Environmental and land use factors affecting phosphate hysteresis patterns of stream water during flood events (Carpathian Foothills,Poland)

Flood events play a substantial role in the circulation of catchment phosphate (PO₄^3?). The purpose of the research was to analyze the factors determining PO₄^3? hysteresis patterns (direction and width) during four types of floods: short and long rainfall floods and snowmelt floods on frozen and thawed soil. The research took place in small catchments (forested, agricultural, mixed‐use) in the Carpathian Foothills in Poland. Anticlockwise hysteresis was identified in the forested catchment during short and long rainfall floods. Under the same conditions, the clockwise direction was observed in the agricultural catchment. In the mixed‐use catchment, the direction of PO₄^3? hysteresis loops was various, driven by the share of water flowing from each part of the catchment. For snowmelt floods, the PO₄^3? hysteresis pattern was similar in all the streams studied (usually clockwise). The direction of PO₄^3? hysteresis loops depends on water circulation patterns, which are determined by the different influx times of particular runoff components. The stream recharge mechanism during a flood event is affected both by the factor initiating the event (precipitation, snowmelt) as well as by land use in the given catchment. Hysteresis loop width was determined by the pool of PO₄^3? in a given catchment during the time period immediately preceding a flood event as well as by the quantity of PO₄^3? flushed out of the soil. The greater a catchment's pool of PO₄^3? and the greater its ability to flush PO₄^3? out of the soil and into surface flow, the wider the hysteresis loops. Copyright © 2012 John Wiley & Sons, Ltd.     

Remanent hysteresis study of dolerite dykes

Saturation remanent hysteresis studies were carried out on numerous dolerite dyke samples from the peninsular India. These studies result in four types of remanent hysteresis curves which indicate that the magnetic material is magnetite or titanomagnetite with variable grain-size having remanent coercive forces (H _cr ) of 8 to 30 mT, requiring saturating fields (H _s ) up to 250 mT. Two extreme types of samples with (1) low coercive forces requiring high saturating fields and (2) high coercive forces requiring low saturating fields are noticed along with the generally observed ones. The Granulometric and Lowrie-Fuller Tests on these samples indicated that the magnetic material i.e., magnetite or titanomagnetite in these rocks is in the form of Multi-Domain (MD), Cation Deficient (CD) and a mixture of these two forms (MD+CD) within.     

基于相关函数理论的动模量和阻尼比计算新方法

基于相关函数理论,提出一种新的计算动三轴试验动模量和阻尼比的方法。假设土体为黏弹性体,采用自相关函数分析应力、应变波形的平均幅值,进而计算动模量;采用互相关函数分析应变滞后于应力时程波形的相位差,进而计算阻尼比。利用饱和珊瑚砂、南京细砂和原状粉质黏土的不排水应变控制分级循环加载试验数据,分析结果表明：动模量和阻尼比计算的相关函数法对不同土样具有普适性;应变幅值小于1×10?4时,相关函数法计算动模量及阻尼比的精度明显优于传统的滞回圈法;应变幅值大于1×10?3时,土体呈现强非线性特性,应力-应变滞回圈不对称,相关函数法计算的阻尼更为可靠。     

土-水特征曲线滞后阻塞模型

基于Young-Laplace方程利用土-水特征曲线估算孔隙分布,借鉴非饱和渗流统计模型,建立了土-水特征曲线的滞后模型。在某一基质吸力下对应的毛细半径上限的毛细水对更大孔隙半径的毛细水具有阻塞作用,阻塞概率与孔隙分布函数直接相关。孔隙分布函数自身属性体现了土体孔隙空间分布的非均匀性。该模型显示：在高基质吸力与低基质吸力阶段,脱湿曲线与吸湿曲线趋近相等;中等基质吸力阶段,脱湿曲线饱和度高于吸湿曲线饱和度,两者的差值存在一个明显的峰值。并采用实例验证了该模型的可靠性,发现该模型对中、细粒土预测效果较好,而砂类土因孔隙分布不符合假设,导致存在较大误差。对于砂类土等特征尺寸较大的土质,引入阻塞概率修正系数,发现最佳修正系数与土-水特征曲线半对数坐标下的土-水特征曲线最大斜率呈反比例关系。     

