1,720,968 research outputs found
Alternative Insight into the “Self-immobilization” Mechanism by New Tethered Zirconocene Catalyst
No full textNew -alkenyl-substituted ansa-bridged bisindenyl zirconium complexes are prepared and tested as self-immobilized catalysts for ethene polymerization. But, even at very high concentration of the tethered complexes and low pressure of ethene, there is no evidence of their insertion into the polyethene chain. A cross polymerization test, performed by copolymerizing the tethered complexes with ethene using rac-Me2Si(2-MeBenzInd)2ZrCl2 (MBI), does not lead to their incorporation into the polyethene chain. However, the corresponding ligand proves to be a suitable comonomer for ethene, and, through copolymerization promoted by MBI, innovative poly(ethene-co-2,2-bis[(1H-inden-3-yl)-hex-5-ene) copolymers are prepared and characterized by 13C NM
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
Seven- and eight-membered saturated fused ring zirconium and titanium metallocenes: a route for the synthesis of elastomeric polypropylene
No full textUnbridged zirconium and titanium catalysts, where a seven or eight-membered ring fused to a cyclopentadiene is associated with a phenyl substituent in position 2, were tested in propene polymerization in order to investigate the possibility to observe a "fluxional behavior", and to obtain stereoblock polypropylene, even in the absence of the aromatic ring, usually present in this kind of catalysts, by introducing the conformational flexibility of the saturated ring as a new parameter. The microstructure, molecular properties and thermal behavior of the polymers obtained showed that it is possible to observe a "fluxional behavior" even by replacing the basic indenyl structure with a slightly flexible saturated ring. Furthermore, this structural feature sensibly increases the stability of the complexes, thus making possible to observe for the first time the oscillating behavior in titanocenes
Random propene/4-methyl-1-pentene copolymers synthesized with C2symmetric highly isospecific metallocenes
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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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