The relationship between community-wide change and patterns of variation and change within the individual is one of the cornerstones of variationist theorising. But while sociolinguistic theory makes clear and testable predictions regarding the use of stable vernacular features across the life-span of the individual, we lack real-time evidence on the age-graded nature of stable variability. Indeed, whereas apparent time research highlights the diachronic stability of (ing), only two research projects have explored its use within the individual speaker. Both report on pre-adult speakers. Our research expands the window of analysis by adding a later age-bracket to the investigation of age-graded variability. We consider the variable realisation of (ing) in a group of individuals between early adulthood and retirement.

Modern machine learning methods are dependent on active optimization research to improve the set of methods available for the efficient and effective extraction of information from large datasets. This, in turn, requires an intense and rigorous study of optimization methods and their possible applications to crucial machine learning applications in order to advance the potential benefits of the field. This thesis provides a study of several modern optimization techniques and supplies a mathematical inquiry into the effectiveness of homotopy methods to attack a fundamental machine learning problem, effective clustering under constraints. The first part of this thesis provides an empirical survey of several popular optimization algorithms, along with one approach that is cutting-edge. These algorithms are tested against deeply challenging real-world problems with vast numbers of local minima, and compares and contrasts the benefits of each when confronted with problems of different natures. The second part of this thesis proposes a new homotopy map for use with constrained clustering problems. This thesis explores the connections between the map and the problem, providing several theorems to justify the use of the map and making use of modern homotopy tracking software to compare an optimization that employs the map with several modern approaches to solving the same problem. / Ph. D.

La première augmentation de la longévité en laboratoire fût observée à la suite d’une intervention nutritionnelle consistant en une réduction de l’apport alimentaire chez le rat. Plus tard, ce phénomène a été reproduit dans de très nombreuses espèces et référé en tant que restriction calorique. Le développement des techniques de biologie moléculaire moderne a permis de montrer dans des organismes modèles simples que cette flexibilité du processus de vieillissement était régulée par des facteurs génétiques. De fait, plusieurs mécanismes cellulaires ont alors pu être identifiés comme responsables de ce contrôle du vieillissement. Ces voies de régulation ont révélées être conservées entre les espèces, depuis les levures jusqu’aux organismes multicellulaires tels que le nématode, la mouche ou la souris, suggérant l’existence d’un programme universel de vieillissement dans le vivant. La levure s’est avéré à plusieurs reprises être un modèle puissant et fiable pour la découverte de gènes impliqués dans ce phénomène. Mon étude a consisté au développement d’un nouveau modèle unicellulaire d’étude du vieillissement à travers l’espèce Schizosaccharomyces pombe appelée aussi levure à fission. La première étape de mon travail a montré que les voies de détection des nutriments gouvernées par la sérine/thréonine protéine kinase A (Pka1) et la sérine/thréonine kinase Sck2 contrôlent le vieillissement chronologique de ces cellules comme il était connu dans la levure Saccharomyces cerevisiae. Ceci permit de valider l’utilisation de la levure à fission pour l’étude du vieillissement. Ensuite, nous avons analysé plus en détail l’effet pro-vieillissement du glucose en étudiant le rôle de sa détection par le récepteur membranaire Git3 couplé à la protéine G (Gpa2) en amont de la kinase Pka1. La perte du signal du glucose par la délétion de Git3 imite partiellement l’effet d’augmentation de longévité obtenu par baisse de la concentration en glucose dans le milieu. De plus, l’effet néfaste du signal du glucose est maintenu en absence de tout métabolisme du glucose suite à la mutation des hexokinases, premières enzymes de la glycolyse. L’ensemble de ces résultats suggèrent que la signalisation du glucose est prédominante sur son métabolisme pour son effet pro-vieillissement. D’autre part, à la fois la suppression de cette signalisation et la baisse de niveau de glucose disponible allongent la durée de vie en corrélation avec une augmentation de la résistance au stress, une hausse d’activité mitochondriale et une baisse de production de radicaux libres. Finalement, le criblage d’une banque de surexpression d’ADNc a permis d’identifier plusieurs gènes candidats responsables de ces effets en aval de la voie de signalisation Git3/PKA. La recherche sur les mécanismes moléculaires du vieillissement propose une nouvelle approche, un nouvel angle de vue, pour la compréhension des fonctions cellulaires et promet d’apporter de précieuses clefs pour mieux comprendre certaines maladies. En effet, le vieillissement est la première cause d’apparition de nombreuses affections comme les cancers, les maladies cardiovasculaires et métaboliques ou les maladies neurodégénératives tels que les syndromes d’Alzheimer et de Parkinson. / The first increase in life span due to man’s intervention was obtained with rats subjected to a diet reduced in calorie intake. Later, this phenomenon was repeated with many other species and referred as diet restriction or calorie restriction. The development of modern Molecular Biology approaches and the use of simple model organisms demonstrated that the rate of aging was regulated by genetic traits. Indeed, several cellular mechanisms were identified as responsible for the control of aging. These regulatory pathways appear to be conserved throughout species, from yeast to multicellular organisms like nematode, fly and mice, thus suggesting the existence of a universal program of aging. Yeast proved several times to be a powerful and reliable model for discovering genes involved in the regulation of aging. My study consisted in developing Schizosaccharomyces pombe (also called fission yeast) as a new unicellular model to study aging. The first step of my work was to show that pathways of nutrient detection through kinases involving Pka1 and Sck2 control chronological aging in S. pombe, as it was previously demonstrated in Saccharomyces cerevisiae. This first work validated the use of fission yeast for the study of aging. Subsequently, we analysed in more detail the pro-aging effect of glucose focusing on the role of its signalling through the G-protein Gpa2-coupled membrane receptor Git3, which acts upstream of Pka1. The loss of the glucose signal due to deletion of Git3 mimics partially the effect of increasing longevity by reducing glucose in the medium. Moreover, detrimental effects of glucose signal are maintained in absence of sugar metabolism following loss of hexokinases, the first enzymes of glycolysis. Together, these results suggest that the pro-aging effects of glucose signalling are predominant over those due to metabolism of this sugar. Moreover, both obliteration of this signalling pathway and decrease of glucose availability extend life span, and correlate with an increase in stress resistance, in mitochondrial activity and a lower production of free radicals. Finally, screening a cDNA-overexpression library allowed us to identify several genes candidates responsible for the effects on longevity downstream of Git3/Pka1. Research in the molecular mechanisms of aging propose holds the promise to bring precious clues as to this mysterious processes affecting all living creatures, and paves the way to unravel the underlying causes of many human diseases. Indeed, aging is the first cause of numerous late-onset pathologies including cancers, cardiovascular diseases or neurodegenerative diseases like Alzheimer and Parkinson syndromes.

The Service Path Attribution Network (SPAN) framework provides a novel, user-centric, connectivity-based approach to ecosystem service assessment and valuation (ESAV). Ecosystem services are delivered to users through the simulated flow of some service medium (i.e., matter, energy, or information) from the ecosystems in which it originates (sources) to the people or assets which it affects (users). Along the way, the service medium may be absorbed by intervening landscape features (sinks) or captured by rival users. Crucially, the service medium is not itself an ecosystem service or benefit but rather an agnostic transport mechanism which establishes connectivity between sources, sinks, rival users, and nonrival users within a delimited study region. Each user then receives benefits or harm from the encountered service medium depending on their specific relationship with it. For example, if surface water is the simulated service medium, it may increase productivity at a hydropower plant but damage farmers in floodplains by drowning their crops. In the SPAN terminology, sources provide provisioning ecosystem services to users with a beneficial relationship with the service medium. Similarly, sinks provide preventive ecosystem services to users with a detrimental relationship with the service medium by reducing the amount flowing to their locations. Notably, within a single SPAN analysis, both sources and sinks may provide ecosystem services given a sufficiently heterogeneous pool of users. The results of a SPAN ESAV analysis are myriad, totalling up to 30 output maps for some services. Taken together, these maps tell the story of which sources provide services to which users, which sinks protect users from harm, which users compete for the same resources (and who wins), and how all of the sources, sinks, rival users, and nonrival users affect one another. Additionally, a SPAN simulation produces maps of the flow paths taken by the service medium from sources to users as well as where and by how much the flow strength is reduced by sinks. Studying these flow paths can help decision makers identify those locations at which management actions would be maximized or minimized depending on their specific development goals. A crowning achievement of this work is that for most ecosystem services the SPAN algorithm's complexity is guaranteed to be linear O(n) in both time and space with respect to the number of discrete locations analyzed. This makes it a viable option for high resolution landscape level ESAV studies using no more than commodity hardware. This dissertation explores the SPAN framework in depth, from its novel conceptual terminology and computational algorithms through to the intended interpretation of its results. In addition to describing the conceptual and mathematical components of this system in detail, this work also provides a complete Literate Program demonstrating the application of the SPAN framework to an assessment of the scenic beauty ecosystem service in Chittenden County, Vermont.

O tempo de vida e o desenvolvimento foliar sempre foram questões que intrigaram a humanidade, para além da questão científica, há um interesse até mesmo estético, uma vez que as folhas senescentes do hemisfério Norte e algumas do hemisfério Sul mudam sua coloração de verde para vermelho ou para um amarelo vistoso. Do ponto de vista científico o tempo de vida foliar está associado à produtividade das plantas, bem como às características estruturais das folhas. No entanto, a maioria dos trabalhos enfoca apenas a folha individualmente e não aborda o ponto que o tempo de vida foliar é, na verdade, um produto das taxas de nascimento e de mortalidade que ocorrem no nível da copa. Este é provavelmente o fator que faz com que haja um grande contraste na literatura sobre o tempo de vida foliar. Do ponto de vista ecológico analisam-se apenas as consequências do tempo de vida foliar, sem levar em consideração os mecanismos fisiológicos responsáveis pela mortalidade. Os trabalhos fisiológicos, por outro lado, enfocam em causas da mortalidade - o aumento na quantidade de hexoses e/ou mudanças nos reguladores de crescimento - sem levar em consideração as conseqüências do tempo de vida foliar. Este trabalho visa integrar estas duas visões. Como o nitrogênio é um dos minerais que possuem um efeito profundo no tempo de vida foliar, este foi usado como ferramenta para modificar o tempo de vida foliar de plantas de Senna alata, uma planta pioneira da família Leguminosae, que apresenta crescimento rápido. Foram realizados dois experimentos. No primeiro foi definida a melhor fonte de nitrogênio para o desenvolvimento da planta usando concentrações iguais de NO3, NH4 e NH4NO3. E no segundo experimento foi estudado o efeito de diferentes concentrações da melhor fonte. Em ambos os casos, a expansão, a biomassa, a fotossíntese (somente no segundo experimento) e teores e composição de carboidratos não estruturais, foram acompanhados para cada folha da planta. No primeiro experimento observou-se que ocorreu um aumento na taxa de mortalidade sem efeito na taxa de iniciação foliar, este fato levou a uma diminuição na longevidade das folhas, o que diminuiu o número de folhas na copa, mas não alterou a estrutura vertical da copa. A quantidade de hexoses na fase de senescência parece estar envolvida com o aumento na taxa de mortalidade através do mecanismo sensor de açúcares e como atuou diminuindo o tempo de senescência das folhas, levou a uma mudança no desenvolvimento foliar. No segundo experimento não houve diferença na mortalidade, mas um aumento na iniciação foliar, assim, conforme a concentração de nitrogênio aumentou, a longevidade das folhas tendeu a aumentar e o número de folhas na copa aumentou, mudando a estrutura vertical desta. Como obervado no primeiro experimento, a baixa concentração de hexoses durante a fase de maturidade pareceu ser o mecanismo que impediu a senescência foliar e que, portanto, modificou o desenvolvimento foliar por aumentar a sua fase de maturidade / Leaf life and development have always been intriguing aspects of nature. Even beyond the scientific scope, the aesthetics of such natural processes, illustrated in many different cases, such as when senescent northern hemisphere leaves (as well as some leaves found in the southern hemisphere) change colors from Green to re dor bright yellow. From a scientific standpoint, leaf life span is related to the plants′ productivity, as well as the structural characteristics of the leave themselves. Unfortunately, most current academic studies focus specifically on leaves, neglecting the fact that leaf life span is intimately related to birth and mortality rates at the canopy. This is possibly the greatest issue surrounding academic controversies and discussions regarding leaf life span. From na ecologic perspective, only the consequences deriving from leaf life are analyzed, while all mortality-related physiological mechanisms are not considered. Physiological studies, on the other hand, focus on causes of mortality - increased amount of hexoses and/or changes in growth regulators - but fail to consider the consequences of leaf life span. This article attempts to integrate both standpoints. As one of the minerals with greatest effect on leaf life span, nitrogen Will be used as a way to alter leaf life span during the experiments. In the first experiment we Will establish the most adequate nitrogen source, using the same NO3, NH4 and NH4NO3 concentrations. In the second experiment, we Will assess the effect of different concentrations in such nitrogen source. The first experiment indicated na increase in the mortality rate with no impact over the leaf initiation process, which decreased leaf life span and the amount of leaves in the canopy, but did not change the canopy vertical structure. The amount of hexoses in the senescence phase is responsible for the mortality rate increase and, by shortening the leaves′ senescence process, ultimately changed the leaves′ development. The second experiment did not indicate changes in the mortality rate, but prompted the leaf initiation process. Therefore, as the nitrogen concentratio increased, so did the leaves′ life span and the amount of leaves in the canopy, altering its vertical structure. During the maturity phase, the low hexose concentration seemed to be the mecanism responsible for hidering the leaf senescence process and, therefore, modified the leaves′ development by the increasing the maturity phase.

