1,720,968 research outputs found
Contribution to numerical study of the behavior of a composite panel under fire for naval industry
No full textPour être commercialisés et installés à bord des navires, les panneaux structuraux tels que les cloisons et les pontsdoivent passer avec succès un essai normalisé de résistance au feu de type ISO 834. De tels essais sont longs et coûteux,les constructeurs de panneaux souhaitent par conséquent maximiser les chances de succès lors du passage de leur produitau test en particulier pour les designs alternatifs que constituent les sandwichs composite.La simulation par éléments finis est un outil pour modéliser le comportement thermomécanique de telles structures.Les codes industriels comme SAMCEF qui a été utilisé dans ce travail sont capables de réaliser des analyses thermiquesavec dégradation et des analyses mécaniques mettant en jeu la gestion du contact, la dégradation des propriétésmécaniques et la perte des structures par ruine.L’enjeu de cette étude est d’abord identifier les spécificités de telles structures particulières par leur taille, leurconception, de déterminer quelles sont les données thermiques et mécaniques nécessaires pour alimenter le modèlenumérique et le cas échéant de les construire à partir des résultats de la réaction au feu des matériaux. Des modèlesnumériques que l’on souhaite robustes et utilisables dans un contexte industriel, sont développés pour déterminer lecomportement thermomécanique de tels panneaux. Ils prennent en compte l’évolution des propriétés thermiques etmécaniques des matériaux en cours de dégradation. Ces modèles doivent permettre par la suite l’estimation desperformances de nouveaux designs lors d’un essai de certification ISO 834.Structural panels used in naval industry such as bulkheads and decks must succeed in standard certification testssuch as ISO 834 to be commercialized and settled on board. As these tests are long and expensive, panel manufacturerswish to maximize chances of success for their panels when submitted to certification tests especially when it comes toalternative designs such as composite sandwich panels.Finite elements analyses are used to model thermo-mechanical behavior. Industrial software such as SAMCEF,which was used to conduct this work, are able to solve thermal analyses with degradation and mechanical analyses involvingcontact conditions, degradation of mechanical properties and loss of structures due to failure.The objective in this study is to first identify characteristics of these structures. They are special due to their size andtheir manufacturing. This study aims also to determine thermal and mechanical data required for numerical modeling.When necessary some data can be computed from results coming from the results of the materials’ reaction to fire.Numerical models are developed to determine thermo-mechanical behavior and are designed to be robust and used inindustrial context. They include the evolution of thermal and mechanical properties during the degradation process. Thesemodels must enable to estimate the performances of innovative designs during an ISO 834 certification test
Matériaux magnétiques nanostructurés dur-doux à architecture contrôlée
No full textParmi les aimants sans terres raresactuellement étudiés, τ-MnAl ferromagnétique est uncandidat à haut potentiel, car il possède despropriétés magnétiques intrinsèques prometteuses.Dans cette thèse, Mn(Fe)AlC a été synthétisé parbroyage mécanique. Les effets du carbone sur lamicrostructure et les propriétés magnétiques ont étéétudiés. Les résultats montrent qu’une pureté élevéede τ-MnAl(C) pouvait être obtenue avec un dopage à2% en atomes de carbone, montrant clairement l’effetstabilisant du carbone. L’alliage Mn54.2Al43.8C2possède les meilleures propriétés magnétiques :aimantation à 2T M2T = 414 kAm-1, aimantationrémanente Mr = 237 kAm-1, coercivité HC = 229 kAm-1et |BH|max = 11,2 kJm-3. HC augmente inversementproportionnellement avec la taille des cristallites de laphase τ et proportionnellement à la teneur en C. Descalculs ab initio confirment l’effet stabilisant etindiquent les positions interstitielles préférentielles ducarbone dans la