1,721,010 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
Size effects in the toughening of brittle materials by heterogeneities: A non-linear analysis of front deformations
No full textInternational audienceTraditional computational approaches in simulating crack propagation in perfectly brittle materials rely on the estimate of stress intensity factors along the rupture front. This proves highly challenging in 3D when the crack geometry departs from very specific cases for which analytical solutions are available, like e.g. the penny-shaped crack geometry. Here, we extend the first-order theory of Gao and Rice (1987), and predict the distribution of the mode I stress intensity factor KI along the front of a tensile coplanar crack that is slightly perturbed from a reference penny-shaped configuration, up to second order in the perturbation amplitude. Our theory is validated against analytical solutions available for embedded elliptical cracks, and its range of validity is further assessed using numerical simulations performed on cosine front perturbations of varying mode and amplitude. It is then used to develop a homogenization framework for the toughness of weakly disordered media. The effective toughness and its fluctuations are bridged quantitatively to the intensity of the toughness fluctuations and their spatial structure. Our theoretical predictions are compared to the results of ~1 million simulations of crack propagation building on our second-order theory and Fast Fourier Transforms. We show that the impact of toughness heterogeneities is size-dependent, as they generally weaken the material when the crack size is lower or comparable to the typical heterogeneity size, but reinforces it otherwise. It results in an apparent R-curve behavior of the brittle composite at the macroscale
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
Towards brittle materials with tailored fracture properties: the decisive influence of the material disorder and its microstructure
No full textInternational audienceConsidering a semi-infinite crack propagating within a plane where the local fracture energy fluctuates due to the presence of microstructural heterogeneities, we emphasize the decisive influence of the material disorder on the effective fracture energy of the composite at a macroscopic scale. Through the use of large-scale numerical simulations of a crack interacting with tough inclusions of varying shape, we show how the disorder intensity and the inclusion geometry modify both quantitatively and qualitatively the toughening behavior with respect to the periodic case, where the inclusions are arranged in an ordered manner. This disorder-induced toughening is then rationalized using a theoretical homogenization framework borrowed from statistical physics. It ultimately allows to propose strategies for the design of disordered composites with improved crack growth resistance and tailored asymmetric fracture properties
Propagation de fissures dans des milieux hétérogènes de grande taille: contributions à l'homogénéisation des propriétés de rupture fragile
Get PDFBeing able to predict the macroscopic response of a material from the knowledge of its constituent at a microscopic or mesoscopic scale has always been the Holy Grail pursued by material science, for it provides building bricks for the understanding of complex structures as well as for the development of tailor-made optimized materials. The homogenization theory constitutes nowadays a well-established theoretical framework to estimate the overall response of composite materials for a broad range of mechanical behaviors. Such a framework is still lacking for brittle fracture, which is a dissipative evolution problem that (ii) localizes at the crack tip and (iii) is related to a structural one.In this work, we propose a theoretical framework based on a perturbative approach of Linear Elastic Fracture Mechanics to model (i) crack propagation in large-scale disordered materials as well (ii) the dissipative processes involved at the crack tip during the interaction of a crack with material heterogeneities. Their ultimate contribution to the macroscopic toughness of the composite is (iii) estimated from the resolution of the structural problem using an approach inspired by statistical physics. The theoretical and numerical inputs presented in the thesis are finally compared to experimental measurements of crack propagation in 3D-printed heterogeneous polymers obtained through digital image correlation.La compréhension du comportement macroscopique d'un matériau à partir de la donnée de ses constituants à l'échelle microscopique a toujours été le Saint Graal en science des matériaux dans la mesure où elle fournit les éléments essentiels à la prédiction de la résistance d'une structure et au développement de matériaux aux propriétés innovantes. Si la théorie de l'homogénéisation constitue un cadre théorique établi pour prédire la réponse effective d'une vaste classe de comportements matériaux, elle ne permet pas à l'heure actuelle de prédire les propriétés effectives en rupture fragile. S'attaquer à cette question suppose de tirer profit des caractéristiques uniques de la rupture fragile qui est (i) un problème d'évolution dissipatif, (ii) localisé en pointe de fissure et (iii) relié à un problème de structure.Dans ce travail, nous proposons un formalisme théorique fondé sur une approche perturbative de la mécanique de la rupture afin de (i) modéliser la propagation de fissure dans les milieux désordonnés de grande taille. L'implémentation numérique de ce modèle nous permet (ii) d'étudier en détail les mécanismes dissipatifs mis en jeu en pointe de fissure lorsqu'une fissure interagit avec des hétérogénéités. Leur contribution au renforcement du matériau à l'échelle macroscopique est finalement (iii) estimée à partir de la résolution du problème de structure à l'aide d'outils empruntés à la physique statistique. Les apports théoriques et numériques de la thèse sont finalement confrontés aux résultats d'expériences de fissuration de polymères hétérogènes imprimés 3D, extraits d'outils de corrélation d'image
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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