Summary: Chemical Engineering Science 59 (2004) 16531666
Complex systems and networks: challenges and opportunities for
chemical and biological engineers
L.A.N. Amaral, J.M. Ottino
Department of Chemical and Biological Engineering, Northwestern University, Robert McCormick School of Engineering, 2145 Sheridan Road,
Evanston, IL 60208-3120, USA
Received 18 September 2003; received in revised form 26 December 2003; accepted 31 January 2004
The di erence between the complicated and the complex is not just quantitative; it is also qualitative. Complexity requires both an
augmentation of the conceptual framework and new tools. In this manuscript we describe the challenges faced when studying complex
systems and describe how scientists from many di erent areas have responded to these challenges. We brie y describe the toolkit used for
studying complex systems: nonlinear dynamics, statistical physics, and network theory. We place particular emphasis on network theory
due to the explosive rate of advance that the ˙eld has recently experienced. We argue that chemical engineering--conversant with a
systems viewpoint that is deeply embedded in its culture and the ability to tackle problems across a broad range of length and time scales
--is in excellent position to master and develop new tools and to tackle the many challenges posed by complex systems. To illustrate this
fact, we brie y review two cases--ecologic food webs and cellular networks--where chemical engineers could have an immediate impact.
? 2004 Elsevier Ltd. All rights reserved.
Keywords: Complex systems; Networks; Nonlinear dynamics; Complexity; Small-world; Scaling; Universality
1. What is a complex system?