Toxic effects of chlortetracycline on maize growth, reactive oxygen species generation and the antioxidant response

The toxicity of chlortetracycline (CTC) on maize (Zea mays L.) growth and reactive oxygen species (ROS) generation was studied. The root and shoot lengths and fresh weights of maize seedlings were inhibited by CTC treatment (p < 0.05). Root length was more sensitive than other parameters with the EC₁₀ value of 0.064 mg/L. The spin trapping technique followed by electron paramagnetic resonance (EPR) analysis was used to quantify the ROS production. The ROS generated in maize roots after exposure to CTC was identified as hydroxyl radical (.OH). The EPR signal intensity correlated positively with the logarithm of CTC concentrations exposed (p < 0.05). The dynamic changes of malondialdehyde (MDA) contents and the antioxidative enzyme activities in maize roots were also determined. As compared to the control group, CTC was found to significantly increase MDA content. Treatment of maize roots with the.OH scavenger sodium benzoate (SB) reduced the MDA content and enhanced the antioxidative enzyme activities. The results demonstrated the harmfulness of CTC at high dose to maize in the early developmental stage, and clarified that the inducement of.OH is one of the mechanisms of CTC toxicity.     

Characterization of particle number size distribution and new particle formation in Southern China

Knowledge of particle number size distribution(PND) and new particle formation(NPF)events in Southern China is essential for mitigation strategies related to submicron particles and their effects on regional air quality,haze,and human health.In this study,seven field measurement campaigns were conducted from December 2013 to May 2015 using a scanning mobility particle sizer(SMPS) at four sites in Southern China,including three urban sites and one background site.Particles were measured in the size range of15-515 nm,and the median particle number concentrations(PNCs) were found to vary in the range of 0.3× 10~4-2.2 × 10~4 cn~(-3) at the urban sites and were approximately 0.2 × 10~4 cm~(-3) at the background site.The peak diameters at the different sites varied largely from 22 to 102 nm.The PNCs in the Aitken mode(25-100 nm) at the urban sites were up to 10 times higher than they were at the background site,indicating large primary emissions from traffic at the urban sites.The diurnal variations of PNCs were significantly influenced by both rush hour traffic at the urban sites and NPF events.The frequencies of NPF events at the different sites were0%-30%,with the highest frequency occurring at an urban site during autumn.With higher SO_2 concentrations and higher ambient temperatures being necessary,NPF at the urban site was found to be more influenced by atmospheric oxidizing capability,while NPF at the background site was limited by the condensation sink.This study provides a unique dataset of particle number and size information in various environments in Southern China,which can help understand the sources,formation,and the climate forcing of aerosols in this quickly developing region,as well as help constrain and validate NPF modeling.     

北京夏季高温高湿和降水过程对大气颗粒物谱分布的影响

2004-07-13～2004-08-23使用TDMPS-APS系统在线测量颗粒物的数浓度谱分布,并于07-16～07-18选取了高温闷热夜晚、日间高温高湿和雨后晴朗干洁3种天气条件,使用多级串联撞击式采样器(MOUDI)测量颗粒物的质量浓度谱分布,结果表明,高温高湿天气条件下颗粒物的污染、尤其细粒子污染严重,导致很低的能见度(2.5km);PM_1.8和PM₁₀的质量浓度分别为170.68μg/m³和249.35μg/m³,细粒子质量浓度占PM10的68%;粒径为50～100nm颗粒物的数浓度最高,为2×10⁴～3×10⁴个/cm³;降雨过程对粗粒子和细粒子均有去除作用,对细粒子的去除作用尤为明显;降雨后PM₁₀和PM_1.8浓度分别比降雨前降低3倍和6倍;降雨过后的晴朗干洁天气有利于新粒子(3～20nm)的生成,生成的新粒子快速长大到50～100nm;随着污染物的累积,以后几天内又变为污染天气.     

优化布点的TOPSIS法研究

针对多目标系统的优化布点问题,尝试提出用改进的TOPSIS法研究水质环境监测点位的优化,并建立改进的TOPSIS法优化模型.实例分析表明,该方法充分利用了优化矩阵的信息,优选结果符合客观实际,可用于环境监测点位的优化布点.     

