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Sagamihara, Japan

The Japan Aerospace Exploration Agency , or JAXA, is Japan's national aerospace agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and the launch of satellites into orbit, and is involved in many more advanced missions, such as asteroid exploration and possible manned exploration of the Moon. Its motto is One JAXA and its corporate slogan is Explore to Realize . Wikipedia.

In this paper, we propose a new design method for Gain-Scheduled Output Feedback (GSOF) controllers for continuous-time Linear Parameter-Varying (LPV) systems via Parameter-Dependent Lyapunov Functions (PDLFs). The GSOF controllers depend solely on scheduling parameters. Although our method requires a line search to obtain suboptimal controllers, it produces practical GSOF controllers, being independent of the derivatives of scheduling parameters. Our method is proved to be no more conservative than conventional design methods via constant Lyapunov functions as well as particularly structured PDLFs. © 2011 Elsevier Ltd. All rights reserved.

Shimizu T.,Japan Aerospace Exploration Agency
Astrophysical Journal | Year: 2011

Sunspot light bridges (LBs) - long bright lanes appearing in umbra - sometimes show dynamical behaviors such as plasma ejections, brightenings, and fast gas flows in the photosphere and lower chromosphere, but we have not understood what causes these dynamics. The Hinode Solar Optical Telescope successfully captured the entire period of the evolution of an LB formed at the southeast of the well-developed sunspot in NOAA Active Region 10953, allowing us to track how magnetic and dynamical properties change with time for 3.5 days. The LB produced chromospheric upward ejections intermittently and recurrently on 2007 April 30, and fewer upward ejections were observed on May 1. We found that G-band intensity features morphologically changed from cellar or patchy on April 30 to filamentary on May 1, although there were small changes in the magnetic flux density and inclination. This suggests that the chromospheric activity is related to the change of morphology in the photosphere. Fast gas flows and a pair of strong enhanced vertical electrical currents were also observed in the photosphere after the filamentary structures were dominant. The end of a large Hα filament (or prominence) was extended very close to the LB on May 1, suggesting that the filamentary structures formed along the LB may be magnetically connected to the large Hα filament and the gas flows may originate far from the LB region, although other mechanisms cannot be ruled out. © 2011. The American Astronomical Society. All rights reserved.

Kawai S.,Japan Aerospace Exploration Agency
Journal of Computational Physics | Year: 2013

This paper proposes a new strategy that is very simple, divergence-free, high-order accurate, yet has an effective discontinuous-capturing capability for simulating compressible magnetohydrodynamics (MHD). The new strategy is to construct artificial diffusion terms in a physically-consistent manner, such that the artificial terms act as a diffusion term only in the curl of magnetic field to capture numerical discontinuities in the magnetic field while not affecting the divergence field (thus maintaining divergence-free constraint). The physically-consistent artificial diffusion terms are built into the induction equations in a conservation law form at a partial-differential-equation level. The proposed method may be viewed as adding an artificial magnetic resistivity to the induction equations, and is inherently divergence-free both ideal and resistive MHD, with and without shock waves, and also both inviscid and viscous flows. The method is based on finite difference method with co-located variable arrangement, and we show that any linear finite difference scheme in an arbitrary order of accuracy can be used to discretize the modified governing equations to ensures the divergence-free and the global conservation constraints numerically at the discretization level. The artificial magnetic resistivity is designed to localize automatically in regions of discontinuity in the curl of magnetic field and vanish wherever the flow is sufficiently smooth with respect to the grid scale, thereby maintaining the desirable high-order accuracy of the employed discretization scheme in smooth regions. Two-dimensional smooth and non-smooth ideal MHD problems are considered to validate the capability of the proposed method. © 2013 Elsevier Inc.

Shimada M.,Japan Aerospace Exploration Agency
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011

This paper proposes a new polarimetric synthetic aperture radar (SAR) (PolSAR) calibration method that applies an incoherent decomposition model to the uncalibrated covariance data measured for the forest and surface and determines the polarimetric distortion matrix (PDM). The Freeman-Durden model is used to express the polarization-dependent signal reflection from and penetration through the forest. Nonlinear equations built for uncalibrated PolSAR data are solved iteratively. This method is applicable to the lower frequency SAR that associates with the polarization-dependent signal penetration through forest canopies. Using the time series Phased-Array-Type L-band SAR (PALSAR) data acquired from the Amazon rainforest for around three years, we confirm that the proposed method succeeds in the PDM estimation and that the calibrated data preserve the polarimetric performance on HH-VV orthogonality, low crosstalks, and ideal polarimetric signature for the corner reflector. This paper also investigates the signal-penetration properties of the forest associated with the L-band SAR. © 2006 IEEE.

Nishizuka N.,Japan Aerospace Exploration Agency | Shibata K.,Kyoto University
Physical Review Letters | Year: 2013

We propose the particle acceleration model coupled with multiple plasmoid ejections in a solar flare. Unsteady reconnection produces plasmoids in a current sheet and ejects them out to the fast shocks, where particles in a plasmoid are reflected upstream the shock front by magnetic mirror effect. As the plasmoid passes through the shock front, the reflection distance becomes shorter and shorter driving Fermi acceleration, until it becomes proton Larmor radius. The fractal distribution of plasmoids may also have a role in naturally explaining the power-law spectrum in nonthermal emissions. © 2013 American Physical Society.

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