Heterogeneous photobleaching in confocal microscopy

Photobleaching was studied during recording of confocal scanning laser microscopy. Studies on fluorescent gels of FITC-labeled dextran were used to evaluate differential bleaching along thez-axis. Differential bleaching along the z-axis was observed and it was seen that this was related to the numerical aperture of the objective in use. This points to the conclusion that photon energy flux density is an important parameter in photobleaching. To check if photon energy flux density heterogeneity is affected by local variation in the refractive index of the sample, photobleaching rates were calculated for different fluorescent objects (sections of seeds, animal cells stained with nuclear stains, immunocytochemistry preparations) and a pronounced similarity was found between photobleaching rates and DIC images.     

Ag+掺杂的立方相Y2O3:Eu纳米晶体粉末发光强度研究

采用化学自燃烧法制备了不同Ag⁺掺杂浓度的Y₂O₃:Eu纳米晶体粉末样品(［Y³⁺］∶［Eu³⁺］∶［Ag⁺］=99∶1∶X，X=0—3.5×10^-2)，以及通过退火处理得到了相应的体材料.根据X射线衍射谱确定所得纳米和体材料样品均为纯立方相.实验表明在纳米尺寸样品中随着Ag离子浓度的增加，荧光发射强度随之增加，当X=2×10^-2时达到最大值，其发光强度比X=0时提高了近50%.当Ag离子浓度继续增加，样品发光强度保持不变.在相应的体材料样品中则没有观察到此现象.通过对各样品的发射光谱，激发光谱，X射线衍射图谱，透射电镜(TEM)照片和荧光衰减曲线的研究，分析了引起纳米样品荧光强度变化的原因是由于Ag离子与表面悬键氧结合，从而使这一无辐射通道阻断，使发光中心Eu³⁺的量子效率提高；Ag⁺的引入所带来的另一个效应是使激发更为有效.这两方面原因使发光效率得到了提高.     

Applications of synchrotron radiation in materials analysis

The synchrotron radiation (SR) emitted by circulating high-energy electrons has extraordinary properties: The light is intensive and bright, it is tunable and highly collimated, and finally, it is linearly polarized. These exceptional properties have initiated a unique revival of many spectroscopies using electromagnetic radiation. The techniques of special concern for materials analysis which are treated in this article are: X-ray absorption, reflection, fluorescence, diffraction and topography. A number of examples will be given in order to illustrate the possibilities of these techniques when SR is used.On leave of absence from Institut für Festkörperforschung, KFA Jülich, D-5170 Jülich, Federal Republic of Germany     

原子力显微镜在生物物理领域的新应用

介绍了原子力显微镜在生物物理领域的最新应用:蛋白质去折叠、DNA拉伸、生物膜受力,通过分析实验得到的力谱,可以获取关于蛋白质、DNA、生物膜结构信息.原子力显微镜不仅能反映测量体系的力学性质,由于其具有独特的时间、空间分辨及实时成像,因而能提供更多信息.     

B_2分子X~3Σ_g~-和A~3Σ_u~-态的势能函数

使用SAC/SAC-CI方法,利用D95(d),6-311g**以及cc-PVTZ等基组,对B2分子的基态(X3Σg-)和第一激发态(A3Σu-)的平衡结构和谐振频率进行了优化计算.通过对3个基组的计算结果的比较,得出了D95(d)基组为3个基组中的最优基组的结论;使用D95(d)基组,利用SAC的GSUM(Group Sum of Operators)方法对基态(X3Σg-),SAC-CI的GSUM方法对激发态(A3Σu-)进行单点能扫描计算,用正规方程组拟合Murrell-Sorbie函数,得到了相应电子态的完整势能函数;从得到的势能函数计算了与基态(X3Σg-)和第一激发态(A3Σu-)相对应的光谱常数(Be,αe,ωe和ωeχe),结果与实验数据吻合.     

GaN氢化物气相外延生长系统的设计与制作

根据GaN氢化物气相外延生长(HVPE)的原理,设计制作了双温区卧式HVPE系统．根据实际生长中出现的问题和CaN样品的测试情况,对系统进行了逐步的调试和改进．     

Effect of the Parameters of Three-Mirror Resonators on the Spectral Characteristics of Single-Pulse Laser Generation with Self-Injection of Priming Radiation

Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency.     

Quadrilateral surface meshes without self-intersecting dual cycles for hexahedral mesh generation

Several promising approaches for hexahedral mesh generation work as follows: Given a prescribed quadrilateral surface mesh they first build the combinatorial dual of the hexahedral mesh. This dual mesh is converted into the primal hexahedral mesh, and finally embedded and smoothed into the given domain. Two such approaches, the modified whisker weaving algorithm by Folwell and Mitchell, as well as a method proposed by the author, rely on an iterative elimination of certain dual cycles in the surface mesh. An intuitive interpretation of the latter method is that cycle eliminations correspond to complete sheets of hexahedra in the volume mesh.

Although these methods can be shown to work in principle, the quality of the generated meshes heavily relies on the dual cycle structure of the given surface mesh. In particular, it seems that difficulties in the hexahedral meshing process and poor mesh qualities are often due to self-intersecting dual cycles. Unfortunately, all previous work on quadrilateral surface mesh generation has focused on quality issues of the surface mesh alone but has disregarded its suitability for a high-quality extension to a three-dimensional mesh.

In this paper, we develop a new method to generate quadrilateral surface meshes without self-intersecting dual cycles. This method reuses previous b-matching problem formulations of the quadrilateral mesh refinement problem. The key insight is that the b-matching solution can be decomposed into a collection of simple cycles and paths of multiplicity two, and that these cycles and paths can be consistently embedded into the dual surface mesh.

A second tool uses recursive splitting of components into simpler subcomponents by insertion of internal two-manifolds. We show that such a two-manifold can be meshed with quadrilaterals such that the induced dual cycle structure of each subcomponent is free of self-intersections if the original component satisfies this property. Experiments show that we can achieve hexahedral meshes with a good quality.