1,721,044 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
Synthesis of ionomers by direct polycondensation of functionnal monomers
No full textCe manuscrit de thèse décrit la synthèse et la caractérisation d'ionomères conducteurs protoniques pour une application en tant que membrane pour pile à combustible. La stratégie adoptée pour la synthèse de ces polymères repose sur la polycondensation directe de monomères fonctionnels. Pour ce faire, et dans le cadre d'un travail important de chimie organique, la synthèse de trois monomères sulfonés ainsi que de trois monomères phosphonés a été réalisée. Différents polymères perfluorés (polyperfluorocyclobutane (PFCB) et polyaryléthers (PAE) (Polyétheréther cétone (PEEK) et Polysulfone (PS), ont été obtenus par polycondensation directe de ces monomères fonctionnalisés. Il a été possible de synthétiser des copolymères séquencés (à blocs) et comportant un ou deux types de fonctions conductrices protoniques. Afin d'établir d'éventuelles relations structure-propriété pour ces polymères et l'influence du solvant dans la morphologie de la membrane, une étude de la morphologie a été réalisée à partir de plusieurs séries de polymères PAE et leurs analogues « statistiques ». Les valeurs de conductivité des polymères à blocs sont, en général, supérieures à celles de leurs analogues « statistiques ». Un PAE obtenu est particulièrement intéressant, il possède à la fois une conductivité (216 mS.cm 1) nettement supérieure au Nafion® et un gonflement plus faible. Le polymère perfluoré (PFCB) obtenu est également très prometteur : la conductivité enregistrée pour ce ionomères est de 138 mS/cm. Ce travail de thèse est, à notre connaissance, le premier exemple de synthèse d'un PFCB sulfoné par polymérisation directe d'un monomère fonctionnel mais il constitue également le premier exemple de synthèse de poly(aryléther)s à blocs sulfonés / phosphonés par copolymérisation directe de deux types de monomères fonctionnelsThis thesis describes the synthesis and characterization of proton conducting polymers for application as membrane for fuel cells (PEMFC). The approach for the synthesis of polymers consists in creating polymers from direct polycondensation of functional monomers, in order to better control their final IEC. Three sulphonated monomers and three phosphonated monomers have been first synthetized. Different types of polyarylethers (one of them is both sulphonated and phosphonated) and one perfluorinated polymer (PFCB) have been synthetised by direct polycondensation of functional monomers. In order to explain the influence of the solvent in the final morphology of the membrane, and the relation between its structure and properties, one morphological study has been realized to the obtained polymers but also to their analogues “statistical” polymers. In general, the blocks polymers obtained the highest values of conductivity. One polyarylether seems particularly interesting, because its conductivity value is much higher than Nafion®’s, and has a smaller swelling value. The perfluorinated polymer has also an interesting conductivity value (138 mS/cm). This thesis work is, to the best of our knowledge, the first example of the synthesis of a sulphonated PFCB obtained by direct polycondensation but also the first example of synthesis of a both sulfonated/phosphonated polyarylethers by direct copolymerisation of to types of functional monomer
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
Chemical stabilization of polymer electrolytes used in Fuel Cells
No full textLa dégradation accélérée des membranes conductrices protoniques en pile est en partie due à une oxydation induite par la production d'H2O2. Cette étude présente une stratégie originale de stabilisation chimique d'une matrice de sPEEK par l'inclusion de nano-charges stabilisantes. Quatre nano-charges ont été préparées par fonctionnalisation de nanoparticules de silice avec des fonctions chimiques organosoufrées (disulfure, tétrasulfure et thiourée). Un protocole spécifique de mise en forme des membranes hybrides a permis d'obtenir des composites présentant des propriétés mécaniques et une conductivité protonique compatibles avec l'application pile. Les fonctions polysulfures permettent de ralentir la dégradation de la matrice de sPEEK durant l'étape de mise en œuvre et d'augmenter sa conductivité au cours d'un vieillissement ex-situ (H2O2). En présence de fonctions tétrasulfures, la membrane sPEEK ne se dégrade pas durant un test de 1200h en OCV à 70°C et 100%HR.One of the origins of the accelerated aging of proton exchange membranes used in Fuel Cells is the oxidation induced by H2O2 formation. This work concerns the development of a new way to chemically stabilize a sPEEK membrane by the addition of stabilizing nano-fillers. Four fillers were synthesized by grafting organosulfur functions (disulfide, tetrasulfide and thiourea) onto silica nanoparticles. A specific protocol to prepare hybrid membranes led to materials with suitable mechanical properties and proton conductivity for fuel cells application. Polysulfides allow a significant decrease of the matrix degradation occurring during membrane processing and also a large increase of the proton conductivity of this matrix during ex-situ aging tests (H2O2). A membrane containing tetrasulfide nano-fillers could withstand 1200h in OCV condition at 70°C and 100%RH, without showing any sign of degradation
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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