Distribution of the Permian Monodiexodina in Karakorum and Kunlun and its Geological Significance

The Permian fusulinoidean genus Monodiexodina is widely distributed in east Tethys. The genus might be an important indicator for the northern margin of Gondwana in northwestern China, but this is disputed. Monodiexodina-bearing areas can be restored as in either northern or southern middle latitudes with a symmetrical distribution between a high latitudinal, cool/cold water climatic realm and a paleotropical, warm water realm. Permian strata bearing Monodiexodina in Karakorum, Muztag Pear, and Buka Daban Pear of the east Kunlun Mountains can be correlated with each other. Faunal analyses and the stratigraphical position of Monodiexodina-bearing strata indicate that both Karakorum, east Kunlun, and the Pamirs were formed in a cool temperate sea area of the northern hemisphere in middle latitudes during the Permian, rather than at the Gondwana margin.     

自重湿陷性黄土场地桩的负摩阻力

通过对郑州-西安客运专线的关中某地钻孔灌注桩在预湿和后湿状态下的静载试验和同步进行的桩身应力测试,探讨了自重湿陷性黄土中桩侧负摩阻力的发生和发展过程,中性点位置的变化过程及桩侧阻力的发挥规律等,对自重湿陷性黄土中桩侧负摩阻力的理论研究及其工程应用具有重要的参考价值。     

井壁破裂与砼的徐变破坏

黄淮地区煤矿井壁破裂大都是由于厚松散覆盖层底部含水层失水固结,地层沉降,导致井壁外侧出现负摩阻力,从而在竖井轴向上形成附加的下拉荷载而引起。这些破裂始见于保护层砼的剥落,而后见壁中砼发育密集的竖直砂浆裂隙,砼中骨料因界面裂隙的发育而被剥离,砼向井内膨胀并呈现“假塑性”等。除这些特征外,从负摩阻力的出现及增荷过程来看,井壁破裂是在轴向高压应力长时间作用下的结果,它涉及的是井壁砼的长期强度,故井壁破裂属于砼徐变破坏。      

Evolution of a carbonate delta generated by gateway‐funnelling of episodic currents

Cool‐water carbonate sedimentation has dominated Mediterranean shelves since the Early Pliocene. Skeletal sand and gravel herein consist of remains of heterozoan organisms, which are susceptible to reworking due to weak early cementation in non‐tropical waters. This study documents the Lower Pleistocene carbonate wedge of Favignana Island (Italy), which prograded from a 5   km wide passage between two palaeo‐islands into a perpendicular, 10 to 15   km wide strait between the palaeo‐islands at one side and Sicily at the other during the Emilian highstand (1·6   Ma to 1·1   Ma). The clinoformed carbonate wedge, which is 50   m thick and 6   km long, formed by east/south‐east progradation of a platform on the submarine sill by currents that were funnelled between the two palaeo‐islands. Platform‐slope clinoforms evolved from initial aggradation (thin and low‐angle) into a progradation phase (thick and high‐angle). Both clinoform types are characterized by a bimodal facies stacking pattern defined by sedimentary structures created by: (i) subaqueous dunes associated with dilute subcritical currents; and (ii) upper‐flow‐regime bedforms associated with sediment‐laden supercritical turbidity currents. Focusing of episodic currents on the platform by funnelling between the islands controlled the downstream formation of a sediment body, here named carbonate delta. The carbonate delta interfingers with subaqueous dune deposits formed in the perpendicular strait. This study uses a reconstruction of bedform dynamics to unravel the evolution of this gateway‐related carbonate accumulation.     

堆载作用下桩体弹性模量对负摩阻力性状的影响

简要分析了桩体弹性模量对于桩体负摩阻力特性的影响机制。低弹性模量桩身压缩是桩顶位移的主要组成部分。在这种情况下桩身压缩对桩的荷载传递影响很大。在复合地基中常用的低刚度桩的桩-土相互作用分析中应当考虑桩身压缩的影响。有限元分析表明,影响桩体负摩阻力特性的桩体弹性模量存在一个临界值,当桩体弹性模量大于此值时,可以忽略桩体弹性模量对桩体负摩阻力性状的影响;桩体弹性模量小于此值时,桩身压缩变形增大,会造成中性点位置上移,桩身中最大附加应力降低。这些变化随着桩体弹性模量的降低而加剧     

偏振光皮肤镜图像分析技术在临床上开发应用的研究——在皮肤肿瘤诊断中的灵敏度与特异度探讨

目的：探讨偏振光皮肤镜（DP）图像分析技术在皮肤肿瘤诊断中的价值。方法：在临床肉眼诊断的基础上,采用DP法对皮肤肿瘤进行辅助诊断,后经组织病理确诊,将诊断结果进行对照与回顾性分析。结果：总结了948例皮肤肿瘤和与其相鉴别的色素性皮损的DP法诊断指征并显示出平均灵敏度88.77%,特异度94.92%,诊断符合率达92.72%,比临床肉眼诊断符合率提高了23.94%。结论：DP法是一种无创性观察体表和表皮下部肉眼无法识别的形态学特征与数字图像技术。它对多种皮肤肿瘤尤其对色素性皮肤肿瘤的判断和良恶性皮损的鉴别诊断具有较好的辅助诊断价值。对减少盲目活检、有效指导手术切除范围和选择合理的治疗方法及术后复诊具有重要意义。     

灌注桩侧摩阻力发挥模式的研究

桩侧摩阻力的发挥主要与桩周土的力学性质、侧向有效压力、桩土的相对位移量、桩土的接触性质、时间效应等有关。采用双曲线侧摩阻力发挥模型,通过分析上海某地区灌注桩的现场试验实测资料,提出了双曲线模型的计算参数取值范围。此外,对桩侧摩阻力的时间效应也作了初步探讨。结果表明：采用双曲线函数对灌注桩侧摩阻力与相对位移间的变化关系进行拟合是合理的;由于各级荷载下桩体沉降同样具有时间性,桩侧摩阻力同时具有明显的时间效应     

颗粒图像测速技术在桩基负摩阻力模型试验中的运用

在桩基负摩阻力的研究中桩土位移需重点关注。作为一种成熟的流场测试手段,颗粒图像测速(paticle image velocimetry, PIV)技术已逐步推广至岩土研究领域,将该技术运用至桩基负摩阻力模型试验,可以弥补传统位移测试方法无法获得位移场分布等缺点。基于试验特点,设计由钢板和有机玻璃壁组成的试验箱,采用千斤顶配合置于土表的载荷板实现对土体加载。试验中,对不同土表超载作用下的土体分层沉降、桩身沉降及轴力进行测定,采用PIV技术对桩端处砂土的位移场实施了采样分析。试验表明,PIV所测位移数值与传统方法测得值吻合较好,PIV分析结果能够直观反映桩基受负摩阻力作用而产生的附加沉降;并且可以判断桩端沉降的影响范围,深度方向基本不超过1.75D（D为直径）,水平方向则基本在桩底边界范围内。最后,总结了PIV技术在模型试验中的运用,提出了几点在今后试验中可待改进的地方。     

A self‐limiting bank erosion mechanism? inferring temporal variations in bank form and skin drag from high resolution topographic data

Fluvial bank erosion rates are often quantified by assuming that the erosion rate is a function of the excess (above a critical threshold) boundary shear stress applied by the flow. Research has shown that the form roughness induced by natural topographic bank features, such as slumps, spurs and embayments, is the dominant component of the spatially‐averaged total shear stress, meaning that form roughness provides an important control on bank erosion rates. However, measuring the relative components of the total shear stress for a natural system is not straightforward. In this work we use the method of Kean and Smith to partition the form and skin drag components of river bank roughness using a time series (2005–2011) of high‐resolution topographic surveys of an eroding bank of the Cecina River in central Italy. This method approximates the form drag component of the roughness along a longitudinal bank profile as a series of user‐defined Gaussian curves. The extracted metrics are used in conjunction with an estimate of the outer region flow velocity to partition the form and skin drag components of the total boundary shear stress according to the Kean and Smith analytical solution. The relative magnitude of the form and skin shear stress at each survey date is analysed alongside DEMs of difference to reveal that intense episodes of erosion are followed by periods of quiescence. We show that this is due to the protection offered by increased form drag roughness following erosion. We conceptualise the dynamic feedbacks that exist between river discharge, bank erosion processes and bank form roughness, into a simple model of the self‐limiting nature of river bank erosion. Copyright © 2015 John Wiley & Sons, Ltd.     

湿陷性黄土场地湿陷下限深度与桩基中性点位置关系研究

湿陷性黄土场地的湿陷下限深度与桩基中性点位置密切相关,为了解决桩基设计方案不当问题,如何准确判定湿陷下限深度显得十分重要。在系统分析并总结宁夏固原桩基系列浸水试验、兰州和平镇黄土浸水试验及其他地区桩基浸水试验研究成果的基础上,揭示了黄土湿陷下限深度与桩基中性点位置确定的相互关系,得出了以下研究成果：（1）指出了均质黄土现场浸水试验水的竖向渗透深度是有限的（一般为20～25 m）,现场黄土湿陷发生的下限深度也是有限的,不宜按室内试验的湿陷系数确定的下限深度来直接评判;（2）给出了室内湿陷性评价试验中湿陷系数 或自重湿陷系数 随地区和深度变化的取值建议,同时,建议在湿陷量计算时引入深度修正系数和地基土浸水机率系数,初步给出大厚度湿陷性黄土场地不同地区湿陷下限深度评价系数 ,可以有效减小湿陷性评价的室内外差异;（3）由室内试验计算确定的湿陷下限深度偏于保守,导致桩基设计过分夸大了负摩阻力的不利作用,造成桩基设计承载力偏低;（4）大厚度湿陷性黄土场地桩的中性点最深位置不宜大于20～25 m,湿陷性评价下限深度小于20 m的场地,宜按评价深度确定中性点位置;给出了桩侧负摩阻力估算方法,并建议桩基负摩阻力平均值取20～35 kPa为宜。