1,720,955 research outputs found
Intra- and Intermolecular Hydrogen Bonding Effects in Cycloadditions between Nitrile Oxides and 4-Benzoylamino-2-cyclopenten-1-ol and its Derivatives
No full textCycloadditions between nitrile oxides and cis-4-benzoylamino-2-cyclopenten-1-ol offer an example in which a strong intramolecular hydrogen bond completely offsets the syn-directing ability of the cyclopentene substituents. Solvents affected the conformational equilibrium of the cyclopentene dipolarophile but did not sizeably influence the cycloaddition selectivity, showing the absence of directing effects between the addends. Removal of the intramolecular hydrogen bond by OH protection or oxidation activated the syn-directing ability of the amido substituent and provided a convenient route to syn stereoselection
The hydrogen bond directing effect in nitrile oxide cycloadditions to allylic substituted cyclopentenes.
No full textA quantitative evaluation of the H-bond directing effect on the stereoselectivity in the cycloaddition of
nitrile oxides to 2-cyclopenten-1-ol and allylic cyclopentenyl amides is reported. In apolar solvents the
H-bond directing effect promotes a high syn stereoselectivity while H-bond acceptor solvents divert the
reactions to the anti face of the dipolarophile. Taft's b parameter gives a good description of the solvent
effect on the H-bond directing effect. The persistence of some syn stereoselectivity even in good H-bond
acceptor solvents points out the existence of some residual hydrogen bond direction. The syn stereoselectivity
in the presence of M(II) salts was also investigated and the results discussed in the light of the
potential application of these scaffolds in nucleoside synthesis
Nitrile oxide cycloaddition to 4-hydroxy-2-cyclopentenone: Solvent effect and selectivity
No full textThe facial selectivity in the nitrile oxide cycloaddition reactions of 4-hydroxy-2-cyclopentenone and its
bulky t-butyloxy derivative is reported. A quantitative evaluation of the solvent effect on the hydrogen
bonding directing ability is given, showing the presence of some syn-stereoselectivity even in good
H-bond acceptor solvents. The stereoselectivities of the O-t-butyl derivative may serve as reference data
for more complex systems and point to the existence of a sole steric effect on the directivity; M(II) ions
did not significantly improve the selectivity. The results are also discussed in light of the potential
application of these scaffolds in the nucleoside analogue synthesis
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
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