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Understanding asymmetry effects at low grafting density on the self-assembly of polyion grafted nanoparticles
No full textGrafting of spherical nanoparticles (NPs) with polymeric ligands has been an effective way of controlling the dispersion state of NPs either in the matrix or in solution. Despite the fast evolving synthesis techniques, it is still experimentally difficult to precisely control the position of tethers on the surface of NPs. At low grafting density, due to the surface anisotropy, a wide range of assemblies could be achieved depending on the position of the tethers on the NP surface. This may pose a challenge in interpreting data from scattering and electron micrographs. In the current manuscript, we use coarse-grained molecular dynamics simulations to study the effect of graft angles (positions) on the self-assembly of NPs grafted with oppositely charged polyions at low grafting density driven by coulombic interactions. Our study shows that the NPs grafted with oppositely charged polyions self-assemble into a wide range of morphologies like dimers, rings, strings, coils, tetramers and aggregates depending on the angle between the grafts. Furthermore, the morphologies obtained in the case of semi-flexible and rigid-chains as tethers are more sensitive to the graft positions (angles) compared to that of flexible chains. Molecular dynamics studies carried out at low grafting densities of the system comprising an equimolar mixture of nanoparticles grafted with polyions at varying grafting angles showed that the polyions grafted at low/high grafting angles preferentially interacted with oppositely charged polyion grafts tethered at low/high graft angles
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
Charge-Driven Self-Assembly of Polyelectrolyte-Grafted Nanoparticles in Solutions
No full textNanoparticle self-assembly in solution has gained immense interest due to the enhanced optical, chemical, magnetic, and electrical properties which manifest at the macroscale. Material properties in bulk are a direct consequence of the morphology of these nanoparticles in solutions. Precise control on the orientation, spatial arrangement, shape, size, composition, and control over the interactions of individual nanoparticles play a key role in enhancing their properties. While previous studies have used asymmetry in the nanoparticle and/or the use of linker grafts, nanoparticles grafted with polyelectrolyte grafts provide us a wide parameter space to control and tune their self-assembly in solutions. In this study, we have performed coarse-grained molecular dynamics simulations to understand the charge-driven self-assembly of spherical nanoparticles grafted with polyelectrolyte chains. Nanoparticles grafted with either positively or negatively charged polyelectrolyte chains self-assemble to different structures driven by both excluded volume and electrostatic interactions. Our study shows that by tuning the graft density, the chain length, and the charge density of the grafts, we could build and control a variety of self-assembled structures ranging from rings, dimers, strings, coil-like aggregates, and disordered-to-ordered aggregates
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