1,721,094 research outputs found
Transition Between Open and Closed Wake in 3D Linear Aerospike Nozzles
No full textLinear aerospike nozzles are envisaged as a possible device able to improve launcher engine performance. One of the most interesting properties of these nozzles is the possibility of a good integration with the vehicle. Tb improve the knowledge of the flow-field and performance of aerospike nozzles, they are studied numerically, with particular attention to the differences between the basic two-dimensional nozzle, usually considered in the design phase, and the more realistic three-dimensional nozzle. The study considers different plug lengths and ambient pressures to assess the role of the linear plug side truncation on the base pressure behavior. Numerical tests are carried out at supersonic flight Mach number. Copyright © 2005 by M. Geron and R. Paciorri.F. Nasuti, F. Sabetta, E. Martelli
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
CFD Boundary Conditions for the Interaction of Rocket Nozzle Flows with Ablating Walls
No full textThermal protection system (TPS) typically use materials which ablate at high temperature for mass-efficient rejection of aerothermal heat load. A reliable numerical procedure that can compute surface recession rate, mass loss, surface heat flux, and surface temperature distribution under general heating conditions is essential to successfully carry out the design of an optimum TPS. Thus, in order to improve estimating of the heat flux over an ablating surface, a flow solver coupled with ablating surface conditions becomes a requirement. A study have been conducted to predict nozzle recession behaviour in
a solid rocket motor nozzle and for broad variations of motor operating conditions
Analysis of the transition process in dual bell nozzles
No full textDual bell nozzles may represent a possible alternative to replace conventional bell nozzles in future launcher first stages. Their main feature is the peculiar shape of the divergent section, displaying two bells jointed by an inflection point. Although this is a non-optimized shape, it allows two different operating modes that provide at high altitude larger expansion ratios than conventional nozzles, while avoiding side-loads at sea-level. The present study addresses the main critical aspects of the design of the nozzle shape. In particular, numerical tests have been carried out to understand the role of the inflection point region and of the second bell profile on the nozzle behavior during the phase of transition between the two operating modes. As a result suggestions are provided to be considered when designing the second bell profile
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
Effect of Wall Shape and Real Gas Properties on Dual Bell Nozzle Flowfields
No full textDual bell nozzle permits two different operating modes, which provide higher performance than conventional bell nozzles, when applied to rocket engines operating from sealevel. During the highly overexpanded mode the separation line is located near the geometrical
discontinuity of the nozzle wall, in a region characterized by a negative value of the wall pressure gradient as in conventional nozzle and where side loads may occur. The characteristics of this region in hot full-scale applications are addressed by means of numerical simulations, and scaling laws are sought for cold sub-scale side loads experiments. In addition, because of the possible effect of wall cooling on the wall pressure gradient and thus on side loads, the relevant role of film cooling is discussed in detail
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