6,367 research outputs found
Evershed clouds as precursors of moving magnetic features around sunspots
The relation between the Evershed flow and moving magnetic features (MMFs) is
studied using high-cadence, simultaneous spectropolarimetric measurements of a
sunspot in visible (630.2 nm) and near-infrared (1565 nm) lines. Doppler
velocities, magnetograms, and total linear polarization maps are calculated
from the observed Stokes profiles. We follow the temporal evolution of two
Evershed clouds that move radially outward along the same penumbral filament.
Eventually, the clouds cross the visible border of the spot and enter the moat
region, where they become MMFs. The flux patch farther from the sunspot has the
same polarity of the spot, while the MMF closer to it has opposite polarity and
exhibits abnormal circular polarization profiles. Our results provide strong
evidence that at least some MMFs are the continuation of the penumbral Evershed
flow into the moat. This, in turn, suggests that MMFs are magnetically
connected to sunspots.Comment: To appear in ApJ Letters, Vol 649, 2006 September 20 issu
An Adaptive Sampling Scheme to Efficiently Train Fully Convolutional Networks for Semantic Segmentation
Deep convolutional neural networks (CNNs) have shown excellent performance in
object recognition tasks and dense classification problems such as semantic
segmentation. However, training deep neural networks on large and sparse
datasets is still challenging and can require large amounts of computation and
memory. In this work, we address the task of performing semantic segmentation
on large data sets, such as three-dimensional medical images. We propose an
adaptive sampling scheme that uses a-posterior error maps, generated throughout
training, to focus sampling on difficult regions, resulting in improved
learning. Our contribution is threefold: 1) We give a detailed description of
the proposed sampling algorithm to speed up and improve learning performance on
large images. We propose a deep dual path CNN that captures information at fine
and coarse scales, resulting in a network with a large field of view and high
resolution outputs. We show that our method is able to attain new
state-of-the-art results on the VISCERAL Anatomy benchmark
Neural mechanisms of resistance to peer influence in early adolescence
During the shift from a parent-dependent child to a fully autonomous adult, peers take on a significant role in shaping the adolescent’s behaviour. Peer-derived influences are not always positive, however. Here we explore neural correlates of inter-individual differences in the probability of resisting peer influence in early adolescence. Using functional magnetic-resonance imaging (fMRI), we found striking differences between 10-year old children with high and low resistance to peer influence in their brain activity during observation of angry hand-movements and angry facial expressions: compared with subjects with low resistance to peer influence, individuals with high resistance showed a highly coordinated brain activity in neural systems underlying perception of action and decision making. These findings suggest that the probability of resisting peer influence depends on neural interactions during observation of emotion-laden actions
Consistent thermodynamic derivative estimates for tabular equations of state
Numerical simulations of compressible fluid flows require an equation of
state (EOS) to relate the thermodynamic variables of density, internal energy,
temperature, and pressure. A valid EOS must satisfy the thermodynamic
conditions of consistency (derivation from a free energy) and stability
(positive sound speed squared). When phase transitions are significant, the EOS
is complicated and can only be specified in a table. For tabular EOS's such as
SESAME from Los Alamos National Laboratory, the consistency and stability
conditions take the form of a differential equation relating the derivatives of
pressure and energy as functions of temperature and density, along with
positivity constraints. Typical software interfaces to such tables based on
polynomial or rational interpolants compute derivatives of pressure and energy
and may enforce the stability conditions, but do not enforce the consistency
condition and its derivatives. We describe a new type of table interface based
on a constrained local least squares regression technique. It is applied to
several SESAME EOS's showing how the consistency condition can be satisfied to
round-off while computing first and second derivatives with demonstrated
second-order convergence. An improvement of 14 orders of magnitude over
conventional derivatives is demonstrated, although the new method is apparently
two orders of magnitude slower, due to the fact that every evaluation requires
solving an 11-dimensional nonlinear system.Comment: 29 pages, 9 figures, 16 references, submitted to Phys Rev
Quiet Sun magnetic fields from space-borne observations: simulating Hinode's case
We examine whether or not it is possible to derive the field strength
distribution of quiet Sun internetwork regions from very high spatial
resolution polarimetric observations in the visible. In particular, we consider
the case of the spectropolarimeter attached to the Solar Optical Telescope
aboard Hinode. Radiative magneto-convection simulations are used to synthesize
the four Stokes profiles of the \ion{Fe}{1} 630.2 nm lines. Once the profiles
are degraded to a spatial resolution of 0\farcs32 and added noise, we infer the
atmospheric parameters by means of Milne-Eddington inversions. The comparison
of the derived values with the real ones indicates that the visible lines yield
correct internetwork field strengths and magnetic fluxes, with uncertainties
smaller than 150 G, when a stray light contamination factor is included
in the inversion. Contrary to the results of ground-based observations at
1\arcsec, weak fields are retrieved wherever the field is weak in the
simulation.Comment: Accepted for publication in ApJ Letter
The formation and disintegration of magnetic bright points observed by Sunrise/IMaX
The evolution of the physical parameters of magnetic bright points (MBPs)
located in the quiet Sun (mainly in the interwork) during their lifetime is
studied. First we concentrate on the detailed description of the magnetic field
evolution of three MBPs. This reveals that individual features follow
different, generally complex, and rather dynamic scenarios of evolution. Next
we apply statistical methods on roughly 200 observed MBP evolutionary tracks.
