High-energy synchrotron x-ray diffraction was utilized to study the local order of liquid sulfur at high-pressure and high-temperature conditions. A temperature driven structure change in liquid sulfur was observed, signified by an order of magnitude reduction in lengths of sulfur chains. The large change in chain length implies that this is a liquid-liquid phase transition in sulfur. The chain breakage may strongly influence the physical properties, such as the semiconductor-metal transition and a drastic decrease in viscosity across the transition.

Understanding the volume collapse phenomena in rare-earth materials remains an important challenge due to a lack of information on 4f electronic structures at different pressures. Here, we report the first high-pressure inelastic X-ray scattering measurement on elemental cerium (Ce) metal. By overcoming the ultralow signal issue in the X-ray measurement at the Ce N-4,N-5-edge, we observe the changes of unoccupied 4f states across the volume collapse transition around 0.8 GPa. To help resolve the longstanding debate on the Anderson-Kondo and Mott-Hubbard models, we further compare the experiments with extended multiplet calculations that treat both screening channels on equal footing. The results indicate that a modest change in the 4f-5d Kondo coupling can well describe the spectral redistribution across the volume collapse, whereas the hybridization between neighboring atoms in the Hubbard model appears to play a minor role. Our study helps to constrain the theoretical models and opens a promising new route for systematic investigation of volume collapse phenomena in rare-earth materials.

Successful development of wind farms relies on the optimal siting of wind turbines to maximize the power capacity under stochastic wind conditions and wake losses caused by neighboring turbines. This paper presents a novel method to quickly generate approximate optimal layouts to support infrastruc-ture design decisions. We model the quadratic integer formulation of the discretized layout design problem with an undirected graph that succinctly captures the spatial dependencies of the design pa-rameters caused by wake interactions. On the undirected graph, we apply probabilistic inference using sequential tree-reweighted message passing to approximate turbine siting. We assess the effectiveness of our method by benchmarking against a state-of-the-art branch and cut algorithm under varying wind regime complexities and wind farm discretization resolutions. For low resolutions, probabilistic infer-ence can produce optimal or nearly optimal turbine layouts that are within 3% of the power capacity of the optimal layouts achieved by state-of-the-art formulations, at a fraction of the computational cost. As the discretization resolution (and thus the problem size) increases, probabilistic inference produces optimal layouts with up to 9% more power capacity than the best state-of-the-art solutions at a much lower computational cost.

A previous study showed that the diffraction from cubic crystals of an icosahedral virus, cowpea mosaic virus (CPMV), was dramatically improved under elevated hydrostatic pressure. This use of pressure may have a significant impact on structural biology if it is found to be generally applicable. There were two types of cubic crystals assigned in either an I23 or P23 space group. They show the same rhombic dodecahedral morphology at atmospheric pressure. The crystals assigned to the 123 space group diffracted X-rays to higher resolution than those with P23 space group. The assignment of P23 space group was owing to the presence of reflections with indices of h + k + l = (2n + 1) (odd reflections), which are forbidden in space group I23. Analysis of the odd reflections from the P23 crystals at atmospheric pressure showed that they can originate from a rotational disorder in the 123 crystals. The odd reflections were eliminated with the application of 3.5 kbar of pressure, which transformed the crystals from the apparently primitive cell to the body-centered I23 space group with dramatic improvement in diffraction. A mechanistic model is proposed to describe the induction of order by rectifying the imperfection, which is consistent with the experimental data.

RATIONALE: Induction module cavity ring-down spectroscopy (IM-CRDS) has been proposed as a rapid and cost-effective alternative to cryogenic vacuum distillation (CVD) and isotope ratio mass spectrometry (IRMS) for the measurement of delta O-18 and delta H-2 values in matrix-bound waters. In the current study, we characterized the performance of IM-CRDS relative to CVD and IRMS and investigated the mechanisms responsible for differences between the methods.

Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems(1). However, soil pH is not an independent regulator of soil fertility-rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep transition from alkaline to acid soils across natural climate gradients(2,3). Although the processes governing this threshold in soil pH are well understood, the threshold has not been quantified at the global scale, where the influence of climate may be confounded by the effects of topography and mineralogy. Here we evaluate the global relationship between water balance and soil pH by extracting a spatially random sample (n = 20,000) from an extensive compilation of 60,291 soil pH measurements. We show that there is an abrupt transition from alkaline to acid soil pH that occurs at the point where mean annual precipitation begins to exceed mean annual potential evapotranspiration. We evaluate deviations from this global pattern, showing that they may result from seasonality, climate history, erosion and mineralogy. These results demonstrate that climate creates a nonlinear pattern in soil solution chemistry at the global scale; they also reveal conditions under which soils maintain pH out of equilibrium with modern climate.

Cavity ring-down spectrometers have generally been designed to operate under conditions in which the background gas has a constant composition. However, there are a number of observational and experimental situations of interest in which the background gas has a variable composition. In this study, we examine the effect of background gas composition on a cavity ring-down spectrometer that measures delta O-18-H2O and delta H-2-H2O values based on the amplitude of water isotopologue absorption features around 7184 cm(-1) (L2120-i, Picarro, Inc.). For background mixtures balanced with N-2, the apparent delta O-18 values deviate from true values by 0.50 +/- 0.001 parts per thousand O-2%(-1) and -0.57 +/- 0.001 parts per thousand Ar%(-1), and apparent delta H-2 values deviate from true values by 0.26 +/- 0.004 parts per thousand O-2 %(-1) and 0.42 +/- 0.004 parts per thousand Ar %(-1). The artifacts are the result of broadening, narrowing, and shifting of both the target absorption lines and strong neighboring lines. While the background-induced isotopic artifacts can largely be corrected with simple empirical or semimechanistic models, neither type of model is capable of completely correcting the isotopic artifacts to within the inherent instrument precision. The development of strategies for dynamically detecting and accommodating background variation in N-2, O-2, and/or Ar would facilitate the application of cavity ring-down spectrometers to a new class of observations and experiments.