(a) Quartz marine sand (color interpreted using the vox2grains algorithm); sample courtesy NRL; imaged by C.S. Willson at APS.  (b) Cretaceous-age sandstone from the Frontier Formation, WY, USA; sample courtesy J. Bhattacharya, G. McMechan & C. White; imaged by C.S. Willson at APS.  (c) Section of a 0.65 micron microfiltration membrane; sample courtesy Millipore Corp; imaged using laser scanning confocal microscopy by J.T. Fredrich at Sandia National Lab.  (d) Trapped nonwetting phase fluid in a packed column; imaged by C.S. Willson at APS.  (e) Silicon carbide foam; sample courtesy Ultramet Corp.; imaged by A.H. Reed at NRL.  (f) Surface of 0.65 micron microfiltration membrane; sample courtesy of Millipore Corp.; imaged by SkyScan  using x-ray nanotomography.  (g) Three-dimensional view of the sandstone from image b.  (h) wetting and nonwetting phases in an unconsolidated sand; imaged by C.S. Willson at APS.  (i) axes of cylinders in a packed bed of cylinders; imaged by A.H. Reed at NRL.