1,721,091 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
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
Experimental and numerical analysis of the failure modes induced in ceramic materials under dynamic loading
No full textDe par leur aptitude à résister à des chargements mécaniques extrêmes, les céramiques sont utilisées comme matériaux constitutifs de blindages. Couplées à une face arrière ductile, elles permettent un gain de poids considérable. Le lien entre les mécanismes d'endommagement générés au sein de la céramique lors de l'impact, et ses propriétés microstructurales n'est pas encore bien compris. L'approche classique adoptée pour leur développement consiste ainsi à itérer entre la fabrication de nouveaux matériaux et l'évaluation de leurs performances via des essais balistiques. Cependant, ce type d'optimisation est coûteux et ne permet que très rarement de tirer des conclusions sur ce lien entre propriétés microstructurales et performances balistiques. Le premier objectif de cette thèse est d'améliorer la compréhension du lien entre microstructure et mécanismes d'endommagement engendrés sous chargement dynamique. Ces résultats visent à enrichir une modélisation, représentative du comportement fragile des matériaux céramiques sous chargement de traction dynamique, et sur une large gamme de vitesses de déformations.Les matériaux céramiques sont hautement sensibles à la présence de défauts. A faible vitesse de déformation, ils présentent une résistance stochastique reliée à la taille du défaut le plus critique du volume sollicité. L'approche classique consiste à utiliser des essais quasi-statiques pour identifier les défauts responsables de la rupture (approche de Weibull) et supposer qu’ils sont aussi à l'origine du processus de rupture sous chargement dynamique. Ce travail remet en question cette hypothèse. A haute vitesse de déformation, de nombreuses fissures s'amorcent simultanément sur de multiples défauts et conduisent à une fragmentation intense et déterministe. Six matériaux céramiques de propriétés microstructurales différentes sont analysés et testés sous chargement dynamique. Des essais dynamiques, hautement instrumentés, de type impact sur tranche, normal et tandem, combinés à une analyse par micro-tomographie des faciès d’endommagement, ont permis de mieux comprendre leurs propriétés de fragmentation. Une technique d'écaillage par impact de plaques sans choc a été développée pour évaluer la sensibilité à la vitesse de déformation de la résistance intrinsèque en traction de matériaux céramiques. La conception de plaques impactrices ondulées a permis de transmettre un chargement contrôlé à l'échantillon testé. Une approche hybride, combinant des simulations numériques et des résultats expérimentaux, a mis en évidence le lien entre leur résistance à l'écaillage et la vitesse de déformation.Une nouvelle méthodologie est proposée pour modéliser le processus de fragmentation induit dans les céramiques à haute vitesse de chargement. Cette approche s'appuie sur l'identification des défauts (essentiellement des porosités) à partir d'analyses micro-tomographiques. Cette description réaliste de la distribution de défauts est implémentée dans le modèle d'endommagement Denoual-Forquin-Hild (DFH) de façon explicite, via des approches dites discrète et continue, pour prédire le comportement sous chargement de traction dynamique. Une confrontation aux résultats d’essais de fragmentation et d'écaillage, a permis une validation de l'approche. Les prédictions de ce modèle micromécanique sont comparées pour une population de défauts déterminée via l'approche de Weibull et à partir d'analyses micro-tomographiques. Cette étude a montré que, pour des matériaux présentant plusieurs populations de défauts, l'approche de Weibull n'est plus correcte à haute vitesse de déformation, et l'utilisation d'une population de défauts identifiée via micro-tomographie est grandement pertinente. Ces résultats soulignent l'importance de considérer les propriétés microstructurales pour réussir à correctement modéliser le comportement de matériaux céramiques à haute vitesse, et ainsi progresser vers l'optimisation des prochaines solutions de blindage céramique.Due to their high resistance to extreme loading conditions, ceramic materials have been extensively investigated to be part of vehicle and body armour protections. Combined to a ductile backing, ceramics are very interesting for lightweight bulletproof systems. The link between damage mechanisms occurring in the ceramic upon impact and its microstructural properties is still not well understood. For this reason, a 'make-and-shot' iterative approach is the common way followed to develop this type of