Preparation and luminescence study of Eu(III) titanate nanotubes and nanowires using carbon nanotubes as removable templates

Eu(III) titanate nanotubes and nanowires have been successfully synthesized by solvothermal method using carbon nanotubes (CNTs) as removable templates. The products were characterized by X-ray diffraction spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry, thermogravimetric and differential thermal analysis. It is demonstrated that CNTs are fully coated with an amorphous Eu₂(TiO₃)₃ layer, which is about 10 nm thick and almost continuous and uniform. After the Eu₂(TiO₃)₃/CNTs composites have been calcined at various temperatures, Eu₂(TiO₃)₃ nanotubes and nanowires are obtained by removing the CNTs templates. The diameter of the Eu₂(TiO₃)₃ nanotubes is 40–60 nm, which is consistent with that of CNTs. Both nanotubes and nanowires have a narrow distribution of diameters. The fluorescence properties of the Eu₂(TiO₃)₃ nanotubes and nanowires calcined at various temperatures have been investigated. The results indicate that when the Eu₂(TiO₃)₃/CNTs composites were calcined at 700 °C for 5 h, the Eu₂(TiO₃)₃ nanotubes obtained can be effectively excited by 395 nm light, and exhibit strong red emission around 616 nm. It is very interesting to discover that a few residual carbons doped in Eu₂(TiO₃)₃ nanotubes and many oxygen vacancies could promote the intensity of red emission peak of Eu³⁺ ions. In addition, Eu₂(TiO₃)₃ nanowires calcined at 900 °C for 5 h also have a strong red emission peak due to many oxygen vacancies and defects formed on the surface of the nanowires and inside them.     

丰中子奇异核17B的实验研究

在兰州重离子加速器国家实验室(HIRFL)放射性次级束流线(RIBLL)上,用束流透射法测量了丰中子奇异核17B与C靶反应的总截面.假定17B具有15B(核芯) 2n结构,采用Gauss HO形式的密度分布和零力程Glauber模型进行计算的结果可以很好地拟合实验数据,并得出17B的密度分布有一个很大的弥散,表明17B是双中子晕核.     

斜入射弹丸速度测量系统研究

天幕靶是用于测量弹丸速度较为普遍的光学测量仪器。在测量弹丸速度时,要求弹道垂直于天幕靶的靶面,当弹道不垂直预定靶面时,弹丸飞越两个天幕靶靶面的实际距离与两靶靶距存在一定的误差,斜入射角度越大误差越大。提出了一种用6个天幕构成天幕阵的速度测量系统。当弹丸以任意方向穿越6个天幕时,测时仪记录弹丸穿越各个天幕的时间间隔,根据这些时间间隔便可以求出弹丸的速度值和速度的飞行方向。该方案解决了弹丸斜入射时速度测量不准的问题,特别适用于枪弹末速度的测量。     

A novel two‐dimensional cobalt(II) coordination polymer with 1,4‐bis(1,2,4‐triazol‐1‐yl­methyl)­benzene

In the crystal structure of the title complex, poly­[[di­azidocobalt(II)]‐di‐μ‐1,4‐bis(1,2,4‐triazol‐1‐yl­methyl)­benzene‐κ⁴N⁴:N^4′], [Co(N₃)₂(bbtz)₂]_n, where bbtz is 1,4‐bis(1,2,4‐triazol‐1‐yl­methyl)­benzene (C₁₂H₁₂N₆), the Co^II atom, which lies on an inversion centre, is six‐coordinated by four N atoms from four bbtz ligands and by two N atoms from two azide ligands, in a distorted octahedral coordination environment. The Co^II atoms are bridged by four bbtz ligands to form a two‐dimensional [4,4]‐network.     

六味药材中重金属含量的测定

采用原子吸收分光光度法和原子荧光光谱法测定 6味中药材中重金属铅、铜、镉、砷、汞的含量。方法操作简便、快速 ,且准确度和精密度高 ,适用于中药材中这 5种重金属的含量测定 ,结果令人满意     

双频磁绝缘线振荡器二维周期结构研究

推导了双频磁绝缘线振荡器（BFMILO）慢波结构的本征方程,并研究了其色散特性和场分布.通过研究发现,通过引入角向分区,使BFMILO慢波结构表现出二维周期性的特点,在该慢波结构中,不同电磁模式集中在角向不同区域,传统磁绝缘线振荡器（MILO）中呈现竞争关系的两个不同电磁模式可以同时独立稳定地参与束-波换能,从而产生双频输出.该分析方法可以适用于多频磁绝缘线振荡器的研究. 关键词： 磁绝缘线振荡器 高频特性 双频 高功率微波     

Heavy-to-light transition form factors and their relations in light-cone QCD sum rules

The light-cone QCD sum rules approach improved by using the chiral current correlator is systematically reviewed and applied to the calculation of all the heavy-to-light form factors, including all the semileptonic and penguin ones. By choosing suitable chiral currents, the light-cone sum rules for all the form factors are greatly simplified and depend mainly on one leading-twist distribution amplitude of the light meson. As a result, relations between these form factors arise naturally. At the considered accuracy, these relations reproduce the results obtained in the literature. Moreover, since the explicit dependence on the leading-twist distribution amplitudes is preserved, these relations may be more useful to simulate the experimental data and extract information on the distribution amplitude.     

Existence of positive solutions for fourth‐order impulsive integral boundary value problems on time scales

This paper is devoted to the existence of positive solutions for a fourth‐order impulsive boundary value problem with integral boundary conditions on time scales. Existence results of at least two and three positive solutions are established via the double fixed point theorem and six functionals fixed point theorem, respectively. Also, an example is given to illustrate the theoretical results. Copyright © 2017 John Wiley & Sons, Ltd.     

求解椭圆边值问题惩罚形式的间断有限元方法

本文提出了一个新的求解二阶椭圆边值问题的惩罚形式间断有限元方法并给出了稳定性和收敛性分析. 特别地,本文建立了间断有限元解的基于余量的后验误差估计,给出了求解间断有限元方程的自适应算法.       

Low-temperature sintering and microwave dielectric properties of Ca2Zn4Ti15O36 ceramics

The sintering behavior, microstructures, and microwave dielectric properties of Ca₂Zn₄Ti₁₅O₃₆ ceramics with B₂O₃ addition were investigated. The crystalline phases and microstructures of Ca₂Zn₄Ti₁₅O₃₆ ceramics with 0-10 wt% B₂O₃ addition were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The sintering temperature of Ca₂Zn₄Ti₁₅O₃₆ ceramic was lowered from 1170 to 930 °C by 10 wt% B₂O₃ addition. Ca₂Zn₄Ti₁₅O₃₆ ceramics with 8 wt% B₂O₃ addition sintered at 990 °C for 2 h exhibited good microwave dielectric properties, i.e., a quality factor (Qf) 11,400 GHz, a relative dielectric constant (ε_r) 41.5, and a temperature coefficient of resonant frequency (τ_f) 94.4 ppm/°C.