Publications

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A model of malicious intrusions in infrastructure facilities is developed, using a network representation of the system structure together with Markov models of intruder progress and strategy. This structure provides an explicit mechanism to estimate the probability of successful breaches of physical security, and to evaluate potential improvements. Simulation is used to analyze varying levels of imperfect information on the part of the intruders in planning their attacks. An example of an intruder attempting to place an explosive device on an airplane at an airport gate illustrates the structure and potential application of the model.

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This report provides a summary of the three-year LDRD (Laboratory Directed Research and Development) project aimed at developing microchemical sensors for continuous, in-situ monitoring of volatile organic compounds. A chemiresistor sensor array was integrated with a unique, waterproof housing that allows the sensors to be operated in a variety of media including air, soil, and water. Numerous tests were performed to evaluate and improve the sensitivity, stability, and discriminatory capabilities of the chemiresistors. Field tests were conducted in California, Nevada, and New Mexico to further test and develop the sensors in actual environments within integrated monitoring systems. The field tests addressed issues regarding data acquisition, telemetry, power requirements, data processing, and other engineering requirements. Significant advances were made in the areas of polymer optimization, packaging, data analysis, discrimination, design, and information dissemination (e.g., real-time web posting of data; see www.sandia.gov/sensor). This project has stimulated significant interest among commercial and academic institutions. A CRADA (Cooperative Research and Development Agreement) was initiated in FY03 to investigate manufacturing methods, and a Work for Others contract was established between Sandia and Edwards Air Force Base for FY02-FY04. Funding was also obtained from DOE as part of their Advanced Monitoring Systems Initiative program from FY01 to FY03, and a DOE EMSP contract was awarded jointly to Sandia and INEEL for FY04-FY06. Contracts were also established for collaborative research with Brigham Young University to further evaluate, understand, and improve the performance of the chemiresistor sensors.

This report details some proof-of-principle experiments we conducted under a small, one year ($100K) grant from the Strategic Environmental Research and Development Program (SERDP) under the SERDP Exploratory Development (SEED) effort. Our chemiresistor technology had been developed over the last few years for detecting volatile organic compounds (VOCs) in the air, but these sensors had never been used to detect VOCs in water. In this project we tried several different configurations of the chemiresistors to find the best method for water detection. To test the effect of direct immersion of the (non-water soluble) chemiresistors in contaminated water, we constructed a fixture that allowed liquid water to pass over the chemiresistor polymer without touching the electrical leads used to measure the electrical resistance of the chemiresistor. In subsequent experiments we designed and fabricated probes that protected the chemiresistor and electronics behind GORE-TEX{reg_sign} membranes that allowed the vapor from the VOCs and the water to reach a submerged chemiresistor without allowing the liquids to touch the chemiresistor. We also designed a vapor flow-through system that allowed the headspace vapor from contaminated water to be forced past a dry chemiresistor array. All the methods demonstrated that VOCs in a high enough concentration in water can be detected by chemiresistors, but the last method of vapor phase exposure to a dry chemiresistor gave the fastest and most repeatable measurements of contamination. Answers to questions posed by SERDP reviewers subsequent to a presentation of this material are contained in the appendix.