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  • Author or Editor: J. Hilborn x
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Abstract  

SLOWPOKE-2 is a 20 kW pool-type research reactor, producing a thermal neutron flux of 1012 n·cm–2·s–1 at five sample sites in the beryllium reflector. Because of its inherent safety, it is the only reactor in the world licensed for unattended operation. The present core contains approximately 900 g highly-enriched uranium (93 wt.% U-235 in U), which could be viewed as a potential source of nuclear weapons material. To overcome proliferation concerns, Atomic Energy of Canada Limited (AECL) has developed a low enrichment fuel containing less than 20 wt.% U-235 in U. The first low enrichment uranium core will be installed in a new SLOWPOKE-2 reactor at the Royal Military College, Kingston, Ontario.

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The rational definition of spatial analysis units is critical to modeling and understanding large-scale ecological processes. This study assessed the relationship between forest-edge habitat pattern and Lyme disease incidence rate when modeled under three designs for spatial data aggregation. Incidence rates were calculated from passive surveillance data reported for 12 counties in the U.S. State of Maryland during 1996–2000. A design using road-bounded polygons that varied in size from 0.002 km 2 to 368 km 2 ( n = 415) was compared with designs that used grid cells of 10 km 2 ( n = 823) and 36 km 2 ( n = 230). Major roads were chosen to approximate bounded populations of deer and humans engaged in outdoor activity around the home (peridomestic activity). While cell boundaries were arbitrary, cell sizes were chosen to eliminate outliers observed in small polygons, and to standardize the presumed zone of exposure. The single variable that explained the most variation in incidence rate across all study designs was percent of herbaceous edge adjacent to forest. The multi-variable model with the strongest explanatory power (R 2 = 0.87) resulted from the road-bounded design. Furthermore, this design controlled for spatial autocorrelation (p = 0.064), which was highly significant in both grid designs (p = 0.002). Findings demonstrate the utility of roads to delimit distinct zones of human-environment interaction, including development intensity and peridomestic contact with wildlife habitat. This study emphasizes the importance of judicious boundary selection to spatial models with the potential for real-world applications in landscape planning and design.

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