富锂正极材料结构设计和表面调控的研究进展

富锂正极材料因具有较高的理论能量密度,被视为极具发展潜能的新一代正极材料,但该材料在循环过程中容量和电压衰减显著,导致其实际商业应用受阻.本文综合评述了通过结构设计和表面调控提高富锂正极材料储锂性能的研究进展,介绍了富锂正极材料的充放电工作机制,及导致其比容量和电压衰减的原因,讨论了近年来通过新型结构设计(如构筑蛋黄-蛋壳中空结构、中空多壳层结构等)和表面调控(如尺寸控制、暴露晶面控制、表面尖晶石化、表面包覆、表面掺杂等）策略,抑制富锂正极材料表面氧析出和晶型转变并稳定材料结构,从而抑制电压和比容量衰减,有效提高电池的循环寿命和库伦效率的相关研究成果,最后,提出了通过结构设计和表面调控提高富锂正极材料电化学性能面临的挑战,并对未来发展方向进行了展望.     

中空多壳层CoFe2O4的制备及锂离子电池性能研究

以二元金属氧化物CoFe₂O₄为研究对象,通过次序模板法制备了CoFe₂O₄中空多壳层结构(HoMS)材料;对其形貌、结构进行了表征;考察了壳层结构与电化学性能之间的关系.电化学测试结果表明,双壳层-核CoFe₂O₄中空球具有最高的放电比容量(1354.4 mA·h/g)、优异的倍率性能和循环稳定性,其独特的结构优势和最优的空腔体积占有率使其在多次循环过程中能始终保持结构和电化学性质的稳定.     

受外来植物入侵的土壤微生物生态学研究进展

外来植物入侵已成为全球性问题,给人类社会、经济和环境带来巨大挑战,因而对外来植物成功入侵机制的研究引起了国内外学者的广泛关注.目前,外来植物成功入侵机制的理论框架主要包括2个方面：外来植物的入侵能力与生态系统的可入侵性.基于上述理论框架,生态学家提出了多个用于解释外来植物成功入侵的机制假说,包括天敌逃避假说、资源可获得性假说等,但这些假说主要针对的是地上植物与草食性动物.近年来的研究证明,外来入侵植物与入侵地土壤微生物以及与自身内生菌之间的相互作用也是其成功入侵的重要机理之一.从菌根共生、固氮菌共生、病原微生物逃避、土壤微生物群落总体结构与功能以及内生菌等方面对国内外关于外来植物入侵的微生物学机制研究进行了总结,并在此基础上探讨了研究中存在的问题及未来的研究方向,以期为外来植物入侵的预防、控制与生境恢复提供依据.     

燃料电池中质子交换膜干涸的热物理机制

本文首次应用有内热源的多孔介质中流体流动与换热理论,对直接甲醇燃料电池中PEM中的传热过程和干涸 现象进行定量研究。建立了相应的数学物理模型并进行了数值求解。计算结果表明:反映水的热容量和膜的内部产热量的 两个无因次参数D和N是影响PEM中传热的主要因素;水的质量流率小和电流密度过高是造成膜干涸的主要原因。     

基于广义线性模型的针刺足三里脊髓背根神经活动解码

神经系统以时空编码形式刻画外部刺激信息, 针刺作为对穴位的机械作用可以等效为对神经系统的一种外部刺激. 为了揭示神经系统如何表达和传递针刺作用, 本文设计了不同频率的针刺动物实验, 即在针刺大鼠足三里穴位时获取脊髓背根神经节电信号. 首先, 经过数据预处理获得单神经元动作电位序列并转化为点过程序列. 其次, 应用广义线性模型(GLM)编码针刺作用, 产生模拟的神经放电序列. 另外, 在模型基础上应用贝叶斯解码, 根据神经放电序列重构针刺随时间变化的位移波形. 最后, 基于时间重标度理论应用分位数分位数(Q-Q)图方法检验编码模型与点过程数据的一致性. 结果表明, GLM能够模拟针刺神经编码, 并正确解码针刺信息. 本文为针刺研究提供了新的视角, 对于构建神经系统与机器接口以改善针刺的临床研究具有潜在意义. 关键词： 针刺 点过程 广义线性模型 神经解码     

