Costly stakeholder participation creates inertia in marine ecosystems

Ecosystems often shift abruptly and dramatically between different regimes in response to human or natural disturbances. When ecosystems tip from one regime to another, the suite of available ecosystem benefits changes, impacting the stakeholders who rely on these benefits. These changes often create some groups who stand to incur large losses if an ecosystem returns to a previous regime. When the participation cost in the decision-making process is extremely high, this can “lock in” ecosystem regimes, making it harder for policy and management to shift ecosystems out of what the majority of society views as the undesirable regime. Public stakeholder meetings often have high costs of participation, thus economic theory predicts they will be dominated by extreme views and often lead to decisions that do not represent the majority viewpoint. Such extreme viewpoints can create strong inertia even when there is broad consensus to manage an ecosystem towards a different regime. In the same manner that reinforcing ecological feedback loops make it harder to exit an ecosystem regime, there are decision-making feedback loops that contribute additional inertia.     

The influence of capillarity on multiphase flow within porous media: a new model for interpreting fluid levels in groundwater monitoring wells in dynamic aquifers

A new approach is presented to calculate the volume of oil in the underground at an oil spill site from fluid levels in monitoring wells. The approach includes the effects of hysteresis due to irregular pore geometry and to phase entrapment. It is possible to explain the drastic changes in the oil thickness in a monitoring well due to the decrease and increase in the groundwater table. A correct evaluation of the oil volume infiltrated underground from an oil spill and the effective control of remediation works can only be done by using the newly developed approach with a consideration of the dynamic changes in the groundwater table.     

Plasticity model for sand under small and large cyclic strains: a multiaxial formulation

This paper presents the multiaxial formulation of a plasticity model for sand under cyclic shearing. The model adopts a kinematic hardening circular cone as the yield surface and three non-circular conical surfaces corresponding to the deviatoric stress ratios at phase transformation, peak strength and critical state. The shape of the non-circular surfaces is formulated in accordance with the experimentally established failure criteria, while their size is related to the value of the state parameter ψ. To simulate cyclic response under small and large shear strain amplitudes without a change in model parameters, it was found necessary to introduce: (a) a non-linear hysteretic (Ramberg–Osgood type) formulation for the strain rate of elastic states and (b) an empirical index of the effect of fabric evolution during shearing which scales the plastic modulus. This index is estimated in terms of a macroscopic second-order fabric tensor, which develops as a function of the plastic volumetric strain increment and the loading direction in the deviatoric plane. Comparison of simulations to pertinent data from 27 resonant column, cyclic triaxial and cyclic direct simple shear tests provide a measure for the overall accuracy of the model.     

强降雨条件下框架预应力锚杆柔性支护结构整体稳定性影响参数分析

为完善框架预应力锚杆柔性支护结构稳定性研究,针对该结构的稳定性分析和设计均未考虑降雨入渗影响的现状,基于GeoStudio软件,分析了黄土地区强降雨条件下的框架预应力锚杆柔性支护结构的整体稳定性影响参数,在分析中考虑了土体含水率变化对摩擦型灌浆锚杆极限抗拔承载力的影响。分析结果表明:降雨持时、降雨强度和地下水位对框架预应力锚杆柔性支护结构的整体稳定性有明显的影响; 土体饱和渗透系数的影响十分显著; 渗透各向异性的影响可以忽略; 降雨条件下框架预应力锚杆柔性支护结构的安全系数变化存在滞后效应:随着降雨持时和土体饱和渗透系数增大,滞后效应逐渐减弱; 降雨强度越大、初始地下水位越高,滞后效应越明显。本文的研究成果能为非饱和黄土地区框架预应力锚杆柔性支护结构考虑降雨影响的设计和施工提供指导。     

Some analytical results on lateral dynamic stiffness for footings supported on hysteretic soil medium

The nonlinearity of the soil affects soil–structure interaction to a considerable extent. For a reliable and safe analysis of soil interaction effects on the dynamic response of structures, a more realistic and relatively straightforward method incorporating the nonlinear hysteretic nature of the underlying soil–foundation system needs to be developed. The present paper models the soil–foundation system as a single degree of freedom spring–dashpot system with nonlinear hysteresis in form of elasto-perfectly plastic behavior. Analytical results for the lateral dynamic stiffness on footing have been presented. An example study has been carried out in case of circular footings. It is shown how the analytical results can be used to get a preliminary idea of the lateral dynamic stiffness of footings on a soil medium prior to a detailed computational geo-mechanics analysis provided the static nonlinear load–deformation characteristic of the soil medium is known and can be modeled by a hysteretic elasto-plastic behavior. The corresponding results are presented in a graphical form. The results have been computed showing parametric variations with the change in the amplitude and dimensionless frequency of the non-dimensional excitation force. Analytical results are also presented for the asymptotic cases at low and very high values of dimensionless frequency parameter.     

