Due to the symmetry breaking, Janus two-dimensional materials possess novel electronic properties such as energy valley and spin polarization. In this research, we predicted the Zeeman-type spin ...splitting and Rashba splitting of monolayer Janus ZrNX (X = Br, I). The Rashba spin splitting and valley splitting can be greatly tuned by the magnetic proximity effect of monolayer H–VTe2, which are dependent on the stacking configurations. There is strong interlayer coupling between Janus ZrNX and VTe2, leading to a sizable valley splitting of 87 meV. The valley splitting can be significantly enlarged by the vertical compression strain, because of the increases of effective Zeeman field and in-plane orbital component. In addition, a helical gap is opened and the dispersion relation of Rashba spin-orbit coupling is obviously modified by in-plane biaxial strain. The Rashba constant and helical gap increase with the in-plane tensile strain, which leads from the larger potential energy difference and magnetic moment of surface V atoms. The greatly tunable spin/valley splittings in ZrNBr/VTe2 heterostructure are of some signification for the development of spintronics/valleytronics and the realization of new functional devices.
•The valley polarization and Rashba SOC of monolayer Janus ZrNX (X = Br, I) are demonstrated.•The valley splitting and Rashba splitting of ZrNBr/VTe2 heterostructure are effectively regulated by stacking configurations.•The factor of greater valley splitting is larger in-plane orbital composition and strong effective Zeeman field.•The helical gap is found and can be manipulated by biaxial strain.
The Kagome lattice is rich in unique electronic and magnetic properties, such as flat band, superconductivity, charge density waves, and so on. In this paper, the magnetic properties, flat and Dirac ...bands of monolayer Mn3Sn3Se2 with Kagome lattice are investigated based on first-principles calculations. A total of four magnetic configurations are considered, and the intrinsic ground state of Mn3Sn3Se2 is identified as the ferromagnetic state. Strain has a significant effect on its magnetic ground state, which changes to an in-plane AFM state when the tensile strain exceeds 5 %. Monolayer Mn3Sn3Se2 has an out-of-plane magnetic anisotropy of up to 0.777 meV, and the Curie temperature is 528 K. The band structure of the FM state is shown to be metallic, and spin polarized flat and Dirac bands appear near the Fermi level, which are degenerate. Monolayer Mn3Sn3Se2 changes to half-metallic when a strain of 1%–2% is applied. Strain and correlation effects can significantly alter the flatness of flat band and the relative energy with Dirac bands. These results not only enrich the family of two-dimensional ferromagnets, but also provide a reference for studying the regulation of flat and Dirac bands.
•The intrinsic Mn3Sn3Se2 monolayer is room-temperature ferromagnetic metal.•The Curie temperature is 528 K and out-of-plane MAE is 0.777 meV.•A tensile strain of 1 %∼2 % makes it a half-metal.•There are flat band and Dirac point near the Fermi level, which are degenerate.•U-value and strain can regulate the degeneracy and the flatness of flat band.
Cobalt-based sulfides with variable valence states and unique physical and chemical properties have shown great potential as oxygen evolution reaction (OER) catalysts for electrochemical ...water-splitting reactions. However, poor morphological characteristics and a small specific surface area limit its further application. Here, hexagonal single-crystal two-dimensional (2D) CoS nanosheets with different thicknesses are successfully prepared by an atmospheric-pressure chemical vapor deposition method. Because of the advantages of the 2D structure, more exposed catalytic active sites, better reactant adsorption ability, accelerated electron transfer, and enhanced electrical conductivities can be achieved from the thinnest 5 nm CoS nanosheets (CoS-5), significantly improving OER performance. The electrochemical tests manifest that CoS-5 show an overpotential of 290 mV at 10 mA cm–2 and a Tafel slope of 65.6 mV dec–1 in the OER in an alkaline solution, superior to those for other thicknesses of CoS, bulk CoS, and RuO2. For the mechanistic investigation, the lowest charge transfer resistance (R ct) and the highest double-layer capacitance (C dl) were obtained for CoS-5, demonstrating the faster OER kinetics and the larger active area. Density functional theory calculations further reveal the enhanced density of states around the Fermi level and higher H2O molecule adsorption energy for thinner CoS nanosheets, promoting its intrinsic catalytic activity. Moreover, the two-electrode system with CoS-5 as the anode and Pt/C as the cathode requires only 1.56 V to attain 10 mA cm–2 in the overall water-splitting reaction. We believe that this study will provide a fresh view for thickness-dependent catalytic performance and offers a new material for the study of electronic and energy devices.
