Preparation of flexible polyhedral particles via concentrated emulsion templating polymerization

This paper presents recent efforts on the preparation of flexible polyhedral particles via concentrated emulsion templating polymerization in which the hydrophilic monomer (acrylamide) and hydrophobic monomer (butyl acrylate) are polymerized simultaneously in the continuous and dispersed phase, respectively. Such templating polymerization has been enhanced in our systems owing to the introduction of acrylamide monomer and their higher polymerization rate in continuous phase as compared with butyl acrylate in dispersed phase. Diffusion between the different phases was also inhibited. Furthermore, the stability of the concentrated emulsion and the molecular weight of the produced poly(butyl acrylate) were found to be significantly affected by the amount of redox initiator. The morphology of the particles could be controlled by varying the volume fraction of the dispersed phase and the polyhedral particles were achieved at higher volume fraction. Copyright © 2005 Society of Chemical Industry     

Generalized Global Monotonicity of Generalized Derivatives

The gradient and the several kinds of its generalizations provide a very efficient tool in characterizing important properties of functions. Convexity and generalized convexity, which are central properties in many branches of Operational Research, can also be characterized by special properties (monotonicity and generalized monotonicity) of the gradient map in the smooth case (Karamardian and Schiable, 1990. JOTA , Vol. 66, pp. 37–46) and by that of the Dini derivatives in the nonsmooth case (Komlosi, 1991. Working paper, Janus Pannonius University; 1992a. Nonsmooth Optimization: Methods and Applications; Proceedings of the IVth International Workshop on Generalized Conuexity , in press; Luc, 1991. Subgradients of quasiconvex functions). It is shown in this paper how quasiconvexity, pseudoconvexity and (strict) pseudoconvexity of lower semicontinuous functions can be characterized via quasimonotonicity and (strict) pseudomcnotonicity of different types of generalized derivatives, including the Dini, Dini-Hadamard, Clarke and Rockafellar derivatives.     

Zirconium-Embedded Polyhedral Oligomeric Silsesquioxane Containing Phosphaphenanthrene-Substituent Group Used as Flame Retardants for Epoxy Resin Composites

A zirconium hybrid polyhedral oligomeric silsesquioxane derivative (Zr–POSS–bisDOPO) is synthesized by the corner-capping and Kabachnik–Fields reactions. It is characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR), and then used as a flame retardant in diglycidyl ether of bisphenol A (DGEBA) to endow epoxy resin (EP) with flame retardancy. The flame retardancy, thermal stability, and mechanical properties of the cured EP/Zr–POSS–bisDOPO composites are investigated. The results show that when Zr–POSS–bisDOPO is added by 5–7 wt%, the EP/Zr–POSS–bisDOPO composites pass the UL-94 V-0 rating test. In addition, they have a better flame-retardant effect than pure EP. The combination of Zr atom embedded in the Si O cubic cage and the two phosphaphenanthrene substituent groups in one corner of cubic cage is expected to realize the Zr/Si/P ternary intramolecular hybrid synergistic effect and achieve the possibility of dispersing metal–POSS cages at a sub-micrometer-scale level into polymer matrix. It also proves that Zr–POSS–bisDOPO produces phosphorus-containing free radicals and terminates the chain reactions in gas phase. Meanwhile the Si O Si and Zr O units are retained in the solid phase, which promote the char formation and enhance the flame retardancy. This kind of Zr-doped POSS will be helpful for developing the new metal–POSS hybrid flame-retardant and polymer composites.     

Preparation and thermal property of hybrid nanocomposites by free radical copolymerization of styrene with octavinyl polyhedral oligomeric silsesquioxane

The poly(styrene‐co‐octavinyl‐polyhedral oligomeric silsesquioxane) (PS–POSS) organic–inorganic hybrid nanocomposites containing various percent of POSS were prepared via one‐step free radical polymerization and characterized by FTIR, high‐resolution ¹H NMR, ²⁹Si NMR, GPC, DSC, and TGA technologies. The POSS contents in these nanocomposites were determined using FTIR calibration curve. The result shows that the POSS contents in nanocomposites can be tailored by varying the POSS feed ratios. On the basis of the POSS contents in the nanocomposites and the ¹H NMR spectra, the number of reacted vinyl groups of each octavinyl‐POSS macromonomer were calculated to be 6–8. DSC and TGA measurements indicate that the incorporation of POSS into PS homopolymer can apparently improve the thermal properties of the polymeric materials. The dramatic T_g and T_dec increases are mainly due to the formation of star and low cross‐linking structure of the nanocomposites, where POSS cores behave as the joint points and hinder the motion and degradation of the polymeric chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Bayesian estimation of Dirichlet mixture model with variational inference

