1,720,954 research outputs found
Effects of Particle Size and Mixture Composition on Propulsive Performance of Gelled and Refrigerated Aluminum-Liquid Oxidizer Propellants
No full textThe propulsive performance of aluminum-liquid oxidizer mixtures is studied using an Eulerian-Eulerian multiphase Computational Fluid Dynamics model. The simulations are performed to capture the high-speed multiphase flow dynamics in a lab-scale rocket motor and predict the propulsive performance parameters. The focus of the study is to examine the effects of particle size and mixture composition on key performance parameters such as chamber pressure, thrust, characteristic velocity, and specific impulse. For nano-aluminum and water propellants, the chamber pressure and thrust increase significantly with decreasing particle diameter; a d−1.6 p correlation is observed. The specific impulse increases with decreasing particle size due to the reduction in two-phase flow losses. However, when the particle size is decreased below 50 nm, a reduction in the specific impulse is observed due to the increase in the oxide content in the particles. The effect of mixture composition is studied by varying the equivalence ratio and H2O2 concentration in the oxidizer. Decreasing the equivalence ratio from 0.943 to 0.71 and increasing the H2O2 concentration in the oxidizer from 0 to 25%increased the peak chamber pressure and peak thrust due to the increase in the propellant burning rates. However, the characteristic velocity and specific impulse are not as strongly affected. Modifying the pH of water also increases the peak chamber pressure and peak thrust without altering the specific impulse significantly. Overall, the computed specific impulses are in the range of 130-175 s, substantially lower than the ideal theoretical specific impulse, thereby highlighting excessive two-phase flow losses for these propellants
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
A computational fluid dynamics model of combustion of nanoaluminum–water propellant strands
No full textA computational fluid dynamics model of combustion of nanoaluminum–water propellants is developed. An unsteady and axisymmetric model of strand combustion is developed to mimic the experimental setup and conditions. The entire time evolution of strand combustion from ignition until steady-state flame propagation through the strand is simulated. A multiphase Eulerian modeling approach is adopted to handle multiple phases and the associated transport processes. The mass, momentum, species, and energy conservation equations are discretized using the Finite Volume Method. A rigorous computational framework with superior accuracy and stability characteristics is developed and implemented. The theoretical and computational framework is first verified and validated by running standard test cases such as Stefan problem, fluidized bed, and constant-volume reactor. Upon verification and validation, the framework is applied to simulate combustion of stoichiometric nanoaluminum–water propellant strands. The particle size is chosen to be 80 nm and pressure range is taken as 1–10 MPa. The temporal evolutions of flow, temperature, and species composition fields are computed and insights into the underlying physicochemical processes are provided. Measurable quantities such as the burning rate and pressure exponent are computed. Both fixed bed and moving bed combustion scenarios are simulated and the effects of particle retainment in the propellant bed and particle agglomeration are studied. It is found that the multiphase flow dynamics strongly affect the burning rate and its pressure exponent. The present study suggests that the combustion of nano-aluminum and water propellants is diffusion-controlled due to agglomeration of particles. Novelty and significance statement A novel theoretical and computational framework is developed to simulate nano-aluminum and water propellant strand combustion. In a paradigm shift in the modeling and simulation approach, a Computational Fluid Dynamics (CFD) approach is adopted to simulate strand burning experiments as closely as possible. A comprehensive multiphase model is developed to resolve all underlying physiochemical processes including boiling of liquid water, multiphase flow dynamics, chemical reactions, and thermal transport. The entire time evolution from ignition until steady-state flame propagation is simulated for an axisymmetric propellant strand. The study provides new insights on the underlying processes that occur during the entire time history of propellant combustion. The simulations demonstrate the importance of multiphase flow dynamics and its impact on propellant combustion. It is discovered that the pressure dependence of burning rate of nano-aluminum and water propellant is primarily due to multiphase flow dynamics and that the combustion of nano-aluminum and water propellants is diffusion-controlled due to agglomeration of particles
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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