Figure 6

Root locus plots of recA to uvrA SISO system. These plots trace the poles of the closed-loop system as the gain K is varied from zero to infinity. The trajectories start at the open-loop poles which are represented by the cross, and could end at the open-loop zeros which are represented by an open circle, or they could go on infinitely in some direction. The different colours represent distinct trajectories of different closed-loop poles. Fig. 6a This is the root locus plot of recA to uvrA system under low level of radiation with negative feedback, where the locus on the real axis goes out of the unit circle quickly and therefore shows small stability margins. (The dotted circle is the unit circle.). Fig. 6b This is the root locus plot of recA to uvrA system under low level of radiation with positive feedback, with some stability margins. Fig. 6c This is the root locus plot of recA to uvrA system under high level of radiation with negative feedback, where a good portion of all three loci stays within the unit circle and therefore exhibits large stability margins. Fig. 6d This is the root locus plot of recA to uvrA system under high level of radiation with positive feedback, which has no stability margin.