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\citet{nderson_Mitchell_Bartlett_2002}: high-speed observations of two interacting colloids. Sonic effects.\\  \citet{Padding_Louis_2006} coarse-graining approach; Langevin does a poor job.  \item {\it Does Payam assume incompressible flow?} I believe so Yes  -- he follows \citet{1959flme.book.....L} pp. 86-88 in setting up the submerged jet; and they assume zero divergence in the velocity field. (Note that the field \& use stress tensor for incompressible flow. (The  derivation in \citet{Broman_Rudenko_2010} also assumes incompressibility.) This means that the sound speed in his model will be infinite!\\ {\it Would there be any point in re-visiting the derivation with incompressibility assumption dropped?}  %\item (Sound speed shouldn't depend on viscosity at except for near-supersonic flow. (\href{http://iopscience.iop.org/0370-1301/66/5/303/pdf/0370-1301_66_5_303.pdf}{Or does it?} \href{http://www.engineeringtoolbox.com/sound-speed-water-d_598.html}{Speed of sound table}, \href{http://resource.npl.co.uk/acoustics/techguides/soundpurewater/content.html#LUBBERS}{$c(T,P)$ fits}.))