Effect of β-Nucleating Agent on the Crystallization,Mechanical Properties,and Heat Resistance of Injection-Molded Isotactic Polypropylene

Injection-molded β-isotactic polypropylene (β-iPP) was prepared with a commercial β-nucleating agent (NT-A). The effect of NT-A on the crystallization, mechanical properties, and heat resistance of β-iPP was investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), polarized light microscopy (PLM), and mechanical and heat deflection tests. DSC and WAXD analysis showed that the content of β-crystals in the nucleated iPP was higher than that of pure iPP, and the content of β-crystals of the core was higher than that of the skin. PLM observations showed that injection-molded iPP had an obvious skin-core structure. NT-A induced abundant β-crystals and resulted in small spherulites which improved the Izod notched impact strength. When the content of NT-A was 0.075wt%, the Izod notched impact strength reached a maximum, 2.6 times more than that of pure iPP. The heat distortion temperature was also improved by NT-A.     

High resolution dynamic cardiac MRI using partial separability of spatiotemporal signals with a novel sampling scheme

The partial separability (PS) of spatiotemporal signals has been exploited to accelerate dynamic cardiac MRI by sampling two datasets (training and imaging datasets) without breath-holding or ECG triggering. According to the theory of partially separable functions, the wider the range of spatial frequency components covered by the training dataset, the more accurate the temporal constraint imposed by the PS model. Therefore, it is necessary to develop a new sampling scheme for the PS model in order to cover a wider range of spatial frequency components. In this paper, we propose the use of radial sampling trajectories for collecting the training dataset and Cartesian sampling trajectories for collecting the imaging dataset. In vivo high resolution cardiac MRI experiments demonstrate that the proposed data sampling scheme can significantly improve the image quality. The image quality using the PS model with the proposed sampling scheme is comparable to that of a commercial method using retrospective cardiac gating and breath-holding. The success of this study demonstrates great potential for high-quality, high resolution dynamic cardiac MRI without ECG gating or breath-holding through use of the PS model and the novel data sampling scheme.     

Determination of bulk viscosity of liquid water via pulse duration measurements in stimulated Brillouin scattering

We present a method by which to determine the bulk viscosity of water from pulse duration measurements of stimulated Brillouin scattering （SBS）. Beginning from a common model of Brillouin scattering, the bulk viscosity is shown to play an important role in Brillouin linewidth determination. Pulse durations of SBS back-reflected optical pulses are measured over the temperature range of 5-40℃. SBS linewidths are de- termined via Fourier transformation of the time-domain results, and the bulk viscosity of water is measured and derived from the obtained values. Our results show that the proposed method for measurement of pulse durations is an effective approach for determining bulk viscosity. The method can be easily extended to determine bulk viscosities of other Newtonian liquids.     

丙烯腈-尿素包合物的形成过程及特征

利用差示扫描量热法(DSC)和X射线衍射(XRD)研究了在不同丙烯腈/尿素投料比情况下的丙烯腈-尿素包合物的形成过程和组成. 实验结果表明DSC是一种研究包合物的客主比及分解热的有效方法. 测定了丙烯腈-尿素包合物的客主比和分解热分别为1.17和5361.53 J/mol. 同时发现丙烯腈-尿素包合物的形成依赖于冷冻时间,在足够长的冷冻时间之后丙烯腈-尿素包合物的组成达到稳定状态. 实验结果表明,丙烯腈分子可能是采用堆叠的方式排布在尿素晶道结构中. XRD结果表明只要丙烯腈分子进入尿素晶格中,丙烯腈-尿素包合物的结构便形成了,并且这种结构与形成过程终了时的结构是一致的. 只要丙烯腈是足量的,包合物中的丙烯腈分子排列会随冷冻时间的延长而增长,直到尿素的晶道结构被丙烯腈分子填满.     

SiN自由基X2∑+, A2Π和B2∑+ 电子态的光谱常数研究

采用内收缩多参考组态相互作用(MRCI)方法, 结合价态范围内的最大相关一致基aug-cc-pV6Z, 计算了SiN自由基X²∑⁺, A²Π 和B²∑⁺电子态的势能曲线. 采用Davidson修正来避免由于MRCI方法本身的大小一致性缺陷产生的误差. 为了提高计算精度, 进一步考虑了相对论修正和核价相关修正对势能曲线的影响. 本文的相对论修正是利用二阶Douglas-Kroll 哈密顿近似在cc-pV5Z基组水平进行的; 同时核价相关修正是在cc-pCV5Z基组水平进行的. 对这些势能曲线进行拟合, 得到各种水平下三个电子态的光谱常数(T_e, R_e, ω_e, ω_ex_e, α_e和B_e), 并详细分析了Davidson修正、相对论修正和核价相关修正对光谱常数的影响. 与其他理论结果和实验数据进行比较, 可知本文的结果更精确、更完整.     

混合溶剂对P3HT:PCBM基太阳能电池的影响

以poly(3-hexylthiophene)(P3HT)为电子给体材料,[6,6]-phenyl-C60-butyric acid methyl ester (PCBM)为电子受体材料,制备了纯氯苯(CB)溶剂、纯氯仿(CF)溶剂和氯苯/氯仿(CB/CF)不同比例混合溶剂的共混体系太阳能电池.研究了不同溶剂及不同比例混合的混合溶剂对电池性能的影响.结果表明:以CB/CF(3/1)为溶剂制备的器件,紫外可见吸收光谱和器件外量子效率曲线显示出红移现象,原子力显微图表明P3HT和PCBM间形成良好的相分离结构.在100 mW/cm2强度光照射下,其开路电压Voc为0.61 V短路电流密度Jsc为9mA/cm2,填充因子FF为57.9％,能量转换效率PCE为3.2％.     

Terfenol-D/PZT磁电复合材料的磁电相位移动研究

采用粘合法制备了叠层结构的块体Terfenol-D/PZT磁电复合材料,测量了不同频率下的磁电回线,采用新的极坐标下的方式做图.从极坐标下的磁电回线中可以看出,随直流磁场的变化,非谐振频率下的磁电相位发生了轻微移动,移动幅度随频率的增加而增加;而在谐振频率下,伴随着巨磁电效应,磁电相位发生了显著移动,移动幅度达到了近90°.与粉末Terfenol-D/环氧树脂/PZT磁电复合材料对比之后表明,非谐振频率下块体Terfenol-D/PZT的磁电相位移动主要由涡流引起;而谐振频率下大幅度相位移动则主要来源于Terfenol-D的磁致弹性变化.     

CVD金刚石中的氮对等离子体刻蚀的影响

采用非对称磁镜场电子回旋共振等离子体分别对沉积过程中掺氮和未掺氮的化学气相沉积金刚石膜进行了刻蚀研究, 结果表明: 掺氮制备的金刚石膜的刻蚀主要集中在晶棱处, 经过4h刻蚀后其表面粗糙度由刻蚀前的4.761 μm下降至3.701 μm, 刻蚀对金刚石膜的表面粗糙度的影响较小; 而未掺氮制备的金刚石膜的刻蚀表现为晶面的均匀刻蚀, 晶粒坍塌,刻蚀4h后其表面粗糙度由刻蚀前的3.061 μm下降至1.083 μm. 刻蚀导致表面粗糙度显著降低. 上述差别的主要原因在于金刚石膜沉积过程中掺氮导致氮缺陷在金刚石晶棱处富集, 晶棱处电子发射加强, 引导离子向晶棱运动并产生刻蚀, 从而加剧晶棱的刻蚀. 而未掺氮金刚石膜,其缺陷相对较少且分布较均匀 ,刻蚀时整体呈现为 (111) 晶面被均匀刻蚀继而晶粒坍塌的现象. 关键词： 掺氮 金刚石膜 刻蚀 非对称磁镜场     

H2S在Fe(100)面吸附的第一性原理研究

基于密度泛函理论第一性原理, 在广义梯度近似下, 研究了表面覆盖度为0.25 ML (monolayer)时硫化氢分子在Fe(100)面吸附的结构和电子性质, 并与单个硫原子吸附结果进行了对比. 结果表明: 硫化氢分子吸附在B2位吸附能最小为-1.23 eV, 最稳定, B1位吸附能最大为-0.01 eV, 最不稳定; 并对硫化氢分子在B1位和B2位吸附后的电子态密度进行了分析, 也表明了吸附在B2位稳定, 且吸附在B2位后硫化氢分子几何结构变化不大; 将硫化氢中硫原子吸附与单个硫原子吸附的电子性质进行了比较, 发现前者吸附作用非常微弱; 同时对吸附后的Fe(100)面进行了对比, 单个硫原子吸附的Fe(100)面电子态密度出现了一系列峰值且离散分布, 生成了硫化亚铁, 表明在硫化氢环境下, 主要是硫化氢析出的硫原子发生了吸附. 关键词： 第一性原理 Fe(100)表面 吸附能 硫化氢     

利用数值再现实现彩虹全息色差评价

为了在计算机制彩色彩虹全息图输出之前定量得到再现像的色彩保真度,提出了一种采用数值再现进行色差评价的方法.首先对彩虹全息图进行了频谱分析,得到再现参量与频谱分布之间的关系;然后采用频域滤波算法实现彩色彩虹全息图数值再现,得到再现像的相对功率谱分布;最后采用CIE1976UCS均匀颜色空间对再现像色差情况进行了计算.设计了7个色块并制作了计算机制真彩色彩虹全息图,以金卤射灯作为照明光源进行了光学再现实验,给出实验结果及分析.研究证明了采用数值再现方法实现对计算彩虹全息再现像光谱分布和色差进行计算分析是一种快速经济的方法.