1,720,990 research outputs found
Measurement Scheduling for Control Invariance in Networked Control Systems
No full textWe discuss a new reachability problem for networked controlled system where a master node - the controller - broadcasts commands to a set of slave nodes, which must take turn to relay back state measurements. This problem finds applications in some robotics and intelligent transportation systems setups. Constraints on communication demand a coupled design of the controller and the measurement schedule. We prove that the problem is formally equivalent to the Pinwheel Problem from scheduling theory, and building on this result we provide conditions for schedulability and reachability. The results are illustrated in three numerical examples
Communication Demand Minimization for Perturbed Networked Control Systems with Coupled Constraints
No full textCommunication scheduling is needed when control loops of several safety-critical systems are closed through a shared communication medium. To enable schedulability, control for each system is designed primarily to minimize its communication demand. In this paper, we study communication demand minimization for a class of perturbed multi-agent networked control systems with a shared communication medium and subject to input and coupled state constraints. First, a framework to design communication schedule and control is recalled such that state and input constraints are satisfied under no coupling assumption. Then, a heuristic method is proposed to decouple state constraints such that the overall communication demand of the systems is minimized. Effectiveness of the proposed results are illustrated through a numerical example
Robust Control Invariance for Networked Control Systems with Output Feedback
No full textThis paper focuses on robust output feedback design for multi-agent networked control systems with a shared communication medium, where each system is subject to state and input constraints. We first compute the communication demand for each system given constant observer and controller gains; we argue that minimization of the communication demand with respect to the control or observer gains is very hard. Then, given a constant observer gain, we compute the minimum communication demand for each system and a corresponding control policy using model predictive control; we argue that the second approach is less difficult to solve and results in a communication demand which is no larger than for a linear controller. We illustrate and compare these design methods by a numerical example
Optimal Control Design for Perturbed Constrained Networked Control Systems
Full text linkThis letter focuses on an optimal control design problem for a class of perturbed networked control systems where a number of systems, subject to state and input constraints, share a communication network with limited bandwidth. We first formulate an optimal control design problem with a constant feedback gain in order to minimize the communication demand for each system while guaranteeing satisfaction of state and input constraints; we show that this optimization problem is very hard to solve. Then, we formulate the same optimal control design problem with a non-constant feedback gain; we argue that this problem is less difficult and results in a lower, or equal, communication demand in comparison to the design with the constant feedback gain. We illustrate and compare these optimal control designs by a simple example
Receding-horizon robust online communication scheduling for constrained networked control systems
No full textThis paper proposes a novel online scheduling approach for perturbed Networked Control Systems (NCS) over lossy networks, subject to state and input constraints and limited network capacity. The paper shows how an online communication schedule can be found for the considered class of systems, as the solution of a constrained optimization problem, which is solved in receding horizon and is proven to be persistently feasible. The resulting online schedule is proven to preserve the system invariance w.r.t. state and input constraints. A communication scheduler is also derived for lossy networks, starting from a feasible baseline schedule calculated offline. Numerical examples are given to illustrate the proposed contributions
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
Control and Communication-Schedule Co-design For Networked Control Systems
Full text linkIn a networked control system (NCS), the control loop is closed through a communication medium. This means that sensor measurements and/or control signals can be exchanged through a communication link. NCSs have many benefits, such as wiring reduction (elimination in the case of wireless communication), installation cost reduction, and simplification of upgrades and restructuring. However, network congestion, impairments of the wireless links (such as bandwidth limitations, packet losses, delays, and noises) may degrade system performance and even cause instability. These issues have motivated a great deal of research over the past 20 years and have given rise to a number of approaches to prevent congestion and compensate for delays and/or packet losses.An interesting class of NCSs that has not received enough attention is an NCS whose systems are uncertain and subject to state and inputs hard constraints.These hard constraints may stem from the system itself, its environment, or be proposed by the designer in order to guarantee safety or a certain performance.The contribution of this thesis is introducing a design framework that guarantees robust constraint satisfaction for a class of multi-agent NCSs with a shared communication medium that is subject to bandwidth limitation and prone to packet losses.The proposed framework is built upon reachability analysis to determine the communication demand for each system such that local constraints are satisfied and scheduling techniques to guarantee satisfaction of the communication demands. The thesis explores offline and online scheduling designs under various communication topologies, optimal control designs under state and output feedback, and scheduling and control co-design for NCSs with hard constraints
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
- …
