Le but de cette étude est d'améliorer les performances, en termes d'espace mémoire et de temps de calcul, des simulations actuelles de l'Interaction mécanique Pastille-Gaine (IPG), phénomène complexe pouvant avoir lieu lors de fortes montées en puissance dans les réacteurs à eau sous pression. Parmi les méthodes de raffinement de maillage, méthodes permettant de simuler efficacement des singularités locales, une approche multi-grille locale a été choisie car elle présente l'intérêt de pouvoir utiliser le solveur en boîte noire tout en ayant un faible nombre de degrés de liberté à traiter par niveau. La méthode Local Defect Correction (LDC), adaptée à une discrétisation de type éléments finis, a tout d'abord été analysée et vérifiée en élasticité linéaire, sur des configurations issues de l'IPG, car son utilisation en mécanique des solides est peu répandue. Différentes stratégies concernant la mise en oeuvre pratique de l'algorithme multi-niveaux ont également été comparées. La combinaison de la méthode LDC et de l'estimateur d'erreur a posteriori de Zienkiewicz-Zhu, permettant d'automatiser la détection des zones à raffiner, a ensuite été testée. Les performances obtenues sur des cas bidimensionnels et tridimensionnels sont très satisfaisantes, l'algorithme proposé se montrant plus performant que des méthodes de raffinement h-adaptatives. Enfin, l'algorithme a été étendu à des problèmes mécaniques non linéaires. Les questions d'un raffinement espace/temps mais aussi de la transmission des conditions initiales lors du remaillage ont entre autres été abordées. Les premiers résultats obtenus sont encourageants et démontrent l'intérêt de la méthode LDC pour des calculs d'IPG. / The aim of this study is to improve the performances, in terms of memory space and computational time, of the current modelling of the Pellet-Cladding mechanical Interaction (PCI),complex phenomenon which may occurs during high power rises in pressurised water reactors. Among the mesh refinement methods - methods dedicated to efficiently treat local singularities - a local multi-grid approach was selected because it enables the use of a black-box solver while dealing few degrees of freedom at each level. The Local Defect Correction (LDC) method, well suited to a finite element discretisation, was first analysed and checked in linear elasticity, on configurations resulting from the PCI, since its use in solid mechanics is little widespread. Various strategies concerning the implementation of the multilevel algorithm were also compared. Coupling the LDC method with the Zienkiewicz-Zhu a posteriori error estimator in orderto automatically detect the zones to be refined, was then tested. Performances obtained on two-dimensional and three-dimensional cases are very satisfactory, since the algorithm proposed is more efficient than h-adaptive refinement methods. Lastly, the LDC algorithm was extended to nonlinear mechanics. Space/time refinement as well as transmission of the initial conditions during the remeshing step were looked at. The first results obtained are encouraging and show the interest of using the LDC method for PCI modelling.

Defect prediction models assist tester practitioners on prioritizing the most defect-prone parts of the software. The approach called Cross-Project Defect Prediction (CPDP) refers to the use of known external projects to compose the training set. This approach is useful when the amount of historical defect data of a company to compose the training set is inappropriate or insufficient. Although the principle is attractive, the predictive performance is a limiting factor. In recent years, several methods were proposed aiming at improving the predictive performance of CPDP models. However, to the best of our knowledge, there is no evidence of which CPDP methods typically perform best. Moreover, there is no evidence on which CPDP methods perform better for a specific application domain. In fact, there is no machine learning algorithm suitable for all domains. The decision task of selecting an appropriate algorithm for a given application domain is investigated in the meta-learning literature. A meta-learning model is characterized by its capacity of learning from previous experiences and adapting its inductive bias dynamically according to the target domain. In this work, we investigate the feasibility of using meta-learning for the recommendation of CPDP methods. In this thesis, three main goals were pursued. First, we provide an experimental analysis to investigate the feasibility of using Feature Selection (FS) methods as an internal procedure to improve the performance of two specific CPDP methods. Second, we investigate which CPDP methods present typically best performances. We also investigate whether the typically best methods perform best for the same project datasets. The results reveal that the most suitable CPDP method for a project can vary according to the project characteristics, which leads to the third investigation of this work. We investigate the several particularities inherent to the CPDP context and propose a meta-learning solution able to learn from previous experiences and recommend a suitable CDPD method according to the characteristics of the project being predicted. We evaluate the learning capacity of the proposed solution and its performance in relation to the typically best CPDP methods. / Modelos de predição de defeitos auxiliam profissionais de teste na priorização de partes do software mais propensas a conter defeitos. A abordagem de predição de defeitos cruzada entre projetos (CPDP) refere-se à utilização de projetos externos já conhecidos para compor o conjunto de treinamento. Essa abordagem é útil quando a quantidade de dados