803 research outputs found
Massive star formation via high accretion rates and early disk-driven outflows
We present an investigation of massive star formation that results from the
gravitational collapse of massive, magnetized molecular cloud cores. We
investigate this by means of highly resolved, numerical simulations of initial
magnetized Bonnor-Ebert-Spheres that undergo collapse and cooling. By comparing
three different cases - an isothermal collapse, a collapse with radiative
cooling, and a magnetized collapse - we show that massive stars assemble
quickly with mass accretion rates exceeding 10^-3 Msol/yr. We confirm that the
mass accretion during the collapsing phase is much more efficient than
predicted by selfsimilar collapse solutions, i.e. dM/dt ~ c^3/G. We find that
during protostellar assembly the mass accretion reaches 20 - 100 c^3/G.
Furthermore, we determined the self-consistent structure of bipolar outflows
that are produced in our three dimensional magnetized collapse simulations.
These outflows produce cavities out of which radiation pressure can be
released, thereby reducing the limitations on the final mass of massive stars
formed by gravitational collapse. Moreover, we argue that the extraction of
angular momentum by disk-threaded magnetic fields and/or by the appearance of
bars with spiral arms significantly enhance the mass accretion rate, thereby
helping the massive protostar to assemble more quickly.Comment: 22 pages, 12 figures, aastex style, accepted for publication in ApJ,
see http://www.ita.uni-heidelberg.de/~banerjee/publications/MassiveStars.pdf
for high resolution figure
Assessing the association between oral hygiene and preterm birth by quantitative light-induced fluorescence
The aim of this study was to investigate the purported link between oral hygiene and preterm birth by using image analysis tools to quantify dental plaque biofilm. Volunteers (Ρ = 91) attending an antenatal clinic were identified as those considered to be âat high riskâ of preterm delivery (i.e., a previous history of idiopathic preterm delivery, case group) or those who were not considered to be at risk (control group). The women had images of their anterior teeth captured using quantitative light-induced fluorescence (QLF). These images were analysed to calculate the amount of red fluorescent plaque (ÎR%) and percentage of plaque coverage. QLF showed little difference in ÎR% between the two groups, 65.00% case versus 68.70% control, whereas there was 19.29% difference with regard to the mean plaque coverage, 25.50% case versus 20.58% control. A logistic regression model showed a significant association between plaque coverage and case/control status (ÎĄ = 0.031), controlling for other potential predictor variables, namely, smoking status, maternal age, and body mass index (BMI)
Global Nonradial Instabilities of Dynamically Collapsing Gas Spheres
Self-similar solutions provide good descriptions for the gravitational
collapse of spherical clouds or stars when the gas obeys a polytropic equation
of state, (with ). We study the behaviors of
nonradial perturbations in the similarity solutions of Larson, Penston and
Yahil, which describe the evolution of the collapsing cloud prior to core
formation. Our global stability analysis reveals the existence of unstable
bar-modes () when . In particular, for the collapse of
isothermal spheres, which applies to the early stages of star formation, the
density perturbation relative to the background, , increases as ,
where denotes the epoch of core formation, and is the cloud
central density. Thus, the isothermal cloud tends to evolve into an ellipsoidal
shape (prolate bar or oblate disk, depending on initial conditions) as the
collapse proceeds. In the context of Type II supernovae, core collapse is
described by the equation of state, and our analysis
indicates that there is no growing mode (with density perturbation) in the
collapsing core before the proto-neutron star forms, although nonradial
perturbations can grow during the subsequent accretion of the outer core and
envelope onto the neutron star. We also carry out a global stability analysis
for the self-similar expansion-wave solution found by Shu, which describes the
post-collapse accretion (``inside-out'' collapse) of isothermal gas onto a
protostar. We show that this solution is unstable to perturbations of all
's, although the growth rates are unknown.Comment: 28 pages including 7 ps figures; Minor changes in the discussion; To
be published in ApJ (V.540, Sept.10, 2000 issue
A PPMAP analysis of the filamentary structures in Ophiuchus L1688 and L1689
We use the PPMAP (Point Process MAPping) algorithm to re-analyse the
\textit{Herschel} and SCUBA-2 observations of the L1688 and L1689 sub-regions
of the Ophiuchus molecular cloud. PPMAP delivers maps with high resolution
(here , corresponding to at ),
by using the observations at their native resolutions. PPMAP also delivers more
accurate dust optical depths, by distinguishing dust of different types and at
different temperatures. The filaments and prestellar cores almost all lie in
regions with (corresponding
to ). The dust temperature, , tends to be correlated
with the dust opacity index, , with low and low tend
concentrated in the interiors of filaments. The one exception to this tendency
is a section of filament in L1688 that falls -- in projection -- between the
two B stars, S1 and HD147889; here and are relatively high, and
there is compelling evidence that feedback from these two stars has heated and
compressed the filament. Filament {\sc fwhm}s are typically in the range
to . Most filaments have line densities in the
range to . If
their only support is thermal gas pressure, and the gas is at the canonical
temperature of , the filaments are highly supercritical. However,
there is some evidence from ammonia observations that the gas is significantly
warmer than this, and we cannot rule out the possibility of additional support
from turbulence and/or magnetic fields. On the basis of their spatial
distribution, we argue that most of the starless cores are likely to disperse
(rather than evolving to become prestellar).Comment: 22 pages, 18 figures, Accepted for publication by MNRAS March 202
Spatial-Distance Cues Influence Economic Decision-Making in a Social Context
Social distance (i.e., the degree of closeness to another person) affects the
way humans perceive and respond to fairness during financial negotiations.
Feeling close to someone enhances the acceptance of monetary offers. Here, we
explored whether this effect also extends to the spatial domain. Specifically,
using an iterated version of the Ultimatum Game in a within-subject design, we
investigated whether different visual spatial distance-cues result in
different rates of acceptance of otherwise identical monetary offers. Study 1
found that participants accepted significantly more offers when they were cued
with spatial closeness than when they were cued with spatial distance. Study 2
replicated this effect using identical procedures but different spatial-
distance cues in an independent sample. Importantly, our results could not be
explained by feelings of social closeness. Our results demonstrate that mere
perceptions of spatial closeness produce analogousâbut independentâeffects to
those of social closeness
Biomarkers of Tuberculosis Severity and Treatment Effect: A Directed Screen of 70 Host Markers in a Randomized Clinical Trial.
More efficacious treatment regimens are needed for tuberculosis, however, drug development is impeded by a lack of reliable biomarkers of disease severity and of treatment effect. We conducted a directed screen of host biomarkers in participants enrolled in a tuberculosis clinical trial to address this need. Serum samples from 319 protocol-correct, culture-confirmed pulmonary tuberculosis patients treated under direct observation as part of an international, phase 2 trial were screened for 70 markers of infection, inflammation, and metabolism. Biomarker assays were specifically developed for this study and quantified using a novel, multiplexed electrochemiluminescence assay. We evaluated the association of biomarkers with baseline characteristics, as well as with detailed microbiologic data, using Bonferroni-adjusted, linear regression models. Across numerous analyses, seven proteins, SAA1, PCT, IL-1β, IL-6, CRP, PTX-3 and MMP-8, showed recurring strong associations with markers of baseline disease severity, smear grade and cavitation; were strongly modulated by tuberculosis treatment; and had responses that were greater for patients who culture-converted at 8weeks. With treatment, all proteins decreased, except for osteocalcin, MCP-1 and MCP-4, which significantly increased. Several previously reported putative tuberculosis-associated biomarkers (HOMX1, neopterin, and cathelicidin) were not significantly associated with treatment response. In conclusion, across a geographically diverse and large population of tuberculosis patients enrolled in a clinical trial, several previously reported putative biomarkers were not significantly associated with treatment response, however, seven proteins had recurring strong associations with baseline radiographic and microbiologic measures of disease severity, as well as with early treatment response, deserving additional study
Genetic structure of Tribolium castaneum populations in mills
We investigated the genetic diversity and differentiation among nine populations of Tribolium castaneum using eight polymorphic loci, including microsatellites and other insertion-deletion polymorphisms (=âindelsâ). Samples were collected in food processing/storage facilities located in Kansas, Nebraska, California, Louisiana, Florida and Puerto Rico. Standard population genetic analysis was applied, and an assignment test was used to assign individuals to their genetic population. All loci were polymorphic across populations, with the number of alleles per locus-population combination varying from three to fourteen. Among 72 locus-by-population combinations, 31 deviated significantly from Hardy-Weinberg equilibrium, which was associated with a deficiency in heterozygosity. Tribolium castaneum populations show some level of genetic structuring. Genetic differentiation between populations, using FST estimates, was significant, with FST varying from 0.018 to 0.149. AMOVA indicated that 8.32% of the variation in allele frequency resulted from comparisons among populations. Genetic distance was not significantly correlated with geographic distance. Correct assignment to the genetic population was possible in only 56% of all individuals. Together, these results revealed that geographically distinct populations of T. castaneum had low to moderate levels of genetic differentiation that was not correlated with geographic distance, and the genotypic profile of the individuals did not provide enough information for fingerprinting them with their source population. Keywords: Tribolium castaneum, Population genetics, Genetic structure, FST, Genetic fingerprintin
Random division of an interval
The well-known relation between random division of an interval and the Poisson process is interpreted as a Laplace transformation. With the use of this interpretation a number of (in part known) results is derived very easily
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