一维自组织临界米堆模型的临界行为

对一维链上的具有固定位置驱动机制和随机位置驱动机制的米堆模型的临界行为进行了数值模拟研究.系统经一个暂态过程后达到一个临界态,雪崩大小的概率统计分布服从"幂指"规律.固定位置驱动机制模型的临界雪崩指数为τs=1.51±0.02和τt=1.83±0.02.随机位置驱动机制的模型的临界雪崩指数为τs=1.01±0.02和τt=1.03±0.02.固定位置驱动机制和随机位置驱动机制的米堆模型属于不同的普适类.     

Mechanical Characteristics of Radial Magnetic Bearing

1 IntroductionThe great majority of docUments about magneticbearings dealt only with the characteristics when thejournal was concentric with the radial magnetic bearing inthe past, and few research involved the ones when thejournal was eccotic with the radial magnetic bearing.For example, the bulk of documents suPPosed thecomponents Fx and F. of magnetic force depended onlyon the cUrred in x and y direchons respeGtively, bac theair gap thickness and the curvatUre of suiface shape werenot co…     

封闭式基金折价交易的期权解释

封闭式基金折价交易是证券市场的一般现象，投资人普遍认为折价交易是“不正常”的，期待“价值回归”。本文用期权理论对封闭式基金进行定价，从而得到了新基金折价交易的科学解释。     

地质样品的一次阴离子色谱法Hf分离及其MC-ICP-MS分析

本文建立了适合MC-ICP-MS测试地质样品中Hf同位素的一次阴离子交换化学分离方法。使用常规的阴离子交换树脂就可以完成Hf与干扰元素和基体元素的分离,避免了当前广泛采用的多次离子交换柱的麻烦,也无需使用特效树脂,HF处理样品后,也不必使用HClO4赶尽HF.Hf的回收率大于90%,过程空白约为50pg。岩石标样的重复分析表明,该方法简单、快速、经济、有效,尤其适合年轻地质样品Hf同位素组成分析。     

Students’ Views of Design in an Engineering Design-Based Science Curricular Unit

Recent reforms in science education have supported the inclusion of engineering and their practices in K-12 curricula. To this end, many classrooms have incorporated engineering units that include design challenges. Design is an integral part of engineering and can help students think in creative and interdisciplinary ways. In this study, we examined students’ conceptions of design during and after participation in a design-based science curriculum unit. Our study was guided by the following research question: What are students’ views of design after participation in an engineering design-based science curriculum unit and how are these views reflected in their enactment throughout the unit? Using a qualitative approach, we examined students’ conversations throughout the enactment of the curriculum and interviews conducted after the completion of the unit. We found that students had complex and diverse views of design, and these views were reflected in their group discussions throughout the curriculum and design challenge. Students most frequently expressed design as learning and as a process of integration into a coherent whole. These aspects of design were also frequently observed in students’ conversations during the unit. Interestingly, we found evidence of students demonstrating several aspects of design throughout the curriculum that were not explicitly expressed during the student interviews. Taken together, these findings support the complex nature of design as seen at the middle school level.

     

A Tour That Creates the Future European Museum Directors Visit China

Approved by the Ministry of Culture, a delegation consisting of 16 curators of national museumsvisited China for exchanges from 20 to 29 September 2013. The curators came from 14 central and eastern European countries （hereinafter referred to as＂CEEC＂） including Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Macedonia, Montenegro, Poland, Romania, Serbia, and Slovenia.