From cropland to cropped field: A robust algorithm for national-scale mapping by fusing time series of Sentinel-1 and Sentinel-2

Detailed and updated maps of actively cropped fields on a national scale are vital for global food security. Unfortunately, this information is not provided in existing land cover datasets, especially lacking in smallholder farmer systems. Mapping national-scale cropped fields remains challenging due to the spectral confusion with abandoned vegetated land, and their high heterogeneity over large areas. This study proposed a large-area mapping framework for automatically identifying actively cropped fields by fusing Vegetation-Soil-Pigment indices and Synthetic-aperture radar (SAR) time-series images (VSPS). Three temporal indicators were proposed and highlighted cropped fields by consistently higher values due to cropping activities. The proposed VSPS algorithm was exploited for national-scale mapping in China without regional adjustments using Sentinel-2 and Sentinel-1 images. Agriculture in China illustrated great heterogeneity and has experienced tremendous changes such as non-grain orientation and cropland abandonment. Yet, little is known about the locations and extents of cropped fields cultivated with field crops on a national scale. Here, we produced the first national-scale 20 m updated map of cropped and fallow/abandoned land in China and found that 77 % of national cropland (151.23 million hectares) was actively cropped in 2020. We found that fallow/abandoned cropland in mountainous and hilly regions were far more than we expected, which was significantly underestimated by the commonly applied VImax-based approach based on the MODIS images. The VSPS method illustrates robust generalization capabilities, which obtained an overall accuracy of 94 % based on 4,934 widely spread reference sites. The proposed mapping framework is capable of detecting cropped fields with a full consideration of a high diversity of cropping systems and complexity of fallow/abandoned cropland. The processing codes on Google Earth Engine were provided and hoped to stimulate operational agricultural mapping on cropped fields with finer resolution from the national to the global scale

Highly active and stable stepped Cu surface for enhanced electrochemical CO₂ reduction to C₂H₄

Electrochemical CO₂ reduction to value-added chemical feedstocks is of considerable interest for renewable energy storage and renewable source generation while mitigating CO₂ emissions from human activity. Copper represents an effective catalyst in reducing CO₂ to hydrocarbons or oxygenates, but it is often plagued by a low product selectivity and limited long-term stability. Here we report that copper nanowires with rich surface steps exhibit a remarkably high Faradaic efficiency for C₂H₄ that can be maintained for over 200 hours. Computational studies reveal that these steps are thermodynamically favoured compared with Cu(100) surface under the operating conditions and the stepped surface favours C₂ products by suppressing the C₁ pathway and hydrogen production

Highly active and stable stepped Cu surface for enhanced electrochemical CO₂ reduction to C₂H₄

Electrochemical CO₂ reduction to value-added chemical feedstocks is of considerable interest for renewable energy storage and renewable source generation while mitigating CO₂ emissions from human activity. Copper represents an effective catalyst in reducing CO₂ to hydrocarbons or oxygenates, but it is often plagued by a low product selectivity and limited long-term stability. Here we report that copper nanowires with rich surface steps exhibit a remarkably high Faradaic efficiency for C₂H₄ that can be maintained for over 200 hours. Computational studies reveal that these steps are thermodynamically favoured compared with Cu(100) surface under the operating conditions and the stepped surface favours C₂ products by suppressing the C₁ pathway and hydrogen production

Metaknowledge Enhanced Open Domain Question Answering with Wiki Documents

The commonly-used large-scale knowledge bases have been facing challenges in open domain question answering tasks which are caused by the loose knowledge association and weak structural logic of triplet-based knowledge. To find a way out of this dilemma, this work proposes a novel metaknowledge enhanced approach for open domain question answering. We design an automatic approach to extract metaknowledge and build a metaknowledge network from Wiki documents. For the purpose of representing the directional weighted graph with hierarchical and semantic features, we present an original graph encoder GE4MK to model the metaknowledge network. Then, a metaknowledge enhanced graph reasoning model MEGr-Net is proposed for question answering, which aggregates both relational and neighboring interactions comparing with R-GCN and GAT. Experiments have proved the improvement of metaknowledge over main-stream triplet-based knowledge. We have found that the graph reasoning models and pre-trained language models also have influences on the metaknowledge enhanced question answering approaches

Risk assessment for comprehensive meteorological disaster of winter wheat based on multisource gridded data : A case study in the upper Huaihe River basin, China

Crop production security is an essential guarantee for the prosperity of country and the well-being of people. In the context of frequent occurrence of extreme weather events, how to comprehensively evaluate the risk of multiple hazards and quantitatively describe spatial differences will be one of the significant topics in agricultural disaster mitigation. In this study, based on the gridded meteorological data and other datasets (crop, socioeconomic, disaster loss, and actual planting location) from 2000 to 2020, multihazard risk model for different growth period was built to assess the comprehensive risk of winter wheat in the upper Huaihe River basin (UHRB), China. The conclusions were as follows: (a) The spatial distribution of continuous rain risk increased gradually from north to south; the area of the highest lodging risk was located in the east; the spatial trend of drought risk was the highest in the south and the lowest in the northeast. (b) The weights of continuous rain, lodging, and drought disasters were 41, 31, and 28%, respectively, which indicated that winter wheat in UHRB was most affected by continuous rain during the harvest period. (c) The spatial distribution of comprehensive disaster risk assessment showed that the higher risk areas were located in the central and southern parts (Huaibin, Linquan, Luoshan). After verification by historical disasters information, the results are credible, providing a concrete scientific basis for implementing regional agricultural disaster response measures

