Room-temperature ferromagnetism in epitaxial bilayer FeSb/SrTiO3(001) terminated with a Kagome lattice

Two-dimensional (2D) magnets exhibit unique physical properties for potential applications in spintronics. To date, most 2D ferromagnets are obtained by mechanical exfoliation of bulk materials with van der Waals interlayer interactions, and the synthesis of single or few-layer 2D ferromagnets with strong interlayer coupling remains experimentally challenging. Here, we report the epitaxial growth of 2D non-van der Waals ferromagnetic bilayer FeSb on SrTiO3(001) substrates stabilized by strong coupling to the substrate, which exhibits in-plane magnetic anisotropy and a Curie temperature above 300 K. In-situ low-temperature scanning tunneling microscopy/spectroscopy and density-functional theory calculations further reveal that a Fe Kagome layer terminates the bilayer FeSb. Our results open a new avenue for further exploring emergent quantum phenomena from the interplay of ferromagnetism and topology for application in spintronics

Orbit: A Unified Simulation Framework for Interactive Robot Learning Environments

We present Orbit, a unified and modular framework for robot learning powered by NVIDIA Isaac Sim. It offers a modular design to easily and efficiently create robotic environments with photo-realistic scenes and high-fidelity rigid and deformable body simulation. With Orbit, we provide a suite of benchmark tasks of varying difficulty -- from single-stage cabinet opening and cloth folding to multi-stage tasks such as room reorganization. To support working with diverse observations and action spaces, we include fixed-arm and mobile manipulators with different physically-based sensors and motion generators. Orbit allows training reinforcement learning policies and collecting large demonstration datasets from hand-crafted or expert solutions in a matter of minutes by leveraging GPU-based parallelization. In summary, we offer an open-sourced framework that readily comes with 16 robotic platforms, 4 sensor modalities, 10 motion generators, more than 20 benchmark tasks, and wrappers to 4 learning libraries. With this framework, we aim to support various research areas, including representation learning, reinforcement learning, imitation learning, and task and motion planning. We hope it helps establish interdisciplinary collaborations in these communities, and its modularity makes it easily extensible for more tasks and applications in the future.Comment: Project website: https://isaac-orbit.github.io

Protein phosphorylation-acetylation cascade connects growth factor deprivation to autophagy

Different from unicellular organisms, metazoan cells require the presence of extracellular growth factors to utilize environmental nutrients. However, the underlying mechanism was unclear. We have delineated a pathway, in which glycogen synthase kinase 3 (GSK3) in cells deprived of growth factors phosphorylates and activates the acetyltransferase KAT5/TIP60, which in turn stimulates the protein kinase ULK1 to elicit autophagy. Cells with the Kat5/Tip60 gene replaced with Kat5(S86A) that cannot be phosphorylated by GSK3 are resistant to serum starvation-induced autophagy. Acetylation sites on ULK1 were mapped to K162 and K606, and the acetylation-defective mutant ULK1(K162,606R) displays reduced kinase activity and fails to rescue autophagy in Ulk1(-/-) mouse embryonic fibroblasts, indicating that acetylation is vital to the activation of ULK1. The GSK3-KAT5-ULK1 cascade seems to be specific for cells to sense growth factors, as KAT5 phosphorylation is not enhanced under glucose deprivation. Distinct from the glucose starvation-autophagy pathway that is conserved in all eukaryotic organisms, the growth factor deprivation response pathway is perhaps unique to metazoan organisms.973 Program [2011CB910800]; NSFC [31130016, 30921005, 31000621]; Fundamental Research Funds for the Central Universities [2010121094]; MOE of China [B06016

Review of calibration strategies for discrete element model in quasi-static elastic deformation

Abstract This study first reviewed theories of the mechanical response of structures under loading, and the discrete element method provides a route for studying mechanical response including elastic deformation and structure failure. However, the direct acquisition of the microscopic parameters from the governing equations of the discrete element method via experiments encounters challenges. One possible strategy to obtain these microscopic parameters is parameter calibration that are widely used by researchers. Secondly, the governing equations and failure criterion of the discrete element method are summarized, and the microscopic parameters that would be calibrated are pinpointed. Next, the principles of classical calibration methods of discrete element method are explicated in detail, alongside the validation and discussion of their properties. Lastly, this study examined the applicability of calibrated parameters and points out that the size ratio, porosity, maximum radius, and minimum radius of particles should be identical in both the geometric calibration model and that for applications

Hydro-Damage Properties of Red-Bed Mudstone Failures Induced by Nonlinear Seepage and Diffusion Effect

