Dr. Yoshio Nishina was a key figure in modem physics in Japan and a world pioneer in many fields of modem science such as nuclear physics, cosmic-ray physics, and radiobiology. He devoted his life to the development of science, so that his beloved country could compete with any other country in science and technology. Unfortunately, he died soon after the Second World War and did not witness the results of his great efforts. To commemorate the centennial of Dr. Nishina' s birth, a Nishina Centennial Symposium was held in Tokyo from December 5 to 7, 1990, under the co-sponsorship of the Nishina Memorial Foundation and RIKEN (the Institute of Physical and Chemical Research). The symposium was entitled Evolutionary Trends in the Physical Sciences. The title of the symposium was very broad and ambitious. Indeed, progress in physics over recent decades has been truly amazing, so much so that the present frontiers of physics extend far beyond the horizons we saw when we were young. Experiments in particle physics have revealed many new particles, and may eventually lead to the clarification of the ultimate structure of matter, though it is not known whether man will ever fully understand how natural forces are unified. At the same time, it is becoming more and more likely that the creation of the universe will finally be discovered by continuing the lines of research into physics that have been pursued over the past decades.

This is the Proceedings of the Taniguchi International Symposium on "Relaxation of Elementary Excitations" which was held October 12-16,1979, at Susono-shi (at the foot of f1t. Fuji) in Japan. The pleasant atmosphere of the Symposium is evidenced in the picture of the participants shown on the next page. The purpose of the symposium was to provide an opportunity for a limited number of active researchers to meet and to discuss relaxation processes and related phenomena not only of excitons and phonons in solids but also electronic and vibrational excitations in molecules and biological systems. First, the lattice relaxation, i.e., multi-phonon process, associated with electronic excitation, which plays important roles in self-trapping of an exciton and a particle (electron and hole) and also in degradation of semi conductor lasers, is discussed. Second, this lattice relaxation is studied as the intermediate state interaction in the second-order optical responses, i.e., in connection with the competitive behavior of Raman scattering and luminescence. Third, relaxation mechanisms and relaxation constants are by spectroscopic methods as well as by genuine nonlinear optical determined phenomena. Conversely the relaxation is decisive in coherent nonlinear optical phenomena such as laser, superradiance, and optical bistability. Fourth, the role played by relaxation processes is discussed for optical phenomena in macromolecules and biological system such as photosynthesis."

Statistical Physics II introduces nonequilibrium theories of statistical mechanics from the viewpoint of the fluctuation-disipation theorem. Emphasis is placed on the relaxation from nonequilibrium to equilibrium states, the response of a system to an external disturbance, and general problems involved in deriving a macroscopic physical process from more basic underlying processes. Fundamental concepts and methods are stressed, rather than the numerous individual applications.

Statistical Physics I discusses the fundamentals of equilibrium statistical mechanics, focussing on basic physical aspects. No previous knowledge of thermodynamics or the molecular theory of gases is assumed. Illustrative examples based on simple materials and photon systems elucidate the central ideas and methods.