1. Department of Physics, Nuclear Research Center Negev, POB 9001, Be'er-Sheva 84190, Israel
2. Department of Physics, Ben-Gurion University of the Negev, POB 653, Be'er-Sheva 84105, Israel
3. Department of Mechanical Engineering, Ben-Gurion University of the Negev, POB 653, Be'er-Sheva 84105, Israel