Estimating the turbulent energy dissipation rate in an airport environment     

Michael Frech 《Boundary-Layer Meteorology》2007,123(3):385-393

This note reports on the influence of aircraft wake vortices on the estimation of the turbulent energy dissipation rate using sonic anemometer measurements near the runway threshold. The wake vortex traces, which are generated at a height of about 65 m and subsequently evolve in ground effect, are clearly visible in the velocity components and temperature. The observed temperature increase of 1 K appears related to the stably stratified atmospheric surface layer. The dissipation rate is estimated from the longitudinal velocity power spectrum for a sample in a nocturnal boundary layer with and without a wake vortex signal. In both cases an inertial subrange is found. For the analyzed sample the estimated dissipation rate is a factor of ten larger compared to the undisturbed sample. Implications for operational wake avoidance systems are discussed.  相似文献   

EVALUATION OF GEOCHEMICAL QUALITY CONTROL IN DETERMINATION OF Mn IN SOILS USING A SEQUENTIAL CHEMICAL EXTRACTION     

DONGDe－ming  FANGChun－sheng 《中国地理科学(英文版)》2002,12(2):166-170

Sequential chemical extraction procedure has been widely used to partition particulate trace metals into vari-ous fractions and to describe the distribution and the statue of trace metals in geo-environment.One sequential chemical extraction procedure was employed here to partition various fractions of Mn in soils.The experiment was designed with quality controlling concept in order to show sampling and analytical error.Experimental results obtained on duplicate analy-sis of all soil samples demonstrated that the precision was less than 10%(at 95% confidence level).The accuracy was estimated by comparing the accepted total concentration of Mn in standard reference materials (SRMs) with the measured sum of the individual fractions.The recovery of Mn from SRM1 and SRM2 was 94.1% and 98.4%,respectively.The detection limit,accuracy and precision of the sequential chemical extraction procedure were discussed in detailed.All the results suggest that the trueness of the analytical method is satisfactory.  相似文献   

Discriminating Bio-Induced and Detrital Sedimentary Processes from Particle Size Distribution of Carbonates and Non-Carbonates in Hard Water Lake Sediments     

F.?ArnaudEmail author 《Journal of Paleolimnology》2005,34(4):519-526

Particle size distribution (PSD) and carbonate content are two of the most frequently used parameters for describing lake sediments. This paper presents a method for rapidly measuring both these parameters using a laser particle-sizer, as well as an original way in which to separately interpret the PSD of the carbonate and non-carbonate fractions. Differential particle size analyses are produced by measuring the PSD of each sample twice. The first PSD is measured using the bulk sample. The second PSD is measured after the carbonate fraction has been completely dissolved by adding hydrochloric acid to the sample. As well as particle size analyses, laser particle-sizers automatically give obscuration values for the samples being analysed. By comparing the obscuration value for the bulk sample with the value for the de-carbonated fraction, the carbonate content of the sediment can be determined. In order to test the accuracy of the method, the results were compared with chemical analyses of carbonate content. This comparison showed that when applied to diatom-rich samples the method underestimates the carbonate content. This is due to the fact that the differential particle size method measures the volume concentrations of the carbonate and non-carbonate fractions, whereas chemical analysis measures the weight concentrations. As diatoms are hollow and have relatively low-densities, differential particle size analyses of diatom-rich samples overestimate the non-carbonate fraction. Despite this limitation, and bearing in mind that laser particle-sizer distributions are expressed in terms of volume percent for each size class and not weight percent, PSDs can provide useful data for interpreting sedimentary processes. One of the main advantages of this method is that it can be used to separate the PSDs of the carbonate (autochthonous) fraction and the non-carbonate (allochthonous) fraction from the PSD of the bulk sample. The value of such an approach was demonstrated by the analysis and interpretation of a 9 m-long core from Lake Bourget in France. An analysis of the bulk sample PSDs plotted as a function of depth showed the consistency of sedimentary processes over the last 7200 years. Amongst these processes, it was possible to identify two modes of clastic material deposition: river-borne fine sedimentation during major floods and gravity reworking of sandy sediment from the lakeshore.  相似文献   

