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Submitted on: 23 June 1999.
Revised on: 31 August 1999.
Accepted on: 22 October 1999.
___________________Frontiers in Mechanical Engineering-Switzerland
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Submitted on: 23 November 2004.
Revised on: 20 January 2005.
Accepted on: 16 March 2005.
___________________Frontiers in Mechanical Engineering-Switzerland
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Submitted on: 05 December 2000.
Revised on: 25 March 2001.
Accepted on: 17 May 2001.
___________________Frontiers in Mechanical Engineering-Switzerland