1,721,035 research outputs found
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
Development of new hybrid composites reinforced by carbon and flax fibers : manufacturing and Mechanical characterization
No full textL’objectif de cette thèse est, d’une part, l’optimisation de la mise en œuvre des matériaux composites àtravers l’étude du comportement des renforts secs en compaction et, d’autre part, le développement et lacaractérisation de matériaux composites stratifiés hybrides renforcés par des fibres de carbone et de lin.Durant la mise en œuvre de ces composites, les renforts sont soumis à un phénomène appelé compactiontransverse. La compréhension de ce mécanisme est importante pour l’amélioration de la mise en œuvre.La connaissance de la capacité de compaction des renforts secs sert également à la prédiction du taux defibres ainsi que de l’épaisseur de la pièce composite finale. Des essais de compaction réalisés sur douzerenforts présentant de différentes solutions techniques ont montré que la capacité de compaction d’unrenfort sec est influencée par plusieurs facteurs. Les résultats obtenus de ce travail portant essentiellementsur les renforts à fibres naturelles (lin) ont montré que ces types de renforts se compactent moinsbien que les renforts à fibres synthétiques (carbone, verre). Ainsi, pour pouvoir améliorer la capacité decompaction de ces renforts naturels, il faut choisir ceux dont le grammage est important, ceux dont lesmèches sont en fibre et non en fil, ceux qui sont unidirectionnels (ou quasi UD) plutôt que des tissés oudes bi-biais. De plus, il faut privilégier les séquences à plusieurs plis aux séquences mono-plis.Face à un fort besoin d’allègement des structures, les matériaux composites sont de plus en plus recherchésdans le secteur industriel notamment dans le domaine des transports. Cependant, les matériaux compositescomme tout autre matériau, en plus d’être mécaniquement performant, doivent remplir d’autresfonctions comme l’amortissement de chocs et de vibrations pour une bonne tenue en service. Pour remplircette double exigence, une des solutions est d’utiliser la technique d’hybridation qui consiste à utiliserau sein d’un même composite des fibres naturelles et synthétiques à la fois afin d’exploiter leursatouts respectifs. Respectivement en raison de leur rigidité et de leur pouvoir amortissant, les fibres decarbone et de lin ont été choisies dans le cadre de cette thèse. La caractérisation des plaques stratifiéesfabriquées en infusion de résine montre que le composite carbone a de meilleures propriétés mécaniqueset microstructurales tandis que le composite lin propose des propriétés amortissantes très intéressantes.Les résultats montrent que l’hybridation du lin avec du carbone permet d’améliorer considérablement lesfaibles propriétés mécaniques du composite lin et les mauvaises propriétés amortissantes du compositecarbone. La séquence d’empilement des couches a une influence significative sur le comportement et lespropriétés des stratifiés hybrides. Nos résultats ont montré que pour avoir une meilleure microstructureles couches de carbone doivent être disposées à l’extérieur. Cette façon d’hybrider permet égalementd’obtenir de meilleures propriétés en flexion et en choc. En revanche, lorsque les couches de lin sontplacées à l’extérieur, le composite hybride a une meilleure capacité d’amortissement. Cette séquenced’empilement garantit aussi une meilleure résistance en indentation. Ainsi, la séquence d’empilementhybride à choisir dépendra du besoin que l’on cherche à satisfaire.Enfin, grâce à une analyse basée sur la théorie classique des stratifiés, il a été démontré dans cette thèsequ’on peut dimensionner des composites stratifiés hybrides malgré que les couches constitutives soientde différente nature avec des propriétés dissemblables.The goal of this thesis is, on the one hand, the optimization of the manufacturing of composite materials through the study of the behavior of dry fibrous reinforcements in compaction and, on the other hand, the development and characterization of hybrid composite laminates reinforced with carbon and flax fibers. During the manufacturing process of these composites, the reinforcements are subjected to a phenomenon called transverse compaction. Understanding this mechanism is important for improving the manufacturing process. Knowledge of the compaction capacity of the dry reinforcements also serves to predict the fiber content as well as the thickness of the final composite part. Compaction tests carried out on twelve reinforcements presenting different technical solutions have shown that the compaction capacity of a dry reinforcement is influenced by several factors. The results obtained from this work, which focuses on natural fiber reinforcements (flax), have shown that these types of reinforcement are less compactable than synthetic fiber reinforcements (carbon, glass). Thus, to be able to improve the compaction capacity of these natural reinforcements, it is necessary to choose those whose area density is important, those whose tows are in fiber not in yarn, those which are unidirectional (or quasi UD) rather than woven or bi-bias. In addition, it is necessary to choose a multi-ply sequence rather than single-ply sequence. Faced with a strong need for lightening structures, composite materials are increasingly sought in the industrial