13,695 research outputs found
Doubled Conformal Compactification
We use Weyl transformations between the Minkowski spacetime and dS/AdS
spacetime to show that one cannot well define the electrodynamics globally on
the ordinary conformal compactification of the Minkowski spacetime (or dS/AdS
spacetime), where the electromagnetic field has a sign factor (and thus is
discountinuous) at the light cone. This problem is intuitively and clearly
shown by the Penrose diagrams, from which one may find the remedy without too
much difficulty. We use the Minkowski and dS spacetimes together to cover the
compactified space, which in fact leads to the doubled conformal
compactification. On this doubled conformal compactification, we obtain the
globally well-defined electrodynamics.Comment: 14 pages, 4 figure
The Quasi-normal Modes of Charged Scalar Fields in Kerr-Newman black hole and Its Geometric Interpretation
It is well-known that there is a geometric correspondence between
high-frequency quasi-normal modes (QNMs) and null geodesics (spherical photon
orbits). In this paper, we generalize such correspondence to charged scalar
field in Kerr-Newman space-time. In our case, the particle and black hole are
all charged, so one should consider non-geodesic orbits. Using the WKB
approximation, we find that the real part of quasi-normal frequency corresponds
to the orbits frequency, the imaginary part of the frequency corresponds to the
Lyapunov exponent of these orbits and the eigenvalue of angular equation
corresponds to carter constant. From the properties of the imaginary part of
quasi-normal frequency of charged massless scalar field, we can still find that
the QNMs of charged massless scalar field possess the zero damping modes in
extreme Kerr-Newman spacetime under certain condition which has been fixed in
this paper.Comment: 30 pages, many figures, to appear in JHE
Neural Feedback Scheduling of Real-Time Control Tasks
Many embedded real-time control systems suffer from resource constraints and
dynamic workload variations. Although optimal feedback scheduling schemes are
in principle capable of maximizing the overall control performance of
multitasking control systems, most of them induce excessively large
computational overheads associated with the mathematical optimization routines
involved and hence are not directly applicable to practical systems. To
optimize the overall control performance while minimizing the overhead of
feedback scheduling, this paper proposes an efficient feedback scheduling
scheme based on feedforward neural networks. Using the optimal solutions
obtained offline by mathematical optimization methods, a back-propagation (BP)
neural network is designed to adapt online the sampling periods of concurrent
control tasks with respect to changes in computing resource availability.
Numerical simulation results show that the proposed scheme can reduce the
computational overhead significantly while delivering almost the same overall
control performance as compared to optimal feedback scheduling.Comment: To appear in International Journal of Innovative Computing,
Information and Contro
Fuzzy Feedback Scheduling of Resource-Constrained Embedded Control Systems
The quality of control (QoC) of a resource-constrained embedded control
system may be jeopardized in dynamic environments with variable workload. This
gives rise to the increasing demand of co-design of control and scheduling. To
deal with uncertainties in resource availability, a fuzzy feedback scheduling
(FFS) scheme is proposed in this paper. Within the framework of feedback
scheduling, the sampling periods of control loops are dynamically adjusted
using the fuzzy control technique. The feedback scheduler provides QoC
guarantees in dynamic environments through maintaining the CPU utilization at a
desired level. The framework and design methodology of the proposed FFS scheme
are described in detail. A simplified mobile robot target tracking system is
investigated as a case study to demonstrate the effectiveness of the proposed
FFS scheme. The scheme is independent of task execution times, robust to
measurement noises, and easy to implement, while incurring only a small
overhead.Comment: To appear in International Journal of Innovative Computing,
Information and Contro
SIMBA: scalable inversion in optical tomography using deep denoising priors
Two features desired in a three-dimensional (3D) optical tomographic image reconstruction algorithm are the ability to reduce imaging artifacts and to do fast processing of large data volumes. Traditional iterative inversion algorithms are impractical in this context due to their heavy computational and memory requirements. We propose and experimentally validate a novel scalable iterative mini-batch algorithm (SIMBA) for fast and high-quality optical tomographic imaging. SIMBA enables highquality imaging by combining two complementary information sources: the physics of the imaging system characterized by its forward model and the imaging prior characterized by a denoising deep neural net. SIMBA easily scales to very large 3D tomographic datasets by processing only a small subset of measurements at each iteration. We establish the theoretical fixedpoint convergence of SIMBA under nonexpansive denoisers for convex data-fidelity terms. We validate SIMBA on both simulated and experimentally collected intensity diffraction tomography (IDT) datasets. Our results show that SIMBA can significantly reduce the computational burden of 3D image formation without sacrificing the imaging quality.https://arxiv.org/abs/1911.13241First author draf
Regularized Fourier ptychography using an online plug-and-play algorithm
The plug-and-play priors (PnP) framework has been recently shown to achieve state-of-the-art results in regularized image reconstruction by leveraging a sophisticated denoiser within an iterative algorithm. In this paper, we propose a new online PnP algorithm for Fourier ptychographic microscopy (FPM) based on the accelerated proximal gradient method (APGM). Specifically, the proposed algorithm uses only a subset of measurements, which makes it scalable to a large set of measurements. We validate the algorithm by showing that it can lead to significant performance gains on both simulated and experimental data.https://arxiv.org/abs/1811.00120Published versio
Regularized Fourier ptychography using an online plug-and-play algorithm
The plug-and-play priors (PnP) framework has been recently shown to achieve state-of-the-art results in regularized image reconstruction by leveraging a sophisticated denoiser within an iterative algorithm. In this paper, we propose a new online PnP algorithm for Fourier ptychographic microscopy (FPM) based on the accelerated proximal gradient method (APGM). Specifically, the proposed algorithm uses only a subset of measurements, which makes it scalable to a large set of measurements. We validate the algorithm by showing that it can lead to significant performance gains on both simulated and experimental data.https://arxiv.org/abs/1811.00120Published versio
DNA Methylation Heterogeneity Patterns in Breast Cancer Cell Lines
Heterogeneous DNA methylation patterns are linked to tumor growth. In order to study DNA methylation heterogeneity patterns for breast cancer cell lines, we comparatively study four metrics: variance, I² statistic, entropy, and methylation state. Using the categorical metric methylation state, we select the two most heterogeneous states to identify genes that directly affect tumor suppressor genes and high- or moderate-risk breast cancer genes. Utilizing the Gene Set Enrichment Analysis software and the ConsensusPath Database visualization tool, we generate integrated gene networks to study biological relations of heterogeneous genes. This analysis has allowed us to contribute 19 potential breast cancer biomarker genes to cancer databases by locating “hub genes” – heterogeneous genes of significant biological interactions, selected from numerous cancer modules. We have discovered a considerable relationship between these hub genes and heterogeneously methylated oncogenes. Our results have many implications for further heterogeneity analyses of methylation patterns and early detection of breast cancer susceptibility
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