1,721,124 research outputs found
Mechanism optimization with a novel objective function: Surface matching with joint dependence on physical condition parameters
No full textThe prediction accuracy of chemical kinetics models can be improved efficiently by using automatic model optimization techniques. In the optimization, an objective function, which quantifies the differences between model responses and experimental data for quantities of interest, is minimized by calibrating the reaction rate parameters of a model within their uncertainty limits. Consequently, the values of the model predictions become closer to those of the measurements. Typically, a point-wise objective function, which is based on function components separately for each measurement over the investigated domain, is used in the model optimization. Quantities of interest are often functions of various physical condition parameters, such as temperature, pressure, and equivalence ratio. However, the point-wise objective function does not consider the correlation between data and their corresponding physical conditions. Thus, in this work, a new objective function is proposed, which uses a surface-matching (SM) method. It evaluates the similarity between surface shapes of the predicted and measured values, which is quantified in form of two user-defined physical condition parameters. By minimizing this function, the joint dependence of model predictions on physical conditions is optimized in conjunction with the point-wise model prediction accuracy. A chemical mechanism of oxymethylene ethers is optimized in this work as an example. The model is calibrated with the point-wise, curve-matching (CM)-based, and SM-based objective functions. The optimized models are compared and the results are discussed. It is shown that the optimization with the SM-based objective function yields improved results for certain cases compared to using the point-wise objective function. This model also provides the best prediction accuracy in terms of joint physical condition dependence. In addition, a better overall performance is achieved by adjusting the ratios between the component functions in the objective function, which demonstrates that the definition of objective functions plays a crucial role for model optimization
A reduced-order model for turbulent reactive sprays in compression ignition engines
No full textIn this work, we present a reduced-order model for transient turbulent reactive sprays in compression ignition engines. The model is an extension of the previously developed cross-sectionally averaged spray model (CAS) (Deshmukh et al., 2021). A transient turbulence model is derived for the gas phase that allows to model the transient scalar dissipation rate, which is a key parameter in non-premixed combustion. Representative chemistry is solved in mixture fraction space interactively with the flow. The turbulent CAS model combined with the combustion model is termed the cross-sectionally averaged reactive turbulent spray (CARTS) model and can represent unsteady non-premixed combustion behavior. The CARTS model is validated against experimental data as well as three-dimensional (3D) numerical simulations. The model is able to reasonably predict the trends of ignition delay time, flame lift-off length, and soot emissions. The computational cost of the CARTS model is orders of magnitude lower than the 3D simulation methods. This low computational cost enables various applications, including but not limited to the rapid screening of novel fuel candidates as well as off-line training of models to be eventually used in closed-loop control
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
Effects of turbulence on variations in early development of hydrogen and iso-octane flame kernels under engine conditions
No full textThe understanding and prediction of the early development of flame kernels are of high practical importance for the robust relight of aviation gas turbines and the control of cycle-to-cycle variations (CCV) of spark-ignition engines. CCV are known to correlate strongly with early flame kernel development and complicate the optimization of such engines in terms of safety, thermal efficiency, and engine emissions. The flame kernel initiated by a spark is initially small, in the very early combustion phase typically smaller than the size of the turbulent integral length scales. Therefore, the development of the flame kernel is dominated by local, intermittent flow fluctuations and can vary under the same nominal conditions. In this study, the effects of turbulence on the early development of premixed iso-octane and hydrogen turbulent flame kernels under realistic engine conditions are investigated through direct numerical simulations. Multiple realizations were simulated under the same nominal conditions for both fuels. Significant variations in flame kernel interactions with turbulence can be identified among different realizations. The fuel consumption rate varies by a factor of two, which is remarkable considering that only statistical differences in the local flow field are present between different realizations. Effects of different flow features of the initial flow fields on the flame kernel development were analyzed. It was found that the flow motion on the scale of the ignition radius, specifically the fluid deformation, which is characterized by the invariants of the strain rate tensor, determines the global shape of the kernel, while the variations of the kernel growth rate are mostly driven by the variations of the smallest turbulent scales. In particular, turbulence influences the flame surface area growth mainly through the tangential strain rate at the flame surface, which is shown to result from the small-scale turbulent motion. Due to differential diffusion effects, hydrogen and iso-octane exhibit significantly different flame responses to curvature, which is comprehensively studied for both fuels. The findings in this study will guide the development of combustion models that are capable to capture variations of the early flame kernels based on the local turbulence dissipation rate.</p
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
- …
