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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
Mécanisme de séchage des colloïdes durs et mous dans une gouttelette
No full textLes films polymères sont essentiels dans diverses applications, de la nanolithographie en électronique à l'emballage, l'impression par jet d'encre et plus encore. Leur utilisation implique souvent le séchage de suspensions polymériques ou colloïdales appliquées sur des substrats. Dans les années 1990, les politiques ont évolué vers l'utilisation de l'eau comme milieu pour réduire les gaz organiques volatils (COV), qui contribuent au réchauffement climatique. Cependant, cela a créé un fossé technologique puisque la plupart des produits utilisaient des solvants organiques, et le mécanisme de séchage des systèmes à base d'eau n'était pas bien compris. Cette thèse explore la synthèse de particules colloïdales en utilisant la polymérisation en dispersion sans tensioactif, en évaluant leur taille et leur température de transition vitreuse (Tg). Les mécanismes de séchage ont été étudiés en utilisant diverses techniques de microscopie et de spectroscopie. Les colloïdes durs et mous ont montré des comportements de séchage différents, les particules dures passant par une phase de gel et les particules molles formant des fronts de coalescence. La présence de tensioactifs influençait considérablement ces mécanismes. Les résultats expérimentaux ont montré que les colloïdes durs créent des ponts capillaires, influencés par l'humidité ambiante. Les systèmes mixtes de colloïdes durs et mous présentaient des comportements de séchage uniques, avec une stratification se produisant lorsque les colloïdes mous étaient en dessous de 30 % de concentration. La tomographie par rayons X a révélé des détails de stratification et des densités de compactage. L'étude conclut que les tensioactifs jouent un rôle crucial dans les mécanismes de séchage, et que la tomographie par rayons X est précieuse pour évaluer les systèmes colloïdaux multi-espèces. Une analyse plus approfondie est nécessaire pour comprendre pleinement ces processus de séchage.Polymer films are essential in various applications, from nanolithography in electronics to packaging, ink-jet printing, and more. Their usage often involves drying polymer or colloidal suspensions applied to substrates. In the 1990s, policies shifted towards using water as a medium to reduce volatile organic gases (VOCs), which contribute to global warming. However, this created a technological gap since most products used organic solvents, and the drying mechanism of water-based systems was not well understood.This thesis explores the synthesis of colloidal particles using surfactant-free dispersion polymerization, evaluating their size and glass transition temperature (Tg). Drying mechanisms were studied using various microscopy and spectroscopy techniques. Hard and soft colloids exhibited different drying behaviors, with hard particles transitioning through a gel phase and soft particles forming coalescence fronts. The presence of surfactants influenced these mechanisms significantly. Experimental results showed that hard colloids create capillary bridges, influenced by environmental humidity. Mixed systems of hard and soft colloids displayed unique drying behaviors, with stratification occurring when soft colloids were below 30% concentration. X-ray tomography revealed detailed stratification and packing densities.The study concludes that surfactants play a crucial role in drying mechanisms, and x-ray tomography is valuable for evaluating multi-species colloidal systems. More in-depth analysis is needed to fully understand these drying processes
Concentrated suspensions : non-Newtonian systems and thixotropy under flow
No full textCette thèse de doctorat a été financée par l’entreprise SIKA spécialisée dans les matériaux de construction. Les trois chapitres de cette thèse correspondent à la tentative de résolution de trois problématiques d’origine industrielle. Dans le premier chapitre, nous avons étudié l’effet de la concentration en particules sur les propriétés d’écoulement de fluides complexes rhéofluidifiants ou rhéoépaississants et démontré l’origine microscopique de cet effet. Dans le second chapitre, nous avons étudié la floculation de particules colloïdales sous faibles perturbations et mis en évidence l’existence, au cours de la reconstruction, d’un maximum du module élastique. Enfin le troisième chapitre est l’étude d’un diagramme de phase de jet de suspensions concentrées. En régime dilué et semi-dilué, les résultats sont conformes à ceux de la bibliographie, en revanche nous avons étudié un nouveau régime à très haute fraction volumique où le jet, instable, se met à osciller. Nous avons montré que ces oscillations étaient dues au rhéoépaississement de la suspension.This thesis has been done in collaboration with the company SIKA, one of the leader if the construction industry. This thesis report is organized in three chapters where each of them tries to answer a problem coming from industrial processes. In the first chapter, we studied the impact of particles concentration on the flowing properties of complex fluids such as shear-thinning and shear-thickening fluids. We demonstrated the importance of local contacts between particles to explain the evolution of the viscosity with the volume fraction. In the second chapter, we studied the aggregation of colloidal attractive suspensions under small perturbations and proved the existence of a maximum of elastic modulus during the rebuilding of the structure. Finally, the third chapter is a study of a phase diagram of a concentrated suspension jets. In the diluted and semi-diluted regimes, we found results in agreement with the bibliography, meanwhile at very high concentration, we studied a new regime where the jet, unstable, is oscillating. We showed those oscillations can be explained by the shear-thickening behaviour of the suspensions at those high concentrations
