Author
Masaki Fujimoto
Other affiliations: University of Tokyo, Tokyo Institute of Technology
Bio: Masaki Fujimoto is an academic researcher from Japan Aerospace Exploration Agency. The author has contributed to research in topics: Magnetosphere & Magnetic reconnection. The author has an hindex of 43, co-authored 156 publications receiving 5656 citations. Previous affiliations of Masaki Fujimoto include University of Tokyo & Tokyo Institute of Technology.
Papers published on a yearly basis
Papers
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TL;DR: BepiColombo as mentioned in this paper is an interdisciplinary mission to explore Mercury, the planet closest to the sun, carried out jointly between the European Space Agency and the Japanese Aerospace Exploration Agency.
429 citations
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Japan Aerospace Exploration Agency1, Nagoya University2, Auburn University3, University of Aizu4, Kobe University5, University of Tokyo6, Graduate University for Advanced Studies7, Hiroshima University8, Tohoku University9, Chiba Institute of Technology10, Kindai University11, National Institute of Advanced Industrial Science and Technology12, Kōchi University13, Rikkyo University14, National Institute of Information and Communications Technology15, Seoul National University16, Planetary Science Institute17, Johns Hopkins University Applied Physics Laboratory18, Centre national de la recherche scientifique19, University of Colorado Boulder20, Meiji University21, German Aerospace Center22, Centre National D'Etudes Spatiales23
TL;DR: The Hayabusa2 spacecraft measured the mass, size, shape, density, and spin rate of asteroid Ryugu, showing that it is a porous rubble pile, and observations of Ryugu's shape, mass, and geomorphology suggest that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation.
Abstract: The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu’s shape, mass, and geomorphology. Ryugu has an oblate “spinning top” shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu’s shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.
402 citations
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Chiba Institute of Technology1, University of Tokyo2, Kōchi University3, Nagoya University4, Rikkyo University5, Japan Aerospace Exploration Agency6, University of Aizu7, National Institute of Advanced Industrial Science and Technology8, Kobe University9, Meiji University10, Graduate University for Advanced Studies11, Planetary Science Institute12, Auburn University13, Tohoku University14, Brown University15, Kindai University16, Centre national de la recherche scientifique17, University of Arizona18, Johns Hopkins University Applied Physics Laboratory19, German Aerospace Center20, Hokkaido University of Education21, Max Planck Society22, University of Stirling23, Nihon University24, Osaka University25, Hitotsubashi University26, Hiroshima University27, Seoul National University28, Paris Diderot University29
TL;DR: Spectral observations and a principal components analysis suggest that Ryugu originates from the Eulalia or Polana asteroid family in the inner main belt, possibly via more than one generation of parent bodies.
Abstract: Additional co-authors: N Namiki, S Tanaka, Y Iijima, K Yoshioka, M Hayakawa, Y Cho, M Matsuoka, N Hirata, N Hirata, H Miyamoto, D Domingue, M Hirabayashi, T Nakamura, T Hiroi, T Michikami, P Michel, R-L Ballouz, O S Barnouin, C M Ernst, S E Schroder, H Kikuchi, R Hemmi, G Komatsu, T Fukuhara, M Taguchi, T Arai, H Senshu, H Demura, Y Ogawa, Y Shimaki, T Sekiguchi, T G Muller, T Mizuno, H Noda, K Matsumoto, R Yamada, Y Ishihara, H Ikeda, H Araki, K Yamamoto, S Abe, F Yoshida, A Higuchi, S Sasaki, S Oshigami, S Tsuruta, K Asari, S Tazawa, M Shizugami, J Kimura, T Otsubo, H Yabuta, S Hasegawa, M Ishiguro, S Tachibana, E Palmer, R Gaskell, L Le Corre, R Jaumann, K Otto, N Schmitz, P A Abell, M A Barucci, M E Zolensky, F Vilas, F Thuillet, C Sugimoto, N Takaki, Y Suzuki, H Kamiyoshihara, M Okada, K Nagata, M Fujimoto, M Yoshikawa, Y Yamamoto, K Shirai, R Noguchi, N Ogawa, F Terui, S Kikuchi, T Yamaguchi, Y Oki, Y Takao, H Takeuchi, G Ono, Y Mimasu, K Yoshikawa, T Takahashi, Y Takei, A Fujii, C Hirose, S Nakazawa, S Hosoda, O Mori, T Shimada, S Soldini, T Iwata, M Abe, H Yano, R Tsukizaki, M Ozaki, K Nishiyama, T Saiki, S Watanabe, Y Tsuda
325 citations
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University of California, Berkeley1, Goddard Space Flight Center2, Centre national de la recherche scientifique3, Swedish Institute of Space Physics4, National Institute of Aerospace5, Boston University6, Princeton University7, University of Colorado Boulder8, Space Sciences Laboratory9, University of Arizona10, Wright State University11, University of Kansas12, University of Tokyo13, Tohoku University14, University of California, Los Angeles15, Max Planck Society16, University of New Brunswick17, Eastern Michigan University18, University of Michigan19, Planetary Science Institute20, United States Naval Research Laboratory21, Jet Propulsion Laboratory22
TL;DR: In this article, the authors used observations of the Mars upper atmosphere made from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft to determine the loss rates of gas from the upper atmosphere to space for a complete Mars year (16 Nov 2014 − 3 Oct 2016).
