1,720,994 research outputs found
Liquid phase hydroformylation of ring substituted styrenes catalyzed by Rh-B and Rh-Zn-B systems supported on silica
No full textRhodium based catalysts supported on silica have been prepared by low temperature reduction of the preadsorbed salts with respectively NaBH4 and Zn(BH4)(2). The catalyst surfaces were characterized by ESCA, XRD and FT-IR spectroscopy, A remarkable boron and zinc surface enrichment resulted from ESCA data in both catalysts. From the FT-IR data it appeared that the bridging CO chemisorption is substantially suppressed, as was observed by others in similar systems, probably because boron and zinc oxide molecules cover most of the catalyst surface blocking the multicenter rhodium sites. Both catalysts are active in the liquid phase ring substituted styrenes hydroformylation. The reaction resulted was truly heterogeneous because no leaching of catalyst was observed. The chemoselectivity was always very high, close to 100%, and regioselectivity appeared to be controlled by the nature of the ring substituents. Evidences were found that the heterogeneous reaction proceeds through elementary steps similar to those proposed for the homogeneous process
Highly selective vapor phase propene hydroformilation catalyzed by Rh/B and Rh-Co/B systems on silica
No full textBifunctional catalysts from pillared clays: Vapour phase conversion of propene to acetone catalyzed by iron and ruthenium containing aluminum pillared bentonites.
No full textCatalysis by Rh/B system: part 2 Higly regioselective vapour phase hydroformylation of propene at atmospheric pressure on Rh/B on silica and silica-alumina
No full textA Rh/B catalyst prepared by reducing rhodium trichloride supported on silica and silica-alumina with NaBH4 at low temperature is used after thermal treatments in the vapour phase, propene hydroformylation in a flow reactor at atmospheric pressure. A good regioselectivity toward normal isomers, that remains constant at increasing temperatures, is detected (S(L) = 0.88). The surface composition of silica-alumina catalysts is apparently not affected by thermal treatments whether in argon or in CO/H-2 or in hydroformylation mixture flow. The geometrical arrangements of the active sites appear to play an important role in controlling the regioselectivity of the catalytic system
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
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