maille quadratique de la phase τ-MnAl.Les alliages Mn51-xFexAl47C2 (x = 0,25, 0,5, 1, 2, 4, 6)ont également été synthétisés par broyagemécanique, montrant une pureté élevée de la phaseτ jusqu'à un taux de substitution de 2% du Mn par duFe. L'ajout de Fe dans MnAl(C) réduit l'aimantationet TC, mais augmente légèrement la valeur de HC. Laspectrométrie 57Fe Mössbauer à 300K a été utiliséepour sonder l'environnement local dans ε-, τ-, β- etγ2-MnFeAl(C). γ2-, ε- et β-MnFeAl(C) présentent unestructure hyperfine quadripolaire alors que τ-Mn50.5Fe0.5Al47C2 montre une structutr hyperfinemagnétique assez complexe. Une expérience despectrométrie Mössbauer effectuée à bassetempérature (10K) et sous champ magnétique (8T)montre un ordre ferromagnétique local non colinéairedes moments magnétiques de Fer par rapport à ladirection du champ appliqué. Le champ hyperfin del’alliage MnFeAl calculé par Wien2k confirme lespropriétés magnétiques et les résultats despectrométrie Mössbauer.Among currently investigated rare-earth-free magnets, ferromagnetic τ-MnAl is a highly potential candidate as having promising intrinsic magnetic properties. In my thesis, Mn(Fe)AlC was synthesized by mechanical alloying method. Effects of carbon on microstructure and magnetic properties were systematically investigated. It was found that high purity of τ-MnAl(C) could be obtained at 2 at.% C doping, showing clearly stabilizing effect of carbon. Mn54.2Al43.8C2 has the best magnetic properties: magnetization at 2T M2T = 414 kAm-1, remanent magnetization Mr = 237 kAm-1, coercivity HC = 229 kAm-1, and |BH|max = 11.2 kJm-3. HC increased inversely with the crystallite size of τ phase and proportionally with C content. Moreover, first principle calculation showed both stabilizing effect and preferable interstitial positions of carbon in tetragonal τ-MnAl. Mn51-xFexAl47C2 (x= 0.25, 0.5, 1, 2, 4, 6) alloys were also synthesized by mechanical alloying method, showing high purity of τ phase up to 2 at.% Fe doping. Adding of Fe on MnAl(C) reduced both magnetization and TC but likely increased slightly HC. 57Fe Mössbauer spectrometry at 300K was used to probe local enviroment in ε-, τ-, β-, and γ2-MnFeAl(C). In which, γ2-, ε-, and β-MnFeAl(C) exhibited a quadrupolar structure while τ -Mn50.5Fe0.5Al47C2 spectrum showed a rather complex magnetic hyperfine splitting. The interaction between Fe and Mn examined by in-field Mössbauer measurement at 10 K and 8 T showed a non-collinear magnetic structure between Fe and Mn with different canting angles at different sites. Hyperfine field of MnFeAl alloy calculated by Win2k supported both magetic properties and Mossbauer results
Modeling of magnetic and optical properties of nanoparticles in medical interest
No full textCette thèse porte sur la modélisation ab initio des ligands et des nanoparticules magnétiques utilisés en médecine (hyperthermie magnétique, imagerie médicale ...). Les calculs sont effectués par le logiciel Quantum Espresso base sur théorie de la fonctionnelle de la densité et LDA + U. L'objectif est d'abord de comprendre la liaison des ligands sur des nanoparticules magnétiques, la nature de l'ionicité dans les particules, puis de décrire le changement d'anisotropie magnétique due aux liaisons chimiques sur la surface, et enfin de décrire la modification des propriétés optiques due également à la liaison de différents ligands sur la surface de nanoparticules hybrides d'or et d'oxyde de fer.This thesis concerns the ab initio modeling of ligands and magnetic nanoparticles used in medicine (magnetic hyperthermia, medical imaging). Calculations are performed by the Quantum Espresso software based on density functional theory and LDA+U. The goal is first to understand the binding of ligands on magnetic nanoparticles, the nature of ionicity in the particles, then to describe the change in magnetic anisotropy due to the chemical bondings on surface, and finally to describe the change in optical properties due also to the bonding of various ligands or clusters on the surface of hybrid gold and iron oxide nanoparticles
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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