Role of the evanescent states in the electron transport in quantum waveguides

Recognizing the computational difficulty due to the exponential behavior of the evanescent states in the calculations of the electron transmission in waveguide structures, the authors propose two transfer matrix methods and apply them to investigate the influence of the evanescent states on the electron wave propagation. The study shows that the effect of the evanescent states on the electron transport is obvious when the electron energy is close to the subband minima. The results show that the calculated transmissions are much enhanced if the evanescent states are omitted in the calculations. For the multiple-stub structures, it is found that the connecting channel length has a critical effect on the electron transmission depending on it larger or smaller than the attenuation lengths of evanescent states. Based on the study of the evanescent states, a new kind of waveguide structures which exhibit quantum modulated transistor action is proposed. (C) 1997 American Institute of Physics.

极低阈值脊形波导GaAs/AlGaAs GRIN-SCH SQW激光二极管

报道了极低阈值电流脊形波导～0.85 μm GaAs/AlGaAs GRIN-SCH SQW激光二极管优化设计、器件制备和特性。获得了2.2～4 mA的极低阈值电流和～0.6 mW/mA的微分量子效率。70℃,3 mW恒功率寿命试验,推测器件平均工作寿命大于4万小时。

Comparative on causes and accumulation of selenium in the tree-rings ambient high-selenium coal combustion area from Yutangba；Hubei；China

IEECAS SKLLQG

近40a来新疆地区太阳辐射状况研究

IEECAS SKLLQG

HIRFL新的束流分配系统

随着CSR的建成和兰州重粒子加速系统(HIRFL)实现质子加速,HIRFL现有的束流传输系统已不能满足越来越多的物理实验对供束时间的要求,为此,对原有的HIRFL的束流输运系统进行了分时供束改造,新的束流分配系统可以在给CSR供束和不供束两种情况下,同时使用SFC和SSC的束流在多个实验终端进行物理实验,介绍了新设计的HIRFL束流分配系统的布局和束流光学计算结果。

Difference of ZSM-5 zeolites synthesized with various templates

ZSM-5 zeolites with similar SUM ratio were synthesized successfully using various templates (n-butylamine (BTA), ethylamine (ETA), isopropylamine (IPA), ethylenediamine (EDA), ethanol (ETL), ethanol-ammonium (ETL-AM) and no template (NT)) under hydrothermal conditions. The samples were characterized by XRD, SEM, XRF, NH3-TPD and BET surface area measurements in order to understand the template effects and the differences of the ZSM-5 samples. The synthesis of ZSM-5 with organic templates was relatively easier than those with inorganic templates and without template. SEM results revealed that ZSM-5 synthesized with different templates had different morphology and particle size. The Si/Al ratio and BET specific surface area of the sample with ethanol as template was the lowest. NH3-TPD results showed that the sample synthesized without template had fewer strong acid sites than others. n-Hexane cracking reaction was carried out over the samples to evaluate the catalytic properties. All ZSM-5 zeolites were effective in n-hexane cracking reaction, especially for the sample synthesized without template. (C) 2004 Elsevier B.V. All rights reserved.

长期施肥对土壤活性有机碳指标的影响

以棕壤长期肥料定位试验地土壤为试材,研究和对比了不同施肥处理耕层土壤各项活性有机碳指标对长期施肥的响应。研究结果表明,长期施用化肥、有机肥以及有机肥配施化肥均显著改变了土壤总有机碳(TOC)含量。与此同时,土壤的轻组有机碳(LFOC)、易氧化有机碳(ROC)和微生物量碳(MBC)含量亦对长期施肥产生与TOC基本一致的响应。相关分析结果表明,土壤的LFOC、ROC和MBC可以作为长期施肥对土壤TOC影响的评价指标,且三者的指示灵敏度依次为MBC>LFOC>ROC。

道地药材牛蒡子适宜产区划分

牛蒡子为两年生菊科植物牛蒡(Arctium lappa L.)的干燥成熟果实,又名大力子。牛蒡在全国各地均有分布,据《中华人民共和国药典》记载,牛蒡子主要有四大产区:东北产区、华东产区、西南产区和华中产区。过去认为牛蒡子以浙江一带所产的为好,目前牛蒡子被认为是关药,以东北产的为佳。目前,有关牛蒡子的道地药材产区仍然存在争议。因此,科学划分牛蒡子的道地产区,不仅可以解决争议,而且对牛蒡的引种栽培具有重要的实践指导意义。本研究运用多元统计方法,确定影响牛蒡子道地性各环境因子的权重,在地理信息系统ArcGis9.0的支持下,进行牛蒡子产地适宜性划分,结果表明:牛蒡的最适宜分布区沿西南-东北方向呈现条带状分布,主要分布在东北、华北和西南地区。与《中华人民共和国药典》中记载的产区基本相近。但是,笔者的研究结果与药典记载也存在差异,华北(包括北京、天津、河北、山西、内蒙古)和西北(宁夏、新疆、陕西、甘肃)也是牛蒡的集中分布区;原来以浙江为主的华东产区,现在以山东为主;东北地区的吉林和黑龙江也是牛蒡子的主产区;西南地区牛蒡子的产区除了四川和重庆外,还包括云南和贵州;在华南和华中地区的分布较少。造成这种情况的原因可能是人为干扰(如人为拔除、除草剂的大量使用等)和气候变化影响。