Practical rearrangement methods for dynamic double‐array dictionaries

Double‐array structures have been widely used to implement dictionaries with string keys. Although the space efficiency of dynamic double‐array dictionaries tends to decrease with key updates, we can still maintain high efficiency using existing methods. However, these methods have practical problems of time and functionality. This paper presents several efficient rearrangement methods to solve these problems. Through experiments using real‐world datasets, we demonstrate that the proposed rearrangement methods are much more practical than existing methods.     

基于LDAP的统一访问控制系统的设计与实现

随着Internet的迅速发展和企业的全球化进程,目录服务的应用为大规模的采集、存储和访问信息提供了一种灵活多变的解决方案。介绍了一个支持用户单点登陆的统一访问控制系统,它基于LDAP目录服务,将各种应用系统的访问控制结合在一起,从而实现了用户统一管理的安全访问。系统采用了中间件技术,有效地解决了大量用户访问LDAP数据库时的系统运行瓶颈问题。     

A lower bound on the probability of conflict under nonuniform access in database systems

Past performance analyses of resource sharing systems have often assumed uniform resource access distributions. This assumption is made for reasons of computational tractability. In some of these analyses it has been conjectured that such an assumption is optimistic, in the sense that it minimizes the probability of resource conflict. In this paper we give conditions on access distributions for which the above conjecture is true and show that these conditions are satisfied for two natural probabilistic models. Our technique can be applied to other resource contention problems.Research supported by NSF and NSA under Grant DMS-9001295.     

Efficient bulk-loading on dynamic metric access methods

This paper presents a new technique and two algorithms to bulk-load data into multi-way dynamic metric access methods, based on the covering radius of representative elements employed to organize data in hierarchical data structures.     

基于动态跳频的频谱接入*

在认知网络中,为了克服频谱接入方案中系统吞吐量普遍偏低的缺点,运用动态跳频技术,提出一种可以使次用户顺利切换到其他信道同时增加系统吞吐量的频谱接入新方案,并利用部分可观察马尔可夫决策过程描述这一问题;最后进行了数值验证。     

A conditional purpose-based access control model with dynamic roles

This paper presents a model for privacy preserving access control which is based on variety of purposes. Conditional purpose is applied along with allowed purpose and prohibited purpose in the model. It allows users using some data for certain purpose with conditions. The structure of conditional purpose-based access control model is defined and investigated through dynamic roles. Access purpose is verified in a dynamic behavior, based on subject attributes, context attributes and authorization policies. Intended purposes are dynamically associated with the requested data object during the access decision. An algorithm is developed to achieve the compliance computation between access purposes and intended purposes and is illustrated with Role-based access control (RBAC) in a dynamic manner to support conditional purpose-based access control. According to this model, more information from data providers can be extracted while at the same time assuring privacy that maximizes the usability of consumers’ data. It extends traditional access control models to a further coverage of privacy preserving in data mining atmosphere. The structure helps enterprises to circulate clear privacy promise, to collect and manage user preferences and consent.     

合成H∞动态观测器存在性问题的研究

本文研究了文献[24]提出的合成H∞动态观测器存在性问题, 针对合成H∞动态观测器存在时需要满足的 一组特殊Sylvester矩阵方程组是否有解进行了讨论, 利用矩阵理论进行相关推导和证明, 得到了此Sylvester矩阵方 程组有解的充分必要条件, 以及有解时解的结构, 缩小了合成H∞动态观测器(UHDO)设计问题中参数的搜索范围, 并给出了该Sylvester矩阵方程组的求解算法, 最后的仿真例子通过解的结构中任意参数的不同取值, 说明了对合成 动态观测器的影响.     

A unified model for joint throughput-overhead analysis of random access mobile ad hoc networks

An analytical framework is developed to study the throughput and routing overhead for proactive and reactive routing strategies in random access mobile ad hoc networks. To characterize the coexistence of the routing control traffic and data traffic, the interaction is modeled as a multi-class queue at each node, where the aggregate control traffic and data traffic are two different classes of customers of the queue. With the proposed model, the scaling properties of the throughput, maximum mobility degree supported by the network and mobility-induced throughput deficiencies are investigated, under both classes of routing strategies. The proposed analytical model can be extended to evaluate various routing optimization techniques as well as to study routing/relaying strategies other than conventional proactive or reactive routing. The connection between the derived throughput result and some well-known network throughput capacity results in the literature is also established.     

一种动态带宽资源预留分配链路接入控制算法

传统的基于带宽请求的固定资源预留链路接入控制算法（BRLAC）不能适应网络状态和业务需求的变化,针对该类算法接入成功率和系统带宽利用率不高的问题,基于概率分析了系统预留带宽的大小,并提出一种动态带宽资源预留分配链路接入控制算法（DBRRA）,该算法通过判断业务流优先级允许动态地从其他业务流调整预留带宽。仿真实验证明,DBRRA算法有较高的接入成功率、系统带宽利用率和较好的时延特性。     

基于微分几何的蛇形机器人移动与操作统一动力学模型研究

蛇形机器人本体是一种多关节串联机构,可以在各种环境中运动,并且当一端固定时可以实现操作.本文提出一种蛇形机器人移动与操作的统一动力学建模方法,统一蛇形机器人移动状态及操作状态的动力学方程.机器人从移动状态到操作状态的转换意味着机构上的重构,即移动状态无固定基座,而操作状态有固定基座.应用虚设机构法在机构学上统一这两种状态(即构形空间中的嵌入关系),利用指数积公式描述这两种状态的运动学方程.在Riemann流形上建立起蛇形机器人移动和操作的动力学模型,并在对动力学模型中各项计算分析的基础上发现机器人操作动力学方程可直接由移动动力学方程退化得到,同时应用子流形的Gauss公式给出证明.由此在微分几何框架下建立蛇形机器人移动与操作的统一动力学模型.按照几何的观点将蛇形机器人移动与操作动力学模型的统一看作是子流形问题,并赋予几何意义.较单独针对蛇形机器人的一种状态(移动或操作)的动力学模型而言,这种统一的动力学模型能够更深刻地揭示蛇形机器人动力学的特征.     

