Effect of As Passivation on Vapor-Phase Epitaxial Growth of Ge on (211)Si as a Buffer Layer for CdTe Epitaxy

We report an investigation of epitaxial germanium grown by chemical vapor deposition (CVD) on arsenic-terminated (211)Si, which is the preferred substrate in the USA for fabrication of night-vision devices based on mercury cadmium telluride (MCT) grown by molecular-beam epitaxy (MBE). The films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), cross-sectional transmission electron microscopy (XTEM), and x-ray diffraction (XRD). Arsenic passivation was found to be effective in preventing cross-contamination of unwanted residual species present inside the reactor chamber and also in prolonging the evolution of layer-by-layer growth of Ge for significantly more monolayers than on nonpassivated Si. The two-dimensional (2D) to three-dimensional (3D) transition resulted in Ge islands, the density and morphology of which showed a clear distinction between passivated and nonpassivated (211)Si. Finally, thick Ge layers (∼250 nm) were grown at 525°C and 675°C with and without As passivation, where the layers grown with As passivation resulted in higher crystal quality and smooth surface morphology.     

Quantification of VX vapor in ambient air by liquid chromatography isotope dilution tandem mass spectrometric analysis of glass bead filled sampling tubes

An analysis method has been developed for determining low parts-per-quadrillion by volume (ppqv) concentrations of nerve agent VX vapor actively sampled from ambient air. The method utilizes glass bead filled depot area air monitoring system (DAAMS) sampling tubes with isopropyl alcohol extraction and isotope dilution using liquid chromatography coupled with a triple-quadrupole mass spectrometer (LC/MS/MS) with positive ion electrospray ionization for quantitation. The dynamic range was from one-tenth of the worker population limit (WPL) to the short-term exposure limit (STEL) for a 24 L air sample taken over a 1 h period. The precision and accuracy of the method were evaluated using liquid-spiked tubes, and the collection characteristics of the DAAMS tubes were assessed by collecting trace level vapor generated in a 1000 L continuous flow chamber. The method described here has significant improvements over currently employed thermal desorption techniques that utilize a silver fluoride pad during sampling to convert VX to a higher volatility G-analogue for gas chromatographic analysis. The benefits of this method are the ability to directly analyze VX with improved selectivity and sensitivity, the injection of a fraction of the extract, quantitation using an isotopically labeled internal standard, and a short instrument cycle time.     

Simple and convenient G-quadruplex-based turn-on fluorescence assay for 3' → 5' exonuclease activity

A selective, oligonucleotide-based, label-free, turn-on fluorescence detection method for 3' → 5' exonuclease activity has been developed using crystal violet as a G-quadruplex-binding probe. The assay is highly simple and rapid, does not require the use of gel-based equipment or radioisotopic labeling, and is amenable to high-throughput and real-time detection. A proof-of-concept of this assay has been demonstrated for prokaryotic Exonuclease III (ExoIII) and human TREX1.     

Modulation of Macrophage Fatty Acid Content and Composition by Exposure to Dyslipidemic Serum in Vitro

Macrophages in arterial walls accumulate lipids leading to the development of atherosclerotic plaques. However, mechanisms underlying macrophage lipid accumulation and foam cell formation are often studied without accounting for risk factors such as dyslipidemia. We investigated the effect of varying concentrations of triglyceride (TG) within physiological range on macrophage fatty acid (FA) accumulation and expression of cholesterol efflux proteins. Human monocytes were cultured in media supplemented with 10% sera containing low (0.7 mmol/L) to high (1.4 mmol/L) TG. The resulting macrophages were harvested after 10 days for analysis of FA content and composition and expression of genes involved in lipid metabolism. Exposure to higher TG and lower HDL concentrations in media increased macrophage lipid content. Macrophages exposed to higher TG had increased total FA content compared with controls (876 μg/mg protein vs. 652 μg/mg protein) and greater proportions of C16:0, C18:1 and C18:2. Macrophage expression of both ABCA1 and ABCG1 cholesterol efflux proteins were reduced when higher TG concentrations were present in the media. Expression of scavenger receptor CD36, involved in lipoprotein uptake, was also downregulated in macrophages exposed to higher TG. Culturing macrophages in conditions of higher versus lower TG influenced macrophage FA content and composition, and levels of regulatory proteins. Replicating in vitro levels of dyslipidemia encountered in vivo may provide an informative model for investigation of atherogenesis.     

Observations and simulations of snow surface temperature on cross-country ski racing courses

Fast skis are essential for an Olympic cross-country skiing athlete. Accurate and timely estimates of the snow surface conditions on a race course are needed to prepare race skis. For training purposes prior to the 2010 Winter Olympics, snow surface and snowpack observations were collected on the cross-country racing track at the Whistler Olympic Park, British Columbia during February 2008 and 2009. During periods with clear skies, snow surface temperatures varied by more than 10 °C around the course while temperatures in the stadium area increased by more than 16 °C from morning to early afternoon. Simulations using the SNOWPACK model of snow surface temperature were within 1 °C of those measured during a four day observation period in the stadium area. Idealized simulations were completed varying cloud cover, slope and aspect. These simulations provided realistic appearing changes in snow surface temperature as a function of time of day.     

