1,721,382 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Thermo-mechanical behavior of a thermoplastic reinforced with glass fibers under cyclic loadings
No full textLes composites à matrice polymère sont de plus en plus utilisés dans le secteur automobile. Afin de remplir les conditions exigeantes du cahier des charges vis-à-vis des conditions de mise en service, les pièces en composite doivent maintenir leur forme géométrique sous des conditions thermo-mécaniques parfois extrêmes. Par exemple, un assemblage de hayon composite est soumis à des contraintes mécaniques élevées associées à des variations de température importantes lors des essais de validation du cahier des charges. Les enjeux de la thèse sont axés sur l’aide à la conception dans le domaine quasi-statique de pièces industrielles injectées en thermoplastique renforcé de fibres discontinues. L’amélioration des outils numériques doit permettre un dimensionnement virtuel optimal de ces pièces en anticipant les variations rencontrées en service et les distorsions résiduelles résultantes de chargements thermo-mécaniques. Cette démarche s’appuie sur la connaissance du comportement thermo-mécanique du matériau de l’étude, celui du renfort de hayon, un polypropylène renforcé à 40% en masse de fibres de verre discontinues, et sur la modélisation du comportement de ce type de matériau.Discontinuous fibers reinforced thermoplastic materials have been widely used for several years in the automotive industry. These parts must resist demanding service life conditions and must meet thermo- mechanical specifications. Indeed, structural automotive spare parts have to endure high temperatures, like a few tens of degrees Celsius, for a long duration, at least a few hours. As an example, a structural part of tailgate is subject to high mechanical loading, associated to strong temperature variations, during the validation test, regarding specifications. The purpose of this work is to improve the design of complex industrial parts, like the tailgate in quasi-static domain, by relying on numerical simulation. One of the challenges related to the use of such material, is to have a reliable virtual design of industrial parts by predicting the geometrical variations during service life conditions, and residual strain. Therefore, it is necessary to characterize and to model the thermo-mechanical behavior of the tailgate material, a polypropylene matrix reinforced with discontinuous glass fibers, with a given mass fraction of 40
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Impact of manufacturing processes on the critical mechanical performances of a hydrofoil : implementation of automated solution
No full textLe travail de thèse a débuté début 2016, dans l’écurie de course au large Absolute Dreamer qui préparait le premier Vendée Globe sur lequel les bateaux de course (jauge IMOCA) étaient équipés d’appendices sustenteurs appelés hydrofoils. Pourquoi ces voiliers de dernière génération ont-ils tous eu des casses de foils, alors que les matériaux et procédés de fabrication (pré-imprégnés carbone époxy) utilisés pour la fabrication de ces pièces existent depuis les années 70 ? On explore les procédés de fabrication complexes de ces pièces très épaisses (>80mm) en cherchant à identifier les mécanismes qui peuvent altérer la résistance en compression : la propriété mécanique « critique » de telles pièces. Des fabrications et caractérisations de plaques et de foils à taille réelle permettent d’une part de mesurer l’impact de certains choix de fabrication mais aussi de faire évoluer les standards de qualification de telles pièces. Ainsi, un essai de flexion est conçu pour à la fois étudier et quantifier la non-linéarité élastique axiale des unidirectionnels, tout en mesurant leur résistance en compression. En parallèle de ces explorations, la maîtrise des procédés de fabrication nous a poussé à essayer des procédés alternatifs, en utilisant un robot de placement de fibres traditionnellement utilisé dans l’aéronautique pour fabriquer des foils de catamaran. Ces travaux permettent à Luc Talbourdet et moi de créer une entreprise – Avel Robotics – qui est aujourd’hui un chantier dédié à la fabrication de foils. Quatre ans après le début des travaux de thèse, trois IMOCA parmi les favoris du prochain Vendée Globe seront équipés de pièces produites par Avel RoboticsThe thesis work started in early 2016, in the sailing team « Absolute Dreamer », which was preparing the first Vendée Globe where the IMOCA sailing boats were allowed to carry lifting appendixes called « hydrofoils ». ‘Why did so many of these boats suffered breakages of hydrofoils as the manufacturing process used to produced them (pre-impregnated carbon/epoxy) had been employed since the seventies?’ was one question to address. We explore the manufacturing processes of these very thick parts (>80mm) while identifying the mechanisms that could alter the composite compressive strength: the critical property of such parts. Plates and full-sized foils are manufactured and tested in order to measure the mechanical impact of some manufacturing choices, and to improve the testing methodology used to qualify these parts. We designed a bending test able to simultaneously highlight and quantify the elastic non-linearity of unidirectional plies, while measuring their compressive strength. In the meantime, we use our manufacturing knowledge to adapt the aeronautical technology of automated fiber placement for the production of catamaran hydrofoils. Luc Talbourdet and myself will use this work to create a small company – Avel Robotics – which is today an hydrofoil shipyard. Four years after the beginning of the thesis, three IMOCAs among the next Vendée Globe favourites’ will be equipped with pieces produced by Avel Robotics
