断续节理岩体随机模型三维离散元数值模拟

针对断续节理岩体提出了一种随机计算模型.在该模型中,假设结构面的形状为正方形,通过岩体结构面的统计分布函数模拟结构面的空间随机分布.给出了随机节理模型的实现方法,对该随机模型的算法可靠性进行了验证.通过单向加载模拟试验研究了节理岩体破坏强度与节理倾角及节理连通率等因素的关系,并与极限平衡条件推导的理论结果进行了比较,分析了数值模拟结果与极限平衡理论结果的异同性,进而验证了节理随机计算模型的可靠性.同时,研究了节理连通率与岩体等效弹性模量之间的影响关系,给出了二者的影响关系式.

一种岩石概率型本构及其应用

在岩石材料非均匀特性的基础上,建立了弹塑性概率材料本构.认为材料单元的切线模量与破坏强度都是服从二参数Weibull分布的随机量,通过用户材料子程序将该本构导入到LS-DYNA3D中,推导了程序流程,分析了导入过程中的关键技术.算例验证表明,应用该本构模拟得出的现象与实验观测完全一致,这是确定性本构无法实现的.

清江茅坪滑坡白岩危岩体崩塌现场测量及其分析

位于茅坪滑坡体后缘的白岩危岩体于2002年8月24日发生了大规模的崩塌。崩落的块石落在滑坡体上，对滑坡体产生了加载作用，影响了该滑坡体的稳定性。为研究茅坪滑坡体的稳定性，有必要弄清滑坡体上崩落块石的堆积情况。论文在对清江隔河岩水库白岩危岩体崩塌现场调查的基础上，估算了崩塌岩体的体积，实地测量了岩体崩塌后堆积体表面块石的尺寸以及各块石空间位置坐标。对测量的结果进行了统计分析。根据所测量的块石尺寸、得到了崩落岩体的块体大小级配累积曲线图和各块石尺度出现的概率，从而阐明了各尺度崩落块石组合情况。根据各块石尺寸和各块石空间位置坐标、分析得到不同尺寸崩落块石落在滑坡体上的空间分布规律，从而为茅坪滑坡的进一步研究打下了基础。

含节理岩块单轴受压试验三维离散元数值模拟

采用三维离散元方法，模拟含节理岩块的单轴受压试验。并针对节理空间分布，给出了解析解与数值计算比较的结果，验证了数值模拟的正确性。当节理正交时，离散元与有限元的计算结果一致。计算结果定量地说明了岩体的各向异性和尺寸效应。

Characteristics of an AC Three-Phase GlidArc Plasma Generator

Experimental Evidence of Critical Sensitivity in Catastrophe

The paper presents an experimental study on critical sensitivity in rocks. Critical sensitivity means that the response of a system to external controlling variable may become significantly sensitive as the system approaches its catastrophic rupture point. It is found that the sensitivities measured by responses on three scales (sample scale, locally macroscopic scales and mesoscopic scale) display increase prior to catastrophic transition point. These experimental results do support the concept that critical sensitivity might be a common precursory feature of catastrophe. Furthermore, our previous theoretical model is extended to explore the fluctuations in critical sensitivity in the rock tests.

Numerical investigation of crack growth in concrete subjected to compression by the generalized beam lattice model

The beam lattice-type models, such as the Euler-Bernoulli (or Timoshenko) beam lattice and the generalized beam (GB) lattice, have been proved very effective in simulating failure processes in concrete and rock due to its simplicity and easy implementation. However, these existing lattice models only take into account tensile failures, so it may be not applicable to simulation of failure behaviors under compressive states. The main aim in this paper is to incorporate Mohr-Coulomb failure criterion, which is widely used in many kinds of materials, into the GB lattice procedure. The improved GB lattice procedure has the capability of modeling both element failures and contact/separation of cracked elements. The numerical examples show its effectiveness in simulating compressive failures. Furthermore, the influences of lateral confinement, friction angle, stiffness of loading platen, inclusion of aggregates on failure processes are respectively analyzed in detail.

应力波峰值变化与岩体结构关系的试验研究

选择了3种有代表性的岩体结构进行冲击试验,分析研究了波形最大峰值变化与岩体结构的关系.试验结果表明:震动峰值随空间衰减、震动峰值延时及其离散性变化均能有效反映岩体结构特点和受扰动程度,也能反映岩体的各向异性.

