This is the second and final issue of the collection of papers that were contributed by friends and colleagues of (Late) Professor P. R. Pat Sethna of the University of Minnesota to commemorate his 70th birthday on May 26, 1993. The first set of contributions was published in Nonlinear Dynamics as the last issue (no. 6) of Vol. 4 in 1993. As circumstances would have it, Professor Sethna was diagnosed with cancer in the fall of 1992 and, after an extended battle with the disease, he passed away on November 4, 1993, just a few days before the first set of contributed papers appeared in print. It is gratifying to report that the organizers of these vi Foreword commemorative issues in Nonlinear Dynamics were able to present to Professor Sethna, on the occasion of his 70th birthday, complete details of the planned commemorative issues. This second set of contributions is dedicated, in memoriam, to Professor P. R. Sethna. As many of you are well aware, Professor Sethna was an active researcher in the field of nonlinear vibrations and dynamics for nearly forty years, making many fundamental and significant contributions to both the theoretical and applied aspects of this field. He was also recognized for his outstanding leadership and administrative abilities, amply demonstrated through his position as the Head of the Department of Aerospace Engineering and Mechanics at the University of Minnesota for twenty-six years (1966-1992).