Phys. Rev. D 98, 083018 (2018) May 2018 [Refereed]

Macroscopic evolution of relativistic charged matter with chirality imbalance
is described by the chiral magnetohydrodynamics (chiral MHD). One such
astrophysical system is high-density lepton matter in core-collapse supernovae
where the chirality...

Bushby, P. J.; Käpylä, P. J.; Masada, Y.; Brandenburg, A.; Favier, B.; Guervilly, C.; Käpylä, M. J.

Astronomy & Astrophysics 612(A97) 16 May 2018 [Refereed]

Context. Convectively driven flows play a crucial role in the dynamo processes that are responsible for producing magnetic activity in stars and planets. It is still not fully understood why many astrophysical magnetic fields have a significant la...

Katsukawa, Y.; Masada, Y.; Shimizu, T.; Sakai, S.; Ichimoto, K.

Proceedings of the SPIE, Volume 10565, id. 1056528 6 pp. (2017). Nov 2017

It is essential to achieve fine pointing stability in a space mission aiming for high resolutional observations. In a future Japanese solar mission SOLAR-C, which is a successor of the HINODE (SOLAR-B) mission, we set targets of angular resolution...

We report the first successful simulation of spontaneous formation of surface
magnetic structures from a large-scale dynamo by strongly-stratified thermal
convection in Cartesian geometry. The large-scale dynamo observed in our
strongly-stratified...

The Astrophysical Journal, Volume 806, Issue 1, article id. 10, 16 pp. Apr 2015 [Refereed]

Effects of magnetic field on stellar differential rotation are studied by
comparing magnetohydrodynamic (MHD) models and their hydrodynamic (HD)
counterparts in the broad range of rotation rate and in varying initial
rotation profile. Fully-compre...

The Astrophysical Journal Letters, Volume 798, Issue 1, article id. L22, 7 pp. Nov 2014 [Refereed]

Magnetorotational instability (MRI) in a convectively-stable layer around the
neutrinosphere is simulated by a three-dimensional model of supernova core. To
resolve MRI-unstable modes, a thin layer approximation considering only the
radial global ...

The mechanism of large-scale dynamos in rigidly rotating stratified
convection is explored by direct numerical simulations (DNS) in Cartesian
geometry. A mean-field dynamo model is also constructed using turbulent
velocity profiles consistently ex...

Publications of the Astronomical Society of Japan, Volume 66, Issue SP1, id.S27 pp. Mar 2014 [Refereed]

Convective dynamo simulations are performed in local Cartesian geometry. We
report the first successful simulation of a large-scale oscillatory dynamo in
rigidly rotating convection without stably stratified layers. A key requirement
for exciting ...

Plasma and Fusion Research 8(1201135) Sep 2013 [Refereed]

A high-speed rendering method for three-dimensional animated volume rendering in a CAVE visualization environment is developed. The proposed method accelerates the standard three-dimensional texture-slicing approach to volume rendering by making u...

The Astrophysical Journal Letters, 772, L1 Jun 2013 [Refereed]

We study the stability of a non-rotating single-component jet using
two-dimensional special relativistic hydrodynamic simulations. By assuming
translational invariance along the jet axis, we exclude the destabilization
effect by Kelvin-Helmholtz m...

The Astrophysical Journal, Volume 778, Issue 1, article id. 11, 14 pp. Apr 2013 [Refereed]

Spherical solar dynamo simulations are performed. Self-consistent, fully
compressible magnetohydrodynamic system with a stably stratified layer below
the convective envelope is numerically solved with a newly developed simulation
code based on the...

Journal of Physics, Volume 454, Issue 1, article id. 012077 Jan 2013 [Refereed]

We developed an application launcher called Multiverse for scientific
visualizations in a CAVE-type virtual reality (VR) system. Multiverse can be
regarded as a type of three-dimensional (3D) desktop environment. In
Multiverse, a user in a CAVE ro...

The Astrophysical Journal, Volume 759, Issue 2, article id. 110, 11 pp. (2012) 759(2) Nov 2012 [Refereed]

Bearing in mind the application of core-collapse supernovae, we study the nonlinear properties of the magnetorotational instability (MRI) by means of three-dimensional simulations in the framework of a local shearing box approximation. By systemat...

The effect of rarefaction acceleration on the propagation dynamics and
structure of relativistically hot jets is studied through relativistic
hydrodynamic simulations. We emphasize the nonlinear interaction of rarefaction
waves excited at the inte...

