Publications

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A NISAC study on the economic effects of a hypothetical H1N1 pandemic was done in order to assess the differential impacts at the state and industry levels given changes in absenteeism, mortality, and consumer spending rates. Part of the analysis was to determine if there were any direct relationships between pandemic impacts and gross domestic product (GDP) losses. Multiple regression analysis was used because it shows very clearly which predictors are significant in their impact on GDP. GDP impact data taken from the REMI PI+ (Regional Economic Models, Inc., Policy Insight +) model was used to serve as the response variable. NISAC economists selected the average absenteeism rate, mortality rate, and consumer spending categories as the predictor variables. Two outliers were found in the data: Nevada and Washington, DC. The analysis was done twice, with the outliers removed for the second analysis. The second set of regressions yielded a cleaner model, but for the purposes of this study, the analysts deemed it not as useful because particular interest was placed on determining the differential impacts to states. Hospitals and accommodation were found to be the most important predictors of percentage change in GDP among the consumer spending variables.

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Nanowires based on the III nitride materials system have attracted attention as potential nanoscale building blocks in optoelectronics, sensing, and electronics. However, before such applications can be realized, several challenges exist in the areas of controlled and ordered nanowire synthesis, fabrication of advanced nanowire heterostructures, and understanding and controlling the nanowire electrical and optical properties. Here, recent work is presented involving the aligned growth of GaN and III-nitride core-shell nanowires, along with extensive results providing insights into the nanowire properties obtained using advanced electrical, optical and structural characterization techniques.

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The Fiber Optic Intrusion Detection System (FOIDS)1 is a physical security sensor deployed on fence lines to detect climb or cut intrusions by adversaries. Calibration of detection sensitivity can be time consuming because, for example, the FiberSenSys FD-332 has 32 settings that can be adjusted independently to provide a balance between a high probability of detection and a low nuisance alarm rate. Therefore, an efficient method of calibrating the FOIDS in the field, other than by trial and error, was needed. This study was conducted to: x Identify the most significant settings for controlling detection x Develop a way of predicting detection sensitivity for given settings x Develop a set of optimal settings for validation The Design of Experiments (DoE) 2-4 methodology was used to generate small, planned test matrixes, which could be statistically analyzed to yield more information from the test data. Design of Experiments is a statistical methodology for quickly optimizing performance of systems with measurable input and output variables. DoE was used to design custom screening experiments based on 11 FOIDS settings believed to have the most affect on WKH types of fence perimeter intrusions were evaluated: simulated cut intrusions and actual climb intrusions. Two slightly different two-level randomized fractional factorial designed experiment matrixes consisting of 16 unique experiments were performed in the field for each type of intrusion. Three repetitions were conducted for every cut test; two repetitions were conducted for every climb test. Total number of cut tests analyzed was 51; the total number of climb tests was 38. This paper discusses the results and benefits of using Design of Experiments (DoE) to calibrate and optimize the settings for a FOIDS sensor

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We present a newly developed microsystem enabled, back-contacted, shade-free GaAs solar cell. Using microsystem tools, we created sturdy 3 {micro}m thick devices with lateral dimensions of 250 {micro}m, 500 {micro}m, 1 mm, and 2 mm. The fabrication procedure and the results of characterization tests are discussed. The highest efficiency cell had a lateral size of 500 {micro}m and a conversion efficiency of 10%, open circuit voltage of 0.9 V and a current density of 14.9 mA/cm{sup 2} under one-sun illumination.

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This work simulated the response of idealized isotopic U-235, U-238, Th-232, and Pu-239 mediums to photonuclear activation with various photon energies. These simulations were conducted using MCNPX version 2.6.0. It was found that photon energies between 14-16 MeV produce the highest response with respect to neutron production rates from all photonuclear reactions. In all cases, Pu-239 responds the highest, followed by U-238. Th-232 produces more overall neutrons at lower photon energies then U-235 when material thickness is above 3.943 centimeters. The time it takes each isotopic material to reach stable neutron production rates in time is directly proportional to the material thickness and stopping power of the medium, where thicker mediums take longer to reach stable neutron production rates and thinner media display a neutron production plateau effect, due to the lack of significant attenuation of the activating photons in the isotopic mediums. At this time, no neutron sensor system has time resolutions capable of verifying these simulations, but various indirect methods are possible and should be explored for verification of these results.