基于均值量化的小波域自同步数字音频水印算法研究

文中提出了一种基于均值量化的小波域自同步数字音频水印算法。该算法是一种盲水印算法,水印提取不需要原始音频信号的参与。算法设计中运用了均值量化的策略,音频信号小波分解后,在低频系数中隐藏水印信息;引入了同步信号的思想,利用同步信号定位水印隐藏位置。实验表明,该算法具有较强的鲁棒性、抗攻击性、抗裁剪性。     

基于博弈论的无意攻击和隐写分析攻击下嵌入水印漏警概率分析(英文)

Steganalysis attack is to statistically estimate the embedded watermark in the watermarked multimedia,and the estimated watermark may be destroyed by the attacker.The existing methods of false negative probability,however,do not consider the influence of steganalysis attack.This paper proposed the game theory based false negative probability to estimate the impacts of steganalysis attack,as well as unintentional attack.Specifically,game theory was used to model the collision between the embedment and steganalysis attack,and derive the optimal building embedding/attacking strategy.Such optimal playing strategies devote to calculating the attacker destructed watermark,used for calculation of the game theory based false negative probability.The experimental results show that watermark detection reliability measured using our proposed method,in comparison,can better reflect the real scenario in which the embedded watermark undergoes unintentional attack and the attacker using steganalysis attack.This paper provides a foundation for investigating countermeasures of digital watermarking community against steganalysis attack.     

基于SIFT特征点和交比值的水印图像抗攻击算法

为提高数字水印图像对常规信号和复杂几何攻击的抵抗能力,利用SIFT(scale invariant feature transform)特征点的稳健性和交比值不变特性,提出了一种数字图像顽健水印算法。首先,在原图像经过NSCT(nonsubsampled contourlet transform)变换后的低频子带系数中提取SIFT特征点并对其进行优化筛选,从中确定满足“近凸正四边形” 的系数区域作为水印嵌入的局部区域,然后利用事先设定好的一些交比值在各局部区域中确定要嵌入水印的具体系数,最后利用奇偶量化调制方法嵌入水印信息。与传统算法相比,在提取水印信息时无需对含水印图像进行几何逆变换。实验结果表明,该算法对常规信号处理及多种几何攻击具有较强的抵抗能力和顽健性。     

Fano Decoding with Timeout: Queuing Analysis

In mobile communications, a class of variable‐complexity algorithms for convolutional decoding known as sequential decoding algorithms is of interest since they have a computational time that could vary with changing channel conditions. The Fano algorithm is one well‐known version of a sequential decoding algorithm. Since the decoding time of a Fano decoder follows the Pareto distribution, which is a heavy‐tailed distribution parameterized by the channel signal‐to‐noise ratio (SNR), buffers are required to absorb the variable decoding delays of Fano decoders. Furthermore, since the decoding time drawn by a certain Pareto distribution can become unbounded, a maximum limit is often employed by a practical decoder to limit the worst‐case decoding time. In this paper, we investigate the relations between buffer occupancy, decoding time, and channel conditions in a system where the Fano decoder is not allowed to run with unbounded decoding time. A timeout limit is thus imposed so that the decoding will be terminated if the decoding time reaches the limit. We use discrete‐time semi‐Markov models to describe such a Fano decoding system with timeout limits. Our queuing analysis provides expressions characterizing the average buffer occupancy as a function of channel conditions and timeout limits. Both numerical and simulation results are provided to validate the analytical results.     

一种新的小波域盲水印算法

文章提出了一种新的小波域鲁棒性水印算法,将载体图像小波变换后的近似子带进行分块,结合HVS,用密钥对子块进行选择,直接进行灰度水印的嵌入。该算法具有嵌入和提取过程十分简单、水印嵌入信息量大、鲁棒性强等突出特点,并能够实现水印盲检测。     

半封闭活塞式和螺杆式冷水机组性能比较

半封闭活塞式和螺杆式冷机组以其各自鲜明的特点得到了广泛的应用。文章分析了开利半封闭活塞式和螺杆式冷水机组的特点,对比在不同温度和不同冷量下的性能,为实际使用打下基础。     

A Robust Algorithm for Watermarking 2D Vector Maps with Low Shape-Distortions

The technique of watermarking has been introduced into 2D vector maps for many potential applications such as protecting the copyright of important GIS （geographical information system） data and tracing the data source of military maps. In most previous works, although the validity of the map data could be preserved during the embedding procedure, the shape-distortions of the map elements are usually neglected which would tend to degrade the invisibility of the watermarking schemes. A shape-preserving algorithm for watermarking 2D vector maps is presented in this paper. A 1D distance sequence extracted from the original map is adopted as the cover data instead of 2D coordinates. A watermark bit is represented by changing the distributions of the cover data. The embedding procedure induces lower shape-distortions than in former works. Experimental results indicate better invisibility of the proposed scheme, as well as its robustness to certain attacks such as map simplification, interpolation, additive noise and most geometric transforms.     

耦合尾喷管堵盖运动的发射箱内流场研究

利用初始冲击波超压完成前后盖开启过程的贮运发射箱已得到广泛应用。为研究含尾喷管堵盖的冲击波超压形成过程及对后易碎盖的作用效果,应用有限元方法并结合动网格技术建立了导弹点火后堵盖的运动模型,并通过实验方法对仿真结果进行了验证。结合计算结果可清晰地看到尾焰流场的形成过程,并得到了冲击波超压在后易碎盖表面的随时间变化曲线。研究表明：受堵盖的影响,冲击波超压首先形成并冲击后易碎盖,燃气由堵盖的边缘向中心汇聚形成主流,在对后易碎盖的冲击时间和作用位置上与冲击波作用有明显的不同;后易碎盖主要受到冲击波超压作用实现碎裂变形,在堵盖运动的投影区域首先达到最大受力,瞬时峰值达5×10⁵ Pa.     

一种可用于图像置乱的新型变换矩阵

以图像信息安全为背景,构造了一种新型变换矩阵W,证明了其周期性,并给出了其周期与Arnold矩阵变换周期的比较.理论分析表明,W-矩阵在二阶和三阶情况下具有比Arnold矩阵更大的周期,因此,在图像置乱处理中具有比Arnold矩阵更大的优势.实验仿真结果验证了这一结论.     

数字图像小波域鲁棒性双水印算法

本文提出了一种数字图像小波域双水印算法,该方法在检测时依据一个参考水印来动态调整主水印序列各部分的可信度,从而尽量减少攻击造成的影响。实验表明,该算法有效降低了检测错误的概率,显著地提高了扩频水印的抗攻击能力。