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Diffusion Reaction Interaction for a Pair of Spheres - ETD ...

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4<br />

that <strong>for</strong> site volumes fractions 10 when the two-sphere problem is explicitly<br />

−<br />

<<br />

included in the N-sink problem, it could improve the bounds on the effective<br />

reaction rate.<br />

1.3 Cell-Cell <strong>Interaction</strong><br />

Bailey and Ollis (1986) outline a number <strong>of</strong> different types <strong>of</strong> cellular<br />

interaction with competition and mutualism described as the two extremes. On<br />

the one hand, competition implies that the presence <strong>of</strong> the second cells results in a<br />

negative effect on the growth rate, i.e. the consumption rate, <strong>of</strong> both cell while<br />

mutualism implies that the two cells are mutually beneficial and hence this<br />

improves the growth rates <strong>of</strong> each species. From published experimental results<br />

(Cooney and McDonald, 1995; Manz, 1999; Raskin et al., 1996; Rauch, 1999;<br />

Stewart et al., 1995 and 1997) it is clear that many if not all <strong>of</strong> these types <strong>of</strong><br />

interaction are occurring within a given system. For instance in a bi<strong>of</strong>ilm, a<br />

highly organized multiphasic system composed <strong>of</strong> cells, water and metabolic<br />

products (Costerton and Stewart, 2001 and De Beer et al., 1994 and 1997),<br />

microbial growth is encouraged by the introduction <strong>of</strong> a substrate (Cao and<br />

Alaerts, 1995), this may stimulate competition between like species <strong>for</strong> say<br />

oxygen (Raskin et al., 1996) or mutualism as a consortium <strong>of</strong> microbes co-<br />

metabolizes hazardous waste (Wanner and Gujer, 1986). There have been many<br />

attempts to solve the biological N-particle system with numerical simulations<br />

while neglecting the importance <strong>of</strong> cellular interaction (Rodriguez, 1983; Beg and<br />

9

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