1,721,033 research outputs found
Numerical Analysis on the Influence of Jets Break-up Model Formulation on Diesel Engines Combustion Computations
No full textThe multidimensional simulation methods available today for spray motion predictions solve the spray equations (including the mass, momentum, and energy changes due to the interaction between the drops and the gas), and also consider drop collision and coalescence phenomena. The most-used breakup spray models in CFD computations are based on an analysis of the instability of a liquid column injected unbroken from the nozzle orifice (in the following WAVE model), or in an analogy between a damped spring-mass system and a liquid column (TAB model). Both models require some empirical constants.
Considering also that the mechanism that controls atomization is not yet well understood, further calculations and experimental comparisons over a range of injection conditions may be useful to improve the prediction capability of these models. In previous work, an analysis was performed to determine the influence of spray breakup model constants setting on the spray tip penetration, using the KIVA II code. The mesh size adopted was quite coarse, but typical of that used in computations of diesel engine combustion. It was outlined that both the TAB and the WAVE models are sensitive mainly to the breakup time constant value; the influence of the other model constants on the tip penetration results is minimal. In spite of the fact that the physics of the two models is very different, the best setting of the constants falls in the same range.
In the present article a further analysis of spray patterns is reported, particularly related to the spray breakup phenomenon. After a brief description of the breakup models, a sensitivity analysis of the main spray features to the model constants is presented. In addition, the numerical data of jet penetration, computed with both the TAB and WAVE models, are compared with literature data for vaporizing and nonvaporizing conditions. In order to improve the numerical predictions, a "hybrid" model is proposed, based on both the TAB and WAVE models. Finally, because the overall goal of the spray computations is to obtain a reliable simulation of the overall diesel combustion process, the influence on combustion computations of breakup modeling is also evaluated and discussed
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
Un contributo alla modellizzazione di fenomeni di evaporazione dei getti di combustibile nei motori a combustione interna
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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
Performance evaluation of simple autoignition models for 3D diesel combustion computations
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