NUMERICAL STUDY OF HYDRODYNAMICS OF MULTIPLE TANDEM JETS IN CROSS FLOW

The hydrodynamics of a single jet and four tandem jets in a cross flow are simulated by using the Computational Fluid Dynamics (CFD) software Fluent. The realizable model is used to close the Reynolds-Averaged equations. The flow characteristics of the jets, including the jet trajectory, the velocity field and the turbulent kinetic energy are obtained with various jet-to-cross flow velocity ratios in the range of 2.38-17.88. It is shown that a single jet penetrates slightly deeper than the first jet in a jet group at the same , although the difference decreases with the decrease of . It is also found that the way in which the velo-city decays along the centerline of the jet is similar for both a single jet and the first jet in a group, and the speed of the decay increases with the decrease of . The downstream jets in a group are found to behave differently due to the sheltering effect of the first jet in the group. Compared with the first jet, the downstream jets penetrate deeper into the cross flow, and the velocity decays more slowly. The circulation zone between the two upstream jets in the front is stronger than those formed between the downstream jets. The Turbulent Kinetic Energy (TKE) sees a distinct double-peak across the cross-sections close to each nozzle, with low values in the jet core and high values in the shear layers. The double-peak gradually vanishes, as the shear layers of the jet merge further away from the nozzle, where the TKE assumes peaks at the jet centerline.     

IK-CPA security implies IE-CCA security in the random oracle model

Key-privacy is a notion of security that is concerned with the key anonymity in public-key encryption.Some popular schemes keep key-privacy,while others do not.Key-privacy has been shown to be orthogonal to data-privacy within one cryptosystem.This paper investigates the relationship between keyprivacy and data-privacy in public-key encryption.We show that the existence of IK-CPA secure cryptosystems implies the existence of IE-CCA secure cryptosystems in the random oracle model.The main contributions include a novel construction of a family of injective one-way trapdoor functions directly based on any IK-CPA secure public-key cryptosystem in the random oracle model.This construction adopts a novel idea in the construction compared to the existing one.The latter was based on unapproximable trapdoor predicates.The novelty of the construction allows to show that the injective trapdoor functions are secure under correlated products with respect to uniform repetitional distribution.That further allows us to conclude,in the random oracle model,that the existence of IK-CPA secure public-key cryptosystems implies the existence of CCA secure cryptosystems by a result of Rosen and Segev.     

基于网络的安全通信系统的研究与设计

本系统结合网络安全通信系统的应用需求和功能需求两方面,在深入研究实现数据加密技术的对称密钥密码体制和公开密钥密码体制的基础上,提出了一套网络安全通信系统的设计方案。实验表明,该系统能确保通信双方能够实现网络中聊天和文件传输的安全,它体现了消息保密性和消息认证性两方面的安全特性。     

基于PERT技术的人员调度研究

人员成本占软件项目总成本的大部分,但是现有的Pert技术未能体现人员计划管理这重要的一环,不合理的活动指派时间可能导致人员闲置或者项目延迟.本文提出一种解决方法,基于Pert技术,结合人员闲置、项目延迟和缓冲区计算活动负责人的指派时间,以此指导项目管理,可有效减少总开销.     

基于惯性权重非线性动态变化的微粒群算法

本文提出一种惯性权重非线性动态变化的微粒群算法(NDPSO),根据微粒在群体中距群体最优位置的远近,选择不同的惯性权重非线性下降指数,每个微粒根据个体状况选择不同的惯性权重.在NDPSO算法中,距最优位置较远区域惯性权重选择较小的下降指数,这样利于微粒较快地飞向群体最优位置,提高算法的全局搜索性能;当微粒飞到距最优位置较近区域时,惯性权重采用较大的下降指数,这样微粒在此区域进行细致的搜索,提高算法的收敛速度.为了研究NDPSO算法的性能,对几种典型高维非线性函数进行了测试.测试结果表明,与其它几种典型的微粒群算法相比,NDPSO明显地提高了算法的性能.     

一种基于中断处理机制的动态反汇编算法

传统的反汇编是静态进行的,它难以处理逻辑陷阱、花指令、代码中的数据、动态控制流等问题,这就导致其最终的反汇编结果可能不完整,存在错误.一段特意设计的代码,可以用动态控制流替代静态控制流;一段特意设计的花指令,可以让静态控制流关系任意复杂,这都将使静态反汇编分析难以进行.让代码运行起来,动态地进行反汇编,可以解决上述静态反汇编遇到的问题.结合计算机的中断处理机制,使得代码的实际执行路径是可知的.针对实际执行到的计算机指令进行反汇编,确保了反汇编结果的准确性;反复执行代码,在时间上进行积累,可以确保反汇编结果的完整性不断增加并趋于完整.     

一个在Horn子句中求解极大缩减的算法

在信念修正理论中,一个核心问题是求解一个公式集合关于事实集合的所有极大协调子集,即极大缩减.本文尝试从算法的角度来解决这一问题,研究在Horn子句中求解所有极大缩减的算法.首先,本文指出并证明了公式集合和事实集合并集的极小不协调子集与公式集合关于事实集合的极大缩减之间的转化关系.其次,给出并证明了Horn子句集合极小不协调的一个必要条件.然后,基于上述两个结论,本文提出了一个在Horn子句中枚举公式集合和事实集合并集的极小不协调子集的交互式算法和一个通过这些极小不协调子集计算所有极大缩减的算法.最后,综合这两个算法,提出了一个在Horn子句中求解所有极大缩减的交互式算法.     

一种基于图像的非均匀单散射参与介质建模方法

针对非均匀单散射参与介质建模问题,提出一种能够保持密度场空间变化细节的建模方法.使用体数据、吸收和散射系数之比分别描述参与介质空间变化的密度分布及光线在其内部的传输特性,通过构建采集图像像素值与它们之间的表达式,将建模问题转化为非线性数值优化问题,求最优解.为了解决高分辨率体数据下大量体素密度值同时求解带来的时间开销大及数值不稳定问题,提出一种符合采集图像像素值明暗分布规律的密度场体数据初始化算法和一种多分辨率体数据逐步求精优化算法;为了快速计算大量体素密度值梯度,提出一种基于GPU的多体素并行梯度计算算法.实验结果表明,提出的方法能够根据采集图像重构烟模型,并保持其细节信息.     

CBCR:采用循环移位的CBC MAC

在现代通信中,消息鉴别码广泛应用于数据的完整性保护和起源认证.文中提出一个基于分组密码的消息鉴别码算法CBCR,它在认证任意长度的消息时都具备可证明安全的保障.CBCR在密码分组链接模式的末端采用循环移位操作,并且对所有消息都加入一个定长的前缀,后者使得它在现实应用中具备一定的灵活性.比如说,这些定长的前缀可以是一些安...     

Image City sharing platform and its typical applications

In this paper,the trend of urban spatial information sharing service from the electronic map to image is analyzed and its sharing framework based on service-oriented architecture is designed.Moreover,the service implementation,feedback data service procedure and its processing service model are explored. Based on the software with independent intellectual property rights,image city of Taizhou is developed as an example to realize various image data and processing servicesLastly,the bright future prospects o...