The method 4 wherein said {HEAD ~ cooling rate} in step is {TAIL ~ about 0.2° C.} per minute or less 
The method 4 wherein said { HEAD ~ cooling rate } in step is { TAIL ~ about 0.2 ° C. } per minute or less
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH