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21.
Some deep-marine channels show striking similarities to fluvial channels, despite major differences in the properties of the flows that they conduct. Some field observations from deep-marine channel deposits within a Late Cretaceous palaeo-canyon in the Rosario Formation of Baja California, Mexico, that bear on these comparisons have been reported. These channel deposits contain erosively based lateral accretion sets. These sets are generally a few metres thick and resemble fluvial point bar deposits. Sediment movement and deposition within these accretion deposits was induced by turbidity currents several to many times thicker than the depth of the channel, moving at several metres per second. The inclined sets define laterally migrating and sinuous channels locally at a high angle to the confining canyon. The instantaneous channel widths varied from 6 to 39 m, the depths from 2·5 to 4 m and the sinuosities from 1·3 to 3·1. Palaeocurrent data, taken mostly from clast imbrication in conglomerates, indicates current modes along the channel thalweg, but with other directions representing either secondary flow (oriented primarily up the point bar) or over-passing canyon-confined flow. It is suggested that, at times, the lower part of the turbidity currents flowing down the channels behaved similarly to within-bank fluvial currents, with a cross-channel component of flow towards the cut bank, and return flow at the bed sweeping up the point bar. At other times, this secondary circulation may be absent or reversed, which may be related to changes in flow thickness, coupling with the overriding flow and possible flow separation. 相似文献
22.
肺内小结节三维重建的表现及临床意义 总被引：2，自引：1，他引：1
目的：探讨肺部结节三维重建的应用价值。材料与方法：常规扫描采用螺旋扫描“10mm/10mm/10mm”（即层厚/每螺旋-圈床进距离/重建间隔,Fov300-360mm,标准算法。53例肺内小结节和100例健康体检（包括平扫无阳性发现者）作三维重建（质量透视法-Volume Rendering),取-720HU为重建域下限。结果：阳性者53例中,单个结节47例（左肺21例,右肺26例）,结节直径（0.5cm-3.0cm),比常规扫描更能检出结节边缘凹凸不平及肿瘤供血血管。2个结节2例均为良性（一例手术病理证实为结核,1例抗炎治疗后吸收痊愈）。双肺多发性结节4例（3例为转移瘤,一例为结核）。常规扫描无阳性发现者100例做三维重建,其中92例作健康体检者检出一个结节（0.5cm);8例有癌性病史患者（食道癌6例,肺癌2例）,检出两例有结节。结论：胸部螺旋CT三维重建能提高病变检出率及肿块周边的特征改变,从而有助于肺部结节的诊断可靠性,值得临床推广应用。 相似文献
23.
This paper presents analytical models to predict the pullout capacity and the load–displacement relationship for shallow single
vertical helical and plate anchors in sand. The models were developed based on the failure mechanism deduced from laboratory
testing and utilize the limit equilibrium technique. Expression was given to estimate the critical depth for a given anchor/soil
conditions, which separates deep from shallow anchors. Furthermore, the radius of influence of a individual anchor on the
ground surface is established, and accordingly, the spacing between anchors can be determined to avoid anchors interactions
between anchors. The proposed theory compared well with the theories and the experimental data available in the literature.
相似文献
Résumé Cet article présente un model analytique pour prédire la résistance à l’arrachement et la relation charge-diplacement pour les ancrages à vis et plats verticaux superficiels ancrés dans le sable. Le model est basé sur le mécanisme de rupture déduit des essais de laboratoire et utilise la méthode d’analyse à l’équilibre limite. En outre, une expression a été proposé pour éstimer la profondeur critique pour un ancrage donné permettant d’identifier l’ancrage comme superficiel ou profond. Le rayon d’influence d’un ancrage à la surface du sable autour de l’ancrage a été établi, et par conséquent, l’espacement entre ancrages peut être déterminer pour éviter toute interaction. La théorie proposée montre une bonne concordance avec des résultats theoriques et expérimentaux rapports dans la literature.
相似文献
24.
YIN Leiming BIAN Lizeng & YUAN Xunlai . Nanjing Institute of Geology Palaeontology Chinese Academy of Sciences Nanjing China . Department of Earth Sciences Nanjing University Nanjing China 《中国科学D辑(英文版)》2004,47(10):880-885
~~Discovery of branched tubular algae and microscopic tubes with annular-helical thickening from the Mesoproterozoic Ruyang Group of Shanxi, North China~~ 相似文献
25.
