1. Toray Research Center, Sonoyama, Otsu, Shiga 520, Japan (V.M., G.K.); Dipartimento di Ingegneria dei Materiali, I-34127 Trieste, Italy (V.S., S.M.); and Materials Department, Kyoto Institute of Technology, Matsugasaki, Kyoto 606, Japan (G.P., T.N.)