Submitted on: 06 January 2005.
Revised on: 24 March 2005.
Accepted on: 14 April 2005.
___________________International Journal of Dynamical Systems and Differential Equations
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Submitted on: 12 July 2011.
Revised on: 30 August 2011.
Accepted on: 20 September 2011.
___________________International Journal of Dynamical Systems and Differential Equations
Submitted on: 23 June 2018.
Revised on: 28 July 2018.
Accepted on: 06 September 2018.
___________________International Journal of Dynamical Systems and Differential Equations
Submitted on: 08 July 2013.
Revised on: 09 September 2013.
Accepted on: 24 September 2013.
___________________International Journal of Dynamical Systems and Differential Equations
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