Nuclear spin relaxation and quasicoherent fluctuations in ordered fluids: A different expression for the high-frequency cutoff

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Abstract
An expression for the contribution to nuclear spin relaxation rates in liquid crystals from fluctuations in the nematic order has been rederived using an ellipsoidal integration volume for the director modes. When the anisotropic elastic constants, viscosities, and cutoff wavelengths are replaced by effective, isotropic values this expression reduces to the familiar ‘‘one-constant’’ formula, a result which cannot be recovered from expressions based on a cylindrical integration volume. The frequency dependence of the spectral density of motion in various limits as well as practical applications to studies of nematic phases is discussed.