Why is the %PD different from the Range %PD in DYNAMICS? - WKB319120
ENVIRONMENT
- DYNAMICS
- DYNAMICS software
ANSWER
The %PD values differ in DYNAMICS because they are calculated using two distinct methods. The standard %PD is derived from cumulant analysis, using the first and second cumulants (µ1 and µ2). In contrast, the Range %PD is obtained through regularization analysis, which is based on the width of histogram peaks. Regularization is better suited for multimodal samples, while cumulant analysis is typically used for monodisperse samples. Generally, cumulant-derived %PD values are lower than those from regularization for monodisperse samples.
ADDITIONAL INFORMATION
The DataGrid view in DYNAMICS shows %PD and then Range (peak number) %PD. The %PD is from the cumulants fit to the autocorrelation function and the %PD in a Range is from a regularization fit.
(Note: You will want to ensure that the Range setting includes your peak because these are predefined in DYNAMICS. To do this, right-click on the DataGrid table and select Peak ranges. Then, specify a value for Range 1 that matches your peak.)
The differences that you see in the cumulants versus regularization fits are related to the way the %PD is calculated.
%PD from cumulant analysis
In the case of cumulant analysis, the %PD is calculated from the first and second cumulants, µ1 and µ2.
%PD from regularization analysis
The Regularization %PD is based on the width of the defined histogram peaks. In general, %PD<15 is considered monodisperse and above this polydisperse.
For monomodal, polydisperse samples, both regularization and cumulants can be used to describe the size distribution. For bimodal (multimodal) samples, only regularization can fit the data properly. In general, for monodisperse samples, you will see that the %PD from cumulant analysis is lower than the %PD from regularization.