Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Palomar Testbed Interferometer   The Palomar Testbed Interferometer (PTI) is a long-baseline infrared
interferometer located at Palomar Observatory, California. It was built as a
testbed for interferometric techniques applicable to the Keck Interferometer.
First fringes were obtained in July 1995. PTI implements a dual-star
architecture, tracking two stars simultaneously for phase referencing and
narrow-angle astrometry. The three fixed 40-cm apertures can be combined
pair-wise to provide baselines to 110 m. The interferometer actively tracks the
white-light fringe using an array detector at 2.2 um and active delay lines
with a range of +/- 38 m. Laser metrology of the delay lines allows for servo
control, and laser metrology of the complete optical path enables narrow-angle
astrometric measurements. The instrument is highly automated, using a
multiprocessing computer system for instrument control and sequencing.

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The categories of this paper are: bayes-an
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The categories of this paper are: nlin
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The categories of this paper are: cond-mat
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The categories of this paper are: supr-con
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The categories of this paper are: q-fin
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The categories of this paper are: physics
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The categories of this paper are: hep-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: mtrl-th
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The categories of this paper are: eess
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The categories of this paper are: plasm-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: econ
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The categories of this paper are: ao-sci
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The categories of this paper are: math