  The non-linear (electric field-dependent) resistivity of the 2D electron
system in silicon exhibits scaling as a function of electric field and electron
density in both the metallic and insulating phases, providing further evidence
for a true metal-insulator transition in this 2D system at B=0. Comparison with
the temperature scaling yields separate determinations of the correlation
length exponent, \nu=1.5, and the dynamical exponent, z=0.8, close to the
theoretical value z=1.
