1,721,295 research outputs found
Liquidi ionici e fluidi supercritici.
No full textLa realizzazione di nuovi processi sostenibili dal punto di vista ambientale deve essere per i chimici moderni il principale obiettivo. In questo contesto si colloca la ricerca di nuovi solventi nei quali sia possibile ottenere processi efficienti e selettivi, anche di tipo industriale. Eccellenti candidati per questo scopo sono i liquidi ionici a temperatura ambiente (RTILs) e i fluidi supercritici (ScFs)
Vanadium catalyzed oxidation with hydrogen peroxide
Full text linkVanadium peroxides are known as very effective oxidants af different organic and inorganic substrates. In this short account reactivity, structural and mechanistic studies concerning the behaviour of peroxovanadates toward a number of different substrates are collected. Homogeneous and two-phases systems are presented, in addition, interesting synthetic results obtained with the use of ionic liquids as reaction media are also presented
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
Mathematical model for the plastic flow of a polycrystalline material medium
No full textLagos, M (Lagos, Miguel)1; Conte, V (Conte, Victor)1. Reprint Address: Lagos, M (reprint author), Univ Talca, Fac Ingn, Campus Los Niches, Curico, Chile.Using a model that gives a realistic description of the plastic flow of polycrystals with refined grain size resulted in discrepancies being found in the postulates of the mathematical theory of plasticity. The new proposed time-dependent mathematical formulation predicts finite ductility, temperature-dependent work strengthening and creep, in remarkable agreement with experiment. Insight is gained into the Bauschinger effect and necking instability. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
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
Bromination of alkynes in ionic liquids - A kinetic investigation
No full textThe kinetic behaviour and the product distributions of brominations of several arylalkynes with Br(2) in the room-temperature ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF(6)] and 1-butyl-3-methylimidazolium. bromide [bmim]Br, have been investigated at different temperatures. In [bmim]Br, alkynes stereospecifically gave the anti addition products, the reactions following a second-order rate law. In [bmim][PF(6)], mixtures of syn and anti addition products were obtained, and the reactions followed a second- or third-order rate law, depending on the structure of the alkyne and the concentration of Br(2). The data obtained for the reactions in [bmim]Br are interpreted on the basis of a mechanism involving a product- and a rate-determining nucleophilic attack by bromide on the alkyne-Br(2) pi complex. The data relating to the electrophilic addition in [bmim][PF6] are explained in terms of the initial formation of a 1:1 alkyne-Br(2) pi complex, the ionisation of which, probably catalysed either by a second halogen molecule or by the imidazolium cation, gives a bromirenium (or beta-bromovinyl cation) Br(-) or [Br(3)](-) intermediate. Such intermediates then collapse to give the corresponding dibromo adduct(s). The kinetic constants and the activation parameters for the reaction in [bmim]Br are compared with those relating to the second-order reaction of the same alkynes with tetrabutylammonium tribromide ([NBu(4)][Br(3)]) in 1,2-dichloroethane (DCE). On the basis of the kinetic data, a significant role for solvent viscosity in determining the reaction rate may be envisaged. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
Possible role of vanadium in biological oxidations. The oxidation of uracil by hydrogen peroxide in acidic aqueous solution
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