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Decentralized adaptive control is considered for systems consisting of multiple interconnected subsystems. It is assumed that each subsystem s parameters are uncertain and the interconnection parameters are not known. In addition, mismatch can exist between each subsystem and its reference model. A strictly decentralized adaptive control scheme is developed, wherein each subsystem has access only to its own state but has the knowledge of all reference model states. The mismatch is estimated online for each subsystem and the mismatch estimates are used to adaptively modify the corresponding reference models. The adaptive control scheme is extended to the case with actuator failures in addition to mismatch.

In this paper, the problem of controlling systems with failures and faults is introduced, and an overview of recent work on direct adaptive control for compensation of uncertain actuator failures is presented. Actuator failures may be characterized by some unknown system inputs being stuck at some unknown (fixed or varying) values at unknown time instants, that cannot be influenced by the control signals. The key task of adaptive compensation is to design the control signals in such a manner that the remaining actuators can automatically and seamlessly take over for the failed ones, and achieve desired stability and asymptotic tracking. A certain degree of redundancy is necessary to accomplish failure compensation. The objective of adaptive control design is to effectively use the available actuation redundancy to handle failures without the knowledge of the failure patterns, parameters, and time of occurrence. This is a challenging problem because failures introduce large uncertainties in the dynamic structure of the system, in addition to parametric uncertainties and unknown disturbances. The paper addresses some theoretical issues in adaptive actuator failure compensation: actuator failure modeling, redundant actuation requirements, plant-model matching, error system dynamics, adaptation laws, and stability, tracking, and performance analysis. Adaptive control designs can be shown to effectively handle uncertain actuator failures without explicit failure detection. Some open technical challenges and research problems in this important research area are discussed.

1Egypt of the Pharaohs and of the Khedivé

By Chien Tao and Foster Barham Zincke

Those particulars of the History of Egypt, and of its present condition, in which it differs from other countries, are factors of the idea this famous name stands for, which must be brought prominently into view in any honest and useful construction of the idea. Something of this kind is what the author of the following work has been desirous of attempting, and so was unable, as he was also unwilling, to pass by any point, or question, which fell within the requirements of his design. His aim, throughout, has been to aid those who have not studied the subject much, or perhaps at all, in understanding what it is in the past, and in the present, that gives to Egypt a claim on their attention. The pictures of things, and the thoughts about them, which he offers to his readers, are the materials with which the idea of Egypt has been built up in his own mind: they will judge how far with, or without, reason. The work had its origin in a tour the author made through the country in the early months of this year. It consists, indeed, of the thoughts that actually occurred to him at the time, and while the objects that called them forth were still before him; with, of course, some[x] pruning, and, here and there, some expansion or addition. They are presented to the reader with somewhat more of methodical arrangement than would have been possible had the hap-hazard sequence, in which the objects and places that suggested them were visited, been adhered to. As he started for Egypt at a few hours’ notice, it did not occur to him to take any books with him. This temporary absence of the means of reference, and verification, will, in some measure, account for the disposition manifested throughout to follow up the trains of thought Egyptian objects quicken in the beholder’s mind. These excursus, however, as they will appear to those who take little interest in the internal, and ask only for the external, incidents of travel, have been retained, not merely because they were necessary for what came to be the design of the work, but also because, had they been excluded, the work would have ceased to be something real; for then it would not have been what it professes to be, that is, a transcript of the thoughts which the sights of Egypt actually gave rise to in the authors mind. Wherstead Vicarage: May 13, 1871. - Summary by from the Introduction to the first edition.