利用微悬臂梁表面应力研究聚N-异丙基丙烯酰胺分子的构象转变

提出了一种基于微悬臂梁传感技术研究大分子折叠/构象转变的新方法.通过分子自组装的方法将热敏性的聚N-异丙基丙烯酰胺(PNIPAM)分子链修饰到微悬臂梁的单侧表面，用光杠杆技术检测温度在20—40℃之间变化时由于微悬臂梁上的PNIPAM分子在水中的构象转变所引起的微悬臂梁变形.实验结果显示：在升温过程中，微悬臂梁的表面应力发生了变化并且导致微悬臂梁产生了弯曲变形，这个过程对应着微悬臂梁上的PNIPAM分子从无规线团构象到塌缩小球构象的构象转变.在降温过程中，微悬臂梁发生了反方向的弯曲变形，这对应着PNIPA 关键词： 构象转变 聚N-异丙基丙烯酰胺分子链 表面应力 微悬臂梁     

沿直线的垂直方向匀速直线运动的带电直线的电场

本文利用相对论变换关系计算了沿直线的垂直方向匀速运动的带电直线的电场.     

基于视觉心理学的SFS流形算法研究

通过视觉方法获取形状在科学研究及工程实践中有着重要作用,灰度图像是最容易获取的视觉信息之一。目前由灰度重构的形状(SFS,shape from shading)受到了广泛的关注,但现有的算法稳定性差、效率低,一直阻碍着SFS方法的推广应用。受近期的视觉心理学研究成果的启发,针对SFS问题,从局部分析入手,即:在图像上,在每一灰度极值点附近,根据灰度单调变化的情况,形成一个椭圆形邻域,对应着表面凹凸区;在每一椭圆域上,形状可用抛物面逼近,其参数可由局部辐射度约束求解;整个图像被椭圆形邻域覆盖,这些覆盖可构成一个二维流形;借助于流形上单位分解函数,各局部抛物面粘合在一起,形成光滑的整体形状;总体形状在整幅图像的灰度约束下再进行全局优化,可得到最终的重构结果。给出了初步算例,算法的稳定性和效率均有大幅度提高。     

A Linear Time Algorithm for Constructing Maximally Symmetric Straight Line Drawings of Triconnected Planar Graphs

Symmetry is one of the most important aesthetic criteria in graph drawing because it reveals structure in the graph. To draw graphs symmetrically, we employ two steps. The first step is to find appropriate automorphisms. The second step is to draw the graph to display the automorphisms. Our aim in this paper is to construct maximally symmetric straight line drawings of triconnected planar graphs in linear time. Previously known algorithms run in quadratic time. We show that an algorithm of Fontet can be used to find an embedding in the plane with the maximum number of symmetries, and present a new algorithm for finding a straight line drawing that achieves that maximum. Both algorithms run in linear time.     

Feature Selection using Fuzzy Support Vector Machines

The feature selection consists of obtaining a subset of these features to optimally realize the task without the irrelevant ones. Since it can provide faster and cost-effective learning machines and also improve the prediction performance of the predictors, it is a crucial step in machine learning. The feature selection methods using support machines have obtained satisfactory results, but the noises and outliers often reduce the performance. In this paper, we propose a feature selection approach using fuzzy support vector machines and compare it with the previous work, the results of experiments on the UCI data sets show that feature selection using fuzzy SVM obtains better results than using SVM.     

贫燃料预混燃烧的回火特性研究

回火问题是贫燃料预混燃烧面临的主要问题之一。本文采用计算和实验相结合的方法研究甲烷与富氢合成气贫预混燃烧的回火现象,得到不同燃料、不同稳定方式之间的回火特性。研究结果表明,回火极限可以关联为丕雷数模型,环形稳定器的回火稳定性最好,其次为杆稳定器,旋流稳定器的稳定性最差;环形稳定的甲烷预混火焰的回火过程为边缘稳定,适当加入边缘空气同轴射流后变为中心回火,且同轴射流速度存在最佳范围可以提高回火稳定性。     

Nd∶NaR(WO_4)_2晶体生长(R=Bi,Y)

采用提拉法生长出了掺钕钨酸铋钠[Nd∶NaBi(WO4)2,简称Nd∶NBW]和掺钕钨酸钇钠[Nd∶NaY(WO4)2,简称Nd∶NYW]晶体,并给出了制备无开裂优质Nd∶NBW和Nd∶NYW晶体的最佳生长工艺参数。从XRD分析得到Nd∶NBW和Nd∶NYW晶体的晶胞参数,并分析了晶体的拉曼光谱,认为二者结构基本相同,为四方晶系、白钨矿结构、I41/a空间群。由吸收光谱可以看出,Nd∶NBW在802nm有较强的吸收峰,Nd∶NYW在804nm、752nm、586nm附近有较强、较宽的吸收峰,二者均适合于LD泵浦;计算了晶体中Nd3+的吸收截面积。     

Preparation of antimicrobial poly(vinyl alcohol) nanofibers containing silver nanoparticles

Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO₃) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO₃ nanofibers became insoluble, while the Ag⁺ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag⁺ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag⁺ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006     

现场拉曼光谱研究乙腈在金电极上的解离吸附行为

利用共焦显微拉曼系统、结合合适的电极表面粗糙方法研究了非水体系 0 1mol/LLiClO4 /CH3CN溶液中 ,乙腈分子在金表面的吸附和解离行为。结果表明非水体系中乙腈可在金表面发生还原反应 ,产物CN- 离子与电极表面作用形成的表面配合物可在较宽的电位区间吸附于电极表面。溶液中的微量水、激光照射以及电极电位均对该反应有较大的影响。通过拉曼谱图的比较得出乙腈分子解离出的CN- 在金电极表面比在银电极表面有更强的吸附作用。     

掺Eu3+硅基材料的发光性质

通过溶胶－凝胶技术制备了掺Eu^3 的硅基材料并测试了其三维荧光光谱、激光谱和发射光谱，结果显示，最佳激发波波长为350nm,最强荧光波长为620nm；在350nm光激发下的发射光谱显示Eu^3 的特征发射光谱，产生4条谱带，分别是577nm(^5D0-^7F0)，588nm(^5D0-^7F1),596nm(^5D0-^7F1)和610nm(^5D0-^7F2)。