An example of an apparatus includes a focusing region to focus a sheath fluid and a particle flow. The apparatus also includes a particle inlet to inject the particle flow into the focusing region. In addition, the apparatus includes a sheath inlet to inject the sheath fluid into the focusing region. Also, the apparatus includes a cut-out disposed on a wall of the sheath inlet to distribute the sheath fluid about the particle flow to focus the particle flow into a linear stream. The apparatus further includes a separation region to apply a force to the particle flow. The force is dependent on a characteristic of a particle in the particle flow.