Este trabalho aborda, de uma forma geral, os sistemas estruturais normalmente adotados no projeto de cúpulas metálicas. Foi dado ênfase a um arranjo derivado do sistema Schwedler, recentemente utilizado em projetos desenvolvidos no interior do estado de São Paulo. O trabalho pode ser divido em duas partes, a primeira delas versando sobre as ligações que compunham o sistema estrutural estudado, e a segunda versando sobre a influência dessas ligações no comportamento da estrutura e sobre a influência da forma de contraventamento. As ligações foram estudadas sob dois aspectos diferentes, que foram: a) revisão e aperfeiçoamento dos critérios de dimensionamento adotados em algumas ligações, e b) proposição de modelos para descrição do comportamento momento-rotação de ligações com dupla tala de alma parafusada e de aparelhos de apoio. A influência do tipo de contraventamento e da rigidez das ligações foi investigada por meio do efeito exercido nos deslocamentos verticais e na distribuição de esforços internos da estrutura. Para tanto, foram utilizados programas computacionais de uso já consagrado, cujos resultados foram comparados entre si. / In a general way, this work deals with structural systems usually adopted in the project of metallic domes. Emphasis was given to a derived arrangement derived of the Schwedler system, recently used in projects developed the state of São Paulo. The work can be divided in two parts, the first one is about the connections that compose the structural system studied, and second one treats the influence of those connections in the structure behavior and the influence in the brace configuration. The connections were studied under two different aspects, that were: a) revision and improvement of the design criteria adopted in some connections, and b) proposition of models for the momentrotation description for double plate connections of web. The influence of the brace type and of the rigidity of the connections were investigated by means of the effect in the vertical displacements and in the distribution of internal efforts of the structure. So, two commercial softwares were used, and the results were compared.

RésuméL’objectif général de cette thèse était d’étudier les capacités d’empan visuo-attentionnel (VA) des lecteurs arabophones. Les recherches ont montré que l’empan VA module le traitement visuel des séquences de lettres et joue à ce titre un rôle important en lecture experte, tel que modélisé dans le cadre du modèle multitraces de lecture experte (Ans, Carbonnel et Valdois, 1998). Il a également été montré que l'empan VA joue un rôle dans l’acquisition de la lecture et qu’une réduction de l’empan VA explique certaines formes de dyslexies développementales. Néanmoins, les études menées jusqu’ici se sont limitées aux langues européennes. Il s’agissait donc d’évaluer la pertinence du concept d’empan VA dans une langue de structure très différente, comme l’arabe. Deux questions principales ont été abordées : la première (Etude 1) portait sur une éventuelle modulation des capacités d’empan VA selon la langue ; elle a été menée chez des lecteurs experts. La seconde (Etude 2) visait à évaluer l’implication de l’empan VA dans les troubles de l’apprentissage de la lecture. Dans l’étude 1, nous avons comparé les performances d’empan VA chez des adultes de langue française, espagnole et arabe. Nous montrons notamment que les capacités d’empan VA sont plus limitées chez les arabophones que chez les français ou les hispanophones. La taille de l’empan VA n’est pas modulée par la transparence de la langue mais pourrait varier selon les contraintes de traitement des mots (traitement parallèle pour le français et l’espagnol mais traitement privilégié de la racine morphologique pour l’arabe). L’étude 2 a porté sur des enfants arabophones de 4ème et 5ème année, bons et mauvais lecteurs, qui ont été soumis à des épreuves de lecture, de conscience phonologique et d’empan VA. Nous montrons que les capacités d’empan VA contribuent à expliquer les performances en lecture de mots et de texte, voyellé et non voyellé, indépendamment des capacités phonologiques des enfants. Comme dans les langues européennes, un sous-groupe d’enfants mauvais lecteurs présente un trouble isolé de l’empan VA. Par contre, la proportion d’enfants présentant un trouble de l’empan VA, isolé ou pas, est beaucoup plus importante que dans les études précédentes portant sur les langues européennes. Ces résultats devraient conduire à proposer de nouveaux outils de diagnostic et de remédiation des troubles d'apprentissage de la lecture chez les lecteurs arabophones. Ils