特种车辆涡轮增压器内部流动特性分析

涡轮增压器是特种动力装备的重要动力部件,良好的密封是保证涡轮增压器正常工作的关键因素,而叶轮高速运转引发的压力不均则是泄漏的重要原因.基于流体力学分析方法建立有限元模型,研究了一种离心泵式密封结构的内部流场分析及流动特性,探讨了压气机端泄漏量、内部压力在不同转速和窄隙出口负压等工况下的变化规律,验证了该密封结构的油气密封性能.结果表明,受高速离心效应影响,该密封结构具备良好的防止压气机端漏油效果,高速运转时会产生漏气.研究结果为改进涡流增压器密封结构提供了参考依据.     

吴友如与晚清小说插图

晚清时期,新的印刷技术——石印术传入我国,石印术的照相技术可以使图画完好无损地得以再现,因此,小说插图的创作再次掀起高潮。吴友如作为晚清时期最有名的风俗画家,主要是为画报绘制插图,同时他也为大量的小说绘制插图。本文以吴友如采用石印术为晚清小说绘制插图为切入点,研究吴友如对于晚清小说插图的贡献。     

一种民间写作的立场

民间写作是指对象、方法、视角均是向下的,指向最底层社会的平民大众,同时指这种民间大众是没有媒介信息能力,没有话语传播能力的,非发声的民间自治的声音。这和主流话语表述的民间话语不一样。民间写作尤其重视民间的发生学,那些受到主流、正统文化压制的语言、行为、事件,甚至包括地方性知识,这需要大量的田野调查,发现一切民间元素相互发生作用的关系史。     

Mechanical and corrosion properties of low-carbon steel prepared by friction stir processing

Low-carbon steel plates were successfully subjected to normal friction stir processing(NFSP) in air and submerged friction stir processing(SFSP) under water, and the microstructure, mechanical properties, and corrosion behavior of the NFSP and SFSP samples were investigated. Phase transformation and dynamic recrystallization resulted in fine-grained ferrite and martensite in the processed zone. The SFSP samples had smaller ferrites(5.1 μm), finer martensite laths(557 nm), and more uniform distribution of martensite compared to the NFSP samples. Compared to the base material(BM), the microhardness of the NFSP and SFSP samples increased by 19.8% and 27.1%, respectively because of the combined strengthening effects of grain refinement, phase transformation, and dislocation. The ultimate tensile strengths(UTSs) of the NFSP and SFSP samples increased by 27.1% and 38.7%, respectively. Grain refinement and martensite transformation also improved the electrochemical corrosion properties of the low-carbon steel. Overall, the SFSP samples had better mechanical properties and electrochemical corrosion resistance than the NFSP samples.     

CoPt-Co hybrid supported on amino modified SiO_2 nanospheres as a high performance catalyst for hydrogen generation from ammonia borane

CoPt-Co hybrids were successfully supported on amino modified SiO_2 nanospheres by a chemical reduction method at a temperature of 278 K.The solid carrier i.e.amino modified SiO_2,provides numerous anchoring sites for the metal nanoparticles(NPs)to improve the dispersion while reducing the size of metal NPs.The supported NPs displayed a narrow particle size distribution on the SiO_2 surface with an average diameter of 12 nm.The XRD results alongside with the binary alloy phase diagram suggest that the resulted NPs are bimetallic,composed of CoPt and amorphous Co.Among the prepared materials,the solid with the specific composition of SiO_2@Pt_(0.1)Co_(0.9)was proved to be effective catalyst for ammonia borane(AB)hydrolysis in aqueous solution.The turnover frequency(TOF)value of the supported nanocatalyst was 25.59mol_(H_2)min~(-1)·mol_M~(-1),almost twice as that of unsupported Pt_(0.1)Co_(0.9)NPs while the activation energy was 37.05 kJ mol~(-1).Furthermore,the SiO_2@Pt_(0.1)Co_(0.9)composite manifested high catalytic activity even after five cycles of reuse.     

基于神经网络动态优化的再入轨迹设计

为解决当飞行器出现破损以及飞行器受干扰时的轨迹优化问题,新一代的再入式飞行器需要有实时在线轨迹优化的能力。神经网络动态优化算法(neural dynamic optimization,NDO)的主要特点是能使神经网络逼近最优解。神经网络动态优化算法可以避免传统的间接法在求解轨迹优化问题时协态变量初值猜测问题。给出了神经网络动态优化的原理,详细介绍了优化流程。仿真结果表明神经网络动态优化算法可以很好的避免协态变量初值猜测问题,具有较强的鲁棒性,能满足实时性要求。     

无人机复垦区植被覆盖度提取方法优选

为探寻无人机遥感对矿业复垦区域植被指数覆盖度的快速提取方法,以四川古蔺某硫磺复垦区为研究对象,通过ZC-6型无人机获取高分辨率遥感影像,采用多种植被指数计算方法作为分类器的选择,使用直方图峰谷法、基本全局阈值法及其融合方法确定图像最佳分割阈值,从而获取研究区植被覆盖度结果.结果表明:不同植被指数分类后的结果有所差异,EXG和VDVI植被指数分类后影像界定较为清晰,而NGBDI指数分类最为模糊;单一直方图峰谷法和基本全局阈值法所得分割结果不理想,而将二者融合后的阈值确定法能结合彼此的优势,弥补灰度不明显或多峰现象的缺点;植被覆盖度(FVC)提取精度显示,基于VDVI提取的人为干预条件下FVC的绝对误差和提取误差分别达到0.0409和7.05％,而基于EXG提取的自然条件下FVC的绝对误差和提取误差分别达到0.0366和6.94％,表明利用VDVI和EXG结合B-H融合的方法可有效用于复垦区条件下的FVC提取.     

近临界紧邻随机游动局部时的重整化极限

Lamperti于1961年证明了在适当条件下, 半直线上一类近临界的紧邻随机游动经过重整化会弱收敛到布朗运动. 考虑过程局部时重整化的极限问题, 运用随机游动的内蕴分枝结构以及非时齐分枝过程重整化极限的结果, 证明了其局部时经过适当的重整化会收敛到布朗运动的局部时.      

爆炸极限实验系统研制及二甲醚/HFC125的可燃性研究

根据ASTM E681-04及ANSI/ASHRAE Standard 34-2007标准,建立了一套全自动可燃性气体爆炸极限实验系统.该系统实际配气比例与设定比例的误差不超过±0.1%,配气比例的不确定度小于0.5%.对几种常见制冷剂的爆炸极限进行了测试,验证了系统的准确性.对二甲醚/HFC125混合气体的爆炸极限进行了实验研究,结果表明,加入HFC125后二甲醚的可燃性范围减小,当HFC125与二甲醚的体积比为4.6时达到临界抑爆点,但HFC125含量较低时对二甲醚的阻燃作用不明显.该测试结果为将二甲醚作为一种环保型制冷剂进行推广应用提供了安全参考.