472 research outputs found
IRIS observations of magnetic interactions in the solar atmosphere between pre-existing and emerging magnetic fields. II. UV emission properties
Multi-wavelength ultraviolet (UV) observations by the IRIS satellite in
active region NOAA 12529 have recently pointed out the presence of long-lasting
brightenings, akin to UV bursts, and simultaneous plasma ejections occurring in
the upper chromosphere and transition region during secondary flux emergence.
These signatures have been interpreted as evidence of small-scale, recurrent
magnetic reconnection episodes between the emerging flux region (EFR) and the
pre-existing plage field. Here, we characterize the UV emission of these
strong, intermittent brightenings and we study the surge activity above the
chromospheric arch filament system (AFS) overlying the EFR. We analyze the
surges and the cospatial brightenings observed at different wavelengths. We
find an asymmetry in the emission between the blue and red wings of the Si IV
1402 \AA{} and Mg II k 2796.3 \AA{} lines, which clearly outlines the dynamics
of the structures above the AFS that form during the small-scale eruptive
phenomena. We also detect a correlation between the Doppler velocity and
skewness of the Si IV 1394 \AA{} and 1402 \AA{} line profiles in the UV burst
pixels. Finally, we show that genuine emission in the Fe XII 1349.4 \AA{} line
is cospatial to the Si IV brightenings. This definitely reveals a pure coronal
counterpart to the reconnection event.Comment: 19 pages, 8 figures + 3 figures in the Appendix; accepted in Ap
Satellite observations of reconnection between emerging and pre-existing small-scale magnetic fields
We report multi-wavelength ultraviolet observations taken with the IRIS
satellite, concerning the emergence phase in the upper chromosphere and
transition region of an emerging flux region (EFR) embedded in the unipolar
plage of active region NOAA 12529. The photospheric configuration of the EFR is
analyzed in detail benefitting from measurements taken with the
spectropolarimeter aboard the Hinode satellite, when the EFR was fully
developed. In addition, these data are complemented by full-disk, simultaneous
observations of the SDO satellite, relevant to the photosphere and the corona.
In the photosphere, magnetic flux emergence signatures are recognized in the
fuzzy granulation, with dark alignments between the emerging polarities,
cospatial with highly inclined fields. In the upper atmospheric layers, we
identify recurrent brightenings that resemble UV bursts, with counterparts in
all coronal passbands. These occur at the edges of the EFR and in the region of
the arch filament system (AFS) cospatial to the EFR. Jet activity is also found
at chromospheric and coronal levels, near the AFS and the observed brightness
enhancement sites. The analysis of the IRIS line profiles reveals the heating
of dense plasma in the low solar atmosphere and the driving of bi-directional
high-velocity flows with speeds up to 100 km/s at the same locations.
Furthermore, we detect a correlation between the Doppler velocity and line
width of the Si IV 1394 and 1402 \AA{} line profiles in the UV burst pixels and
their skewness. Comparing these findings with previous observations and
numerical models, we suggest evidence of several long-lasting, small-scale
magnetic reconnection episodes between the emerging bipole and the ambient
field. This process leads to the cancellation of a pre-existing photospheric
flux concentration of the plage with the opposite polarity flux patch of the
EFR. [...]Comment: 4 pages, 2 figures, to be published in "Nuovo Cimento C" as
proceeding of the Third Meeting of the Italian Solar and Heliospheric
Communit
Description of Anteon seramense (Hymenoptera. Dryinidae), a new species from Indonesia
Anteon seramense sp. nov. is described from Seram Island (Indonesia). Seram is an island
situated in a transition area between the Oriental and the Australian regions. Anteon seramense
can be distinguished from the related Australian species A. giluwense Olmi and
A. chelogynoides (Perkins) by the different sculpture of the scutum (granulated in A. seramense,
punctate and unsculptured among punctures in A. giluwense and A. chelogynoides)
and the different distal apex of the protarsal segment 5 (deeply hollow in A. seramense,
not hollow in A. giluwense and A. chelogynoides). Anteon seramense sp. nov. can be distinguished
from the related Oriental species A. heppneri Olmi and A. thai Olmi by the different
shape of the protarsal segment 5 (basal part slightly longer than distal part in A. seramense,
much longer in A. heppneri and A. thai)
HINODE Observations of Chromospheric Brightenings in the Ca II H Line during small-scale Flux Emergence Events
\ion{Ca}{2} H emission is a well-known indicator of magnetic activity in the
Sun and other stars. It is also viewed as an important signature of
chromospheric heating. However, the \ion{Ca}{2} H line has not been used as a
diagnostic of magnetic flux emergence from the solar interior. Here we report
on Hinode observations of chromospheric \ion{Ca}{2} H brightenings associated
with a repeated, small-scale flux emergence event. We describe this process and
investigate the evolution of the magnetic flux, G-band brightness, and
\ion{Ca}{2} H intensity in the emerging region. Our results suggest that energy
is released in the chromosphere as a consequence of interactions between the
emerging flux and the pre-existing magnetic field, in agreement with recent 3D
numerical simulations.Comment: 12 Pages, 6 Figures, Accepted for publication in ApJ Letter
The Lockman Hole Project: new constraints on the sub-mJy source counts from a wide-area 1.4 GHz mosaic
This paper is part of a series discussing the results obtained in the
