2,118 research outputs found
AJAE Appendix: Optimal Investment in Transportation Infrastructure When Middlemen Have Market Power: A Developing-Country Analysis
The material contained herein is supplementary to the article named in the title and published in the American Journal of Agricultural Economics.Public Economics,
Telomeres in ICF syndrome cells are vulnerable to DNA damage due to elevated DNA:RNA hybrids.
DNA:RNA hybrids, nucleic acid structures with diverse physiological functions, can disrupt genome integrity when dysregulated. Human telomeres were shown to form hybrids with the lncRNA TERRA, yet the formation and distribution of these hybrids among telomeres, their regulation and their cellular effects remain elusive. Here we predict and confirm in several human cell types that DNA:RNA hybrids form at many subtelomeric and telomeric regions. We demonstrate that ICF syndrome cells, which exhibit short telomeres and elevated TERRA levels, are enriched for hybrids at telomeric regions throughout the cell cycle. Telomeric hybrids are associated with high levels of DNA damage at chromosome ends in ICF cells, which are significantly reduced with overexpression of RNase H1. Our findings suggest that abnormally high TERRA levels in ICF syndrome lead to accumulation of telomeric hybrids that, in turn, can result in telomeric dysfunction
Fine Structures of Shock of SN 1006 with the Chandra Observation
The north east shell of SN 1006 is the most probable acceleration site of
high energy electrons (up to ~ 100 TeV) with the Fermi acceleration mechanism
at the shock front. We resolved non-thermal filaments from thermal emission in
the shell with the excellent spatial resolution of Chandra. The thermal
component is extended widely over about ~ 100 arcsec (about 1 pc at 1.8 kpc
distance) in width, consistent with the shock width derived from the Sedov
solution. The spectrum is fitted with a thin thermal plasma of kT = 0.24 keV in
non-equilibrium ionization (NEI), typical for a young SNR. The non-thermal
filaments are likely thin sheets with the scale widths of ~ 4 arcsec (0.04 pc)
and ~ 20 arcsec (0.2 pc) at upstream and downstream, respectively. The spectra
of the filaments are fitted with a power-law function of index 2.1--2.3, with
no significant variation from position to position. In a standard diffusive
shock acceleration (DSA) model, the extremely small scale length in upstream
requires the magnetic field nearly perpendicular to the shock normal. The
injection efficiency (eta) from thermal to non-thermal electrons around the
shock front is estimated to be ~ 1e-3 under the assumption that the magnetic
field in upstream is 10 micro G. In the filaments, the energy densities of the
magnetic field and non-thermal electrons are similar to each other, and both
are slightly smaller than that of thermal electrons. in the same order for each
other. These results suggest that the acceleration occur in more compact region
with larger efficiency than previous studies.Comment: 24 pages, 11 figures, Accepted for publication in ApJ, the paper with
full resolution images in
http://www-cr.scphys.kyoto-u.ac.jp/member/bamba/Paper/SN1006.pd
Thermal and Non-thermal X-Rays from the LMC Super Bubble 30 Dor C
We report on the discovery of thermal and non-thermal X-rays from the shells
of the super bubble (SB) 30 Dor C in the Large Magellanic Cloud (LMC). The
X-ray morphology is a nearly circular shell with a radius of about 40 pc, which
is bright on the northern and western sides. The spectra of the shells are
different from region to region. The southern shell shows clear emission lines,
and is well fitted with a model of a thin-thermal plasma (kT = 0.21keV) in
non-equilibrium ionization (NEI) plus a power-law component. This thermal
plasma is located inside of the H alpha emission, which is the outer edge of
the shell of the SB. The northern and western sides of the SB are dim in H
alpha emission, but are bright in non-thermal (power-law) X-rays with a photon
index of 2.1-2.9. The non-thermal X-ray shell traces the outer boundary of the
radio shell. These features of thin-thermal and non-thermal X-rays are similar
to those of SN 1006, a prototype of synchrotron X-ray shell, but the
non-thermal component of 30 Dor C is about ten-times brighter than that of SN
1006. 30 Dor C is the first candidate of an extragalactic SB, in which
energetic electrons are accelerating in the shell. The age is much older than
that of SN 1006, and hence the particle acceleration time in this SB may be
longer than those in normal shell-like SNRs. We found point-like sources
associated with some of tight star clusters. The X-ray luminosity and spectrum
