数码彩扩机色域匹配模型研究

色域匹配是数码彩扩机实现图像颜色较好再现的关键.首先,采用一种较为实用的方法对CRT显示器进行了标定,运用Beer色料理论预测了彩色相纸的色域.在此基础上,运用非线性压缩算法实现从CRT到彩色相纸的色域匹配,同时提出了虚拟色域的概念,并加以分析研究.结果表明,非线性压缩色域匹配模型对于建立数码彩扩机的颜色管理系统具有重要实用价值.采用这种方法在国家高新技术激光数码彩扩机中取得了高质量的扩印效果.     

Video coding technique with a parametric modelling of noise

This paper presents a video encoding method in which noise is encoded using a novel parametric model representing spectral envelope and spatial distribution of energy. The proposed method has been experimentally assessed using video test sequences in a practical setup consisting of a simple, real-time noise reduction technique and High Efficiency Video Codec (HEVC). The attained results show that the use of the proposed parametric modelling of noise can improve the subjective quality of reconstructed video by approximately 1.8 Mean Opinion Scope (MOS) points (in 11-point scale) related to the classical video coding. Moreover, the present work confirms results attained in the previous works that the usage of even sole noise reduction prior to the encoding provides quality increase.     

Effects of chain extender and uniaxial stretching on the properties of PLA/PPC/mica composites

Poly(lactic acid) (PLA)/poly(propylene carbonate) (PPC)/mica composites with different amount of chain extender (CE) were melt compounded and then processed via two routes (compression molding and uniaxial stretching) into sheets and films. The tensile, thermal, and oxygen barrier properties of all the samples were investigated. Tensile test showed that the tensile strength and elongation at break of all films were much higher than that of all sheets, especially for PLA/PPC/mica with 0.9‐wt% CE composite (CM₃(CE)_0.9) film. The crystallinity of all films increased significantly after uniaxial stretching of sheet samples. The Fourier transform infrared spectroscopy (FTIR) results proved the chemical reactions occurred between PLA/PPC and CE. Scanning electron microscope (SEM) analysis revealed that compatibility and interfacial adhesion of all samples were improved after adding mica and CE, and they were further enhanced after uniaxial stretching. The addition of CE was not favorable to improve the oxygen barrier performance of PLA/PPC/mica sheet samples. However, the oxygen barrier performance of film samples was significantly improved after uniaxial stretching. In particular, the CM₃(CE)_0.9 film had the lowest oxygen permeability coefficient (1.4 × 10^?15 cm³·cm/(cm²·s·Pa)), and this was the best oxygen barrier properties reported in the literature for PLA‐based composites, which was comparable with PA film. This study demonstrated the high efficiency of uniaxial stretching on improvement of properties of composites, which would promote the application of biodegradable polymers in oxygen sensitive food packaging.     

尾喷焰红外辐射特性的小波压缩

本文针对发动机尾喷焰的目标红外特性开展谱分析研究.采用热流法求解辐射传输方程,获得尾喷焰表观红外辐射特性仿真数据,应用多尺度小波分解红外光谱获得小波压缩系数.考察了不同小波函数及小波尺度下红外特性光谱的压缩效果.研究结果表明,基于小波的尾喷焰红外辐射特性光谱数据压缩方法是可行的,尾喷焰红外光谱主要信息基本保留,变量维数压缩可达10倍以上.     

Influence of atmospheric refraction on the performance of an outdoor ultrasonic pulse compression system

Nowadays, many ultrasonic sensory systems are being developed to operate outdoors, where they are finding a variety of applications, such as local positioning, vehicle navigation or obstacle detection. To assure the reliable operation of these systems under any meteorological condition, it is necessary to achieve a thorough comprehension of the effects that the different atmospheric phenomena can have on the propagation of these acoustic waves. This paper deals with one of these phenomena, atmospheric refraction, and its influence on the performance of an ultrasonic system whose signals are detected by matched filtering.     

