Time correlation function, supercooled liquids

In supercooled liquids the BPP expression usually fails to reproduce the observed spin-lattice relaxation times. Instead of a single correlation time x2, it is found that a distribution of correlation times G(lnx2) exists. Indication for a distribution G(lnx2) resulting from a superposition of subensembles with different x2 were reported for supercooled liquids close to Tg [11,349,350]. This implies the existence of a distribution of spin-lattice relaxation rates. Correspondingly, the relaxation function 4>,w (t) of the z-magnetization is... 

S. C. Glotzer, V. N. Novikov, and T. B. Schroeder. Time-dependent, four-point density correlation function description of dynamical heterogeneity and decoupling in supercooled liquids. J. Chem. Phys., 112 (2000), 509-512. 

Gang, H., Novikov, V.N. and Payer, M.D. (2003). Experimental observation of a nearly logarithmic decay of the orientational correlation function in supercooled liquids on the picosecond-to-nanosecond time scales. Phys. Rev. Lett. 90 197401(1 ). 

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