1,720,954 research outputs found
Bis(cyclopropenium)phosphines: Synthesis, Reactivity, and Applications
Get PDFA straightforward route for the preparation of a set of bis(cyclopropenium)-substituted phosphines is reported. Due to their dicationic nature, these ligands depict an excellent π-acceptor character. The effect of the ligand substituent pattern on the catalytic activity of the metal complexes thereof derived is also studied. Whereas sterically demanding biaryl groups directly attached to the phosphorus atom seem to facilitate elementary steps such as the product release from the catalyst, long chain dialkylamino groups on the cyclopropenium units maximize the catalysts solubility and, thus, allow the use of typical apolar solvents such as toluene. Importantly, all new ligands prepared can be easily handled in air. Finally, the impact of the newly prepared dicationic phosphines in hydroarylation reactions is demonstrated. In particular, their use in the synthesis of several naphtho[1,2-b]furanes and naturally occurring naphthalene derivatives such as Calanquinone C is reported
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Synthesis and applications of biscyclopropenium phosphines as ancillary ligands in catalysis
Get PDFThe aim of this thesis was the design of new strong π‐acceptor ligands. In our approach two cyclopropenium substituents were attached to the phosphorus atom of the phosphine in order to introduce enhanced π-acceptor character. These biscyclopropenium phosphines, unlike their polyhalogenated analogues (PF3, P(CF3)3 and PCl3), were air stable. While the variation of the third (non-cationic) substituent attached to the phosphorus of the dicationic phosphine allowed further modification of its electronic properties, the decoration of one cyclopropenium unit with longer aliphatic chains facilitated the solution of the charged species in non-polar solvents like toluene. Furthermore, the BF4- counter-ion of some of the prepared phosphines was exchanged for SbF6- in order to investigate its influence on the reactivity in catalysis later on. Subsequent coordination of these dicationic phosphines to various transition metals afforded the corresponding Au(I), Pt(II), Ir(I) and Ag(I) complexes. The reactivity of the prepared dicationic Au(I)-precatalysts was investigated in the 6-endo-dig cycolisomerization of biphenyl-alkynes with two substituents in internal positions to their corresponding phenanthrene derivatives. After successful optimization, this methodology was applied in the synthesis Calanquinone C. Finally, the substrate scope of the utilized Au(I)-precatalysts was expanded from the synthesis of phenanthrene derivatives to the preparation of naphto-furans.Das Ziel dieser Arbeit war es neue starke π-Akkzeptor Liganden herzustellen. In unserer Herangehensweise wurden zwei Cyclopropenium-Substituenten an das Phosphoratom des hergestellten Phosphins gebunden, um einen verstärkten π-Akkzeptor Charakter einzuführen. Diese synthetisierten Biscyclopropeniumphosphine waren luftstabil im Gegensatz zu ihren polyhalogenierten Analogen (PF3, P(CF3)3 und PCl3). Die Variation des dritten (nicht-kationischen) Substituenten, der an das Phosphoratom des dikationischen Phosphins gebunden ist, erlaubt die Modifikation der elektronischen Eigenschaften der jeweiligen Verbindung. Die Anbringung längerer aliphatischer Ketten an die Cyclopropeniumeinheit ermöglicht die vollständige Lösung des dikationischen Phosphins in nicht-polaren Lösungsmitteln wie Toluol. Außerdem wurde für einige der hergestellten Phosphine das BF4- Gegenion für SbF6- ausgetauscht, um später seinen Einfluss auf die Reakivität in der Katalyse zu untersuchen. Die anschließende Koordinierung dieser dikationischen Phosphine an Übergangsmetalle resultierte in der Isolation der jeweiligen Au(I)-, Pt(II)-, Ir(I)- und Ag(I)- Komplexe. Die Reaktivität der hergestellten Au(I)-präkatalysatoren wurde in der Cycloisomerisierung von Biphenyl-Alkinen mit zwei Substituenten in internen Postionen zu den jeweiligen Phenanthrenderivaten untersucht. Nach erfolgreicher Optimierung wurde diese Methodik in der Synthese von Calanchinon C angewendet. Schließlich wurde der Anwendungsbereich der verwendeten Au(I)-präkatalysatoren von der Synthese von Phenanthrenderivaten zur Herstellung von Naphto-furanen erweitert
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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