the particle suspensions are very dilute lt lt 1 it is justified to assume that the integrated fluorescence intensities are linearly proportional to the total number of beads contained within each droplet and thus provide an accurate measure of local particle concentrations moving away from the parent droplet the absolute densities of both size cuts drop almost monotonically with the density of the larger red particles decreasing more rapidly the green red density ratio 1 1 in the test solution has reached u02dc 3 1 for the sixth droplet situated u02dc 5 mm from the edge of the parent droplet to investigate the mechanisms at work in the transient dep particle separation scheme we developed a simple model for the process and then used a simulation methodology with a single adjustable parameter related to the particle polarizability for comparison to the concentration data plotted in fig3 c particles swept along in the z direction by the rapidly moving finger experience a transverse downward directed dep force induced by the nonuniform electric field created by the parallel electrodes this force acting primarily in the radial r direction as depicted in the cross section of fig1 b may be expressed in standard form as f r u03c0 u03b5 m r 3 re k u2202 e 2 u2202 r 1 in eq 1 r is particle radius u03b5 m is permittivity of the suspension medium e x is magnitude of the transverse electric field and k is the complex frequency dependent clausius mossotti factor k _ u2061 u03c9 u025b _ p u025b _ m u025b _ p 2 u2062 u2062 u025b _ m 2 where.