[1] MIT, Sch Engn, Cambridge, MA 02139 USA
[2] Rensselaer Polytech Inst, Dept Phys Appl Phys & Astron, Troy, NY 12180 USA
[3] US Army ARDEC, Benet Labs, Watervliet, NY 12189 USA
[4] Harvard Univ, Sch Engn & Appl Sci, Cambridge, MA 02138 USA
[5] Australian Natl Univ, Res Sch Phys & Engn, Canberra, ACT 0200, Australia