1. K. Mori, A. Spagnoli, I. Torigoe, I. Murakami, and S. Itoh: Impact Engineering and Application (2001), p.607, Elsevier Science Ltd.
2. K. Mori, A. Spagnoli, Y. Murakami, G. Kondo, and I. Torigoe: NDT & E (2002), p.399, Elsevier Science Ltd.
3. For Example, L. Meirovitch: Elements of Vibration Analysis (McGrawHill, U. S. A. 1986).