Intergranular glassy phase free SiC ceramics retains strength at 1500 °C

We report SiC ceramics sintered with AlN and Sc₂O₃ (or Lu₂O₃) that retain room temperature strength to 1500 °C. The intergranular glassy phase has not been observed in the ceramics due to a designed-sintering additive and, thus, the unsatisfactory effect of glassy phases on the high temperature strength is eliminated.     

毫米波MIMO系统中稀疏度自适应的压缩感知信道估计

利用毫米波MIMO系统的稀疏特性,信道估计可以转化为稀疏信号重构的问题。解决毫米波MIMO稀疏信道估计问题时,传统的OMP方法需要信号的稀疏度作为先验信息,实际系统难以满足此需要。文中引入StOMP算法,根据信号已知的稀疏先验信息确定阈值,并结合动态的阈值调整,提出一种新的StOMP-D算法,实现了稀疏度自适应的毫米波MIMO信道估计。仿真结果表明,所提的方法与传统的LS方法比较,信道估计性能显著提高,并且与稀疏度已知的OMP方法性能十分接近,在稀疏度未知时有明显的优势。     

曲线交叠外推的微动多目标宽带分辨算法

针对传统的微多普勒特征提取技术难以解决多目标分辨和微动参数估计这一问题,该文针对进动多目标,提出一种曲线交叠外推的微动多目标宽带分辨算法。该算法以各个滤波数据点间的相对距离为准则,结合各曲线的历史斜率信息,对交叠点后的点迹进行外推估计,实现各个分量信号微动曲线的区分关联。在此基础上,通过分析各曲线的微动特性差异实现多目标分辨。仿真实验验证了所提算法的有效性和稳定性。     

Crystal anisotropy-dependent shear angle variation in orthogonal cutting of single crystalline copper

Shear deformation that dominates elementary chip formation in metal cutting greatly relies on crystal anisotropy. In the present work we investigate the influence of crystallographic orientation on shear angle in ultra-precision orthogonal diamond cutting of single crystalline copper by joint crystal plasticity finite element simulations and in-situ experiments integrated in scanning electron microscope. In particular, the experimental cutting conditions including a straight cutting edge are the same with that used in the 2D finite element simulations. Both simulations and experiments demonstrate a well agreement in chip profile and shear angle, as well as their dependence on crystallography. A series of finite element simulations of orthogonal cutting along different cutting directions for a specific crystallographic orientation are further performed, and predicated values of shear angle are used to calibrate an extended analytical model of shear angle based on the Ernst–Merchant relationship.     

Influence of impurities on hot-rolled molybdenum for high temperature applications

Refractory metals are crucial for high-temperature applications such as fusion reactors. However, no systematic research has been reported for the influence of the impurities in refectory metals, especially at high temperatures. Our goal is an investigation of the influence of dissolved impurities on the recrystallization behavior of hot-rolled molybdenum (Mo). Two sets of 80%-rolled Mo plates with different purity levels pure Mo and non-pure Mo with the content of impurities, O, C, N, etc. are analyzed. Both isothermal and isochronous annealing experiments demonstrated that the impurities resulted in a reduction of recrystallization temperature and acceleration of texture transformation in a Mo plate. The recrystallization temperature of as-rolled non-pure Mo is about 100 °C lower than that of pure Mo. EBSD results show deformed γ-fiber texture gets weakened while {001}〈110〉 component gets strengthened at 1250 °C for pure Mo and 1150 °C for non-pure Mo, leading to the destabilization of fibrous grains. The XRD and TEM results reveal that the dislocation density of as-rolled non-pure Mo is ~2.4 times that of pure Mo. This discovery deviates from the conventional understanding of impurities or second phase particles in metals, providing better practical knowledge and opportunities to establish the technical parameters of refractory metals for high temperatures applications.     

