Preparation of micron‐size monodispersed PS/P(St/MAA) microspheres by seeded dispersion polymerization

Uniform polystyrene (PSt) particles with the size of 1.9 μm were first prepared via dispersion polymerization, and then used as the seeds in a second‐stage dispersion copolymerization of styrene (St) and methacrylic acid (MAA) to produce carboxyl‐carrying microspheres. The PSt seed particles were swollen by monomer mixture of St and MAA, including an oil‐soluble initiator 2,2′‐azobisiso‐butyronitrile (AIBN), before polymerization. Finally, uniform PS/P(St/MAA) (polydispersity index, PDI = 1.02) microspheres with the size of 2.2 μm were obtained. The average particle size and size distribution of the final microspheres were investigated. MAA contents between 54 and 97 mg/g were detected from the PS/P(St/MAA) particles produced under different conditions. Dispersion medium has great influence on the kinetics of polymerization, due to its effect on the partitioning of monomers, solvents, and initiator in the particle phase, probably as well as on the conformation of the dispersion agent on the surface of the particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3586–3591, 2006     

反应性乳化剂应用于丙烯酸酯类乳液压敏胶的研制

使用正交试验法设计压敏胶配方,得到用反应性乳化剂参与的AA、HEA、BA和EA、M AA等多元共聚物乳液,研究该聚合物应用于压敏胶的初粘、持粘、剥离强度等力学性能。结果表明,在该体系下引发剂用量、反应温度、AA、反应性乳化剂用量对压敏胶乳液综合性能关系密切,其它各因素影响不明显。得到的优化配方为BA(83%)、AA(1%)、HEA(1%)、MM A和EA的混合单体(15%)。     

国内外聚碳酸酯市场及需求分析

聚碳酸酯(PC)综合性能好,其消费与生产增长举世瞩目,在世界五大通用工程塑料中占有重要地位。国内PC生产及消费量虽不大,但潜在市场不可忽视,发展与开拓工程塑料,特别是PC的应用与生产的开发,是我国化学和石化工业发展需要之一。     

Crystallization behavior of carbon nanotubes‐filled polyamide 1010

The nanocomposites of polyamide1010 (PA1010) filled with carbon nanotubes (CNTs) were prepared by melt mixing techniques. The isothermal melt‐crystallization kinetics and nonisothermal crystallization behavior of CNTs/PA1010 nanocomposites were investigated by differential scanning calorimetry. The peak temperature, melting point, half‐time of crystallization, enthalpy of crystallization, etc. were measured. Two stages of crystallization are observed, including primary crystallization and secondary crystallization. The isothermal crystallization was also described according to Avrami's approach. It has been shown that the addition of CNTs causes a remarkable increase in the overall crystallization rate of PA1010 and affects the mechanism of nucleation and growth of PA1010 crystals. The analysis of kinetic data according to nucleation theories shows that the increment in crystallization rate of CNTs/PA1010 composites results from the decrease in lateral surface free energy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3794–3800, 2006     

Effect of the Three Gorges Reservoir on vertical distribution of suspended sediment concentration and estimation accuracy of depth-average concentration in downstream reaches

The sediment regime in the middle Yangtze River has been significantly changed from quasi-equilibrium to nonequilibrium since the impoundment of the Three Georges Reservoir (TGR). To understand the effects of the TGR on vertical distribution of suspended sediment concentration (SSC) and estimation accuracy of mean concentration, vertical sediment concentration and flow velocity data at the Shashi and Jianli hydrological stations in the reach before and after the impoundment were collected. Comparisons and analysis of vertical profiles of SSC before and after the TGR impoundment show that after the impoundment of the TGR, due to the coarsening of sediment particle size, the reduction in sediment load, and the significant decrease in sediment saturation, the vertical distribution of SSC in the downstream reaches became more uneven under medium and low water flows, which was reflected in the vertical gradient and the fluctuation degree of SSC significantly increased. In addition, the depth-average sediment concentrations were calculated by the selected-point method and the mean values calculated by the “multi-point method” were regarded as the “true mean” to evaluate the accuracy of the mean value calculated by the “few-point method.” It was found that the relative errors for the selected-point method were mainly positive before impoundment but mainly negative after impoundment. Additionally, the correction factors of one-point, two-point, and three-point methods and the position of the near-bed substituted point for the five-point method were given to reduce the error when the point measurements were used to calculate the depth-average sediment concentration in the downstream reaches.     

