1,721,267 research outputs found
A multinuclear magnetic resonance study of nitrile oxides
No full textThe 13C NMR signal of the CNO carbon atom in nitrile oxides is in general so broad at room temperature that it is often undetectable. This result has been related to the quadrupolar relaxation mechanism of the adjacent 14N nucleus. The unusual behavior of trimethylsilanecarbonitrile oxide, exhibiting a sharp 13C triplet and a narrow 14N singlet, indicates a dramatic increase in the 14N relaxation time, ascribed to the reduction of the electric field gradient around the 14N nucleus arising from a higher electron density on the adjacent carbon atom. © 1982
Cyclopropyl Building Blocks for Organic Synthesis. Part 125. New Oligocyclic β‐Lactams and β‐Amino Acid Derivatives by Intramolecular Cycloaddition of Bicyclopropylidenyl‐Substituted Nitrones.
No full textCyclopropyl Building Blocks in Organic Synthesis. Part 122. A New Three‐Component Cascade Reaction to Yield 3‐Spirocyclopropanated β‐Lactams.
No full textGoing 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
New Oligocyclic β-Lactams and β-Amino Acid Derivatives by Intramolecular Cycloaddition of Bicyclopropylidenyl-Substituted Nitrones
No full textBicyclopropylidenylalkyl-substituted nitrones 6 and 7 undergo regio- and diastercoselective intramolecular cycloadditions to afford exclusively the ring-fused adducts 8 and 9, respectively. The thermal rearrangement of the cycloadducts 8 and 9 under acidic conditions (TFA) leads to the tricyclic beta-lactams 12 and 14, respectively. Under the reaction conditions, 12 undergoes lactamamide bond cleavage to yield the bicyclic N-trifluoroacetylated beta-amino acid derivative 13
A New Three‐Component Cascade Reaction to Yield 3‐Spirocyclopropanatedβ‐Lactams
No full textA one-pot three-component reaction for the direct conversion of certain alkylhydroxylamine hydrochlorides 8 (alkyl = benzyl, p-methoxybenzyl, benzhydryl, tert-butyl), formaldehyde (9) or an alkyl glyoxylate (10) and bicyclopropylidene (2) to furnish 3-spirocyclopropanated 2-azetidinones 7, 11 has been developed. Microwave heating of mixtures of the three components in the presence of sodium acetate in ethanol for 15-120 min furnished the products 7, 11 in 49-78% yield (7 examples). A new protocol for the oxidative deprotection of the 3-spirocyclopropanated methyl 1-(p-methoxybenzyl)-2-carboxylate 11b-Me provides the beta-lactam building block 17-Me in 90% yield, and the latter can be reprotected and activated with an N-tert-butoxycarbonyl (Boc) group in 82% yield. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
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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