压剪复合冲击下氧化铝陶瓷的剪切响应实验研究

通过对92.93%氧化铝陶瓷进行倾斜板碰撞实验,研究了多晶陶瓷材料在压剪复合冲击下的非弹性变形响应和剪切波传播规律。压剪复合冲击实验由57 mm开槽气体炮驱动铜飞片对陶瓷靶板加载,通过试件内埋植的电磁速度计来测量内部质点速度历程。将纵向粒子速度从感应电动势曲线中分离后得到横向粒子速度历程,发现在压剪复合冲击下由于材料剪切刚度的降低而引起的剪切波衰减。冲击软回收试件的扫描电子显微镜（SEM）观察表明,冲击载荷低于屈服强度时,多晶氧化铝陶瓷中存在沿晶界、气孔的微裂纹成核与扩展,在高于屈服强度的冲击加载下进一步产生了穿晶微裂纹,微裂纹系统导致了材料在卸载后的显著的体积膨胀。     

对本科工科概率统计教学的探索与思考

本科工科概率统计教学是我国工科数学教育中备受关注的一个重要问题,本文从加强教材建设、改善师资队伍的博士化率、提高教师学术水平、建设信息技术平台来改善教学手段和方法、增强教师的教学理论水平等五个方面论述了它们对提高本科工科概率统计教学水平的重要性和迫切性.     

Computational design and simulation of the Mg-Cu system graded density impactors for complex loading experiments

Two types of Mg-Cu composition system graded density impactors used for complex loading (shock loading and quasi-isentropic compression) are designed by the elastic-plastic hydrodynamic method in this paper. Mixtures of metal powders in the Mg-Cu system are cast into a series of 17 and 25 uniform compositions ranging from 100% Mg to 100% Cu. The graded density impactors are launched to the stationary 10 m aluminum film and 12 mm LiF window targets by a two-stage light-gas gun in the National Key Laboratory ...     

A convenient dynamic loading device for studying kinetics of phase transitions and metastable phases using symmetric diamond anvil cells

We have designed and implemented a novel DLD for controlling pressure and compression/decompression rate. Combined with the use of the symmetric diamond anvil cells (DACs), the DLD adopts three piezo-electric (PE) actuators and three static load screws to remotely control pressure in accurate and consistent manner at room temperature. This device allows us to create different loading mechanisms and frames for a variety of existing and commonly used diamond cells rather than designing specialized or dedicated diamond cells with various drives. The sample pressure compression/decompression rate that we have achieved is up to 58.6/43.3?TPa/s, respectively. The minimum of load time is less than 1?ms. The DLD is a powerful tool for exploring the effects of rapid (de)compression on the structure of materials and the properties of materials.     

Pultruded Kenaf Fibre Reinforced Composites: Effect of Different Kenaf Fibre Yarn Tex

Manufacturing high performance composites from natural fibres is one of an ambitious goal currently being pursued by researchers across the globe. The ecological benefits of this material among many others are environmentally friendly and do not cause health problems. In terms of sustainability, the natural fibre is an appropriate alternative candidate to replace the synthetic and other types of reinforcement since it is a renewable resource. In order for natural fibre reinforced composite to become competitive, it has to accommodate the processing avenues of which has long being associated with its synthetic counterpart. Among those proven technology in manufacturing advanced engineering component is pultrusion. In this paper, an attempt has been made to produce pultrudedkenaf fibre reinforced unsaturated polyester composites via pultrusion. The properties of the pultrudedkenaf fibre reinforced composites with different kenaf yarn sizes are reported and compared. Pultruded composites made with smaller tex number i.e. tex 1400 shows better compression properties of as compared to larger tex number. Smaller tex number help to produce better wetting on fibre during production of composites, consequently help to increase its properties. Pultruded composites made with smaller tex number i.e. tex 1400 shows better compression properties of as compared to larger tex number. Smaller tex number help to produce better wetting on fibre during production of composites, consequently help to increase its properties.     

