An intrinsic magnetic topological insulator (TI) is a stoichiometric magnetic compound possessing both inherent magnetic order and topological electronic states. Such a material can provide a ...shortcut to various novel topological quantum effects but remained elusive experimentally for a long time. Here we report the experimental realization of thin films of an intrinsic magnetic TI, MnBi
2
Te
4
, by alternate growth of a Bi
2
Te
3
quintuple layer and a MnTe bilayer with molecular beam epitaxy. The material shows the archetypical Dirac surface states in angle-resolved photoemission spectroscopy and is demonstrated to be an antiferromagnetic topological insulator with ferromagnetic surfaces by magnetic and transport measurements as well as first-principles calculations. The unique magnetic and topological electronic structures and their interplays enable the material to embody rich quantum phases such as quantum anomalous Hall insulators and axion insulators at higher temperature and in a well-controlled way.
Abstract
Effective remaining useful life (RUL) prediction of bearings is essential for the predictive maintenance of rotating machinery. However, the effectiveness of many existing RUL prediction ...methods depends on expert experience and signal processing algorithms, which limiting the application of these methods in real-life scenarios. This study proposes a novel end-to-end deep learning framework consisting of a multi-scale attention-based dilated causal convolutional (MADCC) module and a multi-layer temporal convolutional network (MTCN) to predict the RUL of bearings using raw vibration data. First, the MADCC module extracts multi-scale temporal features of the bearing degradation process (BDP) and provides fused feature vectors (FFVs) containing comprehensive BDP information for the MTCN module. Subsequently, the MTCN module mines deep temporal dependencies hidden in the FFV to predict the RUL of bearings. Ablation experiments are conducted to analyze the contribution of the framework’s components. Three evaluation metrics (root mean square error (RMSE), mean absolute error (MAE), and coefficient of determination (
R
2
)) are used to verify the effectiveness of the proposed framework and other state-of-the-art methods on two public bearing datasets. The experimental results show that the proposed framework achieves the lowest RMSE and MAE and the highest
R
2
, demonstrating excellent performance and potential for RUL prediction of bearings.
Aluminum is a naturally abundant, trivalent charge carrier with high theoretical specific capacity and volumetric energy density, rendering aluminum-ion batteries a technology of choice for future ...large-scale energy storage. However, the frequent collapse of the host structure of the cathode materials and sluggish kinetics of aluminum ion diffusion have thus far hampered the realization of practical battery devices. Here, we synthesize Al
MnO
·nH
O by an in-situ electrochemical transformation reaction to be used as a cathode material for an aluminum-ion battery with a configuration of Al/Al(OTF)
-H
O/Al
MnO
·nH
O. This cell is not only based on aqueous electrolyte chemistry but also delivers a high specific capacity of 467 mAh g
and a record high energy density of 481 Wh kg
. The high safety of aqueous electrolyte, facile cell assembly and the low cost of materials suggest that this aqueous aluminum-ion battery holds promise for large-scale energy applications.
If a bulk material can withstand a high load without any irreversible damage (such as plastic deformation), it is usually brittle and can fail catastrophically1,2. This trade-off between strength and ...fracture toughness also extends into two-dimensional materials space3-5. For example, graphene has ultrahigh intrinsic strength (about 130 gigapascals) and elastic modulus (approximately 1.0 terapascal) but is brittle, with low fracture toughness (about 4 megapascals per square-root metre)3,6. Hexagonal boron nitride (h-BN) is a dielectric two-dimensional material7 with high strength (about 100 gigapascals) and elastic modulus (approximately 0.8 terapascals), which are similar to those ofgraphene8. Its fracture behaviour has long been assumed to be similarly brittle, subject to Griffith's law9-14. Contrary to expectation, here we report high fracture toughness of single-crystal monolayer h-BN, with an effective energy release rate up to one order of magnitude higher than both its Griffith energy release rate and that reported for graphene. We observe stable crack propagation in monolayer h-BN, and obtain the corresponding crack resistance curve. Crack deflection and branching occur repeatedly owing to asymmetric edge elastic properties at the crack tip and edge swapping during crack propagation, which intrinsically toughens the material and enables stable crack propagation. Our in situ experimental observations, supported by theoretical analysis, suggest added practical benefits and potential new technological opportunities for monolayer h-BN, such as adding mechanical protection to two-dimensional devices.
