A book is never the sole accomplishment of the authors. It is built on the foun dation of established mathematics, and it benefits from current developments within the mathematical community. Many colleagues have contributed ideas, comments, and corrections to this volume. There are, first of all, our students C. Bauer, G. Grammel, 1. Greger, S. Grtinvogel, G. Hackl, and D. Szolnoki in Augs burg, and E. Joseph, R.-G. Lai, S. Lin, C.-M. Ou, and H. Wang in Ames. We have received comments from, among others, L. Arnold, V. Ayala, K. Grasse, D. Hinrichsen, R. Johnson, Y. Latushkin, J.L. Massera, F.J. de la Rubia, J. San Martin, L.A.B. San Martin, C. Scherer, H. Sussmann, L. Vargas, and W. Du. Special thanks go to a group of engineers who have helped us to identify important problems and have kept us honest in our claim of applicability of the theory: Ariaratnam, S. Namachchivaya, S. Shaw, S. Sinha, B. Spencer, V. Vittal, and W. Wedig. And we appreciate the work of the anonymous referees of our papers who have helped us in so many ways.