Spatial contributions of diffuse inputs and within-channel processes to the form of stream water phosphorus over storm events

Concentrations of suspended particulate matter (SPM), NO₃-N and P fractions: PO₄-P, dissolved organic P (DOP), particulate P (PP) and bioavailable exchangeable P were examined over 5 storm events in two nested agricultural catchments in NE Scotland: a (51 km²) catchment and its headwater (4 km²). NO₃-N showed anticlockwise hysteresis for all storms in both catchments. In contrast, the headwater showed strong clockwise hysteresis of SPM, dissolved and particulate P concentrations, but which weakened through summer to spring. Less pronounced hysteresis of P forms in the larger catchment was attributed to a combination of factors: a less energetic system, nutrient leaching from the floodplain, a point source of a small sewage treatment works and the occurrence of coarser soil and sediment parent materials with less P adsorption and transport capacity. The headwater exhibited a strong ‘first flush’ effect of sediment and dissolved P, particularly following dry conditions, received a significant transfer of readily-solubilized organic P from the surrounding soils in late summer and after manure applications in winter, and was the likely cause of large sediment associated P signals observed in the 51 km² catchment. Our results suggest that steeper gradient headwaters should be targeted for riparian improvements to mitigate soil erosion from headwater fields. The efficiency of riparian erosion controls is also dependant on the size of the store of fine sediment material within the stream channel and this may be large.     

DEPTH-AVERAGE ANALYSIS OF HYSTERESIS BETWEEN FLOW AND SEDIMENT TRANSPORT UNDER UNSTEADY CONDITIONS

1 INTRODUCTION Flow and sediment transport in natural rivers are generally unsteady, and exhibit temporal and spatial lags. Traditionally, in most hydraulic engineering problems the unsteady flow and sediment transport are approximately treated as steady …     

考古标本岩石磁性的初步研究

讨论了考古标本中所含矿物的磁学性质与古代地球磁场强度测定数据可靠性之间的关系,进行了岩石磁学实验,包括高温、低温磁化率测定、居里温度测定、磁滞回线各参数的测定等．结果表明,文中所用各类标本（陶片、砖、烧土等）的主要载磁矿物为磁铁矿,采用这些标本用Ｔｈｅｌｌｉｅｒ方法进行逐步热退磁实验所测定的古强度数据较为可靠．     

Automatic calibration of soil–water characteristic curves using genetic algorithms

An automatic technique for the determination of the coefficients of models for soil–water characteristic curves (SWCC) or water retention curves (WRC) is presented. The technique is based on optimisation using genetic algorithms, in which the error between predictions and experimental data is minimised by varying the model parameters. The method is powerful and reasonably efficient in finding the best parameters. Four models are analysed including one accounting for hysteresis behaviour. Details of a simple genetic algorithm (SGA) and its complete application are explained. To account for the hysteresis of the SWCC, the models are programmed in a rate form, in which numerical integration is employed to advance the state variables. One advantage of the optimisation presented is that the best curves averaging both the drying and wetting paths are obtained when hysteresis is present.     

循环荷载下饱和岩石的滞后和衰减

通过对饱和砂岩和大理岩的循环荷载实验,分析了饱和岩石在循环荷载下的应力-应变滞后回线、瞬时杨氏模量、泊松比的“X”形变化曲线,以及杨氏模量随应变振幅的增加而减少等滞后现象,并分析了施加外力的应变振幅对衰减的影响,认为岩石在循环荷载作用下的衰减与应变振幅成正比,提出的衰减b值反映了岩石在循环荷载作用下衰减的程度. 岩石的衰减和滞后存在密切的关系,通过饱和岩石的宏观行为,探讨了饱和岩石在循环荷载下的滞后和衰减现象的微观机理,认为孔隙流体流动在岩石的滞后和衰减中起着重要作用,岩石内部的颗粒接触粘合和黏滑摩擦可能是孔隙岩石在循环荷载作用下产生滞后和衰减的原因.