1,720,954 research outputs found
Flow topology in asymmetric coaxial helical vortices and in the wake of wind turbines
No full textLos vórtices helicoidales son uno de los fenómenos fundamentales en la estela de turbinas eólicas. Su interacción, inestabilidad y efecto sobre la energía cinética en la estela aún están bajo investigación activa. Esta tesis trata de los vórtices helicoidales en tres casos de realismo creciente: vórtices paralelos, hélices infinitas y hélices formadas y desintegradas en la estela de la turbina. En el primer tema, estudiamos la topología de flujo inducida por tres y cuatro vórtices puntuales. Estos vórtices generan un flujo estacionario cuando se localizan en los vértices de un polígono regular; de lo contrario, generan un flujo periódico con regiones caóticas. Cuantificamos el mar caótico y el intercambio de masa para tres y cuatro vórtices puntuales y encontramos que el mar caótico crece linealmente a medida que los polígonos del vórtice son perturbados y se alejan de su configuración estacionaria. También estudiamos la evolución de tres y cuatro vórtices de Rankine localizados inicialmente en los vértices de un polígono regular y encontramos que se fusionan o interactúan elásticamente (a diferencia de dos vórtices, que también pueden intercambiar masa sin fusionarse). La topología de flujo de los vórtices que interactúan elásticamente es similar a la de los vórtices puntuales con la misma configuración geométrica; sin embargo, los vórtices de Rankine generan un flujo no estacionario debido a que su interacción los deforma con el tiempo. En el segundo tema, estudiamos el movimiento y el flujo inducido por dos vórtices helicoidales coaxiales e iguales. Determinamos la estabilidad de vórtices simétricos, que se mueven de manera estacionaria, en función de su grosor y paso. Los vórtices asimétricos muestran cuatro tipos de movimiento periódico que, a su vez, determinan la topología del flujo que inducen. En el tercer y último tema, estudiamos la estela detrás de una turbina eólica de dos aspas, caracterizada por vórtices helicoidales. Hay fenómenos en la estela, actualmente no comprendidos del todo, que afectan al rendimiento de los parques eólicos. Uno de ellos es la inestabilidad de los vórtices que desprenden las aspas. Encontramos que el inicio de la inestabilidad depende de la intensidad de la turbulencia corriente arriba. Además, la eficiencia de una segunda turbina en la estela depende de su distancia al punto donde los vórtices se vuelven inestables.Helical vortices are one of the fundamental phenomena in the wake of wind turbines. Their interaction, instability, and effect on the kinetic energy in the wake are still under active research. This thesis deals with helical vortices in three cases of increasing realism: parallel vortices, infinite helices, and helices formed and disintegrated in the wake of the turbine. In the first topic, we studied the flow topology induced by three and four point vortices. These vortices generate a steady flow when they are located on the vertices of a regular polygon; otherwise, they generate a periodic flow with chaotic regions. We quantified the chaotic sea and the mass exchange for three and four point vortices and found that the chaotic sea grows linearly as the vortex polygons are perturbed away from their steady configuration. We also studied the evolution of three and four Rankine vortices initially located on the vertices of a regular polygon and found that they either merge or interact elastically (unlike two vortices, which also can exchange mass without merging). The flow topology of elastically-interacting vortices is similar to that of point vortices with the same geometric configuration; however, Rankine vortices generate unsteady flow because their interaction deforms them over time. In the second topic, we studied the motion and flow induced by two equal coaxial helical vortices. We determined the stability of symmetric, steadily-moving vortices as a function of their thickness and pitch. Asymmetric vortices display four types of periodic motion which in turn determine the flow topology they induce. In the third and final topic, we studied the wake behind a two-bladed wind turbine, characterized by helical vortices. There are wake phenomena that affect wind farms’ performance that are not currently fully understood. One of them is the instability of the vortices shed by the blades. We found that the instability onset depends on the upstream turbulence intensity. Furthermore, the efficiency of a second turbine in the wake depends on its distance to the point where the vortices become unstable
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
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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