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\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 the formulae for the submerged jet, and perhaps solve the time-dependent Navier-Stokes equation.\\ However, it would (arguably) 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 better model with sound might be a more accurate  model (see references below), and 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. \item {\it Which process (sound or vorticity) carries more momentum?} Read \citet{1959flme.book.....L} chapter 8 (p. 245), on sound.