壬基酚聚氧乙烯醚的冲击压缩实验研究

 利用二级轻气炮对有机大分子乳化剂壬基酚聚氧乙烯醚（C₃₅H₆₄O₁₁）进行了系列动高压加载实验。在11~42 GPa冲击压力范围内测量了7个Hugoniot数据。结果表明,在17.8 GPa处,该物质的Hugoniot曲线出现拐折。这一现象意味着在高温高压条件下,壬基酚聚氧乙烯醚体系的分子基团发生了结构性相变。     

基于临界状态的砂土本构模型研究

砂土孔隙比及所受压力是其力学特性的重要影响因素. 本文基于砂土临界状态线特性分析,采用以e-(p/p_a)ξ平面内的线性关系描述其等向压缩线. 通过对比分析两种不同压缩线函数 与临界状态线函数之间的关系提出更适合描述砂土在等向压缩下的参考压缩线,并给出了基于参考压缩线的等向硬化规律. 建议了适用于 描述砂土剪切特性的屈服面函数,并给出利用等向压缩和等p路径确定屈服面形状参数μ的方法. 将不同应力比对应的压缩线作为砂土状态参量参考线,以获取潜在强度M_f与特征状态应力比M_c,进而描述砂土压缩与剪切特性;基于等向压缩与等p路径建立了当前应力比与状态参量参考线之间的相关关系,从而实现了砂土状 态参量参考线由参考压缩线向临界状态线平稳过渡. 建立的砂土本构模型共11个参数,均能够通过常规土工试验或经验获取. 基于模型预测与Toyoura砂的等向压缩、三轴不排水剪切试验及排水剪切试验的对比结果,本文建立的砂土本构模型很好地描述了Toyoura 砂在不同孔隙比和不同压力下的压缩与剪切特性.      

考虑侧面摩擦的侧限压缩模型的数值解法

海上箱筒型基础结构下沉到位后,舱内土体的受力变形可以看作是侧限压缩模型问题,上部荷载引起的侧壁摩擦力与土体应力之间的关系较为复杂。本文通过简化模型,列出了侧限压缩模型的平衡微分方程,分析了方程解析计算时存在的难点,结合摩擦应力边界条件的特点,构造函数迭代法对该方程进行数值求解,展示了计算的收敛过程,得到接触侧面上水平应力和土体表面位移的非线性分布规律,并将其结果与ABAQUS数值模拟结果进行了对比。结果表明,函数迭代法收敛速度较快,计算过程稳定,对其他存在变量耦合边界条件的微分方程数值求解有一定的参考价值。     

A generalized anisotropic and asymmetric yield criterion with adjustable complexity

During the past decades, numerous yield criteria for orthotropic materials, possibly showing tension–compression asymmetry, were developed. Although they were applied successfully to forming simulations, they are usually only adequate for a specific class of materials. The aim of this work is to present a generalized, pressure-independent criterion for plane stress states on the base of a two-dimensional Fourier series. Its complexity is adjustable through the number of considered Fourier coefficients, and thus, albeit using an associated flow rule, virtually any number of experimental data can be captured exactly. The criterion is applicable for materials with or without tension–compression asymmetry.     

基于主成分分析和分层树集合划分的Huffman算法图像压缩研究

互联网的飞速发展,产生了大量的图像信息.为了减少图片占用的存储空间,提高图像质量,提出了一种将主成分分析（PCA）和分层树集合划分（SPIHT）压缩算法相结合的有损图像压缩算法.首先对图像进行主成分分解,选取主要特征值进行压缩,再利用SPIHT算法将图像分解成不同子带的小波系数进行压缩,对SPIHT压缩系数进行哈夫曼编码,实现图像二级压缩.将本文提出的算法与SPIHT、SPIHT的哈夫曼编码、JEPG2000、PCA压缩算法进行了比较,结果表明本算法较其他压缩算法具有更好的性能,在压缩比相同的情况下能获得更高的PNSR和SSIM.