Web应用服务器研究综述

Web应用服务器是Web计算环境下产生的新型中间件，为创建、部署、运行、集成和管理事务性Web应用提供一个跨平台的运行环境，被认为是自关系型数据库以来最令人激动的企业应用技术。诸多IT企业纷纷推出其各自的Web应用服务器产品和系统，学术界也对这种热门领域产生了浓厚的兴趣。在分析Web计算环境下传统中间件发展所遇到的问题的基础上，介绍Web应用服务器的起源和发展、运行模式以及评测基准，然后对Web应用服务器研究现状进行综述，主要包括Web应用服务器的定义、体系结构、组件容器、分布事务处理、负载平衡、高速缓存、Web Service等研究热点和关键技术。根据评测基准，对若干主流Web应用服务器从功能和性能两个文献进行分析和比较。此外，还指出了Web应用服务器目前存在的不足以及未来的发展趋势。

OnceAS/Q:一个面向QoS的Web应用服务器

网络分布计算环境下应用系统的需求多样化和复杂性的增长,要求位于中间件层次的Web应用服务器(web application server,简称WAS)从原来的尽力而为服务模型转变为服务质量(quality of service,简称QoS)保障模型,为具有不同需求的应用分别提供适宜的服务质量保障.目前的WAS系统在此方面仍然比较薄弱.OnceAS/Q是一个面向QoS的WAS系统,它以QoS规约为基础,为不同应用提供不同的QoS保障能力.OnceAS/Q实现了一个应用QoS保障框架,提供了一组QoS服务组件支持具有QoS需求的应用开发和运行.介绍了OnceAS/Q的体系结构和主要组件,详细阐述了两个关键问题,一是QoS规约的定义及其映射,另一个是面向QoS的服务组件和资源的动态重配.OnceAS/Q原型在Ecperf测试基准下,对其QoS保障能力进行了实验.实验数据表明,在较大规模的应用环境下,OnceAS/Q能够提供更好的服务质量,并且开销是可接受的.

LIQUID-PHASE EPITAXY GROWTH AND PROPERTIES OF GAINASSB/ALGAASSB/GASB HETEROSTRUCTURES

The GaInAsSb/AlGaAsSb/GaSb heterostructures were grown by the liquid phase epitaxy (LPE) technique. The materials were characterized by means of optical microscopy, electroprobe microanalysis (EPMA), double-crystal X-ray diffraction, capacitance-voltage (C-V) and Van der Pauw measurments, infrared absorption spectra, photoluminescence and laser Raman scattering. The results show that the materials have fine surface morphology, low lattice mismatch and good homogeneity. Room-temperature light-emitting diodes with an emission wavelength of 2.2-mu-m were obtained by using the GaInAsSb/AlGaAsSb DH structures.

Characterization of deep centers in AlGaAs/InGaAs/GaAs pseudomorphic HEMT structures grown by molecular beam epitaxy and hydrogen treatment

In AlGaAs/InGaAs/GaAs PM-HEMT structures, the characterization of deep centers, the degradation in electrical and optical properties and their effects on electrical performance of the PM-HEMTs have been investigated by DLTS, SIMS, PL and conventional van der Pauw techniques. The experimental results confirm that the deep level centers correlate strongly with the oxygen content in the AlGaAs layer, the PL response of PM-HEMTs, and the electrical performance of the PM-HEMTs. Hydrogen plasma treatment was used to passivate/annihilate these centers, and the effects of hydrogenation were examined.

一种按基因重要度收敛的进化算法

提出基因重要度的概念,通过实验证明基因重要度对于单变量边缘分布算法(Unvaried Marginal Distribution Algo-rithm,UMOA)收敛的重要性.由此提出一种基于基因重要度的进化算法.该算法首先对组成染色体的各基因进行重要度排序,随后对重要度大的基因先进行收敛操作,每次收敛当前重要度最大的基因,直到所有基因全部收敛.实验数据表明,本算法的收敛速度更快,而且更容易求出满意解.

