1,720,957 research outputs found
Biosynthesis of ascochitine: Incorporation studies with advanced precursors
No full textEvidence is presented that the first step of the biosynthesis of ascochitine (1), a metabolite of Ascochyta fabae Speg., involves methylation of a hexaketide, followed by cyclization, reduction to the aldehyde, dehydration, and eventually oxidation of the methyl group at C(7) to a carboxy group
Biosynthesis of ascochitine and synthesis of its biogenetic precursors
No full text' Enzymic trap ' experiments show that the main biosynthetic pathway to ascochitine (1) involves the direct reduction of the enzyme-bound ester into aldehyde (4). Therefore the complete pathway has now been assessed. Various synthetic approaches have been tried to synthesize the precursors: the use of 1,3-dithians, of an organolithium equivalent to the Friedel-Crafts reagent, and of phase-transfer reactions allowed for a good introduction of the label
Biosynthesis of citrinin
No full textThe biosynthetic pathway to citrinin is elucidated by incorporation studies with advanced precursors, the first step of biosynthesis involves methylation of a pentaketide, followed by cyclization, reduction to the ketoaldehyde and then to the hydroxyaldehyde, dehydration, and finally oxidation of the methyl group at C(7) to a carboxy-group
Biosynthesis of austdiol and synthesis of a deuterium labelled biogenetic precursor
No full textIncorporation studies on austdiol (1), a metabolite from Aspergillus ustus were carried out with [1,2-13C2]-acetate, [Me- 13C]-, and [Me-2H3]-methionine. Specific incorporation of 4,6-dihydroxy-3,5-dimethyl-2-(2-oxopropyl)benzaldehyde (2) into austdiol (1) was demonstrated using 2H n.m.r. spectroscopy. The total synthesis of the ketoaldehyde (2), allowing the specific insertion of a label, is described
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
Biosynthesis of citrinin and synthesis of its biogenetic precursors
No full textThe biosynthetic pathway to citrinin has been elucidated by incorporation studies with advanced precursors. These specifically labelled compounds were obtained from labelled citrinin produced by cultures of Penicillium citrinum in the presence of [Me-14C]methionine. The method for testing incorporation specificity is also described
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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