一次夏季雷暴天气过程中闪电活动特征分析

利用探空资料、多普勒天气雷达和闪电定位仪数据,分析了2009年7月30日发生在南京地区一次雷暴天气过程的雷达及闪电数据时空演变特征。结果表明：对流有效位能Ecap比起K指数（IK）等对于对流潜势预报具有更明显的指示作用,0 ℃层和-10 ℃层高度的降低有利于雷暴云的雷电活动;整个过程以负闪为主导,闪电强度越大,闪电频数也越高,每次闪电峰值后,都对应一次谷值;闪电数据与多普勒天气雷达回波叠加后分析发现,回波的生消演变对应着闪电频数和强度的生消演变,负闪主要落在强回波中心区域,正闪零星分布于回波强度梯度较大的区域;雷达径向速度图像特征变化更能揭示闪电发生发展的机制,逆风区对应雷暴中心区域,不仅是强降水的中心区也是闪电的中心区,对逆风区的识别监测能够更好的指导雷暴预警报工作;利用雷达数据计算的云底动能施力参量,能够很好的描述支持闪电起电的热动力特征,云底动能施力对雷电增长的贡献有一段持续传输过程,该参量峰值比频闪峰值和强度峰值都约有0.5 h的提前量。     

Using Chlorine Dioxide to Remove the Fouling of Ultrafiltration Membrane and Control Disinfection By‐Products

Ultrafiltration (UF) can remove natural organic matter (NOM) effectively. Moreover, chlorine dioxide (ClO₂) has been an alternative disinfectant as it forms fewer disinfection by‐products with NOM than chlorination does. Therefore, combining ClO₂ with UF may improve conventional purification processes. In this study, feed water containing humic acid with 4.07 mg/L total organic carbon (TOC) was dosed directly with various amounts of ClO₂ (0, 2, 5, 10, and 15 mg/L) before being filtered through a 5‐kDa UF membrane. With a low dose (2 mg/L ClO₂), UF removed humic acid effectively, as TOC was not detected in the permeate, and the permeate flux increased to about 80% of the initial permeate flux by cross flow. Moreover, the concentrations of ClO, ClO, and trihalomethanes in the permeate were below the United States Environmental Protection Agency guidelines.     

“I Still Have the Old Tradition”: The co-production of sweetgrass basketry and coastal development

Scholars working around the world have drawn attention to the physical and social changes associated with rural gentrification. Case studies from the United States have focused on how these patterns lead to the cultural displacement and replacement of land-based livelihoods, including non-timber forest product (NTFP) practices. Scholars have also documented the persistence of culturally and economically important NTFP practices in urban and suburban areas. We reconcile these disparate outcomes, displacement on the one hand and persistence on the other, by focusing on the social relationships that co-produce land use and livelihood change. Our case investigates how African American sweetgrass basketmakers in Mount Pleasant South Carolina negotiate the complex terrain of a rapidly urbanizing and gentrifying landscape.Analysis of interviews with basketmakers and participant observation at public meetings suggests that gathering materials and selling baskets occur across spaces not typically considered important for NTFP practices. Access to these sites depends upon continually reinforced and negotiated social relationships between a variety of actors. Findings illustrate that, by themselves, development and gentrification are insufficient for explaining livelihood and land use patterns that emerge in places experiencing intensive development. Using a co-production framework, we acknowledge the wide variety of complex trajectories and local power dynamics shaping land use and livelihoods. Findings also have implications for connecting global research on housing, employment, and demographic transitions associated with rural gentrification, to international NTFP research, which is increasingly turning to rural–urban interfaces for insights on how livelihoods are linked to land development and migration.     

