北京市冬季雾霾天人体呼吸高度PM2.5变化特征对气象因素的响应

依据实测北京冬季人体呼吸高度PM_(2.5)质量浓度、湿度、风速、风向、温度数据,利用相关性分析、非线性回归分析、统计分析,分别探讨轻中度空气污染天、一次重污染过程,气象因子对PM_(2.5)质量浓度生成、变化的影响.结果表明:1轻中度污染天,若温度较低、日平均风速较小,湿度大时,湿度是影响PM_(2.5)质量浓度变化的决定性因素;而温度、风速、湿度均较大时,PM_(2.5)质量浓度变化受三者共同作用;当风速、湿度、温度均较小时,PM_(2.5)质量浓度变化主要受前两者影响.这反映出,人体呼吸高度的PM_(2.5)质量浓度变化对气象因子微小变化响应极为敏感.2一次空气质量从良到重度污染的过程中,PM_(2.5)质量浓度积累主要是由于空气湍流较弱、加之湿度大导致的,此外白天西北风、东北风较大,但持续时间短,而夜间东南风、西南风风速较小,持续时间长,也有利于污染物的累积.3短时微小量降雪使温度降低、空气湿度增加,不仅不能降低PM_(2.5)质量浓度,反而使其上升了72%,造成颗粒物浓度的跃升现象.4短时风速较大,风速达到2.0 m·s~(-1),持续2 h,虽然在一定程度上降低局地PM_(2.5)质量浓度,但并不能彻底改变空气质量状况.只有当风速大于3.5 m·s~(-1),且持续4 h以上,才能够迅速地扩散空气中的细颗粒物,空气质量由重度污染转变为优.     

黄磷燃烧特性实验研究与理论分析

基于黄磷燃烧特性实验,对黄磷燃烧的动力学现象进行了实验研究和理论分析。通过观察不同燃烧表面积的黄磷燃烧动力学现象,获得了黄磷的燃烧特性参数,并利用池火模型对黄磷燃烧实验进行了理论分析。研究结果表明：固定表面积的黄磷燃烧时,黄磷的质量损失速率可近似视为某一恒定值,黄磷的质量损失速率与燃烧表面积有关。黄磷燃烧实验火焰最高温度约为1000℃,火焰高度与燃烧表面积有关。池火模型可以对黄磷的燃烧特性参数进行预测和分析,池火模型所预测的火焰高度与实验数据基本相吻合,相对误差小于7％。     

室外风作用下竖井结构内火灾烟气运动规律研究

室外风是影响高层（超高层）建筑火灾蔓延的主要因素。通过数值模拟六个不同火灾场景温度场、能见度及CO浓度场变化过程,定量总结了不同风向、风速条件下侧向全开竖井结构内烟气运动规律。模拟结果发现,迎面风作用下,竖井内会产生较高滞止压力,中性面位置上升,上部烟气加速向竖井下部蔓延,下部烟气通过开口排出;背面风作用下,中性面位置...     

巢湖流域SRTM高程误差的空间分异研究

数字高程模型是进行地学研究的重要基础数据,SRTM、DEM是公众可以免费获取的精度达90m的DEM数据.以我国1:5万DEM为参考数据,以巢湖流域为研究区,利用高程中误差模型和单位面积土地填挖方对SRTM、DEM进行高程精度研究,并分析了高程误差的空间分异规律.结果表明,SRTM、DEM的高程中误差和单位面积土地填挖方随着地貌类型的变化呈现明显的空间分异性,这主要由于SRTM像元精度不高所致.在研究区内的33块样区中,绝大部分都是在二级精度评价标准之内,可见SRTM、DEM整体精度较高.     

