Crash data analysis: collective vs. individual crash level approach

INTRODUCTION: Traffic safety literature has traditionally focused on identification of location profiles where "more crashes are likely to occur" over a period of time. The analysis involves estimation of crash frequency and/or rate (i.e., frequency normalized based on some measure of exposure) with geometric design features (e.g., number of lanes) and traffic characteristics (e.g., Average Annual Daily Traffic [AADT]) of the roadway location. In the recent past, a new category of traffic safety studies has emerged, which attempts to identify locations where a "crash is more likely to occur." The distinction between the two groups of studies is that the latter group of locations would change based on the varying traffic patterns over the course of the day or even within the hour. METHOD: Hence, instead of estimation of crash frequency over a period of time, the objective becomes real-time estimation of crash likelihood. The estimation of real-time crash likelihood has a traffic management component as well. It is a proactive extension to the traditional approach of incident detection, which involves analysis of traffic data recorded immediately after the incident. The units of analysis used in these studies are individual crashes rather than counts of crashes. RESULTS: In this paper, crash data analysis based on the two approaches, collective and at individual crash level, is discussed along with the advantages and shortcomings of the two approaches.     

Effect of the C:N:P ratio on the denitrifying dephosphatation in a sequencing batch biofilm reactor (SBBR)

A series of investigations were conducted using sequencing batch biofilm reactor(SBBR) to explore the influence of C:N:P ratio on biological dephosphatation including the denitrifying dephosphatation and the denitrification process.Biomass in the reactor occurred mainly in the form of a biofilm attached to completely submerged disks.Acetic acid was used as the source of organic carbon.C:N:P ratios have had a significant effect on the profiles of phosphate release and phosphate uptake and nitrogen removal.The highest rates of phosphate release and phosphate uptake were recorded at the C:N:P ratio of 140:70:7.The C:N ratio of 2.5:1 ensured complete denitrification.The highest rate of denitrification was achieved at the C:N:P ratio of 140:35:7.The increase of nitrogen load caused an increase in phosphates removal until a ratio C:N:P of 140:140:7.Bacteria of the biofilm exposed to alternate conditions of mixing and aeration exhibited enhanced intracellular accumulation of polyphosphates.Also,the structure of the biofilm encouraged anaerobic–aerobic as well as anoxic–anaerobic and absolutely anaerobic conditions in a SBBR.These heterogeneous conditions in the presence of nitrates may be a significant factor determining the promotion of denitrifying polyphosphate accumulating organism(DNPAO) development.     

Preparation of reverse osmosis membrane with high permselectivity and anti-biofouling properties for desalination

• Nanoparticle incorporation and anti-biofouling grafting were integrated. • Flux of modified membranes was enhanced without rejection sacrificing. • Anti-biofouling property of modified membranes was improved. High performance is essential for the polyamide (PA) reverse osmosis (RO) membranes during the desalination process. Herein, RO membranes with high permselectivity and anti-biofouling properties were fabricated by nanoparticles incorporation and anti-biofouling grafting. Hydrotalcite (HT) incorporation was performed with a dual role, enhancing water flux and acting as grafting sites. The HT incorporation increased the water flux without sacrificing the salt rejection, compensating for the loss caused by the following grafting reaction. The exposed surface of HT acted as grafting sites for anti-biofouling agent dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOTPAC). The combination of HT incorporation and DMOTPAC grafting endowed RO membranes with high permselectivity and anti-biofouling properties. The water flux of the modified membrane PA-HT-0.06 was 49.8 L/m²·h, which was 16.4% higher than that of the pristine membrane. The salt rejection of PA-HT-0.06 was 99.1%, which was comparable to that of the pristine membrane. As to the fouling of negatively charged lysozyme, the modified membrane’s water flux recovery was superior to that of the pristine membrane (e.g. 86.8% of PA-HT-0.06 compared to 78.2% of PA-pristine). The sterilization rates of PA-HT-0.06 for E. coli and B. subtilis were 97.3% and 98.7%, much higher than those of the pristine membrane (24.0% for E. coli and 26.7% for B. subtilis).     

上海市城市绿地土壤特性及对雨洪削减效应的影响

研究了上海市5个功能区城市绿地土壤的特性,分析了它们在各功能区的分布规律及造成差异的影响因素,并对上海市利用绿地蓄渗雨洪的潜力进行了计算分析.结果表明,上海市城市绿地土壤质地以粘壤土、砂质粘壤土和壤质粘土为主;城市绿地土壤由于受人为活动的影响,土壤物理性质发生了显著变化,土壤容重增大,孔隙度和渗透性降低,压实现象普遍;土壤的入渗速率差异较大,以文教区和居民生活区为最好,其后依次为公园、商业活动区、道路交通区.对绿地面积比为20%的功能区,在一年一遇的设计暴雨重现期内,绿地蓄渗雨水效果随土壤入渗速率的增大而增大,且下凹式绿地的蓄渗效果明显优于平绿地.     

Investigating supportive conditions for participation in voluntary environmental programs

Voluntary environmental programs (VEPs) are commonly construed as contracts between industry and government that encourage businesses to voluntarily mitigate their environmental impacts beyond legal requirements. This research explores conditions under which polluting firms are likely to participate in VEPs. We analyze 34 comparable VEPs whose shared goal is to reduce greenhouse gases emissions, with focus on the alleged influences of three factors drawn from existing scholarship: government supervision; economic instruments; and public disclosure of participants' environmental records. The statistical results show a greater effect from government supervision than complete voluntarism and the positive effect of financial subsidies on firms' participation in VEPs. Although recent debates over regulatory reform have been oriented towards vesting greater discretion in regulatees to better address environmental harms, the findings imply that even in a highly privatized form of regulation, government oversight and assistance are necessary for promoting this new mode of environmental regulation.     

