栅极系统电子返流对离子推力器寿命影响

栅极系统电子返流是离子推力器寿命的主要失效模式之一。以20 cm Xe离子推力器地面运行测试数据为基础,结合离子推力器栅极系统电子返流失效机理,预测了离子推力器在地面测试环境中和空间飞行环境中栅极系统电子返流对寿命的影响。预测结果表明:20 cm Xe离子推力器在地面试验环境中和空间飞行环境中的预期寿命分别为6 600 h和17 000 h。     

车辆驾驶室内噪声建模及分析

驾驶室内噪声是车辆乘坐舒适性的重要指标之一。以某型水泥搅拌车为例,综合考虑驾驶室外噪声源和悬置点振动源的影响,建立较全面的驾驶室声振耦合有限元分析模型。通过有限元仿真分析室内噪声响应和驾驶室结构吸声敏感特性。根据仿真结果提出改进措施,改进前后仿真计算结果与实验测得的结果较为吻合,改进后室内的降噪效果较为理想,降低3 dBA左右,并且低频噪声得到抑制。上述结果充分验证模型和降噪方法的有效性。     

盘景2×4 500 t/d熟料生产线联合粉磨系统介绍

简要介绍了安徽盘景4500t／d熟料生产线采用的由辊压机、V型选粉机和管磨组成的联合粉磨系统及其系统特点;并重点分析介绍了RP170—140辊压机和VRP1200选粉机的结构组成和技术特点。经过有效调整,该项目一期工程的联合粉磨系统已顺利通过了达标达产,其系统产量达到225t／h,水泥电耗≤28kWh／t。     

浅谈常见纤维混凝土的性能与应用

纤维应用于混凝土中具有阻裂、增强、增韧作用,可以有效抵抗微裂纹,改善混凝土的性能,减少应力对混凝土造成的破坏,从而可更好地应用于复杂的施工环境,最大程度地满足施工要求。纤维混凝土常用的纤维有钢纤维、碳纤维、聚丙烯纤维、玄武岩纤维和玻璃纤维等,不同纤维混凝土有着不同性能。具体工程中应根据使用要求,选择适当的纤维混凝土,从而达到最佳的施工效果。     

Inverse synthetic aperture radar range profile compensation of plasma-sheath-enveloped reentry object

The scattering points in a plasma sheath characterized with coupled velocities can cause pulse compression mismatching, which results in displacement and energy diffusion in the one-dimension range profile. To solve this problem, we deduce the echo model of the plasma-sheath-enveloped reentry object. By estimating the coupled velocities, we propose a compensation method to correct the defocus of an inverse synthetic aperture radar (ISAR) image in range dimension to improve the quality of the ISAR images. The simulation results suggest that the echoes from different regions of the surface of the reentry object have various coupling velocities, and the higher the coupled velocity, the more serious the displacement and energy diffusion in the range dimension. Our proposed method can correct the range dimension aberration. Two measurement metrics were used to evaluate the improvement of the compensation method.     

Wideband radar cross-section reduction using plasma-based checkerboard metasurface

For stealth technology, in order to overcome the limitations of thin-layer plasma for electromagnetic waves attenuation and further broaden the radar cross-section (RCS) reduction (RCSR) band of the metasurface, the plasma-based checkerboard metasurface composed of plasma and checkerboard metasurface is investigated to achieve better RCSR. We designed a checkerboard metasurface which can achieve abnormal reflection to reduce RCS and whose −10 dB RCSR bandwidth is from 8.1 to 14.5 GHz, the RCSR principle of it lies in the backscattering cancellation, which depends on the phase difference of artificial magnetic conductor (AMC) units. The designed plasma-based checkerboard metasurface is a thin composite structure, including a checkerboard metasurface, a plasma layer, and an air gap which is between them. Full wave simulations confirm that the plasma-based checkerboard metasurface's ‒10 dB RCS reduction bandwidth and RCS reduction amplitude, are both increased under different polarized waves compared with the only single plasma or the only metasurface. We also introduced the reason and mechanism of the interaction between plasma and the checkerboard metasurface to improve the RCSR effect in detail. As plasma-based checkerboard metasurface does not need the plasma to be too thick for plasma stealth, its application in practical scenarios is easier to implement.     

螺灭杀离心工序工艺及设备优化

对某公司螺灭杀离心工序进行工艺及设备优化后,有效解决了生产的安全环保问题,同时降低了生产成本并提高了自动化生产水平。优化后的工艺和设备可在间歇性生产过滤工序、老旧设备升级等精细化工车间推广。     

建筑材料石膏模盒中氟和磷含量的测定简

在建筑材料中广泛使用石膏模盒因含有磷、氟、有机物等杂质而导致水化时间延长、强度降低等问题.采用标准曲线法对石膏模盒样品中氟和磷的含量进行了测定.     

PVB/KH-560协同改性聚氨酯的合成及膜性能

以聚醚丙二醇(PPG600)、IPDI(异佛尔酮二异氰酸酯)、γ-缩水甘油醚氧丙基三甲氧基硅烷(KH-560)为主要原料,DMPA(2,2-二羟甲基丙酸)扩链合成支链型Si-WPU(硅氧烷水性聚氨酯)预聚体,再与PVB(聚乙烯醇缩丁醛)键合得到协同改性水性聚氨酯(PVB-Si-WPU)乳液,制备成膜。采用FT-IR(红外光谱)和TG(热重分析)法对胶膜进行表征,考察了R(—NCO/—OH)值和KH-560、PVB含量对乳液或胶膜性能的影响。研究结果表明:KH-560和PVB接枝到WPU分子链后,胶膜热稳定性得到一定提高;R值=2.6时,拉伸强度达到5.4 MPa,断裂伸长率降至237%;当KH-560和PVB添加量的质量分数分别等于6%和2%时(相对于纯WPU胶膜),PVB-Si-WPU胶膜的拉伸强度、断裂伸长率分别增长3.78、2.01倍,吸水率由38.0%降到15.4%。可见,KH-560和PVB的引入提高了WPU乳液的综合性能。     

板料成形拉延筋技术研究现状

拉延筋在汽车覆盖件拉深成形中起着十分重要的作用。利用拉延筋可以调节和控制板料的变形程度和变形分布,抑制破裂、起皱、面畸变等多种冲压质量问题的产生。在很多情况下,拉延筋的设置合理与否将决定覆盖件拉深的成败。较系统地总结了板料成形拉延筋技术以及拉延筋作用原理、阻力模型、影响因素等的研究现状。