1,721,022 research outputs found
Analysis of a boundary layer of a granular mixture flowing past a plate at zero incidence
No full textThe present paper reports experiments on the flow field of a grain-water mixture around
a flat, thin plate at zero incidence. The velocity measurements are performed using a
Particle Image Velocimetry (PIV) technique. The Proper Orthogonal Decomposition
(POD) analysis reveals that the degree of organisation of the flow field increases with
the Reynolds number. The displacement thickness of the boundary layers generally
increases downstream and increases slightly with the Reynolds number, which is based
on the length of the plate. The vorticity normal to the plane of the flow has a maximum
value at the leading edge and is almost invariant with respect to the Reynolds number;
additionally, the non-dimensional profiles in the direction normal to the plate show selfsimilarity
in the streamwise direction for a single test, and the profiles are almost
coincident for all tests. The flow divergence is assumed to be an indicator of the
variation of the sediment volume concentration; it indicates an increment of the
sediment volume concentration near the walls of the plate and a spatial periodicity
downstream that is triggered for relatively large Reynolds numbers. The spatial correlation analysis allows the evaluation of the integral length scales that are
successively utilised in modelling the non-local rheology of the mixture. The velocity
profiles have been modelled based on Savage’s model and Bagnold’s experiments, with
further modifications from Ertaş and Halsey (2002) that are represented by pseudoturbulence
modelling of the flow field. Vortices have been detected according to the lambda-2-
criterion given by Jeong and Hussain (1995). The statistics of the vortices indicate that
no preferential size is selected and that at a high Reynolds number, the most energetic
vortices develop near the leading edge
Coupled Effects of non-Newtonian Rheology and Aperture Variability on Flow in a Single Fracture
No full textModeling of non-Newtonian flow in fractured media is essential in hydraulic fracturing and drilling operations, EOR, environmental remediation, and to understand magma intrusions. An important step in the modeling effort is a detailed understanding of flow in a single fracture, as the fracture aperture is spatially variable.
A large bibliography exists on Newtonian and non-Newtonian flow in variable aperture fractures. Ultimately, stochastic or deterministic modeling leads to the flowrate under a given pressure gradient as a function of the parameters describing the aperture variability and the fluid rheology. Typically, analytical or numerical studies are performed adopting a power-law (Oswald-de Waele) model. Yet the power-law model, routinely used e.g. for hydro-fracturing modeling, does not characterize real fluids at low and high shear rates. A more appropriate rheological model is provided by e.g. the four-parameter Carreau constitutive equation, which is in turn approximated by the more tractable truncated power-law model. Moreover, fluids of interest may exhibit yield stress, which requires the Bingham or Herschel-Bulkely model.
This study employs different rheological models in the context of flow in variable aperture fractures, with the aim of understanding the coupled effect of rheology and aperture spatial variability with a simplified model. The aperture variation, modeled within a stochastic or deterministic framework, is taken to be one-dimensional and i) perpendicular; ii) parallel to the flow direction; for stochastic modeling, the influence of different distribution functions is examined. Results for the different rheological models are compared with those obtained for the pure power-law. The adoption of the latter model leads to overestimation of the flowrate, more so for large aperture variability. The presence of yield stress also induces significant changes in the resulting flowrate for assigned external pressure gradient
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
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
Non-Newtonian power-law gravity currents propagating in confining boundaries
Full text linkThe propagation of viscous, thin gravity currents of non-Newtonian liquids in horizontal and inclined channels with semicircular and triangular cross-sections is investigated theoretically and experimentally. The liquid rheology is described by a power-law model with flow behaviour index n, and the volume released in the channel is taken to be proportional to ta, where t is time and a is a non-negative constant.
Some results are generalised to power-law cross-sections. These conditions are representative of environmental flows, such as lava or mud discharges, in a variety of conditions. Theoretical solutions are obtained in self-similar form for horizontal channels, and with the method of characteristics for inclined channels. The position of the current front is found to be a function of the current volume, the liquid rheology,
and the channel inclination and geometry. The triangular cross-section is associated with the fastest or slowest propagation rate depending on whether a < ac or a > ac. For horizontal channels, ac = n=(n+1) < 1, whereas for inclined channels, ac = 1, irrespective of the value of n. Experiments were conducted with Newtonian and power-law liquids by independently measuring the rheological parameters and releasing currents with constant volume (a = 0) or constant volume flux (a = 1) in right triangular and semicircular channels. The experimental results validate the model for horizontal channels and inclined channels with a = 0. For tests in inclined channels with a = 1, the propagation rate of the current front tended to lower values than predicted, and different flow regimes were observed, i.e., uniform flow with normal depth or instabilities resembling roll waves at an early stage of development.
The theoretical solution accurately describes current propagation with time before the transition to longer roll waves. An uncertainty analysis reveals that the rheological parameters are the main source of uncertainty in the experiments and that the model is most sensitive to their variation. This behaviour supports the use of carefully designed laboratory experiments as rheometric tests
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