Accurate and unbiased radiative energy transfer models are critical to our understanding of ecosystem primary productivity, carbon cycling, and climate change. Much of the current research in this area is based on models parameterized for grasslands and broadleaf forests. However, many temperate montane and boreal forests are dominated by conifers, which present unique challenges to modellers. We propose two fundamentally different strategies by which plant canopies optimize solar radiation interception. Laminar canopies (e.g., grasslands, broadleaf trees) are .solar panels. that directly intercept incoming radiant energy. By contrast, conifer canopies are conical anechoic (.without echo.) surfaces that intercept radiant energy by scattering it through the canopy. The properties of anechoic surfaces are well known in acoustical and electrical engineering, but have not been applied in environmental biophysics. We discuss the physical principles of anechoic surfaces, and demonstrate how these principles apply to conifer trees and canopies. A key feature of anechoic interception is low radiance over all wavelengths, which is an emergent property of the system. Using empirical data from boreal forest stands in Riding Mountain National Park (Manitoba, Canada), we demonstrate that conifer canopies have very low near-infrared radiance compared to laminar broadleaf canopies. Vegetation index values for conifers are thereby reduced, resulting in underestimates of primary productivity and other biophysical parameters. We also discuss the adaptive significance of boreal conifer geometry, and consider factors driving selection of laminar versus anechoic canopy architectures.
Landscape complexity in the boreal forest is a function of physiographic complexity (spatial processes) and post-fire successional (temporal) processes operating across scales. In this study we examine the role of succession and topographic complexity in determining the landscape complexity of Riding Mountain National Park, Manitoba, Canada. Landscape complexity is assessed by using multifractal analysis to quantify landscape patterns from Landsat TM imagery. To determine whether complexity changes with age, . young. sites (post-fire stand ages = 11 and 30 years) were matched with adjacent . old. sites (post-fire stand ages ≯ 95 years). The influence of physiography on landscape complexity is examined by comparing sites having . simple. and . complex. physiographies (as determined by fractal surface analysis). The scaling properties of landscape complexity are determined by calculating the multifractal spectrum (Dq) for each site. Landscape complexity increases during early succession; multifractal profiles of 11 year old sites are lower than those of adjacent older stands. However, the multifractal profiles of 30 year old and adjacent older stands are indistinguishable, suggesting that change in landscape complexity occurs within 30 years following fire. Physiographically . complex. sites have consistently greater landscape complexity than adjacent . simple. sites. We conclude that landscape complexity increases over time as succession proceeds, and in space along a gradient from . simple. to . complex. physiographies. It follows that landscape complexity is lowest in early-successional, physiographically . simple. sites and highest in late-successional, physiographically . complex. sites.
Authors:J. Kaczvinsky, J. Fritz, D. Walker, and M. Ebra
The alkaline synthesis of porous phenol-formaldehyde polymers containing iminodiacetic acid is described. Porosity is induced by the addition of a finely divided solid material (template) that is insoluble under the reaction conditions. This template is removed by dissolution after the polymerization is complete. Silica gel, carbonate salts and various other salts are used as templates. Resins containing different phenols are synthesized and their effectiveness for the removal of radioactive cesium and strontium from alkaline concentrated sodium salt brines is examined. This matrix typifies the composition of soluble defense nuclear waste.
Authors:J. Kaczvinsky, J. Fritz, D. Walker, and M. Ebra
The effect of a number of synthetic variables on the affinities of resorcinol-formaldehyde-iminodiacetic acid resins for137Cs and90Sr was determined. Porosity was introduced into the resins by inclusion of CaCO3 as a solid template during the synthesis. Among the variables examined were reaction temperature, reactant ratio, choice of basic catalyst, and amount of added template. Only reaction temperature was found to have a clearly defined influence on affinity. Cesium-137 affinity increased with increasing reaction temperature. Affinity for90Sr was independent of reaction temperature below reflux temperature, but dropped drastically for resins synthesized at reflux. These results are explained mechanistically. The reproducibility of the resin synthesis is also examined.
Authors:R. L. Brodzinski, R. A. Craig, S. D. Fink, W. K. Hensley, N. O. Holt, M. A. Knopf, E. A. Lepel, O. D. Mullen, S. R. Salaymeh, T. J. Samuel, J. E. Smart, M. R. Tinker, and D. D. Walker
An online monitor has been designed, built, and tested that is capable of measuring the residual transuranic concentrations in processed high-level wastes with a detection limit of 370 Bq/ml (10 nCi/ml) in less than six hours. The monitor measures the (α,n) neutrons in the presence of gamma-ray fields up to 1 Sv/h (100 R/h). The optimum design was determined by Monte Carlo modeling and then tempered with practical engineering and cost considerations. A multiplicity counter is used in data acquisition to reject the large fraction of coincident and highly variable cosmic-ray-engendered background events and results in an S/N ratio ~1.
Authors:L. Tandon, E. Hastings, J. Banar, J. Barnes, D. Beddingfield, D. Decker, J. Dyke, D. Farr, J. FitzPatrick, D. Gallimore, S. Garner, R. Gritzo, T. Hahn, G. Havrilla, B. Johnson, K. Kuhn, S. LaMont, D. Langner, C. Lewis, V. Majidi, P. Martinez, R. McCabe, S. Mecklenburg, D. Mercer, S. Meyers, V. Montoya, B. Patterson, R. Pereyra, D. Porterfield, J. Poths, D. Rademacher, C. Ruggiero, D. Schwartz, M. Scott, K. Spencer, R. Steiner, R. Villarreal, H. Volz, L. Walker, A. Wong, and C. Worley
The goal of nuclear forensics is to establish an unambiguous link between illicitly trafficked nuclear material and its origin.
The Los Alamos National Laboratory (LANL) Nuclear Materials Signatures Program has implemented a graded “conduct of operations”
type analysis flow path approach for determining the key nuclear, chemical, and physical signatures needed to identify the
manufacturing process, intended use, and origin of interdicted nuclear material. This analysis flow path includes both destructive
and non-destructive characterization techniques and has been exercized against different nuclear materials from LANL’s special
nuclear materials archive. Results obtained from the case study will be presented to highlight analytical techniques that
offer the critical attribution information.