1,720,960 research outputs found
Characterization of surface-oxides on char under periodically changing oxidation/desorption conditions
No full textA novel experimental method based on periodic swinging of oxidation/desorption reaction stages is used to investigate the formation and release of surface oxides on carbon under mild oxidation conditions. The chemical nature of the carbon-oxygen complex and the key mechanistic features of the interaction between solid carbon and oxygen are assessed by continuous monitoring of CO/CO2 release during the experiments and by probing - via XPS - the chemical nature of oxygen moieties at different stages of the experiments. Sub-bituminous char is used as carbon substrate. The proposed technique turns out to be a simple though effective method to assess the nature and extent of surface oxides formed under different reaction conditions. Results show that oxygen is extensively chemisorbed on carbon as epoxy moieties below ~750 K. At higher temperatures, isomerization into “edge” oxides (ether-hydroxyl and carbonyl-carboxyl functionalities) takes place, followed by oxide decomposition and desorption as CO and CO2. Estimates of the oxygen chemisorption rate as a function of temperature are given. The study provides new insights into the extent and chemical nature of surface oxides on carbons, that represent one key to their successful application in several areas of energy conversion and storage. Oxides affect surface physico-chemical (polarity, wettability) and electrical (capacitance, resistivity) properties, relevant to application of carbons in batteries, supercapacitors and fuel cells. Moreover, understanding surface oxides on carbon is helpful in designing novel concepts of energy conversion from carbon through chemical looping, transient operation of stationary combustors, synthesis of carbon-based catalysts, beneficiation of ash
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
The influence of temperature on the nature and stability of surface-oxides formed by oxidation of char
No full textA coal char has been oxidized isothermally at temperatures comprised between 300 and 1073 K. The pre-oxidized chars have been subjected to Temperature Programmed Desorption (TPD) and to core-level high-resolution X-ray photoelectron spectroscopy (XPS) analysis using Synchrotron radiation to infer the nature of the carbon oxides that populate the surface and their evolution throughout thermochemical processing. For low oxygen coverages and mild oxidation temperatures the prevailing carbon-oxygen moieties are epoxy. Raising the oxidation temperature up to ~723K the edge carbon oxygen complexes (ether-hydroxyl and carbonyl-carboxyl) increase. The amounts of CO + CO2 desorbed during TPD also increase with temperature and duration of oxidation for relatively mild oxidative treatments (temperature below ~723K). Upon further increase of the oxidation temperature the amount of CO + CO2 decrease and the ratio of CO/CO2 increases remarkably. Altogether, results suggest the existence of a strong link between a remarkable shift of surface oxides from epoxy to ether/carbonyl and the desorption of CO and CO2. Moreover, the CO/CO2 ratio during desorption can be well correlated with the relative abundance and stability of epoxy moieties with respect to the “edge” oxides. Results are analyzed in the frame of a semi-lumped kinetic model of carbon oxidation with a focus on the role and nature of surface oxides as intermediates in carbon gasification reactions
The Influence of Mineral Matter on X-Ray Photoelectron Spectroscopy Characterization of Surface Oxides on Carbon
No full textThe chemical structure of coal is very composite, consisting of a heterogeneous carbonaceous matrix with variable degrees of “turbostratic” order and the inclusion and/or exclusion of mineral matter (ash). The formation of surface oxides on carbon has long been recognized as a key to understanding many chemical and physical properties of carbon materials relevant to their consolidated or emerging applications. The extent and nature of surface oxides can effectively be assessed by high-resolution X-ray photoelectron spectroscopy (XPS), which provides excellent insight into the functional nature of C-O moieties. However, the XPS analysis of ash-bearing carbons may be biased by the interfering effects of inorganics with the most relevant spectral ranges, namely the core levels O1s and C1s. The effect of ash components on the spectroscopic characterization of carbon is scrutinized here with reference to a sub-bituminous coal characterized by a fairly large ash content. The coal is subjected to different treatments, including devolatilization, milling, and oxidation. A synthetic carbon (Carboxen) is used as a reference sample for the correct assignment of the carbon–oxygen functionalities in the core-level XPS spectra (C1s and O1s) in the absence of mineral matter. On the opposite side, fly ash from an industrial coal boiler is analyzed to investigate the effects of mineral matter. It is shown that the establishment of non-uniform charging of the sample induced by ash provides a key to the interpretation of the XPS spectra of ash-bearing carbon samples. The positive charge on the surface, referred to as the charging effect, brings about a shift of the core-level binding energies towards higher values. Grinding of the samples or partial combustion emphasizes the charging effect. XPS analysis of the fly ash, where carbon is largely consumed and dispersed in the inorganic matter, confirms that charging arises from non-conductive aluminosilicates. These effects may induce remarkable changes in carbon and oxygen peak shapes and need to be accounted for to obtain correct interpretations of the XPS spectra of ash-rich carbonaceous fuels
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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