Submitted on: 14 October 2001.
Revised on: 01 February 2002.
Accepted on: 14 March 2002.
___________________JOURNAL OF MECHANICS---OXFORD UNIV PRESS
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Submitted on: 12 September 2003.
Revised on: 07 December 2003.
Accepted on: 21 January 2004.
___________________JOURNAL OF MECHANICS---OXFORD UNIV PRESS
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Submitted on: 20 October 2011.
Revised on: 09 February 2012.
Accepted on: 12 March 2012.
___________________JOURNAL OF MECHANICS---OXFORD UNIV PRESS
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