1,720,961 research outputs found
Low-temperature Pd/FER NOx adsorbers: Operando FT-IR spectroscopy and performance analysis
Full text linkA Pd-doped FER zeolite sample is synthesized and investigated for potential use in the low-temperature NOx adsorption. The catalyst is characterized by BET, XRD, TEM, NaCl titration and by in-situ FT-IR spectroscopy following adsorption of CO, NH3 and NO for the characterization of the Pd sites. Over the calcined sample, Pd is present mainly as PdOx clusters/particles; near 13 % of Pd is present in the form of isolated ions. The NOx adsorption / desorption performances at low temperature are investigated by microreactor studies and operando FT-IR upon NO/O2 adsorption followed by TPD under relevant operating conditions, i.e. in the presence of water and carbon dioxide. It is found that NO adsorbs in the form of Pd nitrosyls (hydrated and anhydrous) and nitrates; near 59 μmol/gcat of NOx could be adsorbed, corresponding to a NO/Pd ratio near 0.6. Upon heating, nitrosyls decompose and transform into anhydrous species leading to NO desorption in the low-T region (below 200 °C) and at higher temperature, with maximum near 370 °C. The presence of CO negatively affects the NOx storage capacity, due to a competition of CO and NO over the Pd storage sites
NO adsorption/desorption pathways over Pd/SSZ-13 low temperature NOx adsorbers investigated by operando FT-IR spectroscopy and microreactor study
Full text linkIn this study a Pd-doped SSZ-13 zeolite sample is synthesized, characterized and evaluated for potential use in the low-temperature NOx adsorption. TEM/HR-TEM and in-situ CO/NO adsorptions followed by FT-IR spectroscopy are used to gain information on the nature and accessibility of the Pd sites. It is found that over the calcined sample Pd is present as isolated Pd+ and Pd2+ cations formed by ion exchange with the Bronsted acid sites of the zeolite, and as Pd+ and Pd2+ species belonging to PdOx particles on the external surface of the zeolite. Isolated Pd2+ ions prevail on the calcined fresh sample. The NOx adsorption/desorption performances, investigated by microreactor studies and operando FT-IR under relevant operating conditions, indicate that significant amounts of NO are stored on the catalyst (i.e. ca. 80-95 & mu;mol/gcat of NOx in the temperature range 50-150 degrees C) which suggests the participation in the NOx uptake of both isolated Pdn+ sites and PdOx particles. NO is adsorbed as nitrosyls (anhydrous and hydrated) over both Pd2+ and Pd+; at low temperatures the formation of nitrates is also observed. The NO uptake as nitrosyls occurs with evolution of NO2 according with a NO storage mechanism which implies (i) the initial adsorption of NO on Pd2+, followed by (ii) the reduction of Pd2+ to Pd+ by NO accompanied by NO2 release and eventually (iii) the adsorption of NO on Pd+. The suggested interconversion of Pd2+ into Pd+ during NO adsorption is herein discussed based on FT-IR evidences. The stored NOx species are decomposed upon heating; nitrates are responsible for low temperature NOx desorption (below 200 degrees C), whereas nitrosyls show much higher stability and lead to a high temperature NO desorption (above 200 degrees C). The presence of NO2 in the feed stream increases the NOx adsorption capacity and results in the formation of mainly surface/ bulk nitrates and nitro-compounds at the expense of nitrosyls
An Assessment of Zeolite Framework Effect for Low-Temperature NOX Adsorbers
Full text linkPd-promoted zeolites (Y, ZSM-5, FER, SSZ-13) were prepared and characterized to analyze their properties as low-temperature NOx adsorbers. The samples were investigated by BET and XRD and by in situ FT-IR spectroscopy of CO and NO adsorption to probe the Pd sites and the nature of the adsorbed NOx species. The NOx adsorption/desorption performances at low temperatures were examined by microreactor measurements upon NO/O-2 adsorption followed by TPD in the presence of water and carbon dioxide. It was enlightened that: (i) the zeolite framework influences the Pd dispersion: the smaller the zeolite cage, the higher the Pd dispersion, irrespective of the Si/Al ratio. Accordingly, the following Pd dispersion order has been observed, inversely to the zeolite cage size: Pd/SSZ-13 > Pd/ZSM-5 similar to Pd/FER >> Pd/Y; (ii) Pd is present as isolated Pdn+ species and in PdOx particles; (iii) the Pd dispersion governs the NOx storage capacity: the smaller the zeolite cage, the higher the Pd dispersion and the storage capacity; (iv) NO adsorbs mainly in the form of Pd nitrosyls and nitrates; (v) NO desorption occurs both at a temperature below 200 & DEG;C and in a high-temperature range (near 350 & DEG;C)
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
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