Fig. 4.2.

Time series for System (2.7) with treatment starting at t = 0 for r = 0 (top, left), r = 0.3 (top, right), and r = 0.6 (bottom). The initial condition is the pre-treatment stationary solution. When the proliferation rate r is small (top, left), there is no delay; the number of infected cells (y) decays at a constant rate from the start of treatment. For intermediate proliferation rates (top, right), there may is a weak delay between the start of treatment and the asymptotic clearance of infection. When r is large (bottom), there is a strong delay (about 10 units, here) before the number of uninfected cells (x) reaches equality with the number of infected cells and the number decay rate of infected cells accelerates to its exponential asymptotic rate. Parameter values s = 0.001, q = 0, d = 0.3, b = 5, θ = 1.