干燥工艺对微波复合介质基板性能的影响

该文采用聚四氟乙烯(PTFE)树脂为基体,熔融SiO_2作为填料,通过机械混合、压延成型、热压烧结工艺制备出高频高速电路用微波复合介质基板,重点研究了采用不同干燥工艺对复合物结构、微波介电性能的影响。实验表明,采用旋转蒸干工艺对复合物进行处理时,可在较短的时间内去除有机物质,并能使无机填料与聚合物分散均匀。经热压烧结后,所得基板相对介电常数为2.92~2.94,损耗因子为1.3×10~(-3)。     

Multi-temporal InSAR for Urban Deformation Monitoring:Progress and Challenges

Multi-temporal Interferometric Synthetic Aperture Radar(MT-InSAR) is one of the most powerful Earth observation techniques, especially useful for measuring highly detailed ground deformation over large ground areas. Much research has been carried out to apply MT-InSAR to monitor ground and infrastructure deformation in urban areas related to land reclamation, underground construction and groundwater extraction.This paper reviews the progress in the research and identifies challenges in applying the technology, including the inconsistency in coherent point identification when different approaches are used, the reliability issue in parameter estimation, difficulty in accurate geolocation of measured points, the one-dimensional line-of-sight nature of InSAR measurements, the inability of making complete measurements over an area due to geometric distortions, especially the shadowing effects, the challenges in processing large SAR datasets, the decrease of the number of coherent points with the increase of the length of SAR time series, and the difficulty in quality control of MT-InSAR results.     

西门子S7-PLCSIM对PLC程序的仿真

介绍了S7-PLCSIM这种新仿真软件的特点。说明如何使用此软件模拟S7—300和S7-400PLC的运行，及实现PID调试工具和组态软件WinCC的离线调试。此仿真软件为技术人员调试程序带来方便。     

测地学中的不可逆性──混沌特性之一

在对非线性科学深入研究过程中，曾派生分支出混沌学、协同学、分形理论和耗散理论等，其中，它们内涵着多种特性，包括不可逆性。在地学、测地学中，亦有大量地质现象具不可逆性，如把它们与混沌理论结合，相信我们对许多问题的认识定会有质的升华。     

Greatly improved elevated-temperature cycling behavior of Li1+xMgyMn2−x−yO4+δ spinels with controlled oxygen stoichiometry

A new type of oxygen stoichiometric and Mg-doped LiMn₂O₄ spinel with improved crystallinity and decreased surface area was synthesized by a special “two-step” method: first, calcinate the mixture of metal oxides at “ultra-high” temperatures (950-1100 °C) to obtain an intermediate product with improved crystallinity, larger particle size and oxygen defects; then, anneal the intermediate at relatively low temperatures (600-800 °C) with the addition of extra LiOH to achieve oxygen stoichiometry. These spinels with general formula Li_1+xMg_yMn_2−x−yO_4+δ or (Li, Mg, Mn)₃O_4+δ are oxygen-rich based on chemical analysis (O/(Li+Mg+Mn) ratio larger than 4:3), and they can be called oxygen stoichiometric spinels with metal cation vacancies and rewritten as [Li]_8a[Li_nMg_mMn_{2−n−m−p}□_p]_16d[O₄]_32e. This new kind of materials with controlled oxygen stoichiometry exhibited greatly improved cycling performance and reduced Mn dissolution at elevated temperatures over that of other Mg-doped materials prepared by conventional “one-step” method.     

