Submitted on: 03 April 2010.
Revised on: 20 June 2010.
Accepted on: 31 July 2010.
___________________CHINESE JOURNAL OF PHYSICS---ELSEVIER
Submitted on: 20 August 1999.
Revised on: 06 December 1999.
Accepted on: 09 January 2000.
___________________CHINESE JOURNAL OF PHYSICS---ELSEVIER
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Submitted on: 28 December 2015.
Revised on: 02 March 2016.
Accepted on: 25 April 2016.
___________________CHINESE JOURNAL OF PHYSICS---ELSEVIER
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Submitted on: 19 January 2000.
Revised on: 12 May 2000.
Accepted on: 28 June 2000.
___________________CHINESE JOURNAL OF PHYSICS---ELSEVIER