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INTRODUCTIONTheattentiontothestudyofmetalsinthemarineaerosolparticulatesisincreasingduetotheirenvironmentalecologicaleffectsandcontributiontothebiogeochemicalcycle.Intheaspectofenvironmentalecologicaleffects,first,onthesideofclimate,aerosolswithmetalscanactascloudcondensationoricenuclei,absorbandscattersolarradiation,andaffecttheradiationbudgetontheearth.Therelativelyhighironcontent(5%)ofthedustcanabsorbtheshortwavelengthradiationefficiently.Second,onthesideofecologicaleffects,di~lvedAlse… 相似文献
213.
I~IOWDuceetal.(1980)calculatedthattheair-seaexchangeprocesscouldsupply80%--90%ofthediforedironinputtothephotcrzoneoftheSargassoAsfromairand16%--76%tothecentralNorthPacific.CuisessentialtotheTnarineorganisms,butexcessiveCuistoxictOtheOrganisms.CdandPh... 相似文献
214.
Absolute chronologies in paleoceanographic records are often constructed using the 14C dating of coarse fraction foraminifera (>150 μm). However, due to processes such as changes in sediment sources or abundances, sedimentation rates, bioturbation, reworking, the adsorption of modern carbon, etc., several studies conducted in different environmental settings have shown time-lags between records obtained from various granulometric fractions. In this study, we examined temporal phasing between the coarse foraminifera and fine fractions by studying changes in the abundances of δ18O, the 14C ages of the planktonic foraminifera Globigerinoides ruber (G. ruber, 250–350 μm), and the sediment fine fraction (<63 μm) over the last 45 ka in a core obtained from the northern Caribbean Sea. All of the records were found to be in phase during part of the Holocene (at least for the last ≈6 ka). As determined from δ18O records and 14C ages, the fine fraction was younger than G. ruber during the Last Deglaciation (of 1.89 ka). The coupling between bioturbation and changes in the fine fraction, and G. ruber abundances, as tested using a numerical model of the bioturbation record within a mixed-layer depth of 8 cm, was sufficient to explain the results. 14C age discrepancies increased from 5.64 to 8.5 ka during Marine Isotopic Stages (MIS) 2 and 3, respectively. These chronological discrepancies could not be explained by only one process and seemed to result from the interplay between mechanisms: size-differentiated bioturbation (for 1.5 to 2.5 ka), the adsorption of modern atmospheric CO2 (for 3.04 to 5.92 ka), and variations in sedimentological processes that influenced the fine carbonate fraction. However, even if variations in the mineralogical composition of the fine carbonate fraction were identified using scanning-electron microscopy observations, X-ray diffraction measurements, and geochemical analyses (the mol % MgCO3 of magnesian calcite and the Sr/Ca ratio of the bulk fine fraction), they can not account for the observed age differences. The results presented for core MD03-2628 extend beyond this case study because they illustrate the need for a detailed characterization of the various size fractions prior to paleoclimate signal interpretations, especially for chronological studies. 相似文献
215.
Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration 下载免费PDF全文
Emeline Perret Céline Berni Benoît Camenen Albert Herrero Kamal El Kadi Abderrezzak 《地球表面变化过程与地形》2018,43(7):1416-1430
A reliable estimation of sediment transport in gravel‐bed streams is important for various practical engineering and biological studies (e.g., channel stability design, bed degradation/aggradation, restoration of spawning habitat). In the present work, we report original laboratory experiments investigating the transport of gravel particles at low bed shear stresses. The laboratory tests were conducted under unsteady flow conditions inducing low bed shear stresses, with detailed monitoring of the bed topography using a laser scanner. Effects of bed surface arrangements were documented by testing loose and packed bed configurations. Effects of fine sediments were examined by testing beds with sand, artificial fine sand or cohesive silt infiltrated in the gravel matrix. Analysis of the experimental data revealed that the transport of gravel particles depends upon the bed arrangement, the bed material properties (e.g., size and shape, consolidation index, permeability) and the concentration of fine sediments within the surface layer of moving grains. This concentration is directly related to the distribution of fine particles within the gravel matrix (i.e., bottom‐up infiltration or bridging) and their transport mode (i.e., bedload or suspended load). Compared to loose beds, the mobility of gravel is reduced for packed beds and for beds clogged from the bottom up with cohesive fine sediments; in both cases, the bed shear stress for gravel entrainment increases by about 12%. On the other hand, the mobility of gravel increases significantly (bed shear stress for particle motion decreasing up to 40%) for beds clogged at the surface by non‐cohesive sand particles. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
216.
