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\item In \citet{2013PhRvE..87d2723R} page 5, it is claimed that motion will be a superposition of longitudinal and transverse. Is this true -- won't one of them be unstable (in the case where work done in dragging is less than $T$, say)?  \item In \citet{2013PhRvE..87d2723R} page 5, second column, Payam uses dimensional analysis to justify a steady state approximation used in the paper: the time taken to establish the fluid velocity profile around a section of DNA must be much shorter than the time taken the DNA to move its own length.\\  I want to try to do a better job than Payam's scaling argument: what are the coefficients in the $\# ``$\#  \ll 1$ 1$''  relationship? This might be interesting because of a problem acknowledged in Payam's other paper: that his predictions do not fit the experimental data. %  \begin{itemize}  \item I think $t_{\rm h}\sim \ell/c_{\rm s}$ on physical grounds, but Payam says $t_{\rm h}\sim \ell^2\rho/\eta$ from dimensional analysis. Are these compatible?  %  \begin{itemize}  \item Sound speed shouldn't depend on viscosity at except for near-supersonic flow. \item \href{http://iopscience.iop.org/0370-1301/66/5/303/pdf/0370-1301_66_5_303.pdf}{Or (\href{http://iopscience.iop.org/0370-1301/66/5/303/pdf/0370-1301_66_5_303.pdf}{Or  does it?}\item  \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}. \item  \end{itemize}  \item Payam has (equation 12) $v_{\rm DNA}=F_{\rm ext} \ln(\ell/d)/\eta\ell - \lambda E\ln(1+r_{\rm D}/d)/\eta$, which we use to calculate $t_{\rm D}$. He finds $t_{\rm D}\sim \ell\eta/E\lambda$ -- whence this simplification?