{HEAD ~ Driving elements} maintain {TAIL ~ oscillating tangential vibrations} of the masses about the z axis 
maintain
{ HEAD ~ Driving elements } maintain { TAIL ~ oscillating tangential vibrations } of the masses about the z axis
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH