Aoyama Gakuin University

www.aoyama.ac.jp/en/
Tokyo, Japan

Aoyama Gakuin University , abbreviated AGU, is a Japanese Christian university in Shibuya near Omotesandō, Tokyo, Japan. Aoyama Gakuin University is part of a comprehensive educational institute called Aoyama Gakuin, which includes a kindergarten, an elementary school, junior and senior high schools, and a women's junior college. Aoyama Gakuin's history dates from October 1874, when missionaries from the Methodist Episcopal Church of the United States established three schools. John Franklin Goucher contributed to the establishment of the university. Canadian Methodist missionary Davidson MacDonald played a role in the establishment of Aoyama Gakuin, and his contribution to the improvement of Japan's educational system is considered an important episode in the early history of Japanese-Canadian relations. The institution took its present form in 1949 when Aoyama Gakuin College was established as a comprehensive university.Aoyama Gakuin University is one of the most prestigious private universities in Japan.The university's undergraduate and graduate programs include "literature", "law", "economics", "business", "international politics, economics and communication", "science and engineering","cultural and creative studies". The university also has specialized graduate programs that are designed to train high level specialized professionals, including "international management", "law school", and "professional accounting". Wikipedia.


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Iwasaki J.,University of Tokyo | Mochizuki M.,Aoyama Gakuin University | Nagaosa N.,University of Tokyo | Nagaosa N.,RIKEN
Nature Nanotechnology | Year: 2013

Magnetic skyrmions - vortex-like swirling spin structures with a quantized topological number that are observed in chiral magnets - are appealing for potential applications in spintronics because it is possible to control their motion with ultralow current density. To realize skyrmion-based spintronic devices, it is essential to understand skyrmion motions in confined geometries. Here we show by micromagnetic simulations that the current-induced motion of skyrmions in the presence of geometrical boundaries is very different from that in an infinite plane. In a channel of finite width, transverse confinement results in steady-state characteristics of the skyrmion velocity as a function of current that are similar to those of domain walls in ferromagnets, whereas the transient behaviour depends on the initial distance of the skyrmion from the boundary. Furthermore, we show that a single skyrmion can be created by an electric current in a simple constricted geometry comprising a plate-shaped specimen of suitable size and geometry. These findings could guide the design of skyrmion-based devices in which skyrmions are used as information carriers. © 2013 Macmillan Publishers Limited. All rights reserved.


Inoue T.,Aoyama Gakuin University | Inutsuka S.-I.,Nagoya University
Astrophysical Journal | Year: 2012

Using three-dimensional magnetohydrodynamic simulations, including the effects of radiative cooling/heating, chemical reactions, and thermal conduction, we investigate the formation of molecular clouds in the multi-phase interstellar medium. As suggested by recent observations, we consider the formation of molecular clouds due to accretion of H I clouds. Our simulations show that the initial H I medium is piled up behind the shock waves induced by accretion flows. Since the initial medium is highly inhomogeneous as a consequence of thermal instability, a newly formed molecular cloud becomes very turbulent owing to the development of the Richtmyer-Meshkov instability. The kinetic energy of the turbulence dominates the thermal, magnetic, and gravitational energies throughout the entire 10 Myr evolution. However, the kinetic energy measured using CO-fraction-weighted densities is comparable to the other energies, once the CO molecules are sufficiently formed as a result of UV shielding. This suggests that the true kinetic energy of turbulence in molecular clouds as a whole can be much larger than the kinetic energy of turbulence estimated using line widths of molecular emission. We find that clumps in a molecular cloud show the following statistically homogeneous evolution: the typical plasma β of the clumps is roughly constant 〈β〉 ≃ 0.4; the size-velocity dispersion relation is Δv ≃ 1.5 km s-1 (l/1 pc)0.5, irrespective of the density; the clumps evolve toward magnetically supercritical, gravitationally unstable cores; and the clumps seem to evolve into cores that satisfy the condition for fragmentation into binaries. These statistical properties may represent the initial conditions of star formation. © 2012. The American Astronomical Society. All rights reserved..


Yoneyama J.,Aoyama Gakuin University
Information Sciences | Year: 2012

This paper is concerned with robust sampled-data stabilization for uncertain fuzzy systems. The system is modeled as a continuous-time fuzzy system, while the control input is a zero-order sampled-data signal. When a zero-order control input is considered, the closed-loop system can be seen as an input delay system. Hence, an input delay system approach is introduced for sampled-data control design. Sufficient stability conditions for the closed-loop system are given in terms of linear matrix inequalities (LMIs). Under the assumption that sampling interval is not greater than some prescribed number, stability conditions for fuzzy time-delay systems are given by using Jensen's Inequality, which simplifies conditions with less matrix variables. A design method of robust sampled-data state feedback controller for uncertain fuzzy systems is then proposed. Numerical examples are given to illustrate our robust sampled-data state feedback control design and to show the effectiveness over other existing results. © 2012 Elsevier Inc. All rights reserved.


Nakada T.,Aoyama Gakuin University
Electronic Materials Letters | Year: 2012

Although CIGS solar cells consist of a polycrystalline thin film grown on a glass substrate, more than 20% conversion efficiency has been achieved. The efficiency has reached the same level as polycrystalline silicon solar cells. This high efficiency has not yet been observed in other thin film solar cells including thin film Si and CdTe. Therefore, it is important to understand the mechanisms that allow CIGS solar cells to exhibit high conversion efficiencies. This paper discusses the origin of the high efficiency and demonstrates that it is caused by the unique material properties of CIGS films. © 2012 The Korean Institute of Metals and Materials and Springer Netherlands.


