Occurrence and formation potential of N-nitrosodimethylamine in ground water and river water in Tokyo

N-nitrosodimethylamine (NDMA), a disinfection byproduct of water and wastewater treatment processes, is a potent carcinogen. We investigated its occurrence and the potential for its formation by chlorination (NDMA-FP_2Cl) and by chloramination (NDMA-FP_2NHCl) in ground water and river water in Tokyo. To characterize NDMA precursors, we revealed their molecular weight distributions in ground water and river water. We collected 23 ground water and 18 river water samples and analyzed NDMA by liquid chromatography-tandem mass spectrometry. NDMA-FP_2Cl was evaluated by chlorinating water samples with free chlorine for 24 h at pH 7.0 while residual free chlorine was kept at 1.0-2.0 mgCl₂/L. NDMA-FP_2NHCl was evaluated by dosing water samples with monochloramine at 140 mgCl₂/L for 10 days at pH 6.8. NDMA precursors and dissolved organic carbon (DOC) were fractionated by filtration through 30-, 3-, and 0.5 kDa membranes. NDMA concentrations were <0.5-5.2 ng/L (median: 0.9 ng/L) in ground water and <0.5-3.4 ng/L (2.2 ng/L) in river water. NDMA concentrations in ground water were slightly lower than or comparable to those in river water. Concentrations of NDMA-FP_2Cl were not much higher than concentrations of NDMA except in samples containing high concentrations of NH₃ and NDMA precursors. The increased NDMA was possibly caused by reactions between NDMA precursors and monochloramine unintentionally formed by the reaction between free chlorine and NH₃ in the samples. NDMA precursors ranged from 4 to 84 ng-NDMA eq./L in ground water and from 11 to 185 ng-NDMA eq./L in river water. Those in ground water were significantly lower than those in river water, suggesting that NDMA precursors were biodegraded, adsorbed, or volatilized during infiltration. The molecular weight of NDMA precursors in river water was dominant in the <0.5 kDa fraction, followed by 0.5-3 kDa. However, their distribution was inconsistent in ground water: one was dominant in the <0.5 kDa fraction, and the other in 0.5-3 kDa. Molecular weight distributions of NDMA precursors were very different from those of DOC. This is the first study to reveal the widespread occurrence and characterization of NDMA precursors in ground water.     

周边场地及建筑物对地脉动测试影响的探讨

通过对福州地区场地土地脉动频谱结构的实测,由此来深入研究该地区场地土层的地脉动动力响应,以及周围场地及建筑物对其实测值的影响。场地地脉动测试影响     

浅谈基于性能/位移的抗震设计分析工具——静力弹塑性分析方法

首先介绍了静力弹塑性分析方法的基本假定及基本原理,然后较详细介绍了2类静力弹塑性分析方法并进行了比较分析,在此基础上论述了静力弹塑性分析方法的优点及有待完善的地方,最后指出了静力弹塑性分析方法的研究热点及发展前景。     

正确应用CAD软件提高建筑结构设计质量

针对CAD设计软件使用过程中出现的问题 ,结合PKPM系列微机建筑结构CAD系统软件的应用 ,指出了建筑结构设计中存在的问题 ,分析了产生问题的原因 ,提出了今后设计中应注意的问题     

粉喷桩复合地基承载力测试与探讨

粉喷桩复合地基承载力的确定 ,目前被公认为比较可靠的方法是现场静载荷试验。结合具体工程实测资料 ,分析和讨论现场静载荷试验确定复合地基承载力方法 ,寻求出更理想确定承载力的方法     

网架结构在悬挂荷载作用下的计算

本文对大柱网工业厂房网架屋盖下面设置悬挂吊车等移动荷载类型、网架结构在动、静荷载作用下内力计算及其组合,以及网架秆件疲劳问题进行了一些探讨,并对一些有关网架悬挂的问题提出了看法。     

儿童游乐场所的设计目标与创意

针对目前儿童游乐场的设计现状,设计师普遍存在的态度、观念和思路等问题,提出新的发展观念。通过对儿童喜欢的动画片的成功方式进行分析,总结各个年龄段儿童的特点、喜好、心理活动和行为方式,力图在不断理解儿童游戏特点的过程中探寻游戏的意义,找到能够给孩子们的成长带来积极影响的主题创意。通过一些实例提出摆脱目前贫乏无趣的游戏场模式,从而实现为儿童快乐生活和健康成长而创作的目标,设计出满足儿童需要的作品。     

大型贮水构筑物在湿陷性黄土上的地基处理

湿陷性黄土受水后会产生较大的不均匀沉降 ,从而会危害上部结构的安全。湿陷性黄土地基处理形式很多 ,不同场地、不同的结构形式对这样的地基处理有不同的要求。本文结合工程实例 ,针对大型贮水构筑物建造在湿陷性黄土地基上的地基处理方案选择和施工注意事项进行阐述     

工程勘察在地源热泵系统工程中的重要性

地源热泵系统所利用的热源主要位于地层浅部。它的存在具有普遍性的同时又具有隐蔽性和复杂性,从而决定了地源热泵系统进行工程勘察的必要性,本文从浅层地热能的赋存特征入手阐述工程勘察的必要性,并就工程勘察的程序及注意事项等问题进行了讨论,以希望有关勘察部门在进行地源热泵系统勘察和施工中有所借鉴。     

A new contribution to the finite line-source model for geothermal boreholes

Heat transfer around vertical ground heat exchangers is a common problem for the design and simulation of ground-coupled heat pump (GCHP) systems. Most models are based on step response of the heat transfer rate, and the superposition principle allows the final solution to be in the form of the convolution of these contributions. The step response is thus a very important tool. Some authors propose numerical tabulated values while others propose analytical solutions for purely radial problem as well as axisymmetric problems. In this paper we propose a new analytical model that yields results very similar to the tabulated numerical ones proposed in the literature. Analytical modeling offers better flexibility for a parameterized design.