Submitted on: 20 December 1999.
Revised on: 11 February 2000.
Accepted on: 16 March 2000.
___________________Clean Technologies---MDPI
Submitted on: 06 January 2005.
Revised on: 25 February 2005.
Accepted on: 10 April 2005.
___________________Clean Technologies---MDPI
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Submitted on: 21 August 2011.
Revised on: 27 September 2011.
Accepted on: 24 November 2011.
___________________Clean Technologies---MDPI
Submitted on: 05 January 2021.
Revised on: 27 February 2021.
Accepted on: 23 March 2021.
___________________Clean Technologies---MDPI
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