1,720,957 research outputs found
Catalytic and non-catalytic chemical kinetics of hydrocarbons cracking for hydrogen and carbon materials production
No full textIn the perspective of decarbonizing the chemical and energy industries, the production of hydrogen from the thermal and thermo-catalytic pyrolysis of hydrocarbons has been highlighted as a potentially effective route. Indeed, the "turquoise" hydrogen pathway enables to fixate the carbon content of the feedstock in high-performance, durable and recyclable materials entirely avoiding CO2 emissions. Such multiphase processes include chemical vapor deposition (CVD) and infiltration (CVI), diamond synthesis and the catalytic production of carbon nanotubes (CNTs). All the above involve a homogeneous gas-phase environment where feedstock cracking occurs together with heterogeneous interactions between gas-phase fragments and an active carbon (preform) or catalyst surface.
Mechanistic models provide insights into gas-phase product distribution, untangling the competition between amorphous carbon formation (soot) in the gas-phase and structured carbon deposition. Once the models are developed and validated, kinetic analyses allow the identification of optimal conditions by relating process parameters (temperature, pressure, feedstock, catalyst morphology, etc.) to feedstock conversion, product yields and quality.
This chapter provides an overview of relevant chemical kinetics aspects starting systematically from the description of reaction classes and reference rate parameters used to describe homogeneous gas-phase cracking. Then the formation mechanisms of polycyclic aromatic hydrocarbons and soot is addressed. The latter is a critical aspect as soot formation competes with the synthesis of highly structured and organized carbon materials through heterogeneous mechanisms. These are then discussed specifically focusing on CVD/CVI processes, diamond growth mechanisms and carbon nanotubes synthesis
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
Turquoise hydrogen and carbon materials production from thermal methane cracking: An experimental and kinetic modelling study with focus on carbon product morphology
No full textMethane (CH4) cracking is emerging as a bridge technology for hydrogen (H2) production fostering the transition from current carbon-intensive production processes (e.g. steam reforming) to the fixation of the carbon content of the feedstock in the form of valuable carbon materials. With the valorization of the carbon product being a key factor to lower H2 prices by improving the overall process economics, the understanding and the description of the complex network of homogeneous and heterogeneous reactions involved in CH4 thermal cracking and, in particular, in the formation of valuable carbon and of undesired byproducts (carbon nanoparticles) is key to technology design and operations. In this work we present a systematic experimental study of pure methane cracking in a tubular quartz reactor in the temperature range T = 875–975 °C at initial flow rates QCH4,0 = 30, 45 and 60 ml/min. CH4 conversion and H2 yields have been measured quantitatively and complemented with the identification of key aromatic precursors supporting the interpretation of the mechanistic phenomena aided by an existing chemical kinetic model and chemical kinetic analyses. A careful analysis of the carbon products allowed to explore the different morphologies of deposited carbon and carbon nanoparticles in the gas phase, as well as their strong dependence from homogeneous gas-phase reactivity, motivating further model developments aimed to describe currently missing complex heterogeneous reaction pathways towards a quantitative description of the observed features
Turquoise hydrogen and carbon materials production from thermal methane cracking: An experimental and kinetic modelling study with focus on carbon product morphology
No full textMethane (CH4) cracking is emerging as a bridge technology for hydrogen (H2) production fostering the transition from current carbon-intensive production processes (e.g. steam reforming) to the fixation of the carbon content of the feedstock in the form of valuable carbon materials. With the valorization of the carbon product being a key factor to lower H2 prices by improving the overall process economics, the understanding and the description of the complex network of homogeneous and heterogeneous reactions involved in CH4 thermal cracking and, in particular, in the formation of valuable carbon and of undesired byproducts (carbon nanoparticles) is key to technology design and operations. In this work we present a systematic experimental study of pure methane cracking in a tubular quartz reactor in the temperature range T = 875–975 °C at initial flow rates QCH4,0 = 30, 45 and 60 ml/min. CH4 conversion and H2 yields have been measured quantitatively and complemented with the identification of key aromatic precursors supporting the interpretation of the mechanistic phenomena aided by an existing chemical kinetic model and chemical kinetic analyses. A careful analysis of the carbon products allowed to explore the different morphologies of deposited carbon and carbon nanoparticles in the gas phase, as well as their strong dependence from homogeneous gas-phase reactivity, motivating further model developments aimed to describe currently missing complex heterogeneous reaction pathways towards a quantitative description of the observed features
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
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