1,721,183 research outputs found
Predicting the apparent wall slip when using roughened geometries: A porous medium approach
No full textA common approach to prevent or alleviate wall slip in rotational rheometry is to utilize roughened geometries. While this is a helpful strategy, the presence of the surface roughness introduces a fundamentally different boundary condition, as the flow trough the porous structure needs to be accounted for. In the present work we investigate the use of rough surfaces in rheometry, starting with simple Newtonian fluids. Both structured and randomly structured surfaces are used, i.e. a cross-hatched plate and a sandpaper disc, respectively. We show that the fluid flows within the roughened layer and that the flow in the gap of the rheometer can be modelled as a flow over and through a porous medium. Stokes’ equation and Brinkman’s equation can be coupled at the interface through a suitable stress boundary condition recently developed in the literature that takes the momentum transfer to both the fluid and the solid substrate properly into account [Minale M., Phys Fluids 26, 123102 (2014)]. The predictions of this new model are compared with the experimental results on Newtonian reference fluids and show excellent agreement for the case of the cross-hatched geometry, and satisfactory agreement for the geometry with sandpaper. The analysis provides a way to correct the apparent viscosity by dealing with the extra dissipation in the rough layer using an extrapolation length
Rheo-optical Analysis of Functionalized Graphene Suspensions
No full textWet processing of graphene sheets is a potentially interesting route for the economically viable creation of graphene-based composites. In the present work, flow dichroism and small-angle light scattering are used to investigate the dispersion of functionalized graphene sheets in a suspension and their response to shear flow. In line with expectations from scaling theory at rest, the functionalized graphene sheets are present as Brownian flat sheets, and there is no evidence of significant crumpling. More surprisingly, we find that the rate-dependent orientation of these molecularly thin sheets can be described by numerical predictions for hard spheroidal sheets, making quantitative predictions of the flow-induced orientation possible. Further comparison of the flow-induced orientation of thick gold decahedra with the thin graphene sheets shows that, except for effects of polydispersity, the flow-induced orientation is predicted well quantitatively. Adequate prediction of the effects of flow on the orientation of graphene sheets makes it possible to design wet processed graphene-based composite materials.sponsorship: The authors thank Luiz Lis-Marzan, Jorge Perez-Juste, and Isabel Pastoriza-Santos for providing oblate gold spheroids. J.V. acknowledges the Swiss National Science Foundation (project number 200021-157147), and G.N. acknowledges funding from the NSERC (grant number RGPIN-2017-03783). The authors thank the reviewers for insightful comments on the article, as these comments led us to improve it. (Swiss National Science Foundation|200021-157147, NSERC|RGPIN-2017-03783)status: Publishe
Orientation dynamics of dilute functionalized graphene suspensions in oscillatory flow
No full textsponsorship: J.V. acknowledges the Swiss National Science Foundation Project No. 200021-157147 and G.N. acknowledges funding from the NSERC Grant No. RGPIN-2017-03783. (Swiss National Science Foundation|200021-157147, NSERC|RGPIN-2017-03783)status: Publishe
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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