Thin-Shell Structure of Nanometal Particles

As is well known, the rare-earth and transition-metal elements are the main active components in catalysis because of their special d and f electron structures. In our laboratory, a type of nanometer particle of a transition metal with a rare-earth outer shell was synthesized by a hydrogen arc plasma method, and their microstructures were analyzed by TEM and an X-ray diffraction profile refinement method. The nanoparticles were used as a catalyst in some chemical reactions. The catalytic activities of the nanometer particles with and without a rare-earth thin shell were evaluated by means of the catalytic reactions of toluene, nitrobenzene hydrogenation, and carbon monoxide oxidation. The results of these chemical reactions demonstrated that the nanometer transition metal particles with a rare-earth outer shell possess much higher catalytic activity and selectivity than those particles without a rare-earth outer shell. This means that the rare-earth shell plays an important role in these chemical reactions. This catalytic mechanism of the rare-earth shell is discussed.     

High optical quality ZnO films grown on graphite substrate for transferable optoelectronics devices by ultrasonic spray pyrolysis

ZnO thin films were deposited on graphite substrates by ultrasonic spray pyrolysis method. The effects of substrate temperature and film thickness on the crystalline structure, morphology, and optical properties of the as-grown ZnO films were investigated systemically. Results illustrated that dense ZnO films with hexagonal wurtzite structure were uniformly distributed on the substrate. Strong near-band edge ultraviolet (UV) emission peaks were observed in room temperature photoluminescence (PL) spectra for the samples prepared under optimized parameters, yet the usually observed defect related deep level emissions were nearly undetectable, indicating high optical quality ZnO films could be achieved via this easy process under optimal conditions. The successful growth of polycrystalline ZnO films on graphite offers the significant opportunity to be readily transferred onto any rigid or flexible foreign substrates, since the graphite substrates consist of weakly bonded layer structure.     

2A12铝合金板焊接裂纹分析

研究了CZ状态的铝合金板在退火时退火工艺对机械性能和原始组织的影响,继而对焊接性能产生影响,以及焊接的连接方式对铝合金焊接性能的影响,分析了2A12铝合金板材在焊接时出现裂纹的原因,并提出了解决方法.     

Dynamic response of ultralight all-metallic sandwich panel with 3D tube cellular core to shallow-buried explosives

The underbody of a vehicle system, either military or civil, is typically made of a relatively thin metallic plate, thus vulnerable to mine blast attacks. To improve the blast resistance, a multitude of protective structures have been proposed as attachments to the thin plate. In the present study, a novel ultralight all-metallic sandwich panel with three-dimensional(3D) tube cellular cores mounted to the vehicle underbody was envisioned as such a protective system. A metallic substrate(mimicking vehicle bottom)was placed above the proposed sandwich panel to construct a sandwich-substrate combinative structure. A series of sandwich panels having 3D tube cellular cores were fabricated via argon protected welding and laser welding. Mechanical responses of the combinative structure subjected to the denotation of 6 kg TNT explosives shallow-buried in dry sand were experimentally measured. Full numerical simulations with the method of finite elements(FE) were subsequently carried out to explore the physical mechanisms underlying the observed dynamic performance and quantify the effects of key geometrical parameters and connection conditions of the protective system. The performance of the proposed sandwich panel under shallow-buried explosives was also compared with competing sandwich constructions having equal mass. Finally, a preliminary optimal design of the 3D tube cellular core was carried out.     

基于精确序列模式的网页个性化推荐

Web个性化系统的目标是为用户提供他们想要的或需要的信息,而不必明确询问用户的需求。传统推荐系统的方法是直接收集服务器日志作为Web使用数据,通过分析用户的行为模式,挖掘出用户的兴趣、偏好,然后将系统认为是与用户相关的网页链接向用户推荐。本文应用新的方法——远程代理收集Web使用数据,为数据预处理提供了方便,并提出了精确序列模式的方法进行Web页面推荐,扩展了N—Gram,从而分别提高了网页推荐的准确率和覆盖率。