2,882 research outputs found
Small-scale chromospheric jets above a sunspot light bridge
High-resolution broadband filtergrams of active region NOAA 11271 in Ca ii H
and G band were obtained with the Solar Optical Telescope on board Hinode to
identify the physical driver responsible for the dynamic and small-scale
chromospheric jets above a sunspot light bridge. We identified the jets in the
Ca images using a semi-automatic routine. The chromospheric jets consist of a
bright, triangular-shaped blob that lies on the light bridge, while the apex of
this blob extends into a spike-like structure that is bright against the dark
umbral background. Most of the jets have apparent lengths of less than 1000 km
and about 30% of them have lengths between 1000-1600 km. They are oriented
within +/-35 deg. to the normal of the light bridge axis. Many of them are
clustered near the central part within a 2 arcsec area. The jets are seen to
move rapidly along the light bridge and most of them cannot be identified in
successive images taken with a 2 min cadence. The jets are primarily located on
one side of the light bridge and are directed into the umbral core. The Stokes
profiles at or close to the location of the blobs on the LB exhibit both a
significant net circular polarization and multiple components, including
opposite-polarity lobes. The magnetic field diverges from the light bridge
towards the umbral cores that it separates. In the photosphere there is a
predominantly uni-directional flow with speeds of 100-150 m/s along the light
bridge which is interrupted by a patch of weak motions that also moves along
the light bridge. The dynamic short-lived jets above the LB seem to be guided
by the magnetic field lines. Reconnection events are a likely trigger for such
phenomenon since they occur at locations where the magnetic field changes
orientation sharply. We find no clear relation between the jets and the
photospheric flow pattern.Comment: Accepted for publication in A&A, 9 pages, 7 figure
A bioeconomic model for determining the optimal response to a new weed incursion in Australian cropping systems
Invasions by non-indigenous plant species pose serious economic threats to Australian agricultural industries. When an invasion is discovered a decision has to be made as to whether to attempt to eradicate it, contain it or do nothing. These decisions should be based on long term benefits and costs. This paper describes a bioeconomic simulation framework with a mathematical model representing weed spread linked to a dynamic programming model to provide a means of determining the economically optimal weed management strategies over time. The modelling framework is used to evaluate case study invasive weed control problems in the Australian grains industry.weeds, incursion, bioeconomic model, Crop Production/Industries, Research Methods/ Statistical Methods,
Anomalous flows in a sunspot penumbra
High-resolution spectropolarimetric observations of active region NOAA 11271
were obtained with the spectro-polarimeter on board Hinode to analyze the
properties of an anomalous flow in the photosphere in a sunspot penumbra. We
detect a blue-shifted feature that appeared on the limb-side penumbra of a
sunspot and that was present intermittently during the next two hours. It
exhibited a maximum blue-shift of 1.6 km/s, an area of 5.2 arcsec^2, and an
uninterrupted lifetime of 1 hr. The blue-shifted feature, when present, lies
parallel to red-shifts. Both blue and red shifts flank a highly
inclined/horizontal magnetic structure that is radially oriented in the
penumbra. The low-cadence SP maps reveal changes in size, radial position in
the penumbra and line-of-sight velocity of the blue-shifted feature, from one
scan to the other. There was an increase of nearly 500 G in the field strength
and a marginal reduction in the field inclination of about 10 deg with the
onset of the blue-shifts. In the chromosphere, intense, arc-shaped brightenings
were observed close to the location of the blue-shifts, that extend from the
edge of the umbral core to the penumbra-quiet Sun boundary. The strongest and
largest brightenings were observed about 30 min after the strongest blue-shifts
were detected at the photosphere. The close spatial proximity of the two
phenomenon strongly suggests a causal relationship. The blue-shifted feature
represents plasma motion that could be related to a magnetic structure that
rises in the solar atmosphere and subsequently reconnects with the ambient
chromospheric magnetic field of the sunspot or an inverse Evershed flow, which
would be unique in the photosphere. This transient phenomena is presumably
related to the dynamic stability of the sunspot because the corresponding
umbral core separated two days later at the location of the blue-shifts and
fragmented subsequently.Comment: Accepted for publication in A&A: 8 pages, 8 figure
Racial/Ethnic Disparities in Diabetes Care and Outcomes: A Mixed Methods Study
Limited research has examined racial/ethnic differences in diabetes care and outcomes among primary care patients. This study examined racial/ethnic differences in diabetes care and outcomes among an ambulatory patient population and explored patient perceptions of the patient-provider relationship to inform strategies to improve care delivery. Using data from 62,149 adults with diabetes who received care within Atrium Health in 2013, regression models assessed associations between race/ethnicity and the following outcomes: glycated hemoglobin (HbA1c) tests, low density lipoprotein (LDL) and blood pressure (BP) screening, foot and eye exams, and HbA1c, LDL, and BP control. Eleven patients with diabetes and uncontrolled hypertension participated in three focus groups about their perceptions of the patient-provider relationship. Compared to non-Hispanic Whites, non-Hispanic Blacks had 22% to 73% higher odds of receiving screenings (HbA1c, LDL, BP, foot and eye exams;
Modelling of acoustic transmission through perforated layer
The paper deals with modeling the acoustic transmission through a perforated interface plane separating two halfspaces occupied by the acoustic medium. We considered the two-scale homogenization limit of the standard acoustic problem imposed in the layer with the perforated periodic structure embedded inside. The homogenized transmission conditions govern the interface discontinuity of the acoustic pressure associated with the two halfspaces and the magnitude of the fictitious transversal acoustic velocity. By numerical examples we illustrate this novel approach of modeling the acoustic impedance of perforated interfaces
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