We report direct imaging of standing waves of the nontrivial surface states of topological insulator Bi2Te3 using a scanning tunneling microscope. The interference fringes are caused by the ...scattering of the topological states off Ag impurities and step edges on the Bi2Te3(111) surface. By studying the voltage-dependent standing wave patterns, we determine the energy dispersion E(k), which confirms the Dirac cone structure of the topological states. We further show that, very different from the conventional surface states, backscattering of the topological states by nonmagnetic impurities is completely suppressed. The absence of backscattering is a spectacular manifestation of the time-reversal symmetry, which offers a direct proof of the topological nature of the surface states.
We study the bulk–edge correspondence in topological insulators by taking Fu–Kane spin pumping model as an example. We show that the Kane–Mele invariant in this model is Z2 invariant modulo the ...spectral flow of a single-parameter family of 1+1-dimensional Dirac operators with a global boundary condition induced by the Kramers degeneracy of the system. This spectral flow is defined as an integer which counts the difference between the number of eigenvalues of the Dirac operator family that flow from negative to non-negative and the number of eigenvalues that flow from non-negative to negative. Since the bulk states of the insulator are completely gapped and the ground state is assumed being no more degenerate except the Kramers, they do not contribute to the spectral flow and only edge states contribute to. The parity of the number of the Kramers pairs of gapless edge states is exactly the same as that of the spectral flow. This reveals the origin of the edge–bulk correspondence, i.e., why the edge states can be used to characterize the topological insulators. Furthermore, the spectral flow is related to the reduced η-invariant and thus counts both the discrete ground state degeneracy and the continuous gapless excitations, which distinguishes the topological insulator from the conventional band insulator even if the edge states open a gap due to a strong interaction between edge modes. We emphasize that these results are also valid even for a weak disordered and/or weak interacting system. The higher spectral flow to categorize the higher-dimensional topological insulators is expected.
To improve the wear properties of magnesium alloys, a novel technique for preparing coatings using ultrasonic shot peening was developed, and tungsten carbide (WC) coatings were prepared for the ...first time on the magnesium alloys. The surface morphology, microstructure characteristics, and wear properties were investigated. The findings showed that this method deposited a WC coating with a thickness of 20 μm and a surface hardness of 3.24 GPa on the substrate. A 5 μm composite layer and a 425 μm thick hardened layer existed beneath the coating. The formation mechanism of the hardened layer can be interpreted as dislocation slip and grain refinement, resulting in a hardness of 1.96 GPa at the layer's top. The treated sample exhibited excellent wear resistance due to the high hardness of the WC coating and hardened layer, with a wear volume of 0.737 × 108 μm3, representing a decrease of 49.52% and 35.29% compared to the untreated and ultrasonic shot peening one. The research provides a novel solution to improve the wear properties of magnesium alloys, and it contributes to enhancing magnesium alloys' applicability in practical engineering fields such as aerospace, new energy vehicles, and biomedicine while also contributing to meeting the demand for lightweight manufacturing in these fields.
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•A new approach for preparing coatings using ultrasonic shot peening was proposed•Tungsten carbide coatings were prepared on magnesium alloy by ultrasonic shot peening•The composite and hardened layers were formed beneath the tungsten carbide coatings•The proposed method effectively improves the wear resistance of magnesium alloys due to the high hardness of the coating and hardened layer.
In the present paper, the effect of mechanical ball milling time on the fretting wear of GCr15 steel balls at different displacement amplitudes is investigated. TiC powder coating was fabricated on ...the surface of GCr15 steel balls using various process times, and the fretting wear tests were conducted on an AISI 52100 steel disk with the applied force of 80 N. Additionally, various displacement amplitudes (10 μm, 20 μm, and 60 μm) were selected. Specimen attributes and wear scars were characterized using an inverted metallographic microscope, a microhardness tester, an X-ray diffractometry analyzer, a white light interferometer, and a scanning electron microscope. The results showed that thick and continuous coatings could be obtained at the milling time of 18 h. The specimens processed for a longer milling time demonstrated better fretting wear resistance, which we attribute to higher microhardness of the surface layer. The coefficient of friction and wear volume of specimens at each different displacement amplitude significantly decreased with increasing milling time. As the displacement amplitude increased, the three fretting states were: partial slip coordinated by elastic deformation; partial slip state coordinated by plastic deformation; and gross slip condition. Our observations indicate that mechanical ball milling could be an efficient approach to improve the fretting wear resistance of GCr15 steel balls.
In this study, the tribological properties of three AISI 1045 steel samples were investigated. Two samples were treated with ultrasonic shot peening (USP) and ultrasonic strengthening grinding ...process (USGP), respectively, while the other one was only treated with a polishing process. Sample properties, such as surface morphology, roughness, microhardness, elastic modulus, frictional coefficient, and phase structures were analyzed. Results show that the sample treated with USGP had the best tribological properties. It realized the highest surface roughness, microhardness, and elastic modulus. Compared with a polished sample, the roughness of the sample treated with USGP increased by 157%, and the microhardness and elastic modulus improved by 32.8% and 21.3%, respectively. Additionally, USGP provided an average frictional coefficient of 0.4, decreasing approximately 45% compared to polishing. The possible mechanisms of USGP surface texturing were discussed. The findings denote that USGP could be an efficient approach to improve the fatigue life of some mechanical components.
