1,720,979 research outputs found
Mixing in particulate suspensions sheared at low Reynolds number.
No full textJ'ai étudié expérimentalement, à l'échelle de la taille des particules, les mécanismes à l'origine de l'intensification des transferts ayant lieu dans les suspensions cisaillées de particules non-inertielles et non-Browniennes. Dans un premier temps, l'expérience de Taylor est revisitée en étudiant l'évolution d'une goutte de colorant soumise à un cisaillement périodique. Au-delà d'une amplitude critique de déformation, la présence des particules brise la réversibilité du système et induit une forte dispersion de la goutte de colorant. Ensuite, en m'intéressant au transfert en proche paroi, j'ai montré que la rotation des particules sur la paroi induit un transport à flux constant d'un scalaire jusque dans le bulk de la suspension, brisant la couche limite diffusive. Une solution analytique du profil de concentration dans cette zone est proposée, en bon accord avec les expériences. Finalement, des mesures PIV haute résolution du fluide interstitiel dans le bulk de la suspension ont été réalisées. A partir de ces champs de vitesses, on a reconstruit l'historique d'étirement de lignes matérielles du fluide et ainsi déterminé les lois d'étirement, information fondamentale pour la compréhension du processus de mélange. La présence des particules change les lois d'étirement qui passent de linéaires dans un fluide pur, à exponentielles en présence de particules. Un modèle d'étirements multiplicatifs est proposé, qui prédit quantitativement l'évolution de la moyenne, de la variance, et la forme log-normale des distributions d'étirements mesurées expérimentalement. L'inhomogénéité des étirements dans les suspensions cisaillées implique une large distribution du temps de mélange.Mainly based on experiments, I investigated at a particle scale the mechanisms at the origin of the transfer enhancement in sheared non-Brownian and non-inertial particulate suspensions. First, I revisited Taylor's experiment, investigating the evolution of a drop of dye in a periodic shear. Beyond a critical strain amplitude, the presence of the particles breaks the reversibility of the system and the drop of dye is rapidly dispersed in the surrounding medium. Then, investigating the transfer process in the wall vicinity, I showed that in this region, the rotation of the particles convectively transport a scalar at a constant rate directly from the wall towards the bulk of the suspension, breaking the diffusive boundary layer. An analytical solution for the concentration profile in this region is proposed, in good agreement with experimental measurements. Lastly, high-resolution PIV measurements of the fluid phase were performed in the bulk of the suspension. Using these velocity fields, we reconstructed the stretching histories of fluid material lines to determine the stretching laws, crucial for the understanding of the mixing process. The presence of the particles changes the very nature of the stretching laws from linear, in a pure fluid, to exponential in the presence of particles. A multiplicative stretching model is proposed, which quantitatively predicts the experimentally measured evolution of the mean and the variance of the elongations of the fluid material lines as well as their evolution towards a log-normal distribution. The strong stretching inhomogeneity in sheared suspensions results in a broad distribution of the mixing time
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
Mélange dans les suspensions de particules cisaillées à bas nombre de Reynolds
No full textThe goal of this dissertation is to understand, at the particle scale, the mechanisms at the origin of the transfer enhancement in non-Brownian and non-inertial particulate suspensions.i) Inspired by Taylor’s experiment, I first studied the evolution of a drop of dye in a periodic shear. One can observe that beyond a critical strain amplitude, the presence of particles breaks the reversibility of the system. The drop of dye is thus rapidly dispersed in the surrounding medium. This evolution is well described using an effective diffusion coefficient which is of the same order as the particle diffusion coefficient.ii) We observed a `rolling-coating‘ mechanism which allowed a better understanding of the transfer process in the wall vicinity. In this region, the rotation of the particles convectively transport a scalar at a constant rate directly from the wall towards the bulk of the suspension, breaking the diffusive boundary layer. The evolution of the concentration profiles can be described using a constant flux boundary condition (induced by the `rolling-coating’), and an effective diffusion profile, based on the experimentally measured velocity fluctuations of the fluid phase, which