  The existence of a quiescent core (QC) in the center of turbulent channel
flows was demonstrated in recent experimental and numerical studies. The
QC-region, which is characterized by relatively uniform velocity magnitude and
weak turbulence levels, occupies about $40\%$ of the cross-section at Reynolds
numbers $Re_\tau$ ranging from $1000$ to $4000$. The influence of the QC region
and its boundaries on transport and accumulation of inertial particles has
never been investigated before. Here, we first demonstrate that a QC is
unidentifiable at $Re_\tau = 180$, before an in-depth exploration of
particle-laden turbulent channel flow at $Re_\tau = 600$ is performed. The
inertial spheres exhibited a tendency to accumulate preferentially in
high-speed regions within the QC, i.e. contrary to the well-known concentration
in low-speed streaks in the near-wall region. The particle wall-normal
distribution, quantified by means of Vorono\"i volumes and particle number
concentrations, varied abruptly across the QC-boundary and vortical flow
structures appeared as void areas due to the centrifugal mechanism. The
QC-boundary, characterized by a localized strong shear layer, appeared as a
\emph{barrier}, across which transport of inertial particles is hindered.
Nevertheless, the statistics conditioned in QC-frame show that the mean
velocity of particles outside of the QC was towards the core, whereas particles
within the QC tended to migrate towards the wall. Such upward and downward
particle motions are driven by similar motions of fluid parcels. The present
results show that the QC exerts a substantial influence on transport and
accumulation of inertial particles, which is of practical relevance in
high-Reynolds number channel flow.
