Supernova remnant (SNR) shock waves are the main place where interstellar dust grains are destroyed. However, the dust destruction efficiency in nonradiative shocks is still not well known. One way ...to estimate the fraction of dust destroyed is to compare the difference between postshock gas abundances and preshock medium total abundances when the preshock elemental depletion factors are known. We compare the postshock gas abundances of 16 SNRs in the Large Magellanic Cloud (LMC) with the LMC interstellar medium abundances that we derived based on 69 slow-rotating early B-type stars. We find that, on average, ∼61% of Si-rich dust grains are destroyed in the shock, while the fraction of dust destroyed is only ∼40% for Fe-rich dust grains. This result supports the idea that the high depletion of Fe in the diffuse neutral medium is not caused by the resilience of Fe-rich grains but because of faster growth rate. This work also presents a potential way to constrain the chemical composition of interstellar dust.
We carry out a project to independently measure the distances of supernova remnants (SNRs) in the first quadrant of the Galaxy. In this project, red clump (RC) stars are used as standard candles and ...extinction probes to build the optical extinction (AV)-distance(D) relation in each direction of extinction-known SNRs. The distances of 15 SNRs are determined. Among them, the distances of G65.8-0.5, G66.0-0.0, and G67.6+0.9 are given for the first time. We also obtain 32 upper/lower limits of distances, and the distances to G5.7-0.1, G15.1-1.6, G28.8+1.5, and G78.2+2.1 are constrained. Most of the distances measured by the RC method are consistent with previous results. The RC method provides independent access to the distances of SNRs.
Accurate SHAPE-directed RNA structure determination Deigan, Katherine E; Li, Tian W; Mathews, David H ...
Proceedings of the National Academy of Sciences - PNAS,
01/2009, Volume:
106, Issue:
1
Journal Article
Peer reviewed
Open access
Almost all RNAs can fold to form extensive base-paired secondary structures. Many of these structures then modulate numerous fundamental elements of gene expression. Deducing these structure-function ...relationships requires that it be possible to predict RNA secondary structures accurately. However, RNA secondary structure prediction for large RNAs, such that a single predicted structure for a single sequence reliably represents the correct structure, has remained an unsolved problem. Here, we demonstrate that quantitative, nucleotide-resolution information from a SHAPE experiment can be interpreted as a pseudo-free energy change term and used to determine RNA secondary structure with high accuracy. Free energy minimization, by using SHAPE pseudo-free energies, in conjunction with nearest neighbor parameters, predicts the secondary structure of deproteinized Escherichia coli 16S rRNA (>1,300 nt) and a set of smaller RNAs (75-155 nt) with accuracies of up to 96-100%, which are comparable to the best accuracies achievable by comparative sequence analysis.
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Three supernova remnants (SNRs) form the CTB 37 complex: CTB 37A (G348.5+0.1, associated with the TeV γ-ray source HESS J1714−385), CTB 37B (G348.7+0.3, associated with HESS J1713−381 and the ...magnetar CXOU J171405.7.381031) and G348.5−0.0. We use 21-cm H i absorption measurements to constrain kinematic distances to these SNRs, which have not previously been determined well. We revise the kinematic distance for CTB 37A to be in the range 6.3-9.5 kpc (previously ∼11.3 kpc) because it is beyond the near 3-kpc arm and in front of the far side of the CO cloud at −145 km s−1 towards l= 348.5. G348.5−0.0 has an H i column density (
∼6.1×1021 cm−2) lower than CTB 37A (∼7.1 × 1021 cm−2). Also, G348.5−0.0 does not have the major absorption feature at −107 km s−1 that CTB 37A shows. This is caused by the near 3-kpc arm, so G348.5−0.0 is at a distance of ≤6.3 kpc. CTB 37B is at a distance of ∼13.2 kpc (previously 5-9 kpc) based on: (1) it has an absorption feature at −10 ± 5 km s−1 from the far 3-kpc arm, so CTB 37B is behind it; (2) there is absorption at −30 km s−1 but not at −26 km s−1, which yields the distance value; and (3) the H i column density towards CTB 37B (∼8.3 × 1021 cm−2) is larger than that towards CTB 37A. In summary, CTB 37A, CTB 37B and G348.5+0.0 are all at different distances and are only by chance nearby each other on the sky. In addition, we conclude that CTB 37A and 37B are not associated with the historical supernova AD 393.
