同轴集成式宏微驱动器的温升特性及温控方法

同轴集成式宏微驱动器是参考超磁致伸缩驱动器和音圈电机的结构研究出的一种新型宏微一体的高精度驱动器.由于同轴集成式宏微驱动器时释放的热量会对驱动器各个部件产生损耗,降低工作效率,导致其无法正常工作,因此对驱动器的隔磁筒进行优化,分别对比了隔磁钢和尼龙对GMM棒上温度分布均匀性的影响,并且通过COMSOL软件分析了水冷装置对同轴集成式宏微驱动器内部温度分布的作用.从温度分布图可以发现,尼龙隔磁筒对温度均匀性相较于隔磁钢有很大提升,温度分布均匀度仅为0.71％;水冷装置对温度有着很好的控制,温度了下降30％.说明优化结构对驱动器有很大的前景.     

Adhesive failure of sandwich structures under combined fatigue and thermal loading

Adhesive failure of a sandwich beam made of steel and PTFE is studied under thermal and vibration environment. Superposed stresses model is presented in order to predict the effect of the combination environment. Then, the stress distributions are evaluated by an experimental method. Results show that the proposed model is effective for the study of thermal stress. The stress on the steel beam in the initial crack region is slightly low under thermal environment. Vibration excitation generates cyclic loading on the beam and stress distribution exhibits sensitivity to location and loading frequency. It is observed that the high-stress peak will be provided in combined environment. The fatigue crack growth is monitored, and it is shown that the adhesive failure is strongly temperature-dependent with invariable dynamic excitation. High temperature leads to both the high value of stress intensity and an increase in fatigue. Moreover, stick-slip behavior is observed at the interface of adhesive and base plate.     

Damping elastomer with broad temperature range based on irregular networks formed by end‐linking of hydroxyl‐terminated poly(dimethylsiloxane)

Irregular networks based on the condensation reaction of hydroxyl‐terminated poly(dimethylsiloxane) with cross‐linkers were investigated. The networks have excellent damping properties in a wide temperature range utilizing the viscoelastic relaxation of the irregular network with dangling chains. NMR Cross‐link Density Spectroscopy was used to explore the weight fraction of pendant chains and elastic chains in the elastomer. The transverse relaxation time for the elastomer was studied to explore the influence of pendant chains. The effects of the structure of cross‐linkers and the molecular weight of precursors were studied in detail. Elastomers cross‐linked by tetra‐functional cross‐linker (TEOS) have higher damping properties than the elastomers cross‐linked by tri‐functional cross‐linkers (MTMS and OTMS). A damping elastomer based on irregular networks with effective damping (tanδ > 0.3) temperature range of more than 250°C (from lower than ?60°C to 190°C) was prepared. POLYM. ENG. SCI., 56:97–102, 2016. © 2015 Society of Plastics Engineers     

Crystallographic Structure and Ferroelectricity of (AxLa1−x)2Ti2O7 (A = Sm and Eu) Solid Solutions with High Tc

The solubility and ferroelectric properties of (A_xLa_1?x)₂Ti₂O₇ (A = Sm and Eu) solid solutions were investigated. The crystallographic structure of the solid solutions was studied using X‐ray diffraction and Raman spectroscopy. The solubility limits of Eu and Sm in (A_xLa_1?x) ₂Ti₂O₇ were found to be greater than x = 0.5 and 0.8, respectively. The solid solutions had a monoclinic perovskite‐like layered structure (PLS), similar to that of the pure La₂Ti₂O₇, when x was less than the solubility limit. When x was above the solubility limit the materials were biphase. The biphases of (Sm_xLa_1?x)Ti₂O₇ (x = 0.9) consisted of (Sm_xLa_1?x)₂Ti₂O₇ with PLS and pure Sm₂Ti₂O₇ with pyrochlore structure, and the biphases of (Eu_xLa_1?x)Ti₂O₇ (x = 0.6, 0.7, and 0.8) consisted of (Eu_xLa_1?x)₂Ti₂O₇ with PLS structure and La³⁺ doped Eu₂Ti₂O₇ with pyrochlore structure. The effect of A‐site substitution on the properties of La₂Ti₂O₇ was investigated by measuring the dielectric permittivity and loss at different frequencies and temperatures. The highest piezoelectric constant d₃₃ was 2.8 pC/N for (Sm_0.1La_0.9)Ti₂O₇.     

热压工艺对SiCf/Ti复合材料界面反应层生长影响的数值模拟

提出一个热-力-扩散-反应强耦合相场模型来研究热压烧结制备工艺对连续碳化硅纤维增强钛基复合材料中金属间化合物生长规律的影响。模拟结果表明,在两种不同温度下各个界面反应层(Ti₃SiC₂/Ti₅Si₃C_x/Ti₅Si₃C_x+TiC/TiC)的厚度生长与试验值吻合较好。增大外加压力能促进界面层厚度的生长,但对其中抗拉强度最低的Ti₅Si₃层的生长起显著的抑制作用,同时使各界面反应层由周向拉应力状态逐渐转变为压应力。温度的升高使断裂韧度最大的Ti₃SiC₂层厚度增大,但也使总界面层和Ti₅Si₃层的厚度增加。因此,在制备工艺上适当增加压力并选择合适的温度,得到厚度适宜的界面反应层的同时,尽可能使Ti₅Si₃层变薄和Ti₃Si...     

Preparation of hollow SiC spheres by combustion synthesis

Hollow spherical β-SiC was successfully prepared in argon by combustion synthesis using Si powder and polytetrafluoroethylene (PTFE) powder. The phase composition and morphology of spherical products can be controlled by adjusting the Si/C₂F₄ molar ratio (M_Si/(C2F4)). When M_Si/(C2F4) = 3, the phase content of β-SiC is the highest (up to 85.54%), and hollow spherical products obtained; When M_Si/(C2F4) ≥ 5, the Si/SiC microspheres are solid. The synthesis mechanism of hollow β-SiC microspheres is as follows: Si particles react with PTFE releasing heat. Then unreacted Si absorbs heat to form liquid phase microspheres, which is equivalent to the core template to form β-SiC microspheres by reaction with cracked C. Meanwhile, the silicon diffuses from the core to the shell to form the cavity. This method can synthesize the hollow spherical β-SiC in a simple way without prearranged spherical template and long synthesis cycle.     

合成气生物发酵法制乙醇的研究进展

采用合成气生物发酵法制乙醇具有反应条件温和、产物选择性高、原料来源广泛、低碳可持续发展等优势,是一种具有前景的可再生能源新型生产工艺。文章综述了合成气发酵法制乙醇的微生物种类及对应的适宜操作条件,分析了合成气发酵法制乙醇的Wood-Ljungdahl代谢途径;总结了合成气的广泛来源;分析讨论了过程工艺参数如合成气组成及压力、pH、温度、培养基组分、气液传质对合成气发酵的影响;指出合成气发酵法制乙醇面临的底物传质性能差、乙醇收率低等关键问题,比较了典型反应器在传质方面的差异,归纳了传质强化方法;总结了合成气发酵法制乙醇的工业化进展, 并提出了未来的发展方向。     

固体氧化物电池氧离子电解质研究进展

固体氧化物电池(SOCs)作为一种绿色、高效的全固态能量转换装置,既能在燃料电池模式下将氢、碳、烃、醇等燃料的化学能转化为电能,又能在电解池模式下分解水制氢,在缓解全球能源危机、实现碳中和等方面具有重要意义。然而,SOCs常用的Y₂O₃稳定的ZrO₂(YSZ)电解质材料在1 000 ℃以上才具有较高的离子电导率,但过高的工作温度会提高运行成本,限制材料选择,并降低系统稳定性。因此,降低工作温度一直是SOCs发展的核心问题之一,开发高电导率电解质材料和降低电解质膜厚度是实现SOCs中低温化应用的主要路径。本文从材料开发和薄膜制造两方面对中低温SOCs各类氧离子电解质的研究进展进行梳理,针对ZrO₂、CeO₂、Bi₂O₃及LaGaO₃基固体电解质,系统阐述了异价离子掺杂对提升氧离子电导率和稳定相结构的作用机制,介绍了电解质薄膜的制备技术和导电性能,为发展高性能固体氧化物电池电解质材料提供参考依据。     

一种应用于光缆外破在线监控的模式识别方案

电力通信网络线路常因沿途的工程机械施工,人为外力破坏等行为造成毫无预警的危害和损坏。为了实现对线路外破隐患高效预警,需要在现有预警定位的基础上,加上对碰撞敲击、管孔侵入、机械施工和开盖报警等行为的识别。将分布式光纤传感技术、梅尔频率倒谱系数和径向基神经网络相结合,提出一种可应用于光缆外破在线监控的模式识别方案。测试的总体识别率达97.78%,现场模拟的事件报警准确率高。该方案可广泛应用于长距离管线检测领域。     

Stimulations of strontium-doped calcium polyphosphate for bone tissue engineering to protein secretion and mRNA expression of the angiogenic growth factors from endothelial cells in vitro

The vascularization of tissue-engineered bone is the key problem needed solving before application of tissue-engineered bone in clinical practice. Meanwhile, endothelial cells are the major and important source of seed cells in bone tissue engineering, and significant on promoting vascularization in tissue-engineered bone. Vascularization (namely angiogenesis) is a process mainly controlled by several angiogenic growth factors (VEGF, bFGF and MMP-2) which can be secreted by endothelial cells. Therefore, the research on the stimulations of SCPP to the secretion of the angiogenic growth factors from endothelial cells is very important. This study was performed to determine the ability of strontium-doped calcium polyphosphate (SCPP) to induce angiogenesis by detecting the protein secretion levels and mRNA expression of VEGF, bFGF and MMP-2 from cultured endothelial cells. As a control, we also researched the effect of HA on the mRNA expressions and protein secretion of angiogenic growth factors from cultured endothelial cells. We cultured endothelial cells with SCPP scaffolds containing various concentration of strontium and HA. The results obtained in the MTT and SEM tests indicated that endothelial cells on SCPP scaffold exhibited higher proliferation rate and were easy to get a good spread than them on CPP, the best state of growth and proliferation of cells could be observed on 8%SCPP. The results of ELISA demonstrated that the protein levels of VEGF, bFGF and MMP-2 from cultured endothelial cells increased with the increasing Sr doped in calcium polyphosphate in SCPP groups, the peaks appeared on 8%SCPP. All SCPP groups showed a better ability to stimulate the protein secretion of VEGF, bFGF and MMP-2 from endothelial cells relative to CPP group and HA group. The results of RT-PCR suggested that the 8%SCPP group exhibited a significantly higher mRNA expression of VEGF, bFGF and MMP-2 relative to CPP group and HA group. In conclusion, the results of this study demonstrated that 8%SCPP had obvious promotion for secretion and mRNA expression of angiogenic growth factors from cultured endothelial cells.