Advances in Astronomy, Vol.2012, id. 428757 Apr 2012 [Refereed]

Core-collapse supernovae are dramatic explosions marking the catastrophic end
of massive stars. The only means to get direct information about the supernova
engine is from observations of neutrinos emitted by the forming neutron star,
and through ...

Transaction of the Japan Society for Simulation Technology,Vol.4, No4, pp190-193 2012 [Refereed]

To analyze large scale 3-dimensional data, the modern virtual reality (VR) technology will play important roles in future simulation studies. Various VR visualization programs have been developed to date, including our original VR visualization so...

Hiroyuki R. Takahashi, Takahiro Kudoh, Youhei Masada, Jin Matsumoto

The Astrophysical Journal Letters,Vol.739, article id. L53, 5pp. Aug 2011 [Refereed]

Relativistic Sweet-Parker type magnetic reconnection is investigated by
relativistic resistive magnetohydrodynamic (RRMHD) simulations. As an initial
setting, we assume anti-parallel magnetic fields and a spatially uniform
resistivity. A perturbat...

Jin Matsumoto, Youhei Masada, Eiji Asano, Kazunari Shibata

The Astrophysical Journal, Vol. 733, article id. 18, 15pp Mar 2011 [Refereed]

The nonlinear dynamics of outflows driven by magnetic explosion on the
surface of a compact star is investigated through special relativistic
magnetohydrodynamic simulations. We adopt, as the initial equilibrium state, a
spherical stellar object e...

The Astrophysical Journal, Vol. 727, article id. 106, 9pp Nov 2010 [Refereed]

Based on the characteristics of the magnetorotational instability (MRI) and
the MRI-driven turbulence, we construct a steady model for a geometrically thin
disk using "non-standard" -prescription. The efficiency of the angular
momentum tra...

Monthly Notices of the Royal Astronomical Society: Letters (MNRAS Letters) 411 L26-L30 Nov 2010 [Refereed]

The possible role of magneto-rotational instability (MRI) and its driven MHD
turbulence in the solar interior is studied on the basis of the linear and
nonlinear theories coupling with physical parameters, providing solar rotation
profile inverted...

Revista Mexicana de Astronomia y Astrofísica, Vol. 36, pp. 163-170 (2009) Aug 2009 [Invited]

In ultra dense and hot regions realized in stellar core-collapse, neutrinos take a major role in the energy and momentum transports. We investigate the growth of the magnetorotational instability (MRI) in neutrino viscous media by using linear and...

Axisymmetric magnetorotational instability (MRI) in viscous accretion disks
is investigated by linear analysis and two-dimensional nonlinear simulations.
The linear growth of the viscous MRI is characterized by the Reynolds number
defined as $R_{\...

Publications of the Astronomical Society of Japan (62) 1093-1102 Mar 2008 [Refereed]

We present a theoretical model describing magnetar giant flares on the basis
of solar flare/coronal mass ejection theory. In our model, a preflare activity
plays a crucial role in driving evaporating flows and supplying baryonic
matters into the m...

The central engine of gamma-ray bursts (GRBs) is believed to be a hot and
dense disk with hyperaccretion onto a few solar-mass black hole. We investigate
where the magnetorotational instability (MRI) actively operates in the
hyperaccretion disk, w...

Neutrino radiation takes a major role in the momentum, heat, and lepton
transports in proto-neutron stars (PNSs). These diffusive processes affect the
growth of magnetorotational instability (MRI) in PNSs. We perform a local
linear analysis for th...

We investigate the stability of differentially rotating proto-neutron stars
(PNSs) with a toroidal magnetic field. Stability criteria for nonaxisymmetric
MHD instabilities are derived using a local linear analysis. PNSs are expected
to have much s...

Numerical Modeling of Solar and Stellar Dynamos - Current Status and Future Perspectives -[Invited]

Youhei MASADA

1st Asia-Pacific Conference on Plasma Physics Sep 2017

Spontaneous Formation of Surface Magnetic Structure from Dynamo-maintained Magnetic Flux: The Impact of Strong Stratification[Invited]

Youhei MASADA

COSPAR 2016 (The 41th COSPAR Scientific Assembly : Solar and Stellar Dynamos and Magnetic Flux Emergence, COSPAR 2016 (The 41th COSPAR Scientific Assembly) Jun 2016

Organization of Coherent Magnetic Fields in Turbulent Thermal Convection[Invited]

Youhei MASADA

NASA LWS Workshop on Solar Dynamo Frontiers: Helioseismology, 3D Modeling, and Data Assimilation Jun 2015