ont également des implications potentielles sur les méthodes d’enseignement de la lecture en langue arabe. / AbstractThe aim of this doctoral research was to study the visual-attention (VA) span abilities of Arabic-readers. Previous studies showed that VA span modulates letter string visual processing and plays an important role in expert reading, as modeled in the multitrace memory model (Ans, Carbonnel and Valdois, 1998). The VA span was previously described as a key component of reading acquisition; a reduction in VA span was found to characterize a subgroup of children with developmental dyslexia. Longitudinal and training studies suggest this relation may be causal. However, all previous studies on VA span have been limited to the European languages. Our purpose in this doctoral research was to assess the relevance of the VA span in a language of very different structure, the Arabic language. Two main questions were addressed. In Study 1, we explored potential modulations of VA span skills depending on the language characteristics; this study was conducted on expert readers. Study 2 was designed to investigate the role of VA span in reading acquisition in Arabic children. In Study 1, we compared the VA span performance of skilled readers from three different languages (French, Spanish and Arabic). We show that VA span abilities are reduced in Arabic as compared to French or Spanish. Differences in the size of VA span do not relate to language transparency but may depend on orthographic processing constraints (parallel processing of the word letter string for French and Spanish but privileged processing of the morphological root for Arabic). Study 2 was carried out on Arabic-speaking children, good and poor readers, from 4th and 5th grade. They were administered tests of reading, phonological awareness and VA span. Results show that VA span abilities contribute to explain performance in word and text reading whatever the script (vowelized or not) regardless of the child phonological abilities. As in European languages, a subgroup of poor readers shows an isolated VA span disorder. However, the proportion of children with a VA span disorder (isolated or not) is much higher than in previous studies on European languages. The current findings should allow designing new diagnostic tools and remediation programs for Arabic children with learning disorders. They also have potential implications for the teaching methods of reading in Arabic.

Made available in DSpace on 2016-04-28T20:56:34Z (GMT). No. of bitstreams: 1 Renan de Almeida Sargiani.pdf: 1879594 bytes, checksum: 30d53cbb220f22cadcfb3ef6f994cefd (MD5) Previous issue date: 2013-01-29 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Earlier studies showed that reading performance depends on phonemic awareness skills and visual attention span (VAS). Phonemic awareness refers to sensitivity and intentional control over the smallest speech sounds, i.e., phonemes. Visual attention span refers to the amount of distinct visual elements (letters) that can be processed simultaneously within a given set. There are hardly any studies on these two skills and their role in reading performance among Brazilian Portuguese speakers. This study aims at verifying (1) the existence of relationships between the skills of VAS and phonemic awareness and their relations with the reading performance of Brazilian children and (2) whether these relations would modify during their schooling years. The sample was made up of 48 students (1st, 3rd and 5th grade) from a public elementary school in Sao Paulo (Brazil). Children were assessed in three sessions through a battery of tasks which included single word reading, phonemic awareness, VAS, nonverbal IQ, verbal short-term memory and letter identification threshold. Results showed that VAS and phonemic awareness correlated with performance in reading of regular and irregular words and nonwords from 1st to 5th grade of elementary school. They also indicated that VAS and phonemic awareness play a more important role at the beginning of the learning of reading, i.e., in 1st grade, but continue to be of importance to reading ability in 3rd and 5th grade especially in reading of nonwords. It was also observed that there is a development of reading skills, phonemic awareness and visual attention span with the progress in schooling / Estudos anteriores demonstraram que o desempenho em leitura depende das habilidades de consciência fonêmica e de amplitude visuo-atencional (AVA). A consciência fonêmica se refere à sensibilidade e controle intencional dos menores sons