1,720,967 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
Natural or nature-inspired heterocycles : library of quinolones and cyclotripeptides in the oxepine series
No full textLa synthèse d’hétérocycles fonctionnalisés est particulièrement importante dans le but de proposer de nouvelles molécules bioactives. A partir du pharmacophore 4-hydroxyquinoléine, une fonctionnalisation multiple et divergente a été mise au point. Ce squelette a en effet été « programmé » en un substrat compatible avec une fonctionnalisation C-H séquentielle et sélective. Tout d’abord, la fonctionnalisation en C-8 a été réalisée avec notamment une réaction d’amidation et de méthylation. Ensuite, un système catalytique a entièrement été développé afin de permettre l’arylation sélective en C-2. Après réduction du N-oxyde, un réarrangement de Fries a été utilisé afin d’induire la migration du groupement carbamate de la fonction hydroxyle en C-4 à la position C-3, tout en libérant la fonction hydroxyle en C-4. Cette dernière a ensuite été utilisée comme groupement directeur pour la fonctionnalisation en C-5.Une librairie de plus de cent composés a été créée, dont certains démontrant une puissante activité anti-malarique contre le parasite Plasmodium falciparum.Dans un second temps, notre attention s’est portée sur la synthèse totale de cyclotripeptides hétérocycliques de la famille de la janoxépine, qui possèdent des propriétés biologiques intéressantes. A partir d’acides aminés commerciaux, une stratégie de synthèse mettant en jeu un vinylcyclopropane et une amidine cyclique a été imaginée et une nouvelle méthodologie a été développée pour leur préparation. Ces deux fragments ont ensuite été engagés dans une cascade réactionnelle composée de deux couplages peptidiques et du réarrangement d’oxa-Cope, permettant notamment de réaliser la synthèse formelle de la janoxépine. La synthèse de plusieurs dérivés de cette famille en utilisant cette nouvelle méthodologie sera réalisée par la suite.The synthesis of functionalized heterocycles is particularly important to find new bioactive molecules. Considering the high medicinal potential of the 4-hydroxyquinoline ring, we first established a multiple and divergent functionalization of this pharmacophore. It was “programmed” to obtain a suitable substrate for successive and selective C-H functionalizations of four positions. The C-H functionalization at C-8 was performed by methylation and amidation. Then, a new catalytic system was entirely developed to tackle selective C-2 arylation. After N-oxide cleavage, the protecting carbamate group previously installed on the 4-OH moiety was used to functionalize position C-3 through a Fries rearrangement releasing the 4-OH moiety at the same time, which was then used as a directing group to further functionalize at position C-5.A library of a hundred compounds was built and some of them showed potent antimalarial activity against the parasite Plasmodium falciparum.Then, we focused on the total synthesis of natural cyclotripetides in the janoxepin series, which showed interesting biological activities. Nevertheless, only one total synthesis is described in the literature. Starting from commercially available amino acids, we envisioned a new synthetic strategy involving the coupling between a vinylcyclopropane and a cyclic amidine, both prepared after the development of new methodologies. They were then engaged in a cascade reaction of two peptide couplings and the oxa-Cope rearrangement allowing us to achieve the formal synthesis of janoxepin. This work is still processing with the synthesis of several derivatives and the development of a new route to generate the corresponding oxepine ring
Synthèse de composés hétérocycliques naturels ou d’inspiration naturelle : librairies de quinolones et cyclotripeptides à noyau oxépine
No full textThe synthesis of functionalized heterocycles is particularly important to find new bioactive molecules. Considering the high medicinal potential of the 4-hydroxyquinoline ring, we first established a multiple and divergent functionalization of this pharmacophore. It was “programmed” to obtain a suitable substrate for successive and selective C-H functionalizations of four positions. The C-H functionalization at C-8 was performed by methylation and amidation. Then, a new catalytic system was entirely developed to tackle selective C-2 arylation. After N-oxide cleavage, the protecting carbamate group previously installed on the 4-OH moiety was used to functionalize position C-3 through a Fries rearrangement releasing the 4-OH moiety at the same time, which was then used as a directing group to further functionalize at position C-5.A library of a hundred compounds was built and some of them showed potent antimalarial activity against the parasite Plasmodium falciparum.Then, we focused on the total synthesis of natural cyclotripetides in the janoxepin series, which showed interesting biological activities. Nevertheless, only one total synthesis is described in the literature. Starting from commercially available amino acids, we envisioned a new synthetic strategy involving the coupling between a vinylcyclopropane and a cyclic amidine, both prepared after the development of new methodologies. They were then engaged in a cascade reaction of two peptide couplings and the oxa-Cope rearrangement allowing us to achieve the formal synthesis of janoxepin. This work is still processing with the synthesis of several derivatives and the development of a new route to generate the corresponding oxepine ring.La synthèse d’hétérocycles fonctionnalisés est particulièrement importante dans le but de proposer de nouvelles molécules bioactives. A partir du pharmacophore 4-hydroxyquinoléine, une fonctionnalisation multiple et divergente a été mise au point. Ce squelette a en effet été « programmé » en un substrat compatible avec une fonctionnalisation C-H séquentielle et sélective. Tout d’abord, la fonctionnalisation en C-8 a été réalisée avec notamment une réaction d’amidation et de méthylation. Ensuite, un système catalytique a entièrement été développé afin de permettre l’arylation sélective en C-2. Après réduction du N-oxyde, un réarrangement de Fries a été utilisé afin d’induire la migration du groupement carbamate de la fonction hydroxyle en C-4 à la position C-3, tout en libérant la fonction hydroxyle en C-4. Cette dernière a ensuite été utilisée comme groupement directeur pour la fonctionnalisation en C-5.Une librairie de plus de cent composés a été créée, dont certains démontrant une puissante activité anti-malarique contre le parasite Plasmodium falciparum.Dans un second temps, notre attention s’est portée sur la synthèse totale de cyclotripeptides hétérocycliques de la famille de la janoxépine, qui possèdent des propriétés biologiques intéressantes. A partir d’acides aminés commerciaux, une stratégie de synthèse mettant en jeu un vinylcyclopropane et une amidine cyclique a été imaginée et une nouvelle méthodologie a été développée pour leur préparation. Ces deux fragments ont ensuite été engagés dans une cascade réactionnelle composée de deux couplages peptidiques et du réarrangement d’oxa-Cope, permettant notamment de réaliser la synthèse formelle de la janoxépine. La synthèse de plusieurs dérivés de cette famille en utilisant cette nouvelle méthodologie sera réalisée par la suite
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
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