1,160 research outputs found
Quantitative Molecular MRI of Intervertebral Disc Degeneration
Degeneration of the intervertebral disc (IVD) is the most common cause of back-related disability among North American adults. Low-back-pain and associated disability costs the United States more than 100 billion dollars annually in health care expenditures and reduced productivity. The mechanism of IVD degeneration, especially its biomolecular aspect, is poorly understood in an in vivo setting. Thus there is increasingly a need for the non-invasive diagnosis and quantification of IVD degeneration. MRI is a non-invasive imaging modality capable of producing contrast sensitive to biomolecules. Therefore, the primary objective of this dissertation research project is to develop MRI techniques capable of non-invasive quantification of IVD biomolecular composition in vivo. We further developed three MRI techniques specifically for IVD imaging. Magnetization transfer (MT) MRI, T1ρ MRI and sodium MRI were first separately validated of their specificities for IVD biomolecular components. In doing so, we concluded that MT MRI is sensitive to IVD collagen content, T1ρ MRI is indicative of IVD osmotic pressure, and sodium MRI is sensitive to IVD proteoglycan (PG) content. Next, we applied all three techniques to human subjects in vivo. Due to the inherently low signal-to-noise ratio (SNR) efficiency of sodium MRI, we engineered a custom radio-frequency (RF) surface coil for sodium MRI of human lumbar spine on a 7 T MRI scanner. Cross-correlation of the MT MRI, T1ρ MRI and sodium MRI data with the corresponding Pfirrmann grade revealed that the relative collagen density of IVD increases with degeneration, the IVD osmotic pressure decreases with degeneration, and the IVD PG content decreases with degeneration. By establishing that in vivo MT MRI, T1ρ MRI and sodium MRI can be used to quantify multiple IVD biomolecular characteristics non-invasively, we open up the possibility to conduct longitudinal studies on human subjects as they undergo IVD degeneration. The combination of MT MRI, T1ρ MRI and sodium MRI provides scientists and clinicians with the diagnostic tool to improve our understanding of IVD degeneration, which could benefit future treatment and prognosis of IVD degeneration
Pose-Guided Multi-Granularity Attention Network for Text-Based Person Search
Text-based person search aims to retrieve the corresponding person images in
an image database by virtue of a describing sentence about the person, which
poses great potential for various applications such as video surveillance.
Extracting visual contents corresponding to the human description is the key to
this cross-modal matching problem. Moreover, correlated images and descriptions
involve different granularities of semantic relevance, which is usually ignored
in previous methods. To exploit the multilevel corresponding visual contents,
we propose a pose-guided multi-granularity attention network (PMA). Firstly, we
propose a coarse alignment network (CA) to select the related image regions to
the global description by a similarity-based attention. To further capture the
phrase-related visual body part, a fine-grained alignment network (FA) is
proposed, which employs pose information to learn latent semantic alignment
between visual body part and textual noun phrase. To verify the effectiveness
of our model, we perform extensive experiments on the CUHK Person Description
Dataset (CUHK-PEDES) which is currently the only available dataset for
text-based person search. Experimental results show that our approach
outperforms the state-of-the-art methods by 15 \% in terms of the top-1 metric.Comment: published in AAAI2020(oral
Multi-epoch analysis of the X-ray spectrum of the active galactic nucleus in NGC 5506
We present a multi-epoch X-ray spectroscopy analysis of the nearby
narrow-line Seyfert I galaxy NGC 5506. For the first time, spectra taken by
Chandra, XMM-Newton, Suzaku, and NuSTAR - covering the 2000-2014 time span -
are analyzed simultaneously, using state-of-the-art models to describe
reprocessing of the primary continuum by optical thick matter in the AGN
environment. The main goal of our study is determining the spin of the
supermassive black hole (SMBH). The nuclear X-ray spectrum is photoelectrically
absorbed by matter with column density cm. A
soft excess is present at energies lower than the photoelectric cut-off. Both
photo-ionized and collisionally ionized components are required to fit it. This
component is constant over the time-scales probed by our data. The spectrum at
energies higher than 2 keV is variable. We propose that its evolution could be
driven by flux-dependent changes in the geometry of the innermost regions of
the accretion disk. The black hole spin in NGC 5506 is constrained to be
0.93 at 90% confidence level for one interesting
parameter.Comment: 13 pages, 9 figures. v2: refereed versio
DEUCON: Distributed End-to-End Utilization Control for Real-Time Systems
This paper presents the Distributed End-to-end Utiization CONtrol (DEUCON) algorithm. DEUCON can dynamically enforce desired CPU utilizations on all processors in a dis-tributed real-time system despite uncertainties in the system workload. In contrast to earlier centralized control schemes, DEUCON is a distributed control algorithm that is system-atically designed based on the Distributed Model Predictive Control theory. We decompose the global multi-processor utilization control problem into a set of localized subprob-lems, and design a peer-to-peer control structure where each local controller only needs to coordinate with a small number of neighbor processors. DEUCON can provide utilization guarantees similar to a centralized control algorithm, while significantly reducing the per-controller run-time overhead in terms of both computation and communication. Further-more, it can tolerate considerable network delay and indi-vidual processor failures. Consequently, DEUCON can pro-vide scalable and robust utilization control services for large distributed real-time systems that operate in unpredictable environments
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