Before revision:  The scheme considers two physical stages of the device and models them using two coupled systems , i.e., a system of Poisson and drift-diffusion equations describing the nonequilibrium steady state, and a system of Maxwell and drift-diffusion equations describing the transient stage.
After revision:  The scheme considers two physical stages of the device and models them using two coupled systems : a system of Poisson and drift-diffusion equations describing the nonequilibrium steady state, and a system of Maxwell and drift-diffusion equations describing the transient stage.