The focal mechanism solution on the seismic fault plane can reflect the geometric and kinematic characteristics of faults, and it is an important way to further study the fine structure of fault plane. From the focal mechanism solution of the earthquakes around the Dujiangyan fault in Longmenshan fault zone, we derived the average dip angle of Dujiangyan fault is 45.1° based on the seismic moment tensor theory. In order to refine the fault geometry structure, this paper decomposed it into multiple sub-fault planes along the length and width of the fault plane and forms a number of models A13, B13, A23 a, A23 b, A23 c, B23 a,B23 b and B23 c, then calculated the sub-fault's dip of each model. In order to clarify exactly which one of the fault models is closest to the real fault model, the fault slip was carried out for each model in turn, then compared the surface displacement of each model with GPS observations. The results show that B23 c model with high dip in shallow and small dip in deep is the best model, the lengths of each subfault of Dujiangyan fault from south to north are 33 km, 21 km and 46 km, respectively. When the depth of the fault bottom is about 11 km, the dip angles are 70.56°, 67.41° and 45.55°.When the depth of the fault bottom is about 30 km, The fault dip angles are 44.55°, 29.18° and 44.25°. 相似文献
217.
吴昌 《测绘与空间地理信息》2022,(2):130-131,134
对比分析目前常用的几种实景三维建模方法及适用性,剖析倾斜摄影三维建模技术在几何结构和模型纹理等方面存在的问题,提出了实景三维精细建模的优化方法和技术路线,着重阐述了高低空航摄相结合的关键技术,明显改善了模型效果,提高了建模的质量与效率,为实景三维数字城市建设提供了技术参考. 相似文献
218.
王楠 《沙漠与绿洲气象(新疆气象)》2020,14(2):81-89
利用2015—2018年乌鲁木齐机场航空例行天气报告(METAR报)、ECMWF(European Centre for Medium-Range Weather Forecasting)细网格数值预报产品对影响能见度的主要因子进行分析,提取与低能见度相关性高的物理量作为预报因子,采用SVM方法,分别基于Poly、RBF核函数建立乌鲁木齐机场未来21 h能见度预报模型。结果表明:(1)基于预报因子区间分类的SVM模型物理意义明确,试验结果较好;以RBF为函数建立的SVM模型(SVM-RBF)预报能力更好,其训练样本预测的TS评分0.84,准确率89.20%。(2)SVM-RBF模型的检验样本中,预报准确样本的预报误差整体偏小;在漏报样本中则有能见度越低、预报误差越大的特点,模型的振荡性明显。(3)结合NCEP/NCAR再分析资料研究SVM-RBF模型对天气过程的预报表现,发现模型对于特定天气形势下引发的低能见度天气,预报误差较小且预报提前量较大。 相似文献
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金的地球化学勘查基于金的准确测定,地球化学样品中金含量通常处于ng/g水平,需先进行分离富集,再采用电感耦合等离子体质谱法(ICP-MS)或石墨炉原子吸收光谱法(GFAAS)进行测定。当前,隐伏矿床勘查是地球化学探测技术的发展前沿,金活动态提取技术是寻找隐伏金矿的有效手段之一。相比于全量分析,金的活动态含量更低,需要解决选择性提取、高效预富集与准确测定等一系列难题。本文采用柠檬酸铵与土壤中黏土矿物及次生矿物作用促使吸附和可交换组分的金进入提取液,以硫脲和硫代硫酸钠络合金使活动态金向提取液中扩散,达到选择性提取的目的,建立了提取液中金的预富集及ICP-MS测定方法。实验确定的分析条件为:采用5g/L柠檬酸铵-2g/L硫脲-5g/L硫代硫酸钠为提取剂,提取时间24h,在酸性硫脲介质下用活性炭富集金,金吸附率可达89.6%~109.2%,灰化解吸温度为650~700℃。本方法检出限为0.05ng/g,相对标准偏差(RSD)为9.4%~10.2%,加标回收率为91.2%~93.4%。与已报道的硫酸铁-硫脲-硫代硫酸钠溶液提取再GFAAS测定的方法相比,本方法具有检出限低、测试线性范围宽、测试速度快的优势;应用于森林覆盖区黑龙江东安金矿区地球化学探测试验,金活动态异常与隐伏金矿位置一致。 相似文献