Nadine GUILLOTIN-PLANTARD has been Maitre de Conferences (i.e. Associate Professor) at the University Claude Bernard, Lyon, France since 1998. Here research interests include the study of time and/or space dependent random walks and their applications in computer science, biology and finance. She serves as referee for many journals in mathematics and authored or co-authored more than 20 published journal papers. Rene SCHOTT has been a full Professor at the University Henri Poincare, Nancy, France, since 1987. His research interests include the study of stochastic processes and operator calculus on algebraic structures and their applications in computer science (probabilistic analysis of algorithms, random generators, randomized algorithms, optimization problems). He serves as referee for many journals and international conferences, both in mathematics and in computer science. He is the co-author of eight books and has also authored or co-authored more than 100 published journal and conference proceedings papers. Dr. SCHOTT has received numerous collaborative research grants from such agencies as the National Center for Scientific Research (CNRS), INRIA, National Science Foundation and PROCOPE. He was granted the Silver Medal by the CNRS with the team EURECA-CRIN) in 1987 for his achievements in theoretical computer science. He is a member of the editorial board of International Journal of Mathematics and Computer Science, Scientific Committee of IDAQP, American Mathematical Society, French Mathematical Society and European Association for Theoretical Computer Science.