1,721,032 research outputs found
Optimality with respect to blips
No full textWe consider local minimality with respect to
short duration variations, called ‘blips’. It is shown that for
quadratic differential integrals either there are no such optimal
trajectories, or that all stationary trajectories are local minima
with respect to blips. Conditions on the polynomial matrix that
defines the quadratic integral for the stationary trajectories to
be local minima with respect to blips are derived. We motivate
this problem by the variational principles of mechanics, and
show that if the Hessian of the Lagrangian with respect to the
generalized velocities is positive definite, then the solutions of
the Euler-Lagrange equations are the local minimum of the
action integral w.r.t. blips as variations
Linear-quadratic control and quadratic differential forms
No full textWe consider the infinite time linear-quadratic control problem from a
behavioral point of view. The performance functional is the integral of a quadratic
differential form. A characterization of the stationary trajectories and of the local
minima with respect to (left) compact support variations, as well as their relation
to stability, are obtained. Finally, several theorems are derived that describe the
optimal LQ trajectories with specified initial, and possibly terminal, conditions
Interconnections and symmetries of linear differentialsystems
No full textIn this paper we study the interplay between control problems and symmetries in the context of linear systems. In particular, we establish sufficient conditions under which it is possible to control a symmetric system in order to make it achieve control objectives, without ''breaking'' its symmetry
Observer synthesis in the behavioral approach
No full textThis paper analyzes the observer design problem
in the behavioral context. Observability and detectability notions
are first introduced and fully characterized. Necessary and sufficient
conditions for the existence of an observer, possibly an
asymptotic or an exact one, are introduced, and a complete parameterization
of all admissible observers is given. The problem
of obtaining observers endowed with a (strictly) proper transfer
matrix and the design of observer-based controllers are later
addressed and solved. Finally, the above issues are particularized
to the case of state-space systems, thus showing they naturally
generalize well-known theorems of traditional system theory
Dead beat observer synthesis
No full textIn the paper the observer design problem is investigated in the context of linear left shift invariant discrete behaviors, whose
trajectories have support on the positive axis. Observability and reconstructibility properties of certain manifest variables
from certain others, in the presence of latent variables, are dened and fully characterized. Necessary and sucient conditions
for the existence of either a dead-beat or an exact observer are introduced, and a complete parametrization of all dead-beat
observers is given
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
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
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