Tea polyphenols as a novel reaction-type electrolyte additive in lithium-ion batteries

In this study, we reported tea polyphenols (TP) as a novel, cheap, environment-friendly and easy dissolution in common electrolytes reaction-type electrolyte additive for the graphite anode of the lithium-ion batteries. The TP can capture less stable radical anions that are harmful to oxidation stability of ethylene carbonate (EC) to form stable polymer. To a certain extent, it improved the electrochemical performance of the graphite electrode such as reversible capacity and cyclic stability by charge-discharge test, cyclic voltammetry (CV), scanning electron microscope (SEM), and electrochemical impedance microscope (EIS). The first charge capacities of the graphite electrodes in electrolytes without and with TP were 327.1 and 349.1 mAh g^?1, respectively. The charge capacities were 306.8 and 344.2 mAh g^?1 after 100 cycles and the capacity retention were 93.79 and 98.60%, respectively. The improvement was benefited from the effective scavenging the less stable radical anions and improvement the oxidation stability of EC and formation of a stable, compact and thin solid electrolyte interface (SEI) film with lower resistance.     

Periodic surface nanostructures on polycrystalline ZnO induced by femtosecond laser pulses

Periodic surface nanostructures induced by femtosecond laser pulses on polycrystalline ZnO are presented. By translating the sample line-by-line under appropriate irradiation conditions, grating-like nanostructures with an average period of 160 nm are fabricated. The dependence of surface morphologies on the processing parameters, such as laser fluence, pulse number and laser polarization, are studied by scanning electronic microscope (SEM). In addition, photoluminescence (PL) analysis at room-temperature indicates that the PL intensity of the irradiated area increases significantly compared with the un-irradiated area. Using femtosecond laser pulses irradiation to fabricate periodic surface nanostructures on polycrystalline ZnO is efficient, simple and low cost, which shows great potential applications in ZnO-based optoelectronic devices.     

Prediction of mixed-mode fracture based on an elasto–plastic energy balance criterion

The maximum energy release rate criterion, i.e., G _max criterion, is commonly used for crack propagation analysis. This fracture criterion is based on the elastic macroscopic strength of materials. In the present investigation, however, the G _max criterion has been modified in order to accommodate the consideration of plastic strain energy. This modified criterion is extended to study the fatigue crack growth characteristics of mixed-mode cracks. To predict crack propagation due to fatigue loads, a new elasto–plastic energy model is presented. This new model includes the effects of material properties such as strain hardening exponent n, yield strength σ _y , and fracture toughness and stress intensity factor ranges. The results obtained are compared with those obtained using the commonly employed crack growth law and the experimental data.     

Mathematical problems in the integral-transformation method of dynamic crack

In the investigation on fracture mechanics, the potential function was introduced,and the moving differential equation was constructed. By making Laplace and Fourier transformation as well as sine and cosine transformation to moving differential equations and various responses, the dual equation which is constructed from boundary conditions lastly was solved. This method of investigating dynamic crack has become a more systematic one that is used widely. Some problems are encountered when the dynamic crack is studied.After the large investigation on the problems, it is discovered that during the process of mathematic derivation, the method is short of precision, and the derived results in this method are accidental and have no credibility. A model for example is taken to explain the problems existing in initial deriving process of the integral-transformation method of dynamic crack.     

位移约束集成化处理的连续体结构拓扑优化

为解决多工况下多位移约束的连续体结构拓扑优化问题,引入了K-S函数对位移约束进行集成化处理.在建立优化模型时,基于莫尔定理按ICM方法导出约束点位移与设计变量之间的近似显函数关系,然后采用Lagrange乘子法进行求解.给出三个算例对该方法进行验证,并与ESO法、BESO法、MD法以及均匀化方法的结果进行比较.结果表明:该方法计算效率较高,并且能够计算出更合理的结构拓扑.     

