1,721,049 research outputs found
A lower bound for the height in abelian extensions
No full textAbstractWe produce an absolute lower bound for the height of the algebraic numbers (different from zero and from the roots of unity) lying in an abelian extension of the rationals. The proof rests on elementary congruences in cyclotomic fields and on Kronecker–Weber theorem
Numerical evaluation and experimental comparison of airframe noise for the optimization of next generation aircraft design
No full textIn this paper the airframe noise of civil transport aircraft is numerically evaluated and compared with measurements taken in some european airports with the target of separating the airframe contribution from other noise contributions effective on a typical aircraft. The attention has been focused on airframe noise since it sets a lower limit below whichever reduction of noise generated by engine have no significant effect on the overall noise level perceived by an observer and due to the aircraft flyover. The intensity of airframe noise depends on the aircraft configuration: during the cruise the aircraft exhibit an aerodynamically 'clean' configuration that produces less noise than the configuration assumed by the aircraft during landing and take-off, that usually is referred as 'dirty' one. The configuration with slats extended, flaps down and undercarriage lowered is more noisy than the clean configuration. In this paper the results of numerical simulations performed on common operating aircraft are presented: these simulations allow the contribution breakdown and, therefore, the classification of the most noisy airframe components for the different approach and take-off configurations
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
Design of a morphing test-article for large-scale, high-speed wind tunnel tests of an adaptive wing flap
No full textLarge efforts are currently being spent in Europe for the maturation of innovative technologies enabling the application of morphing systems on next-generation civil transport aircraft. Running along with the CleanSky2 platform, the AirGreen2 project aims to evolve the proofs of concept addressed during the CleanSky program into true-scale demonstrators for a more comprehensive validation of morphing architectures both on the ground and in flight. In this challenging framework, research activities have been carried out to design a novel multi-modal camber morphing flap for the enhancement of the aerodynamic performances of a new-generation regional aircraft. Referring to CFD analyses, very relevant benefits in terms of CLmax increase and stall angle delay were proved to be achievable by properly morphing the camber of the flap; the extra-lift produced by flap cambering resulted more than adequate to allow for takeoff and landing at a single flap deployment angle, in turn much lower than those required by a standard flap in both settings. As a side positive effect, a dramatic simplification of the flap deployment system was shown to be practicable, together with the adoption of fairing-less (no-drag) solutions with flap tracks fully embedded into the wing. In addition, wing aerodynamic efficiency in cruise was demonstrated to be enhanced by locally morphing the tip of the flap still exposed to the aerodynamic flow in flap-retracted configuration. The design and validation of the smart architecture enabling the different morphing modes required for low speed (take-off / landing) and high speed (cruise) conditions, consisted of a complex process involving both wind tunnel and ground tests. To increase the relevance of the wind tunnel test campaign, a large scale-factor (1:3) was selected for the test-article, in combination with the realization of the very same Mach numbers expected in flight. Standing the un-scalability of the flap architecture conceived for ground tests and flight operations, a very challenging design was faced for the test article, in order to define a totally new morphable system (Fig.1), assuring the same functionalities of the true-scale device. The path followed to accomplish this task has been outlined in this work, with emphasis on adopted design philosophy, implemented methodologies, and technological solutions
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