Submitted on: 18 April 2017.
Revised on: 20 May 2017.
Accepted on: 14 July 2017.
___________________APPLIED MATHEMATICAL MODELLING
Submitted on: 03 June 2016.
Revised on: 24 July 2016.
Accepted on: 24 August 2016.
___________________APPLIED MATHEMATICAL MODELLING
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Submitted on: 13 December 2009.
Revised on: 31 March 2010.
Accepted on: 15 May 2010.
___________________APPLIED MATHEMATICAL MODELLING
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