Kathrin Cresswell1, Aziz Sheikh2, Robin Williams3. 1. Usher Institute, University of Edinburgh, Edinburgh EH8 9DX, UK. Electronic address: kathrin.cresswell@ed.ac.uk. 2. Usher Institute, University of Edinburgh, Edinburgh EH8 9DX, UK. 3. Institute for the Study of Science, Technology and Innovation, University of Edinburgh, Edinburgh EH8 9DX, UK.