 coupled equations: $$d_{0}\left( {t + \Delta t} \right) = {\max\limits_{\ }\left\{ {0,d_{0}\left( t \right) + b + g\left( {v_{0}\left( t \right) - i_{v}v_{0}\left( t \right)} \right) - i_{d}d_{0}\left( t \right) + {N\left( {0,\sigma^{0}} \right)}_{0}\left( t \right)} \right\}}$$ $$d_{0}\left( {t + \Delta t} \right) = {\max\limits_{\ }\left\{ {0,d_{0}\left( t \right) + b + g\left( {v_{0}\left( t \right) - i_{v}v_{0}\left( t \right)} \right) - i_{d}d_{0}\left( t \right) + {N\left( {0,\sigma^{0}} \right)}_{0}\left( t \right)} \right\}}$$  The 