históricos de defeitos é inapropriada ou insuficiente para compor o conjunto de treinamento. Embora o princípio seja atrativo, o desempenho de predição é um fator limitante nessa abordagem. Nos últimos anos, vários métodos foram propostos com o intuito de melhorar o desempenho de predição de modelos CPDP. Contudo, na literatura, existe uma carência de estudos comparativos que apontam quais métodos CPDP apresentam melhores desempenhos. Além disso, não há evidências sobre quais métodos CPDP apresentam melhor desempenho para um domínio de aplicação específico. De fato, não existe um algoritmo de aprendizado de máquina que seja apropriado para todos os domínios de aplicação. A tarefa de decisão sobre qual algoritmo é mais adequado a um determinado domínio de aplicação é investigado na literatura de meta-aprendizado. Um modelo de meta-aprendizado é caracterizado pela sua capacidade de aprender a partir de experiências anteriores e adaptar seu viés de indução dinamicamente de acordo com o domínio alvo. Neste trabalho, nós investigamos a viabilidade de usar meta-aprendizado para a recomendação de métodos CPDP. Nesta tese são almejados três principais objetivos. Primeiro, é conduzida uma análise experimental para investigar a viabilidade de usar métodos de seleção de atributos como procedimento interno de dois métodos CPDP, com o intuito de melhorar o desempenho de predição. Segundo, são investigados quais métodos CPDP apresentam um melhor desempenho em um contexto geral. Nesse contexto, também é investigado se os métodos com melhor desempenho geral apresentam melhor desempenho para os mesmos conjuntos de dados (ou projetos de software). Os resultados revelam que os métodos CPDP mais adequados para um projeto podem variar de acordo com as características do projeto sendo predito. Essa constatação conduz à terceira investigação realizada neste trabalho. Foram investigadas as várias particularidades inerentes ao contexto CPDP a fim de propor uma solução de meta-aprendizado capaz de aprender com experiências anteriores e recomendar métodos CPDP adequados, de acordo com as características do software. Foram avaliados a capacidade de meta-aprendizado da solução proposta e a sua performance em relação aos métodos base que apresentaram melhor desempenho geral.

Ce travail de thèse traite de la détection des défauts mécaniques des roulements à billes par analyse de grandeurs mécaniques et électriques dans des machines synchrones à aimants permanents haute vitesse. Le domaine applicatif de ce travail concerne l'aéronautique. Généralement, pour surveiller l'état des roulements à billes dans un actionneur électrique, des mesures vibratoires sont réalisées. Elles permettent, en exploitant le spectre du signal vibratoire, de mettre facilement en évidence la détérioration du roulement. Cette méthode de surveillance est cependant relativement couteuse en termes d'instrumentation et le placement d'un capteur vibratoire dans des équipements à fort degré d'intégration est parfois difficile. Nous proposons dans ce mémoire d'utiliser d'autres grandeurs physiques prélevées sur le système pour réaliser la surveillance de ces défauts. Il peut s'agir de grandeurs mécaniques (vitesse, position par exemple) et de grandeurs électriques (courant statorique, courant onduleur par exemple). L'utilisation de données déjà disponibles dans l'équipement pour les besoins de la commande permet ainsi de supprimer le système d'acquisition vibratoire. A partir d'enregistrements temporels de données réalisées au cours de campagnes d'essais, nous proposons des méthodologies de traitement du signal permettant d'extraire automatiquement des informations sensibles au défaut à surveiller. L'idée finale est de construire des indicateurs de l'état de santé des roulements permettant de prendre « juste à temps » des décisions fiables relatives à la maintenance ou à la sécurisation de l'équipement. Pour construire ces indicateurs, les signatures spécifiques aux défauts de roulements sont étudiées de manière théorique et expérimentale, pour l'ensemble des grandeurs prélevées. Leurs propriétés sont mises en évidence, permettant ainsi de définir les bandes fréquentielles les plus contributives au diagnostic. L'extraction de ces signatures est réalisée dans le domaine fréquentiel selon plusieurs méthodes. Deux types d'indicateurs automatiques différents sont proposés. Le premier est construit directement à partir du spectre d'amplitude des grandeurs par extraction de l'amplitude des harmoniques dans des bandes fréquentielles particulières. Le second intègre une dimension statistique dans l'analyse en exploitant le caractère aléatoire de certains harmoniques pour détecter la présence du défaut. Des critères de comparaison sont définis et utilisés pour étudier les performances des indicateurs proposés pour deux campagnes d'essais avec des roulements artificiellement dégradés, pour différentes vitesses de fonctionnement et pour différents paramètres de réglage des indicateurs. / This Ph.D. thesis deals with detection of mechanical bearings faults by analysis of mechanical and electrical signals in high speed permanent magnet synchronous machine. The application domain of this work concerns aeronautics. Generally, to monitor the ball bearings status in electrical actuator, the vibration measurements are used. They allow, by extracting the vibration spectrum, to easily detect the deterioration of the bearing. This monitoring method is relatively expensive in terms of instrumentation and placing a vibration sensor in equipment with a high integration degree can be difficult. We propose in this paper to use other physical quantities taken from the system to perform the monitoring of these defects. It may be mechanical quantities (for example speed, position) and electrical quantities (for example stator current, power inverter). From time recording of data carried out during test campaigns, we propose signal processing methodologies to automatically extract information sensitive to the monitored fault. The final idea is to construct indicators of bearings health and make decisions relating to maintenance or equipment security. To construct these indicators, specific bearing defects signatures are studied theoretically and experimentally, for all collected variables. The extraction of these signatures is carried out in frequency domain. Two different types of automatic indicators are proposed. The first is constructed directly from the amplitude spectrum by extraction of the harmonic amplitude of the spectrum in particular frequency bands. The second includes a statistical dimension analysis by exploiting the random nature of some harmonics to detect fault presence. Criteria of comparison are defined and used to study the proposed indicators performances for two trial campaigns with artificially degraded bearings, for different speed functioning and for different regulation of indicators parameters.

L’étude d’un critère de distinction des nullités est-elle désuète ? Tant s’en faut. S’inscrivant dans lecontentieux de la théorie des nullités, le critère de distinction actuel est couramment dénoncé.À ce jour, il est enseigné qu’une théorie « moderne » aurait renversé une théorie « classique »distinguant les nullités relatives et absolues selon la gravité du vice de l’acte. Aussi le critère actuel de« l’intérêt protégé » propose-t-il de scinder les nullités selon l’intérêt que la loi décide de préserver.Ici, la nullité est relative lorsque seul un intérêt particulier est protégé par le législateur. Là, unenullité absolue est préférable quand l’intérêt général a guidé l’objectif législatif dans l’édiction de larègle.Séduisant, ce critère n’en demeure pas pour autant convaincant. L’excès condamnable de rigidité ducritère organique laisse place à un excès de souplesse du critère de l’intérêt protégé tout aussiblâmable. Comment distinguer l’intérêt général de l’intérêt privé ? Bien plus, y a-t-il un intérêt àprotéger quand le législateur exige une condition matérielle de formation de l’acte comme la cause oul’objet ? Par où l’on voit qu’à l’insécurité juridique du critère s’adjoint l’artifice des classifications qu’ilengendre. Insatisfaisant, le critère de l’intérêt protégé doit être réprouvé.L’approche historique, essentielle pour comprendre l’origine de la distinction, dévoile la chronologieerronée des théories esquissées. S’ensuit l’abandon d’un critère palliatif pour la substitution d’uncritère plus effectif, dont le fondement n’instaure pas une hiérarchie entre les conditions de formationou les intérêts protégés. Mises sur un pied d’égalité, les nullités seraient distinctes en raison des vicesqui les provoquent, pris dans leur nature, et non dans leur gravité. Fondé sur la nature du vice,personnelle – si le vice affecte le consentement –, matérielle ou illicite – si le vice altère le contrat –,ce nouveau critère de distinction des nullités autoriserait une classification ternaire, avec un régimespécifique à chaque vice. Il permettrait également la redécouverte d’une pluralité de natures desnullités, en tant que sanction ou remède. L’harmonie des catégories s’en trouverait ainsi instaurée, labipolarité décriée abandonnée et la nature véritable des nullités restaurée. / Is the search for a distinction criterion of nullities obsolete ? Far from it. Lying within the litigation ofdoctrine of nullities, the current distinction criterion is frequently denounced.To date, it is taught that a "modern" theory would have reversed a "classical" theory, distinguishingrelative nullities (voidable) from absolute ones (void) according to the gravity of the act’s defect.Therefore, the "protected interest" criterion proposes dividing up nullities according to the interestthe law decides to protect. Here, nullity is relative when a specific interest alone is protected by thelawmaker. There, an absolute nullity is preferred, when general interest guided the legislative purposewhile enacting the rule.Appealing, this criterion does not remain, however, convincing. The blameworthy excess of rigidity ofthe organic criterion makes room for an as much blameful excess of flexibility of the protected interestcriterion. How to distinguish general interest from specific interest ? Furthermore, is there an interestto be protected when the lawmaker demands a material condition for the formation of the act such asthe cause or the object? In any case, to the juridical insecurity of the criterion is affixed the device ofbred classifications. Unsatisfactory, the protected interest criterion must be reprobated.Historical approach, essential for understanding the origin of the distinction, expose the erroneouschronology of the sketched theories. Follows the abandonment of a palliative criterion for a moreeffective one, whose foundation does not establish a hierarchy between the conditions of formation orthe protected interests. Treated on an equal footing, nullities would be distinct because of the defectsthat father them, taken in nature, not in their severity. Based on the nature of the defect, personal – ifthe defect affects the consent –, concrete or illicit – if the defect impairs the contract –, this newdistinction criteria of nullities would allow a ternary classification, with a specific plan for each vice. Itwould also allow the rediscovery of a plurality natures of nullity, as a sanction or remedy. Harmony ofcategories would find itself instituted, disparaged polarity abandoned and true nature of nullitiesrestored.

