基于USBKEY的访问控制方法研究

为了使USBKEY得到更广泛的利用,分析了目前几种不同环境下基于USBKEY访问控制的方法,介绍了各自的工作原理并对各种访问控制方式的优点和缺点进行了比较.在此基础上,提出了在BIOS层实现的基于USBKEY的远程访问控制框架,对USBKEY用户登录系统过程中身份认证和系统资源的访问控制功能进行完善.     

Workflow performance analysis and simulation based on multidimensional workflow net

Workflow model performance analysis plays an important role in the research of workflow techniques and efficient implementation of workflow management. Instances dwelling times (IDT) which consist of waiting times and handle times in a workflow model is a key performance analysis goal. In a workflow model the instances which act as customers and the resources which act as servers form a queuing network. Multidimensional workflow net (MWF-net) includes multiple timing workflow nets (TWF-nets) and the organization and resource information. This paper uses queuing theory and MWF-net to discuss mean value and probability distribution density function (PDDF) of IDT. It is assumed that the instances arrive with exponentially distributed inter-arrival times and the resources handle instances within exponentially distributed times or within constant times. First of all, the mean value and PDDF of IDT in each activity is calculated. Then the mean value and PDDF of IDT in each control structure of a workflow model is computed. According to the above results a method is proposed for computing the mean value and PDDF of IDT in a workflow model. Finally an example is used to show that the proposed method can be effectively utilized in practice.     

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.     

基于不重叠路径熵的网络抗毁性评估方法

通过引入熵的概念,提出了基于不重叠路径数的标准稳定熵指标,用于刻画节点间抗毁性随不重叠路径数变化的规律.在此基础上给出了用于全网抗毁性评估的模型.同时指出了评价模型中涉及的节点间不重叠路径数的计算方法.最后通过算例分析以及与最短路径法相比较,论证了基于不重叠路径熵的模型在网络抗毁性评估方面具有更高的准确性与合理性.     

Boosting performance of multidimensional tores

This paper suggests a speed boosting technique for system area networks in massive parallel multiprocessor computers by decreasing the diameter and increasing the throughput of a pair of opposite simplex rings (a duplex ring), a couple and quadruple of such rings. The result is achieved through replacing a duplex ring with a pair of minimal switched multidimensional rings with different steps in each ring. The decreased diameter and increased throughput of rings appreciably reduce packet delivery delays in system area networks based on the pairs of such rings.     

基于远程直接内存访问的高性能键值存储系统

随着数据与系统规模的不断扩大,网络传输成为了键值存储系统的性能瓶颈。同时,远程直接内存访问(RDMA)技术能够支持高带宽和低时延的数据传输,为键值存储系统设计提供了新的思路。结合高性能网络中的RDMA技术,设计并实现了高性能、低CPU负载的键值存储系统Chequer;结合RDMA原语的特性,重新设计了键值存储系统的基本操作工作流程;并设计了基于线性探测的共享hash表,解决客户端缓存失效的问题以及提高hash命中率来减少客户端的读取轮数,进一步提高了系统的性能。在小规模集群上实现了Chequer系统,并通过实验验证了其性能。     

基于多跳中继的宽带接入网组网成本性能分析*

利用成本分析模型及等性能成本比较方法对基于多跳中继的宽带无线接入网络部署进行了量化分析,并与传统单跳网络部署进行了仿真比较。结果显示,基于中继的网络部署在保证性能的前提下能有效地降低组网成本,增强网络边缘吞吐量,扩大基站覆盖范围。进一步分析表明,无线资源配置方法也对网络的成本增益有一定的影响。复用技术能进一步改善中继网络的成本效益,并有效提升网络性能。     

TACIoT: multidimensional trust-aware access control system for the Internet of Things

Internet of Things environments are comprised of heterogeneous devices that are continuously exchanging information and being accessed ubiquitously through lossy networks. This drives the need of a flexible, lightweight and adaptive access control mechanism to cope with the pervasive nature of such global ecosystem, ensuring, at the same time, reliable communications between trusted devices. To fill this gap, this paper proposes a flexible trust-aware access control system for IoT (TACIoT), which provides an end-to-end and reliable security mechanism for IoT devices, based on a lightweight authorization mechanism and a novel trust modelthat has been specially devised for IoT environments. TACIoT extends traditional access control systems by taking into account trust values which are based on reputation, quality of service, security considerations and devices’ social relationships. TACIoT has been implemented and evaluated successfully in a real testbed for constrained and non-constrained IoT devices.     

CT图像肺及肺病变区域分割方法综述

计算机断层扫描(computed tomography, CT)技术能为新冠肺炎(corona virus disease 2019,COVID-19)和肺癌等肺部疾病的诊断与治疗提供更全面的信息,但是由于肺部疾病的类型多样且复杂,使得对肺CT图像进行高质量的肺病变区域分割成为计算机辅助诊断的重难点问题。为了对肺CT图像的肺及肺病变区域分割方法的现状进行全面研究,本文综述了近年国内外发表的相关文献：对基于区域和活动轮廓的肺CT图像传统分割方法的优缺点进行比较与总结,传统的肺CT图像分割方法因其实现原理简单且分割速度快等优点,早期使用较多,但其存在分割精度不高的缺点,目前仍有不少基于传统方法的改进策略;重点分析了基于卷积神经网络(convolutional neural network, CNN)、全卷积网络(fully convolutional network, FCN)、U-Net和生成对抗网络(generative adversarial network, GAN)的肺CT图像分割网络结构改进模型的研究进展,基于深度学习的分割方法具有分割精度高、迁移学习能力强和鲁棒性高等优点,特...     

