1,721,069 research outputs found
Rate constants of the fulvenallenyl recombination with propargyl and its role in PAH formation: a theoretical and kinetic modeling study
No full textThe temperature- and pressure-dependent rate constants of the reaction of fulvenallenyl (C7H5) and propargyl (C3H3) radicals have been explored using advanced electronic structure methods and kinetics theories. The results show that the head-C3H3 + tail-C7H5 addition is the fastest, followed by the tail + tail addition, and that at typical combustion conditions of 1500 K and 1 atm, the reaction mostly results in collisional stabilization of entrance channel adducts without further cyclization, whereas the well-skipping pathway to fulvalene - a precursor to naphthalene, prevails at high temperatures. The formation of the aromatic two-ring isomers, naphthalene, methylene-indenes, and azulene, can be enhanced only at high temperatures and much lower pressures, when the collisional stabilization of the intermediate wells is not efficient. The computed phenomenological rate constants were consequently simplified using master equation-based lumping and the pseudo steady state approximation to reduce the size of the system. This post-processing confirmed fulvalene as the main two-ring aromatic product and thus, its contribution should be considered in kinetic models. While naphthalene is only a trace product of the C7H5 + C3H3 reaction, it can be formed from fulvalene via H-assisted isomerization. The impact of the updated thermochemistry and rate constants in CRECK and ITV kinetic models on mole fractions of relevant cyclic aromatic species was also analyzed. The results suggest that the relevance of the C7H5 + C3H3 reaction has been likely overestimated in the current literature and needs to be carefully reevaluated by revising the pathways involving the formation and consumption of C7H6 and C7H5 and improving predictions of their precursors, such as unsaturated C4 species in flames
The Fragmentation of Melamine: A Study via Electron-Impact Ionization, Laser-Desorption Ionization, Collision-Induced Dissociation, and Density Functional Calculations of Potential Energy Surface
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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
p-p* vibronic spectrum of ethylene from ab initio calculations of the Franck-Condon factors
No full textMechanism and kinetics of the oxidation of propargyl radical by atomic oxygen
No full textAutomated reaction path discovery tools have been used to map out the C3H3O potential energy surface and determine the prevailing channels for oxidation of the propargyl radical with atomic oxygen. The energy of the stationary points was then evaluated at the CCSD(T)/CBS//ωB97X-D/6-311+G(d,p) level of electronic structure theory. The C3H3 + O total and individual product channel rate constants were evaluated with Rice-Ramsperger-Kassel-Marcus Master Equation calculations combined with variable reaction coordinate transition state theory assessment of barrierless entrance channels. The total reaction rate so determined is in quantitative agreement with experiments, highlighting the relevance of accounting for C3H3 + O recombination on the excited electronic state surface. C2HCHO (propynal) + H are predicted as the prevailing reaction products, followed by CH2CCO (propadienone) + H, with minor contributions from C2H2 + HCO and C2H3 + CO. The calculated rate constants have been utilized in kinetic simulations, which tested the impact of the C3H3 + O reaction on chemical reactivity in premixed laminar flames of acetylene, ethylene, allene, propyne, and benzene. The results displayed macroscopic changes of the model predictions at low pressures (< 0.1 atm) and rich conditions, a reduction in the consumption of propargyl via C3H3 + O, and a substantial decrease in the C2H2 + HCO reactivity to C2H3 + CO. The updated model showed an improved performance in predicting C2 species in the considered flames
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
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