Simple synthesis of honeysuckle-like CuCo2O4/CuO composites as a battery type electrode material for high-performance hybrid supercapacitors

In this paper, porous CuCo₂O₄/CuO composites with novel honeysuckle-like shape (CuCo₂O₄/CuO HCs) have been prepared for the first time by a simple hydrothermal method and followed with an additional annealing process in air. The unique CuCo₂O₄/CuO HCs consisted of dense and slender petals with length of 1.3–1.5 μm and width of about 50 nm, and possessed a specific surface area of 36.09 m² g^?1 with main pore size distribution at 10.63 nm. When used as the electrode materials for supercapacitors, the CuCo₂O₄/CuO HCs exhibited excellent electrochemical performances with a high specific capacity of 350.69 C g^?1 at 1 A g^?1, a rate capability of 78.6% at 10 A g^?1, and 96.2% capacity retention after 5000 cycles at a current density of 5 A g^?1. In addition, a hybrid supercapacitor (CuCo₂O₄/CuO HCs//AC HSC) was assembled using the CuCo₂O₄/CuO HCs as positive electrode and activated carbon (AC) as negative electrode. The HSC device delivered a specific capacity of 187.85 C g^?1 at 1 A g^?1 and a superior cycling stability with 104.7% capacity retention after 5000 cycles at 5 A g^?1, and possessed a high energy density of 41.76 W h kg^?1 at a power density of 800.27 W kg^?1. These outstanding electrochemical performances manifested the great potential of CuCo₂O₄/CuO HCs as a promising battery-type electrode material for the next-generation advanced supercapacitors with high-performance.     

Se doped nickel-molybdenum bimetal sulfide with enhanced electrochemical activity for hydrogen evolution reaction

In this work, we synthesized Se doped MoS₂@Ni₃S₂ with nanosheets coated nanorods structure supported on Ni foam (MoNiSeS). Firstly, MoS₂@Ni₃S₂ (MoNiS) nanorods was synthesized by hydrothermal method. After selenization treatment, MoSe₂ successfully formed on the edge of MoS₂ nanosheets and particle Ni₃S₂ transformed into NiSe, in which MoSe₂ and NiSe acted as new phase in MoNiSeS. The obtained MoNiSeS only needs a low overpotential of 68 mV to reach the current density of 10 mA cm^?2, and has a low Tafel plots of 72.77 mV dec^?1 and good electrochemical durability, whose electrochemical activity is much better than that of MoNiS and NiSeS, implying the introduction of Mo and Se is beneficial to improve the electrocatalytic performance of NiS for HER. In addition, the proper amount of Mo source, which has an effect on the morphology of product, has also been investigated. For MoNiSeS, the typical nanosheets coated nanarods expose more active sites and the synergic effects is good to the improvement of the catalytic activity. Meanwhile, WNiSeS has also been prepared using the same method and the corresponding results show that the electrochemical activity of WNiSeS is much better than that of NiSeS, proving the universality of this strategy.     

贵州省干线公路沥青路面典型病害研究

"十二五"期间,随着贵州省交通建设的飞速发展,干线公路的里程及施工质量也迅速提高。但同时,干线公路沥青路面出现了许多早期病害,并且病害种类也更加多样化。本文对贵州省9个地市的干线公路沥青路面进行了系统调查,并就路面典型病害的成因进行了分析。     

基于振动特征边缘提取的电缆外力扰动智能感知技术

基于微型传感技术、嵌入式边缘计算和LoRa物联网，提出了一种新型的电缆外力扰动分布式监测技术。并针对LoRa数据传输的低密度、窄带宽要求，基于振动信号的时频特征，提出了一种精简化的特征集、状态集和控制集的单包数据装载方法。通过试验初步获得了电缆振动特征集的典型范围，为建立基于物联网窄带通信方式的电缆外力扰动智能预警系统提供了基础。     

芳烃连续重整装置先进控制系统的开发和应用

针对某石化公司芳烃连续重整装置的生产现状、存在问题及需求,为实现节能降耗而进行控制优化,在常规DCS控制的基础上提出了芳烃连续重整装置先进控制系统的控制目标、控制策略、系统结构及控制方案。利用机理建模,单值预估控制来进行先进控制器搭建,应用结果证实了所开发系统实现了质量指标的卡边控制,降低了能耗,提升了装置的平稳性。     

High‐performance printable paper‐like composites derived from plastic flexible film wastes

Owing to lack of proper recycling methods, plastic flexible film wastes are usually directly discarded or incinerated, which brings about severe environmental pollution. Therefore, converting plastic wastes into value‐added products has received more and more attention in recent years. In this work, paper‐like composites derived from plastic flexible film wastes were prepared via the thermally induced phase separation method by adding polyethylene‐graft‐maleic anhydride (PE‐g‐MAH) as a compatibilizer and fumed silica as an additive. The resulting paper‐like composites were characterized by SEM and infrared spectroscopy. Other properties such as mechanical properties, thermal properties, whiteness, printability and adsorption performance were also tested in detail. It was found that remarkable enhancements in mechanical, thermal and printable properties of the paper‐like composites were obtained when nano‐SiO₂ loading was 2.5–3 wt%. Uniformly distributed holes that can endow good printability by providing space for ink or other functional molecules were observed by using SEM. Furthermore, the CIE whiteness value of the resulting composites can reach 91.6%–96.7% on adding nano‐SiO₂. Additionally, the paper‐like composites integrating nano‐SiO₂ and PE‐g‐MAH exhibited good solid ink affinity and high water or oil adsorption capacity. Thus, according to this research, high‐performance printable paper‐like composites used as major components of multifunctional papers can be prepared based on plastic flexible film wastes. © 2019 Society of Chemical Industry     

