1,721,000 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
Experimental contribution to the steady and unsteady analysis of the flow behind a bluff body
No full textDe nouvelles connaissances sur les écoulements autour des véhicules automobiles doivent aujourd'hui être apportées pour envisager une amélioration de leurs performances aérodynamiques. Ce travail de thèse repose sur des études expérimentales, réalisées en soufflerie, permettant l'analyse et la compréhension des mécanismes physiques associés aux écoulements décollés tridimensionnels et instationnaires se développant à l'arrière des véhicules automobiles. Il se concentre plus particulièrement sur la géométrie générique du corps de Ahmed permettant de reproduire les écoulements à l'arrière de véhicule de type bicorps (lunette arrière et culot). L'étude compare deux maquettes de géométrie différente dont l'une permet d'obtenir une zone de recirculation tridimensionnelle sur la lunette arrière et l'autre de conserver l'écoulement attaché. L'analyse et la comparaison des topologies moyennes des écoulements permettent d'évaluer les interactions entre la recirculation 3D et les autres structures en présence. On montre plus particulièrement que l'absence du décollement sur la lunette arrière modifie la topologie de l'écoulement à l'arrière du culot avec une réduction de traînée de l'ordre de 10%. Les résultats montrent que les effets de la recirculation ne sont pas assez importants pour modifier la position des structures tourbillonnaires longitudinales se développant sur les arêtes latérales de la lunette, mais modifient légèrement leur intensité. L'analyse spectrale des fluctuations de vitesse et de pression indique que la recirculation est le siège d'activités instationnaires pseudopériodiques. La Décomposition Orthogonale Propre des champs de vitesse et de pression montre finalement que ces activités sont associées à un mécanisme de battement de la recirculation passant d'une configuration décollée à une configuration attachée et à une émission de structures tourbillonnaires formées par la couche cisaillée de la recirculation.More and more knowledge related to flows behind road vehicles must be provided to improve their aerodynamic performances. This PhD thesis deals with experimental studies carried out in a wind tunnel, and enables analysis and understanding of physical mechanisms related to three-dimensionnal and unsteady separated flows that develop behind road vehicles. More specifically, it focuses on the generic model of Ahmed body that recreates flows behind common fastback cars (rear window and rear part). This study compares two models with different shape, the first one having a sharped edge between the roof and the rear window enabling the development of a separated region, and the second one having a rounded edge preventing separation. Analysis and understanding of the time averaged topology of both flow configurations are performed to characterize interactions between the three-dimensionnal separation and the other structures. More specifically, it is observed that suppressing separated region over the rear window changes the flow topology behind the rear base with a drag reduction of approximately 10%. Results show that the influence of the separated region is not strong enough to modify the location of the longitudinal vortical structures, which develop at each side of the model, but is strong enough to slightly modify their intensity. Spectral analysis of the velocity and pressure fluctuations indicates that the separated region is characterized by pseudo-periodic unsteady activities. Proper Orthogonal Decomposition of instantaneous velocity and pressure fields shows that these activities are respectively related to a flapping mechanism of the separated zone moving between a shrinked state and an enlarged state, and a large scale vortices emmission resulting from the shear layer of the separated region
Experimental investigation of aerodynamic loads modification on wind turbine blades with active flow control
No full textL’énergie éolienne est une source d’énergie propre et renouvelable qui fait partie des moyens pour réduire les émissions de gaz à effet de serre et contrer le réchauffement climatique dans le domaine de la production électrique.L’objectif de la thèse est d’optimiser la production d’énergie éolienne par la réduction des fluctuations de charge induites par la turbulence de la couche limite atmosphérique. Ces fluctuations augmentent la fatigue des pales et réduisent la durée de vie des rotors.Cette réduction des fluctuations de charge est réalisée par le biais d’une approche expérimentale et à l’échelle du laboratoire. Deux actionneurs non conventionnels sont étudiés et testés au sein d’un écoulement contrôlé ensoufflerie: il s’agit d’actionneurs plasma et de jets fluidiques. L’objectif est d’effectuer un contrôle de circulation par une action proche du bord de fuite arrondi de la pale afin de modifier la portance du profil.Dans le cadre du projet SMARTEOLE, les deux stratégies sont d’abord testées en parallèle sur un profil bidimensionnel. Pour cette thèse, les actionneurs plasma sont implémentés autour du bord de fuite arrondi afin d’augmenter ou de réduire la portance. Les performances aérodynamiques ont été modifiées dans la partie linéaire de la courbe de portance. Pour des raisons d’efficacité et de fiabilité, le projet est poursuivi avec des jets fluidiques pour aller vers l’étude des pales et du contrôle d’écoulement