Acknowledgments
This material is based on work supported by the Homeland Security Advanced Research Projects Agency (ARPA) under the contract FA8750-05-C-0212 administered by the Air Force Research Laboratory/Rome; by the Air Force Research Laboratory/Rome under the contract FA8750-06-C-0246; by the Federal Aviation Administration under the contract DTFAWA-04-P-00278/0001; by the Air Force Office of Scientific Research under grant FA9550-07-1-0527 and FA9550-08-1-0157; and by the National Science Foundation under grants CT-0716567, CT-0627493, and IIS-0430402. Any opinions, findings, conclusions, or recommendations expressed in this material are the author's and do not necessarily reflect the views of the sponsoring organizations.