Effect of porosity and crack on the thermoelectric properties of expanded graphite/carbon fiber reinforced cement-based composites

Cement-based composites is a promising type of structural material, which has prospective applications in relieving the urban heat island effect in summer and melted snow with low energy consumption. However, the major drawbacks of cement-based composites are heterogeneity, porosity, and brittleness. Porosity and microcrack have considerable influence on the thermoelectric of cement-based composites applied in large-scale concrete structures in future. This paper studied in detail the effect of porosity and crack on thermoelectric properties of the cement-based composite. The proper pores and cracks in the cement matrix are advantageous to enhance the Seebeck effect, but meanwhile it also reduces the electrical conductivity. So combined with Seebeck effect, electrical conductivity and other factors, it can obtain a comparatively low electrical conductivity (0.063S cm⁻¹) of expanded graphite/carbon fiber reinforced cement-based composites (EG-CFRC), but EG-CFRC manifests the maximum thermoelectric figure of merit (ZT) has reached 2.22 × 10⁻⁷ when the porosity is 3.90%. With different porosity, the Seebeck effect of prepared EG-CFRC was strengthened when the crack existed. The effect is most pronounced by a factor of 2 when the porosity is 28.90%. Therefore, based on stabilizing the conductivity, the crack is fittingly made to have a good effect on the Seebeck coefficient.     

Backtesting portfolio value-at-risk with estimated portfolio weights

This article theoretically and empirically analyzes backtesting portfolio value-at-risk (VaR) with estimation risk in an intrinsically multi-variate framework. It particularly takes into account the estimation of portfolio weights in forecasting portfolio VaR and its impact on backtesting. It shows that the estimation risk from estimating portfolio weights and that from estimating the multi-variate dynamic model make the existing methods in a univariate framework inapplicable. It proposes a general theory to quantify estimation risk applicable to the present problem and suggests practitioners a simple but effective way to implement valid inference to overcome the effect of estimation risk in backtesting portfolio VaR. In particular, we apply our theory to the efficient mean-variance-skewness portfolio for a multi-variate generalized autoregressive conditional heteroscedasticity model with multi-variate general hyperbolic distributed innovations. Some Monte Carlo simulations and an empirical application demonstrate the merits of our method.     

中间相炭微球在锂离子电池负极材料的应用进展

中间相炭微球(MCMB)具有良好锂离子扩散性、导电性和机械稳定性等优势,是目前应用广泛、综合性能优异的锂离子电池负极材料,但较低理论比容量是制约其发展的关键因素。为了获得性能优良的MCMB基锂离子电池负极材料,改性修饰和复合材料已然成为目前研发重点。笔者论述了碳结构、表界面和复合材料等微观结构设计对MCMB负极材料电化学性能的影响。从碳堆积结构类型、有序性、层间距以及球体粒径大小等方面,论述了碳结构微观设计对MCMB电化学性能的影响。发现具有乱层结构的MCMB在充放电过程中内部产生应力较小,且碳结构较稳定,具有优异循环稳定性;内部具有大量微孔或碳层间距较大的MCMB,在充放电过程中可提高锂离子在电极中的迁移速率,并提供更多的储锂空间,一般具有优良的充放电比容量和倍率性能;小粒径MCMB具有较短的锂离子迁移路径和随之增加的比表面积,通常具有较好倍率性能,伴随着可逆比容量和充放电效率的衰减。从表界面碳层改性、包覆和掺杂改性等方面,论述了表界面改性对MCMB电化学性能的影响。表面碳层修饰可增加MCMB与电解液的相容性及其比表面积,提高了与电解液的接触面积及贮锂容量,改善了锂离子电池负极材料的电化学性能;另外,MCMB表面包覆一层无定型碳,可避免其表面与电解液直接接触,减少电化学副反应的产生,提升其可逆比容量。从碳活性物质复合材料、非碳活性物质复合材料等方面,论述了复合材料微观结构设计对MCMB电化学性能的影响。碳活性物质可降低MCMB内部碳层结构的有序性,减少锂离子嵌入过程中的内部应力,提升MCMB循环稳定性。非碳活性物质诱导MCMB生成更加有序的碳层结构,提高MCMB的比表面积,从而改善MCMB表面与电解液分子的接触能力及其嵌锂性能,有利于提升MCMB负极材料可逆比容量、循环性能和倍率性能。MCMB具有高碳层间距和多缺陷位点等结构特征,有利于钠离子自由脱嵌,应用于钠离子电池时具有良好的可逆比容量、循环稳定性和倍率性能。MCMB的不规则定向层状结构经活化等处理具有较高比表面积,可应用于超级电容器电极材料。最后提出在高性能锂离子电池电极材料快速发展的需求下,从微观结构角度设计MCMB纳米复合材料将是MCMB负极材料的研究重点。     

开关磁阻直线电机的设计及其推力优化

设计了一种开关磁阻直线电机,使用JMAG软件对其进行了仿真和优化。进行了推力公式的推导,研究了导通顺序和初始位置对电机推力的影响,并分析了三种典型情况的磁力线分布。对电机的定子和动子的齿部和轭部高度、宽度及铁耗进行仿真优化,得出了最优参数。将有取向硅钢应用于该电机,研究了推力与轧制角的关系,并与使用普通硅钢的开关磁阻直线电机进行了对比,推力有一定提升。提出在动子齿部开切向槽的方案,结果表明,开切向槽对推力的影响较小,并能显著减小推力波动。