1,720,982 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
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
Etude du frittage sélectif par laser : propriétés des matériaux et influence des paramètres du procédé
No full textAdditive manufacturing is attractive because it allows to reduce significantly the development and industrialization phases of part design. Among the promising technologies for thermoplastic parts, the SLS (Selective Laser Sintering) process stands out because of its ability to produce geometries with low dimensional tolerances. This process is based on the displacement of a laser beam that interacts with the powder bed. The attractiveness of additive manufacturing counterbalances, however, with the choice of currently available materials: these are mainly polyamides. Polyaryletherketones (PAEK) suitable to SLS process are still rare on the market and expensive. In this work, various powders have been characterized to deeper understand the properties necessary for their use in SLS and to define their processability temperature window. The absence of suitable PEEK powder led us to develop a new material by blending PEEK with an amorphous thermoplastic, polyethersulfone (PESU). The initially immiscible blends have been compatibilized in order to improve their mechanical properties and to delay their crystallization on cooling. During manufacturing, many process parameters control the melting of the powder, and thus the properties of the parts and their dimensional accuracy. Thus, a statistical analysis of the response of the parameters was led by a design of experiments to extract the most influential parameters. The parametric study, done with the polyamide powder, was carried out by varying five parameters and by looking at their influence on five groups of responses relating to the physical, mechanical and thermal properties as well as to the printing duration of the parts. The design of experiments made it possible to establish the mathematical models of the response surfaces linking the responses to factors and their interactions. These statistical models were used to define an optimal set of parameters. Finally, a combined experimental and numerical simulation approach was conducted to estimate the influence of each laser pass on the degree of crystallinity and the mechanical properties of each layer. The results show that the heating due to the successive laser passes cover a thickness equivalent to 14 deposited layers. However, only the 4 upper layers are significantly thermally affected by the laser pass on a powder layer and thus show an evolution of their degree of crystallinityLa fabrication additive permet de répondre aux exigences de réactivité et de rapidité de création d’un produit industriel en réduisant les phases de développement et d’industrialisation. Parmi les technologies prometteuses pour les pièces en thermoplastiques, le procédé de fusion sur lit de poudre (SLS: Selective Laser Sintering) se distingue en raison de sa capacité de réalisation des géométries à faibles tolérances dimensionnelles. Ce procédé est basé sur le déplacement d’un faisceau laser qui interagit avec le lit de poudre. L’attractivité de la fabrication additive contrebalance cependant avec le choix des matériaux actuellement utilisables: ce sont principalement les polyamides. Les polyaryléthercétones (PAEK) adaptés au procédé SLS sont encore rares sur le marché et couteux. Dans ces travaux, différentes poudres ont été caractérisées pour mieux comprendre les propriétés nécessaires à leur utilisation en SLS et définir leur fenêtre de température de processabilité. L'absence de poudre de PEEK adaptée nous a conduit à élaborer un nouveau matériau en mélangeant le PEEK à un thermoplastique amorphe, le polyethersulfone (PESU). Les mélanges initialement immiscibles ont été compatibilisés dans l’objectif d’améliorer leurs propriétés mécaniques et pour retarder leur cristallisation au refroidissement. Pendant la fabrication, de nombreux paramètres du procédé contrôlent la fusion de la poudre, et ainsi les propriétés des pièces et leur précision dimensionnelle. Ainsi, l'analyse statistique de la réponse de l'ensemble des paramètres a fait l’objet d’un plan d’expériences pour en extraire les paramètres les plus influant. L’étude paramétrique, conduite avec la poudre polyamide, a été réalisée en faisant varier cinq paramètres et en regardant leur influence sur cinq groupes de réponses relatives aux propriétés physico-chimiques, physiques, mécaniques et thermiques ainsi qu’aux durées d’impression des pièces. Le plan d’expériences a permis d’établir les modèles mathématiques des surfaces de réponses liant les réponses aux facteurs et à leurs interactions. Ces modèles statistiques ont été utilisés pour définir un jeu de paramètres optimal. Enfin, une approche combinant expérimental et simulation numérique a été menée pour estimer l’influence de chaque passage du laser sur le taux de cristallinité et les propriétés mécaniques de chaque couche. Les résultats montrent que l’échauffement dû aux passages successifs du laser couvre une épaisseur équivalente à 14 couches déposées. Cependant, seules les 4 couches supérieures sont affectées thermiquement de manière significative par le lasage d’une couche de poudre et montrent ainsi une évolution de leur taux de cristallinité
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
Preliminary assessment of material extrusion (MEX) for medical applications: The effect of hatch angle
Get PDFMaterial extrusion (MEX) is one of the most widely used Additive Manufacturing (AM) technologies owing to its simplicity and accessible cost. The technique is based on the principle of extrusion of thermoplastic material, layer-by-layer, on a building platform through multiple head nozzles. Metal filled filaments, in combination with debinding and sintering cycles, may innovate and transform the traditional functioning of the MEX technique into a cost-effective alternative for the conventional metallic AM processes. In the present document, the optimal printing conditions characterizing LPBF technology were replicated on MEX technology, with the aim of assessing the effects of the printing parameter hatch angle over the material properties and, at the same time, providing a better understanding of the production of medical metal parts via MEX. Indeed, in this particular context, the use of Powder Bed Fusion (PBF) and Directed Energy Deposition (DED) prevails, requiring MEX-based technique extensive research for its applicability. The influence of a specific AM process parameter, the hatch angle, was assessed following a single factor Design of Experiment (DOE), varying over two levels: the optimal Laser Powder Bed Fusion (LPBF) scanning strategy (67°k) and the most common MEX deposition strategy (±45°). Specimens were manufactured, using MEX technology (Ultimaker S5) and AISI 316L filament (BASF Ultrafuse 316L) and tested. Results of the defect analysis, including closed and open porosity, and mechanical properties were collected and statistically compared to determine any difference in the two-deposition strategies. Furthermore, in the analysis, LPBF key characteristics are reported as benchmark values
