Generalized eigenfunctions of relativistic Schrödinger operators. I. Umeda, Tomio — 2006 Electronic Journal of Differential Equations (EJDE) [electronic only]
Generalized eigenfunctions of relativistic Schrödinger operators in two dimensions. Umeda, Tomio; Wei, Dabi — 2008 Electronic Journal of Differential Equations (EJDE) [electronic only]
Radiation conditions and resolvent estimates for relativistic Schrödinger operators Tomio Umeda — 1995 Annales de l'I.H.P. Physique théorique
The nonrelativistic limit for the Weyl quantized Hamlitonians and pseudo-differential operators. Michihiro Nagase; Tomio Umeda — 1992 Forum mathematicum