1,720,977 research outputs found
A Guidance System for Unmanned Air Vehicles based on fuzzy Sets and fixed Waypoints
No full textThe problem of guidance and control of unmanned aerial vehicles (UAVs) has become a topic of research in recent years. Typical projected UAV operations such as surveillance, payload delivery, and search and rescue can be addressed by waypoint-based guidance. Automatic target recognition, for instance, requires that the aircraft approach the possible target from one or more desired directions. In a highly dynamic cooperative UAV environment, the management system, either centralized or decentralized, may switch the waypoint set rapidly to change an aircraft mission depending on external events, pop-up threats, etc.; the new waypoint set may be ill-formed in terms of flyability (maximum turn rates, descent speed, acceleration, etc.).
Fast Unmanned Vehicles Task Allocation with Moving Targets
No full textThis paper presents a fast algorithm for allocation at mission-time of moving targets to a group of unmanned vehicles. A fleet of UAVs must fly through a known environment to reach partially unknown locations, or targets, where three tasks: identification, attack and verification must be performed sequentially. The total mission cost is identified to be the sum of the total times that the UAVs spend completing their tasks, while respecting the task priorities and ensuring the tasks precedence laws. The problem is solved in two steps; the first step is performed off-line and is the most computationally intensive: the environment is subdivided into triangle-shaped areas forming the Tessellation Graph (TG), and the shortest path between each two vertexes couples of the plane is computed using the All-Pairs-Nodes Dijkstra algorithm. The second step, at mission-time, regards management of moving targets and adaptation to the results of the identification phase. Optimal task assignment is performed using the Hungarian algorithm; exact path lengths between vehicles and targets are computed from the off-line computed Dijkstra paths. One parameter is available to tune the optimal task allocation algorithm with respect to desired aggressive/selfish or cooperative behavior
A Fuzzy Approach to the Guidance of Unmanned Air Vehicles Tracking moving Targets
No full textThis paper presents the development of a fuzzy guidance system for unmanned aircraft based on waypoints described in a 5-D space: position in 3-dimensions, desired crossing heading, and speed. The aircraft is assumed to be auto piloted in speed, heading, and flight path angle. The proposed system uses standard Takagi-Sugeno fuzzy controllers that provide speed, heading, and flight path angle references for the autopilots. In particular, the heading guidance law results in a pipeline of two fuzzy controllers depending on the relative distance between aircraft and waypoint. A trajectory optimization algorithm is used to yield a long-distance guidance law blended with a short-distance guidance law as the waypoint approaches. The system handles sets of not directly flyable waypoints, driving the aircraft on flyable trajectories that try to cross the waypoints at a prescribed altitude and heading
Real-Time Unmanned Vehicles Task Allocation with Moving Targets
No full textThe problem of task allocation for a fleet of unmanned aerial vehicles (UAV), in the presence of moving targets, was discussed using a viable algorithms in the real-time sense. It was found that a N UAVs must fly through a partial unknown environment to reach M known locations, or targets, where a set of tasks must be performed. It was found that when the targets were not moving, an optimal solution to the task allocation problem exist. The task allocation problem with obstacle with obstacle avoidance and sequentially constraint was solved with a pipeline procees that performs the most computationally intensive tasks off-line
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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