Comparison of the performances of an automated arrhythmia detector working on original and virtual ECG tracings

Two approaches can be taken to improve the performance of an automatic arrhythmia detector: perfecting the detection algorithms or improving the quality of the investigated traces by preprocessing the original traces. This paper reports on the results of a data preprocessing approach. Preprocessing consists in constructing new traces, which we call virtual. They are mathematically obtained from the original traces and referred to the dominant cardiac electric axis. The classifications obtained with an arrhythmia detector using both virtual and original traces are presented and discussed. By comparing the performance indices obtained under the two different conditions, it can be seen that a diagnosis based on the virtual traces is as acceptable as one based on the original traces. This result should be judged as favorable, since the algorithm was not adjusted or calibrated to the virtual traces, while those who developed it had certainly calibrated the parameters to the original traces.     

蚁群智能模型检测算法

蚁群智能模型检测算法借鉴了自然界中蚂蚁通过信息素相互沟通,从而完成觅食、搬迁等需要协作的复杂社会活动的原理。通过分布在程序控制流图和状态图上的代理,即人工蚂蚁的回溯来跟踪寻找模型中的正确路径和错误路径,人工蚂蚁在控制流图上移动时,分别在正确路径和错误路径上释放两种不同的信息素,通过对两种信息素的对比,可自动定位出程序中引发特定错误的原因。由于人工蚂蚁之间相互独立、并行工作,因此算法能够同时、并行地跟踪多条正确路径和错误路径,也可同时定位出引发多个不同错误的不同原因。通过对中小规模程序的检测,结果表明,该算法是有效的。     

An empirical study on the use of mutant traces for diagnosis of faults in deployed systems

Debugging deployed systems is an arduous and time consuming task. It is often difficult to generate traces from deployed systems due to the disturbance and overhead that trace collection may cause on a system in operation. Many organizations also do not keep historical traces of failures. On the other hand earlier techniques focusing on fault diagnosis in deployed systems require a collection of passing–failing traces, in-house reproduction of faults or a historical collection of failed traces. In this paper, we investigate an alternative solution. We investigate how artificial faults, generated using software mutation in test environment, can be used to diagnose actual faults in deployed software systems. The use of traces of artificial faults can provide relief when it is not feasible to collect different kinds of traces from deployed systems. Using artificial and actual faults we also investigate the similarity of function call traces of different faults in functions. To achieve our goal, we use decision trees to build a model of traces generated from mutants and test it on faulty traces generated from actual programs. The application of our approach to various real world programs shows that mutants can indeed be used to diagnose faulty functions in the original code with approximately 60–100% accuracy on reviewing 10% or less of the code; whereas, contemporary techniques using pass–fail traces show poor results in the context of software maintenance. Our results also show that different faults in closely related functions occur with similar function call traces. The use of mutation in fault diagnosis shows promising results but the experiments also show the challenges related to using mutants.     

MPEG-4视频流长相关特性研究

长相关(Long-RangeDependence,LRD)是MPEG-4视频流基本的统计特性。对内容不同和内容相同但图像质量不同的MPEG-4视频流,用鲁棒性较好的R/S估值方法进行H参数估计,对影响LRD特性的原因进行了研究。通过实验分析,得出结论:MPEG-4视频流的LRD特性与图像质量、表示的内容、以及流量中的帧长突发次数有关。     

On trace inclusion optimization problems

The following four optimization problems over a finite set of traces are considered: (i) find the longest trace that is included in each trace from a given finite set T of traces, (ii) find the shortest trace that is not included in every trace from a given finite set T of traces, (iii) find the shortest trace that includes every trace from a given finite set T of traces, (iv) find the longest trace that does not include each trace from a given finite set T of traces.     

基于GHM多小波算法的功耗分析攻击

功耗分析的密钥获取是基于采集的功耗信号,功耗信号的信噪比是影响分析密钥成功率的重要因素,所以噪声能否被有效去除是提高功耗分析成功率的关键,针对该问题引入了基于GHM多小波的预处理方法。该方法首先对功耗曲线进行GHM多小波阈值去噪处理,其目的是最大限度地去除功耗曲线中不相关的噪声,提高功耗曲线中真实信号的信噪比,从而提高攻击效率。在MEGA16微控制器上,采集固定密钥随机明文的ASE算法的功耗曲线,对比原始功耗曲线与去噪后的功耗曲线执行相关功耗分析。实验结果表明,使用去噪后的功耗曲线执行相关功耗分析所需的功耗曲线减少了89.5%,相关系数平均提高了107.9%,验证了新方法的有效性。     

