EFFECTIVE-MASS THEORY FOR GAAS/GA1-XALXAS QUANTUM WIRES AND CORRUGATED SUPERLATTICES GROWN ON (311)-ORIENTED SUBSTRATES

The electronic structures of GaAs/Ga1-xAlxAs quantum wires (corrugated superlattices) grown on (311)-oriented substrates are studied in the framework of the effective-mass envelope-function method. The electron and hole subband structure and optical transition matrix elements are calculated. When x=1, the results are compared with experiments, and it is found that the direct transition becomes an indirect transition as the widths of well and barrier become smaller.

EFFECTIVE-MASS THEORY FOR SUPERLATTICES GROWN ON (11N)-ORIENTED SUBSTRATES

An effective-mass formulation for superlattices grown on (11N)-oriented substrates is given. It is found that, for GaAs/AlxGa1-xAs superlattices, the hole subband structure and related properties are sensitive to the orientation because of the large anisotropy of the valence band. The energy-level positions for the heavy hole and the optical transition matrix elements for the light hole apparently change with orientation. The heavy- and light-hole energy levels at k parallel-to = 0 can be calculated separately by taking the classical effective mass in the growth direction. Under a uniaxial stress along the growth direction, the energy levels of the heavy and light holes shift down and up, respectively; at a critical stress, the first heavy- and light-hole energy levels cross over. The energy shifts caused by the uniaxial stress are largest for the (111) case and smallest for the (001) case. The optical transition matrix elements change substantially after the crossover of the first heavy- and light-hole energy has occurred.

Some properties of gallium nitride films grown on (0001) oriented sapphire substrates by gas source molecular beam epitaxy

The Raman and photoreflectivity spectra of gallium nitride (GaN) films grown on (0001) oriented sapphire substrates by gas source molecular beam epitaxy (GSMBE) have been investigated. The Raman spectra showed the presence of the E-2(high) mode and a shift in the wavenumber of this mode with respect to the GaN epilayer thickness. The Raman scattering results suggest the presence of stress due to lattice and thermal expansion misfit in the films, and also indicate that the buffer layer play an important role in the deposition of high quality GaN layers. The residual stress changes from tensile to compressive as the epilayer thickness increases. Samples subjected to anneal cycles showed an increase in the mobility due probably to stress relaxation as suggested by an observed shift in the E-2(high) mode in the Raman spectra after annealing.

Structural ordering and interface morphology in symmetrically strained (GaIn)As/Ga(PAs) superlattices grown on off-oriented GaAs(100)

In this work we investigate the structural properties of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of x-ray diffraction, reciprocal-space mapping, and x-ray reflectivity. The multilayers were grown by metalorganic vapor-phase epitaxy on (001) GaAs substrates intentionally off-oriented towards one of the nearest [110] directions. High-resolution triple-crystal reciprocal-space maps recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction clearly show a double periodicity of the x-ray peak intensity that can be ascribed to a lateral and a vertical periodicity occurring parallel and perpendicular to the growth surface. Moreover, from the intensity modulation of the satellite peaks, a lateral-strain gradient within the epilayer unit cell is found, varying from a tensile to a compressive strain. Thus, the substrate off-orientation promotes a lateral modulation of the layer thickness (ordered interface roughness) and of the lattice strain, giving rise to laterally ordered macrosteps. In this respect, contour maps of the specular reflected beam in the vicinity of the (000) reciprocal lattice point were recorded in order to inspect the vertical and lateral interface roughness correlation, A semiquantitative analysis of our results shows that the interface morphology and roughness is greatly influenced by the off-orientation angle and the lateral strain distribution. Two mean spatial wavelengths can be determined, one corresponding exactly to the macrostep periodicity and the other indicating a further interface waviness along the macrosteps. The same spatial periodicities were found on the surface by atomic-force-microscopy images confirming the x-ray results and revealing a strong vertical correlation of the interfaces up to the outer surface.

