基于空时DFT投影实现宽带信号二维角估计

 提出了一种基于空时DFT投影的宽带信号二维角估计算法. 该方法采用3个共面的均匀线阵,每一均匀线阵对宽带信号空间采样,然后进行空时二维DFT变换,在空时频率域对宽带信号进行投影变换,用MUSIC算法实现宽带来波信号方向余弦的估计. 利用3个方向余弦估值进行配对,然后求得来波的方位角和仰角估计. 该方法既保留了投影算法的优点,即不需要源的先验知识;不需变换矩阵和在低信噪比有好的性能,又避免二维谱峰搜索.仿真实验表明了算法是有效的.     

交错级数的审敛法

本文给出交错级数及双项交错级数的一种类型的审敛法，并分别给出判定交错级数及双项交错级数绝对收敛的一种方法。     

一种终端区利用率评估方法研究

终端区利用率量化评估是解决终端区运行瓶颈、挖掘运行潜力的重要前提。现有方法大都面向全空域,指标缺乏通用性。聚焦终端区运行特点,构建了终端区利用率评估指标,基于灰色绝对关联度和主成分分析法,建立了灰色主成分评估模型,并对传统灰色绝对关联度的计算方法进行改进。以20个典型终端区数据为基础,经模糊C均值聚类验证了所提方法有效正确,且可区分性更好,能够满足多个终端区间的横向对比要求;结合广州终端区雷达数据进一步分析,发现方法更加细致地反映了沿时间轴的资源利用情况,满足单个终端区的纵向对比要求,可以为终端区的天气影响评估及流量管理优化策略评估提供论证依据。     

星图匹配制导中的关键技术

为了提高新一代弹道导弹的快速、机动反击能力和射击精度，采用星光，惯性组合制导足最佳的选择。本论文给出了基于双星敏感器的、星图匹配制导系统的关键技术。提出了根据弹道设计导航星表．极大地简化了弹载星表；提出了一种适用于星光制导的凸多边形箅法，合理地减少了匹配的星对角距数目。这两项技术保证了星图匹配制导技术的实用性。提出了一种分离初始定位、定向误差及平台漂移误差方法。采用凸多边形的星图识别算法可同时获得多颗星的瞬时位置，结合恒星在像平面的位置可解算导弹在赤道惯性系和发射点惯性系的三轴姿态，最后，给出了导弹初始定位、定向误差的数学表达式。仿真结果表明了该方法的有效性。     

Keeping Ma’at: An astronomical approach to the orientation of the temples in ancient Egypt

For various reasons, Archaeoastronomy has not been one of the favourite disciplines of the Egyptologists in the past. Probably because of that, important questions such as the orientation of Egyptian temples and the relevance of astronomy in this respect had never been afforded with the necessary seriousness and deepness. The Egyptian–Spanish Mission for the Archaeoastronomy of ancient Egypt has, among its various priorities, the solution of this problem. In order to achieve that, we have measured the orientation of some 330 temples in the Valley, the Delta, the Oases and the Sinai so far. The aim is to find a correct and almost definitive answer to the question of whether the ancient Egyptian sacred constructions were astronomically aligned or not. Our data seem to answer this question in the affirmative sense. Besides, they offer a very interesting new perspective in the field of landscape archaeology, a new discipline hardly worked in Egypt so far, in which terrestrial landscape, dominated by the Nile, and celestial landscape, dominated by the sun and the stars, would combine in order to permit the establishment of Ma’at, the Cosmic Order, on Earth.     

Microstructure,thermophysical property and ablation behavior of high thermal conductivity carbon/carbon composites after heat-treatment

Uni-directional carbon/carbon composites with high thermal conductivity are suitable to supply continuous thermal protection for future reentry vehicles since they could reduce surface temperature and ablation rates simultaneously in harsh environments. In this work, the high thermal conductivity carbon/carbon composites were prepared by chemical vapor infiltration. After heat-treatment, both their open porosity and internal friction increase due to the fiber/matrix thermal expansion mismatch; while their thermal conductive performance become better due to more complete carbon structure. With raising heat-treatment temperature from 1800 °C to 2450 °C, the mass and linear ablation rates of C/C composites with fibers vertical to the oxyacetylene torch for 60 s decrease from 0.66 mg/s and 2.95 μm/s to 0.51 mg/s and 2.05 μm/s respectively. The improved ablation resistance is resulted from the increased thermal conductivity from 282 to 508 W/(m·K) and more carbon fibers exposed to the flame during ablation, which have better oxidation resistance than those of carbon matrix. While such ablation rates become larger for composites with fibers parallel to the flame, from 1.02 mg/s and 3.73 μm/s to 1.28 mg/s and 5.01 μm/s respectively since the ablation occurred more easily through gaps at the fiber/matrix interfaces, which become larger and are always exposed to the flame for this case.     

Crystal orientation and morphology of α lamellae in wrought titanium alloys: On the role of microstructure evolution in β processing

To obtain high-quality aviation forgings of titanium alloys, β forging is an essential processing step which must be considered throughout a production process. In this work, the effect of β forging on the crystal orientation and morphology of lamellar α was experimentally investigated in a two-phase titanium alloy. Strong dynamic recovery during β working resulted in the formation of low-angle grain boundary (LAGB_β) inside β grains. The lamellar α can penetrate through the LAGB_β, leading to similar intra α LAGBs on subgrain boundaries. Deformation banding occurs at high strain rates, and both diffusive and sharp boundaries of deformation bands can be observed. A continuous change of the β orientation in diffusive boundaries results in the formation of fine and disordered α lamellae without intra-lamellar boundary to hold the Burgers orientation relationship (OR). On sharp boundaries, it is prone to producing continuous grain boundary α (α_GB) with a highly similar orientation along the boundaries. Meanwhile, there may exist several lower-angle boundaries within the grain boundary α for a smoother orientation change on the β grain boundary.     

Localization,Exploration, and Navigation Based on Qualitative Angle Information

Abstract

Three of the major problems in building autonomous mobile robots are localization, exploration, and navigation. This paper investigates how well different qualitative methods based on angle information, most of them originally invented for representation of spatial knowledge, are suited for addressing these problems. It combines results from discrete and computational geometry with methods from qualitative spatial reasoning, gaining some new insights on the complexity of robot navigation. It turns out that essentially only with panoramas (special roundviews) the qualitative localization problem can be solved in a satisfactory manner. The exploration problem (qualitative map building), remains difficult for all considered approaches.     

中国沪深股市中羊群行为检验

分散度检验法和横截面收益绝对差检验法是检验证券市场中羊群行为的两种方法。运用这两种方法对中国证券市场进行实证分析，结果表明：在中国的证券市场中确实存在着明显的羊群行为。     

闭合等角转位法的测量精确度

闭合等角转位法广泛地应用于传感器旋转式圆度测量仪、工作台旋转式圆度测量仪或精密轴系的径向、轴向及其综合误差的测量。对闭合等角转位法的测量精确度做了详细的理论分析和实验验证,并提出了正确确定其采样点数的方法。