1,720,953 research outputs found
Modelling for turbulent autoignition with split fuel injection
No full textSplit-injection is applied in automotive diesel engines in order to control heat release and pollution production. Injecting fuel prior to the main fuel injection, known as pilot injection, increases premixing and tends to reduce NOx emission. Injecting a portion of the fuel after the main injection has potential for reducing particulate emissions. In order to meet increasingly stringent emission and fuel consumption regulations, modern automotive diesel injectors have been developed with the capacity to deliver of the order of ten separate injection pulses during a single engine stroke. Simulation methods for split-injection engines are required in order to develop more advanced injection strategies with two or more separate fuel-injections. A range of additional combustion applications involve mixing and combustion between multiple streams such as Exhaust Gas Recirculation (EGR) and dual fuel injections. Modelling for the turbulent combustion interactions in multi-stream problems is developed in this thesis in the context of Conditional Moment Closure (CMC) methods.The CMC approach provides modelling of chemical processes in turbulent flows by linking composition fluctuations to the variation of a small number of conditioning variables such as mixture fraction. In order to achieve good accuracy, the conditioning variables must be chosen to minimise compositional fluctuations around the conditional mean. Split-injection diesel engine operation results in complex combustion behaviour in which a single conditioning variable may be insufficient. However multiple-conditioned moment closures, or even double conditional moment closures (DCMC) have not been exploited previously. The objective of this study is to identify the most appropriate conditioning variables for modelling of split-injection diesel engines and to formulate, validate and demonstrate a practical implementation of the DCMC approach for engine-relevant simulations.The thesis begins by developing a new formulation of the DCMC approach that is applicable to a general set of non-conserved conditioning variables, and a set of numerical solution approaches is demonstrated and verified. The choice of conditioning variables is then investigated through direct numerical simulations of autoignition in a turbulent flow with up to three separate fuel injections. In the case with a single injection, fluctuations around the mixture fraction-conditioned mean arise due to variation in mixture fraction dissipation rate affecting the progress of ignition differently at different points in space. In cases with multiple injections, the repeated addition of unreacted fuel also adds to fluctuations around the conditional mean. The high level of conditional fluctuations leads to large errors when employing singly-conditioned first-order conditional moment closure. Alternative doubly conditional moment closure approaches are tested using a priori and a posteriori analyses. Single conditioned first order closure gives extremely poor agreement with the DNS, and the study indicates that double conditioning on mixture fraction and progress variables, such as the sensible enthalpy, outperforms double conditioning on multiple mixture fractions.The feasibility of the zero-dimensional DCMC approach for practical predictive design calculations is then assessed further through simulations of n-heptane spray ignition in constant volume research vessels with single or multiple injections. The experimental flows are simulated by coupling the zero-dimensional first order double conditional moment closure (0D-DCMC) with a commercial CFD code and an efficient Operator Splitting solution method is demonstrated. The predictions show the same trends as the experimental observations, however ignition delays and lift off lengths agree with the measurements only approximately. Reasons for the discrepancies include the uncertainty in the chemical modelling as well as in the ambient temperature surrounding the spray in the experiments. The modelling of conditional cross-scalar dissipation rate is also found to have a significant influence on the flame evolution, with the limiting cases of modelling corresponding to zero correlation or unity correlation between mixture fraction and progress variable giving unrealistic predictions. Conditional cross-dissipation rate modelling corresponding to negative unity correlation gives reasonable predictions, and an argument for why negative mixture fraction–progress variable correlation is expected to be dominant in autoignitive lifted jet flames involving multiple fuel injections is presented. Other aspects of modelling uncertainty with regard to conditional dissipation rates, presumed joint mixture fraction-progress variable probability density functions and first order source term closures will also contribute to the model error, and further development of models suitable for spray autoignition cases would be beneficial.In comparison with the established three-dimensional singly-conditioned moment closure (3D-CMC), the 0D-DCMC model is a promising approach which is expected to be substantially faster than the 3D-CMC approach in most problems of engineering interest. Not withstanding the imperfect predictions, the ability of the zero-dimensional DCMC to describe the whole split-injection process and to provide new insight into the mechanisms involved is encouraging: this implies that only a few DCMC control volumes may be needed in order to model a wide range of flows involving very complex physics, of which split-injection is just one example, and the DCMC approach is therefore recommended for further development.<br/
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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