32,756 research outputs found
Object Contour and Edge Detection with RefineContourNet
A ResNet-based multi-path refinement CNN is used for object contour
detection. For this task, we prioritise the effective utilization of the
high-level abstraction capability of a ResNet, which leads to state-of-the-art
results for edge detection. Keeping our focus in mind, we fuse the high, mid
and low-level features in that specific order, which differs from many other
approaches. It uses the tensor with the highest-levelled features as the
starting point to combine it layer-by-layer with features of a lower
abstraction level until it reaches the lowest level. We train this network on a
modified PASCAL VOC 2012 dataset for object contour detection and evaluate on a
refined PASCAL-val dataset reaching an excellent performance and an Optimal
Dataset Scale (ODS) of 0.752. Furthermore, by fine-training on the BSDS500
dataset we reach state-of-the-art results for edge-detection with an ODS of
0.824.Comment: Keywords: Object Contour Detection, Edge Detection, Multi-Path
Refinement CN
Opposite polarity field with convective downflow and its relation to magnetic spines in a sunspot penumbra
We discuss NICOLE inversions of Fe I 630.15 nm and 630.25 nm Stokes spectra
from a sunspot penumbra recorded with the CRISP imaging spectropolarimeter on
the Swedish 1-m Solar Telescope at a spatial resolution close to 0.15". We
report on narrow radially extended lanes of opposite polarity field, located at
the boundaries between areas of relatively horizontal magnetic field (the
intra-spines) and much more vertical field (the spines). These lanes harbor
convective downflows of about 1 km/s. The locations of these downflows close to
the spines agree with predictions from the convective gap model (the "gappy
penumbra") proposed six years ago, and more recent 3D MHD simulations. We also
confirm the existence of strong convective flows throughout the entire
penumbra, showing the expected correlation between temperature and vertical
velocity, and having vertical RMS velocities of about 1.2 km/s.Comment: Accepted for publication in A&A (06-March-2013). Minor corrections
made in this version
Chromospheric observations and magnetic configuration of a supergranular structure
Unipolar magnetic regions are often associated with supergranular cells. The
chromosphere above these regions is regulated by the magnetic field, but the
field structure is poorly known. In unipolar regions, the fibrillar arrangement
does not always coincide with magnetic field lines, and polarimetric
observations are needed to establish the chromospheric magnetic topology. In an
active region close to the limb, we observed a unipolar annular network of
supergranular size. This supergranular structure harbours a radial distribution
of the fibrils converging towards its centre. We observed this structure at
different heights by taking data in the FeI 6301-6302 {\AA}, H-\alpha, CaII
8542 \AA\ and the CaII H&K spectral lines with the CRISP and CHROMIS
instruments at the Swedish 1-m Solar Telescope. We performed Milne-Eddington
inversions of the spectropolarimetric data of FeI and applied the weak field
approximation to CaII 8542 \AA\ data to retrieve the magnetic field in the
photosphere and chromosphere. We used magnetograms of CRISP, HINODE/SP and HMI
to calculate the magnetic flux. We investigated the velocity using the
line-of-sight velocities computed from the Milne-Eddington inversion and from
Doppler shift of the K feature in the CaII K spectral line. To describe the
typical spectral profiles characterising the chromosphere above the
supergranular structure, we performed a K-mean clustering of the spectra in
CaIIK. The photospheric magnetic flux is not balanced. The magnetic field
vector at chromospheric heights, retrieved by the weak field approximation,
indicates that the field lines within the supegranular cell tend to point
inwards, and might form a canopy above the unipolar region. In the centre of
the supergranular cell hosting the unipolar region, we observe a persistent
chromospheric brightening coinciding with a strong gradient in the
line-of-sight velocity.Comment: 12 pages, 12 figures, accepted for publication in A&
Ellerman Bombs at high resolution: I. Morphological evidence for photospheric reconnection
High-resolution imaging-spectroscopy movies of solar active region NOAA 10998
obtained with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish 1-m
Solar Telescope show very bright, rapidly flickering, flame-like features that
appear intermittently in the wings of the Balmer H-alpha line in a region with
moat flows and likely some flux emergence. They show up at regular H-alpha
blue-wing bright points that outline magnetic network, but flare upward with
much larger brightness and distinct "jet" morphology seen from aside in the
limbward view of these movies. We classify these features as Ellerman bombs and
present a morphological study of their appearance at the unprecedented spatial,
temporal, and spectral resolution of these observations. The bombs appear along
magnetic network with footpoint extents up to 900km. They show apparent travel
away from the spot along the pre-existing network at speeds of about 1 km/s.
The bombs flare repetitively with much rapid variation at time scales of
seconds only, in the form of upward jet-shaped brightness features. These reach
heights of 600-1200km and tend to show blueshifts; some show bi-directional
Doppler signature, and some seem accompanied with an H-alpha surge. They are
not seen in the core of H-alpha due to shielding by overlying chromospheric
fibrils. The network where they originate has normal properties. The morphology
of these jets strongly supports deep-seated photospheric reconnection of
emergent or moat-driven magnetic flux with pre-existing strong vertical network
fields as the mechanism underlying the Ellerman bomb phenomenon.Comment: 13pages, 10 figures, 2 tables. Accepted for publication in the
Astrophysical Journa
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