Uranium isotope compositions (δ238) and Th/U in carbonates are being explored as paleoredox proxies to study global oceanic anoxia. However, the impact of changes to local depositional environments ...that might cause a decline in δ238U and an increase in Th/U has not been thoroughly investigated. Here we report a decline in δ238U (from +0.1 to -0.3‰) and an increase in Th/U from shallow-marine carbonates during the Paleocene-Eocene thermal maximum at Tingri (south Tibet). Changes of δ238U and Th/U are not fully coupled. The decline in δ238U coincided with a local sea-level fall, whereas the increase in Th/U occurred mainly during a sea-level rise. The decline in δ238U likely results from changes in redox conditions of pore waters and in primary carbonate mineralogy. The increase in Th/U is ascribed to reduced authigenic U(IV) accumulation. Here our results suggest that changes in local depositional environments can cause behavior of δ238U and Th/U resembling that induced by expanded global oceanic anoxia. This finding calls for caution to consider local factors before applying δ238U and Th/U as global paleoredox proxies.
Uranium isotope compositions (δ238U) and Th/U in carbonates are being explored as paleoredox proxies to study global oceanic anoxia. However, the impact of changes to local depositional environments ...that might cause a decline in δ238U and an increase in Th/U has not been thoroughly investigated. Here we report a decline in δ238U (from +0.1 to −0.3‰) and an increase in Th/U from shallow-marine carbonates during the Paleocene-Eocene thermal maximum at Tingri (south Tibet). Changes of δ238U and Th/U are not fully coupled. The decline in δ238U coincided with a local sea-level fall, whereas the increase in Th/U occurred mainly during a sea-level rise. The decline in δ238U likely results from changes in redox conditions of pore waters and in primary carbonate mineralogy. The increase in Th/U is ascribed to reduced authigenic U(IV) accumulation. Our results suggest that changes in local depositional environments can cause behavior of δ238U and Th/U resembling that induced by expanded global oceanic anoxia. This finding calls for caution to consider local factors before applying δ238U and Th/U as global paleoredox proxies.
•Variable carbonate δ238U and Th/U were observed in a PETM section from Tibet.•The decline in carbonate δ238U coincided with a sea-level fall in the CIE recovery.•The Th/U increase mainly occurred during a sea-level rise in the main CIE.•The paired δ238U and Th/U don't support global expansion of ocean anoxia here.
Advances in cryo-electron microscopy (cryo-EM) imaging technologies have led to a rapidly increasing number of cryo-EM density maps. Alignment and comparison of density maps play a crucial role in ...interpreting structural information, such as conformational heterogeneity analysis using global alignment and atomic model assembly through local alignment. Here, we present a fast and accurate global and local cryo-EM density map alignment method called CryoAlign, that leverages local density feature descriptors to capture spatial structure similarities. CryoAlign is a feature-based cryo-EM map alignment tool, in which the employment of feature-based architecture enables the rapid establishment of point pair correspondences and robust estimation of alignment parameters. Extensive experimental evaluations demonstrate the superiority of CryoAlign over the existing methods in terms of both alignment accuracy and speed.
Abstract
Pan-genomes from large natural populations can capture genetic diversity and reveal genomic complexity. Using de novo long-read assembly, we generated a graph-based super pan-genome of rice ...consisting of a 251-accession panel comprising both cultivated and wild species of Asian and African rice. Our pan-genome reveals extensive structural variations (SVs) and gene presence/absence variations. Additionally, our pan-genome enables the accurate identification of nucleotide-binding leucine-rich repeat genes and characterization of their inter- and intraspecific diversity. Moreover, we uncovered grain weight-associated SVs which specify traits by affecting the expression of their nearby genes. We characterized genetic variants associated with submergence tolerance, seed shattering and plant architecture and found independent selection for a common set of genes that drove adaptation and domestication in Asian and African rice. This super pan-genome facilitates pinpointing of lineage-specific haplotypes for trait-associated genes and provides insights into the evolutionary events that have shaped the genomic architecture of various rice species.
The strengthening effect of composites is rather limited in comparison with the excellent properties of graphene due to difficulty in acquiring strong interfacial bonding. To enhance the interfacial ...bonding and reduce the interface mismatch between the matrix and reduced graphene oxide (rGO), a novel strategy in this study is proposed through generating hybrid layered double oxides (LDO) nanoparticles on rGO (LDO@rGO). The 2024Al composites with heterogeneous structure were constructed by ball milling and spark plasma sintering (SPS), which was reinforced by flake-like LDO@rGO-rich zones contained LDO@rGO in the Al matrix with fine grain size of ~1 µm. The yield strength, elongation and fracture energy of 1 vol% LDO@rGO/Al composite with heterogeneous microstructure were 69.6%, 63.9% and 140.5% higher than those of the composite reinforced by uniformly distributed 0.67 vol% graphene oxide (GO), respectively, achieving an improvement in the strength-ductility synergy of the fabricated LDO@rGO/Al composite. The rationally spatial arrays of LDO@rGO-rich and LDO@rGO-free zones are beneficial for promoting the synergistic strengthening of Orowan, solid solution, thermal mismatch and load transfer and simultaneously toughening the composite through enhanced crack deflection and bridging effects. The proposed method offers a promising route for fabricating composite with optimized and improved material properties by coupling interface and heterogeneous structure.
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•Hybrid nano interfacial products improve the bonding between the Al matrix and rGO.•The hierarchical composite reinforced by LDO@rGO-rich zones is constructed.•Tailoring spatial arrays of LDO@rGO-rich zones optimizes the performance.•The strengthening and toughening mechanisms of the composites are analyzed.
