{HEAD ~ The vent position} can be changed from {TAIL ~ an equilibrium position} to a nonequilibrium position 
{ HEAD ~ The vent position } can be changed from { TAIL ~ an equilibrium position } to a nonequilibrium position
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH