Physical,hydrochemical and isotopic characteristics of springs in Beijing,China, compared to historical properties

A physical, hydrochemical and isotopic evaluation of springs in Beijing was conducted in 2009 to reveal apparent changes in the properties of those springs. The results showed that most of the 2nd class springs and more than 50 % of the 1st class springs recorded in the early 1980s were depleted, while the discharges of existing springs have also decreased sharply. In addition, the majority of springs were of the HCO₃–Ca–Mg type and good water quality, with the quality indices changing slightly compared to those recorded 30 years ago. The abundances of ²H, ¹⁸O, and ³H in the springs indicated that most of the springs were of meteoric origin with a relatively close connection to modern atmospheric precipitation. As a result, the springs have a relatively strong renewability within a shallow circulation.     

1.3 GHz超导腔磁通排出效应研究

设计并搭建了一套高精度的磁场测量和补偿系统,并结合中国科学院高能物理研究所(IHEP)的2K超导腔垂直测试平台对1.3 GHz单加速间隙超导腔的磁通排出效应开展了实验研究:利用研制的磁场测量和补偿系统能够精密地测量超导腔赤道位置磁场,并能够将磁场补偿至小于5.0×10-8 T;并对超导腔不同表面温度梯度下的磁通排出效应进行了测量分析;对钉扎了磁场的超导腔进行了射频性能测试,研究了超导腔电阻对磁通钉扎的敏感度,以及在不同电场梯度下超导腔的表面电阻变化情况。结果表明,研制的高精度磁场测量和补偿系统能够满足超导腔磁通排出研究的需求;高的超导腔表面温度梯度有利于磁通的排出;磁通钉扎电阻的敏感度随着加速电场梯度的增加而增大,导致超导腔的性能下降。此实验研究也为后续超导腔的研制奠定了一定基础。     

基于石墨烯/石墨烯卷轴复合薄膜高灵敏度柔性压力传感器

一维导电材料例如纳米线，大量应用于柔性压力传感器中. 但是一维材料和基底之间接触时相互作用力较弱，使得传感器灵敏度、响应时间、和循环寿命等性能指标有待进一步提高. 针对这些问题，设计了石墨烯/石墨烯卷轴多分子层复合薄膜作为传感器导电层. 石墨烯卷轴具有一维结构，而石墨烯的二维结构可以牢固地固定卷轴，以确保高导电性复合薄膜与基底之间的粘附性，同时整体结构的导电通道得到了增加. 由于一维和二维结构的协同效应，实现了应变灵敏度系数3.5 kPa^-1、 响应时间小于50 ms、能够稳定工作1000次以上的压阻传感器.     

Crucial factors affecting the physicochemical properties of sol–gel produced Fe3O4@SiO2–NH2 core–shell nanomaterials

Multifunctional nanomaterials with task-specific physicochemical properties, especially core?Cshell nanostructures with Fe₃O₄ core and NH₂-functional shells (Fe₃O₄@SiO₂?CNH₂), have been extensively investigated as high-performance adsorbents, catalysts and catalyst supports; and in most cases the controllable sol?Cgel technique is the choice for fabrication of this kind of widely applied materials. Herein, we demonstrated that mono-dispersed and spherical Fe₃O₄@SiO₂?CNH₂ nanomaterials with magnetic response core, NH₂-functional shell structure can be facilely prepared by co-condensation of TEOS with APTMS using a versatile sol?Cgel process. It was shown that the proper usage of APTMS and appropriate pre-hydrolysis time of TEOS were crucial and key steps for formation of highly uniform and desirable amino loading Fe₃O₄@SiO₂?CNH₂ materials. The TEOS pre-hydrolysis and the critical time (around 90?min) before the addition of APTMS prove to be vital for uniform structure evolution, while the appropriate concentration of APTMS (~2.28?mmol?L^?1 in our system) leads to well-dispersed materials with relatively high loading of amino functionality. The as-prepared Fe₃O₄@SiO₂?CNH₂ magnetic nanoparticles prepared under optimum conditions possessing superparamagnetic behavior, uniform core?Cshell structure (~200?nm in diameter), relatively large BET surface area (~138?m²/g) and high incorporation of amino-functionality (~2.90?wt?%).