Diurnal variation of dissolved gaseous mercury (DGM) levels in a southern reservoir lake (Tennessee, USA) in relation to solar radiation

Variations of dissolved gaseous mercury (DGM) concentrations in a southern reservoir lake (Cane Creek Lake, Cookeville, TN, USA) in relation to solar radiation were investigated consecutively from June 2003 to May 2004. The daytime DGM levels in the lake exhibited a two-phase diurnal trend; the DGM concentrations rose in the morning, peaked around noontime and then fell in the afternoon through the evening; these trends followed the general pattern of diurnal solar radiation variations. The morning and afternoon phases appeared to be asymmetrical with the former relatively steep and the latter gradual. A variety of daytime DGM level variations other than the typical two-phase diurnal patterns were also observed. For the time spans studied, the daytime mean DGM concentrations of the lake ranged from 12 to 68 pg L(-1) (60-340 fM). The daytime mean DGM levels in the summertime (June, July, August) showed values above 30 pg L(-1) (150 fM) in most cases and a large number of peak DGM concentrations above 50 pg L(-1) (250 fM). The summer DGM levels in the lake appear to be comparable to those observed in the large northern lakes for the summertime. The daytime DGM levels in the lake were found to correlate with solar radiation to various degrees (cases of r values above 0.8: approximately 12% and approximately 18% of the total sampling days for correlation with global solar radiation and UVA radiation, respectively). Correlating trends are recognizable between the daytime mean DGM concentration and the corresponding mean global solar radiation (r = 0.66, p < 0.0005) and between the daytime mean DGM concentration and the corresponding mean UVA radiation (r = 0.62, p < 0.0005).     

Study on two operating conditions of a full-scale oxidation ditch for optimization of energy consumption and effluent quality by using CFD model

The operating condition of an oxidation ditch (OD) has significant impact on energy consumption and effluent quality of wastewater treatment plants (WWTPs). An experimentally validated numerical tool, based on computational fluid dynamics (CFD) model, was proposed to optimize the operating condition by considering two important factors: flow field and dissolved oxygen (DO) concentration profiles. The model is capable of predicting flow pattern and oxygen mass transfer characteristics in ODs equipped with surface aerators and submerged impellers. Performance demonstration and comparison of two operating conditions (existing and improved) were carried out in two full-scale Carrousel ODs at the Ping Dingshan WWTP in Henan, China. A moving wall model and a fan model were designed to simulate surface aerators and submerged impellers, respectively. Oxygen mass transfer in the ditch was predicted by using a unit analysis method. In aeration zones, the mass inlets representing the surface aerators were set as one source of DO. In the whole straight channel, the oxygen consumption was modeled by using modified BOD-DO model. The following results were obtained: (1) the CFD model characterized flow pattern and DO concentration profiles in the full-scale OD. The predicted flow field values were within 1.98 ± 4.28% difference from the actual measured values while the predicted DO concentration values were within −4.71 ± 4.15% of the measured ones, (2) a surface aerator should be relocated to around 15 m from the curve bend entrance to reduce energy loss caused by fierce collisions at the wall of the curve bend, and (3) DO concentration gradients in the OD under the improved operating condition were more favorable for occurrence of simultaneous nitrification and denitrification (SND).     

中房大厦建筑设计构思

中房大厦是集商场、百货公司、写字楼、地下两层车库为一体的,具有国际水平的综合性设施。其建筑设计包括功能组织、技术、经济、交通、环境、造型等诸多方面的内容,建筑师应综合广泛的专业知识与新技术,全面考虑,统一安排。本文主要叙述该大厦在环境布局、功能分区、立面造型等方面的建筑设计与构思。     

The collapse of welded aluminium plate girders—an experimental study

Twenty-two tests conducted to study the collapse behaviour of welded aluminium girders are described. The girders are of varying proportions, have transverse or longitudinal web stiffeners and are subjected to different combinations of shear and bending loads. It is observed that, although shear sway mechanisms similar to those for steel girders do develop, the webs of aluminium girders may fracture in the heat affected zones adjacent to the perimeter welds. These fractures develop at some stage during the formation of the collapse mechanism and are the consequence, rather than the cause, of failure. It is shown that the tension field theory, originally developed for steel girders, may overestimate the shear-carrying capacity of aluminium girders and it is concluded that the theory requires some modification before it can be applied with confidence to aluminium girders.     

浙江省黄龙体育中心主体育场空调通风设计大型体育建筑空调设计系列之一

本文(设计系列之一)介绍了位于杭州市的浙江省黄龙体育中心的主体育场空调通风工程设计,包括设计标准的采用、空调型式、新风系统、排风系统、门厅排烟、空调水系统、以及系统调试、工程验收和存在问题的改进等。     

Central place theory and intercommunity input-output analysis

This paper explores trade hierarchies and interindustry relationships, first in theory, then in the empirical context of a western United States timber economy facing a large reduction in its timber harvest. Principles of central place theory guide construction of a hybrid intercommunity input-output model. A nonsurvey technique for estimating central place trade is developed, and is compared with MRIO methods. The effect of central place dominance on intercommunity multipliers is examined theoretically, as is the nature of feedback linkages in a central place hierarchy. The empirical magnitude of feedback effects is small, and although effects vary in magnitude from community to community, neglect of central place considerations can understate intercommunity sawmill multipliers by as much as 36 percent.     

维也纳机场消防员选择新式作训服

2004年对维也纳施威夏特机场(维也纳国际机场)消防部门来说是至关重要的一年。它需要用更安全、舒适、高效和耐用性能最高质作训服取代现有的服装。因此,消防部门开始对各厂家生产的作训服进行测试和评估。消防员作训服的要求之一就是服装要抗轰燃,即在保持舒适和结构完整的同时还要能够抵抗烈火的直接烧灼和高温的烘烤。获得认可的产品是由泰克斯珀特公司生产的以聚苯并咪脞为面料的防火两件套作训服。与众不同的是,表层材料聚苯并咪唑是抗静电和耐火的,能抗高温。泰克斯珀特首席执行官欧克玛·斯克奈德骄傲地介绍说:“即使是与大火直接接…     

盐碱地区大面积混凝土晒场裂缝原因及防治

夏季盐碱地区大面积现浇混凝土晒场完工一段时间后，往往易出现空鼓、隆起、变形裂缝。其原因与土壤性质、施工工艺、基层结构、现场条件以及混凝土自身收缩等因素有关。本文通过实例分析其裂缝产生的原因，并提出防治措施。