Isotopic fractionation during soil uptake of atmospheric hydrogen

Soil uptake of atmospheric hydrogen (H<sub>2</sub>) and the associated hydrogen isotope effect were studied using soil chambers in a Western Washington second-growth coniferous forest. Chamber studies were conducted during both winter and summer seasons to account for large natural variability in soil moisture content (4–50%) and temperature (6–22 °C). H<sub>2</sub> deposition velocities were found to range from 0.01–0.06 cm s<sup>−1</sup> with an average of 0.033 ± 0.008 cm s<sup>−1</sup> (95% confidence interval). Consistent with prior studies, deposition velocities were correlated with soil moisture below 20% soil moisture content during the summer season. During winter, there was considerable variability observed in deposition velocity that was not closely related to soil moisture. The hydrogen kinetic isotope effect with H<sub>2</sub> uptake was found to range from −24‰ to −109‰. Aggregate analysis of experimental data results in an average KIE of −57 ± 5‰ (95% CI). Some of the variability in KIE can be explained by larger isotope effects at lower (<10%) and higher (>30%) soil moisture contents. The measured KIE was also found to be correlated with deposition velocity, with smaller isotope effects occurring at higher deposition velocities. If correct, these findings will have an impact on the interpretation of atmospheric measurements and modeling of δD of H<sub>2</sub>

Salinity History of Coastal Marshes Reconstructed from Diatom Remains

Sediment cores were collected from three Louisiana coastal marsh ponds, dated with radioisotopes, and analyzed for diatom remains to determine if long-term salinity changes were evident in the sediment record. A diatom-based salinity index formulated from a statistical comparison of available salinity data and changing diatom assemblages demonstrated that diatom remains appear to preserve salinity signals in coastal brackish and salt marsh environments. The salinity index was applied to sediment cores spanning the late 1600s to the 1990s and provided a more complete record of salinity than field data, which were temporally and spatially incomplete. The salinity reconstructions indicated that salinity has increased at two sites and decreased at a third since the early 1900s. The salinity changes are less than 1‰ per decade in all cases, and may be due to natural variability as depicted by the wide range of salinities observed between the late 1600s and 1900. Salinity regimes may be very localized (\u3c2 km from a hydrologic source), indicating single-site studies may not be applicable to regional inferences. This study demonstrates that diatoms can be used to reconstruct past salinity in coastal marsh environments and can provide a useful tool with which to study the changing hydrology of river-influenced ecosystems

Observation of a One-Dimensional Spin-Orbit Gap in a Quantum Wire

Understanding the flow of spins in magnetic layered structures has enabled an increase in data storage density in hard drives over the past decade of more than two orders of magnitude1. Following this remarkable success, the field of 'spintronics' or spin-based electronics is moving beyond effects based on local spin polarisation and is turning its attention to spin-orbit interaction (SOI) effects, which hold promise for the production, detection and manipulation of spin currents, allowing coherent transmission of information within a device. While SOI-induced spin transport effects have been observed in two- and three-dimensional samples, these have been subtle and elusive, often detected only indirectly in electrical transport or else with more sophisticated techniques. Here we present the first observation of a predicted 'spin-orbit gap' in a one-dimensional sample, where counter-propagating spins, constituting a spin current, are accompanied by a clear signal in the easily-measured linear conductance of the system.Comment: 10 pages, 5 figures, supplementary informatio

Industrial Application of Heterostructure Device Simulation,”

Abstract-We give an overview of the state-of-theart of heterostructure RF-device simulation for industrial application based on III-V compound semiconductors. Results for Heterostructure Bipolar Transistors (HBTs) and for High Electron Mobility Transistors (HEMTs) are presented in good agreement with measured data of industrially relevant devices

Zoonosis at the Huanan Seafood Market: A Critique

Since the Hunan Seafood Market (HSM) in Wuhan, China was first suggested as the source of the COVID-19 pandemic in late January 2020, debate has continued over the evidence supporting this claim. Here, we assess the evidence provided in support of zoonotic spillover at the HSM as the origin of human infection of SARS-CoV-2. We find that the datasets and analyses put forward in support of zoonosis are biased, and lack sufficient verifiable data to support this hypothesis. The earliest COVID-19 case at the HSM was not at or near a wildlife stall, the distribution of cases at the HSM is consistent with a Poisson point process model (randomly distributed) and the distribution of wildlife stalls and COVID-19 cases are consistent with independent Poisson point processes. No statistical correlation is found between cases and wildlife stall locations. The random distribution of cases and several isolated clusters is consistent with human-to-human transmission in shared areas such as eating areas, toilets and social gathering areas. Sampling bias is evident in specimen collection at the market, with over-sampling evident in the SW corner of the market relative to the rest of the market. Notwithstanding this bias, environmental positive PCR samples are more consistent with contamination by infected COVID-19 cases and aerosol spread from the HSM toilets, as compared with from wildlife stalls. Although proposed as the intermediate spillover host, raccoon dogs were unlikely to be linked with the outbreak, as they were sold in Wuhan in small numbers, and there is no epidemiological evidence indicating any infection of a raccoon dog, or any other wild or domestic animal, before or during the early pandemic, at any market elsewhere in Wuhan, or even in the rest of China. These considerations indicate that HSM was instead likely a superspreader location, with only tenuous evidence to support a zoonotic spillover there. Consequently, we conclude there is sufficient evidence to indicate the HSM as the source of the pandemic

Nutrient Changes in the Mississippi River and System Responses on the Adjacent Continental Shelf

The Mississippi River system ranks among the world\u27s top 10 rivers in freshwater and sediment inputs to the coastal ocean. The river contributes 90% of the freshwater loading to the Gulf of Mexico, and terminates amidst one of the United States\u27 most productive fisheries regions and the location of the largest zone of hypoxia, in the western Atlantic Ocean. Significant increases in riverine nutrient concentrations and loadings of nitrate and phosphorus and decreases in silicate have occurred this century, and have accelerated since 1950. Consequently, major alterations have occurred in the probable nutrient limitation and overall stoichiometric nutrient balance in the adjacent continental shelf system. Changes in the nutrient balances and reduction in riverine silica loading to, the continental shelf appear to have led to phytoplankton species shifts offshore and to an increase in primary production. The phytoplankton community response, as indicated by long-term changes in biological uptake of silicate and accumulation of biologically bound silica in sediments, has shown how the system has responded to changes in riverine nutrient loadings. Indeed, the accumulation of biologically bound silica in sediments beneath the Mississippi River plume increased during the past two decades, presumably in response to, increased nitrogen loading. The duration, size, and severity of hypoxia has probably increased as a consequence of the increased primary production. Management alternatives directed at water pollution issues within the Mississippi River watershed may have unintended and contrasting impacts on the coastal waters of the northern Gulf of Mexico

Influence of a Cyclonic Eddy on Microheterotroph Biomass and Carbon Export in the Lee of Hawaii

[1] A multi‐platform sampling strategy was used to investigate carbon cycling in a cold‐core eddy that formed in the lee of Hawaii during September 2000. Microheterotroph biomass and 234Th‐derived carbon export rates within the eddy were 2 to 3 times higher than those observed for adjacent waters. If this eddy is representative of other cyclonic eddies that are frequently formed in the lee of Hawaii, then eddy activity may significantly enhance the areal efficiency of the biological pump and facilitate the transfer of organic carbon to organisms inhabiting the mesopelagic and abyssal‐benthic zones of this subtropical ecosystem