1. Ph.D. Student, Nicholas School of the Environment, Duke Univ., Durham, NC 27708 (corresponding author).
2. Assistant Research Scientist, Dept. of Geography and Environmental Engineering, Johns Hopkins Univ., Baltimore, MD 21218.
3. Professor, Dept. of Mathematics and Computer Science, North Carolina Central Univ., Durham, NC 27707.
4. Professor, Nicholas School of the Environment, Duke Univ., Durham, NC 27708.