Concentration in Sequences of Solutions to the Nonlinear Klein-Gordon Equation Zheng YuXi Indiana University Mathematics Journal 1991 text pdf 10.1512/iumj.1991.40.40009 10.1512/iumj.1991.40.40009 en Indiana Univ. Math. J. 40 (1991) 201 - 235 state-of-the-art mathematics http://iumj.org/access/