一种新型的5GHz自适应偏置及可变增益低噪声放大器

该文提出了一种新型的自适应偏置及可变增益低噪声放大器（LNA），利用电荷泵（亦称电压倍增器）将LNA输出信号转换成与LNA射频输入信号功率成比例变化的直流信号，以此信号同时反馈控制LNA的偏置和增益，来实现自适应偏置以及可变增益低噪声放大器。从而极大地改善了LNA的输入线性范围。鉴于5GHz频率下，Bipolar相对于CMOS更好的频率特性和低噪声特性，该项研究采用了BiCMOS工艺，实现了低于3．0dB的噪声系数（高增益状态下）和大约13dBm的输入三阶交调点ⅡP3的控制范围以及大于15dB的增益控制范围。

MOCVD-Grown AlGaN/AlN/GaN HEMT Structure with High Mobility GaN Thin Layer as Channel on SiC

AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with a high-mobility GaN thin layer as a channel are grown on high resistive 6H-SiC substrates by metalorganic chemical vapor deposition. The HEMT structure exhibits a typical two-dimensional electron gas (2DEG) mobility of 1944cm2/(V · s) at room temperature and 11588cm2/(V· s) at 80K with almost equal 2DEG concentrations of about 1.03 × 1013 cm-2 High crystal quality of the HEMT structures is confirmed by triple-crystal X-ray diffraction analysis. Atomic force microscopy measurements reveal a smooth AlGaN surface with a root-mean-square roughness of 0. 27nm for a scan area of 10μm × 10μm. HEMT devices with 0.8μm gate length and 1.2mm gate width are fabricated using the structures. A maximum drain current density of 957mA/mm and an extrinsic transconductance of 267mS/mm are obtained.

Wide-Band Polarization-Independent Semiconductor Optical Amplifier Gate with Tensile-Strained Quasi-Bulk InGaAs

A semiconductor optical amplifier gate based on tensile-strained quasi-bulk InGaAs is developed. At injection current of 80mA,a 3dB optical bandwidth of more than 85nm is achieved due to dominant band-filling effect.Moreover, the most important is that very low polarization dependence of gain (＜0. 7dB),fiber-to-fiber lossless operation current (70～90mA) and a high extinction ratio (＞50dB) are simultaneously obtained over this wide 3dB optical bandwidth (1520～1609nm) which nearly covers the spectral region of the whole C band (1525～1565nm)and the whole L band (1570～ 1610nm). The gating time is also improved by decreasing carrier lifetime. The wideband polarization-insensitive SOA-gate is promising for use in future dense wavelength division multiplexing (DWDM) communication systems.

Investigation of high cycle and Very-High-Cycle Fatigue behaviors for a structural steel with smooth and notched specimens

The high cycle and Very-High-Cycle Fatigue (VHCF) properties of a structural steel with smooth and notched specimens were studied by employing a rotary bending machine with frequency of 52.5 Hz. For smooth specimens, VHCF failure did occur at fatigue cycles of 7.1 x 10(8) with the related S-N curve of stepwise tendency. Scanning Electron Microscopy (SEM) was used for the observations of the fracture surfaces It shows that for smooth specimens the crack origination is surface mode in the failure regime of less than 10(7) cycles While at VHCF regime, the material failed from the nonmetallic inclusion lies in the interior of material, leading to the formation of fisheye pattern. The dimensions of crack initiation region were measured and discussed with respect to the number of cycles to failure. The mechanism analysis by means of low temperature fracture technique shows that the nonmetallic inclusion in the interior of specimen tends to debond from surrounding matrix and form a crack. The crack propagates and results to the final failure. The stress intensity factor and fatigue strength were calculated to investigate the crack initiation properties. VHCF study on the notched specimens shows that the obtained S-N curve decreases continuously. SEM analysis reveals that multiple crack origins are dominant on specimen surface and that fatigue crack tends to initiate from the surface of the specimen. Based on the fatigue tests and observations, a model of crack initiation was used to describe the transition of fatigue initiation site from subsurface to surface for smooth and notched specimens. The model reveals the influences of load, grain size, inclusion size and surface notch on the crack initiation transition. (C) 2010 Elsevier Ltd. All rights reserved

同位旋非对称核物质状态方程

为了确定同位旋非对称核物质状态方程,利用同位旋有关的量子分子动力学理论计算和寻找实验上对于中能重离子碰撞中核子-核子碰撞截面或者对称势非常灵敏的物理观测量——探针.结果发现了几种分别对于核子-核子碰撞截面或者对称势非常灵敏的物理观测量.并对这些探针的机理进行了仔细研究,对以上研究结果进行小结和讨论,并为今后继续深入研究工作提出展望.

长白山地区散射辐射与云的关系

根据中国科学院长白山森林生态系统定位站1982—2001年太阳辐射和云的观测资料对散射辐射及散射比进行了分析,探讨了散射辐射及散射比的日、季节、年际变化特征以及云量、云状、太阳高度角与散射辐射及散射比的关系。结果表明:1)散射辐射日变化特点是,中午最大,早晚较小;季节变化特点是,7月最大,年初和年末较小;年际变化特点是从1982—2001年呈减少趋势;散射比1d中中午最小,7月达到最大值,年际变化为0.38～0.55;2)散射辐射及散射比均随高云量或低云量增加而呈增加趋势;散射辐射日平均量及散射比与总云量和低云量的日平均值均呈线性正相关关系,且与总云量的关系比与低云量的关系更密切;3)不同云相比较,散射辐射和散射比最大的是高积云(Ac),卷云(Ci)次之,较小为对流性积云(积雨云Cb、积云Cu),碧空时散射辐射及散射比最小;4)散射辐射随太阳高度角增加而增大,呈二次函数关系;散射比随太阳高度角增加而减小且呈二次函数关系。

稠油污染土壤的生物修复应用研究

目的研究微生物-植物联合对稠油污染土壤的修复效果,为石油污染土壤生物修复技术的应用提供依据.方法将高效降解菌B2020以及B22发酵产生的生物表面活性剂加入稠油污染土壤,再施用复合肥和柴油补充土壤中的营养物质和代谢底物,分析微生物-植物联合修复的效果.结果试验结果表明,降解效果最好的组合为,处理时间为120 d,菌剂(每kg土中)投加量为50 g,生物表面活性剂(每kg土中)投加量为100 g,复合肥(每kg土中)投加量为0.1 g.结论在植物生长初期(40 d),影响石油污染土壤总石油烃(TPH)降解的显著因子为投加菌剂量;植物生长中期和后期(80 d,120 d),影响TPH降解率的因子为生物表面活性剂和施肥水平.