Hydrodynamic characteristics of a four-compartment periodic anaerobic ba ed reactor

Periodic anaerobic baffled reactor (PABR) is a novel reactor based on the design concept of anaerobic baffled reactor (ABR). Residence time distribution (RTD) studies on both clean and working reactors at the same hydraulic residence time (HRT) of 2 d were carried out to investigate the dead spaces and mixing patterns in PABRs at different organic loading rates (OLRs) in various switching manners and frequencies.The results showed that the fraction of dead space in PABR was similar to that in ABR,which was low in comparison with other reactor designs.Dead space may be divided into two categories,hydraulic and biological.In RTD studies without biomass,the hydraulic dead space in the PABR run in an"every second"switching manner with T=2 d was the lowest whereas that in the PABR run in a T=∞(ABR) switching manner was the highest.The same trend was obtained with the total dead space in RTD studies with biomass no matter what the OLR was.Biological dead space was the major contributor to dead space but affected decreasingly at higher OLR whichever switching manner the PABR run in.The flow patterns within the PABRs were intermediate between plug-flow and perfectly mixed under all the conditions tested.     

基于改进Togawa模型的人员疏散时间预测模型研究

为解决传统疏散模型在计算人员疏散时间时参数不确定的问题,采用离散算法和Fruin模型对传统的Togawa疏散模型进行改进,先将时间离散为多个微小单元,假设各时间单元内人流密度不变,然后通过Fruin模型确定Togawa模型参数值,并运用迭代法累计各单元时间得到疏散时间,提高了计算的精确度.以辽宁工程技术大学博雅楼紧急情况下人员疏散为例进行分析,结果表明,改进的Togawa疏散模型预测的人员疏散时间与实际疏散时间相对误差为3.6％,预测精确度较高.     

新型双循环厌氧反应器的设计与水力特性研究

结合IC与EGSB的特点,同时根据厌氧处理理论,设计了新型双循环厌氧反应器,用于处理高浓度含有毒物质工业废水,并以Li Cl作为示踪剂,对该反应器不同水力停留时间(HRT)下的水力特性进行了研究。结果表明,在无循环时,各HRT下双循环厌氧反应器的C-θ曲线为不对称的单峰曲线。HRT为6,9,12 h时,反应器的死区比例分别为0.165,0.155,0.146。反应器呈推流流态,且随着HRT的增加,推流作用逐渐加强而完全混合作用逐渐减弱。当存在双循环时,在HRT为6,9,12 h的条件下,反应器第一反应区的σ2分别为0.249,0.179,0.113,第二反应区的σ2分别为0.135,0.112,0.106。双循环增大了反应器的返混程度,且与第一反应区相比,第二反应区更趋于推流式。     

基于ARIMA干预模型和对比分析的安徽省“清剿火患”效果研究

为了研究"清剿火患"行动对安徽省火灾形势的抑制作用,采用ARIMA干预模型与火灾数据对比的方法对2007—2012年安徽省火灾统计数据进行了分析。2种ARIMA干预模型都能检测到"清剿火患"行动对季节调整后火灾起数时间序列的抑制效果。根据干预模型,抑制效果在"清剿火患"行动开展后第3个月时出现,火灾立即减少约300起,随后抑制效果逐渐衰减。在"清剿火患"行动开展14个月后,抑制效果几乎衰减为0。通过对比"清剿火患"期间与2009-10—2010-02、2010-10—2011-02的火灾统计数据,发现"清剿火患"行动期间的火灾起数较前两年同期的火灾起数大幅度降低,平均降幅达64%。在此基础上又分析了不同火灾原因、火灾场所和火灾起数的降低情况。对比发现,"清剿火患"期间火灾死亡人数与死亡人数不低于3人的火灾起数均降低为0。     

Modeling the Effects of Extreme Drought on Pollutant Transport Processes in the Yangtze River Estuary

Water resources in the Yangtze River Estuary (YRE), which is the vital water supply for Shanghai, decreased by approximately 2.45 Gm³ in 2006, the second‐worst recorded drought year. A numerical model was developed to investigate the effects of this extreme drought on pollutant transport processes in the YRE. The model was calibrated against observations and displayed good agreement. Residence time, a critical hydrodynamic indicator, was implemented to indicate pollutant transport processes. Numerical experiments were conducted to examine the possibly drought‐induced influences. The model results demonstrated that the influences on pollutant transport processes varied spatially and temporally, and these influences could partly explain the observed temporal and spatial variations of total nitrate in 2006. The area most susceptible to drought is in the north branch with 2‐11 days' extension of residence time. As the drought occurred in both the high and normal water periods, its influences were more significant during the normal water period with saltwater intrusion into the north branch. The drought also introduced a pollutant transport lag in timescale of approximately five days by diminishing the seaward advection flux with freshwater discharge. In 2006, the magnified tidal influence during the drought contributed more than usual to structuring pollutant transport, as the pollutant transport processes were intensely associated with tidal flow and tidal cycle.     

Measuring disaster recovery: bouncing back or reaching the counterfactual state?