No description available.

Le cœur des vertébrés est un organe modulaire qui requiert le " patterning " complexe des champs morphogénétiques cardiogènes et la convergence coordonnée des diverses sous-populations de progéniteurs cardiogéniques. Au moins 7 facteurs de transcription de la famille T-box coopèrent au sein de ces nombreuses sous-populations de progéniteurs cardiogéniques afin de réguler la morphogenèse et l’agencement de multiples structures le long de l’ébauche cardiaque, ce qui explique que les mutations humaines de ces gènes engendrent diverses malformations congénitales cardiaques (MCCs). L’un de ces gènes T-box, Tbx5, dont l’haploinsuffisance génère le syndrome de Holt-Oram (SHO), intervient dans une grande variété de réseaux de régulation géniques (RRGs) qui orchestrent la morphogenèse des oreillettes, du ventricule gauche, de la valve mitrale, des septums inter-auriculaire et inter-ventriculaire, ainsi que du système de conduction cardiaque. La diversité des RRGs impliqués dans la formation de ces structures cardiaques suggère que Tbx5 détient une profusion de fonctions qui ne seront identifiables qu’en répertoriant ses activités moléculaires dans chaque lignée cardiaque examinée isolément. Afin d’aborder cette problématique, une ablation génétique de Tbx5 dans l’endocarde a été réalisée. Cette expérience a démontré le rôle crucial de Tbx5 dans la survie des cellules endocardiques bordant le septum primum et des cardiomyocytes au sein de cette structure embryonnaire qui contribuera à la morphogenèse du septum inter-auriculaire. En outre, cette étude a révélé l’existence d’une communication croisée entre la sous-population de cellules endocardiques Tbx5+ et le myocarde au niveau du septum primum, afin d’assurer la survie des cardiomyocytes, et ultimement de garantir la maturation du septum inter-auriculaire. Nos résultats confirment aussi l’importance de l’interdépendance génétique (Tbx5 et Gata4 ainsi que Tbx5 et Nos3) entre différents loci dans la morphogenèse de la cloison inter-auriculaire, et particulièrement de l’influence que peut avoir l’environnement sur la pénétrance et l’expressivité des communications inter-auriculaires (CIAs) dans le SHO. En outre, puisque les fonctions d’un gène dépendent ordinairement des différents isoformes qu’il peut générer, une deuxième étude a focalisé davantage sur l’aspect transcriptionnel de Tbx5. Cette approche a mené à la découverte de 6 transcrits alternatifs exhibant des fonctions à la fois communes et divergentes. La caractérisation de 2 de ces isoformes a révélé le rôle de l’isoforme long (Tbx5_v1) dans la régulation de la croissance des cardiomyocytes durant la cardiogénèse, tandis que l’isoforme court (Tbx5_v2), préférentiellement exprimé dans le cœur mature, réprime la croissance cellulaire. Il est donc entièrement concevable que les mutations de TBX5 entraînant une troncation de la région C-terminale accroissent la concentration d’une protéine mutée qui, à l’instar de Tbx5_v2, interfère avec la croissance de certaines structures cardiaques. En revanche, la divergence de fonctions de ces isoformes, caractérisée par les disparités de localisation subcellulaire et de d’interaction avec d’autres cofacteurs cardiaques, suggère que les mutations affectant davantage un isoforme favoriseraient l’émergence d’un type particulier de MCC. Finalement, un dernier objectif était d’identifier le ou les mécanisme(s) moléculaire(s) par le(s)quel(s) Tbx5 régule son principal gène cible, Nppa, et d’en extraire les indices qui éclairciraient sa fonction transcriptionnelle. Cet objectif nécessitait dans un premier lieu d’identifier les différents modules cis-régulateurs (MCRs) coordonnant la régulation transcriptionnelle de Nppa et Nppb, deux gènes natriurétiques dont l’organisation en tandem et le profil d’expression durant la cardiogénèse sont conservés dans la majorité des vertébrés. L’approche d’empreinte phylogénétique employée pour scanner le locus Nppb/Nppa a permis d’identifier trois MCRs conservés entre diverses espèces de mammifères, dont un (US3) est spécifique aux euthériens. Cette étude a corroboré que la régulation de l’expression du tandem génique Nppb/Nppa requérait l’activité transcriptionnelle d’enhancers en complément aux promoteurs de Nppa et Nppb. La concordance quasiment parfaite entre les profils d’expression de Tbx5 et de ces deux gènes natriurétiques chez les mammifères, suggère que le gradient d’expression ventriculaire de Tbx5 est interprété par le recrutement de ce facteur au niveau des différents enhancers identifiés. En somme, les études présentées dans cette thèse ont permis de clarifier la profusion de fonctions cardiaques que possède Tbx5. Certaines de ces fonctions émanent de l’épissage alternatif de Tbx5, qui favorise la synthèse d’isoformes dotés de propriétés spécifiques. Les