This paper investigates the surface enhancement treatment of 12Cr17Mn6Ni5N steel weld joints using the Strengthened Grinding Process (SGP) and explores its effect on their surface characteristics and ...tensile performance. The study begins by examining the influence of different SGP durations on the weld joints' surface morphology, microhardness, and residual stress. Subsequently, the tensile properties of the SGP-treated samples are analyzed and the potential mechanisms by which SGP enhances the tensile performance of 12Cr17Mn6Ni5N steel weld joints are discussed. The results reveal that SGP treatment increases the maximum microhardness of 12Cr17Mn6Ni5N steel weld joints to 519.3 HV, marking a 109.9 % improvement as compared to untreated samples. Additionally, the samples’ surface residual stress was changed from residual tensile stress (46.5 MPa) to residual compressive stress (−1253.1 MPa). The SGP-treated samples exhibit a tensile strength of 671.43 MPa, marking an 8.51 % increase as compared to the untreated samples, while also achieving a simultaneous elongation of 16.42 %. The research demonstrates that SGP is an effective method for enhancing the tensile performance of specific mechanical components.
Abstract
The phenomenon of fractional quantum Hall effect (FQHE) was first experimentally observed 33 years ago. FQHE involves strong Coulomb interactions and correlations among the electrons, which ...leads to quasiparticles with fractional elementary charge. Three decades later, the field of FQHE is still active with new discoveries and new technical developments. A significant portion of attention in FQHE has been dedicated to filling factor 5/2 state, for its unusual even denominator and possible application in topological quantum computation. Traditionally, FQHE has been observed in high-mobility GaAs heterostructure, but new materials such as graphene also open up a new area for FQHE. This review focuses on recent progress of FQHE at 5/2 state and FQHE in graphene.
Wire-arc additive manufacturing (WAAM) technology offers an effective approach to fabricating complex metallic components. However, the existing WAAM process is limited in producing a metallic ...component with high mechanical strength. In this study, the ultrasonic strengthening grinding process (USGP) was proposed to enhance the mechanical properties of WAAM-processed 06Cr19Ni9 steel. A multiphase abrasive, comprising zirconia ceramic balls, brown corundum powder, and strengthening liquid, was propelled by an ultrasonic vibration and randomly impacted on the surface of the WAAM-processed sample. Subsequently, a uniaxial tensile test was conducted to evaluate its mechanical properties. The evolutions of microhardness, microstructure, and phase transformation were comprehensively analyzed. The results revealed that UGSP treatment promotes the generation of dendritic grains and dislocations, facilitates phase transitions, and augments stacking fault and twin band sizes. These cumulative effects enhanced the tensile properties of 06Cr19Ni9 steel. The resulted yield strength and tensile strength achieves a value of ∼970 MPa and ∼1032 MPa, respectively, which increased by ∼43.73% and ∼95.96% compared to the untreated sample. The finding suggested that the proposed method has great application prospects in improving mechanical properties of WAAM-processed components and has the advantages of high efficiency, low cost, and small equipment size.
Selective laser melted (SLM) 316L stainless steel (SS) has been widely employed in the fields of designing and manufacturing components with complex shapes and sizes. However, the low yield strength, ...low ultimate tensile stress, and low hardness of SLM 316L SS components hinder its further application. In this work, the strengthening grinding process (SGP) was used to enhance the mechanical properties of SLM 316L SS. The microhardness, residual stress, microstructure, and tensile properties of all the samples were analyzed. The results demonstrate that the SGP induced higher compressive residual stress and microhardness, as well as higher tensile properties. The maximum hardness and residual stress reached 354.5 HV and −446 MPa, respectively, indicating that the SGP resulted in a plastic deformation layer over 150 μm. The possible mechanisms have been discussed in further detail. Compared to the untreated sample, the SGP sample shows a significant improvement in yield strength (YS), ultimate tensile stress (UTS), and elongation (EL), increasing 30%, 25.5%, and 99.1%, respectively. This work demonstrates that SGP treatment could be an efficient approach to simultaneously improving the strength and ductility of the SLM 316L SS, which makes it more suitable for engineering applications.
IgG4-related disease mainly manifests as organomegaly and is accompanied by tissue fibrosis (Mimori, Mod Rheumatol 29(2):213, 2019) which is frequently confused with tumour (Dawei et al., J ...Gastroenterol Hepatol 29(12):1375-8, 2020). There are few reports with of IgG4-related disease with the first clinical manifestation involving the stomach.
We present the case of 46-year-old male patient with a "stomach tumour" as the first manifestation of IgG4-related disease. Gastroscopy showed a mass in the stomach, however, the pathology result was chronic inflammation with IgG4 positivity. CT scans of abdomen showed that the stomach wall was thick, the head of the pancreas was swollen, and retroperitoneal fibrosis was severe.The serum IgG4 level was 75 g/L (normal range 0.03-2.01 g/L).After treatment with methylprednisolone for one month, the symptoms were greatly relieved.
To reduce the suffering of patients and relieve their financial burden, we should consider the possibility of IgG4-related disease when the initial manifestation is a stomach mass.
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