https://doi.org/10.1351/goldbook.MT06760
Mass transport is described by a @[email protected] \(b\), defined by: \[b_{i} = \frac{\nu _{i}}{\boldsymbol{F}_{i}}\] where \(\nu _{i}\) is the average @[email protected] velocity and \(\boldsymbol{F}_{i}\) is the @[email protected] on particle \(i\).