Influence of polymerization conditions on the structure and properties of polyethylene/polypropylene in‐reactor alloy synthesized in the gas phase with a spherical Ziegler–Natta catalyst

A spherical TiCl₄/MgCl₂‐based catalyst was used in the synthesis of in‐reactor polyethylene/polypropylene alloys by polyethylene homopolymerization and subsequent homopolymerization of propylene in the gas phase. Different conditions in the ethylene homopolymerization stage, such as monomer pressure and polymerization temperature, were investigated, and their influences on the structure and properties of in‐reactor alloys were studied. Raising the polymerization temperature is the most effective way of speeding up polymerization and regulating the ethylene content of polyethylene (PE)/polypropylene (PP) alloys, but it will cause a greater increase in the PE‐b‐PP block copolymer fraction (named fraction D) than in the fraction of PP‐block‐PE in which the PP segments have low or medium isotacticity (named fraction A). Although changing ethylene monomer pressure could influence the ethylene content of PE/PP alloys slightly, it is an effective way of regulating the structural distribution. Reducing the monomer pressure will evidently increase fractions A and D. The mechanical properties of the alloys, including impact strength and flexural modulus, can be regulated in a broad range with changes in polymerization conditions. These properties are highly dependent on the amount, distribution, and chain structure of fractions A and D. The impact strength is affected by both fraction A and fraction D in a complicated way, whereas the flexural modulus is mainly determined by the amount of fraction A. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2136–2143, 2006     

钛酸铝材料性能及合成工艺

着重介绍了钛酸铝（Al2TiO3）陶瓷的结构、性能和合成工艺，并对今后发展趋势提出了基本观点。     

不同反应器中氧化反应与水蒸气气化反应协同作用差异性

在?80mm×3000mm气流床和?40mm×200mm流化床中进行了O₂、H₂O、H₂O+O₂气氛下800℃胜利褐煤气化实验，同时在流化床中进行了O₂、H₂O、H₂O+O₂气氛下半焦原位气化实验和H₂O气氛下半焦完全气化实验。比较了2种反应器中氧化反应与水蒸气气化反应协同作用的大小（强弱）；结合实验条件利用缩核模型分别推导了2种反应器中协同作用影响下水蒸气气化反应速率方程；同时，从传质（扩散）速率、动力学、半焦-挥发分相互作用3方面探讨了2种反应器中协同作用存在显著差异的原因。结果发现，气流床中H₂O+O₂气氛下褐煤转化率明显大于H₂O和O₂单独气氛下褐煤转化率之和，其差值稳定在2.11%～4.01%，而在流化床中差值仅为0～0.75%，相对流化床，气流床中协同作用更明显。这是由于，在流化床中水蒸气向炭粒表面扩散的传质速率约为气流床的11%～25%，水蒸气气化过程受气膜扩散控制，炭粒表面水蒸气全部参与气化反应，炭粒表面无“多余”水分子，氧气开孔/扩孔作用提供的活性位“闲置”，而气流床中气化反应为速控步，炭粒表面有“富裕”水分子，可充分利用氧气开孔/扩孔作用提供的活性位，促进作用显著；挥发分-半焦相互作用不是流化床反应器中协同作用不显著的原因。     

A new route for the electrodeposition of platinum-nickel alloy nanoparticles on multi-walled carbon nanotubes

An electrochemical method was developed to deposit platinum (Pt) and nickel (Ni) nanoparticles on multi-walled carbon nanotubes (MWCNTs) through a three-step process. X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) show the alloy formation for Pt and Ni with a ratio of 1:1. The presence of Pt(0), Ni(0), Ni(OH)₂, NiOOH and slight NiO was deduced from XPS data. Electrocatalytic properties of the resulting PtNi/MWCNT electrode for methanol oxidation reaction were investigated. Compared with Pt/MWCNT, an appreciably improved resistance to CO poisoning was observed for the PtNi/MWCNT electrode, which was interpreted by a mechanism based on the bifunctional catalysis. The successful preparation of PtNi/MWCNT nanocomposites opens a new path for an efficient dispersion of the promising electrocatalysts in the direct methanol fuel cells.     

电成像测井资料裂缝识别技术及其应用

利用裂缝图像的颜色（或灰度）和产状特征,结合岩芯标定和常规测井资料,可以有效地识别裂缝,定量判断出裂缝位置、发育程度及裂缝性质,进而定量求取裂缝参数,为探索充填缝的纵横向变化规律奠定基础。     

一种改进的文档图像倾斜检测算法

在分析现有倾斜检测算法基础上,提出一种改进的文档图像倾斜检测算法。该算法首先对文档图像进行图像增强、去噪和二值化处理,然后提取边界线、计算每条边界线的角度,最后计算加权平均得到文档图像的倾斜角度。通过在计算每条边界线的角度过程中引入LMS算法。改进的算法提高了原算法的精确度、稳定性和适应性。实验表明,改进的方法有效可行。     

高陡边坡的监测与稳定性分析

从现场监测仪器获取的位移、应力方面的原始数据入手,绘制出位移、应力随时间变化的曲线图,并运用回归拟合分析方法,在综合分析开挖过程中各种影响因素以及锚固工具对边坡锚固效果的基础上,掌握了边坡的变形趋势及稳定状况。可为预测、预报及整治工程地质灾害等提供可靠的资料和科学的依据,为工程的安全进行提供理论保障。     

信息不对称下的建设项目组织界面管理

建设项目的各参与方隶属于不同的组织体系,界面双方（多方）就会存在极度的信息不对称。以业主和施工承包商为例,分析了二者之间的信息不对称所造成的影响。最后,通过对信息不对称的产生原因分析,从组织层面上提出了一些可能的解决措施,包括：设计合理的契约、应用新的承发包模式、建立统一编码的界面管理信息系统、合理设计组织内部各职能部门界面。     

论茅盾《蚀》三部曲中的时代女性形象

茅盾的"时代女性"人物系列是一个清晰而又复杂的群体,时代女性形象在他的小说中占有非常瞩目的地位,从而形成了一幅绚丽多姿的女性形象艺术画卷。分析茅盾《蚀》三部曲中"时代女性"形象之外在和内在的共同特征,透视作家创作时共同的心理机制,揭示其对茅盾小说创作的正面和负面影响。     

大学英语教学改革中教师激励机制的运用

教师是大学英语教学改革的主导,其能动性的发挥在很大程度上影响着改革的进程.从教师激励角度出发,依照波特一劳勒综合激励理论的观点,探讨了有效的激励措施,激发教师的工作积极性和热情,主动转变教学模式,提高教学质量,努力培养适应时代发展的高素质英语人才.