Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Reflectivity of cholesteric liquid crystals with spatially varying pitch   Solids with spatially varying photonic structure offer gaps to light of a
wider range of frequencies than do simple photonic systems. We solve
numerically the field distribution in a solid cholesteric with a linearly
varying inverse pitch (helical wavevector) using equations we derive for the
general case. The simple idea that the position where the Bragg condition is
locally satisfied is where reflection takes place is only true in part. Here,
reflection is due to a region where the waves are forced to become evanescent,
and the rate of variation of structure determines over which distance the waves
decay and therefore how complete reflection is. The approximate local Bragg-de
Vries schemes are shown to break down in detail at the edges of the gap, and an
analytical estimate is given for the transmission coefficient.

28
The categories of this paper are: alg-geom
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The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
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The categories of this paper are: q-bio
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The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
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The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
31
The categories of this paper are: ao-sci
24
The categories of this paper are: dg-ga