1,721,086 research outputs found
Data-based guarantees of set invariance properties
Full text linkFor a discrete-time linear system, we use data from an open-loop experiment to design directly a linear feedback controller enforcing that a given (polyhedral) set of the state is invariant and given (polyhedral) constraints on the control are satisfied. By building on classical results from model-based set invariance and a fundamental result from Willems et al., the controller designed from data has the following desirable features. The satisfaction of the above properties is guaranteed only from data, it can be assessed by solving a numerically-efficient linear program, and, under a certain rank condition, a data-based solution is feasible if and only if a model-based solution is feasible
An energy function based design of second order sliding modes for automatic generation control
Full text linkThis paper proposes a decentralized Second Order Sliding Mode (SOSM) control strategy for Automatic Generation Control (AGC) in power networks, where frequency regulation is achieved, and power flows are controlled towards their desired values. This work considers a power network partitioned into control areas, where each area is modelled by an equivalent generator including second order turbine-governor dynamics, and where the areas are nonlinearly coupled through the power flows. Asymptotic convergence to the desired state is established by constraining the state of the power network on a suitable sliding manifold. This is designed relying on stability considerations made on the basis of an incremental energy (storage) function. Simulation results confirm the effectiveness of the proposed control approach
A Note on Stabilization via Communication Channel in the presence of Input Constraints
Full text linkThe problem of asymptotic stabilization of a process via communication channel under control input constraints is studied. A solution is proposed which provides encoders, decoders and controllers accomplishing global asymptotic stabilization of the closed-loop system provided that a suitable number of bits is used to encode the information generated by the process. The proposed solution shows interesting features: it employs a number of bits for encoding equal to the relative degree of the system and works in the presence of an adaptive transmission rate.
On feedback stabilization of nonlinear systems under quantization
Full text linkThe aim of this note is to show how the results concerning asymptotic stabilization using quantized feedback, still hold under the assumption of asymptotic stabilizability only. As a consequence, we are able to examine as special interesting cases nonlinear systems which are e.g. globally asymptotically and locally exponentially stabilizable and stabilizable by dynamic observer-based feedback. The results are also discussed for discrete-time nonlinear systems.
Hybrid Feedback Stabilization of Nonlinear Systems with Quantization Noise and Large Delays
Full text linkControl systems over networks with a finite data rate can be conveniently modeled as hybrid (impulsive) systems. For the class of nonlinear systems in feedforward form, we design a hybrid controller which guarantees stability, in spite of the measurement noise due to the quantization, and of an arbitrarily large delay which affects the communication channel. The rate at which feedback packets are transmitted from the sensors to the actuators is shown to be arbitrarily close to the infimal one.
Detecting Faults from Encoded Information
Full text linkThe problem of fault detection for linear continuous-time systems via encoded information is considered. The encoded information is received at a remote location by the monitoring deiice and assessed to infer the occurrence of the fault. A class of faults is considered which allows to use a simple decision logic as monitoring device.
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
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