PBT弹性体微相分离及对其力学性能的影响研究

为了获得微相分离对宽温PBT叠氮聚醚弹性体力学性能的影响规律,用红外光谱分析法(FT-IR)和动态热力学分析法(DMA)研究了PBT叠氮聚醚弹性体产生微相分离的机理和影响因素。用调节硬段含量、交联参数的方法调控其微相分离,控制适当的微相分离程度可显著改善推进剂的力学性能。研究结果表明:在二元醇扩链的弹性体体系中,当硬段含量约为15%时,弹性体发生相对最大比例的微相分离,体现出较佳的综合力学性能。通过微相分离的调控可获得宽温范围内综合力学性能较好的叠氮聚醚推进剂用粘合剂基体材料。     

Early analysis of precise orbit and clock offset determination for the satellites of the global BeiDou-3 system

Eight new-generation BeiDou satellites (BeiDou-3) have been launched into Medium Earth Orbit (MEO), allowing for global coverage since March 2018, and they are equipped with new hydrogen atomic clocks and updated rubidium clocks. Firstly, we analyzed the signals for the carrier-to-noise-density ratio (C/N0) and pseudorange multipath (MP) by using international GNSS (Global Navigation Satellite System) Monitoring and Assessment System (iGMAS) station data, and found that B1C has a lower C/N0, and B2a has the same level of C/N0 as the B1I and B3I signals. For pseudorange multipath, compared with the BeiDou-2 satellites, the obvious systematic variation of MP scatters related to the elevation angle is greatly improved for the BeiDou-3 and BeiDou-3e satellites signals. For the signals of the BeiDou-3 satellites, the order of the Root Mean Square (RMS) values of multipath and noise is B3I?<?B1I?<?B2a?<?B1C. Then, the comparison of the precise orbit determination and clock offset determination for the BeiDou-2, BeiDou-3, and BeiDou-3 experimental (BeiDou-3e) satellites was done by using 10 stations from iGMAS. The 3D precision of the 24?h orbit overlap is 24.55, 25.61, and 23.35?cm for the BeiDou-3, BeiDou-3e, and BeiDou-2 satellites, respectively. BeiDou-3 satellite has a comparable precision to that of the BeiDou-2 satellite. For the precision of clock offset estimation, the Standard Deviation (STD) of the BeiDou-3 MEO satellite is 0.350?ns, which is an improvement of 0.042?ns over that of the BeiDou-2 MEO satellite. The stabilities of the BeiDou-3 and BeiDou-3e onboard clocks are better than those of BeiDou-2 by factors of 2.84 and 1.61 at an averaging time of 1000 and 10,000?s, respectively.     

复合材料构件热压罐成型模具温度均匀性分析

热压罐固化中成型模具的温度分布对复合材料固化质量有显著影响,提高与构件直接接触的模具型面温度均匀性有利于改善内部温度梯度,减小固化变形,提高成型精度。本文以复合材料构件热压罐框架式成型模具为对象,应用有限元方法,分析模具温度的分布,研究模具支撑结构对型板表面温度均匀性的影响。研究表明,支撑板厚度越薄,温度均匀性越好,与进气风口平行方向的支撑板对温度均匀性的影响更为显著,因此可优先考虑增加与进气风口垂直方向支撑板厚度来增加模具刚度。在保持面积不变的前提下,改变散热孔的形状,发现菱形与圆形散热孔具有较强的抗变形能力,而方形散热孔使得型板表面温度分布更加均匀。通过控制散热孔的布局改变风道时,发现T型风道对于改善温度均匀性的效果最佳。     

高温存储对Sn-Pb-Ni凸点界面金属间化合物生长的影响

倒装焊工艺由于具有信号处理速度快、封装密度高、可靠性高等特点，已广泛应用于高密度集成电路封装工艺中。高可靠倒装焊器件的互连焊点通常采用10Sn90Pb等高铅焊料，该焊料具有剪切强度高、可靠性高等优点，但其熔点高、回流工艺窗口窄等特性给封装工艺带来一定难度，此外该焊料在高温存储环境的可靠性有待进一步提高。本文采用Ni元素对10Sn90Pb焊料进行改性，研究高温存储下Sn-Pb-Ni体系凸点的力学性能以及金属间化合物（Intermetallic compound,IMC）的生长演变规律，以此评估Ni元素对10Sn90Pb凸点可靠性的影响。主要结果如下：适量添加Ni元素可以细化10Sn90Pb焊点界面处IMC晶粒，降低高温存储条件下的IMC生长速度，但在一定程度上会降低凸点的剪切强度。0.05%~0.1%含量的Ni元素添加对10Sn90Pb凸点综合性能提升较为显著。     

谐振式加速度计自激振荡电路性能评价方法的研究

针对谐振式加速度计成品率不高、精度低等问题，以石英振梁加速度计为例，采用引进标准信号，将谐振电路作为“黑盒子”，对其开展独立的评价。通过评价电路的驱动电压幅值稳定性、移相稳定性、全温幅值/相位对称性等指标，与加速度计实际指标建立了一一对应的关系，为加速度计研制与性能提升提供了有效依据。实际运用表明，电路噪声性能、温度性能大幅提升，产品成品率从70%提高到了约90%。     

Validation of non-linear split window algorithm for land surface temperature estimation using Sentinel-3 satellite imagery: Case study; Tehran Province,Iran

