[1] Siemens Corp, Corp Res, Syst Dev Technol, Princeton, NJ 08540 USA
[2] City Univ Hong Kong, Kowloon, Hong Kong, Peoples R China
[3] Allegheny Coll, Dept Comp Sci, Meadville, PA 16335 USA
[4] Oxford Brookes Univ, Sch Technol, Oxford OX3 0BP, England