1. C&C Res. Lab., NEC Europe Ltd., Rathausallee 10, 53757 St. Augustin, Germany
2. K. U. Leuven, Dept. Comp. Science, Celestijmemlaan 200A, B-3001, Heverlee-Leuven, Belgium
3. U. Greenwich, Centre for Num. Modelling and Proc. Analysis, Wellington St., Woolwich, London SE18 6PF, UK