material. However, this type of optimisation process is very expensive, time consuming and hardly leads to any conclusions on the link between microstructural features and ballistic performance. The first goal of this PhD is to bring insight on the connection between microstructural properties of the ceramic armour and its failure mechanisms under dynamic loading. The natural second step consists in using these results to improve a modelling, which is representative of ceramic brittle damage under tensile loading on a large range of strain rates.Ceramics are highly sensitive to the presence of inherent defects. Under low loading rate, they have a stochastic strength linked to the size of the most critical defect in the loaded volume. The common approach consists in using quasi-static tests to identify the defects responsible for failure (Weibull approach) and assume that the same ones are causing failure at high loading rates. Such assumption is questioned in the present work. Under high strain rate, numerous cracks are triggered simultaneously from multiple defects, causing an intense and deterministic fragmentation. Six ceramic materials, presenting different microstructural features, are analysed and tested under dynamic conditions in this project. Highly instrumented edge-on impact, normal impact and tandem impact dynamic tests, combined with a micro-tomography analysis of damage patterns, provided a better understanding of the fragmentation properties of the different grades of ceramics. A shockless experimental spalling technique was developed to evaluate the intrinsic tensile strength sensitivity to strain-rate of ceramic materials. To do so, the plate-impact configuration was adapted, using specific flyer-plate geometries designed to generate a tailored loading in the sample. From a hybrid approach mixing numerical simulations and experimental results, the spall-strength of the tested ceramic can be related to a well-controlled loading rate.A new methodology is proposed to model the multiple fragmentation process induced in ceramics under high strain rate. This method is built on the identification of material defects (mainly pores) from micro-tomography analysis. This realistic description of the defect distribution is explicitly implemented in the Denoual-Forquin-Hild (DFH) damage model to predict the dynamic failure behaviour of ceramics under tensile loading, through so-called continuous and discrete approaches. A comparison with experimental results of the fragmentation and spalling tests provided a validation of the approach. Predictions of this micro-mechanical model were compared for a Weibullian distribution of critical defects and a description based on micro-tomography analyses. Comparisons on a large range of strain rates showed that, for materials presenting multiple flaw populations, the Weibull-based solution is highly invalid. In this case, the use of a proper flaw description, obtained via micro-tomography, is much more relevant. These results highlight the importance of considering microstructural features to properly model the failure behaviour of ceramics at high loading rate, and therefore move toward a design of the next generation of ceramic-based armour protections
Experimental characterisation and modelling of the dynamic fracture and fragmentation properties of a projectile ammunition and armour ceramics
No full textCertaines nuances de céramiques, comme les carbures de silicium (SiC) ou les alumines (Al2O3), sont utilisées comme matériaux balistiques en raison de leurs excellentes performances mécaniques, notamment leur dureté, tout en étant légères, là où le gain de masse est un enjeu majeur pour la conception d’équipements militaires de protection individuelle ou de véhicule. Depuis la guerre du Viêt Nam, les céramiques ont été largement utilisées et intégrées comme face avant de blindage bicouche pour stopper la menace des projectiles de type AP (Armour-Piercing) durant un impact balistique. Néanmoins, le projectile provoque un endommagement intense dans la céramique en raison, notamment, d’un chargement de traction dynamique qui se manifeste par une fissuration multiple, appelée fragmentation, particulièrement défavorable à l’intégrité de la protection balistique et à sa capacité à faire face à un second impact. Afin de développer un matériau de blindage plus performant, il est essentiel de comprendre le lien entre la microstructure des céramiques, l’endommagement généré sous impact et leurs performances balistiques.Cette thèse cherche à mieux comprendre le phénomène de fragmentation dynamique généré à hautes vitesses de déformation dans des céramiques à forte ténacité, incluant un matériau aluminé bio-inspiré de la nacre. Cette