In order to study oil-gas-liquid three-phase flow regularity in oil well, the vertical upward three-phase flow dynamic experiment with low velocity was carried out in a large diameter (125 mm i.d.) ...flow loop using the combination sensors of VMEA and mini-conductance probe array and six three-phase flow patterns were defined. VMEA sensor conductance fluctuating signals of five flow patterns with water as the continuous liquid were acquired. And then the multi-scale entropy processing and analysis of them are conducted to describe the dynamics characteristics of the different flow patterns. The study result indicates that the multi-scale entropy reveals the nonlinear dynamics characteristics of flow patterns in different scales and Rate of MSE as a characteristic representing approximately constant increasing rate of sample entropy at low scales sensitively indicates the variation of flow patterns and can act as the efficient criterion of three-phase flow patterns identification. And it is helpful to understand the dynamics mechanism of three-phase flow pattern evolution.
In order to investigate the flow patterns of gas/liquid two phase flow existing widely in Daqing oilfield of China, conductance signals of 104 gas/liquid two phase flow conditions has been acquired ...in concentrating channel on the three phase flow experimental facility of Tianjin University. Firstly, the fluctuating conductance signals are decomposed into seven scale signals and then recurrence plot is employed to analysis the original signal and each scale signal. The results indicate the recurrence plot has perfect identification ability in analyzing the flow patterns of complex gas/liquid flow. Simultaneously, two dimensional attractor morphologic characteristics of each order have been extracted, the effective feature combination used to identify the flow pattern is found through the analysis of attractor morphologic characteristics. The result shows that attractor morphologic characteristics can well reflect the flow pattern transition and it is an effective analysis method of flow pattern identification.
The CFD/CSD coupling method is turning into the main research direction for the static/dynamic aeroelastic analyses. If one wants to use the method for the complex engineering aeroelastic problems, ...he needs to investigate the relative aeroelasfic algorithms, such as the numerical computational method of unsteady aerodynamic forces, equivalent low-dimensional structural fi- nite element model and the solution method of structural dynamic equations, data transfer technique between fluid and structure, the moving grid method, etc. Besides, he also needs to improve the computational efficiency by such as massive parallel CFD algorithm, reduced-order model （ROM） of unsteady aerodynamic forces, etc. In this paper, based on the authors＇ recent investigations, the research progresses in computational aeroelastic methods and their applications to engineering problem are summarized.
According to multi-resolution theory of wavelet, in order to filter, de-noise and to distill the character of signal effectively, The GPS/DR(Global Position System/dead Reckoning) signal was ...decomposed and constructed with the application of wavelet matching method. Without needing exact statistical model of noise, the data is fused in wavelet fields. The parameters and biases of sensors are adjusted and the navigation precision is improved. The device composed of Jupiter GPS and LR-46 piezoelectricity gyro was designed. The experiments were carried out and the results showed that processing the data in wavelet fields can obtain satisfying location precision.
Recurrence quantification analysis method was employed to study the identification of oil/water two-phase flow patterns. The results showed recurrence plot appeared different textures for the ...transitional oil/water two phase flow patterns, and was special for different flow pattern. That indicated the texture of recurrence plot was sensitive to the changes of oil/water two flow patterns, and the recurrence quantification analysis is a useful diagnosis tool in identifying of two phase flow patterns.