Imbibition and dispersion of an aggregate under flow
No full textLe BUT de ma thèse est d’étudier les mécanismes fondamentaux du mélange d’une poudre avec un liquide : Au début du mélange, la poudre et le liquide sont versés dans le mélangeur, des agrégats de poudre communément appelés grumeaux se forment. Ensuite chaque agrégat va évoluer par l’action de plusieurs phénomènes : l’imbibition, phénomène spontané qui désigne l’infiltration d’un liquide dans un milieu poreux par capillarité ; et le phénomène forcé de rupture sous contraintes d’écoulement. A l’état final la poudre est dispersée finement et de façon homogène dans le liquide. Ma thèse est alors structurée en deux parties : l’étude de la cinétique d’imbibition d’un agrégat sphérique immergé ; et l’étude de la rupture d’un agrégat sous contrainte extérieure. La REUSSITE de l’étude provient des expériences approfondies: de la création d’un nouveau procédé de fabrication d’un agrégat grâce à l’impression 3D, jusqu’à la détermination de lois empiriques de nouveaux phénomènes mis en évidence.The GOAL of my PhD is to study the fundamental mechanisms of mixing a powder with a liquid. The mix of focus proceeds as follows:At start, as the powder and the liquid are filled in the mixer, powder aggregates form.Then each powder aggregate evolves under the influence of several phenomena: imbibition, spontaneous phenomenon corresponding to the infiltration of a liquid inside a porous medium by capillarity; and the forced phenomenon of rupture under flow. At last the powder is finely and homogeneously dispersed in the liquid. My PhD is thus organized in two parts: the study of the imbibitions kinetics of a spherical aggregate, and the study of the rupture of an aggregate under flow.The SUCCESS of the study relies on the thorough experiments: from creating a new aggregate manufacturing process using 3D printing, to determining empirical laws corresponding to new phenomena
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
Colloidal suspension under flow : the importance of contacts
No full textNous avons étudié dans notre thèse la microstructure d'une suspension colloïdale concentrée lors de son écoulement. En effet, si la rhéologie des suspensions diluées est bien comprise, le comportement des suspensions concentrées est beaucoup plus difficile à décrire. On sait qu'à faibles vitesses de déformation, si la suspension est suffisamment monodisperse, la suspension est rhéofluidifiante. À plus forts taux de cisaillement, la suspension est
rhéoépaississante. L'une des hypothèses permettant de comprendre ce comportement est la formation de clusters hydrodynamiques, au sein desquels les particules sont maintenues par les forces de lubrification, dont les contacts entre les particules gouvernent le passage vers un
état rhéoépaississant. Dans une première partie, nous avons étudié par simulation numérique (DPD) les contacts
entre particules et l'organisation spatiale des contraintes entre particules au contact. Une deuxième partie, expérimentale, est consacrée à la localisation, par microscopie de fluorescence, des contacts entre particules voisines. Les simulations numériques nous ont montré que le champ de contrainte interparticulaire était en effet fortement anisotrope, mais, contrairement à ce que laissent penser les hypothèses de clusters hydrodynamiques ou les chaînes des forces, cette anisotropie a son axe préférentiel
dans un plan parallèle à la direction de l'écoulement. Les mesures expérimentales nous ont seulement permis d'imager les particules les plus proches au contact, en l'absence d'écoulement. Nous avons montré que le FRET permettait
d'observer les contacts entre particules colloïdales de taille micronique.We have studied the microstructure of concentrated colloidal suspension under flow. Although the rheology of dilute suspensions is well understood, the behavior of concentrated suspensions is much more difficult to describe. In monodisperse solutions, the rheological
behavior of the suspension is shear-thinning. At stronger shear rates, the suspension shear thickens. One of the hypotheses allowing understanding this behavior is the formation of hydrodynamic c1usters, inside which partic1es are maintained by the lubrification forces. We sought to test this hypothesis by following the stress between partic1es with two tools: 1- Numerical simulation by Dissipative Partic1e Dynamics (DPD) 2- Experimental measures of fluorescence transfer between neighbouring partic1es in the suspension. The simulation shows that, although partic1e to not exhibit layering along the flow, the interparticular stress pattern is strongly anisotropie. The propagation of stress no longer occurs in the compression quadrant of the deformation, but in a plane paralle1 to the flow direction. In this regime, of small interpartic1es distances, the hydrodynamic stress between
adjacent partic1es dominates the rheological response.
Experimental measurements show that the FRET allows us to observe the contacts between colloidal micro-partic1es. However, we could not use this technique to visualize a network of contacts in a suspension under flow for several reasons: - The maximum distance observable by FRET is too low and only a small fraction of colloids in contact is actually observed. - Acquisition time of an image is much too long for it to be taken under flow
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
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