Abstract
An advanced control system for the optimal operation and management of autonomous wind-diesel systems is presented. This system minimises the production costs through an on-line optimal scheduling of the power units, which takes into account the technical constraints of the diesel units, as well as short-term forecasts of the load and renewable resources. The power system security is maximised through on-line security assessment modules, which enable the power system to withstand sudden changes in the production of the renewable sources. The control system was evaluated using data from the island of Lemnos, where it has been installed and operated since January 1995. © 1997 Elsevier Science Ltd.

Abstract
Vehicle number plate recognition systems are expected to have numerous applications in traffic surveying and monitoring, e,g. finding stolen cars and controlling access to car parks. In this paper algorithmic improvements to a previous version of a number plate reading system are described. The work builds on the experience gained by the Computer Vision Group at the University of Bristol. This paper addresses the problem of locating the number plate area in the image and proposes a new line based method for number plate location, which is suitable for realtime number plate recognition.

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Abstract
Current data abstraction mechanisms are not adequate to control sharing of state in the general case involving objects in linked structures. The pervading possibility of sharing is a source of errors and an obstacle to language implementation techniques. We present a general extension to programming languages which makes the ability to share state a first class property of a data type, resolving a long-standing flaw in existing data abstraction mechanisms. Balloon types enforce a strong form of encapsulation: no state reachable (directly or transitively) by a balloon object is referenced by any external object. Syntactic simplicity is achieved by relying on a non-trivial static analysis as the checking mechanism. Balloon types are applicable in a wide range of areas such as program transformation, memory management and distributed systems. They are the key to obtaining self-contained composite objects, truly opaque data abstractions and value types-important concepts for the development of large scale, provably correct programs. © Springer-Verlag Berhn Heidelberg 1997.

Abstract
Ambulance control involves distributed group work using a mix of computer and communications technologies. The implementation of computer technologies has had mixed results in this area, evidenced by serious failures in the London Ambulance Service in 1992. Often failures are due to inadequate attention to integration of organizational and technical aspects of work. We report a field study of the organization of one aspect of the work of ambulance control, locating the scene of an emergency. The study was carried out in two ambulance control centres, one predominantly urban and highly computerized and the other largely rural and minimally computerized. Our analysis shows that the particulars of `locating the scene' are best seen in terms of the use of different technologies to link representations and represented. This research has implications for understanding task and context and the integration of technology and organization in design, particularly with respect to using similar computer-based technologies in both ambulance control centres.

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