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Abstract
Relaxation and diffusion in interacting systems including most glass-forming substances involve many-body dynamics. The stretch exponent, n, in the Kohlrasuch correlation function, , is a convenient measure of the many-body relaxation dynamics. Evidences of the importance of the many-body dynamics can be seen from the empirical facts that n either governs or correlates with several general relaxation properties. Two examples of this scenario are shown. The first is the ageing of colloidal glasses. The second is the breakdown of the Stokes–Einstein and the Debye–Stokes–Einstein relations in small molecular glass formers, colloidal particle suspensions and a Lennard-Jones system with rotational degree of freedom. The coupling model has a relation in which n plays a pivotal role in determining relaxation properties. The relation is used once more to explain the findings of the two examples given in this paper.
Acknowledgements
The work was supported by the Office of Naval Research. The author thanks Eric Weeks and Biman Bagchi for sending their data.