Влияние облучения и отжига на термическую стабильность радиационных дефектов в кремнии

Описан отжиг А-центров, дивакансий, А-центров, модифицированных водородом, в n-Si (P ≈ 10^14 см^-3), в отсутствие и при наличии примеси платины, после облучения протонами с энергией 1,8 МэВ. Показано, что энергия активации отжига радиационных дефектов при взаимодействии с водородно-вакансионными дефектами уменьшается с 1,1 до 0,8 эВ при увеличении концентрации платины в кремнии, так как деформационные поля, создаваемые атомами платины, уменьшают энергию переориентации дефектов. Уточнено энергетическое положение в запрещенной зоне кремния донорного уровня А-центра (ЕV + 0,415 эВ) на основании известных данных о положении А-центра, модифицированного атомом углерода (ЕV + 0,38 эВ) или водорода (ЕV + 0,28 эВ).Описано відпал А-центрів, дивакансій, А-центрів, модифікованих воднем, у n-Si (P ≈ 10^14 см^-3), за відсутності та при наявності домішки платини, після опромінення протонами з енергією 1,8 МеВ. Показано, що енергія активації відпалу радіаційних дефектів при взаємодії з воднево-вакансійними дефектами зменшується від 1,1 до 0,8 еВ зі збільшенням концентрації платини в кремнії, оскільки деформаційні поля, які створюються атомами платини, зменшують енергію переорієнтації дефектів. Уточнено енергетичне положення у забороненій зоні кремнію донорного рівня А-центра (ЕV + 0,415 еВ), виходячи із відомих даних щодо положення А-центра, модифікованого атомом вуглецю (ЕV + 0,38 еВ) або водню (ЕV + 0,28 еВ).The annealing of A-centers, divacancies, A-centers modified by hydrogen was described for n-Si (P ≈ 10^14 cm^-3), with and without platinum dopants, after the irradiation by protons with energy 1.8 MeV. It was shown that the activation energy of annealing for radiation defects under their interaction with hydrogen-vacancy defects is decreased from 1.1 to 0.8 eV with the increasing of platinum concentration in silicon, because the deformation fields, creating by platinum atoms, decrease the energy of the defect re-orientation. In the forbidden zone of silicon the energy state for the donor level of A-center (ЕV + 0.415 eV) was specified based on the data about the position of A-center modified by the carbon atom (ЕV + 0.38 eV) or the hydrogen atom (ЕV + 0.28 eV)

Spoken Code-Switching in Written Form? Manifestation of Code-Switching in Computer Mediated Communication

Contains fulltext : 159840.pdf (publisher's version ) (Open Access)22 p

Soil warming increases the number of growing bacterial taxa but not their growth rates

Soil microorganisms control the fate of soil organic carbon. Warming may accelerate their activities putting large carbon stocks at risk of decomposition. Existing knowledge about microbial responses to warming is based on community-level measurements, leaving the underlying mechanisms unexplored and hindering predictions. In a long-term soil warming experiment in a Subarctic grassland, we investigated how active populations of bacteria and archaea responded to elevated soil temperatures (+6°C) and the influence of plant roots, by measuring taxon-specific growth rates using quantitative stable isotope probing and 18O water vapor equilibration. Contrary to prior assumptions, increased community growth was associated with a greater number of active bacterial taxa rather than generally faster-growing populations. We also found that root presence enhanced bacterial growth at ambient temperatures but not at elevated temperatures, indicating a shift in plant-microbe interactions. Our results, thus, reveal a mechanism of how soil bacteria respond to warming that cannot be inferred from community-level measurements

Atmospheric deposition of elements and its relevance for nutrient budgets of tropical forests

Atmospheric deposition is an important component of the nutrient cycles of terrestrial ecosystems, but field measurements are especially scarce in tropical regions. In this study we analysed 15 months of precipitation chemistry collected in an old growth tropical forest located in French Guiana. We measured nutrient inputs via bulk precipitation and throughfall and used the canopy budget model to estimate nutrient fluxes via canopy exchange and dry deposition. Based on this method we quantified net fluxes of macronutrients and compared their contribution to internal cycling rates via litterfall. Our results suggest that while atmospheric deposition of nitrogen was relatively high (13 kg ha−1 year−1), and mainly in organic forms, the N inputs via litterfall were an order of magnitude higher. In contrast to nitrogen, we found that atmospheric deposition of phosphorus (0.5 kg ha−1 year−1) supplied up to one third of the annual litterfall input to the forest floor. Most strikingly, combined annual inputs of potassium via atmospheric deposition (14 kg ha−1 year−1) and canopy leaching (22 kg ha−1 year−1) were three times larger than internal nutrient recycling via litterfall (11 kg ha−1 year−1). We conclude that atmospheric deposition of phosphorus and especially potassium may play an important role in sustaining the productivity of this old-growth tropical rainforest

