While the present invention has been described in conjunction with a preferred embodiment, one of ordinary skill, after reading the foregoing specification, will be able to effect various changes, substitutions of equivalents, and other alterations to the compositions and methods set forth herein. It is therefore intended that the protection granted by Letters Patent hereon be limited only by the definitions contained in the appended claims and equivalents thereof.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Part of the work leading to this invention was carried out with United States Government support provided under a grant from the Department of Energy, Grant No. DE-FG02-90ER60985. Therefore, the U.S. Government has certain rights in this invention.