一类三次曲线的形状分析

基于包络理论与拓扑映射的方法,对一类带有形状参数的三次曲线进行了形状分析,得出了曲线上含有奇点、拐点和曲线为局部凸或全局凸的充分必要条件,这些条件完全由控制多边形和形状参数所决定。进一步讨论了形状参数对形状分布图的影响及其对曲线形状的调节能力。     

Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.     

Silicate-based polymer-nanocomposite membranes for polymer electrolyte membrane fuel cells

Proton-exchange membrane fuel cells have emerged as a promising emission free technology to fulfill the existing power requirements of the 21st century. Nafion^® is the most widely accepted and commercialized membrane to date and possesses excellent electrochemical properties below 80 °C, under highly humidified conditions. However, a decrease in the proton conductivity of Nafion^® above 80 °C and lower humidity along with high membrane cost has prompted the development of new membranes and techniques. Addition of inorganic fillers, especially silicate-based nanomaterials, to the polymer membrane was utilized to partially overcome the aforementioned limitations. This is because of the lower cost, easy availability, high hydrophilicity and higher thermal stability of the inorganic silicates. Addition of silicates to the polymer membrane has also improved the mechanical, thermal and barrier properties, along with water uptake of the composite membranes, resulting in superior performance at higher temperature compared to that of the virgin membrane. However, the degrees of dispersion and interaction between the organic polymer and inorganic silicates play vital roles in improving the key properties of the membranes. Hence, different techniques and solvent media were used to improve the degrees of nanofiller dispersion and the physico-chemical properties of the membranes. This review focuses mainly on the techniques of silicate-based nanocomposite fabrication and the resulting impact on the membrane properties.     

Synthesis of poly(ε‐caprolactone)/clay nanocomposites using polyhedral oligomeric silsesquioxane surfactants as organic modifier and initiator

Poly(ε‐caprolactone)/clay nanocomposites were synthesized by in situ ring‐opening polymerization of ε‐caprolactone in the presence of montmorillonite modified by hydroxyl functionalized, quaternized polyhedral oligomeric silsesquioxane (POSS) surfactants. The octa(3‐chloropropyl) polyhedral oligomeric silsesquioxane was prepared by hydrolytic condensation of 3‐chloropropyltrimethoxysilane, which was subsequently quaternized with 2‐dimethylaminoethanol. Montmorillonite was modified with the quaternized surfactants by cation exchange reaction. Bulk polymerization of ε‐caprolactone was conducted at 110°C using stannous octoate as an initiator/catalyst. Nanocomposites were analyzed by X‐ray diffraction, transmission electron microscopy, thermo gravimetric analysis, and differential scanning calorimetry. Hydroxyl functionalized POSS was employed as a surface modifier for clay which gives stable clay separation for its 3‐D structure and also facilitates the miscibility of polymer with clay in the nanocomposites due to the star architecture. An improvement in the thermal stability of PCL was observed even at 1 wt % of clay loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of phosphorus‐containing polyhedral oligomeric silsesquioxanes via hydrolytic condensation of a modified silane

A simple route to synthesize a new type of phosphorus‐containing polyhedral oligomeric silsesquioxanes (DOPO–POSS) in high yield, by the hydrolytic condensation of a modified silane, is reported. The starting material was a phosphorus‐containing triethoxy silane (DOPO–VTES), which was synthesized by addition reaction between 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and vinyl triethoxy silane (VTES). This product was subjected to hydrolytic condensation using an HCl catalyst in methanol. The new types of phosphorus‐containing POSS were obtained and characterized using ¹H, ¹³C, ²⁹Si‐NMR, MALDI‐TOF MS, XRD, DSC, and FTIR. All of these results suggested that the DOPO–POSS were amorphous mixtures of T₈, T₉(OH), and TGA curve of DOPO–POSS shows that the cage‐like compound has high thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

POSS改性聚合物复合材料力学性能研究进展

介绍了笼型倍半硅氧烷（POSS）的结构、分类以及POSS改性聚合物力学性能的特点和机理,综述了POSS改性聚合物（包括聚烯烃、环氧树脂、聚丙烯酸酯、聚氨酯等）复合材料力学性能的研究进展,并展望了POSS改性聚合物复合材料的发展前景。     

一个三角形网格上等值线图的绘制算法

本文提出一个三角形上曲面插值的新算法，各三角形上的曲面片拼合起来得到的整体曲面是Ｃ连续的。     

铝合金热轧带材“中凸度超标＋中间波浪”板形缺陷的原因分析与改进措施

试验研究了单机架双卷取四辊可逆热轧机生产5182铝合金时,产生＂中凸度超标＋中间波浪＂缺陷的原因。结果表明：工作辊原始凸度太小、道次压下量不合理、乳液喷淋压力太小是导致产生该缺陷的主要原因。通过增大工作辊原始凸度、优化道次压下量、提高乳液喷淋压力可以消除此缺陷。     

氯甲基笼型倍半硅氧烷改性双酚A环氧树脂性能

引言双酚A环氧树脂是目前应用最广、用量最大的环氧树脂,具有良好的化学稳定性、电气绝缘性被广泛应用于涂料和电子电器等领域;然而,双酚A环氧树脂存在耐热性较差和固化后脆性大等缺点,因此如何提高环氧树脂的耐热性及力学性能等是目前改性研究的热点之一[1-5]。而笼型多面体倍半硅氧烷(POSS)是一类具有(RSiO1.5)n通式的纳米材料,因其特殊的分子组成结构使得POSS具     

对萃取槽上平型胶带传动中出现的问题探讨

针对具有多从动轮的平型带传动在萃取槽试车过程中出现的问题,阐明了调试传动带的操作经验,指出了传动设计的不当参数（带宽b、轮缘中凸度１δ１）,以及修改带轮轮缘中凸度的根据。