Flow properties of a dusty-gas point source in a supersonic free stream

By using Lagrangian method, the flow properties of a dusty-gas point source in a supersonic free stream were studied and the particle parameters in the near-symmetry-axis region were obtained. It is demonstrated that fairly inertial particles travel along oscillating and intersecting trajectories between the bow and termination shock waves. In this region,formation of "multi-layer structure" in particle distribution with alternating low- and highdensity layers is revealed. Moreover, sharp accumulation of particles occurs near the envelopes of particle trajectories.

VISCOSITY AND FLOW PROPERTIES OF CONCENTRATED-SOLUTIONS OF CHITOSAN WITH DIFFERENT DEGREES OF DEACETYLATION

The effects of the degree of deacetylation (DD) on the viscosity and flow behaviour of concentrated solutions of chitosan were investigated using 0.2 M CH3COOH and 0.2 M CH3COOH/0.1 M CH3COONa aqueous solutions as solvents. The results indicated that the

超声速气流中含灰气体点源流动特性

采用Lagrange方法，研究了超声速气流中含灰气体点源的流动特性，求得了对称辆附近激波层内的流动参数。计算数值模拟结果揭示了大惯性颗粒在激波层内沿着相互交叉的振荡轨迹运动，颗粒分布形成了高、低密度层交错出现的“多层结构”，而且粒子子在轨迹包络线附近急剧聚集。

Development of a Cell Size Relaxed Scheme for the Direct Simulation Monte Carlo Method

The conventional direct simulation Monte Carlo (DSMC) method has a strong restriction on the cell size because simulated particles are selected randomly within the cell for collisions. Cells with size larger than the molecular mean free path are generally not allowed in correct DSMC simulations. However, the cell-size induced numerical error can be controlled if the gradients of flow properties are properly involved during collisions. In this study, a large cell DSMC scheme is proposed to relax the cell size restriction. The scheme is applied to simulate several test problems and promising results are obtained even when the cell size is greater than 10 mean free paths of gas molecules. However, it is still necessary, of course, that the cell size be small with respect to the flow field structures that must be resolved.

Heat Transfer of Aviation Kerosene at Supercritical Conditions

The heat transfer characteristics of China no. 3 kerosene were investigated experimentally and analytically under conditions relevant to a regenerative cooling system for scramjet applications. A test facility developed for the present study can handle kerosene in a temperature range of 300-1000 K, a pressure range of 2.6-5 MPa, and a mass How rate range of 10-100 g/s. In addition, the test section was uniquely designed such that both the wall temperature and the bulk fuel temperature were measured at the same location along the flowpath. The measured temperature distributions were then used to analytically deduce the local heat transfer characteristics. A 10-component kerosene surrogate was proposed and employed to calculate the fuel thermodynamic and transport properties that were required in the heat transfer analysis. Results revealed drastic changes in the fuel flow properties and heat transfer characteristics when kerosene approached its critical state. Convective heat transfer enhancement was also found as kerosene became supercritical. The heat transfer correlation in the relatively low-fuel-temperature region yielded a similar result to other commonly used jet fuels, such as JP-7 and JP-8, at compressed liquid states. In the high-fuel-temperature region, near and beyond the critical temperature, heat transfer enhancement was observed; hence, the associated correlation showed a more significant Reynolds number dependency.

基于策略的域间访问控制和信息流控制框架

随着互联网及其相关技术的发展，多域环境下的资源共享越来越普遍。域间的资源共享给域间合作带来了便利的同时也带来了安全问题。其中两个关键安全问题是跨域访问控制和跨域信息流控制。本文针对典型的跨域资源共享系统的安全需求，提出了基于策略的跨域访问控制与信息流控制框架。框架包括了授权和访问控制体系结构、授权策略模型、用于生成和维护授权策略的协议和算法、 用于表示和分析跨域信息流的信息流图和用于控制跨域信息流的机制。主要贡献具体体现在以下几个方面： 1）框架的提出使得安全互操作可以以一种无策略协调器的方式进行。在对资源共享进行控制的现有方案中， 其安全互操作都是以基于中心协调器的方式进行，存在如下问题：中心协调器会成为仲裁域间资源共享的瓶颈；有时很难找到一个可信的第三方来持有中心协调器。框架通过以一种无策略协调器的方式使得这些问题得到解决。首先，框架给出一个分布式跨域授权策略模型；根据此模型，跨域策略被分布到每个域，而每个域所保留的策略对于安全违反检测以及资源的访问判定来说是可靠的和完备的。其次，框架给出了协议和算法以在域初始建立合作时生成这样的跨域授权策略，并给出了跨域策略变更的协议和算法。其中，跨域授权策略初始建立与变更过程中的安全违反检测可以在单个域本地进行 — 也就是说, 每个域检查是否有对其自身的安全违反并引导协商以去除违反；对一个域的资源的访问判定由此域自身来确定（根据其保留的策略）。 2）框架给出了一个渐进的策略变更方案。此方案只涉及与策略变更相关的域，并且只涉及到与策略变更相关的策略。在多种情况下，变更不会带来任何安全违反或者只会带来某种类型的安全违反。如果存在任何安全违反，此安全违反也是被限定在相关策略范围内。此方案适合策略变更频繁的动态环境。 3）框架给出了一种面向多域资源共享的信息流控制方案。该方案面向采用了基于角色访问控制（RBAC）策略和单向角色映射的多域环境。方案给出了如何用信息流图来表示和分析跨域信息流的方法。根据与信息扩散相关的需求，给出域内信息安全和域间信息安全的概念。域可以定义域内和域间信息安全需求以控制信息扩散。而且给出了角色划分、角色激活上的限制、角色映射激活上的限制等措施来满足由域定义的需求。

