[1] Pembroke Coll, Cambridge CB2 1RF, England
[2] Univ Cambridge, Dept Chem Engn & Biotechnol, Cambridge CB3 0AS, England
[3] Univ Granada, CSIC, Inst Andaluz Ciencias Tierra, E-18100 Granada, Spain
[4] Univ Granada, Inst Carlos I Fis Teor & Computac, E-18071 Granada, Spain
[5] Kings Coll, Inst Theoret Geophys, Cambridge CB2 1ST, England
[6] Univ Edinburgh, Sch Engn, Edinburgh EH9 3FB, Midlothian, Scotland