声学超表面的非对称声分束特性研究

非对称声分束超表面是由人工微单元结构按照特定序列构建的二维平面结构,可将垂直入射的声波分成两束传播方向和分束比自由调控的透射波,在声功能器件设计及声通信领域具有广泛的应用前景。本文系统研究了一种实现非对称声分束的设计理论和实现方法,基于局域声功率守恒条件研究了声分束器的设计理论、阻抗矩阵分布、法向声强分布、声压场分布等。利用遗传算法对四串联共振腔结构进行参数优化实现了声分束器所需的阻抗矩阵分布,声压场分布表明声波入射到声分束器后在入射侧激发出两列传播方向相反且幅值和衰减系数均相同的表面波,实现了入射侧与透射侧的局域声功率相互匹配。声波经过声分束器后被分为两束透射波,两束透射波的折射角和透射系数与理论值十分吻合,证明了设计理论及实现方法的正确性和可行性。本文的研究工作可以为新型非对称声分束结构设计提供理论参考、设计方法和技术支持,并促进其在工程领域的实际应用。     

发动机机油滤清器虑层强度分析及优化

针对机油滤清器工作工况下进出口压差、机油滤层强度及导流桩高度等问题, 通过试验测试与仿真相结合, 对滤清器初步设计进行了评估及优化, 以确保滤清器在工作工况下进出口压降及滤层强度能满足要求. 首先进行滤层性能试验, 得到滤层的惯性阻力系数和黏性阻力系数; 再通过滤层多孔介质CFD分析, 对滤清器进出口压降进行分析计算. 结果表明: 在-18℃、25℃和70℃的工况下, 进出口压降都小于10kPa, 满足相关要求. 针对滤层的最大主应力超过其抗拉强度的问题, 通过CAE仿真分析, 优化滤层与导流桩间隙, 将滤层最大主应力由110.1MPa降至36.99MPa, 小于其抗拉强度42.8MPa.     

Enhanced Photocatalytic H2-production Activity of CdS Nanoflower using Single Atom Pt and Graphene Quantum Dot as Dual Cocatalysts

Single-atom catalysts have high catalytic activity due to their unique quantum size effects and optimal atom utilization. Herein, visiblelight-responsive photocatalysts were designed by coupling Cd S with graphene quantum dots（GQDs） and platinum single atoms（Pt SAs）. GQDs and Pt SAs were successively loaded on ultrathin Cd S nanosheets through freeze-drying and in-situ photocatalytic reduction. The synergistic effect between Pt SAs and GQDs results in superior photocatalytic activity with a hydr...     

Superconductivity and unconventional density waves in vanadium-based kagome materials AV3Sb5

Recently, the discovery of vanadium-based kagome metal AV₃Sb₅ (A= K, Rb, Cs) has attracted great interest in the field of superconductivity due to the coexistence of superconductivity, non-trivial surface state and multiple density waves. In this topical review, we present recent works of superconductivity and unconventional density waves in vanadium-based kagome materials AV₃Sb₅. We start with the unconventional charge density waves, which are thought to correlate to the time-reversal symmetry-breaking orders and the unconventional anomalous Hall effects in AV₃Sb₅. Then we discuss the superconductivity and the topological band structure. Next, we review the competition between the superconductivity and charge density waves under different conditions of pressure, chemical doping, thickness, and strains. Finally, the experimental evidence of pseudogap pair density wave is discussed.     

Copper-catalyzed diversified annulations between α-diketones and alkynyl α-diketones

Copper-catalyzed divergent annulations between α-diketones and alkynyl α-diketones have been achieved, delivering a series of highly functionalized and biologically important cis-hexahydro-2Hcyclopenta[b]furan(HCPF) and 2-hydroxydihydrofuran-3(2H)-one(HDFO) products with high levels of stereoselectivity under identical conditions. The protocol features the use of earth-abundant copper catalyst, mild conditions, shortening synthetic routes in constructing different molecular frameworks, and reduc...     

Research Advances of Ferroelectric Semiconductors of 2D Hybrid Perovskites toward Photoelectronic Applications

Ferroelectric materials, characterized by the switchable spontaneous polarization(Ps) through reversing the directions of external electric field, exhibit versatile physical attributes that have been extensively used for practical device applications. Two-dimensional(2D) organic-inorganic hybrid perovskites are recently emerging as a robust family of candidate ferroelectrics, termed ferroelectric semiconductors. In particular, the coexistence and/or coupling of ferroelectric polarization with th...     

In-situ monitoring of cell-secreted lactate by electrochemiluminescence sensing under biomimetic microfluidic confinement

Cell migration proceeds in 3D matrices in vivo, which can naturally switch to distinct phenotypes for better invasion in confined microenvironments. The studies of important metabolites under confinement are extremely meaningful for comprehensive insights into cancer metastasis. The integration of cell confinement device and analytical techniques is a key point for in-situ analysis of significant metabolites in vitro.Herein, an electrochemiluminescence(ECL) sensing platform was designed for in-s...     

Crosslinked polyacrylonitrile precursor for S@pPAN composite cathode materials for rechargeable lithium batteries

S@pPAN has become promising cathode materials in rechargeable batteries due to its high compressed density,low E/S ratio,no polysulfide dissolution,no self-discharge,and stable cycling.However,it is a big challenge to enhance its sulfur content which determines its practical specific capacity.Herein,we prepare crosslinked PAN as precursor,leading to effective enhancement of sulfur content up to 55 wt%and a reversible specific capacity of 838 mAh g _composites^-1 at 0.2C.Because of the microporous structure and high specific area,crosslinked PAN provides more space to accommodate sulfur molecule and improve the interfacial reaction of S@pPAN as well.This work provides a promising direction to design S@pPAN for lithium sulfur batteries with high energy density.     

Hollow Fe4C/FeP Nanoboxes with Heterostructure and Carbon Armor for Efficient and Stable Hydrogen Evolution

The heterojunction interfacial modulation of FeP is an effective strategy to regulate the intrinsic activity and stability, which is a major challenge to promote the industrial application of FeP-based electrocatalysts. Herein, hollow Fe₄C/FeP box with heterojunction interface and carbon armor is successfully synthesized, which can expose numerous active sites and protect catalyst from corrosion. Electrochemical measurements show that Fe₄C/FeP exhibits excellent hydrogen ev...     

Low-temperature Li-S batteries enabled by all amorphous con version process of organosulfur cathode

The high degree of crystallinity of discharging in termediates of Li-S batteries(Li₂S₂/Li₂S)causes a severe capacity attenuation at low temperatures.Herein,a sulfur-rich polymer is fabricated,which enables all the discharging in termediates to exist in an amorphous state without long-range order,promoti ng the substantial conversion of discharging intermediates and enhancing Li-S batteries'performance at low temperatures greatly.This cathode material exhibits excellent performance both at room and low temperatures.Even under an extremely low temperature(-40℃),the discharge capacity can remain 67% of that at room temperature.Besides,in-situ UV/Vis spectroscopy and density functional theory calculations reveal that this organosulfur cathode undergoes a new mechanism during discharge.Li₂S₆ and Li₂S₃ are the primary discharging intermediates that are quite different from conventional Li-S batteries.These results provide a new directi on for a broader range of applications of Li-S batteries.