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Cato edited Payam and DNA.tex
almost 11 years ago
Commit id: b9053953341026925a84230eb0d18c4751d036c4
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\item Dimensional analysis argument not fully understood: I guessed $t_{\rm h}\sim \ell/c_{\rm s}$ on physical grounds, but Payam says $t_{\rm h}\sim \ell^2\rho/\eta$ from dimensional analysis. What is the interpretation of Payam's $t_{\rm h}$?
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\begin{itemize}
\item The two $t_{\rm h}$s are measuring different things. Payam's $t_{\rm h}$ is considering the
{\it diffusion
}of of a particle's
momentum, or the momentum via vorticity
of in the fluid; or the characteristic time in the velocity autocorrelation of neighbouring particles. 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 {\it reasoning: what is the physics behind establishing the flow profile $\vec{v}(\vec{x})$ in the fluid around the DNA/jet?}\\