Degradation linear

The Kirchhoff hypothesis of linear strain variation through the laminate thickness applies (prior to degradation, if any after degradation, linear only through the thickness of each lamina). 

The chemical structure of the polyolefins determines their susceptibility to oxidative degradation. Linear polyethylene, in the absence of additives, is more resistant to oxidation that polypropylene that oxidizes rather readily due to the presence of labile tertiary hydrogens. It was demonstrated, for instance, that the molecular weigh of polypropylene sheets in a 138°C oven can drop from 250,000 to approximately 10,000 in 3 h [522]. The process of oxidation was shown to take place according to the following scheme [522] ... 

Measurements with a one layer mesh screen gave results similar to those obtained with porous filters with high intrinsic viscosity of Polyox, severe degradation, linearity in concentration and onset of pressure drop. Also a relaxation time of about 0.1 seconds was obtained when using screens. Any configuration of screens and porous filters in the test section gave the 0.1 seconds relaxation time. The screen was a wire mesh screen with a wire diameter of 0.05 and a separation between wires of 0.125 mm. 

The first barrier to sea water ingress is the bitumen which covers the whole SGI. This bitumen is assumed to degrade linearly in 100 years from full to zero effectiveness, modelled by the bitumen factor k(, = O.Olt (t 100 years). The fuel, and hence the fission products and actinides, is surrounded above and below by at least 300 mm of solidified Pb-Bi coolant, and multiple layers of SS. Using the most pessimistic estimates of corrosion rates and thicknesses, the minimum time for water ingress to the fuel via corrosion directly from above or below is over 40 000 years. This timescale is much longer than that of ingress through the EPR tubes and ECTs hence, this method will be assumed to be the primary means of release and is studied in more detail below. 

Another interesting example of biodegradation by the use of Chryseobacterium eum for the decomposition of photo-degraded linear lower-density polyethylene (LLDPE) [42]. LLDPE is used extensively in agricultural plastics such as films used in greenhouses and mulches. Kim and Jeon [42] discuss the degradation of UV-treated LLDPE with the meso-philic bacterium. 

Interestingly, Eq. (5.21) is the differential equation commonly employed in the context of chemical kinetics to model the dynamics of a chemical species that is produced via a catalytic reaction and degraded linearly (Houston 2001). In particular, the first term on the right-hand side of Eq. (5.21) corresponds to Michaelis-Menten equation, which is commonly used to model the velocity of enzymatic reactions (Houston 2001 Lehninger et al. 2005). Let us close this section by stating that knowing how Eq. (5.21) can be deduced from a stochastic chemical dynamics approach, allows us to better understand its range of validity and its connection with the relevant quantities of the stochastic-description. 

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