A Distributed Parameter Physiologically-Based Pharmacokinetic Model for Dermal and Inhalation Exposure to Volatile Organic Compounds

Estimates of dermal dose from exposures to toxic chemicals are typically derived using models that assume instantaneous establishment of steady-state dermal mass flux. However, dermal absorption theory indicates that this assumption is invalid for short-term exposures to volatile organic chemicals (VOCs). A generalized distributed parameter physiologically-based pharmacokinetic model (DP-PBPK), which describes unsteady state dermal mass flux via a partial differential equation (Fickian diffusion), has been developed for inhalation and dermal absorption of VOCs. In the present study, the DP-PBPK model has been parameterized for chloroform, and compared with two simpler PBPK models of chloroform. The latter are lumped parameter models, employing ordinary differential equations, that do not account for the dermal absorption time lag associated with the accumulation of permeant chemical in tissue represented by permeability coefficients. All three models were evaluated by comparing simulated post-exposure exhaled breath concentration profiles with measured concentrations following environmental chloroform exposures. The DP-PBPK model predicted a time-lag in the exhaled breath concentration profile, consistent with the experimental data. The DP-PBPK model also predicted significant volatilization of chloroform, for a simulated dermal exposure scenario. The end-exposure dermal dose predicted by the DP-PBPK model is similar to that predicted by the EPA recommended method for short-term exposures, and is significantly greater than the end-exposure dose predicted by the lumped parameter models. However, the net dermal dose predicted by the DP-PBPK model is substantially less than that predicted by the EPA method, due to the post-exposure volatilization predicted by the DP-PBPK model. Moreover, the net dermal dose of chloroform predicted by all three models was nearly the same, even though the lumped parameter models did not predict substantial volatilization.     

How Inventory Cost Influences Introduction Timing of Product Line Extensions

In the industry with radical technology push or rapidly changing customer preference, it is firms' common wisdom to introduce high‐end product first, and follow by low‐end product‐line extensions. A key decision in this “down‐market stretch” strategy is the introduction time. High inventory cost is pervasive in such industries, but its impact has long been ignored during the presale planning stage. This study takes a first step toward filling this gap. We propose an integrated inventory (supply) and diffusion (demand) framework and analyze how inventory cost influences the introduction timing of product‐line extensions, considering substitution effect among successive generations. We show that under low inventory cost or frequent replenishment ordering policy, the optimal introduction time indeed follows the well‐known “now or never” rule. However, sequential introduction becomes optimal as the inventory holding gets more substantial or the product life cycle gets shorter. The optimal introduction timing can increase or decrease with the inventory cost depending on the marketplace setting, requiring a careful analysis.     

基于网络效应的竞争性产品微观扩散研究

竞争性产品扩散是成熟市场的重要表现,网络效应的存在不仅改变了传统的扩散模式, 而且对个体采纳行为有重要影响． 但是以往研究竞争性产品扩散侧重于宏观层面的扩散速度和扩散效果,忽略了微观层面个体的个性以及社会交互等特点对产品扩散的影响,因此需要基于网络效应从个体微观层面研究竞争性产品扩散的特点． 首先构建了基于个体间交往关系的直接网络效应函数和基于多种互补产品协同作用下的间接网络效应函数,然后,个体将计算自己当前时刻的收益以及下一时刻的预期收益,并根据预期社会化效益满意决策机制确定下一时刻的产品选择． 通过仿真对扩散系统进行研究,结果表明: 直接网络效应和间接网络效应对竞争性产品扩散具有阶段性影响; 在小世界网络的社会交往结构中竞争性产品扩散效果最好; 个体人数分布、偏好、对环境的判断都对竞争性产品扩散有重要影响．     

中国风能技术扩散的规律及政策影响分析

基于广义Bass模型,对比中国与世界其他风能先进国家在技术创新水平和模仿水平上的差异,考察外生政策冲击对中国风能技术扩散的影响。利用常规Bass模型、广义Bass模型、Logistic模型和Gompertz模型等多个预测模型对中国未来风能技术的扩散趋势进行短期预测,并对其预测精度和结果差异进行对比和分析。研究结果表明,中国风能技术市场的创新水平显著低于其他风能技术较为先进的欧美国家,甚至低于同为发展中国家的印度,模仿水平在所有考察国家中最高;中国风能技术扩散过程受指数冲击和矩形冲击的影响,但两种外部冲击的影响程度均较弱;中国风能技术急速增长的阶段已经过去,且于2010年达到增长的阶段性峰值点,未来的增速将显著放缓。针对上述结论给出促进中国风能长效发展的相关政策建议。     

更新扩散模型与最优广告费用控制

从消费者购买行为的分析,应用贝叶斯风险决策理论,研究了新产品的市场扩散过程,建立了耐用消费品及重复性购买产品的总体市场扩散模型。在考虑广告和已购者信息传播效应基础上,应用最优控制理论,得出了广告费用的最优控制策略。     

Intra-firm Adoption Decisions:: Role of Inter-firm and Intra-firm Variables

The subject of this paper is intra-firm adoption decisions, a relatively unexplored research area in the marketing literature. We develop a conceptual model in which two sets of independent variables are hypothesized to influence the intra-firm adoption decisions, i.e. (1) variables known from the inter-firm diffusion literature, (2) variables specifically relevant for intra-firm analyses of innovation acceptance. Hypotheses are developed and tested in an application in the domain of finance: the intra-firm adoption decisions regarding the common European currency by the treasury, purchasing and sales departments of European companies. Data were obtained from treasury, purchasing and sales managers (441 respondents in total) from companies located in five different European countries. The results of logistic regression show that the proposed intra-firm variables are indeed important explanatory variables that should be included in intra-firm analyses. Moreover, for the inter-firm variables we found differences in the effects between departments, which demonstrates the very need for an intra-firm analysis.     

一个巨灾风险模型破产概率的估计

巨灾风险是目前理论界和保险事务界十分关注的重大问题,如何用数学模型描述巨灾保险经营过程更是其中一个关键性问题,其中运用带干扰的Cramér-Lundberg风险模型描述巨灾保险经营过程是保险理论界比较认同的模型。另外,巨灾所引起的保险索赔分布通常属于重尾分布,比如标准的对数正态分布。在此情形下破产概率的精确表达式一般很难求得,因此破产概率的表达式一般就通过渐近等价估计式进行表达。     

区域品牌能级与区域自主品牌群发展

根据品牌实力、品牌前景、品牌扩散力三项指标,可以评价区域内不同品牌的能级。而由于区域内自主品牌群具有非均衡发展和梯度扩散的特征,要促进区域内整个品牌群系统效应的发挥,就须针对不同能级层次的品牌实施不同的发展策略:重点扶持高能级品牌,提升品牌竞争力,吸引优势资源;构建品牌交流平台,促进较低能级品牌的成长;注重品牌系统生态化,整体提升区域品牌竞争力。     

人力资本与国际技术扩散:基于进口贸易的实证研究

在CH模型的基础上,纳入了人力资本变量,构建了包含人力资本与国外研发共同作用项的进口贸易技术扩散测度模型,并利用我国和15个OECD国家1990-2004年的数据,运用不同的人力资本度量指标对进口贸易技术扩散效应进行了检验。实证结果表明,通过进口贸易传导机制,国外研发的溢出对我国技术进步产生了显著的促进作用,但由于存在人力资本的临界效应,我国人力资本与国外研发溢出还没有很好的结合,基于此本文提出了相应的政策建议。