4,278 research outputs found
Thermohaline instability and rotation-induced mixing II- Yields of 3He for low- and intermediate-mass stars
Context. The 3He content of Galactic HII regions is very close to that of the
Sun and the solar system, and only slightly higher than the primordial 3He
abundance as predicted by the standard Big Bang nucleosynthesis. However, the
classical theory of stellar evolution predicts a high production of 3He by
low-mass stars, implying a strong increase of 3He with time in the Galaxy. This
is the well-known "3He problem". Aims. We study the effects of thermohaline and
rotation-induced mixings on the production and destruction of 3He over the
lifetime of low- and intermediate-mass stars at various metallicities. Methods.
We compute stellar evolutionary models in the mass range 1 to 6M\odot for four
metallicities, taking into account thermohaline instability and
rotation-induced mixing. For the thermohaline diffusivity we use the
prescription based on the linear stability analysis, which reproduces Red Giant
Branch (RGB) abundance patterns at all metallicities. Rotation-induced mixing
is treated taking into account meridional circulation and shear turbulence. We
discuss the effects of these processes on internal and surface abundances of
3He and on the net yields. Results. Over the whole mass and metallicity range
investigated, rotation-induced mixing lowers the 3He production, as well as the
upper mass limit at which stars destroy 3He. For low-mass stars, thermohaline
mixing occuring beyond the RGB bump is the dominant process in strongly
reducing the net 3He yield compared to standard computations. Yet these stars
remain net 3He producers. Conclusions. Overall, the net 3He yields are strongly
reduced compared to the standard framework predictions
Constraining angular momentum transport processes in stellar interiors with red-giant stars in the open cluster NGC6819
Clusters are excellent test benches for verification and improvement of
stellar evolution theory. The recent detection of solar-like oscillations in
G-K giants in the open cluster NGC6819 with Kepler provides us with independent
constraints on the masses and radii of stars on the red giant branch, as well
as on the distance to clusters and their ages. We present, for NGC6819,
evolutionary models by considering rotation-induced mixing ; and the
theoretical low-l frequencies of our stellar models.Comment: Submitted to EPJ Web of Conferences, to appear in the Proceedings of
the 3rd CoRoT Symposium, Kepler KASC7 joint meeting; 2 pages, 1 figur
Does high workload reduce the quality of healthcare? Evidence from rural Senegal
There is a widely held perception that staff shortages in low and middle-income countries (LMICs) lead to excessive workloads, which in turn worsen the quality of healthcare. Yet there is little evidence supporting these claims. We use data from standardised patient visits in Senegal and determine the effect of workload on the quality of primary care by exploiting quasi-random variation in workload. We find that despite a lack of staff, average levels of workload are low. Even at times when workload is high, there is no evidence that provider effort or quality of care are significantly reduced. Our data indicate that providers operate below their production possibility frontier and have sufficient capacity to attend more patients without compromising quality. This contradicts the prevailing discourse that staff shortages are a key reason for poor quality primary care in LMICs and suggests that the origins likely lie elsewhere
F03RS SGR No. 5 (KJL)
A Resolution
To express sincere and heartfelt condolences upon the untimely death of Kurt James Latiolais II of New Iberia, Louisian
Overconfident health workers provide lower quality healthcare
While a growing body of evidence suggests that healthcare workers in low and middle-income countries often provide poor quality of care, the reasons behind such low performance remain unclear. The literature on medical decision-making suggests that cognitive biases, or failures related to the way healthcare providers think, explain many diagnostic errors. This study investigates whether one cognitive bias, overconfidence, defined as the tendency to overestimate one's performance relative to others, is associated with the low quality of care provided in Senegal. We link survey data on the overconfidence of health workers to objective measures of the quality of care they provide to standardised patients – enumerators who pose as real patients and record details of the consultation. We find that about a third of providers are overconfident – meaning that they overestimate their own abilities relative to their peers. We then show that overconfident providers are 26% less likely to manage patients correctly and exert less effort in clinical practice. These results suggest that the low levels of quality of care observed in some settings could be partly explained by the cognitive biases of providers, such as overconfidence. Policies that encourage adequate supervision and feedback to healthcare workers might reduce such failures in clinical decision-making
Castile Evaporite Karst Potential Map of the Gypsum Plain, Eddy County, New Mexico and Culberson County, Texas: A GIS Methodological Comparison
