Update Micro rheology authored by jarlt's avatar jarlt
...@@ -5,15 +5,18 @@ ...@@ -5,15 +5,18 @@
2. Convert the DICF into an MSD 2. Convert the DICF into an MSD
1. Get good estimates for A(q) and B(q) using the following options 1. Get good estimates for A(q) and B(q) using the following options
* fit data with suitable model * fit data with suitable model
* Estimate from g(q,tau_min) and g(q, tau_max) * Estimate from $g(q,\tau_{min})$ and $g(q, \tau_{max})$
2. Estimate mean squared displacement as 2. Estimate mean squared displacement as
MSD(tau; q) = -4/q^2 ln(1 - (g(q,tau)-B(q))/A(q)).
**Note:** This assumes motion in 2D (for 3D the 4 needs to be replaced by 6) $$MSD(\tau; q) = -\frac{4}{q^2} \ln(1 - (g(q,\tau)-B(q))/A(q)).$$
1. This can be displayed in my software by selecting 'Representation'-> 'MSD' in the 'Display & Fit' tab
2. Rather than plotting it for all tau it uses 'MSDcutoff' to suppress values too close to the noise level: if correlation has dropped by more than 'MSDcutoff' (default 85%) it is not plotted and when saving a NaN values is saved. **Note:** This assumes motion in 2D (for 3D the 4 needs to be replaced by 6)
3. MSD(tau; q) can be saved by using 'Save as displayed' button
3. In principle this MSD should be independent of the q used to calculate it, but in practice they differ (if nothing else in the timescales/displacements they can reliably access...). 1. This can be displayed in my software by selecting 'Representation'-> 'MSD' in the 'Display & Fit' tab
2. Rather than plotting it for all $\tau$ it uses 'MSDcutoff' to suppress values too close to the noise level: if correlation has dropped by more than 'MSDcutoff' (default 85%) it is not plotted and when saving a NaN values is saved.
3. MSD$(\tau; q)$ can be saved by using 'Save as displayed' button
4. In principle this MSD should be independent of the q used to calculate it, but in practice they differ (if nothing else in the timescales/displacements they can reliably access...).
3. Extract G* from MSD 3. Extract G* from MSD
1. The 'Microrheology' tab is sometimes hidden: if so, go to 'Select Movies' -> Advanced settings' -> 'Misc' and activate the 'Show u-rheo Tab?' button 1. The 'Microrheology' tab is sometimes hidden: if so, go to 'Select Movies' -> Advanced settings' -> 'Misc' and activate the 'Show u-rheo Tab?' button
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