en rotation. Ces pales sont préalablement testées dans une configuration translationnelle pour évaluer l’effet du contrôle sans les effets de la rotation. Finalement,les pales sont montées sur le banc éolien du laboratoire. Les effets du contrôle sont mis en évidence par les mesures de pression pariétale et de moment de flexion en pied de pale. Le contrôle induit des réductions importantes de fatigue qui motivent la poursuite des travaux dans le domaine du contrôle d’écoulement appliqué aux pales d’éolienne.Wind energy is a clean and renewable source of energy that remains one of the solutions to cut carbon emissions and curb global warming in the field of power generation. The present thesis objective is the optimisation of wind energy production by the all eviation of blade load fluctuations induced by shear and turbulence in the atmospheric boundary layer. These fluctuations increase the blade fatigue and reduce the life duration of the rotors.This load fluctuation all eviation is assessed with an experimental approach and at a laboratory scale. Two not conventional flow control strategies, plasma actuators and fluidic jets, are implemented and tested in the controlled environment of a wind-tunnel to perform a circulation control by acting in the vicinity of the rounded trailing-edge of the blade in order to modify its lift force.In the scope of the SMARTEOLE project, both plasma and fluidic strategies are, as a first step, tested in parallel on a 2D-airfoil. For this thesis, plasma actuators are implemented over the airfoil trailing-edge to increase ordecrease the lift force. Airfoil performances are indeed modified in the linear part of the lift curve. For efficiency and reliability reasons, it is chosen to pursue the work towards the rotational configuration with the fluidic strategy. Blades are then manufactured and tested first in a translational configuration to evaluate the potentialof the fluidic actuation without rotational effects. Then, blades are mounted in the wind turbine bench of the laboratory. The effects of the actuation are demonstrated through surface pressure and flapwise bending moment measurements. Actuation shows important fatigue reduction motivating the pursue of the investigations on active flow control applied to wind turbine blades
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
Theoretical, experimental and numerical study of the cooling airflow and its effects on the aerodynamics of road vehicles
No full textL’écoulement de refroidissement, qui pénètre par les entrées d’air sous le capot des véhicules automobiles,est étudié à partir de trois approches complémentaires : les approches théorique, expérimentale et numérique. Ces trois approches s’appuient sur une maquette simplifiée à culot droit basée sur le corps de Ahmed et équipée d’un compartiment moteur. Les mesures expérimentales montrent que placer la sortie du compartiment moteur au culot de la maquette est plus favorable à une faible traînée de refroidissement qu’une sortie placée au niveau du soubassement. La contribution de la traînée de refroidissement dans la traînée totale peut ainsi varier de 2% à 24%. Les simulations numériques donnent elles accès au débit de refroidissement. Pour les configurations étudiées, les sorties au culot sont là encore les plus favorables puisqu’elles fournissent les débits les plus importants à travers le milieu poreux modélisant un échangeur aérothermique. Par ailleurs, la mise en place d’étanchéités de part et d’autre de l’échangeur améliore significativement le débit de refroidissement où une augmentation d’environ 45% est obtenue. La mise en place d’un modèle analytique permet de relier la traînée et le débit de refroidissement à partir d’une analogie entre les circuits électriques et les écoulements fluides. Il est alors possible de prévoir le sens d’évolution du débit de refroidissement, donc de la performance des échangeurs aérothermiques, à partir d’une modification géométrique interne au compartiment moteur.The cooling airflow, which flows through the underhood of motor vehicles from the inlet sections, is studied by means of three complementary approaches: the theoretical, experimental and numerical approaches. The three approaches use a simplified geometry with a blunt rear end, based on the Ahmed body, and equipped with an engine compartment. The experimental measurements show that locating the outlet section of the engine compartment at the base of the geometry favors low cooling drag values compared to an outlet section located in the underbody. The variation of the cooling drag contribution in the total drag is between2% and 24%, as a function of the location of the outlet. As for the numerical simulations, they provide the cooling flow rates. For the studied configurations, rear end outlets are again the most favorable since they provide the highest flow rates through the porous media that simulates a heat exchanger. Besides, the implementation of sealing above and below the porous media significantly increases the cooling flow rate by45%. An analytical model, based on the analogy between electrical circuits and fluid flows, connects the aerodynamic drag with the cooling flow rate. It is then possible to predict the evolution trend of the cooling flow rate, hence the heat exchangers efficiency, from a geometrical modification inside the engine compartment
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
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
- …
