1,721,337 research outputs found
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
From enantioconvergent to stereodivergent processes in copper-catalyzed asymmetric allylic alkylation
No full textThe copper-catalyzed asymmetric allylic alkylation (AAA) is one of the most powerful methods to introduce a simple alkyl group in allylic position. Copper is particularly known to induce a high γ-selectivity stemming from a SN2' process. This feature has been mainly applied to the alkylation of linear prochiral substrates leading to the formation of stereogenic centers. In sharp contrast, the use of racemic substrates has been scarcely studied. We will present here that this range of substrates could be interesting reaction partners leading to the development of new valuable resolution processes
Copper(I)-catalyzed asymmetric allylic alkylation
No full textLa substitution allylique est une réaction fondamentale pour la formation de liaison C-C. L'emploi de cuivre permet une version catalytique de cette réaction en présence de réactifs organométalliques. Cette thèse s'est axée sur l'utilisation plus spécifique de réactifs de Grignard (alkyle ou aryle) en présence de ligands chiraux phosphorés, tels que des phosphoramidites ou des phosphines amines. Notre méthodologie a été étendue à des substrats allyliques saturés, atteignant des excès moyens de 78% [ee], et à des oléfines électrophiles plus substituées (des systèmes β-disubstitués), qui ont permis un contrôle asymétrique quasi parfait de >99% [ee]. De plus, les substrats allyliques 1,4 dihalogénés sont de puissants inducteurs γ-spécifiques (pour réactifs alkyles ou aryles, jusqu'à γ :α=100 :1), et produisent des synthons chiraux versatiles avec des excès allant jusqu'à 94% [ee]. Ces derniers ont pu être dérivatisés par des procédés nucléophiles ou électrophiles sans perte de leur pureté chirale initiale
Construction of enantioenriched cyclic compounds via asymmetric allylic alkylation and ring closing metathesis
No full textA new strategy to access highly enantioenriched cyclic compounds was studied using ω-ethylenic allylic substrates through a one-pot asymmetric allylic alkylation and ring-closing metathesis. Such starting compounds can be seen as synthetic equivalents of cyclic allylic substrates
Organocatalytic enantioselective construction of mono- and polycyclic structures by domino reactions
No full textIn this manuscript, we are particularly interested in the formation of chiral mono- and polycyclic compounds by organocatalytic domino reactions. In order to understand better the studied reactivities, some generalities about the activation modes used during this work, aminocatalysis and bifunctional thiourea-type catalysis, are firlsty introduced. Afterwards, a study on the synthesis of chiral γ-butenolides from renewable sources by a direct vinyligous Michael addition of Angelicalactone to enals catalysed by an aminal-pyrrolidine catalyst is reported. In the third part, we focused on the reactivity of acyclic 1,2-diketones in organocatalytic domino transformations. Interesting chiral polysubstituted cyclopentanones are synthesized by domino reactions. Finally, β,γ-unsaturated 1,2 dicarbonyl compounds are involved in organocatalytic domino tranformations as bis-electrophiles with various cyclic 1,3-ketoesters forming interesting chiral polysubstituted bicyclo[3.2.1]octanones
New substrates for the copper-catalyzed enantioselective allylic and propargylic substitutions
No full textL'objectif de cette thèse est d'étudier et de développer de nouveaux substrats dans le cadre de la substitution allylique et propargylique catalysée par le cuivre. A cet égard, une étude systématique a été effectuée sur deux types de substrats et de grandes régio et énantiosélectivités ont été atteintes pour ces transformations. De nouvelles synthèses régio et énantiosélectives de chlorures d'énynyles-1,4, chlorures diènyles-1,4, allènes trisubstitués et alcynes terminaux ont été développées qui représentent une contribution importante pour la synthèse organique asymétrique
Development of new highly efficient amino-organocatalysts and of related methodologies
No full textThe field of aminocatalysis, defined as the aptitude of a primary or secondary amine to catalyze reactions using carbonyls such as ketones or aldehydes, has rapidly evolved in the last ten years. These researches have led to considerable efforts in new catalysts developments. Unfortunately, most of the newly designed organocatalysts remain specific, as for the over-studied Michael addition to nitroolefins. Thus, the development of new catalysts with a broad range of applicability would be of great interest. During this phD, we discovered a new family of catalysts called Aminal PYrrolidine (APY). Based on a maximized steric hindrance and modularity of the catalysts, they afford excellent enantioselectivities on a broad range of different reactions. Furthermore, those catalysts were further applied to new highly challenging reactions. They allowed us to discover unprecedented reactions by applying new Michael acceptors and donors. In addition, by combining different modes of catalytic activation (organometallic and enamine) in a single-pot, a new approach for the generation of complex molecules has been explored
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