Huge Tunneling Magnetoresistance in Magnetic Tunnel Junction with Heusler Alloy Co2MnSi Electrodes

Magnetic tunnel junction with a large tunneling magnetoresistance has attracted great attention due to its importance in the spintronics applications. By performing extensive density functional theory calculations combined with the nonequilibrium Green's function method, we explore the spin-dependent transport properties of a magnetic tunnel junction, in which a non-polar SrTiO$_{3}$ barrier layer is sandwiched between two Heusler alloy Co$_{2}$MnSi electrodes. Theoretical results clearly reveal that the near perfect spin-filtering effect appears in the parallel magnetization configuration. The transmission coefficient in the parallel magnetization configuration at the Fermi level is several orders of magnitude larger than that in the antiparallel magnetization configuration, resulting in a huge tunneling magnetoresistance (i.e. $>10^6$), which originates from the coherent spin-polarized tunneling, due to the half-metallic nature of Co$_{2}$MnSi electrodes and the significant spin-polarization of the interfacial Ti 3d orbital.     

基于模糊层次分析法的地铁深基坑施工风险评估

地铁深基坑施工技术复杂、不确定因素多,施工阶段发生风险的概率较大且风险损失后果严重.为降低和控制地铁深基坑施工风险,有必要对其进行风险评估.结合工程实例,先根据工程地质条件和施工方法等对主要施工风险进行辨识;然后采用模糊层次分析法得到风险概率等级,并结合专家调查法对风险后果等级进行评估;最后确定地铁深基坑施工风险等级为IV级,并根据主要风险提出了有针对性的施工风险控制措施,确保施工安全.     

Jet interaction at supersonic cross flow conditions

The thrust produced by lateral jet systems has been successfully used for several years to control the flight trajectory, i.e., the maneuverability of spacecraft in the high atmosphere and in orbit. Recently this technology has also been applied to projectiles and rockets flying in the low atmosphere from sea level up to more than 10 km. At ISL, investigations have been performed with a 90 mm caliber full-scale projectile in order to study a special side jet controlling system at flight speeds of about 1500 m/s, i.e., Mach number at altitudes of 1.5 and 7.5 km. The High Energy ISL Shock Tunnel facility is used as a ground testing facility in which the flow around the projectile is studied at fully duplicated flight conditions. In the test facility the projectile is fixed inside the test chamber and the atmospheric air is set in motion flowing around the projectile test model. The air flow is generated in the ISL Shock Tunnel STB which is equipped for this purpose with a divergent square nozzle with an exit side length of 184 mm. A lateral gas jet is produced by combusting a solid propellant in a combustion chamber, placed inside the projectile. The powder gases are blown out laterally via a nozzle, creating a complex flow field by the interaction of the lateral jet with the external cross flow. Differential interferometry is used to visualize the behavior of the external flow field distorted by the lateral jet outflow. Numerical simulations have been performed based on steady state computations using the conservation equations of mass, momentum and energy. This was done to theoretically predict the development of the flow field around the projectile under the influence of the side jet. As final result the lateral force acting on the projectile is given as force and moment amplification factors, K_F and K_M respectively.Received: 7 May 2002, Accepted: 12 March 2003, Published online: 16 May 2003An abridged version of this paper was presented at the 23rd Int. Symposium on Shock Waves at Fort Worth, Texas, from July 22 to 27, 2001     

双圆盾构隧道施工过程中管片力学性状的原位测试研究

本文介绍了双圆盾构隧道管片在施工过程中结构内力的现场测定试验及结构内力在施工荷载作用下的变化情况。盾构隧道管片内力的计算方法有许多种，但其在实际施工过程中的结构内力及其变化情况许多年来一直没有比较详细的研究。在我国首次进行的双圆盾构隧道施工过程中，隧道股份对双圆隧道管片在拼装、成环、推进等施工过程中的结构内力变化进行了详细的监测分析，掌握了大量的第一手监测数据，对双圆盾构管片在施工过程中的力学特性变化有了比较详细的分析研究。为今后的双圆隧道建设提供了详实的研究基础。     

天津电视塔塔楼风作用风洞模拟实验

通过风洞实验,给出了天津电视塔塔楼表面的平均风压系数、脉动风压系数分布及风压系数变化范围,同时给出了塔楼空气调节系统进排风口附近的环境风压,包括无进排风状态和有进排风状态,还对排风均压室结构的改变对环境的影响进行了试验.     