Shifts in discharge‐concentration relationships as a small catchment recover from severe drought

This paper provides evidence of the recovery of a small, moorland catchment to a severe drought, the most extreme on record in the UK. We present a detailed water quality time series for the post‐drought recovery period, from the first significant storm event at the end of the drought through three very wet months during which time the catchment fully wetted up. High‐frequency observations were obtained using pump water samplers, at 15‐min intervals for storm events and 2 hourly at other times. There are significant shifts in discharge‐concentration response as the catchment wets up; initial behaviour is very different to later storms. Extreme drought may become more common in a warmer world, so it is increasingly important to understand water quality response during and after such episodes, if their impact on water resources and in‐stream ecology is to be better anticipated. Copyright © 2014 John Wiley & Sons, Ltd.     

Residual displacements of RC structures as SDOF systems

Residual displacements are sensitive to ground motion details, hence more random than peak inelastic displacements. Among the factors with systematic impact on residual displacements, the post‐yield‐stiffness‐ratio has been studied thoroughly; its effects are not investigated further. Concerning another important factor, the hysteresis law, past studies have focused on the bilinear model, which does not represent concrete structures. Residual displacements from nonlinear response‐history analyses of bilinear systems are compared to those from models tuned to concrete structures, conforming to modern codes, deficient or intermediate. Deficient‐type structures, with their narrow, almost self‐centering hysteresis loops, develop markedly smaller residual displacements than those with stable energy‐dissipating behavior. A velocity pulse in the motion increases peak inelastic and residual displacements by about the same proportion. As a fraction of the peak inelastic or spectral displacement, residual displacements are on average almost independent of the period and increase when the lateral strength ratio increases, reaching a limit at a lateral strength ratio of 2 to 5. Peak inelastic displacements are a better basis for estimation of residual displacements than spectral ones: the ratio of the two is almost independent of the period, the lateral strength ratio (beyond values of 2 to 3) and velocity pulses. The spectrum of the ratio of residual displacement to peak inelastic or spectral displacement is considered as a random process of period; its mean and variance functions, marginal probability distributions and autocorrelation functions are given in terms of the lateral strength ratio, the hysteresis model and the presence of a velocity pulse. Copyright © 2014 John Wiley & Sons, Ltd.     

Composed analytical models for seismic assessment of reinforced concrete bridge columns

This paper presents general composed analytical models to predict the behavior of reinforced concrete (RC) bridge columns. The analytical models were developed in OpenSees to represent the common hysteretic behavior of RC bridge columns. The proposed composed models can accommodate flexure failure, flexure‐shear failure, and pure shear failure, which are observed in existing RC bridge piers. The accuracy of the models was verified using data from the static cyclic‐loading experiments of 16 single columns and one multi‐column bent and dynamical experiment from two pseudo‐dynamic tests. The results showed that the analytical models could simulate the nonlinear behavior until the post‐failure behavior, including the strength degradation, the buckling of the reinforcement, and the pinching effect. Therefore, a global view of the behavior of reinforcement concrete is prescribed as simply as possible from the academic perspective, and these models are expected to provide sufficient accuracy when applied in engineering practice. Copyright © 2014 John Wiley & Sons, Ltd.     

单环入渗试验与数值反演法结合推求土壤水力参数

单环入渗试验广泛应用于野外测定土壤水力参数。文章在三维非饱和带水分模拟程序VSF基础上,加入了单环入渗水流计算模块,并将改进的VSF与参数优化程序LEVMAR相耦合,构建了适用于单环入渗试验的土壤水力特征参数反演程序VSF-LEVMAR。利用大型室内土槽单环定水头入渗及变水头入渗试验资料,反求水平及垂向饱和入渗系数等土壤水力参数。应用结果表明:该方法既可以利用单环定水头入渗试验单独推求吸湿过程中的土壤水力参数,也可以结合单环定水头入渗与变水头入渗试验同时推求吸湿及脱湿过程中的土壤水力参数。