Ivo BabuškaRID="*"ID="*" Partially supported by the US office of Naval Research under Grant N00014-90-J-1030 and National Science Foundation under grant DMJ-95-01841
Benqi GuoRID="**"ID="**" Partially supported by National Science and Engineering on Research Council of Canada under Grant OGP0046726 and by Research Fellowship of TICAM, University of Texas at Austin during his stay (1996–1997).