12 research outputs found
SPIRiT-Diffusion: Self-Consistency Driven Diffusion Model for Accelerated MRI
Diffusion models are a leading method for image generation and have been
successfully applied in magnetic resonance imaging (MRI) reconstruction.
Current diffusion-based reconstruction methods rely on coil sensitivity maps
(CSM) to reconstruct multi-coil data. However, it is difficult to accurately
estimate CSMs in practice use, resulting in degradation of the reconstruction
quality. To address this issue, we propose a self-consistency-driven diffusion
model inspired by the iterative self-consistent parallel imaging (SPIRiT),
namely SPIRiT-Diffusion. Specifically, the iterative solver of the
self-consistent term in SPIRiT is utilized to design a novel stochastic
differential equation (SDE) for diffusion process. Then -space data
can be interpolated directly during the reverse diffusion process, instead of
using CSM to separate and combine individual coil images. This method indicates
that the optimization model can be used to design SDE in diffusion models,
driving the diffusion process strongly conforming with the physics involved in
the optimization model, dubbed model-driven diffusion. The proposed
SPIRiT-Diffusion method was evaluated on a 3D joint Intracranial and Carotid
Vessel Wall imaging dataset. The results demonstrate that it outperforms the
CSM-based reconstruction methods, and achieves high reconstruction quality at a
high acceleration rate of 10
Accelerating Magnetic Resonance Parametric Mapping Using Simultaneously Spatial Patch-based and Parametric Group-based Low-rank Tensors (SMART)
Quantitative magnetic resonance (MR) parametric mapping is a promising
approach for characterizing intrinsic tissue-dependent information. However,
long scan time significantly hinders its widespread applications. Recently,
low-rank tensor has been employed and demonstrated good performance in
accelerating MR parametricmapping. In this study, we propose a novel method
that uses spatial patch-based and parametric group-based low rank tensors
simultaneously (SMART) to reconstruct images from highly undersampled k-space
data. The spatial patch-based low-rank tensor exploits the high local and
nonlocal redundancies and similarities between the contrast images in
parametric mapping. The parametric group based low-rank tensor, which
integrates similar exponential behavior of the image signals, is jointly used
to enforce the multidimensional low-rankness in the reconstruction process. In
vivo brain datasets were used to demonstrate the validity of the proposed
method. Experimental results have demonstrated that the proposed method
achieves 11.7-fold and 13.21-fold accelerations in two-dimensional and
three-dimensional acquisitions, respectively, with more accurate reconstructed
images and maps than several state-of-the-art methods. Prospective
reconstruction results further demonstrate the capability of the SMART method
in accelerating MR quantitative imaging.Comment: 15 pages, 12 figure
Discovery of a radio lobe in the Cloverleaf Quasar at z = 2.56
The fast growth of supermassive black holes and their feedback to the host
galaxies play an important role in regulating the evolution of galaxies,
especially in the early Universe. However, due to cosmological dimming and the
limited angular resolution of most observations, it is difficult to resolve the
feedback from the active galactic nuclei (AGN) to their host galaxies.
Gravitational lensing, for its magnification, provides a powerful tool to
spatially differentiate emission originated from AGN and host galaxy at high
redshifts. Here we report a discovery of a radio lobe in a strongly lensed
starburst quasar, H1413+117 or Cloverleaf at redshift , based on
observational data at optical, sub-millimetre, and radio wavelengths. With both
parametric and non-parametric lens models and with reconstructed images on the
source plane, we find a differentially lensed, kpc scaled, single-sided radio
lobe, located at to the north west of the host galaxy
on the source plane. From the spectral energy distribution in radio bands, we
find that the radio lobe has an energy turning point residing between 1.5 GHz
and 8 GHz, indicating an age of 20--50 Myr. This could indicate a feedback
switching of Cloverleaf quasar from the jet mode to the quasar mode
ALMA [N \i\i ] 205 \mu m Imaging Spectroscopy of the Lensed Submillimeter galaxy ID 141 at redshift 4.24
We present the Atacama Large Millimeter/submillimeter Array (ALMA)
observation of the Sub-millimeter galaxy (SMG) ID 141 at z=4.24 in the [N II]
205 m line (hereafter [N II]) and the underlying continuum at (rest-frame)
197.6 m. Benefiting from lensing magnification by a galaxy pair at
z=0.595, ID 141 is one of the brightest z SMGs. At the angular resolutions
of to ( kpc), our observation clearly
separates, and moderately resolves the two lensed images in both continuum and
line emission at . Our continuum-based lensing model implies an
averaged amplification factor of and reveals that the de-lensed
continuum image has the S\'ersic index and the S\'ersic radius of
kpc). Furthermore, the reconstructed [N II] velocity
field in the source plane is dominated by a rotation component with a maximum
velocity of km/s at large radii, indicating a dark matter halo mass
of . This, together with the reconstructed velocity
dispersion field being smooth and modest in value ( km/s) over much of
the outer parts of the galaxy, favours the interpretation of ID 141 being a
disk galaxy dynamically supported by rotation. The observed [N II]/CO (7-6) and
[N II]/[C II] 158 m line luminosity ratios, which are consistent with the
