Phase unwrapping algorithms, respectively, based on path-following and discrete cosine transform

This paper describes a path-following phase unwrapping algorithm and a phase unwrapping algorithm based on discrete cosine transform (DCT) which accelerates the Computation and suppresses the propagation of noise. Through analysis of fringe pattern with serious noises simulated in mathematic model, we make a contrast between path-following algorithm and DCT algorithm. The advantages and disadvantages or analytical fringe pattern are also given through comparison of two algorithms. Three-dimensional experimental results have been given to prove the validity of these algorithms. Despite DCT phase unwrapping technique robustness and speed in some cases, it cannot be unwrapping inconsistencies phase. The path-following algorithm can be used in automation analysis of fringe patterns with little influence of noise. (c) 2007 Elsevier GmbH. All rights reserved.

Discrete wavelets transform for signal denoising in capillary electrophoresis with electrochemiluminescence detection

Discrete wavelets transform (DWT). was applied to noise on removal capillary electrophoresis-electrochemiluminescence (CE-ECL) electropherograms. Several typical wavelet transforms, including Haar, Daublets, Coiflets, and Symmlets, were evaluated. Four types of determining threshold methods, fixed form threshold, rigorous Stein's unbiased estimate of risk (rigorous SURE), heuristic SURE and minimax, combined with hard and soft thresholding methods were compared. The denoising study on synthetic signals showed that wave Symmlet 4 with a level decomposition of 5 and the thresholding method of heuristic SURE-hard provide the optimum denoising strategy. Using this strategy, the noise on CE-ECL electropherograms could be removed adequately. Compared with the Savitzky-Golay and Fourier transform denoising methods, DWT is an efficient method for noise removal with a better preservation of the shape of peaks.

光学干涉图像处理中基于质量权值的离散余弦变换解包裹相位

为减少噪声对相位恢复过程的影响,快速得到正确的解包裹相位,提出了一种改进的相位解包裹方法——加权离散余弦变换解包裹算法。该方法把离散余弦变换和标识相位数据好坏的质量权值结合起来,兼有速度快和可靠度高的优势。为验证此算法,对模拟和实验得到的包裹相位图添加随机噪声和散粒噪声,同时采用加权与非加权离散余弦变换算法进行处理,所得到的解包裹结果与未加噪声的解包裹相位值进行比较,结果表明,通过加权离散余弦变换算法恢复的相位图比非加权离散余弦变换算法所恢复的相位图更接近于理想值,而且两种算法的运行速度基本相同,这证明提

频谱泄漏对正弦相位调制干涉测量精度的影响何

在正弦相位调制(SPM)干涉仪中,若调制频率或者采样频率发生变化将使干涉信号出现频谱泄漏,减小了谐波分量的幅值,在测量结果中引入了误差。对频谱泄漏的产生及其对测量精度的影响进行了理论分析,获得了频谱泄漏引入测量误差的计算方法。实验测得频率漂移量在-0.3～0.3 Hz内,得到的频谱泄漏引入的误差为0.3～7.9 nm,当超出这个范围时,频谱泄漏误差将迅速增长。实验结果与模拟分析结果一致。

傅立叶分解法荧光层析成像

本文提出一种基于结构光照明和傅立叶分解方法的荧光层析成像技术，该技术首先将激发光的强度沿着光轴方向调制成余弦函数，然后用此激发光对样品作传统的二维扫描，在每一个扫描位置余弦函数的频率在一定的范围内扫描，同时一一对应地记录下所发出的荧光强度。只要对所纪录的荧光序列做一个简单的傅立叶变换，即可以得到此位置样品沿着光轴方向的荧光团分布。这样通过一个传统的二维扫描，就可以得到一个三维的阳样品分布。

AN EFFICIENT ITERATIVE DFT-BASED CHANNEL ESTIMATION FOR MIMO-OFDM SYSTEMS ON MULTIPATH CHANNELS

In this paper, an efficient iterative discrete Fourier transform (DFT) -based channel estimator with good performance for multiple-input and multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems such as IEEE 802.11n which retain some sub-carriers as null sub-carriers (or virtual carriers) is proposed. In order to eliminate the mean-square error (MSE) floor effect existed in conventional DFT-based channel estimators, we proposed a low-complexity method to detect the significant channel impulse response (CIR) taps, which neither need any statistical channel information nor a predetermined threshold value. Analysis and simulation results show that the proposed method has much better performance than conventional DFT-based channel estimators and without MSE floor effect.

