L 2-Gain analysis and control synthesis of uncertain discrete-time switched linear systems with time delay and actuator saturation

The problem of L ₂-gain analysis and control synthesis is studied for a class of uncertain discrete-time switched linear systems with time delay and saturating actuators by using the multiple Lyapunov functions method. With the state feedback controllers adopted beforehand, an analysis condition on disturbance tolerance is derived under which the operating state trajectory with zero initial condition will remain inside a bounded set in its proximity. Then with this condition at hand, the largest disturbance tolerance level is determined via the solution of a constrained optimisation problem. Then, a sufficient condition for the restricted L ₂-gain over the set of tolerable disturbances is derived. The smallest upper bound on the restricted L ₂-gain is also obtained by solving a constrained optimisation problem. Furthermore, when controller gain matrices are design variables, these optimisation problems are adjusted for solving the control design task. An illustrative numerical example is given to demonstrate the feasibility and effectiveness of the proposed method.     

Multiple Lyapunov functions approach to observer-based H ∞ control for switched systems

This article investigates the issue of H _∞ control for a class of continuous-time switched Lipschitz nonlinear systems. None of the individual subsystems is assumed to be stabilisable with H _∞ disturbance attenuation. Based on a generalised multiple Lyapunov functions (GMLFs) approach, which removes the nonincreasing requirement at switching points, a sufficient condition for the solvability of the H _∞ control problem under a state estimation-dependent switching law is presented. Observers, controllers and a switching law are simultaneously designed. As an extension, a sufficient condition for exponential stabilisability is also given.     

L 2-gain analysis and control synthesis of uncertain switched linear systems subject to actuator saturation

This article addresses the L ₂-gain analysis and control synthesis problem for a class of uncertain switched linear systems with saturating actuators and external disturbances. First, when the controllers are pre-given, an analysis condition on disturbance tolerance is established under which the state trajectory starting from the origin will remain inside a bounded set. By this condition, the problem of estimating disturbance tolerance capability is formulated as a constrained optimisation problem. Then, the restricted L ₂-gain property is analysed over the set of tolerable disturbances. An upper bound on the restricted L ₂-gain is estimated by solving a constrained optimisation problem. Furthermore, when controller gain matrices are design variables, these optimisation problems can be adapted for controller design. All the results are achieved by utilising the multiple Lyapunov functions method and presented in terms of an LMI optimisation-based approach. A numerical example is given to show the effectiveness of the proposed method.     

Constraints on constant-input oscillations of a bandpass sigma-delta modulator structure

This paper presents sets of conditions on the parameters of bandpass sigma–delta modulators for which the oscillations of the state variables remain bounded within a specific square of the state space. The conditions are associated with areas in the parameter space and the system dynamics is illustrated for parameter sets showing examples of typical oscillations, both those which are and those which are not constrained to the specified square. © 1997 by John Wiley & Sons, Ltd.     

Computed tomography in a case of pseudomembranous colitis

Pseudomembranous colitis (PMC) is an infectious colitis usually occurring as a complication of antibiotic therapy. The computed tomography (CT) findings of 10 patients with PMC are reviewed. All patients demonstrated an abnormal large bowel wall with an average thickness of 13 mm (range 7-31 mm). Additional, but less frequent findings included mesenteric inflammation, ascites, pleural effusions, and dilatation of the large or small bowel. Pancolonic involvement was seen in 7 cases, while three patients had focal colitis. Although the CT appearance of PMC is not specific, the diagnosis may be suggested in the proper clinical setting.     

Maximum entropy for periodically correlated processes from nonconsecutive autocovariance coefficients

Abstract.  We consider the maximum entropy extension of a partially specified autocovariance sequence of a periodically correlated process. The sequence may be specified on a non-contiguous set. We give a method which solves the problem completely – it gives the positive definite solution when it exists and reports that it does not exist otherwise. The method is numerically reliable even when the solution is 'almost' semidefinite. It also works when only positive semidefinite extension(s) exist.     

Preparation and properties of RF sputtered indium-tin oxide thin films for applications as heat mirrors in photothermal solar energy conversion

In the present research, in order to deposit indium-tin oxide (ITO) thin films the method of RF reactive sputtering was used. Sputtering of two types indium-tin targets in the presence of oxygen as reactive gas was made. The technological parameters were optimized to obtain films with good quality on different substrates. The films' microstructure was studied by TEM and SAED. To identify the optical properties of the films the methods of infrared spectrometry and laser ellipsometry were used. UV-VIS spectrophotometry showed the high visible transmittance of the RF sputtered ITO films. Heating of the substrates during the films sputtering and their post deposition thermal treatment also were studied. The ultimate goal of the present research activities was to develop new technological processes leading to low-cost, highly effective optical coatings for application in photo thermal solar energy conversion and utilization.     

Uniform Cooling of Alloys

A phase separation process model formed by the Cahn– Hilliard equation and the heat equation is considered. The mobility coefficient in the Cahn–Hilliard equation is assumed to be an increasing function of the temperature. This property is of importance at the latest stage of the cooling process. The existence and uniqueness of a weak solution is proved, and a uniform cooling problem is studied. Obtained results can be used to control the cooling process and to create alloys with a uniform structure. 2000 Mathematics Subject Classification. 35K30, 35Q99, 49J20.