纤锌矿结构Zn1-xMgxO电子结构及吸收光谱的第一性原理研究

采用第一性原理计算方法,计算了纤锌矿结构Zn_1-xMg_xO(x=0,00625,0125,025)的电子结构及吸收光谱. 计算结果表明,Mg的掺入使ZnO的电子结构发生了较大的改变,与Mg邻近的O原子得到电子的数目明显增大,进而O原子返回部分电子给邻近Zn原子. Zn-O间相互作用减弱,禁带宽度变大,这也从同一合金中Zn4s上移的程度得到证实. 其吸收光谱也随着Mg的掺入出现蓝移现象,其吸收边对应波长分别为379, 关键词： 第一性原理计算 电子结构 吸收光谱 纤锌矿结构ZnO     

A straightforward method for wall impedance eduction in a flow duct

The development of the advanced liner technology for aeroengine noise control necessitates the impedance measurement method under realistic flow conditions. Currently, the methods for this need are mainly based on the inverse impedance eduction principle, confronting with the problems of initial guess, high computation cost, and low convergence. In view of this, a new strategy is developed that straightforwardly educes the impedance from the sound pressure information measured on the duct wall opposing to the test acoustic liner embedded in a flow duct. Here, the key insight is that the modal nature of the duct acoustic field renders a summed-exponential representation of the measured sound pressure; thus, the characterizing axial wave number can be readily extracted by means of Prony's method, and further the unknown impedance is calculated from the eigenvalue and dispersion relations based on the classical mode-decomposition analysis. This straightforward method is simple in its basic principle but remarkably has the advantages of ultimately overcoming the drawbacks inherent to the inverse methods, incorporating the realistic multimode nonprogressive wave effects, high computational efficiency, possibly reducing the measurement points, and even avoiding the necessity of the duct exit impedance that bothers perhaps all the existing waveguide methods.     

基于元胞自动机的对向行人交通流仿真研究

基于元胞自动机对对向行人交通流进行仿真研究. 模型利用四个动态参数反映行人移动区域和其视野范围内的实际情况,从而决定行人的行为选择,行人可以根据自身周围的情况选择前进、后退、等待、左右移动、交换位置等行为. 仿真研究不同方向比例与不同系统规模的对向行人流的速度-密度、流量-密度关系. 研究结果表明,系统存在相位转换和临界密度,方向比例和系统规模对行人流的速度-密度、流量-密度关系曲线的形状和系统临界密度值有一定的影响. 关键词： 元胞自动机 对向行人流 动态参数 临界密度     

GDX树脂富集－反相高效液相色谱法分离测定酚类化合物

用ＧＤＸ－５０２树脂富集的酚类化合物，经反相高效液相色谱法分离和检测，具有较好的准确度和精密度。     

Growth and spectral properties of Er:Gd2SiO5 crystal

Er³⁺-doped Gd₂SiO₅ (Er:GSO) single crystal with dimensions of ? 35×40 mm³ has been grown by the Czochralski method. The absorption and fluorescence spectra of the Er:GSO crystal were measured at room temperature. The spectral parameters were calculated based on Judd–Ofelt theory, and the intensity parameters Ω₂, Ω₄ and Ω₆ are obtained to be 6.168×10^?20, 1.878×10^?20, and 1.255×10^?20 cm², respectively. The emission cross-section has been calculated by Fuechtbauer–Ladenbury formula.     

Effect of Environment on the Scattering of Electrons by a Junction of Different Topological Materials

The studies of electron transport through a junction of topological materials in the literature so far ignore the coupling of a topological material to its surrounding environment. Here, the dynamics of an open system through a stochastic Hamiltonian are simulated to investigate the influence of the environment on the scattering of electrons by a junction of different topological materials, such as a Dirac–Weyl magnetic junction and a topological insulator. It is found that, although the detrimental effect of the environment is inevitable, the Landauer conductance can be enhanced via adjusting the system–environment coupling strength. This result supplies the possibilty of changing the transport feature of topological materials by modulating the surrounded environment. It is also demonstrated that a non-Hermitian Hamiltonian can be used to replace the stochastic Hamiltonian for this study, when the system and the environment coupling are weak.     

Phase Modulating of Cu–Ni Nanowires Enables Active and Stable Electrocatalysts for the Methanol Oxidation Reaction

The design and development of non-noble metal alternatives with superior performance and promising long-term stability that is comparable or even better than those of noble-metal-based catalysts is a significant challenge. Here, we report the thermal-induced phase engineering of non-noble-metal-based nanowires with superior electrochemical activity and stability for the methanol oxidation reaction (MOR) under alkaline conditions. The optimized Cu–Ni nanowires deliver an unprecedented mass activity of 425 mA mg⁻¹, which is 4.3 times higher than that of the untreated one. Detailed catalytic investigations show that the enhanced performance is due to the large active area, the increased number of active sites (NiOOH), and fast methanol electrooxidation kinetics. In addition, the generated hollow feature in the nanowires provides a unique void space to release the volume expansion, where the activity can be maintained for 5 h without a distinct activity decay. The present work emphasizes the importance of precisely phase modulating of nanomaterials for the design of non-noble metal electrocatalysts towards the MOR, which opens up a new pathway for the design of cost-effective electrocatalysts with promising activity and long-term stability.     

Interfacial Synthesis of a Monolayered Fluorescent Two-Dimensional Polymer through Dynamic Imine Chemistry

A fluorescent monolayered two-dimensional polymer (2DP) containing both tetraphenylethylene (TPE) and imine linkages is synthesized at air-water interface using the Langmuir-Blodgett method. We designed TPE-based monomers with long distances between the TPE and the imine linkages to avoid the charge transfer and therefore keep the fluorescence. A monolayered 2DP provided with more than 104 μm² in domain size and around 0.8 nm thickness was obtained through a successive Schiff base reaction at air-water interface. The nanostructures and fluorescent property of 2DP films were characterized by optical microscopy, SEM, TEM, AFM and fluorescence spectrum. Most importantly, the tip-enhanced Raman spectroscopy (TERS) was utilized here to confirm the success of the polycondensation of monolayered 2DP.     

Enantioselective Synthesis of Acyclic Stereotriads Featuring Fluorinated Tetrasubstituted Stereocenters

Elaboration of enantioenriched complex acyclic stereotriads represents a challenge for modern synthesis even more when fluorinated tetrasubstituted stereocenters are targeted. We have been able to develop a simple strategy in a sequence of two unprecedented steps combining a diastereoselective aldol-Tishchenko reaction and an enantioselective organocatalyzed kinetic resolution. The aldol-Tishchenko reaction directly generates a large panel of acyclic 1,3-diols possessing a fluorinated tetrasubstituted stereocenter by condensation of fluorinated ketones with aldehydes under very mild basic conditions. The anti 1,3-diols featuring three contiguous stereogenic centers are generated with excellent diastereocontrol (typically >99 : 1 dr). Depending upon the precursors both diastereomers of stereotriads are accessible through this flexible reaction. Furthermore, from the obtained racemic scaffolds, development of an organocatalyzed kinetic resolution enabled to generate the desired enantioenriched stereotriads with excellent selectivity (typically er >95 : 5).