  We study a series array of nonlinear electrical circuit elements that possess
negative differential resistance and find that \emph{heterogeneity} in the
element properties leads to the presence of multiple branches in
current-voltage curves and a non-uniform distribution of voltages across the
elements. An inhomogeneity parameter $r_{max}$ is introduced to characterize
the extent to which the individual element voltages deviate from one another,
and it is found to be strongly dependent on the rate of change of applied
voltage. Analytical expressions are derived for the dependence of $r_{max}$ on
voltage ramping rate in the limit of fast ramping and are confirmed by direct
numerical simulation.
