Jiying Liu

Advanced computational modeling for in vitro nanomaterial dosimetry.

BackgroundAccurate and meaningful dose metrics are a basic requirement for in vitro screening to assess potential health risks of engineered nanomaterials (ENMs). Correctly and consistently quantifying what cells “see,” during an in vitro exposure requires standardized preparation of stable ENM suspensions, accurate characterizatoin of agglomerate sizes and effective densities, and predictive modeling of mass transport. Earlier transport models provided a marked improvement over administered concentration or total mass, but included assumptions that could produce sizable inaccuracies, most notably that all particles at the bottom of the well are adsorbed or taken up by cells, which would drive transport downward, resulting in overestimation of deposition.MethodsHere we present development, validation and results of two robust computational transport models. Both three-dimensional computational fluid dynamics (CFD) and a newly-developed one-dimensional Distorted Grid (DG) model were used to estimate delivered dose metrics for industry-relevant metal oxide ENMs suspended in culture media. Both models allow simultaneous modeling of full size distributions for polydisperse ENM suspensions, and provide deposition metrics as well as concentration metrics over the extent of the well. The DG model also emulates the biokinetics at the particle-cell interface using a Langmuir isotherm, governed by a user-defined dissociation constant, KD, and allows modeling of ENM dissolution over time.ResultsDose metrics predicted by the two models were in remarkably close agreement. The DG model was also validated by quantitative analysis of flash-frozen, cryosectioned columns of ENM suspensions. Results of simulations based on agglomerate size distributions differed substantially from those obtained using mean sizes. The effect of cellular adsorption on delivered dose was negligible for KD values consistent with non-specific binding (> 1 nM), whereas smaller values (≤ 1 nM) typical of specific high-affinity binding resulted in faster and eventual complete deposition of material.ConclusionsThe advanced models presented provide practical and robust tools for obtaining accurate dose metrics and concentration profiles across the well, for high-throughput screening of ENMs. The DG model allows rapid modeling that accommodates polydispersity, dissolution, and adsorption. Result of adsorption studies suggest that a reflective lower boundary condition is appropriate for modeling most in vitro ENM exposures.

A Rapid and Reliable Numerical Method for Predictions of Outdoor Thermal Environment in Actual Urban Areas

To analyze urban thermal environments more rapidly and accurately, a real urban morphology is simulated. Two models are proposed to support Reynolds Averaged Navier Stokes (RANS) simulations including: (1) a Zero-equation (ZEQ) turbulence model for outdoor airflows, and (2) convective heat transfer coefficients (CHTC) on external building surfaces. This study used commercial Computational Fluid Dynamics (CFD) software to implement the newly derived ZEQ turbulence model and CHTC wall boundary conditions. This modified version of CFD software was used to predict the thermal environment of an actual urban area including air temperatures and wind velocities. The simulated air velocities around the buildings are compared with the velocities obtained with the standard k-e (SKE) turbulence model. The air temperatures around the buildings were compared with measured data in the actual outdoor environment. The comparisons show that this simulation method can rapidly and reliably predict a real outdoor thermal environment in an urban area.Copyright

The numerical analysis of outdoor wind and thermal environment in a residential area in Liaocheng, China

With the improvement of peoples living standard, people not only pay attention to the indoor environment, but also the outdoor environment. The paper simulated the outdoor wind environment and thermal environment for the building in its design stage, then suggestions are provided for further design stage using a case study in a residential area in Liaocheng, China. SketchUp is used to establish 3D model and PHOENICS is adopted to simulate wind environment and thermal environment. The evaluation criterion mainly utilized Green Building Evaluation Criteria and Urban Residential Area Thermal Environment Design Criteria and ISO7243. Through the analysis of the wind and thermal environment problems, this paper puts forward measures and suggestions to provide reference for the later planning.