铜/镍箔中间层对铝/钢激光焊接接头组织与力学性能的影响

研究以Ni、Ni/Cu箔片为中间层的铝/钢异种金属激光焊接行为,系统考察Cu/Ni箔片复合中间层的添加对铝/钢异种激光焊接接头组织与性能的影响。利用扫描电子显微镜和能谱仪对焊缝横截面的组织形貌和各区域的元素分布进行观察分析,利用X射线衍射仪对焊接接头的主要物相进行分析,并利用电子万能试验机对焊接接头进行拉伸实验以表征其力学性能,结果表明:Cu/Ni箔片做复合中间层加入时,其中加入0.02 mm厚Cu箔片时焊接接头的最大剪切力提高至1754.72 N;加入0.05 mm厚Cu箔片时的最大剪切力为734.97 N,相比只添加Ni箔片时焊接接头的最大剪切力反而下降。Cu箔片的添加使得铝/钢界面的物相组成、元素分布和微观组织形态发生改变,同时增加了熔池的流动性。在靠近不锈钢侧的Fe-Al脆性相中的部分Fe原子被Cu原子取代生成新的二元韧性相,从而抑制Fe-Al二元脆性金属间化合物的生成,有效改善铝/钢的焊接性。因此,Cu/Ni箔片复合中间层的加入,可以有效地改善铝/钢异种激光焊接过程中的冶金反应,进而提高焊接接头的力学性能。     

超细长空心活塞杆高速车削加工

介绍了长径比接近80∶1的超细长空心杆(活塞杆)的结构特点和加工难点。从理论联系实际的角度出发,分析了细长空心杆车削过程中容易出现的各种缺陷的产生原因,并提出针对性的措施以及提高生产效率的途径。     

大型客机CAT Ⅲ级自动着陆机载设备需求

CAT Ⅲ自动着陆在恶劣天气进场着陆时具有较高的安全性和可靠性,对此类运行机载设备的研究具有重要的意义.本文首先从基本概念及原理出发介绍了进场着陆等级的划分、故障一性能下降和故障-工作两类自动着陆系统以及完成自动着陆的机载自动飞行系统及设备,然后指出决断高度DH和跑道视程RVR对CAT Ⅲ自动着陆机载设备的限制,最后介...     

Automatic target recognition for hyperspectral imagery using high-order statistics

Due to recent advances in hyperspectral imaging sensors many subtle unknown signal sources that cannot be resolved by multispectral sensors can be now uncovered for target detection, discrimination, and identification. Because the information about such sources is generally not available, automatic target recognition (ATR) presents a great challenge to hyperspectral image analysts. Many approaches developed for ATR are based on second-order statistics in the past years. This paper investigates ATR techniques using high order statistics. For ATR in hyperspectral imagery, most interesting targets usually occur with low probabilities and small population and they generally cannot be described by second-order statistics. Under such circumstances, using high-order statistics to perform target detection have been shown by experiments in this paper to be more effective than using second order statistics. In order to further address a challenging issue in determining the number of signal sources needed to be detected, a recently developed concept of virtual dimensionality (VD) is used to estimate this number. The experiments demonstrate that using high-order statistics-based techniques in conjunction with the VD to perform ATR are indeed very effective     

综合评判法确定可靠性门限值

在装备论证过程中，由可靠性目标值合理确定门限值是在整个可靠性要求论证中，十分关键的部分。本文论述的是基于Duane模型，在装备目标值明确的前提下，利用综合评判法确定装备可靠性可能的增长潜力，科学、合理地确定门限值。     

Magnetic Field Topology and Criticality in Geotail Dynamics: Relevance to Substorm Phenomena

Recent observations and analyses seem to suggest that certain dynamical features of the Earth's magnetosphere could resemble the evolution of a complex system near a forced and/or self-organized criticality (FSOC). Here, we review concepts dealing with the phenomenology of criticality and disorder systems in connection with magnetospheric processes. In more detail, we discuss the importance of intermittency, turbulence and local topological disorder in the geomagnetic tail regions, that form a new paradigm for the understanding of the magnetotail dynamics.     

空间环境对聚合物基复合材料性能的影响

文章介绍了空间飞行器工作过程中的空间环境条件。为满足这些要求 ,在设计与选材时须考虑一些因素。此外对某型号任务中使用的P75S/环氧648复合材料耐空间环境条件的性能做了简要评述。     

Parallel operation of shunt active power filters with capacitylimitation control

This paper presents a capacity-limitation technique to enlarge the power capacity that can be handled by the shunt active power filters (APFs). The capacity limited includes the reactive power as well as the amplitude of the distortion current supplied by the APFs. Under capacity-limitation control m+1 APFs supply the load reactive power with m APFs supplying their rated power and one APF supplying a fraction of its rated value. Similarly, n+1 APFs supply the load current harmonic with n APFs supplying the distortion current limited in amplitude and one APF supplying a fraction of its limited amplitude. Advantages of the proposed approach include high flexibility for extending system capacity, high reliability due to no control interconnection, reducing power capacity demand of APF, high modularity due to identical APFs, stable reactive power and harmonic current sharing and its performance is insensitive to parameters mismatch of APFs, cost-effective due to modularization, and so on. Three single-phase 1 KVA APFs are designed and implemented. The effectiveness is demonstrated by some experimental results     

Reconfiguration of flight control systems for actuator failures

We consider the problem of designing fault tolerant control for transient failures in the flight control system caused by harsh electromagnetic environments. We examine principles of fault tolerant design and discuss integrated local supervisory control of these systems. As an example, we present a sample design of a control mixer to achieve fault tolerance in the event of failures in the actuators