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Submitted on: 02 April 2000.
Revised on: 21 May 2000.
Accepted on: 19 July 2000.
___________________AMERICAN JOURNAL OF SCIENCE---AMER JOURNAL SCIENCE
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Submitted on: 05 May 2003.
Revised on: 12 June 2003.
Accepted on: 20 July 2003.
___________________AMERICAN JOURNAL OF SCIENCE---AMER JOURNAL SCIENCE
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