基于W2ID准则的RichModel隐写检测特征选取方法

数字隐写是信息安全领域一个重要分支,其通过将秘密信息嵌入到数字图像、声音、视频等文件中并通过公开信道(如:Email邮箱、微博推文和即时通信等)进行传递,从而实现信息的隐蔽通信.图像自适应隐写是近年来数字隐写技术的研究热点,而Rich Model特征是检测图像自适应隐写的一大类主流高维特征,这类高维特征在实现对图像自适应隐写较高检测正确率的同时,带来了高额的计算开销和和存储开销,并使得隐写检测中的分类器训练变得极为困难.为此,本文提出了一种基于加权类间距离和类内距离差异准则(W2ID准则)的图像Rich Model隐写检测特征选取方法(记为W2ID-α方法).首先,在对Fisher-based方法这一隐写检测特征经典选取方法进行原理分析的基础上,指出该方法可能存在误删有用特征分量、保留冗余和冲突特征分量的不足;然后,通过将"类内距离差异"原则引入到隐写检测特征分量的可分性度量,提出了基于类间距离和类内距离差异的特征可分性度量准则(简记为2ID准则),给出了类内距离差异的一个相关性质;同时,为了合理体现"类间距离"的重要性,本文提出了基于频数统计加权法的权重分配算法,为该准则分配合理权重,使得对特征分量可分性的度量结果相比传统的Fisher准则更为准确;最后,依据W2ID准则的度量结果,基于决策粗糙集α-正域约简方法约简隐写检测特征分量,并在约简特征分量过程中,将每次处理一个特征分量改进为每次处理一组特征分量,以提升决策粗糙集α-正域约简的效率.提出的W2ID-α方法因无需设置可分性下限,避免了阈值设置不准确可能造成去除有用特征分量的问题,从而消除了现有Steganalysis-α隐写检测特征选取方法依赖经验参数的问题.基于数字隐写领域通用的BOSSbase-1.01图像库10 000幅原始图像和基于经典SI-UNIWARD隐写方法生成的多组隐写图像,针对从这些图像组每幅图像中提取的35263维J+SRM特征和17000维GFR特征(两类典型的图像Rich Model隐写检测特征),进行了一系列特征选取实验,结果表明:本文提出的W2ID-α方法能够在大幅降低Rich Model隐写检测特征维数的同时,基于选取后特征的隐写检测提高了对隐写图像的检测正确率,与Fisher-based、Steganalysis-α和PCA-based等现有典型特征选取方法相比具有显著优势,如对嵌入率=0.1的SI-UNIWARD隐写图像,基于提出的W2ID-α方法将J+SRM特征从35 263维降到2723维的同时,还提高了 3.63%的检测正确率.     

基于有限时间跟踪微分器的迭代学习控制

针对迭代学习控制（Iterative learning control,ILC）中的初始状态问题,提出了采用有限时间跟踪微分器安排过渡过程方法,根据迭代学习控制中期望轨迹已知的特点,设计了其参数有明显物理意义并且调节方便的有限时间跟踪微分器. 在此基础上,针对一类具有不确定性的非线性时变系统的迭代学习控制问题,提出了具有对不确定项进行估计的迭代学习控制算法,并应用类Lyapunov方法给出了相关定理证明. 仿真结果表明所提出的方法是有效的.     

Quantum image encryption based on generalized affine transform and logistic map

Quantum circuits of the generalized affine transform are devised based on the novel enhanced quantum representation of digital images. A novel quantum image encryption algorithm combining the generalized affine transform with logistic map is suggested. The gray-level information of the quantum image is encrypted by the XOR operation with a key generator controlled by the logistic map, while the position information of the quantum image is encoded by the generalized affine transform. The encryption keys include the independent control parameters used in the generalized affine transform and the logistic map. Thus, the key space is large enough to frustrate the possible brute-force attack. Numerical simulations and analyses indicate that the proposed algorithm is realizable, robust and has a better performance than its classical counterpart in terms of computational complexity.     

一种解决大规模数据集问题的核主成分分析算法

提出一种大规模数据集求解核主成分的计算方法.首先使用Gram矩阵生成一个Gram-power矩阵,根据线性代数的理论可知,新形成的矩阵和原先的Gram矩阵具有相同的特征向量.因此,可以把Gram矩阵的每一列看成核空间迭代算法的输入样本,这样,无须使用特征分解即可迭代地计算出核主成分.该算法的空间复杂度只有O(m);在大规模数据集的情况下,时间复杂度也降低为O(pkm).实验结果表明了所提出算法的有效性.更为重要的是,在大规模数据集的情况下,当传统的特征分解技术无法使用时,该方法仍然可以提取非线性特征.     