Lignocellulosic nanomaterials for construction and building applications
Full text linkLignocellulosic nanomaterials are nanoscale materials derived from lignocellulosic biomass and having the length ranges from 1 to 100 nm. Generally, lignocellulosic biomass consisting of three main cell wall components, namely, cellulose, hemicellulose, and lignin. Building material represents a variety of materials that are used for construction purpose including wood and timber, fired bricks and clay blocks, steel, concrete, cement composites, etc. Construction and building materials can be simply classified as structural and nonstructural materials. Concrete, wood, and steel are three of the main structural materials. Lignocellulosic nanomaterials are able to enhance the properties of construction and building materials by acting as a reinforcement to the concrete, coating for woods, and nanofiller for polymer composites. This chapter provides an overview on the available types of lignocellulosic nanomaterials and their application in the production of construction and building materials. Limitations and challenges dealing with the application of lignocellulosic nanomaterials were also discussed
Development of thermal super-insulating materials from nano-cellulose fibers
No full textL'objectif de cette thèse est la préparation d’aérogels biosourcés ayant des propriétés de super-isolation thermique. Pour cela, nous avons choisi de développer de nouveaux aérogels à base de nanofibres de cellulose (NFC). Les aérogels ont été préparés par lyophilisation. Dans un premier temps, une analyse des paramètres expérimentaux jouant un rôle sur la morphologie et les propriétés physico-chimiques des aérogels a été réalisée afin d’obtenir les meilleures propriétés d’isolation thermique. Avec une suspension de NFC à 2% en masse, sans ajout de sels et sans faire varier le pH, une lyophilisation réalisée dans des moules d’aluminium à une température de -80°C a permis d’obtenir des aérogels ayant une conductivité thermique de 0,024 W/m.K. Afin de diminuer cette conductivité thermique, nous avons choisi de réduire la taille des pores pour obtenir un effet Knudsen. Pour cela, une nouvelle technique de séchage a été proposée : la lyophilisation par pulvérisation. Les aérogels préparés dans les mêmes conditions expérimentales que précédemment avec cette technique ont des propriétés thermiques super-isolantes (0,018 W/m.K) grâce à la nano-structuration du réseau poreux. Finalement, un nouveau dispositif expérimental a été développé pour caractériser plus finement les propriétés thermiques des aérogels. C’est un dispositif transitoire impulsionnel qui permet d'estimer simultanément la contribution de la conduction solide et gazeuse, l'effet radiatif et la diffusivité thermique grâce à un modèle théorique simple. Ce dispositif permettra d’approfondir l’étude complexe du transfert thermique à travers des matériaux poreux semi-transparents tels que les aérogels.The objective of this thesis is the preparation of renewable aerogels having thermal super-insulating properties. To do it, we designed new aerogels from nanofibrillated cellulose (NFC) by freeze-drying. This technique is simple and has the advantage of not using organic solvents. First of all, the parameters playing a role on the aerogel morphology and physico-chemical properties of the aerogels were analyzed to get the best thermal insulating properties. Using 2 wt% NFC suspensions, without addition of salts, keeping the initial pH, the obtained freeze-dried aerogels in alumina molds at -80 °C have a thermal conductivity of 0.024 W/m.K. In order to reduce the pore size and to improve the thermal insulating properties by Knudsen effect, a new drying technique was proposed: the spray freeze-drying. Aerogels prepared in the same experimental conditions with this technique have thermal super-insulating properties (0.018 W/m.K) thanks to the nanostructuration of the porous network. Finally, a new device was designed to characterize more precisely the thermal properties of aerogels. This is an impulsive transient device, which can estimate simultaneously the contribution of solid and gas conduction, the radiative effect and thermal diffusivity using a simple theoretical model. This device will allow studying complex heat transfer through porous semi-transparent materials such as aerogel
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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