Urea is an important raw material in the chemical industry and is widely used as a nitrogen source in chemical fertilizers. The current industrial urea synthesis not only requires harsh reaction ...conditions, but also consumes most of the NH
obtained through artificial synthesis. The conversion of N
and CO
into urea through electrochemical reactions under ambient conditions represents a novel green urea synthesis method. However, the large-scale promotion of this method is limited by the lack of suitable electrocatalysts. Here, by means of density functional theory computations, we systematically study the catalytic activity of three experimentally available two-dimensional metal borides (MBenes), Mo
B
, Ti
B
, and Cr
B
toward simultaneous electrocatalytic coupling of N
and CO
to produce urea under ambient conditions. According to our results, these three MBenes not only have superior intrinsic basal activity for urea formation, with limiting potentials ranging from -0.49 to -0.65 eV, but also can significantly suppress the competitive reaction of N
reduction to NH
. In particular, 2D Mo
B
and Cr
B
possess superior capacity to suppress surface oxidation and self-corrosion under electrochemical reaction conditions, rendering them relatively promising electrocatalysts for urea production. Our work paves the way for the electrochemical synthesis of urea.
Deep faults could provide fluent channels for geothermal water uplift so that it is one of the targets for high-temperature hydrothermal exploration in orogenic geothermal belt. In the eastern edge ...of the Qinghai Tibet Plateau, significant geothermal potential reflected by hot springs, fumaroles, and sinters, are indeed exposed along a series of lithospheric-scale faults, including the Jinshajiang, the Ganzi-Litang and the Xianshuihe faults. However, as the controlling fault of the eastern edge of the plateau, the Longmenshan Fault has few geothermal manifestations. In order to uncover the role of deep faults in the genesis of high-temperature geothermal systems, a comprehensive chemical and isotopic comparison of geothermal fluid between the Xianshuihe-Anninghe Fault and the Longmenshan-Minjiang Fault was investigated in this paper. According to FixAl modeling and cation geothermometric calculations, the reservoir temperatures of geothermal systems along the Longmenshan Fault are lower than 150 °C with circulation depth of geothermal water less than 4 km while those in the Xianshuihe Fault reaches up to 260 °C with geothermal water circulating as deep as 8 km. Compared to the Xianshuihe Fault, the low reservoir temperatures along the Longmenshan Fault are accompanied by two characteristics of geothermal fluid: (1) no distinctive oxygen shift occurs in stable isotopes of geothermal waters; and (2) little mantle-derived volatiles found in the gaseous components. We propose that, extensional fracture systems are locally formed in the strike-slip movement of the Xianshuihe and Anninghe faults, which not only act as conduits for deep-derived geothermal volatiles, such as metamorphic carbon dioxide and mantle helium, but also enhance the heat convection processes, resulting in the formation of high-temperature geothermal systems. In contrast, in the Longmenshan Thrust Fault, the shallow circulation of geothermal water in closed fracture systems accounts for its lower reservoir temperatures. Therefore, deep extensional fault is a crucial element in forming a high-temperature geothermal system in the eastern edge of the Qinghai Tibet Plateau.
•The reservoir temperature in the Xianshuihe Strike-slip Fault reaches up to 260 °C.•The reservoir temperature in the Longmenshan Thrust Fault is lower than 150 °C.•Deep extensional faults act as convective conduits for both heat and fluid.•Deep extensional fault is critical in forming high-temperature geothermal systems.
Hyperspectral image (HSI) contains complex multiple structures. Therefore, the key problem analyzing the intrinsic properties of an HSI is how to represent the structure relationships of the HSI ...effectively. Hypergraph is very effective to describe the intrinsic relationships of the HSI. In general, Euclidean distance is adopted to construct the hypergraph. However, this method cannot effectively represent the structure properties of high-dimensional data. To address this problem, we propose a sparse-adaptive hypergraph discriminant analysis (SAHDA) method to obtain the embedding features of the HSI in this letter. SAHDA uses the sparse representation to reveal the structure relationships of the HSI adaptively. Then, an adaptive hypergraph is constructed by using the intraclass sparse coefficients. Finally, we develop an adaptive dimensionality reduction mode to calculate the weights of the hyperedges and the projection matrix. SAHDA can adaptively reveal the intrinsic properties of the HSI and enhance the performance of the embedding features. Some experiments on the Washington DC Mall hyperspectral data set demonstrate the effectiveness of the proposed SAHDA method, and SAHDA achieves better classification accuracies than the traditional graph learning methods.
Synthetic two-dimensional (2D) materials without layered bulk allotropes are approaching a new frontier of materials flatland, one with properties richer than those of graphene-like materials. This ...is the case even as only a few chemical elements and blends have shown synthetic 2D forms. While hydrogen and metals are earth-abundant and form numerous compounds, rarely are 2D materials with only robust metal–hydrogen bonds. Here, a large new family of 2D materials is found from metal hydrides by high-throughput computational search augmented with first-principles calculations. There are 110 thermally and dynamically stable 2D materials that range from metallic materials to wide-gap semiconductors. A subgroup of these materials even varies from topological insulators to nodal-loop semimetals as well as from antiferromagnetic semiconductors to ferromagnetic half-metals. Unexpectedly, these monolayers resemble graphene in an ability to form weak interlayer interaction due to the variable multicenter bonding of hydrogen that eliminates the otherwise prevalent dangling bonds, rather than the covalent bonds between stacked layers as in previously reported synthetic 2D materials. This feature will favor potential experimental synthesis of these metal hydride monolayers.