Aluminum induced crystallization of strongly (111) oriented polycrystalline silicon thin film and nucleation analysis

A polycrystalline silicon thin film was fabricated on glass substrate by means of aluminum induced crystallization (AIC). Al and alpha-Si layers were deposited by magnetron sputtering respectively and annealed at 480A degrees C for 1 h to realize layer exchange. The polycrystalline silicon thin film was continuous and strongly (111) oriented. By analyzing the structure variation of the oxidation membrane and lattice mismatch between gamma-Al2O3 and Si, it was concluded that aluminum promoted the formation of (111) oriented silicon nucleus by controlling the orientation of gamma-Al2O3, which was formed at the early stage of annealing.

多Agent群体行为中的扩散趋同综述

为了研究复杂系统及复杂性科学问题,人们提出多Agent模型进行建模和分析.多Agent的群体行为是复杂系统研究所必须解决的问题,而其中的扩散趋同更是相关领域的研究热点.文中首先介绍多Agent群体行为中的扩散趋同现象,然后根据Agent扩散趋同传递的方式、Agent的扩散趋同能力的分布情况和Agent扩散趋同所感知的范围,将相关研究成果中的扩散趋同机制分为3个方面:层次结构性扩散趋同与群集性扩散趋同、平滑扩散趋同与非平滑扩散趋同、邻域扩散趋同与全局扩散趋同.文中对每种模型的特点进行论述和比较分析,最后指出下一步的研究方向.

一种用于软件过程建模的适应性Agent协商

大多软件过程模型是预定义的.在变化的应用环境中,需要由相应人员进行适应性调整.提出一种用于软件过程建模的适应性多边协商模型——AMNM-PA,其采用Agent封装软件过程中所涉及的个体,包含组织、团队、个人等,通过Agent间的协商动态、适应地建立针对给定软件项目的软件过程模型.AMNM-PA基于非静态有限阶段Markov决策过程,采用模型无关的Q学习算法选取协商策略,因此能够支持动态、非预知环境下的适应性协商,从而满足软件过程建模对环境的适应性需求.AMNM-PA已经实施于软件过程管理系统——SoftPM.

一种适应性多边软件过程Agent协商模型研究

软件过程建模是指对软件过程建立模型，并且对模型建立和模型执行提供自动化支持。软件过程建模技术为软件过程的描述、表示、执行、分析、跟踪、变更以及改进提供了方法和工具，从而为软件组织实现软件开发过程的管理和改进提供了有力的支持，对于保证软件组织的软件产品质量，提高开发效率具有重要的理论和实践价值。 软件过程的一个重要特征是极大地依赖于软件开发人员，当软件过程面临各种变化时，正是作为软件过程的主体——软件开发人员的及时反应和应对，使得软件过程能够灵活适应各种软件开发的实际和变化状况；忽视软件开发人员在软件过程中的核心作用，是目前大多软件过程建模方法不适用于软件企业实际应用的原因之一。Agent技术主要基于对人的观察，其已被认识到是软件过程建模领域的重要研究方向之一。然而，相关研究工作并没有很好地体现人在软件过程中的核心作用，其根本原因在于其所采用或关注的是单Agent技术，而非多Agent系统技术。以互联为背景的多Agent系统能够很好地刻画人类的社会性，因此，对于当前以全球性、分布式多点等为主要特点的软件过程而言，采用多Agent系统技术，关注软件过程中所涉及的实体之间的协商、协作、竞争、承诺等特性是将Agent技术应用于软件过程的研究重点。 本文提出一种适应性多边软件过程Agent协商模型AMNM-PA。AMNM-PA基于软件开发者为软件过程中的核心要素并且软件过程为这些核心要素之间的相互协同关系的观点，将软件开发建模描述为代表软件开发者的自治的软件过程Agent（简称过程Agent）之间的协商；在协商中，过程Agent能够在变化的环境下针对各种不同实际应用，以及根据对环境的感知和所拥有的知识，适应、灵活地确立彼此间的协同关系，即建立软件过程。 本文在组织上采用了从模型要素及其相互关系定义、模型要素具体描述到模型实现及验证的逻辑结构。首先，本文给出AMNM-PA的模型定义，对过程Agent的协商所涉及的协商要素及其相互之间的关系进行描述。其次，本文详细描述协商要素中的决策过程，即过程Agent在协商中进行决策所依据的协商策略选择方法及各种可选协商策略；并以决策过程为基础，提出一种多边适应性协商算法，以此给出基于AMNM-PA的适应性多边协商过程的基本算法。随后，本文详细描述了另一协商要素——协商规则，其解决了协商过程的离线和在线灵活性问题，从而为软件过程建模的灵活性提供了解决方案。最后，本文实现了基于AMNM-PA的协商系统，并在该系统的支持下进行了实验研究，验证了AMNM-PA能够在变化的环境中适应性地建立面向实际软件项目的软件过程，并且该软件过程所包含的个体利益能够得到均衡、整体利益较高；同时很好地支持了软件过程建立和执行的灵活性。

