星用介质材料表面充放电效应试验研究

航天器表面介质材料易遭受表面充放电危害。利用30keV单能电子对几种不同的航天介质材料进行了表面充放电模拟试验,测量了不同电子通量辐照下的表面充电电位以及放电脉冲。试验结果表明,聚酰亚胺薄膜在接地处理不当时表面可充至千伏以上,易发生表面放电,且辐照强度越大,放电频率越高。表面镀铝的聚酰亚胺薄膜在不接地时,铝膜成为悬浮导体更加剧了放电的危害。而通过渗碳处理的聚酰亚胺薄膜,其良好的导电性能可有效抵御nA/cm~2量级电子的表面充电。聚四氟乙烯天线罩表面未进行防静电处理时,表面充电电位可达万伏量级,极易发生放电。     

表面粗糙度的光学测量方法

表面粗糙度的光学测量方法,具有非接触、精度高和响应快等优点,致使研究十分引人注目,发展极快。本文简单介绍了几种典型的光学测量原理和方法及一些商品化的仪器。     

Experimental study of effect of post processing on fracture toughness and fatigue crack growth performance of selective laser melting Ti-6Al-4V

For Ti-6Al-4V, a titanium alloy increasingly used in aerospace structure, selective laser melting (SLM) is an attractive additive manufacturing technology, which is attributed to its complex construction capability with high accuracy and good surface quality. In order to obtain qualified mechanical properties, SLM parameters and post processing should be tailored for diverse service conditions. Fracture toughness and fatigue crack growth (FCG) behavior are critical characteristics for damage tolerance evaluation of such metallic structures, and they are affected by post processing technologies significantly. The objective of this study is to obtain the fracture toughness and fatigue crack growth behavior of Ti-6Al-4V manufactured by SLM, and to evaluate the influence of post-SLM thermomechanical treatment and surface machining. Fracture toughness and FCG tests were performed for SLM Ti-6Al-4V in three types of post processing status: as-built, heat treated and hot isostatically pressed (HIPed), respectively. Specimens with as-built and machined surface were tested. The microstructure and fractography were analyzed as well in order to investigate the relevance among manufacture process, microstructure and mechanical properties. The results demonstrate that as-built SLM Ti-6Al-4V presents poor ductility and FCG behavior due to martensitic microstructure and residual stresses. Both heat treatment and hot isostatic pressing improve the plane-stress fracture toughness and FCG performance considerably, while surface machining shows slight effect.     

An Adaptive Network-based Fuzzy Inference System for the detection of thermal and TEC anomalies around the time of the Varzeghan,Iran, (Mw = 6.4) earthquake of 11 August 2012

Anomaly detection is extremely important for forecasting the date, location and magnitude of an impending earthquake. In this paper, an Adaptive Network-based Fuzzy Inference System (ANFIS) has been proposed to detect the thermal and Total Electron Content (TEC) anomalies around the time of the Varzeghan, Iran, (M_w = 6.4) earthquake jolted in 11 August 2012 NW Iran. ANFIS is the famous hybrid neuro-fuzzy network for modeling the non-linear complex systems. In this study, also the detected thermal and TEC anomalies using the proposed method are compared to the results dealing with the observed anomalies by applying the classical and intelligent methods including Interquartile, Auto-Regressive Integrated Moving Average (ARIMA), Artificial Neural Network (ANN) and Support Vector Machine (SVM) methods. The duration of the dataset which is comprised from Aqua-MODIS Land Surface Temperature (LST) night-time snapshot images and also Global Ionospheric Maps (GIM), is 62 days. It can be shown that, if the difference between the predicted value using the ANFIS method and the observed value, exceeds the pre-defined threshold value, then the observed precursor value in the absence of non seismic effective parameters could be regarded as precursory anomaly. For two precursors of LST and TEC, the ANFIS method shows very good agreement with the other implemented classical and intelligent methods and this indicates that ANFIS is capable of detecting earthquake anomalies. The applied methods detected anomalous occurrences 1 and 2 days before the earthquake. This paper indicates that the detection of the thermal and TEC anomalies derive their credibility from the overall efficiencies and potentialities of the five integrated methods.     

