伝播する衝撃波背後の極超音速境界層における流れの不安定性

Tohoku University博士（工学）要約のみthesi

An alternative attractor in gauged NJL inflation

We have investigated the attractor structure for the CMB fluctuations in composite inflation scenario within the gauged Nambu-Jona-Lasinio (NJL) model. Such composite inflation represents an attractor which can not be found in a fundamental scalar model. As is known, the number of inflationary models contains the attractor classified by the $\alpha$-attractor model. It is found that the attractor inflation in the gauged NJL model corresponds to the $\alpha = 2$ case.Comment: 7 pages, 2 figure

Lung Nodule Classification by the Combination of Fusion Classifier and Cascaded Convolutional Neural Networks

Lung nodule classification is a class imbalanced problem, as nodules are found with much lower frequency than non-nodules. In the class imbalanced problem, conventional classifiers tend to be overwhelmed by the majority class and ignore the minority class. We showed that cascaded convolutional neural networks can classify the nodule candidates precisely for a class imbalanced nodule candidate data set in our previous study. In this paper, we propose Fusion classifier in conjunction with the cascaded convolutional neural network models. To fuse the models, nodule probabilities are calculated by using the convolutional neural network models at first. Then, Fusion classifier is trained and tested by the nodule probabilities. The proposed method achieved the sensitivity of 94.4% and 95.9% at 4 and 8 false positives per scan in Free Receiver Operating Characteristics (FROC) curve analysis, respectively.Comment: Draft of ISBI2018. arXiv admin note: text overlap with arXiv:1703.0031

Data-driven h2 model reduction for linear discrete-time systems

We present a new framework of $h^{2}$ optimal model reduction for linear discrete-time systems. Our main contribution is to create optimal reduced order models in the $h^{2}$-norm sense directly from the measurement data alone, without using the information of the original system. In particular, we focus on the fact that the gradient of the $h^{2}$ model reduction problem is expressed using the discrete-time Lyapunov equation and the discrete-time Sylvester equation, and derive the data-driven gradient. In the proposed algorithm, the initial point is chosen as the output of the existing data-driven methods. Numerical experiments are conducted to show that the proposed method produce better reduced order models in the $h^{2}$-norm sense than other data-driven model order reduction approaches.Comment: 8 pages, 3 figure

Decomposition of neutron noise in a reactor into higher-order mode components and investigation of the space and frequency dependence

© 2019 Elsevier Ltd It is a well-known fact that the frequency characteristics of neutron noise induced by the fluctuation of nuclear cross sections have space-dependence that departs from the point kinetics behavior. In this paper, the neutron noise distribution in a two-dimensional BWR core model, which is calculated by solving a two-energy group neutron noise diffusion equation, is decomposed into higher-order mode components using α-mode eigenfunctions. The amplitude and the phase shift of the higher-order mode components have a minor dependence on the frequency, compared to the fundamental mode. Near the neutron noise source, the higher-order mode components account for a major portion of the neutron noise, thereby causing a minor dependence of the neutron noise on the frequency. Near the nodes of the higher-order modes, the fundamental mode is dominant, and the neutron noise exhibits almost the point kinetics behavior. The space dependence and the frequency characteristics of the neutron noise are elucidated by examining the higher order components that are decomposed from the neutron noise distribution

Robustness of predicted CMB fluctuations in Cartan F(R)F(R) gravity

The cosmology of the $F(R)$ gravity rebuilding by the Cartan formalism is investigated. This is called Cartan $F(R)$ gravity. The well-known $F(R)$ gravity has been introduced to extend the standard cosmology, e.g. to explain the cosmological accelerated expansion as the inflation. Cartan $F(R)$ gravity is based on the Riemann-Cartan geometry. The curvature $R$ can separate to two parts, one is derived from the Levi-Civita connection and the other from the torsion. Assuming the matter-independent spin connection, we have successfully rewritten the action of Cartan $F(R)$ gravity into the Einstein-Hilbert action and a scalar field with canonical kinetic and potential terms without any conformal transformations. This feature simplifies building and analysis of new model of inflation. In this paper, we study two models, the power-law model and logarithmic model, and evaluate fluctuations in the cosmological microwave background (CMB) radiation. We found the robustness of CMB fluctuation by the analytical computation and confirm this feature by the numerical calculation.Comment: 14pages, 4figure

量子補正によって改良されたインフレーションのモデル

内容の要約広島大学(Hiroshima University)博士(理学)Doctor of Sciencedoctora