1. a Department of Applied Mathematics , Leeds University , Leeds, LS2 9JT , U.K.
2. b ZXA/ZC, BASF-AG , Kaiser-Wilhelm Strasse 52, Ludwigshafe , D-67056 , Germany
3. c Mantis Numerics Ltd. , 46 The Calls, Leeds , LS2 7EY , U.K.
4. d ZAV/C, Ammoniaklaboratorium M300 , BASF-AG, Ludwigshafen , D-67056 , Germany