diverses interactions combinatoires entre ces isoformes et d’autres facteurs cardiaques au sein des diverses sous-populations de progéniteurs cardiogènes contribuent à l’émergence de RRGs cardiaques divergents. / The vertebrate heart is a modular organ, which requires the complex patterning of the morphogenetic heart fields and the coordinated convergence of the diverse subpopulations of cardiogenic progenitors. At least 7 transcription factors of the T-box family cooperate within these numerous subpopulations of cardiogenic progenitors to regulate the morphogenesis and the layout of multiple structures along the primordial heart tube, which explains that the human mutations of these genes induce various congenital heart defects (CHDs). One of these T-box genes, Tbx5, whose haploinsufficiency generates the Holt-Oram syndrome (HOS), intervenes in a wide variety of gene regulatory networks (GRNs) that orchestrate the morphogenesis of the atria, the left ventricle, the mitral valve, the inter-atrial and inter-ventricular septa, as well as the cardiac conduction system. The diversity of GRNs involved in the formation of these cardiac structures suggests that Tbx5 holds a profusion of functions which will be identifiable only by indexing its molecular activities in each separately examined cardiac lineage. To address this problem, a conditional knockout of Tbx5 in the endocardium was generated. This experiment demonstrated a crucial role of Tbx5 in the survival of the endocardial cells lining the septum primum and the cardiomyocytes within this embryonic structure, which will contribute to the morphogenesis of the inter-atrial septum. Moreover, this study revealed a crosstalk between the Tbx5-positive endocardial cells subpopulation and the myocardium at the level of the septum primum to ensure the survival of cardiomyocytes, and ultimately to guarantee the maturation of the inter-atrial septum. Our results also confirmed the importance of genetic interdependence (Tbx5 and Gata4 as well as Tbx5 and Nos3) between different loci in the morphogenesis of the inter-atrial septum, and particularly the influence that the environment can have on the penetrance and the expressivity of atrial septal defects (ASDs) in the HOS. Besides, since the functions of a gene usually depend on the different isoforms it can generate, a second study focused more on the transcriptional aspect of Tbx5. This approach led to the discovery of 6 alternative transcripts exhibiting both common and specific functions. The characterization of 2 of these isoforms revealed the role of the long isoform (Tbx5_v1) in the regulation of cardiomyocytes growth during cardiogenesis, whereas the short isoform (Tbx5_v2), preferentially expressed in the mature heart, represses cell growth. It is thus entirely conceivable that TBX5 mutations leading to a C-terminal truncation increase the concentration of a mutated protein, which, like Tbx5_v2, interferes with the growth of certain cardiac structures. On the other hand, the divergence of functions of these isoforms, characterized by the disparities of subcellular localization and interaction with other cardiac cofactors, suggests that mutations affecting more one isoform would favor the emergence of a particular type of CHD. Finally, a last objective was to identify one or several molecular mechanism(s) by which Tbx5 regulates its main target gene, Nppa, and to extract clues that might clarify its transcriptional function. This objective required in a first place to identify the various cis-regulatory modules (CRMs) coordinating the transcriptional regulation of Nppa and Nppb, two natriuretic genes whose tandem organization and expression pattern during cardiogenesis are preserved in most vertebrates. The phylogenetic footprint approach employed to scan the Nppb/Nppa locus allowed the identification of three CRMs evolutionary conserved between different mammals species, one of which (US3) is specific to eutherians. This study confirmed that the regulation of the tandem genes Nppb/Nppa required the transcriptional activity of enhancers in complement to Nppa and Nppb promoters. The almost perfect concordance between the expression profiles of Tbx5 and these two natriuretic genes in mammals, suggests that the ventricular expression gradient of Tbx5 is interpreted by the recruitment of this factor to the identified enhancers. Altogether, the studies presented in this thesis allowed clarifying the profusion of Tbx5 cardiac functions. Some of these functions emanate from the alternative splicing of Tbx5, which favors the synthesis of isoforms endowed with specific properties. The diverse combinatorial interactions between these isoforms and other cardiac factors within the various cardiogenic progenitor subpopulations contribute to the emergence of distinct cardiac RRGs.

