Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Acoustic Bubble Dynamics in a Yield-Stress Fluids   Yield-stress fluids naturally trap small bubbles when their buoyancy applies
an insufficient stress to induce local yielding of the material. Under acoustic
excitation, trapped bubbles can be driven into volumetric oscillations and
apply an additional local strain and stress that can trigger yielding and
assist their release. In this paper we explore different regimes of microbubble
oscillation and translation driven by an ultrasound field in a model
yield-stress fluid, a Carbopol microgel. We first analyse the linear bubble
oscillation dynamics to measure the local, high-frequency viscosity of the
material. We then use acoustic pressure gradients to induce bubble translation
and examine the elastic part of the response of the material below yielding. We
find that, at moderate pressure amplitude, the additional stresses applied by
volumetric oscillations and acoustic radiation forces do not lead to any
detectable irreversible bubble motion. At high pressure amplitude, we observe
non-spherical shape oscillations that result in erratic bubble motion. The
shape modes and critical pressures we observe differ from the predictions of a
recent model of shape oscillations in soft solids.Based on our findings, we
discuss possible reasons for the lack of bubble release in Carbopol and suggest
other systems in which ultrasound-assisted bubble rise may be observed.

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The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
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The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
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The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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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: q-bio
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The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn