1,720,981 research outputs found
Liquefying Fuel Combustion in a Lab-scale Vortex Flow Pancake Hybrid Rocket Engine
No full textThe combustion behavior of paraffin-based blends is investigated by a lab-scale vortex flow pancake motor (VFP). A complete pre-burning characterization for different paraffin-based fuel formulations is performed. The tested compositions are based on a micro-crystalline paraffin wax (W1), possibly blended with a styrene-based reinforcing polymer (SEBS-MA). Liquid paraffin (LP) is considered as an additional fuel ingredient for mechanical properties tailoring. The pre-burning characterization of the fuels includes thermal behavior investigation, rheological, tensile and compression analyses. In this preliminary investigation, 12 combustion tests are performed with quasisteady operating conditions. The main observable of interest is the solid fuel regression rate. Effects of the vortex flow combustion on the combustion efficiency are assessed by the characteristic velocity efficiency of the lab-scale system. The pre-burning characterization proves that SEBS-MA is a good candidate for improving the mechanical and thermal characteristics for the blends. LP had a significant impact on decreasing the viscosity of the blends
Effects of Vortex Flow Pancake Hybrid Rocket Engine Operating Parameters on Liquefying Fuel Combustion
No full textExperimental results from the vortex flow pancake hybrid rocket engine implemented at the Space Propulsion Laboratory of Politecnico di Milano are presented. Paraffin-based fuels are tested under quasi-steady and forced transient operating conditions. This preliminary investigation shows a database of more than 30 firings with quasi-steady operating conditions, and 4 runs with oxidizer mass flow rate throttling. The three main engine operating parameters varied in the current research are: (i) the oxidizer mass flow rate, (ii) the combustion chamber height, and (iii) the oxidizer injection velocity. The latter parameter is altered by changing the number of injectors for the oxidizer inlet flow. Throttling is performed on selected fuel formulations. Under the investigated conditions, the quasi-steady tests showed a regression rate decrease for increasing reinforcing polymer mass fraction in the paraffin-based blends. Such a result is due to the augmented viscosity of the melt layer of the formulations as the reinforcing polymer mass fraction increases. At the same time, the regression rate showed no direct dependence on the initial combustion chamber height, while oxidizer injection velocity dependence was identified. Forced transient tests showed an immediate response to throttling for the two investigated fuels
Cellular Structures for Solid Fuel Grain Reinforcement: Mechanical and Combustion Performance in Conventional and Non-Conventional 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
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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