Nature 1999/12/23 $B$K$h$k$H!"468wF}:^$K%.;@1v%$%*%s$r%I!<%W$9(B $B$k$3$H$K$h$C$F7kA|$NG=N($r(B10$BG\$[$I9b$a$k8+9~$_$,$"$k$s$G$9$C(B $B$F!#$=$l$@$1$J$s$G$9$1$I!#(B -- $B;T@n!!<~0l(B (Shuichi ICHIKAWA) <ichikawa@tutkie.tut.ac.jp>