Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Decimetre dust aggregates in protoplanetary discs   The growth of planetesimals is an essential step in planet formation.
Decimetre-size dust agglomerates mark a transition point in this growth
process. In laboratory experiments we simulated the formation, evolution, and
properties of decimetre-scale dusty bodies in protoplanetary discs. Small
sub-mm size dust aggregates consisting of micron-size SiO$_2$ particles
randomly interacted with dust targets of varying initial conditions in a
continuous sequence of independent collisions. Impact velocities were 7.7 m/s
on average and in the range expected for collisions with decimetre bodies in
protoplanetary discs. The targets all evolved by forming dust \emph{crusts}
with up to several cm thickness and a unique filling factor of 31% $\pm$3%. A
part of the projectiles sticks directly. In addition, some projectile fragments
slowly return to the target by gravity. All initially porous parts of the
surface, i.e. built from the slowly returning fragments, are compacted and
firmly attached to the underlying dust layers by the subsequent impacts. Growth
is possible at impact angles from 0$^{\circ}$ (central collision) to
70$^{\circ}$. No growth occurs at steeper dust surfaces. We measured the
velocity, angle, and size distribution of collision fragments. The average
restitution coefficient is 3.8% or 0.29 m/s ejection velocity. Ejecta sizes are
comparable to the projectile sizes. The high filling factor is close to the
most compact configuration of dust aggregates by local compression ($\sim
33$%). This implies that the history of the surface formation and target growth
is completely erased. In view of this, the filling factor of 31% seems to be a
universal value in the collision experiments of all self-consistently evolving
targets at the given impact velocities. We suggest that decimetre and probably
larger bodies can simply be characterised by one single filling factor.

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The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: cs
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The categories of this paper are: bayes-an
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The categories of this paper are: ao-sci
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The categories of this paper are: cond-mat
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The categories of this paper are: stat
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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: gr-qc
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The categories of this paper are: hep-th