Effective Lagrangians involving nucleons coupled to scalar and vector
fields are investigated within the framework of relativistic mean-fiel
d theory. The study presents the traditional Walecka model acid differ
ent kinds of scalar derivative coupling suggested by Zimanyi and Moszk
owski (ZM). it is shown that the equations of state for all these modi
fied ZM models are soft. The real part of the optical potential for th
ese models is obtained. When compared with the usual ZM model, the mod
ified models present the peculiarity of giving simultaneously a smalle
r nucleon effective mass and a smaller incompressibility. This can be
explained through the mesonic nonlinear sealar-vector coupling contain
ed in these modified models.