Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hydrodynamic capture of microswimmers into sphere-bound orbits   Self-propelled particles can exhibit surprising non-equilibrium behaviors,
and how they interact with obstacles or boundaries remains an important open
problem. Here we show that chemically propelled micro-rods can be captured,
with little change in their speed, into close orbits around solid spheres
resting on or near a horizontal plane. We show that this interaction between
sphere and particle is short-range, occurring even for spheres smaller than the
particle length, and for a variety of sphere materials. We consider a simple
model, based on lubrication theory, of a force- and torque-free swimmer driven
by a surface slip (the phoretic propulsion mechanism) and moving near a solid
surface. The model demonstrates capture, or movement towards the surface, and
yields speeds independent of distance. This study reveals the crucial aspects
of activity-driven interactions of self-propelled particles with passive
objects, and brings into question the use of colloidal tracers as probes of
active matter.

10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
6
The categories of this paper are: astro-ph
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph