7,344 research outputs found
Clustering with diversity
We consider the {\em clustering with diversity} problem: given a set of
colored points in a metric space, partition them into clusters such that each
cluster has at least points, all of which have distinct colors.
We give a 2-approximation to this problem for any when the objective
is to minimize the maximum radius of any cluster. We show that the
approximation ratio is optimal unless , by providing a matching
lower bound. Several extensions to our algorithm have also been developed for
handling outliers. This problem is mainly motivated by applications in
privacy-preserving data publication.Comment: Extended abstract accepted in ICALP 2010. Keywords: Approximation
algorithm, k-center, k-anonymity, l-diversit
FSDiffReg: Feature-wise and Score-wise Diffusion-guided Unsupervised Deformable Image Registration for Cardiac Images
Unsupervised deformable image registration is one of the challenging tasks in
medical imaging. Obtaining a high-quality deformation field while preserving
deformation topology remains demanding amid a series of deep-learning-based
solutions. Meanwhile, the diffusion model's latent feature space shows
potential in modeling the deformation semantics. To fully exploit the diffusion
model's ability to guide the registration task, we present two modules:
Feature-wise Diffusion-Guided Module (FDG) and Score-wise Diffusion-Guided
Module (SDG). Specifically, FDG uses the diffusion model's multi-scale semantic
features to guide the generation of the deformation field. SDG uses the
diffusion score to guide the optimization process for preserving deformation
topology with barely any additional computation. Experiment results on the 3D
medical cardiac image registration task validate our model's ability to provide
refined deformation fields with preserved topology effectively. Code is
available at: https://github.com/xmed-lab/FSDiffReg.git.Comment: Accepted as a conference paper at Medical Image Computing and
Computer-Assisted Intervention (MICCAI) conference 202
Occupation-dependent particle separation in one-dimensional non-Hermitian lattices
We unveil an exotic phenomenon arising from the intricate interplay between
non-Hermiticity and many-body physics, namely an occupation-dependent particle
separation for hardcore bosons in a one-dimensional lattice driven by
uni-directional non-Hermitian pumping. Taking hardcore bosons as an example, we
find that a pair of particles occupying the same unit cell exhibit an opposite
non-Hermitian pumping direction to that of unpaired ones occupying different
unit cells. By turning on an intracell interaction, many-body eigenstates split
in their real energies, forming separable clusters in the complex energy plane
with either left-, right-, or bipolar-types of non-Hermitian skin effect
(NHSE). The dependency of skin accumulating directions on particle occupation
is further justified with local sublattice correlation and entanglement entropy
of many-body eigenstates. Dynamically, this occupation-dependent NHSE manifests
as uni- or bi-directional pumping for many-body initial states, allowing for
spatially separating paired and unpaired particles. Similar phenomena also
apply to fermionic systems, unveiling the possibility of designing and
exploring novel non-Hermitian phases originated from particle non-conservation
in subsystems (e.g., orbitals, sublattices, or spin species) and their spatial
configurations.Comment: 18pages, 14 fiugre
Low magnetic field reversal of electric polarization in a Y-type hexaferrite
Magnetoelectric multiferroics in which ferroelectricity and magnetism coexist
have attracted extensive attention because they provide great opportunities for
the mutual control of electric polarization by magnetic fields and
magnetization by electric fields. From a practical point view, the main
challenge in this field is to find proper multiferroic materials with a high
operating temperature and great magnetoelectric sensitivity. Here we report on
the magnetically tunable ferroelectricity and the giant magnetoelectric
sensitivity up to 250 K in a Y-type hexaferrite, BaSrCoZnFe11AlO22. Not only
the magnitude but also the sign of electric polarization can be effectively
controlled by applying low magnetic fields (a few hundreds of Oe) that modifies
the spiral magnetic structures. The magnetically induced ferroelectricity is
stabilized even in zero magnetic field. Decayless reproducible flipping of
electric polarization by oscillating low magnetic fields is shown. The maximum
linear magnetoelectric coefficient reaches a high value of ~ 3.0\times10^3 ps/m
at 200 K.Comment: 9 pages, 5 figures, a couple of errors are correcte
Geometry-dependent skin effect and anisotropic Bloch oscillations in a non-Hermitian optical lattice
The interplay between the non-Hermiticity and dimensionality gives rise to
exotic characteristics in higher dimensions, with one representative phenomenon
known as the geometry-dependent skin effect (GDSE), which refers to that the
localization of extensive eigenstates depends on the system's geometry under
open boundary conditions. In this paper, we demonstrate the emergence of GDSE
in a two-dimensional optical ladder lattice with on-site atom loss, which
can be manifested by anisotropic dynamics of Bloch oscillations in the bulk of
the system. By applying a static force in different directions, the wave-packet
dynamics retrieve the complex energy spectra with either nonzero or zero
spectral winding number, indicating the presence or absence of skin
accumulation in the corresponding directions, respectively. Our results reveal
that the GDSE has an intrinsic anisotropic bulk dynamics independent of
boundary conditions, and offer its realization and detection in quantum
systems.Comment: 16 pages, 13 figure
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