Experimental investigation on the cavity-based scramjet model

The present work focused on improving the engine performance with different fuel equivalence ratios and fuel injections. A scramjet model with strut/cavity integrated configurations was tested under Mach 5.8 flows. The results showed that the strut may sreve as an effective tool in a kerosene-fueled scramjet. The integration of strut/cavities also had great effect on stablizing the combustion in a wide range of fuel equivalence ratio. The one-sdimensional analysis method was used to analyze the main characteristics of the model. The two-stage fuel injection should have better performance in increasing the chemical reaction rate in the first cavity region.

Rate-equation-based circuit model of high-speed semiconductor lasers

Based oil rare equations of semiconductor laser, a symbolically-defined model for optical transmission system performance evaluation and network characterization in both time- and frequency domains is presented. The steady-state and small-signal characteristics, such as current-photon density curve, current-voltage curve, and input impedance, call be predicted from this model. Two important dynamic characteristics, second-order harmonic distortion and two-tone third-order intermodulation products, are evaluated under different driving conditions. Experiments show that the simulated results agree well with the published data. (c) 2007 Wiley Periodicals, Inc.

Stratigraphic Model Predictions of Geoacoustic Properties

Geoacoustic properties of the seabed have a controlling role in the propagation and reverberation of sound in shallow-water environments. Several techniques are available to quantify the important properties but are usually unable to adequately sample the region of interest. In this paper, we explore the potential for obtaining geotechnical properties from a process-based stratigraphic model. Grain-size predictions from the stratigraphic model are combined with two acoustic models to estimate sound speed with distance across the New Jersey continental shelf and with depth below the seabed. Model predictions are compared to two independent sets of data: 1) Surficial sound speeds obtained through direct measurement using in situ compressional wave probes, and 2) sound speed as a function of depth obtained through inversion of seabed reflection measurements. In water depths less than 100 m, the model predictions produce a trend of decreasing grain-size and sound speed with increasing water depth as similarly observed in the measured surficial data. In water depths between 100 and 130 m, the model predictions exhibit an increase in sound speed that was not observed in the measured surficial data. A closer comparison indicates that the grain-sizes predicted for the surficial sediments are generally too small producing sound speeds that are too slow. The predicted sound speeds also tend to be too slow for sediments 0.5-20 m below the seabed in water depths greater than 100 m. However, in water depths less than 100 m, the sound speeds between 0.5-20-m subbottom depth are generally too fast. There are several reasons for the discrepancies including the stratigraphic model was limited to two dimensions, the model was unable to simulate biologic processes responsible for the high sound-speed shell material common in the model area, and incomplete geological records necessary to accurately predict grain-size

Synthesis and characterization of new carbazole/fluorene-based derivatives for blue-light-emitting devices

2,7-Bis(9-ethylcarbazol-3-yl)-9,9-di(2-ethylhexyl)fluorene and a segmented copolymer composed of the same chromophores alternated with hexamethylene fragments were synthesized. The obtained materials possess good solubility in common organic solvents, high thermal stability with 1% weight loss temperature of 350-370 degrees C, and suitable glass transition temperatures. Both derivatives show blue fluorescence in dilute solutions as well as in solid state, demonstrating that excimers are not formed in the thin films. The fluorescence spectra of the materials do not show any peaks in the long-wavelength region even after annealing at 200 degrees C in air. An organic LED with the configuration of ITO/copolymer/Al generates blue electroluminescence with the maximum peak at 416 nm, rather low turn-on voltage (4.0 V), and brightness of about 400 cd/m(2). The heterostructure device based on model derivative emitted stable blue light with low operation voltage (100 cd/m(2) at similar to 11 V) and demonstrated luminescence efficiency of 0.8 cd/A.

Photoluminescence properties of tensile-strained GaAsP/GaInP single quantum wells grown by metal organic chemical vapor deposition

Tensile-strained GaAsP/GaInP single quantum well (QW) laser diode (I-D) structures have been grown by low-pressure metal organic chemical vapor deposition (LP-MOCVD) and related photoluminescence (PL) properties have been investigated in detail. The samples have the same well thickness of 16 nm but different P compositions in a GaAsP QW. Two peaks in room temperature (RT) PL spectra are observed for samples with a composition larger than 0.10. Temperature and excitation-power-dependent PL spectra have been measured for a sample with it P composition of 0.15. It is found that the two peaks have a 35 meV energy separation independent of temperature and only the low-energy peak exists below 85 K. Additionally, both peak intensities exhibit a monotonous increase as excitation power increases. Analyses indicate that the two peaks arise from the intrinsic-exciton recombination mechanisms of electron-heavy hole (e-hh) and electron-light hole (e-hh). A theoretical calculation based oil model-solid theory, taking, into account the spin-orbit splitting energy, shows good agreement with our experimental results. The temperature dependence of PL intensity ratio is well explained using the spontaneous emission theory for e-hh and e-hh transitions. front which the ratio can be characterized mainly by the energy separation between the fill and Ill states.

