An apparatus comprising: a cartridge having a center of rotation and configured to be rotated to cause sedimentation of particles or cells suspended in a sample, the cartridge comprising: a receiving cavity to hold the sample, the receiving cavity having a sample entry hole allowing entry of the sample into the receiving cavity, wherein the receiving cavity is centered on the center of rotation of the cartridge; a second cavity (35, 81) located farther from the center of rotation of the cartridge than the receiving cavity is located from the center of rotation of the cartridge, the second cavity having one or more walls, the second cavity comprising a narrow channel (36, 87) of reduced cross section, the reduced cross-section being smaller than a cross section of the second cavity between a proximal end and a distal end relative to the center of rotation, the narrow channel of reduced cross section being coupled to the distal end of the second cavity farther from the center of rotation than the second cavity; and a passage (37, 38) connecting the receiving cavity and the second cavity, the passage having a cross-sectional area that is smaller than a cross-sectional area of the receiving cavity, wherein the one or more of the walls of the second cavity slant outward and are configured at an angle away from and relative to a radial line, the radial line projected away from the center of rotation of the cartridge and crossing the one or more walls, wherein the cartridge is configured to transfer the sample from the receiving cavity to the second cavity during rotation of the cartridge for sedimentation of the particles or cells. a cartridge having a center of rotation and configured to be rotated to cause sedimentation of particles or cells suspended in a sample, the cartridge comprising: a receiving cavity to hold the sample, the receiving cavity having a sample entry hole allowing entry of the sample into the receiving cavity, wherein the receiving cavity is centered on the center of rotation of the cartridge; a second cavity (35, 81) located farther from the center of rotation of the cartridge than the receiving cavity is located from the center of rotation of the cartridge, the second cavity having one or more walls, the second cavity comprising a narrow channel (36, 87) of reduced cross section, the reduced cross-section being smaller than a cross section of the second cavity between a proximal end and a distal end relative to the center of rotation, the narrow channel of reduced cross section being coupled to the distal end of the second cavity farther from the center of rotation than the second cavity; and a passage (37, 38) connecting the receiving cavity and the second cavity, the passage having a cross-sectional area that is smaller than a cross-sectional area of the receiving cavity, wherein the one or more of the walls of the second cavity slant outward and are configured at an angle away from and relative to a radial line, the radial line projected away from the center of rotation of the cartridge and crossing the one or more walls, a receiving cavity to hold the sample, the receiving cavity having a sample entry hole allowing entry of the sample into the receiving cavity, wherein the receiving cavity is centered on the center of rotation of the cartridge; a second cavity (35, 81) located farther from the center of rotation of the cartridge than the receiving cavity is located from the center of rotation of the cartridge, the second cavity having one or more walls, the second cavity comprising a narrow channel (36, 87) of reduced cross section, the reduced cross-section being smaller than a cross section of the second cavity between a proximal end and a distal end relative to the center of rotation, the narrow channel of reduced cross section being coupled to the distal end of the second cavity farther from the center of rotation than the second cavity; and a passage (37, 38) connecting the receiving cavity and the second cavity, the passage having a cross-sectional area that is smaller than a cross-sectional area of the receiving cavity, wherein the one or more of the walls of the second cavity slant outward and are configured at an angle away from and relative to a radial line, the radial line projected away from the center of rotation of the cartridge and crossing the one or more walls, wherein the cartridge is configured to transfer the sample from the receiving cavity to the second cavity during rotation of the cartridge for sedimentation of the particles or cells.