1,720,985 research outputs found
The Dynamic Structure Factor in non-Entangled Polymer Melts: Theoretical Results and the Stretched-Exponential Approximation
No full textThe dynamic structure factor in non-entangled polymer melts - Theoretical results for real chains and the stretched exponential approximation
No full textThe dynamic structure factor S(Q, t) measured in quasi-elastic scattering experiments (Q being the momentum transfer) is calculated for real poly(dimethyl siloxane) (PDMS) and polyethylene (PE) chains in the molten state at high Q, where chain entanglements are irrelevant. The theoretical lineshapes, obtained within the rotational isomeric states approach, are empirically fitted with the stretched exponential function S(Q, t)= exp[-(t/t)ß]. We find that the stretching exponent ß increases with chain stiffness, in keeping with our previous results for coarse-grained chain models. In particular, for high molar-mass polymers PE has a somewhat larger ß exponent than PDMS, in fair agreement with experimental results. Moreover, the theory predicts a marginal decrease of ß with increasing temperature, due to the increased conformational flexibility. Additionally, the ß exponent for PE is predicted to slightly increase in oligomers at a given T, in qualitative agreement with recent experimental results. © 2002 Elsevier Science B.V. All rights reserved.</p
The stretched exponential approximation to dynamic structure factor in non-entangled polymer melts
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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
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
New polymeric materials for paper and textiles conservation. II. Grafting polymerization of ethyl acrylate/methyl methacrylate copolymers onto linen and cotton
No full textIn the preservation of Cultural Heritage items, the use of polymeric materials for the consolidation and protection of artifacts with historical and artistic value is widely accepted, except for cellulose-based materials, since here there are no suitable products and appropriate application techniques. Grafting polymerization of acrylic monomers onto cellulose chains represents an innovative method of restoration for both artificially and naturally aged textiles. In this article, some results concerning the grafting polymerization of ethyl acryla te/ethyl methacrylate 75/25 and ethyl acrylate/methyl methacrylate/tri fluoroethyl methacrylate 73/24.5/2.5 polymers onto linen and cotton are reported. The effectiveness of grafting polymerization as a method for textiles conservation is discussed. The consolidating and protective effects were investigated by evaluating the mechanical properties and the wetting behavior of the grafted samples, and comparing them with the original and aged substrates. © 2006 Wiley Periodicals, Inc.</p
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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