Click to increase image sizeClick to decrease image size Acknowledgments This paper draws in part on work supported by grants from the Sloan Foundation (Grant No. 2002-10-12, To Launch an Urban Security Initiative Focused on the City of New York, and Grant No. 2000-12-12, To Explore the Possibility of Launching a MetroTech-like Project in New York City) and of the National Science Foundation (Grant No. 0227693, Introduction of Point-of-Service Scanning Technology Linked to Cash Registers in Small Grocery Stores Owned by Minority Communities in New York City, with Professor Michael Greenstein). The assistance of Rose Emma of Polytechnic University is gratefully acknowledged.