3,661 research outputs found

    Health and environmental impact of agricultural intensification: Translating Ecohealth program-derived knowledge into practice

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    International Development Research Centr

    Transformation of microbially-induced protodolomite to dolomite proceeds under dry-heating conditions

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    The genesis of sedimentary dolomite remains an unresolved issue. Protodolomite has been considered as a metastable precursor for some sedimentary dolomites. Through laboratory experiments, much has been learnt about the transformation of protodolomite into dolomite under hydrothermal conditions mimicking those in open diagenetic systems. However, it is still unclear whether such mineral transformation could proceed in closed diagenetic systems, in which the supply of externally-derived fluids is often limited. Here through dry-heating experiments we demonstrated that low-temperature protodolomite converts into dolomite in the absence of external fluid. The starting materials for the recrystallization reactions included two types of protodolomite: biotic protodolomite and its abiotic counterpart. Biotic protodolomite was synthesized by means of a halophilic bacterium at 30 °C. Since the synthesis of abiotic protodolomite normally requires higher temperatures than biotic ones, the abiotic protodolomite samples used herein were prepared at 60 °C and 100 °C. These protodolomites were spherical in shape and composed of nano-globular subunits. Our protodolomite samples contained considerable structural water in the range of 1.4-7 wt%. The water content of protodolomites was linearly correlated with their synthesis temperature, that is, biotic protodolomite had a higher amount of water than its abiotic counterparts. The protodolomite samples were then dry-annealed at temperatures of 100 to 300 °C for two months. The results indicated that the rate of protodolomite-to-dolomite transformation was higher in the reactors using biotic protodolomite than those using abiotic protodolomites. This conversion was likely triggered by the dehydration of structural water within protodolomite. The resulting dolomite mostly retained spherical morphology, whereas its nanosized subunits tended to become rhombohedral. Calcite neoformation was also found to accompany the dolomite formation. Our findings suggest that structural water within protodolomite is an overlooked internal fluid and it might have an impact on the genesis of sedimentary dolomite during burial diagenesis

    The Tongde Picritic Dikes in the Western Yangtze Block: Evidence for Ca. 800-Ma Mantle Plume Magmatism in South China during the Breakup of Rodinia

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    Secondary ion mass spectroscopy U-Pb zircon ages and mineralogical, geochemical, and Nd isotopic data are reported for the Tongde picritic dikes in the Yanbian area of the western Yangtze Block, South China. The picritic dikes, which intruded in the ca. 820-Ma Tongde complex, are dated at 796+-5 Ma. Most of the picritic rocks are highly porphyritic (ca. 15–35 vol% phenocrysts) with dominant olivine (Fo = 82–92) phenocrysts that are high in CaO (up to 0.43 wt%), Cr2O3, and Ni. All the studied rocks are high-Ti and alkaline in composition and exhibit light rare earth element– enriched and “humped” incompatible trace-element patterns, similar to the alkaline basalts within the ocean islands and continental rifts. Variably high εNd(T) values between +6.9 and +8.7 indicate that these rocks were derived from an asthenospheric mantle source with inappreciable crustal contamination. Geochemical modeling suggests a primary melt of 22.7% MgO for batch melting and 21.4% MgO for fractional melting. The high MgO content in the modelled primary magmas implies a minimum melt temperature of >1400˚C and a mantle potential temperature of 1600˚– 1620˚C. The Tongde picritic dikes were therefore generated by melting of an anomalously hot mantle source with a potential temperature ca. 200˚C higher than that of the ambient mid-ocean ridge basalt–source mantle, similar to that of modern mantle plumes. Thus, the Tongde picritic dikes provide solid petrological evidence for the proposed Neoproterozoic mantle plume that led to the breakup of the supercontinent Rodinia

    Smooth-AP: Smoothing the Path Towards Large-Scale Image Retrieval

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    Optimising a ranking-based metric, such as Average Precision (AP), is notoriously challenging due to the fact that it is non-differentiable, and hence cannot be optimised directly using gradient-descent methods. To this end, we introduce an objective that optimises instead a smoothed approximation of AP, coined Smooth-AP. Smooth-AP is a plug-and-play objective function that allows for end-to-end training of deep networks with a simple and elegant implementation. We also present an analysis for why directly optimising the ranking based metric of AP offers benefits over other deep metric learning losses. We apply Smooth-AP to standard retrieval benchmarks: Stanford Online products and VehicleID, and also evaluate on larger-scale datasets: INaturalist for fine-grained category retrieval, and VGGFace2 and IJB-C for face retrieval. In all cases, we improve the performance over the state-of-the-art, especially for larger-scale datasets, thus demonstrating the effectiveness and scalability of Smooth-AP to real-world scenarios.Comment: Accepted at ECCV 202

    Effects of Ru Substitution on Dimensionality and Electron Correlations in Ba(Fe_{1-x}Ru_x)_2As_2

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    We report a systematic angle-resolved photoemission spectroscopy study on Ba(Fe1x_{1-x}Rux_x)2_2As2_2 for a wide range of Ru concentrations (0.15 \leq \emph{x} \leq 0.74). We observed a crossover from two-dimension to three-dimension for some of the hole-like Fermi surfaces with Ru substitution and a large reduction in the mass renormalization close to optimal doping. These results suggest that isovalent Ru substitution has remarkable effects on the low-energy electron excitations, which are important for the evolution of superconductivity and antiferromagnetism in this system.Comment: 4 pages, 4 figure

