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61.
Extracting water from soils is often a critical step for obtaining soil water isotope information. Cryogenic vacuum extraction (CVE), the most widely used laboratory-based removal technique, produces biased isotope composition and the mechanisms causing the biases remain uncertain. Here, we conducted spiking tests on soil samples oven-dried at 105 and 205°C, respectively. The recovery rate and isotopic composition of the extracted water were analysed. Our results show that conventional oven-drying (105°C) was not sufficient to liberate tightly bound water from soils but oven-drying at temperatures above 205°C was. Part of the tightly bound water in soil was extracted by CVE, because the extraction capacity of CVE (heating at 95°C) was equivalent to oven-drying at temperature between 105 and 205°C. Moreover, the two pretreatments yielded markedly differences in water recovery rates. And with increasing ratios of clay contents to water contents, the recovery rates of the pretreated soil at 105°C trended upward above 100%, but that of 205°C trended downward below 100%. Further, the 2H and 18O signatures of the extracted water from the soil pretreated at 205°C were both depleted relative to reference water, but the pretreatment at 105°C showed enriched 18O and depleted 2H. This suggests that oxygen isotope exchange may have occurred between tightly bound water and soil minerals, resulting in enriched 18O in water for the 105°C pretreatments. For the 205°C pretreatment, pre-existing soil water was completely removed and relative to spiking water, isotopic signatures of the extracted water followed equilibrium fractionation law due to incomplete extraction. Therefore, our results suggested that the biased isotopic signatures of water extracted by CVE may be partially due to incomplete extraction and mixture of added water with the residual tightly bound water that pre-exists before spiking. 相似文献
62.
位于陆地与海洋交界的海岸系统,对环境变化反应敏感,海岸沉积是记录区域及全球环境变化的重要载体。但海岸沉积动力环境复杂,多存在沉积物的侵蚀、搬运与再沉积现象,或缺乏14C测年所需的有机质材料,因此年代问题是海岸第四纪地层研究的难点。光释光测年技术(OSL)主要通过石英或长石矿物的释光信号,确定沉积物的埋藏年龄,测年范围从近百年到几十万年。OSL的快速发展为海岸第四纪地层年代确定提供了有利条件,特别是单片再生剂量法的提出,提高了光释光测年结果的准确度和精度。OSL测年需要根据样品的年龄与性质,进行测年矿物、测量程序条件及粒级的选择。文章基于近年来石英和长石光释光测年技术的发展,结合我国海岸第四纪地层断代中已发表的500多个光释光年代数据,探讨光释光测年技术在海岸第四纪沉积物定年中遇到的常见问题及应对策略,包括测年矿物的选择(石英vs.长石)、样品的晒退、剂量率、石英信号的组分、长石包裹体等。对这些问题的认识有助于对光释光测年结果准确度的评估,可以更好地服务于海岸晚第四纪沉积研究。
相似文献63.
????????GNSS_LEO_KPP????????????????????????????GRACE_A??GRACE_B????DOY220/2011??DOY226 /2011??7???????????????JPL?o????????б?????????????????????10??20 cm???о??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? 相似文献
64.
首先,分析了混合星座的特点,并分别讨论了GEO卫星、IGSO卫星和Walker-δ星座的服务性能和星间链路的建立特点;然后,运用邻接矩阵给出混合星座连通性的判断标准,运用任意两颗卫星间相连途径的数目、割点、割边、k-连通度和k-边连通度给出星间链路稳健性的判断标准,并给出了星座达到k-连通所需要的最少星间链路的数目及其构建方式;最后,对模拟的3GEO+3IGSO+24MEO星座构型中各卫星之间的星间链路建立准则、连通性和稳健性进行了分析。 相似文献
65.
基于粗糙集理论的船舶"三漏"故障诊断 总被引:1,自引:0,他引:1
故障诊断是与有效决策密切相关的复杂问题。粗糙集理论可以有效地分析、处理不完备信息。应用粗糙集理论挖掘工具,对故障信息系统“约简”,在故障诊断系统中提取最小诊断条件集,可为设备维护人员提供快捷、有效的诊断依据。对“三漏”问题中机械装配不当故障诊断作了实例分析。 相似文献
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68.
Qun Wang Liqiang Tong Zhaocheng Guo Guang Liu 《International Journal of Digital Earth》2019,12(6):614-624
COSMO-SkyMed is a constellation of four X-band high-resolution radar satellites with a minimum revisit period of 12 hours. These satellites can obtain ascending and descending synthetic aperture radar (SAR) images with very similar periods for use in the three-dimensional (3D) inversion of glacier velocities. In this paper, based on ascending and descending COSMO-SkyMed data acquired at nearly the same time, the surface velocity of the Yiga Glacier, located in the Jiali County, Tibet, China, is estimated in four directions using an offset tracking technique during the periods of 16 January to 3 February 2017 and 1 February to 19 February 2017. Through the geometrical relationships between the measurements and the SAR images, the least square method is used to retrieve the 3D components of the glacier surface velocity in the eastward, northward and upward directions. The results show that applying the offset tracking technique to COSMO-SkyMed images can be used to derive the true 3D velocity of a glacier’s surface. During the two periods, the Yiga Glacier had a stable velocity, and the maximum surface velocity, 2.4?m/d, was observed in the middle portion of the glacier, which corresponds to the location of the steepest slope. 相似文献
69.
研究了无越流补给承压含水层不完整井非稳定流单井排放诱发地壳形变的解析表达,讨论了表达式的计算方案,以20个结点的Hermite求积公式编制了相应的数值积分计算程序,并给出了模拟计算算例,表明了计算方案的可行性。 相似文献
70.
LEO星座参数对GPS掩星数量和时空分布影响的模拟研究 总被引:3,自引:0,他引:3
利用低地球轨道LEO(Low Earth Orbit)卫星上的星载接收机对GPS卫星进行掩星观测反演地球的大气性质,对于气象学和大气研究具有重要意义.与单颗LEO卫星相比,由多个卫星组成的LEO星座观测到的掩星事件在时空分辨率和数量上都有很大的提高.考虑特定的区域,采用数值模拟方法,对不同卫星数和不同星座参数k的玫瑰型星座在一天内所观测的掩星事件的数量和分布进行比较分析,得到相应结论.研究成果对实际发射LEO星座时相关参数的选取具有参考价值. 相似文献