deletions | additions       diff --git a/Payam.tex b/Payam.tex  index 890d270..8bdeb68 100644  --- a/Payam.tex  +++ b/Payam.tex 
...
\item {\it Does Payam assume incompressible flow?} Yes -- he follows \citet{1959flme.book.....L} pp. 86-88 in setting up the submerged jet; they assume zero divergence in the velocity 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, and sonic information transfer will be irrelevant.  \item {\it Should I re-visit the derivation with sound included?}  Method 1: I would have to re-derive derive  the formulae for the submerged jet, jet in a compressible fluid,  and perhaps solve the time-dependent Navier-Stokes equation.\\ Method 2: tack some ad-hoc changes onto the existing work -- e.g. treat the DNA/jet as an extended source of spherical waves. This will be {\it inconsistent} and crude, but probably easier than method 1.\\  In any case, a model with sound might be a more accurate model (see references below). It may also be more illuminating as to how the velocity profile is set up, and the nature of interactions between neighbouring DNA molecules.