软件过程Agent的知识生成方法研究

软件开发过程的不可见是软件项目失败的主要原因之一。为了提高软件开发过程的可见性，研究人员从软件开发过程的表示、软件开发知识的管理和软件开发数据的挖掘等方面提出了相应理论、方法和工具，这些理论、方法和工具对提高软件过程的可见性提供了一定的帮助，但却都有自己的局限性，难以全面覆盖提高软件开发过程可见性的要素。 为此，我们需要进一步融合软件过程建模、知识管理和数据挖掘等领域各自的研究成果，探索一种不但支持从过程资产库提取知识，而且支持对这些知识进行描述和管理，同时还能将这些知识直接用于建立符合组织能力的软件过程模型，并可以根据该软件过程模型生成符合组织中人的能力的软件开发项目计划的完整方法，为提高软件开发过程的可见性提供全面、有力的支持，从而有效保障软件开发的质量和效率。 本文给出一种根据组织的软件过程资产库生成软件过程Agent知识的方法，该方法生成的软件过程Agent知识可被用于建立一种基于组织实体能力的软件过程模型。基于该方法，本文实现了一个软件过程Agent自动生成工具，该工具可以根据指定的软件过程资产库自动生成软件过程Agent实例及其知识。同时本文在应用实例研究中进行了实验验证，证明了该方法的有效性。 本文研究是对基于组织实体能力的软件过程建模方法的扩展和补充。该方法和基于组织实体能力的软件过程建模方法的集成，可有效支持根据组织过程资产库生成组织的软件开发知识并将这些知识进行描述，使其能够被用于建立符合组织能力的软件开发模型，并最终根据特定目标生成符合组织实际能力软件开发项目计划。

Effects of oriented substrates on cell morphology, the cell cycle, and the cytoskeleton in Ros 17/2.8 cells

Absence of gravity or microgravity influences the cellular functions of bone forming osteoblasts. The underlying mechanism, however, of cellular sensing and responding to the gravity vector is poorly understood. This work quantified the impact of vector-directional gravity on the biological responses of Ros 17/2.8 cells grown on upward-, downward- or edge-on-oriented substrates. Cell morphology and nuclear translocation, cell proliferation and the cell cycle, and cytoskeletal reorganization were found to vary significantly in the three orientations. All of the responses were duration-dependent. These results provide a new insight into understanding how osteoblasts respond to static vector-directional gravity.

Multi-agent的协作模型及其应用

本文从经济学和社会心理学角度出发 ,探讨了多种高级认知结构在社会活动中的作用 ,建立了多种高级认知结构的框架 ,研究了这些高级认知结构在多智能体代理系统环境中如何相互作用问题 ,并提出了三个系统模型来刻画这些相互作用。