333 research outputs found
Glycolaldehyde formation via the dimerization of the formyl radical
Glycolaldehyde, the simplest monosaccharide sugar, has recently been detected in low- and high-mass star-forming cores. Following our previous investigation into glycolaldehyde formation, we now consider a further mechanism for the formation of glycolaldehyde that involves the dimerization of the formyl radical, HCO. Quantum mechanical investigation of the HCO dimerization process upon an ice surface is predicted to be barrierless and therefore fast. In an astrophysical context, we show that this mechanism can be very efficient in star-forming cores. It is limited by the availability of the formyl radical, but models suggest that only very small amounts of CO are required to be converted to HCO to meet the observational constraints
How do early-life conditions shape health age profiles late in life?
We investigate how health dynamics late in life vary with early-life conditions. Better early-life conditions are associated with better health outcomes. Education as well as current income and wealth are important mediating factors of this relationship
Close companions around young stars
Multiplicity is a fundamental property that is set early during stellar
lifetimes, and it is a stringent probe of the physics of star formation. The
distribution of close companions around young stars is still poorly constrained
by observations. We present an analysis of stellar multiplicity derived from
APOGEE-2 spectra obtained in targeted observations of nearby star-forming
regions. This is the largest homogeneously observed sample of high-resolution
spectra of young stars. We developed an autonomous method to identify double
lined spectroscopic binaries (SB2s). Out of 5007 sources spanning the mass
range of 0.05--1.5 \msun, we find 399 binaries, including both RV
variables and SB2s. The mass ratio distribution of SB2s is consistent with a
uniform for . The period
distribution is consistent with what has been observed in close binaries (
AU) in the evolved populations. Three systems are found to have 0.1,
with a companion located within the brown dwarf desert. There are not any
strong trends in the multiplicity fraction (MF) as a function of cluster age
from 1 to 100 Myr. There is a weak dependence on stellar density, with
companions being most numerous at stars/pc, and
decreasing in more diffuse regions. Finally, disk-bearing sources are deficient
in SB2s (but not RV variables) by a factor of 2; this deficit is
recovered by the systems without disks. This may indicate a quick dispersal of
disk material in short-period equal mass systems that is less effective in
binaries with lower .Comment: 25 pages, 20 figures. Accepted to A
The APOGEE-2 Survey of the Orion Star Forming Complex: I. Target Selection and Validation with early observations
The Orion Star Forming Complex (OSFC) is a central target for the APOGEE-2
Young Cluster Survey. Existing membership catalogs span limited portions of the
OSFC, reflecting the difficulty of selecting targets homogeneously across this
extended, highly structured region. We have used data from wide field
photometric surveys to produce a less biased parent sample of young stellar
objects (YSOs) with infrared (IR) excesses indicative of warm circumstellar
material or photometric variability at optical wavelengths across the full 420
square degrees extent of the OSFC. When restricted to YSO candidates with H <
12.4, to ensure S/N ~100 for a six visit source, this uniformly selected sample
includes 1307 IR excess sources selected using criteria vetted by Koenig &
Liesawitz and 990 optical variables identified in the Pan-STARRS1 3
survey: 319 sources exhibit both optical variability and evidence of
circumstellar disks through IR excess. Objects from this uniformly selected
sample received the highest priority for targeting, but required fewer than
half of the fibers on each APOGEE-2 plate. We fill the remaining fibers with
previously confirmed and new color-magnitude selected candidate OSFC members.
Radial velocity measurements from APOGEE-1 and new APOGEE-2 observations taken
in the survey's first year indicate that ~90% of the uniformly selected targets
have radial velocities consistent with Orion membership.The APOGEE-2 Orion
survey will include >1100 bona fide YSOs whose uniform selection function will
provide a robust sample for comparative analyses of the stellar populations and
properties across all sub-regions of Orion.Comment: Accepted for publication in ApJ
Extreme Cosmic-Ray-Dominated-Regions: a new paradigm for high star formation density events in the Universe
We examine in detail the recent proposal that extreme
Cosmic-Ray-Dominated-Regions (CRDRs) characterize the ISM of galaxies during
events of high-density star formation, fundamentally altering its initial
conditions (Papadopoulos 2010). Solving the coupled chemical and thermal state
equations for dense UV-shielded gas reveals that the large cosmic ray energy
densities in such systems (U_{CR} (few)x(10^3-10^4) U_{CR,Gal}) will indeed
raise the minimum temperature of this phase (where the initial conditions of
star formation are set) from ~10K (as in the Milky Way) to (50-100)K. Moreover
in such extreme CRDRs the gas temperature remains fully decoupled from that of
the dust, with T_{kin} >> T_{dust}, even at high densities (n(H_2)~10^5--10^6
cm^{-3}), quite unlike CRDRs in the Milky Way where T_k T_{dust} when n(H_2) >=
10^5 cm^{-3}.
