三维荧光与神经网络研究城市河流沉积物孔隙水有机物组成与结构特征

应用三维荧光技术结合自组织神经网络方法,研究典型城市河流沉积物孔隙水中水溶性有机物(DOM)与颗粒性有机物(POM)组成结构及空间分布特征。自组织神经网络是一种非监督神经网络算法,能够从有机物三维光谱中提取不同的荧光组分,表征各组分的含量。沉积物是重要的有机碳库,而沉积物孔隙水中有机物的多寡可直接反映其环境特征。人们对水体中沉积物孔隙水中的DOM与营养盐特征的研究较多,而对POM的研究较少,尤其对重污染城市支流河的研究更少。因此,选取沈阳市白塔堡河为研究对象,沿河源、农村、城市区域河段采集沉积物孔隙水样品,提取DOM与POM,检测样品的三维荧光光谱。DOM的f_450/500值为1.82～1.91,表明DOM主要是微生物源;POM的f_450/500值为1.42～1.68,表明POM主要以陆地输入为主。自组织神经网络解析DOM与POM含有类酪氨酸、类色氨酸、类富里酸与类胡敏酸等物质,类酪氨酸主要源于新鲜的具有高氧化的类蛋白物质,而类色氨酸主要为微生物代谢产物。DOM的各组分丰度之和为POM的2倍,类酪氨酸平均相对丰度在50%以上,类色氨酸的平均相对丰度为18.8%～23.1%,类富里酸相对丰度比类胡敏酸的高,但两者在有机物组分所占比重小。通过主成分分析,DOM与POM特征呈现沿河源、农村、城市区域河段变化,表明白塔堡河深受人类活动的影响。     

基于多元统计的居民消费水平评价模型及应用

为解决传统主成分分析在消费水平评价应用中的局限性,对传统主成分方法作了改进,建立一种新的评价模型,利用此模型对青海城镇居民消费水平进行评价.结果表明:这是一种适合于居民消费水平综合定量评价且切实有效的方法模型,有较强的实践价值.     

Modeling cities

Cities are systems with a large number of constituents and agents interacting with each other and can be considered as emblematic of complex systems. Modeling these systems is a real challenge and triggered the interest of many disciplines such as quantitative geography, spatial economics, geomatics and urbanism, and more recently physics. (Statistical) Physics plays a major role by bringing tools and concepts able to bridge theory and empirical results, and we will illustrate this on some fundamental aspects of cities: the growth of their surface area and their population, their spatial organization, and the spatial distribution of activities. We will present state-of-the-art results and models but also open problems for which we still have a partial understanding and where physics approaches could be particularly helpful. We will end this short review with a discussion about the possibility of constructing a science of cities.     

城市工程地质问题的经济分析

随着城市建设步伐的加快, 人类已面临着许多城市工程地质问题, 此类问题一旦形成则造成经济损失, 预防其发生则需要代价。本文从城市工程地质问题的经济分析着手, 对城市建设的成本进行了研究, 对城市规划、城市建设和城市管理具有现实意义。     

Current trends and analytical methods for evaluation of microplastics in stormwater

Stormwater runoff is an important source of microplastics (plastic particles <5 mm) into the aquatic environment and studies documenting the microplastics abundance and their characteristics are constantly expanding. The lack of standardized methods as well as the development of many analytical techniques to evaluate microplastics greatly influence reported results and calls for a better understanding of approaches adopted by microplastic studies in stormwater. Hence, this paper aims to systematically review currently employed methods for sampling, isolating and identifying microplastics and to summarize the data on the abundance of microplastics in the samples of water, sediment and biota collected from stormwater, stormwater catchment areas and stormwater discharging sites. There were significant methodological variations between the studies throughout the experimental procedures and different techniques including, sieving, digestion (chemical and enzyme), density separation and filtration were reported for microplastics extraction from sample matrix. A combination of visual sorting and spectroscopic approaches such as infrared and Raman was adopted to identify and study microplastic characteristics such as shape, size, color and polymer. The microplastic abundance in each sample matrix was different with relatively high concentrations of smaller size particles (10−500 μm), majorly fibrous shaped (51 %) and polymers of polypropylene (27 %) and polyethylene (26 %). Finally, we conclude by identifying analytical challenges and suggesting appropriate methods that can be implemented to enable effective monitoring and comparison of microplastic contamination in stormwater.     

Efficient Generation of Inflow Conditions for Large Eddy Simulation of Street-Scale Flows

Using a numerical weather forecasting code to provide the dynamic large-scale inlet boundary conditions for the computation of small-scale urban canopy flows requires a continuous specification of appropriate inlet turbulence. For such computations to be practical, a very efficient method of generating such turbulence is needed. Correlation functions of typical turbulent shear flows have forms not too dissimilar to decaying exponentials. A digital-filter-based generation of turbulent inflow conditions exploiting this fact is presented as a suitable technique for large eddy simulations computation of spatially developing flows. The artificially generated turbulent inflows satisfy the prescribed integral length scales and Reynolds-stress-tensor. The method is much more efficient than, for example, Klein’s (J Comp Phys 186:652–665, 2003) or Kempf et al.’s (Flow Turbulence Combust, 74:67–84, 2005) methods because at every time step only one set of two-dimensional (rather than three-dimensional) random data is filtered to generate a set of two-dimensional data with the appropriate spatial correlations. These data are correlated with the data from the previous time step by using an exponential function based on two weight factors. The method is validated by simulating plane channel flows with smooth walls and flows over arrays of staggered cubes (a generic urban-type flow). Mean velocities, the Reynolds-stress-tensor and spectra are all shown to be comparable with those obtained using classical inlet-outlet periodic boundary conditions. Confidence has been gained in using this method to couple weather scale flows and street scale computations.     

