1,721,105 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
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
Thermal ageing of polydicyclopentadiene
No full textLe polydicyclopentadiène (PDCPD) est un polymère thermodurcissable synthétisé à partir de la polymérisation par métathèse par ouverture de cycle, qui présente l'avantage d'un temps de polymérisation court du fait de la présence de doubles liaisons et de l'utilisation de catalyseurs organométalliques. Dans cette thèse, PDCPD est considéré comme un candidat pour des applications en milieu marin, pour lesquelles la question de la durabilité doit être évaluée. L'objectif de ce travail est d'établir un modèle cinétique non empirique pour la prédiction de la durée de vie du PDCPD au cours de l'oxydation thermique. Tout d'abord, la caractérisation par spectroscopie Infrarouge et dosages des peroxydes au cours de l’oxydation a été réalisée afin de mettre en place un modèle cinétique pour le PDCPD sans stabilisant. En particulier, les constantes de vitesse d'initiation ont été identifiées par une étude de la thermolyse des hydroperoxydes; les constantes de vitesse de terminaison ont été obtenues par des expériences spécifiques sous différentes pressions d'oxygène. L'effet du catalyseur sur la cinétique d'oxydation a également été étudié dans ce travail. La consommation de doubles liaisons du polymère entraîne une augmentation significative de la concentration de nœuds de réticulation, puis une augmentation de la contrainte de rupture de PDCPD. Le modèle cinétique créé prédit ces tendances ainsi que l'épaisseur de la couche oxydée. L'effet des stabilisants visant à ralentir la vitesse d'oxydation a également étudié expérimentalement puis modélisé. En particulier, les amines encombrées (HALS) se sont révélées très efficaces et compatibles avec les catalyseurs de la ROMP. Dans la dernière partie, l’effet de l’oxydation thermique du PDCPD sur le comportement de sorption de l’eau a été étudié. Le PDCPD vierge présente une très faible absorption d'eau à cause de sa structure apolaire, alors que le PDCPD vieilli est plus hydrophile en raison de la formation de groupes polaires ce qui peut avoir une influence sur sa durée de vie en milieu marin.Polydicyclopentadiene (PDCPD) is a thermoset polymer synthesized from ring opening metathesis polymerization with the advantage of short processing time due to the presence of double bonds and the use of organometallic catalysts. In this thesis, PDCPD is for example considered as a candidate for the field-joint in a marine environment. The question of the durability of PDCPD has to be assessed. The objective of this work is to establish a non-empirical kinetic model for the lifetime prediction of PDCPD during thermal oxidation. Firstly, the characterization by Infrared spectroscopy and peroxide titration of PDCPD during its thermal oxidation was conducted to set up a kinetic model for additive-free PDCPD. In particular, the initiation rate constants have been identified especially through hydroperoxide decomposition rates; the termination rate constants have been obtained by specific experiments under various oxygen pressures. The consumption of double bonds in the polymer causes a significant increase in crosslink concentration then increasing yield stress of PDCPD. The kinetic model predicts those trends as well as the thickness of the oxidized layer. The effect of stabilizer aimed at slowing down the oxidation rate was also experimentally studied and modeled. In particular, hindered amine stabilizers were shown to be promising candidates with good stabilizing properties and compatible with ROMP catalysts. Lastly, the effect of thermal oxidation of PDCPD on water sorption was investigated. Virgin PDCPD presents very low water absorption due to its apolar groups. Whereas, aged PDCPD shows increased hydrophilicity associated with polar groups build-up (which can probably impact its lifetime in marine conditions
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
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
Ageing of epoxys used for aeronautical bonded assemblies
No full textCette thèse porte sur l’étude multi-échelle du vieillissement d’assemblages collés à base de colle époxy employés dans le domaine aéronautique. Dans leurs conditions de service, ces matériaux sont soumis à un vieillissement humide, qui peut s’accompagner d’un vieillissement thermique essentiellement lors des phases de décollage des avions. De telles conditions rendent difficiles la prédiction de la durée de vie basée uniquement sur le suivi des propriétés mécaniques des assemblages (par des tests de cisaillement simple ou de clivage) lors d’essais de vieillissement normalisés qui prévalent, pour le moment, dans l’industrie. Notre objectif était donc une étude du vieillissement à l’échelle moléculaire afin d’en dériver, à terme, des lois cinétiques prédisant la vitesse de dégradation. Une première étape a mis en lumière les différences existantes entre le vieillissement humide (rupture adhésive) et thermique (rupture cohésive). La rupture cohésive observée en vieillissement thermique nous a conduits à étudier les mécanismes responsables de la chute de ténacité des époxys. Nous avons ainsi étudié les mécanismes de dégradation de l’adhésif, de deux de ses systèmes « représentatifs » (DGEBA-DDS et TGMDA-DDS). L’analyse des produits de dégradation dans ces réseaux et leurs composées modèles nous a conduits à élaborer un schéma cinétique intégrant la réactivité des principaux sites d’oxydation (sites au voisinage de certains hétéroatomes) qui peut décrire en partie l’oxydation des