1,720,959 research outputs found
The manifestation of fluid-transmitted bed shear stress in a smooth annular flume: a comparison of methods
No full textThe most commonly used methods of calculating mean, fluid-transmitted bed shear stresses within a benthic boundary layer have been investigated. The work was carried out in an annular flume 2 m in diameter and 0.40 m deep—the Lab Carousel. This flume is a laboratory equivalent to the Sea Carousel (an in situ flume). A well developed boundary layer 0.02 m thick was confirmed for a range of flows measured using a Laser Doppler Velocimeter (LDV) within the Lab Carousel. There was a good relationship found between flow speed in the Lab Carousel and Sea Carousel, which corresponded well with a direct measurement method (particle tracking) using neutrally buoyant particles. The purpose of this investigation was to compare the accuracies and relative differences of eight ways of determining bed shear stress under smooth bed conditions: five using velocity as a proxy; and three considered direct. The proxy methods investigated were; (1) the Law of the Wall; (2) the Quadratic Stress Law; (3) the Turbulent Kinetic Energy (TKE) method; (4) Prandtl’s seventh power law; (5) and the Reynolds stress calculation. Three ‘direct’ measurements of bed shear stress were: (6) hot film probes; (7) inverting Newton’s second law to define frictional drag through flow deceleration; and (8) numerical simulation. All the methods gave sensible results with the expected trends of increasing stress under increasing flow velocity. The best correlation of the proxy methods was found between Prandtl’s seventh power law and flow deceleration; the other methods over predicting the stress by up to a factor of 10. There was a good coherence between the estimates of stress using an Acoustic Doppler Velocimeter (ADV) and the LDV at 0.15 m above the bed. The use of Sternberg’s constant drag coefficient (CD100 = 3 × 10?3) in stress calculations yielded the greatest over prediction. The hot film probes showed radial differences in stress, which were in general greatest in the middle and lowest near the outer wall. All the methods appear to converge at low current velocities. The TKE and flow deceleration methods showed similar results over a bed roughened with 0.011 m diameter uniform gravel, suggesting that they may be valid for naturally roughened beds
Flow deceleration as a method of determining drag coefficients over roughened flat beds
No full textThe drag coefficient (C D ) is a fundamental parameter in the determination of shear stress or the drag force between a fixed object and fluid moving over it. In natural settings, conventional methods of defining it are largely impractical and so either smooth-bed C D or constant values are used irrespective of bed roughness or flow strength. This paper deals with the determination of C D over naturally roughened beds. The work was carried out in two annular flumes of known, constant water mass. In an otherwise balanced system, flow deceleration is a manifestation of the total drag force exerted at the rigid boundaries (Newton's second law). The inversion of this relationship is used to yield the bed drag coefficients. The advantages of this method include its accurate use over rough and irregular beds, as shown by experiments over patchy and homogeneous gravel beds and over a wide range of Reynolds numbers. The value of C D was found to converge to the constant value of 3 × 10?3 determined by Sternberg [1968] at intermediate velocities, and a reduction in the drag coefficient occurred at high velocities. Results showed that patch spacing did not influence the shear stress value in the case of one-grain-thick gravel patches. A modification of the equipment for field use may give advantages where traditional methods fail due to difficulties in obtaining accurate velocity profile measurements
An evaluation of bed shear stress under turbid flows
No full textThis paper investigates the effect of various turbidity levels on the drag coefficient and bed shear stress in decelerating flows over a smooth bed. Turbid flows were simulated in a laboratory annular flume (Lab Carousel) using clay suspensions of different known mass concentrations. Flow velocity measurements were taken in the turbulent boundary layer and the values of bed drag coefficient and shear stress were calculated using the method of flow deceleration. Results showed that the bed drag coefficient responds significantly to an increase in the suspended sediment concentration (up to 20 g\L) showing a decrease of up to 50% in drag due to turbulence suppression. However, subsequent increases in mass concentration resulted in an increase in the drag coefficient reaching the clear water value at approximately 200 g\L because of the influence of viscosity. Thus the application of the law of the wall in flows of high concentrations of suspended cohesive sediments up to 200 g\L results in overestimation of the bed shear stress
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
- …
