多频率电源下的最大功率传输问题研究

容性负载和感性负载的电抗随频率而变,因此在不同频率下负载获得的最大功率不能简单相加。该文运用Multisim仿真软件和Matlab探讨了2个和3个不同频率源单独作用及同时作用时传递的最大功率和此时的负载阻抗值,并探讨了此问题的困难和意义。     

基于时间序列的中超联赛球队竞技表现稳定性分析

竞技状态是训练学的核心研究概念之一，其会极大地影响运动员竞技表现。竞技表现反映了竞技状态好坏，以往对此内容的研究多集中于优秀运动员个体。为了探讨集体项目中的竞技表现及其影响因素，选择中超联赛作为研究对象。中超联赛是亚洲最好的职业足球联赛之一，代表了中国职业足球的最高水平，受到广泛的关注。通过时间序列分析中的自相关函数和互相关函数对足球比赛表现分析进行实证研究，以2017赛季中国足球超级联赛的240场比赛为样本，探明影响球队竞技状态的表现指标稳定性，并确定对球队战绩影响较大的关键指标。研究结果显示：（1）对联赛排名上游的球队而言，传球成功率、拦截和抢断是较为重要的指标；（2）进球和进攻类指标是强队制胜的关键；（3）联赛排名上游和中游球队比赛表现的整体稳定性要高于下游球队。     

“砍”字出现时代考

出现在唐以前文献里的“砍”字不可信,“砍”字当是宋代出现的新字。     

如何讲好时域取样定理

时域取样定理是"信号与系统"和"数字信号处理"等课程的重要内容,但是,目前高等院校普遍使用的国内外经典教材对这部分内容论述不够清晰,没有证明连续时间信号与离散时间信号频谱的关系,尤其是引入了理想冲激取样过程,物理意义不明确,影响了学生理解。本文对时域取样定理进行了深入的思考,提出了两种讲解思路,教学实践表明,对增强学生对该内容的理解,提高授课质量,有较强的针对性。     

Books,Children, Dogs,Artists: Library Programs for the Entire Family

The promotion of library resources and services is a continuous process for all libraries, especially hospital family resource center libraries. Like public libraries, a family resource center can utilize programs as a pathway for connecting with and developing awareness of library resources and services available to patient families. This column describes the programs currently offered for All Children's Hospital Johns Hopkins Medicine patient families, marketing initiatives to promote these programs, and utilization of grant funding to supplement a program.     

科技期刊青年编辑自我成长要素分析

青年编辑的成长是期刊未来发展的原动力和不竭源泉。文章从职业规划的角度,论述青年编辑自我成长的若干要素:合理规划编辑人生;认识自己与自我定位;加强自我管理(工作效能管理、自我培养以及自我情绪的调节)等。建议置身于新闻出版体制改革大背景和环境中的科技期刊青年编辑应审时度势,增强职业认知和自我管理、自我发展、自我调整意识。     

清钞本《类姓登科考》的几个问题

清钞本《类姓登科考》是一种体例独特、史料价值突出的科举文献,以前学者对其相关信息缺乏相对准确的著录。从藏书印、时人征引、地名变革和避讳改字等角度,对其作者、成书时间进行考证,认为该书确为盛子邺之作,写成于康熙元年之后、康熙四十年之前。该书有较高的史料价值,但也存在一定的错误,参考时需要注意辨别。     

东西方穿越的不同心理诉求

"穿越"这个话题近几年来在东西方的小说和屏幕上屡屡亮相并掀起一阵风潮。国内外对于穿越小说的创作类型、特色、时代背景和意义等都做了相对深入的研究,但在穿越背后所体现的东西方不同心理诉求的论述则相对匮乏。本文从穿越小说所表现的主题入手,分析了东西方穿越小说所传达的不同文化内涵。     

Impact maturity times and citation time windows: The 2-year maximum journal impact factor

Journal metrics are employed for the assessment of scientific scholar journals from a general bibliometric perspective. In this context, the Thomson Reuters journal impact factors (JIFs) are the citation-based indicators most used. The 2-year journal impact factor (2-JIF) counts citations to one and two year old articles, while the 5-year journal impact factor (5-JIF) counts citations from one to five year old articles. Nevertheless, these indicators are not comparable among fields of science for two reasons: (i) each field has a different impact maturity time, and (ii) because of systematic differences in publication and citation behavior across disciplines. In fact, the 5-JIF firstly appeared in the Journal Citation Reports (JCR) in 2007 with the purpose of making more comparable impacts in fields in which impact matures slowly. However, there is not an optimal fixed impact maturity time valid for all the fields. In some of them two years provides a good performance whereas in others three or more years are necessary. Therefore, there is a problem when comparing a journal from a field in which impact matures slowly with a journal from a field in which impact matures rapidly. In this work, we propose the 2-year maximum journal impact factor (2M-JIF), a new impact indicator that considers the 2-year rolling citation time window of maximum impact instead of the previous 2-year time window. Finally, an empirical application comparing 2-JIF, 5-JIF, and 2M-JIF shows that the maximum rolling target window reduces the between-group variance with respect to the within-group variance in a random sample of about six hundred journals from eight different fields.     

The use of training days: finding time for teachers’ professional development

This study was designed to compare the relative efficiency of three methods of presenting and teaching fractions to slow learners at the secondary stage of education.

Thirty‐six first‐year pupils took part in the experiment and were divided into three groups of 12 for instruction in fractions for 14 periods of 40 minutes. Each group was taught by a different method, viz:

Group A, was taught in a formal, traditional method

Group B, used the Cuisenaire (unimodel) material

Group C, used multi‐model materials specially constructed for teaching fractions to slow learners.

At the beginning of the experiment the groups were equivalent in age, intelligence, arithmetical attainment, attainment in fractions, conceptual understanding of fractions, in adjustment to school, attitudes to learning fractions, and socio‐economic status. On re‐assessment on six of the variables at the end of the experiment it was found that each group had improved in each of the six variables tested.

When considering all the results obtained it was concluded that the multi‐model method was the most effective method of teaching fractions to slow learning children at the secondary stage. This method was found to have particular advantage in creating a favourable attitude to learning fractions and in promoting a sound conceptual understanding of fractions. It also produced the greatest mean gain in fraction computation, and seemed to have some slight advantage in aiding the adjustment of pupils to school.