1,720,967 research outputs found
Stability and stabilization of piecewise affine and hybrid systems
No full textIn this paper we present various algorithms both for stability analysis and
state-feedback design for discrete-time piecewise affine systems. As in (Johansson and Rantzer, 1998), our
approach hinges on the use of piecewise quadratic Lyapunov functions that can be computed
as the solution of a set of linear matrix inequalities. We show that the continuity of the
Lyapunov function is not required in the discrete-time case. Moreover, the basic algorithms
are made less conservative by exploiting the switching structure of piecewise affine
systems and by using relaxation procedures
Moving horizon estimation for hybrid systems
No full textIn this paper, by exploiting the equivalence between hybrid systems modeled in the Mixed Logic Dynamical form and Piece-Wise Affine systems, we propose a state smoothing algorithm based on Moving Horizon Estimation (MHE). We provide sufficient conditions on the time horizon and the initial penalties to guarantee asymptotic convergence of the MHE scheme. Moreover we propose an algorithm for the computation of the initial penalties that allows to implement MHE by solving Mixed-Integer Quadratic Programs
Analysis of discrete-time piecewise affine and hybrid systems
No full textIn this paper we present various algorithms both for stability and performance analysis of discrete-time Piece-Wise Affine (PWA) systems. For stability, different classes of Lyapunov functions are considered and it is shown how to compute them through Linear Matrix Inequalities that take into account the switching structure of the systems. We also show that the continuity of the Lyapunov function is not required in the discrete-time case. Moreover, the tradeoff between the degree of conservativeness and computational requirements is discussed. Finally, by using arguments from the dissipativity theory for nonlinear systems, we generalize our approach to analyze the l2-gain of PWA systems
Mixed Logic Dynamical Model of a Hydroelectric Power Plant
No full textIn this work we present the model of a hydroelectric
power plant in the framework of Mixed Logic Dynamical (MLD)
systems. Each outflow unit exhibits a hybrid behavior since flaps,
gates and turbines are controlled with logical inputs and the
outflow dynamics depend on the logical state of the unit. We show
how to derive detailed models of each unit considering not only
standard operating conditions, but also emergencies and startup
and shut-down procedures
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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