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The supernova remnant (SNR) Kes 75/PSR J1846-0258 association can be regarded as a certainty due to the accurate location of young PSR J1846-0258 at the center of Kes 75 and the detected bright ...radio/X-ray synchrotron nebula surrounding the pulsar. We provide a new distance estimate to the SNR/pulsar system by analyzing the HI and 13CO maps, the HI emission and absorption spectra, and the 13CO emission spectrum of Kes 75. That there are no absorption features at negative velocities strongly argues against the widely-used large distance of 19 to 21 kpc for Kes 75, and shows that Kes 75 is within the Solar circle, i.e. a distance d < 13.2 kpc. Kes 75 is likely at a distance of 5.1 to 7.5 kpc because the highest HI absorption velocity is at 95 km s-1, and no absorption is associated with a nearby HI emission peak at 102 km s-1 in the direction of Kes 75. This distance to Kes 75 gives a reasonable luminosity of PSR J1846-0258 and its PWN and also leads to a much smaller radius for Kes 75, so the age of the SNR is consistent with the spin-down age of PSR J1846-0258, confirming this pulsar as the second-youngest in the Galaxy.
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Ring laser gyroscope technique directly senses the Earth’s instantaneous rotation pole (IRP), whose polar motion contains strong retrograde diurnal components induced by external torques due to the ...gravitational attraction of the Moon and Sun. The first direct measurement of this retrograde diurnal motion with three large ring lasers was reported by Schreiber et al. (J Geophys Res 109(B18):B06405,
2004
). Since then many technical improvements led to a significant increase in precision and stability of ring laser gyroscopes; however, precise determination of amplitude and phase at main partial waves has not been given in the literature. In this paper, I will report on determination of the retrograde diurnal motion of the IRP at main partial waves (
O
o
1
,
J
1
,
K
1
,
M
1
,
O
1
,
Q
1
) by the ring laser “G”, located in Wettzell, Germany, which is the most stable one amongst the currently running large ring laser gyroscopes.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this study, we analyze the Aura Microwave Limb Sounder
water vapor data in the tropical upper troposphere and the lower and middle
stratosphere (UTLMS) (from 215 to 6 hPa) for the period from ...August 2004
to September 2017 using time-lag regression analysis and composite analysis
to explore the interannual variations of tropical UTLMS water vapor and
their connections to El Niño–Southern Oscillation (ENSO) and quasi-biennial
oscillation (QBO). Our analysis shows that the interannual tropical UTLMS
water vapor anomalies are strongly related to ENSO and QBO which together
can explain more than half (∼ 50 %–60 %) but not all variance
of the interannual tropical water vapor anomalies. We find that ENSO's
impact is strong in the upper troposphere (∼ 215–∼ 120 hPa) and near the tropopause (∼ 110–∼ 90 hPa), with a ∼ 3-month lag but weak in the
lower and middle stratosphere (∼ 80 to ∼ 6 hPa).
In contrast, QBO's role is large in the lower and middle stratosphere, with
an upward-propagating signal starting at the tropopause (100 hPa) with a
∼ 2-month lag, peaking in the middle stratosphere near 15 hPa
with a ∼ 21-month lag. The phase lag is based on the 50 hPa
QBO index used by many previous studies. This observational evidence
supports that the QBO's impact on the tropical stratospheric water vapor is
from its modulation on the tropical tropopause temperature and then
transported upward with the tape recorder as suggested by many previous
studies. In the upper troposphere, ENSO is more important than QBO for the
interannual tropical water vapor anomalies that are positive during the warm
ENSO phases but negative during the cold ENSO phases. Near the tropopause,
both ENSO and QBO are important for the interannual tropical water vapor
anomalies. Warm ENSO phase and westerly QBO phase tend to cause positive
water vapor anomalies, while cold ENSO phase and easterly QBO phase tend to
cause negative water vapor anomalies. As a result, the interannual tropical
water vapor anomalies near the tropopause are different depending on
different ENSO and QBO phase combinations. In the lower and middle
stratosphere, QBO is more important than ENSO for the interannual tropical
water vapor anomalies. For the westerly QBO phases, interannual tropical
water vapor anomalies are positive near the tropopause and in the lower
stratosphere but negative in the middle stratosphere and positive again
above. Vice versa for the easterly QBO phases.
