Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical and radiographical characterization of silica aerogel for
  Cherenkov radiator   We present optical and X-ray radiographical characterization of silica
aerogels with refractive index from 1.05 to 1.07 for a Cherenkov radiator. A
novel pin-drying method enables us to produce highly transparent hydrophobic
aerogels with high refractive index by shrinking wet-gels. In order to
investigate the uniformity in the density (i.e., refractive index) of an
individual aerogel monolith, we use the laser Fraunhofer method, an X-ray
absorption technique, and Cherenkov imaging by a ring imaging Cherenkov
detector in a beam test. We observed an increase in density at the edge of the
aerogel tiles, produced by pin-drying.

7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
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The categories of this paper are: astro-ph
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th