It is with a great sense of loss that I am writing this small memoriam about Da Ruan. I believe Da, who was full of ideas and energy for new ventures, had a bright future from which all of us would have benefited.
The first time that I met Da was at a conference in Europe. While I can’t recall the conference or city, I can vividly remember our encounter. Da approached me with a question about an issue he was struggling with at the nuclear agency. They were trying to evaluate the safety at some nuclear plants around the world, and they had to deal with the issue of missing information. In the course of our conversation I was impressed by Da’s sophisticated evaluation of the problem as well as his deep concern for the problem of nuclear safety. Over the years, Da had discussed with me many problems which he encountered in his role at the nuclear agency. I always found the problems very challenging and stimulating. On a number of occasions they provided an impetus for some of my research investigations.