加速寿命试验三参数威布尔分布的极小变异-极大似然估计

目的 在加速试验中,对寿命服从三参数威布尔分布的产品进行可靠性评估与寿命预测,解决形状参数小于1时传统方法难以计算的问题。方法 利用三参数威布尔分布与指数分布之间的转换关系,以变异系数误差最小为优化目标,在确定最优位置参数估计值的基础上,应用拟极大似然方法估计分布模型中的其余参数,建立极小变异–极大似然估计（MV-MLE）。根据加速寿命试验中失效机理不变的原则,在失效机理等同条件下,将该方法推广至多应力水平下的可靠寿命评估。结果 在单一应力与多应力水平下,通过仿真模拟验证了所提方法的有效性。与传统方法相比,在小样本条件下,所提方法可提高形状参数（机理等同性参数）估计精度40%以上。结论 所提方法对于三参数威布尔分布的参数估计和寿命评估具有较高精度,能够有效克服传统方法的不足,在加速寿命试验评估中具有良好的应用效果。     

遥感与GIS在河流水质环境背景分析中的应用——以台湾基隆河为例

为了研究河流水质受到流域环境背景和人类活动的影响 ,运用 TM影像和 SPOT影像 ,在地图资料、统计资料以及实测资料的基础上 ,结合遥感和 GIS技术 ,对基隆河水质及其与环境背景和城市污染的关系做了分析 .根据遥感影像灰度值与水体反射率和水中悬浮固体含量之间的相关关系 ,运用 SPOT影像和实测数据将基隆河悬浮固体含量分为 4级 .并进行了基于 GIS专题信息的基隆河流域环境遥感制图 ,通过水体悬浮固体浓度等级与环境背景、排污口的比较 ,通过计算各等级水体与各种环境背景相邻的边界长度 ,得出基隆河悬浮固体含量主要受环境背景和城市排污的影响 .     

喀斯特高镉地质背景区水稻镉的富集、转运特征与机理

西南喀斯特地区土壤镉(Cd)具有"高地质背景、低污染风险"特征,但超过《土壤环境质量农用地土壤污染风险管控标准》风险管制值的区域是否仍具有低风险性,是迫切需要回答的问题.本文在罗甸县喀斯特峰丛谷地选择一个高Cd 土壤水稻种植区,开展土壤-水稻系统Cd含量特征和土壤Cd赋存形态等方面的研究,评价水稻各部位Cd的富集、转运...     

西南典型碳酸盐岩高地质背景区农田重金属化学形态、影响因素及回归模型

土壤重金属化学形态是决定重金属生物活性和生物毒性的重要因素,是科学评价西南碳酸盐岩高地质背景区土壤重金属生态风险的关键.为了探明碳酸盐岩高地质背景区土壤重金属化学形态分布情况,选择贵州省典型碳酸盐岩分布区,以第二次全国土壤普查图斑为采样单元,在农田中采集土壤表层样品309件,利用改进的Tessier七步顺序提取法,分析了As、Cd、Cu、Hg、Ni、Pb和Zn等7种重金属的水溶态（F1）、离子交换态（F2）、碳酸盐结合态（F3）、弱有机结合态（F4）、铁锰氧化物结合态（F5）、强有机结合态（F6）和残渣态（F7）这7种化学形态.结果发现,土壤中重金属As、Cu、Hg、Ni、Pb和Zn残渣态比例均超过50%,有效组分（F1~F3）比例均小于5%,潜在生物有效组分（F4~F6）比例低于45%,活性较低,生态风险不高.Cd的有效组分和潜在生物有效组分占比分别为55.49%和29.37%,远高于其他重金属,基于土壤重金属形态的生态风险远小于基于土壤总量的生态风险.逐步回归方程可以有效建立Cd、Cu和Pb生物有效组分与影响因素之间的关系.重金属全量和pH值是影响碳酸盐岩高地质背景区土壤重金属化学形态的重要因子,受研究区长期土法炼锌活动和碳酸盐岩风化成土过程中重金属元素倾向于在残渣态中富集的影响,土壤有机质（OM）和氧化物含量对土壤重金属化学形态影响相对较小.     

