Anomalous coarsening of self-assembled InAs quantum dots on vicinal GaAs (100) substrates

The formation process of InAs quantum dots (QDs) on vicinal GaAs (1 0 0) substrates is studied by atomic force microscopy (AFM). It is found that after 1.2 MLs of InAs deposition, while the QDs with diameters less than the width of the multi-atomic steps are shrinking, the larger QDs are growing. Photoluminescence measurements of the uncapped QDs correspond well to the AFM structure observations of the QDs. We propose that the QDs undergo an anomalous coarsening process with modified growth kinetics resulting from the restrictions of the finite terrace sizes. A comparison between the QDs on the vicinal GaAs (1 0 0) substrates and the QDs on the exact GaAs (1 0 0) further verifies the effect of the multi-atomic steps on the formation of QDs.

Influence of InAs deposition. thickness on the structural and optical properties of InAs quantum wires

The influence of InAs deposition thickness on the structural and optical properties of InAs/InAlAs quantum wires (QWR) superlattices (SLS) was studied. The transmission electron microscopy (TEM) results show that with increasing the InAs deposited thickness, the size uniformity and spatial ordering of InAs QWR SLS was greatly improved, but threading dislocations initiated from InAs nanowires for the sample with 6 monolayers (MLs) InAs deposition. In addition, the zig-zag features along the extending direction and lateral interlink of InAs nanowires were also observed. The InAs nanowires, especially for the first period, were laterally compact. These structural features may result in easy tunneling and coupling of charge carriers between InAs nanowires and will hamper their device applications to some extent. Some suggestions are put forward for further improving the uniformity of the stacked InAs QWRs, and for suppressing the formation of the threading dislocations in InAs QWR SLS.

Homogeneous Epitaxial Growth of N,N '-di(n-butyl)quinacridone Thin Films on Ag(110)

The structural evolution of the ordered N-N' dibutyl-substituted quinacridone (QA4C) multilayers (3 MLs) has been monitored in situ and in real time at various substrate temperatures using low energy electron diffraction (LEED) during organic molecular beam epitaxy (MBE). Experimental results of LEED patterns clearly reveal that the structure of the multilayer strongly depends on the substrate temperature. Multilayer growth can be achieved at the substrate temperatures below 300 K, while at the higher temperatures we can only get one ordered monolayer of QA4C. Two kinds of structures, the commensurate and incommensurate one, often coexist in the QA4C multilayer. With a method of the two-step substrate temperatures, the incommensurate one can be suppressed, and the commensurate, on the other hand, more similar to the (001) plane of the QA4C bulk crystal, prevails with the layer of QA4C increasing to 3 MLs. The two structures in the multilayers are compressed slightly in comparison to the original ones in the first monolayer.

网络安全操作系统关键技术研究

 本文针对安全操作系统开发和安全操作系统网络适应性方面涉及的关键问题进行研究。从信息系统整体来看，安全操作系统是解决各种安全威胁的基础。在网络环境中，计算机系统面临复杂、多样的安全威胁，尤其是机密信息泄露的威胁。网络环境对安全操作系统的研究和开发实践提出了新的挑战和要求：1) 网络环境中需要多层次安全策略实施框架，而以安全内核为基础的安全操作系统总是将安全功能集中在最小的安全内核中；2) 安全操作系统机密性策略导致的单向信息流动与网络环境下的双向信息交互之间存在冲突，需要引入大量的可信主体；3) 网络环境中独立的节点间缺少必要的信任。

    本文对上述几个方面的关键问题进行研究，并取得如下的创新：

    第一，针对网络环境中多层次安全策略实施要求，探索基于虚拟机环境的安全操作系统体系结构。提出一种基于虚拟机的双内核体系结构，这种体系结构以隔离作为基础，将操作系统分解为可以单独设计、开发、测评的组件。还提出一种基于消息的策略体系结构来约束组件的开发和设计。分析了虚拟机环境下动态内存管理的隔离性问题，提出一种基于BLP模型的安全的内存管理方案。

    第二，对安全操作系统的可信主体进行了研究。 该研究涉及到判定可信主体、确定可信主体的安全需求以及评估可信主体对于整个系统的安全风险等多个方面。本文以信息流分析为基础，利用TE安全规范与MLS策略间的信息流冲突定位可信主体，确定可信主体的安全标签范围，采用风险分析法确定每个可信主体的安全保障级指派。

    第三，针对网络环境中信任缺乏的问题，研究建立远程信任的平台证明技术，尤其关注平台证明的隐私保护问题。本文提出一种隐私隐藏的度量体系结构，并给出了相应的远程平台证明方案，改进了基于TCG的IMA度量体系结构    存在的配置隐私泄露问题。在此基础上，提出一种二进制证明与属性证明结合的混合证明方案。该方案既具有平台配置隐私保护能力又不需要属性证明所必须的在线可信第三方。

    第四，对属性证明的配置隐私保护能力进行研究。本文提出了几种可以被用来攻击属性证明隐私保护的方法：奇异属性法、增量分析法和统计分析法，证实了属性证明并不具有完全的配置隐私保护能力， 需要在设计中满足一定条件才具有隐私保护能力。上述研究也可为属性证明的设计提供参考。

基于点集曲面投影算法的自由曲面匹配

测量数据的精确定位是实现复杂曲面加工检测的关键,针对测量点云数据与NURBS表示的CAD自由曲面模型匹配中求最近点计算方面存在的问题,提出了一种简单、有效的寻找最近点的方法。该方法与由测量点集评估给定曲面上的最近点的传统算法相反,采用点集曲面(point set surface,PSS)投影算法,对给定自由曲面模型上有限个点与不附加任何几何和拓扑信息的散乱点集之间进行粗匹配获得初始位置,进而以最近点迭代算法(ICP)完成测量数据定位的精确调整,达到全局及局部最优的目标。实验结果表明,采用PSS投影算法法寻找最近点不仅效率高,而且能得到全局匹配结果,可以为精匹配提供较好的计算初值,减少了ICP算法进行二次匹配时,迭代次数及执行时间并且精度得到了较大提高。

模拟月壤研制的初步设想

模拟月壤是月球样品的地球化学复制品，作者总结世界上已有的5种模拟月壤JSC-1，MLS．1，MLS-2，MKS-1和FJS-1的研制过程、方法与基本理化性质，认为系列化模拟月壤研制对中国首次月球探测有重要意义，在此基础上，作者提出系列化模拟月壤研制的基本思路．