High-quality GaNAs/GaAs quantum wells with light emission up to 1.44 mu m grown by molecular-beam epitaxy

High-quality GaNAs/GaAs quantum wells with high substitutional N concentrations, grown by molecular-beam epitaxy, are demonstrated using a reduced growth rate in a range of 0.125-1 mu m/h. No phase separation is observed and the GaNAs well thickness is limited by the critical thickness. Strong room-temperature photoluminescence with a record long wavelength of 1.44 mu m is obtained from an 18-nm-thick GaN0.06As0.94/GaAs quantum well. (C) 2005 American Institute of Physics.

4×4热光SOI波导开关阵列

设计并制作了阻塞型和完全无阻塞型4×4热光SOI(silicon-on-insulator)波导开关阵列.开关单元采用了多模干涉耦合器(MMI)-MZI(Mach-Zehnder intederometer)结构的2×2光开关.阻塞型光开关附加损耗为4.8～5.4 dB,串扰为-21.8 dB～-14.5 dB.完全无阻塞型光开关阵列附加损耗为6.6～9.6 dB,串扰为-25.8～-16.8 dB.两者的消光比都在17～25 dB内变化,开关单元功耗小于230 mW.器件的开关时间小于3μs.功耗和开关速度都明显优于SiO_2基和聚合物基的开关阵列.

Design and Fabrication of Thermo-Optic 4×4 Switching Matrix in Silicon-on-Insulator

A rearrangeable nonblocking thermo-optic 4×4 switching matrix,which consists of five 2×2 multimode interference-based Mach-Zehnder interferometer(MMI-MZI) switch elements，is designed and fabricated.The minimum and maximum excess loss for the matrix are 6.6 and 10.4dB,respectively.The crosstalk in the matrix is measured to be between －12 and －19.8dB.The switching speed of the matrix is less than 30μs.The power consumption for the single switch element is about 330mW.

The PPh3 ligand modified Rh/SiO2 catalyst for hydroformylation of olefins

A novel family of hybrid catalyst with high turnover frequency (TOF) and high selectivity towards aldehydes for hydroformylation of olefins could be successfully approached through direct coordination with the PPh3 ligand to the highly dispersed Rh metal particle precursors. A further advantage is that the catalyst is easily prepared and recyclable. The results revealed that hydroformylation of olefins to aldehydes dominantly took place on the surface of PPh3 ligand modified Rh metal particles of the hybrid catalyst. It was found that the formation of chemical coordination bond between the Rh metal particles and the lone-pair electron of PPh3 was evident through the TG and P-31 NMR measurement. Moreover, the addition of PPh3 onto the Rh/SiO2 exert a significant influence on the adsorption state of reactant CO, H-2 and C2H4 on the PPh3-Rh/SiO2 sample, which probably lead to good catalytic performances for hydroformylation of olefins. (C) 2004 Elsevier B.V. All rights reserved.

Preparation and characteristics of nonflammable polyimide materials

The thermal and flame-retardant properties of homo- and copolyimides were evaluated. Those containing sulfone linkages in the backbone were found to be more flame retardant. Both properties were dependent on the composition. A polyimide/silica nanocomposite was obtained through sol-gel processing. The effects of the addition of silica an the dispersion, interfacial adhesion, fire resistance, mechanical properties, and thermal stability of the composites were investigated. SEM analysis showed a good dispersion of silica with a diameter of 50-300 nm in the organic matrices. The addition of silica increased the fire retardancy and mechanical properties of the composites. (C) 2000 John Wiley & Sons, Inc.

沈阳市建成区树种现状分析

通过对沈阳市建成区城市树木的调查分析发现:沈阳市的各土地类型中的树木分布不均,其中,被调查的256块样地中每公顷物种小于或等于5种的样地有113块,占总调查样地的44.14%,每公顷小于或等于10株的样地共43块,占总样地的16.80%;利用树种多度重要性排序及累积贡献率获得了不同土地类型中的主要树种;多个生物多样性指数表明,公园性质的绿地树种多样性最高,企事业单位用地与居住区用地次之,街道类用地较低,而商业金融用地最低;并对沈阳市的树种发展提出建议。