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Submitted on: 30 July 2009.
Revised on: 31 August 2009.
Accepted on: 05 October 2009.
___________________IEEE TRANSACTIONS ON EDUCATION
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Submitted on: 16 January 2005.
Revised on: 27 February 2005.
Accepted on: 17 March 2005.
___________________IEEE TRANSACTIONS ON EDUCATION
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Submitted on: 29 November 2001.
Revised on: 28 December 2001.
Accepted on: 18 February 2002.
___________________IEEE TRANSACTIONS ON EDUCATION