICBEMA and SARFIITIC índices; cumulative and individual probability distributions, scattering diagrams and coordination charts of the voltage sags. / No mundo todo, a reestruturação do setor de energia promovida pela desregulamentação das empresas elétricas trouxe benefícios econômicos para a sociedade, resultando no aumento do interesse pertinente a questão da qualidade de energia. O ambiente competitivo criado pela desregulamentação obriga às empresas elétricas de geração e transmissão a redefinirem seus objetivos a fim de reduzir seus custos operacionais e maximizar seus lucros para garantir sua sobrevivência. Algumas das medidas adotadas para conseguir estes objetivos, tais como o adiamento da manutenção e investimentos de expansão na rede elétrica têm como conseqüência direta a deterioração dos níveis de qualidade e confiabilidade do fornecimento de energia. Em sistemas de distribuição esta situação é mais crítica devido à natureza monopolista das redes de distribuição. Os consumidores estão sujeitos aos interesses lucrativos destas empresas e, por causa disto, geralmente os órgãos reguladores estabelecem metas de confiabilidade e qualidade do fornecimento de energia elétrica a fim de evitar a deterioração da qualidade de fornecimento de energia e penalizar as empresas que violarem estas metas. Um dos problemas da qualidade de energia que basicamente preocupa são as variações de tensão de curta duração, cujos efeitos aumentaram em anos recentes devido ao crescente uso de equipamentos mais sensíveis à variações de tensão. Este trabalho tem como objetivo desenvolver uma metodologia probabilística para analisar as variações de tensão de curta duração em redes de distribuição. Com a metodologia proposta pode-se estimar índices de qualidade de energia associados as variações de tensão de curta duração em sistemas de distribuição, considerando-se a topologia e dados de falha do sistema. Devido à natureza estocástica da freqüência e duração das faltas, sendo o curto circuito a principal causa das variações de tensão de curta duração, a metodologia proposta se baseia em modelos probabilísticos que permitem representar a operação do sistema frente às faltas. A metodologia proposta se baseia na combinação do Método de Monte Carlo com o Método de Soma de Admitâncias. O Método de Monte Carlo com simulação seqüencial é usado para a amostra de cenários de faltas e o Método de Soma de Admitância para estimar as correntes de faltas. Estas correntes de faltas são estimadas usando-se o modelo de coordenadas de fase do sistema de distribuição. Este modelo é usado devido ao desequilíbrio das redes de distribuição causado pelas cargas e pelas linhas aéreas não transpostas. Além disso, a duração das variações de tensão de curta duração é estimada usando-se as curvas de tempo×corrente dos dispositivos de proteção (fusíveis, disjuntores, religadores). Para comprovar a aplicação prática, a metodologia foi testada em um alimentador da Companhia Energética do Maranhão (CEMAR). Os resultados são apresentados como: distribuições de probabilidade dos índices SARFI%V, SARFICBEMA e SARFIITIC; distribuições de probabilidade individual-cumulativa, diagramas de dispersão e cartas de coordenação das variações de tensão de curta duração. A metodologia proposta é uma ferramenta útil tanto para as empresas elétricas como para consumidores, porque permite avaliar o desempenho do sistema frente às variações de tensão de curta duração e estima a compatibilidade entre o sistema e os equipamentos do consumidor.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-09-29T13:41:58Z No. of bitstreams: 1 monalisamarialauro.pdf: 510424 bytes, checksum: 31284a9c9c1e1159695542b7f038ffe8 (MD5) / Approved for entry into archive by Diamantino Mayra (mayra.diamantino@ufjf.edu.br) on 2016-09-30T13:52:54Z (GMT) No. of bitstreams: 1 monalisamarialauro.pdf: 510424 bytes, checksum: 31284a9c9c1e1159695542b7f038ffe8 (MD5) / Made available in DSpace on 2016-09-30T13:52:54Z (GMT). No. of bitstreams: 1 monalisamarialauro.pdf: 510424 bytes, checksum: 31284a9c9c1e1159695542b7f038ffe8 (MD5) Previous issue date: 2010-08-18 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / Na presente dissertação, analisa-se o modo peculiar com que Kant apreende o problema da imortalidade da alma em sua filosofia crítica. Neste intuito, prioriza-se um confronto com as provas racional-teóricas presentes no célebre Fédon mendelssohniano, visto que este é uma notável referência na defesa da imortalidade da alma na Aufklärung. Este confronto permite constatar que o argumento da simplicidade da alma de Mendelssohn constitui-se em um paralogismo transcendental, e que sua defesa da incorruptibilidade da alma não se sustenta quando se respeita a condição crítica de uso esquematizado dos conceitos puros do entendimento. Finalmente, a advertência kantiana contra o uso especulativo da razão para além dos limites da experiência possível revela-se como parte de seu empreendimento de fundamentação de uma moralidade autônoma e plenamente ativa na vida humana. Na perspectiva aberta pela lei moral, a permanência da alma resolve-se como um necessário e sólido postulado da razão prática pura. / This thesis analyzes the particular way in which Kant conceives the issue of the soul’s immortality in his critical philosophy. In order to do that, the focus is set on a confrontation with the rational-theoretical proofs present in Mendelssohn’s Phaedon, since this work is a remarkable reference in the defense of the soul’s immortality during the German Aufklärung. This confrontation allows us to verify that Mendelssohn’s argument of the simplicity of the soul constitutes a transcendental paralogism, and his defense of the incorruptibility of the soul fails when measured by the critical condition of a schematized use of the pure concepts of the understanding. Finally, Kant’s caution against the speculative use of reason beyond the limits of possible experience appears as a part of his undertaking of philosophically grounding a morality which is both autonomous and completely active in human life. Following the perspective opened by the moral law, the duration of the soul is explained as a necessary and firm postulate of pure practical reason.

Abstract Coronary artery disease (CAD) is the leading cause of death in developed countries. In patients with complex CAD, coronary artery bypass grafting (CABG) remains the preferred treatment as it can provide long-lasting results. However, CABG carries a significant risk of excessive perioperative bleeding and other complications, which may deteriorate the prognosis. Transfusion of blood products is generally used to compensate blood loss. However, both bleeding and blood transfusions have been shown to be associated with an adverse outcome. This cohort study aimed to clarify the impact of perioperative bleeding and the use of different blood products in the development of perioperative complications in 2,764 patients undergoing isolated CABG. The universal definition of perioperative bleeding classification (UDPB) was employed to stratify the severity of bleeding. Additionally, the impact of storage time of transfused red blood cells (RBCs) on the outcome was investigated. Increased UDPB classes, particularly classes 3 and 4, were associated with significantly poorer immediate and late outcome. RBC transfusion in patients who underwent elective off-pump CABG was independently associated with increased troponin I release indicating myocardial injury. Prolonged storage duration of transfused RBCs did not affect immediate and late outcome of patients with moderate bleeding. The most remarkable risk factors for stroke after off-pump CABG were any degree of atherosclerosis of the ascending aorta as well as transfusion of platelets and/or solvent/detergent-treated plasma. The UDPB classification appears to be a promising research tool to stratify the severity of perioperative bleeding and to assess its prognostic impact after coronary surgery. Prevention of major bleeding that leads to blood transfusion may protect from myocardial injury and stroke and possibly result in better early and late outcomes. Patients with a diseased ascending aorta could be considered at high risk of stroke because of their risk of generalized atherosclerosis. In case of mildly diseased aorta, the “no-touch” aorta policy should be considered with the intention of preventing postoperative stroke. / Tiivistelmä Sepelvaltimotauti on yleisin kuolinsyy kehittyneissä maissa. Potilailla, joilla on vaikea monen suonen tai vasemman sepelvaltimon päärungon tauti, sepelvaltimoiden ohitusleikkaus on edelleen paras hoitovaihtoehto, koska sillä pystytään saavuttamaan pitkäkestoisia tuloksia. Kuitenkin ohitusleikkaukseen liittyy suuri riski leikkauksen aikaiselle tai jälkeiselle verenvuodolle ja muille haittatapahtumille, jotka osaltaan huonontavat potilaan ennustetta. Vuodon hoitona käytetään yleisesti verensiirtoa. Kuitenkin on osoitettu, että sekä verenvuoto että verituotteiden anto lisäävät riskiä komplikaatioille. Tämän kohorttitutkimuksen tavoitteena oli selvittää tarkemmin leikkauksen yhteydessä ilmenevän vuodon ja siihen liittyvän verensiirron vaikutuksia leikkauksen jälkeisten haittatapahtumien kehittymiseen 2764 ohitusleikatulla potilaalla. Universal Definition of Perioperative Bleeding (UDPB) -luokitusta käytettiin vuodon vaikeusasteen luokittelemiseen. Lisäksi tutkittiin siirrettyjen punasolujen varastointiajan vaikutusta potilaan ennusteeseen. Korkeammat UDPB-luokat, erityisesti luokat 3 ja 4, liittyivät merkittävästi huonompaan lyhyen ja pitkän aikavälin ennusteeseen. Potilailla, joille oli tehty kiireetön ohitusleikkaus ilman sydän-keuhkokoneen käyttöä, punasolujen anto oli itsenäinen riskitekijä suurentuneelle troponiini I -päästölle eli sydänlihasvauriolle. Pidentynyt punasolujen varastointiaika ei ollut yhteydessä lyhyen tai pitkän aikavälin ennusteeseen potilailla, jotka olivat vuotaneet kohtalaisesti. Merkittävimmät riskitekijät ilman sydän-keuhkokonetta tehdyn leikkauksen jälkeiselle aivoinfarktille olivat minkä tahansa asteinen nousevan aortan ateroskleroosi sekä verihiutaleiden ja/tai jääplasman anto. UDPB-luokitus vaikuttaa lupaavalta tutkimustyökalulta verenvuodon vaikeusasteen luokitteluun. Lisäksi sitä voidaan käyttää vuodon ennusteellisen vaikutuksen arvioimiseen ohitusleikkauksen jälkeen. Runsaan verenvuodon ja siihen liittyvän verensiirron ehkäiseminen saattaa suojata potilasta sydänlihasvauriolta ja aivoinfarktilta ja mahdollisesti johtaa parempaan lyhyen ja pitkän aikavälin ennusteeseen. Potilaita, joilla on nousevan aortan ateroskleroosi, voisi pitää suuressa aivoinfarktiriskissä yleisen ateroskleroosiriskin vuoksi. Potilailla, joilla on lieväkin nousevan aortan ateroskleroosi, tulisi harkita aortan jättämistä pihdittämättä aivoinfarktin ehkäisemiseksi.

Dans cette thèse, nous identifions les déterminants de la survie des nouvelles entreprises créées par les jeunes diplômés de l'enseignement supérieur, bénéficiant de prêts bancaires à taux bonifié. Un accent est mis sur l’impact des politiques d’aides publiques. Les données sont issues d’une enquête réalisée en 2013, sous la tutelle de l’Université de Sfax, sur une cohorte de 160 entreprises créées entre le 01/01/2008 et 31/12/2008, soit cinq ans après la création. Le taux de réponse était de 81,25%. Après avoir évoqué la problématique de survie de la petite entreprise nouvellement créée, nous recourons aux modèles de durée, et plus précisément au modèle semi-paramétrique de Cox (1972). L’analyse conduit à mettre en lumière qu’un entrepreneur voit son entreprise plus pérenne, lorsqu’il s’agit d’un homme étudiant qui s’est lancé dans les affaires l’année de l’obtention de son diplôme, ayant un entourage entrepreneurial qui stimule chez lui le goût d’entreprendre et d’indépendance. L’amélioration de la survie découle de la similitude entre l’activité préalable de l’entrepreneur et l’activité de son entreprise, et la détention d’un capital initial de démarrage qui dépasse les 30.000 DT. Les aides octroyées par l’Etat aux nouveaux promoteurs (subvention d’investissement, bourse d’accompagnement, allégement des charges sociales et patronales) ne contribuent pas à diminuer le risque de l’échec entrepreneurial, à l’exception de la prise en charge par l’Etat d’une partie des salaires. Par contre une entreprise bénéficiant d’une formation entrepreneuriale et d’un accompagnement post-création, voit sa probabilité de survie s’accroître. / In this dissertation we identify the determinants of the longevity and the probability of survival of small businesses created by young graduates benefiting from bank loans at enhanced rates. The focus is on the policy impact of public support for the creation of companies. The data are based on a survey conducted in 2013 under the tutelage of the University of Sfax (Tunisia) of a cohort of 160 companies five years after they were first formed. The response rate was 81.25%. After discussing the issue of the survival of newly-established companies and the factors that promote their survival, we use duration models specifically the Cox model (1972). This analysis allows us to shed light on a business is more likely to survive if the entrepreneur is a male who started his business within a year of graduating and comes from an entrepreneurial background, stimulating his entrepreneurial spirit. The improved longevity of small companies ensues from the similarity between the entrepreneur’s previous occupation and the activity of his own company, and from the initial start-up capital if it exceeds 30.000 DT. Aid granted by the State for new promoters (investment subsidy, grant, and reduction in social security contributions) does not help reduce the risk of entrepreneurial failure with the exception of State aid to support a portion of employees’ wages. On the other hand, a company benefiting from entrepreneurial training before creation and from support post-creation sees its probability of survival rise.

Les principaux modèles et représentations du changement organisationnel ont en commun de le considérer, de façon plus ou moins explicite, comme un phénomène dynamique fait de forces ou comme un flux, un mouvement. Mais dans les deux cas, le changement n’est pas directement observé. Il est simplement déduit d’une série d’observations portant (i) soit sur une ‘entité’ qui change - des formes d’organisations ou un ensemble de pratiques - (ii) soit sur une succession de phases, d’étapes ou d’évènements. Ce qui revient, paradoxalement, à observer une série d’immobilités. Notre propos dans cette thèse est d’observer le changement lui-même. Et comme un flux émergent, un mouvement substantiel et absolument indivisible, en référence à la philosophie d’Henri Bergson. / The main models of organizational change have in common that they see change, more or less explicitly, either as a dynamic phenomenon due to forces or as a flow, a movement. But change itself is not directly observed. It is simply inferred from a series of observations that focus on either (i) an entity, or (ii) a sequence of events - phases or steps of an on-going process. So, research in organizational change faces a paradox : understanding change processes leads to representations and explanations that reify the processes in fixed forms (words or diagrams). The aim of this dissertation is to observe change itself and show how it can be thought of as a flow, a movement. The conditions of understanding change as a movement are based on Henri Bergson’s philosophy.

La thématique centrale de cette thèse, située à l’interface entre macroécologie et macroévolution, consiste en l’analyse des dynamiques spatio-temporelles de distribution des ammonites du Pliensbachien inf. de la Téthys de l’Ouest. Deux problématiques sont abordées : comment la similarité compositionnelle des assemblages décroît-elle avec la distance géographique? Quel est le lien entre la taille des aires de répartition des espèces et leur phylogénie, leur durée de vie, et leur position latitudinale?Grâce à une analyse des relations de SDD, nous montrons que plus l’environnement est homogène, plus les ammonites se dispersent librement ; et que leur dispersion sur de grandes distances n’est pas liée à leur morphologie, ce qui suggère qu’elle se faisait essentiellement via une dérive planctonique aux cours des stades juvéniles.Notre étude de l’étendue de la répartition des ammonites révèle que cette caractéristique n’est ni stable, ni propre à un clade. Son héritabilité phylogénétique dépend de la stabilité spatio-temporelle de l’environnement et varie selon l’estimateur de répartition et l’intervalle de temps considérés, et entre des espèces d’un même groupe contemporaines les unes des autres. De plus, l’étendue de répartition n’a pas d’effet sur la durée de vie des espèces. Cette absence de corrélation semble prévaloir chez les ammonoïdes, ce groupe étant connu pour présenter de grandes aires de répartition associées à des courtes durées de vie. Enfin, les étendues latitudinales des ammonites étudiées tendent à être maximales aux basses latitudes et augmentent des moyennes vers les hautes latitudes, conformément à la Règle de Rapoport. Ceci suggère qu’elles étaient vraisemblablement température-dépendantes et qu’un gradient de température des eaux existait au Pliensbachien inf. dans la province NW européenne. / The present work, which lies between macroecology and macroevolution, focuses on the spatio-temporal dynamics of early Pliensbachian ammonites of the western Tethys. Two main questions are addressed: how does inter-assemblage compositional similarity decrease with geographical distance? What is the relationship between species range size and phylogeny, species duration and latitudinal position?Ammonite dispersal dynamics are studied through a multi-scale Similarity Distance Decay analysis. We show that their long-distance dispersal is facilitated when the environment is more homogeneous and that it is not related to their morphology. This suggests that their long-distance dispersal occurred essentially through a passive planktonic drift during the first juvenile stages.We also show that ammonite geographical range size is neither stable, nor clade-specific. Indeed, its phylogenetic heritability depends on the spatio-temporal stability of the environment and it varies according to the range variable chosen, the temporal interval considered, and among contemporary species of the same group. Furthermore, the size of their geographical range has no effect on species duration. In fact, this lack of correlation seems to prevail among ammonoids, as this group is well-known for showing both large geographical distributions and short species durations. Finally, species latitudinal ranges tend to be maximal at low latitudes and to increase from middle to high latitudes during the early Pliensbachian, in accordance with the Rapoport’s rule. This suggests that these ammonites were probably temperature-dependent and that a latitudinal gradient of sea-surface temperature occurred in the NW European province during the early Pliensbachian.

This study determined whether the Hodgkin-Huxley model for unmyelinated nerve fibres could be more comprehensively modified to predict excitation behaviour at Ranvier nodes of a human sensory nerve fibre, as specifically applied to the prediction of temporal characteristics of the human auditory system. The model was developed in three phases. Firstly, the Hodgkin-Huxley model was modified to describe action potential dynamics at Ranvier nodes using recorded ionic membrane current data from single human myelinated peripheral nerve fibres. A nerve fibre cable model, based on a combination of two existing models, was subsequently developed using human sensory nerve fibre morphometric data. Lastly the morphological parameters of the nerve fibre model were changed to resemble a Type I peripheral auditory nerve fibre and coupled to a volume-conduction model of the cochlea. This study is the first to show that the Hodgkin-Huxley model equations can be modified successfully to predict excitation behaviour of a generalised human peripheral sensory nerve fibre without using the Goldman-Hodgkin-Katz equations. The model includes a more comprehensive establishment of temperature dependence of the physiological and electrical parameters compared to existing models. Two versions of the human Type I auditory nerve fibre model were developed, one simulating an undamaged (non-degenerate) fibre and another a damaged (degenerate) fibre. Comparison between predicted and measured results indicated similar transient and persistent sodium, as well as slow potassium ionic membrane currents to those found in generalised sensory nerve fibres. Results confirm that chronaxie, rheobase current, mean latency, threshold and relative refractive periods depend on the amount of degeneracy of fibres. The model could account for threshold differences observed between different asymmetric waveforms. The combination of persistent sodium and slow potassium ionic membrane currents could in part predict non-monotonic excitation behaviour observed experimentally. A simplified method was developed to calculate electrically evoked compound action potential responses following neural excitation. It provided a computationally effective way to obtain an estimate of profile widths from the output of models that calculate neural excitation profiles, and an indirect way to estimate stimulus attenuation by calculating the value of the parameter that produces the best fit to experimental data. Results also confirmed that electrode arrays located closer to the modiolus produce more focussed neural excitation spread than more laterally located arrays. / Thesis (PhD)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

Current economic situation is characterized for deflation and low inflation, low economic growth, and low or negative interest rates, which lead to phenomenon of issuing governments bonds with negative yield. The main goal of this work is to understand the valuation and behavior of bonds with condition of negative interest rates, analyze impacts of negative rates on volatility of bonds. This work also compares the behavior of negative yields of bonds in contrast with positive yields. The contribution of this work consists in the critical evaluation of limitations of the formula for calculating the bond price to fulfill its role if the values of negative interest rates are too low.

Cette thèse propose une analyse novatrice des différences de niveau de chômage entre les hommes et les femmes, en tenant compte, en plus du taux, d'autres dimensions importantes de la question qui ont des répercussions en matière de bien-être pour les individus et la société dans laquelle ils vivent. Elle se compose de trois chapitres contributifs.Le chapitre II propose une extension de la mesure des différences de niveaux chômage entre les hommes et les femmes sur la base de l'indice de Shorrocks. Cet indice prend en compte, en plus du taux de chômage, de la durée moyenne et de l'inégalité dans la distribution des durées de chômage. Le chapitre III part des résultats du chapitre II et propose une analyse purement empirique de l'écart entre les sexes dans le chômage en France. Il examine en outre les différences entre les sexes dans le taux de chômage, la durée moyenne de chômage et la distribution des durées de chômage. Le chapitre fournit également une analyse de la réduction des écarts entre sexes dans le chômage, ainsi qu'une analyse comparative de trois différentes méthodes de décomposition: Yun, Taylor décomposition et Oaxaca. Le chapitre IV présente une analyse de la différence entre les sexes dans le nombre d'épisodes de chômage (vulnérabilité face au chômage) et la distribution de ces épisodes dans la force de travail (répartition inégale de la perte de bien-être engendrée par le chômage). L'importance de la question réside dans le fait que le chômage répétitif peut causer un travail moins bien rémunéré et des emplois précaires et donc conduire à la pauvreté et à l'exclusion sociale. / The thesis provides a novel analysis of the differences in unemployment between males and females, taking into account, in addition to the rate, other important aspects of unemployment that have welfare implications for both individuals and the society where they live. It consists of three contributive chapters.Chapter 2 proposes a measurement of the differences in unemployment between males and females based on an index by Shorrocks. The latter is estimated by quarter for France during the period 2003:1 to 2008:3 using three different methods: synthetic cohort method, Salant's method and a method using directly the interrupted durations. The first method uses the interrupted durations to obtain an estimate of the distribution of completed durations while the Salant method do the same but assume that the labour market is in a steady state. Chapter 3 builds from Chapter 2's results and proposes a purely empirical analysis of the gender gap in unemployment in France. It examines in addition to the gender differences in the unemployment rate, the gender differences in mean duration and distribution of durations. The chapter also provides a comparative analysis of different methods of regression-based decomposition. It finishes with an analysis of the reduction of the gender gap in unemployment in France between 2003 and 2008 Chapter 4 provides an analysis of the gender difference in the number of unemployment spells and the distribution of these spells across the labour force. The importance of the matter relates to the fact that a repetitive unemployment may cause lower paid work and unstable jobs and therefore lead to poverty and social exclusion.

