1,720,969 research outputs found
Free radical controlled polymerization of fluorinated copolymers produced in microemulsion
No full textControlled free-radical polymerization is an emerging technique which can in principle produce macromolecules with well defined microstructure, possibly tailored to specific applications. This work describes the application of such a process to the production of several hundreds of tons of a fluorinated copolymer per year. The aim is to control the microstructure of the product and, in particular, to produce branched macromolecules with relatively uniform chain lengths. The process operates in microemulsion and is complicated by the presence of branching reactions. A complete kinetic model is developed to identify the most appropriate operating conditions to produce copolymers with desired characteristics
Kinetics of the emulsion polymerization of vinylidene fluoride and hexafluoropropylene
No full textThe kinetics of emulsion polymerization of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) has been investigated both experimentally and through the development of an appropriate model. Despite the practical relevance of this copolymer, information about the polymerization kinetics in the literature are rather scarce. A reasonable polymerization mechanism involves quite a number of kinetic parameters, which all need to be evaluated independently. This was obtained by running a limited number of polymerization reactions, but performing a rather accurate characterization of the polymer produced, including the polymerization rate, molecular weight, and chain end group distribution. These quantities allow for the reliable estimation of the involved kinetic parameters. The reliability of the developed model has been assessed by comparison with a second independent set of experimental data, where different operating conditions, in terms of pressure, initial concentration of the initiator, and chain-transfer agent, have been considered
Vinylidenfluoride-hexafluoropropylene copolymers as hybrid electrolyte components for lithium batteries
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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
PTFE- Polystyrene Core-Shell Nanospheres and Nanocomposites
No full textPTFE latexes with particles in the submicrometer size range were employed as seeds in the emulsifier-free styrene emulsion polymerization to obtain PTFE-polystyrene (PS) core-shell nanospheres. Stable latexes were generally obtained. Neither residual PTFE nor secondary nucleation was observed, thus leading to PTFE-PS core-shell latexes. By appropriately choosing the ratio between the styrene monomer and the PTFE seed in the reaction mixture, it is possible to obtain spheres with predetermined sizes and narrow size distribution. In all cases, a slightly hemispherical morphology was observed. Peculiar effects related to the high degree of segregation of PTFE cores and their small size, and possibly to the PTFE/PS interface, were observed
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
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