Cooperative control of a network of multi-vehicle unmanned systems

Development of unmanned systems network is currently among one of the most important areas of activity and research with implications in variety of disciplines, such as communications, controls, and multi-vehicle systems. The main motivation for this interest can be traced back to practical applications wherein direct human involvement may not be possible due to environmental hazards or the extraordinary complexity of the tasks. This thesis seeks to develop, design, and analyze techniques and solutions that would ensure and guarantee the fundamental stringent requirements that are envisaged for these dynamical networks. In this thesis, the problem of team cooperation is solved by using synthesis-based approaches. The consensus problem is defined and solved for a team of agents having a general linear dynamical model. Stability of the team is guaranteed by using modified consensus algorithms that are achieved by minimizing a set of individual cost functions. An alternative approach for obtaining an optimal consensus algorithm is obtained by invoking a state decomposition methodology and by transforming the consensus seeking problem into a stabilization problem. In another methodology, the game theory approach is used to formulate the consensus seeking problem in a "more" cooperative framework. For this purpose, a team cost function is defined and a min-max problem is solved to obtain a cooperative optimal solution. It is shown that the results obtained yield lower cost values when compared to those obtained by using the optimal control technique. In game theory and optimal control approaches that are developed based on state decomposition, linear matrix inequalities are used to impose simultaneously the decentralized nature of the problem as well as the consensus constraints on the designed controllers. Moreover, performance and stability properties of the designed cooperative team is analyzed in presence of actuator anomalies corresponding to three types of faults. Steady state behavior of the team members are analyzed under faulty scenarios. Adaptability of the team members to the above unanticipated circumstances is demonstrated and verified. Finally, the assumption of having a fixed and undirected network topology is relaxed to address and solve a more realistic and practical situation. It is shown that the stability and consensus achievement of the network with a switching structure and leader assignment can still be achieved. Moreover, by introducing additional criteria, the desirable performance specifications of the team can still be ensured and guaranteed

Early preshistoric island archaeology in Cyprus: configuration of formative culture growth from the Pleistocene/Holocene boundary to the mid-3rd millenium B.C.

This dissertation studies the early prehistoric cultures of Cyprus from the beginnings to the Chalcolithic-Early Bronze Age transition in the 3rd millennium BC. Its aim is not to provide a culture-historical review, but to define, examine and explain processes of formative culture change in light of island biogeography and new evidence which has accumulated during the last decade. Current excavations on the South Coast not only indicate what may be the earliest instance of Mediterranean Island colonization, but they also hint at the existence of a proto-neolithic occupation prior to the aceramic Khirokitia Culture. This evidence is interpreted in terms of the causality of Quaternary biogeographic conditions and island colonizations by man and animals. Specifically, the discussion addresses the problem of inhibitive factors, the triggers required to overcome them, and the adaptive responses of the founder populations. Following colonization, excavated and surveyed sites attest to a widely distributed and culturally homogeneous aceramic occupation which lasted for over one millennium before disappearing in a lacuna in the archaeological record. A locational analysis attempts to define the rate of intra-island dispersal of this and the subsequent ceramic cultures, and it is argued that the use of a statistically meaningful sample of datable sites and the demographic trends it evidences contradict the hypothesis of an occupational gap. The themes of cultural continuity vs. discontinuity and demic diffusion are further explored within the framework of absolute chronology. A date-by-date discussion of 14C determinations for the Formative Period in light of advances in calibration and settlement stratigraphy is put in the context of artifactual and paleoenvironmental data and used as the chronometric underpinning for an explanation of the configuration of culture growth in an early island ecosystem. Fieldwork data are appended in a Gazetteer of Early Prehistoric Sites Supplement and a Gazetteer of Pleistocene Fossil Sites