Modelling failure mechanisms to explain rock slope change along the Isle of Purbeck coast,UK

Results are presented of distinct element computer modelling used to examine rates and mechanisms of change in rock slopes and cliffs, where material intact properties determine process and form but the most significant controls are the joint pattern and cross-joint properties. The modelling approach does not appear to have been used before in a geomorphological context and provides an alternative approach for examining cliff development. Field and laboratory data have been collected for the Portland Limestone outcrop of the Isle of Purbeck, central southern England. The Portland Limestome is a hard, shelly, crystalline sediment of the Upper Jurassic. It has a regular discontinuity pattern throughout the outcrop in Purbeck. While joint orientation remains relatively constant, bedding changes from horizontal to vertical, a consequence of the Purbeck Monocline. There are resulting implications for spatial variations in rock slope evolution. The modelling exercise enhances previous knowledge on rock failure mechanisms and slope development along the Purbeck coast and demonstrates its potential in research where landforms are developed in lithified, jointed rock masses. © 1998 John Wiley & Sons, Ltd.     

Non-equilibrium alcohol flooding model for immiscible phase remediation: 1. Equation development

The equations for a compositional model for simulation of a two-phase, three-component system with inter-phase mass transfer are developed. Emphasis is placed on development of inter-phase mass transfer equations for incorporation of rate-limited inter-phase mass transfer. Due to the nature of the three-component systems considered, a single-film model may be inadequate and a two-film model must be utilized. A two-film model accounts for the simultaneous transfer of components in both directions across phase interfaces. The effect of interaction between components on diffusion is considered using a general form of Fick's Law. A Hand Plot representation of ternary phase behavior is chosen since it allows for straightforward calculation of miscibility of bulk phases under conditions of local non-equilibrium. The developed set of equations form the basis for a numerical model to simulate the enhanced removal of non-aqueous phase liquids (NAPLs) from porous media using single-component alcohol floods.     

Characterisation of hydroclimatological trends and variability in the Lake Naivasha basin,Kenya

Recent hydro‐climatological trends and variability characteristics were investigated for the Lake Naivasha basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using a Bayesian change point analysis and modified Mann–Kendall tests, time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes, were analysed for the period 1960–2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35 × 10⁶ m³ year^?1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright © 2015 John Wiley & Sons, Ltd.     

中小体质指数患者腹部能谱CT血管成像双低扫描方案优化

目的:探讨腹部能谱CT血管成像双低扫描方案的可行性和应用价值。方法:前瞻性收集疑腹部病变需行全腹血管CT成像BMI≤25的患者367例。首先按照首诊时间分实验组和对照组,再根据体质指数(BMI)分成两个亚组,BMI≤22为实验1组或对照1组,22相似文献   

Mass rig system for shaking table tests of slender columns

A new mass rig system is proposed to minimize the deficiencies in current shaking table testing setups. This is accomplished by placing the inertial mass on a convex path designed to impose P‐Delta demands on slender cantilever columns. The design and performance of the mass rig system, and the principles used in deriving the equations of motion and their analytical validation against results obtained from shaking table tests, are presented. Formulation of the governing equations of motion was based on Lagrangian mechanics and solved using an implicit linear acceleration method with an adaptive time step formulation. Friction developed in the sliding system was also incorporated in the equations of motion. Experimental results validated the accuracy in the derivation and solution of the equations of motion. Validated by analytical and experimental results, P‐Delta effects were found to increase the displacement demands on slender columns in the low‐frequency range of acceleration input, while in the high‐frequency range P‐Delta effects led to no increase and in some cases even a reduction in displacement demands. Copyright © 2015 John Wiley & Sons, Ltd.     

Evidence of Self‐Organized Criticality in riverbank mass failures: a matter of perspective?

