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The large abundance ratio of 44 Ti/ 56 Ni in Cas A is puzzling. In fact, the ratio seems to be larger than the theoretical constraint derived by Woosley & Hoffman (1991). However, this constraint is obtained on the assumption that the explosion is spherically symmetric, whereas Cas A is famous for the asymmetric form of the remnant. Recently, Nagataki et… (More)

- Shin-ichirou Fujimoto, Masa-aki Hashimoto, Kei Kotake, Shoichi Yamada
- 2006

We investigate synthesis of heavy elements in a collapsar. We have calculated detailed composition of magnetically driven jets ejected from a collapsar, which is based on long-term, magneto-hydrodynamic simulations of a rapidly rotating massive star of 40M ⊙ during core collapse. We follow evolution of abundances of about 4000 nuclides from the collapse… (More)

- Shin-ichirou Fujimoto, Kei Kotake, Shoichi Yamada, Masa-aki Hashimoto, Katsuhiko Sato
- 2006

We perform two-dimensional, axisymmetric, magnetohydrodynamic simulations of the collapse of a rotating star of 40 M ⊙ and in the light of the collapsar model of gamma-ray burst. Considering two distributions of angular momentum, up to ∼ 10 17 cm 2 s −1 , and the uniform vertical magnetic field, we investigate the formation of an accretion disk around a… (More)

- Marc Rayet, Masa-aki Hashimoto
- 1999

The s-process is studied in the He burning core of a M α = 8 M He star using temperature and density profiles obtained with a standard stellar evolution model and an updated nuclear network. We discuss in detail the s-process efficiency for metallicities Z/Z ranging between 1 and 10 −3 in the light of recent nuclear data. We show that 16 O acts as a… (More)

- Masa-aki Hashimoto
- Brain and nerve = Shinkei kenkyū no shinpo
- 2008

Outcome of the treatment on hydrocephalus especially in idiopathic normal pressure hydrocephalus (iNPH) shows the better outcome after shunting operation according to the evolution of the shunt system and the better management of shunt complications, and also, comprehension of the pathophysiology of NPH. The history of shunt system is benefit for the… (More)

We investigate the evolution of a universe with a decaying cosmological term (vacuum energy) that is assumed to be a function of the scale factor. In this model, while the cosmological term increases to the early universe, the radiation energy density is lower than the model with the cos-mological "constant". We find that the effects of the decaying… (More)

We investigate the evolution of a universe with a decaying cosmological term (vacuum energy) that is assumed to be a function of the scale factor. In this model, while the cosmological term increases to the early universe, the radiation energy density is lower than the model with the cos-mological "constant". We find that the effects of the decaying… (More)

- Sunao Nishimura, Kei Kotake, +4 authors Katsuhiko Sato
- 2005

We investigate r-process nucleosynthesis during the magnetohydrodynamical (MHD) explosion of supernova in a massive star of 13 M ⊙. Contrary to the case of the spherical explosion, jet-like explosion due to the combined effects of the rotation and magnetic field lowers the electron fraction significantly inside the layers above the iron core. We find that… (More)

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