1,721,003 research outputs found
Numerical Simulations of Combustion Processes in Hybrid Rocket Engines Using OpenFoam and COOLFluiD Codes
No full textNumerical modeling of combustion processes in hybrid rocket engines
Full text linkNowadays, numerical simulations of combustion processes in hybrid rockets are generally considered as a qualitative tool used mainly to describe the flow field inside the rocket engine. A research effort is
of major importance in order to change this trend. It can be done by obtaining results that are quantitatively accurate, to be used as a support for experimental research, reducing costs, and increasing
efficiency in the development of better fuel formulations. The importance of such an effort relies on the fact that hybrid rockets are one of the most promising technologies in the aerospace propulsion field,
with applications in hypersonic atmospheric flight, launch vehicles' upper stages, and space tourism, which is seen as a prelude for an economically feasible mass access to space. This is possible because
of hybrid propulsion's low cost, intrinsic safety, and operational flexibility with potentially high performances. This research contribution aims to develop an accurate combustion model for traditional rubber-based hybrid rocket fuels (hydroxyl-terminated polybutadiene). Results of the simulations are presented as temperature distribution, axial velocity, and the products' mass fractions. A discussion about local and average fuel regression rates is presented, with particular attention to the effects on
both the local and average regression rate, due to an increase in oxidizer mass flux and in pressure.
Results of the present work suggest that an increase in oxidizer mass flux gives an increase in the average regression rate, while an increase in pressure gives a reduction in the average regression rate
Object oriented techniques for the numerical simulation of combustion processes in hybrid rocket engines
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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
Characterization of a Family of Paraffin-Based Solid Fuels
No full textIn the framework of EU-project ORPHEE, some innovative solid fuel formulations for hybrid rocket propulsion were manufactured and tested in order to overcome the shortcoming of very low fuel regression rates, typical of conventional hybrid rocket fuels. Firing tests were perfomed in a 2D slab burner implemented at SPLab (Space Propulsion Laboratory of Politecnico di Milano). Nano-Al powders and a metal hydride (Magnesium hydride (MgH2)) were used as fillers in paraffin matrices. The highest regression rates were found for the Solid Wax (SW) composition, added with 5% MgH2 mass fraction. At 350 kg/m2s oxygen mass flux, the measured regression rate, averaged in space and time, was 2.5 mm/s, which is approximately five times higher than that of the pure HTPB composition, taken as baseline reference fuel. Compositions added with nano-sized Aluminum powders were compared with those added with MgH2, using gel or solid wax. A rheological investigation and a mechanical characterization were performed, in order to explain the dependence of the regression rate on the nature and size of the metal powder, the viscosity of the paraffin melted layer, the thermodynamic properties of the different paraffins considered in this work
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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