Assessment of dermal absorption by thermogravimetric analysis: Development of a diffusion model based on Fick's second law

On the analyses of carbon atom diffused into grey cast iron during carburisation process

The study employed Fick's second law of diffusion to discover some unknown aspect of carbon diffusion in grey cast iron during carburisation process. Emphasis on the experiments and theoretical modelling were established for better accomplishments. Pulverised palm kernel and eggshell additives of 70 (wt.%) and 30 (wt.%) according to the Voige law of mixture was considered as a continuous medium without considering the atomic nature of the mixture. Furthermore, a kinetic approach was described where a physical model of the substrate immersed in the carbon mixture was established while diffusion equations were modelled to establish the mechanism of carbon diffusion during carburisation. Initial composition and concentration of diffused atom remained constant which are 2.68 and 6.67% carbon. While the carburizing time used varied from 60 min, 90 min, 120 min, 150 min, 180 min and 210 min respectively at constant carburising temperature of 900° The results revealed varying composition gradient of carbon atom ranging from 5.4%, 5.42%, 5.44%, 5.46%, 5.51%, and 5.65 compared to the initial carbon content of 2.68%. The concentration of carbon atom on the substrate surface at varying time implies that the process was non-steady state diffusion which verified Fick's second law of diffusion. Hence, the composition achieved is a function of boundary conditions such as time position and temperature. This novel study will enhance the understanding of heat treat treatment of metals such that their applications in the industry will be numerous.

An inner boundary condition of moisture diffusion model for simulating transient nonlinear moisture transport in Chinese fir

This paper proposed an inner boundary condition of moisture diffusion model for simulating transient nonlinear moisture transport of Chinese fir (Cunninghamia lanceolata). The inner boundary condition is serviced for simulate the moisture diffusion of multi-layer boards and is mainly used for the boundary conditions inside component, which presents the diffusion of moisture between wood and its adjacent wood. Furthermore, the established simulation model contains fiber orientation information and is used to simulate the moisture diffusion under different boundary conditions, which considers the constrained boundary. Simulation of simple boundary condition models and the proposed inner boundary condition model under different boundary conditions for multilayer board specimen exposed to constant temperature and constant humidity with a known initial moisture content, and the model was then validated in a laboratory climate chamber. Different from the simple boundary condition model the direct error of the proposed inner boundary model was less than 2% (moisture content), which indicates the proposed inner boundary condition could improve the accuracy of moisture diffusion model. The results show that the inner boundary condition model can comprehensively analyze the transient nonlinear moisture transfer process in different fiber directions with high accuracy.

Predicting the absorption of chemical vapours

The focus of this review is on the systemic absorption of vapours via skin, including experimental data as well as regression and pharmacokinetic models. Dermal contribution ratios (DCR), i.e. amount absorbed through skin relative to total intake (skin and inhalation) at specified conditions, could be identified or calculated from published data for 33 chemical vapours. The ratios vary from ~0.0002 (vinyl chloride) to ~0.8 (2-butoxyethanol), with hydrophilic chemicals having a higher ratio than lipophilic ones. Multiple regression analysis of these data suggests that the DCR is largely explained by the octanol:water partition coefficient, vapour pressure and molecular weight (R(2)=0.69). Several physiologically-based pharmacokinetic models were identified; however, all describe the absorption of single substances. Regarding predictive models, only two models were found. In conclusion, dermal uptake of chemical vapours needs more attention, as such exposures are common, data are scarce and few predictive models exist.

Detailed modeling of skin penetration--an overview

In recent years, the combination of computational modeling and experiments has become a useful tool that is proving increasingly powerful for explaining biological complexity. As computational power is increasing, scientists are able to explore ever more complex models in finer detail and to explain very complex real world data. This work provides an overview of one-, two- and three-dimensional diffusion models for penetration into mammalian skin. Besides diffusive transport this includes also binding of substances to skin proteins and metabolism. These models are based on partial differential equations that describe the spatial evolution of the transport process through the biological barrier skin. Furthermore, the work focuses on analytical and numerical techniques for this type of equations such as discretization schemes or homogenization (upscaling) techniques. Finally, the work compares different geometry models with respect to the permeability.