Submitted on: 13 January 1998.
Revised on: 27 January 1998.
Accepted on: 05 February 1998.
Maejo International Journal of Science and Technology
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Submitted on: 18 November 2006.
Revised on: 05 December 2006.
Accepted on: 13 December 2006.
Maejo International Journal of Science and Technology
Submitted on: 04 July 2002.
Revised on: 06 August 2002.
Accepted on: 26 August 2002.
Maejo International Journal of Science and Technology
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