Comparison of two- and three-dimensional modeling of invert trap for sewer solid management

In the present study, five different invert trap configurations （rectangular with and without lids on both sides; trapezoidal, trapezoidal with rectangular base and rectangular with trapezoidal base with lids on both sides） were simulated for both two-dimensional （2D） and three-dimensional （3D） flow conditions for three sediment types （sand, styrocell and plastic beads） at six flow rates （0.35, 0.70, 1.05, 1.35, 4.55 and 9.95 L/s） for each trap. Computational fluid dynamics （CFD）-based modeling using FLUENT software with Renormalization Group （RNG） k-e model along with discrete phase model （DPM） were used in the simulations. A hexagonal/tetrahedral and map-type non-uniform grid was chosen to discretize the entire computational domain and a control volume finite difference method was used to solve the governing equations. The flow rates selected in the present study cover the entire range of flow rate expected for dry weather and monsoon. The simulation is capable of differentiating between 2D and 3D modeling of particle trajectories, the effects of flow rate and trap geometry on flow patterns developed in the trap. The sediment retention ratio for 2D is higher than that for 3D modeling for all flow conditions, particle types and model geometry due to inclusion of lateral effects in 3D modeling. The invert trap having rectangular shape with trapezoidal base is found to be the most efficient configuration in both 2D and 3D modeling.     

Comparison of two-and three-dimensional modeling of invert trap for sewer solid management

In the present study, five different invert trap configurations (rectangular with and without lids on both sides; trapezoidal, trapezoidal with rectangular base and rectangular with trapezoidal base with lids on both sides) were simulated for both two-dimensional (2D) and three-dimensional (3D) flow conditions for three sediment types (sand, styrocell and plastic beads) at six flow rates (0.35, 0.70, 1.05, 1.35, 4.55 and 9.95L/s) for each trap. Computational fluid dynamics (CFD)-based modeling using FLUENT software with Renormalization Group (RNG) k-ε model along with discrete phase model (DPM) were used in the simulations. A hexagonal/tetrahedral and map-type non-uniform grid was chosen to discretize the entire computational domain and a control volume finite difference method was used to solve the governing equations. The flow rates selected in the present study cover the entire range of flow rate expected for dry weather and monsoon. The simulation is capable of differentiating between 2D and 3D modeling of particle trajectories, the effects of flow rate and trap geometry on flow patterns developed in the trap. The sediment retention ratio for 2D is higher than that for 3D modeling for all flow conditions, particle types and model geometry due to inclusion of lateral effects in 3D modeling. The invert trap having rectangular shape with trapezoidal base is found to be the most efficient configuration in both 2D and 3D modeling.     

A review of heavy metal contaminations in urban soils, urban road dusts and agricultural soils from China

This paper reviews quite a few heavy metal contamination related studies in several cities from China over the past 10 years. The concentrations, sources, contamination levels, sample collection and analytical tools of heavy metals in urban soils, urban road dusts and agricultural soils were widely compared and discussed in this study. The results indicate that nearly all the concentrations of Cr, Ni, Cu, Pb, Zn, As, Hg and Cd are higher than their background values of soil in China. Among the cities, the contamination levels of the heavy metals vary in a large range. The geoaccumulation index shows that the contamination of Cr, Ni, Cu, Pb, Zn and Cd is widespread in urban soils and urban road dusts of the cities. Generally, the contamination levels of Cu, Pb, Zn and Cd are higher than that of Ni and Cr. Agricultural soils are also significantly influenced by Cd, Hg and Pb derived from anthropogenic activities. The integrated pollution index (IPI) indicates that the urban soils and urban road dusts of the developed cities and the industrial cities have higher contamination levels of the heavy metals. The comparison of the IPIs of heavy metals in urban soils and urban road dusts of Shanghai, Hangzhou, Guangzhou and Hongkong reveals that the contamination levels of the metals in urban road dusts are higher than that in urban soils in the cities. Moreover, the main sources of the metals in urban soils, urban road dusts and agricultural soils are also different.     

半覆水相变V形峡谷场地P波入射下的空间地震动散射频域理论解、验证及特征

克服介质相变、峡谷分层且局部地形覆水导致的固有边界值难题,首次推导并得到了半覆水相变V形峡谷场地对P波激励下的散射理论解,验证理论解的正确性,探究了相变界面的有无、入射波频率和入射角对地表位移的显著影响,突出并重点强调了覆水因素对结果影响的不可忽视性。分析结果表明,(1)以经典算例为标准,对比验证了本文理论解的正确性,解释并澄清了峡谷局部可预测性的微小偏差的来源。(2)与未覆水部位相比,峡谷覆水部位表面位移显著增大;与峡谷满水状态相比,相变面的存在使位移增大的初始位置向峡谷中间移动;不同的入射波频率和入射角下,地面运动情况存在显著差异,随着入射角的增大,水平方向的位移逐渐增大,竖直方向的位移逐渐减小。本文研究可为覆水V形峡谷的长大结构多点地震动的合理输入提供基础性研究依据,兼有理论意义与应用价值。