结合缺失模式的不完整数据模糊聚类

数据的完整性是数据可用性的重要维度。由于数据采集等过程中存在的问题,现实中的数据往往存在缺失。现有的聚类算法在面对不完整数据时一般采用忽略缺失或填补缺失的策略,但是当数据缺失属于非随机缺失时,这样的处理策略会导致聚类精度严重下降。当数据缺失属于非随机缺失时,数据缺失模式与缺失属性的取值相关,因此在不完整对象的相似度量中加入缺失模式相似的度量,提出了两种结合缺失模式的 PCM(Possibilistic c-means)模糊聚类算法:最小化缺失模式距离之和的 PatDistPCM 算法和基于缺失模式聚类的 PatCluPCM 算法。在两个公开数据集上的实验证明, 考虑缺失模式的模糊聚类PatDistPCM和PatCluPCM算法,在对存在非随机缺失的数据进行聚类时 ,能有效提高聚类结果的准确性。     

Exploring approaches to improve the performance of autonomous monitoring with imperfect data in location-aware wireless sensor networks

In recent years, information and sensing technologies have been applied to the construction industry to collect and provide rich information to facilitate decision making processes. One of the applications is using location data to support autonomous crane safety monitoring (e.g., collision avoidance and dangerous areas control). Several location-aware wireless technologies such as GPS (Global Positioning System), RFID (Radio-frequency identification), and Ultra-Wide Band sensors, have been proposed to provide location information for autonomous safety monitoring. However, previous studies indicated that imperfections (errors, uncertainty, and inconsistency) exist in the data collected from those sensors and the data imperfections have great impacts on autonomous safety monitoring system performance. This paper explores five computationally light-weight approaches to deal with the data imperfections, aiming to improve the system performance. The authors built a scaled autonomous crane safety monitoring testbed with a mounted localization system to collect location data and developed five representative test cases based on a live construction jobsite. Seven hundred and sixty location readings were collected at thirty-eight test points from the sensors. Those location data was fed into the reasoning mechanisms with five approaches to generate the safety decisions at those thirty-eight test points and evaluate system performance in terms of precision, recall and accuracy. The results indicate that system performance can be improved if at least ten position readings from sensors can be collected at small intervals at any location along the moving path. However, by including additional data such as velocity and acceleration that may be read from devices mounted on workers, localization error may be significantly reduced. These findings represent a path forward to improve localization accuracy by mixing imperfect data from the sensed environment with supplemental input.     

体素几何模型中物体表面的绘制算法

在体素几何模型中 ,物体由体素表示 ,物体表面由边界体素表示。当体素大小与屏幕像素大小相等时 ,可把边界体素作为点向投影面投影 ,但这样易产生空洞现象和图像走样。基于物体边界体素 ,生成一个绘制表面 ,用光线投射法显示这个绘制表面 ,可以消除空洞现象 ,减轻图像走样。这种算法能生成光滑细腻的图像。本文生成绘制表面的速度比 Dividing Cubes算法生成表面的速度快     

Estimation of vector error correction models with mixed‐frequency data

Vector autoregressive (VAR) models with error‐correction structures (VECMs) that account for cointegrated variables have been studied extensively and used for further analyses such as forecasting, but only with single‐frequency data. Both unstructured and structured VAR models have been estimated and used with mixed‐frequency data. However, VECMs have not been studied or used with mixed‐frequency data. The article aims partly to fill this gap by estimating a VECM using the expectation‐maximization (EM) algorithm and US data on four monthly coincident indicators and quarterly real GDP and, then, using the estimated model to compute in‐sample monthly smoothed estimates and out‐of‐sample monthly forecasts of GDP. Because the model is treated as operating at the highest monthly frequency and the monthly‐quarterly data are used as given (neither interpolated to all‐monthly data, nor aggregated to all‐quarterly data), the application is expected to be unbiased and efficient. A Monte Carlo analysis compares the accuracy of VECMs estimated with the given mixed‐frequency data vs. with their single‐frequency temporal aggregate.     

A nice electricity market design

This paper proposes a nice electricity market design that is efficient and practical, meaningfully satisfying the wants of a market design’s stakeholders. Hence, this new design should be considered by countries that have reformed their electricity sectors or are in the process of doing so.     

Advancing post-earthquake structural evaluations via sequential regression-based predictive mean matching for enhanced forecasting in the context of missing data

After an earthquake, every damaged building needs to be properly evaluated in order to determine its capacity to withstand aftershocks as well as to assess safety for occupants to return. These evaluations are time-sensitive as the quicker they are completed, the less costly the disaster will be in terms of lives and dollars lost. In this direction, there is often not sufficient time or resources to acquire all information regarding the structure to do a high-level structural analysis. The post-earthquake damage survey data may be incomplete and contain missing values, which delays the analytical procedure or even makes structural evaluation impossible. This paper proposes a novel multiple imputation (MI) approach to address the missing data problem by filling in each missing value with multiple realistic, valid candidates, accounting for the uncertainty of missing data. The proposed method, called sequential regression-based predictive mean matching (SRB-PMM), utilizes Bayesian parameter estimation to consecutively infer the model parameters for variables with missing values, conditional based on the fully observed and imputed variables. Given the model parameters, a hybrid approach integrating PMM with a cross-validation algorithm is developed to obtain the most plausible imputed data set. Two examples are carried out to validate the usefulness of the SRB-PMM approach based on a database including 262 reinforced concrete (RC) column specimens subjected to earthquake loads. The results from both examples suggest that the proposed SRB-PMM approach is an effective means to handle missing data problems prominent in post-earthquake structural evaluations.     

时空大数据的缺失数据流关联修复仿真

传统方法对缺失数据进行修复,通常存在填补效果较差、所需时间较长和填补准确度较低等问题。提出一种针对时空大数据的缺失数据流关联修复方法。方法首先利用数据流之间的关联规则创建条件函数依赖,然后对数据流之间的关联相似度进行计算,并通过该相似度结果进一步计算缺失数据的加权值,完成对缺失数据和相应的临界点之间融合情况的检测。最后选择最佳置信度方法决定缺失数据的修复顺序,以实现对时空大数据缺失数据流的修复。经过仿真证明,提出的方法对缺失数据流检测准确,且修复效果好,经过修复的数据流与原始时空大数据十分接近。     

PPT 教学有效性的缺失与提升策略研究

近年来,以PPT为媒介的教学方式得到广泛应用,并在教学过程中发挥着举足轻重的作用。然而这种教学方式的出现也带来了一些问题,这些问题直接影响了教学的效果和质量。本文将仔细分析PPT教学有效性缺失的原因,并针对这些原因提出提升教学有效性的对策和建议。