The role of intergrain junctions in transport critical current irreversibility

The magnetic field dependence of voltage at constant measuring currents of YBa₂Cu₃O_7– bulk ceramics and Bi(Pb)SrCaCuO screen printed films were studied at different temperatures so as to obtain information on critical current irreversibility. Two ranges of these curves were found to show sensitivity to magnetic field. They suggest that the two types of superconducting medium, i.e., the Josephson and Abrikosov medium, result in two different voltage generation mechanisms. It is shown that the Josephson medium plays a role in both low and high magnetic field critical current irreversibility.     

Application of Granular Activated Carbon in the Water Industry

U ntil the mid 1980s granular activated carbon (GAC) was used in only a small number of water-treatment plants in the UK. Since then the material has been installed in over 30 plants, either as a result of an operational decision to treat the water by GAC or for the purpose of full-scale experiments. GAC is used for a variety of reasons including taste and odour control, removal of a wide range of synthetic organic compounds (for example volatile chlorinated solvents, pesticides, oils) of molecular weight 100–500, and adsorption of trihalomethane precursors (molecular weight 10³-10⁵). The performance of different GACs for a particular duty may vary by a factor of 10, and the best GAC for one application may be the worst for another. Thus, to minimize the cost of GAC treatment, it is essential to identify the purpose for which GAC is being used and then to select, by pilot trials or by more rapid laboratory procedures and mathematical modelling, the most appropriate GAC for that particular application.     

Pentachlorophenol adsorption and desorption characteristics of granular activated carbon-II. Kinetics

The kinetics of pentachlorophenol (PCP) adsorption/desorption with Calgon F300 granular activated carbon (GAC) was studied. A previously-developed model of GAC adsorption/desorption kinetics was applied to the case of PCP for both batch and continuous plug-flow liquid conditions. The model predictions were found to be in good agreement with the experimental observations.     

Bearing Capacity of the Granular Bed of a Strip Foundation under an Inclined Eccentric Load

Exact solutions are presented for the bearing capacity of a weighted noncohesive Coulomb bed supporting a strip foundation. The effect of the incline and eccentricity of the load is analyzed on the basis of these solutions. __________ Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 2–7, July–August, 2005.     

流动散体中波的传播规律与振动分形特征

试验测定振动助流时散体颗粒在初始阶段和稳定流动阶段的振动加速度信号,并对流动场中波的传播规律进行分析。把流动中的散体看作弱横观各向同性介质,给出了P波、SH波和SV波的速度表达式,分析了它们在流动散体介质中的传播特点。认为椭球体的偏心率减小,散体间的黏性阻力和内摩擦力降低,松散系数增加,使散体具有更好的流动性。散体颗粒受振运动是一种不规则、复杂和随机的运动,具有分形特征,对其进行了分形分析和模拟。     

生物除磷颗粒污泥的丝状菌膨胀及恢复研究

颗粒污泥的稳定性是影响其在污水处理中广泛应用的重要因素.在SBR反应器中,采用成熟的生物除磷颗粒污泥,探讨了丝状菌膨胀对其除磷能力和稳定性的影响.经过396d的运行,结果表明,丝状菌的存在对颗粒污泥的形成和稳定起重要作用,但当丝状菌过度生长时,反应器的除磷率和污泥最大释磷速率分别降低到60%和26.67 mgP/（gMLVSS·h）以下,出水SS和SVI分别提高到100 mg/L和50 mL/g以上.采用延长沉淀时间、提高搅拌速度以及投加无膨胀的生物除磷颗粒污泥三种策略均可以恢复系统的功能,所需恢复时间分别为53、26和20 d.     

水平向渗透系数变化条件下散体材料桩复合地基固结理论研究及分析

 建立考虑排水影响区土体水平向渗透系数因施工扰动影响而逐渐变化的散体材料桩复合地基的固结定解问题,并求出其一般解。基于实际工程中桩体施工对扰动区土体水平向渗透系数影响的复杂性,选择排水影响区土体水平向渗透系数沿径向分布的3种特殊情况,给出相应特解。根据解析解结果,通过编程计算,绘制出主要因素对复合地基固结过程的影响曲线图,分析排水影响区土体水平向渗透系数变化对散体材料桩复合地基固结性状的影响。研究结果表明：土体渗透性变化对复合地基固结影响显著,桩体施工对周围土体扰动越大,复合地基固结会越慢;考虑土体水平向渗透系数变化的散体材料桩复合地基固结理论较现有的复合地基固结理论更接近实际情况。     

常温下EGSB处理低浓度城市污水的初步研究

通过间歇试验和中试研究,初步探讨了悬浮物、温度和溶解氧对膨胀颗粒污泥床（EGSB）在常温下处理低浓度城市污水的影响。中试结果表明,城市污水中的悬浮物在EGSB中能够得到有效去除,不会在系统中沉积而影响运行效果;EGSB的出水可回流且城市污水的COD浓度低,缓解了温度对系统的影响,EGSB对CODtotal的去除率可保持在70%左右;颗粒污泥的外层兼性菌消耗了溶解氧,保护了产甲烷菌,减轻了溶解氧对颗粒污泥降解城市污水的抑制作用。初步研究结果表明,悬浮物、温度和溶解氧对EGSB在常温下处理低浓度城市污水不会产生不利影响。     

DEM investigation on the breakage of spherical aggregate under multi-contact loadings

Particle crushing is commonly encountered during the storage, transportation, and handling of granular assemblies. This work is aimed at ascertaining the applicability of four particle breakage criteria frequently mentioned in literature. Discrete element method (DEM) simulations were conducted to investigate the crushing of spherical aggregates under multicontact loadings. Mean and major principal stress criteria, octahedral shear stress criterion, and maximal contact force (MCF) criterion were then evaluated based on the obtained DEM results. It is found that the first three parameters all vary with the number of loading contacts, demonstrating they cannot predict the crushing of particles under arbitrary loading configuration. Simulation results indicate that the MCF at crushing is related to the number and the spatial arrangement of loading contacts. Thus, strictly speaking, this parameter cannot uniquely define particle breakage either. The influences of the microstructural heterogeneity on the breakage strength of particle and also on the applicability of MCF criterion are discussed.     

Multi-scale investigation of active failure for various modes of wall movement

Retained backfill response to wall movement depends on factors that range from boundary conditions to the geometrical characteristic of individual particles. Hence, mechanical understanding of the problem warrants multi-scale analyses that investigate reciprocal relationships between macro and micro effects. Accordingly, this study attempts a multi-scale examination of failure evolution in cohesionless backfills. Therefore, the transition of retained backfills from at-rest condition to the active state is modeled using the discrete element method (DEM). DEM allows conducting virtual experiments, with which the variation of particle and boundary properties is straightforward. Hence, various modes of wall movement (translation and rotation) toward the active state are modeled using two different backfills with distinct particle shapes (spherical and nonspherical) under varying surcharge. For each model, cumulative rotations of single particles are tracked, and the results are used to analyze the evolution of shear bands and their geometric characteristics. Moreover, dependencies of lateral pressure coefficients and coordination numbers, as respective macro and micro behavior indicators, on particle shape, boundary conditions, and surcharge levels are investigated. Additionally, contact force networks are visually determined, and their influences on pressure distribution and deformation mechanisms are discussed with reference to the associated modes of wall movement and particle shapes.