On the Mechanism of Time--Delayed Feedback Control
  The Pyragas method for controlling chaos is investigated in detail from the experimental as well as theoretical point of view. We show by an analytical stability analysis that the revolution around an unstable periodic orbit governs the success of the control scheme. Our predictions concerning the transient behaviour of the control signal are confirmed by numerical simulations and an electronic circuit experiment. 
Wolfram Just, Thomas Bernard, Matthias Ostheimer, Ekkehard Reibold,   and Hartmut Benner