Study on Post Foundation of Highway Medium Guardrail

目前高速公路中央分隔带波形梁护栏立柱的实际设置中,普遍存在着由于分隔带地基强度低于压实路基,护栏立柱承载能力偏低,护栏的防护性能达不到设计要求的问题。对粘性土地基中立柱的受力情况进行了分析,并对地基为压实土与回填土两种情况进行了对比,给出了中央分隔带中立柱地基的加固方案。

液桥中不同Prandtl数流体的热毛细对流

本文研究从上面加热的液桥中不同 pr 数流体的热表面张力驱动对流。在 Ma 数相同的条件下,不同 pr 数流体液桥中的温度分布和流场结构定性相似,但定量结果不同。小pr数(pr<<1)流体液桥中的粘性边界层远小于热边界层,最大流函数所在位置向冷端偏移,有较大的流动速度。结果表明,Ma 数是描述这种流动的敏感参数。

有涨落效应的磁流体静力学关系

观测表明,在许多天体物理环境中,涨落场具有不可忽略的重要作用.本文在一阶光滑近似条件下,推导了普通湍流和随机波动两种条件下的磁流体静力学方程组,以及这些方程所要求的自洽性条件.在静力学问题中,涨落的洛伦茨力会对大尺度磁场位形有影响.具体研究这种影响对于解释观测的特征是十分必要的,特别是许多天体物理环境中,磁场(包括涨落磁场δB)是决定能量和动量平衡的重要因素.

基于红外热象技术的金属材料疲劳性能研究方法

金属材料的疲劳极限或疲劳寿命等性能是长寿命机械和结构抗疲劳设计的基本数据,探讨效率高、成本低而又准确的试验新方法,成为相关研究者十分感兴趣的课题。材料在循环载荷作用下产生的塑性变形经不断累积会引起疲劳破坏,这个过程所耗的塑性功绝大部分以热量形式耗散,因此寻找热耗散温度变化过程与疲劳极限及寿命之间的关系很有意义。就此问题,文中引入利用先进的红外热成象技术确定金属材料疲劳性能的试验研究方法,主要从原理和试验方法两方面进行介绍,并对45钢的试验过程和现象作较为详细地阐述,得到较准确的疲劳极限值和基于红外热象技术确定疲劳寿命的重要参量M。

模拟弹塑性碰撞的修正SPH方法

从基本的无网格光滑粒子法SPH(Smoothed Particle Hydrodynamics)近似出发,修正了模拟固体力学中大变形弹塑性碰撞的SPH方法.在边界处采用修正的边界条件,弹塑性分析过程中采用增量理论计算应力,迭代过程中用守恒光滑法进行滤波修正消除拉力不稳定.对SPH方法进行了程序实现,给出了杆弹塑性碰撞的算例.计算分析表明,SPH方法节点的影响域较大、精度较相同节点间距有限元法的结果有一定差距,但是通过增加粒子数量可以提高SPH的精度,保持了其简单性和计算大变形的特性.

Laser-driven inertial ion focusing

A Hohlraum-like configuration is proposed for realizing a simple compact source for neutrons. A laser pulse enters a tiny thin-shelled hollow-sphere target through a small opening and is self-consistently trapped in the cavity. The electrons in the inner shell-wall region are expelled by the light pressure. The resulting space-charge field compresses the local ions into a thin layer that becomes strongly heated. An inward expansion of ions into the shell cavity then occurs, resulting in the formation at the cavity center of a hot spot of ions at high density and temperature, similar to that in inertial electrostatic confinement.

Algorithm of far-field centre estimation based on phase-only matched filter

Estimation of the far-field centre is carried out in beam auto-alignment. In this paper, the features of the far-field of a square beam are presented. Based on these features, a phase-only matched filter is designed, and the algorithm of centre estimation is developed. Using the simulated images with different kinds of noise and the 40 test images that are taken in sequence, the accuracy of this algorithm is estimated. Results show that the error is no more than one pixel for simulated noise images with a 99% probability, and the stability is restricted within one pixel for test images. Using the improved algorithm, the consumed time is reduced to 0.049 s.

Calculations of bond dissociation energies and dipole moments in energetic materials using density-functional methods

We compare the effectiveness of six exchange/correlation functional combinations (Becke/Lee, Yang and Parr; Becke-3/Lee, Yang and Parr; Becke/Perdew-Wang 91; Becke-3/Perdew-Wang 91; Becke/Perdew 86; Becke-3/Perdew 86) for computing C-N, O-O and N-NO2 dissociation energies and dipole moments of five compounds. The studied compounds are hexabydro-1,3,5-trinitro-1,3,5-triazine (RDX), dimethylnitramine, cyanogen, nitromethane and ozone. The Becke-3/Perdew 86 in conjunction with 6-31G

970nm抽运下Tm^3／Yb^3＋共掺氧氟玻璃的频率上转换发光

稀土离子掺杂的氧氟玻璃是一种新型上转换发光材料。制备了Tm^3／Yb^3＋单掺、共掺的摩尔分数为n（SiO2）-0．30，n（PbF2）-0．50，n=（Al2O3）=0．15，n（AlF3）=（0．049-x），n（TmF3）=y，n（YbF3）=x（x=0，0．001，0．010，0．015，0．020，y=0，0．001）系统氧氟玻璃，研究了其上转换发光特性、分析了其上转换发光机理。研究发现，在970nm抽运光源激发下，Tm^3＋单掺时没有可见光上转换发射；而加入Yb^3＋后产生了强的蓝光（452n

Investigation on upconversion luminescence in Er3+/Yb3+ codoped tellurite glasses and fibers

The upconversion properties of Er3+/Yb3+ codoped tellurite glasses and glass fibers with D-shape cladding under 980 mu excitation were investigated. Intense emission bands centered at 531, 546 and 658 nm corresponding to the transitions Er3+: H-2(11/2) -> I-4(15/2) , S-4(3/2) -> I-4(15/2) and F-4(9/2) -> I-4(15/2), respectively, were observed at room temperature. Compared with that in Er3+/Yb3+ codoped tellurite bulk glass, the upconversion luminescence becomes more efficient in the fiber geometry. The dependence of upconversion intensities on fiber geometry and possible upconversion mechanism are discussed and evaluated. The presented Er3+/Yb3+ codoped tellurite fibers with intense upconversion luminescence can be used as potential host materials for upconversion fiber lasers. (c) 2005 Elsevier B.V. All rights reserved.