结构参数对自相似多级蜂窝力学性能的影响

对蜂窝的代表性体积单元(RVE)研究发现,相比于均匀化边界条件,周期性边界条件能更好地预测蜂窝的等效力学性能。基于周期性边界条件,对自相似多级蜂窝进行面内不同方向的拉伸模拟,重点分析了蜂窝孔隙率与多级长度比对拉伸性能的影响。结果表明:自相似多级蜂窝在拉伸过程中会呈现面内各向异性,沿扶手椅方向拉伸时,会在节点六边形的水平连接边处发生断裂;沿锯齿形方向拉伸时,当节点六边形的边长大于壁厚和节点六边形的连接斜边的边长较长的情况下,蜂窝会出现两次拉伸破坏,分别在节点六边形边与节点六边形的连接斜边处,而在其他情况下,则只会在节点六边形连接斜边处发生一次破坏。并且自相似多级蜂窝随着孔隙率或长度比的增大,蜂窝拉伸强度呈现减小的趋势。     

改性酰化壳聚糖缓释肥包膜材料的制备与表征

壳聚糖与辛酰氯酰化反应,制备低取代度的酰化壳聚糖。通过元素分析计算酰化壳聚糖的取代度,并用红外光谱、核磁共振、尿素渗透测试对其结构及渗透性能进行分析和表征。以戊二醛为交联剂,制备了一系列酰化交联壳聚糖膜,用吸水倍率、接触角、X射线衍射仪、热重分析、尿素渗透等对其性能进行分析表征。结果表明,交联使酰化壳聚糖热稳定性提高;酰化交联壳聚糖缓释包膜材料结晶度下降,疏水性提高;随戊二醛含量增加,尿素累积渗透量下降,7 d内尿素累积渗透量由74.7%降低至34.2%,28 d时尿素累积渗透量为76.7%,改性酰化壳聚糖膜缓释性能良好。     

Metasurfaces Atop Metamaterials: Surface Morphology Induces Linear Dichroism in Gyroid Optical Metamaterials

Optical metamaterials offer the tantalizing possibility of creating extraordinary optical properties through the careful design and arrangement of subwavelength structural units. Gyroid‐structured optical metamaterials possess a chiral, cubic, and triply periodic bulk morphology that exhibits a redshifted effective plasma frequency. They also exhibit a strong linear dichroism, the origin of which is not yet understood. Here, the interaction of light with gold gyroid optical metamaterials is studied and a strong correlation between the surface morphology and its linear dichroism is found. The termination of the gyroid surface breaks the cubic symmetry of the bulk lattice and gives rise to the observed wavelength‐ and polarization‐dependent reflection. The results show that light couples into both localized and propagating plasmon modes associated with anisotropic surface protrusions and the gaps between such protrusions. The localized surface modes give rise to the anisotropic optical response, creating the linear dichroism. Simulated reflection spectra are highly sensitive to minute details of these surface terminations, down to the nanometer level, and can be understood with analogy to the optical properties of a 2D anisotropic metasurface atop a 3D isotropic metamaterial. This pronounced sensitivity to the subwavelength surface morphology has significant consequences for both the design and application of optical metamaterials.     

Optical study of charge dynamics along thec-axis in high-Tc superconductors

Comparing the optical spectra withEc for typical high-T _c superconducting cuprates, we discuss the charge dynamics along thec-axis. The plasma energy or the mass anisotropic factorm _* ^c //m _* ^b is one of the key parameters determining the spectrum forEc. In Bi₂Sr₂CaCu₂O₈ and La_2–x Sr _x CuO₄ with a largem _* ^c /m _* ^b , the plasma energy is smaller than the superconducting gap energy, and thus the supercurrent along thec-axis is a kind of Josephson current flowing through insulating layers such as the BiO layers. On the other hand, in YBa₂Cu₃O₇ with a smallm _* ^c /m _* ^a , it seems that the coherent supercurrent flows along thec-axis. Although the spectrum forEc strongly depends on samples, presumably due to the difference in the hole concentration, a clear anisotropy between theab- and thec-directions is observed in the characteristics energy scales such as the plasma energy as well as the reflectivity knee energy.     

