The main objectives of this dissertation are the following. The first objective is concerned with the stabilization of large-scale systems by a decentralized control. The fundamental idea behind this type of control is the stabilization of the isolated subsystems of a large-scale system in such a way that the global stability requirement is also satisfied. For this purpose, a new stability criterion is introduced to identify a class of interconnected systems that can be stabilized by local state feedback. In addition to this, two specific classes of interconnections are presented for which the overall system stability can be ensured by a decentralized approach. A new constructive procedure for the design of decentralized controllers for the identified classes of large-scale systems is discussed. The principal advantages of this design procedure are that it requires a minimal amount of computation and is a systematic procedure eliminating the trial and error arguments as in the earlier methods. The second objective of the dissertation is to investigate the problem of the stabilization of a class of large-scale systems which are composed of identical subsystems and identical interconnections. For this class of systems, certain significant theorems, concerning the qualitative properties are introduced. Following the guidelines set forth by the above theorems, a few different schemes for the decentralized and multilevel control of the aforementioned class of large-scale interconnected systems are presented. The third objective concerns the development of a few different schemes for the design of an asymptotic state estimator for large-scale systems described as interconnections of several low-order subsystems. The most attractive feature of the present schemes is that the majority of the necessary computations are performed at the subsystem level only, thereby leading to a simple and practicable estimator design. Finally, all the above results are illustrated by numerical examples. Further, a comparison study is conducted to show the advantages of the methods and the results in this dissertation in comparison with some results available in the literature.

In the design of large-scale systems the problem is often too large to be approached by a single group. Then the system design problem must be resolved into component subproblems with different groups assigned to work on each subproblem. A. Wayne Wymore's "Tricotyledon Theory of Systems Design" (T3SD) provides a general system theoretic framework for the statement of large-scale system design problems. In this paper some results are developed for the extension of T3SD to the problem of the resolution of system design problems into system component design problems. Initially resolutions with respect to I/O specifications and technologies are defined and examined. Following this, resolutions with respect to merit orderings in which the merit orderings on the component problems have a specified relation with the merit orderings on the original problem are discussed. Ideal, strong and perfect resolutions with respect to merit orderings are defined and relationships among these types of resolutions are discussed. It is shown that trivial strong and ideal resolutions can always be developed from simple resolutions. Perfect resolutions are always ideal resolutions and ideal resolutions are always strong resolutions. Finally it is shown that given a class of simple resolutions there always exists a maximal ideal resolution for that class.

Understanding how institutions affect or shape fisheries performance is an important part of providing practical insights for the development of management strategies that promote sustainable fishing. In the Gulf of California there is widespread evidence of declines in fish stocks upon which small-scale fisheries depend and these declines are largely attributed to policy failures. Using methods commonly used in social sciences, I investigated the formal and informal rules regulating resource use by smallscale fishers from two fishing communities in the Northern Gulf of California (NGC), Bahía de Kino and Bahía de los Ángeles, Mexico, and their effects on fisheries sustainability. Some of the main results are summarized below: a) The percentage of fishers holding fishing rights and actually using them to report and commercialize catch was quite small in both communities (fishing rights are usually in the hands of absentee operators). b) Current policies and policy changes do not reach the fishers in a direct and formalized way in any of these communities, and these policies are shaped with no participation of local fishers. c) Current policy tools show poor performance in practice and have been ineffective (at the moment) in promoting sustainable fishing practices by fishery stakeholders. Neither community has been able to manage their resources sustainably. Results also suggest some potentials that could lead to more sustainable fishing practices in both communities: d) The presence of informal rights (fishers' sense of ownership) over the fishing grounds in the surroundings of their home communities. Generally, local fishers do not conform to or enforce the individual boundaries of the fishing rights they hold (or work under), but they do care about and defend an area that they perceive as belonging to their community as a whole, particularly when there are "outsiders" coming in. e) The presence of strong support from the fishers for implementing improved regulatory measures for local fisheries. Specific recommendations for each case study are provided with the aim of enhancing rules legitimacy and improving management outcomes.

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