corresponding line ratio vs. far-infrared color correlation from local luminous
infrared galaxies, imply a de-lensed star formation rate of (/yr and provide an independent estimate on the size of
the star-forming region kpc in radius.Comment: 13 pages, 6 figures, 2 tables, accepted by ApJ, lensing model code
can be found here https://gitlab.com/cxylzlx/tiny_len
Hdp Code: A Horizontal-Diagonal Parity Code to Optimize i/o Load Balancing
Abstract-With higher reliability requirements in clusters and data centers, RAID-6 has gained popularity due to its capability to tolerate concurrent failures of any two disks, which has been shown to be of increasing importance in large scale storage systems. Among various implementations of erasure codes in RAID-6, a typical set of codes known as Maximum Distance Separable (MDS) codes aim to offer data protection against disk failures with optimal storage efficiency. However, because of the limitation of horizontal parity or diagonal/anti-diagonal parities used in MDS codes, storage systems based on RAID-6 suffers from unbalanced I/O and thus low performance and reliability. To address this issue, in this paper, we propose a new parity called Horizontal-Diagonal Parity (HDP), which takes advantages of both horizontal and diagonal/anti-diagonal parities. The corresponding MDS code, called HDP code, distributes parity elements uniformly in each disk to balance the I/O workloads. HDP also achieves high reliability via speeding up the recovery under single or double disk failure. Our analysis shows that HDP provides better balanced I/O and higher reliability compared to other popular MDS codes
Design of Airborne Large Aperture Infrared Optical System Based on Monocentric Lens
Conventional reconnaissance camera systems have been flown on manned aircraft, where the weight, size, and power requirements are not stringent. However, today, these parameters are important for unmanned aerial vehicles (UAVs). This article provides a solution to the design of airborne large aperture infrared optical systems, based on a monocentric lens that can meet the strict criteria of aerial reconnaissance UAVs for a wide field of view (FOV) and lightness of airborne electro-optical pod cameras. A monocentric lens has a curved image plane, consisting of an array of microsensors, which can provide an image with 368 megapixels over a 100° FOV. We obtained the initial structure of a five-glass (5GS) asymmetric monocentric lens with an air gap, using ray-tracing and global optimization algorithms. According to the design results, the ground sampling distance (GSD) of the system is 0.33 m at 3000 m altitude. The full-field modulation transfer function (MTF) value of the system is more than 0.4 at a Nyquist frequency of 70 lp/mm. We present a primary thermal control method, and the image quality was steady throughout the operating temperature range. This compactness and simple structure fulfill the needs of uncrewed airborne lenses. This work may facilitate the practical application of monocentric lens in UAVs
Identification of Key Areas for Ecosystem Restoration Based on Ecological Security Pattern
Ecosystem degradation and conversion are leading to a widespread reduction in the provision of ecosystem services. It is crucial for the governance of regional land spaces to rapidly identify key areas for ecosystem restoration. Herein, we combined the InVEST Habitat Quality Model with the granularity inverse method to identify ecological sources in Jiashi county, China, based on the “source-corridor” ecological security pattern paradigm. The minimum cumulative resistance model and circuit theory were adopted to diagnose the ecological “pinch points”, barrier points, break points, and key restoration areas for land space. Our results show that: (1) the area of the ecological source and the total length of the ecological corridor were identified as 1331.13 km2 and 316.30 km, respectively; (2) there were 164 key ecological “pinch points” and 69 key ecological barrier points in Jiashi county, with areas of 15.13 km2 and 14.57 km2, respectively. Based on the above ecological security pattern, recovery strategies are put forward to improve regional ecosystem health. This study describes the best practices which can be used to guide the planning and implementation of ecosystem restoration at the local landscape scale
Identification of Key Areas for Ecosystem Restoration Based on Ecological Security Pattern
Ecosystem degradation and conversion are leading to a widespread reduction in the provision of ecosystem services. It is crucial for the governance of regional land spaces to rapidly identify key areas for ecosystem restoration. Herein, we combined the InVEST Habitat Quality Model with the granularity inverse method to identify ecological sources in Jiashi county, China, based on the “source-corridor” ecological security pattern paradigm. The minimum cumulative resistance model and circuit theory were adopted to diagnose the ecological “pinch points”, barrier points, break points, and key restoration areas for land space. Our results show that: (1) the area of the ecological source and the total length of the ecological corridor were identified as 1331.13 km2 and 316.30 km, respectively; (2) there were 164 key ecological “pinch points” and 69 key ecological barrier points in Jiashi county, with areas of 15.13 km2 and 14.57 km2, respectively. Based on the above ecological security pattern, recovery strategies are put forward to improve regional ecosystem health. This study describes the best practices which can be used to guide the planning and implementation of ecosystem restoration at the local landscape scale