The method 1 wherein the step of applying {HEAD ~ alternating forward and reverse bias potentials} is effected by a bipolar signal having a reverse bias potential of significantly larger magnitude than {TAIL ~ said forward bias potential} 
The method 1 wherein the step of applying { HEAD ~ alternating forward and reverse bias potentials } is effected by a bipolar signal having a reverse bias potential of significantly larger magnitude than { TAIL ~ said forward bias potential }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL