WAXS studies on block copolymers of ethylene and propylene

Wide-angle X-ray scattering from presumed block copolymers of polypropylene (PP) and ethylene-propylene copolymer (EPR), i.e., PP-EPR and PP-EPR-PP, synthesized by sequential polymerization with δ-TiCl₃? Et₂AlCl, was examined and compared with WAXS of mechanical blends and chain-transfer mixtures of PP and EPR with comparable compositions. The peak at 2θ = 20° for both the copolymers and the mixtures was attributed to the γ modification of PP in EPR. A strong variation in the ratio of diffraction intensities I₀₄₀/I₁₁₀ of PP in block copolymers and mixtures was explained in terms of crystallite growth in different directions. Analysis of the patterns and calculation of crystallinity, crystallite size, and lattice parameters led to the conclusion that block structure existed in the prepared copolymers.     

关于Lipschitz域上反射Brown运动的游程

本文具体刻画有界 Lipschitz 域上的反射 Brown 运动跨过某给定时刻 t 的离开 Martin 边界的游程．在此基础上,给出 Lipschitz 域上的反射 Brown 运动的边界过程的 L(?)vy 系统．     

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The main circuit topology, control hardware and control sequence of the cathode filament power supply for the HL-2A neutral beam heating system was introduced. Feedback control simulation of main circuit of filament power supply is carried out through MATLAB simulation software. It is found that the ripple factor is about 1%when the current is about 1000A, and the ripple coefficient increases to 3% when the current drops to 200A. Without the AC filter reactor in series L₁ and parallel harmonic filter LC in the low level control cabinet, the output current ripple coefficient becomes larger obviously. It shows that L₁ and LC not only absorb harmonic current, but also filter the chopper waveform after AC voltage regulation to make the output waveform smoother.     

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By using Fluent software with the Eulerian multiphase model and Non-equilibrium boiling model, the subcooled flow boiling heat transfers was numerically simulated in the plain upward vertical tubes under the condition of one-side heating. The influences of the different mass flux, inlet temperatures and heat flux on the heat transfer coefficient, the void fraction and heat transfer deterioration were investigated.     

Ethylene–propylene copolymerization with bis(β‐enaminoketonato) titanium complexes activated with modified methylaluminoxane

Ethylene–propylene copolymerization, using [(Ph)NC(R₂)CHC(R₁)O]₂TiCl₂ (R₁ = CF₃, Ph, or t‐Bu; R₂ = CH₃ or CF₃) titanium complexes activated with modified methylaluminoxane as a cocatalyst, was investigated. High‐molecular‐weight ethylene–propylene copolymers with relatively narrow molecular weight distributions and a broad range of chemical compositions were obtained. Substituents R₁ and R₂ influenced the copolymerization behavior, including the copolymerization activity, methylene sequence distribution, molecular weight, and polydispersity. With small steric hindrance at R₁ and R₂, one complex (R₁ = CF₃; R₂ = CH₃) displayed high catalytic activity and produced copolymers with high propylene incorporation but low molecular weight. The microstructures of the copolymers were analyzed with ¹³C NMR to determine the methylene sequence distribution and number‐average sequence lengths of uninterrupted methylene carbons. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5846–5854, 2006     

Highly soluble and optically transparent poly (ether imide)s based on 2,6‐ or 2,7‐bis(3,4‐dicarboxyphenoxy)naphthalene dianhydride and aromatic bis(ether amine)s bearing trifluoromethyl groups

Two series of novel fluorinated poly(ether imide)s (coded IIIA and IIIB ) were prepared from 2,6‐bis(3,4‐dicarboxyphenoxy)naphthalene dianhydride and 2,7‐bis(3,4‐dicarboxyphenoxy)naphthalene dianhydride, respectively, with various trifluoromethyl‐substituted aromatic bis(ether amine)s by a standard two‐step process with thermal or chemical imidization of the poly(amic acid) precursors. These fluorinated poly(ether imide)s showed good solubility in many organic solvents and could be solution‐cast into transparent, flexible, and tough films. These films were nearly colorless, with an ultraviolet–visible absorption edge of 364–386 nm. They also showed good thermal stability with glass‐transition temperatures of 221–298 °C, 10% weight loss temperatures in excess of 489 °C, and char yields at 800 °C in nitrogen greater than 50%. The 2,7‐substituted IIIB series also showed better solubility and higher transparency than the isomeric 2,6‐substituted IIIA series. In comparison with nonfluorinated poly (ether imide)s, the fluorinated IIIA and IIIB series showed better solubility, higher transparency, and lower dielectric constants and water absorption. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5909–5922, 2006     

ZI纵向计数数据模型的影响分析

基于EM算法和Laplace逼近, 本文给出了研究ZI (即含0较多的)纵向计数数据模型的影响分析方法. 为了识别含0较多的分组计数数据中的强影响点, 本文将ZI纵向数据模型中取值为0的数据赋予一定的权重; 而把随机效应看作缺失数据; 在此基础上引入EM算法, 从而应用完全数据对数似然函数的条件期望以及相应的$Q$距离函数进行影响分析; 并进一步应用Laplace逼近方法简化EM算法中的积分计算. 在此基础上, 基于数据删除模型和局部影响分析方法导出了适用于ZI纵向计数数据模型的诊断统计量. 本文也通过实际计数数据的例子验证了诊断统计量的有效性.     

交换自同构群的若干结果

借助于环论的方法研究了具有交换自同构群的有限群,提出了一种新的自同构构作技术,并用之证明了这样的非交换有限群具有非循环的中心子群,以及其每个极大子群的中心子群也都非循环.     

金属氧化物薄膜的多离子束反应共溅射模型(Ⅱ)——数值计算与结果讨论

结合实验中的工艺技术参数,以Pb,Ti两金属靶的反应共溅射为例,对我们提出的金属氧化物薄膜的多离子束反应共溅射模型进行数值计算,分别得出了各靶的溅射速率R,反应腔中反应气体分压p以及衬底Pb,Ti的金属单质和氧化物所占的有效面积百分比与反应共溅射中直接可调的物理量,即反应气体总量Q和溅射离子束流J的关系.计算结果表明,该模型揭示了反应溅射具有滞回效应的本质特征,反映了反应共溅射中相关参数的相互影响与相互耦合的特点,给出了薄膜中组分原子百分比及其氧化物的形态与溅射工艺的关系,指出了多离子束反应共溅射中稳恒溅 关键词：     

添加助剂的钙钛矿型氧化物NdMO_3上的甲烷氧化偶联——Ⅱ.15% Li_2O/NdMO_3(M=Cr、Mn、Fe、Co、Ni)上的OCM反应研究

在添加了15%Li_2O的NdMO_3(M=Cr、Mn、Fe、Co、Ni)上进行了甲烷氧化偶联(OCM)反应研究.通过改变反应气中CH_4:O_2浓度比,在氧化态和“脱氧态”催化剂上的CH_4脉冲反应,探讨了表面吸附氧和晶格氧在OCM反应中的作用以及NdMO_3中不同金属离子(M)对OCM反应活性的影响等.