1,720,973 research outputs found
Geometric methods for output regulation in discrete-time switching systems with preview
No full textThis contribution is focused on a geometric methodology devised to achieve optimization, expressed as the minimization of the l2 norm of the tracking error, of regulation transients caused by instantaneous, wide parameter variations occurring in discrete-time, linear systems. The regulated system switching law is assumed to be completely known a priori in a given time interval. A set of feedback regulators, designed according to the internal model principle, guarantee closed-loop asymptotic stability and asymptotic tracking of the reference signal generated by an exosystem, for each regulated system (i.e., for each pair to-be-controlled system/exosystem). The compensation scheme for optimization of transients consists of feedforward actions on the regulation loop and switching policies for suitably setting the states of the feedback regulators and those of the exosystems at the switching times. The theoretical bases of this approach comprise (i) a geometric interpretation, specifically aimed at discrete-time stabilizable and detectable systems, of the multivariable autonomous regulator problem and (ii) a non-recursive solution, still aimed at discrete-time stabilizable systems, of the finite-horizon optimal control problem with final state wieghted by a generic quadratic function, based on a characterization of the structural invariant subspaces of the associated singular Hamiltonian system holding on the sole, fairly general, assumptions that guarantee the existence of the stabilizing solution of the corresponding discrete algebraic Riccati equation
Optimal Filtering, Fault Detection and Isolation for Linear Discrete Time Systems in a Noisy Environment
No full textDisturbed fault detection and isolation problems for linear state models in a noisy environment
No full textCo-positive lyapunov functions for the stabilization of positive switched systems
No full textIn this paper, exponential stabilizability of continuous-time positive switched systems is investigated. For two-dimensional systems, exponential stabilizability by means of a switching control law can be achieved if and only if there exists a Hurwitz convex combination of the (Metzler) system matrices. In the higher dimensional case, it is shown by means of an example that the existence of a Hurwitz convex combination is only sufficient for exponential stabilizability, and that such a combination can be found if and only if there exists a smooth, positively homogeneous and co-positive control Lyapunov function for the system. In the general case, exponential stabilizability ensures the existence of a concave, positively homogeneous and co-positive control Lyapunov function, but this is not always smooth. The results obtained in the first part of the paper are exploited to characterize exponential stabilizability of positive switched systems with delays, and to provide a description of all the switched equilibrium points of an affine positive switched system. © 1963-2012 IEEE
Is stabilization of switched positive linear systems equivalent to the existence of an Hurwitz convex combination of the system matrices?
No full textAbstract|In this paper exponential stabilizability
of continuous-time positive switched systems is in-
vestigated. It is proved that, when dealing with two-
dimensional systems, exponential stabilizability can
be achieved if and only if there exists an Hurwitz
convex combination of the (Metzler) system matrices.
However, for systems of higher dimension this is not
true.
In general, exponential stabilizability corresponds
to the existence of a (positively homogeneous, concave
and co{positive) control Lyapunov function, but this
function is not necessarily smooth. The existence of
an Hurwitz convex combination is equivalent to the
stronger condition that the system is not only expo-
nentially stable, but it also admits a smooth control
Lyapunov function. These two conditions, in turn, are
equivalent to the fact that the stabilizing switching
law can always be based on a linear co{positive control
Lyapunov function. Finally, the characterization of
exponential stabilizability is exploited to provide a
description of all the \switched equilibrium points"
of a positive ane switched system
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
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