23Co14Ni12Cr3Mo超高强度钢DCB试样在3.5%NaCl溶液中的应力腐蚀开裂行为

23Co14Ni12Cr3Mo超高强度钢具有优异的强韧性配合,逐步取代现役的超高强度钢,被广泛地应用于起落架等航空关键承力构件中。研究了23Co14Ni12Cr3Mo超高强度钢的应力腐蚀开裂(SCC)行为,对该材料的安全可靠应用具有重要的意义。采用双悬臂(DCB)试样研究了23Co14Ni12Cr3Mo超高强度钢在3.5%NaCl溶液中的SCC分叉行为,为该材料在航空航天领域安全可靠地使用提供了理论数据。采用扫描电子显微镜(SEM)对试验开裂后的断口形貌进行了表征,采用X射线电子衍射技术(XRD)结合能谱(EDS)技术对腐蚀产物进行分析。结果表明应力腐蚀裂纹扩展分叉,断口形貌在裂纹扩展前期、中期和后期分别为穿晶(TG)形貌、穿晶伴随沿晶(IG)形貌并含有二次微裂纹以及沿晶脆性断裂。该超高强度钢腐蚀产物主要包括Fe、Cr、Co的氧化物,结合Co、Cr、Ni、Mo在应力腐蚀过程中的变化,讨论了裂纹扩展分叉机理。     

F3 layer feature under low and medium solar activity observed at a Chinese low latitude station Fuke

Ionogram observations from the ionosonde at Fuke (9.5°N geomagnetic latitude), a Chinese low latitude station, in 2010–2012 are analyzed to present the features of F3 layer under low and moderate solar activity conditions. Structure of the ionogram, displaying the F3 layer, was more distinct and clear during MSA than LSA periods especially during spring to summer. Start time of occurrence of the F3 layer is about at 0830–0900 LT and is approximately the same for LSA and MSA conditions. The average duration time of the F3 layer occurrence was 181 min per day under F_10.7 = 75 condition, 263 min in F_10.7 = 99 and 358 min in F_10.7 = 125, respectively. The differences of h′F2 and h′F3 exhibited obvious semiannual variation observed at Fuke from March 2010 to June 2012 and increased with increasing solar activity. The difference of foF2 and foF3 in the months February, March, September, October and November is less evident in the middle solar activity period 2011–2012 than the low solar activity 2010 and in the other period it shows a slight increase (0.5 MHz) or keeps constant. The results show that the solar activity dependence of the F3 layer occurrence at low latitude away from the magnetic equator is different from that at near the magnetic equator.     

太阳F10.7指数准27天振荡的小波分析

利用1956-2003年的F10.7日均值数据,采用Morlet小波变换方法,分析了准27天振荡的特征及与太阳活动11年周期(Schwabe周期)的关系.结果表明,F10.7的准27天振荡的幅度和周期存在明显的短期变化现象,不同年里变化的程度差别很大,有些年里起伏非常剧烈,在几天到几十天的很短时间里,幅度变化达十几倍,周期可变化数天,甚至发生十几天的突变;有些年里,幅度变化很大但起伏很小,周期也比较稳定.准27天振荡的年平均幅度存在明显的逐年变化,与太阳活动显著相关.一般说来,F10.7越高,准27天振荡的幅度就越大,然而在太阳活动19周峰年,F10.7比其他活动周的值都高,但准27天振荡的幅度却比其他活动周低.准27天振荡的周期也有明显的逐年变化,除了个别年(如1987年),年平均周期在24至31天之间变化,与太阳活动周期没有明显的关系.48年的平均周期为27.3天.从总体看,周期有逐渐缩短的趋势,48年里周期大约减少了1.5天.造成准27天振荡起伏的因素非常复杂,有待深入研究.      

00Cr17Ni14Mo2不锈钢的性能研究

本文研究了00C r17N i14Mo2不锈钢材料的的性能,证明其具有很好的机械性能、焊接性能和耐腐蚀性能,从用户和研究开发的角度探讨了其在压力容器、化工装置等领域的应用。     

铝合金与不锈钢的连接技术

阐述了钎焊、摩擦焊技术在铝合金与不锈钢连接中的应用情况.此外,介绍了液相扩散连接、爆炸焊、超声波焊、表面活化连接等新型连接技术.     

