564,053 research outputs found
Propagating wave in active region-loops, located over the solar disk observed by the Interface Region Imaging Spectrograph
We aim to ascertain the physical parameters of a propagating wave over the
solar disk detected by the Interface Region Imaging Spectrograph (IRIS). Using
imaging data from the IRIS and the Solar Dynamic Observatory (SDO), we tracked
bright spots to determine the parameters of a propagating transverse wave in
active region (AR) loops triggered by activation of a filament. Deriving the
Doppler velocity of Si IV line from spectral observations of IRIS, we have
determined the rotating directions of active region loops which are relevant to
the wave. On 2015 December 19, a filament was located on the polarity inversion
line of the NOAA AR 12470. The filament was activated and then caused a C 1.1
two-ribbon flare. Between the flare ribbons, two rotation motions of a set of
bright loops were observed to appear in turn with opposite directions.
Following the end of the second rotation, a propagating wave and an associated
transverse oscillation were detected in these bright loops. In 1400 A channel,
there was bright material flowing along the loops in a wave-like manner, with a
period of ~128 s and a mean amplitude of ~880 km. For the transverse
oscillation, we tracked a given loop and determine the transverse positions of
the tracking loop in a limited longitudinal range. In both of 1400 A and 171 A
channels, approximately four periods are distinguished during the transverse
oscillation. The mean period of the oscillation is estimated as ~143 s and the
displacement amplitude as between ~1370 km and ~690 km. We interpret these
oscillations as a propagating kink wave and obtain its speed of ~1400 km s-1.
Our observations reveal that a flare associated with filament activation could
trigger a kink propagating wave in active region loops over the solar disk.Comment: Accepted for publication in A&
Interatomic collisions in two-dimensional and quasi-two-dimensional confinements with spin-orbit coupling
We investigate the low-energy scattering and bound states of two
two-component fermionic atoms in pure two-dimensional (2D) and quasi-2D
confinements with Rashba spin-orbit coupling (SOC). We find that the SOC
qualitatively changes the behavior of the 2D scattering amplitude in the
low-energy limit. For quasi-2D systems we obtain the analytic expression for
the effective-2D scattering amplitude and the algebraic equations for the
two-atom bound state energy. Based on these results, we further derive the
effective 2D interaction potential between two ultracold atoms in the quasi-2D
confinement with Rashba SOC. These results are crucial for the control of the
2D effective physics in quasi-2D geometry via the confinement intensity and the
atomic three-dimensional scattering length.Comment: 13pages, 5 figure
Momentum relaxation due to polar optical phonons in AlGaN/GaN heterostructures
Using the dielectric continuum (DC) model, momentum relaxation rates are calculated for electrons confined in quasi-two-dimensional (quasi-2D) channels of AlGaN/GaN heterostructures. Particular attention is paid to the effects of half-space and interface modes on the momentum relaxation. The total momentum relaxation rates are compared with those evaluated by the three-dimensional phonon (3DP) model, and also with the Callen results for bulk GaN. In heterostructures with a wide channel (effective channel width >100 Ã…), the DC and 3DP models yield very close momentum relaxation rates. Only for narrow-channel heterostructures do interface phonons become important in momentum relaxation processes, and an abrupt threshold occurs for emission of interface as well as half-space phonons. For a 30-Ã… GaN channel, for instance, the 3DP model is found to underestimate rates just below the bulk phonon energy by 70% and overestimate rates just above the bulk phonon energy by 40% compared to the DC model. Owing to the rapid decrease in the electron-phonon interaction with the phonon wave vector, negative momentum relaxation rates are predicted for interface phonon absorption in usual GaN channels. The total rates remain positive due to the dominant half-space phonon scattering. The quasi-2D rates can have substantially higher peak values than the three-dimensional rates near the phonon emission threshold. Analytical expressions for momentum relaxation rates are obtained in the extreme quantum limits (i.e., the threshold emission and the near subband-bottom absorption). All the results are well explained in terms of electron and phonon densities of states
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