1,721,017 research outputs found
The detailed acoustic signature of a micro-confined cavitation bubble
Full text linkNumerous scenarios exist for a cavitation bubble growing in a liquid. We focus here on cavitation phenomena within water under static tension in a confined environment. Drawing inspiration from the natural materials in plants, we design a novel experimental setup where a micrometric volume of water is confined by a hydrogel-based material. We show that, submerging the sample in a hypertonic solution, the water within the cavity is placed under tension and the acoustic emission produced by the resulting bubble nucleation is precisely detected. This new experimental procedure is able to strongly reduce the acoustic reflections occurring at the hydrogel/air interface with more classical techniques. We also propose a mathematical model to characterise the pressure wave emitted in order to correctly take into account the dissipation effect induced by the visco-elastic behaviour of the confining hydrogel. Both bubble resonant frequency and damping are captured by the model and quantitatively match the values found in the experiments
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
Biomechanics of fast motions in plant kingdom
No full textDans cette thèse, nous nous intéressons à la biomécanique de deux mouvements parmi les plus rapides du règne végétal. La première partie porte sur l’étude théorique du mouvement permettant la capture de proies par les pièges de l’utriculaire, des outres déformables de taille millimétrique refermées par une porte flexible. Un modèle dynamique, élaboré à partir d’ingrédients mécaniques, hydrodynamiques et élastiques, permet de relier la différence de pression entre l’intérieur et l’extérieur du piège à la position de la porte via deux équations différentielles couplées. Le modèle permet de capturer la dynamique de fonctionnement du piège et de prédire l’intégralité des comportements observés dans la nature via l’ajout d’un bruit stochastique. La seconde partie est consacrée au mouvement d’éjection des spores par les sporanges de fougères. Notre étude à la fois expérimentale et théorique permet de révéler le caractère remarquable de l’anneau, une structure spécialisée du sporange, dont la nature poroélastique lui confère un comportement comparable à celui d’une catapulte autonome. Les différentes phases du mouvement : ouverture, déclenchement par cavitation, fermeture rapide et recharge éventuelle sont observées via imagerie ultra-rapide. La courbure de l’anneau au cours du mouvement est mesurée expérimentalement puis comparée aux prédictions théoriques pour chacune des phases du mouvement. Cette étude nous permet d’identifier les différents processus physiques à l’origine du mouvement et de déterminer les paramètres caractéristiques de l’anneau : raideur, perméabilité membranaire et pression osmotique interne, ainsi que la pression négative de cavitation.In this PhD work, we focus on the biomechanics of two motions among the fastest in plant kingdom. The first part is a theoretical study of the motion leading to a prey capture by the bladderwort’s traps, elastic millimeter-sized bladders closed by a flexible door. A dynamical model, based on mechanical, elastic and hydrodynamic ingredients, links the pressure difference between the trap and its surroundings with the door position by the means of two coupled ordinary differential equations. The model captures the dynamics of the trap and predicts all the range of behaviors found in nature by including stochastic noise in the system. The second part focuses on the fern sporangium motion allowing the spores dispersal. Our experimental and theoretical studies point out the remarkable character of the annulus, a specialized structure of the sporangium, as it behaves as an autonomous catapult due to its poroelastic nature. The different stages of the motion: opening, triggering by cavitation, fast closure and eventual reloading are observed using ultra-fast imaging. The annulus curvature is measured experimentally and then compared to the theoretical predictions for each motion phase. This study enables us to identify the physical processes governing the complete motion and to determine the characteristic parameters of the annulus: stiffness, permeability and internal osmotic pressure, and also the negative cavitation pressure
Nucleation and dynamics of cavitation bubbles in confined and stretched liquids : experiments on microfabricated systems and molecular dynamics simulations
No full textDans cette thèse, nous nous sommes intéressés à la cavitation de bulles de vapeur dans un liquide confiné sous tension (c’est-à-dire sous pression négative). Ce travail s’est développé en étudiant deux aspects différents mais complémentaires : la simulation numérique et l’expérience biomimétique. L’étude numérique utilise la simulation par dynamique moléculaire d’un liquide confiné dans une cellule solide. Cette méthode nous a permis d’étudier précisément l’effet de l’interaction entre le solide et le liquide (angle de contact), mais aussi de la géométrie sur la nucléation de bulles de vapeur. Nous avons également étudié l’interaction entre deux cellules voisines, et ainsi par comparaison avec un modèle, nous avons mis en évidence une corrélation entre deux évènements de cavitation ainsi que les paramètres importants dans ce phénomène. L’étude expérimentale, quant à elle, a été réalisée sur un dispositif en hydrogel de polymère inspiré de systèmes naturels. Cette méthode nous permet d’étudier un système ayant des caractéristiques mécaniques proches des observations naturelles sur les sporanges de fougères tout en pouvant contrôler sa géométrie. Nous avons alors mis en évidence l’effet de l’épaisseur des parois entre cellules permettant d’observer des cavitations isolées ou groupées de plusieurs centaines de bulles. La taille des cellules permet de mesurer des vitesses de propagation allant jusqu’à plus de 800 m/s. A l’aide d’un modèle acoustique nous avons mis en évidence les paramètres importants dans cette propagation.In this work, we have been interested in the cavitation process of vapor bubbles in a confined and stretched liquid. We have followed two complimentary points of view: numerical simulation and biomimetical experiments. For the numerical study we have used molecular dynamics simulations of a liquid confined in a solid cell. This method allows us to study precisely the effect of the interaction between the solid and the liquid (contact angle), and also the geometrical properties on the nucleation of vapor bubbles. We have also studied the interaction between two neighboring cells, and by comparing with a model, we have shown a correlation between two cavitation events and the important parameters taking place in this phenomenon. For the experimental study, we have used polymer hydrogel devices inspired from natural systems (ferns sporangia). This method allows us to study a system having almost the same mechanical properties as the natural one, and showing the possibility to control its geometry. We have shown that the wall thickness between the cells can control the propagation properties from isolated cavitation to grouped propagation (up to several hundreds of bubbles). The cell size controls the propagation velocity, up to values of 800 m/s. We have shown by comparing with an acoustical model the important parameters that control this phenomenon
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
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