da fala, isto é, os fonemas. A amplitude visuo-atencional se refere à quantidade de elementos visuais distintos (letras) que podem ser processados simultaneamente dentro de um conjunto. Ainda são escassas as pesquisas sobre essas duas habilidades e seu papel no desempenho em leitura em falantes do português do Brasil. No presente estudo, verificou-se (1) a existência de relações entre as habilidades de AVA e de consciência fonêmica e o desempenho em leitura em crianças brasileiras e (2) se essas relações se modificavam com o progresso na escolarização. Participaram desse estudo 48 alunos do 1º ano, 3º ano e 5º ano do ensino fundamental de uma escola pública de São Paulo. As crianças foram avaliadas em três sessões por meio de uma bateria que incluía tarefas de leitura de palavras isoladas, tarefas de consciência fonêmica, tarefas de EVA, Q.I. não verbal, memória verbal de curto prazo e limiar de identificação de letras. Demonstrou-se que a AVA e a consciência fonêmica se correlacionam com o desempenho em leitura de palavras regulares, irregulares e pseudopalavras desde o 1º até o 5º ano do ensino fundamental. Os resultados indicam que a AVA e a consciência fonêmica desempenham um papel mais importante no 1º ano da aprendizagem da leitura, mas continuam tendo um papel relevante no 3º ano e no 5º ano principalmente na leitura de pseudopalavras. Observou-se também que ocorre uma evolução das habilidades de leitura, consciência fonêmica e amplitude visuoatencional com o progresso na escolarização

L'adhésion des revêtements est l'objectif premier de tout système afin de pouvoir apporter les propriétés de surface voulues par projection thermique. De façon conventionnelle, des traitements de sablage sont régulièrement employés afin de promouvoir des phénomènes d'ancrage mécanique entre les deux matériaux mis en contact.Néanmoins, selon la nature même des matériaux, un certain nombre de limitations peuvent être observées aussi bien d'un point de vue usage que tenue. Une fragilisation des surfaces peut en effet être remarquée dès lors qu'ils'agit du traitement de matériaux ductiles. Pour palier certaines de ces contraintes, des traitements palliatifs sont alors recherchés parmi lesquels les traitements laser apparaissent particulièrement bénéfiques dont la texturation laser. Les revêtements barrière thermique sont l'application visée de cette étude avec comme objectif une optimisation de leur durabilité à chaud (oxydation, fluage). Une sous-couche d'accroche est habituellement déposée mais les modes d'endommagement recensés semblent se concentrer autour de cette dernière. L'objectif de c etravail a donc visé à remplacer la sous-couche par une topographie de surface spécifique du substrat générée partexturation laser et permettant un ancrage mécanique suffisant aux chargement mécaniques et thermiques subis par les aubes de turbines hautes températures.Lors de l'interaction laser-matière, une élévation en température de l'extrême surface jusqu'à la température defusion et de vaporisation du matériau peut être observée et permettre la formation de motifs. Les dimensions de tels motifs sont donc liées à l¿énergie par impulsion et au nombre d¿impulsions. Pour valider de tels effets, les mécanismes de perçage ont donc été étudiés grâce à une modélisation thermo hydraulique et une validation postmortem des échantillons. Les dimensions des motifs alors contrôlées, le remplissage des surfaces texturées par des particules fondues projetées par le procédé APS a été étudié afin de minimiser le nombre de défauts proche de l'interface. Deux modes de rupture ont pu être identifiés en fonction de la morphologie de surface pour descontraintes de traction et de cisaillement. Les fissures se propagent à l'interface jusqu'à avoir des changements dedirection. L'énergie de propagation de la fissure augmente donc jusqu'à atteindre une valeur limite correspondant àla ténacité du revêtement. Dans ce cas, la tenue n'est pas fonction de la surface totale en contact mais de larépartition spatiale et l'ouverture des motifs, la seule limite de la tenue du revêtement restant la cohésion du dépôt.D'un point de vue applicatif, le but de cette étude a été de caractériser les modes d'endommagements de systèmes barrière thermique sans sous-couche pour des conditions rencontrées en service. Les mécanismes d'endommagement dus à l'oxydation et à l'allongement viscoplastique à 1100C ont donc été isolés par des essais àdes flux thermiques isothermes et cyclés, de fluage et de fatigue thermomécanique. Le traitement laser modifiant localement la microstructure des surfaces, une modification des