Oceanic biogeochemical controls on global dynamics of persistent organic pollutants

Understanding and quantifying the global dynamics and sinks of persistent organic pollutants (POPs) is important to assess their environmental impact and fate. Air-surface exchange processes, where temperature plays a central role in controlling volatilization and deposition, are of key importance in controlling global POP dynamics. The present study is an assessment of the role of oceanic biogeochemical processes, notably phytoplankton uptake and vertical fluxes of particles, on the global dynamics of POPs. Field measurements of atmospheric polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins (PCDDs), and furans (PCDFs) are combined with remote sensing estimations of oceanic temperature, wind speed, and chlorophyll, to model the interactions between air-water exchange, phytoplankton uptake, and export of organic matter and POPs out of the mixed surface ocean layer. Deposition is enhanced in the mid-high latitudes and is driven by sinking marine particulate matter, rather than by a cold condensation effect. However, the relative contribution of the biological pump is a function of the physical-chemical properties of POPs. It is concluded that oceanic biogeochemical processes play a critical role in controlling the global dynamics and the ultimate sink of POPs.     

Soy isoflavones and fatty acids: effects on bone tissue postovariectomy in mice

Osteoporosis is a silent disease that leads to fragility fractures that can diminish quality of life and contribute to death. With no ideal drug treatment available to manage osteoporosis, soy isoflavones (ISO), and omega-3 long chain PUFAs in fish oil (FO) may be integral in a dietary strategy that prevents bone loss. The overall objective of this study was to determine if combining ISO with omega-3 long chain PUFAs resulted in greater protection against the loss of bone mineral and skeletal weakening in ovariectomized mice. Ovariectomized CD-1 mice were randomized to control diet or a diet containing ISO alone (250 mg of genistein + 250 mg of daidzein/kg diet), FO alone (7% menhaden oil), or ISO + FO. Each dietary intervention prevented the loss of bone mineral density (BMD) in the femur and preserved femur strength, but only FO, either alone or combined with ISO, resulted in a higher BMD of lumbar vertebra (LV). Most notably, FO + ISO resulted in a higher peak load of LV4, indicating that vertebra were more resistant to fracture. Whether a dietary strategy providing FO in combination with ISO attenuates bone loss in postmenopausal women awaits investigation.     

Plant reestablishment 15 years after the debris avalanche at Mount St Helens,Washington

Vegetation has slowly reestablished on the debris avalanche deposit in the 15 years after the 1980 eruption of Mount St. Helens that created a 60-km(2) debris avalanche, the largest landslide in recorded history. There has been a gradual increase in species richness and cover, but only 61% of the species present on the mountain before the eruption have established on the debris avalanche deposit. Plant cover averages 38% and is extremely patchy. Life form composition changed over successional time, because part of the avalanche deposit was invaded by introduced plant species aerially seeded to reduce erosion, the site offers the opportunity to compare successional processes occurring with and without introduced species. Long-term recovery trends and effects of nonnative species on succession are important to understand since plant reestablishment practices often rely on nonnative species for enhancing vegetation recovery of denuded sites along road sides, strip mines, or other human-generated clearing. Fifteen years after the eruption and 10 years since the invasion by introduced species, plots invaded by nonnative species had greater vegetation cover and more native plant richness than plots that were not inundated. Significantly greater mortality of conifers occurred in the plots dominated by introduced species shortly after the invasion of those species, but no difference in conifer mortality occurred in the last 5 years. Even so, the plots dominated by introduced species still have fewer conifer trees. Thus, the short-term pulse of conifer mortality after the invasion of introduced species may have long-term effects on the recovery of the dominant vegetation. It will likely be decades before there is 100% plant cover on the debris avalanche deposit and a century or more before full recovery of the vegetation system.     

Impacts of urban environmental elements on residential housing prices in Guangzhou (China)

The amenity value provided by urban green spaces, water bodies and good environmental quality is difficult to assess and incorporate into urban planning and development. Developers and governments in China hitherto have seldom objectively factored these attributes into property pricing and associated decisions. The hedonic pricing method offers an appropriate approach to gauge such external benefits which contribute to real-estate transaction prices. This study explored the impacts of key environmental elements with a bearing on residential housing value in Guangzhou, including window orientation, green-space view, floor height, proximity to wooded areas and water bodies, and exposure to traffic noise. Four large private housing estates composed of multi-storied blocks with similar design and price bracket, catering to the mass property market, were sampled. Transaction price data and structural attributes of 652 dwelling units were acquired directly from developers. Data on environmental attributes were collected in the field. Two functional hedonic pricing method models, linear and semi-log, were constructed. The semi-log model offered comparatively stronger explanatory power and more reliable estimation. High floor on the multi-storey tenement blocks contributed implicitly 9.2% to the selling price. View of green spaces and proximity to water bodies raised housing price, contributing notably at 7.1% and 13.2%, respectively. Windows with a southern orientation with or without complementary eastern or northern views added 1% to the price. Proximity to nearby wooded area without public access was not significant, expressing the pragmatic mindset in the hedonic behavior. Exposure to traffic noise did not influence willingness-to-pay, implying tolerance of the chronic environmental nuisance in the compact city. The study demonstrates that hedonic pricing method could be applied in the Chinese context with an increasingly expanding and privatized property market. It could inform the decisions of policy makers and property developers concerning land selling and buying, land conversion, property development, urban nature conservation, and design of ecological green-space networks.