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对外掺杂碱土金属Mg的B40硼笼的储氢性能进行了密度泛函理论研究. 结果表明, B40笼含有2个六元环与4个七元环. 多个Mg原子对B40笼进行外掺杂时不会发生成簇现象, 有利于进一步储氢. Mg原子外掺杂的B40笼对H2分子的平均吸附能介于物理吸附与化学吸附之间(0.1~0.8 eV). 体系的储氢密度达到7.60%(质量分数). 储氢结构能在常温常压下释放H2分子, 因此, Mg原子外掺杂的B40笼比Mg合金具有更好的储氢性能.  相似文献   
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周晓锋  高雷 《中国物理》2007,16(7):2028-2032
Nanofluids or liquids with suspended nanoparticles are likely to be the future heat transfer media, as they exhibit higher thermal conductivity than those of liquids. It has been proposed that nanoparticles are apt to congregate and form clusters, and hence the interaction between nanoparticles becomes important. In this paper, by taking into account the interaction between nearest-neighbour inclusions, we adopt the multiple image method to investigate the effective thermal conductivity of nanofluids. Numerical results show that then the thermal conductivity ratio between the nanoparticles and fluids is large, and the two nanoparticles are close up and even touch, and the point-dipole theory such as Maxwell--Garnett theory becomes rough as many-body interactions are neglected. Our theoretical results on the effective thermal conductivity of CuO/water and Al热传导率 多极化 物理 相互作用nanofluids, thermal conductivity, multipolar interactionProject supported by the National Natural Science Foundation of China (Grant No~10204017) and the Natural Science of Jiangsu Province, China (Grant No~BK2002038).2006-07-062006-08-21Nanofluids or liquids with suspended nanoparticles are likely to be the future heat transfer media, as they exhibit higher thermal conductivity than those of liquids. It has been proposed that nanoparticles are apt to congregate and form clusters, and hence the interaction between nanoparticles becomes important. In this paper, by taking into account the interaction between nearest-neighbour inclusions, we adopt the multiple image method to investigate the effective thermal conductivity of nanofluids. Numerical results show that then the thermal conductivity ratio between the nanoparticles and fluids is large, and the two nanoparticles are close up and even touch, and the polnt-dipole theory such as Maxwell-Garnett theory becomes rough as many-body interactions are neglected. Our theoretical results on the effective thermal conductivity of CuO/water and Al2O3/water nanofluids are in good agreement with experimental data.  相似文献   
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周晓锋  方浩宇  唐春梅 《物理学报》2019,68(5):53601-053601
本文使用密度泛函理论中的广义梯度近似对扩展三明治结构graphene-2Li-graphene的几何结构、电子性质和储氢性能进行计算研究.计算得知:位于单层石墨烯中六元环面心位上方的单个Li原子与基底之间的结合能最大(1.19 eV),但小于固体Li的实验内聚能(1.63 eV),然而,在双层石墨烯之间的单个Li原子与基底的结合能增加到3.41 eV,远大于固体Li的实验内聚能,因此位于双层石墨烯之间的多个Li原子不会成簇,有利于进一步储氢.扩展三明治结构graphene-2Li-graphene中每个Li原子最多可以吸附3个H_2分子,储氢密度高达10.20 wt.%,超过美国能源部制定的5.5 wt.%的目标.该体系对1—3个H_2分子的平均吸附能分别为0.37,0.17和0.12 eV,介于物理吸附和化学吸附(0.1—0.8 eV)之间,因此该体系可以实现常温常压下对H_2的可逆吸附.通过对态密度分析可知,每个Li原子主要通过电场极化作用吸附多个H_2分子.动力学和巨配分函数计算表明graphene-2Li-graphene结构对H_2分子具有良好的可逆吸附性能.该研究可以为开发良好的储氢材料提供一个好的研究思路,为实验工作提供理论依据.  相似文献   
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杨梅缺硼症状与硼肥施用技术研究   总被引:4,自引:0,他引:4  
为矫治杨梅缺硼症状,采用了喷施和土施硼肥技术。调查和试验结果表明,杨梅硼元素缺乏的典型生理症状为叶小、枝梢丛生、枯梢、花量少,且不结果或很少结果。喷施0,2%硼砂液或0.2%硼砂 0.5%尿素液能明显矫治杨梅缺硼症状,改善春、夏两梢生长指标,提高坐果率,从而提高单株产量。土施硼肥也能取得较好的矫治效果,施用量以硼砂100g/株为佳;同时,土施处理在生产实际中还表现出良好的后续效应。  相似文献   
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