1,720,969 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Reliable computation of H infini central controllers near the optimum
Get PDFProjet META2The state-space formulas for the usual H central controller become singular when approaching the optimum gopt. A new approach is taken to circumvent this difficulty. It consists of extending the notion of central controller to include proper controllers with a feedthrough term. While such controllers are still derived from the usual Riccati solutions X and Y, their feedthrough gain can be selected so as to neutralize the singularities near gopt. This provides numerically stable formulas for the controller parameters and eliminates the discontinuity between the realizations of nearly optimal and of reduced-order optimal central controllers. The advantages of this method are illustrated on a few examples
A convex parametrization of suboptimal hinfini controllers
Get PDFProjet META2A new parametrization is proposed for suboptimal H controllers of order no larger than the plant order. Here such controllers are generated from pairs of symmetric matrices (X,Y) constrained by two Riccati matrix inequalities and some positivy requirements. Interestingly, the Riccati expressions and the positivity conditions are exactly those arising in the usual state-space solution of suboptimal H problems. When working with the inverses R and S of X and Y, respectively, the constraints can be rewritten as linear matrix inequalities which define a convex parameter set. This sets up a convenient framework to handle design objectives which can be reflected in terms of (R,S). Examples of such objectives include reduced-order H design and the avoidance of pole/zero cancellation between the plant and the controller
Variations on the Author
Get PDF“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
Get PDFWe 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
A new representation of Hinfini suboptimal controllers
No full textProjet META2Elementary state-space concepts are used to derive a transparent solution to the stationary H control problem. The main contribution of this solution is a novel representation of suboptimal controllers in terms of a pair of parametric Riccati equations with a coupling constraint. Unlike the classical parametrization in terms of linear fractional transformation, this state-space representation has a homogeneous Riccati formulation which should help to make the most out of the suboptimal controller diversity. Potential applications include the design of reduced-order controllers and more generally the selection of suboptimal controllers to meet or optimize additional constraints
On the game Riccati equations arising in Hinfini control problems
Get PDFProjet META2In the state-space approach to H optimal control, feasibility of some closed-loop attenuation g is characterized in terms of a pair of game Riccati equations depending on g. This paper is concerned with the properties of these equations as g varies. The most general problem is considered (D11 0) and a thorough analysis of the variations of the Riccati solutions provides insight into the behavior near the optimum and into the dependence on g of the suboptimality conditions. In addition, concavity is established for a criterion which synthesizes the three conditions X 0, Y 0, and p(XY) < g 2. As a result, a numerically reliable Newton scheme can be devised to compute the optimal g. Most presented results are extensions of earlier contributions. The main concern here is to provide a complete and synthetic overview as well as results and formulas tailored to the development of numerically-sound algorithms
A new representation of Hinfini suboptimal controllers
Get PDFProjet META2Elementary state-space concepts are used to derive a transparent solution to the stationary H control problem. The main contribution of this solution is a novel representation of suboptimal controllers in terms of a pair of parametric Riccati equations with a coupling constraint. Unlike the classical parametrization in terms of linear fractional transformation, this state-space representation has a homogeneous Riccati formulation which should help to make the most out of the suboptimal controller diversity. Potential applications include the design of reduced-order controllers and more generally the selection of suboptimal controllers to meet or optimize additional constraints
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
- …
