Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Demonstration experiments for solid state physics using a table top
  mechanical Stirling refrigerator   Liquid free cryogenic devices are acquiring importance in basic science and
engineering. But they can also lead to improvements in teaching low temperature
an solid state physics to graduate students and specialists. Most of the
devices are relatively expensive, but small sized equipment is slowly becoming
available. Here, we have designed several simple experiments which can be
performed using a small Stirling refrigerator. We discuss the measurement of
the critical current and temperature of a bulk YBa2Cu3O(7-d) (YBCO) sample, the
observation of the levitation of a magnet over a YBCO disk when cooled below
the critical temperature and the observation of a phase transition using ac
calorimetry. The equipment can be easily handled by students, and also used to
teach the principles of liquid free cooling.

27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph