Observation and analysis of near-surface atmospheric aerosol optical properties in urban Beijing

Year-round measurements of the mass concentration and optical properties of fine aerosols(PM_2.5) from June 2009 to May 2010 at an urban site in Beijing were analyzed.The annual mean values of the PM_2.5 mass concentration,absorption coefficient（Ab）,scattering coefficient（Sc） and single scattering albedo（SSA）at 525 nm were 67±66μg/m³,64 ±62 Mm^-1,360 ±405 Mm^-1 and 0.82 ±0.09,respectively.The bulk mass absorption efficiency and scattering efficiency of the PM_2.5 at 525 nm were 0.78 m²/g and 5.55 m²/g,respectively.The Ab and Sc showed a similar diurnal variation with a maximum at night and a minimum in the afternoon,whereas SSA displayed an opposite diurnal pattern.Significant increases in the Ab and Sc were observed in pollution episodes caused by the accumulation of pollutants from both local and regional sources under unfavorable weather conditions.Aerosol loadings in dust events increased by several times in the spring,which had limited effects on the Ab and Sc due to the low absorption and scattering efficiency of dust particles.The frequency of haze days was the highest in autumn because of the high aerosol absorption and scattering under unfavorable weather conditions.The daily PM_2.5concentration should be controlled to a level lower than 64 μg/m³ to prevent the occurrence of haze days according to its exponentially decreased relationship with visibility.     

含孔软铁磁材料Mindlin板中弹性波散射问题

基于考虑磁弹相互作用的Mindlin板弯曲波动方程，采用波函数展开法，分析研究 了含孔软铁磁材料Mindlin板中弹性波散射与动应力集中问题，给出了问题的分析 解和数值算例. 通过分析发现：磁感应强度对动弯矩集中系数和动剪力集中系数有 增加的作用，特别是在低频的情况下.     

INFLUENCE OF ASIAN DUSTS ON THE PHYSICOCHEMICAL PROPERTIES OF ATMOSPHERIC AEROSOLS IN TAIWAN DISTRICT USING THE PENGHU ISLANDS AS AN EXAMPLE

1. Introduction In the early months of each year, Asian dusts transport frequently from Northwest China and Mongolia to the Pa-cific-Rim countries (Kagawa et al., 2001; Uno et al., 2002). It causes significant environmental effects such as ambient air quality deterioration, atmospheric visibility impairment, radiation energy reduction, mineral deposition, and acid rain neutralization (Terada et al., 2002; Zhang & An, 1999). During Asian dust periods, significant increases of atmos-pheric …     

EFFECTS OF FINELY DISPERSED METALLIC PALLADIUM ON MICROSTRUCTURE AND PROPERTIES OF NANOCOMPOSITES PRODUCED BY SOL-GEL TECHNIQUE

Nanosized palladium particles were incorporated into mesoporous silica matrix to obtain nanocomposites using the sol-gel technique. Effects of the finely dispersed metallic palladium on the microstructure and properties of the nanocomposites were investigated. By means of X-ray diffraction and optical absorption, it was found that palladium particles were 5-9 nm in diameter and their uniform dispersion in the mesoporous silica depended on both the content of the palladium and the structural features of the silica matrix. The results showed that the mixing method of preparation led to wider size distribution of the nanosized particles as compared to the immersion method, but dispersed degree was reduced. Although the incorporation of nanosized palladium particles could not substantially induce significant structural changes of the matrix, the apparent red-shifted optical absorptions for the nanocomposites were observed as compared to the parent monolithic silica, particularly with increase in palladium loading and calcination temperature.     

SYNTHESIS AND CHARACTERIZATION OF SURFACE-HYPERBRANCHED MAGNETITE NANOPARTICLE FOR BOVINE SERUM ALBUMIN IMMOBILIZATION

A hyperbranched polyamidoamine polymer was synthesized on the surface of magnetite nanoparticles to enhance bovine serum albumin (BSA) immobilization efficiency. The amount of immobilized bovine serum albumin (BSA) on the surface-hyperbranched magnetite nanoparticle was up to 2.5 times as much as that of magnetite nanoparticle modified with only amino silane.     

相变材料接触熔化的研究

对有关相变材料接触熔化的研究成果进行了全面的综述, 内容包括:封闭空间的接 触熔化、围绕热源的接触熔化、滑动接触熔化、滚动接触熔化、冰的压力熔化、接 触熔化的量级分析与修正、由液体边界层内的热扩散引起的熔化、不连续接触点上 熔化与润滑、固体内部传热的影响、玻璃的软化与接触熔化.     

结构静动力屈曲问题研究进展

近几十年来，结构的静动力屈曲问题一直是力学工作者极为关注的一个前沿课题．本文总结和综述了这一研究领域的几个基本问题：屈曲问题的分类、动态屈曲问题的特点及其特征量；介绍了屈曲问题的处理方法和目前已取得的成果；总结评述了人们关心的热点问题；屈曲问题的模型分析和实验技术、动态屈曲判别准则．     

四边固定载流矩形薄板的磁弹性稳定性分析

本文针对四边固定载流矩形薄板,利用Mathieu方程解的稳定性,研究其在电磁场与机械荷载共同作用下的磁弹性稳定性问题。首先在载流薄板的磁弹性非线性运动方程、物理方程、几何方程、洛仑兹力表达式及电动力学方程的基础上,导出了载流薄板在电磁场与机械荷载共同作用下的磁弹性动力稳定方程,然后应用Galer-kin方法将稳定方程整理为Mathieu方程的标准形式,并将薄板的动力稳定性问题归结为对Mathieu方程的求解。利用Mathieu方程的稳定解区域与非稳定解区域的分界,即方程系数λ和η的本征值关系,得出了磁弹性问题失稳临界状态的判别方程。通过具体算例,给出了四边固定载流矩形薄板的磁弹性动力失稳临界状态与相关参量之间的关系曲线,并对计算结果及其变化规律进行了分析讨论。     

白洋淀内水体的流动特征研究

研究了风对白洋淀内水体循环流动的影响，研究指出：(1)风应力可看作是水体循环 的主要驱动力. (2)在风应力的作用下，水体表层的流动主方向与风的方向一致，下层水体 的流动方向与表层方向相逆或近似相逆. (3)表层以下水体流动复杂，次表层水平流动有明 显的双涡结构. (4)淀底地形对水体垂向流动影响很大，垂向速度变化复杂，垂向上有双涡 流动现象. 从动力学角度研究了淀内水体流动的情况.     

多胞材料的力学行为

多胞材料具有独特的力学性质,其工程应用日益增加.人造多胞材料可以分为蜂窝材料和泡沫材料两类.本文介绍了这两类材料在不同载荷条件下力学行为的研究概况.对于某些天然材料(木材和松质骨)的多胞结构及其模型也作了简要介绍.