Using multiple indexes for efficient subsequence matching in time-series databases

A time-series database is a set of data sequences, each of which is a list of changing values of an object in a given period of time. Subsequence matching is an operation that searches for such data subsequences whose changing patterns are similar to a query sequence in a time-series database. This paper addresses a performance issue of time-series subsequence matching. First, we quantitatively examine the performance degradation caused by the window size effect, and then show that the performance of subsequence matching with a single index is not satisfactory in real applications. We claim that index interpolation is a fairly effective tool to solve this problem. Index interpolation performs subsequence matching by selecting the most appropriate one from multiple indexes built on windows of their distinct sizes. For index interpolation, we need to decide the sizes of windows for multiple indexes to be built. In this paper, we solve the problem of selecting optimal window sizes from the perspective of physical database design. Given a set of pairs 〈length, frequency〉 of query sequences to be performed in a target application and a set of window sizes for building multiple indexes, we devise a formula that estimates the overall cost of all the subsequence matchings performed in a target application. By using this formula, we propose an algorithm that determines the optimal window sizes for maximizing the performance of entire subsequence matchings. We formally prove the optimality as well as the effectiveness of the algorithm. Finally, we show the superiority of our approach by performing extensive experiments with a real-life stock data set and a large volume of synthetic data sets.     

基于ERwin模型的ERP系统研究

在论述中国加入WTO后ERP系统应用现状的基础上,分析了关系数据库的建模方法,重点对用ERwin这一关系数据库应用开发的优秀CASE工具的应用进行了研究,提出了ERP系统的功能模块的组成,借助ERwin建立了ERP系统的信息模型,给出了其逻辑模式和物理模式的视图及其向具体数据库物理结构的转换方法。以SQLServer作为后台数据库支持,Delphi为前台界面开发工具,建立了一个ERP系统。为企业的ERP的研究和应用提供了一种方法和思路。     

基于MC13233的ZigBee物理层分析与设计

以Freesacle公司的ZigBee RF4CE芯片MC13233为基础,依据嵌入式硬件构件的规范设计了硬件各模块。介绍MC13233的ZigBee物理层的模型。详细阐述MC13233的ZigBee物理层的设计方法,具体实现RF收发器的工作模式设置、物理层数据收发、CCA/ED/LQI,并给出了物理层正确性和可靠性测试。     

一种高性能低VOC尼龙6复合材料的研究

通过研究基料、无机填料、增韧剂、润滑剂对尼龙6(PA6)复合材料的物理性能、VOC的影响,得到一种高性能低VOC的PA6复合材料。结果表明:以PA6 IM为基料、滑石粉为无机填料、EPDM 3092M为增韧剂、E525为润滑剂的尼龙6复合材料,具有高性能、低VOC的优点。     

Modeling temperature effects on a Coriolis mass flowmeter

Coriolis mass flowmeters are used for many applications, including as transfer standards for proficiency testing and liquified natural gas (LNG) custody transfer. We developed a model to explain the temperature dependence of a Coriolis meter down to cryogenic temperatures. As a first step, we tested our model over the narrow temperature range of 285 K to 318 K in this work. The temperature dependence predicted by the model agrees with experimental data within ± 0.08 %; the model uncertainty is 0.16 % (95 % confidence level) over the temperature range of this work.Here, basic concepts of Coriolis flowmeters will be presented, and correction coefficients will be proposed that are valid down to 5 K based on literature values of material properties.     

基于网络的塑性成形物理模拟系统的构建

提出基于网络的塑性成形模拟系统方案,将网络信息传递快捷、直观的特点同塑性成形模拟技术的科学预测作用结合起来,改善目前塑性加工生产中存在的信息交流方式落后、生产周期长、适应性差、不能满足现代生产和市场需要等问题。构建的系统方案应用到发动机连杆锻造过程中。应用物理模拟技术研究连杆、曲轴等锻件的成形过程,揭示出锻造过程中坯料的流动和充填情况;测定成形力、错移力等重要工艺参数,为合理制定锻造工艺方案和设计可靠的模具结构提供了有力的保障,实现了设计、制造和模拟仿真等部门之间信息和图像的快捷传递。     

Cooperative Decode‐and‐Forward Relaying for Secure Multicasting

In this paper, secure multicasting with the help of cooperative decode‐and‐forward relays is considered for the case in which a source securely sends a common message to multiple destinations in the presence of a single eavesdropper. We show that the secrecy rate maximization problem in the secure multicasting scenario under an overall power constraint can be solved using semidefinite programing with semidefinite relaxation and a bisection technique. Further, a suboptimal approach using zero‐forcing beamforming and linear programming based power allocation is also proposed. Numerical results illustrate the secrecy rates achieved by the proposed schemes under secure multicasting scenarios.     

涂敷介质目标的雷达散射截面

在金属目标表面涂敷吸波材料可以有效地抑制雷达散射截面,增强雷达目标的隐身性能.因此,精确的计算涂敷 介质目标的雷达散射截面(Radar Cross Section, RCS)尤为重要。文中提出了一种基于物理光学(Physical Optics, PO)的方法 来计算复杂涂敷介质目标的RCS。首先以涂敷两层介质的平板为例将FEKO 软件计算结果作为参照验证该算法的精确度, 然后分别以涂敷两层介质的平板和复杂的导弹为例体现该算法的效率。     

诺克斯事务所的非标准化建筑进程

文章通过分析荷兰诺克斯事务所在三个不同领域——研究、艺术和建筑方面的工作,力图探寻其设计技巧与方法论的关系。设计技巧从纯物理模型到类比计算再到现在的脚本编写,这种进步亦反映出科学技术进步对当代建筑设计的影响。     

基于异常样品剔除的酒醅近红外定量分析模型的精度提升

目的 利用异常识别算法识别出原数据集中存在的奇异点,以建立预测精度更高的酒醅定量分析模型。方法 采用集群分析思维,利用马氏距离、主成分马氏距离、蒙特卡罗交叉验证法对108个样本进行异常样品识别及剔除,以光谱-理化值共生距离算法进行样品集的划分,划分比例为3:1。结果 酒醅水分近红外定量分析模型经马氏距离处理后预测精度达到最高,预测相关系数上升了0.43%,预测均方根误差下降了6.94%;酒醅酸度近红外定量分析模型经马氏距离处理后预测精度达到最高,预测相关系数上升了0.02%,预测均方根误差下降了0.20%;酒醅还原糖近红外定量分析模型经蒙特卡罗处理后,预测相关系数上升了8.74%,预测均方根误差下降了42.14%;酒醅淀粉近红外定量分析模型经蒙特卡罗处理后预测精度达到最高,预测相关系数上升了2.81%,预测均方根误差下降了57.80%。结论 经过验证,剔除异常样品可建立出预测精度更高的酒醅定量分析模型。