RF-MBE Grown AlGaN/GaN HEMT Structure with High Al Content

A Si doped AlGaN/GaN HEMT structure with high Al content (x= 44%) in the barrier layer is grown on sapphire substrate by RF-MBE. The structural and electrical properties of the heterostructure are investigated by the triple axis X-ray diffraction and Van der Pauw-Hall measurement, respectively. The observed prominent Bragg peaks of the GaN and AlGaN and the Hall results show that the structure is of high quality with smooth interface.fabricated and characterized. Better DC characteristics, maximum drain current of 1.0A/mm and extrinsic transconductance of 218mS/mm are obtained when compared with HEMTs fabricated using structures with lower Al mole fraction in the AlGaN barrier layer. The results suggest that the high Al content in the AlGaN barrier layer is promising in improving material electrical properties and device performance.

Heteroepitaxial Growth and Heterojunction Characteristics of Voids-Free n-3C-SiC on p-Si(100)

Highly oriented voids-free 3C-SiC heteroepitaxial layers are grown on φ50mm Si (100) substrates by low pressure chemical vapor deposition (LPCVD). The initial stage of carbonization and the surface morphology of carbonization layers of Si(100) are studied using reflection high energy electron diffraction (RHEED) and scanning electron microscopy (SEM). It is shown that the optimized carbonization temperature for the growth of voids-free 3S-SiC on Si (100) substrates is 1100 ℃. The electrical properties of SiC layers are characterized using Van der Pauw method. The I-V, C-V, and the temperature dependence of I-V characteristics in n-3C-SiC-p-Si heterojunctions with AuGeNi and Al electrical pads are investigated. It is shown that the maximum reverse breakdown voltage of the n-3C-SiC-p-Si heterojunction diodes reaches to 220V at room temperature. These results indicate that the SiC/Si heterojunction diode can be used to fabricate the wide bandgap emitter SiC/Si heterojunction bipolar transistors (HBT's).

Improved Epitaxy of 3C-SiC Layers on Si(100) by New CVD/LPCVD System

Single crystalline 3C-SiC epitaxial layers are grown on φ50mm Si wafers by a new resistively heated CVD/LPCVD system, using SiH_4, C_2H_4 and H_2 as gas precursors. X-ray diffraction and Raman scattering measurements are used to investigate the crystallinity of the grown films. Electrical properties of the epitaxial 3C-SiC layers with thickness of 1 ～ 3μm are measured by Van der Pauw method. The improved Hall mobility reaches the highest value of 470cm~2/(V·s) at the carrier concentration of 7.7 * 10~(17)cm~(-3).

Broadly Tunable Grating-Coupled External Cavity Laser With Quantum-Dot Active Region

A broadly tunable and high-power grating-coupled external cavity laser with a tuning range of more than 200 nm and a similar to 200-mW maximum output power was realized, by utilizing a gain device with the chirped multiple quantum-dot (QD) active layers and bent waveguide structure. The chirped QD active medium, which consists of QD layers with InGaAs strain-reducing layers different in thickness, is beneficial to the broadening of the material gain spectrum. The bent waveguide structure and facet antireflection coating are both effective for the suppression of inner-cavity lasing under large injection current.

Surface Plasmon Resonances of Cu Nanowire Arrays

Surface plasmon resonances of arrays of parallel copper nanowires, embedded in ion track-etched polycarbonate membranes, were investigated by systematic changes of nanowires’ topology and arrays area density. The extinction spectra exhibit two peaks which are attributed to interband transitions of Cu bulk metal and to a dipolar surface plasmon resonance, respectively. The resonances were investigated as a function of wire diameter and length, mean distance between adjacent wires, and angle of incidence of the light field with respect to the long wire axis. The dipolar peak shifts to larger wavelengths with increasing diameter and length, and diminishing mean distance between adjacent wires. Additionally, the shape effect on the dipolar peak is investigated.