3,062 research outputs found
Some Like It Hot: Linking Diffuse X-ray Luminosity, Baryonic Mass, and Star Formation Rate in Compact Groups of Galaxies
We present an analysis of the diffuse X-ray emission in 19 compact groups of
galaxies (CGs) observed with Chandra. The hottest, most X-ray luminous CGs
agree well with the galaxy cluster X-ray scaling relations in and
, even in CGs where the hot gas is associated with only the
brightest galaxy. Using Spitzer photometry, we compute stellar masses and
classify HCGs 19, 22, 40, and 42 and RSCGs 32, 44, and 86 as fossil groups
using a new definition for fossil systems that includes a broader range of
masses. We find that CGs with total stellar and HI masses
M are often X-ray luminous, while lower-mass CGs only sometimes exhibit
faint, localized X-ray emission. Additionally, we compare the diffuse X-ray
luminosity against both the total UV and 24 m star formation rates of each
CG and optical colors of the most massive galaxy in each of the CGs. The most
X-ray luminous CGs have the lowest star formation rates, likely because there
is no cold gas available for star formation, either because the majority of the
baryons in these CGs are in stars or the X-ray halo, or due to gas stripping
from the galaxies in CGs with hot halos. Finally, the optical colors that trace
recent star formation histories of the most massive group galaxies do not
correlate with the X-ray luminosities of the CGs, indicating that perhaps the
current state of the X-ray halos is independent of the recent history of
stellar mass assembly in the most massive galaxies.Comment: 20 pages, 7 figures, accepted for publication in Ap
Erratum: Multimedia Dispersion Relation for Surface Electromagnetic Waves. (The Journal of Chemical Physics (1975) 62 (1674))
Rapid, -insensitive, dual-band quasi-adiabatic saturation transfer with optimal control for complete quantification of myocardial ATP flux
Purpose: Phosphorus saturation-transfer experiments can quantify metabolic
fluxes non-invasively. Typically, the forward flux through the creatine-kinase
reaction is investigated by observing the decrease in phosphocreatine (PCr)
after saturation of -ATP. The quantification of total ATP utilisation
is currently under-explored, as it requires simultaneous saturation of
inorganic phosphate (Pi) and PCr. This is challenging, as currently available
saturation pulses reduce the already-low -ATP signal present.
Methods: Using a hybrid optimal-control and Shinnar-Le-Roux method, a
quasi-adiabatic RF pulse was designed for the dual-saturation of PCr and Pi to
enable determination of total ATP utilisation. The pulses were evaluated in
Bloch equation simulations, compared with a conventional hard-cosine DANTE
saturation sequence, before application to perfused rat hearts at 11.7 Tesla.
Results: The quasi-adiabatic pulse was insensitive to a -fold variation
in , producing equivalent saturation with a 53% reduction in delivered
pulse power and a 33-fold reduction in spillover at the minimum effective
. This enabled the complete quantification of the synthesis and
degradation fluxes for ATP in 30-45 minutes in the perfused rat heart. While
the net synthesis flux ( mM/s, SEM) was not significantly different
from degradation flux ( mM/s, ) and both measures are
consistent with prior work, nonlinear error analysis highlights uncertainties
in the Pi-to-ATP measurement that may explain a trend suggesting a possible
imbalance.
Conclusion: This work demonstrates a novel quasi-adiabatic dual-saturation RF
pulse with significantly improved performance that can be used to measure ATP
turnover in the heart in vivo.Comment: 26 pages, Accepted at Magnetic Resonance in Medicine, 24/11/2020
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Convergence of bark investment according to fire and climate structures ecosystem vulnerability to future change
Fire regimes in savannas and forests are changing over much of the world. Anticipating the impact of these changes requires understanding how plants are adapted to fire. Here we test whether fire imposes a broad selective force on a key fire-tolerance trait, bark thickness, across 572 tree species distributed worldwide. We show that investment in thick bark is a pervasive adaptation in frequently burned areas across savannas and forests in both temperate and tropical regions where surface fires occur. Geographic variability in bark thickness is largely explained by annual burned area and precipitation seasonality. Combining environmental and species distribution data allowed us to assess the vulnerability to future climate and fire conditions: tropical rainforests are especially vulnerable, whereas seasonal forests and savannas are more robust. The strong link between fire and bark thickness provides an avenue for assessing the vulnerability of tree communities to fire and demands inclusion in global models
Possible Applications of Surface Electromagnetic Waves to Measure Absorption Coefficients
We Show that Surface Electromagnetic Waves Can Probably Be Used to Measure the Absorption Coefficients of Materials overlaying Metals. the Proposed Experimental Method is Illustrated in the Infrared Frequency Range using Water, Teflon, and Polyethylene as Sample Materials
Control of the Mitotic Cleavage Plane by Local Epithelial Topology
For nearly 150 years, it has been recognized that cell shape strongly influences the orientation of the mitotic cleavage plane (e.g. Hofmeister, 1863). However, we still understand little about the complex interplay between cell shape and cleavage plane orientation in epithelia, where polygonal cell geometries emerge from multiple factors, including cell packing, cell growth, and cell division itself. Here, using mechanical simulations, we show that the polygonal shapes of individual cells can systematically bias the long axis orientations of their adjacent mitotic neighbors. Strikingly, analysis of both animal epithelia and plant epidermis confirm a robust and nearly identical correlation between local cell topology and cleavage plane orientation in vivo. Using simple mathematics, we show that this effect derives from fundamental packing constraints. Our results suggest that local epithelial topology is a key determinant of cleavage plane orientation, and that cleavage plane bias may be a widespread property of polygonal cell sheets in plants and animals.Engineering and Applied Science
The Veterans Affairs Medical Center's Contribution to Plastic Surgery Education
Veterans Affairs (VA) medical centers have played a major role in graduate medical education since the 1940s. Currently, the VA health system operates 168 medical centers across the United States and supports the clinical training of more than 41 200 medical residents annually. Teaching hospitals within the VA provide subspecialty medical and surgical care and perform the majority of complex and high-risk surgical procedures.
The diversity of pathologic conditions requiring a plastic surgery skill set are prominent within the VA population: cancer reconstruction, hand surgery, facial fractures, and burn care. Educational opportunities are ample. Plastic surgery residents in university-based training programs typically rotate at the VA hospital for several months each year. This study examines the relationship between the plastic surgery service and resident education within the VA hospitals
Fabrication of high-entropy nitrides and carbonitrides
In high-entropy alloys, the use of multiple principle alloying elements is known to entropically stabilize the material. Refractory nitrides and carbides of transition metals are widely known for their ultra high-temperature stability and their high hardness, properties that make them valuable materials for extreme environments, such as coating the exterior of hypersonic flight vehicles and the interior of nuclear reactors. By creating entropy-stabilized complex solid solutions of nitrides and carbides, one can take advantage of the inherent favorable properties of these materials, as well as increased thermal stability and solid solution strengthening. Five-metal systems are chosen using first-principles calculations to describe the energetic distribution of possible atomic configurations, in order to identify systems that are likely to form an entropy-stabilized solid solution. Bulk samples of equiatomic, hexanery (5-metal), high-entropy refractory nitrides and carbonitrides were then fabricated to demonstrate this concept, by using a combination of high-energy ball milling, spark plasma sintering, and hot pressing. The uniformity of the microstructures is characterized, and single-phase solid solutions are achieved, thus demonstrating the ability to entropically stabilize multi-component random mixtures of refractory carbides and nitrides.
This work is supported by the U.S. Office of Naval Research MURI program (Grant No. N00014-15- 1-2863
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