1,720,958 research outputs found
An online algorithm for constrained POMDPs
No full textThis work seeks to address the problem of planning in the presence of uncertainty and constraints. Such problems arise in many situations, including the basis of this work, which involves planning for a team of first responders (both humans and robots) operating in an urban environment. The problem is framed as a Partially-Observable Markov Decision Process (POMDP) with constraints, and it is shown that even in a relatively simple planning problem, modeling constraints as large penalties does not lead to good solutions. The main contribution of the work is a new online algorithm that explicitly ensures constraint feasibility while remaining computationally tractable. Its performance is demonstrated on an example problem and it is demonstrated that our online algorithm generates policies comparable to an offline constrained POMDP algorithm.United States. Office of Naval Research (grant N00014-07-1-0749
An intelligent cooperative control architecture
Get PDFThis paper presents an extension of existing cooperative control algorithms that have been developed for multi-UAV applications to utilize real-time observations and/or performance metric(s) in conjunction with learning methods to generate a more intelligent planner response. We approach this issue from a cooperative control perspective and embed elements of feedback control and active learning, resulting in an new intelligent Cooperative Control Architecture (iCCA). We describe this architecture, discuss some of the issues that must be addressed, and present illustrative examples of cooperative control problems where iCCA can be applied effectively.United States. Air Force Office of Scientific Research (grant FA9550-08-1-0086)Boeing Scientific Research Laboratorie
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Planning under uncertainty and constraints for teams of autonomous agents
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 155-164).One of the main advantages of unmanned, autonomous vehicles is their potential use in dangerous situations, such as victim search and rescue in the aftermath of an urban disaster. Unmanned vehicles can complement human first responders by performing tasks that do not require human expertise (e.g., communication) and supplement them by providing capabilities a human first responder would not have immediately available (e.g., aerial surveillance). However, for unmanned vehicles to work seamlessly and unintrusively with human responders, a high degree of autonomy and planning is necessary. In particular, the unmanned vehicles should be able to account for the dynamic nature of their operating environment, the uncertain nature of their tasks and outcomes, and the risks that are inherent in working in such a situation. This thesis therefore addresses the problem of planning under uncertainty in the presence of risk. This work formulates the planning problem as a Markov Decision Process with constraints, and offers a formal definition for the notion of "risk". Then, a fast and computationally efficient solution is proposed. Next, the complications that arise when planning for large teams of unmanned vehicles are considered, and a decentralized approach is investigated and shown to be efficient under some assumptions. However some of these assumptions place restrictions - specifically on the amount of risk each agent can take. These restrictions hamper individual agents' ability to adapt to a changing environment. Hence a consensus-based approach that allows agents to take more risk is introduced and shown to be effective in achieving high reward. Finally, some experimental results are presented that validate the performance of the solution techniques proposed.by Aditya Undurti.Ph.D
Variations on the Author
Get PDF“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
Get PDFWe 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
Optimal trajectories for maneuvering reentry vehicles
Get PDFThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.Includes bibliographical references (p. 187-189).Many demanding aerospace missions today require maneuverable re-entry vehicles that can fly trajectories that have stringent path and terminal constraints, including those that cannot be written as drag or energy constraints. This work presents a method based on trajectory optimization techniques to assess the capabilities of the re-entry vehicle by computing the landing and re-entry footprints while meeting these conditions. The models used also account for important non-linear effects seen during hypersonic flight. Several different vehicles are studied, and the effects of parameters such the maximum G-loading, stagnation point heat rate, and the maximum L/D are analyzed.by Aditya Undurti.S.M
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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