1,720,956 research outputs found
Lyapunov-based second-order sliding mode control for a class of uncertain reaction-diffusion processes
No full textThis paper addresses the design of a distributed, second-order sliding-mode based, tracking controller for a class of uncertain diffusion-reaction processes. Spatially varying uncertain parameters and mixed boundary conditions, along with the presence of an uncertain distributed disturbance, characterize the considered class of processes. The paper presents a constructive Lyapunov-based stability analysis which leads to simple tuning conditions for the controller parameters, The good performance of the proposed control systems are verified by means of computer simulations
Unknown Input Observer with sliding mode disturbance estimator for the Diffusion PDE
No full textIn this note an Unknown Input Observer and a disturbance estimator are proposed for a class of distributed parameter systems. The 1D diffusion equation subject to an uncertain exogenous input is dealt with, and point-wise measurements are considered. The observer/estimator design is carried out by making reference to a finite dimensional modal decomposition of the solution. A combined state and output transformation is applied to the resulting finite dimensional approximation, yielding a special form for the transformed system that allows the implementation of a linear observer for reconstructing the system state and a sliding mode observer for reconstructing the unknown input. Numerical simulations show the applicability of the suggested approach to the considered class of PDEs
Sliding-mode Boundary Control of Uncertain Reaction-Diffusion Processes with Spatially Varying Parameters
No full textThe primary concern of the present paper is the stabilization problem of a one-dimensional uncertain reaction-diffusion process powered with a Dirichlet type actuator from one of the boundaries. The heat flux at the controlled boundary is the only measured signal, the uncertain diffusion and reaction parameters are admitted to be spatially varying, and the system is also affected by a sufficiently smooth boundary disturbance, which is not available for measurements and can be also unbounded in magnitude. The proposed robust synthesis is based on a dynamic input extension, and it is formed by the relay control algorithm and a linear term, suitably combined. A continuous stabilizing boundary control law is suggested to achieve exponential stability under some restrictions on the uncertain parameters spatial profiles characteristics. A Lyapunov-based functional analysis is invoked to establish the global exponential stability in the Sobolev space W1, 2(0, 1). The proof is accompanied by a set of simple tuning rules for the controller parameters. The effectiveness of the developed control scheme is supported by simulation results
On the Lyapunov-based second-order SMC design for some classes of distributed parameter systems
No full textThis paper addresses the Lyapunov-based design of second-order sliding mode controllers in the domain of distributed parameter systems (DPSs). To the best of our knowledge, the recent authors' publications (Orlov et al., 2010, Continuous state-feedback tracking of an uncertain heat diffusion process. Syst. Control Lett., 59, 754-759; Orlov et al., 2011, Exponential stabilization of the uncertain wave equation via distributed dynamic input extension. IEEE Trans. Autom. Control, 56, 212-217; Pisano et al., 2011, Tracking control of the uncertain heat and wave equation via power-fractional and sliding-mode techniques. SIAM J. Control Optim., 49, 363-382) represent the seminal applications of second-order sliding mode control techniques to DPSs. A Lyapunov-based framework of analysis was found to be appropriate in the above publications. While reviewing the main existing results in this new field of investigation, the paper provides the novelty as well and gives several hints and perspectives for the generalization, listing some open problems
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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