[1] Univ Wollongong, Sch Math & Appl Stat, Inst Math & Its Applicat, Wollongong, NSW 2522, Australia
[2] Mahidol Univ, Fac Sci, Dept Math, Bangkok 10400, Thailand
[3] CHE, Ctr Excellence Math, Bangkok 10400, Thailand
[4] Univ Adelaide, Sch Math Sci, Nanomech Grp, Adelaide, SA 5005, Australia