A large scale height galactic component of the diffuse 2-60 keV background

The diffuse 2-60 keV X-ray background has a galactic component clearly detectable by its strong variation with both galactic latitude and longitude. This galactic component is typically 10 percent of the extragalactic background toward the galactic center, half that strong toward the anticenter, and extrapolated to a few percent of the extragalactic background toward the galactic poles. It is acceptably modeled by a finite radius emission disk with a scale height of several kiloparsecs. The averaged galactic spectrum is best fitted by a thermal spectrum of kT about 9 keV, a spectrum much softer than the about 40 keV spectrum of the extragalactic component. The most likely source of this emission is low luminosity stars with large scale heights such as subdwarfs. Inverse Compton emission from GeV electrons on the microwave background contributes only a fraction of the galactic component unless the local cosmic ray electron spectrum and intensity are atypical

Nonlinear Dynamics in Ecosystem Response to Climatic Change: Case Studies and Policy Implications

Many biological, hydrological, and geological processes are interactively linked in ecosystems. These ecological phenomena normally vary within bounded ranges, but rapid, nonlinear changes to markedly different conditions can be triggered by even small differences if threshold values are exceeded. Intrinsic and extrinsic ecological thresholds can lead to effects that cascade among systems, precluding accurate modeling and prediction of system response to climate change. Ten case studies from North America illustrate how changes in climate can lead to rapid, threshold-type responses within ecological communities; the case studies also highlight the role of human activities that alter the rate or direction of system response to climate change. Understanding and anticipating nonlinear dynamics are important aspects of adaptation planning since responses of biological resources to changes in the physical climate system are not necessarily proportional and sometimes, as in the case of complex ecological systems, inherently nonlinear

Nutrient concentration patterns in streams draining alpine and subalpine catchments, Fraser Experimental Forest, Colorado

Streamwater samples were collected during 1987-1988 from two adjacent gauged watersheds, the subalpine-alpine East St. Louis and the Fool Creek Alpine, in the Fraser Experimental Forest, Colorado. The study objective was to compare the relationships between streamwater discharge and ion concentration in alpine and alpine-subalpine watersheds at a site receiving low inputs of atmospheric contaminants. Streamwater discharge accounts for much of the variation in ion concentration. Trajectories of time, discharge, and ion concentration suggest that patterns of nutrient flux are controlled primarily by the magnitude of streamwater discharge, and seasonal differences in the relative contributions of snowmelt and soil water. In the subalpine catchment, increased streamwater discharge accounted for most of the decline in concentration of ions, with high concentrations in soil water relative to precipitation. This relationship was not seen in the alpine catchment, probably because of the influence of large diurnal variation in the ratio of snowmelt to soil water. In both catchments, ions with comparatively high concentrations in precipitation and the snowpack relative to soil water showed less concentration decline with increased streamwater discharge. The recurring nature of the trajectories, especially in the subalpine catchment, suggests that the time, discharge, and ion concentration patterns may represent a general characteristic in moderate-sized, undisturbed Rocky Mountain catchments which do not receive high inputs of airborne contaminants. © 1992

Effect of clear cutting on nutrient fluxes in a subalpine forest at Fraser, Colorado

Nutrient fluxes were investigated on a forested and a clearcut plot in a mixed conifer high elevation (2900 m) forest at the Fraser Experimental Forest in Fraser, Colorado, USA. Plots were located on a coarse loamy mixed Dystric Cryochrept with relatively high base saturation (30-90%) and underlain by an impermeable clay subsoil. Following harvest in late 1984, annual mean NO₃ concentrations of 195 to 198 &#956;mol l^-1 were observed from 1988 through 1990 and concentrations were still above reference levels in 1993. Total nitrogen loss attributable to leaching following harvest was estimated at 48kg ha^-1 over 8 years. Over this same period, atmospheric nitrogen inputs exceeded annual outflow of NH₄ plus NO₃ from the control plots by approximately 11 kg N ha^-1. A slight enrichment Of SO₄ and Cl was observed from the harvested plot in 1986 but concentrations later fell below control plot levels, apparently due to dilution by the increased discharge from the harvested plot which was three to four times that from the control plot. <br> Elevated Ca, Mg, and Na concentrations followed a similar pattern to NO₃ due to exchange reactions, while a depression in alkalinity of about one-third the amount of NO₃ found was also observed. Enrichment of K occurred primarily in water collected at less than 1 m depth. Increases in base cation loss due to leaching after harvest were about twice the amount that can be accounted for by the increased flux of NO₃, SO₄, and Cl anions. The excess reflects the increased water flux and consequent leaching of base cations in association with HCO₃ and organic anions

