1,721,024 research outputs found
Incorporation of transition-metal complexes in functionalized mesoporous silica and their activity toward the oxidation of aromatic amines
No full textThe highly ordered mesoporous material HISiO2 was prepared at room temperature and low pH utilizing a high concentration of nonionic surfactant to achieve a hexagonal ordered phase with a pore size of similar to3.5 nm. The grafted amino ligand was covalently bonded to the internal pore surface of HISiO2 through a silanation procedure. Thereby, immobilized transition-metal-aquo complexes such as Mn-II-aquo (I), Cu-II-aquo (II), Co-II-aquo (III), and Zn-II-aquo (IV) were coordinated to the supported wall without impregnation on the surface. Diffuse reflectance spectroscopy (DRS) and electron paramagnetic resonance (EPR) studies observed that a proportion of the Mn-II complex was oxidized to a higher oxidation state, particularly Mn-IV. The kinetics and mechanism of redox reactions between o-aminophenol, o-phenylenediamine, and p-pheneylenediamine and the incorporated transition-metal-aquo-propylamine complexes have been investigated. The oxidation products of the amines have been monitored by UV-vis spectroscopy. The reaction follows first-order kinetics, and the rate constant of the oxidation of amines decreases in the following order: Mn-IV/Mn-II --> Cu-II --> Con --> Zn-II. This trend is attributed to the reduction potential of the metal ions in the reaction medium. The most obvious feature of the oxidation reaction of amines with complexes III and IV is that there is a well-defined induction time, whose rate depends on the reactivity and the initial concentration of these amines, prior to a rapid growth in the production of the oxidation product of amines. The experimental results indicate that the outer-sphere mechanism is probably followed in this redox system. Extensive studies of the transition-metal complexes on HISiO2 have been conducted before and after the redox reaction by a wide variety of characterization techniques which include powder X-ray diffraction, DRS, the Bnxnauer-Emmett-Teller method for nitrogen adsorption and surface area measurements, NMR, EPR, and IR
Kinetics and mechanism of the sorption of some aromatic amines onto amberlite IRA-904 anion-exchange resin
No full textThe kinetics of the sorption of aromatic amines such as o-aminophenol (o-AP), o-phenylenediamine (o-PDA), and phenylenediamine (p-PDA) onto Amberlite anion-exchange resin in chloride form was investigated in batch experiments spectrophotometrically at different temperatures. The sorption rate is zero order in all amines sorbed, increasing directly in the order: p-PDA < o-PDA < o-AP, which corresponds to the sequence of the electrostatic contributions to the sorption interactions. The attainment of sorption equilibrium of aromatic amines is seen to be similar. The diffusion coefficients (D) have been calculated by using Fick's equation from the second portions of the sorption/desorption curves; D values ranged from 0.7 to 2.8 x 10(-9) cm(2)/s. These results, reflecting the diffusion mechanism, were ascribed to intraparticle diffusion. Arrhenius parameters for the diffusion process and the thermodynamic quantities for the process of equilibrium sorption have been estimated. The effect of a chemical oxidation reaction on intraparticle diffusion was investigated by measuring the intraparticle diffusion of amines during the redox reaction
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
Characteristic mechanisms of the homogeneous and heterogeneous oxidation of aromatic amines with transition metal-oxalate complexes
No full textThe oxidation-reduction reactions of aromatic amines {o-aminophenol (o-AP), o-phenylenediamine (o-PDA) and p-phenylenediamine (p-PDA)} with Co(III)-, Mn(III)-, and Cu(II)-oxalate complexes have been investigated in homogeneous and heterogeneous systems. The kinetics of the redox reaction of both systems have been studied spectrophotometrically. The redox products were identified and characterised by diffuse reflectance spectroscopy (DRS), and mass spectrometry. The redox reactions follow first-order kinetics with respect to each of the reactants and first order in [amines] in homogeneous and heterogeneous (supported complexes on Amberlite IRA 904 anion-exchange resin) phases, respectively. However, the specific oxidation rate of the amines is found to follow the order, p-PDA > o-AP > o-PDA. The effect of the oxalate anion on the reaction rate of both systems was examined. There is a significant difference in the behaviour of the oxidation of o-AP and o-, p-PDA with all the metal complexes in both systems. Moreover, the oxidation of o-AP and o-, p-PDA appears to follow the outer- and inner-sphere mechanistic classification, respectively
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