Intertwined Dirac cones induced by anisotropic coupling in antiferromagnetic topological insulator

Antiferromagnetic topological insulators (AFM TIs), which host magnetically gapped Dirac-cone surface states and exhibit many exotic physical phenomena, have attracted great attention. The coupling between the top and bottom surface states becomes significant and plays a crucial role in its low-energy physics, as the thickness of an AFM TI film decreases. Here, we find that the coupled surface states can be intertwined to give birth to a set of $2n$ brand new Dirac cones, dubbed \emph{intertwined Dirac cones}, through the anisotropic coupling due to the $n$-fold crystalline rotation symmetry $C_{nz}$ ($n=2, 3, 4, 6$) in the presence of an out-of-plane electric field. Interestingly, we also find that the warping effect further drives the intertwined Dirac-cone state into a quantum anomalous Hall phase with a high Chern number ($C=n$). Then, we demonstrate the emergent six intertwined Dirac cones and the corresponding Chern insulating phase with a high Chern number ($C=3$) in MnBi$_2$Te$_4$$/$(Bi$_2$Te$_3$)$_{\mathrm{m}}/$MnBi$_2$Te$_4$ heterostructures through first-principles calculations. This work discovers a new intertwined Dirac-cone state in AFM TI thin films and also reveals a new mechanism for designing the quantum anomalous Hall state with a high Chern number.Comment: 7 pages, 4 figures+supplemental material

Study on Noise Source Analysis and Control Method of Gas Station

With the rapid development of economy, environmental issues have attracted more and more attention from all walks of life. As a new type of efficient energy, urban gas plays a vital role in promoting the healthy development of cities and mitigating urban air pollution. As the hub of urban gas, gas stations play the role of gas distribution, peak regulation and pressure regulation, and are necessary facilities for the safe and stable operation of urban gas pipeline network. With the increase of the number of urban gas stations, the noise problem generated by the stations is becoming increasingly prominent, which seriously affects the quality of people’s life and social environment. Based on the analysis of the causes of gas station noise, this paper analyzes the noise control strategy of gas station

Continuous and comprehensive atmospheric observations in Beijing : a station to understand the complex urban atmospheric environment

Peer reviewe

The effect of COVID-19 restrictions on atmospheric new particle formation in Beijing

During the COVID-19 lockdown, the dramatic reduction of anthropogenic emissions provided a unique opportunity to investigate the effects of reduced anthropogenic activity and primary emissions on atmospheric chemical processes and the consequent formation of secondary pollutants. Here, we utilize comprehensive observations to examine the response of atmospheric new particle formation (NPF) to the changes in the atmospheric chemical cocktail. We find that the main clustering process was unaffected by the drastically reduced traffic emissions, and the formation rate of 1.5 nm particles remained unaltered. However, particle survival probability was enhanced due to an increased particle growth rate (GR) during the lockdown period, explaining the enhanced NPF activity in earlier studies. For GR at 1.5-3 nm, sulfuric acid (SA) was the main contributor at high temperatures, whilst there were unaccounted contributing vapors at low temperatures. For GR at 3-7 and 7-15 nm, oxygenated organic molecules (OOMs) played a major role. Surprisingly, OOM composition and volatility were insensitive to the large change of atmospheric NOx concentration; instead the associated high particle growth rates and high OOM concentration during the lockdown period were mostly caused by the enhanced atmospheric oxidative capacity. Overall, our findings suggest a limited role of traffic emissions in NPF.Peer reviewe

Acoustic attenuation prediction and analysis of perforated hybrid mufflers with non-uniform flow based on frequency domain linearized Navier-Stokes equations

The three-dimensional frequency-domain linearized Navier-Stokes equations (LNSEs) with consideration of eddy viscosity are developed to evaluate the acoustic attenuation performance of perforated hybrid mufflers in the presence of non-uniform flow. The computations are performed in two steps: time averaged flow variables are acquired by using steady-state computational fluid dynamics (CFD) method and then mapped into the acoustic mesh, and the acoustic perturbation variables are obtained by solving frequency-domain LNSEs, where the sound-absorbing material is treated as an equivalent fluid with complex sound speed and density. The predictions of transmission losses of the two-pass perforated hybrid mufflers in the presence of non-uniform flow are in good consistencies with the measurements, which verifies the correctness of LNSEs. The effect of Mach numbers on acoustic attenuation performance of the mufflers with different filling densities and perforated components is investigated in detail. The transmission loss of the mufflers with various filling densities are increased by complex airflow in the lower frequency range. For the mufflers where not all components have been perforated, the flow lowers low-frequency resonance peak. The influence of complex airflow on acoustic attenuation performance of all configurations is weakened at higher frequencies

