1. Leeds Institute of Fluid Dynamics (LIFD), School of Mechanical Engineering, University of Leeds, LS2 9JT Leeds, U.K.
2. Department of Chemical Engineering, Imperial College London, SW7 2AZ London, U.K.
3. ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, OX11 0QX Didcot, U.K.