基于空间尺度效应的山东省PM2.5浓度时空变化及空间分异地理探测

基于PM_2.5遥感数据,采用Theil-Sen Median趋势分析和Mann-Kendall显著性检验,分析2000~2021年山东省PM_2.5浓度时空变化特征,结合地理探测器,在省-市-县三级空间尺度上探测影响山东省PM_2.5浓度空间分异的影响因子影响力.结果表明：①时间上,2000~2021年山东省ρ（PM_2.5）均值在38.15~88.63 μg·m^-3之间,略微高于《环境空气质量标准》中可吸入颗粒物的二级标准限值（35 μg·m^-3）.在年际尺度上,2013年是ρ（PM_2.5）变化的峰值年,其值为83.36 μg·m^-3,据此将山东省PM_2.5浓度变化趋势分为两个阶段：持续上升和快速下降阶段.在季节尺度上,PM_2.5浓度呈现“夏低冬高,春秋居中”分布特征和先降后升的“U”型变化规律.②空间上,山东省PM_2.5浓度呈现出“西高东低”的空间分布格局,PM_2.5浓度高值区分布山东省西部地区,低值区则分布在东部半岛地区.PM_2.5浓度空间变化趋势呈现显著的空间异质性,极显著下降的区域主要分布在东部半岛地区.③因子探测结果表明,气候因子是影响山东省PM_2.5浓度空间分异的重要影响因素,平均气温对山东省PM_2.5浓度空间分异的影响最高,q值为0.512.省-市-县多尺度探测结果显示,影响PM_2.5浓度空间分异的影响因子及其影响力在不同空间尺度上具有差异性.省级尺度上,平均气温、日照时数和坡度是影响PM_2.5浓度空间分异的主要影响因子;市级尺度上,降水、高程和相对湿度是影响PM_2.5空间分异的主要影响因子;县级尺度上,降水、平均气温和日照时数是影响PM_2.5浓度空间分异的主要影响因子.     

青藏高原四季日照时数年际、年代际变化趋势分析

利用1961-2007年青藏高原日照时数资料,通过统计方法初步分析了近47年青藏高原四季日照时数的年际、年代际变化特征,得到以下几点初步认识：青藏高原四季日照时数整体上均呈现自东南向西北增加的特点,其空间变化也存在明显的区域差异：青藏高原西部和中部日照时数增加,高原东南部和北部呈减少的趋势。近47年来青藏高原四季日照时数年际和年代际变化明显,总体均呈减少趋势,20世纪60年代以偏少为主,70年代和80年代整体偏多,90年代和21世纪初高原日照时数以偏少为主,各年代之间日照时数区域差异明显。     

Comparison of Ground Water Bacterial Cell Sizes from the Agricultural, Domestic and Industrial Areas of Mysore District, Karnataka State, India

A two-year study on temporal variations in the ground water heterotrophic bacterial cell sizes of free living bacteria(FLB)and particle bound bacteria(PBB)from the agricultural,domestic and industrial areas was carried out from Februar y2005 to January 2007.The overall mean cell length of FLB and PBB was similar in all the ground water studied.However,the season wise grouped data revealed significant seasonal changes in cell length of FLB and PBB,as smaller bacteria were noticed during rainy season in the ground water in agricultural area in both the years,and only in the second year of study in domestic and industrial areas.Generally,it was noticed that there were summer maximum and rainy minimum values of the cell length of PBB in the ground water in agricultural,domestic and industrial areas in the second year of study.The Pearson's correlations showed the presence of 8(in agricultural area),5(in domestic)and 3(in industrial) significant correlations with environmental(Physico-chemical)parameters,respectively.The regression analysis revealed that as much as 12%of variation in the mean length of FL Bwas due to NO3( )in agricultural area and 9%due to total solids( )indomestic area.However,the 8% variation in bacterial cell size of FLB was due to Mg( )in industrial area.Whereas,13%variation in mean length of PBB was due to S04( )in agncultural area and 10%due to total anions of strong acid(TASA)( )in domestic area.Furthermore,10% of variation Was due to PO4( )in industrial area.Thus,the statistical analysis revealed that several environmental variables were potentially responsible for some of the temporal variations in aquatic heterotrophic bacterial cell size,suggesting probably the stressed environment in these ecosystems.     