In statistical modeling, parameter estimation is an essential and challengeable task. Estimation of the parameters in the Dirichlet mixture model (DMM) is analytically intractable, due to the integral expressions of the gamma function and its corresponding derivatives. We introduce a Bayesian estimation strategy to estimate the posterior distribution of the parameters in DMM. By assuming the gamma distribution as the prior to each parameter, we approximate both the prior and the posterior distribution of the parameters with a product of several mutually independent gamma distributions. The extended factorized approximation method is applied to introduce a single lower-bound to the variational objective function and an analytically tractable estimation solution is derived. Moreover, there is only one function that is maximized during iterations and, therefore, the convergence of the proposed algorithm is theoretically guaranteed. With synthesized data, the proposed method shows the advantages over the EM-based method and the previously proposed Bayesian estimation method. With two important multimedia signal processing applications, the good performance of the proposed Bayesian estimation method is demonstrated.     

Bezier三角曲面凸性的证明

Bezier曲面造型是计算机图形学的重要研究方向,在实际工作中有着非常广泛的应用.讨论了二次及三次Bezier三角曲面凸性的充分必要条件,这些条件对于控制曲面造型中的保凸性有重要意义.     

复合材料POSS/TX-10/Bent的制备及其吸附性能

以多面齐聚倍半硅氧烷(POSS)、TX-10型非离子表面活性剂为改性剂对膨润土(Bent)进行复合改性制备了复合材料(POSS/TX-10/Bent),并利用亚甲基蓝研究了其吸附性能。采用XRD、XPS、EA、FTIR、SEM对POSS/TX-10/Bent进行了组成与结构表征。结果表明,POSS和TX-10型非离子表面活性剂都成功插入到膨润土层间,使得复合材料层间距增大,疏水性增强。吸附实验表明,在30℃、pH为6.52(原始值)的条件下,复合材料投加量5 g/L、吸附180 min时效果最佳。在同等吸附条件下,复合改性膨润土对亚甲基蓝的吸附能力远大于未改性的膨润土。吸附过程更符合准二级动力学模型,平衡吸附数据与Langmuir等温吸附曲线吻合较好,吸附是一个自发的吸热过程,POSS/TX-10/Bent对亚甲基蓝的理论最大吸附量为253.81 mg/g。     

On the Range of the Common Cycle Time in a Road Network

In a coordinated road network, the optimal common cycle time is determined by evaluating the performance of the network in the given range of cycles. Normally, this range is determined by users’ experience. And a large range of common cycle time, e.g. \[0,0\] is chosen, which requires long computation time. This study considers that the optimal common cycle time ranges between the minimal and maximal value of intersections’ individual optimal cycle time. It is proved mathematically from the convexity condition, that the delay of the network and each individual intersection are convex functions of the cycle time according to Webster delay model. Finally, 2 000 random cases for the network composed of two intersections and of eight intersections are created to underline the proposed conclusions. The results of all cases confirm the validity, and show up to 90% improvement in computation time to compare with experience range. The signal optimization tool, Synchro, is also used to validate the conclusion by 50 random cases. The results confirm reliability further.     

面向多面体模型的非规则程序SIMD投机优化技术

多面体模型具有规范化、健壮性、灵活性等特点,被认为是最有前途的编译优化技术之一,SIMD优化是重要应用领域之一。由于静态编译技术的限制,大量非规则循环无法建立多面体模型,例如复杂依赖关系,导致无法利用该模型实现SIMD循环优化与代码生成。文章通过分析、利用SIMD优化所需的程序运行剖面信息,将静态编译未知情况转化为已知情况,为多面体模型建立创造条件。SPEC2000和PolyBench的测试结果显示,通过本文提出的方法,可将适用多面体模型的非规则循环个数提高2．3倍,经过SIMD优化后,平均加速比提高了1．53倍。