Fig. 1.
Examples of manmade and natural small particles. (a) Commercial glass spheres (after [37]). (b) Sahara desert sand (after [38]). (c) Dry sea-salt particles (after [39]). (d) A 6-mm-diameter falling raindrop. (e) 40-nm-diameter gold particles (after [40]). (f) Interplanetary dust particle U2012C11 collected by a NASA U2 aircraft. (g) Red blood cells.