173 research outputs found
MHD Equilibrium and Stability of Spherical Tokamak Plasma with Current Hole
The potential characteristics of spherical tokamak configurations with current hole are investigated from the point of view of magnetohydrodynamic (MHD) equilibrium and stability. The effect of the toroidal shear flows is also considered by using a modified Grad-Shafranov equation. Linear and nonlinear stability for low-n kink modes and intermediate-n ballooning mode is analyzed by means of numerical simulations
X-ray Observation of Mars with Suzaku at Solar Minimun
Mars was observed in X-rays during April 3-5 2008 for 82 ksec with the
Japanese Suzaku observatory. Mars has been known to emit X-rays via the
scattering of solar X-rays and via the charge exchange between neutral atoms in
the exosphere and solar wind ions. Past theoretical studies suggest that the
exospheric neutral density may vary by a factor of up to 10 over the solar
cycle. To investigate a potential change of the exospheric charge exchange
emission, Mars was observed with Suzaku at solar minimum. Significant signals
were not detected at the position of Mars in the energy band of 0.2-5 keV. A 2
sigma upper limit of the O VII line flux in 0.5-0.65 keV was 4.3
ph cm s. Comparing this upper limit to the past Chandra and
XMM-Newton observations conducted near solar maximum, it was found that the
exospheric density at solar minimum does not exceed that near solar maximum by
more than 6-70 times.Comment: 17 pages, 7 figures, accepted for publication in PAS
Dynamics of spherical tokamak plasma on the internal reconnection event
Nonlinear magnetohydrodynamic (MHD) simulations are executed to investigate the dynamical behavior of the relaxation phenomenon observed in spherical tokamak (ST) plasma that is known as the Internal Reconnection Event (IRE). The simulation results successfully reproduce several key features of IRE, and the physical mechanisms are revealed. A sudden collapse of the pressure profile takes place as a result of a nonlinear time development of a pressure-driven instability. A magnetic reconnection induced between the internal and the external magnetic field is found to play a crucial role in determining the nature of the overall process, namely, the rapid expulsion of the plasma heat energy due to the pressure imbalance along the reconnected field lines, and the large distortion in the overall shape. The resultant deformations in overall shape of the plasma are in good agreement with the experimental observations
Dust grain growth and the formation of the extremely primitive star SDSS J102915+172927
Dust grains in low-metallicity star-forming regions may be responsible for
the formation of the first low-mass stars. The minimal conditions to activate
dust-induced fragmentation require the gas to be pre-enriched above a critical
dust-to-gas mass ratio Dcr=[2.6--6.3]x10^-9 with the spread reflecting the
dependence on the grain properties. The recently discovered Galactic halo star
SDSS J102915+172927 has a stellar mass of 0.8 Msun and a metallicity of
Z=4.5x10^-5 Zsun and represents an optimal candidate for the dust-induced
low-mass star formation. Indeed, for the two most plausible Population III
supernova progenitors, with 20 Msun and 35 Msun, the critical dust-to-gas mass
ratio can be overcome provided that at least 0.4 Msun of dust condenses in the
ejecta, allowing for moderate destruction by the reverse shock. Here we show
that even if dust formation in the first supernovae is less efficient or strong
dust destruction does occur, grain growth during the collapse of the parent gas
cloud is sufficiently rapid to activate dust cooling and likely fragmentation
into low-mass and long-lived stars. Silicates and magnetite grains can
experience significant grain growth in the density range 10^9 /cc < nH<10^12
/cc by accreting gas-phase species (SiO, SiO2, and Fe) until their gas-phase
abundance drops to zero, reaching condensation efficiencies =1. The
corresponding increase in the dust-to-gas mass ratio allows dust-induced
cooling and fragmentation to be activated at 10^12 /cc < nH < 10^14 /cc, before
the collapsing cloud becomes optically thick to continuum radiation. We show
that for all the initial conditions that apply to the parent cloud of SDSS
J102915+172927, dust-driven fragmentation is able to account for the formation
of the star.Comment: 8 pages, 4 figures, submitted to MNRA
Enhancement of Terrestrial Diffuse X-ray Emission Associated With Coronal Mass Ejection and Geomagnetic Storm
We present an analysis of a Suzaku observation taken during the geomagnetic
storm of 2005 August 23-24. We found time variation of diffuse soft X-ray
emission when a coronal mass ejection hit Earth and caused a geomagnetic storm.
The diffuse emission consists of fluorescent scattering of solar X-rays and
exospheric solarwind charge exchange. The former is characterized by a neutral
oxygen emission line due to strong heating of the upper atmosphere during the
storm time, while the latter is dominated by a sum of C V, C VI, N VI, N VII, O
VII, and O VIII emission lines due to the enhanced solar wind flux in the
vicinity of the exosphere. Using the solar wind data taken with the ACE and
WIND satellites,a time correlation between the solar wind and the strong O VII
line flux were investigated. We estimated necessary column densities for the
solar X-ray scattering and exospheric SWCX. From these results, we argue that a
part of the solar wind ions enter inside the magnetosphere and cause the SWCX
reaction.Comment: 33 pages, 16 figures, accepted for publication in PAS
The origin of the most iron-poor star
We investigate the origin of carbon-enhanced metal-poor (CEMP) stars starting
from the recently discovered star SMSS J031300 (Keller et al.
