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Submitted on: 03 December 2006.
Revised on: 28 February 2007.
Accepted on: 04 April 2007.
___________________International Journal of Biomathematics
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Submitted on: 19 January 2014.
Revised on: 01 March 2014.
Accepted on: 11 March 2014.
___________________International Journal of Biomathematics
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Submitted on: 05 February 2000.
Revised on: 22 March 2000.
Accepted on: 10 May 2000.
___________________International Journal of Biomathematics
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