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81.
地磁场相对强度研究方法 总被引:1,自引:0,他引:1
主要介绍了地磁场相对强度研究的两种方法:常规归一化方法和假-Thellier方法的基本原理和做法,探讨了前者选择不同归一化参数的一般原则,并对比了两种方法的差异,指出地磁场相对强度研究方法在目前海洋沉积物定年研究中的应用方向和前景。 相似文献
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铌钽精矿标准物质在监控选冶样品分析的过程起到重要作用,在选厂及冶金系统有很大的需求,国内外的文献检索均未发现铌钽精矿标准物质的报道;而铌钽矿物的性质决定了铌钽精矿的粉碎粒度及均匀性对铌钽精矿标准物质的研制提出了更高的要求。本文阐述了4个铌钽精矿标准物质的研制过程,铌钽精矿采集于宜春及尼日利亚铌钽选厂,样品经气流粉碎和高铝球磨两次细碎及机械混匀后,随机抽取包装好的样品进行均匀性和稳定性检验及定值。采用电感耦合等离子体发射光谱法与质谱法(ICP-OES/MS)进行均匀性和稳定性检验,结果表明样品的均匀性和稳定性良好。采用多个实验室协同测试的定值方式,利用不同原理的分析方法对此样品的铌钽等12个元素进行定值,给出了各定值元素的认定值和不确定度。4个铌钽精矿标准物质Ta(Nb)_2O_5的含量为9. 89%、20. 55%、40. 79%、53. 69%,形成一个从粗精矿到精矿较为完整的含量体系,可以满足选冶试验各阶段流程样品分析对标准物质的需求。 相似文献
84.
Andrew T. Fullhart Thijs J. Kelleners Dave G. Chandler James P. McNamara Mark S. Seyfried 《水文研究》2019,33(17):2323-2336
Integrated watershed models can be used to calculate streamflow generation in snow‐dominated mountainous catchments. Parameterization of water flow is often complicated by the lack of information on subsurface hydraulic properties. In this study, bulk density optimization was used to determine hydraulic parameters for the upper and lower regolith in the GEOtop model. The methodology was tested in two small catchments in the Dry Creek Watershed in Idaho and the Libby Creek Watershed in Wyoming. Modelling efficiencies for profile‐average soil–water content for the two catchments were between 0.52 and 0.64. Modelling efficiencies for stream discharge (cumulative stream discharge) were 0.45 (0.91) and 0.54 (0.94) for the Idaho and Wyoming catchments, respectively. The calculated hydraulic properties suggest that lateral flow across the upper–lower regolith interface is an important driver of streamflow in both the Idaho and Wyoming watersheds. The overall calibration procedure is computationally efficient because only two bulk density values are optimized. The two‐parameter calibration procedure was complicated by uncertainty in hydraulic conductivity anisotropy. Different upper regolith hydraulic conductivity anisotropy factors had to be tested in order to describe streamflow in both catchments. 相似文献
85.
Seasonal transition of hydrological processes in a slow‐moving landslide in a snowy region
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Hikaru Osawa Yuki Matsushi Sumio Matsuura Takashi Okamoto Tatsuya Shibasaki Hiroyuki Hirashima 《水文研究》2018,32(17):2695-2707
A comprehensive understanding of seasonal hydrological dynamics is required to describe the influence of pore‐water pressure on the stability of landslides in snowy regions. This study reports on the results of continuous meteorological and hydrological observations over 2 years on a landslide body comprising Neogene sedimentary rocks in northern Japan, where a thick (3–5 m) seasonal snowpack covers the land surface. Monitoring of the volumetric water content in shallow unsaturated zones (<0.8 m depth) and pore‐water pressure in saturated bedrock at depths of 2.0 and 5.2 m revealed clear seasonality in hydrological responses to rainfall and meltwater supply. During snow‐free periods, both the shallow soil moisture and deep pore‐water pressure responded rapidly to intense rainwater infiltration. In contrast, during snowmelt, the deep pore pressure fluctuated in accordance with the daily cycle of meltwater input, without notable changes in shallow moisture conditions. During occasional foehn events that cause intense snow melting in midwinter, meltwater flows preferentially through the layered snowpack, converging to produce a localized water supply at the ground surface. This episodically triggers a significant rise in pore‐water pressure. The seasonal differences in hydrological responses were characterized by a set of newly proposed indices for the magnitude and quickness of increases in the pressure head near the sliding surface. Under snow‐covered conditions, the magnitude of the pressure increase tends to be suppressed, probably owing to a reduction in infiltration caused by a seasonal decrease in the permeability of surface soils, and effective pore‐water drainage through the highly conductive colluvial layer. Deep groundwater flow within bedrock remained in a steady upwelling state, enhanced by increasing moisture in shallow soils under snow cover, reflecting the convergence of subsurface water from surrounding hillslopes. 相似文献
86.
The current research deals with the dispersion of fine settling particles in a fluid flowing through an icecovered channel under the laminar flow condition. An analytical solution of the two-dimensional convection-diffusion equation, based on the multi-scale homogenization technique, is obtained. To validate the current study, analytical results for the dispersion coefficient are compared with the available earlier research work. Moreover, the proposed analytical solutions for mean concentration... 相似文献
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Water temperatures in mountain streams are likely to rise under future climate change, with negative impacts on ecosystems and water quality. However, it is difficult to predict which streams are most vulnerable due to sparse historical records of mountain stream temperatures as well as complex interactions between snowpack, groundwater, streamflow and water temperature. Minimum flow volumes are a potentially useful proxy for stream temperature, since daily streamflow records are much more common. We confirmed that there is a strong inverse relationship between annual low flows and peak water temperature using observed data from unimpaired streams throughout the montane regions of the United States' west coast. We then used linear models to explore the relationships between snowpack, potential evapotranspiration and other climate-related variables with annual low flow volumes and peak water temperatures. We also incorporated previous years' flow volumes into these models to account for groundwater carryover from year to year. We found that annual peak snowpack water storage is a strong predictor of summer low flows in the more arid watersheds studied. This relationship is mediated by atmospheric water demand and carryover subsurface water storage from previous years, such that multi-year droughts with high evapotranspiration lead to especially low flow volumes. We conclude that watershed management to help retain snow and increase baseflows may help counteract some of the streamflow temperature rises expected from a warming climate, especially in arid watersheds. 相似文献
89.
砂雨法是开展砂质土层和构筑物离心试验应用广泛的模型制备技术,以密实程度与均匀性为关键控制对象,直接关系试验结果的准确性和可靠性。针对砂雨装置、控制要素和均匀度测试等几个方面,概况总结了国内外离心模型砂雨法制备技术的研究进展与暴露的关键问题,归纳了现有砂雨装置的基本组成、操控特点和分类方法,阐述了稳态密实度范围及影响关键因素。综述模型空间均匀度的不同量测与评价方法,评述了各自优缺点与归一化评价标准。综合现状与不足,讨论了离心模型砂雨法制备技术的发展方向与趋势。 相似文献
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