1,721,008 research outputs found
Catalysis by metal nanoparticles supported on functional organic polymers
No full textThe preparation and catalytic applications of dispersed metal catalysts supported on organic functional polymers are presented. The advantages of these catalysts, such as the easy tailoring with respect to the nature of the used support, the "nanoscale" size control of metal crystallites by the polymer framework, the high accessibility and consequent catalytic activity in a proper liquid or liquid-vapor reaction systems are stressed. Various proposed catalytic processes making use of these materials are presented and evaluated, including multifunctional catalysis, e.g. redox-acid. Interesting peculiar aspects such as the enhancement of the hydrogenation rate by nitrogen containing moieties anchored to the polymer backbone are emphasised. When suitable, a comparison with catalysts based on inorganic supports is given
Macromolecule-palladium complexes as catalysts for the synthesis of hydrogen peroxide
No full textCommercial resin supports containing aromatic nitrogen bases as functional groups have been used as macromolecular ligands for palladium(II), thus yielding insoluble macromolecule-metal complexes. Preliminary tests were run with these materials as catalysts for the preparation of hydrogen peroxide from carbon monoxide, oxygen, and water. Pretreatment of the catalyst with an organic solvent was found to be necessary in order to achieve catalytic activity. The best results (turnover number = 6) were obtained with pretreatment in dioxane
Catalysis by metal nanoparticles supported on functionalized polymers
No full textThis contribution is a brief review dealing with metal catalysts prepared on functionalized polymers. The following topics will be touched: i) preparation and properties of metal catalysts based on functionalized polymers; ii) methods for the characterization of these catalysts; iii) effect of mass transport phenomena on the overall rate of a process and on the selectivity in complex reaction systems; iv) deactivation of the polymer-based catalysts; v) applications - selective hydrogenations, one-pot synthesis of methyl isobutyl ketone, removal of nitrates from water. A particular attention is paid to the comparison of polymer-based metal catalysts with those supported on inorganic materials. The mechanical and chemical stability vs. the activity and the cost of the catalysts are discussed. The emphasis will be put on the main advantages of polymer-based catalysts, stemming from easily controlled micro- or macroporous nature and hydrophobic-hydrophilic properties, from the possibility to attach various special functional groups, precise and well defined metal loading and metal distribution in the final catalyst. In the part describing the methods for the characterization of metal polymer-based catalysts, the techniques as evaluation of the mobility on the basis of electron spin resonance and pulse field gradient spin echo NMR will be discussed
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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