Root properties of vegetation communities and their impact on the erosion resistance of river dikes

Predicted climate change and the associated sea level rise poses an increased threat of flooding due to wave overtopping events at sea and river dikes. To safeguard the land from flooding it is important to keep the soil erosion resistance at the dikes high. As plant roots can be very effective in reducing soil erosion rates by concentrated flow, the main goal of this study is to explore the variability in root system characteristics of five dike vegetation communities along the Scheldt River (Belgium) and to assess their effectiveness in controlling soil erosion rates during concentrated flow. This study is the first one to investigate systematically the erosion‐reducing potential of the root properties of representative dike vegetation communities in a temperate humid climate. Results show that the presence of Urtica dioica resulted in large differences in root length density (RLD) among dike vegetation communities. Observed RLD values in the topsoil ranged from 129 to 235 km m^‐3 for dike vegetation communities without U. dioica, while smaller values ranging from 22 to 58 km m^?3 were found for vegetation communities with U. dioica. The erosion‐reducing effect of the dike vegetation communities was estimated based on a global Hill curve model, linking the RLD to the soil detachment ratio (SDR; i.e. the ratio of the soil detachment rate for root‐permeated topsoils to the soil detachment rate for root‐free topsoils). Concentrated flow erosion rates are likely to be reduced to 13–16% of the erosion rates for root‐free topsoils if U. dioica is absent compared to 22–30% for vegetation communities with U. dioica. Hence, to maintain a high resistance of the soil against concentrated flow erosion it is important to avoid the overgrowth of grassland by U. dioica through an effective vegetation management. Copyright © 2016 John Wiley & Sons, Ltd.     

陕西旬阳县210国道6号边坡变形特征初步研究

通过现场工程地质勘探、室内物理力学实验并利用FLAC2D数值分析软件对陕西旬阳县某堆积层边坡进行变形特征的实例分析,考查了坡体岩土体的粘聚力、内摩擦角数值与坡脚开挖深度的变化后,得出浅层岩土体较深层岩土体的滑动趋势与滑动位移均较大,并且浅层岩土体滑移变形对深层岩土体具有牵引力作用。最后对该类型堆积层坡体滑动的防治措施提出了一些看法。     

Approximation approach to the SRM based on root decomposition in the simulation of spatially varying ground motions

The spectral representation method(SRM) is widely used to simulate spatially varying ground motions.This study focuses on the approximation approach to the SRM based on root decomposition,which can improve the efficiency of the simulation.The accuracy of the approximation approach may be affected by three factors: matrix for decomposition,distribution of frequency interpolation nodes and elements for interpolation.The influence of these factors on the accuracy of this approach is examined and the following conclusions are drawn.The SRM based on the root decomposition of the lagged coherency matrix exhibits greater accuracy than the SRM based on the root decomposition of the cross spectral matrix.The equal energy distribution of frequency interpolation nodes proposed in this study is more effective than the counter pith with an equal spacing.Elements for interpolation do not have much of an effect on the accuracy,so interpolation of the elements of the decomposed matrix is recommended because it is less complicated from a computational efficiency perspective.     

“Belonging” in the gentrified Golden Horn/Halic neighbourhoods of Istanbul

Mainstream gentrification research predominantly examines experiences and motivations of the middle-class gentrifier groups, while overlooking experiences of non-gentrifying groups including the impact of in situ local processes on gentrification itself. In this paper, I discuss gentrification, neighbourhood belonging and spatial distribution of class in Istanbul by examining patterns of belonging both of gentrifiers and non-gentrifying groups in historic neighbourhoods of the Golden Horn/Halic. I use multiple correspondence analysis (MCA), a methodology rarely used in gentrification research, to explore social and symbolic borders between these two groups. I show how gentrification leads to spatial clustering by creating exclusionary practices and eroding social cohesion, and illuminate divisions that are inscribed into the physical space of the neighbourhood.     

水稻籽实及其根系土壤中镉含量的相关性研究——以几个金土地工程土地整理区为例

通过对水稻籽实（大米）及其根系土壤中镉含量的相关性研究表明：酸性水稻土壤区域,根系土中的镉与水稻籽实中的镉相关系数为0．971,说明大米中镉积累与土壤环境中镉含量密切相关。碱性水稻土壤区域,水稻根系土中的镉与水稻籽实中的镉相关系数为0．265,大米中镉含量较低,碱性土壤中镉不易活化而原地淀积,则根系土壤中镉对大米中镉的富集贡献小。水稻根系土壤中有机质（Org）与镉相关系数为0．59,也较为显著。土壤中有机质对重金属元素镉具正吸附作用,有机质含量越高,重金属元素镉呈难吝硫化物而原地淀积。     

Regional Temperature Forecast for the Next Day in Hong Kong

For a century or so, the Hong Kong Observatory (HKO) has been providing temperature forecast for the whole of Hong Kong with the HKO Headquarters as the reference location. In recent decades, due to spreading of population from the main urban center to satellite towns, there is an increasing demand for regional temperature forecasts. To support such provision, the HKO has developed a regression model to provide objective guidance to forecasters in formulating forecasts of maximum and minimum temperatures for the next day at various locations in Hong Kong. In this paper, the regression model is presented, together with the assessment of its performance. Based on the verification of one year of forecasts, it is found that the root mean square errors (RMSEs) of maximum (minimum) temperature forecasts are from about 1.3 to 2.1 (1.1 to 1.4) degrees, respectively. The regression model is shown to have generally out-performed the operational regional spectral model then operated by HKO. Regional temperature forecast methods of other meteorological or research centers are also surveyed. Equipped with the regression model, the HKO has launched an online regional temperature forecast service for the next day in Hong Kong since March 2008.     

Simulation of spatially correlated earthquake ground motions for engineering purposes

A new model to simulate spatially correlated earthquake ground motions is developed. In the model, the main factors that characterize three distinct effects of spatial variability, namely, the incoherency effect, the wave-passage effect and the site-response effect, are taken into account, and corresponding terms/parameters are incorporated into the well known model of uniform ground motions. Some of these terms/parameters can be determined by the root operation, and others can be calculated directly. The proposed model is fi rst verif ied theoretically, and examples of ground motion simulations are provided as a further illustration. It is proven that the ensemble expected value and the ensemble auto-/cross-spectral density functions of the simulated ground motions are identical to the target spectral density functions. The proposed model can also be used to simulate other correlated stochastic processes, such as wave and wind loads.     

泥沙颗粒生长生物膜后起动的实验研究——Ⅱ.起动流速计算

泥沙颗粒生长生物膜后,起动流速发生了较大变化.根据生长生物膜后的泥沙起动流速实验数据,考虑天然水体中,生物膜填充于颗粒与颗粒之间形成除水以外新的介质,将生物膜的作用模化为生物膜作用产生的粘连力,再考虑生物膜随时间变化的特性以及基底物理特性的影响等因素,结合泥沙颗粒之间由于薄膜水产生的黏结力、重力等,研究了颗粒在滑动和滚...     

剪切速率对凝聚力和摩擦角的影响规律

为提高生产速度,指导生产,以饱和细粒土为实验材料,研究剪切速率的变化对样品凝聚力和摩擦角的影响.     

树根桩在厂房扩建工程地基处理中的应用

在苏南某工业厂房扩建工程中,为了妥善解决新旧熔炉区的不均匀沉降,通过多方案的比选,最终采用树根桩托换技术进行地基加固。并且对新旧熔炉区的基础进行了化学植筋连接和防渗漏处理。