1,721,072 research outputs found
Estimation of the region of attraction for state-dependent Riccati equation controllers
No full textA new method for estimating a higher bound of the region of attraction of a nonlinear system is developed for state-dependent Riccati equation controller. The methodology can be applied to SDRE-controlled systems for improving the stability properties of such systems. The method calculates a Lyapumov function for the linearized system near the origin, and is then applied to the complete nonlinear system. The generation of a grid in a region of the state space is necessary, and the procedure must be run on the grid points, resulting in a computationally intensive procedure especially for large size systems. The procedure is similar with the only difference being the overvaluing matrix, which has to be found with respect to the closed loop matrix resulting from the SDRE control. This implies that the SDRE has to be solved pointwise because the closed form solution is not known in general, which makes the gridding of the state space necessary
Cooperative Task Assignment using Dynamic Ranking
No full textThe paper presents a novel approach to the decentralized task assignment for multiple cooperative unmanned air systems, in a multiple target-multiple task environment. The vehicles (or agents) may have complete or partial a priori information about the targets that populate the scenario. Each vehicle autonomously computes the cost for servicing each task available at each target using a path planning algorithm, taking into account obstacles, pop-up threats, and weights the total path cost including potential risk areas. Vehicles assign an initial ranking to each task, and then exchange their ranking information with the others. Each agent then updates the ranking of its tasks using a non linear dynamic programming algorithm that is proven to be stable and to converge to an equilibrium point. The ranking dynamics is initially formulated as a continuous time system, and then time-discretized depending on available data, and transmission rate among the network. Stability of the network and independence of steady state values from the data rate are proved analytically. Current studies are directed towards the effect of communication delays. The validity and performance of the proposed method are verifed via extensive numerical simulation, and compared with alternate techniques such as an optimal MILP based integrated task assignment and path planning solver. Copyright © 2007 International Federation of Automatic Control All Rights Reserved
Cooperative path planning and task assignment for unmanned air vehicles
No full textThis article presents a review and a novel approach to the decentralized path planning and task assignment for multiple cooperative unmanned air systems, in multiple target, and multiple task environment. The vehicles (or agents) may have complete or partial a priori information about the targets that populate the scenario. Each vehicle autonomously computes the cost for servicing each task available at each target using a path planning algorithm, taking into account obstacles, pop-up threats, and weights the total path cost including potential risk areas. Vehicles assign an initial ranking to each task, and then exchange their ranking information with the others. Each agent then updates the ranking of its tasks using a non-linear dynamic programming algorithm that is proven to be stable and to converge to an equilibrium point where each vehicle is assigned to a different task. The ranking dynamics is initially formulated as a continuous time system, and then time-discretized depending on available data, and transmission rate among the network. Stability of the network and independence of steady-state values from the data rate are evaluated analytically, and via simulation
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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