X70钢在包头土壤环境中的腐蚀规律研究

通过在内蒙古包头土壤中室内埋设试样的方法,考察了土壤温度、含水量以及埋设时间对X70钢腐蚀情况的影响,利用失重法和电化学极化曲线方法测定了腐蚀速率.通过SEM和EDS对腐蚀形貌和腐蚀产物进行了观察与分析.实验结果表明,腐蚀速率在埋设60天内一直没有达到稳定,并随温度的升高而增加,在45℃、10%含水量土壤中埋设15天时达最大值;腐蚀程度随时间的延长而加剧;当埋设时间和温度相同时,X70钢在10%含水量土壤中腐蚀严重,在20%含水量的包头土壤中腐蚀轻微;X70钢的腐蚀机理主要是均匀腐蚀和点蚀,腐蚀产物主要为Fe的氧化物.     

应用CGE模型量化分析中国实施能源环境税政策的可行性

应用一个可计算一般均衡(CGE)模型对中国若干工业行业按照差别税率对所投入的煤炭和油气产品征收从价能源环境税的情况进行了量化模拟,预测了该项政策在中国实施的可行性;并在量化模拟和分析之后得出如下结论:即征收能源环境税有助于促进工业部门,尤其是能源密集型行业,节能、降耗、改善能源消费结构和削减SO2 和CO2 污染排放,但该项政策的实施并不能够从根本上促进能源利用效率的提高,反而易对宏观经济造成负面影响,因此在中国目前现阶段不宜作为主要能源环境政策备选方案     

非致死剂量的四溴双酚A胁迫下蚯蚓的生长和抗氧化防御反应

以自然土壤为介质,考察赤子爱胜蚓(Eisenia fetida)的生长抑制率、蛋白质含量、超氧化物歧化酶(SOD)活性、谷胱甘肽转移酶(GST)活性等指标,进行了急性(14 d)、亚急性(28 d)暴露下四溴双酚A(tetrabromobisphenol A,TBBPA)非致死剂量胁迫对蚯蚓的生长和抗氧化防御效应研究。结果表明:在急性试验中TBBPA对蚯蚓的生长抑制均存在显著的剂量效应关系,而在亚急性暴露期,400 mg·kg~(-1)时显著抑制蚯蚓的生长(P<0.05);TBBPA对蚯蚓体内蛋白含量影响,在急性试验中各处理间差异不显著(P=0.712),进入亚急性期蛋白质含量在400 mg·kg~(-1)时被显著诱导(P=0.039,P<0.05);TBBPA对蚯蚓SOD酶活性的影响,在急性试验中50 mg·kg~(-1)时被显著诱导(P<0.01),在亚急性试验中400 mg·kg~(-1)时SOD酶活性显著升高(P<0.05);TBBPA对蚯蚓GST酶活性影响,在急性试验中400 mg·kg~(-1)时呈现显著诱导效应(P<0.05),在亚急性期各处理间差异不显著(P=0.428)。蚯蚓生长抑制率、蛋白质含量、体内各生化酶系对TBBPA暴露的时间效应和剂量效应的敏感性存在不同程度差异,应依据污染暴露指标的有效性和敏感性选择多时间段检测和多指标进行土壤安全评价诊断。     

农村生活垃圾产生特征及分类收集模式

以南京市高淳县的一个村为研究对象,依托新建的农村生活垃圾分类收集系统,对该区域生活垃圾的产生量、组成成分及其动态变化进行了调查研究,从垃圾分类收集模式的运行效果和经济可行性对其进行了分析。结果表明,该地区农村人均垃圾产生量为0.4 kg/d ,但随季节有一定的波动,这主要是由食品类消费的季节性变动而引起。垃圾组成以有机垃圾为主,约占55%,可回收垃圾、其他垃圾和有害垃圾所占比例分别为30.5%、14.2%和0.34%。通过认真的宣传和指导,村民在较短的时间内基本都可以做到正确分类;垃圾分类收集系统的户均建设成本为21元,运行费用比分类收集前每户每月增加3.2元 。     

Soil enzymatic activities and microbial community structure with di erent application rates of Cd and Pb

This study focused on the changes of soil microbial diversity and potential inhibitory effects of heavy metals on soil enzymatic activities at different application rates of Cd andor Pb. The soil used for experiments was collected from Beijing and classified as endoaquepts. Pots containing 500 g of the soil with different Cd andor Pb application rates were incubated for a period of 0, 2, 9, 12 weeks in a glasshouse and the soil samples were analyzed for individual enzymes, including catalase, alkaline phosphatase and dehydrogenase, and the changes of microbial community structure. Results showed that heavy metals slightly inhibited the enzymatic activities in all the samples spiked with heavy metals. The extent of inhibition increased significantly with increasing level of heavy metals, and varied with the incubation periods. The soil bacterial community structure, as determined by polymerase chain reaction-denaturing gradient gel electrophoresis techniques, was different in the contaminated samples as compared to the control. The highest community change was observed in the samples amended with high level of Cd. Positive correlations were observed among the three enzymatic activities, but negative correlations were found between the amounts of the heavy metals and the enzymatic activities.