2014). We show that the elemental abundances observed on the surface of SMSS
J031300 can be well fit by the yields of faint, metal free, supernovae. Using
properly calibrated faint supernova explosion models, we study, for the first
time, the formation of dust grains in such carbon-rich, iron-poor supernova
ejecta. Calculations are performed assuming both unmixed and uniformly mixed
ejecta and taking into account the partial destruction by the supernova reverse
shock. We find that, due to the paucity of refractory elements beside carbon,
amorphous carbon is the only grain species to form, with carbon condensation
efficiencies that range between (0.15-0.84), resulting in dust yields in the
range (0.025-2.25)M. We follow the collapse and fragmentation of a
star forming cloud enriched by the products of these faint supernova explosions
and we explore the role played by fine structure line cooling and dust cooling.
We show that even if grain growth during the collapse has a minor effect of the
dust-to-gas ratio, due to C depletion into CO molecules at an early stage of
the collapse, the formation of CEMP low-mass stars, such as SMSS J031300, could
be triggered by dust cooling and fragmentation. A comparison between model
predictions and observations of a sample of C-normal and C-rich metal-poor
stars supports the idea that a single common pathway may be responsible for the
formation of the first low-mass stars.Comment: 14 pages, 8 figures, accepted for publication in ApJ. Rephrased
sentence in section 5 to avoid text overlap with arXiv:1307.2239 in their
model descriptio
Determination of the genetic structure of remnant Morus boninensis Koidz. trees to establish a conservation program on the Bonin Islands, Japan
BACKGROUND: Morus boninensis, is an endemic plant of the Bonin (Ogasawara) Islands of Japan and is categorized as "critically endangered" in the Japanese red data book. However, little information is available about its ecological, evolutionary and genetic status, despite the urgent need for guidelines for the conservation of the species. Therefore, we adopted Moritz's MU concept, based on the species' current genetic structure, to define management units and to select mother tree candidates for seed orchards. RESULTS: Nearly all individuals of the species were genotyped on the basis of seven microsatellite markers. Genetic diversity levels in putative natural populations were higher than in putative man-made populations with the exception of those on Otouto-jima Island. This is because a limited number of maternal trees are likely to have been used for seed collection to establish the man-made populations. A model-based clustering analysis clearly distinguished individuals into nine clusters, with a large difference in genetic composition between the population on Otouto-jima Island, the putative natural populations and the putative man-made populations. The Otouto-jima population appeared to be genetically differentiated from the others; a finding that was also supported by pairwise F(ST )and R(ST )analysis. Although multiple clusters were detected in the putative man-made populations, the pattern of genetic diversity was monotonous in comparison to the natural populations. CONCLUSION: The genotyping by microsatellite markers revealed strong genetic structures. Typically, artificial propagation of this species has ignored the genetic structure, relying only on seeds from Otouto-jima for replanting on other islands, because of a problem with inter-specific hybridization on Chichi-jima and Haha-jima Islands. However, this study demonstrates that we should be taking into consideration the genetic structure of the species when designing a propagation program for the conservation of this species
Mechanisms for eukaryotic response and adaptation to hypoxia
科学研究費助成事業(科学研究費補助金)研究成果報告書:基盤研究(B)2009-2011課題番号:2138005
Effects of the anti-RANKL antibody denosumab on joint structural damage in patients with rheumatoid arthritis treated with conventional synthetic disease-modifying antirheumatic drugs (DESIRABLE study): a randomised, double-blind, placebo-controlled phase 3 trial.
ObjectiveTo evaluate the efficacy of denosumab in suppressing joint destruction when added to conventional synthetic disease-modifying antirheumatic drug (csDMARD) therapy in patients with rheumatoid arthritis (RA).MethodsThis was a multi-centre, randomised, double-blind, parallel-group, placebo-controlled phase 3 study in Japan. Patients with RA aged ≥20 years receiving csDMARDs were randomly assigned (1:1:1) to denosumab 60 mg every 3 months (Q3M), denosumab 60 mg every 6 months (Q6M) or placebo. The change in the modified total Sharp score (mTSS) and effect on bone mineral density (BMD) at 12 months was evaluated.ResultsIn total, 654 patients received the trial drugs. Denosumab groups showed significantly less progression of joint destruction. The mean changes in the mTSS at 12 months were 1.49 (95% CI 0.99 to 1.99) in the placebo group, 0.99 (95% CI 0.49 to 1.49) in the Q6M group (p=0.0235) and 0.72 (95% CI 0.41 to 1.03) in the Q3M group (p=0.0055). The mean changes in bone erosion score were 0.98 (95% CI 0.65 to 1.31) in the placebo group, 0.51 (95% CI 0.22 to 0.80) in the Q6M group (p=0.0104) and 0.22 (95% CI 0.09 to 0.34) in the Q3M group (p=0.0001). No significant between-group difference was observed in the joint space narrowing score. The per cent change in lumbar spine (L1-L4) BMD in the placebo, Q6M and Q3M groups were -1.03%, 3.99% (p<0.0001) and 4.88% (p<0.0001). No major differences were observed among safety profiles.ConclusionsDenosumab inhibits the progression of joint destruction, increases BMD and is well tolerated in patients with RA taking csDMARD
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