1. Graduate
School of Advanced Mathematical Sciences, Meiji University, Tokyo, Japan
2. School
of Mathematics, University of Edinburgh, Edinburgh, U.K.
3. Laboratory
for High Performance Ceramics, Empa, Swiss Federal Laboratories for
Materials Science and Technology, Dübendorf, Switzerland
4. Department
of Physics, Budapest University of Technology and Economics, H-1111 Budapest, Budafoki út 8, Hungary