1. a Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge, MA 02139, USA
2. b Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge, MA 02139, USA
3. c Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge, MA 02139, USA
4. d Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge, MA 02139, USA
5. e U.S. Army Cold Regions Research and Engineering Laboratory Hanover, NH 03755, USA
6. f U.S. Army Cold Regions Research and Engineering Laboratory Hanover, NH 03755, USA