1,720,994 research outputs found
The disturbance decoupling problem for jumping hybrid systems
No full textThe problem considered here consists in decoupling the output of a hybrid system from an unknown disturbance by means of state feedback, while assuring global asymptotic stability of the closed-loop dynamics. The considered hybrid systems are characterized by the coupling of a linear flow dynamics with a discontinuous jump dynamics. Suitable geometric methods and tools are introduced and, assuming that the linear flow dynamics is reachable, a general sufficient solvability condition is given. A more restrictive sufficient solvability condition that can be checked by a simple, finite procedure is also given. This provides a practical way to construct solutions in many situations
The Output Regulation Problem with Stability for Linear Switching Systems: A Geometric Approach
No full textThis work presents a solution for the output regulation problem with quadratic stability under arbitrary switching in linear switching systems. The extension to other stability requirements, like asymptotic stability in particular, is also considered and it is shown to affect only few specific features of the proposed solution. The main reason is that the geometric approach, which is at the basis of the developed methodology, establishes a neat separation between the structural aspects and the stability aspects of the problem. For the same reason, continuous-time systems and discrete-time systems are given a unified treatment as far as the structural issues are concerned, while different technicalities characterize the discussion of the stability issues
Preface
No full textComplex dynamical systems emerge in a variety of disciplines and domains, rang- ing from those that deal with physical processes (biology, genetics, environmental sciences, etc.) to those that concern man-made systems (engineering, energy, fi- nance, etc.). Indeed, in these fields, it is becoming more and more common to refer to dynamical structures such as systems of systems, hybrid systems and multimodal systems. In brief, the former ones consist of many interconnected dynamical sys- tems with various topological patterns and hierarchical relations; the second ones are dynamical systems that exhibit dynamics of a different nature, both continu- ous and discrete; the third ones are dynamical systems whose behavior may vary during their life-cycle owing to different operating conditions or depending on the occurrence of some events. The dynamical structures with these characteristics are currently modelled as, e.g., multi-agent systems, hybrid impulsive systems, switch- ing systems, implicit switching systems, and so on..
Unknown-input state observers for hybrid dynamical structures
No full textThis chapter investigates the unknown-input state observation problem for hybrid dynamical systems with state jumps. The problem considered is that of deriving an asymptotic estimate of a linear function of the state of a given system in the presence of unknown inputs. The systems addressed are hybrid dynamical systems which exhibit a continuous-time linear behaviour except at isolated points of the time axis, where their state shows abrupt changes ruled by an algebraic linear equation. The systems belonging to this class are also known as linear impulsive systems. It will be assumed that the time interval between two consecutive state discontinuities is lower bounded by a positive real constant. The presence of unknown inputs precludes, in general, the possibility of asymptotically estimating the whole system state, but may permit the asymptotic estimation of a linear function of the state. Thus, the objective of this chapter is to state and prove necessary and sufficient conditions for the existence of solutions to this problem, in the context of linear impulsive systems. The methodology adopted is structural, based on the use of properly defined geometric objects and properties. A general necessary and sufficient condition is proven first. Then, under more restrictive, yet acceptable in contexts of practical interest, assumptions, a constructive necessary and sufficient condition is shown. The latter condition can be checked by an algorithmic procedure, since it is based on subspaces which can be easily computed and on properties which can be systematically ascertained. Special attention is paid to the synthesis of asymptotic observers whose state has the minimal possible dimension, briefly referred to as minimal-order observers
A Geometric Approach to Output Regulation for Discrete-Time Switched Linear Systems
No full textThis paper considers the problem of asymptotic output regulation by dynamic feedback for discrete-time switched linear systems, with the requirement of asymptotic stability of the regulation loop. Using the methods of the geometric approach, sufficient conditions for solvability of the problem, under suitable assumptions, are shown. A synthesis procedure is outlined
A Geometric Approach to Output Regulation for Linear Switching Systems
No full textThis paper considers the problem of asymptotic output regulation by output dynamic feedback for continuous-time linear switching systems, with the requirement of asymptotic stability of the regulation loop. Using tools and methods of the geometric approach, necessary and sufficient conditions for the existence of solutions, under suitable assumptions, are found. A synthesis procedure is outlined in case a stronger sufficient condition holds. The case of different stability requirements, in particular that of quadratic stability, is discussed
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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