下颌髁突运动中心轨迹测量分析系统

20世纪90年代以来，虽然下颌运动轨迹的研究热点和难点已向髁突运动中心研究发展；然而目前，国际及国内尚未有商品化的髁突运动中心运动轨迹描记仪，国内也未见有关髁突运动中心运动轨迹研究成果的报道，为了获得下颌上任一点（包括髁突运动中心）的三维运动轨迹，以便为医学研究提供手段。首先利用计算机图形学技术和已有的三维六自由度下颌运动轨迹描记仪（MT1602）来获得下颌运动轨迹的原始数据，然后根据刚体运动规律，进行软件编程，自行设计并建立了一个髁突运动中心运动轨迹显示分析系统，该系统是用Microsoft Visual C^ 6.0髁突编写计算机程序自行开发的，可根据需要随时对系统软件进行功能补充和修改，整个系统有较强的可维护性和可升级性，实践表明，该系统可方便地获得地下颌上任一点（包括髁突运动中心）的三维运动轨迹，是一个实用的下颌髁突运动中心轨迹测量分析系统。     

MPEG-4流的多分形小波模型仿真及性能分析

本文采用多分形小波模型（MWM）对MPEG—4视频流进行仿真,其母小波采用Haar小波,并利用一阶统计、二阶统计和多分形分析的方法,对模型在刻画流量的主要统计特性（如概率密度分布、LRD特性、突发性和多分形特征）方面的性能进行了评估,其结果为：MWM模型是一个简单的和有实用价值的MPEG—4视频流的仿真模型,它可以很好地刻画出流量的全局统计特性和多分形特征,但此模型也有缺陷,对于具有高突发性的视频流量的刻画能力较弱,需要我们在以后的研究工作中加以完善。     

三角网格表面等残留高度刀轨生成算法

针对截平面法规划的三角网格表面的刀轨长度较长、加工表面残留高度不均匀的问题,提出一种基于改进截平面法的等残留高度刀轨生成算法.首先在估算刀触点轨迹线垂直方向曲率半径的基础上,计算刀触点轨迹投影线并对其进行修正,去除其中冗余的投影点;然后由修正后的刀触点轨迹投影线构造驱动表面,利用驱动表面和网格表面迭代计算刀触点轨迹线;最后由刀触点轨迹线计算无干涉刀轨.与截平面法生成的刀轨进行比较分析的结果表明,文中算法生成的刀轨长度较小且获得的残留高度保持均匀,适合于三角网格表面表示的复杂表面的精加工.     

NTFS系统存储介质上文件操作痕迹分析

计算机用户通过文件系统存取数据，文件和文件夹的操作(如增加、删除、修改)会在存储介质上留下痕迹，这些痕迹与文件系统有关。NTFS文件系统以簇为单位分配和回收外存空间，通过主文件表来进行管理。文章从计算机取证角度探讨NTFS文件系统下访问文件(夹)的方法，研究NTFS文件系统下文件和文件夹的操作痕迹，并与FAT文件系统中的痕迹进行比较。     

Privately Finding Specifications

Buggy software is a reality and automated techniques for discovering bugs are highly desirable. A specification describes the correct behavior of a program. For example, a file must eventually be closed once it has been opened. Specifications are learned by finding patterns in normal program execution traces versus erroneous ones. With more traces, more specifications can be learned more accurately. By combining traces from multiple parties that possess distinct programs but use a common library, it is possible to obtain sufficiently many traces. However, obtaining traces from competing parties is problematic: By revealing traces, it may be possible to learn that one party writes buggier code than another. We present an algorithm by which mutually distrusting parties can work together to learn program specifications while preserving their privacy. We use a perturbation algorithm to obfuscate individual trace values while still allowing statistical trends to be mined from the data. Despite the noise introduced to safeguard privacy, empirical evidence suggests that our algorithm learns specifications that find 85 percent of the bugs that a no-privacy approach would find.     

Enhancing synchronous collaboration by using interactive visualisation of modelled traces

This article addresses issues related to traces modelling for formally describing human interactions of people engaged in a synchronous collaborative learning activity. The objective is to propose models and tools for representing, transforming, sharing and visualising traces of users’ experiences. The traces here represent the users’ activities in their interactions with the learning platform. Our proposition is based on reflexive learning defined as the ability to interact with the situation, in order to meet one’s own limitations. This work takes place in the ITHACA project which aims at developing an on-line learning platform that uses interaction traces as knowledge sources on, and for, the learners’ learning as individuals or groups. In this paper, we propose a general framework for trace management and sharing, a generic model of synchronous collaborative activity based on the notion of interaction modes that we specialized for whiteboard sharing and text chatting, and a conceptual framework for modelling the exploitation of modelled traces, in particular for interactive visualisation on the user side. This article extends our previous work [1] on the instrumented prototypes, by presenting our theorisation of the interactive visualisation of modelled traces.     

