Some transport phenomena in classical liquids and neutron scattering

Our knowledge in liquid physics and particularly in the field of non-equilibrium phenomena has increased enormously during the last two decades. The reasons are two-fold: (a) the application of the slow neutron inelastic scattering technique to the liquid state has supplied us with very valuable fundamental data and has stimulated theoretical work and (b) the application of molecular dynamics computations to problems of liquid dynamics has profoundly deepened our understanding of fundamental dynamical quantities. The combination of the two ways of research has shown how to approach the solution of classical questions: for instance to what small wave length domain may we apply the normal hydrodynamical equations. And when these equations cease to exist what would be a good theoretical continuation into the short wave length domain. The modern techniques have shown that normal hydrodynamics is useful down to wave lengths approximately ten atomic distances. Thereafter kinetic effects of atomic nature take over. It is also shown that periodic waves are transmitted through insulator liquids like argon and neon to wave lengths of the abovementioned order whereas periodic waves with wave lengths of order two atomic distances are transmitted through liquid metals like rubidium and lead. (author)