Compact images of spaces with a weaker metric topology

If X is a space that can be mapped onto a metric space by a one-to-one mapping, then X is said to have a weaker metric topology. In this paper, we give characterizations of sequence-covering compact images and sequentially-quotient compact images of spaces with a weaker metric topology. The main results are that (1) Y is a sequence-covering compact image of a space with a weaker metric topology if and only if Y has a sequence of point-finite cs-covers such that for each y ∈ Y. (2) Y is a sequentially-quotient compact image of a space with a weaker metric topology if and only if Y has a sequence of point-finite cs*-covers such that for each y ∈ Y. Supported by the NNSF(10471084) of China.     

Maximizing lifetime of a wireless sensor network via joint optimizing sink placement and sensor-to-sink routing

Wireless sensor networks typically contain hundreds of sensors. The sensors collect data and relay it to sinks through single hop or multiple hop paths. Sink deployment significantly influences the performance of a network. Since the energy capacity of each sensor is limited, optimizing sink deployment and sensor-to-sink routing is crucial. In this paper, this problem is modeled as a mixed integer optimization problem. Then, a novel layer-based diffusion particle swarm optimization method is proposed to solve this large-scaled optimization problem. In particular, two sensor-to-sink binding algorithms are combined as inner layer optimization to evaluate the fitness values of the solutions. Compared to existing methods that the sinks are selected from candidate positions, our method can achieve better performance since they can be placed freely within a geometrical plane. Several numerical examples are used to validate and demonstrate the performance of our method. The reported numerical results show that our method is superior to those existing. Furthermore, our method has good scalability which can be used to deploy a large-scaled sensor network.     

轴对称压差系统的自相似解

考察了二维压差系统的轴对称活塞均匀膨胀而产生的自相似流动.在轴对称和自相似假设下,该问题可以简化为一个自治的非线性常微分方程组的自由边值问题.通过对常微分方程组的积分曲线性质的详细分析,建立该自由边值问题正光滑解的整体存在性.     

The influence of organo-modified sepiolite on the flame-retardant and thermal properties of intumescent flame-retardant polylactide composites

Polylactide (PLA) composites based on intumescent flame-retardant (IFR) and organo-modified sepiolite (OSEP) were prepared via direct melt compounding. The uniform dispersion of OSEP in the PLA matrix was observed by TEM, but some agglomerates still existed at the high loading. Tensile results showed that high loading of the conventional IFR led to a reduction in tensile strength of PLA composites; however, replacing a portion of the IFR with modified sepiolite in the PLA matrix improved this result. The thermal degradation temperature of the PLA/IFR/OSEP composites determined by thermogravimetric analysis was lower than that of neat PLA, as a consequence of the catalyzed carbonization induced by the addition of IFR and OSEP. The formulation with 13 mass% IFR and 2 mass% OSEP exhibited the highest LOI value of 32 vol% and also reached UL-94 V-0 rating in the vertical burning tests. Furthermore, the co-addition of IFR and OSEP gave rise to a significant reduction in peak heat release rate (PHRR) and total heat release (THR) of PLA composites during combustion, particularly in the case of PLA/IFR13/OSEP2 (82% reduction in PHRR and 69% in THR). The excellent fire resistance of PLA/IFR13/OSEP2 could be attributed to that IFR catalyzed carbonization of PLA to form the char, while OSEP resulted in further stabilization in the charred layers.     

Investigation of thermal decomposition of polymer nanocomposites with different char residues

The pyrolysis process of polypropylene (PP), PP‐based nanoclay composites, acrylonitrile‐butadiene‐styrene (ABS), and ABS/metal hydroxide nanorods (MHR)/grapheme nanosheets (GNS) composites in a cone calorimeter test was simulated with a recently developed numerical codes, the Federal Aviation Administration ThermaKin. First, the heat release rate (HRR) and the surface temperature as a function of time were compared with experiment data. With reasonable input parameters, the pyrolysis behaviors were predicted reasonably. Subsequently, the influence of the properties of char residue on the HRR was discussed. The char residue of PP/nanoclay acted as a heat transfer barrier, while the char layer of ABS/MHR/GNS acted as a mass transfer barrier. Finally, the sensitivity of the residue characteristic parameters to the model output was discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Molecular simulations of host-guest interactions between zeolite framework STW and its organic structure-directing agents

Zeolites have been widely applied in many chemical processes owing to their featured microporous framework structures. Organic structure-directing agents (OSDAs) play an important role during of the formation of zeolite frameworks via non-bonding host-guest interactions. Understanding these interactions is crucial to the design of OSDAs and the synthesis of target zeolites. Here, we report a molecular simulation study in the host-guest interactions between zeolite framework STW and 21 alkylated imidazolium and pyrazolium cations that have been used as the OSDAs for the synthesis of STW-type zeolites. We find that OSDAs that have successfully directed the formation of STW exhibit stronger host-guest interactions than unsuccessful ones. Furthermore, we find all successful OSDAs possess relatively more negative atomic charges on nitrogen atoms and smaller dipole moments. According to this finding, we have designed seven new alkylated imidazolium and pyrazolium cations that may be suitable for zeolite STW, and verified their structure-directing capability by molecular simulation calculations.     

ITER纵场的电磁分析与电源系统的概念设计

进行了ITER纵场磁体电源系统的概念设计.首先,对ITER主机基于循环对称算法,借助ANSYS软件进行了电磁的分析,然后根据电磁分析得到的结果,设计了ITER纵场磁体电源的拓扑结构,分析了整流器的输出电压波形;其次,基于电磁分析的结果,设计了ITER纵场磁体失超保护系统,并计算了磁体失超保护电路中的关键部件-电容和电阻...     

可调谐激光吸收光谱法与气相色谱法监测甲烷的对比研究

甲烷是一种重要的温室气体,它对大气中温室效应的贡献仅次于二氧化碳.针对环境空气中甲烷的测定,从测量原理、测量过程和测量装置等方面比较了可调谐二极管激光吸收光谱和气相色谱法两种测量方法.结果表明用上述两种方法测得的甲烷的日变化趋势具有良好的一致性.相比较而言,后者造价更低,并且更方便.     

Effect of annealing temperature on photocatalytic activity of ZnO thin films prepared by sol-gel method

Zinc oxide thin films are deposited on Si and quartz substrates using the sol-gel method. The thin films, annealed at 400, 600 and 800 °C respectively, are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), ultraviolet-visible spectrophotometer (UV-Vis), fluorescence spectrometer (FL) and the photocatalytic activity is tested by the decomposition of methyl orange dye under UV illumination. The results show that the mean grain size, surface-to-volume ratio, rms roughness and degradation efficiency of the thin films increases with increasing annealing temperature. In particular, ZnO thin film annealed at 800 °C exhibits the highest photocatalytic activity, degrading methyl orange by almost 88% in 180 min. Photocatalytic reaction mechanism of the ZnO thin films is discussed in detail, and the oxygen defects are proposed to be the active sites of the ZnO photocatalyst.     

高分子基础实验的优化与改革

为适应高分子材料与工程专业实验分层次教学改革的要求,结合我院高分子材料与工程专业的具体实际,在教学内容设计中融入科学、节约、环保的理念,对高分子基础实验体系、内容、组织与运行、教学方法与手段进行了整体优化和改革。使实验成本得到降低,污染物明显减少,实验教学效果得到显著提高,实现了高分子专业基础实验教学效益的最大化。