基于分块分形的工业CT图像缺陷自动定位算法

针对传统的缺陷定位必须经过图像分割和缺陷提取等步骤,识别过程比较麻烦而且费时,提出了一种基于分块分形的工业CT图像缺陷自动定位算法.该方法首先对图像进行分块处理,对每个分块区域进行分形维数计算.通过分形维数频域分布直方图进行阈值处理,标记边缘块,最后通过连通区域处理标记块,进而对缺陷进行标记定位.通过对含有不同缺陷数目的固体火箭发动机模型工业CT图像处理,均可以准确地定位缺陷.实验结果表明,该方法能有效、准确地自动定位工业CT图像缺陷,且具有较强的鲁棒性.     

How the environment determines banking efficiency: a comparison of banking firms in Taiwan,Hong Kong,and Mainland China

This study uses the three‐stage data envelopment analysis (DEA) model to explore the true managerial efficiency of the banking firms in Taiwan, Hong Kong, and Mainland China. The empirical results indicate that the environmental conditions have a significant impact on banking efficiency. When the country‐specific situations are important factors in explaining efficiency difference, the common frontier estimates obtained by neglecting those factors can generate biased and overestimated inefficiency levels. With findings obtained from the slack variable analyses, the current study can provide inefficient banks with ways to reduce their input waste through the adjustment of input allocations. The findings also confirm the importance of the three‐stage DEA and its applications in determining the true managerial efficiencies of banks. Without the three‐stage DEA, the management could be misguided when making strategic decisions and conducting inappropriate resource allocation.     

Influence of groove type on welding-induced residual stress,deformation and width of sensitization region in a SUS304 steel butt welded joint

To join a medium or thick plate weldment with a full penetration, a groove is usually prepared in the space between two sections of metal. Because weld metal needs to be deposited within the groove to form the joint, it is expected that different groove type will require different heat input, which may consequently have influence on welding residual stress and deformation. Generally, different groove corresponds to different bead layout, so it can be foreseen that the groove type has a significant effect on temperature history, shape and size of heat affected zone, and region of sensitization in certain alloys such as austenitic stainless steel. The influences of groove type on residual stress, angular distortion and width of sensitization region in a SUS304 butt-welded joint were investigated by means of numerical simulation and experiment. Based on ABAQUS code, a computational approach with considering thermo-mechanical coupling behaviors, moving heat source, strain hardening and annealing effect was developed to simulate temperature profile, stress field and deformation in multi-pass joint. Welding temperature cycles, residual stress distributions and deformations in V, K and X groove joints were calculated through using the proposed computational procedure. Meanwhile, experiments were carried out to obtain residual stress distributions and angular distortions. Through comparing the numerical results and the measured data, the effectiveness and accuracy of the developed computational approach were verified. The simulation results show that groove type has a significant influence on welding residual stress distribution, angular distortion and width of sensitization region.     

一类饱和非有理系统状态反馈设计

本文研究了一类饱和非有理系统状态反馈镇定问题.通过线性分式表示技术,这类非有理系统可以转化为带有两个非线性回路的线性时不变(linear time-invariant,LTI)系统.假设非有理函数项分别满足局部扇形区间不等式以及局部Lipschitz条件,提出了两种基于LMI条件的镇定方法.最后,举例证明了所提出方法的有效性.     

基于聚类和局部区域的彩色图像分割方法

针对现有图像多阈值分割方法存在的分割不够准确、计算复杂度较高等问题,利用Otsu多阈值分割的思想,提出一种基于聚类和局部区域的彩色图像多阈值分割方法.获取彩色图像的H分量直方图;在综合考虑以H分量划分的颜色范围的前提下对直方图中的H分量进行聚类,依次选取各类中的最大值作为对应局部区域的边界;分别搜索局部区域内的最小H分量值,将其作为彩色图像的分割阈值.实验结果表明,与现有方法相比,该方法具有较高的分割准确性和更快的计算速度.     

