稀有糖的合成方法研究

稀有糖广泛存在于天然产物及药物分子中, 并发挥着重要的生物作用. 药物分子的糖基多样化修饰使得稀有糖的合成受到越来越多的关注. 从以普通糖为原料合成稀有糖和以非糖化合物为原料合成稀有糖两个方面综述了近年来的稀有糖合成进展.     

Strain-Compensated InGaAs/InAlAs Quantum Cascade Detector of 4.5 μm Operating at Room Temperature

We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron transfer on a cascade of quantum levels which is designed to provide longitudinal optical phonon extraction stairs. By careful structure design and growth, the whole epilayer has a residual strain toward InP substrate of only -2.8× 10^-4. A clear narrow band detection spectrum centered at 4.5 μm has been observed above room temperature for a device with 200／times 200 ×μm^2 square mesa.     

High-Duty-Cycle Operation of GaAs/AlGaAs Quantum Cascade Laser above Liquid Nitrogen Temperature

We present a detailed study of λ- 9.75 μm GaAs/AlGaAs quantum cascade lasers. For a coated 2-rmm-long and 40-μm-wide laser, an optical power of 85 μ W is observed at 95% duty cycle at 80K. At a moderate driving pulse （1 kHz and 1% duty cycle）,the device presents a peak power more than 20mW even at 120K. At 80K, the fitted result of threshold current densities shows evidence of potential cw operation.     

Magnetic properties and magnetoresistance of HfFe2Ge2-type Dy1-xGdxMn6Ge6 (x=0.1－0.6) compounds

The magnetic properties and magnetoresistance effects of Dy_{1-x}Gd_xMn_6Ge_6 (x=0.1－0.6) compounds have been studied by magnetic properties and resistivity measurements in applied magnetic fields up to 5T. The compounds with x=0.1, 0.2, 0.4 and 0.5 order antiferromagnetically at 425, 428, 430 and 432K, respectively, and there are second magnetic phase transitions below 100K. The compound with x=0.6 exhibits a transition from ferrimagnetic to antiferromagnetic, then to ferrimagnetic state again with decreasing temperature. Furthermore, it displays a field-induced metamagnetic transition, and its threshold field decreases with increasing temperature. The magnetoresistance curve of the compound with x=0.6 in applied magnetic fields up to 5T is presented and the magnetoresistance effects are related to the metamagnetic transitions.     

微孔分子筛主-客体复合体系及其电子转移过程

沸石分子筛是一类带有规则微孔结构的硅铝酸盐晶体,因其骨架具有独特的电子给受能力而备受关注．由此,许多以微孔分子筛为主体的电子转移体系被构建并深入研究．与溶液相中自由基的快速衰减不同,产生于微孔分子筛内部的自由基受其纳米孔道的限制,具有有限的迁移率和较长的寿命,有助于人们利用传统光谱技术确定反应机理．本文主要对当前微孔分子筛主-客体复合体系中的电子转移过程和机制的研究现状加以论述．     

Single-mode surface-emitting distributed feedback quantum-cascade lasers based on hybrid waveguide structure

Surface-emitting distributed feedback quantum-cascade lasers operating at λ≈7.8 μm are demonstrated. The metal-covered second-order grating is shallow-etched into the surface of a thin InGaAs contact and cladding layer. This forms a hybrid waveguide and used to achieve relatively low waveguide losses and high coupling strengths. The devices exhibit stable single-mode operation from 90 to 130 K with a side mode suppression ratio above 20 dB. A slope efficiency of 194 mW/A is obtained at 90 K, which is twice higher than that of the Fabry-Perot counterpart.     

用气体摆的原理制作平衡姿态传感器

在柱状的密闭腔内沿轴向对称的位置设置2根平行的热敏丝,腔内近热源处的气体由于密度小向上运动,腔壁处密度大的气体受重力场作用向下运动,形成气体摆,气体的密度差是由温度差引起的.将2根热敏丝r1和r2组成惠斯通电桥的2个可变臂,它们既做热源,又兼敏感元件.通电时,热敏丝加热腔内气体,当两根热敏丝平置时,由于受气流影响相同,r1=r2,电桥输出的电压为零,当它们倾斜时,热敏丝受不同气流影响,r1≠r2,电桥输出电压不为零.平衡姿态传感器就是根据倾斜角度和温度的关系设计的.     

功能性两亲嵌段共聚物的研究进展

功能性两亲嵌段共聚物因自身独特的性质而在靶向输送、控制释放、分子识别等领域得到广泛的应用.本文对这类嵌段共聚物的合成方法、其胶束的形成机理、制备形式、表征手段以及一些常见的具有光学活性的两亲嵌段共聚物及其应用进行了综述.     

High-Power and Low-Threshold-Current-Density GaAs/AlGaAs Quantum Cascade Lasers

We report on the realization of GaAs/AlGaAs quantum cascade lasers with an emission wavelength of 9.1 μm above the liquid nitrogen temperature. With optimal current injection window and ridge width of 24 and 60μm respectively, a peak output power more than 500mW is achieved in pulsed mode operation. A low threshold current density Jth = 2.6 kA/cm^2 gives the devices good lasing characteristics. In a drive frequency of i kHz, the laser operates up to 20% duty cycle.