Comment on "Shear-induced quench of long-range correlations in a liquid mixture"

Recently, Wada [Phys. Rev. E 69, 031202 (2004)] presented an analysis of the long-range nature of concentration fluctuations in a binary liquid mixture subjected to a concentration gradient in a uniform shear flow as a function of the wave number k of the fluctuations. Specifically, he argued that the presence of a uniform shear causes the intensity of the concentration fluctuations to crossover from the well-known k(-4) dependence at large wave numbers to a k(-4/3) dependence for small wave numbers. The purpose of this comment is to point out that the wave-number dependence of the concentration fluctuations to be expected in realistic experimental conditions will be affected by gravity and finite-size effects.