TABLE 1.
A glossary of the important quantities discussed in the article, along with the corresponding units (m = meter, s = seconds, M = mole)
| Quantity | Symbol | Typical units |
|---|---|---|
| Microscopic length scale | λ | m |
| Diffusion coefficient | D | m2 s−1 |
| Microscopic diffusion timescale | δt = λ2/4D | s |
| Association rate | k+ | M−1 s−1 |
| Dissociation rate | k− | s−1 |
| Equilibrium dissociation constant |  |
M |
| Mean surface density of receptors | R0 | No. of molecules/m2 |
| Surface density of receptors inside clusters | R′0 | No. of molecules/m2 |
| Bound receptor fraction at time t | p(t) | Dimensionless |
| Ligand density profile close to the surface at time t | ρ(t) | No. of molecules/m3 |
| Return to origin probability density for a surface with R0 receptors per unit area |  |
m−1 |
| Return to origin probability density for a perfectly absorbing surface | q(t) | m−1 |
| Probability of nonabsorption upon contact | γ | Dimensionless |
| Timescale of exponential decay (Eq. 11a) | te | s |