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Boundary Layers in Planes of Symmetry, Part II: Calculations for Laminar and Turbulent Flow
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Analysis of turbulent flow in channels roughened by two-dimensional ribs and three-dimensional blocks. Part I: Resistance
No full textThe characteristics of a turbulent flow in channels with two-dimensional ribs and three-dimensional blocks are investigated in the context of surface roughness effects. Reynolds-averaged Navier-Stokes equations, coupled with the k-omega turbulence model with near-wall treatment, are solved by a finite-volume method. Calculations are carried out for ribs with square, triangular, semicircular and wavy cross-sections over a range of rib spacing (pitch) and Reynolds numbers. The pitch that yields maximum resistance is identified for each roughness. For all cases, the space-averaged velocity profile exhibits a logarithmic region, with a roughness function that varies logarithmically with the roughness Reynolds number. The roughness function depends on the rib shape and pitch ratio but is independent of the absolute rib size. Analysis with three-dimensional blocks reveals similar but more complex behavior. A logarithmic region exists in the velocity profile but with much smaller block heights compared to ribs. The different block arrangements exhibit quite distinct flow characteristics but the differences tend to vanish as the block height decreases. In general, a Reynolds-averaged numerical model successfully describes the principal features of wall roughness that have hitherto fore been the purview of experimental correlations. Part II of the paper extends the model to study heat transfer from a rough surface. (c) 2007 Elsevier Inc. All rights reserved
Analysis of turbulent flow in channels roughened by two-dimensional ribs and three-dimensional blocks. Part II: Heat transfer
No full textThe heat-transfer characteristics of a turbulent flow in channels with two-dimensional ribs and three-dimensional blocks are investigated in the context of surface roughness effects. This Part II of a two-part paper focuses on heat transfer while Part I was devoted to resistance. Reynolds-averaged Navier-Stokes equations, coupled with the k-omega-t (2) over bar-epsilon(t) turbulence model with near-wall treatment for velocity and temperature fields, are solved by a finite-volume method. Calculations are carried out for two-dimensional ribs with square, triangular, semicircular and wavy cross-sections over a range of rib spacing (pitch) and Reynolds numbers. It is found that heat transfer and flow resistance behave in a similar manner, with highest heat transfer occurring when the resistance is maximum. For all cases, the space-averaged temperature profile exhibits a logarithmic region, with a "heat-transfer roughness function" that varies with a constant power of the roughness Reynolds number. The constant power in the formula is found to be slightly larger than that in existing experimental correlations. Analysis of flow with three-dimensional blocks reveals similar characteristics. A log region exists in the space-averaged temperature profile for all cases for which the velocity profile has a log region. (c) 2007 Published by Elsevier Inc
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
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