一种基于朴素贝叶斯分类的特征选择方法

由于朴素贝叶斯文本分类中的独立假设前提,使得在特征选择步骤能否准确有效地选出能代表文本的特征显得尤为重要,而特征选择标准中的MI标准与TFIDF标准其优缺正好互补,因此在用朴素贝叶斯文本分类方法中的多项式模型实现了一个web页面分类系统-WEBCAT的基础上,提出将MI标准与TFIDF标准结合进行特征选择.实验显示:用改进的方法可以更准确地选出能代表文本的特征,文本分类结果也比单独使用TFIDF标准或单独使用MI标准进行特征选择的分类结果更加精确.     

基于TFIDF特征选择方法的改进

TFIDF是常用的特征提取方法,但是该方法存在着很多不足。首先这个方法忽视了如果某词条仅仅在一个类别的文档集中存在次数多,在其他类别中存在次数少,则能说明该词条可以很好地反映类别特征。再者TFIDF忽视了特征与类别的关系。本文提出了改进的TFIDF策略,并结合简单距离向量分类方法与传统的TFIDF进行分类比较,得到了很好的分类效果,试验证明了其可行性。     

中文文本分类技术比较研究

文本分类中特征选择、权重计算及分类算法三个阶段中都存在一些经典方法,在实际的中文文本分类任务中,如何从各阶段不同方法的组合中找到一个好的组合成为值得研究的问题。比较研究中文文本分类中各阶段经典方法的不同组合对分类效果的影响结果表明:采用CHI特征选择方法、TFIDF权重计算方法及SVM分类方法的组合为最佳组合。     

基于空间向量模型的垃圾文本过滤方法

针对垃圾文本识别计算的需求特性,应用VSM文本聚类算法思想,综合现有TFIDF算法特点,提出一种基于VSM和改进的TFIDF特征项提取算法.本方法在对垃圾文本高聚类特征项权值进行放大的同时,有效减小由二类数据样本数量偏差对计算结果带来的影响,提高了垃圾文本过滤识别效率和准确率.为垃圾文本识别提供了一种新的改进算法选择.     

基于信息熵的TFIDF文本分类特征选择算法研究

特征权值的选择是文本分类技术的基础环节.在详细分析文本分类技术特点的基础上,基于信息熵理论建立了TF_IDF的改进算法模型;并根据实际工程数据,验证了算法模型的有效性.理论分析和实例验证表明该算法弥补了传统TFIDF算法没有考虑词条文本类间分布的不足,能更好的体现特征词条的权重,从而能有效提高分类的精确度.     

基于TFIDF的社区问答系统问句相似度改进算法

针对社区问答系统问句相似度计算问题,提出了一种改进的TFIDF算法.按照用户的查询意图对问句进行分类,根据特征词在类别中的分布对权值进行调整;将问句的主题词归入特征项进行TFIDF计算.实验结果表明,本文改进的TFIDF算法的P@3比传统的TFIDF算法提高了7.66%,比TFIDF-IG算法提高了5.31%,而且P@5和P@10也有不同程度的提高,与传统TFIDF算法和参考改进算法相比,该算法明显提高了检索性能.      

面向中文新闻话题检测的多向量文本聚类方法

基于多向量模型,给出一种将话题主题信息与话题文本信息相结合的多向量话题表示方式,使用较低的维度来准确表示一个话题.针对传统TFIDF方法在文本分类问题中对特征项在各个类中分布情况考虑不充分的问题,给出了一种TFIDF改进方法.在TDT4的中文语料上,与传统向量空间模型进行了对比实验.实验结果表明,给出的话题表示方法和TFIDF改进算法能够在较低的维度上,使聚类的准确率得到较大提升.     

基于朴素贝叶斯的档案分类研究

通过对甘肃省档案局数据资源的分析研究,并与朴素贝叶斯分类算法相结合,实现对档案资源分类应用的研究.根据档案数据的特征,选用TFIDF(term frequency-inverse document frequency)算法进行选取符合档案文本主题的属性.样本实验结果证明,该分类模型适用于档案文本资源的分类,实现了档案资源自动分类的功能.相较于传统朴素贝叶斯分类方法,所提出的分类模型针对档案资源的分类效率提高了1%~2%.     

基于TF-IDF的网页新闻分类的研究与应用

文本分类作为处理和组织大量文本数据的关键技术,为用户准确、快速查找所需信息提供依据。通过TFIDF算法计算文本词汇的词频,并根据词频排序选择特征项,再用Simhash和余弦相似度算法计算文本之间的相似度,最后采用准确率和召回率为评价标准,根据评价结果分析两种算法的优劣。     

基于朴素贝叶斯的垃圾邮件分类系统的设计

结合垃圾邮件分类系统的具体要求,在传统规则分类方法的基础上引入机器学习的知识,给出了系统体系结构和特征提取算法,试验了一种对新邮件计算所属类别后验概率的方法,并详细讨论了一个基于朴素贝叶斯方法的个性化垃圾邮件分类系统的设计。提出的分TFIDF特征子集提取算法和朴素贝叶斯方法对邮件进行分类具有较好的分类精度,应用朴素贝叶斯方法在新邮件到达的同时对其进行分类,具有较好的分类速度。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

英文诗歌中的喻类修辞

为了有助于提高英文爱好者的个人情操、文化素养和学习兴趣,以及专业人员对英语学习和研究进行多途径的探索,本文通过一些精选诗歌的引证和分析,着重论述了喻类修辞法在英文诗歌中的运用其及效果。     

Man Is Unable to Change the Miserable Life——Analysis of the Arrangement of Four Characters in The Glass Menagerie

Tennessee Williams is considered as one of the most important American playwrights since World War II.The Glass Menagerie is his first successful drama,which describes a tragic situation of family and means to say that Man is unable to change the miserable life,no matter whatever means he try,This essay focuses on the analysis of the arrangement of the four main characters:Laura.Amanda,Jim and Tom to reveal the theme.Laura is fragile.Amanda is brave.Jim is vital.Tom is sensible.And all of them develop and try the different means to struggle against life,but fail tragically.With the evidence,the paper comes to conclusion naturally that Man is unable to change the miserable life,and he dooms to fail.     

Characterization of root-nodulating bacteria on Retama raetam in arid Tunisian soils

The aim of this study is to investigate the diversity of Retama raetam root-nodule bacteria isolated from arid regions of Tunisia. Twelve isolates, chosen as representative for different 16S rRNA gene patterns, were characterized by 16S rRNA gene sequencing and phenotypic analysis. Isolates were assigned to Sinorhizobium, Rhizobium and Agrobacterium. Symbiotic properties of Sinorhizobium and Rhizobium isolates showed a large diversity in their capacity to infect their host plant and fix atmospheric nitrogen. Strain RK 22 identified as Rhizobium was the most effective isolate.     

An Affordable Accurate Evaluation of the Binding Conformations Predicted by Molecular Docking Studies in Bio-System

正Recently,docking has been widely used to predict the binding-modes of protein-inhibitors,when the crystal complexes structure was absent.Most docking algorithms are able to generate a large number of probable conformations,it,however,is difficult to effectively evaluate these docking poses and identify the most reasonable bindingmode.In the present study,on the basis of the crystallographic data of human 3-hydroxy-3-methylglutaryl coenzyme     

WIMAX与WI-FI技术分析及联合组网

介绍了WiMAX与Wi-Fi两种无线宽带接入技术,并对两者之间的关系及相互之间的影响做了对比及分析,并对WiMAX的关键技术进行了详细说明,最后对两者的联合组网方式做了简单的探讨。