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Submitted on: 16 July 2009.
Revised on: 17 October 2009.
Accepted on: 28 November 2009.
___________________DIFFERENTIATION---ELSEVIER SCI LTD
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Submitted on: 19 October 1999.
Revised on: 24 January 2000.
Accepted on: 16 March 2000.
___________________DIFFERENTIATION---ELSEVIER SCI LTD
Submitted on: 19 June 2003.
Revised on: 10 October 2003.
Accepted on: 16 November 2003.
___________________DIFFERENTIATION---ELSEVIER SCI LTD
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