We show that both analytic and numerical evidence points to the existence of a critical angle of eta approximate to 60 degrees-70 degrees in viscous fingers and diffusion-limited aggregates growing in a wedge. The significance.of this angle is that it is the typical angular spread of a major finger. For wedges with an angle larger than 2 eta, two fingers can coexist. Thus a finger with this angular spread is a kind of building block for viscous fingering patterns and diffusion-limited aggregation clusters in radial geometry. [References: 21]
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