1,721,507 research outputs found
Analysis of n-heptane auto-ignition characteristics using computational singular perturbation
No full textTo provide insights into auto-ignition characteristics in low temperature combustion (LTC) engine conditions, computational singular perturbation (CSP) analysis is used to gain fundamental understanding into classification of ignition regimes in n-heptane air mixtures in the presence of temperature and composition inhomogeneities. Parametric studies are conducted using high-fidelity simulations with detailed chemistry and transport. In particular, a key interest is to understand different ignition behavior of the n-heptane mixture at the negative-temperature coefficient (NTC) versus the non-NTC conditions. The CSP analysis for the reference homogeneous system yields the number of exhausted modes (M) at various stages during the ignition event. In addition, the merging of two explosive modes is observed at the onset of auto-ignition. For the one-dimensional system, the M profiles along with the importance index (IT) measured in the upstream of the ignition front are used to determine whether the front propagation is the spontaneous (IT → 0) or deflagrative (IT → 1) regime. At the relatively large temperature fluctuation considered herein, the mixture at non-NTC conditions shows initially a deflagration front which is subsequently transitioned into a spontaneous ignition front. For the mixtures at the NTC conditions which exhibit two-stage ignition behavior, the 1st stage ignition front is found to be more likely in the deflagration regime. On the other hand, the 2nd stage ignition front occurs almost always in the spontaneous regime because the upstream mixture contains active radical species produced by the preceding 1st stage ignition front. The effects of differently correlated equivalence ratio stratification are also considered and the results are shown to be consistent with previous findings
Classification of ignition regimes in HCCI combustion using computational singular perturbation
No full textThe computational singular perturbation (CSP) technique is applied as an automated diagnostic tool to classify ignition regimes encountered in homogeneous charge compression ignition (HCCI) engines. Various model problems representing HCCI combustion are simulated using high-fidelity computation with detailed chemistry for hydrogen-air system. The simulation data are then analyzed by CSP. In a homogeneous system, the occurrence of two branches of explosive eigenvalues characterizes chain-branching and thermal ignition. Their merging point serves as a good indicator of the completion of the explosive stage of ignition. However, the merging point diagnostics is insufficient to differentiate spontaneous ignition from deflagration. As an alternate method, the active reaction zones are first identified by the locus of minimum number of fast exhausted time scales (based on user-specified error thresholds). Subsequently, the relative importance of transport and chemistry is determined in the region ahead of the reaction zone. A new index IT, defined as the sum of the absolute values of the importance indices of diffusion and convection of temperature to the slow dynamics of temperature, serves as a criterion to differentiate spontaneous ignition from deflagration regimes. These diagnostic tools are applied to 1D and 2D ignition problems under laminar and turbulent mixture conditions, respectively, allowing automated detection of different ignition regimes at different times and location during the ignition events. The implication of the results in the context of modeling autoignition of nearly homogeneous turbulent mixtures is discussed. © 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved
Gender differences in access to information and adoption of climate-smart agriculture practices in Uganda: The role of women's empowerment
No full textPrepared by Rashid Khan , Christine Bosch, Edward Kato, Elizabeth Bryan , Regina Birner, Thomas Daum, Saurabh Gupta, and Claudia Ringle
Can social trust improve governance in India?
No full textRohit Sinha and Saurabh Gupta point to citizen-led initiatives that could help bridge the trust deficit between India’s political elite and the electorate
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
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