In situ synthesis of star copolymers consisting of a polyhedral oligomeric silsesquioxane core and poly(2,5-benzimidazole) arms for high-temperature proton exchange membrane fuel cells

Star copolymers with good film-forming and mechanical properties were in situ synthesized for fabricating proton exchange membranes. The monomers of 3,4-diaminobenzoic acid were first grafted onto glycidyl-polyhedral oligomeric silsesquioxane (G-POSS) cores and then propagated to the poly(2,5-benzimidazole) (ABPBI) chains. The introduction of the star copolymer improves the movement of the ABPBI polymer chains, resulting in a lower internal viscosity and larger free volume that favor increased membrane flatness and absorbilities of water and phosphoric acid molecules, respectively. It was found that the star copolymers with 1.0 wt% of incorporated POSS (ABPBI-1.0POSS) had the best balance of the acid retentivity and film-forming property as well as mechanical properties that are desirable for proton exchange membranes without PA loss operating at high temperatures. The enhanced cell performance characteristics obtained using the ABPBI-1.0POSS-based membranes indicate that star copolymers are promising materials for use in high-temperature proton exchange membrane fuel cells.     

Local cubic and bicubic C surface interpolation with linearly varying boundary normal

An algorithm for the interpolation of a ‘mesh of points’ in 3-space by a C¹ surface is developed. At each point, the surface normal can be specified. The surface is constructed locally and consists of cubic and bicubic patches to match the underlying mesh facets. The surface construction is special in that it generates a piecewise parametric surface such that the normal along patch boundaries varies linearly.     

High-Performance Low-k Poly(dicyclopentadiene) Nanocomposites as Achieved via Reactive Blending with Norbornene-Functionalized Larger POSS

Low dielectric constant (k) polymers with excellent comprehensive properties are useful materials in the microelectronics industry as matrix resins or encapsulation layers. With the inherent low polarization, high reactivity, good processability, and low cost, poly(dicyclopentadiene) (PDCPD) has received considerable attention as low-k materials. However, its practical application is limited by the relatively high thermal expansion and k value. Herein, three norbornene-functionalized polyhedral oligomeric silsesquioxanes (POSSs) with T₈, T₁₀, and T₁₂ polyhedral cores are synthesized and employed for enhancing the dielectric and comprehensive properties of PDCPD via reactive blending. The results show that these POSSs have good compatibility with PDCPD matrix and nano-dispersed POSSs particles could be obtained. As a result, the materials’ properties can be largely enhanced by varying the POSS content and POSS size. Especially, PT₁₂N₁₂-40 (40 wt% of T₁₂N₁₂) shows the lowest k value (2.1) and coefficient of thermal expansion (63.4 ppm°C⁻¹), highest glass transition temperature (202.5 °C), yield strength (78.0 MPa), and elastic modulus (2.36 GPa), along with excellent hydrophobicity. This study highlights a useful strategy to fabricate high-performance low-k polymer nanocomposites by using larger POSS and reactive blending, which provides useful materials for the future microelectronic industry and high frequency communication.     

Non‐convex model for sensor network localization based on connectivity

In this paper, a new model utilizing all the information derived from connectivity‐based sensor network localization is introduced. The connectivity information between any pair of nodes is modeled as convex and non‐convex constraints. The localization problem is solved by searching for a solution that would satisfy all the constraints established in the problem. A two‐objective evolutionary algorithm called Pareto Archived Evolution Strategy (PAES) is used to solve the localization problem. The solution can reach the most suitable configuration of the unknown nodes because the information on both convex and non‐convex constraints related to connectivity has been utilized. From simulation results, a relationship between the communication range and accuracy is obtained. Furthermore, a two‐level range connectivity‐based sensor network localization method is proposed to enrich the connectivity information. The two‐level range/indication of connectivity between each pair of nodes would indicate three levels of connectivity: strong, weak, or nil. A comparison on accuracy between the one‐level and two‐level ranges of connectivity is carried out by simulation using six different topological networks all containing 100 nodes. Simulation results have shown that better solution can be obtained by using two‐level range connectivity compared with the usual one‐level range connectivity‐based localization. Copyright © 2012 John Wiley & Sons, Ltd.     

Modifications of carbon for polymer composites and nanocomposites

The various forms of carbon used in composite preparation include mainly carbon-black, carbon nanotubes and nanofibers, graphite and fullerenes. This review presents a detailed literature survey on the various modifications of the carbon nanostructures for nanocomposite preparation focusing upon the works published in the last decade. The modifications of each form of carbon are considered, with a compilation of structure-property relationships of carbon-based polymer nanocomposites. Modifications in both bulk and surface modifications have been reviewed, with comparison of their mechanical, thermal, electrical and barrier properties. A synopsis of the applications of these advanced materials is presented, pointing out gaps to motivate potential research in this field.     

凸性数据的样条修匀及其应用

借助于样条技术 ,给出了利用先验信息对初始估计进行修正的新方法 .这些先验信息可以包含数据的凸性以及增减性 .同时讨论了这种数据处理方法在生存分析尤其是精算等领域中的应用 .     

Resource allocation in OFDMA networks based on interior point methods

This paper studies a joint optimization problem of sub‐carrier assignment and power allocation in orthogonal frequency division multiple access (OFDMA) wireless networks. A major challenge in solving the optimization problem is non‐convexity caused by the combinatorial nature of sub‐carrier assignment problem and/or non‐convex objective functions. To address the combinatorial complexity, we formulate the resource allocation problem as an optimization problem with continuous variables. We propose a novel approach based on a penalty function method and an interior point method (PM/IPM) to solve the problem. In specific, using a two‐step implementation, the penalty method is applied first to convert the non‐convex feasible region to a convex one. Then, the interior point method is deployed to solve the problem which is non‐convex only in the objective function. To evaluate the performance of PM/IPM, we apply a genetic algorithm (GA) that achieves near optimal solutions of the problem by iterative searching. Copyright © 2009 John Wiley & Sons, Ltd.     

板形控制技术及应用

概述了板形控制原理.根据有载辊缝形状方程,分析了影响板形、板凸度的诸项因素,综合介绍了板形控制技术及发展趋势.     

张力平面参数曲线的几何性态

给出了一种分析平面参数曲线奇拐点和凸性的方法。这种方法在几何上直观，对于四阶代数曲线和非代数曲线的几何性态分析都是有效的。将它应用于基于指数函数的张力平面参数曲线，以及基于双曲Ｂ－样条函数的张力Ｂ－样条平面参数曲线的研究，解决了这些曲线的奇拐点和凸性等几何性态问题。     

广义η-偏差函数的一些性质

将η-偏差函数ηK(t)和线性偏差函数λ(K)的几个结果推广到了广义η-偏差函数ηK(a,t)和广义线性偏差函数λ(a,K),并得到了它们满足的几个不等式.