1. Department of Aerospace, Physics and Space Sciences, Florida Institute of Technology, Melbourne, FL 32901, USA
2. Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA
3. Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
4. Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA