ABSTRACT
The author first met Ralph Kleinman about 15 years ago when she first visited the Delaware math department. She discovered that at some of the engineering meetings, he would be the only person she knew. The author gradually came to realize that he was one of these rare and valuable people who form a bridge between the engineering community and the mathematics community. Ralph and the author worked together on the editorial board of the SIAM Journal of Applied Math; when she sent him e-mail asking for help, he would always respond immediately with good advice and encouragement. She discusses two problems that she talked to Ralph about at the IMA during the spring of 1997. The first is the question of whether data measured on a half-space uniquely determines a compactly supported perturbation in the sound speed. The other problem is related to the detection and identification of underwater mines.