GRAZED STUBBLE HEIGHT AS A CRITERION FOR CONTROLLING SEDIMENT PRODUCTION FROM GRAZING LANDS1

ABSTRACT: Efforts by state and federal agencies to develop standards and guidelines for protecting and enhancing water quality on grazing lands have led to suggestions that grazed stubble height criteria could be used to determine when cattle should be removed from a specific pasture or grazing area. Until recently only indirect scientific evidence from agronomy and laboratory studies gave support to the stubble height concept. Consequently, a grazing study was initiated on a Montana ranch in 1997 to determine the reduction in overland sediment achieved by grazing a pasture to a predetermined stubble height. Treatments consisted of 7 cm (3 in) grazed, 7 cm (3 in) clipped or mowed, 15 cm (6 in) grazed; 15 cm (6 in) clipped and untreated or natural forage plant height. The five treatments were used in a two‐year trial spanning 1997 to 1999. At the conclusion of this study the magnitude of sediment production was related to the number of intense rain events during the March through June period rather than total precipitation. There was a significant year effect in terms of sediment accumulation (P < 0.01) but no year by treatment effect (P = 0.11). Even though a significant difference in sediment accumulation was detected between the shorter and taller stubble heights (P = 0.04) in both 1998 and 1999, the difference could not be explained by grazed stubble height alone. Close grazing (7 cm stubble) consistently ranked lowest in sediment production (P < 0.01) among all treatments, including the ungrazed control. These results suggest that changes in plant community structure and microtopographic caused by grazing influence sediment entrapment (retention) on hillslopes more than those caused by plant height.     

中空结构可燃物竖直向上火蔓延特性实验研究*

为探究中空结构固体可燃物竖直向上火蔓延的特征规律,针对不同试样内径(d)的瓦楞纸圆管进行竖直向上的火蔓延实验研究,探讨试样内径对其竖直向上火蔓延特性的影响。结果表明:其火蔓延过程可以分为火焰发展、稳定蔓延和火焰衰弱3个阶段,蔓延过程中对流换热占据主导地位;平均火焰高度随d的增大先增大后略微减小,在d=70 mm时达到最大;火蔓延速率和质量损失速率均随d的增大而增大,并且质量损失速率与d存在较好的线性关系;火蔓延速率与热释放速率呈现出较好的幂次关系。可以发现在一定范围内,中空结构可燃物的内径越大其火灾危险性越高。     

广州城区冬季大气边界层气溶胶激光雷达探测

激光雷达是大气边界层气溶胶和云的一个高效探测工具。2010年12月利用Mie散射激光雷达对广州城区冬季大气边界层进行系统观测,分析讨论了测站地域上空大气气溶胶的消光系数垂直分布和时间变化的主要特征。结果表明:冬季广州大气边界层气溶胶主要分布在1100m以下区域,气溶胶分布具有多层结构;大气边界层高度稳定分布在500~620m左右,边界层高度日变化不明显;冬季广州气溶胶源较为稳定并且变化慢;广州城区气溶胶浓度白天比晚上大,峰值出现11颐00~14颐00左右,谷值出现在20颐00左右。     

磁场对扩散火焰特性的影响

通过磁场对扩散火焰特性影响的研究，可以发现磁场能够改变火焰的燃烧特性，使火焰的温度升高，而火焰的高度有所降低。这能使我们更精确地了解实际火灾过程中火焰的燃烧特性，掌握火灾的特点，为减灾和灭灾提供有益的参考。     

Prediction of Annual Streambank Erosion for Sequoia National Forest,California

Many bank erosion models have limitations that restrict their use in wildland settings. Scientists and land managers at the Sequoia National Forest would like to understand the mechanisms and rates of streambank erosion to evaluate management issues and post‐wildfire effects. This study uses bank erosion hazard index (BEHI) and near‐bank stress (NBS) methods developed in Rosgen (2006 Watershed Assessment of River Stability and Sediment Supply [WARSSS]) for predicting streambank erosion in a geographic area that is dominated by colluvium and in which streambank erosion modeling has not been previously evaluated. BEHI evaluates bank susceptibility to erosion based on bank angle, bank and bankfull height, rooting depth and density, surface protection, and stratification of material within the banks. NBS assesses energy distribution against the bank measured as a ratio of bankfull near‐bank maximum depth to mean bankfull depth. We compared BEHI classes and NBS to actual bank erosion measured from 2008 to 2012. This index predicted streambank erosion with clear separation among BEHI ratings with R² values of 0.76 for extreme, 0.37 for high/very high, 0.49 for moderate, and 0.70 for low BEHI. The relationships between measured erosion and BEHI extend the application of BEHI/NBS to a new region where they can inform management priorities, afforestation, stream/riparian restoration projects, and potentially burned area rehabilitation.     

氯化镉和敌敌畏突发胁迫下斑马鱼的行为差异

采用计算机摄像跟踪技术,以正常水体中斑马鱼的行为变化为基础,比较突发性氯化镉和敌敌畏污染胁迫下斑马鱼的个体行为(游动速度、深度、转弯次数和加速度)和鱼群行为(平均距离和分散度)的变化规律.研究结果表明:斑马鱼在两种污染物突发性胁迫下,行为反应快速且敏感,游动行为响应与污染物种类和暴露时间直接相关;两种不同类型的污染胁迫...