门限密码学中的离散傅里叶变换

基于离散傅里叶变换提出了一种通用的门限密码学中恢复分享秘密的算法。该算法是离散傅里叶变换在门限密码学中的首次应用。利用该算法，门限密码体制可以有效地达到鲁棒性和自适应安全性。同时，引入了设计有效的鲁棒自适应安全的门限密码体制的新的通用技术。

DCT变换域乘嵌入图像水印的检测算法

目前大多数水印算法采用线性相关的方法检测水印，但是，当原始媒体信号不服从高斯分布，或者水印不是以加嵌入方式嵌入到待保护的媒体对象中时，该方法存在一定的问题．数字水印的不可感知性约束决定了水印检测是一个弱信号检测问题，利用这一特性，首先从图像DCT（discrete cosine transfom）交流变换系数的统计特性出发，应用广义高斯分布来建立其统计分布模型，然后将水印检测问题转化为二元假设检验问题，以非高斯噪声中弱信号检测的基本理论作为乘嵌入水印的理论检测模型，推导出优化的乘嵌入水印检测算法，并对检测算法进行了实验．结果表明，对于未知嵌入强度的乘水印的盲检测，提出的水印检测器具有良好的检测性能．因此，该检测器能在数字媒体数据的版权保护方面得到了实际的应用．

地形可视性分析中观察点设置问题研究

观察点设置问题是地形可视性分析中的一类重要问题，对该问题的研究可以在空间信息辅助决策、通信、旅游、野生动物保护等领域发挥重大作用。本文在对地形可视性分析中观察点设置问题现有研究成果总结和分析基础上对该问题展开深入研究。 首先，针对现有解决方法只从智能算法或地形数据表示方法单一角度进行分析和研究的局限性，提出了一种问题相关的智能算法和数据表示方法相结合的解决问题新框架。该框架考虑了解决观察点设置问题时智能算法的优点和数据表示方式的特点相互配合问题，目的是充分发挥二者各自的优势以提高观察点设置问题解决的准确度与效率。 其次，在深入分析观察点设置问题本身特点的基础上，结合隶属云理论的基本理论和方法，对经典模拟退火算法从退温函数设计、温度产生过程、状态生成过程三方面进行了问题相关的改进，提出了一种适于观察点设置问题的改进模拟退火算法(Improved Simulated Annealing algorithm, ISA)。该算法一方面保持了经典模拟退火算法的稳定倾向特性，保证了算法满足伴随退火温度的不断下降，对恶化的新状态越来越难于接受这一模拟退火算法的最基本特征；另一方面其退火温度的连续性随机变化特性和隐含的“回火升温”过程，则有利于算法有效拒绝恶化解，加速算法收敛，能够更好地满足观察点设置问题对于算法收敛速度的要求。 再次，在分析地形数据的精度、误差等因素对观察点设置问题的解决准确性和解决效率影响程度的基础上，提出了一种基于离散余弦变换的地形数据内插方法(Discrete Cosine Transformation Interpolation method, DCTI)。新方法将传统空域上的地形内插转换到变换域上进行，同时充分利用了离散余弦变换的熵保持特性和能量压缩特性，简化了变换域上的内插过程，提高了地形数据内插的效率和精度。DCTI方法与其他现有典型地形数据内插方法相比，对地形可视性信息获取的准确性和效率影响最小，为平衡观察点设置问题解决过程中时间效率和准确度之间的关系，最终有效地解决观察点设置问题提供了数据基础。 最后，从智能算法和地形数据相结合的角度出发，提出了一种基于ISA和DCTI相结合的观察点设置问题多分辨率处理方法(Multi-Resolution Processing method, MRP)。新方法将模拟退火算法的逐次退火特点和地形数据的多分辨率表示充分结合，达到了发挥算法数据相结合的综合优势的目的。与现有单纯基于模拟退火算法的解决方法相比，在问题解决准确度保持不变的前提下，基于MRP方法的观察点设置问题解决的平均耗时减少85%~95%，为实际工程应用问题的解决提供了一条重要途径。

基于非均匀DCT的量化索引调制隐写

基于量化索引调制(QIM)的隐写技术正日益受到隐写分析的威胁。该文将通常在DCT域隐写的做法改为在非均匀DCT域进行,将参数作为密钥,提出了一种NDCT-QIM图像隐写方法。由于在攻击者猜测的域中,嵌入信号具有扩散性,NDCT-QIM方法不利于隐写分析对隐写特征的检测,分析和实验表明,它能够更好地抵御基于梯度能量、直方图及小波统计特征等常用统计量的隐写分析,增强了隐写的隐蔽性。

Local Feature Based Geometric-Resistant Image Information Hiding

Watermarking aims to hide particular information into some carrier but does not change the visual cognition of the carrier itself. Local features are good candidates to address the watermark synchronization error caused by geometric distortions and have attracted great attention for content-based image watermarking. This paper presents a novel feature point-based image watermarking scheme against geometric distortions. Scale invariant feature transform (SIFT) is first adopted to extract feature points and to generate a disk for each feature point that is invariant to translation and scaling. For each disk, orientation alignment is then performed to achieve rotation invariance. Finally, watermark is embedded in middle-frequency discrete Fourier transform (DFT) coefficients of each disk to improve the robustness against common image processing operations. Extensive experimental results and comparisons with some representative image watermarking methods confirm the excellent performance of the proposed method in robustness against various geometric distortions as well as common image processing operations.

