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圆柱体构件中非轴对称人造缺陷偏心圆孔的超声探伤一直是无损检测的难点。基于脉冲反射原理设计超声实验平台,根据检测回波信号判定偏心圆孔缺陷所呈现的特征。在实验研究基础上,针对声场在圆柱体工件内部的传播情况,根据惠更斯原理以圆柱体为发射声源,基于k-wave仿真工具箱建立仿真平台,并利用声学传感器接收声波信号,设计的仿真平台能够实现360°同时刻采集工件的发射信号,同时利用传播过程中声压强弱的变化构建声场模型。根据采集的信号采用逆时反演重构模型,直观可视化地重构了内部缺陷的位置形状信息。 相似文献
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Christopher Zambakari 《African Security Review》2016,25(1):44-62
In this paper, I critically analyse the doctrine of the Responsibility to Protect (RtoP), as it relates to the responsibility of intervening forces towards the people they claim to protect and the challenges that the situation in Libya now poses in the region and for the African Union (AU). I focus most of my attention on the coercive elements of the RtoP framework (Pillar III). This is the most contested element in the framework. Three questions guide this article: were there legitimate grounds to justify an external intervention in Libya? In the words of Hugh Roberts in Who Said Gaddafi Had to Go, ‘[w]hat if anything has Libya got in exchange for all the death and destruction that have been visited on it’ since 2011? What are the practical implications and consequences of the North Atlantic Treaty Organization (NATO) intervention, led by the United States (US), for regional peace? I discuss the problems surrounding the US–NATO intervention, followed by an analysis of the various positions and narratives leading up to the intervention, the framing and justifications provided for the intervention, and an analysis of the AU's proposal for the resolution of the Libyan crisis. I analyse the various debates that took place in the US (Pentagon/White House), at the United Nations, among scholars in the West and in Africa, and among various actors who tried to broker a ceasefire in Libya before and during the intervention. I conclude with a discussion of the implications for regional peace. 相似文献
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For a given set S of nonnegative integers the partitioning problem asks for a partition of S into two disjoint subsets S1 and S2 such that the sum of elements in S1 is equal to the sum of elements in S2. If additionally two elements (the kernels) r1, r2 ∈ S are given which must not be assigned to the same set Si, we get the partitioning problem with kernels. For these NP‐complete problems the authors present two compound algorithms which consist both of three linear greedylike algorithms running independently. It is shown that the worst‐case performance of the heuristic for the ordinary partitioning problem is 12/11, while the second procedure for partitioning with kernels has a bound of 8/7. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 593–601, 2000 相似文献
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经典的数字信道化思想的实施都是建立在一组硬件滤波器构成的并行多路,虽然能实时处理,但随着处理数据带宽的增大和子信道频率分辨率的增加,设备开销将线性增长,整体可靠性也必然下降.基于信号的检测理论,在利用时频分析工具得到的时频图上进行信号检测,提出了检测去噪法.针对宽带数据背景噪声的特点,提出了噪声基底的3种估计算法:去大留小法、对数统计法和频移均值法,并线面结合对噪声基底进行平滑,实现了天电干扰的去除.通过实际接收到的某短波信号检验,证明了算法的有效性. 相似文献