Submitted on: 17 June 2006.
Revised on: 23 September 2006.
Accepted on: 09 November 2006.
___________________Alexandria Engineering Journal
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Submitted on: 28 November 1998.
Revised on: 12 March 1999.
Accepted on: 17 April 1999.
___________________Alexandria Engineering Journal
Submitted on: 29 August 2017.
Revised on: 02 November 2017.
Accepted on: 31 December 2017.
___________________Alexandria Engineering Journal
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