Boron, as a unique element nearest to carbon in the periodic table, has been predicted to form many distinctive two‐dimensional (2D) structures that significantly differ from other well‐studied 2D ...materials, owning to its exceptional ability to form strong covalent two‐center‐two‐electron bonds as well as stable electron‐deficient multi‐center‐two‐electron bonds. Until recently, the successful syntheses of atomically thin crystalline 2D boron sheets (i.e., borophenes) provoked growing passion in 2D boron crystals. In this feature article, we present a survey of the latest achievements on 2D boron structures, starting from a concise introduction of the structures and properties of the bulk allotropes of boron, boron clusters, and especially potential building blocks for 2D boron crystals. Then we review important achievements and the current status of research on single‐layered metallic borophene, and discuss 2D few‐layered boron sheets, from their possible structures to tunable properties and potential applications in electronics, spintronics, and photoelectronics. We also systematically investigate the stability and functionalization of 2D icosahedral boron sheets in comparison with borophenes through first‐principles studies. Finally, we present an outlook on the advance in fabrications of 2D boron sheets, and the challenges and prospects in the realm of 2D boron crystals.
Boron bulk allotropes and clusters with unique bonding and structures have drawn long‐standing interest. Now, boron of a new dimensionality, namely 2D boron crystals, has emerged into the vision of scientific communities, especially with the success of their experimental synthesis achieved in the last year. Here, we review state‐of‐the‐art experimental and theoretical achievements on 2D boron crystals, with special attention paid to their possible structures, tunable properties, and potential applications.
Cancer-associated fibroblasts (CAFs) have been widely reported to promote tumor angiogenesis. However, the underlying mechanisms of the proangiogenic switch of CAFs remain poorly understood. This ...study aims to clarify the mechanisms underlying the proangiogenic switch of CAFs.
NIH/3T3 cells were treated with B16 and B16F10-derived exosomes. Then the CAFs markers and proangiogenic factors were detected by RT-PCR and Western blot. CCK-8 assay, transwell migration assay, tube formation assay, and in vivo Matrigel plug assay were conducted to determine the proangiogenic capability of CAFs. Western blot and AG490 were used to investigate the role of Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway in the proangiogenic switch of CAFs. Bioinformatics analysis, luciferase reporter assay, microRNA mimic and inhibitor, and xenograft models were used to investigate the role of mmu-miR-155-5p (miR-155) in the proangiogenic switch of CAFs.
In this study, we show that melanoma cell-secreted exosomes can induce reprogramming of fibroblasts into CAFs and that exosomal miR-155 can trigger the proangiogenic switch of CAFs. Mechanistically exosomal miR-155 can be delivered into fibroblasts and promote the expression of proangiogenic factors, including vascular endothelial growth factor A (VEGFa), fibroblast growth factor 2 (FGF2), and matrix metalloproteinase 9 (MMP9), by directly targeting suppressor of cytokine signaling 1 (SOCS1). Downregulation of SOCS1 activates JAK2/STAT3 signaling pathway and elevates the expression levels of VEGFa, FGF2, and MMP9 in fibroblasts. Treatment with exosomes containing overexpressed miR-155 can promote angiogenesis, and the reduction of miR-155 in melanoma cell-secreted exosomes alleviates angiogenesis in vitro and in vivo.
These results demonstrate that by promoting the expression of proangiogenic factors in recipient fibroblasts via SOCS1/JAK2/STAT3 signaling pathway, melanoma cell-secreted exosomal miR-155 can induce the proangiogenic switch of CAFs. Although tumor angiogenesis is modulated by various factors, exosomal miR-155 may be a potential target for controlling melanoma angiogenesis and used to set up novel strategies to treat melanoma.
Autophagy is an essential catabolic process that orchestrates cellular homeostasis and plays dual roles in tumor promotion and suppression. However, the mechanism by which autophagy affects the ...self-renewal of cancer stem cells (CSCs) remains unclear. In this study, we investigated whether autophagy activation contributes to CSC properties of head and neck squamous cell carcinoma (HNSCC). The results showed that the autophagy level and CSC properties of HNSCC cells were elevated in response to several adverse conditions, including treatment with cisplatin, starvation, and hypoxia. Pretreatment with autophagy inhibitors, such as 3-MA and chloroquine, diminished the CSC properties acquired under adverse conditions. In addition, the isolated CSCs were endowed with stronger autophagic activity than non-CSCs, and the CSC properties were dampened when autophagy was inhibited either by 3-MA, chloroquine, or Beclin1 knockdown. Notably, the tumor-initiating activity of CSCs was decreased upon knocking down Beclin1. Further study revealed that FOXO3, a substrate for autophagy, was enriched in the nucleus of cells with lower autophagy levels. Nuclear FOXO3 directly bound to the promoter region of SOX2 and negatively regulated its transcriptional activity. Overexpression of FOXO3 decreased the expression of SOX2 and thereby impaired the CSC phenotype both in vitro and in vivo. Taken together, our findings suggest that the activation of autophagy is essential for the acquisition of CSC properties in adverse conditions and the self-renewal of CSCs. We clarify the role of autophagy in regulating the CSC phenotype and demonstrate that the noncanonical FOXO3/SOX2 axis is the intrinsic regulatory mechanism.