H.264视频感兴趣区域加密算法

为了对视频的隐私区域进行加密,提出一种基于FMO和骑士巡游思想的H.264视频感兴趣区域加密的算法。首先确定视频中包含的感兴趣区域的范围,之后对感兴趣区域内部宏块的宏块类型参数使用SHA-1生成的流密码异或加密,并对条带组序号使用骑士巡游思想置乱加密。实验分析表明,该算法可以有效地保护视频中的隐私区域,并且可以在安全性、加密效率和编码效率取得较好的折中。     

Analysis of General Ideal Proportional Navigation Guidance Laws

In this work, the capture region of the general ideal proportional navigation guidance law is analyzed with the following constraints: (i) the target's input acceleration is subject to independent or magnitude saturation, and (ii) the missile's input acceleration is subject to magnitude saturation. In addition to the case of unbounded maneuverability of missile with or without knowing the target acceleration, the necessary and sufficient condition for a bounded maneuvering missile that captures a nonmaneuvering target is also derived. Furthermore, the conditions that result in zero impact velocity are discovered and discussed in some of the cases. The capture regions that cannot be obtained analytically are determined numerically by a powerful classifier, the least square support vector machines. To have the capture region ready for least square support vector machines, all the state variables are transformed into modified polar variables and non‐dimensionalized to reduce the number of independent variables. In order to make the implementation possible in real time, an approximation of the Gaussian radial basis function is adopted to obtain the corresponding nonlinear feature mapping function. Through numerous numerical experiments, the proposed technique is found to be adequate for storing the capture region in an onboard fire control computer.     

JPEG图像双重压缩偏移量估计的篡改区域自动检测定位

目的 为了解决现有图像区域复制篡改检测算法只能识别图像中成对的相似区域而不能准确定位篡改区域的问题,提出一种基于JPEG(joint photographic experts group)图像双重压缩偏移量估计的篡改区域自动检测定位方法。方法 首先利用尺度不变特征变换(SIFT)算法提取图像的特征点和相应的特征向量,并采用最近邻算法对特征向量进行初步匹配,接下来结合特征点的色调饱和度(HSI)彩色特征进行优化匹配,消除彩色信息不一致引发的误匹配;然后利用随机样本一致性(RANSAC)算法对匹配对之间的仿射变换参数进行估计并消除错配,通过构建区域相关图确定完整的复制粘贴区域;最后根据对复制粘贴区域分别估计的JPEG双重压缩偏移量区分复制区域和篡改区域。结果 与经典SIFT和SURF(speeded up robust features)的检测方法相比,本文方法在实现较高检测率的同时,有效降低了检测虚警率。当第2次JPEG压缩的质量因子大于第1次时,篡改区域的检出率可以达到96%以上。 结论 本文方法可以有效定位JPEG图像的区域复制篡改区域,并且对复制区域的几何变换以及常见的后处理操作具有较强的鲁棒性。     

利用层间相关性的岩心CT图像半自动分割方法

目的 由于岩心CT图像分辨率不高,目标边界较为模糊,无法完全自动化地对岩心CT图像的目标分割和提取。为保证效果,在分割过程中往往需要进行人为干预。但作为3维重建的岩心CT图像,图像数据规模较大,达到成百上千帧。如果对每一帧都进行人为干预,工作量将会很大。针对这种情况提出一种在保证分割效果的前提下只需进行少量人为干预的高效实用的分割方法。方法 先对CT图像中的某一帧设定分割阈值,利用CT图像层间相关性对相邻帧自动计算合适的分割阈值,从而分割出整个CT图中的目标。并根据需要,选定其中分割效果较好的一帧,其他帧根据此帧进行自动区域生长修复,从而更加完善分割效果。还可以手工修复其中一帧中的目标,其余帧的所有相关目标将会自动进行识别和修复。结果 通过对多组不同数据规模和分辨率的岩心CT图像进行实验测试,使用本文方法均可达到期望的分割效果,并且分割速度较大津分割法提高近1倍,与固定阈值分割方法速度相当。结论 岩心CT图像分割方法充分利用图像层间相关性,可快速有效地批量提取具有连续性的序列图像中的目标。     

Energy-efficient control of nanosatellites during distributed region formation flying

In this paper, we present an energy-efficient method for distributed region formation flying of nanosatellites. The proposed framework consists of two concurrent sub-schemes that include estimation and formation. In the estimation sub-scheme, unlike the existing methods on satellite formation flying, that assume the availability of the reference orbital elements to all followers, here, a distributed estimator is developed so that the follower nanosatellites estimate the position of the leader in its orbital slot. In the formation sub-scheme, we consider a region formation strategy which is an efficient method in dealing with the formation of a large number of nanosatellites. We propose an optimal region following formation method based on the receding horizon control (RHC) using the estimated reference orbital elements. Subsequently, an algorithm is presented to solve the proposed energy-efficient formation flying method. Finally, the simulation result is presented that illustrates the purposed method improves the power consumption for each nanosatellite with respect to the existing non-optimal region formation flying controllers.