频率标准用超导铌腔内表面处理工艺研究

频率标准用超导铌腔内表面的处理是影响超导腔Q值的最大因素。本文首先通过理论分析确定了超导腔Q与表面剩余电阻的关系,其次通过一系列的表面处理工艺来保证超导腔内表面的剩余电阻尽量小,最后通过实验得到了超导腔的Q值为1.9E9,与理论计算结果相近,证明了表面处理的有效性。     

GPS total electron content and surface latent heat flux variations before the 11 March 2011 M9.0 Sendai earthquake

The present paper describes the variations of the GPS total electron content (TEC) from the International GNSS service network and surface latent heat flux (SLHF) from the Scientific Computing Division of the National Center for Atmospheric Research (NCAR) before the 11 March 2011 M9.0 Sendai earthquake, respectively. The analysis shows pronounced enhancements in the GPS TEC and SLHF a few days prior to the earthquake event. The maximum increase in the GPS TEC was about 30 TECu with an extended spatial distribution on a geomagnetically quiet day (Dst ? −20 nT, between two moderate geomagnetic storms), 8 March, 3 days prior to the earthquake. This giant positive disturbance was possibly associated with the impending disastrous earthquake and contributed from the enhanced solar radiation. Moreover, there were several anomalous regions of SLHF on the global map, but an area of enhanced SLHF very close to the epicenter. The purpose of this paper is to report the existence of the changes in surface and ionosphere, and show the potential application of multi-source data to identify seismic precursors.     

Fronts and thermohaline structure of the Brazil–Malvinas Confluence System

Fronts and thermohaline structure of the Brazil–Malvinas Confluence System (BMCS) are studied from climatic data, “Marathon Exp. Leg.8, 1984” data, and Sea surface temperature (SST) data base “ds277-Reynolds” (1981–2000). The South Atlantic Central Water (SACW) is divided in two main types: tropical (TW) and subtropical water (ST). Water masses, Fronts, Inter-Frontal and Frontal Zones are analysed and classified: (a) the water masses: Tropical Low-Salinity Water, Tropical Surface Water, Tropical Tropospheric Water, Subtropical Low-Salinity Water, Subtropical Surface Water, Subtropical Tropospheric Water. T,S characteristics of intermediate, deep and bottom water defined by different authors are confirmed and completed; (b) the Inter-Frontal Zones: Tropical/Brazil Current Zone, Subtropical Zone and Subantarctic Zone; (c) the Frontal Zones: Subtropical, Subantarctic and Polar, and (d) the Fronts: Subtropical Front of the Brazil Current, Principal Subtropical Front, North Subtropical Front, Subtropical Surface Front, South Subtropical Front, Subantarctic Surface Front, Subantarctic Front and Polar Front. Several stable T–S relationships are found below the friction layer and at the Fronts. The maximum gradient of the oceanographic characteristics occurs at the Brazil Current Front, which can be any of the subtropical Fronts, depending on season. Minimum mean depth of the pycnocline coincides with the Fronts of the BMCS, indicating the paths of low-salinity shelf waters into the open ocean. In the work it is shown how to recover the horizontal and vertical thermohaline structure of waters from satellite data RSMAS SST.     

航天柔性展开结构技术及其应用研究进展

综述了航天柔性展开结构的技术特点及其在航天器中的研究应用情况，围绕航天柔性展开结构应用涉及的薄膜褶皱、充气张力结构的屈曲失稳、展开动力学、精度测试、刚化材料等关键理论和技术基础，评述了航天柔性结构技术应用中的关键问题及未来研究重点，最后给出了航天柔性展开结构技术的未来发展趋势。     

一种飞机操纵面驼峰型颤振随高度变化特性研究

飞机操纵面旋转和安定面弯曲模态频率较近时易耦合形成一种速度阻尼特性随高度显著变化的驼峰型颤振。某飞机垂尾颤振分析表明超过一定高度后驼峰型颤振分支阻尼峰值会超过结构阻尼系数,成为临界颤振型,并且随飞行高度增加阻尼峰值迅速增加。针对上述情况采用了三种方案抑制驼峰型颤振,算例表明降低30%安定面弯曲刚度,增加25%结构质量,操纵面旋转频率增加60%以上均能有效抑制高空驼峰型颤振。