2,366 research outputs found
Critical Surface for Explosions of Rotational Core-Collapse Supernovae
The effect of rotation on the explosion of core-collapse supernovae is
investigated systematically in three-dimensional simulations. In order to
obtain the critical conditions for explosion as a function of mass accretion
rate, neutrino luminosity, and specific angular momentum, rigidly rotating
matter was injected from the outer boundary with an angular momentum, which is
increased every 500 ms. It is found that there is a critical value of the
specific angular momentum, above which the standing shock wave revives, for a
given combination of mass accretion rate and neutrino luminosity, i.e. an
explosion can occur by rotation even if the neutrino luminosity is lower than
the critical value for a given mass accretion rate in non-rotational models.
The coupling of rotation and hydrodynamical instabilities plays an important
role to characterize the dynamics of shock revival for the range of specific
angular momentum that are supposed to be realistic. Contrary to expectations
from past studies, the most rapidly expanding direction of the shock wave is
not aligned with the rotation axis. Being perpendicular to the rotation axis on
average, it can be oriented in various directions. Its dispersion is small when
the spiral mode of the standing accretion shock instability (SASI) governs the
dynamics, while it is large when neutrino-driven convection is dominant. As a
result of the comparison between 2D and 3D rotational models, it is found that
m=!0 modes of neutrino-driven convection or SASI are important for shock
revival around the critical surface.Comment: First revised version, submitted to ApJ, 14 pages, 13 figures, 2
table
ETS-5, ETS-6, and COMETS projects in Japan
Three satellite communication projects now in progress in Japan are described. The first is a project to establish a telecommunication network for tele-education, TV conference, and tele-medicine in the Asia-Pacific region by using the Japan's Engineering Test Satellite-5 (ETS-5). The second is a project of the ETS-6 satellite, to be launched in 1993, for inter-satellite communication, mobile and fixed communication, and millimeter wave personal communication experiments. The third is a project of the Communications and Broadcasting Engineering Test Satellite (COMETS), to be launched in 1997, for advanced mobile satellite communication, inter-satellite link, and advanced broadcasting experiments at higher frequencies
The importance of Nuclear Weapons Free Zones
Some say that it is nothing but an illusion to think of a world totally without nuclear weapons. This might be true. Nonetheless, although the total abolition of nuclear weapons seems, at present, to be quite difficult, promoting Nuclear Weapons Free Zones (NWFZs) from a regional standpoint might encourage further large-scale non-proliferation processes. NWFZs are important elements to be brought into the debate when dealing with the non-proliferation of nuclear weapons on a global scale. Also for regional security reasons, NWFZs are crucial. In particular, there is a need for an NWFZ in Northeast Asia
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Social cognition-based content instruction for communicative competence in Japanese middle school English
This project demonstrates how English teachers in Japan can conduct purposeful and meaningful lessons for middle school low-intermediate students. The teaching approach used for this project is based on Content-Based Instruction (CBI)
Propagation research in Japan
L-band propagation measurements for land-mobile, maritime, and aeronautical satellite communications have been carried out by using the Japanese Engineering Test Satellite-Five (ETS-5) which was launched in Aug. 1987. This paper presents propagation characteristics for each of the mobile satellite communication channels
Simultaneous Measurement of Torsional Oscillator and NMR of Very Dilute 3He in Solid 4He
We have investigated the NMR properties of dilute 3He impurities in solid 4He
contained in a torsional oscillator (TO) by the simultaneous measurement of the
NMR and the torsional oscillator response of the so-called supersolid 4He. From
measurements on samples with one hundred to a few hundred ppm of 3He, we have
found three different states of 3He. The first is the homogeneously distributed
isolated 3He atom in a solid matrix of 4He. The second is the 3He cluster in a
homogeneous 4He matrix, which appears below the phase separation temperature of
a solid mixture. The third is the 3He cluster in some nonuniform part of a 4He
crystal. We find that 3He atoms contained in the third component remain in a
nearby location even above the phase separation temperature. Based on the fact
that even a ppm of 3He affects the supersolid response in a TO below and above
the phase separation temperature, we propose that the nonuniform part of a
crystal that holds the third type of 3He and thus has a higher local
concentration of 3He plays an important role in the supersolid phenomenon in a
TO.Comment: 5 pages, 5 figures, Accepted for publication in Physical Review
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