Modeling and optimization of semiconductor manufacturing process with neural networks

A neural network-based process model is proposed to optimize the semiconductor manufacturing process. Being different from some works in several research groups which developed neural network-based models to predict process quality with a set of process variables of only single manufacturing step, we applied this model to wafer fabrication parameters control and wafer lot yield optimization. The original data are collected from a wafer fabrication line, including technological parameters and wafer test results. The wafer lot yield is taken as the optimization target. Learning from historical technological records and wafer test results, the model can predict the wafer yield. To eliminate the "bad" or noisy samples from the sample set, an experimental method was used to determine the number of hidden units so that both good learning ability and prediction capability can be obtained.

协同环境中共有资源的细粒度协作访问控制策略

在军事和商业领域中,由多个自治域形成的协作群体对共有资源(如客体、应用程序以及服务等)的访问问题越来越受到重视.协作中的基本事实是:尽管这些自治域有共同的目标,但同时有不同的自身利益.为了有效地保护共有资源,把“信任”的概念引入了协作访问控制中,并在基于量化权限的思想上,提出了细粒度的协作访问控制策略.在该策略里,权限的使用形式是元权限,也就是单位权限,它是访问共有客体权限的一个划分,可为多个域中不同用户所拥有.当访问共有资源时,参与者们所拥有的元权限的值之和以及人数必须达到规定的权限门限值和人数值,并且访问时间是所有参与者的共同许可访问时间段,这使得可以对协作资源进行有效地分布控制.另外,还引入了元权限的使用时间段约束.最后,证明了该细粒度协作访问控制策略关于协作系统的状态转换是保持安全的.

基于安全状态域的网络评估模型

将基于攻击图的评估与依赖标准的评估相结合,提出了一种基于安全状态域(security state region,简称SSR)的网络安全评估模型(security-state-region-based evaluation model,简称SSREM).该模型将攻击的影响分为攻击能力改变和环境改变,通过两者之间的因果关系建立数学模型,提出了安全状态域趋向指数的概念,借助Matlab进行攻击趋势的曲面拟合,进而进行安全状态域的划分和网络的安全性评估.实验结果表明,依据SSREM进行的评估能够通过安全状态城和安全状态域趋向指数反映网络进入不同状态的难易程度,对网络安全性量化评估具有借鉴意义.

一种基于身份的多信任域网格认证模型

分析了现有的网格认证框架中存在的问题，提出了一种基于身份的多信任域网格认证模型．该模型以基于身份的PKI为基础，避免了基于传统PKI的认证框架的诸多缺点．同时，该模型提供了跨信任域的双向实体认证功能．模拟试验表明，该认证模型比基于传统PKI的认证框架更轻量、更高效．而且由于该模型可以在多信任域的环境下工作，故而比W Mao提出的只能在单一信任域中工作的认证框架更符合网格认证的实际需要．

基于角色的受限委托模型

角色委托是RBAC模型需要支持的一种重要安全策略.它的主要思想是系统中的主动实体将角色委托给其他主动实体,以便以前者名义执行特定的工作.角色委托者要对委托角色的使用负责,所以对委托角色进行使用限制是整个模型的关键组成部分.目前已有一些模型扩展了RBAC模型以支持角色委托,但是这些模型对委托限制的支持非常有限.提出了角色委托限制的需求,包括临时性限制、常规角色关联性限制、部分性限制和传播限制.并且,给出了一个支持临时性限制和常规角色关联性限制的基于角色的委托模型.给出模型的形式化描述,为模型在实际环境中的应用奠定了基础.

基于对象关系的位置相关数据库模型及其移动持续查询处理策略

近年来，人们对位置相关的信息服务进行了较为大量的研究，这些工作主要以移动对象数据库及空间数据库框架为基础，探讨如何有效地支持位置相关的查询等问题．然而，另一类重要的数据类型——位置相关的数据(10cation dependent data，LDD)，却没有得到人们足够的重视．目前，LDD的研究主要集中在概念应用层，缺乏完善的数据库模型(包括数据类型及查询操作等)及有效的查询处理方法．为了解决上述问题，提出一种基于对象关系数据库模型的位置相关数据模型(object—relational database based LDD model，ORLDD)。在ORLDD中，定义了完整的位置相关数据类型及查询操作，给出了相关的移动持续查询处理方法，并阐述了在对象关系数据库系统PostgreSQL上的实现方法．实验结果表明，该方法具有良好的查询处理性能及灵活性．

基于角色的管理模型隐式授权分析

基于角色的管理模型被用于管理大型RBAC(role-based access control)系统的授权关系,UARBAC具有可扩展、细粒度等优点.UARBAC的管理操作包含隐式授权.隐式授权分析说明UARBAC管理操作的两类缺陷,包括两个定义缺陷,即无法创建客体和虚悬引用,以及一个实施缺陷,即不支持最小授权.通过修改管理操作更正定义缺陷,提出实施缺陷的改进方案.定义实施最小授权的最小角色匹配问题,证明该问题是NP难,并给出基于贪心算法的可行方案,帮助管理员选择合适的管理操作将最小角色集合授予用户.

ISO9000在软件组织的实施模型

中国计算机学会