Predicting the initiation of static liquefaction of cross‐anisotropic sands under multiaxial stress conditions

Experimental evidence has shown that the liquefaction instability of sands can be affected by its material density, stress state, and inherent anisotropy. In order to predict the initiation of the static liquefaction of inherent cross‐anisotropic sands under multidimensional stress conditions, a rational constitutive model is needed. An elastoplasticity model able to capture the influences of intermediate principal stress ratio (b  = (σ ₂ ? σ ₃)/(σ ₁ ? σ ₃)) and loading direction on stress–strain relationships and volumetric properties was proposed. The yield function was formulated to be controlled by Lode angle, loading direction, and material state; the stress–dilatancy was a material state‐dependent function. After using the existing drained hollow cylinder tests to validate the proposed model, this model was used to simulate the existing undrained hollow cylinder tests. During this simulation, the second‐order work criterion was used to determine the initiation of static liquefaction. The results showed that an increase in both the intermediate principal stress ratio and the loading angle induces a decrease in the second‐order work. Static liquefaction is initiated more easily at a stress state with a large intermediate principal stress ratio and a large loading angle, and the mobilized friction angle at the instability points decreases with the intermediate principal stress ratio and the loading angle. Copyright © 2017 John Wiley & Sons, Ltd.     

SANISAND-FN: An evolving fabric-based sand model accounting for stress principal axes rotation

SANISAND is the name of a family of bounding surface plasticity constitutive models for sand within the framework of critical state theory, which have been able to realistically simulate the sand behavior under conventional monotonic and cyclic loading paths. In order to incorporate the important role of evolving fabric anisotropy, one such model was modified within the framework of the new anisotropic critical state theory and named SANISAND-F model. Yet the response under continuous stress principal axes rotation requires further modification to account for the effect of ensuing noncoaxiality on the dilatancy and plastic modulus. This modification is simpler than what is often proposed in the literature, since it does not incorporate an additional plastic loading mechanism and/or multiple dilatancy and plastic modulus expressions. The new model named SANISAND-FN is presented herein and is validated against published data for loading that includes drained stress principal axes rotation on Toyoura sand.     

Escaping the Territorially Trapped East Asian Developmental State Thesis

Using a multiscalar approach, there has been a recent increase in geographic critiques of the East Asian developmental state thesis (DST). These critiques argue that the existing DST literature is epistemologically caught in a territorial trap. There has been less concern, however, about the methodology related to this research. In this article, I suggest that scholars consider not only the epistemological perspective but also the methodological dimension to effectively exploit the less territorially trapped DST research. Based on these analyses, this article emphasizes that interdisciplinary research using a multiscalar methodology and epistemology is required to better explain economic development in East Asia.     

华南李家沱剖面寒武纪纽芬兰世海水氧化还原性质演化及其驱动因素

大气-海洋含氧量的演化对埃迪卡拉纪-寒武纪转折期的后生动物大爆发事件具有重要影响.为探讨寒武纪纽芬兰世中国南方海洋氧化还原性质的演化及其初级生产力、海水硫酸盐浓度等演化驱动因素, 分析了李家沱剖面纽芬兰世留茶坡组和小烟溪组微量元素、有机碳含量、有机碳同位素、总硫含量、黄铁矿硫同位素等.该剖面沉积于斜坡-盆地环境且出露齐全.该剖面上V/Sc、Th/U及Mo、U、V、Ni、Cu等元素的富集系数呈现出5个变化旋回, 其中留茶坡组中上部和小烟溪组中部各存在一氧化环境段, 其余层段处于缺氧环境, 而Re/Mo则显示仅在小烟溪组中部水体出现过短暂的氧化环境和含有游离H₂S的硫化环境, 其余层段处于没有游离H₂S的缺氧非硫化环境.Ba、Ni、Cu、Zn、Cd等微量元素的富集系数及TOC表明: 留茶坡组的有机质沉降量和埋藏量都明显小于上覆小烟溪组; 而在小烟溪组中, 其中部有机质的沉降量和埋藏量最低, 下部最高, 上部次之.TOC/TS、TS以及黄铁矿硫同位素的垂向演化趋势等都显示李家沱剖面纽芬兰世大都处于低海水硫酸盐浓度环境.低海水硫酸盐浓度是造成李家沱剖面纽芬兰世缺氧水体未富集游离H₂S的主要原因.大气含氧量的升高是导致李家沱剖面小烟溪组中部出现短暂氧化环境以及近硫化环境的主要原因.      

Tectonic Stress State Changes Before and After the Wenchuan Ms 8.0 Earthquake in the Eastern Margin of the Tibetan Plateau

Crustal tectonic activities are essentially the consequences of the accumulation and release of in situ stress. Therefore, studying the stress state near active faults is important for understanding crustal dynamics and earthquake occurrences. In this paper, using in situ stress measurement results obtained by hydraulic fracturing in the vicinity of the Longmenshan fault zone before and after the Wenchuan Ms 8.0 earthquake and finite element modeling, the variation of stress state before and after the Wenchuan Ms 8.0 earthquake is investigated. The results show that the shear stress, which is proportional to the difference between principal stresses, increases with depth and distance from the active fault in the calm period or after the earthquakes, and tends to approach to the regional stress level outside the zone influenced by the fault. This distribution appears to gradually reverse with time and the change of fault properties such as frictional strength. With an increase in friction coefficient, low stress areas are reduced and areas with increased stress accumulation are more obvious near the fault. In sections of the fault with high frictional strengths, in situ stress clearly increases in the fault. Stress accumulates more rapidly in the fault zone relative to the surrounding areas, eventually leading to a stress field that peaks at the fault zone. Such a reversal in the stress field between the fault zone and surrounding areas in the magnitude of the stress field is a potential indicator for the occurrence of strong earthquakes.     

岩石力学实验在地应力测试中的应用

介绍了应力解除法的基本原理、测试步骤及计算过程,采用实验室测得的弹性模量、泊松比及现场应力解除获得的三维膨胀变形数据,由线性虎克定律即可计算出应力解除前岩体中应力的大小和方向。以济宁煤田安居煤矿为例,获得3个测点的最大主应力、中间主应力及最小主应力的大小、方向、倾角,总结了安居煤矿井底车场附近的原岩应力分布规律。     

夏季南大洋南极大磷虾种群分布、结构及生长研究

利用2007/2008年和2008/2009年南极夏季高速采集器和IKMT网走航采样样品,结合同步环境调查资料,研究了南极大磷虾(Euphausia superba)的水平分布、生长状况及种群结构。结果表明,南极大磷虾在威德尔海域丰度高于普里兹湾海域,两个海域的磷虾丰度都低于历史同期。从两个年度南极考察的整个调查海区来看,南极大磷虾处于正常生长状态,但也存在个别生长状况较差站位,推测与海冰回退时间较晚或叶绿素浓度较低有关。利用高速采集器采集的大磷虾样品,在海冰边缘区域站位,未成体磷虾占有很大比例;而在海冰已经消退较长时间的海域,成体磷虾占比例较大,这反映了大磷虾未成体与成体不同的分布特征。南极大磷虾在不同海域种群结构存在一定的差异,对种群补充产生一定的影响。     

Population distribution,structure and growth condition of Antarctic krill （Euphausia superba Dana） during the austral summer in the Southern Ocean

Antarctic krill （Euphausia superba Dana） was collected using a High Speed Collector and an Isaac-Kidd midwater trawl （IKMT） net during the austral summer of 2007/2008 and 2008/2009 in the circumpolar and Prydz Bay regions of the Southern Ocean, respectively. Combined with the simultaneous recording of environmental factors, spatial distribution, population structure and growth condition of E. superba were studied. The abundance of E. superba in the Weddell Sea was higher than in Prydz Bay. However, the abundance of E. superba in both the Weddell Sea and Prydz Bay was lower than figures reported in previous krill surveys for the same time period. With respect to the total study area, E. superba displayed a normal growing state during the two expeditions. E. superba grew relatively poorly in some stations, which may be due to the late retreat of sea ice or lower chlorophyll a concentrations. The number of juvenile E. superba collected using the High Speed Collector was proportionally greater in stations located at the edge of the sea ice, while adults dominated in long-term non-ice regions. This phenomenon reflects the different distribution pattern between juvenile and adult krill. The population structure of E. superba differed between sea regions, which may affect recruitment.     

Monitoring stress levels on rice with heavy metal pollution from hyperspectral reflectance data using wavelet-fractal analysis

Remote sensing allows monitoring heavy metal pollution in crops for agricultural production and food security. This paper presents an approach to wavelet-fractal analysis for exploring a set of sensitive spectral parameters to monitor the heavy metal pollution levels in rice crops from hyperspectral reflectance data. Hyperspectral and biochemical data were collected from three study farms in Changchun, Jilin Province, China. Our study explored the fractal dimension of reflectance with wavelet transform (FDWT) that demonstrated a better performance than other existing methods. Our results obtained in this study show that the red edge position (REP) was the most sensitive indicator for monitoring the heavy metal pollution levels in rice crops among common indices. As compared with REP, the FDWT is more sensitive to biochemical composition, namely with respect to chlorophyll concentrations, N, Cu and Cd. The established linear models showed a correlation coefficient (R²) above 0.70, model efficiency (ME) above 0.65 and a root mean square error (RMSE) below 3.5. Minimum FDWT values occurred in rice with Level II pollution followed by Level I pollution, and finally the safe level. This study suggests that wavelet transform is well suited as a spectral analysis method to eliminate noise and amplify the stress information from heavy metals. The wavelet transform in conjunction with fractal analysis is promising for detecting heavy metal-induced stress in rice crops.     

CINRAD/CC雷达速调管运行状态控制

速调管性能直接影响到雷达探测的回波质量、运行成本和使用时间,目前使用和维护好速调管是雷达站提高业务质量和降低成本的主要环节之一.从云南6部CINRAD/CC雷达近年来的运行情况看,使用和维护好速调管是十分重要和必要的.以德宏、普洱的速调管使用维护为个例,在速调管工作原理的基础上,结合前期实际工作中经验,以收集极波形、发射功率和地物回波变化三项指标来判断运行性能状况.通过多年分析总结,电子枪通常是速调管的易损和易老化部件,对此主要提出速调管使用初期宜适当调高电子枪灯丝电流以使灯丝充分激活和保证新管具有较好的真空度;中期宜灯丝电流略低运行;晚期速调管的阴极发射能力可能会有所下降,在此时可又适当调高灯丝电流,以保证雷达探测的回波质量.通过对速调管工作阶段提出分段运行的新措施和建议,从实际效果看,在不影响探测质量的前提下应能提高速调管的使用时间,供同行探讨.对其他型号CINRAD雷达也应有较好的借鉴.