1,963 research outputs found
Disks in the Arches cluster -- survival in a starburst environment
Deep Keck/NIRC2 HK'L' observations of the Arches cluster near the Galactic
center reveal a significant population of near-infrared excess sources. We
combine the L'-band excess observations with K'-band proper motions, to confirm
cluster membership of excess sources in a starburst cluster for the first time.
The robust removal of field contamination provides a reliable disk fraction
down to our completeness limit of H=19 mag, or about 5 Msun at the distance of
the Arches. Of the 24 identified sources with K'-L' > 2.0 mag, 21 have reliable
proper motion measurements, all of which are proper motion members of the
Arches cluster. VLT/SINFONI K'-band spectroscopy of three excess sources
reveals strong CO bandhead emission, which we interpret as the signature of
dense circumstellar disks. The detection of strong disk emission from the
Arches stars is surprising in view of the high mass of the B-type main sequence
host stars of the disks and the intense starburst environment. We find a disk
fraction of 6 +/- 2% among B-type stars in the Arches cluster. A radial
increase in the disk fraction from 3 to 10% suggests rapid disk destruction in
the immediate vicinity of numerous O-type stars in the cluster core. A
comparison between the Arches and other high- and low-mass star-forming regions
provides strong indication that disk depletion is significantly more rapid in
compact starburst clusters than in moderate star-forming environments.Comment: 51 pages preprint2 style, 22 figures, accepted by Ap
Deep near-infrared imaging of W3 Main: constraints on stellar cluster formation
Embedded clusters like W3 Main are complex and dynamically evolving systems
that represent an important phase of the star formation process. We aim at the
characterization of the entire stellar content of W3 Main in a statistical
sense to identify possible differences in evolutionary phase of the stellar
populations and find clues about the formation mechanism of this massive
embedded cluster. Methods. Deep JHKs imaging is used to derive the disk
fraction, Ks-band luminosity functions and mass functions for several
subregions in W3 Main. A two dimensional completeness analysis using artificial
star experiments is applied as a crucial ingredient to assess realistic
completeness limits for our photometry. We find an overall disk fraction of 7.7
2.3%, radially varying from 9.4 3.0 % in the central 1 pc to 5.6
2.2 % in the outer parts of W3 Main. The mass functions derived for three
subregions are consistent with a Kroupa and Chabrier mass function. The mass
function of IRSN3 is complete down to 0.14 Msun and shows a break at M
0.5 Msun. We interpret the higher disk fraction in the center as evidence for a
younger age of the cluster center. We find that the evolutionary sequence
observed in the low-mass stellar population is consistent with the observed age
spread among the massive stars. An analysis of the mass function variations
does not show evidence for mass segregation. W3 Main is currently still
actively forming stars, showing that the ionizing feedback of OB stars is
confined to small areas ( 0.5 pc). The FUV feedback might be influencing
large regions of the cluster as suggested by the low overall disk fraction.Comment: 15 pages, 13 figures, accepted by A&
The globular cluster NGC 2419: a crucible for theories of gravity
We present the analysis of a kinematic data set of stars in the globular
cluster NGC 2419, taken with Keck/DEIMOS. Combined with a reanalysis of deep
HST and Subaru imaging data, which provide an accurate luminosity profile of
the cluster, we investigate the validity of a large set of dynamical models of
the system, which are checked for stability via N-body simulations. We find
that isotropic models in either Newtonian or Modified Newtonian Dynamics (MOND)
are ruled out with extremely high confidence. However, a simple Michie model in
Newtonian gravity with anisotropic velocity dispersion provides an excellent
representation of the luminosity profile and kinematics. In contrast, with MOND
we find that Michie models that reproduce the luminosity profile either
over-predict the velocity dispersion on the outskirts of the cluster if the
mass to light ratio is kept at astrophysically-motivated values, or else they
under-predict the central velocity dispersion if the mass to light ratio is
taken to be very small. We find that the best Michie model in MOND is a factor
of 10000 less likely than the Newtonian model that best fits the system. A
likelihood ratio of 350 is found when we investigate more general models by
solving the Jeans equation with a Markov-Chain Monte Carlo scheme. We verified
with N-body simulations that these results are not significantly different when
the MOND external field effect is accounted for. If the assumptions that the
cluster is in dynamical equilibrium, spherical, not on a peculiar orbit, and
possesses a single dynamical tracer population of constant M/L are correct, we
conclude that the present observations provide a very severe challenge for
MOND. [abridged]Comment: 25 pages, 19 figures, accepted for publication in Ap
Opting out increases HIV testing in a large sexually transmitted infections outpatient clinic
