Video denoising via spatially adaptive coefficient shrinkage and threshold adjustment in Surfacelet transform domain

Many video denoising methods originated from methods designed for processing static two-dimensional images. Videos would be processed frame by frame, a process with a relatively high computational complexity, without taking into account the correlation information between frames. In this paper, a video denoising method using coefficient shrinkage and threshold adjustment based on Surfacelet transform (CSTA-ST) is proposed, which processes multiple frames of a video as an ensemble. Spatial correlation is used to define a weighted spatial energy. Each Surfacelet transform (ST) coefficient has a corresponding estimated energy value, in which the ST coefficients are grouped by. The similarity of the ST coefficients in a group determines the threshold of each ST coefficient. In addition, according to the neighborhood information of ST coefficients, the threshold is adjusted by a threshold adjustment factor. The coefficient shrinkage parameter is determined based on the adjusted threshold, and the ST coefficients are shrunk. Finally, the denoised video is obtained by the inverse ST using the shrunk coefficients. In experiments, video sequences with noise are tested, and the denoised results of the proposed method are compared with that of current denoising methods. The experimental results show that the proposed method significantly improves the peak signal-to- noise ratio (PSNR) and the structural similarity (SSIM) for various levels of noise and motion, and the ideal denoised visual effect is obtained.     

一种新的自适应子波预滤波器设计

基于一般的紧支撑尺度函数,本文设计了一咎单参数且具有良好逼近性能的新的自适应ＦＩＲ预滤波器,分析和模拟结果与表明这种预波滤算法具有较高的逼近精度和较快的逼近速度。     

AlGaAs／AlAs体系DBR的MOCVD生长及表征

设计并利用MOCVD在（311）GaAs衬底上生长了12．5个周期的Al0．6Ga0．4As／AlAs黄绿光分布式Bragg反射（DBR）体系，测量了白光反光谱及其外延片峰值波长分布，反射率90％以上，波长不均匀性在1．0％以下；利用了X射线双晶衍射对其进行结构表征，580nm波长DBR结构周期为84．5nm。     

Web应用系统的安全威胁及其防护

对Web应用系统的安全威胁进行了分析,提出了相应的Web安全防护措施。现阶段的安全解决方案均把重点放在网络层,当应用层被攻击（如SQL（结构查询语言）注入攻击、跨站脚本攻击、恶意代码等）时,传统的网络层安全设备,如防火墙、IDS（入侵检测系统）／IPS（入侵防御系统）等形同虚设,无能力阻挡攻击。文中注重分析在众多因素综合影响下,使Web应用潜在的隐患轻易暴露在互联网之下,承受较大的风险,并且叙述了服务器端和客户端的安全防护技术。     

基于像素相似性与Graph-Cut的图像自动分割

采用Graph cut的图像分割分为交互式分割与自动分割,为了弥补交互式分割需要用户的参与、分割结果依赖种子点的选取与模型的建立、需要用户的进一步修正才能得到满意结果等不足,介绍基于相似性的自动图像分割。该方法采用Mean-shift平滑图像、转换成YCbCr空间后将图像分割成若干区域块等方法,建立合适的能量函数后利用最大流/最小割定理求最小割。并通过实验证明,该方法在自动性、准确性、时间效率方面都获得较好结果。     

基于互协方差的L型嵌套阵列二维波达方向估计

为了解决L型均匀阵列波达方向（DOA）估计分辨率较低、估计信源数受限于阵元数、估计精度易受信噪比影响等问题,提出一种基于互协方差的L型嵌套阵列二维DOA估计算法。利用不同子阵间互协方差矩阵产生较长无冗余阵元的虚拟阵列,消除噪声干扰;利用虚拟阵列及其共轭矩阵构建等效协方差矩阵,实现虚拟阵列信号的解相干;采用旋转不变子空间技术对等效协方差矩阵进行处理,得到目标的角度信息;基于虚拟阵列等效信源的唯一性进行空间信源的角度匹配。对所提算法的DOA估计有效性进行仿真验证,结果表明,在阵元数相同情况下,该算法与L型均匀阵列相比在低信噪比环境下拥有更高的估计精度,能够辨识更多的空间信源。     

一种具有角速度量测的多站无源目标跟踪方法

为提高多站无源目标跟踪系统的跟踪性能,将无源目标跟踪系统获取的目标角速度测量表示为目标在笛卡尔坐标系下位置与速度的非线性形式,进而提出了一种同时利用目标角度和角速度量测来提高被动跟踪精度的方法。结合Cramer-Rao下界理论,分析了在利用角速度量测信息后无源目标跟踪系统跟踪性能的改善情况。基于不敏卡尔曼非线性状态估计方法,给出了具有角速度多站无源跟踪方法的一种具体实现流程。仿真与试验结果表明,具有角速度量测的无源跟踪系统具有更优目标运动参数的估计精度。     

中文信息智能处理技术的研究

信息的智能处理技术是中文信息处理中的重要课题,其主要包括智能搜索和信息获取。而自然语言处理和理解技术是智能信息处理的核心。讨论自然语言理解应用于智能搜索和信息获取的若干问题,阐述标注、分析搜索要求以及完善基于词典的知识库的处理手段,特别是语料库语言学在这些环节的应用情况。同时,对中文信息获取技术涉及的具体语言处理技术也做了较为详尽的论述,包括词典与知识库、词切分和词性标注、信息获取的短语句法及语义分析和信息获取的过程。     

Effect of Sintering Temperature on Microstructure, Electrical Properties, and Thermal Expansion of Perovskite-Type La0.8Ca0.2CrO3 Complex Oxides Synthesized by a Combustion Method

Perovskite-type La_0.8Ca_0.2CrO₃ complex oxides were synthesized by a combustion method. Microstructural evolution, electrical properties, and thermal expansion behavior of the ceramics were investigated in the sintering temperature range of 1250°C to 1450°C. It was found that the electrical conductivity (σ _e) remarkably improved with increasing sintering temperature from 1250°C to 1400°C, ascribed to the development of microstructural densification, whereas it declined slightly above 1400°C due to generation of excessive liquid. The specimen sintered at 1400°C had a maximum conductivity of 31.6 S cm^?1 at 800°C, and lowest activation energy of 0.148 eV. The improvement of the thermal expansion coefficient (TEC) with increasing sintering temperature was monotonic as a result of the microstructural densification of the materials. The TEC of La_0.8Ca_0.2CrO₃ sintered at 1400°C was about 10.5 × 10^?6 K^?1, being consistent with other components as high-temperature conductors. With respect to microstructure, electrical properties, and thermal expansion, the preferable sintering temperature was ascertained to be about 1400°C, which is much lower than for the traditional solid-state reaction method.