基于散射实验极化靶的2.5T/1.3K的动态核极化(DNP)系统的开发

动态核极化法(Dynamic Nuclear Polarization, DNP)是利用热平衡下的电子在磁场中的高自旋极化率转移到原子核自旋的技术,从而极大的提高原子核自旋极化率。多种动态极化靶材料已广泛的用于自旋物理散射实验。本文介绍一种简单实用,共同开发的日本山形大学DNP系统,包括超导磁场,氦4蒸发恒冷器,微波系统以及NMR核磁共振检测系统,测得中子靶材料氘带丁醇(D-butanol)中氘核的极化率在2.5T/1.3K达到+6.5%。     

提升广告价值人人网并购56网 视频网站发展路径呈现两极化

56网转投人人旗下,是继盛大收购酷6、新浪入股土豆后的最新一起视频网站并购案。而这次并购或许预示着国内视频网站第二波收购浪潮的到来人人网收购56网,试图寻找新的增长点。而56网希望背靠人人网这棵大树,早日脱贫。9月27日,人人网宣布将以8000万美元全资收购国内视频分享网站56网,此交易将在2011年第四季度内完成。受这一消息的影响,人人公司股价在当日上涨4.5%,     

基于肤色的自适应光照法定位运动人体研究

为了解决自然环境下,环境光照变化和复杂背景等因素对视频监视和目标识别带来的干扰,提出了一种基于人体肤色特征遵循环境光照变化规律的自适应光照法运动人体定位方法。自适应光照法,即在HSV颜色模型下,分别计算不同光照条件下所有肤色像素点的平均色调H、平均饱和度S、平均亮度V;再计算不同光照条件下每幅帧图像所有像素点的相对亮度值μ;以相对亮度值为横坐标,肤色的H、S、V的平均值分别作为纵坐标,拟合出肤色相对于亮度的规律公式,通过自动选取阈值,进一步消除了环境光照变化对肤色检测的影响,使肤色区域定位更为准确,且计算量小、不需要消耗大量的存储空间和处理时间。以一年为周期采集并处理和分析了大量不同季节和时段的视频图像数据,实验结果表明,在运动区域查找人体肤色,自适应光照法提高了复杂自然环境下光照下对运动人体定位的实时性和准确性。     

Caging dynamics in a granular fluid

We report an experimental investigation of the caging motion in a uniformly heated granular fluid for a wide range of filling fractions, varphi. At low varphi the classic diffusive behavior of a fluid is observed. However, as varphi is increased, temporary cages develop and particles become increasingly trapped by their neighbors. We statistically analyze particle trajectories and observe a number of robust features typically associated with dense molecular liquids and colloids. Even though our monodisperse and quasi-2D system is known to not exhibit a glass transition, we still observe many of the precursors usually associated with glassy dynamics. We speculate that this is due to a process of structural arrest provided, in our case, by the presence of crystallization.     

Oscillatory persistent currents in self-assembled quantum rings

We report the direct measurement of the persistent current carried by a single electron by means of magnetization experiments on self-assembled InAs/GaAs quantum rings. We measured the first Aharonov-Bohm oscillation at a field of 14 T, in perfect agreement with our model based on the structural properties determined by cross-sectional scanning tunneling microscopy measurements. The observed oscillation magnitude of the magnetic moment per electron is remarkably large for the topology of our nanostructures, which are singly connected and exhibit a pronounced shape asymmetry.     

Thermal fluctuations and rubber elasticity

The effects of thermal elastic fluctuations in rubbery materials are examined. It is shown that, due to their interplay with the incompressibility constraint, these fluctuations qualitatively modify the large-deformation stress-strain relation, compared to that of classical rubber elasticity. To leading order, this mechanism provides a simple and generic explanation for the peak structure of Mooney-Rivlin stress-strain relation and shows good agreement with experiments. It also leads to the prediction of a phonon correlation function that depends on the external deformation.     

电偶腐蚀对先进封装铜蚀刻工艺的影响

在先进封装的铜种子层湿法蚀刻工艺中,电镀铜镀层的蚀刻存在各向异性的现象。研究结果表明,在磷酸、双氧水的蚀刻液体系中,因电偶腐蚀造成的凸点电镀铜蚀刻量约为铜种子层蚀刻量的4.9倍。通过分析凸点上锡、镍镀层的能谱数据及蚀刻效果,发现该凸点结构中的锡、镍镀层表面存在钝化层,导致锡、镍镀层的蚀刻量远低于铜镀层。在加入不同添加剂的蚀刻液中,通过络合铜或破坏锡、镍镀层表面钝化层的方法,均能达到抑制凸点上铜镀层发生电偶腐蚀的效果。其中,复合型添加剂可以使凸点上铜镀层的横向蚀刻量降低约82%,并且添加剂无残留风险。