基金This paper was supported by a scholarship under the Post-doctoral Program from Research Affairs and Graduate School, Khon Kaen University （58227）. This research was funded by a fellowship from the Royal Golden Jubilee Ph.D. Program of the Thailand Research Fund （TRF） and a grant from the Division of Research Administration, Khon Kaen University. Additional support was provided by a Thailand Research Fund Basic Research grant （BRG 5680008）. We are appreciative of the final editing done by John S. Parsons.