1,721,071 research outputs found
Azobenzene containing polymers: what is yet viable with aged liquid crystals
No full textA Commentary on the paper ”Photochromic liquid crystalline polymers. Main chain and side chain polymers containing azobenzene mesogens„, by A. S. Angeloni, D. Caretti, C. Carlini, E. Chiellini, G. Galli, A. Altomare, R. Solaro and M. Laus. First published in Liquid Crystals, 4, 513‐527 (1989)
Homo- and co-polymerization of styrene with ethylene by novel nickel catalysts
No full textThe homopolymerization of styrene has been studied by using catalysts based on bis(alpha -nitroacetophenonate)Nickel(II) [Ni(naph)(2)] and bis(hexafluoroacetylacetonate)Nickel(II) [Ni(hfacac)(2)] precursors and methylalumoxane (MAO) as co-catalyst. The former system displayed at room temperature a higher activity as compared with other previously reported nickel catalysts, giving rise to a substantially atactic polystyrene with a quite low molecular weight. The use of the basic and bulky tricyclohexylphosphine (PCy3) as ancillary ligand allowed to increase both molecular weight (similar to 20,000 Da) and isotacticity degree (similar to 50%) of the polymer. On the contrary, the use of the less basic triphenylphosphine (PPh3) caused a reduction of isotacticity degree. On increasing the reaction temperature at 70 degreesC, even in absence of the phosphine ligand, both catalytic systems gave a polymer characterized by about 50% isotacticity degree. A significant further increase of isotacticity degree (65-70%) was obtained when a AlMe3 free MAO was adopted in combination with the above nickel precursors. The GC/MS analysis of the oligomeric products allowed us to conclude that styrene insertion is mainly of secondary type. The above catalytic systems were found also to copolymerize ethylene with styrene, giving rise mainly to oligomeric products. (C) 2001 Elsevier Science Ltd. All rights reserved
Polymeric photoinitiators having benzoin methylether moieties connected to the main chain through the benzyl aromatic ring and their activity for ultraviolet-curable coatings
No full textSynthesis and chiroptical properties of optically active photochromic polymers with side-chain L-lactic residues connected to trans-azobenzene moieties bearing a formyl electron-withdrawing group
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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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