Design and Verification of On-Line Monitoring & Controlling System of Tensioner

Tensioner for deep water pipe-laying vessel is a type of engineering equipment that is applied in sub-sea pipeline laying. Based on the designed tensioner body for S-lay vessel, with the capacity of 200t and can meet the requirements of 3000m water-depth pipe-laying, the corresponding monitoring and controlling system need to be designed. Firstly, the programs of on-line monitoring and controlling system are proposed, and then the software and hardware of the system are designed. In addition, the man-machine interaction interface of the system is developed. This research could provide the guidance for the design of the on-line monitoring and controlling system of 200t tensioner. The test is carried out to verify the functions of the designed on-line monitoring& controlling system. The test results show that the designed system is reliable and also have good maneuverability

Confirmatory factor analysis of posttraumatic stress symptoms assessed by the Impact of Event Scale-Revised in Chinese earthquake victims: Examining factor structure and its stability across sex

The current study investigated the factor structure of posttraumatic stress symptoms assessed by the Impact Event Scale-Revised (IES-R) in a large sample of individuals from China who recently experienced a destructive earthquake. The results of the confirmatory factor analysis indicated that a four-factor structure (intrusion, avoidance-numbing, hyperarousal, and sleep disturbance) emerged as the model best fit in total sample, female and male subsamples, respectively. Moreover, multiple-group confirmatory factor analysis further demonstrated that the four-factor model was quite stable across sex. Implication and limitations for the results are discussed. (C) 2010 Elsevier Ltd. All rights reserved

Super synergy between photocatalysis and ozonation using bulk g-C3N4 as catalyst: A potential sunlight/O-3/g-C3N4 method for efficient water decontamination

The recent thrust in utilizing g-C3N4 as a metal-free photocatalyst has led to accelerated attention in environmental decontamination. Despite of enormous efforts paid on material modification, the overall efficiency is still limited, especially for decomposition of chemically stable contaminants and mineralization of organics. Here, we coupled bulk g-C3N4 (GCN-T and GCN-D synthesized from thiourea and dicyandiamide, respectively) photocatalysis with ozonation for mineralization of oxalic acid (OA) and p-hydroxybenzoic acid (PHBA) under UV and visible-light irradiation. The compelling experiments confirmed that bulk g-C3N4 could trigger a super synergy between photocatalysis and ozonation under visible light. The apparent rate constant of OA removal by Vis/O-3/GCN-D was 20.6 times as great as the sum of that in Vis/GCN-D and ozonation. The TOC removal of PHBA by Vis/O-3/GCN-D was 98.0%, which was about 39.3% higher than the sum of that in Vis/GCN-D and ozonation. The high conduction band (CB) position of g-C3N4 proved to be crucial for the synergy between photocatalysis and ozonation. GCN-D possessed a similar to 0.10V upshifted CB level compared to GCN-T, resulting in a 1.30 times higher photocatalytic ozonation activity. More negative CB potential benefited photoinduced electron capture by ozone molecules, thus significantly enhanced charge separation as well as the decay of ozone eventually with generation of abundant hydroxyl radicals (center dot OH). Exceptionally, Vis/O-3/GCN-D exhibited stronger oxidizing ability than UV/O-3/GCN-D for OA degradation with the same light intensity. The reason was that the photolysis of ozone occurred under UV and partly inhibited ozone capturing photoinduced electrons. The amount of generated center dot OH thus decreased in UV/O-3/GCN-D instead with the formation of a few atomic oxygen species (O(D-1)). This study puts forward new application of the easily obtained bulk g-C3N4 and may drive the advance of sunlight/O-3/g-CsN4 method for efficient and green water decontamination using sunlight as energy source. (C) 2015 Elsevier B.V. All rights reserved

Understanding the Role of Geometric and Electronic Structure in Bioinspired Catalyst Design: the Case of Formate Dehydrogenase

The design of bioinspired synthetic inorganic molecular complexes is challenging, due to a lack of understanding of enzyme action and the degree to which that action can be translated into mimics. Exemplary of this challenge is the reversible conversion of formate into CO2 by formate dehydrogenase (FDH) enzymes with Mo/W centers in large molybdopterin cofactors. Despite numerous efforts to synthesize Mo/W-containing molecular complexes, none have been demonstrated to reproduce the full reactivity of FDH. Here, we carry out a large-scale, high-throughput screening study on all mononuclear Mo/W complexes currently deposited in Cambridge Structural Database (CSD). Using density functional theory, we systematically investigate the individual effects of metal identity, ligand identity, oxidation state, and coordination number on structural, electronic and catalytic properties. We compare our results on molecular complexes with quantum mechanics/molecular mechanics simulations on a representative FDH enzyme to further elucidate the influence of the enzyme environment. These comparisons reveal that the enzyme environment primarily influences the metal-local geometry, and these metal-local structural variations can improve catalysis. Through a series of computational mutations on molecular complexes, we extend beyond the CSD structures to further identify the limits of varied chalcogen and metal identity. This broad set and comparison reveal relatively little variation of electronic properties of the metal center due to the presence of the enzyme environment or changes in metal-distant ligand chemistry. Instead, these properties are found to be much more sensitive to the identity of the metal and the nature of the bound terminal chalcogen