1,720,969 research outputs found
Studies on sulfur poisoning and development of advanced anodic materials for waste-to-energy fuel cells applications
No full textBiomass is the renewable energy source with the most potential penetration in energy market for its positive environmental and socio-economic consequences: biomass live cycles for energy production is carbon neutral; energy crops promote alternative and productive utilizations of rural sites creating new economic opportunities; bioenergy productions promote local energy independence and global energy security defined as availability of energy resource supply. Different technologies are currently available for energy production from biomass, but a key role is played by fuel cells which have both low environmental impacts and high efficiencies. High temperature fuel cells, such as molten carbonate fuel cells (MCFC), are particularly suitable for bioenergy production because it can be directly fed with biogas: in fact, among its principal constituents, methane can be transformed to hydrogen by internal reforming; carbon dioxide is a safe diluent; carbon monoxide is not a poison, but both a fuel, because it can be discharged at the anode, and a hydrogen supplier, because it can produce hydrogen via the water-gas shift reaction. However, the utilization of biomass derived fuels in MCFC presents different problems not yet solved, such as the poisoning of the anode due to byproducts of biofuel chemical processing. The chemical compound with the major negative effects on cell performances is hydrogen sulfide. It reacts with nickel, the main anodic constituent, forming sulfides and blocking catalytic sites for electrode reactions. The aim of this work is to study the hydrogen sulfide effects on MCFC performances for defining the poisoning mechanisms of conventional nickel-based anode, recommending selection criteria of sulfur-tolerant materials, and selecting advanced anodes for MCFC fed with biogas. © 2010 Elsevier B.V. All rights reserved
Multiple regression analysis of hydrogen sulphide poisoning in molten carbonate fuel cells used for waste-to-energy conversions
No full textBioenergy addresses three important social concerns: security of energy supply, mitigation of greenhouse gas emissions and development of agriculture. Bioenergy is the energy generated by either direct or indirect combustion of biomass, which is non-fossil organic material of both vegetable and animal origins. Different technologies are currently available for bioenergy production, but fuel cells are one of the most interesting devices because of their environmental benefits and their high efficiency. In particular, molten carbonate fuel cells are suitable devices for waste-to-energy conversion because of their ability to be fed with biogas, which is biomass-derived gas rich in methane and carbon dioxide. Indeed, methane can be internally reformed to hydrogen, carbon dioxide is a safe diluent preventing electrolyte loss, and carbon monoxide acts both as a hydrogen supplier and as an actual fuel. Unfortunately, biogas impurities, such as sulfur, halogen and nitrogen compounds, cause adverse effects on cell performances. The most dangerous impurities are sulfur compounds, among whom hydrogen sulphide is the predominant and the most harmful chemicals. It reacts with nickel-based anode to form nickel sulphides, that block catalytic sites, slowing hydrogen oxidation down, and change the anode wettability in molten carbonates, compromising the optimal electrolyte distribution within cell components. Poisoning mechanism of hydrogen sulphide depends on operating conditions such as current density, anodic gas composition, temperature and pressure. The aim of this work is to study hydrogen sulphide effects on MCFCs by means of multiple regression analysis. The mathematical approach gives us tools to define the main sulfur poisoning mechanism under MCFC operating conditions, quantify the effects of the main parameters affecting poison actions, such as current density, hydrogen and hydrogen sulphide, and identify their mutual interactions. Also it is possible to formulate a multivariate model to predict sulfur poisoning. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
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
Numerical modelling of MCFC cathode degradation in terms of morphological variations
No full textThis paper describes the numerical modelling of a key material-stability issue within the realm of Molten Carbonate Fuel Cells (MCFC). Differential models have been developed for the 2D and 3D distributions of current density as well as peroxide and carbon dioxide concentrations. By suitable variations of the integration domain - based on the agglomerate concept - one can describe the morphological and attending electrocatalytic evolution of porous NiO electrodes. On the basis of electrochemical data recorded during the operation of a laboratory MCFC, we have shown that this model is able to rationalise the evolution of cathode conditions leading to both improvements of electrocatalytic performance - such as lithiation - and degradation - such as agglomeratio
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
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