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251.
In order to evaluate the influence of the measuring technique on the determination of (micro‐)aggregation in soil and sediment samples, results of grain size distributions of undispersed silty soil samples obtained by the sieve‐pipette method are compared with those obtained using a laser diffraction grain size analyser, the Coulter LS‐100. Reduced major axis relationships are calculated which may be used to convert Coulter LS‐100 results to those obtained by the sieve‐pipette method. The relationships obtained are very similar to the reduced major axis relationships established for dispersed silty soil samples. The results also show that the Coulter LS measurements have a systematic bias compared to the sieve‐pipette data. This implies that, if the percentage of (micro‐)aggregation is determined, the (interpretation of the) results will be strongly dependent on the measurement technique used. Using the calibration relationships that were established, nomographs can be developed to predict the level of sieve‐pipette (micro‐) aggregation from Coulter LS‐100 data. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
252.
筑坝堆石料由于尺寸较大,必须对其按一定比例缩尺后才能用来开展室内三轴试验。但缩尺前后颗粒形状难免会有差异,如何评价颗粒形状变化对堆石料变形特性的影响是十分重要的。引入了高精度的三维激光扫描技术对紫坪铺面板坝筑坝堆石料2.5~5、5~10、10~20 mm以及20~40 mm 4个粒径组的颗粒进行了空间形状分析,在此基础上进一步开展了单一粒组的三轴试验,研究了4个粒组的颗粒形状指标与颗粒破碎率的相关性。试验表明,紫坪铺堆石料颗粒破碎率随着其平均球度的增加而减小,并且呈近似半对数线性关系;随着围压的增加,颗粒形状对颗粒破碎的影响逐渐减弱,颗粒强度的影响逐渐增大。紫坪铺堆石料的颗粒强度随着颗粒尺寸的增加逐渐减小,但其破碎率反而随着颗粒尺寸的增加而逐渐减小,主要是因为试验所采用的紫坪铺堆石料颗粒尺寸越小时,其形状越不规则。因此,研究缩尺效应对颗粒破碎率的影响时,要同时考虑颗粒尺寸和颗粒形状。 相似文献
253.
Malorie Dierick Éric Pili Nelly Assayag Pierre Agrinier 《Geostandards and Geoanalytical Research》2017,41(3):397-409
A new method for accurate determination of oxygen isotopes in uranium oxides encountered in the nuclear fuel cycle was developed using the conventional BrF5 fluorination technique. Laser‐assisted fluorination was tested for comparison. We focused on fine powders of triuranium octoxide (U3O8), uranium dioxide (UO2±x with 0 ≤ x ≤ 0.25), uranium trioxide (UO3.nH2O, with 0.8 ≤ n ≤ 2) and diuranates (M2U2O7.nH2O, with M = NH4, Na or Mg0.5 and 0 ≤ n ≤ 6). Fluorination at room temperature and heating under vacuum at 150 °C are shown to eliminate both adsorbed and structural water from the powder samples. Precision fit for purpose of δ18O values (± 0.3‰, 1s) and oxygen yields (close to 100%) were obtained for U3O8 and UO2 where oxygen is only bound to uranium. A lower precision was observed for UO3.nH2O and M2U2O7.nH2O where oxygen is both present in the structural H2O and bonded to uranium and where the extracted O2(g) can be contaminated by NF3 and NOx compounds. Laser‐assisted fluorination gave shifted δ18O values between +0.8 and +1.4‰ for U3O8, around ?0.8‰ for UO3.nH2O and between ?3.9 and ?4.5‰ for M2U2O7.nH2O (± 0.3‰, 1s) compared with the conventional method. 相似文献
254.
利用NSIDC公布的ICESat运行期间的19个任务期的观测数据, 采用重复轨迹分析方法估计近年来南极冰盖高程的时空变化。结果表明,南极大陆冰盖整体上呈现消融趋势,基于不同的GIA模型和ICESat激光测高数据的南极大陆冰盖高程变化的趋势约为 -1.17~-1 cm/a。 相似文献
255.
Ultra‐rapid topographic surveying for complex environments: the hand‐held mobile laser scanner (HMLS)
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Terrestrial laser scanning is the current technique of choice for acquiring high resolution topographic data at the site scale (i.e. over tens to hundreds of metres), for accurate volume measurements or process modelling. However, in regions of complex topography with multiple local horizons, restricted lines of sight significantly hinder use of such tripod‐based instruments by requiring multiple setups to achieve full coverage of the area. We demonstrate a novel hand‐held mobile laser scanning technique that offers particular promise for site‐scale topographic surveys of complex environments. To carry out a survey, the hand‐held mobile laser scanner (HMLS) is walked across a site, mapping around the surveyor continuously en route. We assess the accuracy of HMLS data by comparing survey results from an eroding coastal cliff site with those acquired by a state‐of‐the‐art terrestrial laser scanner (TLS) and also with the results of a photo‐survey, processed by structure from motion and multi‐view stereo (SfM‐MVS) algorithms. HMLS data are shown to have a root mean square (RMS) difference to the benchmark TLS data of 20 mm, not dissimilar to that of the SfM‐MVS survey (18 mm). The efficiency of the HMLS system in complex terrain is demonstrated by acquiring topographic data covering ~780 m2 of salt‐marsh gullies, with a mean point spacing of 4.4 cm, in approximately six minutes. We estimate that HMLS surveying of gullies is approximately 40 times faster than using a TLS and six times faster than using SfM‐MVS. © 2013 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. 相似文献
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257.
一种激光收敛测量方法及其精度评估 总被引:1,自引:0,他引:1
结合传统收敛测量和全站仪测量两种测量方法的优势,提出了一种新的收敛测量方法。传统收敛测量方法存在着操作要求高,施工干扰多,不易长期监测等缺点;全站仪测量方法由于采用间接测量策略,测点间的距离需要进行解算,施测精度较低。新方法延用了全站仪测量方法所采用的激光测距技术,同时也延用了传统收敛测量方法采用的直接测量距离策略。借助于目前市场上成熟的激光测距产品,研制和加工了新方法所需的测量装置。它由5个部分组成,依次为激光测距仪、测距仪底座、测量基点连杆、连接套筒、测量基座。按照一定的实施步骤,在程潮铁矿采空区的地面隧道进行了测量精度在现场工程环境下的试验评估。试验结果表明,新方法的成本低廉、操作简捷、稳定性好,施测精度可达到0.7 mm,有利于收敛监测在地下工程建设过程中的普及应用。 相似文献
258.
激光加工技术在珠宝首饰业中的应用越来越广泛。介绍了该技术的基本特点以及其在珠宝首饰业中的典型应用现状。这些技术涉及激光焊接、激光快速原型技术、激光打标、激光雕刻和激光切磨钻石等领域。激光焊接比传统的焊接技术具有显著的优点;快速原型技术的引入大大缩短了从首饰图样到制出原版的时间;激光打标和激光雕刻的使用丰富了首饰表面处理的手段,可进一步满足首饰个性化需求;激光切磨钻石原石可达到最小的损耗。激光加工技术在珠宝首饰业中发挥着越来越重要的作用。 相似文献
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