Anomalous properties in normal and superconducting states of Sc2Ir4-x Si x due to flat band effect driven by spin-orbit coupling

Abstract Correlation effect may be induced by the flat band(s) near the Fermi energy, as demonstrated in twisted graphene, Kagome materials, and heavy Fermion materials. Unconventional superconductivity may arise from this correlation effect and show deviation from the phonon-mediated pairing as well as the Landau Fermi liquid in the normal state. Here, we report the anomalous properties in normal and superconducting states in the Laves phase superconductor Sc2Ir4-x Si x with a kagome lattice and silicon doping. By doping silicon to the iridium sites, a phase diagram with nonmonotonic and two-dome-like doping dependence of the superconducting transition temperature T c was observed. The samples in the region of the second dome, including Sc2Ir3.5Si0.5 with the optimal T c, exhibit non-Fermi liquid behavior at low temperatures after superconductivity is suppressed, as evidenced by the divergence of the specific heat coefficient and the semiconducting-like resistivity, together with a strong superconducting fluctuation in the optimally doped samples. Combined with first-principles calculations, we attribute the anomalous properties in normal and superconducting states to the correlation effect, which is intimately induced by the flat band effect when considering the strong spin-orbit coupling

TiO2-FTCS modified superhydrophobic PVDF electrospun nanofibrous membrane for desalination by direct contact membrane distillation

The major challenges for electrospun membranes used in direct contact membrane distillation (DCMD) process are insufficient pore wetting resistance related with hydrophobicity and pore structure of membrane surface. A novel super-hydrophobization method containing first coating TiO2 nanoparticles on membrane surface by the low temperature hydrothermal process and then the TiO2 coated membrane being fluorosilanized with low surface energy material of 1H, 1H, 2H, 2H-perfluorododecyl trichlorosilane (FTCS) was employed to modify the virgin polyvinylidene fluoride electrospun nanofiber membrane (PVDF ENM). Results showed that this TiO2-FTCS modified membrane possessed high hydrophobicity (157.1 degrees), high mean roughness (4.63 mu m), considerable wetting resistance (158 kPa), well-distributed pore size (0.81 mu m), reasonable surface porosity (57%) and modest membrane thickness (55 mu m). These combined properties made the modified PVDF ENM an attractive candidate for DCMD. High flux and stable desalination performances were achieved during short-term DCMD process (73.4 LMH permeate flux, 99.99% salt rejection) using 3.5 wt% NaCl solution. Long-term DCMD process with actual reverse osmosis brine as feed solution also showed high performance (40.5 LMH, 99.98%). These results exceeded those of commercial PVDF membrane and unmodified PVDF ENM significantly, suggesting the potential for PVDF ENM in DCMD applications

Design and Synthesis of Vandetanib Derivatives Containing Nitroimidazole Groups as Tyrosine Kinase Inhibitors in Normoxia and Hypoxia

Sixteen novel epidermal growth factor receptor (EGFR)/vascular endothelial growth factor (VEGF)-2 inhibitors (nitroimidazole-substituted 4-anilinoquinazoline derivatives (16a–p)) were designed and prepared via the introduction of a nitroimidazole group in the piperidine side chain and modification on the aniline moiety of vandetanib. Preliminary biological tests showed that comparing with vandetanib, some target compounds exhibited excellent EGFR inhibitory activities and anti-proliferative over A549/H446 cells in hypoxia. Meanwhile, several of the above compounds demonstrated better bioactivity than vandetanib in VEGF gene expression inhibition. Owing to the excellent IC50 value (1.64 μmol/L), the inhibition ratios of 16f over A549 and H446 cells were 62.01% and 59.86% at the concentration of 0.5 μM in hypoxia, respectively. All of these results indicated that 16f was a potential cancer therapeutic agent in hypoxia and was worthy of further development