1,720,981 research outputs found
Nonlinear regulation for linear fat plants: the constant reference/disturbance case
No full textIn this paper, the output regulation problem for linear time invariant systems is considered, for the case of fat plants and constant exogenous signals, including both references to be tracked and (measured or unmeasured) disturbances to be rejected. It is shown that nonlinear (in particular, piecewise linear solutions) of the regulator equations are optimal solutions when either (input or state) constraints or very reasonable performance indices are introduced; hence, such solutions might be preferable to the standard, well known and easy linear solutions
Nonlinear output regulation for over-actuated linear systems
No full textWe present results for the definition of nonlinear steady-state manifolds achieving output regulation for input-saturating over-actuated systems. By defining steady-state manifolds of polynomial form and exposing the structure of the studied systems, we derive homogeneous polynomial equations corresponding to the steady-state conditions and present existence conditions for their solution. The numerical computation of the polynomial feedforward inputs that satisfy the zero-error steady state is performed by solving a sum-of-squares program. The solution to this convex problem maximizes the set of exogenous signals for which regulation can be achieved inside the given input bounds
Relaxed stabilizability conditions for hybrid linear systems on periodic time domains
No full textIn this paper, we consider the problem of designing stabilizing feedback control laws for hybrid linear systems defined on periodic time domains. In this context, requiring the existence of a Lyapunov function decreasing simultaneously along flow and jump dynamics is a rather conservative condition. We propose then relaxed conditions for analysis and design that allow to systematically redistribute negativity of a candidate Lyapunov function between the continuous-time and the discrete-time compo- nents. Interestingly, such redistribution is performed dynamically by suitably assigning the behavior over the time interval of a time-varying component of the function. Finally, it is shown that the latter selection, in the design scenario, may be recast in terms of a reachability problem for a LTI extended system
Piecewise polynomial Lyapunov functions for stability and nonlinear L_2m-gain computation of saturated uncertain systems
No full textIn this paper we provide sufficient conditions for regional asymptotic and nonlinear L2m gain estimation of linear systems subject to saturations and/or deadzones, based on piecewise polynomial Lyapunov functions. By using sum-of-squares relaxations, these conditions are formulated in terms of linear matrix inequalities for the global case, and bilinear ones for the regional case. The results are provided for both the cases with and without structured parametric uncertainties. Example studies are used to comparatively illustrate the proposed techniques
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
- …
