1,720,953 research outputs found
Reinforcement of the ballast railways : optimization of the ballast bonding process by coupling numerical and experimental approaches
No full textLe collage du ballast est un procédé consistant à verser un liant sur l’ensemble d’agrégats rocheux qu’est le ballast afin d’en limiter les déplacements, et par conséquent les opérations de maintenance très coûteuses en temps et en moyens. Pour comprendre et optimiser le procédé de collage du ballast utilisé en exploitation ferroviaire par la SNCF, le développement d’un modèle numérique de colle à ballast est proposé ainsi que son exploitation dans un code de calcul par éléments discrets LMGC90, basé sur l’approche NonSmooth Contact Dynamics. Pour développer ce modèle, une approche combinant expérimentations en laboratoire et expérimentations numériques est proposée, expérimentations menées à différentes échelles. Dans un premier temps, des essais expérimentaux de traction sont réalisés sur des reproductions de contacts entre grains de ballast collés. Ces essais ont fourni des données locales utilisées pour calibrer les deux paramètres d’une première loi de contact cohésive numérique simple, de type Dugdale : la résistance cohésive maximale d’un contact, et la distance de séparation au-delà de laquelle on considère le contact décollé. Un deuxième modèle développé par Venzal, plus précis, a également été paramétré grâce aux essais expérimentaux unitaires. Il est entre autre traduit par une raideur initiale, une contrainte maximale, et un endommagement progressif du contact cohésif. Ces modèles sont ensuite exploités grâce à la plateforme LMGC90 dédiée à la modélisation de milieux divisés pour réaliser des simulations " modèles " de caractérisation macroscopique de milieu granulaire collé, puis des simulations appliquées à la problématique ferroviaire. Ainsi, des essais numériques de compression triaxiale effectués sur un milieu granulaire polyédrique cohésif ont mis en évidence l'importance du choix du modèle de cohésion : les simulations réalisées avec la loi Dugdale ne permettent pas de respecter l'application d'une pression isotrope sur les parois de l'échantillon pour les intensités de cohésion élevées, en raison de la forte déformation du milieu. Les essais réalisés avec la loi Venzal restent significatifs, et permettent d'expliquer l'évolution de la résistance du système grâce à l'évolution de l'endommagement des contacts cohésifs. Au départ, l'échantillon s'endommage fortement car la dilatation volumique de l'échantillon nécessite la rupture des contacts intervenant activement dans la résistance du milieu ; sur cette période, la résistance au cisaillement du système augmente drastiquement. Elle finit par baisser pour se stabiliser une fois la détérioration des contacts cohésifs suffisante. Des essais de résistance latérale expérimentaux et numériques ont également été conduits, avec différentes configurations de collage. Les essais expérimentaux, en plus de fournir des données de référence, prouvent que l’ajout de la cohésion dans le massif ballasté en augmente la résistance latérale, et quantifient ce renforcement (jusqu’à atteindre une amélioration de 43% pour un collage de la banquette en profondeur). Un collage surfacique de la banquette propose un renforcement de 22% pour une moindre quantité de colle. Les essais numériques de résistance latérales montrent que la cohésion peut agir sur deux aspects différents : renforcer le réseau de résistance qui s’oppose déjà au mouvement latéral de la traverse, ou ajouter un réseau d’opposition supplémentaire en plus du préexistant. Ces travaux offrent ainsi un outil numérique permettant de répondre à la problématique ferroviaire soulevée et proposent différentes pistes de réflexion.Ballast gluing is a process that consists in spreading a binder on the ballast as a set of rocky aggregates in order to limit its movements, and consequently the maintenance operations, which are very costly in time and resources. To understand and optimize the ballast gluing process used in railway operations by the SNCF, the development of a numerical model of ballast glue is proposed as well as its exploitation in a discrete element calculation code LMGC90, based on the NonSmooth Contact Dynamics approach.To develop this model, an approach combining laboratory and numerical experiments is proposed, experiments conducted at different scales. In a first step, experimental tensile tests are carried out on reproductions of contacts between bonded ballast grains. These tests provided local data used to calibrate the two parameters of a first simple numerical cohesive contact law, of Dugdale type: the maximum cohesive resistance of a contact, and the separation distance beyond which the detached contact is considered.A second law developped by Venzal, more precise, is also calibrated. It is described by an initial stiffness, a maximal strain and allows the contact to damage.These models are then exploited thanks to the LMGC90 platform dedicated to the modeling of divided media to carry out "model" simulations, and then simulations applied to railway issues.Thus, numerical tests of triaxial compression carried out on a cohesive polyhedral granular medium have highlighted the importance of the cohesion law used : simulations executed with Dugdale law and important cohesion intensity cannot respect the application of an isotropic pressure on the sample because of the importance of its strain. Tests realized with Venzal law are meaningful, and link the evolution of sample shearing resistance to the evolution of contact cohesion damage. At first, the sample quickly damage itself, because its volumic expansion breaks the cohesion of contacts which actively take part of the medium resistance ; at the same time, the system shearing resistance increase considerably. It decreases and stabilizes when the cohesion damage is sufficient.Experimental and numerical lateral resistance tests have also been conducted, with different bonding configurations. Experimental tests, in addition to providing reference data, prove that adding cohesion to the ballasted mass increases its lateral strength, and quantify this reinforcement (up to a 43% improvement for deep bench bonding). A surface gluing of the seat offers a 22% reinforcement for a lower quantity of glue. Numerical lateral strength tests show that cohesion can act on two different aspects: reinforcing the resistance network that already opposes the lateral movement of the cross member, or adding an additional opposition network on top of the pre-existing one. This work thus offers a numerical tool to respond to the railway problem raised and proposes various avenues for reflection
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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