粉细砂的真三轴试验与强度特性

采用柔性真三轴仪对上海粉细砂进行了一系列不同中主应力系数条件下的真三轴试验,针对中主应力对粉细砂强度特性的影响进行了系统分析。基于真三轴试验结果对Mohr-Coulomb强度准则的形状函数进行了改进,并采用试验结果对强度准则进行验证。结果表明,建立在真三轴试验基础上的强度准则能更准确地反映砂土三维应力状态下的强度特性。     

真三维状态下土体强度及变形分叉影响

通过引入应力Lode角建立合理的角隅函数描述偏平面形状,对三维Mohr-Coulmb强度准则进行修正,使之能合理反映中主应力比对土体峰值内摩擦角的影响。修正后的准则在偏平面上的强度线与Lade-Duncan准则相似,但更具灵活性,预测结果更符合松砂真三轴试验结果。由于土体在加载过程中常发生应变局部化现象,导致其强度得不到充分发挥。基于非共轴塑性模型的分叉分析研究了应变局部化发生对土体强度发挥的影响,通过与密砂真三轴试验结果对比表明,分叉强度能合理反映在不同中主应力比条件下应变局部化发生对土体强度的降低作用。     

浙江慈溪市土地生态质量调查和评估

土壤、大气、水和农产品质量共同构成土地生态质量的内涵。通过慈溪市基本农田质量调查试点项目,开展了高精度土壤地球化学调查和农产品、灌溉水、大气质量调查,建立了土地生态质量评估模型。以土壤地球化学质量评估为基础,进行了大气、水、农产品综合质量评估,以及慈溪市农用地土地生态质量评价。评价显示,慈溪市农用地土地生态质量绝大部分优良,只有局部如城市周边等地存在生态风险。试点成果为浙江省国土资源特别是基本农田的数量、质量和生态管护并重的精细化管理提供了示范和依据。     

水环境及水产品中汞的测定与形态分析进展

概要总结了世界各地对水环境及水产品中汞的测定与形态分析的研究成果,涵盖样品采集、储存、传递与处理,各种色谱(薄层色谱、气相色谱、液相色谱、电色谱和离子色谱)分离分析方法及其联用技术,以及分光光度法、电化学法、原子吸收光谱和原子荧光光谱的应用等。并对未来发展提出了改进建议。     

青海省锶产品发展思考

锶是一种十分活泼的碱土金属,随着世界工业技术的不断发展,锶的使用领域也随之逐步扩大。锶及锶的化合物用途广泛,是发展高新技术不可缺少的重要材料。青海省锶资源极为丰富,应充分发挥锶资源的优势,采用国内外先进技术,提高资源综合利用率,积极发展锶产品的深加工,逐步形成锶工业产业链,提高产品的附加值,满足市场需要,变资源优势为经济优势,形成新的经济增长点。     

基于NDIS-HOOK技术的个人防火墙的研究与实现

介绍了NDIS系统结构以及在Windows 2000/NT下NDIS-HOOK的原理,并给出了一个基于NDIS-HOOK技术的个人防火墙驱动程序--Packet.sys.利用该驱动程序,可方便地实现基于Windows的个人防火墙.     

锡林浩特草原区域MODIS LAI产品真实性检验与误差分析

本文研究了LAI产品真实性检验的指标和方法,建立了LAI产品真实性检验的流程,将遥感产品真实性检验误差分解为模型误差、数据定量化差异和尺度效应3个方面。以内蒙古锡林浩特草原为研究区,结合实测数据和Landsat TM数据建立NDVI-LAI模型,得到LAI验证参考"真值",据此"真值"按照本文的流程对MODIS LAI产品进行验证,分析了研究区MODIS LAI产品真实性检验的误差来源。研究表明,该研究区的MODIS LAI(MOD15A2)产品相对高估约25%。各个误差因素中,LAI遥感模型差异对于结果影响最大,MODIS LAI模型高估了该区域草地LAI(高估约44.2%);数据定量差异的影响也比较大,MODIS地表反射率数据与Landsat TM地表反射率数据的差异造成了约16.2%的低估;尺度效应的影响较小,造成约3.1%的低估,其中NDVI-LAI模型的尺度效应带来2.4%的低估,NDVI数据的尺度效应造成约0.7%的低估。