Evaluation of a combined wavelet and a combined principal component analysis classification system for BCG diagnostic problem

Heart disease is one of the main factor causing death in the developed countries. Over several decades, variety of electronic and computer technology have been developed to assist clinical practices for cardiac performance monitoring and heart disease diagnosis. Among these methods, Ballistocardiography (BCG) has an interesting feature that no electrodes are needed to be attached to the body during the measurement. Thus, it is provides a potential application to asses the patients heart condition in the home. In this paper, a comparison is made for two neural networks based BCG signal classification models. One system uses a principal component analysis (PCA) method, and the other a discrete wavelet transform, to reduce the input dimensionality. It is indicated that the combined wavelet transform and neural network has a more reliable performance than the combined PCA and neural network system. Moreover, the wavelet transform requires no prior knowledge of the statistical distribution of data samples and the computation complexity and training time are reduced.

多尺度分解与相位反褶积提高海上地震资料分辨率和信噪比

Offshore seismic exploration is full of high investment and risk. And there are many problems, such as multiple. The technology of high resolution and high S/N ratio on marine seismic data processing is becoming an important project. In this paper, the technology of multi-scale decomposition on both prestack and poststack seismic data based on wavelet and Hilbert-Huang transform and the theory of phase deconvolution is proposed by analysis of marine seismic exploration, investigation and study of literatures, and integration of current mainstream and emerging technology. Related algorithms are studied. The Pyramid algorithm of decomposition and reconstruction had been given by the Mallat algorithm of discrete wavelet transform In this paper, it is introduced into seismic data processing, the validity is shown by test with field data. The main idea of Hilbert-Huang transform is the empirical mode decomposition with which any complicated data set can be decomposed into a finite and often small number of intrinsic mode functions that admit well-behaved Hilbert transform. After the decomposition, a analytical signal is constructed by Hilbert transform, from which the instantaneous frequency and amplitude can be obtained. And then, Hilbert spectrum. This decomposition method is adaptive and highly efficient. Since the decomposition is based on the local characteristics of the time scale of data, it is applicable to nonlinear and non-stationary processes. The phenomenons of fitting overshoot and undershoot and end swings are analyzed in Hilbert-Huang transform. And these phenomenons are eliminated by effective method which is studied in the paper. The technology of multi-scale decomposition on both prestack and poststack seismic data can realize the amplitude preserved processing, enhance the seismic data resolution greatly, and overcome the problem that different frequency components can not restore amplitude properly uniformly in the conventional method. The method of phase deconvolution, which has overcome the minimum phase limitation in traditional deconvolution, approached the base fact well that the seismic wavelet is phase mixed in practical application. And a more reliable result will be given by this method. In the applied research, the high resolution relative amplitude preserved processing result has been obtained by careful analysis and research with the application of the methods mentioned above in seismic data processing in four different target areas of China Sea. Finally, a set of processing flow and method system was formed in the paper, which has been carried on in the application in the actual production process and has made the good progress and the huge economic benefit.

Numerical Analyses of Discrete Gust Response for an Aircraft

Based on Navier-Stokes equations and structural and flight dynamic equations of motion, dynamic responses in vertical discrete gust flow perturbation are investigated for a supersonic transport model. A tightly coupled method was developed by subiterations between aerodynamic equations and dynamic equations of motion. First, under the assumption of rigid-body and single freedom of motion in the vertical plunging, the results of a direct-coupling method are compared with the results of quasi-steady model method. Then, gust responses for the one-minus-cosine gust profile arc analyzed with two freedoms of motion in plunging and pitching for the airplane configurations with and without the consideration of structural deformation.

Effect of Rock Mass Structure and Block Size on the Slope Stability-Physical Modeling and Discrete Element Simulation

This paper studies the stability of jointed rock slopes by using our improved three-dimensional discrete element methods (DEM) and physical modeling. Results show that the DEM can simulate all failure modes of rock slopes with different joint configurations. The stress in each rock block is not homogeneous and blocks rotate in failure development. Failure modes depend on the configuration of joints. Toppling failure is observed for the slope with straight joints and sliding failure is observed for the slope with staged joints. The DEM results are also compared with those of limit equilibrium method (LEM). Without considering the joints in rock masses, the LEM predicts much higher factor of safety than physical modeling and DEM. The failure mode and factor of safety predicted by the DEM are in good agreement with laboratory tests for any jointed rock slope.