边坡可靠度风险评价分析     

李东升  刘东燕 《中国地质灾害与防治学报》2005,16(2):150-153

确定性设计安全系数法由于简单易行得到了广泛的应用。可靠度方法在一定程度上弥补了确定性设计中不能考虑实际工程中岩体参数离散性的问题，使设计更加符合实际情况。函数连分式方法在边坡一次二阶矩概率设计中可以方便地计算出状态函数对各随机变量的偏导数，也可使传统安全系数法和可靠度分析有机结合。考虑经济最优的原则，结合风险分析来确定可靠度法设计中的可靠度数值问题。由安全系数和可靠性共同度量边坡系统的稳定性，建立传统安全系数与可靠度理论耦合的边坡稳定二元体系，可有效地考虑边坡系统内实际存在的不确定性和相关性，使边坡的稳定性评价更加客观精确，为边坡安全和滑坡灾害的风险性管理提供理论和方法。  相似文献   

岩土材料塑性损伤模型及拱坝的变形局部化分析     

陈新  杨强  周维垣 《岩土力学》2007,28(5):865-870

常规的弹塑性模型难以模拟材料破坏时由于内部损伤累积引起的变形局部化带形成过程。将岩土材料抽象为含有孔洞的球形体胞单元的集合体,采用一个标量--孔洞体积百分比来刻划单元的损伤程度,基于细观损伤力学提出了一个适用于岩土材料的塑性损伤模型。将该模型通过用户子程序嵌入到大型有限元商业软件MRAC中,研究岩土材料的局部化剪切带形成过程。采用该模型,成功地对平面应力条件下岩土材料单轴受压和单轴受拉试件的局部化破坏分别进行了数值模拟。采用该模型,对拱坝在超水载作用下的变形局部化进行了研究,数值计算结果表明,上游坝踵处最先发生变形局部化现象。  相似文献   

植物稳定同位素研究进展与展望   总被引：6，自引：0，他引：6  

吴绍洪  潘韬  戴尔阜 《地理科学进展》2006,25(3):1-11

植物稳定同位素是近年来在地理学、生态学研究中逐步广泛应用的研究手段, 具有综合长 期生物地球化学过程和联系不同系统成分的特点, 国际上已经展开了较为广泛的应用, 国内也有 相关研究。本文对国内外植物C、H、O 稳定同位素研究的回顾, 显示植物稳定同位素与环境因子, 如气温、湿度、降水、环境稳定同位素组成等密切相关。目前植物稳定同位素技术主要应用于历史 时期环境气候的重建, 恢复大气CO₂ 同位素组成以及CO₂ 浓度的变化趋势。本文根据植物稳定同 位素的特点和研究基础, 认为植物稳定同位素方法不仅可以用来重建历史时期气候, 而且在区域 环境差异及其生态效应研究上有着重要应用前景。  相似文献   

Seasonal variability of phytoplankton biomass and composition in the major water masses of the Indian Ocean sector of the Southern Ocean     

《Polar Science》2014,8(3):283-297

Long-term changes in phytoplankton biomass and community composition are important in the ecosystem and biogeochemical cycle in the Southern Ocean. We aim to ultimately evaluate changes in phytoplankton assemblages in this region on a decadal scale. However, yearly continuous data are lacking, and long-term datasets often include seasonal variability. We evaluated the seasonal changes in phytoplankton abundance/composition across latitudes in the Indian Ocean sector of the Southern Ocean via multi-ship observations along the 110°E meridian from 2011 to 2013. The chlorophyll a concentration was 0.3–0.5 mg m⁻³ in the Subantarctic Zone (40–50°S) and 0.4–0.6 mg m⁻³ in the Polar Frontal Zone (50–60°S); pico-sized phytoplankton (<10 μm), mainly haptophytes, were dominant in both zones. In the Antarctic Divergence area (60–65°S), the chlorophyll a concentration was 0.6–0.8 mg m⁻³, and nano-sized phytoplankton (>10 μm), mainly diatoms, dominated. Chlorophyll a concentrations and phytoplankton community compositions were the same within a latitudinal zone at different times, except during a small but distinct spring bloom that occurred north of 45°S and south of 60°S. This small seasonal variation means that this part of the Southern Ocean is an ideal site to monitor the long-term effects of climate change.  相似文献   