nacre artificielle est, a priori, plus réfractaire aux fissures que les céramiques conventionnelles car elle se caractérise par une haute ténacité statique en raison d’une microstructure spécifique de type « Brique-Mortier » (ou BM) reproduite dans le matériau appelé ici MAINa.Some ceramic grades, such as silicon carbide (SiC) or alumina (Al2O3), are used as ballistic materials thanks to their excellent mechanical performances, such as their hardness, while being light, where weight gain is a major issue for the design of military equipment for personal and vehicle protection. Since the Vietnam War, ceramics have been largely used and integrated as front face in bilayer shielding to stop the threat of AP (Armour Piercing)-type projectiles during a ballistic impact. Nevertheless, the projectile leads to an intense damage in the ceramic due to, amongst other phenomena, a dynamic tensile loading that manifests by multiple cracking, called fragmentation, particularly unfavourable for the integrity of the ballistic protection and its capacity to deal with a second impact. In order to develop a more performing shielding material, it is essential to understand the link between the microstructure of ceramics, the damage generated under impact and their ballistic performances.This thesis seeks to better understand the dynamic fragmentation phenomenon generated at high strain rates in high fracture-toughness ceramics, including a bio-inspired alumina material mimicking nacre microstructure. This artificial nacre is, a priori, more crack resistant than conventional ceramics as it is characterised by a high static fracture-toughness due to its specific “Brick-and-Mortar” (or BM) microstructure reproduced in the material called here MAINa
Experimental testing and numerical modelling of the tensile and compressiondamage in Ultra-High Performance Concrete under impact loading
No full textCette thèse présente des recherches expérimentales et numériques sur les Bétons à Ultra-Hautes Performances (BHUP) en vue de favoriser leur application technique en tant que structures de protection. Le modèle couplé DFHcoh-KST, décrivant à la fois le comportement confiné et l'endommagement en traction, est sélectionné pour simuler un problème d'impact aux éléments finis (FE) Abaqus/Explicit. Les paramètres matériaux sont identifiés pour deux formulations de Ductal® avec fibres utilisant des techniques expérimentales existantes: tels que les essais de compression quasi-oedométrique (Q-OC), les essais de flexion et les essais d'écaillage à la barre de Hopkinson. L'étude du comportement en traction des BUHP est ensuite étendue à des vitesses de déformation de 103 à 104 s-1 grâce à des essais d'impact sur plaque. Une technique expérimentale novatrice utilisant un système de ‘pulse-shaping’ permettant une vitesse de chargement constante dans l'échantillon est conçue par simulation numérique et expérimentée en utilisant le lanceur à gaz installé au laboratoire 3SR. De plus une modélisation du processus de fragmentation sous chargement de traction dynamique a été développée à l'aide d'approches continue et discrète en se basant sur des analyses par tomographie aux rayons X des distributions des pores des BUHP. Ces travaux de modélisation permettent d'expliciter le rôle de la microstructure sur la sensibilité à la vitesse de déformation de la résistance à la traction et de la densité de fissures générée dans les matériaux étudiés.This thesis presents experimental and numerical investigations of Ultra-High Performance Concretes (UHPC) in view of intensifying their application as protective structures.The coupled DFHcoh-KST model, describing both confined behavior and tensile damage, is selected to simulate impact problem using the Finite Element (FE) code Abaqus/Explicit. The material parameters are identified for two Ductal® formulations with fibres using existing experimental techniques: such as Quasi-Oedometric Compression (Q-OC) tests, bending tests and spalling tests at the Hopkinson bar. The investigation of the tensile response of UHPC is then extended at strain rates in the range of 103 - 104 s-1 through plate-impact tests. A new testing technique employing a pulse shaping system to ensure a constant loading rate in the specimen is designed using numerical simulation and experienced using the single-stage gas gun installed in the 3SR laboratory. Finally, the UHPC fragmentation under dynamic tension is simulated with discrete and continuous approaches based on X-ray Computed Tomography (CT) analysis of the UHPC pore distributions. This methodology contributes to understanding the role of the microstructure on the observed strain-rate sensitivity of tensile strength and crack density
- …