Castile Formation gypsum crops out over ,1,800 km2 in the western Delaware Basin where it forms the majority of the Gypsum Plain. Karst development is well recognized in the Gypsum Plain (i.e., filled and open sinkholes with associated caves); however, the spatial occurrence has been poorly known. In order to evaluate the extent and distribution of karst development within the Castile portion of the Gypsum Plain, combined field and Geographic Information System (GIS) studies were conducted, which enable a first approximation of regional speleogenesis and delineate karst-related natural resources for management. Field studies included physical mapping of 50, 1-km2 sites, including identification of karst features (sinkholes, caves, and springs) and geomorphic mapping. GIS-based studies involved analyses of karst features based on public data, including Digital Elevation Model (DEM), Digital Raster Graphic, (DRG) and Digital Orthophoto Quad (DOQ) formats. GIS analyses consistently underestimate the actual extent and density of karst development, based on karst features identified during field studies. However, DOQ analyses coupled with field studies appears to produce accurate models of karst development. As a result, a karst potential map of the Castile outcrop region was developed which reveals that karst development within the Castile Formation is highly clustered. Approximately 40% of the region effectively exhibits no karst development (,1 feature/km2). Two small regions (,3 km2 each) display intense karst development (.40 features/km2) located within the northern extent of the Gypsum Plain, while many regions of significant karst development (.15 features/km2) are distributed more widely. The clustered distribution of karst development suggests that speleogenesis within the Castile Formation is dominated by hypogenic, transverse processes
The inner circumstellar disk of the UX Ori star V1026 Sco
The UX Ori type variables (named after the prototype of their class) are
intermediate-mass pre-main sequence objects. One of the most likely causes of
their variability is the obscuration of the central star by orbiting dust
clouds. We investigate the structure of the circumstellar environment of the
UX~Ori star V1026 Sco (HD 142666) and test whether the disk inclination is
large enough to explain the UX Ori variability. We observed the object in the
low-resolution mode of the near-infrared interferometric VLTI/AMBER instrument
and derived H- and K-band visibilities and closure phases. We modeled our AMBER
observations, published Keck Interferometer observations, archival MIDI/VLTI
visibilities, and the spectral energy distribution using geometric and
temperature-gradient models. Employing a geometric inclined-ring disk model, we
find a ring radius of 0.15 +- 0.06 AU in the H band and 0.18 +- 0.06 AU in the
K band. The best-fit temperature-gradient model consists of a star and two
concentric, ring-shaped disks. The inner disk has a temperature of
1257^{+133}_{-53} K at the inner rim and extends from 0.19 +- 0.01 AU to 0.23
+- 0.02 AU. The outer disk begins at 1.35^{+0.19}_{-0.20} AU and has an inner
temperature of 334^{+35}_{-17} K. The derived inclination of
48.6^{+2.9}_{-3.6}deg approximately agrees with the inclination derived with
the geometric model (49 +- 5deg in the K band and 50 +- 11deg in the H band).
The position angle of the fitted geometric and temperature-gradient models are
163 +- 9deg (K band; 179 +- 17deg in the H band) and 169.3^{+4.2}_{-6.7}deg,
respectively. The narrow width of the inner ring-shaped model disk and the disk
gap might be an indication for a puffed-up inner rim shadowing outer parts of
the disk. The intermediate inclination of ~50deg is consistent with models of
UX Ori objects where dust clouds in the inclined disk obscure the central star
Perception and prediction of simple object interactions
For humans, it is useful to be able to visually detect an object's physical properties. One potentially important source of information is the way the object moves and interacts with other objects in the environment. Here, we use computer simulations of a virtual ball bouncing on a horizontal plane to study the correspondence between our ability to estimate the ball's elasticity and to predict its future path. Three experiments were conducted to address (1) perception of the ball's elasticity, (2) interaction with the ball, and (3) prediction of its trajectory. The results suggest that different strategies and information sources are used for passive perception versus actively predicting future behavior
Lunar laser ranging in infrfared at hte Grasse laser station
For many years, lunar laser ranging (LLR) observations using a green
wavelength have suffered an inhomogeneity problem both temporally and
spatially. This paper reports on the implementation of a new infrared detection
at the Grasse LLR station and describes how infrared telemetry improves this
situation. Our first results show that infrared detection permits us to densify
the observations and allows measurements during the new and the full Moon
periods. The link budget improvement leads to homogeneous telemetric
measurements on each lunar retro-reflector. Finally, a surprising result is
obtained on the Lunokhod 2 array which attains the same efficiency as Lunokhod
1 with an infrared laser link, although those two targets exhibit a
differential efficiency of six with a green laser link
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