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F. Spahn, Nicole Albers, Miodrag Sremcevic (Univ. Potsdam/Germany)
Collisions of granular particles result either in coagulation, restitution or fragmentation. These outcomes are determined by the impact speed, the masses and the material of the collision partners. Coagulation takes place at low impact velocities so that attractive forces and dissipation prevent a post collisional separation. Fragmentation occurs if the impact energy is sufficient to break internal bonds. We derive kinetic equations for these cases including the combined dynamics of the velocity and mass distribution. In the pure sticking limit (no fragmentation or restitution) the classical Smoluchowski equation is reproduced. We calculate a threshold velocity for coagulation in binary collisions of visco-elastic particles including adhesion. Significant modifications of the classical coagulation equations in a certain mass range arise from the consideration of these phase borders. In the case of planetary growth, for instance, this causes the largest particles to grow rapidly at the expense of the majority of the smaller dust grains. Fragmentation and gas drag additionally amplify this tendency well before the gravitation becomes important for the ``classical'' runaway growth.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.