    TAI-SARNET: Deep Transferred Atrous-Inception CNN for Small Samples SAR ATR

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    Since Synthetic Aperture Radar (SAR) targets are full of coherent speckle noise, the traditional deep learning models are difficult to effectively extract key features of the targets and share high computational complexity. To solve the problem, an effective lightweight Convolutional Neural Network (CNN) model incorporating transfer learning is proposed for better handling SAR targets recognition tasks. In this work, firstly we propose the Atrous-Inception module, which combines both atrous convolution and inception module to obtain rich global receptive fields, while strictly controlling the parameter amount and realizing lightweight network architecture. Secondly, the transfer learning strategy is used to effectively transfer the prior knowledge of the optical, non-optical, hybrid optical and non-optical domains to the SAR target recognition tasks, thereby improving the model\u2019s recognition performance on small sample SAR target datasets. Finally, the model constructed in this paper is verified to be 97.97% on ten types of MSTAR datasets under standard operating conditions, reaching a mainstream target recognition rate. Meanwhile, the method presented in this paper shows strong robustness and generalization performance on a small number of randomly sampled SAR target datasets

    Structurally-informed Mutagenesis of a Stereochemically Promiscuous Aldolase Produces Mutants that Catalyse the Diastereoselective Syntheses of all Four Stereoisomers of 3-Deoxy-Hexulosonic acid

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    [Image: see text] A 2-keto-3-deoxygluconate aldolase from the hyperthermophile Sulfolobus solfataricus catalyzes the nonstereoselective aldol reaction of pyruvate and d-glyceraldehyde to produce 2-keto-3-deoxygluconate (d-KDGlc) and 2-keto-3-deoxy-d-galactonate (d-KDGal). Previous investigations into curing the stereochemical promiscuity of this hyperstable aldolase used high-resolution structures of the aldolase bound to d-KDGlc or d-KDGal to identify critical amino acids involved in substrate binding for mutation. This structure-guided approach enabled mutant variants to be created that could stereoselectively catalyze the aldol reaction of pyruvate and natural d-glyceraldehyde to selectively afford d-KDGlc or d-KDGal. Here we describe the creation of two further mutants of this Sulfolobus aldolase that can be used to catalyze aldol reactions between pyruvate and non-natural l-glyceraldehyde to enable the diastereoselective synthesis of l-KDGlc and l-KDGal. High-resolution crystal structures of all four variant aldolases have been determined (both unliganded and liganded), including Variant 1 with d-KDGlc, Variant 2 with pyruvate, Variant 3 with l-KDGlc, and Variant 4 with l-KDGal. These structures have enabled us to rationalize the observed changes in diastereoselectivities in these variant-catalyzed aldol reactions at a molecular level. Interestingly, the active site of Variant 4 was found to be sufficiently flexible to enable catalytically important amino acids to be replaced while still retaining sufficient enzymic activity to enable production of l-KDGal

    Space-time crystals of trapped ions

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    Spontaneous symmetry breaking can lead to the formation of time crystals, as well as spatial crystals. Here we propose a space-time crystal of trapped ions and a method to realize it experimentally by confining ions in a ring-shaped trapping potential with a static magnetic field. The ions spontaneously form a spatial ring crystal due to Coulomb repulsion. This ion crystal can rotate persistently at the lowest quantum energy state in magnetic fields with fractional fluxes. The persistent rotation of trapped ions produces the temporal order, leading to the formation of a space-time crystal. We show that these space-time crystals are robust for direct experimental observation. We also study the effects of finite temperatures on the persistent rotation. The proposed space-time crystals of trapped ions provide a new dimension for exploring many-body physics and emerging properties of matter.Comment: updated to the version published in PR

    Biomimetic lipid-bilayer anode protection for long lifetime aqueous zinc-metal batteries

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    The practical application of rechargeable aqueous zinc batteries is impeded by dendrite growth, especially at high areal capacities and high current densities. Here, this challenge is addressed by proposing zinc perfluoro(2-ethoxyethane)sulfonic (Zn(PES)2) as a zinc battery electrolyte. This new amphipathic zinc salt, with a hydrophobic perfluorinated tail, can form an anode protecting layer, in situ, with a biomimetic lipid-bilayer structure. The layer limits the anode contact with free H2O and offers fast Zn2+ transport pathways, thereby effectively suppressing dendrite growth while maintaining high rate capability. A stable, Zn2+-conductive fluorinated solid electrolyte interphase (SEI) is also formed, further enhancing zinc reversibility. The electrolyte enables unprecedented cycling stability with dendrite-free zinc plating/stripping over 1600 h at 1 mA cm−2 at 2 mAh cm−2, and over 380 h under an even harsher condition of 2.5 mA cm−2 and 5 mAh cm−2. Full cell tests with a high-loading VS2 cathode demonstrate good capacity retention of 78% after 1000 cycles at 1.5 mA cm−2. The idea of in situ formation of a biomimetic lipid-bilayer anode protecting layer and fluorinated SEI opens a new route for engineering the electrode–electrolyte interface toward next-generation aqueous zinc batteries with long lifetime and high areal capacities
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