Defects in the functional oxides play an important role in electronic devices like metal oxide semiconductor field effect transistors (MOSFETs) and resistive random-access memories (ReRAMs). The continuous scaling of CMOS has brought the Si MOSFET to its physical technology limit and the replacement of Si channel with Ge channel is required. However, the performance of Ge MOSFETs suffers from Ge/oxide interface quality and reliability problems, which originates from the charge traps and defect states in the oxide or at the Ge/oxide interface. The sub-oxide layers composed of GeII states at the Ge/GeO2 interface seems unavoidable with normal passivation methods like hydrogen treatment, which has poor electrical properties and is related to the reliability problem. On the other hand, ReRAM works by formation and rupture of O vacancy conducting filaments, while how this process happens in atomic scale remains unclear. In this thesis, density functional theory is applied to investigate the defect behaviours in oxides to address existing issues in these electronic devices. In chapter 3, the amorphous atomic structure of doped GeO2 and Ge/GeO2 interface networks are investigated to explain the improved MOSFET reliability observed in experiments. The reliability improvement has been attributed to the passivation of valence alternation pair (VAP) type O deficiency defects by doped rare earth metals. In chapter 4, the oxidation mechanism of GeO2 is investigated by transition state simulation of the intrinsic defect diffusion in the network. It is proposed that GeO2 is oxidized from the Ge substrate through lattice O interstitial diffusion, which is different from SiO2 which is oxidized by O2 molecule diffusion. This new mechanism fully explains the strange isotope tracer experimental results in the literature. In chapter 5, the Fermi level pinning effect is explored for metal semiconductor electrical contacts in Ge MOSFETs. It is found that germanides show much weaker Fermi level pinning than normal metal on top of Ge, which is well explained by the interfacial dangling bond states. These results are important to tune Schottky barrier heights (SBHs) for n-type contacts on Ge for use on Ge high mobility substrates in future CMOS devices. In chapter 6, we investigate the surface and subsurface O vacancy defects in three kinds of stable TiO2 surfaces. The low formation energy under O poor conditions and the +2 charge state being the most stable O vacancy are beneficial to the formation and rupture of conducting filament in ReRAM, which makes TiO2 a good candidate for ReRAM materials. In chapter 7, we investigate hydrogen behaviour in amorphous ZnO. It is found that hydrogen exists as hydrogen pairs trapped at oxygen vacancies and forms Zn-H bonds. This is different from that in c-ZnO, where H acts as shallow donors. The O vacancy/2H complex defect has got defect states in the lower gap region, which is proposed to be the origin of the negative bias light induced stress instability.

