deletions | additions       diff --git a/Payam.tex b/Payam.tex  index d5fe788..ac825fe 100644  --- a/Payam.tex  +++ b/Payam.tex 
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\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 No! They are measuring different things. Payam's $t_{\rm h}\sim \ell^2\rho/\eta$ is considering the diffusion of momentum information about a particle (I think this is the characteristic time in the decay of the velocity autocorrelation). My $t_{\rm h}$ is about pure information flow.     \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}. fits}.)  \item   \end{itemize}