Mesoscale dispersion

Study [25] concluded that this fire performance is probably due to filler-induced increased char formation, because the reductions in PHRR are roughly comparable for all four composites, despite their morphological variations (ranging from very good nanoscale and mesoscale dispersions for the MMT-based nanocomposites to rather poor dispersions and conventional composite structures for the magadiite-based composites [25]). In addition, when the fire behavior of these PET nanocomposites [25] was compared with that of PS nanocomposites [47] (based on both alkylquinolinium- and alkylammonium-modified MMT), it was suggested that the thermally stable quinolinium surfactants are more effective in fire-resistance improvement than the alkylammonium surfactants [25]. 

J. Wescott et al Atomistic, mesoscale and finite element simulation of nanofube dispersion in polymers. VDI Berichte 1940, 23-24 (2006)... 

The dynamic viscosity and storage modulus of the melt polymer can characterize (1) the degree of dispersity (i.e., intercalation) of the nanocomposite polymer [1,2], (2) the dripping tendency in mesoscale or large-scale fires [3,4], and (3) the structure of the char layer formed during pyrolysis in mesoscale or large-scale fires [5-7]. 

Prasanna K. Jog, Valeriy V. Ginzburg, Rakesh Srivastava, Jeffrey D. Weinhold, Shekhar Jain, and Walter G. Chapman, Application of Mesoscale Field-Based Models to Predict Stability of Particle Dispersions in Polymer Melts... 

As a third advantage, polymer particles in dispersions allow one to control or imprint an additional length scale into a polymer bulk material, given by the diameter of the particle, which is offered by the process of film formation. That way, polymer materials can be generated employing rational structure design not only on the molecular scale, but also on the mesoscale. 

Mesocopic flows are important to understand because they hold the key to the interaction between the macroscopic flow and the microstructural inhomogeneities. This is especially true in colloidal flows, which involve colloidal mixtures, thermal fluctuations and particle-particle interactions. Dynamic processes occurring in the granulation of colloidal agglomerate in solvents are severely influenced by coupling between the dispersed microstructures and the global flow. On the mesoscale, this... 

The static stability of the air stream usually changes as it moves into and out of the urban area, typically becoming less and more stable, respectively. However it should not be assumed that the boundary layer profiles over the urban area and downwind are identical to the equilibrium states found in neutral, stable and unstable boundary layers over flat terrain. In fact as the flow adjusts characteristic distortions of the air flow profiles occur on these scales, such as blocked flow, unsteady slope flows, gravity currents and boundary layer jets especially near hills, coasts and urban/rural boundaries. These distorted profiles (which are ignored in most mesoscale atmospheric models) significantly affect dispersion (e.g. Hogstrom and Smedman, [274] Owinoh et al., [477]). 

As explained in Table 2.4, these mesoscale models take many hours to compute a single meteorological situation. Nevertheless, they are sufficiently reliable that they are used operationally in the USA for short term forecasts and for computing the future scenarios of air quality in large urban areas. For complex dispersion e.g. from a localised source, stochastic simulations are sometimes used, (e.g. NAME model of UK Met Office, Maryon and Buckland [396] (1995)). Even then their predictions have to be supplemented with more detailed input on the properties of the turbulence. 

Theoretical analysis together with the results of field experiments and numerical simulations are fast approximate models, FAM s, over mesoscale distances are being developed even when the air flow and meteorology is quite complex. These models are useful as estimates and provide input velocity fields for practical dispersion computations Section 2.4 when many scenarios are needed in a short time. 

In terms of FAM, the most basic method for estimating dispersion on the mesoscale (where crz becomes equal to or greater than h) is to assume that the concentration profile is approximately constant below the top of the boundary layer, so that for a continuous source Qs, and for steady meteorological conditions,... 

CFD-based models use high-resolution grids to develop a detailed representation of the wind field and are typically used to investigate wind fields within urban (obstacle-rich) environments. The models incorporate detailed representations of each obstacle in the environment and provide the only possible approach to the computation of flows deep within urban canyons (a capability not offered by mesoscale meteorological models). A recent field study of dispersion in New York City provided... 

Evaluation of the suitability of mesoscale NWP models for use in dispersion modeling is based on following criteria ... 

We have determined that nudging the models with the WTM surface observations alone appeared to have very limited impact on the mesoscale weather and dispersion forecasts. It is basically three-dimensional (two horizontal dimensions plus time) data assimilation over a small area. The impulses caused by the data insertion dissipated rapidly within 3 h after the turnoff of data nudging regardless of the length of relaxation time scale for model adjustment and nudging period. However, impulses caused by FDDA... 

Based on these results, it is reasonable to hypothesize that FDDA with ACARS data could significantly improve the quality of mesoscale NWP and the subsequent dispersion prediction in the atmospheric boundary layer. The hypothesis needs to be systematically tested. 

An advanced mesoscale model may perform well in some cases but not in others, and the model responses to data assimilation are likely to vary with weather scenarios. There would be a potential benefit of using several model winds separately to run HPAC. A composite result of the HPAC runs would give a more complete depiction of the potential surface-based transport of hazardous agents. Also, the latest version of HPAC allows us to display dispersion output within a geographic information system (GIS) environment. We should explore all possible GIS applications in dispersion modeling and damage assessment. 

The horizontal airflow in the BL often consists of synoptic-scale (> 1000 km) and mesoscale (10-1000 km) circulations, and microscale ( 1 km) turbulence. Their time scales are days, 1 to 24 h, and less than 1 h, respectively. The impact of toxic dispersion on a synoptic scale or large mesoscale is generally not threatening to health, while for small mesoscale (< 100 km) and microscale, the impact can be life threatening because of accumulated doses over a relatively small area. Small-scale... 

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