The southeast Tibetan Plateau is a region with high level seismic activity and strong hydrothermal activity. Several large (7.5 > M > 7) historical earthquakes have occurred in the Litang fault zone ...(LFZ), eastern Tibetan Plateau since 1700. Litang Ms 5.1 earthquake occurred On Sept 23, 2016, indicating the reactivation of the LFZ. This study was undertaken to elucidate spatial-temporal variations of the hot spring gas geochemistry along the LFZ from Jun 2010 to April 2016. The chemical components, He, Ne and C isotropic ratios of bubbling gas samples taken from 18 hot springs along LFZ were investigated. Helium isotope ratios (3He/4He) measured in hot springs varied from 0.06 to 0.93 Ra (Ra = air 3He/4He = 1.39 × 10−6), with mantle-derivd He up to 11.1% in the LFZ (assuming R/Ra = 8 for mantle) indicated the fault was a crustal-scale feature that acts as a conduit for deep fluid from the mantle. CO2 concentrations of the majority of hot spring gas samples were ≥80 vol%, CO2/3He ratios varied from 1.4 to 929.5 × 1010, and δ13CCO2 values varied from −19.2‰ to −2.3‰ (vs. PDB). The proportions of mantle-derived CO2 varied from 0 to 1.8%. Crustal marine limestone was the major contributor (>75%) to the carbon inventory of the majority of hot spring gas samples. Before Litang Ms 5.1 earthquake, the 3He/4He ratios obviously increased in the Heni spring from May 2013 to Apr 2016. The geographical distribution of the mantle-derivd He decreased from east to west along 30°N in the southeast Tibetan Plateau relative to a corresponding increase in the radiogenic component. The gas geochemical data suggested that the upwelling mantle fluids into the crust play an important role in seismic activity in the strike-slip faults along 30°N in the southeast Tibetan Plateau.
•Gas geochemistry of hot springs along Litang fault, Southeast Tibetan Plateau were surveyed.•Mantle-derived He decreased from east to west along 30°N.•Upwelling mantle fluids well related with seismic activity in the strike-slip faults.
•The time series of stable isotopes were observed simultaneously in three hot springs.•The isotopes of all three hot springs changed before and after a major earthquake.•The amplitudes of isotopic ...variations are related to the seismic energy density.
Earthquake-related hydrogeochemical changes are considered a possible means of identifying earthquake precursors. This work investigated the time series of hydrogen and oxygen stable isotopes at three hot springs in Kangding with different temperatures, namely, the Erdaoqiao, Longtougou, and Guanding hot springs, located in the Xianshuihe fault zone, one of the most active seismic fault zones in China. The hot springs were observed with a sampling frequency of 3 or 4 days for one year. The results showed that the three hot springs were recharged by meteoric water, and there was a slight water–rock interaction at the Longtougou hot spring. The different isotopic compositions of the three hot springs were related to the recharge and groundwater circulation environment. Temporal anomalies in the stable isotope values at the three hot springs occurred synchronously; these anomalies were closely related to the 2019 Mw 5.8 Changning earthquake, indicating possible earthquake-related changes. Moreover, the amplitudes of stable isotope variations at the three hot springs were closely related to the seismic energy density, and the background isotopic changes were related to the water temperature and flow. These findings reflect the hydrological cycle processes of geothermal water in the Kangding geothermal area on the eastern margin of the Tibetan Plateau. Simultaneously observed temporal variations in hydrogen and oxygen stable isotopes among multiple hot springs may have relevance for distinguishing earthquake precursors.
Spatial features retrieved from satellite data play an important role for improving crop classification. In this study, we proposed a deep-learning-based time-series analysis method to extract and ...organize spatial features to improve parcel-based crop classification using high-resolution optical images and multi-temporal synthetic aperture radar (SAR) data. Central to this method is the use of multiple deep convolutional networks (DCNs) to extract spatial features and to use the long short-term memory (LSTM) network to organize spatial features. First, a precise farmland parcel map was delineated from optical images. Second, hundreds of spatial features were retrieved using multiple DCNs from preprocessed SAR images and overlaid onto the parcel map to construct multivariate time-series of crop growth for parcels. Third, LSTM-based network structures for organizing these time-series features were constructed to produce a final parcel-based classification map. The method was applied to a dataset of high-resolution ZY-3 optical images and multi-temporal Sentinel-1A SAR data to classify crop types in the Hunan Province of China. The classification results, showing an improvement of greater than 5.0% in overall accuracy relative to methods without spatial features, demonstrated the effectiveness of the proposed method in extracting and organizing spatial features for improving parcel-based crop classification.
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