非线性二阶周期边值问题的正解(英文)

周期边值问题是非线性分析中的一个重要课题,它在许多实际问题中有着广泛的应用.论文应用锥拉伸和锥压缩不动点定理研究非线性二阶周期边值问题正解的多重性.以一类线性问题的格林函数为工具,证明了周期边值问题至少有两个正周期解的结论.     

20CrMnTi齿轮轴裂纹分析

采用光学显微镜分析、化学成分分析和力学性能试验,对20CrMnTi齿轮裂纹进行分析。结果表明,齿轮裂纹属于钢材存在皮下裂纹,严重的硫化物和大颗粒氧化物夹杂,造成应力集中,是齿轮裂纹的原因之一。热处理工艺不当是造成齿轮裂纹的另一重要原因。     

液液萃取一气质联用法检测水中IPMP与IBMP

对液液萃取(LLE)-气相色谱质谱(GC/MS)法测定饮用水中异嗅物质2-甲氧基-3-异丙基吡嗪(2-methoxy-3-3isopropyl pyrazine,IPMP)及2-甲氧基-3-异丁基吡嗪(2-methoxy-3-3isobutyl pyrazine,IBMP)的方法进行了探讨,确定了最佳萃取条件,萃取时间为4 min,NaCl加入量为60g·L-1,pH值为4左右.在选定条件下,IPMP和IBMP在20～500 μg·L-1的范围内具有良好的线性关系,相关系数r＞0.995;方法回收率为72.0％～103.6％;相对标准偏差RSD＜8％.     

利用变进制数量化位置信息的一种有效算法

提出了一种在有限个位置中，对一定数目脉冲所在位置信息进行量化的方案。这种方案可以将帧压缩到无损压缩的极限，并且可以利用ＤＳＰ芯片的特性高速完成压缩与解压处理。     

赋权有向图最短路问题的新解法--前趋法

Dijkstra算法被公认为解决最短路问题的最好算法,但它的缺陷之一是不能解决存在负权的最短路问题.一种解决这类问题的新方法--前趋法可弥补Dijkstra算法的这一缺陷.实例表明、前趋法是一种解决存在负权的最短路问题的行之有效的简便算法.     

Synthesis,structure and biological activity of diorganotin derivatives with pyridyl functionalized bis(pyrazol‐1‐yl)methanes

Three pyridyl functionalized bis(pyrazol‐1‐yl)methanes, namely 2‐[(4‐pyridyl)methoxyphenyl] bis(pyrazol‐1‐yl)methane (L¹), 2‐[(4‐pyridyl)methoxyphenyl]bis(3,5‐dimethylpyrazol‐1‐yl)methane (L²) and 2‐[(3‐pyridyl)methoxyphenyl]bis(pyrazol‐1‐yl)methane (L³) have been synthesized by the reactions of (2‐hydroxyphenyl)bis(pyrazol‐1‐yl)methanes with chloromethylpyridine. Treatment of these three ligands with R₂SnCl₂ (R = Et, n‐Bu or Ph) yields a series of symmetric 2:1 adducts of (L)₂SnR₂Cl₂ (L = L¹, L² or L³), which have been confirmed by elemental analysis and NMR spectroscopy. The crystal structures of (L²)₂Sn(n‐Bu)₂Cl₂·0.5C₆H₁₄ and (L³)₂SnEt₂Cl₂ determined by X‐ray crystallography show that the functionalized bis(pyrazol‐1‐yl)methane acts as a monodentate ligand through the pyridyl nitrogen atom, and the pyrazolyl nitrogen atoms do not coordinate to the tin atom. The cytotoxic activity of these complexes for Hela cells in vitro was tested. Copyright © 2010 John Wiley & Sons, Ltd.     

引发剂用量对ABS树脂冲击强度的影响

采用种子乳液聚合技术，以K2S2O8为引发剂合成了一系列PB－g－SAN接枝共聚物。并与SAN树脂进行共混，制得了ABS树脂。考察了引发剂K2S2O8用量对PB－g－SAN接枝共聚物的接枝率及制得的ABS树脂的冲击 强度的影响。研究了PB－g－SAN接枝共聚物的接枝率与ABS树脂的冲击强度间的关系。讨论了乳液聚合过程中K2S2O8的引发、扩散机理。     

对大学生学习武术动机的研究

本文主要分析了大学生在武术课教学过程中学习动机的类型和学习动机对学习成绩及身体素质的影响．研究表明，具有问接远景性学习动机的学生比具有直接近景性学习动机的学生的学习成绩和身体素质有明显的提高．所以，学习动机对学生学习成绩和身体素质的提高起着重要的作用．     

Preparation and performance of sulfur–carbon composite based on hollow carbon nanofiber for lithium-sulfur batteries

A unique structured hollow carbon nanofiber–sulfur composite material (HCF–S) was fabricated and characterized in lithium-sulfur batteries. It is found that a part of spherical sulfur particles are located in the voids formed by the intertwined fibers and the others are confined in hollow channel of the HCF. The high conductive and porous HCF favors the construction of stable three-dimensional conducting network and convenient infiltration of the electrolytes into the cathode. The HCF–S cathode exhibits excellent electrochemical performance in the electrolyte with LiNO₃. By contrast, the ionic liquid electrolyte provides insufficient shuttle suppression and weakens ion transport, which leads to poor cycle and rate capability.