多级安全OS与DBMS模型的信息流及其一致性分析

数据库安全与操作系统安全密不可分,如果多级安全DBMS的安全策略不违反OS的安全策略,那么可以使用多级安全OS的安全机制来实现DBMS的部分安全功能,如强制访问控制.信息流分析使我们能更好地理解安全策略的意义和内容.该文给出了多级安全OS模型和以该模型为基础的多级安全DBMS模型,首次详细分析了它们在强制访问控制策略下的信息流集合.经过主客体的映射后,证明了数据库与操作系统的信息流集合是一致的,这个结论保证了利用OS的机制来实现DBMS的强制访问控制的合理性.

基于信息流的可信操作系统度量架构

将信息流和可信计算技术结合,可以更好地保护操作系统完整性.但现有的可信计算度量机制存在动态性和效率方面的不足,而描述信息流的Biba完整性模型在应用时又存在单调性缺陷.本文将两者结合起来,基于Biba模型,以可信计算平台模块TPM为硬件信任根,引入信息流完整性,并提出了可信操作系统度量架构:BIFI.实验表明,BIFI不仅能很好地保护信息流完整性,而且对现有系统的改动很少,保证了效率.

基于授权策略的RBAC信息流控制

RBAC没有明确定义非法信息流，也没有提供信息流控制机制．RBAC系统中主体的访问操作 可以引起客体之间的信息流，使用户访问到未授权的信息．首次从授权策略的角度形式化地定义了 RBAC非法信息流，提出了一个检测RBAC配置中用户可以引起的非法信息流的算法，给出了一个动态 信息流控制算法．确保了RBAC访问控制目标的实现，增强了RBAC系统的安全性．

带敏感标签的SELinux安全策略信息流分析方法

针对SELinux操作系统中多安全策略的实现方式,文中在信息流分析方法的基础上引入了多级安全敏感标签,以自动机与线性时态逻辑为理论基础,提出了一种改进的信息流分析方法,对SELinux安全策略的完整性与机密性进行验证.

船载综合信息显示系统半实物仿真设计与实现

针对船载综合信息显示系统在实体船舶内开发不方便的问题,提出了一种半实物仿真系统的设计与实现方法。结合"科学三号"海洋科学考察船的综合信息显示系统的设计和开发过程,从体系结构、信息流程和实现方法3个方面对半实物仿真系统的设计和实现过程进行了探索。实践结果表明,这种半实物仿真系统一方面可以为实际系统的体系结构、信息流程设计提供支持,另一方面可以为实际系统应用软件的开发提供较为真实的环境,有效的缩短开发时间和降低开发风险。

RADIATION EFFECTS ON POLY(VINYLIDENE FLUORIDE)

Melt-crystallized poly(vinylidene fluoride)s (PVF2) with different crystallization histories were irradiated with gamma-rays within the range of irradiation doses 0-83 Mrad. The effects on the crystalline structure and mechanical properties have been measured, compared, and discussed. The degree of crystallinity of the samples was found to increase with radiation dose. The differential scanning calorimeter scans of the quenched samples indicate that there are two melting peaks, and that the area of the lower temperature peak increases while the area of higher temperature peak decreases with increasing dose. Yield stress and breaking stress for all samples are not significantly affected by irradiation but elongation at break is.

供应链中物流及信息流管理

供应链管理使企业在变化的市场环境中有效地与其它企业合作 ,取得集体竞争优势。本文首先讨论了后勤学与供应链管理的定义和之间的关系。本文认为供应链管理的核心是物流与信息流的控制。物流控制决策主要包括操作层次的库存补充和运输路径规划 ,以及战略层次的设施地点规划。信息流管理跨越部门与企业的界限将相关的应用集成起来。动态联盟协调各企业内部的生产经营活动 ,战略性地决定物流与信息流的构形。

基于IDEF&UML的生产过程管理系统的建模研究

提出了IDEF与UML两者结合的系统建模方法,能够有效地避免IDEF对信息过程流建模和UML语义描述精确性及使用灵活性的不足.该方法采用IDEF0进行系统功能建模,用IDEF1x和UML模型进行信息建模和面向对象的软件系统设计.用该方法设计的沈阳某冶金设备有限公司的基于组件的生产过程管理系统模型具有良好的维护性、可扩展性和重用性,证明了该方法的可行性.