在EBEX-2000实验资料中湍流耗散率、长度尺度和结构参数特征

采用2000年8月在美国加州棉花地两个高度上应用超声三分量仪、快速响应温度和湿度仪进行的EBEX-2000 (International Energy Balance Experiment, 2000, 简称EBEX-2000) 风速三分量、温度和湿度湍流实验观测数据, 计算分析了在不同稳定度下的湍流能量和热量耗散率和湍流结构参数特征.并与Kansas和长白山原始森林湍流实验得到的结果进行了比较, 得到了一些湍流特征量在不同下垫面情况下的一些有意义的特征.     

美国加利福尼亚因约县更新世特科帕湖中的海泡石

一、引言 Sheppard和Gude(1968)在更新世特科帕湖(Lake Tecopa)小于2μm的泥岩碎片中辨认出了海泡石。他们推断海泡石是自生的,而别的粘土矿物则是碎屑成因的,而且他们还建议进一步取样,以确定海泡石的分布及其与别的粘土矿物的关系。本文作者在特科帕湖的粘土中采了158个样品,只有43个样含海泡石,本文只涉及那些含海泡石的样品,不管其含量多少。更新世特科帕湖约23公里长,18公里宽,位于Mojave Desert地区,在加利福尼亚因约县(Inyo County)东南的死谷(Death Val-     

The Structure of A Turbulent Jet in A Crossfiow--Effect of Jet-Crossfiow Velocity

A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. Thejet-to-crossflow velocity ratio (R) varies in the range of 2 ～ 16; both vertical jets and inclined jets without excess streamwisemomentum are considered. The numerical results of the standard two-equation k-~ model show that the turbulent structurecan be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R >4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallelwith the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details andscalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20 ～ 60.The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated,with distinct double concentration maxima; the aspect ratio is found to be around 1.2. A loss in vertical momentum is ob-served and the added mass coefficient of the jet motion is found to be approximately 1. On the other hand, for weak jets instrong crossflow, i.e. R≤ 2, the lee of the jet is characterized by a negative pressure region. Although the double vortexflow can still be noted, the scalar field becomes more symmetrical and no longer bifurcated. The similarity coeffcients are al-so noticeably different. The predicted jet flow characteristics and mixing rates are well supported by experimental and field data     

南极冰盖15万年的气候记录

第四纪经历了若干次冰期和间冰期。自首次在格陵兰西北部世纪营地打钻提取冰岩芯以来,又先后在南极洲伯德站、东方站、多姆C和格陵兰的戴依3四个地点打了五个穿透末次冰期层位的深钻孔。对这些冰岩芯中稳定同位素氧18含量及冰内杂质的化学成份分析研究结果,为地球的古气候及古环境提供了极为珍贵的资料。     

洞穴黑色沉积的成因

洞穴黑色沉积由几种不同物质构成。本文主要论述的有锰矿、煤烟、鸟粪、沥青和腐殖酸盐。锰呈一种黑色薄层盖在洞壁及河流冲积物上,也可呈斑点状存在于洞穴碳酸钙沉积物上,或作为一种黑色充填沉积。在黑色沉积中已发现了几种不同的锰矿,有钠水锰矿、杂硬锰矿(硬锰矿)、钙硬锰矿、锂硬锰矿和钡镁锰矿,这些可通过简单的化学实验进行鉴定。火把和提灯产生的煤烟往往沉积在洞顶和洞壁上部。在新墨西哥州瓜德罗普山的黑洞中发现地面燃烧的煤烟已由渗流水带入洞穴中。洞底鸟粪沉积中的灰份是过去鸟粪燃烧的证据。深褐色到黑色的鸟粪沉积可通过鸟粪的气味、屎粒特征、骨头、羽毛或昆虫的存在来识别,若鸟炎分解后则有较高的磷酸盐含量。洞穴中略带黑色的有机腐殖酸盐和其它酸质物必须在化学实验基础上由 x 射线的衍射术及红外线吸收光谱的分析来鉴定。虽然氧化锰是洞中最普遍的黑色物,但它仅是可能造成染色的色剂之一。本文之目的是论述洞穴中存在的几种黑色沉积,以便指导读者鉴别它们。     

利用卫星数据监测城市区域存在的问题及解决方法

1.引言城市化的影响对发达和不发达国家都存在。现势性而又详细的信息对于城市规划十分重要。遥感方法可以提供这方面的某些信息。世界各地对用陆地卫星 MSS 数据进行城市区域分类作过很多研究。其成果之一就是建立了适用于遥感的城市区域分类系统。第一级是城市(建成区),第二级进一步细分成居住区、商业区、工业区和空地等,用陆地卫星 MSS 资料进行第二级或更低一级的划分成效不大。     

土地分类方法

所有景观都能分成更小的单位。一些单位可能是独特的(如陨石坑),但大多数则是由一些重复的地形所组成,而这些地形本身则由更小的景观单位,如山顶、腰坡、谷底等锒嵌而成。本文,我们将探讨为不同目的而发展的、已应用于土地研究的各种方法,同时也将研究土地分类的一些哲理与方法论问题。方法澳大利亚联邦科学与工业研究组织土地研究处从事土地分类研究已二十多年了。调查目的是为了确定一个地区的主要类型,评价自然资源。     

SEDIMENT MANAGEMENT IN HYDROELECTRIC PROJECTS

Withdrawal of water from a river into a canal involves the construction of a barrage or a dam across the river depending on whether the river is perennial or not. The design of the reservoir upstream of the dam and of the canal requires consideration of the sediment load carried by the river in case the river is sediment-laden. The basic equations concerning morphological changes in such rivers are discussed with particular reference to computation of reservoir sedimentation. The hydraulics of lined canals carrying wash load is examined from the point of view of limiting transport capacity and changes in frictional resistance. Lastly, the methods of design of sediment extraction devices like settling basins and vortex chambers are presented.     

Seasonal fluctuations of tissue mercury contents in the European shore crab Carcinus maenas from low and high contamination areas (Ria de Aveiro, Portugal)

The main objective was to study the seasonal variation of mercury concentrations in different tissues (muscle, hepatopancreas and gills) of Carcinus maenas from low and high Hg contaminated areas, a valuable resource in temperate estuaries and a possible pathway for human uptake. Individuals of two size classes (around 35 and 55 mm cephalothorax wide) were captured monthly between March 1999 and May 2000 in two areas of Ria de Aveiro: in the main navigation channel that connects the lagoon to the sea, and in the inner lagoon area heavily contaminated by mercury (maximum Hg in sediments of 5.4 microg g(-1)). Pronounced decreases in salinity and temperature and reduced food availability in winter seemed to be the responsible for the decline of the crab condition index (0.75-0.45) in larger individuals. Muscle and hepatopancreas exhibited higher mercury concentrations than gills, with concentrations in the contaminated site ranging from 0.03 to 0.63 microg g(-1) and 0.02 to 0.34 microg g(-1), respectively. Linear regressions between muscle and hepatopancreas (r=0.94, p<0.001) and muscle and gills (r=0.97, p<0.001) suggested a rapid redistribution of mercury inside the organism. During winter, a rapid elimination of mercury was found in the three analysed tissues followed by uptake. Larger crabs presented elimination rates from 18 to 34 ng g(-1) per week, while the smaller crabs showed lower elimination rates (10-24 ng g(-1) per week). The uptake was similar in both size classes (11-15 ng g(-1) and 8.1-15 ng g(-1) per week, respectively for large and small crabs). Our results suggest that C. maenas harvested in the contaminated areas must be considered with caution, since Hg concentrations were found to exceed the threshold concentration allowed for human consumption (0.5 microg g(-1)).