1. Norwegian Defence Research Establishment (FFI), P.O. Box 25, N-2027 Kjeller, Norway, GPMS, Institut de Génétique et Microbiologie, Bât 400, Université Paris-Sud, 91405 Orsay cedex, France, Unilabs Telelab AS, P.O. Box 1868, Gulset, N-3703 Skien, Norway, and Borregaard Ind. Ltd., P.O. Box 162, N-1701 Sarpsborg, Norway