Characteristics and genesis of maghemite in Chinese loess and paleosols: Mechanism for magnetic susceptibility enhancement in paleosols

Morphological characteristics and microstructures of magnetic minerals extracted from Chinese loess and paleosols were investigated using powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Our results indicate that maghemite in loess–paleosol sequences was transformed from magnetite through oxidation of magnetite. Maghemite transformed from eolian magnetite during chemical weathering has low-angle grain boundaries among maghemite nano-crystals. Some nano-crystalline maghemites with nanoporous texture resulted from microbe-induced precipitation of magnetite or transformation of poorly crystalline ferric Fe (oxy)hydroxides in presence of Fe-reducing bacteria. Aggregates of euhedral maghemite nano-crystals were transformed from magnetite magnetosomes. Both microbe-induced nanoporous magnetite and microbe-produced magnetite magnetosomes are directly related to microbial activities and pedogenesis of the paleosols. It is proposed that the formation of nano-crystalline maghemite with superparamagnetic property in paleosol results in the enhancement of magnetic susceptibility, although the total amount (weight percent) of magnetic minerals in both paleosol and loess units is similar. Our results also show that nano-crystalline and nanoporous magnetite grains prefer to transform into maghemite in semi-arid soil environments instead of hematite, although hematite is a thermodynamically stable phase. This result also indicates that a decrease in crystal size will increase stability of maghemite. It is also inferred that surface energy of maghemite is lower than that of hematite.     

Least-squares wave-path migration

We present a new least-squares migration method called least-squares wave-path migration. The proposed method combines an iterative conjugate-gradient solver with a stationary-phase wave-path migration operator. Numerical tests demonstrate that (i) least-squares wave-path migration is computationally more efficient than and almost as accurate as Kirchhoff least-squares migration, and (ii) many of the artefacts seen in wave-path migration images are suppressed after several conjugate-gradient iterations. Previous results have shown that 3D wave-path migration is up to 100 times faster than a standard 3D Kirchhoff migration, but sometimes at the cost of reduced quality. With the proposed least-squares wave-path migration method, the image quality in wave-path migration can be improved at an acceptable increase in computational cost.     

中国海相油气田勘探实例(之一) 四川盆地罗家寨大型气田的发现和探明

罗家寨气田发现于2000年,是四川盆地迄今为止发现的储量规模最大的一个气田,2002年探明储量为581.08×108m3。其下三叠统飞仙关组储层由碳酸盐岩蒸发台地边缘优质鲕粒滩白云岩构成,圈闭面积大,构造幅度高,具有一定的埋藏隐蔽性。论述了气田的发现和探明过程,气藏地质的特征,以及对碳酸盐岩气藏勘探的启示。     

综合管理信息系统的应用是设计院规范管理体制提高市场竞争力的重要途径

本文针对国内勘察设计企业管理现状和存在的问题,阐述了综合信息管理系统开发的必要性及其实施时各方面的要求及策略。     

Microorganisms in Lianxian lateritic gold deposit in Guangdong and their effects on leaching of heavy metals

Microorganisms in the lateritic profiles of the Lianxian gold deposit in Guangdong were cultured, isolated and identified. The microorganisms include bacteria such as Bacillus, Enterobacter, Pseudomonas, Lactobacillus, Actinetobacter, Aeromona, Listeria, Agrobacteriura, Cotyttebacteriurn, and Moraxella, fungi such as Penicillium, Alter naria, Cladosporium, Saccharcornyces, Mucor, and the chemoautotrophic Thiobacillu.~. It is shown in a leaching experiment that the microorganisms can accelerate the leaching of Cu, Cd, Zn, and that the G- bacteria are most efficient for leaching Cu, Zn and the G^ bacteria are better for leaching Cd.     

Slope stability evaluation using Back Propagation Neural Networks

The Yudonghe landslide, located in western Hubei Province of China, consists of eastern and western subunits as well as a main landslide mass with upper and lower slip surfaces. As an important landslide close to Shuibuya Dam on the Qing River, its stability is crucial, as the slide might reactivate because of a change in ground-water level caused by filling of the Shuibuya Reservoir. Existing weakness zones, growth of ruptures, the downslope attitude of geologic strata, and water infiltration, which reduced the strength of rocks and soils, have been found to be the most important factors contributing to the Yudonghe landslide. With regard to the landslide processes, it can be noted that the original large-scale slide activity was due to erosion by the Qing River, the second sliding resulted from the fall of blocks from the head scarp, and the final activity was the growth of the eastern and western secondary slides. A base failure was the main type of slope movement, however, it was obvious that more than one sliding event occurred, as inferred from striations and fractures detected by microstructure analysis of soils along the failure surfaces. Slope instability was evaluated by the method of Back Propagation Neural Networks (BPNN), in which a four-layer BPNN model with five input nodes, two hidden layers, and two output nodes was constructed using a training data set of landslide samples throughout the Qing River area. The predicted results of this analysis showed that the factor of safety was 1.10, which indicates that the Yudonghe landslide is currently in a marginally stable condition.     

木荚红豆人工林C库及其分配研究

对木荚红豆人工林C贮量及其分配的研究表明,木荚红豆人工林C贮量为227.9t/hm2,其中生物量C库和死有机质C库分别为117.1t/hm2和110.8t/hm2,分别占C库总量的51.4%和48.6%;乔木层C库和土壤有机质C库分别占林分总C库的49.4%和47.1%;林下植被层、枯枝落叶层、粗木质残体C库总共仅占生态系统C库的3.5%,对生态系统C吸存的贡献较小.     

Semi‐analytical solution to one‐dimensional consolidation for unsaturated soils with semi‐permeable drainage boundary under time‐dependent loading

This paper presents semi‐analytical solutions to Fredlund and Hasan's one‐dimensional consolidation of unsaturated soils with semi‐permeable drainage boundary under time‐dependent loadings. Two variables are introduced to transform two coupled governing equations of pore‐water and pore‐air pressures into an equivalent set of partial differential equations, which are easily solved by the Laplace transform. The pore‐water pressure, pore‐air pressure and settlement are obtained in the Laplace domain. Crump's method is adopted to perform the inverse Laplace transform in order to obtain semi‐analytical solutions in time domain. It is shown that the present solutions are more general and have a good agreement with the existing solutions from literatures. Furthermore, the current solutions can also be degenerated into conventional solutions to one‐dimensional consolidation of unsaturated soils with homogeneous boundaries. Finally, several numerical examples are provided to illustrate consolidation behavior of unsaturated soils under four types of time‐dependent loadings, including instantaneous loading, ramp loading, exponential loading and sinusoidal loading. Parametric studies are illustrated by variations of pore‐air pressure, pore‐water pressure and settlement at different values of the ratio of air–water permeability coefficient, depth and loading parameters. Copyright © 2017 John Wiley & Sons, Ltd.