Isotopic Oxygen Exchange and EPR Studies of Superoxide Species on the SrF2/La2O3 Catalyst

By using the in situ IR spectroscopy, the superoxide species (O₂⁻), characterized by the O–O stretching peak at 1130 cm⁻¹, was detected on the SrF₂/La₂O₃ catalyst at temperatures up to 973 K. The introduction of ¹⁸O₂ isotope caused the 1130 cm⁻¹ peak to shift to lower wavenumbers (1095 and 1064 cm⁻¹), consistent with the assignment of the spectra to the superoxide species. A good correlation between the rate of the disappearance of the O₂⁻ species and that of the formation of C₂H₄ was observed, suggesting that O₂⁻ was the active oxygen species responsible for the oxidative coupling of methane (OCM) on the SrF₂/La₂O₃ catalyst. This conclusion was reinforced by the EPR experiments (g_xx = 2.0001, g_yy = 2.0045, g_zz = 2.0685), showing that O₂⁻ was the only paramagnetic oxygen species detectable on the O₂-preadsorbed SrF₂/La₂O₃ catalyst. These results suggest that superoxide O₂⁻ can be a stable active oxygen species, whose role in the OCM reaction cannot be overlooked.     

Synthesis and characterization of poly(butyl acrylate)/silica and poly(butyl acrylate)/silica/poly(methyl methacrylate) composite particles

Poly(butyl acrylate)/poly(methyl methacrylate) (PBA/PMMA) core–shell particles embedded with nanometer‐sized silica particles were prepared by emulsion polymerization of butyl acrylate (BA) in the presence of silica particles preabsorbed with 2,2′‐azobis(2‐amidinopropane)dihydrochloride (AIBA) initiator and subsequent MMA emulsion polymerization in the presence of PBA/silica composite particles. The morphologies of the resulting PBA/silica and PBA/silica/PMMA composite particles were characterized, which showed that AIBA could be absorbed effectively onto silica particles when the pH of the dispersion medium was greater than the isoelectric potential point of silica. The critical amount of AIBA added to have stable dispersion of silica particles increased as the pH of the dispersion medium increased. PBA/silica composite particles prepared by in situ emulsion polymerization using silica preabsorbed with AIBA showed higher silica absorption efficiency than did the PBA/silica composite particles prepared by direct mixing of PBA latex and silica dispersion or by emulsion polymerization in which AIBA was added after the mixing of BA and silica. The PBA/silica composite particles exhibited a raspberrylike morphology, with silica particles “adhered” to the surfaces of the PBA particles, whereas the PBA/silica/PMMA composite latex particles exhibited a sandwich morphology, with silica particles mainly at the interface between the PBA core and the PMMA shell. Subsequently, the PBA/silica/PMMA composite latex obtained had a narrow particle size distribution and good dispersion stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3425–3432, 2006     

Kinetic Treatment for copolymerization of styrene or methyl methacrylate with N-phenylmaleimide

Shirota‘s kinetic model and our kinetic model were used to treat the kinetic data of styrene (St) and N-phenylmaleimide (PMI) copolymerization in which chaxge-transfer complex (CTC) was formed. The results obtained by Shirota‘s kinetic model were disagreed with the experiments and the experimental phenomena could not be explained. The kinetic data of all feed fractions can be treated with our kinetic model, and the experimental phenomena can be explained from the propagation constants and reactivity ratios. Our kinetic model is also suitable for the kinetic data of methyl methacrylate (MMA) and PMI copolymerization in which CTC can not be formed.     

基于课堂教学的多媒体课件设计分析

随着教学水平的提高,目前我国大部分的课堂教学都采用多媒体课件进行教学.然而在多媒体课件的设计方面却存在着非常明显的问题,如屏幕所呈现的内容与课本所呈现的内容基本一样,课件的实际作用无法体现,加剧学生的机械性思维固疾.师生之间缺少良好的沟通,导致教学水平一直难以得到质的提升.本文就课堂教学的多媒体课件设计的现状、出现的原因,以及课堂教学多媒体课件的正确设计方法进行简要的论述,以提高提高多媒体的使用效率.     

R2O-RO-Al2O3-B2O3-SiO2系统在骨质瓷中的应用

实验采用正交实验法和对比实验，通过对R2O-RO-AlO3-B2O3-SiO2系统的成釉机理分析及熔融特性、熔体的粘度和表面张力等性能的测试，探讨了该系统在骨质瓷中的应用。     

气候变化背景下流域生态需水预估−以好溪流域为例

为探究未来气候变化对流域生态需水量的影响,保障河流生态需水量,针对好溪流域进行生态需水量计算 及预测。基于好溪流域气象数据及下垫面条件建立流域生态需水模型,并根据 GF1-WFV 遥感影像数据订正后的 地表反射率和作物种植结构提升模型模拟精度。选择 CanESM2气候模式下的 RCP2.6、RCP4.5 和 RCP8.5 这 3 种 排放情景,建立气候变化背景下流域生态需水预测方法,计算现状年并预测未来年份的生态需水量及生态需水保 障程度。结果表明,基于光学遥感影像进行数据订正后,模型模拟精度有所提升,率定期的模型精度 R2从 0.80 提 升为 0.85,验证期的 R2从 0.75 提升至 0.78。应用提升精度后的模型进行生态需水预测,在 RCP2.6、RCP4.5 和 RCP8.5 情景下,2025—2100 年的年均生态需水分别增加了 0.27 亿、0.21 亿和 0.29 亿 m3,其中 RCP8.5 情景下生态 需水保障程度最高,RCP4.5 情景下生态需水保障程度最低。     

A social recommendation method based on opinion leaders

With the rapid development of information technology, social media has been widely used, and Internet information has been exploded, and consumers may experience information overload. Recommender systems using the social recommendation method that integrates social relationship information can provide users with target information that meets their needs. However, most of the existing methods only rely on the user’s ordinary friends to make recommendations, neglecting another influential group, the opinion leaders. In this study, we propose a new social recommendation method based on opinion leaders. The proposed method assumes that the influence of the opinion leader on the user is much greater than that of the user’s ordinary friends. The experimental results on two real datasets show that the proposed method not only has a better recommendation effect than the state-of-the-art recommendation algorithms, but also has a good performance in the cases of cold-start users.

     

基于OLPP符号表示的时间序列分类算法

基于符号表示的时间序列分类方法是时间序列数据挖掘的关键技术。大部分现有方法主要针对单个时间序列样本进行符号表示,没有考虑样本间的近邻关系对符号化分类的影响。对此提出一种基于正交局部保持映射(Orthogonal Locality Preserving Projection,OLPP)的时间序列符号表示方法。使用OLPP对原始数据集进行维数约减,利用信息增益寻找维数约减后数据的最佳符号投影区间,采用多重系数分箱技术(Multiple Coefficient Binning,MCB)将降维后数据表示成符号序列。该算法在20个时间序列数据集上的分类效果好于已有方法,有效利用样本间的近邻关系能够显著提高算法的分类性能。     

基于局部概率抽样的标签噪声过滤方法

分类学习任务中,在获取数据的过程中会不可避免地产生噪声,特别是标签噪声的存在不仅使得学习模型更复杂,而且容易造成过拟合并导致分类器泛化能力的下降。标签噪声过滤算法虽然在一定程度上可以解决上述问题,但是仍然存在噪声识别能力较差、分类效果不够理想以及过滤效率低等问题。针对这些问题,提出一种基于标签置信度分布的局部概率抽样方法来进行标签噪声过滤。首先利用随机森林分类器对样本的标签进行投票,从而获取每个样本的标签置信度;然后根据标签置信度的大小,将样本划分为易识别样本和难识别样本;最后分别采用不同的过滤策略对样本进行过滤。实验结果表明,在标签噪声存在的情况下,所提方法在大多数案例上能够保持较高的噪声识别能力,并且在分类泛化性能上也具有明显优势。