1,721,243 research outputs found
A numerically robust method of moments with number density function reconstruction and its application to soot formation, growth and oxidation
No full textSeveral method of moments (MOM) models were developed recently to describe the evolution of soot particle populations. However, especially soot oxidation is still very challenging in MOM, as pointwise information of the underlying soot particle number density function (NDF) is usually unknown and thus, the prediction of smallest particles that oxidize completely is not easy. The recently proposed Extended Quadrature Method of Moments (EQMOM) (Yuan, Laurent, & Fox, 2012) has the potential to resolve this issue providing a continuous NDF reconstruction based on the set of transported moments. While its general suitability for soot was already demonstrated in the literature, the EQMOM moment inversion procedure reveals several numerical difficulties.
In this work, we propose an EQMOM modification called split-based EQMOM that builds upon the general idea of EQMOM to represent the NDF by a weighted sum of superimposed, non-negative, continuous kernel density functions (KDFs), avoiding, however, the numerical problems of its original version. The model is based on a split of the entire NDF into a sum of overlaying density functions, whose evolution is governed by individual population balance equations (PBFs). These PBFs are derived and implemented in a novel Monte Carlo (MC) framework which is applied to simulate two fuel-rich burner-stabilized laminar premixed flames with different sooting behaviours. Results are compared to a classical MC model to demonstrate the suitability. Next, the MC data is used to assess the suitability of lognormal, gamma and inverse Gaussian distributions to approximate the NDF shape by employing the Wasserstein metric as criterion. This information is finally used to formulate an improved EQMOM soot model, which is then evaluated for both fuel-rich and oxidizing conditions. For the latter, the two-stage burner experiments of Echavarria, Jaramillo, Sarofim, & Lighty (2011) is considered, where particle oxidation is the dominant process. It is demonstrated that the proposed MOM model allows an accurate and numerically robust description of soot formation, growth and also oxidation
Experimental and numerical study on the effect of oxymethylene ether-3 (OME3) on soot particle formation
Full text linkThe reduction and control of particulate matter generated by fossil fuel combustion are among the main issues for actual and future combustion devices due to the increasingly stringent emission regulations. Recently, various fuels have been investigated as a potential substitute or additive for diesel and gasoline. This work focuses on how oxymethylene ether-3 (OME3), the smallest promising OME compound, affects carbon particulate formation when blended with ethylene in burner-stabilized premixed flames at different equivalence ratios. Particle size distribution (PSD) and Laser-Induced Fluorescence (LIF) and Incandescence (LII) along with numerical (Conditional Quadrature Method of Moments – CQMOM, based on D'Anna physico-chemical soot model) investigations were conducted to study particle formation and growth in pure ethylene and ethylene/OME3 flames. The soot volume fraction and PSD indicate a reduction in the total number and the size of the soot particles at all equivalence ratios, while the number of small nanoparticles remains almost unchanged. The CQMOM model is able to predict similar trends for the soot volume fraction and, using the entropy maximization concept, the general shape of the PSD for both pure ethylene and OME3-blended flames, compared to the experimental measurements. Further, carbon particulate matter was thermophoretically sampled in the highest equivalence ratio conditions and spectroscopically analyzed. The soot structure was investigated using UV–Visible and Raman spectroscopy, finding a slightly higher aromaticity for the pure ethylene soot. FTIR analysis showed that carbon particulate matter produced from an OME3-doped flame contained larger amounts of oxygen, mainly in the form of C[dbnd]O
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
Chemical reactor network modeling in the context of solid fuel combustion under oxy-fuel atmospheres
Full text linkA multi-phase chemical reactor network (CRN) is developed and applied to investigate solid fuel combustion under oxy-fuel atmospheres in a laboratory-scale combustion chamber. The development of a novel solid-gas plug flow reactor (sPFR) allows the full coupling of solid and gas phase processes to increase the fidelity in CRN modeling. Together with the recently developed solid-gas perfectly stirred reactor (sPSR), the new sPFR is applied within a multi-phase reactor network to model the complex features of the investigated application. To design an initial reactor network, a hybrid experimental and computational fluid dynamics (CFD)-driven approach is being pursued, taking into account both global and local information on flow and temperature fields. Initially, an in-depth investigation of the physical processes is conducted, covering solid fuel conversion processes such as devolatilization and char conversion, along with the thermochemical characteristics of the flue gas. In particular, the prediction of carbon monoxide (CO) emissions is analyzed in detail by means of sensitivity analyses. Based on the findings of the sensitivity study, the network complexity of the initial reactor network is increased to enable an accurate prediction of the CO formation in comparison to the experiments. Finally, the formation of nitric oxides (NOx), sulfur oxides (SOx), and aromatic pollutants is discussed, highlighting the importance of detailed chemistry in solid fuel combustion at technically relevant scales
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