1,720,987 research outputs found
Aminophosphonite-phosphite and aminophosphonite-phosphinite ligands with mixed chirality: preparation and catalytic applications in asymmetric hydrogenation and hydroformylation
No full textAminophosphonite-phosphite and aminophosphonite-phosphinite chiral ligands with mixed stereogenic elements have been prepared in good yields from chiral α-aminoalcohols such as 2-(hydroxymethyl)pyrrolidine and 2-N-ethylammino-1-butanol. These new ligands have been fully characterized; the Rh(I) complexes have been tested in catalytic hydrogenation and hydroformylation reactions. Enantioselectivities up to 70% have been obtained in asymmetric hydrogenation of α-acetamidocinnamic acid, methyl ester; enantioselectivities higher than 30% and regioselectivities higher than 98% have been obtained in asymmetric hydroformylation of vinyl acetate
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
Chiral Aminophosphonite-phosphite and Aminophosphonite-phosphinite Ligands in Asymmetric Hydroformylation of Carbapenem Antibiotics Precursors.
No full textThe greater part of the transition metals known as excellent catalysts for asymmetric synthesis has optically active diphosphine ligands as source of chirality; in spite of the great variety of chiral ligands available there is still demand for the development of catalysts which display the requirements of high enantioselectivity, diastereoselectivity and productivity in fine chemicals, fragrances, flavours, agrochemicals. Spurred by these observations we have developed some “mixed” electrondeficient aminophosphonite-phosphite and aminophosphonite-phosphinite. The term “mixed” indicates that the ligands gather one or more stereogenic sp3 carbon atoms of an alpha-aminoalcohol with the (R) or (S) atropisomeric chirality of the 1,1’-binaphthyl moiety. The Rh(I)-complexes derived from these chiral ligands can be valuable catalysts in hydroformylation of Carbapenem antibiotics precursors.
Same selected results are summarized in the table
New chiral ligands for the enantioselective catalysis with transition metal complexes
No full textWe have prepared new ligands based on the combination of the atropisomeric chirality with the chirality of stereogenic carbon atoms.
The ligands are prepared according to the scheme 1, and are obtained in good yield by the condensation of one or two optically pure (R) or (S) 1,1’Binaphthyl[1] group and chiral not racemic aminoalcohols derived from the “chiral pool”.
The aminoalcohols of choice are -N-ethylamino buthanol and 2-Pyrrolidinemethanol; with these chiral substrates we have prepared two different types of ligands: 6 and 7.
By a combination of NMR techniques we have fully characterized the ligands and the correspondent Rh(I), Pd(II), Pt(II) complexes.
Rhodium complexes based on type 6 and type 7 ligands have demonstrated to be active catalysts in the asymmetric hydrogenation of N-protected dehydroaminoacids.
[1] We are indebted to Prof. F. Faraone and with his coworker C.G. Arena for the detailed description of the preparation of 1,1’Binaphtyl-2,2’ diylphosphite cloride
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