Note that the subscript letter 'a' and superscript letter 'b' in the abstract have not copied correctly, and the fractions have been written in a single line.
RGMIA digitization. CAVAL 2011
Abstract removed Lyn 25/9/12. Permission granted, in perpetuity, RGMIA version. MA 6/9/12. Supporting documentation added to dark upload - HD 15/11/19