129 research outputs found
Scalar perturbations in braneworld cosmology
We study the behaviour of scalar perturbations in the radiation-dominated era
of Randall-Sundrum braneworld cosmology by numerically solving the coupled bulk
and brane master wave equations. We find that density perturbations with
wavelengths less than a critical value (set by the bulk curvature length) are
amplified during horizon re-entry. This means that the radiation era matter
power spectrum will be at least an order of magnitude larger than the
predictions of general relativity (GR) on small scales. Conversely, we
explicitly confirm from simulations that the spectrum is identical to GR on
large scales. Although this magnification is not relevant for the cosmic
microwave background or measurements of large scale structure, it will have
some bearing on the formation of primordial black holes in Randall-Sundrum
models.Comment: 17 pages, 7 figure
Local Probe Isomerization in a One-Dimensional Molecular Array
Synthesis of one-dimensional molecular arrays with tailored stereoisomers is
challenging yet has a great potential for application in molecular opto-,
electronic- and magnetic-devices, where the local array structure plays a
decisive role in the functional properties. Here, we demonstrate construction
and characterization of dehydroazulene isomer and diradical units in
three-dimensional organometallic compounds on Ag(111) with a combination of
low-temperature scanning tunneling microscopy and density functional theory
calculations. Tip-induced voltage pulses firstly result in the formation of a
diradical species via successive homolytic fission of two C-Br bonds in the
naphthyl groups, which are subsequently transformed into chiral dehydroazulene
moieties. The delicate balance of the reaction rates among the diradical and
two stereoisomers, arising from an in-line configuration of tip and molecular
unit, allows directional azulene-to-azulene and azulene-to-diradical local
probe isomerization in a controlled manner. Furthermore, we found that the
diradical moiety hosts an open-shell singlet with antiferromagnetic coupling
between the unpaired electrons, which can undergo an inelastic spin transition
of 91 meV to the ferromagnetically coupled triplet state
The Subaru Deep Field Project: Lyman Emitters at Redshift of 6.6
We present new results of a deep optical imaging survey using a narrowband
filter () centered at 9196 \AA ~ together with , ,
, , and broadband filters in the sky area of the Subaru
Deep Field which has been promoted as one of legacy programs of the 8.2m Subaru
Telescope. We obtained a photometric sample of 58 Ly emitter candidates
at 6.5 -- 6.6 among strong -excess () objects together with a color criterion of . We then obtained optical spectra of 20 objects in our -excess
sample and identified at least nine Ly emitters at -- 6.6
including the two emitters reported by Kodaira et al. (2003). Since our
Ly emitter candidates are free from strong amplification of
gravitational lensing, we are able to discuss their observational properties
from a statistical point of view. Based on these new results, we obtain a lower
limit of the star formation rate density of yr Mpc at , being
consistent with our previous estimate. We discuss the nature of star-formation
activity in galaxies beyond .Comment: 49 pages, 16 figures, PASJ, Vol. 57, No. 1, in pres
ALS mutations in the TIA-1 prion-like domain trigger highly condensed pathogenic structures
筋萎縮性側索硬化症(ALS)の発症機構の一端を解明 --タンパク質の高密度な凝縮構造が鍵--. 京都大学プレスリリース. 2022-09-13.T cell intracellular antigen-1 (TIA-1) plays a central role in stress granule (SG) formation by self-assembly via the prion-like domain (PLD). In the TIA-1 PLD, amino acid mutations associated with neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS) or Welander distal myopathy (WDM), have been identified. However, how these mutations affect PLD self-assembly properties has remained elusive. In this study, we uncovered the implicit pathogenic structures caused by the mutations. NMR analysis indicated that the dynamic structures of the PLD are synergistically determined by the physicochemical properties of amino acids in units of five residues. Molecular dynamics simulations and three-dimensional electron crystallography, together with biochemical assays, revealed that the WDM mutation E384K attenuated the sticky properties, whereas the ALS mutations P362L and A381T enhanced the self-assembly by inducing β-sheet interactions and highly condensed assembly, respectively. These results suggest that the P362L and A381T mutations increase the likelihood of irreversible amyloid fibrillization after phase-separated droplet formation, and this process may lead to pathogenicity
Holographic Formulation of Quantum Supergravity
We show that supergravity with a cosmological constant can be
expressed as constrained topological field theory based on the supergroup
. The theory is then extended to include timelike boundaries with
finite spatial area. Consistent boundary conditions are found which induce a
boundary theory based on a supersymmetric Chern-Simons theory. The boundary