227 citations
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TL;DR: In this article, the authors show that the roll-up vortex can be detected even from single-spacecraft measurements and that the velocity of a fraction of low-density, magnetospheric plasmas exceeds that of the magnetosheath flow.
Abstract: [1] Recent numerical simulations suggest that as soon as the Kelvin-Helmholtz instability (KHI) has grown nonlinearly to form a highly rolled-up vortex, plasma mixing is inevitably achieved within the vortex. Identification of rolled-up vortices by in situ measurements is therefore an important task as a step to establish the mechanism by which solar wind plasmas enter the magnetosphere and to understand conditions under which the vortices form. In the present study we show that the rolled-up vortices are detectable even from single-spacecraft measurements. Numerical simulations of the KHI indicate that in the rolled-up vortex the tailward speed of a fraction of low-density, magnetospheric plasmas exceeds that of the magnetosheath flow. This feature appears only after a vortex is rolled up and thus can be used as a marker of roll-up. This signature was indeed found in the Cluster multispacecraft measurements of the rolled-up vortices at the flank magnetopause. By use of this marker, we have searched for events consistent with the roll-up from Geotail observations showing quasi-periodic plasma and field fluctuations in the flank low-latitude boundary layer (LLBL) under northward interplanetary magnetic field (IMF), presumably associated with KH waves. The survey shows that such rolled-up events do occur on both dawn and dusk flanks and are not rare for northward IMF conditions. In addition, in all the rolled-up cases, magnetosheath-like ions are detected on the magnetospheric side of the boundary. These findings indicate that the KHI plays a nonnegligible role in the formation of the flank LLBL under northward IMF.
182 citations
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TL;DR: Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging.
Abstract: The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed and updated. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eotvos experiment, tests of local Lorentz invariance and clock experiments. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and a growing family of other binary pulsar systems is yielding new tests, especially of strong-field effects. Current and future tests of relativity will center on strong gravity and gravitational waves.
3,394 citations
01 Apr 2003
TL;DR: The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it as mentioned in this paper, and also presents new ideas and alternative interpretations which further explain the success of the EnkF.
Abstract: The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.
2,975 citations
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TL;DR: Insights into the underlying structural principles of indigenous microbial phyllosphere populations will help to develop a deeper understanding of the phyllospheric microbiota and will have applications in the promotion of plant growth and plant protection.
Abstract: Our knowledge of the microbiology of the phyllosphere, or the aerial parts of plants, has historically lagged behind our knowledge of the microbiology of the rhizosphere, or the below-ground habitat of plants, particularly with respect to fundamental questions such as which microorganisms are present and what they do there. In recent years, however, this has begun to change. Cultivation-independent studies have revealed that a few bacterial phyla predominate in the phyllosphere of different plants and that plant factors are involved in shaping these phyllosphere communities, which feature specific adaptations and exhibit multipartite relationships both with host plants and among community members. Insights into the underlying structural principles of indigenous microbial phyllosphere populations will help us to develop a deeper understanding of the phyllosphere microbiota and will have applications in the promotion of plant growth and plant protection.
1,450 citations
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TL;DR: Magnetospheric multiscale (MMS) as mentioned in this paper is a NASA four-spacecraft constellation mission to investigate magnetic reconnection in the boundary regions of the Earth's magnetosphere.
Abstract: Magnetospheric Multiscale (MMS), a NASA four-spacecraft constellation mission launched on March 12, 2015, will investigate magnetic reconnection in the boundary regions of the Earth's magnetosphere, particularly along its dayside boundary with the solar wind and the neutral sheet in the magnetic tail. The most important goal of MMS is to conduct a definitive experiment to determine what causes magnetic field lines to reconnect in a collisionless plasma. The significance of the MMS results will extend far beyond the Earth's magnetosphere because reconnection is known to occur in interplanetary space and in the solar corona where it is responsible for solar flares and the disconnection events known as coronal mass ejections. Active research is also being conducted on reconnection in the laboratory and specifically in magnetic-confinement fusion devices in which it is a limiting factor in achieving and maintaining electron temperatures high enough to initiate fusion. Finally, reconnection is proposed as the cause of numerous phenomena throughout the universe such as comet-tail disconnection events, magnetar flares, supernova ejections, and dynamics of neutron-star accretion disks. The MMS mission design is focused on answering specific questions about reconnection at the Earth's magnetosphere. The prime focus of the mission is on determining the kinetic processes occurring in the electron diffusion region that are responsible for reconnection and that determine how it is initiated; but the mission will also place that physics into the context of the broad spectrum of physical processes associated with reconnection. Connections to other disciplines such as solar physics, astrophysics, and laboratory plasma physics are expected to be made through theory and modeling as informed by the MMS results.
1,228 citations