Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Sense and sensitivity: How ALMA receivers work   In previous articles, we described how electromagnetic waves emitted from
objects in the sky are collected by the ALMA antennas (Anatomy of ALMA), and
how they are combined in order to produce images. Before these images can be
processed, they are picked up by the antennas and concentrated by the large
main mirror and a smaller secondary mirror in the so called focal point of each
antenna. In order to process the data they must be first converted to
electromagnetic waves of a lower frequency and amplified. This is the role of
the ALMA receivers. In principle they work like a normal AM receiver, but at
much higher frequencies. Here we describe how they work and what makes them
special.

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The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: q-bio
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The categories of this paper are: hep-lat
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The categories of this paper are: cmp-lg
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The categories of this paper are: acc-phys
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The categories of this paper are: supr-con
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The categories of this paper are: hep-th
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The categories of this paper are: eess
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The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: physics
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin