45,314 research outputs found
Transition from Ferromagnetism to Antiferromagnetism in GaMnN
Using density functional theory, we study the magnetic stability of the
GaMnN alloy system. We show that unlike GaMnAs, which
shows only ferromagnetic (FM) phase, GaMnN can be stable in either
FM or antiferromagnetic phases depending on the alloy concentration. The
magnetic order can also be altered by applying pressure or with charge
compensation. A unified model is used to explain these behaviors.Comment: 4 pages, 4 figure
Detection of a new methanol maser line with ALMA
Aims. We aimed at investigating the structure and kinematics of the gaseous
disk and outflows around the massive YSO S255 NIRS3 in the S255IR-SMA1 dense
clump. Methods. Observations of the S255IR region were carried out with ALMA at
two epochs in the compact and extended configurations. Results. We
serendipitously detected a new, never predicted, bright maser line at about
349.1 GHz, which most probably represents the CHOH A transition. The emission covers most of the 6.7 GHz methanol maser emission
area of almost 1 in size and shows a velocity gradient in the
same sense as the disk rotation. No variability was found on the time interval
of several months. It is classified as Class II maser and probably originates
in a ring at a distance of several hundreds AU from the central star.Comment: 4 pages, 4 figures, accepted by Astronomy and Astrophysic
Pre-flare coronal dimmings
In this paper, we focus on the pre-flare coronal dimmings. We report our
multiwavelength observations of the GOES X1.6 solar flare and the accompanying
halo CME produced by the eruption of a sigmoidal magnetic flux rope (MFR) in
NOAA active region (AR) 12158 on 2014 September 10. The eruption was observed
by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamic Observatory
(SDO). The photospheric line-of-sight magnetograms were observed by the
Helioseismic and Magnetic Imager (HMI) aboard SDO. The soft X-ray (SXR) fluxes
were recorded by the GOES spacecraft. The halo CME was observed by the white
light coronagraphs of the Large Angle Spectroscopic Coronagraph (LASCO) aboard
SOHO.} {About 96 minutes before the onset of flare/CME, narrow pre-flare
coronal dimmings appeared at the two ends of the twisted MFR. They extended
very slowly with their intensities decreasing with time, while their apparent
widths (89 Mm) nearly kept constant. During the impulsive and decay phases
of flare, typical fanlike twin dimmings appeared and expanded with much larger
extent and lower intensities than the pre-flare dimmings. The percentage of 171
{\AA} intensity decrease reaches 40\%. The pre-flare dimmings are most striking
in 171, 193, and 211 {\AA} with formation temperatures of 0.62.5 MK. The
northern part of the pre-flare dimmings could also be recognized in 131 and 335
{\AA}.} To our knowledge, this is the first detailed study of pre-flare coronal
dimmings, which can be explained by the density depletion as a result of the
gradual expansion of the coronal loop system surrounding the MFR during the
slow rise of the MFR.Comment: 6 pages, 8 figures, to be accepted for publication by A&
Nonconical theory of flow past slender wing bodies with leading-edge separation
Nonconical theory of flow past slender wing bodies with leading edge separatio
Non-damping oscillations at flaring loops
Context. QPPs are usually detected as spatial displacements of coronal loops
in imaging observations or as periodic shifts of line properties in
spectroscopic observations. They are often applied for remote diagnostics of
magnetic fields and plasma properties on the Sun. Aims. We combine imaging and
spectroscopic measurements of available space missions, and investigate the
properties of non-damping oscillations at flaring loops. Methods. We used the
IRIS to measure the spectrum over a narrow slit. The double-component Gaussian
fitting method was used to extract the line profile of Fe XXI 1354.08 A at "O
I" window. The quasi-periodicity of loop oscillations were identified in the
Fourier and wavelet spectra. Results. A periodicity at about 40 s is detected
in the line properties of Fe XXI, HXR emissions in GOES 1-8 A derivative, and
Fermi 26-50 keV. The Doppler velocity and line width oscillate in phase, while
a phase shift of about Pi/2 is detected between the Doppler velocity and peak
intensity. The amplitudes of Doppler velocity and line width oscillation are
about 2.2 km/s and 1.9 km/s, respectively, while peak intensity oscillate with
amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period
of about 155 s is identified in the Doppler velocity and peak intensity of Fe
XXI, and AIA 131 A intensity. Conclusions. The oscillations at about 40 s are
not damped significantly during the observation, it might be linked to the
global kink modes of flaring loops. The periodicity at about 155 s is most
likely a signature of recurring downflows after chromospheric evaporation along
flaring loops. The magnetic field strengths of the flaring loops are estimated
to be about 120-170 G using the MHD seismology diagnostics, which are
consistent with the magnetic field modeling results using the flux rope
insertion method.Comment: 9 pages, 9 figures, 1 table, accepted by A&
High-Efficient Parallel CAVLC Encoders on Heterogeneous Multicore Architectures
This article presents two high-efficient parallel realizations of the context-based adaptive variable length coding (CAVLC) based on heterogeneous multicore processors. By optimizing the architecture of the CAVLC encoder, three kinds of dependences are eliminated or weaken, including the context-based data dependence, the memory accessing dependence and the control dependence. The CAVLC pipeline is divided into three stages: two scans, coding, and lag packing, and be implemented on two typical heterogeneous multicore architectures. One is a block-based SIMD parallel CAVLC encoder on multicore stream processor STORM. The other is a component-oriented SIMT parallel encoder on massively parallel architecture GPU. Both of them exploited rich data-level parallelism. Experiments results show that compared with the CPU version, more than 70 times of speedup can be obtained for STORM and over 50 times for GPU. The implementation of encoder on STORM can make a real-time processing for 1080p @30fps and GPU-based version can satisfy the requirements for 720p real-time encoding. The throughput of the presented CAVLC encoders is more than 10 times higher than that of published software encoders on DSP and multicore platforms
Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare
We analyzed high-cadence sit-and-stare observations acquired with the
Hinode/EIS spectrometer and HXR measurements acquired with RHESSI during an
M-class flare. During the flare impulsive phase, we observe no significant
flows in the cooler Fe XIII line but strong upflows, up to 80-150 km/s, in the
hotter Fe XVI line. The largest Doppler shifts observed in the Fe XVI line were
co-temporal with the sharp intensity peak. The electron density obtained from a
Fe XIII line pair ratio exhibited fast increase (within two minutes) from the
pre-flare level of 5.01x10^(9) cm^(-3) to 3.16x10^(10) cm^(-3) during the flare
peak. The nonthermal energy flux density deposited from the coronal
acceleration site to the lower atmospheric layers during the flare peak was
found to be 1.34x10^(10) erg/s/cm^(2) for a low-energy cut-off that was
estimated to be 16 keV. During the decline flare phase, we found a secondary
intensity and density peak of lower amplitude that was preceded by upflows of
15 km/s that were detected in both lines. The flare was also accompanied by a
filament eruption that was partly captured by the EIS observations. We derived
Doppler velocities of 250-300 km/s for the upflowing filament material.The
spectroscopic results for the flare peak are consistent with the scenario of
explosive chromospheric evaporation, although a comparatively low value of the
nonthermal energy flux density was determined for this phase of the flare. This
outcome is discussed in the context of recent hydrodynamic simulations. It
provides observational evidence that the response of the atmospheric plasma
strongly depends on the properties of the electron beams responsible for the
heating, in particular the steepness of the energy distribution.Comment: 13 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
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