http://reply.papertrans.cn/3/224/22352/22352-31.png
http://reply.papertrans.cn/3/224/22352/22352-32.png
http://reply.papertrans.cn/3/224/22352/22352-33.png
Submitted on: 20 October 2000.
Revised on: 25 November 2000.
Accepted on: 23 December 2000.
Moscow University Mechanics Bulletin
http://reply.papertrans.cn/3/224/22352/22352-35.png
Submitted on: 22 September 2004.
Revised on: 15 October 2004.
Accepted on: 28 October 2004.
Moscow University Mechanics Bulletin