Developing efficient noble-metal-free catalysts for the electrochemical N2 reduction reaction (NRR) under ambient conditions shows promise in fertilizer production and hydrogen storage. Here, as a ...proof-of-concept prototype, we design and implement an Fe–N/C–carbon nanotube (CNT) catalyst derived from a metal–organic framework and carbon-nanotube-based composite with built-in Fe–N3 active sites. This catalyst exhibits enhanced NRR activity with NH3 production (34.83 μg·h–1·mg–1 cat.), faradaic efficiency (9.28% at −0.2 V vs RHE), selectivity, and stability in 0.1 M KOH aqueous media under mild conditions. Experimental and theoretical results both reveal that Fe–N3 species are the primary catalytically active centers for the NRR. This work provides insight into precise construction of more efficient and stable NRR electrocatalysts and further expands the possibilities of transition metal–nitrogen–carbon (M–N–C)-based nanomaterials in NRR fields.
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•Polyimide aerogels are prepared by incorporating TFMB into BPDA/ODA backbones.•These fluorinated aerogels show ultralow dielectric constants and loss tangents.•Moisture-resistance is ...dramatically enhanced by adding a small quantity of TFMB.•These fluorinated aerogels exhibit superior lipophilicity.
Conventional polyimide aerogels made from biphenyl-3,3′,4,4′-tetracarboxylic dianydride (BPDA) and 4,4′-oxidianiline (ODA) exhibit poor resistance to moisture and mechanical properties. In this work, a versatile diamine, 2,2′-bis-(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB), is introduced to BPDA/ODA backbone to modify the comprehensive performance of this aerogel. Among all formulations, the resulted polyimide aerogels exhibit the lowest shrinkage and density as well as highest porosity, at the ODA/TFMB molar ratio of 5/5. Dielectric constants and loss tangents of the aerogels fall in the range of 1.29–1.33 and 0.001–0.004, respectively, and more TFMB fractions results in a slightly decrease of dielectric constant and loss tangent. In addition, moisture-resistance of the aerogels are dramatically enhanced as the water absorption decreasing from 415% for BPDA/ODA to 13% for the polyimide aerogel at the ODA/TFMB molar ratio of 7/3, and even to 4% for the homo-BPDA/TFMB polyimide aerogel, showing a superhydrophobic characteristic, which is a great advantage for polyimide aerogels used as low dielectric materials. Meanwhile, all of formulations of aerogels exhibit high absorption capacities for oils and common organic solvents, indicating that these fluorinated polyimide aerogels are good candidates for the separation of oils/organic solvents and water. Mechanical properties and thermal stability of the polyimide aerogels are also raised to varying degrees due to the rigid-rod biphenyl structure introduced by TFMB.
•Exposure to PFASs was inversely associated with the risk of type 2 diabetes.•Serum PFOA was positively associated with fasting plasma glucose in controls.•PFNA, PFUnDA, PFOS and 6:2 Cl-PFESA may ...disturb lipid metabolism in human.
Associations between per- and polyfluoroalkyl substances (PFASs) and the incidence of type 2 diabetes are controversial in epidemiological studies. In addition, limited data are available for assessing the health effects of novel PFAS alternatives. Our study evaluated the effects of PFAS exposure on type 2 diabetes by estimating the associations of PFASs in human serum with the risk of type 2 diabetes and levels of glycemic biomarkers and lipid fractions. The case-control study consisted of 304 participants from Shandong Province, East China, half of which were diagnosed with type 2 diabetes. Logistic regression showed that most PFASs were inversely associated with the risk of type 2 diabetes after adjusting for age, sex, and body mass index. However, concentrations of perfluorooctanoic acid (PFOA) in the control group were positively associated with fasting plasma glucose levels (β = 0.04, 95% confidence interval (CI): 0.0003, 0.08), which may promote the development of type 2 diabetes. Furthermore, each log-unit increase in the concentrations of perfluorononanoic acid (PFNA), perfluoroundecanoic acid (PFUnDA), and 6:2 chlorinated polyfluoroalkyl ether sulfonic acid (Cl-PFESA) were associated with a total cholesterol increase (i.e., 17.49% (95% CI: 0.93%, 34.90%), 17.49% (95% CI: 4.71%, 31.83%), and 17.49% (95% CI: 4.71%, 31.83%), respectively). Positive associations were also observed between PFNA, PFUnDA, perfluorooctane sulfonate (PFOS), and 6:2 Cl-PFESA and low-density lipoprotein cholesterol. However, no associations between PFASs and hemoglobin A1c, triglycerides, or high-density lipoprotein cholesterol reached statistical significance, nor associations between PFAS mixtures and outcomes of interest. In conclusion, the significant correlations between serum PFASs and glycemic biomarkers and lipid fractions indicated that PFAS exposure may be a potential diabetogenic factor. To the best of our knowledge, this is the first study to assess the associations between novel Cl-PFESAs and type 2 diabetes, although the inverse associations observed require clarification in future studies.