Yoneyama J.,Aoyama Gakuin University
Fuzzy Sets and Systems | Year: 2013

This paper is concerned with robust H∞ filtering for Takagi-Sugeno sampled-data fuzzy systems with uncertain parameters. Takagi-Sugeno fuzzy system can describe a wide class of nonlinear systems, and is widely used in many engineering fields. Recently, system analysis and control design for nonlinear systems based fuzzy system approach have been active. The system is usually modelled as a continuous-time system, while in practical situations the observation is taken at discrete instants. Such an observation can be represented as a delayed signal. First it is shown that the error system which stems from an original fuzzy system and a sampled-data filter becomes a system with time-varying delay. Sufficient conditions for the error system to achieve the robust stability with H∞ disturbance attenuation are given in terms of linear matrix inequalities(LMIs). We derive such conditions via output delay system approach under the assumption that sampling-time is not greater than some prescribed number. Based on such conditions, we propose a robust H∞ sampled-data filter design for a fuzzy system. We consider two different cases for the premise variables in our filter design. Numerical examples are given to illustrate our robust H ∞ sampled-data filtering. © 2012 Elsevier B.V.


Ohira Y.,Aoyama Gakuin University
Physical Review Letters | Year: 2013

Perpendicular collisionless shocks propagating into partially ionized plasmas are investigated by two-dimensional hybrid particle simulations. It is shown that some neutral particles leak into the upstream region from the downstream region, the leaking neutral particles become pickup ions in the upstream region and modify the shock structure, the pickup ions are preferentially accelerated, and plasma instabilities are excited by the pickup ions in the upstream and downstream regions. © 2013 American Physical Society.


Inoue T.,Aoyama Gakuin University
Astrophysical Journal | Year: 2012

The linear stability of a current sheet that is subject to an impulsive acceleration due to shock passage with the effect of a guide magnetic field is studied. We find that a current sheet embedded in relativistically magnetized plasma always shows a Richtmyer-Meshkov-type instability, while the stability depends on the density structure in the Newtonian limit. The growth of the instability is expected to generate turbulence around the current sheet, which can induce the so-called turbulent reconnection, the rate of which is essentially free from plasma resistivity. Thus, the instability can be applied as a triggering mechanism for rapid magnetic energy release in a variety of high-energy astrophysical phenomena such as pulsar wind nebulae, gamma-ray bursts, and active galactic nuclei, where the shock wave is thought to play a crucial role. © 2012. The American Astronomical Society. All rights reserved.


Ohira Y.,Aoyama Gakuin University
Astrophysical Journal | Year: 2012

In this paper, we investigate effects of neutral particles on shocks propagating into the partially ionized medium. We find that for 120 km s -1 < ush < 3000 km s-1 (ush is the shock velocity), about 10% of upstream neutral particles leak into the upstream region from the downstream region. Moreover, we investigate how the leakage neutral particles affect the upstream structure of the shock and particle accelerations. Using four-fluid approximations (upstream ions, upstream neutral particles, leakage neutral particles, and pickup ions), we provide analytical solutions of the precursor structure due to leakage neutral particles. It is shown that the upstream flow is decelerated in the precursor region and the shock compression ratio becomes smaller than without leakage neutral particles, but the total compression ratio does not change. Even if leakage of neutral particles is small (a few percent of total upstream particles), this smaller compression ratio of the shock can explain steep gamma-ray spectra from young supernova remnants. Furthermore, leakage neutral particles could amplify the magnetic field and heat the upstream region. © 2012. The American Astronomical Society. All rights reserved.


Yoneyama J.,Aoyama Gakuin University
Applied Soft Computing Journal | Year: 2011

In practice, the system is often modeled as a continuous-time fuzzy system, while the control input is applied only at discrete instants. This system is called a sampled-data control system. In this paper, robust guaranteed cost control for uncertain sampled-data fuzzy systems is discussed. A guaranteed cost control where a quadratic cost function is bounded by a certain scalar, not only stabilizes a system but also considers a control performance. A typical sampled-data control is the zero-order input, which can be represented as a piecewise-continuous delay. Here we take a delay system approach to the sampled-data guaranteed cost control problem. The closed-loop system with a sampled-data state feedback controller becomes a system with time-varying delay. First, guaranteed cost control performance conditions for the closed-loop system are given in terms of linear matrix inequalities (LMIs). Such conditions are derived by using Leibniz-Newton formula and free weighting matrix method for fuzzy systems under the assumption that sampling time is not greater than some prescribed scalar. Then, a design method of robust guaranteed cost state feedback controller for uncertain sampled-data fuzzy systems is proposed. Examples are given to illustrate our robust sampled-data guaranteed cost control design. © 2010 Elsevier B.V. All rights reserved.


Yoneyama J.,Aoyama Gakuin University
Fuzzy Sets and Systems | Year: 2010

Robust H∞ sampled-data control for uncertain fuzzy systems is discussed. In many practical situations, a system is modeled as a continuous-time fuzzy system, while the control input is the zero-order hold, which can be represented as a piecewise-continuous delay. Here we take a delay system approach to the H∞ sampled-data control problem. The closed-loop system with a sampled-data state feedback controller becomes a system with time-varying delay. First, H∞ performance conditions for the closed-loop system are given in terms of linear matrix inequalities (LMIs). Such conditions are derived by using the Leibniz-Newton formula and free-weighting matrix method for fuzzy time-delay systems under the assumption that sampling time is not greater than some prescribed number. Then, a design method for a robust H∞ sampled-data state feedback controller for uncertain fuzzy systems is proposed. Numerical examples are given to illustrate our robust H∞ sampled-data state feedback control design. © 2009 Elsevier B.V. All rights reserved.

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