1,720,976 research outputs found
Study of direct gas injection into stagnation zone of blunt nose at hypersonic flow
No full textDirect gas injection in the shocked or compressed region has importance in many applications from drag control to ignition and pressure gain combustion. This numerical study is focused on direct light gas injection into the stagnation zone of a blunt nose at hypersonic speed, aiming to achieve efficient active drag control. The direct injection of a inert gas helium and a reactive gas hydrogen in the stagnation zone of bow-shock, are compared numerically with the air injection at hypersonic flow Mach 6 with freestream conditions according to the Earth’s altitude of 10 km. The two-dimensional axisymmetric numerical simulations are performed by adaptive mesh refinement and solving compressible Euler equations for multiple thermally perfect species with a reactive source term using AMROC solver. The hydrogen combustionand ignition is modelled using one-step reaction mechanism. The pressure drag on the blunt nose has been compared for different injection pressure ratios for all three gas injections and it was concluded that the sonic injection (at Mach = 1) of light gases He and H2 provides similar performance in the pressure drag reduction up to 77%, as compared to air injection, with 62.5% and 73.5% lesser mass flow rate, respectively. In case of supersonic gas injection (at Mach = 2), the inert gas helium injection performs relatively better (up to 82% pressure drag reduction) or comparable to supersonic air injection for lesser mass flow rates. Various flow features in the short and long penetration modes of sonic and supersonic gas injections are also analyzed in the reactive and non-reactive flow-fields
Numerical investigation of detonation propagation through small orifice holes
Get PDFThe propagation of a detonation wave along a tube filled with a hydrogen-oxygen mixture, diluted with argon in the presence of obstacles with small orifice hole has been investigated numerically. The numerical simulations are performed in a two-dimensional domain using adaptive mesh refinement and by solving compressible Euler equations for multiple thermally perfect species with a reactive source term. The premixed mixture of H2: O2: Ar at a ratio 2: 1:7 at 10.0 kPa and 298 K has been used in a 90 mm diameter tube with a detonation wave travelling from one end. It was observed that a single orifice placed at 200 mm from one end of the tube, with varying diameters of 6, 10, 14, 16, 18, 30, and 50 mm show an initial decoupling of the detonation wave into a shockwave and flame front. Along the tube the detonation wave fails to propagate for orifice diameters less than \lambda, while it propagates by different re-initiation pathways for orifice diameters greater than \lambda, where \lambda is the cell-width for regular detonation propagation. This paper details the observed detonation re-initiation and failure in a detonation re-initiation mechanism for the cases considered
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
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
Oblique detonation wave control with O<sub>3</sub> and H<sub>2</sub>O<sub>2</sub> sensitization in hypersonic flow
No full textThis numerical study investigates the effects of adding a small amount of ignition promoters for controlling the wedge-induced oblique shock wave (OSW) to oblique detonation wave (ODW) transition in a premixed hydrogen–air mixture at hypersonic speeds. The time-dependent two-dimensional compressible Euler equations for multiple thermally perfect species with a reactive source term are solved using adaptive mesh refinement and detailed chemical kinetics. The wedge with a fixed angle of 26
◦ exhibits abrupt to smooth transitions for freestream Mach numbers 7–9 (speeds 2.8–3.2 km/s) at a pressure of 20 kPa and a temperature of 300 K. The small amount (1000 PPM by vol.) of H
2O
2 and O
3 is found to be effective at significantly reducing the initiation length for the oblique detonation transition for all Mach numbers, which suggests a practical approach to increase the operating flight range for oblique detonation wave engine with a finite length wedge. At Mach number 8, the abrupt OSW to ODW transition turns towards a smooth transition with a small amount of H
2O
2 and O
3 addition. Comparatively, O
3 addition was found to be effective in reducing the ODW initiation length by promoting reactivity behind even a weaker oblique shock at low Mach number 7, for abrupt transition, while H
2O
2 addition was more effective than O
3 at high Mach numbers 8 and 9, during a smooth transition. The maximum 73% and 80% reduction in initiation length of ODW was observed with 10,000 PPM H
2O
2 and O
3 addition, respectively, during an abrupt OSW to ODW transition at Mach 7.
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