How should one measure the recovery of a locale from a disaster? The measurement is crucial from a public policy and administration standpoint to determine which places should receive disaster assistance, and it affects the performance evaluation of disaster recovery programmes. This paper compares two approaches to measuring recovery: (i) bouncing back to pre‐disaster conditions; and (ii) attaining the counterfactual state. The former centres on returning to normalcy following disaster‐induced losses, whereas the latter focuses on attaining the state, using quasi‐experimental design, which would have existed if the disaster had not occurred. Both are employed here to assess two housing recovery indicators (total new units and their valuations) in Hurricane Katrina‐affected counties (rural and urban). The examination reveals significantly different outcomes for the two approaches: counties have not returned to their pre‐disaster housing conditions, but they do exhibit counterfactual recovery. Moreover, rural counties may not be as vulnerable as assumed in the disaster recovery literature.     

Regional and Temporal Differences in Nitrate Trends Discerned from Long‐Term Water Quality Monitoring Data

Riverine nitrate (NO₃) is a well‐documented driver of eutrophication and hypoxia in coastal areas. The development of the elevated river NO₃ concentration is linked to anthropogenic inputs from municipal, agricultural, and atmospheric sources. The intensity of these sources has varied regionally, through time, and in response to multiple causes such as economic drivers and policy responses. This study uses long‐term water quality, land use, and other ancillary data to further describe the evolution of river NO₃ concentrations at 22 monitoring stations in the United States (U.S.). The stations were selected for long‐term data availability and to represent a range of climate and land‐use conditions. We examined NO₃ at the monitoring stations, using a flow‐weighting scheme meant to account for interannual flow variability allowing greater focus on river chemical conditions. River NO₃ concentration increased strongly during 1945‐1980 at most of the stations and have remained elevated, but stopped increasing during 1981‐2008. NO₃ increased to a greater extent at monitoring stations in the Midwest U.S. and less so at those in the Eastern and Western U.S. We discuss 20th Century agricultural development in the U.S. and demonstrate that regional differences in NO₃ concentration patterns were strongly related to an agricultural index developed using principal components analysis. This unique century‐scale dataset adds to our understanding of long‐term NO₃ patterns in the U.S.     

污染源减排时刻和减排比例对北京市PM_(2.5)浓度的影响

利用Model-3/CMAQ及京津冀地区高分辨率排放源清单,选取文献[19]中污染峰值当天启动50%污染源削减方案的同时,进一步设置了3种污染源控制方案(峰值当天启动75%源削减;峰值日前1d、2d开始启动25%源削减),比较了峰值日前启动适量减排与峰值日当天启动大幅度减排的效果差异.结果表明:污染峰值当天启动50%、75%减排时,北京市PM2.5浓度下降率分布不均匀,高值区集中于PM2.5浓度高值区,减排后PM2.5浓度分布较减排前均匀.提前1~2d启动25%源削减时,峰值日北京市PM2.5浓度整体下降.城、郊PM2.5下降率均表现为当天减排50%小于提前1d开始减排25%;当天启动减排提高到75%时,城区PM2.5下降率大于提前2d启动25%减排,郊区表现为峰值前2d启动25%削减优于当天减排75%.将峰值前1d、2d启动25%减排分别与当天启动50%、75%减排时北京市峰值日PM2.5浓度下降率相减,北京市绝大部分区域下降率差值为正;峰值前1d、2d启动25%减排分别比峰值日启动50%、75%减排时北京市平均PM2.5多下降4.7μg/m3(6%)、2.9μg/m3(4%).综上所述,在污染峰值来临之前采取适量减排较污染当天才启动大幅度减排更有利于北京市整体空气质量达标.     

水解酸化处理黄麻生物脱胶废水试验

针对黄麻生物脱胶废水浓度高、处理难度大的问题,采用水解酸化与膜生物反应器组合工艺对黄麻生物脱胶废水进行了处理试验。考察水解酸化池对COD、氨氮、木质素等的去除效果;并通过调节试验条件,考察水力停留时间、pH值、温度等因素对水解酸化效果的影响,得出处理黄麻生物脱胶废水的最佳实验条件。结果表明,水解酸化预处理工艺提高了废水的可生化性,对COD、氨氮均有较高的去处效率,对于降低纤维素的聚合度、促成纤维素的水解起到了关键的作用,为后续的好氧处理创造了有利条件。试验在水力停留时间10 h下,COD与氨氮去处率最高分别达35%,40%;影响水解酸化的因素主要为pH值和水力停留时间。     

时间压力视角下人格特征与VDT视觉搜索绩效的关系及形成机理*

为合理选拔和培训特定情境下的视觉搜索安检人员,从时间压力视角分析大五人格特征与视觉显示终端（visual display terminal,VDT）的视觉搜索绩效的关系。通过变量分析和设计,提出VDT视觉搜索绩效影响因素理论模型;运用Visual Studio设计实验模拟视觉搜索安检任务,采集绩效及眼动数据;最后进行有中介的调节模型检验。研究结果表明:不同人格特征的VDT视觉搜索绩效存在差异;所有人格特征的搜索策略随机指数随时间压力的增加而降低,但调整强度在不同人格特征之间存在差异,严谨性人格调整幅度最大;时间压力通过搜索策略的中介作用（部分）间接调节人格特征与VDT视觉搜索绩效的关系;较高和较低时间压力下,严谨性人格通过有效的搜索策略调整,绩效最好;中等时间压力下,开放性人格的绩效最好。研究结果可为视觉搜索作业人员的选拔和培训提供理论依据。