We have undertaken the largest survey for outflows within the Galactic plane using simultaneously observed and data. Out of a total of 919 ATLASGAL clumps, 325 have data suitable to identify ...outflows, and 225 (69% 3%) show high-velocity outflows. The clumps with detected outflows show significantly higher clump masses ( ), bolometric luminosities ( ), luminosity-to-mass ratios ( ), and peak H2 column densities ( ) compared to those without outflows. Outflow activity has been detected within the youngest quiescent clump (i.e., weak) in this sample, and we find that the outflow detection rate increases with , , , and , approaching 90% in some cases (UC H ii regions = 93% 3%; masers = 86% 4%; HC H ii regions = 100%). This high detection rate suggests that outflows are ubiquitous phenomena of massive star formation (MSF). The mean outflow mass entrainment rate implies a mean accretion rate of , in full agreement with the accretion rate predicted by theoretical models of MSF. Outflow properties are tightly correlated with , , and and show the strongest relation with the bolometric clump luminosity. This suggests that outflows might be driven by the most massive and luminous source within the clump. The correlations are similar for both low-mass and high-mass outflows over 7 orders of magnitude, indicating that they may share a similar outflow mechanism. Outflow energy is comparable to the turbulent energy within the clump; however, we find no evidence that outflows increase the level of clump turbulence as the clumps evolve. This implies that the origin of turbulence within clumps is fixed before the onset of star formation.
Context.
The derived physical parameters for young H
II
regions are normally determined assuming the emission region to be optically thin. However, this assumption is unlikely to hold for young H
...II
regions such as hyper-compact H
II
(HC H
II
) and ultra-compact H
II
(UC H
II
) regions and leads to underestimation of their properties. This can be overcome by fitting the SEDs over a wide range of radio frequencies.
Aims.
The two primary goals of this study are (1) to determine the physical properties of young H
II
regions from radio SEDs in the search for potential HC H
II
regions, and (2) to use these physical properties to investigate their evolution.
Methods.
We used the
Karl G. Jansky
Very Large Array (VLA) to observe the
X
-band and
K
-band with angular resolutions of ~1.7′′ and ~0.7′′, respectively, toward 114 H
II
regions with rising-spectra (
α
1.4 GHz
5 GHz
>0). We complement our observations with VLA archival data and construct SEDs in the range of 1−26 GHz and model them assuming an ionization-bounded H
II
region with uniform density.
Results.
Our sample has a mean electron density of
n
e
= 1.6 × 10
4
cm
−3
, diameter diam = 0.14 pc, and emission measure EM = 1.9 × 10
7
pc cm
−6
. We identify 16 HC H
II
region candidates and 8 intermediate objects between the classes of HC H
II
and UC H
II
regions. The
n
e
, diam, and EM change, as expected, but the Lyman continuum flux is relatively constant over time. We find that about 67% of Lyman-continuum photons are absorbed by dust within these H
II
regions and the dust absorption fraction tends to be more significant for more compact and younger H
II
regions.
Conclusions.
Young H
II
regions are commonly located in dusty clumps; HC H
II
regions and intermediate objects are often associated with various masers, outflows, broad radio recombination lines, and extended green objects, and the accretion at the two stages tends to be quickly reduced or halted.
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Bone defect caused by trauma, neoplasia, congenital defects, or periodontal disease is a major cause of disability and physical limitation. The transplantation of bone marrow mesenchymal stem cells ...(BMSCs) promotes bone repair and regeneration. However, it has been shown that most BMSCs die within a short period after transplantation. During apoptosis, BMSCs generate a large number of apoptotic cell–derived extracellular vesicles (ApoEVs). This study aims to understand the potential role of ApoEVs in craniofacial bone defect repair and regeneration. First, we confirmed that BMSCs undergo apoptosis within 2 d after transplantation into the defect of the cranium. Abundant ApoEVs were generated from apoptotic BMSCs. Uptake of ApoEVs efficiently promoted the proliferation, migration, and osteogenic differentiation of recipient BMSCs in vitro. ApoEVs from cells in the middle stage of apoptosis were the most efficient to enhance the regenerative capacity of BMSCs. Moreover, a critical size bone defect model in rats was used to evaluate the osteogenic property of ApoEVs in vivo. Local transplantation of ApoEVs promoted bone regeneration in the calvarial defect. Mechanistically, ApoEVs promoted new bone formation by increasing intracellular reactive oxygen species to activate JNK signaling. This study reveals a previously unknown role of the dying transplanted BMSCs in promoting the viability of endogenous BMSCs and repairing the calvarial defects. Since it could avoid several adverse effects and limits of BMSC cytotherapy, treatment of ApoEVs might be a promising strategy in craniofacial bone repair and regeneration.
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