But instead of assuming a [*[single]{}*]{} outer gap with [*[only]{}*]{} an outgoing current, and no restriction on azimuthal directions, they use various physical processes (including pair production which depends sensitively on the local electric field and the local radius of curvature, surface field structure, reflection of $e^{\pm}$ pairs because of mirroring and resonant scattering) to determine the three-dimensional geometry of the outer gap. In their model, two outer gaps and both outgoing and incoming currents are in principle allowed, but it turns out that outgoing currents dominate the emitted radiation intensities. Furthermore, the three dimensional structure of outer gaps is completely determined by pair production conditions. Since the potential drop of the gap is $\Delta V\approx 6.6\times 10^{12}f^2_0B_{12}P^{-2}\;{\mbox{Volts}}$, where $P=2\pi /\Omega $ is the rotation period, $\Omega$ is the rotation angular velocity, $B_{12}$ is the surface magnetic field in units of 10$^{12}$ Gauss, $f_0=h(<r>)/R_L$, $h(<r>)$ is the average vertical separation of the gap boundaries in the (${\bf{\Omega}}$, ${\bf{\mu}}$) plane and $R_L=c/\Omega$ is the light cylinder radius, and $<r>$ is the average distance to the gap; its value depends on magnetic inclination angle $\alpha$ ($<r>\sim R_L/2$). The particle current passing through the gap is $\dot{N}_{gap}=3\times 10^{30}f_0\xi B_{12}P^{-2}\;{\mbox{s$^{-1}$}}$, where $\xi=\Delta\Phi/2\pi$; $\Delta\Phi$ is 