结构平稳随机地震反应时域分析:方法

给出了三种常用的随机地震地面运动过程模型,即理想白噪声模型、金井清模型、改进金井清模型的相关函数表达式.引入状态向量,在状态空间中建立地震地面运动激励下的结构振动方程,并求解出结构的复模态特性和复模态反应.利用复模态叠加法推导出线性时不变多自由度体系在这三种随机地震动激励下的平稳协方差反应的解析式,可在时域内直接计算结构随机反应的统计特征.该方法物理概念清晰,结论简便明确,可作为实际工程结构平稳随机地震反应的实用分析方法.     

Stress induced time dependent behavior of clayey soils

It is shown that time compression curve obtained from one-dimensional consolidation curve in the laboratory may include six phases. These are initial compression, first primary compression, transition from first primary compression to second primary compression, second primary compression, and transition from second primary compression to creep and lastly creep. This paper attempts to identify the quantitative beginnings and characteristics of these phases. A mathematical characteristic of all the soils that follow primary consolidation as per Terzaghi’s one dimensional consolidation theory is derived. It is known as the constant of primary consolidation. It is used to study the beginning of secondary consolidation and its effects on primary consolidation. Another characteristic of soils for creep and total absence of primary compression is derived. Methods are suggested for the determination of coefficients of Primary and Secondary consolidations and the compression index.     

A new criterion for strength of frozen sand under quick triaxial compression considering effect of confining pressure

The strength of frozen soils has been one of the most extensively studied aspects in frozen soil mechanics. When carrying out deep excavations using freezing methods, high stress states are often encountered. Therefore, the strength of frozen soils under high confining pressures is of major concern. This paper first reviews the present failure criteria for frozen soils, especially with regard to the effect of confining pressure on the strength. It is suggested that the strength consists of two components, cohesion and friction, and can be expressed by the Mohr–Coulomb criterion and in the framework of the Drucker–Prager criterion. However, these two components are both dependent on the stress state. Duncan’s equation for the friction angle is extended to frozen soils. A frozen Lanzhou fine sand is taken as study subject. The frozen sand is compressed at a high strain rate under three different temperatures and under a wide range of confining pressure. Experimental results have confirmed the generally recognized principle that the strength increases with the confining pressure up to certain value. Thereafter, it decreases with continued increase in confining pressure. Experimental data from our own tests and literature are fitted to the new criterion, which shows its validity.     

基于小波理论的遥感压缩软件的比较

本文选取了商业化比较好的基于小波压缩原理的三个压缩软件 ,采用国际上通用的反映压缩影像质量还原精度的 PSNR(最佳峰值信噪比 )法 ,主要从压缩速度、压缩比率、压缩影像的还原质量等几方面对这些压缩软件的性能进行了比较 ,从而为今后更好地使用这些软件提供借鉴。     

一种减少块效应的自适应后处理算法

针对在基于块变换的图像编码技术尤其在甚低速率视频编码技术中，块斑严重影响图像的主观质量问题，提出了一种复杂度低且效果比较明显的消除块效应的自适应后处理技术。模拟结果表明，该方法能够同时提高图像的客观峰值信噪比和主观视觉效果，具有较高的实用意义。     

基于自适应四叉树分割的遥感图像压缩算法

遥感图像具有不同于一般图像的特点,针对遥感图像对压缩算法的特殊要求,提出了自适应四叉树分割算法实现图像的分块,以各像块的均值近似表示该像块的灰度值,从而以尺量少的数值获得对原始图像的最佳逼近,再对辐近误差进行自适应分割和基于像块方差的自适应量化,最后对各分量进行Huffman编码.实验表明,本算法能表现出良好的实用性能,比JPEG算法更适用于遥感图像的压缩.     

水稻时域散射特征分析及其应用研究

通过对肇庆试验区1996年和1997年获取的多时相、多模式雷达卫星（RADARSAT）数据分析，从图像上直接提取地物的后向散射系数，结合实地测量水稻的生长结构参数，建立了水稻生长模型，分析了不同生长周期（从80天到120－125天）4种类型水稻的时域散射特性。利用1997年4月至7月获取的7景标准模式雷达卫星数据，对试验区内三个县和两个行政区共5000km^2面积范围内的作物进行分类和水稻产量预估算，水稻类型分类及面积量算精度达91％。结果表明：利用雷达遥感数据进行水稻种植面积量算和估产需要水稻生长期间三个时相的数据，即插秧期、抽穗期、收割前期。若能够获得多参数雷达图像，可以用插秧期和收割前期的两个时相图像来代替上述的三个时相图像同样可以达到种植面积量算和估产的效果。这一结果充分说明多时相雷达卫星数据对我国南方水稻长势监测及估产具有明显优势和潜力。     

基于整数小波变换的多光谱图像无损压缩

多光谱图像一般都采用预测方法去除空间冗余和谱内冗余实现无损压缩。通过用提升方法构造整数小波变换, 将变换方法用于去除空间冗余；通过分类方法构造谱间预测器，用预测方法去除谱间冗余，两者相结合，实现无损压缩。由于变换方法的去相关性能良好，使该方法压缩效果大大改善。     

数字滤波器的频谱窗和噪声压缩度

根据傅里叶理论导出了数字滤波器的频谱窗，根据随机过程理论导出了数字滤波的噪声压缩度。通过对二项式系数数字滤波器和多项式系数数字滤波器和频谱窗和噪声压缩度的分析，发现前者对噪声具有较强的压缩作用，同时能保持信号的凹凸性，是一种优于后者的数字滤波器。     

河口表层悬浮泥沙气象卫星遥感定量模式研究

分析了HRIS光谱图像帧序列的相关性 ,并针对这一特性 ,提出了利用D2 PCM方法 ,降低光谱图像序列的谱相关和空间相关 ,减少图像中的冗余 ,从而实现光谱图像的压缩。该方法提高了压缩比和压缩效率 ,算法运算量小 ,快速。