In recent years, land surface temperature (LST) has become critical in environmental studies and earth science. Remote sensing technology enables spatiotemporal monitoring of this parameter on large scales. This parameter can be estimated by satellite images with at least one thermal band. Sentinel-3 SLSTR data provide LST products with a spatial resolution of 1 km. In this research, direct and indirect validation procedures were employed to evaluate the Sentinel-3 SLSTR LST products over the study area in different seasons from 2018 to 2019. The validation method was based on the absolute (direct) evaluation of this product with field data and comparison (indirect) evaluation with the MODIS LST product and the estimated LST using the non-linear split-window (NSW) algorithm. Also, two emissivity estimation methods, (1) NDVI thresholding method (NDVI-THM) and (2) classification-based emissivity method (CBEM), were used to estimate the LST using the NSW method according to the two thermal bands of Sentinel-3 images. Then, the accuracy of these methods in estimating LST was evaluated using field data and temporal changes of vegetation, which the NDVI-THM method generated better results. For indirect evaluation between the Sentinel-3 LST product, MODIS LST product, and LST estimated using NSW, four filters based on spatial and temporal separates between pairs of pixels and pixel quality were used to ensure the accuracy and consistency of the compared pairs of a pixel. In general, the accuracy results of the LST products of MODIS and Sentinel-3, and LST estimated using NSW showed a similar trend for LST changes during the seasons. With respect to the two absolute and comparative validations for the Sentinel-3 LST products, summer with the highest values of bias (?1.24 K), standard deviation (StDv = 2.66 K), and RMSE (2.43 K), and winter with the lowest ones (bias of 0.14 K, StDv of 1.13 K, and RMSE of 1.12 K) provided the worst and best results for the seasons in the period of 2018–2019, respectively. According to both absolute and comparative evaluation results, the Sentinel-3 SLSTR LST products provided reliable results for all seasons on a large temporal and spatial scale over our studied area.     

高温铝合金电磁超声检测回波特性及因素分析

针对高温铝合金在线检测条件下，温度对铝合金电磁超声检测回波特性的影响规律尚不明确、高温检测时缺陷定量/定位补偿困难这一难题，以螺旋线圈电磁超声换能器（EMAT）为例，建立了高温铝合金EMAT检测过程的场路耦合有限元模型；研究了温度对EMAT激励/接收换能效率、EMAT激励/接收电路的功率分配特性、超声传播过程中的扩散/介质衰减特性、回波幅值和超声声速等因素的影响规律；研制了耐高温EMAT探头，对20~500℃高温铝合金试样进行了检测实验，并测定了高温铝合金的超声介质衰减系数和超声声速。在仿真和实验相结合的基础上，分析了高温检测时超声回波幅值变化特性及其影响因素。结果表明：对于铝合金这类非铁磁性金属材料，导致高温时超声回波幅值下降的主要原因是超声介质衰减系数随着温度的升高而增大，其次为高温时EMAT激励/接收电路的功率分配特性的改变。在激励EMAT在试样表面形成的洛伦兹力不变的条件下，其所激励的超声波回波幅值具有随着温度的增加而增加的特点，可以有效减缓超声回波幅值下降的趋势。     

钛合金表面抗激光涂层损伤特性及热效应影响研究

实验研究了钛合金和高反射型陶瓷涂层材料抗连续型激光烧蚀的损伤及温度分布特性，并从热效应影响角度对比分析了二者在抗激光损伤效果方面的差异性。研究结果表明：相比于钛合金，高反射型陶瓷涂层材料能有效增强钛合金基底抗激光损伤的能力；在同等激光功率密度辐照下，陶瓷涂层材料能有效提升钛合金基底耐受激光辐照的时间长度。实验结果表明该陶瓷涂层材料的激光损伤阈值比钛合金高约5.8倍。实验发现陶瓷涂层温升速率高于钛合金，但由于陶瓷材料具有较高的反射特性，以及良好的热吸收和热传导特性，因此能使由激光辐照产生的热量在其表面较快地扩散，而降低向基底方向传导的程度，最终提升陶瓷涂层的抗激光损伤阈值。     

星载微波传感器大气温湿度物理反演算法研究

针对我国下一代静止轨道微波探测器资料应用的需求,对微波50~60GHz和183GHz的温湿遥感通道开展了不同大气条件下探测敏感高度的模拟,发现大气散射对微波探测影响明显,尤其是近地面通道,在未来数据应用时需加以注意。提出一种基于一维变分的大气温湿度廓线物理反演算法。以美国最新一代气象卫星Suomi NPP搭载的ATMS(Advanced Technology Microwave Sounder)获取的观测资料为研究对象,RTTOV(Radiative Transfer for TOVS)快速辐射传输模式为前向算子,利用一维变分算法开展了温湿度廓线反演单点试验。研究发现:地表参数对微波亮温,尤其是地面通道影响较大。同时,反演所需背景场对反演结果影响较明显,反演所得温度与背景场较接近。     

高主流湍流度下密度比对涡轮导叶全气膜冷却特性的影响

为了研究高主流湍流度下二次流密度比对涡轮导叶全气膜冷却特性的影响,使用热色液晶测量了在主流湍流度为15%,二次流密度比为1.0和1.5下三维涡轮导叶的气膜冷却效率和换热系数。二次流与主流质量流量比为7.0%和12.5%。结果表明:二次流密度比增大可以降低冷气射流的动量,小流量比工况下,在叶片前缘和压力面前半段,动量较低的二次流在高主流湍流度的影响下更易耗散,增大二次流密度比使冷却效率明显降低;大流量比工况下,二次流动量降低使气膜孔后区域冷气贴附性增强,气膜冷却效率和冷气覆盖效果均得到提升。小流量比工况下,二次流密度比增大对叶片表面换热的影响较小;大流量比工况下,二次流密度比增大使吸力面中弦区域和压力面后半段的平均换热系数比分别降低15%和25%。