An innovative method to model run-out phenomena in micro-milling by using cutting force signal
Get PDFThis work deals with the modeling of micro-milling processes by considering the phenomena generated by the transition from conventional size to the micro-scale machining. The concomitant effects of different cutting regimes, and the deviation of the cutting edges from their theoretical trajectories due to tool run-out, are important aspects to be considered during the process modeling. Several models are available in literature to describe how ploughing and shearing regimes influence cutting forces and how the tool run-out impacts on the actual chip thickness. In a previous authors research, a comprehensive model was published achieving a good agreement with the experimental data, but its calibration requires the measurement of the width of the micro-milled slots. This practice is time consuming and subjected to experimental errors, while a calibration of the model based only on the elaboration of the cutting force signal appears a promising strategy. Starting from the mathematical description of the geometrical model, a new equation to compute the tool run-out parameters was found. The parameters depend on eight variables that must be calculated from tool geometry, material composition, cutting parameters and the cutting force signal. An experimental procedure was developed to compare the prediction achieved by the new method and the conventional technique
Etude du frittage sélectif par laser : propriétés des matériaux et influence des paramètres du procédé
No full textLa fabrication additive permet de répondre aux exigences de réactivité et de rapidité de création d’un produit industriel en réduisant les phases de développement et d’industrialisation. Parmi les technologies prometteuses pour les pièces en thermoplastiques, le procédé de fusion sur lit de poudre (SLS: Selective Laser Sintering) se distingue en raison de sa capacité de réalisation des géométries à faibles tolérances dimensionnelles. Ce procédé est basé sur le déplacement d’un faisceau laser qui interagit avec le lit de poudre. L’attractivité de la fabrication additive contrebalance cependant avec le choix des matériaux actuellement utilisables: ce sont principalement les polyamides. Les polyaryléthercétones (PAEK) adaptés au procédé SLS sont encore rares sur le marché et couteux. Dans ces travaux, différentes poudres ont été caractérisées pour mieux comprendre les propriétés nécessaires à leur utilisation en SLS et définir leur fenêtre de température de processabilité. L'absence de poudre de PEEK adaptée nous a conduit à élaborer un nouveau matériau en mélangeant le PEEK à un thermoplastique amorphe, le polyethersulfone (PESU). Les mélanges initialement immiscibles ont été compatibilisés dans l’objectif d’améliorer leurs propriétés mécaniques et pour retarder leur cristallisation au refroidissement. Pendant la fabrication, de nombreux paramètres du procédé contrôlent la fusion de la poudre, et ainsi les propriétés des pièces et leur précision dimensionnelle. Ainsi, l'analyse statistique de la réponse de l'ensemble des paramètres a fait l’objet d’un plan d’expériences pour en extraire les paramètres les plus influant. L’étude paramétrique, conduite avec la poudre polyamide, a été réalisée en faisant varier cinq paramètres et en regardant leur influence sur cinq groupes de réponses relatives aux propriétés physico-chimiques, physiques, mécaniques et thermiques ainsi qu’aux durées d’impression des pièces. Le plan d’expériences a permis d’établir les modèles mathématiques des surfaces de réponses liant les réponses aux facteurs et à leurs interactions. Ces modèles statistiques ont été utilisés pour définir un jeu de paramètres optimal. Enfin, une approche combinant expérimental et simulation numérique a été menée pour estimer l’influence de chaque passage du laser sur le taux de cristallinité et les propriétés mécaniques de chaque couche. Les résultats montrent que l’échauffement dû aux passages successifs du laser couvre une épaisseur équivalente à 14 couches déposées. Cependant, seules les 4 couches supérieures sont affectées thermiquement de manière significative par le lasage d’une couche de poudre et montrent ainsi une évolution de leur taux de cristallinité.Additive manufacturing is attractive because it allows to reduce significantly the development and industrialization phases of part design. Among the promising technologies for thermoplastic parts, the SLS (Selective Laser Sintering) process stands out because of its ability to produce geometries with low dimensional tolerances. This process is based on the displacement of a laser beam that interacts with the powder bed. The attractiveness of additive manufacturing counterbalances, however, with the choice of currently available materials: these are mainly polyamides. Polyaryletherketones (PAEK) suitable to SLS process are still rare on the market and expensive. In this work, various powders have been characterized to deeper understand the properties necessary for their use in SLS and to define their processability temperature window. The absence of suitable PEEK powder led us to develop a new material by blending PEEK with an amorphous thermoplastic, polyethersulfone (PESU). The initially immiscible blends have been compatibilized in order to improve their mechanical properties and to delay their crystallization on cooling. During manufacturing, many process parameters control the melting of the powder, and thus the properties of the parts and their dimensional accuracy. Thus, a statistical analysis of the response of the parameters was led by a design of experiments to extract the most influential parameters. The parametric study, done with the polyamide powder, was carried out by varying five parameters and by looking at their influence on five groups of responses relating to the physical, mechanical and thermal properties as well as to the printing duration of the parts. The design of experiments made it possible to establish the mathematical models of the response surfaces linking the responses to factors and their interactions. These statistical models were used to define an optimal set of parameters. Finally, a combined experimental and numerical simulation approach was conducted to estimate the influence of each laser pass on the degree of crystallinity and the mechanical properties of each layer. The results show that the heating due to the successive laser passes cover a thickness equivalent to 14 deposited layers. However, only the 4 upper layers are significantly thermally affected by the laser pass on a powder layer and thus show an evolution of their degree of crystallinit
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