Duarte Valério is a research assistant at the Technical University of Lisbon. He works in the field of control engineering, studying the control of dynamic systems using fractional order derivatives; the use of autonomous, pro-active, interacting systems applied to distributed plants; and the control of plants to produce electricity from sea wave energy.José Sá da Costa is Professor of Control Engineering at the Technical University of Lisbon and Head of the Centre of Intelligent Systems of the Institute of Mechanical Engineering, Lisbon. His research interests include fractional systems, fault tolerant control, surgery robots, active noise and vibration control, and control in health and ocean wave energy devices.