1,720,958 research outputs found
On the preservation of co-positive Lyapunov functions under Padédiscretization for positive systems
Get PDFIn this paper the discretization of switched and
non-switched linear positive systems using Padé approximations
is considered. We show:
1) first order diagonal Padé approximation preserves both
linear and quadratic co-positive Lyapunov functions,
higher order transformations need an additional condition
on the sampling time1;
2) positivity need not be preserved even for arbitrarily small
sampling time for certain Padé approximations.
Sufficient conditions on the Padé approximations are given to
preserve positivity of the discrete-time system. Finally, some
examples are given to illustrate the efficacy of our results
Essentially negative news about positive systems
Get PDFIn this paper the discretisation of switched and non-switched linear positive systems using Padé approximations is considered. Padé
approximations to the matrix exponential are sometimes used by
control engineers for discretising continuous time systems and for
control system design. We observe that this method of approximation is not suited for the discretisation of positive dynamic systems,
for two key reasons. First, certain types of Lyapunov stability are
not, in general, preserved. Secondly, and more seriously, positivity
need not be preserved, even when stability is. Finally we present an
alternative approximation to the matrix exponentialwhich preserves
positivity, and linear and quadratic stability
Combined performance and stability optimisation via central transfer case active control in four-wheeled vehicles
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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
Designing On-Demand Four-Wheel-Drive Vehicles via Active Control of the Central Transfer Case
No full textNew driveline architectures equipped with torquebiasing
devices such as active differentials and active transfer
cases have yielded a new generation of on-demand four-wheel-drive vehicles, where the torque distribution between left and right and between front and rear axles can actively be modulated online. This allows one to design active vehicle-control systems that are capable of altering, via electronic control, the behavior of a car dictated from its mechanical layout, e.g., understeering and oversteering characteristics. This paper proposes a control strategy that optimizes vehicle performance while guaranteeing vehicle stability and drivability by actively controlling the transfer case. The performance of the overall control strategy is assessed on both a multibody simulator and an instrumented test vehicle
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