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461.
This study addresses the measures chosen by students when selecting or constructing indices to properties of distributions of data. A series of individual teaching experiments were conducted to provide insight into the development of five 4th to 8th grade students’ conceptualizations of distribution over the course of 8 weeks of instruction. During the course of the teaching experiment (emergent) statistical tasks and analogous teacher activities were created and refined in an effort to support the development of understanding. In the process of development, attempts were made by students to coordinate center and variability when constructing measures to index properties of distributions. The results indicate that consideration of representativeness was a major factor that motivated modification of approaches to constructing indices of distributions, and subsequent coordination of indices of variation and center. In particular, the defining features of student's self-constructed “typical” values and notions of spread were examined, resulting in a model of development constituting eight “categories” ranging from the construction of values that did not reflect properties of the data (Category 1) to measures employing conceptual use of the mean in combination with other indices of center and spread (Category 8). 相似文献
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可持续发展的几何自动推理平台(SGARP)支持用户发展多种多样基于规则的机器自动推理或人机交互推理方法,但缺乏处理符号计算的模块,其解题能力仍有待加强.质点法是最近发展的继面积法之后又一个能对可构造型几何命题生成可读机器证明的具有完全性的算法.基于一种在SGARP中快捷实现符号计算功能的方法,对质点法机器证明算法进行了新的实现.新添加的质点法模块使得用户能更便捷地验证更多的几何定理,从而使SGARP能更好地满足用户学习与发展几何机器推理的需求. 相似文献
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针对现有的网络安全态势预测方法正确性和合理性难以得到保证,同时不能有效应对不确定情况的问题,设计了一种基于最小二乘支持向量机(Least square support vector machine, LSSVM)和改进证据理论的网络安全态势预测方法。首先,将由多源传感器采集的历史标记数据作为样本数据,实现对LSSVM的训练,然后,将当前采集的数据输入LSSVM进行分类,并通过混淆矩阵获得数据对应每个类的概率,为了有效地对采集的数据进行进一步融合,将各类转换为证据,同时将数据相对每个类的概率作为证据的基本信度分配,采用改进的DS证据合成规则对各证据进行融合,实现对网络安全态势的预测,最后,设计了基于LSSVM和改进DS证据合成规则的网络安全状态预测算法。在MATLAB环境下进行实验,实验表明了文中方法能对网络的安全态势进行实时精确的预测,与其它方法相比,具有更高的预测精度,是一种可行的网络安全态势预测方法。 相似文献
466.
Taghrid S. Hafez Hisham Abdallah A. Yosef Hala M. Abou Yousef Eman F. Al-Amrousi Mohamed Refat H. Mahran 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2277-2285
Dialkyl phosphites attack 6-(Aryliminomethyl)furobenzopyran-5-ones at the imine-carbon atom to give new phosphonate 1:1 adducts. The obtained compounds regenerate the starting materials upon thermolysis under reduced pressure. Structures of the new products were attested by compatible analytical and spectroscopic measurements. Insecticidal activity tests assured that some new compounds show marked potency against adults of Aphis gossypii (Glover), which infests cotton crops. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献
467.
S. Agnello A. Alessi F. M. Gelardi R. Boscaino A. Parlato S. Grandi A. Magistris 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(1):25-31
We report experimental investigation by electron paramagnetic resonance (EPR) measurements of room temperature γ-ray irradiation
effects in sol-gel Ge doped amorphous SiO2. We used materials with Ge content from 10 up to 104 part per million (ppm) mol obtained with different preparations. These latter gave rise to samples characterized by different
extents of oxygen deficiency, estimated from the absorption band at ~5.15 eV of the Ge oxygen deficient centers (GeODC(II)).
The irradiation at doses up to ~400 kGy induces the E'-Ge, Ge(1) and Ge(2) paramagnetic centers around g ~ 2 with concentrations
depending on Ge and on GeODC(II) content. We found correlation between Ge(2) and GeODC(II) contents, supporting the suggestion
that the latter defect is the precursor of Ge(2). Even if the concentration of E'-Ge and Ge(1) defects cannot be strictly
related to GeODC(II) one, the concentration growth of these paramagnetic defects with irradiation evidences that the radiation
sensitivity is enhanced by the oxygen deficiency for Ge doping above 1000 ppm mol and it is reduced below 100 ppm mol. Moreover,
the investigation of samples with different GeODC(II) concentration but fixed Ge content has shown that the oxygen deficiency
enhances the overall radiation sensitivity for [GeODC(II)]/[Ge] in the range 10-3
10-2. 相似文献
468.
应急预案的优劣关系到突发事件的处理效果,要判断应急预案的优劣则需要对应急预案进行评估.基于事件的流程构建突发事件应急预案评价指标体系,采用层次分析法确定各级指标权重,基于模糊-证据理论,将专家评语转化为mass函数,并综合专家评价信息合成为指标mass函数.之后根据权重修正mass函数,建立完整的突发事件应急预案评价模... 相似文献
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