自重体积力作用下坡体张应力及坡面位移的变化规律

为了提高对边坡体力学行为的认识,借助于FLAC有限差分软件的数值模拟,并结和相似理论的推导验证,研究了在仅有自重体积力作用的条件下,线弹性边坡体的一些力学特征及其与相关变量或物理力学参数的相关关系。没有外载荷影响时边坡地表最大主应力和最小主应力分别平行和垂直于地表,当深度增加时,主应力的取向逐渐变成竖直和水平两个方向,坡面处既有张应力区也有拉应力区,坡脚处亦存在较大的张应力,这是自重体积力作用下边坡体应力分布的一般性特征,在本文和前人的研究中都能体现。本文还重点揭露了：坡角线性增加时坡顶最大张应力的变化速率表现为：快——慢——快; 沿坡顶面竖直向下张应力随深度增加线性减小; 小变形条件下边坡应力场与弹性模量无关; 最后验证了满足相似理论的坡体,坡面对应点的位移比是其几何尺寸比的平方倍。本文不仅是对既有研究成果的进一步补充,而且为以后研究复杂条件下边坡体的力学特征奠定了基础,对于理论和实践都有一定的启发意义。     

Exact solutions to the equations of perfect gases through Lie group analysis and substitution principles

In this paper we consider the equations that govern the motion of perfect gases. We explicitly characterize some classes of steady solutions in two and three space dimensions, by introducing invertible point transformations suggested by Lie group analysis; moreover, by using various transformations known as substitution principles, new steady and unsteady solutions are constructed.     

自适应卡尔曼滤波在移动卫星通讯系统中的应用

研究了自适应卡尔曼滤波技术在移动卫星通讯系统中的应用.首先分析长时间工作的移动卫星通讯系统对导航定位系统的要求,其次通过对系统建模建立系统方程,利用GPS信息和激光陀螺惯性导航系统(LINS)信息建立量测方程.为了避免滤波发散,卡尔曼滤波算法采用Sage&Husa算法.最后给出在北京西郊跑车实验的结果.实验结果表明采用自适应卡尔曼滤波技术的LINS/GPS组合导航系统可以有效地改善移动卫星通讯系统的性能.     

Nearly-Hamiltonian Structure for Water Waves with Constant Vorticity

We show that the governing equations for two-dimensional gravity water waves with constant non-zero vorticity have a nearly-Hamiltonian structure, which becomes Hamiltonian for steady waves.      

后台阶流动的数值模拟

访述了大涡模拟的基本思想，指出大涡模拟的效率主要取决于四个因素，即流动中须有大尺度涡存在、合理的计算格式、合适的滤波器和亚格子应力模型。在深入考虑粘性不可压缩流Navier—Stokes方程各个子项作用的基础上，提出二阶全展开Euler—Taylor—Galerkin有限元方法作为大涡模拟的离散格式，并采用Gauss滤波器，对典型算例——后台阶处的流动进行大涡模拟，计算结果与相关文献符合的很好。从计算结果还可以看出大涡模拟与二阶全展开ETG有限元方法的结合在捕捉涡系及反映涡动时变过程方面具有明显的优势，说明大涡模拟适合于边界几何形状复杂区域流动的模拟。同时应用二阶全展开ETG有限元方法对低雷诺数粘性不可压缩后台阶流动进行了计算，得到与相关文献符合良好的计算结果，即该方法也可独立用于对低雷诺数粘性不可压缩流动的计算。     

Tm3+/Yb3 :LiYF4单晶的高效近红外量子剪裁及其在光伏电池中的应用

采用改进的坩埚下降法成功地生长了Tm/Yb共掺氟化钇锂单晶. 该单晶体具有每吸收一个蓝色光子并能发射出2个1000 nm近红外光子的下转换发光效应. 测定了样品的激发光谱、发射光谱和荧光衰减曲线. 在465 nm蓝光激发下观察到由Yb³⁺：²F_5/2→²F_7/2能级跃迁所致的960～1050 nm 波段的发射带,此发光带源于Tm³ 对Yb³ 离子的能量下转换过程. 应用Inokuti-Hirayama模型,研究了晶体的能量转换过程,结果表明Tm³ 向Yb³ 的能量传递是一个电偶极子相互作用机制过程. 当Tm³ 与Yb³ 离子的掺杂浓度为0.49mol%与5.99mol%时,单晶的量子剪裁效率达到最大值167.5%.     

非晶碳氧化硅纳米线的合成与光致发光

利用直流电弧放电合成非晶碳氧化硅(SiCO)纳米线,不使用催化剂和模板,独立的SiCO 纳米线沉积在石墨锅的表面．通过XRD、SEM、TEM、XPS、FTIR等对SiCO纳米线进行了表征．结果表明,纳米线长度为20～100 μm,直径为10～100 nm,Si原子同C原子和氧原子分享成键组成SiCO单元．SiCO纳米线的光致发光谱在454和540 nm呈现了强而稳定的白色发光峰． SiCO纳米线的生长机制为等离子辅助气―固生长机制．     

Effect of cooling rate in [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xNbx alloy system on magnetic properties

The effect of cooling rate on the thermal stability and soft magnetic properties of [(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]_100-xNb_x (x = 5, 6, 7, 8 at. %) system was investigated. The alloys were produced into the form of ribbon and cylindrical rod by melt-spinning and injection casting, respectively. Their structure, thermal, mechanical and soft magnetic properties were investigated by x-ray diffraction, differential scanning calorimetry, universal testing machine and vibrating sample magnetometer, respectively. All of the alloys were identified as fully amorphous by X-ray diffraction. It turned out that the rod samples had exceptionally high saturation fields reaching 3.0 kOe, which is key properties for sensor application. Also, among these Fe,Co-based samples, the Fe_35.25 Co_35.25 B_18.8 Si_4.70 Nb₆ ribbon exhibits the highest saturation magnetization with 142.1 emu/g.     

Application of multi-buffer layer of (Zn,Mg)O/CdS in Cu2ZnSn(S,Se)4 solar cells

(Zn,Mg)O (ZMO) buffer layer has attracted attention for having the potential to control the conduction band offset of buffer layer and large band-gap (Eg) Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber interface, where the ZMO layer is deposited by the sputtering. However, the solar cell efficiency is decreased with the ZMO layer as compared with the CdS layer. The decrease in conversion efficiency is attributed to the sputtering damage on the absorber and high light reflection from the surfaces of CZTSSe solar cells. To completely suppress the damage, a CdS layer with very thin thickness of 20 nm is inserted between the ZMO layer and the CZTSSe layer. In addition, MgF₂ layers are deposited on CZTSSe solar cells as anti-reflection coating. Ultimately, the solar cell with multi-buffer layer of ZMO/thin-CdS is almost same level as that with the CdS layer. Therefore, the multi-buffer layer can be an appropriate buffer layer of the large-Eg CZTSSe layer.