17 research outputs found
Ambiguity of black hole entropy in loop quantum gravity
We reexmine some proposals of black hole entropy in loop quantum gravity
(LQG) and consider a new possible choice of the Immirzi parameter which has not
been pointed out so far. We also discuss that a new idea is inevitable if we
regard the relation between the area spectrum in LQG and that in the
quasinormal mode analysis seriously.Comment: 4 pages, 1 figure, error corrected, PRD published versio
The universal area spectrum in single-horizon black holes
We investigate highly damped quasinormal mode of single-horizon black holes
motivated by its relation to the loop quantum gravity. Using the WKB
approximation, we show that the real part of the frequency approaches the value
for dilatonic black hole as conjectured by Medved et al. and
Padmanabhan. It is surprising since the area specrtum of the black hole
determined by the Bohr's correspondence principle completely agrees with that
of Schwarzschild black hole for any values of the electromagnetic charge or the
dilaton coupling. We discuss its generality for single-horizon black holes and
the meaning in the loop quantum gravity.Comment: 5 pages, 1 figure, references and comments adde
The Fate of a Five-Dimensional Rotating Black Hole via Hawking Radiation
We study the evolution of a five-dimensional rotating black hole emitting
scalar field radiation via the Hawking process for arbitrary initial values of
the two rotation parameters and . It is found that any such black hole
whose initial rotation parameters are both nonzero evolves toward an asymptotic
state
, where this constant is independent
of the initial values of and .Comment: 6 pages, 6 figure
Continuous area spectrum in regular black hole
We investigate highly damped quasinormal modes of regular black hole coupled
to nonlinear electrodynamics. Using the WKB approximation combined with
complex-integration technique, we show that the real part of the frequency
disappears in the highly damped limit. If we use the Bohr's correspondence
principle, the area spectrum of this black hole is continuous. We discuss its
implication in the loop quantum gravity.Comment: 5 pages, 1 figure
Quantitative Assessment of Thyroid Nodules Using Dual-Energy Computed Tomography: Iodine Concentration Measurement and Multiparametric Texture Analysis for Differentiating between Malignant and Benign Lesions
Background and Objectives. Thyroid nodules are increasingly being detected during cross-sectional imaging of the neck and chest. The purpose of this study is to investigate the efficacy of dual-energy computed tomography (DECT) using iodine concentration measurement and multiparametric texture analysis of monochromatic images for differentiating between benign and malignant thyroid nodules. Materials and Methods. This retrospective study included 34 consecutive patients who presented with thyroid nodules and underwent noncontrast DECT between 2015 and 2016. Manual segmentation of each thyroid nodule by monochromatic imaging (40, 60, and 80 keV) was performed, and an in-house developed MATLAB-based texture analysis program was used to extract 41 textures. Iodine material decomposition and CT attenuation slopes were also measured. Histopathologic findings of ultrasound-guided biopsies over a follow-up period of at least one year were used as reference standards. Basic descriptive statistics and areas under receiver operating characteristic curves (AUCs) were evaluated. Results. The 34 nodules comprised 14 benign nodules and 20 malignant nodules. Iodine content and Hounsfield unit curve slopes did not differ significantly between benign and malignant thyroid nodules (P=0.480–0.670). However, significant differences in the texture features of monochromatic images were observed between benign and malignant nodules: histogram mean and median, co-occurrence matrix contrast, gray-level gradient matrix (GLGM) skewness, and mean gradients and variance of gradients for GLGM at 80 keV (P=0.014–0.044). The highest AUC was 0.77, for the histogram mean and median of images acquired at 80 keV. Conclusions. Texture features extracted from monochromatic images using DECT, specifically acquired at high keV, may be a promising diagnostic approach for thyroid nodules. A further large study for incidental thyroid nodules using DECT texture analysis is required to validate our results
Design Studies on a High-Power Wide-Band RF Combiner for Consolidation of the Driver Amplifier of the J-PARC RCS
A power upgrade of the existing 8 kW solid-state driver amplifier is required for the acceleration of high intensity proton beams in the J-PARC 3 GeV rapid cycling synchrotron (RCS). The development of a 25 kW amplifier with gallium nitride (GaN) HEMTs and based on 6.4 kW modules is ongoing. The combiner is a key component to achieve such a high output power over the wide bandwidth required for multi-harmonic rf operation. This paper presents a preliminary design of the combiner. The circuit simulation setup and results, including the realistic magnetic core characteristics and frequency response of the cables are reported
Prostatic urinary tract visualization with super-resolution deep learning models
In urethra-sparing radiation therapy, prostatic urinary tract visualization is important in decreasing the urinary side effect. A methodology has been developed to visualize the prostatic urinary tract using post-urination magnetic resonance imaging (PU-MRI) without a urethral catheter. This study investigated whether the combination of PU-MRI and super-resolution (SR) deep learning models improves the visibility of the prostatic urinary tract. We enrolled 30 patients who had previously undergone real-time-image-gated spot scanning proton therapy by insertion of fiducial markers. PU-MRI was performed using a non-contrast high-resolution two-dimensional T2-weighted turbo spin-echo imaging sequence. Four different SR deep learning models were used: the enhanced deep SR network (EDSR), widely activated SR network (WDSR), SR generative adversarial network (SRGAN), and residual dense network (RDN). The complex wavelet structural similarity index measure (CW-SSIM) was used to quantitatively assess the performance of the proposed SR images compared to PU-MRI. Two radiation oncologists used a 1-to-5 scale to subjectively evaluate the visibility of the prostatic urinary tract. Cohen's weighted kappa (k) was used as a measure of agreement of inter-operator reliability. The mean CW-SSIM in EDSR, WDSR, SRGAN, and RDN was 99.86%, 99.89%, 99.30%, and 99.67%, respectively. The mean prostatic urinary tract visibility scores of the radiation oncologists were 3.70 and 3.53 for PU-MRI (k = 0.93), 3.67 and 2.70 for EDSR (k = 0.89), 3.70 and 2.73 for WDSR (k = 0.88), 3.67 and 2.73 for SRGAN (k = 0.88), and 4.37 and 3.73 for RDN (k = 0.93), respectively. The results suggest that SR images using RDN are similar to the original images, and the SR deep learning models subjectively improve the visibility of the prostatic urinary tract