1,721,016 research outputs found
A particle swarm approach for flight path optimization in a constrained environment
No full textPotentials of Particle Swarm Optimization techniques in the field of flight path generation are investigated in this paper. The objective is the development of a particle swarm-based procedure performing off-line two-dimensional flight path optimizations compliant with operational constraints. Assuming a typical surveillance mission, such constraints are defined in terms of "target" and "no-fly" zones, desired flight time on targets, fixed way-points and landing areas. Flight path is described through a discrete number of suitable flight parameters varying within defined ranges, each particle of the swarm being represented by a numerical combination of these parameters. A novel obstacle avoidance model based on the evaluation of a so-called area function has been introduced. All trajectories, made up of circular arcs and straight lines, start from a specified point with fixed velocity vector, ending within a selected landing area. Both single-objective and multi-objective optimization procedures have been formulated and implemented. The former minimize the total flight path length; the latter also try to maximize the trajectory length covered over specified target areas. Sensitivity studies with increasing problem complexity have been performed changing both number and positions of "target" and "no-fly" zones in order to assess the effectiveness as well as the robustness of the proposed approach. Algorithm capability in finding the optimum path through non-circular and concave obstacles has also been tested. Finally computational time monitoring allowed making a preliminary assessment of Particle Swarm Optimization suitability for practical applications. © 2012 Elsevier Masson SAS
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
Intersubjectivity in primary and secondary education: a review study
No full textIn this literature review on the dynamics of intersubjectivity in primary and secondary education, we summarise and examine articles published in the last 10 years. This concept is considered relevant in education, in particular to enhance different types of collaborative learning situations. The articles were selected from several databases, all in English and blindly peer-reviewed. From the 157 articles appearing when limiting the contexts to primary and secondary education, 25 empirical studies were selected because they focused on the collaborative activities of students-students and/or teacher-students. We are also interested in understanding the role that technology may play in such process. Additionally, research where some types of digital technologies were used was contrasted with studies with analogical technologies. The selected articles were analysed with the aim of highlighting ideas and critical concepts featuring the process of producing intersubjectivity. As relevant dimensions, we identified: (a) teachers’ role; (b) cultural and/ or intercultural dimension; (c) the role of cognitive aspects; (d) the role of social dimension, and (e) the role of space-time. Finally, implications for future empirical studies and educational practices are outline
Multiobjective Particle Swarm Optimization technique as an effective tool for aircraft requirements analysis
No full textIn this paper, a multi-objective particle swarm optimization (MOPSO) procedure has been developed and applied in the field of aircraft requirement analysis. In order to identify useful set-up schemes for algorithm control parameters, the optimisation procedure has been preliminarily verified with test-case functions. Moreover, specific tools have been implemented to improve MOPSO effectiveness in finding Pareto front as wide and uniform as possible. The optimization procedure has been subsequently applied to the preliminary definition of a civil transport aircraft configuration. Both maximum takeoff weight and block time have been selected as objective functions to be minimized. At the end of optimization process, useful sensitivity curves, showing cruise speed requirement effects on aircraft main characteristics, have been obtained. Finally, a comparison with a similar task driven by a genetic algorithm has been performed in order to highlight some advantages offered by MOPSO procedure
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
The role of the ATPase inhibitor factor 1 (IF(1)) in cancer cells adaptation to hypoxia and anoxia
No full textThe physiological role of the mitochondrial ATP synthase complex is to generate ATP through oxidative phosphorylation. Indeed, the enzyme can reverse its activity and hydrolyze ATP under ischemic conditions, as shown in isolated mitochondria and in mammalian heart and liver. However, what occurs when cancer cells experience hypoxia or anoxia has not been well explored. In the present study, we investigated the bioenergetics of cancer cells under hypoxic/anoxic conditions with particular emphasis on ATP synthase, and the conditions driving it to work in reverse. In this context, we further examined the role exerted by its endogenous inhibitor factor, IF1, that it is overexpressed in cancer cells. Metabolic and bioenergetic analysis of cancer cells exposed to severe hypoxia (down to 0.1% O2) unexpectedly showed that Δψm is preserved independently of the presence of IF1 and that ATP synthase still phosphorylates ADP though at a much lower rate than in normoxia. However, when we induced an anoxia-mimicking condition by collapsing ΔμΗ+ with the FCCP uncoupler, the IF1-silenced clones only reversed the ATP synthase activity hydrolyzing ATP in order to reconstitute the electrochemical proton gradient. Notably, in cancer cells IF1 overexpression fully prevents ATP synthase hydrolytic activity activation under uncoupling conditions. Therefore, our results suggest that IF1 overexpression promotes cancer cells survival under temporary anoxic conditions by preserving cellular ATP despite mitochondria dysfunction
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