1. ASTUOM , K. J. , BOHLIN , T. , and WENSMAHK , S. 1965 , Technical Paper TP. 18.150 I.B.M. Nordic Laboratory , Sweden .
2. GAINES , P. E. 1970 , Ph.D. Tlicsis , Imperial College , London University ; 1971, Proceedings Fourth UK AC Control Convention., Manchester, f.E.E. Conference Publication No. 78 .