343 research outputs found
A Chemical Composition Survey of the Iron-Complex Globular Cluster NGC 6273 (M 19)
Recent observations have shown that a growing number of the most massive
Galactic globular clusters contain multiple populations of stars with different
[Fe/H] and neutron-capture element abundances. NGC 6273 has only recently been
recognized as a member of this "iron-complex" cluster class, and we provide
here a chemical and kinematic analysis of > 300 red giant branch (RGB) and
asymptotic giant branch (AGB) member stars using high resolution spectra
obtained with the Magellan-M2FS and VLT-FLAMES instruments. Multiple lines of
evidence indicate that NGC 6273 possesses an intrinsic metallicity spread that
ranges from about [Fe/H] = -2 to -1 dex, and may include at least three
populations with different [Fe/H] values. The three populations identified here
contain separate first (Na/Al-poor) and second (Na/Al-rich) generation stars,
but a Mg-Al anti-correlation may only be present in stars with [Fe/H] > -1.65.
The strong correlation between [La/Eu] and [Fe/H] suggests that the s-process
must have dominated the heavy element enrichment at higher metallicities. A
small group of stars with low [alpha/Fe] is identified and may have been
accreted from a former surrounding field star population. The cluster's large
abundance variations are coupled with a complex, extended, and multimodal blue
horizontal branch (HB). The HB morphology and chemical abundances suggest that
NGC 6273 may have an origin that is similar to omega Cen and M 54.Comment: Accepted for Publication in The Astrophysical Journal; 50 pages; 18
figures; 8 tables; higher resolution figures are available upon request or in
the published journal articl
Carbon monoxide poisoning: novel magnetic resonance imaging pattern in the acute setting
The presentation of carbon monoxide (CO) poisoning is non-specific and highly variable. The diagnosis is made when a compatible history and examination occur in a patient with elevated carboxyhaemoglobin levels. The severity of intoxication is difficult to assess accurately based on laboratory markers alone. Magnetic resonance imaging (MRI) has been shown to have superior sensitivity to computed tomography for the detection of abnormalities post CO poisoning. We report a novel imaging pattern on MRI undertaken in the acute setting in a patient with CO intoxication. We also discuss the management and follow up of patients with CO poisoning
Carbon monoxide poisoning: Novel magnetic resonance imaging pattern in the acute setting
The presentation of carbon monoxide (CO) poisoning is non-specific and highly variable. The diagnosis is made when a compatible history and examination occur in a patient with elevated carboxyhaemoglobin levels. The severity of intoxication is difficult to assess accurately based on laboratory markers alone. Magnetic resonance imaging (MRI) has been shown to have superior sensitivity to computed tomography for the detection of abnormalities post CO poisoning. We report a novel imaging pattern on MRI undertaken in the acute setting in a patient with CO intoxication. We also discuss the management and follow up of patients with CO poisoning
The First Detection of Blue Straggler Stars in the Milky Way Bulge
We report the first detections of Blue Straggler Stars (BSS) in the bulge of
the Milky Way galaxy. Proper motions from extensive space-based observations
along a single sight-line allow us to separate a sufficiently clean and
well-characterized bulge sample that we are able to detect a small population
of bulge objects in the region of the color-magnitude diagram commonly occupied
young objects and blue strgglers. However, variability measurements of these
objects clearly establish that a fraction of them are blue stragglers. Out of
the 42 objects found in this region of the color-magnitude diagram, we estimate
that at least 18 are genuine BSS. We normalize the BSS population by our
estimate of the number of horizontal branch stars in the bulge in order to
compare the bulge to other stellar systems. The BSS fraction is clearly
discrepant from that found in stellar clusters. The blue straggler population
of dwarf spheroidals remains a subject of debate; some authors claim an
anticorrelation between the normalised blue straggler fraction and integrated
light. If this trend is real, then the bulge may extend it by three orders of
magnitude in mass. Conversely, we find that the genuinely young (~5Gy or
younger) population in the bulge, must be at most 3.4% under the most
conservative scenario for the BSS population.Comment: ApJ in press; 25 pages, 6 figures, 2 table
Dynamic Coupling and Allosteric Behavior in a Nonallosteric Protein â€
Long-range intraprotein interactions give rise to many important protein behaviors. Understanding how energy is transduced through protein structures to either transmit a signal or elicit conformational changes is therefore a current challenge in structural biology. In an effort to understand such linkages, multiple V→A mutations were made in the small globular protein eglin c. The physical responses, as mapped by NMR spin relaxation, residual dipolar couplings (RDCs), and scalar couplings, illustrate that the interior of this non-allosteric protein forms a dynamic network and that local perturbations are transmitted as dynamic and structural changes to distal sites as far as 16 Å away. Two basic types of propagation responses were observed: contiguous pathways of enhanced (attenuated) dynamics with no change in structure; and dispersed (non-contiguous) changes in methyl rotation rates that appear to result from subtle deformation of backbone structure. In addition, energy transmission is found to be unidirectional. In one mutant, an allosteric conformational change of a side chain is seen in the context of a pathway of propagated changes in ps-ns dynamics. The observation of so many long-range interactions in a small, rigid system lends experimental weight to the idea that all well-folded proteins inherently possess allosteric features [Gunasekaran et al. (2004) Proteins 57, 433−443], and that dynamics are a rich source of information for mapping and gaining mechanistic insight into communication pathways in individual proteins
Common Representation of Information Flows for Dynamic Coalitions
We propose a formal foundation for reasoning about access control policies
within a Dynamic Coalition, defining an abstraction over existing access
control models and providing mechanisms for translation of those models into
information-flow domain. The abstracted information-flow domain model, called a
Common Representation, can then be used for defining a way to control the
evolution of Dynamic Coalitions with respect to information flow
Stellar Proper Motions in the Galactic Bulge from deep HST ACS/WFC Photometry
We present stellar proper motions in the Galactic bulge from the Sagittarius
Window Eclipsing Extrasolar Search (SWEEPS) project using ACS/WFC on HST.
Proper motions are extracted for more than 180,000 objects, with >81,000
measured to accuracy better than 0.3 mas/yr in both coordinates. We report
several results based on these measurements: 1. Kinematic separation of bulge
from disk allows a sample of >15,000 bulge objects to be extracted based on
>6-sigma detections of proper motion, with <0.2% contamination from the disk.
This includes the first detection of a candidate bulge Blue Straggler
population. 2. Armed with a photometric distance modulus on a star by star
basis, and using the large number of stars with high-quality proper motion
measurements to overcome intrinsic scatter, we dissect the kinematic properties
of the bulge as a function of distance along the line of sight. This allows us
to extract the stellar circular speed curve from proper motions alone, which we
compare with the circular speed curve obtained from radial velocities. 3. We
trace the variation of the {l,b} velocity ellipse as a function of depth. 4.
Finally, we use the density-weighted {l,b} proper motion ellipse produced from
the tracer stars to assess the kinematic membership of the sixteen transiting
planet candidates discovered in the Sagittarius Window; the kinematic
distribution of the planet candidates is consistent with that of the disk and
bulge stellar populations.Comment: 71 pages, 30 figures, ApJ Accepte
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