are consistent with those of young clusters of massive stars. Point-like
sources with non-thermal spectra are also found in the SB. These may be
background objects (AGNs) or stellar remnants (neutron stars or black holes).Comment: 11 pages, 6 figures, Accepted for publication in ApJ, the paper with
full resolution images in
http://www-cr.scphys.kyoto-u.ac.jp/member/bamba/Paper/30DorC.pd
Bimetallic Coordination Insertion Polymerization of Unprotected Polar Monomers: Copolymerization of Amino Olefins and Ethylene by Dinickel Bisphenoxyiminato Catalysts
Dinickel bisphenoxyiminato complexes based on highly substituted p- and m-terphenyl backbones were synthesized, and the corresponding atropisomers were isolated. In the presence of a phosphine scavenger, Ni(COD)_2, the phosphine-ligated syn-dinickel complexes copolymerized α-olefins and ethylene in the presence of amines to afford 0.2–1.3% α-olefin incorporation and copolymerized amino olefins and ethylene with a similar range of incorporation (0.1–0.8%). The present rigid catalysts provide a bimetallic strategy for insertion polymerization of polar monomers without masking of the heteroatom group. The effects of the catalyst structure on the reactivity were studied by comparisons of the syn and anti atropisomers and the p- and m-terphenyl systems
Accretion Disk Spectra of the Ultra-luminous X-ray Sources in Nearby Spiral Galaxies and Galactic Superluminal Jet Sources
Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and
Galactic superluminal jet sources share the common spectral characteristic that
they have unusually high disk temperatures which cannot be explained in the
framework of the standard optically thick accretion disk in the Schwarzschild
metric. On the other hand, the standard accretion disk around the Kerr black
hole might explain the observed high disk temperature, as the inner radius of
the Kerr disk gets smaller and the disk temperature can be consequently higher.
However, we point out that the observable Kerr disk spectra becomes
significantly harder than Schwarzschild disk spectra only when the disk is
highly inclined. This is because the emission from the innermost part of the
accretion disk is Doppler-boosted for an edge-on Kerr disk, while hardly seen
for a face-on disk. The Galactic superluminal jet sources are known to be
highly inclined systems, thus their energy spectra may be explained with the
standard Kerr disk with known black hole masses. For ULXs, on the other hand,
the standard Kerr disk model seems implausible, since it is highly unlikely
that their accretion disks are preferentially inclined, and, if edge-on Kerr
disk model is applied, the black hole mass becomes unreasonably large (> 300
M_solar). Instead, the slim disk (advection dominated optically thick disk)
model is likely to explain the observed super-Eddington luminosities, hard
energy spectra, and spectral variations of ULXs. We suggest that ULXs are
accreting black holes with a few tens of solar mass, which is not unexpected
from the standard stellar evolution scenario, and that their X-ray emission is
from the slim disk shining at super-Eddington luminosities.Comment: ApJ, accepte
Chandra Observations of A Galactic Supernova Remnant Vela Jr.: A New Sample of Thin Filaments Emitting Synchrotron X-Rays
A galactic supernova remnant (SNR) Vela Jr. (RX J0852.04622, G266.61.2)
shows sharp filamentary structure on the north-western edge of the remnant in
the hard X-ray band. The filaments are so smooth and located on the most outer
side of the remnant. We measured the averaged scale width of the filaments
( and ) with excellent spatial resolution of {\it Chandra}, which are
in the order of the size of the point spread function of {\it Chandra} on the
upstream side and 49.5 (36.0--88.8) arcsec on the downstream side,
respectively. The spectra of the filaments are very hard and have no line-like
structure, and were well reproduced with an absorbed power-law model with
2.67 (2.55--2.77), or a {\tt SRCUT} model with = 4.3
(3.4--5.3) Hz under the assumption of . These results
imply that the hard X-rays are synchrotron radiation emitted by accelerated
electrons, as mentioned previously. Using a correlation between a function
and the SNR age, we estimated the
distance and the age of Vela Jr.: the estimated distance and age are 0.33
(0.26--0.50) kpc and 660 (420--1400) years, respectively. These results are
consistent with previous reports, implying that --age relation may be
a useful tool to estimate the distance and the age of synchrotron X-ray
emitting SNRs.Comment: 19 pages, 8 figures, ApJ, in pres
- …
