1,720,984 research outputs found
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
Thermodynamic Analysis of a Turboprop Engine with Intercooling and Heat Recovery
No full textIn many modern gas turbine engine ground-based power plants, used for power generation, several auxiliary systems are integrated with the main gas generator to improve the generated output power or reduce fuel consumption. Two of the most effective practices are regeneration and intercooling. The first recovers part of the enthalpy in exhaust gas to pre-heat air before introducing it into the combustion chamber. The second cools the air during compression to reduce the work, and consequently obtain more power at the output shaft. These techniques are not used in gas turbine engines for propulsion mainly due to the extra weight and size caused by the heat exchangers and more complex flow patterns that result. However, if we could overcome these difficulties by means of compact heat exchangers the same benefits obtained for the ground-based plants could be obtained for aero engines. In particular the turboprop engine seems to be the best suited to this purpose due to its smaller mass flow rate and gas path. A thermodynamic cycle analysis shows the advantages of introduction of regeneration and intercooling in a turboprop engine in terms of increased power and reduced fuel consumption
Fuel Consumption Reduction and Weight Estimate of an Intercooled-Recuperated Turboprop Engine
No full textThe introduction of intercooling and regeneration in a gas turbine engine can lead to performance improvement and fuel consumption reduction. Moreover, as first consequence of the saved fuel, also the pollutant emission can be greatly reduced. Turboprop seems to be the most suitable gas turbine engine to be equipped with intercooler and heat recuperator thanks to the relatively small mass flow rate and the small propulsion power fraction due to the exhaust nozzle. However, the extra weight and drag due to the heat exchangers must be carefully considered. An intercooled-recuperated turboprop engine is studied by means of a thermodynamic numeric code that, computing the thermal cycle, simulates the engine behavior at different operating conditions. The main aero engine performances, as specific power and specific fuel consumption, are then evaluated from the cycle analysis. The saved fuel, the pollution reduction, and the engine weight are then estimated for an example case
Off-design performances of a gas turbine engine with heat recovery and intercooling
No full textThe reduction of fuel consumption and pollutant emissions have become one of the main requirements of modern gas turbine aero engines. To pursue this aim engineers are developing new techniques to improve the efficiency of the thermodynamic cycle of new engines. In particular the attention is focused on the possibility to introduce practices as heat regeneration and staged-intercooled compression process on these engines. These practices, that change considerably the features of the working cycle of the engine, are well known and widely used in ground based power plants, but until now they have not been transferred on aero engines, mainly for problems of extra weight and size. However now these problems seem to be overcome by new technology, and the possibility to have intercooled-recuperated gas turbine engines on a plane has become real. A thermodynamic code that simulates the behavior of a gas turbine engine at different engine and operating conditions has been developed. In this paper are presented the main results obtained with the code, simulating the behavior of a turboprop engine in which both intercooling and regeneration are introduced. An off-design analysis is then performed to compare the behavior difference between the two engines when operate at different conditions respect to the design point. © 2012 by Roberto Andriani
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
Off-design characteristics of low-fuel consumption gas turbine engine for long-range UAV
No full textUAVs are becoming of always greater importance, both for civil and military uses. Some UAV missions require a flight length of many hours, sometimes lasting more than two days. In these cases, the engine fuel consumption characteristics become of primary importance. In this sense, it is interesting to study the effects of some techniques, as intercooling and regeneration, on the engine power and fuel consumption, in particular in a turboprop engine, commonly used for this kind of missions. These effects have been studied by means of a thermodynamic numeric program that simulates the behavior of a turboprop engine with intercooling and regeneration, or with regeneration only. The program allows to do a parametric study, computing the main engine characteristics, as thermal efficiency, specific power and specific fuel consumption, for different operating conditions. After the parametric study, an off-design analysis has been performed, to see how the main engine parameters change
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