1,720,958 research outputs found
A set based approach for SFDI on small commercial aircraft
No full textThe problem of detecting and isolating faults on duplex sensor architecture in a small commercial aircraft is considered. The use of a Set-Based approach involving a bank of consistency signal generators is proposed. In particular, by exploiting the knowledge of dynamic relations between command inputs and sensed variables in discrete time, sensor measurements accuracy has been estimated also in the presence of bounded disturbances and model uncertainties. Then, a Health Measurement Voting Supervisor detects and isolates faulty sensor. Numerical simulations involving a nonlinear aircraft mathematical model subject to atmospheric disturbance and sensor noise are performed in order to show the practical applicability of the proposed technique
A robust constrained model predictive control scheme for norm-bounded uncertain systems with partial state measurements
No full textA robust model predictive control scheme for a class of constrained norm-bounded uncertain discrete-time linear systems is developed under the hypothesis that only partial state measurements are available for feedback. The proposed strategy involves a two-phase procedure. Initialization phase is devoted to determining an admissible, though not optimal, linear memoryless controller capable to formally address the input rate constraint; then, during on-line phase, predictive capabilities complement the designed controller by means of N steps free control actions in a receding horizon fashion. These additive control actions are obtained by solving semidefinite programming problems subject to linear matrix inequalities constraints. As computational burden grows linearly with the control horizon length, an example is developed to show the effectiveness of the proposed approach for realistic control problems: the design of a flight control law for a flexible unmanned over-actuated aircraft, where the states of the flexibility dynamics are not measurable, is discussed, and a numerical implementation of the controller within a nonlinear simulation environment testifies the validity of the proposed approach and the possibility to implement the algorithm on an onboard computer
A reconfigurable aircraft control scheme based on an hybrid Command Governor supervisory approach
No full textIn this paper, we adopt the hybrid supervisory control architecture developed in [1] for constrained control systems. The strategy is based on Command Governor (CG) ideas and is tailored to jointly take into account time-varying set-points/constraints and unpredictable anomalies in the nominal dynamical plant behaviour. The main contribution is to develop a low-computational demanding predictive scheme known in literature as the command governor (CG) for the supervision of non- linear dynamical systems subject to sudden switchings amongst operating conditions and time-varying constraints by preserving its basic properties. In order to show the effectiveness of proposed approach, we show significant simulations on the P92 commercial aircraft used for general aviation purposes. © 2014 American Automatic Control Council
A norm-bounded robust MPC strategy with partial state measurements
No full textIn this paper a robust MPC scheme based on a partial-state availability is developed for uncertain discrete-time linear systems described by structured norm-bounded model uncertainties and subject to saturation and rate of variation constraints. The algorithm is based on the minimization, at each time instant, of a semi-definite convex optimization problem subject to Linear Matrix Inequalities (LMI) feasibility constraints which are derived by a judicious use of S-Procedure arguments. Numerical comparisons with competitor algorithms are finally reported by dealing with the control augmentation problem of an High Altitude Performance Demonstrator (HAPD) unmanned aircraft with redundant control surfaces
A Receding Horizon Control scheme with partial state measurements: Control Augmentation of a flexible UAV
No full textIn this paper the implementation of an Output Feedback Receding Horizon Control (RHC) algorithm for constrained uncertain discrete-time linear systems subject to norm-bounded Linear Fractional Representation (LFR) model uncertainties has been developed. Performance and effectiveness of the proposed strategy have been numerically tested by considering the control augmentation problem of an High Altitude Performance Demonstrator (HAPD) unmanned aircraft with redundant control surfaces. © 2013 IEEE
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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