deletions | additions       diff --git a/Payam.tex b/Payam.tex  index 4b7b9fd..e5ffdd5 100644  --- a/Payam.tex  +++ b/Payam.tex 
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\item The two $t_{\rm h}$s are measuring different things. Payam's $t_{\rm h}$ is considering the {\it diffusion }of a particle's momentum: the characteristic time in the velocity autocorrelation. My $t_{\rm h}$ is about information flow via sonic waves: this is much smaller than the vorticity time-scale.\\  I want to think about {\it which time scale is more appropriate in this context and why?}  \item So, {\it what should the time-scale be from physical }physical {\it  reasoning: what is the physics behind establishing the flow profile $\vec{v}(\vec{x})$ in the fluid around the DNA/jet?} \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.