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