融合交互意图的图神经网络协同过滤算法

传统的协同过滤方法很大程度上以一种统一的方式进行建模,未从交互意图的细粒度上考虑建模关系。为此提出一种融合交互意图的图神经网络协同过滤算法（INTNGCF）。首先,通过将边分解成多个潜在空间来识别潜在意图;其次,利用交互意图融合层确定这些潜在意图的重要性;最后,生成用户对项目的预测评分。在三个真实数据集上与七种基线模型进行对比实验,结果表明,提出的算法与其他先进的推荐模型相比具有一定的性能优势。     

基于坐标—灰度交织映射的视频麦克风声音复原系统

区别于声学麦克风,视频麦克采用高帧率摄像机,利用声音震动引起周围物体的帧间图像细微差异,对声音进行复原。模拟人脑v2皮层位置亮度交织神经网络,提出一种基于二维对数的坐标—灰度交织映射算法。算法将视频帧图像矩阵与函数构造矩阵交织映射,产生混沌吸引子保留并放大帧间图像微差异,并构造基于该算法的视频麦克风声音复原系统。仿真实验表明,该视频麦克风系统可以从薯片袋子的高帧率视频中复原声音信号,相比于传统算法降低了40%的计算量,同时保持语音复原质量。     

基于双策略协同进化的QPSO算法及其应用

为更好地提升量子粒子群优化算法（QPSO）的局部挖掘和全局搜索能力,提出了一种改进的QPSO算法（DSQPSO）。在改进算法中引入了双策略协同进化的思路调整粒子的位置更新公式。为充分体现个体粒子挖掘的优势和群体共同引导的特点,提出了两种吸引点构造的思路,做到个体和种群更好地融合以及信息的互通;分别考虑了最优平均位置与全局最优和粒子的历史最优之间的联系,对粒子搜索范围作出了重新定义;此外,在迭代过程中,借助随机扰动机制对全局最优位置进行调整,以保持种群的多样性。通过18个测试函数将DSQPSO算法与PSO、QPSO、RQPSO和LQPSO四种算法在收敛精度和鲁棒性方面进行对比;进而在两个具体的工程优化问题上,应用改进算法与八个智能算法进行了寻优结果比较。实验表明DSQPSO算法无论在基准测试中还是在工程应用上,其计算精度和收敛效果均有明显优势。     

Fluorescence of poly(di-n-alkylsilane)s in room-temperature solution

A comprehensive study of the electronic absorption and emission spectra and the fluorescence quantum yield and lifetime of seven poly(di-n-alkylsilane)s and of three isotopically labelled poly(di-n-hexylsilane)s in hydrocarbon solution at room temperature is reported. Also reported are fluorescence polarization and carbon tetrachloride quenching of fluorescence of poly(di-n-hexylsilane). The observed fluorescence spectra, quantum yield, and polarization depend on the selected excitation energy in a very characteristic fashion, whereas the fluorescence lifetime does not; however, it depends on the selected emission energy. These characteristic dependencies are qualitatively accounted for by the previously proposed segment distribution model if one assumes that the photophysical behavior at higher excitation energies is strongly affected by the presence of a low-lying weakly allowed state in short-segment chromophores and the behavior at lower excitation energies is dictated by the selective excitation of emitting long-segment chromophores.     

Infrared reflectance and transmission spectra of semiconducting non-stoichiometric CdGe x As2

The infrared reflectance and transmission spectra of amorphous CdGe _x As₂ were investigated to study the amorphous structure with varying Ge content. The mid-infrared optical absorption edges of amorphous CdGe _x As₂ with 0<x<1.2, were observed in the range 1.6–1.7 m, indicating a structural similarity in short-range order throughout. Comparing the reflectance and transmission spectra of amorphous and devitrified crystalline phases established that the structures of amorphous CdGe _x As₂ transformed from the CdAs₂ basic structure to the chalcopyrite (CdGeAs₂) structure, as one progressed fromx=0 tox=1.2. The infrared spectra were interpreted interactively with radial distribution function, magnetic susceptibility, density measurements, and crystallization studies. The crystallization behaviour of amorphous CdGe _x As₂ that was heat treated at different temperatures was investigated using far-infrared transmission spectra.