1,721,081 research outputs found
Electrochemical Engineering aspects of a direct borohydride fuel cell
No full textFuel cells (FCs) are clean power sources for both large-scale and portable applications, as they provide a viable method to convert the chemical energy of fuel directly into electrical energy. The most developed FC is the H2ǁO2 system, which uses hydrogen as fuel. However, issues have been observed with the use of hydrogen, such as sourcing, the safety of handling and storage problems. Direct borohydride fuel cells (DBFCs) are liquid FCs that address some of these issues. They are composed of both BH4 - fuel, which oxidises at the anode, and hydrogen peroxide (or O2), which reduces at the cathode. Their many advantages, such as their high theoretical specific energy (up to 17 kW h kg-1) and high theoretical cell voltage (up to 3.02 V), have attracted increasing interest. Borohydride is also available in a solid state (sodium borohydride, NaBH4) or as an aqueous electrolyte up to 30 weight percent (wt.%), where it remains unchanged in a strong alkaline solution with a half-life of around 270 days at pH 13.9 (25 o C). Moreover, the final product of the borohydride oxidation reaction (BOR) is metaborate (NaBO2), which is not harmful to the environment and can be reused to produce sodium borohydride again. Finally, borohydride FCs can operate under ambient conditions and in an air-free environment, which makes them more convenient for portable and anaerobic applications (such as in space and underwater). The main challenges to their commercialisation, however, are the selectivity of the anode catalysts and their substrate materials. Many publications have investigated noble metals (e.g. platinum, gold, palladium, etc.) as candidate materials, but none have found an anode catalyst able to meet the needs of both high catalytic activity towards BH4 - oxidation and low activity towards its hydrolysis. Experimentally, Pt catalysts have shown a higher activity rate (by a factor of 10) and lower onset potential of BH4 - oxidation compared to Au. Bimetallic ii electrocatalysts (e.g. Au-Pt, Pt-Ni, Pt-Zn) have also presented considerable cell performance in contrast to single-metal catalysts. As Pt0.75-Ir0.25/Ti and Pt0.25-Ir0.75/Ti anode catalysts have not been studied in DBFCs, this research considers them. Employing 3D electrode materials, such as reticulated metals, is expected to enhance the reactants’ mass transport, avoid channel blocking, fully utilise the active sites, minimise the amount of noble metal required and thus simultaneously reduce electrode costs and increase cell power output. Moreover, optimising the operational conditions (temperature, reactant compositions, background materials, flow rate, etc.) of DBFCs will improve their performance. Therefore, the aim of this research is to investigate approaches to increase the overall performance and efficiency of a DBFC with the following research objectives: investigate the use of Pt-Ir alloys supported by titanium as anode materials for DBFCs; discover the optimal anode geometry among different 3D electrode materials by determining the volumetric mass-transfer coefficient using a limiting-current technique; and find the maximum power density of a DBFC using the optimal electrode through manipulation of operating conditions and electrolyte compositions. Pt0.75-Ir0.25/Ti and Pt0.25-Ir0.75/Ti anode catalysts have been characterised and evaluated, Pt0.75-Ir0.25/Ti being the most effective electrode for direct NaBH4 oxidation. Its reaction parameters – including the activation energy ("# #), the charge-transfer coefficient (α), the total number of electrons exchanged (z), the heterogeneous rate constant (ka) of the BH4 - oxidation process and reaction order (β) – were 18.6 kJ mol-1 , 0.59, 5.3, 0.40 cm s-1 and 0.87, respectively. Among 3D electrode materials, the fine mesh showed the best performance. Finally, the operating conditions were discovered to have a significant influence on the cell power density. For example, the cell performance showed a dependence on the operating temperature, that is, the reaction kinetics at the anode and cathode were promoted when it rose. The peak power density also increased dramatically, from 93 to 162 mW cm-2 (~75%), when the temperature elevated from 25 to 65 o C. Keywords: borohydride oxidation, 3D electrode, iridium, limiting current, mass transport, platinum, porous electrode, operating condition
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
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
Bibliographie générale
Get PDFAbdulkarim (M.) 1997 Recherches sur la cité d’Émèse à l’époque romaine, thèse de doctorat, Université de Versailles. Abdulkarim (M.) & Olesti-Vila (l.) 2007 « Les centuriationes dans la province romaine de Syrie : nouvelles perspectives d’étude », Syria 84, p. 249-276. Abdulsalam (A.) 1990 Al-Aqalim al-Jughrafiya al-Souriya [Les régions géographiques syriennes], Université de Damas, Damas. Abel (F.-M.) 1933 « Oronte et Līṭāni », Journal of the Palestine Oriental Society 13, p. 147-158. Abel ..
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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