When {HEAD ~ the vent} is moved to a nonequilibrium position, it is located within one of the two cells and is not in direct relation to {TAIL ~ the vent follower} 
When { HEAD ~ the vent } is moved to a nonequilibrium position , it is located within one of the two cells and is not in direct relation to { TAIL ~ the vent follower }
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL