A Physiologically-Based Pharmacokinetic Model Assessment of Methyl t-Butyl Ether in Groundwater for a Bathing and Showering Determination

Methyl t -butyl ether (MTBE) is a gasoline additive that has appeared in private wells as a result of leaking underground storage tanks. Neurological symptoms (headache, dizziness) have been reported from household use of MTBE-affected water, consistent with animal studies showing acute CNS depression from MTBE exposure. The current research evaluates acute CNS effects during bathing/showering by application of physiologically-based pharmacokinetic (PBPK) techniques to compare internal doses in animal toxicity studies to human exposure scenarios. An additional reference point was the delivered dose associated with the acute Minimum Risk Level (MRL) for MTBE established by the Agency for Toxic Substances and Disease Registry. A PBPK model for MTBE and its principal metabolite, t -butyl alcohol (TBA) was developed and validated against published data in rats and humans. PBPK analysis of animal studies showed that acute CNS toxicity after MTBE exposure can be attributed principally to the parent compound since the metabolite (TBA) internal dose was below that needed for CNS effects. The PBPK model was combined with an exposure model for bathing and showering which integrates inhalation and dermal exposures. This modeling indicated that bathing or showering in water containing MTBE at 1 mg/L would produce brain concentrations ˜1000-fold below the animal effects level and twofold below brain concentrations associated with the acute MRL. These findings indicate that MTBE water concentrations of 1 mg/L or below are unlikely to trigger acute CNS effects during bathing and showering. However, MTBE's strong odor may be a secondary but deciding factor regarding the suitability of such water for domestic uses.     

A Physiologically Based Pharmacokinetic Assessment of Tetrachloroethylene in Groundwater for a Bathing and Showering Determination

A two-step methodology is described to make a health-based determination for the bathing and showering use of the water from a private well contaminated with volatile organic chemicals. The chemical perchloroethylene (PERC) is utilized to illustrate the approach. First, a chemical-specific exposure model is used to predict the concentration of PERC in the shower air, shower water, and in the air above the bathtub. Second, a physiologically based pharmacokinetic (PBPK) model is used to predict the concentration of PERC delivered to the target tissue, the brain, since the focus is on neurological endpoints. The simulation exercise includes concurrent dermal and inhalation routes of exposure. A reference target tissue level (RTTL) in the brain is estimated using the PBPK model. A hazard index based on this benchmark guideline is used to make a regulatory determination for bathing and showering use of the contaminated water.     

The Dynamics of Pre‐ and Post‐purchase Service and Consumer Evaluation of Online Retailers: A Comparative Analysis of Dissonance and Disconfirmation Models*

This article explores the theoretical underpinnings of the dissonance framework in online consumer satisfaction formation process. Specifically, we suggest that any discrepancy between pre‐ and post‐purchase service performance would help determine consumers’ evaluations of online vendors. Drawing upon cognitive dissonance theory, a conceptual model is developed and tested in two different studies (preliminary and main studies). Using data from 191 college students collected longitudinally, the preliminary study demonstrates the validity and reliability of the measurements. Using a comparative analysis, the main study then tests our conceptual model as well as various competing models, including the expectation–confirmation model, with a sample of 292 online consumers. The results in both studies support our main prediction that the service encountered in different stages establishes dissonance. Specifically, we find that dissonance explains online consumers’ satisfaction process to a substantial extent, as compared with disconfirmation under the same conditions in online retailers. This study contributes to providing an alternative yet substantial approach for expectation–confirmation theory, reflecting the overarching nature of online shopping.     

Tests for Trend in Developmental Toxicity Experiments with Correlated Binary Data

In this article, the operating characteristics of recently proposed tests for trend in correlated binary data arising in laboratory studies of developmental toxicity are examined using both computer-generated and experimental data. Specifically, we consider adjusted Cochran-Armitgc tests based on the Rao-Scott transformation which are of the same general form as that for uncorrelated data. In addition, generalized score tests based on generalized estimating equations allowing for extra-binomial variation in the data are discussed. Specific forms of these statistics demonstrating favorable type I and type II error rates are identified and recommended for use in practice. The application of these tests is illustrated using data from studies of developmental toxicity that have been reported in the literature.     

46家国内企业使命陈述的实证分析

本文根据弗雷德·R·戴维提出的九要素标准对国内46家企业的使命陈述进行了实证分析和评价。结果发现:(1)国内企业在制定使命陈述的时候最关注的要素是产品和服务、观念,其次是市场、关心员工、技术和自我认知等要素,而最不关注的是对公众形象的关切要素和顾客要素。(2)根据九要素评价标准,国内企业在使命陈述制定水平上尚须提高。(3)高科技企业的使命陈述比传统型企业的要好,在具体评价指标上,高科技企业也要好于传统型企业。另外,服务型企业的使命陈述与生产制造型企业也有差异,部分要素的偏重有所不同。(4)国内企业的使命陈述比较重视创新精神,还有部分企业的使命陈述表现出较强的民族情感。     

Connecticut's Dioxin Ambient Air Quality Standard

Connecticut is the first state in the country to have adopted an ambient air quality standard for dioxins at 1 pg/m³, 2,3,7,8-TCDD equivalents, as annual average. This paper describes the scientific basis and the methodology used by the State Department of Health Services (the risk assessment agency) in assisting the Department of Enviromental Protection (the risk management agency) to establish a health-based dioxin standard. This standard protects the public health from the aggregate effect of all sources of dioxin emissions in the vapor and particulate phases. The risk assessment methodology included: a limit on total daily dioxin exposure from all media and sources based on reproductive effects; a multimedia nonsource-specific exposure assessment; an apportionment by media of the health-based limit (including background dosing rate); an evaluation of inhalation bioavailability and cancer risk based on a calculation of a range of upperbound cancer risk estimates using different potency, bioavailability, and particle phase assumptions.     

在线品牌社群产品知识与结构洞：互依自我的调节

在线品牌社群本质上是社会网络,而结构洞是社会网络中关系形成的关键节点。以产品知识为前因,研究成员嵌入在线品牌社群结构洞位置的原因以及结构洞位置对品牌社群承诺和品牌承诺的影响,同时探讨互依自我在产品知识与结构洞之间的调节效应以及品牌社群承诺在结构洞与品牌承诺之间的中介效应。通过网上调研平台“问卷星”收集500份有效问卷,采用自我中心网的关系数据,通过UCINET软件计算结构洞位置,再使用偏最小二乘法进行实证检验。研究结果表明,产品知识对结构洞位置的占据有正向影响,互依自我对产品知识与结构洞位置之间的关系起正向调节作用,结构洞位置通过品牌社群承诺的完全中介作用影响品牌承诺。研究结论在理解社会网络与在线品牌社群之间的关系方面具有理论意义,对于在线品牌社群建构社会网络具有实践意义。     

SLOW INFORMATION DIFFUSION AND THE INERTIAL BEHAVIOR OF DURABLE CONSUMPTION

This paper studies the aggregate dynamics of durable and nondurable consumption under slow information diffusion (SID) due to noisy observations and learning within the permanent income hypothesis framework. We show that SID can significantly improve the model's predictions on the joint behavior of income, durable consumption, and nondurable consumption at the aggregate level. Specifically, we find that SID can significantly improve the model's predictions for: (i) smoothness in durable and nondurable consumption, (ii) autocorrelation of durable consumption, and (iii) contemporaneous correlation between durable and nondurable consumption.