•The structure of Mg(OH)2/LDH coating is tailored by roughness of Mg alloy surface.•FPG coating on Mg substrate with the lowest roughness has denser and thicker structure. significantly improving the ...corrosion resistance.•FPG composite coating has the best corrosion resistance and good biocompatibility.
Corrosion-resistant and biocompatible films were fabricated on AZ91D Mg alloy substrates by varying their roughness levels using metallographic preparation and subsequent hydrothermal procedures. The coated films comprised a mixed structure of Mg(OH)2 and Mg-Al layered double hydroxides (LDH) and exhibited excellent compactness. Coating film thickness increased with decreasing surface roughness. Corrosion resistance was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy. Metallographic pretreatment influenced the chemical activity of the Mg alloy surface and helped modulate the dissolution rate of the Mg17Al12 phase during the hydrothermal procedure. With decreasing roughness of the Mg substrate, the Al3+ concentration gradually increased, accelerating the in-situ formation of the Mg(OH)2/LDH composite coating and improving its crystallinity. A thick and dense Mg(OH)2/LDH coating was synthesized on the Mg substrate with the least roughness, substantially improving the corrosion resistance of the AZ91D alloy. The lowest corrosion current density ((5.73 ± 2.75) × 10−8 A·cm−2) was achieved, which was approximately three orders of magnitude less than that of bare AZ91D. Moreover, the coating demonstrated biocompatibility with no evident cytotoxicity, cellular damage, and hemolytic phenomena. This study provides an effective method for preparing coatings on Mg alloy surfaces with excellent corrosion resistance and biocompatibility.
Timely and effective identification and monitoring of tool wear is important for the milling process. However, traditional methods of tool wear estimation have run into difficulties due to under ...small samples with less prior knowledge. This article addresses this issue by employing a multisensor tool wear estimation method based on blind source separation technology. Stationary subspace analysis (SSA) technology is applied to transform multisensor signals to stationary and nonstationary sources without prior information of signals. Ten dimensionless time-frequency indices of the nonstationary signal are extracted to train least squares support vector regression (LS-SVR) to obtain a tool wear estimation model for small samples. The analysis and comparison of one benchmark tool wear dataset and tool wear experiments verify the feasibility and effectiveness of the proposed method and outperform other two current methods.
To improve the mechanical strength and ductility of Al-20Si matrix composites, a novel strategy was proposed by constructing nanoparticle-rich zones (NPR) in where SiC nanoparticles were embedded ...into fine-grain high-entropy alloy particles (SiC@HEA). Due to the specific arrangement of SiC in HEA reinforcement, the mechanical properties of as-fabricated Al composites with hierarchical microstructure were improved significantly. The influences of hierarchical structure and interface between the NPR zones and Al matrix on tensile strength and ductility were systematically studied. The results show that the designed composite exhibits NPR zones and nanoparticle-free (NPF) zones, leading to a typical bimodal structure. The NPR zones have a higher density of geometrically necessary dislocations (GND) than NPF zones, and hence it can act as “hard” regions by enhanced dislocation strengthening and grain refinement. The large Al grains in NPF zones actet as “soft” regions to promote plastic deformation. The SiC@HEA/Al interface featured a dual-layer, including the inner layer (∼200 nm) of Ni2Si, FeNi, Ni3Si2, and FeSi phases, and the outer layer (∼300 nm) of Ni5Si2, Ni2Si, and FeNi phases. A good combination of tensile strength (251 MPa) and elongation (9%) was realized in SiC@HEA/Al composite. This study provides a new route to fabricate composites with enhanced both strength and ductility.
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•The arrays of SiC inside HEA reinforcement is tailored by shift-speed ball milling.•The hierarchical composite reinforced by SiC@HEA is constructed.•Hybrid interfacial products improve the Al/SiC@HEA interface.•The composites can achieve combination of high strength and desirable ductility.
The precipitates obtained by EPE technology from the 9Cr-1.7W-0.4Mo-Co ferritic heat-resistant steel subject to isothermal aging were investigated using SEM, TEM and XRD. The particle size ...distribution and the coarsening kinetics of M
C
with duration of isothermal aging were also analyzed with or without consideration of Laves phase. The results show that the isolated dislocations were detected in delta ferrite interior, and the precipitates on delta ferrite and martensite boundaries are obviously larger than other locations. Fe
W-Laves phase can only be found as duration of aging time to 2000 h, and is preferential to form adjacent to M
C
particles. The small M
C
particles firstly coarsen, but the large M
C
are relatively stable during short aging. The total coarsening rate of M
C
precipitates is 9.75 × 10
m
s
, and the coarsening of M
C
depends on the formation of Laves phase.
Vehicular communications in future sixth-generation (6G) networks are expected to leverage integrated sensing and communications (ISAC) and mobile edge computing (MEC) techniques. However, the rapid ...proliferation of vehicle user equipment (V-UE) and the diversity of ISAC-aided and MEC-empowered vehicular communication and computation services demand a more intelligent and efficient resource allocation framework for next-generation vehicular networks. To address this issue, we propose a comprehensive ISAC-aided vehicle-to-everything (V2X) MEC framework, where V-UEs can offload their tasks to the edge server collocated at the roadside unit (RSU). We aim to minimise the long-term average total service delay of all V-UEs by jointly optimising the offloading decisions of all V-UEs, the computation resource allocation at the ISAC-aided RSU, the transmission power and the allocation of resource blocks for all V-UEs, where the total service delay of a V-UE includes the task processing delay and the transmission delay if the V-UE offloads its task to the RSU. To solve the formulated mixed integer non-linear programming problem, we design a multi-agent deep deterministic policy gradient (MADDPG)-based offloading optimisation and resource allocation algorithm (MADDPG-O2RA2). Simulation results demonstrate that our proposed algorithm outperforms the benchmarks in terms of convergence and the long-term average delay among all V-UEs.
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