1,721,113 research outputs found
Reversible Addition Fragmentation chain Transfer (RAFT) polymerization of methyl acrylate: Detailed structural investigation via coupled Size Exclusion Chromatography-Electrospray Ionization Mass Spectrometry (SEC-ESI-MS)
No full textThe on-line coupling of size exclusion chromatography (SEC) with electrospray ionization mass spectrometry (ESI-MS) was applied to study the polymeric product spectrum generated by the (strongly rate retarded) 2,2′-azobisisobutyronitrile (AIBN) and 1,1′-azobis(cyclohexanecarbonitrile) (ACHCN) initiated, cumyl dithiobenzoate (CDB) mediated methyl acrylate (MA) polymerization in detail. Products corresponding to the polymeric reversible addition fragmentation chain transfer (RAFT) agent and the combination and disproportionation termination products (with both cumyl, cyanocyclohexyl, and cyanoisopropyl end groups) along with a product stream arising from an oxidation process of the polymeric RAFT agent yielding sulfines and thioesters could be clearly identified. Termination products associated with the intermediate radical, that is, three- or four-armed star polymers, were not present. There is a degree of ambiguity over the disproportionation product of the macroRAFT radical. The experiments suggest that either the RAFT intermediate disproportionation product or the actual RAFT intermediate radical is present in the ESI-MS spectrum
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
The reversible addition-fragmentation chain transfer process and the strength and limitations of modeling: Comment on "The magnitude of the fragmentation rate coefficient"
No full textThere is appreciable uncertainty concerning the magnitude of the fragmentation rate coefficient of the intermediate radical in reversible addition-fragmentation chain transfer (RAFT) polymerizations. A large proportion of the experimental and theoretical evidence suggests that it is a stable species with a lifetime longer than 0.0001 s. This is particularly the case when the intermediate macro-RAFT radical is stabilized by a phenyl group attached to the radical center or has a poor leaving group. Although the occurrence to some extent of irreversible termination reactions cannot be excluded, we argue that such reactions are more likely to be a result of slow fragmentation of the intermediate macro-RAFT radical
Chain length dependent termination in butyl acrylate free-radical polymerization studied via stationary and pulsed laser initiated RAFT polymerization
No full textThe chain-length dependence of the termination rate coefficient, k t, in butyl acrylate free-radical polymerization has been determined by two independent methods, RAFT-SP-PLP and RAFT-CLD-T, both employing control of radical chain length by reversible addition fragmentation chain transfer (RAFT) polymerization. Within RAFT-SP-PLP, the polymerization induced by a laser single pulse is monitored via near-IR spectroscopy with a time resolution of microseconds. In RAFT-CLD-T, isothermal reaction rate measurements are carried out via DSC under stationary polymerization conditions. The resulting k t data refer to the situation of living/controlled radical polymerization, where both radical chain length and monomer conversion increase during the course of the reaction. The RAFT-SP-PLP measurements were carried out at 60°C and two pressures, 5 and 1000 bar. The RAFT-CLD-T experiments were run at ambient pressure and at two temperatures, 60 and 80°C, respectively. In absolute value, the termination rate coefficients for identical pressure and temperature deduced from the two methods differ by less than a factor of 2. For the dependence of kt on chain length, i, almost identical information is provided by the two techniques. The chain-length dependence of kt may be described by the power-law expression kt(i) = k t(1,1)i-α with, however, α being different for short-chain and long-chain radicals. RAFT-SP-PLP yields α1 = 1.25 for the short-chain regime from 1 < i < 30, and α2 = 0.22 for chain lengths above i = 50. RAFT-CLD-T results in α1 = 1.04 and α2 = 0.20 in identical chain length regimes. k t(1,1) values are found to be close to 1 × 109 L mol-1 s-1. © 2005 American Chemical Society
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
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