Effect of diamond-like carbon (DLC) on the properties of the NiTi alloys

NiTi alloy has found wide application in the biomedical field due to its unique shape memory effect, superelasticity and biocompatibility. However, the materials are vulnerable to surface corrosion and the most serious issue is out-diffusion of toxic Ni ions from the substrate into body tissues and fluids. In this paper, NiTi alloys were coated with diamond-like carbon (DLC) fabricated by plasma immersion ion implantation and deposition (PIIID) to improve their corrosion resistance and blood compatibility without sacrificing their shape memory effect and superelasticity. The structure of the films and the depth profiles between the films and substrate were studied using Raman spectroscopy and XPS, respectively. The phase transformation temperature, superelasticity, anticorrosion behavior and Ni ions release of the coated and uncoated sample were investigated by DSC, tensile tests, potentiodynamic polarization and AAS, respectively. The hemocompatibilty of the coated and uncoated samples was measured using clotting time and platelet adhesion. The results shows that the films is DLC accompanying with the formation of the mixing layer, and the DLC films can markedly improve the corrosion resistance and the hemocompatibility, obviously increase the ratio of albumin-to-fibrinogen and effectively block the Ni ions release of the NiTi alloys without sacrificing its superelasticity and changing its phase transformation temperature. The research results suggest DLC films prepared by PIIID could improve the in vivo performance of NiTi alloys implanted into the human body.     

基于相关性阈值的NSCT图像去噪方法研究

利用非下采样Contourlet变换(NSCT)平移不变性、多分辨率、多方向的优点,提出一种基于尺度相关与阈值去噪相结合的非下采样Contourlet变换图像去噪方法。首先对噪声图像进行非下采样Contourlet变换,得到各个尺度各个方向子带的系数,然后采用相关系数归一的方法,结合Bayesian自适应阈值来达到更好的去噪效果。仿真实验表明,该方法在提高去噪后图像的峰值信噪比的同时,有效保留了图像的纹理信息,避免伪吉布斯现象,改善了图像的视觉效果。     

基于粒子群算法的轨道电路补偿电容故障诊断方法

为了延长轨道电路传输距离,改善传输效果。本文提出一种机车信号感应电压幅值包络仿真模型,它是基于均匀传输线理论,通过补偿电容对机车信号感应电压幅值包络的影响规律,使用改进粒子群算法得到当前状态下补偿电容的最优值,进而对补偿电容的故障进行诊断。仿真结果表明,这种诊断方法是可行和有效的,能快速准确地定位故障补偿电容,替补偿电容的故障诊断提供了新的有效手段。     

Preparation and characterization of a PMMA/Ce(OH)3, Pr2O3/graphite nanosheet composite

An easy process for the synthesis of poly(methyl methacrylate)/Ce(OH)₃, Pr₂O₃/graphite nanosheet (PMMA/Ce(OH)₃, Pr₂O₃/NanoG) composite was developed. Graphite nanosheets (NanoG) were prepared by treating the expanded graphite with sonication in aqueous alcohol solution. The PMMA/Ce(OH)₃, Pr₂O₃/NanoG composites were prepared via in situ polymerization of MMA monomer in the presence of graphite nanosheets and Ce(OH)₃, Pr₂O₃ through reverse micelle template, in which the methyl methacrylate was designated as the oily phase. The composites were then dispersed with chloroform and coated on glass slides to form films. Scanning and transmission electron microscopy were used to characterize the structure and dispersion of the graphite nanosheets and the composites. The results showed that the high-aspect-ratio structure of the nanosheets played an important role in forming a conducting network in the PMMA matrix. From thermogravimetric analysis, the introduction of graphite nanosheets and inorganic nanopartices exhibited a beneficial effect on the thermal stability of PMMA.     

基于主题和链接分析的微博社区发现算法

针对传统社区发现方法大多基于链接或主题关系, 且没有考虑获取微博用户社会信息时的限制, 无法有效识别微博中多个社区的问题, 提出了一种综合基于主题和链接分析的微博社区发现算法来挖掘微博中多个社区。算法首先研究微博用户的链接及博文主题特性, 定义了链接相关度和主题相关度公式; 然后推出用户总相关度公式, 以此来计算节点间的传递概率, 用改进后的标签传递算法对用户分类; 最终划分出兴趣相似且社会联系紧密的用户群。真实数据集上的仿真实验验证了该方法的合理性和有效性。     

杂交粒子群算法在列车运行调整中的应用研究

针对列车运行调整存在约束条件多、求解难度大等问题, 结合城市轨道交通列车运行特点, 建立了优化的列车运行调整模型。在此基础上, 引入遗传算法中的杂交思想, 采用改进后的粒子群算法对此模型进行求解, 给出了求解算法的具体步骤, 并采用西安地铁2号线数据进行仿真验证。结果表明, 采用杂交粒子群算法解决列车运行调整问题是一种有效的方法, 并且其优化能力优于标准粒子群算法。     

一类非线性四阶常微分方程边值问题正解的存在性

用一种较简单的方法建立了非线性四阶常微分方程边值问题{u（4）（t）=f（t,u9t）,u″（t）0,t∈（0,1） u（0）=u（1）=u″（0）=u″（1）,正解的存在性结果,对非线性项f只要求其满足一个局部条件．     

随机指标鞅序列的收敛性

主要讨论了以停时序列{τn}n∈N作为鞅序列{xn}n∈N的指标时,序列{xτn}n∈N的收敛性问题.     

刘勰与曹操诗学观念之比较

《文心雕龙》中的《明诗》篇,主要论述诗歌的历史沿革,但其中些许微言大义,在一定程度上揭示了诗歌创作的基本特质。《文心雕龙》广泛涉及各种问题,结构严谨,论述周详,有很强的系统性和完整性。但其在《明诗》论述四言诗时对魏晋时期的大诗人曹操之字未提。夲论文试从"通变"和"新变"等方面论述,意在探讨刘勰偏见之缘由。     

预应力混凝土箱型梁桥温度效应分析

参考我国公路、铁路和英国规范不同的温度梯度规定,对某大跨径连续梁桥进行温度效应计算,对结构的内力和变形进行分析比较,得出可供设计和施工参考的结论。