多格式海量数据统一存取的索引结构

为提高多格式海量数据统一存取效率,提出了一种基于Hadoop的分布式数据读取模式。并通过对海量数据非主键索引结构的研究,结合统一存取的描述理念,提出了基于HDFS的一种可适用于B-树和R-树及其变种的层次索引结构,改变了原键—值存储在非主键索引结构中的劣势。通过提出Hadoop缓冲策略、基于随机读取的新数据传输模型以及相应的查询处理策略,进一步降低了数据传输开销。实验表明,该系列方法优化了统一存取中随机存取效率,减少了相应的查询响应时间和数据传输开销,提高了多格式海量数据统一存取的性能。     

A dynamic programming branch and bound algorithm for pure integer programming

Several algorithms for linear integer programming have been proposed in which one or more of the conditions are relaxed to produce a solvable problem form. Reimposing these relaxed conditions can lead to a branch and bound process. In this paper an alternative relaxation is proposed in which the integer conditions are maintained but the feasibility conditions are relaxed in a special way. Reimposing feasibility by sequentially setting variables creates the branch and bound process. In special cases, the algorithm reverts to the normal form of dynamic programming.The algorithm is applicable to both linear and non-linear pure integer problems. It has been programmed to solve pure $\text{0}\text{1}$ problems and results of computational experience with some linear problems previously used in the literature are given.     

A dynamic access control scheme based upon the knapsack problem

A new dynamic access control scheme for information protection systems is proposed in this paper. The main idea of it is inspired by the concept of the trapdoor knapsack problem proposed by Merkle and Hellman. Since the knapsack problem is an NP-complete problem, the security of access control is achieved henceforth. Our scheme associates each user with some user keys and each file with some file keys. There is a positive integer set of S′; through a simple formula on keys and S′, the corresponding access privilege can be easily revealed in the protection system. Moreover, by employing our scheme, insertion or deletion of the user/file can be processed effectively with only a few previously defined keys and locks required to be modified.     

Policy-based spectrum access control for dynamic spectrum access network radios

We describe the design of a policy-based spectrum access control system for the Defense Advanced Research Projects Agency (DARPA) NeXt Generation (XG) communications program to overcome harmful interference caused by a malfunctioning device or a malicious user. In tandem with signal-detection-based interference-avoidance algorithms employed by cognitive software-defined radios (SDR), we design a set of policy-based components, tightly integrated with the accredited kernel on the radio device. The policy conformance and enforcement components ensure that a radio does not violate machine understandable policies, which are encoded in a declarative language and which define stakeholders’ goals and requirements. We report on our framework experimentation, illustrating the capability offered to radios for enforcing policies and the capability for managing radios and securing access control to interfaces changing the radios’ policies.     

UDPF: A unified data provision framework for developing dynamic resource-oriented embedded applications

With the popularity of various embedded applications, there is increasing demand for automatic updates with low bandwidth overhead. In this paper, a developing framework based on the Android platform called the Unified Data Provision Framework (UDPF) is proposed. The UDPF provides a framework with which developers are able to build applications with modules that are decoupled from each other. In the UDPF, applications are divided into two independent layers: the front-end and back-end. Developers are able to publish updates for their applications in the minimal replacement unit with low bandwidth overhead, and it is not necessary to re-install the applications. We build a social network application using UDPF and conduct a performance evaluation that demonstrates the effectiveness of UDPF.     

A unified dynamic model for locomotion and manipulation of a snake-like robot based on differential geometry

A snake-like robot, whose body is a seried-wound articulated mechanism, can move in various environments. In addition, when one end is fixed on a base, the robot can manipulate objects. A method of dynamic modeling for locomotion and manipulation of the snake-like robot is developed in order to unify the dynamic equations of two states. The transformation from locomotion to manipulation is a mechanism reconfiguration, that is, the robot in locomotion has not a fixed base, but it in manipulation ha...     

Fully dynamic metric access methods based on hyperplane partitioning

Metric access methods based on hyperplane partitioning have the advantage, compared to the ball partitioning-based ones, that regions do not overlap. The price is less flexibility for controlling the tree shape, especially in the dynamic scenario, that is, upon insertions and deletions of objects. In this paper we introduce a technique called ghost hyperplanes, which enables fully dynamic data structures based on hyperplane partitioning. We apply the technique to Brin's GNAT static index, obtaining a dynamic variant called EGNAT, which in addition we adapt to secondary memory. We show experimentally that the EGNAT is competitive with the M-tree, the baseline for this scenario. We also apply the ghost hyperplane technique to Voronoi trees, obtaining a competitive dynamic structure for main memory.     

面向服务的工作流动态访问控制模型

访问控制是提高工作流系统安全的重要机制.基于角色的访问控制(RBAC)被绝大多数工作流系统所采用,已成为工作流领域研究的热点.基于传统的RBAC模型,从工作流访问控制模型与流程模型分离的角度出发,提出了一种面向服务的工作流动态访问控制模型--SWDAC模型.模型中引入服务和上下文的概念,加强了对动态工作流系统的描述能力,并有效增强了访问控制的灵活性和系统的安全性.该访问控制模型已在自主研发的基于J2EE的工作流管理平台中实施.