Mycorrhizal hyphal turnover as a dominant process for carbon input into soil organic matter

The atmospheric concentration of CO2 is predicted to reach double current levels by 2075. Detritus from aboveground and belowground plant parts constitutes the primary source of C for soil organic matter (SOM), and accumulation of SOM in forests may provide a significant mechanism to mitigate increasing atmospheric CO2 concentrations. In a poplar (three species) plantation exposed to ambient (380 ppm) and elevated (580 ppm) atmospheric CO2 concentrations using a Free Air Carbon Dioxide Enrichment (FACE) system, the relative importance of leaf litter decomposition, fine root and fungal turnover for C incorporation into SOM was investigated. A technique using cores of soil in which a C-4 crop has been grown (delta C-13 -18.1 parts per thousand) inserted into the plantation and detritus from C-3 trees (delta C-13 -27 to -30 parts per thousand) was used to distinguish between old (native soil) and new (tree derived) soil C. In-growth cores using a fine mesh (39 mu m) to prevent in-growth of roots, but allow in-growth of fungal hyphae were used to assess contribution of fine roots and the mycorrhizal external mycelium to soil C during a period of three growing seasons (1999-2001). Across all species and treatments, the mycorrhizal external mycelium was the dominant pathway (62%) through which carbon entered the SOM pool, exceeding the input via leaf litter and fine root turnover. The input via the mycorrhizal external mycelium was not influenced by elevated CO2, but elevated atmospheric CO2 enhanced soil C inputs via fine root turnover. The turnover of the mycorrhizal external mycelium may be a fundamental mechanism for the transfer of root-derived C to SOM

The Wellesley News (12-01-1966)

https://repository.wellesley.edu/wcnews/1090/thumbnail.jp

Can Current Moisture Responses Predict Soil CO2 Efflux Under Altered Precipitation Regimes? A Synthesis of Manipulation Experiments

As a key component of the carbon cycle, soil CO2 efflux (SCE) is being increasingly studied to improve our mechanistic understanding of this important carbon flux. Predicting ecosystem responses to climate change often depends on extrapolation of current relationships between ecosystem processes and their climatic drivers to conditions not yet experienced by the ecosystem. This raises the question to what extent these relationships remain unaltered beyond the current climatic window for which observations are available to constrain the relationships. Here, we evaluate whether current responses of SCE to fluctuations in soil temperature and soil water content can be used to predict SCE under altered rainfall patterns. Of the 58 experiments for which we gathered SCE data, 20 were discarded because either too few data were available, or inconsistencies precluded their incorporation in the analyses. The 38 remaining experiments were used to test the hypothesis that a model parameterized with data from the control plots (using soil temperature and water content as predictor variables) could adequately predict SCE measured in the manipulated treatment. Only for seven of these 38 experiments, this hypothesis was rejected. Importantly, these were the experiments with the most reliable datasets, i.e., those providing high-frequency measurements of SCE. Accordingly, regression tree analysis demonstrated that measurement frequency was crucial; our hypothesis could be rejected only for experiments with measurement intervals of less than 11 days, and was not rejected for any of the 24 experiments with larger measurement intervals. This highlights the importance of high-frequency measurements when studying effects of altered precipitation on SCE, probably because infrequent measurement schemes have insufficient capacity to detect shifts in the climate-dependencies of SCE. We strongly recommend that future experiments focus more strongly on establishing response functions across a broader range of precipitation regimes and soil moisture conditions. Such experiments should make accurate measurements of water availability, they require high-frequency SCE measurements and they should consider both instantaneous responses and the potential legacy effects of climate extremes. This is important, because we demonstrated that at least for some ecosystems, current moisture responses cannot be extrapolated to predict SCE under altered rainfall

Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO-Virgo Run O3b

We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC-2020 March 27 17:00 UTC). We conduct two independent searches: A generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate. © 2022. The Author(s). Published by the American Astronomical Society