涡带工况下混流式水轮机转轮动应力特性分析

近年来,国内一些大型混流式转轮出现了不同程度的裂纹问题,对机组安全运行构成了威胁。研究表明,水力激励引起的混流式水轮机转轮叶片动应力是引起叶片疲劳破坏的主要原因之一。文中首先对高水头小负荷的涡带工况下混流式水轮机内流场进行非定常CFD计算,得到涡带工况下叶片表面不同时刻的水压力载荷,并利用流固耦合方法对转轮进行结构场瞬态特性计算,分析转轮叶片的动应力特性。结果表明由于水压力脉动引起的转轮叶片上的振动交变动应力是混流式水轮机疲劳破坏的主要原因之一。计算结果可为其它水轮机转轮的动应力特性分析和疲劳分析提供参考。     

Nanostructural CoSnC anode prepared by CoSnO3 with improved cyclability for high-performance Li-ion batteries

Stannate, CoSnO₃, which mixes the elements Co and Sn evenly at the atomic level, was used as precursor to prepare CoSnC by a modified carbothermal reduction method. The synthesis process was characterized by differential thermal analysis (DTA) and X-ray diffraction (XRD). The particle feature was evaluated by transmission electron microscopy (TEM). The results indicated the as-prepared composite has a well-coated carbon layer that effectively prevents the encapsulated, low melting point alloy from out-flowing in a high-temperature treatment process. In addition, this structure, CoSn_x grains surrounded by carbon, prevents aggregation and pulverization of nanosized, tin-based alloy particles during charge/discharge cycling and improves the cycling stability of the alloy. The synthesized CoSnC integrates the merits of intermetallic compounds and nanosized anode materials and delivers a reversible capacity of 450 mA h g⁻¹ with a capacity retention of 72% after 50 cycles.     

Nonlinear vibration induced by the water-film whirl and whip in a sliding bearing rotor system

Many industrial applications and experiments have shown that sliding bearings often experience fluid film whip due to nonlinear fluid film forces which can cause rotor-stator rub-impact failures. The oil-film whips have attracted many studies while the water-film whips in the water lubricated sliding bearing have been little researched with the mechanism still an open problem. The dynamic fluid film forces in a water sliding bearing are investigated numerically with rotational, whirling and squeezing motions of the journal using a nonlinear model to identify the relationships between the three motions. Rotor speed-up and slow-down experiments are then conducted with the rotor system supported by a water lubricated sliding bearing to induce the water-film whirl/whip and verify the relationship. The experimental results show that the vibrations of the journal alternated between increasing and decreasing rather than continuously increasing as the rotational speed increased to twice the first critical speed, which can be explained well by the nonlinear model. The radial growth rate of the whirl motion greatly affects the whirl frequency of the journal and is responsible for the frequency lock in the water-film whip. Further analysis shows that increasing the lubricating water flow rate changes the water-film whirl/whip characteristics, reduces the first critical speed, advances the time when significant water-film whirling motion occurs, and also increases the vibration amplitude at the bearing center which may lead to the rotor-stator rub-impact. The study gives the insight into the water-film whirl and whip in the water lubricated sliding bearing.     

考虑迟滞行为的重型车辆轮胎原地转向阻力矩研究

重型车辆原地转向阻力矩是影响其转向系统设计与控制性能的关键参数之一,精确可靠的阻力矩模型对提升转向驱动系统的设计水平、稳定性与控制能力有重要作用。为建立可精确复现实际转向工况的阻力矩模型,将轮胎转向时胎面单元变形产生的弹性迟滞摩擦力与Maxwell迟滞模型结合,提出考虑轮胎迟滞行为的原地转向阻力矩模型,可对轮胎任意换向下的阻力矩进行有效预测。基于重型车辆单轴转向系统测试台,试验探究转向频率、转向角幅值和垂直载荷对阻力矩的影响规律;基于典型迟滞行为设计系统转向角输入,明确原地转向阻力矩模型对擦除特性、多值特性、同余特性和返回点记忆性的复现能力与其实际迟滞行为。试验结果表明,该模型可以复现擦除特性、同余特性和多值特性的典型迟滞行为,这与标准迟滞系统一致,具有普遍性,但重型车辆转向阻力矩在返回点记忆特性上存在特殊性,即仅在轮胎回转角大于蓄力角度时才表现出良好的返回点记忆特性。综上可为重型车辆原地转向阻力矩研究提供有价值的模型参考。