Defect prediction models assist tester practitioners on prioritizing the most defect-prone parts of the software. The approach called Cross-Project Defect Prediction (CPDP) refers to the use of known external projects to compose the training set. This approach is useful when the amount of historical defect data of a company to compose the training set is inappropriate or insufficient. Although the principle is attractive, the predictive performance is a limiting factor. In recent years, several methods were proposed aiming at improving the predictive performance of CPDP models. However, to the best of our knowledge, there is no evidence of which CPDP methods typically perform best. Moreover, there is no evidence on which CPDP methods perform better for a specific application domain. In fact, there is no machine learning algorithm suitable for all domains. The decision task of selecting an appropriate algorithm for a given application domain is investigated in the meta-learning literature. A meta-learning model is characterized by its capacity of learning from previous experiences and adapting its inductive bias dynamically according to the target domain. In this work, we investigate the feasibility of using meta-learning for the recommendation of CPDP methods. In this thesis, three main goals were pursued. First, we provide an experimental analysis to investigate the feasibility of using Feature Selection (FS) methods as an internal procedure to improve the performance of two specific CPDP methods. Second, we investigate which CPDP methods present typically best performances. We also investigate whether the typically best methods perform best for the same project datasets. The results reveal that the most suitable CPDP method for a project can vary according to the project characteristics, which leads to the third investigation of this work. We investigate the several particularities inherent to the CPDP context and propose a meta-learning solution able to learn from previous experiences and recommend a suitable CDPD method according to the characteristics of the project being predicted. We evaluate the learning capacity of the proposed solution and its performance in relation to the typically best CPDP methods. / Modelos de predição de defeitos auxiliam profissionais de teste na priorização de partes do software mais propensas a conter defeitos. A abordagem de predição de defeitos cruzada entre projetos (CPDP) refere-se à utilização de projetos externos já conhecidos para compor o conjunto de treinamento. Essa abordagem é útil quando a quantidade de dados históricos de defeitos é inapropriada ou insuficiente para compor o conjunto de treinamento. Embora o princípio seja atrativo, o desempenho de predição é um fator limitante nessa abordagem. Nos últimos anos, vários métodos foram propostos com o intuito de melhorar o desempenho de predição de modelos CPDP. Contudo, na literatura, existe uma carência de estudos comparativos que apontam quais métodos CPDP apresentam melhores desempenhos. Além disso, não há evidências sobre quais métodos CPDP apresentam melhor desempenho para um domínio de aplicação específico. De fato, não existe um algoritmo de aprendizado de máquina que seja apropriado para todos os domínios de aplicação. A tarefa de decisão sobre qual algoritmo é mais adequado a um determinado domínio de aplicação é investigado na literatura de meta-aprendizado. Um modelo de meta-aprendizado é caracterizado pela sua capacidade de aprender a partir de experiências anteriores e adaptar seu viés de indução dinamicamente de acordo com o domínio alvo. Neste trabalho, nós investigamos a viabilidade de usar meta-aprendizado para a recomendação de métodos CPDP. Nesta tese são almejados três principais objetivos. Primeiro, é conduzida uma análise experimental para investigar a viabilidade de usar métodos de seleção de atributos como procedimento interno de dois métodos CPDP, com o intuito de melhorar o desempenho de predição. Segundo, são investigados quais métodos CPDP apresentam um melhor desempenho em um contexto geral. Nesse contexto, também é investigado se os métodos com melhor desempenho geral apresentam melhor desempenho para os mesmos conjuntos de dados (ou projetos de software). Os resultados revelam que os métodos CPDP mais adequados para um projeto podem variar de acordo com as características do projeto sendo predito. Essa constatação conduz à terceira investigação realizada neste trabalho. Foram investigadas as várias particularidades inerentes ao contexto CPDP a fim de propor uma solução de meta-aprendizado capaz de aprender com experiências anteriores e recomendar métodos CPDP adequados, de acordo com as características do software. Foram avaliados a capacidade de meta-aprendizado da solução proposta e a sua performance em relação aos métodos base que apresentaram melhor desempenho geral.

Plusieurs industries manipulent des substances liquides et gazeuses qui circulent souvent dans de longues canalisations. La technique d'ondes guidées est couramment utilisée dans ce domaine. Cette technique est en progrès continu. Dans cette thèse, un système d'inspection a été conçu et développé. Il est basé sur des transducteurs piézoélectriques qui génèrent des ondes guidées de torsion pouvant se propager le long du tube testé. Les signaux réfléchis des défauts et singularités rencontrés sont détectés aussi par des capteurs piézoélectriques. Des simulations numériques utilisantpar la méthode d'éléments finis standard et la méthode Wave Finite Element(WFEM) ont été effectuées afin de vérifier et de visualiser le phénomène de propagation des ondes dans des tubes intacts et endommagés. Un ensemble de tests a été mis en place sur des tubes droits et courbés avec deux matériaux différents: PVC et acier. L'interaction entre les ondes générées et les défauts usinés a été prouvée.Les résultats numériques et expérimentaux confirment certaines caractéristiques spécifiques concernant le coefficient de réflexion de l'onde. Par la suite, un pipeline industriel d'environ soixante mètres de long et contenant plusieurs défauts et singularités a été testé par le système d'inspection. Les signaux enregistrés ont soumis certains traitements numériques afin de les rendre exploitables. Les signaux traités sont