Pour des applications médicales ou en histoire de l'art, un système compact de production de rayonnement X monochromatique à haut flux par effet Compton nécessite de disposer d’une source laser impulsionnelle de forte puissance moyenne avec des durées de quelques picosecondes. Pour atteindre un haut flux de rayonnement X, le laser devra être injecté dans une cavité Fabry-Perot de haute finesse afin d’atteindre les puissances laser moyennes requises. Par conséquent, le laser devra avoir une bonne qualité de mode et de faibles bruits. Afin d’atteindre ces objectifs, nous avons étudié la réalisation d’oscillateurs à blocage de modes passif délivrant des puissances moyennes de plus de 10 W avec des impulsions d’une durée entre 10 et 20 ps. Au cours de ce travail, deux oscillateurs de haute puissance moyenne ont été conçus et réalisés : l’un à pompage radial avec Nd:YAG comme milieu de gain et l’autre à pompage longitudinal avec comme milieu de gain Nd:YVO4. Le développement du second oscillateur a donné lieu à une étude expérimentale de la réduction de la durée des impulsions qui nous permet d’ajuster la durée entre 46 ps et 12 ps en régime de blocage de modes passif. Les résultats expérimentaux ont été expliqués à l’aide d’une simulation numérique et une solution analytique a été trouvée pour prédire la durée des impulsions. Enfin, une étude des caractéristiques des bruits de l’oscillateur Nd:YVO4 a été réalisée. Ces mesures ont permis de mettre en évidence qu’un oscillateur de forte puissance moyenne a les capacités pour être aussi peu bruyant que des oscillateurs de faible puissance et à faibles bruits. En résumé nous avons développé un oscillateur puissant (20W), à une longueur d’onde de 1064 nm, avec des durées d’impulsions courtes (15 ps), une bonne qualité de faisceau (M2<1,2) et de faibles bruits (gigue temporelle <1,2 ps RMS 100Hz-1MHz non asservi). Par conséquent, notre oscillateur puissant est un excellent candidat pour faire partie de la machine compacte de rayonnement X monochromatique et à haut flux. / For medical or cultural heritage applications, a compact, monochromatic, Compton x-ray source system needs a powerful, few picosecond laser source. To obtain high-x-ray-flux, the laser should be coupled to a high-finesse Fabry-Perot cavity to reach the required laser power. Therefore, the laser should have a good beam quality and low noises. In order to reach theses requirements, we have studied passive mode-locking oscillators delivering more than 10 W average power and between 10 and 20 ps pulse duration.Two high-power oscillators have been designed and implemented: a side-pumped Nd:YAG and an end-pumped Nd:YVO4 oscillator. With the second oscillator, we have studied the experimental reduction of pulse duration. We obtained a decrease from 46 ps to 12 ps in the continuous-wave mode-locked regime. Those experimental results have been explained by a numerical simulation and furthermore, we have developed an analytical solution to predict the pulse duration of such oscillator. Finally, we studied the noise characteristics of the Nd:YVO4 oscillator. Our measurements have shown that a high-power oscillator might be as low-noise as other low-power, low-noise oscillators. In conclusion, we have developed a powerful (20W), 1064nm-wavelength, short-pulses (15ps), good-beam-quality (M2<1.2) and low-noise free-running oscillator (timing jitter <1.2 ps RMS 100Hz-1MHz). Therefore, our high-power oscillator is an excellent candidate to be part of a compact, high-flux, monochromatic x-ray source.