1,721,102 research outputs found
Reduction of certain steroidal 19-sulfonic esters with metal hydrides
No full textFor biosynthetic studies we required steroids labeled with 2H and 3H at C 19. The isotopic hydrogens could be introduced sequentially by stepwise reduction of appropriate 19 oxygenated substrates. The key step of the projected sequence was the conversion of the C10 hydroxymethyl to a methyl. The approaches via the hydrogenolysis of steroidal 19 sulfonic esters with metal hydrides was explored and is described. Under conditions tested only 1-2% of the needed C 10 methyl steroids were formed
Preparation of 19 hydroxypregnenolone 3 acetate and 3 methyl ether
No full textThe synthesis of the title compounds is presented. The functionalization of the C-19 carbon was carried out by photolysis of the appropriate 5α-bromo-6β-hydroxy analogs. Certain improvements of synthetic procedures are described in detail
C-19 chiral steroids: The synthesis of (19R)- and (19S)-[19-3H,2H,1H]-3β-hydroxyandrost-5-en-17-ones
No full textTwo synthesis of C-19 chiral steroids are documented by the preparation of (19 R)- and (19 S)-[19-3H,2H,1H]-3β-hydroxyandrost-5-en-17-ones (4) and (5)
Reaction of saturated (5α- and 5β-) 19-hydroxy steroids with mixed phosphorus and halogen containing reagents
No full textAttempts to convert saturated (5α- and 5β-) 19-hydroxylated steroids to 19-halogenated analogues with the use of mixed phosphorus and halogen containing reagents are described. The 19-halogenated analogues were not obtained, but certain transformations in the 5α series and rearrangements in the 5β series were noted and are discussed
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
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