The development of useful structure-function relationships for materials that exhibit correlated nanoscale disorder requires adequately large atomistic models which today are obtained mainly via ...theoretical simulations. Here, we exploit our recent advances in structure-refinement methodology to demonstrate how such models can be derived directly from simultaneous fitting of 3D diffuse- and total-scattering data, and we use this approach to elucidate the complex nanoscale atomic correlations in the classical relaxor ferroelectric PbMg
Nb
O
(PMN). Our results uncover details of ordering of Mg and Nb and reveal a hierarchical structure of polar nanoregions associated with the Pb and Nb displacements. The magnitudes of these displacements and their alignment vary smoothly across the nanoregion boundaries. No spatial correlations were found between the chemical ordering and the polar nanoregions. This work highlights a broadly applicable nanoscale structure-refinement method and provides insights into the structure of PMN that require rethinking its existing contentious models.
Atmospheric methane grew very rapidly in 2014 (12.7 ± 0.5 ppb/year), 2015 (10.1 ± 0.7 ppb/year), 2016 (7.0 ± 0.7 ppb/year), and 2017 (7.7 ± 0.7 ppb/year), at rates not observed since the 1980s. The ...increase in the methane burden began in 2007, with the mean global mole fraction in remote surface background air rising from about 1,775 ppb in 2006 to 1,850 ppb in 2017. Simultaneously the 13C/12C isotopic ratio (expressed as δ13CCH4) has shifted, now trending negative for more than a decade. The causes of methane's recent mole fraction increase are therefore either a change in the relative proportions (and totals) of emissions from biogenic and thermogenic and pyrogenic sources, especially in the tropics and subtropics, or a decline in the atmospheric sink of methane, or both. Unfortunately, with limited measurement data sets, it is not currently possible to be more definitive. The climate warming impact of the observed methane increase over the past decade, if continued at >5 ppb/year in the coming decades, is sufficient to challenge the Paris Agreement, which requires sharp cuts in the atmospheric methane burden. However, anthropogenic methane emissions are relatively very large and thus offer attractive targets for rapid reduction, which are essential if the Paris Agreement aims are to be attained.
Plain Language Summary
The rise in atmospheric methane (CH4), which began in 2007, accelerated in the past 4 years. The growth has been worldwide, especially in the tropics and northern midlatitudes. With the rise has come a shift in the carbon isotope ratio of the methane. The causes of the rise are not fully understood, and may include increased emissions and perhaps a decline in the destruction of methane in the air. Methane's increase since 2007 was not expected in future greenhouse gas scenarios compliant with the targets of the Paris Agreement, and if the increase continues at the same rates it may become very difficult to meet the Paris goals. There is now urgent need to reduce methane emissions, especially from the fossil fuel industry.
Key Points
Atmospheric methane is rising; its carbon isotopic ratio has become more depleted in C‐13
The possible causes of the change include an increase in emissions, with changing relative proportions of source inputs, or a decline in methane destruction, or both
If this rise continues, there are significant consequences for the UN Paris Agreement
Objective
Validate and assess the limitations of the Shear Compression 0 Specimen (SCS0) as a simple shear specimen for quasi-static and dynamic large strain loading conditions. Propose a simple data ...reduction procedure, using a simple, back of the envelope method, as a first approximation for the strain, as opposed to cumbersome numerical simulations and avoid the use of ad-hoc data reduction factors.
Methods
Static and dynamic finite elements simulations were performed in which the large deformation options was turned on and off. Assessment of the Lode parameter in each case and evaluation of the accuracy of the specimen’s strains and stresses as determined through simple data reduction and full numerical simulations.
Results
The SCS0 was shown to undergo simple shear, both statically and dynamically, as evidenced from the very low values of the Lode parameter. The calculated stress is in excellent agreement with the measured one, determined using simple strength of materials definitions. When assuming the corresponding kinematics, it is observed that the calculated and the measured strain diverge to an extent of about 25%. This discrepancy is shown to result from the assumption of large geometrical deformations in the numerical model as opposed to the simple analytical kinematics.
Conclusion
The conclusion is that the SCS0 is now fully validated, and the experimentalist will decide which strain approximation is suitable, between analytical and numerical.
