where T = 2π ω is the period of oscillation, with angular frequency ω. The Gor'kov potential is derived under the assumption that boundaries are far away from the region of interest, which is not the case here; however, a recent study of Baasch et al. showed that the validity can extend to close proximity to a boundary. In case of some cells, the Gor'kov potential is even valid, when the particle is touching the wall.