基于曲线投影动态聚类模型的大气质量监测布点研究

聚类数和聚类方法是聚类分析研究的核心,具有重要的实用价值。针对各单项大气质量监测指标的不相容问题,在投影寻踪动态聚类模型的基础上,通过引入S型曲线作为投影方式,提出了基于曲线投影动态聚类的大气质量监测布点研究新方法。从理论上讲,作为一种完全由数据驱动的方法,该模型充分体现了投影寻踪聚类的设计思想,能把最佳聚类数和对应的聚类结果的分析有机地融合在一起,具有物理意义清晰,可操作性强等特点。实例应用结果表明,通过把待研究地区大气监测点多维指标综合成一维投影指标,并利用免疫进化算法优化目标函数,模型能提供明确、客观及稳健的监测布点最佳方案,实现大气质量监测经济性和代表性的平衡。上述研究可为其它非线性、非正态高维数据分类问题开辟一条新途径。     

雄安新区土壤重金属地球化学监测关键问题探讨

为构建雄安新区土壤环境质量监控网,系统获取雄安新区建设前后土壤重金属地球化学数据,长期监测新区建设过程中土壤重金属的变化趋势,在分析雄安新区土地质量地球化学调查监测数据和土壤重金属元素地球化学空间变异特征的基础上,采用统计学方法估算构建新区土壤地球化学监测网所需要的采样密度、采样数量和采样周期等参数,为后续新区土壤重金属地球化学长期监测工作提供参考.结果表明,调查区重金属As、 Cd、 Cu、 Hg和Pb元素变异系数>36%,属于高度变异元素; Cd、 Cu和Pb元素块金系数均>75%,其高度富集是在较高自然背景上出现了人为源的叠加.在置信水平P为95%和90%时,对样本平均值允许误差Δ分别为5%、 10%和15%的条件下,同时对新区土壤中8种重金属As、 Cd、 Cr、 Cu、 Hg、 Ni、 Pb和Zn进行土壤环境质量监测,最少合理采样数分别为1 077个、 270个、 120个和767个、 192个、 86个.土壤各重金属元素可监测最小变化量(MDC)介于0.0025～2.54 mg·kg^-1之间.在不同的重金属年变化速率下土壤重金属监测所需要的...     

直升机电力作业非线性动态安全评价模型

为有效提高直升机电力作业安全评价能力,落实通用航空作业标准化和规范化管理,本文以直升机电力作业中人员因素、直升机设备因素、电力作业设备因素、自然环境因素、机场环境因素、组织因素、规章管理因素7个模块为一级指标建立安全评价指标体系。结合多位专家给出的概率语义值,基于模糊集与改进的证据融合理论量化各指标风险程度,同时采用三角模糊数法确定中间节点条件概率,最后利用贝叶斯网络模型灵活推理能力,提出直升机电力作业非线性动态安全评价模型。通过对某通用航空公司直升机电力作业安全状况评价分析可知,企业组织因素、电力作业设备因素以及人员因素为主要薄弱环节,需加强管理,可通过提高从业人员的安全防范意识、提高设备可靠性以及加强人员培训等措施对风险进行预防。     

缸内直喷汽油车细小颗粒物排放特性研究

选取三辆满足国六排放标准的缸内直喷汽油车进行常温冷启动WLTC循环排放试验,研究不同车辆排放的粒径在23nm以上的固态颗粒物、6nm以上包含挥发性/半挥发性组分的颗粒物数量排放特性,并进行了比较研究.结果发现,在缸内直喷汽油车排放的6~30nm范围内包含挥发性/半挥发性物质的细颗粒物主要产生在WLTC循环减速段､高速段和超高速段;30~2500nm范围的挥发性/半挥发性的颗粒物主要在超高速段生成;其它工况下,23nm以上固态颗粒物在颗粒物数量排放中占主体.试验研究还发现GPF对6~30nm大小的细颗粒物捕集效果不佳,并且GPF再生时会产生高浓度6~30nm大小的细颗粒物排放.颗粒物碳质成分分析表明挥发性/半挥发性细颗粒物对法规测量的23~2500nm颗粒物的数量排放影响甚微,但对颗粒物质量排放影响明显.     

板料成形数值模拟中网格结点编号优化算法研究

提出一种用于板料成形数值模拟的网格结点编号优化算法。该算法用各个结点的相邻单元结点编号总和除以该结点相邻单元数 ,所得的结点商作为重新结点编号的依据 ,对板料成形模拟的四边形单元结点编号进行优化 ,减少了带宽 ,减少有限元的计算贮存量 ,缩短了板料成形数值模拟的计算时间