Influence of aggregate pre-wetting and fly ash on mechanical properties of lightweight concrete

This study has examined the mechanical properties of lightweight aggregate concrete with a density of 1800 kg/m3. The effects of the following parameters on the concrete properties have been analyzed: the pre-wetting time of the lightweight aggregate and the percentage of pulverized fly ash used as cementitious replacement material. The strength of the lightweight aggregate was found to be the primary factor controlling the strength of high-strength lightweight concrete. An increase in the cementitious content from 420 to 450 kg/m3 does not significantly increase the strength of lightweight aggregate concrete. The relationship between the flexural and compressive strength at 28 days can be represented by the equation fr=0.69/fck. The elastic modulus was found to be much lower than that of normal weight concrete, ranging from 15.0 to 20.3 GPa. The addition of PFA increases the slump and density of lightweight aggregate concrete.     

Evaluation of leachate recirculation on nitrous oxide production in the Likang Landfill,China

Landfill leachate recirculation is efficient in reducing the leachate quantity handled by a leachate treatment plant. However, after land application of leachate, nitrification and denitrification of the ammoniacal N becomes possible and the greenhouse gas nitrous oxide (N2O) is produced. Lack of information on the effects of leachate recirculation on N2O production led to a field study being conducted in the Likang Landfill (Guangzhou, China) where leachate recirculation had been practiced for 8 yr. Monthly productions and fluxes of N2O from leachate and soil were studied from June to November 2000. Environmental and chemical factors regulating N2O production were also accessed. An impermeable top liner was not used at this site; municipal solid waste was simply covered by inert soil and compacted by bulldozers. A high N2O emission rate (113 mg m-2 h-1) was detected from a leachate pond purposely formed on topsoil within the landfill boundary after leachate irrigation. A high N2O level (1.09 micrograms L-1) was detected in a gas sample emitted from topsoil 1 m from the leachate pond. Nitrous oxide production from denitrification in leachate-contaminated soil was at least 20 times higher than that from nitrification based on laboratory incubation studies. The N2O levels emitted from leachate ponds were compared with figures reported for different ecosystems and showed that the results of the present study were 68.7 to 88.6 times higher. Leachate recirculation can be a cost-effective operation in reducing the volume of leachate to be treated in landfill. However, to reduce N2O flux, leachate should be applied to underground soil rather than being irrigated and allowed to flow on topsoil.     

Measurements of sulfur dioxide and formaldehyde in Taipei using a differential optical absorption spectrometer

Taipei, the capital city of Taiwan, lies in a basin, and its topography prevents the dispersion of pollutants in the city. As a continuation of our air quality study, from February 1999 through June 1999, we measured the concentrations of SO2 at six different locations and of formaldehyde at five locations using a differential optical absorption spectrometer (DOAS). The average concentration of SO2 varied from 3.5 to 6.6 ppb. The average concentration was highest at Toucheng because of its proximity to point sources. The level in Hsientien was close to that in Toucheng, with Hsinyu showing the lowest concentrations. The DOAS and the Taiwan Air Quality Monitoring Network (TAQMN) measurements for SO2 were highly correlated (r2 > 0.9) for Toucheng, Panchiao, and Hsientien. However, DOAS SO2 concentrations were 2 times higher for Hsientien and slightly lower for Panchiao than the TAQMN concentrations were. The average concentration of formaldehyde varied from 7 to 10 ppb. Diurnal variation of formaldehyde closely followed the variation of ozone, especially when the 1-hr peak ozone concentration was > 60 ppb. Photochemical formation accounted for the ambient levels of formaldehyde in Taipei. Concentration of formaldehyde became significant on days when O3 concentration was high. Our results indicate that DOAS can replace conventional measurement techniques.     

APPLICATION OF A SINGLE RESERVOIR OPERATION POLICY TO A RAIN WATER CISTERN SYSTEM1

The operation policy for a single reservoir is applied to a rain water cistern system because the functions of a cistern are similar to a simple single reservoir. Since the cistern is a closed system, water loss is negligible. In this study, a dynamic programming analysis has been made to study the effects of the probable weekly rainfall and the water storage in the cistern towards the water consumption policy. The result of this study indicates that the water consumption rate should be adjusted into a lower rate when the water storage in the cistern is low and/or when the expected probable weekly rainfall is low if the owner of the cistern does not want to risk the chance of an empty cistern. The demand for a reliable method for forecasting weekly rainfall is evident in this study.     

Groundwater protection on Long Island,New York: a study in management capacity

Through their powers to regulate land use and their responsibilities for public water supply, local governments are critical players in groundwater protection. Unfortunately, the demands of groundwater protection are high, and many local governments do not have the ability or capacity to develop and implement appropriate management strategies. This paper analyzes groundwater protection experiences on Long Island, New York, a place where groundwater dependence is high, and threats to groundwater are serious. Long Island's experiences highlight the need to approach capacity building for groundwater protection broadly, concentrating on factors such as political commitment and citizen support; enhancement of local technical competency through linkages and support from state and federal governments; and strengthening of institutional arrangements at all levels.     

Determination of volatile organic compounds in workplace air by multisorbent adsorption/thermal desorption-GC/MS

Investigation of volatile organic compounds (VOCs) was first conducted in the air of class-100 cleanrooms at liquid crystal display (LCD) fabrication facilities. Air samples were collected on multisorbent tubes (including Carbopack B, Carbopack C, and Carbosieve S-III) and analyzed using adsorption/thermal desorption coupled with gas chromatography-mass spectrometry (GC-MS). Optimal conditions lead to average recoveries in the range of 96.2-98.2%, and method detection limits between 0.38 and 0.78 ppb, under the condition of 1-l sampling volume and 80% relative humidity. The method appears to be accurate, sensitive, simple and well-suited for determining VOC distributions from various stages of LCD manufacturing process and temporal variations of the analyte concentrations. About 15 VOCs were identified in workplace air. The major pollutants such as propylene glycol methyl ether acetate (PGMEA), butyl acetate, and acetone that are commonly used in the opto-electronics industry were detected and accurately quantified with the established method.     

决策科学与DSS

要实现科学管理,必须掌握决策的科学,并在决策过程中运用现代管理的基本工具——计算机,以辅助决策,提高组织效能。本文正是以“国家环境质量决策支持系统”为分析范例,从决策科学与DSS技术的结合上介绍了决策模式分析,决策模型建立和决策选择,综述了DSS概念,结构和建立初始系统,并通过自适应的设计和应用过程形成最终系统的开发方法。文中列举了一些国内外开发应用DSS的实例,并指出在高层次复杂决策问题上,目前的DSS支持手段还是比较薄弱的