Substrate surface atomic structure influence on the growth of InAlAs quantum dots

We have examined the influence of substrate surface orientation on self-assembled InAlAs/AlGaAs quantum dots grown on (0 0 1) and (n 1 1) A/B (n = 3, 5) GaAs substrates by molecular beam epitaxy (MBE). Preliminary characterizations have been performed using photoluminescence (PL) and transmission electron microscopy (TEM). The PL emission energies of quantum dots on high Miller index surface are found to be strongly dependent on the atomic-terminated surface (A or B surface) of the substrate. We observed that there were planar ordering larger islands on (3 1 1)B surface compared to (0 0 1) surface, in contrast, a rough interface and smaller "grains" on (3 1 1)A surface, this result is identical with PL emission energy from these islands. We propose that the rapid strain-induced surface "roughening" impedes the formation of 3D islands on A surface, and indicating that this is a promising approach of the realization of ordering distribution on (3 1 1)B plane for devices such as red-emitting semiconductor quantum dots lasers. (C) 1999 Elsevier Science B.V. All rights reserved.

Characteristics of triangle and square InP/InGaAsP microlasers

Directional emission triangle and square InGaAsP/InP lasers have been fabricated by standard photolithography, inductively coupled plasma etching technique combined with wet chemical etching process. In this article, the characteristics of the microcavity lasers are presented. For an equilateral triangle microcavity laser with the side length of 30 mu m, we got the laser spectra fitted very well with the mode wavelength formulate LIP to the 8(th) transverse mode at room temperature. But the laser spectra are usually more complex than the formulae for the lasers, especially for the lasers with a smaller side length. For a square microcavity laser with side length of 20 mu m, we observed the mode competition between the Fabry-Perot (FP) modes and Whispering-Gallery (WG) modes at 200K. The output spectra below the threshold have the mode interval of FP modes with a large mode interval, and the laser spectra agree very well with the WG modes, which have mode interval less than the FP modes. The output spectra are dominated by the FP modes below the threshold, because the FP modes have a higher output coupling efficiency than the WG modes.

Edge dislocation of b=[001]/2 in the InAs nanostructure on InP(001)

The self-organized InAs/In0.52Al0.48As nanostructure were grown on InP (001) using molecular beam epitaxy (MBE). The nanostructure has been studied using transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The edge dislocations with the Burgers vector b = ([001]/2) and extending along the [$(110) over bar $] direction are observed. The results show that in the region near an edge dislocation, no InAs wires were formed, while in the regions free of dislocation, wire-like nanostructures were formed. The mechanisms for the formation of the [001]/2 edge dislocations were discussed.

基于JMF的跨平台视频点播系统的设计与实现

利用Java媒体框架(JMF)开发的视频点播系统具有开发简单、跨平台、提供QoS保证和交互性好等优点,具有广泛的应用前景.介绍了JMF应用编程接口的特点和结构,阐述了基于JMF开发的跨平台的视频点播系统的整体结构设计,并详细介绍了基于RTP的实时媒体传输、基于RTCP的拥塞控制、完整VCR操作和穿越NAT等关键技术的具体实现.

无线自组网络中基于簇结构的安全方案

无线自组网络是一种不需要基础通信设施的自组织网络，正得到越来越多的应用．当前自组网络的安全性研究正成为一个热点．对基于簇结构的自组网络进行了安全分析，并且针对存在的安全问题提出了新的安全解决方案．主要贡献在于：①提出了一个保护簇首的安全机制；②针对节点簇间漫游的安全隐患，提出一个基于请求的节点信息共享机制，并给出了相应的算法．对该方案进行了仿真实验，结果显示，该方案具有充分的可行性．与已有方案相比，该方案具有较完善的安全机制，网络性能也较好．

TAE模式的分析和改进

TAE(tweakable authenticated encryption)模式是一种基于可调分组密码的加密认证模式.研究结果表明,安全的可调分组密码不是安全的TAE模式的充分条件.只有当可调分组密码是强安全的时候,TAE模式才是安全的.同时,还给出了TAE模式的一些改进,得到模式MTAE(modified tweakable authenticat edencryption),并且证明了其安全性.

非结构化P2P系统Overlay优化技术综述

非结构化P2P Overlay网络的结构松散,网络中资源的分布没有明确的限制,这使得非结构化P2P Overlay网络中的资源搜索在很大程度上依赖于通信开销巨大的泛洪法,因而非结构化P2P系统在伸缩性,可用性等方面,存在明显的不足.非结构化P2P Overlay网络的上述特点决定了非结构化P2P Overlay优化技术的重要性.本文分四大类别,对非结构化P2P Overlay优化技术进行了介绍,分析比较了各类方法的优劣以及它们的适用场合,并在此基础上对未来工作进行了展望.

基于TPM的可信文件系统CIVFS的研究和实现

本文提出一种利用可信计算技术增强文件系统可信性的方法，以Linux为基础，设计实现了一个可信文件系统原型CIVFS。CIVFS是一个结合加密和完整性校验两种保护措施的文件系统，它借助堆式文件系统技术，嵌入在Linux内核中，添加了文件加密和完整性校验模块，利用TPM芯片提供的可信计算和安全存储等功能，增强了对系统安全组件和数据的安全保护。

Study on biomass circulation and gasification performance in a clapboard-type internal circulating fluidized bed gasifier

We investigated the solid particle flow characteristics and biomass gasification in a clapboard-type internal circulating fluidized bed reactor. The effect of fluidization velocity on particle circulation rate and pressure distribution in the bed showed that fluidization velocities in the high and low velocity zones were the main operational parameters controlling particle circulation. The maximum internal circulation rates in the low velocity zone came almost within the range of velocities in the high velocity zone, when uH/umf = 2.2-2.4 for rice husk and uH/umf = 3.5-4.5 for quartz sand. In the gasification experiment, the air equvalence ratio (ER) was the main controlling parameter. Rice husk gasification gas had a maximum heating value of around 5000 kJ/m3 when ER = 0.22-0.26, and sawdust gasification gas reached around 6000-6500 kJ/m3 when ER = 0.175-0.24. The gasification efficiency of rice husk reached a maximum of 77% at ER = 0.28, while the gasification efficiency of sawdust reached a maximum of 81% at ER = 0.25.

Isolation and Characterization of a Methomyl-Degrading Paracoccus sp mdw-1

Methomyl, an extremely toxic pesticide, is widely used in agriculture. A strain named mdw-1 capable of degrading methomyl rapidly was successfully isolated from activated sludge in this study. It could utilize methomyl as the sole carbon or nitrogen source. The optimal temperature and medium pH for its growth and methomyl biodegradation were 30 degrees C and 7.0, respectively. It was identified as a Paracoccus sp. according to its morphological features, physiological and biochemical characteristics, and phylogenetic analysis based on the sequence of 16S rDNA. Gas chromatography-mass spectrometry (GC-MS) analysis showed that methomyl could be completely transformed to S-methyl-N-hydroxythioacetamidate in 10 h of incubation with the isolate mdw-1.