systèmes simples DGEBA-DDS et TGMDA-DDS mais devra être converti en modèle de co-oxydation (c’est-à-dire intégrant la participation simultanée de plusieurs sites) à la fois pour décrire plus complétement l’oxydation des systèmes simples mais surtout pour traiter des matériaux industriels de formulation complexe. Dans une dernière partie, nous nous sommes intéressés à la spécificité des assemblages collés lors d’un vieillissement humide. Cette dernière partie montre la nécessité de bien comprendre les phénomènes de diffusion à l’interface, et dans des matériaux oxydés, pour pouvoir prédire la durée de vie des adhésifs époxys employés pour les assemblages collés.This thesis deals with a multi-scale study of the ageing of bonded assemblies based on epoxy adhesive used in the aeronautical field. In service conditions, these materials are subjected to humid ageing, which can be accompanied by thermal ageing essentially during the take-off phases of aircraft. Such conditions make it difficult to predict lifetime based only on the study of the mechanical properties of the assemblies (by single lap shear stress or wedge tests) in standardized ageing tests, which, for the moment, prevail in the industry. Our objective was therefore a study of ageing at the molecular scale in order to derive forward kinetic laws predicting the kinetics of degradation. A first step highlighted the differences between humid ageing (adhesive failure) and thermal aging (cohesive failure). The cohesive rupture observed in thermal ageing led us to study the mechanisms responsible for the decrease in toughness of the epoxies. We studied the mechanisms of degradation of the adhesive as well as two of its "representative" systems (DGEBA-DDS and TGMDA-DDS). The analysis of degradation products in these networks and their model compounds led us to develop a kinetic scheme introducing the reactivity of the main oxidation sites (site near certain heteroatoms) which can partly describe the oxidation of simple systems. In the future, DGEBA-DDS and TGMDA-DDS will have to be converted into a co-oxidation model (that means integrating the simultaneous participation of several sites) to describe entirely the oxidation of simple systems but especially for handled industrial materials of complex formulation. In a last part, we were interested in the specificity of bonded assemblies during humid aging. This last section displays the need to understand diffusion phenomena at the interface, and in oxidized materials, to predict the lifetime of epoxy adhesives used for bonded assemblies
Study of water aging of urethane dimethacrylate polymerized at high temperature and pressure
No full textLa pérennité des biomatériaux est au cœur des préoccupations des médecins et des patients. L’étude de leur dégradation in vitro pourrait permettre d’appréhender leur comportement clinique à long terme. Ce travail se concentre sur le vieillissement en milieu humide de polymères d’uréthane dimétacrylate (UDMA) polymérisés à haute température et sous haute pression (HT/HP) utilisés dans des blocs de matériaux composites usinables à usage dentaire et présente pour objectif d’étudier : le rôle de la pression de polymérisation HT/HP, les interactions entre l’eau et le polymère d’UDMA HT/HP, et l’influence de l’eau sur les propriétés de l’UDMA HT/HP. Il a été montré que :- La méthode de polymérisation HT/HP est un procédé pertinent, permettant d’améliorer les propriétés initiales de l’UDMA avec notamment une augmentation de la température de transition vitreuse.- Les interactions eau-UDMA semblent régies par la nature chimique de l’UDMA. La diffusion semble obéir à la loi de Fick et abouti à une quantité maximale d’eau absorbée d’environ 3,5 % à 37°C.- La pression de polymérisation n’a pas semblé influencer la solubilité ni la diffusion de l’eau.- La polymérisation sous HT/HP n’empêche pas la diffusion de l’eau au sein de la matrice d’UDMA ni l’altération de ses propriétés mécaniques. Néanmoins, elle permet d’améliorer significativement les propriétés initiales du polymère, accroissant ainsi l’écart entre les propriétés initiales du biomatériau et les propriétés limites d’utilisation.The durability of biomaterials concerns of doctors and patients. The study of their degradation in vitro could make it possible to understand their long-term clinical behavior. This work focuses on the wet aging of urethane dimethacrylate (UDMA) polymers polymerized at high temperature and under high pressure (HT/HP) used in blocks of machinable composite materials for dental use and has the objective of studying: the role of HT/HP polymerization pressure, the interactions between water and the UDMA HT/HP polymer, and the influence of water on the properties of UDMA HT/HP. It has been shown that: - The HT/HP polymerization method is a relevant process, making it possible to improve the initial properties of UDMA with in particular an increase in the glass transition temperature.- Water-UDMA interactions seem depend on the chemical nature of UDMA. Diffusion appears to obey Fick's law and results in a maximum amount of water absorption of about 3.5% at 37°C.- The polymerization pressure did not seem to influence the solubility or the diffusion of water.- Polymerization under HT/HP does not prevent the diffusion of water within the UDMA matrix nor the alteration of its mechanical properties. Nevertheless, it makes it possible to significantly improve the initial properties of the polymer, thus increasing the gap between the initial properties of the biomaterial and the limiting properties of use
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