1,720,979 research outputs found
Hypersonic high altitude aerothermodynamics of a space re-entry vehicle
No full textThe analysis of the rarefaction effects in the prediction of the main aerothermal loads of a space re-entry vehicle is presented. It is well known that the Navier–Stokes equations fail in rarefied regimes and therefore other approaches must be used. In the present paper different configurations have been simulated by using the Direct Simulation Monte Carlo method. Moreover, slip flow boundary conditions have been implemented in a Navier–Stokes code in order to extend the validity of such a continuum method in the transitional flow regime. Finally, bridging-formulae for the high altitude aerodynamics of winged bodies have also been used. For the tuning of the methodologies, two simple geometries have been analysed, specifically designed to study the phenomenon of shock wave boundary layer interaction: the first one is a hollow cylinder flare, for which experimental data are also available; the second one is the geometry of a test article that was designed and tested at the Italian Aerospace Research Centre. The other two configurations that have been taken into account are an experimental winged re-entry vehicle and a capsule, for which global aerodynamic coefficients and local wall heating have been determined using different computational approaches. The Navier–Stokes code with slip flow boundary conditions has shown good predictive capabilities of the size of the recirculation bubble compared with the experimental results in the hollow cylinder flare test case; however, for the winged vehicle and capsule case, the CFD results are not fully satisfactory and the Monte Carlo method remains the most reliable approach, together with the bridging formulae, that provide good results for the global aerodynamic coefficients
Supercritical methane heat transfer modeling in rocket engine cooling channels
No full textLiquid propellants, which are typically used for regenerative cooling of rocket thrust chambers, can flow in channels at supercritical pressures and in the neighborhood of pseudo-critical temperature (near-critical fluid). This could be for instance the case for the envisioned liquid-oxygen/liquid-methane engines with chamber pressures larger than about 50 bar. When the fluid is in such a near-critical condition, deterioration in heat transfer can occur if the heat transfer level is higher than a threshold value. In this study detailed three-dimensional numerical analyses are performed to study the coupled wall/coolant environment of an electrically-heated test article designed in order to investigate the thermo-fluid dynamic behavior of methane inside a rectangular cooling channel which can be representative of a regenerative system. Different coolant pressure and surface roughness levels are considered in order to understand their influence on the heat transfer capability of the cooling system. Results evidence that the heat transfer deterioration can be mitigated either by increasing the coolant pressure or by increasing the surface roughness. In the latter case, a penalty in terms of coolant pressure drop is expected
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
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
Advanced Models for Prediction of High Altitude Aero-Thermal Loads of a Space Re-Entry Vehicle
No full text- …