MBPs are found to be formed by the strengthening of an equipartition field
patch, which initially exhibits a moderate downflow. During the evolution,
strong downdrafts with an average velocity of 2.4 km/s set in. These flows,
taken together with the concurrent strengthening of the field, suggest that we
are witnessing the occurrence of convective collapses in these features,
although only 30% of them reach kG field strengths. This fraction might turn
out to be larger when the new 4 m class solar telescopes are operational as
observations of MBPs with current state of the art instrumentation could still
be suffering from resolution limitations. Finally, when the bright point
disappears (although the magnetic field often continues to exist) the magnetic
field strength has dropped to the equipartition level and is generally somewhat
weaker than at the beginning of the MBP's evolution. Noteworthy is that in
about 10% of the cases we observe in the vicinity of the downflows small-scale
strong (exceeding 2 km/s) intergranular upflows related spatially and
temporally to these downflows.Comment: 19 pages, 13 figures; final version published in "The Astrophysical
Journal
Electrocatalytic Oxidation of Cyanide on Copper-doped Cobalt Oxide Electrodes
[EN] Copper and copper oxides are well-known excellent catalysts in several chemical processes, but their low mechanical and electrochemical stability restrict their direct utilization as electrodes in electrolytic processes. In this work, the incorporation of copper into cobalt oxide (CuxCo3-xO4) is presented as an excellent approach to obtain highly active and robust copper-based electrocatalysts. Particularly, the electrocatalytic performance of Ti-supported CuxCo3-xO4 electrodes (with 0 <= x <= 1.5) has been studied for the oxidation' of cyanide in alkaline media. Cyclic voltammetry and electrolysis runs show an outstanding effect of Cu on the activity, efficiency and kinetics of spinel CuxCo3-xO4 electrodes for CN(-)electro-oxidation. Despite being active oxides with high activity towards water oxidation, copper saturated (x=1.0) and oversaturated (x=1.5) spinels exhibit unprecedented 100% current efficiencies for the electro-oxidation of CN- in aqueous electrolyte. In situ surface enhanced Raman spectroscopy (SERS) reveals the specific adsorption of CN- ions on surface Cu species to be involved in the electrocatalytic oxidation mechanism. This electrocatalytic activity has been attributed to surface Cu(II) in the spinel lattice. Furthermore, the CuxCo3-xO4 electrodes also display high electrochemical stability. Therefore, they are considered excellent candidates for the sustainable electrochemical elimination of highly toxic cyanides.Financial support from the Spanish Ministerio de Economia y Competitividad and FEDER funds (MAT2016-76595-R, IJCI-2014-20012) and from the Generalitat Valenciana (PROMETEO2013/038) is gratefully acknowledged.Berenguer, R.; La Rosa-Toro, A.; Quijada, C.; Morallon, E. (2017). Electrocatalytic Oxidation of Cyanide on Copper-doped Cobalt Oxide Electrodes. Applied Catalysis B Environmental. 207:286-296. https://doi.org/10.1016/j.apcatb.2017.01.078S28629620
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