Magnetic properties and local structure studies of Zn doped ferrites

A series of nano-particle zinc-doped ferrites samples Zn_xFe_3 − xO₄ (x = 0, 0.17, 0.33, 0.50, and 0.67) were prepared with the hydrothermal method, and the effects of Zn doping on the magnetic properties and local structures of the samples were studied. By increasing zinc content from 0 to 0.33, the saturated magnetization M_s measured with the vibrating sample magnetometry (VSM) method increases, while it decreases by further Zn doping. The experimental results of extended X-ray absorption fine structure (EXAFS) show that most of dopant Zn atoms occupy A site, and only a few Fe atoms at B site are substituted by Zn atoms. The Neel's two-sublattice model and the molecular field analysis of Yafet–Kittel (Y–K) spin-ordering using the three-sublattice model are compared to explain the experimental phenomena. The Y–K angle between the magnetic moments at A and B sublattices is found changing due to the decrease of A–O–B exchange interaction, which shows that the magnetic moments at B site are no longer rigidly parallel to the few remained magnetic moments at A site.     

Effects of heat input on the low power Nd:YAG pulse laser conduction weldability of magnesium alloy AZ61

The effects of heat input on the low power Nd:YAG pulse laser conduction weldability of magnesium alloy AZ61 plates were investigated. The results show that for a hot-extruded AZ61 magnesium alloy plate laser conduction welding, the penetration depth and area of welds cross-section increased with an increase of the heat input. The microstructure of a band zone, which is located in the fusion zone (FZ) and close to the fusion boundary, evolved with an increase of the heat input. Moreover, an increase of the heat input increased the tendency of the formation of solidification cracking and liquation cracking. The porosities and average diameters of pores increased with an increase of the heat input but reduced sharply when a relatively large heat input was achieved. In addition, the degree of formation of craters increased linearly with an increase of the heat input.     

Resistive switching of silicon-rich-oxide featuring high compatibility with CMOS technology for 3D stackable and embedded applications

This paper discusses the resistive switching devices based on highly compatible silicon-rich-oxide, including silicon monoxide (SiO) and SiO _x N _y material, which can be fabricated by low temperature process, and thus fully compatible with the back-end CMOS technology. The demonstrated SiO based RRAM suitable for 3D stackable applications shows repeatable unipolar resistive switching behavior with excellent on/off resistance ratio and good retention performance, but a little bit high switching voltage. The presented silicon-rich silicon-oxynitride RRAM device can effectively reduce the switching voltages (∼1 V) and shows good retention capability under 180°C baking as well as fast speed, giving great potentials for 3D stackable and embedded applications. The switching mechanisms in the studied devices are discussed. The method of switching voltage reduction through nitrogen doping, as a kind of defect engineering, can provide some guidelines for RRAM design.     

硅胶及其负载酸在糖化学中的应用研究进展

硅胶及其负载酸在有机合成中有着极其广泛的应用.结合我们的研究工作,系统综述了硅胶及其负载酸在糖化学中的应用研究进展.主要内容包括它们在糖苷化、官能团转化以及水解反应方面的应用.     

Effect of the optimal velocity function on traffic phase transitions in lattice hydrodynamic models

The original lattice hydrodynamics models of traffic flow are extended to take into account the complex acceleration behavior of drivers. A new optimal velocity function which considers the stepwise acceleration effect and fits the observed data better is introduced. The stability conditions of these two models are obtained by using the linear stability theory. It is shown that the modified optimal velocity function has a remarkable influence on the neutral stability curve and the traffic phase transitions. In a certain vehicle’s density and driver’s sensitivity region, tri-stable states will occur. In addition, the properties of the multiple phases also depend on the asymmetry of the optimal velocity function and the stage number of multi-phase transitions is closely related to the turning points of the optimal velocity function. The validity and correctness of the analytical results is confirmed by numerical simulations.     

Superhard nitride-based nanocomposites: role of interfaces and effect of impurities

Recently, a hardness similar to that of diamond has been reported for a quasiternary, nitride-based nanocomposite. The related, quasibinary nanocomposite "nc-TiN/a-Si3N4," which may be regarded as the prototype of the family of superhard nc-metal-N/a-Si3N4 systems, also exhibits a significant hardness enhancement. Extensive density-functional theory calculations indicate that the superhardness is related to the preferential formation of TiN(111) polar interfaces with a thin beta-Si3N4-derived layer. The strength of TiN in the 111 direction is similar to that of the weakest bonding direction in diamond. Oxygen impurities cause a significant reduction of the interface strength.     

垂直轴风机的结构受力分析及其优化

风力发电机的应力分析是保障其安全运行乃至结构设计的基础．垂直轴风机的支撑结构一般都是超静定的,主要承受风载及高速旋转引起的离心力,因此对风轮重量有严格的要求．在结构总体设计时必须先对其进行力学分析,并进行受力优化,才能进行详细的零部件设计,数值分析往往只在设计基本定型后才能进行．一些风机在大风时发生飞车事故,其原因都是因为结构受力不合理导致关键部位应力过大或强度不足所引发的．本文针对垂直轴风机叶片和支撑系统,首先对支点位置进行优化,并推导出叶片、支撑杆、斜拉索等的受力公式,为此类部件的设计提供广适性的力学方法,并对垂直轴风机的一些关键安全性问题进行讨论．     

Metallic Single‐Unit‐Cell Orthorhombic Cobalt Diselenide Atomic Layers: Robust Water‐Electrolysis Catalysts

The bottleneck in water electrolysis lies in the kinetically sluggish oxygen evolution reaction (OER). Herein, conceptually new metallic non‐metal atomic layers are proposed to overcome this drawback. Metallic single‐unit‐cell CoSe₂ sheets with an orthorhombic phase are synthesized by thermally exfoliating a lamellar CoSe₂‐DETA hybrid. The metallic character of orthorhombic CoSe₂ atomic layers, verified by DFT calculations and temperature‐dependent resistivities, allows fast oxygen evolution kinetics with a lowered overpotential of 0.27 V. The single‐unit‐cell thickness means 66.7 % of the Co²⁺ ions are exposed on the surface and serve as the catalytically active sites. The lowered Co²⁺ coordination number down to 1.3 and 2.6, gives a lower Tafel slope of 64 mV dec^?1 and higher turnover frequency of 745 h^?1. Thus, the single‐unit‐cell CoSe₂ sheets have around 2 and 4.5 times higher catalytic activity compared with the lamellar CoSe₂‐DETA hybrid and bulk CoSe₂.     

基于行为动力学的智能机器人导航行为演化研究

运用非线性微分方程动力系统稳定性和分岔理论,通过行为状态变量定义了机器人奔向目标行为和避障行为两种行为模式;将两种行为相结合,与控制各行为权值的行为模式模型一起构成了基于动态方法的智能机器人行为动力学模型.分析了机器人导航中行为状态变量及参数的演化规律,通过计算机实例仿真,验证了该方法应用于机器人导航的可行性.