仅知失效数的指数型元件失效率的估计

目的基于仅知失效元件数而不知其确切寿命的试验数据,对指数型元件的失效率进行估计。方法设在时刻t_0=0以n个指数型元件进行寿命试验,但仅在时刻t_0t_1…t_k记录失效的元件数,即在[t_0,t_1],[t_1,t_2],…,[t_(k-1),t_k]内可以观测到失效的元件数,但失效元件的确切寿命未知,将各时间段内的失效元件数分别记为r_1,r_2,…,r_k,在t_k时刻未失效的元件数记为r_(k+1)。采用改进的条件中数的方法,计算元件在[t_0,t_1],[t_1,t_2],…,[t_(k-1),t_k],[t_k,∞]的条件中位寿命分别为μ_1,μ_2,…,μ_k,μ_(k+1),将[t_(i-1),t_i]内失效的r_i个元件的寿命均近似看作μ_i,未失效的r_(k+1)个元件的寿命近似看作(t_k+μ_(k+1))/2,进而估计元件的失效率,并对此方法进行仿真。结果仿真结果表明,改进后的估计结果得到改善。结论对于此类数据,改进的条件中位数方法可以有效估计元件的失效率,并可应用于实际。     

北京市不同区域大气气溶胶粒子中水溶性离子的特征

在北京市两个区域同时采集不同粒径的气溶胶粒子,利用离子色谱分析了样品中的水溶性无机离子组分．研究发现,城乡结合带采集的总水溶性离子浓度比郊区高．两地水溶性离子浓度有明显的季节变化趋势,SO4^2-浓度冬季最高,而夏季许多离子浓度普遍较低,NO3^-质量中值直径随季节变化有明显的不同．Na^ 浓度受地表植被影响较大．两地NO3^-,SO4^2-,NH4^ ,K^ 四种离子间的相关系数很好,可能是因为这些离子的来源相似．     

Two-way left turn lane or raised median? A truck safety based study

Introduction: Due to their size and weight, trucks require more space and time to make left turns when exiting or entering a roadway. Therefore, appropriate median treatments are critical for roadways with substantial truck traffic. The two-way left-turn lane (TWLTL) and raised median (RM) are the two types of median most commonly used to improve roadway mobility and manage roadway accessibility. However, previous studies on these median treatments have focused primarily on the general traffic conditions and geometric roadway features without considering the truck traffic impact. Method: To fill this gap, this study investigates the truck impacts on TWLTL and RM by considering two major influencing factors – truck percentage and roadway access point density. First, a negative binomial regression is developed to analyze the relationship between crash frequency and various influencing factors. Next, the crash rate difference analysis between the TWLTL and RM is conducted to identify critical points for these two factors. Results: The findings indicate that, compared with RM, TWLTL has significantly higher crash frequency, especially for roadways with a higher percentage of trucks. This suggests that the percentage of trucks should be taken into consideration when selecting an appropriate type of roadway median.     

Impact of a proposed revision of the IESTI equation on the acute risk assessment conducted when setting maximum residue levels (MRLs) in the European Union (EU): A case study

ABSTRACT

Proposals to update the methodology for the international estimated short-term intake (IESTI) equations were made during an international workshop held in Geneva in 2015. Changes to several parameters of the current four IESTI equations (cases 1, 2a, 2b, and 3) were proposed. In this study, the overall impact of these proposed changes on estimates of short-term exposure was studied using the large portion data available in the European Food Safety Authority PRIMo model and the residue data submitted in the framework of the European Maximum Residue Levels (MRL) review under Article 12 of Regulation (EC) No 396/2005. Evaluation of consumer exposure using the current and proposed equations resulted in substantial differences in the exposure estimates; however, there were no significant changes regarding the number of accepted MRLs. For the different IESTI cases, the median ratio of the new versus the current equation is 1.1 for case 1, 1.4 for case 2a, 0.75 for case 2b, and 1 for case 3. The impact, expressed as a shift in the IESTI distribution profile, indicated that the 95th percentile IESTI shifted from 50% of the acute reference dose (ARfD) with the current equations to 65% of the ARfD with the proposed equations. This IESTI increase resulted in the loss of 1.2% of the MRLs (37 out of 3110) tested within this study. At the same time, the proposed equations would have allowed 0.4% of the MRLs (14 out of 3110) that were rejected with the current equations to be accepted. The commodity groups that were most impacted by these modifications are solanacea (e.g., potato, eggplant), lettuces, pulses (dry), leafy brassica (e.g., kale, Chinese cabbage), and pome fruits. The active substances that were most affected were fluazifop-p-butyl, deltamethrin, and lambda-cyhalothrin.     