铁路施工期岩溶地质宏观预测专家系统研究

岩溶的发育受到多种因素控制,具有不确定性,在结合宜万铁路齐岳山隧道、八字岭隧道、野三关隧道、马鹿青隧道以及渝怀铁路圆梁山隧道等多座岩溶地区山岭隧道的岩溶洞穴发育分布特征分析研究的基础上,提出了包括地层岩性、地质构造、地形地貌、地表水、地下水、隧道设计等因素在内的隧道工程岩溶超前预报的地质分析指标体系,明确了岩溶灾害发生危险性的高、中、低3个等级的工程地质标志性特征,应用专家评价法研究了各个指标的权重,构建了超前地质预报专家系统知识库,研制了山岭隧道岩溶超前地质预报专家系统,通过宜万铁路具体隧道工程的实际应用探讨了专家系统预测的可靠性。     

城市地下空间开发对地下水环境影响的初步研究

本文以南京地铁、玄武湖水底交通隧道为例,初步分析了玄武湖水底交通隧道对地下水环境的潜在影响。这种潜在影响主要表现在三个方面：阻滞地下水的排泄,引起地下水位的升降,诱发玄武湖水与古河道水的贯通。结果则是地下水污染加剧,城市生态环境的恶化。     

An experimental investigation of combined turbulent free and forced evaporation

The wide variation in correlations available in the literature for predicting water evaporation rates in a moving air stream necessitated a new investigation to determine which correlations can be considered reliable. Water evaporation measurements were made from a heated pool (a class-A pan) into a low speed wind tunnel. The evaporation regime examined combined turbulent free and turbulent forced convection over the range 0.1 < Gr_m/Re² < 10.0. The data includes the range in which combined convection modes are important, as well as the limits where either free or forced convection effects may dominate. The data are compared to several evaporation correlations based on laboratory wind tunnel data. These historical correlations do not produce consistent estimates in predicting evaporation rates. It is believed that the apparent inconsistencies arise because many correlations do not adequately describe the appropriate evaporation regimes for which they are valid. A new correlation using the combined free/forced convection Sherwood number has been developed to predict evaporation rates for a moving air stream. This correlation allows the results of this study to be extended to other evaporating conditions (i.e. variation in surface geometry and air turbulence levels) than those described here. For a 95% confidence limit, the Sherwood number correlation matches the data within ±7.9%.     

水动力试验和流噪声测试

在模型表面上涂敷低表面能涂层会降低航行体阻力和噪声．因此，对水筒中流噪声的测量数据重复性、误差和数据的可信度等，必须有正确的测量和分析方法．在相同时期内，用相对比较法，从模型内测量同一模型的流噪声，其测量数据的重复性好，误差小于２ｄＢ．在８ｋＨｚ４０ｋＨｚ频率范围内，水筒中环境所造成的背景噪声小，这时信噪比大，噪声的测量能较好地反映出涂层的降噪效果．而低频时≤５ｋＨｚ，循环系统引起较高的背景噪声，可能会掩盖涂层的降噪效果．但低频时，相对比较法中，噪声的降低确是涂层引起的结果．     

利用灰色模型预测巷道围岩变形

利用灰色系统理论，用少量的非等时的实测数据，建立非等时的灰色ＧＭ（１，１）模型，同时将实测数据经拉格朗日插值后形成等时时序，建立等时的灰色ＧＭ（１，１）模型，通过模型预测结果的比较，得到了在利用灰色模型进行巷道围岩变形预测时比较理想的模型。