Submitted on: 08 June 2008.
Revised on: 18 July 2008.
Accepted on: 11 August 2008.
___________________International Journal of Mathematics and Physics
Submitted on: 23 October 2008.
Revised on: 25 January 2009.
Accepted on: 07 March 2009.
___________________International Journal of Mathematics and Physics
Submitted on: 11 April 2014.
Revised on: 23 July 2014.
Accepted on: 19 August 2014.
___________________International Journal of Mathematics and Physics
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