Multilevel modeling in traffic safety research: two empirical examples illustrating the consequences of ignoring hierarchies

OBJECTIVES: This commentary illustrates the advantages of multilevel modeling compared to statistical techniques that ignore hierarchies, based on two empirical traffic safety examples. METHODS: The common concept shared by different definitions of multilevel modeling is identified and illustrated. Each definition defines multilevel modeling in its own way but they all refer to hierarchies. Conceptual issues inherently related to hierarchies are then pointed out and illustrated. RESULTS: Broadly speaking there are two important consequences of ignoring a hierarchical structure in the data. The first consequence, underestimation of standard errors, is illustrated with data from an observational study on seatbelt behavior. Two effects that were significant at the 5% level in a single-level model were no longer found to be significant in a two-level model. The single-level model is therefore bound to lead to erroneous conclusions regarding variables that could have an impact on seatbelt use and, ultimately, on increasing the level of traffic safety. The second consequence, related to contextual information, is illustrated with data from a roadside survey on drink driving. Of particular interest is the relationship between Traffic Count, an aggregated level 2 explanatory variable and Odds of drink driving, an individual level 1 dependent variable. CONCLUSIONS: Like every statistical technique, multilevel models should be used with caution and reservation. However, given certain limitations, multilevel modeling is very useful and valuable to traffic safety research.     

Photochemistry of hydrolytic iron (III) species and photoinduced degradation of organic compounds. A minireview

On the basis of the research literature of the last fifty years, we have reviewed the photochemical properties of different hydrolytic Fe(III) species and the photodegradation of organic compounds in aqueous solutions initiated by them (mainly including low-molecular-weight Fe(III)-OH complexes, Fe(III) oxides (Fe2O3) and Fe(III) hydroxides (FeOOH)). Furthermore, the feasibility and prospects of the novel photochemical methods of using Fe(III) salts and oxides in wastewater treatments are being discussed in this paper.     

Photoinduced addition of the fungicide anilazine to cyclohexene and methyl oleate as model compounds of plant cuticle constituents

Photoreactions, initiated by sunlight irradiation, between organochlorine pesticides and olefinic compounds of plant cuticles have been postulated. Concerning the formation of bound residues, which so far have not been detectable by common analytical techniques, photoaddition reactions are of main interest. In order to study the photochemical behavior of chlorinated fungicides, anilazine was irradiated in cyclohexene and methyl oleate as model compounds for olefinic plant cuticle constituents. Anilazine extensively reacted with the cis-double bond of both model compounds via radical mechanisms. In addition to a dechlorinated photoproduct several addition products were formed showing plausible reaction pathways for the formation of bound residues in plant cuticles. Photoproducts were isolated by preparative HPLC and analyzed by HPLC, MS, 1H-, and 13C-NMR.     

Microcalorimetric studies of the toxic action of La3+ in mitochondria isolated from Star-cross 288 chicken heart tissue cells

The thermogenic curves of the metabolism of mitochondria isolated from the heart of chicken Star-cross 288 and the effect of La3+ on it were studied by using an LKB-2277 BioActivity Monitor, ampoule method, at 37 degrees C. After isolation from the chicken heart tissue, mitochondria still have metabolic activity and can live for a long time by using the stored nutrients. From the thermogenic curves, we obtained the thermokinetic equations under different conditions. The kinetics show that La3+ has changed the metabolism completely.     

1979年蒸发盐研究

<正> 对近代盐沼蒸发盐(在干燥的潮上环境中形成的蒸发盐)文献的编集和对古代盐沼蒸发盐层序的识别,如同过去十多年的情况一样,在1979年蒸发盐报告中,继续占着主要地位。在七月号的《地质学》杂志上,I.M.West等论述了埃及地中海沿岸现代盐沼中的石膏结核。这些石膏结核是在砂质盐沼沉积物中由于超盐(hypersallne)地下水的沉淀作用而生长的透镜状石膏晶体的增大而形成的。West等对埃及现代的盐沼结核和他们认为是在同样环境中形成的英格兰下波倍克建造(上侏罗统)中的石膏结核作了比较。透镜状石膏晶体,象West等所描述的石膏原结     

不列颠哥伦比亚省海兰—伐利斑岩铜矿床周围铷和锶的原生分布

前言 根据契利安—安第斯(Chilcan And-es)地区近年来的地球化学研究结果,Arm-brust 等(1971)和 Oyarzun(1971,1974认为 Rb 和 Sr 是产于蚀变安山岩和玄武岩中斑岩铜矿床的潜在指示剂,但后者发现这对于蚀变花岗岩侵入体作地球化学对比不太适合。Warren 等(1974)提出把 Ba 和 Sr 作为寻找火山岩中矿体的地球化学手段。这些应用的地球化学和地质学根据与斑岩铜矿床有关的某些类型的热液蚀变中 Rb 的普遍富集和 Sr 的减少有关。     

热液矿床中金属及伴生元素的来源

绪论 热液矿床中金属及伴生元素的来源,长期来一直是地质学家们争论的课题之一。自阿格利科拉(AgricoIa)时期以来,认为有四种可能性,列述如下: (1) 元素来自地球深部。地幔常被认为是可能的来源,甚至更深的部位也曾有人提及。 (2) 元素来自结晶的岩浆体。一些研究者倾向于基性岩浆,另一些人倾向于形成花岗闪长岩和花岗岩的酸性岩浆。如果这些岩浆岩出露于地表或者能在     

生油岩石油成熟度测量的新方法

<正> 前言公认的石油形成理论都假定生物为石油的来源。海相和陆相成因的有机质聚集起来并在早期成岩阶段转变成非晶质的、不溶的、含烃的所谓干洛根物质(Dow,1977)。当沉积物进一步埋藏时,沉积物的温度就升高,最后达到某一温度点,开始出现干洛根的热裂解(Tissot 等,1971;de Tran 等,     

应用石油地球化学找油(加拿大西部盆地的例子)

引言 在勘探过程的早期阶段,石油地球化学能够帮助预测盆地中各种类型烃的分布。在地质上不复杂的加拿大西部盆地,是表明地球化学实际应用于烃类勘探的一个极好的地区。