SP-345 Evolution of the Solar System

FIGURE 6.7.1. Simple model of negative diffusion.


FIGURE 6.7.1. Simple model of negative diffusion. The region of collision is shown (above) for two particles, one with guiding center at x1 = r - r' and another with guiding center at x2 = r' - r. Both particles are oscillating radially with amplitude x0. In the x1 x2 diagram (below) collisions can take place if x1 + x2 is located inside the triangle. If a perfectly inelastic collision takes place in the domain a the guiding center x2 is transmitted outward through r'. If the collision takes place in domain b, a similar inward transmission of the guiding center at x1 takes place. If the density increases with r, the collision frequency is larger in domain a than in domain b, with the result that the diffusion goes outward; i.e., toward the higher density region. Hence the diffusion coefficient is negative.

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