Method development for compositional analysis of low molecular weight poly(vinyl acetate) by matrix-assisted/laser desorption-mass spectrometry and its application to analysis of chewing gum

The influence of the sample preparation parameters (the choice of the solvent and of the matrix:analyte ratio) was investigated and optimal conditions were established for MALDI mass spectrometry analysis of the pristine low molecular weight polyvinyl acetate (PVAc). It was demonstrated that comparison of polymer’s and solvent’s Hansen solubility parameters could be used as a guide when choosing the solvent for MALDI sample preparation. The highest intensity PVAc signals were obtained when ethyl acetate was used as a solvent along with the lowest matrix–analyte ratio (2,5-dihydroxybenzoic acid was used as a matrix in all experiments). The structure of the PVAc was established with high accuracy using the matrix-assisted laser desorption/ionization-Fourier transform mass spectrometry (MALDI-FTMS) analysis. It was demonstrated that PVAc undergoes unimolecular decomposition by losing acetic acid molecules from its backbone under the conditions of FTMS measurements. Number and weight average molecular weights as well as polydispersity indices were determined with both MALDI-TOF and MALDI-FTMS methods. The sample preparation protocol developed was applied to the analysis of a chewing gum and the molecular weight and structure of the polyvinyl acetate present in the sample were established. Thus, it was shown that optimized MALDI mass spectrometry could be used successfully for characterization of polyvinyl acetate in commercially available chewing gum.     

时滞效应对弹性地基上梁主共振响应影响分析

本文研究了弹性地基上梁主共振响应的时滞效应．基于Hamilton原理,建立了时滞影响下弹性地基上梁的非线性运动微分方程,采用多尺度法,求得了时滞效应下主共振响应调制方程以及稳定性条件．通过数值算例,分析了时滞和调谐参数影响下主共振响应的峰值及幅频响应特性．结果表明,地基反力中的时滞效应对主共振响应影响较大,会导致共振域偏移,在一定区间内,响应幅值随时滞变化先减小再增大,呈现出周期性,并导致幅频曲线弯曲程度增大．     

高功率准分子激光主振荡功率放大系统光学元件的稳定性

为了分析高功率准分子激光主振荡功率放大(MOPA)系统中各光学元件稳定性对靶面光斑定位精度的影响,建立了分析模型,利用分析结果指导高稳定性镜架设计以满足系统实验需求。根据高功率准分子激光MOPA系统特点,有效地简化了系统光路,建立了系统光路模型;按照系统打靶精度要求,利用三维坐标变换和光线追迹法,计算得到了系统单个光学元件稳定性对靶面光斑定位精度的影响规律;最后,对自行设计的镜架进行了稳定性测量。计算结果表明,反射镜的旋转变化和透镜垂直光轴的平移变化是影响靶面光斑定位精度的主要因素,且主放大光路中反射镜在X方向和Y方向上最大的变化范围分别不能超过0.8和1.6μrad。实际测量结果表明,设计的镜架在X方向和Y方向最大的变化范围分别为0.6和0.81μrad,满足系统实验要求。     

标准镜的高精度柔性支撑镜框的优化设计

为了实现干涉仪标准镜中光学元件的高精度定位,设计了一种柔性支撑镜框,研究了该结构的力学模型、结构参数、定位精度和透镜变形。首先,根据材料力学原理将柔性镜框等效为一个弹簧系统;根据力学方程和几何关系,建立了透镜中心位置与柔性结构的挠度之间的二元方程。然后,分析了安装位置、温度、结构参数对透镜位置以及作用力的影响。最后,应用有限元仿真分析了所设计结构的力学性能,并进行对比验证。结果表明,数值仿真分析的结果与有限元仿真结果基本相同,柔性镜框的柔性结构厚度最优值为1.5 mm。该设计方案完全满足干涉仪标准镜对镜框在定位精度、稳定性方面的要求。     

第一性原理研究KDP晶体中Ba取代K点缺陷

 用基于第一性原理的CASTEP模拟了Ba替代K缺陷前后形成的电子结构和能态密度。发现晶体能带宽度降至6.4 eV左右,对应着380 nm的双光子吸收,这一结果可以解释掺Ba晶体在紫外波段的吸收现象。Ba替代K点缺陷仅使其周围的晶格及电子结构发生轻微畸变,对晶体整体结构影响不大。     

基于红外波段光谱吸收的小型化湿度探测系统

 探测系统的光源选择为垂直腔面发射激光器,选定水汽在1.854 μm的吸收峰。系统自动在直接测量法与谐波测量法之间切换,能够适应高低湿度环境。在低湿度环境检测中,利用二次谐波与一次谐波的比值来定标湿度,有效去除了光源不稳定对测量带来的影响;过采样的A/D转换结合数字锁相放大（DLIA）技术,提高了检测精度。系统通过以太网接口,可以实现远程数据采集。     

双喷嘴乳粒发生器的研制及初步应用

 叙述了双喷嘴乳粒发生器的工作原理、设计关键点及设计思路,利用该发生器开展了双层乳粒的制备实验研究工作。研制的双喷嘴乳粒发生器在喷嘴处的3层管的位置能够通过简单调节达到同心,使得双层乳粒包覆的可靠性得到提高。研究了制备的乳粒的分散性和稳定性,并分析了形成双层乳粒的油相和水相的流速比,结果证明：利用所研制的双喷嘴乳粒发生器可以容易地制备出单分散性双层乳粒,油相与水相的流速比为0.3~15.0时,可形成双层乳粒。     

基于发射光谱的DF激光器光腔温度与粒子数分布

 建立了谱线增益系数与温度、粒子数分布之间及谱线增益系数与谱线强度之间的关系式,对一台燃烧驱动DF激光器的发射光谱进行了测量,利用发射光谱数据计算得到光腔温度为381.4 K,分布在振动态能级1与0,振动能级2与1,振动能级3与2的粒子数之比分别为0.60～0.62, 0.676 4, 0.71～0.74。     

气流对水面的冲击效果

通过实验研究了在气流冲击下水面的凹陷情况,并通过理论计算予以解释.结果表明凹陷的体积和深度主要与气流速度、玻璃管内径和玻璃管底部到水面上的距离有关的结论.     

Density functional theory study of neutral AlS_n(n=2-9) clusters

This paper investigates the geometrical structures and relative stabilities of neutral AlS n(n = 2-9) using the density functional theory.Structural optimisation and frequency analysis are performed at the B3LYP/6-311G(d) level.The ground state structures of the AlS n show that the sulfur atoms prefer not only to evenly distribute on both sides of the aluminum atom but also to form stable structures in AlS n clusters.The structures of pure S n are fundamentally changed due to the doping of the Al atom.The fragmentation energies and the second-order energy differences are calculated and discussed.Among neutral AlS n(n = 2-9) clusters,AlS 4 and AlS 6 are the most stable.