The ornamental design for a centrifuge, as shown and described.
FIG. 1 is a perspective view of the centrifuge design, showing its top, front, and right sides.
FIG. 2 is a front view of the centrifuge design.
FIG. 3 is a rear view of the centrifuge design.
FIG. 4 is a left-side view of the centrifuge design.
FIG. 5 is a right-side view of the centrifuge design.
FIG. 6 is a top view of the centrifuge design; and,
FIG. 7 is a bottom view of the centrifuge design.
The broken lines illustrate portions of the centrifuge that form no part of the claimed design.
A characteristic feature of the ornamental design is the polished metallic surface material covering the major surfaces of the centrifuge. The metallic surface is illustrated in FIGS. 1-7 by oblique line shading.