1,720,977 research outputs found
Investigation of thermal effects on heterogeneous exothermic reactions and their impact on kinetics studies
No full textExperiments and modelling were performed to investigate CO oxidation over a Pd-Rh monolith. We focused on thermal effects and hysteresis, to validate by modelling a thermal explanation of the results. Different feed composition (0.07-4% vol. CO) and heating rates (0.5-5 degrees C/min) have been used to reproduce both ignition and extinction stages, up to 300 degrees C, thus measuring the catalyst activity under transient conditions. The heating rate plays a marginal role in producing hysteresis, whereas the reactants concentration appears the real cause, because of its effect on the rate of heat production. A significant increase of the monolith temperature compared to the inlet gas is measured after ignition. The local overheating of the catalyst surface explains the hysteresis observed. When the reactor thermal control is based on the internal temperature, instead of the inlet one, the hysteresis appears dramatically different. The choice of the temperature used to control the oven, and report the activity results, may induce very misleading indications, including inexistent multiple steady-states. A model accounting for the thermal dynamics of the solid predicts the observed hysteresis, even with simple rate equations. That supports the thermal explanation for the direct hysteresis. The estimated activation energy is quite reasonable and compare well with literature. Preexponential factors accommodate for the weakening of the adiabatic channel critical assumption, less and less realistic as the reaction heat increases. The overall conclusion is that the local temperature can vary widely, in time and space, and any kinetic study not accounting for a precise knowledge of that will inevitably produce poorly representative parameter estimates. The limitation can be overcome with spatially-resolved measurements
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
CuO/La0.5Sr0.5CoO3 nanocomposites in TWC
No full textIn this contribution several La0.5Sr0.5CoO3 based nanocomposites have been prepared and tested for application as Three-Ways Catalysts (TWC), aiming to develop Platinum Group Metal (PGM)-free catalysts. To reach this objective we designed and realized nanocomposites in which active CuO nanoparticles are deposited on La0.5Sr0.5CoO3. This perovskite is active in oxidation and is characterized by high oxygen anion mobility; copper is active in reduction: catalytic bifunctionality is thus built-in via a tailor-made and controlled nano-composition. The supporting perovskite was prepared following the "citrate" route. The deposition was carried out by means of the Ammonium-Driving-Deposition precipitation (ADP) to highly disperse CuO on La0.5Sr0.5CoO3. In a precedent paper we focused on nanocomposites obtained using LaCoO3 as a support because this perovskite is active in oxidation. Sr-doped LaCoO3, in addition, is characterized by a more relevant presence of oxygen vacancies and mobility and the desire of comparing these systems is to better investigate the different role played by all these aspects on the interaction between highly dispersed CuO nanoparticles and perovskite and on the catalytic activity. The copper amount on the nanocomposite surface does not increase linearly with the nominal composition reaching a plateau: migration below the surface is observed for the nanocomposite with 30 wt.% of Cu. The surface composition of the perovskite is modified by the copper deposition which causes the decrease of A-cations surface segregation and enhances the presence of cobalt suggesting a certain synergy; the reducibility of the perovskite is also greatly favored by deposition. Both model reactions (CO oxidation and CO assisted NO reduction) and reactions with a synthetic automotive exhaust mixture, including 10% steam, and oxygen, were carried out. We compared the results with the ones obtained in similar reactions with CuO/LaCoO3. Different interaction and synergy were observed with respect to CuO/La0.5Sr0.5CoO3. Sr-doping, in fact, enhances oxygen mobility affecting the reducing character of the nanodispersed CuO and thus the reactivity under different conditions. The deposition of copper oxide significantly increases the activity of the nanocomposites in CO oxidation (about 100% conversion at 200 degrees C) and in CO + NO (50% conversion at 250 degrees C, more than 80% at 400 degrees C) reactions. When compared with the corresponding CuO/LaCoO3, the more significant difference has been observed in nanocomposites poorer in CuO, which became highly active at lower temperature. On simulated gasoline engine exhaust the nanocomposites always improve the oxidation activity compared to the parent perovskite, while the NO reduction is quantitative in the absence of O-2. The activity on a mixture simulating actual gasoline-engine exhaust proves that ADP synthesis provides materials with a higher activity compared to wet impregnation (WI), thanks to a higher dispersion of copper. NO reduction in fuel-rich conditions is activated at approx. 300 degrees C, (400 degrees C on WI sample), when significant amount of O-2 is still in the mixture. This feature completes the good performance in absence of noble critical metals that are promising facts to develop PGM-free catalysts for the automotive industry
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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