Nonlinear robust H-infinity filtering for a class of uncertain systems via convex optimization

A new approach for robust H-infinity filtering for a class of Lipschitz nonlinear systems with time-varying uncertainties both in the linear and nonlinear parts of the system is proposed in an LMI framework. The admissible Lipschitz constant of the system and the disturbance attenuation level are maximized simultaneously through convex multi-objective optimization. The resulting H-infinity filter guarantees asymptotic stability of the estimation error dynamics with exponential convergence and is robust against nonlinear additive uncertainty and time-varying parametric uncertainties. Explicit bounds on the nonlinear uncertainty are derived based on norm-wise and element-wise robustness analysis.     

Input-to-state stabilization for nonlinear dual-rate sampled-data systems via approximate discrete-time model

The problem of state feedback stabilization of nonlinear sampled-data systems is considered under the “low measurement rate” constraint. A dual-rate control scheme is proposed that utilizes a numerical integration scheme to approximately predict the current state. Given an approximate discrete-time model of a sampled nonlinear plant and given a family of controllers that stabilizes the plant model in input-to-state sense, we show that under some standard assumptions the closed loop dual-rate sampled data system is input-to-state stable in the semiglobal practical sense.     

The Top-Down Strategy for Building EuroWordNet: Vocabulary Coverage, Base Concepts and Top Ontology

This paper describes two fundamental aspects in the process of building of the EuroWordNet database. In EuroWordNet we have chosen for a flexible design in which local wordnets are built relatively independently as language-specific structures, which are linked to an Inter-Lingual-Index (ILI). To ensure compatibility between the wordnets, a core set of common concepts has been defined that has to be covered by every language. Furthermore, these concepts have been classified via the ILI in terms of a Top Ontology of 63 fundamental semantic distinctions used in various semantic theories and paradigms. This paper first discusses the process leading to the definition of the set of Base Concepts, and the structure and the rationale of the Top Ontology.     

Temporal Sampling of Enzymes from Live Cells by Localized Electroporation and Quantification of Activity by SAMDI Mass Spectrometry

Measuring changes in enzymatic activity over time from small numbers of cells remains a significant technical challenge. In this work, a method for sampling the cytoplasm of cells is introduced to extract enzymes and measure their activity at multiple time points. A microfluidic device, termed the live cell analysis device (LCAD), is designed, where cells are cultured in microwell arrays fabricated on polymer membranes containing nanochannels. Localized electroporation of the cells opens transient pores in the cell membrane at the interface with the nanochannels, enabling extraction of enzymes into nanoliter‐volume chambers. In the extraction chambers, the enzymes modify immobilized substrates, and their activity is quantified by self‐assembled monolayers for matrix‐assisted laser desorption/ionization (SAMDI) mass spectrometry. By employing the LCAD‐SAMDI platform, protein delivery into cells is demonstrated. Next, it is shown that enzymes can be extracted, and their activity measured without a loss in viability. Lastly, cells are sampled at multiple time points to study changes in phosphatase activity in response to oxidation by hydrogen peroxide. With this unique sampling device and label‐free assay format, the LCAD with SAMDI enables a powerful new method for monitoring the dynamics of cellular activity from small populations of cells.     

Optimization of gear ratio and power distribution for a multimotor powertrain of an electric vehicle

The architecture and design of the propulsion system of electric vehicles are highly important for the reduction of energy losses. This work presents a powertrain composed of four electric motors in which each motor is connected with a different gear ratio to the differential of the rear axle. A strategy to reduce energy losses is proposed, in which two phases are applied. Phase 1 uses a divide-and-conquer approach to increase the overall output efficiency by obtaining the optimal torque distribution for the electric motors. Phase 2 applies a genetic algorithm to find the optimal value of the gear ratios, in which each individual of each generation applies Phase 1. The results show an optimized efficiency map for the output torque and speed of the powertrain. The increase in efficiency and the reduction of energy losses are validated by the use of numerical experiments in various driving cycles.     

Localization in time and space for wireless sensor networks: An efficient and lightweight algorithm

In many applications that use Wireless Sensor Networks (WSNs), detected events need to be localized in both time and space. As a result, sensor nodes need to have precisely synchronized clocks as well as to be localized in a common spatial reference system. While synchronization and localization algorithms have been proposed to solve these problems independently, in this work we propose to combine both synchronization and localization into a single problem that we refer to as the time–space localization problem. We then propose a novel and efficient time–space localization algorithm for wireless sensor networks which we refer to as the Lightness algorithm. Our proposed algorithm not only takes advantage of the additional hardware resources required by the positioning mechanism in order to improve the performance and scalability of synchronization, but also benefits from the additional communication needed by the synchronization mechanism in order to decrease positioning errors. We also present an extensive set of experiments to evaluate the performance of our algorithm. Our results indicate clearly that our proposed scheme is scalable while keeping a low synchronization error and a low communication overhead. Our results also indicate that the additional packets needed to compute clocks’ drift have the ability to decrease the positioning errors to almost one third of the initial positioning.     

Decentralized robust output feedback control for control affine nonlinear interconnected systems

In this paper, a scheme for decentralized robust control for control affine nonlinear interconnected systems using linear matrix inequalities (LMIs) is presented. Based on the Lyapunov theory, sufficient conditions for closed-loop stability of a nonlinear system, reference input tracking, and disturbance attenuation over its operating-range are obtained. Then, achieving these sufficient conditions are formulated as local LMI optimization problems. By solving the appropriately defined local problems, provided the obtained sufficient conditions are satisfied, the closed-loop stability, input tracking, and disturbance attenuation over the operating-range of the system are guaranteed. The designed controller is linear whose implementation is straightforward. An example is given to illustrate the proposed methodology.     

Multi‐loop control synthesis for unstable systems and its application: An approach based on µ interaction measure

This paper presents a new practical framework for multi‐loop controller design in which controllers are designed independently, i.e. a controller in one loop is designed without exploiting information of other controllers. The method is based on the (block) diagonal approximation of a system that is different from its (block) diagonal elements. The focus of this work is on unstable systems and the approximated systems are obtained by minimizing an upper bound of a scaled ??_∞ norm for the error systems. This extends the applicability of conventional µ‐interaction measure to a more general scenario. The proposed approach is applied to a numerical example and to a simulated industrial boiler system. Copyright © 2008 John Wiley & Sons, Ltd.