高温超导磁通跳跃过程中的磁致伸缩效应

文中基于超导磁通动力学理论,考虑电磁力与热激活对磁通运动的影响,基本模型包括由等效电阻率随超导体温度和磁场变化的磁通扩散方程,以及比热随超导体温度变化的热传导方程组成.在此基础上,用数值方法求解了这组非线性磁热耦合方程,主要研究了有磁通跳跃状发生状态时环境温度和外磁场速度对于高温超导磁致伸缩的影响.结果表明:磁通进入超...     

Using partial correlation to enhance structural equation modeling of functional MRI data

In functional magnetic resonance imaging (fMRI) data analysis, effective connectivity investigates the influence that brain regions exert on one another. Structural equation modeling (SEM) has been the main approach to examine effective connectivity. In this paper, we propose a method that, given a set of regions, performs partial correlation analysis. This method provides an approach to effective connectivity that is data driven, in the sense that it does not require any prior information regarding the anatomical or functional connections. To demonstrate the practical relevance of partial correlation analysis for effective connectivity investigation, we reanalyzed data previously published [Bullmore, Horwitz, Honey, Brammer, Williams, Sharma, 2000. How good is good enough in path analysis of fMRI data? NeuroImage 11, 289–301]. Specifically, we show that partial correlation analysis can serve several purposes. In a pre-processing step, it can hint at which effective connections are structuring the interactions and which have little influence on the pattern of connectivity. As a post-processing step, it can be used both as a simple and visual way to check the validity of SEM optimization algorithms and to show which assumptions made by the model are valid, and which ones should be further modified to better fit the data.     

电子商务平台系统互动性对顾客感知价值的影响

随着现代知识经济和网络经济的到来,电子商务这一互联网时代的特殊模式吸引着越来越多的企业和消费者.电子商务平台应该通过系统互动性的设计提升顾客感知价值,维系与顾客的稳固关系,已成为国内外学者和企业家共同关注的话题.研究首先通过文献及访谈研究,提出研究假设;其次,通过实验设计的方式采集数据研究不同的系统互动机制对顾客感知价值的影响;最后通过统计分析验证假.研究结论显示电子商务网站系统互动机制的层次不同,顾客感知价值也不同,同时这种影响受到顾客个人使用经验和个人创新性的调节作用.     

交变磁场作用下高温超导体温度变化研究

高温超导体在交变的磁场作用下,由于磁通的运动引起能量损耗,损耗的能量一部分通过超导体表面传递到冷却剂中,另一部分将使得超导体的温度升高。文中用数值的方法研究了外加磁场速度在0.0005T/s—5T/s变化情况下超导体的温度变化;当外磁场的速度由小到大变化时,超导板的状态会发生从稳定→不稳定(磁通跳跃)→稳定的变化;慢变磁场作用下超导体的温度在接近冷却剂温度的温区作微幅的周期性变化,当外加磁场速度比较大时,超导体发生磁通跳跃,温度也呈跳跃性变化,进一步加大外磁场速度,磁通和温度呈准周期的振荡型变化,而且振荡幅值随外磁场速度的增加逐渐减小,最后振荡消失,超导体在更高的温区稳定运行,温度呈周期性变化。     

Will learning to solve one-step equations pose a challenge to 8th grade students?

Assimilating multiple interactive elements simultaneously in working memory to allow understanding to occur, while solving an equation, would impose a high cognitive load. Element interactivity arises from the interaction between elements within and across operational and relational lines. Moreover, operating with special features (e.g. negative pronumeral) poses additional challenge to master equation solving skills. In an experiment, 41 8th grade students (girls = 16, boys = 25) sat for a pre-test, attended a session about equation solving, completed an acquisition phase which constituted the main intervention and were tested again in a post-test. The results showed that at post-test, students performed better on one-step equations tapping low rather than high element interactivity knowledge. In addition, students performed better on those one-step equations that contained no special features. Thus, both the degree of element interactivity and the operation with special features affect the challenge posed to 8th grade students on learning how to solve one-step equations.     

Anomalous magnetothermal effect in the spin- Heisenberg XXZ chain

The low-temperature thermomagnetic power of the spin- Heisenberg XXZ chain is exactly calculated by the Bethe ansatz. For finite magnetic fields, the magnetothermal effects arise due to the breakdown of the spin-reversal symmetry. For finite interaction strengths, we find the thermomagnetic coefficient (magnetic Seebeck coefficient) changes sign at certain temperature and magnetic field. This peculiar feature is interpreted as an effect of the competition between the interaction strength and the external magnetic field.     

水平圆管通道内热磁对流的实验研究

由于温度分布不均匀而导致磁场中的磁性流体受到非平衡的磁场力作用,而发生流动的现象,称为热磁对流。它是一种由体积力驱动的类似自然对流的流动,可以通过设计合适的磁场来控制热磁对流的强度和方向。本文对水平圆管通道内热磁对流进行了实验研究,测量了通道内及壁面的温度分布,并通过两种不同的方法根据实验测得的温度分布估算了热磁对流的流量和速度的大小。     

多粒度不确定语言信息下的多阶段交互式群体评价方法

针对目前多阶段交互式群体评价研究较少且评价信息多为精确数或区间数的问题,以及大多数交互式群体评价缺乏对评价信息质量判断的不足,提出了一种新的多粒度不确定语言信息下的多阶段交互式群体评价方法.首先,定义了一个多粒度语言转换函数,将多粒度不确定语言信息一致转换为同一粒度下的不确定语言信息;其次,给出了一个语言型稳定性指标,以探讨交互终止的条件;最后,基于2个诱导不确定纯语言算子,分别对评价信息进行"横向"和"纵向"集结.实例分析验证了该方法的有效性与合理性.     

Mathematic education in a cultural setting

The paper develops some proposals for curriculum development in mathematics based on an analysis of the intercultural transmission of mathematical knowledge. By introducing a concept of culture which calls for an analysis of individual and social behaviours, we are lead to recognize ‘ethnomathematics’ as a form of structured knowledge and to recognize ‘matheracy’ as a characteristic behaviour of human beings. Upon these two concepts, we introduce a theoretical framework for curriculum development in mathematics.

Curricular space is conceptualized as a three‐dimensional space with components, contents, methods and objectives considered solidarily. This relies upon an epistemology of action, based on an integration of episteme, techne and praxis. This allows for an approach in which theory and practice are in a dialectical relationship. Special reference is made to the problems of mathematical education for culturally differentiated groups, and in particular to the situation in third‐world countries.