因具备高速、灵活和高精度的特点,移动式激光扫描被广泛用于地铁隧道的监测系统中。针对现有数据处理方法的里程配准误差大、数据利用率低的问题,本文提出了从扫描到后处理的一体化数据转换方法。在预扫描阶段,对隧道进行预标定,根据速度曲线的概率密度确定噪声界限;在正式扫描阶段,标定小车匀速运动的开始计速点,仅在惯导速度超限的情况下更新里程;在后处理阶段,首次基于激光点云数据生成360°全景图用于病害监测,提高了用户交互性。试验结果表明,本文方法在50 m内的测量误差小于1.2 mm,优于已有的螺旋扫描方法。因此,本文方法更适用于传感器精度低,测量频率高,且监测隧道较长的移动式激光扫描系统。同时,生成的全景图为隧道病害监测提供新的发展方向。 相似文献
26.
在印尼塔里阿布铁矿项目岩心钻探施工中,其地层既具有泥岩、页岩、粘土岩的遇水膨胀、坍塌,又有凝灰岩、火山灰岩的遇水溶解及硅化石英岩的“打滑”,以及粉状铁矿取心难的特点。易出现卡钻、粘钻等孔内事故。通过大胆的探索,形成了针对该地区岩心钻探施工的一套施工工艺,取得了良好的钻探技术效果。详细介绍了印尼塔里阿布岛铁矿项目岩心钻探施工技术。 相似文献
27.
The Conservation of Helicity in Hurricane Andrew （1992） and the Formation of the Spiral Rainband 总被引：5，自引：0，他引：5
The characteristics of helicity in a hurricane are presented by calculating the MM5 model output in addition to theoretical analysis. It is found that helicity in a hurricane mainly depends on its horizontal component, whose magnitude is about 100 to 1000 times larger than its vertical component. It is also found that helicity is approximately conserved in the hurricane. Since the fluid has the intention to adjust the wind shear to satisfy the conservation of helicity, the horizontal vorticity is even larger than the vertical vorticity, and the three-dimensional vortices slant to the horizontal plane except in the inner eye. There are significant horizontal vortices and inhomogeneous helical flows in the hurricane. The formation of the spiral rainband is discussed by using the law of horizontal helical flows. It is closely related to the horizontal strong vortices and inhomogeneous helical flows. 相似文献
28.
直接测量岩石表面降低的高度是测算当前地表侵蚀速率的有效方法。本文介绍了一种便携式高精度游标螺旋测微装置的组成和原理。在原装置的基础上,增加了"T"型杆和底托套,并利用改造后的装置在唐山地区进行了野外实测试验。本次共测量98个测点,每个测点测量5-15次,获得1005条数据。其中极差小于0.1mm的点共74个,占所有点的75.5%;平均偏差小于0.1mm的点共87个,占所有点的88.8%,标准偏差小于0.1mm的点共86个,占所有点的87.8%,表明该设备在0.1mm数量级精密度良好。通过研究发现,在侵蚀速率较高的地区,利用高精度游标式螺旋测微装置直接在野外测量岩石侵蚀速率具有一定的可行性,并且可以通过改进装置或增加测量点的方法进一步提高测量准确度。 相似文献
29.
320排动态容积CT脑血管数字减影（DSA）可为颅内动脉瘤病人提供4DDSA成像信息,这一技术的关键是宽体检测器和ConeXact锥束重建算法。本文对目前常见锥束扫描重建算法进行了分析和比较,特别是近几年发展起来的Feldkamp类,Grangeant类,Katsevich类和ConeXact锥束重建算法。应用方面对30例颅内动脉瘤患者进行了宽探测器平台下动态容积扫描,一次成像获得满意图像,无阶梯伪影,并与计算机断层血管造影（CTA）、常规DSA对比,320排CTDSA检查可作为颅内动脉瘤筛选和术后复查一种方法,与CTA相比320排CT动态容积成像和功能成像有明显的优势。 相似文献
30.
Giovanni Spagnoli 《Marine Georesources & Geotechnology》2017,35(4):578-585
Helical piles present a possible alternative to driven displacement piles in the offshore sector. While this type of pile is used widely in the onshore environment, design methods tend to be highly empirical and there is considerable uncertainty around the bearing resistance and the installation resistance required to install large diameter piles necessary to resist uplift. The paper combines a theoretical model for estimating torque resistance from the literature with a cone penetration test (CPT)-based model originally developed to estimate the axial resistance of helical piles and to predict the installation torque required to install piles in sand. The model appears to be able to capture the general installation behavior of piles across a range of scales and in various sand states. 相似文献