[1] Penn State Univ, Dept Phys, University Pk, PA 16802 USA
[2] Penn State Univ, Dept Biol, Mueller Lab 208, University Pk, PA 16802 USA
[3] Univ Padua, Dipartimento Fis Galileo Galilei, I-35131 Padua, Italy
[4] Ist Nazl Fis Mat, I-35131 Padua, Italy