Fig. 1.
Timescales for processes relevant to grain dynamics: τs is the stopping time of the grain, given by Eq. (4); 
is the inverse grain gyrofrequency given by Eq. (6); τch(0) is the time for a neutral grain to acquire a negative charge; and τch(−1) is the time for a grain of charge −1 to become neutral. The top panel is for the core center, and the bottom is for the envelope.
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