南方某水库底层溶解氧分布特征及低氧成因分析

以南方某水库为例,通过2013年4月至2014年3月的监测数据研究底层溶解氧(bottom dissolved oxygen,BDO)和底层水温(bottom temperature,BT)、p H值、电导率、浊度(TU)、TP、TN、COD、总有机碳(TOC)、Chl-a间的关系,以阐明该水库BDO的时空分布特征及低氧成因。结果表明,BDO春、夏季浓度低,秋、冬季(枯水期)浓度较高,进水口附近的DO浓度普遍高于库中、库心;低氧现象主要发生在夏季(5—8月);水越深、水温越低,BDO下降趋势显著(P0.05);浊度、TOC与BDO为正相关关系。BDO与叶绿素a呈现显著正相关,在底层浮游植物中,蓝藻门占绝对优势,BDO浓度与蓝藻的垂直迁移有关。表明水库BDO在时间上的变化趋势受温度的影响,而空间上的变化受到水动力的影响,低氧现象的发生受到水体垂直密度分层的影响。     

热带地区水库水温分层特性研究

为探讨热带地区水库水温分层特征,采用垂向一维水温数学模型对海南省南渡江干流某拟建大型水库开展了水库垂向热分层结构和下泄水温过程研究,并探讨了叠梁门分层取水措施对低温水的改善效果。研究结果表明:①受水库湖泊特性和气候特征影响,海南热带地区水库水温总体也呈现随季节变化的分层结构,在冬季水温趋于同温,夏季水温分层逐渐加强且显著,年内垂向最大温差可达11.8℃,由于海南主汛期为9～10月,汛后水库蓄热能力明显减弱。②水库下泄水温呈现低温水明显、高温水较弱的规律,最大降幅9.7℃,最大升幅仅为1.0℃。③叠梁门分层取水措施的运用,加强了水库垂向分层状态,对低温水的改善效果显著,最大低温水影响降低为2.3℃。     

Characteristics of thermal stratification in head area of Three Gorges Reservoir and ecological effects in different operation periodsEI北大核心CSCD

为了解三峡水库库首2003—2018年的水温变化特征及其对生态环境的影响,基于庙河断面实测资料,采用LSTM-Logistic模型模拟分析了库首多年水温结构特性,并探讨了其变化对库区支流库湾水华的影响和对坝下鱼类产卵水温的影响。结果表明：LSTM-Logistic模型能较好地适用于三峡水库,准确地模拟水温的逐日变化过程;2006—2013年,三峡水库库首每年4—6月均出现了水温分层现象,从2014年开始,水温垂向差异变小,水温不分层,且春季、秋季和冬季水温升高,下泄水温进一步平坦化;三峡水库库首水温长期变暖的趋势,会使支流库湾倒灌异重流潜入深度上移,从而改变异重流倒灌形式,降低库湾水华风险;梯级水库蓄水缓解了春季下泄低温水的不利影响,但秋冬季水温的升高对中华鲟繁殖造成了进一步威胁。     

An assessment of climate change and stratification in Lake Kariba (Zambia–Zimbabwe)

Lake Kariba is a monomictic reservoir, isothermal in winter (June–August), and stratified for the rest of the year. Its temperature has increased since the 1990s, with some researchers suggesting it now has a stronger and more stable thermocline as a result. It was also claimed that the depth of the epilimnion had decreased, and nutrient depletion has led to a decrease in the depth of the euphotic zone, algal biomass and primary productivity. A re‐analysis of the data suggests this view is incorrect. The epilimnion is more homogenous now than in the 1980s, with less vertical variation in temperature and dissolved oxygen in the upper 20 m of the lake. The depth of the euphotic zone has not changed since the 1960s, and the algal biomass and primary productivity have increased. The thermocline appears to have weakened with temperature and density gradients being much smaller than in the 1980s because of a more rapid rate of warming in deeper water. The reasons for this phenomenon are not clear, although evaporative cooling at the surface may contribute to it. There was a significant increase in Birgean heat budgets over time, although there was none for stability. This may be explained by the fact that the lake is monomictic, cooling to 22°C in winter, with a new cycle of stratification beginning each year, and it may be affected by variable factors such as evaporation, rainfall, river flow and internal wave movements.     

