基于无线传感器网络的市政下水道可燃气体监测系统设计及应用

为防止下水道可燃气体积聚引发爆炸事故,利用无线传感器网络技术设计了市政下水道可燃气体监测系统.实测结果表明:气体传感器监测数据相对误差在2.0%以内,无线数据收发设备的年发送成功率达到98.0%,满足工程运用需求,系统具有较高的可靠性和稳定性.结合无线网络覆盖范围广、实时在线的特点,该系统实现了对不同区域下水道内可燃气体浓度的远程监测,为下水道的安全预警提供了有效依据.     

基于最大熵原理的城市防洪标准方案优选智能评价模型

影响城市防洪标准的因素众多,为处理统计数据的模糊性和随机性,根据城市防洪标准的政治效果、社会效果、经济效果、环境生态效果综合最优原则,基于统计数据的变异性,根据主观性最小、最合乎自然、偏差最小的最大熵原理和使各方案对各分类级别的加权广义距离平方和最小的模糊理论建立目标函数,然后用加速遗传算法解此目标函数,得各指标权重,进而计算出各城市防洪标准方案的相对贴近度,从而建立方案优选智能评价模型,对城市防洪标准方案进行优选.应用结果表明,方案3(500年一遇的城市防洪标准)既能降低防洪费用,又能达到较好的防洪效益.此模型的评价结果与其他方法虽有差异,但经过具体分析,智能评价方法所得结果是合理、客观的.     

河流水环境质量综合评价方法比较研究

提出了对河流水环境质量综合评价方法的基本要求,对水环境质量评价方法的现状进行了研究,并通过对各种方法的 比较,探讨了今后水环境质量综合评价方法的发展方向。     

Emissions of reduced sulphur compounds from the surface of primary and secondary wastewater clarifiers at a Kraft Mill

Emissions of reduced sulphur compounds (RSCs) from the primary and secondary clarifiers at a Kraft mill were measured for respectively 8 and 22 days using a floating flux chamber. In the primary clarifier, dimethyl disulphide (DMDS) had the highest mean flux (0.83 microg s(-1) m(-2)) among all RSCs, and the mean flux of total reduced sulphur (TRS) was 1.53 microg s(-1) m(-2). At the secondary clarifier, dimethyl sulphide (DMS) had the highest mean flux (0.024 microg s(-1) m(-2)), and the mean flux of total reduced sulphur (TRS) was 0.025 microg s(-1) m(-2). Large variations in fluxes as a function of sampling date were observed in both clarifiers. Emission fluxes of DMS from the secondary clarifier were correlated with temperature in the flux chamber and with the biological and chemical oxygen demands (BOD and COD) of the wastewater. Emission rates of RSCs from the clarifiers were found to be insignificant by comparison with other mill sources.     

Transfer of metals from soil to vegetables in an area near a smelter in Nanning, China

A field survey was conducted to investigate the metal contamination in soils and vegetables, and to evaluate the possible health risks to local population through foodchain transfer near a smelter in Nanning, southern China. Contamination levels in soils and vegetables with cadmium (Cd), lead (Pb), zinc (Zn) and copper (Cu) were measured, and transfer factors (TF) from soils to vegetable plants and its health risk (risk index, RI) were calculated accordingly. Results showed that both soils and vegetables from villages 1 and 2 (V1 and V2, 1500 m and 500 m from the smelter) were heavily contaminated, compared to a village 50 km from the smelter. Geometric mean of Cd and Pb concentrations in vegetables for V1 and V2, respectively, were 0.15 and 0.24 mg Cd kg(-1) and 0.45 and 0.38 mg Pb kg(-1) (on fresh weight basis). Oral intake of Cd and Pb through vegetables poses high health risk to local residents. Risk indices for V1 and V2, respectively, were 3.87 and 7.42 for Cd, and 1.44 and 13.5 for Pb. The complexity of metal contamination and their health risks are also discussed.     

Nitrogen loss through lateral seepage in near-trench paddy fields

A near-trench paddy field experiment with five urea application rates (0-360 kg N ha(-1) in 90-kg increments) was conducted on a paddy soil in the Taihu Lake Region of China to elucidate N losses through lateral seepage during three rice (Oryza sativa L.) growing seasons. The total N (Nt), NH4(+) -N, and NO3(-) -N concentrations in the lateral seepage water increased with increasing N rates. The seasonal Nt fluxes by lateral seepage varied from 6.8 to 25.6 kg N ha(-1) for urea application rates of 90 to 360 kg N ha(-1). Lateral seepage accounted for 4.7 to 6.6% of the Nt applied, implying that lateral seepage was an important pathway of N loss from near-trench paddy fields. The cumulative N loss via lateral seepage was significantly related to N fertilization rate (P = 0.05). Floodwater level was also identified as a main factor affecting N losses via lateral seepage from paddy fields, as indicated by a positive linear relationship (R2 = 0.43) between floodwater level and daily lateral flow during the flooded period (P = 0.05). Under the conditions of these experiments, a shallow floodwater depth of 50 mm, urea application rates of 90 kg N ha(-1) or less, and no rainfall within 1 wk after N application reduced N losses by lateral seepage from paddy fields.     

Adsorption of Pb and Cd on the natural surface coatings (NSCs) in the presence of organochlorine pesticides: a preliminary investigation

Adsorption of Pb and Cd in the presence and absence of organochlorine pesticides (OCPs) on natural surface coatings (NSCs), which were collected in the Nanhu Lake in Changchun, China, was measured in order to investigate the effect of the OCPs on the adsorption of heavy metals on the NSCs. Adsorption of Pb/Cd was carried out under controlled laboratory conditions (mineral salt solution with defined species, ionic strength 0.05 mol/l, 25 degrees C and pH 6.0) with initial Pb and Cd concentrations ranging from 0.2 to 2.5 mol/l. The classical Langmuir adsorption isotherm was applied to estimate the equilibrium coefficients of the adsorption of Pb and Cd on the NSCs. Adsorption interference between Pb/Cd and the OCPs on the NSCs indicated that the adsorption of Pb/Cd on the NSCs was influenced by the OCPs, and competitive adsorption between Pb and the OCPs was observed while adsorption of Cd was enhanced by addition of the OCPs. Adsorption data fit the Langmuir isotherm well for the NSCs treated with the OCPs at different equilibrium concentrations. The results showed that the amount of adsorbed Pb decreased by more than 40% while the amount of adsorbed Cd increased by over 60% with an increase in the initial concentrations of the OCPs ranging from 0 to 5.0 microg/l and that adsorption of Pb/Cd on the NSCs was strongly affected by the OCPs. This preliminary study highlights the importance of the OCPs on the NSCs in controlling the transport, fate, biogeochemistry, bioavailability and toxicity of trace metals in aquatic environments.     

关于不确定度评定中两个问题的讨论

通过对环境监测仪器分析不确定度评定中,标准不确定度和相对标准不确定度的单位来源以及关于相对标准不确定度两种计算方法的讨论,得出标准不确定度是有量纲的、相对标准不确定度是无量纲的;最大允许误差较易获得,用这种方法计算不确定度有很好的可靠性。相对标准偏差计算不确定度则结果更好。     

巧用Premiere Pro 2.0 制作艺术倒计时片头

Premiere Pro 2.0 是用于编辑影视作品的专业软件,可以编辑和制作电影、DV、栏目包装、字幕、网络视频、电子相册等.本文介绍了其自带的制作倒计时片头效果模板的使用方法,提出了利用Premiere Pro 2.0视频转场特效结合专业制图软件制作艺术倒计时效果的具体方法.     

论大学生职业生涯教育的现状及其对策

目前,高校对开展大学生职业生涯教育的重要性尚未有足够认识,职业生涯教育和辅导的保障机制也还不够完善,高校课程、专业设置等还不能为职业生涯教育提供有效支持。因此,要不断建立、完善职业生涯教育和辅导体系,推动高校招生教育体制改革,完善大学生职业生涯教育配套机制,以提高高校人才培养质量,促进大学生就业质量和水平,推动高校健康发展。