Photocatalytic nitrogen fixation reaction can harvest the solar energy to convert the abundant but inert N2 into NH3. Here, utilizing metal–organic framework (MOF) membranes as the ideal assembly of ...nanoreactors to disperse and confine gold nanoparticles (AuNPs), we realize the direct plasmonic photocatalytic nitrogen fixation under ambient conditions. Upon visible irradiation, the hot electrons generated on the AuNPs can be directly injected into the N2 molecules adsorbed on Au surfaces. Such N2 molecules can be additionally activated by the strong but evanescently localized surface plasmon resonance field, resulting in a supralinear intensity dependence of the ammonia evolution rate with much higher apparent quantum efficiency and lower apparent activation energy under stronger irradiation. Moreover, the gas-permeable Au@MOF membranes, consisting of numerous interconnected nanoreactors, can ensure the dispersity and stability of AuNPs, further facilitate the mass transfer of N2 molecules and (hydrated) protons, and boost the plasmonic photocatalytic reactions at the designed gas–membrane–solution interface. As a result, an ammonia evolution rate of 18.9 mmol gAu –1 h–1 was achieved under visible light (>400 nm, 100 mW cm–2) with an apparent quantum efficiency of 1.54% at 520 nm.
A crucial issue restricting the application of direct alcohol fuel cells (DAFCs) is the low activity of Pt‐based electrocatalysts for alcohol oxidation reaction caused by the reaction intermediate ...(CO*) poisoning. Herein, a new strategy is demonstrated for making a class of sub‐monolayer YOx/MoOx‐surface co‐decorated ultrathin platinum nanowires (YOx/MoOx–Pt NWs) to effectively eliminate the CO poisoning for enhancing methanol oxidation electrocatalysis. By adjusting the amounts of YOx and MoOx decorated on the surface of ultrathin Pt NWs, the optimized 22% YOx/MoOx–Pt NWs achieve a high specific activity of 3.35 mA cm−2 and a mass activity of 2.10 A mgPt−1, as well as the enhanced stability. In situ Fourier transform infrared (FTIR) spectroscopy and CO stripping studies confirm the contribution of YOx and MoOx to anti‐CO poisoning ability of the NWs. Density functional theory (DFT) calculations further reveal that the surface Y and Mo atoms with oxidation states allow COOH* to bind the surface through both the carbon and oxygen atoms, which can lower the free energy barriers for the oxidation of CO* into COOH*. The optimal NWs also show the superior activities toward the electro‐oxidation of ethanol, ethylene glycol, and glycerol.
A new class of sub‐monolayer YOx/MoOx‐surface‐co‐decorated ultrathin platinum (Pt) nanowires is demonstrated to effectively boost alcohol oxidation electrocatalysis. The surface Y and Mo atoms make the free energies of CO* and COOH* be decoupled on the nanowire surfaces, lowering the energy barriers for the oxidation of CO* into COOH*.
Oriented arrays of polyaniline (PANI) nanorods grown on expanded graphite (EG) nanosheets are fabricated by in situ polymerization to achieve excellent electrochemical properties for applications as ...supercapacitor electrodes. EG serves as an excellent 3D conductive skeleton that supports a highly electrolytic accessible surface area of redox-active PANI and provides a direct path for electrons. The porous and ordered nanostructure provides a larger contact surface area for the intercalation/deintercalation of protons into/out of active materials and shortens the path length for electrolyte ion transport. The maximum specific capacitance of 1665 F g–1 at 1 A g–1 is observed in the PANI/EG electrode with 10% EG content. The composite electrode material also exhibits significant rate capability and good long-term cycling stability. The results demonstrate that PANI is effectively utilized with the assistance of EG conductive skeletons in the electrode. Such 3D composite nanoarchitecture is very promising for the next generation of high-performance electrochemical supercapacitors.
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