Mesoscale modeling studies

In this chapter, we describe our recent mesoscale modeling studies of the interactions between spherical nanoparticles and model cell membranes [73-75]. Although these studies are not comprehensive, they demonstrate the techniques that could be used to further explore the mechanisms of nanoparticle-membrane interactions. Initially, we describe the use of hybrid selfconsistent field theory to study the phase behavior of small (radius Rp < 10 nm) spherical nanoparticles near a lipid bilayer. Depending on the nanoparticle size and interaction parameters... 

Bharadwaj, R.K., Bunning, T.J., and Farmer, B.L. (2000). A mesoscale modelling study of nematic liquid crystals confined to ellipsoidal domains, Liq. Cryst. 27 591-603. 

Sewell and co workers [145-148] have performed molecular dynamics simulations using the HMX model developed by Smith and Bharadwaj [142] to predict thermophysical and mechanical properties of HMX for use in mesoscale simulations of HMX-containing plastic-bonded explosives. Since much of the information needed for the mesoscale models cannot readily be obtained through experimental measurement, Menikoff and Sewell [145] demonstrate how information on HMX generated through molecular dynamics simulation supplement the available experimental information to provide the necessary data for the mesoscale models. The information generated from molecular dynamics simulations of HMX using the Smith and Bharadwaj model [142] includes shear viscosity, self-diffusion [146] and thermal conductivity [147] of liquid HMX. Sewell et al. have also assessed the validity of the HMX flexible model proposed by Smith and Bharadwaj in molecular dynamics studies of HMX crystalline polymorphs. 

In this chapter we focus on atomistic predictions of thermophysical and mechanical properties of HMX crystals and liquid important to the development of reliable mesoscale equations of state. The outline of the remainder of the chapter is as follows In section 2 we describe briefly the philosophy and overall approach we have taken to force field development, including the results of quantum chemistry calculations for HMX and smaller model compounds that were used in the force field parameterization. The focus of section 3 is on the properties of liquid HMX, for which experimental data are completely lacking. Structural, thermal, and mechanical properties of the three pure crystal polymorphs of HMX are presented in section 4, where the results are compared to the available experimental data. At the ends of sections 3 and 4 we discuss briefly the importance of the various properties with mesoscale models of high explosives, with an emphasis on conditions relevant to weak shock initiation. We conclude in section 5, and provide our opinions (and justifications, based on our interactions with mesoscale modelers) regarding which HMX properties and phenomena should comprise the next targets for study via atomistic simulation. 

Lenz C-J, Muller F, Schliinzen KH (2000) The sensitivity of mesoscale chemistry transport model results to boundary values. Environ Monit Assess 65 287-298 L6pez SD, Liipkes C, Schliinzen KH (2005) The effects of different k-e-closures on the results of a micro-scale model for the flow in the obstacle layer. Meteorol Z 14 839-848 Muller F, Schliinzen KH, Schatzmann M (2000) Test of numerical solvers for chemical reaction mechanisms in 3D air quality models. Environ Model Softw 15 639-646 Schliinzen KH (1990) Numerical studies on the inland penetration of sea breeze fronts at a coastline with tidally flooded mudflats. Beitr Phys Atmos 63 243-256 Schliinzen KH, Katzfey JJ (2003) Relevance of subgrid-scale land-use effects for mesoscale models. Tellus 55A 232-246... 

Our studies show that the MM5/11P. C conjugation can provide useful prediction of airborne transport of hazardous materials near the surface. It also demonstrates that the accuracy of HPAC computation strongly depends on the performance of MM5. The forecast skill of mesoscale models is likely to be a function of weather scenarios and the terrain over which the models are being run. Because the numerical techniques are different and the model physics (e.g., PBL, surface, and moist processes) vary considerably among different mesoscale meteorological models, we anticipate that there would be discrepancies between the predictions of individual models. 

Note that the order of these steps is important. Indeed, it is very rare for a successful mesoscale model to result from simply studying the results from a microscale simulation that is not specifically designed to test a particular assumption or hypothesis. In general, a microscale simulation will produce an enormous quantity of data if all flow variables are stored at every time step, and it is not realistic to expect that such data sets will reveal the correct form of the mesoscale models without some a priori understanding of the physics. On the other hand, microscale simulations offer an invaluable and often unique tool for sorting out the validity of a proposed mesoscale model because they contain all of the microscale variables, many of which are impossible to measure in laboratory experiments. 

Wei Wang and Yanpei Chen, Mesoscale Modeling Beyond Local Equilibrium Assumptionfor Multiphase Mow Mao Ye, HuaLi, YinfengZhao, Tao Zhang, andZhongminLiu, MTO Processes Development The Key of Mesoscale Studies... 

Contrary to the convective internal boundary layer, a stable IBL develops when warmer air is advected from an upstream warmer land (or sea) sttrface to a cooler sea downstream. This situation is shown in Fig. lOc. The main difference between convective and stable IBLs is that the heat flux is directed upward (from a warm sea to cooler air) for a convective IBL and downward (from warm air to a cooler sea) for a stable IBL. A two-dimensional nirmerical mesoscale model was used by J. R. Garratt to investigate the internal structure and growth of a stably stratified IBL beneath warm continental air flowing over a cooler sea. An analytical model was also used by Garratt to study a stable IBL, and excellent agreement with the numerical results was found. This analytical model states that... 

Methanol to olefins (MTO), which provides a new route to produce light olefins such as ethylene and propylene from abundant natural materials (e.g., coal, natural gas or biomass), has been recently industrialized by the Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences. In this contribution, the process development of MTO is introduced, which emphasizes the importance of mesoscale studies and focuses on three aspects a mesoscale modeling approach for MTO catalyst pellet, coke formation and control in MTO reactor, and scaling up of the microscale-MTO fluidized bed reactor to pilot-scale fluidized bed reactor. The challenges and future directions in MTO process development are also briefed. 

Simulations of physical properties of realistic Pt/support nanoparticle systems can provide interaction parameters that are used by molecular-level simulations of self-organization in CL inks. Coarse-grained MD studies presented in the section Mesoscale Model of Self-Organization in Catalyst Layer Inks provide vital insights on structure formation. Information on agglomerate formation, pore space morphology, ionomer structure and distribution, and wettability of pores serves as input for parameterizations of structure-dependent physical properties, discussed in the section Effective Catalyst Layer Properties From Percolation Theory. CGMD studies can be applied to study the impact of modifications in chemical properties of materials and ink composition on physical properties and stability of CLs. 

Mesoscale modeling uses a basic unit just above the molecular scale, and is particularly useful for studying the behavior of polymers and soft materials. It can model even larger molecular systems, but with the commensurate trade-off... 

In this study, the DPM calculations on the microscale have been performed neglecting the influence of the liquid on the particle dynamics. Such simplification can be made only when the fraction of particles covered with hquid film is relative small. To consider the influence of liquid, the submicro- and mesoscale models can be employed. On the submicroscale, detailed simulation of particle impacts with different Hquid amount can be performed to predict energy dissipation. The mesoscale model can be used to approximate wetted surface fractions of particles in different zones. Transferring the data from both scales to the DPM calculations gives a possibility to consider liquid. 

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