1,721,068 research outputs found
Collective diffusion in charge-stabilized suspensions: Concentration and salt effects
Get PDFThe authors present a joint experimental-theoretical study of collective diffusion properties in aqueous suspensions of charge-stabilized fluorinated latex spheres. Small-angle x-ray scattering and x-ray photon correlation spectroscopy have been used to explore the concentration and ionic-strength dependence of the static and short-time dynamic properties including the hydrodynamic function H (q), the wave-number-dependent collective diffusion coefficient D (q), and the intermediate scattering function over the entire accessible range. They show that all experimental data can be quantitatively described and explained by means of a recently developed accelerated Stokesian dynamics simulation method, in combination with a modified hydrodynamic many-body theory. In particular, the behavior of H (q) for de-ionized and dense suspensions can be attributed to the influence of many-body hydrodynamics, without any need for postulating hydrodynamic screening to be present, as it was done in earlier work. Upper and lower boundaries are provided for the peak height of the hydrodynamic function and for the short-time self-diffusion coefficient over the entire range of added salt concentrations.Fil: Gapinski, J.. A. Mickiewicz University; PoloniaFil: Patkowski, A.. A. Mickiewicz University; PoloniaFil: Banchio, Adolfo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Holmqvist, P.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Meier, Guillermo Enrique. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Lettinga, M.P.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Nägele, G.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; Alemani
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
Tuning Shear Banding and Wall Slip in Entangled Polyelectrolytes by Intermolecular Interactions
No full textThe study of flow instabilities such as shear banding and wall slip in entangled polymers is of great significance for both fundamental science and industry. There is, however, an ongoing debate in the polymer rheology community whether shear banding is generic for polymers. This discussion is involved as the molecular mechanism for shear banding in entangled polymers is poorly known and the interplay of shear banding with wall slip makes the problem even more complicated. Therefore we try to answer three questions in this thesis: 1) Is shear banding a generic phenomenon for entangled polymers or a more system-specific phenomenon? 2) Will the shear banded systems always show classic shear banded velocity profiles, with a constant shear rate within both bands, independent of the applied shear rate? 3) What is the molecular mechanism for shear banding in entangled polymers?
In order to address these questions, we performed in this thesis standard rheology measurements, birefringence and velocity profile experiments in order to characterize the linear and non-linear flow behavior of polymers for which the interactions and properties can be tuned. Polyelectrolytes are a logical choice, as both the interactions and particle properties can be tuned by varying the ionic strength. To access the generic character, we used two different polyelectrolytes, namely the semi-flexible xanthan and DNA. In addition, we synthesized an attractive polymer system namely DNA grafted with PNIPAm, which becomes hydrophobic above a critical temperature. This allowed us to also access the effect of attraction.
We demonstrate that shear banding and wall slip in entangled xanthan and DNA can be finely tuned by intermolecular interactions such as the electrostatic repulsions and intermolecular attraction. For xanthan and DNA we observe sharp shear banding at low ionic strength, though for DNA there is a strong competition with wall slip. The sharp interfaces broaden upon addition of salt, up to a point at high salt where no shear bands are observed and the velocity profile becomes linear. We introduced a new analysis method to quantify this broadening and also the difference between a shear thinning factor as obtained from the rheological flow curve and the velocity profile. For the attractive PNIPAm-DNA we find a reentrant behavior as upon increasing temperature first wall slip is suppressed in favor of shear band formation, while shear banding is suppressed when the system tends to gel. These observations suggest that shear band formation is generic for polymers when they are sufficiently stiff and when the friction between the polymers is low. Shear banding is suppressed when the disentangled polymers can easily collapse either by screening the charges along its backbone or increasing attraction. The mechanism of suppression is related with the widening of the interface. We claim that generally polymeric systems that display a curvature in the velocity profile which is stronger than expected from the rheology, do display shear banding, but with an interface which is too broad for the gap of the shear cell geometry.status: Publishe
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
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