Submitted on: 30 December 2013.
Revised on: 15 January 2014.
Accepted on: 31 January 2014.
SCRIPTA MATERIALIA
http://reply.papertrans.cn/3/278/27716/27716-22.png
http://reply.papertrans.cn/3/278/27716/27716-23.png
http://reply.papertrans.cn/3/278/27716/27716-24.png
http://reply.papertrans.cn/3/278/27716/27716-25.png
http://reply.papertrans.cn/3/278/27716/27716-26.png
http://reply.papertrans.cn/3/278/27716/27716-27.png
http://reply.papertrans.cn/3/278/27716/27716-28.png
http://reply.papertrans.cn/3/278/27716/27716-29.png
Submitted on: 09 September 1999.
Revised on: 23 September 1999.
Accepted on: 12 October 1999.
SCRIPTA MATERIALIA