1,721,199 research outputs found
Exponential input-to-state stability of globally Lipschitz time-delay systems under sampled-data noisy output feedback and actuation disturbances
No full textIn this paper we deal with the problem of global exponential practical stability preservation for globally Lipschitz time-delay systems, by Euler emulation of continuous-time dynamic output feedback controllers affected by measurement noises and actuation disturbances. Nonlinear time-delay systems not necessarily affine in the control input are studied. It is shown that, if the continuous-time closed-loop system at hand is globally exponentially stable and the maps describing the plant and the continuous-time dynamic output feedback controller are globally Lipschitz, then, under suitably fast sampling, the Euler emulation of the continuous-time controller at hand preserves the global exponential stability of the sampled-data closed-loop system (no matter whether periodic or aperiodic sampling is used). In the case of bounded measurement noises and bounded actuation disturbances affecting the control law, it is proved that, under suitable fast sampling, (global) exponential input-to-state stability with respect to both these external inputs is guaranteed. A generalisation of the Halanay's inequality is used as a tool in order to prove the results. The existence of a Lyapunov-Krasovskii functional for the continuous-time closed-loop system is sufficient to ensure the preservation of the global exponential practical stability. On the other hand, the explicit knowledge of a Lyapunov-Krasovskii functional allows us to compute an upper bound for the sampling period. An example is presented which validates the theoretical results
On Global Exponential Stability Preservation under Sampling for Globally Lipschitz Delay-Free and Retarded Systems
No full textThe paper shows that the global exponential stability property is preserved, under suitable fast sampling, whenever the dynamics of the system at hand is described by globally Lipschitz functions. The Halanay's inequality is used in order to prove this result. Both fully nonlinear delay-free and fully nonlinear retarded systems are investigated
Synchronization of Multi-Agent Systems under Time-Varying Network via Time-Delay Approach to Averaging
No full text
ANALYSIS OF THE COOLANT DENSITY REACTIVITY COEFFICIENT IN LFRs AND SFRs VIA MONTE CARLO PERTURBATION/SENSITIVITY
No full textThe coolant density effect represents one of the main reactivity feedback in LFR and SFR. These reactivity feedback effects are often calculated via direct perturbation in Monte Carlo codes. This work presents a new approach for reactivity coefficient calculations based on Perturbation Theory. New methods were implemented in a extended Serpent version and are here verified against reference results for spatial coolant reactivity maps. In the paper, a detailed investigation of the effect of the calculation parameters and the applicability range of the perturbation calculations is presented. The main advantage of the present approach is the capability of providing, within a single Monte Carlo run, several reactivity coefficients. This feature is demonstrated via the reactivity feedback decomposition in energy, space, isotope and reaction in the ALFRED lead cooled reactor case. The obtained decompositions suggest that the reactivity coefficient is the result of large opposite effect. A preliminary uncertainty quantification analysis shows that 208-Pb cross sections uncertainties have a large impact on keff estimates in the ALFRED reactor
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
Practical Stability Preservation Under Sampling, Actuation Disturbance and Measurement Noise, for Globally Lipschitz Time-Delay Systems
No full textA small-gain-theorem-like approach to nonlinear observability via finite capacity channels
No full textThe paper is concerned with observation of discrete-time, nonlinear, deterministic, and maybe chaotic systems via communication channels with finite data rates, with a focus on minimum data-rates needed for various types of observability. With the objective of developing tractable techniques to estimate these rates, the paper discloses benefits from regard to the operational structure of the system in the case where the system is representable as a feedback interconnection of two subsystems with inputs and outputs. To this end, a novel estimation method is elaborated, which is alike in flavor to the celebrated small gain theorem on input-to-output stability. The utility of this approach is demonstrated for general nonlinear time-delay systems by rigorously justifying an experimentally discovered phenomenon: Their topological entropy stays bounded as the delay grows without limits. This is extended on the studied observability rates and appended by constructive finite upper bounds independent of the delay. It is shown that these bounds are asymptotically tight for a time-delay analog of the bouncing ball dynamics. Team Tamas Keviczk
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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