KM6低温泵新型测温系统研制

低温泵是KM6环境模拟器最主要的高真空获得设备,其二级冷头(板)的温度变化对低温泵的抽气性能有直接的影响,因此对低温泵内部实施全面、准确的温度监测对于保障低温泵的稳定、可靠运行具有重要的意义。文章详细介绍了新研制的低温泵测温系统的软、硬件结构、测温元器件的选型及安装工艺、系统测试等内容。该新型测温系统已经成功投入使用,能够准确地提供试验过程中低温泵内部的温度状况,大大提高了低温泵运行异常时的分析手段,为试验的顺利进行提供了有力的保障。     

Validity assessment of SAMOSA retracking for fully-focused SAR altimeter waveforms

We demonstrate in this work how we can take advantage of known unfocused SAR (UF-SAR) retracking methods (e.g. the physical SAMOSA model) for retracking of fully-focused SAR (FF-SAR) waveforms. Our insights are an important step towards consistent observations of sea surface height, significant wave height and backscatter coefficient (wind speed) with both UF-SAR and FF-SAR. This is of particular interest for SAR altimetry in the coastal zone, since coastal clutter may be filtered out more efficiently in the high-resolution FF-SAR waveform data, which has the potential to improve data quality. We implemented a multi-mission FF-SAR altimetry processor for Sentinel-3 (S3) and Sentinel-6 Michael Freilich (S6), using a back-projection algorithm, and analysed ocean waveform statistics compared to multilooked UF-SAR. We find for Sentinel-3 that the averaged power waveforms of UF-SAR and FF-SAR over ocean are virtually identical, while for Sentinel-6 the FF-SAR power waveforms better resemble the UF-SAR zero-Doppler beam. We can explain and model the similarities and differences in the data via theoretical considerations of the waveform integrals. These findings suggest to use the existing UF-SAR SAMOSA model for retracking S3 FF-SAR waveforms but the SAMOSA zero-Doppler beam model for S6 FF-SAR waveforms, instead. Testing the outlined approach over short track segments, we obtain range biases between UF-SAR and FF-SAR lower than 2 mm and significant wave height biases lower than 5 cm.     

激光选区熔化成型316L不锈钢工艺参数研究

针对激光选区熔化成型316L不锈钢工艺参数选择问题,采用单因素条件变量分析法,在激光选区熔化过程中,分析了激光功率、扫描速度对316L不锈钢成型零件表面粗糙度、致密度、硬度和尺寸偏差的影响规律。结果表明：当激光功率降低或者扫描速度提高时,内部能量密度减小,粉末熔化量减少,试样表面球化效应增强,孔隙缺陷增多,试样致密度减小、硬度降低;当激光功率提高或者扫描速度降低时,内部能量密度增大,粉末被过度烧蚀,产生较大的尺寸偏差,所形成熔道易塌陷,导致层间结合较差,试样性能降低。当激光功率为300 W、扫描速度为1000 mm/s时,能量密度适中,形成了较好的冶金结合,抗拉强度可达753 MPa,上表面硬度HRB能达到97.22。该项研究为316L不锈钢激光选区熔化工艺参数的合理选择提供了参考。     

基于液体金属的接触PIM抑制方法和实验验证

接触非线性是射频设备和电路中产生无源互调（passive intermodulation，PIM）信号的重要原因之一。基于对接触结点射频等效电路的分析，提出了一种基于共晶镓铟合金（eutectic gallium-indium，EGaIn）的PIM抑制方法。EGaIn不同于传统的焊锡，它可以在室温下实现接触结位置上的稳定、可重构连接。首先分析了射频（radio frequency，RF）下的金属接触结的电路模型。其次设计并实现了两个包含不同金属接触结构且工作在2.6GHz的平面倒F天线（planar inverted F antenna，PIFA）。最后比较了EGaIn焊接前后PIFA的互调水平，其中对PIM指标的最大抑制程度为35dB。验证了EGaIn可以在室温下对PIFA的接触结点进行可重构焊接，这为电连接中的非线性抑制提供了一种参考方法。     

Ergodic sum rate for uplink NOMA transmission in satellite-aerial-ground integrated networks

The application of Non-Orthogonal Multiple Access (NOMA) technology into satellite-aerial-ground integrated networks can meet the requirements of ultra-high rate and massive connectivity for the Sixth-Generation (6G) communication systems. We consider an uplink NOMA scenario for such a satellite-aerial-ground integrated network where multiple users communicate with satellite under the help of an Unmanned Aerial Vehicle (UAV) as an aerial relay equipped with a phased array. Supposing that buffer-aided decode-and-forward protocol is adopted at the UAV relay, we first formulate an optimization problem to maximize Ergodic Sum Rate (ESR) of the considered system subject to individual power constraint and quality-of-service constraint of each user. Then, with known imperfect channel state information of each user, we propose a joint power allocation and robust Beam Forming (BF) iterative algorithm to maximize ESR for the user-to-UAV link. Besides, to take the advantages of Free-Space Optical (FSO) and millimeter Wave (mmWave) communications, we present a switch-based hybrid FSO/mmWave scheme and a robust BF algorithm for the UAV-to-satellite link to achieve higher rate. Moreover, a closed-form ESR expression is derived. Finally, the effectiveness and correctness of the proposed solutions are verified by numerical simulations, and the performance evaluation results show that the proposed solutions not only achieve performance enhancement and robustness, but also outperform the orthogonal multiple access significantly.