Experimental study and electromechanical model analysis of the nonlinear deformation behavior of IPMC actuators

This paper develops analytical electromechanical formulas to predict the mechanical deformation of ionic polymer–metal composite(IPMC) cantilever actuators under DC excitation voltages. In this research, IPMC samples with Pt and Ag electrodes were manufactured, and the large nonlinear deformation and the effect of curvature on surface electrode resistance of the IPMC samples were investigated experimentally and theoretically. A distributed electrical model was modified for calculating the distribution of voltage along the bending actuator. Then an irreversible thermodynamic model that could predict the curvature of a unit part of an IPMC actuator is combined with the electrical model so that an analytical electromechanical model is developed. The electromechanical model is then validated against the experimental results obtained from Pt-and Ag-IPMC actuators under various excitation voltages. The good agreement between the electromechanical model and the actuators shows that the analytical electromechanical model can accurately describe the large nonlinear quasi-static deflection behavior of IPMC actuators.     

欧拉圆盘不同能量耗散机理之间的关联

本文研究了欧拉圆盘运动过程中盘厚度以及盘面与水平面夹角α两因素对能量耗散的影响. 得出圆盘厚度与直径之比x对能量变化中各项因子的影响: x很小时, 质心在竖直方向上的动能变化和重力势能变化是系统能量耗散的主要因素; 当x>0.4142时, 圆盘绕与之平行的轴的转动动能变化成为主要因素, 并给出圆盘厚度可忽略的条件. 模拟了滚动摩擦、空气黏滞等不同能量耗散方式与x,α的关系, 导出各种耗散方式在圆盘运动的过程中的转变规律, 并指出x=0.1733, α>18°时能量耗散形式为纯滚动摩擦, 这修正了文献[26]结论.     

脑电信号的标度分析及其在睡眠状态区分中的应用

脑电信号具有长程幂律相关性及多重分形的标度特性,并随生理病理状态改变.本文首次针对睡眠脑电信号应用单重分形去趋势波动分析(detrended fluctuation analysis,简记为DFA)方法与多重分形奇异谱对睡眠脑电信号的标度特征进行系统的对比研究.发现DFA标度指数α对于不同导联和样本组间的差异较为敏感,随睡眠状态的变化不规律;而多重分形奇异强度区间Δα随睡眠状态的变化更为规律,睡眠Ⅰ期至Ⅳ期不断增大,并且导联间差异和样本组间差异均较小.多重分形Δα参数更适合作为判定睡眠状态的定量参数.     

也谈中学生自学能力的培养

利用自编学案诱导学生分步自学,培养学生的自学习惯;加强学生阅读能力的培养,结合物理学科知识的联系,让学生比较、归纳,促使学生掌握自学方法;强化信息题的训练,培养信息处理能力,实现自学能力的有效提升.     

Hemi[hexa­aqua­magnesium(II)] (μ‐2,6‐bis{[bis­(carboxyl­ato­methyl)­amino]­methyl}‐4‐chloro­phenolato)­bis­[di­aqua­magnesium(II)] decahydrate

The crystal structure of the title compound, [Mg(H₂O)₆]_0.5[Mg₂(C₁₆H₁₄ClN₂O₉)(H₂O)₄]·10H₂O, shows that this bi­nuclear complex consists of two Mg centres in distorted octahedral geometry, joined by an oxo bridge which is a derivative of the deprotoned hydroxy group of the phenolate in the ligand mol­ecule. In the anion, the coordination sphere of each Mg^II ion is completed by two carboxyl­ates, a tertiary N atom and two water mol­ecules. The inner coordination spheres for the Mg^II ions are very similar, both in ligand sets and in geometry. Each unit of the binuclear complex has one negative charge neutralized by a neighbouring hydrated cation, [Mg(H₂O)₆]²⁺, in which the Mg atom lies on an inversion centre. In each cell, there are 34 water mol­ecules and most of them participate in the formation of hydrogen bonds, which contribute greatly to the stability of the whole structure.