基于高光谱图像解混的海洋绿藻检测算法

提出了一种基于线性混合模型的高光谱图像绿藻面积估计算法。利用端元提取算法,自动获取图像中绿藻端元的光谱曲线,根据得到的端元及原始图像,通过全约束最小二乘算法,求得绿藻端元的丰度图,丰度图作为绿藻面积的估计结果。算法能够有效克服由于高光谱图像分辨率不足造成的绿藻面积估计不准确的问题,实现亚像素水平的绿藻面积估计。利用2013年6月29日获取的GOCI传感器获取的8波段光谱图像展开实验,计算得到当日绿藻覆盖面积为321 km2,与HJ-1B卫星的实测结果高度接近,相比于NDVI等传统算法具有明显优势。方法为绿藻灾害预警和监测提供了一条新的解决思路和技术途径,具有较高的应用价值。     

横向电阻区对IGBT过电流关断能力的影响研究

针对绝缘栅双极晶体管(IGBT)在过电流关断测试中被烧毁的问题,设计了三种不同的横向电阻区结构。为了分析器件的失效机理,研究不同结构横向电阻区对过电流关断能力的影响,借助Sentaurus TCAD仿真工具构建了器件模型,模拟了器件的整个过电流关断过程。对三种结构器件在过电流关断过程中的内部关键物理参量的变化情况进行分析,发现不同长度的横向电阻区对空穴的抽取效率不同,进而可以影响到电流密度分布。当电阻区增加到一定长度时,可以有效提升过电流关断能力,避免器件烧毁失效。     

基于图模型的小尺寸飞行器地面试验中位姿估计方法

在多飞行器地面试验位姿估计中,由于跟踪算法导致的跟踪轨迹不连续会使得位姿估计产生累积误差,为了实现位姿的精确估计,提出了一种基于图模型的全局位姿估计非线性优化方法。首先,建立了一个飞行器地面视觉位姿估计系统。然后根据飞行器上特征点的数目提出了一种向量交叉式的飞行器位姿解算方法,求解得到数据已关联飞行器位姿估计值。利用中介坐标系法求解得到轨迹段初始位姿节点在测量坐标系下的值,最后,在图模型基础上下,对整个量测过程中飞行器的位姿估计结果进行非线性全局优化减小线性算法的累积误差,并通过仿真与实际实验对飞行器位姿估计算法的可行性与精度进行验证。实验结果表明:在测量范围为6 000 mm×6 000 mm×3 000 mm的范围内,飞行器尺寸约为400 mm,特征点三维定位精度为2.9 mm的条件下,基于非线性优化的飞行器位姿估计算法的理论精度分别可达0.5°(3σ)与3 mm (3σ),实际绝对测量精度分别可达1.3°(3σ)与4 mm (3σ),基本满足地面试验对多飞行器编队算法开发以及制导控制系统性能长时间评估稳定可靠、精度高、抗干扰能力强等要求。     

相干激光引信在云雾干扰下的回波特性研究

为分析相干激光引信在云雾干扰下的探测性能,基于Mie散射理论和Monte Carlo方法建立了相干激光引信在云雾中的探测模型,仿真获取相干激光引信在多种云雾干扰场景下的探测回波,分析回波信号的时域和频域特性,以及云雾能见度、探测位置和探测角度对回波特性的影响。研究结果表明,相干激光引信可利用回波频域特征准确探测和识别目标,且不易受云雾能见度、探测位置和探测角度等因素的影响。结果证明:相干激光引信在云雾干扰下具有优良的探测性能。     

基于FPGA的深空图像实时边缘检测算法与实现

航天器的导航控制是深空探索的重要关键技术之一。随着探索距离越来越远,传统地面站控制的局限性越发明显,因此航天器自主导航成为深空探索的发展方向。边缘检测是光学自主导航系统中定位天体目标的关键算法之一,为了满足星载计算机计算的实时性要求,文中提出了一种优化的Canny边缘检测算法和FPGA电路架构来优化Canny边缘检测算法中的非极大值抑制并采用动态单阈值,使其能够以较少的资源占用在FPGA上以流水线架构实现。该方法在保证边缘提取精度地前提下满足光学自主导航实时性的要求,对复杂的星体目标也具有较好的鲁棒性。