Controllable synthesis of high loading LiFePO4/C nanocomposites using bimodal mesoporous carbon as support for high power Li-ion battery cathodes

Mesoporous LiFePO₄/C composites containing 80 wt% of highly dispersed LiFePO₄ nanoparticles (4–6 nm) were fabricated using bimodal mesoporous carbon (BMC) as continuous conductive networks. The unique pore structure of BMC not only promises good particle connectivity for LiFePO₄, but also acts as a rigid nano-confinement support that controls the particle size. Furthermore, the capacities were investigated respectively based on the weight of LiFePO₄ and the whole composite. When calculated based on the weight of the whole composite, it is 120 mAh·g^?1 at 0.1 C of the high loading electrode and 42 mAh·g^?1 at 10 C of the low loading electrode. The electrochemical performance shows that high LiFePO₄ loading benefits large tap density and contributes to the energy storage at low rates, while the electrode with low content of LiFePO₄ displays superior high rate performance, which can mainly be due to the small particle size, good dispersion and high utilization of the active material, thus leading to a fast ion and electron diffusion.     

Crack Patching: Analysis and Design

Bonded composite patches are frequently used to retard crack growth. This repair procedure is usually referred to as crack patching. The present paper outlines the various methods for the analysis and design of fiber composite patches in thin and thick structures. As illustrative examples the repair of fatigue cracks in the wing skins of Mirage III aircraft, of surface flaws in Macchi landing wheels, and of cracks in a truss is considered.     

Organocatalytic Enantioselective Mukaiyama–Mannich Reaction of Isatin-Derived Ketimines for the Synthesis of Oxindolyl-β3, 3-Amino Acid Esters

Mukaiyama–Mannich reactions of ester enolate equivalents with aldimines have been elegantly used for the asymmetric synthesis of β-amino acids; nevertheless, the corresponding asymmetric reaction employing ketimines are unexplored. Herein, the first organocatalytic enantioselective Mukaiyama–Mannich reaction employing isatin-derived ketimines with unsubstituted silyl ketene acetals is disclosed towards the scalable synthesis of 2-oxoindolinyl-β^{3, 3}-amino acid esters at room temperature with excellent enantioselectivities (ee >99.5 %). Ultra-low catalyst loadings (as low as 250 ppm) could be used for the quantitative product formation with high enantiopurity. The synthetic utility of this protocol has been showcased in the short formal synthesis of pharmaceutically demanded (+)-AG-041R, a potent gastrin/CCK-B receptor antagonist.     

The effect of Pt nanoparticles distribution on the removal of cyanide by TiO2 coated Al-MCM-41 in blue light exposure

With an aim to enhance the photocatalytic activity, Pt loaded TiO₂–Al-MCM-41 catalysts with high surface area were synthesized by a multistep route. The waste of the rice processing, rice husk (RH), was used as the precursor for the extraction of silica. The diffuse reflectance and photoluminescence spectroscopy revealed the extension of the absorption edge in the visible region and exciton trapping nature of the dispersed platinum. The structural analysis was carried out by XRD, whereas X-ray photoelectron spectroscopy identified the chemical states of the components of the synthesized powders. The BET surface area measurements revealed the reduction in the surface area and pore volume with the increasing platinum loading. TEM micrographs showed the uniform distribution of TiO₂ and Pt nanoparticles at the surface of Al-MCM-41. The photocatalytic efficiency of the synthesized powders as photocatalysts was obtained for the removal of 100 ppm CN⁻ from aqueous solution in fluorescent blue light exposure. Compared to unsupported TiO₂, the Pt-loaded catalysts exhibited substantially high activity for the removal of CN⁻. A plausible mechanism for the removal of cyanide ions was proposed. The catalysts showed excellent stability and reproducibility in the successive use.     

眼科病床安排的优化模型

根据不同类型眼科病人手术时间的限制情况,建立了入院安排的整数规划模型,通过具体计算结果定量分析了模型的使用情况.运用统计分析方法给出病人大致入院时间,并建立使所有病人在系统内平均逗留时间最短的病床比例分配模型.