1,721,037 research outputs found
Extending the dynamic range of detectors for average particle/droplet imaging methods
No full textLaser-based diagnostic methods are being applied to more and more flows of theoretical and practical interest and are revealing interesting new flow features. Imaging particles or droplets in Nephelometry and Laser Sheet Dropsizing methods requires a tradeoff between maximised signal to noise ratio, without over-saturating the detector. Droplet imaging results in lognormal pdf (probability density function) distribution of pixel intensity. It is possible to fit a lognormal distribution to the histogram of pixels intensities. If pixel intensities are clipped at a saturated value it is possible to estimate a presumed pdf shape without the effects of saturation from the lognormal fit to the unsaturated histogram. Information about presumed shapes of the pixel intensity pdf is used to generate corrections that can be applied to data to account for saturation. The effects of even slight saturation are shown to be a significant source of error on the derived average. It is found that errors on the determined average exceed 5% when the number of saturated samples exceeds 3% of the total. This study also attempts to delineate limits, within which, the detector saturation can be accurately corrected. It is demonstrated that a simple method for reshaping the clipped part of the pixel intensity histogram makes accurate corrections to account for saturated pixels. These outcomes can be used to correct a saturated signal, quantify the effect of saturation on a derived average and offer a method to correct the derived average in the case of slight to moderate saturation of pixels
Effect of fuel dilution on jet flames in a heated and diluted co-flow
No full textimaged by laser diagnostic techniques are presented. The measurements are of nonpremixed jet flames in a hot and highly diluted co-flow. These conditions emulate those of Moderate and Intense Low Oxygen Dilution (MILD) combustion. This paper presents results on the effect of O2 co-flow level and fuel dilution on the structure of the flames for a fixed jet Reynolds number. A reduction of O2 in the oxidant stream is shown to lead to a substantial suppression of both OH and H2CO levels. Within lifted flames, in comparison to the fluctuating levels of OH, H2CO levels remain constant. Although beyond the aim of the current investigation, a peripheral observation has been made that flames in a lower O2 co-flow stabilise at jet velocities which are lifted at higher O2 levels.http://www.mecheng.adelaide.edu.au/aspacc05
Effect of Reynolds number on the spatial distribution of OH and formaldehyde in jet flames in a heated and diluted co-flow
No full textThe spatial distribution of OH, formaldehyde (H2CO) and temperature imaged by laser diagnostic techniques are presented. The measurements are of nonpremixed jet flames in a hot and highly diluted co-flow. These conditions emulate those of Moderate and Intense Low Oxygen Dilution (MILD) combustion. This paper presents some results on the effect of O2 co-flow level and jet Reynolds number on the structure of the flames for various fuels (each diluted by hydrogen 1:1 vol/vol). A reduction of O2 levels is shown to lead to a substantial suppression of OH and a drop in peak temperatures. For strained flames, increased dilution of O2 also leads to reduction of H2CO. Reynolds number effects on the radial profiles of the flame species considered are shown to be minor compared to O2 levels. The drop of the peak temperature in a low O2 co-flow leads to a reduction of thermal gradients and hence a laminarisation of these flames. Strain rate does have a significant effect on the relative levels of H2CO however, with levels increasing markedly with higher Reynolds number.P R Medwell, P A M Kalt, and B B Dallyhttp://www.mecheng.adelaide.edu.au/aspacc05/noframes.htm
Calibrations for planar laser nephelometry in densely seeded two-phase flows
No full textNephelometry is a laser based imaging technique, which uses the signal of light scattered off particles to provide information about the local number density of these particles. In densely seeded flows of practical interest, such as pulverised coal flames, particle loadings can become very high, to the point where the incident laser beam is severely attenuated. Therefore, measurements in flows are hampered by these practical difficulties, and there are limited data at these conditions. Laser attenuation experiments were conducted in suspensions of spherical particles in water at various concentrations. Results enabled the formulation of a calibration for the effects of diffuse scatter and laser sheet extinction. A model for the distribution of light through a densely seeded, light-scattering medium is developed and is compared to experimental results. It is demonstrated that the scattered signal may be considered proportional to the local particle concentration multiplied by the incident laser power. The incident laser power varies as a function of the attenuation by obscurement. The current laser sheet extinction model may be implemented for both collimated and diverging light, in addition to nonhomogenously seeded scattering media. This correction for planar nephelometry images thus extends the technique to provide pseudo-quantitative data for instantaneous particle concentration measurements.Peter A. M. Kalt and Cristian H. Birze
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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