May 2000 - December 2000
October 1999 - May 2000
May 1999 - October 1999
October 1998 - May 1999
June 1998 - October 1998
July 1997 - June 1998
July 1996 - June 1997
July 1995 - June 1996
January 1994 - June 1995
December 1993 - December 1993
July 1991 - November 1993
July 1983 - June 1991