The relative contributions of unicellular and filamentous diazotrophs to N2 fixation in the South China Sea and the upstream Kuroshio     

《Deep Sea Research Part I: Oceanographic Research Papers》2014

We studied the seasonal, diel, and vertical distribution of phytoplankton N₂ fixation to understand the relative contributions of unicellular and filamentous nitrogen fixers (diazotrophs) to N₂ fixation and nitrogen recycling in the northern South China Sea (SCS) and the neighboring upstream Kuroshio. N₂-fixation rates were measured by the ¹⁵N₂ tracer technique (addition by bubble) on unicellular (<10 or 20 µm) and the filamentous diazotrophs (>10 or 20 µm, mostly Trichodesmium and Richelia) fractionated by 10- or 20-µm mesh sizes. The mean depth-integrated total (unicellular+filamentous) N₂-fixation rates in the SCS (51.7±6.2 µmol N m⁻² d⁻¹) averaged 1/3 of that in the Kuroshio (142.7±29.6 µmol N m⁻² d⁻¹), with higher rates in the winter than in other seasons in the SCS and the opposite seasonal pattern in the Kuroshio. Unicellular diazotrophs contributed 65% of the total N₂ fixation in the SCS, which were negatively correlated with surface temperature and, as for total N₂ fixation, were higher in the winter when Trichodesmium spp. were scarce. In comparison, the unicellular diazotrophs contributed 50% of total N₂ fixation in the Kuroshio, and their contributions were not significantly correlated with surface temperature. In both the SCS and the Kuroshio, the unicellular N₂ fixation was more important during the night than during the day, and in the deep euphotic layer than in the surface layer, even in the daytime. Our results show that the unicellular diazotrophs were important N₂ fixers and contributed significantly to N₂ fixation in the tropical marginal seas, more so in the SCS than the Kuroshio.  相似文献   

Estimating evapotranspiration fraction by modeling two-dimensional space of NDVI/albedo and day-night land surface temperature difference: A comparative study   总被引：1，自引：0，他引：1  

Jingxue YangYunpeng Wang 《Advances in water resources》2011,34(4):512-518

Three simple models estimating the evapotranspiration fraction (EF) were tested, validated and compared with available data from NDVI/albedo and day-night land surface temperature difference (DT). They were analyzed using ground based measurements collected by the energy balance Bowen ratio system at the 11 enhanced facilities located at the Southern Great Planes of the USA between April 2001 and May 2005. One model was superior in predicting the EF. It used an extension of the Priestly-Taylor equation and a relation between the normalized difference vegetation index (NDVI) and DT.  相似文献   

东海盆地西湖凹陷凝析油和轻质油生源母质剖析   总被引：2，自引：0，他引：2  

许婷  侯读杰  曹冰 《地球化学》2015,44(3):289-300

东海盆地西湖凹陷所分析的原油样品主要为凝析油和轻质油,黄岩构造带与平湖斜坡带原油的生源母质特征存在明显区别:黄岩构造带原油中C29甾烷占优势,C27、C28甾烷有一定含量,表明母质以陆源高等植物为主,水生生物占一定比例的贡献,二萜类化合物中富含源于裸子植物针叶树脂的成分,原油Pr/Ph值大于5.0,富含升补身烷和重排补身烷,表明其来自富含黏土、沉积环境呈氧化性的泥岩或煤系烃源岩;平湖斜坡带原油中C29甾烷占明显优势,母质中陆源高等植物占重要比例,二萜类化合物中富含源于裸子植物松柏目树脂的成分,原油Pr/Ph值大部分大于4.0,其富含补身烷,重排补身烷含量变化较大,表明原油母质主要形成于氧化环境,源岩岩性有所区别。两个构造带原油均已成熟,但成熟度略有不同。  相似文献