{HEAD ~ The melt circulation} through the conduits is caused by the difference in the levels and densities of the melt in {TAIL ~ these vessels} 
{ HEAD ~ The melt circulation } through the conduits is caused by the difference in the levels and densities of the melt in { TAIL ~ these vessels }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL