Observation of Electrospinning Behavior of Nanoscale Fibers by a High-Speed Camera

Electrospinning is regarded as an effective method to generate nanoscale fibers. However, we believe that the mechanism of the formation of nanoscale fibers by Electrospinning has not yet been fully investigated. In this study, the jet behavior under various conditions was observed with a high-speed camera with short exposure periods. The behaviors of stable and unstable jets were compared. The effect of bending instability on the deposition pattern of jets was examined at different voltages and concentrations. In addition, the diameters of nanoscale fibers were analyzed as a function of sampling position.     

A Silicon Plasma-Based Wideband Modulator

Theoretical and experimental analysis has been performed for surface oriented silicon plasma-based p,i,n structures used to control high power level, broadband devices. It is shown that these structures are very promising for their use as modulators in the millimeter and submillimeter wave range.     

Isolation and Purification of a Novel Long－chain Acyl Catechin from Lipophilic Tea Polyphenols

Llpophilic tea polyphenols (LTP) was prepared by esterification of green tea polyphenols (GTP) with hexadecanoyl chloride. A novel long-chaln acyl catechin was isolated and purified from LTP by high-speed countercurrent chromatography (HSCCC).Its molecular structure was elucidated as epigallocatechin-3-O-gallate-4‘-O-hexadecanate by elemental analysis, IR, MS and ^1H NMR spectra.     

数字散斑法在局域剪切带三维变形研究中的应用

在适当的温度、应变率和预变形下,合金材料的拉伸试验中,将会出现伴随应力锯齿形跌落的雪崩式剪切变形带,即波特文-勒夏特利埃(Portevin-Le Chatelier,PLC)效应。利用高速数字摄像系统(分辨力1000 frames/s)并结合数字散斑干涉法(Digital speckle pattern interferometry,DSPI)和数字散斑相关法设计了一套光学变形测量系统,实现了拉伸试验中对试件表面三维变形的实时、精确测量。利用该光学系统对铝铜合金试件在拉伸试验中产生的跳跃传播的局域剪切带瞬态成核过程进行捕捉。通过结合数字散斑相关法得到的面内变形定量结果和数字散斑干涉法得到的表现离面变形的条纹图,再现了剪切变形带成核和传播瞬间的三维变形过程。     

数字高速分幅相机中光学分幅系统的设计与分析

使用光学辅助设计软件ZEMAX设计了用于四通道数字高速分幅相机的光学分幅系统，并结合机械设计软件SOLIDWORKS，在ZEMAX的非序列模式下建立了光学分幅系统的三维立体仿真模型。成像质量达到了衍射极限，动态极限空间分辨率为16lp／mm。模拟分析结果表明成像质量理想，符合设计要求。     

Non-isothermal crystallization of polyethylenes as function of cooling rate and concentration of short chain branches

Non-isothermal crystallization and melting of metallocene-catalyzed polyethylene was analyzed using the power-compensating calorimetry as function of both cooling rate and branch-degree ranging from 1 to 300 K min^–1, and from 0 to 72 hexyl-branches per 1000 carbon atoms, respectively. The onset crystallization temperature decreases linearly with increasing logarithm of cooling rate. The slope of this dependence increases with increasing branch-degree, which is explained by a stronger inhibition of the crystallization by the branches and the decreasing diffusion rate of molecules. The melting endotherms reveal a clear reduction of the crystallinity in the entire temperature range with increasing cooling rate.The authors gratefully acknowledge financial support by Deutsche Forschungsgemeinschaft (DFG). Samples of polyethylenes were kindly provided by Omya GmbH (Germany), or tailor-synthesized by Dr. S. Rudolph (Martin Luther University Halle-Wittenberg, Germany). Samples of adamantane and of liquid crystal M24 (4-cyano-4-octyloxybiphenyl) were kindly provided by Dr. S. Neuenfeld (Merck KGaA, Germany). Thanks are due to Dr. C. Gabriel (Friedrich Alexander University Erlangen-Nurnberg) for the molecular characterization of poly(ethylene-co-1-octene)s.     

甲烷/空气预混气体火焰的传播特征

利用高速纹影摄像等技术探讨了密闭管道内不同当量比的甲烷/空气预混气体火焰的传播特征。结果表明,当甲烷含量接近当量值时,预混气体火焰传播中会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程,逐渐由层流燃烧转变成湍流燃烧,并形成Tulip火焰结构;当甲烷含量偏离当量值一定程度时,预混火焰呈现出典型的层流燃烧特征,不会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程。Tulip火焰结构形成于火焰传播速度迅速降低的区间里,且只有当减速阶段的最大加速度的绝对值大于某一数值时才能形成;Tulip火焰结构是预混火焰由层流燃烧向湍流燃烧转变的一个中间过程。     

高速逆流色谱与硅胶柱色谱结合分离制备高纯度芦荟素异构体

芦荟素是芦荟叶中主要的蒽醌类成分,通常以芦荟素A和B两种非对映异构体形式并存,目前已成为许多芦荟产品质量控制指标之一。采用高速逆流色谱和硅胶柱色谱结合的方法,从老芦荟干粉中分离制备了高纯度的芦荟素A(纯度为98%)和芦荟素B(纯度为96%)样品,并采用快原子轰击质谱(FAB-MS)和核磁共振氢谱(1H NMR)以及GOESY(gradient-enhanced nuclear Overhauser effect spectroscopy)等方法对所得的两个芦荟素异构体的立体构象进行了确认。该法具有制备量大和分离效率高的特点。     

高速逆流色谱法分离纯化黄芪中的芒柄花素和毛蕊异黄酮

采用高速逆流色谱法(HSCCC),以正己烷-氯仿-甲醇-水组成二相系统作为固定相与流动相,对黄芪的乙酸乙酯粗提 物进行了分离纯化。 结果发现:以正己烷-氯仿-甲醇-水(体积比为1.5∶3∶3∶2)组成的系统可以从黄芪的乙酸乙酯粗 提物中分离出毛蕊异黄酮,纯度可达95％以上,并可以初步纯化芒柄花素;接着用正己烷-氯仿-甲醇-水(体积比为4∶4∶5 ∶4)组成的系统进一步纯化芒柄花素,其纯度达95％以上。利用该方法,可以对中药黄芪中的异黄酮进行快速的分离和纯 化。     

高速碰撞SPH方法模拟中的初始光滑长度和粒子间距

采用光滑粒子流体动力学方法对高速碰撞问题作数值模拟,分析初始光滑长度和非一致粒子间距对计算结果的影响,提出修正光滑长度法,并引入XSPH速度纠错公式.数值结果表明,初始光滑长度越大,弹丸的刚性越小,h₀的合理取值范围应为d₀<h₀≤1.5d₀;粒子间距越小,材料的刚性越小.非一致粒子间距和均匀粒子分布的计算结果吻合的较好.