1,720,959 research outputs found
Synthesis of Syndiotactic Polystyrene Macromonomers End Capped with Bromine Atoms: a Tool for a New Investigation of Styrene Polymerization Mechanism Catalyzed by Monocyclopentadienyl Titanium Compounds
No full textSyndiotactic polystyrene samples end capped with bromine atoms in benzylic position have been synthesized by terminating the syndiospecific styrene polymerization catalyzed by Cp*TiBn(3)/B(C(6)F(5))(3)/Al-Oct(3) (CP* = eta(5)-C(5)(CH(3))(5); Bn = CH(2)Ph, Oct = (CH(2))(7)CH(3)) with N-bromosuccinimide (NBS) and 2-bromo-2-phenylethylisocyanate (BPEI). The chemical structure of the different polymer end groups was assessed by mono and bidimensional NMR techniques. The evaluation of the relative concentrations of the end Groups permitted to V Give new insights into the bromination reaction and syndiospecific styrene polymerization mechanism. A specific bromination of the methine carbon of the growing polymer chain bound to the titanium catalyst was observed when NBS was used as terminating agent. The formation of Ti(III) hydrido complexes in the activation reaction was proved as well as the role of these species as active catalyst in syndiospecific styrene polymerization
Iron(III) Complexes of Bidentate Nitrogen Ligands as Catalysts in Atom Transfer Radical Polymerization of Styrene
No full textThree iron(III) complexes of bidentate nitrogen ligands, namely 3,5-dimethyl-bispyrazolylmethane (bpzm), 2,2-dipyridyl (bipy) and 1,1-bis(4,4-dimethyl-1,3-oxazolyn-2-yl)-ethane (box), have been tested in atom transfer radical polymerization (ATRP) of styrene at 120 ◦C using the 1,1,2,2-tetraphenyl-1,2- ethanediol (TPED) initiator under reverse protocol. Good control of the polymerization reaction and narrow average molecular weight distribution (PDI) have been found for the TPED/FeCl3/box catalyst whereas TPED/FeCl3/bpzm and TPED/FeCl3/bipy produce linear dependence ofMn vs polymerization time but PDI values broader than that expected for a controlled mechanism. Attempts to clarify the performances of these catalysts were carried out, evaluating the formation constants ˇIII and the electrochemical parameters E1/2 of the FeCl3/L adducts (L = bpzm; bipy; box) by means of UV–vis spectroscopy and cyclic voltammetry, respectively. A regular increase of both ˇIII and E1/2 values was observed as the Lewis basic properties of the ligands increase in the order bpzm< bipy < box. The best performances of the FeCl3/box catalyst have been thus attributed to the highest formation constant that produce easy and reversible reduction of the iron(III) metal centre to the corresponding iron(II). Lower reducibility and reversibilitywere found for the iron(III)/iron(II) redox couple in FeCl3/bipy and FeCl3/bpzm in agreement with the modest performances in ATRP of styrene of these complexes
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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