Probing Distinctive Electron Conduction in Multilayer Rhenium Disulfide

Charge carrier transport in multilayer van der Waals (vdW) materials, which comprise multiple conducting layers, is well described using Thomas–Fermi charge screening (λ_TF) and interlayer resistance (R_int). When both effects occur in carrier transport, a channel centroid migrates along the c‐axis according to a vertical electrostatic force, causing redistribution of the conduction centroid in a multilayer system, unlike a conventional bulk material. Thus far, numerous unique properties of vdW materials are discovered, but direct evidence for distinctive charge transport behavior in 2D layered materials is not demonstrated. Herein, the distinctive electron conduction features are reported in a multilayer rhenium disulfide (ReS₂), which provides decoupled vdW interaction between adjacent layers and much high interlayer resistivity in comparison with other transition‐metal dichalcogenides materials. The existence of two plateaus in its transconductance curve clearly reveals the relocation of conduction paths with respect to the top and bottom surfaces, which is rationalized by a theoretical resistor network model by accounting of λ_TF and R_int coupling. The effective tunneling distance probed via low‐frequency noise spectroscopy further supports the shift of electron conduction channel along the thickness of ReS₂.     

Giant Enhancements of Perpendicular Magnetic Anisotropy and Spin‐Orbit Torque by a MoS2 Layer

2D transition metal dichalcogenides have attracted much attention in the field of spintronics due to their rich spin‐dependent properties. The promise of highly compact and low‐energy‐consumption spin‐orbit torque (SOT) devices motivates the search for structures and materials that can satisfy the requirements of giant perpendicular magnetic anisotropy (PMA) and large SOT simultaneously in SOT‐based magnetic memory. Here, it is demonstrated that PMA and SOT in a heavy metal/transition metal ferromagnet structure, Pt/[Co/Ni]₂, can be greatly enhanced by introducing a molybdenum disulfide (MoS₂) underlayer. According to first‐principles calculation and X‐ray absorption spectroscopy (XAS), the enhancement of the PMA is ascribed to the modification of the orbital hybridization at the interface of Pt/Co due to MoS₂. The enhancement of SOT by the role played by MoS₂ is explained, which is strongly supported by the identical behavior of SOT and PMA as a function of Pt thickness. This work provides new possibilities to integrate 2D materials into promising spintronics devices.     

镍基单晶高温合金研究进展

单晶高温合金因具有较高的高温强度、优异的蠕变与疲劳抗力以及良好的抗氧化性、抗热腐蚀性、组织稳定性和使用可靠性,广泛应用于涡轮发动机等先进动力推进系统涡轮叶片等部件。由于采用定向凝固工艺消除了晶界,单晶高温合金明显减少了降低熔点的晶界强化元素,提高了合金的初熔温度,能够在较高温度范围进行固溶和时效处理,其高温强度比等轴晶和定向柱晶高温合金也大幅度提高。经过几十年的发展,单晶高温合金已经在合金设计方法、组织结构与力学性能关系、纯净化冶炼工艺和定向凝固工艺等方面取得了重要进展。从单晶高温合金成分特点、合金元素作用、强化机理、力学性能各向异性、凝固过程及缺陷控制、单晶制备工艺等方面,简要介绍了单晶高温合金的主要研究进展。     

MgO/Pd底层对CoSiB/Pd多层膜垂直磁各向异性及热稳定性的影响EI北大核心CSCD

采用磁控溅射方法在玻璃基片上制备以MgO/Pd为底层的CoSiB/Pd多层膜样品,研究MgO底层厚度t对CoSiB/Pd多层膜垂直磁各向异性(perpendicular magnetic anisotropy,PMA)的影响,分析具有MgO/Pd底层的多层膜的热稳定性。通过对样品的反常霍尔效应的测试分析发现,底层中引入MgO层能够提高其PMA性能,当t为3.5 nm时,样品的矩形度最好。对最佳样品MgO(3.5 nm)/Pd(3 nm)/[CoSiB(0.5 nm)/Pd(0.8 nm)]2/Ta(2 nm)的磁滞回线进行测试,其有效磁各向异性常数K eff达到2.0×10^5 J/m^3。热稳定性分析发现,当退火温度为200℃时,样品的K eff达到最大值2.6×10^5 J/m^3;当退火温度达到400℃时,样品仍能保持良好的PMA性能。     

用减压膜蒸馏淡化罗布泊地下苦咸水

考察了减压膜蒸馏过程淡化高浓度盐溶液过程中温度、浓度、真空度对膜通量的影响,结果表明:膜的渗透通量与温度的倒数呈指数关系,高真空度下膜的通量与膜两侧水蒸气分压平方根的差呈直线关系,这种直线关系说明了水蒸气在膜孔内的传质过程是以扩散为主;当盐溶液浓度达到一定量时,浓度的增大对膜通量的影响较小.将减压膜蒸馏应用于新疆罗布泊地区地下苦咸水的淡化处理,可获得馏出液电导率均小于10μS/cm的较好效果.