analysés afin d'identifier et de distinguer les réflexions des défauts de celles des singularités structurés. La méthode WFEM a été employée pour construire une base de données numérique des coefficients de réflexion en variant la profondeur et les extensions axiale et circonférentielle du défaut modélisé. Le calcul a été établi en fonction de la fréquence. La corrélation des tailles des défauts est effectuée en balayant la base de données numérique pour trouver la combinaison appropriée de dimensions pour un défaut donné. Les réflexions à partir des singularités structurées (coudes, blocs de béton, colliers, et les soudures) sont traitées ainsi en comparant des coefficients de réflexion obtenus par WFEM à ceux évalués expérimentalement. Enfin, on a étudié numériquement l'effet de la position angulaire d'un défaut sur les coefficients de réflexion et de transmission tout en excitant à différents types d'ondes. La méthode WFE est aussi utilisée pour effectuer le calcul. Cette étude donne un guide à la localisation circonférentielle des défauts dans les tubes. / Long pipelines are widely used in several industries transporting liquid or gas. The guided wave technique is commonly used in this field and it is under continuing progress. In this thesis, an inspection system has been designed and developed. Piezoelectric transducers are employed to generate torsional guided waves that could propagate along the tested pipe; and receive reflected signals from encountered features and damages. Numerical simulations using standard FE and Wave Finite Element methods have been carried out in order to verify and visualize the wave propagation phenomenon in both intact and damaged pipes. A set of tests has been performed on straight and curved pipes with two different materials: PVC and steel. The interaction between generated waves and machined defects has been proven. Numerical and experimental results confirm some specific features in the wave reflection coefficient. Thereafter, an industrial pipeline of about sixty meters long and containing several features has been tested by the inspection system.Recorded signals had submitted some numerical treatments in order to make them interpretable. Processed signals are analyzed to identify defects reflections from structured singularities echoes. The Wave Finite Element Method (WFEM) has been used to construct a numerical database of reflection coefficients from modelled defects by varying thickness, axial and circumferential extents. Calculation was made depending on frequency. The approximation of defect sizes is carried out by sweeping the numerical database to find the suitable combination of dimensions fora given defect. Reflections from structural singularities (elbows, concrete blocks,clamps, and welds) are treated as well by comparing reflection coefficients obtained by WFEM to those evaluated experimentally. Finally, a numerical investigation deals with the effect of defect angular-position on reflection and transmission coefficients while exciting by different types of waves. The spectral method Wave Finite Element has been used to carry out calculation. This study gives guidance to circumferential localization of defects in pipes.

Fundamental understanding of the behaviour of nuclear fuel has been of great importance. Enhancing this knowledge not only by means of experimental observations, but also via multi-scale modelling is of current interest. The overall goal of this thesis is to understand the impact of atomic interactions on the nuclear fuel material properties. Two major topics are tackled in this thesis. The first topic deals with non-stoichiometry in uranium dioxide (UO2) to be addressed by empirical potential (EP) studies. The second fundamental question to be answered is the effect of the atomic fraction of americium (Am), neptunium (Np) containing uranium (U) and plutonium (Pu) mixed oxide (MOX) on the material properties.UO2 has been the reference fuel for the current fleet of nuclear reactors (Gen-II and Gen-III); it is also considered today by the Gen-IV International Forum for the first cores of the future generation of nuclear reactors on the roadmap towards minor actinide (MA) based fuel technology. The physical properties of UO2 highly depend on material stoichiometry. In particular, oxidation towards hyper stoichiometric UO2 – UO2+x – might be encountered at various stages of the nuclear fuel cycle if oxidative conditions are met; the impact of physical property changes upon stoichiometry should therefore be properly assessed to ensure safe and reliable operations. These physical properties are intimately linked to the arrangement of atomic defects in the crystalline structure. The first paper evaluates the evolution of defect concentration with environment parameters – oxygen partial pressure and temperature by means of a point defect model, with reaction energies being derived from EP based atomic scale simulations. Ultimately, results from the point defect model are discussed, and compared to experimental measurements of stoichiometry dependence on oxygen partial pressure and temperature. Such investigations will allow for future discussions about the solubility of different fission products and dopants in the UO2 matrix at EP level.While the first paper answers the central question regarding the dominating defects in non-stoichiometry in UO2, the focus of the second paper was on the EP prediction of the material properties, notably the lattice parameter of Am, Np containing U and Pu MOX as a function of atomic fractions.The configurational space of a complex U1-y-y’-y’’PuyAmy’Npy’’O2 system, was assessed via Metropolis-Monte Carlo techniques. From the predicted configuration, the relaxed lattice parameter of Am, Np bearing MOX fuel was investigated and compared with available literature data. As a result, a linear behaviour of the lattice parameter as a function of Am, Np content was observed, as expected for an ideal solid solution. These results will allow to support and increase current knowledge on Gen-IV fuel properties, such as melting temperature, for which preliminary results are presented in this thesis, and possibly thermal conductivity in the future. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished