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

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the end, Tsao (2001) claimed that the permeable sink can always be well<br />

represented by an impermeable sink model.<br />

Keep in mind that it is very unlikely that any two spheres are exactly the<br />

same size two key examples are: typical biological cells range is 1 – 100<br />

micrometers (Alberts et al., 1998) and population models <strong>of</strong> ripening and<br />

coarsening where the size <strong>of</strong> the spheres are always changing (Lifshitz and<br />

Pitaevskii, 1981; Voorhees and Schaefer, 1987). Furthermore any insight arising<br />

from size difference cannot be illuminated within the context <strong>of</strong> these four<br />

studies.<br />

As seen in diverse cultures <strong>of</strong> microorganisms, variation in crystal growth<br />

rates, and coalesences <strong>of</strong> particles, size variation is very common. Work <strong>for</strong> two<br />

particles <strong>of</strong> varying sizes is limited (Voorhees and Schaefer, 1987; Tsao, 2002;<br />

Stoy 1989a, 1989b and 1991). Voorhees and Schaefer (1987), used bispherical<br />

coordinates (Morse and Feshbach 1953) where the two particles have constant<br />

concentrations, differ in size and are far apart, to correlate experimental results <strong>for</strong><br />

coarsening. Here the authors have neglected to consider the impact proximity<br />

may have on the surface concentration <strong>of</strong> the two spheres, furthermore this<br />

method tends to an unphysical infinite reaction rate when the two spheres are in<br />

contact. Tsao (2002) obtained a solution <strong>for</strong> the two impermeable sink problem<br />

with first order reactions occurring at the surface <strong>of</strong> both spheres. Using the<br />

bispherical expansions (Ross, 1968 and 1970) he generated a series solution <strong>for</strong><br />

any combination <strong>of</strong> diffusion-limited to reaction-limited conditions <strong>for</strong> the two<br />

sinks. Tsao (2002) determined that the interaction is significantly influenced by<br />

5

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