rheological and other properties of the solvent: matrix system, but dominates scattering by the ternary mixture. If matrix scattering is not entirely negligible, there are established, reliable ways to isolate the probe scattering, based on spectral subtraction at the level of the field correlation function.

Because probe particles very nearly do not interact with each other, the field correlation function for probe diffusion reduces (up to normalization constants) to the incoherent scattering function $$g^{(1s)}(q,t) =  \langle \exp(\imath q \Delta x(t))\rangle.
 \label{eq:g1sandr}$$ with $\Delta x(t)$ being the component parallel to ${\bf q}$ of $\mathbf{\Delta r}(t) = {\bf r}_{i}(t+\tau) -  {\bf r}_{i}(\tau)$. Probe motions perpendicular to $\mathbf{q}$ do not contribute to $g^{(1s)}(q,t)$. In moving from eq \[eq:g1qgeneral\] to eq \[eq:g1sandr\], terms of eq \[eq:g1qgeneral\] in which $i \neq j$ were taken to average to zero, because the relative positions of dilute probes are very nearly uncorrelated. An expression formally identical to eq \[eq:g1sandr\] describes diffusion measurements using pulsed-field-gradient nuclear magnetic resonance, though with this method $q$ has an entirely different meaning, namely in the simplest case $q = \gamma \delta g$, where $\gamma$ is the gyromagnetic ratio, $\delta$ is a pulse width, and $g = dB/dz$ is the field gradient.

The averages 