聚苯乙烯的催化裂解研究

由于塑料性质稳定,难以自然降解,其废弃物不仅严重污染环境,更造成了资源浪费.因此,废旧塑料的再资源化对环境保护和可持续发展有着重要意义.废塑料再资源化回收技术是指将废塑料热裂解或催化裂解、回收燃料油和化工原料的技术~([1,2]).     

Molecular associations in acacia gums

The tendency of polysaccharides to associate in aqueous solution has long been recognised. Molecular associations can profoundly affect their performance in a given application due to its influence on the molecular weight, shape and size. This will ultimately determine how the molecules will interact with each other, with other molecules and with water. There are several factors, such as hydrogen bonding, hydrophobic association, ion mediated association, electrostatic interaction, concentration dependence and the presence of proteinaceous components, which affect this behaviour. Our objective is to highlight the role of the proteinaceous component, present in acacia gum, to promote associations when the gum is subjected to various processing treatments such as maturation, spray drying and irradiation. The results demonstrate the ability of the proteinaceous component to promote hydrophobic associations which influence the size and proportion of the arabinogalactan high molecular weight component (AGP). Heat treatment in solid state (maturation) increases the hydrophobic character of the gum and hence its emulsification performance. Spray drying also involves aggregation through hydrophobic association but changes the surface properties of peptide moieties to become more hydrophilic compared to the association promoted by the maturation treatment in the solid state. Irradiation induced cross-linking, in the presence of unsaturated gas, was used to introduce C–C bonds into the carbohydrate moiety and thus confirms the hydrophobic association prompted by the heat used in the maturation and spray drying. This association can be reversed by treatments, such as filtration or high pressure homogenisation. The results reported here reconcile the contradiction about structure of gum arabic proposed by the wattle-blossom and twisted hairy rope models and shows that the AGP fraction is basically an aggregated fraction made up of AG units stabilized by low molecular weight highly proteinaceous components.

LMI conditions for global robust stability of delayed neural networks with discontinuous neuron activations

Without assuming that the neuron activations are bounded, some delay-independent criteria for interval delayed neural networks with discontinuous neuron activations are derived to guarantee global robust stability by using the generalized Lyapunov method and linear matrix inequality (LMI) technique. The obtained results improve and extend those given in earlier literature, and two numerical examples are also given to show the effectiveness of our results.     

用于燃料电池的聚乙烯醇/纤维素/聚乙二醇碱性阴离子交换复合膜的制备及性能

通过对聚乙烯醇(PVA)/季铵化羟乙基乙氧基纤维素(QHECE)共混膜进行聚乙二醇(PEG)聚塑化改性, 采用物理-化学交联联用法制备了PVA/QHECE/PEG碱性阴离子交换复合膜. 通过交流(AC)阻抗、 傅里叶变换红外光谱(FTIR)、 扫描电子显微镜(SEM)、 热重分析(TGA)、 气相色谱(GC)和拉伸实验等手段考察了不同PEG添加量对膜的离子电导率、 分子结构、 微观形貌、 热稳定性、 力学强度、 甲醇渗透率和耐碱稳定性等性能. 结果表明, PEG的加入(除最小比例外)提高了膜的离子电导率和力学强度并使其柔韧性增大. 同时, 膜的热稳定性比未添加PEG时提高了40℃. 将PVA/QHECE/PEG膜在80℃, 6 mol/L KOH浓碱溶液中浸渍处理264 h, 膜的电导率从1.06×10^-3 S/cm提高到3.88×10^-3 S/cm, 而膜的外观和力学强度及含水率未发生明显变化, 表明该膜具有很好的耐碱化学稳定性. 此外, 以3 mol/L甲醇溶液为测试目标, 膜的甲醇渗透率<10^-7 cm²/s, 仅为商业用Nafion^®膜的1/20~1/40.     

高强度聚乙烯醇水凝胶微球的制备

以三氯甲烷/丙酮为凝固液, 用高压静电技术制备了高强度、物理交联的聚乙烯醇(PVA)水凝胶微球. 研究了凝固液组成、PVA溶液浓度、温度和湿度、电场强度、进样速度及微球冷冻次数等对PVA微球的形貌、粒径和强度的影响. 结果表明, 采用常压水蒸气控制PVA溶液温度与湿度的高压静电技术, 可克服高浓度PVA溶液在强电场下出现微丝现象, 形成的水凝胶微球具有强度高、粒径在一定范围内可控的特点.     

