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Submitted on: 02 July 2013.
Revised on: 27 September 2013.
Accepted on: 04 November 2013.
___________________Ingenieria y Competitividad---UNIV VALLE, FAC INGENIERIA
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Submitted on: 25 May 2000.
Revised on: 21 July 2000.
Accepted on: 09 August 2000.
___________________Ingenieria y Competitividad---UNIV VALLE, FAC INGENIERIA