state space is constructed from states of the boundary supersymmetric
Chern-Simons theory on the punctured two sphere and naturally satisfies the
Bekenstein bound, where area is measured by the area operator of quantum
supergravity.Comment: 30 pages, no figur
Self Excitation of the Tunneling Scalar Field in False Vacuum Decay
A method to determine the quantum state of a scalar field after
-symmetric bubble nucleation has been developed recently. The method has
an advantage that it concisely gives us a clear picture of the resultant
quantum state. In particular, one may interpret the excitations as a particle
creation phenomenon just as in the case of particle creation in curved
spacetime. As an application, we investigate in detail the spectrum of quantum
excitations of the tunneling field when it undergoes false vacuum decay. We
consider a tunneling potential which is piece-wise quadratic, hence is simple
enough to allow us an analytical treatment. We find a strong dependence of the
excitation spectrum upon the shape of the potential on the true vacuum side. We
then discuss features of the excitation spectrum common to general tunneling
potentials not restricted to our simple model.Comment: 24 pages, uuencoded compressed postscript fil
Environmental Effects on Evolution of Cluster Galaxies in a LCDM Universe
We investigate environmental effects on evolution of bright cluster galaxies
in a dominated cold dark matter universe using a combination of
dissipationless N-body simulations and a semi-analytic galaxy formation model.
The N-body simulations enable us to calculate orbits of galaxies in simulated
clusters. Therefore we can incorporate stripping of cold gas from galactic
disks by ram pressure from intracluster medium into our model. In this paper we
study how ram pressure stripping (RPS) and small starburst induced by a minor
merger affect colors, star formation rates, and morphologies of cluster
galaxies. We find that the RPS is not important for colors and SFRs of galaxies
in the cluster core if star formation time-scale is properly chosen, because
the star formation is sufficiently suppressed by consumption of the cold gas in
the disks. Then observed color and SFR gradients can be reproduced without the
RPS. The small starburst triggered by a minor merger hardly affects the SFRs
and colors of the galaxies as well. We also examine whether these two processes
can resolve the known problem that the major merger-driven bulge formation
scenario predict too few galaxies of intermediate bulge-to-total luminosity
ratio (B/T) in clusters. When the minor burst is taken into account, the
intermediate B/T population is increased and the observed morphology gradients
in clusters are successfully reproduced. When the minor burst is considered,
the RPS also plays an important role in formation of the intermediate B/T
galaxies. We present redshift evolution of morphological fractions predicted by
our models. The predicted number ratios of the intermediate B/T galaxies to the
bulge-dominated galaxies show nearly flat or slightly increasing trends with
increasing redshift.Comment: 12 pages, 9 figures, accepted for publication in ApJ (v587 n2 April
20, 2003
Spectral evolution of GRB 060904A observed with Swift and Suzaku -- Possibility of Inefficient Electron Acceleration
We observed an X-ray afterglow of GRB 060904A with the Swift and Suzaku
satellites. We found rapid spectral softening during both the prompt tail phase
and the decline phase of an X-ray flare in the BAT and XRT data. The observed
spectra were fit by power-law photon indices which rapidly changed from to within a few hundred
seconds in the prompt tail. This is one of the steepest X-ray spectra ever
observed, making it quite difficult to explain by simple electron acceleration
and synchrotron radiation. Then, we applied an alternative spectral fitting
using a broken power-law with exponential cutoff (BPEC) model. It is valid to
consider the situation that the cutoff energy is equivalent to the synchrotron
frequency of the maximum energy electrons in their energy distribution. Since
the spectral cutoff appears in the soft X-ray band, we conclude the electron
acceleration has been inefficient in the internal shocks of GRB 060904A. These
cutoff spectra suddenly disappeared at the transition time from the prompt tail
phase to the shallow decay one. After that, typical afterglow spectra with the
photon indices of 2.0 are continuously and preciously monitored by both XRT and
Suzaku/XIS up to 1 day since the burst trigger time. We could successfully
trace the temporal history of two characteristic break energies (peak energy
and cutoff energy) and they show the time dependence of while the following afterglow spectra are quite stable. This fact
indicates that the emitting material of prompt tail is due to completely
different dynamics from the shallow decay component. Therefore we conclude the
emission sites of two distinct phenomena obviously differ from each other.Comment: 19 pages, 9 figures, accepted for publication in PASJ (Suzaku 2nd
Special Issue
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