1,720,957 research outputs found
Electron paramagnetic resonance spectra of CeO2 catalyst for CO oxidation
No full textThe EPR spectra of freshly prepared CeO2 samples as well as of samples used as a catalyst in the oxidation of CO to CO2 are reported. Attribution of these patterns to oxygen species O-2(-), O-2, O- or to Ce3+ ions is discussed and dynamic phenomena involving these species are described. Bottlenecked systems between conduction electrons and Ce3+ ions are envoked to explain the observation of the Ce3+ EPR spectrum up to temperatures of about 370 K. Oxygen-deficient systems are obtained when the sample is used as a catalyst for CO oxidation in the presence of pyrex or quartz powder as a diluent, showing that the latter can play some role in stabilizing such species
AGING OF FRESH AND USED CA-SR-CUPRATE-BASED CATALYSTS
No full textAn ageing degeneration process was observed in a Ca-Sr-cuprate catalyst, both unused and after use in an NO decomposition reaction. The formation of strongly interacting dipoles (SIDs) by Cu2+ and oxygen ions perturbs the layerlike structure, which is typical of Sr3Cu5O8 species and is also characteristic of the present catalyst when it is fresh. This phenomenon was observed with both unused and used aged samples. Furthermore, in the case of the used catalysts, the degeneration process lead to the disappearance of both the layerlike crystal structure and of the SID systems. However, the samples recover their properties when recalcined
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
La-Ce-Ca perovskites as catalysts for exhaust gas depollution
No full textA series of La1-xCexCoO3+delta perovskite-type catalysts, with x ranging from 0 to 0.20, showed to be quite active for reduction of NO by CO (reaction 1) and for oxidation of CO by air oxygen (reaction 2) at temperatures ranging from 373 to 723 K. Analysis by X-ray diffraction, electron probe microanalysis, temperature-programmed desorption-temperature-programmed reaction and electron paramagnetic resonance, coupled with catalytic activity data, showed that the active sites on these catalysts are very likely localised onto Co ions, which coordinate O-2(-) ions as intermediates for reaction 2, the latter taking place essentially through a suprafacial mechanism. For reaction 1, taking place through both a suprafacial and an intrafacial mechanism, the Co-based sites play also an additional role, favouring the electron transfer from site to site and so enhancing the transfer of oxygen species from surface to bulk and vice versa. Ce ions seem to act only as a stabiliser of O-2(-) ions, helping in keeping them at the catalyst surface
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
LA-EU CUPRATES AS CATALYSTS FOR PHENOL OXIDATION
No full textA set of six La2-xEuxCuO4+δ oxides were prepared, with x ranging from 0 to 1.33. They were characterized by various techniques, including, in addition to chemical analysis, surface area and porosity measurements, XRD, SEM-EPMA, EPR, and electric resistivity measurements. All the oxides proved to be good catalysts for the oxidation of phenol with hydrogen peroxide and, under proper reaction conditions, a high selectivity to p-benzoquinone was obtained with each solid. Different selectivities to hydroquinone or to catechol were also obtained, depending on the value of x. The best catalytic performance was obtained in any case at relatively low temperatures (≤70°C). Increasing the temperature beyond 70°C led only to fast wasting of hydrogen peroxide and to faster oxidation of the products to CO2, without any advantage on yield to the desired products. A competition exists between the reactants for adsorption on the same surface sites. Phenol is adsorbed very strongly, although it can be displaced rather easily by hydrogen peroxide. The results of the characterization analysis indicate that catalytic activity is very probably connected with the presence of Cu ions forming anisotropic quantum spin fluid (AQSF) or glass (AQSG) structures. When the catalyst becomes inactive, AQSF and AQSG disappear and strongly oxygen-deficient copper clusters form
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