[1] Boston Univ, Dept Mech Engn, Boston, MA 02215 USA
[2] Boston Univ, Dept Elect & Comp Engn, Boston, MA 02215 USA
[3] Ecole Polytech Fed Lausanne, Neuchatel, Switzerland
[4] Boston Univ, Div Mat Sci & Engn, Boston, MA 02215 USA
[5] Boston Univ, Dept Phys, 590 Commonwealth Ave, Boston, MA 02215 USA