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Electrochemical reduction of 1,1-diaryl-substituted ethenes in dimethylformamide
No full textThe cathodic behaviour of 1,1-diaryl-substituted ethenes (Ar)PhC=CH 2 (where Ar = phenyl-2-naphthyl-, 2-pyridyl-, 2-thienyl-, 2-furyl-) at a Hg cathode in N,N-dimethylformamide (DMF) and 0.1 mol dm-3 tetraethylammonium tetrafluoroborate (TEAF), was investigated by cyclic voltammetry and controlled potential electrolysis experiments. In cyclic voltammetry, at a potential scan rate of 0.2 V s-1 all substrates showed an irreversible reduction peak [(Ep.c) between -2.27 and -2.54 V vs. saturated calomel electrode (SCE)]. Controlled potential coulometries indicated that the apparent charge number of the process involved ranges from 1 to 2. The reduction products were characterised as (Ar)PhCH-Me (1-aryl-1-phenylethanes) and (Ar)PhCH-[CH2]2-CHPh(Ar) (1,4-diaryl-1,4-diphenylbutanes). The charge number of the process and the ratio between the two different reduction products depended strongly on the structure and concentration of the substrate. Exhaustive electrolyses performed in the presence of variable amounts of D2O or in [2H 7]DMF allowed us to suggest that two distinct pathways are involved in the reduction process, leading to the monomeric and dimeric product, respectively. Hypotheses on the nature of the two reduction mechanisms are discusse
Electron paramagnetic resonance studies and effects of vanadium in Saccharomyces cerevisiae
No full textVanadium uptake by whole cells and isolated cell walls of the yeast Saccharomyces cerevisiae was studied. When orthovanadate was added to wild-type S. cerevisiae cells growing in rich medium, growth was inhibited as a function of the VO4(3-) concentration and the growth was completely arrested at a concentration of 20 mM of VO4(3-) in YEPD. Electron paramagnetic resonance (EPR) spectroscopy was used to obtain structural and dynamic information about the cell-associated paramagnetic vanadyl ion. The presence of EPR signals indicated that vanadate was reduced by whole cells to the vanadyl ion. On the contrary, no EPR signals were detected after interaction of vanadate with isolated cell walls. A 'mobile' and an 'immobile' species associated in cells with small chelates and with macromolecular sites, respectively, were identified. The value of rational correlation time tau r indicated the relative motional freedom at the macromolecular site. A strongly 'immobilized' vanadyl species bound to polar sites mainly through coulombic attractions was detected after interaction of VO2+ ions with isolated cell walls
Solubility of nitric oxide (NO) in lipid aggregates as monitored by nuclear magnetic resonance
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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
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
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