couches d'oxydes a tout d'abord pu être identifiée.En effet, contrairement aux traitements conventionnels où la croissance d'oxyde n'est pas constante (point limitant de la durée de vie du système), l'apparition de spinelles et d'une couche dense d'alumine protectrice en surface des matériaux texturés a pu être observée. L'ancrage mécanique ainsi créé a démontré alors une durée de vie nettement améliorée face à des conditions extrêmes. / Coating adhesion is requiered to rpomote specific surface properties by thermal spraying. Conventional prior-surface treatments have been developed to create anchoring zones but the adhesion strenght and their applications are limited. Laser surface texturing increases and adapts the adhesion surface. Therefore, two interface failure modes have been related to texture morphologies for tensile and shear stresses. The energy released rate at the interface increases up to coating toughness when the crack path is sharp. Mixed-mode failures have been observed with adhesive and cohesive cracks around and above pattern respectively. So, the adhesion stengyh is function of the contact aera precisely linked to pattern distribution and morphology. Thermal barrier coating system without bond coat life-span has been evaluated for thermomechanical stresses (YSZ coating on single crystal based Nickel). The bond coat has been remplaced by an adapted substrate surface topography. According ti the laser parameters (energy per pulse, pulse numbers) pattern morphology can be created. Therefore, textured surface filling by melted particles has been studies to minimize interface defaults and created mixed-mode failures for during plasma spray coatings. The drilling mechanisms have been evaluated by numerical modeling and experimental analysis. The pattern dimensions and heat affected zones has been identified. The laser treatment changes the microstructure locally.Oxydation tests have been performed to study the surface pre-tratments effects on oxide nature and mass gain rate. The damaging mechanisms ave been studied under isotherm and cyclic high temperature tests and also under creeping and thermo-mechanical fatigue tests. Grit-blasting change the natural oxides, limits life-span and bucking failure mode have been obeserved. Natural oxides have been analyzed for the textured substraes also but anchoring mechanism enables large life-span under high temperature tests. Mechanical applied stresses (constant and cyclic) validate the beneficial effects of patterned surfaces. The interface is stronger than the coating toughness and the patterns do not create early cracks under thermo-mechanical solicitations.

<p>This PhD thesis, consisting of an introduction, four papers, and some supplementary results, studies the problem of finding an <i>optimal realization</i> of a given finite metric space: a weighted graph which preserves the metric's distances and has minimal total edge weight. This problem is known to be NP-hard, and solutions are not necessarily unique.</p><p>It has been conjectured that <i>extremally weighted</i> optimal realizations may be found as subgraphs of the <i>hereditarily optimal realization</i> Γ_d, a graph which in general has a higher total edge weight than the optimal realization but has the advantages of being unique, and possible to construct explicitly via the <i>tight span</i> of the metric.</p><p>In Paper I, we prove that the graph Γ_d is equivalent to the 1-skeleton of the tight span precisely when the metric considered is <i>totally split-decomposable</i>. For the subset of totally split-decomposable metrics known as <i>consistent</i> metrics this implies that Γ_d is isomorphic to the easily constructed <i>Buneman graph</i>.</p><p>In Paper II, we show that for any metric on at most five points, any optimal realization can be found as a subgraph of Γ_d.</p><p>In Paper III we provide a series of counterexamples; metrics for which there exist extremally weighted optimal realizations which are not subgraphs of Γ_d. However, for these examples there also exists at least one optimal realization which is a subgraph.</p><p>Finally, Paper IV examines a weakened conjecture suggested by the above counterexamples: can we always find some optimal realization as a subgraph in Γ_d? Defining <i>extremal</i> optimal realizations as those having the maximum possible number of shortest paths, we prove that any embedding of the vertices of an extremal optimal realization into Γ_d is injective. Moreover, we prove that this weakened conjecture holds for the subset of consistent metrics which have a 2-dimensional tight span</p>