March 1988; received Ph. D. from the University of Tokyo April 1985–March 1990; Research Associate at the Department of Mathematics, College of Arts and Sciences, the University of Tokyo April 1990–March 1992; Associate Professor at the Department of Mathematics, College of Arts and Sciences, the University of Tokyo April 1992–March 2010; Associate Professor at the Department of Mathematical Sciences, the University of Tokyo April 2010; Professor at the Department of Mathematical Sciences, the University of Tokyo