Dissipative particle dynamics simulation of wettability alternation phenomena in the chemical flooding process

Wettability alternation phenomena is considered one of the most important enhanced oil recovery (EOR) mechanisms in the chemical flooding process and induced by the adsorption of surfactant on the rock surface. These phenomena are studied by a mesoscopic method named as dissipative particle dynamics (DPD). Both the alteration phenomena of water-wet to oil-wet and that of oil-wet to water-wet are simulated based on reasonable definition of interaction parameters between beads. The wetting hysteresis phenomenon and the process of oil-drops detachment from rock surfaces with different wettability are simulated by adding long-range external forces on the fluid particles. The simulation results show that, the oil drop is liable to spread on the oil-wetting surface and move in the form of liquid film flow, whereas it is likely to move as a whole on the water-wetting surface. There are the same phenomena occuring in wettability-alternated cases. The results also show that DPD method provides a feasible approach to the problems of seepage flow with physicochemical phenomena and can be used to study the mechanism of EOR of chemical flooding.

Abnormal phenomenon of ac Stark splitting in magneto-optical traps

We experimentally study the ac Stark splitting in D2 line of cold Rb-87 atoms. The frequency span between the Autler-Townes doublets is obviously larger than that derived from theoretical calculation. Two physical effects, which increase the effective Rabi frequency, contribute to the splitting broadening. First, atoms tend to distribute in strong lield places of a inhomogeneous red-detuned light field. Second, atoms reabsorb scattered light when they are huge in number and high in density.

Characteristics of polypyrrole (PPy) nano-tubules made by templated ac electropolymerization

Electrochemical alternating current (ac) method designed for the synthesis of polypyrrole (PPy) nano-tubule arrays is the topic of this paper. Two-step anodic aluminum oxide (AAO) membrane is used as a template. The morphology of PPy nano-tubules is observed by SEM and discussed. FTIR spectra exhibit that the peaks of PPy nano-tubules shift compared to conventional PPy film. (c) 2005 Elsevier Ltd. All rights reserved.

Polarized spectral analysis of Ho3+ ions in biaxial YAlO3 crystal for 2 mu m lasers

An Ho3+-doped YAlO3 (Ho : YAP) single crystal has been grown by the Czochralski technique. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of the crystal are measured at room temperature. The spectroscopic parameters are calculated based on Judd-Ofelt theory, and the effective phenomenological intensity parameters Omega(2,eff), Omega(4,eff) and Omega(6,eff) are obtained to be 2.89 x 10(-20), 2.92 x 10(-20) and 1.32 x 10(-20) cm(2), respectively. The room-temperature fluorescence lifetime of the Ho3+ 5I(7) -> I-5(8) transition is measured to be 8.1 ms. Values of the absorption and emission cross-sections with different polarizations are presented for the I-5(7) manifold, and the polarized gain cross-section curves are also provided and discussed.

The evolution of intermediate castration virulence and ant coexistence in a spatially structured environment

Theory suggests that spatial structuring should select for intermediate levels of virulence in parasites, but empirical tests are rare and have never been conducted with castration (sterilizing) parasites. To test this theory in a natural landscape, we co

四川美姑、汉源黑颈鹤迁徙停歇地环境调查

Eight Black-necked Cranes(Grus nigricollis)were banded with satellite transmitters in the spring of 2005 and 2006 at Dashanbao in Yunnan and Caohai in Guizhou.Six of the banded cranes completed at least one migration between their wintering and breeding grounds.Townships where these birds stopped over include:Wusihe,Henan,Nimei,Liyuan,Yidong,Sanjiaoping,and Huangmu in Hanyuan County,and Liuhong,Yiguojie,Nongzuo,Lamuajue,Bingtu,Wagu,Equgulongmen,and Niha in Meigu County.We surveyed stop-over sites in Hanyuan...

Alternative cold response modes in Chlorella (Chlorophyta, Trebouxiophyceae) from Antarctica

Chlorella was known to show enhanced antifreeze capability after cold hardening. We isolated Chlorella strains NJ-7 and NJ-18, which display alternative cold response modes from rock surfaces in Antarctica. On the basis of 18S ribosomal (rRNA) sequences, NJ-7 is an Antarctic type of Chlorella vulgaris; NJ-18 is also a 'true' Chlorella species but differs from any previously reported species in structure. NJ-7 partially retained the enhancing effects of low temperature cultivation on freeze tolerance, which correlates with an increase of C18:3-fatty acid content and up-regulation of two antifreeze protein genes. NJ-18, however, showed stable freeze tolerance regardless of the precultivation temperature. We propose that cold response modes vary widely in Chlorella and that the adaptation of C. vulgaris to Antarctica may serve as a model system for the evolution of antifreeze mechanisms in a single species of photosynthetic microorganism.