334 research outputs found
Monitoring cell infiltration into the myocardial infarction site using micrometer-sized iron oxide particles-enhanced magnetic resonance imaging
The cell infiltration into the myocardial infarction (MI) site was studied using magnetic resonance imaging (MRI) with micrometer-sized iron oxide particles (MPIO) as cell labeling probes. MI is a leading cause of global death and disability. However, the roles of inflammatory cells and stem cells during the post-MI remodeling and repair processes are yet to be discovered. This study was to develop noninvasive MRI techniques to monitor and quantify the cellular infiltration into the MI site. MPIO can produce pronounced signal attenuation at regions of interest in MRI. Therefore, cells labeled with these particles can be detected after they are activated and home to the MI site. In the first project, MPIO of various doses were injected into the mouse blood stream 7 days before the MI surgery. Serial MRI was performed at various time points post-MI to monitor the inflammatory cell infiltration into the MI site. Significant signal attenuation caused by labeled cells, in particular macrophages, was observed at the MI site. The study suggests an optimal imaging window should be from 7 to 14 days post-MI, during which the MR signal was inversely proportional to the MPIO dose. The study also suggests an optimal MPIO dose should be between 9.1 and 14.5 µg Fe/g body weight. In the second project, mesenchymal stem cells labeled with MPIO were transplanted into the mouse bone marrow 14 days before the MI surgery. Serial MRI was performed at various time points post-MI to monitor the labeled cells, which mobilized from the bone marrow and homed to the MI site. All the MRI findings were further confirmed by histology. In addition to revealing the characteristics of cell infiltration during MI, this study also provides noninvasive MRI techniques to monitor and potentially quantify labeled cells at the pathological site. The technique can also be used to investigate the function of cells engaged in MI and to test the effect on cell infiltration caused by any treatment strategies.Ph.D.Committee Chair: Sang Hyun Cho; Committee Co-Chair: Tom C.-C. Hu; Committee Member: Autumn Schumacher; Committee Member: Chris C.-K. Wang; Committee Member: John N. Oshinski; Committee Member: Nathan E. Yanasa
Realization of a three-dimensional photonic topological insulator
Confining photons in a finite volume is in high demand in modern photonic
devices. This motivated decades ago the invention of photonic crystals,
featured with a photonic bandgap forbidding light propagation in all
directions. Recently, inspired by the discoveries of topological insulators
(TIs), the confinement of photons with topological protection has been
demonstrated in two-dimensional (2D) photonic structures known as photonic TIs,
with promising applications in topological lasers and robust optical delay
lines. However, a fully three-dimensional (3D) topological photonic bandgap has
never before been achieved. Here, we experimentally demonstrate a 3D photonic
TI with an extremely wide (> 25% bandwidth) 3D topological bandgap. The sample
consists of split-ring resonators (SRRs) with strong magneto-electric coupling
and behaves as a 'weak TI', or a stack of 2D quantum spin Hall insulators.
Using direct field measurements, we map out both the gapped bulk bandstructure
and the Dirac-like dispersion of the photonic surface states, and demonstrate
robust photonic propagation along a non-planar surface. Our work extends the
family of 3D TIs from fermions to bosons and paves the way for applications in
topological photonic cavities, circuits, and lasers in 3D geometries
Efficient Bayesian Uncertainty Estimation for nnU-Net
The self-configuring nnU-Net has achieved leading performance in a large
range of medical image segmentation challenges. It is widely considered as the
model of choice and a strong baseline for medical image segmentation. However,
despite its extraordinary performance, nnU-Net does not supply a measure of
uncertainty to indicate its possible failure. This can be problematic for
large-scale image segmentation applications, where data are heterogeneous and
nnU-Net may fail without notice. In this work, we introduce a novel method to
estimate nnU-Net uncertainty for medical image segmentation. We propose a
highly effective scheme for posterior sampling of weight space for Bayesian
uncertainty estimation. Different from previous baseline methods such as Monte
Carlo Dropout and mean-field Bayesian Neural Networks, our proposed method does
not require a variational architecture and keeps the original nnU-Net
architecture intact, thereby preserving its excellent performance and ease of
use. Additionally, we boost the segmentation performance over the original
nnU-Net via marginalizing multi-modal posterior models. We applied our method
on the public ACDC and M&M datasets of cardiac MRI and demonstrated improved
uncertainty estimation over a range of baseline methods. The proposed method
further strengthens nnU-Net for medical image segmentation in terms of both
segmentation accuracy and quality control
Development of a 3-D Position Sensitive Neutron Detector Based on Organic Scintillators with Double Side SiPM Readout
A 3-D position sensitive neutron detector is being developed based on a
plastic scintillator array. A double side SiPM readout is used to determine the
depth of interaction (DOI) in each scintillator unit. In the preliminary test,
the DOI in a 254 x 6 x 6 mm3 SP101 plastic scintillator is measured at
different positions using a collimated Co-60 source. The SiPM (KETEK PM6660)
signals are recorded by a 2.5 GS/s digital oscilloscope. The DOI results are
calculated using both the amplitude and the temporal information. Position
resolutions (FWHM) of 2.5 cm and 6.6 cm are realized, respectively. A detector
based on a 2-D array is capable of recording the 3-D position information of
the incident neutron. The 3-D detector is to be used together with a neutron
time projection chamber as a directional fast neutron detector. According to
the simulation results, the angular resolution (8 degree FWHM) is much better
than that of a typical neutron scatter camera.Comment: 7 pages, 7 figures, submitted to IEEE NSS MIC 201
A new fracture permeability model of CBM reservoir with high-dip angle in the southern Junggar Basin, NW China
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was funded by the National Major Research Program for Science and Technology of China (2016ZX05043-001), the National Natural Science Fund of China (grant nos. 41602170 and 41772160), the Royal Society International Exchanges-China NSFC Joint Project (grant nos. 4161101405 and RG13991-10), and Key Research and Development Projects of the Xinjiang Uygur Autonomous Region (2017B03019-01).Peer reviewedPublisher PD
Acoustic higher-order topological insulator on a Kagome lattice
High-order topological insulators (TIs) are a family of recently-predicted
topological phases of matter obeying an extended topological bulk-boundary
correspondence principle. For example, a two-dimensional (2D) second-order TI
does not exhibit gapless one-dimensional (1D) topological edge states, like a
standard 2D TI, but instead has topologically-protected zero-dimensional (0D)
corner states. So far, higher-order TIs have been demonstrated only in
classical mechanical and electromagnetic metamaterials exhibiting quantized
quadrupole polarization. Here, we experimentally realize a second-order TI in
an acoustic metamaterial. This is the first experimental realization of a new
type of higher-order TI, based on a breathing Kagome lattice, that has zero
quadrupole polarization but nontrivial bulk topology characterized by quantized
Wannier centers (WCs). Unlike previous higher-order TI realizations, the corner
states depend not only on the bulk topology but also on the corner shape; we
show experimentally that they exist at acute-angled corners of the Kagome
lattice, but not at obtuse-angled corners. This shape dependence allows corner
states to act as topologically-protected but reconfigurable local resonances.Comment: 15 pages, 4 figure
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