These dramatically different star formation initial conditions will: a) boost
the Jeans mass of UV-shielded gas regions by factors of ~10--100 with respect
to those in quiescent or less extreme star forming systems, and b) "erase" the
so-called inflection point of the effective equation of state (EOS) of
molecular gas. Both these effects occur across the entire density range of
typical molecular clouds, and may represent {\it a new paradigm for all
high-density star formation in the Universe}, with cosmic rays as the key
driving mechanism, operating efficiently even in the high dust extinction
environments of extreme starbursts...Comment: 10 pages, 5 figures, accepted with minor modifications for
publication in the MNRAS (the follow-up paper to Papadopoulos 2010, ApJ, 720,
226
Sam68 regulates EMT through alternative splicing–activated nonsense-mediated mRNA decay of the SF2/ASF proto-oncogene
Expression levels of SF2/ASF are controlled by Sam68 mediated activation of splicing-induced mRNA decay
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Variability in Asian parents’ English and mathematics skills: A family-based study
What explains parental English word reading and mathematics performance? The present study examined whether parent-, family-, and child-related variables explain parents’ English word reading and mathematics performances among two groups of Asian parents. The data were collected from 152 Hong Kong and 280 Cebu City (Philippines) parents who learn English as a second language. The academic performances of their children (Hong Kong: Mean age = 8.72 years; Cebu City; Mean age = 6.59 years) were also measured. Regression analysis results suggested that, across both groups, parents with higher education levels tended to perform better in English word reading. In addition, in Hong Kong, but not the Philippines, family income was a unique correlate of parental English word reading performance, whereas in the Philippines, but not Hong Kong, the parent’s own mathematics skill and the child’s own English word reading skill were also uniquely associated with parental English performance. Across both groups, parents’ mathematics skills were associated with better literacy skills. In addition, in Hong Kong, more positive attitudes toward mathematics were additionally predictive of better mathematics performance, as were children’s own mathematics performances. In the Philippines only, mothers tended to be poorer in mathematics than fathers. Such results underscore the complexity of family related literacy and mathematics, including family status and intergenerational effects
Large-Scale Evidence for the Effect of the COLIA1 Sp1 Polymorphism on Osteoporosis Outcomes: The GENOMOS Study
BACKGROUND: Osteoporosis and fracture risk are considered to be under genetic control. Extensive work is being performed to identify the exact genetic variants that determine this risk. Previous work has suggested that a G/T polymorphism affecting an Sp1 binding site in the COLIA1 gene is a genetic marker for low bone mineral density (BMD) and osteoporotic fracture, but there have been no very-large-scale studies of COLIA1 alleles in relation to these phenotypes. METHODS AND FINDINGS: Here we evaluated the role of COLIA1 Sp1 alleles as a predictor of BMD and fracture in a multicenter study involving 20,786 individuals from several European countries. At the femoral neck, the average (95% confidence interval [CI]) BMD values were 25 mg/cm (2) (CI, 16 to 34 mg/cm (2)) lower in TT homozygotes than the other genotype groups ( p < 0.001), and a similar difference was observed at the lumbar spine; 21 mg/cm (2) (CI, 1 to 42 mg/cm (2)), ( p = 0.039). These associations were unaltered after adjustment for potential confounding factors. There was no association with fracture overall (odds ratio [OR] = 1.01 [CI, 0.95 to 1.08]) in either unadjusted or adjusted analyses, but there was a non-significant trend for association with vertebral fracture and a nominally significant association with incident vertebral fractures in females (OR = 1.33 [CI, 1.00 to 1.77]) that was independent of BMD, and unaltered in adjusted analyses. CONCLUSIONS: Allowing for the inevitable heterogeneity between participating teams, this study—which to our knowledge is the largest ever performed in the field of osteoporosis genetics for a single gene—demonstrates that the COLIA1 Sp1 polymorphism is associated with reduced BMD and could predispose to incident vertebral fractures in women, independent of BMD. The associations we observed were modest however, demonstrating the importance of conducting studies that are adequately powered to detect and quantify the effects of common genetic variants on complex diseases
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