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.     

Simple and Explicit Estimating Functions for a Discretely Observed Diffusion Process

We consider a one-dimensional diffusion process X , with ergodic property, with drift b ( x , θ) and diffusion coefficient a ( x , θ) depending on an unknown parameter θ that may be multidimensional. We are interested in the estimation of θ and dispose, for that purpose, of a discretized trajectory, observed at n equidistant times t_i = iΔ , i = 0, ..., n . We study a particular class of estimating functions of the form ∑ f (θ, X _{t i −1}) which, under the assumption that the integral of f with respect to the invariant measure is null, provide us with a consistent and asymptotically normal estimator. We determine the choice of f that yields the estimator with minimum asymptotic variance within the class and indicate how to construct explicit estimating functions based on the generator of the diffusion. Finally the theoretical study is completed with simulations.     

形象资源与公共关系活动

在现代社会中 ,形象已经成为一种资源——形象资源。形象资源就其特征和发挥作用的方式来看 ,与主体的公共关系活动存在着十分密切的关系 ,具有高度的一致性。因此 ,将公共关系活动与形象资源的培植与开发活动紧密结合起来 ,才能取得最佳的效果。     

Discretely Observed Diffusions: Approximation of the Continuous-time Score Function

We discuss parameter estimation for discretely observed, ergodic diffusion processes where the diffusion coefficient does not depend on the parameter. We propose using an approximation of the continuous-time score function as an estimating function. The estimating function can be expressed in simple terms through the drift and the diffusion coefficient and is thus easy to calculate. Simulation studies show that the method performs well.     

网络虚拟社区与幼儿教育的实证分析——以南京市鼓楼区幼儿园网站为例

选取幼儿园网站作为观察视角，以问卷调查为研究方法，对家长对以幼儿园网站为代表的虚拟社区的认同状况、家长对幼儿园网站在幼儿教育方面的评价状况以及虚拟社区之中信息交流的模式进行统计分析。研究结果表明，网络虚拟社区是当前中国城市年轻父母幼儿教育的一个重要的知识来源。家长对网络虚拟社区作为幼儿教育知识途径的认同状况，取决于使用媒介的习惯与人的因素合力的结果，其中教育程度和年龄是重要的变量。对幼儿园网站的总体评价和在幼儿人格成长、知识技能进步等具体方面的评价存在差异。幼儿园网站之上形成的虚拟社区中存在着传播权力不平衡的状况，其信息交流模式是一种综合模式。     

基于企业集群的技术创新扩散激励机制研究

通过对企业集群内部技术创新扩散的特征和活动进行分析,揭示了企业集群在保持创新扩散持续性过程中所存在的障碍,利用激励理论中的委托--代理理论,搭建起企业集群内部技术创新扩散激励机制框架,借鉴"锦标机制"方法构建了企业集群技术创新扩散激励机制模型并对其加以分析,得出相关激励制度为企业集群整体采取有效措施进行技术创新扩散激励提供了理论依据。     

基于Tsallis分布及跳扩散过程的欧式期权定价

准确描述资产价格的运行规律是进行衍生产品定价及风险控制的基础。受金融市场外部环境的影响,资产收益率常常具有尖峰厚尾和偏尾的现象,为了准确地描述资产价格的运动规律,本文利用具有长程记忆及统计反馈性质的Tsallis熵分布和一类更新过程,建立了跳-反常扩散的股票价格运动模型。利用随机微分和鞅方法,在风险中性的条件下,得到了欧式期权的定价公式,该公式推广了文献11和21的相应结论。最后,利用上证指数数据分别计算出了各模型的参数以及对资产收益率拟合的平均绝对误差,数据分析结果表明本文模型与文献11和21相比其平均绝对误差分别减小了10.4%和25.1%。说明了本文模型对资产收益率尖峰厚尾及偏尾等现象的捕捉更为准确。     

对于尝试-重购新产品扩散模型的改进：logit模型及NILS估计

在现有的尝试-重购模型的基础上,本文构建了一个更加合理的logit形式的尝试-重购模型。发展出一套适用于该模型的估计方法和检验方法,并用Monte Carlo随机模拟实验对此方法的有效性进行验证。经检验,随着样本数据量的增加和样本标准差的减小,无论是模型参数的估计误差,还是单参数显著性检验的效力,以及犯第一类错误的可能性都表现出合理的变化趋势。该模型可以用于快速消费品新产品的销量预测和营销组合分析。     

梁启超对古希腊史的引介和传播

梁启超流亡日本后,编写了多部有关希腊历史的论著。与此同时,他还通过创办报刊和撰写评论,积极向国人推荐和评介有关的世界史著,介绍西方古典时期的思想文化,比较中国和希腊历史之间的异同,从而将古希腊历史知识引入了中国。梁启超的引介满足了国人了解外国历史的需求,开阔了国人的视野,激发了青年人探寻世界知识和外国文化的热情。     

镁合金微弧氧化中的传质研究

分别采用扫描电镜（SEM）、能谱仪（EDS）和电感耦合等离子体发射光谱仪（ICP—AES）等手段,研究了镁合金在微弧氧化过程中的传质过程．通过研究发现在微弧氧化过程中存在许多传质过程,这些传质过程包括：基体中的合金元素向膜层与电解液中的传质;电解液中的离子向膜层与基体中的传质．这些传质过程对膜层的生成有重要影响,它可以影响合金元素在膜层中的分布以及物相的生成．