scales linearly with the distance from the wall. The analytical solution for the concentration profile, based on an incomplete gamma function, is in good agreement with experimental measurements.iii) Lastly, high-resolution PIV measurements of the fluid phase were performed in the bulk of the suspension. Using these velocity fields, we reconstructed the stretching histories of fluid material lines to determine the stretching laws, crucial for the understanding of the mixing process. This complete characterization of the kinematics of deformation in sheared suspensions reveals that the presence of the particles changes the very nature of the stretching laws from linear, in a pure fluid, to exponential in the presence of particles. According to the quality of the measured velocity fields, two very important quantities were determined : the local shear rate distribution, and their persistency times. Based on these two quantities, one can describe the stretching history of material lines using a multiplicative model which consists of a sequence of uncorrelated stretching cycles. This simple model quantitatively predicts the experimentally measured evolution of the mean and the variance of the elongations of the fluid material lines as well as their evolution towards a log-normal distribution. The strong stretching inhomogeneity in sheared suspensions results in a broad distribution of the mixing time.L'objectif de cette thèse principalement expérimentale est de comprendre, à l'échelle de la taille des particules, les mécanismes à l'origine de l'intensification des transferts ayant lieu dans les suspensions de particules non-inertielles et non-Browniennes soumises à un cisaillement. i) En s'inspirant de l'expérience de Taylor, j'ai d'abord étudié l'évolution d'une goutte de colorant soumise à un cisaillement périodique. On observe qu'au-delà d'une amplitude de déformation critique, la présence des particules brise la réversibilité du système. La goutte de colorant est alors rapidement dispersée dans le milieu environnant. Cette évolution est bien décrite par un coefficient de diffusion effectif qui est du même ordre que celui caractérisant l'agitation des particules. ii) Nous avons mis en évidence un mécanisme de `rolling-coating' qui permet de comprendre le processus de transfert en proche paroi. Dans cette zone, la rotation des particules induit un transport à flux constant du scalaire de la paroi vers le bulk de la suspension, court-circuitant ainsi la couche limite diffusive. L'évolution des profils de concentration peut être décrite avec une condition limite de flux constant (conséquence du `rolling-coating') et un profil de diffusion effectif, déterminé par la mesure des fluctuations de vitesse du fluide interstitiel, qui croit linéairement avec la distance à la paroi. La solution analytique proposée, basée sur une fonction gamma incomplète, prédit quantitativement l'évolution de ces profils. iii) Finalement, des mesures PIV haute résolution du fluide interstitiel dans le bulk de la suspension ont été réalisées. A partir de ces champs de vitesses, on a pu reconstruire l'historique d'étirement de lignes matérielles du fluide et ainsi déterminer les lois d'étirement, information fondamentale pour la compréhension du processus de mélange. Cette caractérisation complète de la cinématique de déformation dans les suspensions cisaillées montre que la présence des particules change la nature des lois d'étirement qui passent de linéaires dans un fluide pur, à exponentielles en présence de particules. La qualité des champs de vitesses mesurés par PIV nous a par ailleurs permis d'extraire deux grandeurs très importantes : la distribution des taux de cisaillements locaux ainsi que leur temps de persistance. A partir de ces deux quantités, on peut décrire l'historique d'étirement des lignes matérielles comme un processus multiplicatif qui consiste en une succession de cycles d'étirements décorrélés. Ce modèle simple prédit quantitativement l'évolution de la moyenne, de la variance, et la forme log-normale des distributions d'étirements mesurées expérimentalement. La forte inhomogénéité des étirements dans les suspensions cisaillées implique une large distribution du temps de mélang
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
L'expérience de Taylor dans une suspension de particules
Full text linkNous re-visitons l'expérience de Taylor dans une suspension de particules soumise à un cisaillement périodique afin d'étudier l'effet de la diffusion induite par cisaillement sur la dispersion d'une goutte de colorant. Au delà d'une déformation critique, la dispersion de la goutte augmente fortement. Le coefficient de diffusion effectif de la goutte est mesuré et comparé à celui des particules
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
- …
