A scaleable document clustering approach for large document corpora

In this paper, the scalability and quality of the contextual document clustering (CDC) approach is demonstrated for large data-sets using the whole Reuters Corpus Volume 1 (RCV1) collection. CDC is a form of distributional clustering, which automatically discovers contexts of narrow scope within a document corpus. These contexts act as attractors for clustering documents that are semantically related to each other. Once clustered, the documents are organized into a minimum spanning tree so that the topical similarity of adjacent documents within this structure can be assessed. The pre-defined categories from three different document category sets are used to assess the quality of CDC in terms of its ability to group and structure semantically related documents given the contexts. Quality is evaluated based on two factors, the category overlap between adjacent documents within a cluster, and how well a representative document categorizes all the other documents within a cluster. As the RCV1 collection was collated in a time ordered fashion, it was possible to assess the stability of clusters formed from documents within one time interval when presented with new unseen documents at subsequent time intervals. We demonstrate that CDC is a powerful and scaleable technique with the ability to create stable clusters of high quality. Additionally, to our knowledge this is the first time that a collection as large as RCV1 has been analyzed in its entirety using a static clustering approach.     

中俄天然气贸易安全格局与态势

中俄天然气合作对两国天然气贸易安全具有重要影响。已有研究对于天然气贸易安全评价以定性分析为主,近年来越来越多的研究开始采用定量方法评价天然气贸易安全。本文基于HHI指数(赫芬达尔-赫希曼指数),构建了天然气进口和出口安全评价体系,科学评估了在不同因素影响下中俄天然气贸易安全格局与态势。研究表明：中国天然气进口多元化程度逐渐提升,从俄罗斯进口天然气比例呈上升趋势在均衡中国天然气进口来源、降低中国天然气进口风险总体具有积极作用;俄罗斯逐渐增加的天然气出口潜力对于提升中国进口安全产生正向作用;价格因素对中国天然气贸易安全影响显著;俄罗斯出口中国的天然气占俄罗斯天然气出口总量的比例提升在一定程度上对俄罗斯天然气出口安全产生积极影响;中国不断增加的天然气进口潜力带来的正效应相对抵消了俄罗斯主要天然气出口国天然气需求下降带来的负效应;近年来天然气价格下跌,对俄罗斯天然气出口安全产生明显负效应;未来几年,中俄天然气贸易量的急剧增加将使中国天然气进口集聚程度提升,应防范天然气进口风险上升。     

Seroprevalence of SARS-CoV-2 infection among children in Children’s Hospital Zagreb during the initial and second wave of COVID-19 pandemic in Croatia

IntroductionThe study aimed to investigate the prevalence and titres of anti-SARS-CoV-2 antibodies in children treated at the Children’s Hospital Zagreb in the first and the second wave of the COVID-19 pandemic. Statistical significance of difference at two time points was done to determine how restrictive epidemiological measures and exposure of children to COVID-19 infection affect this prevalence in different age groups.Materials and methodsAt the first time point (13th to 29th May 2020), 240 samples and in second time point (24th October to 23rd November 2020), 308 serum samples were tested for anti-SARS-CoV-2 antibodies by enzyme-linked immunosorbent assay (ELISA) and electrochemiluminescence immunoassay (ECLIA). Confirmation of results and titre determination was done using virus micro-neutralization test. Subjects were divided according to gender, age and epidemiological history.ResultsSeroprevalence of anti-SARS-CoV-2 antibodies differs significantly in two time points (P = 0.010). In first time point 2.9% of seropositive children were determined and in second time point 8.4%. Statistically significant difference (P = 0.007) of seroprevalence between two time points was found only in a group of children aged 11-19 years. At the first time point, all seropositive children were asymptomatic with titre < 8. At the second time point, 69.2% seropositive children were asymptomatic with titre ≥ 8.ConclusionsThe prevalence of anti-SARS-CoV-2 antibodies was significantly lower at the first time point than at the second time point. Values of virus micro-neutralization test showed that low titre in asymptomatic children was not protective at the first time point but in second time point all seropositive children had protective titre of anti-SARS-CoV-2 antibodies.     

The impact of structured teaching methods on the quality of education in Brazil

This paper estimates the impact of the use of structured methods on the quality of education for students in primary public school in Brazil. Structured methods encompass a range of pedagogical and managerial instruments applied in the educational system. In recent years, several municipalities in the state of São Paulo have contracted out private educational providers to implement these structured methods in their schooling systems. Their pedagogical proposal involves structuring of curriculum content, development of teacher and student textbooks, and the training and supervision of teachers and instructors. Using a difference-in-differences estimation strategy, we find that the 4th- and 8th-grade students in the municipalities with structured methods performed better in Portuguese and mathematics than did students in municipalities not exposed to these methods. We find no differences in passing rates. A robustness test supports the assumption that there is no unobserved municipal characteristics associated with proficiency changes over time that may affect the results.     

THE EFFECT OF IDENTIFICATION AND DIFFERENTIAL TREATMENT OF GIFTED ELEMENTARY SCHOOL PUPILS

Within the framework of a comprehensive research project entitled “The effects of identification and specific treatment of gifted pupils”, this paper deals with the problem of the effects of such a procedure on the attitudes of pupils, their parents, and teachers regarding giftedness and gifted individuals. Attention was mainly directed towards the effects of identification on the development of personality characteristics of the gifted pupils, on relations between gifted and other pupils, on the characteristics of teachers necessary for work with the gifted, on the controversy about separation of the gifted into special classes or schools, and on society's obligations to the gifted. The results of this two year follow‐up study are based on a comparison of the data from the initial and the final surveys of an experimental and a control group of subjects.

     

Evaluation of Energy Saving Operational Modes for Industrial Fracture Connected Processes on the Basis of Incubation Time Fracture Criterion

A problem for a central crack in a plate subjected to plane strain conditions is investigated.Mode Ⅰ crack loading is created by a dynamic pressure pulse applied at a large distance from the crack.It was found that for a certain combination of amplitude and duration of the pulse applied,the energy transmitted to the sample has a strongly marked minimum,meaning that with the pulse amplitude or duration moving away from the optimal values,minimum energy required for initiation of crack growth increases rapidly.The results obtained indicate a possibility to optimise energy consumption of different industrial processes connected with fracture.Much could be gained in,for example,drilling or rock pounding where energy input accounts for the largest part of the process cost.Presumably further investigation of the effect observed can make it possible to predict optimal energy saving parameters,i.e.frequency and amplitude of impacts,for industrial devices,e.g.bores,grinding machines,and hence significantly reduce the process cost.The prediction can be given based on the parameters of the media fractured (material parameters,prevalent crack length and orientation,etc.).     

对波黑医学院校的综合评估

按照国际标准对波黑的5所医学院进行了内部评估和外部评估,参与者包括医学院管理人员、教师、学生以及外部评估专家.评估内容包括10个项目:学校宗旨和目标、课程、管理、教师、学生、设施和技术、经费情况、国际关系、内部质量保证和发展规划.结果表明,内部评估中有的学校高估了自己的总体表现,有的学校明显高估或低估自己在某些项目上的表现.评估工作表明,即使在复杂和不利的条件下,对医学教育进行建设性的、有组织的评估也是可能的.