A laser flash photolysis, matrix isolation, and DFT investigation of (η-C6H5Y)Cr(CO)3 (Y = NH2, OCH3, H, CHO, or CO2CH3)

The quantum yield for arene displacement from (η⁶-C₆H₅Y)Cr(CO)₃ was measured in 1,1,2-trifluorotrichloroethane (Y = NH₂, OCH₃, H, CHO, or CO₂CH₃). Values of 0.24, 0.27, 0.15, 0.17, and 0.32 were obtained respectively (λ_exc. = 355 nm). These values are significantly higher than those measured for photoinduced arene loss in hydrocarbon solvents using the same excitation wavelength. Laser flash photolysis of (η⁶-C₆H₅Y)Cr(CO)₃ in 1,1,2-trifluorotrichloroethane (λ_exc. = 355 nm) resulted in the rapid formation (<10 ns) of Cr(CO)₆. Matrix isolation experiments on (η⁶-C₆H₅Y)Cr(CO)₃ (Y = H or CHO) at 12 K in CH₄ or CO-doped CH₄ matrixes using monochromatic irradiation confirmed the presence of two discrete excited states, one leading to CO-loss and the other to arene-loss. The results correlate with the calculated electron drift in the excited state derived from density functional theory and time dependent density functional theory calculations.     

可用于高速摄影脉冲氙灯的研究

为了研究储能电容初始电压、电极间距、充气压及灯管内径等条件对脉冲氙灯电流脉冲和发光脉冲的影响,在电极间距100~300mm、充气压13.33~53.32kPa、灯管内径6~12mm、储能电容初始电压1.75~4.25kV的条件下,分别测量了脉冲氙灯的电流脉冲和发光脉冲的变化状况。测量得到脉冲氙灯的电流脉冲宽度和发光脉冲宽度均在15~45μs之间。对比发现:储能电容初始电压较高有助于获得高峰值、窄脉宽且滞后时间短的电流脉冲;具有较高充气压或较长电极间距的脉冲氙灯其电流脉冲与发光脉冲的峰值较小、脉冲宽度较大,且发光脉冲滞后时间较长;较粗灯管内径虽然可以增加电流脉冲的峰值,但电流脉冲的宽度被增宽,发光脉冲峰值减小,发光脉冲宽度展宽,且延长了发光脉冲的滞后时间.     

漫谈Flash中的引导动画

Flash是Macromedia公司推出的动态界面制作工具。它是当前最优秀、应用最广泛的网页矢量动画设计软件。它不仅应用在因特网上,现在许多电视广告、电脑游戏的片头和片尾、多媒体课件制作上等等都是用Flash来做成的。Flash动画与传统动画一样,引导动画的制作与技巧也是很重要的一部分。这篇文章是本人这几年的《Flash动画制作》教学过程中总结出来的一些关于Flash中各种制作引导动画的技巧,写出来与各位老师交流沟通,互相学习探讨。     

OneNAND Flash的操作性能与应用研究

与NOR Flash和NAND Flash比较,新器件OneNAND Flash体系结构具有存储容量大、快速读取、快速编程和上电自启动等综合优点.分析和探讨了OneNAND Flash的读数、编程和擦除等操作时序,提供若干OneNAND Flash的应用参考方案.     

Multifunctional nanocomposites based on tetraethylenepentamine-modified graphene oxide/epoxy

Composites based on epoxy/graphene were investigated for thermal-mechanical performance. Initially, few-layer graphene oxide (GO) was modified with tetraethylenepentamine (GO-TEPA) in a reaction assisted by microwave radiation. GO and GO-TEPA samples were characterized for their structure and morphology. Composites containing 0.1, 0.3 and 0.5 wt.% of GO and GO-TEPA were prepared, and the effect of fillers on the morphology of cryofractured regions of epoxy matrix was observed through electron microscopy images. Dynamic mechanical thermal analysis (DMA) tests revealed increases of approximately 20 °C in glass transition. Moreover, when compared to neat polymer, composites containing 0.5 wt.% of GO-TEPA gained up to 103% in thermal conductivity (obtained by flash laser). Finally, nanoindentation analyses showed increases of 72% in Young's modulus and 143% in hardness for the same sample. The system is characterized as multifunctional nanocomposites because of the simultaneous gains in thermal and mechanical properties. The best results of the multifunctional composites were strongly associated with the chemical modification of the GO by TEPA.     

超快扫描量热技术表征高分子结晶动力学

高分子结晶行为是高分子材料加工过程研究的热点,因为高分子组分和加工工艺控制着高分子结晶及其产物性能。差示扫描量热仪(DSC)是研究高分子结晶动力学常规手段。但是,普通DSC所能达到的最快降温速率一般无法抑制较快的样品结晶,结晶行为将在等温结晶动力学测试之前发生,因此可进行等温结晶的研究温度范围局限于较低结晶过冷度的高温区域。近年来,具有超快速升降温扫描速率和精准控温的快速扫描芯片量热仪(FSC,其商业化版本Flash DSC 1)得到了广泛应用。FSC可以抑制高分子样品在升降温过程中的结晶成核,避免对之后的结晶动力学测试产生影响。因此FSC技术将高分子结晶动力学的研究温度区间延伸至具有较大过冷度的低温区,加深了我们对高分子结晶成核机理以及高分子工业加工过程的理解。本文首先介绍了由初级成核方程描述的高分子结晶动力学原理,初级成核自由能位垒(?G~*)和扩散活化能位垒(?U)分别控制了高低温区的结晶动力学。我们还总结了FSC技术的发展,包括氮化硅薄膜芯片技术、快速扫描量热仪、商业化Flash DSC 1在不同高分子结晶熔融行为研究中的应用。然后介绍表征高分子等温结晶动力学的方法,其中包括样品制备、质量估算、消除热历史、临界扫描速率的确定等,并举例介绍FSC在高分子结晶动力学研究中的应用,涵盖高分子总结晶动力学、结晶成核动力学、高分子焓松弛对结晶成核的影响、FSC联用技术等方面。应用举例中对应形貌和结晶信息,分析了通过FSC测试得到的结晶成核动力学特点。另外通过比较不同结构特点的高分子,总结了我们对结晶动力学行为的基本理解。总之,FSC技术是一种能够提供相转变动力学和热力学信息的高效工具,特别是应用于分析只能在快速扫描中得到的样品结构变化信息。同时我们希望本文能够帮助读者考虑超快扫描量热技术在其他材料研究上的应用,包括合金、药物、生物大分子等。     

基于Flash实现网络课程平台的编著与应用

以Flash技术为基础,自主开发了《网络课程编著与发布平台》。该平台选择了使用Flash技术来表现网络课程的结构、教学内容、交互功能等,使得教师和学生在建设、管理和使用网络课程时更为简单、直观、灵活、个性和美观。文中以该平台为例,详细分析了利用Flash技术可以实现高校网络课程的多种功能。     

基于日志的闪存文件系统的设计

日志文件系统的主要设计思想是跟踪文件系统的变化,在日志节点中记录对文件所作的修改信息.FAT、JFFS、YAFFS等文件系统由于擦写频率过高,对闪存储介质的某些块造成较大的负担从而导致存芯片失效.文章设计的基于日志的闪存文件系统对存取采用的是追加模式,能很好地均衡读写频率,将该系统应用于嵌入式GIS系统,取得较好的效果,但在效率上还有待提高.     

闪光照相底片成像非线性校正技术研究

介绍了利用黑密度~穿透光程关系曲线对底片接收方式下的闪光照相图像进行非线性校正的方法. 根据闪光照相成像原理, 在光场均匀、散射均匀的条件下, 图像的黑密度是照相客体的穿透光程的单调函数. 当有一定的散射分布时, 相当于校正图像中叠加了一本底成分, 利用先验知识可以扣除. 因此可以用黑密度~穿透光程关系曲线进行闪光照相图像的非线性校正. 利用本方法对一三棱柱照相客体的图像进行了非线性校正, 处理结果证实了该方法的有效性.     

Study on volatility and flash point of the pseudo binary mixtures of sunflower-based biodiesel + methylcyclohexane

The transesterification of sunflower seed oil was carried out in supercritical ethanol without using any catalyst to produce biodiesel. In the present work, methylcyclohexane was added to enhance the vapor pressure of biodiesel. The vapor pressures of mixtures of biodiesel + methylcyclohexane as a function of temperature were measured by comparative ebulliometry with an inclined ebulliometer. The vapor pressures versus composition at different temperatures were obtained. Experimental data of vapor pressures and equilibrium temperatures were correlated by the Antoine equation. A mathematical model was used to predict the flash point of the pseudo binary mixtures. With the regular solution theory, the predictive flash point displays agreement with the experimental data obtained by closed cup test.