超磁致伸缩作动器的磁路设计

论述了超磁致伸缩作动器的基本原理,根据三种偏置磁场优缺点,选用增加单独线圈产生偏置磁场。在磁路分析的基础上,采用有限元仿真的方法,分析了不同参数和结构对各个组成部分的磁场影响。     

Anticipatory postural adjustments during cutting manoeuvres in football and their consequences for knee injury risk

Abstract

Anticipatory postural adjustments (APAs), i.e. preparatory positioning of the head, the trunk and the foot, are essential to initiate cutting manoeuvres during football games. The aim of the present study was to determine how APA strategies during cutting manoeuvres are influenced by a reduction of the time available to prepare the movement.

Thirteen football players performed different cutting tasks, with directions of cutting either known prior to the task or indicated by a light signal occurring 850, 600 or 500 ms before ground contact.

With less time available to prepare the cutting manoeuvre, the head was less orientated towards the cutting direction (P = 0.033) and the trunk was even more rotated in the opposite direction (P = 0.002), while the foot placement was not significantly influenced. Moreover, the induced higher lateral trunk flexion correlated with the increased knee abduction moment (r = 0.41; P = 0.009).

Increasing lateral trunk flexion is the main strategy used to successfully perform a cutting manoeuvre when less time is available to prepare the movement. However, higher lateral trunk flexion was associated with an increased knee abduction moment and therefore an increased knee injury risk. Reducing lateral trunk flexion during cutting manoeuvres should be part of training programs seeking the optimisation of APAs.     

一个重要的概率不等式及其应用

我们通过对随机变量X的分类和r的不同取值分别比较矩EXr和EXr-2的大小,同时指出可以利用这些结果解决其他的数学问题。     

50Hz正弦磁场对细胞超氧产率及细胞增殖的影响

中国仓鼠肺成纤维细胞（CHL）和人脐静脉内皮细胞（HUVEC）受磁场辐照后,采用荧光光度法检测细胞的超氧产率和采用噻唑蓝比色分析法检测细胞的增殖情况。50Hz、0．4mT正弦磁场辐照30min引起CHL细胞和HUVEC细胞的超氧产率分别较对照组增加12％和19％：该磁场辐照24h导致CHL细胞和HUVEC细胞的数目分别较对照组上调9％和10％。提示50Hz、0.4mT正弦磁场促进CHL细胞和HUVEC细胞的增殖,可能与超氧自由基产率的上调有关。     

New types of topological superconductors under local magnetic symmetries

We classify gapped topological superconducting (TSC) phases of one-dimensional quantum wires with local magnetic symmetries, in which the time-reversal symmetry is broken, but its combinations with certain crystalline symmetries, such as , , and , are preserved. Our results demonstrate that an equivalent BDI class TSC can be realized in the or superconducting wire, which is characterized by a chiral Z^c invariant. More interestingly, we also find two types of totally new TSC phases in the and superinducting wires, which are beyond the known AZ class, and are characterized by a helical Z^h invariant and Z^h⊕Z^c invariants, respectively. In the Z^h TSC phase, Z pairs of Majorana zero modes (MZMs) are protected at each end. In the case, the MZMs can be either chiral or helical, and even helical-chiral coexisting. The minimal models preserving or symmetry are presented to illustrate their novel TSC properties and MZMs.     

强磁场下液态金属在竖直平板外的自由对流换热

托克马克装置中面向等离子体部件在不同的位置存在很大的温差,导致面向等离子体部件表面液态金属产生自由对流。以此为背景,实验研究液态金属受横向磁场影响下竖直壁面上的自由对流换热规律。实验采用K型热电偶测量环境与壁面两侧的温度,利用多普勒超声波测速仪测量壁面上的液态金属速度,分析不同磁场强度和加热热流密度条件对竖直平板外表面的流动与换热影响规律。研究表明：竖直平板的局部换热系数与特征长度成反比,即距加热平板起始段越远换热越弱,同时增强加热功率使表面换热系数增加。在强磁场条件下,壁面边界层的流动与换热均普遍被抑制;但是在弱磁场下,增加磁场会强化平板表面的自由对流与换热,根据实验结果发现该转折点出现在磁相互作用数为1~4的范围。     

电磁场动量流密度的应用

阐述了由电磁场动量流密度张量求电磁场合力的方法,举例说明对于同一个问题可以用多种积分限计算的物理原因．     

基于小波包降噪的地磁场干扰数据分析

针对在港口消磁站附近港口日常作业时产生的磁场干扰以及地球地磁日变对港口消磁站的磁场测量造成严重干扰的现象,采用基于小波包降噪的办法进行干扰抑制处理.该办法通过对干扰源进行分析及实验模拟,得出磁场干扰的原因及特征.通过实际磁场测量数据分析,得出消磁站附近港口日常作业时产生的磁场干扰对地磁场Z分量造成的影响.采用小波包降噪算法,通过小波包基变化,重构受干扰磁场数据,进行干扰抑制处理.处理结果表明,此方法能够有效抑制干扰,对提高港口消磁站磁场测量的准确性有积极意义.     

量子信息处理及其核磁共振实现（英文）

量子特性在信息领域中有着独特的功能,在提高运算速度、确保信息安全、增大信息容量和提高检测精度等方面可能突破现有经典信息系统的极限。我们以液态NMR技术实现量子信息处理中的应用主题开展研究,所取得的成果包括：1）利用NMR实验实现了两个无直接耦合自旋之间的量子密集编码和三个量子位之间的量子密集编码过程。实验结果表明：量子密集编码只需传送N-1个量子位便可以传递N个经典位的信息。2）利用NMR实验实现了三种多量子算法;提出了一种实现n阶耦合变换的理论方法,根据这种方法可实现任意量子位的Deutsch-Jozsa算法。3）提出了一种基于量子克隆的量子编码和纠错方案。该方案一方面说明了量子克隆与量子纠错存在一定程度上的联系,另一方面也反映出一些量子克隆过程本身具有一定的抗消相干的能力。4）提出用二维NMR中的多量子相干实现无消相干子空间（DFS）,并在实验上验证了该DFS的避错能力。本方法有效地利用了甲基中三个磁等价的氢核,把原本需要四个化学位移各不相同的核自旋构造的二逻辑位的DFS变成了只需两个化学位移各不相同的核自旋体系构造的二逻辑位的DFS,虽然用的核自旋数“更少”,却能避免更多的错误算符。用多量子相干作为量子计算中的量子位,是一种全新的概念,可以充分利用磁等价的原子核自旋来构造多个量子位,从而扩展了可利用的量子位的数目。     

The Sun’s mysteries from space — II

In the concluding part of our article we discuss problems of coronal heating and coronal holes and solar winds.