1. Division of Dynamics,Chalmers University of Technology, Hörsalsvägen 7A,Gothenburg 412 96, Sweden
2. Division of Vascular Surgery,Stanford University, 300 Pasteur Dr.,Always Building M121,Stanford, CA 94305
3. Mathematical Sciences,Chalmers University of Technology and University of Gothenburg, Chalmers tvärgata 3,Gothenburg 412 58, Sweden
4. Department of Cardiothoracic Surgery,Stanford University, Falk Building, 870 Quarry Road,Palo Alto, CA 94304