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81.
Developing sound or reliable statistical models for analyzing motor vehicle crashes is very important in highway safety studies. However, a significant difficulty associated with the model development is related to the fact that crash data often exhibit over-dispersion. Sources of dispersion can be varied and are usually unknown to the transportation analysts. These sources could potentially affect the development of negative binomial (NB) regression models, which are often the model of choice in highway safety. To help in this endeavor, this paper documents an alternative formulation that could be used for capturing heterogeneity in crash count models through the use of finite mixture regression models. The finite mixtures of Poisson or NB regression models are especially useful where count data were drawn from heterogeneous populations. These models can help determine sub-populations or groups in the data among others. To evaluate these models, Poisson and NB mixture models were estimated using data collected in Toronto, Ontario. These models were compared to standard NB regression model estimated using the same data. The results of this study show that the dataset seemed to be generated from two distinct sub-populations, each having different regression coefficients and degrees of over-dispersion. Although over-dispersion in crash data can be dealt with in a variety of ways, the mixture model can help provide the nature of the over-dispersion in the data. It is therefore recommended that transportation safety analysts use this type of model before the traditional NB model, especially when the data are suspected to belong to different groups. 相似文献
82.
针对小本体PP装置抽真空排出的含有纯度极高的丙烯气体排入大气这一现状 ,提出了合适的水气分离措施及工艺操作 ,以利于将排空丙烯彻底回收并避免环境污染 ,提高了装置的经济效益 相似文献
83.
欧阳征标 《深圳大学学报(理工版)》1991,(Z2)
本文研究了负反馈放大电路的方框图分析法中的基本放大电路的输入输出端口的选择问题,给出了一个选择原则:若所选择的基本放大电路的输入输出端口不会导致放大电路的负反缋组态的改变,则这样的选择是合适的.反之则是不合适的。文中针对可能的4种组态的负反馈电路验证了这个选择原则. 相似文献
84.
85.
一种基于人工免疫理论的入侵检测模型 总被引:1,自引:0,他引:1
谢建全 《数字社区&智能家居》2006,(11)
基于智能技术的异常检测正成为IDS研究的一个重要方向,其研究目标主要是提高检测系统的准确性、实时性、高效性以及自适应性,借鉴生物免疫系统的计算机免疫系统将成为解决入侵检测问题的有效手段。本文分析了生物免疫系统的原理,结合生物免疫理论,提出一种基于检测代理的分布式网络入侵检测免疫模型。 相似文献
86.
Monfette Marie-Eve; Grimard Fran?ois; Ivers Hans; Blais Marie-Claude; Lavoie Vicky; Boisvert Jean-Marie 《Canadian Metallurgical Quarterly》2006,38(3):261
The popularity of the Fear of Negative Evaluation scale (FNE; Watson & Friend, 1969) stems from the centrality of this construct in personality, social and clinical psychology. In order to meet the needs of the Francophone researchers community, Kéroack, Boisvert, and Prévost (1987) traduced the short version of this instrument. Since social anxiety is most salient in adolescence, there is a need for normative and psychometric data for this population. This research aims at documenting the psychometric properties and norms for Francophone adolescents. Five hundred and seventy-eight participants aged from 14 to 19 years completed the French versions of the short FNE and the Social Avoidance and Distress scale. The factorial structure, the internal consistency and the convergent validity analyses confirm the traduction's quality and the questionnaire's validity. Norms are presented separately for females and males. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
87.
88.
Bilal Alataş Erhan Akin 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2006,10(3):230-237
In this paper, a genetic algorithm (GA) is proposed as a search strategy for not only positive but also negative quantitative
association rule (AR) mining within databases. Contrary to the methods used as usual, ARs are directly mined without generating
frequent itemsets. The proposed GA performs a database-independent approach that does not rely upon the minimum support and
the minimum confidence thresholds that are hard to determine for each database. Instead of randomly generated initial population,
uniform population that forces the initial population to be not far away from the solutions and distributes it in the feasible
region uniformly is used. An adaptive mutation probability, a new operator called uniform operator that ensures the genetic
diversity, and an efficient adjusted fitness function are used for mining all interesting ARs from the last population in
only single run of GA. The efficiency of the proposed GA is validated upon synthetic and real databases. 相似文献
89.
本文介绍了一种用于发电机的微机反时限负序电流保护装置。装置兼有显示I2及I22t和压缩数据打印功能。为了保证宽频率范围内的测量准确度,采用了自适应采样,装置具有准确、可靠的特点,便于运行和试验。文中简述了硬件、软件和样机试验结果。 相似文献
90.
There are about 75,000 pedestrian crashes in the United States each year. Approximately 5000 of these crashes are fatal, accounting for 12% of all roadway deaths. On college campuses, pedestrian exposure and crash-risk can be quite high. Therefore, we analyzed pedestrian crashes on the campus of the University of North Carolina at Chapel Hill (UNC) as a test case for our spatially-oriented prototype tool that combines perceived-risk (survey) data with police-reported crash data to obtain a more complete picture of pedestrian crash-risk. We use spatial analysis techniques combined with regression models to understand factors associated with risk. The spatial analysis is based on comparing two distributions, i.e. the locations of perceived-risk with police-reported crash locations. The differences between the two distributions are statistically significant, implying that certain locations on campus are perceived as dangerous, though pedestrian crashes have not yet occurred there, and there are actual locations of police-reported crashes that are not perceived to be dangerous by pedestrians or drivers. Furthermore, we estimate negative binomial regression models to combine pedestrian and automobile exposure with roadway characteristics and spatial/land use information. The models show that high exposure, incomplete sidewalks and high crosswalk density are associated with greater observed and perceived pedestrian crash-risk. Additionally, we found that people perceive a lower risk near university libraries, stadiums, and academic buildings, despite the occurrence of crashes. 相似文献