A growing body of field, theoretical and numerical modelling studies suggests that predicting river response to even major changes in input variables is difficult. Rivers are seen to adjust rapidly and variably through time and space as well as changing independently of major driving variables. Concepts such as Self‐Organized Criticality (SOC) are considered to better reflect the complex interactions and adjustments occurring in systems than traditional approaches of cause and effect. This study tests the hypothesis that riverbank mass failures which occurred both prior to, and during, an extreme flood event in southeast Queensland (SEQ) in 2011 are a manifestation of SOC. Each wet‐flow failure is somewhat analogous to the ‘avalanche’ described in the initial sand‐pile experiments of Bak et al. (Physical Review Letters, 1987, 59(4), 381–384) and, due to the use of multitemporal LiDAR, the time period of instability can be effectively constrained to that surrounding the flood event. The data is examined with respect to the key factors thought to be significant in evaluating the existence of SOC including; non‐linear temporal dynamics in the occurrence of disturbance events within the system; an inverse power‐law relation between the magnitude and frequency of the events; the existence of a critical state to which the system readjusts after a disturbance; the existence of a cascading processes mechanism by which the same process can initiate both low‐magnitude and high‐magnitude events. While there was a significant change in the frequency of mass failures pre‐ and post‐flood, suggesting non‐linear temporal dynamics in the occurrence of disturbance events, the data did not fit an inverse power‐law within acceptable probability and other models were found to fit the data better. Likewise, determining a single ‘critical’ state is problematic when a variety of feedbacks and multiple modes of adjustment are likely to have operated throughout this high magnitude event. Overall, the extent to which the data supports a self‐organized critical state is variable and highly dependent upon inferential arguments. Investigating the existence of SOC, however, provided results and insights that are useful to the management and future prediction of these features. Copyright © 2014 John Wiley & Sons, Ltd.     

Bi‐directional coupled tuned mass dampers for the seismic response control of two‐way asymmetric‐plan buildings

This paper proposes bi‐directional coupled tuned mass dampers (BiCTMDs) for the seismic response control of two‐way asymmetric‐plan buildings subjected to bi‐directional ground motions. The proposed BiCTMD was developed from the three‐degree‐of‐freedom modal system, which represents the vibration mode of a two‐way asymmetric‐plan building. The performance of the proposed BiCTMD for the seismic response control of elastic two‐way asymmetric‐plan buildings was verified by investigating the reductions of the amplitudes of the associated frequency response functions. In addition, the investigation showed that the proposed BiCTMD is effective in reducing the seismic damage of inelastic asymmetric‐plan buildings. Therefore, the BiCTMD is an effective approach for the seismic response control of both elastic and inelastic two‐way asymmetric‐plan buildings. Copyright © 2010 John Wiley & Sons, Ltd.     

新型半主动调谐质量阻尼器减震性能的数值模拟

为了改良被动式调谐质量阻尼器(TMD)对建筑结构的减震效果,本文提出了一种新型的可实时调节频率和电涡流阻尼的半主动调谐质量阻尼器(SATMD)。由Hilbert-Huang变换(HHT)识别出结构的瞬时频率,通过基于HHT的控制算法实时调节SATMD的质量进行频率的调谐;通过基于线性二次型高斯(LQG)的控制算法实时调整磁导间距来调节电涡流阻尼系数。为了验证SATMD对建筑结构的减震效果,以一单自由度结构模型为例进行地震响应模拟,同时采用一经优化设计的被动TMD作为对比,并考虑由于主结构的累积损伤等引起自身频率下降而造成被动TMD的去谐效应。以主结构的加速度和位移时程峰值、整体均方根值及TMD的耗能性能作为评价指标,对比了SATMD在主结构发生损伤前后对被动TMD的改良效果。数值模拟结果表明,在主结构发生损伤前后,SATMD均比经优化设计的被动TMD有更好的减震效果及耗能能力。     

Identification of strength equilibrium rock slopes: Further statistical considerations

Strength equilibrium slopes are rock slopes whose gradient θ and rock mass strength (RMS) are in adjustment. The identification of such slopes depends on the accurate specification of the strength equilibrium envelope. Previous attempts to delimit the envelope are reviewed and modifications are proposed that permit its more rigorous statistical definition. Because θ can be measured much more reliably than RMS, the structural relation between these variables is estimated by regressing RMS on θ, and the strength equilibrium envelope is defined by the 95 per cent confidence limits. The analysis is performed on a data set of 268 rock slopes, representing all the data on RMS and θ hitherto employed in published studies of strength equilibrium slopes.