In January 2007, opt-out HIV testing replaced provider-initiated testing at the sexually transmitted infections (STI) outpatient clinic in Amsterdam, The Netherlands. The effect of the opt-out strategy on the uptake of HIV testing was studied and factors associated with refusal of HIV testing were identified. Data routinely collected at the STI clinic were analysed separately for men who have sex with men (MSM) and heterosexuals. Logistic regression analysis was used to identify factors associated with opting out. In 2007, 12% of MSM and 4% of heterosexuals with (presumed) negative or unknown HIV serostatus declined HIV testing. Refusals gradually decreased to 7% and 2% by the year end. In 2006, before the introduction of opt-out, 38% of MSM and 27% of heterosexuals declined testing. The proportion of HIV-positive results remained stable among MSM, 3.4% in 2007 versus 3.7% in 2006, and among heterosexuals, 0.2% in 2007 versus 0.3% in 2006. In both groups factors associated with opting out were: age >or=30 years, no previous HIV test, the presence of STI-related complaints and no risky anal/vaginal intercourse. Among heterosexuals, men and non-Dutch visitors refused more often; among MSM, those warned of STI exposure by sexual partners and those diagnosed with gonorrhoea or syphilis refused more often. An opt-out strategy increased the uptake of HIV testing. A sharp increase in testing preceeded a more gradual increase, suggesting time must pass to optimise the new strategy. A small group of visitors, especially MSM, still opt out. Counselling will focus on barriers such as fear and low risk perception among high-risk visitors considering opting ou
Keck Adaptive Optics Observations of the Protostellar Disk around Radio Source I in the Orion Kleinmann-Low Nebula
We have made the first detection of a near-infrared counterpart associated
with the disk around Radio Source "I," a massive protostar in the Kleinmann-Low
Nebula in Orion using imaging with laser guide star adaptive optics on the Keck
II telescope. The infrared emission is evident in images acquired using L' (3.8
microns) and Ms (4.7 microns) filters and is not detectable at K' (2.1
microns). The observed morphology strongly suggests that we are seeing some
combination of scattered and thermal light emanating from the disk. The disk is
also manifest in the L'/Ms flux ratio image. We interpret the near-infrared
emission as the illuminated surface of a nearly edge-on disk, oriented so that
only the northern face is visible; the opposite surface remains hidden by the
disk. We do not see infrared radiation associated directly with the star
proposed to be associated with Source "I." The data also suggest that there is
a cavity above and below the disk that is oriented perpendicular to the disk,
and is sculpted by the known, strong outflow from the inner disk of Source I.
We compare our data to models of a protostar with a surrounding disk, envelope,
and wind-blown cavity in order to elucidate the nature of the disk around Radio
Source I.Comment: 22 pages, 7 figures. Accepted for publication to Ap
DOMINO++: Domain-aware Loss Regularization for Deep Learning Generalizability
Out-of-distribution (OOD) generalization poses a serious challenge for modern
deep learning (DL). OOD data consists of test data that is significantly
different from the model's training data. DL models that perform well on
in-domain test data could struggle on OOD data. Overcoming this discrepancy is
essential to the reliable deployment of DL. Proper model calibration decreases
the number of spurious connections that are made between model features and
class outputs. Hence, calibrated DL can improve OOD generalization by only
learning features that are truly indicative of the respective classes. Previous
work proposed domain-aware model calibration (DOMINO) to improve DL
calibration, but it lacks designs for model generalizability to OOD data. In
this work, we propose DOMINO++, a dual-guidance and dynamic domain-aware loss
regularization focused on OOD generalizability. DOMINO++ integrates
expert-guided and data-guided knowledge in its regularization. Unlike DOMINO
which imposed a fixed scaling and regularization rate, DOMINO++ designs a
dynamic scaling factor and an adaptive regularization rate. Comprehensive
evaluations compare DOMINO++ with DOMINO and the baseline model for head tissue
segmentation from magnetic resonance images (MRIs) on OOD data. The OOD data
consists of synthetic noisy and rotated datasets, as well as real data using a
different MRI scanner from a separate site. DOMINO++'s superior performance
demonstrates its potential to improve the trustworthy deployment of DL on real
clinical data.Comment: 12 pages, 5 figures, 5 tables, Accepted by the International
Conference on Medical Image Computing and Computer Assisted Intervention
(MICCAI) 202
Independent large scale duplications in multiple M. tuberculosis lineages overlapping the same genomic region
Mycobacterium tuberculosis, the causative agent of most human tuberculosis, infects one third of the world's population and kills an estimated 1.7 million people a year. With the world-wide emergence of drug resistance, and the finding of more functional genetic diversity than previously expected, there is a renewed interest in understanding the forces driving genome evolution of this important pathogen. Genetic diversity in M. tuberculosis is dominated by single nucleotide polymorphisms and small scale gene deletion, with little or no evidence for large scale genome rearrangements seen in other bacteria. Recently, a single report described a large scale genome duplication that was suggested to be specific to the Beijing lineage. We report here multiple independent large-scale duplications of the same genomic region of M. tuberculosis detected through whole-genome sequencing. The duplications occur in strains belonging to both M. tuberculosis lineage 2 and 4, and are thus not limited to Beijing strains. The duplications occur in both drug-resistant and drug susceptible strains. The duplicated regions also have substantially different boundaries in different strains, indicating different originating duplication events. We further identify a smaller segmental duplication of a different genomic region of a lab strain of H37Rv. The presence of multiple independent duplications of the same genomic region suggests either instability in this region, a selective advantage conferred by the duplication, or both. The identified duplications suggest that large-scale gene duplication may be more common in M. tuberculosis than previously considere
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