how to get the velocities from the dcd file

From: Alessio Alexiadis (
Date: Mon Mar 05 2007 - 09:25:49 CST

Hi everybody,
Im sure this is a very silly question but I really couldnt find any solution in the Users Guide or on the Tutorials.
  Im simulating the flow of water inside carbon nanotubes and I wanted to calculate the average velocity at certain locations of the tube.
The idea is to get some streaming velocity profiles averaging the velocities of the molecules that cross a certain surface dS. Nothing new, it was done in many papers on the subject (see for instance Travis and Gubbins, Poiseulle flow of Lennard-Jones fluids in narrow slit pores, Journal of Chemical Physics, vol. 112, num. 4, 2000, pages 1984-1994) and it should be a simple task.
  The point is that I couldnt find any way to access the velocities from the trajectory file. Im thinking something like the tcl command
$sel get {x y z}
But for the velocities instead of the coordinates. Can anybody help me?
  Thanks in advance

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