deletions | additions       diff --git a/Payam.tex b/Payam.tex  index cec3d0e..576a06c 100644  --- a/Payam.tex  +++ b/Payam.tex 
...
\item Why does the hydrodynamic disturbance travel diffusively rather than at the sound speed?  \item Some reading about propagation of hydrodynamic information:\\  \citet{Hinch_1975} application of Langevin equation to fluid suspensions; takes account of includes  fluid inertia  and interaction with suspension.\\ \citet{Ladd_1993} short-time motion of colloidal particles: theory.\\  \citet{1995PhyA..214..185E},  \citet{Espanol_Rubio_Zuniga_1995} for discussion of how HD disturbances propagate, and evidence for faster-than-vorticity interaction. One considers incompressible and the other considers compressible; the vorticity time-scale is not the only important time-scale.\\