稀磁半导体CoTiO2薄膜结构和磁性研究

通过对靶磁控反应溅射法和原位退火工艺制备了系列CoTiO2薄膜样品.研究发现,掺杂量对薄膜的磁性和结构有很大的影响.通过X射线衍射仪和振动样品磁强计对样品的结构和磁性进行了分析,发现制备的样品中较少的掺杂显示明显的室温铁磁性并且没有Co金属存在,但是随着掺杂的增加,部分Co以微小的颗粒存在,而且在超顺磁极限之下,使薄膜的磁性受到超顺磁相的影响.     

Numerical study of an unsteady free convective magnetohydrodynamic flow of a dissipative fluid along a vertical plate subject to a constant heat flux

A new method is presented to solve the transient free convection MHD flow of a dissipative fluid along a semi-infinite vertical plate with mass transfer, the surface of which is exposed to a constant heat flux. The non-linear system of partial differential equations is numerically solved by means of the network simulation method, based on the thermo–electric analogy. This method permits the direct visualisation and evolution of the local and/or integrated transport variables (temperatures, velocities, concentrations and fluxes) at any point or section of the medium. At the same time, the solution for both transient and steady-state problems is obtained, the only requirement being finite-difference schemes for the spatial variable, while its programming does not involve manipulation of the sophisticated mathematical software that is inherent in other numerical methods. The technique is always stable and convergent. Velocity, temperature and concentration profiles, local skin-friction, local Nusselt and local Sherwood numbers are plotted for air. The influence of the viscous dissipation, buoyancy ratio parameter, Schmidt number and magnetic parameter on heat and mass transfer and on the time needed to reach the steady-state are discussed.     

Models relating mixture composition to the density and strength of foam concrete using response surface methodology

There have been several investigations in the past on the influence of mixture composition on the properties of foam concrete. Conventionally strength is related to density alone and few models have been developed relating strength with density, porosity, gel–space ratio, etc. Very little work has been reported in the literature in predicting the properties of foam concrete from the knowledge of its mixture proportions. This paper discusses the development of empirical models for compressive strength and density of foam concrete through statistically designed experiments. The response surface plots helps in visually analysing the influence of factors on the responses. The relative influence of fly ash replacement on strength and density of foam concrete is studied by comparing it with mixes without fly ash and brought out that replacement of fine aggregate with fly ash will help in increase in the strength of foam concrete at lower densities allowing high strength to density ratio. Confirmatory tests have shown that the relation developed by statistical treatment of experimental results can act as a guideline in the mixture proportion of foam concrete.     

On Destabilization via Active Stiffness

Corless and Leitmann [2] have shown that a damped simple oscillator can be destabilized by varying the spring stiffness. The present note establishes that this result is closely related to the variational approach to absolute stability theory [1,6] both in substance and in method of proof. In particular, several key ideas employed in [2] appear in the work of Brockett [1].     

透视操作的空间意义建构

透视法由最初绘画空间的表现方法逐渐演变为一种建构空间意义的操作手段,被建筑师广泛应用于空间意义和情感的营造之中.以建筑实例分析为基础,系统论述了透视操作建构空间意义的可能性.     

轴心受压FRP约束圆形混凝土柱应力-应变模型

外包纤维复合材料(FRP)可以有效的提高混凝土柱的承载力和延性.本文系统总结了现有的几种FRP约束混凝土柱应力-应变模型,通过对已有大量试验研究结果的分析,指出FRP约束圆形混凝土柱的性能主要取决于FRP对混凝土柱的约束效果,引入约束效应系数ξ.并以约束效应系数ξ为主要参数,提出了FRP约束圆形混凝土柱三阶段应力-应变模型.该模型能较好的反映FRP约束混凝土柱应力-应变关系的特点,模型计算结果与试验数据吻合较好.     

基于非对称阿基米德Copula的多变量水文干旱联合概率研究

推导了5种常用3维非对称阿基米德Copulas函数的条件Copulas和密度函数,阐述了这类Copulas函数研究水文干旱特性联合分布的应用技术问题。以渭河流域北洛河状头站的径流序列为例,干旱变量的边际分布参数分别采用矩法、概率权重法、极大似然法和遗传算法进行计算和选优,并进行了分布函数拟合度检验。变量相依性的度量表明干旱变量间有较强的相依性;根据AIC,BIC和RMSE准则,M12 Copula拟合效果最优。最后,进行了M12 Copula的拟合度检验,计算了北洛河状头站3维水文干旱变量组合的联合概率、条件概率和相应的重现期。     

应用改进的稳健设计法分析深梁抗剪强度

为深梁的试验、设计和施工提供基本依据,应用改进的稳健设计法,并引入新的信噪比,考虑剪跨比、混凝土强度、水平箍筋屈服强度和竖向箍筋屈服强度等因素.用软化桁架模型分析钢筋混凝土深梁抗剪强度,并应用改进的稳健设计法对影响深梁抗剪强度的因素进行分析,得出了各种影响因素的重要程度.深梁的抗剪强度对混凝土强度这个因素最为敏感,剪跨比次之,水平钢筋屈服强度、竖向钢筋屈服强度影响最小.与田口方法相比改进的稳健设计法的分析结果与试验结果吻合较好,应用更加准确、方便.     

基于ETM遥感影像的海岸线提取与验证研究

利用ETM遥感数据,以黄河三角洲为研究区域,运用边缘检测方法中的Soble算法和修复归一化水体指数法（MNDWI）两种方法对该地区的两种海岸线类型--人工海岸和淤泥质海岸进行海岸线提取研究,并验证评价海岸线提取效果。结果表明,Soble算法提取的海岸线准确度更高,在淤泥质海岸提取中表现更为明显,相对误差由0.025%降低为0.018%。