A Dynamical Model for Pion Photo- and Electroproduction on the Nucleon S.S. Kamalov, S.N. Yang, D. Drechsel, L. Tiator Phys. Rev. C 64 (2001) 032201or nucl-th/0006068 Phys. Rev. Lett. 83, (1999) 4494 and nucl-th/0107017