Local isotropy, or the statistical isotropy of small scales, is one of the basic assumptions underlying Kolmogorov’s theory of universality of small-scale turbulent motion. The literature is replete with studies purporting to examine its validity and limitations. While, until the midseventies or so, local isotropy was accepted as a plausible approximation at high enough Reynolds numbers, variou...

We derive sum rules for the effective dielectric function ee(v) of a polycrystalline material, under the assumption of macroscopic isotropy. If the material comprising the polycrystal is a quasi-one-dimensional or quasiplanar Drude metal, we predict that part of the oscillator strength of the polycrystal is pushed up in frequency to form an ‘‘impurity’’ band of confined plasmonlike excitations....