Possibilities and limitations of migration modelling

Example 1 Ten 4 cm diameter circular 200 tm thick plastic film pieces are mounted on a stainless steel wire and placed in a glass vial containing 100 ml solvent. What percentage of the additives initially contained in the plastic migrate into the liquid over the 24 hour period (Dp = 2.10E-10 cm /s) Note that the plastic additives are readily soluble in the solvent, the solvent has low viscosity and the solvent does not swell the plastic. Because the additives are readily soluble in the solvent Kpp = 1 can be assumed in eqn 8.10. The volume of the plastic is  

With a = 39.8 one uses the values for a equal to infinity ( ) in Table 8.1 for the roots of tan q = -a- q . Carrying out calculations with eqn 8.12 for the fraction of additive migrating at time t to what would migrate at f = o°  

Note that for the summation the second term is quite small. Because the mass balance for migration out of plastic into a liquid (eqn 8.17) shows 

Therefore, the percentage of additive that has migrated from the polymer in 24 hours according to eqn 8.19 is 46.1%  

Example 2 Solve Example 1 using eqn 8.13 and compare the two results. Starting with a = 39.8 and T = 0.181 from Example 1 calculate the value for using eqn 8.14  

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BRANDSCH, J., MERCEA, p. and PiRiNGER o., 2000, Possibilities and limitations of migration modelling, in Piringer, O.-G. and Baner, A. L., Plastic Packaging Materials for Food, Wiley-VCH, Weinheim, New York. 

A generic problem with profile methods that iterate is the possibility of profile wander (also called matrix migration). This occurs when sequences found in early rounds of the iterative search are not found in later rounds of the search. This problem affects both PSI-BLAST and HMMER. This means that one should record all the intermediate steps so that these lost members of the family can be recovered. Profile wander only becomes a problem for large protein families, and therefore the cause of the profile wander may be related to the limits of modeling using profiles. 

Models of biosphere transport have been developed. 5,6) As is the case for geosphere transport models, the data base for parameters in the biosphere models is limited. The scope of available data is being expanded, (7-9) but careful assessment is needed of the validity of the data, the validity of the models, and the need for the data and models to be site-specific. One site-specific factor to consider is the possibility that geosphere migration could extend for considerable distances from the repository radioactivity might therefore enter the biosphere in an environment different from that of the repository site. 

Recent work demonstrates that chemokines are not limited in their function to their ability to attract cells and initiate cell mobility, but have multiple other functions (58-64). The possibility that C-C chemokines may directly affect (via autocrine action) pleural mesothelial cells was not recognized until recently (65). Pleural injury results in the death of mesothelial cells and denudation of the mesothelial basement membrane. Repair of the mesothelium without fibrosis requires local proliferation and migration of mesothelial cells into the injured area. In a model of mechanical pleural injury, the C-C chemokine MCP-1 was found to play a central role in the repair process. MCP-1 induces proliferative and haptotactic responses in pleural mesothelial cells. 

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