Multiple ionization of atom clusters by intense soft X-rays from a free-electron laser

Intense radiation from lasers has opened up many new areas of research in physics and chemistry, and has revolutionized optical technology. So far, most work in the field of nonlinear processes has been restricted to infrared, visible and ultraviolet light, although progress in the development of X-ray lasers has been made recently. With the advent of a free-electron laser in the soft-X-ray regime below 100 nm wavelength, a new light source is now available for experiments with intense, short-wavelength radiation that could be used to obtain deeper insights into the structure of matter. Other free-electron sources with even shorter wavelengths are planned for the future. Here we present initial results from a study of the interaction of soft X-ray radiation, generated by a free-electron laser, with Xe atoms and clusters. We find that, whereas Xe atoms become only singly ionized by the absorption of single photons, absorption in clusters is strongly enhanced. On average, each atom in large clusters absorbs up to 400 eV, corresponding to 30 photons. We suggest that the clusters are heated up and electrons are emitted after acquiring sufficient energy. The clusters finally disintegrate completely by Coulomb explosion.     

Protein images obtained by STM, AFM and TEM.

Scanning tunnelling microscopy and atomic force microscopy, one scanning the tunnelling current and the other the repulsive atomic force between same and probe, can give high-quality surface topographies of proteins, which have been difficult to obtain by more conventional methods such as transmission electron microscopy.     

SSPD的低抖动SFQ信号读数

运用单磁通量量子(SFQ)读取技术的超导单光子探测器(SSPD)可以实现低抖动信号的读出。通过优化SFQ读出电路的电路参数,输入电流灵敏度被改善到10μA以下,且该结果比SSPD典型的临界电流小。实验使用脉冲发生器作为输入脉冲源,结果显示测出的SFQ读出电路的抖动值远低于目前测量装置系统超过15μA的抖动电流值。SSPD连接到SFQ读出电路的测量抖动值在37 ps的半高全宽(FWHM)时的SSPD偏置电流约为18μA,这是对传统的没有SFQ读出电路,抖动为67 ps的FWHM的显著提高。     

A gravitationally lensed quasar with quadruple images separated by 14.62 arcseconds

Gravitational lensing is a powerful tool for the study of the distribution of dark matter in the Universe. The cold-dark-matter model of the formation of large-scale structures (that is, clusters of galaxies and even larger assemblies) predicts the existence of quasars gravitationally lensed by concentrations of dark matter so massive that the quasar images would be split by over 7 arcsec. Numerous searches for large-separation lensed quasars have, however, been unsuccessful. All of the roughly 70 lensed quasars known, including the first lensed quasar discovered, have smaller separations that can be explained in terms of galaxy-scale concentrations of baryonic matter. Although gravitationally lensed galaxies with large separations are known, quasars are more useful cosmological probes because of the simplicity of the resulting lens systems. Here we report the discovery of a lensed quasar, SDSS J1004 + 4112, which has a maximum separation between the components of 14.62 arcsec. Such a large separation means that the lensing object must be dominated by dark matter. Our results are fully consistent with theoretical expectations based on the cold-dark-matter model.     

一种双腔体二甲基硅氧烷液体变焦透镜

针对PDMS(二甲基硅氧烷)液体变焦透镜在使用过程中常会发生边缘脱落从而影响透镜性能甚至毁坏整个器件的问题,提出了一种基于单点金刚石切削和软刻蚀工艺的双腔体可调焦透镜模型,该模型相比仅由单PDMS腔体和PDMS薄膜粘合的结构,能有效防止在大变形条件下变形膜边缘脱落,从而更大可能地保证透镜正常工作.测试结果表明:相比于单腔体的模型,该透镜在保留可调焦透镜性能的同时,具有更好的工作稳定性.     

基于核密度估计尺度空间的目标跟踪算法

为能够准确表示目标颜色分布、适应目标尺寸连续变化,提出了一种新的序列图像目标跟踪算法。该算法首先计算目标区域颜色概率分布的核密度估计函数,然后通过规整化每一帧输入图像像素在此函数上的取值生成目标概率分布图。最后通过检测多尺度规范化Laplacian滤波的极值,实现目标的定位和尺寸描述。与基于直方图的算法比较并结合大量真实序列图像上的实验验证表明,该算法更好地描述了目标颜色特征,提高了跟踪算法的精度。     

堆载预压-强夯法在软基处理中的应用

本文结合福建某港区软土地基处理,详细介绍了堆载预压——强夯法在软土地基加固处理中的施工要点,并通过现场检测试验,表明了这种方法在软土地区应用的可行性。     

锚贴钢板和粘钢加固钢筋混凝土梁受剪性能的比较

锚贴钢板加固法是一种新型补强加固方法.本文通过对1根锚钢加固的钢筋混凝土梁和2根对比梁进行了受剪性能的试验研究.结果表明：锚贴钢板加固能够提高梁的抗剪承载力;改善梁的破坏形态;抑制梁斜裂缝的发展;且锚钢加固施工简单,施工质量容易得到保证.     

应用有限元计算无界冲击电场

绝缘材料承受冲击电压试验时，其电场有两个明显的特征：动态性和无界性。应用有限元的Newmark算法可以方便地计算动态电场。应用映射无限元可以有效地计算无界域。本文着重介绍应用具有映射无限元的Newmark算法解决绝缘材料承受冲击电压陡度时电场分布的计算问题。根据计算可知．样品尺寸大于0．5m．波头Tf小于0．12μs．就需用动态电场的解法来计算它的电位分布．为使映射无限元能嫫拟无限远处的电场分布．其插值形函数必须采用指数衰减形式。     

主体分子D.D与茴香醛包结物的超分子异构现象

1,1,6,6-四苯基-2,4-己二炔-1,6-二醇（D．D）与茴香醛在不同的结晶条件下形成主客体分子物质的量比分别为2：1和1：2的包结物晶体。x-射线单晶衍射测试结果表明,在2：1（h／g）包结物晶体中,D．D通过形成闭合氢键网,构筑了1维zigzag主体分子框架超结构,形成的隧道框架对茴香醛具有识别作用;在1：2（h／g）包结物晶体中,主体分子采取0维框架超结构,按2,次螺旋轴呈zigzag形状排列,茴香醛分子与主体分子通过OH…O强氢键作用进入主体分子构筑的隧道。它们互为超分子异构体。产生异构体的原因是,在前者包结物晶体中,主体分子采取邻位交叉式构象,而在后者的包结物晶体中,主体分子采取对位交叉式构象,因此,它们又是超分子构象异构体。     

棕榈科麒麟血竭与百合科剑叶血竭HPLC指纹图谱分析与比较

采用反相高效液相色谱法,首次建立了进口棕榈科麒麟血竭和国产百合科剑叶血竭HPCL指纹图谱,运用相对指保留指纹谱的方法,对获得的图谱进行数据化处理,得出重叠率、n强峰、特征峰群和特征指纹峰检出率等参数。从中找出不同血竭品种所含化合物之间的相互关系及特征。结果表明,进口血竭与国产血竭的HPLC指纹图谱差异明显,同一品种不同产地国产血竭指纹谱极为相似,但主成分含量有一定的差别。