Fabrication of Covalently Linked PAH/PVS Layer-by-layer Assembled Multilayers via a Post-photochemical Cross-linking Strategy

A post-photochemical cross-linking strategy was successfully demonstrated to enhance the stability of polyelectrolyte poly(allylamine hydrochloride)(PAH)/poly(vinylsulfonic acid sodium salt)(PVS) multilayers. Conventional polyelectrolyte multilayers of PAH/PVS are usually fabricated through electrostatic layer-by-layer(LbL) assembly, resulting in poor stability, especially in basic solutions, which leads to the urgent demand for converting weak electrostatic interactions into covalent bonds to enhance the stability of the multilayers. This stability problem has been ultimately addressed by post-infiltrating a photosensitive cross-linking agent, 4,4'-diazostilbene-2,2'- disulfonic acid disodium salt(DAS), into the LbL assembled films to initiate the photochemical reaction to cross-link the multilayers. The obviously improved stability of the photo-cross-linked multilayers was demonstrated through experiments with basic solution treatments. Compared to the complete decomposition of uncross-linked multilayers in basic solution, over 74.4% of the covalently cross-linked multilayers were retained under the same conditions, even after a longer duration of basic solution treatment.     

Synchronization of time varying delayed complex networks via impulsive control

In this paper, we investigate the problem of synchronization for the time varying delayed complex dynamical networks via impulsive control method, several sufficient synchronization conditions are given, and we consider the impulsive control matrices are time varying delayed matrices. Furthermore, we found impulsive control does not always play an active role in synchronization although impulsive control strategy is cheaper and simpler than other control strategy. Finally, numerical simulations are also given to demonstrate the effectiveness of the proposed schemes.     

Synchronized stability in a reaction–diffusion neural network model

The reaction–diffusion neural network consisting of a pair of identical tri-neuron loops is considered. We present detailed discussions about the synchronized stability and Hopf bifurcation, deducing the non-trivial role that delay plays in different locations. The corresponding numerical simulations are used to illustrate the effectiveness of the obtained results. In addition, the numerical results about the effects of diffusion reveal that diffusion may speed up the tendency to synchronization and induce the synchronized equilibrium point to be stable. Furthermore, if the parameters are located in appropriate regions, multiple unstability and bistability or unstability and bistability may coexist.     

Delay effect on schedule in shuttle bus transportation controlled by capacity

We study a bus schedule in a shuttle bus transportation system controlled by capacity. The motion of shuttle buses depends on the inflow rate of passengers, the number of buses, and the delayed increase of buses. The bus schedule is closely related to the dynamic motion of buses. The delayed increase of buses has an important effect on the arrival of buses. We present the delayed piecewise map model for the dynamics of shuttle buses with the delayed increase. The motion of buses changes from a stable state to an unstable state and vice versa with increasing the inflow rate. The arrival of shuttle buses oscillates with various periods in the unstable state. The dynamic transitions change highly with the delayed increase of buses. We clarify the effect of the delayed increase on the bus schedule.     

A risk analysis based on a two-stage delayed diagnosis regression model with application to chronic disease progression

This paper presents a two-stage regression model for quantifying different stages of a disease progression with delayed diagnosis time and for identifying the risk factors associated with each stage. Conventional chronic disease progression studies reported replied on the assumption that the time of the confirmation of a disease state by diagnosis is the start time of this disease state. Clearly this will lead to biased estimates of progression since the disease state should have already occurred before the diagnosis, but the true occurrence time is unknown. This later confirmation is called the delayed diagnosis in this paper and a delay-time modelling procedure is developed for the identification of the unknown stages of progression. A hazard-based regression model is also proposed for a further risk analysis. We apply the developed methods to hepatitis C data and the analysis shows that considering the delayed diagnosis significantly improved the model fit in comparison with the conventional model. We also find that the risk factors associated with each stage are more significant, particularly in the second stage of progression, than those based on the conventional model. We conclude that such delayed phenomena in diagnosis should be taken into account when modelling the chronic disease progression process and conducting related risk analysis.