Nonlinear catastrophes caused by geological fluids are a fundamental issue in rock mechanics and the geoengineering hazard field. For the consideration of hydrodynamic force on red-bed mudstone softening damage, X-ray visualization tests on the fissure flow in mudstone block failure under hydrodynamic force was performed in this study based on block scale, and the physical phenomena of fissure seepage and nonlinear diffusion were further explored. A new method for evaluating the hydro-damage degrees of rocks using an X-ray image analysis was proposed, and the quantitative relation of diffusion coefficients of hydro-damage and seepage was established. The research results revealed that the hydrodynamic force promoted the fluid-filled fissure behavior in mudstone specimen failure. Furthermore, the seepage and diffusion phenomena of fluid in rocks during failures were indicated using X-ray imaging. A dual mechanical behavior was presented in the nonlinear seepage and abnormal diffusion of a red mudstone geological body under hydrodynamic conditions. The damaged degree of mudstone was aggravated by the effect of hydrodynamic force, and the initial seepage–diffusion coefficient with respect to lower hydro-damage was larger than the final seepage–diffusion coefficient with respect to higher hydro-damage of rocks with a decreasing nonlinear trend

Variations in Permeability and Mechanical Properties of Basaltic Rocks Induced by Carbon Mineralization

Carbon capture, utilization, and storage (CCUS/CCS) is a strategic choice for ensuring energy security and reducing carbon dioxide emissions across the globe. The injection of CO2 into the basaltic reservoir is one strategy for the permanent disposal of carbon emissions. Basaltic rocks, which are widely distributed in Hainan Island, are capable of CO2 geological sequestration. In this study, the reaction of CO2-NaOH/Ca(OH)2-basaltic rocks under conditions of 6.0 M Pa and 30 °C was performed using basaltic samples collected from the Fushan area of the Hainan Province to evaluate the sequestration of CO2 in basalt by mineralization. Then, the effect of CO2 mineralization on the permeability and mechanical properties of basaltic rocks was evaluated using X-ray computer tomography and triaxial compression testing at 21.0 MPa. In addition, microwave technology was used to irradiate the basaltic rocks before mineralization. Changes in the permeability of basalt before and after mineralization and microwave irradiation were simulated numerically, and their effects on the mechanical strength deterioration of basalt were analyzed according to the rock mechanics using triaxial testing. Based on these results, a new method for the induction of basalt deterioration, mineralization, CO2 injectivity, and storage capacity using microwave irradiation is proposed for use in CCUS/CCS engineering

HIV/AIDS Knowledge, Depression, and HIV-Related Stigma Among Elderly Men in Rural China: A Hierarchical Regression Analysis

This study explored the current status and influencing factors of HIV-related stigma among elderly men (≥50 years old) in rural Chengdu, China. A structured face-to-face interview survey was conducted among 286 elderly males from three towns in Chengdu using convenience sampling, 240 men (83.9%) who had heard of HIV/AIDS were included in the analysis. Hierarchical regression was used to examine the associated factors of HIV-related stigma, including demographic variables, HIV/AIDS knowledge level, receiving HIV/AIDS-related health education in the past year, depression, and anxiety, and to examine the moderating effect of educational level on HIV/AIDS knowledge and HIV-related stigma. Hierarchical regression analysis showed that men with lower HIV/AIDS knowledge scores, primary school or below educated, and depression had higher HIV-related stigma total score and social stigma dimensional scores than their counterparts. In addition, living alone was associated with higher HIV-related stigma, and elderly men with lower monthly income and those without HIV/AIDS-related health education in the past year had higher levels of social stigma. Higher HIV/AIDS knowledge score was significantly associated with lower HIV-related stigma level among those with middle school or above education level, but no such effect in those with primary school or below. In conclusion, the HIV-related stigma level among elderly men in rural Chengdu was high and positively associated with depression. HIV/AIDS education should target elderly men with low education, living alone, and low income, and interventions to promote mental health may work together to reduce HIV-related stigma in the rural elderly population

Molecular Basis of Wnt Activation via the DIX Domain Protein Ccd1

Ministry of Science and Technology of China [2007CB914400, 2011CB910803]; National Natural Science Foundation of China [31070643]; Tsinghua University [09THZ02235]The Wnt signaling plays pivotal roles in embryogenesis and cancer, and the three DIX domain-containing proteins, Dvl, Axin, and Ccd1, play distinct roles in the initiation and regulation of canonical Wnt signaling. Overexpressed Dvl has a tendency to form large polymers in a cytoplasmic punctate pattern, whereas the biologically active Dvl in fact forms low molecular weight oligomers. The molecular basis for how the polymeric sizes of Dvl proteins are controlled upon Wnt signaling remains unclear. Here we show that Ccd1 up-regulates canonical Wnt signaling via acting synergistically with Dvl. We determined the crystal structures of wild type Ccd1-DIX and mutant Dvl1-DIX(Y17D), which pack into "head-to-tail" helical filaments. Structural analyses reveal two sites crucial for intra-filament homo-and hetero-interaction and a third site for inter-filament homo-assembly. Systematic mutagenesis studies identified critical residues from all three sites required for Dvl homo-oligomerization, puncta formation, and stimulation of Wnt signaling. Remarkably, Ccd1 forms a hetero-complex with Dvl through the "head" of Dvl-DIX and the "tail" of Ccd1-DIX, depolymerizes Dvl homo-assembly, and thereby controls the size of Dvl polymer. These data together suggest a molecular mechanism for Ccd1-mediated Wnt activation in that Ccd1 converts latent polymeric Dvl to a biologically active oligomer(s)