Scholte波与含泥沙两相流介质属性关系的分析及仿真验证

基于四种超声悬浮液模型Urick, Urick-Ament, HT, Mcclements分析了Scholte波在两相流体与多孔介质固体界面处的传播特性. 结合各模型的复波数表达式建立含泥沙流体-多孔介质固体界面波特征方程, 分析了Scholte波速与两相流体积含量、粒径等介质属性的关系. 通过仿真实验获得界面波信号, 运用时延估计获得Scholte波速与泥沙含量、粒径的关系, 发现所得的波速与Urick-Ament和HT理论有相对好的一致性. 关键词： Scholte波 两相流体 多孔介质 泥沙含量     

Quantum anomalous Hall effect and related topological electronic states

Over a long period of exploration, the successful observation of quantized version of anomalous Hall effect (AHE) in thin film of magnetically doped topological insulator (TI) completed a quantum Hall trio—quantum Hall effect (QHE), quantum spin Hall effect (QSHE), and quantum anomalous Hall effect (QAHE). On the theoretical front, it was understood that the intrinsic AHE is related to Berry curvature and U(1) gauge field in momentum space. This understanding established connection between the QAHE and the topological properties of electronic structures characterized by the Chern number. With the time-reversal symmetry (TRS) broken by magnetization, a QAHE system carries dissipationless charge current at edges, similar to the QHE where an external magnetic field is necessary. The QAHE and corresponding Chern insulators are also closely related to other topological electronic states, such as TIs and topological semimetals, which have been extensively studied recently and have been known to exist in various compounds. First-principles electronic structure calculations play important roles not only for the understanding of fundamental physics in this field, but also towards the prediction and realization of realistic compounds. In this article, a theoretical review on the Berry phase mechanism and related topological electronic states in terms of various topological invariants will be given with focus on the QAHE and Chern insulators. We will introduce the Wilson loop method and the band inversion mechanism for the selection and design of topological materials, and discuss the predictive power of first-principles calculations. Finally, remaining issues, challenges and possible applications for future investigations in the field will be addressed.     

Precursor Based on Polyborylborazine for BN Fiber: Preparation and Rheology Properties

A polyborylborazine precursor for hexagonal boron nitride (h-BN) was obtained by reaction of boron trichloride with methylamine and its structure was characterized by ¹¹BNMR, ¹³CNMR, ¹HNMR, and FTIR. The results show that the molecular precursor consists of borazine rings connected via a cross-linked network. The results of shear rheological tests indicated that the polymer is capable of being melt spun at moderate temperature, which implies that the structure of the molecular chains of the precursor polymer is branched. The precursor polymer was spun into a continuous polymer fiber in the melt state and then subsequently heat-treated under NH₃ up to 1000°C for conversion into BN fibers. Its surface morphology was observed by scanning electron microscopy (SEM); the fiber was free of defects and cavities.     

Improved Performance of On-line Atom Trapping in Flame Furnace Atomic Absorption Spectrometry by Chemical Vapor Generation: Determination of Cadmium in High-Salinity Water Samples

ABSTRACT

On-line atom trapping inside a nickel flame furnace using chemical vapor generation for sample introduction was proposed for the determination of trace cadmium by flame atomic absorption spectrometry (AAS). Cadmium volatile species was generated upon reaction with potassium borohydride and then flushed into a flame furnace for on-line trapping by a flow of nitrogen carrier gas. The middle part of the flame furnace, where the carrier gas impacts, is cooled by the gas flow, and this provides a fine strategy for on-line atom trapping for the purpose of preconcentration. A stainless steel plate is put on the top of the flame burner in the middle to form a flame-free zone, which also greatly lowers the temperature of the flame furnace and facilitates the atom-trapping process. Due to the introduction of chemical vapor generation, matrix effect was greatly alleviated compared with direct pneumatic nebulization for on-line atom trapping in flame furnace AAS. With trapping time of 35 s, the current approach achieved an excellent limit of detection of 20 ng L^?1. The proposed method was successfully applied for the quantification of cadmium in high-salinity samples.     

具有高隔离度的双陷波超宽带多入多出天线

提出了一款具有高隔离度的双陷波超宽带多入多出（UWB MIMO）天线。该天线由两个相同的半切超宽带天线单元倒置构成。通过在天线底板刻蚀栅栏型缺陷地解耦结构,使该MIMO天线的隔离度提高至25 dB。此外,在天线半圆形辐射贴片上刻蚀两个方向相反的“L”型缝隙,实现了双陷波的功能,分别抑制了802.16无线城域网WiMAX（3.2～3.7 GHz）和WLAN（5.15～5.85 GHz）信号对天线系统的干扰。实验结果表明,该天线在3～11 GHz工作带宽内的隔离度大于25 dB,包络相关系数（ECC）小于0.004;第一个陷波频段为3.0～3.7 GHz,第二个陷波频段为5.1～5.85 GHz,有效抑制了WiMAX和WLAN的信号干扰。     

Real-time phase measurement and correction of dynamic multimode beam using a single spatial light modulator

In this Letter,a novel system for adaptively correcting the phase of a dynamic multimode beam is proposed.While using merely one spatial light modulator,the phase measurement of the first-order diffraction pattern and the correction of the zeroth diffraction order are simultaneously realized.The real-time experimental result is obtained at a control rate of 10 Hz.The power-in-the-bucket value is improved from 38.5%to 61.8%,even with fundamental mode content that is consistently below 30%.To the best of our knowledge,this is the first implementation of real-time adaptive correction of the entire multimode beam.     

A reconfigurable terahertz polarization converter based on metal–graphene hybrid metasurface

A metal-graphene hybrid metasurface polarization converter is designed in this Letter.The unit cell of the hybrid metasurface is composed of a butterfly-shaped structure whose branches are connected by multi-layer graphene sheets.The proposed device can be reconfigured from linear-to-circular polarization to cross-polarization by changing the Fermi energy of graphene.The simulation results show that for three-layer graphene,the device acts as a linear-to-circular polarization converter when EF=0 eV and switches to a cross-polarization converter when EF=0.5 eV.Compared with single-layer graphene,the device with three-layer graphene can maintain the cross-polarization conversion performance under low Fermi energy.Furthermore,two equivalent circuits in the x and y directions are developed to understand the working mechanism of the device.     

Optical Trapping with Focused Surface Waves

Near-field optical trapping can be realized with focused evanescent waves that are excited at the water–glass interface due to the total internal reflection, or with focused plasmonic waves excited on the water–gold interface. Herein, the performance of these two kinds of near-field optical trapping techniques is compared using the same optical microscope configuration. Experimental results show that only a single-micron polystyrene bead can be trapped by the focused evanescent waves, whereas many beads are simultaneously attracted to the center of the excited region by focused plasmonic waves. This difference in trapping behavior is analyzed from the electric field intensity distributions of these two kinds of focused surface waves and the difference in trapping behavior is attributed to photothermal effects due to the light absorption by the gold film.