Host dependent thermal stability and frequency upconversion of Er^3＋-doped heavy metal oxyfluoride germanate glasses

The upconversion properties of Er^3＋-doped heavy metal oxyfluoride germanate glasses under 975 nm excitation have been investigated. The intense green （551 and 529 nm） and relatively weak red （657 nm） emissions corresponding to the transitions ^4S3/2→^4I15/2, ^2H11/2→^4 I15/2 and ^4F9/2 →^4I15/2, respectively, were simultaneously observed at room temperature. The content of PbF2 has an important influence on the upconversion luminescence emission. With increasing content of PbF2, the intensities of green （529 nm） and red （657 nm） emissions increase slightly, while the green emission （551 nm） increases markedly. These results suggest that PbF2 has an influence on the green （551 nm） emission more than on the green （529 nm） and red （657 nm） emissions.     

杂多酸催化合成乙酸乙酯

回流吸附法制备的负载型12-钨磷酸(HPW/C)是合成乙酸乙酯的高效催化剂。最佳反应条件下乙醇转化率达96％,酯化选择性100％。催化剂的高活性是由于HPW在活性炭上高度分散,使活性位增多,有效酸量增大。HPW/C还具有热稳定性高和不易流失等优点。     

Incorporation Behaviour of Arsenic and Phosphorus in GaAsP／GaAs Grown by Solid Source Molecular Beam Epitaxy with a GaP Decomposition Source

The incorporation behaviour of arsenic and phosphorus in the GaAsP ternary alloy under phosphorus-rich conditions is studied based on the incorporation coefficient model and the growth diffusion model combined with the alloy composition data obtained by high resolution x-ray diffraction analysis. It is found that As adatoms have longer surface lifetime and longer migration length than those of P adatoms, which leads to an arsenic incorporation efficiency much higher than that of phosphorous. With the increase of arsenic flux, the surface lifetime of arsenic adatoms decreases due to the competition of As adatoms. The detailed analysis and discussion are given here.     

Application of Electron-Shelving Detection via 423 nm Transition in Calcium-Beam Optical Frequency Standard

A new scheme of small compact optical frequency standard based on thermal calcium beam with application of 423 nm shelving detection and sharp-angle velocity selection detection is proposed. Combining these presented techniques, we conclude that a small compact optical frequency standard based on thermal calcium beam will outperform the commercial caesium-beam microwave dock, like the 5071 Cs clock （from Hp to Agilent, now Symmetricom company）, both in accuracy and stability.     

Effect of Cu doping on the magnetic and electrical properties of n=2 Ruddlesden-Popper manganates

A series of polycrystalline Cu-doped n=2 Ruddlesden-Popper manganates La1.2Sr1.8CuzMn（2-x）O7 （x=0, 0.04, 0.13） were synthesized by the solid state reaction method. The effect of Cu doping on the magnetic and transport properties has been studied. It is found that Cu substitution for Mn greatly affects the magnetic and electrical properties of the parent phase La1.2Sr1.8Mn2O7. With the increase of Cu content, the system undergoes a transition from longrange ferromagnetic order to the spin glass state and further to an antiferromagnetic order. A little of Cu dopant can lead to the samples showing semiconductor or insulator behaviour in the whole observed temperature range while the parent phase has a metal-insulator transition. These samples show colossal magnetoresistance at low temperatures and the value of it decreases with increasing Cu content.     

卤化铅调整Tm3+/Yb3+共掺碲酸盐玻璃上转换发光研究

研究了卤化铅调整Tm3+/Yb3+共掺碲酸盐玻璃的热稳定性能、Raman光谱和上转换发光光谱,分析了Tm3+/Yb3+共掺氧卤碲酸盐玻璃的上转换发光机理.结果发现:混合卤化铅调整Tm3+/Yb3+共掺碲酸盐玻璃具有好的热稳定性能、低的声子能量、强的上转换蓝光.这表明混合卤化铅调整Tm3+/Yb3+共掺碲酸盐玻璃是一种上转换蓝光激光器的潜在基质材料.     

卤化铅调整Tm3+/Yb3+共掺碲酸盐玻璃上转换发光研究

研究了卤化铅调整Tm³⁺/Yb³⁺共掺碲酸盐玻璃的热稳定性能、Raman 光谱和上转 换发光光谱，分析了Tm³⁺/Yb³⁺共掺氧卤碲酸盐玻璃的上转换发光 机理.结果发 现：混合卤化铅调整Tm³⁺/Yb³⁺共掺碲酸盐玻璃具有好的热稳定性 能、低的声 子能量、强的上转换蓝光.这表明混合卤化铅调整Tm³⁺/Yb³⁺共掺碲 酸盐玻璃是一种上转换蓝光激光器的潜在基质材料. 关键词： 氧卤碲酸盐玻璃 上转换光谱 发光机理 上转换蓝光激光器     

2003年全国各地高考数学模拟试题选析——数列

1　高考回顾数列是高中代数的重要内容之一 ,由于它既具有函数特征 ,又能构成独特的递推关系 ,使得它既与中学数学其他部分知识如 :函数、方程、不等式、解析几何、二项式定理等有较紧密的联系 ,又有自己鲜明的特征 ,因此它是历年高考考查的重点、热点和难点 ,在高考中占有极其重要的地位 ,试题往往综合性强、难度大 ,承载着考察学生数学思维能力和分析、建模、解决问题的能力以及函数与方程的思想 ,转化与化归的思想、分类讨论的思想 .从近几年试题来看 ,数列部分内容的分值约占总分的 12 %左右 ,大多为一道选择题或填空题 ,一道解答题 .而…     

带积分环节的隶属度函数中心自适应模糊控制器设计

自适应变论域模糊控制是改变模糊控制性能的主要方法之一,针对自适应变论域模糊控制器的稳定性设计这一难题,将输入和输出的隶属度函数分别用论域值表示成解析形式;针对典型模糊控制系统没有考虑积分环节带来的稳态误差问题,设计一种积分器,并从减小控制规则数目的角度出发设计了针对积分环节的控制规则库;引进Lyapunov函数,设计了输入隶属度函数论域值的自适应律和输出隶属度函数中心取值的自适应律,最后针对Duffing非线性系统仿真,结果表明设计的变论域模糊控制器是可行的。     

地方医学高校以人为本的开放实验室研究探索

从以人为本的教学理念出发,提出了开设地方医学院校化学开放实验室,以培养学生的综合素质和创新能力为目标,满足不同层次学生需求,构建了以“学生为中心、创新能力为主线、自主学习、多元化评价体系”为核心的开放实验室教学观念。探讨了医学类院校采取开放实验室的意义,并利用开放实验室的教学经验对实验教学提供一定的借鉴意义,以期提高高校的实验教学质量。