Abstract:
An analysis is presented of the Rayleigh component of the dynamic structure factor of a fluid under the influence
of gravity and of a stationary temperature gradient. A conservative force like gravity in the absence of a
temperature gradient modifies the Rayleigh spectrum, but not the integrated intensity. A dissipative thermodynamic
force, like a temperature gradient, yields a modification of the Rayleigh spectrum and an enhancement of the
Rayleigh-line intensity which varies as k^-4 with the wave number k of the fluctuations. In the presence of both
gravity and a temperature gradient, this k^-4 growth law of the nonequilibrium fluctuations saturates for very small
wave numbers.