Reliable and Energy-Efficient Routing for Static Wireless Ad Hoc Networks with Unreliable Links

Energy efficient routing and power control techniques in wireless ad hoc networks have drawn considerable research interests recently. In this paper, we address the problem of energy efficient reliable routing for wireless ad hoc networks in the presence of unreliable communication links or devices or lossy wireless link layers by integrating the power control techniques into the energy efficient routing. We consider both the case when the link layer implements a perfect reliability and the case when the reliability is implemented through the transport layer, e.g., TCP. We study the energy efficient unicast and multicast when the links are unreliable. Subsequently, we study how to perform power control (thus, controlling the reliability of each communication link) such that the unicast routings use the least power when the communication links are unreliable, while the power used by multicast is close to optimum. Extensive simulations have been conducted to study the power consumption, the end-to-end delay, and the network throughput of our proposed protocols compared with existing protocols.     

室温中波红外碲镉汞探测器激光辐照饱和特性的仿真

针对室温工作的光伏型碲镉汞中波红外探测器激光辐照饱和特性进行了仿真,结果表明,中红外激光对碲镉汞材料的加热效应以及光照导致零偏压阻抗降低,是影响探测器输出量子效率的重要因素。利用一维数值仿真方法,建立了室温碲镉汞pn结的模型,计算了稳态激光辐照下器件量子效率以及零偏压阻抗。理论计算了激光辐照下的稳态温度分布近似模型,并将温度场分布耦合到仿真计算中,发现衬底厚度会影响芯片的温升,从而显著影响器件饱和阈值的大小。另外,计算表明,随着光照强度的增加,器件的零偏压阻抗降低,并将仿真结果与实测芯片参数进行了比较。计算分析为设计高饱和辐照度阈值的中波红外碲镉汞探测器提供了参考。     

基于梯度能带结构的高速非制冷中波红外HgCdTe探测器

报道了基于梯度能带结构的高速室温中波红外HgCdTe器件,器件设计为n-on-p同质结结构,在300 K的零偏压条件下达到了1.33 ns（750 MHz）的总的响应时间,相对于非制冷的碲镉汞器件和工作于高偏压下的碲镉汞APD器件响应速度有所提高。基于一维模型的分析表明,吸收层中的组分梯度可以形成内置电场并改变了载流子的输运特性,该模型由不同组分梯度的HgCdTe器件的实验对比验证。因此,此项工作优化了高速HgCdTe中波红外探测器的设计,并为设计超快中波红外光电探测器提供了一种可行的思路。     

基于视觉权值的分块颜色直方图图像检索算法

为了进一步提高基于颜色直方图的图像检索系统工作效率, 本文以人眼视觉感知特性为基础, 结合局部图像相关性, 提出了一种基于视觉权值的分块颜色直方图图像检索新方法. 该方法首先对图像进行分块处理, 并计算出图像子块的颜色直方图; 然后结合反映局部区域变化的像素点颜色复杂度, 计算出图像子块的视觉权值; 最后利用视觉权值对子块颜色直方图进行加权处理, 并根据加权颜色直方图进行图像检索. 仿真实验结果表明, 本文算法能够准确和高效地查找出用户所需内容的彩色图像, 并且具有较好的查准率和查全率.     

A novel color image watermarking scheme in nonsampled contourlet-domain

Geometric distortion is known as one of the most difficult attacks to resist, for it can desynchronize the location of the watermark and hence causes incorrect watermark detection. It is a challenging work to design a robust color image watermarking scheme against geometric distortions. Based on the support vector regression (SVR) and nonsubsampled contourlet transform (NSCT), we propose a new color image watermarking algorithm with good visual quality and reasonable resistance toward geometric distortions in this paper. Firstly, the geometrically invariant space is constructed by using color image normalization, and a significant region is obtained from the normalized color image by utilizing the invariant centroid theory. Then, the NSCT is performed on the green channel of the significant region. Finally, the digital watermark is embedded into host color image by modifying the low frequency NSCT coefficients, in which the HVS masking is used to control the watermark embedding strength. In watermark detection, according to the high correlation among different channels of the color image, the digital watermark can be recovered by using SVR technique. Experimental results show that the proposed color image watermarking is not only invisible and robust against common image processing operations such as filtering, noise adding, and JPEG compression etc., but also robust against the geometrical distortions.     

面向安全关键嵌入式系统的时钟同步设计

为了满足安全关键性实时嵌入式系统对实时行为正确性和确定性的要求,本文应用ETSEC网络控制器的硬件时间戳特性, ReWorks嵌入式实时操作系统的实时特性,结合IEEE 1588精密度时钟同步协议,设计并实现了一个面向安全关键性领域的时钟同步系统原型.其同步精度达到100纳秒以内,并通过软件插桩测试和验证了该时钟同步系统的正确性和精度.