sector, particularly in the transport sector. However, composite materials like any other material, in addition to being mechanically efficient, must perform other functions such as damping shock and vibration for good performance in service. To meet this double requirement, one of the solutions is to use the hybridization technique which consists in using within the same composite natural and synthetic fibers at the same time in order to exploit their respective advantages. Respectively because of their rigidity and their damping capacity, the carbon and flax fibers were chosen in the context of this thesis. The characterization of the laminate composite plates manufactured with resin infusion process shows that the carbon composite has better mechanical and microstructural properties while the flax composite offers very interesting damping properties. The results show that hybridization of flax with carbon considerably improves the low mechanical properties of the flax composite and the poor damping properties of the carbon composite. The stacking sequence of layers has a significant influence on the behavior and properties of the hybrid laminates. Our results showed that to have a better microstructure the carbon layers must be put outside. This way of hybridizing also makes it possible to obtain better properties in flexion and shock. By contrast, when the flax layers are placed outside, the hybrid composite has a better damping capacity. This stacking sequence also guarantees a better indentation strength. Thus, the hybrid stacking sequence to choose will depend on the need that is sought to meet. Finally, thanks to an analysis based on classical laminate theory, it has been demonstrated in this thesis that hybrid composite laminates can be dimensioned despite the fact that the constituent layers are of different types with dissimilar properties
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
Influence of natural fibers on curing kinectis of biobased resins
No full textLe développement de composites à matrices biosourcées et renforcées par des fibres naturelles est une solution envisagée par les industriels pour répondre aux problématiques environnementales. Cependant, la méconnaissance des interactions qui se produisent durant la mise en oeuvre entre les fibres naturelles et la résine pendant la réticulation ne permet pas d'obtenir des procédés de fabrication stabilisés et rend l'industrialisation à grande échelle difficile. Cette étude propose d'évaluer l'influence de la présence de fibres de lin sur la cinétique de réticulation d'une résine époxy-amine biosourcée. Pour ce faire, une approche multi-échelle couplant résultats expérimentaux et numériques a été utilisée en comparant des échantillons de résine pure, de composites renforcés par des fibres de verre, de lin sèches ou humides. La présence d'eau dans les fibres naturelles accélère la cinétique de réticulation du système époxy-amine. A l'inverse, l'absence d'eau dans les fibres naturelles semble inhiber la réaction de réticulation amenant à une diminution de la réactivité de la résine polyépoxyde. Il a également été mis en évidence que la présence d'eau pendant la fabrication a un impact sur la cohérence et la qualité du réseau tridimensionnel final. En parallèle de ces résultats expérimentaux, une étude numérique à l'échelle atomique réalisée grâce à des simulations en dynamique moléculaire a permis d'obtenir de nouvelles clés de compréhension de l'influence des fibres naturelles sur la cinétique de réticulation d'une résine époxy-amine biosourcée. En effet au-delà de l'action chimique, les molécules d'eau ont une action purement physique sur la formation du réseau tridimensionnel.The development of composites made of biobased matrices reinforced with natural fibres is a solution considered to meet environmental constraints of industry. However, the lack of knowledge on the interactions that occur during processing between natural fibers and the resin during crosslinking does not allow one to obtain stabilized manufacturing processes and makes large-scale industrialization more difficult. This study proposes to evaluate the influence of the presence of flax fibres on the crosslinking kinetics of a biobased epoxy-amine resin. For this purpose, a multi-scale approach coupling experimental and numerical results was used by comparing samples of pure resin, composites reinforced with glass fibers, dry flax fibers or wet flax fibres. The presence of water in natural fibers accelerates the crosslinking reaction of the epoxy-amine system. Conversely, the absence of water in natural fibers seems to inhibit the crosslinking reaction leading to a lower reactivity of the polyepoxy resin. It has also been shown that the presence of water during the manufacturing process has an impact on the consistency and quality on the final three-dimensional network. In parallel with these experimental results, a numerical study at the atomic scale was carried out using molecular dynamics simulations and revealed new ways in understanding the influence of natural fibres on the crosslinking kinetics of an epoxy resin. Indeed, beyond the chemical action, water molecules have a purely physical action on the formation of the three-dimensional network
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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