more diamond age wizradry

there's a nice piece in the Diamond Age (neal stephonson) about aerial nanotech defensive systems - one throwaway remark about them is that the attacks they have to withstand are from more nanotech distributed nodes, and so any system cannot operate an "impermeable shield" (shades of star wars) but instead must "hack the mean free path"
and its left as an exercise for the reader to figure out what this means (basically, the defensive net has to be long enough that for a set of random walks (c.f. Einstein: Brownian motion) the probability of any attacking node making it through the defensive nodes (i.e. the number of variances of the path length) is vanishingly small - like
Hiro Protagonists "usual car chase" in Snow Crash, this is a masterpiece of minimalism...

another interesting point is the throwaway remark about forensic geeks carrying cards to help identify which "species" of cookie cutter has been used on a victim, by looking at the arcs of intersection of the shockwave (circular, or part of solid angle intersecting a sphere?) with the skin, leaving a set of curves - given the shockwave does most its damage at a fixed distance from the two "epicenters", this means the radius of curvature of the intersection with skin is fixed, so you can tell the initial velocity (assuming its largely mass independent - I suppose the slowdown is dependent mainly on the size of cookie cutter fragments and viscosity of humans, rather than the interital mass:)

doesn't really bear close examination near breakfast:)