Spin transfer torques

This tutorial article introduces the physics of spin transfer torques in magnetic devices. Our intention is that it be accessible to beginning graduate students. We provide an elementary discussion of the mechanism of spin transfer torque and review the theoretical and experimental progress in this field. This article is meant to set the stage for the articles which follow in this volume of the Journal of Magnetism and Magnetic Materials, which focus in more depth on particularly interesting aspects of spin-torque physics and highlight unanswered questions that might be productive topics for future research.     

Magnetization reversal of sub-micron ferromagnetic tunnel junctions in external magnetic fields

Sub-micron sized magnetic tunnel junctions are fabricated by electron beam lithography. Magnetoresistance measurements were done at crossed easy- and hard-axis fields and the critical switching curves for 3 different sub-μm junctions are discussed. Single domain like switching according to the Stoner and Wohlfarth model can be achieved, but Néel coupling effects and AAF stray field effects have to be controlled.     

Tunnel numbers of small knots do not go down under connected sum

Let and be two knots in and , the tunnel numbers of them. In this paper, we show that if both and are small, then . Moreover we show that for any small knots .

     

Controlling the near vortex wake of a swept half-wing by means of mini-flaps

The effect of mini-flaps on the flow pattern in the near vortex wake behind a model swept half-wing is investigated. The distributions of the time-average flow velocity were measured in a subsonic wind tunnel, in a section normal to the freestream velocity vector located at a distance of 3.8 wing half-spans from its trailing edge. When mini-flaps are mounted on both upper and lower wing surfaces, two vortices (tip and auxiliary) of the same sign are observable in the above-mentioned flow section; they are separated by an extended region of vorticity of the opposite sign. The model angle-of-attack effect on the intensities of the tip and auxiliary vortices is estimated.     

黄土公路隧道病害治理实例研究

黄土物理力学性质相对较差,具有大孔隙、湿陷性强、强度低的特点,加之黄土区的地形地貌、地质条件比较复杂,导致黄土隧道修筑过程中病害较多。利用SIR2000型探地雷达、RSM-SY5非金属声波探测仪和BJSD-2型激光限界仪等多种方法对某黄土公路隧道病害进行了探测,探测表明隧道洞身出现环向和横向裂缝,衬砌厚度不足,局部地段存在集中涌水和渗漏水,根据探测结果对隧道病害成因进行了详细的分析。在此基础上结合黄土隧道的基本特征,有针对性地提出了锚喷加固、套衬加仰拱、套衬和下加固围岩3套病害治理方案。并利用数值模拟对隧道治理前后围岩稳定性和衬砌结构受力状态进行了分析,结果表明治理方案衬砌受力状态基本对称,结构的安全系数有较大的提高。     

一种新的C_(60)二维畴拓扑结构

利用低温扫描隧道显微镜对吸附在硫醇膜表面的二维C6 0 岛进行研究 ,首次观察到化学键分辨的C6 0 分子结构 ,并发现一种新型的C6 0 二维取向畴界 .这种畴界仅仅由于两边C6 0 分子的取向不同而存在 ,附近没有结构缺陷 ,畴界附近C6 0 阵列的位置平移序和键取向序都得到了保持 .     

圆形硐室岩爆机制及其突变理论分析

硐室岩爆机制是围岩中处于极限状态的塑性变形集中区承载能力下降时,其中完好岩体部分以弹性方式卸载,当后者释放的弹性能超过前者形变耗散的能量时便发生岩爆．以岩体等效应变为状态变量,建立了硐室岩爆的突变模型,给出岩爆释放地震能计算式．分析表明: 岩爆发生条件与岩体的升降模量比及岩体裂隙发育程度有关;对于特定冲击倾向的岩体,存在相应的临界软化区深度,当满足岩爆发生条件,且软化区深度达到临界深度时会发生岩爆．     

Aerodynamic force measurement using 3-component accelerometer force balance system in a hypersonic shock tunnel

A new three-component accelerometer force balance has been designed, calibrated and tested in hypersonic shock tunnel (HST2) of Indian Institute of Science. The newly designed balance is able to measure aerodynamic forces (within test time of one millisecond) on test models at angles of attack from 0 to 12°. Two models, a blunt cone with after body and a blunt cone with after body and frustum are used to establish the accuracy of the force balance. The tests were conducted for the above two configurations with a constant Mach number of 8 and total enthalpy of 2.0 MJ/kg. The effectiveness of the balance is demonstrated by comparing the forces and moments of measured data with AGARD models. The flow fields around the test model are simulated using a 3D axisymmetric Navier–Stokes solver and the simulated results were compared with the measured values. Measured and computed force data are matched within ±10% for two different models tested here. The accuracy of the force balance is also estimated with the Newtonian theory and the values are approximately ±10% for the axial component and ±8% for the normal and pitching moment components.      

抗战前清华航空研究考察

1932年起,清华大学为适应中国航空建设需要,开始发展航空教育与研究,在国内 首次建成5英尺航空风洞,并设计建造当时远东最大的15英尺航空风洞,由于抗战全面爆 发,15英尺航空风洞建成前夕被毁。本文着重从时代背景、师资、图书设备、航空风洞的 建设与意义等方面考察了抗战全面爆发前清华大学航空研究与教学概况。清华大学航空教学 与研究取得的成果,为抗战期间以及抗战胜利以后中国航空事业发展,做出了重要贡献。