Measurement of Atmospheric Deposition Under Forest Canopies: Some Recommendations for Equipment and Sampling Design

Quantification of the forest water flux provides valuable information for the understanding of forest ecosystem functioning. As such, throughfall (and stemflow to a lesser extent) has been frequently measured. Although throughfall collection may seem relatively simple, the requirements to obtain reliable estimates are often underestimated. This review addresses the criteria to take into account when working out the sampling procedure, from the selection of equipment to implementation in the field. Sound sampling of the forest water flux is difficult due to its high spatial and temporal variation. The high costs entailed by the ideal sampling design often prohibit its implementation. Different procedures are available, some of which are compromises between the aim of the study (monitoring or experimental study, short or long term objectives, absolute or relative estimates, quality of the assessment to be achieved) and the available means.     

多种方法测量全国辐射环境监测质量考核样对比研究

介绍了有源效率刻度法及实验室γ谱无源效率刻度系统(LabSOCS)在样品活度浓度分析中的原理,利用多型号低本底高纯锗γ谱仪,通过生态环境部辐射环境监测技术中心(下称技术中心)提供的沉降物考核样品,进行了两种分析方法的对比分析,对LabSOCS软件可靠性进行验证并对比不同型号探测器性能.两种方法所得核素活度浓度结果与技术...     

Distribution of perfluorinated alkyl substances in marine shellfish along the Chinese Bohai Sea coast

Perfluorinated alkyl substances (PFASs) are emerging persistent organic pollutants, which pose a threat to human health primarily by dietary exposure, especially through seafood. Bohai Sea (a semi-closed sea located north of China) is an important shellfish aquaculture area that is possibly highly-polluted with PFASs. In this study, we first evaluated contamination by PFASs in a total of 230 samples of marine shellfish from the Bohai Sea. Samples included five important shellfish species, collected from important aquaculture spots distributed around the Bohai Sea. Samples were analyzed by an ultra-fast liquid chromatography-tandem mass spectrometry method, which could simultaneously detect 23 PFASs in shellfish. Our research verified that PFASs have become a threat to the safety of shellfish products in this area. Furthermore, contamination by PFASs in shellfish changed depending on the components of PFASs, the species of shellfish, and the sampling sites. Many of the 23 target compounds contributed to the high detection ratio (>50%) as follows: perfluorooctanoic acid (PFOA)?>?perfluorononanoic acid?>?perfluorodecanesulfonic acid?>?perfluorooctanesulfonic acid (PFOS). Compared with other dominant components, PFOA not only had the highest detection percentage in shellfish samples (98.3%), but its detection level contributed to 87.2% of total PFASs concentrations, indicating that PFOA is the major threat to the safety of shellfish products. The highest level of PFAS was found in clams (62.5?ng?g^?1 wet weight of PFOA). The concentration of total PFAS in different shellfish species showed the following trend: clams?>?mussels?>?scallops?>?whelks?>?oysters. The maximum concentration of total PFAS or PFOA was found in Shouguang. The total concentration of PFOS and its precursor were highest in Cangzhou, possibly due to local industrial activities. The results presented in this paper provide new data on the contamination of marine shellfish along the Bohai Sea coasts in China, and constitute a reference for future monitoring of contamination by emerging contaminants in Bohai coast.