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.     

Zoned-partitioning of tree-like access methods

The performance of access methods and the underlying disk system is a significant factor in determining the performance of database applications, especially with large sets of data. While modern hard disks are manufactured with multiple physical zones, where seek times and data transfer rates vary significantly across the zones, there has been little consideration of this important disk characteristic in designing access methods (indexing schemes). Instead, conventional access methods have been developed based on a traditional disk model that comes with many simplifying assumptions such as an average seek time and a single data transfer rate. The paper proposes novel partitioning techniques that can be applied to any tree-like access methods, both dynamic and static, fully utilizing zoning characteristics of hard disks. The index pages are allocated to disk zones in such a way that more frequently accessed index pages are stored in a faster disk zone. On top of the zoned data placement, a localized query processing technique is proposed to significantly improve the query performance by reducing page retrieval times from the hard disk.     

Estimating secondary school catchment areas and the spatial equity of access

Following the Educational Reform Act of 1988, families in England and Wales have been free to identify a preferred school for their children’s secondary education. However, as part of this open selection, the demand from parents opting to send their children to the best performing schools far outstrips the supply of available places at them, and consequently many schools ration places using entry criteria that favour those pupils domiciled close to the school. Through this geographic selection process, choice is spatially sorted and access to the best schools is often crucially dependent upon where parents live. After illustrating this problem, this paper develops an automated modelling technique that can be used to define and map school catchment areas based on the home locations of pupils attending every publically funded school in England. It then develops this framework to create a web based decision support tool to aid parents seeking secondary school places.     

对象关系型空间数据库的访问方式的改进

对象关系型空间数据库使得地理空间对象可以作为一种新的类型存储到空间数据库中。然而索引访问方式与数据类型是紧密联系的。为了使空间数据库用户为每个新空间数据类型建立自己的索引,同时减轻工作量,对将GiST索引框架引入到空间数据库进行了介绍,并分析了GiST框架下的空间索引的好处与劣势。在此基础上,实现了访问效率较高的GiST R*树索引,并对其时间效率和空间效率进行测试。     

基于多维混沌系统的自适应加密算法

提出了一种基于多维混沌系统的自适用加密算法,先从矩阵的某个元素开始遍历各个元素.根据图像的行的遍历顺序来决定的列的置乱顺序,再根据列的遍历顺序来对行进行置乱.然后使用三维Liu混沌系统对置乱后的图像进行加密.理论分析和实验表明,该方案具有良好的密码特性.     

基于多维标度的动态网络选择算法

异构无线网络的网络选择问题中,除了考虑多属性的网络参数外,还需考虑无线信道的时变性特征。针对这两个考虑因素,提出了一种基于多维标度的新的动态网络选择算法,可将多属性判决的网络选择问题近似转化为一个低维的拟合构图,并能反映不同时刻同个网络的变化。仿真结果表明,在不考虑负载的情况下,提出的算法能有效地选择出适合于移动终端当前业务的网络,并能在低维坐标系中直观地观察网络间的区别。     

基于多维功能索引的服务匹配方法

服务匹配是面向服务架构(SOA)中的重要问题,为了解决现有服务匹配方法中功能匹配不准确和匹配效率低的问题,提出一种基于多维功能索引的服务匹配方法.该方法首先对应用领域中的基本功能操作进行了定义,基于定义的功能操作给出Web服务的功能描述,进而引入两级索引机制建立服务的多维功能索引,最后在索引基础上给出了服务匹配和相关性排序算法.测试结果表明,该方法在服务匹配准确度上与现有方法相比有10%左右的提高,同时具有较优的时间性能.     

基于多维度特征分析的KPI异常检测

为帮助运维人员提前发现未知风险,减少因异常风险带来的损失,提出多种特征融合的异常检测方法.对关键性能指标(KPI)进行多维度的特征提取,使用主成分分析方法(PCA)进行降维,对降维后的数据按照时序模式,使用小波分解提取出高频特征与低频特征,使用极限梯度提升(XGBoost)模型进行异常检测.实验结果表明,该方法有较好的...     

A clustering method based on multidimensional texture analysis

Considering the analogy between image segmentation and cluster analysis, the aim of this paper is to adapt statistical texture measures to describe the spatial distribution of multidimensional observations. The main idea is to consider the cluster cores as domains characterized by their specific textures in the data space. The distribution of the data points is first described as a multidimensional histogram defined on a multidimensional regular array of sampling points. In order to evaluate locally a multidimensional texture, a co-occurrence matrix is introduced, which characterizes the local distribution of the data points in the multidimensional data space. Several local texture features can be computed from this co-occurrence matrix, which accumulates spatial and statistical information on the data distribution in the neighborhoods of the sampling points. Texture features are selected according to their ability to discriminate different distributions of data points. The sampling points where the local underlying texture is evaluated are categorized into different texture classes. The points assigned to these classes tend to form connected components in the data space, which are considered as the cores of the clusters.