利用细模态气溶胶光学厚度估计PM2.5

本文利用2013年1月AERONET北京站的气溶胶光学深度(AOD)、气溶胶细模态比例(η)以及地面监测的细颗粒物质量浓度(PM2.5)数据建立AODf与PM2.5的线性回归关系,并利用2013年2月1-15日验证该方法。结果表明,利用2013年1月建立的回归方法能够有效估算灰霾期间细颗粒物质量浓度,获得PM2.5的均值为85μg/m3,均方根误差为50μg/m3。利用气溶胶细模态订正方法估算的灰霾组分气溶胶光学深度(AODf)与细颗粒物质量浓度的相关系数大于气溶胶总光学深度与PM2.5的相关系数,这表明灰霾期间以PM2.5为代表的细模态颗粒物成为气溶胶消光的主体,且AOD与PM2.5的关系转化为AODf与PM2.5的相关关系时,相关程度提高。垂直分布修正在灰霾时对改善AOD与PM2.5相关关系作用不明显;当相对湿度大于80%时,湿度订正效果受到较大限制。     

Effect of Initial Stress Conditions on the Threshold Shear Strain of Nanjing＇s Saturated Fine Sand

By using GDS dynamic hollow cylinder torsional apparatus,a series of cyclic torsional triaxial tests under complex initial consolidation condition are performed on Nanjing saturated fine sand. The effects of the initial principal stress direction α0,the initial ratio of deviatoric stress η0,the initial average effective principal stress p0 and the initial intermediate principal stress parameter b0 on the threshold shear strain γt of Nanjing saturated fine sand are then systematically investigated. The results show that γt increases as η0,p0 and b0 increase respectively,while the other three parameters remain constant. α0 has a great influence on γt,which is reduced when α0 increases from 0° to 45° and increased when α0 increases from 45° to 90°. The effect of α0 on γt plays a leading role and the effect of η0 will weaken when α0 is approximately 45°.     

Air–water two-phase flow modeling of turbulent surf and swash zone wave motions

Wave breaking and wave runup/rundown have a major influence on nearshore hydrodynamics, morphodynamics and beach evolution. In the case of wave breaking, there is significant mixing of air and water at the wave crest, along with relatively high kinetic energy, so prediction of the free surface is complicated. Most hydrodynamic studies of surf and swash zone are derived from single-phase flow, in which the role of air is ignored. Two-phase flow modeling, consisting of both phases of water and air, may be a good alternative numerical modeling approach for simulating nearshore hydrodynamics and, consequently, sediment transport. A two-phase flow tool can compute more realistically the shape of the free surface, while the effects of air are accounted for. This paper used models based on two-dimensional, two-phase Reynolds-averaged Navier–Stokes equations, the volume-of-fluid surface capturing technique and different turbulence closure models, i.e., k–ε, k–ω and re-normalized group (RNG). Our numerical results were compared with the available experimental data. Comparison of the employed method with a model not utilizing a two-phase flow modeling demonstrates that including the air phase leads to improvement in simulation of wave characteristics, especially in the vicinity of the breaking point. The numerical results revealed that the RNG turbulence model yielded better predictions of nearshore zone hydrodynamics, although the k–ε model also gave satisfactory predictions. The model provides new insights for the wave, turbulence and means flow structure in the surf and swash zones.     

Pore water pressure increment model for saturated Nanjing fine sand subject to cyclic loading

Three groups of dynamic triaxial tests were performed for saturated Nanjing fine sand subjected to uniform cyclic loading. The tested curves of the excess pore water pressure (EPWP) ratio variation with the ratio of the number of cycles are provided. The concept of the EPWP increment ratio is introduced and two new concepts of the effective dynamic shear stress ratio and the log decrement of effective stress are defined. It is found that the development of the EPWP increment ratio can be divided into three stages: descending, stable and ascending. Furthermore, at the stable and ascending stages, a satisfactory linear relationship is obtained between the accumulative EPWP increment ratio and natural logarithm of the effective dynamic shear stress ratio. Accordingly, the EPWP increment ratio at the number of cycles N has been deduced that is proportional to the log decrement of effective stress at the cycle number N-1, but is independent of the cyclic stress amplitude. Based on the analysis, a new EPWP increment model for saturated Nanjing fine sand is developed from tested data fitting, which provides a better prediction of the curves of EPWP generation, the number of cycles required for initial liquefaction and the liquefaction resistance.     

遥感与化探信息在川西北地区找矿中的应用

四川省西北部是我国岩金矿床分布的重点地区之一,尤以微细浸染型金矿床为主.该区有刷经寺联合村、嘎拉、金木达等大中型与超大型金矿床,充分显示出金矿成矿的良好前景.在对区域成矿规律及成矿条件的认识基础上充分利用遥感技术,建立了以NW、E-W及近S-N向为主的区域构造格架,优化了蚀变信息提取方案.结合区域化探特征建立了区域遥感及地球化学综合找矿模式.综合区域遥感、地质、化探信息,利用GIS进行了预测选区.     

