The major concerns in state-of-the-art model reduction algorithms are: achieving accurate models of sufficiently small size, numerically stable and efficient generation of the models, and preservation of system properties such as passivity. Algorithms such as PRIMA generate guaranteed-passive models, for systems with special internal structure, using numerically stable and efficient Krylov-subspace iterations. Truncated Balanced Realization (TBR) algorithms, as used to date in the design automation community, can achieve smaller models with better error control, but do not necessarily preserve passivity. In this paper we show how to construct TBR-like methods that guarantee passive reduced models and in addition are applicable to state-space systems with arbitrary internal structure.

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Parallel computing has become an affordable reality forcing a shift in the programming paradigm from sequential to concurrent applications, specially those who demand much computational power or with large search spaces like SAT-solvers. In this context we present the research, planning and implementation of PMSat: a parallel version of MiniSAT with MPI (Message Passing Interface) technology, to be executed in clusters or grids of computers. The main features of the program are described: search modes, search space pruning and share of learnt clauses. An analysis of its performance and load balance is also presented.

The reduction of greenhouse gas emissions is a major contemporary challenge. This has prompted the requirements concerning energy efficiency for ships, among other things. Improvement in efficiency of ship operations could be achieved by reducing unnecessary power consumption by induction motors. Specifically, the occurrence of power quality disturbances, such as frequency and voltage deviations, voltage unbalances, and voltage harmonics, can cause an extraordinary increase in the power losses occurring in induction motors, as well as an unnecessary increase in the output power. Furthermore, excessive power quality disturbances are often interconnected with failures of on-board equipment, and in extreme cases, these may even pose a threat to safety at sea. Consequently, strict power quality monitoring of on-board microgrids can also contribute to improving safety while afloat. In this study, a dedicated tool for power quality monitoring is proposed, namely the coefficient of voltage energy efficiency, which has a value proportional to the power losses occurring in induction motors under power quality disturbances. INDEX TERMS Energy efficiency, induction motors, marine technology, power systems, power quality.