Tetragonal tungsten bronzes (TTBs), an important class of oxides known to exhibit ferroelectricity, undergo complex distortions, including rotations of oxygen octahedra, which give rise to either ...incommensurately or commensurately modulated superstructures. Many TTBs display broad, frequency-dependent relaxor dielectric behavior rather than sharper frequency-independent normal ferroelectric anomalies, but the exact reasons that favor a particular type of dielectric response for a given composition remain unclear. In this contribution the influence of incommensurate/commensurate displacive modulations on the onset of relaxor/ferroelectric behavior in TTBs is assessed in the context of basic crystal-chemical factors, such as positional disorder, ionic radii and polarizabilities, and point defects. We present a predictive crystal-chemical model that rationalizes composition–structure–properties relations for a broad range of TTB systems.
Detailed 222radon (222Rn) flux maps are an essential pre-requisite for the use of radon in atmospheric transport studies. Here we present a high-resolution 222Rn flux map for Europe, based on a ...parameterization of 222Rn production and transport in the soil. The 222Rn exhalation rate is parameterized based on soil properties, uranium content, and modelled soil moisture from two different land-surface reanalysis data sets. Spatial variations in exhalation rates are primarily determined by the uranium content of the soil, but also influenced by soil texture and local water-table depth. Temporal variations are related to soil moisture variations as the molecular diffusion in the unsaturated soil zone depends on available air-filled pore space. The implemented diffusion parameterization was tested against campaign-based 222Rn soil profile measurements. Monthly 222Rn exhalation rates from European soils were calculated with a nominal spatial resolution of 0.083∘ × 0.083∘ and compared to long-term direct measurements of 222Rn exhalation rates in different areas of Europe. The two realizations of the222Rn flux map, based on the different soil moisture data sets, both realistically reproduce the observed seasonality in the fluxes but yield considerable differences for absolute flux values. The mean 222Rn flux from soils in Europe is estimated to be 10 mBq m-2 s-1 (ERA-Interim/Land soil moisture) or 15 mBq m-2 s-1 (GLDAS (Global Land Data Assimilation System) Noah soil moisture) for the period 2006–2010. The corresponding seasonal variations with low fluxes in winter and high fluxes in summer range in the two realizations from ca. 7 to ca. 14 mBq m-2 s-1 and from ca. 11 to ca. 20 mBq m-2 s-1, respectively. These systematic differences highlight the importance of realistic soil moisture data for a reliable estimation of 222Rn exhalation rates. Comparison with observations suggests that the flux estimates based on the GLDAS Noah soil moisture model on average better represent observed fluxes.
Background: Elevated Epstein–Barr virus (EBV) antibody titers are risk factors for multiple sclerosis (MS), but the strength and consistency of this association are not well characterized.
...Objectives: The objectives of this study were to determine whether this association is confounded by vitamin D or modified by gender or race, and the usefulness of EBV nuclear antigen (EBNA) antibodies as a marker for MS.
Methods: We conducted a prospective study among US military personnel. Antibody titers against EBV antigens were measured in serum samples from 222 individuals who developed MS and 444 age, sex, and race/ethnicity matched controls. Conditional logistic regression was used to estimate relative risks.
Results: MS risk increased with increasing titers of anti-EBNA complex (p < 10−9) and anti-EBNA-1 (p = 5.8 × 10−9) titers. MS risk was 36-fold higher among individuals with anti-EBNA complex IgG titers ≥320 than among those with titers <20 (95% confidence interval CI 9.6–136), and 8-fold higher among those with anti-EBNA-1 ≥320 than among those with anti-EBNA-1 <20 (95% CI 2.6–23). These associations were consistent across gender and race/ethnicity groups and independent from 25-hydroxyvitamin D levels. Areas under the receiver operating characteristic (ROC) curves were 0.67 for EBNA complex and 0.65 for EBNA-1.
Conclusions: Serum titers of pre-onset anti-EBNA antibodies are strong, robust markers of MS risk and could be useful in an MS risk score.
Haemosporidian parasites in the genus Plasmodium were recently detected through molecular screening in the Galapagos Penguin (Spheniscus mendiculus). We summarized results of an archipelagowide ...screen of 3726 endemic birds representing 22 species for Plasmodium spp. through a combination of molecular and microscopy techniques. Three additional Plasmodium lineages were present in Galapagos. Lineage A-infected penguins, Yellow Warblers (Setophaga petechia aureola), and one Medium Ground Finch (Geospiza fortis) was detected at multiple sites in multiple years. The other 3 lineages were each detected at one site and at one time; apparently, they were transient infections of parasites not established on the archipelago. No gametocytes were found in blood smears of infected individuals; thus, endemic Galapagos birds may be dead-end hosts for these Plasmodium lineages. Determining when and how parasites and pathogens arrive in Galapagos is key to developing conservation strategies to prevent and mitigate the effects of introduced diseases. To assess the potential for Plasmodium parasites to arrive via migratory birds, we analyzed blood samples from 438 North American breeding Bobolinks (Dolichonyx oryzivorus), the only songbird that regularly migrates through Galapagos. Two of the ephemeral Plasmodium lineages (B and C) found in Galapagos birds matched parasite sequences from Bobolinks. Although this is not confirmation that Bobolinks are responsible for introducing these lineages, evidence points to higher potential arrival rates of avian pathogens than previously thought. Parásitos de la familia Haemosporidia, del género Plasmodium recientemente fueron detectados por medio de análisis moleculares en el pingüino de las Galápagos (Spheniscus mendiculus). Resumimos los resultados de un análisis, extendido a lo largo del archipiélago, de 3726 aves endémicas representando a 22 especies para Plasmodium spp. mediante la combinación de técnicas moleculares y de microscopía. Tres linajes adicionales de Plasmodium estuvieron presentes en las Galápagos. El linaje A infectó pingüinos, individuos Setophaga petechia aureola y a un individuo de Geospiza fortis en sitios múltiples y en varios años. Los otros 3 linajes fueron detectados cada uno en un sitio y en un tiempo específico; aparentemente, fueron infecciones transitorias de parásitos no establecidos en el archipiélago. No se encontraron gametocitos en los frotis de sangre de individuos infectados; por esto, las aves endémicas de las Galápagos pueden ser hospederos finales de estos linajes de Plasmodium. Determinar cuándo y cómo llegaron los parasitos y los patógenos a las Galápagos es clave para desarrollar estrategias de conservación para prevenir y mitigar los efectos de las enfermedades introducidas. Para evaluar el potencial de llegada de Plasmodium en aves migratorias, analizamos muestras de sangre de 438 Dolichonyx oryzivorus en época reproductiva. Esta ave es la única canora que migra regularmente a través de las Galápagos. Dos de los linajes efímeros de Plasmodium (B y C) que se hallaron en las aves de las Galápagos coincidieron con secuencias de parásitos del ave canora. Aunque esto no confirma que Dolichonyx oryzivorus sea responsable de introducer estos linajes, la evidencia apunta a un potencial más alto de tasas de llegada de patógenos aviares de lo que se pensaba previamente.
Over the past decade, the RMCProfile software package has evolved into a powerful computational framework for atomistic structural refinements using a reverse Monte Carlo (RMC) algorithm and multiple ...types of experimental data. However, realizing the full potential of this method, which can provide a consistent description of atomic arrangements over several length scales, requires a computational speed much higher than that permitted by the current software. This problem has been addressed via substantial optimization and development of RMCProfile, including the introduction of the new parallel‐chains RMC algorithm. The computing speed of this software has been increased by nearly two orders of magnitude, as demonstrated using the refinements of a simulated structure with two distinct correlation lengths for the atomic displacements. The new developments provide a path for achieving even faster performance as more advanced computing hardware becomes available. This version of RMCProfile permits refinements of atomic configurations of the order of 500 000 atoms (compared to the current limit of 20 000), which sample interatomic distances up to 10 nm (versus 3 nm currently). Accurate, computationally efficient corrections of the calculated X‐ray and neutron total scattering data have been developed to account for the effects of instrumental resolution. These corrections are applied in both reciprocal and real spaces, thereby enabling RMC fitting of an atomic pair distribution function, which is obtained as the Fourier transform of the total‐scattering intensity, over the entire nanoscale distance range accessible experimentally.
The computing speed of reverse Monte Carlo structure refinements has been improved by up to two orders of magnitude, which significantly expands the capabilities of this method.
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