Effect of Post-Annealing on Structural and Electrical Properties of ZnO:In Films

Indium-doped ZnO(ZnO:In) films are deposited on quartz substrates by rf magnetron sputtering. The effects of post-annealing on structural, electrical, optical and Raman properties are investigated by x-ray diffraction,Raman scattering, Hall measurement and first-principles calculation. The results indicate that all of the ZnO:In films have excellent crystallinity with a preferred ZnO(002) orientation. It is found that the incorporation of In can dramatically increase the intensity of the 274 cm~(-1) Raman mode. However, both post-annealing treatment and increasing O_2 partial pressure in the process of preparing thin films can reduce the intensity of the 274 cm~(-1) mode or even eliminate it, and relax compressive stress of the ZnO:In film judged by analyzing the shifts of the(002) Bragg peaks and E_2(high) mode. Finally, the origin of the 274 cm~(-1) mode is inferred to be the vibration of Zn interstitial(Zni) defects, which play a crucial role in the high electron concentration and low resistivity of ZnO:In films annealed in an appropriate temperature range(450–600℃).     

Microstructure and photocatalytic activity of titanium dioxide nanoparticles

Titanium dioxide nanoparticles with an average diameter of about 10 nm are fabricated using a sintering method. The degradation of methyl orange indicates that the photocatalytic efficiency is greatly enhanced, which is measured to be 62.81%. Transmission electron microscopy is used to investigate the microstructure of TiO 2 nanoparticles in order to correlate their photocatalytic properties. High-resolution transmission electron microscopy examinations show that all the nanoparticles belong to the anatase phase, and pure edge dislocations exist in some nanoparticles. The great enhancement of photocatalytic efficiency is attributed to two factors, the quantum size effect and the surface defects in the nanoparticles.     

Characteristics analysis of acupuncture electroencephalograph based on mutual information Lempelben-Ziv complexity

As a convenient approach to the characterization of cerebral cortex electrical information, electroencephalograph (EEG) has potential clinical application in monitoring the acupuncture effects. In this paper, a method composed of the mutual information method and Lempel-Ziv complexity method (MILZC) is proposed to investigate the effects of acupuncture on the complexity of information exchanges between different brain regions based on EEGs. In the experiments, eight subjects are manually acupunctured at ‘Zusanli’acupuncture point (ST-36) with different frequencies (i.e., 50, 100, 150, and 200 times/min) and the EEGs are recorded simultaneously. First, MILZC values are compared in general. Then average brain connections are used to quantify the effectiveness of acupuncture under the above four frequencies. Finally, significance index P values are used to study the spatiality of the acupuncture effect on the brain. Three main findings are obtained: (ⅰ) MILZC values increase during the acupuncture; (ⅱ) manual acupunctures (MAs) with 100 times/min and 150 times/min are more effective than with 50 times/min and 200 times/min; (ⅲ) contralateral hemisphere activation is more prominent than ipsilateral hemisphere's. All these findings suggest that acupuncture contributes to the increase of brain information exchange complexity and the MILZC method can successfully describe these changes.     

直接甲醇燃料电池阳极流道两相流动的拟沸腾模型(I)流动压力降的计算

本文分析了直接甲醇燃料电池阳极流道中存在的气液两相流动现象。通过与传统加热管中流动沸腾现象进行比拟,首次提出了“拟沸腾”的概念,建立了气液两相流压力降模型。基于在建的活化面积为100 cm2的DMFC极板的蛇行流场设计,计算了阳极流道的压力降,分析了各分压力降对总压降的影响。计算结果表明:对于小活化面积的电池,在小电流密度下运行时,流道中扩散层表面的“非活化点”处滞留的气泡核心对主流有较大的附加摩擦阻力作用。     

基于悬臂梁的光纤光栅线性调谐

理论上对不同厚度的“凸”字形悬臂梁的调谐能力进行了分析,实验中选用适当尺寸的悬臂梁,对粘贴基上的光纤光栅的反射波长实现了线性调谐,并观察到由于梁轴向应力的梯度分布造成的啁啾输出现象,指出选用长度较短的光栅可以减小谱的展宽量。