硼含量及横向取样对定向凝固Ni_3Al合金持久性能的影响

硼的添加增强了晶界的结合力 ,使合金相界面的位错组态改变 ,提高了持久断裂寿命 ;硼的添加细化晶粒 ,增加界面数 ,使持久寿命下降。Ni3Al定向凝固横向试样持久性能不稳定与取样位置有关     

新乡上空电离层总电子含量的经验模式

基于电离层总电子含量与太阳活动性之间的线性相关关系,利用在新乡长期测量所得的电离层总电子含量的资料,得出了总电子含量的一种经验模式。      

Negative VTEC with spherical harmonic expansion model under different solar activity conditions

The Earth’s ionosphere can be described by a spherical harmonic (SH) expansion up to a specific degree. However, there exist negative vertical total electron content (VTEC) values in the global ionosphere map (GIM) with the SH expansion model. In this contribution, we specifically investigated the negative VTEC values that are induced by the SH expansion model and validated the performance of the inequality-constrained least squares (ICLS) method in eliminating the negative VTEC values. The GPS data from 2004 to 2017 was selected to cover one solar cycle and the experiments under different solar activity conditions were analyzed. The results in our work show that the occurrence of the negative VTEC values is attributed to the deficiency of the SH expansion model when the VTEC itself is small instead of the unevenly distribution of the GNSS stations. The negative VTEC values appear periodically in the temporal domain, showing apparently one year and half year periods. During one year, two peaks in June and December can be observed in the time series of the negative VTEC values. The number of negative VTEC values in June is obvious larger than that in December. During one solar cycle, the number of negative VTEC values under quiet solar activity condition is obvious larger than that under strong solar activity condition. In the spatial domain, the appearance of the negative VTEC values is strongly related with the movement of the subsolar point. In the latitude of the subsolar point has the largest magnitude, the negative values will appear on the opposite hemisphere and the further from the subsolar point the more negative values. The maximum number of the negative VTEC values in the southern hemisphere appears in June, while the peak value in the northern hemisphere appears in December. The maximum number of negative VTEC values in the southern hemisphere is generally larger than that in the northern hemisphere. In addition, the negative VTEC values are distributed both at middle latitude and high latitude in the southern hemisphere, while they are mainly distributed at high latitude in the northern hemisphere. When the ICLS method is used, the negative VTEC values can be eliminated efficiently and it has nearly no influence on the positive VTEC values. The ICLS method can also improve the receiver’s differential code bias (DCB) and significantly decrease the unreasonable negative slant TEC (STEC) values along the lines of sight. Using the final GIM product of the Jet Propulsion Laboratory (JPLG) as a reference, the root mean square (RMS) of the ICLS solution shows maximum 25%, 20% and 45% improvement relative to the least squares (LS) solution at northern high latitude, southern middle latitude and southern high latitude, respectively.     

电子产品中铅焊接金脆问题浅析

针对航天电子产品广泛采用的Sn-Pb焊料在镀金表面焊接形成焊点的工艺,分析了工业及国内外航天相关标准文件中对焊接后焊点中含金量的要求以及焊点含金量、时效、器件不同封装形式对焊点可靠性的影响,并深入分析了合金焊点金相组织结构,最后介绍了一般去金工艺要求与去金不到位而导致器件失效案例。     

含气率对液力透平影响的非定常分析

为了研究含气率对液力透平内部压力的影响，以比转速为84.5的单级单吸离心泵反转作液力透平并对其内部流场进行CFD瞬态数值模拟，获得了气体在液力透平内的分布规律以及气液两相介质下透平内部流场的压力脉动变化规律。结果表明:从蜗壳进口到叶轮出口,含气率逐渐增加，含气率等于0.2时蜗壳出口、叶轮进口气体的尾迹效应明显，分布不够均匀。叶轮出口有气体聚集现象，气体体积分数越高，聚集现象越明显。进口含气率对透平蜗壳、叶轮内各点的相对压力分布影响明显，各点的相对压力随着透平进口含气率增加而降低。含气率小于0.05时其对透平内各监测点的压力脉动主频幅值影响不大，含气率大于0.05后其对液力透平内各监测点的压力脉动主频幅值有影响，含气率越高，压力脉动主频幅值越小。不同含气率下液力透平蜗壳周向、径向以及叶轮内的压力脉动主频均等于叶轮叶片的转动频率。