Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Null Lagrangians in linear theories of micropolar type and few other
  generalizations of elasticity   In the context of linear theories of generalized elasticity including those
for homogeneous micropolar media, quasicrystals, piezoelectric and
piezomagnetic media, we explore the concept of null Lagrangians. For obtaining
the family of null Lagrangians we employ the sufficient conditions of H. Rund.
In some cases a non-zero null Lagrangian is found and the stored energy admits
a split into a null Lagrangian and a remainder. However, the null Lagrangian
vanishes whenever the relevant elasticity tensor obeys certain symmetry
conditions which can be construed as an analogue of the Cauchy relations.

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The categories of this paper are: quant-ph
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The categories of this paper are: nlin
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The categories of this paper are: astro-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: eess
30
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: acc-phys
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-th
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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: adap-org
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The categories of this paper are: cond-mat
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The categories of this paper are: chao-dyn