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The ability to resolve spatially and identify chemically atoms in defects would greatly advance our understanding of the correlation between structure and property in materials. This is particularly important in polycrystalline materials, in which the grain boundaries have profound implications for the properties and applications of the final material. However, such atomic resolution is still extremely difficult to achieve, partly because grain boundaries are effective sinks for atomic defects and impurities, which may drive structural transformation of grain boundaries and consequently modify material properties. Regardless of the origin of these sinks, the interplay between defects and grain boundaries complicates our efforts to pinpoint the exact sites and chemistries of the entities present in the defective regions, thereby limiting our understanding of how specific defects mediate property changes. Here we show that the combination of advanced electron microscopy, spectroscopy and first-principles calculations can provide three-dimensional images of complex, multicomponent grain boundaries with both atomic resolution and chemical sensitivity. The high resolution of these techniques allows us to demonstrate that even for magnesium oxide, which has a simple rock-salt structure, grain boundaries can accommodate complex ordered defect superstructures that induce significant electron trapping in the bandgap of the oxide. These results offer insights into interactions between defects and grain boundaries in ceramics and demonstrate that atomic-scale analysis of complex multicomponent structures in materials is now becoming possible. 相似文献
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本文调查了上海市百岁老人的性别、职业和谱系,并绘制了57个完整的寿命谱系图,其中男性10名(占总数的17.5%),女性47名(占82.5%).男性中脑力劳动者4名(占男性总数的40%),体力劳动者6名(占60%);女性中脑力劳动者1人(占女性总数的2.1%),体力劳动者3人(占6.4%),操持家务者43人(占91.5%).有长寿家族史者40人(占寿命家族史清楚者的70.2%),无长寿家族史者17人(占29.8%).百岁老人配偶寿长≥70岁者,其已故子女的平均寿命高于配偶<70岁的.作者认为长寿是遗传的,并着重从遗传和环境两方面分析了女寿星数明显多于男寿星数的原因. 相似文献
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艾摩尔 《华东师范大学学报(自然科学版)》2004,2004(1):40-44
在二次损失函数下,作者研究了多元线性模型协方差矩阵的MINQUE估计和简单估计的比较问题,其中多元线性模型的设计矩阵和离散矩阵可以不满秩,得到了一个充分和必要条件。 相似文献
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心肌宁冲剂按1.75g/kg,0.875g/kg剂量,每天早晚分两次灌胃给药,连续7天,均能明显对抗垂体后叶素所诱发的大鼠急性心肌缺血的心电图改变。 相似文献
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该文通过34只罗猴头颈实验研究,从中决定罗猴的颅脑损伤容限.当颅脑受到冲击时,颅壳发生局部变形瞬间,大脑亦发生变形,致使颅内压升高.利用这些结果来确定它的损伤机制,以模拟宇航员在冲击载荷下的创伤分析模型,将有助于进行临床创伤治疗和宇航弹射时的防护. 相似文献
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