事件日志的批量迹与过程模型的多视角对齐方法

在业务过程发现的一致性检测中,现有事件日志与过程模型的多视角对齐方法一次只能获得一条迹与过程模型的最优对齐;并且最优对齐求解中的启发函数计算复杂,以致最优对齐的计算效率较低。为此,提出一种基于迹最小编辑距离的、事件日志的批量迹与过程模型的多视角对齐方法。首先选取事件日志中的多条迹组成批量迹,使用过程挖掘算法得到批量迹的日志模型;进而获取日志模型与过程模型的乘积模型及其变迁系统,即为批量迹的搜索空间;然后设计基于Petri网变迁序列集合与剩余迹的最小编辑距离的启发函数来加快A*算法;最后设计可调节数据和资源视角所占权重的多视角代价函数,在乘积模型的变迁系统上提出批量迹中每条迹与过程模型的多视角最优对齐方法。仿真实验结果表明,相比已有工作,在计算批量迹与过程模型间的多视角对齐时,所提方法占用更少的内存空间和使用更少的运行时间。该方法提高了最优对齐的启发函数计算速度,可以一次获得批量迹的所有最优对齐,进而提高了事件日志与过程模型的多视角对齐效率。     

Trace-based mobility modeling for multi-hop wireless networks

Realistic and scenario-dependent mobility modeling is crucial for the reliable performance evaluation of multi-hop networks. In the last decade, a significant number of synthetic mobility models have been proposed. However, only a few of these models have been validated by realistic movement traces. In the last few years, several of such traces have been collected, analyzed, and made available to the community. This paper provides a comprehensive and up-to-date survey of (1) available movement traces, (2) modeling/analyses of these traces, and (3) synthetic mobility models. The focus of the paper is on mobility traces/models that include position information. The contribution of this paper is to summarize the research that has been done in the area of mobility modeling over the last few years and present challenges for future work.     

Post-processing in wireless sensor networks: Benchmarking sensor trace files for in-network data aggregation

Wireless sensor network research usually focuses on the reliable and efficient collection of data. In this paper we target on the next step in the lifetime of traces: we aim at investigating and evaluating, by qualitative and quantitative means, data repositories of already collected measurements. Concerning the collected datasets, several important topics arise like the need of exchanging traces between researchers using a common representation of the traces and the need for common classification of the traces based on a commonly agreed set of statistical characteristics for in retrospect utilization. In order to qualitatively address these issues, we propose the use of a novel set of metrics focusing on the in-network data-aggregation problem class. These metrics enable reliable evaluation of algorithms using the same benchmark traces (both in average cases and “stressful” setups) removing the need for running algorithms in a real testbed, at least in the initial development stage. We present the results of our research as a first approach for addressing this problem, and in order to confirm our method, we characterized several traces with the proposed metrics. We validate the metrics by predicting the performance of three data-aggregation schemes using the available traces and checking the results by actually running the algorithms.     

电磁兼容技术及其在PCB设计中的应用

在印制电路板的电路设计阶段就进行电磁兼容性(EMC)设计是非常重要的。本文介绍了电磁兼容技术及其在印制电路板中的应用，从印制电路板的选取到元器件的布置以及地线、电源线和信号线的设计，最后结合PROTEL公司的PROTEL99SE软件，给出了一种在PCB设计中减少电磁干扰的设计方法。     

基于通讯行为轮廓挖掘条件非频繁行为的方法

条件非频繁行为是指带有属性值的频数较低事件轨迹所记录的行为。从记录的事件日志中挖掘条件非频繁行为是业务过程优化的主要内容之一。已有的方法删除低频次行为,较少考虑模块网间数据流角度下的条件非频繁行为。基于此,文中提出了基于通讯行为轮廓挖掘条件非频繁行为的方法。以模块网间的通讯行为轮廓理论为基础,首先,通过给定的业务过程源模型查找其可执行事件日志,并且找出频数较低的事件轨迹,添加相关属性及属性值,即可得到条件非频繁轨迹；其次,通过计算不同模块网间通讯特征的条件依赖数值,确定条件不频繁轨迹是否删除或保留,从而得到优化事件日志,进而挖掘出优化通讯模型；最后,通过仿真实验验证了该方法的可行性。     

A metamodel for the compact but lossless exchange of execution traces

Understanding the behavioural aspects of a software system can be made easier if efficient tool support is provided. Lately, there has been an increase in the number of tools for analysing execution traces. These tools, however, have different formats for representing execution traces, which hinders interoperability and limits reuse and sharing of data. To allow for better synergies among trace analysis tools, it would be beneficial to develop a standard format for exchanging traces. In this paper, we present a graph-based format, called compact trace format (CTF), which we hope will lead the way towards such a standard. CTF can model traces generated from a variety of programming languages, including both object-oriented and procedural ones. CTF is built with scalability in mind to overcome the vast size of most interesting traces. Indeed, the design of CTF is based on the idea that call trees can be transformed into more compact ordered acyclic directed graphs by representing similar subtrees only once. CTF is also supported by our trace analysis tool SEAT (Software Exploration and Analysis Tool).