framework of a wide international collaboration - the Lockman Hole Project -
aimed at improving the extensive multiband coverage available in the Lockman
Hole region, through novel deep, wide-area, multifrequency (60, 150, 350 MHz,
and 1.4 GHz) radio surveys. This multifrequency, multi-band information will be
exploited to get a comprehensive view of star formation and active galactic
nucleus activities in the high-redshift Universe from a radio perspective. In
this paper, we present novel 1.4 GHz mosaic observations obtained with the
Westerbork Synthesis Radio Telescope. With an area coverage of 6.6 deg2, this
is the largest survey reaching an rms noise of 11 uJy/beam. In this paper, we
present the source catalogue (~6000 sources with flux densities S>55 uJy
(5sigma), and we discuss the 1.4 GHz source counts derived from it. Our source
counts provide very robust statistics in the flux range 0.1<S<1 mJy, and are in
excellent agreement with other robust determinations obtained at lower and
higher flux densities. A clear excess is found with respect to the counts
predicted by the semi-empirical radio sky simulations developed in the
framework of the Square Kilometre Array Simulated Skies project. A preliminary
analysis of the identified (and classified) sources suggests this excess is to
be ascribed to star-forming galaxies, which seem to show a steeper evolution
than predicted.Comment: accepted for publication on MNRAS. New version that corrects latex
errors and contain the correct version of figure 1
Multiwavelength Observations of Small-Scale Reconnection Events triggered by Magnetic Flux Emergence in the Solar Atmosphere
The interaction between emerging magnetic flux and the pre-existing ambient
field has become a "hot" topic for both numerical simulations and
high-resolution observations of the solar atmosphere. The appearance of
brightenings and surges during episodes of flux emergence is believed to be a
signature of magnetic reconnection processes. We present an analysis of a
small-scale flux emergence event in NOAA 10971, observed simultaneously with
the Swedish 1-m Solar Telescope on La Palma and the \emph{Hinode} satellite
during a joint campaign in September 2007. Extremely high-resolution G-band,
H, and \ion{Ca}{2} H filtergrams, \ion{Fe}{1} and \ion{Na}{1}
magnetograms, EUV raster scans, and X-ray images show that the emerging region
was associated with chromospheric, transition region and coronal brightenings,
as well as with chromospheric surges. We suggest that these features were
caused by magnetic reconnection at low altitude in the atmosphere. To support
this idea, we perform potential and linear force-free field extrapolations
using the FROMAGE service. The extrapolations show that the emergence site is
cospatial with a 3D null point, from which a spine originates. This magnetic
configuration and the overall orientation of the field lines above the emerging
flux region are compatible with the structures observed in the different
atmospheric layers, and remain stable against variations of the force-free
field parameter. Our analysis supports the predictions of recent 3D numerical
simulations that energetic phenomena may result from the interaction between
emerging flux and the pre-existing chromospheric and coronal field.Comment: In press for Ap
The performance of differential point positioning using low-cost GNSS in comparison to DInSAR for monitoring coseismic displacement of the Provenzana–Pernicana fault system (Mt. Etna, 2018 December eruptive phase)
Mt. Etna is a perfect laboratory for testing new approaches and new technologies in a very active geodynamic environment. It offers, in fact, the opportunity for measuring active crustal deformation, related to volcanic activity as well as to seismic faulting on its flanks. In this work, a network of low-cost/low-power Global Navigation Satellite System stations has been installed and tested on Mt. Etna, across a very active fault, the Provenzana–Pernicana system, cutting its north-eastern flank. During the test period, a lateral eruption occurred (starting on 2018 December 24), with a forceful dyke intrusion that stressed all the flanks of the volcano, soliciting all the main faults dissecting the edifice. Also the Provenzana–Pernicana fault system, where this network was recording, was activated during the dyke intrusion, producing a significant seismic swarm. The low-cost/low-power network data analysis allowed the fault slip during the intrusion to be clearly traced in time and space at all the stations lying on the hangingwall mobile block of the fault. All the stations lying south of the fault trace showed an eastward displacement, in very good agreement with the usual kinematics of the fault and the temporal duration of the M 3.5 December 24 earthquake, related to the seaward dislocation of the eastern mobile flank of the volcano, promoted and accelerated by dyke emplacement on the upper part of the edifice
fatigue life evaluation of car front halfshaft
Abstract The present paper is the result of the collaboration between the Engineering Department of Messina University and the car company Maserati S.p.A. The aim of this paper is to determine the T-N torsion fatigue curve at R= -1 of the mechanical system "front halfshaft" of an existing car. In particular, experimental fatigue tests were carried out in the laboratories of the Engineering Department of the University of Messina. Torsion fatigue tests of the entire mechanical system were carried out on 15 different front halfshafts. Evaluations of the crack propagation and of failure analysis were made to determine the causes of breakage. In conclusion, the T-N fatigue curve of the mechanical system "front halfshaft" has been obtained
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