Stabilization in a chemostat with sampled and delayed measurements

We study chemostat models with constant substrate input concentrations. We allow growth functions that are not necessarily monotone. The measurement is the substrate concentration, which is piecewise constant with a nonconstant delay, so only sampled observations are available. Under new conditions on the size of the delay and on the largest sampling interval, we solve the problem of asymptotically stabilizing a componentwise positive equilibrium point with the dilution rate as the control. We use a new Lyapunov approach