3,817 research outputs found
Limb Event Brightenings and Fast Ejection Using IRIS Mission Observations
The Interface Region Imaging Spectrograph (IRIS) of the NASA small explorer
mission provides significantly more complete and higher resolution spectral
coverage of the dynamical conditions inside the chromosphere and transition
region (TR) than has heretofore been available. Near the solar limb high
temporal, spatial (0.3") and spectral resolution observations from the
ultraviolet IRIS spectra reveal high-energy limb event brightenings (LEBs) at
low chromospheric heights, around 1 Mm above the limb. They can be
characterized as explosive events producing jets. We selected two events
showing spectra of a confined eruption just off or near the quiet Sun limb, the
jet part showing obvious moving material with short duration large Doppler
shifts in three directions identified as macrospicules on slit-jaw (SJ) images
in Si IV and He II 304 A. The events are analyzed from a sequence of very close
rasters taken near the central meridian and the South pole limb. The processed
SJ images and the simultaneously observed fast spectral sequences having large
Doppler shifts, with a pair of red shifted elements together with a faster blue
shifted element from almost the same position, are analyzed. Shifts correspond
to velocities of up to 100 km/s in projection on the plane of the sky. The
occurrence of erupting spicules and macrospicules from these regions is noticed
from images taken before and after the spectra. The cool low first ionization
potential (FIP) element simultaneous line emissions of the MgII h and k
resonance lines do not clearly show a similar signature due to optical
thickness effects but the Si IV broad-band SJ images do. The bidirectional
plasma jets ejected from a small reconnection site are interpreted as the
result of coronal loop-loop interactions leading to reconnection in nearby
sites.Comment: 24 pages, 16 figures., Accepted in Sol. Phy
Polar Coronal Plumes as Tornado-Like Jets
We examine the dynamical behavior of white light polar plume structures in
the inner corona that are observed from the ground during total solar eclipses,
based on their EUV hot and cool emission line counterparts observed from space.
EUV observations from SDO/AIA of a sequence of rapidly varying coronal hole
structures are analyzed. Evidence of events showing acceleration in the 1.25 Mk
line of Fe XII at 193 A is given. The structures along the plume show an
outward velocity of about 140 kms-1 that can be interpreted as an upwards
propagating wave in the 304 A and 171 A lines; higher speeds are seen in 193 A
(up to 1000 km/s). The ejection of the cold He II plasma is delayed by about 4
min in the lowest layer and more than 12 min in the highest level compared to
the hot 193 A behavior. A study of the dynamics using time-slice diagrams
reveals that a large amount of fast ejected material originates from below the
plume, at the footpoints. The release of plasma material appears to come from a
cylinder with quasi-parallel edge-enhanced walls. After the initial phase of a
longitudinal acceleration, the speed substantially reduces and the ejecta
disperse into the environment. Finally, the detailed temporal and spatial
relationships between the cool and hot components were studied with
simultaneous multi-wavelength observations, using more AIA data. The
outward-propagating perturbation of the presumably magnetic walls of polar
plumes supports the suggestion that Alfven waves propagate outwardly along
these radially extended walls.Comment: 17 pages, 10 figures, accepted in Ap
Interaction-assisted propagation of Coulomb-correlated electron-hole pairs in disordered semiconductors
A two-band model of a disordered semiconductor is used to analyze dynamical
interaction induced weakening of localization in a system that is accessible to
experimental verification. The results show a dependence on the sign of the
two-particle interaction and on the optical excitation energy of the
Coulomb-correlated electron-hole pair.Comment: 4 pages and 3 ps figure
Circular photon drag effect in bulk tellurium
The circular photon drag effect is observed in a bulk semiconductor. The
photocurrent caused by a transfer of both translational and angular momenta of
light to charge carriers is detected in tellurium in the mid-infrared frequency
range. Dependencies of the photocurrent on the light polarization and on the
incidence angle agree with the symmetry analysis of the circular photon drag
effect. Microscopic models of the effect are developed for both intra- and
inter-subband optical absorption in the valence band of tellurium. The shift
contribution to the circular photon drag current is calculated. An observed
decrease of the circular photon drag current with increase of the photon energy
is explained by the theory for inter-subband optical transitions. Theoretical
estimates of the circular photon drag current agree with the experimental data.Comment: 8 pages, 4 figure
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