Combining random sampling and census strategies - Justification of inclusion probabilities equal to 1

Very often values of a size variable are known for the elements of a population we want to sample. For example, the elements may be clusters, the size variable denoting the number of units in a cluster. Then, it is quite usual to base the selection of elements on inclusion probabilities which are proportionate to the size values. To estimate the total of all values of an unknown variable for the units in the population of interest (i.e. for the units contained in the clusters) we may use weights, e.g. inverse inclusion probabilities. We want to clarify these ideas by the minimax principle. Especially, we will show that the use of inclusion probabilities equal to 1 is recommendable for units with high values of the size measure. AMS Classification 2000: Primary 62D05. Secondary 62C20     

分层教学在工厂电气控制没备课程中的尝试

分层教学思想旨在课堂教学中面向全体学生,促使人人成功.分层教学指协调教学目标和要求,将教学要求置于各层次学生的最近发展区之中,同时调动学生学习可能性中的易变因素,使教学要求与学生的学习可能性相互适应.通过实施分层授课、分层训练、分层辅导、分层评价,以达到各类学生接受效应、共振效应.使各类学生的索质达到分层发展的目的.     

Effects of selective water withdrawal schemes on thermal stratification in Kouris Dam in Cyprus

Thermal stratification and its seasonal variations in Kouris Dam in Cyprus were simulated, and the impact of five different water withdrawal schemes was studied, using the 2‐D, laterally averaged CE‐QUAL‐W2 reservoir model. Based on the model simulations, it was found that the thermal stratification of the reservoir is significant for most of the year. Most importantly, a complete mixing of the water column, triggered by seasonal variations in meteorological conditions, occurs in late‐January. Predicted thermal stratification and water temperature profiles in the reservoir are noticeably affected by water withdrawal schemes. It was found that deep‐water withdrawals tend to facilitate heat transfer in the water column and deepen the water mixing layer (epilimnion), especially from September to the following January. These study results suggest that it is prudent for Kouris Dam to integrate selective water withdrawal schemes into reservoir management by using the water withdrawal effects on thermal stratification for different water quality management strategies.     

QC方法——特性要因图、巴雷托图和层别法的运用

经济的全球化发展推动了现代制造企业质量管理体系的建立和不断完善。虽然中国制造企业已经开展质量管理并获得了有益的经验,然而,目前我国制造企业质量管理仍存在很大不足。结合实际,重点阐述了如何运用QC方法特性要因图(鱼骨图)、巴雷托图和层别法历来改善企业生产过程中出现的质量问题,从而提高产品品质、降低产品的生产成本。     

Risk‐based approach for assessing the effectiveness of flow management in controlling cyanobacterial blooms in rivers

Cyanobacterial blooms present significant water quality problems worldwide. Flow management is considered to be one of the most promising approaches for combating the cyanobacterial bloom problem in rivers. In this paper, a new method for evaluating the effectiveness of flow management strategies in reducing the risk of cyanobacterial blooms is developed and applied to the River Murray at Morgan, South Australia. As stratification has been shown to be a necessary condition for significant growth of certain cyanobacteria species, the method uses estimates of the probability that stratification events of various durations will occur in conjunction with estimates of population growth during stratified conditions to determine the probability that blooms of various magnitudes will occur. The results of the case study indicate that the probability that blooms of the cyanobacterium Anabaena circinalis exceeding 15 000 cells/ml will occur in any given year under summer entitlement flow conditions is 11.7%, which is in excellent agreement with results obtained using a Poisson–Bayesian approach applied to 17 years of historical data of cell densities of Anabaena circinalis at the study site. The results obtained also indicate that increasing inflows into South Australia by 10 000 Ml/day, which is the maximum achievable increase given current operational constraints, would not have a significant impact on the occurrence of blooms exceeding 15 000 cells/ml. An additional flow of 19 900 Ml/day into South Australia would be required to reduce the probability of occurrence of blooms exceeding 15 000 cells/ml to 0.01%. Copyright © 2004 John Wiley & Sons, Ltd.     

施工方案优选方法的探讨

施工方案优选涉及的因素较多，决策者应从系统的观点出发，综合考虑各种因素进行比选。模糊层次综合评价和灰色关联分析应用于方案优选均能取得较好效果。通过对这两种方法的分析，对比，揭示了两者的异同，并在此基础上阐明了两者的适用范围及在实际应用中应注意的相关问题。