薄壁试件脉冲热像法深度检测模型分析

脉冲热像法作为红外热像检测中具有定量分析能力的方法,其主要检测模型温差函数法在薄壁试件的缺陷深度检测时存在失效问题.为找出建模过程中的缺陷,以理想脉冲激励下一维有限形式的解析解替代原温差函数模型中的近似解,在温差曲线和温差导数曲线中,对模型中的核心参数峰值温差时间和峰值斜率时间的使用特性进行了比较分析.结果显示:峰值温差时间由参考点决定,而不由测试点决定,峰值温差时间不具备对缺陷深度的定量检测能力;峰值斜率时间的适用范围受到测试点与参考点实际深度之比的限制,根据给出的适用性判据公式求得该比值的上限在0.5附近,判据公式可作为使用峰值斜率时间的理论依据.     

卫星导航接收机陷波器级联抑制窄带干扰研究

为了在有用信号失真较小的情况下有效抑制具有一定带宽的窄带干扰,本文首先推导了IIR陷波带宽控制参数α与陷波带宽和陷波深度的定量表达式,在统筹考虑陷波频率、陷波带宽、陷波深度和实时性基础上提出了基于多级开环IIR陷波器级联的滤波算法。每一级IIR滤波器负责抑制一个子带内的干扰,在保证陷波深度的条件下实现较为陡峭的带阻特性,在窄带干扰被有效抑制的情况下使有用信号失真达到最小。仿真结果验证了算法的有效性。
     

飞机结构腐蚀损伤尺寸的关联性分析与探讨

基于某型水上飞机结构材料铝合金的外场腐蚀普查数据,建立了腐蚀深度与腐蚀面积的相关性计算模型,经研究发现,这两者有着较好的关联关系。所以,在外场腐蚀普查过程中可以通过测量腐蚀损伤表面积,预测腐蚀深度的大小,因而本文可以为获得飞机结构腐蚀深度提供一种简单而可行的预测方法。     

Snow depth retrieval by using robust estimation algorithm to perform multi-SNR and multi-system fusion in GNSS-IR

Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) technology provides a new means of snow depth detection. Multi-satellite and multi-Signal-to-Noise Ratio (SNR) provide more data for daily high-precision snow depth retrieval, but also face the problem of data fusion and effective utilization. Therefore, this study proposes a robust estimation algorithm based on multi-satellite and multi-SNR fusion applied to the observations of a GNSS station in Alaska. This study uses four solutions (S_avg, S_med, S_{RE_avg} and S_{RE_med}) to carry out multi-system fusion snow depth inversion and precision comparison research. The S_avg has more obvious disadvantages, which is not suitable for snow depth assessment. The S_{RE_avg} and S_{RE_med} have better snow depth retrieval effects in the snowy periods. The correlation coefficient (R), root mean square error (RMSE) and mean error (ME) of the calculated snow depth using the robust estimation algorithm with respect to the nearest in-situ measurements reached 0.759, 3.7 cm and ?1.4 cm, respectively. Compared with the S_med, the R is increased by 2.0 %, the RMSE corresponds to an improvement of 2.6 %. Moreover, the ME of the snow depth retrievals, as an indicator of the measurement bias, has significantly decreased by 6.7 %. The result also shows that the snow depth inversion by the robust estimation algorithm is more consistent with the in-situ measurements, further extending and advancing the optimal algorithm for snow depth retrieval.     

Study of aerosol anomaly associated with large earthquakes (M>6)

We present the variation of unusual atmospheric phenomena, aerosols, to understand the preseismic irregularities for two major earthquakes in Japan. We consider aerosol optical depth and Angstrom exponent data retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Terra satellite to establish possible connections between earthquakes and the generation of aerosols. Variation of the aerosol parameters shows significant changes before the April 15, 2016, Kumamoto earthquake ($M=7.0,h=10$ km) and the November 21, 2016, Fukushima earthquake ($M=6.9$ and $h=9$ km), where M indicates the Richter magnitude and h indicates the focal depth. To identify the source of the aerosol particles, we use the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT-4). This model uses both Lagrangian and Eulerian approaches to compute trajectories and establish a source-receptor relationship. We compute backward trajectories to check whether the aerosol generated near the epicenter is due to the preseismic processes or is transported from other areas. From our results, we conclude the fine-mode aerosols are generated in the vicinity of the epicenter, 3–7 days before the earthquakes.     

负电子亲和半导体的二次电子发射

根据0.8keV≤Epomax≤5keV的负电子亲和(negative electron affinity,NEA)半导体二次电子发射(secondary electron emission,SEE)的特性，初级电子产额R，现有的次级电子产额δ的通用公式和实验数据，分别推导并实验证明了NEA金刚石的δ在0.5Epomax≤Epo≤10Epomax, GaN在2keV≤Epomax≤5keV, NEA金刚石的δ在08keV≤Epo≤3keV, GaN在08keV≤Epomax≤2keV的特殊公式;其中Epomax为δ达到最大值时的Epo, Epo为初级电子入射能。推导出了08keV≤Epomax≤5keV时NEA半导体的内部二次电子到达发射极表面后逃逸到真空中的概率B。还提出了计算08keV≤Epomax≤5keV NEA半导体1/α的方法;其中1/α为二次电子的平均逃逸深度。分析结果表明，B和1/α的理论研究有助于研究不同样品制备方法对NEA半导体中SEE的定量影响，从而生产出理想的NEA发射体，如NEA金刚石。