Prescribed Burning and Mastication Effects on Surface Fuels in Southern Pine Beetle-killed Loblolly Pine Plantations

Surface fuels were characterized in loblolly pine (Pinus taeda L.) plantations severely impacted by southern pine beetle (Dendroctonus frontalis Ehrh.) (SPB) outbreaks in the upper South Carolina Piedmont. Prescribed burning and mastication were then tested as fuel reduction treatments in these areas. Prescribed burning reduced fuelbed continuity by consuming litter (Oi layer), duff (Oe + Oa), and woody surface fuels (1-, 10-, and 100-h timelag size classes) immediately after the treatment. Total loading of 1- and 10-h fuels in burned stands (3.1 Mg ha−1) remained significantly lower than that in the control (no treatment) (5.6 Mg ha−1) in the 2nd year post-treatment. However, 100- and 1000-h fuels increased post-burn due to accelerated failure of remaining pine snags and totaled 14.5 Mg ha−1 in the 2nd year post-treatment which was not significantly different than the control (17.3 Mg ha−1). Mineral soil exposure averaged 73% of burned stands after consumption of the duff layer in many areas. Custom low, moderate, and high load fuel models were developed for SPB-killed stands and produced simulated fire behavior (flame length and rate of spread) similar to two standard slash-blowdown fuel models (SB2 and SB3) when input to the BehavePlus fire modeling system. Mastication resulted in a compacted (bulk density = 131.3 kg m−3) and continuous layer of woody debris that averaged 15.1 cm in depth. Equations were developed for estimating masticated debris load and utilize fuelbed depth as input. The masticated debris load averaged 192.4 Mg ha−1 in the 1st year post-treatment and was significantly higher than total fuel loading in burned (16.3 Mg ha−1) and control (24.3 Mg ha−1) stands. The treatments tested in this study provide different options for preparing SPB-killed areas for reforestation activities and may produce short-term reductions in fire hazard

Hixon Center Ground Breaking

On November 20, 2014 the William & Mary Law School celebrated the groundbreaking of the James A. and Robin L. Hixon Center for Experiential Learning and Leadership

Structure sensitivity in adsorption and decomposition of NO on Ir

The adsorption and decomposition of NO on planar Ir(210) and nanofaceted Ir(210) with tunable facet sizes (5-14 nm) have been studied by means of temperature programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT). Evidence has been found for structure sensitivity in adsorption sites and thermal decomposition of NO on planar Ir(210) versus those on faceted Ir(210). Both planar and faceted Ir(210) surfaces are very active for NO decomposition with high selectivity to N₂. Heating NO-saturated planar Ir(210) leads to desorption of large amounts of N₂ and small amounts of NO together with traces of N₂O. Annealing NO-saturated faceted Ir(210) also produces large amounts of N₂ and small amounts of NO without the formation of N₂O. Adsorption of NO at 300 K on both surfaces is predominantly molecular. On planar Ir(210) NO adsorbs on atop sites for the entire NO coverage range. On faceted Ir(210) that contains (110) and {311} faces, NO adsorbs on bridge and atop sites at low NO coverage while only on atop sites at high NO coverage. No evidence has been found for size effects in the thermal decomposition of NO over faceted Ir(210) for average facet size ranging from 5 to 14 nm