淄博市大气降尘矿物组合特征及其环境意义

用多晶X-射线衍射法对淄博市中心城区逐月采集的大气降尘矿物组成及其含量进行了分析。研究结果表明:淄博市大气降尘的矿物组合比较稳定,降尘中以源于自然成因的石英、长石和粘土质矿物为主,质量分数变化范围为59.1%～95.1%。降尘中的石膏和方解石与大气化学反应有关,其中石膏质量分数为36.3%～1.0%,反映了大气SO₂污染具有明显的时间性特征。降尘中的赤铁矿源于高温工业活动,含量变化幅度最小。气象因素可能是导致降尘中石膏含量变化的主要原因,降尘中石膏含量的变化是大气酸污染程度的重要矿物指示剂。     

饱和南京细砂孔压增量模型的普适性研究

循环荷载作用下饱和砂土的孔压增长规律是土动力学的核心内容之一。基于笔者在给定相对密度、均等固结条件下饱和南京细砂的不排水等幅循环三轴试验结果建立的孔压增量模型,进一步进行了不同相对密度、不同固结比条件下饱和南京细砂的不排水等幅循环三轴试验,将上述均等固结的孔压增量模型拓展为适用于不同相对密度、均等和非均等固结条件的孔压增量模型。采用拓展后的孔压增量模型对试验结果进行分析的结果表明：通过该孔压增量模型预测验证试验的孔压与验证试验测试的孔压具有较好的一致性,说明该孔压增量模型具有普适性。     

Runoff initiation in a preserved semiarid Caatinga small watershed,Northeastern Brazil

This study analyses some hydrological driving forces and their interrelation with surface‐flow initiation in a semiarid Caatinga basin (12 km²), Northeastern Brazil. During the analysis period (2005 – 2014), 118 events with precipitation higher than 10 mm were monitored, providing 45 events with runoff, 25 with negligible runoff and 49 without runoff. To verify the dominant processes, 179 on‐site measurements of saturated hydraulic conductivity (Ksat) were conducted. The results showed that annual runoff coefficient lay below 0.5% and discharge at the outlet has only occurred four days per annum on average, providing an insight to the surface‐water scarcity of the Caatinga biome. The most relevant variables to explain runoff initiation were total precipitation and maximum 60‐min rainfall intensity (I₆₀). Runoff always occurred when rainfall surpassed 31 mm, but it never occurred for rainfall below 14 mm or for I₆₀ below 12 mm h^?1. The fact that the duration of the critical intensity is similar to the basin concentration time (65 min) and that the infiltration threshold value approaches the river‐bank saturated hydraulic conductivity support the assumption that Hortonian runoff prevails. However, none of the analysed variables (total or precedent precipitation, soil moisture content, rainfall intensities or rainfall duration) has been able to explain the runoff initiation in all monitored events: the best criteria, e.g. failed to explain 27% of the events. It is possible that surface‐flow initiation in the Caatinga biome is strongly influenced by the root‐system dynamics, which changes macro‐porosity status and, therefore, initial abstraction. Copyright © 2016 John Wiley & Sons, Ltd.     

Predicting physical equations of soil detachment by simulated concentrated flow in Ultisols (subtropical China)

Soil detachment in concentrated flow is due to the dislodging of soil particles from the soil matrix by surface runoff. Both aggregate stability and shear strength of the topsoil reflect the erosion resistance of soil to concentrated runoff, and are important input parameters in predicting soil detachment models. This study was conducted to develop a formula to predict soil detachment rate in concentrated flow by using the aggregate stability index (As), root density (R_d) and saturated soil strength (σ_s) in the subtropical Ultisols region of China. The detachment rates of undisturbed topsoil samples collected from eight cultivated soil plots were measured in a 3.8 m long, 0.2 m wide hydraulic flume under five different flow shear stresses (τ = 4.54, 9.38, 15.01, 17.49 and 22.54 Pa). The results indicated that the stability index (As) was well related with soil detachment rate, particularly for results obtained with high flow shear stress (22.54 Pa), and the stability index (As) has a good linear relationship with concentrated flow erodibility factors (K_c). There was a positive linear relationship between saturated soil strength (σ_s) and critical flow shear stress (τ_c) for different soils. A significant negative exponential relationship between erodibility factors (K_c) and root density (R_d) was detected. This study yielded two prediction equations that allowed comparison of their efficiency in assessing soil detachment rate in concentrated flow. The equation including the root density (R_d) may have a better correlation coefficient (R² = 0.95). It was concluded that the formula based on the stability index (As), saturated soil strength (σ_s) and root density (R_d) has the potential to improve methodology for assessing soil detachment rate in concentrated flow for the subtropical Chinese Ultisols. Copyright © 2012 John Wiley & Sons, Ltd.