四氟硼酸化1-烷基—3-甲基咪唑离子液体对小鼠的急性经口毒性

采用寇式改良法研究了四氟硼酸化1-烷基—3-甲基咪唑离子液体对小鼠的急性毒性,考察了烷基侧链长度对毒性的影响,同时采用HE染色法观察了离子液体对小鼠胃、小肠、大肠、肝和肾组织的损害.结果表明,4种离子液体([Cnmim] BF4,n=10、12、14、18)对小鼠的肠、肝、肾等组织均有损伤,其LD50值在56.16 ～214.18 mg·kg-1之间,为中等毒性.四氟硼酸化1-烷基—3-甲基咪唑离子液体对小鼠的急性毒性与烷基侧链长度有关,当碳链长度为14时,毒性最强.     

黄河口湿地表层沉积物中磷赋存形态的分析

于2009年4月在黄河口湿地采集表层沉积物,利用改进后的SEDEX方法对沉积物样品进行了磷形态的分析.结果表明,表层沉积物中总磷含量变化范围为12.12~25.37μmol·g-1,平均值为20.70μmol·g-1,其中自生磷灰石磷和碎屑磷灰石磷为表层沉积物中磷的主要赋存形式.中值粒径与各形态磷含量密切相关,弱吸附态磷、自生磷灰石磷、活性有机磷含量与中值粒径呈显著负相关关系;碎屑磷灰石磷含量与中值粒径呈显著正相关关系.有机质含量影响各形态磷在沉积物中含量,弱吸附态磷、活性有机磷、自生磷灰石磷含量均随TOC含量增加而升高.包括弱吸附态磷、活性有机磷和铁结合态磷在内的生物可利用磷含量变化为1.15~6.74μmol·g-1,平均值为4.27μmol·g-1,占总磷的摩尔分数为6.35%~30.4%.     

吸气式管道尺寸及温差对烟颗粒输运的影响

在火灾标准燃烧室中,用扫描电迁移粒谱仪测量单孔采样的吸气管道内5种标准试验火烟雾颗粒浓度和粒径分布的变化,分析管道输运中管道参数对烟颗粒数目浓度损耗和中位径的影响.结果表明,在管道输运中,平均粒径相对较小的热解和阴燃烟雾颗粒.其小于0.1μm的超细颗粒部分的浓度损耗随管道长度的增加而增大,且烟颗粒平均粒径随管道增长而增大.而明火烟雾在管道输运中,由于管道与高温烟雾的温差增大,导致0.1～1 μm颗粒的管壁沉积损耗增大,使烟颗粒数浓度下降,中位径减小了几个纳米.火灾早期,火灾阴燃和热解期间小于0.1 μm的烟颗粒数目浓度占15%以上,因此,用较短的管道或者管道分级预警的方式可以减少滞留时间,提高极早期感烟探测的灵敏度.     

塔里木盆地气溶胶粒度分布研究

使用Series 210收集了塔里木盆地内6个不同地点的气溶胶,获取了该地区气溶胶的粒度分布,并计算了对应的气溶胶数量中位直径。研究发现:在自然情况下,气溶胶分布遵循双峰分布的规律,其中第一峰值通常出现在0.5μm附近,第二峰值出现在3μm附近;由于采样点的气象条件、地表情况等差异所致,不同采样地点的峰位和峰面积有一定的差异;各采样点气溶胶分布规律显示,绝大多数气溶胶粒子粒径小于1μm。自然条件下,大多数采样点气溶胶粒子数量中位直径小于1μm。     

环境对某型飞机典型结构部位疲劳寿命影响分析

目的 研究环境对飞机典型结构部位疲劳寿命的影响。方法 选取某型机机身连接壁板、机翼壁板、机翼内部大梁结构、平尾接头及垂尾接头的典型模拟件为研究对象,开展实验室加速腐蚀与随机载荷谱交替试验、载荷谱疲劳试验,分析环境对典型结构部位模拟件表面涂层损伤、疲劳断裂位置、疲劳源及中值寿命的影响,建立环境对结构部位疲劳寿命影响关系。结果 采用载荷作用后结构部位模拟件疲劳中值寿命与加速腐蚀环境-疲劳寿命后试样的疲劳中值寿命比值,估算环境对结构部位模拟件疲劳寿命的影响,比值k=1.2~2.5,且比值k越大,说明环境对试样的疲劳寿命影响越大。结论 采用载荷作用后结构部位模拟件疲劳中值寿命与加速环境-疲劳寿命后试样的疲劳中值寿命比值,可初步估算环境对结构部位模拟件疲劳寿命的影响,且试验结果表明,外部环境较内部环境对试样疲劳寿命的影响更大。     

The influence of confounding factors on the relationship between muscle contraction level and MF and MPF values of EMG signal: a review

The purpose of this article is to gather results of studies on the relationship between median frequency (MF) and mean power frequency (MPF) and the level of muscle contraction, and to use those results to discuss the differences in the trends according to factors related to measurement technique and subject. Twenty-one studies with 63 cases for upper limb muscles and nine studies with 31 cases for lower limb muscles were analysed. Most results showed an increase in parameters with an increased level of muscle contraction, only some studies showed a decrease. The influence on parameters of the level of muscle contraction and factors such as subjects, type of contraction, muscle length and electrodes was analysed for each muscle. It was concluded that when analysing the influence of different factors on MF and MPF, because those factors interact they should be considered together, not separately.