About the depolymerization of cellulose propionate to segments with low DP

Low molecular weight cellulose propionate (CP) segments were synthesized by depolymerization with HBr under esterification conditions using either a commercial CP with residual hydroxyl groups (DS_OH ca. 0.4) or a tripropionate (CTP). The depolymerization using CTP yielded segments having a minimum DP of as low as 7, whereas the depolymerization of the commercial CP resulted in segments having a minimum DP of 50. Differences were also seen in the rate of depolymerization and the Mark-Houwink exponent, which declined from 1 to 0.6 below DP 100 and 30 for commercial CP and CTP, respectively. The results are consistent with the hypothesis that branching is induced by transglycosidation when OH-containing cellulose derivatives are depolymerized with HBr in aprotic solution.     

The simulation of dynamic crack propagation using the cohesive segments method

The cohesive segments method is a finite element framework that allows for the simulation of the nucleation, growth and coalescence of multiple cracks in solids. In this framework, cracks are introduced as jumps in the displacement field by employing the partition of unity property of finite element shape functions. The magnitude of these jumps are governed by cohesive constitutive relations. In this paper, the cohesive segments method is extended for the simulation of fast crack propagation in brittle solids. The performance of the method is demonstrated in several examples involving crack growth in linear elastic solids under plane stress conditions: tensile loading of a block; shear loading of a block and crack growth along and near a bi-material interface.     

基于直线检测的遥感影像道路提取方法

针对传统的高分辨率遥感影像中提取道路精度低问题,提出了一种基于改进直线检测道路的方法。首先将彩色图像梯度计算运用到经典的直线段检测(LSD)算法中,实现遥感影像直线提取。根据相邻两条直线关系设置6个直线合并规则,然后判断直线间的区域是否为候选道路区域。以候选区域为种子点,生长其他直线间的区域。最后提取面状道路及优化,同时也对道路交叉路口进行提取。实验结果表明使用提出方法所提取道路区域更加完整。     

基于听觉感知特征的环境声分类

大多数环境声是不和谐的,比语声和乐声更加不平稳。针对传统时频分析的不足,提出一种基于听觉感知的环境声特征提取方法。针对研究的小样本问题,采用支持向量机(Support Vector Machine,SVM)作为分类算法,对环境声进行分类。仿真结果表明所用特征及方法是有效的。     

用瞬态诱发耳声发射信号识别听神经病

听神经病是一种特殊的感音神经性耳聋,目前对其病变部位和发病机理的认识仍有争议,诊断方法也较为复杂。该文探讨利用瞬态诱发耳声发射(TEOAE)信号识别听神经病的可行性。采用前馈神经网络,以TEOAE信号的自回归模型功率谱为特征,对正常耳和听神经病耳的TEOAE信号进行分类识别,总正确率可达88.67%,说明了利用TEOAE信号对听神经病进行识别的可行性。该方法对听神经病的识别具有一定意义,若应用于新生儿听力筛查中,将有助于降低新生儿听神经病的漏检率。     

对苯二甲酸乙二醇酯-ε-己内酯共聚酯中硬链段结晶特性研究

利用广角X射线衍射和傅里叶变换红外光谱研究了对苯二甲酸乙二醇酯-ε-己内酯(TCL)共聚酯中对苯二甲酸乙二醇酯(ET)硬链段的晶区结构和结晶特性。结果表明,在ET硬段含量较高的TCL共聚酯中,ET链段的结晶特性与纯的聚对苯二甲酸乙二醇酯(PET)基本相同。ET硬段晶区的尺寸和结晶度均随链段序列长度的减小而减小。     

1,5-萘二异氰酸酯与1,4-丁二醇基为基质的多嵌段聚氨酯弹性体的合成与性能

利用 1 ,5_萘二异氰酸酯 (NDI)和 1 ,4_丁二醇 (BDO)为均匀硬质分子单体 ,与不同软质分子单体 (聚醚、聚酯、聚硅氧烷 )缩合制备多嵌段聚氨酯弹性体 ,详细研究了硬嵌段相 (NDI)弹性体的结构与性能间的关系 ,发现随着硬嵌段相长度的增加 ,或者氨基甲酸酯中胺基与聚醚、聚酯、聚硅氧烷中软段氧原子间氢键的减弱 ,都导致微相分离程度的增加 ,造成聚合物熔点和熔化热的升高。硬嵌段相熔化的多峰行为是由于形成了NDI/BDO半微晶区 ,在退火时转变为更加有序的结晶微区 ,当温度高于 1 80℃时 ,由于氢键的断裂 ,NDI/BDO硬嵌段发生分解反应 ,该过程源于不很有序的硬嵌段半结晶微区。当温度高于 2 5 0℃时 ,发生快速的分解。在动态力学行为方面 ,NDI基聚醚弹性体比其它硅氧烷基的弹性体展示了更高的硬嵌段区的稳定性 ,同时 ,在使用温度范围内 ,也显示出最高的储能模量值 ,表明刚性对温度的依赖性 ,以及NDI/BDO硬嵌段中活性填料的显著影响     

Pointed binary encompassing trees: Simple and optimal

For n disjoint line segments in the plane we construct in optimal O(nlogn) time and linear space an encompassing tree of maximum degree three such that at every vertex v all edges of the tree that are incident to v lie in a halfplane bounded by the line through the input segment which v is an endpoint of. In particular, this tree is pointed since every vertex has an incident angle greater than π. Such a pointed binary tree can be augmented to a minimum pseudo-triangulation. It follows that every set of disjoint line segments in the plane has a constrained minimum pseudo-triangulation whose maximum vertex degree is bounded by a constant.     

基于听觉模型的自相关谱语音信号的重构

研究如何从听觉模型的自相关谱中恢复出原始的声音信号.从短时自相关函数中得到原始信号的傅立叶变换的幅度值,然后利用迭代算法仅从傅立叶变换的幅度值中恢复语音信号.