1,720,955 research outputs found
Automatic mechanism generation for pyrolysis of di-tert-butyl sulfide
No full textThe automated Reaction Mechanism Generator (RMG), using rate parameters derived from ab initio CCSD(T) calculations, is used to build reaction networks for the thermal decomposition of di-tert-butyl sulfide. Simulation results were compared with data from pyrolysis experiments with and without the addition of a cyclohexene inhibitor. Purely free-radical chemistry did not properly explain the reactivity of di-tert-butyl sulfide, as the previous experimental work showed that the sulfide decomposed via first-order kinetics in the presence and absence of the radical inhibitor. The concerted unimolecular decomposition of di-tert-butyl sulfide to form isobutene and tert-butyl thiol was found to be a key reaction in both cases, as it explained the first-order sulfide decomposition. The computer-generated kinetic model predictions quantitatively match most of the experimental data, but the model is apparently missing pathways for radical-induced decomposition of thiols to form elemental sulfur. Cyclohexene has a significant effect on the composition of the radical pool, and this led to dramatic changes in the resulting product distribution
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
Predicting organosulfur chemistry in fuel sources
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.Cataloged from PDF version of thesis.Includes bibliographical references.Desulfurization of fossil fuels with supercritical water (SCW) has been the topic of many studies over the past few decades. This process does not require the use of any catalyst, eliminates the need for a hydrogen feed, and minimizes coke formation. Previous research has shown that it has the potential to be a viable commercial process, and recent experimental studies have proven that water acts as one hydrogen source for sulfur removal in this process. However, the exact desulfurization mechanism is largely unknown, as are many other reaction mechanisms involving sulfur compounds. Recent work has greatly expanded our ability to build comprehensive reaction mechanisms automatically for the decomposition of organic sulfur compounds using the automated Reaction Mechanism Generator (RMG). This thesis presents the implementation of this and other tools to investigate chemical processes relevant to our use of fuel sources containing sulfur compounds, and it shows some steps that have been taken to improve our predictions for these mechanisms and those that will be generated in the future. Previous investigations had focused on the pyrolysis of small sulfur compounds containing less than six heavy atoms, so RMG is first used to study the pyrolysis of t-butyl sulfide. A detailed reaction mechanism is then presented for the SCW desulfurization of hexyl sulfide. Comprehensive kinetic mechanisms for these larger molecules are likely to include thousands of reactions, so RMG builds this model in a systematic and unbiased way using a database of ab initio data. This database is expanded with potentially relevant thermochemical and kinetic parameters using transition state theory and quantum chemical calculations at the CBS-QB3 and CCSD(T)-F12 levels of theory. With these data, as well as previously calculated rates for hydrocarbon and sulfur kinetics, RMG is used to build a reaction mechanism for the conversion of hexyl sulfide to hydrogen sulfide, pentane, and carbon monoxide in the presence of SCW. This mechanism is validated with results from batch and flow reactor experiments, and predictions are accurate within a factor of two for reactant and major product concentrations. Analysis of the proposed mechanism shows that the molecular addition of water to the carbonsulfur double-bond in hexanethial is a key step in the SCW process, as this not only leads to the desulfurization of the compound, but also prevents the thioaldehyde from undergoing addition reactions with other hydrocarbons in a process that could eventually form coke. Thus, this work not only has implications in the SCW desulfurization process, but in the overall crude oil upgrading process as well. The calculated kinetic and thermochemical parameters are used to generate predictive reaction mechanisms for other processes relevant in fuel chemistry, such as the geological formation of oil and gas from kerogen. This not only allows us to model experimental work investigating the effect sulfur compounds have on the oil-to-gas process, but we also explore how these effects differ at geological conditions and timescales. And as the possible applications of RMG grow, the need for accurate parameters in mechanism generation become even more critical. A thermochemical database is generated for a wide variety of sulfur compounds using the highaccuracy CCSD(T)-F12/cc-pVTZ-F12 method, and this provides a basis for the investigation of organosulfur chemistry with tighter uncertainty.by Caleb Andrew Class.Ph. D
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
Supercritical Water Treatment of Crude Oil and Hexylbenzene: An Experimental and Mechanistic Study on Alkylbenzene Decomposition
No full textHigh concentrations of fuel-range hydrocarbons may be recovered from heavier alkyl-aromatic compounds in crude oil after supercritical water (SCW) treatment. Arabian Heavy (AH) crude oil was treated in SCW and analyzed using two-dimensional gas chromatography (GC × GC-FID). Cracking mechanisms were investigated using the model compound hexylbenzene under similar SCW treatment conditions. The results of the model compound experiments were compared to predictions of a kinetic model built by the Reaction Mechanism Generator (RMG). AH crude cracked significantly during SCW treatment. The GC-observable mass fraction increased by 90%. We conducted studies on the distilled samples of crude oil and found that significant changes in the composition of the SCW-treated heavy fraction occurred. Significant formation of aliphatic hydrocarbons and small-chain BTX-type compounds were found in the SCW-processed samples. Hexylbenzene conversions differed between the crude oil studies and the model compound studies. The mechanistic model for the cracking of hydrocarbons during SCW treatment of the model compound hexylbenzene predicted the observed major liquid products toluene, styrene, and ethylbenzene. The selectivity of ethylbenzene and styrene changed over time. The apparent conversion of styrene into ethylbenzene was possibly via a reverse disproportionation reaction. Ultimately, a mechanism was built that serves as a basis for understanding the kinetics of hydrocarbon cracking in SCW.Saudi Aramco (Contract 6600023444
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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