[1] Mt Holyoke Coll, Dept Phys, S Hadley, MA 01075 USA
[2] Univ Colorado, ATLAS Inst, Boulder, CO 80309 USA
[3] Michigan State Univ, Dept Phys, Lyman Briggs Coll, E Lansing, MI 48824 USA
[4] Univ Coll Dublin, Sch Educ, Dublin, Ireland
[5] Univ Colorado, Dept Phys, Boulder, CO 80309 USA