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High-Order Spherical Harmonics Methods for Radiative Heat Transfer and Applications in Combustion Simulations
Full text linkThe study of radiative transfer within participating gaseous and particulate media has become increasingly important in the prediction of the combustion process of hydrocarbons for various scientific and industrial applications. The radiative transfer equation (RTE) is an integro-differential equation in five independent variables describing the physical process of radiative transfer. The angular dependency of the RTE makes it exceedingly difficult to solve by deterministic methods. Several approximate deterministic methods for the RTE have been developed over time. Two most promising candidates, the discrete ordinates method (DOM) and the spherical harmonics PN method, are often used to solve the RTE even though both of them have their limitations. The DOM discretizes the entire solid angle by a finite number of ordinate directions and integrals over direction are replaced by numerical quadrature. DOM is relatively simple to implement but suffers from ray effects and false scattering and requires an iterative solution for scattering media or reflecting surfaces. On the other hand, the spherical harmonics PN method is a spectral method that solves the RTE by approximating the angular distribution of the intensity by a truncated series of spherical harmonics. Despite the popularity of the lowest order of the PN method, i.e., the P1 method, the potential of high-order PN methods has never been fully explored. This is partly due to cumbersome mathematics, and to lack of research in this area compared with the effort and progress made in its most popular counterpart, the DOM. Increasing of the order of PN is expected to overcome the difficulty of optically thin and optically intermediate conditions or domains with optically thin and optically intermediate regions, which is the motivation for this research. The Photon Monte Carlo (PMC) method is so far the most accurate method; unlike the DOM/FVM and PN methods, the stochastic PMC method gives an exact solution to the RTE. However, the PMC method can be computationally expensive since a large number of rays must be traced, which prevents it from wider applications in evaluating radiative transfer within combustion simulations.This study focuses on a recently-developed general PN formulation consisting of N(N+1)/2 second-order elliptic PDEs and their Marshak's boundary conditions for arbitrary 3-D geometries. The number of equations and unknowns can be further reduced to (N+1)^2/4 for two-dimensional geometries by taking advantage of the geometric characteristics of spherical harmonics. Special boundary conditions, including symmetry/specular reflection boundaries, walls with specified radiative flux, cyclic boundaries and mixed diffuse-specular surfaces have also been developed for high-order PN methods. The high-order PN methods (up to the order of 7) have been implemented within the finite volume-based OpenFOAM open-source libraries. The performance of high-order PN methods is demonstrated by solving a number of examples covering a wide range of different geometries and varying radiative properties including coupled simulations of a turbulent jet flame and a frozen snapshot study of a high-temperature oxy-natural gas burner. The goal of these examples is to test the performances of the high-order PN methods with respect to all kinds of factors, e.g., order of PN, overall optical thickness, geometry, homogeneity of radiative properties, etc., as well as to verify the finite volume implementations of the high-order PN method on OpenFOAM
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
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Determination of temperature and concentration from radiometric measurements in combustion systems
Full text linkDespite that combustion diagnostics have reached high levels of refinement, it remains difficult to make quantitatively accurate nonintrusive measurements of temperature and species concentrations in realistic combustion environments. The goal of the present study is to develop nonintrusive spectral radiation tools to allow efficient high-fidelity determination of temperature and species concentrations in laminar and turbulent combustion systems. Temperature and concentrations are deduced from medium-to-coarse resolution measurements of spectral transmissivity and emitted intensity for homogeneous gas media, nonhomogeneous gas media and turbulent systems considering the turbulence radiation interaction (TRI). For a homogeneous gas medium, by minimizing the differences between measured and predicted transmissivity spectra, an inverse radiation model is developed to retrieve temperature and species concentrations simultaneously using the the Levenberg-Marquardt optimization method. This model has been validated by experimental measurements. The developed inverse radiation model is used to determine the optimal wavenumber range and resolution by retrieving temperature and species concentrations from a homogeneous gas column for a wide range of temperatures and concentrations. Multiple factors, including spectral region, spectral resolution, temperature and concentration range, and susceptibility to systematic error and random error have been considered. Results are obtained for homogeneous mixtures containing CO2, H2O or CO with N2.In nonhomogeneous gas media, transmissvities are not sensitive to temperature and concentration distributions, making it impossible to reconstruct temperature and species concentrations fields from transmissivity spectra. Another inverse calculation model is developed using measured line-of-sight emitted spectral intensity data to retrieve temperature profiles. Because intensity spectra are also not sensitive to concentration profiles, this model can only deduce the temperature profile together with an average concentration. Due to the ill-posedness of this inverse problem, additional conditions or criteria are needed to be imposed to determine the most realistic solution. Most regularization methods transform an ill-posed inverse problem into a well-behaved one by adding auxiliary information based on desired or assumed characteristics. Tikhonov regularization imposes smoothness to the solution by adding a regularization term. Tikhonov regularization has been shown to be suitable for solving these ill-posed problems, but it is difficult to select an appropriate regularization parameter, especially for nonlinear problems. A new regularization selection method based on the theory of the discrepancy principle and the L-curve criterion is proposed and shows good generality for different temperature profile inversions. Several types of temperature profiles are retrieved accurately using this method.For a turbulent system, the nonlinear interaction between turbulence and radiation has profound effects and cannot be neglected when developing inverse radiation tools. In the presence of TRI, temperature and concentration can never be measured directly. An inverse radiation model considering how turbulence and radiation interact along the detector's line-of-sight has been developed to deduce time-averaged and root-mean-square (rms) values of temperature and concentrations as well as the turbulent length scale from the time-averaged transmissivity and its rms spectrum for a single turbulent gas as well as a turbulent gas mixture
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
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
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