653 research outputs found
Gravitational Wave Background from Population III Stars
We estimate the gravitational wave (GW) background from Population III (Pop
III) stars using the results from our hydrodynamic simulations (Suwa et al.
2007). We calculate gravitational waveforms from matter motions and anisotropic
neutrino emissions for single Pop III stars. We find that the GW amplitudes
from matter motions are dominant until just after bounce, but those from
neutrinos dominate later on at frequencies below Hz in the GW
spectrum. Computing the overall signal produced by the ensemble of such Pop III
stars, we find that the resultant density parameter of the GW background peaks
at the amplitude of in the frequency interval
Hz. We show that such signals, depending on the formation rate of
Pop III stars, can be within the detection limits of future planned
interferometers such as DECIGO and BBO in the frequency interval of Hz. Our results suggest that the detection of the GW background from Pop
III stars can be an important tool to supply the information about the star
formation history in the early universe.Comment: 4 pages, 3 figures, accepted for publication in ApJ
Explosion geometry of a rotating 13 star driven by the SASI-aided neutrino-heating supernova mechanism
By performing axisymmetric hydrodynamic simulations of core-collapse
supernovae with spectral neutrino transport based on the isotropic diffusion
source approximation scheme, we support the assumption that the
neutrino-heating mechanism aided by the standing accretion shock instability
and convection can initiate an explosion of a 13 star. Our results
show that bipolar explosions are more likely to be associated with models which
include rotation. We point out that models, which form a north-south symmetric
bipolar explosion, can lead to larger explosion energies than for the
corresponding unipolar explosions.Comment: 5 pages, 4 figures; accepted for publication in PASJ Letter
Magneto-driven Shock Waves in Core-Collapse Supernova
We perform a series of two-dimensional magnetohydrodynamic simulations of the
rotational core-collapse of a magnetized massive star. We employ a realistic
equation of state and take into account the neutrino cooling by the so-called
leakage scheme. In this study we systematically investigate how the strong
magnetic field and the rapid rotation affect the propagation of the shock
waves. Our results show that in the case of the strong initial poloidal
magnetic field, the toroidal magnetic field amplified by the differential
rotation, becomes strong enough to generate a tightly collimated shock wave
along the rotational axis. On the other hand, in the case of the weak initial
magnetic field, although the differential rotation amplifies toroidal magnetic
field over the long rotational period, the launched shock wave is weak and the
shape of it becomes wider. The former case is expected to be accompanied by the
formation of the so-called magnetar. Our models with rapid rotation and strong
magnetic field can create a nozzle formed by the collimated shock wave. This
might be the analogous situation of the collapsar that is plausible for the
central engine of the Gamma-Ray Bursts.Comment: 21 pages, 6 figures, Accepted to ApJ. A paper with high-resolution
figures available at
"http://www-utap.phys.s.u-tokyo.ac.jp/~takiwaki/res/index-j.html
Molecular characterization of O-methyltransferases involved in isoquinoline alkaloid biosynthesis in Coptis japonica
O-Methyltransferases, which catalyze the production of small molecules in plants, play a crucial role in determining biosynthetic pathways in secondary metabolism because of their strict substrate specificity. Using three O-methyltransferase (OMT) cDNAs that are involved in berberine biosynthesis, we investigated the structure that was essential for this substrate specificity and the possibility of creating a chimeric enzyme with novel substrate specificity. Since each OMT has a relatively well-conserved C-terminal putative S-adenosyl-L-methionine-binding domain, we first exchanged the N-terminal halves of different OMTs. Among the 6 combinations that we tested for creating chimeric OMTs, 5 constructs produced detectable amounts of recombinant proteins, and only one of these with an N-terminal half of 6-OMT and a C-terminal half of 4′-OMT (64′-OMT) showed methylation activity with isoquinoline alkaloids as a substrate. Further enzymological analysis of 64′-OMT reaction product indicated that 64′-OMT retained the regio-specificity of 6-OMT. Further examination of the N-terminal region of 64′-OMT showed that about 90 amino acid residues in the N-terminal half were critical for reaction specificity. The creation of OMTs with novel reactivity is discussed
Post-event Processing Predicts Cortisol Recovery
There is growing evidence that individuals with social anxiety show impaired cortisol recovery after experiencing social evaluative stressors. Yet, little is known regarding the cognitive processes underlying such impaired cortisol recovery. The present study examined the effect of post-event processing (PEP), referred to as repetitive thinking about social situations, on cortisol recovery following a social stressor. Forty-two non-clinical university students (23 women, 19 men, mean age = 22.0 ± 2.0 years) completed the Trier Social Stress Test (TSST), followed by a thought sampling procedure which assessed the frequency of PEP reflecting the TSST. A growth curve model showed PEP and social anxiety interactively predicted cortisol recovery. In particular, PEP predicted impaired cortisol recovery in those with low levels of social anxiety but not in those with high levels of social anxiety, which contradicted the initial hypothesis. These findings suggest that PEP is differentially associated with cortisol recovery depending on levels of social anxiety. The possible mechanisms underlying these findings were discussed in terms of protective inhibition framework
Distance to G14.33-0.64 in the Sagittarius Spiral Arm: H2O Maser Trigonometric Parallax with VERA
We report on trigonometric parallax measurements for the Galactic star
forming region G14.33-0.64 toward the Sagittarius spiral arm. We conducted
multi-epoch phase-referencing observations of an H2O maser source in
G14.33-0.64 with the Japanese VLBI array VERA. We successfully detected a
parallax of 0.893+/-0.101 mas, corresponding to a source distance of
1.12+/-0.13 kpc, which is less than half of the kinematic distance for
G14.33-0.64. Our new distance measurement demonstrates that the Sagittarius arm
lies at a closer distance of ~1 kpc, instead of previously assumed ~2-3 kpc
from kinematic distances. The previously suggested deviation of the Sagittarius
arm toward the Galactic center from the symmetrically fitted model (Taylor &
Cordes 1993) is likely due to large errors of kinematic distances at low
galactic longitudes. G14.33-0.64 most likely traces the near side of the
Sagittarius arm. We attempted fitting the pitch angle of the arm with other
parallax measurements along the arm, which yielded two possible pitch angles of
i=34.7+/-2.7 degrees and i=11.2+/-10.5 degrees. Our proper motion measurements
suggest G14.33-0.64 has no significant peculiar motion relative to the
differential rotation of the Galaxy (assumed to be in a circular orbit),
indicating that the source motion is in good agreement with the Galactic
rotation.Comment: 14 pages, 7 figures, to appear in PASJ Vol. 62, No.
Contribution of Majoron to Hubble tension in gauged U(1) Model
In this paper, we analyze parameter regions that can alleviate the Hubble
tension in the U(1) model with the broken lepton number
U(1) symmetry. As new particles, this model has a U(1)
gauge boson and a Majoron , which can affect the early universe and
the effective number of neutrino species . If and
simultaneously exist in the early universe, - interaction
processes such as occur. The
comparison of between the cases with and without the
- interaction processes shows that these processes make a small
contribution of to , and it does not need
to be considered for the alleviation of the Hubble tension. Based on these
facts, we calculated for various Majoron parameters without the
- interaction processes to search parameters that could alleviate
the Hubble tension. As a result, we found that the U(1)
gauge boson and Majoron can alleviate the Hubble tension in some parameter
regions, and there is a non-trivial synergy contribution between and
. Moreover, the parameter region with a lighter mass
MeV and a larger coupling is excluded because it
predicts too large , i.e. . The favored
and restricted regions of the Majoron parameters depend on the parameters
because of the presence of the contribution and synergy one.Comment: 24 pages, 4 figure
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