空心微珠/Al复合材料的动态压缩力学性能和吸能特性

利用分离式霍普金森压杆（split Hopkinson pressure bar,SHPB）系统对空心微珠体积分数为0.4的空心微珠/1199Al复合泡沫在1 700~2 900s^-1应变率范围内的动态压缩力学性能、吸能性能进行了研究,还利用SEM扫描电镜对压缩试件断口进行微观组织分析,与准静态条件下材料的压缩力学性能及压缩变形机制进行了对比。结果表明,空心微珠/1199Al复合泡沫是一种应变率敏感材料,与准静态结果相比,在高应变率下复合材料的流动应力和塑性应变有明显的增大,应变率硬化效应对复合材料的流动应力的影响明显大于应变硬化的影响。复合材料的准静态和动态压缩变形机制存在一定差异,动态载荷作用下,空心微珠/1199Al复合泡沫内部空心微珠的压缩和基体材料的充填同时发生,组分之间具有良好的协调变形能力。

     

Novel miniature high power ring filter

The power handling capability of high temperature superconducting (HTS) filters is limited due to current concentration at the edges of the superconducting films. This problem can be overcome by using ring resonator, which employs the edge current free and reduces the current concentration. However, this kind of filter has large size. In order to reduce the cost and size and increase the power handling capability, in this paper a HTS photonic bandgap (PBG) structure filter is developed. The proposed pass band filter with PBG structure exhibits center frequency 12.23 GHz, steepness (about 35 dB/GHz), bandwidth (−3 dB bandwidth is 0.045 GHz), and low insertion loss (about −0.5 dB), and can handle input power up to 1 W (this value was limited by the measurement instrument used in the experiment). The size is reduced by 25%, insertion loss reduced by 37.5%, and steeper roll-off of the filter is also obtained compared with that in published literature.     

Tutorial review on validation of liquid chromatography–mass spectrometry methods: Part I

This is the part I of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS) and discuss specific issues that arise with MS (and MS/MS) detection in LC (as opposed to the “conventional” detectors). The Part I briefly introduces the principles of operation of LC–MS (emphasizing the aspects important from the validation point of view, in particular the ionization process and ionization suppression/enhancement); reviews the main validation guideline documents and discusses in detail the following performance parameters: selectivity/specificity/identity, ruggedness/robustness, limit of detection, limit of quantification, decision limit and detection capability. With every method performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to determine it, specifically in the case of LC–MS methods.     

Co1−xFe2+xO4 (x = 0.1, 0.2) anode materials for rechargeable lithium-ion batteries

A cobalt-poor or iron rich bicomponent mixture of Co_0.9Fe_2.1O₄/Fe₂O₃ and Co_0.8Fe_2.2O₄/Fe₂O₃ anode materials have been successfully prepared using simple, cost-effective, and scalable urea-assisted auto-combustion synthesis. The threshold limit of lower cobalt stoichiometry in CoFe₂O₄ that leads to impressive electrochemical performance was identified. The electrochemical performance shows that the Co_0.9Fe_2.1O₄/Fe₂O₃ electrode exhibits high capacity and rate capability in comparison to a Co_0.8Fe_2.2O₄/Fe₂O₃ electrode, and the obtained data is comparable with that reported for cobalt-rich CoFe₂O₄. The better rate performance of the Co_0.9Fe_2.1O₄/Fe₂O₃ electrode is ascribed to its unique stoichiometry, which intimately prefers the combination of Fe₂O₃ with Co_1−xFe_2+xO₄ and the high electrical conductivity. Further, the high reversible capacity in Co_0.9Fe_2.1O₄/Fe₂O₃ and Co_0.8Fe_2.2O₄/Fe₂O₃ electrodes is most likely attributed to the synergistic electrochemical activity of both the nanostructured materials (Co_1−xFe_2+xO₄ and Fe₂O₃), reaching beyond the well-established mechanisms of charge storage in these two phases.     

静电自组装方法合成的具有多孔三维网络结构的Fe_3O_4/石墨烯复合材料作为高性能锂离子电池负极材料(英文)

采用静电自组装方法,分两步合成Fe(OH)3/GO前驱体(GO:氧化石墨烯),再通过水热反应和600°C高纯氮气气氛下煅烧,获得了Fe3O4/石墨烯复合材料.通过X射线衍射(XRD)、扫描电镜(SEM)、高分辨透射电镜(HRTEM)、拉曼(Raman)光谱等多种分析,发现该复合材料具有三维多孔石墨烯网络结构.把合成的这种Fe3O4/石墨烯复合材料作为锂离子电池负极材料,电化学测试结果表明其具有优良的电化学性能:首次放电容量为1390 mAh·g-1,50次循环后容量为819 mAh·g-1.通过对比实验表明,三维石墨烯网络结构的形成对复合材料的电化学循环稳定性起着关键作用.     

尖晶石型LiMn1.9Al0.1O3.95F0.05材料的制备及其增强的倍率性能

通过溶胶-凝胶和高温固相掺杂反应可控合成了形貌均匀、结晶性好的尖晶石型LiMn_1.9Al_0.1O_3.95F_0.05正极材料,探究了Al部分取代Mn、F部分取代O后对结构的影响,测试并比较了电极材料的倍率性能和循环充放电性能. 结果表明,尖晶石型LiMn_1.9Al_0.1O_3.95F_0.05和LiMn₂O₄有同样的晶型,但电极较传统的LiMn2O4电极倍率稳定性有显著提高. 在连续混合（如0.1C、0.5C和1C）充放电150次后,LiMn_1.9Al_0.1O_3.95F_0.05电极的容量仍能保持90%以上.     

对中专学生体育能力与培养的探讨

本文通过对中专学生体育能力的概念、范畴、结构的理论探讨，得出如下结论：体育能力是人们独立地、科学地从事体育锻炼作身体活动的能力。它的结构是体育认知能力、身体活动能力、体育技术和运动技能诸因素构成的个性身心的综合体。中专学生体育能力的结构是一个多层次，多因素的系统。系统中各个因素相互联系，相互作用，互相制约。本文并对在教育实践中培养中专学生体育能力的主要途径进行总结和研究。     

中学生数学学习选择能力研究

中学生的数学学习选择能力是一个值得引起关注的问题.本文从数学研究中的选择、数学学习选择能力的概念、数学学习选择能力与数学思维品质等角度,在有关文献的基础上对数学学习选择能力进行研究.     

最小载流元件对送电线路通流能力影响的解决方案

分析了最小载流元件对送电线路通流能力的影响,并探讨了最小载流元件对送电线路通流能力影响的解决方案