1. CSIRO Mathematics; Informatics and Statistics Division; Locked Bag 17, North Ryde New South Wales 2113 Australia
2. School of Engineering and Information Technology; The University of New South Wales; Canberra ACT 2600 Australia
3. Aizu Research Cluster for Medical Engineering and Informatics; Research Center for Advanced Information Science and Technology, The University of Aizu; Fukushima Japan