Figure 4.

Contour plot of log₁₀(N_V) from Equations (6) (full lines) and (8) (dashed lines), in the P and N range 0–100. The lines are the loci of the points where log₁₀(N_V) equals 0.0 (red), 0.4, 0.8, 1.2, and 1.6 (black), as indicated on the right side of the figure. The blue line represents P = 0.14N, while the black dotted line is the bisectrix N = P, plotted to emphasize the symmetry of the contour lines.