聚吡咯/多壁碳纳米管及其聚氨酯导电复合材料的制备和性能

以羧基化多壁碳纳米管(MWCNTs)做模版剂,采用化学氧化法将吡咯(Py)在羧基化MWCNTs表面聚合制备PPy/MWCNTs导电材料,将其添加到溶剂型聚氨酯(PU)溶液中制备了PPy/MWCNTs/PU导电复合材料,研究了Py用量对PPy/MWCNTs及其PU复合材料性能的影响.研究表明,随Py用量的增加,PPy/MWCNTs的长度不变,管径增大,sp~2和sp~3杂化C含量先提高后减少,N的掺杂梯度降低,PPy/MWCNTs的导电率高于羧基化MWCNTs和PPy.当Py用量为羧基化MWCNTs的20%时,其导电率最大.PPy/MWCNTs中N元素的掺杂程度及其管径变化是引起PPy/MWCNTs/PU复合材料的性能不同的主要原因.增加Py用量,MWCNTs中亲水的羧基因对PPy掺杂而消耗,相同导电材料用量时纳米导电粒子数目相对减少,PPy/MWCNTs/PU复合材料的耐水性能提高,定向应力、储能模量和玻璃化温度降低,导电率先增加后减小.当Py用量为羧基化MWCNTs的15%时,导电率最大.     

磷钼酸作为低温碳燃料电池的碳间接电氧化介质

以磷钼酸作为低温下碳间接电氧化的介质构建新型碳燃料电池。通过线性电位扫描和计时电流法研究不同碳材料、不同反应条件、不同反应时间、不同磷钼酸浓度对碳间接电氧化性能的影响。采用循环伏安法研究碳在磷钼酸介质中的间接电氧化机理。研究结果表明,椰壳活性炭的间接电氧化活性要明显高于煤和煤质活性炭。以磷钼酸为介质时,采用光照与升温80oC避光的条件均可以提高碳间接电氧化性能,且提高程度接近。由循环伏安测试分析出磷钼酸中+6价Mo可将碳氧化,且被还原成+5价Mo,随后又在阳极上重新被电氧化回+6价Mo,通过该过程将从碳材料上获得的电子转移到阳极上,从而实现碳在低温条件下的间接电氧化过程。并且通过对光照条件的分析,证实光对磷钼酸催化碳电氧化反应有两方面的促进作用:一方面光的热效应使反应温度升高,从而提高反应速率;另一方面磷钼酸利用其特有结构吸收光能,提高磷钼酸与碳的反应速率,且后者促进作用更明显。以VO2+/VO2+为阴极构建的碳燃料电池全电池室温下功率是0.087m W?cm-2,验证了碳燃料电池在常温条件下运行的可行性。     

橡胶在动态载荷下的能量损耗分析

以交联密度不同的同类轮胎胎面胶A1和A2为研究对象,通过动态拉伸实验得到储能模量及损耗模量随频率变化的曲线.建立了黏弹性广义Maxwell模型来定量分析不同温度的橡胶在不同频率的动态载荷下的能量损耗.采用非线性规划的方法分别在低频(10~25 Hz)及高频(25~60 Hz)下拟合模量-频率曲线,得到黏弹性广义Maxwell模型的参数值.采用有限元软件Abaqus模拟胎面胶动态拉伸过程并计算胎面胶的损耗角正切,得到不同温度下胎面胶的损耗角正切随激振频率的变化规律,通过和实验结果的比较证明文中所述黏弹性广义Maxwell模型及其参数获取方法可准确应用于胎面胶的动态拉伸性能分析.预测了在不同温度及频率下每一循环载荷周期中胎面胶的应力-应变迟滞回线以及单位体积胶料的能量损耗,阐释了不同温度下的胎面胶的能量损耗随频率的变化规律,同时结合2种胎面胶的交联密度测试数据分析了胶料的构效关系.     

氮掺杂纳米管包覆金属钴催化苯甲醇和苯胺一步N-烷基化反应

通过直接热解三聚氰胺、硝酸钴和葡萄糖混合物制备氮掺杂碳纳米管包覆金属钴催化剂(Co@NCNT).Co@NCNT具有较大的比表面积、均匀的氮分布以及包覆结构.在苯甲醇和苯胺一步法N-烷基化反应中Co@N CNT具有较高的催化活性,且循环4次反应活性没有明显的变化.控制实验和中毒实验表明金属Co和N对催化活性起着重要的作用,同时金属Co是中间产物N-苄叉苯胺加氢的主要活性位.     

Solvability of finite groups

H is called an ? _p -embedded subgroup of G, if there exists a p-nilpotent subgroup B of G such that H _p ∈ Syl _p (B) and B is ? _p -supplemented in G. In this paper, by considering prime divisor 3, 5, or 7, we use ? _p -embedded property of primary subgroups to investigate the solvability of finite groups. The main result is follows. Let E be a normal subgroup of G, and let P be a Sylow 5-subgroup of E. Suppose that 1 < d ? |P| and d divides |P|. If every subgroup H of P with |H| = d is ?₅-embedded in G, then every composition factor of E satisfies one of the following conditions: (1) I/C is cyclic of order 5, (2) I/C is 5′-group, (3) I/C ? A₅.     

Combined separable signals based neuro-fuzzy Hammerstein–Wiener model

Hammerstein–Wiener model can describe a large number of complicated industrial processes. In this paper, a novel identification method for neuro-fuzzy based Hammerstein–Wiener model is presented. A neuro-fuzzy system with correlation analysis based non-iterative parameter updating algorithm is proposed to model the static nonlinearity of Hammerstein–Winer processes. As a result, the proposed method not only avoid the inevitable restrictions on static nonlinear function encountered by using the polynomial approach, but also overcomes the problems of initialization and convergence of the model parameters, which are usually resorted to trial and error procedure in the existing iterative algorithms used for the identification of Hammerstein–Winer model. In addition, combined separable signals are adopted to identify the Hammerstein–Wiener process, resulting in the identification problem of the linear model separated from that of nonlinear parts. Moreover, one part of the input signals is extended to more general signals, such as binary signals, Gaussian signals or other modulated signals. Examples are used to illustrate the effectiveness of the proposed method.     

The p-th moment stability of solutions to impulsive stochastic differential equations driven by G-Brownian motion

In this paper, we consider a class of impulsive stochastic differential equations driven by G-Brownian motion (IGSDEs in short). By means of the G-Lyapunov function method, some criteria on p-th moment stability and p-th moment asymptotical stability for the trivial solutions of IGSDEs are established. An example is presented to illustrate the efficiency of the obtained results.     

Universal arcs in local tournaments

An arc $uv$ of a digraph $D$ is called universal if $uv$ and $w$ are in a common cycle for any vertex $w$ of $D$. In this paper we characterize local tournaments whose every arc is universal.     

Delay‐dependent criteria on the global attractivity of Nicholson's blowflies model with patch structure

In this paper, we investigate the effect of delay on the asymptotic behavior of Nicholson's blowflies model with patch structure and multiple time‐varying delays. By using the fluctuation lemma and some differential inequality technique, delay‐dependent criteria are obtained for the global attractivity of the addressed system. Meanwhile, some numerical examples are given to illustrate the feasibility of the theoretical results. Copyright © 2017 John Wiley & Sons, Ltd.