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